BACKGROUND

Insulin resistance has a causal role in type 2 diabetes. Serum levels of retinol-binding protein 4 (RBP4), a protein secreted by adipocytes, are increased in insulin-resistant states. Experiments in mice suggest that elevated RBP4 levels cause insulin resistance. We sought to determine whether serum RBP4 levels correlate with insulin resistance and change after an intervention that improves insulin sensitivity. We also determined whether elevated serum RBP4 levels are associated with reduced expression of glucose transporter 4 (GLUT4) in adipocytes, an early pathological feature of insulin resistance.

METHODS

We measured serum RBP4, insulin resistance, and components of the metabolic syndrome in three groups of subjects. Measurements were repeated after exercise training in one group. GLUT4 protein was measured in isolated adipocytes.

RESULTS

Serum RBP4 levels correlated with the magnitude of insulin resistance in subjects with obesity, impaired glucose tolerance, or type 2 diabetes and in nonobese, nondiabetic subjects with a strong family history of type 2 diabetes. Elevated serum RBP4 was associated with components of the metabolic syndrome, including increased body-mass index, waist-to-hip ratio, serum triglyceride levels, and systolic blood pressure and decreased high-density lipoprotein cholesterol levels. Exercise training was associated with a reduction in serum RBP4 levels only in subjects in whom insulin resistance improved. Adipocyte GLUT4 protein and serum RBP4 levels were inversely correlated.

CONCLUSIONS

RBP4 is an adipocyte-secreted molecule that is elevated in the serum before the development of frank diabetes and appears to identify insulin resistance and associated cardiovascular risk factors in subjects with varied clinical presentations. These findings provide a rationale for antidiabetic therapies aimed at lowering serum RBP4 levels.

As our knowledge of type 1 (insulin-dependent) diabetes increases, so does our appreciation for the pathogenic complexity of this disease and the challenges associated with its treatment. Many new concepts about the pathogenesis of this disorder have arisen. The role of genetics versus environment in disease formation has been questioned, and the basis on which type 1 diabetes is characterised and diagnosed is the subject of much debate. Additionally, the care and treatment of patients with type 1 diabetes has seen a rapid evolution; with genetically engineered insulins, glucose monitoring devices, and algorithms all contributing to a decrease in disease-related complications. We focus this seminar on these changing views, and offer a new perspective on our understanding of the pathogenesis of type 1 diabetes and on principles for therapeutic management of patients with this disorder.

To identify structural characteristics of the closely related cell surface receptors for insulin and IGF-I that define their distinct physiological roles, we determined the complete primary structure of the human IGF-I receptor from cloned cDNA. The deduced sequence predicts a 1367 amino acid receptor precursor, including a 30-residue signal peptide, which is removed during translocation of the nascent polypeptide chain. The 1337 residue, unmodified proreceptor polypeptide has a predicted Mr of 151,869, which compares with the 180,000 Mr IGF-I receptor precursor. In analogy with the 152,784 Mr insulin receptor precursor, cleavage of the Arg-Lys-Arg-Arg sequence at position 707 of the IGF-I receptor precursor will generate alpha (80,423 Mr) and beta (70,866 Mr) subunits, which compare with approximately 135,000 Mr (alpha) and 90,000 Mr (beta) fully glycosylated subunits.

Two cell lines have been established from insulinomas obtained by targeted expression of the simian virus 40 T antigen gene in transgenic mice. These cell lines, designated MIN6 and MIN7, produce insulin and T antigen and have morphological characteristics of pancreatic beta cells. MIN6 cells exhibit glucose-inducible insulin secretion comparable with cultured normal mouse islet cells, whereas MIN7 cells do not. Both cell lines produce liver-type glucose transporter (GT) mRNA at high level. Brain-type GT mRNA is also present at considerable level in MIN7 cells, but is barely detectable in MIN6 cells, suggesting that exclusive expression of the liver-type GT is related to glucose-inducible insulin secretion. MIN6 cells do not express either major histocompatibility (MHC) class I or class II antigens on the cell surface. However, treatment with interferon-gamma induces high levels of MHC class I antigens, and a combination of interferon-gamma and tumor necrosis factor-alpha induces a MHC class II antigen on the cell surface. These results emphasize that the MIN6 cell line retains physiological characteristics of normal beta cells. The MIN6 cell line will be especially useful to analyze the molecular mechanisms by which beta cells regulate insulin secretion in response to extracellular glucose concentrations. We discuss a possible role of GT isoforms in glucose sensing by beta cells.

Insulin-like growth factor-I (IGF-I) is a mitogen for prostate epithelial cells. To investigate associations between plasma IGF levels and prostate cancer risk, a nested case-control study within the Physicians' Health Study was conducted on prospectively collected plasma from 152 cases and 152 controls. A strong positive association was observed between IGF-I levels and prostate cancer risk. Men in the highest quartile of IGF-I levels had a relative risk of 4.3 (95 percent confidence interval 1.8 to 10.6) compared with men in the lowest quartile. This association was independent of baseline prostate-specific antigen levels. Identification of plasma IGF-I as a predictor of prostate cancer risk may have implications for risk reduction and treatment.

The adverse metabolic consequences of obesity are best predicted by the quantity of visceral fat. Excess glucocorticoids produce visceral obesity and diabetes, but circulating glucocorticoid levels are normal in typical obesity. Glucocorticoids can be produced locally from inactive 11-keto forms through the enzyme 11beta hydroxysteroid dehydrogenase type 1 (11beta HSD-1). We created transgenic mice overexpressing 11beta HSD-1 selectively in adipose tissue to an extent similar to that found in adipose tissue from obese humans. These mice had increased adipose levels of corticosterone and developed visceral obesity that was exaggerated by a high-fat diet. The mice also exhibited pronounced insulin-resistant diabetes, hyperlipidemia, and, surprisingly, hyperphagia despite hyperleptinemia. Increased adipocyte 11beta HSD-1 activity may be a common molecular etiology for visceral obesity and the metabolic syndrome.

Diabetes, a disease in which carbohydrate and lipid metabolism are regulated improperly by insulin, is a serious worldwide health issue. Insulin is secreted from pancreatic beta cells in response to elevated plasma glucose, with various factors modifying its secretion. Free fatty acids (FFAs) provide an important energy source as nutrients, and they also act as signalling molecules in various cellular processes, including insulin secretion. Although FFAs are thought to promote insulin secretion in an acute phase, this mechanism is not clearly understood. Here we show that a G-protein-coupled receptor, GPR40, which is abundantly expressed in the pancreas, functions as a receptor for long-chain FFAs. Furthermore, we show that long-chain FFAs amplify glucose-stimulated insulin secretion from pancreatic beta cells by activating GPR40. Our results indicate that GPR40 agonists and/or antagonists show potential for the development of new anti-diabetic drugs.

BACKGROUND

It is uncertain whether treatment of mild gestational diabetes mellitus improves pregnancy outcomes.

METHODS

Women who were in the 24th to 31st week of gestation and who met the criteria for mild gestational diabetes mellitus (i.e., an abnormal result on an oral glucose-tolerance test but a fasting glucose level below 95 mg per deciliter [5.3 mmol per liter]) were randomly assigned to usual prenatal care (control group) or dietary intervention, self-monitoring of blood glucose, and insulin therapy, if necessary (treatment group). The primary outcome was a composite of stillbirth or perinatal death and neonatal complications, including hyperbilirubinemia, hypoglycemia, hyperinsulinemia, and birth trauma.

RESULTS

A total of 958 women were randomly assigned to a study group--485 to the treatment group and 473 to the control group. We observed no significant difference between groups in the frequency of the composite outcome (32.4% and 37.0% in the treatment and control groups, respectively; P=0.14). There were no perinatal deaths. However, there were significant reductions with treatment as compared with usual care in several prespecified secondary outcomes, including mean birth weight (3302 vs. 3408 g), neonatal fat mass (427 vs. 464 g), the frequency of large-for-gestational-age infants (7.1% vs. 14.5%), birth weight greater than 4000 g (5.9% vs. 14.3%), shoulder dystocia (1.5% vs. 4.0%), and cesarean delivery (26.9% vs. 33.8%). Treatment of gestational diabetes mellitus, as compared with usual care, was also associated with reduced rates of preeclampsia and gestational hypertension (combined rates for the two conditions, 8.6% vs. 13.6%; P=0.01).

CONCLUSIONS

Although treatment of mild gestational diabetes mellitus did not significantly reduce the frequency of a composite outcome that included stillbirth or perinatal death and several neonatal complications, it did reduce the risks of fetal overgrowth, shoulder dystocia, cesarean delivery, and hypertensive disorders. (ClinicalTrials.gov number, NCT00069576.)

In the fruit fly Drosophila, four insulin genes are coexpressed in small clusters of cells [insulin-producing cells (IPCs)] in the brain. Here, we show that ablation of these IPCs causes developmental delay, growth retardation, and elevated carbohydrate levels in larval hemolymph. All of the defects were reversed by ectopic expression of a Drosophila insulin transgene. On the basis of these functional data and the observation that IPCs release insulin into the circulatory system, we conclude that brain IPCs are the main systemic supply of insulin during larval growth. We propose that IPCs and pancreatic islet beta cells are functionally analogous and may have evolved from a common ancestral insulin-producing neuron. Interestingly, the phenotype of flies lacking IPCs includes certain features of diabetes mellitus.

The global prevalence of obesity is increasing across most ages in both sexes. This is contributing to the early emergence of type 2 diabetes and its related epidemic. Having either parent obese is an independent risk factor for childhood obesity. Although the detrimental impacts of diet-induced maternal obesity on adiposity and metabolism in offspring are well established, the extent of any contribution of obese fathers is unclear, particularly the role of non-genetic factors in the causal pathway. Here we show that paternal high-fat-diet (HFD) exposure programs β-cell 'dysfunction' in rat F(1) female offspring. Chronic HFD consumption in Sprague-Dawley fathers induced increased body weight, adiposity, impaired glucose tolerance and insulin sensitivity. Relative to controls, their female offspring had an early onset of impaired insulin secretion and glucose tolerance that worsened with time, and normal adiposity. Paternal HFD altered the expression of 642 pancreatic islet genes in adult female offspring (P < 0.01); genes belonged to 13 functional clusters, including cation and ATP binding, cytoskeleton and intracellular transport. Broader pathway analysis of 2,492 genes differentially expressed (P < 0.05) demonstrated involvement of calcium-, MAPK- and Wnt-signalling pathways, apoptosis and the cell cycle. Hypomethylation of the Il13ra2 gene, which showed the highest fold difference in expression (1.76-fold increase), was demonstrated. This is the first report in mammals of non-genetic, intergenerational transmission of metabolic sequelae of a HFD from father to offspring.

This is a consensus statement from an international group, mostly of clinical endocrinologists. MEN1 and MEN2 are hereditary cancer syndromes. The commonest tumors secrete PTH or gastrin in MEN1, and calcitonin or catecholamines in MEN2. Management strategies improved after the discoveries of their genes. MEN1 has no clear syndromic variants. Tumor monitoring in MEN1 carriers includes biochemical tests yearly and imaging tests less often. Neck surgery includes subtotal or total parathyroidectomy, parathyroid cryopreservation, and thymectomy. Proton pump inhibitors or somatostatin analogs are the main management for oversecretion of entero-pancreatic hormones, except insulin. The roles for surgery of most entero-pancreatic tumors present several controversies: exclusion of most operations on gastrinomas and indications for surgery on other tumors. Each MEN1 family probably has an inactivating MEN1 germline mutation. Testing for a germline MEN1 mutation gives useful information, but rarely mandates an intervention. The most distinctive MEN2 variants are MEN2A, MEN2B, and familial medullary thyroid cancer (MTC). They vary in aggressiveness of MTC and spectrum of disturbed organs. Mortality in MEN2 is greater from MTC than from pheochromocytoma. Thyroidectomy, during childhood if possible, is the goal in all MEN2 carriers to prevent or cure MTC. Each MEN2 index case probably has an activating germline RET mutation. RET testing has replaced calcitonin testing to diagnose the MEN2 carrier state. The specific RET codon mutation correlates with the MEN2 syndromic variant, the age of onset of MTC, and the aggressiveness of MTC; consequently, that mutation should guide major management decisions, such as whether and when to perform thyroidectomy.

BACKGROUND

Type 1 diabetes mellitus is a T-cell-mediated autoimmune disease that leads to a major loss of insulin-secreting beta cells. The further decline of beta-cell function after clinical onset might be prevented by treatment with CD3 monoclonal antibodies, as suggested by the results of a phase 1 study. To provide proof of this therapeutic principle at the metabolic level, we initiated a phase 2 placebo-controlled trial with a humanized antibody, an aglycosylated human IgG1 antibody directed against CD3 (ChAglyCD3).

METHODS

In a multicenter study, 80 patients with new-onset type 1 diabetes were randomly assigned to receive placebo or ChAglyCD3 for six consecutive days. Patients were followed for 18 months, during which their daily insulin needs and residual beta-cell function were assessed according to glucose-clamp-induced C-peptide release before and after the administration of glucagon.

RESULTS

At 6, 12, and 18 months, residual beta-cell function was better maintained with ChAglyCD3 than with placebo. The insulin dose increased in the placebo group but not in the ChAglyCD3 group. This effect of ChAglyCD3 was most pronounced among patients with initial residual beta-cell function at or above the 50th percentile of the 80 patients. In this subgroup, the mean insulin dose at 18 months was 0.22 IU per kilogram of body weight per day with ChAglyCD3, as compared with 0.61 IU per kilogram with placebo (P<0.001). In this subgroup, 12 of 16 patients who received ChAglyCD3 (75 percent) received minimal doses of insulin (< or =0.25 IU per kilogram per day) as compared with none of the 21 patients who received placebo. Administration of ChAglyCD3 was associated with a moderate "flu-like" syndrome and transient symptoms of Epstein-Barr viral mononucleosis.

CONCLUSIONS

Short-term treatment with CD3 antibody preserves residual beta-cell function for at least 18 months in patients with recent-onset type 1 diabetes.

In type 2 diabetes, chronic hyperglycemia is suggested to be detrimental to pancreatic beta cells, causing impaired insulin secretion. IL-1beta is a proinflammatory cytokine acting during the autoimmune process of type 1 diabetes. IL-1beta inhibits beta cell function and promotes Fas-triggered apoptosis in part by activating the transcription factor NF-kappaB. Recently, we have shown that increased glucose concentrations also induce Fas expression and beta cell apoptosis in human islets. The aim of the present study was to test the hypothesis that IL-1beta may mediate the deleterious effects of high glucose on human beta cells. In vitro exposure of islets from nondiabetic organ donors to high glucose levels resulted in increased production and release of IL-1beta, followed by NF-kappaB activation, Fas upregulation, DNA fragmentation, and impaired beta cell function. The IL-1 receptor antagonist protected cultured human islets from these deleterious effects. beta cells themselves were identified as the islet cellular source of glucose-induced IL-1beta. In vivo, IL-1beta-producing beta cells were observed in pancreatic sections of type 2 diabetic patients but not in nondiabetic control subjects. Similarly, IL-1beta was induced in beta cells of the gerbil Psammomys obesus during development of diabetes. Treatment of the animals with phlorizin normalized plasma glucose and prevented beta cell expression of IL-1beta. These findings implicate an inflammatory process in the pathogenesis of glucotoxicity in type 2 diabetes and identify the IL-1beta/NF-kappaB pathway as a target to preserve beta cell mass and function in this condition.

Chronic liver disease is a major cause of morbidity and mortality in the United States. Although often used to detect liver disease, the prevalence and etiology of elevated aminotransferases are unknown. We analyzed data on adults ages 17 yr and older (N = 15,676) from the Third National Health and Nutrition Examination Survey (1988-1994). Participants were classified as having elevated aminotransferase levels if either aspartate aminotransferase or alanine aminotransferase was elevated above normal. Aminotransferase elevation was classified as "explained" if there was laboratory evidence of hepatitis B or C infection, iron overload, or if there was a history of alcohol consumption. Analyses were weighted to provide national estimates. The prevalence of aminotransferase elevation in the United States was 7.9%. Aminotransferase elevation was more common in men compared to women (9.3% vs 6.6%, p = 0.002), in Mexican Americans (14.9%) and non-Hispanic blacks (8.1%) compared to non-Hispanic whites (7.1%, p < 0.001). High alcohol consumption, hepatitis B or C infection and high transferrin saturation were found in only 31.0% of cases. Aminotransferase elevation was unexplained in the majority (69.0%). In both men and women, unexplained aminotransferase elevation was significantly associated with higher body mass index, waist circumference, triglycerides, fasting insulin, and lower HDL; and with type 2 diabetes and hypertension in women (all p < 0.05). Aminotransferase elevation was common in the United States, and the majority could not be unexplained by alcohol consumption, viral hepatitis or hemochromatosis. Unexplained aminotransferase elevation was strongly associated with adiposity and other features of the metabolic syndrome, and thus may represent nonalcoholic fatty liver disease.

Obesity and type 2 diabetes are characterized by decreased insulin sensitivity, elevated concentrations of free fatty acids (FFAs), and increased macrophage infiltration in adipose tissue (AT). Here, we show that FFAs can cause activation of RAW264.7 cells primarily via the JNK signaling cascade and that TLR2 and TLR4 are upstream of JNK and help transduce FFA proinflammatory signals. We also demonstrate that F4/80(+)CD11b(+)CD11c(+) bone marrow-derived dendritic cells (BMDCs) have heightened proinflammatory activity compared with F4/80(+)CD11b(+)CD11c(-) bone marrow-derived macrophages and that the proinflammatory activity and JNK phosphorylation of BMDCs, but not bone marrow-derived macrophages, was further increased by FFA treatment. F4/80(+)CD11b(+)CD11c(+) cells were found in AT, and the proportion and number of these cells in AT is increased in ob/ob mice and by feeding wild type mice a high fat diet for 1 and 12 weeks. AT F4/80(+)CD11b(+)CD11c(+) cells express increased inflammatory markers compared with F4/80(+)CD11b(+)CD11c(-) cells, and FFA treatment increased inflammatory responses in these cells. In addition, we found that CD11c expression is increased in skeletal muscle of high fat diet-fed mice and that conditioned medium from FFA-treated wild type BMDCs, but not TLR2/4 DKO BMDCs, can induce insulin resistance in L6 myotubes. Together our results show that FFAs can activate CD11c(+) myeloid proinflammatory cells via TLR2/4 and JNK signaling pathways, thereby promoting inflammation and subsequent cellular insulin resistance.

The cytoarchitecture of human islets has been examined, focusing on cellular associations that provide the anatomical framework for paracrine interactions. By using confocal microscopy and multiple immunofluorescence, we found that, contrary to descriptions of prototypical islets in textbooks and in the literature, human islets did not show anatomical subdivisions. Insulin-immunoreactive beta cells, glucagon-immunoreactive alpha cells, and somatostatin-containing delta cells were found scattered throughout the human islet. Human beta cells were not clustered, and most (71%) showed associations with other endocrine cells, suggesting unique paracrine interactions in human islets. Human islets contained proportionally fewer beta cells and more alpha cells than did mouse islets. In human islets, most beta, alpha, and delta cells were aligned along blood vessels with no particular order or arrangement, indicating that islet microcirculation likely does not determine the order of paracrine interactions. We further investigated whether the unique human islet cytoarchitecture had functional implications. Applying imaging of cytoplasmic free Ca2+ concentration, [Ca2+]i, we found that beta cell oscillatory activity was not coordinated throughout the human islet as it was in mouse islets. Furthermore, human islets responded with an increase in [Ca2+]i when lowering the glucose concentration to 1 mM, which can be attributed to the large contribution of alpha cells to the islet composition. We conclude that the unique cellular arrangement of human islets has functional implications for islet cell function.

Recombinant bacterial plasmids have been constructed that contain complementary DNA prepared from rat islets of Langerhans messenger RNA. Three plasmids contain cloned sequences representing the complete coding region of rat proinsulin I, part of the preproinsulin I prepeptide, and the untranslated 3' terminal region of the mRNA. A fourth plasmid contains sequences derived from the A chain region of rat preproinsulin II.

BACKGROUND

The association of triglycerides with incident cardiovascular disease remains controversial. Although triglyceride levels are typically obtained in the fasting state, postprandial hypertriglyceridemia may play an important role in atherosclerosis.

OBJECTIVE

To determine the association of triglyceride levels (fasting vs nonfasting) and risk of future cardiovascular events.

METHODS

Prospective study of 26,509 initially healthy US women (20,118 fasting and 6391 nonfasting) participating in the Women's Health Study, enrolled between November 1992 and July 1995 and undergoing follow-up for a median of 11.4 years. Triglyceride levels were measured in blood samples obtained at time of enrollment.

METHODS

Hazard ratios for incident cardiovascular events (nonfatal myocardial infarction, nonfatal ischemic stroke, coronary revascularization, or cardiovascular death).

RESULTS

At baseline, triglyceride levels in fasting as well as nonfasting women correlated with traditional cardiac risk factors and markers of insulin resistance. During a median follow-up of 11.4 years, 1001 participants experienced an incident cardiovascular event (including 276 nonfatal myocardial infarctions, 265 ischemic strokes, 628 coronary revascularizations, and 163 cardiovascular deaths), for an overall rate of 3.46 cardiovascular events per 1000 person-years of follow-up. After adjusting for age, blood pressure, smoking, and use of hormone therapy, both fasting and nonfasting triglyceride levels predicted cardiovascular events. Among fasting participants, further adjustment for levels of total and high-density lipoprotein cholesterol and measures of insulin resistance weakened this association (fully adjusted hazard ratio [95% confidence interval] for increasing tertiles of triglyceride levels: 1 [reference], 1.21 [0.96-1.52], and 1.09 [0.85-1.41] [P = .90 for trend]). In contrast, nonfasting triglyceride levels maintained a strong independent relationship with cardiovascular events in fully adjusted models (hazard ratio [95% confidence interval] for increasing tertiles of levels: 1 [reference], 1.44 [0.90-2.29], and 1.98 [1.21-3.25] [P = .006 for trend]). In secondary analyses stratified by time since participants' last meal, triglyceride levels measured 2 to 4 hours postprandially had the strongest association with cardiovascular events (fully adjusted hazard ratio [95% confidence interval] for highest vs lowest tertiles of levels, 4.48 [1.98-10.15] [P<.001 for trend]), and this association progressively decreased with longer periods of fasting.

CONCLUSIONS

In this cohort of initially healthy women, nonfasting triglyceride levels were associated with incident cardiovascular events, independent of traditional cardiac risk factors, levels of other lipids, and markers of insulin resistance; by contrast, fasting triglyceride levels showed little independent relationship.

The extracellular space is an environment hostile to unmodified polypeptides. For this reason, many eukaryotic proteins destined for exposure to this environment through secretion or display at the cell surface require maturation steps within a specialized organelle, the endoplasmic reticulum (ER). A complex homeostatic mechanism, known as the unfolded protein response (UPR), has evolved to link the load of newly synthesized proteins with the capacity of the ER to mature them. It has become apparent that dysfunction of the UPR plays an important role in some human diseases, especially those involving tissues dedicated to extracellular protein synthesis. Diabetes mellitus is an example of such a disease, since the demands for constantly varying levels of insulin synthesis make pancreatic beta-cells dependent on efficient UPR signaling. Furthermore, recent discoveries in this field indicate that the importance of the UPR in diabetes is not restricted to the beta-cell but is also involved in peripheral insulin resistance. This review addresses aspects of the UPR currently understood to be involved in human disease, including their role in diabetes mellitus, atherosclerosis, and neoplasia.

OBJECTIVE

Prolonged sedentary time is ubiquitous in developed economies and is associated with an adverse cardio-metabolic risk profile and premature mortality. This study examined the associations of objectively assessed sedentary time and breaks (interruptions) in sedentary time with continuous cardio-metabolic and inflammatory risk biomarkers, and whether these associations varied by sex, age, and/or race/ethnicity.

RESULTS

Cross-sectional analyses with 4757 participants (≥ 20 years) from the 2003/04 and 2005/06 US National Health and Nutrition Examination Survey (NHANES). An Actigraph accelerometer was used to derive sedentary time [< 100 counts per minute (cpm)] and breaks in sedentary time. Independent of potential confounders, including moderate-to-vigorous exercise, detrimental linear associations (P for trends < 0.05) of sedentary time with waist circumference, HDL-cholesterol, C-reactive protein, triglycerides, insulin, HOMA-%B, and HOMA-%S were observed. Independent of potential confounders and sedentary time, breaks were beneficially associated with waist circumference and C-reactive protein (P for trends <0.05). There was limited evidence of meaningful differences in associations with biomarkers by age, sex, or race/ethnicity. Notable exceptions were sex-differences in the associations of sedentary time and breaks with HDL-cholesterol, and race/ethnicity differences in the association of sedentary time with waist circumference with associations detrimental in non-Hispanic whites, null in Mexican Americans, and beneficial in non-Hispanic blacks.

CONCLUSIONS

These are the first population-representative findings on the deleterious associations of prolonged sedentary time with cardio-metabolic and inflammatory biomarkers. The findings suggest that clinical communications and preventive health messages on reducing and breaking up sedentary time may be beneficial for cardiovascular disease risk.

Prediabetes (intermediate hyperglycaemia) is a high-risk state for diabetes that is defined by glycaemic variables that are higher than normal, but lower than diabetes thresholds. 5-10% of people per year with prediabetes will progress to diabetes, with the same proportion converting back to normoglycaemia. Prevalence of prediabetes is increasing worldwide and experts have projected that more than 470 million people will have prediabetes by 2030. Prediabetes is associated with the simultaneous presence of insulin resistance and β-cell dysfunction-abnormalities that start before glucose changes are detectable. Observational evidence shows associations between prediabetes and early forms of nephropathy, chronic kidney disease, small fibre neuropathy, diabetic retinopathy, and increased risk of macrovascular disease. Multifactorial risk scores using non-invasive measures and blood-based metabolic traits, in addition to glycaemic values, could optimise estimation of diabetes risk. For prediabetic individuals, lifestyle modification is the cornerstone of diabetes prevention, with evidence of a 40-70% relative-risk reduction. Accumulating data also show potential benefits from pharmacotherapy.

Although recent studies show that adipose tissue macrophages (ATMs) participate in the inflammatory changes in obesity and contribute to insulin resistance, the properties of these cells are not well understood. We hypothesized that ATMs recruited to adipose tissue during a high-fat diet have unique inflammatory properties compared with resident tissue ATMs. Using a dye (PKH26) to pulse label ATMs in vivo, we purified macrophages recruited to white adipose tissue during a high-fat diet. Comparison of gene expression in recruited and resident ATMs using real-time RT-PCR and cDNA microarrays showed that recruited ATMs overexpress genes important in macrophage migration and phagocytosis, including interleukin-6 (IL-6), inducible nitric oxide synthase (iNOS), and C-C chemokine receptor 2 (CCR2). Many of these genes were not induced in ATMs from high-fat diet-fed CCR2 knockout mice, supporting the importance of CCR2 in regulating recruitment of inflammatory ATMs during obesity. Additionally, expression of Apoe was decreased, whereas genes important in lipid metabolism, such as Pparg, Adfp, Srepf1, and Apob48r, were increased in the recruited macrophages. In agreement with this, ATMs from obese mice had increased lipid content compared with those from lean mice. These studies demonstrate that recruited ATMs in obese animals represent a subclass of macrophages with unique properties.

Arterial stiffness is a growing epidemic associated with increased risk of cardiovascular events, dementia, and death. Decreased compliance of the central vasculature alters arterial pressure and flow dynamics and impacts cardiac performance and coronary perfusion. This article reviews the structural, cellular, and genetic contributors to arterial stiffness, including the roles of the scaffolding proteins, extracellular matrix, inflammatory molecules, endothelial cell function, and reactive oxidant species. Additional influences of atherosclerosis, glucose regulation, chronic renal disease, salt, and changes in neurohormonal regulation are discussed. A review of the hemodynamic impact of arterial stiffness follows. A number of lifestyle changes and therapies that reduce arterial stiffness are presented, including weight loss, exercise, salt reduction, alcohol consumption, and neuroendocrine-directed therapies, such as those targeting the renin-angiotensin aldosterone system, natriuretic peptides, insulin modulators, as well as novel therapies that target advanced glycation end products.

OBJECTIVE

We examined the role of butyric acid, a short-chain fatty acid formed by fermentation in the large intestine, in the regulation of insulin sensitivity in mice fed a high-fat diet.

METHODS

In dietary-obese C57BL/6J mice, sodium butyrate was administrated through diet supplementation at 5% wt/wt in the high-fat diet. Insulin sensitivity was examined with insulin tolerance testing and homeostasis model assessment for insulin resistance. Energy metabolism was monitored in a metabolic chamber. Mitochondrial function was investigated in brown adipocytes and skeletal muscle in the mice.

RESULTS

On the high-fat diet, supplementation of butyrate prevented development of insulin resistance and obesity in C57BL/6 mice. Fasting blood glucose, fasting insulin, and insulin tolerance were all preserved in the treated mice. Body fat content was maintained at 10% without a reduction in food intake. Adaptive thermogenesis and fatty acid oxidation were enhanced. An increase in mitochondrial function and biogenesis was observed in skeletal muscle and brown fat. The type I fiber was enriched in skeletal muscle. Peroxisome proliferator-activated receptor-gamma coactivator-1alpha expression was elevated at mRNA and protein levels. AMP kinase and p38 activities were elevated. In the obese mice, supplementation of butyrate led to an increase in insulin sensitivity and a reduction in adiposity.

CONCLUSIONS

Dietary supplementation of butyrate can prevent and treat diet-induced insulin resistance in mouse. The mechanism of butyrate action is related to promotion of energy expenditure and induction of mitochondria function.