Liver nuclear ethanol metabolizing systems (NEMS) producing acetaldehyde and 1-hydroxyethyl free radicals.
Biotransformation of ethanol by liver nuclei was studied. The formation of acetaldehyde was determined by GC/FID. The 1-hydroxyethyl (1HEt) formation was established by spin trapping of the radical with N-t-butyl-alpha-phenylnitrone (PBN) followed by GC/MS. Liver nuclei, free of endoplasmic reticulum, cytosol or mitochondria, were able to biotransform ethanol to acetaldehyde in the presence of NADPH under air. Only 22% activity was observed in the absence of the cofactor. Twenty-six percent of the NADPH-dependent activity and 47% of the NADPH-independent activity were observable under nitrogen. Aerobic biotransformation was inhibited by CO, SKF 525A, 4-methylpyrazole and by diethyldithiocarbamate. This suggests that CYP2E1 is involved in the process. However, the formation of acetaldehyde was able to proceed under a pure CO atmosphere. The lack of inhibitory effects of 2-mercapto-1-methylimidazol and thiobenzamide excludes the potential participation of the NADPH flavin monooxigenase system. The formation of hydroxyl radicals in the process is suggested by the partial inhibitory effect of 5 mM mannitol and 5 mM sodium benzoate and by the fact that the 1HEt was detected. The NADPH-dependent anaerobic ethanol biotransformation pathway was stimulated by FAD and inhibited to some extent by iron chelators. The relevance of a liver nuclear ethanol biotransformation, generating reactive metabolites, such as acetaldehyde and free radicals, nearby DNA, nuclear proteins and lipids is discussed.
Castro
G D
GD
Centro de Investigaciones Toxicológicas (CEITOX)-CITEFA/CONICET, Buenos Aires, Argentina.
Delgado de Layño
A M
AM
Castro
J A
JA
D000079:Acetaldehyde / Q000378:metabolism*; D000818:Animals; D001711:Biotransformation; D002467:Cell Nucleus / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism*; D005609:Free Radicals; D008099:Liver / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D009249:NADP / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley
D005609:Free Radicals; D000431:Ethanol; D009249:NADP; D000079:Acetaldehyde