ABSTRACT
Mammalian catechol-O-methyltransferases(COMT)are an important class of conjugative enzymes,which play a key role in the metabolism and inactivation of catechol neurotransmitters,catechol es-trogens and a wide range of endobiotics and xenobiotics that bear the catechol group.Currently,COMT inhibitors are used in combination with levodopa for the treatment of Parkinson's disease in clinical practice.The crucial role of COMT in human health has raised great interest in the development of more practical assays for highly selective and sensitive detection of COMT activity in real samples,as well as for rapid screening and characterization of COMT inhibitors as drug candidates.This review summarizes recent advances in analytical methodologies for sensing COMT activity and their applications.Several lists of biochemical assays for measuring COMT activity,including the probe substrates,along with their analytical conditions and kinetic parameters,are presented.Finally,the challenges and future perspec-tives in the field,such as visualization of COMT activity in vivo and in situ,are highlighted.Collectively,this review article overviews the practical assays for measuring COMT activities in complex biological samples,which will strongly facilitate the investigations on the relevance of COMT to human diseases and promote the discovery of COMT inhibitors via high-throughput screening.
ABSTRACT
Daphnetin is quickly eliminated in rats after dosing, but the mechanism remains unclear. This study was aimed to investigate the in vitro metabolism of daphnetin using rat liver S9 fractions (RLS9). The metabolites formed in RLS9 were identified and the kinetic parameters for different metabolic pathways were determined. HPLC-DAD-MS analysis showed that daphnetin was biotransformed to six metabolites, which were identified as 7 or 8 mono-glucuronide and mono-sulfate, 8-methylate, and 7-suflo-8-methylate. Methylation and glucuronidation of daphnetin exhibited the Michaelis-Menten kinetic characteristics, whereas the substrate inhibition kinetic and the two-site kinetic were observed for 8-sulfate and 7-sulfate formations. Of the 3 conjugation pathways, the intrinsic clearance rate for sulfation was highest, followed by methylation and glucuronidation. By in vitro-in vivo extrapolation of the kinetic data measured in RLS9, the hepatic clearance were estimated to be 54.9 mL·min-1·kg-1 which is comparable to the system clearance (58.5 mL·min-1·kg-1) observed in rats. In conclusions, the liver might be the main site for daphnetin metabolism in rats. Sulfation, methylation and glucuronidation are important pathways of the hepatic metabolism of daphnetin in rats.
ABSTRACT
Catechol O-methyltransferase (COMT), one of the endogenous phase II metabolizing enzymes, expressed by chromosome 22. COMT catalyzes the transfer of a methyl group from common methyl donor S-adenosyl-L-methionine (AdoMet or SAM) to one of the catechol hydroxyls. COMT participates in the metabolism of many catechols in vivo, e.g. dopamine, epinephrine, noradrenaline, estradiol. Furthermore COMT also plays important roles in the metabolism of xenobiotic catechols from food and drug. COMT play a critical role in the management of catechols. Metabolism disorders of COMT can cause many diseases or an increased risk of diseases, e.g. Pakinson diseases, schizophrenia, and breast cancer. In this review, we explains the relationship of COMT and related-diseases through expounding disease caused by the COMT metabolic disorders. Finally, we hope that there will be more effective treatments for the COMT metabolism related diseases.