Glutamate-Mediated Down-Regulation of the Multidrug-Resistance Protein BCRP/ABCG2 in Porcine and Human Brain Capillaries

Abstract

Breast cancer resistance protein (BCRP) functions as a major molecular gatekeeper at the blood-brain barrier. Considering its impact on access to the brain by therapeutic drugs and harmful xenobiotics, it is of particular interest to elucidate the mechanisms of its regulation. Excessive glutamate concentrations have been reported during epileptic seizures or as a consequence of different brain insults including brain ischemia. Previously, we have demonstrated that glutamate can trigger an induction of the transporter P-glycoprotein. These findings raised the question whether other efflux transporters are affected in a comparable manner. Glutamate exposure proved to down-regulate BCRP transport function and expression in isolated porcine capillaries. The reduction was efficaciously prevented by coincubation with N-methyl-d-aspartate (NMDA) receptor antagonist MK-801. The involvement of the NMDA receptor in the down-regulation of BCRP was further confirmed by experiments showing an effect of NMDA exposure on brain capillary BCRP transport function and expression. Pharmacological targeting of cyclooxygenase-1 and -2 (COX-1 and -2) using the nonselective inhibitor indomethacin, COX-1 inhibitor SC-560, and COX-2 inhibitor celecoxib revealed a contribution of COX-2 activity to the NMDA receptor's downstream signaling events affecting BCRP. Translational studies were performed using human capillaries isolated from surgical specimens of epilepsy patients. The findings confirmed a glutamate-induced down-regulation of BCRP transport activity in human capillaries, which argued against major species differences. In conclusion, our data reveal a novel mechanism of BCRP down-regulation in porcine and human brain capillaries. Moreover, together with previous data sets for P-glycoprotein, the findings point to a contrasting impact of the signaling pathway on the regulation of BCRP and P-glycoprotein. The effect of glutamate and arachidonic acid signaling on BCRP function might have implications for brain drug delivery and for radiotracer brain access in epilepsy patients and patients with other brain insults.

The expression of inflammatory markers and their potential influence on efflux transporters in drug‐resistant mesial temporal lobe epilepsy tissue

“…It is also possible that the activity of COX‐2—not its expression—is what correlates with P‐gp expression. This could also explain why we observed no relationship between COX‐2 and BCRP expression, in contrast to previous findings from Salvamoser and colleagues …”

Regulation of ABC efflux transporters at blood-brain barrier in health and neurological disorders

“…These authors provided evidence for the contribution of NMDA/COX-2 cascade to the down regulation of BCRP expression and activity in porcine capillaries. Moreover, using human capillaries isolated from surgical specimens of epilepsy patients, they were able to confirm a glutamate-induced down-regulation of BCRP expression and activity in human capillaries, which argued against major species differences (Salvamoser et al, 2015). In similar study, the same group showed that MRP2 expression and activity increased significantly in porcine and human BBB models after exposure to glutamate.…”

“…While Yousif et al showed a significant increase in BCRP expression at rat BBB mediated by NMDA/COX-2 cascade (Yousif et al, 2012), a recent report by Salvamoser et al showed that glutamate exposure decreased BCRP expression and activity in isolated porcine capillaries (Salvamoser et al, 2015). These authors provided evidence for the contribution of NMDA/COX-2 cascade to the down regulation of BCRP expression and activity in porcine capillaries.…”

Drug-Resistant Epilepsy: Multiple Hypotheses, Few Answers

“…In addition, evidence from in vitro and in vivo rodent studies suggests that targeting this pathway could control P-gp expression and activity levels, and thus, help increase ASD brain penetration and improve ASD efficacy to control seizures in drug-resistant epilepsy (131, 137–139). One study of Salvamoser et al (140) showed that exposing isolated porcine brain capillaries and human brain capillaries from ASD-resistant patients with FCD to glutamate resulted in reduced BCRP protein expression levels. This finding is in contrast with data from human studies comparing BCRP expression between control and epileptic human brain tissue (89, 90, 92, 95), and unpublished data from our lab clearly demonstrate seizure-induced upregulation of BCRP protein expression and activity levels in brain capillaries from chronic epileptic rats.…”