Metabolism of melatonin by cytochrome P450s in rat liver mitochondria and microsomes

Abstract

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 (NAS), 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 Km value) and higher Vmax for melatonin 6-hydroxylation and O-demethylation for both high-affinity and low-affinity components as compared to 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 P-450s metabolize melatonin principally by 6-hydroxylation, with O-demethylation representing a minor metabolic pathway.

Melatonin, mitochondria, and the skin

“…Cytochrome P450-mediated 6-hydroxylation and O-demethylation of melatonin in these organelles was first described in the liver [65]; however, it has become clear that these reactions may occur in other tissues, including skin. Several forms of cytochrome P450 (CYP1A, CYP3A, and CYP2E) responsible for the melatonin metabolism in hepatic mitochondria are found in the skin [66] and the production of 6-hydroxymelatonin and N -acetylserotonin was detected in different skin cells [41].…”

“…It is clear that there are at least two major pathways of melatonin metabolism in mitochondria [62, 65], each consisting of different types of reactions and playing special physiological roles in skin cells. Pseudoperoxidase oxidation of melatonin by cytochrome c is involved in H 2 O 2 -mediated signaling pathways via regulation H 2 O 2 efflux from mitochondria to cytoplasm.…”

Melatonin Inhibits Benzene-Induced Lipid Peroxidation in Rat Liver

“…This suggests that CYP 450 2E1 activity varies with melatonin concentration. Semak et al (44) believe that microsomal CYP 450 2E1 plays a smaller role in melatonin-O-demethylation in rat liver. Both endogenous and administered melatonin are known to metabolise in humans principally by 6-hydroxylation, with O-demethylation representing a relatively minor pathway.…”

Melatonin and Circadian Rhythm: Aging, Cancer, and Mechanism

“…Data indicate the crucial role played by the methoxy substituent. Various investigations were carried out on metabolism with rat and human subjects [12]- [15]. The principal products are 6-hydroxymelatonin (Figure 1) and N-acetylseratonin (Figure 2) from O-demethylation.…”