Glutathione export from human erythrocytes andPlasmodium falciparummalaria parasites

Abstract

Glutathione export from uninfected human erythrocytes was compared with that from cells infected with the malaria parasite Plasmodium falciparum using two separate methods that distinguish between oxidized (GSSG) and reduced (GSH) glutathione. One involved enzymatic recycling with or without thiol-masking; the other involved rapid derivatization followed by HPLC. Glutathione efflux from uninfected erythrocytes under physiological conditions occurred predominantly as GSH. On exposure of the cells to oxidative challenge, efflux of GSSG exceeded that of GSH. Efflux of both species was blocked by MK571, an inhibitor of mammalian multidrug-resistance proteins. Glutathione efflux from parasitized erythrocytes was substantially greater than that from uninfected erythrocytes. Under physiological conditions, the exported species was GSH, whereas under energy-depleted conditions, GSSG efflux occurred. Glutathione export from parasitized cells was inhibited partially by MK571 and more so by furosemide, an inhibitor of the 'new permeability pathways' induced by the parasite in the host erythrocyte membrane. Efflux from isolated parasites occurred as GSH. On exposure to oxidative challenge, this GSH efflux decreased, but no GSSG export was detected. These results are consistent with the view that the parasite supplies its host erythrocyte with GSH, much of which is exported from the infected cell via parasite-induced pathways.

A disrupted transsulphuration pathway results in accumulation of redox metabolites and induction of gametocytogenesis in malaria

“…Indeed, previous studies have hinted at increase in homocysteine levels in the serum of malaria patients Also, attempts have been made to quantify levels of glutathione in the host RBCs and the spent medium. These studies have relied on conventional methods for measuring these metabolites and there is lack of agreement among different reports about the absolute values and the form of glutathione being effluxed2212223. We, therefore, resorted to the use of mass spectrometry (MS) based quantification of homocysteine (HCy), reduced glutathione (GSH) and oxidized glutathione (GSSG) intracellularly as well as in the spent medium of P. falciparum infected RBC (iRBC).…”

“…The ability to shift the redox homeostasis of the host is shared by many other viruses, bacteria and protozoa. As shown in Table 1, many infections caused by intracellular pathogens result in a 2-4-fold decrease in the GSH: GSSG ratio of the host cell221222324252627282930313233. Importantly, this altered redox state is often utilized by the pathogen to facilitate its pathogenesis and/or transmission.…”

“…Previous studies have stressed on the importance of GSH/GSSG levels as de novo biosynthesis of GSH is critical for parasite survival23. However, the values currently available in the literature are variable2212223. There is a discord in the values reported by different groups and a lack of agreement with regard to the form of glutathione being effluxed.…”

Glutathione-deficient Plasmodium berghei parasites exhibit growth delay and nuclear DNA damage

“…It is possible that P. falciparum is incapable of uptaking sufficient amounts of GSH from the mature RBC to allow parasite survival during the erythrocytic cycle [32, 33]. Furthermore, P. falciparum infected RBC display increased GSH efflux [34], which may result in a decrease in GSH available for parasite uptake. P. berghei prefers to invade young erythrocytes (reticulocytes), which are metabolically different from mature RBC, supporting the hypothesis that host environment have an impact in parasite growth and survival [34, 35].…”

“…Furthermore, P. falciparum infected RBC display increased GSH efflux [34], which may result in a decrease in GSH available for parasite uptake. P. berghei prefers to invade young erythrocytes (reticulocytes), which are metabolically different from mature RBC, supporting the hypothesis that host environment have an impact in parasite growth and survival [34, 35]. Differences between both species should be taken into consideration and the GSH uptake in P. berghei be further evaluated, since the pbggcs-ko parasites have reduced but detectable GSH levels.…”