Stratifying the management of type 2 diabetes (T2D) has to take into account marked variability in patient phenotype due to heterogeneity in its pathophysiology, different stages of the disease process, and multiple other patient factors including comorbidities. The focus here is on the very challenging subgroup of patients with T2D who are overweight or obese with insulin resistance (IR) and the most refractory hyperglycemia due to an inability to change lifestyle to reverse positive energy balance. For this subgroup of patients with T2D, we question the dogma that IR is primarily harmful to the body and should be counteracted at any cost. Instead we propose that IR, particularly in this high-risk subgroup, is a defense mechanism that protects critical tissues of the cardiovascular system from nutrient-induced injury. Overriding IR in an effort to lower plasma glucose levels, particularly with intensive insulin therapy, could therefore be harmful. Treatments that nutrient off-load to lower glucose are more likely to be beneficial. The concepts of "IR as an adaptive defense mechanism" and "insulin-induced metabolic stress" may provide explanation for some of the unexpected outcomes of recent major clinical trials in T2D. Potential molecular mechanisms underlying these concepts; their clinical implications for stratification of T2D management, particularly in overweight and obese patients with difficult glycemic control; and future research requirements are discussed.

The concept that excess superoxide production from mitochondria is the driving, initial cellular response underlying diabetes complications has been held for the past decade. However, results of antioxidant-based trials have been largely negative. In the present review, the data supporting mitochondrial superoxide as a driving force for diabetic kidney, nerve, heart, and retinal complications are reexamined, and a new concept for diabetes complications--mitochondrial hormesis--is presented. In this view, production of mitochondrial superoxide can be an indicator of healthy mitochondria and physiologic oxidative phosphorylation. Recent data suggest that in response to excess glucose exposure or nutrient stress, there is a reduction of mitochondrial superoxide, oxidative phosphorylation, and mitochondrial ATP generation in several target tissues of diabetes complications. Persistent reduction of mitochondrial oxidative phosphorylation complex activity is associated with the release of oxidants from nonmitochondrial sources and release of proinflammatory and profibrotic cytokines, and a manifestation of organ dysfunction. Restoration of mitochondrial function and superoxide production via activation of AMPK has now been associated with improvement in markers of renal, cardiovascular, and neuronal dysfunction with diabetes. With this Perspective, approaches that stimulate AMPK and PGC1α via exercise, caloric restriction, and medications result in stimulation of mitochondrial oxidative phosphorylation activity, restore physiologic mitochondrial superoxide production, and promote organ healing.

Observational studies have reported different effects of adiposity on cardiovascular risk factors across age and sex. Since cardiovascular risk factors are enriched in obese individuals, it has not been easy to dissect the effects of adiposity from those of other risk factors. We used a Mendelian randomization approach, applying a set of 32 genetic markers to estimate the causal effect of adiposity on blood pressure, glycemic indices, circulating lipid levels, and markers of inflammation and liver disease in up to 67,553 individuals. All analyses were stratified by age (cutoff 55 years of age) and sex. The genetic score was associated with BMI in both nonstratified analysis (P = 2.8 × 10(-107)) and stratified analyses (all P < 3.3 × 10(-30)). We found evidence of a causal effect of adiposity on blood pressure, fasting levels of insulin, C-reactive protein, interleukin-6, HDL cholesterol, and triglycerides in a nonstratified analysis and in the <55-year stratum. Further, we found evidence of a smaller causal effect on total cholesterol (P for difference = 0.015) in the ≥55-year stratum than in the <55-year stratum, a finding that could be explained by biology, survival bias, or differential medication. In conclusion, this study extends previous knowledge of the effects of adiposity by providing sex- and age-specific causal estimates on cardiovascular risk factors.

Vascular endothelial growth factor (VEGF) blockers have been developed for the treatment of proliferative diabetic retinopathy (PDR), the leading cause of visual impairments in the working-age population in the Western world. However, limitations to anti-VEGF therapies may exist because of the local production of other proangiogenic factors that may cause resistance to anti-VEGF interventions. Thus, novel therapeutic approaches targeting additional pathways are required. Here, we identified a sulfated derivative of the Escherichia coli polysaccharide K5 [K5-N,OS(H)] as a multitarget molecule highly effective in inhibiting VEGF-driven angiogenic responses in different in vitro, ex vivo, and in vivo assays, including a murine model of oxygen-induced retinopathy. Furthermore, K5-N,OS(H) binds a variety of heparin-binding angiogenic factors upregulated in PDR vitreous humor besides VEGF, thus inhibiting their biological activity. Finally, K5-N,OS(H) hampers the angiogenic activity exerted in vitro and in vivo by human vitreous fluid samples collected from patients with PDR. Together, the data provide compelling experimental evidence that K5-N,OS(H) represents an antiangiogenic multitarget molecule with potential implications for the therapy of pathologic neovessel formation in the retina of patients with PDR.

Inflammation and lipid accumulation are hallmarks of muscular pathologies resulting from metabolic diseases such as obesity and type 2 diabetes. During obesity, the hypertrophy of visceral adipose tissue (VAT) contributes to muscle dysfunction, particularly through the dysregulated production of adipokines. We have investigated the cross talk between human adipocytes and skeletal muscle cells to identify mechanisms linking adiposity and muscular dysfunctions. First, we demonstrated that the secretome of obese adipocytes decreased the expression of contractile proteins in myotubes, consequently inducing atrophy. Using a three-dimensional coculture of human myotubes and VAT adipocytes, we showed the decreased expression of genes corresponding to skeletal muscle contractility complex and myogenesis. We demonstrated an increased secretion by cocultured cells of cytokines and chemokines with interleukin (IL)-6 and IL-1β as key contributors. Moreover, we gathered evidence showing that obese subcutaneous adipocytes were less potent than VAT adipocytes in inducing these myotube dysfunctions. Interestingly, the atrophy induced by visceral adipocytes was corrected by IGF-II/insulin growth factor binding protein-5. Finally, we observed that the skeletal muscle of obese mice displayed decreased expression of muscular markers in correlation with VAT hypertrophy and abnormal distribution of the muscle fiber size. In summary, we show the negative impact of obese adipocytes on muscle phenotype, which could contribute to muscle wasting associated with metabolic disorders.

The aim of this study was to determine the effects of single and repeated episodes of clamped hypoglycemia on fibrinolytic balance, proinflammatory biomarkers, proatherothrombotic mechanisms, and endothelial function. Twenty healthy individuals (12 male and 8 female) were studied during separate 2-day randomized protocols. Day 1 consisted of either two 2-h hyperinsulinemic (812 ± 50 pmol/L)-euglycemic (5 ± 0.1 mmol/L) or hyperinsulinemic (812 ± 50 pmol/L)-hypoglycemic (2.9 ± 0.1 mmol/L) clamps. Day 2 consisted of a single 2-h hyperinsulinemic-hypoglycemic clamp. Two-dimensional Doppler ultrasound was used to determine brachial arterial endothelial function. Plasminogen activator inhibitor 1, vascular cell adhesion molecule-1, intracellular adhesion molecule-1, E-selectin, P-selectin, TAT (thrombin/antithrombin complex), tumor necrosis factor-α, and interleukin-6 responses were increased (P < 0.05) during single or repeated hypoglycemia compared with euglycemia. Endogenous and exogenous nitric oxide (NO)-mediated vasodilation were both impaired by repeated hypoglycemia. Neuroendocrine and autonomic nervous system (ANS) responses were also blunted by repeated hypoglycemia (P < 0.05). In summary, acute moderate hypoglycemia impairs fibrinolytic balance; increases proinflammatory responses, platelet activation, and coagulation biomarkers; and reduces NO-mediated endothelial function in healthy individuals. Repeated episodes of hypoglycemia further impair vascular function by additionally reducing exogenously NO-mediated endothelial function and increasing coagulation biomarkers. We conclude that despite reduced neuroendocrine and ANS responses, antecedent hypoglycemia results in greater endothelial dysfunction and an increased proatherothrombotic state compared with a single acute episode of hypoglycemia.

Short-chain fatty acids (SCFAs) are the main products of dietary fiber fermentation and are believed to drive the fiber-related prevention of the metabolic syndrome. Here we show that dietary SCFAs induce a peroxisome proliferator-activated receptor-γ (PPARγ)-dependent switch from lipid synthesis to utilization. Dietary SCFA supplementation prevented and reversed high-fat diet-induced metabolic abnormalities in mice by decreasing PPARγ expression and activity. This increased the expression of mitochondrial uncoupling protein 2 and raised the AMP-to-ATP ratio, thereby stimulating oxidative metabolism in liver and adipose tissue via AMPK. The SCFA-induced reduction in body weight and stimulation of insulin sensitivity were absent in mice with adipose-specific disruption of PPARγ. Similarly, SCFA-induced reduction of hepatic steatosis was absent in mice lacking hepatic PPARγ. These results demonstrate that adipose and hepatic PPARγ are critical mediators of the beneficial effects of SCFAs on the metabolic syndrome, with clearly distinct and complementary roles. Our findings indicate that SCFAs may be used therapeutically as cheap and selective PPARγ modulators.

The understanding of the etiology of type 1 diabetes (T1D) remains limited. One objective of the Diabetes Virus Detection (DiViD) study was to collect pancreatic tissue from living subjects shortly after the diagnosis of T1D. Here we report the insulin secretion ability by in vitro glucose perifusion and explore the expression of insulin pathway genes in isolated islets of Langerhans from these patients. Whole-genome RNA sequencing was performed on islets from six DiViD study patients and two organ donors who died at the onset of T1D, and the findings were compared with those from three nondiabetic organ donors. All human transcripts involved in the insulin pathway were present in the islets at the onset of T1D. Glucose-induced insulin secretion was present in some patients at the onset of T1D, and a perfectly normalized biphasic insulin release was obtained after some days in a nondiabetogenic environment in vitro. This indicates that the potential for endogenous insulin production is good, which could be taken advantage of if the disease process was reversed at diagnosis.

Spontaneous glucose uptake by brown adipose tissue (BAT) is lower in overweight or obese individuals and in diabetes. However, BAT metabolism has not been previously investigated in patients with type 2 diabetes during controlled cold exposure. Using positron emission tomography with (11)C-acetate, (18)F-fluoro-deoxyglucose ((18)FDG), and (18)F-fluoro-thiaheptadecanoic acid ((18)FTHA), a fatty acid tracer, BAT oxidative metabolism and perfusion and glucose and nonesterified fatty acid (NEFA) turnover were determined in men with well-controlled type 2 diabetes and age-matched control subjects under experimental cold exposure designed to minimize shivering. Despite smaller volumes of (18)FDG-positive BAT and lower glucose uptake per volume of BAT compared with young healthy control subjects, cold-induced oxidative metabolism and NEFA uptake per BAT volume and an increase in total body energy expenditure did not differ in patients with type 2 diabetes or their age-matched control subjects. The reduction in (18)FDG-positive BAT volume and BAT glucose clearance were associated with a reduction in BAT radiodensity and perfusion. (18)FDG-positive BAT volume and the cold-induced increase in BAT radiodensity were associated with an increase in systemic NEFA turnover. These results show that cold-induced NEFA uptake and oxidative metabolism are not defective in type 2 diabetes despite reduced glucose uptake per BAT volume and BAT "whitening."

Single nucleotide polymorphism (SNP) rs10911021 at the glutamate-ammonia ligase (GLUL) locus has been associated with an increased risk of coronary heart disease in individuals with type 2 diabetes. The effect of this SNP on mortality was investigated among 1,242 white subjects with type 2 diabetes from the Joslin Kidney Study (JKS) (n = 416) and the Gargano Mortality Study (GMS) (n = 826). During a mean follow-up of 12.8 ± 5.8 and 7.5 ± 2.2 years, respectively, a total of 215 and 164 deaths were observed in the two studies. In both cohorts, the all-cause mortality rate significantly increased with the number of rs10911021 risk alleles, with allelic hazard ratios (HRs) of 1.32 (95% CI 1.07-1.64, P = 0.01), 1.30 (1.10-1.69, P = 0.04), and 1.32 (1.12-1.55, P = 0.0011), respectively, in the JKS, the GMS, and the two studies combined. These associations were not affected by adjustment for possible confounders. In the JKS, for which data on causes of death were available, the HR for cardiovascular mortality was 1.51 (1.12-2.04, P = 0.0077) as opposed to 1.15 (0.84-1.55, P = 0.39) for mortality from noncardiovascular causes. These findings point to SNP rs10911021 as an independent modulator of mortality in patients with type 2 diabetes and, together with the previous observation, suggest that this results from an effect of this variant on cardiovascular risk.

The role of glucose-stimulated release of GLP-1 in the development of obesity and type 2 diabetes is unclear. We assessed GLP-1 response to oral glucose in a large study population of lean and obese men and women with normal and impaired glucose regulation. Circulating concentrations of glucose, insulin, and GLP-1 during an oral glucose tolerance test (OGTT) were analyzed in individuals with normal glucose tolerance (NGT) (n = 774), prediabetes (n = 525), or screen-detected type 2 diabetes (n = 163) who attended the Danish ADDITION-PRO study (n = 1,462). Compared with individuals with NGT, women with prediabetes or type 2 diabetes had 25% lower GLP-1 response to an OGTT, and both men and women with prediabetes or type 2 diabetes had 16-21% lower 120-min GLP-1 concentrations independent of age and obesity. Obese and overweight individuals had up to 20% reduced GLP-1 response to oral glucose compared with normal weight individuals independent of glucose tolerance status. Higher GLP-1 responses were associated with better insulin sensitivity and β-cell function, older age, and lesser degree of obesity. Our findings indicate that a reduction in GLP-1 response to oral glucose occurs prior to the development of type 2 diabetes and obesity, which can have consequences for early prevention strategies for diabetes.

Several single nucleotide polymorphisms (SNPs) associated with type 2 diabetes mellitus (T2DM) have been identified, but there is little information on their role in populations at high risk for T2DM. We genotyped SNPs at 63 T2DM loci in 3,421 individuals from a high-risk American Indian population. Nominally significant (P < 0.05) associations were observed at nine SNPs in a direction consistent with the established association. A genetic risk score derived from all loci was strongly associated with T2DM (odds ratio 1.05 per risk allele, P = 6.2 × 10(-6)) and, in 292 nondiabetic individuals, with lower insulin secretion (by 4% per copy, P = 4.1 × 10(-6)). Genetic distances between American Indians and HapMap populations at T2DM markers did not differ significantly from genomic expectations. Analysis of U.S. national survey data suggested that 66% of the difference in T2DM prevalence between African Americans and European Americans, but none of the difference between American Indians and European Americans, was attributable to allele frequency differences at these loci. These analyses suggest that, in general, established T2DM loci influence T2DM in American Indians and that risk is mediated in part through an effect on insulin secretion. However, differences in allele frequencies do not account for the high population prevalence of T2DM.

Insulin detemir (DET) reduces glycemia comparably to other long-acting insulin formulations but causes less weight gain. Insulin signaling in the brain is catabolic, reducing food intake. We hypothesized that DET reduces weight gain, relative to other insulins, owing to increased transport into the central nervous system and/or increased catabolic action within the brain. Transport of DET and NPH insulin into the cerebrospinal fluid (CSF) was compared over several hours and after the administration of different doses peripherally in rats. DET and NPH had comparable saturable, receptor-mediated transport into the CSF. CSF insulin remained elevated significantly longer after intraperitoneal DET than after NPH. When administered acutely into the 3rd cerebral ventricle, both DET and NPH insulin reduced food intake and body weight at 24 h, and both food intake and body weight remained lower after DET than after NPH after 48 h. In direct comparison with another long-acting insulin, insulin glargine (GLAR), DET led to more prolonged increases in CSF insulin despite a shorter plasma half-life in both rats and mice. Additionally, peripheral DET administration reduced weight gain and increased CSF insulin compared with saline or GLAR in mice. Overall, these data support the hypothesis that DET has distinct effects on energy balance through enhanced and prolonged centrally mediated reduction of food intake.

Neurogenin3 (NEUROG3) is a basic helix-loop-helix transcription factor required for development of the endocrine pancreas in mice. In contrast, humans with NEUROG3 mutations are born with endocrine pancreas function, calling into question whether NEUROG3 is required for human endocrine pancreas development. To test this directly, we generated human embryonic stem cell (hESC) lines where both alleles of NEUROG3 were disrupted using CRISPR/Cas9-mediated gene targeting. NEUROG3(-/-) hESC lines efficiently formed pancreatic progenitors but lacked detectible NEUROG3 protein and did not form endocrine cells in vitro. Moreover, NEUROG3(-/-) hESC lines were unable to form mature pancreatic endocrine cells after engraftment of PDX1(+)/NKX6.1(+) pancreatic progenitors into mice. In contrast, a 75-90% knockdown of NEUROG3 caused a reduction, but not a loss, of pancreatic endocrine cell development. We conclude that NEUROG3 is essential for endocrine pancreas development in humans and that as little as 10% NEUROG3 is sufficient for formation of pancreatic endocrine cells.

Despite treatment advances, diabetic eye disease remains a leading cause of visual acuity (VA) loss worldwide. No methods to prospectively determine which patients will gain or lose vision exist, limiting individualized risk assessment and management. We investigated whether noninvasive, readily obtainable spectral domain optical coherence tomography parameters were correlated with VA in eyes with current or resolved center-involved diabetic macular edema (DME). Images were evaluated for disorganization of the retinal inner layers (DRIL), cysts, epiretinal membranes, microaneurysms, subretinal fluid, and outer layer disruption/reflectivity. DRIL affecting ≥50% of the 1-mm central retinal zone was associated with worse VA in all eyes, eyes with current edema, and eyes with resolved edema. Furthermore, early 4-month change in DRIL extent predicted VA change from baseline to 1 year. These data suggest that DRIL is a robust predictor of VA in eyes with present or previous DME and more highly correlated with VA than other widely used measures, such as retinal thickness. If further studies confirm DRIL as a predictive biomarker of future VA, physicians would gain a new tool of substantial clinical and investigative importance that could significantly change the approach to ophthalmic counseling and therapeutic management in patients with diabetes.

Type 2 diabetes is associated with increased fracture risk and delayed fracture healing; the underlying mechanism, however, remains poorly understood. We systematically investigated skeletal pathology in leptin receptor-deficient diabetic mice on a C57BLKS background (db). Compared with wild type (wt), db mice displayed reduced peak bone mass and age-related trabecular and cortical bone loss. Poor skeletal outcome in db mice contributed high-glucose- and nonesterified fatty acid-induced osteoblast apoptosis that was associated with peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α) downregulation and upregulation of skeletal muscle atrogenes in osteoblasts. Osteoblast depletion of the atrogene muscle ring finger protein-1 (MuRF1) protected against gluco- and lipotoxicity-induced apoptosis. Osteoblast-specific PGC-1α upregulation by 6-C-β-d-glucopyranosyl-(2S,3S)-(+)-5,7,3',4'-tetrahydroxydihydroflavonol (GTDF), an adiponectin receptor 1 (AdipoR1) agonist, as well as metformin in db mice that lacked AdipoR1 expression in muscle but not bone restored osteopenia to wt levels without improving diabetes. Both GTDF and metformin protected against gluco- and lipotoxicity-induced osteoblast apoptosis, and depletion of PGC-1α abolished this protection. Although AdipoR1 but not AdipoR2 depletion abolished protection by GTDF, metformin action was not blocked by AdipoR depletion. We conclude that PGC-1α upregulation in osteoblasts could reverse type 2 diabetes-associated deterioration in skeletal health.