Autoprotection against acetaminophen toxicity in cultured rat hepatocytes: the effect of pretreatment and growth factors

To evaluate the effect of acetaminophen pretreatment and growth factors on acetaminophen hepatotoxicity in cultured rat hepatocytes, rat hepatocytes in primary culture were exposed to acetaminophen 8 mM after pretreatment with either acetaminophen 1 mM, treatment with growth factors (EGF and HGF), or no treatment. Growth response was measured by changes in DNA, [3H]thymidine incorporation and mRNA of growth related proteins, cell damage by leakage of LDH to the medium and changes in ATP, and protection against toxicity by changes in glutathione, cytochrome p450 and the expression of glutathione-S-transferase and Cyp1A2. Pretreatment with acetaminophen induced growth response, weaker than that of growth factors, but pretreatment and growth factors reduced cell damage equally effectively. Glutathione and glutathione-S-transferase increased more by growth factors than by pretreatment, but both conditions reduced Cyp1A2 to near zero. Pretreatment and growth factors protect against acetaminophen toxicity by suppressing the expression of Cyp1A2, thereby reducing the production of the intermediate N-acetyl-p-benzoquinone imine (NAPQI). Suppression of Cyp1A2 expression by pretreatment is assumed to be due to a growth-stimulating effect of low concentrations of acetaminophen.