Date Published: February 23, 2018
Publisher: Public Library of Science
Author(s): Luiza Almeida Figueiredo, Thais Fuscaldi Rebouças, Sebastião Rodrigo Ferreira, Gabriela Flavia Rodrigues-Luiz, Rodrigo Cambraia Miranda, Ricardo Nascimento Araujo, Ricardo Toshio Fujiwara, Rui Lu.
While diseases caused by nematodes remains a considerable drawback for the livestock, agriculture and public health, anthelmintics drug resistance has been observed over the past years and is a major concern for parasite control. Ivermectin, initially considered as a highly potent drug, currently presents a reduced anti-helminthic efficacy, which is influenced by expression of several ATP-binding cassette transporters (ABC), among them the P-glycoproteins (Pgps). Here we present some evidences of Pgps dominance during Ivermectin resistance/susceptibility using Pgps double silencing in C. elegans and the phylogenetic relationship of Pgps among nematodes, which strengthen the use of this model for study of drug resistance in nematodes. Firstly, we evaluated the quantitative gene expression of 12 out the 15 known Pgps from resistant and WT strains of C. elegans, we demonstrated the upregulation of Pgps 12 and 13 and downregulation of all remaining Pgps in ivermectin resistant strain. By using an RNAi loss-of-function approach we observed that Pgp 12 gene silencing reverts the resistance phenotype to ivermectin, while Pgp 4 gene silencing does not alter the resistance phenotype but induces a resistance in wild type strain. Interestingly, the dual silencing of Pgp 12 and Pgp 4 expression demonstrates the dominance of phenotype promoted by Pgp 12 silencing. Finally, in silico analysis reveals a close relationship between Pgps from C. elegans and several nematodes parasites. Taken together, our results indicate that Pgp 12 is crucial for the resistance to ivermectin and thus a good candidate for further studies aiming to develop specific inhibitors to this transporter, allowing the continuous use of ivermectin to control the burden on animal and human health inflicted by nematode parasites globally.
Diseases caused by nematodes remains a considerable drawback for the livestock, agriculture and public health, contributing to increasing production costs, decreased food supply and deficits in host health [1–2]. Programs for parasite control are culturally performed through employment of anthelmintics and the improper use of these drugs for treatment of human and animal populations, like underdosing, contributes to selection of resistant parasites [3–5]. Ivermectin is an important macrocyclic lactone (ML) and the most commonly used drug to treat parasitic nematode infections of the gastrointestinal tract, the lungs, filarial infections and infestations with arthropods . The ubiquitous use of this drug has led to the selection of resistance in several target species including Cooperia oncophora , Haemonchus contortus , Ostertagia spp. , Trichostrongylus spp. , Onchocerca volvulus [4, 9–10] and Dirofilaria immitis [11–12].
Initially considered as a highly potent drug, ivermectin has now a reduced anti-helminthic efficacy and therefore research on the possible mechanisms of resistance are important, especially in the light of the negative effects of diseases caused by parasitic nematodes in animal [31–32] and in human [33–34] healthcare. Previous studies revealed the involvement of Pgps in the development of ivermectin resistance in various nematodes [16, 19–20], including the free-living nematode, C. elegans [35–37]. We have confirmed some of these results and extended the study on the role of Pgps in ivermectin resistance developed by C. elegans to show that Pgp 4 might be directly related to susceptible phenotype and that Pgp 12 directly related to resistant phenotype in this worm. In addition, we show that Pgps 1 to 13 of C. elegans have a close phylogenetic relationship to Pgps of other parasitic nematodes.
In conclusion, here we show that Pgp 12 is a good candidate for further studies aiming to develop specific inhibitors to this transporter so that ivermectin can still be used to control the burden on animal and human health inflicted by nematode parasites globally.