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4-hydroxynonenal detoxification by mitochondrial glutathione S-transferase is compromised by short-term ethanol
Juanjuan Chen1, Steven Schenker, George I Henderson
1Department of Medicine, Division of Gastroenterology and Nutrition, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78284, USA. chenj1@uthscsa.edu
Background:
4-Hydroxynonenal (HNE), a toxic lipid peroxidation product, has been implicated in mitochondrial damage in rat liver by ethanol consumption. The present study assessed the effects of short-term in vivo ethanol exposure on HNE detoxification by mitochondrial glutathione S-transferase (GST).
Methods:
Male Sprague Dawley rats were administered 5 doses of ethanol (4 g/kg) at 12 hr intervals by gavage. Pair-fed rats that received isocaloric dextrose instead of ethanol served as controls. Mitochondrial and submitochondrial fractions were prepared from the livers. Mitochondrial contents of HNE and HNE-glutathione conjugate were measured by high-performance liquid chromatography. GST isoforms were identified by Western blots in submitochondrial fractions.
Results:
Whereas there was an 80% increase in mitochondrial HNE content after ethanol consumption, there was a 42% decrease in the content of HNE-glutathione conjugate, compared with controls (p< 0.05). After ethanol exposure, the GST activities toward HNE in intact mitochondria and in the membranous fraction were decreased by 37% and 45% (p< 0.05), respectively, whereas that in the aqueous fraction was unchanged. Kinetic analysis of HNE conjugation by the membrane-associated GST showed that ethanol decreased the V(max) nearly by half (p< 0.05), whereas it did not affect the K(m). HNE conjugation by the aqueous GST demonstrated a higher K(m) than that of the membrane-associated GST, although its kinetics were not significantly altered by ethanol. Immunochemical analysis with Western blots demonstrated that both the membranous and the aqueous fractions of mitochondria contain GST-alpha and GST-mu isoforms, whereas GST-pi was absent.
Conclusions:
HNE detoxification by mitochondrial GST is compromised by short-term ethanol consumption, which may contribute to elevated mitochondrial HNE content and hence its toxicity in the ethanol-exposed liver.