Melanin: Benefits, Dosage, Contraindications

Dermatological Effect

Melanin from natural sources possesses a wide range of biological activities, including protection against UV rays, enzymatic lysis, and damage from oxidants. Additionally, it has been demonstrated that melanin chelates metal ions and acts as a physiological redox buffer. The use of melanin in cosmetics and sunscreens has been adopted by many manufacturers to mimic the natural role of these molecules in the skin. Traditionally, eumelanins play an antioxidant and photoprotective role in dark-skinned phenotypes, while pheomelanins have been implicated in increased skin cancer susceptibility for individuals with the red-haired phenotype due to their photosensitizing and pro-oxidant properties.

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Antioxidant

Melanins from various sources exhibit significant antioxidant activity. Studies have observed that melanin protects melanocytes and keratinocytes from DNA damage caused by hydrogen peroxide, indicating that the pigment has an essential antioxidant role in the skin. Melanin extracted from tea leaves has been shown to inhibit low-density lipoprotein oxidation, supporting the idea of an inhibitory effect of melanin against peroxide radicals. Another study suggested that complex melanins, consisting of eumelanin and pheomelanin fractions, have an antioxidant effect due to the action of eumelanins, while pheomelanins tend to provoke a pro-oxidant effect. Thus, the antioxidant behavior of melanin should be considered as due to a combination of two opposite effects. But since eumelanin is the predominant fraction in most biological organs, an antioxidant effect related to eumelanin is mostly observed.

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Immuno-modulator

A number of studies have shown that plant and synthetic melanin can modulate cytokine production and enhance several immune parameters. Recently, it has been demonstrated that both animal and fungal melanin (derived from rats and Aspergillus fumigatus respectively) also modulate cytokine production. Sava et al (2001) extracted melanin-like pigments (MLP) from black tea and showed that oral administration of MLP to mice significantly stimulated splenic lymphoid tissue. Later, Hung et al demonstrated that melanin extracted from different tea species induced cytokine production, with green tea melanin being at least 100 times more active than black tea melanin. The immunostimulant effects of melanin preparations from 30 traditional medicinal plants have been studied and patented by Pasco et al (2005). The authors reported that the most active melanins were found in Allium sativum, Tabebuia spp., Serenoa repens, and Echinacea spp.

Anti-inflammatory

Animal studies have reported that melanin interferes with prostaglandins, leukotrienes, and/or other complement systems involved in inflammation. El-Obeid et al (2016) studied the anti-inflammatory effect of Nigella sativa L melanin in the treatment of formalin-induced rat paw edema. The results showed that the topical application of melanin has a strong anti-inflammatory action and that melanin is more effective than hydrocortisone.

Gastroprotective

Melanin may prevent the formation of gastric ulcers induced by ulcerogenic agents such as indomethacin. Additionally, melanin may lead to the reconstitution of mucus levels in ethanol-depleted gastric cell walls. Recently, it has been shown that pure melanin extracted from Nigella sativa seeds strongly protects against ulcers induced by alcohol, indomethacin, stress, or the combined ulcerogenic action of stress and aspirin.

Hepato-protective

Melanin extracted from different tea species exhibits protective effects against hydrazine-induced liver damage. Sava et al. (2003) showed that administering melanin-like pigments (MLP) derived from tea to rats 30 minutes before hydrazine administration prevented both severe hepatic intoxication and the increase of serum alanine transaminase (ALT) activity in the liver. Additionally, the treatment was associated with low concentrations of malondialdehyde (MDA) and decreased glutathione levels in the liver. Recently, ElObeid et al. (2015) demonstrated that melanin from Nigella sativa L. prevented carbon tetrachloride (CCl4) induced liver damage in Wistar rats. Pretreatment of rats with melanin led to a significant reduction in CCl4-induced aspartate aminotransferase (AST), ALT, and MDA levels.

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Purifying

Research has shown that various drugs and other chemicals, such as organic amines, metals, and polycyclic aromatic hydrocarbons, easily bind to melanin and are retained in pigmented tissues for long periods. The physiological significance of this metal-binding property of melanin is unclear, but it is suggested that melanin protects pigmented cells and adjacent tissues by adsorbing potentially harmful substances, which are then slowly released at non-toxic concentrations. Many studies suggest that the specific retention of drugs and metals by melanin initially protects cells but also serves as a depot that slowly releases accumulated compounds and may lead to toxicity if overexposed.

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