Metabolism of melatonin in the skin: Why is it important?
Melatonin is produced in almost all living taxa and is probably 2-3 billion years old. Its pleiotropic activities are related to its local concentration that is secondary to its local synthesis, delivery from distant sites and metabolic or non-enzymatic consumption. This consumption generates metabolites through indolic, kynuric and cytochrome P450 (CYP) mediated hydroxylations and O-demethylation or non-enzymatic processes, with potentially diverse phenotypic effects. While melatonin acts through receptor-dependent and receptor-independent mechanisms, receptors for melatonin metabolites remain to be identified, while their receptor-independent activities are well documented. The human skin with its main cellular components including malignant cells can both produce and rapidly metabolize melatonin in cell-type and context-dependent fashion. The predominant metabolism in human skin occurs through indolic, CYP-mediated and kynuric pathways with main metabolites represented by 6-hydroxymelatonin, N1-acetyl-N2-formyl-5-methoxykynuramine (AFMK), N1-acetyl-5-methoxykynuramine (AMK), 5-methoxytryptamine, 5-methoxytryptophol and 2-hydroxymelatonin. AFMK, 6-hydroxymelatonin, 2-hydroxymelatonin and probably 4-hydroxymelatonin can potentially be produced in epidermis through UVB-induced non-enzymatic melatonin transformation. The skin metabolites are also the same as those produced in lower organisms and plants indicating phylogenetic conservation across diverse species and adaptation by skin of the primordial defense mechanism. As melatonin and its metabolites counteract or buffer environmental stresses to maintain its homeostasis through broad-spectrum activities, both melatoninergic and degradative pathways must be precisely regulated, because the nature of phenotypic regulations will depend on local concentration of melatonin and its metabolites. These can be receptor-mediated or represent non-receptor regulatory mechanisms.
Department of Dermatology, University of Alabama at Birmingham, Birmingham, AL, USA.|VA Medical Center, Birmingham, AL, USA.
Andrzej T
AT
Slominski
Department of Biochemistry, Belarusian State University, Minsk, Belarus.
Igor
I
Semak
Department of Dermatology, Allergology and Venerology, University of Lübeck, Lübeck, Germany.
Tobias W
TW
Fischer
Department of Dermatology, University of Alabama at Birmingham, Birmingham, AL, USA.
Tae-Kang
TK
Kim
Department of Dermatology, Allergology and Venerology, University of Lübeck, Lübeck, Germany.
Konrad
K
Kleszczyński
Johann Friedrich Blumenbach Institute of Zoology and Anthropology, University of Göttingen, Göttingen, Germany.
Ruediger
R
Hardeland
Department of Cellular and Structural Biology, UT Health Science Center, San Antonio, TX, USA.
Russel J
RJ
Reiter
D000818:Animals; D002384:Catalysis; D006224:Cricetinae; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004817:Epidermis / Q000378:metabolism; D005260:Female; D006706:Homeostasis; D006801:Humans; D007211:Indoles / Q000737:chemistry; D015603:Keratinocytes / Q000378:metabolism; D008297:Male; D008550:Melatonin / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism*; D008745:Methylation; D009154:Mutation; D018384:Oxidative Stress; D010641:Phenotype; D010802:Phylogeny; D012867:Skin / Q000378:metabolism* / Q000528:radiation effects; D014466:Ultraviolet Rays
D007211:Indoles; C487380:N-(2-(5-methoxy-2-oxo-2,3-dihydro-1H-indol-3-yl)ethyl)acetamide; C002465:methoxytryptophol; D003577:Cytochrome P-450 Enzyme System; D008550:Melatonin; C012365:6-hydroxymelatonin
AFMK; AMK; melatonin; metabolism; skin