Effect of oxygen free radicals, hypoxia and pH on the release of liver lysosomal enzymes.

We investigated the effect of acidic environment, hypoxia and oxygen free radicals on the release of beta-glucuronidase from rat liver lysosomes. A lysosomal enriched fraction from the homogenate of rat liver was prepared, using differential centrifugation technique. Exogenous oxygen free radicals were generated using xanthine-xanthine oxidase system. The release of beta-glucuronidase activity was measured from the lysosomes. The lysosomal fraction was exposed to various pH (8.0, 7.4, 6.5, 6.0, 5.5) and pO2 (454, 172, 96, 57,34 mm Hg) separately or to a combination of low pH (5.5, 6.5) and low pO2 (34, 57 mm Hg). The changes in pH or pO2 separately did not cause any increase in the release of beta-glucuronidase activity. The presence of oxygen free radicals at each pH or pO2 resulted in about a 3-fold increase in the release of beta-glucuronidase. A combination of very low pO2 and pH (pO2 (mm Hg)/pH; 34/5.5, 34/6.5) resulted in an increased release of beta-glucuronidase from lysosomes. Oxygen free radicals in the presence of both low pO2 and pH resulted in a further increase in the release of beta-glucuronidase. These data indicate that oxygen free radicals and not the alterations in pH and/or pO2 are primarily responsible for the disruption of lysosomes.