Registration Dossier

Administrative data

Endpoint:
basic toxicokinetics in vitro / ex vivo
Type of information:
experimental study
Adequacy of study:
key study
Study period:
circa 1979
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: The study was not conducted according to guideline/s and GLP but the report contains sufficient data for interpretation of study results

Data source

Reference
Reference Type:
publication
Title:
THE INTERACTION OF ALIPHATIC NITRO COMPOUNDS WITH THE LIVER MICROSOMAL MONOOXYGENASE SYSTEM
Author:
Sakurai, H., Hermann, G., Ruf, H.H. and Ullrich, V.
Year:
1980
Bibliographic source:
Biochemical Pharmacology, Vol. 29. pp. 341-345

Materials and methods

Objective of study:
metabolism
Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
Liver microsomal metabolism of nitromethane was examined.
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
Nitromethane was obtained from Fluka AG.

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male

Administration / exposure

Route of administration:
other: in vitro study: compounds were added to the incubation mixtures as 1 M methanolic solutions.
Vehicle:
other:
Duration and frequency of treatment / exposure:
Based on a graph in the report, the production of nitrite and formaldehyde from nitromethane was measured at 2, 4, 6 and 8 minutes. Nitromethane was added once to the liver microsomal mixture.
Doses / concentrations
Remarks:
Doses / Concentrations:
50 mM nitromethane
No. of animals per sex per dose:
No data
Control animals:
yes, concurrent no treatment

Results and discussion

Preliminary studies:
Not applicable.

Toxicokinetic / pharmacokinetic studies

Details on absorption:
Not applicable.
Details on distribution in tissues:
Not applicable.
Details on excretion:
Not applicable.

Metabolite characterisation studies

Metabolites identified:
yes
Details on metabolites:
Formaldehyde and nitrite formation from nitromethane by rat liver microsomes in the presence of NADPH and dioxygen. The stoichiometry
of nitrite to formaldehyde formation in the case of nitromethane was exactly 1:1. The specific activity (+/-S.E.M) for nitromethane was 0.2 +/-0.1.

Any other information on results incl. tables

The observation that addition of nitromethane to an oxidized rat liver microsomal suspension did not result in a substrate binding difference spectrum like the other nitro compounds, but gave rise to a peak at 437 nm, was unexpected. With the aid of e.p.r.-spectroscopy, this was interpreted as the formation of a cytochrome P450-NO complex.

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information): bioaccumulation potential cannot be judged based on study results
This study demonstrated that nitromethane can be metabolized by cytochrome P450 to formaldehyde and nitrate.
Executive summary:

It was previously shown that liver microsomes from phenobarbital pretreated rats can convert 2-nitropropane to acetone and nitrate in the presence of NADPH and dioxygen. The investigation was now extended to the compounds phenylnitromethane, w-nitrostyrene, nitrocyclohexane and nitromethane, which were also denitrificated but with weaker specific activities than 2-nitropropane. Untreated rats and 3-methylcholanthrene induced animals yielded microsomes with even lower activities. The observation that addition of nitromethane to an oxidized rat liver microsomal suspension did not result in a substrate binding difference spectrum like the other nitro compounds, but gave rise to a peak at 437 nm, was unexpected. With the aid of e.p.r.-spectroscopy, this was interpreted as the formation of a cytochrome P450-NO complex. Parallel to this complex formation, oxidized rat liver microsomes catalyzed the production formaldehyde from nitromethane in an NADPH-independent reaction. In contrast, liver microsomes from phenobarbital pretreated pigs produced a normal substrate binding spectrum with nitromethane and were unable to release formaldehyde from nitromethane. Reduced liver microsomes from all sources yielded a cytochrome P450-ligand spectrum with peaks around 453 nm, which probably reflects the formation of a ferrous cytochrome P450-nitrosoalkane complex.