Rodent Models Of Type 2 Diabetes Research Articles

Evaluating the effectiveness of a novel somatostatin receptor 2 antagonist, ZT-01, for hypoglycemia prevention in a rodent model of type 2 diabetes.

Background: Elevated levels of somatostatin blunt glucagon counterregulation during hypoglycemia in type 1 diabetes (T1D) and this can be improved using somatostatin receptor 2 (SSTR2) antagonists. Hypoglycemia also occurs in late-stage type 2 diabetes (T2D), particularly when insulin therapy is initiated, but the utility of SSTR2 antagonists in ameliorating hypoglycemia in this disease state is unknown. We examined the efficacy of a single-dose of SSTR2 antagonists in a rodent model of T2D. Methods: High-fat fed (HFF), low dose streptozotocin (STZ, 35mg/kg)-induced T2D and HFF only, nondiabetic (controls-no STZ) rats were treated with the SSTR2 antagonists ZT-01/PRL-2903 or vehicle (n = 9-11/group) 60min before an insulin tolerance test (ITT; 2-12U/kg insulin aspart) or an oral glucose tolerance test (OGTT; 2g/kg glucose via oral gavage) on separate days. Results: This rodent model of T2D is characterized by higher baseline glucose and HbA1c levels relative to HFF controls. T2D rats also had lower c-peptide levels at baseline and a blunted glucagon counterregulatory response to hypoglycemia when subjected to the ITT. SSTR2 antagonists increased the glucagon response and reduced incidence of hypoglycemia, which was more pronounced with ZT-01 than PRL-2903. ZT-01 treatment in the T2D rats increased glucagon levels above the control response within 60min of dosing, and values remained elevated during the ITT (glucagon Cmax: 156 ± 50 vs. 77 ± 46pg/mL, p < 0.01). Hypoglycemia incidence was attenuated with ZT-01 vs. controls (63% vs. 100%) and average time to hypoglycemia onset was also delayed (103.1 ± 24.6 vs. 66.1 ± 23.6min, p < 0.05). ZT-01 administration at the OGTT onset increased the glucagon response without exacerbating hyperglycemia (2877 ± 806 vs. 2982 ± 781), potentially due to the corresponding increase in c-peptide levels (6251 ± 5463 vs. 14008 ± 5495, p = 0.013). Conclusion: Treatment with SSTR2 antagonists increases glucagon responses in a rat model of T2D and results in less hypoglycemia exposure. Future studies are required to determine the best dosing periods for chronic SSTR2 antagonism treatment in T2D.

Regulation of the intestinal Na+/H+ exchanger NHE3 by AMP-activated kinase is dependent on phosphorylation of NHE3 at S555 and S563.

Electroneutral NaCl transport by Na+/H+ exchanger 3 (NHE3, SLC9A3) is the major Na+ absorptive mechanism in the intestine and decreased NHE3 activity contributes to diarrhea. Patients with diabetes often experience gastrointestinal adverse effects and medications are often a culprit for chronic diarrhea in type 2 diabetes (T2D). We have shown previously that metformin, the most widely prescribed drug for the treatment of T2D, induces diarrhea by inhibition of Na+/H+ exchanger 3 (NHE3) in rodent models of T2D. Metformin was shown to activate AMP-activated protein kinase (AMPK), but AMPK-independent glycemic effects of metformin are also known. The current study is undertaken to determine whether metformin inhibits NHE3 by activation of AMPK and the mechanism by which NHE3 is inhibited by AMPK. Inhibition of NHE3 by metformin was abolished by knockdown of AMPK-α1 or AMPK-α2. AMPK activation by 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR) phosphorylated NHE3 at S555. S555 is the primary site of phosphorylation by protein kinase A (PKA), but AMPK phosphorylated S555 independently of PKA. Using Mass spectrometry, we found S563 as a newly recognized phosphorylation site in NHE3. Altering either S555 or S563 to Ala was sufficient to block the inhibition of NHE3 activity by AMPK. NHE3 inhibition is dependent on ubiquitination by the E3 ubiquitin ligase Nedd4-2 and metformin was shown to induce NHE3 internalization via Nedd4-2-mediated ubiquitination. AICAR did not increase NHE3 ubiquitination when S555 or S563 was mutated. We conclude that AMPK activation inhibits NHE3 activity and NHE3 inhibition is associated with phosphorylation of NHE3 at S555 and S563.NEW & NOTEWORTHY We show that AMP-activated protein kinase (AMPK) phosphorylates NHE3 at S555 and S563 to inhibit NHE3 activity in intestinal epithelial cells. Phosphorylation of NHE3 by AMPK is necessary for ubiquitination of NHE3.

1-LB: Evaluating the Effectiveness of the Novel Somatostatin Receptor Antagonist (SSTR2a) ZT-01 for Hypoglycemia Prevention in a Rodent Model of Type 2 Diabetes

Background: Few pharmacological strategies exist to prevent hypoglycemia in diabetes, other than reducing the intensity of glucose-lowering therapy. SSTR2a treatment increases glucagon counterregulation and reduces the time spent in hypoglycemia in rodent models of type 1 diabetes (T1D), but the utility of this approach in type 2 diabetes (T2D) is unclear. The purpose of this study was to test the effect of acute SSTR2a treatment in a rodent model of hypoglycemia in T2D. Methods: High fat fed (HFF), low dose streptozotocin (35 mg/kg) T2D rats received SSTR2a treatment (subcutaneous ZT-01 3 mg/kg) or vehicle (N=9-11/group) 60 min before the induction of hypoglycemia using rapid-acting insulin (12 U/kg). Glycemia, glucagon and c-peptide levels were measured intermittently pre- and post-dosing. Results: T2D in the rats was characterized by significantly higher baseline glucose (21.8 ± 4.7 vs 6.5 ± 0.7 mmol/L, p&amp;lt;0.05) and HbA1c (8.6 ± 0.6% vs 5.5 ± 0.5%; p&amp;lt;0.0001) levels relative to HFF controls (n=3). T2D rats also displayed reduced c-peptide levels relative to controls (3.1 ± 1.3 vs 6.1 ± 1.2 ng/ml, p&amp;lt;0.05). During hypoglycemic challenge (T2D rats only), SSTR2a elevated glucagon levels relative to vehicle treatment (glucagon Cmax: 156 ± 50 vs 77 ± 46 pg/ml, p&amp;lt;0.01) and reduced the incidence of hypoglycemia by ~40% (5/8 SSTR2a treated vs 9/9 vehicle treated rats). In those that developed hypoglycemia, the average time to hypoglycemia onset was delayed (103.1± 24.6 vs 66.1 ± 23.6 min, p&amp;lt;0.05) with SSTR2a compared to vehicle. Conclusion: SSTR2a treatment increases glucagon levels in this rodent model of T2D, which appears to reduce the risk for hypoglycemia following bolus insulin dosing. Disclosure N. C. D'souza: None. M. Nejad-mansouri: None. R. Liggins: Employee; Zucara Therapeutics, Stock/Shareholder; Zucara Therapeutics. O. Chan: None. M. C. Riddell: Advisory Panel; Zealand Pharma A/S, Zucara Therapeutics, Indigo Diabetes, Consultant; Lilly Diabetes, Eli Lilly and Company, Jaeb Center for Health Research, Speaker's Bureau; Dexcom, Inc., Novo Nordisk, Sanofi, Stock/Shareholder; Supersapiens, Zucara Therapeutics. P. Zaree bavani: None. J. Aiken: None. E. G. Hoffman: None. S. C. Atherley: None. S. Champsi: None. N. Aleali: None. D. Shakeri: None. M. El-zahed: None. N. Akbarian: None. Funding GlycoNet (CD-85)

Sustained inhibition of NPY/AgRP neuronal activity by FGF1.

In rodent models of type 2 diabetes (T2D), central administration of FGF1 normalizes elevated blood glucose levels in a manner that is sustained for weeks or months. Increased activity of NPY/AgRP neurons in the hypothalamic arcuate nucleus (ARC) is implicated in the pathogenesis of hyperglycemia in these animals, and the ARC is a key brain area for the antidiabetic action of FGF1. We therefore sought to determine whether FGF1 inhibits NPY/AgRP neurons and, if so, whether this inhibitory effect is sufficiently durable to offer a feasible explanation for sustained diabetes remission induced by central administration of FGF1. Here, we show that FGF1 inhibited ARC NPY/AgRP neuron activity, both after intracerebroventricular injection in vivo and when applied ex vivo in a slice preparation; we also showed that the underlying mechanism involved increased input from presynaptic GABAergic neurons. Following central administration, the inhibitory effect of FGF1 on NPY/AgRP neurons was also highly durable, lasting for at least 2 weeks. To our knowledge, no precedent for such a prolonged inhibitory effect exists. Future studies are warranted to determine whether NPY/AgRP neuron inhibition contributes to the sustained antidiabetic action elicited by intracerebroventricular FGF1 injection in rodent models of T2D.

Is Type 2 Diabetes a Primary Mitochondrial Disorder?

Diabetes mellitus is the most common endocrine disturbance in inherited mitochondrial diseases. It is essential to increase awareness of the correct diagnosis and treatment of diabetes in these patients and screen for the condition in family members, as diabetes might appear with distinctive clinical features, complications and at different ages of onset. The severity of mitochondrial-related diabetes is likely to manifest on a large scale of phenotypes depending on the location of the mutation and whether the number of affected mitochondria copies (heteroplasmy) reaches a critical threshold. Regarding diabetes treatment, the first-choice treatment for type 2 diabetes (T2D), metformin, is not recommended because of the risk of lactic acidosis. The preferred treatment for diabetes in patients with mitochondrial disorders is SGLT-2i and mitochondrial GLP-1-related substances. The tight relationship between mitochondrial dysfunction, reduced glucose-stimulated insulin secretion (GSIS), and diabetes development in human patients is acknowledged. However, despite the well-characterized role of mitochondria in GSIS, there is a relative lack of data in humans implicating mitochondrial dysfunction as a primary defect in T2D. Our recent studies have provided data supporting the significant role of the mitochondrial respiratory-chain enzyme, cytochrome c oxidase (COX), in regulating GSIS in a rodent model of T2D, the Cohen diabetic sensitive (CDs) rat. The nutritionally induced diabetic CDs rat demonstrates several features of mitochondrial diseases: markedly reduced COX activity in several tissues, increased reactive oxygen production, decreased ATP generation, and increased lactate dehydrogenase expression in islets. Moreover, our data demonstrate that reduced islet-COX activity precedes the onset of diabetes, suggesting that islet-COX deficiency is the primary defect causing diabetes in this model. This review examines the possibility of including T2D as a primary mitochondrial-related disease. Understanding the critical interdependence between diabetes and mitochondrial dysfunction, centering on the role of COX, may open novel avenues to diagnose and treat diabetes in patients with mitochondrial diseases and mitochondrial dysfunction in diabetic patients.

Diabetes induces remodeling of the left atrial appendage independently of atrial fibrillation in a rodent model of type-2 diabetes

BackgroundDiabetic patients have an increased predisposition to thromboembolic events, in most cases originating from thrombi in the left atrial appendage (LAA). Remodeling of the LAA, which predisposes to thrombi formation, has been previously described in diabetic patients with atrial fibrillation, but whether remodeling of the LAA occurs in diabetics also in the absence of atrial fibrillation is unknown. To investigate the contribution of diabetes, as opposed to atrial fibrillation, to remodeling of the LAA, we went from humans to the animal model.MethodsWe studied by echocardiography the structure and function of the heart over multiple time points during the evolution of diabetes in the Cohen diabetic sensitive rat (CDs/y) provided diabetogenic diet over a period of 4 months; CDs/y provided regular diet and the Cohen diabetic resistant (CDr/y), which do not develop diabetes, served as controls. All animals were in sinus rhythm throughout the study period.ResultsCompared to controls, CDs/y developed during the evolution of diabetes a greater heart mass, larger left atrial diameter, wider LAA orifice, increased LAA depth, greater end-diastolic and end-systolic diameter, and lower E/A ratio—all indicative of remodeling of the LAA and left atrium (LA), as well as the development of left ventricular diastolic dysfunction. To investigate the pathophysiology involved, we studied the histology of the hearts at the end of the study. We found in diabetic CDs/y, but not in any of the other groups, abundance of glycogen granules in the atrial appendages , atria and ventricles, which may be of significance as glycogen granules have previously been associated with cell and organ dysfunction in the diabetic heart.ConclusionsWe conclude that our rodent model of diabetes, which was in sinus rhythm, reproduced structural and functional alterations previously observed in hearts of human diabetics with atrial fibrillation. Remodeling of the LAA and of the LA in our model was unrelated to atrial fibrillation and associated with accumulation of glycogen granules. We suggest that myocardial accumulation of glycogen granules is related to the development of diabetes and may play a pathophysiological role in remodeling of the LAA and LA, which predisposes to atrial fibrillation, thromboembolic events and left ventricular diastolic dysfunction in the diabetic heart.

Effect of Empagliflozin and Liraglutide on the Nucleotide-Binding and Oligomerization Domain-Like Receptor Family Pyrin Domain-Containing 3 Inflammasome in a Rodent Model of Type 2 Diabetes Mellitus

ObjectivesChronic inflammation has been identified as an important driver of cardiovascular disease in type 2 diabetes (T2D) and can lead to a higher risk of cardiovascular events and rehospitalization. Empagliflozin or liraglutide represent 2 classes of drugs with proven efficacy in the treatment of T2D to reduce macrovascular complications; however, the exact mechanism behind their cardioprotective properties remains incompletely understood. The nucleotide-binding and oligomerization domain-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome is implicated in the progression of cardiovascular disease and linked to the progression of cardiovascular risk factors, such as T2D. MethodsWe set out to determine whether the sodium-glucose cotransporter-2 inhibitor, empagliflozin, or the glucagon-like peptide-1 receptor antagonist, liraglutide, modified components of NLRP3 in a rodent model of T2D, which recapitulates many of the features of humans with T2D. Empagliflozin and liraglutide were used for 8 weeks in a 32-week-old rat model of T2D and compared with an age- and sex-matched control. After treatment, left ventricular tissue samples and blood plasma were obtained for immunoblotting and an interleukin-1β enzyme-linked immunossay. NLRP3, apoptosis-associated speck-like protein, pro-caspase-1 as well as the cleaved caspase-1 subunits p12 and p10 were assessed by Western blot. ResultsGoto-Kakizaki rats demonstrated increased NLRP3 inflammasome activation, but neither empagliflozin nor liraglutide demonstrated any impact across the NLRP3 inflammasome pathways or interleukin-1β levels. ConclusionsThe data suggest that the cardioprotective benefits demonstrated by sodium-glucose cotransporter-2 inhibitors and glucagon-like peptide-1 receptor antagonists occur independently of the NLRP3 inflammasome.

Insulin Resistance is Mechanistically Linked to Hepatic Mitochondrial Remodeling in Nonalcoholic Fatty Liver Disease

Insulin resistance and altered hepatic mitochondrial function are central features of type 2 diabetes (T2D) and non-alcoholic fatty liver (NAFL), but the etiological role of these processes in disease progression remains unclear. We investigated the molecular links between insulin resistance, mitochondrial remodeling, and hepatic lipid accumulation in a rodent model of T2D / NAFL. Livers from obese, insulin resistant mice displayed augmented mitochondrial content and increased TCA cycle and pyruvate dehydrogenase (PDH) activities. Insulin sensitization with pioglitazone mitigated pyruvate-driven TCA cycle activity and PDH activation via both covalent (PDK4 and PDP2) and allosteric (intracellular pyruvate availability) mechanisms. Interestingly, improvements in insulin sensitivity and mitochondrial function were entirely dissociated from changes in hepatic triglycerides, diacylglycerides or fatty acids. Instead, we show that the mitochondrial phospholipid cardiolipin undergoes pathological remodeling in livers from obese mice and that this is reversed by insulin sensitization. Our findings identify targetable mitochondrial features of T2D and NAFLD and highlight the benefit of insulin sensitization in managing the clinical burden of obesity-associated disease.

Sustained Diabetes Remission Induced by the Central Action of Fibroblast Growth Factor-1 (FGF-1) Requires Activation of Integrin Receptor aνß3

The brain is implicated in the antidiabetic effects of members of the fibroblast growth factor (FGF) peptide family. Previously, we reported that a single intracerebroventricular (icv) injection of FGF-1 induces remission of hyperglycemia that is sustained for weeks in rodent models of type 2 diabetes (T2D). The integrin receptor ανβ3 plays a key role in FGF-1 signaling, and crosstalk between ανβ3 and the FGF-1-FGF receptor (FGF-R) complex is necessary for increased DNA synthesis and proliferation in cultured cells. These cellular responses downstream of FGF-1-FGFR-ανβ3 result from sustained (e.g., lasting for 5 hours) activation of the extracellular signal-regulated kinase (ERK) signal transduction pathway. In cultured fibroblasts, prolonged ERK activation induced by FGF-1 is not replicated with a mutant FGF-1 peptide (R50E) that activates FGFR normally, but does not activate ανβ3 signaling. Similarly, we report that whereas icv FGF-1 (3 µg) induces phosphorylation of ERK1/2 at both early (20 minute) and late (5 hr) time points in hypothalamic punches obtained from wild type mice, icv injection of the same dose of R50E elicited this effect only at the early time point. Thus, R50E fails to activate hypothalamic FGF-1-FGFR-ανβ3 signaling in vivo. To investigate whether activation of ανβ3 is required for the prolonged antidiabetic effect of icv FGF-1, diabetic ob/ob mice received a single injection of either vehicle (Veh), recombinant FGF-1 (3 µg), or R50E (3 µg). Whereas R50E mimicked the effect of native FGF-1 to reduce food intake, body weight and blood glucose for the first week after icv injection (P&amp;lt;0.001 vs. Veh), the mutant peptide failed to elicit the sustained diabetes remission observed in animals receiving icv FGF-1. We conclude that signaling by the full FGF-1-FGFR-ανβ3 complex is necessary for the effect of FGF-1 signaling in the brain to elicit sustained remission of diabetic hyperglycemia in rodent models of T2D. Disclosure J. Scarlett: None. J.M. Brown: None. B.N. Phan: None. E.L. Khav: None. M.E. Matsen: None. N.K. Acharya: None. H.T. Nguyen: None. A. Secher: Employee; Self; Novo Nordisk A/S. Stock/Shareholder; Self; Novo Nordisk A/S. Employee; Spouse/Partner; Gubra. R. Jorgensen: Employee; Self; Novo Nordisk Inc.. G.J. Morton: None. M.W. Schwartz: Consultant; Self; Novo Nordisk A/S. Research Support; Self; Novo Nordisk A/S.

Pleiotropic Effects of Totum-63—Simultaneous Targeting of Multiple Diabetes Mediators

In 2015, 30.3 million Americans had diabetes, and 84.1 million Americans had prediabetes. Up to 70% of individuals with prediabetes will eventually develop type 2 diabetes (T2D). Additional intervention strategies are needed to manage prediabetes. The pathophysiology of T2D is complex and characterized by alterations in many tissues. We have previously shown that Totum-63 is effective to prevent glucose homeostasis impairments in rodent models of T2D. In an open phase I/II clinical study, Totum-63 also improved glucose and insulin responses to a standardized breakfast in healthy subjects. In order to better understand the mechanisms involved in the beneficial effects of Totum-63, we have conducted early interventions with oral administration of Totum-63 in high fat-fed mice and in db/db mice. Body weight gain and fat mass accumulation, known as early mediators of insulin-sensitivity defectiveness, were markedly lowered. Liver and skeletal muscle insulin signaling pathways were activated in a similar fashion despite lower circulating insulin levels, suggesting an improvement in insulin sensitivity. Hepatic triglyceride content, known as a powerful inductor of liver insulin resistance, was reduced. Totum-63 administration increased liver gene expression of FGF-21, which has been involved in the regulation of many metabolic pathways. In db/db mice, Totum-63 administration delayed the defect of insulin secretion, suggesting a protective role on pancreatic beta-cells. Finally, Totum-63 also showed preventive effects on high fat diet-induced gut microbiota dysbiosis, that has been postulated as a key driver of many metabolic disturbances. In conclusion, Totum-63 displays pleiotropic beneficial effects on tissues known as major contributors to T2D development. Totum-63 is a promising intervention strategy to prevent T2D development, and is currently under investigation in phase II clinical trial. Disclosure V. Chavanelle: Employee; Self; Valbiotis. Y.F. Otero: Employee; Self; Valbiotis. P. Sirvent: Employee; Self; Valbiotis. P.D. Cani: Research Support; Self; Tate&amp;Lyle. Consultant; Self; Biocodex. Stock/Shareholder; Self; A-Mansia Biotech SA. Research Support; Self; Pilèje, Valbiotis. S. Peltier: Board Member; Self; Valbiotis.

Chronic Beta2‐Adrenergic Receptor Stimulation Improves Whole‐Body Glucose Homeostasis through Skeletal Muscle Metabolic Reprogramming

Type 2 diabetes (T2D) has emerged as a major health problem worldwide. Since skeletal muscle (SKM) is the major site of insulin‐stimulated glucose disposal in the body, SKM insulin resistance plays a crucial role in the pathogenesis of this disorder. Drugs that could enhance or mimic insulin action in SKM hold great therapeutic potential for the treatment of obesity and T2D.Previous work carried out with cultured SKM cells indicates that activation of SKM β2‐adrenergic receptors (β2‐ARs) can promote glucose uptake. In rodent models of T2D, chronic administration of clenbuterol, a selective β2‐AR agonist, greatly improves glucose tolerance. However, the mechanism and in vivo tissue(s) responsible for the actions of clenbuterol are still unclear. This study was designed to test the hypothesis that the beneficial metabolic effects of clenbuterol observed in vivo are mediated by SKM β2‐ARs. For this purpose, we generated mice that lack β2‐ARs or the Gαs subunit selectively in SKM (SKM‐β2‐AR‐KO and SKM‐Gs‐KO mice, respectively). We also generated transgenic mice expressing a Gs‐DREADD selectively in SKM (SKM‐Gs‐DREADD mice).As expected, chronic administration of clenbuterol via drinking water improved glucose tolerance in wild‐type (WT) mice without affecting glucose‐stimulated insulin secretion or insulin tolerance. The SKM selectivity of this chronic clenbuterol effect was confirmed using SKM‐β2‐KO, SKM‐Gs‐KO, and SKM‐Gs‐DREADD mice. RNA‐seq and functional data indicated increases in SKM glucose accumulation, glycolysis, and glycogen synthesis following chronic treatment, suggesting a switch of SKM metabolism towards enhanced glucose utilization.Multiple components of known, but also less studied metabolic pathways seem to be simultaneously involved in mediating the beneficial metabolic effects of chronic β2‐AR stimulation.Our study represents a striking example of the complexity of β2‐AR signaling in vivo. Further analysis of β2‐AR signaling pathways in SKM could help identify potential drug targets for new T2D treatments.Support or Funding InformationThis research was funded by the Intramural Research Program of the NIDDK.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Glucose enhances rat islet function via stimulating CART expression

Cocaine- and amphetamine-regulated transcript (CART) is an anorexigenic peptide widely expressed in the central and peripheral nervous systems, as well as in endocrine cells. CART is markedly upregulated in the β-cells of several rodent models of type-2 diabetes. The stimulatory effect of exogenous CART peptide on insulin secretion is cAMP dependent. Glucose is the most important regulator of islet function. However, the role of CART in glucose-potentiated insulin secretion remains unclear. Here, our results showed that glucose time- and dose-dependently elicited CART mRNA expression in rat islets. Both the glucokinase agonist GKA50 and the long-acting GLP-1 analogue exendin-4 increased CART mRNA expression. The protein kinase A (PKA) inhibitor H89 and the inactivation of cAMP response element-binding protein (CREB) suppressed forskolin-stimulated CART mRNA expression. Furthermore, CART overexpression amplified insulin secretion from rat islets in response to glucose and forskolin, and ameliorated dexamethasone-impaired insulin secretion. These findings suggest that islet-derived CART is involved, at least in part, in high glucose-potentiated pancreatic β-cell function.

Early intervention with glucagon-like peptide 1 analog liraglutide prevents tau hyperphosphorylation in diabetic db/db mice.

Increasing evidence has shown that type 2 diabetes (T2D) is a risk factor for Alzheimer's disease. Neurofibrillary tangles, which consist of hyperphosphorylated tau and misfolded microtubules, is one of the neuropathological hallmarks of Alzheimer's disease. Db/db mice, a rodent model of T2D, also exhibited age-dependent tau hyperphosphorylation. Glucagon-like peptide-1 (GLP-1) mimetics, a type of drug used in T2D, has been found to have neuroprotective effects. The aim of this study was to explore the potential effects of liraglutide (a GLP-1 analog), or insulin, on tau phosphorylation in T2D animals. Male db/db mice (3-3.5 weeks) were daily injected subcutaneously with liraglutide (n = 27), insulin (n = 27), or saline (n = 26), and five to seven mice were killed every 2 weeks for analysis of plasma and cerebrospinal (CSF) insulin levels by ELISA, and protein levels in the hippocampal formation by western blot. We found that db/db mice treated with saline exhibited an age-dependent decrease in CSF insulin and an increase in hippocampal tau phosphorylation. Liraglutide injection reversed the CSF insulin to ~1 mIU/L by the end of 8 weeks treatment, and prevented the hyperphosphorylation of tau protein in the hippocampal formation. By contrast, insulin injection had no effects on CSF insulin or phosphorylation of tau protein. In summary, this study indicates that early GLP-1 analog intervention prevented the age-dependent tau hyperphosphorylation in T2D mice brain, probably by facilitating sequential activation in an insulin signaling pathway reflected in increased basal activation of Akt and basal suppression of glycogen synthase kinase-3 beta.

Targeting the association of calgranulin B (S100A9) with insulin resistance and type 2 diabetes

Calgranulin B (S100A9) was recognized as a candidate type 2 diabetes (T2D) gene in the genomic profiling of muscle from a rodent model of T2D and identifying the human orthologs of genes localized in T2D susceptibility regions. Circulating and S100A9 expressions in muscle and adipose tissue, isolated fat cells, and mouse models were evaluated. A common 5'-upstream single-nucleotide polymorphism (SNP; rs3014866) for S100A9 was analyzed, as well as the effects of weight loss and treatments in vitro with recombinant S100A9. S100a9 expression was increased in muscle of diabetic mice (1.6-fold, p = 0.002), and in muscle from subjects with impaired glucose tolerance (∼4-fold, p = 0.028; n = 34). The rs3014866 SNP was associated with circulating S100A9 and the risk of T2D, having TT carriers at 28 % (p = 0.03) lower risk (n = 1,450). Indeed, increased circulating S100A9 (∼4-fold, p = 0.03; n = 206) and subcutaneous (2-fold, p = 0.01) and omental (1.4-fold, p = 0.04) S100A9 gene expressions (n = 83) in TT carriers run in parallel to decreased fasting glucose and glycated hemoglobin. Accordingly, metformin led to increased S100A9 mRNA in ex vivo-treated adipose tissue explants (n = 5/treatment). Otherwise, obese subjects showed a compensatory increase in circulating and S100A9 expressions in adipose (n = 126), as further demonstrated by decreased levels after diet- (-34 %, p = 0.002; n = 20) and surgery-induced (-58 %, p = 0.02; n = 8) weight loss. Lipopolysaccharide led to increased S100A9 in adipose from mice (n = 5/treatment) while recombinant S100A9 downregulated inflammation in adipocytes (n = 3/treatment). Current findings support the strategy of testing differentially expressed genes in mice and human orthologs associated with T2D. The increased S100A9 reported for obesity and insulin resistance may be envisioned as a compensatory mechanism for inflammation.

Fasting hyperglycemia in the Goto-Kakizaki rat is dependent on corticosterone: a confounding variable in rodent models of type 2 diabetes

SUMMARYThe Goto-Kakizaki (GK) rat is an inbred model of type 2 diabetes (T2D); GK rats are lean but have hyperglycemia and increased gluconeogenesis. However, fasting hyperglycemia in other commonly used rodent models of T2D is associated with increased corticosterone, and thus the underlying mechanism for hyperglycemia differs significantly from T2D in humans. Information regarding corticosterone in the GK rat is not readily available. We studied 14- to 16-week-old GK rats in comparison with age-matched control Wistar-Kyoto (WK) rats. GK rats had lower body weights (WK: 343±10 g vs GK: 286±9 g, P<0.01), but higher plasma glucose concentrations (WK: 132±1.5 mg/dl vs GK: 210±11.7 mg/dl, P<0.01). This was associated with an ∼twofold increase in PEPCK1 expression (P<0.05). However, these findings were also associated with elevations in plasma corticosterone and urinary corticosterone excretion. Ketoconazole (KTZ) treatment in GK rats reduced plasma corticosterone, fasting glucose (GK: 218±15 mg/dl vs GK-KTZ: 135±19 mg/dl, P<0.01) and rates of glucose production [GK: 16.5±0.6 mg/(kg-minute) vs GK-KTZ: 12.2±0.9 mg/(kg-minute), P<0.01]. This was associated with an ∼40% reduction in hepatic PEPCK1 expression as well as a 20% reduction in alanine turnover. Thus, hypercorticosteronemia might contribute to the diabetic phenotype of GK rats and should be considered as a potential confounder in rodent models of T2D.

The Cardioprotective Effects of Adiponectin in the ZDF Heart Following Ischemia Are Associated with a Significant Attenuation of Myocardial ICAM‐1 Expression

Ischemic heart disease (IHD) is significantly enhanced in type 2 diabetes (T2D) and inflammation is associated with IHD and T2D. The adipocytokine, adiponectin (APN), which has anti‐inflammatory actions, is chronically reduced in type 2 diabetes. APN may link inflammation, T2D and IHD. We examined if a globular form of adiponectin was cardioprotective in the Zucker Diabetic Fatty (ZDF) rodent model of T2D and if the cardioprotection was associated with myocardial expression of ICAM‐1, a key adhesion molecule and marker of coronary microvascular dysfunction. ZDF (n=14) rats and their lean controls ZLC (n=13) were subjected to 30 minutes of LAD occlusion and 120 minutes of reperfusion. Animals were treated with either PBS or recombinant globular adiponectin (1.0 μg/g). At R120, the extent of myocardial infarction was measured. Myocardial ICAM‐1 expression was also quantified immunohistochemically. We found that adiponectin treatment significantly attenuated the enhanced myocardial infarction in the ZDF model of T2D (p&lt;0.05). The reduced infarction was associated with a significant reduction in myocardial ICAM‐1 expression (p&lt;0.05). These findings suggest that adiponectin treatment protects against I/R injury in the T2D heart. The cardioprotective action may be related to reduced coronary microvascular inflammation enhancing PMN sequestration and PMN‐mediated tissue injury. Supported by NIH HL 58859.