Received for publication May 13, 2005.
Revised March 13, 2006.
Accepted for publication March 14, 2006.

Comparative Metabolism of Geranyl Nitrile and Citronellyl Nitrile in Mouse, Rat and Human Hepatocytes

Abstract

Geranyl nitrile (GN) and citronellyl nitrile (CN) are fragrance components used in consumer and personal care products. Differences in the clastogenicity of these two terpenes are postulated to result from differential biotransformation, presumably involving the conjugated nitrile moiety. The metabolic clearance and biotransformation of GN and CN were compared in primary hepatocytes from mice, rats and humans. For determination of intrinsic clearance, GN and CN were incubated with hepatocytes in sealed vials and the headspace was sampled periodically by solid phase microextraction and analyzed by GC/MS. For metabolite identification, GN and CN were incubated with hepatocytes from each species for 60 min and reaction mixtures were extracted and analyzed by mass spectroscopy. Both GN and CN were rapidly metabolized in hepatocytes from all species (T1/2 0.7-11.6 min). Within a species, intrinsic clearance was similar for both compounds, and increased in the order human < rat << mouse. Major common pathways for biotransformation of GN and CN involved 1) epoxidation of the 6-alkenyl moiety followed by conjugation with GSH, 2) hydroxylation of the terminal methyl group(s) followed by direct conjugation with glucuronic acid in rodents or further oxidation to the corresponding acid in human cells and 3) hydroxylation of the allylic C5 position. No evidence for either phase I or phase II metabolism of the conjugated nitrile moiety was obtained. Thus the presumed metabolic basis for differences in genotoxicity remains elusive.

Key words: drug clearance, hepatocytes, in vitro-in vivo prediction, mass spectrometry