Haem products reversibly reduce red blood cell deformability

Abstract

In falciparum malaria, but not in septicaemia, the deformability of the entire erythrocyte population is reduced in proportion to disease severity. This is a major determinant of survival as it compromises microcirculatory blood flow through vessels partially obstructed by cytoadherent parasitized erythrocytes. We hypothesized that rigidification is caused by haem products produced by the parasite. Red blood cell deformability (LORCA) was measured in erythrocytes exposed to increasing concentrations of haemin (synthetic haemozoin, the malaria pigment), and haemoglobin. Lipid and protein oxidation was assayed as thiobarbituric reactive substances (TBARS) and sulphhydryl groups respectively. The protective effects of N-acetylcysteine were also assessed. A dose and time-dependent incorporation of haemin into RBC and oxidation a protein SH groups was observed. TBARS production and changes in the fatty acid pattern, as indicators of lipid peroxidation were not observed. Haemin, and to a much lesser extend haemoglobin and B-haematin reduced red cell deformability in a dose dependent manner. These pathophysiological processes were prevented, and also largely reversed, by the therapeutic antioxidant N-acetycysteine. The results suggest that the effect of haemin on the RBC membrane does not result from oxidative damage of membrane lipids but from direct binding or incorporation of haem, affecting the oxidative status of proteins and the reciprocal interactions between the membrane and cytoskeleton proteins. This may provide a novel approach to the treatment of potentially lethal malaria.