Blood-to-Testis Transport of Ribavirin Involves Carrier-Mediated Processes at the Blood-Testis Barrier

Ribavirin, an antiretroviral agent targeting the hepatitis C virus, causes male reproductive toxicity. This study investigated the mechanism of ribavirin transport at the blood-testis barrier (BTB). In vivo mouse integration plot analysis after intravenous administration revealed that the net influx clearance of [³H]ribavirin in the testis was 3.6-fold greater than that of [¹⁴C]D-mannitol, a paracellular transport marker, implying transcellular transport of ribavirin across the BTB. Moreover, [³H]ribavirin uptake by TM4 cells, mouse-derived Sertoli cells, was time- and concentration-dependent, with a K_m value of 2.49 mM. S-[(4-nitrophenyl)methyl]-6-thioinosine, an inhibitor of Na⁺-independent equilibrative nucleoside transporters (ENTs), strongly inhibited the [³H]ribavirin uptake by TM4 cells at 100 µM. Compared to the uptake of [³H]adenosine, a typical endogenous nucleoside, [³H]ribavirin uptake was relatively similar to ENT2 transport. [³H]Ribavirin uptake was also observed in mouse ENT2-expressing Xenopus laevis oocytes, and gene silencing via the transfection of ENT2 small interfering RNA significantly reduced the [³H]ribavirin transport into TM4 cells by 13%. Taken together, these results suggest that ENT2 partially contributes to ribavirin transport at the BTB.