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Malaria remains one of the most common human infections worldwide. In endemic areas, malaria is a leading cause of morbidity and mortality and it imposes significant socioeconomic burdens on the people affected. Monocytes are part of the immune system controlling parasite burden and protecting the host against malaria infection. Monocytes play their protective roles against malaria via phagocytosis, cytokine production and antigen presentation. Though monocytes are crucial for clearance of malaria infection, they have also been shown to cause adverse clinical outcomes. In this review, we discuss recent findings regarding the role of monocytes in malaria via mechanisms such as parasite detection and clearance, pro-inflammatory activities, and activation of other immune components. We also highlight the role of different monocyte subsets, and other myeloid cells that are involved in malaria infection. However, more investigations are required in order to explore the exact roles of these monocytes in malaria infection.

Recent advancement in molecular medicine has seen applications of advanced biotechnology tools such as aptamer technology in therapeutics and diagnostics. Aptamer technology has witnessed various approaches including “Click-Chemistry” towards modifying aptamer structure to improve its potentials, but limited studies have reported the influence of such alteration on aptamer's specificity and affinity for their targets. Here, we utilized square wave voltammetry (SWV) electrochemical sensing based on heme to show the effects of cholesterol-triethylene-glycol (COL-TEG) modification of protoporphyrin-IX DNA-aptamers (OKA_24 and OKA_26) on their affinity for heme. Binding was evaluated by immobilizing 5 μM of heme onto cysteamine-glutaraldehyde-coated gold-electrode to construct electrochemical biosensor. Sensing of native/modified-aptamer was achieved by incubating their varying concentrations (9.76 nM - 10 μM) with heme-coated gold-electrode in HKSCM buffer pH 5, for 15 min. Chloroquine (2.5 μM) and non-binding HPIX-aptamer (2.5 μM) served as controls. Ferrocene was the redox solution used for SWV analysis. Protoporphyrin-IX DNA-aptamers specificity for heme was not tarnish by lipid conjugation. Selective binding of 2.5 μM of COL-TEG-OKA_24 and COL-TEG-OKA_26 to heme induced peak-current reduction by 30.68% and 24% respectively. Incubation of OKA_24 and OKA_26 aptamers produced resistance to current flow through the heme-coated gold-electrode by 23.21% and 14.4 8% respectively. Affinity SWV reveals that cholesterol conjugation decreases the affinity of COL-TEG-OKA_24 (KD = 4 7.13 ± 3.767 nM) and COL-TEG-OKA_24 (KD = 84.6 ± 8.7 nM) by 3- fold. There is a need to check the impact of such alteration on inhibition of heme to hemozoin polymerization, a process mediated by Plasmodium falciparum.

Objective: To isolate and characterize RNA aptamers that are specific to human CD36 protein using systematic evolution of ligands by exponential enrichment (SELEX) technology to identify candidates for adjunct therapy to reverse the binding of Plasmodium-infected erythrocytes. Methods: RNA aptamers were isolated using nitrocellulose membrane-based SELEX and binding analysis was screened using an electrophoretic mobility shift assay and enzyme-linked oligonucleotide assay. Results: Thirteen cycles of nitrocellulose membrane-based SELEX yielded three aptamers (RC60, RC25, RC04) exhibiting high binding against CD36 protein as shown on electrophoretic mobility shift assay. The sequence analysis revealed a G-quadruplex sequence within all the isolated aptamers that might contribute to aptamer binding and thermodynamic stability. The specificity assay further showed that RC60 and RC25 were highly specific to CD36. The competitive inhibition assay demonstrated that RC60 and RC25 shared a similar binding epitope recognized by mAb FA6-152, a specific monoclonal antibody against CD36. Conclusions: RC60 and RC25 are promising candidates as anti-cytoadherence for severe malaria adjunct therapy.

Malaria is one of the most devastating infectious diseases that caused millions of clinical cases annually despite decades of prevention efforts. Recent cases of Plasmodium falciparum resistance against the only remaining class of effective antimalarial (artemisinin) in South East Asia may soon pose a significant threat. Hence, the identification of new antimalarial compounds with a novel mode of action is necessary to curb this problem. Protein kinase has been implicated as a valid target for drug development in diseases such as cancer and diabetes in humans. A similar approach is now recognized for the treatment of protozoan-related disease including malaria. Few Plasmodium protein kinases that are not only crucial for their survival but also have unique structural features have been identified as a potential target for drug development. In this review, studies on antimalarial drug development exploiting the size of Plasmodium protein kinase ATP gatekeeper over the past 15 years are mainly discussed. The ATP-binding site of Plasmodium protein kinases such as Pf CDPK1, Pf CDPK4, Pf PKG, Pf PK7, and Pf PI4K showed great potential for selective and multi-target inhibitions owing to their smaller or unique ATP-gatekeeper amino acid subunits compared to that of human protein kinase. Hence it is a feasible solution to identify a new class of active antimalarial agents with a novel mode of action and longer clinical life-span.

Bee bread (BB) has traditionally been used as a dietary supplement to treat liver problems. This study evaluated the therapeutic effects of Heterotrigona itama BB from Malaysia on obesity-induced hepatic lipid metabolism disorder via the regulation of the Keap1/Nrf2 pathway. Male Sprague Dawley rats were fed with either a normal diet or high-fat diet (HFD) for 6 weeks to induce obesity. Following 6 weeks, obese rats were treated either with distilled water (OB group), BB (0.5 g/kg body weight/day) (OB + BB group) or orlistat (10 mg/kg body weight/day) (OB + OR group) concurrent with HFD for another 6 weeks. BB treatment suppressed Keap1 and promoted Nrf2 cytoplasmic and nuclear translocations, leading to a reduction in oxidative stress, and promoted antioxidant enzyme activities in the liver. Furthermore, BB down-regulated lipid synthesis and its regulator levels (SIRT1, AMPK), and up-regulated fatty acid β-oxidation in the liver of obese rats, being consistent with alleviated lipid levels, improved hepatic histopathological changes (steatosis, hepatocellular hypertrophy, inflammation and glycogen expression) and prevented progression to non-alcoholic steatohepatitis. These results showed the therapeutic potentials of H. itama BB against oxidative stress and improved lipid metabolism in the liver of obese rats possibly by targeting the Keap1/Nrf2 pathway, hence proposing its role as a natural supplement capable of treating obesity-induced fatty liver disease.

Oxidative stress contributes to major complications of obesity. This study intended to identify whether orlistat could mitigate myocardial damage in obese animal models. The tested rats were divided into two groups and fed either with normal chow (n = 6 per group) or with a high-fat diet (HFD) for 6 weeks to induce obesity (n = 12 per group). Obese rats were further subjected to treatment either with distilled water (OB group) or orlistat 10 mg/kg/day (OB + OR group). Key indices of oxidative stress, inflammation, and apoptosis were assessed using an immunohistochemical-based technique and real-time PCR. The OB group showed significant increases of oxidative stress markers (TBARs and PCO), with significant decreases of anti-oxidant markers (Nrf2, SOD, CAT, and GPx). Furthermore, mRNA expression of pro-inflammatory markers (TNF-α and NF-κβ) and pro-apoptosis markers (Bax, Caspase-3, Caspase-8, and Caspase-9) were significantly upregulated in the OB group. Obese rats developed pathological changes of myocardial damages as evidenced by the presence of myocardial hypertrophy and inflammatory cells infiltration. Orlistat dampened the progression of myocardial damage in obese rats by ameliorating the oxidative stress, and by inhibiting NF-κβ pathway and caspase-dependent cell apoptosis. Our study proposed that orlistat could potentially mitigate oxidative stress-linked myocardial damage by mitigating inflammation and apoptosis, thus rationalizing its medical usage.

Dibutyl phthalate (DBP) produced by Streptomyces sp. H11809 exerted inhibitory activity against human GSK-3β (Hs GSK-3β) and Plasmodiumfalciparum 3D7 (Pf 3D7) malaria parasites. The current study aimed to determine DBP’s plausible mode of action against Hs GSK-3β and Pf 3D7. Molecular docking analysis indicated that DBP has a higher binding affinity to the substrate-binding site (pocket 2; −6.9 kcal/mol) than the ATP-binding site (pocket 1; −6.1 kcal/mol) of Hs GSK-3β. It was suggested that the esters of DBP play a pivotal role in the inhibition of Hs GSK-3β through the formation of hydrogen bonds with Arg96/Glu97 amino acid residues in pocket 2. Subsequently, an in vitro Hs GSK-3β enzymatic assay revealed that DBP inhibits the activity of Hs GSK-3β via mixed inhibition inhibitory mechanisms, with a moderate IC50 of 2.0 µM. Furthermore, the decrease in Km value with an increasing DBP concentration suggested that DBP favors binding on free Hs GSK-3β over its substrate-bound state. However, the antimalarial mode of action of DBP remains unknown since the generation of a Pf 3D7 DBP-resistant clone was not successful. Thus, the molecular target of DBP might be indispensable for Pf survival. We also identified nocardamine as another active compound from Streptomyces sp. H11809 chloroform extract. It showed potent antimalarial activity with an IC50 of 1.5 μM, which is ~10-fold more potent than DBP, but with no effect on Hs GSK-3β. The addition of ≥12.5 µM ferric ions into the Pf culture reduced nocardamine antimalarial activity by 90% under in vitro settings. Hence, the iron-chelating ability of nocardamine was shown to starve the parasites from their iron source, eventually inhibiting their growth.

Introduction: Plasmodium falciparum (P. falciparum) is a deadly protozoan that is accountable for malaria and chloroquine was the first-line antimalarial drug before its withdrawal and replaced by artemisinin. To date, several studies showed that P. falciparum had regained its sensitivity towards chloroquine after its withdrawal for decades. By understanding the basic principle and mechanism of chloroquine resistance in P. falciparum, at the molecular level, it would be valuable prior to the re-introduction of chloroquine as a first-line anti-malarial drug for malaria treatment. Thus, this study was conducted to determine the chloroquine resistance level of long preserved lab-adapted P. falciparum strain. Methodology: By using 14 years (2006-2020) cryopreserved chloroquine-sensitive (3D7) and chloroquine-resistant (W2) lab-adapted P. falciparum strains, the strains were subjected to continuous culture for three months before in vitro drug susceptibility assay and single nucleotide polymorphisms (SNP) analysis on Pfcrt and Pfmdr-1 gene for both strains. Results: This study shows the IC50 chloroquine of lab-adapted P. falciparum 3D7 and W2 strains were at 32.98 nM and 691.21 nM, respectively and both strains showed 3-fold higher IC50 when compared to their susceptibility before cryopreserved (3D7; 13.84nM and W2; 208.27 nM). The SNPs result showed a consistent amino acid substitution at position 76 (K to T) on PfCRT and 86 (N to Y) in Pfmdr-1 gene which concordance with other studies before preservation. Conclusion: Thus, this study shows that long cryopreserved of lab-adapted P. falciparum increases the chloroquine resistance level but not exhibited any change in susceptibility.

Typhoid fever, also known as typhoid, is a life-threatening bacterial infection that remains a global health concern. The infection is associated with a significant morbidity and mortality rate, resulting in an urgent need for specific and rapid detection tests to aid prevention and management of the disease. The present review aims to assess the specificity and sensitivity of the available literature on the immunodiagnostics of typhoid fever. A literature search was conducted using three databases (PubMed, ProQuest and Scopus) and manual searches through the references of identified full texts to retrieve relevant literature published between 1 January 2011 and 31 December 2020. Of the 577 studies identified in our search, 12 were included in further analysis. Lipopolysaccharides (LPS) and hemolysin E (HlyE) were the most frequently studied antigens. The specimens examined in these studies included serum and saliva. Using blood culture as the gold standard, anti-LPS IgA gave the highest sensitivity of 96% (95% CI: 93–99) and specificity of 96% (95% CI: 93–99) for distinguishing between typhoid cases and healthy controls, whereas the combination of anti-LPS and anti-flagellin total IgGAM gave the highest sensitivity of 93% (95% CI: 86–99) and specificity of 95% (95% CI: 89–100) for distinguishing typhoid cases and other febrile infections. A comparably high sensitivity of 92% (95% CI: 86–98) and specificity of 89% (95% CI: 78–100) were shown in testing based on detection of the combination of anti-LPS (IgA and IgM) and anti-HlyE IgG as well as a slightly lower sensitivity of 91% (95% CI: 74–100) in the case of anti-50kDa IgA. Anti-50kDa IgM had the lowest sensitivity of 36% (95% CI: 6–65) against both healthy and febrile controls. The development of a rapid diagnostic test targeting antibodies against lipopolysaccharides combined with flagellin appeared to be a suitable approach for the rapid detection test of typhoid fever. Saliva is added benefit for rapid typhoid diagnosis since it is less invasive. As a result, further studies could be done to develop additional approaches for adopting such samples.

Melioidosis is a severe disease caused by Burkholderia pseudomallei (B. pseudomallei), a Gram-negative environmental bacterium. It is endemic in Southeast Asia and Northern Australia, but it is underreported in many other countries. The principal routes of entry for B. pseudomallei are skin penetration, inhalation, and ingestion. It mainly affects immunocompromised populations, especially patients with type 2 diabetes mellitus. The laboratory diagnosis of melioidosis is challenging due to its non-specific clinical manifestations, which mimic other severe infections. The culture method is considered an imperfect gold standard for the diagnosis of melioidosis due to its low sensitivity. Antibody detection has low sensitivity and specificity due to the high seropositivity among healthy people in endemic regions. Antigen detection using various proteins has been tested for the rapid determination of B. pseudomallei; however, it presents certain limitations in terms of its sensitivity and specificity. Therefore, this review aims to frame the present knowledge of a potential target known as the Burkholderia invasion protein D (BipD), including future directions for its detection using an aptamer-based sensor (aptasensor).

A feature of mature Plasmodium falciparum parasitized red blood cells is their ability to bind surface molecules of the microvascular endothelium via the parasite-derived surface protein Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1). This ligand is associated with the cytoadherence pathology observed in severe malaria. As pRBC treated with effective anti-malarial drugs are still able to cytoadhere, there is therefore a need to find an adjunct treatment that can inhibit and reverse the adhesion process. One semi-synthetic, sulfated polysaccharide has been identified that is capable of inhibiting and reversing sequestration of pRBC on endothelial cells in vitro under physiological flow conditions. Furthermore, it exhibits low toxicity in the intrinsic (APTT assay) and extrinsic (PT assay) clotting pathways, as well as exhibiting minimal effects on cell (HUVEC) viability (MTT proliferation assay). These findings suggest that carbohydrate-based anti-adhesive candidates may provide potential leads for therapeutics for severe malaria.

Malaria is a life-threatening parasitic infection occurring in the endemic areas, primarily in children under the age of five, pregnant women, and patients with human immunodeficiency virus and acquired immunodeficiency syndrome (HIV)/(AIDS) as well as non-immune individuals. The cytoadherence of infected erythrocytes (IEs) to the host endothelial surface receptor is a known factor that contributes to the increased prevalence of severe malaria cases due to the accumulation of IEs, mainly in the brain and other vital organs. Therefore, further study is needed to discover a new potential anti-adhesive drug to treat severe malaria thus reducing its mortality rate. In this review, we discuss how the aptamer technology could be applied in the development of a new adjunct therapy for current malaria treatment.

Malaria is a disease that causes enormous human morbidity and mortality. One feature of mature Plasmodium falciparum-infected erythrocytes leading to the development of severe malaria is thought to be cytoadherence and blockage of the microvasculature. Therefore, an understanding of mechanisms that mediate parasite adhesion leading to malaria pathology is needed to yield new treatments for malaria. However, to date, cytoadherence-associated pathology is still under debate. Is cytoadherence needed to develop severe malaria? This review will discuss the available information on associations of cytoadherence with the development of severe malaria.