This study was designed to investigate the protective effect of a methanol extract of Chungkookjang (CKJ) on high glucose induced oxidative stress in LLC-PK 1 cells (renal tubular epithelial cells), which are susceptible to oxidative stress. Freeze dried CKJ powder was extracted with methanol, and the extract solution was concentrated, and then used in this study. To determine the protective effect of CKJ extract, oxidative stress was induced by exposing of LLC-PK 1 cells to high glucose (30 mM) or normal glucose (5 mM) for 24 hr. Exposure of LLC-PK 1 cells to high glucose for 24 hr resulted in a significant (p<0.05) decrease in cell viability, catalase, SOD and GSH-px activity and a significant (p<0.05) increase in intracellular ROS level and thiobarbituric acid reactive substances (TBARS) formation in comparison to the cells treated with 5 mM glucose. CKJ extract treatment decreased intracellular ROS level and TBARS formation, and increased cell viability and activities of antioxidant enzymes including catalase, SOD and GSH-px in high glucose pretreated LLC-PK 1 cells. These results suggest that CKJ extract may be able to protect LLC-PK 1 cells from high glucose-induced oxidative stress, partially through the antioxidative defense systems.

This study investigated the hypoglycemic effect of fermented soymilk extract (FSE) in STZ-induced diabetic mice. FSE was prepared via fermentation of soymilk with Bacillus subtilis followed by methanol extraction. The hypoglycemic effect was determined by inhibitory activities against α-glucosidase and α-amylase as well as the alleviation of postprandial glucose level. The non-fermented soymilk extract (SE) was used as control in this experiment. FSE showed higher (p＜0.05) inhibitory activities than SE against α-glucosidase and α-amylase. The IC 50 values of FSE for α-glucosidase and α-amylase were 0.77 and 0.94 mg/mL, respectively, which were comparable or even superior to those of acarbose (0.79 and 0.68 mg/mL, respectively). In addition, a further suppression on the postprandial blood glucose levels were observed in the FSE than SE group for both STZ-induced diabetic mice and normal mice. Furthermore, FSE significantly lowered the incremental area under the curve (AUC) in the diabetic mice and the AUC in normal mice corroborated the hypoglycemic effect of FSE (p＜0.05). Results from this study suggest that FSE may help decrease the postprandial blood glucose level via inhibiting α-glucosidase and α-amylase and the usefulness of FSE was proven to be better than SE.

To further the goal of isolating Bacillus sp. from commercial chungkukjang (CKJ) for a development of a probiotic dietary adjunct using soymilk or milk, antioxidant activity of CKJ purchased from the Sunchang Traditional Village in Chunbook province was examined. Six CKJ samples were evaluated and 3 were selected based on the results of the physicochemical analysis and sensory evaluation for further antioxidant study. IC 50 for DPPH scavenging activity of methanol extracts of CKJ ranged from 238.1 to 345.7 μg/mL. CKJ exhibited over 80% scavenging of •OH and ONOO-at concentrations of 100 μg/mL and 250 μg/mL, respectively. O 2 -and NO scavenging activities of three CKJ were increased in a dose dependent manner with the concentration tested from 100 to 1000 μg/mL. In this study, the methanol extract of CKJ exhibited a great reduction capability and powerful free radical scavenging activity, especially against OH -and ONOO -, which are the most toxic radicals responsible for oxidative damage in the body. However, radical scavenging effects of CKJ on DPPH, O 2 -, and nitrite radical were rather moderate. In conclusion, CKJ may reduce the oxidative stress in the body by scavenging the free radicals.

We investigated whether the fermented soymilk extract (FSE) has protective effects against high glucose-induced oxidative stress in human umbilical vein endothelial cells (HUVECs). FSE was prepared via fermentation of soymilk with Bacillus subtilis followed by methanol extraction. To determine the protective effect of FSE, oxidative stress was induced by exposing of HUVECs to the high glucose (30 mM) for 48 hr. Exposure of HUVECs to high glucose for 48 hr resulted in a significant (p<0.05) decrease in cell viability, catalase, SOD and GSH-px activity and a significant (p<0.05) increase in intracellular ROS level and thiobarbituric acid reactive substances (TBARS) formation in comparison to the cells treated with 5.5 mM glucose. However, at concentration of 0.1 mg/mL, FSE treatment decreased intracellular ROS level and TBARS formation, and increased cell viability and activities of antioxidant enzymes including catalase, SOD and GSH-px in high glucose pretreated HUVEC. These results suggest that FSE may be able to protect HUVECs from high glucose-induced oxidative stress, partially through the antioxidative defense systems.