Ethanol suppresses ureagenesis in rat hepatocytes: role of acetaldehyde.
We proposed previously that closure of voltage-dependent anion channels (VDAC) in the mitochondrial outer membrane after ethanol exposure leads to suppression of mitochondrial metabolite exchange. Because ureagenesis requires extensive mitochondrial metabolite exchange, we characterized the effect of ethanol and its metabolite, acetaldehyde (AcAld), on total and ureagenic respiration in cultured rat hepatocytes. Ureagenic substrates increased cellular respiration from 15.8 ± 0.9 nmol O(2)/min/10(6) cells (base line) to 29.4 ± 1.7 nmol O(2)/min/10(6) cells in about 30 min. Ethanol (0-200 mM) suppressed extra respiration after ureagenic substrates (ureagenic respiration) by up to 51% but not base line respiration. Urea formation also declined proportionately. Inhibition of alcohol dehydrogenase, cytochrome P450 2E1, and catalase with 4-methylpyrazole, trans-1,2-dichloroethylene, and 3-amino-1,2,3-triazole restored ethanol-suppressed ureagenic respiration by 46, 37, and 66%, respectively. By contrast, inhibition of aldehyde dehydrogenase with phenethyl isothiocyanate increased the inhibitory effect of ethanol on ureagenic respiration by an additional 60%. AcAld, an intermediate product of ethanol oxidation, suppressed ureagenic respiration with an apparent IC(50) of 125 μM. AcAld also inhibited entry of 3-kDa rhodamine-conjugated dextran in the mitochondrial intermembrane space of digitonin-permeabilized hepatocytes, indicative of VDAC closure. In conclusion, AcAld, derived from ethanol metabolism, suppresses ureagenesis in hepatocytes mediated by closure of VDAC.
Center for Cell Death, Injury, and Regeneration, Medical University of South Carolina, Charleston, South Carolina 29425, USA.
Ekhson L
EL
Holmuhamedov
Christoph
C
Czerny
Craig C
CC
Beeson
John J
JJ
Lemasters
D000079:Acetaldehyde / Q000378:metabolism*; D000426:Alcohol Dehydrogenase / Q000378:metabolism; D000818:Animals; D002374:Catalase / Q000378:metabolism; D002492:Central Nervous System Depressants / Q000493:pharmacokinetics* / Q000494:pharmacology; D019392:Cytochrome P-450 CYP2E1 / Q000378:metabolism; D020536:Enzyme Activators / Q000494:pharmacology; D000431:Ethanol / Q000493:pharmacokinetics* / Q000494:pharmacology; D022781:Hepatocytes / Q000378:metabolism*; D008297:Male; D008930:Mitochondria, Liver / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D014508:Urea / Q000378:metabolism*; D050994:Voltage-Dependent Anion Channels / Q000378:metabolism
D002492:Central Nervous System Depressants; D020536:Enzyme Activators; D050994:Voltage-Dependent Anion Channels; D000431:Ethanol; D014508:Urea; D000426:Alcohol Dehydrogenase; D002374:Catalase; D019392:Cytochrome P-450 CYP2E1; D000079:Acetaldehyde