Chemistry of Melanins

Itô, Shôsuke; Wakamatsu, Kazumasa

doi:10.1002/9780470987100.ch15

Cited by 49 publications

(46 citation statements)

References 197 publications

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“…The most studied eumelanins are black-to-brown insoluble pigments derived at least in part from the oxidative polymerization of L-DOPA via 5,6-dihydroxyindole intermediates (Prota 2000; Wakamatsu and Ito, 2002). Pheomelanins are yellow-to-reddish brown, alkali-soluble, sulfur-containing pigments derived from the oxidation of cysteinyldopa precursors via benzothiazine and benzothiazole intermediates (Ito and Wakamatsu, 2006). NM pigments are extensively discussed in the following chapters of this review and will not be addressed in this chapter.…”

Section: Definition Classification and Basic Physicochemical Propmentioning

confidence: 99%

Interactions of iron, dopamine and neuromelanin pathways in brain aging and Parkinson's disease

Zucca

Segura‐Aguilar

Ferrari

et al. 2017

Progress in Neurobiology

546

482

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There are several interrelated mechanisms involving iron, dopamine, and neuromelanin in neurons. Neuromelanin accumulates during aging and is the catecholamine-derived pigment of the dopamine neurons of the substantia nigra and norepinephrine neurons of the locus coeruleus, the two neuronal populations most targeted in Parkinson’s disease. Many cellular redox reactions rely on iron, however an altered distribution of reactive iron is cytotoxic. In fact, increased levels of iron in the brain of Parkinson’s disease patients are present. Dopamine accumulation can induce neuronal death; however, excess dopamine can be removed by converting it into a stable compound like neuromelanin, and this process rescues the cell. Interestingly, the main iron compound in dopamine and norepinephrine neurons is the neuromelanin-iron complex, since neuromelanin is an effective metal chelator. Neuromelanin serves to trap iron and provide neuronal protection from oxidative stress. This equilibrium between iron, dopamine, and neuromelanin is crucial for cell homeostasis and in some cellular circumstances can be disrupted. Indeed, when neuromelanin-containing organelles accumulate high load of toxins and iron during aging a neurodegenerative process can be triggered. In addition, neuromelanin released by degenerating neurons activates microglia and the latter cause neurons death with further release of neuromelanin, then starting a self-propelling mechanism of neuroinflammation and neurodegeneration. Considering the above issues, age-related accumulation of neuromelanin in dopamine neurons shows an interesting link between aging and neurodegeneration.

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Section: Definition Classification and Basic Physicochemical Propmentioning

confidence: 99%

Interactions of iron, dopamine and neuromelanin pathways in brain aging and Parkinson's disease

Zucca

Segura‐Aguilar

Ferrari

et al. 2017

Progress in Neurobiology

546

482

View full text Add to dashboard Cite

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“…13 Subsequently, the late 1960s through the 1980s witnessed great advances in the development of quantitative approaches based on oxidative degradation and reductive hydrolysis of natural pigments to generate meaningful insight into aspects of the molecular structures of melanins. 14,15 Shosuke Ito refined many of these analytical approaches, and his methods are currently the best approaches available for deriving molecular information about melanins. 16 Specifically, the yields of PTCA, pyrrole-2,3-dicarboxylic acid (PDCA), and 4-AHP produced by degradation techniques are routinely used to infer the relative contributions of specific molecular monomers, but not their chemical connectivity, to the overall architecture of the pigment.…”

Section: A Journeymentioning

confidence: 99%

The Red and the Black

2010

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Pigmentation, which is primarily determined by the amount, the type, and the distribution of melanin, shows a remarkable diversity in human populations, and in this sense, it is an atypical trait."sE. J. Parra.Melanin is found throughout the human body, skin, eye, brain, hair, and inner ear, yet its molecular structure remains elusive. Researchers have characterized the molecular building blocks of melanin but have not been able to describe how those components fit together in the overall architecture of the pigment. Melanin is categorized into two distinct classes, pheomelanin (red) and eumelanin (black). Although these classes share a common biosynthetic origin, specific molecular reactions occurring early in pigment production differentiate these two types. Pure eumelanin is found throughout nature, which has allowed researchers to characterize and quantify its chemical properties. However, pure pheomelanin is not observed in nature and rarely makes up more than ∼25% of the total melanin present. In this Account, we explore our current understanding of the structure and reactivity of the red and black pigments.Epidemiological studies of skin and ocular cancers suggest that increasing relative proportions of pheomelanin correlate with increased risk factors for these diseases. Therefore, understanding the factors that control the relative abundance of the two pigments has become increasingly important. Consequently, researchers have worked to elucidate the chemistry of pheomelanin to determine whether the pigment could cause these cancers and, if so, by what mechanisms. The photoactivation of oxygen by pheomelanin in the UV-A range could contribute to the development of UV-induced cancers: recent measurement of the surface photoionization threshold of intact melanosomes reveals a lower photoionization potential for pheomelanin than eumelanin. A complementary study of intact human melanosomes isolated from different colored irides reveals that the absorption coefficient of the melanosome decreases with increasing pheomelanin content. These results suggest that the epidemiological data may simply result from an increased exposure of the underlying tissues to UV light.

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“…The physic-chemical properties of MN particles, e.g., aggregation, have been studied and reviewed extensively before. 1,[14][15][16] For example, it has been shown that the MN particles present in ink sacs of cuttlefish are aggregates of much smaller MN particulate units. 17 Although this model of MNmacroaggregates composed of MN-microparticles may not be applicable to all MN that are present in vivo or the MN synthesized in the lab.…”

Section: Introductionmentioning

confidence: 99%

Dark- or Light-Colored Melanins: Generating Pigments Using Fe2+ and H2O2

Vercruysse

Russell²,

Knight³

et al. 2017

Preprint

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We have studied the formation of melanin-like pigments from catechol or pyrogallol and a wide range of other phenolic compounds using Fe 2+ and H 2 O 2 . Combining UV_Vis spectroscopic measurements and size-exclusion chromatography analyses we evaluated the impact of the intensity of the oxidation reaction by varying the concentration of H 2 O 2 present in the reaction mixtures. All compounds tested, except tyrosine, reacted readily leading to mixtures that were black, brown or yellow-orange in color. For many compounds tested, the use of increasing concentrations of H 2 O 2 resulted in either precipitation of the pigment or the formation of a soluble, lighter-colored pigment. With catechol or pyrogallol as model compounds, and using different concentrations of H 2 O 2 , several materials were synthesized, purified and dried. The physic-chemical properties of these materials were compared to the properties of melanin-like pigments synthesized from the same precursors using air-oxidation in an alkaline environment. For both precursors, a distinct chemical change, as judged from FT-IR spectroscopy, was introduced in the melanin structures when using H 2 O 2 as the oxidizing agent and the relative intensity of this distinct signal strengthened with increasing concentration of H 2 O 2 used in the reaction. In general, our results suggest that depending on the precursor molecule and the intensity of the oxidizing reaction conditions involved, light-or dark-colored melanin-like pigments can be generated. This may be an important factor when evaluating the visible outlook of histological or archeological specimens: the presence of a lighter color or the absence of a dark color may not necessarily mean the absence of melanin-like biomolecules.

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Chemistry of Melanins

Cited by 49 publications

References 197 publications

Interactions of iron, dopamine and neuromelanin pathways in brain aging and Parkinson's disease

Interactions of iron, dopamine and neuromelanin pathways in brain aging and Parkinson's disease

The Red and the Black

Dark- or Light-Colored Melanins: Generating Pigments Using Fe2+ and H2O2

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