Fig 1.
OCT2-mediated metformin and MPP+ uptake.
Time-dependent uptake of metformin (A, 1000 μM) and MPP+ (B, 50 μM) into OCT2-expressing HEK-cells and corresponding vector controls. Uptake of metformin (C) and MPP+ (D) in HEK-VC and HEK-OCT2 cells after three minutes. Data are presented as the mean ± standard error (4–8 experiments each on two to four separate days, i.e., n = 8–29).
Fig 2.
Inhibitors of OCT2-mediated metformin (1000 μM) and MPP+ (50 μM) transport identified in a screen of 125 drugs most commonly prescribed in Germany.
(A) Inhibition of metformin transport. (B) Inhibition of MPP+ transport. Each bar represents one compound tested in HEK-OCT2 cells at a concentration of 20 μM. Bars showing a statistically significant (one-sample t test) inhibition are shaded in black. Data are presented as the mean +/- standard error (at least two experiments each on two or more separate days, i.e., n = 4–15). Negative inhibition values indicate enhanced OCT2-dependent substrate uptake in cells incubated with the respective test drug compared with vehicle-treated cells; ASS, acetylsalicylic acid.
Fig 3.
Substrate-dependent differences in the inhibitory profiles and concentration-dependent inhibition of metformin uptake.
(A) Correlation analysis between inhibition of OCT2-mediated metformin and inhibition of OCT2-mediated MPP+ uptake in HEK-OCT2 cells. Drugs were tested at 20 μM. Substrate concentrations were 1000 μM for metformin and 50 μM for MPP+ (data are presented as the mean ± standard error, Spearman's rank-order correlation test). (B) Bland-Altman plot (bias and limits of agreement) for the inhibition of OCT2-mediated metformin and MPP+ uptake. Average of % inhibition of metformin uptake and % inhibition of MPP+ is plotted against the difference between % inhibition of metformin uptake and % inhibition of metformin uptake, LoA, limits of agreement. Simvastatin, simvastatin lactone
Fig 4.
Correlation between inhibition of OCT2-mediated metformin, MPP+, and ASP+ uptake in HEK-OCT2 cells.
(A) Shown are drugs which were tested for each of the three substrates (n = 75). Drugs were tested at 20 μM. The size of the balls represents the inhibition of ASP+ uptake. Black balls, positive values; white balls, negative values. ASP+ data are from Kido et al. (2011). (B) Venn diagram showing unique and common / overlapping inhibitors of metformin, MPP+, and ASP+ uptake, respectively, by the human OCT2 transporter. Shown are only those drugs which were tested for each of the three substrates (n = 75) and which inhibit uptake of the respective substrate by more than 50%.
Fig 5.
Concentration-dependent inhibition of OCT2-mediated metformin uptake into HEK-OCT2 cells.
Shown is the inhibition of metformin uptake by psychoactive (A) and non-psychoactive drugs (B). Data are presented as the mean ± standard error (at least three experiments each on two separate days, i.e., n = 6).
Table 1.
Comparison of IC50 values for inhibition of OCT2-dependent uptake of metformin and maximum therapeutic plasma concentrations in humans.