wunsch a_skin eye and brain

8/14/2019 WUNSCH A_Skin Eye and Brain

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Wunsch A: Skin, Eye and Brain

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HUMAN LIGHT RESPONSE VIA SKIN, EYE AND BRAIN

Wunsch, Alexander

International Light Association, Belgium

ABSTRACT

Ultraviolet light from sunlight unfolds avariety of different photophysical andphotochemical activities in human skin,which are controlled and reacted upon bytwo photoendocrinologically activeantagonistic organs in the brain, namely thepituitary and pineal gland, under the controlof the eye.

There are also two organs for lightreception, namely skin and eye. Thesesystems have been attuned by the course ofevolution under the frequent influence ofsunlight. Human genes only know how toreact upon bright light with the spectralcomposition of sunlight. Understanding thisheliotropic logic behind the coordinationprocesses between skin, visual andenergetic portion of the retina andphotoendocrine regulation in the brain isessential for creating a reliable concept ofhealthy artificial lighting.

Keywords: Photoendocrinology, pituitary and

pineal gland antagonism, photochemical lightreactions, stress.

1. INTRODUCTION

Bright light is, amongst other environmentalstimuli, a major releasing factor for stressreactions (5, 6, 12). Darkness for humans isa stimulus for regeneration reactions andsleep. The circadian stress hormoneconcentrations and the melatonin curveshow clear variations depending on light,acting as an antagonistic system controlledby pituitary and pineal gland. Without lightentering the eye an involution of the pituitarygland can be observed after a while (7).

Ocular phototransduction under brightlighting conditions leads to systemic stressreactions (12) with increased production ofCRH (Corticotropin Releasing Hormone),POMC (ProOpioMelanoCortin), ACTH(AdrenoCorticoTrophic Hormone) and otherpituitary hormones like TSH (ThyroidStimulating Hormone) and GonadotropicReleasing Hormone (GnRH) through the

hypothalamic pituitary axis (HPA) (8). Whilethe production of the pituitary hormones isincreased, the production of melatonin in thepineal gland is suppressed and vice versa.The pituitary gland functions are mainlyassociated with day and summer tasks, thepineal gland rules over night and winter.

Dermal phototransduction leads to localstress reactions in the skin tissue under themediation of the same hormonalcomponents, except TSH and GnRH. Theaction spectrum for dermal light stress is wellknown since the groundbreaking research ofNiels Ryberg Finsen, the father of modernphototherapy and winner of the Nobel prizefor medicine in 1903 (3). It is associated withthe photochemical potential of ultravioletradiation in the UVA and UVB range andleads to a number of photochemicalreactions. Most of these reactions aredestructive photo-oxidations which concernnearly all pituitary hormones and otherbiomolecules with chromophoric groups,while only one reaction is a photosynthesis,namely the production of the hormoneCalcitriol or so called Vitamin D (12).

Recent discoveries have unveiled theaction spectrum of the optical radiationwhich seems to be most effective in inducingthe endocrine reaction in the HPA which islocated in the short wave segment of thevisible spectrum with a sensitivity peak ofaround 460 nm. But not only the wavelengthor color temperature of the visible radiation,but also the light intensity seems to beimportant for photoendocrine efficiency.

Even if science today discovers thatdifferent wavelengths in the visible range ofthe spectrum show different reactions inhumans, under the evolutionary viewpointthis is not a new piece of information.Finsen, over 100 years ago, described aphotodermatic reaction showing a spectralopponency in a number of simple organismslike salamanders or earthworms whichalways follow the same logic. Regarding thereactions after photic stimulation, blue andviolet light is associated with bright light andred light is associated with darkness (3).


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2. SUNLIGHT REACTIONS

Natural sunlight has a given spectralcomposition which is altered byenvironmental factors, seasons and localclimate conditions. The spectral componentsin the UV range underlie the most significantvariations depending on these alteringfactors and show also the highestphotochemical potential and activity in thebody. This particular range of radiation canonly enter the skin but not the eye. Theocular lens provides filtering properties whichmake sure that the delicate retinal structuresare protected from this aggressive part of theoptical spectrum. Nevertheless the bodyneeds orientation regarding theenvironmental UV concentration tocoordinate dermal and systemic stressreactions and hormone production. Thereason for this informational demand lies inthe significance of the UV reactions in theskin: 20 minutes under sunlight can lead to aproduction of 25 000 international units ofVitamin D, but also, depending on individualconditions, to a severe erythema andinflammatory skin reaction. Vasoactivesubstances are liberated in the capillarylayers of the skin which lead to a dermalpooling effect by widening the vessels.

Dermal pooling is a shift of blood andliquid from inside the body into the

vascularised and outer layers of the skin.Under extreme conditions, the skin can takemore than 60% of the whole bloodcontingent of the body (1). If a normalindividual has about 5 liters of blood, thisequates to an amount of more than 3 liters.This seems to be a very high amount, butcan be better understood if one knows, thatthe skin is one of the largest organs in thebody with a mass of about 12 kg (withoutsubcutaneous fat layers). Massive dermalpooling can lead to a lethal condition ofcirculatory shock reaction if not sufficiently

counteracted, even the loss of 1 liter of bloodcan be rather harmful. This dermal poolingeffect has been used therapeutically sincethe 1920s to treat high blood pressure.

The systemic stress reaction is capableof counteracting excessive dermal poolingeffects, because the catecholaminesconstrict the vessels, raise the bloodpressure and increase the heart activity. Inaddition, a hormone of the posterior lobe ofthe pituitary gland, ADH (AntiDiureticHormone) is directly released into the blood

stream and induces water retention in thekidneys. For the control of the inflammatoryskin reactions, the cortisol is liberatedtogether with the adrenaline. Thesecontrolling mechanisms seem to be soessential that the liberation of the stress

hormones is not only provided by the HPA,but there are also accessory stress hormonereleasing systems located in the hair folliclesin the skin as well, which have been recentlydiscovered (13).

A second reason for compensatorystimulation of pituitary secretion activityunder bright light conditions is thecircumstance that there is a hormonal drainor loss caused by the UV radiation whichenters the skin. All of these hormonalsubstances are photosensitive (2) becausethey carry chromophoric groups in theirmolecular structure which lead to anabsorption of photon energy in the UV range.The photon energy destroys or deactivatesthese molecules as a consequence ofabsorption. As the hormone levels arecontrolled by feedback loops, the destructionof certain amounts of these hormones in theskin leads to an increased production in theendocrine organs.

These light reactions described abovehave been essential for survival under thedifferent climatic and lighting conditions on

earth. Under the pressure of evolution it hasfinally turned out that survival has beeneasier for those organisms which couldsomehow foresee the content of UV in theenvironment and thereby anticipate theadequate pituitary activity needed forhormonal balance. In natural sunlight a highamount of UV is always accompanied byhigh levels of brightness and, whats evenmore significant, a high content of blueradiation. While UV is invisible, blue can bedetected by the eye and thus can be used asa parameter for indirect extrapolative

measurement of ultraviolet radiation.This system seems to be ingenious, but it

only works under natural sunlight conditions.As soon as there is artificial fluorescent lightinvolved, the system begins to malfunction:the bright artificial light with high colortemperature triggers adaptive endocrinestress reactions against high environmentalUV radiation which does not exist. Thisinduces a hormonal imbalance which can bedetrimental for health, especially under longterm conditions.


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3. ARTIFICIAL LIGHT AND HEALTH

Reviewing the recent publicationsconcerning healthy light, a focus uponcircadian effectiveness and melatonin canbe noticed. It mostly appears as if thiscircadian or chronobiological effectiveness isused as a quality label for healthy lighting.The equation circadian effective = healthyhas to be thoroughly examined. This kind ofartificial light can be used for therapeuticalpurposes in treating SAD and other circadiandisorders. It can also be used in helping shiftworkers to cope with their unhealthy workingconditions. But these examples give no proofthat this light is healthy, it only shows acertain therapeutic potential. For the largestpart of a population it might be healthier touse chronobiologically and endocrinologicallyneutral light sources in order not to interferewith their individual endocrine regulationsystems.

For photometrical purposes andsimplified reflections on the functions of thecircadian system it might be practical to lookonly at the suppression of the hormone ofdarkness (melatonin) in terms of a markersubstance for endocrine reagibility, but thisapproach only touches the surface of ahighly complex system: humanendocrinology. From the medical viewpoint,it seems to be more important to look at the

increased secretion of pituitary hormones.The Proopiomelanocortin (POMC) is a veryinteresting candidate for further investigation,because it is a multi purpose peptide whichshows the link between light influence andsystemic stress, even on the molecular andgenetic level. It is the precursor molecule forACTH (which controls the secretion ofcatecholamines and cortisol), -MSH and -Endorphin. If the body needs ACTH, thisalways comes along with -MSH and -Endorphin. In the central nervous system -Endorphin reduces pain, in the periphery it

acts as an immune modulator. -MSH is themelanocyte stimulating hormone whichstimulates pigmentation (sic!), but it alsoincreases the heart rate, the concentration oflipoproteins in the blood and stimulates theactivity of the thyroid gland. All thesehormones are deeply involved in thedevelopment of civilizations diseases. Inindustrialized societies about 50% of thepopulation die from cardio-vascular diseases(CVD) which are the consequence of highblood pressure and a disturbance in the

lipoprotein and cholesterol metabolism.Another 30% develop deadly forms ofcancer, which are mostly hormonedependent/sensitive and also the result of amalfunctioning immune system.Catecholamines, gonadotropic hormones,

steroids and hormones of the thyroid glandare the major influences in this field and theyare all hormones under pituitary control (4).The development of these diseases iscertainly the result of multiple factors, so itwill be difficult to prove the role of artificiallighting for this outcome, but the findings inphotoendocrinology indicate at least apromoting effect of circadian effective lightsources.

4. CIRCADIAN LIGHTING AND VISION

The human eye has two pathways for theprocessing of light signals. The optical part isresponsible for vision processes while theenergetic pathway controls the HPA via theretino-hypothalamic tract. For visionpurposes it is better if the surrounding lightdoes not contain high amounts of blue andviolet wavelengths. The higher refraction forshort wavelengths which occurs in opticalmedia appears also in the eye. This causesa chromatic aberration effect with negativeconsequences for sharp vision. The differentwavelengths focus on different planes in andaround the focus plane of the retina. Due tophotooxidative effects (9, 11), the blue andviolet radiation also promotes chemicalreactions in the optical media of the eye andin the fovea centralis. We find a number ofmechanisms in the eye which provide bettervision on one hand and less photooxidativestress and damage on the other, in order toreduce the negative effects of blue light onvision. First the number of blue receptors isup to 20 times less compared to the numberof red cones in the fovea centralis (10).Secondly there is a concentration of lutein, ayellow pigment which filters out excrecentportions of blue and shows also antioxidativeproperties. The concentration of thisprotection substance is reduced in the eyesof elderly people. Ophthalmologists havediscovered that there is some evidence thatthe age related reduction of lutein isfunctionally compensated by the increasedblur in the lens, which is also promoted byblue and ultraviolet light. As a consequencethey replace the lens in cataract surgery by acolored one, which filters out the blueportions in order to protect the macula from


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further degeneration. This shows that eventhe structures of the eye wear out,depending on age and the amount of lightwhich has to be processed during a personslifetime. The question is, is it only thesunlight which is responsible for the

increasing incidence of age related maculardegeneration, which is found in 30% of thepopulation over 70 years of age inindustrialized nations? These people stay90% of their time inside buildings whileunder the influence of artificial light, whichhas to be taken into account as well. Weindeed find that there is a large number oflight sources in our environment whichproduce high amounts of photooxidativepotent light, such as mercury vapor lampswith high color temperature and TFTcomputer screens.

5. CONCLUSION

Epidemiologic data show that the incidencefor civilization related health problems likecardio-vascular diseases, cancer, immunedeficiency, osteoporosis and age relatedmacular degeneration is rising. All thesedisorders are photochemically andendocrinologically related to the influence oflight (12). Artificial light has become themajor photonic influence in modernsocieties. The tendency in artificial lighting is

the ubiquitous use of mercury vapor lightsources with high color temperature. Thisparameter indicates high portions ofphotochemically and chronobiologicallyactive radiation in the spectrum, which isalso hindering sharp vision. From themedical viewpoint the question arises as towhether the use of mercury vapor light has apromoting effect on a number of thesediseases of civilization. In terms ofprevention of hormonal disorder andimprovement of vision in healthy individuals,it may be better to use artificial light sources

with a low content of blue and low colortemperature and go for alternatives to themercury vapor light sources.

REFERENCES

1 BRAUCHLE A. Handbuch derNaturheilkunde. Leipzig: Reclam 1935.

2 DANNENBERG, H. Ueber dieUltraviolettabsorption der Steroide. Berlin: deGruyter, 1940.

3 FINSEN NR. Ueber die Bedeutung derchemischen Strahlen des Lichts fr Medicinund Biologie. Leipzig: Vogel, 1899.

4 HARBUZ MS et al. Hypothalamo-pituitary-adrenal axis and chronic immune activation.Ann. N. Y. Acad. Sci. 992 , 99-106, 2003.

5 HOLLWICH F. The Influence of OcularLight Perception on Metabolism in Man andAnimal. New York: Springer 1979

6 JORES A. Aenderungen desHormongehaltes der Hypophyse mit demWechsel von Licht und Dunkelheit. Klin.Wschr. 14 , 1713, 1935b.

7 MARX H. Hypophysre Insuffizienz beiLichtmangel. Klin. Wschr. 24/25 , 18-21,1946.

8 MILLER DB et al. Neuroendocrine aspectsof the response to stress. Metabolism 51 , 5-10, 2002.

9 OMATA, Y et al. Intra- and extracellularreactive oxygen species generated by bluelight. J. Biomed. Mater. Res. A, 77A , 3,470-477, 2006.

10 REA, M et al. A model ofphototransduction by the human circadiansystem. Brain Res Rev 50 , 213-228, 2005.

11 ROTENBERG, S et al. Extracellularenvironment as one mediator of blue light induced mitochondrial suppression. Dent.Mat. 22 , 8, 759-764, 2005.

12 SILBERNAGL, S et al. Taschenatlas derPhysiologie. Stuttgart : Thieme, 2001

13 SLOMINSKI, A et al. DifferentialExpression of a Cutaneous Corticotropin-Releasing Hormone System. Endocrinology145 (2), 941-950, 2004.

Author:Alexander WunschPhysicianBergheimer Strasse 11669115 HeidelbergGermanyPhone: +49-6221-602344Fax: +49-6221-161596e-mail: [email protected]

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