Endocytosis by liver cells during suppression of intralysosomal proteolysis.

The lysosomotropic agent chloroquine is widely used as a specific inhibitor of intralysosomal proteolysis in isolated hepatocytes. It was shown that in vitro chloroquine reversibly inhibited purified cathepsins H, B, L in concentrations less than those observed inside lysosomes in vivo. However, administration of high doses of chloroquine to rats (30-50 mg/kg i.p. as a single or repeated injections) was followed by increased cathepsin D and cysteine proteinase activities, as well as other lysosomal enzymes. Chloroquine administration did not induce any changes of carbon particles phagocytosis by liver cells (macrophages); modifications of fluid-phase (125I-PVP uptake) and receptor-mediated endocytosis (125I-asialo-fetuin uptake) were noted. Chloroquine administered in vivo reproduced some symptoms of lysosomal storage diseases (especially during repeated drug administration).