Falciparum Malaria: Diagnostic Tools, Therapeutic Advances, and Future Opportunities

By Tabish Qidwai

Falciparum Malaria: Diagnostic Tools, Therapeutic Advances, and Future Opportunities discusses the current state of therapeutic options for malaria, antimalarial drugs and drug targets. The book also covers recent progress in the development of vaccines and other approaches for malaria treatment, prevention and control and explores diagnostic tools and biomarkers. Sections examine potential biomarkers and their applications, molecular diagnostic tools, multi-omic approaches for the characterization of therapeutic action of potential new antimalarials, therapeutic advances in falciparum malaria, antimalarial drugs, targeting parasite apicoplast for antimalarial drug discovery, cellular and adjunctive therapies for malaria treatment, and future opportunities.

With contributions from experts in the field, this book is an ideal resource for academics, researchers, graduates and industry engaged in malaria research, its diagnosis, and treatment.

• Reviews current therapeutic strategies of falciparum malaria
• Covers antimalarial drugs, peptides, vaccines and RNAi approaches against malaria
• Explores antimalarial drug targets in parasites
• Discusses biomarkers and new diagnostic tools

• Language: English
• Publisher: Academic Press
• Release date: Apr 14, 2024
• ISBN: 9780323957830

Book preview

Preface

Tabish Qidwai

I would like to congratulate and express my heartfelt thanks to all the authors for their valuable contribution to the book titled Falciparum Malaria: Diagnostic Tools, Therapeutic Advances, and Future Opportunities.

In this book, the authors offer valuable discussions on the current state of therapeutic options for malaria, antimalarial drugs, and drug targets. The book also covers recent progress in the development of approaches for malaria treatment, prevention, and control and explores diagnostic tools and biomarkers. The book could be beneficial for scientists, researchers, and healthcare providers and also the general public to remain updated with the current work happening worldwide.

The book consists of 12 chapters and 2 parts. The first part consists of five chapters which deals diagnosis and biomarkers. The second part consists of seven chapters focusing on the therapeutic advances in falciparum malaria. In this part, both drug and nondrug approaches have been covered.

As an editor, I would like to express my deepest thanks to the editorial team and production staff of the publishers for their technical support and for successful completion of the book in all possible ways. All the authors of the book chapters are acknowledged for their sincere support and contributions. In addition to this, finally, I would like to thank all the well-wishers, and the Almighty, who are behind this achievement.

Part I

Diagnostics and biomarkers in falciparum malaria

Outline

Chapter 1 Molecular mechanism of inflammatory signaling pathway in severe malaria pathogenesis

Chapter 2 Exploration of potential biomarkers and their applications for detection of malaria

Chapter 3 Laboratory diagnosis of malaria: an update

Chapter 4 Molecular diagnostic tools in detection of mixed parasite infections: current scenario and challenges

Chapter 5 Multiomics approaches in the development of therapy against malaria

Chapter 1

Molecular mechanism of inflammatory signaling pathway in severe malaria pathogenesis

Divya Bhatt and Dnyaneshwar Umrao Bawankule,    Bioprospection and Product Development, CSIR-Central Institute of Medicinal and Aromatic Plants, Lucknow, Uttar Pradesh, India

Abstract

Malaria is a severe infectious disease that affects humans and is caused by the parasite called plasmodium. A thorough understanding of the delicate balance that exists between the host’s immune system and the parasite’s virulence mechanism in severe malaria pathogenesis is critical for the development of successful immunological therapies. In a malaria infection, the protective actions of the innate immune system help the host to regulate rapidly increasing parasite burden. To fight the parasite infection, the host releases a large number of proinflammatory cytokines as a means of protecting itself against malaria complications. However, excessive proinflammatory cytokine production during infection may produce serious pathologies. The balance between pro- and antiinflammatory responses that is needed to fight off infections while avoiding pathogenesis may not always be achieved, which can lead to pathogenesis. Therefore, a better understanding of how the host and the parasite interact together is important for the development of effective vaccines and adequate combination therapy for treating severe malaria pathogenesis.

Keywords

Malaria; inflammation; cytokine storm; pathogenesis

1.1 Introduction

Malaria remains one of the serious parasitic infections that has affected the economy and medical stability worldwide. Malaria results from plasmodium parasite infection, transmitted by the female Anopheles mosquito. Plasmodium falciparum (P. falciparum) is the most severe malaria-causing species and often results in damage to vital organs. Other species of plasmodium that infect humans include P. vivax, P. ovale, P. malariae, and P. knowlesi (Martinsen et al., 2008). It is now well understood that the cytokine storm is what produces illness and pathology in infectious diseases (Clark et al., 2008). There is not enough information regarding the protective immunity in malaria disease. However, it has been found that the immune system dysregulation is the governing process during severe malaria complications such as severe malarial anemia (SA) and cerebral malaria (CM). Therefore, a better understanding of immunopathology and mechanism of protective immunity would help in better drug development (Angulo and Fresno, 2002). Malaria results in high inflammatory stage with an acute span of fever, nausea, and headache, generally due to the massive release of merozoites into the blood stream upon erythrocytes rupture, leading to elevated parasitemia and anemia. The parasite products (hemozoin, glycosylphosphatidylinositol (GPI) anchors, parasite DNA, and uric acid) and the molecules released from erythrocytes trigger an inflammatory cascade, upregulating the cytokine levels of IL-6, IL-1β, TNF-α, IFN-γ, and IL-12 (Mavondo et al., 2019). Generally, death by malaria results due to the involvement of systemic, single or multiorgan pathology, which includes hypoglycemia, metabolic acidosis, respiratory distress, renal failure, coagulopathy, pulmonary edema, shock, and cerebral involvement (seizures and coma). These processes are triggered by several mechanisms such as the generation of inflammatory response due to the production of excessive cytokines by the innate immune system, site-specific localization of parasites promoting a huge accumulation of bioactive products that trigger the proinflammatory immune response in the spleen, brain, lungs, kidney, liver, and placenta (Nebl et al., 2005). The host also manifests stage- and species-specific immunity, which is complex due to the requirement of repeated infection for the generation and maintenance of the protective immunity. The blood parasite keeps increasing exponentially if not arrested by the immune system or antimalarial drugs (Stevenson and Riley, 2004). The antiparasite defense of the host and the parasite virulence properties are the primary cause of the severe pathology during malaria. It is critical to have a thorough knowledge of the delicate balance that exists between the two systems. Metabolic, vascular, and erythropoietic balances may further exacerbate infection outcomes. Therefore, a deeper knowledge of the processes guiding the immunological balance toward severe consequences of parasite infection is critical to further reducing morbidity and death.

Hence, based on parasite and host coevolution, we created an overview of current understanding regarding parasite virulence factors that cause immunomodulation, the host’s innate response, and pathogenic processes during severe malaria infection. This overview is also represented in Fig. 1.1.

Figure 1.1 Inflammatory signaling pathway in activated immune cells during malaria pathogenesis. MAPK, mitogen-activated protein kinase; ERK, extracellular-signal-regulated kinase; JNK, c-jun N-terminal kinase; CD36, cluster of differentiation 36; TLR, toll-like receptors; NLRP3, NOD-LRR- and pyrin domain-containing protein 3; ASC, apoptosis-associated speck-like protein containing a CARD; IRAK4, interleukin-1 receptor-associated kinase 4; CGAS, cyclic GMP-AMP synthase; GPI, glycosylphosphatidylinositols; PLCγ2, phospholipase C-gamma-2; IRF7, interferon regulatory factor-7; STING, stimulator of interferon genes; TBK, TANK-binding kinase-1.

1.2 Pathogen-associated molecular patterns during malaria pathogenesis

The liver stage of malaria was found to be completely silent with no symptoms exhibited by the host, while blood-stage malaria is characterized by a fatal illness. The host usually detects parasites immediately to mediate innate immune response, which aims to neutralize infection and build protective adaptive immunity (Miller et al., 2014). When the immune system gets dysregulated, the protective response leads to pathogenesis. Therefore, understanding the mechanism of parasite sensing and the signaling pathway leading to protective immunity is required (Liehl et al., 2015). Hosts usually respond to infection through sensing conserved molecules of the pathogen termed pathogen-associated molecular patterns (PAMPs), such as bacterial LPS, fungal glucans, peptidoglycan, and microbial DNA and RNA (Takeuchi and Akira, 2010). The host detects the PAMPs through pathogen-recognition receptors (PRRs), danger-associated molecular patterns (DAMPs) are endogenous factors released due to infection and exert danger signaling, for example, SP100 family of proteins, HSP70, and degraded hyaluronic acid (Tang et al., 2012). The innate immune system has several PRRs at cellular locations such as the outer surface of the plasma membrane, the outer membrane of the mitochondria, and cytosol to recognize PAMP and DAMP, which upon activation by specific signaling pathways lead to the production of cytokines and chemokines. Some transmembrane PRRs are toll-like receptors (TLRs), CD36, MARCO, and CD204 (Underhill and Ozinsky, 2002). The common pathologies associated with malaria are usually manifested during blood stage. After every 48 hour, the parasite (P. falciparum) rapidly multiplies to produce multiple merozoites from fully developed schizont and release into the blood stream. The merozoites, if alive, invade the erythrocyte while the macrophages and dendritic cells deal with the dead merozoites. Along with the waste products, hemozoin enveloped in the digestive vacuole of the parasite also enters into circulation (Gazzinelli et al., 2014). This process of releasing of parasite and waste keep repeating and so is the release of protective components (e.g., inflammatory cytokines) produced by active innate immune system after every erythrocyte cycle, which causes recurrent episode of chills, fever, headache, and malaise upon systemic TNF-α production and altering glucose homeostasis (Hirako et al., 2018). PAMPs and PRRs, which are linked with the inflammatory signaling in severe malaria pathogenesis, are identified and described in their mechanism of interaction and activation of signaling pathways.

1.2.1 Glycosylphosphatidylinositol

Glycosylphosphatidylinositol (GPI) originated in P. falciparum, the first malarial PAMP and is one of the toxins leading to the severity of malaria due to stimulation of the proinflammatory response of innate immune cells. It has a significant role in parasite invasion in erythrocytes through anchoring the parasite proteins to the plasma membrane. If GPI protein moiety is not bound with the membrane, it is recognized by the innate immune system (Naik et al., 2000). The purified protein of GPI has led to a macrophage-induced proinflammatory effect. In the mouse model, the GPI administration mimics the pathology related to hypoglycemia, pyrexia, TNF-a-induced sepsis, and cachexia. Several other reports proved that GPI triggers immune response with macropage-induced production of IL-1 and TNF-α, endothelial and leukocytes triggered VCAM-1, ICAM-1, and E-selectin and nitric oxide synthase expression by macrophages and endothelial cells through various signaling pathways (Schofield et al., 1996). Also, GPI renders protective immunity by the production of anti-GPI antibodies against parasite-induced illness. It was reported that the GPI-induced inflammatory mediators by macrophages were primarily mediated by heterodimer TLR2-TLR1and not much by TLR4 (Zhu et al., 2009).

1.2.2 Plasmodium DNA

Pichyangkul et al. (2004) first reported that P. falciparum schizonts possess soluble components that instigate dendritic cell–derived cytokine and chemokine production through TLR9-MyD88 signaling cascade. These soluble components were later identified as DNA, TLR-9 primarily targets the CpG motifs in DNA. P. vivax is known to possess higher CpG motifs (~2000) as compared with P. falciparum (~300), which results in comparatively higher fever induction ability of P. vivax (Wu and Chen, 2014). The phagocytic process governs the uptake of merozoites, DNA–protein–hemozoin complex, parasite nuclear material, and DNA-bound immune complexes mediating the DNA entry to immune cell endosomes, which are later fused to lysosome and form phagolysosomes. Phagolysosome has an acidic environment, which releases the DNA to be recognized by TLR9 and activates the signaling pathway (MAPK and NF-kB) followed by cytokine and chemokine production (Parroche et al., 2007). The cytosolic DNA sensors also help in DNA recognition after the contents of the phagolysosome are released into the cytosol. cGAS-sensing dsDNA, a cytosolic sensor, activates STINGTBK1-IRF3 signaling by recognizing the AT-rich motifs of DNA to produce type I IFNs. AIM2 cytosolic DNA sensor results in caspase 1 and inflammasome activation to produce IL-1 and IL-18. However, vigorous production of IL-1 and IL-18 requires both TLR and inflammasome signaling (Gowda and Wu, 2018).

1.2.3 Plasmodium RNA

RNA is recognized by the innate immune system in both the liver and blood stages of malaria. In the liver stage, RNA is recognized by MDA5 in the cytosol, while blood-stage RNA is recognized in the dendritic cell’s phagolysosomes by TLR7 and leads to the production of type I IFN (Spaulding et al., 2016). This production of type 1 IFN is characterized as the earliest response of cytokines in blood-stage malaria. The dendritic and macrophage cells uptake the parasites and their components, leading to RNA entry into the endosome and producing type I IFN response through TLR7 signaling and mediate upregulatory induction of proinflammatory cytokines (IFN-g and IL-12) (Baccarella et al., 2013).

1.2.4 Hemozoin

Hemozoin is an inorganic crystal produced during heme detoxification and released into circulation from the parasite’s food vacuole after the erythrocyte lysis. In the circulation, monocytes and macrophages uptake these hemozoin and initiate production of interleukin-1β (IL-1β) through NOD-like receptor containing pyrin domain 3 (NLRP3) inflammasome complex activation. Hemozoin carries parasitic DNA into the endosome to get recognized by TLR9 (Parroche et al., 2007). After ingestion of infected RBCs, the neutrophils and macrophages meet apoptotic death and release the parasite materials such as DNA, hemozoin, RNA, and other components. This is because of the inert and indigestible nature of hemozoin, which hinders the innate immune response of macrophages by making them immunosuppressive and less functional upon oxidative damage (Olivier et al., 2014). Once the released parasite components get recognized by cytosolic PRRs, several signaling pathways get activated, such as DNA-mediated cGAS STING-TBK1-IRF3 signaling, RNA-induced IRF3 signaling, AIM2 inflammasome signaling, STING signaling, and NLRP12 inflammasome activation (Gowda and Wu, 2018).

1.2.5 Uric acid

Uric acid is the physiological oxidation product of nucleic acid metabolism, released by dying cells in large amounts, and finally forms insoluble crystals of monourate. Uric acid is considered one of the important plasma antioxidants with known antiinflammatory effects in vascular diseases (Orengo et al., 2009). However, unregulated and excess uric acid formation creates pathogenesis, including severe inflammatory conditions. This pathogenesis induced by uric acid is governed by the NLRP3 inflammasome (Braga et al., 2017). Uric acid is thus a danger signal that triggers an inflammatory cascade necessary for the host’s survival.

1.3 Immune evasion phenotypes instigate severe malaria pathogenesis

During the asexual stage of malaria, plasmodium parasites invade the red blood cells and become mature after a 48-hour replication cycle. Parasite-infected red blood cells (pRBCs) are bound to undergo changes in morphological and rheological properties to escape the spleen, an immunological effector organ, and filter out the pRBC’s from the bloodstream. pRBCs acquire a new set of properties, including the expression of multiple cell surface proteins, which could bind to several receptors in cell endothelium to protect it from passing through the spleen (Schofield and Grau, 2005). This leads to severe pathology due to the accumulation of parasites in several target organs that decrease oxygen delivery due to obstruction in blood flow. However, targeting this parasite mechanism of the parasite to evade the spleen could be helpful for the development of novel antimalarial therapies (Cooke et al., 2001).

1.3.1 Endothelial sequestration

During the course of development, pRBC transforms from biconcave shape to round form with increased permeability and rigidity of their membranes, which may lead to blockage of blood flow, making them prone to spleen clearance mechanism (Ishioka et al., 2016). However, pRBCs circumvent clearance by binding to the microvasculature through endothelial cells (Trager et al., 1966). Parasites encode several proteins in their genome, which are then transferred to the surface of the plasma membrane by encompassing parasitophorous vacuole and host cytosol. The polymorphic proteins of P. falciparum are exported to the knob-like structure in the pRBC’s surface to interact with several host receptors to evade host immune response (Cunningham et al., 2010). Some of these proteins are named as P. falciparum erythrocyte membrane protein 1 (PfEMP1), subtelomeric variant open-reading frame (stevor), and repetitive interspersed families of polypeptides (RIFINs), respectively. PfEMP1, stevor, and RIFIN all are involved in mediating adherence and therefore initiate severe malaria development (Ishioka et al., 2016). Among several receptors mediating cytoadherence, thrombospondin (TSP) and CD36 were the first being identified. In this league, E-selectin, ICAM-1, and VCAM-1 were later identified (Chen et al., 2000). The greatly polymorphic molecules PfEMP-1 and RIFIN in P. knowlesi have been named variant surface antigens (VSAs) due to their tendency to change the antigen in chronic infection. The sequestration mechanism is also found in other plasmodium species of humans (P. vivax) and rodents (P. chabaudi) (Gilks et al., 1990). PfEMP-1 encoded by var genes is known to adhere to host cells through several molecules such as CD36, thrombospondin, heparin sulfate, ICAM-1, CR1, and CSA through various domains having cysteine-rich interdomain regions (CIDRs) and Duffy binding–like ligand (DBL) to mediate escape from splenic clearance mechanism. The inhibition of the dendritic cell maturation and their potential to activate T cells was observed upon binding of PfEMP-1 with CD36 (Urban et al., 2001). Also, the PfEMP-1 binding with NK lysis receptors leads to NK cells mediating killing of pRBCs (Wolf et al., 2017). These studies thus suggest that besides escape from splenic clearance, PfEMP-1 also plays a role in suppressing immune function. RIFINs are known to exist as two subfamilies based on their structures: type-A RIFINs have downstream inserts of 25 amino acids in the motif of plasmodium export element (PEXEL) and are present in the membrane of pRBC’s, while Type-B RIFINs do not have PEXEL and present inside the parasite (Fernandez et al., 1999). Type-A RIFINs bound to the antigen of the A blood group and were observed to form larger rosettes than Type-B RIFINs, which bind to the RBCs of O blood group through glycophorin A and form smaller rosettes (Saito et al., 2017). The human proteins leukocyte-associated immunoglobulin-like receptor-1 (LAIR1) and leukocyte immunoglobulin-like receptor-B1 (LILRB1) are generally expressed on the surface of B cells and myeloid T-cell subset and NK cells. LILRB1 was found to play an inhibitory role upon binding to the MHC class I (Trowsdale et al., 2015). RIFIN-LAIR1 binding leads to the downregulation of NK cell response and impedes human B cells–induced IgM production. LAIR1 also interferes cellular activation by binding to the collagenous molecules. This highlights the significant role of RIFIN protein in the immune escape mechanism useful for parasite (Yui and Inoue, 2021). However, further studies are required to investigate the mechanism behind PfEMP-1 interaction with immune cell molecules and their impact on malaria pathogenesis. As there are more than 100 RIFIN genes and only the role of a few have been studied for immune escape strategies, more research is demanded to elucidate the role of existing and discovering novel