Regional variation in adipose tissue lipoprotein lipase activity: association with plasma high density lipoprotein levels

Progression to Obesity: Variations in Patterns of Metabolic Fluxes, Fat Accumulation, and Gastrointestinal Responses

Obesity is a multifactorial disorder that is remarkably heterogeneous. It presents itself in a variety of phenotypes that can be metabolically unhealthy or healthy, associate with no or multiple metabolic risk factors, gain extreme body weight (super-responders), as well as resist obesity despite the obesogenic environment (non-responders). Progression to obesity is ultimately linked to the overall net energy balance and activity of different metabolic fluxes. This is particularly evident from variations in fatty acids oxidation, metabolic fluxes through the pyruvate-phosphoenolpyruvate-oxaloacetate node, and extracellular accumulation of Krebs cycle metabolites, such as citrate. Patterns of fat accumulation with a focus on visceral and ectopic adipose tissue, microbiome composition, and the immune status of the gastrointestinal tract have emerged as the most promising targets that allow personalization of obesity and warrant further investigations into the critical issue of a wider and long-term weight control. Advances in understanding the biochemistry mechanisms underlying the heterogenous obesity phenotypes are critical to the development of targeted strategies to maintain healthy weight.

Sex differences in the associations between adiposity distribution and cardiometabolic risk factors in overweight or obese individuals: a cross-sectional study

Background

We aimed to assess the associations between adiposity distribution and cardiometabolic risk factors among overweight and obese adults in China, and to demonstrate the sex differences in these associations.

Methods

A total of 1221 participants (455 males and 766 females) were included in this study. Percentage of body fat (PBF) of the whole body and regional areas, including arm, thigh, trunk, android, and gynoid, were measured by the dual-energy X-ray absorptiometry method. Central adiposity was measured by waist circumference. Clustered cardiometabolic risk was defined as the presence of two or more of the six cardiometabolic risk factors, namely, high triglyceride, low high density lipoprotein, elevated glucose, elevated blood pressure, elevated high sensitivity C-reactive protein, and low adiponectin. Linear regression models and multivariate logistic regression models were used to assess the associations between whole body or regional PBF and cardiometabolic risk factors.

Results

In females, except arm adiposity, other regional fat (thigh, trunk, android, gynoid) and whole-body PBF are significantly associated with clustered cardiometabolic risk, adjusting for age, smoking, alcohol drinking, physical activity, and whole-body PBF. One-SD increase in Z scores of the thigh and gynoid PBF were significantly associated with 80 and 78% lower odds of clustered cardiometabolic risk (OR: 0.20, 95%CI: 0.12–0.35 and OR: 0.22, 95%CI: 0.12–0.41). Trunk, android and whole-body PBF were significantly associated with higher odds of clustered risk with OR of 1.90 (95%CI:1.02–3.55), 2.91 (95%CI: 1.75–4.85), and 2.01 (95%CI: 1.47–2.76), respectively. While in males, one-SD increase in the thigh and gynoid PBF are associated with 94% (OR: 0.06, 95%CI: 0.02–0.23) and 83% lower odds (OR: 0.17, 95%CI: 0.05–0.57) of clustered cardiometabolic risk, respectively. Android and whole-body PBF were associated with higher odds of clustered cardiometabolic risk (OR: 3.39, 95%CI: 1.42–8.09 and OR: 2.45, 95%CI: 1.53–3.92), but the association for trunk PBF was not statistically significant (OR: 1.16, 95%CI: 0.42–3.19).

Conclusions

Adiposity distribution plays an important role in the clustered cardiometabolic risk in participants with overweight and obese and sex differences were observed in these associations. In general, central obesity (measured by android PBF) could be the best anthropometric measurement for screening people at risk for CVD risk factors for both men and women. Upper body fat tends to be more detrimental to cardiometabolic health in women than in men, whereas lower body fat is relatively more protective in men than in women.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-021-11316-4.

Sex Differences in the Association of Body Composition and Cardiovascular Mortality

Background To determine whether differences in body composition contribute to sex differences in cardiovascular disease (CVD) mortality, we investigated the relationship between components of body composition and CVD mortality in healthy men and women. Methods and Results Dual energy x-ray absorptiometry body composition data from the National Health and Nutrition Examination Survey 1999-2004 and CVD mortality data from the National Health and Nutrition Examination Survey 1999-2014 were evaluated in 11 463 individuals 20 years of age and older. Individuals were divided into 4 body composition groups (low muscle mass-low fat mass-the referent; low muscle-high fat; high muscle-low fat, and high muscle-high fat), and adjusted competing risks analyses were performed for CVD versus non-CVD mortality. In women, high muscle/high fat mass was associated with a significantly lower adjusted CVD mortality rate (hazard ratio [HR], 0.58; 95% CI, 0.39-0.86; P=0.01), but high muscle/low fat mass was not. In men, both high muscle-high fat (HR, 0.74; 95% CI, 0.53-1.04; P=0.08) and high muscle-low fat mass (HR, 0.40; 95% CI, 0.21-0.77; P=0.01) were associated with lower CVD. Further, in adjusted competing risks analyses stratified by sex, the CVD rate in women tends to significantly decrease as normalized total fat increase (total fat fourth quartile: HR, 0.56; 95% CI, 0.34-0.94; P<0.03), whereas this is not noted in men. Conclusions Higher muscle mass is associated with lower CVD and mortality in men and women. However, in women, high fat, regardless of muscle mass level, appears to be associated with lower CVD mortality risk. This finding highlights the importance of muscle mass in healthy men and women for CVD risk prevention, while suggesting sexual dimorphism with respect to the CVD risk associated with fat mass.

The "adipose tissue expandability" hypothesis: a potential mechanism for insulin resistance in obese youth

Obesity has become a major global health challenge of the 21st century, as it is associated with the onset of type 2 diabetes (T2D) and cardiovascular complications, even at a very early age in life. The root causes of pediatric obesity remain incompletely understood. The obesity epidemic together with the relationship of obesity to the growing population burden of chronic disease presents unprecedented research opportunities and challenges. Decades of obesity-related research funded by governments around the world have yielded many important discoveries about both etiological pathways and preventive or therapeutic interventions. Yet, there is a sense that the problem is outpacing these research efforts. Obesity poses a significant risk for the development of cardiovascular disease (CVD) , diabetes and certain cancers thereby shortening life expectancy. Nevertheless, many obese individuals do not develop any of these comorbidities. One hypothesis explaining this dilemma is that total body fat is not the culprit of adverse health in obesity rather the relative proportion of lipids in various fat depots is what determines the metabolic risk. In this review, we describe the role of altered fat partitioning in youth onset obesity and its relation to fatty liver and T2D during adolescence.

Cardiovascular and Metabolic Heterogeneity of Obesity: Clinical Challenges and Implications for Management

The prevalence of obesity has increased globally over the last 2 decades. Although the body mass index has been a convenient and simple index of obesity at the population level, studies have shown that obesity defined by body mass index alone is a remarkably heterogeneous condition with varying cardiovascular and metabolic manifestations across individuals. Adipose tissue is an exquisitely active metabolic organ engaged in cross-talk between various systems; perturbation of adipose tissue results in a pathological response to positive caloric balance in susceptible individuals that directly and indirectly contributes to cardiovascular and metabolic disease. Inadequate subcutaneous adipose tissue expansion in the face of dietary triglycerides leads to visceral and ectopic fat deposition, inflammatory/adipokine dysregulation, and insulin resistance. Conversely, preferential fat storage in the lower body depot may act as a metabolic buffer and protect other tissues from lipotoxicity caused by lipid overflow and ectopic fat. Translational, epidemiological, and clinical studies over the past 30 years have clearly demonstrated a strong link between visceral and ectopic fat and the development of a clinical syndrome characterized by atherogenic dyslipidemia, hyperinsulinemia/glucose intolerance, hypertension, atherosclerosis, and adverse cardiac remodeling/heart failure. This relationship is even more nuanced when clinical entities such as metabolically healthy obesity phenotype and the obesity paradox are considered. Although it is clear that the accumulation of visceral/ectopic fat is a major contributor to cardiovascular and metabolic risk above and beyond the body mass index, implementation of fat distribution assessment into clinical practice remains a challenge. Anthropometric indexes of obesity are easily implemented, but newer imaging-based methods offer improved sensitivity and specificity for measuring specific depots. Lifestyle, pharmacological, and surgical interventions allow a multidisciplinary approach to overweight/obesity that may improve outcomes and align with a public health message to combat the growing epidemic of obesity worldwide and to build healthier lives free of cardiovascular diseases.

Relationships between Rodent White Adipose Fat Pads and Human White Adipose Fat Depots

The objective of this review was to compare and contrast the physiological and metabolic profiles of rodent white adipose fat pads with white adipose fat depots in humans. Human fat distribution and its metabolic consequences have received extensive attention, but much of what has been tested in translational research has relied heavily on rodents. Unfortunately, the validity of using rodent fat pads as a model of human adiposity has received less attention. There is a surprisingly lack of studies demonstrating an analogous relationship between rodent and human adiposity on obesity-related comorbidities. Therefore, we aimed to compare known similarities and disparities in terms of white adipose tissue (WAT) development and distribution, sexual dimorphism, weight loss, adipokine secretion, and aging. While the literature supports the notion that many similarities exist between rodents and humans, notable differences emerge related to fat deposition and function of WAT. Thus, further research is warranted to more carefully define the strengths and limitations of rodent WAT as a model for humans, with a particular emphasis on comparable fat depots, such as mesenteric fat.

Normal-weight obesity: implications for cardiovascular health

We sought to review the epidemiological features and clinical implications of normal-weight obesity. The concept of normal-weight obesity has been recently reported as an important risk factor for cardiovascular disease, metabolic dysregulation, and poor functional outcomes. However, in clinical practice, normal-weight obesity is not commonly recognized. In this review, we examine the clinical significance and important epidemiological outcomes of normal-weight obesity and describe other variants of adiposity and adiposity-related metabolic status. The incorporation of measures of body fat content and distribution in the clinical setting could allow more accurate identification of adiposity-related long-term risk. This could in turn lead to early lifestyle changes and behavioral modifications that are essential to the treatment of obesity.

Change in Intra-Abdominal Fat Predicts the Risk of Hypertension in Japanese Americans

In Japanese Americans, intra-abdominal fat area measured by computed tomography is positively associated with the prevalence and incidence of hypertension. Evidence in other populations suggests that other fat areas may be protective. We sought to determine whether a change in specific fat depots predicts the development of hypertension. We prospectively followed up 286 subjects (mean age, 49.5 years; 50.4% men) from the Japanese American Community Diabetes Study for 10 years. At baseline, subjects did not have hypertension (defined as blood pressure ≥140/90 mm Hg) and were not taking blood pressure or glucose-lowering medications. Mid-thigh subcutaneous fat area, abdominal subcutaneous fat area, and intra-abdominal fat area were directly measured by computed tomography at baseline and 5 years. Logistic regression was used to estimate odds of incident hypertension over 10 years in relation to a 5-year change in fat area. The relative odds of developing hypertension for a 5-year increase in intra-abdominal fat was 1.74 (95% confidence interval, 1.28-2.37), after adjusting for age, sex, body mass index, baseline intra-abdominal fat, alcohol use, smoking status, and weekly exercise energy expenditure. This relationship remained significant when adjusted for baseline fasting insulin and 2-hour glucose levels or for diabetes mellitus and pre-diabetes mellitus classification. There were no significant associations between baseline and change in thigh or abdominal subcutaneous fat areas and incident hypertension. In conclusion, in this cohort of Japanese Americans, the risk of developing hypertension is related to the accumulation of intra-abdominal fat rather than the accrual of subcutaneous fat in either the thigh or the abdominal areas.

Interrelationships between changes in anthropometric variables and computed tomography indices of abdominal fat distribution in response to a 1-year physical activity–healthy eating lifestyle modification program in abdominally obese men

The objectives were to (i) measure the effects of a 1-year lifestyle modification program on body fat distribution/anthropometric variables; (ii) determine the interrelationships between changes in all these variables; and (iii) investigate whether there is a selective reduction in deep (DSAT) vs. superficial subcutaneous adipose tissue (SSAT) at the abdominal level following a 1-year lifestyle modification program. Anthropometric variables, body composition and abdominal and midthigh fat distribution were assessed at baseline and after 1 year in 109 sedentary, dyslipidemic and abdominally obese men. Reductions in anthropometric variables, skinfold thicknesses (except the trunk/extremity ratio) and fat mass as well as an increase in fat-free mass were observed after 1 year (p < 0.0001). Decreases in abdominal adipose tissue volumes were also noted (–23%, –26%, –18%, –19%, –17%, p < 0.0001 for total adipose tissue, visceral adipose tissue, subcutaneous adipose tissue, DSAT and SSAT, respectively). Adipose tissue areas at midthigh also decreased (–18%, –18%, –17%, p < 0.0001 for total, deep, and subcutaneous adipose tissue, respectively). A reduction (–9%, p < 0.0001) in low-attenuation muscle area and an increase (+1%, p < 0.05) in normal-attenuation muscle area were also observed. There was a positive relationship between changes in visceral adipose tissue and changes in DSAT (r = 0.65, p < 0.0001) or SSAT (r = 0.63, p < 0.0001). Although absolute changes in DSAT were greater than changes in SSAT, relative changes in both depots were similar, independent of changes in visceral adipose tissue. The 1-year lifestyle modification program therefore improved the body fat distribution pattern and midthigh muscle quality in abdominally obese men.

Adipose tissue renin-angiotensin-aldosterone system (RAAS) and progression of insulin resistance

This review focuses on the expression of the key components of the renin-angiotensin-aldosterone axis in fat tissue. At the center of this report is the role of RAAS in normal and excessive fat mass enlargement, the leading etiology of insulin resistance. Understanding the expression and regulation of RAAS components in various fat depots allows insight not only into the processes by which these complex patterns are modified by the enlargement of adipose tissue, but also into their impact on local and systemic response to insulin.

Sex dimorphism and depot differences in adipose tissue function

Obesity, characterized by excessive adiposity, is a risk factor for many metabolic pathologies, such as type 2 diabetes mellitus (T2DM). Numerous studies have shown that adipose tissue distribution may be a greater predictor of metabolic health. Upper-body fat (visceral and subcutaneous abdominal) is commonly associated with the unfavorable complications of obesity, while lower-body fat (gluteal-femoral) may be protective. Current research investigations are focused on analyzing the metabolic properties of adipose tissue, in order to better understand the mechanisms that regulate fat distribution in both men and women. This review will highlight the adipose tissue depot- and sex-dependent differences in white adipose tissue function, including adipogenesis, adipose tissue developmental patterning, the storage and release of fatty acids, and secretory function. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

Fat depots, free fatty acids, and dyslipidemia

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

Thigh circumference and low ankle brachial index in US adults: results from the National Health and Nutrition Examination Survey 1999-2004

OBJECTIVE

Recent studies have suggested that smaller thighs are a disadvantage for health and survival, but the association of thigh circumference with atherosclerosis remains uncertain. The purpose of this study was to investigate the association between thigh circumference and peripheral arterial disease (PAD), as measured by ankle brachial index (ABI).

METHODS

This study used data from the National Health and Nutrition Examination Survey (1999-2004), in which participants' ABI and thigh circumference were measured simultaneously. A total of 5716 participants (2959 men and 2757 women) were included in the final analysis. A diagnosis of PAD was determined on the basis of ABI <0.9.

RESULTS

The overall prevalence of PAD in this sample was 6.6%. Thigh circumference of those with PAD was 50.1cm compared to 52.2 cm for those without PAD (p < 0.0001). After adjusting for potential covariates, the prevalence of PAD generally decreased as thigh circumference increased up to 55 cm. In the first quantile (smallest thigh circumference), men and women had as much as a 4.8-fold (95% CI, 2.28-10.29) and a 3-fold (95% CI, 1.45-6.18) increased risk of PAD, respectively. Above 55 cm, PAD was no longer related to thigh circumference.

CONCLUSIONS

Small thigh circumference may be associated with PAD, as measured by ABI.

Association of adipose tissue blood flow with fat depot sizes and adipokines in women

OBJECTIVE

To explore possible associations between adipose tissue (AT) blood flow (ATBF), AT depot sizes and adipocyte-derived hormones (adipokines) in women.

SUBJECTS

In all, 43 healthy women were divided into four groups: normal-weight (n=11) and obese (n=11) pre-menopausal women and normal-weight (n=10) and obese (n=11) post-menopausal women.

METHODS

Fasting levels of adipokines were obtained, and a single-slice computed tomography scan at the level of L4-L5 was used to estimate fat depot sizes. ATBF was assessed by xenon washout while in a fasting state and after oral glucose load. We also measured glucose, insulin and non-esterified fatty acids.

RESULTS

Total, subcutaneous and visceral AT areas strongly correlated with ATBF (all P<0.001). Circulating leptin levels strongly and inversely correlated with ATBF (P=0.001), but this association did not remain after adjustment for body mass index. Adiponectin was not associated with blood flow.

CONCLUSION

ATBF is closely linked to subcutaneous and visceral AT size. Further analyses are needed to determine possible mediators of this association, including mechanistic studies to assess a putative role for leptin as a significant modulator of blood flow.

Abdominal and gynoid adipose distribution and incident myocardial infarction in women and men

OBJECTIVE

The relationships between objectively measured abdominal and gynoid adipose mass with the prospective risk of myocardial infarction (MI) has been scarcely investigated. We aimed to investigate the associations between fat distribution and the risk of MI.

SUBJECTS

Total and regional fat mass was measured using dual-energy X-ray absorptiometry (DEXA) in 2336 women and 922 men, of whom 104 subsequently experienced an MI during a mean follow-up time of 7.8 years.

RESULTS

In women, the strongest independent predictor of MI was the ratio of abdominal to gynoid adipose mass (hazard ratio (HR)=2.44, 95% confidence interval (CI) 1.79-3.32 per s.d. increase in adipose mass), after adjustment for age and smoking. This ratio also showed a strong association with hypertension, impaired glucose tolerance and hypertriglyceridemia (P<0.01 for all). In contrast, the ratio of gynoid to total adipose mass was associated with a reduced risk of MI (HR= 0.57, 95% CI 0.43-0.77), and reduced risk of hypertension, impaired glucose tolerance and hypertriglyceridemia (P<0.001 for all). In men, gynoid fat mass was associated with a decreased risk of MI (HR=0.69, 95% CI 0.48-0.98), and abdominal fat mass was associated with hypertriglyceridemia (P for trend 0.02).

CONCLUSION

In summary, fat distribution was a strong predictor of the risk of MI in women, but not in men. These different results may be explained by the associations found between fat distribution and hypertension, impaired glucose tolerance and hypertriglyceridemia.

Gluteofemoral body fat as a determinant of metabolic health

Body fat distribution is an important metabolic and cardiovascular risk factor, because the proportion of abdominal to gluteofemoral body fat correlates with obesity-associated diseases and mortality. Here, we review the evidence and possible mechanisms that support a specific protective role of gluteofemoral body fat. Population studies show that an increased gluteofemoral fat mass is independently associated with a protective lipid and glucose profile, as well as a decrease in cardiovascular and metabolic risk. Studies of adipose tissue physiology in vitro and in vivo confirm distinct properties of the gluteofemoral fat depot with regards to lipolysis and fatty acid uptake: in day-to-day metabolism it appears to be more passive than the abdominal depot and it exerts its protective properties by long-term fatty acid storage. Further, a beneficial adipokine profile is associated with gluteofemoral fat. Leptin and adiponectin levels are positively associated with gluteofemoral fat while the level of inflammatory cytokines is negatively associated. Finally, loss of gluteofemoral fat, as observed in Cushing's syndrome and lipodystrophy is associated with an increased metabolic and cardiovascular risk. This underlines gluteofemoral fat's role as a determinant of health by the long-term entrapment of excess fatty acids, thus protecting from the adverse effects associated with ectopic fat deposition.

Abdominal obesity: the cholesterol of the 21st century?

Cardiovascular disease (CVD) is a leading cause of morbidity and death in many countries worldwide. With the help of epidemiological, metabolic and clinical studies conducted over the past decades, the key factors contributing to the development of CVD have been identified. In this regard, several modifiable (hypertension, smoking, elevated cholesterol or low-density lipoprotein-cholesterol concentrations, reduced levels of high-density lipoprotein-cholesterol, type 2 diabetes) and nonmodifiable (age, sex, genetic predisposition) CVD risk factors have been recognized. Although better acute care and chronic pharmacological management have contributed to reduce CVD mortality, CVD morbidity remains very high. It has been proposed that this situation could be the consequence of the evolving landscape of CVD risk factors, which include, among others, poor nutritional habits and a reduction in physical activity contributing to the epidemic of obesity sweeping the world. However, obesity is heterogeneous both in terms of its etiology and its metabolic complications. Body fat distribution, especially visceral adipose tissue accumulation, has been found to be a major correlate of a cluster of diabetogenic and atherogenic abnormalities that has been described as the metabolic syndrome. The importance of abdominal obesity in association with the development of CVD and type 2 diabetes has been recognized in several studies, beyond the contribution of overall obesity. Additional evidence also suggests that the CVD risk related to the hyperglycemic state observed in subjects with the metabolic syndrome or type 2 diabetes is largely explained by the high prevalence of the metabolic complications of abdominal obesity. Although the presence of the metabolic syndrome clearly increases CVD risk, its clinical diagnosis is not sufficient to classify a patient at high risk for a cardiovascular event because attention must also be paid to the presence of traditional risk factors in the calculation of global CVD risk. The additional information provided by the metabolic syndrome to the risk attributed to traditional risk factors in the calculation of global CVD risk has been defined as global cardiometabolic risk. The fight against abdominal obesity as a major cause of CVD morbidity and mortality will require major societal changes and the involvement of dieticians, kinesiologists and behaviour modification specialists in clinical practice to reshape our physical activity and dietary habits. Finally, the early prevention of overweight/obesity/abdominal obesity in children, starting as early as conception, and the identification of key drivers of unhealthy nutritional and sedentary behaviours are the cornerstone of a successful comprehensive plan to fight CVD morbidity.

Regional body fat distribution and metabolic profile in postmenopausal women

The aim of the study was to examine how body fat distribution variables were associated with metabolic parameters in a sample of 113 postmenopausal women not receiving hormone therapy (56.9 +/- 4.4 years, 28.4 +/- 5.1 kg/m(2)). Body fat distribution variables (visceral adipose tissue [AT], subcutaneous AT, and total midthigh AT) were measured using computed tomography; body fat mass was assessed by hydrostatic weighing; insulin sensitivity was determined with the euglycemic-hyperinsulinemic clamp; fasting plasma glucose (FPG) and 2-hour plasma glucose (2hPG) concentrations were measured by a 75-g oral glucose load; and (high-sensitivity) C-reactive protein (hs-CRP) was measured using a highly sensitive assay. After controlling for fat mass, visceral AT was positively associated with plasma triglyceride, hs-CRP, FPG, and 2hPG, and negatively associated with high-density lipoprotein cholesterol (HDL-C) and insulin sensitivity. Total midthigh AT was negatively associated with apolipoprotein B, FPG, and 2hPG, and positively associated with insulin sensitivity. Stepwise multiple regression analyses including abdominal visceral AT, subcutaneous AT and total midthigh AT as independent variables showed that abdominal visceral AT best predicted the variance in plasma triglyceride, HDL-C, low-density lipoprotein peak particle size, hs-CRP, FPG, 2hPG, and insulin sensitivity. Abdominal subcutaneous AT was a significant predictor of only insulin sensitivity, whereas total midthigh AT predicted HDL-C, low-density lipoprotein peak particle size, and apolipoprotein B. These multivariate analyses also indicated that total midthigh AT was favorably related to these outcomes, whereas abdominal visceral AT and subcutaneous AT were unfavorably related. These results confirmed that abdominal visceral fat is a critical correlate of metabolic parameters in postmenopausal women. In addition, a higher proportion of AT located in the total midthigh depot is associated with a favorable metabolic profile.

The association between dyslipidaemia and obesity in Chinese men after adjustment for insulin resistance

Obesity is associated with dyslipidaemia characterised by increased fasting triglyceride and decreased high-density lipoprotein (HDL) concentrations. Causes for obesity-associated dyslipidaemia include insulin resistance, excessive caloric intake, increased free fatty acid production and disturbances in the counter-regulatory hormones. We examined the relationships between lipid parameters and obesity before and after adjustment of insulin resistance in 902 Hong Kong Chinese men. After adjustment for age, smoking and insulin resistance, increasing body mass index (BMI) and waist-to-hip ratio (WHR) remained closely associated with increased concentrations of triglyceride and apolipoprotein B (apo B), increased ratios between low-density lipoprotein (LDL) and HDL (LDL/HDL), and that between apo B and LDL (apo B/LDL), increased fasting and 2-h plasma glucose and insulin, as well as decreased concentrations of HDL, HDL2 and apolipoprotein A-I (apo A-I). On stepwise multiple regression analysis using age, BMI, WHR, insulin resistance and fasting plasma glucose as independent variables, BMI and WHR were the major determinants for the variance of triglyceride, HDL and its subfractions, LDL/HDL, apo B and apo B/LDL. Age was the most important predictor for total cholesterol and LDL. Insulin resistance only explained less than 1% of the variance in triglyceride and apo B. This was compared to a variance between 10 and 16% in these parameters as explained by BMI and/or WHR. In conclusion, obesity is associated with dyslipidaemia in Chinese men, characterised by increased plasma triglyceride, apo B, LDL/HDL, apo B/LDL, and decreased HDL, HDL2 and apo A-I concentrations. Obesity independent of insulin resistance, in particular central adiposity as reflected by increased WHR, was the most important independent variable for many of these lipid abnormalities. Our results emphasised the multifactorial linkage between obesity and dyslipidaemia.

Familial resemblance of plasma lipids, lipoproteins and postheparin lipoprotein and hepatic lipases in the HERITAGE Family Study

The familial aggregation of lipids and lipoproteins and plasma postheparin triglyceride lipases was investigated in 86 Caucasian families participating in the HERITAGE Family study, a study investigating the role of genetic factors in the adaptation to exercise training and its relationships with cardiovascular disease risk factors. Accordingly, sedentary subjects were recruited, tested for a battery of measurements, exercise trained for 20 weeks, and were re-measured. The present report includes plasma levels of total cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol and triglycerides, and postheparin plasma lipoprotein lipase (LPL) and hepatic lipase (HL) activities measured in 437 sedentary individuals (171 parents and 266 adult offspring) before training. Significant familial resemblance was observed for all the age-adjusted phenotypes. The pattern of familial correlations reveals no spouse correlations but significant parent-offspring and sibling correlations for total cholesterol, HDL-cholesterol and LDL-cholesterol with heritability (h2) estimates of 62%, 83%, and 50%, respectively. For plasma triglyceride concentrations (h2 = 55%) and HL activity (h2 = 40%), significant spouse correlations were found in addition to parent-offspring and sibling correlations, suggesting that common familial environment in addition to genetic factors contribute to the familial resemblance. For plasma LPL activity, there was no spouse correlation, but sex differences were found in the familial correlations with higher heritabilities in female pairs (h2 = 76%) compared to male pairs (h2 = 30%) and opposite-sex pairs (h2 = 44%). These results confirm the findings of previous family studies showing that genetic factors are major determinants of the familial resemblance in plasma lipids and lipoproteins and suggest the presence of sex differences in the heritability of postheparin LPL activity.

The relation of plasma triglyceride, apolipoprotein B, and high-density lipoprotein cholesterol to postheparin lipoprotein lipase activity is dependent on apolipoprotien E polymorphism

Postheparin plasma (PH)-lipoprotein lipase (LPL) activity has been reported to be a significant correlate of plasma triglyceride and high-density lipoprotein cholesterol (HDL-C) levels. However, some studies have failed to observe these associations. In this regard, apolipoprotein (apo) E polymorphism may play an important role, since the apo E2 isoform has unfavorable effects on the catabolism of triglyceride-rich lipoprotein particles. We have thus examined the relationships between PH-LPL activity and plasma lipoprotein-lipid levels within groups of men classified on the basis of apo E phenotypes, to verify whether apo E polymorphism could alter these associations. In men carrying the apo E2 isoform (n = 12), PH-LPL activity showed a strong negative correlation with plasma triglyceride (r = -.72, P < .01), very-low-density lipoprotein (VLDL) triglyceride ([VLDL-TG] r = -.83, P < .001), and VLDL cholesterol ([VLDL-C] r = -.57, P < .05) levels and a positive correlation with plasma HDL-C (r = .87, P < .001) and HDL2-C (r=.90, P < .001) concentrations. These correlations were also noted for plasma apo B levels (r = -.65, P < .05), VLDL-apo B concentrations (r= -.76, P < .01), and the HDL-C to cholesterol ratio (r = .85, P < .001). In contrast, none of these associations were found in men carrying the apo E4 isoform (n = 11). In men homozygous for the apo E3 isoform (n = 29), PH-LPL activity was only significantly correlated with plasma HDL2-C levels (r = .46, P < .01). Results of the present study indicate that PH-LPL activity is related to plasma triglyceride, VLDL-TG, VLDL-C, VLDL-apo B, apo B, and HDL-C levels and the HDL-C to cholesterol ratio in men carrying the apo E2 isoform, but not in men homozygous for the apo E3 isoform or among apo E4 carriers. Thus, apo E polymorphism appears to modulate the effect of variation in PH-LPL activity on the plasma lipoprotein profile.

Does lipoprotein or hepatic lipase activity explain the protective lipoprotein profile of premenopausal women?

Numerous studies have reported that women have a lipoprotein profile suggestive of a reduced risk of coronary heart disease (CHD). We have therefore tested whether the "protective" lipoprotein profile of women could be explained by differences in hepatic lipase (HL) or lipoprotein lipase (LPL) activities. In the present study, 14 non-obese healthy premenopausal women had higher plasma concentrations of high-density lipoprotein cholesterol (HDL-C), HDL2-C, HDL3-C, and HDL-apolipoprotein (apo) AI, and a higher ratio of HDL-C to low-density lipoprotein cholesterol (LDL-C) than 17 non-obese healthy men. Women also had lower plasma triglyceride (TG), HDL-TG, and apo B levels than men. Plasma postheparin LPL (PH-LPL) and HL activities showed no significant sex dimorphism, whereas abdominal and femoral adipose tissue (AT)-LPL activities were significantly higher in women (P < .005). In men, PH-LPL activity correlated significantly with plasma HDL2-C (r = .52, P < .05), LDL-C (r = -.47, P < .05), and apo B (r = -.56, P < .01) levels, as well as with the HDL-C/LDL-C ratio (r = .67, P < .005). No such relationships were found in women, with the exception of HL activity, which was negatively correlated with HDL-apo AI levels. In both genders, abdominal AT-LPL activity showed no significant association with plasma lipoprotein levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Dyslipidaemia and obesity

Obesity is frequently associated with a dyslipidaemic state. Several metabolic and epidemiological studies published in the 1980s have, however, emphasized the importance of considering the regional distribution of body fat in the assessment of the health hazards of obesity. The development of imaging techniques such as computed tomography has also allowed it to be established that the fat located in the abdominal cavity, i.e. the visceral adipose tissue, was the critical correlate of the metabolic complications found in abdominal obesity which include insulin resistance and hyperinsulinaemia, glucose intolerance, hypertriglyceridaemia, hypoalphalipoproteinaemia and increased concentrations of dense LDL particles. Furthermore, since several genes are involved in the regulation of plasma lipoprotein-lipid levels and they have been reported to show polymorphism, visceral obesity should be considered as a permissive factor that exacerbates an individual's susceptibility to dyslipidaemia and premature coronary heart disease rather than a primary regulator of the dyslipidaemic state observed in visceral obese patients. Finally, as insulin resistance and the level of visceral adipose tissue are two main correlates of the dyslipidaemic state which characterizes abdominal obesity, treatment should be aimed at reducing visceral fat and improving insulin sensitivity. Prospective studies are clearly warranted to evaluate the potential benefits of such interventions on the incidence of coronary heart disease.

Is body fat loss a determinant factor in the improvement of carbohydrate and lipid metabolism following aerobic exercise training in obese women?

Thirty-one obese, premenopausal women aged 35.4 +/- 5.1 (SD) years exercised for 90 minutes at approximately 55% of maximal aerobic power (VO2max) four to five times a week for a period of 6 months. The training program induced a significant increase in VO2max (P < .001) and significant improvements in carbohydrate and lipid metabolism, as reflected by decreased plasma insulin (INS) concentrations measured in the fasting state and after glucose (GLU) ingestion (INS area, P < .001), by reduced plasma cholesterol (C) and low-density lipoprotein cholesterol (LDL-C) levels (P < .001), and by increased ratios of high-density lipoprotein cholesterol (HDL-C)/LDL-C and HDL2-C/HDL3-C (P < .05 and P < .001, respectively). Changes in body fat mass were positively associated with changes in the INS area/GLU area ratio (r = .49, P < .05) and with changes in very-low-density lipoprotein triglycerides ([VLDL-TG] r = .49, P < .05). Furthermore, changes in the INS area were positively associated with changes in VLDL-TG (r = .51, P < .05). Although no significant mean change in body composition was observed, important individual variation was noted. Twenty women showed a reduction in body fat mass (mean reduction, 2.63 +/- 2.2 kg), whereas 11 women showed an increase in adipose mass (mean increase, 2.79 +/- 2.36 kg). Comparable increases in VO2max were observed between the two groups. The group that showed a decrease in body fat mass with exercise also had significant improvements in carbohydrate and lipid metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of exercise and feeding on the activity of lipoprotein lipase in nine different adipose depots of guinea pigs

1. The activity of lipoprotein lipase (LPL) was measured in whole adipose tissue from 9 identified adipose depots of sedentary, fasting adult guinea pigs and following 30 min of exercise or voluntary ingestion of chow, and in adipocyte and stromal-vascular fractions from exercised specimens. 2. In sedentary, fasting specimens, LPL activity was up to 4 times higher in the small intermuscular depots than in the perirenal and epididymal depot (Table 1). 3. LPL activity increased significantly after feeding only in the large superficial depot, groin, and in the perirenal depot. LPL activity decreased after exercise only in the 2 intermuscular depots and in small anterior superficial depots. These effects of exercise were consistently greater in males than in females (Table 3). 4. Following exercise, there was up to twice as much LPL in the adipocytes as in the stromal-vascular fraction of the intermuscular depots, about 50% more in adipocytes from the minor superficial depots and about equal quantities in the 2 fractions of the intra-abdominal and groin depots (Table 2). 5. The data demonstrate the physiological inhomogeneity of both superficial and internal adipose depots, and are consistent with the hypothesis that LPL originating from adipose tissue may enter the circulation.

Genetic aspects of susceptibility to obesity and related dyslipidemias

Obesity has a multifactorial origin. However, although environmental variables undoubtedly play a role in the development of obesity, it is now clear that genetic variation is also involved in the determination of an individual's susceptibility to body fat accumulation. In addition, it is also widely accepted that obesity is not a single homogeneous phenotype. It is also heterogeneous regarding its causes and metabolic complications. The regional distribution of body fat appears to be an important correlate of the metabolic complications that have been related to obesity. Due to their higher accumulation of abdominal fat, men are generally more at risk for the metabolic complications of obesity than women whereas some obese women, with large gluteal-femoral adipose depots may have a cosmetic problem which may not necessarily require medical intervention. Several studies have been conducted to understand the mechanisms by which abdominal obesity is related to diabetes, hypertension and cardiovascular disease. It appears that the increased risk of abdominal obesity is the result of complex hormonal and metabolic interactions. Studies in genetic epidemiology have shown that both total body fatness and the regional distribution of body fat have a significant genetic component. Standardized intervention studies using an identical twin design have shown that individuals that have the same genetic background tend to show similar changes in body fat and in plasma lipoprotein levels when exposed to standardized caloric excess or energy restriction. Finally, although abdominal obesity is a significant risk factor for cardiovascular disease, not every abdominal obese subject will experience metabolic complications, suggesting that some obese individuals may be more susceptible than others. Variation in several genes relevant to lipid and lipoprotein metabolism may alter the relation of abdominal obesity to dyslipoproteinemias. Abdominal obesity should therefore be considered as a factor that exacerbates an individual's susceptibility to cardiovascular disease.