CHLOROQUINE ACCUMULATION AND ALTERATIONS OF PROTEOLYSIS AND PINOCYTOSIS IN THE RAT CONCEPTUS IN VITRO

Abstract-The teratogenicity of chloroquine (CQ) has been hypothesized to result from its effects on lysosomal function, specifically the ability of the visceral yolk sac (VYS) to capture and degrade external macromolecules. Using the rat whole embroyo culture system, we evaluated the ability of CQ to accumulate in conceptal tissues and its effects on aspects of VYS function known to be important in the uptake and processing of nutrients. When CQ was added directly to the culture medium, it was found to accumulate rapidly in conceptal tissues, particuarly the VYS. Tissue concentrations of CQ in the embryo proper reached approximately lo-fold those in the medium, whereas concentrations in the VYS exceeded by lOO-fold the medium concentration within a 4-hr exposure on gestational day (GD) 10. Embryotoxic concentrations of CQ (lO-30pM) enhanced the activity of lysosomal cysteine proteinases measured in vitro under optimum pH conditions in both embryonic and VYS homogenates after a 26-hr treatment from GD 10-11. A different pattern of response in enzyme activity was observed between embryos and VYSs that could be attributed to the preferential accumulation of CQ in the VYS. Nonembryotoxic concentrations of CQ (l-7.5 PM) induced a concentration-dependent i crease in VYS enzyme activity that peaked in conceptuses exposed to 20 PM CQ (an intermediate mbryotoxic concentration). The enhanced cysteine proteinase activity was time dependent and appeared to increas