bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of exercise carbohydrate metabolism by estrogen and progesterone in women
Authors: D'Eon Tara M. , Sharoff Carrie , Chipkin Stuart R. , Grow Dan , Ruby Brent C. , Braun Barry
Published: March 2015

To assess the roles of endogenous estrogen (E2) and progesterone (P4) in regulating exercise carbohydrate use, we used pharmacological suppression and replacement to create three distinct hormonal environments: baseline (B), with E2 and P4 low; estrogen only (E), with E2 high and P4 low; and estrogen/progesterone (E + P), with E2 and P4high. Blood glucose uptake (Rd), total carbohydrate oxidation (CHOox), and estimated muscle glycogen utilization (EMGU) were assessed during 60 min of submaximal exercise by use of stable isotope dilution and indirect calorimetry in eight eumenorrheic women. Compared with B (1.26 ± 0.04 g/min) and E + P (1.27 ± 0.04 g/min), CHOox was lower with E (1.05 ± 0.02 g/min). Glucose Rd tended to be lower with E and E + P relative to B. EMGU was 25% lower with E than with B or E + P. Plasma free fatty acids (FFA) were inversely related to EMGU ( r 2 = 0.49). The data suggest that estrogen lowers CHOox by reducing EMGU and glucose Rd. Progesterone increases EMGU but not glucose Rd. The opposing actions of E2 and P4 on EMGU may be mediated by their impact on FFA availability or vice versa.
Insulin resistance, intramyocellular lipid content, and plasma adiponectin in patients with type 1 diabetes
Authors: Perseghin Gianluca , Lattuada Guido , Danna Massimo , Sereni Lucia Piceni , Maffi Paola , De Cobelli Francesco , Battezzati Alberto , Secchi Antonio , Del Maschio Alessandro , Luzi Livio
Published: March 2015

Insulin resistance is a key pathogenic factor of type 2 diabetes (T2DM); in contrast, in type 1 diabetes (T1DM) it is considered a secondary alteration. Increased intramyocellular lipid (IMCL) content accumulation and reduced plasma adiponectin were suggested to be pathogenic events of insulin resistance in T2DM. This study was designed to assess whether IMCL content and plasma adiponectin were also associated with the severity of insulin resistance in T1DM. We studied 18 patients with T1DM, 7 older and overweight/obese patients with T2DM, and 15 nondiabetic, insulin-resistant offspring of T2DM parents (OFF) and 15 healthy individuals (NOR) as appropriate control groups matched for anthropometric features with T1DM patients by means of the euglycemic hyperinsulinemic clamp combined with the infusion of [6,6-2H2]glucose and 1H magnetic resonance spectroscopy of the calf muscles. T1DM and T2DM patients showed reduced insulin-stimulated glucose metabolic clearance rate (MCR: 5.1 ± 0.6 and 3.2 ± 0.8 ml · kg–1 · min–1) similar to OFF (5.3 ± 0.4 ml · kg–1 · min–1) compared with NOR (8.5 ± 0.5 ml · kg–1 · min–1, P < 0.001). Soleus IMCL content was increased in T1DM (112 ± 15 AU), T2DM (108 ± 10 AU) and OFF (82 ± 13 AU) compared with NOR (52 ± 7 AU, P < 0.05) and the result was inversely proportional to the MCR ( R2 = 0.27, P < 0.001); an association between IMCL content and Hb A1c was found only in T1DM ( R2 = 0.57, P < 0.001). Fasting plasma adiponectin was reduced in T2DM (7 ± 1 μg/ml, P = 0.01) and OFF (11 ± 1 μg/ml, P = 0.03) but not in T1DM (25 ± 6 μg/ml), whose plasma level was increased with respect to both OFF ( P = 0.03) and NOR (16 ± 2 μg/ml, P = 0.05). In conclusion, in T1DM, T2DM, and OFF, IMCL content was associated with insulin resistance, demonstrating that IMCL accretion is a marker of insulin resistance common to both primary genetically determined and secondary metabolic (chronic hyperglycemia) alterations. The increased adiponectin levels in insulin-resistant patients with T1DM, in contrast to the reduced levels found in patients with T2DM and in OFF, demonstrated that the relationship of adiponectin to insulin resistance in humans is still unclear.
Insulin/IGF-I-signaling pathway: an evolutionarily conserved mechanism of longevity from yeast to humans
Authors: Barbieri Michelangela , Bonafè Massimiliano , Franceschi Claudio , Paolisso Giuseppe
Published: March 2015

Although the underlying mechanisms of longevity are not fully understood, it is known that mutation in genes that share similarities with those in humans involved in the insulin/insulin-like growth factor I (IGF-I) signal response pathway can significantly extend life span in diverse species, including yeast, worms, fruit flies, and rodents. Intriguingly, the long-lived mutants, ranging from yeast to mice, share some important phenotypic characteristics, including reduced insulin signaling, enhanced sensitivity to insulin, and reduced IGF-I plasma levels. Such genetic homologies and phenotypic similarities between insulin/IGF-I pathway mutants raise the possibility that the fundamental mechanism of aging may be evolutionarily conserved from yeast to mammals. Very recent findings also provide novel and intriguing evidence for the involvement of insulin and IGF-I in the control of aging and longevity in humans. In this study, we focus on how the insulin/IGF-I pathway controls yeast, nematode, fruit fly, and rodent life spans and how it is related to the aging process in humans to outline the prospect of a unifying mechanism in the genetics of longevity.
Postnatal oxytocin alleviates adverse effects in adult rat offspring caused by maternal malnutrition
Authors: Olausson Hanna , Uvnäs-Moberg Kerstin , Sohlström Annica
Published: March 2015

Repeated oxytocin administration to adult rats causes a long-term decrease of plasma levels of corticosterone and blood pressure and stimulates growth and fat retention. Maternal undernutrition increases blood pressure and plasma corticosterone in adult offspring. We hypothesized that oxytocin treatment early in life would alleviate adverse effects of intrauterine food restriction. Male pups from ad libitum-fed and food-restricted (fed 60% of ad libitum intake) dams were injected with oxytocin or saline in days 1–14 after birth. At 4 mo, blood pressure, plasma levels of corticosterone, and adiposity were assessed. Oxytocin treatment decreased blood pressure independently of nutrition, whereas the increased plasma levels of corticosterone were lowered to normal levels in food-restricted offspring. Blood pressure and adiposity were not affected by in utero food restriction, whereas birth and adult weight were. In conclusion, postnatal events may alleviate adverse effects caused by in utero food restriction. In contrast to more severe food restriction, a moderate general food restriction during gestation had no effect on blood pressure in the offspring.
Interaction of glucagon and epinephrine in the control of hepatic glucose production in the conscious dog
Authors: Gustavson Stephanie M. , Chu Chang An , Nishizawa Makoto , Farmer Ben , Neal Doss , Yang Ying , Donahue E. Patrick , Flakoll Paul , Cherrington Alan D.
Published: March 2015

Epinephrine increases net hepatic glucose output (NHGO) mainly via increased gluconeogenesis, whereas glucagon increases NHGO mainly via increased glycogenolysis. The aim of the present study was to determine how the two hormones interact in controlling glucose production. In 18-h-fasted conscious dogs, a pancreatic clamp initially fixed insulin and glucagon at basal levels, following which one of four protocols was instituted. In G + E, glucagon (1.5 ng · kg−1· min−1; portally) and epinephrine (50 ng · kg−1· min−1; peripherally) were increased; in G, glucagon was increased alone; in E, epinephrine was increased alone; and in C, neither was increased. In G, E, and C, glucose was infused to match the hyperglycemia seen in G + E (∼250 mg/dl). The areas under the curve for the increase in NHGO, after the change in C was subtracted, were as follows: G = 661 ± 185, E = 424 ± 158, G + E = 1,178 ± 57 mg/kg. Therefore, the overall effects of the two hormones on NHGO were additive. Additionally, glucagon exerted its full glycogenolytic effect, whereas epinephrine exerted its full gluconeogenic effect, such that both processes increased significantly during concurrent hormone administration.
Effects of fasting and glucocorticoids on hepatic gluconeogenesis assessed using two independent methods in vivo
Authors: Goldstein Richard E. , Rossetti Luciano , Palmer Brett A. J. , Liu Rong , Massillon Duna , Scott Melanie , Neal Doss , Williams Phillip , Peeler Benjamin , Cherrington Alan D.
Published: March 2015

The purpose of this study was to compare the assessment of gluconeogenesis (GNG) in the overnight- and prolonged-fasted states and during chronic hypercortisolemia using the arteriovenous difference and [14C]phospho enolpyruvate-liver biopsy techniques as well as a combination of the two. Two weeks before a study, catheters and flow probes were implanted in the hepatic and portal veins and femoral artery of dogs. Animals were studied after an 18-h fast ( n = 8), a 42- or 66-h fast ( n = 7), and an 18-h fast plus a continuous infusion of cortisol (3.0 μg · kg−1· min−1) for 72 h ( n = 7). Each experiment consisted of an 80-min tracer ([3-3H]glucose and [U-14C]alanine) and dye equilibration period (−80 to 0 min) and a 45-min sampling period. In the cortisol-treated group, plasma cortisol increased fivefold. In the overnight-fasted group, total GNG flux rate (GNGflux), conversion of glucose 6-phosphate to glucose (GNGG-6- P→Glc), glucose cycling, and maximal GNG flux rate (GNGmax) were 0.95 ± 0.14, 0.65 ± 0.06, 0.62 ± 0.06, and 0.70 ± 0.09 mg · kg−1· min−1, respectively. In the prolonged-fasted group, they were 1.50 ± 0.18, 1.18 ± 0.13, 0.40 ± 0.07, and 1.28 ± 0.10 mg · kg−1· min−1, whereas in the cortisol-treated group they were 1.64 ± 0.33, 0.99 ± 0.29, 1.32 ± 0.24, and 0.91 ± 0.13 mg · kg−1· min−1. These results demonstrate that GNGG-6- P→Glcand GNGmaxwere almost identical. However, these rates were 15–38% lower than GNGfluxgenerated by a combination of the two methods. This difference was most apparent in the steroid-treated group, where the combination of the two methods (GNGflux) detected a significant increase in gluconeogenic flux.
Impaired oxidative phosphorylation in skeletal muscle of intrauterine growth-retarded rats
Authors: Selak Mary A. , Storey Bayard T. , Peterside Iyalla , Simmons Rebecca A.
Published: March 2015

Intrauterine growth retardation (IUGR) has been linked to the development of type 2 diabetes in later life. We have developed a model of uteroplacental insufficiency, a common cause of intrauterine growth retardation, in the rat. Early in life, the animals are insulin resistant and by 6 mo of age they develop diabetes. Glycogen content and insulin-stimulated 2-deoxyglucose uptake were significantly decreased in muscle from IUGR rats. IUGR muscle mitochondria exhibited significantly decreased rates of state 3 oxygen consumption with pyruvate, glutamate, α-ketoglutarate, and succinate. Decreased pyruvate oxidation in IUGR mitochondria was associated with decreased ATP production, decreased pyruvate dehydrogenase activity, and increased expression of pyruvate dehydrogenase kinase 4. Such a defect in IUGR mitochondria leads to a chronic reduction in the supply of ATP available from oxidative phosphorylation. Impaired ATP synthesis in muscle compromises energy-dependent GLUT4 recruitment to the cell surface, glucose transport, and glycogen synthesis, which contribute to insulin resistance and hyperglycemia of type 2 diabetes.
Free fatty acids increase basal hepatic glucose production and induce hepatic insulin resistance at different sites
Authors: Lam Tony K. T. , Van de Werve Gérald , Giacca Adria
Published: March 2015

To investigate the sites of the free fatty acid (FFA) effects to increase basal hepatic glucose production and to impair hepatic insulin action, we performed 2-h and 7-h Intralipid + heparin (IH) and saline infusions in the basal fasting state and during hyperinsulinemic clamps in overnight-fasted rats. We measured endogenous glucose production (EGP), total glucose output (TGO, the flux through glucose-6-phosphatase), glucose cycling (GC, index of flux through glucokinase = TGO − EGP), hepatic glucose 6-phosphate (G-6- P) content, and hepatic glucose-6-phosphatase and glucokinase activities. Plasma FFA levels were elevated about threefold by IH. In the basal state, IH increased TGO, in vivo glucose-6-phosphatase activity (TGO/G-6- P), and EGP ( P < 0.001). During the clamp compared with the basal experiments, 2-h insulin infusion increased GC and in vivo glucokinase activity (GC/TGO; P < 0.05) and suppressed EGP ( P< 0.05) but failed to significantly affect TGO and in vivo glucose-6-phosphatase activity. IH decreased the ability of insulin to increase GC and in vivo glucokinase activity ( P < 0.01), and at 7 h, it also decreased the ability of insulin to suppress EGP ( P < 0.001). G-6- P content was comparable in all groups. In vivo glucose-6-phosphatase and glucokinase activities did not correspond to their in vitro activities as determined in liver tissue, suggesting that stable changes in enzyme activity were not responsible for the FFA effects. The data suggest that, in overnight-fasted rats, FFA increased basal EGP and induced hepatic insulin resistance at different sites. 1) FFA increased basal EGP through an increase in TGO and in vivo glucose-6-phosphatase activity, presumably due to a stimulatory allosteric effect of fatty acyl-CoA on glucose-6-phosphatase. 2) FFA induced hepatic insulin resistance (decreased the ability of insulin to suppress EGP) through an impairment of insulin's ability to increase GC and in vivo glucokinase activity, presumably due to an inhibitory allosteric effect of fatty acyl-CoA on glucokinase and/or an impairment in glucokinase translocation.
Quantitative assessment of anaplerosis from propionate in pig heart in vivo
Authors: Martini Wenjun Z. , Stanley William C. , Huang Hazel , Rosiers Christine Des , Hoppel Charles L. , Brunengraber Henri
Published: March 2015

Normal cardiac metabolism requires continuous replenishment (anaplerosis) of catalytic intermediates of the citric acid cycle. Little is known about the quantitative aspects of propionate as a substrate of in vivo anaplerosis; therefore, we measured the rate of propionate entry into the citric acid cycle in hearts of anesthetized pigs. [U-13C3]propionate (0.25 mM) was infused in a coronary artery branch for 1 h via an extracorporeal perfusion circuit, and cardiac biopsies were analyzed for the mass isotopomer distribution of citric acid cycle intermediates. Infusion of propionate did not affect myocardial oxygen consumption, heart rate, or contractile function. In the infused territory, propionate infusion did not affect uptake of glucose and lactate but decreased free fatty acid uptake by one-half ( P < 0.05). Propionate extraction and uptake were 57.4 ± 3.3% and 0.078 ± 0.009 μmol · min−1· g−1. Anaplerosis from propionate, calculated from the mass isotopomer distribution of succinate, accounted for 8.9 ± 1.3% of the citric acid cycle flux. Propioylcarnitine release accounted for only 0.033 ± 0.002% of propionate uptake. Methylcitrate did not accumulate. Thus administration of a low concentration of propionate appears to be a convenient and safe way to boost anaplerosis in the heart.
Adiponectin expression in adipose tissue is reduced in first-degree relatives of type 2 diabetic patients
Authors: Lihn A. S. , Østergård T. , Nyholm B. , Pedersen S. B. , Richelsen B. , Schmitz O.
Published: March 2015

Adiponectin is suggested to be an important mediator of insulin resistance. Therefore, we investigated the association between adiponectin and insulin sensitivity in 22 healthy first-degree relatives (FDR) to type 2 diabetic patients and 13 matched control subjects. Subcutaneous adipose tissue biopsies were taken before and after a hyperinsulinemic euglycemic clamp. FDR subjects were insulin resistant, as indicated by a reduced Mvalue (4.44 vs. 6.09 mg · kg−1· min−1, P < 0.05). Adiponectin mRNA expression was 45% lower in adipose tissue from FDR compared with controls ( P < 0.01), whereas serum adiponectin was similar in the two groups (6.4 vs. 6.6 μg/ml, not significant). Insulin infusion reduced circulating levels of adiponectin moderately (11–13%) but significantly in both groups ( P < 0.05). In the control group, adiponectin mRNA levels were negatively correlated with fasting insulin ( P < 0.05) and positively correlated with insulin sensitivity ( P < 0.05). In contrast, these associations were not found in the FDR group. In conclusion, FDR have reduced adiponectin mRNA in subcutaneous adipose tissue but normal levels of circulating adiponectin. Adiponectin mRNA levels are positively correlated with insulin sensitivity in control subjects but not in FDR. These findings indicate dysregulation of adiponectin gene expression in FDR.
Pathways for glucose disposal after meal ingestion in humans
Authors: Woerle Hans J. , Meyer Christian , Dostou Jean M. , Gosmanov Niyaz R. , Islam Nazmul , Popa Emilia , Wittlin Steven D. , Welle Stephen L. , Gerich John E.
Published: March 2015

To characterize postprandial glucose disposal more completely, we used the tritiated water technique, a triple-isotope approach (intravenous [3-H3]glucose and [14C]bicarbonate and oral [6,6-2H2]glucose) and indirect calorimetry to assess splanchnic and peripheral glucose disposal, direct and indirect glucose storage, oxidative and nonoxidative glycolysis, and the glucose entering plasma via gluconeogenesis after ingestion of a meal in 11 normal volunteers. During a 6-h postprandial period, a total of ∼98 g of glucose were disposed of. This was more than the glucose contained in the meal (∼78 g) due to persistent endogenous glucose release (∼21 g): splanchnic tissues initially took up ∼23 g, and an additional ∼75 g were removed from the systemic circulation. Direct glucose storage accounted for ∼32 g and glycolysis for ∼66 g (oxidative ∼43 g and nonoxidative ∼23 g). About 11 g of glucose appeared in plasma as a result of gluconeogenesis. If these carbons were wholly from glucose undergoing glycolysis, only ∼12 g would be available for indirect pathway glycogen formation. Our results thus indicate that glycolysis is the main initial postprandial fate of glucose, accounting for ∼66% of overall disposal; oxidation and storage each account for ∼45%. The majority of glycogen is formed via the direct pathway (∼73%).
Effect of weight loss on VLDL-triglyceride and apoB-100 kinetics in women with abdominal obesity
Authors: Mittendorfer Bettina , Patterson Bruce W. , Klein Samuel
Published: March 2015

The effects of obesity and weight loss on lipoprotein kinetics were evaluated in six lean women [body mass index (BMI): 21 ± 1 kg/m2] and seven women with abdominal obesity (BMI: 36 ± 1 kg/m2). Stable isotope tracer techniques, in conjunction with compartmental modeling, were used to determine VLDL-triglyceride (TG) and apolipoprotein B-100 (apoB-100) secretion rates in lean women and in obese women before and after 10% weight loss. VLDL-TG and VLDL-apoB-100 secretion rates were similar in lean and obese women. Weight loss decreased the rate of VLDL-TG secretion by ∼40% (from 0.41 ± 0.05 to 0.23 ± 0.03 μmol · kg fat-free mass−1· min−1; P < 0.05). The relative decline in VLDL-TG produced from nonsystemic fatty acids, derived from intraperitoneal and intrahepatic TG, was greater (61 ± 7%) than the decline in VLDL-TG produced from systemic fatty acids, predominantly derived from subcutaneous TG (25 ± 8%; P < 0.05). Weight loss did not affect VLDL-apoB-100 secretion rate. We conclude that weight loss decreases the rate of VLDL-TG secretion in women with abdominal obesity, primarily by decreasing the availability of nonsystemic fatty acids. There is a dissociation in the effect of weight loss on VLDL-TG and apoB-100 metabolic pathways that may affect VLDL particle size.
BMP-2 inhibits proliferation of human aortic smooth muscle cells via p21Cip1/Waf1
Authors: Wong Gail A. , Tang Vincent , El-Sabeawy Faten , Weiss Robert H.
Published: March 2015

Bone-morphogenetic proteins (BMP)-2 and -7, multifunctional members of the transforming growth factor (TGF)-β superfamily with powerful osteoinductive effects, cause cell cycle arrest in a variety of transformed cell lines by activating signaling cascades that involve several cyclin-dependent kinase inhibitors (CDKIs). CDKIs in the cip/kip family, p21Cip1/Waf1and p27Kip1, have been shown to negatively regulate the G1 cyclins and their partner cyclin-dependent kinase proteins, resulting in BMP-mediated growth arrest. Bone morphogens have also been associated with antiproliferative effects in vascular tissue by unknown mechanisms. We now show that BMP-2-mediated inhibition of platelet-derived growth factor (PDGF)-stimulated human aortic smooth muscle cell (HASMC) proliferation is accompanied by increased levels of p21 protein. Antisense oligodeoxynucleotides specific for p21 attenuate BMP-2-induced inhibition of proliferation when transfected into HASMCs, demonstrating that BMP-2 inhibits PDGF-stimulated proliferation of HASMCs through induction of p21. Whether p21-mediated induction of cell cycle arrest by BMP-2 sets the stage for osteogenic differentiation of vascular smooth muscle cells, ultimately leading to vascular mineralization, remains to be investigated.
A highly sensitive and specific assay for determination of IGF-I bioactivity in human serum
Authors: Chen Jian-Wen , Ledet Thomas , Ørskov Hans , Jessen Niels , Lund Sten , Whittaker Jonathan , De Meyts Pierre , Larsen Maj Britt , Christiansen Jens Sandahl , Frystyk Jan
Published: March 2015

At present, the circulating bioactivity of insulin-like growth factor I (IGF-I) is estimated by immunological measurements of IGF-I levels. However, immunoassays ignore the modifying effects of the IGF-binding proteins (IGFBPs) on the interaction between IGF-I and the IGF-I receptor (IGF-IR). Therefore, we developed an IGF-I kinase receptor activation assay (KIRA) based on cells transfected with the human IGF-IR gene. The bioassay was sensitive (detection limit 0.08 μg/l), specific (cross-reactivity of insulin, insulin analogs, and proinsulin was <1%; IGF-II cross-reactivity was 12%), and accurate (within- and between-assay coefficients of variation <7 and <15%). The operational range of the assay (0.25–10.0 μg/l) allowed for determination of IGF-I bioactivity in serum from patients with, for example, growth hormone deficiency, type 1 diabetes, and acromegaly. Addition of IGFBPs dose dependently reduced the KIRA signal, whereas addition of IGF-II to preformed complexes (1:1 molar ratio) of IGF-I and IGFBP dose dependently increased IGF-I bioactivity by displacement of bound IGF-I. In conclusion, the KIRA will enable us to compare IGF-I bioactivity with existing immunological measurements of IGF-I in serum and, hopefully, to elucidate the factors that determine IGF-I bioactivity in vivo.
Effects of reduced free fatty acid availability on skeletal muscle PDH activation during aerobic exercise
Authors: Stellingwerff Trent , Watt Matthew J. , Heigenhauser G. J. F. , Spriet Lawrence L.
Published: March 2015

This study investigated the effect of reduced free fatty acid (FFA) availability on pyruvate dehydrogenase activation (PDHa) and carbohydrate metabolism during moderate aerobic exercise. Eight active male subjects cycled for 40 min at 55% V˙o2 peakon two occasions. During one trial, subjects ingested 20 mg/kg body mass of the antilipolytic drug nicotinic acid (NA) during the hour before exercise to reduce FFA. Nothing was ingested in the control trial (CON). Blood and expired gas measurements were obtained throughout the trials, and muscle biopsy samples were obtained immediately before exercise and at 5, 20, and 40 min of exercise. Plasma FFA were lower in the NA trial (0.13 ± 0.01 vs. 0.48 ± 0.03 mM, P < 0.05), and the respiratory exchange ratio (RER) was increased with NA (0.93 ± 0.01 vs. 0.89 ± 0.01, P < 0.05), resulting in a 14.5 ± 1.8% increase in carbohydrate oxidation compared with CON. PDHa increased rapidly in both trials at exercise onset but was ∼15% higher ( P < 0.05) throughout exercise in the NA trial (2.44 ± 0.19 and 2.07 ± 0.12 mmol · kg wet muscle−1· min−1for NA and CON at 40 min). Muscle glycogenolysis was 15.3 ± 9.6% greater in the NA trial vs. the CON trial but did not reach statistical significance. Glucose 6-phosphate contents were elevated ( P < 0.05) in the NA trial at 30 and 40 min of exercise, but pyruvate and lactate contents were unaffected. These data demonstrate that the reduction of exogenous FFA availability increased the activation of PDH and carbohydrate oxidation during moderate aerobic exercise in men. The increased activation of PDH was not explained by changes in muscle pyruvate or the ATP/ADP ratio but may be related to a decrease in the NADH/NAD+ratio or an epinephrine-induced increase in calcium concentration.
Regulation of 5′AMP-activated protein kinase activity and substrate utilization in exercising human skeletal muscle
Authors: Wojtaszewski Jørgen F. P. , MacDonald Christopher , Nielsen Jakob N. , Hellsten Ylva , Hardie D. Grahame , Kemp Bruce E. , Kiens Bente , Richter Erik A.
Published: March 2015

The metabolic role of 5′AMP-activated protein kinase (AMPK) in regulation of skeletal muscle metabolism in humans is unresolved. We measured isoform-specific AMPK activity and β-acetyl-CoA carboxylase (ACCβ) Ser221phosphorylation and substrate balance in skeletal muscle of eight athletes at rest, during cycling exercise for 1 h at 70% peak oxygen consumption, and 1 h into recovery. The experiment was performed twice, once in a glycogen-loaded (glycogen concentration ∼900 mmol/kg dry wt) and once in a glycogen-depleted (glycogen concentration ∼160 mmol/kg dry wt) state. At rest, plasma long-chain fatty acids (FA) were twofold higher in the glycogen-depleted than in the loaded state, and muscle α1 AMPK (160%) and α2 AMPK (145%) activities and ACCβ Ser221phosphorylation (137%) were also significantly higher in the glycogen-depleted state. During exercise, α2 AMPK activity, ACCβ Ser221phosphorylation, plasma catecholamines, and leg glucose and net FA uptake were significantly higher in the glycogen-depleted than in the glycogen-loaded state without apparent differences in muscle high-energy phosphates. Thus exercise in the glycogen-depleted state elicits an enhanced uptake of circulating fuels that might be associated with elevated muscle AMPK activation. It is concluded that muscle AMPK activity and ACCβ Ser221phosphorylation at rest and during exercise are sensitive to the fuel status of the muscle. During exercise, this dependence may in part be mediated by humoral factors.
Bovine growth hormone-transgenic mice have major alterations in hepatic expression of metabolic genes
Authors: Olsson Bob , Bohlooly-Y Mohammad , Brusehed Ola , Isaksson Olle G. P. , Ahrén Bo , Olofsson Sven-Olof , Oscarsson Jan , Törnell Jan
Published: March 2015

Transgenic mice overexpressing growth hormone (GH) have been extensively used to study the chronic effects of elevated serum levels of GH. GH is known to have many acute effects in the liver, but little is known about the chronic effects of GH overexpression on hepatic gene expression. Therefore, we used DNA microarray to compare gene expression in livers from bovine GH (bGH)-transgenic mice and littermates. Hepatic expression of peroxisome proliferator-activated receptor-α (PPARα) and genes involved in fatty acid activation, peroxisomal and mitochondrial β-oxidation, and production of ketone bodies was decreased. In line with this expression profile, bGH-transgenic mice had a reduced ability to form ketone bodies in both the fed and fasted states. Although the bGH mice were hyperinsulinemic, the expression of sterol regulatory element-binding protein (SREBP)-1 and most lipogenic enzymes regulated by SREBP-1 was reduced, indicating that these mice are different from other insulin-resistant models with respect to expression of SREBP-1 and its downstream genes. This study also provides several candidate genes for the well-known association between elevated GH levels and cardiovascular disease, e.g., decreased expression of scavenger receptor class B type I, hepatic lipase, and serum paraoxonase and increased expression of serum amyloid A-3 protein. We conclude that bGH-transgenic mice display marked changes in hepatic genes coding for metabolic enzymes and suggest that GH directly or indirectly regulates many of these hepatic genes via decreased expression of PPARα and SREBP-1.
Response to sex hormones differs in atherosclerosis-susceptible and -resistant mice
Authors: Potier Mylène , Karl Michael , Elliot Sharon J. , Striker Gary E. , Striker Liliane J.
Published: March 2015

Genetic factors that determine the degree of susceptibility to atherosclerosis may also influence the effects of estrogens and progestins in arterial vessel disease. We examined and compared estrogen receptor (ER) and progesterone receptor (PR) expression and the effects of 17β-estradiol (E2) and progesterone (P) on collagen synthesis and matrix metalloproteinase (MMP) activities in the aortic arch and in cultured aortic smooth muscle cells (ASMC) of atherosclerosis-susceptible (C57Bl6/J, B6) or -resistant (C3H/HeJ, C3H) mice. ERα, ERβ, and PR levels were higher in the aorta and ASMC of atherosclerosis-susceptible B6 mice. In transfection studies using an estrogen response element-driven reporter plasmid, E2 elicited a >2-fold increase in luciferase activity in ASMC of B6 (B6-ASMC), which demonstrated the transcriptional activity of ER in atherosclerosis-susceptible cells. Importantly, the response of endogenous target genes to E2 and P was different in B6-ASMC and C3H-ASMC. E2 decreased collagen synthesis but had no effect on MMP activities in B6-ASMC. P decreased MMP-2 and MMP-9 activity in B6-ASMC. In contrast, E2 increased MMP-2 and decreased MMP-9 activity but had no effect on collagen synthesis in C3H-ASMC. P had no effect on collagen synthesis and MMP activity in C3H-ASMC. These differences in response to sex hormones may have important implications for women who receive hormone replacement therapy.
Protein tyrosine phosphatases: the quest for negative regulators of insulin action
Authors: Asante-Appiah Ernest , Kennedy Brian P.
Published: March 2015

Type 2 diabetes is increasing at an alarming rate worldwide, and there has been a considerable effort in several laboratories to identify suitable targets for the design of drugs against the disease. To this end, the protein tyrosine phosphatases that attenuate insulin signaling by dephosphorylating the insulin receptor (IR) have been actively pursued. This is because inhibiting the phosphatases would be expected to prolong insulin signaling and thereby facilitate glucose uptake and, presumably, result in a lowering of blood glucose. Targeting the IR protein tyrosine phosphatase, therefore, has the potential to be a significant disease-modifying strategy. Several protein tyrosine phosphatases (PTPs) have been implicated in the dephosphorylation of the IR. These phosphatases include PTPα, LAR, CD45, PTPε, SHP2, and PTP1B. In most cases, there is evidence for and against the involvement of the phosphatases in insulin signaling. The most convincing data, however, support a critical role for PTP1B in insulin action. PTP1B knockout mice are not only insulin sensitive but also maintain euglycemia (in the fed state), with one-half the level of insulin observed in wild-type littermates. Interestingly, these mice are also resistant to diet-induced obesity when fed a high-fat diet. The insulin-sensitive phenotype of the PTP1B knockout mouse is reproduced when the phosphatase is also knocked down with an antisense oligonucleotide in obese mice. Thus PTP1B appears to be a very attractive candidate for the design of drugs for type 2 diabetes and obesity.
Thyroid status, but not insulin status, affects expression of avian uncoupling protein mRNA in chicken
Authors: Collin Anne , Taouis Mohammed , Buyse Johan , Ifuta Ndey B. , Darras Veerle M. , Van As Pieter , Malheiros Ramon D. , Moraes Vera M. B. , Decuypere Eddy
Published: March 2015

The aim of this study was to investigate the hormonal regulation of the avian homolog of mammalian uncoupling protein (avUCP) by studying the impact of thyroid hormones and insulin on avUCP mRNA expression in chickens ( Gallus gallus). For 3 wk, chicks received either a standard diet (control group), or a standard diet supplemented with triiodothyronine (T3; T3 group) or with the thyroid gland inhibitor methimazole (MMI group). A fourth group received injections of the deiodinase inhibitor iopanoic acid (IOP group). During the 4th wk of age, all animals received two daily injections of either human insulin or saline solution. The results indicate a twofold overexpression of avUCP mRNA in gastrocnemius muscle of T3 birds and a clear downregulation (−74%) in MMI chickens compared with control chickens. Insulin injections had no significant effect on avUCP mRNA expression in chickens. This study describes for the first time induction of avUCP mRNA expression by the thermogenic hormone T3in chickens and supports a possible involvement of avUCP in avian thermogenesis.
Thiazolidinediones upregulate impaired fatty acid uptake in skeletal muscle of type 2 diabetic subjects
Authors: Wilmsen Hubertina M. , Ciaraldi Theodore P. , Carter Leslie , Reehman Nabeela , Mudaliar Sunder R. , Henry Robert R.
Published: March 2015

We examined the regulation of free fatty acid (FFA, palmitate) uptake into skeletal muscle cells of nondiabetic and type 2 diabetic subjects. Palmitate uptake included a protein-mediated component that was inhibited by phloretin. The protein-mediated component of uptake in muscle cells from type 2 diabetic subjects (78 ± 13 nmol · mg protein-1· min-1) was reduced compared with that in nondiabetic muscle (150 ± 17, P < 0.01). Acute insulin exposure caused a modest (16 ± 5%, P < 0.025) but significant increase in protein-mediated uptake in nondiabetic muscle. There was no significant insulin effect in diabetic muscle (+19 ± 19%, P = not significant). Chronic (4 day) treatment with a series of thiazolidinediones, troglitazone (Tgz), rosiglitazone (Rgz), and pioglitazone (Pio) increased FFA uptake. Only the phloretin-inhibitable component was increased by treatment, which normalized this activity in diabetic muscle cells. Under the same conditions, FFA oxidation was also increased by thiazolidinedione treatment. Increases in FFA uptake and oxidation were associated with upregulation of fatty acid translocase (FAT/CD36) expression. FAT/CD36 protein was increased by Tgz (90 ± 22% over control), Rgz (146 ± 42%), and Pio (111 ± 37%, P < 0.05 for all 3) treatment. Tgz treatment had no effect on fatty acid transporter protein-1 and membrane-associated plasmalemmal fatty acid-binding protein mRNA expression. We conclude that FFA uptake into cultured muscle cells is, in part, protein mediated and acutely insulin responsive. The basal activity of FFA uptake is impaired in type 2 diabetes. In addition, chronic thiazolidinedione treatment increased FFA uptake and oxidation into cultured human skeletal muscle cells in concert with upregulation of FAT/CD36 expression. Increased FFA uptake and oxidation may contribute to lower circulating FFA levels and reduced insulin resistance in skeletal muscle of individuals with type 2 diabetes following thiazolidinedione treatment.
Glucagon and regulation of glucose metabolism
Authors: Jiang Guoqiang , Zhang Bei B.
Published: March 2015

As a counterregulatory hormone for insulin, glucagon plays a critical role in maintaining glucose homeostasis in vivo in both animals and humans. To increase blood glucose, glucagon promotes hepatic glucose output by increasing glycogenolysis and gluconeogenesis and by decreasing glycogenesis and glycolysis in a concerted fashion via multiple mechanisms. Compared with healthy subjects, diabetic patients and animals have abnormal secretion of not only insulin but also glucagon. Hyperglucagonemia and altered insulin-to-glucagon ratios play important roles in initiating and maintaining pathological hyperglycemic states. Not surprisingly, glucagon and glucagon receptor have been pursued extensively in recent years as potential targets for the therapeutic treatment of diabetes.
The hot IVGTT two-compartment minimal model: an improved version
Authors: Toffolo Gianna , Cobelli Claudio
Published: March 2015

The two-compartment minimal model (2CMM) interpretation of a labeled intravenous glucose tolerance test (IVGTT) is a powerful tool to assess glucose metabolism in a single individual. It has been reported that a derived 2CMM parameter describing the proportional effect of glucose on insulin-independent glucose disposal can take physiologically unplausible negative values. In addition, precision of 2CMM parameter estimates is sometimes not satisfactory. Here we resolve the above issues by presenting an improved version of 2CMM that relies on a new assumption on the constant component Rd0 of insulin-independent glucose disposal. Here Rd0 is not fixed to 1 mg · kg−1 · min−1but instead is expressed as a fraction of steady-state glucose disposal. The new 2CMM is identified on the same stable labeled IVGTT data base on which the original 2CMM was formulated. A more reliable insulin-independent glucose disposal portrait is obtained while that of insulin action remains unchanged. The new 2CMM also improves the precision with which model parameters and metabolic indexes are estimated.
Activation of α2-adrenergic receptors blunts epinephrine-induced lipolysis in subcutaneous adipose tissue during a hyperinsulinemic euglycemic clamp in men
Authors: Stich Vladimir , Pelikanova Tereza , Wohl Petr , Sengenès Coralie , Zakaroff-Girard Alexia , Lafontan Max , Berlan Michel
Published: March 2015

The aim of this study was to investigate whether hyperinsulinemia modifies adrenergic control of lipolysis, with particular attention paid to the involvement of antilipolytic α2-adrenergic receptors (AR). Eight healthy male subjects (age: 23.9 ± 0.9 yr; body mass index: 23.8 ± 1.9) were investigated during a 6-h euglycemichyperinsulinemic clamp and in control conditions. Before and during the clamp, the effect of graded perfusions of isoproterenol (0.1 and 1 μM) or epinephrine (1 and 10 μM) on the extracellular glycerol concentration in subcutaneous abdominal adipose tissue was evaluated by using the microdialysis method. Both isoproterenol and epinephrine induced a dose-dependent increase in extracellular glycerol concentration when infused for 60 min through the microdialysis probes before and during hours 3 and 6 of the clamp. The catecholamine-induced increase was significantly lower during the clamp than before it, with the inhibition being more pronounced in hour 6 of the clamp. Isoproterenol (1 μM)-induced lipolysis was reduced by 28 and 44% during hours 3 and 6 of the clamp, respectively, whereas the reduction of epinephrine (100 μM)-induced lipolysis was significantly greater (by 63 and 70%, P < 0.01 and P < 0.04, respectively) during the same time intervals. When epinephrine was infused in combination with 100 μM phentolamine (a nonselective α-AR antagonist), the inhibition of epinephrine (10 μM)-induced lipolysis was only of 19 and 40% during hours 3 and 6 of the clamp, respectively. The results demonstrate that, in situ, insulin counteracts the epinephrine-induced lipolysis in adipose tissue. The effect involves 1) reduction of lipolysis stimulation mediated by the β-adrenergic pathway and 2) the antilipolytic component of epinephrine action mediated by α2-ARs.
Spared bone mass in rats treated with thyroid hormone receptor TRβ-selective compound GC-1
Authors: Freitas Fatima R. S. , Moriscot Anselmo S. , Jorgetti Vanda , Soares Antonio G. , Passarelli Marisa , Scanlan Thomas S. , Brent Gregory A. , Bianco Antonio C. , Gouveia Cecilia H. A.
Published: March 2015

Thyrotoxicosis is frequently associated with increased bone turnover and decreased bone mass. To investigate the role of thyroid hormone receptor-β (TRβ) in mediating the osteopenic effects of triiodothyronine (T3), female adult rats were treated daily (64 days) with GC-1 (1.5 μg/100 g body wt), a TRβ-selective thyromimetic compound. Bone mass was studied by dual-energy X-ray absorptiometry of several skeletal sites and histomorphometry of distal femur, and the results were compared with T3-treated (3 μg/100 g body wt) or control animals. As expected, treatment with T3significantly reduced bone mineral density (BMD) in the lumbar vertebrae (L2-L5), femur, and tibia by 10–15%. In contrast, GC-1 treatment did not affect the BMD in any of the skeletal sites studied. The efficacy of GC-1 treatment was verified by a reduction in serum TSH (–52% vs. control, P < 0.05) and cholesterol (–21% vs. control, P < 0.05). The histomorphometric analysis of the distal femur indicated that T3but not GC-1 treatment reduced the trabecular volume, thickness, and number. We conclude that chronic, selective activation of the TRβ isoform does not result in bone loss typical of T3-induced thyrotoxicosis, suggesting that the TRβ isoform is not critical in this process. In addition, our findings suggest that the development of TR-selective T3analogs that spare bone mass represents a significant improvement toward long-term TSH-suppressive therapy.
Gene expression profiles and protein balance in skeletal muscle of burned children after β-adrenergic blockade
Authors: Herndon David N. , Dasu Mohan R. K. , Wolfe Robert R. , Barrow Robert E.
Published: March 2015

Propranolol, a nonselective β-blocker, has been shown effective in hypermetabolic burn patients by decreasing cardiac work, protein catabolism, and lipolysis. This study investigates the effect of propranolol on gene and protein expression changes in skeletal muscle of burned children by use of high-density oligonucleotide arrays to establish the genetic profiles and stable isotope technique to quantitate protein synthesis. Thirty-seven children (mean age 9.7 ± 1.1 yr) were randomized into groups to receive placebo ( n = 23) or propranolol ( n = 14) titrated to reduce heart rate by 15%. Children had >40% total body surface area burns (mean 43 ± 5.6%). Protein net balance was determined by stable-isotope infusion technique. Total RNA from muscle biopsies was isolated, labeled, and cRNA hybridized to the HG-U95Av2 Affymetrix array. Mean net balance of protein synthesis and breakdown was –14.3 ± 12.9 nmol · min–1· 100 ml leg volume–1for placebo and +69.3 ± 34.9 nmol · min–1· 100 ml leg volume–1in the propranolol-treated children ( P = 0.012). Comparison of 12,000 genes in burned children receiving placebo showed increased expression of two genes with time, whereas children receiving propranolol showed increased expression of nine genes with a decrease in five genes. We conclude that burned children receiving propranolol showed a significant upregulation in genes involved in muscle metabolism and downregulation of an important enzyme involved in gluconeogenesis and insulin resistance compared with burned children receiving placebo. The upregulation of genes involved in muscle metabolism correlates well with the increase in net protein balance across the leg.
Skeletal muscle lipid metabolism with obesity
Authors: Hulver Matthew W. , Berggren Jason R. , Cortright Ronald N. , Dudek Ronald W. , Thompson R. Peter , Pories Walter J. , MacDonald Kenneth G. , Cline Gary W. , Shulman Gerald I. , Dohm G. Lynis , Houmard Joseph A.
Published: March 2015

The objectives of this study were to 1) examine skeletal muscle fatty acid oxidation in individuals with varying degrees of adiposity and 2) determine the relationship between skeletal muscle fatty acid oxidation and the accumulation of long-chain fatty acyl-CoAs. Muscle was obtained from normal-weight [ n = 8; body mass index (BMI) 23.8 ± 0.58 kg/m2], overweight/obese ( n = 8; BMI 30.2 ± 0.81 kg/m2), and extremely obese ( n = 8; BMI 53.8 ± 3.5 kg/m2) females undergoing abdominal surgery. Skeletal muscle fatty acid oxidation was assessed in intact muscle strips. Long-chain fatty acyl-CoA concentrations were measured in a separate portion of the same muscle tissue in which fatty acid oxidation was determined. Palmitate oxidation was 58 and 83% lower in skeletal muscle from extremely obese (44.9 ± 5.2 nmol · g−1 · h−1) patients compared with normal-weight (71.0 ± 5.0 nmol · g−1 · h−1) and overweight/obese (82.2 ± 8.7 nmol · g−1 · h−1) patients, respectively. Palmitate oxidation was negatively ( R = −0.44, P = 0.003) associated with BMI. Long-chain fatty acyl-CoA content was higher in both the overweight/obese and extremely obese patients compared with normal-weight patients, despite significantly lower fatty acid oxidation only in the extremely obese. No associations were observed between long-chain fatty acyl-CoA content and palmitate oxidation. These data suggest that there is a defect in skeletal muscle fatty acid oxidation with extreme obesity but not overweight/obesity and that the accumulation of intramyocellular long-chain fatty acyl-CoAs is not solely a result of reduced fatty acid oxidation.
Association between plasma zinc concentration and zinc kinetic parameters in premenopausal women
Authors: Yokoi Katsuhiko , Egger Norman G. , Ramanujam V. M. Sadagopa , Alcock Nancy W. , Dayal Hari H. , Penland James G. , Sandstead Harold H.
Published: March 2015

The objective of this study was to measure relationships between plasma zinc (Zn) concentrations and Zn kinetic parameters and to measure relationships of Zn status with taste acuity, food frequency, and hair Zn in humans. The subjects were 33 premenopausal women not taking oral contraceptives and dietary supplements containing iron and Zn. Main outcomes were plasma Zn concentrations, Zn kinetic parameters based on the three-compartment mammillary model using 67Zn as a tracer, electrical taste detection thresholds, and food frequencies. Lower plasma Zn was significantly ( P < 0.01) associated with smaller sizes of the central and the lesser peripheral Zn pools, faster disappearance of tracer from plasma, and higher transfer rate constants from the lesser peripheral pool to the central pool and from the central pool to the greater peripheral pool. The break points in the plasma Zn-Zn kinetics relationship were found between 9.94 and 11.5 μmol/l plasma Zn. Smaller size of the lesser peripheral pool was associated with lower frequency of beef consumption and higher frequency of bran breakfast cereal consumption. Hypozincemic women with plasma Zn <10.7 μmol/l or 700 ng/ml had decreased thresholds of electrical stimulation for gustatory nerves. Our results based on Zn kinetics support the conventional cutoff value of plasma Zn (10.7 μmol/l or 700 ng/ml) between normal and low Zn status.
Zinc modulates mRNA levels of cytokines
Authors: Bao Bin , Prasad Ananda S. , Beck Frances W. J. , Godmere Michele
Published: March 2015

Zinc plays an important role in cell-mediated immune function. Altered cellular immune response resulting from zinc deficiency leads to frequent microbial infections, thymic atrophy, decreased natural killer activity, decreased thymic hormone activity, and altered cytokine production. In this study, we examined the effect of zinc deficiency on IL-2 and IFN-γ in HUT-78 (Th0) and D1.1 (Th1) cell lines and TNF-α, IL-1β, and IL-8 in the HL-60 (monocyte-macrophage) cell line. The results demonstrate that zinc deficiency decreased the levels of IL-2 and IFN-γ cytokines and mRNAs in HUT-78 after 6 h of PMA/ p-phytohemagglutinin (PHA) stimulation and in D1.1 cells after 6 h of PHA/ionomycin stimulation compared with the zinc-sufficient cells. However, zinc deficiency increased the levels of TNF-α, IL-1β, and IL-8 cytokines and mRNAs in HL-60 cells after 6 h of PMA stimulation compared with zinc-sufficient cells. Actinomycin D study suggests that the changes in the levels of these cytokine mRNAs were not the result of the stability affected by zinc but might be the result of altered expression of these cytokine genes. These data demonstrate that zinc mediates positively the gene expression of IL-2 and IFN-γ in the Th1 cell line and negatively TNF-α, IL-1β, and IL-8 in the monocyte-macrophage cell line. Our study shows that the effect of zinc on gene expression and production of cytokines is cell lineage specific.