PB-PK derived metabolic constants, hepatotoxicity, and lethality of BrCCl3 in rats pretreated with chlordecone, phenobarbital, or mirex.

Pharmacokinetic modeling has been very useful in examining the complex relationships between exposure concentration and target tissue dose. This study utilizes a physiologically based pharmacokinetic (PB-PK) modeling approach for assessing the metabolism of BrCCl3 and to investigate its relationship with hepatotoxicity and lethality. Male Sprague-Dawley rats maintained for 15 days on normal diet (control), or on diets containing either chlordecone (CD, 10 ppm), phenobarbital (PB, 225 ppm) or mirex (M, 10 ppm), were used in gas uptake studies to determine the kinetic constants of BrCCl3 metabolism. Four initial concentrations of BrCCl3 at approximately 30, 200, 700, and 3000 ppm were used for each group. The uptake data were analyzed by computer simulation using a PB-PK model containing relevant tissue solubilities and physiological parameters as well as an equation describing the behavior of BrCCl3 in the closed chamber atmosphere. Liver injury was assessed by serum enzyme elevations (alanine aminotransferase, aspartate aminotransferase, and sorbitol dehydrogenase) and histopathological examination, at 24 hr after the exposure to BrCCl3. Another group of similarly pretreated rats was exposed to BrCCl3 and observed over a 14-day period for mortality. Dietary exposures resulted in increased Vmaxc value for BrCCl3 metabolism as compared to control (3.55 +/- 0.14 mg/hr/kg) for PB (8.52 +/- 0.28 mg/hr/kg) and M (5.06 +/- 0.19 mg/hr/kg) but not for CD (3.92 +/- 0.19 mg/hr/kg). Kfc, the first-order rate constant for BrCCl3 metabolism, was decreased after PB (12.9 +/- 0.5 hr-1/kg) and increased after M (17.6 +/- 0.5 hr-1/kg), but unchanged after CD (15.5 +/- 0.6 hr-1/kg) exposure as compared to control (15.0 +/- 0.3 hr-1/kg). The total amount of BrCCl3 metabolism at any initial concentration employed remained unchanged in all the pretreated groups as compared to control. However, the amount of BrCCl3 metabolized through saturable pathway only, at higher initial concentrations, was increased in the PB and M pretreated groups, but not in the CD pretreated group. It is concluded that the rates of metabolism of BrCCl3 were unchanged after CD pretreatment as compared to control, while PB and M pretreatment alter both the saturable and first-order rates. Serum enzymes were significantly increased in all the groups after exposure to BrCCl3 at 200 and 700 ppm concentrations. The increase was more pronounced in PB and M pretreated groups as compared to control and CD pretreated groups. Similarly, histopathological examination of liver showed alterations in the lobular architecture, the extent of alterations being dependent on the dose of BrCCl3 and the pretreatment.(ABSTRACT TRUNCATED AT 400 WORDS)