Direct or Indirect Skin Lipid-Ordering Effect of Pyrrolidone Carboxylate Sodium After Topical Treatment with Penetration Enhancers

Abstract

The structural changes in the lipid of the excised skin of nude mice and the porcine stratum corneum was investigated by in vitro treatment with vitamin C, oleic acid, or DMSO. The CH₂ stretching vibrational peaks of lipid near 2920 cm⁻¹ (asymmetric) and 2850 cm⁻¹ (symmetric) shifted to higher wavenumber due to the lipid-disorder after in vitro treatment with above enhancers. The spectral shift of the asymmetric CH₂ band was more sensitive than that of the symmetric CH₂ band. The higher wavenumber of CH₂ stretching bands decreased gradually to the lower region after co-treatment or posttreatment with pyrrolidone carboxylate sodium (PCA Na). Such a decrease was dependent on the PCA Na concentration and the time of treatment. The higher the concentration of PCA Na used, the lower value of the permeability coefficient of vitamin C through the excised skin and the downward spectral shift of asymmetric CH₂ band were obtained. When PCA Na coexisted with vitamin C in the cell donor compartment, a competitive effect between PCA Na and vitamin C was found. The oleic acid was supposed to directly insert it into the lipid structure to form a rigid structure, leading to larger spectral shift of both stretching bands but lesser restoring ability after PCA Na treatment. However, DMSO only displaces water from the lipid head groups and protein domain of skin to indirectly loosen the lipid structure, resulting in lesser spectral shift of the CH₂ stretching bands to higher region, which was easier and better restoration after PCA Na application. The PCA Na enabled to restore the disordered lipid structure to order state might be attributed to PCA Na previously penetrated into skin and then absorbed water to directly or indirectly rearrange the disordered lipid bilayer structure.