Evidencing the Role of Erythrocytic Apoptosis in Malarial Anemia

Infectious and obstetric determinants of anemia among pregnant women in Southwest Ethiopia

Background

Anaemia, characterized by low red blood cell or haemoglobin levels, impairs oxygen transport in the body and poses a major global public health issue, particularly affecting pregnant women and children. This study focuses on identifying the factors contributing to anaemia among pregnant women receiving antenatal care (ANC) at Mizan-Tepi University Teaching Hospital (MTUTH) in southwest Ethiopia.

Methods

A hospital-based unmatched case-control study was conducted from July 1 to August 30, 2022, involving 370 pregnant women (90 with anaemia and 280 without). Data collection included questionnaires, laboratory tests (Hgb and stool examination), and anthropometric measurements. SPSS version 21 was used for data analysis, with binary logistic regression identifying factors associated with anaemia. The significance level was set at a p-value <0.05.

Results

The study achieved a 100% response rate for both cases and controls. Factors identified as determinants of anaemia among pregnant women included malaria infection (AOR = 7.83, 95% CI: 3.89-15.8), hookworm infection (AOR = 2.73, 95% CI: 1.39-5.34), short birth interval (AOR = 7.11, 95% CI: 3.59-14.2), and history of unsafe abortion (AOR = 5.40, 95% CI: 2.46-11.8).

Conclusion

This study found that malaria infection, hookworm infection, birth interval <33 months, and a history of unsafe abortion are factors contributing to anaemia in pregnant women. Strategies such as distributing insecticide-treated bed nets (ITNs) to combat malaria, improving sanitation, anthelmintic drugs, promoting family planning to prevent unwanted pregnancies and unsafe abortions, and providing preconception care can help reduce the incidence of anaemia.

Association of apoptosis-related variants to malaria infection and parasite density in individuals from the Brazilian Amazon

BACKGROUND

In malaria infection, apoptosis acts as an important immunomodulatory mechanism that leads to the elimination of parasitized cells, thus reducing the parasite density and controlling immune cell populations. Here, it was investigated the association of INDEL variants in apoptotic genes-rs10562972 (FAS), rs4197 (FADD), rs3834129 and rs59308963 (CASP8), rs61079693 (CASP9), rs4647655 (CASP3), rs11269260 (BCL-2), and rs17880560 (TP53)-and the influence of genetic ancestry with susceptibility to malaria and parasite density in an admixed population from the Brazilian Amazon.

METHODS

Total DNA was extracted from 126 malaria patients and 101 uninfected individuals for investigation of genetic ancestries and genotypic distribution of apoptosis-related variants by Multiplex PCR. Association analyses consisted of multivariate logistic regressions, considering the following comparisons: (i) DEL/DEL genotype vs. INS/DEL + INS/INS; and (ii) INS/INS vs. INS/DEL + DEL/DEL.

RESULTS

Individuals infected by Plasmodium falciparum had significantly higher African ancestry proportions in comparison to uninfected controls, Plasmodium vivax, and mixed infections. The INS/INS genotype of rs3834129 (CASP8) seemed to increase the risk for P. falciparum infection (P = 0.038; OR = 1.867; 95% CI 0.736-3.725), while the DEL/DEL genotype presented a significant protective effect against infection by P. falciparum (P = 0.049; OR = 0.446; 95% CI 0.185-0.944) and mixed infection (P = 0.026; OR = 0.545; 95% CI 0.281-0.996), and was associated with lower parasite density in P. falciparum malaria (P = 0.009; OR = 0.383; 95% CI 0.113-1.295). Additionally, the INS/INS genotype of rs10562972 (FAS) was more frequent among individuals infected with P. vivax compared to P. falciparum (P = 0.036; OR = 2.493; 95% CI 1.104-4.551), and the DEL/DEL genotype of rs17880560 (TP53) was significantly more present in patients with mono-infection by P. vivax than in individuals with mixed infection (P = 0.029; OR = 0.667; 95% CI 0.211-1.669).

CONCLUSIONS

In conclusion, variants in apoptosis genes are associated with malaria susceptibility and parasite density, indicating the role of apoptosis-related genetic profiles in immune responses against malaria infection.

Plasmodium falciparum infection of human erythroblasts induces transcriptional changes associated with dyserythropoiesis

During development down the erythroid lineage, hematopoietic stem cells undergo dramatic changes to cellular morphology and function in response to a complex and tightly regulated program of gene expression. In malaria infection, Plasmodium spp parasites accumulate in the bone marrow parenchyma, and emerging evidence suggests erythroblastic islands are a protective site for parasite development into gametocytes. Although it has been observed that Plasmodium falciparum infection in late-stage erythroblasts can delay terminal erythroid differentiation and enucleation, the mechanism(s) underlying this phenomenon are unknown. Here, we apply RNA sequencing after fluorescence-activated cell sorting of infected erythroblasts to identify transcriptional responses to direct and indirect interaction with P falciparum. Four developmental stages of erythroid cells were analyzed: proerythroblast, basophilic erythroblast, polychromatic erythroblast, and orthochromatic erythroblast. We found extensive transcriptional changes in infected erythroblasts compared with that in uninfected cells in the same culture, including dysregulation of genes involved in erythroid proliferation and developmental processes. Although some indicators of cellular oxidative and proteotoxic stress were common across all stages of erythropoiesis, many responses were specific to cellular processes associated with developmental stage. Together, our results evidence multiple possible avenues by which parasite infection can induce dyserythropoiesis at specific points along the erythroid continuum, advancing our understanding of the molecular determinants of malaria anemia.

Plasmodium falciparum infection of human erythroblasts induces transcriptional changes associated with dyserythropoiesis

During development down the erythroid lineage, hematopoietic stem cells undergo dramatic changes to cellular morphology and function in response to a complex and tightly regulated program of gene expression. In malaria infection, Plasmodium spp . parasites accumulate in the bone marrow parenchyma, and emerging evidence suggests erythroblastic islands are a protective site for parasite development into gametocytes. While it has been observed that Plasmodium falciparum infection of late-stage erythroblasts can delay terminal erythroid differentiation and enucleation, the mechanism(s) underlying this phenomenon are unknown. Here, we apply RNA-seq after fluorescence-activated cell sorting (FACS) of infected erythroblasts to identify transcriptional responses to direct and indirect interaction with Plasmodium falciparum . Four developmental stages of erythroid cells were analyzed: proerythroblast, basophilic erythroblast, polychromatic erythroblast, and orthochromatic erythroblast. We found extensive transcriptional changes in infected erythroblasts compared to uninfected cells in the same culture, including dysregulation of genes involved in erythroid proliferation and developmental processes. Whereas some indicators of cellular oxidative and proteotoxic stress were common across all stages of erythropoiesis, many responses were specific to cellular processes associated with developmental stage. Together, our results evidence multiple possible avenues by which parasite infection can induce dyserythropoiesis at specific points along the erythroid continuum, advancing our understanding of the molecular determinants of malaria anemia.

Key Points

Erythroblasts at different stages of differentiation have distinct responses to infection by Plasmodium falciparum . P. falciparum infection of erythroblasts alters expression of genes related to oxidative and proteotoxic stress and erythroid development.

Eryptosis as a New Insight in Malaria Pathogenesis

Eryptosis is a programmed cell death-like process that occurs in red blood cells. Although the red blood cells are anucleated, there are similarities between eryptosis and apoptosis, such as increased calcium efflux, calpain activation, phosphatidylserine exposure, cell blebbing and cell shrinkage. Eryptosis occurs physiologically in red blood cells, as a consequence of the natural senescence process of these cells, but it can also be stimulated in pathological situations such as metabolic syndromes, uremic syndromes, polycythemia vera, anemias such as sickle cell anemia and thalassemia, and infectious processes including Plasmodium infection. Infection-induced eryptosis is believed to contribute to damage caused by Plasmodium, but it’s still a topic of debate in the literature. In this review, we provided an overview of eryptosis mechanisms and its possible pathogenic role in malaria.

High Prevalence of Asymptomatic Malarial Anemia and Association with Early Conversion from Asymptomatic to Symptomatic Infection in a Plasmodium falciparum Hyperendemic Setting in Cameroon

Asymptomatic malarial parasitemia is highly prevalent in Plasmodium falciparum endemic areas and often associated with increased prevalence of mild to moderate anemia. The aim of this study was to assess the prevalence of anemia during asymptomatic malaria parasitemia and its interplay with persistent infection in highly exposed individuals. A household-based longitudinal survey was undertaken in a malaria hyperendemic area in Cameroon using multiplex nested polymerase chain reaction to detect plasmodial infections. Residents with P. falciparum asymptomatic parasitemia were monitored over a 3-week period with the aid of structured questionnaires and weekly measurements of axillary temperatures. Of the 353 individuals included (median age: 26 years, range 2-86 years, male/female sex ratio 0.9), 328 (92.9%) were positive for malaria parasitemia of whom 266 (81.1%) were asymptomatic carriers. The prevalence of anemia in the study population was 38.6%, of which 69.2% were asymptomatic. Multivariate analyses identified high parasitemia (> 327 parasites/µL) and female gender as associated risk factors of asymptomatic malarial anemia in the population. Furthermore, risk analyses revealed female gender and anemia at the time of enrolment as key predictors of early development of febrile illness (< 3 weeks post enrolment) among the asymptomatic individuals. Together, the data reveal an extremely high prevalence of asymptomatic malaria parasitemia and anemia in the study area, unveiling for the first time the association of asymptomatic malarial anemia with early clinical conversion from asymptomatic to symptomatic infection. Furthermore, these findings underscore the negative impact of asymptomatic malaria parasitemia on individual health, necessitating the development of appropriate control and preventive measures.

The Multiple Facets of Iron Recycling

The production of around 2.5 million red blood cells (RBCs) per second in erythropoiesis is one of the most intense activities in the body. It continuously consumes large amounts of iron, approximately 80% of which is recycled from aged erythrocytes. Therefore, similar to the “making”, the “breaking” of red blood cells is also very rapid and represents one of the key processes in mammalian physiology. Under steady-state conditions, this important task is accomplished by specialized macrophages, mostly liver Kupffer cells (KCs) and splenic red pulp macrophages (RPMs). It relies to a large extent on the engulfment of red blood cells via so-called erythrophagocytosis. Surprisingly, we still understand little about the mechanistic details of the removal and processing of red blood cells by these specialized macrophages. We have only started to uncover the signaling pathways that imprint their identity, control their functions and enable their plasticity. Recent findings also identify other myeloid cell types capable of red blood cell removal and establish reciprocal cross-talk between the intensity of erythrophagocytosis and other cellular activities. Here, we aimed to review the multiple and emerging facets of iron recycling to illustrate how this exciting field of study is currently expanding.

Phenotypic differences between highlanders and lowlanders in Papua New Guinea

OBJECTIVES

Altitude is one of the most demanding environmental pressures for human populations. Highlanders from Asia, America and Africa have been shown to exhibit different biological adaptations, but Oceanian populations remain understudied [Woolcock et al., 1972; Cotes et al., 1974; Senn et al., 2010]. We tested the hypothesis that highlanders phenotypically differ from lowlanders in Papua New Guinea, as a result of inhabiting the highest mountains in Oceania for at least 20,000 years.

MATERIALS AND METHODS

We collected data for 13 different phenotypes related to altitude for 162 Papua New Guineans living at high altitude (Mont Wilhelm, 2,300-2,700 m above sea level (a.s.l.) and low altitude (Daru, <100m a.s.l.). Multilinear regressions were performed to detect differences between highlanders and lowlanders for phenotypic measurements related to body proportions, pulmonary function, and the circulatory system.

RESULTS

Six phenotypes were significantly different between Papua New Guinean highlanders and lowlanders. Highlanders show shorter height (p-value = 0.001), smaller waist circumference (p-value = 0.002), larger Forced Vital Capacity (FVC) (p-value = 0.008), larger maximal (p-value = 3.20e -4) and minimal chest depth (p-value = 2.37e -5) and higher haemoglobin concentration (p-value = 3.36e -4).

DISCUSSION

Our study reports specific phenotypes in Papua New Guinean highlanders potentially related to altitude adaptation. Similar to other human groups adapted to high altitude, the evolutionary history of Papua New Guineans appears to have also followed an adaptive biological strategy for altitude.

Apoptotic mimicry as a strategy for the establishment of parasitic infections: parasite- and host-derived phosphatidylserine as key molecule

The establishment of parasitic infection is dependent on the development of efficient strategies to evade the host defense mechanisms. Phosphatidylserine (PS) molecules are pivotal for apoptotic cell recognition and clearance by professional phagocytes. Moreover, PS receptors are able to trigger anti-inflammatory and immunosuppressive responses by phagocytes, either by coupled enzymes or through the induction of regulatory cytokine secretion. These PS-dependent events are exploited by parasites in a mechanism called apoptotic mimicry. Generally, apoptotic mimicry refers to the effects of PS recognition for the initiation and maintenance of pathogenic infections. However, in this context, PS molecules can be recognized on the surface of the infectious agent or in the surface of apoptotic host debris, leading to the respective denomination of classical and non-classical apoptotic mimicry. In this review, we discuss the role of PS in the pathogenesis of several human infections caused by protozoan parasites.

Eryptosis of non-parasitized erythrocytes is related to anemia in Plasmodium berghei low parasitema malaria of Wistar rats

It is known that premature elimination of non-parasitized RBCs (nRBCs) plays an important role in the pathogenesis of malarial anemia, in which suicidal death process (eryptosis) of nRBCs has been suggested to be involved. To check this possibility, we investigate eryptosis during infection of P. berghei ANKA in Wistar rats, a malaria experimental model that, similar to human malaria, the infection courses with low parasitemia and acute anemia. As expected, P. berghei ANKA infection was marked by low parasite burdens that reached a mean peak of 3% between days six and nine post-infection and solved spontaneously. A significant reduction of the hemoglobin levels (~ 30%) was also observed on days subsequent to the peak of parasitemia, persisting until day 16 post-infection. In eryptosis assays, it was observed a significant increase in the levels of PS-exposing nRBC, which coincided with the reduction of hemoglobin levels and was positively related to anemia. In addition to PS externalization, eryptosis of nRBC induced by P. berghei infection was characterized by cytoplasm calcium influx, but not caspases activity. These results confirm our previous studies evidencing a pro-eryptotic effect of malaria infection on nRBCs and show that a caspase-independent eryptotic process is implicated in anemia induced by P. berghei ANKA infection in Wistar rats.

Manipulating Eryptosis of Human Red Blood Cells: A Novel Antimalarial Strategy?

Malaria is a major global health burden, affecting over 200 million people worldwide. Resistance against all currently available antimalarial drugs is a growing threat, and represents a major and long-standing obstacle to malaria eradication. Like many intracellular pathogens, Plasmodium parasites manipulate host cell signaling pathways, in particular programmed cell death pathways. Interference with apoptotic pathways by malaria parasites is documented in the mosquito and human liver stages of infection, but little is known about this phenomenon in the erythrocytic stages. Although mature erythrocytes have lost all organelles, they display a form of programmed cell death termed eryptosis. Numerous features of eryptosis resemble those of nucleated cell apoptosis, including surface exposure of phosphatidylserine, cell shrinkage and membrane ruffling. Upon invasion, Plasmodium parasites induce significant stress to the host erythrocyte, while delaying the onset of eryptosis. Many eryptotic inducers appear to have a beneficial effect on the course of malaria infection in murine models, but major gaps remain in our understanding of the underlying molecular mechanisms. All currently available antimalarial drugs have parasite-encoded targets, which facilitates the emergence of resistance through selection of mutations that prevent drug-target binding. Identifying host cell factors that play a key role in parasite survival will provide new perspectives for host-directed anti-malarial chemotherapy. This review focuses on the interrelationship between Plasmodium falciparum and the eryptosis of its host erythrocyte. We summarize the current knowledge in this area, highlight the different schools of thoughts and existing gaps in knowledge, and discuss future perspectives for host-directed therapies in the context of antimalarial drug discovery.

Microfluidic analysis of red blood cell deformability as a means to assess hemin-induced oxidative stress resulting from Plasmodium falciparum intraerythrocytic parasitism

Hemolytic anemia is one of the hallmarks of malaria and leads to an increase in oxidized heme (hemin) within the plasma of infected individuals. While scavenger proteins sequester much of the circulating heme, it has been hypothesized that extracellular heme may play a central role in malaria pathogenesis. We have previously developed the multiplex fluidic plunger (MFP) device for the measurement of red blood cell (RBC) deformability. Here, we demonstrate that the measurement of changes in RBC deformability is a sensitive method for inferring heme-induced oxidative stress. We further show that extracellular hemin concentration correlates closely with changes in RBC deformability and we confirm that this biophysical change correlates with other indicators of cell stress. Finally, we show that reduced erythrocyte deformability corresponds with both erythrophagocytosis and RBC osmotic fragility. The MFP microfluidic device presents a simple and potentially inexpensive alternative to existing methods for measuring hemolytic cell stress that could ultimately be used to perform clinical assessment of disease progression in severe malaria.

Insights into the Cytoadherence Phenomenon of Plasmodium vivax: The Putative Role of Phosphatidylserine

Plasmodium vivax is the most geographically widespread and the dominant human malaria parasite in most countries outside of sub-Saharan Africa and, although it was classically recognized to cause benign infection, severe cases and deaths caused by P. vivax have remarkably been reported. In contrast to Plasmodium falciparum, which well-known ability to bind to endothelium and placental tissue and form rosettes is related to severity of the disease, it has been a dogma that P. vivax is unable to undergo cytoadherent phenomena. However, some studies have demonstrated that red blood cells (RBCs) infected by P. vivax can cytoadhere to host cells, while the molecules participating in this host–parasite interaction are still a matter of speculation. In the present overview, we address the evidences currently supporting the adhesive profile of P. vivax and, additionally, discuss the putative role of phosphatidylserine—a cell membrane phospholipid with cytoadhesive properties that has been detected on the surface of Plasmodium-parasitized RBCs.