Background: The erythrocytic stage of the life cycle of the malaria parasite, Plasmodium falciparum, consists of trophozoite, schizont and gametocyte stages in humans. Various anti-malarial agents target different stages of the parasite to produce treatment outcomes. This study reports on the stage-specific anti-malarial activity of heptaphylline and imperatorin against human P. falciparum in addition to their cytotoxicity and selectivity indices (SI). Methods: The compounds were isolated from Clausena anisata using column chromatography and their structures elucidated using NMR spectroscopy. The anti-malarial activity was determined by measuring the trophozoitocidal, schizonticidal and gametocytocidal activities of the compounds using the SYBR green assay. Cytotoxicity was evaluated using the tetrazolium-based colorimetric assay. Results: Heptaphylline and imperatorin produced trophozoitocidal, schizonticidal and gametocytocidal activities with IC₅₀s of 1.57 (0.2317)–26.92 (0.3144) µM with those of artesunate (the standard drug) being 0.00024 (0.0036)–0.0070 (0.0013) µM. In the cytotoxicity assay, the compounds produced CC_50S greater than 350 µM and SI of 13.76–235.90. Also, the trophozoitocidal and schizonticidal activities of the compounds were more pronounced than their gametocytocidal activity. Imperatorin was 42.04% more trophozoitocidal than hepthaphyline. However, hepthaphyline has more schizonticidal and gametocytocidal properties than imperatorin. Conclusion: Heptaphylline and imperatorin are promising anti-malarial agents, since they possess potent anti-malarial activity with weak cytotoxicity on RBCs. However, imperatorin is a better anti-malarial prophylactic agent whereas heptaphylline is a better malaria treatment agent.

Antimalarial resistance has hampered the effective treatment of malaria, a parasitic disease caused by Plasmodium species. As part of our campaign on phenotypic screening of phenylhydrazones, a library of six phenylhydrazones was reconstructed and evaluated for their in vitro antimalarial and in silico receptor binding and pharmacokinetic properties. The structures of the phenylhydrazone hybrids were largely confirmed using nuclear magnetic resonance techniques. We identified two compounds which exhibited significant antimalarial potential against the ring stage (trophozoite) of 3D7 chloroquine-sensitive (CS) strain and DD2 chloroquine-resistant (CR) strains of Plasmodium falciparum with monosubstituted analogs bearing meta or para electron-donating groups showing significant activity in the single-digit micromolar range. Structure activity relationship is presented showing that electron-donating groups on the substituent hydrophobic pharmacophore are required for antimalarial activity. Compounds PHN6 and PHN3 were found to be the most potent with pIC₅₀s (calculated form in vitro IC₅₀s) of 5.37 and 5.18 against 3D7 CS and DD2 CR strains, respectively. Our selected ligands (PHN3 and PHN6) performed better when compared to chloroquine regarding binding affinity and molecular stability with the regulatory proteins of Plasmodium falciparum, hence predicted to be largely responsible for their in vitro activity. Pharmacokinetic prediction demonstrated that the phenylhydrazones may not cross the blood-brain barrier and are not P-glycoprotein (P-gp) substrates, a good absorption of 62 to 69, and classified as a category IV compound based on toxicity grading.

Malaria is a major public health problem, prevalent in Africa and endemic in Ghana. Besides the use of artemisinin combination therapy, plant medicine is well‐recognised and accepted in Ghana. Decoctions of Azadirachta indica (AI) leaves and Khaya senegalensis (KS) stem bark are traditionally used for treating malaria. However, these decoctions are bitter, bulky and unstable compared to solid dosage forms. This study sought to formulate decoctions from these plants into capsules to tackle these setbacks. The maximum wavelength of absorption and the amount per dose of both plants’ decoctions (120 mL) were determined. Four absorbents (bentonite, magnesium carbonate, microcrystalline cellulose and kaolin) at four concentrations (25, 50, 75 and 100 mg/dose) were used to formulate the decoctions into granules. The granules were assessed to select the best extract‐absorbent granules for encapsulation and quality assessment. Antiplasmodial activity and cytotoxicity of the formulated capsules were also determined. AI containing 35 mg/dose of kaolin with a percentage release of 97.31 ± 0.74% and good flow properties was encapsulated. KS containing 50 mg/dose of bentonite with a percentage release of 97.54 ± 0.88% and good flow properties was encapsulated. Formulated capsules from both plants passed all quality control tests performed, with disintegration times of 10.01 ± 0.34 and 4.48 ± 0.23 min, and cumulative drug release of 78.13 ± 0.37% and 95.63 ± 1.00%, for AI and KS, respectively. AI (IC ₅₀ , 2.74 ± 0.70 μg/mL) and KS (IC ₅₀ , 24.37 ± 4.19 μg/mL) had good to moderate antiplasmodial activity (IC ₅₀ ≤ 50 μg/mL) using the SYBR green assay. Cytotoxicity studies also indicated that both AI and KS were selective for the Plasmodium parasite. The formulated capsules could therefore be used as an alternative to their bitter decoctions.

Finished herbal antimalarials are widely used in Ghana, although scientific reports regarding their antiplasmodial activity and safety of these products are limited. This study, therefore, assessed the antiplasmodial activities and safety of three widely distributed antimalarial polyherbal products. These products (samples A, B and C) were obtained through a minisurvey conducted in the Accra and Kumasi Metropolises. The SYBR Green fluorescence antiplasmodial assay was conducted on different stages of chloroquine‐resistant and chloroquine‐sensitive strains of P. falciparum. Cytotoxicity and subacute toxicity were assessed following MTT assay and OECD guidelines, respectively. Samples A, B and C yielded IC ₅₀ (μg/mL) values of 0.869 ± 0.10, 0.828 ± 0.05 and 3.07 ± 0.098, respectively, against the chloroquine‐sensitive (3D7) strain at the trophozoite stage. At the schizont stage, samples A, B and C exhibited moderate to weak activities with IC ₅₀ (μg/mL) values of 9.96 ± 0.63, 7.71 ± 1.63 and 13.66 ± 1.91, respectively. At the gametocyte stage, samples A, B and C displayed moderate to weak activity with IC ₅₀ (μg/mL) values of 13.59 ± 0.49, 17.92 ± 0.814 and 59.65 ± 1.61, respectively. Parasite inhibition against the chloroquine‐resistant strain (Dd2) at the trophozoite stage demonstrated good antiplasmodial activities for samples A and B, with IC ₅₀ (μg/mL) values of 0.939 ± 0.04 and 0.318 ± 0.01, respectively. Sample C yielded an IC ₅₀ (μg/mL) value of 15.09 ± 0.319. In conclusion, the three products are antiplasmodial agents and are safe in the rodent model.