Quantification of naphthyl conjugates. Comparison of high-performance liquid chromatography and selective enzyme hydrolysis methods

Effects of molybdate and pentachlorophenol on the sulfation of alpha-naphthol

Sulfation is the conjugation of chemicals with sulfate, which usually decreases, but occasionally increases, their biological effects. The phenol-sulfotransferase inhibitor pentachlorophenol (PCP) is often used to distinguish the biological effects of a chemical from its sulfate conjugate. Recently, molybdate has been shown to decrease the hepatic concentration of 3'-phosphoadenosine 5'-phosphosulfate (PAPS), the cosubstrate for sulfation. Therefore, the present study was designed to compare the effectiveness and specificity of molybdate and PCP as inhibitors of sulfation. Alpha-naphthol (125 and 250 micromol/kg, i.p.) was administered to rats and the sulfate and glucuronide conjugates excreted into urine were quantified for this comparison. Molybdate (5.0, 7.5, and 10 mmol/kg) decreased the 24-h cumulative urinary excretion of the sulfate conjugate of the lower dose of alpha-naphthol by 54, 53, and 55%, respectively, with corresponding compensatory increases in glucuronide excretion at the two lower doses of molybdate. PCP (20, 40, and 80 micromol/kg) similarly decreased the sulfation of alpha-naphthol by 48, 38, and 41%, respectively, but prevented compensatory increases in glucuronide excretion. Molybdate (2.5, 5.0, and 7.5 mmol/kg) decreased the sulfation of the higher dose of alpha-naphthol by 21, 30, and 44%, respectively, again with corresponding compensatory increases in glucuronide excretion. In contrast, PCP did not decrease significantly the sulfation of the higher dose of alpha-naphthol. These data suggest that molybdate is equally or more effective than PCP at inhibiting sulfation of alpha-naphthol, and appears to be more specific.

Conjugation of organic compounds in isolated hepatocytes from a marine fish, the plaice, Pleuronectes platessa

A method is described for the preparation of viable hepatocytes from a marine fish, the plaice. Their ability to detoxify organic compounds was measured by the formation of glucuronic acid and sulphate conjugates with the model substrates 1-naphthol and phenolphthalein. 1-Naphthol was conjugated three- to four-fold faster than phenolphthalein and glucuronidation predominated with both substrates. Strong substrate inhibition of glucuronidation was observed with 200 microM 1-naphthol or phenolphthalein. No measurable sulphate conjugation was detected with phenolphthalein. Treatment of fish with 3-methylcholanthrene induced formation of both glucuronide and sulphate conjugates by two- to three-fold. Compared with rat hepatocytes, the extent of sulphation was 100-fold lower in plaice hepatocytes whereas glucuronide formation was only 10-fold lower. The observations indicate that isolated plaice hepatocytes provide a suitable system for studies of the detoxication of xenobiotic pollutants in fish liver.

Isolation and characterization of the four antipyrine glucuronides and determination of their urinary excretion pattern in man by a reversed-phase h.p.l.c. assay

A large-scale procedure for the isolation of four urinary glucuronides in antipyrine metabolism is described; the isolated compounds are used as standards in a direct h.p.l.c. assay. The four glucuronides were characterized by u.v. and 1H-n.m.r. spectroscopy, and after hydrolysis by a t.l.c. assay of the corresponding aglycones. A reversed-phase h.p.l.c. assay procedure has been developed for the direct quantification of the four antipyrine glucuronides; this separates 3-hydroxymethyl-antipyrine glucuronide, 4,4'-dihydroxy-antipyrine glucuronide, norantipyrine glucuronide and 4-hydroxy-antipyrine glucuronide in a single run. Urinary elimination patterns of these glucuronides have been determined in five female and five male volunteers after antipyrine (1200 mg) administration. The direct assay of urinary glucuronides enables the simultaneous determination of glucuronidation activities and four different phase-I metabolites of antipyrine in vivo.