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 β cell (HOMA-β) 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-β 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, β-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-β-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 β-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.

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.

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 β-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 β-cell exocytosis as a putative common defect observed in these rodent models.

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.

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.

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).

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.

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)-1β 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 β (Rβ) or Akt expression; however Rβ-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.

Long-term effects of a new billiopancreatic diversion surgery on plasma glucose in Goto-Kakizaki rats

AIM: To observe the effects of a new billiopancreatic diversion (NBPD) surgery and duodenal-jejunal bypass (DJB) on plasma glucose and blood lipids in Goto-Kakizaki (GK) rats, and to explore the possible mechanisms involved.

METHODS: Thirty rats were randomly divided into an NBPD group, a DJB group and a sham operation group. Body weight, plasma glucose and blood lipids were measured before and after surgery. Morphology of islet cells was observed 48 weeks after surgery.

RESULTS: One week after surgery, random plasma glucose level decreased from 9.729 mmol/L ± 0.652 mmol/L to 17.743 mmol/L ± 3.734 mmol/L in the NBPD group, from 9.367 mmol/L ± 1.118 mmol/L to 16.500 mmol/L ± 3.272 mmol/L in the DJB group, and both were significantly lower than those in the sham operation group. Twenty-four weeks after surgery, random plasma glucose level rose to 14.233 mmol/L ± 2.759 mmol/L in the NBPD group. However, random plasma glucose level was still maintained at 14.233 mmol/L ± 2.759 mmol/L in the DJB group, which was significantly lower than those in the NBPD and sham-operation groups. Forty-eight weeks after surgery, the number of islet cells in the DJB group was more than those in the other two groups.

CONCLUSION: Both NBPD and DJB can decrease plasma glucose in GK rats in the early stage after surgery, but long-term effect of NBPD is not satisfactory. Biliopancreatic diversion may be an important factor in early stage. Changes in the digestive tract may be the most important factor involved in the surgical treatment of type 2 diabetes.

In vitro effects of bis(1,2-dimethyl-3-hydroxy-4-pyridinonato)oxidovanadium(IV), or VO(dmpp)2, on insulin secretion in pancreatic islets of type 2 diabetic Goto-Kakizaki rats

Vanadium compounds have been explored as therapy of diabetes, and most studies have focussed on insulin mimetic effects, i.e. reducing hyperglycemia by improving glucose sensitivity and thus glucose uptake in sensitive tissues. We have recently shown that bis(1,2-dimethyl-3-hydroxy-4-pyridinonato)oxidovanadium(IV), VO(dmpp)2, has promising effects when compared to another vanadium compound, bis(maltolato)oxidovanadium(IV), BMOV, and insulin itself, in isolated adipocytes and in vivo in Goto-Kakizaki (GK) rats, an animal model of hereditary type 2 diabetes (T2D).We now have investigated in GK rats whether VO(dmpp)2 also modulates another important defect in T2D, impaired insulin secretion. VO(dmpp)2, but not BMOV, stimulated insulin secretion from isolated GK rat pancreatic islets at high, 16.7mM, but not at low–normal, 3.3 mM, glucose concentration. Mechanistic studies demonstrate that the insulin releasing effect of VO(dmpp)2 is due to its interaction with several steps in the stimulus-secretion coupling for glucose, including islet glucose metabolism and K-ATP channels, L-type Ca2+ channels, modulation by protein kinases A and C, as well as the exocytotic machinery. In conclusion, VO(dmpp)2 exhibits properties of interest for treatment of the insulin secretory defect in T2D, in addition to its well-described insulin mimetic activity.

Glucagon secretion after metabolic surgery in diabetic rodents

Excessive or inadequate glucagon secretion promoting hepatic gluconeogenesis and glycogenolysis is believed to contribute to hyperglycemia in patients with type 2 diabetes. Currently, metabolic surgery is an accepted treatment for obese patients with type 2 diabetes and has been shown to improve glycemic control in Goto-Kakizaki (GK) rats, a lean animal model for type 2 diabetes. However, the effects of surgery on glucagon secretion are not yet well established. In this study, we randomly assigned forty 12- to 14-week-old GK rats to four groups: control group (GKC), sham surgery (GKSS), sleeve gastrectomy (GKSG), and gastric bypass (GKGB). Ten age-matched Wistar rats served as a non-diabetic control group (WIC). Glycemic control was assessed before and 4 weeks after surgery. Fasting- and mixed-meal-induced plasma levels of insulin and glucagon were measured. Overall glycemic control improved in GKSG and GKGB rats. Fasting insulin levels in WIC rats were similar to those for GKC or GKSS rats. Fasting glucagon levels were highest in GKGB rats. Whereas WIC, GKC, and GKSS rats showed similar glucagon levels, without any significant meal-induced variation, a significant rise occurred in GKSG and GKGB rats, 30 min after a mixed meal, which was maintained at 60 min. Both GKSG and GKGB rats showed an elevated glucagon:insulin ratio at 60 min in comparison with all other groups. Surprisingly, the augmented post-procedural glucagon secretion was accompanied by an improved overall glucose metabolism in GKSG and GKGB rats. Understanding the role of glucagon in the pathophysiology of type 2 diabetes requires further research.

Hyperinsulinemia induces hepatic iron overload by increasing liver TFR1 via the PI3K/IRP2 pathway

Dysmetabolic iron overload syndrome (DIOS) is frequently observed, but the underlying mechanism remains unclear. We propose the hypothesis that hyperinsulinemia, a common characteristic of DIOS, may stimulate liver transferrin receptor 1 (TFR1) expression via the PI3K/iron regulatory protein 2 (IRP2) pathway, leading to the occurrence of DIOS. The hepatic iron content, serum iron parameters, and expressions of TFRs and IRPs in the liver were determined in rats with temporary or long-lasting hyperinsulinemia induced by acute or chronic administration of insulin. The effect of insulin on TFR1 expression and its molecular mechanism were determined in HL-7702 cells in vitro. It was found that long-lasting hyperinsulinemia significantly increased TFR1 expression in the liver and induced mild-to-moderate hepatic iron overload, which was accompanied by a normal level of serum iron. Insulin markedly upregulated both protein and mRNA levels of TFR1 in HL-7702 cells. The stability of TFR1 mRNA stability, together with expression of IRPs expression, were both significantly increased by insulin treatment. Insulin-induced TFR1 expression was blocked by IRP2, but not by IRP1 interference, and disappeared when HL-7702 cells were pretreated with LY294002, triciribine hydrate, or rapamycin. In conclusion, the findings of this study indicate that hyperinsulnemia could induce hepatic iron overload by upregulating liver TFR1 via the PI3K/AKT/mTOR/IRP2 pathway, which may be one of the main reasons for the occurrence of DIOS.

A new biliopancreatic diversion surgery decreases plasma glucose and lipids in Goto-Kakizaki rats

AIM: To observe the effects of a new biliopancreatic diversion (NBPD) surgery and duodenal-jejunal bypass (DJB) surgery on plasm glucose and lipids in Goto-Kakizaki (GK) rats and investigate the possibility of surgical treatment of diabetes.

METHODS: Thirty rats were randomly and equally divided into a sham operation group, a NBPD group or a DJB group. The NBPD group and the DJB group underwent NBPD and DJB, respectively, and the sham operation group underwent a sham operation. Body weight, random plasma glucose, OGTT and blood lipids were measured before and after surgery.

RESULTS: One week after surgery, random plasma glucose levels decreased from 17.088 mmol/L ± 3.708 mmol/L to 9.200 mmol/L ± 1.000 mmol/L in the NBPD group and from 17.180 mmol/L ± 3.383 mmol/L to 9.620 mmol/L ± 0.794 mmol/L in the DJB group, respectively, and both were significantly lower than those in the sham operation group. Four weeks postoperatively, fasting cholesterol decreased from 3.220 mmol/L ± 0.185 mmol/L to 3.100 mmol/L ± 0.424 mmol/L in the DJB group and from 3.100 mmol/L ± 0.424 mmol/L to 2.550 mmol/L ± 0.691 mmol/L in the NBPD group.

CONCLUSION: DJB and NBPD decrease plasma glucose and lipids in GK rats possibly via mechanisms associated with diversion of biliopancreatic juice that results in incomplete food digestion and absorption and improves lipid metabolism and plasma glucose.

Liraglutide protects pancreatic beta cells during an early intervention in Gato-Kakizaki rats

BACKGROUND

Glucagon-like peptide-1 (GLP-1) analogues have emerged as insulin secretagogues and are widely used in type 2 diabetic patients. GLP-1 analogues also demonstrate a promotion of beta cell proliferation and reduction of apoptosis in rodents. In the present study, we investigated the protection of pancreatic beta cells by early use (at the age of 2 weeks) of GLP-1 analogue, liraglutide in Gato-Kakizaki (GK) rats and explored the underlying mechanisms.

METHODS

The effects of liraglutide on glucose tolerance were evaluated by intraperitoneal glucose tolerance test (IPGTT) and insulin release tests (IRT). Ki67 and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) immunostaining, Western blots and real-time polymerase chain reaction were applied to evaluate cell proliferation, apoptosis and related gene expressions.

RESULTS

Our results demonstrated that early use of liraglutide improved glucose tolerance during liraglutide treatment in GK rats. Liraglutide increased pancreatic insulin contents and markedly reduced beta cell apoptosis. Liraglutide also downregulated pro-apoptotic gene expressions and reduced intra-islet macrophage infiltration.

CONCLUSIONS

This experiment reported for the first time that early use of liraglutide could protect beta cell failure in pre-diabetic GK rats through reduction of beta cell apoptosis and ameliorating islet inflammation.

Evaluation of hypoglycemic activity of total lignans from Fructus Arctii in the spontaneously diabetic Goto-Kakizaki rats

ETHNOPHARMACOLOGICAL RELEVANCE

Fructus Arctii, called "Niubangzi" in China (Great burdock achene in English), is a well-known Chinese Materia Medica. It is the dried ripe fruit of Arctium lappa L. (family Asteraceae) and was included in the Chinese pharmacopoeia for its traditional therapeutic actions. Meanwhile it has been utilized extensively in a number of classical drug formulas as a major component for the treatment of noninsulin-dependent diabetes mellitus. It has also been reported recently that the clinical use of Fructus Arctii resulted in a satisfactory hypoglycemic effect in diabetic patients. The aim of this study was to investigate hypoglycemic activity of total lignans from Fructus Arctii (TLFA) in Goto-Kakizaki (GK) rats, a spontaneous type 2 diabetic animal model, and the mechanism of its hypoglycemic activity.

MATERIALS AND METHODS

Male GK rats and normal Wistar rats were used in this study, GK rats fed twice daily were given TLFA (300 mg/kg) or nateglinide (50mg/kg) orally before each meal for 12 weeks. Besides common evaluation indexes of hypoglycemic activity such as blood glucose level, oral glucose tolerance test (OGTT), glycated hemoglobin, as well as lipid metabolism parameters such as cholesterol (CHOL), triglycerides (TG), et al., in rat serum. The effects of TLFA on insulin secretion and pancreas tissue sections, the levels of serum glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), and the α-glucosidase inhibitory activity of TLFA in vitro were investigated.

RESULTS

TLFA demonstrated stable and long-lasting hypoglycemic activity in GK rats and showed significant improvement in glucose tolerance in glucose fed hyperglycemic GK rats. Both TLFA and nateglinide controlled the glycosylated hemoglobin levels of the experimental animals very well. Stimulation of insulin secretion was proved to be one of the hypoglycemic mechanism of TLFA, promoting the release of GLP-1 should be another one, and ɑ-glucosidase inhibitory activity of TLFA also contributes to its hypoglycemic activity. In this study, we didn't found that TLFA could effect the body weight of GK rats, which was also verified by the changes of biochemical parameters of blood in experimental rats.

CONCLUSION

The results of this study indicates that TLFA has significant hypoglycemic potential in GK rats, and it may be acting through stimulating insulin secretion, promoting the release of GLP-1, and decreasing intestinal absorption of glucose.

Management of diabetic complications: a chemical constituents based approach

ETHNOPHARMACOLOGICAL RELEVANCE

Long term hyperglycemia leads to development of complications associated with diabetes. Diabetic complications are now a global health problem without effective therapeutic approach. Hyperglycemia and oxidative stress are important components for the development of diabetic complications. Over the past few decades, herbal medicines have attracted much attention as potential therapeutic agents in the prevention and treatment of diabetic complications due to their multiple targets and less toxic side effects. This review aims to assess the current available knowledge of medicinal herbs for attenuation and management of diabetic complications and their underlying mechanisms.

MATERIAL AND METHODS

Bibliographic investigation was carried out by scrutinizing classical text books and peer reviewed papers, consulting worldwide accepted scientific databases (SCOPUS, PUBMED, SCIELO, NISCAIR, Google Scholar) to retrieve available published literature. The inclusion criteria for the selection of plants were based upon all medicinal herbs and their active compounds with attributed potentials in relieving diabetic complications. Moreover, plants which have potential effect in ameliorating oxidative stress in diabetic animals have been included.

RESULTS

Overall, 238 articles were reviewed for plant literature and out of the reviewed literature, 127 articles were selected for the study. Various medicinal plants/plant extracts containing flavonoids, alkaloids, phenolic compounds, terpenoids, saponins and phytosterol type chemical constituents were found to be effective in the management of diabetic complications. This effect might be attributed to amelioration of persistent hyperglycemia, oxidative stress and modulation of various metabolic pathways involved in the pathogenesis of diabetic complications.

CONCLUSION

Screening chemical candidate from herbal medicine might be a promising approach for new drug discovery to treat the diabetic complications. There is still a dire need to explore the mechanism of action of various plant extracts and their toxicity profile and to determine their role in therapy of diabetic complications. Moreover, a perfect rodent model which completely mimics human diabetic complications should be developed.

Food-intake dysregulation in type 2 diabetic Goto-Kakizaki rats: hypothesized role of dysfunctional brainstem thyrotropin-releasing hormone and impaired vagal output

Thyrotropin-releasing hormone (TRH), a neuropeptide contained in neural terminals innervating brainstem vagal motor neurons, enhances vagal outflow to modify multisystemic visceral functions and food intake. Type 2 diabetes (T2D) and obesity are accompanied by impaired vagal functioning. We examined the possibility that impaired brainstem TRH action may contribute to the vagal dysregulation of food intake in Goto-Kakizaki (GK) rats, a T2D model with hyperglycemia and impaired central vagal activation by TRH. Food intake induced by intracisternal injection of TRH analog was reduced significantly by 50% in GK rats, compared to Wistar rats. Similarly, natural food intake in the dark phase or food intake after an overnight fast was reduced by 56-81% in GK rats. Fasting (48h) and refeeding (2h)-associated changes in serum ghrelin, insulin, peptide YY, pancreatic polypeptide and leptin, and the concomitant changes in orexigenic or anorexigenic peptide expression in the brainstem and hypothalamus, all apparent in Wistar rats, were absent or markedly reduced in GK rats, with hormone release stimulated by vagal activation, such as ghrelin and pancreatic polypeptide, decreased substantially. Fasting-induced Fos expression accompanying endogenous brainstem TRH action decreased by 66% and 91%, respectively, in the nucleus tractus solitarius (NTS) and the dorsal motor nucleus of the vagus (DMV) in GK rats, compared to Wistar rats. Refeeding abolished fasting-induced Fos-expression in the NTS, while that in the DMV remained in Wistar but not GK rats. These findings indicate that dysfunctional brainstem TRH-elicited vagal impairment contributes to the disturbed food intake in T2D GK rats, and may provide a pathophysiological mechanism which prevents further weight gain in T2D and obesity.

Gastric bypass surgery improves glucose metabolism possibly by decreasing ghrelin levels in Goto-Kakizaki rats

AIM: To investigate the influence of gastric bypass (GBP) surgery on glucose metabolism in Goto-Kakizaki (GK) rats and to explore the possible mechanisms involved.

METHODS: Twenty male GK rats and 10 male Wistar rats were randomized into three groups: GK operation group, GK sham operation group and Wistar sham operation group. The GK operation group underwent gastric bypass surgery. The levels of fasting plasma glucose (FPG), glycosylated hemoglobin (HbAlc), serum insulin (INS) and ghrelin were monitored 1 week before surgery and 1, 2, 4, 8 and 12 weeks after surgery.

RESULTS: In the GK operation group, FPG level decreased from (11.36 ± 1.14) mmol/L before surgery to (8.36 ± 0.62) mmol/L 12 weeks after surgery, and HbAlc from (8.91 ± 0.36)% to (6.35 ± 0.46)%. Serum INS increased from (32.70 ± 2.37) mIU/L before surgery to (55.14 ± 5.45) mIU/L 12 weeks after surgery, while serum ghrelin level decreased from (928.53 ± 58.66) pg/mL to (367.83 ± 27.78) pg/mL. All the above parameters differed significantly between before surgery and 12 weeks after surgery (all P < 0.05).

CONCLUSION: GBP can significantly improve glycometabolism in GK rats possibly by decreasing ghrelin levels and promoting insulin secretion.

Combating Combination of Hypertension and Diabetes in Different Rat Models

Rat experimental models are used extensively for studying physiological mechanisms and treatments of hypertension and diabetes co-existence. Each one of these conditions is a major risk factor for cardiovascular disease (CVD), and the combination of the two conditions is a potent enhancer of CVD. Five major animal models that advanced our understanding of the mechanisms and therapeutic approaches in humans are discussed in this review: Zucker, Goto-Kakizaki, SHROB, SHR/NDmcr-cp and Cohen Rosenthal diabetic hypertensive (CRDH) rats. The use of various drugs, such as angiotensin-converting enzyme (ACE) inhibitors (ACEIs), various angiotensin receptor blockers (ARBs), and calcium channel blockers (CCBs), to combat the effects of concomitant pathologies on the combination of diabetes and hypertension, as well as the non-pharmacological approach are reviewed in detail for each rat model. Results from experiments on these models indicate that classical factors contributing to the pathology of hypertension and diabetes combination—Including hypertension, hyperglycemia, hyperinsulinemia and hyperlipidemia—can now be treated, although these treatments do not completely prevent renal complications. Animal studies have focused on several mechanisms involved in hypertension/diabetes that remain to be translated into clinical medicine, including hypoxia, oxidative stress, and advanced glycation. Several target molecules have been identified that need to be incorporated into a treatment modality. The challenge continues to be the identification and interpretation of the clinical evidence from the animal models and their application to human treatment.

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 α-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 α-glucosidase in the small intestine were suggested as possible mechanisms related with the postprandial hypoglycemic effect of MLE.