Comparative assessment of the access of albendazole, fenbendazole and triclabendazole toFasciola hepatica: effect of bile in the incubation medium

Abstract

The work reported here describes the comparative ability of albendazole (ABZ), fenbendazole (FBZ) and triclabendazole (TCBZ) to penetrate through the tegument of mature Fasciola hepatica, and the influence of the physicochemical composition of the incubation medium on the drug diffusion process. The data obtained from the trans-tegumental diffusion kinetic studies were complemented with the determination of lipid-to-water partition coefficients (octanol-water) for the benzimidazole (BZD) anthelmintic drugs assayed. Sixteen-week-old F. hepatica were obtained from untreated artificially infected sheep. The flukes were incubated (37 degrees C) over 60 and 90 min in incubation media (pH 7.4) prepared with different proportions of ovine bile and Krebs' Ringer Tris (KRT) buffer (100, 75, 50, 25 and 0% of bile) containing either ABZ, FBZ or TCBZ at a final concentration of 5 nmol/ml. After the incubation time expired, the liver fluke material was chemically processed and analysed by high performance liquid chromatography (HPLC) to measure drug concentrations within the parasite. Additionally, the octanol-water partition coefficients (PC) for each molecule were calculated (as an indicator of drug lipophilicity) using reversed phase HPLC. The 3 BZD molecules were recovered from F. hepatica at both incubation times in all incubation media assayed. The trans-tegumental diffusion of the most lipophilic molecules ABZ and FBZ (higher PC values) tended to be greater than that observed for TCBZ. Interestingly, the uptake of ABZ by the liver flukes was significantly greater than that measured for TCBZ, the most widely used flukicidal BZD compound. This differential uptake pattern may be a relevant issue to be considered to deal with TCBZ-resistant flukes. Drug concentrations measured within the parasite were lower in the incubations containing the highest bile proportions. The highest total availabilities of the 3 compounds were obtained in liver flukes incubated in the absence of bile. Altogether, these findings demonstrated that the entry of the drug into a target parasite may not only depend on a concentration gradient, the lipophilicity of the molecule and absorption surface, but also on the physicochemical composition of the parasite's surrounding environment.

Understanding the main route of drug entry in adult Fasciola hepatica: Further insights into closantel pharmacological activity

“…Only 7.4 % of drug available in ovine bile was able to diffuse into the parasite. Similar results were previously described by Alvarez et al (2004) starvation (Skuce and Fairweather, 1990). In addition, CLS reduces the availability of ATP, needed (for example) for the energy-demanding processes of gametogenesis and oogenesis, and it has been associated in cattle with a decrease in parasite egg production (Hanna et al, 2006).…”

“…The acquisition of broad-spectrum anthelmintics by liver flukes could be by passive diffusion through their tegument (Alvarez et al, 2000(Alvarez et al, , 2001. However, drug diffusion depends on different factors, such as molecule lipophilicity, molecular size, concentration gradient, surface area of contact between drug and parasite (Mottier et al 2006) and the physico-chemical properties of the surrounding parasite environment (Alvarez et al, 2004). Clearly, under ex vivo conditions, the presence of bile modified the diffusion and accumulation of CLS into the parasite, decreasing it by 72 % compared with that observed after incubation in RPMI medium.…”

Inhibition of cytochrome P450 activity enhances the systemic availability of triclabendazole metabolites in sheep

“…While the FMO system was found as the main enzymatic pathway involved in the sulphoxidation of TCBZ (yielding ∼77% of TCBZSO production), both enzymatic systems participate in a similar proportion in the sulphonation reaction to form the sulphone metabolite. Studies on ex vivo drug diffusion into TCBZ‐susceptible Fasciola hepatica , demonstrated that TCBZ, TCBZSO and TCBZSO 2 have the capability to penetrate the fluke′s tegument (Alvarez et al. , 2004).…”

A transmission electron microscope study on the route of entry of triclabendazole into the liver fluke,Fasciola hepatica

“…The tegument plays an important role in the uptake of nutrients such as glucose and amino acids into the liver fluke, in addition to roles in sensory perception, osmoregulation and protection against the host's immune response, for example (Fairweather et al 1999). The tegument of trematode and cestode parasites has been shown to be the primary site of anthelmintic entry (Alvarez et al 2000, 2001, 2004, 2007; Mottier et al 2003, 2006 a ). Similarly, the cuticle has been demonstrated as an important interface of drug uptake in nematodes (Ho et al 1990; Sims et al 1996; Cross et al 1998).…”