Combined chemical and electron microscopic studies of pheomelanosomes in human red hair.

This study clarified the fine structure of pheomelanosomes in human red hair by quantifying the contents of pheomelanin and eumelanin and by identifying the fine structure of melanocytes and melanosomes based on their melanogenesis type in follicles. Out of 5 red-haired subjects, 3 were found to exhibit pheomelanogenesis in follicles, while the remaining 2 were found to have a mixed type melanogenesis of pheomelanin and eumelanin. Melanocytes in the pheomelanic follicles contained spherical melanosomes which revealed sequences of development identical to those seen in the pheomelanosomes of mice and guinea pigs. In contrast, the follicles of mixed type melanogenesis contained 2 different populations of melanocytes, i.e., one with synthesis of spherical melanosomes such as seen in the pheomelanic follicles and the other with synthesis of ellipsoidal-lamellar (filamentous) granules of eumelanosome form. It was concluded that (a) visual differentiation of hair color does not always reflect the melanogenesis type in human red hair, (b) chemical analysis of melanogenesis type corresponds well to the fine structural differentiation of eumelanosomes and pheomelanosomes, and (c) human pheomelanosomes are spherical granules with microvesicular (vesiculoglobular) and proteinaceous matrices on which melanin deposition is spotty and granular.