Zinc and syringic acid have metabolic and antioxidant medicinal potentials. A novel zinc(II)-syringic acid complex with improved anti-hyperglycaemic and antioxidant potential was developed. Zinc(II) was complexed with syringic acid in a 1:2 molar ratio and characterized using FT-IR, 1H NMR and LC-MS. Different experimental models were used to compare the anti-hyperglycaemic and antioxidant properties between the complex and precursors. A Zn(II)-bisyringate.2H2O complex was formed. The in vitro radical scavenging and Fe3+ reducing antioxidant, antiglycation, and α-glucosidase inhibitory activities of the complex were 1.8-5.2 folds stronger than those of the syringic acid precursor and comparable to those of the positive controls. The complex possessed an increased ability to inhibit lipid peroxidation (by 1.6-1.7 folds) and glutathione depletion (2.8-3 folds) relative to syringic acid in Chang liver cells and liver tissues isolated from rats. The complex exhibited a higher glucose uptake effect (EC50 = 20.4 and 386 µM) than its precursors (EC50 = 71.1 and 6460 µM) in L6-myotubes and psoas muscle tissues isolated from rats, respectively, which may be linked to the observed increased cellular zinc uptake potentiated by complexation. Tissue glucose uptake activity was accompanied by increased hexokinase activity, suggesting increased glucose utilization. Moreover, treatment increased tissue phospho-Akt/pan-Akt ratio. The complex had strong molecular docking scores than syringic acid with target proteins linked to diabetes. The presence of two syringic acid moieties and Zn(II) in the complex influenced its potency. The complex was not hepatotoxic and myotoxic in vitro. Zinc-syringic acid complexation may be a novel promising therapeutic approach for diabetes and oxidative complications.
Keywords: Antioxidant; Bioactive synergism; Complexation; Glycaemic control; Syringic acid; Zinc mineral.
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