The phenobarbital-type induction of rat liver microsomal monooxygenases by perfluorodecalin

Effect of a Perfluorochemical Emulsion on the Rat Hepatic Mixed Function Oxidase System

The perfluorochemical components of synthetic oxygen transporting emulsions may persist in hepatic tissue. After a single 30% blood exchange with the perfluorochemical emulsion, Fluosol-DA 20%, the effects on the microsomal metabolism of 7-methoxycoumarin and 7-ethoxycoumarin were studied over a 9 week period. Fluosol-DA treated animals were compared with controls (sham) and hetastarch-treated controls. Changes in dealkylase activities were compared with induction by phenobarbitone and 3-methylcholanthrene. The liver to body weight ratio increased by 49% in Fluosol-DA-treated rats over the controls at 1 week and the microsomal protein was increased in the Fluosol-DA-treated rats after 4 and 9 weeks. Fluosol-DA treatment induced 7-methoxycoumarin demethylase with peak differences occurring at 1 week and a Vmax 75% greater than controls. Fluosol-DA was a more potent inducer of demethylase than phenobarbitone. In addition, 7-ethoxycoumarin de-ethylase was induced by Fluosol-DA with a peak induction at 4 weeks. The Vmax at 4 weeks in Fluosol-DA-treated rats was 122% greater than control. In this case, Fluosol-DA produced less induction in de-ethylase than 3-methylcholanthrene. These studies show that Fluosol-DA induces more than one form of cytochrome P450 and the effects resemble those of phenobarbitone more than those of 3-methylcholanthrene. Hetastarch, a plasma expander, did not affect liver weights, microsomal protein content, or the cytochrome P450 system.

Stimulatory effect of the CYP1A1 inducer 2,3,7,8-tetrachlorodibenzo-p-dioxin on the reproduction of HIV-1 in human lymphoid cell culture

1. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) was an inducer of microsomal benzo[alpha]pyrene hydroxylase (AHH) and 7-ethoxyresorufin O-deethylase (EROD) in MT-4 human lymphoid cell culture. 2. The monoclonal antibody (Mab), 1-7-1 and the immunodepleted polyclonal antibody (Pab), anti-CYP1A1(-A2), inhibit AHH and EROD activities pre-induced by 10 nM TCDD in MT-4 cells. Hence, the specific monooxygenase isoform induced in the lymphoid cells by TCDD appears to be CYP1A1 the expression of which is mediated by the Ah receptor. 3. Incubation of MT-4 cells with TCDD at 10, 50 and 150 nM for 1.5 and 48 h followed by infection of the cells with human immunodeficiency virus 1 (HIV-1) was accompanied by a 3-6-fold increase in the activity of viral RNA-dependent DNA-polymerase. The most marked effect on reverse transcriptase activity occurred with 10 nM TCDD 5-9 days after HIV-1 infection. 4. In the same period there was accumulation of viral protein, determined by ELISA, with a 4-8-fold increase in production of viral protein. The above effects of TCDD have been observed even when MT-4 cells were washed 1.5 h after beginning the incubation with TCDD.

Detection of the enzymatic activity of cytochrome P-450 enzymes by high-performance liquid chromatography

The reactions catalysed by the various cytochrome P-450 enzymes are reviewed with respect to the analysis of products by high-performance liquid chromatography (HPLC). Especially biotransformation reactions of purified cytochrome P-450 enzymes in a reconstituted system and in microsomes mainly of rat liver origin are considered. Emphasis is put on the specificity of product formation due to the individual isozymes of cytochrome P-450. It is shown that the presence of eight cytochrome P-450 isozymes can be monitored and determined by specific product formation after HPLC analysis, which is an important parameter in toxicological studies.

The effect of moderate haemodilution with Fluosol-DA or Hespan on the nonmicrosomal acetylation of sulphadimidine in the rat

The effects of Fluosol-DA (Fluosol) and Hespan haemodilution on the nonmicrosomal acetylation of sulphadimidine were studied in male rats. Fluosol increased the acetylsulphadimidine percent excreted in urine, the metabolic formation rate constant (kf), and the formation clearance (CLF) for 72 h after haemodilution without any significant changes in the sulphadimidine apparent volume of distribution (Vd) or total body clearance (CL). Hespan haemodilution increased the acetylsulphadimidine percent excreted in urine only at 48 h while significantly decreasing the sulphadimidine clearance, urinary excretion rate constant (ku), and renal clearance (CLR) for 72 h. The enhanced N-acetyltransferase activity after Fluosol haemodilution may have therapeutic consequences for concomitantly given drugs metabolized by this enzyme.

Acute effects of moderate Fluosol-DA hemodilution on hepatic microsomal and nonmicrosomal metabolism in rats

Fluosol has been shown to alter the disposition of several drugs immediately after its administration. Investigations in this laboratory established that the disposition of several drug markers requiring the hepatic microsomal cytochrome P-450 isoenzymes was time dependent for 72 hours. It was an additional purpose of the research to determine if the nonmicrosomal sulfation and acetylation pathways were also influenced by Fluosol hemodilution in a time dependent manner. Rats were moderately hemodiluted with Fluosol and received an intravenous dose of a drug marker 24, 48, or 72 hours after hemodilution. The formation clearance (ClF) of specific metabolites was used as the pharmacokinetic measure of a specific enzymatic activity. 3-Hydroxymethyl antipyrine ClF (phenobarbital inducible microsomal cytochrome P-450 isoenzymes) increased 300% only at 48 hours. Acetylsulfamethazine ClF (nonmicrosomal acetylation) increased 287% and 162% at 24 and 48 hours, respectively. Acetaminophen sulfate ClF (nonmicrosomal sulfation) decreased 30% only at 48 hours. Substantial evidence shows that cytochrome P-450 content is induced at 72 hours and remains induced for an unprecedented length of time by the PFCs in Fluosol. Therefore, it was unexpected that 3-hydroxymethyl antipyrine ClF was not increased at 72 hours. Several possible explanations are discussed for the unexpected findings.