Phenobarbital pretreatment in vivo and in vitro and the effect of hepatotoxicity of d-galactosamine in rat hepatocytes in culture.
Galactosamine (GalN) is a known hepatotoxic compound, acting by depletion of uracil nucleotides. The relation between an active cytochrome P-450 system (CYP) and the hepatotoxicity of GalN was studied in rat hepatocytes that were pretreated with phenobarbital (PB) in vivo or in vitro. A 24-hr in vitro pretreatment of cultured hepatocytes with PB resulted in a significant decrease in GalN toxicity as measured by lactate dehydrogenase (LDH) leakage. Furthermore, GalN treatment resulted in an increase in the activity of the PB-induced forms of CYP (namely CYP 2B1/2) as measured by 7-pentoxyresorufin O-depentylase (PROD) activity. This increase was not found after GalN treatment of microsomes. GalN had no effect on the concentration of the apoenzymes. GalN administration to hepatocytes of in vivo PB-pretreated rats resulted in a similar effect of GalN on the activity of the CYP enzymes but PB in vivo had no effect on GalN toxicity. These results suggest that GalN treatment may result in a significant increase in the specific activity of CYP 2B1/2 enzymes (PROD), without an obvious increase in the amount of PB-induced apoenzymes. This phenomenon was measurable only in intact cells. No direct relation is assumed between the activity of the CYP apoenzymes and the decrease in GalN toxicity after PB treatment. The toxicity of Galn was inhibited by PB treatment in vitro.
Toussaint
M J
MJ
Department of Veterinary Pathology, Utrecht University, POB 80.158, 3508 TD Utrecht, The Netherlands.
De Wit
M M
MM
Blaauboer
B J
BJ
Nederbragt
H
H