Failure of homeostatic model assessment of insulin resistance to detect marked diet-induced insulin resistance in dogs

MIRA: Myocardial insulin resistance app for clinical practice

BACKGROUND AND OBJECTIVE

Type 2 diabetes (T2D) is a prevalent disease characterized by insulin resistance (IR), leading to energy disruptions in myocardial cells and increasing cardiovascular (CV) risk. Current diagnostic methods are either systemic, thus lacking tissue-specific information, or invasive. The hyperinsulinemic euglycemic clamp (HEC) combined with [18F]FDG-PET images, only used in clinical trials, allow to assess regional IR and identify phenotypes within T2D, linking myocardial IR to higher CV risk. However, phenotyping is not easily accessible, creating a need for alternative assessment tools. Thus, we propose a myocardial IR model to address these gaps and improve T2D management.

METHODS

The study included forty-two patients with T2D who enrolled in a clinical trial (NCT02248311) and who underwent biochemical analyses, anthropometric measurements and [18F]FDG PET/CT imaging before and after HEC with. Patients were phenotyped into mIR and mIS according to poor or good uptake after HEC, respectively. The proposed predictive model was based on stepwise regression including feature selection to provide an estimate of myocardial IS and thus IR=1/IS by using biochemical parameters in T2D. A software application, the myocardial IR app (MIRA), was developed using MATLAB.

RESULTS

MIRA was developed as a myocardial IR estimator (R2=0.97, p=7.1 × 10-7, error=1.24) for patients with T2D. Moreover, since HEC is not allowed in rutinary clinical practice, the application includes a prediction of the expected myocardial HEC [18F]FDG uptake from baseline uptake (r=0.52, p=5 × 10-4, R2=0.60). The app also yields the patient's phenotype, either mIR or mIS, according to poor or good uptake after HEC. Enhanced CV risk exposure due to altered T2D biomarkers and associated to mIR is also provided with highlighted features.

CONCLUSIONS

We hereby present MIRA, a myocardial IR calculation app to manage myocardial-specific affectation in T2D, as well as to provide with patient phenotyping and CV risk assessment.

Fibroblast growth factor 21 improves insulin sensitivity by modulating the bile acid-gut microbiota axis in type Ⅱ diabetic mice

BACKGROUND

Fibroblast growth factor 21 (FGF21) is an important regulator of glycolipid metabolism. However, whether the gut microbiota is related to the anti-diabetic and obesity effects of FGF21 remains unclear.

METHODS

Our research used KO/KO db/db male mice and streptozotocin (STZ)-induced to simulate the construction of two type II diabetic mellitus (T2DM) models, and detected impaired glucose tolerance in the model by using the ipGTT and ITT assays, and collected feces from the model mice for sequencing of the intestinal flora and the content of short-chain fatty acids. H＆E staining was used to detect changes in intestinal tissue, the serum levels of LPS and GLP-1 were detected by ELISA.

RESULTS

In this study, we found that FGF21 significantly improved insulin sensitivity, attenuated intestinal lesions, and decreased serum lipopolysaccharide (LPS) concentrations in T2DM mice. Moreover, FGF21 reshaped the gut microbiota and altered their metabolic pathways in T2DM mice, promoting the production of short-chain fatty acids (SCFAs) and the secretion of glucagon-like peptide 1 (GLP-1). Fecal transplantation experiments further confirmed that feces from FGF21-treated diabetic mice demonstrated similar effects as FGF21 in terms of anti-diabetic activity and regulation of gut microbiota dysbiosis. Additionally, the antibiotic depletion of gut microbiota abolished the beneficial effects of FGF21, including increased GLP-1 secretion and fecal SCFA concentration. Additionally, the FGF21 effects of ameliorating intestinal damage and suppressing plasma LPS secretion were suppressed. All these findings suggest that FGF21 prevents intestinal lesions by modifying the gut microbiota composition. Furthermore, FGF21 affected bile acid synthesis by inhibiting CYP7A1, the key enzyme of bile acid synthesis.

CONCLUSSION

Therefore, FGF21 enriched beneficial bacteria by preventing bile acid synthesis and stimulating the secretion of the intestinal hormone GLP-1 via the increased production of gut microbiota metabolites, thereby exerting its anti-diabetic effects.

Methods for estimating insulin resistance from untargeted metabolomics data

CONTEXT

Insulin resistance is associated with multiple complex diseases; however, precise measures of insulin resistance are invasive, expensive, and time-consuming.

OBJECTIVE

Develop estimation models for measures of insulin resistance, including insulin sensitivity index (SI) and homeostatic model assessment of insulin resistance (HOMA-IR) from metabolomics data.

DESIGN

Insulin Resistance Atherosclerosis Family Study (IRASFS).

SETTING

Community based.

PARTICIPANTS

Mexican Americans (MA) and African Americans (AA).

MAIN OUTCOME

Estimation models for measures of insulin resistance, i.e. SI and HOMA-IR.

RESULTS

Least Absolute Shrinkage and Selection Operator (LASSO) and Elastic Net regression were used to build insulin resistance estimation models from 1274 metabolites combined with clinical data, e.g. age, sex, body mass index (BMI). Metabolite data were transformed using three approaches, i.e. inverse normal transformation, standardization, and Box Cox transformation. The analysis was performed in one MA recruitment site (San Luis Valley, Colorado (SLV); N = 450) and tested in another MA recruitment site (San Antonio, Texas (SA); N = 473). In addition, the two MA recruitment sites were combined and estimation models tested in the AA recruitment sample (Los Angeles, California; N = 495). Estimated and empiric SI were correlated in the SA (r2 = 0.77) and AA (r2 = 0.74) testing datasets. Further, estimated and empiric SI were consistently associated with BMI, low-density lipoprotein cholesterol (LDL), and triglycerides. We applied similar approaches to estimate HOMA-IR with similar results.

CONCLUSIONS

We have developed a method for estimating insulin resistance with metabolomics data that has the potential for application to a wide range of biomedical studies and conditions.

The Novel Peptide Chm-273s Has Therapeutic Potential for Metabolic Disorders: Evidence from In Vitro Studies and High-Sucrose Diet and High-Fat Diet Rodent Models

The aim of this study was to develop a novel peptide potentially applicable for the treatment of metabolic conditions, such as obesity and type 2 diabetes (T2D). We identified CHM-273S from the list of peptides from milk hydrolysate obtained by HPLC/MS-MS. In vitro analysis of primary murine fibroblasts indicated the potential of CHM-273S to upregulate IRS2 mRNA expression. CHM-273S showed a prominent anorexigenic effect in mice with the induction of a key mechanism of leptin signaling via STAT3 in the hypothalamus as a possible effector. In the animal model of metabolic disease, CHM-273S alleviated glucose intolerance and insulin resistance, and induced phosphorylation of Akt at Ser473 and Thr308 in the hepatocytes of high-sucrose diet-fed rats. In a murine model of T2D, CHM-273S mitigated high-fat diet-induced hyperglycemia and insulin resistance and improved low-grade inflammation by diminishing serum TNFα. Mice treated with chronic CHM-273S had a significant reduction in body weight, with a lower visceral fat pad weight and narrow adipocytes. The effects of the peptide administration were comparable to those of metformin. We show the potential of CHM-273S to alleviate diet-induced metabolic alterations in rodents, substantiating its further development as a therapeutic for obesity, T2D, and other metabolic conditions.

Analysis of insulin resistance using the non-linear homeostatic model assessment index in overweight canines

Background and Aim:

Diabetes mellitus is a carbohydrate metabolism disorder produced mainly by a deficit in insulin production or insulin resistance. The homeostatic model assessment (HOMA) is a broad method for estimating insulin resistance and β-cell function. This study aimed to evaluate the stages of insulin resistance using non-linear HOMA index analysis in normoglycemic normal weight and obese canines.

Materials and Methods:

Insulin resistance was evaluated using the mathematical HOMA non-linear model in canines with different body and glycemic conditions. Forty canines were studied, including 20 normoglycemic normal weight canines and 20 normoglycemic obese canines. Chi-square statistical test was applied, in which the body condition and HOMA non-linear index were evaluated. The Spearman correlation test was conducted to evaluate the glycemic and insulin variables in both types of canines.

Results:

The Spearman correlation presented a correlation between increased blood glucose levels and insulin in obese canines, with a correlation of 0.79, while no significant changes in insulin were found in normal weight canines with different blood glucose levels, with a correlation of −0.11. The analysis of the non-linear HOMA index showed significant differences between non-linear HOMA insulin resistance in normal weight and obese canines, with a Chi-square statistic of 16.9424 and p = 0.000039. Canine with increased HOMA 2 showed higher levels of insulin with increasing blood glucose compared to those with normal HOMA 2.

Conclusion:

The HOMA 2 is a marker for evaluating increased insulin resistance in obese dogs and can be used to determine patients at risk for glycemic alterations.

Associations between adherence to the dietary approaches to stop hypertension (DASH) diet and six glucose homeostasis traits in the Microbiome and Insulin Longitudinal Evaluation Study (MILES)

BACKGROUND AND AIMS

The DASH diet conveys protection against type 2 diabetes mellitus (T2D) Via plant-based and non-plant-based recommendations. Research has not identified which glucose homeostasis pathways are improved. We examined associations between adherence to a DASH diet and six glucose homeostasis traits, probing whether associations could be attributed to the plant-based (DASH-P) and/or non-plant based (DASH-NP) components.

METHODS AND RESULTS

We included data from 295 adults without T2D (age 59.3 ± 9.00 years; 63.46% non-Hispanic White and 36.54% African American, self-reported race ancestry) participating in the Microbiome and Insulin Longitudinal Evaluation Study (MILES). An oral glucose tolerance test (OGTT) yielded fasting plasma glucose, insulin, C-peptide, and insulin secretion, sensitivity, and disposition index. Habitual dietary intake was assessed by food frequency questionnaire (FFQ). Associations between DASH components and glucose homeostasis traits were examined, controlling for demographics, body mass index (BMI), physical activity, and energy intake. For significant associations, the models were repeated with scores for DASH-P and DASH-NP as predictors in the same model. DASH and DASH-P scores were inversely associated with fasting plasma glucose (DASH:β = -0.036 ± 0.012,P = 0.005; DASH-P: β = -0.04 ± 0.017,P = 0.002), and positively associated with insulin sensitivity (DASH:β = 0.022 ± 0.012,P = 0.042; DASH-P: = 0.036 ± 0.015,P = 0.014). The DASH score was also associated with disposition index (β = 0.026 ± 0.013,P = 0.038), but this association did not reach significance with DASH-P (β = 0.035 ± 0.018,P = 0.051). No associations were observed with DASH-NP score (all P > 0.05).

CONCLUSIONS

DASH diet is associated with improvement in specific glucose homeostasis traits, likely arising from increased plant-based foods. Such research may help tailor future dietary advice to specific metabolic risk, and to food groups most effective at improving these.

Canine Geriatric Syndrome: A Framework for Advancing Research in Veterinary Geroscience

Biological aging is the single most important risk factor for disease, disability, and ultimately death in geriatric dogs. The effects of aging in companion dogs also impose significant financial and psychological burdens on their human caregivers. The underlying physiologic processes of canine aging may be occult, or early signs of aging may be ignored because of the misconception that biological aging is natural and therefore inevitable. The ability to detect, quantify, and mitigate the deleterious processes of canine aging would greatly enhance veterinary preventative medicine and animal welfare. In this paper we propose a new conceptual framework for aging in dogs, the Canine Geriatric Syndrome (CGS). CGS consists of the multiple, interrelated physical, functional, behavioral, and metabolic changes that characterize canine aging as well as the resulting clinical manifestations, including frailty, diminished quality of life, and age-associated disease. We also identify potential key components of a CGS assessment tool, a clinical instrument that would enable veterinarians to diagnose CGS and would facilitate the development and testing of interventions to prolong healthspan and lifespan in dogs by directly targeting the biological mechanisms of aging. There are many gaps in our knowledge of the mechanisms and phenotype of aging in dogs that must be bridged before a CGS assessment tool can be deployed. The conceptual framework of CGS should facilitate identifying these gaps and should stimulate research to better characterize the processes and effects of aging in dogs and to identify the most promising preventative strategies to target these.

Is methylprednisolone acetate-related insulin resistance preventable in cats?

Methylprednisolone acetate (MPA) is often prescribed to cats despite being recognized eventually as diabetogenic. To assess MPA-related insulin resistance and evaluate the efficacy of metformin or an obesity and diabetes mellitus (O&D) adjuvant diet as protective factors, a randomized clinical trial was conducted with 28 owned cats undergoing glucocorticoid therapy. A single MPA dose of 20 mg intramuscularly was administered to each cat. Controls (n=10) received only MPA. In the diet group (n=9), replacement of their habitual diet by ad-libitum feeding of a feline commercial O&D diet (Equilíbrio O&D, Total Alimentos ADM) was made. In the metformin group (n=9), metformin chlorhydrate 25mg/cat PO/q24h was administered for 30 days. All patients were clinically evaluated at baseline (T0), day 15 (T15), and day 30 (T30) and blood draw for complete blood count, serum biochemistry, and determination of insulin concentrations. Fasting Insulin Sensitivity Index (SI), Amended Insulin to Glucose Ratio (AIGR), Homeostatic Model Assessment of Insulin Resistance (HOMA-IR), and Homeostatic Model Assessment of beta-cell function (HOMA-B) were calculated based on fasting glycemia and insulinemia. All groups showed significantly higher levels (p < 0.05) of neutrophils, albumin, glucose, cholesterol, triglycerides, and serum insulin at T15. Patients in the metformin group showed also higher SI, AIGR, and HOMA-IR results at T15. Also, at T15, reduced levels (p < 0.05) of eosinophils, lymphocytes, and creatinine were documented in all groups. An MPA single dose induced changes in insulin sensitivity in cats; however, neither metformin nor O&D feeding used in this study was effective as protective factors against MPA-related insulin resistance.

A preliminary evaluation of the circulating leptin/adiponectin ratio in dogs with pituitary-dependent hyperadrenocorticism and concurrent diabetes mellitus

Leptin and adiponectin are thought to modulate insulin sensitivity and pancreatic β-cell function, but there is limited information regarding the adipokine status of hyperglycemic dogs with hyperadrenocorticism. This study aimed to determine whether alterations in the leptin/adiponectin ratio, insulin sensitivity, and/or pancreatic β-cell function are associated with diabetes mellitus (DM) in dogs with pituitary-dependent hyperadrenocorticism (PDH). A total of 48 client-owned dogs were included in this prospective observational study: 20 dogs with PDH (10 normoglycemic and 10 with DM), 15 dogs with DM, and 13 healthy dogs. The serum concentrations of leptin, adiponectin, resistin, interleukin (IL)-1β, IL-6, IL-10, IL-18, and tumor necrosis factor (TNF)-α were measured, and homeostatic model assessment indices (HOMAs) were calculated and compared among the groups. Serum leptin was significantly higher in PDH dogs with and without DM than in healthy and DM dogs, and it was lower in DM dogs than in PDH dogs without DM. Serum adiponectin was significantly lower in PDH dogs with DM than in healthy and PDH dogs, and it was significantly lower in DM dogs than in healthy dogs. Serum IL-10 was significantly higher in PDH dogs with DM than in healthy and PDH dogs without DM. The leptin/adiponectin ratio was significantly higher in PDH dogs with DM than in normoglycemic PDH dogs. Serum IL-6 concentrations were significantly higher in DM dogs than in healthy dogs. Serum IL-1β concentration was significantly higher in DM dogs than in healthy dogs and PDH dogs with DM and without DM. Serum TNF-α and IL-18 concentrations were not different among groups. The HOMA_{β-cell function} was significantly lower in PDH dogs with DM than in normoglycemic PDH dogs, while HOMA_{insulin sensitivity} was significantly lower in PDH dogs with DM than in healthy dogs. These results suggest that adipokine dysregulation, a reduction in insulin sensitivity, and a further impairment in pancreatic β-cell function might predispose PDH dogs to DM. Further longitudinal study will be necessary to confirm this result.

Chronic mirabegron treatment increases human brown fat, HDL cholesterol, and insulin sensitivity

BACKGROUNDMirabegron is a β3-adrenergic receptor (β3-AR) agonist approved only for the treatment of overactive bladder. Encouraging preclinical results suggest that β3-AR agonists could also improve obesity-related metabolic disease by increasing brown adipose tissue (BAT) thermogenesis, white adipose tissue (WAT) lipolysis, and insulin sensitivity.METHODSWe treated 14 healthy women of diverse ethnicities (27.5 ± 1.1 years of age, BMI of 25.4 ± 1.2 kg/m2) with 100 mg mirabegron (Myrbetriq extended-release tablet, Astellas Pharma) for 4 weeks in an open-label study. The primary endpoint was the change in BAT metabolic activity as measured by [18F]-2-fluoro-d-2-deoxy-d-glucose (18F-FDG) PET/CT. Secondary endpoints included resting energy expenditure (REE), plasma metabolites, and glucose and insulin metabolism as assessed by a frequently sampled intravenous glucose tolerance test.RESULTSChronic mirabegron therapy increased BAT metabolic activity. Whole-body REE was higher, without changes in body weight or composition. Additionally, there were elevations in plasma levels of the beneficial lipoprotein biomarkers HDL and ApoA1, as well as total bile acids. Adiponectin, a WAT-derived hormone that has antidiabetic and antiinflammatory capabilities, increased with acute treatment and was 35% higher upon completion of the study. Finally, an intravenous glucose tolerance test revealed higher insulin sensitivity, glucose effectiveness, and insulin secretion.CONCLUSIONThese findings indicate that human BAT metabolic activity can be increased after chronic pharmacological stimulation with mirabegron and support the investigation of β3-AR agonists as a treatment for metabolic disease.TRIAL REGISTRATIONClinicaltrials.gov NCT03049462.FUNDINGThis work was supported by grants from the Intramural Research Program of the NIDDK, NIH (DK075112, DK075116, DK071013, and DK071014).

Relationships Between Gut Microbiota, Metabolome, Body Weight, and Glucose Homeostasis of Obese Dogs Fed with Diets Differing in Prebiotic and Protein Content

Obesity is a major issue in pets and nutritional strategies need to be developed, like promoting greater protein and fiber intake. This study aimed to evaluate the effects of dietary protein levels and prebiotic supplementation on the glucose metabolism and relationships between the gut, microbiota, metabolome, and phenotype of obese dogs. Six obese Beagle dogs received a diet containing 25.6% or 36.9% crude protein, with or without 1% short-chain fructo-oligosaccharide (scFOS) or oligofructose (OF), in a Latin-square study design. Fecal and blood samples were collected for metabolite analysis, untargeted metabolomics, and 16S rRNA amplicon sequencing. A multi-block analysis was performed to build a correlation network to identify relationships between fecal microbiota, metabolome, and phenotypic variables. Diets did not affect energy homeostasis, but scFOS supplementation modulated fecal microbiota composition and induced significant changes of the fecal metabolome. Bile acids and several amino acids were related to glucose homeostasis while specific bacteria gathered in metavariables had a high number of links with phenotypic and metabolomic parameters. It also suggested that fecal aminoadipate and hippurate act as potential markers of glucose homeostasis. This preliminary study provides new insights into the relationships between the gut microbiota, the metabolome, and several phenotypic markers involved in obesity and associated metabolic dysfunctions.

Metabolic and Immunological Effects of Intermittent Fasting on a Ketogenic Diet Containing Medium-Chain Triglycerides in Healthy Dogs

In several species, intermittent fasting (IF) has been shown to have beneficial effects, including delayed aging, increased lifespan, increased insulin sensitivity, reduced ischemic tissue damage, delayed onset of neurodegenerative disease and improved neuronal repair following injury. However, the metabolic and immunological effects of IF have not been well-established in dogs. The aim of this study was to examine the effects of a 48 h IF regimen using a low fat and a high fat diet in healthy dogs by quantifying the metabolic, hormonal, and immunological changes. We hypothesized that IF dogs would have higher blood ketone and ghrelin concentrations, lower blood leptin, insulin and glucose concentrations, and signs of immunosuppression compared to dogs eating daily. Ten healthy adult dogs were randomized into three group and underwent three feeding regimes in a 3 × 3 Latin square design: twice a day feeding on a low fat (23% energy from fat; LF) diet, 48 h fasting on a low fat diet, and 48 h fasting on a high fat enriched with medium-chain triglycerides (68% energy from fat; HF) diet. Body weight, food intake, activity, blood glucose, β-hydroxybutyrate, leptin, ghrelin, and insulin were measured. Lymphocyte proliferation and neutrophil/macrophage phagocytosis and respiratory burst were measured as markers of immune function. Nuclear magnetic resonance spectroscopy was used to relatively quantify plasma metabolites. When the dogs were IF on a HF diet, they had the highest concentration of blood ketones (mean 0.061 mmol/L, SD 0.024), whereas they had the lowest concentration (mean 0.018 mmol/L, SD 0.004) when fed daily. Blood glucose and insulin concentrations were lower in IF dogs on a HF diet compared to daily feeding or IF on a LF diet. There was an increase in plasma β-hydroxybutyrate concentrations, and a reduction in glucose and insulin concentrations when dogs were IF on a HF diet. There was only a decline in the immune parameters studied when the dogs were IF on a LF diet, which was not seen when on the HF diet. The results of this study indicate the potential of IF to be further investigated as a potential beneficial feeding regime for dogs.

A novel measure of glucose homeostasis (or loss thereof) comprising the joint dynamics of glucose, insulin, glucagon, and cortisol

Quantification of disturbances in glucose-insulin homeostasis has been the cornerstone of appraising insulin resistance and detecting early-stage diabetes. Metabolic homeostasis arises from feedback and feed-forward interactions among (at least) all four of glucose, insulin, glucagon, and cortisol. Quantifying such tetrapartite interactions in the fasting (endogenously regulated) state overnight could elucidate very early regulatory disruption. In the present study, healthy subjects without diabetes (ND; n = 20) and patients with Type 2 diabetes (T2D; n = 21) were investigated by repeated overnight blood sampling of all four of glucose, insulin, glucagon, and cortisol concentrations. To obviate confounding by hormone-specific disappearance rates, analyses were performed at the level of production (glucose) or secretion (insulin, glucagon, and cortisol) rates estimated by regularized deconvolution analysis. Then, a novel method for quantifying the loss of homeostasis among glucose, insulin, and glucagon (and, when available, cortisol) secretion patterns was developed. Potential early stage prediabetic candidates were identified. The new methodology avoids many of the difficulties encountered in the conventional estimation of insulin-glucose sensitivity or resistance, while incorporating the dynamics of the key coregulators under fasting conditions.

Circulating Sphingolipids, Insulin, HOMA-IR, and HOMA-B: The Strong Heart Family Study

Experimental studies suggest ceramides may play a role in insulin resistance. However, the relationships of circulating ceramides and related sphingolipids with plasma insulin have been underexplored in humans. We measured 15 ceramide and sphingomyelin species in fasting baseline samples from the Strong Heart Family Study (SHFS), a prospective cohort of American Indians. We examined sphingolipid associations with both baseline and follow-up measures of plasma insulin, HOMA of insulin resistance (HOMA-IR), and HOMA of β-cell function (HOMA-B) after adjustment for risk factors. Among the 2,086 participants without diabetes, higher levels of plasma ceramides carrying the fatty acids 16:0 (16 carbons, 0 double bond), 18:0, 20:0, or 22:0 were associated with higher plasma insulin and higher HOMA-IR at baseline and at follow-up an average of 5.4 years later. For example, a twofold higher baseline concentration of ceramide 16:0 was associated with 14% higher baseline insulin (P < 0.0001). Associations between sphingomyelin species carrying 18:0, 20:0, 22:0, or 24:0 and insulin were modified by BMI (P < 0.003): higher levels were associated with lower fasting insulin, HOMA-IR, and HOMA-B among those with normal BMI. Our study suggests lowering circulating ceramides might be a target in prediabetes and targeting circulating sphingomyelins should take into account BMI.

Homeostasis Model Assessment of Insulin Resistance and Survival in Patients With Diabetes and Acute Coronary Syndrome

OBJECTIVE

Insulin resistance has been linked to development and progression of atherosclerosis and is present in most patients with type 2 diabetes. Whether the degree of insulin resistance predicts adverse outcomes in patients with type 2 diabetes and acute coronary syndrome (ACS) is uncertain.

DESIGN

The Effect of Aleglitazar on Cardiovascular Outcomes after Acute Coronary Syndrome in Patients with Type 2 Diabetes Mellitus trial compared the peroxisome proliferator-activated receptor-α/γ agonist aleglitazar with placebo in patients with type 2 diabetes and recent ACS. In participants not treated with insulin, we determined whether baseline homeostasis model assessment of insulin resistance (HOMA-IR; n = 4303) or the change in HOMA-IR on assigned study treatment (n = 3568) was related to the risk of death or major adverse cardiovascular events (cardiovascular death, myocardial infarction, and stroke) in unadjusted and adjusted models. Because an inverse association of HOMA-IR with N-terminal pro-B-type natriuretic peptide (NT-proBNP) has been described, we specifically examined effects of adjustment for the latter.

RESULTS

In unadjusted analysis, twofold higher baseline HOMA-IR was associated with lower risk of death [hazard ratio (HR): 0.79, 95% CI: 0.68 to 0.91, P = 0.002]. Adjustment for 24 standard demographic and clinical variables had minimal effect on this association. However, after further adjustment for NT-proBNP, the association of HOMA-IR with death was no longer present (adjusted HR: 0.99, 95% CI: 0.83 to 1.19, P = 0.94). Baseline HOMA-IR was not associated with major adverse cardiovascular events, nor was the change in HOMA-IR on study treatment associated with death or major adverse cardiovascular events.

CONCLUSIONS

After accounting for levels of NT-proBNP, insulin resistance assessed by HOMA-IR is not related to the risk of death or major adverse cardiovascular events in patients with type 2 diabetes and ACS.

Association between site-specific bone mineral density and glucose homeostasis and anthropometric traits in healthy men and women

OBJECTIVE

Patients with type 2 diabetes mellitus have an increased risk of fracture despite normal or increased bone mineral density (BMD). Studies on the relationship of glucose homeostasis with BMD phenotypes have been inconclusive because distinguishing the roles of insulin resistance and hyperglycaemia in bone remodelling is challenging. In this study, we sought to define the relationship of site-specific BMD with glucose homeostasis traits and anthropometric traits.

DESIGN/PATIENTS/MEASUREMENTS

In a cross-sectional study, we examined 787 subjects from the Mexican-American Coronary Artery Disease (MACAD) cohort who had undergone euglycaemic-hyperinsulinaemic clamps, oral glucose tolerance testing and dual X-ray absorptiometry. Glucose homeostasis traits included insulinogenic index (IGI30), insulin sensitivity (M value), insulin clearance (MCRI), fasting insulin, fasting glucose and 2-hour glucose. Univariate and multivariate analyses were performed to assess the association of glucose homeostasis and anthropometric traits with site-specific BMD.

RESULTS

Two-hour glucose was negatively associated with arm BMD in women, which remained significant in multivariate analysis (β = -.15, P = .0015). Positive correlations between fasting insulin and BMD at weight-bearing sites, including pelvis (β = .22, P < .0001) and legs (β = .17, P = .001) in women and pelvis (β = .33, P < .0001) in men, lost significance after multivariate adjustment. Lean mass exhibited strong independent positive associations with BMD at multiple sites in both sexes.

CONCLUSION

Our findings suggest that (i) anabolic effects of insulin might work via mechanical loading from lean mass; (ii) a direct negative effect of increasing glucose might be more prominent at cortical-bone-rich sites in women; and (iii) lean mass is a strong positive predictor of bone mass.

Physiologic Interpretation of GWAS Signals for Type 2 Diabetes

This chapter reviews both statistical and physiologic issues related to the pathophysiologic effects of genetic variation in the context of type 2 diabetes. The goal is to review current methodologies used to analyze disease-related quantitative traits for those who do not have extensive quantitative and physiologic background, as an attempt to bridge that gap. We leverage mathematical modeling to illustrate the strengths and weaknesses of different approaches and attempt to reinforce with real data analysis. Topics reviewed include phenotype selection, phenotype specificity, multiple variant analysis via the genetic risk score, and consideration of multiple disease-related phenotypes. Type 2 diabetes is used as the example, not only because of the extensive existing knowledge at the genetic, physiologic, clinical, and epidemiologic levels, but also because type 2 diabetes has been at the forefront of complex disease genetics, with many examples to draw from.

The Effect of Anthocyanin-Rich Purple Vegetable Diets on Metabolic Syndrome in Obese Zucker Rats

Consumption of highly colored fruits and vegetables rich in anthocyanins has been associated with numerous health benefits. Purple carrots (PC) and purple potatoes (PP) have higher anthocyanin concentrations and higher biological activities compared with less pigmented cultivars. We hypothesized that substitution of the majority of carbohydrate in a high fat diet with PP or PC, for 8 weeks, would improve insulin resistance and hypertension, major components of metabolic syndrome, compared with orange carrots (OC), white potatoes (WP) or a control, high fat, sucrose-rich diet (HFD) in obese Zucker rats. After 8 weeks of feeding, intraperitoneal glucose tolerance test, intraperitoneal insulin tolerance test (ipITT), and invasive hemodynamic tests were performed. The PP group had better glucose tolerance compared with the WP and the HFD groups and higher insulin sensitivity as measured by the ipITT and homeostatic model assessment of insulin resistance (P = .018) compared with the HFD without having any effect on blood pressure. The PC reduced left ventricular pressure compared with both the HFD (P = .01) and the OC (P = .049) groups and reduced systolic and diastolic blood pressures compared with the HFD group (P = .01 and <.0001, respectively) without having any effect on glucose homeostasis. The PC animals consumed more and were more obese than other groups, possibly obscuring any benefit of this vegetable on glucose tolerance. The bioactives in the vegetables responsible for blood pressure and glucose homeostasis could be different, and their effects could be independent of each other. The specific bioactives of each vegetable and their molecular targets remain to be identified. Nonetheless, incorporation of purple vegetables in functional food products may provide metabolic/cardiovascular benefits in the background of a high-fat diet that promotes obesity.

Immunometabolic parameters in overweight dogs during weight loss with or without an exercise program

The influence of physical activity on metabolic health in overweight dogs is unknown. This study was conducted to evaluate biomarkers of immunometabolic health in relation to changes in physical activity and adiposity. Client-owned overweight dogs participated in a 12-wk intervention based on caloric restriction combined with a training program (fitness and diet [FD] group, n = 8), or caloric restriction alone (diet-only [DO] group, n = 8). Physical activity was monitored by accelerometry. All dogs were fed the same diet and achieved similar weight loss. Fasting blood samples were collected before and after 6- and 12-wk intervention. Insulin resistance was evaluated from plasma insulin and C-peptide as well as homeostasis model assessment. Inflammation and dyslipidemia were evaluated from circulating leptin, adiponectin, C-reactive protein (CRP), monocyte chemoattractant factor-1 (MCP-1), interleukin-8 (IL-8), and cholesterol. Accelerometer counts in both groups were high compared with previous reports of physical activity in overweight dogs. No difference in blood parameters was evident between groups, evaluated by linear mixed-effects model (P > 0.05). Within the groups, the following changes were significant by t-test (P < 0.05): leptin decreased in both groups. Within the FD group, IL-8, MCP-1, and CRP decreased at 6 wk and IL-8 and cholesterol at 12 wk. Within the DO group, C-peptide and HOMA decreased at 6 wk and C-peptide at 12 wk. We conclude that, for both groups, weight loss resulted in minor indications of improved immunometabolic health, whereas this level of physical activity did not add further benefits.

Renal Denervation Reverses Hepatic Insulin Resistance Induced by High-Fat Diet

Activation of the sympathetic nervous system (SNS) constitutes a putative mechanism of obesity-induced insulin resistance. Thus, we hypothesized that inhibiting the SNS by using renal denervation (RDN) will improve insulin sensitivity (S_I) in a nonhypertensive obese canine model. S_I was measured using euglycemic-hyperinsulinemic clamp (EGC), before (week 0 [w0]) and after 6 weeks of high-fat diet (w6-HFD) feeding and after either RDN (HFD + RDN) or sham surgery (HFD + sham). As expected, HFD induced insulin resistance in the liver (sham 2.5 ± 0.6 vs. 0.7 ± 0.6 × 10^-4 dL ⋅ kg^-1 ⋅ min^-1 ⋅ pmol/L^-1 at w0 vs. w6-HFD [P < 0.05], respectively; HFD + RDN 1.6 ± 0.3 vs. 0.5 ± 0.3 × 10^-4 dL ⋅ kg^-1 ⋅ min^-1 ⋅ pmol/L^-1 at w0 vs. w6-HFD [P < 0.001], respectively). In sham animals, this insulin resistance persisted, yet RDN completely normalized hepatic S_I in HFD-fed animals (1.8 ± 0.3 × 10^-4 dL ⋅ kg^-1 ⋅ min^-1 ⋅ pmol/L^-1 at HFD + RDN [P < 0.001] vs. w6-HFD, [P not significant] vs. w0) by reducing hepatic gluconeogenic genes, including G6Pase, PEPCK, and FOXO1. The data suggest that RDN downregulated hepatic gluconeogenesis primarily by upregulating liver X receptor α through the natriuretic peptide pathway. In conclusion, bilateral RDN completely normalizes hepatic S_I in obese canines. These preclinical data implicate a novel mechanistic role for the renal nerves in the regulation of insulin action specifically at the level of the liver and show that the renal nerves constitute a new therapeutic target to counteract insulin resistance.

Scientific Statement on the Diagnostic Criteria, Epidemiology, Pathophysiology, and Molecular Genetics of Polycystic Ovary Syndrome

Polycystic ovary syndrome (PCOS) is a heterogeneous and complex disorder that has both adverse reproductive and metabolic implications for affected women. However, there is generally poor understanding of its etiology. Varying expert-based diagnostic criteria utilize some combination of oligo-ovulation, hyperandrogenism, and the presence of polycystic ovaries. Criteria that require hyperandrogenism tend to identify a more severe reproductive and metabolic phenotype. The phenotype can vary by race and ethnicity, is difficult to define in the perimenarchal and perimenopausal period, and is exacerbated by obesity. The pathophysiology involves abnormal gonadotropin secretion from a reduced hypothalamic feedback response to circulating sex steroids, altered ovarian morphology and functional changes, and disordered insulin action in a variety of target tissues. PCOS clusters in families and both female and male relatives can show stigmata of the syndrome, including metabolic abnormalities. Genome-wide association studies have identified a number of candidate regions, although their role in contributing to PCOS is still largely unknown.

Early Clinical Detection of Pharmacologic Response in Insulin Action in a Nondiabetic Insulin-Resistant Population

Background

Insulin resistance heightens the risk for type 2 diabetes mellitus and cardiovascular disease. Amelioration of insulin resistance may reduce this risk. The thiazolidinedone class of insulin sensitizers improves insulin action in individuals with insulin-resistant diabetes and nondiabetic individuals. However, there are few reports on the time of onset of such effects independent of reversal of glucotoxicity.

Objective

The goal of our study was to test whether the thiazolidinedione pioglitazone has prominent early metabolic effects that can be detected in an obese, nondiabetic, insulin-resistant population.

Methods

We conducted a randomized, double-blind, placebo-controlled, parallel-group trial in men with nondiabetic insulin resistance using a hyperinsulinemic euglycemic clamp technique (at low and high doses of insulin at 10 and 40 mU/m²/min, respectively). The patients were given 30 mg daily oral pioglitazone or placebo for 28 days. Patients underwent a baseline clamp before initiation of treatment, and again at 14 and 28 days of treatment.

Results

Compared with placebo, under high-dose hyperinsulinemia, pioglitazone led to significant increases in glucose disposal rates (GDR) of 1.29 mg/kg/min (90% CI, 0.43–2.15; 39%; P=0.008) that were detectable at 2 weeks of treatment and persisted at 4 weeks of treatment. Under low-dose hyperinsulinemia, significant increases in GDR of 0.40 mg/kg/min (90% CI, 0.17–0.62; 95%; P=0.003) were observed at 4 weeks of treatment. These responses were accompanied by robust suppression of free fatty acids under hyperinsulinemic conditions, and by significant increases in circulating basal total adiponectin at 2 and 4 weeks of treatment.

Conclusions

Significant changes in insulin action across multiple insulin-sensitive tissues can be detected within 2 weeks of initiation of insulin-sensitizing therapy with pioglitazone in obese patients with nondiabetic insulin resistance. ClinicalTrials.gov identifier: NCT01115712.

Insulin secretion and sensitivity in healthy adults with low vitamin D are not affected by high-dose ergocalciferol administration: a randomized controlled trial

BACKGROUND

Epidemiologic data suggest that low serum 25-hydroxyvitamin D [25(OH)D] increases insulin resistance and the risk of type 2 diabetes. Few interventional trials have assessed the effect of vitamin D on insulin metabolism, and published results are discordant.

OBJECTIVE

The goal of this study was to perform a detailed assessment of the effect of ergocalciferol administration on glucose and insulin metabolism in healthy people with low total 25(OH)D(total).

DESIGN

This was a 12-wk, double-blinded, randomized controlled trial. We enrolled 90 healthy volunteers aged 18-45 y with serum 25(OH)D ≤20 ng/mL (by immunoassay) and administered 50,000 IU ergocalciferol/wk or placebo for 12 wk. Primary endpoints were change in first-phase insulin response and insulin sensitivity as measured by intravenous glucose tolerance test. Secondary endpoints included change in homeostasis model assessment of insulin resistance; fasting glucose, insulin, and lipids; body mass index (BMI); and blood pressure.

RESULTS

On-study 25(OH)D(total) was assessed by liquid chromatography-tandem mass spectrometry. In the treated group, 25(OH)D(total) rose from 18 ± 7 to 43 ± 12 ng/mL (P < 0.001) with no change in the placebo group. Despite this increase, at 12 wk, there were no between-group differences in either insulin response or insulin sensitivity; nor were there differences in any measured secondary endpoints. There was no evidence of effect modification by sex, race, glucose tolerance status, baseline 25(OH)D(total), or BMI.

CONCLUSION

In healthy persons with low 25(OH)D(total), ergocalciferol administration for 12 wk normalizes 25(OH)D(total) but does not improve insulin secretion, insulin sensitivity, or other markers of metabolic health.

High-fat diet-induced insulin resistance does not increase plasma anandamide levels or potentiate anandamide insulinotropic effect in isolated canine islets

Background

Obesity has been associated with elevated plasma anandamide levels. In addition, anandamide has been shown to stimulate insulin secretion in vitro, suggesting that anandamide might be linked to hyperinsulinemia.

Objective

To determine whether high-fat diet-induced insulin resistance increases anandamide levels and potentiates the insulinotropic effect of anandamide in isolated pancreatic islets.

Design and Methods

Dogs were fed a high-fat diet (n = 9) for 22 weeks. Abdominal fat depot was quantified by MRI. Insulin sensitivity was assessed by the euglycemic-hyperinsulinemic clamp. Fasting plasma endocannabinoid levels were analyzed by liquid chromatography-mass spectrometry. All metabolic assessments were performed before and after fat diet regimen. At the end of the study, pancreatic islets were isolated prior to euthanasia to test the in vitro effect of anandamide on islet hormones. mRNA expression of cannabinoid receptors was determined in intact islets. The findings in vitro were compared with those from animals fed a control diet (n = 7).

Results

Prolonged fat feeding increased abdominal fat content by 81.3±21.6% (mean±S.E.M, P<0.01). In vivo insulin sensitivity decreased by 31.3±12.1% (P<0.05), concomitant with a decrease in plasma 2-arachidonoyl glycerol (from 39.1±5.2 to 15.7±2.0 nmol/L) but not anandamide, oleoyl ethanolamide, linoleoyl ethanolamide, or palmitoyl ethanolamide. In control-diet animals (body weight: 28.8±1.0 kg), islets incubated with anandamide had a higher basal and glucose-stimulated insulin secretion as compared with no treatment. Islets from fat-fed animals (34.5±1.3 kg; P<0.05 versus control) did not exhibit further potentiation of anandamide-induced insulin secretion as compared with control-diet animals. Glucagon but not somatostatin secretion in vitro was also increased in response to anandamide, but there was no difference between groups (P = 0.705). No differences in gene expression of CB1R or CB2R between groups were found.

Conclusions

In canines, high-fat diet-induced insulin resistance does not alter plasma anandamide levels or further potentiate the insulinotropic effect of anandamide in vitro.