Renal transport of gossypol in the rabbit

Determination of age and gender differences in biochemical processes affecting the disposition of 2-butoxyethanol and its metabolites in mice and rats to improve PBPK modeling

2-Butoxyethanol (BE) is the most widely used glycol ether solvent. BEs major metabolite, butoxyacetic acid (BAA), causes hemolysis with significant species differences in sensitivity. Several PBPK models have been developed over the past two decades to describe the disposition of BE and BAA in male rats and humans to refine health risk assessments. More recent efforts by Lee et al. [Lee, K.M., Dill, J.A., Chou, B.J., Roycroft, J.H., 1998. Physiologically based pharmacokinetic model for chronic inhalation of 2-butoxyethanol. Toxicol. Appl. Pharmacol. 153, 211-226] to describe the kinetics of BE and BAA in the National Toxicology Program (NTP) chronic inhalation studies required the use of several assumptions to extrapolate model parameters from earlier PBPK models developed for young male rats to include female F344 and both sexes of B6C3F1 mice and the effects of aging. To replace these assumptions, studies were conducted to determine the impact of age, gender and species on the metabolism of BE, and the tissue partitioning, renal acid transport and plasma protein binding of BAA. In the current study, the Lee et al. PBPK model was updated and expanded to include the further metabolism of BAA and the salivary excretion of BE and BAA which may contribute to the forestomach irritation observed in mice in the NTP study. The revised model predicted that peak blood concentrations of BAA achieved following 6 h inhalation exposures are greatest in young adult female rats at concentrations up to 300 ppm. This is not the case predicted for old (> or =18 months) animals, where peak blood concentrations of BAA in male and female mice were similar to or greater than female rats. The revised model serves as a quantitative tool for integrating an extensive pharmacokinetic and mechanistic database into a format that can readily be used to compare internal dosimetry across dose, route of exposure and species.

Effects of gossypol on the motility of mammalian sperm

The effects of the male contraceptive gossypol on the motility of mammalian spermatozoa are reviewed. The role of sperm motility in the processes of fertilization and the effect of the drug on these processes determine its effectiveness as a contraceptive. The promising male contraceptive potential of gossypol is discussed in the context of the serious adverse effects of the agent.

Kinetic characterization of the inhibition of purified cynomolgus monkey lactate dehydrogenase isozymes by gossypol

This report describes the results of the first step in a sequence of experiments designed to test the hypothesis that the sperm-specific isozyme of lactate dehydrogenase (LDH-C4), is a site of action of the potential male contraceptive agent gossypol. Cynomolgus monkey LDH-A4, LDH-B4 and LDH-C4 were purified and kinetically characterized. LDH-A4 and LDH-B4 exhibited "linear mixed-type" inhibition by gossypol with both lactate and pyruvate as variable substrates. LDH-C4 also exhibited "linear mixed-type" inhibition with lactate as substrate. However, the C4 isozyme exhibited "parabolic mixed-type" inhibition by gossypol and substrate inhibition with pyruvate as substrate, the latter due to abortive complex formation. Of the three isozymes, LDH-C4 exhibited the lowest apparent Km for pyruvate and the highest apparent Km for lactate. The LDH-C4 form was found to be the most sensitive isozyme to gossypol inhibition, since it had the lowest apparent Ki values for gossypol inhibition. The effect of gossypol on coenzyme binding to LDH-C4 was examined and gossypol binding was found to inhibit binding and release of NADH but not NAD+, an effect possibly due to its interaction with the more hydrophobic loop region of LDH-C4.