Malaria 2017: Update on the Clinical Literature and Management

Hesitancy towards R21/Matrix-M malaria vaccine among Ghanaian parents and attitudes towards immunizing non-eligible children: a cross-sectional survey

BACKGROUND

The newly developed malaria vaccine called "R21/Matrix-M malaria vaccine" showed a high safety and efficacy level, and Ghana is the first country to approve this new vaccine. The present study aimed to evaluate the rate of vaccine hesitancy (VH) towards the newly developed malaria vaccine among parents who currently have children who are not eligible for the vaccine but may be eligible in the near future. Additionally, the study aimed to identify the factors that could potentially influence VH.

METHODS

A cross-sectional survey using both online-based questionnaires and face-to-face interviews was conducted in Ghana from June to August 2023. The survey specifically targeted parents of ineligible children for vaccination, including those aged less than 5 months or between 3 and 12 years. The Parent Attitudes about Childhood Vaccination (PACV) scale was used to assess parental VH.

RESULTS

A total of 765 people participated in this study. Their median age was 36.0 years with an interquartile range of 31.0-41.0 years, 67.7% were females, 41.8% completed their tertiary education, 63.3% were married, 81.6% worked in non-healthcare sectors, and 59.7% reported that their monthly income was insufficient. About one-third (34.5%) of the parents were hesitant to give their children the R21/Matrix-M malaria vaccine. The following predictors were associated with VH: working in the healthcare sector (adjusted odds ratio (AOR) = 0.50; 95% confidence interval (CI) 0.30-0.80; p = 0.005), having the other parent working in the healthcare sector (AOR = 0.54; 95% CI 0.30-0.94; p = 0.034), and not taking scheduled routine vaccinations (AOR = 1.90; 95% CI 1.27-2.84; p = 0.002).

CONCLUSIONS

Addressing VH is crucial for optimizing R21/Matrix-M vaccine coverage in Ghana's malaria control strategy. By tackling VH issues, Ghana can effectively safeguard children's health in malaria-prone areas.

Derivatives of Amaryllidaceae Alkaloid Ambelline as Selective Inhibitors of Hepatic Stage of Plasmodium berghei Infection In Vitro

The incidence rate of malaria and the ensuing mortality prompts the development of novel antimalarial drugs. In this work, the activity of twenty-eight Amaryllidaceae alkaloids (1-28) belonging to seven different structural types was assessed, as well as twenty semisynthetic derivatives of the β-crinane alkaloid ambelline (28a-28t) and eleven derivatives of the α-crinane alkaloid haemanthamine (29a-29k) against the hepatic stage of Plasmodium infection. Six of these derivatives (28h, 28m, 28n and 28r-28t) were newly synthesized and structurally identified. The most active compounds, 11-O-(3,5-dimethoxybenzoyl)ambelline (28m) and 11-O-(3,4,5-trimethoxybenzoyl)ambelline (28n), displayed IC₅₀ values in the nanomolar range of 48 and 47 nM, respectively. Strikingly, the derivatives of haemanthamine (29) with analogous substituents did not display any significant activity, even though their structures are quite similar. Interestingly, all active derivatives were strictly selective against the hepatic stage of infection, as they did not demonstrate any activity against the blood stage of Plasmodium infection. As the hepatic stage is a bottleneck of the plasmodial infection, liver-selective compounds can be considered crucial for further development of the malaria prophylactics.

Synthesis and Antiplasmodial Activity of Bisindolylcyclobutenediones

Malaria is one of the most dangerous infectious diseases. Because the causative Plasmodium parasites have developed resistances against virtually all established antimalarial drugs, novel antiplasmodial agents are required. In order to target plasmodial kinases, novel N-unsubstituted bisindolylcyclobutenediones were designed as analogs to the kinase inhibitory bisindolylmaleimides. Molecular docking experiments produced favorable poses of the unsubstituted bisindolylcyclobutenedione in the ATP binding pocket of various plasmodial protein kinases. The synthesis of the title compounds was accomplished by sequential Friedel-Crafts acylation procedures. In vitro screening of the new compounds against transgenic NF54-luc P. falciparum parasites revealed a set of derivatives with submicromolar activity, of which some displayed a reasonable selectivity profile against a human cell line. Although the molecular docking studies suggested the plasmodial protein kinase PfGSK-3 as the putative biological target, the title compounds failed to inhibit the isolated enzyme in vitro. As selective submicromolar antiplasmodial agents, the N-unsubstituted bisindolylcyclobutenediones are promising starting structures in the search for antimalarial drugs, albeit for a rational development, the biological target addressed by these compounds has yet to be identified.

4-Arylthieno[2,3-b]pyridine-2-carboxamides Are a New Class of Antiplasmodial Agents

Malaria causes hundreds of thousands of deaths every year, making it one of the most dangerous infectious diseases worldwide. Because the pathogens have developed resistance against most of the established anti-malarial drugs, new antiplasmodial agents are urgently needed. In analogy to similar antiplasmodial ketones, 4-arylthieno[2,3-b]pyridine-2-carboxamides were synthesized by Thorpe-Ziegler reactions. In contrast to the related ketones, these carboxamides are only weak inhibitors of the plasmodial enzyme PfGSK-3 but the compounds nevertheless show strong antiparasitic activity. The most potent representatives inhibit the pathogens with IC₅₀ values in the two-digit nanomolar range and exhibit high selectivity indices (>100).

Structure-activity relationships in a series of antiplasmodial thieno[2,3-b]pyridines

BACKGROUND

Malaria is one of the most prevalent tropical infectious diseases. Since recently cases of artemisinin resistance were reported, novel anti-malarial drugs are required which differ from artemisinins in structure and biological target. The plasmodial glycogen synthase kinase-3 (PfGSK-3) was suggested as a new anti-malarial drug target. 4-Phenylthieno[2,3-b]pyridines were previously identified as selective PfGSK-3 inhibitors with antiplasmodial activity. The present study aims at identifying a molecular position on this scaffold for the attachment of side chains in order to improve solubility and antiplasmodial activity. Furthermore, the role of axial chirality in the compound class for antiplasmodial activity and PfGSK-3 inhibition was investigated.

METHODS

4-Phenylthieno[2,3-b]pyridines with substituents in 4-position of the phenyl ring were docked into the ATP binding site of PfGSK-3. The compounds were synthesized employing a Thorpe reaction as final step. The enantiomers of one congener were separated by chiral HPLC. All derivatives were tested for inhibition of asexual erythrocytic stages of transgenic NF54-luc Plasmodium falciparum. Selected compounds with promising antiplasmodial activity were further evaluated for inhibition of HEK293 cells as well as inhibition of isolated PfGSK-3 and HsGSK-3. The kinetic aqueous solubility was assessed by laser nephelometry.

RESULTS

The para position at the 4-phenyl ring of the title compounds was identified as a suitable point for the attachment of side chains. While alkoxy substituents in this position led to decreased antiplasmodial activity, alkylamino groups retained antiparasitic potency. The most promising of these congeners (4h) was investigated in detail. This compound is a selective PfGSK-3 inhibitor (versus the human GSK-3 orthologue), and exhibits improved antiplasmodial activity in vitro as well as better solubility in aqueous media than its unsubstituted parent structure. The derivative 4b was separated into the atropisomers, and it was shown that the (+)-enantiomer acts as eutomer.

CONCLUSIONS

The attachment of alkylamino side chains leads to the improvement of antiplasmodial activity and aqueous solubility of selective PfGSK-inhibitors belonging to the class of 4-phenylthieno[2,3-b]pyridines. These molecules show axial chirality, a feature of high impact for biological activity. The findings can be exploited for the development of improved selective PfGSK-3 inhibitors.

Antiparasitic phytotherapy perspectives, scope and current development

Tropical protozoan diseases are currently a major public health problem throughout the world and are strongly linked with poverty, this combined with a lack of commercial markets for potential drugs has created a large burden on the health and economic development of low-income and middle-income countries in Africa, Asia, and the Americas. Due to the low research interest and the high increase of resistance against the existing treatments, as well as increasing inefficiency, toxicity, prolonged treatment schedules and costs, there is an urgent need for cost-effective, safe and easy-to-administer, new effective compounds with novel mechanisms of action. Several studies of crude plant extracts have already identified potential compounds to treat Chagas’ disease, Leishmaniasis, Toxoplasmosis, Giardiasis, and Malaria among other protozoan parasites. Natural compounds of medicinal plants have shown lower toxicity together with higher specificity, creating an optimistic view of new treatments for diseases. Out of 1010 new active substances approved as drugs for medical conditions by regulatory agencies during the past 25 years, 490(48.5%) were from a natural origin.

Level of circulating steroid hormones in malaria and cutaneous leishmaniasis: a case control study

Epidemiological and clinical studies have shown a great difference in the severity and prevalence of infectious diseases in men and women and various studies have shown that the key immunological factors are affected by sex-associated hormones. Considering the role of sex hormones in various infections, the current study aimed to determine the level of sex hormones in patients with cutaneous leishmaniasis (CL) and malaria and compare it with those of healthy controls. The survey was designed as a case-control study. Peripheral blood was collected from thirty male malaria patients, sixty patients (equal number of both sexes) with cutaneous leishmaniasis and ninety healthy subjects. Disease confirmations were done through microscopic examination of either peripheral blood smears, in case of malaria, or Giemsa-stained lesion imprint slides for CL. The level of testosterone, progesterone and estrogen were measured in malaria and CL patients along with healthy subjects, using an ELISA commercial kit. Age of participants was 18-35 years (mean 25.39 ± 4.70) for CL patients and 14-41 years (mean 27.63 ± 9.09) for malaria patients. Differences between the age of patients and the healthy subjects were insignificant. The level of testosterone in malaria patients (1.44 ± 0.12 ng/mL) was lower than control group (1.46 ± 0.06, ng/mL) but the differences were not statistically significant (p > .05). The concentration of testosterone in CL patients (1.49 ± 0.03 ng/mL) was higher than those of control group (1.46 ± 0.06 ng/mL), and the difference was statistically significant (p  = 0.05). Although the concentration of estrogen and progesterone in CL patients were lower than controls, still the differences were not statistically significant (p > 0.05). Findings of the current study demonstrated a significant difference in the serum level of testosterone in CL patients in comparison with the healthy subjects whereas such difference was not seen in malaria patients.

Metabolism of primaquine in normal human volunteers: investigation of phase I and phase II metabolites from plasma and urine using ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry

BACKGROUND

Primaquine (PQ), an 8-aminoquinoline, is the only drug approved by the United States Food and Drug Administration for radical cure and prevention of relapse in Plasmodium vivax infections. Knowledge of the metabolism of PQ is critical for understanding the therapeutic efficacy and hemolytic toxicity of this drug. Recent in vitro studies with primary human hepatocytes have been useful for developing the ultra high-performance liquid chromatography coupled with high-resolution mass spectrometric (UHPLC-QToF-MS) methods for simultaneous determination of PQ and its metabolites generated through phase I and phase II pathways for drug metabolism.

METHODS

These methods were further optimized and applied for phenotyping PQ metabolites from plasma and urine from healthy human volunteers treated with single 45 mg dose of PQ. Identity of the metabolites was predicted by MetaboLynx using LC-MS/MS fragmentation patterns. Selected metabolites were confirmed with appropriate standards.

RESULTS

Besides PQ and carboxy PQ (cPQ), the major plasma metabolite, thirty-four additional metabolites were identified in human plasma and urine. Based on these metabolites, PQ is viewed as metabolized in humans via three pathways. Pathway 1 involves direct glucuronide/glucose/carbamate/acetate conjugation of PQ. Pathway 2 involves hydroxylation (likely cytochrome P450-mediated) at different positions on the quinoline ring, with mono-, di-, or even tri-hydroxylations possible, and subsequent glucuronide conjugation of the hydroxylated metabolites. Pathway 3 involves the monoamine oxidase catalyzed oxidative deamination of PQ resulting in formation of PQ-aldehyde, PQ alcohol and cPQ, which are further metabolized through additional phase I hydroxylations and/or phase II glucuronide conjugations.

CONCLUSION

This approach and these findings augment our understanding and provide comprehensive view of pathways for PQ metabolism in humans. These will advance the clinical studies of PQ metabolism in different populations for different therapeutic regimens and an understanding of the role these play in PQ efficacy and safety outcomes, and their possible relation to metabolizing enzyme polymorphisms.

Effect of artemisinin and neurectomy of pterygoid canal in ovalbumin-induced allergic rhinitis mouse model

Background

Allergic rhinitis (AR), characterized by sneezing, nasal itching and rhinorrhea, affects a large number of population. This study aimed to explore the effects of artemisinin alone or combined with neurectomy of pterygoid canal in ovalbumin-induced AR mouse model and illustrate the underlying mechanisms.

Methods

Allergic symptoms were evaluated to verify inhibitory effect of artemisinin alone or combined with neurectomy of pterygoid canal on AR. Serum levels of histamine, immunoglobulin E (IgE) and inflammatory factors TNF, INF-γ, IL-1β IL-10, IL-4 and IL-5 were measured by ELISA. The mRNA levels of TNF, INF-γ, IL-1β and IL-10 in local lymph nodes were measured by RT-qPCR. The total and phosphorylated levels of ERK and JNK were assessed by Western blot. CD4⁺CD25⁺Foxp3⁺ T (Treg) cells were analyzed by flow cytometry.

Results

Artemisinin significantly relieved the behavior symptoms of AR mice. The administration of artemisinin strikingly suppressed the expression of histamine, IgE and inflammatory factors. An increased Treg cell proportion and inhibited ERK phosphorylation were observed in artemisinin-treated groups as compared to those in the AR group. Moreover, artemisinin plus neurectomy of pterygoid almost abolished the behavioral score increase in AR mice.

Conclusions

These results indicated that artemisinin exhibited anti-allergic effect by inhibiting ERK activation and increasing Treg cell proportion, which subsequently decreased the expressions of allergic mediators. In addition, artemisinin combined with neurectomy of pterygoid showed better efficacy than artemisinin alone.

Electronic supplementary material

The online version of this article (10.1186/s13223-018-0249-6) contains supplementary material, which is available to authorized users.

Modeling and resistant alleles explain the selectivity of antimalarial compound 49c towards apicomplexan aspartyl proteases

Toxoplasma gondii aspartyl protease 3 (TgASP3) phylogenetically clusters with Plasmodium falciparum Plasmepsins IX and X (PfPMIX, PfPMX). These proteases are essential for parasite survival, acting as key maturases for secreted proteins implicated in invasion and egress. A potent antimalarial peptidomimetic inhibitor (49c) originally developed against Plasmepsin II selectively targets TgASP3, PfPMIX, and PfPMX To unravel the molecular basis for the selectivity of 49c, we constructed homology models of PfPMIX, PfPMX, and TgASP3 that were first validated by identifying the determinants of microneme and rhoptry substrate recognition. The flap and flap-like structures of several reported Plasmepsins are highly flexible and critically modulate the access to the binding cavity. Molecular docking of 49c to TgASP3, PfPMIX, and PfPMX models predicted that the conserved phenylalanine residues in the flap, F344, F291, and F305, respectively, account for the sensitivity toward 49c. Concordantly, phenylalanine mutations in the flap of the three proteases increase twofold to 15-fold the IC₅₀ values of 49c. Compellingly the selection of mutagenized T. gondii resistant strains to 49c reproducibly converted F344 to a cysteine residue.

Malaria

Malaria is caused in humans by five species of single-celled eukaryotic Plasmodium parasites (mainly Plasmodium falciparum and Plasmodium vivax) that are transmitted by the bite of Anopheles spp. mosquitoes. Malaria remains one of the most serious infectious diseases; it threatens nearly half of the world's population and led to hundreds of thousands of deaths in 2015, predominantly among children in Africa. Malaria is managed through a combination of vector control approaches (such as insecticide spraying and the use of insecticide-treated bed nets) and drugs for both treatment and prevention. The widespread use of artemisinin-based combination therapies has contributed to substantial declines in the number of malaria-related deaths; however, the emergence of drug resistance threatens to reverse this progress. Advances in our understanding of the underlying molecular basis of pathogenesis have fuelled the development of new diagnostics, drugs and insecticides. Several new combination therapies are in clinical development that have efficacy against drug-resistant parasites and the potential to be used in single-dose regimens to improve compliance. This ambitious programme to eliminate malaria also includes new approaches that could yield malaria vaccines or novel vector control strategies. However, despite these achievements, a well-coordinated global effort on multiple fronts is needed if malaria elimination is to be achieved.