Release Of Non-esterified Fatty Acids Research Articles

PKC Activation is Required for TSH-mediated Lipolysis via Perilipin Activation

Adipocytes express TSH receptors, and TSH can stimulate cAMP-dependent protein kinase, perilipin phosphorylation, and lipolysis in human and mouse 3T3-L1 adipocytes. TSH activates PKC in thyrocytes. Since PKC has been implicated in lipolysis in adipocytes, we examined whether the family of conventional isoforms of PKC (cPKC) is a target of TSH in adipocytes, and whether cPKC is required for TSH-stimulated lipolysis. Differentiated 3T3-L1 and subcutaneous abdominal human adipocytes in culture were treated with TSH in the presence or absence of either PKC inhibitor Gö6976 (inhibits PKCα, βI) or Gö6983 (inhibits PKCα, βI, βII, γ, δ). Activation of cPKC was assessed by phospho-(ser) PKC substrate antibody immunoblot analysis. Perilipin phosphorylation was measured by SDS-PAGE electromobility shift followed by anti-perilipin immunoblot analysis. Lipolysis was quantified by the amount of nonesterified fatty acids (NEFAs) released into the medium. TSH strongly and significantly activated cPKC in differentiated human and 3T3-L1 adipocytes from undetectable levels in control conditions. This cPKC stimulation in human adipocytes by TSH was reduced significantly by 40% or 48% in the presence of PKC inhibitor Gö6983 or Gö6976, respectively. Gö6976 inhibited TSH-stimulated human adipocyte perilipin phosphorylation and NEFA release by 80% and 50%, respectively. We conclude that cPKC is activated by TSH in human differentiated adipocytes. Based on the effects of cPKC inhibition, cPKC activation is required for TSH-stimulated perilipin phosphorylation and lipolysis in human differentiated adipocytes.

Relationship of glucose and oleate metabolism to cardiac function in lipin-1 deficient (fld) mice

Lipin-1 is the major phosphatidate phosphatase (PAP) in the heart and a transcriptional coactivator that regulates fatty acid (FA) oxidation in the liver. As the control of FA metabolism is essential for maintaining cardiac function, we investigated whether lipin-1 deficiency affects cardiac metabolism and performance. Cardiac PAP activity in lipin-1 deficient [fatty liver dystrophy (fld)] mice was decreased by >80% compared with controls. Surprisingly, oleate oxidation and incorporation in triacylglycerol (TG), as well as glucose oxidation, were not significantly different in perfused working fld hearts. Despite this, [³H]oleate accumulation in phosphatidate and phosphatidylinositol was increased in fld hearts, reflecting the decreased PAP activity. Phosphatidate accumulation was linked to increased cardiac mammalian target of rapamycin complex 1 (mTORC1) signaling and endoplasmic reticulum (ER) stress. Transthoracic echocardiography showed decreased cardiac function in fld mice; however, cardiac dysfunction was not observed in ex vivo perfused working fld hearts. This showed that changes in systemic factors due to the global absence of lipin-1 could contribute to the decreased cardiac function in vivo. Collectively, this study shows that fld hearts exhibit unchanged oleate esterification, as well as oleate and glucose oxidation, despite the absence of lipin-1. However, lipin-1 deficiency increases the accumulation of newly synthesized phosphatidate and induces aberrant cell signaling.

Metabolic characteristics of human subcutaneous abdominal adipose tissueafter overnight fast

Subcutaneous abdominal adipose tissue is one of the largest fat depots and contributes the major proportion of circulating nonesterified fatty acids (NEFA). Little is known about aspects of human adipose tissue metabolism in vivo other than lipolysis. Here we collated data from 331 experiments in 255 healthy volunteers over a 23-year period, in which subcutaneous abdominal adipose tissue metabolism was studied by measurements of arterio-venous differences after an overnight fast. NEFA and glycerol were released in a ratio of 2.7:1, different (P < 0.001) from the value of 3.0 that would indicate no fatty acid re-esterification. Fatty acid re-esterification was 10.2 ± 1.4%. Extraction of triacylglycerol (TG) (fractional extraction 5.7 ± 0.4%) indicated intravascular lipolysis by lipoprotein lipase, and this contributed 21 ± 3% of the glycerol released. Glucose uptake (fractional extraction 2.6 ± 0.3%) was partitioned around 20-25% for provision of glycerol 3-phosphate and 30% into lactate production. There was release of lactate and pyruvate, with extraction of the ketone bodies 3-hydroxybutyrate and acetoacetate, although these were small numerically compared with TG and glucose uptake. NEFA release (expressed per 100 g tissue) correlated inversely with measures of fat mass (e.g., with BMI, r(s) = -0.24, P < 0.001). We examined within-person variability. Systemic NEFA concentrations, NEFA release, fatty acid re-esterification, and adipose tissue blood flow were all more consistent within than between individuals. This picture of human adipose tissue metabolism in the fasted state should contribute to a greater understanding of adipose tissue physiology and pathophysiology.

Fatty Acids, Obesity, and Insulin Resistance: Time for a Reevaluation

There is a widespread acceptance in the literature that plasma nonesterified fatty acids (NEFA), also called free fatty acids (FFA), can mediate many adverse metabolic effects, most notably insulin resistance. Elevated NEFA concentrations in obesity are thought to arise from an increased adipose tissue mass. It is also argued that the process of fatty acid mobilization from adipose tissue, normally suppressed by insulin, itself becomes insulin resistant—thus, lipolysis is further increased, potentially leading to a vicious cycle. Although we have also accepted this model for many years (1,2), recently there has been a steady accumulation of data, both in the literature and from our own research, that has forced us to realize that this simple story is not always true. Here we review the background to the idea of “fatty acids as metabolic villains,” together with data from the literature and from our own studies, which tend to show another side to the fatty acids/insulin resistance story. We will first examine the relationship between systemic concentrations of NEFA and obesity/insulin resistance and then study adipose tissue in the obese state with regard to its adaptation for NEFA release. NEFA circulate in the plasma bound to plasma albumin. Their function was largely elucidated in the 1950s through the work of Vincent Dole (3) at the Rockefeller Institute in New York and Robert Gordon (4,5) at the National Institutes of Health. Gordon demonstrated the origin of plasma NEFA from adipose tissue and their use by tissues such as the liver and myocardium, but not the brain. We now recognize that NEFA are the vehicle by which triacylglycerol (TG) stored in adipose tissue is transported to its sites of utilization. NEFA turnover is rapid, with a plasma half-life around 2–4 min (6). The only significant site of NEFA liberation …

Lipid mobilization and inflammatory responses during the transition period of dairy cows

The transition period of dairy cattle is characterized by dramatic changes in metabolism and host defense mechanisms that are associated with increased disease. Intense lipid mobilization from tissue stores is an important metabolic adaptation during the transition period that results in significant release of non-esterified fatty acids (NEFA) into the blood stream. Whereas these fatty acids are important sources of energy during times of increased metabolic demands, elevated concentrations of NEFA are known to disrupt several immune and inflammatory functions. This review will discuss the implications of lipid mobilization on inflammatory responses with special emphasis on leukocytes and endothelial cell functions during the transition period of dairy cows.

Leptin Induces Nitric Oxide-Mediated Inhibition of Lipolysis and Glyceroneogenesis in Rat White Adipose Tissue

Leptin is secreted by white adipose tissue (WAT) and induces lipolysis and nonesterified fatty acid (NEFA) oxidation. During lipolysis, NEFA efflux is the result of triglyceride breakdown, NEFA oxidation, and re-esterification via glyceroneogenesis. Leptin's effects on glyceroneogenesis remain unexplored. We investigated the effect of a long-term treatment with leptin at a physiological concentration (10μg/L) on lipolysis and glyceroneogenesis in WAT explants and analyzed the underlying mechanisms. Exposure of rat WAT explants to leptin for 2 h resulted in increased NEFA and glycerol efflux. However, a longer treatment with leptin (18 h) did not affect NEFA release and reduced glycerol output. RT-qPCR showed that leptin significantly downregulated the hormone-sensitive lipase (HSL), cytosolic phosphoenolpyruvate carboxykinase (Pck1), andPPARγgenes. In agreement with its effect on mRNA, leptin also decreased the levels of PEPCK-C and HSL proteins. Glyceroneogenesis, monitored by [1-14C] pyruvate incorporation into lipids, was reduced. Because leptin increases nitric oxide (NO) production in adipocytes, we explored the role of NO in the leptin signaling pathway. Pretreatment of explants with the NO synthase inhibitor N?-nitro-L-arginine methyl ester eliminated the effect of leptin on lipolysis, glyceroneogenesis, and expression of theHSL,Pck1, andPPARγgenes. The NO donorS-nitroso-N-acetyl-DL penicillamine mimicked leptin effects, thus demonstrating the role of NO in these pathways. The inverse time-dependent action of leptin on WAT is consistent with a process that limits NEFA re-esterification and energy storage while reducing glycerol release, thus preventing hypertriglyceridemia.

Feedback modeling of non-esterified fatty acids in rats after nicotinic acid infusions

A feedback model was developed to describe the tolerance and oscillatory rebound seen in non-esterified fatty acid (NEFA) plasma concentrations following intravenous infusions of nicotinic acid (NiAc) to male Sprague-Dawley rats. NiAc was administered as an intravenous infusion over 30 min (0, 1, 5 or 20 μmol kg−1 of body weight) or over 300 min (0, 5, 10 or 51 μmol kg−1 of body weight), to healthy rats (n = 63), and serial arterial blood samples were taken for measurement of NiAc and NEFA plasma concentrations. Data were analyzed using nonlinear mixed effects modeling (NONMEM). The disposition of NiAc was described by a two-compartment model with endogenous turnover rate and two parallel capacity-limited elimination processes. The plasma concentration of NiAc was driving NEFA (R) turnover via an inhibitory drug-mechanism function acting on the formation of NEFA. The NEFA turnover was described by a feedback model with a moderator distributed over a series of transit compartments, where the first compartment (M 1) inhibited the formation of R and the last compartment (M N) stimulated the loss of R. All processes regulating plasma NEFA concentrations were assumed to be captured by the moderator function. The potency, IC 50, of NiAc was 45 nmol L−1, the fractional turnover rate k out was 0.41 L mmol−1 min−1 and the turnover rate of moderator k tol was 0.027 min−1. A lower physiological limit of NEFA was modeled as a NiAc-independent release (k cap) of NEFA into plasma and was estimated to 0.032 mmol L−1 min−1. This model can be used to provide information about factors that determine the time-course of NEFA response following different modes, rates and routes of administration of NiAc. The proposed model may also serve as a preclinical tool for analyzing and simulating drug-induced changes in plasma NEFA concentrations after treatment with NiAc or NiAc analogues.

Lipid Mobilization in Transition Dairy Cows Alters Endothelial Inflammatory Response

A hallmark of the transition period in dairy cows is intense lipid mobilization. This mechanism of adaptation is necessary to fulfill the energy deficits experienced by cows in late gestation and early lactation. Lipid mobilization is a dynamic process involving lipolysis and lipogenesis. During the transition period, the rate of lipolysis surpasses that of lipogenesis, inducing the release of non-esterified fatty acids (NEFA) into the blood stream. As a consequence, increased NEFA concentrations disrupt systemic lipid homeostasis not only quantitatively, but also relative to composition. Previous research demonstrated that enhanced lipolysis during the transition period altered the fatty acid composition of different organs and cell populations including blood, liver, adipose tissue, and peripheral blood mononuclear cells. A common change was the increment in the concentrations of saturated fatty acids (palmitic and stearic). Although increments in plasma NEFA are linked to transition cow diseases such as ketosis and displaced abomasum, less is known about the consequences of shifts in fatty acid profiles of endothelial cells and how these changes contribute to dairy cows increased susceptibility to disease. Immune responses are highly dependent on the interactions between immune cells with the vasculature. Indeed, endothelial cells regulate the trafficking of the immune cell migration to and from tissues. We hypothesize that shifts in plasma NEFA content and composition in transition dairy cows modify endothelial cells inflammatory response by enhancing lipid mediator biosynthesis and expression of adhesion molecules.

Enhanced glycogen metabolism in adipose tissue decreases triglyceride mobilization

Adipose tissue is a primary site for lipid storage containing trace amounts of glycogen. However, refeeding after a prolonged partial fast produces a marked transient spike in adipose glycogen, which dissipates in coordination with the initiation of lipid resynthesis. To further study the potential interplay between glycogen and lipid metabolism in adipose tissue, the aP2-PTG transgenic mouse line was utilized since it contains a 100- to 400-fold elevation of adipocyte glycogen levels that are mobilized upon fasting. To determine the fate of the released glucose 1-phosphate, a series of metabolic measurements were made. Basal and isoproterenol-stimulated lactate production in vitro was significantly increased in adipose tissue from transgenic animals. In parallel, basal and isoproterenol-induced release of nonesterified fatty acids (NEFAs) was significantly reduced in transgenic adipose tissue vs. control. Interestingly, glycerol release was unchanged between the genotypes, suggesting that enhanced triglyceride resynthesis was occurring in the transgenic tissue. Qualitatively similar results for NEFA and glycerol levels between wild-type and transgenic animals were obtained in vivo during fasting. Additionally, the physiological upregulation of the phosphoenolpyruvate carboxykinase cytosolic isoform (PEPCK-C) expression in adipose upon fasting was significantly blunted in transgenic mice. No changes in whole body metabolism were detected through indirect calorimetry. Yet weight loss following a weight gain/loss protocol was significantly impeded in the transgenic animals, indicating a further impairment in triglyceride mobilization. Cumulatively, these results support the notion that the adipocyte possesses a set point for glycogen, which is altered in response to nutritional cues, enabling the coordination of adipose glycogen turnover with lipid metabolism.

Activin B inhibits lipolysis in 3T3-L1 adipocytes

Activin B, consisting of two inhibin βB (INHBB) subunits, is a hormone known to affect gonadal function, reproduction and fetal development. We have reported that INHBB and activin B receptors are highly expressed in adipocytes suggesting that activin B may have local effects in adipose tissue. In this study, we investigate the effect of activin B on lipolysis, measured as release of non-esterified fatty acids and free glycerol. Recombinant activin B decreased lipolysis in a concentration-dependent manner and increased intracellular triglyceride content in 3T3-L1 adipocytes. siRNA-mediated knock-down of INHBB expression increased lipolysis, and this effect was abolished by addition of recombinant activin B. In line with its inhibitory effect on lipolysis, activin B caused a down regulation of the expression of adipose triglyceride lipase and hormone sensitive lipase, key genes involved in lipolysis. In summary, we suggest that activin B is a novel adipokine that inhibits lipolysis in a paracrine or autocrine manner.

Rates of lipid fluxes in adipose tissue in vivo after a mixed meal in morbid obesity

Although insulin resistance in obesity is established, information on insulin action on lipid fluxes, in morbid obesity, is limited. This study was undertaken in morbidly obese women to investigate insulin action on triacylglycerol fluxes and lipolysis across adipose tissue. A meal was given to 26 obese (age 35+/-1 years, body mass index 46+/-1 kg m(-2)) and 11 non-obese women (age 38+/-2 years, body mass index 24+/-1 kg m(-2)). Plasma samples for glucose, insulin, triglycerides and non-esterified fatty acids (NEFAs) were taken for 360 min from a vein draining the abdominal subcutaneous adipose tissue and from the radial artery. Adipose tissue blood flow was measured with (133)Xe. In obese vs non-obese: (1) Arterial glucose was similar, but insulin was increased (P=0.0001). (2) Adipose tissue blood flow was decreased (P=0.0001). (3) Arterial triglycerides (P=0.0001) and NEFAs (P=0.01) were increased. (4) Lipoprotein lipase was decreased (P=0.0009), although the arteriovenous triglyceride differences were similar. (5) Veno-arterial NEFA differences across the adipose tissue were similar. (6) NEFA fluxes and hormone-sensitive lipase-derived glycerol output from 100 g adipose tissue were not different. (7) Total adipose tissue NEFA release was increased (P=0.02). In morbid obesity: (a) hypertriglycerinemia could be attributed to a defect in the postprandial dynamic adjustment of triglyceride clearance across the adipose tissue, partly caused by blunted BF; and (b) postprandially, there is an impairment of adipose tissue to buffer NEFA excess, despite hyperinsulinemia.

Regulation of adipose triglyceride lipase by fasting and refeeding in avian species

Lipolysis in fat tissue is a process that is not fully understood. Increasing knowledge of the process could allow for increased feed efficiency and reduced fat content, which would lower feeding costs for poultry production. Adipose triglyceride lipase (ATGL) is an adipose-specific enzyme that cleaves at the Sn-1 position of triglycerides, releasing nonesterified fatty acids (NEFA) into the bloodstream. Adipose triglyceride lipase has recently been cloned in avian species. For further understanding of how ATGL responds to environmental stimuli, we fasted 21-d-old Ross 308 broiler chickens for 24 h. Adipose and liver tissues were collected before the fasting period and at its conclusion, as well as 4, 8, 12, and 24 h after being refed. Blood samples were also collected at these time points. Additionally, tissue samples were collected from 30 quails subjected to the same fasting period, with refeeding time points of 2, 4, and 8 h. Adipose triglyceride lipase in tissue samples was analyzed via Western blot and quantitative real-time PCR. Protein and RNA levels of ATGL were high in the birds after the fasting period. Ribonucleic acid levels quickly returned to control levels following refeeding. Protein levels, however, remained high in the chicken throughout the 4- and 8-h refeeding time points. For the quail samples, ATGL protein returned to normal levels at 8 h. To relate the release of NEFA into the blood with ATGL expression, plasma analysis was done. Nonesterified fatty acids were significantly higher after the fasting period than the control and returned to control levels by 4 h after refeeding. The quick return of the RNA to control levels suggests that ATGL production was stimulated during the fasting period but inhibited once food was reintroduced. The immediately lowered NEFA levels suggest that the residual high amounts of ATGL protein shown by Western blot were no longer functioning. This suggests the existence of a mechanism to inactivate the active form of ATGL, possibly through posttranslational modification of the protein.

The role of the lipogenic pathway in the development of hepatic steatosis

Non-alcoholic fatty liver disease (NAFLD) represents a wide spectrum of diseases, ranging from simple fatty liver (hepatic steatosis) through steatosis with inflammation and necrosis to cirrhosis. NAFLD, which is strongly associated with obesity, insulin resistance and type 2 diabetes, is now well recognized as being part of the metabolic syndrome. The metabolic pathways leading to the development of hepatic steatosis are multiple, including enhanced non-esterified fatty acid release from adipose tissue (lipolysis), increased de novo fatty acids (lipogenesis) and decreased β-oxidation. Recently, several mouse models have helped to clarify the molecular mechanisms leading to the development of hepatic steatosis in the pathogenesis of NAFLD. This review describes the models that have provided evidence implicating lipogenesis in the development and/or prevention of hepatic steatosis.

Long-term pioglitazone treatment enhances lipolysis in rat adipose tissue

The insulin-sensitizing effects of thiazolidinediones are believed to depend at least in part on reductions in circulating levels of nonesterified fatty acids (NEFA). The mechanisms that mediate the reductions in NEFA are not fully understood and could involve reductions in adipose tissue lipolysis, increases in glyceroneogenesis and NEFA reesterification in triglycerides in adipose tissue and increases in NEFA metabolism by oxidative tissues. In a congenic strain of spontaneously hypertensive rats that fed a high-sucrose diet to promote features of the metabolic syndrome, we studied the effects of chronic pioglitazone treatment over 4 months on adipose tissue lipolysis and NEFA metabolism. We observed significant increases in basal and adrenaline-stimulated NEFA and glycerol release, and near-total suppression of NEFA reesterification in epididymal adipose tissue isolated from rats chronically treated with pioglitazone. However, pioglitazone-treated rats also exhibited significant increases in mitochondrial DNA levels in adipose tissue (3.2-fold increase, P=0.001) and potentially greater sensitivity to the antilipolytic effects of insulin than untreated controls. In addition, chronic pioglitazone treatment was associated with increased palmitate oxidation in soleus muscle, reduced fasting levels of serum NEFA and triglycerides, as well as reduced serum levels of insulin and increased serum levels of adiponectin. Despite suppressing NEFA reesterification and increasing basal and adrenaline-stimulated lipolysis, chronic pioglitazone treatment may decrease circulating NEFA levels in part by increasing adipose tissue sensitivity to the antilipolytic effects of insulin and by enhancing NEFA oxidation in skeletal muscle.

Cell death–inducing DFF45-like effector C is reduced by caloric restriction and regulates adipocyte lipid metabolism

Members of the cell death–inducing DFF45-like effector (CIDE) gene family have been shown to regulate lipid metabolism. In this article, we report that the third member of the human CIDE family, CIDEC, is down-regulated in response to a reduced caloric intake. The down-regulation was demonstrated by microarray and real-time polymerase chain reaction analysis of subcutaneous adipose tissue in 2 independent studies on obese patients undergoing treatment with a very low calorie diet. By analysis of CIDEC expression in 65 human tissues, we conclude that human CIDEC is predominantly expressed in subcutaneous adipocytes. Together, these observations led us to investigate the effect of decreased CIDEC expression in cultured 3T3-L1 adipocytes. Small interfering RNA–mediated knockdown of CIDEC resulted in an increased basal release of nonesterified fatty acids, decreased responsiveness to adrenergic stimulation of lipolysis, and increased oxidation of endogenous fatty acids. Thus, we suggest that CIDEC is a regulator of adipocyte lipid metabolism and may be important for the adipocyte to adapt to changes in energy availability.

Synergistic Effect ofVespaAmino Acid Mixture on Lipolysis in Rat Adipocytes

The effect of Vespa amino acid mixture (VAAM) on the release of lipolytic products was examined in isolated rat adipocytes. Concentrations of 112.5 to 225 ppm of VAAM showed significantly greater release of non-esterified fatty acids (NEFA) and glycerol than the same concentrations of casein amino acid mixture (CAAM). The integrated relative release of NEFA and glycerol was lower in response to individual administration of amino acids comprising VAAM than to VAAM itself. Further, amino acids mixtures deficient in a single amino acid comprising VAAM showed significantly lower release of lipolytic products than VAAM. These data suggest that the synergistic effect of VAAM on the release of lipolytic products is a function of concurrent exposure to the unique composition of amino acids found in VAAM as compared to the effect of exposure to the same individual un-mixed amino acids or to a mixture lacking one of the amino acids comprising VAAM.

Pyruvate Dehydrogenase Kinase 4

OBJECTIVE—Pyruvate dehydrogenase complex (PDC) serves as the metabolic switch between glucose and fatty acid utilization. PDC activity is inhibited by PDC kinase (PDK). PDC shares the same substrate, i.e., pyruvate, as glyceroneogenesis, a pathway controlling fatty acid release from white adipose tissue (WAT). Thiazolidinediones activate glyceroneogenesis. We studied the regulation by rosiglitazone of PDK2 and PDK4 isoforms and tested the hypothesis that glyceroneogenesis could be controlled by PDK.RESEARCH DESIGN AND METHODS—Rosiglitazone was administered to Zucker fa/fa rats, and then PDK4 and PDK2 mRNAs were examined in subcutaneous, periepididymal, and retroperitoneal WAT, liver, and muscle by real-time RT-PCR. Cultured WAT explants from humans and rats and 3T3-F442A adipocytes were rosiglitazone-treated before analyses of PDK2 and PDK4 mRNA and protein. Small interfering RNA (siRNA) was transfected by electroporation. Glyceroneogenesis was determined using [1-14C]pyruvate incorporation into lipids.RESULTS—Rosiglitazone increased PDK4 mRNA in all WAT depots but not in liver and muscle. PDK2 transcript was not affected. This isoform selectivity was also found in ex vivo–treated explants. In 3T3-F442A adipocytes, Pdk4 expression was strongly and selectively induced by rosiglitazone in a direct and transcriptional manner, with a concentration required for half-maximal effect at 1 nmol/l. The use of dichloroacetic acid or leelamine, two PDK inhibitors, or a specific PDK4 siRNA demonstrated that PDK4 participated in glyceroneogenesis, therefore altering nonesterified fatty acid release in both basal and rosiglitazone-activated conditions.CONCLUSIONS—These data show that PDK4 upregulation in adipocytes participates in the hypolipidemic effect of thiazolidinediones through modulation of glyceroneogenesis.

Effects of trans-10, cis-12 conjugated linoleic acid on gene expression and lipid metabolism of adipose tissue of growing pigs

The objective of the present study was to determine the effects of trans-10, cis-12 conjugated linoleic acid (CLA) in adipose tissue explant cultures of growing pigs on the following responses: lipogenesis (measured as rate of (14)C-labeled glucose incorporation over a subsequent 2-h incubation in the presence or absence of insulin), lipolysis (release of non-esterified fatty acid over a 2-h incubation in the presence or absence of isoproterenol), activities of lipogenic enzymes, and mRNA abundance of fatty acid synthase (FAS). Adipose tissue explants from nine growing pigs (78 +/- 3 kg) were cultured in 199 medium with insulin, dexamethasone and antibiotics for 4, 12, 24, and 48 h. The treatments were 1) control: 100 microM polyvinyl alcohol (PVA); 2) pGH: 100 ng/mL porcine growth hormone (pGH) plus 100 microM PVA; 3) CLA200: 200 microM trans-10, cis-12 CLA; 4) CLA50: 50 microM trans-10, cis-12 CLA, and 5) LA: 200 microM linoleic acid. Fatty acids were added along with PVA (2:1), respectively, for 24 h. Explants were collected after each culture period and assayed for lipogenesis. Transcripts of FAS mRNA were quantified by real-time RT-PCR after 24 and 48 h. Lipolysis and activities of FAS, glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, and NADP-malate dehydrogenase were determined after 48 h. As expected, glucose incorporation was decreased (P < 0.05) in response to pGH treatment (positive control). LA had no effect on any parameter evaluated. Treatment with trans-10, cis-12 CLA decreased FAS activity (P < 0.05), but NADPH-generating enzymes were unaffected by treatments. Consistent with reduction in FAS activity, both lipid synthesis and FAS mRNA abundance were reduced with chronic CLA treatment, pGH increased baseline and stimulated lipolysis (P < 0.05) after 48 h of culture, while CLA treatment had no effect on non-esterified fatty acid release. Results of this study showed that trans-10, cis-12 CLA alters lipogenesis but has no effect on lipolysis in cultures of pig adipose tissue.

Effect of nutrition on the GH responsiveness of liver and adipose tissue in dairy cows

Dairy cows enter a period of energy insufficiency after parturition. In liver, this energy deficit leads to reduced expression of the liver-specific GH receptor transcript (GHR1A) and decreased GHR abundance. As a consequence, hepatic processes stimulated by GH, such as IGF-I production, are reduced. In contrast, adipose tissue has been assumed to remain fully GH responsive in early lactation. To determine whether energy insufficiency causes contrasting changes in the GH responsiveness of liver and adipose tissue, six lactating dairy cows were treated for 4 days with saline or bovine GH when adequately fed (AF, 120% of total energy requirement) or underfed (UF, 30% of maintenance energy requirement). AF cows mounted robust GH responses in liver (plasma IGF-I and IGF-I mRNA) and adipose tissue (epinephrine-stimulated release of non-esterified fatty acids in plasma, IGF-I mRNA, and p85 regulatory subunit of phosphatidylinositol 3-kinase mRNA). Reductions of these responses were seen in the liver and adipose tissue of UF cows and were associated with decreased GHR abundance. Reduced GHR abundance occurred without corresponding reductions of GHR1A transcripts in liver or total GHR transcripts in adipose tissue. In contrast, undernutrition did not alter the abundance of proteins involved in the early post-receptor signaling steps. Thus, a feed restriction reproducing the energy deficit of early lactation depresses GH actions not only in liver but also in adipose tissue. It remains unknown whether a similar reduction of GH action occurs in the adipose tissue of early lactating dairy cows.

Obesity and Atherogenic Dyslipidemia

Obesity is associated with an increased risk of coronary heart disease, in part due to its strong association with atherogenic dyslipidemia, characterized by high triglycerides and low high-density lipoprotein (HDL) cholesterol. There has been substantial research effort focused on the mechanisms of the link between obesity and atherogenic dyslipidemia, both in the absence and presence of insulin resistance. After a brief overview of the epidemiology of atherogenic dyslipidemia, this article details the known molecular mechanisms of adipocyte function and its relationship to apoB-containing lipoprotein assembly and metabolism, both in the healthy as well as in the obese states. We also discuss the pathophysiology of low HDL cholesterol in obesity and the implications for cardiovascular disease risk.