Drug transport mechanisms in helminth parasites: passive diffusion of benzimidazole anthelmintics

MOTTIER, L.; ALVAREZ, L.; CEBALLOS, L.; LANUSSE, C.

EXPERIMENTAL PARASITOLOGY

ACADEMIC PRESS INC ELSEVIER SCIENCE

Año: 2006 vol. 113 p. 49 - 57

0014-4894

  Anthelmintic molecules must reach their receptors inside target parasites to finally exert the pharmacological effect. Previous work indicates that the main route of entry of antiparasitic drugs into helminth parasites would be through the external surface of the worms. However, it has not been demonstrated until now if trans-tegumental/cuticular penetration over oral ingestion is the most important way of entry of benzimidazole anthelmintics into their target parasites. Even more, it has neither been shown if this phenomenon would be regulated by passive diffusion or active transport. The goal of the work reported here was to determine the main processes involved on the entry of benzimidazole anthelmintic molecules into the three main classes of helminth parasites. Adult specimens of Moniezia benedeni (cestode), Fasciola hepatica (trematode) and Ascaris suum (nematode) were incubated in Krebs Ringer Tris buffer (pH 7.4, 37oC) (1 g parasite/10 ml incubation medium) for 15, 45 and 90 min, respectively, in the presence of a concentration gradient of fenbendazole, oxfendazole or triclabendazole sulphoxide (1-30 nmol/ml, n= 4). Dead specimens were also incubated with the same drug concentration gradient. Liver flukes with the oral route closed off by ligation were incubated with TCBZSO in the presence or absence of bovine serum albumin. After the incubation times elapsed, samples of parasite material were chemically extracted and prepared for high performance liquid chromatography analysis to measure drug/metabolite concentrations. Equal drug concentrations were measured inside ligated and non-ligated liver flukes demonstrating that BZD do mainly penetrate by trans-tegumental diffusion. The higher the concentration of BZD molecules in the incubation medium, the greater their concentration inside the helminth parasites. High correlations were obtained after linear regression analysis between initial drug concentration in the incubation medium and drug concentration measured inside the nematode, cestode and trematode parasites (r>0.98). The results obtained demonstrated that the main mechanism of entry of benzimidazole anthelmintics into target helminth parasites is passing through the external surface of them and drug accumulation occurs by a passive diffusion process.