The putative P-gp inhibitor telmisartan does not affect the transcellular permeability and cellular uptake of the calcium channel antagonist verapamil in the P-glycoprotein expressing cell line MDCK II MDR1

Abstract

Verapamil is used in high doses for the treatment of cluster headache. Verapamil has been described as a P-glycoprotein (P-gp, ABCB1) substrate. We wished to evaluate in vitro whether co administration of a P-gp inhibitor with verapamil could be a feasible strategy for increasing CNS uptake of verapamil. Fluxes of radiolabelled verapamil across MDCK II MDR1 monolayers were measured in the absence and presence of the putative P-gp inhibitor telmisartan (a clinically approved drug compound). Verapamil displayed a vectorial basolateral-to-apical transepithelial efflux across the MDCK II MDR1 monolayers with a permeability of 5.7 × 10(-5) cm sec(-1) compared to an apical to basolateral permeability of 1.3 × 10(-5) cm sec(-1). The efflux could be inhibited with the P-gp inhibitor zosuquidar. Zosuquidar (0.4 μmol/L) reduced the efflux ratio (PB-A/PA-B) for verapamil 4.6-1.6. The presence of telmisartan, however, only caused a slight reduction in P-gp-mediated verapamil transport to an efflux ratio of 3.4. Overall, the results of the present in vitro approach indicate, that clinical use of telmisartan as a P-gp inhibitor may not be an effective strategy for increasing brain uptake of verapamil by co-administration with telmisartan.

Keywords: Blood–brain barrier; P-glycoprotein; cluster headache; telmisartan; verapamil.

Figure 1

Transepithelial transport of [³H]-verapamil (12 μmol/L) across MDCK II (MDR1) in the apical to basolateral (closed circles) and the basolateral to apical direction (closed squares). Data show accumulation of verapamil on the acceptor side as a function of time. Data points represent the means, while error bars designate the standard deviations (n = 9, N = 3).

Figure 2

(A) The apparent transepithelial permeability of [3H]-verapamil (12 μmol/L) in the apical to basolateral (grey bars) and basolateral to apical (white bars) direction across MDCK II (MDR1) cells in the presence or absence of zosuquidar (ZSQ, 0.4 μmol/L). Data represent the means ± SD (n = 9, N = 3). (B) Efflux ratios for [3H]-verapamil (12 μmol/L) across MDCK II (MDR1) cells in the presence or absence of zosuquidar (ZSQ, 0.4 μmol/L). Data points represent the calculated efflux ratio for individual cell culture passages (n = 9). Efflux ratio was calculated as the ratio between the basolateral to apical and the apical to basolateral apparent permeability from means of three filters (N = 3) for each treatment and direction. Connected data points originate from the same cell culture passage.

Figure 3

(A) The apparent transepithelial permeability of ³H-verapamil (12 μmol/L) in the apical to basolateral direction across MDCK II (MDR1) cells in the presence or absence of telmisartan (TEL, 2.4 μmol/L). Data points represent the mean permeability of three filter supports (N = 3) of six different passages (n = 6). Lines between data points indicate how the data points are paired within each of the six cell passages. The effect of zosuquidar on the A-B transport of verapamil was statistically significant in a paired t-test (P = 0.0465). (B) Efflux ratio for ³H-verapamil (12 μmol/L) across MDCK II (MDR1) cells in the presence or absence of telmisartan (TEL, 2.4 μmol/L). Data points represent the calculated efflux ratios for six individual passages (n = 6). Lines between data points indicate how the data points are paired within each of the six cell passages.

Figure 4

Amount of ³H-verapamil remaining on filter supports including MDCK II (MDR1) cells after an apical to basolateral transport experiment in the presence or absence of telmisartan (TEL, 2.4 μmol/L) or zosuquidar (ZSQ, 0.4 μmol/L). Data were collected from three to six different passages with three filter supports for each treatment and passage (n = 3–6, N = 3). Bars in the scatter plot designate the mean amount of ³H-verapamil found for each treatment. The effect of both telmisartan and zosuquidar on the uptake of verapamil was statistically significant in an unpaired t-test (P < 0.0001).

Figure 5

(A) Transepithelial transport of [³H]-digoxin (0.03 μmol/L) across MDCK II (MDR1) cells as a function of time, in the apical to basolateral (closed circles) and the basolateral to apical direction (closed squares). Data show accumulation of digoxin on the acceptor side as a function of time. Data points represent the means, while error bars designate the standard deviations (n = 3, N = 3). (B) The apparent transepithelial permeability of [³H]-digoxin (0.03 μmol/L) in the apical to basolateral (grey bars) and basolateral to apical (white bars) direction across MDCK II (MDR1) cells in the presence or absence of telmisartan (TEL, 2.4 μmol/L). Data represent the means ± SD (n = 3, N = 3).

Figure 6

Amount of ³H-digoxin remaining on filter supports including MDCK II (MDR1) cells after an apical to basolateral transport experiment in the presence or absence of telmisartan (2.4 μmol/L). Data were collected from three different passages with three filter support for each treatment and passage (n = 3, N = 3). Bars in the scatter plot designate the mean amount of ³H-digoxin found for each treatment.