Synergisms in Alpha‑glucosidase Inhibition and Antioxidant Activity of Camellia sinensis L. Kuntze and Eugenia uniflora L. Ethanolic Extracts

Background: Camellia sinensis, the most consumed and popular beverages worldwide, and Eugenia uniflora, a Brazilian native species, have been already confirmed to have beneficial effects in the treatment of diabetes mellitus. However, their potential acting together against an enzyme linked to this pathology has never been exploited. Objective: The aim of this study was to evaluate the inhibitory properties of individual and combined ethanolic extracts of the leaves of C. sinensis and E. uniflora over alpha‑glucosidase, a key digestive enzyme used on the Type 2 diabetes mellitus (T2DM) control. In addition, their inhibitory activity against 2,2‑diphenyl‑1‑picrylhydrazyl radical (DPPH•) and peroxyl radicals was also assayed. Materials and Methods: Enzyme inhibition and antioxidant potential were assessed based on in vitro assays. Total phenolic compounds, carotenoids, and chlorophylls A and B were achieved using spectrophotometric methods. Results: E. uniflora was almost 40 times more active on alpha‑glucosidase than C. sinensis and combined extracts showed a significant synergistic effect with an obtained IC₅₀ value almost 5 times lower than the theoretical value. C. sinensis extract was twice more active than E. uniflora concerning DPPH•, in contrast, E. uniflora was almost 10 times more effective than C. sinensis on inhibition of peroxyl radicals with a significant synergistic effect for combined extracts. The extracts activities may be related with their phytochemicals, mainly phenolic compounds, and chlorophylls. Conclusion: Combined C. sinensis and E. uniflora ethanolic extracts showed synergistic effect against alpha‑glucosidase and lipid peroxidation. These herbal combinations can be used to control postprandial hyperglycemia and can also provide antioxidant defenses to patients with T2DM.