Identification of intermediate pathways of 4-hydroxynonenal metabolism in the rat.
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 omega-hydroxylation by cytochrome P450 4A enzymes and conjugation with thiol groups and therefore is the most likely candidate for the formation of omega-hydroxylated HNE-mercapturic acid conjugates excreted in rat urine.
Alary
Jacques
J
Laboratoire des Xénobiotiques, UMR 1089, INRA-Institut National de la Recherche Agronomique, 180 Chemin de Tournefeuille, BP3, 31931 Toulouse Cedex 9, France.
Fernandez
Yvette
Y
Debrauwer
Laurent
L
Perdu
Elisabeth
E
Guéraud
Françoise
F
D000111:Acetylcysteine / Q000737:chemistry / Q000378:metabolism / Q000652:urine; D000447:Aldehydes / Q000737:chemistry / Q000378:metabolism* / Q000652:urine; D000818:Animals; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003600:Cytosol / Q000737:chemistry; D008401:Gas Chromatography-Mass Spectrometry; D005978:Glutathione / Q000737:chemistry / Q000378:metabolism; D006900:Hydroxylation; D007668:Kidney / Q000378:metabolism; D007783:Lactones / Q000737:chemistry / Q000378:metabolism; D008862:Microsomes, Liver / Q000378:metabolism; D010084:Oxidation-Reduction; D051381:Rats; D017208:Rats, Wistar; D021241:Spectrometry, Mass, Electrospray Ionization; D013440:Sulfides / Q000737:chemistry / Q000378:metabolism; D014316:Tritium
D000447:Aldehydes; D007783:Lactones; D013440:Sulfides; D014316:Tritium; D005978:Glutathione; C027576:4-hydroxy-2-nonenal; D000111:Acetylcysteine