Decreased stability of digestive gland lysosomes from the common musselMytilus edulis L. byin vitro generation of oxygen-free radicals

Abstract

A consequence of xenobiotic exposure is oxidative stress resulting from one electron metabolism with the concomitant generation of oxygen-derived free radicals. The growing interest in molluscs as sentinels of environmental pollution has prompted studies on the responsiveness of lysosomal membranes from the common marine mussel,Mytilus edulis L. to oxidative stress by the oxyradicalgenerating hypoxanthine/xanthine oxidase reaction. We report that oxyradicals generated external to the lysosomal membrane cause a decrease in the stability of the lysosomal membrane, thereby resulting in leakage of enzymes from this organelle. This leakage can be prevented by catalase but not by hydroxyl radical scavenging agents. Superoxide dismutase appears to be a major enzyme exhibiting latent activity upon attack of lysosomes by oxyradicals but does not afford sufficient protection to prevent enzyme leakage under the conditions studied. Further, non-fluorescent dihydrorhodamine 123 is converted to highly fluorescent products after uptake into the lysosomal compartment of digestive gland cells suggesting that oxyradicals may be produced within the lysosomal compartment in association with the pinocytotic activity of the digestive cells. Thus, a consequence of xenobiotic-mediated proliferation of oxyradicals might be the release of potent hydrolytic enzymes into the cytosol with ensuing enzyme degradation and damage to other organelles.