Melanin-based pigments

Generally, the phenotype that predisposes an individual to an increased risk of skin cancer is red or blond hair, blue eyes, and fair skin. These characteristics are surrogate measure of the sensitivity of the skin to sun exposure and the tendency to develop nevi, freckles, and sunburns based on the skin type. Freckles, which may appear abruptly after the first high dose of UV radiation sun exposure, represent clones of mutated melanocytes, and their presence is associated with an increased risk of melanoma.12 The Fitzpatrick classification of skin type is used to determine the response pattern of the skin to UV radiation and assess the risk for melanoma. There are six Fitzpatrick skin types Type I skin always burns and never tans, type II skin burns easily and tans rarely, type III skin burns sometimes and tans usually, type IV skin burns rarely and always tans, type V skin always tans and is moderately pigmented (brown), and type VI skin always tans and is darkly pigmented (black). Fitzpatrick I and II skin types are commonly affected by NMSC and MM. The susceptibility to skin cancer, both NMSC and MM, is related to the melanin content of the skin and the skin s response to UV radiation. 

Histochemical evidence for melanins in caries lesions has been presented, based on silver staining and bleaching by hydrogen peroxide. These reports, however, are contradictory as far as the pigment location is concerned circumventing the lesion (Opdyke, 1962), diffuse throughout the lesion (Ermin, 1968), and superficial (Meyer and Baume, 1966). 

The solubilization of eumelanins has been attempted under a variety of conditions. Table IV summarizes the results obtained with some native melanins (300). A melanin is considered completely solubilized if the solution does not scatter light. So far only two approaches have been successful, one of which is based on treating the pigment with Solulene 100 (0.1 M solution of dimethyl- -dodecyl-n-undecyl ammonium hydroxide in toluene incubation for 2.5 hr at 75 C). Such solutions were used in the characterization and quantitative determination of melanins (124,301). The extinction coefficient (absorption at 400 nm) for hair melanin was of the order of 3000 Af" cm per indole unit, while that of melanoma melanin was only about 70% that of synthetic dopa melanin (124). The mechanism of the Solulene solubilization process is unknown, and degradation of the pigment cannot be excluded. Interestingly, full neutralization of the melanin solution in Solulene with acetic acid did not precipitate the pigment (302). 

The possible biophysical consequences of the introduction of new physical models of melanins are stimulating and puzzling at the same time. New fields of investigation are open to test these models, in particular, the role of melanins in the inner ear and the functional significance of neuromelanin in the brain. Theoretical hypotheses on this last topic (373,374) are based on the electronic structure and physicochemical behavior of such pigments. 

Melanocytes produce pigments of complex heterogeneous polyphenol-like structure, known collectively as melanins. In humans, melanins play a major role in photoprotection based on their radical scavenging abilities. They are responsible for the production of different colored patterns in hair and superficial epidermis. 

Compounds derived from amino acids include cellular proteins, hormones, neu-rotransmitters, creatine phosphate, the heme of hemoglobin and the cytochromes, the skin pigment melanin, and the purine and pyrimidine bases of nucleotides and nucleic acids. In fact, all of the nitrogen-containing compounds of the body are synthesized from amino acids. Many of these pathways are outlined in the following chapters of the book. 

Hundreds of applications have been mentioned in the Zweig (1968) review acids, alkaloids, amino acids, antibiotics, antioxidants, food and feed additives, bases and amines, bile acids, carbonyls, dyes, enzymes, lipids, hydrocarbons, hormones, indoles, natural products, peptides, proteins, pesticides, plant growth regulators, pharmaceutical products, phenols, pigments (chlorophylls, xanthophylls, porphyrins, melanin, pterins, pteridines, anthocyanins, ilavonoids, etc.), polymers, purine and pyrimidine derivatives, quinones, RNA, DNA, organic sulfur compounds, steroids, sugars, toxins, vitamins, inorganic ions, and others. 

A baseline clinical study is conducted to analyse melanin pigmentafion for participants with no skin pigmentation disorder of different skin phototypes (SPT) using on Fitzpatrick classification as shown in Table 1. Based on Fitzpatrick skin phototype (SPT) classification, it accepted that -... 

In this paper, we have developed a skin pigmentation model for melanin pigment (eumelanin /pheomelanin) analysis. The proposed model is based on modified Beer-Lambert law of skin reflectance model. Clinical study involving 118 participants with three different skin phototypes (SPTs) is conducted. In the study, it was found that the pheomelanin concentration is -4.6E5 5.4E-6 moles/1 for SPT III, -5.9E-5 6.4E-6 moles/1 for SPT IV, and -8.2E-5 9.8E-6 moles/1 for SPT V) and the eumelanin concentration is 9.7E-5 7.3E-6... 

In some senses enzymes with copper at their active sites act in an opposite manner to those with zinc at their active sites. Copper-based enzymes are responsible for carrying out oxidation reactions which lead to formation of organic stmc-tural polymers such a collagen and melanin (responable for protection against UV radiation). Copper-based enzymes have two copper atoms in the Cu(I) oxidation state at their active site to which molecular oxygen becomes bound. Figure 26.33 shows the action of the copper-based enzyme tyrosinase which oxidises the amino acid tyrosine to produce dopachrome, the precursor of the melanin pigments. 

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