Abstract
Filariae are parasitic nematodes that are transmitted to their definitive host as third-stage larvae by arthropod vectors like mosquitoes. Filariae cause diseases including: lymphatic filariasis with distressing and disturbing symptoms like elephantiasis; and river blindness. Filarial diseases affect millions of people in 73 countries throughout the topics and sub-tropics. The drugs available for mass drug administration, (ivermectin, albendazole and diethylcarbamazine), are ineffective against adult filariae (macrofilariae) at the registered dosing regimen; this generates a real and urgent need to identify effective macrofilaricides. Emodepside, a veterinary anthelmintic registered for treatment of nematode infections in cats and dogs, is reported to have macrofilaricidal effects. Here, we explore the mode of action of emodepside using adult Brugia malayi, one of the species that causes lymphatic filariasis. Whole-parasite motility measurement with Worminator and patch-clamp of single muscle cells show that emodepside potently inhibits motility by activating voltage-gated potassium channels and that the male is more sensitive than the female. RNAi knock down suggests that emodepside targets SLO-1 K channels. We expressed slo-1 isoforms, with alternatively spliced exons at the RCK1 (Regulator of Conductance of Potassium) domain, heterologously in Xenopus laevis oocytes. We discovered that the slo-1f isoform, found in muscles of males, is more sensitive to emodepside than the slo-1a isoform found in muscles of females; and selective RNAi of the slo-1a isoform in female worms increased emodepside potency. In Onchocerca volvulus, that causes river blindness, we found two isoforms in adult females with homology to Bma-SLO-1A and Bma-SLO-1F at the RCK1 domain. In silico modeling identified an emodepside binding pocket in the same RCK1 region of different species of filaria that is affected by these splice variations. Our observations show that emodepside has potent macrofilaricidal effects and alternative splicing in the RCK1 binding pocket affects potency. Therefore, the evaluation of potential sex-dependent effects of an anthelmintic compound is of importance to prevent any under-dosing of one or the other gender of nematodes once given to patients.
Highlights
Emodepside as a macrofilaricideFilariae are parasitic nematodes that reside in the definitive host which are always mammals
We demonstrate selectively knocking down the slo-1a splice variant in female B. malayi increases emodepside efficacy, signifying a dominant suppressor role for SLO-1A
When we treated the slo-1 knock down worms with 300nM emodepside and measured their motility over a period of two hours, we found that worms treated with slo-1 specific dsRNA were resistant to emodepside as compared to lacZ dsRNA treated control worms (Fig 3C)
Summary
Emodepside as a macrofilaricideFilariae are parasitic nematodes that reside in the definitive host which are always mammals. The adult females release microscopic juveniles, microfilariae, which are ingested during a blood meal by the arthropod vectors. These microfilariae develop in the arthropod host to the infectious third-stage larvae which can be transmitted to the mammalian host during a subsequent blood meal. The filaroide species that are responsible for most of the morbidity are Wuchereria bancrofti, Brugia malayi and Brugia timori that cause lymphatic filariasis (including elephantiasis), and Onchocerca volvulus that causes river blindness (onchocerciasis) [1]. These diseases occur mostly in sub-Saharan Africa and Southeast Asia and affect 168 million people. The MDA programs have been successful in several countries, but the filarial diseases still persist, and have not been eliminated [2]
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