Effects of mulberry leaf polysaccharide on oxidative stress in pancreatic β-cells of type 2 diabetic rats

OBJECTIVE: To explore and discuss the effects and mechanisms of mulberry leaf polysaccharide (MLP) on oxidative stress in pancreatic β-cells of type 2 diabetic rats.

MATERIALS AND METHODS: The model of diabetic rats was established by inducing the Sprague-Dawley (SD) rats with high-sugar and high-fat diet for 6 weeks and then giving them streptozotocin (STZ) by single intraperitoneal injection. The mulberry leaf polysaccharide was administered via gavage daily for 8 weeks, and the tissue morphology was observed through electron microscopy. The levels of fasting blood glucose (FBG), free fatty acid (FFA), triglycerides (TG), low-density lipoprotein cholesterol (LDL-C), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α) were detected. The content of malondialdehyde (MDA) and the activity of superoxide dismutase (SOD) in the pancreas were tested. The activities of mitochondrial cytochrome C oxidase (CCO) and succinate dehydrogenase (SDH) in the pancreatic cell were examined.

RESULTS: Compared with the normal control group, the level of FBG increased (p < 0.01), the levels of FFA, TG, LDL-C, IL-6, and TNF-α were higher (p < 0.05), the content of MDA increased (p < 0.05) and the activity of SOD, CCO and SDH declined (p < 0.05) in the model group. In comparison with the model group, the level of FBG in the group intervened by mulberry leaf polysaccharide decreased [(23.9 ± 2.5) vs. (16.8 ± 2.1) mmol•L-1]; the levels of FFA, TG and LDL-C dropped from (1.18 ± 0.24), (2.95 ± 0.65) and (2.18 ± 0.46) mmol•L-1 to (0.65 ± 0.14), (2.20 ± 0.45) and (1.08 ± 0.42) mmol•L-1, respectively; the levels of IL-6 and TNF-α declined from (60.78 ± 5.02) ng•L-1 and (2.34 ± 0.42) μg•L-1 to (30.94 ± 3.02) ng•L-1 and (1.02 ± 0.12) μg•L-1, respectively; the content of MDA w as reduced from (1.38 ± 0.21) μmol•g-1 to (0.78 ± 0.12) μmol•g-1; the activities of SOD, CCO and SDH increased from (25.32 ± 3.58) KU•g-1, (15.00 ± 1.58) mmol•g-1 and (3.23 ± 0.32) KU•g-1 to (32.87 ± 2.62) KU•g-1, (18.30 ± 1.78) mmol•g-1 and (5.62 ± 0.38) KU•g-1, respectively; the electron microscopy results indicated that the intervention of mulberry leaf polysaccharide could improve the morphological structure of the pancreatic β-cells.

CONCLUSIONS: The mulberry leaf polysaccharide can lower down the levels of inflammatory mediators and free fatty acid in the diabetic rats, alleviate oxidative stress injury, improve the mitochondrial functions of islet cells and protect the pancreatic β-cells.

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