Modified SADI-S in non-obese diabetic rats: Description of the surgical technique.

Background: Single anastomosis duodenoileal bypass with sleeve gastrectomy (SADI-S) is a predominantly malabsorptive technique that has shown excellent results in morbid obese patients. The aim of this study is to establish a rodent model modifying the SADI-S technique by performing a proximal duodenojejunal anastomosis. This model can be useful for the study of glucose metabolism without malabsorption observed after the SADI-S technique. Methods: Goto-Kakizaki rats, a genetic model of non-obese and non-hypertensive type 2 diabetes mellitus, that develop hyperglycemia at an early age was used. Surgery consisted in a sleeve gastrectomy, duodenojejunal anastomosis and duodenal exclusion using three different techniques: duodenal transection (DT), duodenal ligation with hem-o-lock (DLH), and duodenal ligation with suture (DLS). Surgery time, weight loss, morbidity and mortality were recorded. Results: A total of 16 animals were subjected to surgical intervention and overall mortality was 25 %, with the DT group showing the highest mortality rate (42.9 %). No differences were observed among groups in terms of weight loss. Conclusion: The surgical technique described in this work is feasible and reproducible. Weight loss is comparable regardless of the technique used for duodenal exclusion.

Characterization of gut microbial and metabolite alterations in faeces of Goto Kakizaki rats using metagenomic and untargeted metabolomic approach.

BACKGROUND: In recent years, the incidence of type 2 diabetes (T2DM) has shown a rapid growth trend. Goto Kakizaki (GK) rats are a valuable model for the study of T2DM and share common glucose metabolism features with human T2DM patients. A series of studies have indicated that T2DM is associated with the gut microbiota composition and gut metabolites. We aimed to systematically characterize the faecal gut microbes and metabolites of GK rats and analyse the relationship between glucose and insulin resistance. AIM: To evaluate the gut microbial and metabolite alterations in GK rat faeces based on metagenomics and untargeted metabolomics. METHODS: Ten GK rats (model group) and Wistar rats (control group) were observed for 10 wk, and various glucose-related indexes, mainly including weight, fasting blood glucose (FBG) and insulin levels, homeostasis model assessment of insulin resistance (HOMA-IR) and homeostasis model assessment of ß cell (HOMA-ß) were assessed. The faecal gut microbiota was sequenced by metagenomics, and faecal metabolites were analysed by untargeted metabolomics. Multiple metabolic pathways were evaluated based on the differential metabolites identified, and the correlations between blood glucose and the gut microbiota and metabolites were analysed. RESULTS: The model group displayed significant differences in weight, FBG and insulin levels, HOMA-IR and HOMA-ß indexes (P < 0.05, P < 0.01) and a shift in the gut microbiota structure compared with the control group. The results demonstrated significantly decreased abundances of Prevotella sp. CAG:604 and Lactobacillus murinus (P < 0.05) and a significantly increased abundance of Allobaculum stercoricanis (P < 0.01) in the model group. A correlation analysis indicated that FBG and HOMA-IR were positively correlated with Allobaculum stercoricanis and negatively correlated with Lactobacillus murinus. An orthogonal partial least squares discriminant analysis suggested that the faecal metabolic profiles differed between the model and control groups. Fourteen potential metabolic biomarkers, including glycochenodeoxycholic acid, uric acid, 13(S)-hydroxyoctadecadienoic acid (HODE), N-acetylaspartate, ß-sitostenone, sphinganine, 4-pyridoxic acid, and linoleic acid, were identified. Moreover, FBG and HOMA-IR were found to be positively correlated with glutathione, 13(S)-HODE, uric acid, 4-pyridoxic acid and allantoic acid and ne-gatively correlated with 3-α, 7-α, chenodeoxycholic acid glycine conjugate and 26-trihydroxy-5-ß-cholestane (P < 0.05, P < 0.01). Allobaculum stercoricanis was positively correlated with linoleic acid and sphinganine (P < 0.01), and 2-methyl-3-hydroxy-5-formylpyridine-4-carboxylate was negatively associated with Prevotella sp. CAG:604 (P < 0.01). The metabolic pathways showing the largest differences were arginine biosynthesis; primary bile acid biosynthesis; purine metabolism; linoleic acid metabolism; alanine, aspartate and glutamate metabolism; and nitrogen metabolism. CONCLUSION: Metagenomics and untargeted metabolomics indicated that disordered compositions of gut microbes and metabolites may be common defects in GK rats.

Selectively bred rodent models for studying the etiology of type 2 diabetes: Goto-Kakizaki rats and Oikawa-Nagao mice.

Type 2 diabetes (T2D) is a polygenic disease and studies to understand the etiology of the disease have required selectively bred animal models with polygenic background. In this review, we present two models; the Goto-Kakizaki (GK) rat and the Oikawa-Nagao Diabetes-Prone (ON-DP) and Diabetes-Resistant (ON-DR) mouse. The GK rat was developed by continuous selective breeding for glucose tolerance from the outbred Wistar rat around 50 years ago. The main cause of spontaneous hyperglycemia in this model is insulin secretion deficiency from pancreatic ß-cells and mild insulin resistance in insulin target organs. A disadvantage of the GK rat is that environmental factors have not been considered in the selective breeding. Hence, the GK rat may not be suitable for elucidating predisposition to diabetes under certain environmental conditions, such as a high-fat diet. Therefore, we recently established two mouse lines with different susceptibilities to diet-induced diabetes, which are prone and resistant to the development of diabetes, designated as the ON-DP and ON-DR mouse, respectively. The two ON mouse lines were established by continuous selective breeding for inferior and superior glucose tolerance after high-fat diet feeding in hybrid mice of three inbred strains. Studies of phenotypic differences between ON-DP and ON-DR mice and their underlying molecular mechanisms will shed light on predisposing factors for the development of T2D in the modern obesogenic environment. This review summarizes the background and the phenotypic differences and similarities of GK rats and ON mice and highlights the advantages of using selectively bred rodent models in diabetes research.

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.

A Holistic View of the Goto-Kakizaki Rat Immune System: Decreased Circulating Immune Markers in Non- Obese Type 2 Diabetes.

Type-2 diabetes is a complex disorder that is now considered to have an immune component, with functional impairments in many immune cell types. Type-2 diabetes is often accompanied by comorbid obesity, which is associated with low grade inflammation. However,the immune status in Type-2 diabetes independent of obesity remains unclear. Goto-Kakizaki rats are a non-obese Type-2 diabetes model. The limited evidence available suggests that Goto-Kakizaki rats have a pro-inflammatory immune profile in pancreatic islets. Here we present a detailed overview of the adult Goto-Kakizaki rat immune system. Three converging lines of evidence: fewer pro-inflammatory cells, lower levels of circulating pro-inflammatory cytokines, and a clear downregulation of pro-inflammatory signalling in liver, muscle and adipose tissues indicate a limited pro-inflammatory baseline immune profile outside the pancreas. As Type-2 diabetes is frequently associated with obesity and adipocyte-released inflammatory mediators, the pro-inflammatory milieu seems not due to Type-2 diabetes per se; although this overall reduction of immune markers suggests marked immune dysfunction in Goto-Kakizaki rats.

Lifelong soya consumption in males does not increase lifespan but increases health span under a metabolic stress such as type 2 diabetes mellitus.

Soya consumption can decrease oxidative stress in animal models. Moreover, phytoestrogens such as genistein, present in soya, can mimic some of the beneficial effects of estrogens and are devoid of significant side effects, such as cancer. In this study, we have performed a controlled lifelong study with male OF1 mice that consumed either a soya-free diet or a soya-rich diet. We show that, although we found an increase in the expression and activity of antioxidant enzymes in soya-consuming mice, it did not increase lifespan. We reasoned that the soya diet could not increase lifespan in a very healthy population, but perhaps it could extend health span in stressed animals such as type 2 diabetic Goto Kakizaki (GK) rats. Indeed, this was the case: we found that male GK rats consuming a soya-rich diet developed the disease at a lower rate and, therefore, lived longer than soya-free diet-consuming rats.

Effect of berberine on hyperglycaemia and gut microbiota composition in type 2 diabetic Goto-Kakizaki rats.

BACKGROUND: A recent investigation showed that the prevalence of type 2 diabetes mellitus (T2DM) is 12.8% among individuals of Han ethnicity. Gut microbiota has been reported to play a central role in T2DM. Goto-Kakizaki (GK) rats show differences in gut microbiota compared to non-diabetic rats. Previous studies have indicated that berberine could be successfully used to manage T2DM. We sought to understand its hypoglycaemic effect and role in the regulation of the gut microbiota. AIM: To determine whether berberine can regulate glucose metabolism in GK rats via the gut microbiota. METHODS: GK rats were acclimatized for 1 wk. The GK rats were randomly divided into three groups and administered saline (Mo), metformin (Me), or berberine (Be). The observation time was 8 wk, and weight, fasting blood glucose (FBG), insulin, and glucagon-like peptide-1 (GLP-1) were measured. Pancreatic tissue was observed for pathological changes. Additionally, we sequenced the 16S rRNA V3-V4 region of the gut microbiota and analysed the structure. RESULTS: Compared with the Mo group, the Me and Be groups displayed significant differences in FBG (P < 0.01) and GLP-1 (P < 0.05). A significant decrease in weight and homeostatic model assessment-insulin resistance was noted in the Be group compared with those in the Me group (P < 0.01). The pancreatic islets of the Me- and Be-treated rats showed improvement in number, shape, and necrosis compared with those of Mo-treated rats. A total of 580 operational taxonomic units were obtained in the three groups. Compared to the Mo group, the Me and Be groups showed a shift in the structure of the gut microbiota. Correlation analysis indicated that FBG was strongly positively correlated with Clostridia_UCG-014 (P < 0.01) and negatively correlated with Allobaculum (P < 0.01). Body weight showed a positive correlation with Desulfovibrionaceae (P < 0.01) and a negative correlation with Akkermansia (P < 0.01). Importantly, our results demonstrated that Me and Be could significantly decrease Bacteroidetes (P < 0.01) and the Bacteroidetes/Firmicutes ratio (P < 0.01). Furthermore, Muribaculaceae (P < 0.01; P < 0.05) was significantly decreased in the Me and Be groups, and Allobaculum (P < 0.01) was significantly increased. CONCLUSION: Berberine has a substantial effect in improving metabolic parameters and modulating the gut microbiota composition in T2DM rats.

Selectively Bred Diabetes Models: GK Rats, NSY Mice, and ON Mice.

The polygenic background of selectively bred diabetes models mimics the etiology of type 2 diabetes. So far, three different rodent models (Goto-Kakizaki rats, Nagoya-Shibata-Yasuda mice, and Oikawa-Nagao mice) have been established in the diabetes research field by continuous selective breeding for glucose tolerance from outbred rodent stocks. The origin of hyperglycemia in these rodents is mainly insulin secretion deficiency from the pancreatic ß-cells and mild insulin resistance in insulin target organs. In this chapter, we summarize backgrounds and phenotypes of these rodent models to highlight their importance in diabetes research. Then, we introduce experimental methodologies to evaluate ß-cell exocytosis as a putative common defect observed in these rodent models.

The insulin resistance is reversed by exogenous 3,5,3'triiodothyronine in type 2 diabetic Goto-Kakizaki rats by an inflammatory-independent pathway.

PURPOSE: Diabetes mellitus (DM) has a multifactorial etiology that imparts a particular challenge to effective pharmacotherapy. Thyroid hormone actions have demonstrated beneficial effects in diabetic as well as obese rats. In both conditions, inflammation status plays a crucial role in the development of insulin resistance. Taking this into consideration, the present study aimed to demonstrate another possible pathway of thyroid hormone action on insulin sensitivity in a spontaneous type 2 diabetic rat model: the Goto-Kakizaki (GK) rats. GK animals present all typical hallmarks of type 2 DM (T2DM), except the usual peripheric inflammatory condition, observed in the other T2DM animal models. METHODS: GK rats were treated or not with 3,5,3'triiodothyronine (T3). Insulin sensitivity, glucose tolerance, and proteins related to glucose uptake and utilization were evaluated in the skeletal muscle, white adipose tissue, and liver. RESULTS: GK rats T3-treated presented enhanced insulin sensitivity, increased GLUT-4 content in the white adipose tissue and skeletal muscle, and increased hexokinase and citrate synthase content in skeletal muscle. Both non-treated and T3-treated GK rats did not present alterations in cytokine content in white adipose tissue, skeletal muscle, liver, and serum. CONCLUSIONS: These results indicate that T3 improves insulin sensitivity in diabetic rats by a novel inflammatory-independent mechanism.

A sea cucumber (Holothuria leucospilota) polysaccharide improves the gut microbiome to alleviate the symptoms of type 2 diabetes mellitus in Goto-Kakizaki rats.

Diabetes mellitus has become a worldwide concern in recent years. In this study, the effect of Holothuria leucospilota polysaccharide (HLP) on type 2 diabetes mellitus (T2DM) was investigated in Goto-Kakizaki (GK) rats. The results showed that HLP significantly improved glucose intolerance and regulated blood lipid and hormone levels (p < 0.05). Pathological analysis showed that HLP repaired the impairments of the pancreas and colon in diabetic rats. In addition, a high dose of HLP (200 mg/kg) significantly upregulated the gene expression of peroxisome proliferator-activated receptor-α (PPAR-α), peroxisome proliferator-activated receptor-γ (PPAR-γ), phosphoinositide 3-kinase (PI3K), protein kinase B (PKB/AKT), glucose transporter-4 (GLUT4) and anti-apoptotic (Bcl-2), and downregulated the mRNA levels of pro-apoptotic (Bax) and cluster of differentiation 36 (CD36) in diabetic rats (p < 0.05). Furthermore, HLP treatment increased the short-chain fatty acid-producing bacteria and decreased the opportunistic bacterial pathogen in the feces of diabetic rats. These results demonstrated that HLP has the potential to ameliorate T2DM in GK rats.

Effects of Resveratrol in Goto-Kakizaki Rat, a Model of Type 2 Diabetes.

Resveratrol exhibits a pleiotropic, favorable action under various pathological conditions, including type 2 diabetes. However, its anti-diabetic effects in animal models and human trials have not been fully elucidated. The aim of the present study was to determine whether resveratrol is capable of inducing beneficial changes in the Goto-Kakizaki rat, a spontaneous model of diabetes, which in several aspects is similar to type 2 diabetes in humans. Goto-Kakizaki (GK) rats and control Sprague-Dawley (SD) rats were treated intragastrically with resveratrol (20 mg/kg b.w./day) for 10 weeks. Then, a glucose tolerance test was performed and levels of some adipokines in blood were measured. Moreover, lipid contents in skeletal muscle and liver tissues, along with the expression and phosphorylation of pivotal enzymes (AMP-activated protein kinase-AMPK, acetyl-CoA carboxylase-ACC, protein kinase B-Akt) in these tissues were determined. Histology of pancreatic islets was also compared. GK rats non-treated with resveratrol displayed a marked glucose intolerance and had increased lipid accumulation in the skeletal muscle. Moreover, upregulation of the expression and phosphorylation of AMPK, ACC and Akt was shown in the muscle tissue of GK rats. Those rats also had an abnormal structure of pancreatic islets compared with control animals. However, treatment with resveratrol improved glucose tolerance and prevented lipid accumulation in the skeletal muscle of GK rats. This effect was associated with a substantial normalization of expression and phosphorylation of ACC and Akt. In GK rats subjected to resveratrol therapy, the structure of pancreatic islets was also clearly improved. Moreover, blood adiponectin and leptin levels were partially normalized by resveratrol in GK rats. It was revealed that resveratrol ameliorates key symptoms of diabetes in GK rats. This compound improved glucose tolerance, which was largely linked to beneficial changes in skeletal muscle. Resveratrol also positively affected pancreatic islets. Our new findings show that resveratrol has therapeutic potential in GK rats.

Therapeutic effects of stem cells from human exfoliated deciduous teeth on diabetic peripheral neuropathy.

OBJECTIVE: To evaluate the therapeutic potential of stem cells from human exfoliated deciduous teeth (SHED) for diabetic peripheral neuropathy. METHODS: The biological characteristics of SHED were identified by flow cytometric study and evaluation of differentiation potential. Using high-fat feeding, diabetes was induced in GK rats, and SHED were transplanted into the caudal veins of these rats. Immunohistochemical analysis was used to compare the capillary to muscle fiber ratio and intra-epidermal nerve fiber density between SHED- and saline-treated diabetic rats. Further, the expressions of angiogenesis-related and neurotrophic factors were quantified by real-time PCR and western blot. RESULTS: SHED had a capacity of multiple differentiation and shared typical characteristics of mesenchymal stem cells. SHED transplantation relieved diabetic neuropathic pain, enabled functional recovery of the peripheral nerves, and increased the capillary to muscle fiber ratio and intra-epidermal nerve fiber density compared to the saline group and normal controls. Real-time PCR results showed that the expressions of CD31, vWF, bFGF, NGF, and NT-3 in the skeletal muscles were higher in the SHED group than in the saline groups. Western blot results indicated that the levels of the CD31 and NGF proteins were higher in the SHED transplantation group than the saline group. CONCLUSION: SHED transplantation ameliorated diabetic peripheral neuropathy in diabetic GK rats. Thus, systemic application of SHED could be a novel strategy for the treatment of diabetic peripheral neuropathy.

Lupinus mutabilis Extract Exerts an Anti-Diabetic Effect by Improving Insulin Release in Type 2 Diabetic Goto-Kakizaki Rats.

Lupinus mutabilis (LM) is a legume part of Bolivian traditional diet that has a nutraceutical property reducing blood glucose levels. The prevalence of type 2 diabetes is increasing worldwide thus; the search for novel anti-diabetic drugs is needed. Based on its traditional use, we evaluated the anti-diabetic effect of LM in the spontaneously diabetic Goto-Kakizaki (GK) rat, a model of type 2 diabetes and in Wistar (W) rats as healthy control. LM seeds hydroethanolic extract, analyzed by gas chromatography-mass spectrometry and high-performance liquid chromatography-high resolution mass spectrometry, is a complex mixture of volatile and non-volatile components. A single oral administration of LM extract (2000 mg/kg b.w.) improved glucose tolerance during the oral glucose tolerance test (OGTT) (30⁻120 min) in GK and W rats (p < 0.0001). The long-term treatment with LM (1000 mg/kg b.w.), for 21 days, improved the area under the curve (AUC) of glucose during OGTT at day 20, in both GK (p < 0.01) and W rats (p < 0.01). The HbA1c (GK rats, p < 0.05 and W rats, p < 0.0001) and the non-fasting glucose (GK rats, p < 0.05) were also reduced. LM increased both serum insulin levels (2.4-fold in GK rats and 2.5-fold W rats), and the glucose-induced (16.7 mM glucose) insulin release in isolated islets from treated animals (6.7-fold in GK rats, and 6.6-fold in W rats). Moreover, LM (10 mg/mL) stimulated in vitro glucose induced (16.7 mM glucose) insulin release in batch incubated GK and W rat islets (p < 0.0001). In perifused GK rat islets, insulin release in 16.7 mM glucose was increased 95.3-fold compared to untreated islets (p < 0.0001), while no significant differences were found in perifused W rat islets. The LM mechanism of action, evaluated using inhibitory compounds of the insulin secretion pathway, showed that LM-dependent insulin secretion was reduced 42% by diazoxide (p < 0.001), 70% by nifedipine (p < 0.001), 86.7% by H89 (p < 0.0001), 70.8% by calphostine-C (p < 0.0001) and 93% by pertussis toxin (p < 0.0001). A similar effect was observed in W rats islets. Our findings provide evidence that LM has an anti-diabetic effect through stimulation of insulin release. The effect is-dependent on L-type calcium channel, protein kinase A and C systems, and G protein-coupled exocytosis and is partially mediated by K-ATP channels.

Type 2 diabetes impairs odour detection, olfactory memory and olfactory neuroplasticity; effects partly reversed by the DPP-4 inhibitor Linagliptin.

Recent data suggest that olfactory deficits could represent an early marker and a pathogenic mechanism at the basis of cognitive decline in type 2 diabetes (T2D). However, research is needed to further characterize olfactory deficits in diabetes, their relation to cognitive decline and underlying mechanisms.The aim of this study was to determine whether T2D impairs odour detection, olfactory memory as well as neuroplasticity in two major brain areas responsible for olfaction and odour coding: the main olfactory bulb (MOB) and the piriform cortex (PC), respectively. Dipeptidyl peptidase-4 inhibitors (DPP-4i) are clinically used T2D drugs exerting also beneficial effects in the brain. Therefore, we aimed to determine whether DPP-4i could reverse the potentially detrimental effects of T2D on the olfactory system.Non-diabetic Wistar and T2D Goto-Kakizaki rats, untreated or treated for 16 weeks with the DPP-4i linagliptin, were employed. Odour detection and olfactory memory were assessed by using the block, the habituation-dishabituation and the buried pellet tests. We assessed neuroplasticity in the MOB by quantifying adult neurogenesis and GABAergic inhibitory interneurons positive for calbindin, parvalbumin and carletinin. In the PC, neuroplasticity was assessed by quantifying the same populations of interneurons and a newly identified form of olfactory neuroplasticity mediated by post-mitotic doublecortin (DCX) + immature neurons.We show that T2D dramatically reduced odour detection and olfactory memory. Moreover, T2D decreased neurogenesis in the MOB, impaired the differentiation of DCX+ immature neurons in the PC and altered GABAergic interneurons protein expression in both olfactory areas. DPP-4i did not improve odour detection and olfactory memory. However, it normalized T2D-induced effects on neuroplasticity.The results provide new knowledge on the detrimental effects of T2D on the olfactory system. This knowledge could constitute essentials for understanding the interplay between T2D and cognitive decline and for designing effective preventive therapies.

Amaranthus caudatus Stimulates Insulin Secretion in Goto-Kakizaki Rats, a Model of Diabetes Mellitus Type 2.

Diabetes Mellitus Type 2 prevalence is increasing worldwide; thus efforts to develop novel therapeutic strategies are required. Amaranthus caudatus (AC) is a pseudo-cereal with reported anti-diabetic effects that is usually consumed in food preparations in Bolivia. This study evaluated the anti-diabetic nutraceutical property of an AC hydroethanolic extract that contains mainly sugars and traces of polyphenols and amino acids (as shown by nalysis with liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR)), in type 2 diabetic Goto-Kakizaki (GK) rats and healthy Wistar (W) rats. A single oral administration of AC extract (2000 mg/kg body weight) improved glucose tolerance during Oral Glucose Tolerance Tests (OGTT) in both GK rats and in W rats. Long-term treatment (21 days) with AC (1000 mg/kg b.w.) improved the glucose tolerance evaluated by the area under the curve (AUC) of glucose levels during the OGTT, in both GK and W rats. The HbA1c levels were reduced in both GK (19.83%) and W rats (10.7%). This effect was secondary to an increase in serum insulin levels in both GK and W rats and confirmed in pancreatic islets, isolated from treated animals, where the chronic AC exposure increased the insulin production 4.1-fold in GK and 3.7-fold in W rat islets. Furthermore, the effect of AC on in vitro glucose-dependent insulin secretion (16.7 mM glucose) was concentration-dependent up to 50 mg/mL, with 8.5-fold increase in GK and 5.7-fold in W rat islets, and the insulin secretion in perifused GK and W rat islets increased 31 and nine times, respectively. The mechanism of action of AC on insulin secretion was shown to involve calcium, PKA and PKC activation, and G-protein coupled-exocytosis since the AC effect was reduced 38% by nifedipine (L-type channel inhibitor), 77% by H89 (PKA inhibitor), 79% by Calphostine-C (PKC inhibitor) and 20% by pertussis toxin (G-protein suppressor).

Insulin does not rescue cortical and trabecular bone loss in type 2 diabetic Goto-Kakizaki rats.

In type 2 diabetes mellitus (T2DM), the decreased bone strength is often associated with hyperglycemia and bone cell insulin resistance. Since T2DM is increasingly reported in young adults, it is not known whether the effect of T2DM on bone would be different in young adolescents and aging adults. Here, we found shorter femoral and tibial lengths in 7-month, but not 13-month, Goto-Kakizaki (GK) T2DM rats as compared to wild-type rats. Bone µCT analysis showed long-lasting impairment of both cortical and trabecular bones in GK rats. Although insulin treatment effectively improved hyperglycemia, it was not able to rescue trabecular BMD and cortical thickness in young adult GK rats. In conclusion, insulin treatment and alleviation of hyperglycemia did not increase BMD of osteopenic GK rats. It is likely that early prevention of insulin resistance should prevail over treatment of full-blown T2DM-related osteopathy.

Avocado oil induces long-term alleviation of oxidative damage in kidney mitochondria from type 2 diabetic rats by improving glutathione status.

Hyperglycemia and mitochondrial ROS overproduction have been identified as key factors involved in the development of diabetic nephropathy. This has encouraged the search for strategies decreasing glucose levels and long-term improvement of redox status of glutathione, the main antioxidant counteracting mitochondrial damage. Previously, we have shown that avocado oil improves redox status of glutathione in liver and brain mitochondria from streptozotocin-induced diabetic rats; however, the long-term effects of avocado oil and its hypoglycemic effect cannot be evaluated because this model displays low survival and insulin depletion. Therefore, we tested during 1 year the effects of avocado oil on glycemia, ROS levels, lipid peroxidation and glutathione status in kidney mitochondria from type 2 diabetic Goto-Kakizaki rats. Diabetic rats exhibited glycemia of 120-186 mg/dL the first 9 months with a further increase to 250-300 mg/dL. Avocado oil decreased hyperglycemia at intermediate levels between diabetic and control rats. Diabetic rats displayed augmented lipid peroxidation and depletion of reduced glutathione throughout the study, while increased ROS generation was observed at the 3rd and 12th months along with diminished content of total glutathione at the 6th and 12th months. Avocado oil ameliorated all these defects and augmented the mitochondrial content of oleic acid. The beneficial effects of avocado oil are discussed in terms of the hypoglycemic effect of oleic acid and the probable dependence of glutathione transport on lipid peroxidation and thiol oxidation of mitochondrial carriers.

Left ventricular pressure-volume measurements and myocardial gene expression profile in type 2 diabetic Goto-Kakizaki rats.

The Goto-Kakizaki (GK) rat, a non-obese model of type 2 diabetes mellitus (T2DM), was generated by the selective inbreeding of glucose-intolerant Wistar rats. This is a convenient model for studying diabetes-induced cardiomyopathy independently from the effects of the metabolic syndrome. We investigated the myocardial functional and structural changes and underlying molecular pathomechanisms of short-term and mild T2DM. The presence of DM was confirmed by an impaired oral glucose tolerance in the GK rats compared with the age-matched nondiabetic Wistar rats. Data from cardiac catheterization showed that in GK rats, although the systolic indexes were not altered, the diastolic stiffness was increased compared with nondiabetics (end-diastolic-pressure-volume-relationship: 0.12 ± 0.04 vs. 0.05 ± 0.01 mmHg/µl, P < 0.05). Additionally, DM was associated with left-ventricular hypertrophy and histological evidence of increased myocardial fibrosis. The plasma pro-B-type natriuretic peptide, the cardiac troponin-T, glucose, and the urinary glucose concentrations were significantly higher in GK rats. Among the 125 genes surveyed using PCR arrays, DM significantly altered the expression of five genes [upregulation of natriuretic peptide precursor-A and connective tissue growth factor, downregulation of c-reactive protein, interleukin-1ß, and tumor necrosis factor (TNF)-α mRNA-level]. Of the altered genes, which were evaluated by Western blot, only TNF-α protein expression was significantly decreased. The ECG recordings revealed no significant differences. In conclusion, while systolic dysfunction, myocardial inflammation, and abnormal electrical conduction remain absent, short-term and mild T2DM induce the alteration of cardiac TNF-α at both the mRNA and protein levels. Further assessments are required to reveal if TNF-α plays a role in the early stage of diabetic cardiomyopathy development.

Neurolytic celiac plexus block enhances skeletal muscle insulin signaling and attenuates insulin resistance in GK rats.

Non-insulin-dependent diabetes mellitus (NIDDM) is associated with chronic inflammatory activity and disrupted insulin signaling, leading to insulin resistance (IR). The present study investigated the benefits of neurolytic celiac plexus block (NCPB) on IR in a rat NIDDM model. Goto-Kakizaki rats fed a high-fat, high-glucose diet to induce signs of NIDDM were randomly divided into NCPB and control groups; these received daily bilateral 0.5% lidocaine or 0.9% saline injections into the celiac plexus, respectively. Following 14 and 28 daily injections, rats were subject to oral glucose tolerance tests (OGTTs) or sacrificed for the analysis of serum free fatty acids (FFAs), serum inflammatory cytokines and skeletal muscle insulin signaling. Compared with controls, rats in the NCPB group demonstrated significantly (P<0.05) lower baseline, 60-min and 120-min OGTT values, lower 120-min serum insulin, lower IR [higher insulin sensitivity index (ISI1) and lower ISI2) and lower serum FFAs, tumor necrosis factor-α, interleukin (IL)-1ß and IL-6. Conversely, NCPB rats exhibited higher basal and insulin-stimulated skeletal muscle glucose uptake and higher skeletal muscle insulin receptor substrate-1 (IRS-1) and glucose transporter type 4 expression. There were no differences between the groups in insulin receptor ß (Rß) or Akt expression; however Rß-Y1162/Y1163 and Akt-S473 phosphorylation levels were higher and IRS-1-S307 phosphorylation were lower in NCPB rats than in the controls. These results indicate that NCPB improved insulin signaling and reduced IR, possibly by inhibiting inflammatory cytokine release.

Type 2 diabetes-induced neuronal pathology in the piriform cortex of the rat is reversed by the GLP-1 receptor agonist exendin-4.

Type 2 diabetes (T2D) patients often present olfactory dysfunction. However, the histopathological basis behind this has not been previously shown. Since the piriform cortex plays a crucial role in olfaction, we hypothesize that pathological changes in this brain area can occur in T2D patients along aging. Thus, we determined potential neuropathology in the piriform cortex of T2D rats, along aging. Furthermore, we determined the potential therapeutic role of the glucagon-like peptide-1 receptor (GLP1-R) agonist exendin-4 to counteract the identified T2D-induced neuropathology. Young-adult and middle-aged T2D Goto-Kakizaki rats were compared to age-matched Wistars. Additional Goto-Kakizaki rats were treated for six weeks with exendin-4/vehicle before sacrifice. Potential T2D-induced neuropathology was assessed by quantifying NeuN-positive neurons and Calbindin-D28k-positive interneurons by immunohistochemistry and stereology methods. We also quantitatively measured Calbindin-D28k neuronal morphology and JNK phosphorylation-mediated cellular stress. PI3K/AKT signalling was assessed by immunohistochemistry, and potential apoptosis by TUNEL.We show T2D-induced neuronal pathology in the piriform cortex along aging, characterized by atypical nuclear NeuN staining and increased JNK phosphorylation, without apoptosis. We also demonstrate the specific vulnerability of Calbindin-D28k interneurons. Finally, chronic treatment with exendin-4 substantially reversed the identified neuronal pathology in correlation with decreased JNK and increased AKT phosphorylation.Our results reveal the histopathological basis to explain T2D olfactory dysfunction. We also show that the identified T2D-neuropathology can be counteracted by GLP-1R activation supporting recent research promoting the use of GLP-1R agonists against brain diseases. Whether the identified neuropathology could represent an early hallmark of cognitive decline in T2D remains to be determined.