Oral and topical absorption, disposition kinetics, and the metabolic fate of trans-methyl styryl ketone in the male Fischer 344 rat.

trans-Methyl styryl ketone (MSK; trans-4-phenyl-3-buten-2-one) is a beta-unsaturated ketone that has a wide range of uses in industry and is present in numerous consumer products. Although MSK has been shown to be positive in several in vitro mutagenic assays, it does not seem to be overtly toxic in animal models. This lack of toxicity may relate to its poor absorption and/or rapid elimination. However, little is known about the fate of MSK in the body. Studies were conducted to characterize the absorption, and disposition kinetics of MSK after intravenous, oral, and topical administration to male Fischer 344 rats. After intravenous administration of [14C]MSK (20 mg/kg, 120 microCi/kg), blood concentration-time data could be characterized with a biexponential equation and apparent first-order elimination kinetics. The following pharmacokinetic parameter values were obtained (mean +/- SD): terminal disposition half-life, 17.7 +/- 0.08 min; apparent steady-state volume of distribution, 0.89 +/- 0.14 liters/kg; systemic body clearance, 68.9 +/- 10.0 ml/kg *min; and mean residence time, 13.1 +/- 2.2 min. Within 48 hr, 95.5% of the dose was excreted in the urine and 2.7% in the feces. The major blood metabolite after intravenous administration was identified by GC/MS as the 4-phenyl-3-buten-2-ol (methyl styryl carbinol). After oral administration of [14C]MSK (200 mg/kg, 100 microCI/kg), approximately 96.6% of the dosed radioactivity was recovered in the urine and 4.8% in the faces within 48 hr. Major urinary metabolites identified by LC-MS/MS and quantified by HPLC radioassay were N-phenylacetyl-L-glycine (64.9% of dose) and N-benzyl-L-glycine (9.9% of dose). Parent compound could not be detected in the blood after oral administration, and 14C-equivalents in the blood never exceeded 1.3% of the dose. Results suggest near-total presystemic elimination of the oral dose. After topical application of [14C]MSK (250 mg/kg, 50 microCi/kg), > 60% of the dose was absorbed, and the majority of the dose was excreted into the urine (55% of dose) in the form of metabolites. Urinary metabolites were similar to those described after oral administration. 14C-equivalents were not detected in the blood at any time after topical administration. These results indicate that MSK is almost totally metabolized before systemic distribution after oral or topical administration. The systemic exposure dose of MSK seems to be exceedingly low at the doses studied herein.