Effect of chloroquine on the form and function of hepatocyte lysosomes. Morphologic modifications and physiologic alterations related to the biliary excretion of lipids and proteins.

ABSTRACT

In these experiments, we tested the hypothesis that chloroquine, a lysosomotropic agent which modifies protein and lipid metabolism by hepatocyte lysosomes, would alter the biliary excretion of lipids and lysosomal enzymes. We treated male rats for 5 days with intraperitoneal chloroquine (50 mg/kg body wt, n = 9) or saline (n = 8) and collected bile for 6 h via bile fistulas; rats were then killed and livers homogenized for biochemical analyses or processed for electron microscopy. Chloroquine markedly increased the biliary excretion of three lysosomal enzymes (mean +/- SEM) expressed as milliunits of activity per gram liver N-acetyl-beta-glucosaminidase (24.4 +/- 2.7 vs. 12.5 +/- 1.4, p less than 0.01), beta-glucuronidase (26.4 +/- 4.7 vs. 10.9 +/- 1.4, p less than 0.01), and beta-galactosidase (9.8 +/- 1.7 vs. 5.5 +/- 0.8, p less than 0.05). In contrast, biliary outputs of enzymes associated with other organelles (e.g., alkaline phosphodiesterase I and lactic dehydrogenase) were unaffected by chloroquine treatment. Biliary cholesterol secretion was decreased after chloroquine administration (0.28 +/- 0.02 mumol/g liver vs. 0.39 +/- 0.03 mumol/g liver, p less than 0.01), but bile acid and phospholipid secretion were not altered; as a result, cholesterol saturation of bile decreased by 22% (p less than 0.05). Hepatic activities of all three lysosomal enzymes were increased after chloroquine administration (p less than 0.04); activities of enzymes associated with mitochondria, plasma membrane, endoplasmic reticulum, and cell sap were not altered. Morphometric analysis of electron micrographs of rat livers demonstrated a marked increase (p less than 0.001) in the number of lysosomelike vesicles and autophagic vacuoles in the vicinity of bile canaliculi after chloroquine administration; also, the number of canalicular microvilli decreased (p less than 0.003) after chloroquine treatment. We conclude that altered hepatic lysosomal morphology and function after chloroquine is accompanied by marked changes in outputs of lipids and lysosomal enzymes into bile. These findings call attention to a possible role for hepatic lysosomes in modulating biliary protein and lipid secretion.