Phosphodiesterase Type 5 Inhibitors Greatly Affect Physicochemical Properties of Model Lipid Membranes

Abstract

Although phosphodiesterase type 5 inhibitors are widely used and well-studied drugs, the potential benefits of their application in the treatment of various diseases and new drug delivery systems, including liposome forms, are still being discussed. In this regard, the role of the lipid matrix of cell membranes in the pharmacological action of the inhibitors is of special interest. It was shown that sildenafil, vardenafil, and tadalafil caused a significant decrease in the boundary potential of model membranes composed of palmitoyloleoylphosphatidylcholine or its mixture with cholesterol, by 70-80 mV. The reduction in the membrane dipole potential induced by inhibitors led to a 20-25% increase in the conductance of cation-selective pores formed by the antimicrobial peptide gramicidin A. The addition of sildenafil or vardenafil also led to a significant decrease in the temperature of the main phase transition of dipalmytoylphosphatidylcholine, by about 1.5 °C, while tadalafil did not change the melting temperature. Sildenafil, vardenafil, and tadalafil enhanced the pore-forming activity of the antifungal polyene antibiotic nystatin by 11, 13, and 2 times, respectively. This fact might indicate the induction of membrane curvature stress by the inhibitors. The data obtained might be of special interest for the development of lipid-mediated forms of drugs.

Keywords: gramicidin A; ion channel; lipid bilayers; lipid melting; liposomes; membrane boundary potential; nystatin; phosphodiesterase type 5 inhibitors; sildenafil; tadalafil; vardenafil.

Figure 1

(a) The dependence of the changes in the boundary potential of the POPC membranes (Δφ_b) on the concentration of sildenafil (□), vardenafil (Δ), and tadalafil (♦) in the aqueous solution. The bilayer bathed in 0.1 M KCl at pH 7.4 (V = 50 mV). (b) The dependences of (Δφ_b(max)/Δφ_b(C)) on 1/C in POPC membranes. (c) The dependence of the changes in the dipole potential of the POPC membranes (Δφ_d) on the concentration of tested PDE-5 inhibitors.

Figure 2

(a) Current fluctuations corresponding to openings and closures of single GrA channels in the absence (control) and presence of 100 μM of sildenafil, vardenafil, and tadalafil (V = 200 mV). (b) G–V curves of single GrA in the absence (●) and presence of 100 µM of sildenafil (□), vardenafil (Δ), and tadalafil (♦). The membranes were composed of POPC and bathed in 2.0 M KCl (pH 7.4).

Figure 3

Heating thermograms of DPPC unilamellar liposomes in the absence (control, black line) and presence of sildenafil (a), vardenafil (b), and tadalafil (c) in the liposome suspension at concentrations of 10 μM (red lines), 50 μM (green lines), and 100 μM (blue lines).

Figure 4

The effects of PDE-5 inhibitors on the steady-state transmembrane current induced by one-side addition of Nys. The moments of the addition of 100 µM of sildenafil (a), vardenafil (b), or tadalafil (c) to the bilayer bathing solution are indicated by arrows. The lipid bilayers were composed of POPC/Chol (67/33 mol%) and bathed in 2.0 M KCl, pH 7.4 (V = 50 mV).