Wifredo Ricart

Irisin Is Expressed and Produced by Human Muscle and Adipose Tissue in Association With Obesity and Insulin Resistance

CONTEXT Recently irisin (encoded by Fndc5 gene) has been reported to stimulate browning and uncoupling protein 1 expression in sc adipose tissue of mice. OBJECTIVE The objective of the study was to investigate FNDC5 gene expression in human muscle and adipose tissue and circulating irisin according to obesity, insulin sensitivity, and type 2 diabetes. DESIGN, PATIENTS, AND MAIN OUTCOME MEASURE Adipose tissue FNDC5 gene expression and circulating irisin (ELISA) were analyzed in 2 different cohorts (n = 125 and n = 76); muscle FNDC5 expression was also evaluated in a subcohort of 34 subjects. In vitro studies in human preadipocytes and adipocytes and in induced browning of 3T3-L1 cells (by means of retinoblastoma 1 silencing) were also performed. RESULTS In both sc and visceral adipose tissue, FNDC5 gene expression decreased significantly in association with obesity and was positively associated with brown adipose tissue markers, lipogenic, insulin pathway-related, mitochondrial, and alternative macrophage gene markers and negatively associated with LEP, TNFα, and FSP27 (a known repressor of brown genes). Circulating irisin and irisin levels in adipose tissue were significantly associated with FNDC5 gene expression in adipose tissue. In muscle, the FNDC5 gene was 200-fold more expressed than in adipose tissue, and its expression was associated with body mass index, PGC1α, and other mitochondrial genes. In obese participants, FNDC5 gene expression in muscle was significantly decreased in association with type 2 diabetes. Interestingly, muscle FNDC5 gene expression was significantly associated with FNDC5 and UCP1 gene expression in visceral adipose tissue. In men, circulating irisin levels were negatively associated with obesity and insulin resistance. Irisin was secreted from human adipocytes into the media, and the induction of browning in 3T3-L1 cells led to increased secreted irisin levels. CONCLUSIONS Decreased circulating irisin concentration and FNDC5 gene expression in adipose tissue and muscle from obese and type 2 diabetic subjects suggests a loss of brown-like characteristics and a potential target for therapy.

The relationship of serum osteocalcin concentration to insulin secretion, sensitivity and disposal with hypocaloric diet and resistance training

CONTEXT Bone has recently been described as exhibiting properties of an endocrine organ by producing osteocalcin that increases insulin sensitivity and secretion in animal models. OBJECTIVE AND DESIGN We aimed to evaluate circulating osteocalcin in association with insulin sensitivity and insulin secretion in three different studies in nondiabetic subjects: one cross-sectional study in 149 men (using minimal model), and two longitudinal studies in two independent groups (one formed by 26 women, and the other by 9 men and 11 women), after a mean of 7.3 and 16.8% weight loss, and after a mean of 8.7% weight loss plus regular exercise. RESULTS In the cross-sectional study, circulating osteocalcin was associated with insulin sensitivity, mainly in lean subjects, and with insulin secretion (only in lean subjects). A mean of 16.8%, but not 7.3% weight loss, led to significant increases in circulating osteocalcin. However, a mean of 8.7% weight loss plus regular exercise led to the more pronounced effects on the serum osteocalcin concentration, which increased in parallel to reduced visceral fat mass, unchanged thigh muscle mass, and increased leg strength and force. The postintervention serum levels of osteocalcin were associated with both insulin sensitivity (r = 0.49; P = 0.03) and fasting triglycerides (r = -0.54; P = 0.01). The change in visceral fat was the parameter that best predicted the change in serum osteocalcin, once age, body mass index, and insulin sensitivity changes were controlled for (P = 0.002). CONCLUSION Circulating osteocalcin could mediate the role of bone as an endocrine organ in humans.

The TNF-alpha gene Nco I polymorphism influences the relationship among insulin resistance, percent body fat, and increased serum leptin levels.

Tumor necrosis factor-α (TNF-α), acting as a modulator of gene expression in adipocytes, is implicated in the development of insulin resistance and obesity. The aim of this study was to investigate whether the Nco I polymorphism of the TNF-a gene influences the relationship among insulin resistance, percent body fat, and serum leptin levels. A sample of 38 subjects (19 men, mean age 36.2 ± 1.9 years, BMI 28.8 ± 1.2 kg/m2, range 22.2–35.7; and 19 women, age 34.9 ± 1.4 years, BMI 28.1 ± 0.8 kg/m2, range 19–37.9) was divided into two groups on the basis of the Nco I genotype. Twenty-three subjects were (+/+) homozygotes for the presence of the Nco I restriction site that is associated with a guanine at position −308 of the TNF-a promoter. Of the other subjects, 12 were (+/−) heterozygotes and 3 (−/−) homozygotes for the absence of the restriction site, resulting from a guanine-to-adenine substitution at position −308 of the TNF-a promoter. This substitution (termed TNF-2) leads to higher rate of transcription of TNF-a than the wild-type allele TNF-1 in vitro. TNF-1 (+/+) and TNF-2 (+/− and −/−) groups of subjects were comparable in sex, age, BMI, waist-to-hip ratio, and several skinfold measurements. Basal serum insulin was greater (14.2 ± 2 vs. 9.2 ± 0.9 mlM, P = 0.041) in the TNF-2 group in the presence of comparable serum glucose concentration. The integrated area under the curve of serum insulin concentrations, measured in response to a 75-g oral glucose challenge, and the percent body fat, measured by bioelectric impedance, were significantly increased in TNF-2 subjects (226.8 ± 33 vs. 139.4 ± 17.8 mU/l, P = 0.032; 33.6 ± 2.8 vs. 24.9 ± 2%, P = 0.01). TNF-2 subjects also showed a decreased insulin sensitivity index, as determined by the frequently sampled intravenous glucose tolerance test with minimal model analysis (1.9 ± 0.4 vs. 3.05 ± 0.3 min−1 · mU−1 · 1−1 P = 0.03). These differences were more marked among women. Paralleling the known relationship between insulin and leptin levels, serum leptin concentration was clearly increased in the TNF-2 group (19.6 ± 3.4 vs. 11.1 ± 1.5 ng/ml, P = 0.03). Therefore, (+/−) heterozygotes and (−/−) homozygotes may be more susceptible to developing insulin resistance and increased percent body fat. Results of the present study suggest that TNF-αNco I polymorphism may exacerbate the alterations in leptin levels normally found among insulin-resistant subjects.

MiRNA Expression Profile of Human Subcutaneous Adipose and during Adipocyte Differentiation

Background Potential regulators of adipogenesis include microRNAs (miRNAs), small non-coding RNAs that have been recently shown related to adiposity and differentially expressed in fat depots. However, to date no study is available, to our knowledge, regarding miRNAs expression profile during human adipogenesis. Thereby, the aim of this study was to investigate whether miRNA pattern in human fat cells and subcutaneous adipose tissue is associated to obesity and co-morbidities and whether miRNA expression profile in adipocytes is linked to adipogenesis. Methodology/Principal Findings We performed a global miRNA expression microarray of 723 human and 76 viral mature miRNAs in human adipocytes during differentiation and in subcutaneous fat samples from non-obese (n = 6) and obese with (n = 9) and without (n = 13) Type-2 Diabetes Mellitus (DM-2) women. Changes in adipogenesis-related miRNAs were then validated by RT-PCR. Fifty of 799 miRNAs (6.2%) significantly differed between fat cells from lean and obese subjects. Seventy miRNAs (8.8%) were highly and significantly up or down-regulated in mature adipocytes as compared to pre-adipocytes. Otherwise, 17 of these 799 miRNAs (2.1%) were correlated with anthropometrical (BMI) and/or metabolic (fasting glucose and/or triglycerides) parameters. We identified 11 miRNAs (1.4%) significantly deregulated in subcutaneous fat from obese subjects with and without DM-2. Interestingly, most of these changes were associated with miRNAs also significantly deregulated during adipocyte differentiation. Conclusions/Significance The remarkable inverse miRNA profile revealed for human pre-adipocytes and mature adipocytes hints at a closely crosstalk between miRNAs and adipogenesis. Such candidates may represent biomarkers and therapeutic targets for obesity and obesity-related complications.

Targeting the Circulating MicroRNA Signature of Obesity

BACKGROUND Genomic studies have yielded important insights into the pathogenesis of obesity. Circulating microRNAs (miRNAs) are valuable biomarkers of systemic diseases and potential therapeutic targets. We sought to define the circulating pattern of miRNAs in obesity and examine changes after weight loss. METHODS We assessed the genomewide circulating miRNA profile cross-sectionally in 32 men and after surgery-induced weight loss in 6 morbidly obese patients. The most relevant miRNAs were cross-sectionally validated in 80 men and longitudinally in 22 patients (after surgery-induced weight loss). We evaluated the effects of diet-induced weight loss in 9 obese patients. Thirty-six circulating miRNAs were associated with anthropometric variables in the initial sample. RESULTS In the validation study, morbidly obese patients showed a marked increase of miR-140-5p, miR-142-3p (both P < 0.0001), and miR-222 (P = 0.0002) and decreased levels of miR-532-5p, miR-125b, miR-130b, miR-221, miR-15a, miR-423-5p, and miR-520c-3p (P < 0.0001 for all). Interestingly, in silico targets leukemia inhibitory factor receptor (LIFR) and transforming growth factor receptor (TGFR) of miR-140-5p, miR-142-3p, miR-15a, and miR-520c-3p circulated in association with their corresponding miRNAs. Moreover, a discriminant function of 3 miRNAs (miR-15a, miR-520c-3p, and miR-423-5p) was specific for morbid obesity, with an accuracy of 93.5%. Surgery-induced (but not diet-induced) weight loss led to a marked decrease of miR-140-5p, miR-122, miR-193a-5p, and miR-16-1 and upregulation of miR-221 and miR-199a-3p (P < 0.0001 for all). CONCLUSIONS Circulating miRNAs are deregulated in severe obesity. Weight loss-induced changes in this profile and the study of in silico targets support this observation and suggest a potential mechanistic relevance.

Serum Visfatin Increases With Progressive β-Cell Deterioration

Visfatin has shown to be increased in type 2 diabetes but to be unrelated to insulin sensitivity. We hypothesized that visfatin is associated with insulin secretion in humans. To this aim, a cross-sectional study was conducted in 118 nondiabetic men and 64 (35 men and 29 women) type 2 diabetic patients. Type 1 diabetic patients with long-standing disease (n = 58; 31 men and 27 women) were also studied. In nondiabetic subjects, circulating visfatin (enzyme immunoassay) was independently associated with insulin secretion (acute insulin response to glucose [AIRg] from intravenous glucose tolerance tests) but not with insulin sensitivity (Si) or other metabolic or anthropometric parameters, and AIRg alone explained 8% of visfatin variance (β = −0.29, P = 0.001). Circulating visfatin was increased in type 2 diabetes (mean 18 [95% CI 16–21] vs. 15 ng/ml [13–17] for type 2 diabetic and nondiabetic subjects, respectively; P = 0.017, adjusted for sex, age, and BMI), although this association was largely attenuated after accounting for HbA1c (A1C). Finally, circulating visfatin was found to be increased in patients with long-standing type 1 diabetes, even after adjusting for A1C values (37 ng/ml [34–40]; P < 0.0001, adjusted for sex, age, BMI, and A1C compared with either type 2 diabetic or nondiabetic subjects). In summary, circulating visfatin is increased with progressive β-cell deterioration. The study of the regulation and role of visfatin in diabetes merits further consideration.

Circulating omentin concentration increases after weight loss

BackgroundOmentin-1 is a novel adipokine expressed in visceral adipose tissue and negatively associated with insulin resistance and obesity. We aimed to study the effects of weight loss-induced improved insulin sensitivity on circulating omentin concentrations.MethodsCirculating omentin-1 (ELISA) concentration in association with metabolic variables was measured in 35 obese subjects (18 men, 17 women) before and after hypocaloric weight loss.ResultsBaseline circulating omentin-1 concentrations correlated negatively with BMI (r = -0.58, p < 0.001), body weight (r = -0.35, p = 0.045), fat mass (r = -0.67, p < 0.001), circulating leptin (r = -0.7, p < 0.001) and fasting insulin (r = -0.37, p = 0.03). Circulating omentin-1 concentration increased significantly after weight loss (from 44.9 ± 9.02 to 53.41 ± 8.8 ng/ml, p < 0.001). This increase in circulating omentin after weight loss was associated with improved insulin sensitivity (negatively associated with HOMA value and fasting insulin, r = -0.42, p = 0.02 and r = -0.45, p = 0.01, respectively) and decreased BMI (r = -0.54, p = 0.001).ConclusionAs previously described with adiponectin, circulating omentin-1 concentrations increase after weight loss-induced improvement of insulin sensitivity.

Profiling of Circulating MicroRNAs Reveals Common MicroRNAs Linked to Type 2 Diabetes That Change With Insulin Sensitization

OBJECTIVE This study sought to identify the profile of circulating microRNAs (miRNAs) in type 2 diabetes (T2D) and its response to changes in insulin sensitivity. RESEARCH DESIGN AND METHODS The circulating miRNA profile was assessed in a pilot study of 12 men: 6 with normal glucose tolerance (NGT) and 6 T2D patients. The association of 10 circulating miRNAs with T2D was cross-sectionally validated in an extended sample of 45 NGT vs. 48 T2D subjects (65 nonobese and 28 obese men) and longitudinally in 35 T2D patients who were recruited in a randomized, double-blinded, and placebo-controlled 3-month trial of metformin treatment. Circulating miRNAs were also measured in seven healthy volunteers before and after a 6-h hyperinsulinemic-euglycemic clamp and insulin plus intralipid/heparin infusion. RESULTS Cross-sectional studies disclosed a marked increase of miR-140-5p, miR-142-3p, and miR-222 and decreased miR-423-5p, miR-125b, miR-192, miR-195, miR-130b, miR-532-5p, and miR-126 in T2D patients. Multiple linear regression analyses revealed that miR-140-5p and miR-423-5p contributed independently to explain 49.5% (P < 0.0001) of fasting glucose variance after controlling for confounders. A discriminant function of four miRNAs (miR-140-5p, miR-423-5p, miR-195, and miR-126) was specific for T2D with an accuracy of 89.2% (P < 0.0001). Metformin (but not placebo) led to significant changes in circulating miR-192 (49.5%; P = 0.022), miR-140-5p (−15.8%; P = 0.004), and miR-222 (−47.2%; P = 0.03), in parallel to decreased fasting glucose and HbA1c. Furthermore, while insulin infusion during clamp decreased miR-222 (−62%; P = 0.002), the intralipid/heparin mixture increased circulating miR-222 (163%; P = 0.015) and miR-140-5p (67.5%; P = 0.05). CONCLUSIONS This study depicts the close association between variations in circulating miRNAs and T2D and their potential relevance in insulin sensitivity.

Adipocytokines and Insulin Resistance: The possible role of lipocalin-2, retinol binding protein-4, and adiponectin

It is well known that adipocytes and resident macrophages that have migrated to adipose tissue produce and secrete a variety of biologically active mediators (adipocytokines), which are thought to contribute to the development of insulin resistance, type 2 diabetes, and cardiovascular disease (1). The abnormal function of adipocytes may play an important role in the development of a chronic low-grade proinflammatory state associated with obesity (2). For example, adipocyte hypertrophy appears to lead to an imbalance between pro- and anti-inflammatory adipokines. The secretion of interleukin (IL)-6, IL-8, monocyte chemoattractant protein-1, and granulocyte colony–stimulating factor have been positively correlated with adipocyte size. Adipose tissue is an important inflammatory source in obesity and type 2 diabetes, not only because of cytokines produced from the adipocyte itself, but also because of infiltration by proinflammatory macrophages (3). Not only do adipocytes, but also adipose tissue macrophage numbers, increase with obesity and participate in inflammatory pathways of obese individuals. Macrophages from adipose tissue are responsible for almost all adipose tissue tumor necrosis factor (TNF)-α and significant amounts of IL-6 production. Macrophages migrating to adipose tissue in response to high-fat feeding overexpress proinflammatory cytokines. Different cytokines synthesized by adipocytes or by macrophages from adipose tissue may induce insulin resistance, such as IL-6, TNF-α, leptin, resistin, adiponectin, retinol binding protein-4 (RBP4), or lipocalin-2 (LCN2). This review focuses on the latter adipocytokines, hinting at their role in obesity-associated insulin resistance. LCN2 (or neutrophil gelatinase-associated lipocalin) is a recently identified adipokine that belongs to the superfamily of lipocalins (such as RBP4), which seems to affect glucose metabolism and insulin sensitivity (4). LCN2 protein has been implicated in diverse actions, such as apoptosis and innate immunity, and is expressed in several tissues, including neutrophils, liver, kidney, adipocytes, and macrophages (5). Lipocalins comprise a class of proteins that are …

Metformin alters the gut microbiome of individuals with treatment-naive type 2 diabetes, contributing to the therapeutic effects of the drug

Metformin is widely used in the treatment of type 2 diabetes (T2D), but its mechanism of action is poorly defined. Recent evidence implicates the gut microbiota as a site of metformin action. In a double-blind study, we randomized individuals with treatment-naive T2D to placebo or metformin for 4 months and showed that metformin had strong effects on the gut microbiome. These results were verified in a subset of the placebo group that switched to metformin 6 months after the start of the trial. Transfer of fecal samples (obtained before and 4 months after treatment) from metformin-treated donors to germ-free mice showed that glucose tolerance was improved in mice that received metformin-altered microbiota. By directly investigating metformin–microbiota interactions in a gut simulator, we showed that metformin affected pathways with common biological functions in species from two different phyla, and many of the metformin-regulated genes in these species encoded metalloproteins or metal transporters. Our findings provide support for the notion that altered gut microbiota mediates some of metformins antidiabetic effects.