Dientamoeba fragilis associated with microbiome diversity changes in acute gastroenteritis patients.

This study examined the correlation between intestinal protozoans and the bacterial microbiome in faecal samples collected from 463 patients in New Zealand who were diagnosed with gastroenteritis. In comparison to traditional microscopic diagnosis methods, Multiplexed-tandem PCR proved to be more effective in detecting intestinal parasites. Among the identified protozoans, Blastocystis sp. and Dientamoeba fragilis were the most prevalent. Notably, D. fragilis was significantly associated with an increase in the alpha-diversity of host prokaryotic microbes. Although the exact role of Blastocystis sp. and D. fragilis as the primary cause of gastroenteritis remains debatable, our data indicates a substantial correlation between these protozoans and the prokaryote microbiome of their hosts, particularly when compared to other protists or patients with gastroenteritis but no detectable parasitic cause. These findings underscore the significance of comprehending the contributions of intestinal protozoans, specifically D. fragilis, to the development of gastroenteritis and their potential implications for disease management.

Validation of a chloroquine-induced cell death mechanism for clinical use against malaria.

An alternative antimalarial pathway of an 'outdated' drug, chloroquine (CQ), may facilitate its return to the shrinking list of effective antimalarials. Conventionally, CQ is believed to interfere with hemozoin formation at nanomolar concentrations, but resistant parasites are able to efflux this drug from the digestive vacuole (DV). However, we show that the DV membrane of both resistant and sensitive laboratory and field parasites is compromised after exposure to micromolar concentrations of CQ, leading to an extrusion of DV proteases. Furthermore, only a short period of exposure is required to compromise the viability of late-stage parasites. To study the feasibility of this strategy, mice malaria models were used to demonstrate that high doses of CQ also triggered DV permeabilization in vivo and reduced reinvasion efficiency. We suggest that a time-release oral formulation of CQ may sustain elevated blood CQ levels sufficiently to clear even CQ-resistant parasites.

Development of metronidazole-resistant lines of Blastocystis sp.

Metronidazole (MTR) is frequently used for the treatment of Blastocystis infections, but with variable effectiveness, and often with treatment failures as a possible result of drug resistance. We have developed two Blastocystis MTR-resistant (MTR(R)) subtype 4 WR1 lines (WR1-M4 and WR1-M5), with variable susceptibility to a panel of anti-protozoal agents including various 5-nitroimidazoles, nitazoxanide and furazolidone. WR1-M4 and WR1-M5 were developed and assessed over an 18-month period and displayed persistent MTR resistance, being more than 2.5-fold less susceptible to MTR than the parent isolate. The MTR(R) lines grew with a similar g time to WR1, but were morphologically less consistent with a mixture of size. All Blastocystis isolates and the MTR(R) lines were most susceptible to the 5-nitroimidazole drug ronidazole. WR1-M5 was apparently cross-resistant to satranidazole and furazolidone, and WR1-M4 was cross-resistant to nitazoxanide. These MTR(R) lines now provide a valuable tool for the continued assessment of the efficacy and mechanism of action of new and established drugs against a range of Blastocystis sp. subtypes, in order to identify a universally effective drug and to facilitate understanding of the mechanisms of drug action and resistance in Blastocystis.

Drug-induced permeabilization of parasite's digestive vacuole is a key trigger of programmed cell death in Plasmodium falciparum.

Having previously characterized chloroquine (CQ)-induced programmed cell death (PCD) hallmarks in the malaria parasite Plasmodium falciparum and delineating a pathway linking these features, the roles of non-classical mediators were investigated in this paper. It was shown that the later stages of this pathway are Ca(2+)-dependent and transcriptionally regulated. Moreover, it was demonstrated for the first time that micromolar concentrations of CQ partially permeabilized the parasite's digestive vacuole (DV) membrane and that this important upstream event appears to precede mitochondrial dysfunction. This permeabilization of the DV occurred without rupture of the DV membrane and was reminiscent of lysosome-mediated cell death in mammalian cells. As such micromolar concentrations of CQ are found in the patient's plasma after initial CQ loading, this alludes to a clinically relevant antimalarial mechanism of the drug which has yet to be recognized. Furthermore, other 'non-antimalarial' lysosomotropic compounds were also shown to cause DV permeabilization, triggering PCD in both CQ-sensitive and -resistant parasites. These findings present new avenues for antimalarial developments, which induce DV destabilization to kill parasites.

A programmed cell death pathway in the malaria parasite Plasmodium falciparum has general features of mammalian apoptosis but is mediated by clan CA cysteine proteases.

Several recent discoveries of the hallmark features of programmed cell death (PCD) in Plasmodium falciparum have presented the possibility of revealing novel targets for antimalarial therapy. Using a combination of cell-based assays, flow cytometry and fluorescence microscopy, we detected features including mitochondrial dysregulation, activation of cysteine proteases and in situ DNA fragmentation in parasites induced with chloroquine (CQ) and staurosporine (ST). The use of the pan-caspase inhibitor, z-Val-Ala-Asp-fmk (zVAD), and the mitochondria outer membrane permeabilization (MOMP) inhibitor, 4-hydroxy-tamoxifen, enabled the characterization of a novel CQ-induced pathway linking cysteine protease activation to downstream mitochondrial dysregulation, amplified protease activity and DNA fragmentation. The PCD features were observed only at high (µM) concentrations of CQ. The use of a new synthetic coumarin-labeled chloroquine (CM-CQ) showed that these features may be associated with concentration-dependent differences in drug localization. By further using cysteine protease inhibitors z-Asp-Glu-Val-Asp-fmk (zDEVD), z-Phe-Ala-fmk (zFA), z-Phe-Phe-fmk (zFF), z-Leu-Leu-Leu-fmk (zLLL), E64d and CA-074, we were able to implicate clan CA cysteine proteases in CQ-mediated PCD. Finally, CQ induction of two CQ-resistant parasite strains, 7G8 and K1, reveals the existence of PCD features in these parasites, the extent of which was less than 3D7. The use of the chemoreversal agent verapamil implicates the parasite digestive vacuole in mediating CQ-induced PCD.

Effect of plasmodial RESA protein on deformability of human red blood cells harboring Plasmodium falciparum.

During intraerythrocytic development, Plasmodium falciparum exports proteins that interact with the host cell plasma membrane and subplasma membrane-associated spectrin network. Parasite-exported proteins modify mechanical properties of host RBCs, resulting in altered cell circulation. In this work, optical tweezers experiments of cell mechanical properties at normal physiological and febrile temperatures are coupled, for the first time, with targeted gene disruption techniques to measure the effect of a single parasite-exported protein on host RBC deformability. We investigate Pf155/Ring-infected erythrocyte surface antigen (RESA), a parasite protein transported to the host spectrin network, on deformability of ring-stage parasite-harboring human RBCs. Using a set of parental, gene-disrupted, and revertant isogenic clones, we found that RESA plays a major role in reducing deformability of host cells at the early ring stage of parasite development, but not at more advanced stage. We also show that the effect of RESA on deformability is more pronounced at febrile temperature, which ring-stage parasite-harboring RBCs can be exposed to during a malaria attack, than at normal body temperature.