Exploration of antifilarial potential and possible mechanism of action of the root extracts of Saxifraga stracheyion on cattle filarial parasite Setaria cervi

Extracts of Euphorbia hirta Linn. (Euphorbiaceae) and Rauvolfia vomitoria Afzel (Apocynaceae) demonstrate activities against Onchocerca volvulus microfilariae in vitro

Background

Onchocerciasis transmitted by Onchocerca volvulus is the second major cause of blindness in the world and it impacts negatively on the socio-economic development of the communities affected. Currently, ivermectin, a microfilaricidal drug is the only drug recommended for treating this disease. There have been speculations, of late, concerning O. volvulus resistance to ivermectin. Owing to this, it has become imperative to search for new drugs. World-wide, ethnomedicines including extracts of Euphorbia hirta and Rauvolfia vomitoria are used for treating various diseases, both infectious and non-infectious.

Method

In this study extracts of the two plants were evaluated in vitro in order to determine their effect against O. volvulus microfilariae. The toxicity of the E. hirta extracts on monkey kidney cell (LLCMK2) lines was also determined.

Results

The investigations showed that extracts of both plants immobilised microfilariae at different levels in vitro and, therefore, possess antifilarial properties. It was found that all the E. hirta extracts with the exception of the hexane extracts were more effective than those of R. vomitoria. Among the extracts of E. hirta the ethyl acetate fraction was most effective, and comparable to that of dimethanesulphonate salt but higher than that of Melarsoprol (Mel B). However, the crude ethanolic extract of E. hirta was found to be the least toxic to the LLCMK2 compared to the fractionated forms.

Conclusions

Extracts from both plants possess antifilarial properties; however, the crude extract of E. hirta was found to be least toxic to LLCMK2.

Biochemical composition and metabolic pathways of filarial worms Setaria cervi: search for new antifilarial agents

The main problem regarding the chemotherapy of filariasis is that no safe and effective drug is available yet to combat the adult human filarial worms. Setaria cervi, the causal organism of setariasis and lumbar paralysis in cattle, is routinely employed as a model organism for conducting biochemical and enzymatic studies on filarial parasites. In view of the practical difficulties in procuring human strains of Wuchereria bancrofti and Brugia malayi for drug screening, the bovine filarial parasite S. cervi, resembling the human species in having microfilarial periodicity and chemotherapeutic response to known antifilarial agents, is widely used as a model in such studies. For a rational approach to antifilarial chemotherapy, knowledge of the biochemical composition and metabolic pathways of this helminth parasite may be of paramount importance, so that more potent antifilarial agents based on specific drug targets can be identified in drug discovery programmes. The present review provides an update on the biochemistry of the important metabolic pathways functioning within this potentially important bovine parasite, that have so far been studied, and on those that need to be investigated further so as to identify novel drug targets that can be exploited for designing new antifilarial drugs.

Macrofilaricidal and microfilaricidal effects of Neurolaena lobata, a Guatemalan medicinal plant, on Brugia pahangi

Twelve extracts of 11 Guatemalan medicinal plants were initially screened in vitro for potential macrofilaricidal activity against Brugia pahangi, a lymphatic dwelling filarial worm, using concentrations from 125 to 1000 μg ml−1 of each extract that could be dissolved in the culture medium. Of 12 extracts used, the ethanol extract of leaves of Neurolaena lobata showed the strongest activity against the motility of adult worms. Subsequently, the extract of N. lobata was extensively examined in vitro for macro- and micro-filaricidal effects using a series of concentrations of 500, 250, 100, 50 and 10 μg ml−1. The effects were assessed by worm motility, microfilarial release by female worms and a MTT assay. The effect on the motility of adult worms was observed in a concentration- and time-dependent manner. The time required to stop motility of both sexes of adult worms was 6 h at 500 μg ml−1, 24 h at 250 μg ml−1, and 3 days for females and 4 days for males at 100 μg ml−1. The movement of females ceased at 4 days at a concentration of 50 μg ml−1 whereas the motility of males was only reduced. The loss of worm's viability was confirmed by the MTT assay and was similar to the motility results. These concentrations, including 10 μg ml−1, prevented microfilarial release by females in a concentration- and time-dependent manner. Concentrations higher than 100 μg ml−1 even induced mortality of the microfilariae. The present study suggested that the ethanol extract of Neurolaena lobata has potential macro- and micro-filaricidal activities.