Effect of penetration enhancers and iontophoresis on the FT-IR spectroscopy and LHRH permeability through porcine skin

The present study explores the effect of enhancer and iontophoresis on the in vitro permeability of luteinizing hormone releasing hormone (LHRH) through porcine epidermis and biophysical changes in the stratum corneum lipids by Fourier transform infrared (FT-IR) spectroscopy. Enhancers (e.g. ethanol, 10% oleic acid in combination with ethanol and 10% oleic acid in combination with propylene glycol) pretreatment increased (P<0.05) the permeability coefficient of LHRH. Propylene glycol alone did not increase the permeability (P>0.05) of LHRH through the epidermis. Iontophoresis further increased the permeability of LHRH (P<0.05) through the enhancers (ethanol, 10% oleic acid in combination with ethanol, propylene glycol and 10% oleic acid in combination with propylene glycol) pretreated epidermis in comparison to the control (without enhancer pretreated epidermis). This shows that iontophoresis can synergize with enhancers, such as 10% oleic acid in combination with ethanol and 10% oleic acid in combination with propylene glycol, to provide an additional driving force to maintain and control the target flux of LHRH. The FT-IR spectroscopic study was performed to investigate the effect of the above enhancers and iontophoresis on the biophysical changes in the stratum corneum lipids. Pretreatment of the stratum corneum with 10% oleic acid in combination with ethanol, and 10% oleic acid in combination with propylene glycol followed by iontophoresis shifted the antisymmetric peak position with reference to the control (without enhancer and iontophoresis) from 2919.3+/-0.7 to 2927.6+/-4.1, and 2919.3+/-0.7 to 2924.2+/-1.9 cm(-1), respectively. Thus, the combination of enhancer and iontophoresis increased the average acyl chain disorder (lipid fluidity). The synergism in enhancement of the permeability of LHRH through the epidermis by iontophoresis in combination with enhancers (10% oleic acid in combination with ethanol, and 10% oleic acid in combination with propylene glycol) may be due to greater fluidization of the stratum corneum lipids.