Plasma free fatty acid storage in subcutaneous and visceral adipose tissue in postabsorptive women

Bidirectional communication between brain and visceral white adipose tissue: Its potential impact on Alzheimer's disease

A variety of axes between brain and abdominal organs have been reported, but the interaction between brain and visceral white adipose tissue (vWAT) remains unclear. In this review, we summarized human studies on the association between brain and vWAT, and generalized their interaction and the underlying mechanisms according to animal and cell experiments. On that basis, we come up with the concept of the brain-vWAT axis (BVA). Furthermore, we analyzed the potential mechanisms of involvement of BVA in the pathogenesis of Alzheimer's disease (AD), including vWAT-derived fatty acids, immunological properties of vWAT, vWAT-derived retinoic acid and vWAT-regulated insulin resistance. The proposal of BVA may expand our understanding to some extent of how the vWAT impacts on brain health and diseases, and provide a novel approach to study the pathogenesis and treatment strategies of neurodegenerative disorders.

Effects of SGLT2 inhibition on lipid transport in adipose tissue in type 2 diabetes

SGLT2 inhibition induces an insulin-independent reduction in plasma glucose causing increased lipolysis and subsequent lipid oxidation by energy-consuming tissues. However, it is unknown whether SGLT2 inhibition also affects lipid storage in adipose tissue. Therefore, we aimed to determine the effects of SGLT2 inhibition on lipid storage and lipolysis in adipose tissue. We performed a randomized, double-blinded, placebo-controlled crossover design of 4 weeks of empagliflozin 25 mg and placebo once-daily in 13 individuals with type 2 diabetes treated with metformin. Adipose tissue fatty acid uptake, lipolysis rate and clearance were measured by 11C-palmitate PET/CT. Adipose tissue glucose uptake was measured by 18F-FDG PET/CT. Protein and gene expression of pathways involved in lipid storage and lipolysis were measured in biopsies of abdominal s.c. adipose tissue. Subjects were weight stable, which allowed us to quantify the weight loss-independent effects of SGLT2 inhibition. We found that SGLT2 inhibition did not affect free fatty acids (FFA) uptake in abdominal s.c. adipose tissue but increased FFA uptake in visceral adipose tissue by 27% (P < 0.05). In addition, SGLT2 inhibition reduced GLUT4 protein (P = 0.03) and mRNA content (P = 0.01) in abdominal s.c. adipose tissue but without affecting glucose uptake. In addition, SGLT2 inhibition decreased the expression of genes involved in insulin signaling in adipose tissue. We conclude that SGLT2 inhibition reduces GLUT4 gene and protein expression in abdominal s.c. adipose tissue, which could indicate a rebalancing of substrate utilization away from glucose oxidation and lipid storage capacity through reduced glycerol formation.

Influence of Free Fatty Acid Concentrations and Weight Loss on Adipose Tissue Direct Free Fatty Acid Storage Rates

CONTEXT

The factors that determine the recycling of free fatty acids (FFA) back into different adipose tissue depots via the direct storage pathway are not completely understood.

OBJECTIVE

To assess the interactions between adipocyte factors and plasma FFA concentrations that determine regional FFA storage rates.

DESIGN

We measured direct adipose tissue FFA storage rates before and after weight loss under high FFA (intravenous somatostatin and epinephrine) and low (intravenous insulin and glucose) FFA concentrations.

SETTING

Mayo Clinic Clinical Research Unit.

PATIENTS

Sixteen premenopausal women, body mass index 30 to 37 kg/m2.

INTERVENTION

Comprehensive lifestyle weight loss program.

MAIN OUTCOME MEASURE

Direct FFA storage rates in upper and lower body subcutaneous fat.

RESULTS

Over the entire range of FFA and under isolated conditions of elevated FFA concentrations, the storage rates of FFA into upper and lower body subcutaneous fat per unit lipid were associated with concentrations, not adipocyte fatty acid storage factors. Under low FFA conditions, direct FFA storage rates were related to adipocyte CD36 content, not tissue level content of fatty acid storage factors. Weight loss did not change these relationships.

CONCLUSIONS

The regulation of direct FFA storage under low FFA concentration conditions appears to be at the level of the cell/adipocyte content of CD36, whereas under high FFA concentration conditions, direct FFA storage at the tissue level is predicted by plasma FFA concentrations, independent of adipocyte size or fatty acid storage factors. These observations offer novel insights into how adipose tissue regulates direct FFA storage in humans.

Proteome analysis of human adipocytes identifies depot-specific heterogeneity at metabolic control points

Adipose tissue is a primary regulator of energy balance and metabolism. The distribution of adipose tissue depots is of clinical interest because the accumulation of upper-body subcutaneous (ASAT) and visceral adipose tissue (VAT) is associated with cardiometabolic diseases, whereas lower-body glutealfemoral adipose tissue (GFAT) appears to be protective. There is heterogeneity in morphology and metabolism of adipocytes obtained from different regions of the body, but detailed knowledge of the constituent proteins in each depot is lacking. Here, we determined the human adipocyte proteome from ASAT, VAT, and GFAT using high-resolution Sequential Window Acquisition of all Theoretical (SWATH) mass spectrometry proteomics. We quantified 4,220 proteins in adipocytes, and 2,329 proteins were expressed in all three adipose depots. Comparative analysis revealed significant differences between adipocytes from different regions (6% and 8% when comparing VAT vs. ASAT and GFAT, 3% when comparing the subcutaneous adipose tissue depots, ASAT and GFAT), with marked differences in proteins that regulate metabolic functions. The VAT adipocyte proteome was overrepresented with proteins of glycolysis, lipogenesis, oxidative stress, and mitochondrial dysfunction. The GFAT adipocyte proteome predicted the activation of peroxisome proliferator-activated receptor α (PPARα), fatty acid, and branched-chain amino acid (BCAA) oxidation, enhanced tricarboxylic acid (TCA) cycle flux, and oxidative phosphorylation, which was supported by metabolomic data obtained from adipocytes. Together, this proteomic analysis provides an important resource and novel insights that enhance the understanding of metabolic heterogeneity in the regional adipocytes of humans.NEW & NOTEWORTHY Adipocyte metabolism varies depending on anatomical location and the adipocyte protein composition may orchestrate this heterogeneity. We used SWATH proteomics in patient-matched human upper- (visceral and subcutaneous) and lower-body (glutealfemoral) adipocytes and detected 4,220 proteins and distinguishable regional proteomes. Upper-body adipocyte proteins were associated with glycolysis, de novo lipogenesis, mitochondrial dysfunction, and oxidative stress, whereas lower-body adipocyte proteins were associated with enhanced PPARα activation, fatty acid, and BCAA oxidation, TCA cycle flux, and oxidative phosphorylation.

Regulation of direct adipose tissue free fatty acid storage during mixed meal ingestion and high free fatty acid concentration conditions

We found that direct free fatty acid (FFA) storage (fatty acid cycling back into adipose tissue) in leg vs. abdominal subcutaneous fat is related to regional differences in adipose tissue diacylglycerol acyltransferase (DGAT) activity under high-FFA conditions and to differences in adipose tissue acyl-CoA synthetase (ACS)activity under meal ingestion conditions. We also found that direct FFA storage rates in leg fat were significantly less in physically active than sedentary adults. Direct FFA storage into adipocytes relates to body fat distribution. Adipose tissue CD36, ACS, and DGAT may account for some of the between-depot and interindividual variability in FFA storage. These studies were to test whether CD36, ACS, or DGAT might be important for direct palmitate storage under meal ingestion or high-FFA conditions. We measured upper (UBSQ) and lower body subcutaneous (LBSQ) adipose tissue FFA storage rates by infusing palmitate tracers intravenously and performing adipose biopsies under hypoinsulinemic (high-FFA) and mixed-meal conditions. We recruited five postmenopausal women, physically active males (5) and females (5), and sedentary males (5) and females (5). We found that 1) the ratio of UBSQ to LBSQ DGAT activity predicted the ratio of palmitate storage [adjusted R = 0.25, F = 8.0, P = 0.01, 95% CI (0.07, 0.48)] under high-FFA conditions; 2) the ratio of UBSQ to LBSQ ACS activity predicted the ratio of palmitate storage under meal conditions [adjusted R = 0.18, F = 6.3, P = 0.02, 95% CI (0.12, 1.28)]; 3) LBSQ direct palmitate storage rates were significantly less in physically active than sedentary and 4) adipose tissue CD36 protein content, ACS, or DGAT activities did not independently predict palmitate storage rates. We conclude that physically active adults have lesser fatty acid cycling back into adipose tissue and that adipose ACS and DGAT may affect competition between UBSQ and LBSQ adipose for direct palmitate storage.

Sex and Depot Differences in Palmitoleic Acid Content of Human Blood and Fat

Palmitoleic acid has been classified as an insulin-sensitizing lipokine, but evidence for this from human studies has been inconsistent. We hypothesized that this is related to either the types of samples or conditions under which samples are collected. We measured plasma palmitoleic acid and total free fatty acids (FFA) using ultra-performance liquid chromatography in blood samples collected from 34 adults under a variety of conditions. We collected duplicate samples of adipose (n = 10), FFA (n = 9), and very low density lipoprotein triacylglycerol (VLDL-TAG) (n = 7) to measure the palmitoleic acid as a percentage of total fatty acids. We tested whether the percentage of palmitoleic acid was correlated with insulin resistance, as measured by homeostatic model of insulin resistance (HOMA-IR). Adipose stearoyl-coenzyme A desaturase 1 (SCD-1) protein was measured by capillary Western blotting. FFA-palmitoleic acid percentage increased as a function of total FFA and was greater (p < 0.005) in females than males. Adipose palmitoleic acid percentage was greater in females than males (p < 0.001), as was adipose SCD-1. Palmitoleic acid was greater in femoral fat than in abdominal fat in both females and males (p < 0.001), and correlated positively with HOMA-IR only in females. The test-retest reliability values for percentage palmitoleic acid were 7 ± 10% for adipose, 24 ± 26% for VLDL, and 53 ± 31% for FFA. Because FFA-palmitoleic acid percentage varies as a function of total FFA, investigators should re-evaluate how palmitoleic acid data is presented. The positive relationship between adipose palmitoleic acid and HOMA-IR in females suggests that it is not a potent insulin-sensitizing lipokine in humans.

Relevance of human fat distribution on lipid and lipoprotein metabolism and cardiovascular disease risk

PURPOSE OF REVIEW

Upper body abdominal and lower body gluteofemoral fat depot masses display opposing associations with plasma lipid and lipoprotein and cardiovascular disease (CVD) risk profiles. We review developments on adipose tissue fatty acid metabolism in the context of body fat distribution and how that might be related to adverse lipid and lipoprotein profiles and CVD risk.

RECENT FINDINGS

Recent data have confirmed the paradoxical relationship of upper abdominal and lower body gluteofemoral adiposity and CVD risk. Mechanistically, this is likely to reflect the different ways fat depots handle lipid storage and release, which impacts directly and indirectly on lipid and lipoprotein metabolism. The upper body enhances immediate fat storage pathway with rapid uptake of dietary-derived fatty acids, whereas the lower body fat depot has a reduced lipid turnover accommodating a slower fat redistribution. Body fat distribution and the fat depots' ability to undergo appropriate expansion when fat storage is required, rather than overall body fatness, appear as the important determinant of metabolic health.

SUMMARY

A focus on fat distribution in overweight people, preferably using precise imaging methods, rather than quantifying total body fatness, is likely to provide the medical community with better tools to stratify and treat patients with obesity-related complications.

Epicardial Fat Thickness and Free Fatty Acid Level are Predictors of Acute Ischemic Stroke with Atrial Fibrillation

BACKGROUND

Increased epicardial fat is known to be associated with the presence and chronicity of atrial fibrillation (AF). Free fatty acids (FFAs) are major components of epicardial fat; however, their potential association with AF in ischemic stroke has not been investigated. We aimed to assess the performance of echocardiographic epicardial fat thickness (EFT) and plasma FFA level in identifying patients with ischemic stroke and AF.

METHODS

We enrolled a total of 214 consecutive patients (mean age, 66.8 ± 12.3 years; 39.7% women) diagnosed with acute ischemic stroke between March 2011 and June 2014. The patients were divided into two groups: ischemic stroke with AF (n = 35, 16.4%) and ischemic stroke without AF (n = 179, 83.6%).

RESULTS

The ischemic stroke with AF group showed significantly higher serum FFA level (1379.7 ± 717.5 vs. 757.8 ± 520.5 uEq/L, p < 0.0001) and EFT (6.5 ± 1.2 vs. 5.3 ± 1.2 mm, p < 0.001) than the group without AF. Multivariable logistic regression analysis demonstrated that age (odds ratio [OR], 1.112), serum FFA level (OR, 1.002), and EFT (OR, 1.740) were independently associated with the ischemic stroke group with AF. EFT and FFA significantly improved the goodness-of-fit and discriminability of the simple regression model including age as a covariate (log likelihood difference, 21.35; p < 0.001; c-index difference, 17.9%; p < 0.001).

CONCLUSIONS

High EFT and serum FFA level were associated with ischemic stroke in patients with AF. Echocardiographic EFT and serum FFA level can play a significant role in identifying ischemic stroke with AF.

Depot-specific differences in fat mass expansion in WT and ob/ob mice

The study was designed to investigate the cellular mechanisms underlying the differential fat expansion in different fat depots in wild type (WT) and ob/ob (OB) mice. At 6 weeks old, no differences in fat mass were found between SAT and VAT in WT mice, while O-SAT showed significantly higher weight than that of O-VAT. The average adipocyte size of SAT (~ 4133.47 μm2) was smaller than that of VAT (~ 7438.91 μm2) in OB mice. O-SAT preadipocytes gained higher triglyceride contents and higher levels of PPARγ and C/EBPα than did O-VAT preadipocytes upon in vitro differentiation. W-SAT and W-VAT displayed no significant differences in fatty acid uptake, while 1.36 fold significantly higher fatty acid uptake was found in O-SAT compared to O-VAT. Approximately 52% of the radioactivity recovered in cellular lipids was found in TAG in O-SAT, which was significantly higher than the other three adipocyte types. Significantly more radiolabelled oleic acid was β-oxidized to CO2 in adipocytes from O-VAT than that from O-SAT. ATP production was significantly lower in W-SAT compared with W-VAT, whereas no significantly ATP level was observed between O-SAT and O-VAT. Expression of UCP-1 in SAT from either WT or OB mice was significantly higher than the counterpart of VAT, which demonstrated higher uncoupled respiration and lower oxidative phosphorylation in SAT. Together, a combined increase in adipogenesis and FA uptake, and decreases in β-oxidation and ATP production, contributed to greater expansion of SAT compared to VAT in obese mice.

A cellular model for the investigation of depot specific human adipocyte biology

Upper-body adiposity is associated with increased metabolic disease risk, while lower-body adiposity is paradoxically protective. Efforts to understand the underlying mechanisms require appropriate and reproducible in vitro culture models. We have therefore generated immortalised (_im) human preadipocyte (PAD) cell lines derived from paired subcutaneous abdominal and gluteal adipose tissue. These cell lines, denoted _imAPAD and _imGPAD display enhanced proliferation and robust adipogenic capacities. Differentiated _imAPAD and _imGPAD adipocytes synthesize triglycerides de novo and respond lipolytically to catecholamine-stimulation. Importantly the cells retain their depot-of-origin 'memory' as reflected by inherent differences in fatty acid metabolism and expression of depot-specific developmental genes. These features make these cell lines an invaluable tool for the in vitro investigation of depot-specific human adipocyte biology.

Differences in the serum nonesterified Fatty Acid profile of young women associated with a recent history of gestational diabetes and overweight/obesity

Background

Nonesterified fatty acids (NEFA) play pathophysiological roles in metabolic syndrome and type 2 diabetes (T2D). In this study, we analyzed the fasting NEFA profiles of normoglycemic individuals at risk for T2D (women with a recent history of gestational diabetes (GDM)) in comparison to controls (women after a normoglycemic pregnancy). We also examined the associations of NEFA species with overweight/obesity, body fat distribution and insulin sensitivity.

Subjects and Methods

Using LC-MS/MS, we analyzed 41 NEFA species in the fasting sera of 111 women (62 post-GDM, 49 controls). Clinical characterization included a five-point oral glucose tolerance test (OGTT), biomarkers and anthropometrics, magnetic resonance imaging (n = 62) and a food frequency questionnaire. Nonparametric tests with Bonferroni correction, binary logistic regression analyses and rank correlations were used for statistical analysis.

Results

Women after GDM had a lower molar percentage of total saturated fatty acids (SFA; 38.55% vs. 40.32%, p = 0.0002) than controls. At an explorative level of significance several NEFA species were associated with post-GDM status (with and without adjustment for body mass index (BMI) and HbA1c): The molar percentages of 14:0, 16:0, 18:0 and 18:4 were reduced, whereas those of 18:1, 18:2, 20:2, 24:4, monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA) and total n-6 NEFA were increased. BMI and the amount of body fat correlated inversely with several SFA and MUFA and positively with various PUFA species over the whole study cohort (abs(ρ)≥0.3 for all). 14:0 was inversely and BMI-independently associated with abdominal visceral adiposity. We saw no correlations of NEFA species with insulin sensitivity and the total NEFA concentration was similar in the post-GDM and the control group.

Conclusion

In conclusion, we found alterations in the fasting NEFA profile associated with a recent history of gestational diabetes, a risk marker for T2D. NEFA composition also varied with overweight/obesity and with body fat distribution, but not with insulin sensitivity.

Alterations in oral [1-(14)C] 18:1n-9 distribution in lean wild-type and genetically obese (ob/ob) mice

Obesity may result from altered fatty acid (FA) disposal. Altered FA distribution in obese individuals is poorly understood. Lean wild-type C57BL/6J and obese C57BL/6Job/ob mice received an oral dose of [1-(14)C]18:1n-9 (oleic acid), and the radioactivity in tissues was evaluated at various time points. The (14)C concentration decreased rapidly in gastrointestinal tract but gradually increased and peaked at 96 h in adipose tissue, muscle and skin in lean mice. The (14)C concentration was constant in adipose tissue and muscle of obese mice from 4 h to 168 h. (14)C-label content in adipose tissue was significantly affected by genotype, whereas muscle (14)C-label content was affected by genotype, time and the interaction between genotype and time. There was higher total (14)C retention (47.7%) in obese mice than in lean mice (9.0%) at 168 h (P<0.05). The (14)C concentrations in the soleus and gastrocnemius muscle were higher in obese mice than in lean mice (P<0.05). Perirenal adipose tissue contained the highest (14)C content in lean mice, whereas subcutaneous adipose tissue (SAT) had the highest (14)C content and accounted for the largest proportion of total radioactivity among fat depots in obese mice. More lipid radioactivity was recovered as TAG in SAT from obese mice than from lean mice (P<0.05). Gene expression suggested acyl CoA binding protein and fatty acid binding protein are important for FA distribution in adipose tissue and muscle. The FA distribution in major tissues was altered in ob/ob mice, perhaps contributing to obesity. Understanding the disparity in FA disposal between lean and obese mice may reveal novel targets for the treatment and prevention of obesity.

Understanding multifactorial influences on the continuum of maternal weight trajectories in pregnancy and early postpartum: study protocol, and participant baseline characteristics

BACKGROUND

Maternal and offspring immediate and long-term health are affected by pregnancy weight gain and maternal weight. This study was designed to determine feasibility of: 1) recruiting a socio-economically and racially/ethnically diverse sample of pregnant women into a longitudinal observational study, including consenting the women for serial biologic specimen evaluations; 2) implementing comprehensive assessments (including biologic, anthropometric, behavioral, cognitive/psychosocial and socio-demographic, and cultural measures) at multiple time points over the study period, including collecting biologic specimens at planned and unplanned pregnancy delivery times; and 3) retaining the sample for one year into the postpartum period. Additionally, the study will provide preliminary data of associations among hypothesized predictors, mediators and moderators of pregnancy and post-partum maternal and infant weight trajectories. The study was conceptualized under a Biopsychosocial Model using a lifespan approach. Study protocol and baseline characteristics are described.

METHODS/DESIGN

We sought to recruit a sample of 100 healthy women age 18-45 years, between 28-34 weeks gestation, with singleton pregnancies, enrolled in care prior to 17 weeks gestation. Women provide written consent for face-to-face (medical history, anthropometrics, biologic specimens), and paper-and-pencil assessments, at five time points: baseline (third trimester), delivery-associated, and 6-weeks, 3-months and 6-months postpartum. Additional telephone-based assessments (diet, physical activity and breastfeeding) administered baseline and three-months postpartum. Infant weights are collected until 1-year of life. We seek to retain 80% of participants at six-months postpartum and 80% of offspring at 12-months. 110 women were recruited. Sample characteristics include: mean age 28.3 years, BMI 25.7 kg/m(2), and gestational age at baseline visit of 32.5 weeks. One-third of cohort was non-white, over a quarter were Latina, and almost a quarter were non-US born. The cohort majority was multigravida, had graduated high school and/or had higher levels of education, and worked outside the home.

DISCUSSION

Documentation of study feasibility and preliminary data for theory-driven hypothesis of maternal and child factors associated with weight trajectories will support future large scale longitudinal studies of risk and protective factors for maternal and child health. This research will also inform intervention targets facilitating healthy maternal and child weight.

Effects of increased free fatty acid availability on adipose tissue fatty acid storage in men

CONTEXT

A portion of free fatty acids (FFA) released from adipose tissue lipolysis are re-stored in adipocytes via direct uptake. Rates of direct adipose tissue FFA storage are much greater in women than men, but women also have greater systemic FFA flux and more body fat.

OBJECTIVE

We tested the hypotheses that experimental increases in FFA in men would equalize the rates of direct adipose tissue FFA storage in men and women.

DESIGN

We used a lipid emulsion infusion to raise FFA in men to levels seen in post-absorptive women. Direct FFA storage (μmol · kg fat(-1) · min(-1)) rates in abdominal and femoral fat was assessed using stable isotope tracer infusions to measure FFA disappearance rates and an iv FFA radiotracer bolus/timed biopsy.

SETTING

These studies were performed in a Clinical Research Center.

PARTICIPANTS

Data from 13 non-obese women was compared with that from eight obese and eight non-obese men.

INTERVENTION

The men received a lipid emulsion infusion to raise FFA.

MAIN OUTCOME MEASURES

We measured the rates of direct FFA storage in abdominal and femoral adipose tissue.

RESULTS

The three groups were similar in age and FFA flux by design; obese men had similar body fat percentage as non-obese women. Despite matching for FFA concentrations and flux, FFA storage per kg abdominal (P < .01) and femoral (P < .001) fat was less in both lean and obese men than in non-obese women. Abdominal FFA storage rates were correlated with proteins/enzymes in the FFA uptake/triglyceride synthesis pathway in men.

CONCLUSION

The lesser rates of direct FFA adipose tissue in men compared with women cannot be explained by reduced FFA availability.

Adipose tissue diacylglycerol acyltransferase activity and blood lipoprotein triglyceride enrichment in women with abdominal obesity

Previous studies have suggested altered triglyceride (TG) storage in patients with abdominal obesity and blood lipid disorders.

OBJECTIVE

We hypothesized that women with abdominal obesity and a dysmetabolic profile have low DGAT activity in their abdominal fat compartments.

METHODS

Paired omental (OM) and subcutaneous (SC) adipose tissue samples were obtained surgically from 39 women undergoing abdominal hysterectomies. Body composition and fat distribution were measured by dual energy x-ray absorptiometry and computed tomography. DGAT activity was measured by acylation of sn-l,2-diacylglycerol with [(14)C] oleoyl-CoA in microsomal fractions isolated from whole adipose tissue homogenates. DGAT activity was calculated on the basis of picomoles (pmol) TG synthesized in the assay per min per mg lipid, per μg protein or per 1000 cells.

RESULTS

No depot differences were found when DGAT activity was reported per μg microsomal protein or per 1000 cells. DGAT activity in either depot was not associated with adipocyte diameters and blood lipid profile variables. DGAT activity per mg lipid was higher in OM than in abdominal SC adipose tissue (0.43 ± 0.20 vs. 0.34 ± 0.18 pmol/min/mg lipid, p < 0.05). OM DGAT activity was negatively correlated with OM adipocyte diameter and visceral adipose tissue area (r = -0.43, p < 0.01 and r = -0.38, p < 0.05 respectively). Plasma total, LDL and HDL TG levels were negatively associated with OM DGAT activity independent of total body fat mass (r = -0.39, p < 0.05, r = -0.46, p < 0.001 and r = -0.40, p < 0.05 respectively).

CONCLUSION

A defect in adipose tissue DGAT activity is predictive of adiposity and blood lipoprotein TG enrichment only when considering activity per tissue lipid mass.

Systemic free fatty acid disposal into very low-density lipoprotein triglycerides

We measured the incorporation of systemic free fatty acids (FFA) into circulating very low-density lipoprotein triglycerides (VLDL-TGs) under postabsorptive, postprandial, and walking conditions in humans. Fifty-five men and 85 premenopausal women with BMI 18-24 (lean) and 27-36 kg/m(2) (overweight/obese) received an intravenous bolus injection of [1,1,2,3,3-(2)H5]glycerol (to measure VLDL-TG kinetics) and either [1-(14)C]palmitate or [9,10-(3)H]palmitate to determine the proportion of systemic FFA that is converted to VLDL-TG. Experiments started at 0630 h after a 12-h overnight fast. In the postabsorptive protocol, participants rested and remained fasted until 1330 h. In the postprandial protocol, volunteers ingested frequent portions of a fat-free smoothie. In the walking protocol, participants walked on a treadmill for 5.5 h at ∼3× resting energy expenditure. Approximately 7% of circulating FFA was converted into VLDL-TG. VLDL-TG secretion rates (SRs) were not statistically different among protocols. Visceral fat mass was the only independent predictor of VLDL-TG secretion, explaining 33-57% of the variance. The small proportion of systemic FFA that is converted to VLDL-TG can confound the expected relationship between plasma FFA concentration and VLDL-TG SRs. Regulation of VLDL-TG secretion is complex in that, despite a broad spectrum of physiological FFA concentrations, VLDL-TG SRs did not vary based on different acute substrate availability.

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.

Epicardial and subcutaneous adipose tissue Fatty acids profiles in diabetic and non-diabetic patients candidate for coronary artery bypass graft

INTRODUCTION

We have recently shown that in high cholesterol-fed rabbits, the sensitivity of epicardial adipose tissue to changes in dietary fat is higher than that of subcutaneous adipose tissue. Although the effects of diabetes on epicardial adipose tissue thickness have been studied, the influence of diabetes on profile of epicardial free fatty acids (FFAs) has not been studied. The aim of this study is to investigate the effect of diabetes on the FFAs composition in serum and in the subcutaneous and epicardial adipose tissues in patients undergoing coronary artery bypass graft (CABG).

METHODS

Forty non-diabetic and twenty eight diabetic patients candidate for CABG with >75% stenosis participated in this study. Fasting blood sugar (FBS) and lipid profiles were assayed by auto analyzer. Phospholipids and non-estrified FFA of serum and the fatty acids profile of epicardial and subcutaneous adipose tissues were determined using gas chromatography method.

RESULTS

In the phospholipid fraction of diabetic patients' serum, the percentage of 16:0, 18:3n-9, 18:2n-6 and monounsaturated fatty acids (MUFAs) was lower than the corresponding values of the non-diabetics; whereas, 18:0 value was higher. A 100% increase in the amount of 18:0 and 35% decrease in the level of 18:1n-11 was observed in the diabetic patients' subcutaneous adipose tissue. In epicardial adipose tissue, the increase of 18:0 and conjugated linolenic acid (CLA) and decrease of 18:1n-11, w3 (20:5n-3) and 22:6n-3 were significant; but, the contents of arachidonic acid and its precursor linoleic acid were not affected by diabetes.

CONCLUSION

The fatty acids' profile of epicardial and subcutaneous adipose tissues is not equally affected by diabetes. The significant decrease of 16:0 and w3 fatty acids and increase of trans and conjugated fatty acids in epicardial adipose tissue in the diabetic patients may worsen the formation of atheroma in the related arteries.

Body composition determines direct FFA storage pattern in overweight women

Direct FFA storage in adipose tissue is a recently appreciated pathway for postabsorptive lipid storage. We evaluated the effect of body fat distribution on direct FFA storage in women with different obesity phenotypes. Twenty-eight women [10 upper body overweight/obese (UBO; WHR >0.85, BMI >28 kg/m(2)), 11 lower body overweight/obese (LBO; WHR <0.80, BMI >28 kg/m(2)), and 7 lean (BMI <25 kg/m(2))] received an intravenous bolus dose of [9,10-(3)H]palmitate- and [1-(14)C]triolein-labeled VLDL tracer followed by upper body subcutaneous (UBSQ) and lower body subcutaneous (LBSQ) fat biopsies. Regional fat mass was assessed by combining DEXA and CT scanning. We report greater fractional storage of FFA in UBSQ fat in UBO women compared with lean women (P < 0.01). The LBO women had greater storage per 10(6) fat cells in LBSQ adipocytes compared with UBSQ adipocytes (P = 0.04), whereas the other groups had comparable storage in UBSQ and LBSQ adipocytes. Fractional FFA storage was significantly associated with fractional VLDL-TG storage in both UBSQ (P < 0.01) and LBSQ (P = 0.03) adipose tissue. In conclusion, UBO women store a greater proportion of FFA in the UBSQ depot compared with lean women. In addition, LBO women store FFA more efficiently in LBSQ fat cells compared with UBSQ fat cells, which may play a role in development of their LBO phenotype. Finally, direct FFA storage and VLDL-TG fatty acid storage are correlated, indicating they may share a common rate-limiting pathway for fatty acid storage in adipose tissue.

Short-term regional meal fat storage in nonobese humans is not a predictor of long-term regional fat gain

Although body fat distribution strongly predicts metabolic health outcomes related to excess weight, little is known about the factors an individual might exhibit that predict a particular fat distribution pattern. We utilized the meal fatty acid tracer-adipose biopsy technique to assess upper and lower body subcutaneous (UBSQ and LBSQ, respectively) meal fat storage in lean volunteers who then were overfed to gain weight. Meal fatty acid storage in UBSQ and LBSQ adipose tissue, as well as daytime substrate oxidation (indirect calorimetry), was measured in 28 nonobese volunteers [n = 15 men, body mass index = 22.1 ± 2.5 (SD)] before and after an ∼8-wk period of supervised overfeeding (weight gain = 4.6 ± 2.2 kg, fat gain = 3.8 ± 1.7 kg). Meal fat storage (mg/g adipose tissue lipid) in UBSQ (visit 1: 0.78 ± 0.34 and 1.04 ± 0.71 for women and men, respectively, P = 0.22; visit 2: 0.71 ± 0.24 and 0.90 ± 0.37 for women and men, respectively, P = 0.08) and LBSQ (visit 1: 0.60 ± 0.23 and 0.48 ± 0.29 for women and men, respectively, P = 0.25; visit 2: 0.62 ± 0.24 and 0.65 ± 0.23 for women and men, respectively, P = 0.67) adipose tissue did not differ between men and women at either visit. Fractional meal fatty acid storage in UBSQ (0.31 ± 0.15) or LBSQ (0.19 ± 0.13) adipose tissue at visit 1 did not predict the percent change in regional body fat in response to overfeeding. These data indicate that meal fat uptake trafficking in the short term (24 h) is not predictive of body fat distribution patterns. In general, UBSQ adipose tissue appears to be a favored depot for meal fat deposition in both sexes, and redistribution of meal fatty acids likely takes place at later time periods.

Storage rates of circulating free fatty acid into adipose tissue during eating or walking in humans

We measured subcutaneous adipose tissue free fatty acid (FFA) storage rates in postprandial and walking conditions to better understand the contributions of this pathway to body fat distribution. Palmitate tracers were infused intravenously and fat biopsies collected to measure palmitate storage in upper- (UBSQ) and lower-body subcutaneous (LBSQ) fat in 41 (17 men) and 40 (16 men) volunteers under postprandial and under postabsorptive walking conditions, respectively. Postprandial palmitate storage was greater in women than men in UBSQ (0.50±0.25 vs. 0.33±0.37 μmol⋅kg fat(-1)⋅min(-1); P=0.007) and LBSQ fat (0.37±0.25 vs. 0.22±0.20 μmol⋅kg fat(-1)⋅min(-1); P=0.005); storage rates were significantly greater in UBSQ than LBSQ fat in both sexes. During walking, UBSQ palmitate storage did not differ between sexes, whereas LBSQ storage was greater in women than men (0.40±0.22 vs. 0.25±0.15 μmol⋅kg fat(-1)⋅min(-1); P=0.01). In women only, walking palmitate storage was significantly greater in LBSQ than UBSQ fat. Adipocyte CD36 and diacylglycerol acyltransferase (DGAT) correlated with LBSQ palmitate storage in the postprandial and walking condition, respectively. We conclude that UBSQ fat is the preferred postprandial FFA storage depot for both sexes, whereas walking favors storage in LBSQ fat in women. Transmembrane transport (CD36) and esterification into triglycerides (DGAT) may be rate-limiting steps for LBSQ FFA storage during feeding and exercise.

Similar VLDL-TG storage in visceral and subcutaneous fat in obese and lean women

OBJECTIVE

Excess visceral fat accumulation is associated with the metabolic disturbances of obesity. Differential lipid redistribution through lipoproteins may affect body fat distribution. This is the first study to investigate VLDL-triglyceride (VLDL-TG) storage in visceral fat.

RESEARCH DESIGN AND METHODS

Nine upper-body obese (UBO; waist circumference >88 cm) and six lean (waist circumference <80 cm) women scheduled for elective tubal ligation surgery were studied. VLDL-TG storage in visceral, upper-body subcutaneous (UBSQ), and lower-body subcutaneous (LBSQ) fat were measured with [9,10-(3)H]-triolein-labeled VLDL.

RESULTS

VLDL-TG storage in visceral fat accounted for only ~0.8% of VLDL-TG turnover in UBO and lean women, respectively. A significantly larger proportion of VLDL-TG turnover was stored in UBSQ (~5%) and LBSQ (~4%) fat. The VLDL-TG fractional storage was similar in UBO and lean women for all regional depots. VLDL-TG fractional storage and VLDL-TG concentration were correlated in UBO women in UBSQ fat (r = 0.68, P = 0.04), whereas an inverse association was observed for lean women in visceral (r = -0.89, P = 0.02) and LBSQ (r = -0.87, P = 0.02) fat.

CONCLUSIONS

VLDL-TG storage efficiency is similar in all regional fat depots, and trafficking of VLDL-TG into different adipose tissue depots is similar in UBO and lean women. Postabsorptive VLDL-TG storage is unlikely to be of major importance in the development of preferential upper-body fat distribution in obese women.

Free fatty acid storage in human visceral and subcutaneous adipose tissue: role of adipocyte proteins

OBJECTIVE

Because direct adipose tissue free fatty acid (FFA) storage may contribute to body fat distribution, we measured FFA (palmitate) storage rates and fatty acid (FA) storage enzymes/proteins in omental and abdominal subcutaneous fat.

RESEARCH DESIGN AND METHODS

Elective surgery patients received a bolus of [1-(14)C]palmitate followed by omental and abdominal subcutaneous fat biopsies to measure direct FFA storage. Long chain acyl-CoA synthetase (ACS) and diacylglycerol acyltransferase activities, CD36, fatty acid-binding protein, and fatty acid transport protein 1 were measured.

RESULTS

Palmitate tracer storage (dpm/g adipose lipid) and calculated palmitate storage rates were greater in omental than abdominal subcutaneous fat in women (1.2 ± 0.8 vs. 0.7 ± 0.4 μmol · kg adipose lipid(-1) · min(-1), P = 0.005) and men (0.7 ± 0.2 vs. 0.2 ± 0.1, P < 0.001), and both were greater in women than men (P < 0.0001). Abdominal subcutaneous adipose tissue palmitate storage rates correlated with ACS activity (women: r = 0.66, P = 0.001; men: r = 0.70, P = 0.007); in men, CD36 was also independently related to palmitate storage rates. The content/activity of FA storage enzymes/proteins in omental fat was dramatically lower in those with more visceral fat. In women, only omental palmitate storage rates were correlated (r = 0.54, P = 0.03) with ACS activity.

CONCLUSIONS

Some adipocyte FA storage factors correlate with direct FFA storage, but sex differences in this process in visceral fat do not account for sex differences in visceral fatness. The reduced storage proteins in those with greater visceral fat suggest that the storage factors we measured are not a predominant cause of visceral adipose tissue accumulation.

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.

Tracing the fate of dietary fatty acids: metabolic studies of postprandial lipaemia in human subjects

Most postprandial studies have investigated the response of a single meal, yet the ingestion of sequential meals is more typical in a Western society. The aim of this review is to explain how natural and stable isotope tracers of fatty acids have been used to investigate the metabolism of dietary fat after single and multiple meals, with a focus on in vivo measurements of adipose tissue metabolism. When stable isotope tracers are combined with arteriovenous difference measurements, very specific measurements of metabolic flux across tissues can be made. We have found that adipose tissue is a net importer of dietary fat for 5 h following a single test meal and for most of the day during a typical three-meal eating pattern. When dietary fat is cleared from plasma, some fatty acids ‘spillover’ into the plasma and contribute up to 50% of postprandial plasma NEFA concentrations. Therefore, plasma NEFA concentrations after a meal reflect the balance between intracellular and extracellular lipolysis in adipose tissue. This balance is altered after the acute ingestion of fructose. The enzyme lipoprotein lipase is a key modulator of fatty acid flux in adipose tissue and its rate of action is severely diminished in obese men. In conclusion, in vivo studies of human metabolism can quantify the way that adipose tissue fatty acid trafficking modulates plasma lipid concentrations. This has implications for the flux of fatty acids to tissues that are susceptible to ectopic fat deposition such as the liver and muscle.

Inclusion of flaxseed in hay- and barley silage diets increases alpha-linolenic acid in cow plasma independent of forage type

Feeding flaxseed to cattle may be a means of increasing omega-3 fatty acid levels in ruminant products, but possible interactions with conserved forages have not been investigated. Twelve Holstein cows were used in a replicated 4 × 4 Latin Square experiment. Cows were fed one of four 50:50 forage:concentrate diets (DM basis): hay (hay control, HC), hay plus 15% ground flaxseed (hay-flaxseed, HF), barley silage (silage control, SC), and barley silage plus 15% ground flaxseed (silage-flaxseed, SF). Plasma concentrations of alpha-linolenic acid (ALA) did not differ between SC and HC diets. Flaxseed increased ALA (P < 0.05), but levels were not influenced by forage type. Flaxseed slightly increased 18:2n-6 (P < 0.05) and some n-6 and n-3 elongation and desaturation products, particularly arachidonic acid (ARA) and eicosapentaenoic acid (EPA). Flaxseed also increased C18:0 (P < 0.05) with this increase being greater (P < 0.01) for cows fed SF than HF. Feeding flaxseed also increased plasma C18:1-trans isomers (P < 0.01), predominantly vaccenic acid (VAA, 18:1-t11), with this increase being greater (P < 0.05) in cows fed HF than SF. Although conjugated linoleic acid (CLA) was increased (P < 0.001) with flaxseed it was not influenced by forage type (P = 0.06). Overall, feeding flaxseed increased plasma ALA, EPA, ARA and CLA independently of forage type. Feeding flaxseed with silage, however, resulted in more 18:0, while feeding flaxseed with hay resulted in greater accumulations of plasma 18:1-trans isomers mainly in the form of VAA.

Combined gene and protein expression of hormone-sensitive lipase and adipose triglyceride lipase, mitochondrial content, and adipocyte size in subcutaneous and visceral adipose tissue of morbidly obese men

AIMS

Lipotoxicity in obesity might be a failure of adipocytes to respond sufficiently adequate to persistent energy surplus. To evaluate the role of lipolytic enzymes or mitochondria in lipotoxicity, we studied expression levels of genes and proteins involved in lipolysis and mitochondrial DNA (mtDNA) content.

METHODS

As differences in lipid metabolism between men and women are extremely complex, we recruited only men (lean and morbidly obese) and collected subcutaneous and visceral adipose tissue during abdominal surgery for real-time PCR gene expression, protein expression, and microscopic study.

RESULTS

Although mRNA levels of hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) were increased in visceral adipose tissue of morbidly obese men, this was not paralleled by alterations in protein expression and phosphorylation of HSL and ATGL. mtDNA content of visceral adipose tissue was increased in morbidly obese men as compared to lean controls (p < 0.013). Positive correlations were observed between visceral adipocyte size and serum triacylglycerol (r = 0.6, p < 0.007) as well as between visceral adipocyte size and CRP (r = 0.6, p < 0.009) in analyses performed separately in obese men.

CONCLUSION

Lipotoxicity of morbidly obese men might be related to the quantitative impact of the visceral fat depot rather than to important dysregulation of involved lipolytic enzymes or adipocyte mitochondria.

A novel ELISA for measuring CD36 protein in human adipose tissue

CD36 is a transmembrane protein present in many tissues that is believed to facilitate inward fatty acid transport. Western blotting is the most widely used method to measure tissue CD36 protein content, but it is time consuming, technically demanding, and semiquantitative. To more precisely measure adipose tissue CD36 content we developed an enzyme linked immunosorbent assay (ELISA) after establishing that: 1) the anti-CD36 antibodies gave a single distinct band on traditional Western blots, and 2) the vast majority of adipocyte CD36 resides in the plasma membrane. By using serial dilutions of each sample and including a calibrator sample and quality control sample on each plate, we could achieve inter- and intra-assay variability of ∼ 10%. We found that CD36 content in omental and abdominal subcutaneous adipose tissue varied over a 2-5-fold range depending upon the means of data expression (per units of tissue protein, weight, or lipid). Omental CD36 content in women decreased markedly (P = 0.01) as a function of fat cell size. For the most part, tissue CD36 content was not correlated with CD36 mRNA. This ELISA method for tissue CD36 content should enhance research into the role of this protein on tissue fatty acid uptake.

Meal fat storage in subcutaneous adipose tissue: comparison of pioglitazone and glipizide treatment of type 2 diabetes

Treatment of type 2 diabetes (T2DM) with pioglitazone changes abdominal fat in the opposite direction as treatment with glipizide. To determine whether these two medications affect adipose tissue meal fatty acid storage differently we studied 19 T2DM treated with either pioglitazone (n = 8) or glipizide (n = 11) and 11 non-DM control subjects matched for age, BMI, abdominal and leg fat. A breakfast mixed meal containing [1-(14)C]triolein was given and abdominal and femoral subcutaneous (sc) adipose tissue biopsies were collected 6 and 24 h later to measure meal fatty acid storage. The portion of meal fatty acids stored in upper body sc and lower body sc adipose tissue did not differ between non-DM and T2DM subjects either at 6 or 24 h. Likewise, meal fatty acid storage did not differ between the T2DM participants treated with pioglitazone or glipizide. We conclude that meal fatty acid storage in upper body and lower body sc adipose tissue is not abnormal in T2DM patients treated with pioglitazone or glipizide.

Relationship between plasma free fatty acid, intramyocellular triglycerides and long-chain acylcarnitines in resting humans

We hypothesized that plasma non-esterified fatty acids (NEFA) are trafficked directly to intramyocellular long-chain acylcarnitines (imLCAC) rather than transiting intramyocellular triglycerides (imTG) on the way to resting muscle fatty acid oxidation. Overnight fasted adults (n = 61) received intravenous infusions of [U-(13)C]palmitate (0400-0830 h) and [U-(13)C]oleate (0800-1400 h) labelling plasma NEFA, imTG, imLCAC and im-non-esterified FA (imNEFA). Two muscle biopsies (0830 and 1400 h) were performed following 6 h, overlapping, sequential palmitate/oleate tracer infusions. Enrichment of plasma palmitate was approximately 15 times greater than enrichment of imTG, imNEFA-palmitate and im-palmitoyl-carnitine. Fatty acid enrichment in LCAC was correlated with imTG and imNEFA; there was a significant correlation between imTG concentrations and imLCAC concentrations in women (r = 0.51, P = 0.005), but not men (r = 0.30, P = 0.11). We estimated that approximately 11% of NEFA were stored in imTG. imTG NEFA storage was correlated only with NEFA concentrations (r = 0.52, P = 0.004) in women and with V(O(2),peak) (r = 0.45, P = 0.02) in men. At rest, plasma NEFA are trafficked largely to imTG before they enter LCAC oxidative pools; thus, imTG are an important, central pool that regulates the delivery of fatty acids to the intracellular environment. Factors relating to plasma NEFA storage into imTG differ in men and women.

Higher free fatty acid uptake in visceral than in abdominal subcutaneous fat tissue in men

Visceral adipose tissue has been shown to have high lipolytic activity. The aim of this study was to examine whether free fatty acid (FFA) uptake into visceral adipose tissue is enhanced compared to abdominal subcutaneous tissue in vivo. Abdominal adipose tissue FFA uptake was measured using positron emission tomography (PET) and [(18)F]-labeled 6-thia-hepta-decanoic acid ([(18)F]FTHA) and fat masses using magnetic resonance imaging (MRI) in 18 healthy young adult males. We found that FFA uptake was 30% higher in visceral compared to subcutaneous adipose tissue (0.0025 +/- 0.0018 vs. 0.0020 +/- 0.0016 micromol/g/min, P = 0.005). Visceral and subcutaneous adipose tissue FFA uptakes were strongly associated with each other (P < 0.001). When tissue FFA uptake per gram of fat was multiplied by the total tissue mass, total FFA uptake was almost 1.5 times higher in abdominal subcutaneous than in visceral adipose tissue. In conclusion, we observed enhanced FFA uptake in visceral compared to abdominal subcutaneous adipose tissue and, simultaneously, these metabolic rates were strongly associated with each other. The higher total tissue FFA uptake in subcutaneous than in visceral adipose tissue indicates that although visceral fat is active in extracting FFA, its overall contribution to systemic metabolism is limited in healthy lean males. Our results indicate that subcutaneous, rather than visceral fat storage plays a more direct role in systemic FFA availability. The recognized relationship between abdominal visceral fat mass and metabolic complications may be explained by direct effects of visceral fat on the liver.

Fatty acid metabolism in the elderly: effects of dehydroepiandrosterone and testosterone replacement in hormonally deficient men and women

CONTEXT

Aging, low dehydroepiandrosterone (DHEA), and testosterone are associated with increased adiposity and metabolic risk. Treatment with these hormones may improve these abnormalities.

OBJECTIVE

The objective of the study was to determine effects of aging, DHEA, or testosterone replacement on adiposity, meal fat partitioning, and postabsorptive lipolysis.

DESIGN

This was a cross-sectional, 2-yr, double-blind, randomized, placebo-controlled trial.

SETTING

The study was conducted in the general community.

PATIENTS

Elderly women and men (>or=60 yr) with low DHEA sulfate (women and men) and bioavailable testosterone (men) concentrations and young adults.

INTERVENTIONS

Thirty elderly women each received 50 mg DHEA or placebo daily for 2 yr. Thirty elderly men received 75 mg DHEA, 29 received 5 mg testosterone (patch), and 32 received placebo daily for 2 yr. Thirty young women and 32 young men served as controls.

MAIN OUTCOME MEASURES

In vivo measures of meal fat storage into sc fat, postabsorptive lipolysis, and regional adiposity at baseline and after treatment.

RESULTS

At baseline, the elderly had more body fat, greater systemic lipolysis (women, P = 0.0003; men, P < 0.0001) adjusted for resting energy expenditure, greater meal fat oxidation (women, P = 0.026; men, P = 0.0025), and less meal fat storage in sc fat (women, P = 0.0139; men, P= 0.0006). Although testosterone treatment increased meal fat storage into upper- vs. lower-body fat in elderly men, neither hormone affected regional adiposity, meal fat oxidation, or systemic lipolysis.

CONCLUSIONS

Aging, in the context of low DHEA sulfate (women and men) and bioavailable testosterone (men) concentrations, is associated with changes in meal fat partitioning and postabsorptive lipolysis that are not corrected by DHEA and only partly corrected by testosterone replacement.

Sexual differences in the control of energy homeostasis

The prevalence of obesity has reached epidemic proportion with enormous costs in both human lives and healthcare dollars spent. Obesity-related metabolic disorders are much lower in premenopausal women than men; however, there is a dramatic increase following menopause in women. The health risks associated with obesity vary depending on the location of adipose tissue. Adipose tissue distributed in the abdominal visceral carry a much greater risk for metabolic disorders than does adipose tissue distributed subcutaneously. There are distinct sex-dependent differences in the regional fat distribution, women carry more fat subcutaneously whereas men carry more fat viscerally. Males and females differ with respect to their regulation of energy homeostasis. Peripheral adiposity hormones such as leptin and insulin as well as sex hormones directly influence energy balance. Sexual dimorphisms in energy balance, body fat distribution, and the role sex hormones have in mediating these differences are the focus of this review.

Visceral and subcutaneous adipose tissue diacylglycerol acyltransferase activity in humans

Diacylglycerol acyltransferase (DGAT) could be a rate limiting step in triglyceride (TG) synthesis as it is the final step in this pathway. As such, between depot differences in DGAT activity could influence regional fat storage. DGAT activity and in vitro rates of direct free fatty acid (FFA) storage were measured in abdominal subcutaneous and omental adipose tissue samples from 12 nonobese (BMI<30 kg/m2) and 23 obese men and women (BMI>30 kg/m2) undergoing elective surgery. DGAT activity was greater in omental than in abdominal subcutaneous adipose tissue from nonobese patients (2.0+/-0.9 vs. 0.9+/-0.3 pmol/min/mg lipid, respectively, P=0.003), but not from obese patients (1.4+/-0.6 vs. 1.7+/-0.7 pmol/min/mg lipid, respectively, P=0.10). DGAT activity per unit adipose weight was negatively correlated with adipocyte size (P<0.01) and positively correlated with direct FFA storage in omental (P<0.001) but not in abdominal subcutaneous fat. Tissue DGAT activity varies as a function of adipocyte size, but this relationship differs between visceral and abdominal subcutaneous fat in obese and nonobese humans. Our results are consistent with the hypothesis that interindividual variations in DGAT activity may be an important regulatory step in visceral adipose tissue FFA uptake/storage.

Lipolysis and lipid mobilization in human adipose tissue

Triacylglycerol (TAG) stored in adipose tissue (AT) can be rapidly mobilized by the hydrolytic action of the three main lipases of the adipocyte. The non-esterified fatty acids (NEFA) released are used by other tissues during times of energy deprivation. Until recently hormone-sensitive lipase (HSL) was considered to be the key rate-limiting enzyme responsible for regulating TAG mobilization. A novel lipase named adipose triglyceride lipase/desnutrin (ATGL) has been identified as playing an important role in the control of fat cell lipolysis. Additionally perilipin and other proteins of the surface of the lipid droplets protecting or exposing the TAG core of the droplets to lipases are also potent regulators of lipolysis. Considerable progress has been made in understanding the mechanisms of activation of the various lipases. Lipolysis is under tight hormonal regulation. The best understood hormonal effects on AT lipolysis concern the opposing regulation by insulin and catecholamines. Heart-derived natriuretic peptides (i.e., stored in granules in the atrial and ventricle cardiomyocytes and exerting stimulating effects on diuresis and natriuresis) and numerous autocrine/paracrine factors originating from adipocytes and other cells of the stroma-vascular fraction may also participate in the regulation of lipolysis. Endocrine and autocrine/paracrine factors cooperate and lead to a fine regulation of lipolysis in adipocytes. Age, anatomical site, sex, genotype and species differences all play a part in the regulation of lipolysis. The manipulation of lipolysis has therapeutic potential in the metabolic disorders frequently associated with obesity and probably in several inborn errors of metabolism.

Distribution of body fat and risk of coronary heart disease in men and women

PURPOSE OF REVIEW

Earlier studies investigating the risk of developing coronary heart disease in relation to body fat distribution showed inconsistent results, and any sex-related difference in disease risk has not been adequately examined. This review aims to assess current findings on the prospective association between body fat distribution measures and coronary heart disease in men and women.

RECENT FINDINGS

Current epidemiologic evidence suggests that waist circumference and waist-hip ratio, as indicators of abdominal adiposity, are positively related to coronary heart disease in men and women independently of body mass index and conventional coronary heart disease risk factors. But the magnitude and shape of the associations for these abdominal adiposity indices varied with adjustments for mediating and confounding factors. Interestingly, hip waist circumference was inversely associated with coronary heart disease after adjusting for waist circumference. Because waist and hips are positively correlated but have separate and opposite associations with coronary disease, using waist circumference alone may provide underestimated risk estimate if hip girth is not accounted for in the calculation of this risk.

SUMMARY

For adipose tissue distribution assessment to be clinically useful, the ideal adiposity phenotype should provide a single risk estimate that captures the separate 'effects' of abdominal and peripheral adiposity. Although far from perfect, waist-hip ratio may capture separate effects of central and peripheral adiposity. This simple and inexpensive measure could be used to help improve coronary heart disease risk assessment.

Why are we shaped differently, and why does it matter?

Body fat distribution is an important predictor of metabolic abnormalities in obese humans. Dysregulation of free fatty acid (FFA) release, especially from upper body subcutaneous adipose tissue, appears to contribute substantially to these metabolic disturbances. Why different individuals preferentially store fat in upper vs. lower body subcutaneous fat or subcutaneous vs. visceral fat is not completely understood. Current evidence suggests that defects in regional lipolysis are not the cause of net fat retention in larger fat depots. Regional variations in the storage of fatty acids, both meal derived and direct reuptake, and storage of circulating FFAs that may help to explain why some depots expand at the expense of others have been reported. We review the quantitative data on regional lipolysis, meal, and FFA storage in adults to provide an overview of fat balance differences in adults with different fat distribution patterns.