Impact of body composition on very-low-density lipoprotein-triglycerides kinetics

TG/HDL Ratio Is an Independent Predictor for Estimating Resting Energy Expenditure in Adults with Normal Weight, Overweight, and Obesity

Factors that determine resting energy expenditure (REE) remain under investigation, particularly in persons with a high body mass index (BMI). The accurate estimation of energy expenditure is essential for conducting comprehensive nutrition assessments, planning menus and meals, prescribing weight and chronic disease interventions, and the prevention of malnutrition. This study aimed to: (a) determine the contribution of cardiometabolic biomarkers to the inter-individual variation in REE in persons categorized by BMI; and (b) assess the contribution of these biomarkers in the prediction of REE when persons of varying BMI status were categorized by their glycemic and metabolic syndrome status. Baseline data from 645 adults enrolled in diet intervention trials included REE measured by indirect calorimetry, body composition by dual energy X-ray absorptiometry, anthropometrics, and cardiometabolic biomarkers. Multivariate linear regression modeling was conducted to determine the most parsimonious model that significantly predicted REE by BMI category, metabolic syndrome status, and glycemic status. Modeling with the traditional predictors (age, sex, height, weight) accounted for 58-63% of the inter-individual variance in REE. When including age, sex, height, weight and fat-free mass as covariates, adding TG/HDL to regression modeling accounted for 71-87% of the variance in REE. The finding that TG/HDL is an independent predictor in estimating REE was further confirmed when participants were categorized by metabolic syndrome status and by glycemic status. The clinical utility of calculating the TG/HDL ratio not only aids health care providers in identifying patients with impaired lipid metabolism but can optimize the estimation of REE to better meet therapeutic goals for weight and disease management.

Emerging Evidence of Pathological Roles of Very-Low-Density Lipoprotein (VLDL)

Embraced with apolipoproteins (Apo) B and Apo E, triglyceride-enriched very-low-density lipoprotein (VLDL) is secreted by the liver into circulation, mainly during post-meal hours. Here, we present a brief review of the physiological role of VLDL and a systemic review of the emerging evidence supporting its pathological roles. VLDL promotes atherosclerosis in metabolic syndrome (MetS). VLDL isolated from subjects with MetS exhibits cytotoxicity to atrial myocytes, induces atrial myopathy, and promotes vulnerability to atrial fibrillation. VLDL levels are affected by a number of endocrinological disorders and can be increased by therapeutic supplementation with cortisol, growth hormone, progesterone, and estrogen. VLDL promotes aldosterone secretion, which contributes to hypertension. VLDL induces neuroinflammation, leading to cognitive dysfunction. VLDL levels are also correlated with chronic kidney disease, autoimmune disorders, and some dermatological diseases. The extra-hepatic secretion of VLDL derived from intestinal dysbiosis is suggested to be harmful. Emerging evidence suggests disturbed VLDL metabolism in sleep disorders and in cancer development and progression. In addition to VLDL, the VLDL receptor (VLDLR) may affect both VLDL metabolism and carcinogenesis. Overall, emerging evidence supports the pathological roles of VLDL in multi-organ diseases. To better understand the fundamental mechanisms of how VLDL promotes disease development, elucidation of the quality control of VLDL and of the regulation and signaling of VLDLR should be indispensable. With this, successful VLDL-targeted therapies can be discovered in the future.

Adipocyte Proteins and Storage of Endogenous Fatty Acids in Visceral and Subcutaneous Adipose Tissue in Severe Obesity

OBJECTIVE

This study tested whether substrate concentrations or fatty acid storage proteins predict storage of endogenous lipids in visceral adipose tissue (VAT) and upper body subcutaneous adipose tissue (UBSQ) fat.

METHODS

The day prior to surgery, 25 patients undergoing bariatric procedures received an infusion of autologous [1-¹⁴ C]triolein-labeled very low-density lipoprotein (VLDL) particles, and during surgery, they received a continuous [U-¹³ C]palmitate infusion/bolus [9,10-³ H]palmitate tracer. VAT and UBSQ fat were collected to measure VLDL-triglyceride (TG) storage, direct free fatty acid (FFA) storage rates, CD36 content, lipoprotein lipase (LPL), acyl-CoA synthetase, diacylglycerol acetyl-transferase, and glycerol-3-phosphate acyltransferase activities.

RESULTS

Storage of VLDL-TG and FFA-palmitate in UBSQ and VAT was not different. Plasma palmitate concentrations correlated with palmitate storage rates in UBSQ and VAT (r = 0.46, P = 0.02 and r = 0.46, P = 0.02, respectively). In VAT, VLDL-TG storage was correlated with VLDL concentrations (r = 0.53, P < 0.009) and LPL (r = 0.42, P < 0.05). In UBSQ, VLDL-TG storage was correlated with LPL (r = 0.42, P < 0.05). CD36, acyl-CoA synthetase, glycerol-3-phosphate acyltransferase, and diacylglycerol acetyl-transferase were not correlated with VLDL-TG or palmitate storage.

CONCLUSIONS

Adipose storage of VLDL-TG is predicted by VLDL-TG concentrations and LPL; FFA concentrations predict direct adipose tissue FFA storage rates.

Metabolic communication during exercise

The coordination of nutrient sensing, delivery, uptake and utilization is essential for maintaining cellular, tissue and whole-body homeostasis. Such synchronization can be achieved only if metabolic information is communicated between the cells and tissues of the entire organism. During intense exercise, the metabolic demand of the body can increase approximately 100-fold. Thus, exercise is a physiological state in which intertissue communication is of paramount importance. In this Review, we discuss the physiological processes governing intertissue communication during exercise and the molecules mediating such cross-talk.

Visceral fat does not contribute to metabolic disease in lipodystrophy

OBJECTIVES

Lipodystrophies are characterized by regional or generalized loss of adipose tissue and severe metabolic complications. The role of visceral adipose tissue (VAT) in the development of metabolic derangements in lipodystrophy is unknown. The study aim was to investigate VAT contribution to metabolic disease in lipodystrophy versus healthy controls.

METHODS

Analysis of correlations between VAT volume and biomarkers of metabolic disease in 93 patients and 93 age/sex-matched healthy controls.

RESULTS

Patients with generalized lipodystrophy (n = 43) had lower VAT compared with matched controls, while those with partial lipodystrophy (n = 50) had higher VAT versus controls. Both groups with lipodystrophy had lower leg fat mass versus controls (p < 0.05 for all; unpaired t-test). In both generalized and partial lipodystrophy, there was no correlation between VAT and glucose, triglycerides or high-density lipoprotein cholesterol (p > 0.05 for all; Spearman correlation). In controls matched to patients with generalized or partial lipodystrophy, VAT correlated with glucose (R = 0.42 and 0.36), triglycerides (R = 0.36 and 0.60) and high-density lipoprotein cholesterol (R = -0.34 and -0.64) (p < 0.05 for all; Spearman correlation).

CONCLUSIONS

In contrast to healthy controls, metabolic derangements in lipodystrophy did not correlate with VAT volume. These data suggest that, in lipodystrophy, impaired peripheral subcutaneous fat deposition may exert a larger effect than VAT accumulation on the development of metabolic complications. Interventions aimed at increasing functional subcutaneous adipose tissue may provide metabolic benefit.

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.

Lipoprotein lipase activity does not predict very low-density lipoprotein-triglyceride fatty acid oxidation during exercise

Exercise lowers plasma triglyceride levels, but the physiological mechanisms remain not fully elucidated. Lipoprotein lipase (LPL) is a key enzyme in facilitating fatty acid uptake from lipoproteins. As exercise increases the efficiency of very low-density lipoprotein-triglyceride (VLDL-TG) oxidation, we hypothesized that muscle LPL activity would be a rate-limiting step and predict VLDL-TG Fatty acids oxidation during exercise. Sixteen healthy, lean subjects (eight men and eight women) were examined before and during an acute exercise bout (90 minutes at 50% of VO2-max). Heparin-releasable LPL activity was measured in muscle and adipose tissue biopsies. Breath ¹⁴ CO₂ was measured after a primed-constant infusion of ex vivo labeled [¹⁴ C]-triolein VLDL-TG. Fractional VLDL-TG storage was measured in adipose tissue biopsies. Exercise did not affect muscle LPL activity (P=.30). No association was observed between muscle LPL activity and VLDL-TG oxidation, neither in the basal state (P=.17) nor during exercise (P=.83). Exercise did not affect upper body or lower body adipose tissue LPL activity (both P=.92). The basal adipose tissue fractional VLDL-TG storage (abdominal.13%±9%; femoral 17%±10% (P=.18)) was not associated with upper body (P=.56) or lower body (P=.44) subcutaneous adipose tissue LPL activity. Muscle LPL activity does not predict VLDL-TG oxidation during rest or exercise. In addition, adipose tissue LPL activity was not associated with VLDL-TG storage during rest. This suggests that LPL activity is present in excess of what is required to facilitate lipid uptake for oxidation during both rest and exercise.

VLDL Triglyceride Kinetics in Lean, Overweight, and Obese Men and Women

CONTEXT

High-plasma very low-density lipoprotein (VLDL) triglyceride (TG) concentration and alterations in VLDL-TG metabolism are associated with cardiometabolic disease.

OBJECTIVE

This study sought to evaluate the interrelationships among factors purported to regulate VLDL-TG metabolism in a large cohort of men and women with a wide range in body adiposity and fat distribution but without diabetes.

SUBJECTS AND DESIGN

We assessed body composition and fat distribution, plasma insulin concentration, free fatty acid availability, and basal VLDL-TG and VLDL-apoB-100 (VLDL particle number) kinetics in 233 lean, overweight, and obese men and women.

RESULTS

We found that: 1) plasma VLDL-TG concentration is determined primarily by VLDL-TG secretion rate (SR) in men and by VLDL-TG clearance rate in women; 2) there is a dissociation between VLDL-TG and VLDL-apoB-100 SRs, and VLDL-apoB-100 SR only explains ∼30% of the variance in VLDL-TG SR; 3) ∼50% of people with obesity have high plasma VLDL-TG concentration due to both an increased VLDL-TG SR and a decreased rate of VLDL-TG plasma clearance, and they have lower plasma high-density lipoprotein-cholesterol concentration and more intra-abdominal and liver fat than those with normal VLDL-TG concentration; and 4) fat-free mass, liver fat content and the rate of free fatty acid release into plasma are independent predictors (with a sex × race interaction) of VLDL-TG SR.

CONCLUSIONS

The regulation of plasma VLDL-TG concentration is complex and influenced by multiple metabolic factors. Many people with obesity have normal plasma VLDL-TG concentrations and kinetics, whereas those with high plasma VLDL-TG concentrations have increased VLDL-TG SR and other markers of cardiometabolic disease risk.

Oral intake of a combination of glucosyl hesperidin and caffeine elicits an anti-obesity effect in healthy, moderately obese subjects: a randomized double-blind placebo-controlled trial

Background

We have previously shown that a combination of glucosyl hesperidin (G-hesperidin) plus caffeine reduces accumulation of body fat, whereas G-hesperidin or caffeine alone shows little effect on high-fat diet-induced obesity in mice. The aim of this study is to evaluate the anti-obesity effect of G-hesperidin plus caffeine on body fat and serum TG in healthy subjects with moderately high body mass index (BMI) and serum TG. Since we considered that there are individual differences in caffeine sensitivity, we conducted dose-finding study of caffeine combined with G-hesperidin.

Methods

Seventy-five healthy subjects with moderately high BMI (24–30 kg/m²) and serum TG (100–250 mg/dl) were divided and assigned to 12-week intervention with daily intakes of 500 mg of G-hesperidin with or without 25, 50, or 75 mg of caffeine, or placebo in a randomized double-blind placebo-controlled design .

Results

After intervention, decreases in abdominal fat area (AFA), especially subcutaneous fat area (SFA), were significantly greater in the G-hesperidin with 50-mg caffeine group (AFA:-8.4 ± 21.9 v.s. 16.3 ± 34.1 cm²; p < 0.05, SFA: -9.3 ± 17.1 v.s. 11.2 ± 18.3 cm²; p < 0.01) and in the G-hesperidin with 75-mg caffeine group (AFA:-17.0 ± 31.4 v.s. 16.3 ± 34.1 cm²; p < 0.01, SFA: -12.4 ± 18.7 v.s. 11.2 ± 18.3 cm²; p < 0.01) than in the placebo group. Fat-decreasing effects of G-hesperidin were enhanced dose-dependently by caffeine addition. BMI decreases were significantly greater in the G-hesperidin with 75-mg caffeine group than in the placebo group (-0.56 ± 0.74 v.s. -0.02 ± 0.58 kg/m²; p < 0.05). G-hesperidin with/without caffeine had no effect on serum TG (p > 0.05 v.s. placebo).

Conclusions

These data suggested that a combination of 500-mg G-hesperidin with 50- or 75-mg caffeine may be useful for the prevention or treatment of obesity.

Trial registration

UMIN Clinical Trials Registry 000019241.

Menopausal Status and Abdominal Obesity Are Significant Determinants of Hepatic Lipid Metabolism in Women

Background

Android fat distribution (abdominal obesity) is associated with insulin resistance, hepatic steatosis, and greater secretion of large very low‐density lipoprotein (VLDL) particles in men. Since abdominal obesity is becoming increasingly prevalent in women, we aimed to investigate the relationship between android fat and hepatic lipid metabolism in pre‐ and postmenopausal women.

Methods and Results

We used a combination of stable isotope tracer techniques to investigate intrahepatic fatty acid synthesis and partitioning in 29 lean and 29 abdominally obese women (android fat/total fat 0.065 [0.02 to 0.08] and 0.095 [0.08 to 0.11], respectively). Thirty women were premenopausal aged 35 to 45 and they were matched for abdominal obesity with 28 postmenopausal women aged 55 to 65. As anticipated, abdominal obese women were more insulin resistant with enhanced hepatic secretion of large (404±30 versus 268±26 mg/kg lean mass, P<0.001) but not small VLDL (160±11 versus 142±13). However, postmenopausal status had a pronounced effect on the characteristics of small VLDL particles, which were considerably triglyceride‐enriched (production ratio of VLDL₂‐ triglyceride:apolipoprotein B 30±5.3 versus 19±1.6, P<0.05). In contrast to postmenopausal women, there was a tight control of hepatic fatty acid metabolism and triglyceride production in premenopausal women, whereby oxidation (r_s=−0.49, P=0.006), de novo lipogenesis (r_s=0.55, P=0.003), and desaturation (r_s=0.48, P=0.012) were closely correlated with abdominal obesity‐driven large VLDL‐triglyceride secretion rate.

Conclusions

In women, abdominal obesity is a major driver of hepatic large VLDL particle secretion, whereas postmenopausal status was characterized by increased small VLDL particle size. These data provide a mechanistic basis for the hyperlipidemia observed in postmenopausal obesity.

Lean body mass, not FFA, predicts VLDL-TG secretion rate in healthy men

OBJECTIVE

Triglyceride is a risk factor for cardiovascular disease. However, the impact of body composition and free fatty acid (FFA) levels on very-low-density-lipoprotein triglyceride (VLDL-TG) secretion remains controversial. The aim was to identify predictors of VLDL-TG secretion in a data set compiled from seven previously published studies.

METHODS

VLDL-TG kinetics was studied in 96 healthy men covering a wide span in body composition. A primed-constant infusion of ex vivo labeled [1-(14)C]-triolein VLDL-TG was used. Body composition was determined by dual X-ray absorptiometry and computed tomography scanning. Energy expenditure was measured by indirect calorimetry. Palmitate flux was measured by a [9,10-(3)H]-palmitate infusion.

RESULTS

VLDL-TG secretion rate correlated significantly with body mass index (BMI), lean body mass (LBM), total fat mass, resting energy expenditure (REE), and insulin. A trend toward an inverse relationship between VLDL-TG secretion rate and FFA concentration was observed. In mixed model linear regression analysis, VLDL-TG secretion rate was positively associated with LBM (P = 0.03), and VLDL-TG clearance rate was inversely related to total fat mass (P < 0.01).

CONCLUSIONS

LBM is a predictor of VLDL-TG secretion in healthy men, whereas FFA availability is not associated with VLDL-TG secretion. The work suggests reporting VLDL-TG secretion rates normalized for LBM when comparing subjects with differences in body composition.

Ten weeks of aerobic training does not result in persistent changes in VLDL triglyceride turnover or oxidation in healthy men

OBJECTIVE

Very low density lipoprotein triglyceride (VLDL-TG) and free fatty acids (FFA) constitute a substantial proportion of human energy supply both at rest and during exercise. Exercise acutely decreases VLDL-TG concentration, and VLDL-TG clearance is increased after an exercise bout. However, the effects of long-term training are not clear.

DESIGN

The aim was to investigate long-term effects of training by direct assessments of VLDL-TG and palmitate kinetics and oxidation in healthy lean men (n=9) at rest, before and after a 10-week training program, compared with a non-training control group (n=9).

METHODS

VLDL-TG kinetics were assessed by a primed constant infusion of [1-14C]VLDL-TG, and VLDL-TG oxidation by specific activity (14CO2) in expired air. The metabolic study days were placed 60-72 h after the last exercise bout.

RESULTS

Palmitate kinetics and oxidation were assessed by a 2 h constant infusion of [9,10-(3)H]palmitate. In the training group (n=9), maximal oxygen uptake increased significantly by ≈20% (P<0.05), and the insulin sensitivity (assessed by the hyperinsulinemic-euglycemic clamp) improved significantly (P<0.05). Despite these metabolic improvements, no changes were observed in VLDL-TG secretion, clearance, or oxidation or in palmitate kinetics.

CONCLUSION

We conclude that 10 weeks of exercise training did not induce changes in VLDL-TG and palmitate kinetics in healthy lean men.

Kinetics and utilization of lipid sources during acute exercise and acipimox

Overweight is associated with abnormalities of lipid metabolism, many of which are reversed by exercise. We investigated the impact of experimental antilipolysis and acute exercise on lipid kinetics and oxidation from VLDL-TG, plasma FFA, and "residual lipids" in overweight men (n = 8) using VLDL-TG and palmitate tracers in combination with muscle biopsies in a randomized, placebo-controlled design. Participants received placebo or acipimox on each study day (4 h of rest, 90 min of exercise at 50% V(O(2 max))). Exercise suppressed VLDL-TG secretion significantly during placebo but not acipimox (placebo-rest: 64.2 ± 9.4; placebo-exercise: 48.3 ± 8.0; acipimox-rest: 55.2 ± 13.4; acipimox-exercise: 52.0 ± 10.9). Resting oxidation of VLDL-TG FA and FFA was significantly reduced during acipimox compared with placebo, whereas "residual lipid oxidation" increased significantly [VLDL-TG oxidation (placebo: 18 ± 3 kcal/h; acipimox: 11 ± 2 kcal/h), FFA oxidation (placebo: 14 ± 2 kcal/h; acipimox: 4 ± 0.5 kcal/h), and residual lipid oxidation (placebo: 3 ± 5 kcal/h; acipimox: 14 ± 5 kcal/h)]. Additionally, during exercise on both placebo and acipimox, oxidation of VLDL-TG and FFA increased, but the relative contribution to total lipid oxidation diminished, except for FFA, which remained unchanged during acipimox. Residual lipid oxidation increased significantly during exercise in both absolute and relative terms. Changes in selected cellular enzymes and proteins provided no explanations for kinetic changes. In conclusion, suppressed FFA availability blunts the effect of exercise on VLDL-TG secretion and modifies the contribution of lipid sources for oxidation.

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.

Postprandial VLDL-triacylglycerol secretion is not suppressed in obese type 2 diabetic men

AIMS/HYPOTHESIS

Type 2 diabetes is characterised by insulin resistance and increased post-absorptive secretion of VLDL-triacylglycerol (VLDL-TAG). Whether postprandial suppression of endogenous VLDL-TAG secretion is abnormal--a finding that would link hyperlipidaemia and type 2 diabetes--remains unclear.

METHODS

Eight type 2 diabetic men and eight healthy men were studied before and after a fat-free test meal (40% of resting energy expenditure). VLDL-TAG kinetics were assessed using a primed-constant infusion of ex vivo labelled [1-(14)C]triolein VLDL-TAG using non-steady-state calculations.

RESULTS

Type 2 diabetic men had a higher basal VLDL-TAG secretion rate and concentration than healthy men (mean ± SD secretion rate 137 ± 61 vs 78 ± 30 μmol/min, respectively [p = 0.03]; median concentration 1.03 [range 0.58-1.75] vs 0.33 [0.13-1.14] mmol/l, respectively [p < 0.01]). Postprandially, the VLDL-TAG secretion rate decreased in healthy men (p < 0.01), but remained unchanged in diabetic men (p = 0.47). The VLDL-TAG concentration increased in diabetic men and decreased in healthy men postprandially (p < 0.05). The difference in VLDL-TAG secretion rate between the two groups approached significance (p = 0.06) and the relative change in VLDL-TAG secretion rate was significantly different (p = 0.01) between the two groups. Basal VLDL-TAG clearance was significantly lower in diabetic men (diabetic men 133 [49-390] ml/min; healthy controls 215 [137-933] ml/min [p < 0.05]). After meal ingestion, clearance decreased in healthy men (p = 0.03), but was unchanged in diabetic men (p = 0.58).

CONCLUSIONS/INTERPRETATION

Obese type 2 diabetic men have impaired postprandial suppression of VLDL-TAG secretion compared with lean healthy men, contributing to their postprandial lipaemia and hypertriacylglycerolaemia.

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.

Impaired insulin-mediated antilipolysis and lactate release in adipose tissue of upper-body obese women

Upper-body/visceral obesity is associated with abnormalities of free fatty acid (FFA) metabolism and greater risk of developing type 2 diabetes compared with lower-body obesity. In lean subjects lipolysis is readily suppressed by insulin; however, metabolic inflexibility with respect to antilipolysis is a frequent finding in obesity, partly determined by body composition. This study investigates effects of insulin on regional adipose tissue lipolysis and lactate levels in upper-body overweight/obese (UBO), lower-body overweight/obese (LBO), and lean women. The microdialysis technique was used to assess adipose tissue glycerol and lactate concentrations in abdominal and femoral fat during a 5-h basal period and a 2-h hyperinsulinemic euglycemic clamp. The main findings were that the antilipolytic effect of insulin was attenuated in abdominal fat of UBO (glycerol reduction, abd (%): UBO 40.4 (-14 to 66), LBO 46.0 (-8 to 66), lean 66.2 (2-78), ANOVA, P < 0.05), and in femoral fat in both obese groups (glycerol reduction, fem (%): UBO 44.4 (35-67), LBO 44.4 (0-63), lean 65.0 (43-79), ANOVA, P < 0.05). Further, abdominal fat insulin-mediated increase in lactate concentration was greater in lean women compared with UBO women (lactate increase, abd (%): UBO -6.1 (-37.1 to 57.4), LBO 16.5 (-32.2 to 112.5), lean 51.4 (-45.7 to 162.9), P < 0.05), whereas no differences were found between groups in femoral fat (lactate increase, fem (%), UBO -12.9 (-43 to 24), LBO 12.7 (-30.7 to 92), lean 27.6 (-9.5 to 123.8), not significant). Respiratory exchange ratio (RER) increased significantly and similarly in all groups. So, UBO women were metabolically inflexible with respect to insulins antilipolytic and lactate increasing effects in abdominal adipose tissue. These phenomena are probably both consequences of insulin resistance of adipose tissue.

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.

Dual metabolic defects are required to produce hypertriglyceridemia in obese subjects

OBJECTIVE

Obesity increases the risk of cardiovascular disease and premature death. However, not all obese subjects develop the metabolic abnormalities associated with obesity. The aim of this study was to clarify the mechanisms that induce dyslipidemia in obese subjects.

METHODS AND RESULTS

Stable isotope tracers were used to elucidate the pathophysiology of the dyslipidemia in hypertriglyceridemic (n=14) and normotriglyceridemic (n=14) obese men (with comparable body mass index and visceral fat volume) and in normotriglyceridemic nonobese men (n=10). Liver fat was determined using proton magnetic resonance spectroscopy, and subcutaneous abdominal and visceral fat were measured by magnetic resonance imaging. Serum triglycerides in obese subjects were increased by the combination of increased secretion and severely impaired clearance of triglyceride-rich very-low-density lipoprotein(1) particles. Furthermore, increased liver and subcutaneous abdominal fat were linked to increased secretion of very-low-density lipoprotein 1 particles, whereas increased plasma levels of apolipoprotein C-III were associated with impaired clearance in obese hypertriglyceridemic subjects.

CONCLUSIONS

Dual metabolic defects are required to produce hypertriglyceridemia in obese subjects with similar levels of visceral adiposity. The results emphasize the clinical importance of assessing hypertriglyceridemic waist in obese subjects to identify subjects at high cardiometabolic risk.

Effects of exercise on VLDL-triglyceride oxidation and turnover

Lipids are important substrates for oxidation at rest and during exercise. Aerobic exercise mediates a delayed onset decrease in total and VLDL-triglyceride (TG) plasma concentration. However, the acute effects of exercise on VLDL-TG oxidation and turnover remain unclear. Here, we studied the acute effects of 90 min of moderate-intensity exercise in healthy women and men. VLDL-TG kinetics were assessed using a primed constant infusion of ex vivo labeled [1-(14)C]triolein VLDL-TG. Fractional VLDL-TG-derived fatty acid oxidation was measured from (14)CO(2) specific activity in expired air. VLDL-TG concentration was unaltered during exercise and early recovery, whereas non-VLDL-TG concentration decreased significantly.VLDL-TG secretion rate decreased significantly during exercise and remained suppressed during recovery. Total VLDL-TG oxidation rate was unaffected by exercise. However, the contribution of VLDL-TG oxidation to total energy expenditure fell from 14 ± 9% at rest to 3 ± 4% during exercise. We conclude that VLDL-TG fatty acids are quantitatively important oxidative substrates under basal postabsorptive conditions but remain unaffected during 90-min moderate-intensity exercise and, thus, become relatively less important during exercise. Lower VLDL secretion rate during exercise may contribute to the decrease in TG concentrations during and after exercise.

Basal and insulin mediated VLDL-triglyceride kinetics in type 2 diabetic men

OBJECTIVE

Increased very-low-density lipoprotein triglycerides (VLDL-TG) concentration is a central feature of diabetic dyslipidemia. The objective was to compare basal and insulin mediated VLDL-TG kinetics, oxidation, and adipose tissue storage in type 2 diabetic and healthy (nondiabetic) men.

RESEARCH DESIGN AND METHODS

Eleven type 2 diabetic and 11 healthy men, matched for BMI and age, were included. Ex vivo-labeled VLDL-TG tracers, blood and breath samples, fat biopsies, indirect calorimetry, and body composition measures were applied to determine VLDL-TG kinetics, VLDL-TG fatty acids (FA) oxidation, and storage in regional adipose tissue before and during a hyperinsulinemic euglycaemic clamp.

RESULTS

VLDL-TG secretion was significantly greater in diabetic compared with healthy men (basal: 86.9 [31.0] vs. 61.9 [30.0] μmol/min, P = 0.03; clamp: 60.0 [26.2] vs. 34.2 [17.9] μmol · min⁻¹, P = 0.01). The insulin mediated suppression of VLDL-TG secretion was significant in both groups. VLDL-TG clearance was lower in diabetic men (basal: 84.6 [32.7] vs. 115.4 [44.3] ml · min⁻¹, P = 0.08; clamp: 76.3 [30.6] vs. 119.0 [50.2] ml · min⁻¹, P = 0.03). During hyperinsulinemia fractional VLDL-TG FA oxidation was comparable, but in percentage of energy expenditure (EE), significantly higher in diabetic men. Basal VLDL-TG storage was similar, but significantly greater in abdominal compared with leg fat.

CONCLUSIONS

Increased VLDL-TG in type 2 diabetic men is caused by greater VLDL-TG secretion and less so by lower VLDL-TG clearance. The ability of hyperinsulinemia to suppress VLDL-TG secretion appears preserved. During hyperinsulinemia VLDL-TG FA oxidation is significantly increased in proportion of EE in type 2 diabetic men. Greater basal abdominal VLDL-TG storage may help explain the accumulation of upper-body fat in insulin-resistant individuals.

Femoral adipose tissue may accumulate the fat that has been recycled as VLDL and nonesterified fatty acids

OBJECTIVE

Gluteo-femoral, in contrast to abdominal, fat accumulation appears protective against diabetes and cardiovascular disease. Our objective was to test the hypothesis that this reflects differences in the ability of the two depots to sequester fatty acids, with gluteo-femoral fat acting as a longer-term "sink."

RESEARCH DESIGN AND METHODS

A total of 12 healthy volunteers were studied after an overnight fast and after ingestion of a mixed meal. Blood samples were taken from veins draining subcutaneous femoral and abdominal fat and compared with arterialized blood samples. Stable isotope-labeled fatty acids were used to trace specific lipid fractions. In 36 subjects, adipose tissue blood flow in the two depots was monitored with (133)Xe.

RESULTS

Blood flow increased in response to the meal in both depots, and these responses were correlated (r(s) = 0.44, P < 0.01). Nonesterified fatty acid (NEFA) release was suppressed after the meal in both depots; it was lower in femoral fat than in abdominal fat (P < 0.01). Plasma triacylglycerol (TG) extraction by femoral fat was also lower than that by abdominal fat (P = 0.05). Isotopic tracers showed that the difference was in chylomicron-TG extraction. VLDL-TG extraction and direct NEFA uptake were similar in the two depots.

CONCLUSIONS

Femoral fat shows lower metabolic fluxes than subcutaneous abdominal fat, but differs in its relative preference for extracting fatty acids directly from the plasma NEFA and VLDL-TG pools compared with chylomicron-TG.

Lipoprotein subclass patterns in women with polycystic ovary syndrome (PCOS) compared with equally insulin-resistant women without PCOS

OBJECTIVES

Women with polycystic ovary syndrome (PCOS) are more insulin resistant and display an atherogenic lipid profile compared with normal women of similar body mass index (BMI). Insulin resistance (IR) at least partially underlies the dyslipidemia of PCOS, but it is unclear whether PCOS status per se confers additional risk.

RESEARCH DESIGN AND METHODS

Using a case-control design, we compared plasma lipids and lipoprotein subclasses (using polyacrylamide gel tube electrophoresis) in 70 women with PCOS (National Institutes of Health criteria) and 70 normal women pair matched for age, BMI, and IR (homeostasis model assessment-IR, quantitative insulin sensitivity check index, and the Avignon Index). Subjects were identified as having a (less atherogenic) type A pattern consisting predominantly of large low-density lipoprotein (LDL) subfractions or a (more atherogenic) non-A pattern consisting predominantly of small-dense LDL subfractions.

RESULTS

Total, high-density lipoprotein, or LDL cholesterol, or triacylglycerol did not differ between the groups, but very low-density lipoprotein levels (P<0.05) were greater in women with PCOS, whereas a non-A LDL profile was seen in 12.9% compared with 2.9% of controls (P<0.05, chi2). Multiple regression analysis revealed homeostasis model assessment-IR and waist circumference to be independent predictors of very low-density lipoprotein together explaining 40.2% of the overall variance. Logistic regression revealed PCOS status to be the only independent determinant of a non-A LDL pattern (odds ratio 5.48 (95% confidence interval 1.082-27.77; P<0.05).

CONCLUSIONS

Compared with women matched for BMI and IR, women with PCOS have potentially important differences in lipid profile with greater very low-density lipoprotein levels and increased rates of a more atherogenic non-A LDL pattern.

Postabsorptive VLDL-TG fatty acid storage in adipose tissue in lean and obese women

Adipose tissue lipoprotein lipase (LPL) is a necessary enzyme for storage of very-low-density lipoprotein-triglyceride (VLDL-TG), but whether it is a rate-determining step is unknown. To test this hypothesis we included 10 upper-body obese (UBO), 11 lower-body obese (LBO), and 8 lean women. We infused ex vivo-labeled VLDL-(14)C-TG and then performed adipose tissue biopsies to understand the relationship between VLDL-TG storage and LPL activity in femoral and upper-body subcutaneous fat. Both fractional tracer storage and rate of storage of the VLDL-TG tracer were evaluated. VLDL-TG storage was also examined as a function of regional adipose tissue blood flow (ATBF), insulin, VLDL-TG turnover, regional fat mass, fat-free mass (FFM), and fat cell size. LPL activity per adipocyte was significantly greater in obese than lean women but not significantly different per gram lipid. Both VLDL-TG fractional tracer storage per kg lipid and VLDL-TG storage rate per kg lipid were similar in abdominal and femoral fat in all three groups and were not significantly different between groups. Multiple regression analysis identified FFM and femoral fat mass as significant independent predictors of VLDL-TG fractional tracer storage and insulin as a significant predictor of VLDL-TG fatty acid storage rate. LPL activity, ATBF, and VLDL-TG turnover did not predict VLDL-TG storage. We conclude that lower FFM and greater plasma insulin are associated with greater VLDL-TG deposition in abdominal subcutaneous and femoral fat. Greater femoral fat mass signals greater femoral VLDL-TG storage. We suggest that the differences in VLDL-TG storage in abdominal and femoral fat that occur with progressive obesity are regulated through mechanisms other than LPL activity.

Exercise training increases hepatic endoplasmic reticulum (er) stress protein expression in MTP-inhibited high-fat fed rats

The purpose of the study was: (1) to determine the effects of microsomal triglyceride transfer protein (MTP) inhibition on endoplasmic reticulum (ER) stress in liver, and (2) to determine if this response is altered in exercise-trained rats. Female Sprague-Dawley rats (6 weeks) fed either a standard (SD) or a high-saturated fat (HF; 43% as energy) diet were trained (Tr) or kept sedentary (Sed) for 6 week. Exercise training consisted of continuous running on a motor-driven rodent treadmill 5 times/week. Ten days before the end of these interventions, rats were administrated (ip) daily a MTP inhibitor (MTPX) or a placebo (P). MTPX injection resulted in a large (p < 0.01) liver triacylglycerol (TAG) accumulation in SD and HF-fed rats (approximately 200 mg g(-1)), irrespective of the training status, while plasma TAG levels were largely (approximately 80%) decreased (p < 0.01). MTPX injection in HF but not in SD-fed animals resulted in an increase in BiP/GRP78, ATF6, PERK, and XBP-1 mRNA levels, (p < 0.01) indicating an increase in the unfolding protein response (UPR) to ER stress. Interestingly, exercise training in rats fed the HF diet resulted in a further increase in BiP/GRP78 and XBP-1 mRNA levels in MTPX animals (p < 0.01). It is concluded that: (1) ER stress induced by MTPX occurs only in HF-fed rats despite the fact that liver TAG levels were largely increased in both dietary models; (2) the increase in gene expression of UPR markers with training may constitute a protective mechanism against ER stress in liver.

VLDL-TG kinetics: a dual isotope study for quantifying VLDL-TG pool size, production rates, and fractional oxidation in humans

Very-low-density lipoproteins (VLDLs) are large, complex particles containing both surface proteins (e.g., ApoB100) and core lipids, e.g., cholesterol and triglycerides (TG). Whereas ApoB100 kinetics have been thoroughly studied, accurate measurement of VLDL-TG kinetics have proven difficult due to either complex mathematics or laborious procedures. The present study was therefore designed to measure VLDL-TG kinetics by dual isotope ex vivo labeled VLDL-TG tracers and well-established kinetics equations (bolus injection or the primed continuous infusion). Ten healthy Caucasian men [age, 23 +/- 3 yr old (mean +/- SD); body mass index, 24.7 +/- 1.3 kg/m(2)] were included in the study. VLDL-TG rate of appearance (Ra) was measured using a dual-tracer technique ([9,10-(3)H]-labeled VLDL-TG and [1-(14)C]-labeled VLDL-TG) to allow comparison of various bolus decay curve fits with the Ra obtained by the primed continuous infusion (PCI; considered the gold standard). In addition, VLDL-TG fatty acid oxidation was measured as (14)CO(2) in exhaled breath, using the hyamine trapping technique. Following a bolus injection, tracer decay was better described by a biexponential than a monoexponential fit (r(2) = 0.99 +/- 0.01 vs. 0.97 +/- 0.04, respectively, P = 0.01). VLDL-TG Ra calculated using the PCI correlated significantly with the biexponential fit (rho = 0.62, P < 0.05), whereas this was not the case for the monoexponential fit (rho = -0.18, P = not significant). VLDL-TG Ra using the best fit of the bolus injection method (biexponential) was less than values obtained by the constant infusion technique [biexponential, 34.3 (range, 27.1-69.6) vs. PCI, 44.4 (range, 33.0-72.7), P < 0.05]. Fractional oxidation of VLDL-TG was 37.2 +/- 8.8% at 240 min corresponding to 198.8 +/- 55.9 kcal/day or 10.6 +/- 3.3% of resting energy expenditure (REE). Our data demonstrate that VLDL-TG Ra measured by a biexponential fit to a bolus decay curve correlates well with VLDL-TG Ra measured by a primed continuous infusion, and therefore that a "second" peripheral VLDL-TG compartment with rapid exchange of TG exists. VLDL-TG volume of distribution is therefore greater than previously anticipated. Finally our data supports that VLDL-TG contributes quantitatively to REE.

Gender differences in lipid metabolism and the effect of obesity

There are many differences between men and women, and between lean and obese subjects, in fatty acid and very low-density lipoprotein triglyceride and apolipoprotein B-100 metabolism. Currently, observations in this area are predominantly descriptive. The mechanisms responsible for sexual dimorphism in lipid metabolism are largely unknown.