Figure 3.

The effect of tetrahydrocarbazole analogs on mitochondrial membrane potential. (a) Representative TMRM-staining images of HEK293 cells pretreated for 1 h with the indicated tetrahydrocarbazoles (10 μM) or Dimebon (10 μM) as a positive control, relative to DMSO-treated control (scale bar, 100 μm). (b) Quantification of the average TMRM-staining signals showing relative intensity for commercially available analogs of the tetrahydrocarbazole lead structure upon 1 h pretreatment of HEK293 cells (10 μM). The bars highlighted with single- and double-stripes represent the most active compounds 5781464 and 5781441, which, respectively, possess N-(1-benzylpiperidin-4-yl) and N-(1-phenethylpiperidin-4-yl) groups at their R² position. (c) Quantification of average TMRM intensity for synthesized tetrahydrocarbazole derivatives tested at 10 μM. The marked single-striped bars represent the analogous structures similar to 5781464, possessing N-(1-benzylpiperidin-4-yl) at their R² position, and double-striped bars represent derivative compounds similar to 5781441, which contain N-(1-phenethylpiperidin-4-yl) group at the R² position. (d) Quantification of average dose-dependent TMRM relative intensities for three select tetrahydrocarbazoles tested at six different concentrations relative to Dimebon. The EC₅₀ of all analogs tested lies at low micromolar range. All the values are normalized to DMSO value, which is set to 1. (n.s., non-significant; *P<0.05, **P<0.01 and ***P<0.001; n=8). DMSO, dimethyl sulfoxide; TMRM, tetramethylrhodamine methyl ester.