Role of oxygen free radicals and pH on the release of cardiac lysosomal enzymes.

We investigated the effect of exogenous oxygen free radicals and various pH on the release of lysosomal hydrolases from dog myocardial lysosomes. A lysosomal enriched fraction from the homogenate of dog heart was prepared, using differential centrifugation technique. Exogenous oxygen free radicals were generated using xanthine-xanthine oxidase system. The release of lysosomal hydrolases was measured from the lysosomal enriched fraction. There was about 3-fold increase in the release of cathepsin D and beta-N-acetylglucosaminidase activities in the preparations treated with xanthine-xanthine oxidase as compared to those without such treatment. The presence of superoxide dismutase, an oxygen free radical scavenger, prevented the release of cathepsin D and beta-N-acetylglucosaminidase from the lysosomes. Sonication and lubrol treatments, which are known to cause membrane disruption, also induced the release of these enzymes from lysosomal enriched fraction. However, this release was not prevented by superoxide dismutase. The changes in pH (4.5, 5.5, 6.0, 6.5, 7.4, 8.0) alone did not cause any increase in the enzyme release. The presence of oxygen free radicals at each pH resulted in a similar increase in the release of cathepsin D and beta-N-acetylglucosaminidase. These studies suggest that oxygen free radicals and not the alterations in pH are primarily responsible for the release of lysosomal hydrolases. Oxygen free radicals, in addition to their direct myocardial damaging effect, may also be responsible for the cardiac damage through the release of lysosomal enzymes.