Serum Myostatin is Upregulated in Obesity and Correlates with Insulin Resistance in Humans.

Obesity and type 2 diabetes mellitus have reached an epidemic level, thus novel treatment concepts need to be identified. Myostatin, a myokine known for restraining skeletal muscle growth, has been associated with the development of insulin resistance and type 2 diabetes mellitus. Yet, little is known about the regulation of myostatin in human obesity and insulin resistance. We aimed to investigate the regulation of myostatin in obesity and uncover potential associations between myostatin, metabolic markers and insulin resistance/sensitivity indices. Circulating active myostatin concentration was measured in the serum of twenty-eight severely obese non-diabetic patients compared to a sex and age matched lean and overweight control group (n=22). Insulin resistance/sensitivity was assessed in the obese group. Skeletal muscle and adipose tissue specimens from the obese group were collected during elective bariatric surgery. Adipose tissue samples from lean and overweight subjects were collected during elective abdominal surgery. Myostatin concentration was increased in obese compared to lean individuals, while myostatin adipose tissue expression did not differ. Muscle myostatin gene expression strongly correlated with expression of metabolic genes such as IRS1, PGC1α, SREBF1. Circulating myostatin concentration correlated positively with insulin resistance indices and negatively with insulin sensitivity indices. The best correlation was obtained for the oral glucose insulin sensitivity index. Our results point to an interesting correlation between myostatin and insulin resistance/sensitivity in humans, and emphasize its need for further evaluation as a pharmacological target in the prevention and treatment of obesity-associated metabolic complications.

Ultralong TE In Vivo 1 H MR Spectroscopy of Omega-3 Fatty Acids in Subcutaneous Adipose Tissue at 7 T.

BACKGROUND: Omega-3 (n-3) fatty acids (FA) play and important role in neural development and other metabolic diseases such as obesity and diabetes. The knowledge about the in vivo content and distribution of n-3 FA in human body tissues is not well established and the standard quantification of FA is invasive and costly. PURPOSE: To detect omega-3 (n-3 CH3 ) and non-omega-3 (CH3 ) methyl group resonance lines with echo times up to 1200 msec, in oils, for the assessment of n-3 FA content, and the n-3 FA fraction in adipose tissue in vivo. STUDY TYPE: Prospective technical development. POPULATION: Three oils with different n-3 FA content and 24 healthy subjects. FIELD STRENGTH/SEQUENCE: Single-voxel MR spectroscopy (SVS) with a point-resolved spectroscopy (PRESS) sequence with an echo time (TE) of 1000 msec at 7 T. ASSESSMENT: Knowledge about the J-coupling evolution of both CH3 resonances was used for the optimal detection of the n-3 CH3 resonance line at a TE of 1000 msec. The accuracy of the method in oils and in vivo was validated from a biopsy sample with gas chromatography analysis. STATISTICAL TESTS: SVS data were compared to gas chromatography with the Pearson correlation coefficient. RESULTS: T2 relaxation times in oils were assessed as follows: CH2 , 65 ± 22 msec; CH3 , 325 ± 7 msec; and n-3 CH3 , 628 ± 34 msec. The n-3 FA fractions from oil phantom experiments (n = 3) were in agreement with chromatography analysis and the comparison of in vivo obtained data with the results of chromatography analysis (n = 5) yielded a significant correlation (P = 0.029). DATA CONCLUSION: PRESS with ultralong-TE can detect and quantify the n-3 CH3 signal in vivo at 7 T. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:71-82.

Adiponectin regulates aquaglyceroporin expression in hepatic stellate cells altering their functional state.

BACKGROUND AND AIM: Obesity is a major risk factor for liver fibrosis and tightly associated with low levels of adiponectin. Adiponectin has antifibrogenic activity protecting from liver fibrosis, which is mainly driven by activated hepatic stellate cells (HSC). Aquaporins are transmembrane proteins that allow the movement of water and, in case of aquaglyceroporins (AQPs), of glycerol that is needed in quiescent HSC for lipogenesis. Expression of various AQPs in liver is altered by obesity; however, the mechanisms through which obesity influences HSCs activation and AQPs expression remain unclear. This study aimed to identify obesity-associated factors that are related to HSC AQPs expression activation and lipid storage. METHODS: Correlations between serum adipokine levels and hepatic AQPs gene expression were analyzed from a cohort of obese patients. AQP and fibrotic gene expression was determined in a HSC line (LX2) and in a hepatocyte cell line (HepG2) after stimulation with adiponectin using quantitative real-time polymerase chain reaction. RESULTS: We found that serum adiponectin significantly correlated with liver AQP3, AQP7, AQP9 gene expressions. In vitro, adiponectin induced upregulation of AQP3 gene and AQP3 protein expression in human HSCs, but not in hepatocytes, while AQP7, AQP9 remained undetectable. Accordingly, HSC stimulated with adiponectin increased glycerol uptake, lipogenic gene expression, and lipid storage while downregulating activation/fibrosis markers. CONCLUSIONS: These findings demonstrate that adiponectin is a potent inhibitor of HSC activation and induces AQPs expression. Thus, low serum levels of adiponectin could be a mechanism how obesity affects the functional state of HSC, thereby contributing to obesity-associated liver fibrosis.

Osteopontin promotes aromatase expression and estradiol production in human adipocytes.

Breast and endometrial cancer are often estrogen dependent, and their incidence and mortality are increased by obesity in postmenopausal women. Osteopontin (OPN) is a cytokine strongly upregulated in adipose tissue (AT) in obesity. OPN function is potentiated by cleavage by matrix metalloproteinases (MMP). OPN and MMPs play a role in cancer development and are prognostic markers in breast cancer progression. While induction of the estrogen-synthesizing enzyme aromatase by TNFa and IL1 has been shown in preadipocytes, an impact of OPN on aromatase expression in AT has not been investigated yet. Gene expression was determined in AT samples of 21 morbidly obese and matched non-obese subjects. Primary human adipocytes were treated with full-length OPN or MMP-cleaved OPN (cOPN). Protein and mRNA expressions were analyzed from cell lysates, or cells were subsequently supplied with testosterone to determine estradiol production and for indirect co-culture with the estrogen-dependent MCF-7 cell line. Aromatase expression strongly correlated with gene expression of OPN and various MMPs in visceral and MMPs in subcutaneous AT, but not with TNFα expression in both tissues. In vitro, cOPN more effectively than full-length OPN upregulated aromatase mRNA in adipocytes and significantly increased aromatase protein level and estradiol production, leading to increased MCF-7 growth in indirect co-culture. OPN and MMPs are upregulated in AT in obesity, and MMP-cleaved OPN is particularly effective in inducing aromatase activity in human adipocytes. Thereby, obesity-induced OPN expression in AT may contribute to estradiol production and thus to the association of obesity with estrogen-dependent cancers.

Immunological blockade of adipocyte inflammation caused by increased matrix metalloproteinase-cleaved osteopontin in obesity.

OBJECTIVE: Osteopontin (OPN) is upregulated in adipose tissue (AT) in obesity and contributes to subclinical inflammation, adipocyte dysfunction, and insulin resistance. OPN effects can be increased by cleavage by matrix metalloproteinases (MMP). This study aimed at investigating the presence of OPN cleavage products in human AT in obesity and their impact on adipocyte function and immunological blockade of these effects. METHODS: AT of severely obese and control donors was investigated for OPN and MMP expression and the presence of OPN cleavage fragments. Primary adipocytes were isolated from human donors for in vitro investigation of cleaved OPN effects. RESULTS: OPN and MMP-9 expression was highly correlated in AT from obese donors, and increased levels of cleaved OPN were detected in AT from obese individuals. The in vitro effect of OPN on adipocyte inflammation and insulin resistance was enhanced by protease cleavage, which could finally be blocked with a monoclonal antibody directed against the MMP cleavage site of OPN. CONCLUSIONS: These findings show that MMP cleavage of OPN in AT occurs in obesity, thereby enhancing OPN's inflammatory and pro-diabetic activity on adipocytes. Specifically targeting MMP-cleaved OPN opens avenues for prevention and treatment of obesity-induced type 2 diabetes.

Insulin-like growth factor 1 predicts post-load hypoglycemia following bariatric surgery: a prospective cohort study.

Postprandial hypoglycemia is a complication following gastric bypass surgery, which frequently remains undetected. Severe hypoglycemic episodes, however, put patients at risk, e.g., for syncope. A major cause of hypoglycemia following gastric bypass is hyperinsulinemic nesidioblastosis. Since pancreatic islets in nesidioblastosis overexpress insulin-like growth factor 1 (IGF-1) receptor α and administration of recombinant IGF-1 provokes hypoglycemia, our main objective was to investigate the occurrence of post-load hypoglycemia one year after bariatric surgery and its relation to pre- and post-operative IGF-1 serum concentrations. We evaluated metabolic parameters including 2 h 75 g oral glucose tolerance test (OGTT) and measured IGF-1 serum concentration in thirty-six non-diabetic patients (29 f/7 m), aged 41.3±2.0 y with a median (IQR) BMI of 30.9 kg/m2 (27.5-34.3 kg/m2), who underwent elective bariatric surgery (predominantly gastric bypass, 83%) at our hospital. Post-load hypoglycemia as defined by a 2 h glucose concentration <60 mg/dl was detected in 50% of patients. Serum insulin and C-peptide concentration during the OGTT and HOMA-IR (homeostatic model assessment-insulin resistance) were similar in hypoglycemic and euglycemic patients. Strikingly, pre- and post-operative serum IGF-1 concentrations were significantly higher in hypoglycemic patients (p = 0.012 and p = 0.007 respectively). IGF-1 serum concentration before surgery negatively correlated with 2 h glucose concentration during the OGTT (rho = -0.58, p = 0.0003). Finally, IGF-1 serum concentrations before and after surgery significantly predicted post-load hypoglycemia with odds ratios of 1.28 (95%CI:1.03-1.55, p = 0.029) and 1.18 (95%CI:1.03-1.33, p = 0.015), respectively, for each 10 ng/ml increment. IGF-1 serum concentration could be a valuable biomarker to identify patients at risk for hypoglycemia following bariatric surgery independently of a diagnostic OGTT. Thus, IGF-1 testing could help to prevent a significant complication of gastric bypass surgery.

Circulating betatrophin correlates with atherogenic lipid profiles but not with glucose and insulin levels in insulin-resistant individuals.

AIMS/HYPOTHESIS: The newly identified liver- and fat-derived hormone, betatrophin, has recently been linked to insulin resistance and pancreatic beta cell growth in mice. These preclinical findings have suggested betatrophin as a potential candidate for novel glucose-lowering treatment concepts involving beta cell regeneration. However, the role of betatrophin in human insulin resistance and type 2 diabetes is currently unknown. Hence, the aim of this study was to investigate circulating betatrophin concentrations in two distinct cohorts with insulin resistance. METHODS: Betatrophin concentrations were analysed in (1) age- and sex-matched lean (n = 20) and morbidly obese individuals (n = 19), and (2) age-, sex- and BMI-matched non-diabetic (n = 19) and type 2 diabetic individuals (n = 18). RESULTS: Betatrophin concentrations did not differ between lean and morbidly obese or between non-diabetic and type 2 diabetic participants. No association was found with variables of beta cell function and glucose homeostasis. However, betatrophin did correlate significantly with plasma atherogenic lipids including total cholesterol, LDL-cholesterol and apolipoprotein B in morbidly obese and type 2 diabetic patients but not in controls. Insulin-resistant individuals with hypercholesterolaemia (≥5.2 mmol/l) had significantly higher betatrophin concentrations than those with normal cholesterol (<5.2 mmol/l). CONCLUSIONS/INTERPRETATION: Betatrophin is a recently identified hormone, the circulating concentrations of which are unaltered in human insulin resistance but correlate significantly with atherogenic lipid profiles in high-risk cohorts with morbid obesity or type 2 diabetes. Betatrophin could therefore be a novel pathomechanistic player in dysfunctional lipid metabolism associated with high cardiovascular risk.

A protein-enriched low glycemic index diet with omega-3 polyunsaturated fatty acid supplementation exerts beneficial effects on metabolic control in type 2 diabetes.

AIMS: The current study aims to investigate practicability and effects of a combined dietary intervention with increased relative protein content supplemented with omega-3 polyunsaturated fatty acids (PUFA) on metabolic control and inflammatory parameters in a real life situation in type 2 diabetes patients. METHODS: In this observational study we advised thirty mostly obese patients with type 2 diabetes to follow a protein-enriched diet with carbohydrates of low glycemic index (low GI) and moderate fat reduction supplemented with omega-3 PUFA for 24 weeks. Primary efficacy parameter was the change in HbA1c; secondary parameters included changes in systemic inflammation (measured by ultrasensitive C-reactive protein, usCRP), body weight, waist circumference, fat mass. The study is registered at clinicaltrials.gov (NCT01474603). RESULTS: The dietary intervention significantly reduced the primary efficacy variable HbA1c from a baseline value of 63±11mmol/mol to 59±14mmol/mol (P=0.033) and 56±12mmol/mol (P=0.001) after 12 and 24 weeks, respectively. In addition, usCRP decreased significantly at 24 weeks (P=0.039). Waist circumference, an important indicator for cardiometabolic-risk and silent inflammation, decreased from baseline 116.0±14.1cm to 114.9±13.5cm (P=0.019), 114.0±14.4cm (P=0.001), and 112.7±13.4cm (P=0.049), after 3, 12 and 24 weeks, respectively. CONCLUSION: Counseling a protein enriched and low glycemic index diet supplemented with long-chain omega-3 PUFA in a real-life clinical setting improves glycemic control and also reduces waist circumference and silent inflammation in overweight or obese patients with type 2 diabetes.

Autoimmune aspects of type 2 diabetes mellitus - a mini-review.

Autoimmunity is a well-known pathogenic component in type 1 diabetes (T1DM). The assumption that the pathogenesis of type 2 diabetes (T2DM) also encompasses autoimmune aspects is recognized increasingly, based on the presence of circulating autoantibodies against ß cells, self-reactive T cells, but also on the glucose-lowering efficacy of some immunomodulatory therapies in T2DM. The identification of these autoantibodies in elderly patients with slowly progressive manifestation of diabetes led to the introduction of a distinct clinical entity termed latent autoimmune diabetes of the adult (LADA), which combines features of both T1DM and T2DM. The autoantibody cluster differs in patients with LADA from patients with T1DM, but their presence indicates steady progression towards ß-cell death and subsequent need for initiation of insulin treatment in a shorter period of time compared to autoantibody-negative T2DM patients. Autoimmune aspects in T2DM are not solely restricted to autoantibodies and thus LADA. They include the self-reactive T cells or defects in regulatory T cells (Tregs), which have been detected in autoantibody-negative T2DM patients as well. One contributor to the autoimmune activation in T2DM seems to be the chronic inflammatory state, characteristic of this disease. Upon inflammation-induced tissue destruction, cryptic 'self' antigens can trigger an autoimmune response, which in turn accelerates ß-cell death. Both innate and adaptive immune system components, specifically macrophages and self-reactive T cells, contribute to an increased secretion of inflammatory cytokines involved in inflammatory and autoimmune processes. However, the extent to which inflammation overlaps with autoimmunity is not known. Our review focuses on autoimmune involvement in T2DM, with an emphasis on LADA and the humoral immune response, on the involvement of chronic inflammation in autoimmunity, and specifically the role of B and T cells as links between inflammatory and autoimmune reactions. We will further stress the consequences of autoimmune activation for T2DM patients and present novel therapeutic approaches for T2DM management that rely on immune modulation.

Treatment with n-3 polyunsaturated fatty acids overcomes the inverse association of vitamin D deficiency with inflammation in severely obese patients: a randomized controlled trial.

UNLABELLED: Obesity affects the vitamin D status in humans. Vitamin D and long-chain n-3 polyunsaturated fatty acids (PUFA) provide benefit for the prevention of fractures and cardiovascular events, respectively, and both are involved in controlling inflammatory and immune responses. However, published epidemiological data suggest a potential interference of n-3 PUFA supplementation with vitamin D status. Therefore, we aimed to investigate in a randomized controlled clinical trial whether treatment with long chain n-3 PUFA affects vitamin D status in severely obese patients and potential interrelations of vitamin D and PUFA treatment with inflammatory parameters. Fifty-four severely obese (BMI ≥ 40 kg/m2) non-diabetic patients were treated for eight weeks with either 3.36 g/d EPA and DHA or the same amount of butter fat as control. Changes in serum 25-hydroxy-vitamin D [25(OH)D] concentrations, plasma fatty acid profiles and circulating inflammatory marker concentrations from baseline to end of treatment were assessed. At baseline 43/54 patients were vitamin D deficient (serum 25(OH)D concentration <50 nmol/l). Treatment with n-3 PUFA did not affect vitamin D status (P = 0.91). Serum 25(OH)D concentration correlated negatively with both IL-6 (P = 0.02) and hsCRP serum concentration (P = 0.03) at baseline. Strikingly, the negative correlations of 25(OH)D with IL-6 and hsCRP were lost after n-3 PUFA treatment. In conclusion, vitamin D status of severely obese patients remained unaffected by n-3 PUFA treatment. However, abrogation of the inverse association of 25(OH)D concentration with inflammatory markers indicated that n-3 PUFA treatment could compensate for some detrimental consequences of vitamin D deficiency. TRIAL REGISTRATION: ClinicalTrials.gov NCT00760760.

Impaired local production of proresolving lipid mediators in obesity and 17-HDHA as a potential treatment for obesity-associated inflammation.

Obesity-induced chronic low-grade inflammation originates from adipose tissue and is crucial for obesity-driven metabolic deterioration, including insulin resistance and type 2 diabetes. Chronic inflammation may be a consequence of a failure to actively resolve inflammation and could result from a lack of local specialized proresolving lipid mediators (SPMs), such as resolvins and protectins, which derive from the n-3 polyunsaturated fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). We assessed obesity-induced changes of n-3-derived SPMs in adipose tissue and the effects of dietary EPA/DHA thereon. Moreover, we treated obese mice with SPM precursors and investigated the effects on inflammation and metabolic dysregulation. Obesity significantly decreased DHA-derived 17-hydroxydocosahexaenoic acid (17-HDHA, resolvin D1 precursor) and protectin D1 (PD1) levels in murine adipose tissue. Dietary EPA/DHA treatment restored endogenous biosynthesis of n-3-derived lipid mediators in obesity while attenuating adipose tissue inflammation and improving insulin sensitivity. Notably, 17-HDHA treatment reduced adipose tissue expression of inflammatory cytokines, increased adiponectin expression, and improved glucose tolerance parallel to insulin sensitivity in obese mice. These findings indicate that impaired biosynthesis of certain SPM and SPM precursors, including 17-HDHA and PD1, contributes to adipose tissue inflammation in obesity and suggest 17-HDHA as a novel treatment option for obesity-associated complications.

Long-chain n-3 PUFAs reduce adipose tissue and systemic inflammation in severely obese nondiabetic patients: a randomized controlled trial.

BACKGROUND: Chronic adipose tissue inflammation is a hallmark of obesity, triggering the development of associated pathologies, particularly type 2 diabetes. Long-chain n-3 PUFAs reduce cardiovascular events and exert well-established antiinflammatory effects, but their effects on human adipose tissue inflammation are unknown. OBJECTIVE: We investigated whether n-3 PUFAs reduce adipose tissue inflammation in severely obese nondiabetic patients. DESIGN: We treated 55 severely obese nondiabetic patients, scheduled to undergo elective bariatric surgery, with 3.36 g long-chain n-3 PUFAs/d (EPA, DHA) or an equivalent amount of butterfat as control, for 8 wk, in a randomized open-label controlled clinical trial. The primary efficacy measure was inflammatory gene expression in visceral and subcutaneous adipose tissue samples (subcutaneous adipose tissue and visceral adipose tissue), collected during surgery after the intervention. Secondary efficacy variables were adipose tissue production of antiinflammatory n-3 PUFA-derived eicosanoids, plasma concentrations of inflammatory markers, metabolic control, and the effect of the Pro12Ala PPARG polymorphism on the treatment response. RESULTS: Treatment with n-3 PUFAs, which was well tolerated, decreased the gene expression of most analyzed inflammatory genes in subcutaneous adipose tissue (P < 0.05) and increased production of antiinflammatory eicosanoids in visceral adipose tissue and subcutaneous adipose tissue (P < 0.05). In comparison with control subjects who received butterfat, circulating interleukin-6 and triglyceride concentrations decreased significantly in the n-3 PUFA group (P = 0.04 and P = 0.03, respectively). The Pro12Ala polymorphism affected the serum cholesterol response to n-3 PUFA treatment. CONCLUSIONS: Treatment with long-chain n-3 PUFAs favorably modulated adipose tissue and systemic inflammation in severely obese nondiabetic patients and improved lipid metabolism. These effects may be beneficial in the long-term treatment of obesity. This trial was registered at clinicaltrials.gov as NCT00760760.