Protein-Bound Anthocyanin Compounds of Purple Sweet Potato Ameliorate Hyperglycemia by Regulating Hepatic Glucose Metabolism in High-Fat Diet/Streptozotocin-Induced Diabetic Mice

Purple sweet potato is known as a rich source of protein and anthocyanins. Anthocyanins can form complexes with protein present in food products through non-covalent forces or covalent bonds during processing, transportation, and storage as their protein affinity. We evaluated the hypoglycemic effects of protein-bound anthocyanin compounds of purple sweet potato (p-BAC-PSP) and free anthocyanin compounds of purple sweet potato (FAC-PSP) in high-fat diet/streptozotocin-induced diabetic mice. The results showed that administration of both p-BAC-PSP and FAC-PSP improved diabetic condition, as evidenced by the improvement of glucose tolerance and lipid metabolism, and the decrease of oxidative stress and liver damage. For the mechanism study, we have found that p-BAC-PSP and FAC-PSP induced the expression of AMP-activated protein kinase in liver. With p-BAC-PSP or FAC-PSP treatment, glucose transporter type 2, the protein levels of glucokinase, and insulin receptor α were found to be improved significantly (p < 0.05). Glycolysis key genes, phosphofructokinase and pyruvate kinase, were upregulated in two treatment groups, while gluconeogenic genes, glucose-6-phosphatase and phosphoenolpyruvate carboxykinase, were downregulated. Our findings suggested that p-BAC-PSP has great potential as a dietary supplement with hypoglycemic activity for general, pre-diabetic, and diabetic population.