Pathogenic potential of adipose tissue and metabolic consequences of adipocyte hypertrophy and increased visceral adiposity

Post-weaning voluntary exercise exerts long-term moderation of adiposity in males but not in females in an animal model of early-onset obesity

Given the alarming increase in childhood, adolescent and adult obesity there is an imperative need for understanding the early factors affecting obesity and for treatments that may help prevent or at least moderate it. Exercise is frequently considered as an effective treatment for obesity however the empirical literature includes many conflicting findings. In the present study, we used the OLETF rat model of early-onset hyperphagia-induced obesity to examine the influence of early exercise on peripheral adiposity-related parameters in both males and females. Rats were provided voluntary access to running wheels from postnatal day (PND) 22 until PND45. We examined fat pad weight (brown, retroperitoneal, inguinal and epididymal); inguinal adipocyte size and number; and leptin, adiponectin, corticosterone and creatinine levels. We also examined body weight, feeding efficiency and spontaneous intake. Early voluntary exercise reduced intake, adiposity and leptin in the OLETF males following a sharp reduction in adipocyte size despite a significant increase in fat cell number. Exercising males from the lean LETO control strain presented stable intake, but reduced body fat, feeding efficiency and increased plasma creatinine, suggesting an increment in muscle mass. OLETF females showed reduced feeding efficiency and liver fat, and a significant increase in brown fat. Exercising LETO control females increased intake, body weight and creatinine, but no changes in body fat. Overall, OLETF rats presented higher adiponectin levels than controls in both basal and post-exercise conditions. The results suggest an effective early time frame, when OLETF males can be successfully "re-programmed" through voluntary exercise; in OLETF females the effect is much more moderate. Findings expose sex-dependent peripheral mechanisms in coping with energy challenges.

The relationship of omental and subcutaneous adipocyte size to metabolic disease in severe obesity

Objective

Several studies have reported the existence of a subgroup of obese individuals with normal metabolic profiles. It remains unclear what factors are responsible for this phenomenon. We proposed that adipocyte size might be a key factor in the protection of metabolically healthy obese (MHO) individuals from the adverse effects of obesity.

Subjects

Thirty-five patients undergoing bariatric surgery were classified as MHO (n = 15) or metabolically unhealthy obese (MUO, n = 20) according to cut-off points adapted from the International Diabetes Federation definition of the metabolic syndrome. Median body mass index (BMI) was 48 (range 40–71).

Results

There was a moderate correlation between omental adipocyte size and subcutaneous adipocyte size (r = 0.59, p<0.05). The MHO group had significantly lower mean omental adipocyte size (80.9±10.9 µm) when compared with metabolically unhealthy patients (100.0±7.6 µm, p<0.0001). Mean subcutaneous adipocyte size was similar between the two groups (104.1±8.5 µm versus 107.9±7.1 µm). Omental, but not subcutaneous adipocyte size, correlated with the degree of insulin resistance as measured by HOMA-IR (r = 0.73, p<0.0005), as well as other metabolic parameters including triglyceride/HDL-cholesterol ratio and HbA1c. Twenty-eight patients consented to liver biopsy. Of these, 46% had steatohepatitis and fibrosis. Fifty percent (including all the MHO patients) had steatosis only. Both omental and subcutaneous adipocyte size were significantly associated with the degree of steatosis (r = 0.66, p<0.0001 and r = 0.63, p<0.005 respectively). However, only omental adipocyte size was an independent predictor of the presence or absence of fibrosis.

Conclusion

Metabolically healthy individuals are a distinct subgroup of the severely obese. Both subcutaneous and omental adipocyte size correlated positively with the degree of fatty liver, but only omental adipocyte size was related to metabolic health, and possibly progression from hepatic steatosis to fibrosis.

Attenuation of obesity by early-life food restriction in genetically hyperphagic male OLETF rats: peripheral mechanisms

The alarming increase in childhood, adolescent and adult obesity has exposed the need for understanding early factors affecting obesity and for treatments that may help prevent or moderate its development. In the present study, we used the OLETF rat model of early-onset hyperphagia induced obesity, which become obese as a result of the absence of CCK(1) receptors, to examine the influence of partial food restriction on peripheral adiposity-related parameters during and after chronic and early short-term food restriction. Pair feeding (to the amount of food eaten by control, LETO rats) took place from weaning until postnatal day (PND) 45 (early) or from weaning until PND90 (chronic). We examined fat pad weight (brown, retroperitoneal, inguinal and epididymal); inguinal adipocyte size and number; and plasma leptin, oxytocin and creatinine levels. We also examined body weight, feeding efficiency and spontaneous intake after release from food-restriction. The results showed that chronic food restriction produced significant reductions in adiposity parameters, hormones and body weight, while early food restriction successfully reduced long-term body weight, intake and adiposity, without affecting plasma measurements. Early (and chronic) dieting produced promising long-term effects that may imply the reorganization of both peripheral and central mechanisms that determine energy balance and further support the theory suggesting that early interventions may effectively moderate obesity, even in the presence of a genetic tendency.

Adipose tissue-specific regulation of angiotensinogen in obese humans and mice: impact of nutritional status and adipocyte hypertrophy

BACKGROUND

The adipose tissue renin-angiotensin system (RAS) has been implicated in the pathophysiology of obesity and dysfunction of adipose tissue. However, neither regulation of angiotensinogen (AGT) expression in adipose tissue nor secretion of adipose tissue-derived AGT has been fully elucidated in humans.

METHODS

Human subcutaneous abdominal adipose tissue (SAT) biopsies were performed for 46 subjects with a wide range of body mass index (BMI). Considering the mRNA level of AGT and indices of body fat mass, the amount of adipose tissue-derived AGT secretion (A-AGT-S) was estimated. Using a mouse model of obesity and weight reduction, plasma AGT levels were measured with a newly developed enzyme-linked immunosorbent assay (ELISA), and the contribution of A-AGT-S to plasma AGT levels was assessed.

RESULTS

A-AGT-S was substantially increased in obese humans and the value was correlated with the plasma AGT level in mice. A-AGT-S and plasma AGT were higher in obese mice, whereas lower in mice with weight reduction. However, the AGT mRNA levels in the liver, kidney, and aorta were not altered in the mouse models. In both humans and mice, the AGT mRNA levels in mature adipocytes (MAs) were comparable to those in stromal-vascular cells. Coulter Multisizer analyses revealed that AGT mRNA levels in the MAs were inversely correlated with the average size of mature adipocytes.

CONCLUSIONS

This study demonstrates that adipose tissue-derived AGT is substantially augmented in obese humans, which may contribute considerably to elevated levels of circulating AGT. Adipose tissue-specific regulation of AGT provides a novel insight into the clinical implications of adipose tissue RAS in human obesity.

Increased fat due to estrogen deficiency induces bone loss by elevating monocyte chemoattractant protein-1 (MCP-1) production

Ovariectomy (OVX)-induced estrogen withdrawal resulted in both bone loss and an increase in fat. We observed elevated osteoclast (OC) formation by bone marrow-derived macrophages treated with medium conditioned by fats from OVX mice, but not from sham-operated mice. Fats from OVX mice expressed and secreted higher levels of monocyte chemoattractant protein-1 (MCP-1) than those from sham-operated mice. Increased fat resulting from estrogen deficiency is thus responsible for bone loss due to enhanced OC formation, which is, at least partly, a consequence of elevated MCP-1 production.

High-molecular-weight adiponectin is selectively reduced in women with polycystic ovary syndrome independent of body mass index and severity of insulin resistance

CONTEXT

High-molecular-weight (HMW) adiponectin contributes to insulin resistance (IR), which is closely associated with the pathophysiology of polycystic ovary syndrome (PCOS). Abnormalities in adipocyte function have been identified in PCOS and potentially contribute to lower adiponectin concentrations.

OBJECTIVE

Our objective was to determine which variables in plasma and adipose tissue influence HMW adiponectin in a well characterized cohort of women with PCOS.

DESIGN

This was a cross-sectional study.

SETTINGS AND PARTICIPANTS

A teaching hospital. Women with PCOS (n = 98) and body mass index (BMI)-matched controls (n = 103) (including 68 age-, BMI-, and IR-matched pairs).

INTERVENTIONS

A standard 75-g oral glucose tolerance test was performed for each participant. Subcutaneous adipose tissue samples were taken by needle biopsy for a subset of PCOS women (n = 9) and controls (n = 8).

MAIN OUTCOME MEASURES

Serum levels of HMW adiponectin and their relation to indices of insulin sensitivity, body composition, and circulating androgens as well as adipose tissue expression levels of ADIPOQ, TNFalpha, PPARgamma, and AR were assessed.

RESULTS

HMW adiponectin was significantly lower in women with PCOS compared with both BMI- and BMI- and IR-matched controls (P = 0.009 and P = 0.027, respectively). Although BMI and IR were the main predictors of HMW adiponectin, an interaction between waist to hip ratio and plasma testosterone contributed to its variance (P = 0.026). Adipose tissue gene expression analysis demonstrated that AR and TNFalpha (P = 0.008 and P = 0.035, respectively) but not ADIPOQ mRNA levels were increased in PCOS compared with controls.

CONCLUSIONS

HMW adiponectin is selectively reduced in women with PCOS, independent of BMI and IR. Gene expression analysis suggests that posttranscriptional/translational modification contributes to reduced HMW adiponectin in PCOS.

[Adipose tissue as a therapeutic target in obesity]

Obesity is characterized by an increase of adipose tissue as a result of a positive imbalance between food intake and energy expenditure. Recent studies have indicated that adipocyte function is more complex than expected, since these cells have multiple functions and are integrated in a homeostatic network to optimize energy resources. As metabolic sensors in the body, adipocytes and the surrounding stromal vascular cells produce and secrete autocrine, paracrine and endocrine factors, able to regulate aspects involved in the development of adipocytes, as well as effects in peripheral organs important for metabolism. Regulation of these endocrine factors could lead to new therapeutic approaches targeted at aspects related to adipogenesis, preadipocyte proliferation and differentiation, inflammatory cytokine release and secretion, adipose tissue vascularization, and regulation of lipid metabolism or, alternatively, regulation of energy dissipation in mitochondria. In the study of the mechanisms of adipogenesis and remodulation of adipose tissue with respect to adipocyte size and function, an alternative and unorthodox strategy to improve obesity-associated metabolic complications could consist of increasing the storage capacity of adipose tissue to prevent a toxic response known as lipotoxicity.

Aging and regional differences in fat cell progenitors - a mini-review

Fat mass and fat tissue distribution change dramatically throughout life. In old age, fat becomes dysfunctional and is redistributed from subcutaneous to intra-abdominal visceral depots as well as other ectopic sites, including bone marrow, muscle and the liver. These changes are associated with increased risk of metabolic syndrome. Fat tissue is a nutrient storage, endocrine and immune organ that undergoes renewal throughout the lifespan. Preadipocytes, which account for 15-50% of cells in fat tissue, give rise to new fat cells. With aging, declines in preadipocyte proliferation and differentiation likely contribute to increased systemic exposure to lipotoxic free fatty acids. Age-related fat tissue inflammation is related to changes that occur in preadipocytes and macrophages in a fat depot-dependent manner. Fat tissue inflammation frequently leads to further reduction in adipogenesis with aging, more lipotoxicity and activation of cellular stress pathways that, in turn, exacerbate inflammatory responses of preadipocytes and immune cells, establishing self-perpetuating cycles that lead to systemic dysfunction. In this review, we will consider how inherent, age-related, depot-dependent alterations in preadipocyte function contribute to age-related fat tissue redistribution and metabolic dysfunction.

Maternal capital and the metabolic ghetto: An evolutionary perspective on the transgenerational basis of health inequalities

There is particular interest in understanding socioeconomic and ethnic variability in health status. The developmental origins of disease hypothesis emphasize the importance of growth patterns across the life-course in relation to noncommunicable disease risk. The physiological components of cardiovascular risk, collectively termed the metabolic syndrome, derive in part from a disparity between the homeostatic "metabolic capacity" of vital organs and the "metabolic load" induced by large tissue masses, a rich diet and sedentary behavior. From an evolutionary perspective, the risk of such disparity is decreased by maternal physiology regulating offspring growth trajectory during gestation and lactation. Maternal capital, defined as phenotypic resources enabling investment in the offspring, allows effective buffering of the offspring from nutritional perturbations and represents the environmental niche initially occupied by the offspring. Offspring growth patterns are sensitive to the magnitude of maternal capital during early windows of plasticity. Offspring life-history strategy can then respond adaptively to further factors across the life-course, but only within the context of this initial maternal influence on growth. Maternal somatic capital is primarily gained or lost across generations, through variable rates of fetal and infant growth. I argue that the poor nutritional experience of populations subjected to colonialism resulted in a systematic loss of maternal capital, reflected in downward secular trends in stature. Accelerating the recovery of somatic capital within generations overloads metabolic capacity and exacerbates cardiovascular risk, reflected in increased disease rates in urbanizing and emigrant populations. Public health policies need to benefit metabolic capacity without exacerbating metabolic load.

Dysregulation of lipolysis and lipid metabolism in visceral and subcutaneous adipocytes by high-fat diet: role of ATGL, HSL, and AMPK

This study investigated the molecular mechanisms by which a high-fat diet (HFD) dysregulates lipolysis and lipid metabolism in mouse epididymal (visceral, VC) and inguinal (subcutaneous, SC) adipocytes. Eight-weeks of HFD feeding increased adipose triglyceride lipase (ATGL) content and comparative gene identification-58 (CGI-58) expression, whereas hormone-sensitive lipase (HSL) phosphorylation and perilipin content were severely reduced. Adipocytes from HFD mice elicited increased basal but blunted epinephrine-stimulated lipolysis and increased diacylglycerol content in both fat depots. Consistent with impaired adrenergic receptor signaling, HFD also increased adipose-specific phospholipase A(2) expression in both fat depots. Inhibition of E-prostanoid 3 receptor increased basal lipolysis in control adipocytes but failed to acutely alter the effects of HFD on lipolysis in both fat depots. In HFD visceral adipocytes, activation of adenylyl cyclases by forskolin increased HSL phosphorylation and surpassed the lipolytic response of control cells. However, in HFD subcutaneous adipocytes, forskolin induced lipolysis without detectable HSL phosphorylation, suggesting activation of an alternative lipase in response to HFD-induced suppression of HSL in VC and SC adipocytes. HFD also powerfully inhibited basal, epinephrine-, and forskolin-induced AMP kinase (AMPK) activation as well peroxisome proliferator-activated receptor gamma coactivator-1alpha expression, citrate synthase activity, and palmitate oxidation in both fat depots. In summary, novel evidence is provided that defective adrenergic receptor signaling combined with upregulation of ATGL and suppression of HSL and AMPK signaling mediate HFD-induced alterations in lipolysis and lipid utilization in VC and SC adipocytes, which may play an important role in defective lipid mobilization and metabolism seen in diet-induced obesity.

Adipocyte turnover: relevance to human adipose tissue morphology

OBJECTIVE

Adipose tissue may contain few large adipocytes (hypertrophy) or many small adipocytes (hyperplasia). We investigated factors of putative importance for adipose tissue morphology.

RESEARCH DESIGN AND METHODS

Subcutaneous adipocyte size and total fat mass were compared in 764 subjects with BMI 18-60 kg/m(2). A morphology value was defined as the difference between the measured adipocyte volume and the expected volume given by a curved-line fit for a given body fat mass and was related to insulin values. In 35 subjects, in vivo adipocyte turnover was measured by exploiting incorporation of atmospheric (14)C into DNA.

RESULTS

Occurrence of hyperplasia (negative morphology value) or hypertrophy (positive morphology value) was independent of sex and body weight but correlated with fasting plasma insulin levels and insulin sensitivity, independent of adipocyte volume (beta-coefficient = 0.3, P < 0.0001). Total adipocyte number and morphology were negatively related (r = -0.66); i.e., the total adipocyte number was greatest in pronounced hyperplasia and smallest in pronounced hypertrophy. The absolute number of new adipocytes generated each year was 70% lower (P < 0.001) in hypertrophy than in hyperplasia, and individual values for adipocyte generation and morphology were strongly related (r = 0.7, P < 0.001). The relative death rate (approximately 10% per year) or mean age of adipocytes (approximately 10 years) was not correlated with morphology.

CONCLUSIONS

Adipose tissue morphology correlates with insulin measures and is linked to the total adipocyte number independently of sex and body fat level. Low generation rates of adipocytes associate with adipose tissue hypertrophy, whereas high generation rates associate with adipose hyperplasia.

The obesity paradox, weight loss, and coronary disease

PURPOSE

Because obesity is a cardiovascular risk factor but is associated with a more favorable prognosis among cohorts of cardiac patients, we assessed this "obesity paradox" in overweight and obese patients with coronary heart disease enrolled in a cardiac rehabilitation and exercise training (CRET) program, making this assessment in patients classified as overweight/obese using both traditional body mass index (BMI) and percent body fat assessments. Additionally, we assessed the efficacy and safety of purposeful weight loss in overweight and obese coronary patients.

PATIENTS AND METHODS

We retrospectively studied 529 consecutive CRET patients following major coronary events before and after CRET, and compared baseline and post program data in 393 overweight and obese patients (body mass index [BMI] > or =25 kg/m(2)) divided by median weight change (median=-1.5%; mean +2% vs -5%, respectively). In addition, we assessed 3-year total mortality in various baseline BMI categories as well as compared mortality in those with high baseline percent fat (>25% in men and >35% in women) versus those with low baseline fat.

RESULTS

Following CRET, the overweight and obese with greater weight loss had improvements in BMI (-5%; P <.0001), percent fat (-8%; P <.0001), peak oxygen consumption (+16%; P <.0001), low-density lipoprotein cholesterol (-5%; P <.02), high-density lipoprotein cholesterol (+10%; P <.0001), triglycerides (-17%; P <.0001), C-reactive protein (-40%; P <.0001), and fasting glucose (-4%; P=.02), as well as marked improvements in behavioral factors and quality-of-life scores. Those with lower weight loss had no significant improvements in percent fat, low-density lipoprotein cholesterol, triglycerides, C-reactive protein, and fasting glucose. During 3-year follow-up, overall mortality trended only slightly lower in those with baseline overweightness/obesity who had more weight loss (3.1% vs 5.1%; P=.30). However, total mortality was considerably lower in the baseline overweight/obese (BMI > or =25 kg/m(2)) than in 136 CRET patients with baseline BMI <25 kg/m(2) (4.1% vs 13.2%; P <.001), as well as in those with high baseline fat compared with those with low fat (3.8% vs 10.6%; P <.01).

CONCLUSIONS

Purposeful weight loss with CRET in overweight/obese coronary patients is associated with only a nonsignificant trend for lower mortality but is characterized by marked improvements in obesity indices, exercise capacity, plasma lipids, and inflammation, as well as behavioral factors and quality of life. Although an "obesity paradox" exists using either baseline BMI or baseline percent fat criteria, these results support the safety and potential long-term benefits of purposeful weight loss in overweight and obese patients with coronary heart disease.

Obesity and chronic kidney disease

This article summarizes the current hypotheses that link visceral obesity and kidney malfunction and provides information on the epidemiology and renal pathology resulting from visceral obesity.

Estrogen exposure, obesity and thyroid disease in women with severe pulmonary hypertension

Severe pulmonary hypertension is a lethal group of disorders which preferentially afflicts women. It appears that in recent years the patient profile has shifted towards older, obese, and postmenopausal women, suggesting that endocrine factors may be important. Several studies have revealed an increased prevalence of thyroid disease in these patients, but no studies have evaluated for a coexistence of endocrine factors. In particular, no studies have attempted to evaluate for concurrent thyroid disease, obesity and long-term estrogen exposure in patients.

88 patients attending the Pulmonary Hypertension Association 8th International meeting completed a questionnaire and were interviewed. Information was collected regarding reproductive history, height, weight, and previous diagnosis of thyroid disease.

46% met criteria for obesity. 41% reported a diagnosis of thyroid disease. 81% of women reported prior use of hormone therapy. 70% reported greater than 10 years of exogenous hormone use. 74% of female patients reported two or more of potentially disease modifying endocrine factors (obesity, thyroid disease or estrogen therapy).

The coexistent high prevalence in our cohort of exogenous estrogen exposure, thyroid disease and obesity suggests that an interaction of multiple endocrine factors might contribute to the pathogenesis of pulmonary hypertension and may represent epigenetic modifiers in genetically-susceptible individuals.

Development of obesity in the Otsuka Long-Evans Tokushima Fatty rat

Understanding the early factors affecting obesity development in males and females may help to prevent obesity and may lead to the discovery of more effective treatments for those already obese. The Otsuka Long-Evans Tokushima Fatty (OLETF) rat model of obesity is characterized by hyperphagia-induced obesity, due to a spontaneous lack of CCK(1) receptors. In the present study, we focused on the behavioral and physiological aspects of obesity development from weaning to adulthood. We examined body weight, feeding efficiency, fat pad [brown, retroperitoneal, inguinal and epydidimal (in males)] weight, inguinal adipocyte size and number, leptin and oxytocin levels, body mass index, waist circumference, and females' estrous cycle structure. In the males, central hypothalamic gene expression was also examined. OLETF rats presented overall higher fat and leptin levels, larger adipocytes, and increased waist circumference and BMI from weaning until adulthood, compared with controls. Analysis of developmental patterns of gene expression for hypothalamic neuropeptides revealed peptide-specific patterns that may underlie or be a consequence of the obesity development. Analysis of the developmental trajectories toward obesity within the OLETF strain revealed that OLETF females developed obesity in a more gradual manner than the males, presenting delayed obesity-related "turning points," with reduced adipocyte size but larger postweaning fat pads and increased adipocyte hyperplasia compared with the males. Intake decrease in estrus vs. proestrus was significantly less in OLETF vs. Long-Evans Tokushima Otsuka females. The findings highlight the importance of using different sex-appropriate approaches to increase the efficacy of therapeutic interventions in the treatment and prevention of chronic early-onset obesity.

Adiposopathy and bariatric surgery: is 'sick fat' a surgical disease?

OBJECTIVE

To review how bariatric surgery in obese patients may effectively treat adiposopathy (pathogenic adipose tissue or 'sick fat'), and to provide clinicians a rationale as to why bariatric surgery is a potential treatment option for overweight patients with type 2 diabetes, hypertension, and dyslipidaemia.

METHODS

A group of clinicians, researchers, and surgeons, all with a background in treating obesity and the adverse metabolic consequences of excessive body fat, reviewed the medical literature regarding the improvement in metabolic disease with bariatric surgery.

RESULTS

Bariatric surgery improves metabolic disease through multiple, likely interrelated mechanisms including: (i) initial acute fasting and diminished caloric intake inherent with many gastrointestinal surgical procedures; (ii) favourable alterations in gastrointestinal endocrine and immune responses, especially with bariatric surgeries that reroute nutrient gastrointestinal delivery such as gastric bypass procedures; and (iii) a decrease in adipose tissue mass. Regarding adipose tissue mass, during positive caloric balance, impaired adipogenesis (resulting in limitations in adipocyte number or size) and visceral adiposity are anatomic manifestations of pathogenic adipose tissue (adiposopathy). This may cause adverse adipose tissue endocrine and immune responses that lead to metabolic disease. A decrease in adipocyte size and decrease in visceral adiposity, as often occurs with bariatric surgery, may effectively improve adiposopathy, and thus effectively treat metabolic disease. It is the relationship between bariatric surgery and its effects upon pathogenic adipose tissue that is the focus of this discussion.

CONCLUSIONS

In selective obese patients with metabolic disease who are refractory to medical management, adiposopathy is a surgical disease.

Comorbidities of obesity

Obesity, especially visceral adiposity, is associated with morbidity and mortality through endocrine and mechanical processes. Clinical manifestations due to effects of obesity on the cardiovascular, respiratory, gastrointestinal, musculoskeletal, immune, and integumentary systems have been described. Further studies are needed to understand the pathologic processes underlying these clinical manifestations to improve disease prevention.

Fatty acid composition of epicardial and subcutaneous human adipose tissue

BACKGROUND

Epicardial adipose tissue has special properties that distinguish it from the more widely studied depots of adipose tissue.

OBJECTIVES

We undertook this study to investigate regional differences between epicardial and subcutaneous adipose tissue fat composition, as well as associations between these measures and metabolic variables.

METHODS

Epicardial and subcutaneous peripheral adipose tissue were collected during coronary artery bypass grafting from 42 patients (ages 37-65) with coronary artery disease (CAD). The fatty acid composition of adipose tissue was determined by gas liquid chromatography (GLC).

RESULTS

The saturated fatty acids, including myristic acid (14:0), palmitic acid (16:0), and stearic acid (18:0), were higher, and the unsaturated fatty acids, including palmitoleic acid (16:1n-7), oleic acid (18:1n-9), linoleic acid (18:2n-6), and linolenic acid (18:3n-3), were lower than the subcutaneous adipose tissue. The presence of hypertension was positively correlated with the 16:1n-7 (r = 0.407, P = 0.032) and 18:1n-11(r = 0.370, P = 0.027), and negatively correlated with 18:1n-9 (r = -0.367, P = 0.036) and 18:2n-6 (r = -0.446, P = 0.006) contents of epicardial adipose tissue after adjustment for body mass index.

CONCLUSIONS

Regional differences may be observed in fatty acid composition, suggesting a depot specific impact of stored fatty acids on adipocyte function and metabolism.

Hoofbeats, zebras, and insights into insulin resistance

In this issue of the JCI, Semple and colleagues report phenotypic evaluation of patients with a germline mutation in the gene encoding serine/threonine kinase AKT2 (see the related article beginning on page 315). Their findings support the idea that the postreceptor actions of insulin in the liver--suppression of gluconeogenesis and stimulation of lipogenesis--are mediated through divergent pathways that can be uncoupled. The results appear to refine the arrangement of crucial steps along these pathways and show how comprehensive study of the phenotype, "deep phenotyping," of patients who carry rare mutations might complement other types of experiments to elucidate complex pathways and mechanisms.

Insulin resistance without obesity induced by cotton pellet granuloma in mice

Obesity leads to insulin resistance because the larger adipocytes in obese persons secrete proinflammatory cytokines that cause chronic inflammation in adipose tissue. This, in turn, leads to the alteration of adipokine secretion, which can induce insulin resistance. However, the development of insulin resistance without obesity is still obscure. We aimed to use an animal inflammation model with cotton pellet granuloma (CPG) in adipose tissue to characterize insulin resistance formation. We found that CPG in epididymal white adipose tissue (WAT), rather than in interscapular brown adipose tissue, impaired insulin sensitivity, and glucose utilization, and that it decreased levels of phosphoinsulin receptor and phospho-Akt in both muscle and liver tissue, but that it did not modify the body weight or food intake in mice. Macrophage infiltration in adipose tissue, leukocyte counts, monocyte chemoattractant protein-1, and interleukin-6 were elevated in CPG-treated mice. However, we found a marked decrease of plasma adiponectin only in the WAT group, which might have been because of the lower level of peroxisome proliferator-activated receptor-gamma in WAT. These results show that granuloma formation in WAT by implantation of a cotton pellet may induce insulin resistance under nonobese condition through circulating inflammatory mediators, especially the low level of adiponectin.

"Sick fat," metabolic disease, and atherosclerosis

Atherosclerotic coronary heart disease (CHD) is the most common cause of morbidity and mortality among men and women in developed nations. The obesity epidemic contributes to the increasing prevalence of high blood sugar (as may be found in patients with diabetes mellitus and metabolic syndrome), high blood pressure, and dyslipidemia--all CHD risk factors. Metabolic syndrome describes the common clinical finding wherein component CHD risk factors cluster within a single patient, but this term does not identify any unified pathophysiologic process. However, a component of the metabolic syndrome is abdominal obesity, which does reflect an anatomic manifestation of a "common-soil" pathophysiologic process that promotes the onset of CHD risk factors, and thus increases CHD risk. Adiposopathy ("sick fat") is anatomically characterized by visceral adiposity and adipocyte hypertrophy; it is manifested physiologically by a net increase in release of free fatty acids and by pathogenic adipose tissue metabolic/immune responses that promote metabolic disease and increase CHD risk. Understanding the relation of adiposopathy to CHD risk factors and recognizing the importance of treating both the "cause and effect" of metabolic diseases are critical toward a comprehensive approach in reducing CHD risk. Regarding the "cause," clinicians and their patients should be diligent regarding appropriate nutritional and lifestyle interventions that may favorably affect health. Regarding the "effect," clinicians and their patients should be equally diligent toward appropriate pharmaceutical interventions that reduce CHD risk factors when nutritional and lifestyle interventions do not sufficiently achieve desired metabolic treatment goals.

Does nicotinic acid (niacin) lower blood pressure?

Nicotinic acid (niacin) is a well-established treatment for dyslipidaemia - an important cardiovascular disease (CVD) risk factor. However, niacin may also reduce blood pressure (BP), which is another important CVD risk factor. This review examines the limited publicly available data on niacin's BP effects. Acute administration of immediate-release niacin may lower BP because of niacin's acute vasodilatory effects. Although not always supported by clinical trial data, the package insert of a prescription, extended-release niacin describes niacin-induced acute hypotension. From a chronic standpoint, larger studies, such as the Coronary Drug Project, suggest that niacin may lower BP when administered over a longer period of time. Post hoc analyses of some of the more recent niacin clinical trials also support a more chronic, dose-dependent, BP-lowering effect of niacin. Because laropiprant [a prostaglandin D(2) (PGD(2)) type 1 (DP1) receptor antagonist] does not attenuate niacin's BP-lowering effects, it is unlikely that any chronic lowering of BP by niacin is due to dilation of dermal vessels through activation of the DP1 receptor by PGD(2.) Further research is warranted to evaluate the extent and mechanisms of niacin's effects on BP.

Saturated fatty acid-mediated inflammation and insulin resistance in adipose tissue: mechanisms of action and implications

This review highlights the inflammatory and insulin-antagonizing effects of saturated fatty acids (SFA), which contribute to the development of metabolic syndrome. Mechanisms responsible for these unhealthy effects of SFA include: 1) accumulation of diacylglycerol and ceramide; 2) activation of nuclear factor-kappaB, protein kinase C-, and mitogen-activated protein kinases, and subsequent induction of inflammatory genes in white adipose tissue, immune cells, and myotubes; 3) decreased PPARgamma coactivator-1 alpha/beta activation and adiponectin production, which decreases the oxidation of glucose and fatty acids (FA); and 4) recruitment of immune cells like macrophages, neutrophils, and bone marrow-derived dendritic cells to WAT and muscle. Several studies have demonstrated potential health benefits of substituting SFA with unsaturated FA, particularly oleic acid and (n-3) FA. Thus, reducing consumption of foods rich in SFA and increasing consumption of whole grains, fruits, vegetables, lean meats and poultry, fish, low-fat dairy products, and oils containing oleic acid or (n-3) FA is likely to reduce the incidence of metabolic disease.

Xanthohumol influences preadipocyte differentiation: implication of antiproliferative and apoptotic effects

There is interest in the research of natural compounds that may interfere with the adipocyte life cycle, due to the growing prevalence of obesity and related complications. We aimed at studying the effect of xanthohumol (XN), a Humulus lupulus L. prenylflavonoid, on adipocytes measuring differentiation, proliferation, and apoptosis in 3T3-L1 cells. XN reduced differentiation, as revealed by decreased lipid content and peroxisome proliferator-activated receptor gamma expression, an effect more pronounced when cells were treated before or during differentiation induction. XN also decreased proliferation, as measured by sulforhodamine staining (IC(50) between 26 and 12 microM for 24, 48, and 72 h), and preadipocyte Ki67 expression. Apoptosis was increased in preadipocytes and adipocytes. NF-kappaB activity was stimulated by XN in preadipocytes. Results suggest that XN may reduce adipocyte number, contributing to adipocyte hypertrophy. Taking into consideration the consequences of adipocyte hypertrophy, XN does not seem to improve the metabolic profile associated with obesity.

White adipose tissue as endocrine organ and its role in obesity

Due to the public health problem represented by obesity, the study of adipose tissue, particularly of the adipocyte, is central to the understanding of metabolic abnormalities associated with the development of obesity. The concept of adipocyte as endocrine and functional cell is not totally understood and can be currently defined as the capacity of the adipocyte to sense, manage, and send signals to maintain energy equilibrium in the body. Adipocyte functionality is lost during obesity and has been related to adipocyte hypertrophy, disequilibrium between lipogenesis and lipolysis, impaired transcriptional regulation of the key factors that control adipogenesis, and lack of sensitivity to external signals, as well as a failure in the signal transduction process. Thus, dysfunctional adipocytes contribute to abnormal utilization of fatty acids causing lipotoxicity in non-adipose tissue such as liver, pancreas and heart, among others. To understand the metabolism of the adipocyte it is necessary to have an overview of the developmental process of new adipocytes, regulation of adipogenesis, lipogenesis and lipolysis, endocrine function of adipocytes and metabolic consequences of its dysfunction. Finally, the key role of adipose tissue is shown by studies in transgenic animals or in animal models of diet-induced obesity that indicate the contribution of adipose tissue during the development of metabolic syndrome. Thus, understanding of the molecular process that occurs in the adipocyte will provide new tools for the treatment of metabolic abnormalities during obesity.

Adipose tissue and skeletal muscle plasticity modulates metabolic health

Obesity, accumulation of adipose tissue, develops when energy intake exceeds energy expenditure. Adipose tissue is essential for buffering the differences between energy intake and expenditure by accumulating lipids while skeletal muscle is the energy burning machine. Here we adopted the concept that (i) adipose tissue ability to regulate the storage capacity for lipids as well as (ii) dynamic regulation of muscle and adipose tissue secretory and metabolic activity is important for maintaining the metabolic health. This might be at least in part related to tissue plasticity, a phenomenon enabling dynamic modulation of the tissue phenotype in different physiological and pathophysiological situations. Recent advances in our understanding of the complex endocrine function of adipose tissue in regulating lipid metabolism, adipogenesis, angiogenesis, extracellular matrix remodelling, inflammation and oxidative stress prompted us to review the role of tissue plasticity--dynamic changes in adipose tissue and skeletal muscle metabolic and endocrine phenotype--in determining the difference between metabolic health and disease.

Is adiposopathy (sick fat) an endocrine disease?

OBJECTIVE

To review current consensus and controversy regarding whether obesity is a 'disease', examine the pathogenic potential of adipose tissue to promote metabolic disease and explore the merits of 'adiposopathy' and 'sick fat' as scientifically and clinically useful terms in defining when excessive body fat may represent a 'disease'.

METHODS

A group of clinicians and researchers, all with a background in endocrinology, assembled to evaluate the medical literature, as it pertains to the pathologic and pathogenic potential of adipose tissue, with an emphasis on metabolic diseases that are often promoted by excessive body weight.

RESULTS

The data support pathogenic adipose tissue as a disease. Challenges exist to convince many clinicians, patients, healthcare entities and the public that excessive body fat is often no less a 'disease' than the pathophysiological consequences related to anatomical abnormalities of other body tissues. 'Adiposopathy' has the potential to scientifically define adipose tissue anatomic and physiologic abnormalities, and their adverse consequences to patient health. Adiposopathy acknowledges that when positive caloric balance leads to adipocyte hypertrophy and visceral adiposity, then this may lead to pathogenic adipose tissue metabolic and immune responses that promote metabolic disease. From a patient perspective, explaining how excessive caloric intake might cause fat to become 'sick' also helps provide a rationale for patients to avoid weight gain. Adiposopathy also better justifies recommendations of weight loss as an effective therapeutic modality to improve metabolic disease in overweight and obese patients.

CONCLUSION

Adiposopathy (sick fat) is an endocrine disease.

Dyslipidemia in insulin resistance: clinical challenges and adipocentric therapeutic frontiers

The ever-increasing rates of obesity and diabetes worldwide have the potential to further fuel the epidemic of cardiovascular disease that we are experiencing today. To slow this epidemic successfully, insulin resistance and associated lipid abnormalities that frequently accompany it are key clinical targets. Yet, we are still challenged to reach the mandated clinical goals for lipids that would minimize the development and progression of cardiovascular disease. Adoption of a comprehensive approach by clinicians, in line with recent recommendations for stricter treatment goals for the at-risk patient, is essential to achieving cardiovascular risk reduction. The challenge for clinicians is integrating strategies, approaches and treatments that address the multiple metabolic defects in patients with insulin resistance and dyslipidemia. New perspectives can help effectively meet this ongoing challenge. Emerging evidence suggests that adipose tissue is intimately involved in the inter-relationships between insulin resistance and dyslipidemia. The future probably involves therapeutic strategies that directly target adipose tissue to optimally reduce cardiometabolic risk.