Dataset Information

Drug transporter, P-glycoprotein (MDR1), is an integrated component of the mammalian blood-testis barrier.

ABSTRACT: Throughout spermatogenesis, leptotene spermatocytes traverse the blood-testis barrier (BTB) to enter the adluminal compartment of the seminiferous epithelium for continued development. At the same time, the integrity of the BTB, which is constituted by co-existing tight junctions (TJ), basal ectoplasmic specializations (basal ES) and desmosome-like junctions, must be maintained since a breach in barrier function can result in spermatogenic arrest and even infertility. There is evidence to suggest that drug transporters may function at the BTB, but little is known about how they contribute to spermatogenesis. In this study, we investigate the role of P-glycoprotein (P-gp), a drug efflux pump, in BTB dynamics. A survey by RT-PCR revealed several transporter genes to be expressed by the testis, including Mdr1 (gene symbol for P-gp), Mrp1, Abcc5 and Slc15a1. It was also demonstrated that P-gp localizes to the BTB in all stages of the seminiferous epithelial cycle in the adult rat testis, as well as to the Sertoli cell-elongated spermatid interface in stages VII and VIII. We continued our study by examining the levels of several transporters in the testis following oral administration of Adjudin, a compound known to affect Sertoli-germ cell adhesion. In this experiment, the steady-state levels of P-gp, MRP1, ABCG1 and SLC15A1 were all found to increase by several-fold within hours of Adjudin treatment during junction restructuring. More importantly, an increase in P-gp association with TJ proteins (e.g., occludin, claudin-11 and JAM-A) was noted when testis lysates from Adjudin-treated rats were used for co-immunoprecipitation experiments, suggesting that P-gp may enhance BTB function during Sertoli-germ cell junction restructuring.

SUBMITTER: Su L

PROVIDER: S-EPMC2783494 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature

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Drug transporter, P-glycoprotein (MDR1), is an integrated component of the mammalian blood-testis barrier.

Su Linlin L Cheng C Yan CY Mruk Dolores D DD

The international journal of biochemistry & cell biology 20090829 12

Throughout spermatogenesis, leptotene spermatocytes traverse the blood-testis barrier (BTB) to enter the adluminal compartment of the seminiferous epithelium for continued development. At the same time, the integrity of the BTB, which is constituted by co-existing tight junctions (TJ), basal ectoplasmic specializations (basal ES) and desmosome-like junctions, must be maintained since a breach in barrier function can result in spermatogenic arrest and even infertility. There is evidence to sugges ...[more]

PMID: 19720156

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Project description:The adenosine triphosphate-binding cassette transporter P-glycoprotein (ABCB1/Abcb1a) restricts at the blood-brain barrier (BBB) brain distribution of many drugs. ABCB1 may be involved in drug-drug interactions (DDIs) at the BBB, which may lead to changes in brain distribution and central nervous system side effects of drugs. Positron emission tomography (PET) with the ABCB1 substrates (R)-[(11)C]verapamil and [(11)C]-N-desmethyl-loperamide and the ABCB1 inhibitor tariquidar has allowed direct comparison of ABCB1-mediated DDIs at the rodent and human BBB. In this work we evaluated different factors which could influence the magnitude of the interaction between tariquidar and (R)-[(11)C]verapamil or [(11)C]-N-desmethyl-loperamide at the BBB and thereby contribute to previously observed species differences between rodents and humans. We performed in vitro transport experiments with [(3)H]verapamil and [(3)H]-N-desmethyl-loperamide in ABCB1 and Abcb1a overexpressing cell lines. Moreover we conducted in vivo PET experiments and biodistribution studies with (R)-[(11)C]verapamil and [(11)C]-N-desmethyl-loperamide in wild-type mice without and with tariquidar pretreatment and in homozygous Abcb1a/1b((-/-)) and heterozygous Abcb1a/1b((+/-)) mice. We found no differences for in vitro transport of [(3)H]verapamil and [(3)H]-N-desmethyl-loperamide by ABCB1 and Abcb1a and its inhibition by tariquidar. [(3)H]-N-Desmethyl-loperamide was transported with a 5 to 9 times higher transport ratio than [(3)H]verapamil in ABCB1- and Abcb1a-transfected cells. In vivo, brain radioactivity concentrations were lower for [(11)C]-N-desmethyl-loperamide than for (R)-[(11)C]verapamil. Both radiotracers showed tariquidar dose dependent increases in brain distribution with tariquidar half-maximum inhibitory concentrations (IC50) of 1052 nM (95% confidence interval CI: 930-1189) for (R)-[(11)C]verapamil and 1329 nM (95% CI: 980-1801) for [(11)C]-N-desmethyl-loperamide. In homozygous Abcb1a/1b((-/-)) mice brain radioactivity distribution was increased by 3.9- and 2.8-fold and in heterozygous Abcb1a/1b((+/-)) mice by 1.5- and 1.1-fold, for (R)-[(11)C]verapamil and [(11)C]-N-desmethyl-loperamide, respectively, as compared with wild-type mice. For both radiotracers radiolabeled metabolites were detected in plasma and brain. When brain and plasma radioactivity concentrations were corrected for radiolabeled metabolites, brain distribution of (R)-[(11)C]verapamil and [(11)C]-N-desmethyl-loperamide was increased in tariquidar (15 mg/kg) treated animals by 14.1- and 18.3-fold, respectively, as compared with vehicle group. Isoflurane anesthesia altered [(11)C]-N-desmethyl-loperamide but not (R)-[(11)C]verapamil metabolism, and this had a direct effect on the magnitude of the increase in brain distribution following ABCB1 inhibition. Our data furthermore suggest that in the absence of ABCB1 function brain distribution of [(11)C]-N-desmethyl-loperamide but not (R)-[(11)C]verapamil may depend on cerebral blood flow. In conclusion, we have identified a number of important factors, i.e., substrate affinity to ABCB1, brain uptake of radiolabeled metabolites, anesthesia, and cerebral blood flow, which can directly influence the magnitude of ABCB1-mediated DDIs at the BBB and should therefore be taken into consideration when interpreting PET results.

Dataset Information

Drug transporter, P-glycoprotein (MDR1), is an integrated component of the mammalian blood-testis barrier.

Publications

Drug transporter, P-glycoprotein (MDR1), is an integrated component of the mammalian blood-testis barrier.

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