Induction of P-Glycoprotein Function can be Measured with [F]MC225 and PET.

P-Glycoprotein (P-gp) is an efflux pump located at the blood-brain barrier (BBB) that contributes to the protection of the central nervous system by transporting neurotoxic compounds out of the brain. A decline in P-gp function has been related to the pathogenesis of neurodegenerative diseases. P-gp inducers can increase the P-gp function and are considered as potential candidates for the treatment of such disorders. The P-gp inducer MC111 increased P-gp expression and function in SW480 human colon adenocarcinoma and colo-320 cells, respectively. Our study aims to evaluate the P-gp inducing effect of MC111 in the whole brain , using the P-gp tracer [F]MC225 and positron emission tomography (PET). Eighteen Wistar rats were treated with either vehicle solution, 4.5 mg/kg of MC111 (low-dose group), or 6 mg/kg of MC111 (high-dose group). Animals underwent a 60 min dynamic PET scan with arterial-blood sampling, 24 h after treatment with the inducer. Data were analyzed using the 1-tissue-compartment model and metabolite-corrected plasma as the input function. Model parameters such as the influx constant () and volume of distribution () were calculated, which reflect the P-gp function. P-gp and pregnane xenobiotic receptor (PXR) expression levels of the whole brain were assessed using western blot. The administration of MC111 decreased and of [F]MC225 in the whole brain and all of the selected brain regions. In the high-dose group, whole-brain was decreased by 34% (-high-dose = 0.20 ± 0.02 vs -control = 0.30 ± 0.02; < 0.001) and in the low-dose group by 7% (-low-dose = 0.28 ± 0.02 vs -control = 0.30 ± 0.02; = 0.42) compared to controls. Whole-brain was decreased by 25% in the high-dose group (-high-dose = 5.92 ± 0.41 vs -control = 7.82 ± 0.38; < 0.001) and by 6% in the low-dose group (-low-dose = 7.35 ± 0.38 vs -control = 7.82 ± 0.37; = 0.38) compared to controls. values did not vary after treatment. The treatment did not affect the metabolism of [F]MC225. Western blot studies using the whole-brain tissue did not detect changes in the P-gp expression, however, preliminary results using isolated brain capillaries found an increasing trend up to 37% in treated rats. The decrease in and values after treatment with the inducer indicates an increase in the P-gp functionality at the BBB of treated rats. Moreover, preliminary results using brain endothelial cells also sustained the increase in the P-gp expression. In conclusion, the results verify that MC111 induces P-gp expression and function at the BBB in rats. An increasing trend regarding the P-gp expression levels is found using western blot and an increased P-gp function is confirmed with [F]MC225 and PET.