Immune changes of Schistosoma japonicum infections in various rodent disease models.

Rodent models for Schistosoma japonicum infections have demonstrated that these animals possess a degree of resistance to schistosome infections that may be both T and B lymphocyte-mediated. However, their exact role is not well-defined and other immune mechanisms are likely to also play a role in protecting against infection. Immunosuppressed and immunocompetent reed voles (Microtus fortis, Mf), rats and mice (n=24/group) were infected with S. japonicum, and animals were sacrificed 42 days later under anesthesia. Neither worms nor eggs were observed in infected immunosuppressed Mf or rats, with the exception of one rat that presented with few eggs. In immunosuppressed mice, changes in the number and size of the worms were not significantly different compared to immunocompetent mice, but worm fecundity was affected. The size and number of granulomas in immunosuppressed animals was also reduced. Analysis of serum antibodies specific to schistosome adult worm antigen at 3 weeks post-infection demonstrated that the levels of antibodies in the sera of rats were significantly higher than in Mf and mice. In addition, Mf serum levels of IL-4 and IL-12 were significantly higher than levels observed in rats and mice. Antibodies and cytokines in the sera of Mf peaked 3 weeks post-infection and then began to decrease, while antibody responses in rats and mice increased gradually between weeks 3-7 post-infection. It is possible that T and B cells have a dual role in both mediating protection and exacerbating disease outcomes.

In vitro potentiation of antimalarial activities by daphnetin derivatives against Plasmodium falciparum.

OBJECTIVE: To screen the antimalarial compounds of daphnetin derivatives against Plasmodium falciparum in vitro. METHOD: Plasmodium faciparum (FCC1) was cultured in vitro by a modified method of Trager and Jensen. Antimalarial compounds were screened by microscopy-based assay and microfluorimetric method. RESULTS: DA79 and DA78 showed potent antimalarial activity against Plasmodium falciparum cultured in vitro. CONCLUSION: Though the relationship between the structures of daphnetin derivatives and their antimalarial activities has not been clarified yet, this study may provide a new direction for discovery of more potential antimalarial compounds.

[In vitro effect of daphnetin on cytochrome C oxidase and ribonucleotide reductase of plasmodium falciparum].

OBJECTIVE: To test the in vitro effect of daphnetin on cytochrome C oxidase (COX) and ribonucleotide reductase (RNR) activity of Plasmodium falciparum. METHODS: P. falciparum (FCC1/HN) was cultured in vitro using the method of Trager and Jensen. The effect of daphnetin and daphnetin-Fe complex on COX and RNR activity of P. falciparum was tested by ultraviolet spectrophotometer and electron spin resonance (ESR) respectively. RESULT: The parasites synchronized with sorbitol in vitro was treated by daphnetin and daphnetin-Fe complex. The inhibition level of the COX activity by daphnetin after being treated for 2, 4, 8 and 12 h were 0.6%, 73% and 80% respectively and the inhibition level by daphnetin at different concentrations (0.1, 1, 100 and 1 mmol/L) for 6h was 3%, 31%, 53% and 84%, respectively. No considerable effect was observed on the COX activity of P. falciparum treated with daphnetin-Fe complex. The tyrosyl free radical was tested to reflect the RNR activity of P. falciparum at various times by ESR. The inhibition level by daphnetin for 1, 2, 3 and 4 h were 7%, 51%, 69% and 75% respectively, while the values treated by daphnetin-Fe complex were 8%, 6%, 11% and 9% respectively. The inhibition level by daphnetin at different concentrations (0.1, 1, 100 and 1 mmol/L) for 6 h was 3%, 31%, 58% and 93% respectively and while the values treated by daphnetin-Fe complex were 8%, 6%, 11% and 9%. CONCLUSION: Daphnetin significantly reduces the COX and RNR activities of Plasmodium falciparum in vitro.

[Additive therapeutic effect of a combination of artemether and daphnetin against Plasmodium berghei in mice].

OBJECTIVE: To investigate the therapeutic effect of a combination of artemether and daphnetin against Plasmodium berghei ANKA strain in mice. METHODS: Groups of P. berghei infected mice were treated with various oral doses of artemether and daphnetin according to "4-day suppress assay". Thin blood smears were made on the fifth day after inoculation of parasites and the parasitemia reduction rate was calculated. The ED50 values obtained were plotted on isobolograms. A combined action of artemether and daphnetin was assessed. RESULTS: Artemether 0.4 mg/(kg x d) x 4d exhibited no detectable antimalarial effect, while artemether 0.4 mg/(kg x d) x 4d combined with daphnetin 7.7 mg/kg. d x 4d showed potent antiparasile efficacy. The ED50s of artemether in combination with daphnetin were lower than that of single artemether or daphnetin. The R-values were higher than 0.4, but lower than 2.7. CONCLUSION: The combination of artemether with daphnetin showed an additive antiparasile effect.

Comparative study on schizontocidal activity of recrystallized or crude daphnetin against malaria parasites.

OBJECTIVE: To compare the schizontocidal activity of recrystallized or crude daphnetin against malaria parasites in vivo. METHODS: Schizontocidal activity of recrystallized or crude daphnetin at various dosages was assessed in mice infected with Plasmodium berghei ANKA using a "4-day suppress assay". RESULTS: The comparison of the reduction rate of parasitemia caused by either recrystallized or crude dephnetin showed that ED(50) of crude daphnetin was 18.36 mg/kg, with 95% confidence limit of 5.96-56.54 mg/kg while ED50 of recrystallized daphnetin was 11.46 mg/kg, with 95% confidence limit of 8.63-15.22 mg/kg. CONCLUSION: The results indicate that the efficacy of recrystallized daphnetin is 37.6% higher than that of crude daphnetin.

[Effect of daphnetin on SOD activity and DNA synthesis of Plasmodium falciparum in vitro].

OBJECTIVE: To investigate the effect of daphnetin on superoxide dismutase (SOD) activity and DNA synthesis in P. falciparum in vitro. METHODS: The effect of daphnetin, daphnetin-Fe complex and desferrioxamine B on SOD activity of P. falciparum (P.f) FCC1 in vitro was determined with a SOD test-kit. The level of DNA synthesis of P.f synchronized cultured in vitro at various developmental stages after treatment of daphnetin or desferrioxamine B was assayed by fluorescein Hoechest 33258. RESULTS: The total SOD activity decreased by 60% after daphnetin treatment while it only decreased by 22% if treated with desferrioxamine B. No effect on SOD activity of P.f treated with daphnetin-Fe complex was observed. The level of DNA synthesis of P.f trophozoites in synchronized in vitro culture was significantly lower than that of the control. CONCLUSION: Daphnetin lowered SOD activity and decreased DNA synthesis of P.f in vitro.

In vitro antimalarial effect of daphnetin relating to its iron-chelating activity.

OBJECTIVE: To investigate the in vitro antimalarial effect of daphentin relating to its iron-chelating activity. METHODS: Schizontocidal activity of daphnetin and desferrioxamine B was tested through an in vitro assay based on the routine in vitro cultivation of Plasmodium faciparum FCC1 strain. The iron-chelating ability of each was measured by the fluorescent probe calcein. RESULTS: Daphnetin exhibited a modest iron-chelating ability compared with the powerful iron-chelator desferrioxamine B. In vitro test at the range of 0-12 mumol/L daphnetin showed a dose-dependent schizontocidal activity which could be inhibited if mixed with Fe2+ in a ratio of 2:1. CONCLUSION: The dose-dependent antimalarial activity of daphnetin is related to its iron-chelating activity.