Preparation, Evaluation of Propolis Extract Gel and exploring its Antioxidant, Antimicrobial Activity

Background: Propolis is a wax-like resin which is produced by different types of bees by mixing resinous secretions of plants with beeswax and other products of bees' metabolism. However, this natural product contains a group of compounds that are responsible for various propolis activities including antimicrobial, anticancer, antioxidant, antiviral, and others. This study aims to prepare different gel formulae that contain various concentrations of propolis extract using two different polymers and to evaluate their physical properties, antioxidant, and antimicrobial activities. Method: Propolis was extracted depending on the hydroalcoholic method; six different gel formulae (P-1 to P-6) were prepared with different concentrations of propolis extract (0.5, 1, and 1.5%) using two different polymers; carbopol-934 and poloxamer-407, in concentrations of 0.5 and 25% respectively. The formulae were evaluated physically for their visual appearance, pH, viscosity, spreadability, and physiological compatibility with the skin. The anti-microbial activities were investigated by well diffusion method against various bacterial species including Staphylococcus aureus (gram+), Pseudomonas aeruginosa (gram-), Enterococcus fecalis (gram+) and against one fungal species which is Candida albicans. Also, the antioxidant activity was determined utilizing 2,2-Diphenyl-1-picrylhydrazyl (DPPH) assay. Finally, a stability test was carried out for the chosen formula. Results: The six formulae (P-1 to P-6) were successfully prepared and evaluated and they were acceptable in their physical appearance and consistency, pH reading was in the range of 5.33±0.08 to 5.72±0.02 (p>0.05), a study of the skin irritation revealed no undesirable side effect, while the viscosity was in the range of 128.99±0.07 to 248.54±1.04 Pa.s (p>0.05), also the carbopol-934 containing formulae revealed good spreadability (1.495±0.075 to 5.15±0.35 mg.cm/s, p>0.05), in comparison to poloxamer-407 containing ones. Both carbopol-934 and poloxamer-407 containing formulae exhibited antimicrobial activity but the P-3 formula had the largest inhibition zone against C. Albicans (16.1mm), and only P-2, P-5 and P-6 were active against pseudomonas aeruginosa (12mm in all), while P-2 had the largest inhibition zone against enterococcus fecalis (13.2 mm), P-2 and P-5 showed the largest activity against staphylococcus aureus (15.5 and 14.6 mm respectively). The carbopol-934-containing formulae exhibited higher antioxidant activity than those with poloxamer-407, and the best-calculated IC50 belonged to P-2 (1.19 mg/ml). Conclusion: All the prepared formulae showed antimicrobial and antioxidant activities with some controversial results. However, P-2 (1% propolis extract and 0.5% carbopol-934), was active against all types of the tested microorganism, and had the best-calculated IC50, in addition to that it was a stable formula.