Comparative disposition and metabolism of paraherquamide in sheep, gerbils, and dogs.

The disposition and metabolism of paraherquamide (PHQ), a potent and broad-spectrum anthelminthic, were examined in sheep, dogs, and gerbils. The metabolism of PHQ in these species was extensive and marked by significant species differences both in vitro and in vivo. In sheep and gerbils, PHQ metabolism occurs mainly at the pyrrolidine moiety, generating several metabolites that, for the most part, retained nematodicidal activity in vitro. In dogs, the dioxepene group was also extensively metabolized, ultimately resulting in formation of a catechol and loss of pharmacological activity. After oral administration of [3H]PHQ to intact sheep, gerbils, and dogs, the majority of the administered radioactivity was recovered in feces. Intact PHQ accounted for 0% (dogs) to approximately 30% (sheep and gerbils) of drug-related material in feces. A detailed investigation of the composition of the intestinal content of sheep indicated that a significant amount of the dose was still present in the rumen 24 h after dose and that PHQ underwent significant dehydration in the cecum. The oral pharmacokinetic parameters of PHQ in sheep and dogs suggest that its absorption is rapid in both species but that its apparent elimination rate is significantly higher in the dog (t(1/2) approximately 1.5 h) than it is in sheep (t(1/2) approximately 8.5 h). The short elimination half-life and the absence of PHQ or other active components in the dog gastrointestinal tract provide a potential explanation of the lack of efficacy of PHQ in this species.

A novel 4-oxo-2(E)-nonenal-derived endogenous thiadiazabicyclo glutathione adduct formed during cellular oxidative stress.

Cellular oxidative stress causes increased lipid peroxidation with the concomitant formation of DNA and protein reactive bifunctional electrophiles. Glutathione (GSH) detoxifies these bifunctional electrophiles by forming GSH adducts. Several years ago we discovered 4-oxo-2(E)-nonenal (ONE) as a major bifunctional electrophile derived from lipid hydroperoxides. We have now made the unexpected discovery that glutathione-S-transferase (GST)-mediated GSH addition to ONE occurs primarily to C-1 of the alpha,beta-unsaturated ketone rather than to C-3 of the alpha,beta-unsaturated aldehyde. The resulting intermediate rapidly undergoes two intramolecular cyclizations followed by two separate dehydration reactions to provide an unusual thiadiazabicyclo-ONE-GSH adduct (TOG). Quantification of intracellular TOG was performed using stable isotope dilution liquid chromatography-multiple reaction monitoring/mass spectrometry after the addition of ONE to cells or as an endogenously derived adduct during peroxide-induced oxidative stress. TOG represents the first member of a new class of thiadiazabicyclo GSH adducts that are formed through GST-mediated addition of GSH to reactive intermediates containing the ONE motif during intracellular oxidative stress. ONE formation can potentially result from free radical pathways as well as cyclooxygenase- and lipoxygenase-mediated pathways. Its aldo-keto reductase-mediated reduction product, 4-oxo-2(E)-nonenol (ONO), was also formed and converted to GSH adducts similar to those formed by 4-hydroxy-2(E)-nonenal (HNE). ONO is isomeric with HNE; therefore, protein and peptide adducts ascribed to arise solely from reactions with endogenous HNE will need to be re-appraised.