Transdermal delivery of selected statins formulated in grapeseed oil emulsions

Abstract

Hypercholesterolemia can be described as high levels of low-density lipoproteins (LDL) that accumulate in the cells of the body including the liver, spleen and the intestines. Cholesterol is eliminated by increasing high-density lipoproteins (HDL) through the use of statins. Although statins are seen as the first-line treatment of hypercholesterolemia, patient compliance is decreased by the side effects statins possess after oral administration. These side-effects can be reduced by utilising alternative routes of administration, such as the transdermal route. For a statin or any other pharmaceutical active ingredient (API) to pass through the skin, they must exert the ideal physicochemical properties. When the statins were investigated, it was observed they did not possess ideal physicochemical properties for transdermal drug delivery. Therefore, to enhance the penetration of the non-ideal statins through the stratum corneum, an oil-in-water (o/w) nano-emulsion containing 2% (w/w) of the respective statin and 8% (w/w) grapeseed oil was formulated. After the o/w nano-emulsions were formulated and characterised, a nano-emulgel was formulated and subsequently characterised. For each of these formulations with the respective statins, membrane release studies, skin diffusion studies and tape stripping were performed to evaluate if the APIs were released from the dosage form, diffused systemically (transdermally) and permeated the skin (topically). Statistical analysis was then performed to analyse the variances between the means of the membrane release studies, skin diffusion studies and tape stripping to determine whether topical or transdermal delivery was achieved. After skin diffusion studies, in vitro cytotoxicity studies were performed on normal immortalised human keratinocytes (HaCaT) cells. Both the statins (alone, dissolved in methanol) and the nano-emulsions with the different APIs were tested by means of methylthiazol tetrazolium (MTT) assay and neutral red (NR) assay. This was done to determine if the selected statins in their formulations were safe for application on the human skin. After results were determined of the MTT and NR, the IC50 (concentration at which 50% of the cell growth is inhibited) values were established. It was evident that lovastatin and simvastatin were the most cytotoxic and rosuvastatin was the least cytotoxic of all the statins. It must however be mentioned that the concentrations tested on the HaCaT cells during the cytotoxic testing were much higher than the amounts that diffused through the skin during the in vitro diffusion study and that these 2% formulations would be safe for transdermal application.