Melanin in human irides of different color and age of donors

Wielgus, Albert R.; Sarna, Tadeusz

doi:10.1111/j.1600-0749.2005.00268.x

Cited by 91 publications

(96 citation statements)

References 53 publications

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“…43,44 Wielgus and Sarna address the DHI/ DHICA ratio of colored human irides through their reported chemical degradation analyses. 45 Hydrogen peroxide degradation of melanosomes from several different colored irides yields a fairly constant PTCA/PDCA ratio, reflective of a constant DHI/ DHICA ratio for melanosomes isolated from different colored irides. Thus, the change in the observed absorption coefficients is representative of the relative contributions of the two different pigments, pheomelanin and eumelanin.…”

Section: Discussionmentioning

confidence: 99%

The Ultraviolet Absorption Coefficient of Melanosomes Decreases with Increasing Pheomelanin Content

Peles

Simon

2010

J. Phys. Chem. B

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Uveal melanosomes from the iridal stroma contain both eumelanin and pheomelanin, the ratio of which varies with iris color. Herein, we report the absorption coefficient at λ ) 244 nm for individual human iridal stroma melanosomes from dark brown and blue-green irides. The melanosomes are nearly identical in size, but differ in the relative concentration composition, ranging from a eumelanin/pheomelanin ratio of 14.8:1 (dark brown) to 1.3:1 (blue-green or hazel). The absorption coefficient of the melanosome decreases as its pheomelanin content increases. The origin of this decrease is attributed to a corresponding decrease in the number of UV-absorbing chromophores, reflecting the different molecular volumes of the monomeric building blocks of the two pigments. In agreement with reported data on synthetic pigments, the absorption coefficient of pheomelanin is found to be slightly larger than that for eumelanin at λ ) 244 nm (by a factor of 1.2). On the basis of the reported optical properties of synthetic models, this result suggests that the absorption of pheomelanin is less than eumelanin at wavelengths of biological relevance (∼315-400 nm).

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Section: Discussionmentioning

confidence: 99%

The Ultraviolet Absorption Coefficient of Melanosomes Decreases with Increasing Pheomelanin Content

Peles

Simon

2010

J. Phys. Chem. B

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“…3,8 Recent measurements performed on blue irides using electron spin resonance spectroscopy detected less melanin in medium blue irides than in light blue irides. 9 It was postulated that this surprising finding could be related to the localization of pigment granules in the outermost iridal layers. 9 Difficulties 4,9 in performing separate wet measurements on the ABL and SL have precluded the in loco verification of this hypothesis, however.…”

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“…9 It was postulated that this surprising finding could be related to the localization of pigment granules in the outermost iridal layers. 9 Difficulties 4,9 in performing separate wet measurements on the ABL and SL have precluded the in loco verification of this hypothesis, however.…”

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confidence: 99%

“…These changes suggest that the lighter shades and the hue transitions toward blue observed in lightly pigmented irides may be associated to a relatively higher content of melanin in the SL, which may be also related to existence of light blue irides with melanin contents higher than those measured for medium blue irides. 9 To illustrate the latter possibility, we performed another experiment in which we considered two simulated lightly pigmented specimens A and B.…”

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Qualitative assessment of undetectable melanin distribution in lightly pigmented irides

Baranoski

Lam

2007

J. Biomed. Opt.

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Abstract.A longstanding issue in biomedical research concerns the biophysical factors affecting the color diversity of the human irides and its connection with ocular diseases. Although the pigmentation and morphological characteristics of heavily and moderately pigmented irides have been extensively discussed in the literature, similar studies are scarce for lightly pigmented irides. We present computer experiments indicating that the spectral signature of these specimens may be directly affected by still undetectable melanin distributions in the outermost iridal layers. Our findings represent in silico evidence of this relationship which, in turn, may have implications in the investigation of the higher risk of death from metastatic ocular melanoma verified in individuals with light-colored irides.

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“…Wielgus and Sarna address the DHICA/DHI ratio of colored human irides; by chemical degradation analyses, they find a constant DHICA:DHI ratio for melanosomes isolated from different colored irides. 56 Thus changes in the observed …”

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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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Melanin in human irides of different color and age of donors

Cited by 91 publications

References 53 publications

The Ultraviolet Absorption Coefficient of Melanosomes Decreases with Increasing Pheomelanin Content

The Ultraviolet Absorption Coefficient of Melanosomes Decreases with Increasing Pheomelanin Content

Qualitative assessment of undetectable melanin distribution in lightly pigmented irides

The Red and the Black

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