Systemic and regional free fatty acid metabolism in type 2 diabetes

Adiposity, type 2 diabetes and atherosclerotic cardiovascular disease risk: Use and abuse of the body mass index

The worldwide prevalence of individuals with an elevated body weight has increased steadily over the past five decades. Billions of research dollars have been invested to improve our understanding of the causes and consequences of having an elevated body weight. All this knowledge has, however, failed to influence populational body weight trajectories of most countries around the world. Research on the definition of "obesity" has also evolved. Body mass index (BMI), the most commonly used tool to make its diagnosis, has major limitations. In this review article, we will highlight evidence from observational studies, genetic association studies and randomized clinical trials that have shown the remarkable inter-individual differences in the way humans store energy as body fat. Increasing evidence also suggests that, as opposed to weight inclusive, lifestyle-based approaches, weight-centric approaches advising people to simply eat less and move more are not sustainable for most people for long-term weight loss and maintenance. It is time to recognize that this outdated approach may have produced more harm than good. On the basis of pathophysiological, genetic and clinical evidence presented in this review, we propose that it may be time to shift away from the traditional clinical approach, which is BMI-centric. Rather, emphasis should be placed on actionable lifestyle-related risk factors aiming at improving overall diet quality and increasing physical activity level in the general population.

Similar insulin regulation of splanchnic FFA and VLDL-TG in men with nonalcoholic hepatic steatosis and steatohepatitis

This study aimed to determine whether obese men with nonalcoholic fatty liver disease (NAFLD) display differences between those with simple steatosis versus steatohepatitis (NASH) in splanchnic and hepatic FFA and VLDL-triglycerides (VLDL-TG) balances. The study involved 17 obese men with biopsy-proven NAFLD (9 with NASH and 8 with simple steatosis). We used hepatic vein catheterization in combination with [3H]palmitate and [14C]VLDL-TG tracers to measure splanchnic palmitate and VLDL-TG uptake and release rates during basal and hyperinsulinemic conditions. Indocyanine green was used to measure splanchnic plasma flow. Splanchnic palmitate uptake was similar in the two groups and significantly reduced during hyperinsulinemia (NASH: 62 (48-77) versus 38 (18-58) μmol/min; simple steatosis: 62 (46-78) versus 45 (25-65) μmol/min, mean (95% CI), basal versus clamp periods, respectively, P = 0.02 time-effect). Splanchnic palmitate release was also comparable between groups and nonsignificantly diminished during hyperinsulinemia. The percent palmitate delivered to the liver originating from visceral adipose tissue lipolysis was similar and unchanged by hyperinsulinemia. Splanchnic uptake and release of VLDL-TG were similar between groups. Hyperinsulinemia suppressed VLDL-TG release (P <0.05 time-effect) in both groups. Insulin-mediated glucose disposal was similar in the two groups (P = 0.54). Obese men with NASH and simple steatosis have similar splanchnic uptake and release of FFA and VLDL-TG and a similar proportion of FFA from visceral adipose tissue lipolysis delivered to the liver. These results demonstrate that the splanchnic balances of FFA and VLDL-TG do not differ between obese men with NASH and those with simple steatosis.

Insulin regulation of regional lipolysis in upper-body obese and lean humans

BACKGROUND

Upper-body obesity (UBO) results in insulin resistance with regards to free fatty acid (FFA) release; how this differs by fat depot and sex between adults with UBO and lean adults is unknown. We tested the hypothesis that insulin suppression of FFA release from the splanchnic bed, leg fat, and upper-body nonsplanchnic (UBNS) adipose tissue would be impaired in UBO.

METHODS

Fourteen volunteers with UBO (7 men and 7 women) and 14 healthy volunteers with normal weight (7 men and 7 women) participated in studies that included femoral artery, femoral vein, and hepatic vein catheterization. We then measured leg and splanchnic plasma flow as well as FFA kinetics (using isotopic tracers) under overnight fasting as well as low- and high-dose insulin infusion using the insulin clamp technique.

RESULTS

We found the expected insulin resistance in UBO; the most quantitatively important difference between adults with UBO and lean adults was greater FFA release from UBNS adipose tissue when plasma insulin concentrations were in the postprandial, physiological range. There were obesity, but not sex, differences in the regulation of splanchnic FFA release and sex differences in the regulation of leg FFA release.

CONCLUSION

Reversing the defects in insulin-regulated UBNS adipose tissue FFA release would have the greatest effect on systemic FFA abnormalities in UBO.

FUNDING

These studies were supported by the US Public Health Service (grants DK45343 and DK40484), the Novo Nordic Foundation (grant NNF18OC0031804 and NNF16OC0021406), and the Independent Research Fund Denmark (grant 8020-00420B).

Aging adipose tissue, insulin resistance, and type 2 diabetes

With the increase of population aging, the prevalence of type 2 diabetes (T2D) is also rising. Aging affects the tissues and organs of the whole body, which is the result of various physiological and pathological processes. Adipose tissue has a high degree of plasticity and changes with aging. Aging changes the distribution of adipose tissue, affects adipogenesis, browning characteristics, inflammatory status and adipokine secretion, and increases lipotoxicity. These age-dependent changes in adipose tissue are an important cause of insulin resistance and T2D. Understanding adipose tissue changes can help promote healthy aging process. This review summarizes changes in adipose tissue ascribable to aging, with a focus on the role of aging adipose tissue in insulin resistance and T2D.

Adipocyte hypertrophy associates with in vivo postprandial fatty acid metabolism and adipose single-cell transcriptional dynamics

Adipocyte hypertrophy is associated with metabolic complications independent of obesity. We aimed to determine: 1) the association between adipocyte size and postprandial fatty acid metabolism; 2) the potential mechanisms driving the obesity-independent, hypertrophy-associated dysmetabolism in vivo and at a single-cell resolution. Tracers with positron emission tomography were used to measure fatty acid metabolism in 40 men and women with normal or impaired glucose tolerance (NCT02808182), and single nuclei RNA-sequencing (snRNA-seq) to determine transcriptional dynamics of subcutaneous adipose tissue (AT) between individuals with AT hypertrophy vs. hyperplasia matched for sex, ethnicity, glucose-tolerance status, BMI, total and percent body fat, and waist circumference. Adipocyte size was associated with high postprandial total cardiac fatty acid uptake and higher visceral AT dietary fatty acid uptake, but lower lean tissue dietary fatty acid uptake. We found major shifts in cell transcriptomal dynamics with AT hypertrophy that were consistent with in vivo metabolic changes.

Multiomics Analysis-Based Biomarkers in Diagnosis of Polycystic Ovary Syndrome

Polycystic ovarian syndrome is an utmost communal endocrine, psychological, reproductive, and metabolic disorder that occurs in women of reproductive age with extensive range of clinical manifestations. This may even lead to long-term multiple morbidities including obesity, diabetes mellitus, insulin resistance, cardiovascular disease, infertility, cerebrovascular diseases, and ovarian and endometrial cancer. Women affliction from PCOS in midst assemblage of manifestations allied with menstrual dysfunction and androgen exorbitance, which considerably affects eminence of life. PCOS is recognized as a multifactorial disorder and systemic syndrome in first-degree family members; therefore, the etiology of PCOS syndrome has not been copiously interpreted. The disorder of PCOS comprehends numerous allied health conditions and has influenced various metabolic processes. Due to multifaceted pathophysiology engaging several pathways and proteins, single genetic diagnostic tests cannot be supportive to determine in straight way. Clarification of cellular and biochemical pathways and various genetic players underlying PCOS could upsurge our consideration of pathophysiology of this syndrome. It is requisite to know pathophysiological relationship between biomarker and their reflection towards PCOS disease. Biomarkers deliver vibrantly and potent ways to apprehend the spectrum of PCOS with applications in screening, diagnosis, characterization, and monitoring. This paper relies on the endeavor to point out many candidates as potential biomarkers based on omics technologies, thus highlighting correlation between PCOS disease with innovative technologies. Therefore, the objective of existing review is to encapsulate more findings towards cutting-edge advances in prospective use of biomarkers for PCOS disease. Discussed biomarkers may be fruitful in guiding therapies, addressing disease risk, and predicting clinical outcomes in future.

Adipose Tissue Inflammation Is Not Related to Adipose Insulin Resistance in Humans

The role of adipose tissue (AT) inflammation in AT function in humans is unclear. We tested whether AT macrophage (ATM) content, cytokine gene expression, and senescent cell burden (markers of AT inflammation) predict AT insulin resistance measured as the insulin concentration that suppresses lipolysis by 50% (IC50). We studied 86 volunteers with normal weight or obesity at baseline and a subgroup of 25 volunteers with obesity before and after weight loss. There was a strong positive relationship between IC50 and abdominal subcutaneous and femoral fat cell size (FCS). The positive, univariate relationships between IC50 and abdominal AT inflammatory markers CD68, CD14, CD206 ATM/100 adipocytes, senescent cells, IL-6, and TNF-α mRNA were not significant after adjustment for FCS. A 10% weight loss significantly reduced IC50; however, there was no reduction in adipose ATM content, senescent cells, or cytokine gene expression. Our study suggests that commonly used markers of AT inflammation are not causally linked to AT insulin resistance, whereas FCS is a strong predictor of AT insulin resistance with respect to lipolysis.

Nicotinamide Mononucleotide Prevents Free Fatty Acid-Induced Reduction in Glucose Tolerance by Decreasing Insulin Clearance

The NAD-dependent deacetylase SIRT1 improves β cell function. Accordingly, nicotinamide mononucleotide (NMN), the product of the rate-limiting step in NAD synthesis, prevents β cell dysfunction and glucose intolerance in mice fed a high-fat diet. The current study was performed to assess the effects of NMN on β cell dysfunction and glucose intolerance that are caused specifically by increased circulating free fatty acids (FFAs). NMN was intravenously infused, with or without oleate, in C57BL/6J mice over a 48-h-period to elevate intracellular NAD levels and consequently increase SIRT1 activity. Administration of NMN in the context of elevated plasma FFA levels considerably improved glucose tolerance. This was due not only to partial protection from FFA-induced β cell dysfunction but also, unexpectedly, to a significant decrease in insulin clearance. However, in conditions of normal FFA levels, NMN impaired glucose tolerance due to decreased β cell function. The presence of this dual action of NMN suggests caution in its proposed therapeutic use in humans.

100th anniversary of the discovery of insulin perspective: insulin and adipose tissue fatty acid metabolism

Insulin inhibits systemic nonesterified fatty acid (NEFA) flux to a greater degree than glucose or any other metabolite. This remarkable effect is mainly due to insulin-mediated inhibition of intracellular triglyceride (TG) lipolysis in adipose tissues and is essential to prevent diabetic ketoacidosis, but also to limit the potential lipotoxic effects of NEFA in lean tissues that contribute to the development of diabetes complications. Insulin also regulates adipose tissue fatty acid esterification, glycerol and TG synthesis, lipogenesis, and possibly oxidation, contributing to the trapping of dietary fatty acids in the postprandial state. Excess NEFA flux at a given insulin level has been used to define in vivo adipose tissue insulin resistance. Adipose tissue insulin resistance defined in this fashion has been associated with several dysmetabolic features and complications of diabetes, but the mechanistic significance of this concept is not fully understood. This review focusses on the in vivo regulation of adipose tissue fatty acid metabolism by insulin and the mechanistic significance of the current definition of adipose tissue insulin resistance. One hundred years after the discovery of insulin and despite decades of investigations, much is still to be understood about the multifaceted in vivo actions of this hormone on adipose tissue fatty acid metabolism.

Association between Neck Circumference and the Risk of Decreased Estimated Glomerular Filtration Rate in the General Population of China: A Cross-Sectional Study

Background

The burden of chronic kidney disease is increasing substantially worldwide. Neck circumference (NC), an anthropometric index for upper-body adiposity, has been recognized as an indicator of cardiometabolic diseases. However, the association between NC and renal dysfunction has not been fully disclosed.

Objectives

The aim of this study was to investigate the association between NC and estimated glomerular filtration rate (eGFR) in the general population in China.

Methods

A total of 8805 participants (3322 men and 5483 women) were enrolled in this study. Logistic regression analysis was conducted to examine the association between NC and eGFR. The male and female subjects were divided into four groups according to the NC quartiles. The primary outcome was defined as an eGFR ≤ 90 mL/min/1.73 m².

Results

Logistic regression analysis revealed that in both sexes, higher NC was significantly associated with a higher risk of decreased eGFR even after fully adjusting for age, other anthropometric indexes, traditional risk factors for chronic kidney diseases, and sociologic risk factors (quartile 1 as a reference; the odds ratios [95% confidence intervals] were as follows: quartile 2, 1.26 [0.99-1.59]; quartile 3, 1.40 [1.07-1.83]; and quartile 4, 1.71 [1.22-2.38], in men; quartile 2, 1.14 [0.95-1.37]; quartile 3, 1.31 [1.03-1.66]; and quartile 4, 1.32 [1.04-1.68], in women). Stratified analyses suggested that the association was significant among subjects with prediabetes or normal serum uric acid levels and those without cardiovascular diseases (CVD). Among subjects with CVD, the association persisted only in males. When the subjects were stratified according to blood pressure or BMI, the association persisted among male subjects with abnormal blood pressure and was strengthened among male subjects who were overweight/obese, while the association disappeared among female subjects.

Conclusions

NC is independently associated with the risk of decreased eGFR in the general population in China, indicating that NC could contribute to renal dysfunction risk assessment.

Insulin and β-adrenergic receptors mediate lipolytic and anti-lipolytic signalling that is not altered by type 2 diabetes in human adipocytes

Control of fatty acid storage and release in adipose tissue is fundamental in energy homeostasis and the development of obesity and type 2 diabetes. We here take the whole signalling network into account to identify how insulin and β-adrenergic stimulation in concert controls lipolysis in mature subcutaneous adipocytes obtained from non-diabetic and, in parallel, type 2 diabetic women. We report that, and show how, the anti-lipolytic effect of insulin can be fully explained by protein kinase B (PKB/Akt)-dependent activation of the phosphodiesterase PDE3B. Through the same PKB-dependent pathway β-adrenergic receptor signalling, via cAMP and PI3Kα, is anti-lipolytic and inhibits its own stimulation of lipolysis by 50%. Through this pathway both insulin and β-adrenergic signalling control phosphorylation of FOXO1. The dose–response of lipolysis is bell-shaped, such that insulin is anti-lipolytic at low concentrations, but at higher concentrations of insulin lipolysis was increasingly restored due to inhibition of PDE3B. The control of lipolysis was not altered in adipocytes from diabetic individuals. However, the release of fatty acids was increased by 50% in diabetes due to reduced reesterification of lipolytically liberated fatty acids. In conclusion, our results reveal mechanisms of control by insulin and β-adrenergic stimulation — in human adipocytes — that define a network of checks and balances ensuring robust control to secure uninterrupted supply of fatty acids without reaching concentrations that put cellular integrity at risk. Moreover, our results define how selective insulin resistance leave lipolytic control by insulin unaltered in diabetes, while the fatty acid release is substantially increased.

Large mid-upper arm circumference is associated with metabolic syndrome in middle-aged and elderly individuals: a community-based study

BACKGROUND

The mid-upper arm circumference (MUAC) is a proxy for subcutaneous fat in the upper body and is a reliable screening measure for identifying individuals with abnormal regional fat distribution. The purpose of this study was to evaluate the association between MUAC and metabolic syndrome (MetS) in middle-aged and elderly individuals.

METHODS

We measured the MUAC in a cross-sectional sample with a total of 9787 subjects aged 40 years and older. The measurement of MUAC is performed on the right arm using a non-elastic tape held midway between the acromion and the olecranon processes in duplicate, with the arm hanging loosely at the side of the body. The MetS was defined according to the Joint Statement of the International Diabetes Federation Task Force on Epidemiology and Prevention.

RESULTS

MUAC was positively correlated with waist circumference (r = 0.437, P < 0.001), BMI (r = 0.334, P < 0.001), fasting insulin (r = 0.348, P < 0.001), HOMA-IR (r = 0.134, P < 0.001), triglycerides (r = 0.138, P < 0.001), SBP (r = 0.124, P < 0.001), and DBP (r = 0.123, P < 0.001), and inversely correlated with adiponectin (r = - 0.147, P < 0.001) and HDL-cholesterol (r = - 0.176, P < 0.001) after adjusting for age and gender. Compared with the lowest quartile group, the odds ratios were substantially higher for MetS (OR 1.77; 95% CI 1.51-2.09, P for trend< 0.001) in the highest MUAC quartile group after adjustment for potential cofounder.

CONCLUSION

Large mid-upper arm circumference is significantly associated with metabolic syndrome in middle-aged and elderly individuals.

Lymphatic drainage affects lipolytic activity of femoral adipose tissue in women

It has been shown that many molecules released by adipose tissue (AT) into interstitial fluid can reach the bloodstream preferentially via lymphatic system. Worsened lymphatic drainage may alter interstitial fluid (ISF) composition and thus affect microenvironment of adipocytes. Nevertheless, the effect of lymphatic drainage on AT functions remains unknown. Therefore, we analyzed the lipolytic activity of femoral AT in two groups of premenopausal women similar in adiposity but differing in the efficiency of lymphatic drainage of lower body as assessed by lymphoscintigraphy. Levels of lipolytic markers were assessed in plasma and ISF collected by skin blister technique in femoral area. In addition, microdialysis was used to monitor lipolysis of AT in vivo. Our results indicate that worsened lymphatic drainage is associated with lower in vivo lipolytic index and reduced lipolytic responsiveness of femoral AT to adrenergic stimuli. Thus, efficiency of lymphatic drainage appears to play a role in the regulation of AT metabolism. Accordingly, worsened lymphatic drainage could contribute to the resistance of lower body AT to intentional weigh loss.

Errors in measuring plasma free fatty acid concentrations with a popular enzymatic colorimetric kit

OBJECTIVES

Our goal was to test whether an enzymatic, colorimetric assay, the WAKO NEFA kit, provides information equivalent to liquid chromatography (LC) LC-based measures of free fatty acid (FFA).

DESIGN & METHODS

We reanalyzed nadir FFA samples from 109 volunteers from a previous study where we demonstrated that maximal suppression of FFA concentrations predicts metabolic abnormalities in humans; the results from the WAKO NEFA kit, which has been widely used for over three decades, could not replicate our findings. We conducted additional studies to directly compare results from this kit to our LC-mass spectrometry (LC/MS) method that was validated by our LC-UV detection method.

RESULTS

Plasma samples with FFA concentrations ranging from 0.015 to 1.813 mmol/L were measured both by LC-mass spectrometry (LC/MS) and by the WAKO NEFA kit. Despite good overall agreement (R² = 0.86), the slope was significantly different from 1.0 and the intercept was significantly different from zero. The results from the kit were especially discrepant with FFA concentrations <0.200 and >1.000 mmol/L. Some of the discrepancy was related to the use of oleate as the standard solution for the kit and the substrate specificity of the kit enzymes for different fatty acids. Despite attempts to improve the kit by modifying the reaction time, sample volume and the types of standard solutions, we could not obtain a satisfactory agreement between the WAKO NEFA results and LC/MS.

CONCLUSIONS

The WAKO NEFA kit should not be used when high precision and accuracy of FFA concentrations over a wide range is required.

Palmitate is not an effective fuel for pancreatic islets and amplifies insulin secretion independent of calcium release from endoplasmic reticulum

The aim of the study was to determine the acute contribution of fuel oxidation in mediating the increase in insulin secretion rate (ISR) in response to fatty acids. Measures of mitochondrial metabolism, as reflected by oxygen consumption rate (OCR) and cytochrome c reduction, calcium signaling, and ISR by rat islets were used to evaluate processes stimulated by acute exposure to palmitic acid (PA). The contribution of mitochondrial oxidation of PA was determined in the presence and absence of a blocker of mitochondrial transport of fatty acids (etomoxir) at different glucose concentrations. Subsequent to increasing glucose from 3 to 20 mM, PA caused small increases in OCR and cytosolic calcium (about 20% of the effect of glucose). In contrast, the effect of PA on ISR was almost 3 times that by glucose, suggesting that the metabolism of PA is not the dominant mechanism mediating PA's effect on ISR. This was further supported by lack of inhibition of PA-stimulated OCR and ISR when blocking entry of PA into mitochondria (with etomoxir), and PA's lack of stimulation of reduced cytochrome c in the presence of high glucose. Consistent with the lack of metabolic stimulation by PA, an inhibitor of calcium release from the endoplasmic reticulum, but not a blocker of L-type calcium channels, abolished the PA-induced elevation of cytosolic calcium. Notably, ISR was unaffected by thapsigargin showing the dissociation of endoplasmic reticulum calcium release and second phase insulin secretion. In conclusion, stimulation of ISR by PA was mediated by mechanisms largely independent of the oxidation of the fuel.

Differential effect of subcutaneous abdominal and visceral adipose tissue on cardiometabolic risk

Metabolic and cardiovascular diseases are increasing worldwide due to the rise in the obesity epidemic. The metabolic consequences of obesity vary by distribution of adipose tissue. Visceral and ectopic adipose accumulation are associated with adverse cardiometabolic consequences, while gluteal-femoral adipose accumulation are negatively associated with these adverse complications and subcutaneous abdominal adipose accumulation is more neutral in its associations. Gender, race and ethnic differences in adipose tissue distribution have been described and could account for the observed differences in risk for cardiometabolic disease. The mechanisms behind the differential impact of adipose tissue on cardiometabolic risk have started to be unraveled and include differences in adipocyte biology, inflammatory profile, connection to systemic circulation and most importantly the inability of the subcutaneous adipose tissue to expand in response to positive energy balance.

Fatty acid uptake and blood flow in adipose tissue compartments of morbidly obese subjects with or without type 2 diabetes: effects of bariatric surgery

Body fat accumulation, distribution, and metabolic activity are factors in the pathophysiology of obesity and type 2 diabetes (T2D). We investigated adipose blood flow, fatty acid uptake (FAU), and subcutaneous and visceral fat cellularity in obese patients with or without T2D. A total of 23 morbidly obese (mean body mass index = 42 kg/m²) patients were studied before and 6 mo after bariatric surgery; 15 nonobese subjects served as controls. Positron emission tomography was used to measure tissue FAU (with ¹⁸F-FTHA) and blood flow (with H₂¹⁵O); MRI was used for fat distribution and fat biopsy for adipocyte size. Obese subjects had subcutaneous hyperplasia and hypertrophy and lower blood flow; when expressed per cell, flow was similar to controls. FAU into subcutaneous and visceral depots was increased in the obese; per unit tissue mass, however, FAU was similar to controls but reduced in skeletal muscle. Fatty acid fractional extraction in subcutaneous fat and muscle was only increased in obese patients with T2D. We conclude that surgery reduces subcutaneous fat hyperplasia and hypertrophy; subcutaneous blood flow and FAU decrease in absolute terms and per cell while fractional FAU remains unchanged in T2D. In the obese, subcutaneous blood flow is a determinant of FAU and is coupled with cellularity; efficiency of FAU is enhanced in subcutaneous fat and muscle in T2D.

Very-long-chain ω-3 fatty acid supplements and adipose tissue functions: a randomized controlled trial

Background: Increased omega-3 (n-3) fatty acid consumption is reported to benefit patients with metabolic syndrome, possibly due to improved adipose tissue function.Objective: We tested the effects of high-dose, very-long-chain ω-3 fatty acids on adipose tissue inflammation and insulin regulation of lipolysis.Design: A double-blind, placebo-controlled study compared 6 mo of 3.9 g eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)/d (4.2 g total ω-3/d; n = 12) with a placebo (4.2 g oleate/d; n = 9) in insulin-resistant adults. Before and after treatment, the volunteers underwent adipose tissue biopsies to measure the total (CD68⁺), pro- (CD14⁺ = M1), and anti- (CD206⁺ = M2) inflammatory macrophages, crown-like structures, and senescent cells, as well as a 2-step pancreatic clamping with a [U-¹³C]palmitate infusion to determine the insulin concentration needed to suppress palmitate flux by 50% (IC_{50(palmitate)}f).Results: In the ω-3 group, the EPA and DHA contributions to plasma free fatty acids increased (P = 0.0003 and P = 0.003, respectively), as did the EPA and DHA content in adipose tissue (P < 0.0001 and P < 0.0001, respectively). Despite increases in adipose and plasma EPA and DHA in the ω-3 group, there were no significant changes in the IC_{50(palmitate)}f (19 ± 2 compared with 24 ± 3 μIU/mL), adipose macrophages (total: 31 ± 2/100 adipocytes compared with 33 ± 2/100 adipocytes; CD14⁺: 13 ± 2/100 adipocytes compared with 14 ± 2/100 adipocytes; CD206⁺: 28 ± 2/100 adipocytes compared with 29 ± 3/100 adipocytes), crown-like structures (1 ± 0/10 images compared with 1 ± 0/10 images), or senescent cells (4% ± 1% compared with 4% ± 1%). There were no changes in these outcomes in the placebo group.Conclusions: Six months of high-dose ω-3 supplementation raised plasma and adipose ω-3 fatty acid concentrations but had no beneficial effects on adipose tissue lipolysis or inflammation in insulin-resistant adults. This trial was registered at clinicaltrials.gov as NCT01686568.

Impaired adipose tissue lipid storage, but not altered lipolysis, contributes to elevated levels of NEFA in type 2 diabetes. Degree of hyperglycemia and adiposity are important factors

BACKGROUND

Elevated levels of circulating non-esterified fatty acids (NEFA) mediate many adverse metabolic effects. In this work we aim to determine the impact of type 2 diabetes (T2D), glycemic control and obesity on lipolysis regulation.

DESIGN AND PARTICIPANTS

20 control and 20 metformin-treated T2D subjects were matched for sex (10M/10 F), age (58±11 vs 58±9 y) and BMI (30.8±4.6 vs 30.7±4.9kg/m²). In vivo lipolysis was assessed during a 3h-OGTT with plasma glycerol and NEFA levels. Subcutaneous adipose tissue (SAT) biopsies were obtained to measure mRNA and metabolite levels of factors related to lipolysis and lipid storage and to assess in vitro lipolysis in isolated subcutaneous adipocytes.

RESULTS

Plasma NEFA AUC during the OGTT where higher 30% (P=0.005) in T2D than in control subjects, but plasma glycerol AUC and subcutaneous adipocyte lipolysis in vitro were similar, suggesting that adipose tissue lipolysis is not altered. Expression in SAT of genes involved in lipid storage (FABP4, DGAT1, FASN) were reduced in T2D subjects compared with controls, but no differences were seen for genes involved in lipolysis. T2D subjects had elevated markers of beta-oxidation, α-hydroxybutyrate (1.4-fold, P<0.01) and β-hydroxybutyrate (1.7-fold, P<0.05) in plasma. In multivariate analysis, HbA1c, visceral adipose tissue volume and sex (male) were significantly associated with NEFA AUC in T2D subjects.

CONCLUSIONS

In T2D subjects, NEFA turnover is impaired, but not due to defects in lipolysis or lipid beta-oxidation. Impaired adipose NEFA re-esterification or de novo lipogenesis is likely to contribute to higher NEFA plasma levels in T2D. The data suggest that hyperglycemia and adiposity are important contributing factors for the regulation of plasma NEFA concentrations.

Feasibility of simultaneous 18F-FDG PET/MRI for the quantitative volumetric and metabolic measurements of abdominal fat tissues using fat segmentation

BACKGROUND

Quantification of volume and inflammatory activity in the fat tissue is important because these are closely related to type 2 diabetes mellitus and cardiovascular disease. Fluorine-18 fluorodeoxyglucose (F-FDG) PET/computed tomography (CT) has been utilized to measure the metabolic activity of fat tissue. In this study, we assessed the feasibility of simultaneous PET/magnetic resonance (MR) in metabolic and volumetric measurements of fat tissue and the potential advantage over PET/CT.

METHODS

Twenty-four healthy individuals were enrolled, who underwent simultaneous F-FDG PET/MRI. Twenty-five F-FDG PET/CT scans were selected. Isocontour volumes of interest (VOIs) were used to segment and separate visceral fat (VF) and abdominal subcutaneous fat (SF) in using the MR image (T1 DIXON VIBE sequence) of PET/MR and the CT image of PET/CT. Volume, mean standardized uptake value of VF, and SF VOIs were calculated.

RESULTS

Overlap between F-FDG PET and VF VOI was better in F-FDG PET/MR than PET/CT. The mean standardized uptake value of VF was associated with the degree of intestinal uptake on F-FDG PET/CT, but not on F-FDG PET/MR. Volumetric and metabolic measurements using F-FDG PET/MR showed an excellent reproducibility, with a high intraclass correlation coefficient between different observers (0.951-0.997). The measured metabolic activity was higher in VF than SF.

CONCLUSION

We established a method for the quantitative measurement of volume and metabolic status of abdominal VF and SF using simultaneous F-FDG PET/MR. F-FDG PET/MR has an advantage over F-FDG PET/CT in terms of being less confounded by intestinal uptake. This method could be used to assess the inflammatory activity of fat tissue, which is a major risk factor for type 2 diabetes mellitus and cardiovascular disease.

Secondary hypertriglyceridemia in children and adolescents

Secondary dyslipidemia with predominant hypertriglyceridemia may occur as a consequence of both common and rare causes. After accounting for obesity and associated insulin resistance, clinicians should carefully consider other contributing factors and conditions. Genetic background and causative factors prevail during gestation, infancy, and childhood and continue in adults. Elevations in triglyceride (TG) are associated with transfer of TG to high-density lipoprotein (HDL) and low-density lipoprotein (LDL) resulting in lipolysis, HDL degradation, and formation of atherogenic LDL particles. Defining and treating the underlying cause is the first step toward restoring the lipids and lipoproteins to normal, especially in cases with severe hypertriglyceridemia, who are at risk for acute pancreatitis. Disorders involving the liver, kidney, endocrine, and immune systems and medications need to be considered. Rare diseases such as lipodystrophy and glycogen storage disease are particularly challenging, and there have been promising new developments. Treatment depends on the severity; prevention of acute pancreatitis being a priority in severe cases and lifestyle modification being a foundation for general management followed by targeting TG and predictors of coronary artery disease such as LDL cholesterol and non-HDL cholesterol, when they exceed cutpoints.

Androgens, body fat Distribution and Adipogenesis

Androgens are regulators of important adipocyte functions such as adipogenesis, lipid storage, and lipolysis. Through depot-specific impact on the cells of each fat compartment, androgens could modulate body fat distribution patterns in humans. Testosterone and dihydrotestosterone have been shown to inhibit the differentiation of preadipocytes to lipid-storing adipocytes in several models including primary cultures of human adipocytes from both men and women. Androgen effects have also been observed on some markers of lipid metabolism such as LPL activity, fatty acid uptake, and lipolysis. Possible depot-specific and sex-specific effects have been observed in some but not all models. Transformation of androgen precursors to active androgens or their inactivation by enzymes that are expressed and functional in adipose tissue may contribute to modulate the local availability of active hormones. These phenomena, along with putative depot-specific interactions with glucocorticoids may contribute to human body fat distribution patterns.

Influence of weight gain rate on early life nutritional status and body composition of children

OBJECTIVE

To evaluate the influence of the weight gain rate at 4-6 months on nutritional status and body composition in children between 4 and 7 years of age.

METHODS

Retrospective cohort study, sample of 257 children. Data collection was performed in two stages, with the first relating to retrospective data of weight gain from birth to the first 4-6 months of life in the patient records. Measurements of weight, height, waist circumference, and body composition in children between ages 4 and 7 years were obtained. Nutritional status was assessed by the BMI/age. Control variables, such as pregnancy, breastfeeding, lifestyle, and sociodemographics, were studied. Descriptive analysis and multiple linear regression were performed.

RESULTS

In the nutritional status assessment, the prevalence of overweight observed was 24.9%. After adjusting for control variables, it was found that the increase of the WGR at 4-6 months of age explained the occurrence of higher BMI/age, percentage of total body fat, body fat percentage in the android region, and waist circumference in children between 4 and 7 years of age.

CONCLUSION

The increase of the WGR in the first months of life can lead to the occurrence of higher values of parameters of nutritional status and body composition in later life.

Adipose tissue insulin resistance in adolescents with and without type 2 diabetes

BACKGROUND

The incidence of type 2 diabetes mellitus (T2D) is increasing in youth, yet little is known about the underlying pathophysiology. Decreased insulin suppression of lipolysis and elevated non-esterified free fatty acid (NEFA) concentrations are known to be associated with insulin resistance and T2D in adults, but less is known about the relationship in adolescents.

OBJECTIVES

This study aimed to assess adipose tissue insulin resistance (IR; insulin suppression of lipolysis) and its metabolic correlates in lean, obese and T2D adolescents.

METHODS

Forty-seven lean, obese and T2D youth underwent hyperinsulinaemic (80 mU*m(-2) *min(-1)) euglycaemic clamps. NEFAs were measured at baseline and during steady state. Insulin-mediated suppression of lipolysis (%NEFA suppression from baseline) was calculated, and metabolic risk factors were assessed by %NEFA suppression tertile.

RESULTS

There was expected variability in %NEFA suppression within obese and T2D youth, but a subset had significantly reduced suppression of lipolysis. NEFA suppression tertile was significantly inversely associated with fasting triglycerides (P = 0.0001), log alanine aminotransferase (ALT; P = 0.02) and low-density lipoprotein cholesterol (P = 0.0002).

CONCLUSIONS

Marked adipose tissue IR occurs in some obese and T2D adolescents, which may result in release of triglycerides into the circulation and liver deposition of fatty acids, as evidenced by higher ALT in poor NEFA suppressors.

Effects of acute glucocorticoid blockade on metabolic dysfunction in patients with Type 2 diabetes with and without fatty liver

To investigate the potential of therapies which reduce glucocorticoid action in patients with Type 2 diabetes we performed a randomized, double-blinded, placebo-controlled crossover study of acute glucocorticoid blockade, using the glucocorticoid receptor antagonist RU38486 (mifepristone) and cortisol biosynthesis inhibitor (metyrapone), in 14 men with Type 2 diabetes. Stable isotope dilution methodologies were used to measure the rates of appearance of glucose, glycerol, and free fatty acids (FFAs), including during a low-dose (10 mU·m⁻² ·min⁻¹) hyperinsulinemic clamp, and subgroup analysis was conducted in patients with high or low liver fat content measured by magnetic resonance spectroscopy (n = 7/group). Glucocorticoid blockade lowered fasting glucose and insulin levels and improved insulin sensitivity of FFA and glycerol turnover and hepatic glucose production. Among this population with Type 2 diabetes high liver fat was associated with hyperinsulinemia, higher fasting glucose levels, peripheral and hepatic insulin resistance, and impaired suppression of FFA oxidation and FFA and glycerol turnover during hyperinsulinemia. Glucocorticoid blockade had similar effects in those with and without high liver fat. Longer term treatments targeting glucocorticoid action may be useful in Type 2 diabetes with and without fatty liver.

Insulin-mediated suppression of lipolysis in adipose tissue and skeletal muscle of obese type 2 diabetic men and men with normal glucose tolerance

AIMS/HYPOTHESIS

Impaired regulation of lipolysis and accumulation of lipid intermediates may contribute to obesity-related insulin resistance and type 2 diabetes mellitus. We investigated insulin-mediated suppression of lipolysis in abdominal subcutaneous adipose tissue (AT) and skeletal muscle (SM) of obese men with normal glucose tolerance (NGT) and obese type 2 diabetic men.

METHODS

Eleven NGT men and nine long-term diagnosed type 2 diabetic men (7 ± 1 years), matched for age (58 ± 2 vs 62 ± 2 years), BMI (31.4 ± 0.6 vs 30.5 ± 0.6 kg/m(2)) and [Formula: see text] (28.9 ± 1.5 vs 29.5 ± 2.4 ml kg(-1) min(-1)) participated in this study. Interstitial glycerol concentrations in AT and SM were assessed using microdialysis during a 1 h basal period and a 6 h stepwise hyperinsulinaemic-euglycaemic clamp (8, 20 and 40 mU m(-2) min(-1)). AT and SM biopsies were collected to investigate underlying mechanisms.

RESULTS

Hyperinsulinaemia suppressed interstitial SM glycerol concentrations less in men with type 2 diabetes (-7 ± 6%, -13 ± 9% and -27 ± 9%) compared with men with NGT (-21 ± 7%, -38 ± 8% and -53 ± 8%) (p = 0.014). This was accompanied by increased circulating fatty acid and glycerol concentrations, a lower glucose infusion rate (21.8 ± 3.1 vs 30.5 ± 2.0 μmol kg body weight(-1) min(-1); p < 0.05), higher hormone-sensitive lipase (HSL) serine 660 phosphorylation, increased saturated diacylglycerol (DAG) lipid species in the muscle membrane and increased protein kinase C (PKC) activation in type 2 diabetic men vs men with NGT. No significant differences in insulin-mediated reduction in AT interstitial glycerol were observed between groups.

CONCLUSIONS/INTERPRETATION

Our results suggest that a blunted insulin-mediated suppression of SM lipolysis may promote the accumulation of membrane saturated DAG, aggravating insulin resistance, at least partly mediated by PKC. This may represent an important mechanism involved in the progression of insulin resistance towards type 2 diabetes.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01680133.

Spillover of Fatty acids during dietary fat storage in type 2 diabetes: relationship to body fat depots and effects of weight loss

Spillover of lipoprotein lipase-generated fatty acids from chylomicrons into the plasma free fatty acid (FFA) pool is an important source of FFA and reflects inefficiency in dietary fat storage. We measured spillover in 13 people with type 2 diabetes using infusions of a [(3)H]triolein-labeled lipid emulsion and [U-(13)C]oleate during continuous feeding, before and after weight loss. Body fat was measured with dual energy X-ray absorptiometry and computed tomography. Participants lost ∼14% of body weight. There was an ∼38% decrease in meal-suppressed FFA concentration (P < 0.0001) and an ∼23% decrease in oleate flux (P = 0.007). Fractional spillover did not change (P = NS). At baseline, there was a strong negative correlation between spillover and leg fat (r = -0.79, P = 0.001) and a positive correlation with the trunk-to-leg fat ratio (R = 0.56, P = 0.047). These correlations disappeared after weight loss. Baseline leg fat (R = -0.61, P = 0.027) but not trunk fat (R = -0.27, P = 0.38) negatively predicted decreases in spillover with weight loss. These results indicate that spillover, a measure of inefficiency in dietary fat storage, is inversely associated with lower body fat in type 2 diabetes.

Pathophysiology of human visceral obesity: an update

Excess intra-abdominal adipose tissue accumulation, often termed visceral obesity, is part of a phenotype including dysfunctional subcutaneous adipose tissue expansion and ectopic triglyceride storage closely related to clustering cardiometabolic risk factors. Hypertriglyceridemia; increased free fatty acid availability; adipose tissue release of proinflammatory cytokines; liver insulin resistance and inflammation; increased liver VLDL synthesis and secretion; reduced clearance of triglyceride-rich lipoproteins; presence of small, dense LDL particles; and reduced HDL cholesterol levels are among the many metabolic alterations closely related to this condition. Age, gender, genetics, and ethnicity are broad etiological factors contributing to variation in visceral adipose tissue accumulation. Specific mechanisms responsible for proportionally increased visceral fat storage when facing positive energy balance and weight gain may involve sex hormones, local cortisol production in abdominal adipose tissues, endocannabinoids, growth hormone, and dietary fructose. Physiological characteristics of abdominal adipose tissues such as adipocyte size and number, lipolytic responsiveness, lipid storage capacity, and inflammatory cytokine production are significant correlates and even possible determinants of the increased cardiometabolic risk associated with visceral obesity. Thiazolidinediones, estrogen replacement in postmenopausal women, and testosterone replacement in androgen-deficient men have been shown to favorably modulate body fat distribution and cardiometabolic risk to various degrees. However, some of these therapies must now be considered in the context of their serious side effects. Lifestyle interventions leading to weight loss generally induce preferential mobilization of visceral fat. In clinical practice, measuring waist circumference in addition to the body mass index could be helpful for the identification and management of a subgroup of overweight or obese patients at high cardiometabolic risk.

Fat depots, free fatty acids, and dyslipidemia

Body fat deposition and excess free fatty acid (FFA) metabolism contribute to dyslipidemia and the adverse health consequences of obesity. Individuals with upper body obesity have impaired functioning of adipocytes, the primary fatty acid storage site. Excess visceral fat is strongly associated with impaired suppression of FFA release in response to insulin, as well as with hypertriglyceridemia and low concentrations of high density lipoprotein (HDL) cholesterol. High FFA concentrations can induce insulin resistance in muscle and liver. Furthermore, failure of hyperinsulinemia to normally suppress FFA is associated with impaired carbohydrate oxidation and muscle glucose storage, reduced hepatic insulin clearance and elevated triglycerides. Understanding the impact of body fat distribution on FFA metabolism and dyslipidemia is critical for determining the link between overweight and obesity and cardiovascular disease risk. In the current review, we will explore the relationship between adipose tissue, body fat depots, and FFA metabolism.

Neck circumference is correlated with triglycerides and inversely related with HDL cholesterol beyond BMI and waist circumference

BACKGROUND

Neck circumference, beyond a measure of obesity, is a unique fat depot with increasing significance. This study aimed to investigate the association between neck circumference and biomarkers, indicators of cardiovascular risk.

METHODS

During 2009, 490 volunteers (46 ± 16 years, 40% men) were consecutively enrolled to the study (participation rate 85%). Biochemical analyses were performed through established procedures, and after 12-h fasting and glucose, total cholesterol, high-density lipoprotein and low-density lipoprotein cholesterol, triglycerides, cystatin C, uric acid and high-sensitivity C-reactive protein were measured. Anthropometric, lifestyle and dietary characteristics were also recorded to account for potential confounders. Additive linear and logistic regression models were used to evaluate the association between neck circumference and biomarkers of cardiometabolic risk.

RESULTS

A positive association between neck circumference and systolic and diastolic blood pressure, glucose, triglycerides, uric acid and high-sensitivity C-reactive protein, and a negative association with high-density lipoprotein cholesterol were revealed (all ps < 0.05); models were adjusted for age, gender, years of school, smoking, physical activity status, MedDietScore and alcohol intake. The relationship between neck circumference and high-density lipoprotein cholesterol, glucose, triglycerides and uric acid remained significant when models were further stratified by body mass index class and abnormal waist circumference.

CONCLUSION

Neck circumference was found to be a powerful indicator of atherogenic dyslipidaemia above and beyond central obesity indicators.

A new role for lipocalin prostaglandin d synthase in the regulation of brown adipose tissue substrate utilization

In this study, we define a new role for lipocalin prostaglandin D synthase (L-PGDS) in the control of metabolic fuel utilization by brown adipose tissue (BAT). We demonstrate that L-PGDS expression in BAT is positively correlated with BAT activity, upregulated by peroxisome proliferator-activated receptor γ coactivator 1α or 1β and repressed by receptor-interacting protein 140. Under cold-acclimated conditions, mice lacking L-PGDS had elevated reliance on carbohydrate to provide fuel for thermogenesis and had increased expression of genes regulating glycolysis and de novo lipogenesis in BAT. These transcriptional differences were associated with increased lipid content in BAT and a BAT lipid composition enriched with de novo synthesized lipids. Consistent with the concept that lack of L-PGDS increases glucose utilization, mice lacking L-PGDS had improved glucose tolerance after high-fat feeding. The improved glucose tolerance appeared to be independent of changes in insulin sensitivity, as insulin levels during the glucose tolerance test and insulin, leptin, and adiponectin levels were unchanged. Moreover, L-PGDS knockout mice exhibited increased expression of genes involved in thermogenesis and increased norepinephrine-stimulated glucose uptake to BAT, suggesting that sympathetically mediated changes in glucose uptake may have improved glucose tolerance. Taken together, these results suggest that L-PGDS plays an important role in the regulation of glucose utilization in vivo.

Body adipose distribution among patients with type 2 diabetes mellitus

SUMMARY

Both diabetes mellitus (DM) and obesity are prevalent in adults. The relationship between DM and body adipose tissue (AT) distribution is complex and although it has been investigated extensively, the subject remains controversial. Although a causal association between DM and obesity and AT distribution cannot be established on the basis of existing data, it is possible to conclude from many studies that gene, serum sex steroids level, daily physical activity and food supply can be the risk of obesity and AT redistribution factor among type 2 DM patients (T2DM). Obesity and AT redistribution of T2DM patients can increase the risk of insulin resistant (IR), cardiovascular disease and many other disorders. Even though obesity and AT redistribution screening or prophylactic treatment in all patients with T2DM is not being recommended at present, such patient populations should be given general guidelines regarding exercise, food intake control, and even medicinal treatment. The extent of diagnostic and therapeutic interventions should be based on the individual's risk profile.:

Lipocalin prostaglandin D synthase and PPARγ2 coordinate to regulate carbohydrate and lipid metabolism in vivo

Mice lacking Peroxisome Proliferator-Activated Receptor γ2 (PPARγ2) have unexpectedly normal glucose tolerance and mild insulin resistance. Mice lacking PPARγ2 were found to have elevated levels of Lipocalin prostaglandin D synthase (L-PGDS) expression in BAT and subcutaneous white adipose tissue (WAT). To determine if induction of L-PGDS was compensating for a lack of PPARγ2, we crossed L-PGDS KO mice to PPARγ2 KO mice to generate Double Knock Out mice (DKO). Using DKO mice we demonstrated a requirement of L-PGDS for maintenance of subcutaneous WAT (scWAT) function. In scWAT, DKO mice had reduced expression of thermogenic genes, the de novo lipogenic program and the lipases ATGL and HSL. Despite the reduction in markers of lipolysis in scWAT, DKO mice had a normal metabolic rate and elevated serum FFA levels compared to L-PGDS KO alone. Analysis of intra-abdominal white adipose tissue (epididymal WAT) showed elevated expression of mRNA and protein markers of lipolysis in DKO mice, suggesting that DKO mice may become more reliant on intra-abdominal WAT to supply lipid for oxidation. This switch in depot utilisation from subcutaneous to epididymal white adipose tissue was associated with a worsening of whole organism metabolic function, with DKO mice being glucose intolerant, and having elevated serum triglyceride levels compared to any other genotype. Overall, L-PGDS and PPARγ2 coordinate to regulate carbohydrate and lipid metabolism.

The effect of a very low calorie diet on insulin sensitivity, beta cell function, insulin clearance, incretin hormone secretion, androgen levels and body composition in obese young women

OBJECTIVE

Evaluation of the effect of an 8-week very low calorie diet (VLCD, 500-600 kcal daily) on weight, body fat distribution, glucose, insulin and lipid metabolism, androgen levels and incretin secretion in obese women.

METHODS

Seventeen overweight women (BMI > 28) were recruited to the study. Glucose, insulin and lipid metabolism were evaluated by euglycemic clamp technique, indirect calorimetry and an oral glucose tolerance test (OGTT). Insulin sensitivity was calculated as glucose disposal rate (GDR) and insulin sensitivity index (ISI), and also by HOMA-IR. Insulin secretion rate (ISR) was calculated from plasma C-peptide measurements. Secretion of glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic peptide (GIP) was measured during an oral glucose tolerance test. Abdominal fat distribution was assessed by dual x-ray absorptiometry scan and computed tomography.

RESULTS

Ten women completed the intervention. The subjects lost an average 11% of their baseline weight. There was a significant loss of subcutaneous abdominal fatty tissue (p < 0.01) and intra-abdominal fatty tissue (p =0.05). Whole body (HOMA-IR) (p < 0.05) insulin sensitivity increased significantly, but peripheral (ISI) insulin sensitivity was unaltered after weight loss. GIP increased (p < 0.05) and GLP-1 was unaltered after the dietary intervention. Insulin responses did not differ before and after dietary intervention, however, a significant increase in insulin clearance (p < 0.05) was observed. The weight loss resulted in a significant decrease in free testosterone.

CONCLUSION

A VLCD is an effective weight loss treatment, which results in an immediate improvement in several metabolic parameters.

Defects in GLP-1 response to an oral challenge do not play a significant role in the pathogenesis of prediabetes

CONTEXT

There has been much speculation as to whether defects in glucagon-like peptide-1 (GLP-1) secretion play a role in the pathogenesis of type 2 diabetes and the progression from normal glucose tolerance to prediabetes and diabetes.

OBJECTIVE

Our objective was to determine whether fasting and postchallenge concentrations of active and total GLP-1 decrease as glucose tolerance and insulin secretion worsen across the spectrum of prediabetes.

DESIGN

This was a cross-sectional study.

SETTING

The study was performed in the clinical research unit of an academic medical center.

PARTICIPANTS

Participants included 165 subjects with a fasting glucose below 7.0 mmol/liter and not taking medications known to affect gastrointestinal motility or glucose metabolism.

INTERVENTION

Intervention included a 2-h, 75-g oral glucose tolerance test with insulin, C-peptide, glucagon, and GLP-1 measurements at seven time points.

MAIN OUTCOME MEASURE

We evaluated the association of integrated, incremental active, and total GLP-1 concentrations with integrated, incremental glucose response to 75 g oral glucose.

RESULTS

After accounting for covariates, there was no evidence of a relationship of incremental glucose concentrations after oral glucose tolerance test with active and total GLP-1 (r(s) = -0.16 and P = 0.14, and r(s) = 0.00 and P > 0.9, respectively). There also was no association of GLP-1 concentrations with insulin secretion and action.

CONCLUSIONS

The lack of association of GLP-1 concentrations with glucose tolerance status and with insulin secretion and action in a cohort encompassing the full spectrum of prediabetes strongly argues against a significant contribution of defects in GLP-1 secretion to the pathogenesis of prediabetes.

Comparison of visceral fat and liver fat as risk factors of metabolic syndrome

The principal objective of this study was to determine whether visceral fat or liver fat is a more relevant risk factor for metabolic syndrome. A total of 98 subjects aged 18-65 yr, who visited a health promotion center in a university hospital, were enrolled in this study. Metabolic syndrome was diagnosed based on the modified National Cholesterol Education Program's Adult Treatment Panel III report (NCEP-ATPIII) criteria. We defined the visceral obesity as a visceral fat area of ≥ 100 cm(2) which was acquired by CT at the L4-5 level. To evaluate fatty liver, we applied a liver-to-spleen attenuation ratio ≤ 1.1 as measured by CT at the T12 level. We employed binary logistic regression models that used the presence or absence of metabolic syndrome as a dependent variable and age, sex, and the presence or absence of visceral obesity and fatty liver as independent variables. Visceral obesity was not found to be an independent variable as a risk factor of metabolic syndrome (odds ratio 2.7; 95% confidence interval 0.55-13.30), but fatty liver was found to be significant in this model (odds ratio 71.3; 95% CI 13.04-389.53). Our study suggests that liver fat may be a more important risk factor than visceral fat in terms of its association with metabolic syndrome.

Increased very low density lipoprotein (VLDL) secretion, hepatic steatosis, and insulin resistance

Insulin resistance (IR) affects not only the regulation of carbohydrate metabolism but all aspects of lipid and lipoprotein metabolism. IR is associated with increased secretion of VLDL and increased plasma triglycerides, as well as with hepatic steatosis, despite the increased VLDL secretion. Here we link IR with increased VLDL secretion and hepatic steatosis at both the physiologic and molecular levels. Increased VLDL secretion, together with the downstream effects on high density lipoprotein (HDL) cholesterol and low density lipoprotein (LDL) size, is proatherogenic. Hepatic steatosis is a risk factor for steatohepatitis and cirrhosis. Understanding the complex inter-relationships between IR and these abnormalities of liver lipid homeostasis will provide insights relevant to new therapies for these increasing clinical problems.

Storage of circulating free fatty acid in adipose tissue of postabsorptive humans: quantitative measures and implications for body fat distribution

OBJECTIVE

Preferential upper-body fat gain, a typical male pattern, is associated with a greater cardiometabolic risk. Regional differences in lipolysis and meal fat storage cannot explain sex differences in body fat distribution. We examined the potential role of the novel free fatty acid (FFA) storage pathway in determining body fat distribution in postabsorptive humans and whether adipocyte lipogenic proteins (CD36, acyl-CoA synthetases, and diacylglycerol acyltransferase) predict differences in FFA storage.

RESEARCH DESIGN AND METHODS

Rates of postabsorptive FFA (palmitate) storage into upper-body subcutaneous (UBSQ) and lower-body subcutaneous (LBSQ) fat were measured in 28 men and 53 premenopausal women. Stable and radiolabeled palmitate tracers were intravenously infused followed by subcutaneous fat biopsies. Body composition was assessed with a combination of dual-energy X-ray absorptiometry and computed tomography.

RESULTS

Women had greater FFA (palmitate) storage than men in both UBSQ (0.37 ± 0.15 vs. 0.27 ± 0.18 μmol · kg(-1) · min(-1), P = 0.0001) and LBSQ (0.42 ± 0.19 vs. 0.22 ± 0.11 μmol · kg(-1) · min(-1), P < 0.0001) fat. Palmitate storage rates were significantly greater in LBSQ than UBSQ fat in women, whereas the opposite was true in men. Plasma palmitate concentration positively predicted palmitate storage in both depots and sexes. Adipocyte CD36 content predicted UBSQ palmitate storage and sex-predicted storage in LBSQ fat. Palmitate storage rates per kilogram fat did not decrease as a function of fat mass, whereas lipolysis did.

CONCLUSIONS

The FFA storage pathway, which had remained undetected in postabsorptive humans until recently, can have considerable, long-term, and sex-specific effects on body fat distribution. It can also offer a way of protecting the body from excessive circulating FFA in obesity.

Different fatty acids inhibit apoB100 secretion by different pathways: unique roles for ER stress, ceramide, and autophagy

Although short-term incubation of hepatocytes with oleic acid (OA) stimulates secretion of apolipoprotein B100 (apoB100), exposure to higher doses of OA for longer periods inhibits secretion in association with induction of endoplasmic reticulum (ER) stress. Palmitic acid (PA) induces ER stress, but its effects on apoB100 secretion are unclear. Docosahexaenoic acid (DHA) inhibits apoB100 secretion, but its effects on ER stress have not been studied. We compared the effects of each of these fatty acids on ER stress and apoB100 secretion in McArdle RH7777 (McA) cells: OA and PA induced ER stress and inhibited apoB100 secretion at higher doses; PA was more potent because it also increased the synthesis of ceramide. DHA did not induce ER stress but was the most potent inhibitor of apoB100 secretion, acting via stimulation of autophagy. These unique effects of each fatty acid were confirmed when they were infused into C57BL6J mice. Our results suggest that when both increased hepatic secretion of VLDL apoB100 and hepatic steatosis coexist, reducing ER stress might alleviate hepatic steatosis but at the expense of increased VLDL secretion. In contrast, increasing autophagy might reduce VLDL secretion without causing steatosis.

Palmitate induces apoptosis in Schwann cells via both ceramide-dependent and independent pathways

Peripheral neuropathy has been reported to prevail in obese or pre-diabetic individuals, yet its etiology remains unknown. Palmitate, a saturated fatty acid increased in obesity and diabetes, is known to induce apoptosis in multiple types of cells and this effect may be mediated by ceramide, a member of the sphingolipid family. To clarify whether de novo ceramide synthesis from palmitate contributes to apoptosis of Schwann cells, we cultured immortalized mouse Schwann cells (IMS) and rat primary Schwann cells with palmitate, a ceramide analogue C2-ceramide as well as inhibitors of the de novo ceramide synthesis (myriocin and fumonisin B1). Apoptosis of IMS detected by nuclear staining and cell membrane inversion was significantly increased by incubation with palmitate for 48 h in a dose-dependent fashion. This enhanced apoptosis was partially but significantly suppressed by myriocin and fumonisin B1. Western blot analysis and immunostaining revealed that palmitate clearly activated caspase-3 in IMS. Unexpectedly, the ceramide synthesis inhibitors failed to suppress the palmitate-induced caspase-3 activation in spite of complete restoration in ceramide accumulation. The results seemed relevant to the observations that C2-ceramide did not activate caspase-3 while provoking apoptosis with a clear dose-dependency. In agreement, the pro-apoptotic action of C2-ceramide was not attenuated by caspase inhibitors that partially suppressed palmitate-induced apoptosis. These results in IMS were well reproducible in rat primary Schwann cells, indicating that the observed phenomena are not specific to the cell line. Collectively, we have reached a conclusion that palmitate induces apoptosis in Schwann cells via both a ceramide-mediated, caspase-3-independent pathway and ceramide-independent, caspase-3-dependent pathways. Given the fact that palmitate and ceramide are increased in obese or pre-diabetic subjects, these lipids may be implicated in the pathogenesis of peripheral neuropathy observed in these disorders.

Development and validation of a high-throughput screening assay for human long-chain fatty acid transport proteins 4 and 5

Dietary long-chain fatty acid (LCFA) uptake across cell membranes is mediated principally by fatty acid transport proteins (FATPs). Six subtypes of this transporter are differentially expressed throughout the human and rodent body. To facilitate drugs discovery against FATP subtypes, the authors used mammalian cell lines stably expressing the recombinant human FATP4 and 5 and developed a high-throughput screening (HTS) assay using a 96-well fluorometric imaging plate reader (FLIPR). LCFA uptake signal-to-background ratios were between 3- and 5-fold. Two 4-aryl-dihydropyrimidinones, j3 and j5, produced inhibition of FATP4 with a half-maximal inhibitory concentration (IC(50)) of 0.21 and 0.63 microM, respectively, and displayed approximately 100-fold selectivity over FATP5. The US Drug Collection library was screened against the FATP5. A hit rate of around 0.4% was observed with a Z' factor of 0.6 +/- 0.2. Two confirmed hits are bile acids, chenodiol and ursodiol with an IC(50) of 2.4 and 0.22 microM, respectively. To increase throughput, a single time point measurement in a 384-well format was developed using the Analyst HT, and the results are comparable with the 96-well format. In conclusion, the FATP4 and 5 cell-based fluorescence assays are suitable for a primary drug screen, whereas differentiated cell lines are useful for a secondary drug screen.

Effect of conjugated linoleic acid on body fat, tumor necrosis factor alpha and resistin secretion in spontaneously hypertensive rats

Conjugated linoleic acid (CLA) is a naturally occurring group of dienoic derivaties of linoleic acid found mainly in beef and dairy products. CLA has been reported to reduce body fat, as well as to possess anticarcinogenic, antiatherogenic and procatabolic activities in animals. The objective of this study was to evaluate the effect of CLA supplementation to spontaneously hypertensive rats (SHR) on body fat, biochemical parameters of serum related tumor necrosis factor alpha (TNF-alpha) and resistin secretion. Thirty rats were divided in three groups, the first group of spontaneously hypertensive rats received a standard diet (V-SHR group, n=10), a second group of SHR was fed 1.5% of conjugated linoleic acid (CLA-SHR group, n=10) and the third was the control, non-hypertensive group (KW, n=10) also on a standard diet including 7.5% of sunflower oil during eight weeks. After CLA diet administration, spontaneously hypertensive rats showed a significant reduction in blood pressure, serum glucose, cholesterol and triacylglycerols, together with reduction of index of body fat, pericardic, abdominal and epididymal adipose tissue. These effects were accompanied by a decrease in the secretion of TNF-alpha and resistin.

Adipose tissue expandability, lipotoxicity and the Metabolic Syndrome--an allostatic perspective

While the link between obesity and type 2 diabetes is clear on an epidemiological level, the underlying mechanism linking these two common disorders is not as clearly understood. One hypothesis linking obesity to type 2 diabetes is the adipose tissue expandability hypothesis. The adipose tissue expandability hypothesis states that a failure in the capacity for adipose tissue expansion, rather than obesity per se is the key factor linking positive energy balance and type 2 diabetes. All individuals possess a maximum capacity for adipose expansion which is determined by both genetic and environmental factors. Once the adipose tissue expansion limit is reached, adipose tissue ceases to store energy efficiently and lipids begin to accumulate in other tissues. Ectopic lipid accumulation in non-adipocyte cells causes lipotoxic insults including insulin resistance, apoptosis and inflammation. This article discusses the links between adipokines, inflammation, adipose tissue expandability and lipotoxicity. Finally, we will discuss how considering the concept of allostasis may enable a better understanding of how diabetes develops and allow the rational design of new anti diabetic treatments.

Pathophysiology and aetiology of impaired fasting glycaemia and impaired glucose tolerance: does it matter for prevention and treatment of type 2 diabetes?

Prior to the development of type 2 diabetes, glucose levels increase into the prediabetic states of isolated impaired fasting glycaemia (i-IFG), isolated impaired glucose tolerance (i-IGT), or combined IFG/IGT. A better understanding of the aetiology and pathophysiology of the prediabetic states might give a basis for the development of individualised prevention and treatment strategies for type 2 diabetes. Several studies have examined mechanisms and potential aetiological factors leading to the development of the different prediabetic states. The pathophysiology of i-IFG seems to include the following key defects: reduced hepatic insulin sensitivity, stationary beta cell dysfunction and/or chronic low beta cell mass, altered glucagon-like peptide-1 secretion and inappropriately elevated glucagon secretion. Conversely, the prediabetic state i-IGT is characterised by reduced peripheral insulin sensitivity, near-normal hepatic insulin sensitivity, progressive loss of beta cell function, reduced secretion of glucose-dependent insulinotropic polypeptide and inappropriately elevated glucagon secretion. Individuals developing combined IFG/IGT exhibit severe defects in both peripheral and hepatic insulin sensitivity as well as a progressive loss of beta cell function. The aetiologies of i-IFG and i-IGT also seem to differ, with i-IFG being predominantly related to genetic factors, smoking and male sex, while i-IGT is predominantly related to physical inactivity, unhealthy diet and short stature. Since the transition from the prediabetic states to overt type 2 diabetes is characterised by a non-reversible vicious cycle that includes severe deleterious effects on glucose metabolism, there are good reasons to use the well-established aetiological and pathophysiological differences in i-IFG, i-IGT and IFG/IGT to design individualised preventive strategies.

Visceral fat dominant distribution in male type 2 diabetic patients is closely related to hepatic insulin resistance, irrespective of body type

Background

All previous studies that investigated the association between abdominal fat distribution and insulin resistance evaluated subcutaneous and visceral fat area and/or volume, but these values were not related to the body type of each subject. In the present study we have examined the association between abdominal fat distribution and peripheral (muscle)/hepatic sensitivity to insulin using the visceral to abdominal subcutaneous fat area ratio (VF/SF ratio) in male patients with type 2 diabetes mellitus. This ratio defines the predominancy of visceral or subcutaneous abdominal adiposity, independent of the body type of each individual.

Methods

Thirty-six type 2 diabetic male patients underwent a euglycemic insulin clamp (insulin infusion rate = 40 mU/m²·min) with 3-³H-glucose to measure insulin-mediated total body (primarily reflects muscle) glucose disposal (TGD) and suppression of endogenous (primarily reflects liver) glucose production (EGP) in response to a physiologic increase in plasma insulin concentration. Abdominal subcutaneous (SF) and intraabdominal visceral fat (VF) areas were quantitated with magnetic resonance imaging (MRI) at the level of L_4–5.

Results

TGD and TGD divided by steady state plasma insulin concentration during the insulin clamp (TGD/SSPI) correlated inversely with body mass index (BMI), total fat mass (FM) measured by ³H₂O, SF and VF areas, while VF/SF ratio displayed no significant relationship with TGD or TGD/SSPI. In contrast, EGP and the product of EGP and SSPI during the insulin clamp (an index hepatic insulin resistance) correlated positively with VF/SF ratio, but not with BMI, FM, VF or SF.

Conclusion

We conclude that, independent of the individual's body type, visceral fat dominant accumulation as opposed to subcutaneous fat accumulation is associated with hepatic insulin resistance, whereas peripheral (muscle) insulin resistance is more closely related to general obesity (i.e. higher BMI and total FM, and increased abdominal SF and VF) in male patients with type 2 diabetes.