Combination of the insulin sensitizer, pioglitazone, and the long-acting GLP-1 human analog, liraglutide, exerts potent synergistic glucose-lowering efficacy in severely diabetic ZDF rats

Bioengineered Nanomedicines Targeting the Intestinal Fc Receptor Achieve the Improved Glucoregulatory Effect of Semaglutide in a Type 2 Diabetic Mice Model

The oral administration of the glucagon-like peptide-1 analogue, semaglutide, remains a hurdle due to its limited bioavailability. Herein, neonatal Fc receptor (FcRn)-targeted nanoparticles (NPs) were designed to enhance the oral delivery of semaglutide. The nanocarriers were covalently linked to the FcRn-binding peptide FcBP or the affibody molecule ZFcRn that specifically binds to the human FcRn (hFcRn) in a pH-dependent manner. These FcRn-targeted ligands were selected over the endogenous ligands of the receptor (albumin and IgG) due to their smaller size and simpler structure, which could facilitate the transport of functionalized NPs through the tissues. The capacity of FcRn-targeted semaglutide-NPs in controlling the blood glucose levels was evaluated in an hFcRn transgenic mice model, where type 2 diabetes mellitus (T2DM) was induced via intraperitoneal injection of nicotinamide followed by streptozotocin. The encapsulation of semaglutide into FcRn-targeted NPs was translated in an improved glucoregulatory effect in T2DM-induced mice when compared to the oral free semaglutide or nontargeted NP groups, after daily oral administrations for 7 days. Notably, a similar glucose-lowering response was observed between both FcRn-targeted NPs and the subcutaneous semaglutide groups. An increase in insulin pancreatic content and a recovery in β cell mass were visualized in the mice treated with FcRn-targeted semaglutide-NPs. The biodistribution of fluorescently labeled NPs through the gastrointestinal tract demonstrated that the nanosystems targeting the hFcRn are retained longer in the ileum and colorectum, where the expression of FcRn is more prevalent, than nontargeted NPs. Therefore, FcRn-targeted nanocarriers proved to be an effective platform for improving the pharmacological effect of semaglutide in a T2DM-induced mice model.

Liraglutide provides cardioprotection through the recovery of mitochondrial dysfunction and oxidative stress in aging hearts

Glucagon-like peptide-1 receptor (GLP-1R) agonists improve cardiovascular dysfunction via the pleiotropic effects behind their receptor action. However, it is unknown whether they have a cardioprotective action in the hearts of the elderly. Therefore, we examined the effects of GLP-1R agonist liraglutide treatment (LG, 4 weeks) on the systemic parameters of aged rats (24-month-old) compared to those of adult rats (6-month-old) such as electrocardiograms (ECGs) and systolic and diastolic blood pressure (SBP and DBP). At the cellular level, the action potential (AP) parameters, ionic currents, and Ca²⁺ regulation were examined in freshly isolated ventricular cardiomyocytes. The LG treatment of aged rats significantly ameliorated the prolongation of QRS duration and increased both SBP and DBP together with recovery in plasma oxidant and antioxidant statuses. The prolonged AP durations and depolarized membrane potentials of the isolated cardiomyocytes from the aged rats were normalized via recoveries in K⁺ channel currents with LG treatment. The alterations in Ca²⁺ regulation including leaky-ryanodine receptors (RyR2) could be also ameliorated via recoveries in Na⁺/Ca²⁺ exchanger currents with this treatment. A direct LG treatment of isolated aged rat cardiomyocytes could recover the depolarized mitochondrial membrane potential, the increase in both reactive oxygen and nitrogen species (ROS and RNS), and the cytosolic Na⁺ level, although the Na⁺ channel currents were not affected by aging. Interestingly, LG treatment of aged rat cardiomyocytes provided a significant inhibition of activated sodium-glucose co-transporter-2 (SGLT2) and recoveries in the depressed insulin receptor substrate 1 (IRS1) and increased protein kinase G (PKG). The recovery in the ratio of phospho-endothelial nitric oxide (pNOS3) level to NOS3 protein level in LG-treated cardiomyocytes implies the involvement of LG-associated inhibition of oxidative stress-induced injury via IRS1-eNOS-PKG pathway in the aging heart. Overall, our data, for the first time, provide important information on the direct cardioprotective effects of GLP-1R agonism with LG in the hearts of aged rats through an examination of recoveries in mitochondrial dysfunction, and both levels of ROS and RNS in left ventricular cardiomyocytes.

Novel insulin sensitizer MSDC-0602K improves insulinemia and fatty liver disease in mice, alone and in combination with liraglutide

Insulin sensitizers and incretin mimetics are antidiabetic agents with vastly different mechanisms of action. Thiazolidinedione (TZD) insulin sensitizers are associated with weight gain, whereas glucagon-like peptide-1 receptor agonists can induce weight loss. We hypothesized that combination of a TZD insulin sensitizer and the glucagon-like peptide-1 receptor agonist liraglutide would more significantly improve mouse models of diabetes and nonalcoholic steatohepatitis (NASH). Diabetic db/db and MS-NASH mice were treated with the TZD MSDC-0602K by oral gavage, liraglutide (Lira) by s.c. injection, or combination 0602K+Lira. Lira slightly reduced body weight and modestly improved glycemia in db/db mice. Comparatively, 0602K-treated and 0602K+Lira-treated mice exhibited slight weight gain but completely corrected glycemia and improved glucose tolerance. 0602K reduced plasma insulin, whereas Lira further increased the hyperinsulinemia of db/db mice. Surprisingly, 0602K+Lira treatment reduced plasma insulin and C-peptide to the same extent as mice treated with 0602K alone. 0602K did not reduce glucose-stimulated insulin secretion in vivo, or in isolated islets, indicating the reduced insulinemia was likely compensatory to improved insulin sensitivity. In MS-NASH mice, both 0602K or Lira alone improved plasma alanine aminotransferase and aspartate aminotransferase, as well as liver histology, but more significant improvements were observed with 0602K+Lira treatment. 0602K or 0602K+Lira also increased pancreatic insulin content in both db/db and MS-NASH mice. In conclusion, MSDC-0602K corrected glycemia and reduced insulinemia when given alone, or in combination with Lira. However, 0602K+Lira combination more significantly improved glucose tolerance and liver histology, suggesting that this combination treatment may be an effective therapeutic strategy for diabetes and NASH.

A glucagon-like peptide-1 analog, liraglutide, ameliorates endothelial dysfunction through miRNAs to inhibit apoptosis in rats

Background and Aims

Many studies have revealed that glucagon-like peptide-1 has vasoprotective effects. In this study, we investigated whether liraglutide suppressed endothelial dysfunction and explored the mechanism involved.

Methods

Experimental diabetes was induced through combined high-fat diet administration and intraperitoneal streptozotocin injections. Rats were randomly divided into the following four groups: control, diabetes, diabetes + a low liraglutide dose (0.2 mg/kg/d), and diabetes + a high liraglutide dose (0.4 mg/kg/d). Endothelial function and metabolic parameters were measured after 8 weeks of treatment. miRNA arrays were analyzed to identify the differentially expressed miRNAs.

Results

We found that liraglutide significantly improved aortic endothelial function in diabetic rats. Liraglutide inhibited miR-93-5p, miR-181a-5p and miR-34a-5p expression, and activated miR-26a-5p expression. miRNA mimic transfection experiments indicated negative relationships between miR-93-5p, miR-181a-5p, miR-34a-5p, and miR-26a-5p and Sirt1, Creb, Bcl-2, and Pten expression, respectively. Moreover, liraglutide increased Sirt1, Creb, and Bcl-2 expression levels and reduced Pten expression level.

Conclusion

Our results demonstrate the role of key miRNAs in the liraglutide-mediated regulation of endothelial cell function in diabetic rats.

Liraglutide reduces hepatic glucolipotoxicity‑induced liver cell apoptosis through NRF2 signaling in Zucker diabetic fatty rats

The primary aim of the present study was to evaluate the effects of liraglutide on glucolipotoxicity-induced liver cell apoptosis and the underlying mechanisms in Zucker diabetic fatty (ZDF) rats. The results revealed that liraglutide significantly decreased the body weight, hyperglycemia and hyperlipidemia of ZDF rats relative to those of Zucker lean (ZL) rats (P<0.05). Furthermore, the reduced liver cell apoptosis was observed in the ZDF rats following 6 weeks of liraglutide therapy. These data validated the beneficial effects of liraglutide on diabetic and obese ZDF rats. In addition, novel data was obtained that demonstrated that liraglutide treatment increased the expression of the antioxidant transcription factor nuclear factor-erythroid 2-related factor 2 (NRF2), as well as the transcription of downstream target genes, including nicotinamide adenine dinucleotide phosphate quinone dehydrogenase 1 and heme oxygenase-1 (P<0.05). Additionally, serum and hepatic GSH and SOD levels increased following liraglutide therapy (P<0.05). Hence, it was proposed that liraglutide may enhance the antioxidant activity of liver cells by activating the NRF2 signaling pathway, thereby reducing liver cell apoptosis induced by glucolipotoxicity in ZDF rats, which may shed light on the application of liraglutide in the treatment of diabetes- and obesity-induced liver injury.

MicroRNA-223 is a crucial mediator of PPARγ-regulated alternative macrophage activation

Polarized activation of adipose tissue macrophages (ATMs) is crucial for maintaining adipose tissue function and mediating obesity-associated cardiovascular risk and metabolic abnormalities; however, the regulatory network of this key process is not well defined. Here, we identified a PPARγ/microRNA-223 (miR-223) regulatory axis that controls macrophage polarization by targeting distinct downstream genes to shift the cellular response to various stimuli. In BM-derived macrophages, PPARγ directly enhanced miR-223 expression upon exposure to Th2 stimuli. ChIP analysis, followed by enhancer reporter assays, revealed that this effect was mediated by PPARγ binding 3 PPARγ regulatory elements (PPREs) upstream of the pre-miR-223 coding region. Moreover, deletion of miR-223 impaired PPARγ-dependent macrophage alternative activation in cells cultured ex vivo and in mice fed a high-fat diet. We identified Rasa1 and Nfat5 as genuine miR-223 targets that are critical for PPARγ-dependent macrophage alternative activation, whereas the proinflammatory regulator Pknox1, which we reported previously, mediated miR-223-regulated macrophage classical activation. In summary, this study provides evidence to support the crucial role of a PPARγ/miR-223 regulatory axis in controlling macrophage polarization via distinct downstream target genes.

The anti-diabetic effects of GLP-1-gastrin dual agonist ZP3022 in ZDF rats

AIMS/HYPOTHESIS

Combination treatment with exendin-4 and gastrin has proven beneficial in treatment of diabetes and preservation of beta cell mass in diabetic mice. Here, we examined the chronic effects of a GLP-1-gastrin dual agonist ZP3022 on glycemic control and beta cell dysfunction in overtly diabetic Zucker Diabetic Fatty (ZDF) rats.

METHODS

ZDF rats aged 11 weeks were dosed s.c., b.i.d. for 8 weeks with vehicle, ZP3022, liraglutide, exendin-4, or gastrin-17 with or without exendin-4. Glycemic control was assessed by measurements of HbA1c and blood glucose levels, as well as glucose tolerance during an oral glucose tolerance test (OGTT). Beta cell dynamics were examined by morphometric analyses of beta and alpha cell fractions.

RESULTS

ZP3022 improved glycemic control as measured by terminal HbA1c levels (6.2±0.12 (high dose) vs. 7.9±0.07% (vehicle), P<0.001), as did all treatments, except gastrin-17 monotherapy. In contrast, only ZP3022, exendin-4 and combination treatment with exendin-4 and gastrin-17 significantly improved glucose tolerance and increased insulin levels during an OGTT. Moreover, only ZP3022 significantly enhanced the beta cell fraction in ZDF rats, a difference of 41%, when compared to the vehicle group (0.31±0.03 vs. 0.22±0.02%, respectively, P<0.05).

CONCLUSION

These data suggest that ZP3022 may have therapeutic potential in the prevention/delay of beta cell dysfunction in type 2 diabetes.

Effects of 1-Methylnicotinamide (MNA) on Exercise Capacity and Endothelial Response in Diabetic Mice

1-Methylnicotinamide (MNA), which was initially considered to be a biologically inactive endogenous metabolite of nicotinamide, has emerged as an anti-thrombotic and anti-inflammatory agent with the capacity to release prostacyclin (PGI2). In the present study, we characterized the effects of MNA on exercise capacity and the endothelial response to exercise in diabetic mice. Eight-week-old db/db mice were untreated or treated with MNA for 4 weeks (100 mg·kg-1), and their exercise capacity as well as NO- and PGI2-dependent response to endurance running were subsequently assessed. MNA treatment of db/db mice resulted in four-fold and three-fold elevation of urine concentrations of MNA and its metabolites (Met-2PY + Met-4PY), respectively (P<0.01), but did not affect HbA1c concentration, fasting glucose concentration or lipid profile. However, insulin sensitivity was improved (P<0.01). In MNA-treated db/db mice, the time to fatigue for endurance exercise was significantly prolonged (P<0.05). Post-exercise Δ6-keto-PGF1α (difference between mean concentration in the sedentary and exercised groups) tended to increase, and post-exercise leukocytosis was substantially reduced in MNA-treated animals. In turn, the post-exercise fall in plasma concentration of nitrate was not affected by MNA. In conclusion, we demonstrated for the first time that MNA improves endurance exercise capacity in mice with diabetes, and may also decrease the cardiovascular risk of exercise.

Effects of the glucagon-like peptide-1 receptor agonist liraglutide in juvenile transgenic pigs modeling a pre-diabetic condition

Background

The glucagon-like peptide-1 receptor (GLP1R) agonist liraglutide improves glycemic control and reduces body weight of adult type 2 diabetic patients. However, efficacy and safety of liraglutide in adolescents has not been systematically investigated. Furthermore, possible pro-proliferative effects of GLP1R agonists on the endocrine and exocrine pancreas need to be further evaluated. We studied effects of liraglutide in adolescent pigs expressing a dominant-negative glucose-dependent insulinotropic polypeptide receptor (GIPR^dn) in the beta-cells, leading to a pre-diabetic condition including disturbed glucose tolerance, reduced insulin secretion and progressive reduction of functional beta-cell mass.

Methods

Two-month-old GIPR^dn transgenic pigs were treated daily with liraglutide (0.6-1.2 mg per day) or placebo for 90 days. Glucose homeostasis was evaluated prior to and at the end of the treatment period by performing mixed meal and intravenous glucose tolerance tests (MMGTT and IVGTT). Finally animals were subjected to necropsy and quantitative-stereological analyses were performed for evaluation of alpha- and beta-cell mass, beta-cell proliferation as well as acinus-cell proliferation.

Results

MMGTT at the end of the study revealed 23% smaller area under the curve (AUC) for glucose, a 36% smaller AUC insulin, and improved insulin sensitivity, while IVGTT showed a 15% smaller AUC glucose but unchanged AUC insulin in liraglutide- vs. placebo-treated animals. Liraglutide led to marked reductions in body weight gain (-31%) and food intake (-30%) compared to placebo treatment, associated with reduced phosphorylation of insulin receptor beta (INSRB)/insulin-like growth factor-1 receptor beta (IGF1RB) and protein kinase B (AKT) in skeletal muscle. Absolute alpha- and beta-cell mass was reduced in liraglutide-treated animals, but alpha- and beta-cell mass-to-body weight ratios were unchanged. Liraglutide neither stimulated beta-cell proliferation in the endocrine pancreas nor acinus-cell proliferation in the exocrine pancreas, excluding both beneficial and detrimental effects on the pig pancreas.

Conclusions

Although plasma liraglutide levels of adolescent transgenic pigs treated in our study were higher compared to human trials, pro-proliferative effects on the endocrine or exocrine pancreas or other liraglutide-related side-effects were not observed.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0431-2) contains supplementary material, which is available to authorized users.

Effect of bariatric surgery combined with medical therapy versus intensive medical therapy or calorie restriction and weight loss on glycemic control in Zucker diabetic fatty rats

Bariatric surgery rapidly improves Type 2 diabetes mellitus (T2DM). Our objective was to profile and compare the extent and duration of improved glycemic control following Roux-en-Y gastric (RYGB) bypass surgery and vertical sleeve gastrectomy (SG) and compare against calorie restriction/weight loss and medical combination therapy-based approaches using the Zucker diabetic fatty rat (ZDF) rodent model of advanced T2DM. Male ZDF rats underwent RYGB (n = 15) or SG surgery (n = 10) at 18 wk of age and received postsurgical insulin treatment, as required to maintain mid-light-phase glycemia within a predefined range (10-15 mmol/l). In parallel, other groups of animals underwent sham surgery with ad libitum feeding (n = 6), with body weight (n = 8), or glycemic matching (n = 8) to the RYGB group, using food restriction or a combination of insulin, metformin, and liraglutide, respectively. Both bariatric procedures decreased the daily insulin dose required to maintain mid-light-phase blood glucose levels below 15 mmol/l, compared with those required by body weight or glycemia-matched rats (P < 0.001). No difference was noted between RYGB and SG with regard to initial efficacy. SG was, however, associated with higher food intake, weight regain, and higher insulin requirements vs. RYGB at study end (P < 0.05). Severe hypoglycemia occurred in several rats after RYGB. RYGB and SG significantly improved glycemic control in a rodent model of advanced T2DM. While short-term outcomes are similar, long-term efficacy appears marginally better after RYGB, although this is tempered by the increased risk of hypoglycemia.

Pathophysiological and pharmacological rationale for the use of exenatide once weekly in patients with type 2 diabetes

INTRODUCTION

A new formulation of exenatide has become available recently that is the first antidiabetic medication for type 2 diabetes mellitus (T2DM) dosed on a weekly schedule. This review summarizes the pharmacology, efficacy, and safety of exenatide once weekly (exenatide QW). The results are interpreted in terms of the pathophysiology of T2DM, as well as the pharmacology of the new formulation.

METHODS

Relevant literature on exenatide QW and diabetes was identified through PubMed database searches from inception until September 2013.

DISCUSSION

In the new once-weekly formulation of exenatide, the exenatide molecule is dispersed in microspheres. Following subcutaneous injection, these microspheres degrade in situ and slowly release active agent. In clinical trials, therapy with exenatide QW as monotherapy or in combination with other antidiabetic treatments was associated with reductions in glycated hemoglobin (-1.3% to -1.9%), fasting plasma glucose (-32 to -41 mg/dL), and body weight (-2.0 to -3.7 kg). These outcomes were achieved without an associated increase in the rate of hypoglycemic episodes, except when exenatide QW was used in combination with sulfonylureas. The primary tolerability issues in the trials were gastrointestinal adverse events, particularly during the first weeks of use, although the rate of nausea during startup with exenatide QW was lower than that with the related agents, exenatide twice daily and liraglutide once daily.

CONCLUSIONS

Exenatide QW may be particularly well suited to patients who desire the benefits associated with glucagon-like peptide-1 receptor agonists, including significant glycemic control, low risk of hypoglycemia, and moderate weight loss, but prefer the convenience of once-weekly dosing.

Genetically engineered pig models for diabetes research

Diabetes mellitus (DM) has emerged into a steadily increasing health problem and the predicted future dimension of the global DM epidemic is alarming: an increase from currently 346 million to over 400 million affected people worldwide by the year 2030 was extrapolated. Thus concerted research efforts are imperative to gain insight into disease mechanisms and to expand the basis for development of preventive and therapeutic strategies. Diabetic rodent models have traditionally been used to follow these goals, but have limitations for translational research. The pig is another classical animal model for diabetes research. Genetic engineering now facilitates tailoring pig models which mimic human disease mechanisms at the molecular level. This article reviews the existing genetically engineered pig models for diabetes research and their current and future applications. Further, the potential role of the pig as donor of pancreatic islets for xenotransplantation or as host for growing human pancreas is outlined.

Oral salmon calcitonin attenuates hyperglycaemia and preserves pancreatic beta-cell area and function in Zucker diabetic fatty rats

BACKGROUND AND PURPOSE

Oral salmon calcitonin (sCT), a dual-action amylin and calcitonin receptor agonist, improved glucose homeostasis in diet-induced obese rats. Here, we have evaluated the anti-diabetic efficacy of oral sCT using parameters of glycaemic control and beta-cell morphology in male Zucker diabetic fatty (ZDF) rats, a model of type 2 diabetes.

EXPERIMENTAL APPROACH

Male ZDF rats were treated with oral sCT (0.5, 1.0 or 2 mg·kg(-1) ) or oral vehicle twice daily from age 8 to 18 weeks. Zucker lean rats served as control group. Fasting and non-fasted blood glucose, glycosylated haemoglobin (HbA1c) and levels of pancreas and incretin hormones were determined. Oral glucose tolerance test and i.p. glucose tolerance test were compared, and beta-cell area and function were evaluated.

KEY RESULTS

Oral sCT treatment dose-dependently attenuated fasting and non-fasted hyperglycaemia during the intervention period. At the end of the study period, oral sCT treatment by dose decreased diabetic hyperglycaemia by ∼9 mM and reduced HbA1c levels by 1.7%. Furthermore, a pronounced reduction in glucose excursions was dose-dependently observed for oral sCT treatment during oral glucose tolerance test. In addition, oral sCT treatment sustained hyperinsulinaemia and attenuated hyperglucagonaemia and hypersecretion of total glucagon-like peptide-1 predominantly in the basal state. Lastly, oral sCT treatment dose-dependently improved pancreatic beta-cell function and beta-cell area at study end.

CONCLUSIONS AND IMPLICATIONS

Oral sCT attenuated diabetic hyperglycaemia in male ZDF rats by improving postprandial glycaemic control, exerting an insulinotropic and glucagonostatic action in the basal state and by preserving pancreatic beta-cell function and beta-cell area.

Murine models for pharmacological studies of the metabolic syndrome

Metabolic syndrome has been described as the association of insulin resistance, hypertension, hyperlipidemia and obesity. Its prevalence increased dramatically, mainly in developed countries. Animal models are essential to understand the pathophysiology of this syndrome. This review presents the murine models of metabolic syndrome the most often used in pharmacological studies. The most common metabolic syndrome models exhibit a non-functional leptin pathway, or metabolic disorders induced by high fat diets. In a first part, and after a short introduction on leptin, its receptor and mechanism of action, we provide a detailed description of each model: SHROB, SHHF, JCR:LA-cp, Zucker, ZDF, Wistar Ottawa Karlsburg W, and Otsuka Long-Evans Tokushima Fatty rats, ob/ob, db/db, agouti yellow and Mc4R KO mice. The second part of this review is dedicated to metabolic syndrome models obtained by high fat feeding.

Glucagon-like peptide 1 prevents reactive oxygen species-induced endothelial cell senescence through the activation of protein kinase A

OBJECTIVE

Endothelial cell senescence is an important contributor to vascular aging and is increased under diabetic conditions. Here we investigated whether the antidiabetic hormone glucagon-like peptide 1 (GLP-1) could prevent oxidative stress-induced cellular senescence in endothelial cells.

METHODS AND RESULTS

In Zucker diabetic fatty rats, a significant 2-fold higher level of vascular senescence was observed compared with control lean rats. Dipeptidyl-peptidase 4 (DPP-4) inhibition significantly increased GLP-1 levels in these animals and reduced senescence almost to lean animal levels. In vitro studies with human umbilical vein endothelial cells showed that GLP-1 had a direct protective effect on oxidative stress (H(2)O(2))-induced senescence and was able to attenuate oxidative stress-induced DNA damage and cellular senescence. The GLP-1 analogue exendin-4 provided similar results, whereas exendin fragment 9-39, a GLP-1 receptor antagonist, abolished this effect. Intracellular signaling by the phosphoinositide 3-kinase (PI3K)/Akt survival pathway did not appear to be involved. Further analysis revealed that GLP-1 activates the cAMP response element-binding (CREB) transcription factor in a cAMP/protein kinase A (PKA)-dependent manner, and inhibition of the cAMP/PKA pathway abolished the GLP-1 protective effect. Expression analysis revealed that GLP-1 can induce the oxidative defense genes HO-1 and NQO1.

CONCLUSIONS

Dipeptidyl-peptidase 4 inhibition protects against vascular senescence in a diabetic rat model. In vitro studies with human umbilical vein endothelial cells showed that reactive oxygen species-induced senescence was attenuated by GLP-1 in a receptor-dependent manner involving downstream PKA signaling and induction of antioxidant genes.

Synergistic effect of the human GLP-1 analogue liraglutide and a dual PPARalpha/gamma agonist on glycaemic control in Zucker diabetic fatty rats

AIM/HYPOTHESIS

Combination therapies are increasingly common in the clinical management of type 2 diabetes. We investigated to what extent combined treatment with the human glucagon-like peptide-1 (GLP-1) analogue liraglutide and the dual PPARalpha/gamma agonist ragaglitazar would improve glycaemic control in overtly diabetic Zucker diabetic fatty (ZDF) rats.

METHODS

Ninety overtly diabetic male ZDF rats were stratified into groups with matched haemoglobin A1c (HbA1c) (9.0+/-0.1%). Liraglutide (15 and 50 microg/kg subcutaneously twice daily), ragaglitazar (1 and 3 mg/kg perorally once daily) and their vehicles were studied as monotherapy and in combination in a 3x3 factorial design.

RESULTS

After 4-week treatment, synergistic effects on HbA1c, non-fasting morning blood glucose (BG) and/or 24-h BG profiles were observed with three of the four combinations. The relationship between plasma insulin and BG in combination-treated animals approached that of historical lean ZDF rats representing normal glucose homeostasis, suggesting that insulin secretion and insulin sensitivity were markedly improved. Increased insulin immunostaining in islets further supports the improved beta-cell function and/or insulin sensitivity in combination-treated animals. The synergistic effect on glycaemic control was found without a similar synergistic increase in beta-cell mass in the combination groups.

CONCLUSIONS/INTERPRETATION

Our data demonstrate that combination treatment with a human GLP-1 analogue and a dual PPARalpha/gamma agonist through distinct mechanism of actions synergistically improves glycaemic control in the ZDF rat.