The Providence Mutation (βK82D) in Human Hemoglobin Substantially Reduces βCysteine 93 Oxidation and Oxidative Stress in Endothelial Cells.

The highly toxic oxidative transformation of hemoglobin (Hb) to the ferryl state (HbFe4+ ) is known to occur in both in vitro and in vivo settings. We recently constructed oxidatively stable human Hbs, based on the Hb Providence (βK82D) mutation in sickle cell Hb (βE6V/βK82D) and in a recombinant crosslinked Hb (rHb0.1/βK82D). Using High Resolution Accurate Mass (HRAM) mass spectrometry, we first quantified the degree of irreversible oxidation of βCys93 in these proteins, induced by hydrogen peroxide (H2 O2 ), and compared it to their respective controls (HbA and HbS). Both Hbs containing the βK82D mutation showed considerably less cysteic acid formation, a byproduct of cysteine irreversible oxidation. Next, we performed a novel study aimed at exploring the impact of introducing βK82D containing Hbs on vascular endothelial redox homeostasis and energy metabolism. Incubation of the mutants carrying βK82D with endothelial cells resulted in altered bioenergetic function, by improving basal cellular glycolysis and glycolytic capacity. Treatment of cells with Hb variants containing βK82D resulted in lower heme oxygenase-1 and ferritin expressions, compared to native Hbs. We conclude that the presence of βK82D confers oxidative stability to Hb and adds significant resistance to oxidative toxicity. Therefore, we propose that βK82D is a potential gene-editing target in the treatment of sickle cell disease and in the design of safe and effective oxygen therapeutics.