Histopathological changes in juvenile Schistosoma haematobium harboured in hamsters treated with artemether

Effect of artesunate and artemether against Clonorchis sinensis and Opisthorchis viverrini in rodent models

Food-borne trematodiasis is an emerging public health problem and there is a need to develop novel treatment options. We examined the in vivo efficacy of single oral doses of artesunate and artemether administered to rodents experimentally infected with either Clonorchis sinensis or Opisthorchis viverrini. Rats infected with adult C. sinensis were administered artesunate or artemether at doses of 75, 150 or 300 mg/kg. Hamsters infected with adult O. viverrini were administered artesunate or artemether at doses of 200, 400 or 600 mg/kg. Treatment efficacy was assessed according to reductions in worm burden compared with infected but untreated control animals. Worm burden reductions of 98.6-100% were found in C. sinensis-infected rats after a single dose of artesunate and artemether at 150 mg/kg. Administration of artesunate and artemether at a dose of 400mg/kg to O. viverrini-infected hamsters resulted in worm burden reductions of 77.6% and 65.5%, respectively. However, both drugs showed toxic effects when administered to O. viverrini-infected hamsters at a dose > or =400mg/kg. Our study demonstrates that artesunate and artemether possess excellent clonorchicidal activities in vivo. These findings provide a foundation for subsequent clinical trials. More laboratory investigations are warranted to investigate further the opisthorchicidal properties of the artemisinins.

Development of antischistosomal drugs in China, with particular consideration to praziquantel and the artemisinins

Remarkable achievements have been made in the control of schistosomiasis in China, with chemotherapy playing a seminal role. From the early 1950s through the early 1980s, Chinese scientists made considerable progress in discovery and development of compounds with antischistosomal properties, including antimonials, non-antimonials and various effective principles stemming from traditional herbs. However, only few compounds entered clinical testing, while others were abandoned mainly due to their toxicity and poor efficacy. The advent of praziquantel in the 1970s changed the landscape of research and development of drugs for treatment and morbidity control of schistosomiasis. The main Chinese contributions to enhance the understanding of the antischistosomal drug praziquantel are reviewed here, including issues of metabolism, antibody-dependency, host immune factors, stage-specific susceptibility and resistance. Over the past 25 years, researchers from China successfully developed artemether and artesunate, two derivatives from the antimalarial artemisinin, as promising drugs against Schistosoma japonicum. Laboratory investigations showed that the artemisinins display their highest activity against the juvenile stages of the parasite. These findings were consistently confirmed in randomised controlled trials; repeated oral administration of artemether or artesunate was safe and efficacious in the prevention of patent S. japonicum infections. The key findings are reviewed here, and emphasis is placed on how it stimulated research outside of China on other human schistosome species.

Schistosoma japonicum: In vitro effects of artemether combined with haemin depend on cultivation media and appraisal of artemether products appearing in the media

We recently found that the exposure of schistosomes in vitro to artemether plus haemin can lead to parasite death, while exposure to each compound singly had no effect. Since these observations might be relevant to understanding the mechanism of action of artemether against schistosomes, we conducted additional experiments. First, we performed a comparative appraisal of Schistosoma japonicum survival after incubation in two media, namely Hanks' balanced salt solution (HBSS) and RPMI 1640, supplemented with inactivated calf serum, antibiotics and different concentrations of artemether and/or haemin. Worm mortalities were consistently higher and occurred faster in HBSS when compared to RPMI 1640. Second, we investigated the behaviour of artemether in different chemical systems, including reduced glutathione or cysteine, in the presence of haemin or ferrous sulfate. Cleavage of the endoperoxide bridge of artemether occurred in all experiments, consistently forming five different products, of which one has not been described previously. Third, RPMI 1640 and HBSS media were supplemented with artemether and haemin in the presence of S. japonicum. The consumption of artemether in RPMI 1640 was much faster than in HBSS. Trace amounts of artemether and five free radical reaction products of artemether could be detected in RPMI 1640 after 24-48 h. In contrast, large amounts of artemether remained without the formation of free radical products in HBSS under the same conditions. These findings coincide with significantly higher schistosome mortalities employing HBSS instead of RPMI 1640. Our results suggest that it is artemether or an active metabolite thereof (most likely a carbon-centred free radical), rather than any free radical reaction product that is harmful for the worms. We speculate that schistosomes ingest artemether and cleave it in their gut. This cleavage is induced by haemin or another iron-containing molecule. These findings might be a further step forward in elucidating the mechanism of action of artemether against schistosomes.

Recent investigations of artemether, a novel agent for the prevention of schistosomiasis japonica, mansoni and haematobia

Two decades ago, a group of Chinese scientists discovered the antischistosomal properties of artemether, a derivative of the antimalarial drug artemisinin. However, it was only recently that the importance of this finding was recognized internationally, following a collaborative effort between Chinese, European and African scientists, who investigated the effects of artemether against the major human schistosome species. Laboratory studies revealed that artemether exhibits the highest activity against juvenile stages of the parasites, while adult worms are significantly less susceptible. There was no indication of neurotoxicity following repeated high doses of artemether given fortnightly for up to 5 months. Randomized controlled clinical trials confirmed that artemether, orally administered at a dose of 6 mg/kg once every 2-3 weeks, results in no drug-related adverse effects, and significantly reduces the incidence and intensity of schistosome infections. The risk that these treatment regimens might select for resistance, particularly for resistant-plasmodia, appears to be low. Combined treatment with artemether and praziquantel, given to animals harbouring juvenile and adult schistosome worms, resulted in significantly higher worm burden reductions than each drug administered singly. In conclusion, artemether-integrated with other control strategies-has considerable potential for reducing the current burden of schistosomiasis in different epidemiological settings.

The potential of artemether for the control of schistosomiasis

Schistosomiasis continues to rank--following malaria--at the second position of the world's parasitic diseases in terms of the extent of endemic areas and the number of infected people. There is yet no vaccine available and the current mainstay of control is chemotherapy with praziquantel used as the drug of choice. In view of concern about the development of tolerance and/or resistance to praziquantel, there is a need for research and development of novel drugs for the prevention and cure of schistosomiasis. Interestingly, derivatives of artemisinin, which are already effectively used in the treatment of malaria, also exhibit antischistosomal properties. Significant advances have been made with artemether, the methyl ether derivative of artemisinin. We review the discovery of the antischistosomal activity of artemether by Chinese scientists two decades ago; the detailed laboratory studies of the susceptibility of, and effect on, the different developmental stages of Schistosoma japonicum, Schistosoma mansoni and Schistosoma haematobium to artemether; the possible mechanism of action and the potential long-term toxicity. Finally, we look at the effect of combined treatment with artemether and praziquantel; and clinical findings thus far obtained from randomised controlled trials with oral artemether for the prevention of patent infections and morbidity. The review intends to create a forum for strategic discussion of how these laboratory and clinical findings could be translated into public health actions. We conclude that artemether--as part of integrated current control measures and adapted to specific socio-ecological and epidemiological settings--has considerable potential to significantly reduce the current burden of schistosomiasis in many parts of the world.