Purine Nucleoside Phosphorylase Inhibition Rebalances Purine Metabolism and Attenuates Organ Damage in Sickle Cell Mice

Red blood cells (RBCs) contain the highest purine nucleoside phosphorylase (PNP) level per cell volume, yet the role of PNP in the pathogenesis of sickle cell disease (SCD) is incompletely understood, highlighting an important gap in our knowledge of the disease. Previously, we reported increased PNP release by RBCs and accelerated purine nucleoside metabolism with increased production of pro-oxidant, pro-inflammatory and vasculotoxic byproducts in children with SCD and animal models of hemolytic injury. Thus, we hypothesized that PNP inhibition would reduce hemolysis and attenuate end-organ damage in SCD. In adult patients with SCD (n = 63), plasma PNP levels were markedly elevated compared to controls (n = 27; p < 0.001) and correlated positively with LDH (r = 0.6032, p < 0.0001) and negatively with haemoglobin (r = -0.4523, p = 0.0002). SCD mice also showed accelerated purine metabolism compared to controls. Treatment with the PNP inhibitor 8-aminoguanosine (8-AG) increased inosine and guanosine and reduced downstream vasculotoxic byproducts hypoxanthine (p = 0.036), xanthine (p = 0.004) and guanine (p = 0.047), indicating efficient PNP inhibition. 8-AG treatment rebalanced the purine metabolome in SCD mice to favour protective over harmful purine metabolites without negatively affecting haematological parameters. This was associated with reduced hemolysis and decreased splenomegaly, hepatomegaly, and hepatic and renal injury. This study suggests that PNP is an important erythrocytic damage-associated molecular pattern molecule involved in the complex pathophysiology of SCD and proposes PNP inhibitors as a new therapeutic option for SCD and other hemolytic diseases.