Percutaneous penetration enhancement effect of essential oil of mint (Mentha haplocalyx Briq.) on Chinese herbal components with different lipophilicity

ObjectiveTo investigate the percutaneous penetration effect of essential oil of mint from Mentha haplocalyx Briq. on the complex active components in Chinese herbal external preparations, and assess its toxicity on the skin cells.MethodsThe cytotoxicity of mint oil on HaCaT keratinocytes and CCC-ESF-1 fibroblasts was measured using an MTT assay. Five model drugs with a wide range of lipophilicity, namely osthole, tetramethylpyrazine, ferulic acid, puerarin, and geniposide, were tested using in vitro permeation studies to investigate the percutaneous penetration enhancement effect of mint oil. Secondary structure alterations of skin stratum corneum (SC) were measured using Fourier transform infrared spectroscopy (FTIR). Saturation solubilities and SC/vehicle partition coefficients of the five model drugs with and without mint oil were also determined to understand the potential mechanisms of the essential oil.ResultsHalf maximal inhibitory concentration (IC50) values of mint oil were significantly higher in HaCaT and CCC-ESF-1 cell lines than values in the well-established and standard penetration enhancer Azone.ConclusionsMint oil at proper concentration could effectively facilitate percutaneous penetration of both lipophilic and hydrophilic drugs, and exhibit higher efficiency for moderate hydrophilic drugs. Mechanisms of penetration enhancement by mint oil could be explained with saturation solubility, SC/vehicle partition coefficient and the secondary structure change of SC.