Although the morphologic changes and the biochemical/metabolic lesions that occur in the red cell (RBC) in the hereditary hemolytic anemias have been well described, the actual mechanisms responsible for the shortened RBC survival remain unclear. It is proposed that impaired pentose phosphate shunt function and increased RBC susceptibility to oxidant stress are common denominators in the shortened RBC survival seen in the hereditary hemolytic anemias due to defects other than glucose-6-phosphate dehydrogenase (G6PD) deficiency. The objectives of the proposed studies are: 1) to evaluate the RBC antioxidant defense system in hereditary hemolytic anemias due to membranopathies or due to enzymopathies other than G6PD deficiency, and 2) to examine the novel hypothesis that the activity of the enzymes hexokinase and phosphoglucose isomerase and not that of G6PD control the rate of glucose oxidation through the pentose phosphate shunt.
The specific aims of this project are: 1) to evaluate and interrelate the in vitro measures of RBC antioxidant defense (Heinz body formation, reduced glutathione content and stability, pentose phosphate shunt function) with the adenosine triphosphate, glycolytic intermediate, NADP and NADPH concentrations of the RBC in the various hereditary hemolytic anemias, 2) to correlate these measures of antioxidant defense with in vitro RBC survival, 3) to determine the antioxidant capabilities of normal RBC separated on a continuous density gradient, 4) to determine the ability of the RBC to oxidize alternative hexoses through the pentose phosphate shunt under hypoglycemic conditions, 5) to determine the effects of the glycolytic intermediates which may accumulate in the RBC in various hemolytic anemias on the activity of the pentose phosphate shunt in RBC hemolysates and, if pentose shunt dysfunction is observed, to determine if the metabolic block is at the level of hexokinase, phosphoglucose isomerase, or G6PD. These studies are of potential clinical significance since the only therapeutic modalities available for the treatment of severe, chronic hemolytic anemia are splenectomy and/or blood transfusion, both of which carry a significant risk of morbidity and mortality. If our hypothesis proves to be correct, then the clinial use of antioxidants and/or dietary manipulations may become important new therapeutic modalities for this group of debilitating disorders.
