Involvement of lysosomal proteolysis in hepatocyte cytotoxicity induced by Cu(II) or Cr(VI)

Previously we showed that the redox active Cu (II) and Cr (VI) were very powerful at inducing reactive oxygen species ("ROS") formation in hepatocytes and furthermore "ROS" scavengers prevented Cu (II) and Cr (VI) induced hepatocyte cytotoxicity [1,2]. In the following it is shown that hepatocyte cytotoxicity induced by Cu (II) and Cr (VI) were preceded by lysosomal proteolysis as demonstrated by tyrosine release. Hepatocyte lysosomal proteolysis was also prevented by leupeptin and pepstatin (lysosomal protease inhibitors). Cu (II) and Cr (VI) induced cytotoxicity was also prevented by leupeptin and pepstatin. A marked increase in Cu (II) and Cr (VI) induced hepatocyte toxicity also occurred if the lysosomal toxins gentamicin or aurothioglucose were added at the same time as the Cu (II) and Cr (VI). Furthermore destabilizing lysosomal membranes beforehand by preincubating the hepatocytes with gentamicin or aurothioglucose prevented Cu (II) and Cr (VI) induced hepatocyte cytotoxicity. It is proposed that Cu (II) and Cr (VI) induced cytotoxicity involves lysosomal damage that causes the release of cytotoxic digestive enzymes as a result of lysosomal membrane damage by "ROS".