Iron, anemia and hepcidin in malaria

Malaria and iron have a complex but important relationship. Plasmodium proliferation requires iron, both during the clinically silent liver stage of growth and in the disease-associated phase of erythrocyte infection. Precisely how the protozoan acquires its iron from its mammalian host remains unclear, but iron chelators can inhibit pathogen growth in vitro and in animal models. In humans, iron deficiency appears to protect against severe malaria, while iron supplementation increases risks of infection and disease. Malaria itself causes profound disturbances in physiological iron distribution and utilization, through mechanisms that include hemolysis, release of heme, dyserythropoiesis, anemia, deposition of iron in macrophages, and inhibition of dietary iron absorption. These effects have significant consequences. Malarial anemia is a major global health problem, especially in children, that remains incompletely understood and is not straightforward to treat. Furthermore, the changes in iron metabolism during a malaria infection may modulate susceptibility to co-infections. The release of heme and accumulation of iron in granulocytes may explain increased vulnerability to non-typhoidal Salmonella during malaria. The redistribution of iron away from hepatocytes and into macrophages may confer host resistance to superinfection, whereby blood-stage parasitemia prevents the development of a second liver-stage Plasmodium infection in the same organism. Key to understanding the pathophysiology of iron metabolism in malaria is the activity of the iron regulatory hormone hepcidin. Hepcidin is upregulated during blood-stage parasitemia and likely mediates much of the iron redistribution that accompanies disease. Understanding the regulation and role of hepcidin may offer new opportunities to combat malaria and formulate better approaches to treat anemia in the developing world

Cord Blood Hepcidin: Cross-Sectional Correlates and Associations with Anemia, Malaria, and Mortality in a Tanzanian Birth Cohort Study.

Hepcidin, the master regulator of bioavailable iron, is a key mediator of anemia and also plays a central role in host defense against infection. We hypothesized that measuring hepcidin levels in cord blood could provide an early indication of interindividual differences in iron regulation with quantifiable implications for anemia, malaria, and mortality-related risk. Hepcidin concentrations were measured in cord plasma from a birth cohort (N = 710), which was followed for up to 4 years in a region of perennial malaria transmission in Muheza, Tanzania (2002-2006). At the time of delivery, cord hepcidin levels were correlated with inflammatory mediators, iron markers, and maternal health conditions. Hepcidin levels were 30% (95% confidence interval [CI]: 12%, 44%) lower in children born to anemic mothers and 48% (95% CI: 11%, 97%) higher in placental malaria-exposed children. Relative to children in the lowest third, children in the highest third of cord hepcidin had on average 2.5 g/L (95% CI: 0.1, 4.8) lower hemoglobin levels over the duration of follow-up, increased risk of anemia and severe anemia (adjusted hazard ratio [HR] [95% CI]: 1.18 [1.03, 1.36] and 1.34 [1.08, 1.66], respectively), and decreased risk of malaria and all-cause mortality (adjusted HR [95% CI]: 0.78 [0.67, 0.91] and 0.34 [0.14, 0.84], respectively). Although longitudinal measurements of hepcidin and iron stores are required to strengthen causal inference, these results suggest that hepcidin may have utility as a biomarker indicating children's susceptibility to anemia and infection in early life

Profiling the Essential Nature of Lipid Metabolism in Asexual Blood and Gametocyte Stages of Plasmodium falciparum

SummaryDuring its life cycle, Plasmodium falciparum undergoes rapid proliferation fueled by de novo synthesis and acquisition of host cell lipids. Consistent with this essential role, Plasmodium lipid synthesis enzymes are emerging as potential drug targets. To explore their broader potential for therapeutic interventions, we assayed the global lipid landscape during P. falciparum sexual and asexual blood stage (ABS) development. Using liquid chromatography-mass spectrometry, we analyzed 304 lipids constituting 24 classes in ABS parasites, infected red blood cell (RBC)-derived microvesicles, gametocytes, and uninfected RBCs. Ten lipid classes were previously uncharacterized in P. falciparum, and 70%–75% of the lipid classes exhibited changes in abundance during ABS and gametocyte development. Utilizing compounds that target lipid metabolism, we affirmed the essentiality of major classes, including triacylglycerols. These studies highlight the interplay between host and parasite lipid metabolism and provide a comprehensive analysis of P. falciparum lipids with candidate pathways for drug discovery efforts

Inhibition of resistance-refractory P. falciparum kinase PKG delivers prophylactic, blood stage, and transmission-blocking antiplasmodial activity

The search for antimalarial chemotypes with modes of action unrelated to existing drugs has intensified with the recent failure of first-line therapies across Southeast Asia. Here, we show that the trisubstituted imidazole MMV030084 potently inhibits hepatocyte invasion by Plasmodium sporozoites, merozoite egress from asexual blood stage schizonts, and male gamete exflagellation. Metabolomic, phosphoproteomic, and chemoproteomic studies, validated with conditional knockdown parasites, molecular docking, and recombinant kinase assays, identified cGMP-dependent protein kinase (PKG) as the primary target of MMV030084. PKG is known to play essential roles in Plasmodium invasion of and egress from host cells, matching MMV030084's activity profile. Resistance selections and gene editing identified tyrosine kinase-like protein 3 as a low-level resistance mediator for PKG inhibitors, while PKG itself never mutated under pressure. These studies highlight PKG as a resistance-refractory antimalarial target throughout the Plasmodium life cycle and promote MMV030084 as a promising Plasmodium PKG-targeting chemotype

Clinical and biological heterogeneity of multisystem inflammatory syndrome in adults following SARS-CoV-2 infection: a case series

ImportanceMultisystem inflammatory syndrome in adults (MIS-A) is a poorly understood complication of SARS-CoV-2 infection with significant morbidity and mortality.ObjectiveIdentify clinical, immunological, and histopathologic features of MIS-A to improve understanding of the pathophysiology and approach to treatment.DesignThree cases of MIS-A following SARS-CoV-2 infection were clinically identified between October 2021 – March 2022 using the U.S. Centers for Disease Control and Prevention diagnostic criteria. Clinical, laboratory, imaging, and tissue data were assessed.FindingsAll three patients developed acute onset cardiogenic shock and demonstrated elevated inflammatory biomarkers at the time of hospital admission that resolved over time. One case co-occurred with new onset Type 1 diabetes and sepsis. Retrospective analysis of myocardial tissue from one case identified SARS-CoV-2 RNA. All three patients fully recovered with standard of care interventions plus immunomodulatory therapy that included intravenous immunoglobulin, corticosteroids, and in two cases, anakinra.ConclusionMIS-A is a severe post-acute sequela of COVID-19 characterized by systemic elevation of inflammatory biomarkers. In this series of three cases, we find that although clinical courses and co-existent diseases vary, even severe presentations have potential for full recovery with prompt recognition and treatment. In addition to cardiogenic shock, glucose intolerance, unmasking of autoimmune disease, and sepsis can be features of MIS-A, and SARS-CoV-2 myocarditis can lead to a similar clinical syndrome

Hepcidin regulation in Malaria

Epidemiological observations have linked increased host iron with malaria susceptibility. At the same time, blood-stage malaria infection is associated with potentially life-threatening anemia. To improve our understanding of these relationships, this work presents an examination of the mechanisms controlling the upregulation of the hormone hepcidin, the master regulator of iron metabolism, in malaria infection. Chapter 2 presents data from a mouse model of malaria infection which indicate that hepcidin upregulation in malaria infection is associated with increased activity of the sons of mothers against decapentaplegic (Smad) signaling pathway. Although the canonical Smad pathway activators, bone morphogenetic proteins (Bmp) are not increased at the message level following infection, activin B, which has been recently shown to increase hepcidin through the Smad signaling pathway in conditions of inflammation and infection, is upregulated in the livers of malaria-infected mice. Chapter 3 shows that both activin B and the closely related protein activin A upregulate hepcidin in vitro and in vivo. Chapter 3 also explores the effects of the activin-binding protein follistatin in both systems and in the same malaria-infected mouse model as presented in Chapter 2. The work presented in Chapter 4 extends these studies to human infections by demonstrating that activin A protein co-increases with hepcidin in human serum during malaria infection. Taken together, these findings are consistent with a novel role for activin proteins in controlling hepcidin upregulation in the context of malaria infection. This work may form a basis for the development of novel therapeutics that speed recovery from malarial anemia by inhibiting activins’ actions. Chapter 5 examines the role of infected red blood cell-derived microparticles in the initial recognition of a P. falciparum malaria infection, and subsequent hepcidin upregulation. Microparticles stimulate production of cytokines from peripheral blood mononuclear cells (PBMC), which also upregulate activin A message in response to both microparticles and whole infected red blood cells. These data are consistent with a model in which malaria-derived stimuli such as microparticles trigger the systemic release of activin proteins, which then act on the liver to upregulate hepcidin. Evidence has shown that cytokine levels at birth are related to malaria risk. In Chapter 6, hepcidin is measured in cord blood samples from participants in a large-scale clinical study in a malaria-endemic area, and shown to be elevated in cord blood from neonates with a clinical history of placental malaria. Cord blood hepcidin is also compared to birth levels of iron markers and other cytokines, and future clinical outcomes. Finally, the contributions of DNA methylation levels to cord hepcidin and cytokine levels are assessed by comparison of CpG methylation, at sites in genes encoding hepcidin and cytokines, to the serum concentrations of the genes’ protein products. Several intriguing associations are noted which indicate a possible novel role for DNA methylation in the determination of birth cytokine and hepcidin levels. Chapter 7 synthesizes the data presented in this thesis, interprets the possible significance of the major findings, and offers suggestions for future work.</p

Hepcidin Regulation in Malaria

Epidemiological observations have linked increased host iron with malaria susceptibility. At the same time, blood-stage malaria infection is associated with potentially life-threatening anemia. To improve our understanding of these relationships, this work presents an examination of the mechanisms controlling the upregulation of the hormone hepcidin, the master regulator of iron metabolism, in malaria infection. Chapter 2 presents data from a mouse model of malaria infection which indicate that hepcidin upregulation in malaria infection is associated with increased activity of the sons of mothers against decapentaplegic (Smad) signaling pathway. Although the canonical Smad pathway activators, bone morphogenetic proteins (Bmp) are not increased at the message level following infection, activin B, which has been recently shown to increase hepcidin through the Smad signaling pathway in conditions of inflammation and infection, is upregulated in the livers of malaria-infected mice. Chapter 3 shows that both activin B and the closely related protein activin A upregulate hepcidin in vitro and in vivo. Chapter 3 also explores the effects of the activin-binding protein follistatin in both systems and in the same malaria-infected mouse model as presented in Chapter 2. The work presented in Chapter 4 extends these studies to human infections by demonstrating that activin A protein co-increases with hepcidin in human serum during malaria infection. Taken together, these findings are consistent with a novel role for activin proteins in controlling hepcidin upregulation in the context of malaria infection. This work may form a basis for the development of novel therapeutics that speed recovery from malarial anemia by inhibiting activins’ actions. Chapter 5 examines the role of infected red blood cell-derived microparticles in the initial recognition of a P. falciparum malaria infection, and subsequent hepcidin upregulation. Microparticles stimulate production of cytokines from peripheral blood mononuclear cells (PBMC), which also upregulate activin A message in response to both microparticles and whole infected red blood cells. These data are consistent with a model in which malaria-derived stimuli such as microparticles trigger the systemic release of activin proteins, which then act on the liver to upregulate hepcidin. Evidence has shown that cytokine levels at birth are related to malaria risk. In Chapter 6, hepcidin is measured in cord blood samples from participants in a large-scale clinical study in a malaria-endemic area, and shown to be elevated in cord blood from neonates with a clinical history of placental malaria. Cord blood hepcidin is also compared to birth levels of iron markers and other cytokines, and future clinical outcomes. Finally, the contributions of DNA methylation levels to cord hepcidin and cytokine levels are assessed by comparison of CpG methylation, at sites in genes encoding hepcidin and cytokines, to the serum concentrations of the genes’ protein products. Several intriguing associations are noted which indicate a possible novel role for DNA methylation in the determination of birth cytokine and hepcidin levels. Chapter 7 synthesizes the data presented in this thesis, interprets the possible significance of the major findings, and offers suggestions for future work.This thesis is not currently available on ORA