Cosmeceutical Critique

Melatonin update, Part 2


 

Recall that melatonin displays multiple biological functions, acting as an antioxidant, cytokine, neurotransmitter, and global regulator of the circadian clock, the latter for which it is best known.1-3 At the cutaneous level, melatonin exhibits antioxidant (direct, as a radical scavenger; indirect, through upregulating antioxidant enzymes), anti-inflammatory, photoprotective, tissue regenerative, and cytoprotective activity, particularly in its capacity to preserve mitochondrial function.4-8

Dr. Leslie S. Baumann

Melatonin also protects skin homeostasis,6 and, consequently, is believed to act against carcinogenesis and potentially other deleterious dysfunctions such as hyperproliferative/inflammatory conditions.5 Notably, functional melatonin receptors are expressed in human skin and hair follicles, where melatonin is also produced, further buttressing the critical role that melatonin plays in skin health.5 Melatonin also displays immunomodulatory, thermoregulatory, and antitumor functions.9 The topical application of melatonin has been demonstrated to diminish markers of reactive oxygen species as well as reverse manifestations of cutaneous aging.5

Melatonin is both produced by and metabolized in the skin. The hormone and its metabolites (6-hydroxymelatonin, N1-acetyl-N2-formyl-5-methoxykynuramine [AFMK], N-acetyl-serotonin, and 5-methoxytryptamine) reduce UVB-induced oxidative cell damage in human keratinocytes and melanocytes, and also act as radioprotectors.6

Melatonin has been shown to protect human dermal fibroblasts from UVA- and UVB-induced damage.9 In addition, melatonin and its metabolites have been demonstrated to suppress the growth of cultured human melanomas, and high doses of melatonin used in clinical trials in late metastatic melanoma stages have enhanced the efficacy of or diminished the side effects of chemotherapy/chemo-immunotherapy.9

UVB and melatonin in the lab

In a 2018 hairless mouse study in which animals were irradiated by UVB for 8 weeks, Park et al. showed that melatonin displays anti-wrinkle activity by suppressing reactive oxygen species- and sonic hedgehog-mediated inflammatory proteins. Melatonin also protected against transepidermal water loss and prevented epidermal thickness as well as dermal collagen degradation.10

Also that year, Skobowiat et al. found that the topical application of melatonin and its active derivatives (N1-acetyl-N2-formyl-5-methoxykynurenine and N-acetylserotonin) yielded photoprotective effects pre- and post-UVB treatment in human and porcine skin ex vivo. They concluded that their results justify additional investigation of the clinical applications of melatonin and its metabolites for its potential to exert protective effects against UVB in human subjects.8

Although the preponderance of previous work identifies melatonin as a strong antioxidant, Kocyigit et al. reported in 2018 on new in vitro studies suggesting that melatonin dose-dependently exerts cytotoxic and apoptotic activity on several cell types, including both human epidermoid carcinoma and normal skin fibroblasts. Their findings showed that melatonin exhibited proliferative effects on cancerous and normal cells at low doses and cytotoxic effects at high doses.11

Melatonin as a sunscreen ingredient

Further supporting its use in the topical armamentarium for skin health, melatonin is a key ingredient in a sunscreen formulation, the creation of which was driven by the need to protect the skin of military personnel facing lengthy UV exposure. Specifically, the formulation containing avobenzone, octinoxate, oxybenzone, and titanium dioxide along with melatonin and pumpkin seed oil underwent a preclinical safety evaluation in 2017, as reported by Bora et al. The formulation was found to be nonmutagenic, nontoxic, and safe in animal models and is deemed ready to test for its efficacy in humans.12 Melatonin is also among a host of systemic treatment options for skin lightening.13

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