Interaction of antidepressant drug, clomipramine, with model and biological stratum corneum membrane as studied by electron paramagnetic resonance.

The interactions of tricyclic antidepressant drug, clomipramine (CLO), with pig ear stratum corneum (SC) and model membranes were investigated by electron paramagnetic resonance (EPR) spin labeling to get some insight into the possible application of this drug in transdermal delivery. The changes in membrane characteristics caused by CLO in the regions that are close to the water-lipid interfaces and the central parts of the membranes were searched. The experimental results were supported by computer simulation of EPR spectra, which showed heterogeneity of the membranes composed of regions with different fluidity characteristics. CLO was effective in both parts of the layers, indicating intercalation of the drug into model membranes as well as into the pig ear SC. Introduction of various molar ratios of CLO caused a decrease in the order parameter and an increase in the rotational diffusion of nitroxide moiety in different membrane regions as well as an increase in the polarity of spin probe environment. It also changed the number of resolved spectral components, which reflects the heterogeneity of the membrane. The fluidizing effect of CLO on pig ear SC throughout the whole membrane layers indicates that CLO penetrates into the SC, which is important for its transdermal delivery.

EPR investigation of clomipramine interaction with phosphatidylcholine membranes in presence and absence of cholesterol.

The effects of tricylic antidepressant clomipramine (CLO) on the membrane properties of saturated dimyristoyl phosphatidylcholine and dipalmitoyl phosphatidylcholine as well as on unsaturated egg yolk phosphatidylcholine liposomes were investigated by the electron paramagnetic resonance spin-labeling technique, in combination with the simulation of the spectra, taking into account that the membrane is heterogeneous and composed of the regions with different fluidity characteristics. Different spin labels, monitoring membrane properties in the upper and inner parts of the membrane, were used. In general, two spectral components, having different motional characteristics, were detected in all liposomes investigated. In liposomes with saturated chains, CLO decreased the phase-transition temperature, disordered the membrane, and increased polarity in the upper part of the membrane. However, less impact was observed in liposomes with unsaturated chains. In dipalmitoyl phosphatidylcholine liposomes, it also induced molecular rearrangements near the pretransition temperature. The presence of 30 mol% cholesterol increased the fluidizing effect of CLO and modified the lateral diffusion of nitroxide in the inner part of the membrane. A unique anomalous increase in diffusion of nitroxide, dependent on CLO concentration, was detected in the temperature region where the phosphatidylcholine membrane without cholesterol experiences the phase transitions. Since the changes in the central part of the membrane were even more pronounced than in the upper part of the membrane, it could be concluded that CLO incorporates into the membrane with its hydrophobic ring parallel to the phospholipid chains.

EPR spin label study of walnut oil effects on phosphatidylcholine membranes.

Effects of walnut oil (WO) on dynamic and thermodynamic properties of 0-50 wt% cholesterol (CH) containing dimyristoylphosphatidylcholine (DMPC) and 10 wt% CH containing dipalmitoylphosphatidylcholine (DPPC) membrane dispersions were studied by electron paramagnetic resonance (EPR), using 5-doxyl stearic acid (5-DSA) and 16-doxyl stearic acid (16-DSA). Incorporation of 10 wt% WO alone decreased the phase transition temperature and created depth-dependent effects at the gel phase. The order increased close to the head region and decreased in the hydrocarbon core of the DMPC bilayer. For DPPC, the order decreased both close to head region and in the hydrocarbon core. Ten weight percent WO did not have considerable effect at the fluid phase for both DMPC and DPPC. Incorporation of 40 wt% WO into DMPC created an abrupt decrease in the maximum hyperfine splitting values after 305 K. The effect of 10 wt% WO in CH containing DMPC dispersions was dependent on the CH concentration. An increase and a decrease in the order were observed at low and high CH concentrations, respectively. Incorporation of WO created different effects on fluidity of 10 wt% CH containing DMPC and DPPC dispersions. Close to the head group region, the order in DMPC increased both in the gel and fluid phases; but for DPPC, an opposite effect was observed in both of the phases. In the hydrocarbon core of the bilayer, addition of 10 wt% WO into 10 wt% CH containing DMPC decreased the order in the gel phase and WO did not affect the order in the fluid phase. For DPPC, WO effects were observed to alter with temperature. In the studied temperature range, order parameters, diffusion constants and effective tilt angles were obtained from simulations of the spectra using Microscopic Order Macroscopic Disorder (MOMD) and Vary Anisotropic Reorientation (VAR) models. For 16-DSA, spectra were also simulated using two domains with EPRSIM.