The influence of methyl substitution on the N-demethylation and N-oxidation of normethadone in animal species

Microsomal N-oxidation of long chain N,N-dimethylalkylamines: quantitative structure-activity relationships

N,N-Dimethylalkylamines CmH2m+1N(CH3)2 (m = 4 to 18) undergo in vitro N-oxidation to the corresponding amine oxides by mouse liver microsomes. The relative oxidisability of these compounds is parabolically dependent on structural and physico-chemical characteristics (with a maximum at m 12) and is controlled by at least three factors: lipophilicity, stereochemistry and the nucleophilicity of the compounds under evaluation. The results from the QSAR study support this multifactorial view.

Comparative activation of 3,3'-dichlorobenzidine and related benzidines to mutagens in the Salmonella typhimurium assay by hepatic S9 and microsomes from rats pretreated with different inducers of cytochrome P-450

The metabolic basis of the differential activation of 4 benzidines--3,3'-dichlorobenzidine (DCB), benzidine (BZ), o-tolidine (TOL) and o-dianisidine (DIN)--to mutagens was examined in the Ames test, using Salmonella typhimurium TA98. For each benzidine congener, the comparative activation by 3 rat liver enzyme systems--(i) postmitochondrial supernatant (S9), (ii) S9 + acetylcoenzyme A (S9-Ac) and (iii) microsomes--and the effect thereon of animal pretreatment with 3 cytochrome P-450 inducers--DCB, 3-methylcholanthrene (MC) and phenobarbital (PB)--were examined. DCB was the most activated of the benzidines, with activation by the 3 systems being in the order: S9 = S9-Ac greater than microsomes, whereas dianisidine and tolidine were the least activated. Benzidine was activated only in the S9 systems but the S9-catalyzed activation of benzidine, unlike that of DCB, was enhanced by added acetylcoenzyme A. Pretreatment with either DCB, MC or PB enhanced the activation of DCB, decreased that of benzidine, and had no effect on that of tolidine or dianisidine. The enhanced DCB activation was most pronounced with DCB pretreatment and was 2.5-fold, 2-fold, and 3-fold, in S9-Ac, S9, and microsomes, respectively. The microsomal-catalyzed DCB activation was inhibited by the cytochrome P-450 inhibitors 2,4-dichloro-6-phenylphenoxyethylamine and alpha-naphthoflavone by 93% and 48%, respectively. DCB, but not its congeners, elicited NADPH-dependent metabolite complex formation with microsomal cytochrome P-450. The results show that DCB is the most mutagenic of the 4 benzidines under conditions of cytochrome-P-450-catalyzed activation and suggest that the DCB activation may be catalyzed most effectively by cytochrome P-450 species induced specifically by the compound itself.

The role of naloxone infusions in the treatment of overdoses of long half-life narcotic agonists: application to nor-methadone

This report describes the use of a naloxone infusion at a rate of 300 micrograms/h to provide constant antagonism of the respiratory depressant effects of a near fatal nor-methadone dose in a 2 year old boy. The terminal half-life for nor-methadone was calculated to be 13.5 h. The results indicate that a single dose of a narcotic antagonist with a short half-life (e.g. naloxone) will probably be inadequate to provide long lasting reversal of the effects of overdoses of long half-life narcotic agonists, and that continuous infusion may be the preferable to repeated bolus doses.

Interaction of ligands with cytochrome P-450. On the 442 nm spectral species generated during the oxidative metabolism of pyridine

When added to aerobic rabbit liver microsomal fractions fortified with an NADPH-generating system, pyridine initially produces a type II difference spectrum such as is observed with other aromatic amines. There is a time-dependent conversion of this perturbation into a new spectral species characterized by an absorbance maximum at 442 nm and a minor peak at 389 nm. Experiments with inhibitors of the cytochrome P-450-dependent electron-transport chain suggest that these species originate from binding to the haemoprotein of metabolic intermediate(s) derived from the amine substrate. Analysis of the incubation mixtures by t.l.c., high-pressure liquid chromatography, u.v.- and mass-spectrometry reveals the presence of a single metabolite arising from cytochrome P-450-catalysed oxidation of the heteroaromatic tertiary amine, which was identified as pyridine N-oxide, obviously accounting for adduct formation. This view is supported by comparative studies on the spectral changes generated by exogenous amine oxide with NADPH-reduced cytochrome P-450. Moreover, dithiothreitol, a potent N-oxidase inhibitor, strongly suppresses development of the 442 nm and 389 nm complexes. The ability of forming low-spin adducts with ferrous cytochrome P-450 absorbing around 440 nm appears to be an inherent property of different types of N-oxides. Considering the dipole character of the N+-O- function, a co-ordinate iron-oxygen bond is proposed to be formed in these complexes.

The differentiation of N-oxidation and N-dealkylation of N-ethyl-N-methylaniline by rabbit liver microsomes as distinct metabolic routes

1. N-Oxidation and N-dealkylation were shown to be separate routes of metabolism for N-ethyl-N-methylaniline. 2. N-Dealkylation, but not N-oxidation, is enhanced when NADH is present in addition to the NADPH-regenerating cofactors. 3. Some inhibitors, e.g. p-chloromercuribenzoate, inhibit N-dealkylation to a very much greater extent than they do N-oxidation. 4. N-Dealkylation is affected more by 'ageing' of the microsomal preparation or by the presence of bile salts, than is N-oxidation. 5. N-Oxidation followed by N-O-alpha-carbon migration of oxygen is only implicated to a very minor extent in the N-dealkylation process.