Sex-specific differences in organic anion transporting polypeptide 1a4 (Oatp1a4) functional expression at the blood–brain barrier in Sprague–Dawley rats

BACKGROUND: Targeting endogenous blood–brain barrier (BBB) transporters such as organic anion transporting polypeptide 1a4 (Oatp1a4) can facilitate drug delivery for treatment of neurological diseases. Advancement of Oatp targeting for optimization of CNS drug delivery requires characterization of sex-specific differences in BBB expression and/or activity of this transporter. METHODS: In this study, we investigated sex differences in Oatp1a4 functional expression at the BBB in adult and prepubertal (i.e., 6-week-old) Sprague–Dawley rats. We also performed castration or ovariectomy surgeries to assess the role of gonadal hormones on Oatp1a4 protein expression and transport activity at the BBB. Slco1a4 (i.e., the gene encoding Oatp1a4) mRNA expression and Oatp1a4 protein expression in brain microvessels was determined using quantitative real-time PCR and western blot analysis, respectively. Oatp transport function at the BBB was determined via in situ brain perfusion using [(3)H]taurocholate and [(3)H]atorvastatin as probe substrates. Data were expressed as mean ± SD and analyzed via one-way ANOVA followed by the post hoc Bonferroni t-test. RESULTS: Our results showed increased brain microvascular Slco1a4 mRNA and Oatp1a4 protein expression as well as increased brain uptake of [(3)H]taurocholate and [(3)H]atorvastatin in female rats as compared to males. Oatp1a4 expression at the BBB was enhanced in castrated male animals but was not affected by ovariectomy in female animals. In prepubertal rats, no sex-specific differences in brain microvascular Oatp1a4 expression were observed. Brain accumulation of [(3)H]taurocholate in male rats was increased following castration as compared to controls. In contrast, there was no difference in [(3)H]taurocholate brain uptake between ovariectomized and control female rats. CONCLUSIONS: These novel data confirm sex-specific differences in BBB Oatp1a4 functional expression, findings that have profound implications for treatment of CNS diseases. Studies are ongoing to fully characterize molecular pathways that regulate sex differences in Oatp1a4 expression and activity.