ayurvedic drug discovery_review

Review

10.1517/17460441.2.12.1631 2007 Informa UK Ltd ISSN 1746-0441 1631

1. Introduction

2. Modern drug discovery versus

ayurvedic products-based

drug discovery

3. Ayurvedic drug discovery:

essential considerations

and requirements

4. Ayurvedic medicine: what

it can offer?

5. Ayurvedic literature

6. Recent developments in

ayurvedic medicine

7. Development of new

therapeutic compounds from

medicinal plants of Ayurveda

8. Mechanism of action of

ayurvedic drug compounds

9. Reverse pharmacology: a road

to ayurvedic drug discovery

10. Ayurvedic drug discovery:

possible present and

future directions

11. Tools and methodologies

in ayurvedic drug discovery

12. Selection criteria for herbs

and herbal preparations

13. Major challenges in ayurvedic

drug discovery

14. Ayurvedic drug development

in India: government and

private sectors

15. Conclusion

16. Expert opinion

Ayurvedic drug discovery Premalatha Balachandran & Rajgopal Govindarajan University of Mississippi , National Center for Natural Products Research , Research Institute of Pharmaceutical Sciences , School of Pharmacy, MS, 38677 , USA

Ayurveda is a major traditional system of Indian medicine that is still being successfully used in many countries. Recapitulation and adaptation of the older science to modern drug discovery processes can bring renewed interest to the pharmaceutical world and offer unique therapeutic solutions for a wide range of human disorders. Eventhough time-tested evidences vouch immense therapeutic benefits for ayurvedic herbs and formulations, several important issues are required to be resolved for successful imple-mentation of ayurvedic principles to present drug discovery methodologies. Additionally, clinical examination in the extent of efficacy, safety and drug interactions of newly developed ayurvedic drugs and formulations are required to be carefully evaluated. Ayurvedic experts suggest a reverse-pharmacology approach focusing on the potential targets for which ayurvedic herbs and herbal products could bring tremendous leads to ayurvedic drug discovery. Although several novel leads and drug molecules have already been discovered from ayurvedic medicinal herbs, further scientific explorations in this arena along with customization of present technologies to ayurvedic drug manufacturing principles would greatly facilitate a standardized ayurvedic drug discovery.

Keywords: Ayurveda , ayurvedic discovery , ayurvedic leads , drug discovery , medicinal plants , traditional medicine

Expert Opin. Drug Discov. (2007) 2(12):1631-1652

1. Introduction

Ayurveda is a traditional Indian system of medicine that includes medical practices and beliefs as it relates to the prevention and treatment of diseases, health, well-being and spiritual healing, in which all have evolved as a part of the indigenous culture. ayurvedic medicinal products are time-tested over centuries and together with recent extensive research on the medicinal chemistry, pharma-cology and clinical aspects of many of these herbal products, their beneficial properties are continuously proving to be useful [1] . The components used in ayurvedic medicine provide an attractive basis for the development of novel pharmaceutical products that can either act as active single-molecule medications by themselves or as components of multimodel (combination of western and ayurvedic medicines) therapeutic regimens [1] . The ultimate objective in drug discovery is to manufacture safe and effective remedies, especially with the immense solutions already put forth by the traditional Indian (ayurvedic, sidhha, unani) and Chinese medicines drug discovery from herbalplant products always remained a compelling approach [2] . Ayurvedic plants or its proven herbal formulations could platform a foundation step for standard drug discovery methodologies with close guidance from ayurvedic principles. Indeed, pharma-ceutical companies in many countries, including those in developed countries, are finding it promising to adopt strategies for therapeutic channels from what have been long known as merely traditional remedies [3] . Ayurvedic drug discovery cannot only offer renewal interest to the pharmaceutical world [101] , but also benefits to patients by bringing closer-to-nature (by virtue of its source-material) and

Ayurvedic drug discovery

1632 Expert Opin. Drug Discov. (2007) 2(12)

cheaper (by cutting down the conventional drug-manufacturing costs) forms of therapy. Although the potential benefits envisaged from ayurvedic drug discovery are numerous, the radical changes required for implementing them into pre-existing standardized approaches of drug discovery pose immense challenges [4] .

2. Modern drug discovery versus ayurvedic products-based drug discovery

Drug discovery involves multi-disciplinary research efforts to identify active molecules with desirable biological effects. Major steps in drug discovery include synthesis, identification, screening and assaying of chemical compounds. Drug development also demands a multi-disciplinary approach, but with a focused track to develop a single drug molecule. It involves testing the lead molecules identified in drug discovery processes against precisely defined target molecule(s). Through a range of preclinical and clinical trials, drug compounds are eventually evaluated for their therapeutic utilities against specific diseases in humans [5] .

The present trend in the drug discovery methodology has gotten its roots or origin from simple resources, such as plant and mineral sources, as well as from many accidental discoveries. Although innumerable examples of such successful drug compounds can be readily identifiable (e.g., paclitaxel, statins, quinine, vinblastine), the sustained enthusiasm on the use of herbal-based resources for newer drug discovery has only gotten dampened lately (since the early 1980s) [6,7] . This is because of several reasons that accompany the pace and focus of modern technological advancements in drug discovery, the streamlined screening processes of compound libraries, the molecular understanding on disease processes and desirability for target-specific therapeutic solutions [8] . Without doubt, scientific milestones, such as the human genome sequencing and ultra-high-throughput screening, have revolutionized present-day drug discovery methodologies [9-11] . However, despite these advents and transformations in drug discovery, it becomes important to note that new drug discovery continues to act as a challenge and successful outcomes occur only at a very slow rate (10 years per drug on average) with extreme use of man-hours and funding (a few billion US dollars per drug) [12] . Newer diseases emerge all the time and existing diseases (such as cancer, AIDS, diabetes etc.) still pose life-threatening dangers. In the light of all of these situations, considering alternative forms of medicines, especially from those scientific roots that are the initial basis of todays modern drug discovery and matured independently into valuable medical disciplines by themselves, should prove to be highly beneficial. Recent understanding on the human genome and the structural characterization of human proteins are beginning to offer clearer views by which diverse chemical structures in plant products are acting on precise biological targets [13] . Reinforcing further active efforts on alternate

medical utilities, especially by researching on the extent of effectiveness and safety of their medicinal products [14] , could offer newer and extremely valuable directions to drug leads. Although some pharmaceutical companies have already marched significant strides from traditional medicinal products, complete recapitulation of the older sciences like Ayurveda in accordance to modern drug standards are difficult, if not impossible. Nevertheless, continued and renewed enthusiasm on traditional medical resources is anticipated to bring more unique and successful remedies in the near future.

3. Ayurvedic drug discovery: essential considerations and requirements

Standardized ayurvedic drug discovery process necessitates the consideration of several factors, which can be broadly grouped under two major categories. First, it demands incorporation of alternative steps in addition to present drug development processes to establish a more versatile ayurvedic-library screen [102] rather than a limiting chemical-library screen. The prospects of this wide-screening approach could be numerous, but essentially allow the characterization of extremely diverse chemical compounds to successfully identify druggable ayurvedic leads with defined biochemical specificities [7] . Also, it has recently been reported that natural products-based extract libraries, as opposed to existing chemical libraries, comprise predominantly (> 90%) compounds whose structure follows Lipinskis rule-of-five properties [15] , which are ideal for oral administrations. Such chemical characteristics can only be found in drug molecules that have already made their entry to the market [7] . Second, ayurvedic drug discovery mandates the inclusion of existing knowledge on ayurvedic medicines and the blending of known principles of ayurvedic science with modern drug development technologies for more successful investigational drugs. Based on these requirements, ayurvedic practitioners and researchers have recently proposed many effective, yet feasible, methods that could facilitate detailed experimenta-tion on ayurvedic herbs and products for eventual imple-mentation of standardized ayurvedic drug discovery methodologies [1,16,17] . In this review, a broad outline on the scientific aspects and resources available on ayurvedic medicine, and its pertinence to present and potential future drug development strategies, along with the major scientific challenges to be faced, are discussed. Mechanistic aspects on ayurvedic plant actions and biochemical evidences on ayurvedic formulations, reviewed in other recent articles [1,2,18] , are excluded.

4. Ayurvedic medicine: what it can offer?

The ayurvedic system of medicine in India dates back to 3000 BC and prescribes remedies for a wide range of disorders, diseases and conditions [17] . Ayurvedic classic

Balachandran & Govindarajan

Expert Opin. Drug Discov. (2007) 2(12) 1633

texts, Charak Samhita and Sushrut Samhita , describe > 700 medicinal plants [1] of therapeutic value against both infectious and non-infectious disease conditions. These herbs are categorized based on their appearance, taste, digestive effects, safety, efficacy, dosage and therapeutic benefits [7] . In India, 3000 plants of proven medicinal value are found [19] , and > 6000 plants are known to be used in traditional, folk and herbal medicines [19] . An overwhelming number of pharmaceuticals companies in India (a total of 7000) manufacture Ayurvedic medicines along with two other tradi-tional forms of medicines, the siddha medicines (revitalizing and rejuvenating form of medicine developed by ancient sages [Siddhars] for subsequent future generations) and the unani medicines (a system of medicine based on the balance of the elements in the body that originated 980 AD in Persia, but was popularized in India) [20] . These indigenous medical practices continue to prove beneficial for millions of people in India, Sri Lanka and Nepal, despite the significant prevalence and accessibility of western medicine. The impor-tance of ayurvedic medicine is not only reflected in its successful influence on other traditional systems. such as unani, Chinese and Tibetan medicine, but also its present modern applications in Pakistan, Bangladesh, China and Tibet. Traditional plant medications are estimated to fulfill nearly three quarters of all the medicinal needs of the people in developing countries [19] , and some form of other alternative medicines are used for therapeutic, food-additive and cosmetic benefits by millions in developed countries. In spite of these proven track records of traditional medicines, a statistical analysis indicates only a poor representation of its value in the global market and its commonly held perception of unconventionality compared with modern medicines [21] .

5. Ayurvedic literature

Ayurveda offers extensive information about the herbal drug products and their therapeutic uses. The ayurvedic know-ledge has been spread over 100 books containing > 100,000 recipes documented by ayurvedic physicians and scholars. Besides these major resources (described later), there exist a even larger number of recipes that are being used on a daily basis, but are unpublished. Although the documented ayurvedic knowledge chiefly assists ayurvedic practitioners, by virtue of its utility they can also be used as a resource for scientific research and drug discovery processes. Some of the most commonly used reference materials for ayurvedic drugs and products are given in this section.

The ayurvedic formulary of India , published by the government of India, contains a total of 636 compound formula tions with the volume I containing 444 formula-tions, the volume II containing 192 formulations and the volume III containing 192 formulations [103] . Ayurvedic formulae and preparations include aqueous liquids, oils, powders, tablets, pills and others ( Asava , arishta , ark, avaleh ,

kvath , curn , guggulu , grita , taila , dravak , kshara , lepa , vati , gutika , rasayana , parpati , bhasma , mandura , rasa yoga and lauha ). It also includes 27 single drugs of animal origin, 42 single drugs of mineral origin, 271 single drugs of plant origin accompanied with disease indication indices [104] .

The ayurvedic pharmacopeia of India includes in-depth details on 326 ayurvedic plants, such as botanical names and identification criteria, standard measures for various parts of the plants, physical tests and determinations, quan-titative data for vegetable drugs, limits for chlorides, sulfates, sulfated ash, arsenic, mercury, iron, lead and other heavy metals present in the drugs with complete official testing methodologies [104] . A total of three volumes of ayurvedic pharmacopeia have been published by the Indian govern-ment, with a total of 258 monographs. A total of 80 monographs were published in the volume I, 78 mono-graphs in the volume II and 100 monographs in the volume III. The work on remaining single drugs of plant, animal, mineral/metal and marine origin and multi-ingredients formulations is presently being carried out in 30 different ayurvedic and other scientific research institutions [103] .

The Materia Medica of Ayurveda consists of an extremely rich armamentarium of natural drugs, derived from the plants, minerals, animals and marine sources. These drugs are used as monotherapies or in simple combinations, which are otherwise referred to as polypharmaceuticals. The forms in which these are used are varied, such as extracted juices, decoctions, infusions, distillates, powders, tablets, pills, confections, syrups, fermented liquids, medicated oil, bhasmas (resultant of incineration) and many more. The Materia Medica of Ayurveda is an exhaustive publication that describes simple, safe and proven remedies including remedies for common ailments [103] .

The Treatise on Indian medicinal plants , edited by A Chatterjee and SC Pakrashi (1991), is a five volume treatise with each volume containing 180 325 pages. These books contain > 800 medicinal plants. It also served as a search engine for many scientific studies and clinical trials conducted on ayurvedic therapies during the last five decades [104] . A recent book on the scientific basis of ayurvedic therapies, edited by LC Mishra, also summarizes many of these findings [22] .

The Compendium of Indian medicinal plants , edited by R Rastogi and BN Mehrotra, is a total of five volumes published so far with 518 1016 pages per volume [103] .

The Indian herbal pharmacopeia (2002) contains 52 monographs on widely used medicinal plants in India with scientific evidences on therapeutic effects.

In addition, the Pharmacopeia of India (1996) covers additional botanical monographs on clove, guggul, opium, mentha, senna and ashwagantha. Several other lifetime works of many eminent pharmacologists could be found in different ayurvedic and natural product-based scientific institutions of India. For example, the experimental



pharmacology research works on indigenous drugs of India conducted by Sir RN Chopra (considered as the father of Indian pharmacology) can be found at the Regional Research Laboratory (RRL), Jammu-Tawi [17] .

6. Recent developments in ayurvedic medicine

Ayusoft (2004 ) is a recently developed, interactive software that chiefly assists ayurvedic practitioners. It contains several databases on various ayurvedic drugs along with the network of diet patterns, lifestyles, diseases and treatment principles. This software acts as a quick reference guide or index for practitioners to aid in the diagnostic and treatment aspects. The software is based on the prakruthi (ayurvedic disease diagnosis) section of the ayurvedic texts [105] .

Ayugenomics [23] is a body of literature aimed at understanding the ayurvedic concepts of Prakruthi from a pharmacogenomics perspective. It offers a basis for inter-individual variations in diagnosis, drug efficacy and toxicity, hence the development of customized therapeutic approaches.

Herboprint [24] uses three-dimentional HPLC and attempts to develop tools for activity-based standardization of botanicals.

7. Development of new therapeutic compounds from medicinal plants of Ayurveda

The phytochemical analytical studies of ayurvedic medicinal plants is an area of thrust and significant investigation as it offers a direct path for the emergence of newer therapeutic agents. Furthermore, when the structures of the active principles are identified, it provides a platform for synthetic and medicinal chemists to alter the efficacy or toxicity properties or even create analogs with similar or varied phar-macological actions. So far, among a list of frequently used ayurvedic medicinal plants, 43% of it has undergone human clinical trials studies and 62% of it has been subjected to animal studies [25] . Ayurvedic drugs, such as guggul , brahmi , ashwangantha , amlaki , guduchi , kutki , shatavari and shunthi , have also shown clinical promises for therapeutic usage [25] . In relevance to future ayurvedic drug discovery, one could categorize ayurvedic plants as follows:

Those on which suffi cient leads are available and their biological targets are known. Some well-known ayurvedic leads and their molecular targets for cancer therapy are discussed in detail in a recent review by Aggarwal et al. [18] and a summary of ayurvedic plants and their biological targets are listed in Table 1 .

Those with proven medicinal value and with considerable availability of scientifi c evidences ( Table 2 and 3 ).

Those with signifi cant potentials to offer novel drugs, but for which substantial experimentation needs to be performed (see Section 12).

8. Mechanism of action of ayurvedic drug compounds

Ayurvedic system of medicine is founded on the principle that disease occurs due to the derangement of the functional vital energies in the body ( vata [air + ether] or the kinetic energy; pitta [fire] or the thermal energy and kapha [earth + water] or the potential energy), as well as the loss of mutual coordination between them. ayurvedic drugs are formulated to rejuvenate the deranged state to a healthy state so to restore the harmony between body and nature. The extreme chemical diversity of compounds in ayurvedic drug formulations simultaneously targets most systems of the body, resulting in an array of potent and diverse biochemical outcomes. Many scientific studies corroborate ayurvedic principles and the basis for ayurvedic drug action have been extensively reviewed recently [18,22,26,27] . Based on the scientific literature published so far, it also becomes evident that some of the components used in ayurvedic formula-tions or multi-herb extracts do not possess major biological activities by themselves, but instead act as potenti ators or moderators of the efficacy and toxicity effects of the major active principles. For example, non-therapeutic components, such as milk and ghee, are added to Semecarpus anacardium formulations to moderate its hot, acrid and dry nature [28,106] . Similarly in amalaki ( Emblica officinalis )-based rejuvenators, such as chyavnan prasha avaleha , although amalaki is the main ingredient, the formulation contains > 25 herbs that are added for synergistic and counter-balancing effects. In addition to that, a sweetener, such as raw sugar or honey that has no biological activity, has been added to moderate its pungent taste. The herbs in this preparation insure that the sweet is properly digested and cause no adverse reaction [107] . Triphala , another ayurvedic formulation, is a combination of amla ( Emblica officinalis ), bibhitaki ( Terminalia belerica ) and haritaki ( T. chebula ), in which all these three herbs act synergistically as laxative and helps digestion [108] . Thus, multi-ingredient herbal compounds in ayurvedic sciences are rendered both effective and safe in treating human ailments. Although these principles have been shown to successfully offer prevention and treatment of many diseases, it also reminds the confounding issues of new drug discovery from ayurvedic herbs (standardization and precise utilization of various herbal components in the generation of active drug formulations) [14] .

9. Reverse pharmacology: a road to ayurvedic drug discovery

Although conventional drug discovery starts with lead identification and optimization followed by in vivo pre clinical studies (Phase I) and human clinical trials (Phase II and Phase III), ayurvedic drug discovery was recently proposed [29] to preferably work in a reverse pharmacology direction with stages described in Figure 1 .



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se.



The advocation of reverse pharmacology in ayurvedic sciences was initiated by eminent vaidyas , including Mahamahopadhyaya Gananath Sen [17] , and since then has evolved as a powerful scientific approach for newer drug discovery. The reverse pharmacology approach is described by Ashok DB Vaidya as a newer academic discipline that integrates documented clinical and experimental hits with leads by trans-disciplinary exploratory studies. The further development of leads into drug candidates is triggered by experimental and clinical research. Thus, ayurvedic drug discovery follows a retrogressive path based on clinical observations noted with herbal products.

The Indian Council of Scientific and Industrial Research (CSIR) and the Indian Council for Medical Research (ICMR) have successfully conducted many clinical trials

based on reverse-pharmacology and their respective directors have detailed the prospects of this approach in national and international forums [109] for future drug discoveries. Some of the plants that have been successfully analyzed by this approach include Mucuna pruriens for Parkinsons disease, Zingiber officinale for nausea/vomiting, Picrorhiza kurroa for hepatitis, Curcuma longa for oral cancer, Panchavalkal spp. for burns and wounds and Azadirachta indica for malaria.

10. Ayurvedic drug discovery: possible present and future directions

Recent trends indicate that ayurvedic drug discovery and therapeutics can take several possible reverse-pharmacology

Table 2 . List of Ayurvedic botanicals with potential for drug discovery [103] .

Botanical name Ayurvedic/ Common Name

Disease conditions

Acorus calamus Vacha Obesity, hypertension, speech disorders, sedative, transquilizer, mental distress

Adhatoda zeylanica Vasa Bronchiolar constriction

Anethum sowa Soya Appetiser, carminative

Asparagus racemosus Shatavari Aphrodisiac, dysuria, galactogogue, leucorrohea, peptie ulcer

Azadirachta indica Nimba Gastritis, bleeding piles, wounds, fumigative, disinfectant againstbacterial and viral infections

Berberis aristata Daruharidra Liver disorders, conjuctivitis, dysentery, anti-pyretic, antiperidoic, diaphoretic

Boerhaavia diffusa Punarnava Eye diseases, diabetes, anti-diuretic, hepatoprotective, infl ammation

Crataeva nurvala Varuna Erysipelas, lymphadenopathy, urolithiasis

Cassia augustifolia Rechani, markhandi Severe constipation

Centella asiatica Mandukparni Neurological problems

Commiphora wightii Balsamodendron mukul Arthritis

Emblica offi cinalis Amalaki (Amla) Anaemia, jaundice, haemorrhage, acidity, immune stimulant

Eugenia jambolana Jamboo Diabetes

Ferula foetida Hingu (Heeng) Septic conditions, digestive stimulant, expectorant, carminative

Mallotus philippinensis Kampillak (Kamila) Anthelminthic, aphrodisiac

Moringa oleifera Shigru (Sehanjana) Abcess, septic conditions, wound healing, piles, infl ammation, neuritis, joint diseases

Myristica fragrans Jaiphal Nausea and vomiting, diarrhea, leucorrhoea

Nelumbo nucifera Kamal beej/Kamal Gatta Hypoglycemic

Piper longum (root) Pippalimool Malaria, insomnia, worms, piles

Phyllanthus emblica amla Anti-ageing

Psoralea corylifolia Bakuchi Vitiligo, bronchial asthma

Saraca asoca Ashok Meno-metrorrhagia, neurological disorders, spasmogenic, uterine infections

Terminalia arjuna Arjun Cardiac disorders

Terminalia chebula Haritaki (harad) Laxative

Trachyspermum ammi Yavani Anthelminthic, spasmogenic carminative

Tribulus terrestris Goksura (Gokkru) Diuretic, aphrodisiac, lithontriptic



Table 3 . Classifi cation of botanicals according to their effi cacy towards various diseases.

Health disorders Botanicals with scientifi c evidence

Allergies [52] Cleodendrum seratum, Benincasa hispida, Aquilaria agallocha, Albizzia lebbeck, Curcuma longa, Inula racemosa, Galphimia glauca, Picrorhiza kurroa, Adhatoda vasica

Alzhemiers disease [53] Bacopa monniera, Centella asiatica, Convolvulus pluricaulis, Eugenia caryophyllus, Glycyrrhiza glabra, Hydrocotyl asiatica, Lawsonia inermis, Nardostachys jatamansi, Poenia emodi, Pongamia pinnata, Tinospora cordifolia, Withania somnifera

Antimutagens [54] Terminalia arjuna/chebula/bellerica, Ocimum sanctum, Glycyrrhiza glabra, Semecarpus anacardium, Embilica offi cinalis, Cinnamomum cassia, Withania somnifera, Centella asiatica

Arthritis [55] Vanda roxburghii, Commiphora mukul, Semecarpus anacardium, Crataeva nurvala, Hemidesmus indicus, Andrographis paniculata, Aglaia roxburghiana

Bronchial asthma [56] Picrorrhiza kurroa, Solanum spp, Tylophora indica, Boswellia serrata

Cancer (benign and malignant) [57]

Withania somnifera, Aloe vera, Coleus forskohlii, Andrographis paniculata, Santalum album, Picrorrhiza kurroa, Semecarpus anacardium, Ocimum sanctum, Calotrophis procera, Plumbago rosea, Nigella sativa, Embilica offi cinalis

Colon diseases [58] Zingiber offi cinale, Acorus calamus, Aegle marmelos, Withania somnifera, Bacopa monniera

Constipation [59] Aloe vera, Plantago ovata, Cassia senna, Rheum offi cinale, Prunus persica, Terminalia chebula, Cassia fi stula, Mallotus philippinensis, Ricinus communis

Dermatophytes [60] Cassia tora, Hydnocarpus laurifolia, Pongamia pinnata, Argemone mexicana, Ricinus communis, Plumbago zeylanica, Psoralea corylifolia

Diabetes mellitus [61] Momordica charantia, Trigonella foenum, Coccinia indica, Pterocapus marsupium, Ficus bengalensis

Diarrhea and dysentery [62] Holarrhena antidysenterica, Myristica fragrans, Dioscorea oppositifolia, Psidium guajava, Musa paradisiaca, Nelumbo nucifera, Ficus bengalensis, Acorus calamus, Clerodendrum phlomidis, Piper nigrum, Berberis aristata, Punica granatum, Tinospora cordifolia, Calotrophis procera, Valeriana offi cinalis

Emetics [63] Azadirachta indica, Randia dumatorum, Cucumis sativus, Luffa echinata, Embelia ribes, Salix caprea, Toddalia asiatica, Pongamia pinnata

Enema [63] Randia dumatorum, Holarrhena antidysenterica, Saussurea costus, Luffa echinata, Acorus calamus, Aegle marmelose

Epilepsy [64] Withania somnifera, Semecarpus anacardium

Gastroduodenal ulcers [65] Musa sapientum, Bacopa monniera, Eclipta alba, Abies pindrow, Benincasa hispida, Centella asiatica, Convolvulus pluricaulis, Pongamia pinnata, Garcinia indica, Zingiber offi cinale, Asparagus racemosus, Aegle marmelos

Gynecological disorders [66] Saraca indica, Aloe vera, Glycyrrhiza glabra, Curcuma longa, Nardostachys jatamansi, Zingiber offi cinale, Commiphora mukul, Withania somnifera, Tinospora cordifolia, Asparagus racemosus

Heart diseases [67] Terminalia arjuna, Aloe vera, Coleus forskohlii, Inula racemosa, Andrographis paniculata, Centella asiatica, Piper longum, Picrorhiza kurroa, Commiphora mukul

Hepatic disorders [68] Andrographis paniculata, Annona atemoya, Boerhavia diffusa, Eclipta alba, Terminalia chebula, Semecarpus anacardium, Phyllanthus niruri/amarus, Picrorrhiza kurroa, Podophyllum hexandrum, Tinospora cordifolia

Thyroid dysfunction (hyperthyrodism) [69]

Azadirachta indica, Momordica charantia, Convolvulus pluricaulis, Emblica offi cinalis, Ocimum sanctum, Piper betel, Rauwolfi a serpentina, Trigonella foenum, Moringa oleifera, Lithospermum offi cinale, Lithospermum ruderale, Allium sativum, Nelumbo nucifera, Aloe vera, Aegle marmelos

Thyroid dysfunction (hypothyroidism) [69]

Bauhinia variegata, Echhornia crassipes, Bauhinia purpurea, Commiphora mukul, Withania somnifera, Achyranthes aspera, Saussurea lappa

Hyperacidity [70] Embilica offi cinalis, Glycyrrhiza glabra, Asparagus racemosus, Eclipta alba, Trichosanthes dioica, Adhatoda vasica, Cocos nucifera

Immune modulation [71] Terminalia chebula, Embilica offi cinalis, Piper longum, Gycyrrhiza glabra, Allium sativum, Commiphora mukul, Tinospora cordifolia, Withania sominifera, Aloe vera

Indigestion [72] Zingiber offi cinale, Foeniculum vulgare, Curcuma longa, Mentha piperita



tracks, with overlapping steps with each other. The following are three major tracks that are anticipated to progress at an increased pace in the near future.

i) New drug discovery, or more particularly widespread use of known ayurvedic drugs, could result as a natural direction when ayurvedic medications with proven abilities are further subjected to well-designed and analyzed human clinical trials. In this approach, ayurvedic formulations per se are scrutinized for the extent of efficacy and toxicity using precise biological and clinical end point assays, critical drug interactions and inter-individual variability measures.

This method is quite feasible in countries where ayurvedic medicines are commonly practiced and where there is a drive for more use of natural medicines in place of conven-tional medicines that are either less effective or ineffective for a given problem. Such an approach would also be ideal for promising ayurvedic formulations that are not amenable for standardized in vitro biological assays (e.g., cell culture-based) and other laboratory-based exploratory studies. However, whenever the use of in vivo methodologies (such as whole-animal studies) that have traditionally been used to test ayurvedic products are possible, they should be

Table 3 . Classifi cation of botanicals according to their effi cacy towards various diseases (continued).

Health disorders Botanicals with scientifi c evidence

Male reproductive disorders [73] Asparagus racemosus, Cynomorium coccineum, Mucuna pruriens, Piper longum, Tribulus terrestris, Trichopus zeylanicus, Vanda tessellata, Withania somnifera, Zingiber offi cinale

Obesity [74] Commiphora mukul, Terminalia chebula, Terminalia belerica, Embilica offi cinalis, Picrorrhiza kurroa, Curcuma longa, Plantago ovata

Parkinsons disease [75] Withania somnifera, Bacopa monniera, Centella asiatica, Sida cordifolia, Mucuna pruriens

Psychiatric disorders [76] Withania somnifera, Ocimum sanctum, Bacopa monniera, Convolvulus pluricaulis, Centella asiatica

Purgatives [63] Picrorrhiza kurroa, Ricinus communis, Terminalia chebula, Terminalia belerica, Embilica offi cinalis, Euphorbia neriifolia, Indigofera tinctoria, Cassia fi stula

Sciatica [77] Commiphora mukul, Vitex negundo, Ricinus communis, Pluchea lanceolata, Sida cordifolia, Tinospora cordifolia

Urolithiasis [78] Crateva nurvala, Tribulus terrestris, Bergenea ligulata

Exploratory stageTolerability studies

Doseresponse studiesDruginteraction studies

In vitro and In vivo assaysfor Safety and Efficacy

Experimental stageMolecular targets

Signaling pathwaysReceptor pathways

Structure elucidation andCrystallization of drug-target

complexes

Experiential stageDiagnosis

DocumentationFollow-up

Clinical observations

Figure 1 . Reverse pharmacology approach for ayurvedic drug discovery. Reverse pharmacology concept adapted from Patwardhan et al. (2004) [1] and Vaidya (2002) [29] .



OH

HO

HO

O

OH

Gallic acid

VascineS

SO

Allicin

N

NOH

SO

O

OH

OH

OHH

S E

RS S R

R

Andrographolide

O

O

OHHO OH

OHO

O

OH

Bacoside AO OH

H

H

HHO

S

SRR

RRRRR

RR

Boswellic acid

O

O

H H

H S

R RS S

Z

Guggulosterone

O O

OHO

OOH

E E

Curcumin

OHO

Eugenol

O

OO

O

OHH H

HOH

HO O

OHH

O

OH

OH

OH

HO O

OH R R

R

RRRR

S SS

S SS S

SS

SS

S

Glycyrrhizin

HO

HO

OH

O

NH2

S

L-dopa

O

O

O

OOH

OHHO

HO

Ellagic acid

NO

OO

E E

Piperine

OO

OO

OHHO OH

H

O

OHH

H

O

OHE

R

R

RS S

S

SSS S

S

Kutkoside

NH

NOH

H

H

OO

OO

O

OO

OS

SS

R

R

R

Reserpine

OH

HO

OH

E

Reservatol

O

HOH

OS

SS R

Tinocordifolin

O O

O

H

H

O O

H

H

H

S

SSSS

S

R

R

R

Withaferin A 8-Gingerol

HOO

O OH

4S

6-Gingerol

HOO

O OH

6S

Figure 2 . Structures of Ayurvedic leads.



adequately used to validate ayurvedic products before escalating to human clinical trials.

ii) Ayurvedic medications per se are subjected to a higher level of (more rigorous analysis than the previous) scientific exploratory studies comprising both in vitro / ex vivo components (metabolic and activity evaluation assays) and in vivo (preclinical and clinical) components. Heterogeneous crude extracts containing a mixture of compounds (2 100 compounds) are subjected to biological activity-based (e.g., whole animal model testing for response elicitations) or assay-based screening (e.g., antimicrobial challenge studies) and fractionation methods. These response-based studies narrows down complex mixtures to single-molecule or fewer-combination (2 10 compounds) mixtures. The subsequent validation of these refined prepa-rations for efficacy and toxicity studies by human clinical trials for the diseases originally targeted by the ayurvedic formulations should be conducted. Identification and isolation procedures in this approach would probably involve several rounds of chemical purification as well as synthesis measures to scale-up drug compounds. Approximately, lower milligram (1 10 mg) levels of active compounds are required for bio-assaying and at least a few grams (1 10 g) of pure or semipure compounds are required for lead identification [30] . Such an approach is suitable for both proven and potential forms of Ayurveda therapeutic formulations and can be conducted at any place where the quantity and quality of the authentic ayurvedic drug products is not a problem. Difficulties in this approach could arise when more than one compound at varying orders of concentration is responsible for a desired biological or a therapeutic response, which is many a time the case with ayurvedic herbs. In that case, even extensive end point characterizations (such as K i or IC 50 values for a potential enzyme inhibitor) of many of the active components in a mixture may not sufficiently identify discernible clues for a therapeutically effective few-compound mixture.

iii) The last track is the elementary analysis of ayurvedic herbs (and not ayurvedic products) that are described in ayurvedic texts and pharmacopeias, for identification and isolation of active single-molecule drugs. Being an exhaus-tive venture for identifying active and potent single mole-cules, the procedure becomes quite complex for certain plant compounds that tend to occur as bonded complexes with similarly structured and often inactive compounds. If the molecular profiling of active ingredients is successful, then these catalogued compounds can be subsequently subjected to conventional drug discovery steps. The beginning step, which extensively use combinatorial screening library of compounds from ayurvedic plant extracts is excepted. As mentioned in the previous approach, over coming difficulties posed by the multi-active ingredients that are present at varying orders of concentrations (and contributing to different levels of therapeutic benefits) need to be carefully considered. Even though this approach has

higher probability of identifying single-molecule active compounds from designated ayurvedic herbs (e.g., curcumin in turmeric, guggulosterone from guggul), it also suffers the selective disadvantage of not taking into account the supplemental benefits offered by trace-levels compounds additionally present in those herbal plants (as opposed to original ayurvedic preparations). Such an approach is also feasible in any part of the world provided the resources, infrastructure and methodology are available.

The first two processes are shot-gun approaches to make an extensive use of the known properties on the ayurvedic plants and medications and bring ayurvedic formulations to the market in a relatively shorter period. It encompasses optimistic approaches to find superior ayurvedic formula-tions and drug products among the existing herbal preparations or even to develop new drug compounds. Multi-ingredient mixtures are also gaining significance in the drug discovery field because they yield drug preparations of superior clinical value compared with monotarget drugs. However, in the light of the lack of available data on the successful use of ayurvedic products in different ethnic population, metabolic enzymes involved in detoxifying ingredients and toxicity issues need to be carefully considered. The last approach uses the pharmacognostic sources of ayurvedic drugs for streamlined drug discovery approaches, beginning with the identification of the active compounds from ayurvedic plants. Even though this approach is intensely time consuming, relatively expensive and requires major modifications in the early drug discovery methodologies, it has a higher probability of identifying novel drug molecules or chemical structures for experimentation on directed structural alterations and lead optimizations.

11. Tools and methodologies in ayurvedic drug discovery

The evaluation of ayurvedic herbs (or products) lays out several stages that demand the use of modern analytical tools for compound screening and analysis. The mixture of compounds in multi-ingredient formulations or in ayurvedic plants often requires to be simplified into simple and pure (or semipure) single- or fewer-combination molecules. This is achieved by preparing concentrated ayurvedic plant extracts and fractionating and purifying them into sufficient quantities for assaying purposes. Recent high-resolution separation technologies, such as HPLC and tandem mass spectrometry have indeed revolutionized compound separation and fractionation procedures in a relatively time-conserving manner. The HPLC effluents can be directly ionized (electrospray ionization or atmospheric pressure ionization) and can be further analyzed by mass spectrometry techniques [31] (e.g., Fourier transform ion cyclotron resonance mass spectrometry) for a precise determination of molecular masses and other relevant compound parameters. On the other hand, high-resolution NMR spectroscopy



analysis could greatly facilitate analysis or even could help the elucidation of the structure of novel ayurvedic compounds. An array of sophisticated analytical techniques [32] (e.g., ultra-pressure liquid chromatography, supercritical fluid chromatography, capillary electrophoresis), combinatorial techniques (e.g., high-resolution mass spectroscopy with two-dimensional NMR) and high-throughput online assays (continuous-flow enzymatic analysis) that are presently used in conventional drug discovery processes can also be customized for ayurvedic drug discovery processes. Although these modern instruments will surely facilitate the chemical analysis of ayurvedic compounds at an incredibly rapid pace and with lower amounts (nanogram or lower microgram levels of pure compounds), chemical derivatizations guided by structureactivity relationships and traditional medicinal chemistry approaches can also be used wherever scaling-up becomes a factor. For compounds exhibiting absolute difficulties for the purification from ayurvedic plant matrices, circumventing measures could be taken to assay and market them as fractionated or semipurified complexes.

12. Selection criteria for herbs and herbal preparations

One of the major points, which often also becomes an issue that has to be carefully considered in ayurvedic drug discovery, is the nature of the source materials. The selection of potential herbal leads would essentially depend on several selection criteria. These include relevance to disease preva-lence and thrust areas of present research where therapeutic alternatives are not available, easy availability of ingredients and raw materials, necessity for single- or multi-ingredient formulations, modes of compound extractions and purifica-tions, desirability for wide-spectrum benefits within a range of disorders, innovativeness in the material used, shelf-life required for the newer ayurvedic formulations, extent of efficacy and toxic side effects, scope for commercial-ization and availability of previous preclinical and clinical data [110] on those ayurvedic compounds. Additional factors that have to be considered in ayurvedic drug discovery, but not necessarily in conventional drug discovery processes, are the use of appropriate plant parts (e.g., leaves, barks, dried roots), the preparatory forms (powders, enriched extracts, tender shoot extracts etc.) and the processing methods and durations (shade-dried leaves, freshly harvested seed-pods etc.).

Several workshops and conferences are now conducted in different parts of India for an active implementation of research and clinical validations of ayurvedic plants described in ayurvedic texts. A recently held National Innovative Foundation workshop on ayurvedic drugs (2004) has concluded that the selective herbs listed in Table 4 should be used for various disease conditions [110] . In concurrence to that, several Indian scientific research institutes have agreed to conduct clinical trials on these medicinal plants.

13. Major challenges in ayurvedic drug discovery

Ayurvedic drug discovery beginning with elementary analysis of ayurvedic plants is one of the main approaches that have received significant attention so far in new drug discovery. Even with this approach, the time consumed from compound analysis and cataloging of ingredients to manufacturing final drug products is enormous. Many a time, enthusiasm in this approach weakens when the multi-component beneficial activity of herbal medicines can-not be closely or even nearly reproduced by single-molecule or fewer-combination drugs. Compared with this approach, other proposed approaches for developing modern medica-tions from ayurvedic formulations lag behind even in terms of clinical initiatives. Much of this is because of the inherent technical difficulties in understanding and implementing the ayurvedic theories to present drug manufacturing and drug delivery practices. The lack of expertise to develop and produce these formulations on a large scale basis and successful fitting of available ayurvedic resources to present high-through screening methodologies, creates additional hindrances [33] . In addition, difficulties in conducting the pharmacokinetic, pharmacodynamic and bioequivalence studies with specialized ayurvedic formulations also signifi-cantly retard new drug discovery ideas. Moreover, the lack of precise pharmacological end points of multi-ingredient formulations and massive interferences by fluorescent and light-scattering compounds in ayurvedic formulations, bring daunting difficulties in assay developments. Furthermore, the lack of characterized animal models for preclinical examination of ayurvedic formulations poses a new type of challenges. One other general limitation is the failure of ayurvedic disease descriptions and treatment modalities to comply with perfect curative paths in the present days scenarios. This is because of differences in the disease forms described in ayurvedic texts as opposed to the present-world disease presentations. The complexities in understanding the older nomenclatures, disease descriptions, and their correla-tion to modern disease symptoms and courses also pose inconveniences. The changes in the properties of the medicinal plants due to alterations in soil conditions, climatic factors and other environmental reasons over time also complicate the ayurvedic drug discovery issues. Studies on the Saraca asoca plant, which was broadly described in ayurvedic texts as an effective herb for menorrhagia and other uterine problems, had only shown to be therapeuti-cally effective against ovulatory dysfunctional uterine bleeding in recent clinical trials and not for other types of uterine dysfunctions [34,35] . Although the multiple factors described above could very well contribute to such inaccuracies, finely tuned recharacterizations of the ayurvedic plants for precise therapeutic effects and outcome become a major necessity.

Although the above-mentioned factors definitely create hurdles in handling the ayurvedic sources for drug discovery,



Table 4 . Selective herbs that should be used for various disease conditions, as concluded by the Indian National Innovative Foundation workshop on ayurvedic drugs (2004) [110].

Disease/disorder Medicinal plant

Gastrointestinal and hepatic diseases and disorders

Peptic ulcer

Hyperacidity Constipation

Murraya koenigi (leaf) Aristolocehia bracteata Ricinus communis Aeglemarmelos + Cynodon dactylon + Eclipta alba

Diarrhoea

Liver damage Jaundice

Abutilon indicum Asparagus racemosus + rice grain Solanum tilobatum Zingiber offi cinale Cassia sophora Justicia gendurussa Cascaria esculenta + Phyllanthus fraternus Citrus limon + Ervattamia heyneana Pergularia daemia + rice grain Coccinia indica Gymnosporia spinosa

Dermal problems (including burn injury, sepsis, eczema, herpes infection and leucoderma)

Heritiera littoralis Ervattamia heyneana Azadirachta indica Maytenus emarginatus Piper betel Euphorbia hirta + Madhuca indica Aneilema nudifl ora + Aquilaria agallocha + Citrus limon Lawsonia inermis + Santalum album Azadirachta indica Cyclea peltata+ Cocos nucifera Allium sativum + Musa sp. + Nicotiana sp. Andrographis alata Semecarpus anacardium + Ricinus communis Vernonia cineria

Diabetes Holarrhena pubescens Ficus racemosa + Prosopis julifl ora + Sapindus laurifoius + Bougainvillea spectabilis Ficus glomerata Aristolochia bracteata

Odema and urinary infections Oedema of legs Urinary infection

Daemia extensa Dracena ternifl ora

Miscarriages and infertility Abortion prevention

Frequent miscarriage

Citrus limon + Ixora nigricans Aegle marmelos + Putranjiva roxburghi Aristolochia bracteata

Respiratory disorders and miscellaneous diseases

Cough

Cough and asthma

Cuminum cyminum + Piper nigrum + Zingiber offi cinale Allium sativum + Cissus quadrangularis + Piper nigrum Adhatoda vasica + Cuminum cyminum + Coriandrum sativum Piper betel + Zingiber offi cinale

Infant cough Asthma

Aegle marmelos + Zingiber offi cinale Allium sativum + Chenopodium album + Cuminum cyminum + Piper longum + Sachharum offi cinarum + Syzygium aromaticum + Zingiber offi cinale Cinnamomum verum + Curcuma longa + Elettaria cardamomum + Syzygium aromaticum + Zingiber offi cinale



none of it necessarily poses a complete technical impasse for ayurvedic drug discovery. However, there are few immediate and practical challenges, viz availability of the ayurvedic source materials, clinical evaluation of efficacy and safety of ayurvedic medicines, problems on ayurvedic drug formula-tions and ayurvedic drugdrug interactions, which would require more serious considerations for ayurvedic drug devel-opment initiatives. These critical issues are discussed at length in the following sections, along with some possible alternatives to overcome such shortcomings.

13.1 Availability of raw materials for an ayurvedic discovery path Any drug discovery process mandates availability of source raw materials that are adequately and qualitatively sufficient to obtain enough active principles both for initial clinical evaluation and for further scaling up processes to meet the market demand. The major source for ayurvedic drug discovery is the medicinal plants described in ayurvedic texts. Clear shortage of required raw materials is one of the major reasons why reverse-pharmacology approaches are less commonly practiced in drug discovery processes. Technical limitations to produce desired amounts of active components even when medicinal plants are adequately available pose another key issue for the ayurvedic pharmaceutical industries. Naturally, this constraint is carried on as a failure to meet required market demand even when the drug product proves to be therapeutically effective in clinical trials. Alternate initiatives that could circumvent inadequacy problems include either synthetic or semisynthetic development of the plant drug compounds [36,37] . Guggul, an antichloesetrol drug isolated from Commiphora mukul , is one of the best examples for such synthetic versions developed in circumventing inadequacy or supply problems [7] .

Although the availability of the resource for some medicinal plants is not a problem, heavy metal contaminations and alterations in ingredients due to other environmental pollutants can make them difficult or unsuitable for drug development [38,39] . Additional issues include segregation of phenotypically identical plants and identification of

differences within a plant type (variability factors within a species) [2] . Recent developments in molecular characteriza-tion studies not only greatly facilitate the understanding of the species and genetic variability in medicinal plants, but also help in dissecting finer plant properties including contraindications and quality-control measures [11] . In this regard, Indian drug manufacturers generally follow the World Health Organization guidelines for identifying heavy-metal and mycotoxin contamination, adulterations in plant products and for processing techniques including harvesting and storage requirements [20] .

Distinct plant breeding strategies for conservation of nearly extinct medicinal plants, large-scale cultivation of medicinal plants for bulk production, understanding of habitats role (climatic, soil and other environmental influence) on the composition and content of medicinal plants, incorporation of modern processing and storage methods and implementing strict quality-control standardization methods are some of the efforts needed to generate quality raw materials from rare ayurvedic plants showing promise for new drug discovery. Cross-breeding and plant biotechnology techniques (genetic transformation, micropropagation tissue culture, cryopreservation) could also diversify the medicinal value of well-studied ayurvedic plants [4] . Selective enrichment of desired plant components or reduction of toxic plant components by genetic engineering techniques should also be practiced for better resource managements.

13.2 Clinical evaluation of effi cacy and safety of ayurvedic medicines The ayurvedic drug formulations are based on medicinal plant extracts and products that have been safely used for thousands of years. For most part, this assures a time-tested selection process for various plant drugs available in the ayurvedic pharmacopeias. However, ayurvedic medicinal preparations (liquid kashayams [aqueous or oily extracts] or powders) often use extremely low concentrations of active ingredients and many of these ingredients have been shown to operate in conjunction (by covalent or

Table 4 . Selective herbs that should be used for various disease conditions, as concluded by the Indian National Innovative Foundation workshop on ayurvedic drugs (2004) [110] (continued).

Disease/disorder Medicinal plant

Bronchial asthma

Dry cough and asthma Bronchitis Ear pain and tooth ache Ear pain

Cold

Acorus calamus + Glycyrrhiza glabra + Sida stipulata + Trigonella foenum-graceum Arum sp. + Piper nigrum + Nigella sativa + Zingiber offi cinale Curcuma longa + Rubia cordifolia + Zingiber offi cinale Pongamia pinnata Azadirachta indica + Hemidesmus indicus + Vitex negundo Acorus calamus + Allium sativum + Azadirachta indica + Ferula asafoetida Ocimum sanctum + Piper nigrum Ocimum sanctum + Zingiber offi cinale



non-covalent bonding) with other natural substances (e.g., tannins, carbohydrates, minerals) in the body. The key goal in ayurveda-based drug discovery is the development of a single-molecule or a fewer-combination drug formulations that faithfully represents the drug actions noticed in tradi-tional multi-ingredient ayurvedic formulations. Although ayurvedic texts mention that multi-ingredient formulation can overcome key therapeutic drug delivery issues, such as low bioavailability, and less potency, it can also pose serious disadvantages including susceptibility to toxicities (hepatotoxicity and nephrotoxicity) and drugbotanical interactions especially in the light of present-day diet, environ ment and lifestyle patterns. Also, the active parent-drug molecules and the metabolites of each of these parent drug compounds complicate the pharmacokinetic understanding of multi-ingredient formulations, which would become easier when single or fewer-combination drug molecules are developed. Sometimes the isolated new compounds may not completely comply with original ayurvedic descriptions and, hence, it might become essential to revalidate their efficacy and safety by in vitro/in vivo studies and clinical evaluations. Although extensive clinical evaluation as used in conventional drug discovery (such as randomized clinical trials) may not be feasible all the time for ayurvedic drug products, a carefully designed case-study process could help addressing if activity and safety are attained within measurable parameters. Case study trials essentially evaluate the traditional uses of a drug in the existing clinical settings and have also been recommended by the NIH and the National Center for Complementary and Alternative Medicine [40] for ayurvedic practitioners. The knowledge available from ayurvedic literature can guide the usual ethical considerations and dose and dosage forms. For all new (single) molecular entities identified from ayurvedic plants, the dose and dosing-regimens are evaluated based on therapeutic concentrations, elimination pathways and pharmacokinetic parameters (bioavailability, clearance, volume of distribution, half-life, plasma-protein binding, AUC). These processes closely follow and parallel conventional drug pipeline assays as well as help to consolidate resources in a manufac-turing unit. In cases and diseases (e.g., cancer) where single-molecule compounds fail to offer adequate therapeu-tic solutions and where ayurvedic theories firmly support multi-drug treatment modalities [26] , further clinical evaluation for potency and toxicity studies could be planned in the presence of one or more secondary active ingredients.

13.3 Problems on ayurvedic drug formulations, dosage and delivery, and their evaluation Ayurvedic formulations are often dispensed in specialized preparations, such as arka (saturated aqueous solutions prepared by distillation), asava (non-boiled fermentation products), arishta (boiled fermentation products), churnams

(fine powders), ghrithams (ghee preparations), lehyams (jaggary syrup preparations), lepam (ointments), panakam (aqueous extracts), thailam (medicated oils), bhasma (incinerated metals or minerals), sinduram (drugs prepared by sublimation) etc . On the contrary, modern drugs require convenient formulations mainly in the form of tablets, capsules, injectables or oral-liquid (syrups) preparations.

A heavy-metal content of ayurvedic medicine has been another hot topic of concern for its consumers, especially after the publication of reference [38] in the Journal of American Medical Association. In ayurveda, there is a class of medicine called rasaushadha (herbo-mineral/metallic formulations) that contains minerals and metals in the form of bhasmas (incinerated metals) in addition to herbs. Ayurveda clearly recognized and established all the symptoms of heavy metal toxicity at least 3000 years ago, and has advocated stringent standards to use the metals therapeutically only after eliminating its toxic effects by processing [111] . Rasa shastra is the section which describes the use of metals, gems, minerals in formulations to treat incurable chronic diseases. These non-herbal ingredients are first purified and then burnt several times and converted into ash ( bhasma) . Some of the metals are burnt up to 100 times to nullify their toxic effects. These ultra-fine particles should be able to float on water, which indicates the non-existence of heavy metals in the preparation. Although modern chemical testing may give positive result for the presence of heavy metals, according to Ayurveda, these metals have been converted to non-toxic form, which is safe for internal use, and it could even not be possible to recover metals from such preparations [41] . These trans-formed forms of metals acts as carriers and catalysts, helping the herbs to reach their desired site of action and also increase their bioavailability. The proper dose and duration of intake of these medicines are extremely important and they should only be prescribed and taken under the guidance of ayurvedic practitioners who are experts in this particular field of medicine [42,112] .

The manufacture of many ayurvedic drugs in tablets or in a capsule forms require fine grounding and processing of crude herbs and its products. Particle sizes alter herbal properties due the physical and chemical alterations in plant compounds that occur during the blending, compression and filling processes. Such dosage forms are not found to be successful for ayurvedic products due to problems encountered by therapeutic efficacy and compliance issues [4] . However, these problems could be largely avoided when single active molecules are developed from ayurvedic plant products. Iwu, in his book Ethno-medicine as drug discovery , discussed the solubility issues in drugs discovery in detail and these issues seem to be fit for ayurvedic drug products as well. Although the active constituents predominantly occur naturally as soluble salts or organic complexes with solubility-enhancing matrices, the extraction processes often lead to the dissociation of these organic compounds from



the water-soluble components, resulting in production of insoluble extractives [43] . Meticulous experimentation or customization of present drug delivery techniques would help in handling some of the first-pass and bioavailability issues with ayurvedic drug products.

13.4 Drugbotanical interactions Plant product-based drug interactions are alarmingly rising in countries where traditional plant medicines act as health-care component (e.g., India and China) as well as in others regions of the world where herbal supplemental drugs are extensively used (e.g., US). The occurrences and reporting on the drugbotanical interaction are also anticipated to reach far more heights in the near future because of the worldwide market for herbal medicine expecting to reach a tune of $26 billion by the year 2011 [113] . Drug interactions often result in pharmacokinetic (e.g., increased clearance or reduced half-life) or pharmacodynamic altera-tions (e.g., increased blood-clotting time or reduced glucose levels) or, more frequently, in some level of both. Drugbotanical interactions mainly occur because of herbal components inducing or inhibiting (or acting as a substrate) the drug-metabolizing cytochrome P450 (CYP) enzymes (e.g., CYP3A4, CYP2D6, CYP2C9) and/or drug-transporting proteins, such as P-glycoprotein, breast cancer resistance protein and organic anion transporting peptides. Although the predominant mechanisms of induction or inhibition are thought to be due to modulation of the levels of the transcription factors, such as pregnane-X-receptor and constitutive androstane receptor that control the mRNA expression levels of these genes, a number of other mecha-nistic possibilities for drug interactions are only yet to be discovered. Although plants products, such as St. Johns Wort extract and grapefruit (or cranberry) juices are exten-sively studied at the moment for their interactions [44,45] , the majority of ayurvedic plant products are not yet completely evaluated for their interaction with other prescription drugs. Some of the well-assessed and available reports on drug interactions with ayurvedic products are summarized in Table 5 . Guggul or guggulipid, an antihyperlipidemic and antiarthritis ayurvedic drug, is reported to interact with azathiopurine, statins and a number of anticancer agents. Laxative herbs (e.g., Aloe ) have been found to cause a serious hypokalemic cardiac effect when co-administered with potassium-lowering drugs. Bitter melon can induce severe hypoglycemic effects when co-administered with other anti-diabetic agents. For some plant compounds, the constituents and the proportions of those constituents, depending on the type and form of plant products administered, largely determine the presence or the extent of the interaction. For example, garlic ( Allium sativum ) is commonly used as dehyd rated garlic powder, garlic oil or aged garlic preparations. Although dehydrated garlic powder contains two main groups of organo-sulfur constituents, that is, S -alkylcysteine (mostly allicin) and -glutamyl- S -alkylcyteines,

the -glutamyl- S -alkylcyteines are completely hydrolyzed to mainly S -allylcysteine and S -1-propenylcysteine with no presence of volatile sulfides in aged garlic preparation. Allicin, the major active component in garlic, is also converted to a concentrate of allylic mono-, di- and tri-sulfides in dispersed oil during steam-distillation process of garlic oil generation. Allicin is also the major ingredient responsible for lowering blood cholesterol levels that possibly inhibits key enzymatic reactions in the cholesterol biosynthetic pathway. Depending on the form of garlic preparation, the extent and magnitude of cholesterol-lowering effects of garlic products would vary distinctly to a measurable extent. Garlic powder and aged garlic are also known to have antithrombolytic activity that may contribute to additional cardiovascular effects. Earlier clinical studies on garlic supplements and HIV-1 protease inhibitors (saquinavir) showed distinct pharmacokinetic alterations and CYP3A involvement [46] , whereas other follow-up studies with different CYP3A substrates (midazolam, alprazolam) did not show any CYP3A-based drug interactions [47,48] . This suggests multiple factors including the form of garlic supple-ments and substrate dependence in interaction with CYP3A might be important in understanding garlic-based drug interaction. Garlic products have also been shown to signifi-cantly decrease CYP2E1 activity [47] , but not CYP2D6 and CYP1A2 activities [48] . Although the content of active components in herbal extracts with respect to both composi-tion and uniformity is a major issue in understanding drugherb interactions, patient compliance and other related issues also creates distinct challenges in managing drugherb interactions. Missing reports or misreports of patients usage of herbal products to their healthcare providers, significant lack of prospective studies available with plant products especially in a disease context (as opposed to studies in healthy volunteers), lack of governmental regulations resulting in large variation in the quality of commercial products and magnitudes of herbdrug interactions as well as inability to extrapolate or predict results from one herbal product to another, still remain prominent issues to address.

14. Ayurvedic drug development in India: government and private sectors

The Indian government agencies, such as the Department of Biotechnology, the Ministry of Health and Family Welfare, ICMR and CSIR, have brought significant initiatives for ayurvedic drug discovery and development. The Department of Biotechnology initiated the network program on bio-prospecting of biological wealth using biotechnological tools and this includes bio-prospecting of molecules and genes for product development. As mentioned earlier, the CSIR and the ICMR have successfully implemented a reverse-pharmacology approach in many of their drug discovery processes. The CSIR has adopted this new path



through the New Millenium Indian Leadership Initiative and this team has a network of 19 CSIR laboratories along with several research and development institutions, as a multi-disciplinary approach. It is aimed at studying and researching various diseases, such as diabetes, arthritis and hepatitis, paving the way for new hits and leads. The government of India has framed good manufacturing practice regulations to improve the standard and quality of manufactured ayurvedic drugs. New rules delineating the essential infrastructure, manpower and quality-control requirements came into force during the year 2000 and reinforced as part of the Drugs and Cosmetics act of 1940 [49] . As a result, ayurvedic medicine-manufacturing firms are obligated to comply with these rules and use only the ingredients from the recommended resource materials. For any type of newer formulations, documented safety and efficacy data are necessitated for further develop-ment as a drug product [50] . An exclusive department called AYUSH was also established by the Indian govern-ment in 1995 to specifically promote the indigenous medicinal system. Prioritized areas include standardization of drugs, enhancement of availability of raw materials, research and development, information communication, education and awareness as well as larger involvement of the national system in delivering healthcare. The Indian government also established several new laboratories exclu-sively for traditional Indian medicine drug testing, and is preesemtly upgrading existing laboratories to test herbal medicines for safety and quality requirements for licensing purposes [50] . To protect the intellectual property rights of ayurvedic drugs, the Ministry of Health and Family

Welfare has also established a traditional-knowledge digital library that will particularly aid in traditional knowledge resource classification (TKRC) [51] . The TKRC is similar to and in accordance with the international patent classification system that acts as a bridge between the ayurvedic knowledge and patent examiners. This would promote accuracies in granting research patents on ayurvedic drug formulations [50] .

Private pharmaceutical companies in India have also immensely renewed their interest in favor of ayurvedic drug discovery and development. Indian pharmaceutical companies, such as Himalaya Drug Company (HDC), Emami, Aswini, Ayur, Dabur India Limited and Cholayil Pharma, have already patented many of their herbal and ayurvedic products both in India and others parts of the world. The ayurvedic products manufactured by HDC are exported to as many as 60 countries all over the world and its herbal laxative preparation has been recently patented in the US. HDCs ayurvedic products are also registered as a pharmaceutical specialty in many countries (e.g., Switzerland). Dabur India Limited, considered as one of the leading Indian pharmaceutical companies, owns about 30 patents in the US alone. It is also one of the only two pharmaceutical companies in the world to introduce Paclitaxel, an anticancer drug. Daburs research foundation also possesses the infrastructure for unique eco-friendly drug extracting and processing procedures from plant resources. Zandu Indian Pharmaceuticals manufactures about 300 health-promoting ayurveda-based products using hundreds of medicinal herbs and herb extracts [114] .

Table 5 . Ayurvedic herbdrug interactions.

Ayurvedic medicine Drugs Symptoms of interactions

Evolvulus alsinoides [79] (Shankhapushpi syrup)

Phenytoin Co-administration reduces anti-epileptic activity and serum levels of phenytoin

Withanolides from Withania somnifera [80] Digoxin assay Falsely lowers digoxin values with MEIA assay

Guggul lipid from Commiphora mukul [115] Aspirin Increase the activity of aspirin leading to bleeding problems

Areca catechu [81] Prednisone and salbutamol Inadequate control of asthma

Allium sativum [82] Warfarin Increased INR

Momoridica charantia [83] Chlorpropamide Less glucosuria

Glycyrrhiza glabra [84] Prednisolone Increase plasma concentrations

Tamarindus indica [85] Aspirin Increase availability of aspirin

Trigonella foenum-graecum (Fenugreek) [86]

Warfarin Increased INR

Camellia sinensis (Green tea) [87] Warfarin Increased INR

Foeniculum vulgare (Fennel) [88] Enalapril Cough suppression

Zingiber offi cinale (Ginger) [89] NSAIDS No effect of NSAIDS

Citrus paradisi (Grapefruit juice) [90] Fluoxedine and trazodone Serotonin syndrome

INR: International normalized ratio; MEIA: Microparticle enzyme immunoassay; NSAID: Nonsteroidal anti-infl ammatory drug.



Despite significant strides in herbal pharmaceuticals, Indias present share is only of $1 billion out of US$62 billion in the global herbal market (< 2% of the global market share), ranking only in the third position. China seems to do better than India by holding 30% of the global herbal market share, ranking second overall. However, it is widely considered that a huge opportunity is still awaiting the Indian pharmaceutical companies and institutions by way of new innovations, patents and trademarks. Incorporation of modern pharmaceutical, biotechnological and chemical tools is firmly believed to bring a new leverage in ayurvedic drug discovery by way of fusion of traditional and modern medicines [114] .

15. Conclusion

The mechanistic basis of action of medicinal herbs used in ayurvedic Indian medicine, especially in the context of understanding disease processes in molecular terms, is pav-ing the way for identifying new drug compounds as well as new drug targets. At the same time, the present and increased prevalence of diseases that are not completely amenable to therapeutic control by modern medicines is creating a surge in the interest of pharmaceutical companies in developing new solutions from therapeutic principles put forth by tradi-tional medicines. These trends suggest that drug discovery efforts from natural products and specifically from those described in traditional medicines, will undoubtedly offer more significant drug leads for future development. This review presents ayurvedic drug discovery approaches suggested by ayurvedic experts in the context of new drug discovery as well as the practical challenges connecting traditional ayurvedic resources to present drug discovery methodologies. Conformation of ayurvedic drug discovery to modern drug standards and regulations requires signifi-cant customization and up-scaling efforts besides the stan-dardized drug discovery steps. Careful evaluation of ayurvedic herbs and herb products in accordance to present-day practice of drug evaluation and pre-clinical trials is anticipated to bring more successful therapeutic outcomes to the worlds medicine.

16. Expert opinion

Ayurvedic drugs are used by Indian populations as mainstream, alternative, complementary or integrative forms of medicines. Several joint-ventures of western and ayurvedic medical specialty centers are successfully being initiated in India (e.g., Mohans diabetes specialty center and Arya Vaidyas pharmacy in Chennai) to offer multimodal treatment options incorporating advantages put forth by both medical streams. Moreover, it is also common to notice medical practitioners suggesting the incorporation of natural medicine-based procedures and medications in the regularly prescribed modern drugs to handle disorders such as

diabetes, jaundice, renal failure, chicken pox, herpes viral infections etc. Furthermore, multiherbal ayurvedic formulatory drugs have been clearly identified to possess much lesser side effects or toxicities compared with the modern drug-based monotherapy used in treating diseases such as cancer. Despite much of its clinical success in developing countries, there is a significant backlog in the standardized ayurvedic drug discovery efforts to go beyond what has slowly emerged so far. Furthermore, as the global use of ayurvedic knowledge is strikingly minimal, ayurvedic medicine is still stigmatized as one of the unconventional forms of medicine in many parts of the world.

Ayurvedic drug discovery incorporating modern trends in compound identification and clinical screening would help in the widespread use of ayurvedic drugs, uncovering potentials and benefits described in ayurvedic classics. In order to successfully compete for a significant stake in the global market, there is a pressing need for ayurvedic practitioners and scientists to systematically evaluate the therapeutic potentials of ayurvedic products as per standard-ized regulations (e.g., World Health Organization guide-lines). Although the word systematic research may inspire images of large and expensive clinical trials, case-study trials suggested by the Office of Alternative Medicine at the NIH [40] is a simplistic research design with a multitude of advantages. It is less expensive and particularly suited for ayurvedic practitioners in a smaller clinical setting. The essential elements include maintenance of records of diagnosis, pre-treatment and examination schedules, docu-mentation of treatment details including clinical status of the patients, documentation of clinical observations includ-ing side effects and drug responses and inter-individual variations in treatment responses. These studies form the initial basis for reverse-pharmacology approaches in drug discovery and provide valuable contributions to the existing body of knowledge on a given subject of interest. In addition to triggering new drug discovery interests, further standardizations, dose determinations, toxicity profile identifications and quality-control measurements will also help to identify safe and effective ayurvedic drugs and formulations.

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