Optimization of phenolic extraction from Syzygium samarangense fruit and its protective properties against glucotoxicity-induced pancreatic β-cell death

Abstract

Long-term exposure to high glucose levels causes glucotoxicity in pancreatic β-cells associated with diabetes mellitus. The presence of natural antioxidant phenolic compounds, including the compounds from Syzygium samarangense, may help mitigate this metabolic disorder. This study aimed to optimize microwave-assisted extraction (MAE) for maximum phenolic recovery and assess the protective properties of Syzygium samarangense extract (SSE) against pancreatic β-cell mortality caused by glucotoxicity. We demonstrated that the MAE-based response surface methodology provided higher concentrations of total phenolics than the conventional reflux method (10.21 ± 0.22 mg GAE/g and 6.44 ± 0.13 mg GAE/g, respectively). According to in vitro studies, the percentage of viable rat insulinoma cell lines (INS-1 cells) was significantly lower when cultured in high glucose (HG) medium (40 mM) than in normal glucose medium (11.1 mM). Upon treatment of INS-1 cells with SSE (10, 50, and 100 µg/ml) in combination with HG, SSE exhibited a protective effect on the cell viability and inhibited cell apoptosis. In addition, SSE reduced intracellular superoxide ion concentrations in a dose-dependent manner. We conclude that the phenolics of SSE could function as antioxidants, thereby protecting pancreatic β-cells against glucotoxicity-induced apoptosis.