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.

Lipotoxicity,caused by intracellular lipid accumulation,accelerates the degenerative process of cellular senescence,which has implications in cancer development and therapy.Previously,camitine palmi-toyltransferase 1C (CPT1C),a mitochondrial enzyme that catalyzes carnitinylation of fatty acids,was found to be a critical regulator of cancer cell senescence.However,whether loss of CPT1C could induce senescence as a result of lipotoxicity remains unknown.An LC/MS-based lipidomic analysis of PANC-1,MDA-MB-231,HCT-116 and A549 cancer cells was conducted after siRNA depletion of CPT1C.Cellular lipotoxicity was further confirmed by lipotoxicity assays.Significant changes were found in the lipidome of CPT1 C-depleted cells,including major alterations in fatty acid,diacylglycerol,triacylglycerol,oxidative lipids,cardiolipin,phosphatidylglycerol,phosphatidylcholine/phosphatidylethanolamine ratio and sphingomyelin.This was coincident with changes in expressions of mRNAs involved in lipogenesis.Histological and biochemical analyses revealed higher lipid accumulation and increased malondialde-hyde and reactive oxygen species,signatures of lipid peroxidation and oxidative stress.Reduction of ATP synthesis,loss of mitochondrial transmembrane potential and down-regulation of expression of mito-chondriogenesis gene mRNAs indicated mitochondrial dysfunction induced by lipotoxicity,which could further result in cellular senescence.Taken together,this study demonstrated CPT1C plays a critical role in the regulation of cancer cell lipotoxicity and cell senescence,suggesting that inhibition of CPT1C may serve as a new therapeutic strategy through induction of tumor lipotoxicity and senescence.