title: Nicotinamide N-methyltransferase catalyses the N-methylation of the endogenous β-carboline norharman: evidence for a novel detoxification pathway.
abstract: Nicotinamide N-methyltransferase (NNMT) is responsible for the N-methylation of nicotinamide to 1-methylnicotinamide. Our recent studies have demonstrated that NNMT regulates cellular processes fundamental to the correct functioning and survival of the cell. It has been proposed that NNMT may possess β-carboline (BC) N-methyltransferase activity, endogenously and exogenously produced pyridine-containing compounds which, when N-methylated, are potent inhibitors of Complex I and have been proposed to have a role in the pathogenesis of Parkinson's disease. We have investigated the ability of recombinant NNMT to N-methylate norharman (NH) to 2-N-methylnorharman (MeNH). In addition, we have investigated the toxicity of the BC NH, its precursor 1,2,3,4-tetrahydronorharman (THNH) and its N-methylated metabolite MeNH, using our in vitro SH-SY5Y NNMT expression model. Recombinant NNMT demonstrated NH 2N-methyltransferase activity, with a Km of 90 ± 20 µM, a kcat of 3 × 10(-4) ± 2 × 10(-5) s(-1) and a specificity constant (kcat/Km) of 3 ± 1 s(-1) M(-1) THNH was the least toxic of all three compounds investigated, whereas NH demonstrated the greatest, with no difference observed in terms of cell viability and cell death between NNMT-expressing and non-expressing cells. In NNMT-expressing cells, MeNH increased cell viability and cellular ATP concentration in a dose-dependent manner after 72 and 120 h incubation, an effect that was not observed after 24 h incubation or in non-NNNT-expressing cells at any time point. Taken together, these results suggest that NNMT may be a detoxification pathway for BCs such as NH.
authors.affiliation: Institute of Pharmaceutical Science, King's College London, London SE1 9NH, U.K.
authors.forename: Martin G
authors.initials: MG
authors.lastname: Thomas
authors.affiliation: Department of Clinical Sciences, School of Medicine, Universitá Politecnica delle Marche, Ancona, Italy.
authors.forename: Davide
authors.initials: D
authors.lastname: Sartini
authors.affiliation: Department of Clinical Sciences, School of Medicine, Universitá Politecnica delle Marche, Ancona, Italy.
authors.forename: Monica
authors.initials: M
authors.lastname: Emanuelli
authors.affiliation: Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands.
authors.forename: Matthijs J
authors.initials: MJ
authors.lastname: van Haren
authors.affiliation: Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Universiteitsweg 99, 3584 CG Utrecht, The Netherlands.
authors.forename: Nathaniel I
authors.initials: NI
authors.lastname: Martin
authors.affiliation: Department of Chemistry, Imperial College London, London SW7 2AZ, U.K.
authors.forename: David M
authors.initials: DM
authors.lastname: Mountford
authors.affiliation: Institute of Pharmaceutical Science, King's College London, London SE1 9NH, U.K.
authors.forename: David J
authors.initials: DJ
authors.lastname: Barlow
authors.affiliation: Departmento de Bioquímica, Universidade Federal do Rio Grande do Sul, Instituto de Ciências Básicas da Saúde, Rua Ramiro Barcelos, Porto Alegre 90035 003, Brazil.
authors.forename: Fábio
authors.initials: F
authors.lastname: Klamt
authors.affiliation: Department of Medicine, University of Birmingham, Edgbaston, Birmingham B15 2TH, U.K.
authors.forename: David B
authors.initials: DB
authors.lastname: Ramsden
authors.affiliation: Institute of Pharmaceutical Science, King's College London, London SE1 9NH, U.K.
authors.forename: Madeehah
authors.initials: M
authors.lastname: Reza
authors.affiliation: Institute of Pharmaceutical Science, King's College London, London SE1 9NH, U.K.
authors.forename: Richard B
authors.initials: RB
authors.lastname: Parsons
mesh_terms: D002243:Carbolines / Q000378:metabolism*; D002384:Catalysis; D045744:Cell Line, Tumor; D006801:Humans; D008745:Methylation; D050903:Nicotinamide N-Methyltransferase / Q000378:metabolism*
chemical_list: D002243:Carbolines; C010262:norharman; D050903:Nicotinamide N-Methyltransferase
keywords: biotransformation; detoxification; enzyme kinetics; methylation; toxicology; β-carbolines