INTERACTION BETWEEN CHEMICALS AND MELANIN

Various drugs and other chemicals, such as organic amines, metals, pol ycyclic aromatic hydrocarbons, etc., are bound to melanin and retained in pigmented tissues for long periods. The physiological significance of the binding is not evident, but it has been suggested that the mel anin protects the pigmented cells and adjacent tissues by adsorbing po tentially harmful substances, which then are slowly released in nontox ic concentrations. Long-term exposure, on the other hand, may build up high levels of noxious chemicals, stored on the melanin, which ultima tely may cause degeneration in the melanin-containing cells, and secon dary lesions in surrounding tissues. In the eve, e.g., and in the inne r ear, the pigmented cells are located close to the receptor cells, an d melanin binding may be an important factor in the development of som e ocular and inner ear lesions. In the brain, neuromelanin is present in nerve cells in the extrapyramidal system, and the melanin affinity of certain neurotoxic agents may be involved in the development of par kinsonism, and possibly tardive dyskinesia. In recent years, various c arcinogenic compounds have been found to accumulate selectively in the pigment cells of experimental animals, and there are many indications of a connection between the melanin affinity of these agents and the induction of malignant melanoma.