Pathogenesis of Plasmodium falciparum anaemia: metabolic modifications and signalling in red blood cells exposed to ferric protoporphyrin IX or malaria pigment

The pathogenesis of severe anaemia in children with P.falciparum (P.f.) malaria, has not been clarified, yet. Increased level of oxidation and signs of accelerated senescence have been demonstrated in human red blood cells co-cultured, but not infected by P.f (URBC)(Omodeo et al Blood, 2003). In addition, URBC show a marked decrease in cell deformability -a major determinant of microcirculatory obstruction and increased splenic clearance - and higher sensitivity to haemolysis. We have shown that ferric protoporphyrin IX (FP) and to a lesser extent beta haematin (BH,the synthetic haemozoin) contribute to URBC damage by reducing RBC deformability and inducing lipid and thiol oxidation of proteins leading to membrane destabilization and RBC lysis. This is counteracted by the reducing agent N-acetylcysteine (NAC) (Omodeo et al, Europ.J.Haematol, 2005). Here we report that FP, but not BH induce a dose- and time-dependent tyrosine phosphorylation (P-Tyr) (tyr 8 and 21) of Band 3, due to the oxidation of critical thiol groups of the membrane phosphatase PTP1B. The activity of glyceraldehyde 3 phosphate dehydrogenase and aldolase, two glycolytic enzymes bound to the cytosolic terminus of Band 3, is also increased. Moreover, treatment with FP leads to phosphatidylserine (PS) exposure as confirmed by annexin binding and enhanced sensitivity of RBC to phospholipase A2. FP-induced Band 3 P-Tyr and PS exposure may lead to earlier recognition and uptake of RBC by macrophages contributing to malaria anaemia. The capability of NAC of preventing FP-induced Band 3 phosphorylation is in agreement with the beneficial effects of NAC in clinical practice as adjunctive treatment in severe malaria anaemia and other RBC dysfunctions.