Novel modulators of poly(ADP-ribose)polymeraseCsaba Szabo1, Pal Pacher2 and Raymond A. Swanson3

1 Department of Surgery, University of Medicine and Dentistry, New Jersey Medical School, 185 South Orange Avenue, University

Heights Newark, NJ 07103, USA2 Section on Oxidative Stress Tissue Injury, Laboratory of Physiological Studies, National Institutes of Health and National Institute

on Alcohol Abuse and Alcoholism, 5625 Fishers Lane, Bethesda, MD 20892-9413, USA3 Department of Neurology, University of California and Veterans Affairs Center, 4150 Clement Street, San Francisco, CA 94121,

USA

Opinion TRENDS in Pharmacological Sciences Vol.27 No.12

The nuclear enzyme poly(ADP-ribose) polymerase(PARP)-1 has an important role in regulating cell deathand cellular responses to DNA repair. Pharmacologicalinhibitors of PARP have entered clinical testing as cyto-protective agents in cardiovascular diseases and asadjunct antitumor therapeutics. Initially, it was assumedthat the regulation of PARP occurs primarily at the levelof DNA breakage: recognition of DNA breaks was con-sidered to be the primary regulator (activator) or thecatalytic activity of PARP. Recent studies have providedevidence that PARP-1 activity can also be modulated byseveral endogenous factors, including various kinases,purines and caffeine metabolites. There is a genderdifference in the contribution of PARP-1 to stroke andinflammatory responses, which is due, at least in part, toendogenous estrogen levels. Several tetracycline anti-biotics are also potent PARP-1 inhibitors. In this article,we present an overview of novel PARP-1 modulators.

IntroductionPoly(ADP-ribose) polymerase (PARP)-1 is the best-studiedisoform of a family of multifunctional nuclear enzymes.Activated PARP uses NAD+ and transfers ADP-riboseunits to nuclear target proteins. Poly(ADP-ribosyl)ationis involved in the regulation of DNA repair, gene transcrip-tion, cell-cycle progression, cell death, chromatin functionand genomic stability [1,2].

Pharmacological inhibitors ofPARPhaveenteredclinicaltesting as cytoprotective agents in cardiovascular diseases,and are being considered as both monotherapy and incombination with chemotherapy for cancer treatment [2].The cytoprotective effects of PARP inhibitors comprise inhi-bition of the pathological overactivation of the enzyme andprevention of cell necrosis by overuse of cellular NAD+ poolsand promotion of cellular energetic failure [1,2]. The use ofPARP inhibitors as anticancer agents exploits the fact thatthe repair of certain types of cellular damage related toantitumor agents relies almost exclusively on the functionalintegrity of PARP [3]. Another distinct mode of action ofPARP inhibitors relates to the downregulation of variouspro-inflammatory signal transduction pathways [1,2] andsuppression of chemokine, cytokine, adhesion molecule

Corresponding author: Szabo, C. (szabocsaba@aol.com).Available online 19 October 2006.

www.sciencedirect.com 0165-6147/$ – see front matter . Published by Elsevier Ltd. doi:10.101

and free-radical-generating enzyme expression at thetranscriptional level.

Initially, it was assumed that PARP (a constitutiveenzyme) is regulated primarily by its ability to recognizebroken DNA strands via its zinc fingers [1]. Endogenousoxidants and free radicals (e.g. peroxynitrite) were lateradded to the list of ‘classical’ triggers of DNA single-strandbreakage (e.g. ionizing radiation and genotoxic com-pounds) [4]. Conditions that can produce reactive radicalsand oxidants within the cell, including hypoxia–reoxygena-tion [5], elevated extracellular glucose concentration [6–9],Ca2+ [10] and angiotensin II [11,12], have been identifiedas endogenous activators of PARP. Allosteric regulation ofauto(poly-ADP-ribosyl)ation by Mg2+, Ca2+, polyamines,ATP and the histones H1 and H3 has also been demon-strated [13]. Furthermore, the degree to which PARP isactivated by DNA damage can be regulated by otherfactors. For example, PARP-1 phosphorylation by themito-gen-activated protein kinase (MAPK) extracellular-signal-regulated kinase (ERK)2 seems to be necessary formaximal PAPR-1 activation [14]. In cell cultures, ERK2inhibition by either pharmacological agents or small inter-fering RNA downregulation attenuates PARP-1 activationafter DNA damage [14]. This regulatory effect on PARP-1might be a mechanism by which inhibitors of the ERK2signaling cascade reduce cell death rates following ische-mia–reperfusion [15]. Given the central role of PARP-1 inboth cell death and inflammation, these results indicatethat the effects of ERK2 on PARP-1 activity could be ageneral mechanism through which ERK2 influences cellsurvival. Similarly, calmodulin-dependent protein kinase(CaMK)IId might also activate PARP-1 by phosphorylation[16], and PARP can modulate AKT kinase (protein kinaseB) [17] and JNK [18] kinase activities. Importantly, recentstudies have identified the kinesin superfamily protein(KIF)4 [19], and sirtuin or silent mating-type informationregulation 2 homolog (Sirt1) [20] as endogenous inhibitorsof PARP-1.

Most of the these observations can be placed in thecontext of pathophysiological alterations: PARP and signaltransduction pathways in the context of inflammation,PARP and re-oxygenation in the context of stroke and heartattacks, PARP and elevated glucose levels in the context ofdiabetic complications, and PARP and angiotensin II in the

6/j.tips.2006.10.003

Opinion TRENDS in Pharmacological Sciences Vol.27 No.12 627

context of hypertension and cardiac hypertrophy. Untilrecently, however, essentially no information was availableabout the physiological regulation of PARP, for which wenow provide an overview.

Gender-specific regulation of PARP-1Early pioneering work by Jackowski and Kun in the early1980s highlighted the role of thyroid hormones asregulators of PARP activity [21]. Administration of thethyroid hormone L-triiodothyronine in concentrations thatinduce cardiac ventricular enlargement was shown toinhibit the PARP-1 activity of cardiomyocyte nuclei, witha simultaneous augmentation of RNA synthesis [21]. Con-sequent studies have also demonstrated that hepaticPARP-1 activity in rats is controlled by thyroid hormones[22,23]. The concentrations of the thyroid hormones usedwere, in most cases, higher than the physiologicallyrelevant concentrations. Nevertheless, the regulation ofPARP-1 by these hormones merits renewed interest usingthe experimental tools that are now available.

Recent studies have expanded on the concept thatendogenous physiological factors, conditions and media-tors can regulate PARP-1. Several groups [24,25] haveconfirmed earlier observations [26] that PARP inhibitionor PARP-1 deficiency is protective in stroke. Surprisingly,however, PARP inhibitors confer their protection in malemice only. By contrast, the absence of functional PARP-1 orpharmacological PARP inhibition is not beneficial to theoutcome of ischemic stroke in female mice [24,25]. Similarobservations have been noted in rodent models of shock orinflammation [27]. The endotoxin-induced inflammatoryand vascular responses are cooperatively regulated bygender and PARP. Production of the inflammatory med-iator tumor necrosis factor (TNF)-a, endotoxin-inducedmortality and the development of endotoxin-inducedendothelial dysfunction aremarkedly attenuated in femalemice (compared with male mice), and they are also reducedby PARP inhibitors in male mice. However, pharmacolo-gical inhibition of PARP fails to provide further protectionin female animals. In fact, PARP inhibition in male ani-mals, and female gender provided comparable protectionagainst several inflammatory and cardiovascular para-meters that were investigated, although no combinationeffects of the two protective factors were noted [27].Consistent with these findings, in circulating leukocytes,a potent PARP inhibitor regulated lipopolysaccharide(LPS)-induced PARP activation only in male animals[27]. In a subsequent series of investigations conductedin porcine models of thoracoabdominal aortic ischemia–reperfusion injury, the inhibition of cardiovascularcollapse by PARP inhibitors was observed only in maleanimals [28].

What, then, is responsible for this marked genderdifference? Although the issue requires further investiga-tion, several studies indicate the possible importance offemale sex hormones – at least in shock- or inflammation-related studies [27]. Several findings highlight thepotential involvement of the main female sex hormone,17-b-estradiol, for the observed effects: (i) the genderdifference regarding LPS-induced TNF-a productionis partially diminished in ovarectomized animals;

www.sciencedirect.com

(ii) poly(ADP-ribosyl)ation is attenuated by estrogen inmale animals challenged with endotoxin in vivo; and (iii)there is a difference in the degree of PARP activationbetween cells incubated in male versus female rat serum.

However, estrogen does not seem to inhibit PARPactivation directly. When recombinant PARP and estrogenare mixed, the catalytic activity of PARP does not seem tobe affected. However, an interesting in vitro interactionhas been reported among PARP, the estrogen receptor andDNA; this interaction is further reinforced by the presenceof estrogen [27]. A model of interaction has been proposedbetween PARP-1 and the estrogen receptor a in which astable complex might sequester PARP-1 to specific regionson DNA, making it difficult for the zinc fingers of theenzyme to access and recognize DNA breakpoints (withoutwhich its activation would be inhibited). It has beenhypothesized that this action contributes to the observedeffects of estrogen in vivo [27], although a direct linkremains to be demonstrated. An additional mode of actionmight be the antioxidant property of the female sex hor-mones, which can exert cytoprotective effects, sometimesin surprisingly low (1–10 nmol/l) concentrations [29].

Pharmacological importance of gender-specific PARP-1regulationWhat is the applicability of this gender difference inPARP-dependent responses to physiological genderdifferences, to other animal models of disease and, ulti-mately, to humans? Clearly, PARP inhibitors are notalways ineffective in female animals. Female nonobesediabetic (NOD) mice undergo autoimmune b-cell lossand a disease that resembles type 1 diabetes. In thesemice, PARP inhibition is of major therapeutic benefit[7,30]. Also, PARP inhibitors are protective in female sheepsubjected to shock, or burn and smoke inhalation damage[31]. Thus, the limit of the applicability of these gender-specific findings must be established.

An area that requires more-extensive investigation ismyocardial infarction and gender. It is known from humanepidemiological studies that females are protected – to asignificant degree because of estrogen – against cardiovas-cular disease, and this protection disappears after meno-pause [32]. It remains to be tested whether this protectionis related to a ‘baseline’ PARP inhibitory effect of femalesex hormones.

New modulators of PARP-1 activityVitamin D might be an additional endogenous regulator ofPARP [33]. Using purified PARP enzyme, the active form ofvitaminD3, 1,25-dihydroxyvitaminD3, was identified as aninhibitor of PARP activity with an IC50 of 0.2 mMand 3 mMin cell-free and cell-based PARP assays, respectively [33].However, vitamin D3 itself had no effect on PARP activityat more than 100 times this concentration in the cell-freeassay. VitaminD3 haswell-documented anti-inflammatoryeffects in various experimental models of disease (forreview, see Refs [34,35]). However, the extent to whichthis action influences the wide-ranging effects of vitaminD3 is yet to be determined.

ATP [13,36] and certain purines, includinghypoxanthine and inosine, are endogenous inhibitors of

628 Opinion TRENDS in Pharmacological Sciences Vol.27 No.12

PARP[37].However, it isunclearwhether the concentrationrange of these substances is within the physiological orpathophysiological range. Recent studies demonstrate thatmany other xanthine derivatives (metabolites of caffeine,including 1-methylxanthine and 1,7-dimethylxantine) haveconsiderable PARP inhibitory activity and are more potentthan hypoxanthine as endogenous inhibitors of this enzyme(caffeine itself has onlymodest inhibitory effects) [38]. Like-wise, theophylline (which is present in tea and is used totreat lung pathologies because of its bronchodilator andantioxidant–anti-inflammatory properties) exerts PARPinhibitory effects in human pulmonary epithelial cells[39]. The plasma levels of these compounds [40] are in arange that is consistent with the PARP inhibitory propertyof the compounds, such that drinking coffee and tea mightaffect cellular PARP activity in vivo.

Another line of investigation demonstrates that somecommon antibiotics of tetracycline class, including doxycy-cline and minocycline, are relatively potent inhibitors ofPARP, with inhibition occurring in the high nanomolarrange. Thus, these compounds are less potent than are thelatest generation of PARP inhibitors but they are compar-able in potency to earlier compounds of the isoquinolinoneand phenanthridinone classes [41]. The inhibition by tet-racycline antibiotics – which is similar to that caused by

Figure 1. Endogenous and exogenous regulators and modulators of PARP-1 activity. End

1 or by inhibiting the binding of NAD+ to the active site of the enzyme. The former m

nicotinamide (NA), NAD+ metabolites, caffeine metabolites and vitamin D. PARP-1 act

CaMKIId, and PKC), by Sirt1 and through binding to KIF4. PARP can also modulate

endogenously formed metabolites, theophylline and tetracycline antibiotics might als

endogenous regulators, and it is conceivable that the processes regulated by PARP (e.g.

multitude of factors and influences. Abbreviations: ER, estrogen receptor; TR, thyroid h

www.sciencedirect.com

most of the ‘professional’ PARP inhibitor compounds – iscompetitive and occurs by preventing the PARP substrateNAD from binding to the active center of the enzyme [41].Minocycline has recently received attention as a possibletherapy for neurodegenerative disease and it has beenreported to exert cytoprotective and anti-inflammatoryeffects in vitro [42,43]. Minocycline can reduce rates ofneuronal death after excitotoxicity and ionizing radiationin culture [44,45] and in animal models of stroke [45–48],Parkinson’s disease [49,50], Huntington’s disease [51] andamyotrophic lateral sclerosis [52]. The neuroprotectiveeffects of minocycline have been attributed to both reducedinflammation and a direct effect on neuronal survival[44,45,48,52,53]. All of these actions are consistent withits function as a PARP inhibitor.

The identification of doxycycline as a PARP inhibitor[41] represents the third proposed therapeutic mode ofaction for this compound – the first being the originalantibiotic effect and the second being the inhibitory effecton matrix metalloproteinases (MMPs) [54]. Doxycycline isof major benefit in multiple cardiovascular diseases,including myocardial ischemia–reperfusion and heart fail-ure [55,56]; either its MMP inhibitory effect or its PARPinhibitory effect (or a combination of the two, or anotherunidentified action) could be its mode of action.

ogenous factors can affect PARP-1 activity either by forming a complex with PARP-

ight include estrogen (E) and thyroid hormones (T), and the latter might include

ivity can also be modulated through phosphorylation by kinases (e.g. MAPK and

kinase (e.g. AKT and JNK) activity. Exogenous factors such as caffeine and its

o modulate PARP activity. Overall, PARP seems to be subject to multiple lines of

DNA repair and cellular NAD homeostasis) are under similarly dynamic control by a

ormone receptor.

Opinion TRENDS in Pharmacological Sciences Vol.27 No.12 629

Concluding remarksSome implications of the findings discussed relate tothe current clinical trials of PARP inhibitors. If some ofthe endogenous compoundsmentioned are inhibitors of theenzyme, plasma levels of these molecules might influencephysiological or pathophysiological parameters and, ulti-mately, the outcome of the trials. For instance, possiblegender differences in cancer trials with PARP inhibitorsmight require investigation (this issue is less important incardiovascular trials with PARP inhibitors becausemost women develop stroke or heart attack only aftermenopause, when the regulation of PARP activity by estro-gen is expected to be diminished). In many clinical trials,coffee drinking is discouraged. The observation that caf-feine metabolites can suppress PARP activity could neces-sitate the exclusion of coffee from clinical trials involvingPARP inhibitors.

The safety and risks associated with chronic or repeatedadministration of PARP inhibitors are currently underdebate because of the role of PARP in the maintenanceof genomic integrity [2,57]. The recent studies demonstrat-ing that PARP activity is dynamically regulated by amultitude of factors and compounds (some of which –e.g. coffee and tetracycline antibiotics – are consideredto be safe and well tolerated) favor a more permissive viewof the chronic use of PARP inhibitors, perhaps at doses andconcentrations at which inhibition is only partial.

In light of the data showing the PARP inhibitory effect oftetracyclines (coupled with the established safety profile ofdoxycycline and minocycline), the possible therapeuticbenefit of the combination of doxycycline or minocyclinewith anticancer chemotherapeutics could be explored, aswith the recent attempts to investigate the combinationtherapy of novel ultrapotent PARP inhibitors with che-motherapeutic agents such as temozolomide.

In conclusion, a growing body of data demonstrates thatPARP activity is dynamically regulated bymany activatorsand inhibitors (Figure 1). These observations necessitatethe revision of some of the views of PARP as a regulator ofhealth and disease, and highlight new points regarding thedesign and interpretation of clinical trials involving PARPinhibitors.

AcknowledgementsThis work was supported in part by the Intramural Research Program ofthe National Institutes of Health and National Institute on Alcohol Abuseand Alcoholism (to P.P.) and by grant R01 from the National Institutes ofHealth (to C.S. and R.S.).

References1 Virag, L. and Szabo, C. (2002) The therapeutic potential of poly(ADP-

ribose) polymerase inhibitors. Pharmacol. Rev. 54, 375–4292 Jagtap, P. and Szabo, C. (2005) Poly(ADP-ribose) polymerase and

the therapeutic effects of its inhibitors. Nat. Rev. Drug Discov. 4,421–440

3 Graziani, G. et al. (2005) PARP-1 inhibition to treat cancer, ischemia,inflammation. Pharmacol. Res. 52, 1–4

4 Szabo, C. et al. (1996) DNA strand breakage, activation of poly(ADP-ribose) synthetase, and cellular energy depletion are involved in thecytotoxicity of macrophages and smooth muscle cells exposed toperoxynitrite. Proc. Natl. Acad. Sci. U. S. A. 93, 1753–1758

5 Gilad, E. et al. (1997) Protection by inhibition of poly(ADP-ribose)synthetase against oxidant injury in cardiac myoblasts in vitro. J.Mol. Cell. Cardiol. 29, 2585–2597

www.sciencedirect.com

6 Garcia Soriano, F. et al. (2001) Diabetic endothelial dysfunction: therole of poly(ADP-ribose) polymerase activation. Nat. Med. 7, 108–113

7 Pacher, P. et al. (2002) The role of poly(ADP-ribose) polymeraseactivation in the development of myocardial and endothelialdysfunction in diabetes. Diabetes 51, 514–521

8 Du, X. et al. (2003) Inhibition of GAPDH activity by poly(ADP-ribose)polymerase activates three major pathways of hyperglycemic damagein endothelial cells. J. Clin. Invest. 112, 1049–1057

9 Pacher, P. and Szabo, C. (2005) Role of poly(ADP-ribose) polymerase-1activation in the pathogenesis of diabetic complications: endothelialdysfunction, as a common underlying theme. Antioxid. Redox Signal. 7,1568–1580

10 Yakovlev, A.G. et al. (2000) A role of the Ca2+/Mg2+-dependentendonuclease in apoptosis and its inhibition by poly(ADP-ribose)polymerase. J. Biol. Chem. 275, 21302–21308

11 Szabo, C. et al. (2004) Angiotensin II-mediated endothelialdysfunction: role of poly(ADP-ribose) polymerase activation. Mol.Med. 10, 28–35

12 Pillai, J.B. et al. (2006) Poly(ADP-ribose) polymerase-1-deficient miceare protected from angiotensin II-induced cardiac hypertrophy. Am. J.Physiol. Heart Circ. Physio. 291, H1545–H1553

13 Kun, E. et al. (2004) Regulation of the enzymatic catalysis of poly(ADP-ribose) polymerase by dsDNA, polyamines, Mg2+, Ca2+, histones H1

and H3, and ATP. Biochemistry 43, 210–21614 Kauppinen, T.M. et al. (2006) Direct phosphorylation and regulation of

poly(ADP-ribose) polymerase-1 by extracellular signal-regulatedkinases 1/2. Proc. Natl. Acad. Sci. U. S. A. 103, 7136–7141

15 Alessandrini, A. et al. (1999) MEK1 protein kinase inhibition protectsagainst damage resulting from focal cerebral ischemia. Proc. Natl.Acad. Sci. U. S. A. 96, 12866–12869

16 Kim, M.Y. et al. (2004) NAD+-dependent modulation of chromatinstructure and transcription by nucleosome binding properties ofPARP-1. Cell 119, 803–814

17 Veres, B. et al. (2003) Decrease of the inflammatory response andinduction of the Akt/protein kinase B pathway by poly-(ADP-ribose)polymerase 1 inhibitor in endotoxin-induced septic shock. Biochem.Pharmacol. 65, 1373–1382

18 Xu, Y. et al. (2006) Poly(ADP-ribose) polymerase-1 signaling tomitochondria in necrotic cell death requires RIP1/TRAF2-mediatedJNK1 activation. J. Biol. Chem. 281, 8788–8795

19 Midorikawa, R. et al. (2006) KIF4 motor regulates activity-dependentneuronal survival by suppressing PARP-1 enzymatic activity. Cell 125,371–383

20 Kolthur-Seetharam, U. et al. (2006) Control of AIF-mediated cell deathby the functional interplay of SIRT1 and PARP-1 in response to DNAdamage. Cell Cycle 5, 873–877

21 Jackowski, G. and Kun, E. (1983) The effect of in vivo treatment withtriiodothyronine on the in vitro synthesis of protein–poly(ADP)-riboseadducts by isolated cardiocyte nuclei and the separation of poly(ADP)-ribosylated proteins by phenol extraction and electrophoresis. J. Biol.Chem. 258, 12587–12593

22 Cesarone, C.F. et al. (1994) Hepatic poly(ADP-ribose) polymeraseactivity in rat is controlled by thyroid hormones. Biochem. Biophys.Res. Commun. 203, 1548–1553

23 Giannoni, P. et al. (1995) In vitro effect of 3,5,30-triiodothyronine onpoly(ADP-ribosyl)ation of DNA topoisomerase I. Ital. J. Biochem. 44,129–136

24 Hagberg, H. et al. (2004) PARP-1 gene disruption inmice preferentiallyprotects males from perinatal brain injury. J. Neurochem. 90, 1068–1075

25 McCullough, L.D. et al. (2005) Ischemic nitric oxide and poly(ADP-ribose) polymerase-1 in cerebral ischemia: male toxicity, femaleprotection. J. Cereb. Blood Flow Metab. 25, 502–512

26 Eliasson, M.J. et al. (1997) Poly(ADP-ribose) polymerase genedisruption renders mice resistant to cerebral ischemia. Nat. Med. 3,1089–1095

27 Mabley, J.G. et al. (2005) Gender differences in the endotoxin-inducedinflammatory and vascular responses: potential role of poly(ADP-ribose) polymerase activation. J. Pharmacol. Exp. Ther. 315, 812–820

28 Hauser, B. et al. (2006) The PARP-1 inhibitor ino-1001 facilitateshemodynamic stabilization without affecting DNA repair in porcinethoracic aortic cross-clamping-induced ischemia/reperfusion.Shock 25,633–640

630 Opinion TRENDS in Pharmacological Sciences Vol.27 No.12

29 Kuohung, W. et al. (2001) Tamoxifen, esterified estradiol, andphysiologic concentrations of estradiol inhibit oxidation of low-density lipoprotein by endothelial cells. Am. J. Obstet. Gynecol. 184,1060–1063

30 Suarez-Pinzon, W.L. et al. (2003) Poly(ADP-ribose) polymeraseinhibition prevents spontaneous and recurrent autoimmunediabetes in NOD mice by inducing apoptosis of islet-infiltratingleukocytes. Diabetes 52, 1683–1688

31 Shimoda,K. et al. (2003)Effect of poly(ADP-ribose) synthetase inhibitiononburnand smoke inhalation injury in sheep.Am.J. Physiol. LungCell.Mol. Physiol. 285, L240–L249

32 Mehilli, J. et al. (2005) Gender and myocardial salvage afterreperfusion treatment in acute myocardial infarction. J. Am. Coll.Cardiol. 45, 828–831

33 Mabley, J.G. et al. (2003) Vitamine D3 is an inhibitor of poly(ADP)-ribose synthase. FASEB J. 17, 1123–1124

34 Yee, Y.K. et al. (2005) Vitamin D receptor modulators for inflammationand cancer. Mini Rev. Med. Chem. 5, 761–778

35 Nagpal, S. et al. (2005) Noncalcemic actions of vitamin D receptorligands. Endocr. Rev. 26, 662–687

36 Bauer, P.I. et al. (2005) The influence of ATP on poly(ADP-ribose)metabolism. Int. J. Mol. Med. 16, 321–324

37 Virag, L. and Szabo, C. (2001) Purines inhibit poly(ADP-ribose)polymerase activation and modulate oxidant-induced cell death.FASEB J. 15, 99–107

38 Geraets, L. et al. (2006) Caffeine metabolites are inhibitors of thenuclear enzyme poly(ADP-ribose)polymerase-1 at physiologicalconcentrations. Biochem. Pharmacol. 72, 902–910

39 Moonen, H.J. et al. (2005) Theophylline prevents NAD+ depletion viaPARP-1 inhibition in human pulmonary epithelial cells. Biochem.Biophys. Res. Commun. 338, 1805–1810

40 Tang-Liu, D.D. et al. (1983) Disposition of caffeine and its metabolitesin man. J. Pharmacol. Exp. Ther. 224, 180–185

41 Alano, C.C. et al. (2006) Minocycline inhibits poly(ADP-ribose)polymerase-1 at nanomolar concentrations. Proc. Natl. Acad. Sci.U. S. A. 103, 9685–9690

42 Domercq, M. and Matute, C. (2004) Neuroprotection by tetracyclines.Trends Pharmacol. Sci. 25, 609–612

43 Elewa, H.F. et al. (2006) Minocycline for short-term neuroprotection.Pharmacotherapy 26, 515–521

Elsevier joins major healt

Elsevier has joined with scientific publishers and le

patientINFORM, a groundbreaking initiative to help p

gap. patientINFORM is a free online service de

Elsevier provides voluntary health organizations wi

biomedical journals immediately upon publication

voluntary health organizations integrate the informat

text of selected research ar

patientINFORM has been created to enable patients

options online access to the most up-to-date, rel

For more information, visit

www.sciencedirect.com

44 Tikka, T. et al. (2001) Minocycline, a tetracycline derivative, isneuroprotective against excitotoxicity by inhibiting activation andproliferation of microglia. J. Neurosci. 21, 2580–2588

45 Morimoto, N. et al. (2005) Minocycline inhibits oxidative stress anddecreases in vitro and in vivo ischemic neuronal damage. Brain Res.1044, 8–15

46 Yrjanheikki, J. et al. (1998) Tetracyclines inhibit microglial activationand are neuroprotective in global brain ischemia. Proc. Natl. Acad. Sci.U. S. A. 95, 15769–15774

47 Yrjanheikki, J. et al. (1999) A tetracycline derivative, minocycline,reduces inflammation and protects against focal cerebral ischemiawith a wide therapeutic window. Proc. Natl. Acad. Sci. U. S. A. 96,13496–13500

48 Fox, C. et al. (2005) Minocycline confers early but transient protectionin the immature brain following focal cerebral ischemia–reperfusion.J. Cereb. Blood Flow Metab. 25, 1138–1149

49 Du, Y. et al. (2001) Minocycline prevents nigrostriatal dopaminergicneurodegeneration in the MPTP model of Parkinson’s disease. Proc.Natl. Acad. Sci. U. S. A. 98, 14669–14674

50 Wu, D.C. et al. (2002) Blockade of microglial activation isneuroprotective in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridinemouse model of Parkinson disease. J. Neurosci. 22, 1763–1771

51 Chen, M. et al. (2000) Minocycline inhibits caspase-1 and caspase-3expression and delays mortality in a transgenic mouse model ofHuntington disease. Nat. Med. 6, 797–801

52 Zhu, S. et al. (2002)Minocycline inhibits cytochrome c release anddelaysprogression of amyotrophic lateral sclerosis in mice. Nature 417, 74–78

53 Kraus, R.L. et al. (2005) Antioxidant properties of minocycline:neuroprotection in an oxidative stress assay and direct radical-scavenging activity. J. Neurochem. 94, 819–827

54 Peterson, J.T. (2004) Matrix metalloproteinase inhibitor developmentand the remodeling of drug discovery. Heart Fail. Rev. 9, 63–79

55 Wang, W. et al. (2002) Peroxynitrite-induced myocardial injury ismediated through matrix metalloproteinase-2. Cardiovasc. Res. 53,165–174

56 Villarreal, F.J. et al. (2003) Early short-term treatment withdoxycycline modulates postinfarction left ventricular remodeling.Circulation 108, 1487–1492

57 Graziani, G. and Szabo, C. (2005) Clinical perspectives of PARPinhibitors. Pharmacol. Res. 52, 109–118

h information initiative

ading voluntary health organizations to create

atients and caregivers close a crucial information

dicated to disseminating medical research.

th increased online access to our peer-reviewed

, together with content from back issues. The

ion into materials for patients and link to the full

ticles on their websites.

seeking the latest information about treatment

iable research available for specific diseases.

www.patientinform.org