The skin’s endogenous antioxidant network
Roger L. McMullen in Antioxidants and the Skin, 2018
There are two types of biological melanin present in skin and hair: eumelanin and pheomelanin (Figure 3.23).38 Eumelanin is responsible for dark color pigmentation and results in brown and black tones. Pheomelanin, on the other hand, is a red and yellow pigment and is more predominantly found in fair-skinned individuals, e.g., individuals with red hair contain greater quantities of pheomelanin than eumelanin. The synthesis of both types of melanin begins with the aromatic amino acid tyrosine in a reaction that is catalyzed by the enzyme, tyrosinase. This results in the formation of 3,4-dihydroxyphenylalanine (DOPA) which further undergoes conversion to dopaquinone. At this point, two separate reaction pathways proceed for the synthesis of eumelanin and pheomelanin (see Appendix 2 for a schematic of melanin synthesis).
Revisioning Cellular Bioenergetics
Aruna Bakhru in Nutrition and Integrative Medicine, 2018
The pecten, which is enlarged in birds enduring hypoxia, thirst, and hunger during long-distance migrations, may serve as an adaptive coping mechanism to meet “energy and nutrient needs under extreme conditions, by a marginal but critical, melanin-initiated conversion of light to metabolic energy, coupled to local metabolite recycling” (Goodman & Bercovich, 2008, p. 190). This is substantiated by data showing that pheomelanin can be reduced to molecular oxygen (Ye et al., 2006). In addition, the lability and polymeric heterogeneity of melanin, stacked in a disordered nano-aggregate architecture, helps to explain its “thermodynamically cheap means for broadband light absorption” (Goodman & Bercovich, 2008, p. 197). In other words, micro-spatial changes in melanin conformation can produce instability in electron states, causing alterations in the direct biochemical milieu of melanin that instigate repletion of metabolic intermediates and up-regulate local anaplerosis (Goodman & Bercovich, 2008). Especially critical is that light can stimulate NADPH by way of melanin, and generate oxygen and water through catalase via the hydrogen peroxide flowing through the pecten (Goodman & Bercovich, 2008).
Ocular Tumors
Ching-Yu Cheng, Tien Yin Wong in Ophthalmic Epidemiology, 2022
It has been reported that iris color is a risk factor for the development of uveal melanoma.45,47 The most affected eye colors are light-color irises while brown-colored eyes are the least affected.45,49 Recent studies have determined the potential link of higher risk to the difference of melanin molecules in the iris. Eumelanin and pheomelanin both are present in the iris; the distinction lies with the ratio of these types of melanin. Lighter-colored eyes contain a higher degree of pheomelanin and lower amounts of eumelanin, while in darker eyes the distribution is opposite.50 Pheomelanin is more phototoxic than eumelanin, causing an increased propensity of developing radical oxygen species and decreased antioxidant potential when exposed to light, both of which can cause damage to DNA.51,52 Additionally, recent studies have identified three single-nucleotide polymorphisms in pigment genes HERC2, OCA4, and IRF4, which are known risk factors linked tocutaneous melanoma; however, further studies are needed to confirm these observations reading uveal melanoma.53
Novel tyrosinase inhibitory peptide with free radical scavenging ability
Published in Journal of Enzyme Inhibition and Medicinal Chemistry, 2019
Zhiwei Shen, Yujiao Wang, Zhen Guo, Tingyuan Tan, Yi Zhang
Melanin is a natural pigment present widely in living organisms. The primary role of melanin is to reduce the skin damage caused by ultraviolet (UV) radiation. On one hand, it serves as a physical barrier and absorbent filter that scatters and limits the penetration of UV radiation7. On the other hand, it also can scavenge harmful free radicals induced by the UV radiation7–9. However, excessive accumulation and overproduction of melanin can result in the development of physiological abnormalities such as pigment spots, chloasma, freckles, age spots, and even melanoma, as well as neurodegeneration-associated diseases such as the Parkinson’s disease10–12. Furthermore, overproduction of melanin in vegetables accelerates corruption, leading to the loss of nutrients and economic wastage13,14.
Effect of ultraviolet radiation on the Nrf2 signaling pathway in skin cells
Published in International Journal of Radiation Biology, 2021
Alena Ryšavá, Jitka Vostálová, Alena Rajnochová Svobodová
Melanocytes are the second most abundant epidermal element (1–2%), situated in the basal layer and with an origin in neural crests. They are small, rounded cells with numerous long cytoplasmic appendixes that penetrate the epidermal stratum basale and stratum spinosum (Figure 1) (Kanitakis 2002; Mescher 2016). Melanocytes synthesize the melanin pigments, in particular eumelanin, pheomelanin, and mixed melanin, which participate in skin coloring and represent one protection mechanism against solar radiation. Synthesis of melanin arises from L-tyrosine and requires the enzyme tyrosinase (Slominski et al. 2004, Slominski, Zmijewski et al. 2012). Melanin has the ability to scatter UV rays and absorb UV, visible and infrared radiation as well as scavenge reactive oxygen and nitrogen species (ROS, RNS) that have been produced. However, melanin synthesis itself generates ROS, especially the synthesis of lighter variant pheomelanin (Smit et al. 2008). Moreover, pheomelanin can undergo photosensitization that results in the generation of superoxide radicals, hydroxyl radicals and hydrogen peroxide (Slominski et al. 2004). From this point of view, pheomelanin also has pro-oxidative properties and can participate in photoaging and carcinogenic processes (see below). In addition to melanin synthesis, melanocytes secrete a wide range of signal molecules such as cytokines (tumor necrosis factor-α (TNF-α), interleukins), catecholamines and nitric oxide in response to a number of stimuli (including UV radiation) and, via these molecules, influence other epidermal and dermal cells (Svobodová and Vostálová 2010).
Novel formulations for topical delivery of tranexamic acid: assessing the need of epidermal targeting for hyperpigmentation disorders
Published in Expert Opinion on Drug Delivery, 2023
Piyush Verma, Khushwant S. Yadav
Pigmentation or coloration of skin is influenced by genetic factors and physiological factors. Darker skin tones are associated with high melanin levels [23]. Hyperpigmentation disorders are associated with high melanin production, which is produced as a result of bodies biosynthetic pathway called melanin cycle [24]. Melanin production takes place in melanocyte cells which are present in epidermal layer of skin. Melanin cells are produced from its precursor cells, melanoblasts [25].
Related Knowledge Centers
- Melanocyte
- Neuromelanin
- Redox
- Amino Acid
- Tyrosine
- Cysteine
- Benzothiazine
- Parkinson's Disease
- Ultraviolet
- Melanoma