A novel ex vivo skin model for the assessment of the potential transcutaneous anti-inflammatory effect of topically applied Harpagophytum procumbens extract

Using ex vivo skin as a model, this work tested the hypothesis that the major pharmacologically active components of topically applied Harpagophytum procumbens (H. procumbens) can elicit anti-inflammatory responses in deeper tissues post-transcutaneous delivery. Using Franz-type diffusion cells, ethanol extract of powdered H. procumbens tuber was dosed onto freshly excised porcine skin. After 24 h the receptor phase was recovered, analysed for the major glycosides of DC, then used directly to dose further freshly excised skin membranes. After 6 h the skin was recovered and probed for the expression of the three major enzymes involved in the inflammatory factors: cyclooxygenase (COX-2) and its product prostaglandin E2 (PGE-2), lipoxygenase (5-LOX), and inducible nitric oxide (iNOS), using immunocytochemistry and Western blotting analyses. It was found that the receptor phase at 24 h contained (0.8, 25, 1.8, 3 × 10−3) μmol mL−1 of harpagoside, harpagide, verbascoside, 8-O-p-coumaroyl-harpagide, respectively. When applied to skin, this solution effectively inhibited the expression of COX-2 and its product PGE-2. However, it did not have a significant effect on either 5-LOX or iNOS compared to control samples (PBS only). These data support the hypothesis that the transcutaneous delivery of H. procumbens can treat inflammation in deeper tissues such as in arthritis. Moreover, a novel ex vivo model has been described for assessing the potential anti-inflammatory activity of permeants delivered to deeper subcutaneous regions.