Molecular factors that are associated with early developmental arrest of intraerythrocytic Plasmodium falciparum

Profiling molecular factors associated with pyknosis and developmental arrest induced by an opioid receptor antagonist and dihydroartemisinin in Plasmodium falciparum

Malaria continues to be a devastating disease, largely caused by Plasmodium falciparum infection. We investigated the effects of opioid and cannabinoid receptor antagonists on the growth of intraerythrocytic P. falciparum. The delta opioid receptor antagonist 7-benzylidenenaltrexone (BNTX) and the cannabinoid receptor antagonists rimonaband and SR144528 caused growth arrest of the parasite. Notably BNTX and the established antimalarial drug dihydroartemisinin induced prominent pyknosis in parasite cells after a short period of incubation. We compared genome-wide transcriptome profiles in P. falciparum with different degrees of pyknosis in response to drug treatment, and identified 11 transcripts potentially associated with the evoking of pyknosis, of which three, including glutathione reductase (PfGR), triose phosphate transporter (PfoTPT), and a conserved Plasmodium membrane protein, showed markedly different gene expression levels in accordance with the degree of pyknosis. Furthermore, the use of specific inhibitors confirmed PfGR but not PfoTPT as a possible factor contributing to the development of pyknosis. A reduction in total glutathione levels was also detected in association with increased pyknosis. These results further our understanding of the mechanisms responsible for P. falciparum development and the antimalarial activity of dihydroartemisinin, and provide useful information for the development of novel antimalarial agents.

Copper Homeostasis for the Developmental Progression of Intraerythrocytic Malarial Parasite

Malaria is one of the world’s most devastating diseases, particularly in the tropics. In humans, Plasmodium falciparum lives mainly within red blood cells, and malaria pathogenesis depends on the red blood cells being infected with the parasite. Non-esterified fatty acids (NEFAs), including cis-9-octadecenoic acid, and phospholipids have been critical for complete parasite growth in serum-free culture, although the efficacy of NEFAs in sustaining the growth of P. falciparum has varied markedly. Hexadecanoic acid and trans-9-octadecenoic acid have arrested development of the parasite, in association with down-regulation of genes encoding copper-binding proteins. Selective removal of Cu⁺ ions has blockaded completely the ring–trophozoite–schizont progression of the parasite. The importance of copper homeostasis for the developmental progression of P. falciparum has been confirmed by inhibition of copper-binding proteins that regulate copper physiology and function by associating with copper ions. These data have provided strong evidence for a link between healthy copper homeostasis and successive developmental progression of P. falciparum. Perturbation of copper homeostasis may be, thus, instrumental in drug and vaccine development for the malaria medication. We review the importance of copper homeostasis in the asexual growth of P. falciparum in relation to NEFAs, copper-binding proteins, apoptosis, mitochondria, and gene expression.

In vitro antiplasmodial activity of cepharanthine

BACKGROUND

New classes of anti-malarial drugs are needed to control the alarming Plasmodium falciparum resistance toward current anti-malarial therapy. The ethnopharmacological approach allows the discovery of original chemical structures from the vegetable biodiversity. Previous studies led to the selection of a bisbenzylisoquinoline, called cepharanthine and isolated from a Cambodian plant: Stephania rotunda. Cepharanthine could exert a mechanism of action different from commonly used drugs. Potential plasmodial targets are reported here.

METHODS

To study the mechanism of action of cepharanthine, a combined approach using phenotypic and transcriptomic techniques was undertaken.

RESULTS

Cepharanthine blocked P. falciparum development in ring stage. On a culture of synchronized ring stage, the comparisons of expression profiles showed that the samples treated with 5 μM of cepharanthine (IC90) were significantly closer to the initial controls than to the final ones. After a two-way ANOVA (p-value < 0.05) on the microarray results, 1,141 probes among 9,722 presented a significant differential expression.A gene ontology analysis showed that the Maurer's clefts seem particularly down-regulated by cepharanthine. The analysis of metabolic pathways showed an impact on cell-cell interactions (cytoadherence and rosetting), glycolysis and isoprenoid pathways. Organellar functions, more particularly constituted by apicoplast and mitochondrion, are targeted too.

CONCLUSION

The blockage at the ring stage by cepharanthine is described for the first time. Transcriptomic approach confirmed that cepharanthine might have a potential innovative antiplasmodial mechanism of action. Thus, cepharanthine might play an ongoing role in the progress on anti-malarial drug discovery efforts.

Perturbation of copper homeostasis is instrumental in early developmental arrest of intraerythrocytic Plasmodium falciparum

Background

Malaria continues to be a devastating disease. The elucidation of factors inducing asexual growth versus arrest of Plasmodium falciparum can provide information about the development of the parasite, and may help in the search for novel malaria medication. Based on information from genome-wide transcriptome profiling of different developmental stages of P. falciparum, we investigated the critical importance of copper homeostasis in the developmental succession of P. falciparum with regard to three aspects of copper function. These were:1) inhibition of copper-binding proteins, 2) copper-ion chelation, and 3) down-regulated expression of genes encoding copper-binding proteins associated with a specific growth-promoting factor.

Results

Inhibition of copper-binding proteins with tetrathiomolybdate (TTM) caused cessation of growth of the parasite. TTM arrested the parasite irreversibly during the trophozoite to schizont stage progression. Target molecules for TTM may be present in P. falciparum. The involvement of copper ions in developmental arrest was also investigated by copper-ion chelating methods, which indicated a critical function of reduced copper ions (Cu¹⁺) in the parasite during the early developmental stage. Copper ions, not only in the parasite but also in host cells, were targets of the chelators. Chelation of Cu¹⁺caused blockage of trophozoite progression from the ring stage. Profound growth arrest was detected in parasites cultured in a chemically defined medium containing hexadecanoic acid alone as a growth-promoting factor. This developmental arrest was associated with down-regulated expression of genes encoding copper-binding proteins. Cis-9-octadecenoic acid completely prevented the down-regulation of gene expression and developmental arrest that were observed with the use of hexadecanoic acid.

Conclusions

The critical importance of copper homeostasis in early developmental stages of P. falciparum was confirmed. Perturbation of copper homeostasis induced profound and early developmental arrest of P. falciparum. These findings should help to elucidate the mechanisms behind the development of P. falciparum, and may be applied in the development of effective antimalarial strategies.