Deleterious effects of xanthine oxidase on rat liver endothelial cells after ischemia/reperfusion

AbstractPrevious studies have demonstrated that reactive oxygen species are involved in ischemic injury. The present work was undertaken to determine in vivo the role of xanthine oxidase in the oxygen free radical production during rat liver ischemia and to examine the activity of antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase) during the same period. Our results indicate a 4-fold increase in xanthine oxidase activity between 2 and 3 hours of normothermic ischemia, in parallel with a decrease in cell viability. Moderate hypothermia delays both events. Under the same conditions, the activity of oxygen radical scavenging enzymes remains unchanged. Moreover, we have compared in vitro the susceptibility of isolated liver cells to an oxidative stress induced by O2·−, H2O2 and OH. Our results reveal that endothelial cells are much more susceptible to reactive oxygen species than hepatocytes, probably because they lack H2O2-detoxifying enzymes. These findings suggest that xanthine oxidase might play a major role in the ischemic injury mainly at the level of the sinusoidal space where most endothelial cells are located

Biological functions of lysosomal membrane-associated glycoproteins

Lysosomes are the final repository of degradation products from the extracellular and intracellular spaces. The lysosomal membrane forms a unique vacuole participating in both endocytosis and autophagocytosis. It is extremely resistant to degradation by lysosomal hydrolases, maintains an acidic intralysosomal environment, transports amino acids and oligosaccharides produced by lysosomal hydrolases, interacts and fuses with other membrane organelles, such as endosomes and phagosomes, and with the plasma membrane.Biomedical Reviews 1997; 8: 119-125

Endocytosis of hyaluronidase-1 by the liver

International audienceIt has been suggested that intracellular hyaluronidase-1 (Hyal-1), considered as a lysosomal enzyme, originates from the endocytosis of the serum enzyme. To check this proposal we have investigated the uptake of recombinant human hyaluronidase-1 (rhHyal-1) by mouse liver and its intracellular distribution, making use of centrifugation methods. Experiments were performed on wild type mice injected with 125I-rhHyal-1 and on null mice (Hyal-1 -/-) injected with the unlabelled enzyme. Mice were euthanized at increasing times after injection Activity of the unlabelled enzyme was determined by zymography. Intracellular distribution of the Hyal-1 was investigated by differential and isopycnic centrifugation. Results indicated that rhHyal-1 is endocytosed by the liver, mainly by sinusoidal cells and follows the intracellular pathway described for many endocytosed proteins that find themselves eventually in lysosomes. However, Hyal-1 endocytosis has some particular features. Endocytosed rhHyal-1 is quickly degraded. Its distribution after differential centrifugation differs from the distribution of β-galactosidase, taken as reference enzyme of lysosomes. After isopycnic centrifugation in a sucrose gradient, endocytosed rhHyal-1 behaves like β-galactosidase soon after injection but Hyal-1 distribution is markedly less affected than the distribution of β-galactosidase by a prior injection of Triton WR-1339 to the mice. This agent is a specific density perturbant of lysosomes. Behaviour in centrifugation of endogenous liver Hyal-1, identified by HA zymography exhibits some kinship with the behaviour of the endocytosed enzyme, suggesting that it could originate from an endocytosis of the serum enzyme. Overall, these results could be explained by supposing that active endocytosed Hyal-1 is mainly present in early lysosomes. Although its degradation half-time is short, Hyal-1 could exert its activity owing to a constant supply of active molecules from the blood

Effects of wine on cellular and endocellular membranes <em>in vitro</em>

Several observations suggest that wine consumption could have beneficial effects on health by preventing cardiovascular diseases. Apparently, ethanol is not the only component responsible for these effects, phenolic substances: tanins, flavonoids may have an important role. As these compounds are able to affect biological membranes, we investigated the effect of wine in vitro on two model membranes: the lysosomal membrane and the red cell membrane. The integrity of rat liver lysosomal membrane was assessed by measuring the latency of Nacetylglucosaminidase, a lysosomal enzyme, when the organelles are subjected to free radicals of oxygen in the presence of different concentrations of wine. The state of red cell membrane was followed by determining hemolysis caused by phospholipase C. Our results show that low concentrations of red wine prevent the deterioration of the membrane of lysosomes induced by oxygen free radicals generated by the xanthine-xanthine oxidase system and oppose hemolysis induced by treating red cells with Clostridium welchii phospholipase C. White wine is considerably less efficient. As similar effects can be obtained with some phenolic compounds, it is probable that the membrane protective effects of red wine that we describe, originate from its content in these substances