¹⁴C-labeled Pulegone and Metabolites Binding to α2u-globulin in Kidneys of Male F-344 Rats∗

∗This research was supported in part by the Intramural Research Program of the National Institutes of Health, National Institute of Environmental Health Sciences.

Abstract

Pulegone is a major constituent of pennyroyal oil and a minor component of peppermint oil. Pulegone is biotransformed to menthofuran and menthones (diastereomeric menthone and isomenthone) in pennyroyal and peppermint as well as in rodents. Pulegone and menthofuran are hepatotoxic to rodents, and menthones are less toxic. The metabolism and disposition of pulegone and menthofuran were previously studied in rodents, and higher concentrations of pulegone- and menthofuran-derived radioactivity were observed in male than female rat kidney. One explanation is the association of pulegone and metabolites with a male rat-specific protein, α2u-globulin. To test this hypothesis, male and female rats were dosed orally with ¹⁴C-labeled pulegone (80 mg/kg, 120 μCi/kg) or menthofuran (60 mg/kg, 120 μCi/kg) or menthones (80 mg/kg, 120 μCi/kg) in corn oil, and the kidney cytosol was prepared 24 h after dosing. An equilibrium dialysis experiment showed that in all three studies the radioactivity was associated with kidney cytosol proteins of male but not female rats. The chemicals present in the male rat kidney cytosol after dialysis were extracted with dichloromethane and characterized by high-performance liquid chromatography (HPLC) and gas chromatography/mass spectrometry (GC-MS). All parent compounds were detected, and the metabolites characterized included piperitone from pulegone or menthones treatment, menthones and possibly 8-hydroxymenthones from pulegone treatment, and mintlactones (diastereomeric mintlactone and isomintlactone) and 7a-hydroxymintlactone from menthofuran treatment. Analysis of the male rat kidney cytosol by a gel filtration column demonstrated that the retention was due to reversible binding of these chemicals with the male rat-specific protein α2u-globulin. However, binding of pulegone and/or metabolites to α2u-globulin did not produce accumulation of this protein in the kidney.

Notes

∗This research was supported in part by the Intramural Research Program of the National Institutes of Health, National Institute of Environmental Health Sciences.