n-(2-(5-methoxy-2-oxo-2-3-dihydro-1h-indol-3-yl)ethyl)acetamide and 6-hydroxymelatonin

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, N

Topics: Animals; Catalysis; Cricetinae; Cytochrome P-450 Enzyme System; Epidermis; Female; Homeostasis; Humans; Indoles; Keratinocytes; Male; Melatonin; Methylation; Mutation; Oxidative Stress; Phenotype; Phylogeny; Skin; Ultraviolet Rays

In the present study we provide direct evidence for the involvement of rat microsomal cytochrome P450s in melatonin O-demethylation and hydroxylation at two different positions: 2 and 6, as well as generation of N(1)-acetyl-N(2)-formyl-5-methoxy-kynuramine (AFMK) and two unknown products. Moreover, we found that mitochondrial cytochrome P450s also converts melatonin into AFMK, N-acetylserotonin, 2-hydroxymelatonin, 6-hydroxymelatonin and the same two unknown products. Eadie-Hofstee plots for 6-hydroxylation and O-demethylation reactions were curvilinear for all tested fractions, suggestive of involvement of at least two components, one with a high affinity and low capacity, and another with a low affinity and high capacity. Mitochondrial cytochrome P450s exhibited higher affinity (suggesting lower K(m) value) and higher V(max) for melatonin 6-hydroxylation and O-demethylation for both high-affinity and low-affinity components as compared with microsomal enzymes. The intrinsic clearance for melatonin hydroxylation by high- and low-affinity components displayed the highest values in all tested fractions, indicating that both mitochondrial and microsomal cytochrome P450s metabolize melatonin principally by 6-hydroxylation, with O-demethylation representing a minor metabolic pathway.

Topics: Animals; Chromatography, High Pressure Liquid; Cytochrome P-450 Enzyme Inhibitors; Cytochrome P-450 Enzyme System; Kinetics; Kynuramine; Liver; Male; Melatonin; Microsomes, Liver; Mitochondria, Liver; Rats; Rats, Wistar; Serotonin; Spectrometry, Mass, Electrospray Ionization