Verapamil P-glycoprotein Transport across the Rat Blood-Brain Barrier: Cyclosporine, a Concentration Inhibition Analysis, and Comparison with Human Data

Abstract

To predict the magnitude of P-glycoprotein (P-gp)-based drug interactions at the human blood-brain barrier (BBB), rodent studies are routinely conducted where P-gp is chemically inhibited. For such studies to be predictive of interactions at the human BBB, the plasma concentration of the P-gp inhibitor must be comparable with that observed in the clinic. Therefore, we determined the in vivo EC 50 of P-gp inhibition at the rat BBB using verapamil as a model P-gp substrate and cyclosporine A (CsA) as the model P-gp inhibitor. Under isoflurane anesthesia, male Sprague-Dawley rats were administered i.v. CsA to achieve pseudo steady-state CsA blood concentrations ranging from 0 to ϳ12 M. Then, an i.v. tracer dose of [ 3 H]verapamil was administered, and 20 min after verapamil administration, the animals were sacrificed for determination of blood, plasma, and brain 3 H radioactivity by scintillation counting. The percentage increase in the brain/blood 3 H radioactivity (relative to 0 M CsA) was described by the Hill equation with E max , 1290%; EC 50 , 7.2 M; and ␥, 3.8. Previously, using [11 C]verapamil, we have shown that the human brain/blood 11 C radioactivity was increased by 79% at 2.8 M CsA blood concentration. At an equivalent CsA blood concentration, the rat brain/blood 3 H radioactivity was increased by a remarkably similar extent of 75%. This is the first time that an in vivo CsA EC 50 of P-gp inhibition at the rat BBB has been determined and the magnitude of such inhibition was compared between the rat and the human BBB at the same blood CsA concentration.

Progress in Brain Penetration Evaluation in Drug Discovery and Development

“…Using daunorubicin, digoxin, and cyclosporine A as P-gp substrates, we observed that the IC 50 of quinidine and verapamil in human, monkey, canine, rat, and mouse P-gp-transfected cells could vary by 6-fold, although the majority of the IC 50 values are within 2-fold. In contrast, the K p of verapamil increased by 78% in rats and 75% in humans where plasma concentration of cyclosporine was 2.8 M, indicating no species difference for verapamil-cyclosporine DDI (Hsiao et al, 2006).…”

Species Differences in Blood-Brain Barrier Transport of Three Positron Emission Tomography Radioligands with Emphasis on P-Glycoprotein Transport

“…11 C]verapamil in the human and rat brain after treatment with low doses of the potent in vivo P-gp inhibitor cyclosporin A (CsA), they did not observe any species differences (Hsiao et al, 2006). Other explanations could be species differences in blood-brain barrier transport that are not related to P-gp function, but rather to other causes, e.g., tightness of the endothelial cell tight junctions or expression of other active efflux transporters.…”

“…In vivo evidence for species differences in P-gp function has so far only been reported by one group, who compared rats and guinea pigs and found that higher concentrations of the P-gp inhibitor GF-120918 were needed in guinea pigs than in rats to achieve the same increase in brain concentrations of an undisclosed P-gp substrate (Cutler et al, 2006). In contrast, when Hsiao et al (2006) compared the increase of […”

Characterization of P-Glycoprotein Humanized Mice Generated by Chromosome Engineering Technology: Its Utility for Prediction of Drug Distribution to the Brain in Humans

“…Since previously reported P-gp humanized mice did not express functional P-gp at the BBB (Sadiq et al, 2015), the hMDR1-MAC mouse is the first P-gp humanized mouse model expressing functional P-gp in brain capillaries. Furthermore, the mice may be valuable for predicting P-gpmediated drug-drug interactions at the BBB, although the effect of a P-gp inhibitor on the brain distribution of drugs is limited in a clinical setting (Sasongko et al, 2005;Hsiao et al, 2006;Muzi et al, 2009;Wagner et al, 2009;Bauer et al, 2015).…”