Fat Cell Hypertrophy Research Articles

Can bisphenol A diglycidyl ether (BADGE) administration prevent steroid-induced femoral head osteonecrosis in the early stage?

Steroid-induced osteonecrosis of the femoral head (ONFH) is associated with increase of intraosseous pressure caused by elevating of adipogenesis and fat cell hypertrophy in the bone marrow, which subsequently decreases the blood flow in the femoral head and finally resulting in bone ischemia. The early femoral head-preserving method has mainly focused on the conventional core decompression procedure. However, it only achieves a slight decrease in intra-medullary pressure with limited clinical outcome. The crucial point in prevention is to achieve a thorough decompression of intra-medullary pressure and improvement of microcirculation of the femoral head. Bisphenol-A-diglycidyl ether (BADGE), an antagonism of PPAR-γ(Peroxisome proliferator-activated receptor gamma), has been shown to successfully reverse bone marrow adipogenesis and fat cell hypertrophy, enhances proliferation of osteoblasts, inhibit osteoclastogenesis. Therefore, we hypothesized that BADGE administration may be an appropriate novel method for the prevention of early stage steroid-induced ONFH.

Fibrolipomatous hamartoma of the digital branches of the median nerve

Fibrolipomatous Hamartoma is an idiopathic disorder which may be related to hypertrophy of mature fat cells and fibroblasts in the epineurium. It is a rare condition most commonly affects the median nerve. Presentation is usually before 30 years of age.Some of them are presented with signs and symptoms of nerve entrapment and some are associated with macrodactyly (macrodystrophia lipomatosa) with gross cosmetic abnormality. MRI can be an important preoperative diagnostic tool. Biopsy and histopathology report can confirm the pathology.This report describes a case of Fibrolipomatous Hamartoma of the digital branches of left index and middle fingers of median nerve associated with macrodactyly. A 25-year old male patient having this problem came to Apollo Hospitals Dhaka with abnormally large left index and middle finger. Debulking by excision of the lipomatous tissue along the digital branches of median nerve was performed. Three weeks postoperatively, the patient had no major complaints and the mass decreased in size without any motor or functional losses. Sensory function also found near normal with a small area of numbness at the tip of the left index finger.DOI: http://dx.doi.org/10.3329/pulse.v4i1.6967Pulse Vol.4 January 2010 p.40-42

Exploiting anti-obesity mechanism of Clerodendrum phlomidis against two different models of rodents

Roots of Clerodendrum phlomidis are used by the local people of Dibrugarh district of Assam state India as a dietary supplement for treating weight issues and are also mentioned in the traditional system of Indian medicine as a remedy for obesity. We examined the anti-obesity effect of Clerodendrum phlomidis (family Verbenaceae) L. roots against cafeteria diet (CD) and progesterone-induced obesity. In CD-induced model obesity was induced by feeding CD for 48-days and increase in body weight and fat storage was suppressed co-administration with methanolic extract of Clerodendrum phlomidis (MECP) at 400 mg/kg. Blood analysis showed that the levels of triglyceride and cholesterol were significantly lowered by MECP administration and there is subsequent rise in HDLcholesterol level. From this experiment, we demonstrated that MECP is effective in ameliorating the CD-induced hyperglycemia, hyperinsulimenia, dyslepidemia, increase in wet weight of white adipose tissue, and hypertrophy of fat cells. In drug induced obesity model hyperphagia was induced by progesterone (10 mg/kg s.c.) for 28 days and was suppressed by co-administration with MECP in dose dependent manner. It is tempting to speculate that these protective effects shown by Clerodendrum phlomidis is by multiple mechanisms. MECP contains β-sitosterol in the abundant quantity because of the structural similarity it do the physical competition with natural sterols while absorption of food stuffs from GIT and moreover the crude saponin and flavonoid has been reported for it’s the appetit suppressant property and hence reduces hyperphagia produced by progesterone. This is the first report demonstrating that Clerodendrum phlomidis is effective in ameliorating insulin resistance and visceral obesity induced by CD and Progesterone. Key words: Adipocyte, cafeteria diet, clerodendrum phlomidis, hyperphagia, hypertrophy, progesterone

Lipogenic enzyme activities and glucose uptake in fat tissue of dyslipemic, insulin-resistant rats: Effects of fish oil

Objective The purposes of the present work were twofold: (1) investigate same mechanisms involved in the development of fat cell hypertrophy in the experimental model of dyslipidemia and whole-body insulin resistance induced in rats chronically fed a sucrose-rich diet (SRD); and (2) analyze the possible beneficial effect of fish oil on these mechanisms. Methods For 6 mo, male Wistar rats received a sucrose-rich diet (62.5% w/w sucrose, 8% corn oil) or a control diet in which sucrose was replaced by starch. After this period, the sucrose-fed animals were divided randomly into two groups: the first one continued with the same diet up to 8 mo and the second one received the same diet, but with corn oil replaced by 7% fish oil + 1 % corn oil. Rats were fed with this diet for the next 2 mo. Results Although an enlarged fat cell lipolysis and an impaired insulin-stimulated glucose uptake were present in the fat cells of SRD-fed rats, an increase of several key enzymes of the novo lipogenesis could be one of the possible mechanisms involved in visceral adiposity. The addition of dietary fish oil restored or improved the above abnormalities. Conclusion This study shows possible mechanisms conditioning the influence of nutrients on the development and management of dyslipidemia, insulin sensitivity, and fat cell accretion, all abnormalities present in the metabolic syndrome.

Secretory products from human adipocytes stimulate proinflammatory cytokine secretion from human endothelial cells

Hyperplasia and hypertrophy of fat cells can be found in obesity and increased adiposity is associated with endothelial dysfunction as an early event of atherosclerosis. However, it is unclear whether human adipocytes directly influence endothelial protein secretion. To study the crosstalk between fat and endothelial cells, human umbilical venous endothelial cells (HUVECs) were cultured in infranatants (Adipo) of primary differentiated human adipocytes. Interestingly, significantly increased secretion of 23 cytokines and chemokines from HUVECs was detected in four independent experiments after Adipo stimulation by protein array analysis detecting a total of 174 different proteins. Among those, time-dependent Adipo-induced upregulation of cytokine secretion in HUVECs was confirmed by ELISA for interleukin (IL)-8, monokine induced by gamma interferon, macrophage inflammatory protein (MIP)-1beta, MIP-3alpha, monocyte chemoattractant protein-1, and IL-6. Factors besides adiponectin, leptin, resistin, and tumor necrosis factor alpha appear to mediate these stimulatory effects. Our findings suggest that endothelial cell secretion is significantly influenced towards a proinflammatory pattern by adipocyte-secreted factors.

Use of the microdialysis technique to assess lipolytic responsiveness of femoral adipose tissue after 12 sessions of mechanical massage technique

Adipocytes in femoral areas are known to be metabolically 'silent'. Changes related to fat cell hypertrophy may be involved in the formation of cellulite. A mechanical massage technique, with circulatory and dermotrophic properties, has been shown to have an impact on clinical evaluations (i.e. changes in morphometric measurements) in cellulite areas. Whether this technique affected lipolytic responsiveness in subcutaneous adipose tissue of cellulite areas was not known. Using a microdialysis technique in subcutaneous adipose tissue, a study was carried out to test the in situ incidence of a mechanical massage technique in terms of adipose tissue responsiveness to a lipolytic challenge. Nine healthy women volunteers with cellulite (grade > or = 2) were included and treated with 12 sessions of mechanical massage technique (Endermologie). Microdialysis has been carried out in the femoral adipose tissue in order to assess lipolytic responsiveness via glycerol determination following perfusion of a lipolytic agent (0.1, 1 and 10 microm isoproterenol). Clinical evaluations (measurements of waist, thighs and skin fold) were carried out in parallel. All evaluations were performed before and after treatment. The studied intervention lowered resting dialysate glycerol levels in femoral adipose tissue. The lipid-mobilizing effect of isoproterenol was enhanced after 1 month of treatment. In addition, a clear decrease of morphometric measurements (mean decrease on thighs perimeter: 3.1 to 3.3 cm, P < 0.01) was observed. These results suggest an increase in the lipolytic responsiveness of femoral adipose tissue in women with cellulite having undergone 12 sessions of mechanical massage.

A Rabbit Model of Hormone-induced Early Avascular Necrosis of the Femoral Head

Objective To establish an experimental model of early stage avascular necrosis of the femoral head (ANFH) caused by corticosteroid in adult rabbits and to observe the pathological changes with various imaging techniques. Methods ANFH was induced by a combination of hypersensitivity vasculitis caused by injection of horse serum and subsequent administration of a high dose of corticosteroid. The pathological changes were detected with digital radiography (DR), computed tomography (CT), magnetic resonance imaging (MRI), ink artery infusion angiography, hematoxylin–eosin staining, and immunohistochemistry. Results The imageological and pathological changes corresponded to the clinical characteristics of early stage ANFH. DR showed bilaterally increased bone density, an unclear epiphyseal line, and blurred texture of cancellous bone. CT showed spot-like low-density imaging of cancellous bone, thinner cortical bone, osteoporosis, and an unclear epiphyseal line. MRI showed bone marrow edema and spot-like high signals in T2-weighted imaging in cancellous bone. Ink artery infusion angiography showed fewer obstructed blood vessels in the femoral head. HE staining of pathological sections showed fewer trabeculae and thin bone, an increased proportion of empty osteocyte lacunae, decreased hematopoiesis, thrombosis, and fat cell hypertrophy. Immunohistochemistry showed attenuated expression of vascular endothelial growth factor in osteoblasts and chondrocytes, and on the inner membrane of blood vessels. Conclusion Experimental rabbit model of early stage ANFH caused by corticosteroid can be successfully established and provide the foundation for developing effective methods to treat early stage ANFH.

Surgical and Molecular Advances in Osteonecrosis: Editorial Comment

Surgical and Molecular Advances in Osteonecrosis: Editorial Comment

Preventive effects of puerarin on alcohol-induced osteonecrosis.

Alcohol can induce adipogenesis by bone marrow stromal cells and may cause osteonecrosis of the femoral head. Currently, there are no medications available to prevent alcohol-induced osteonecrosis. We hypothesized puerarin, a Chinese herbal medicine with antioxidative and antithrombotic effects, can prevent alcohol-induced adipogenesis and osteonecrosis. Both bone marrow stromal cells (in vitro) and mice (in vivo) were treated either with ethanol or with ethanol and puerarin, with an untreated group serving as a control. In the in vitro study, the number of adipocytes, contents of triglycerides, and levels of PPAR gamma mRNA expression were decreased and alkaline phosphatase activity, contents of osteocalcin, and levels of osteocalcin mRNA expression were increased in cells treated with both alcohol and puerarin, compared with cells treated with alcohol only. In the in vivo study, marrow necrosis, fat cell hypertrophy and proliferation, thinner and sparse trabeculae, diminished hematopoiesis, and increased empty osteocyte lacunae in the subchondral region of the femoral head were observed in mice treated with alcohol. However, no such changes were seen in femoral heads of mice treated with alcohol and puerarin. The data suggest puerarin can inhibit adipogenic differentiation by bone marrow stromal cells both in vitro and in vivo and prevents alcohol-induced osteonecrosis in this model.

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

When caloric intake exceeds caloric expenditure, the positive caloric balance and storage of energy in adipose tissue often causes adipocyte hypertrophy and visceral adipose tissue accumulation. These pathogenic anatomic abnormalities may incite metabolic and immune responses that promote Type 2 diabetes mellitus, hypertension and dyslipidemia. These are the most common metabolic diseases managed by clinicians and are all major cardiovascular disease risk factors. ‘Disease’ is traditionally characterized as anatomic and physiologic abnormalities of an organ or organ system that contributes to adverse health consequences. Using this definition, pathogenic adipose tissue is no less a disease than diseases of other body organs. This review describes the consequences of pathogenic fat cell hypertrophy and visceral adiposity, emphasizing the mechanistic contributions of genetic and environmental predispositions, adipogenesis, fat storage, free fatty acid metabolism, adipocyte factors and inflammation. Appreciating the full pathogenic potential of adipose tissue requires an integrated perspective, recognizing the importance of ‘cross-talk’ and interactions between adipose tissue and other body systems. Thus, the adverse metabolic consequences that accompany fat cell hypertrophy and visceral adiposity are best viewed as a pathologic partnership between the pathogenic potential adipose tissue and the inherited or acquired limitations and/or impairments of other body organs. A better understanding of the physiological and pathological interplay of pathogenic adipose tissue with other organs and organ systems may assist in developing better strategies in treating metabolic disease and reducing cardiovascular disease risk.

Effects of modified alternate-day fasting regimens on adipocyte size, triglyceride metabolism, and plasma adiponectin levels in mice

Calorie restriction (CR) affects adipocyte function and reduces body weight. However, the effects of alternate-day fasting (ADF) on adipose biology remain unclear. This study examined the effects of ADF and modified ADF regimens on adipocyte size, triglyceride (TG) metabolism, and adiponectin levels in relation to changes in body weight and adipose mass. Twenty-four male C57BL/6J mice were randomized for 4 weeks among 1) ADF-25% (25% CR on fast day, ad libitum on alternate day), 2) ADF-50% (50% CR on fast day), 3) ADF-100% (100% CR on fast day), and 4) control (ad libitum). The body weight of ADF-100% mice was lower than that of the other groups (P < 0.005) after treatment. Adipose tissue weights did not change. Inguinal and epididymal fat cells were 35-50% smaller (P < 0.01) than those of controls in ADF-50% and ADF-100% animals after treatment. Net lipolysis was augmented (P < 0.05) in ADF-100% mice, and the contribution from glyceroneogenesis to alpha-glycerol phosphate increased in ADF-50% and ADF-100% mice, whereas fractional and absolute de novo lipogenesis also increased in ADF-50% and ADF-100% animals, consistent with an alternating feast-fast milieu. Plasma adiponectin levels were not affected. In summary, modified ADF (ADF-50%) and complete ADF (ADF-100%) regimens modulate adipocyte function, despite there being no change in body weight or adipose tissue weight in the former group.

Hypertrophy and hyperplasia of abdominal adipose tissues in women

To examine the expression of selected transcription factors involved in adipogenesis and genes related to lipid metabolism in abdominal subcutaneous and omental fat tissue. We obtained subcutaneous and omental adipose tissue samples from 40 women undergoing abdominal hysterectomies (age: 47+/-5 years; BMI 27.9+/-5.3 kg/m(2)). We measured isolated adipocyte size and metabolism, and detailed measures of body fat accumulation and body fat distribution were obtained (dual-energy X-ray absorptiometry and computed tomography, respectively). Adipocyte size of both subcutaneous and omental fat were increased with higher body fat mass values, with similar regression slopes in each compartment. In contrast, with higher body fat mass values, fat accumulation was progressively higher in the subcutaneous than in the visceral fat compartment, suggesting hyperplasia in the subcutaneous fat compartment. Messenger RNA levels of CEBPalpha, PPARgamma2, SREBP1c and genes related to lipid metabolism (LPL, FABP4, DGAT1, DGAT2, PLIN and HSL) were significantly higher in subcutaneous than in omental fat tissue (P< or =0.001 for all). Only subcutaneous expression of these genes tracked with obesity levels as reflected by significant positive associations between subcutaneous fat CEBPalpha, SREBP1c and DGAT2 expression and total body fat mass (r=0.37, r=0.41, r=0.57, respectively, P< or =0,05), fat percentage (r=0.40, r=0.39, r=058, respectively, P< or =0,05) and subcutaneous adipose tissue area (r=0.36, r=0.38, r=0.58, respectively, P< or =0,05). Omental adipose tissue expression levels of these genes were not significantly related to adiposity measures. These results show that in obese women, hyperplasia is predominant in the subcutaneous fat depot, whereas fat cell hypertrophy is observed both in the omental and subcutaneous compartments.

Secretory products from human adipocytes impair endothelial function via nuclear factor κB

Hyperplasia and hypertrophy of fat cells can be found in obesity, and increased adiposity is associated with endothelial dysfunction as an early event of atherosclerosis. However, it is unclear whether human adipocytes directly influence endothelial function. To study the crosstalk between fat and endothelial cells, human umbilical venous endothelial cells (HUVECs), and human coronary artery endothelial cells (HCAECs) were cultured in infranatants (Adipo) of primary differentiated human adipocytes. Interestingly, incubation of HUVECs and HCAECs with Adipo significantly increased monocyte adhesion 7.3 and 2.2-fold, respectively. VCAM-1, ICAM-1, and E-selectin in HUVECs were upregulated 3.9, 3.0, and 9.5-fold, respectively, under these conditions. Furthermore, Adipo significantly stimulated NFκB activity 1.9-fold. The NFκB inhibitor MG-132 and heat inactivation significantly reversed Adipo-stimulated monocyte adhesion. TNFα-neutralizing antibodies partly reversed Adipo-induced monocyte adhesion. In contrast, thiazolidinedione-pretreatment of human adipocytes did not alter the effects of Adipo. Adipo did not show cytotoxic effects. Taken together, we demonstrate that endothelial dysfunction is induced by adipocyte-secreted factors via NFκB partly dependent on TNFα.

Dexamethasone-induced adipogenesis in primary marrow stromal cell cultures

In steroid-induced osteonecrosis, hypertrophy and hyperplasia of marrow fat cells and lipid deposition of osteocytes can be found in the femoral head. However, the precise reason is not clear yet. The aim of this study was to observe the effect of dexamethasone (Dex) on differentiation of marrow stromal cells (MSCs), and to investigate the pathobiological mechanism of steroid-induced osteonecrosis. MSCs in cultures were treated with increasing concentrations of Dex (0, 10(-9), 10(-8), 10(-7), and 10(-6) mol/L) continuously for 21 days. The cells, which were exposed to 0 mol/L (control) or 10(-7) mol/L Dex for 4 - 21 days, were then cultured for 21 days without Dex. MSCs were stained with Sudan III. Number of adipocytes was counted under a light microscope. The activity of alkaline phosphatase (ALP) of MSCs treated with 0, 10(-8), 10(-7), and 10(-6) mol/L Dex for 12 days, and that treated with 0 mol/L and 10(-7) mol/L Dex for 8, 10, or 12 days were determined. The levels of triglycerides, osteocalcin and cell proliferation of MSCs treated with 0 mol/L and 10(-7) mol/L Dex were detected. The mRNA expression levels of adipose-specific 422 (aP2) gene and osteogenic gene type I collagen in MSCs treated with 0 mol/L and 10(-7) mol/L Dex for 6 days were analyzed by whole-cell dot-blot hybridization. Statistical analysis was performed using Student's t test and analysis of variance. P values less than 0.05 were considered significant statistically. The number of adipocytes in cultures increased with the duration of MSCs' exposure to Dex and the concentration of Dex. The level of ALP activity in the MSCs decreased with concentration of Dex. In the control group, it was 8.69 times of that in the 10(-7) mol/L Dex group on day 12 (t = 20.51, P < 0.001). The level of triglycerides in 10(-7) mol/L Dex group was 3.40 times of that in the control (t = 11.00, P < 0.001). The levels of cell proliferation and osteocalcin in the control were 1.54 and 2.42 times of that in the 10(-7) mol/L Dex group respectively. As compared to the control, the mRNA expression of adipose-specific 422 (aP2) gene in 10(-7) mol/L Dex group was significantly increased (t = 36.48, P < 0.001), and that of osteogenic gene type I collagen was decreased (t = 42.07, P < 0.001). Dex can directly induce the differentiation of MSCs into a large number of adipocytes and inhibit their osteogenic differentiation, which provide a novel explanation for the pathologic changes of steroid-induced osteonecrosis.

Omega‐3 PUFA of marine origin limit diet‐induced obesity in mice by reducing cellularity of adipose tissue

Omega-3 PUFA of marine origin reduce adiposity in animals fed a high-fat diet. Our aim was to learn whether EPA and DHA could limit development of obesity and reduce cellularity of adipose tissue and whether other dietary FA could influence the effect of EPA/DHA. Weight gain induced by composite high-fat diet in C57BL/6J mice was limited when the content of EPA/DHA was increased from 1 to 12% (wt/wt) of dietary lipids. Accumulation of adipose tissue was reduced, especially of the epididymal fat. Low ratio of EPA to DHA promoted the effect. A higher dose of EPA/DHA was required to reduce adiposity when admixed to diets that did not promote obesity, the semisynthetic high-fat diets rich in EFA, either alpha-linolenic acid (ALA, 18:3 n-3, the precursor of EPA and DHA) or linoleic (18:2 n-6) acid. Quantification of adipose tissue DNA revealed that except for the diet rich in ALA the reduction of epididymal fat was associated with 34-50% depression of tissue cellularity, similar to the 30% caloric restriction in the case of the high-fat composite diet. Changes in plasma markers and adipose gene expression indicated improvement of lipid and glucose metabolism due to EPA/DHA even in the context of the diet rich in ALA. Our results document augmentation of the antiadipogenic effect of EPA/DHA during development of obesity and suggest that EPA/DHA could reduce accumulation of body fat by limiting both hypertrophy and hyperplasia of fat cells. Increased dietary intake of EPA/DHA may be beneficial regardless of the ALA intake.

Circulation intraosseuse : de la physiologie à la pathologie

Blood flow within bones is unique in two ways: the blood circulates within a closed cavity in which pressure must remain constant, a feat achieved in part thanks to the considerable distensibility of the intraosseous vessels and, above all, veins; the intraosseous circulation allows traffic of minerals between the blood and bone tissue and sends the blood cells produced within the bone marrow into the systemic circulation. In contrast, the arterioles and capillaries within bones have the same anatomic structure as those located elsewhere in the body and are susceptible to arteriosclerosis, arteritis, or thrombosis. The mechanisms that regulate blood flow within bone are incompletely understood, probably because they are difficult to study in vivo. The cytokines and growth factors that regulate intraosseous angiogenesis also regulate bone remodeling, and close links exist between the blood supply to bone and bone formation and resorption : most diseases characterized by increased bone resorption are associated with increased bone vascularization. The vascular bud located at the center of bone multicellular units (BMUs) may determine the timing of bone resorption and bone formation. Avascular bone necrosis and bone infarction may result from acute blood vessel occlusion (thrombosis, lipid emboli, fat cell hypertrophy with compression of intraosseous capillaries), whereas arteriosclerosis may contribute to the development of osteoporosis.

Dietary fish oil reverse epididymal tissue adiposity, cell hypertrophy and insulin resistance in dyslipemic sucrose fed rat model

The present work was designed to assess the possible benefits of (7% w/w) dietary fish oil in reversing the morphological and metabolic changes present in the adipose tissue of rats fed an SRD for a long time. With this purpose, in the epididymal fat tissue, we investigated the effect of dietary fish oil upon: i) the number, size and distribution of cells, ii) the basal and stimulated lipolysis, iii) the lipoprotein lipase (LPL) and the glucose 6-phosphate dehydrogenase activities, and iv) the antilipolytic action of insulin. The study was conducted on rats fed an SRD during 120 days with fish oil being isocaloric substituted for corn oil for 90–120 days in half the animals. Permanent hypertriglyceridemia, insulin resistance and abnormal glucose homeostasis were present in the rats before the source of fat in the diet was replaced. The major new findings of this study are the following: i) Dietary fish oil markedly reduced the fat pads mass, the hypertrophy of fat cells and improved the altered cell size distribution. ii) The presence of fish oil in the diet corrected the inhibitory effect of high sucrose diet upon the antilipolytic action of insulin, reduced the “in vitro” enhanced basal lipolysis and normalized isoproterenol-stimulated lipolysis. Fat pads lipoprotein lipase activity decreased reaching values similar to those observed in age-matched controls fed a control diet (CD). These effects were not accompanied by any change in rat body weight. All these data suggest that the dyslipemic rats fed a moderate amount of dietary fish oil constitute a useful animal model to study diet-regulated insulin action.

Impaired beta-adrenergic signaling pathway in white adipocytes of suckling fa/fa Zucker rats: a defect in receptor coupling.

In fa/fa Zucker rats, leptin receptor deficiency is responsible for both a deficit of energy expenditure and hyperphagia which lead to massive obesity and insulin resistance in adulthood. This obesity is also characterised by alterations of the beta-adrenergic signaling pathway. To determine whether alterations in beta-adrenergic pathway could occur at the onset of obesity when fa/fa rats are not yet hyperinsulinemic. Fourteen-day-old suckling fa/fa and Fa/fa littermates (from heterozygous lean (Fa/fa) female and homozygous obese (fa/fa) male mating). Membranes were prepared from isolated adipocytes after collagenase treatment of inguinal adipose tissue. The response of adenylyl-cyclase activity to stimulation by isoprenaline, GTPgamma-S or forskolin was studied. Bmax and Kd of (beta1+beta2) and of beta3 adrenoceptors were measured using 3H-CGP saturation binding experiments. mRNA concentration of beta1- and beta3-AR was determined by semi-quantitative RT-PCR. G(s)alpha protein was quantified by Western blotting and Gi protein by ADP-ribosylation. Despite an almost normal body weight, inguinal fat pad weight was increased two-fold by the expression of fa mutation. This increase was entirely accounted for by fat cell hypertrophy (x2.5 in volume). In fa/fa compared to Fa/fa pups, response of adenylyl cyclase to isoprenaline was decreased two-fold but responses to GTPgammaS or forskolin were unchanged. Density of (beta1+beta2) and beta3-AR was not affected by the fa/fa genotype, as well as G(s)alpha and Gi concentration. Response of inguinal fat cells to catecholamines was decreased without any quantitative modifications of the different elements of the adenylyl cyclase cascade. This suggests an alteration in the coupling between beta-AR and G proteins. Due to the important increase in fat cell volume we hypothesize that changes in the physical properties of plasma membranes and/or changes in cytoskeleton-extracellular-matrix interactions could disturb the beta-adrenergic pathway responsiveness. In addition to the excess of lipid storage, which occurs very early at the onset of obesity, the impairment of the responsiveness to catecholamines reported in this study might worsen the obesity syndrome.

Effect of diet on fat cell size and hormone-sensitive lipase activity.

This study was designed to examine the relationship between diet-induced insulin resistance/hyperinsulinemia, fat cell hypertrophy, and hormone-sensitive lipase (HSL) to elucidate whether an attenuated HSL activity leads to obesity. Female Fischer 344 rats were fed either a low-fat, complex-carbohydrate diet or a high-fat, refined-sugar (HFS) diet for 2 wk, 2 mo, or 6 mo. Adipose tissue morphology and HSL activity as well as plasma free fatty acid and glycerol levels were determined at these times. No differences between groups were seen after 2 wk except the previously reported hyperinsulinemia in the HFS animals. At both 2 and 6 mo, the HFS animals demonstrated adipocyte hypertrophy. Basal and stimulated HSL activities and plasma glycerol were significantly elevated in the HFS group. There was a positive correlation between adipocyte size and HSL activity for both basal and stimulated states. These results demonstrate that an attenuated HSL activity is not observed with the onset of insulin resistance/hyperinsulinemia and therefore does not play a role in the development of obesity.

Relationship of visceral adipose tissue to metabolic risk factors for coronary heart disease: Is there a contribution of subcutaneous fat cell hypertrophy?

Visceral adipose tissue (VAT) accumulation is an important correlate of the metabolic complications found in obese patients. The aim of this study was to evaluate the respective contribution of VAT deposition versus subcutaneous abdominal or femoral fat cell hypertrophy as correlates of the metabolic risk profile in 69 men and 65 premenopausal women (aged 35 ± 5 years) with a wide range of fatness (body mass index, 18 to 57 kg/m 2). In both genders, VAT accumulation was positively correlated with fasting plasma insulin, triglyceride (TG), and low-density lipoprotein (LDL)-apolipoprotein B (apo B) levels and the cholesterol (CHOL)/high-density lipoprotein (HDL)-CHOL ratio (.24 ≤ r ≤ .71, P < .05). A similar pattern of positive relationships was found between subcutaneous abdominal fat cell weight and metabolic risk variables in men and women (.33 ≤ r ≤ .60, P < .01). Positive associations were also observed in women between femoral fat cell weight and fasting plasma insulin, TG, and CHOL levels and the CHOL HDL-CHOL ratio (.29 ≤ r ≤ .42, P < .05). However, only plasma TG concentrations and the CHOL HDL-CHOL ratio were positively correlated with femoral fat cell weight in men ( r = .30, P < .05). To better investigate the relationships between the metabolic risk profile and hypertrophic subcutaneous obesity, individuals with small versus large subcutaneous abdominal adipocytes were matched according to VAT accumulation. Men with large abdominal fat cells displayed higher plasma TG and LDL-apo B levels compared with men characterized by small abdominal adipocytes ( P < .05). Stepwise multiple regression analyses showed that subcutaneous abdominal fat cell weight was the best independent variable predicting plasma TG and LDL-apo B levels in men. No significant difference was found in the metabolic profile of subjects displaying small versus large femoral adipocytes. Taken together, these results suggest that for a given VAT deposition, the presence of hypertrophied subcutaneous abdominal adipocytes in men appears to be associated with further deterioration in the metabolic risk profile. On the other hand, the hypertrophy of femoral adipocytes does not further alter the metabolic complications generally related to obesity in both men and women.