A Novel Chemical Enhancer Approach for Transdermal Drug Delivery with C17-Monoglycerol Ester Liquid Crystal-forming Lipid

Transdermal administration of drugs represents an excellent alternative to conventional pharmaceutical dosage forms. However, insufficient penetration of the active pharmaceutical substance through the skin is a common problem. Thus, in the present study we evaluated the skin permeation enhancing ability of liquid crystal (LC) topical formulations. A recently developed LC-forming lipid, C17- monoglycerol ester (MGE), was evaluated and compared with glycerol monoolate (GMO), which is considered as the gold standard for LC formulations. We initially prepared LC formulations containing drugs with different physiochemical properties (tranexamic acid [TXA], 4-methoxy-salicylic acid [4-MS], catechin [CC], and calcein [Cal]), and confirmed the LC phase structures in the prepared formulations using a polarizing light microscope and a small-angle X-ray scattering (SAXS). The physicochemical properties of these formulations were also assessed using a viscometer and a zetasizer. The release rate of the drugs from the LC formulations was determined using a dialysis release method. The skin penetration-enhancing ability of LC formulations was also investigated in an in vitro skin permeation study. The results showed that both MGE- and GMO-LC-forming lipids shared the same behavior in terms of their birefringence indexes, LC phase structures, particle sizes, and zeta potentials. Both the MGE- and GMO-LC formulations managed to improve the skin permeation for various drugs with a range of physiochemical properties. However, MGE formulations showed lower viscosity, faster drug release rate, and better skin penetration-enhancing ability than GMO formulations, strongly suggesting that the low viscosity of MGELC-forming lipids might influence drug diffusivity and permeability through the skin. The present MGELC formulation might be utilized as a promising new topical formulation for therapeutic drugs and cosmetic ingredients.