الفهرس 
? INTRODUCTION AND AIM OF THE WORK
Pigmentation BiologyOnly 14 pages are availabe for public view
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Abstract
ABSTRACT
Skin pigmentation is the outcome of melanin synthesis by epidermal melanocytes and its distribution to the surrounding keratinocytes. UVR causes an increase in the size of melanocytes, tyrosinase activity, number of melanosomes transferred to keratinocytes and number of active melanocytes. PGs are lipid molecules produced by multiple cell types. UVR stimulates the release of PGs in the skin. PGF2α analogues are new class of eye drops used to control ocular hypertension with a proven safety and efficacy. Periocular skin hyperpigmentation was reported as a side effect of these medications. The aim of this study is to compare the effect of three PGF2α analogues (Latanoprost, Bimatoprost and Travoprost) on skin pigmentation in guinea pigs. The effect of NB-UVB on skin pigmentation of the same animal was also evaluated both alone and in combination with each of the three drugs. The comparison was done clinically and histopathologically. The present study had been conducted on 18 female adult wild guinea pigs classified into 3 groups according each analogue of PGF2α. The hair was shaved from 4 red/brown areas on the dorsal skin of each animal and treated as follows; area 1 (with purified water and served as control), area 2 (with PGF2α analogues), area 3 (exposed to NB-UVB) and area 4 (with PGF2α analogues and exposed to NB-UVB). Skin biopsies from each area were stained with H&E, MF and DOPA stains. Morphometric measurements were conducted on MF-stained sections to determine the ESA as well as that of the MPSA in µm2. The MPSA/ESA percentage was calculated and the results were statistically analyzed. At the end of this study, the skin in area 2 & 3 showed darkening, nearly at the same level, while that in area 4 showed more darkening. Area 1 showed no or very minimal pigmentation. These observations were demonstrated in all animal groups. Morphometric evaluation revealed an increase of melanin density that was marked in area 4, moderate in areas 2 & 3 and very minimal in area 1. Latanoprost was the highest inducer of pigmentation than other analogues. All PGF2α analogues were found to increase skin pigmentation at the site of application. This could be attributed to their role in increasing melanogenesis through inducing the tyrosinase activity. Marked increase in pigmentation was found when NB-UVB was combined with every member of the PGF2α analogues. This could be through two mechanisms. The first is that NB-UVB stimulates the release of endogenous PGs and so adding more exogenous PG may have an additive effect. The second is the synergism of exogenous PG and other mediators released on exposure to NB-UVB. This work indicates that PGF2α analogues have an important role in increasing skin pigmentation which is augmented when combined with NB-UVB. It is recommended to test the effect of different concentrations of PGF2α analogues, different vehicles as well as treatment duration to achieve the best outcome. Further studies are suggested to evaluate the role of these drugs in the treatment of hypo- and depigmented skin disorders e.g. vitiligo.