Endogenous inhibitors of death proteins inhibit the progression of hemolytic injury

Abstract

Priming dose of butoxyethanol (BE, 500 mg/kg, po) protects female SD rats against LD90 dose of BE administered 7 d later. Incubation of naïve RBCs with the plasma of LD90 BE treated rats obtained 8 h later (with < 1 mM butoxyacetic acid, BAA, hematotoxic metabolite of BE, t1/2(BAA) = 2.5 h, t1/2(BE) = 0.2 h) led to cytotoxicity. Priming dose causes hemolysis from 3 to 24 h. Why BE-initiated hemolysis continues beyond 4 half lives of BAA is unknown. We hypothesized that death proteins viz. calpain, cytosolic phospholipase A2 (CAP, cPLA2) released from lysed RBCs, upon activation by plasma Ca2+ mediate the progression of BAA-initiated hemolysis. Plasma CAP activity and incubation of naïve RBCs with CAP confirmed the role of CAP in the progression of hemolysis. Rats recovered from the priming dose hemolytic episode, exhibit lower hemolysis after challenge with LD90 BE dose on 7 d. We hypothesized that overexpression of survival factors such as inhibitors of CAP and cPLA2 viz. calpastatin and annexin I (CAST and ANX) in the new RBCs imparts resistance against progression of hemolysis mediated by these death proteins. Presence of higher CAST levels in the RBCs of primed rats till only 1 d suggests that CAST alone may protect the new RBCs initially. Overexpression of ANX in primed and 90% reticulocytosis-induced rat RBCs implicates its role in the resiliency of new RBCs against progression of hemolysis. Moreover, protein patterns in Coomassie stained gels of control and primed rat RBCs imply involvement of other survival factors (ankyrin, band 3, adducin) in the resiliency of new RBCs. The roles of these survival factors in resiliency of new RBCs and cPLA2 in the progression of hemolysis remain to be investigated.