Lower Plasma Free Fatty Acid Research Articles

Vascular dysfunction in Type 2 diabetes: emerging targets for therapy

Vascular dysfunction associated with Type 2 diabetes is initially manifested in the pre-diabetic condition and continuously expressed as this complex disease progresses to include other cardiovascular complications that collectively increase patient risk to morbidity and mortality. Many factors are known to affect vascular function and this review focuses on the role of adipokines and obesity in this process. Growing evidence suggests that adipose-derived adipokines, such as cytokines, chemokines and hormones, plays a significant role in the regulation of vascular function. Inhibition of vascular reactive oxygen species (ROS) formation and lowering plasma free fatty acid level are all potential therapeutic targets for type 2 diabetes-induced vascular dysfunction. Bariatric surgery is a relatively new and more aggressive treatment for the morbidly obese patient that also results in an instant and obvious improvement of vascular function through as yet unexplained mechanisms. These therapies show great promise for the prevention and cure of diabetes-induced vascular dysfunction.

Comparison of the antilipolytic effects of an A1 adenosine receptor partial agonist in normal and diabetic rats

Elevated plasma free fatty acid (FFA) concentrations play a role in the pathogenesis of type 2 diabetes (2DM). Antilipolytic agents that reduce FFA concentrations may be potentially useful in the treatment of 2DM. Our previous observation that CVT-3619 lowered plasma FFA and triglyceride concentrations in rats and enhanced insulin sensitivity in rodents with dietary-induced forms of insulin resistance suggested that it might be of use in the treatment of patients with 2DM. The present study was undertaken to compare the antilipolytic effects of CVT-3619 in normal (Sprague Dawley, SD) and Zucker diabetic fatty (ZDF) rats. ZDF rats had significantly higher fat pad weight, glucose, insulin and FFA concentrations than those of SD rats. EC(50) values for forskolin-stimulated FFA release from isolated adipocytes from SD and ZDF rats were 750 and 53 nM, respectively (p < 0.05). Maximal forskolin stimulation of FFA release was significantly (p < 0.01) less in ZDF rats (133 +/- 60 microM) compared with SD rats (332 +/- 38 microM). EC(50) values for isoproterenol to increase lipolysis in adipocytes from SD and ZDF rats were 2 and 7 nM respectively. Maximal isoproterenol-stimulated lipolysis was significantly (p < 0.01) lower in adipocytes from ZDF rats (179 +/- 23 microM) compared with SD rats (343 +/- 27 microM). Insulin inhibited lipolysis in adipocytes from SD rats with an IC(50) value of 30 pM, whereas adipocytes from ZDF rats were resistant to the antilipolytic actions of insulin. In contrast, IC(50) values for CVT-3619 to inhibit the release of FFA from SD and ZDF adipocytes were essentially the same (63 and 123 nM respectively). CVT-3619 inhibited lipolysis more than insulin in both SD (86 vs. 46%, p < 0.001) and ZDF (80 vs. 13%, p < 0.001) adipocytes. In in vivo experiments, CVT-3619 (5 mg/kg, PO) lowered FFA to a similar extent in both groups. Plasma concentrations of CVT-3619 were not different in SD and ZDF rats. There was no significant difference in the messenger RNA expression of the A(1) receptors relative to beta-actin expression in adipocytes from SD (0.98 +/- 0.2) and ZDF rats (0.99 +/- 0.3). The antilipolytic effects of CVT-3619 appear to be independent of insulin resistance and animal model.

Effect of curcumin supplementation on blood glucose, plasma insulin, and glucose homeostasis related enzyme activities in diabetic db/db mice

We investigated the effect of curcumin on insulin resistance and glucose homeostasis in male C57BL/KsJ-db/db mice and their age-matched lean non-diabetic db/+ mice. Both db/+ and db/db mice were fed with or without curcumin (0.02%, wt/wt) for 6 wks. Curcumin significantly lowered blood glucose and HbA 1c levels, and it suppressed body weight loss in db/db mice. Curcumin improved homeostasis model assessment of insulin resistance and glucose tolerance, and elevated the plasma insulin level in db/db mice. Hepatic glucokinase activity was significantly higher in the curcumin-supplemented db/db group than in the db/db group, whereas glucose-6-phosphatase and phosphoenolpyruvate carboxykinase activities were significantly lower. In db/db mice, curcumin significantly lowered the hepatic activities of fatty acid synthase, beta-oxidation, 3-hydroxy-3-methylglutaryl coenzyme reductase, and acyl-CoA: cholesterol acyltransferase. Curcumin significantly lowered plasma free fatty acid, cholesterol, and triglyceride concentrations and increased the hepatic glycogen and skeletal muscle lipoprotein lipase in db/db mice. Curcumin normalized erythrocyte and hepatic antioxidant enzyme activities (superoxide dismutase, catalase, gluthathione peroxidase) in db/db mice that resulted in a significant reduction in lipid peroxidation. However, curcumin showed no effect on the blood glucose, plasma insulin, and glucose regulating enzyme activities in db/+ mice. These results suggest that curcumin seemed to be a potential glucose-lowering agent and antioxidant in type 2 diabetic db/db mice, but had no affect in non-diabetic db/+ mice.

Rosiglitazone Prevents Free Fatty Acid-Induced Vascular Endothelial Dysfunction

Elevated plasma free fatty acid (FFA) levels contribute significantly to insulin resistance, while thiazolidinediones (TZDs) improve insulin resistance and lower plasma FFA levels in diabetic patients by acting as agonists of the peroxisome proliferator-activated receptor-γ (PPARγ). In particular, the TZD rosiglitazone improves endothelial function and increases nitric oxide release in patients with type 2 diabetes. It would be expected that reducing FFA by activating PPARγ would improve triglyceride/heparin-induced endothelial dysfunction. This randomized, double blind, placebo-controlled study examined the effects of 8 mg of rosiglitazone daily or placebo, given orally for 3 weeks to 16 healthy males. All subjects received 20% Intralipid, a triglyceride emulsion, and heparin by intravenous infusion to achieve FFA levels known to produce endothelial dysfunction and insulin resistance. Forearm blood flow (FBF) responses to acetylcholine, an endothelium-dependent vasodilator, and nitroglycerine, an endothelium-independent vasodilator, were measured in both arms by strain-gauge plethysmography. Circulating levels of C-reactive protein (CRP) and asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, also were measured. Rosiglitazone administration did not alter FBF reactivity. Infusing triglyceride and heparin substantially increased plasma FFA concentrations, increased FBF in both study groups, and lowered endothelium-dependent vasodilation by 38%. Reduced reactivity to acetylcholine was observed in placebo recipients but not in those given rosiglitazone. In neither group did infusion of triglyceride/heparin influence endothelium-independent vasodilation in response to nitroglycerine. Levels of CRP remained unchanged, but insulin sensitivity and plasma ADMA levels decreased in the presence of elevated FFA levels in both study groups. In this trial rosiglitazone mitigated the increase in FFA levels following triglyceride/heparin infusion and also prevented FFA-induced endothelial dysfunction. These effects were observed in healthy individuals before any change in insulin sensitivity or plasma ADMA concentration.

Critical role of cholesterol ester transfer protein in nicotinic acid-mediated HDL elevation in mice

Nicotinic acid is a commonly used anti-dyslipidemic agent that increases plasma levels of HDL-cholesterol and decrease triglycerides (TG), and VLDL- and LDL-cholesterol. The most well-studied effect of nicotinic acid is its ability to lower plasma free fatty acids, which has been observed in humans and many animal models. However, its ability to raise HDL in humans has not been replicated in animal models, which precludes studying the mechanism of HDL elevation. Here we studied lipid-modulating effects of nicotinic acid in mice carrying genomic DNA fragments that drive expression of various human genes in the mouse liver. Treatment with nicotinic acid reduced serum levels of HDL cholesterol in wild-type and human apolipoprotein B100 (apoB100)-transgenic mice. In contrast, nicotinic acid treatment of mice that express human cholesteryl ester transfer protein (CETP), with or without concomitant apoB100 expression, resulted in a significant increase of HDL cholesterol and reduction of TG, VLDL- and LDL-cholesterol. These data demonstrate a critical role of CETP in nicotinic acid-mediated HDL elevation, and suggest that mice carrying the human CETP gene may be useful animal models for studying the HDL-elevating effect of nicotinic acid.

Combined Use of Rosiglitazone and Fenofibrate in Patients With Type 2 Diabetes

Elevated plasma free fatty acid (FFA) levels are responsible for much of the insulin resistance in obese patients with type 2 diabetes. To lower plasma FFA levels effectively and long term, we have treated eight obese patients with type 2 diabetes for 2 months with placebo followed by 2 months of treatment with a combination of rosiglitazone (RGZ) (8 mg/day) and fenofibrate (FFB) (160 mg/day) in a single-blind placebo-controlled study design. Compared with placebo, RGZ/FFB lowered mean 24-h plasma FFA levels 30% (P < 0.03) and mean 24-h glucose levels 23% (P < 0.03) and increased insulin-stimulated glucose uptake (glucose rate of disappearance [G(R)(d)], determined using euglycemic-hyperinsulinemic clamp) 442% (P < 0.01), oral glucose tolerance (area under the curve for 3-h oral glucose tolerance test) 28% (P < 0.05), and plasma adiponectin levels 218% (P < 0.01). These RGZ/FFB results were compared with results obtained in five patients treated with RGZ alone. RGZ/FFB prevented the fluid retention usually associated with RGZ (-1.6 vs. 5.6%, P < 0.05), lowered fasting plasma FFA more effectively than RGZ alone (-22 vs. 5%, P < 0.05), and tended to be more effective than RGZ alone in lowering A1C (-0.9 vs. -0.4%) and triglyceride levels (-38 vs. -5%) and increasing G(Rd) (442 vs. 330%). We conclude that RGZ/FFB is a promising new therapy for type 2 diabetes that lowers plasma FFA more than RGZ alone and in contrast to RGZ does not cause water retention and weight gain.

Recent findings concerning thiazolidinediones in the treatment of diabetes

Thiazolidinediones (TZDs) are peroxisomal proliferator-activated receptor (PPAR)-γ agonists. They increase insulin action through several mechanisms including: stimulation of the expression of genes that increase fat oxidation and lower plasma free fatty acid levels; increased expression, synthesis and release of adiponectin; and stimulation of adipocyte differentiation resulting in more and smaller fat cells. TZDs lower blood sugar comparably to sulfonylureas and metformin. The clinical use of TZDs is limited due to the long duration of time required before they reach their full blood sugar-lowering action (3 – 4 months) and adverse effects such as fluid retention, resulting in excessive weight gain and occasionally in peripheral and/or pulmonary oedema and congestive heart failure. Troglitazone, a TZD that has since been removed from the market because of hepatoxicity, has been demonstrated to decrease the progression from normal or impaired glucose tolerance to overt Type 2 diabetes mellitus. Pioglitazone, another TZD, marginally decreased the incidence of cardiovascular complications in patients with Type 2 diabetes mellitus (PROactive trial). Other, as yet, unapproved uses of TZDs include: non-alcoholic fatty liver disease, in which TZDs reduced hepatic fat accumulation and improved liver function tests; polycystic ovary syndrome, where TZDs improved ovulation, hirsutism and endothelial dysfunction; and lipodystrophies, where TZDs increased body fat (marginally) and decrease liver size. Lastly, because PPAR-α and -γ agonists improve atherosclerotic vascular disease and insulin sensitivity, respectively, dual PPAR-α/γ agonists, which are currently undergoing clinical trials, may be useful in treating patients with the metabolic syndrome.

Free Fatty Acids Produce Insulin Resistance and Activate the Proinflammatory Nuclear Factor-κB Pathway in Rat Liver

To study mechanisms by which free fatty acids (FFAs) cause hepatic insulin resistance, we have used euglycemic-hyperinsulinemic clamping with and without infusion of lipid/heparin (to raise or to lower plasma FFAs) in alert male rats. FFA-induced hepatic insulin resistance was associated with increased hepatic diacylglycerol content (+210%), increased activities of two serine/threonine kinases (protein kinase C-delta and inhibitor of kappaB [IkappaB] kinase-beta), increased activation of the proinflammatory nuclear factor-kappaB (NF-kappaB) pathway (IkappaB kinase-beta, +640%; IkappaB-alpha, -54%; and NF-kappaB, +73%), and increased expression of inflammatory cytokines (tumor necrosis factor-alpha, +1,700% and interleukin-1beta, +440%) and plasma levels of monocyte chemoattractant protein-1 (+220%). We conclude that FFAs caused hepatic insulin resistance, which can produce overproduction of glucose and hyperglycemia, and initiated inflammatory processes in the liver that could potentially result in the development of steatohepatitis.

Effects of free fatty acids on plasma resistin and insulin resistance in awake rats

Resistin has been postulated to play a role in obesity-related insulin resistance. To explore this possibility, we have investigated effects of acute euglycemic (5.2 ± 0.1 mmol/L) hyperinsulinemia (96 ± 8 μU/mL) with and without concurrent infusion of lipid plus heparin (to raise or lower plasma free fatty acid [FFA] levels) on glucose turnover and plasma resistin levels in alert rats. Plasma FFA concentrations increased during lipid/heparin (L/H) infusion (from 0.82 to 2.86 mmol/L, P < .001) and decreased (from 0.83 to 0.21 mmol/L, P < .001) in controls who were infused with insulin but not with L/H. L/H infusion reduced insulin suppression of endogenous glucose production by ∼90% (from 28.9 to 3.1 mg· kg −1 · min −1, P < .001) and insulin-stimulated glucose uptake (glucose rate of disappearance) by 78% (from 30.8% to 6.9%, P < .001). Plasma resistin levels increased by 46% (from 39.9 to 58.4 μg/L, P < .05) during L/H infusion and did not change in controls (39.7 vs 39.3 μg/L). Plasma ghrelin levels decreased by 41% (from 892 to 584 ng/L, P < .05) in response to hyperinsulinemia, whereas concurrent L/H infusion had no additional effect on ghrelin levels (584 ± 67 vs 548 ± 82 ng/L). In summary, we found that FFA induced hepatic insulin resistance, and to a lesser extent, peripheral insulin resistance was associated with elevated plasma resistin levels. We conclude that FFA-induced release of resistin may contribute to the development of FFA-induced insulin resistance in rats.

Glucose ingestion during exercise blunts exercise-induced gene expression of skeletal muscle fat oxidative genes

Ingestion of carbohydrate during exercise may blunt the stimulation of fat oxidative pathways by raising plasma insulin and glucose concentrations and lowering plasma free fatty acid (FFA) levels, thereby causing a marked shift in substrate oxidation. We investigated the effects of a single 2-h bout of moderate-intensity exercise on the expression of key genes involved in fat and carbohydrate metabolism with or without glucose ingestion in seven healthy untrained men (22.7 +/- 0.6 yr; body mass index: 23.8 +/- 1.0 kg/m(2); maximal O(2) consumption: 3.85 +/- 0.21 l/min). Plasma FFA concentration increased during exercise (P < 0.01) in the fasted state but remained unchanged after glucose ingestion, whereas fat oxidation (indirect calorimetry) was higher in the fasted state vs. glucose feeding (P < 0.05). Except for a significant decrease in the expression of pyruvate dehydrogenase kinase-4 (P < 0.05), glucose ingestion during exercise produced minimal effects on the expression of genes involved in carbohydrate utilization. However, glucose ingestion resulted in a decrease in the expression of genes involved in fatty acid transport and oxidation (CD36, carnitine palmitoyltransferase-1, uncoupling protein 3, and 5'-AMP-activated protein kinase-alpha(2); P < 0.05). In conclusion, glucose ingestion during exercise decreases the expression of genes involved in lipid metabolism rather than increasing genes involved in carbohydrate metabolism.

Mitochondrial Glycerol-3-phosphate Acyltransferase-1 Is Essential inLiver for the Metabolism of ExcessAcyl-CoAs

In vitro studies suggest that the mitochondrial glycerol-3-phosphate acyltransferase-1 (mtGPAT1) isoform catalyzes the initial and rate-controlling step in glycerolipid synthesis and aids in partitioning acyl-CoAs toward triacylglycerol synthesis and away from degradative pathways. To determine whether the absence of mtGPAT1 would increase oxidation of acyl-CoAs and restrict the development of hepatic steatosis, we fed wild type and mtGPAT1-/- mice a diet high in fat and sucrose (HH) for 4 months to induce the development of obesity and a fatty liver. Control mice were fed a diet low in fat and sucrose (LL). With the HH diet, absence of mtGPAT1 resulted in increased partitioning of acyl-CoAs toward oxidative pathways, demonstrated by 60% lower hepatic triacylglycerol content and 2-fold increases in plasma beta-hydroxybutyrate, acylcarnitines, and hepatic mRNA expression of mitochondrial HMG-CoA synthase. Despite the increase in fatty acid oxidation, liver acyl-CoA levels were 3-fold higher in the mtGPAT1-/- mice fed both diets. A lack of difference in CPT1 and FAS mRNA expression between genotypes suggested that the increased acyl-CoA content was not because of increased de novo synthesis, but instead, to an impaired ability to use long-chain acyl-CoAs derived from the diet, even when the dietary fat content was low. Hyperinsulinemia and reduced glucose tolerance on the HH diet was greater in the mtGPAT1-/- mice, which did not suppress the expression of the gluconeogenic genes glucose-6-phosphatase and phosphoenolpyruvate carboxykinase. This study demonstrates that mtGPAT1 is essential for normal acyl-CoA metabolism, and that the absence of hepatic mtGPAT1 results in the partitioning of fatty acids away from triacylglycerol synthesis and toward oxidation and ketogenesis.

Inhibition of adipose tissue lipolysis increases intramuscular lipid and glycogen use in vivo in humans

This study investigates the consequences of inhibition of adipose tissue lipolysis on skeletal muscle substrate use. Ten subjects were studied at rest and during exercise and subsequent recovery under normal, fasting conditions (control trial, CON) and following administration of a nicotinic acid analog (low plasma free fatty acid trial, LFA). Continuous [U-13C]palmitate and [6,6-2H2]glucose infusions were applied to quantify plasma free fatty acid (FFA) and glucose oxidation rates and to estimate intramuscular triacylglycerol (IMTG) and glycogen use. Muscle biopsies were collected to measure 1) fiber type-specific IMTG content; 2) allosteric regulators of hormone-sensitive lipase (HSL), glycogen phosphorylase, and pyruvate dehydrogenase; and 3) the phosphorylation status of HSL at Ser563 and Ser565. Administration of a nicotinic acid analog (acipimox) substantially reduced plasma FFA rate of appearance and subsequent plasma FFA concentrations (P < 0.0001). At rest, this substantially reduced plasma FFA oxidation rates, which was compensated by an increase in the estimated IMTG use (P < 0.05). During exercise, the progressive increase in FFA rate of appearance, uptake, and oxidation was prevented in the LFA trial and matched by greater IMTG and glycogen use. Differential phosphorylation of HSL or relief of its allosteric inhibition by long-chain fatty acyl-CoA could not explain the increase in muscle TG use, but there was evidence to support the contention that regulation may reside at the level of the glucose-fatty acid cycle. This study confirms the hypothesis that plasma FFA availability regulates both intramuscular lipid and glycogen use in vivo in humans.

Inhibition Of Adipose Tissue Lipolysis Increases Intramuscular Lipid Use In Type 2 Diabetes Patients

Numerous studies have reported the association between elevated plasma free fatty acid (FFA) concentrations, intramyocellular triacylglycerol (IMTG) accumulation and the development of insulin resistance. Excess IMTG accretion is the result of an imbalance between FFA uptake, IMTG deposition and its subsequent mobilisation and/or oxidation. Recent data indicate that this imbalance, and not the actual size or distribution of the IMTG pool, is responsible for the development of insulin resistance. Therefore, the turnover of the IMTG pool should form a major therapeutic target in the prevention and treatment of skeletal muscle insulin resistance. PURPOSE To investigate the consequences of adipose tissue lipolytic inhibition on skeletal muscle substrate use. METHODS Ten type 2 diabetes patients were studied at rest, during exercise and subsequent recovery under normal, fasting conditions (CON) and following administration of a nicotinic acid analogue (LFA). Continuous [U-13C]palmitate and [6,6-2H2]glucose infusions were applied to quantify plasma FFA and glucose oxidation rates, and to estimate intramyocellular lipid and glycogen use. Muscle biopsies were collected before and after exercise to determine net changes in fibre type specific lipid and glycogen content. RESULTS In the LFA trial, plasma FFA rate of appearance was effectively reduced, resulting in 2–5 fold lower plasma FFA concentrations (P<0.001). Plasma FFA oxidation rates were substantially reduced at rest, during exercise and recovery in the LFA trial, which was compensated by an increase in both IMTG and endogenous carbohydrate use. Plasma glucose disposal rates did not differ between trials. During exercise, IMTG use averaged 0.18 ± 0.05 vs 0.08 ± 0.03 g/min in the LFA and CON trial, respectively (P<0.01). In accordance to these tracer data, a greater net decline in type I and type II muscle fiber lipid content was observed following exercise in the LFA vs the CON trial (P<0.05). CONCLUSION This study shows that plasma FFA availability regulates IMTG use and introduces adipose tissue lipolytic inhibition as a means to augment IMTG use in type 2 diabetes patients. The latter seems to represent an effective strategy to improve whole-body insulin sensitivity.

Inhibition Of Adipose Tissue Lipolysis Increases Intramuscular Lipid Use In Type 2 Diabetes Patients

Numerous studies have reported the association between elevated plasma free fatty acid (FFA) concentrations, intramyocellular triacylglycerol (IMTG) accumulation and the development of insulin resistance. Excess IMTG accretion is the result of an imbalance between FFA uptake, IMTG deposition and its subsequent mobilisation and/or oxidation. Recent data indicate that this imbalance, and not the actual size or distribution of the IMTG pool, is responsible for the development of insulin resistance. Therefore, the turnover of the IMTG pool should form a major therapeutic target in the prevention and treatment of skeletal muscle insulin resistance. PURPOSE To investigate the consequences of adipose tissue lipolytic inhibition on skeletal muscle substrate use. METHODS Ten type 2 diabetes patients were studied at rest, during exercise and subsequent recovery under normal, fasting conditions (CON) and following administration of a nicotinic acid analogue (LFA). Continuous [U-13C]palmitate and [6,6-2H2]glucose infusions were applied to quantify plasma FFA and glucose oxidation rates, and to estimate intramyocellular lipid and glycogen use. Muscle biopsies were collected before and after exercise to determine net changes in fibre type specific lipid and glycogen content. RESULTS In the LFA trial, plasma FFA rate of appearance was effectively reduced, resulting in 2–5 fold lower plasma FFA concentrations (P<0.001). Plasma FFA oxidation rates were substantially reduced at rest, during exercise and recovery in the LFA trial, which was compensated by an increase in both IMTG and endogenous carbohydrate use. Plasma glucose disposal rates did not differ between trials. During exercise, IMTG use averaged 0.18 ± 0.05 vs 0.08 ± 0.03 g/min in the LFA and CON trial, respectively (P<0.01). In accordance to these tracer data, a greater net decline in type I and type II muscle fiber lipid content was observed following exercise in the LFA vs the CON trial (P<0.05). CONCLUSION This study shows that plasma FFA availability regulates IMTG use and introduces adipose tissue lipolytic inhibition as a means to augment IMTG use in type 2 diabetes patients. The latter seems to represent an effective strategy to improve whole-body insulin sensitivity.

Enterostatin decreases postprandial pancreatic UCP2 mRNA levels and increases plasma insulin and amylin

This study investigated the chronic effect of enterostatin on body weight and some of the associated changes in postprandial metabolism. Rats were adapted to 6 h of food access/day and a choice of low-fat and high-fat (HF) food and then given enterostatin or vehicle by an intraperitoneally implanted minipump delivering 160 nmol enterostatin/h continuously over a 5-day infusion period. Enterostatin resulted in a slight but significant reduction of HF intake and body weight. After the last 6-h food access period, enterostatin-treated animals had lower plasma triglyceride and free fatty acid but higher plasma glucose and lactate levels than control animals. Enterostatin infusion resulted in increased uncoupling protein-2 (UCP2) expression in various tissues, including epididymal fat and liver. UCP2 was reduced in the pancreas of enterostatin-treated animals, and this was associated with increased plasma levels of insulin and amylin. Whether these two hormones are involved in the observed decreased food intake due to enterostatin remains to be determined. As lipid metabolism appeared to be altered by enterostatin, we measured peroxisome proliferator-activated receptor (PPAR) expression in tissues and observed that PPARalpha, -beta, -gamma1, and -gamma2 expression were modified by enterostatin in epididymal fat, pancreas, and liver. This further links altered lipid metabolism with body weight loss. Our data suggest that alterations in UCP2 and PPARgamma2 play a role in the control of insulin and amylin release from the pancreas. This implies that enterostatin changes lipid and carbohydrate metabolic pathways in addition to its effects on food intake and energy expenditure.

Uncoupling proteins in human heart

Abnormal energetic activity in heart failure correlates inversely with plasma free-fatty-acid concentrations. However, the link between energetic and metabolic abnormalities is unknown. To investigate this association, we obtained blood samples from 39 patients undergoing coronary artery bypass graft surgery. Patients fasted overnight before samples were taken. When plasma free-fatty-acid concentrations were raised, cardiac mitochondrial uncoupling proteins (UCP) increased (isoform UCP2, p<0.0001; isoform UCP3, p=0.0036) and those of glucose transporter (GLUT4) protein decreased (cardiac, p=0.0001; skeletal muscle, p=0.0006). Consequently, energy deficiency in heart failure might result from increased mitochondrial UCPs (ie, less efficient ATP synthesis) and depleted GLUT4 (ie, reduced glucose uptake). New treatment to correct these energy defects would be to simultaneously lower plasma free fatty acids and provide an alternative energy source.

Blood pressure and cardiac autonomic nervous system in obese type 2 diabetic patients: effect of metformin administration

Background Hyperinsulinemia/insulin resistance and elevated plasma free fatty acids (FFA) levels are involved in the hypertension and cardiac sympathetic overactivity. Metformin improves insulin action and lower plasma FFA concentrations. We investigate the possible effect of metformin on arterial blood pressure (BP) and cardiac sympathetic nervous system. Methods One hundred twenty overweight type 2 diabetic patients were treated by placebo ( n = 60) + diet or metformin (850 mg twice daily) ( n = 60) + diet for 4 months, to evaluate the effect of metformin treatment on the cardiac autonomic nervous system. Insulin resistance was measured by the Homeostasis Model Assessment (HOMA) index. Heart rate variability (HRV) assessed cardiac sympathovagal balance. Results Metformin treatment, but not placebo treatment, was associated with a decrease in fasting plasma glucose ( P < .05), insulin ( P < .05), triglyceride ( P < .05), and FFA ( P < .03) concentrations and HOMA index ( P < .03). Metformin treatment was also associated with a significant improvement in cardiac sympathovagal balance but not in mean arterial BP. Furthermore, in a multivariate analysis, delta change in sympathovagal balance index (LF/HF ratio) were associated with delta change in plasma FFA concentrations and HOMA index independently of gender and delta change in plasma triglyceride and HbA1c concentrations. Conclusions Our study demonstrated that metformin treatment might be useful for improving cardiac sympathovagal balance in obese type 2 diabetic patients.

Adipose-specific peroxisome proliferator-activated receptor γ knockout causes insulin resistance in fat and liver but not in muscle

Syndrome X, typified by obesity, insulin resistance (IR), dyslipidemia, and other metabolic abnormalities, is responsive to antidiabetic thiazolidinediones (TZDs). Peroxisome proliferator-activated receptor (PPAR) gamma, a target of TZDs, is expressed abundantly in adipocytes, suggesting an important role for this tissue in the etiology and treatment of IR. Targeted deletion of PPARgamma in adipose tissue resulted in marked adipocyte hypocellularity and hypertrophy, elevated levels of plasma free fatty acids and triglyceride, and decreased levels of plasma leptin and ACRP30. In addition, increased hepatic glucogenesis and IR were observed. Despite these defects, blood glucose, glucose and insulin tolerance, and insulin-stimulated muscle glucose uptake were all comparable to those of control mice. However, targeted mice were significantly more susceptible to high-fat diet-induced steatosis, hyperinsulinemia, and IR. Surprisingly, TZD treatment effectively reversed liver IR, whereas it failed to lower plasma free fatty acids. These results suggest that syndrome X may be comprised of separable PPARgamma-dependent components whose origins and therapeutic sites may reside in distinct tissues.

Free fatty acids trigger apoptosis and inhibit cell cycle progression in human vascular endothelial cells

Plasma free fatty acid (FFA) concentrations are increased in states of insulin resistance and impair endothelial function. Because the underlying mechanisms are largely unknown, we examined selected, purified FFAs' (100-300 micromol/l, 24-48 h) action on apoptosis, cell cycle distribution, and associated gene/protein expression in human umbilical vein endothelial cells (HUVECs). Stearic acid, but not oleic acid, time and concentration dependently increased endothelial apoptosis by fivefold (n=6, P<0.01), whereas polyunsaturated FFAs (PUFAs; linoleic, gamma-linolenic, and arachidonic acid) exerted proapoptotic activity only at 300 micromol/l (P<0.05). Proapoptotic FFA action increased with FFAs' number of double bonds and with protein expression of the apoptosis promotor bak. The G0/G1 cell cycle arrest (n=6, P<0.05) induced by stearic acid (+14%) and PUFAs (+30%) is reflected by up-regulation of p21(WAF-1/Cip1). In addition, all FFAs concentration dependently reduced (P<0.05) gene/protein expression of clusterin (-54%), NF-kappaB's inhibitor, IkappaBalpha (-50%), endothelin-1 (-44%), and endothelial NO synthase (-44%). Plasma samples obtained from individuals with elevated plasma FFAs (372+/-22 micromol/l) increased endothelial apoptosis by 4.2-fold (P<0.001, n=10) compared with intra-individually matched low plasma FFA (56+/-21 micromol/l) conditions, underlining the results obtained by defined FFA stimulation. In conclusion, FFA structure differently affects endothelial cell proliferation and apoptosis, both representing key factors in the development of micro- and macrovascular dysfunction.

High-fat diet elevates resting intramuscular triglyceride concentration and whole body lipolysis during exercise.

This study determined the role of intramuscular triglyceride (IMTG) and adipose lipolysis in the elevated fat oxidation during exercise caused by a high-fat diet. In four separate trials, six endurance-trained cyclists exercised at 50% peak O2 consumption for 1 h after a two-day control diet (22% fat, CON) or an isocaloric high-fat diet (60% fat, HF) with or without the ingestion of acipimox, an adipose lipolysis inhibitor, before exercise. During exercise, HF elevated fat oxidation by 72% and whole body lipolysis [i.e., the appearance rate of glycerol in plasma (Ra glycerol)] by 79% compared with CON (P < 0.05), and this was associated with a 36% increase (P < 0.05) in preexercise IMTG concentration. Although acipimox lowered plasma free fatty acid (FFA) availability, HF still increased fat oxidation and Ra glycerol to the same magnitude above control as the increase caused by HF without acipimox (i.e., both increased fat oxidation 13-14 micromol.kg(-1).min(-1)). In conclusion, the marked increase in fat oxidation after a HF diet is associated with elevated IMTG concentration and whole body lipolysis and does not require increased adipose tissue lipolysis and plasma FFA concentration during exercise. This suggests that altered substrate storage in skeletal muscle is responsible for increased fat oxidation during exercise after 2 days of an HF diet.