Effects of sevuparin on rosette formation and cytoadherence of Plasmodium falciparum infected erythrocytes.

In severe falciparum malaria cytoadherence of parasitised red blood cells (PRBCs) to vascular endothelium (causing sequestration) and to uninfected red cells (causing rosette formation) contribute to microcirculatory flow obstruction in vital organs. Heparin can reverse the underlying ligand-receptor interactions, but may increase the bleeding risks. As a heparin-derived polysaccharide, sevuparin has been designed to retain anti-adhesive properties, while the antithrombin-binding domains have been eliminated, substantially diminishing its anticoagulant activity. Sevuparin has been evaluated recently in patients with uncomplicated falciparum malaria, and is currently investigated in a clinical trial for sickle cell disease. The effects of sevuparin on rosette formation and cytoadherence of Plasmodium falciparum isolates from Thailand were investigated. Trophozoite stages of P. falciparum-infected RBCs (Pf-iRBCs) were cultured from 49 patients with malaria. Pf-iRBCs were treated with sevuparin at 37°C and assessed in rosetting and in cytoadhesion assays with human dermal microvascular endothelial cells (HDMECs) under static and flow conditions. The proportion of Pf-iRBCs forming rosettes ranged from 6.5% to 26.0% (median = 12.2%). Rosetting was dose dependently disrupted by sevuparin (50% disruption by 250 µg/mL). Overall 57% of P. falciparum isolates bound to HDMECs under static conditions; median (interquartile range) Pf-iRBC binding was 8.5 (3.0-38.0) Pf-iRBCs/1000 HDMECs. Sevuparin in concentrations ≥ 100 µg/mL inhibited cytoadherence. Sevuparin disrupts P. falciparum rosette formation in a dose dependent manner and inhibits cytoadherence to endothelial cells. The data support assessment of sevuparin as an adjunctive treatment to the standard therapy in severe falciparum malaria.

Antimalarial drug susceptibility of Plasmodium vivax in the Republic of Korea.

The antimalarial susceptibility of ring stage (> 80%) Plasmodium vivax from the Republic of Korea, where long incubation-period strains are prevalent, was evaluated using the schizont maturation inhibition technique. During 2005-2007, susceptibility to seven antimalarial drugs was evaluated with 24 fresh isolates. The geometric mean (95% confidence interval) 50% inhibition concentration (IC(50)) were quinine 60 (54-75) ng/mL, chloroquine 39 (22-282) ng/mL, piperaquine 27 (17-58) ng/mL, mefloquine 39 (35-67) ng/mL, pyrimethamine 138 (89-280) ng/mL, artesunate 0.6 (0.5-0.8) ng/mL, and primaquine 122 (98-232) ng/mL. Positive correlations were found between quinine and mefloquine (r = 0.6, P = 0.004), piperaquine and chloroquine (r = 0.6, P = 0.008), and piperaquine and primaquine IC(50) values (r = 0.5, P = 0.01). Compared with P. vivax in Thailand, P. vivax in the Republic of Korea was more sensitive to quinine and mefloquine, but equally sensitive to chloroquine and artesunate.

Platelet-induced autoagglutination of Plasmodium falciparum-infected red blood cells and disease severity in Thailand.

The relationship of the platelet-mediated autoagglutination of Plasmodium falciparum-infected red blood cells (IRBCs) to disease severity was investigated in 182 Thai patients with falciparum malaria; it was evident in 43% of uncomplicated malaria (n=63), 41% of severe malaria (n=104), and 100% of cerebral malaria (n=15; P=.001) isolates. The median (range) number of IRBCs in agglutinates per 1000 IRBCs was significantly higher in cerebral malaria (6 [3-42]) than in severe (0 [0-52]) and uncomplicated (0 [0-24]) malaria (P=.01). In multivariate analyses, high parasitemia and cerebral malaria were associated independently with parasite agglutination.