K 88Ultraviolet radiation and melanogenesis in pigment-containing cells of the human eye
K. U. Loeffler, M. Sahm, P. Seifert
Introduction: Ultraviolet radiation (UVR) is responsible for numerous cutaneous malignancies and has also been implicated in a variety of ocular diseases. A characteristic way for skin melanocytes to react to UVR is an increase in melanin to absorb the damaging rays and thus protect other cell organelles. Not much is known, however, about such a response in ocular pigmented cells. We were therefore interested to see whether UVR would produce a similar reaction in pigmented cells of the human eye.
Methods: Iris melanocytes, iris pigment epithelial cells (IPE), and choroidal melanocytes were isolated from apparently healthy human donor eyes and cultured under regular conditions. Semiconfluent cultures were exposed to UVR (280-380 nm) for 30, 60 and 120 sec. In addition, some cultures were incubated with a -methyl-p-tyrosine, a protein that inhibits melanogenesis. Irradiated cells were compared to non-irradiated controls morphologically as well as by measuring cell number and melanin content 10 days after radiation. Selected samples were also examined by transmission electron microscopy (TEM).
Results: In each of the experimental cultures, the number of cells decreased markedly compared to the control. The extent of cell reduction was correlated with the length of UVR exposure. In contrast, total melanin content in all cultures decreased only moderately despite the reduced number of cells, resulting in an increase of melanin per given number of cells. Treatment with the a -methyl-p-tyrosine, however, did not reduce significantly the melanin content of the respective cultures, and TEM showed no morphologic evidence of increased melanogenesis.
Conclusions: In summary, we found that in our experimental set-up, UVR reduced the proliferation of cultures of human ocular pigmented cells. There was no evidence of increased melanogenesis. Both biochemical and morphological data, however, support the conclusion that UVR applied in vitro to ocular pigmented cells results in a predominant survival of more densely pigmented cells within a given cell type.
Universitäts-Augenklinik, Sigmund-Freud-Str.25, D-53105 Bonn