Expression and Immunolocalization of Xenobiotic Transporters at the Human Blood-Testis Barrier

The blood‐testis barrier (BTB) is formed by basal tight junctions between adjacent Sertoli cells of the seminiferous tubules and functions as a physical barrier to protect developing germ cells in the adluminal compartment from reproductive toxicants. Multiple xenobiotics are known to cross into the male genital tract (MGT) including male contraceptives, cancer chemotherapeutics, and environmental toxicants, although the mechanism(s) for their movement into the MGT is(are) largely unknown. Previous studies showed that several ATP‐binding cassette (ABC) and solute carrier (SLC) superfamily transporters are expressed in the testes and could potentially facilitate the disposition of xenobiotics into the MGT through concurrent uptake and efflux mechanisms. This study aimed to determine the expression and localization of xenobiotic transporters that may facilitate transepithelial transport across the human BTB. We used immunofluorescence staining to determine the cellular localization of these transporters in the several cell types found in human testes. OAT1, OAT2, OCTN1, and MRP3 were primarily localized to the basal membrane of Sertoli cells, whereas OCTN2, MRP6, and MRP7 were localized to both the basal membrane of Sertoli cells and the peritubular myoid cells that surround the basal membrane of Sertoli cells. Interestingly, CNT2 was localized to the lateral membranes of Sertoli cells and the peritubular myoid cells. OCT1, OCT2, and OCT3 were localized to the peritubular myoid cells and the Leydig cells, although there was moderate staining of spermatogenic cell membranes. However, definitive staining of CNT1, OAT3, MATE1, MATE2, OATP1A2, OATP1B1, OATP1B3, OATP1C1, OATP2A1, OATP2B1, OATP3A1, OATP4A1, and OATP6A1 was not observed due to non‐specific antibody staining or an absence of staining. The localization of CNT2, OAT1, OAT2, OCT1, OCT2, OCT3, OCTN1, OCTN2, MRP3, MRP6, and MRP7 suggests these transporters may contribute to the mechanism(s) by which xenobiotics can cross the BTB. Taken together, the localization of these pharmacologically relevant transporters provides insight into the selectivity of drug disposition across the BTB and may be useful in developing tools to understand and overcome the pharmacokinetic and pharmacodynamic difficulties presented by the BTB. Support or Funding Information 5R01GM123643‐045R01GM129777‐02 P30CA023074