The molecular mechanism of acylation stimulating protein regulation of adipophilin and perilipin expression: involvement of phosphoinositide 3-kinase and phospholipase C

The novel adipokine acylation stimulating protein (ASP) is involved in lipid metabolism and obesity‐related disorders. Adipophilin and perilipin, two members of the lipid droplet protein family, participate not only in fat storage within adipocytes, but also in ectopic lipid deposition in the form of cytoplasmic triglyceride (TG) droplets within many types of mammalian cells. During differentiation to mature adipocytes, mechanisms controlling the synthesis and turnover of these lipid droplet proteins are only partially understood, the mechanisms regulating gene/protein expression as yet unidentified. In our previous study, ASP has been shown to regulate adipophilin and perilipin expression to facilitate TG synthesis during 3T3‐L1 cell differentiation. Our aim in this study was to provide insight into the physiological importance of phosphoinositide 3‐kinase (PI3K) and phospholipase C (PLC) in ASP‐triggered alteration of adipophilin and perilipin expression. We found that acute (2.5 h) inhibition of PLC or PI3K results in a decrease in mRNA and protein of perilipin and adipophilin at any time during differentiation. The fact that there is such a rapid change even with mRNA levels suggests a rapid turnover of both mRNA and protein independent of a direct ASP effect. Also, the presence of these inhibitors blocked the ASP stimulatory effects with a maximal decrease in gene and protein expression of adipophilin (?45% and ?60%, respectively, P < 0.01) and perilipin (?96% and ?63%, respectively, P < 0.01 and P < 0.05). These findings provide further understanding of the adipogenic properties of ASP in adipocytes. J. Cell. Biochem. 112: 1622–1629, 2011. © 2011 Wiley‐Liss, Inc.     

Isocaloric intake of a high‐fat diet promotes insulin resistance and inflammation in Wistar rats

The aim of this study was to investigate the effect of isocaloric intake from a high‐fat diet (HFD) on insulin resistance and inflammation in rats. Male Wistar rats were fed on an HFD (n = 12) or control diet (n = 12) for 12 weeks. Subsequently, all animals were euthanized, and blood glucose, insulin, free fatty acids, C‐reactive protein, lipid profile, cytokines and hepatic‐enzyme activity were determined. Carcass chemical composition was also analyzed. During the first and the twelfth weeks of the experimental protocol, the oral glucose tolerance test and insulin tolerance test were performed and demonstrated insulin resistance (P < 0.05) in the HFD group. Although food intake (g) was lower (P < 0.05) in the HFD group compared with the control group, the concentration of total cholesterol, low‐density lipoprotein, C‐reactive protein and liver weight were all significantly higher. The kinase inhibitor of κB, c‐Jun N‐terminal kinase and protein kinase B expressions were determined in the liver and skeletal muscle. After an insulin stimulus, the HFD group demonstrated decreased (P = 0.05) hepatic protein kinase B expression, whereas the kinase inhibitor of κB phospho/total ratio was elevated in the HFD muscle (P = 0.02). In conclusion, the isocaloric intake from the HFD induced insulin resistance, associated with impaired insulin signalling in the liver and an inflammatory response in the muscle. Copyright © 2012 John Wiley & Sons, Ltd.     

Diet and Exercise Interventions Reduce Intrahepatic Fat Content and Improve Insulin Sensitivity in Obese Older Adults

Both obesity and aging increase intrahepatic fat (IHF) content, which leads to nonalcoholic fatty liver disease (NAFLD) and metabolic abnormalities such as insulin resistance. We evaluated the effects of diet and diet in conjunction with exercise on IHF content and associated metabolic abnormalities in obese older adults. Eighteen obese (BMI ≥30 kg/m²) older (≥65 years old) adults completed a 6‐month clinical trial. Participants were randomized to diet (D group; n = 9) or diet + exercise (D+E group; n = 9). Primary outcome was IHF quantified by magnetic resonance spectroscopy (MRS). Secondary outcomes included insulin sensitivity (assessed by oral glucose tolerance), body composition (assessed by dual‐energy X‐ray absorptiometry), physical function (VO_2peak and strength), glucose, lipids, and blood pressure (BP). Body weight (D: ?9 ± 1%, D+E: ?10 ± 2%, both P < 0.05) and fat mass (D: ?13 ± 3%, D+E ?16 ± 3%, both P < 0.05) decreased in both groups but there was no difference between groups. IHF decreased to a similar extent in both groups (D: ?46 ± 11%, D+E: ?45 ± 8%, both P < 0.05), which was accompanied by comparable improvements in insulin sensitivity (D: 66 ± 25%, D+E: 68 ± 28%, both P < 0.05). The relative decreases in IHF correlated directly with relative increases in insulin sensitivity index (ISI) (r = ?0.52; P < 0.05). Improvements in VO_2peak, strength, plasma triglyceride (TG), and low‐density lipoprotein–cholesterol concentration, and diastolic BP occurred in the D+E group (all P < 0.05) but not in the D group. Diet with or without exercise results in significant decreases in IHF content accompanied by considerable improvements in insulin sensitivity in obese older adults. The addition of exercise to diet therapy improves physical function and other obesity‐ and aging‐related metabolic abnormalities.     

Effect of linseed oil and macadamia oil on metabolic changes induced by high‐fat diet in mice

The effects of linseed oil (LO) and macadamia oil (MO) on the metabolic changes induced by a high‐fat diet (HFD) rich in saturated fatty acid were investigated. For the purpose of this study, the vegetable oil present in the HFD, i.e. soybean oil (SO) was replaced with LO (HFD‐LO) or MO (HFD‐MO). For comparative purposes, a group was included, which received a normal fat diet (NFD). Male Swiss mice (6‐week old) were used. After 14 days under the dietary conditions, the mice were fasted for 18 h, and experiments were then performed. The HFD‐SO, HFD‐LO and HFD‐MO groups showed higher glycaemia (p < 0.05 versus NFD). However, no significant effect was observed on glycaemia, liver gluconeogenesis and liver ketogenesis when SO was replaced by either LO or MO. The body weight and the sum of epididymal, mesenteric, retroperitoneal and inguinal fat weights were higher (p < 0.05) in the HFD‐SO and HFD‐MO groups as compared with the NFD group. However, there was no significant difference in these parameters between the NFD and HFD‐LO groups. Thus, the protective role of LO on lipid accumulation induced by an HFD rich in saturated fatty acid is potentially mediated by the high content of ?‐3 polyunsaturated fatty acid in LO. Copyright © 2013 John Wiley & Sons, Ltd.     

Endocannabinoid dysregulation in the pancreas and adipose tissue of mice fed with a high-fat diet

Objective: In mice, endocannabinoids (ECs) modulate insulin release from pancreatic β‐cells and adipokine expression in adipocytes through cannabinoid receptors. Their pancreatic and adipose tissue levels are elevated during hyperglycemia and obesity, but the mechanisms underlying these alterations are not understood. Methods and Procedures: We assessed in mice fed for up to 14 weeks with a standard or high‐fat diet (HFD): (i) the expression of cannabinoid receptors and EC biosynthesizing enzymes (N‐acyl‐phosphatidyl‐ethanolamine‐selective phospholipase D (NAPE‐PLD) and DAGLα) and degrading enzymes (fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL)) in pancreatic and adipose tissue sections by immunohistochemical staining; (ii) the amounts, measured by liquid chromatography–mass spectrometry, of the ECs, 2‐AG, and anandamide (AEA). Results: Although CB₁ receptors and biosynthetic enzymes were found mostly in α‐cells, degrading enzymes were identified in β‐cells. Following HFD, staining for biosynthetic enzymes in β‐cells and lower staining for FAAH were observed together with an increase of EC pancreatic levels. While we observed no diet‐induced change in the intensity of the staining of EC metabolic enzymes in the mesenteric visceral fat, a decrease in EC concentrations was accompanied by lower and higher staining of biosynthesizing enzymes and FAAH, respectively, in the subcutaneous fat. No change in cannabinoid receptor staining was observed following HFD in any of the analyzed tissues. Discussion: We provide unprecedented information on the distribution of EC metabolic enzymes in the pancreas and adipose organ, where their aberrant expression during hyperglycemia and obesity contribute to dysregulated EC levels.     

High‐Fat Diet Feeding Elevates Skeletal Muscle Uncoupling Protein 3 Levels But Not Its Activity in Rats

Objective: The objective of this study is to test the impact of high‐fat diet (HFD) feeding on skeletal muscle (SM) uncoupling protein 3 (UCP3) expression and its association with mitochondrial ion permeability and whole‐body energy homeostasis. Research Methods and Procedures: Sprague–Dawley rats were fed ad libitum either a HFD (60% of energy from fat, n = 6) or a low‐fat diet (12% of energy from fat, n = 6) for 4 weeks. Twenty‐four‐hour energy expenditure was measured by indirect calorimetry in the last week of the dietary treatment. Blood samples were collected for plasma leptin and free fatty acid assays, and mitochondria were isolated from hindlimb SM for subsequent determinations of UCP3 levels and mitochondrial ion permeability. Results: Plasma leptin levels were higher in rats fed the HFD despite the same body weight in two groups. The same dietary treatment also rendered a 2‐fold increase in plasma free fatty acid and SM UCP3 protein levels (Western blot) compared with the group fed the low‐fat diet. However, the elevated UCP3 protein levels did not correlate with mitochondrial swelling rates, a measure of mitochondrial chloride, and proton permeability, or with 24‐hour energy expenditure. Discussion: The high correlation between the levels of plasma free fatty acid levels and SM UCP3 suggests that circulating free fatty acid may play an important role in UCP3 expression during the HFD feeding. However, the dissociation between the UCP3 protein levels and 24‐hour energy expenditure as well as mitochondrial ion permeability suggests that mitochondrial proton leak mediated by muscle UCP3 may not be a major contributor in energy balance in HFD feeding, and other regulatory mechanisms independent of gene regulation may be responsible for the control of UCP3‐mediated uncoupling activity.     

Hormone and pharmaceutical regulation of ASP production in 3T3‐L1 adipocytes

Several studies have demonstrated increases in acylation stimulating protein (ASP), and precursor protein C3 in obesity, diabetes and dyslipidemia, however the nature of the regulation is unknown. To evaluate chronic hormonal and pharmaceutical mediated changes in ASP and potential mechanisms, 3T3‐L1 adipocytes were treated with physiological concentrations of relevant hormones and drugs currently used in treatment of metabolic diseases for 48 h. Medium ASP production and C3 secretion were evaluated in relation to changes in adipocyte lipid metabolism (cellular triglyceride (TG) mass, non‐esterified fatty acid (NEFA) release and real‐time FA uptake). Chylomicrons increased ASP production (up to 411 ± 133% P < 0.05), while leptin, triiodothyronine, and β‐blockers atenolol and propranolol had no effect. Dexamethasone, lovastatin, rosiglitazone and rimonabant decreased ASP production (?53 to ?85%, P < 0.05), associated with a decrease in the precursor protein C3 (?37% to ?65%, P < 0.01). By contrast, epinephrine, progesterone, testosterone, angiotensin II and metformin also decreased ASP (?54% to ?100%, P < 0.05), but without change in precursor protein C3, suggesting a direct effect on convertase activity, possibly mediated by interference (except metformin) due to marked increases in NEFA (5.6–31‐fold, increased P < 0.05). Both lovastatin and metformin induced decreases in ASP were also associated with decreased TG mass (maximal ?60%, P < 0.05) and real‐time FA uptake (maximum ?75%, P < 0.05), suggesting a change in adipocyte differentiation status. These in vitro results are consistent with in vivo ASP profiles in subjects, and suggest that ASP may be regulated through precursor C3 availability, convertase activity and differentiation status. J. Cell. Biochem. 109: 896–905, 2010. © 2010 Wiley‐Liss, Inc.     

Low‐carbohydrate High‐fat Diets: Regulation of Energy Balance and Body Weight Regain in Rats

The aim of the current investigations was to examine the effects of a low‐carbohydrate high‐fat diet (LC‐HFD) on body weight, body composition, growth hormone (GH), IGF‐I, and body weight regain after stopping the dietary intervention and returning the diet back to standard laboratory chow (CH). In study one, both adolescent and mature male Wistar rats were maintained on either an isocaloric LC‐HFD or CH for 16 days before having their diet switched. In study two, mature rats were maintained on either LC‐HFD or CH for 16 days to determine the effects of the LC‐HFD on fat pad weight. LC‐HFD leads to body weight loss in mature rats (P < 0.01) and lack of body weight gain in adolescent rats (P < 0.01). Despite less body weight, increased body fat was observed in rats maintained on LC‐HFD (P < 0.05). Leptin concentrations were higher (P < 0.05), and IGF‐I (P < 0.01) concentrations were reduced in the LC‐HFD rats. When the diet was returned to CH following LC‐HFD, body weight regain was above and beyond that which was lost (P < 0.01). The LC‐HFD resulted in increased body fat and had a negative effect upon both GH and IGF‐I concentrations, which might have implications for the accretion and maintenance of lean body mass (LBM), normal growth rate and overall metabolic health. Moreover, when the LC‐HFD ceases and a high‐carbohydrate diet follows, more body weight is regained as compared to when the LC‐HFD is consumed, in the absence of increased energy intake.     

Large size cells in the visceral adipose depot predict insulin resistance in the canine model

Adipocyte size plays a key role in the development of insulin resistance. We examined longitudinal changes in adipocyte size and distribution in visceral (VIS) and subcutaneous (SQ) fat during obesity‐induced insulin resistance and after treatment with CB‐1 receptor antagonist, rimonabant (RIM) in canines. We also examined whether adipocyte size and/or distribution is predictive of insulin resistance. Adipocyte morphology was assessed by direct microscopy and analysis of digital images in previously studied animals 6 weeks after high‐fat diet (HFD) and 16 weeks of HFD + placebo (PL; n = 8) or HFD + RIM (1.25 mg/kg/day; n = 11). At 6 weeks, mean adipocyte diameter increased in both depots with a bimodal pattern only in VIS. Sixteen weeks of HFD+PL resulted in four normally distributed cell populations in VIS and a bimodal pattern in SQ. Multilevel mixed‐effects linear regression with random‐effects model of repeated measures showed that size combined with share of adipocytes >75 µm in VIS only was related to hepatic insulin resistance. VIS adipocytes >75 µm were predictive of whole body and hepatic insulin resistance. In contrast, there was no predictive power of SQ adipocytes >75 µm regarding insulin resistance. RIM prevented the formation of large cells, normalizing to pre‐fat status in both depots. The appearance of hypertrophic adipocytes in VIS is a critical predictor of insulin resistance, supporting the deleterious effects of increased VIS adiposity in the pathogenesis of insulin resistance.     

Mice Deficient in Phosphofructokinase‐M Have Greatly Decreased Fat Stores

Synthesis of triacylglycerol requires the glucose‐derived glycerol component, and glucose uptake has been viewed as the rate‐limiting step in glucose metabolism in adipocytes. Furthermore, adipose tissue contains all three isoforms of the glycolytic enzyme phosphofructokinase (PFK). We here report that mice deficient in the muscle isoform PFK‐M have greatly reduced fat stores. Mice with disrupted activity of the PFK‐M distal promoter were obtained from Lexicon Pharmaceuticals, developed from OmniBank OST#56064. Intra‐abdominal fat was measured by magnetic resonance imaging of the methylene proton signal. Lipogenesis from labeled glucose was measured in isolated adipocytes. Lipolysis (glycerol and free fatty acid release) was measured in perifused adipocytes. Intra‐abdominal fat in PFK‐M–deficient female mice (5–10 months old) was 17 ± 3% of that of wild‐type littermates (n = 4; P < 0.02). Epididymal fat weight in 15 animals (7–9.5 months) was 34 ± 4% of control littermate (P < 0.002), with 10–30% lower body weight. Basal and insulin‐stimulated lipogenesis in PFK‐M–deficient epididymal adipocytes was 40% of the rates in cells from heterozygous littermates (n = 3; P < 0.05). The rate of isoproterenol‐stimulated lipolysis in wild‐type adipocytes declined ～10% after 1 h and 50% after 2 h; in PFK‐M–deficient cells it declined much more rapidly, 50% in 1 h and 90% in 2 h, and lipolytic oscillations appeared to be damped (n = 4). These results indicate an important role for PFK‐M in adipose metabolism. This may be related to the ability of this isoform to generate glycolytic oscillations, because such oscillations may enhance the production of the triacylglycerol precursor α‐glycerophosphate.     

Maté Tea Inhibits In Vitro Pancreatic Lipase Activity and Has Hypolipidemic Effect on High‐fat Diet‐induced Obese Mice

The inhibitory effects of maté tea (MT), a beverage produced with leaves from Ilex paraguariensis, in vitro lipase activity and on obesity in obese mice models were examined. For the in vitro experiment, porcine and human pancreatic lipase (PL) activities were determined by measuring the rate of release of oleic acid from hydrolysis of olive oil emulsified with taurocholate, phospholipids, gum arabic, or polyvinyl alcohol. For the in vivo experiments, animals were fed with a standard diet (SD, n = 10) or high‐fat diet (HFD, n = 30) for 16 weeks. After the first 8 weeks on the HFD, the animals were treated with 1 and 2 g/kg of body weight of MT. The time course of the body weight and obesity‐related biochemical parameters were evaluated. The results showed that MT inhibited both porcine and human PL (half‐maximal inhibitory concentration = 1.5 mg MT/ml) and induced a strong inhibition of the porcine lipase activity in the hydrolysis of substrate emulsified with taurocholate + phosphatidylcholine (PC) (83 ± 3.8%) or PC alone (62 ± 4.3%). MT suppressed the increases in body weight (P < 0.05) and decreased the serum triglycerides and low‐density lipoprotein (LDL)‐cholesterol concentrations at both doses (from 190.3 ± 5.7 to 135.0 ± 8.9 mg/dl, from 189.1 ± 7.3 to 129.3 ± 17.6 mg/dl; P < 0.05, respectively) after they had been increased by the HFD. The liver lipid content was also decreased by the diet containing MT (from 132.6 ± 3.9 to 95.6 ± 6.1 mg/g of tissue; P < 0.05). These results suggest that MT could be a potentially therapeutic alternative in the treatment of obesity caused by a HFD.     

Taurine supplementation prevents morpho-physiological alterations in high-fat diet mice pancreatic β-cells

Taurine (Tau) is involved in beta (β)-cell function and insulin action regulation. Here, we verified the possible preventive effect of Tau in high-fat diet (HFD)-induced obesity and glucose intolerance and in the disruption of pancreatic β-cell morpho-physiology. Weaning Swiss mice were distributed into four groups: mice fed on HFD diet (36 % of saturated fat, HFD group); HTAU, mice fed on HFD diet and supplemented with 5 % Tau; control (CTL); and CTAU. After 19 weeks of diet and Tau treatments, glucose tolerance, insulin sensitivity and islet morpho-physiology were evaluated. HFD mice presented higher body weight and fat depots, and were hyperglycemic, hyperinsulinemic, glucose intolerant and insulin resistant. Their pancreatic islets secreted high levels of insulin in the presence of increasing glucose concentrations and 30 mM K⁺. Tau supplementation improved glucose tolerance and insulin sensitivity with a higher ratio of Akt phosphorylated (pAkt) related to Akt total protein content (pAkt/Akt) following insulin administration in the liver without altering body weight and fat deposition in HTAU mice. Isolated islets from HTAU mice released insulin similarly to CTL islets. HFD intake induced islet hypertrophy, increased β-cell/islet area and islet and β-cell mass content in the pancreas. Tau prevented islet and β-cell/islet area, and islet and β-cell mass alterations induced by HFD. The total insulin content in HFD islets was higher than that of CTL islets, and was not altered in HTAU islets. In conclusion, for the first time, we showed that Tau enhances liver Akt activation and prevents β-cell compensatory morpho-functional adaptations induced by HFD.     

Medium‐Chain Fatty Acids Attenuate Agonist‐Stimulated Lipolysis,Mimicking the Effects of Starvation

Objective: To test the hypothesis that incorporation of medium‐chain fatty acids (FAs) into adipocyte triglycerides alters intracellular lipolysis. Research Methods and Procedures: 3T3‐L1 adipocytes were pretreated with octanoate for various incubation periods. After the removal of exogenous FAs, cells were incubated with different lipolytic agonists. To determine the effects on lipolysis, we measured the following: the release of glycerol and FAs, lipase activity, protein levels of hormone‐sensitive lipase (HSL), and perilipin A; translocation of HSL; phosphorylation of perilipin A; and levels of cellular adenosine triphosphate, cyclic adenosine monophosphate, and H₂O₂. To compare the effects of starvation with those caused by octanoate pretreatment, we measured glycerol release and H₂O₂ generation in rat adipocytes of starved donors. Results: Pretreatment of adipocytes with octanoate in vitro increased basal lipolysis but decreased the cellular response for agonists. The same effects were seen in starvation in vivo. Preincubation with octanoate for 48 hours did not affect basal lipase activity, HSL, and perilipin protein levels, but it reduced agonist‐stimulated perilipin phosphorylation and HSL translocation toward fat droplets. This was associated with a reduction in basal cellular adenosine triphosphate levels and agonist‐stimulated cyclic adenosine monophosphate generation. Starvation and octanoate pretreatment both increased intracellular H₂O₂ concentrations, which might also contribute to the inhibition on agonist‐stimulated lipolysis. Discussion: Pretreatment with octanoate seems to induce changes in adipocyte lipolysis in a pattern mimicking the effects of starvation. Such changes could contribute, in part, to weight loss in animals and humans associated with dietary medium‐chain FAs.     

Adiponectin Oligomers and Ectopic Fat in Liver and Skeletal Muscle in Humans

We aimed at determining which circulating forms of the adipokine adiponectin that increases lipid oxidation in liver and skeletal muscle are related to ectopic fat in these depots in humans. Plasma total‐, high‐molecular weight (HMW)‐, middle‐molecular weight (MMW)‐, and low‐molecular weight (LMW) adiponectin were quantified by an enzyme‐linked immunosorbent assay. Their relationships with liver‐ and intramyocellular fat, measured using ¹H magnetic resonance spectroscopy, were investigated in 54 whites without type 2 diabetes. Liver fat, adjusted for gender, age, and total body fat, was associated only with HMW adiponectin (r = ?0.35, P = 0.012), but not with total‐, MMW‐, or LMW adiponectin. In addition, subjects with fatty liver (liver fat ≥5.56%, n = 15) had significantly lower HMW‐ (P = 0.04), but not total‐, MMW‐, or LMW adiponectin levels, compared to controls (n = 39). Similarly, intramyocellular fat correlated only with HMW (r = ?0.32, P = 0.039), but not with the other circulating forms of adiponectin. These data indicate that, among circulating forms of adiponectin, HMW is strongly related to ectopic fat, thus possibly representing the form of adiponectin regulating lipid oxidation in liver and skeletal muscle.     

Fat Depot‐specific Impact of Visceral Obesity on Adipocyte Adiponectin Release in Women

Our objective was to examine omental and subcutaneous adipocyte adiponectin release in women. We tested the hypothesis that adiponectin release would be reduced to a greater extent in omental than in subcutaneous adipocytes of women with visceral obesity. Omental and subcutaneous adipose tissue samples were obtained from 52 women undergoing abdominal hysterectomies (age: 47.1 ± 4.8 years; BMI: 26.7 ± 4.7 kg/m²). Adipocytes were isolated and their adiponectin release in the medium was measured over 2 h. Measures of body fat accumulation and distribution were obtained using dual‐energy X‐ray absorptiometry and computed tomography, respectively. Adiponectin release by omental and subcutaneous adipocytes was similar in lean individuals; however, in subsamples of obese or visceral obese women, adiponectin release by omental adipocytes was significantly reduced while that of subcutaneous adipocytes was not affected. Omental adipocyte adiponectin release was significantly and negatively correlated with total body fat mass (r = ?0.47, P < 0.01), visceral adipose tissue area (r = ?0.50, P < 0.01), omental adipocyte diameter (r = ?0.43, P < 0.01), triglyceride levels (r = ?0.32, P ≤ 0.05), cholesterol/high‐density lipoprotein (HDL)‐cholesterol (r = ?0.31, P ≤ 0.05), fasting glucose (r = ?0.39, P ≤ 0.01), fasting insulin (r = ?0.36, P ≤ 0.05), homeostasis model assessment index (r = ?0.39, P ≤ 0.01), and positively associated with HDL‐cholesterol concentrations (r = 0.33, P ≤ 0.05). Adiponectin release from subcutaneous cells was not associated with any measure of adiposity, lipid profile, or glucose homeostasis. In conclusion, compared to subcutaneous adipocyte adiponectin release, omental adipocyte adiponectin release is reduced to a greater extent in visceral obese women and better predicts obesity‐associated metabolic abnormalities.     

Abnormal immune responses in fa/fa Zucker rats and effects of feeding conjugated linoleic acid

Objective: The objective of this study was to characterize immune function in the fa/fa Zucker rat, and to determine the effects of feeding conjugated linoleic acid (CLA) isomers on immune function. Methods and Procedures: Lean and fa/fa Zucker rats were fed for 8 weeks nutritionally complete diets with different CLA isomers (%wt/wt): control (0%), c9t11 (0.4%), t10c12 (0.4%), or MIX (0.4% c9t11 + 0.4% t10c12). Isolated splenocytes were used to determine phospholipid (PL) fatty acid composition and cell phenotypes, or stimulated with mitogen to determine their ability to produce cytokines, immunoglobulins (Ig), and nitric oxide (NO). Results: Splenocyte PL of fa/fa rats had a higher proportion of total monounsaturated fatty acids and n ?3 polyunsaturated fatty acids (PUFA), and lower n ?6 PUFA and n ?6‐to‐n ?3 PUFA ratio (P < 0.05). Feeding CLA increased the content of CLA isomers into PL, but there were lower proportions of each CLA isomer in fa/fa rats. Splenocytes of fa/fa rats produced more amounts of IgA, IgG, and IgM, NO, and interleukin‐1β (IL‐1β), IL‐6, and tumor necrosis factor‐α (TNF‐α) (P < 0.05). Obese rats fed the t10c12 diet produced less TNF‐α and IL‐1β (lippopolysaccharide (LPS), P < 0.05). Splenocytes of fa/fa rats produced less concanavalin A (ConA)‐stimulated IL‐2 (P < 0.0001) than lean rats, except fa/fa rats fed the c9t11 diet (P < 0.05). Discussion: The c9t11 and t10c12 CLA isomers were incorporated into the membrane PL of the fa/fa Zucker rat, but to a lesser extent than lean rats. Splenocytes of obese rats responded in a proinflammatory manner and had reduced T‐cell function and feeding the t10c12 and c9t11 CLA isomers may improve some of these abnormalities by distinct methods.     

Adipocytes IGFBP‐2 Expression in Prepubertal Obese Children

Aims of the study were to measure insulin‐like growth factor‐binding protein‐2 (IGFBP‐2) expression by abdominal subcutaneous adipocytes and to assess the relationship between IGFBP‐2 expression, circulating IGFBP‐2, obesity, and insulin sensitivity in obese children. Thirty‐eight obese children were recruited. Insulin sensitivity was assessed by intravenous glucose tolerance test and body composition by total‐body dual‐energy X‐ray absorptiometry. Serum free and total IGF‐I, IGFBP‐2, adiponectin, and leptin were measured. Relative quantification of IGFBP‐2 mRNA by subcutaneous adipose tissue biopsies was obtained using real‐time PCR. Circulating IGFBP‐2 was positively associated with insulin sensitivity, in agreement with previous studies. IGFBP‐2 expression was associated with fat mass percentage (r = 0.656; P < 0.02), insulin sensitivity (r = ?0.604; P < 0.05), free IGF‐I (r = 0.646; P < 0.05), and leptin (r = 0.603; P < 0.05), but not with circulating IGFBP‐2 (r = 0.003, P = ns). The association between IGFBP‐2 expression and adiposity (r = 0.648; P < 0.05) was independent of insulin sensitivity (covariate). In conclusion, circulating IGFBP‐2 was positively associated with insulin sensitivity. IGFBP‐2 was expressed by subcutaneous abdominal adipocytes of obese children and increased with adiposity, independently from the level of insulin sensitivity. IGFBP‐2 expression may potentially be one of the local mechanisms used by adipocytes to limit further fat gain.     

Perilipin Expression in Human Adipose Tissues: Effects of Severe Obesity,Gender, and Depot

Objective: Perilipins are phosphoproteins that are localized to the surface of triacylglycerol droplets within adipocytes where they regulate the rate of lipolysis. We sought to determine the effects of severe obesity and depot [omental (Om) vs. subcutaneous (Sc)] on perilipin expression in the adipose tissue of individuals. Research Methods and Procedures: Samples of Om and Sc adipose tissues obtained at surgery from severely obese subjects and fat aspirations from nonobese subjects were analyzed for perilipin protein and mRNA levels by Northern and Western analysis. Results: Perilipin A (periA) was the major perilipin expressed in adipose tissues. periA mRNA relative abundance was significantly lower in Sc adipose tissue from severely obese compared to that from nonobese subjects. Western blotting of adipose tissue extracts showed that periA protein levels expressed relative to tissue protein or fat cell surface area were significantly lower (～ ?40%) in abdominal Sc adipose tissue from severely obese compared to that from nonobese subjects. However, the calculated mass of perilipin per fat cell did not differ between the two groups. Perilipin mRNA levels were higher in Sc compared to Om adipose tissue from obese individuals (p < 0.025; n = 26; 17 women, 9 men); however, periA protein levels did not differ. In addition, perilipin protein, but not mRNA, levels were higher in Sc adipose tissue from obese men than from women (p < 0.025). Discussion: Variations in perilipin expression may contribute to the higher basal lipolytic rates observed in obese compared to nonobese individuals and in obese women compared to obese men.     

2型糖尿病内脏脂肪含量与胰岛β细胞功能及胰岛素抵抗的关系研究

目的:研究2型糖尿病患者内脏脂肪含量与胰岛β细胞功能及胰岛素抵抗的关系。方法:对65例初诊2型糖尿病患者采用256 CT平脐经L4、5水平进行扫描并测量皮下及内脏脂肪含量,并以BMI不同进行分组,即体重正常组、超重组、肥胖组。采用稳态模式评估法(HOMA)计算胰岛素抵抗指数、胰岛B细胞分泌功能,测量入组患者的相关人体指标、空腹血生化检查指标。结果:超体重组、肥胖组患者腰围、体重指数(body mass index, BMI)、甘油三酯(triglyceride, TG)、低密度脂蛋白胆固醇(low density lipoprotein cholesterol, LDL-C)、空腹血糖,(fasting blood-glucose, FBG)、空腹胰岛素(fasting insulin, FINS)INS、稳态模型胰岛素抵抗指数(Homeostatic Model Assessment for Insulin Resistance, HOMA-IR)、胰岛β细胞功能指数(Homeostasis model assessment-β,HOMA-β)指标肥胖组、超重组均明显高于正常体重组(P0.05),超体重组、肥胖组内脏脂肪含量、内脏脂肪面积、皮下脂肪含量、脂肪总含量、脂肪百分比,超重组、肥胖组均明显高于正常体重组(P0.05),且肥胖组各项指标明显高于超重组(P0.05)。多元回归分析显示腹部脂肪总含量、内脏脂肪含量、皮下脂肪含量、内脏脂肪面积、BMI与胰岛素抵抗呈正相关,而其中内脏脂肪含量及面积关系最密切。结论:内脏脂肪含量是2型糖尿病胰岛素抵抗及B细胞功能变化的独立影响因素。