Glutathione and Mercapturic Acid Conjugations in the Metabolism of Naphthalene and 1-Naphthyl N-Methylcarbamate (Carbaryl)

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Abstract
The formation of glutathione (GSH) conjugate in the detoxification of [1- C]-naphthalene and [naphthyl- C]-carbaryl was investigated using rat liver homogenate. The mercapturic acid conjugate in rats was also investigated by collection of urine after intraperitoneal injection of C substrates. The formation of water-soluble metabolites in vitro from naphthalene was dependent on the amount of glutathione added, but this was not seen in carbaryl metabolism. In vitro, the metabolism of [l-14C]-naphthalene produced 50% GSH conjugates in the incubation mixture, whereas in vivo the metabolism of this compound produced 65% mercapturic acid conjugate in the urine. There was no evidence of GSH or mercapturic acid conjugate in the metabolism of [naphthyl-14C-carbaryl in vitro and in vivo. This conclusion was made by comparing the nature and chemical characteristics of GSH and mercapturic acid conjugates formed in [1- C]-naphthalene metabolism. With the aid of the specific enzyme (e.g. g-glucuronldase and sulfatase) and acid hydrolysis, the water-soluble metabolites of [naphthyl-14Cj-carbaryl were tentatively recognized as glucuronide or sulfate conjugated mainly with 5,6-dihydro-5,6-dihydroxycarbaryl or N-hydroxy-methyl carbaryl and their hydrolytic products. This data demonstrated that the substituent group on the naphthalene molecule may affect the significance of GSH conjugation.

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