The Protective Effect of Sericin on AML12 Cells Exposed to Oxidative Stress Damage in a High-Glucose Environment.

Two types of sericin peptides with high molecular weight (HS) and low molecular weight (LS) were obtained by the green water boiling ultrasonic method and the Ca(OH)2 ultrasonic method, respectively. In this experiment, a high-glucose medium was used to simulate a high-glucose environment in the body, and appropriate concentrations of normal alpha mouse liver 12 (AML12) hepatocytes were exposed to a series of concentrations of HS and LS. The effects of the two sericin peptides on AML12 cells in a high-glucose environment were investigated in detail in terms of oxidative stress and inflammatory factor expression in cells. HS and LS-groups reduced the levels of oxidative stress, inflammation, and tumor necrosis factor (TNF), and the latter significantly reduced the levels of TNF-α, interleukin (IL)-6, and nuclear factor (NF)-κB in AML12 cells. Additionally, it significantly reduced the oxidative stress damage caused by the high-glucose environment compared with normal AML12 cells. These results indicate that sericin may be an antioxidant recovered from industrial waste, and has potential and for use in the reduction of environmental pollution and the development of functional foods with antioxidation and antihyperglycemic effect.

Investigation of the Repairing Effect and Mechanism of Oral Degraded Sericin on Liver Injury in Type II Diabetic Rats.

In the sericulture and silk production industry, sericin is discharged in the degumming wastewater, resulting in a large amount of wasted natural protein and environmental pollution. This study investigated the effect of degraded sericin recovered by the Ca(OH)2-ultrasound degumming method (a green process) on liver injury in T2D rats. After 4 weeks of dietary sericin supplementation, the liver masses and organ coefficients of the T2D rats improved compared with those of the model rats that were not fed sericin. Oral sericin activated the damaged PI3K/AKT/AMPK pathway to enhance glycogen synthesis, accelerate glycolysis, and inhibit gluconeogenesis. The protein expression levels of the inflammatory factors NF-κB, IL-6, and TNF-α in the T2D model group were up to two times higher than in the normal group. However, all three T2D groups that received oral sericin showed significant decreases in these factors to the level found in the normal group, indicating that inflammation in the body was significantly reduced. These results show that the sericin protein might improve glycogen synthesis, accelerate glycolysis, and inhibit gluconeogenesis by enhancing the anti-oxidation capability and reducing inflammatory reactions. Therefore, sericin recovered by Ca(OH)2 degradation has potential use in the development of functional health foods that can lower blood sugar.

Enhancing the In Vitro Biological Activity of Degraded Silk Sericin and Its Analog Metabolites.

Two sericins of high and low molecular weight (HS and LS) were prepared from commercial silkworm cocoon silk with a boiling water and Ca(OH)2 solution with ultrasonic treatments, respectively. This study first investigated the release concentration of the two abovementioned sericins in simulated saliva, gastric juice, and intestinal juice (pH 6.8, 2.0, and 7.4, respectively) within 10 h. The results showed that the order of sericin release rate and its amount in the simulated environment was gastric juice > saliva > intestinal juice. Second, the molecular weights of both sericin metabolites formed by in vitro enzymatic degradation were lower than 15 kDa. The α-glucosidase inhibitory activities of both sericins and their analog metabolites were positively correlated with their concentrations. The IC50 values of the HS- and LS-derived metabolites were 1.02 ± 0.12 mg/mL and 0.91 ± 0.15 mg/mL, respectively, which were five to seven times lower than those of both original sericins. The total antioxidant capacities and hydroxyl radical scavenging capacities of both metabolites were enhanced by one- to three-fold compared with HS and LS. These results indicate that both sericins, regardless of molecular size, have significantly enhanced antioxidant, superoxide free radical scavenging, and glycosidase inhibitory activities after simulated metabolism, and that LS is better than HS regardless of simulated digestion. These results confirm that sericin is important in the sustainable development and utilization of silk resources, especially the reduction in environmental pollution, and provides new ideas for the development of adjuvant treatments for diabetes and the development of foods with anti-hyperglycemic functions.

Degraded Sericin Significantly Regulates Blood Glucose Levels and Improves Impaired Liver Function in T2D Rats by Reducing Oxidative Stress.

Sericin could be degraded well into low-molecular-weight sericin (SS) through a novel and environmentally friendly recycling process using an ultrasonically degumming method in Ca(OH)2 aqueous solution. The oral administration of the SS has an evidently hypoglycemic effect on STZ-induced T2D rats. At oral doses of 2.5 and 5% SS for four weeks, the fasting blood glucose decreased by over 60% compared with that in the untreated model group. Oral glucose tolerance and insulin tolerance were ameliorated by the peptide treatment. The serum insulin level was reduced by approximately 35%, the insulin resistance index was reduced by more than 66%. The 8-hydroxy-2 deoxyguanosine level showed a large reduction of 20%, and the total antioxidant activities significantly increased. Hematoxylin-eosin staining and fluorescent immunostaining sections showed that liver and pancreas damage was partly recovered in T2D rats. In summary, oral SS demonstrated evidently hypoglycemic effects mainly related to reducing oxidative stress in the damaged liver and pancreas of T2D rats. Therefore, these results have suggested that the degraded sericin has a potential use in SS-based healthy functional food or hypoglycemic drugs as a waste recovered from sericulture resources.

Significantly hypoglycemic effect of a novel functional bread rich in mulberry bark and improving the related functions of liver, pancreas, and kidney, on T2D mice.

To develop a novel functional food with lowering blood glucose for diabetics, the mixed bread containing mulberry branch bark powder (MBBP) was used for the oral administration of the type 2 diabetic (T2D) mice induced by streptozocin (STZ), high-fat and high-sugar diet for 7 weeks. 5%, 10%, and 15% MBBP bread diets had a significatively positive influence on the biochemical indicators, histological examination, and immunohistochemistry observations in T2D mice. The 15% MBBP-rich bread diet evidently retarded loss weight of T2D mice, and decreased in FBG by about 55% and in glycosylated hemoglobin (HbA1c) levels by about 30%. Its glucose tolerance and serum insulin levels were very close to normal level. The abnormal lipid metabolism and insulin-related index of T2D mice in both the 10% and 15% MBBP bread diet groups were partly reversed. The Western blotting results showed that the expression levels of key proteins in PI3K/AKT signaling pathway were decreased and expression levels of immunoproteins PPARγ, TNF-α, P65, and IL6 were increased. In general, oral MBBP bread diets effectively restored some functions and repaired damage to the pancreas, liver, and kidney in T2D mice. Therefore, MBBP is potential to develop into a novel functional food additive with significantly hypoglycemic effect.

Antioxidant and Hemolysis Protective Effects of Polyphenol-Rich Extract from Mulberry Fruits.

BACKGROUND: Mulberry fruits are a superior source of polyphenol, especially anthocyanins that contribute potentially to the beneficial effects which include reducing the risk of cardiovascular diseases and cancers with antioxidant, anti-inflammatory, and chemoprotective properties. OBJECTIVES: In this study, purification of the polyphenol-rich extract from mulberry fruit (MPE) was purified and assessed the activities of antioxidant and hemolysis protective in vivo and in vitro. MATERIALS AND METHODS: Antioxidant activities in vitro was measured by quantifying its 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity, reducing power and Fe2+-chelating ability. MPE was purified by high-pressure liquid chromatography (HPLC) and analyzed individual polyphenols using liquid chromatography-mass spectrometry (LC-MS)/MS. RESULTS: The total polyphenol content was 147.69 ± 0.02 mg gallic acid equivalents (GAE)/g dried weight (DW) in the extract and 403.55 ± 0.02 mg GAE/g DW in the purified extract. Further identification by HPLC-ultraviolet-visible and LC-MS/MS analysis indicated in MPE, an anthocyanin compound, cyanidin-3-O-glucoside. With regard to in vitro assays, MPE possessed antioxidant effect, especially in Fe2+ chelating ability with an IC50 value of 1.016 mg/mL. The protective effects on mouse red blood cell hemolysis and lipid peroxidation ex vivo were dose and time dependent. CONCLUSION: It indicates that MPE could be a good candidate for future biomedical applications to promote human health with limited side effects. SUMMARY: Mulberry fruit is an excellent source of polyphenols, in particular, anthocyanins, which has infinite health benefits. This study determined the predominant anthocyanin, cyanidin-3-glucoside, could possibly be the rationale behind the antioxidant and antihemolytic effect of MPE. Results indicate that MPE could be a good candidate for future biomedical applications to promote human health with limited side effects. Abbreviations used: MPE: Purification of the polyphenol-rich extract from mulberry fruit, LC-MS: Liquid chromatography-mass spectrometry, HPLC: High-pressure liquid chromatography, DPPH: 2,2-diphenyl-1-picrylhydrazyl scavenging activity, RBC: Red blood cell, GAE: Gallic acid equivalent, FeCl2: Ferrous chloride, H2O2: Hydrogen peroxide, EDTA-2Na: Ethylenediaminetetraacetic acid disodium salt, PBS: Phosphate-buffered saline, TCA: Trichloroacetic acid, TBA: 2-thiobarbituric acid, FeSO4: Ferrous sulphate, MDA: Malondialdehyde, VC: Vitamin C, DW: Dried weight.