Blueberries possess abundant anthocyanins, which benefit eye health. The purpose of this study was to explore the protective functional role of blueberry anthocyanin extract (BAE) and its predominant constituents, malvidin (Mv), malvidin‐3‐glucoside (Mv‐3‐glc), and malvidin‐3‐galactoside (Mv‐3‐gal), on high glucose‐ (HG‐) induced injury in human retinal capillary endothelial cells (HRCECs). The results showed that BAE, Mv, Mv‐3‐glc, and Mv‐3‐gal enhanced cell viability (P < 0.05 versus the HG group at 24 h); decreased the reactive oxygen species (ROS, P < 0.01 versus the HG group both at 24 and 48 h); and increased the enzyme activity of catalase (CAT) and superoxide dismutase (SOD) (P < 0.05 versus the HG group both at 24 and 48 h). Mv could greatly inhibit HG‐induced Nox4 expression both at 24 and 48 h (P < 0.05), while BAE and Mv‐3‐gal downregulated Nox4 only at 48 h (P < 0.05). Mv, Mv‐3‐glc, and Mv‐3‐gal also changed nitric oxide (NO) levels (P < 0.05). BAE and Mv‐3‐glc also influenced angiogenesis by decreasing the vascular endothelial cell growth factor (VEGF) level and inhibiting Akt pathway (P < 0.05). Moreover, Mv and Mv‐3‐glc inhibited HG‐induced intercellular adhesion molecule‐1 (ICAM‐1, P < 0.001) and nuclear factor‐kappa B (NF‐κB) (P < 0.05). It indicated that blueberry anthocyanins protected HRCECs via antioxidant and anti‐inflammatory mechanisms, which could be promising molecules for the development of nutraceuticals to prevent diabetic retinopathy.

Blueberries are rich in bioactive anthocyanins, with a high level of malvidin, which is associated with antioxidant benefits that contribute to reducing the risk of diabetes. The objective of this study was to investigate the hypoglycemic and hypolipidemic effects of blueberry anthocyanin extract (BAE), malvidin (Mv), malvidin-3-glucoside (Mv-3-glc), and malvidin-3-galactoside (Mv-3-gal) in both human hepatocarcinoma cell line HepG2 and in a high-fat diet combining streptozotocin-induced diabetic mice. High glucose treatment significantly increased hepatic oxidative stress up to 6-fold and decreased HepG2 cell viability. Pretreatment with BAE, Mv, Mv-3-glc and Mlv-3-gal significantly mitigated these damages by lowering the reactive oxygen species (ROS) by 87, 80, 76, and 91%, and increasing cell viability by 88, 79, 73, and 98%, respectively. These pretreatments also effectively inhibited hyperglycemia and hyperlipidemia, respectively by reducing the expression levels of enzymes participating in gluconeogenesis and lipogenesis and enhancing those involved in glycogenolysis and lipolysis, via adenosine monophosphate-activated protein kinase (AMPK) signaling pathway in HepG2 cells. To determinate the role of AMPK in BAE-induced reaction of glucose and lipid metabolism in vivo, doses of 100 mg/kg (blueberry anthocyanin extracts - low concentration, BAE-L) and 400 mg/kg (blueberry anthocyanin extracts - high concentration, BAE-H) were administrated per day to diabetic mice for 5 weeks. BAE treatments had a significant (P < 0.05) effect on body weight and increased the AMPK activity, achieving the decrease of blood- and urine-glucose, as well as triglyceride and total cholesterol. This research suggested that anthocyanins contributed to the blueberry extract-induced hypoglycemia and hypolipidemia effects in diabetes and BAE could be a promising functional food or medicine for diabetes treatment.