The transport of the Rooibos tea flavonoid aspalathin across the skin and the intestinal epithelium
ABSTRACT The aqueous extract of rooibos has been used for more than three hundred years since its discovery by the indigenous people. Currently, rooibos is gaining popularity in the cosmetic industry and incorporation of rooibos extracts in topical cosmetic formulations has become a fashionable trend. Both topical and intestinal absorption of rooibos tea were investigated. The transport of aspalathin in the unfermented (green) rooibos aqueous extracts and aqueous solution of pure aspalathin were studied. The percutaneous permeation experiments were conducted with vertical Franz diffusion cells using human female abdominal skin obtained from patients who underwent cosmetic surgery. The green rooibos extract and pure aspalathin solution buffered in phosphate buffer system (pH 5.5) were applied to the skin for 12 hours. Samples of the permeants were obtained from the receptor fluid phase and from the stratified layers of the skin by using the tape-stripping technique and analysed by HPLC. In vitro intestinal epithelial transport experiments were carried out by using Caco-2 cell monolayers, isolated and cultured from human colonic adenocarcinoma cells, in a six-well transwell system. The green rooibos extract and pure aspalathin solution buffered in phosphate buffer (pH 7.4) were applied on to the cell monolayers and incubated for 2 hours. Samples were obtained from the basolateral phase at predetermined time intervals and analysed by HPLC. Less than 0.1 % of the applied dose of aspalathin permeated the skin. Most of the permeated aspalathin accumulated in the stratum corneum. Close to 100 % of aspalathin was transported across the Caco-2 cell monolayers at a concentration dependent manner. Better absorption of aspalathin was observed using the green rooibos extract than with the pure aspalathin solution across the Caco-2 cell monolayers.