TY - JOUR
T1 - Nicotinamide N-methyltransferase catalyses the N-methylation of the endogenous ß-carboline norharman: evidence for a novel detoxification pathway
AU - Parsons, Richard Bramwell
AU - Sartini, Davide
AU - Emanuelli, Monica
AU - Van Haren, Matthijs J.
AU - Martin, Nathaniel I.
AU - Mountford, David Mark
AU - Barlow, David John
AU - Klamt, Fábio
AU - Ramsden, David B.
AU - Reza, Madeehah
PY - 2016/9/27
Y1 - 2016/9/27
N2 - 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 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 to 2-N-methylnorharman. In addition, we have investigated the toxicity of the β-carboline norharman, its precursor 1,2,3,4-tetrahydronorharman and its N-methylated metabolite 2-N-methylnorharman, using our in vitro SH-SY5Y NNMT expression model. Recombinant NNMT demonstrated norharman 2N-methyltransferase activity, with a Km of 90 ± 20 µM, a kcat of 3 x 10-4 ± 2 x 10-5 s-1 and a specificity constant (kcat/Km) of 3 ± 1 s-1 M-1. 1,2,3,4-Tetrahydronorharman was the least toxic of all three compounds investigated, whereas norharman 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, 2-N-methylnorharman increased cell viability and cellular ATP concentration in a dose-dependent manner after 72 and 120 h incubation, an effect which 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 β-carbolines such as norharman.
AB - 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 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 to 2-N-methylnorharman. In addition, we have investigated the toxicity of the β-carboline norharman, its precursor 1,2,3,4-tetrahydronorharman and its N-methylated metabolite 2-N-methylnorharman, using our in vitro SH-SY5Y NNMT expression model. Recombinant NNMT demonstrated norharman 2N-methyltransferase activity, with a Km of 90 ± 20 µM, a kcat of 3 x 10-4 ± 2 x 10-5 s-1 and a specificity constant (kcat/Km) of 3 ± 1 s-1 M-1. 1,2,3,4-Tetrahydronorharman was the least toxic of all three compounds investigated, whereas norharman 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, 2-N-methylnorharman increased cell viability and cellular ATP concentration in a dose-dependent manner after 72 and 120 h incubation, an effect which 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 β-carbolines such as norharman.
U2 - 10.1042/BCJ20160219
DO - 10.1042/BCJ20160219
M3 - Article
SN - 0264-6021
VL - 473
SP - 3253
EP - 3267
JO - Biochemical Journal
JF - Biochemical Journal
ER -