Pharmacodynamics of antimalarial chemotherapy

Isolation and identification of carotenoid-producing yeast and evaluation of antimalarial activity of the extracted carotenoid(s) against P. falciparum

Plasmodial resistance to a variety of plant-based antimalarial drugs has led toward the discovery of more effective antimalarial compounds having chemical or biological origin. Since natural compounds are considered as safer drugs, in this study, yeast strains were identified and compared for the production of carotenoids that are well-known antioxidants and this metabolite was tested for its antiparasitic activity. Plasmodium falciparum 3D7 strain was selected as the target parasite for evaluation of antimalarial activity of yeast carotenoids using in vitro studies. Data were analyzed by FACS (fluorescence-activated cell sorter) and counted via gold standard Giemsa-stained smears. The extracted yeast carotenoids showed a profound inhibitory effect at a concentration of 10^-3 µg/µl and 10^-4 µg/µl when compared to β- carotene as control. SYBR Green1 fluorescent dye was used to confirm the decrease in parasitaemia at given range of concentration. Egress assay results suggested that treated parasite remained stalled at schizont stage with constricted morphology and were darkly stained. Non-toxicity of carotenoids on erythrocytes and on human liver hepatocellular carcinoma cells (HepG2 cells) was shown at a given concentration. This report provides strong evidence for antimalarial effects of extracted yeast carotenoids, which can be produced via a sustainable and cost-effective strategy and may be scaled up for industrial application.

Antimalarial activity of plumbagin in vitro and in animal models

Background

Plumbagin is the major active constituent in several plants including Plumbago indica Linn. (root). This compound has been shown to exhibit a wide spectrum of biological and pharmacological activities. The present study aimed to evaluate the in vitro and in vivo antimalarial activity of plumbagin including its acute and subacute toxicity in mice.

Methods

In vitro antimalarial activity of plumbagin against K1 and 3D7 Plasmodium falciparum clones were assessed using SYBR Green I based assay. In vivo antimalarial activity was investigated in Plasmodium berghei-infected mouse model (a 4-day suppressive test).

Results

Plumbagin exhibited promising antimalarial activity with in vitro IC₅₀ (concentration that inhibits parasite growth to 50%) against 3D7 chloroquine-sensitive P. falciparum and K1 chloroquine-resistant P. falciparum clones of 580 (270–640) and 370 (270–490) nM, respectively. Toxicity testing indicated relatively low toxicity at the dose levels up to 100 (single oral dose) and 25 (daily doses for 14 days) mg/kg body weight for acute and subacute toxicity, respectively. Chloroquine exhibited the most potent antimalarial activity in mice infected with P. berghei ANKA strain with respect to its activity on the reduction of parasitaemia on day 4 and the prolongation of survival time.

Conclusions

Plumbagin at the dose of 25 mg/kg body weight given for 4 days was safe and produced weak antimalarial activity. Chemical derivatization of the parent compound or preparation of modified formulation is required to improve its systemic bioavailability.

Emerging artemisinin resistance in the border areas of Thailand

Emergence of artemisinin resistance has been confirmed in Cambodia and the border areas of Thailand, the well-known hotspots of multidrug resistance Plasmodium falciparum. It appears to be spreading to the western border of Thailand along the Thai-Myanmar border, and will probably spread to other endemic areas of the world in the near future. This raises a serious concern on the long-term efficacy of artemisinin-based combination therapies, as these combination therapies currently constitute the last effective and most tolerable treatment for multidrug-resistant Plasmodium falciparum. Attempts have been made by a diverse array of stakeholders to prevent the emergence of new foci of artemisinin resistance, as well as to limit the spread of resistance to the original foci. The success in achieving this goal depends on effective integration of containment and surveillance programs with other malaria control measures, with support from both basic and operational research.