Purpose: To study the effect of Ethyl acetate (EtAc), 1:1 ratio of EtAc and Ethanol (EtOH) and 2:1 ratio of chloroform (C) and methanol (M) on the extent of lipid extraction from the stratum corneum (SC) and in vitro passive and iontophoretic transport of insulin through porcine epidermis.
Methods: The porcine epidermis was pretreated for 40 min with the following solvents: 1) EtAc or EtAc:EtOH (1:1) and 2) C:M (2:1), which is a standard solvent combination for lipid extraction. Franz diffusion cells and Scepter iontophoretic power source were used for the transport studies. Cathodal iontophoresis was performed at 0.2 mA/cm2 current density. Fourier transform infrared spectroscopy (FTIR) studies were performed to assess the extent of lipid extraction. Thin layer chromatography (TLC) and gas chromatography (GC) were used to quantitate the different classes of lipid and identify the composition of the fatty acids, respectively, extracted by solvent(s) treatments.
Results: Insulin flux was found to be significantly (P < 0.05) greater through solvent pretreated epidermis compared to untreated controls during both passive and iontophoretic transport. Pretreatment with EtAc:EtOH (1:1) exhibited an insulin flux of 15.29 x 10(-8) nmoles/ cm2/h compared to 52.71 x 10(-8) nmoles/ cm2/h during passive and iontophoretic transport, respectively. The passive and iontophoretic flux of insulin through EtAc:EtOH (1:1) pretreated epidermis was significantly greater (P < 0.05) than EtAc treated epidermis. The SC treated with solvents showed a decrease in peak areas of C-H stretching absorbances in comparison to untreated SC. A greater percent decrease in peak areas was obtained by EtAc:EtOH(1:1), in comparison to EtAc alone. Epidermal resistance measurements revealed its strong correlation with the amount of lipids present in the epidermis. The lipids extracted consisted of six series of ceramides, fatty acids. triglycerides, cholesterol, cholesterol esters, cholesterol sulfate and phospholipids.
Conclusions: The SC lipid extraction using suitable solvents followed by iontophoresis can synergistically enhance the transepidermal transport of insulin.