Induction of Multidrug Tolerance in Plasmodium falciparum by Extended Artemisinin Pressure

Plasmodium falciparum resistance to artemisinin derivatives in Southeast Asia threatens global malaria control strategies. Whether delayed parasite clearance, which exposes larger parasite numbers to artemisinins for longer times, selects higher-grade resistance remains unexplored. We investigated whether long-lasting artemisinin pressure selects a novel multidrug-tolerance profile. Although 50% inhibitory concentrations for 10 antimalarial drugs tested were unchanged, drug-tolerant parasites showed higher recrudescence rates for endoperoxides, quinolones, and an antifolate, including partner drugs of recommended combination therapies, but remained susceptible to atovaquone. Moreover, the age range of intraerythrocytic stages able to resist artemisinin was extended to older ring forms and trophozoites. Multidrug tolerance results from drug-induced quiescence, which enables parasites to survive exposure to unrelated antimalarial drugs that inhibit a variety of metabolic pathways. This novel resistance pattern should be urgently monitored in the field because this pattern is not detected by current assays and represents a major threat to antimalarial drug policy.     

Study on testicular response to prolong artemisinin‐based combination therapy treatments in guinea pigs

Artemisinin‐based combination therapies (ACTs) are first‐line agents in malaria chemotherapy, but often abused in malaria endemic countries including Nigeria. This study investigated the effects of prolong treatment of artesunate–amodiaquine (ATS–Amod), artesunate‐sulfadoxine‐pyrimethamine (ATS–SP) and artemether–lumefantrine (ATM–Lum) on testicular indices in guinea pigs. Sixty‐five pigs were grouped into 13 (n = 5 per group). Six groups were given standard or double therapeutic dose equivalents of ATS–Amod, ATS‐SP or ATM–Lum daily for 14 day and sacrificed 24 hr after treatments. Six other groups (recovery groups) received similar drug treatments but allowed to recover for 14 day before sacrificed. Control group received distilled water. ATS–Amod, ATS–SP and ATM–Lum, respectively, decreased (p < .01) sperm count (17.7%, 37.7% and 33.8%), motility (48.6%, 50% and 51.4%), viability (32.7%, 43.7% and 35.9%) and morphology (123.5%, 0% and 0%), compared to control. These effects were reversed in recovery animals. Also, they decreased (p < .01) luteinising hormone and testosterone serum levels, without affecting follicle‐stimulating hormone. Testicular malondialdehyde level was elevated, and glutathione was decreased, while catalase and superoxide dismutase enzymes were unaffected by the drugs. The alterations were all reversed in recovery animals. The study reveals that prolong administration of ACTs results in reversible alteration of sperm parameters and reduction of testosterone which is partly attributable to oxidative stress.     

More insights into the pharmacological effects of artemisinin

Artemisinin is one of the most widely prescribed drugs against malaria and has recently received increased attention because of its other potential biological effects. The aim of this review is to summarize recent discoveries of the pharmaceutical effects of artemisinin in basic science along with its mechanistic action, as well as the intriguing results of recent clinical studies, with a focus on its antitumor activity. Scientific evidence indicates that artemisinin exerts its biological activity by generating reactive oxygen species that damage the DNA, mitochondrial depolarization, and cell death. In the present article review, scientific evidence suggests that artemisinin is a potential therapeutic agent for various diseases. Thus, this review is expected to encourage interested scientists to conduct further preclinical and clinical studies to evaluate these biological activities.     

Fighting drug-resistant Plasmodium falciparum: the challenge of artemisinin resistance

Following a decade-long scale up of malaria control through vector control interventions, the introduction of rapid diagnostic tests and highly efficacious Artemisinin-based Combination Therapy (ACT) along with other measures, global malaria incidence declined significantly. The recent development of artemisinin resistance on the Cambodia-Thailand border, however, is of great concern. This review encompasses the background of artemisinin resistance in Plasmodium falciparum, its situation, especially in the Greater Mekong Sub-region (GMS), and the responses taken to overcome this resistance. The difficulties in defining resistance are presented, particularly the necessity of measuring the clinical response to artemisinins using the slow parasite-clearance phenotype. Efforts to understand the molecular basis of artemisinin resistance and the search for molecular markers are reviewed. The markers, once identified, can be applied as an efficient tool for resistance surveillance. Despite the limitation of current surveillance methods, it is important to continue vigilance for artemisinin resistance. The therapeutic efficacy “in vivo study'’ network for monitoring antimalarial resistance in the GMS has been strengthened. GMS countries are working together in response to artemisinin resistance and aim to eliminate all P. falciparum parasites. These efforts are crucial since a resurgence of malaria due to drug and/or insecticide resistance, program cuts, lack of political support and donor fatigue could set back malaria control success in the sub-region and threaten malaria control and elimination if resistance spreads to other regions.     

Holotransferrin enhances selective anticancer activity of artemisinin against human hepatocellular carcinoma cells

Artemisinin, also termed qinghaosu, is extracted from the traditional Chinese medicine ar- temesia annua L. （the blue-green herb） in the early 1970s, which has been confirmed for effectively treating malaria, Additionally, emerging data prove that artemisinin exhibits anti-cancer effects against many types of cancers such as leukemia, melanoma, etc. Artemisinin becomes cytotoxic in the presence of ferrous iron. Since iron influx is high in cancer cells, artemisinin and its analogs selectively kill can- cer cells with increased intracellular iron concentrations. This study is aimed to investigate the selective inhibitory effects of artemisinin on SMMC-7721 cells in vitro and determine the effect of holotransfer- fin, which increases the concentration of ferrous iron in cancer cells, combined with artemisinin on the anticancer activity. MTT assay was used for assessing the proliferation of SMMC-7721 cells treated with artemisinin. The induction of apoptosis and inhibition of colony formation in SMMC-7721 cells treated with artemisinin were determined by TdT-mediated dUTP nick end labeling （TUNEL） and col- ony formation assay, respectively. The results showed that artemisinin at various concentrations signifi- cantly inhibited growth, colony formation and cell viability of SMMC-7721 cells （P〈0.05）, likely due to induction of apoptosis of SMMC-7721 cells. Of interest, it was found that incubation of artemisinin combined with holotransferrin sensitized the growth inhibitory effect of artemisinin on SMMC-7721 cells （P〈0.01）. Our data suggest that treatment with artemisinin leads to inhibition of viability and pro- liferation, and apoptosis of SMMC-7721 ceils. Furthermore, we observed that holotransferrin signifi- cantly enhanced the anti-cancer activity of artemisinin. This study may provide a potential therapeutic choice for liver cancer.     

Parasitaemia and gametocytaemia after treatment with chloroquine, pyrimethamine/sulfadoxine, and pyrimethamine/sulfadoxine combined with artesunate in young Gambians with uncomplicated malaria

As part of a study to assess the infectivity of gametocytes after treatment with four antimalarial regimens, the efficacy of each treatment was also determined. From September to December 1998, 598 children with uncomplicated malaria were treated; 135 received chloroquine (CQ) alone, 276 received pyrimethamine/sulfadoxine (Fansidar, PSD) alone, 113 received PSD with a single dose of artesunate (PSD + 1ART) and 74 received PSD combined with three doses of artesunate (PSD + 3ART). On day 28 19/63 (30.2%; 95% C.I. 19.2% to 43.1%) of children treated with CQ alone, 5/134 (3.7%; 95% C.I. 1.2% to 8.5%) treated with PSD alone, 1/71 (1.4%, 95% C.I. 0.0% to 7.9%) treated with PSD + 1ART and 0/45 (0.0%; 95% C.I. 0.0% to 7.9%) treated with PSD + 3ART were parasitaemic. The proportion of children with gametocytes on day 7 after treatment with CQ alone was 16/89 (18.0%; 95% C.I. 10.6% to 27.6%), 98/174 (56.3%; 95% C.I. 48.6% to 63.8%) after treatment with PSD alone, 8/70 (11.4%; 95% C.I. 5.1% to 21.3%) after treatment with PSD + 1ART and 4/46 (8.7%; 95% C.I., 2.4% to 20.8%) after treatment with PSD + 3ART. CQ thus has a lower efficacy than PSD or either of the PSD and artesunate combinations. Use of PSD alone as an alternative first line treatment results in a very high post-treatment gametocyte prevalence that is likely to enhance transmission. There would be greater and more sustainable benefits from using PSD and artesunate combinations.     

高效液相色谱-串联质谱法测定健康人体血浆中青蒿素浓度及其药代动力学研究

目的 建立测定血浆中青蒿素(抗疟药)的高效液相色谱-串联质谱法,研究青蒿素在健康人体内的药代动力学.方法 10名健康男性志愿者,单剂口服青蒿素片1000 mg;用高效液相色谱-串联质谱法测定血药浓度.结果 本方法 检测青蒿素的线性范围为4～1 000 μg·L-1,最低定量限为4μg·L-1;口服青蒿素1 000 mg后,Cmax为(466.50±120.15)μg·L-1,AUC0-24h为(2.78±0.85)mg·h·L-1,AUC0-∞为(2.82±0.87)mg·h·L-1,t1/2为(3.58±0.86)h,tmax为(2.15±0.91)h.结论 该方法操作简便、快速、灵敏度高,适于青蒿素类药物的药代动力学研究.