The incretin hormones glucagon-like peptide-1 and glucose-dependent insulinotropic peptide are secreted by enteroendocrine cells and augment glucose-induced insulin secretion in response to food ingestion in a glucose-dependent manner. The mechanism forms the basis for incretin-based therapies in type 2 diabetes. However, the insulinotropic effect of incretins is diminished in type 2 diabetic patients, due in part to reduced expression of incretin receptors as a consequence of glucotoxicity. In this issue of Diabetologia, Kang et al (DOI: 10.1007/s00125-012-2776-x) provide evidence that in addition to glucotoxicity, lipotoxicity also affects incretin receptor expression and signalling in insulin-secreting cells and isolated islets. In animal models of diabetes, the authors show that co-administration of a lipid-lowering drug with a dipeptidyl peptidase-4 inhibitor or a glucagon-like peptide-1 agonist improved glucose tolerance and beta-cell mass. These novel findings provide convincing support for the notion that restoring normal circulating lipid levels in type 2 diabetes might help improve the efficacy of incretin-based therapies.
Fatty acids; Glucagon-like peptide-1; Glucose-dependent insulinotropic peptide; Incretin; Lipotoxicity
Type 1 diabetes results from a chronic autoimmune process continuing for years after presentation. We tested whether treatment with teplizumab (a Fc receptor non-binding anti-CD3 monoclonal antibody), after the new-onset period, affects the decline in C-peptide production in individuals with type 1 diabetes.
In a randomised placebo-controlled trial we treated 58 participants with type 1 diabetes for 4–12 months with teplizumab or placebo at four academic centres in the USA. A central randomisation centre used computer generated tables to allocate treatments. Investigators, patients, and caregivers were blinded to group assignment. The primary outcome was a comparison of C-peptide responses to a mixed meal after 1 year. We explored modification of treatment effects in subgroups of patients.
Thirty-four and 29 subjects were randomized to the drug and placebo treated groups, respectively. Thirty-one and 27, respectively, were analysed. Although the primary outcome analysis showed a 21.7% higher C-peptide response in the teplizumab-treated group (0.45 vs 0.371; difference, 0.059 [95% CI 0.006, 0.115] nmol/l) (p=0.03), when corrected for baseline imbalances in HbA1c levels, the C-peptide levels in the teplizumab-treated group were 17.7% higher (0.44 vs 0.378; difference, 0.049 [95% CI 0, 0.108] nmol/l, p=0.09). A greater proportion of placebo-treated participants lost detectable C-peptide responses at 12 months (p=0.03). The teplizumab group required less exogenous insulin (p<0.001) but treatment differences in HbA1c levels were not observed. Teplizumab was well tolerated. A subgroup analysis showed that treatment benefits were larger in younger individuals and those with HgbA1c <6.5% at entry. Clinical responders to teplizumab had an increase in circulating CD8 central memory cells 2 months after enrolment compared with non-responders.
This study suggests that deterioration in insulin secretion may be affected by immune therapy with teplizumab after the new-onset period but the magnitude of the effect is less than during the new-onset period. Our studies identify characteristics of patients most likely to respond to this immune therapy.
This work was supported by grants 2007-502, 2007-1059 and 2006-351 from the JDRF and grants R01 DK057846, P30 DK20495, UL1 RR024139, UL1RR025780, UL1 RR024131 and UL1 RR024134 from the NIH.
Autoimmunity; Immune therapy; Type 1 diabetes
We sought to derive and validate a cardiovascular disease (CVD) prediction algorithm for older adults with diabetes, and evaluate the incremental benefit of adding novel circulating biomarkers and measures of subclinical atherosclerosis.
As part of the Cardiovascular Health Study (CHS), a population-based cohort of adults aged ≥65 years, we examined the 10 year risk of myocardial infarction, stroke and cardiovascular death in 782 older adults with diabetes, in whom 265 events occurred. We validated predictive models in 843 adults with diabetes, who were followed for 7 years in a second cohort, the Multi-Ethnic Study of Atherosclerosis (MESA); here 71 events occurred.
The best fitting standard model included age, smoking, systolic blood pressure, total and HDL-cholesterol, creatinine and the use of glucose-lowering agents; however, this model had a C statistic of 0.64 and poorly classified risk in men. Novel biomarkers did not improve discrimination or classification. The addition of ankle–brachial index, electrocardiographic left ventricular hypertrophy and internal carotid intima–media thickness modestly improved discrimination (C statistic 0.68; p=0.002) and classification (net reclassification improvement [NRI] 0.12; p=0.01), mainly in those remaining free of CVD. Results were qualitatively similar in the MESA, with a change in C statistic from 0.65 to 0.68 and an NRI of 0.09 upon inclusion of subclinical disease measures.
Standard clinical risk factors and novel biomarkers poorly discriminate and classify CVD risk in older adults with diabetes. The inclusion of subclinical atherosclerotic measures modestly improves these features, but to develop more robust risk prediction, a better understanding of the pathophysiology and determinants of CVD in this patient group is needed.
Biological markers; Cardiovascular diagnostic techniques; Cardiovascular disease; Cohort; Diabetes; Regression analysis; Risk factors
Ankyrin repeat domain 26 (ANKRD26) is a newly described gene located at 10p12 in humans, a locus identified with some forms of hereditary obesity. Previous studies showed that partial inactivation of Ankrd26 causes hyperphagia, obesity and gigantism in mice. We hypothesized that Ankrd26 mutant (MT) mice could develop diabetes and we sought to establish if the observed phenotype could be solely related to the development of obesity or could be caused by a direct action of Ankrd26 in peripheral tissues.
To test the hypothesis, a full metabolic characterization of the Ankrd26 MT mice under ad libutim feeding or placed under two different calorie restricted dietary regimens was completed.
Highly obese Ankrd26 MT mice develop an unusual form of diabetes in which white adipose tissue (WAT) is insulin sensitive, while other tissues are insulin resistant. When obese MT mice were placed on a food-restricted diet their weight and glucose homeostasis returned to normal. Additionally, when young MT mice were placed on a pair-feeding diet with normal mice, they maintained a normal body weight but showed better glucose tolerance than normal mice, an increased responsiveness of WAT to insulin and enhanced phosphorylation of the insulin receptor.
These findings show that the Ankrd26 protein has at least two functions in mice. One is to control the response of WAT to insulin and the other is to control appetite, which when mutated leads to hyperphagia and diabetes in an obesity-dependent manner.
Ankrd26; calorie restriction; diabetes; insulin sensitivity; obesity; WAT
Pregnancies complicated by diabetes have a higher risk of adverse outcomes for mothers and children, including predisposition to disease later in life, e.g. metabolic syndrome and hypertension. We hypothesised that adverse outcomes from diabetic pregnancies may be linked to compromised placental function, and sought to identify cellular and molecular abnormalities in diabetic placenta.
Using a mouse model of diabetic pregnancy, placental gene expression was assayed at mid-gestation and cellular composition analysed at various stages. Genome-wide expression profiling was validated by quantitative PCR and tissue localisation studies were performed to identify cellular correlates of altered gene expression in diabetic placenta.
We detected significantly altered gene expression in diabetic placenta for genes expressed in the maternal and those expressed in the embryonic compartments. We also found altered cellular composition of the decidual compartment. In addition, the junctional and labyrinth layers were reduced in diabetic placenta, accompanied by aberrant differentiation of spongiotrophoblast cells.
Diabetes during pregnancy alters transcriptional profiles in the murine placenta, affecting cells of embryonic and maternal origin, and involving several genes not previously implicated in diabetic pregnancies. The molecular changes and abnormal differentiation of multiple cell types precede impaired growth of junctional zone and labyrinth, and of placenta overall. Regardless of whether these changes represent direct responses to hyperglycaemia or are physiological adaptations, they are likely to play a role in pregnancy complications and outcomes, and to have implications for developmental origins of adult disease.
Diabetic placenta; Diabetic pregnancy; Gene expression profiling; Gene regulation; Hyperglycaemia; Junctional layer; Maternal diabetes; Placental insufficiency; Spongiotrophoblast; Transcription factors
IRS-1 serine phosphorylation is often elevated in insulin resistance models, but confirmation in vivo in humans is lacking. We therefore analysed IRS-1 phosphorylation in human muscle in vivo.
We used HPLC-electrospray ionisation (ESI)-MS/MS to quantify IRS-1 phosphorylation basally and after insulin infusion in vastus lateralis muscle from lean healthy, obese non-diabetic and type 2 diabetic volunteers.
Basal Ser323 phosphorylation was increased in type 2 diabetic patients (2.1±0.43, p≤0.05, fold change vs lean controls). Thr495 phosphorylation was decreased in type 2 diabetic patients (p≤0.05). Insulin increased IRS-1 phosphorylation at Ser527 (1.4±0.17, p≤0.01, fold change, 60 min after insulin infusion vs basal) and Ser531 (1.3±0.16, p≤0.01, fold change, 60 min after insulin infusion vs basal) in the lean controls and suppressed phosphorylation at Ser348 (0.56±0.11, p≤0.01, fold change, 240 min after insulin infusion vs basal), Thr446 (0.64±0.16, p≤0.05, fold change, 60 min after insulin infusion vs basal), Ser1100 (0.77±0.22, p≤0.05, fold change, 240 min after insulin infusion vs basal) and Ser1142 (1.3±0.2, p≤0.05, fold change, 60 min after insulin infusion vs basal).
We conclude that, unlike some aspects of insulin signalling, the ability of insulin to increase or suppress certain IRS-1 phosphorylation sites is intact in insulin resistance. However, some IRS-1 phosphorylation sites do not respond to insulin, whereas other Ser/Thr phosphorylation sites are either increased or decreased in insulin resistance.
Insulin resistance; IRS-1; Mass spectrometry; Serine; Phosphorylation; Threonine; Type 2 diabetes
We sought to determine the mRNA transcriptome of all major human pancreatic endocrine and exocrine cell subtypes, including human alpha, beta, duct and acinar cells. In addition, we identified the cell type-specific distribution of transcription factors, signalling ligands and their receptors.
Islet samples from healthy human donors were enzymatically dispersed to single cells and labelled with cell type-specific surface-reactive antibodies. Live endocrine and exocrine cell subpopulations were isolated by FACS and gene expression analyses were performed using microarray analysis and quantitative RT-PCR. Computational tools were used to evaluate receptor–ligand representation in these populations.
Analysis of the transcriptomes of alpha, beta, large duct, small duct and acinar cells revealed previously unrecognised gene expression patterns in these cell types, including transcriptional regulators HOPX and HDAC9 in the human beta cell population. The abundance of some regulatory proteins was different from that reported in mouse tissue. For example, v-maf musculoaponeurotic fibrosarcoma oncogene homologue B (avian) (MAFB) was detected at equal levels in adult human alpha and beta cells, but is absent from adult mouse beta cells. Analysis of ligand–receptor interactions suggested that EPH receptor–ephrin communication between exocrine and endocrine cells contributes to pancreatic function.
This is the first comprehensive analysis of the transcriptomes of human exocrine and endocrine pancreatic cell types—including beta cells—and provides a useful resource for diabetes research. In addition, paracrine signalling pathways within the pancreas are shown. These results will help guide efforts to specify human beta cell fate by embryonic stem cell or induced pluripotent stem cell differentiation or genetic reprogramming.
Alpha cell; Beta cell; Paracrine signalling; Transcription factor
Recent functional characterisations of genome-wide association study (GWAS) loci suggest that cis-regulatory variation may be a common paradigm for complex disease susceptibility. Several studies point to a similar mechanism at the transcription factor 7-like 2 (TCF7L2) GWAS locus for type 2 diabetes. To address this possibility, we carried out an in vitro scan of this diabetes-associated locus to fine-map cis-regulatory sequences within this genomic interval.
A systematic cell-based enhancer strategy was employed to interrogate all sequences within the 92 kb type-2-diabetes-association interval for cis-regulatory activity in a panel of cell lines (HCT-116, Neuro-2a, C2C12, U2OS, MIN6 and HepG2). We further evaluated chromatin state at a subset of these regions in HCT-116 and U2OS cells and examined allelic-specific enhancer properties at the type-2-diabetes-associated single nucleotide polymorphism (SNP) rs7903146.
In total, we assigned cis-regulatory activity to approximately 30% (9/28) of constructs tested. Notably, a subset of enhancers was active across multiple cell lines and overlapped with key epigenetic markers suggestive of cis-regulatory sequences. We further replicated the allelic-specific properties for SNP rs7903146 in pancreatic beta cells and additionally demonstrate identical allelic-specific enhancer effects in other cell lines.
These results provide a detailed map of cis-regulatory elements within the TCF7L2 GWAS locus and support the hypothesis of cis-regulatory variation leading to type 2 diabetes predisposition. The detection of allelic-specific effects for SNP rs7903146 in multiple cell lines further alludes to the likelihood of a peripheral defect in disease aetiology.
GWAS; cis-Regulatory elements; TCF7L2; Type 2 diabetes
IL-12 is an important cytokine in early inflammatory responses and is implicated in the immunemediated pathogenesis of pancreatic islets in diabetes. However, little is known about the direct effects of IL-12 on islets and beta cells.
In this study, beta cell function, gene expression and protein production were assessed in primary human donor islets and murine beta cell lines in response to stimulation with IL-12 or a pro-inflammatory cytokine cocktail (TNF-α, IL-1β and IFN-γ).
The pro-inflammatory cytokine cocktail induced islet dysfunction and potently increased the expression and production of IL-12 ligand and IL-12 receptor in human islets. In human islets, the receptor for IL-12 co-localised to the cell surface of insulin-producing cells. Both IL-12 ligand and IL-12 receptor are expressed in the homogeneous beta cell line INS-1. IL-12 induced changes in gene expression, including a dose-dependent upregulation of IFNγ (also known as IFNG), in INS-1 cells. A neutralising antibody to IL-12 directly inhibited IFNγ gene expression in human donor islets induced by either IL-12 or pro-inflammatory cytokine stimulation. Functionally, IL-12 impaired glucose-stimulated insulin secretion (GSIS) in INS-1 cells and human donor islets. A neutralising antibody to IL-12 reversed the beta cell dysfunction (uncoupling of GSIS or induction of caspase-3 activity) induced by pro-inflammatory cytokines.
These data identify beta cells as a local source of IL-12 ligand and suggest a direct role of IL-12 in mediating beta cell pathology.
Diabetes; Human; Interleukin-12; Islets; Pro-inflammatory cytokines
Since it has been shown that polycystic ovary syndrome (PCOS) is highly inherited and characterised by insulin resistance, we hypothesised that male siblings of PCOS women would also be insulin resistant. Thus, our aim was to assess insulin sensitivity and metabolic parameters in brothers of women with PCOS and male control individuals.
Seventeen brothers of PCOS women and 28 male control volunteers were assessed with 75 g OGTTs and euglycaemic–hyperinsulinaemic clamps. PCOS index women were identified using criteria developed at the 1990 National Institutes of Health conference.
Brothers and control individuals were similar in terms of BMI, waist circumference, percentage body fat and BP. However, brothers had increased triacylglycerol (p=0.02), plasminogen activator inhibitor-1 (PAI-1; p=0.02), factor VIII (p=0.02), 2 h glucose (p<0.001), AUCglucose (p<0.001) and AUCinsulin (p<0.001). Insulin sensitivity was reduced by 38% in brothers (p<0.001), and this was primarily due to a 65% decrease in insulin-stimulated non-oxidative carbohydrate metabolism (p<0.001). These differences remained significant after adjustment for age and BMI, except for triacylglycerol, PAI-1 and fasting glucose. The main findings also persisted after excluding individuals with impaired glucose tolerance or diabetic siblings. Significant interactions with BMI status were found for sex hormone-binding globulin, androstenedione, PAI-1 and AUCinsulin, which were significantly altered only in obese brothers (vs control individuals).
Brothers of PCOS women are characterised by decreased insulin sensitivity and glucose tolerance, as well as hypercoagulability, independently of obesity. Therefore, brothers of PCOS women may have inherited the insulin resistance and metabolic syndrome typical of PCOS.
PMID: 17898989 CAMSID: cams3751
Impaired glucose tolerance; Insulin resistance; Male siblings; Metabolic syndrome; Polycystic ovary syndrome
Type 1 diabetes is a common autoimmune disease that has genetic and environmental determinants. Variations within the IL2 and IL2RA (also known as CD25) gene regions are associated with disease risk, and variation in expression or function of these proteins is likely to be causal. We aimed to investigate if circulating concentrations of the soluble form of CD25, sCD25, an established marker of immune activation and inflammation, were increased in individuals with type 1 diabetes and if this was associated with the concentration of C-peptide, a measure of insulin production that reflects the degree of autoimmune destruction of the insulin-producing beta cells.
We used immunoassays to measure sCD25 and C-peptide in peripheral blood plasma from patient and control samples.
We identified that sCD25 was increased in patients with type 1 diabetes compared with controls and replicated this result in an independent set of 86 adult patient and 80 age-matched control samples (p = 1.17 × 10−3). In 230 patients under 20 years of age, with median duration-of-disease of 6.1 years, concentrations of sCD25 were negatively associated with C-peptide concentrations (p = 4.8 × 10−3).
The 25% increase in sCD25 in patients, alongside the inverse association between sCD25 and C-peptide, probably reflect the adverse effects of an on-going, actively autoimmune and inflammatory immune system on beta cell function in patients.
Electronic supplementary material
The online version of this article (doi:10.1007/s00125-013-3113-8) contains peer-reviewed but unedited supplementary material, which is available to authorised users.
Autoimmune; Blood; Case–control; CD25; C-peptide; IL-2; IL-2RA Immunoassay; Peripheral; sCD25; Soluble cytokine receptor; Type 1 diabetes
Advances in type 2 diabetes genetics have raised hopes that genetic testing will improve disease prediction, prevention and treatment. Little is known about current physician and patient views regarding type 2 diabetes genetic testing. We hypothesised that physician and patient views would differ regarding the impact of genetic testing on motivation and adherence.
We surveyed a nationally representative sample of US primary care physicians and endocrinologists (n=304), a random sample of non-diabetic primary care patients (n=152) and patients enrolled in a diabetes pharmacogenetics study (n=89).
Physicians and patients favoured genetic testing for diabetes risk prediction (79% of physicians vs 80% of non-diabetic patients would be somewhat/very likely to order/request testing, p=0.7). More patients than physicians (71% vs 23%, p<0.01) indicated that a ‘high risk’ result would be very likely to improve motivation to adopt preventive lifestyle changes. Patients favoured genetic testing to guide therapy (78% of patients vs 48% of physicians very likely to request/recommend testing, p<0.01) and reported that genetic testing would make them ‘much more motivated’ to adhere to medications (72% vs 18% of physicians, p<0.01). Many physicians (39%) would be somewhat/very likely to order genetic testing before published evidence of clinical efficacy.
Despite the paucity of current data, physicians and patients reported high expectations that genetic testing would improve patient motivation to adopt key behaviours for the prevention or control of type 2 diabetes. This suggests the testable hypothesis that ‘genetic’ risk information might have greater value to motivate behaviour change compared with standard risk information.
Diabetes prediction; Genetic risk; Genetic testing; Medication adherence; Patient motivation; Type 2 diabetes
Few studies have investigated the relationship between predefined dietary patterns and type 2 diabetes incidence; little is known about the generalisability of these associations. We aimed to assess the association between predefined dietary patterns and type 2 diabetes risk in European populations.
From among a case-cohort of 12,403 incident diabetes cases and 16,154 subcohort members nested within the prospective European Prospective Investigation into Cancer and Nutrition study, we used data on 9,682 cases and 12,595 subcohort participants from seven countries. Habitual dietary intake was assessed at baseline with country-specific dietary questionnaires. Two diet-quality scores (alternative Healthy Eating Index [aHEI], Dietary Approaches to Stop Hypertension [DASH] score) and three reduced rank regression (RRR)-derived dietary-pattern scores were constructed. Country-specific HRs were calculated and combined using a random-effects meta-analysis.
After multivariable adjustment, including body size, the aHEI and DASH scores were not significantly associated with diabetes, although for the aHEI there was a tendency towards an inverse association in countries with higher mean age. We observed inverse associations of the three RRR-derived dietary-pattern scores with diabetes: HRs (95% CIs) for a 1-SD difference were 0.91 (0.86, 0.96), 0.92 (0.84, 1.01) and 0.87 (0.82, 0.92). Random-effects meta-analyses revealed heterogeneity between countries that was explainable by differences in the age of participants or the distribution of dietary intake.
Adherence to specific RRR-derived dietary patterns, commonly characterised by high intake of fruits or vegetables and low intake of processed meat, sugar-sweetened beverages and refined grains, may lower type 2 diabetes risk.
Electronic supplementary material
The online version of this article (doi:10.1007/s00125-013-3092-9) contains peer-reviewed but unedited supplementary material, which is available to authorised users.
Alternative Healthy Eating Index; Case-cohort; Dietary Approaches to Stop Hypertension; Dietary patterns; Reduced rank regression; Type 2 diabetes
We report a genome-wide association study of type 2 diabetes in an admixed sample from Mexico City and describe the results of a meta-analysis of this study and another genome-wide scan in a Mexican-American sample from Starr County, TX, USA. The top signals observed in this meta-analysis were followed up in the Diabetes Genetics Replication and Meta-analysis Consortium (DIAGRAM) and DIAGRAM+ datasets.
We analysed 967 cases and 343 normoglycaemic controls. The samples were genotyped with the Affymetrix Genome-wide Human SNP array 5.0. Associations of genotyped and imputed markers with type 2 diabetes were tested using a missing data likelihood score test. A fixed-effects meta-analysis including 1,804 cases and 780 normoglycaemic controls was carried out by weighting the effect estimates by their inverse variances.
In the meta-analysis of the two Hispanic studies, markers showing suggestive associations (p<10−5) were identified in two known diabetes genes, HNF1A and KCNQ1, as well as in several additional regions. Meta-analysis of the two Hispanic studies and the recent DIAGRAM+ dataset identified genome-wide significant signals (p<5×10−8) within or near the genes HNF1A and CDKN2A/CDKN2B, as well as suggestive associations in three additional regions, IGF2BP2, KCNQ1 and the previously unreported C14orf70.
We observed numerous regions with suggestive associations with type 2 diabetes. Some of these signals correspond to regions described in previous studies. However, many of these regions could not be replicated in the DIAGRAM datasets. It is critical to carry out additional studies in Hispanic and American Indian populations, which have a high prevalence of type 2 diabetes.
Genome-wide association; Hispanics; Meta-analysis; Type 2 diabetes
We aimed to quantify the associations between change in objectively measured sedentary and moderate-to-vigorous physical activity (MVPA) times and self-reported television viewing over 6 years and change in a clustered cardiometabolic risk score (CCMR), including and excluding waist circumference (CCMR without adiposity component, CCMRno adip), and its individual components, among the adult children of people with type 2 diabetes.
In 171 adults (mean ± SD age 42.52 ± 6.30 years; 46% men) with a parental history of diabetes (ProActive UK), physical activity accelerometer measures and self-reported television viewing were assessed at baseline and a mean ± SD of 6.27 ± 0.46 years later. Associations between change in sedentary time, MVPA time and television viewing and cardiometabolic risk and mediation by adiposity change were examined by multiple linear regression and the product of coefficients method, respectively.
Greater increases in sedentary time (h/day) were associated with larger increases in clustered cardiometabolic risk (CCMR: 0.08 [95% CI 0.01, 0.15]; CCMRno adip: 0.08 [0.01, 0.16]) and triacylglycerol (0.15 [0.01, 0.29]), independent of baseline sedentary and MVPA times, change in MVPA time and other confounders. No evidence was found for mediation by change in waist circumference and BMI for the associations with CCMRno adip and triacylglycerol. Greater increases in MVPA time (h/day) were associated with larger decreases in waist circumference (−3.86 [−7.58, −0.14]), independently of baseline MVPA and sedentary times, change in sedentary time and other confounders. Television viewing was not independently associated with any of the cardiometabolic outcomes.
Increasing sedentary time is independently related to increasing clustered cardiometabolic risk and triacylglycerol in adults at high risk of developing diabetes. Strategies to prevent diabetes might target reducing sedentary time.
Trial registration ISRCTN61323766
Electronic supplementary material
The online version of this article (doi:10.1007/s00125-013-3102-y) contains peer-reviewed but unedited supplementary material, which is available to authorised users.
Adiposity; Cardiovascular disease risk; Longitudinal study; Moderate-to-vigorous physical activity; Sedentary behaviour; Television viewing
Despite years of appreciating the potential role of environment to influence the pathogenesis of type 1 diabetes, specific agents or mechanisms serving in such a capacity remain ill defined. This is exceedingly disappointing as the identification of factors capable of modulating the disease, either as triggers or regulators of the autoimmune response underlying type 1 diabetes, would not only provide clues as to why the disorder develops but, in addition, afford opportunities for improved biomarkers of disease activity and the potential to design novel therapeutics capable of disease abatement. Recent improvements in sequencing technologies, combined with increasing appreciation of the role of innate and mucosal immunity in human disease, have stirred strong interest in what is commonly referred to as the ‘gut microbiota’. The gut (or intestinal) microbiota is an exceedingly complex microenvironment that is intimately linked with the immune system, including the regulation of immune responses. After evaluating evidence supporting a role for environment in type 1 diabetes, this review will convey current notions for contributions of the gut microbiota to human health and disease, including information gleaned from studies of humans and animal models for this autoimmune disorder.
Bacteria; Environment; Gut microbiome; Immunology; Innate immunity; Microbiota; Mucosal immunity; NOD mice; Review; Type 1 diabetes
The beta cell transcriptional factor musculoaponeurotic fibrosarcoma oncogene family A (MafA) regulates genes important for beta cell function. Loss of nuclear MafA has been implicated in beta cell dysfunction in animal models of type 2 diabetes. We sought to establish if nuclear MafA is less abundant in beta cell nuclei in humans with type 2 diabetes.
Pancreas obtained at surgery from five non-diabetic individuals and six individuals with type 2 diabetes was immunostained for insulin, glucagon and MafA.
Beta cell nuclear MafA was markedly decreased in type 2 diabetes (1.6±1.2% vs 46.3±8.3%, p<0.001).
Beta cell nuclear MafA is markedly decreased in humans with type 2 diabetes, which may contribute to impaired beta cell dysfunction.
Beta cell; Glucotoxicity; MafA
Few data are available about intakes and food sources of trans-fatty acids (TFAs) or their associations with cardiometabolic outcomes in Asian people who consume a prudent diet but are experiencing rapid nutritional transitions. We aimed to investigate the relationships between TFA biomarkers and type 2 diabetes and cardiovascular risk factors in Chinese individuals.
Erythrocyte fatty acids were measured by gas chromatography among 3,107 men and women (50–70 years) recruited from urban and rural areas in Beijing and Shanghai, China.
Total trans-18:1 and two trans-18:2 isomers were detected and accounted for 0.37% of the total fatty acids in the erythrocytes. Concentrations of TFAs were higher in women than men, and in urban than rural residents. Of the TFAs, trans-18:1, but not trans-18:2, showed a modest association with dairy consumption (β=0.27), but not with other foods. After adjustment for BMI, social-demographic, lifestyle and dietary factors and other TFAs, erythrocyte trans-18:1 was shown to be associated with a lower risk of type 2 diabetes (OR comparing extreme quartiles=0.68, 95% CI=0.48, 0.97, ptrend=0.02), as well as 20–50% lower odds of central obesity, dyslipidaemia, hyperglycemia, insulin resistance and chronic inflammation. In contrast, trans-18:2 fatty acids were positively associated with high triacylglycerol (ptrend<0.001) and LDL-cholesterol (ptrend=0.03) levels, but not with diabetes and other cardiometabolic risk factors.
Among middle-aged and older Chinese individuals with overall low erythrocyte TFAs levels, trans-18:1 might serve as a marker of dairy intake. Higher trans-18:1 levels were associated with a lower risk of type 2 diabetes, whereas higher trans-18:2 levels were associated with dyslipidaemia.
Biomarkers; Diet; Dyslipidaemia; trans-Fatty acids; Type 2 diabetes
Hyperglycaemia disproportionately affects African-Americans (AfAs).
We tested the transferability of 18 single-nucleotide polymorphisms (SNPs)
associated with glycaemic traits identified in European ancestry (EuA)
populations in 5,984 non-diabetic AfAs.
We meta-analysed SNP associations with fasting glucose (FG) or
insulin (FI) in AfAs from five cohorts in the Candidate Gene Association
Resource. We: (1) calculated allele frequency differences, variations in
linkage disequilibrium (LD), fixation indices (Fsts) and
integrated haplotype scores (iHSs); (2) tested EuA SNPs in AfAs; and (3)
interrogated within ±250 kb around each EuA SNP in AfAs.
Allele frequency differences ranged from 0.6% to 54%.
Fst exceeded 0.15 at 6/16 loci, indicating modest population
differentiation. All iHSs were <2, suggesting no recent positive
selection. For 18 SNPs, all directions of effect were the same and
95% CIs of association overlapped when comparing EuA with AfA. For
17 of 18 loci, at least one SNP was nominally associated with FG in AfAs.
Four loci were significantly associated with FG (GCK,
p=5.8 × 10-8;
MTNR1B, p=8.5 ×
10-9; and FADS1,
p=2.2 × 10-4) or FI
(GCKR, p=5.9 ×
10-4). At GCK and MTNR1B
the EuA and AfA SNPs represented the same signal, while at
FADS1, and GCKR, the EuA and best AfA
SNPs were weakly correlated (r2<0.2),
suggesting allelic heterogeneity for association with FG at these loci.
Few glycaemic SNPs showed strict evidence of transferability from EuA
to AfAs. Four loci were significantly associated in both AfAs and those with
EuA after accounting for varying LD across ancestral groups, with new
signals emerging to aid fine-mapping.
African ancestry; Genetics; Genome-wide association; LD mapping; Minorities; Type 2 diabetes
Aims/hypothesis The appearance of autoantibodies (Ab) before diabetes onset has mainly been studied in young children. However, most patients develop type 1 diabetes after age 15. In first-degree relatives under age 40, we investigated the frequency of seroconversion to (persistent) Ab-positivity, progression to diabetes and baseline characteristics of seroconverters according to age.
Methods Abs against insulin (IAA), GAD (GADA), IA-2 (IA-2A) and zinc transporter 8 (ZnT8A-CRCW) were measured during follow-up of 7170 first-degree relatives.
Results We identified 379 (5.3%) Ab+ relatives at first sampling and 224 (3.1%) at a later time point. Most seroconversions occurred after age 10 (63%). During follow-up Abs persisted more often in initially Ab+-relatives (76%) than in seroconverters (53%; p < 0.001). In both groups diabetes developed at a similar pace and almost exclusively in case of Ab-persistence (136 of 139 prediabetics). For both, progression was more rapid if Abs appeared before age 10. Baseline characteristics at seroconversion did not vary significantly according to age except for higher proinsulin levels and proinsulin:C-peptide ratio's between age 10 and 20 (p < 0.002).
Conclusions/interpretation Seroconversion to (persistent) Ab-positivity occurs regardless of age. Although the progression rate to diabetes is higher under age 10, later seroconverters (up to age 40) have similar characteristics when compared with age-matched initially Ab+ relatives and generate an important minority of prediabetic relatives, hence warranting their identification and eventually enrolment in prevention trials.
Autoantibodies; First-degree relatives; GAD; IA-2; Insulin; Prediabetes; Proinsulin; Seroconversion; Type 1 diabetes; Zinc transporter 8
In an Indian birth cohort, higher maternal homocysteine concentration in pregnancy was associated with lower birthweight of the offspring. Lower maternal vitamin B12 and higher folate concentrations were associated with higher offspring insulin resistance. Disordered one-carbon metabolism during early development may increase later metabolic risk. We explored these associations in another birth cohort in India at three age points.
We measured plasma vitamin B12, folate and homocysteine concentrations at 30 ± 2 weeks’ gestation in 654 women who delivered at one hospital. Neonatal anthropometry was recorded, and the children’s glucose and insulin concentrations were measured at 5, 9.5 and 13.5 years of age. Insulin resistance was estimated using HOMA of insulin resistance (HOMA-IR).
Maternal homocysteine concentrations were inversely associated with all neonatal anthropometric measurements (p < 0.05), and positively associated with glucose concentrations in the children at 5 (30 min; p = 0.007) and 9.5 years of age (120 min; p = 0.02). Higher maternal folate concentrations were associated with higher HOMA-IR in the children at 9.5 (p = 0.03) and 13.5 years of age (p = 0.03). Maternal vitamin B12 concentrations were unrelated to offspring outcomes.
Maternal vitamin B12 status did not predict insulin resistance in our cohort. However, associations of maternal homocysteine and folate concentrations with birth size, and with childhood insulin resistance and glycaemia in the offspring, suggest a role for nutritionally driven disturbances in one-carbon metabolism in fetal programming of diabetes.
Electronic supplementary material
The online version of this article (doi:10.1007/s00125-013-3086-7) contains peer-reviewed but unedited supplementary material, which is available to authorised users.
Child; Folate; Homocysteine; Insulin resistance; Pregnancy; Programming; Vitamin B12
Type 2 diabetes is characterised by progressive beta cell dysfunction, with changes in gene expression playing a crucial role in its development. MicroRNAs (miRNAs) are post-transcriptional regulators of gene expression and therefore alterations in miRNA levels may be involved in the deterioration of beta cell function.
Global TaqMan arrays and individual TaqMan assays were used to measure islet miRNA expression in discovery (n = 20) and replication (n = 20) cohorts from individuals with and without type 2 diabetes. The role of specific dysregulated miRNAs in regulating insulin secretion, content and apoptosis was subsequently investigated in primary rat islets and INS-1 cells. Identification of miRNA targets was assessed using luciferase assays and by measuring mRNA levels.
In the discovery and replication cohorts miR-187 expression was found to be significantly increased in islets from individuals with type 2 diabetes compared with matched controls. An inverse correlation between miR-187 levels and glucose-stimulated insulin secretion (GSIS) was observed in islets from normoglycaemic donors. This correlation paralleled findings in primary rat islets and INS-1 cells where overexpression of miR-187 markedly decreased GSIS without affecting insulin content or apoptotic index. Finally, the gene encoding homeodomain-interacting protein kinase-3 (HIPK3), a known regulator of insulin secretion, was identified as a direct target of miR-187 and displayed reduced expression in islets from individuals with type 2 diabetes.
Our findings suggest a role for miR-187 in the blunting of insulin secretion, potentially involving regulation of HIPK3, which occurs during the pathogenesis of type 2 diabetes.
Electronic supplementary material
The online version of this article (doi:10.1007/s00125-013-3089-4) contains peer-reviewed but unedited supplementary material, which is available to authorised users.
Glucose-stimulated insulin secretion; HIPK3; Islets; MicroRNA; Type 2 diabetes
Intramyocellular lipids, including diacylglycerol (DAG) and ceramides, have been linked to insulin resistance. This randomised repeated-measures study examined the effects of diet-induced weight loss (DIWL) and aerobic exercise (EX) on insulin sensitivity and intramyocellular triacylglycerol (IMTG), DAG and ceramide.
Sixteen overweight to obese adults (BMI 30.6±0.8; 67.2±4.0 years of age) with either impaired fasting glucose, or impaired glucose tolerance completed one of two lifestyle interventions: DIWL (n=8) or EX (n=8). Insulin sensitivity was determined using hyperinsulinaemic–euglycaemic clamps. Intramyocellular lipids were measured in muscle biopsies using histochemistry and tandem mass spectrometry.
Insulin sensitivity was improved with DIWL (20.6± 4.7%) and EX (19.2±12.9%). Body weight and body fat were decreased by both interventions, with greater decreases in DIWL compared with EX.Muscle glycogen, IMTG content and oxidative capacity were all significantly (p<0.05) decreased with DIWL and increased with EX. There were decreases in DAG with DIWL (−12.4±14.6%) and EX (−40.9±12.0%). Ceramide decreased with EX (−33.7± 11.2%), but not with DIWL. Dihydroceramide was decreased with both interventions. Sphingosine was decreased only with EX. Changes in total DAG, total ceramides and other sphingolipids did not correlate with changes in glucose disposal. Stearoyl-coenzyme A desaturase 1 (SCD1) content was decreased with DIWL (−19.5± 8.5%, p<0.05), but increased with EX (19.6±7.4%, p<0.05). Diacylglycerol acyltransferase 1 (DGAT1) was unchanged with the interventions.
Diet-induced weight loss and exercise training both improved insulin resistance and decreased DAG, while only exercise decreased ceramides, despite the interventions having different effects on IMTG. These alterations may be mediated through differential changes in skeletal muscle capacity for oxidation and triacylglycerol synthesis.
Ceramide; Diacylglycerol; Insulin resistance; Skeletal muscle
ETA receptor activation increases glomerular permeability to albumin (Palb) and elevates pre-inflammatory markers in hyperglycaemic (HG) rats.
Male Sprague-Dawley rats were given streptozotocin (STZ), n=32 or saline (sham,), n=32. Half of the animals in each group received the ETA-selective antagonist, ABT-627 (atrasentan; p.o.), beginning immediately after hyperglycaemia was confirmed. Glomeruli were isolated by sieving techniques and Palb determined from the change in glomerular volume induced by oncotic gradients of albumin. Glomerular nephrin expression was assessed by immunofluorescence, whereas urinary nephrin was measured by immunoassay.
Three and six weeks after STZ injection, proteinuria was significantly increased compared to sham controls and was significantly reduced by ABT-627 treatment. Palb was also increased at 3 and 6 wk post-STZ; ABT-627 had no effect on Palb or protein excretion in sham rats. In glomeruli isolated from HG rats, incubation with BQ-123, a selective ETA antagonist, reduced Palb, whereas BQ-788, a selective ETB antagonist had no effect (n=6 rats/group, 5-8 glomeruli/rat). Glomerular and plasma content of soluble inter-cellular adhesion molecule-1 (sICAM-1) and monocyte chemoattractant protein-1 (MCP-1) were significantly increased 6 wk after STZ (ELISA). ABT-627 attenuated these increases. After 6 weeks of hyperglycaemia, glomerular nephrin expression was decreased with a concurrent increase in urinary nephrin excretion; ABT-627 prevented glomerular nephrin loss in the HG rats (n=5-8 rats in the eight groups).
These observations support the hypothesis that ET-1, via the ETA receptor, directly increases glomerular permeability to albumin, possibly via nephrin loss, as well as early inflammation in the HG rat.
diabetic nephropathy; endothelin-1; sICAM-1; MCP-1; albuminuria; glomerular permeability; Palb; nephrin
Delivery of the gene for human vascular endothelial growth factor (VEGF, also known as VEGFA) to both the transplanted islets and the surrounding tissue may promote islet revascularisation and survival. We previously showed the effective delivery of VEGF gene to rat myocardium by an ultrasound-mediated gene-transfer method named ultrasound-targeted microbubble destruction (UTMD). Here we examined the effect of non-viral VEGF delivery using UTMD on transplanted islets in vivo.
A marginal number of human islets were transplanted into livers of mice which were a model for diabetes. Then, non-viral plasmid vectors encoding VEGF (VEGF group, n=11) or the gene for green fluorescent protein (GFP) (GFP group, n=7) were introduced into the host liver by UTMD. Transplantation without gene delivery was performed as a control (no-UTMD group, n=8). Blood glucose, serum human insulin, C-peptide levels and the revascularisation in graft islets were evaluated.
Restoration of euglycaemia occurred in 13% in the no-UTMD group and 14% in the GFP group, whereas 73% mice in the VEGF group became euglycaemic at day 30 (p<0.05 in no-UTMD vs VEGF). Serum human insulin and C-peptide were significantly higher in the VEGF group at day32 (insulin: no-UTMD, 17±8; GFP, 37±17; VEGF, 109±26 pmol/l, respectively, p<0.05; C-peptide: no-UTMD, 68±38; GFP, 115±58; VEGF, 791±230 pmol/l, respectively, p<0.05). Vessel density in graft islets was significantly higher in the VEGF group (no-UTMD, 169±36; GFP, 227± 39; VEGF, 649±51 counts/mm2, respectively, p<0.05)
Delivery of VEGF gene to host liver using UTMD promoted islet revascularisation after islet transplantation and improved the restoration of euglycaemia.
Gene therapy; Human vascular endothelial growth factor; Islet transplantation; Non-viral gene delivery; Revascularisation