NM isolated from the human SN is present in a large, aggregated structure, composed of three major components, melanin, protein, and lipid, with different electron density. Melanin polymer has the highest density and the protein component shows intermediate density, whereas the third lipid component is translucent. Melanin component is a mixture of melanin classes, black–brown ‘eumelanin’ and yellow–red ‘pheomelanin’ in a ratio of 4∼3 to 1. Eumelanin is composed of indole derivatives produced by autooxidation of dopamine, whereas pheomelanin contains benzothiazine molecules from incorporated cysteine or GSH with dopamine–quinone derived from dopamine by autooxidation. The protein components are covalently bound to NM, make up 5–15% of the isolated molecule, and include mostly lysosomal proteins, in addition to mitochondria-, cytosol-, and endoplasmic reticulum-associated protein, as detected by subcellular proteomics. The protein components are derived from a reaction of melanin polymer and proteins, or dopamine (quinone) bound to cysteinyl residue of peptide chains. The lipid components account for up to 20% of the mass and are identified to be 1% cholesterol and 14% poly-isoprenoid dolichol. The lipid component is adsorbed to NM, not integrated in the structure. It was proposed that NM granules originate from lipofuscin, a lipid-containing pigment, but this hypothesis is now challenged by the fact that lipofuscin is localized in the lysosomes and produced also in glia and distributed ubiquitously in the brain. Show
The higher structure of the NM molecule is a multilayer three-dimensional structure similar to synthetic and naturally occurring melanin, as shown by X-ray diffraction studies. More recently, atomic force microscopy has revealed a spherical structure of NM granules with a diameter of ∼30 nm. The spherical structure of NM is composed of a pheomelanin core with a higher oxidation potential and a less redox-reactive eumelanin surface. However, this model cannot explain the occurrence of free sulfhydryl (SH) residues on the NM surface. NM binds iron most strongly, and zinc, copper, manganese, chromium, cobalt, mercury, lead, and cadmium for 1.5% of the mass, and other 2–5% is due to sodium, potassium calcium and other inorganic compounds. Iron binds to NM at two distinct sites, the catechol groups forming metal centers in a lattice and the small-sized iron–oxygen frameworks in an insoluble NM matrix. In dopamine neurons of the SN, iron binds mainly to NM and accounts for 10–20% of the total iron, and the remainder is stored in microglia as bound to ferritin. View chapterPurchase book Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9780123741059004809 Cryptococcosis ( Cryptococcus neoformans and Cryptococcus gattii)John E. Bennett MD, in Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases, 2020 MelaninThe production of melanin is observed in many fungi, including some pathogenic species.43C. neoformans possesses a laccase, an enzyme that catalyzes the conversion of diphenolic compounds such asl-3,4-dihydroxyphenylalanine (DOPA), norepinephrine, epinephrine, and other related aromatic compounds to quinones, which rapidly autopolymerize to form melanin. The production of this pigment can help identify the yeast in the laboratory, but it is also a major virulence factor for the yeast. Laccase is bound to the inner aspect of the yeast's cytoplasmic membrane, and a site-directed mutant for the gene encoding for it has been created. This laccase-negative or albino mutant has been attenuated for virulence in animal models.161 One proposed mechanism by which melanin may protect the yeast is through its ability to act as an antioxidant, and it has been shown that yeast cells without the ability to form melanin are more susceptible to oxidative stress. Other potential mechanisms by which melanin protects the yeast from host damage involve the following: (1) cell wall support or integrity, (2) alteration in cell wall charge, (3) interference with T-cell response, (4) abrogation of antibody-mediated phagocytosis, and (5) protection from temperature changes and antifungal agents. It remains unclear whether the catecholamine-rich CNS, with its excellent substrates for melanin formation, provides some tissue tropism or a rich environment that enhances this yeast's ability to produce disease. For instance, it has clearly been shown that melanin is formed in yeast cells within the brain.162,163 View chapter on ClinicalKey Lasers and Other Energy-Based TherapiesJean L. Bolognia MD, in Dermatology, 2018 Treatment of Melanin-Containing LesionsEphelides and LentiginesSince melanin has a broad absorption spectrum (seeFig. 136.3), many lasers can be used to treat melanin-containing lesions. At the lower end of the therapeutic window, the penetration of green lasers is limited to the superficial papillary dermis. These lasers are best utilized for epidermal pigmented lesions. Thus, the frequency-doubled Nd:YAG (532 nm), either Q-switched or normal mode, effectively treats lentigines and ephelides in most skin types with limited recurrence36. Of note, in patients with a history of systemic gold therapy, Q-switched lasers can induce darkening of these pigmented lesions. Additional lasers, e.g. the 800 nm diode, as well as IPL can also be used to treat epidermal pigmented lesions (Table 137.3). While the PDL is most commonly used for vascular lesions, 595 nm light is also well absorbed by melanin and can be used to treat pigmented lesions. By incorporating compression, the vascular component of the skin is blanched out and melanin-containing lesions can be targeted. Newer PDL systems have incorporated such a “compression handpiece”. In general, the Q-switched ruby and alexandrite lasers are more effective when treating more deeply situated pigmented lesions (e.g. nevus of Ota), as these wavelengths have an increased depth of penetration. Q-switched ruby (694 nm) laser light is better absorbed by melanin than is alexandrite (755 nm) laser light, which might be an advantage in lighter-skinned individuals, but problematic in darker-skinned patients, given the increased likelihood of nonspecific heating of normal epidermal melanin. Q-switched Nd:YAG laser light is much less well absorbed by melanin, but reaches deeply into the skin; therefore, it is primarily used to treat dermal pigmented lesions. For the treatment of lentigines, ephelides, and café-au-lait macules as well as nevus of Ota, understanding these profiles allows one to choose the optimal device. The clinical response of pigmented lesions to Q-switched lasers is determined by where the pigment is localized (epidermal, dermal or mixed) and whether it is intracellular or extracellular, as well as the composition of the pigment (usually melanin)37. Benign Melanocytic NeviLaser removal of acquired and congenital nevi is controversial since no specimen is submitted for tissue diagnosis and margin assessment. Furthermore, the future biologic behavior of laser-resistant cells and the effect (if any) of laser thermal injury on these cells is unknown. Since the clinical standard of care is excision for any atypical pigmented lesion, laser treatment of melanocytic lesions should only be considered for clinically banal lesions in patients with no personal or family history of melanoma. Both acquired and congenital melanocytic nevi have been treated with Q-switched ruby, alexandrite, and Nd:YAG lasers38. The 694 and 755 nm devices can improve the appearance of acquired junctional melanocytic nevi without scarring39. In general, smaller and thinner lesions are typically more treatment-sensitive. While congenital nevi can be lightened, complete eradication is much more difficult and recurrence is common. Laser therapy decreases the number of pigmented nevus cells in the papillary dermis, but is unlikely to affect deeper seated, non-pigmented cells that are closely associated with adnexal structures. This has been demonstrated histologically as persistent nests of nevus cells in the mid papillary and deeper dermis at depths of 0.16–0.44 mm. Deeper components of these nevi located within muscle or under fascia will also remain unaffected by laser surgery. View chapter on ClinicalKey Metabolism of Amino AcidsGerald Litwack Ph.D., in Human Biochemistry, 2018 MelaninMelanin is derived from tyrosine, and more directly from DOPA. Melanin is a family of pigments having different colors. In this case, DOPA is the product of the enzyme, tyrosinase (diphenol oxidase). Differently from tyrosine hydroxylase, tyrosinase, a copper enzyme, uses molecular oxygen directly [without tetrahydrobiopterin (BH4)] as is the case with tyrosine hydroxylase) to form DOPA from tyrosine. The synthesis of melanin occurs in the melanocyte, and the reactions starting with tyrosine are shown in Fig. 13.25.  Figure 13.25. Synthesis of melanin from tyrosine. DHI, dihydroxyindole; DHICA, dihydroxyindole catecholamine. In the presence of cysteine another pigment called pheomelanin can be formed that has a red-yellow color compared to eumelanin that has a brown color. Melanins are the pigments that produce the color of the eye. The arrows at the top of the structures of eumelanin and pheomelanin indicate the point at which polymerization can occur. After the formation of DOPA from tyrosine, the further conversion of DOPA to DOPAquinone follows. Then, a number of intermediates are formed ending in indolequinone that polymerizes to form melanin. The more common product is eumelanin (brown) but in the presence of cysteine, pheomelanin can be formed (red to yellow). Melanin is formed primarily in the melanocyte, located in the inner layers of the skin where melanin and carotene blend to produce the skin color as well as the color in the eyes and hair. Red hair is produced by pheomelanin in spherical melanosomes (melanin granules). Black-colored melanin is formed in oblong melanosomes. Melanin granules are distributed uniformly in the skin cell in order to absorb UV rays from the sun and protect, at least partially, from injurious rays. View chapterPurchase book Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9780123838643000132 Spectral Imaging in DermatologyD. Ho, ... R.M. Levenson, in Imaging in Dermatology, 2016 MelaninMelanin is obviously a prominent skin constituent, and is associated (perhaps causally) in melanomagenesis [60]. Unfortunately, at least for imaging scientists, melanin proves to be not autofluorescent (or only very weakly autofluorescent) when excited in the visible range, although it is apparently possible to induce bright yellow autofluorescence of melanin by combining exposure to peroxide compounds with UV irradiation [61]. Native melanin autofluorescence, however, can be generated using femtosecond-pulse excitation or single-photon NIR illumination [62,63]. It is thought that melanin autofluorescence may be induced by stepwise two-photon excitation, which allows for a brief interval in the arrival of the two photons, as opposed to the requirement for near-simultaneous cooccurrence that seems necessary for exciting other cellular fluorophores. Under conditions of nanosecond irradiation, with a relatively lower total photon flux, melanin autofluorescence becomes more readily detectable and, intriguingly, the peak melanin emission from malignant melanomas differs from that of benign nevi, possibly reflecting alterations in the pheomelanin and eumelanin contributions [64]. Similar findings using pump-probe imaging for enhancement of the spectral signal to segment melanin distribution have been reported (see Pump-Probe Microscopy section, below). View chapterPurchase book Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9780128028384000182 Design and Evaluation of Ophthalmic Delivery FormulationsVandana Soni, ... Rakesh K. Tekade, in Basic Fundamentals of Drug Delivery, 2019 13.10.6 Melanin BindingOcular melanin is found in the retina and influences the ocular BA of the topically applied drug. Drug binding to melanin affects drug response, toxicity, and duration of activity, which may be due to its distribution and retention in pigmented ocular tissues. Melanin binds to the drugs by electrostatic and van der Waals forces or by simple charge transfers (Rimpelä et al., 2016). Melanin binding in the iris–ciliary body influences the drug concentrations in anterior ocular tissues as well as drug response. Melanin binding may significantly lower the pharmacological activity. Drugs similar to ephedrine and timolol bind to the melanin with an intense binding efficiency. Melanin loaded drugs are not available for receptor and for absorption, hence require large dosage for action (Gaudana et al., 2010). Melanin also absorbs the excess radiation via facilitating the transmittance of visible light to the retina. It also serves as a photoprotector by quenching reactive oxygen species, as well as other radicals, created as a result of the elevate oxygen dependency of the retina for its metabolism (Rozanowska et al., 2009). Melanin additionally can bind various pharmaceuticals that can produce ocular toxicity. View chapterPurchase book Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9780128179093000133 Mechanisms and Morphology of Cellular Injury, Adaptation, and Death1Margaret A. Miller, James F. Zachary, in Pathologic Basis of Veterinary Disease (Sixth Edition), 2017 Melanin.Melanin is the pigment responsible for the color of the hair, skin, and iris. It also colors the leptomeninges in black-faced sheep (Fig. 1-44) and cattle and may be present multifocally in oral mucosa in various species. Localized deposits of melanin (melanosis) are common in the aortic intima in ruminants with pigmented coats and in the lungs (Fig. 1-45) of red or black pigs. The localized deposits in congenital melanosis are merely a color change and not a lesion because they are not a response to injury and have no ill effect on the animal. The melanocytes that synthesize and secrete melanin are derived from the neural crest and migrate to the site of pigment production during embryonic development of the structure. In the skin, melanocytes reside in the stratum basale of the epidermis and follicular epithelium. Melanin is formed in organelles called melanosomes, then transferred through dendritic cell processes to adjacent keratinocytes. In the keratinocyte, melanin granules are mainly in the apical cytoplasm, where they may shield the nucleus from ultraviolet light. Histologically, melanin granules are small (usually less than 1 µm in diameter), brown, and nonrefractile. How do you get melanin?Eating vitamin C–rich foods like citrus, berries, and leafy green vegetables may optimize melanin production. Taking a vitamin C supplement may help as well. 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What food is high in melanin?Best melanin rich foods for hair are:. Red Cabbage. Rich in: Vitamin C, Sulphur. Benefits: Vitamin C is antioxidant-rich and essential against greying hair. ... . Avocado. Rich in: Vitamin E. ... . Dark Chocolate. Rich in: Antioxidants; Vitamins A, B, C, D, E. ... . Carrots. Rich in: Beta-carotene, Antioxidants.. How and where is melanin produced?The process of melanin synthesis and distribution is called melanogenesis, a process that is based on melanocytes present among the basal cells of the epidermis. Pigments formed in melanocyte melanosomes are then stored in the basal layer of epidermal cells, as well as in dermal macrophages, which become melanophores.
Where do you find melanin?Melanin is found in several areas of the human body including: Skin where it provides skin color. Hair. Pupils or irises of the eyes.
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