title: Ethanol metabolism by HeLa cells transduced with human alcohol dehydrogenase isoenzymes: control of the pathway by acetaldehyde concentration.
abstract: BACKGROUND
  Human class I alcohol dehydrogenase 2 isoenzymes (encoded by the ADH1B locus) have large differences in kinetic properties; however, individuals inheriting the alleles for the different isoenzymes exhibit only small differences in alcohol elimination rates. This suggests that other cellular factors must regulate the activity of the isoenzymes.
  
  
  METHODS
  The activity of the isoenzymes expressed from ADH1B*1, ADH1B*2, and ADH1B*3 cDNAs was examined in stably transduced HeLa cell lines, including lines which expressed human low K(m) aldehyde dehydrogenase (ALDH2). The ability of the cells to metabolize ethanol was compared with that of HeLa cells expressing rat class I alcohol dehydrogenase (ADH) (HeLa-rat ADH cells), rat hepatoma (H4IIEC3) cells, and rat hepatocytes.
  
  
  RESULTS
  The isoenzymes had similar protein half-lives in the HeLa cells. Rat hepatocytes, H4IIEC3 cells, and HeLa-rat ADH cells oxidized ethanol much faster than the cells expressing the ADH1B isoenzymes. This was not explained by high cellular NADH levels or endogenous inhibitors; but rather because the activity of the β1 and β2 ADHs was constrained by the accumulation of acetaldehyde, as shown by the increased rate of ethanol oxidation by cell lines expressing β2 ADH plus ALDH2.
  
  
  CONCLUSIONS
  The activity of the human β2 ADH isoenzyme is sensitive to inhibition by acetaldehyde, which likely limits its activity in vivo. This study emphasizes the importance of maintaining a low steady-state acetaldehyde concentration in hepatocytes during ethanol metabolism.
authors.affiliation: Department of Medicine, Indiana University School of Medicine, Roudebush VA Medical Center, Indianapolis, Indiana.
authors.forename: Michinaga
authors.initials: M
authors.lastname: Matsumoto
authors.forename: Izabela
authors.initials: I
authors.lastname: Cyganek
authors.forename: Paresh C
authors.initials: PC
authors.lastname: Sanghani
authors.forename: Won Kyoo
authors.initials: WK
authors.lastname: Cho
authors.forename: Suthat
authors.initials: S
authors.lastname: Liangpunsakul
authors.forename: David W
authors.initials: DW
authors.lastname: Crabb
mesh_terms: D000079:Acetaldehyde / Q000378:metabolism*; D000426:Alcohol Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D000444:Aldehyde Dehydrogenase / Q000235:genetics / Q000378:metabolism; D000483:Alleles; D000818:Animals; D006528:Carcinoma, Hepatocellular; D045744:Cell Line, Tumor; D002492:Central Nervous System Depressants / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism*; D006367:HeLa Cells; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D002492:Central Nervous System Depressants; D007527:Isoenzymes; D009243:NAD; D000431:Ethanol; C489332:ADH1B protein, human; D000426:Alcohol Dehydrogenase; D000444:Aldehyde Dehydrogenase; D000079:Acetaldehyde