Prevention of Schistosoma japonicum infection in mice with long-acting praziquantel implants

Praziquantel promotes protection against Schistosoma japonicum infection in mice

Praziquantel (PZQ) is the first line drug for the treatment of schistosomiasis. Several studies have confirmed that PZQ regulates host immunity, and we have recently found that pretreatment with PZQ enhances resistance against Schistosoma japonicum infection in buffaloes. We speculate that PZQ induces physiological changes in mice that prevent S. japonicum infection. To test this hypothesis and provide a practical measure to prevent S. japonicum infection, we determined the effective dose (the minimum dose), protection period and onset time of protection by comparing the worm burden, female worm burden and egg burden in PZQ-pretreated mice and blank control mice. Morphological differences between parasites were observed by measuring the total worm length, oral sucker, ventral sucker and ovary. The levels of cytokines, nitrogen monoxide (NO), 5-hydroxytryptamine (5-HT) and specific antibodies were measured using kits or soluble worm antigens. Hematological indicators on day 0 were analyzed in mice that received PZQ on days -15, -18, -19, -20, -21 and -22. The PZQ concentrations in plasma and blood cells were monitored using high performance liquid chromatography (HPLC). The effective dose was found to be two oral administrations (interval of 24 h) at 300 mg/kg body weight (BW) or one injection at 200 mg/kg BW, and the protection period of PZQ injection was 18 days. The optimal preventive effect was observed at two days post-administration, with a >92% worm reduction rate and significant worm reduction until 21 days after administration. Adult worms from PZQ-pretreated mice were runtish showing a shorter length, smaller organs and fewer eggs in the uteri of females. Detection of cytokines, NO, 5-HT and hematological indicators showed that PZQ induced immune-physiological changes, including higher levels of NO, IFN-γ and IL-2, and a lower level of TGF-β. No significant difference in the anti-S. japonicum specific antibody levels was observed. The PZQ concentrations in plasma and blood cells 8 and 15 days post-administration were lower than the detection limit. Our results confirmed that pretreatment with PZQ promotes the protection of mice against S. japonicum infection within 18 days. Although we observed some immune-physiological changes in the PZQ-pretreated mice, the exact mechanisms involved in the preventive effect require further study.

Transdermal praziquantel administration attenuates hepatic granulomatosis in mice infected with Schistosoma japonicum

Liver granuloma is a major pathogenic factor responsible for schistosomiasis, and no effective drugs or therapy methods to treat it have been found so far. Praziquantel (PZQ) has shown some anti-schistosomal effect, but little information is available about the effect of PZQ-prolonged administration on granuloma formation around schistosome eggs. Herein, we investigated the effect of PZQ on hepatic granuloma formation by treating the mice infected with Schistosoma japonicum using a long-term PZQ transdermal delivery. The results showed that the mean area of granulomas in the group treated with PZQ transdermal agent was (175.47 ± 116.73) × 10(3) μm(2) at the 49th day postinfection and (71.96 ± 45.99) × 10(3) μm(2) at the 56th day, while that in the control group was (304.51 ± 140.55) × 10(3) μm(2) and (526.44 ± 268.06) × 10(3) μm(2), respectively. The content of hydroxyproline in the livers of mice approached to the normal level on the 154th day in the treatment group, but it continued to increase from the 28th day to the 154th day after infection in the control group and nontreatment group. The ALT activity in serum of mice in the treatment group was also significantly lower than that in the control group (*P ≤ 0.05). Our results suggest that the long-term PZQ transdermal delivery is critical in the therapeutic approach to control the progress of hepatic schistosomiasis induced by egg granulomas.

Praziquantel treatment in trematode and cestode infections: an update

Status and emerging issues in the use of praziquantel for treatment of human trematode and cestode infections are briefly reviewed. Since praziquantel was first introduced as a broadspectrum anthelmintic in 1975, innumerable articles describing its successful use in the treatment of the majority of human-infecting trematodes and cestodes have been published. The target trematode and cestode diseases include schistosomiasis, clonorchiasis and opisthorchiasis, paragonimiasis, heterophyidiasis, echinostomiasis, fasciolopsiasis, neodiplostomiasis, gymnophalloidiasis, taeniases, diphyllobothriasis, hymenolepiasis, and cysticercosis. However, Fasciola hepatica and Fasciola gigantica infections are refractory to praziquantel, for which triclabendazole, an alternative drug, is necessary. In addition, larval cestode infections, particularly hydatid disease and sparganosis, are not successfully treated by praziquantel. The precise mechanism of action of praziquantel is still poorly understood. There are also emerging problems with praziquantel treatment, which include the appearance of drug resistance in the treatment of Schistosoma mansoni and possibly Schistosoma japonicum, along with allergic or hypersensitivity reactions against praziquantel treatment. To cope with and overcome these problems, combined use of drugs, i.e., praziquantel and other newly introduced compounds such as triclabendazole, artemisinins, and tribendimidine, is being tried.