Melanin is a polymer of quinone and hydroquinone monomer units found throughout the animal and plant kingdoms. In addition to its function in pigmentation, melanin also binds various drugs and chemicals in animals. With this function, melanin protects the pigmented cells and adjacent tissues by absorbing harmful substances, which then are slowly released in nontoxic concentrations. Long-term exposure, on the other hand, builds up high levels of noxious chemicals, stored on the melanin, which ultimately causes degeneration in the melanin-containing cells, and secondary lesions in surrounding tissues. In the eye and in the inner ear, the pigmented cells are located close to the receptor cells, and melanin binding may be an important factor in the development of some ocular and inner ear lesions. In the brain, neuromelanin is present in nerve cells in the extrapyramidal system, and melanin affinity of certain neurotoxic agents may be involved in the development of parkinsonism and tardive dyskinesia. There also seems to be a correlation between the induction of melanoma and melanin affinity of carcinogenic compounds found in the pigment cells of animals.
Key words : Melanin, chemicals, toxicity
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