Genetic basis of pigmentation and its disorders

Absorption mechanisms of human melanin in the visible, 400-720 nm

In this paper we propose that human melanin absorbs visible radiation through two distinct mechanisms: one that is in effect over the entire visible range and is linear in wavelength, and a second one that is evident at wavelengths in the range 400-500 nm and is exponential in frequency. These mechanisms are apparent in all human diffuse reflectance spectra that we have collected. We show that the absorber is the same in all human volunteer skin samples. By studying the diffuse reflection spectra of DOPA-melanin in solution and DOPA-melanin in powder form, we find that we can correlate the absorption mechanisms, one with melanin in solution (a low molecular weight form) and the other with melanin in powder (a high molecular weight form). Therefore, we propose that melanin exists in two distinct states. This model is of biologic significance, as it provides a reasonable interpretation for the diffuse reflection spectra obtained from delayed pigment (UVB-induced) and immediate pigment (UVA-induced). Delayed pigment appears as an increase of both forms of melanin (neomelanogenesis), whereas immediate pigment appears as an increase in the higher molecular weight form with a commensurate decrease in the lower molecular weight form: the two mechanisms change independently of each other. Finally, we show that we can distinguish spectroscopically between the delayed pigment and the immediate pigment.

Iris pigmentation and behavioral inhibition

Two independent investigations of the association between the temperamental dimensions of inhibition and lack of inhibition to the unfamiliar, on the one hand, and the degree of pigmentation of the iris, on the other, revealed a statistically significant relation in Caucasian children between behavioral inhibition to the unfamiliar and blue irises and uninhibited behavior and brown irises. Several biochemical interpretations of this association were discussed and it was suggested that these behavioral styles might be influenced by biological factors that are partially marked by eye color in Caucasian populations.

Effects of melanin-induced free radicals on the isolated rat peritoneal mast cells

Pheomelanin from human red hair (RHM) produces considerably more cellular damage in Ehrlich ascites carcinoma cells when subjected to radiations of wavelength 320-700 nm than eumelanin from black hair (BHM). Irradiation of RHM generated large amounts of superoxide while BHM did not produce detectable amounts of superoxide. The present investigations describe the effects of irradiation of mast cells in the presence of various natural and synthetic melanins. Irradiation of mast cells in the presence of RHM and red hair melanoprotein released large amounts of histamine while BHM and synthetic melanins prepared from dopa, cysteinyldopa, or a mixture of dopa and cysteinyldopa did not release histamine. The release of histamine at lower concentrations of RHM was not accompanied by the release of 51Cr from chromium-loaded cells, suggesting that this release was of noncytotoxic nature. On the other hand, the release of histamine at higher concentrations of RHM was due to cell lysis since both histamine and cytoplasmic marker 51Cr were released to the same extent. The release evoked by large concentration RHM was not inhibited by superoxide dismutase or catalase. This suggests that the cell lysis under these conditions was not due to H2O2 or O-2. The finding that mast cells release histamine when irradiated in the presence of RHM suggests that the immediate and late-phase reactions seen in sunburn may in part be due to the release of mediators from these cells.