Perhexilene: effects on hepatic lysosomal function in rats.

1. Perhexilene, a long-acting anti-anginal drug, can induce adverse effects on the liver which may be dose-dependent. At high concentrations, perhexilene causes marked morphological changes in hepatocyte lysosomes. The current study examined the effect of 'therapeutic' doses of perhexilene on hepatic lysosomal function, particularly the biliary release of lysosomal enzymes, using an isolated perfused rat liver (IPRL) model. 2. Pharmacokinetic studies demonstrated that clearance of single doses of perhexilene by the perfused rat liver was dose-dependent and established a 'therapeutic' dose of 0.6 mg using the IPRL. A 5 day pretreatment regimen of 20 mg/kg per day was shown to produce 'therapeutic' perhexilene concentrations of 150-210 ng/ml. 3. At perhexilene concentrations equating the 'therapeutic' range in man, the major effect of perhexilene was at the biliary pole of the hepatocyte. In 5 day pretreatment dose studies, lysosomal enzyme excretion into bile was markedly increased. In single dose studies, the increase in biliary lysosomal enzyme output partially reflected an increase in bile water production which was not seen with the 5 day pretreatment regimen. Hepatic and perfusate lysosomal enzyme activities were not affected. 4. This selective effect of perhexilene on hepatocyte-to-bile lysosomal excretion may reflect intracellular lysosomal drug localization.

Pharmacologic perturbation of rat liver lysosomes: effects on release of lysosomal enzymes and of lipids into bile.

Hepatocyte lysosomes disassemble materials derived from intracellular sources, including lipid-containing membranes, by a process called autophagy. In addition, hepatocyte lysosomes can release their contents into bile by exocytosis. Therefore, using both in vivo and in vitro models, we tested the hypothesis that acute pharmacologic induction of autophagy would modify the biliary excretion of lysosomal protein and of lipids. We treated rats with a single dose of chloroquine (10 mg/kg), glucagon (1 mg/kg), or control solutions and collected bile via bile fistulas. Both chloroquine and glucagon immediately caused a marked and parallel decrease in biliary excretion of three lysosomal enzymes, N-acetyl-beta-glucosaminidase, beta-glucuronidase, and beta-galactosidase, to 25%-30% of baseline values (p less than 0.01). This decrease was sustained for 2 h after glucagon and 4 h after chloroquine administration. In contrast, biliary lipid changes were minor: a slight lowering of biliary cholesterol secretion after chloroquine (p less than 0.05), but no change in biliary bile acids, cholesterol, and phospholipid secretion after glucagon. Changes in biliary excretion of lysosomal enzymes accompanying chloroquine and glucagon administration were associated with morphologic evidence of autophagy as assessed by electron microscopy and by increased fragility of hepatic lysosomes as assessed by latency of N-acetyl-beta-glucosaminidase. These in vivo changes in biliary lysosomal enzyme excretion induced by chloroquine and glucagon were confirmed in vitro using the isolated perfused rat liver. Thus, acute induction of autophagy results in conservation of hepatic lysosomal protein and has virtually no effect on biliary lipid excretion.

Ethanol impairs biliary lysosomal enzyme release in rats.

The effects of ethanol on hepatic lysosomes are poorly documented. This study examined the biliary release of lysosomal enzymes, a marker of the hepatocyte-to-bile excretory pathway, after ethanol administration in the isolated perfused rat liver model. At concentrations similar to those reached in human plasma during social drinking, ethanol markedly decreased biliary lysosomal enzyme output and bile flow in the rat. Ethanol did not affect hepatic activities or the release into perfusate of lysosomal and other subcellular marker enzymes. Hence, ethanol may potentially inhibit hepatocyte-to-bile excretion of other compounds processed through lysosomes.