Diabetes is prevalent worldwide, with >90% of the cases identified as Type 2 diabetes. High blood sugar (hyperglycemia) is the hallmark symptom of diabetes, with prolonged and uncontrolled levels contributing to subsequent complications. Animal models have been used to study these complications, which include retinopathy, nephropathy, and peripheral neuropathy. More recent studies have focused on cognitive behaviors due to the increased risk of dementia/cognitive deficits that are reported to occur in older Type 2 diabetic patients. In this review, we collate the data reported from specific animal models (i.e., mouse, rat, zebrafish) that have been examined for changes in both retina/vision (retinopathy) and brain/cognition, including db/db mice, Goto-Kakizaki rats, Zucker Diabetic Fatty rats, high-fat diet-fed rodents and zebrafish, and hyperglycemic zebrafish induced by glucose immersion. These models were selected because rodents are widely recognized as established models for studying diabetic complications, while zebrafish represent a newer model in this field. Our goal is to (1) summarize the published findings relevant to these models, (2) identify similarities in cellular mechanisms underlying the disease progression that occur in both tissues, and (3) address the hypothesis that hyperglycemic-induced changes in retina precede or predict later complications in brain.

As one of the most abundant plant polyphenols in the human diet, (-)-epicatechin (EC) can improve insulin sensitivity and regulate glucose homeostasis. However, the primary mechanisms involved in EC anti-T2DM benefits remain unclear. The present study explored the effects of EC on the gut microbiota and liver transcriptome in type 2 diabetes mellitus (T2DM) Goto-Kakizaki rats for the first time. The findings showed that EC protected glucose homeostasis, alleviated systemic oxidative stress, relieved liver damage, and increased serum insulin. Further investigation showed that EC reshaped gut microbiota structure, including inhibiting the proliferation of lipopolysaccharide (LPS)-producing bacteria and reducing serum LPS. In addition, transcriptome analysis revealed that the insulin signaling pathway may be the core pathway of the EC anti-T2DM effect. Therefore, EC may modulate the gut microbiota and liver insulin signaling pathways by the gut-liver axis to alleviate T2DM. As a diet supplement, EC has promising potential in T2DM prevention and treatment.

Vascular endothelial insulin resistance (IR) is an important risk factor in the development of vascular complications in diabetes. Prolonged endoplasmic reticulum stress (ERS) contributes to the development and progression of endothelial IR. The current study assessed the effects and mechanism of nebivolol on vascular IR in Goto-Kakizaki (GK) rats and endothelial IR induced by high glucose (33.3 mmol/L) associated with high insulin (10-7 mol/L) in human aortic endothelial cells (HAECs). Rats were divided into Wistar, Wistar + Neb (Wistar rats treated with nebivolol, 10 mg/kg, ig), GK, and GK + Neb (GK rats treated with nebivolol, 10 mg/kg, ig). GK rats showed hyperglycemia, dyslipidemia, impaired glucose homeostasis, metabolic IR, reduced relaxation to insulin, and lower serum nitric oxide (NO) level. Treatment with nebivolol for 4 months ameliorated insulin\'s vasorelaxation and NO production, and relieved dyslipidemia in GK rats. Additionally, nebivolol increased glucose uptake and NO level in the endothelial IR group in vitro. Nebivolol increased aortic expressions of IRS-1/PI3K/Akt/eNOS relative proteins and GLUT4 and reduced expressions of ERS markers (ATF6, GRP78, and CHOP, p-JNK/JNK). Furthermore, both nebivolol and TUDCA (ERS inhibitor) alleviated the attenuated IRS-1PI3K/Akt/eNOS pathway and enhanced ERS in HAECs IR. Tunicamycin (ERS inducer) not only induced endothelial IR but also blocked nebivolol\'s alleviation on the IRS-1PI3K/Akt/eNOS pathway and ERS. Nebivolol ameliorated endothelial IR partially by inhibiting ERS and then regulating the IRS-1/PI3K/Akt/eNOS signal.

Obesity is associated with the development of insulin resistance (IR) and type-2 diabetes mellitus (T2DM); however, not all patients with T2DM are obese. The Goto-Kakizaki (GK) rat is an experimental model of spontaneous and non-obese T2DM. There is evidence that the intestine contributes to IR development in GK animals. This information prompted us to investigate small intestine remodeling in this animal model.
Four-month-old male Wistar (control) and GK rats were utilized for the present study. After removing the small intestine, the duodenum, proximal jejunum, and distal ileum were separated. We then measured villi and muscular and mucosa layer histomorphometry, goblet cells abundance, total myenteric and submucosal neuron populations, and inflammatory marker expression in the small intestinal segments and intestinal transit of both groups of animals.
We found that the GK rats exhibited decreased intestinal area (p < 0.0001), decreased crypt depth in the duodenum (p = 0.01) and ileum (p < 0.0001), increased crypt depth in the jejunum (p < 0.0001), longer villi in the jejunum and ileum (p < 0.0001), thicker villi in the duodenum (p < 0.01) and ileum (p < 0.0001), thicker muscular layers in the duodenum, jejunum, and ileum (p < 0.0001), increased IL-1β concentrations in the duodenum and jejunum (p < 0.05), and increased concentrations of NF-κB p65 in the duodenum (p < 0.01), jejunum and ileum (p < 0.05). We observed high IL-1β reactivity in the muscle layer, myenteric neurons, and glial cells of the experimental group. GK rats also exhibited a significant reduction in submucosal neuron density in the jejunum and ileum, ganglionic hypertrophy in all intestinal segments studied (p < 0.0001), and a slower intestinal transit (about 25%) compared to controls.
The development of IR and T2DM in GK rats is associated with small intestine remodeling that includes marked alterations in small intestine morphology, local inflammation, and reduced intestinal transit.

Type 2 diabetes mellitus (T2DM) is one of the most prevalent endocrine diseases in the world. Recent studies have shown that dysbiosis of the gut microbiota may be an important contributor to T2DM pathogenesis. However, the mechanisms underlying the roles of the gut microbiome and fecal metabolome in T2DM have not been characterized. Recently, the Goto-Kakizaki (GK) rat model of T2DM was developed to study the clinical symptoms and characteristics of human T2DM. To further characterize T2DM pathogenesis, we combined multi-omics techniques, including 16S rRNA gene sequencing, metagenomic sequencing, and metabolomics, to analyze gut microbial compositions and functions, and further characterize fecal metabolomic profiles in GK rats. Our results showed that gut microbial compositions were significantly altered in GK rats, as evidenced by reduced microbial diversity, altered microbial taxa distribution, and alterations in the interaction network of the gut microbiome. Functional analysis based on the cluster of orthologous groups (COG) and Kyoto Encyclopedia of Genes and Genomes (KEGG) annotations suggested that 5 functional COG categories belonged to the metabolism cluster and 33 KEGG pathways related to metabolic pathways were significantly enriched in GK rats. Metabolomics profiling identified 53 significantly differentially abundant metabolites in GK rats, including lipids and lipid-like molecules. These lipids were enriched in the glycerophospholipid metabolic pathway. Moreover, functional correlation analysis showed that some altered gut microbiota families, such as Verrucomicrobiaceae and Bacteroidaceae, significantly correlated with alterations in fecal metabolites. Collectively, the results suggested that an altered gut microbiota is associated with T2DM pathogenesis.

This study was aimed to investigate the mechanism of Danzhi Jiangtang Capsules( DJC) in the treatment of diabetic macrovascular disease in Goto-Kakizaki( GK) rats. The diabetic macrovascular disease rat model was induced by feeding high-fat and high-sugar combined with endothelial nitric oxide synthase( NOS) inhibitor N-nitro-L-arginine methyl ester( L-NAME)( 0. 1 g·L-1·d-1). According to the random array table,the model rats were randomly divided into the model group,DJC groups( 1 260,630,320 mg·kg-1),atorvastatin group( 105 mg·kg-1) and metformin group( 10 mg·kg-1),with 12 rats in each group. The rats received gavage administration for 8 weeks. Twelve Wistar rats were selected as the normal control group. The changes of body weight,water intake,blood glucose,plasma total cholesterol( TC),triglyceride( TG),high density lipoprotein( HDL-C),low density lipoprotein( LDL-C),interleukin( IL-1β),IL-6,tumor necrosis factor( TNF-α),nitric oxide( NO),endothelin( ET-1) were observed in these rats. Aortic tissue was taken and the pathological changes were observed by HE staining. RT-PCR was used to detect the mRNA levels of IL-1β,IL-6,and TNF-α in rat aorta. RT-PCR of the stem loop was used to detect the levels of miRNA-126,miRNA-155,miRNA-146 a,and miRNA-21 in rat plasma and aortic tissue. The canonical correlation between miRNAs and inflammatory factors was then analyzed. The results showed that DJC increased the rat body weight,lowered water intake,reduced the random blood glucose,reversed the rat aorta tissue damage,reduced serum TC,TG,LDL-C,ET-1,IL-1β,IL-6,TNF-α,as well as miRNA-155,miRNA-146 a and miRNA-21 levels in serum,elevated plasma HDL-C,NO content,reduced the aorta mRNA of IL-1β,IL-6,TNF-α,and the miRNA-155,miRNA-146 a and miRNA-21,elevated miRNA-126 expression in aorta. Aortic miRNA-126,miRNA-155,miRNA-146 a and miRNA-21 expression levels were typically correlated with the expression of inflammatory factors,among which miRNA-126 was negatively correlated,miRNA-155,miRNA-146 a and miRNA-21 were positively correlated with the factors. These results suggested that DJC had therapeutic effects on diabetic macrovascular diseases,and the mechanism of action may be related to the regulation of miRNA-126,miRNA-155,miRNA-146 a and miRNA-21 levels,as well as the reduction of inflammatory factors and vascular inflammatory response.

The present study was carried out to investigate the hypoglycemic effect of soy isoflavones from hypocotyl in GK diabetic rats. A single administration and long-term administration tests were conducted in GK diabetic rats to test the hypoglycemic effect of soy isoflavones. At the end of long-term administration trial, blood protein, cholesterol, triglyceride, glycosylated serum protein, C-reactive protein, insulin, aminotransferase, lipid peroxide, interleukin-6, tumor necrosis factor-α were estimated. Inhibition of soy isoflavones against α-amylase and α-glucosidase, as well as on glucose uptake into brush border membrane vesicles or Caco-2 cells were determined in vitro. In single administration experiment, soy isoflavones reduced postprandial blood glucose levels in GK rats. In long-term administration, hypoglycemic effect of soy isoflavones was first observed at week 12 and maintained till week 16. A significant reduction in fasting blood glucose, C-reactive protein, and lipid peroxide was noted at week 16. However, there was no significant treatment effect on blood insulin. Furthermore, soy isoflavone administration resulted in significant decreases in glycosylated serum protein, tumor necrosis factor-α, and interleukin-6. Other biochemical parameters, such as protein, cholesterol, triglyceride and aminotransferases were not modified, however. The results in vitro showed that soy isoflavones showed a potent inhibitory effect on intestinal α-glucosidase, but not on pancreatic α-amylase. Soy isoflavones also decreased glucose transport potency into brush border membrane vesicles or Caco-2 cells. It is concluded that soy isoflavones from hypocotyl, performs hypoglycemic function in GK rats with type 2 diabetes, maybe via suppression of carbohydrate digestion and glucose uptake in small intestine.

BACKGROUND: Sitagliptin, a dipeptidyl peptidase-4 (DPP-4) inhibitor used in type 2 diabetes therapy, has demonstrated protective effects in diabetic chronic kidney disease, in part due to its pleiotropic actions. However, its potential direct effects on the kidney are still not completely defined. Here, by means of proteomics and miRNA profiling, we have further unveiled the role of sitagliptin in oxidative stress, as well as the underlying mechanisms.
METHODS: Renal cortex samples from 9-month-old wild-type (Wistar), type II diabetic Goto-Kakizaki (GK) and sitagliptin-treated GK rats (GK+Sita) (10 mg kg-1 per day) were subjected to quantitative miRNA transcriptomic array, immunohistochemistry and Western blot studies. Renal GK and GK+Sita samples were also analyzed by differential in-gel electrophoresis. Bioinformatic tools were used to find out the relationships between altered proteins and related miRNA expression. Studies were also carried out in cultured tubular cells to confirm in vivo data.
RESULTS: Diabetic GK rats exhibited proteinuria, renal interstitial inflammatory infiltrates and fibrosis, which improved by 20 weeks of sitagliptin treatment. Proteomic analysis of diabetic GK and Wistar rats showed a differential expression of 39 proteins mostly related to oxidative stress and catabolism. In addition, 15 miRNAs were also significantly altered in GK rats.
CONCLUSIONS: Treatment with sitagliptin was associated with modulation of antioxidant response in the diabetic kidney, involving a downregulation of miR-200a, a novel Keap-1 inhibitor and miR-21, coincidentally with the clinical and the morphological improvement. These data further support the concept that DPP-4 inhibitors could exert a direct reno-protective effect in patients with diabetic nephropathy.

Progressive metabolic complications accompanied by oxidative stress are the hallmarks of type 2 diabetes. The precise molecular mechanisms of the disease complications, however, remain elusive. Exercise-induced nontherapeutic management of type 2 diabetes is the first line of choice to control hyperglycemia and diabetes associated complications. In this study, using 11-month-old type 2 Goto-Kakizaki (GK) rats, we have investigated the effects of exercise on mitochondrial metabolic and oxidative stress in the pancreas. Our results showed an increase in theNADPHoxidase enzyme activity and reactive oxygen species (ROS) production inGKrats, which was inhibited after exercise. Increased lipid peroxidation and protein carbonylation andSODactivity were also inhibited after exercise. Interestingly, glutathione (GSH) level was markedly high in the pancreas ofGKdiabetic rats even after exercise. However,GSH-peroxidase andGSH-reductase activities were significantly reduced. Exercise also induced energy metabolism as observed by increased hexokinase and glutamate dehydrogenase activities. A significant decrease in the activities of mitochondrial ComplexesII/IIIandIVwere observed in theGKrats. Exercise improved only ComplexIVactivity suggesting increased utilization of oxygen. We also observed increased activities of cytochrome P450s in the pancreas ofGKrats which was reduced significantly after exercise.SDS-PAGEresults have shown a decreased expression ofNF-κB, Glut-2, andPPAR-ϒ inGKrats which was markedly increased after exercise. These results suggest differential oxidative stress and antioxidant defense responses after exercise. Our results also suggest improved mitochondrial function and energy utilization in the pancreas of exercisingGKrats.

OBJECTIVE: To explore application of targeted contrast enhanced ultrasonography in diagnosis of early stage vascular endothelial injury and diabetic nephropathy.
METHODS: Targeted SonoVue-TM microbubble was prepared by attaching anti-TM monoclonal antibody to the surface of ordinary microbubble SonoVue by biotin - avidin bridge method and ultrasonic instrument was used to evaluate the developing situation of targeted microbubble in vitro. Twenty 12-week-old male GK rats and 20 Wistar rats were enrolled in this study, and were randomly divided into targeted angiography group and ordinary angiography group. Targeted microbubbles SonoVue-TM or general microbubble SonoVue were rapidly injected to the rats via tail vein; the developing situation of the two contrast agents in rats kidneys was dynamically observed. Time-intensity curve was used to analyze rat kidney perfusion characteristics in different groups.
RESULTS: Targeted ultrasound microbubble SonoVue-TM was successfully constructed, and it could be used to develop an external image. Targeted microbubbles SonoVue-TM enabled clear development of experimental rat kidney. Time-intensity curve shapes of rat kidney of the two groups showed as single apex with steep ascending and slowly descending branch. Compared with the control group, the rising slope of the GK rat renal cortex, medulla in targeted angiography group increased (P < 0.05); the peak intensity of medulla increased (P < 0.05), and the total area under the curve of medulla increased (P < 0.05). Compared with control group, the ascending branch of the GK rat in renal cortex, medulla in ordinary angiography group increased (P < 0.05). The peak intensity of the curve increased (P < 0.05), and the total area under the curve increased (P < 0.05). Compared with the ordinary angiography group, the peak of GK rat medulla curve in targeted angiography group intensity increased (P < 0.05), and the total area under the curve increased (P < 0.05).
CONCLUSIONS: Targeted microbubbles SonoVue-TM can make a clear development of experimental rat kidney, its stable performance meet the requirement of ultrasonic observation time limit, and it can reflect early changes of blood perfusion in GK rat kindey.