Artemisinin effectiveness in erythrocytes is reduced by heme and heme-containing proteins

Abstract

Artemisinin loses its antimalarial activity on prolonged exposure to erythrocytes, especially alpha-thalassemic erythrocytes. In this report, we show that the major artemisinin-inactivating factor in cytosol of normal erythrocytes was heat-labile but a heat-stable factor from alpha-thalassemic cells also played a significant role in reducing artemisinin effectiveness, which was shown to be heme released from hemoglobin (Hb). Studies of fractionated lysate from genetically normal erythrocytes revealed that the protein fraction with molecular weight greater than 100 kDa was capable of reducing artemisinin effectiveness more readily than lower molecular weight fraction. Catalase and Hb A, but not selenoprotein glutathione peroxidase, were capable of reducing artemisinin effectiveness. Hemin (ferriprotoporphyrin IX) also reduced artemisinin effectiveness in a concentration- and time-dependent manner. It is concluded that heme and heme-containing proteins in erythrocyte are largely responsible for reducing artemisinin effectiveness and may contribute to resistance of Plasmodium falciparum infecting alpha-thalassemic erythrocytes observed in vitro.

Stability of Peroxide Antimalarials in the Presence of Human Hemoglobin

“…The degradation of artemisinin or Hb reported in previous studies (1,14,21,28,30,38) can most likely be explained by Hb denaturation and subsequent heme release mediated by organic solvents (21), reducing agents (7), or buffers or the use of a higher temperature (11,12,24,34). The stability of peroxide antimalarials with oxyHb is consistent with their antimalarial efficacy in vivo, the absence of toxicity toward healthy erythrocytes, and the notion that free heme or iron is required for peroxide activation and subsequent antimalarial activity.…”

“…These studies suggested reduction of the peroxide bond by the bound heme moiety of Hb, resulting in either decreased artemisinin concentration (1) or potency (28), Hb degradation (21), or alkylation of globin (38) or heme (14,30). Inconsistencies are apparent among these findings and are suggested to result from variations in the Hb oxidation state and conformational stability (21).…”

Stimulatory Effects of Dihydroartemisinin on the Leucocyte Population of Wistar Albino Rats

“…The increases in the total white blood cell count; the percentage neutrophils count and the percentage lymphocyte counts were significant at p<0.01 level of significance which shows that the haemopoesis stimulation effect of DHA was very potent. These effects of dihydroartemisinin on haemopoesis confirm the observation in a previous that the action of artemisinins as antimalarials is linked io their action on intrcellular hemin (Meshnick et al, 1994;Ponmee et al, 2007). Since the white blood cells constitute the disease fighting army of the body, this potent white blood cell population explosion effect of dihydroartemisinin on the blood is a very important aspect of its parasite fighting and elimination strategies as dihydroartemisinin is 90% bound to plasma proteins.…”

Extracellular Heme Enhances the Antimalarial Activity of Artemisinin

“…Pre-incubation of artemisinin with hemin for 6 h decreases the antimalarial activity of artemisinin because of the instability of active intermediates. 29) But in our study, we added hemin and artemisinin into the culture media simultaneously; thus, allowing the short-lived intermediates to act at the parasitic targets. This is relevant to the rapid onset of artemisinin in vivo when the drug is administered and reaches the systemic circulation where it reacts with heme in plasma.…”