Intestinal absorption of S-(pentachlorobutadienyl)glutathione and S-(pentachlorobutadienyl)-L-cysteine, the glutathione and cysteine S-conjugates of hexachlorobuta-1,3-diene.

The bioactivation of the nephrotoxin hexachlorobuta-1,3-diene (HCBD) involves hepatic formation and biliary excretion of S-(pentachlorobutadienyl)glutathione (PCBG). The intestinal absorption of PCBG was studied in vivo by introducing PCBG or its metabolite, S-(pentachlorobutadienyl)-L-cysteine (PCBC), into rat intestines via a biliary cannula and measuring PCBG and PCBC concentrations in portal blood. When PCBG was infused into the intestine, both PCBG and PCBC were found in the blood; the highest metabolite concentrations (0.9 nmol/ml for PCBG and 1 nmol/ml for PCBC) were observed 30 min after infusing the S-conjugate. Higher blood PCBC concentrations were observed after PCBC infusion than after PCBG infusion. Transport studies in CaCo-2 cells, a human intestinal cell line, showed that application of PCBG (0.1 mM) to the apical side of the cells resulted in a 2.4-fold accumulation of PCBG in the basolateral chamber after 24 hr; in this time, the cells metabolized 69% of the applied PCBG to PCBC. Addition of glutathione (1 mM), gamma-glutamyl-p-nitroanilide (1 mM), or probenecid (1 mM) to the apical chamber diminished the active transport of PCBG. With PCBC, no active apical or basolateral transport was observed. The experiments are the first demonstration of the intestinal absorption of the S-conjugates of HCBD, which is an important step in their translocation from the liver to the kidney.

Biosynthesis and biliary excretion of S-conjugates of hexachlorobuta-1,3-diene in the perfused rat liver.

The formation and biliary excretion of the glutathione and cysteine S-conjugates of hexachlorobutadiene were studied in the isolated perfused rat liver. Infusion of increasing amounts of hexachlorobutadiene led to an increase in total metabolite excretion. Partitioning of glutathione conjugate release between bile and perfusate depended on the rate of substrate infusion: S-(1,2,3,4,4-pentachlorobutadienyl)glutathione (PCBG) appeared quantitatively in bile at low hexachlorobutadiene infusion rates, and increasing amounts of the glutathione conjugate were found in the perfusate as infusion rates were increased. The cysteine S-conjugate, S-(1,2,3,4,4-pentachlorobutadienyl)-L-cysteine, was not detected in the perfusate, but the amounts found in the bile were correlated with the concentrations of the glutathione conjugate. Depletion of hepatic glutathione concentrations decreased PCBG formation. Hence, at moderate hexachlorobutadiene infusion rates, PCBG is exclusively excreted into bile, indicating that intestinal absorption of PCBG or its metabolites is required for the induction of kidney damage in vivo.

Single- and multiple-dose pharmacokinetics of R-(-)-and S-(+)-prenylamine in man.

The pharmacokinetics of S-(+)- and R-(-)-prenylamine was studied in eight healthy volunteers given single and repeated oral doses of the racemic drug. Distinct differences in various pharmacokinetic parameters were found between the S- and R-enantiomer. The maximum plasma concentrations and AUCs of the R-enantiomer exceeded those of the S-enantiomer five-fold; the apparent oral clearance of the S-form was five-times and the renal clearance three-times higher than of the R-form. Acid catalyzed hydrolysis of urine samples released more S-prenylamine, indicating stereoselective glucuronidation of unchanged prenylamine. Plasma protein binding also differed between the two enantiomers, generally with a higher unbound fraction of the S-form, whereas analysis of the bound fractions showed that prenylamine was bound to different plasma proteins with inverse stereoselectivity.

Enantioselective disposition of R-(-)- and S-(+)-prenylamine in the rat.

The disposition of R- and S-prenylamine was investigated in male Wistar rats after i.v. and p.o. dosage of 2 mg/kg racemic prenylamine. Concentrations of the enantiomers were determined in plasma, lung, heart, spleen, liver kidney and muscle tissue within a period of 5 h after dosage. In addition, plasma protein binding was assayed in vitro with racemic drug and found to be similar for the two enantiomers. Except for plasma samples after i.v. administration the concentrations of the S-enantiomer exceeded those of the R-enantiomer.

Simultaneous determination of R- and S-prenylamine in plasma and urine by reversed-phase high-performance liquid chromatography.

A high-performance liquid chromatographic method for the determination of R- and S-prenylamine in human plasma and urine is described. It involves a two-step liquid-liquid extraction of prenylamine from biological material and preparation of diastereomeric urea derivatives with R-(-)-naphthylethyl isocyanate, a chiral fluorescence marker. Separation and quantitation of the diastereomeric prenylamine derivatives are carried out by a reversed-phase high-performance liquid chromatographic system with fluorimetric detection. The limit of determination is less than 2 ng of enantiomer per ml of urine and less than 1 ng of enantiomer per ml of plasma. A preliminary kinetic study on one healthy volunteer who had received a single oral dose of racemic prenylamine (100-mg film tablet) showed distinctly higher plasma and urine concentrations of the R-enantiomer.