The Ultraviolet Absorption Coefficient of Melanosomes Decreases with Increasing Pheomelanin Content

The definition of the concentration of pheomelanin in the skin is an issue of great interest because in the case of being influenced by UV radiation, it manifests itself as a prooxidant, causing various skin disorders including melanoma that might help to explain the relatively high incidence of skin cancer among individuals with red hair. The ESR spectra of red hair samples were investigated. It was found that at low microwave power, they are characterized by two types of spectra. Red hair ESR signals result from a superposition of two spectral shapes, a singlet spectrum as a result of the existence of eumelanin and a triplet spectrum as a result of the existence of pheomelanin. At high microwave power, only triplet spectra shape was detected, caused by saturation of the eumelanin singlet. Using different concentration ratios of black to red hair, we measured ESR spectra and plotted the ratio values in each sample against a measured 'g-factor' (experimental). We found that there is a linear relationship between these two parameters. So, it is evident that using these results, the concentration ratio of pheomelanin to eumelanin in a sample of hair can be easily determined by an almost noninvasive method. This can be considered a potential advantage for many practical activities compared with other invasive methods. The concentration dependence curve of pheomelanin (µg/mg) on gexp-factor in an ESR spectrum of hair has been designed, which allows the determination of the amount of pheomelanin in hair of any color.

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“…It is confirmed that melanin plays the most important protective role against UV radiation in the skin …”

Section: Introductionmentioning

confidence: 83%

“…In most of these experiments, the hair is treated using different chemical methods. The specific eumelanin and pheomelanin degradation products were used as markers …”

Section: Introductionmentioning

confidence: 99%

Electron spin resonance (ESR/EPR) of free radicals observed in human red hair: a new, simple empirical method of determination of pheomelanin/eumelanin ratio in hair

Chikvaidze

Partskhaladze

Gogoladze

2014

Magnetic Reson in Chemistry

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“…We demonstrated 18 that the average path length, s, through half of the ellipsoidal melanosome is given by…”

Section: Experimental Methodsmentioning

confidence: 98%

Ultraviolet Absorption Coefficients of Melanosomes Containing Eumelanin As Related to the Relative Content of DHI and DHICA

Peles

Lin

Wakamatsu

et al. 2010

J. Phys. Chem. Lett.

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Central to understanding the photochemical function(s) of melanosomes is the determination of their absorption properties and an understanding of how the absorption varies with the molecular composition of melanin. Herein, the absorption coefficients for melanosomes containing predominantly eumelanin, a polymeric pigment derived from the molecular precursors 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA), are reported for λ = 244 nm. The absorption coefficient varies with the DHICA/DHI ratio, determined from chemical degradation analyses. With increasing DHICA content, the absorption coefficient of the melanosome increases. This observation is consistent with reported extinction coefficients, which reveal that at 244 nm, the extinction coefficient of DHICA is a factor of ∼2.1 greater than that of DHI. The melanosome absorption coefficients are compared to predicted values based on a linear combination of the absorption of the constituent monomers. SECTION Biophysical Chemistry Eumelanin is a commonly occurring pigment derived from the molecular precursors 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA).1-4 Even though the molecular structure of eumelanin remains elusive, exquisite analytical techniques have been developed that enable determination of the relative contributions of these two precursors to the overall pigment. 2,5Studies of eumelanins from different tissues exhibit a wide range of DHICA/DHI ratios. [5][6][7][8] However, how such changes in the molecular composition affect the eumelanic UV absorption coefficient has not been examined for natural systems.

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“…57 At first glance, one might assume that this means pheomelanin has a smaller absorption cross section than eumelanin. Such a conclusion would be in stark contrast to studies on synthetic pigments, where comparable absorption coefficients are observed.…”

Section: Red and Black Simon And Pelesmentioning

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 Ultraviolet Absorption Coefficient of Melanosomes Decreases with Increasing Pheomelanin Content

Cited by 15 publications

References 56 publications

Electron spin resonance (ESR/EPR) of free radicals observed in human red hair: a new, simple empirical method of determination of pheomelanin/eumelanin ratio in hair

Electron spin resonance (ESR/EPR) of free radicals observed in human red hair: a new, simple empirical method of determination of pheomelanin/eumelanin ratio in hair

Ultraviolet Absorption Coefficients of Melanosomes Containing Eumelanin As Related to the Relative Content of DHI and DHICA

The Red and the Black

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