Non-esterified Fatty Acid Metabolism Research Articles

Perilipin 5 improves hepatic lipotoxicity by inhibiting lipolysis.

Abnormal metabolism of nonesterified fatty acids (NEFAs) and their derivatives has been reported to be the main cause of intracellular lipotoxic injury. Normally, NEFAs are stored in lipid droplets (LDs) in the form of triglyceride (TG), which could reduce the lipotoxicity of cytosolic NEFAs. Previous studies have implicated that Perilipin 5 (Plin5), an LD-binding protein, regulates the storage and hydrolysis of TG in LD. However, its roles and underlying mechanisms in the liver remain unknown. Here we found that Plin5 expression was increased in steatotic livers. Using Plin5 knockout mice, we found that Plin5 deficiency resulted in reduced hepatic lipid content and smaller-sized LDs, which was due to the elevated lipolysis rate and fatty acid utilization. Plin5-deficient hepatocytes showed increased mitochondria proliferation, which could be explained by the increased expression and activity of PPARα stimulated by the increased NEFA levels. Meanwhile, Plin5-deficient livers also exhibited enhanced mitochondrial oxidative capacity. We also found that Plin5 deficiency induces lipotoxic injury in hepatocytes, attributed to lipid peroxidation. Mechanistically, we found that Plin5 blocks adipose triglyceride lipase (ATGL)-mediated lipolysis by competitively binding to comparative gene identification-58 (CGI-58) and disrupting the interaction between CGI-58 and ATGL. Plin5 is an important protective factor against hepatic lipotoxicity induced by NEFAs generated from lipolysis. This provides an important new insight into the regulation of hepatic lipid storage and relation between lipid storage and lipotoxicity.

Effect of Growth Hormone on Dawn Phenomenon in Healthy Adults

The purpose of this study was to investigate the involvement of growth hormone in the diurnal variation of insulin sensitivity in healthy adults. Afternoon (16:00 hr) or night (23:00 hr) pretreatment with a subcutaneous injection of normal saline, human growth hormone to mimic the normal nocturnal rise in growth hormone, or octreotide to inhibit endogenous growth hormone secretion to create a state of relative nocturnal growth hormone deficiency, was given 16 hours before undergoing the modified insulin suppression test in healthy subjects. The morning and evening experiments were separated by an interval of at least 3 days. Thus, each subject was tested on six separate occasions arranged in a random order. A higher value of the steady-state plasma glucose (SSPG) is indicative of lower insulin sensitivity. Plasma glucose, serum insulin, insulin-like growth factor-1, nonesterified fatty acids (NEFA), and metabolic clearance rate of insulin (MCRI) were measured. In the normal saline and human growth hormone groups, SSPG levels were lower in the morning than in the evening. Evening SSPG levels, MCRI, and NEFA concentrations were higher in the participants treated with normal saline and growth hormone than in the octreotide group. Differences in SSPG levels between the morning and evening values were higher in the participants pretreated with normal saline and growth hormone than in those treated with octreotide. A diurnal variation in insulin sensitivity existed in healthy subjects. These results provided direct evidence that the role of growth hormone in regulating insulin sensitivity might be related to changes in the MCRI and the metabolism of NEFA in healthy subjects.

Citrulline reduces glyceroneogenesis and induces fatty acid release in visceral adipose tissue from overweight rats.

High-fat diet (HFD) increases visceral adipose tissue (AT). Our aim was to evaluate whether citrulline (CIT) affected nonesterified fatty acid (NEFA) metabolism in AT from HFD-fed rats. Rats were fed for 8 weeks with either a control diet (CD) or HFD. Retroperitoneal AT explants were exposed to 2.5 mmol/L CIT for 24 h. We analyzed lipolysis, beta-oxidation, glyceroneogenesis, and the expression of the key associated enzymes. CIT doubled NEFA release selectively in HFD AT. Phosphorylation of hormone-sensitive lipase was upregulated 50 and 100% by CIT in CD and HFD AT, respectively. Under CIT, beta-oxidation increased similarly whatever the diet, whereas glyceroneogenesis, which permits NEFA re-esterification, was downregulated 50 and 80% in CD and HFD AT, respectively. In the latter, the important decrease in re-esterification probably explains the rise of NEFA release. A pretreatment with the nitric oxide synthase inhibitor N ω-nitro-l-arginine methyl ester abolished CIT effects. These results demonstrate direct lipolytic and antiglyceroneogenic effects of CIT on CD and HFD AT. The selective CIT-mediated NEFA release from HFD AT was probably the consequence of the drastic decrease in glyceroneogenesis and nitric oxide was a mediator of CIT effects. These results provide evidence for a direct action of CIT on AT to reduce overweight.

Plasma non-esterified fatty acid levels in children and their relationship with sex steroids

ObjectivePuberty is associated with decreased insulin sensitivity. Sexual hormones have been related with the onset of insulin resistance, but their relationship with non-esterified fatty acids (NEFA) remains unexplored. The aim of this study was to evaluate circulating NEFA levels in population-based samples of prepubertal children and adolescents and to analyze the association of NEFA with obesity, insulin resistance, and sexual hormones in adolescents. ExperimentalThe studied population included 854 randomly selected 6–8-year-old children and 822 children aged 12–16years. NEFA levels were determined using a commercial kit. Testosterone and estradiol levels were determined by RIA, and insulin and sex hormone binding protein by IRMA. HOMA was calculated as an indicator of insulin resistance. ResultsNEFA levels were lower in adolescents than in 6–8-year-old children, and decreased progressively with age between 12-year-olds and 16-year-olds. No significant differences in NEFA levels were observed between obese and non-obese adolescents. NEFA were not correlated with insulin or HOMA in 12–16-year-old girls, and appear negatively correlated with these variables in boys. Insulin and HOMA were negatively correlated with SHBG levels in both sexes adjusting by age but NEFA levels were not. ConclusionsNEFA levels decrease with age in adolescents and are not significantly increased in obese children, supporting the fact that the decreased insulin sensitivity at this age is not affecting NEFA metabolism. Although SHBG is related to insulin and HOMA independently of age in both sexes, SHBG levels are not associated with NEFA.

Short communication: High insulin concentrations inhibit fatty acid oxidation-related gene expression in calf hepatocytes cultured in vitro

In dairy cows, ketosis is an important disease associated with negative energy balance, which leads to low blood glucose levels and high blood nonesterified fatty acid levels. The liver is the most active organ in cows for the metabolism of nonesterified fatty acids. Insulin is an anabolic hormone that plays numerous roles in the metabolism of carbohydrates, lipids, and proteins, as well as being a potent regulator of fatty acid oxidation. In this study, using fluorescent quantitative reverse-transcription PCR, ELISA, and primary hepatocytes cultured in vitro, we examined the effect of insulin (0, 5, 10, 20, 50, and 100nmol/L) on fatty acid oxidation by monitoring mRNA and protein expression levels of key enzymes: long-chain acyl-coenzyme A synthetase, carnitine palmitoyltransferase I, and long-chain acyl-coenzyme A dehydrogenase. The results showed that the mRNA and protein expression of long-chain acyl-coenzyme A synthetase, carnitine palmitoyltransferase I, and long-chain acyl-coenzyme A dehydrogenase was markedly decreased when the concentration of insulin in the media was increased. These findings indicate that high levels of insulin significantly inhibit the expression of genes related to fatty acid oxidation and consequently results in a decreased level of fatty acid oxidation in calf hepatocytes.

Adipose Tissue Dysfunction in Humans: A Potential Role for the Transmembrane Protein ENPP1

Adipose tissue (AT) helps to regulate body fat partitioning and systemic lipid/glucose metabolism. We have recently reported lipid/glucose metabolism abnormalities and increased liver triglyceride content in an AT-selective transgenic model overexpressing ectonucleotide pyrophosphatase/phosphodiesterase-1 (ENPP1), the AdiposeENPP1-Tg mouse. The aim of the study was to test the translational hypothesis that AT-ENPP1 overexpression associates with AT dysfunction (changes in AT gene expression, plasma fatty acid, and adipokine levels), increased liver triglyceride deposition, and systemic insulin resistance in humans. A total of 134 young normoglycemic men and women were subjected to body composition studies, hyperinsulinemic-euglycemic clamps, and AT needle biopsy. Twenty men also had liver/muscle nuclear magnetic resonance spectroscopy. Predetermined measures included AT expression of ENPP1 and other lipid metabolism/inflammation genes, plasma adipokines, and nonesterified fatty acid (NEFA) levels, liver/muscle triglyceride content, and the systemic glucose disposal rate. After statistical adjustment for body fat content, increasing AT-ENPP1 was associated with up-regulation of genes involved in NEFA metabolism and inflammation, increased postabsorptive NEFA levels, decreased plasma adiponectin, increased liver triglyceride content, and systemic insulin resistance in men. In women, there were no changes in plasma adiponectin, NEFAs, or glucose disposal rate associated with increasing AT-ENPP1, despite increased expression of lipid metabolism and inflammation genes in AT. Increased AT-ENPP1 is associated with AT dysfunction, increased liver triglyceride deposition, and systemic insulin resistance in young normoglycemic men. These findings are concordant with the AdiposeENPP1-Tg phenotype and identify a potential target of therapy for health complications of AT dysfunction, including type 2 diabetes and cardiovascular disease.

Dietary Pulse Consumption and Arterial Damage in Type 2 Diabetes

s / Can J Diabetes 36 (2012) S2eS22 S10 tissues insulin resistance and inflammation. In the present study, we investigated the effect of 4-phenylbutyrate (4-PBA), a chemical chaperon that prevents ER stress, on the regulation of tissues’ nonesterified fatty acids metabolism and diet-induced insulin resistance. Research Design and Methods: Control (chow fed) vs. diabetic (high-fat/high-fructose fed + small dose streptozotocin-treated e HFHFS) male Wistar rats were treated with 4-PBA (1g/kg/day) by oral gavage for 6 weeks. At the end of the treatment period, [8, 9-3H]-palmitate was infused during an euglycemic ehyperinsulinemic clamp followed by an i.v. bolus of [1-14C]-2bromopalmitate at steady-state to determine oxidative and non-oxidative nonesterified fatty acid (NEFA) metabolism in tissues. Results: HFHFS-fed rats displayed insulin resistance with high levels of fasting glucose and insulin. Increased NEFA fractional uptake by the gastrocnemius and reduced myocardial NEFA nonoxidative disposal was observed. Animals treated with 4-PBA displayed greater plasmatic NEFA rate of appearance and clearance. 4-PBA normalized gastrocnemius fractional uptake and increased NEFA oxidation and fractional uptake by the liver. SCAT of treated rats are characterized larger SC adipocytes with greater fractional and net NEFA uptake. In vitro, 4-PBA inhibits differentiation of adipocytes precursors but stimulates fatty acids uptake by mature adipocytes. Conclusions: Redistribution of NEFA fluxes by 4-PBA treatment does not restore insulin sensitivity in a nutritional model of T2D but reduced fasting glucose.

Effect of Alipogene Tiparvovec (AAV1-LPLS447X) on Postprandial Chylomicron Metabolism in Lipoprotein Lipase-Deficient Patients

Lipoprotein lipase-deficient (LPLD) individuals display marked chylomicronemia and hypertriglyceridemia associated with increased pancreatitis risk. The aim of this study was to determine the effect of i.m. administration of an adeno-associated viral vector (AAV1) for expression of LPL(S447X) in muscle (alipogene tiparvovec, AAV1-LPL(S447X)) on postprandial chylomicron metabolism and on nonesterified fatty acid (NEFA) and glycerol metabolism in LPLD individuals. In an open-label clinical trial (CT-AMT-011-02), LPLD subjects were administered alipogene tiparvovec at a dose of 1 × 10(12) genome copies per kilogram. Two weeks before and 14 wk after administration, chylomicron metabolism and plasma palmitate and glycerol appearance rates were determined after ingestion of a low-fat meal containing (3)H-palmitate, combined with (continuous) iv infusion of [U-(13)C]palmitate and [1,1,2,3,3-(2)H]glycerol. After administration of alipogene tiparvovec, the triglyceride (TG) content of the chylomicron fraction and the chylomicron-TG/total plasma TG ratio were reduced throughout the postprandial period. The postprandial peak chylomicron (3)H level and chylomicron (3)H area under the curve were greatly reduced (by 79 and 93%, 6 and 24 h after the test meal, respectively). There were no significant changes in plasma NEFA and glycerol appearance rates. Plasma glucose, insulin, and C-peptide also did not change. Intramuscular administration of alipogene tiparvovec resulted in a significant improvement of postprandial chylomicron metabolism in LPLD patients, without inducing large postprandial NEFA spillover.

Diabetes Health, Residence & Metabolism in Asians: the DHRMA study, research into foods from the Indian subcontinent - a blinded, randomised, placebo controlled trial

BackgroundCoronary heart disease (CHD) is highly prevalent amongst the South Asian communities in Britain. The reasons for this excess CHD risk are multifactorial, but in part relate to a susceptibility to diabetes mellitus - where the aberrant metabolism of non-esterified fatty acids (NEFA) and glucose are likely to underpin vascular disease in this population. Dietary intervention is an important and first line approach to manage increased CHD risk. However, there is limited information on the impact of the South Asian diet on CHD risk.Methods/DesignThe Diabetes Health, Residence & Metabolism in Asians (DHRMA) study is a blinded, randomised, placebo controlled trial that analyses the efficacy of reduced glycaemic index (GI) staples of the South Asian diet, in relation to cardio-metabolic risk factors that are commonly perturbed amongst South Asian populations - primarily glucose, fatty acid and lipoprotein metabolism and central adiposity. Using a 10-week dietary intervention study, 50 healthy South Asians will be randomised to receive either a DHRMA (reduced GI) supply of chapatti (bread), stone ground, high protein wheat flour and white basmati rice (high bran, unpolished) or commercially available (leading brand) versions chapatti wheat flour and basmati rice. Volunteers will be asked to complete a 75g oral glucose tolerance test at baseline and at 10-weeks follow-up, where blood metabolites and hormones, blood pressure and anthropometry will also be assessed in a standardised manner.DiscussionIt is anticipated that the information collected from this study help develop healthy diet options specific (but not exclusive) for South Asian ethnic communities.Trial registrationCurrent Controlled Trials ISRCTN02839188

The beta-1 adrenergic antagonist, atenolol, decreases acylation stimulating protein, exercise capacity and plasma free fatty acids in men with type 2 diabetes

Background and aimsAtenolol is a beta-1 adrenergic antagonist commonly prescribed for the treatment of systemic hypertension or coronary artery disease yet its use in individuals with type 2 diabetes mellitus (T2DM) is controversial due to potentially negative side effects on insulin resistance. Non-esterified fatty acid (NEFA) metabolism is altered in T2DM especially under conditions of metabolic stress such as exercise or the postprandial state. We evaluated atenolol effects on circulating NEFA and related hormones in men with T2DM during acute cardiorespiratory exercise in both the fasting and postprandial state, including the adipokine acylation stimulating protein (ASP) which stimulates adipose tissue NEFA uptake. Methods and resultsTen men with T2DM underwent four 1-h exercise sessions at 60% of their maximal oxygen uptake (VO2max) under the following conditions: 1) fasting (F), and 2) 2 h postprandial (PP) without medication; and 3) fasting (F-Atenolol), and 4) 2 h postprandial (PP-Atenolol) after a one-week treatment with atenolol. Results were tested for the effects of atenolol via two-way ANOVA for the F vs F-Atenolol and PP vs PP-Atenolol states separately. Atenolol treatment decreased fasting and postprandial glycerol (p < 0.0001) and NEFA (p < 0.0001), postprandial epinephrine (p = 0.048), postprandial cortisol (p = 0.02), postprandial ASP (p = 0.04) and postprandial dopamine (p < 0.004). ConclusionAtenolol alters fatty acid metabolism and associated metabolic hormones including ASP during exercise in men with T2DM and its effects are more apparent during conditions of stress such as the postprandial state, acute exercise and obesity.

Down-regulation of hepatic ApoB100 expression during hot season in transition dairy cows

Heat stress is recognized as one of the main factors adversely affecting yield, reproduction and health of dairy ruminants. The peripartum period is the most critical phase for dairy cows. The interaction between heat stress and physiological stress imposed by the peripartum, might worsen the metabolic status of transition dairy cows. Therefore, the objective of the present study was to investigate the effect of hot season on metabolic status and on hepatic apolipoprotein B100 (ApoB100) expression during the peripartum period in Holstein dairy cows. Twenty-four multiparous Holstein cows were utilized in the study. Twelve cows gave birth in spring (SP: 28 March to 30 April). The remaining 12 cows gave birth in summer (SU: 15 June to 2 July). The two groups were balanced for parity and body condition score (BCS) and monitored from −30 to 35d relative to calving. Values of air temperature (°C) and relative humidity (%) were recorded at 1h intervals and were utilized to calculate the temperature–humidity index (THI). Milk production and BCS were recorded weekly. Blood samples were taken at 0800h from the jugular vein −30, −18, and −4d prepartum and 3, 17, and 35d postpartum. Plasma was analyzed for glucose, urea, cholesterol, β-OH butyrate (BHBA), non-esterified fatty acids (NEFA) and ApoB100. Liver biopsies were performed on d −30, 3, and 35 relative to day of calving, and tissue samples were used for histopathological examination, and for ApoB100 mRNA and protein determination. Milk yield in SU cows was lower than in their SP counterparts. During summer, transition cows showed lower glucose and cholesterol, higher NEFA and BHBA, had lower liver ApoB100 gene and protein expression and higher lipid accumulation in liver compared with transition cows during spring. The current study provides the first evidence about the negative effects of hot season on ApoB100 gene and protein expression in transition dairy cows. The down-regulation of ApoB100 expression together with higher circulating NEFA and altered lipid metabolism are likely to be responsible for the higher risk of liver lipidosis in transition SU cows. These metabolic conditions make transition cows more susceptible to metabolic diseases during hot season.

Increased Postprandial Nonesterified Fatty Acid Appearance and Oxidation in Type 2 Diabetes Is Not Fully Established in Offspring of Diabetic Subjects

BackgroundIt has been proposed that abnormal postprandial plasma nonesterified fatty acid (NEFA) metabolism may participate in the development of tissue lipotoxicity and type 2 diabetes (T2D). We previously found that non-diabetic offspring of two parents with T2D display increased plasma NEFA appearance and oxidation rates during intravenous administration of a fat emulsion. However, it is currently unknown whether plasma NEFA appearance and oxidation are abnormal during the postprandial state in these subjects at high-risk of developing T2D.MethodologyPalmitate appearance and oxidation rates and glycerol appearance rate were determined in eleven healthy offspring of two parents with T2D (positive family history, FH+), 13 healthy subjects without first-degree relatives with T2D (FH-) and 12 subjects with T2D at fasting, during normoglycemic hyperinsulinemic clamp and during continuous oral intake of a standard liquid meal to achieve steady postprandial NEFA and triacylglycerols (TG) without and with insulin infusion to maintain similar glycemia in all three groups.Principal FindingsPlasma palmitate appearance and oxidation were higher at fasting and during the clamp conditions in the T2D group (all P<0.05). In the postprandial state, palmitate appearance, oxidative and non oxidative rates were all elevated in T2D (all P<0.05) but not in FH+. Both T2D and FH+ displayed elevated postprandial TG vs. FH- (P<0.001). Acute correction of hyperglycemia during the postprandial state did not affect these group differences. Increased waist circumference and BMI were positively associated with elevated postprandial plasma palmitate appearance and oxidation.Conclusions/SignificancePostprandial plasma NEFA intolerance observed in subjects with T2D is not fully established in non-diabetic offspring of both parents with T2D, despite the presence of increased postprandial plasma TG in the later. Elevated postprandial plasma NEFA appearance and oxidation in T2D is observed despite acute correction of the exaggerated glycemic excursion in this group.

A Model of NEFA Dynamics with Focus on the Postprandial State

To improve the understanding of the mechanisms underlying the behavior of plasma non-esterified fatty acids (NEFA) in the postprandial state, we have developed a physiology-based mathematical model of plasma NEFA dynamics. Known physiological mechanisms are quantified and used to describe NEFA dynamics. Insulin is the major regulator of NEFA metabolism in the postprandial state. Plasma NEFA levels are thus highly dependent on the insulin concentration, the insulin sensitivity of adipose tissue, and the maximal lipolytic rate. In the postabsorptive state, e.g., at low insulin, adipose tissue lipolysis results in a net export of NEFA from adipose tissue to other tissues. Postprandially, the rise in insulin results in: Decreased lipolysis; a higher rate of lipoprotein lipase (LPL) activity; and decreased NEFA uptake and reesterification by adipose tissue stimulation of reesterification. The result is a drop in plasma NEFA after a carbohydrate containing meal. When insulin returns to postabsorptive levels, a rebound in plasma NEFA often occurs. This rebound is due to a restoration of lipolysis, a decrease in NEFA reesterification by adipose tissue and an increased LPL-as insulin activates LPL with a delay of several hours. In conclusion, movements of NEFA depend strongly on insulin-with postprandial plasma NEFA being almost inversely related to the insulin concentration in healthy humans. The model provides an integrative view of NEFA dynamics and a framework for quantitative and conceptual understanding of plasma NEFA fluxes.

Effects of coronary artery disease and percutaneous intervention on the cardiac metabolism of nonesterified fatty acids and insulin: Implications of diabetes mellitus

Nonesterified fatty acids (NEFA) and insulin have been implicated in the pathogenesis of diabetes mellitus (Type 2 diabetes) and coronary artery disease (CAD). We hypothesized that intracardiac levels of insulin and NEFA within the aortic root, coronary sinus and systemic venous levels would be different in patients with coronary atherosclerosis and/or diabetes. We also studied the metabolic cardiac response following percutaneous coronary intervention (PCI). A total of 67 subjects (42 males; mean age 60 +/- 11 years) were recruited, of which three groups were identified: Group I - those with no CAD or Type 2 diabetes (n = 17); Group II - those with CAD but no Type 2 diabetes (n = 40); and Group III - patients with Type 2 diabetes and CAD (n = 10). Of the whole cohort, 34 patients (51%) proceeded to PCI. NEFA and insulin levels were analysed using enzymatic colorimetric and a monoclonal immuno-autoanalyser techniques, respectively. Subsequently, fractional extraction (FFE) of both variables was calculated. Nonesterified fatty acids and insulin concentrations were lower in the aortic root versus coronary sinus (both P < 0.05). FFE of NEFA was 2x higher in Group I (P < 0.01) with a sevenfold reduction in insulin FFE in Group III. Following PCI, systemic NEFA levels increased significantly (P < 0.05) with no significant change seen within the coronary sinus (P = NS), whilst a reduction in insulin concentrations at all three sites was observed (all P < 0.01). No significant difference in FFE of NEFA was seen after PCI when comparing Groups II and III. There was a drop in insulin extraction in Group II (nondiabetic subjects, from 12% to -4%, P = 0.04), compared with an increase seen in Group III (Type 2 diabetes patients, from -4% to 3%, P = 0.03). There is an intracardiac gradient of NEFA and insulin in Groups I-III. Cardiac NEFA metabolism was higher in those with mild CAD compared with those with obstructive CAD whereas intracardiac insulin extraction was lower in Group III (diabetic) patients. PCI was associated with a systemic rise in NEFA, with a reduction in insulin levels and cardiac utilization, but these effects were blunted in diabetic patients.

A pilot study of the effects of pioglitazone and rosiglitazone on de novo lipogenesis in type 2 diabetes

Treatment of type 2 diabetes mellitus (T2DM) patients with pioglitazone results in a more favorable lipid profile, and perhaps more favorable cardiac outcomes, than treatment with rosiglitazone. Pioglitazone treatment increases VLDL-triacylglycerol clearance, but the role of de novo lipogenesis (DNL) has not been explored, and no direct comparison has been made between the thiazolidinediones (TZDs). Twelve subjects with T2DM and hypertriacylglyceridemia were randomized to either rosiglitazone or pioglitazone treatment. Stable isotope infusion studies were performed at baseline and after 20 weeks of treatment. Both treatments reduced glucose and HbA(1c) concentrations equally. Pioglitazone treatment resulted in a 40% reduction in hepatic DNL (P < 0.01) and in a 25% reduction in hepatic glucose production (P < 0.05), while rosiglitazone did not significantly change either parameter, although comparisons of changes between treatments were not significantly different. These pilot results indicate that pioglitazone reduces hepatic DNL while rosiglitazone does not. Larger follow-up studies are required to confirm differential effects of these agents definitively. The reduction in DNL may underlie altered assembly or atherogenicity of lipoprotein particles and may reflect PPARalpha or other non-PPARgamma actions on the liver by pioglitazone. These differences might help explain previously reported differences in lipid profiles and cardiovascular disease outcomes for rosiglitazone and pioglitazone.

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.

NEFA minimal model parameters estimated from the oral glucose tolerance test and the meal tolerance test

The kinetics of nonesterified fatty acid (NEFA) metabolism in humans requires quantification to facilitate understanding of diseases like type 1 and 2 diabetes, metabolic syndrome, and obesity, and the mechanisms underpinning various interventions. Oral glucose tolerance tests (OGTT) and glucose meal tolerance tests (MTT) are potentially useful procedures for enabling quantification of NEFA kinetics because they both cause transitory, but substantial, declines and then rebounds in plasma NEFA concentrations in response to physiologically relevant increases in plasma glucose. The Boston MINIMAL model of NEFA kinetics was developed to analyze data from the intravenous glucose tolerance test (IVGTT), but in this work, we present for the first time its application to modeling NEFA data from both OGTT and MTT studies. This model enables estimation of SFFA (micromol.l(-1).min(-1)) (a parameter describing the maximum rate of lipolysis), and KFFA (%/min) (a parameter related to NEFA oxidation rate). The model could well describe the trajectories of NEFA concentrations following an OGTT (R2 in excess of 0.97) but was not as successful with the MTT (R2>0.65). Model parameters derived from analysis of OGTT and MTT data were well identified with coefficients of variation generally less than 15%. Type 2 diabetes, body mass index, and dietary treatment (high-fat vs. high-glycemic-index diets) were all shown to have significant effects on model parameters. Modeling plasma NEFA concentrations over 24 h has helped to identify and quantify the extent that periprandial NEFA peaks and nocturnal elevation in plasma NEFA can be accounted for by our model.

A novel minimal model to describe NEFA kinetics following an intravenous glucose challenge

Dynamics of nonesterified fatty acid (NEFA) metabolism in humans requires quantification if we are to understand the etiology of such diseases as type 1 and 2 diabetes, as well as metabolic syndrome and obesity, or if we are to elucidate the mechanism of action of various interventions. We present a new compartmental model that employs the pattern of plasma glucose concentrations in healthy young adults to predict dynamic changes that occur in plasma NEFA concentrations during either a glucose-only intravenous glucose tolerance test, or an insulin-modified intravenous tolerance test, or a modified protocol during which variable-rate glucose infusions were administered to prevent plasma glucose from declining below 100 mg/dl. The model described all of the major features of NEFA response to an intravenous glucose tolerance test, including an initial latency phase, a phase during which plasma NEFA concentrations plummet to a nadir, and a rebound phase during which plasma NEFA concentrations may rise to a plateau concentration, which may be substantially higher than the initial basal NEFA concentration. This model is consistent with physiological processes and provides seven adjustable parameters that can be used to quantify NEFA production (lipolysis) and utilization (oxidation). When tested on data from the scientific literature, the range in estimated rate of lipolysis was 24-36 micromol.l(-1).min(-1) and for NEFA oxidation rate was 25-54 micromol.l(-1).min(-1). All model parameters were well identified and had coefficients of variation < 15% of their estimated values. It is concluded that this model is suitable to describe NEFA kinetics in human subjects.

Impaired Plasma Nonesterified Fatty Acid Tolerance Is an Early Defect in the Natural History of Type 2 Diabetes

Abnormal plasma nonesterified fatty acid (NEFA) metabolism may play a role in the development of type 2 diabetes. Our objectives were to demonstrate whether there is a defect in insulin-mediated suppression of plasma NEFA appearance (RaNEFA) and oxidation (OxNEFA) during enhanced intravascular triacylglycerol lipolysis early in the natural history of type 2 diabetes, and if so, to determine whether other mechanisms than reduced insulin-mediated suppression of intracellular lipolysis are involved. These are cross-sectional studies. The studies were performed at an academic clinical research center. Nine healthy subjects with both parents with type 2 diabetes (FH+) and nine healthy subjects with no first-degree relatives with type 2 diabetes (FH-) with similar anthropometric features were included in the studies. Pancreatic clamps and iv infusion of stable isotopic tracers ([1,1,2,3,3-(2)H5]-glycerol and [U-(13)C]-palmitate or [1,2-(13)C]-acetate) were performed while intravascular triacylglycerol lipolysis was simultaneously clamped by iv infusion of heparin plus Intralipid at low (fasting) and high insulin levels. Oral nicotinic acid (NA) was used to inhibit intracellular lipolysis. RaNEFA and OxNEFA were determined. During heparin plus Intralipid infusion at high plasma insulin levels, and despite similar intravascular lipolytic rates, FH+ had higher RaNEFA and OxNEFA than FH- (RaNEFA: 17.4+/-6.3 vs. 9.2+/-4.2; OxNEFA: 4.5+/-1.8 vs. 2.3+/-1.5 micromol/kg lean body mass/min), independent of NA intake, gender, age, and body composition. In the presence of NA, insulin-mediated suppression of RaNEFA was still observed in FH-, but not in FH+. Increased RaNEFA and OxNEFA during intravascular lipolysis at high insulin levels occur early in the natural history of type 2 diabetes.

Adaptations of Mammary Uptake and Nutrient Use to Once-Daily Milking and Feed Restriction in Dairy Cows

The aim of this study was to gain a clearer understanding of the different levels of regulation involved in the reduction in milk yield in response to once-daily milking and feed restriction. The treatments were designed as a 2×2 factorial arrangement of 2 milking frequencies (once- or twice-daily milking) and 2 feeding levels (70 or 98% of requirements determined 1 wk before the trial). The cows were surgically prepared to study the net mammary balance of the nutrients that are precursors of milk components. Mammary efficiency in synthesizing milk components was estimated using a milk output:mammary uptake ratio. No interaction was observed between the effects of milking frequency and feeding level on milk and blood parameters except for milk protein yield, milk fatty acid profile, and nonesterified fatty acids metabolism. Once-daily milking and feed restriction reduced milk yield by 5.1 and 2.9 kg/d and fat-corrected milk yield by 4.2 and 4.1 kg/d, respectively. Both treatments induced a decrease in mammary blood flow. Once-daily milking led to a reduction in the extraction rate of glucose but no changes to the lactose output:glucose uptake ratio. Feed restriction did not change the glucose extraction rate but tended to improve the lactose output:glucose uptake ratio. Under once-daily milking, the slight increase in milk fat content (0.34 percentage units) was linked to a depressed uptake of glucose and acetate but without any variations in the uptake of β-hydroxybutyrate and total glycerol and in the efficiency of acetate and β-hydroxybutyrate conversion to short- and medium-chain fatty acids in milk. The decline in milk fat and protein contents (−0.43 and −0.23 percentage units, respectively) under feed restriction was associated with relatively similar reductions in the mammary uptake of all nutrients and with enhanced conversion of the glucose taken up by the mammary gland and used for lactose synthesis. As a result, once-daily milking and feed restriction seem to affect milk yield through mechanisms that may be different and relatively independent.