Antioxidant and Antiglycation Activities of Syzygium paniculatum Gaertn and Inhibition of Digestive Enzymes Relevant to Type 2 Diabetes Mellitus.

Advanced glycation end-products (AGEs) may be a contributing factor in the development of diabetes-specific vascular pathologies that affect the retina, glomerulus and peripheral nerves. In this study, Australian native food plant species Syzygium paniculatum was investigated for activities relevant to Type 2 diabetes mellitus including inhibition of α-amylase, α-glucosidase and protein glycation. A methanolic extract of the leaves showed the strongest α-amylase inhibition (IC50 = 14.29 ± 0.82 μg/mL, p < 0.05) when compared with other extracts. For inhibition of α-glucosidase, the strongest inhibition was shown for the water, methanolic and acetone extracts of leaves with IC50 values ranging from 4.73 ± 0.96 to 7.26 ± 0.92 μg/mL. In the BSA-glucose model, fruit and leaf extracts inhibited formation of protein-bound fluorescent AGEs with IC50 values ranging between 11.82 ± 0.71 and 96.80 ± 13.41 μg/mL. Pearson's correlation analysis showed that the AGE inhibition significantly correlated with DPPH (rp = -0.8964, p < 0.05) and ABTS (rp = -0.8326, p < 0.05). α-amylase inhibitory activities strongly correlated with DPPH (rp = -0.8964, p < 0.001). α-glucosidase inhibition strongly correlated with TPC (rp = -0.9243, p < 0.05), FRAP (rp = -0.9502, p < 0.01), DPPH (rp = -0.9317, p < 0.01) and ABTS (rp = -0.9486, p < 0.01). This study provides a strong rationale for further investigation aimed at isolating and identifying the active compounds responsible for the observed effects on targets relevant to diabetes.