Diabetes News

Objective:

We hypothesized that intranasal insulin (I-I) delivery targets the nervous system while avoiding potential adverse systemic effects when compared to subcutaneous insulin (S-I) for experimental streptozotocin (STZ)-induced diabetic peripheral neuropathy (DPN).

Research Design and Methods:

I-I or S-I 0.87 IU daily or placebo were delivered in separate cohorts of diabetic and non-diabetic CD1 mice during 8 months of diabetes. Radiolabeled insulin detection was used to compare delivery and biodistribution for I-I and S-I. Biweekly behavioral testing, and monthly electrophysiological and quantitative studies assessed progression of DPN. At and prior to endpoint, morphometric analysis of DRG, peripheral nerve, distal epidermal innervation, and specific molecular markers were evaluated.

Results:

Radiolabeled I-I resulted in more rapid and concentrated delivery to the spinal cord and DRG, with less systemic insulin exposure. When compared to S-I or intranasal placebo, I-I reduced overall mouse mortality and sensory loss, while improving neuropathic pain and electrophysiological/morphological abnormalities in diabetic mice. I-I restored mRNA and protein levels of phosphoinositide 3-kinase (PI3K)/Akt, cyclic AMP response element binding protein (CREB), and glycogen synthase kinase 3β (GSK-3β) to near normal levels within diabetic DRGs.

Interpretation:

I-I slows the progression of experimental DPN in STZ mice, avoids adverse effects associated with S-I treatment, and prolongs lifespan when compared to S-I. I-I may be a promising approach for the treatment of DPN.

Objective:

Metabolic syndrome (MetS) has been associated with increased prevalence of aortic valve calcium (AVC) and with increased progression of aortic stenosis. The purpose of this study was to determine whether MetS is associated with increased risks for the development of new (“incident”) AVC or for progression of established AVC, as assessed by computed tomography (CT).

Research Design and Methods:

The relationships of MetS or its components, as well as of diabetes mellitus (DM) to risks for incident AVC or AVC progression were studied among participants with CT scans performed at baseline and at either Year 2 or Year 3 examinations in the Multi-Ethnic Study of Atherosclerosis (MESA).

Results:

Of 5,723 MESA participants meeting criteria for inclusion, 1,674 had MetS by Adult Treatment Panel (ATP) III criteria, while 761 had DM. Among the 5,123 participants without baseline AVC, risks for incident AVC; adjusted for time between scans, age, gender, race/ethnicity, LDL, lipid lowering meds and smoking; were increased significantly for MetS (OR 1.67, 95% CI: 1.21, 2.31) or DM (OR 2.06, 95% CI: 1.39, 3.06). In addition, there was an increase in incident AVC risk with increasing number of MetS components. Similar results were found using the International Diabetes Federation MetS criteria. Among the 600 participants (10.5%) with baseline AVC, neither MetS nor DM was associated with AVC progression.

Conclusions:

In the MESA cohort, MetS was associated with a significant increase in incident (“new”) AVC, raising the possibility that MetS may be a potential therapeutic target to prevent AVC development.

Objective.

Type 1 diabetes arises from the actions of multiple genetic and environmental risk factors. Considerable success at identifying common genetic variants that contribute to type 1 diabetes risk has come from genetic association (primarily case-control) studies. However, such studies have limited power to detect genes containing multiple rare variants that contribute significantly to disease risk.

Research Design and Methods.

The Type 1 Diabetes Genetics Consortium (T1DGC) has assembled a collection of 2,496 multiplex type 1 diabetes families from 9 geographical regions containing 2,658 affected sib-pairs (ASPs). We describe the results of a genome-wide scan for linkage to type 1 diabetes in the T1DGC family collection.

Results.

Significant evidence of linkage to type 1 diabetes was confirmed at the HLA region on chromosome 6p21.3 (LOD=213.2). There was further evidence of linkage to T1D on 6q which could not be accounted for by the major linkage signal at the HLA class II loci on chromosome 6p21. Suggestive evidence of linkage (LOD≥2.2) was observed near CTLA4 on chromosome 2q32.3 (LOD=3.28) and near INS (LOD=3.16) on chromosome 11p15.5. Some evidence for linkage was also detected at two regions on chromosome 19 (LODS=2.84 and 2.54).

Conclusions.

Five non-HLA chromosome regions showed some evidence of linkage to type 1 diabetes. A number of previously proposed type 1 diabetes susceptibility loci, based on smaller ASP numbers, showed limited or no evidence of linkage to disease. Low frequency susceptibility variants or clusters of loci with common alleles could contribute to the linkage signals observed.

Objective:

To investigate the role of desnutrin in adipose tissue triacylglycerol (TAG) and fatty acid metabolism.

Design:

We generated transgenic mice overexpressing desnutrin in adipocytes (aP2-desnutrin) and also performed adenoviral-mediated overexpression of desnutrin in 3T3-L1 adipocytes.

Results:

aP2-desnutrin mice were leaner with decreased adipose tissue TAG content and smaller adipocyte size. Overexpression of desnutrin increased lipolysis but did not result in increased serum fatty acid levels or ectopic TAG storage. We found increased cycling between diacylglycerol and TAG, increased fatty acid oxidation in adipocytes from these mice, as well as improved insulin sensitivity.

Conclusions:

In conclusion, we show that by increasing lipolysis, desnutrin overexpression causes reduced adipocyte TAG content and attenuation of diet-induced obesity. Furthermore, desnutrin-mediated lipolysis promotes fatty acid oxidation and reesterification within adipocytes.

Objective:

Ghrelin is the only known peripheral hormone to increase ingestive behaviour. However, its role in the physiological regulation of energy homeostasis is unclear since deletion of ghrelin or its receptor does not alter food intake or body weight in mice fed a normal chow diet. We hypothesized over expression of ghrelin in its physiological tissues would increase food intake and body weight.

Research Design and Methods:

We used bacterial artificial chromosome transgenesis to generate a mouse model with increased ghrelin expression and production in stomach and brain. We investigated the effect of ghrelin over expression on food intake and body weight. In addition, we measured energy expenditure and determined glucose tolerance, glucose stimulated insulin release and peripheral insulin sensitivity.

Results:

Ghrelin transgenic mice exhibited increased circulating bioactive ghrelin which was associated with hyperphagia, increased energy expenditure, glucose intolerance, decreased glucose stimulated insulin secretion and reduced leptin sensitivity.

Conclusion:

This is the first report of a transgenic approach suggesting ghrelin regulates appetite under normal feeding conditions and provides evidence that ghrelin plays a fundamental role in regulating β-cell function.

Objective

Non-Fc-binding anti-CD3 specific antibodies represent a promising therapy for preserving C-peptide production in subjects with recent onset type 1 diabetes (T1D). However, the mechanisms by which anti-CD3 exerts its beneficial effect are still poorly understood and it is questionable whether this therapeutic approach will prove durable in its ability to impart metabolic preservation without additional actions designed to maintain immunological tolerance. We took advantage of the NOD mouse model to test whether rapamycin – a compound well known for its immunomodulatory activity in mice and humans – could increase the therapeutic effectiveness of anti-CD3 treatment in T1D.

Research Design and Methods

Rapamycin was administered to diabetic NOD mice simultaneously with anti-CD3, or to NOD mice cured by anti-CD3 therapy. The ability of this combined therapy to revert T1D and maintain a state of long-term tolerance was monitored and compared to that of anti-CD3 therapy alone.

Results

Rapamycin inhibited the ability of anti-CD3 to revert disease without affecting the frequency/phenotype of T cells. Rapamycin also reinstated diabetes in mice whose disease was previously reversed by anti-CD3. Withdrawal of rapamycin in these latter animals promptly restored a normoglycemic state.

Conclusions

These findings indicate that, when combined with anti-CD3, rapamycin exerts a detrimental effect on the disease outcome in NOD mice as long as it is administered. These results suggest strong caution at combining these treatments in T1D patients.

Objective:

Glucagon-like peptide-1 receptor (GLP-1R) agonists are used to treat type 2 diabetes and transient GLP-1 administration improved cardiac function in humans following acute myocardial infarction (MI) and percutaneous revascularization. However, the consequences of GLP-1R activation prior to ischemic myocardial injury remain unclear.

Research Design and Methods:

We assessed the pathophysiology and outcome of coronary artery occlusion in normal and diabetic mice pre-treated with the GLP-1R agonist liraglutide.

Results:

Male C57BL/6 mice were treated twice daily for 7 d with liraglutide or saline followed by induction of MI. Survival was significantly higher in liraglutide-treated mice. Liraglutide reduced cardiac rupture (12/60 vs. 46/60; P=0.0001), and infarct size (21±2% vs. 29±3%, P=0.02), and improved cardiac output (12.4±0.6 vs. 9.7±0.6; ml/min; P=0.002). Liraglutide also modulated the expression and activity of cardioprotective genes in the mouse heart including Akt, GSK3β, PPARβ-, Nrf-2, and HO-1. The effects of liraglutide on survival were independent of weight loss. Moreover, liraglutide conferred cardioprotection and survival advantages over metformin, despite equivalent glycemic control, in diabetic mice with experimental MI. The cardioprotective effects of liraglutide remained detectable 4 days following cessation of therapy and may be partly direct, as liraglutide increased cyclic AMP formation and reduced the extent of caspase-3 activation in cardiomyocytes in a GLP-1R-dependent manner in vitro.

Conclusions:

These findings demonstrate that GLP-1R activation engages pro-survival pathways in the normal and diabetic mouse heart, leading to improved outcomes and enhanced survival following MI in vivo.

Objective.

Obesity is a known risk factor for Type 2 diabetes (T2DM). However, most obese individuals do not develop diabetes because they adapt to insulin resistance by increasing beta-cell mass and insulin secretion. Islet pathology in T2DM is characterized by beta-cell loss, islet amyloid derived from islet amyloid polypeptide (IAPP) and increased beta cell apoptosis characterized by endoplasmic reticulum (ER) stress. We hypothesized that IAPP-induced ER stress distinguishes successful versus unsuccessful islet adaptation to insulin resistance.

Research Design and Methods.

To address this we fed wild type (WT) and human IAPP transgenic rats (HIP rats) either 10 weeks of regular chow or high fat diet and prospectively examined the relationships between: 1) beta cell mass and turnover, 2) beta cell ER stress 3) insulin secretion and 4) insulin sensitivity.

Results.

A high fat diet led to comparable insulin resistance in WT and HIP rats. WT rats compensated with increased insulin secretion and beta cell mass. In contrast, in HIP rats neither beta cell function or mass compensated for the increased insulin demand, leading to diabetes. The failure to increase beta cell mass in HIP rats was due to ER stress induced beta cell apoptosis that increased in proportion to diet induced insulin resistance.

Conclusions.

IAPP-induced ER stress distinguishes the successful versus unsuccessful islet adaptation to a high fat diet in rats. These studies are consistant with the hypothesis that IAPP oligomers contribute to increased beta-cell apoptosis and beta cell failure in humans with Type 2 diabetes.

Objective:

To investigate early events leading to microvascular cell loss in diabetic retinopathy.

Research Design and Methods:

FOXO1 was tested in vivo by DNA binding activity and by nuclear translocation in microvascular cells in retinal trypsin digests. In vivo studies were undertaken in STZ rats and ZDF rats using the TNF specific blocker, pegsunercept or by inhibiting FOXO1 with RNAi. Microvascular cell apoptosis, formation of pericyte ghosts and acellular capillaries were measured. Upstream and downstream effects of high glucose induced FOXO1 were tested on rat microvascular endothelial cells (RMEC) by siRNA in vitro.

Results:

DNA binding or nuclear translocation of FOXO1 was elevated in type 1 and type 2 diabetic retinas, which was reduced by TNF inhibition. Diabetes stimulated microvascular cell apoptosis and pericyte ghost and acellular capillary development was inhibited by FOXO1 siRNA. High glucose in vitro decreased FOXO1 phosphorylation and DNA binding activity and decreased Akt phosphorylation in RMEC. High glucose stimulated FOXO1 DNA binding activity was mediated through TNF- and formation of reactive oxygen species (ROS), while inhibitors of TNF and ROS and FOXO1 siRNA reduced high glucose enhanced RMEC apoptosis. The caspase-3/7 activity and capacity of high glucose to increase mRNA levels of several genes that regulate RMEC activation and apoptosis were knocked down by FOXO1 siRNA.

Conclusion:

FOXO1 plays an important role in rat retinal microvascular cell loss in type-1 and -2 diabetic rats and can be linked to the effect of high glucose on FOXO1 activation.

Objective:

Metformin, an oral glucose-lowering drug, is taken up in hepatocytes by the organic cation transporter (OCT) 1 and in renal epithelium by OCT2. In these cells, the multidrug and toxin extrusion 1 (MATE1) protein, encoded by the SLC47A1 gene, is responsible for the excretion of metformin into the bile and urine, respectively. We studied the effect of single nucleotide polymorphisms (SNPs) in the SLC47A1 gene on the HbA1c lowering effect of metformin

Research Design and Methods:

We identified all incident metformin users in the Rotterdam Study, a population-based cohort study. Associations between twelve tagging SNPs in the SLC47A1 gene and change in HbA1c level were analyzed.

Results:

One-hundred and sixteen incident metformin users were included in the study sample. The rs2289669 G>A SNP was significantly associated with metformin response. For the other SNPs, no associations were found. For each minor A allele at rs2289669, the HbA1c reduction was 0.30 % (95% CI -0.51, -0.10; p=0.005) larger. After Bonferroni correction for multiple testing, the p-value was 0.045.

Conclusions:

The rs2289669 G>A SNP is associated with a reduction in HbA1c level, consistent with a reduction in MATE1 transporter activity. These results suggest that the transporter MATE1, encoded by SLC47A1, may have an important role in the pharmacokinetics of metformin, although replication is necessary.