Metabolism of the genotoxicant 2-nitropropane to a nitric oxide species.
The mechanisms by which the paint constituent 2-nitropropane (2-NP) exerts genotoxicity and hepatocarcinogenicity are poorly understood. The hypothesis was tested that nitric oxide (NO) is a hepatic metabolic intermediate generated from 2-NP and/or its anionic tautomer propane 2-nitronate (P2N). Incubations of liver microsomes from phenobarbital-pretreated rats or mice with 2-NP or P2N gave spectra with Soret maxima at 448 nm which indicated the presence of a ferrous-NO complex. Levels of 3':5'-cyclic guanosine monophosphate (cGMP) and nitrite were measured by ELISA assay and HPLC, respectively, in freshly isolated mouse hepatocytes. Levels of cGMP generated within 3 h in cells by 2-NP, P2N (5 mM each) or the diethylamine/NO complex [Et2NNO(N==O)]Na (0.6 mM), an NO precursor, were 6, 15 and 34 times, respectively, those seen in control hepatocytes. Production of cGMP following treatment with 2-NP was linear with time of incubation; cGMP generation from P2N reached its peak already after 1 h. cGMP levels observed in incubates with 1-nitropropane and 2-deutero 2-nitropropane (5 mM), 2-NP isomers devoid of genotoxic properties, were significantly lower than those seen in the presence of 2-NP. Inclusion in the incubate of methylene blue, which inhibits NO-mediated reactions, decreased cGMP formation in hepatocytes with [Et2NNO(N==O)]Na, but increased it in cells with 2-NP or P2N. The production of nitrite from 2-NP, P2N or [Et2NNO(N==O)]Na mirrored cGMP formation. The results suggest that 2-NP and its nitronate generate an NO species in cells which may mediate, or contribute to, 2-NP genotoxicity.
Kohl
C
C
Medical Research Council Toxicology Unit, University of Leicester, UK.
Morgan
P
P
Gescher
A
A
D000818:Animals; D006152:Cyclic GMP / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D006834:Hydrazines / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D008297:Male; D008751:Methylene Blue / Q000494:pharmacology; D051379:Mice; D008807:Mice, Inbred BALB C; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D009573:Nitrites / Q000378:metabolism; D009589:Nitrogen Oxides; D009595:Nitroparaffins / Q000378:metabolism*; D011407:Propane / Q000031:analogs & derivatives* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012997:Solvents / Q000378:metabolism*; D013053:Spectrophotometry
D006834:Hydrazines; D009573:Nitrites; D009589:Nitrogen Oxides; D009595:Nitroparaffins; D012997:Solvents; C069720:propane-2-nitronate; D009569:Nitric Oxide; C084012:1,1-diethyl-2-hydroxy-2-nitrosohydrazine; C016617:2-nitropropane; D006152:Cyclic GMP; D008751:Methylene Blue; D011407:Propane