Brain glucose hypometabolism and hippocampal inflammation in Goto-Kakizaki rats

Brain glucose hypometabolism and neuroinflammation are early pathogenic manifestations in neurological disorders. Neuroinflammation may also disrupt leptin signaling, an adipokine that centrally regulates appetite and energy balance by acting on the hypothalamus and exerting neuroprotection in the hippocampus. The Goto-Kakizaki (GK) rat is a non-obese type 2 diabetes mellitus (T2DM) animal model used to investigate diabetes-associated molecular mechanisms without obesity jeopardizing effects. Wistar and GK rats received the maintenance adult rodent diet. Also, an additional control group of Wistar rats received a high-fat and high-sugar diet (HFHS) provided by free consumption of condensed milk. All diets and water were provided ad libitum for eight weeks. Brain glucose uptake was evaluated by 2-deoxy-2-[fluorine-18] fluoro-D-glucose under basal (saline administration) or stimulated (CL316,243, a selective β3-AR agonist) conditions. The animals were fasted for 10-12 h, anesthetized, and euthanized. The brain was quickly dissected, and the hippocampal area was sectioned and stored at -80°C in different tubes for protein and RNA analyses on the same animal. GK rats exhibited attenuated brain glucose uptake compared to Wistar animals and the HFHS group under basal conditions. Also, the hippocampus of GK rats displayed upregulated leptin receptor, IL-1β, and IL-6 gene expression and IL-1β and the subunit of the transcription factor NF-κB (p-p65) protein expression. No significant alterations were detected in the hippocampus of HFHS rats. Our data indicated that a genetic predisposition to T2DM has significant brain deteriorating features, including brain glucose hypometabolism, neuroinflammation, and leptin signaling disruption in the hippocampal area.

Protective Effect of Salvianolic Acid B in Goto-kakizaki Rats Complicated with Macroangiopathy / 中国药师

Objective:To study the protective effect and possible mechanism of salvianolic acid B in GK rats complicated with macroangiopathy. Methods:Totally 32 GK rats were randomly divided into four groups:the model group and low,middle and high dose salvianolic acid B groups(40,80 and 160 mg·kg - 1 ),and 8 Wistar rats were used as the normal group. All of GK rats were giv-en high-glucose and high-fat diet. After 16 weeks,GK rats were orally administrated with 10 mg·kg - 1 ·d - 1 N-ω-nitro-L-arginine methyl ester for 8 weeks. At the beginning and the end of the experiment,blood glucose and blood pressure were measured,abdominal aortic blood was collected after anesthesia,thoracic aorta was used to make paraffin sections after bloodletting to observe vasculopathy and the expression of VEGF was detected by Western-blot. Results:The blood glucose was increased in all GK rats with no statistical significance between the drug group and the model group(P > 0. 05). At the end of the experiment,the blood pressure was significant-ly increased in GK rats,indicating that salvianolic acid B could notably reduce the blood pressure in GK rats in a dose-dependent man-ner with statistical significance(P < 0. 05);and it could also remarkably reduce the total white blood cell count and differential blood count,and ameliorate the lesion extent and reduce VEGF expression. Conclusion:Salvianolic acid B has protective effects on aorta in GK rats,and its mechanism may be related with blood pressure lowering,anti-inflammation and reduction of VEGF expression.

The establishment of diabetic peripheral neuropathy model in spontaneous diabetic GK rats / 天津医药

Objective To establish a simple diabetic peripheral neuropathy (DPN) rat model with the high fat-fed in GK rats. Methods A total of 30 GK rats (7-8 weeks) were fed with high-fat diet to establish the DPN model. Thirty normal Wistar rats were fed with ordinary diet (control group). The blood-sugar value, body mass, water-intake and food-intake were monitored every week in two groups. The serum level of glycosylated hemoglobin, the right sciatic nerve conduction velocity were detected at 8, 12 and 16 weeks respectively. The left sciatic nerve was used for HE and TUNEL staining. Results The manifestations of polydipsia, polyphagia and growth retardation were gradually appeared in GK rats. After 12 and 16 weeks, the blood-sugar and glycosylated hemoglobin were significantly increased in GK rats compared with those of normal Wistar rats (P 0.05). The sciatic nerve pathological features and Schwann cell apoptosis suggested that the model of DPN was successfully established (apoptosis index, P <0.01). Conclusion GK rats fed by high-fat diet are the satisfactory models of the DPN in experimental research. And 12-week is a suitable and economical time for molding.

Amelioration effect of duodenal-jejunal bypass surgery on insulin-resistance in Goto-Kakizaki rats / 中国实验动物学报

Objective To establish a Goto-Kakizaki ( GK) rat model of duodenal-jejunal bypass( DJB) and ob-serve the changes in insulin-resistance after surgery, and to explore the mechanism of DJB surgery in treatment of type 2 di-abetes mellitus.Methods Male Goto-kakizaki diabetic rats(GK,n=36)were used as experiment group and 18 healthy male Wistar rats as blank group.GK rats were randomly divided into two groups: diabetic control group and DJB surgery group ( n=18) .Euglycemic-hyperinsulinemic clamp technique was performed in 6 rats randomly taken from each group at third week, sixth week and ninth week after surgery, respectively.The expression levels of Gck, G6P, PEPCK mRNA in the liver and GLUT4 content on skeletal muscle cell plasma membrance were detected one week after the clamp test. Results In the DJB surgery group at the end of third week and sixth week after surgery, the levels of glucose infusion rates and the expression levels of Gck, G6P, PEPCK mRNA in the liver showed no statistically significant difference as com-pared with the diabetic control group (P>0.05).In the DJB surgery group at the end of 9th week after surgery, the glu-cose infusion rate and expression level of Gck mRNA in the liver were significantly higher, and the expression of G6P and PEPCK mRNA was significantly lower than those in the diabetic control group ( P0.05 for all) .Conclusions Our results indicate that the mechanism of DJB surgery improving blood glucose level may be closely related to the amel-ioration of insulin-resistance in the liver, thereby augmenting glucose uptake and inhibiting gluconeogenesis in liver through the regulation of glucose metabolism-related enzymes.There is no significant improvement in insulin-resistance in the skele-tal muscles during the experiment period.This result implies that the effect of DJB surgery on type 2 diabetes is related to the duration of therapy.

Protective effect of catalpol on diabetic rat aorta and its antioxidant mechanisms / 中国病理生理杂志

AIM:To investigate the protective effect of catalpol on Goto-kakizaki (GK) rat aorta and to ex-plore its antioxidant mechanisms.METHODS:Six-month-old GK rats (n=45) were randomly divided into diabetic model group, metformin (100 mg· kg-1· d-1) group, and high-dose (100 mg· kg-1· d-1), medium-dose (50 mg· kg-1· d-1) and low-dose (10 mg· kg-1· d-1) catalpol groups.The healthy male Wistar rats (n=10) were used as control group.The rats in control and model groups were given a same volume of saline .All reagents were administered by oral ga-vage for 12 weeks.Blood glucose and lipids were detected by an automatic biochemical analyzer .Serum reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) levels were detected by commercial kits .The expression of nuclear factor E2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) in the thoracic aorta was determined by Western blotting .The pathological changes of the thoracic aorta were observed by HE staining.The ultrastructural changes of the thoracic aorta were observed under electron microscope .RESULTS:Af-ter catalpol treatment , the levels of blood glucose and blood lipids were decreased significantly , and serum levels of ROS and MDA were significantly decreased , but the activity of SOD and T-AOC were significantly enhanced .The protein ex-pression of Nrf2 and HO-1 in the thoracic aorta were significantly increased , the thoracic aortic lesions indicated by HE staining significantly reduced , and the thoracic aortic damage under ultrastructural observation was attenuated slightly . CONCLUSION:Catalpol effectively protects GK rat thoracic aorta , which may be associated with decreasing blood lipids , reducing oxidative stress and activating Nrf 2/ARE/HO-1 signaling pathways.

Effect of the combination of metformin and fenofibrate on glucose homeostasis in diabetic Goto-Kakizaki rats

Metformin has been reported to increase the expression of the glucagon-like peptide-1 (GLP-1) receptor in pancreatic beta cells in a peroxisome proliferator-activated receptor (PPAR)-alpha-dependent manner. We investigated whether a PPARalpha agonist, fenofibrate, exhibits an additive or synergistic effect on glucose metabolism, independent of its lipid-lowering effect, when added to metformin. Non-obese diabetic Goto-Kakizaki (GK) rats were divided into four groups and treated for 28 days with metformin, fenofibrate, metformin plus fenofibrate or vehicle. The random blood glucose levels, body weights, food intake and serum lipid profiles were not significantly different among the groups. After 4 weeks, metformin, but not fenofibrate, markedly reduced the blood glucose levels during oral glucose tolerance tests, and this effect was attenuated by adding fenofibrate. Metformin increased the expression of the GLP-1 receptor in pancreatic islets, whereas fenofibrate did not. During the intraperitoneal glucose tolerance tests with the injection of a GLP-1 analog, metformin and/or fenofibrate did not alter the insulin secretory responses. In conclusion, fenofibrate did not confer any beneficial effect on glucose homeostasis but reduced metformin's glucose-lowering activity in GK rats, thus discouraging the addition of fenofibrate to metformin to improve glycemic control.

The effect of duodenal-jejunal bypass on the expression of ileum proglucagon mRNA in Goto-Kakizaki type 2 diabetic rats / 中华内分泌外科杂志

Objective To investigate the effect of duodenal-jejunal bypass(DJB) on glucose metabolism and the expression of ileum proglucagon mRNA in Goto-Kakizaki (GK) type 2 diabetic rats.Methods 18 male GK rats and 1 8 male Wistar rats were randomly divided into 4 groups:GK operation group(group A),GK sham operation group(group B),Wistar operation group (group C),Wistar sham operation group (group D).There were 9 rats in each group.The fasting blood glucose and GLP-1 levels were measured before and at the 8th weekafter surgery.Oral glucose tolerance test was measured,and the area under blood glucose concentration curve wascalculated.Ileum tissues were obtained 8 weeks postoperatively and reverse transcriptase polymerase chain reac-tion was used to detect ileum PG mRNA expression after the operation.Results At the 8th week after surgery,the fasting blood glucose of group A decreased from(8.73 ± 1.30) mmol/L to(5.86 ±0.57) mmol/L(P ＜0.05).Area under blood glucose concentration curve decreased from preoperative(60.23 ± 5.14)mmol · h/L to (47.80 ±1.79) mmol· h/L(P ＜ 0.05).Fasting serum GLP-1 in group A increased from (7.69 ± 0.74) pmol/L to (29.00 ±4.85) pmol/L while postprandial GLP-1 increased from(15.74 ± 5.71) pmol/L to (45.78 ± 7.26) pmol/L (P ＜0.05).At the 8th week after surgery,the ileum PG mRNA level in group A was significantly higher than that in group B(P ＜ 0.05).Conclusions DJB can directly improve glucose metabolism in non-obese type 2 diabetic rats,and the operation has no hypoglycemic effect on normal blood glucose.The increased expression of ileum PG mRNA might contribute to the hypoglycemic effect of the surgery.

Postprandial hypoglycemic effect of mulberry leaf in Goto-Kakizaki rats and counterpart control Wistar rats

Postprandial hypoglycemic effect of mulberry leaf (Morus alba L.) was compared in two animal models: Goto-Kakizaki (GK) rats, a spontaneous non-obese animal model for type II diabetes, and their counterpart control Wistar rats. First, the effect of a single oral administration of mulberry leaf aqueous extract (MLE) on postprandial glucose responses was determined using maltose or glucose as substrate. With maltose-loading, MLE reduced peak responses of blood glucose significantly in both GK and Wistar rats (P < 0.05), supporting the inhibition of alpha-glucosidase by MLE in the small intestine. With glucose-loading, MLE also significantly reduced blood glucose concentrations, measured at 30 min, in both animal models (P < 0.01), proposing the inhibition of glucose transport by MLE. Next, dried mulberry leaf powder (MLP) was administered for 8 weeks by inclusion in the diet. By MLP administration, fasting blood glucose was significantly reduced at weeks 4 and 5 (P < 0.05), but then returned to values that were similar to those of the control at the end of experimental period in GK rats. Insulin, HOMA-IR, C-reactive protein, and triglycerides tended to be decreased by MLP treatment in GK rats. All other biochemical parameters were not changed by MLP administration in GK rats. Collectively, these findings support that MLE has significant postprandial hypoglycemic effect in both non-obese diabetic and healthy animals, which may be beneficial as food supplement to manage postprandial blood glucose. Inhibitions of glucose transport as well as alpha-glucosidase in the small intestine were suggested as possible mechanisms related with the postprandial hypoglycemic effect of MLE.