Localization of multidrug resistance-associated proteins along the blood-testis barrier in rat, macaque, and human testis

Abstract

The blood-testis barrier (BTB) prevents the entry of many drugs into seminiferous tubules, which can be beneficial for therapy not intended for the testis but may decrease drug efficacy for medications requiring entry to the testis. Previous data have shown that some of the transporters in the multidrug resistance-associated protein (MRP) family (ABCC) are expressed in the testis. By determining the subcellular localization of these transporters, their physiologic function and effect on drug disposition may be better predicted. Using immunohistochemistry (IHC), we determined the site of expression of the MRP transporters expressed in the testis, namely, MRP1, MRP4, MRP5, and MRP8, from immature and mature rats, rhesus macaques, and adult humans. We determined that in all species MRP1 was restricted to the basolateral membrane of Sertoli cells, MRP5 is located in Leydig cells, and MRP8 is located in round spermatids, whereas MRP4 showed species-specific localization. MRP4 is expressed on the basolateral membrane of Sertoli cells in human and nonhuman primates, but on the apical membrane of Sertoli cells in immature and mature rats, representing a potential caution when using rat models as a means for studying drug disposition across the BTB. These data suggest that MRP1 may limit drug disposition into seminiferous tubules, as may MRP4 in human and nonhuman primates but not in rats. These data also suggest that MRP5 and MRP8 may not have a major impact on the penetration of drugs across the BTB.

Fig. 1.

MRP1 localization in the testis. Immunohistochemical staining for MRP1 in formalin-fixed paraffin-embedded immature (A) or mature (B) rat testes, mature rhesus macaque (C), or mature human (D) is shown at magnification 40×. Black bar in panel A indicates length of 10 microns. Arrows indicate positive (brown) staining for proteins.

Fig. 2.

MRP4 localization in the testis. Immunohistochemical staining for MRP4 in formalin-fixed paraffin-embedded immature (A) or mature (B) rat testes, mature rhesus macaque (C), mature human (D), mature mouse (E), or MRP4⁻/⁻ mouse (F) is shown at magnification 40×. Black bar in panel A indicates length of 10 microns. Arrows indicate positive (brown) staining for proteins.

Fig. 3.

MRP5 localization in the testis. Immunohistochemical staining for MRP5 in formalin-fixed paraffin-embedded immature (A) or mature (B) rat testes, mature rhesus macaque (C), or mature human (D) is shown at magnification 40×. Black bar in panel A indicates length of 10 microns. Arrows indicate positive (brown) staining for proteins.

Fig. 4.

MRP8 localization in the testis. Immunohistochemical staining for MRP8 in formalin-fixed paraffin-embedded mature rhesus macaque (A) or mature human (B) is shown at 40 × magnification. Black bar in panel A indicates length of 10 microns. Arrows indicate positive (brown) staining for proteins.