Protective Effect of Merbau (Intsia bijuga) Extract on Hydrogen Peroxide-Treated HaCaT Human Keratinocytes and Its Formulation as Antioxidant Cream

Background: The excessive generation of ROS in the skin results in oxidative stress that can contribute to premature skin aging, inflammation, and skin carcinogenesis. To prevent these detrimental effects, the development of herbal medicine with a potent antioxidant activity into cosmetic products is required. This study aims to formulate cream that contains a safe and effective concentration of merbau (Intsia bijuga), which has been shown to have a strong antioxidant activity. Methods: Powdered merbau wood was macerated with methanol and the dried extract was evaluated for its cytotoxic effect and antioxidant activity on human keratinocytes cell line using MTS assay. Five cream formulations containing the extract were made and subjected to stability and physical evaluations, including organoleptic, types of cream, pH, viscosity, and homogeneity. Results: Cytotoxicity assay revealed that merbau extracts had an IC50 of 181.3 μg/mL (95% confidence interval (CI): 165.4 - 200.1 µg/mL). At a concentration of 31.25 μg/mL, the extract exhibited a protective effect against H2O2-induced oxidative stress, comparable to vitamin E. Five cream formulas that were developed demonstrated good physical properties that fulfilled the evaluation parameters, including o/w type of cream, homogenous, and stable based on centrifugation and freeze-thaw cycle tests. The pH values were between 5.65 ± 0.067 - 7.4 ± 0.050, while the viscosity values were between 131 ± 1.249 - 56,011 ± 2,729.27 mPa.s. All cream formulas exhibited shear-thinning properties upon increasing shear stress. Conclusion: Overall, this study has successfully formulated several cream formulations containing merbau extract at a concentration that shows antioxidant activity.