Abstract
Jerusalem artichoke (Helianthus tuberosus Linne, HTL) and chungkookjang (CKJ; fermented soybeans) both modulate energy and glucose metabolism. However, the mechanism and their additive effects are unknown. We investigated whether the consumption of HTL and CKJ altered insulin sensitivity, insulin secretion capacity and β-cell survival in type 2 diabetic animals. Rats were divided into partially pancreatectomized (Px) diabetic rats, and sham operated non-diabetic control rats and all fed high fat diets. Diabetic rats were sub-divided into an untreated diabetic control group and those fed 5% HTL, 5% CKJ or 5% HTL+5% CKJ for 8 weeks. HTL+CKJ treatment reduced visceral fat without modulating energy intake compared to the diabetic-control. Glucose tolerance was improved in an ascending order of diabetic-control, CKJ, HTL, HTL+CKJ, and normal-control, but by different mechanisms. CKJ and CKJ+HTL, but not HTL, increased first and second phase insulin secretion in comparison to the diabetic-control at hyperglycemic clamp. However, glucose infusion rates (mg/kg bw/min) were increased by and CKJ+HTL (13.5), but not HTL (9.4) or CKJ (9.5) alone, and HTL and CKJ+ HTL decreased hepatic glucose compared to diabetic-control during the hyperinsulinemic euglycemic study and were associated with decreased triglyceride accumulation and increased glycogen storage. The improved hepatic insulin sensitivity by HTL and CKJ+HTL was explained by potentiated insulin signaling (tyrosine phosphorylation of insulin receptor substrate 2→phosphorylation of Akt) and phosphorylation of AMPK→phosphorykation of acetyl Co carboxlase in comparison to diabetic-control and decreased PEPCK expression. Absolute β-cell mass was increased by CKJ (23.4mg) and CKJ+HTL (26.3 mg) by increasing proliferation compared to the diabetic-control (21.26 mg). Although HTL lowered β-cell apoptosis, it did not increase β-cell mass (20.8 mg). In conclusions, HTL and CKJ enhanced glucose tolerance in different manners, and exhibited partially additive and complementary effects by reversing insulin resistance and enhancing β-cell function in diabetic rats.
Highlights
East Asians have traditionally maintained good glycemic control [1]
We previously reported that 8 week consumption of the fermented soybean food, chungkookjang (20% of the diet), increases β-cell function and mass and attenuates insulin resistance in type 2 diabetic rats [6,7]
Jerusalem artichoke (Helianthus tuberosus Linne) is a native plant to North America in the daisy family; its tubers are available in the produce section of many grocery stores in worldwide including Korea and are a common commercial source of inulin
Summary
East Asians have traditionally maintained good glycemic control [1]. the incidence of diabetes is increasing due to low quality diets early in life and greater consumption of animal fats and less activity in later life [2,3]; changes which exacerbate insulin resistance [3] and lead to type 2 diabetes [2,4]. We previously reported that 8 week consumption of the fermented soybean food, chungkookjang (20% of the diet), increases β-cell function and mass and attenuates insulin resistance in type 2 diabetic rats [6,7]. Jerusalem artichoke may improve insulin sensitivity since inulin, its major component, decreases the synthesis of triglycerides and fatty acids in the liver and lowers their circulating levels in rats [8,9]. It decreases fasting serum glucose levels in healthy humans [10], which may be related to its fructan and coumarins such as ayapin and scopletin [8]. The anti-diabetic effects of moderate amounts of chungkookjang (soybeans fermented with Bacilli spp.) and Jerusalem artichoke were determined in type 2 diabetic rats and some of the potential mechanisms explored
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