Effets préventifs et immunomodulateurs d’une posologie optimale de praziquantel et de l’extrait aqueux des parties aériennes de Sida pilosa Retz. (Malvaceae) sur l’infection à Schistosoma mansoni dans un modèle murin

Abstract

Schistosomiasis is a parasitic disease caused by flatworms of Schistosoma genus. The morbidity related to schistosomiasis is mainly caused by the tissue-embolized eggs laid by adult worms, that induce a granulomatous response which leads to tissue injuries and fibrosis. One of the major challenges of schistosomiasis chemotherapy is the inefficacy of praziquantel (PZQ) at the initial stage of the infection and related therapeutic failures. The establishment of an effective therapeutic regimen during the initial stage of the infection that would protect against the severe pathology became a necessity. Thus, this work was undertaken to evaluate the preventive and immunomodulatory activities of an optimal praziquantel therapeutic regimen and the aqueous extract of Sida pilosa Retz. arial parts on the acute and granulomatous phases of Schistosoma mansoni infection in mice. In order to find an optimal effective PZQ therapeutic regimen during the initial stage of infection, S. mansoni-infected mice were divided into four groups receiving different PZQ regimens from day 1 post-infection (p.i). It was 100 mg/kg/day for five consecutive days (PZQ1), 100 mg/kg/day for 28 days (PZQ2), 18 mg/kg/day for 28 days (PZQ3) and a single dose of 500 mg/kg (PZQ4). In order to evaluate the preventive and immunomodulatory activities of S. pilosa aqueous extract (EASp) during the phases of S. mansoni infection, its cercaricidal activity was evaluated by monitoring the viability of cercariae incubated with concentrations of EASp (31.25 – 1000 μg/mL) during 150 min. Afterwards, infected mice were treated orally with EASp at the doses of 100 and 200 mg/kg (EASp100 and EASp200). Heathy control group (TS), Infected-untreated group (TI), pharmacological control group (TPh) and reference control group corresponding to PZQ3 were formed. The treatment started on day 1 p.i and ended on day 28 p.i. In order to assess the modifications occurring in the acute phase of the infection, a pool of mice was sacrificed on the 36th day p.i, while the second pool of mice sacrificed at 56th days p.i allowed to evaluate the effectiveness of different treatments during the granulomatous phase of the infection. In addition to the mortality rate, parasitological burden, liver function tests, hepatic and splenic oxidative status as well as the histopathological analysis of the liver and the intestine were evaluated. The serum levels and the hepatic expression of genes of pro and anti-inflammatory cytokines and chemokines were also measured. The results of this study showed that during the acute and granulomatous phases of the infection, treatment with PZQ led to a significant reduction (p <0.001) of the worm burden and the hepatic and intestinal eggs loads in PZQ2 and PZQ3 groups in comparison to TI group. This reduction was greater in the PZQ3 group (p<0.001) than in the PZQ1 and PZQ4 groups. Interestingly, in PZQ3 group, the hepatic and splenic oxidative status as well as hepatic function parameters were preserved. A significant reduction (p <0.001) of the granulomas number and volume was observed in PZQ2 and PZQ3 groups in comparison to TI group. Regarding the immune response, the serum levels of pro-inflammatory cytokines (IFN-γ and TNF-α) were significantly decreased at both infection phases in PZQ2 and PZQ3 groups in comparison to TI group, while during the granulomatous phase, the serum level and the genes expression of profibrotic cytokines (IL-13 and FGF-1) were normalized in PZQ2 and PZQ3 groups. In PZQ3 group, the genes of the immunoregulatory factors (IL-10,TGF-β and RANTES) were overexpressed in comparison to those of TI group. Interestingly, a mortality rate of 82% was recorded in the PZQ2 group in contrast to the PZQ3 group where no mortality was noted. These results allowed us to select the PZQ regimen of 18 mg/kg/day for 28 consecutive days as the most effective one. Regarding the effect of S. pilosa aqueous extract S. mansoni cercariae, with a LC50 of 296.11 μg/mL after 150 min of incubation, EASp exhibited a significant cercaricidal activity. In addition, the preventive treatment with EASp at doses of 100 and 200 mg/kg led to a significant reduction (p<0.001) of the worm burden and the hepatic and intestinal eggs loads at both phases in comparison to TI group. The treatment of infected mice with EASp has significantly maintained the liver and spleen oxidative status and the hepatic biochemical parameters in normal ranges. The treatment with EASp also resulted to a reduction (p <0.001) of the granulomas number and volume in the liver and intestine of infected mice. Similarly, the serum levels of INF-γ and TNF-α remained significantly lower in EASp100 (p <0.01) and EASp200 (p <0.001) groups in comparison to those of the TI group. A reduction of the serum level IL-13 was recorded in EASp100 group (p<0.05). In addition, the genes expression of MIP-1α and FGF-1 was significantly reduced (p <0.001) in the mice’s liver of EAsp100 and EASp200 groups in comparison to those of TI group, while the liver gene expression of IL-10, TGF-β, RANTES and FoxP3 was increased Finally, no difference was observed between healthy control group (TS) and the pharmacological control group, except the lymphocyte count, which was significantly high (p <0.001) in the TPh group, suggesting a potential immunostimulatory activity of the aqueous extract of S. pilosa. This study revealed that the praziquantel regimen of 18 mg/kg/day for 28 days (PZQ3) as well as the aqueous extract of S. pilosa aerial parts administered at the early stage of the S. mansoni infection protect the host against S. mansoni pathology by preserving the hepatic, splenic and intestinal function and by modulating the immune response during S.mansoni infection.