Identification and characterization of the Fasciola hepatica sodium- and chloride-dependent taurine transporter.

Bulut Hamali,Sandra Pichler,Martina Molin,Marion Holy,Oliver Kudlacek,Michael Freissmuth,Melanie Burger,Klaus Schicker,Eva Maria Sehr,Elisabeth Wischnitzki,Kathrin Jaentsch,Robert M Greenberg

doi:10.1371/journal.pntd.0006428

Bulut Hamali, Sandra Pichler + Show 10 more

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https://doi.org/10.1371/journal.pntd.0006428

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Abstract

The parasitic liver fluke Fasciola hepatica infests mainly ruminants, but it can also cause fasciolosis in people, who ingest the metacercariae encysted on plants. The drug of choice to treat fasciolosis is triclabendazole (TBZ), which has been on the market for several decades. This is also true for the other available drugs. Accordingly, drug-resistant flukes have been emerging at an increasing rate making it desirable to identify alternative drug targets. Here, we focused on the fact that adult F. hepatica persists in the hostile environment of the bile ducts of infected organisms. A common way to render bile acids less toxic is to conjugate them to taurine (2-aminoethanesulfonic acid). We cloned a transporter from the solute carrier-6 (SLC6) family, which was most closely related to the GABA-transporter-2 of other organisms. When heterologously expressed, this F. hepatica transporter supported the high-affinity cellular uptake of taurine (KM = 12.0 ± 0.5 μM) but not of GABA. Substrate uptake was dependent on Na+- and Cl- (calculated stoichiometry 2:1). Consistent with the low chloride concentration in mammalian bile, the F. hepatica transporter had a higher apparent affinity for Cl- (EC50 = 14±3 mM) than the human taurine transporter (EC50 = 55±7 mM). We incubated flukes with unconjugated bile acids in the presence and absence of taurine: taurine promoted survival of flukes; the taurine transporter inhibitor guanidinoethansulfonic acid abolished this protective effect of taurine. Based on these observations, we conclude that the taurine transporter is critical for the survival of liver flukes in the bile. Thus, the taurine transporter represents a candidate drug target.

Highlights

Liver flukes of the genus Fasciola are parasitic trematodes, which infest mammals all over the world
The liver fluke F. hepatica imposes an economic burden by infesting domestic ruminants
Transcripts encoding the orthologue of the human taurine transporter SLC6A6 were identified from a sequence database including mRNA data of adult F. hepatica [22]

Summary

Introduction

Liver flukes of the genus Fasciola are parasitic trematodes, which infest mammals all over the world. People are infested by ingestion of metacercariae encysted on plants or ingestion of water containing metacercariae This can give rise to regional pockets of endemic infections, e.g. on the Bolivian Altiplano [6], but it is relevant to human health worldwide: conservative estimates indicate that more than 2.5 million people are infested and suffer from various forms of fasciolosis [7]. The juvenile flukes migrate to the liver—presumably using the curvature of the abdominal wall as a guidance clue [11]. They subsequently burrow through the liver capsule and feed on the tissue for several weeks, until they are mature. By contrast with F. hepatica, the Chinese liver fluke Clonorchis sinensis invades the bile duct within two days after excysting. In spite of the differences in their life cycles, F. hepatica, C. sinensis and O. viverrini eventually face the same hostile environment of the bile

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