Identification of Intermediate Pathways of 4-Hydroxynonenal Metabolism in the Rat

• Published in: Chemical research in toxicology 2003-03, Vol.16 (3), p.320-327
• Main Authors: Alary, Jacques, Fernandez, Yvette, Debrauwer, Laurent, Perdu, Elisabeth, Guéraud, Françoise
• Format: Article
• Language: English
• Subjects: 1,4-Dihydroxynonene; 4-Hydroxy-2-nonenal; Acetylcysteine - chemistry; Acetylcysteine - metabolism; Acetylcysteine - urine; aldehyde dehydrogenase; Aldehydes - chemistry; Aldehydes - metabolism; Aldehydes - urine; Animals; Chromatography, High Pressure Liquid - methods; Cytosol - chemistry; Gas Chromatography-Mass Spectrometry; Glutathione - chemistry; Glutathione - metabolism; Hydroxylation; Kidney - metabolism; Lactones - chemistry; Lactones - metabolism; Life Sciences; mercapturic acid; Microsomes, Liver - metabolism; Oxidation-Reduction; Rats; Rats, Wistar; Spectrometry, Mass, Electrospray Ionization; Sulfides - chemistry; Sulfides - metabolism; thioethers; Tritium
• ISSN: 0893-228X; 1520-5010
• DOI: 10.1021/tx025671k

The formation of 4-hydroxy-2-nonenal (HNE) conjugates with glutathione (GSH) by Michael addition and subsequent cleavage to yield the related mercapturic acid (MA) conjugates are a major detoxication process. To characterize the metabolic pathways involved in the formation of urinary HNE−MA conjugates in the rat, the metabolism of HNE−thioethers (HNE−GSH, HNE−MA, and HNE−Cys) by rat liver and kidney cytosolic fractions was investigated. The experimental results showed that HNE−GSH is a good substrate for cytosolic incubations whereas HNE−MA and HNE−Cys are poorly metabolized. About 80% of the urinary MA conjugates originate from the primary and major HNE metabolite, namely, the hemiacetalized HNE−GSH. The direct reduction of HNE−GSH by a cytosolic aldo-keto reductase (NADPH) leads to 1,4-dihydroxynonene−GSH (DHN−GSH) and subsequently to DHN−MA. The direct oxidation of HNE−GSH by aldehyde dehydrogenase (NAD)+ leads to 4-hydroxynonenoic−lactone−GSH, the partial hydrolysis of which occurs at physiological pH and accounts for the corresponding 4-hydroxynonenoic−GSH. Both the spontaneous- and the glutathione S-transferases-catalyzed retro-Michael cleavages of HNE−GSH and HNA−lactone−GSH are the source of HNE and HNA−lactone, respectively. This latter compound, with both lipophilic and electrophilic properties, is available for microsomal ω-hydroxylation by cytochrome P450 4A enzymes and conjugation with thiol groups and therefore is the most likely candidate for the formation of ω-hydroxylated HNE−mercapturic acid conjugates excreted in rat urine.