Differential protection by rat UDP-glucuronosyltransferase 1A7 against Benzo[a]pyrene-3,6-quinone- versus Benzo[a]pyrene-induced cytotoxic effects in human lymphoblastoid cells

Toxicol Appl Pharmacol. 2000 Jan 1;162(1):34-43. doi: 10.1006/taap.1999.8815.


UDP-glucuronosyltransferase 1A7 (UGT1A7) is a polyaromatic hydrocarbon (PAH)-inducible UGT with activity toward various benzo[a]pyrene (B[a]P) metabolites. To investigate the influence of rat UGT1A7 on B[a]P-induced cytotoxicity, human lymphoblastoid L3 cells were transfected with pMF6 (control expression vector), p167Dtk2 (microsomal epoxide hydrolase expression vector), or p167Dtk2-1A7 (epoxide hydrolase/UGT1A7 coexpression vector), and the cell populations were compared for sensitivity to B[a]P-induced effects. B[a]P inhibited cell proliferation and decreased relative cell survival of p167Dtk2 and p167Dtk2-1A7 cells to a similar extent. Metabolism studies using [(3)H]B[a]P revealed increased formation of glucuronide conjugates of B[a]P-4,5-diol, 3-OH-, or 9-OH-B[a]P and an unidentified metabolite by p167Dtk2-1A7 cells, but the presence of unconjugated metabolites suggested that glucuronidation capacity may be limited. No differences between p167Dtk2 and p167Dtk2-1A7 L3 cells were observed in the growth inhibitory effects of 3-OH-B[a]P or B[a]P-7,8-diol, but p167Dtk2-1A7-expressing cells were found to be less sensitive to B[a]P-3,6-quinone-induced effects on cell proliferation and relative cell survival. The effect was also observed in AHH-1 lymphoblastoid cells expressing UGT1A7 without epoxide hydrolase. The UGT1A7-expressing AHH-1 cells were also less sensitive to growth inhibition by B[a]P-1,6-quinone and B[a]P-6,12-quinone. Flow cytometric analysis of vehicle and B[a]P-3, 6-quinone-exposed cell populations showed an association between UGT1A7 expression and resistance to B[a]P-3,6-quinone-induced apoptosis and loss of cell viability. These data suggest that UGT1A7 may be preferentially active toward B[a]P-quinones and that UGT1A7 may represent the PAH-inducible UGT activity previously implicated in protection against toxic redox cycling by B[a]P-3,6-quinone.

Publication types

  • Comparative Study

MeSH terms

  • Animals
  • Apoptosis / drug effects
  • Benzo(a)pyrene / pharmacokinetics
  • Benzo(a)pyrene / toxicity*
  • Benzopyrenes / toxicity*
  • Blotting, Western
  • Cell Division / drug effects
  • Cell Line
  • Cell Survival / drug effects
  • Chromatography, High Pressure Liquid
  • Drug Interactions
  • Epoxide Hydrolases / physiology
  • Flow Cytometry
  • Genetic Vectors / physiology
  • Glucuronides / metabolism
  • Glucuronosyltransferase / physiology*
  • Herpesvirus 4, Human / genetics
  • Humans
  • Lymphocytes / cytology
  • Lymphocytes / drug effects*
  • Rats
  • Transfection


  • Benzopyrenes
  • Glucuronides
  • Benzo(a)pyrene
  • benzo(a)pyrene-3,6-quinone
  • Glucuronosyltransferase
  • UDP-glucuronosyltransferase, UGT1A7
  • Epoxide Hydrolases