Melanin: benefits, dosage, contraindications

Dermatological effect

Melanin from natural sources has a wide range of biological activities, including protection against UV rays, enzymatic lysis, and damage caused by oxidants. Furthermore, melanin has been shown to chelate metal ions and act as a physiological redox buffer. The use of melanin in cosmetics and sunscreens has been adopted by many manufacturers aiming to mimic the natural role of these molecules in the skin. Traditionally, eumelanins have an antioxidant and photoprotective role in dark-skinned phenotypes, whereas pheomelanins have been implicated in the increased susceptibility to skin cancer of 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 plays an important antioxidant role in the skin. Melanin extracted from tea leaves has been found to inhibit the oxidation of low-density lipoproteins, which supports the idea of a melanin inhibitory effect against peroxyl radicals. Another study has suggested that complex melanins, composed of fractions of eumelanin and pheomelanin, exhibit an antioxidant effect due to the action of eumelanins, while pheomelanins tend to cause a pro-oxidant effect. Thus, the antioxidant behavior of melanin should be considered as resulting from a combination of two opposing effects. But because eumelanin is the predominant fraction in most biological tissues, an antioxidant effect associated with eumelanin is mainly observed.

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Immunomodulator

A number of studies have shown that plant and synthetic melanin can modulate cytokine production and improve several immune parameters. Recently, it has been shown that animal and fungal melanin (derived respectively from rat and Aspergillus fumigatus) also modulates 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, green tea melanin being at least 100 times more active than black tea melanin. The immunostimulatory effects of melanin preparations from 30 traditional medicinal plants were 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 topical application of melanin has a strong anti-inflammatory effect and that melanin is more effective than hydrocortisone.

Gastroprotective

Melanin can prevent the formation of gastric ulcers induced by ulcerogenic agents such as indomethacin. In addition, melanin can lead to the restoration of mucus levels in ethanol-depleted gastric cell walls.rnrnRecently, 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.rnrn

Hepatoprotective

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

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Depurative

Studies have shown that various drugs and other chemicals, such as organic amines, metals, and polycyclic aromatic hydrocarbons, bind readily to melanin and are retained in pigmented tissues for long periods. The physiological significance of this metal-binding property of melanin is not clear, but one suggestion is that melanin protects pigmented cells and adjacent tissues by adsorbing potentially harmful substances, which are then slowly released at non-toxic concentrations.rnrnNumerous 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 can lead to toxicity in cases of overexposure.rnrn

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