Quantitative Analysis of Eumelanin and Pheomelanin in Humans, Mice, and Other Animals: a Comparative Review

Abstract

The color of hair, skin, and eyes in animals mainly depends on the quantity, quality, and distribution of the pigment melanin, which occurs in two types: black to brown eumelanin and yellow to reddish pheomelanin. Microanalytical methods to quantify the amounts of eumelanin and pheomelanin in biological materials were developed in 1985. The methods are based on the chemical degradation of eumelanin to pyrrole-2,3,5-tricarboxylic acid and of pheomelanin to aminohydroxyphenylalanine isomers, which can be analyzed and quantitated by high performance liquid chromatography. This review summarizes and compares eumelanin and pheomelanin contents in various pigmented tissues obtained from humans, mice, and other animals. These methods have become valuable tools to study the functions of melanin, the control of melanogenesis, and the actions and interactions of pigmentation genes. The methods have also found applications in many clinical studies. High levels of pheomelanin are found only in yellow to red hairs of mammals and in red feathers of birds. It remains an intriguing question why lower vertebrates such as fishes do not synthesize pheomelanin. Detectable levels of pheomelanin are detected in human skin regardless of race, color, and skin type. However, eumelanin is always the major constituent of epidermal melanin, and the skin color appears to be determined by the quantity of melanin produced but not by the quality.

Variations in skin colour and the biological consequences of ultraviolet radiation exposure

“…[1][2][3][4][5][6] Human skin colour is determined by the total quantity of melanin, the proportion between the brown-black eumelanin and the yellow-red pheomelanin, and its distribution through the epidermis. [7][8][9] The type and amount of melanin is under the control of several genes with a great number of alleles, resulting in wide variations of skin colours. Assessment of skin colour according to Fitzpatrick's phototype classification system, originally created for caucasian skin and based on self-reported erythema sensitivity and tanning ability, 10 is extensively used by dermatologists, despite limitations in relation to quantification and reliability.…”

Has removal of excess cysteine led to the evolution of pheomelanin?

“…In humans, large amounts of pheomelanin and small amounts of eumelanin are characteristic of red hair, fair skin, freckling, and green irides [25], phenotypes that are more common at high latitudes [10]. If the removal of excess cysteine has adaptive value, this should be reflected in human pigmentation patterns.…”

Genetics, development and evolution of adaptive pigmentation in vertebrates

“…By comparison, variation in human skin color among ethnic groups has less to do with melanin ratio or even the number of melanocytes present, but instead is largely due to differences in melanosome size, number and density in the epidermis (Barsh, 2005). Birds, like mammals, produce both pigment types (for a review, see Mundy, 2005), but reptiles lack pheomelanin (Ito and Wakamatsu, 2003), suggesting that either reptiles have the lost the ability to produce pheomelanin or that mammals and birds independently have evolved the ability to produce pheomelanin. Given the similarities in the genetic and developmental mechanisms of pheomelanin production in birds and mammals (Boswell and Takeuchi, 2005), it seems unlikely that they have evolved independently, although this question warrants further investigation.…”