The identification of the UV degradants of melatonin and their ability to scavenge free radicals

Abstract

Ultraviolet (UV) light is known to induce the generation of free radicals in biological tissues such as skin. Of these free radicals, the O2-. and particularly the.OH radical can induce cellular damage including lipid peroxidation. Thus, the use of antioxidants to prevent such damage induced by UV irradiation has received much attention recently. One such antioxidant, which has the potential to be incorporated into sunscreens, is the pineal secretory product melatonin. One of the concerns of using melatonin in sunscreens is its photostability. In the present study, we investigated the photostability of melatonin subjected to UV irradiation. In addition, we used liquid chromatography mass spectrometry (LC-MS) to identify the degradants and we also assessed the ability of the degradants to inhibit O2-. generation as well as lipid peroxidation in rat brain homogenate. The results show that UV irradiation of melatonin (0.1 mg/mL) using a 400-W lamp for 2 hr caused a significant decline of melatonin to 18% of its original concentration after 20 min, with the decline continuing until the melatonin concentration reaches zero at 120 min. The LC-MS results show that the degradants of melatonin are 6-hydroxymelatonin and N1-acetyl-N2-formyl-5-methoxykynurenamine (AFMK). These degradants were able to provide equipotent activity against potassium cyanide (KCN)-induced superoxide generation compared to non-irradiated melatonin. Thus, the study shows that although melatonin is rapidly degraded by UV irradiation, the degradants retain antioxidant activity, making melatonin a likely candidate for inclusion in sunscreens.

The role of melatonin in the light of current knowledge

“…This hormone is a more effective antioxidant than glutathione and vitamins E and C. In recent years, the presence of melatonin metabolites in the skin (AFMK, AMK) has been found. They arise, among other things, as a result of the non-enzymatic pathway (caused by UV radiation) [14]. This finding confirms not only the existence of metabolic pathway induced by UV, but also the already mentioned antioxidant activity.…”

“…Fibroblasts play a crucial role in the processes of skin aging -they are responsible for the synthesis of extracellular matrix components such as collagen, glycosaminoglycans, and elastin. It has been observed that heme oxygenase 1 (HO-1) plays an important role in the protection of fibroblasts, and melatonin enhances the expression of this enzyme, which confirms its protective properties for cells [3,[12][13][14][15][16][18][19][20][21]. Melatonin also plays an important oncostatic role through slowing the growth of tumors and inhibiting angiogenesis within them.…”

“…This system includes the epidermis, dermis and hair follicles. It is likely that the MAS has evolved as a result of the defense mechanisms against environmental factors, in particular UV radiation [3,[10][11][12][13][14][15]. The antioxidant activity of melatonin is mediated by binding to nuclear receptors ROR/RZR and stimulation of gene expression of the main antioxidant enzymes (catalase, glutathione peroxidase).…”

“…During this process, the hydroxyl radicals are scavenged, and the resulting adverse events are reduced directly or indirectly by reducing lipid peroxidation, protein oxidation, as well as mitochondrial and DNA damage. The melatonin metabolites AFMK and AMK are more potent free radical scavengers than melatonin itself [3,[12][13][14][15][16].…”

Melatonin Natural Health Products and Supplements: Presence of Serotonin and Significant Variability of Melatonin Content

“…Because melatonin has been suggested to be unstable under some storage conditions, and melatonin is known to occur naturally in medicinal plants, this raises potential pitfalls that may lead to degradation or modification of the melatonin content in these supplements, especially with such a wide diversity of matrices. 13 …”