Propolis is a natural, sticky substance, found in beehives. It is primarily known for its effectiveness – it has antiviral properties, it helps healing wounds and protects cracked skin. Due to its complexity and diverse structure, examination of propolis is difficult, but highly needed. Tests of permeability through skin are common. In vivo or in vitro tests may be used for this purpose. In vitro tests with Franz diffusion cells are more likely to be used in a case like ours.
The purpose of this study was to develop an HPLC analytical method, which would help us determine the content of propolis components passing through the skin. The chromatographic conditions needed to be optimised for the diversity of propolis components and to provide a reasonably good separation in a reasonably fast analysis. For this reason we tested multiple mobile phases, concentrations of compounds and different columns, until we found a satisfactory combination. Then we carried out an experiment, which included three donor solutions: tincture of propolis, propolis ointment and dry propolis.
The experiment was carried out with Franz's diffusion cells, and because of the similarity to human skin, we chose porcine ear skin for the membrane. What we most wanted to see was whether the components of propolis permeate through skin at all and if they do, how much and what components are those. We also wanted to examine the difference in permeability from different donor solutions. After the analysis there were too many visible peaks in the chromatograms to focus on all of them, so we selected five largest and well-separated peaks – five unknown ingredients that we were able to detect on most acceptor sides in case of most donor solutions.
The results of the experimental work showed best permeability through skin in the case of tincture of propolis and propolis ointment. Permeability from dry propolis was barely detectable. Using UV-spectra, we were able to identify the derivative of chrysin.
This study allowed us to see that propolis permeates in significant concentrations, but for more detailed results (identification of all components) it would be necessary to use LC-MS/MS system.
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