Latanoprost-induced Pigmentation in Human Iridial Melanocytes Is Fibroblast Dependent

Abstract

Abstract: : Purpose: The prostaglandin F2 alpha derivative, Latanoprost, used in the treatment of glaucoma, can induce pigmentation in the iris of pateints with brown, hazel or heterochromatic eye colour. The mechanism by which Latanoprost induces pigmentation in the iris is not established although it does not appear to induce proliferation of iridial melanocytes. Our aim was to develop an in vitro model in which to investigate Latanoprost-induced iridial pigmentation. Methods:Human iridial melanocytes were established and expanded in MCDB 153 medium. The pigmentory responses to LT and PGF2 alpha were then examined in melanocytes on their own (In MCDB 153 or Green's media) or in co-culture with epithelial cells (both non-ocular human epidermal keratinocytes and iris pigment epithelial cells), mesenchymal cells (non-ocular dermal fibroblasts and iridial fibroblasts) or both epithelial and mesenchymal cells. Melanogenesis was assessed after a minimum of 4 days culture with prostanoids, using dopa oxidase activity. FP expression on human iridial fibroblasts and melanocytes was investigated using an immunofluorescent technique using antibody to the prostaglandin F2 alpha receptor and RT-PCR. Results:Iridial melanocytes did not show a convincing increase in dopa oxidase (one of the key enzymes involved in pigment production) when cultured on their own but in the presence of fibroblasts (from ocular and non-ocular sources) there was a significant increase (25-30%) in dopa oxidase activity in response to 10 ^-7 to 10 ^-5 M LT and PGF2 alpha. Co-culture of melanocytes with epithelial cells, while leading to increased dopa oxidase acitivity in the melanocytes, did not lead to any melanogenic response to LT and PGF2 alpha. FP receptor expression was detected on fibroblasts but not melanocytes by immunocytochemistry and RT-PCR. The melanocyte-fibroblast model developed in this study also showed that LT and PGF2 alpha increased dopa oxidase acitivity in melanocytes from donors with brown eyes but not donors with blue eyes. Conclusions:Our data suggest that LT may be inducing pigmentation in the human iris indirectly through the FP receptor on adjacent fibroblasts.

Keywords: melanocytes • receptors: pharmacology/physiology • cell-cell communication