bluuebunny/crossref_metadata_2025 huggingface dataset:
Androgen therapy improves muscle mass and strength but not muscle quality: results from two studies
Authors: Schroeder E. Todd , Terk Michael , Sattler Fred R.
Published: March 2015

The relationship of strength to muscle area was used to assess change in muscle quality after anabolic interventions. Study 1: asymptomatic human immunodeficiency virus-positive men (39 ± 9 yr) were randomized to nandrolone (600 mg/wk) ± resistance training (RT). Study 2: older healthy men (72 ± 5 yr) were randomized to oxandrolone (20 mg/day) or placebo. Maximum voluntary strength was determined by the 1-repetition maximum (1-RM) method for leg press, flexion and extension, and cross-sectional area of leg muscles by MRI. From study week 0 to study week 12, muscle quality was unchanged with nandrolone, oxandrolone, or oxandrolone placebo, respectively, for total thigh muscles (1.23 ± 0.012 vs. 1.27 ± 0.29 kg/cm2; 9.0 ± 1.1 vs. 8.9 ± 1.2 N/cm2; 8.9 ± 1.2 vs. 8.9 ± 1.9 N/cm2) and hamstrings (0.41 ± 0.08 vs. 0.43 ± 0.07 kg/cm2; 0.90 ± 0.14 vs. 0.95 ± 0.016 N/cm2; 0.94 ± 0.23 vs. 0.93 ± 0.21 N/cm2). Lower-extremity 1-RM strength increased several times greater with RT+nandrolone (51–63% increases) than with nandrolone alone (4.7–16%), despite similar increases in muscle area; therefore, muscle quality increased from 1.13 ± 0.17 to 1.51 ± 0.18 kg/cm2 (+36 ± 19%; P < 0.001) for total thigh muscle, 0.37 ± 0.10 to 0.53 ± 0.08 kg/cm2 (+49 ± 39%; P < 0.001) for hamstrings, and 0.73 ± 0.19 to 1.07 ± 0.16 kg/cm2 (+55 ± 36%; P < 0.001) for quadriceps. Thus androgen therapy alone did not improve muscle quality, but the addition of RT to nandrolone produced substantive improvements.
Mechanisms of the free fatty acid-induced increase in hepatic glucose production
Authors: Lam Tony K. T. , Carpentier André , Lewis Gary F. , van de Werve Gérald , Fantus I. George , Giacca Adria
Published: March 2015

The associations between obesity, insulin resistance, and type 2 diabetes mellitus are well documented. Free fatty acids (FFA), which are often elevated in obesity, have been implicated as an important link in these associations. Contrary to muscle glucose metabolism, the effects of FFA on hepatic glucose metabolism and the associated mechanisms have not been extensively investigated. It is still controversial whether FFA have substantial effects on hepatic glucose production, and the mechanisms responsible for these putative effects remain unknown. We review recent progress in this area and try to clarify controversial issues regarding the mechanisms responsible for the FFA-induced increase in hepatic glucose production in the postabsorptive state and during hyperinsulinemia.
Maternal GHRH plasmid administration changes pituitary cell lineage and improves progeny growth of pigs
Authors: Khan Amir S. , Fiorotto Marta L. , Cummings Kathleen K. , Pope Melissa A. , Brown Patricia A. , Draghia-Akli Ruxandra
Published: March 2015

Previous studies from our laboratory have demonstrated that administration of a myogenic plasmid that encodes a protease-resistant growth hormone-releasing hormone (HV-GHRH) to pregnant rat dams augmented long-term growth in first-generation progeny. In the present study, gilts were injected intra-muscularly at day 85 of gestation with 0, 0.1, 0.5, 1, or 5 mg of the HV-GHRH-expressing plasmid and were then electroporated. Piglets were weighed and bled periodically from birth to 100 kg. Piglets from gilts treated with 1 and 5 mg of HV-GHRH plasmid were larger at birth and weaning compared with controls. These two groups reached 100 kg 9 days earlier than the other groups. GHRH levels were increased at birth in piglets from treated gilts. IGF-I levels were significantly increased in the 5-mg group beginning at 21 days of age compared with controls. Pituitaries from the 5-mg group contained a significantly increased number of somatotrophs and lactotrophs from birth to 100 kg. This study confirms that enhanced maternal GHRH production results in intergenerational growth augmentation and that the magnitude of the response is dose dependent. The similarity of the response across species suggests that the effect is likely exerted as a fundamental component of gestational and developmental physiology.
Gonadectomy of adult male rats reduces contractility of isolated cardiac myocytes
Authors: Golden Kish L. , Marsh James D. , Jiang Yang , Brown Tiane , Moulden Jerome
Published: March 2015

Sex-related differences in cardiac function have been well documented. The extent to which sex hormones are responsible for these differences is unclear. The current study was designed to determine whether castration and androgen replacement resulted in changes in functional expression of genes encoding the L-type calcium channel and Na/Ca exchanger in isolated rat ventricular myocytes. Sixteen weeks of castration produced a 50% decline in dihydropyridine receptor expression levels and a 16% ( P < 0.05) increase in time to peak shortening. Furthermore, cardiac myocytes isolated from castrated animals also displayed an 18% ( P < 0.001) increase in time to relengthening and an 80% decrease in Na/Ca exchanger gene expression when compared with intact controls. Testosterone treatment of castrated animals completely reversed these effects. These results provide the first evidence that androgens regulate functional expression of the L-type calcium channel and the Na/Ca exchanger in isolated rat ventricular myocytes and thus may play a role in modulating cardiac performance in males and thereby contribute to the observed gender differences in cardiac function.
Glucagon's actions are modified by the combination of epinephrine and gluconeogenic precursor infusion
Authors: Gustavson Stephanie M. , Chu Chang An , Nishizawa Makoto , Farmer Ben , Neal Doss , Yang Ying , Vaughan Suzan , Donahue E. Patrick , Flakoll Paul , Cherrington Alan D.
Published: March 2015

It was previously shown that glucagon and epinephrine have additive effects on both gluconeogenic and glycogenolytic flux. However, the changes in gluconeogenic substrates may have been limiting and thus may have prevented a synergistic effect on gluconeogenesis and a reciprocal inhibitory effect on glycogenolysis. Thus the aim of the present study was to determine if glucagon has a greater gluconeogenic and a smaller glycogenolytic effect in the presence of both epinephrine and clamped gluconeogenic precursors. Two groups (Epi and G + Epi + P) of 18-h-fasted conscious dogs were studied. In Epi, epinephrine was increased, and in G + Epi + P, glucagon and epinephrine were increased. Gluconeogenic precursors (lactate and alanine) were infused in G + Epi + P to match the rise that occurred in Epi. Insulin and glucose levels were also controlled and were similar in the two groups. Epinephrine and precursor administration increased glucagon's effect on gluconeogenesis (4.5-fold; P < 0.05) and decreased glucagon's effect on glycogenolysis (85%; P = 0.08). Thus, in the presence of both hormones, and when the gluconeogenic precursor supply is maintained, gluconeogenic flux is potentiated and glycogenolytic flux is inhibited.
T3increases lactate transport and the expression of MCT4, but not MCT1, in rat skeletal muscle
Authors: Wang Yuxiang , Tonouchi Mio , Miskovic Dragana , Hatta Hideo , Bonen Arend
Published: March 2015

Triiodothyronine (T3) regulates the expression of genes involved in muscle metabolism. Therefore, we examined the effects of a 7-day T3treatment on the monocarboxylate transporters (MCT)1 and MCT4 in heart and in red (RG) and white gastrocnemius muscle (WG). We also examined rates of lactate transport into giant sarcolemmal vesicles and the plasmalemmal MCT1 and MCT4 in these vesicles. Ingestion of T3markedly increased circulating serum T3( P < 0.05) and reduced weight gain ( P < 0.05). T3upregulated MCT1 mRNA (RG +77, WG +49, heart +114%, P < 0.05) and MCT4 mRNA (RG +300, WG +40%). However, only MCT4 protein expression was increased (RG +43, WG +49%), not MCT1 protein expression. No changes in MCT1 protein were observed in any tissue. T3treatment doubled the rate of lactate transport when vesicles were exposed to 1 mM lactate ( P < 0.05). However, plasmalemmal MCT4 was only modestly increased (+13%, P < 0.05). We conclude that T31) regulates MCT4, but not MCT1, protein expression and 2) increases lactate transport rates. This latter effect is difficult to explain by the modest changes in plasmalemmal MCT4. We speculate that either the activity of sarcolemmal MCTs has been altered or else other MCTs in muscle may have been upregulated.
cPLA2α-evoked formation of arachidonic acid and lysophospholipids is required for exocytosis in mouse pancreatic β-cells
Authors: Juhl Kirstine , Høy Marianne , Olsen Hervør L. , Bokvist Krister , Efanov Alexander M. , Hoffmann Else K. , Gromada Jesper
Published: March 2015

Using capacitance measurements, we investigated the effects of intracellularly applied recombinant human cytosolic phospholipase A2(cPLA2α) and its lipolytic products arachidonic acid and lysophosphatidylcholine on Ca2+-dependent exocytosis in single mouse pancreatic β-cells. cPLA2α dose dependently (EC50= 86 nM) stimulated depolarization-evoked exocytosis by 450% without affecting the whole cell Ca2+current or cytoplasmic Ca2+levels. The stimulatory effect involved priming of secretory granules as reflected by an increase in the size of the readily releasable pool of granules from 70–80 to 280–300. cPLA2α-stimulated exocytosis was antagonized by the specific cPLA2inhibitor AACOCF3. Ca2+-evoked exocytosis was reduced by 40% in cells treated with AACOCF3or an antisense oligonucleotide against cPLA2α. The action of cPLA2α was mimicked by a combination of arachidonic acid and lysophosphatidylcholine (470% stimulation) in which each compound alone doubled the exocytotic response. Priming of insulin-containing secretory granules has been reported to involve Cl-uptake through ClC-3 Cl-channels. Accordingly, the stimulatory action of cPLA2α was inhibited by the Cl-channel inhibitor DIDS and in cells pretreated with ClC-3 Cl-channel antisense oligonucleotides. We propose that cPLA2α has an important role in controlling the rate of exocytosis in β-cells. This effect of cPLA2α reflects an enhanced transgranular Cl-flux, leading to an increase in the number of granules available for release, and requires the combined actions of arachidonic acid and lysophosphatidylcholine.
Insulin inhibits glucose production by a direct effect in diabetic depancreatized dogs during euglycemia
Authors: Gupta Neehar , Sandhu Harmanjit , Goh Tracy , Shah Keyur , Wiesenthal Stephanie R. , Yoshii Hidenori , Chong Victor , Lam Tony K. T. , Haber C. Andrew , Williams Wendy , Tchipashvili Vaja , Giacca Adria
Published: March 2015

In our previous studies in nondiabetic dogs and humans, insulin suppressed glucose production (GP) by both an indirect extrahepatic and a direct hepatic effect. However, insulin had no direct effect on GP in diabetic depancreatized dogs under conditions of moderate hyperglycemia. The present study was designed to investigate whether insulin can inhibit GP by a direct effect in this model under conditions of euglycemia. Depancreatized dogs were made euglycemic (∼6 mmol/l), rather than moderately hyperglycemic (∼10 mmol/l) as in our previous studies, by basal portal insulin infusion. After ∼100 min of euglycemia, a hyperinsulinemic euglycemic clamp was performed by giving an additional infusion of insulin either portally (POR) or peripherally at about one-half the rate (½ PER) to match the peripheral venous insulin concentrations. The greater hepatic insulin load in POR resulted in greater suppression of GP (from 16.5 ± 1.8 to 12.2 ± 1.6 μmol · kg−1· min−1) than ½ PER (from 17.8 ± 1.9 to 15.6 ± 2.0 μmol · kg−1· min−1, P < 0.001 vs. POR), consistent with insulin having a direct hepatic effect in suppressing GP. We conclude that the direct effect of insulin to inhibit GP is present in diabetic depancreatized dogs under conditions of acutely induced euglycemia. These results suggest that, in diabetes, the prevailing glycemic level is a determinant of the balance between insulin's direct and indirect effects on GP.
Effects of GH on urea, glucose and lipid metabolism, and insulin sensitivity during fasting in GH-deficient patients
Authors: Nørrelund Helene , Djurhuus Christian , Jørgensen Jens Otto Lunde , Nielsen Søren , Nair K. Sreekumaran , Schmitz Ole , Christiansen Jens Sandahl , Møller Niels
Published: March 2015

Fasting-related states of distress pose major health problems, and growth hormone (GH) plays a key role in this context. The present study was designed to assess the effects of GH on substrate metabolism and insulin sensitivity during short-term fasting. Six GH-deficient adults underwent 42.5 h of fasting on two occasions, with and without concomitant GH replacement. Palmitate and urea fluxes were measured with the steady-state isotope dilution technique after infusion of [9,10-3H]palmitate and [13C]urea. During fasting with GH replacement, palmitate concentrations and fluxes increased by 50% [palmitate: 378 ± 42 (GH) vs. 244 ± 12 μmol/l, P < 0.05; palmitate: 412 ± 58 (GH) vs. 276 ± 42 μM, P = 0.05], and urea turnover and excretion decreased by 30–35% [urea rate of appearance: 336 ± 22 (GH) vs. 439 ± 43 μmol · kg–1 · h–1, P < 0.01; urea excretion: 445 ± 43 (GH) vs. 602 ± 74 mmol/24 h, P < 0.05]. Insulin sensitivity (determined by a euglycemic hyperinsulinemic clamp) was significantly decreased [M value: 1.26 ± 0.06 (GH) vs. 2.07 ± 0.22 mg · kg–1 · min–1, P < 0.01] during fasting with GH replacement. In conclusion, continued GH replacement during fasting in GH-deficient adults decreases insulin sensitivity, increases lipid utilization, and conserves protein.
Characterization of leptin pulse dynamics and relationship to fat mass, growth hormone, cortisol, and insulin
Authors: Koutkia Polyxeni , Canavan Bridget , Johnson Michael L. , DePaoli Alex , Grinspoon Steven
Published: March 2015

To investigate the regulation of leptin secretion and pulsatility by fat mass, we performed overnight leptin sampling every 20 min for 12 h and compared leptin dynamics with total body and regional fat measurements in 20 healthy male subjects. Simultaneous growth hormone (GH), cortisol, and insulin levels were assessed to determine relatedness and synchronicity during overnight fasting. Deconvolution analyses were performed to determine simultaneous hormonal dynamics, synchronicity, and interrelatedness using cross-correlation and cross-approximate entropy (X-ApEn) analyses. Subjects demonstrated 4.7 ± 0.4 leptin pulses/12 h. Leptin secretion correlated highly with total body fat ( r = 0.78, P < 0.001) and regional fat depots. In contrast, leptin pulsatility did not correlate with total fat ( r = 0.07, P = 0.785) or other measures of fat. There was synchronicity between GH and leptin (lag -39 minutes), cortisol and leptin (lag -211 min), and leptin and insulin, with leptin following insulin by 275 min. The mean random X-ApEn was significant between leptin and GH (0.854 ± 0.030), cortisol (0.891 ± 0.023), and insulin (0.868 ± 0.034), demonstrating a high degree of regularity and pattern frequency. These data demonstrate differential regulation of leptin secretion and pulsatility in adipocytes and suggest that the leptin pulse generator is extrinsic to fat, whereas fat mass acts as an amplifier to modulate secretion and amplitude for a given pulsatility. We demonstrate synchronicity between leptin and GH, cortisol, and insulin. The directionality of the cross correlation suggests a temporal construct in which changes in leptin follow those of insulin but precede those of GH and cortisol during overnight fasting.
Stimulation of glucose uptake by chronic vanadate pretreatment in cardiomyocytes requires PI 3-kinase and p38 MAPK activation
Authors: Tardif Annie , Julien Nathalie , Chiasson Jean-Louis , Coderre Lise
Published: March 2015

Vanadate, an inhibitor of tyrosine phosphatases, has insulin-mimetic properties. It has been shown that acute vanadate administration enhances glucose uptake independently of phosphatidylinositol (PI) 3-kinase and p38 MAPK. However, therapeutic vanadate use requires chronic administration, and this could potentially involve a different signaling pathway(s). Thus, we examined the mechanisms by which chronic vanadate exposure (16 h) stimulates glucose uptake in primary cultures of adult cardiomyocytes. The effect of vanadate on the activation of insulin-signaling molecules was evaluated 60 min after its withdrawal and in the absence of insulin. We therefore evaluated the persistent effect of vanadate on the insulin-signaling cascade. Our results demonstrate that preincubation with low vanadate concentrations (25–75 μM) induces a dose-dependent increase in glucose uptake. The augmentation of this process was not due to alterations in GLUT1 or GLUT4 protein levels, transcription, or de novo protein synthesis. Chronic vanadate exposure was associated with activation of the insulin receptor, insulin receptor substrate-1 (IRS-1), PKB/Akt, and p38 MAPK. Furthermore, inhibition of PI 3-kinase or p38 MAPK by wortmannin and PD-169316, respectively, significantly inhibited vanadate-mediated glucose uptake in cardiomyocytes. Thus, over time, different (albeit overlapping) signaling cascades may be activated by vanadate.
PTHrP stimulated by the calcium-sensing receptor requires MAP kinase activation
Authors: MacLeod R. John , Chattopadhyay Naibedya , Brown Edward M.
Published: March 2015

Increases in extracellular calcium concentration ([Ca2+]o) stimulate from normal and malignant cells secretion of parathroid hormone-related protein (PTHrP), a major mediator of humoral hypercalcemia of malignancy. Because the calcium-sensing receptor (CaR) is a determinant of calcium-regulated hormone secretion, we examined whether HEK cells stably transfected with human CaR secreted PTHrP in response to CaR stimulation. Increases in [Ca2+]oor neomycin and Gd3+all substantially increased PTHrP secretion in CaR-HEK cells but had no effect on nontransfected cells. CaR activation likewise increased PTHrP transcripts. PD-098059 and U-0126, inhibitors of the mitogen-activated protein kinase kinase MEK1/2, abolished CaR-stimulated secretion but had no effect on basal secretion. An inhibitor of p38 MAP kinase, SB-203580, also attenuated CaR-stimulated secretion. Western analysis revealed that CaR activation caused a robust increase in MEK1/2 and p38 MAP kinase phosphorylation. A Src family kinase inhibitor, PP2, blocked both basal and CaR-stimulated secretion. We conclude that CaR specifically mediates the effect of increasing [Ca2+]oon PTHrP synthesis and secretion and that activated MEK1/2 and p38 MAP kinases are determinants of the CaR's stimulation of PTHrP secretion.
Combination therapy with PPARγ and PPARα agonists increases glucose-stimulated insulin secretion in db/dbmice
Authors: Yajima Ken , Hirose Hiroshi , Fujita Haruhisa , Seto Yoshiko , Fujita Hiroshi , Ukeda Kaname , Miyashita Kiichi , Kawai Toshihide , Yamamoto Yukihiro , Ogawa Takeo , Yamada Taketo , Saruta Takao
Published: March 2015

Although peroxisome proliferator-activated receptor (PPAR)γ agonists ameliorate insulin resistance, they sometimes cause body weight gain, and the effect of PPAR agonists on insulin secretion is unclear. We evaluated the effects of combination therapy with a PPARγ agonist, pioglitazone, and a PPARα agonist, bezafibrate, and a dual agonist, KRP-297, for 4 wk in male C57BL/6J mice and db/db mice, and we investigated glucose-stimulated insulin secretion (GSIS) by in situ pancreatic perfusion. Body weight gain in db/db mice was less with KRP-297 treatment than with pioglitazone or pioglitazone + bezafibrate treatment. Plasma glucose, insulin, triglyceride, and nonesterified fatty acid levels were elevated in untreated db/db mice compared with untreated C57BL/6J mice, and these parameters were significantly ameliorated in the PPARγ agonist-treated groups. Also, PPARγ agonists ameliorated the diminished GSIS and insulin content, and they preserved insulin and GLUT2 staining in db/db mice. GSIS was further increased by PPARγ and -α agonists. We conclude that combination therapy with PPARγ and PPARα agonists may be more useful with respect to body weight and pancreatic GSIS in type 2 diabetes with obesity.
Inhibition of Foxo1 function is associated with improved fasting glycemia in diabetic mice
Authors: Altomonte Jennifer , Richter Anja , Harbaran Sonal , Suriawinata Jenny , Nakae Jun , Thung Swan N. , Meseck Marcia , Accili Domenico , Dong Hengjiang
Published: March 2015

Excessive hepatic glucose production is a contributing factor to fasting hyperglycemia in diabetes. Insulin suppresses hepatic glucose production by inhibiting the expression of two gluconeogenic enzymes, phospho enolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G-6-Pase). The forkhead transcription factor Foxo1 has been implicated as a mediator of insulin action in regulating hepatic gluconeogenesis, and a Foxo1 mutant (Foxo1-Δ256), devoid of its carboxyl domain, has been shown to interfere with Foxo1 function and inhibit gluconeogenic gene expression in cultured cells. To study the effect of Foxo1-Δ256 on glucose metabolism in animals, the Foxo1-Δ256 cDNA was delivered to the livers of mice by adenovirus-mediated gene transfer. Hepatic Foxo1-Δ256 production resulted in inhibition of gluconeogenic activity, as evidenced by reduced PEPCK and G-6-Pase expression in the liver. Mice treated with the Foxo1-Δ256 vector exhibited significantly reduced blood glucose levels. In contrast, blood glucose levels in control vector-treated animals remained unchanged, which coincided with the lack of alterations in the expression levels of PEPCK and G-6-Pase. When tested in diabetic db/db mice, hepatic production of Foxo1-Δ256 was shown to reduce fasting hyperglycemia. Furthermore, we showed that hepatic Foxo1 expression was deregulated as a result of insulin resistance in diabetic mice and that Foxo1-Δ256 interfered with Foxo1 function via competitive binding to target promoters. These results demonstrated that functional inhibition of Foxo1, caused by hepatic expression of its mutant, is associated with reduced hepatic gluconeogenic activity and improved fasting glycemia in diabetic mice.
Central stimulatory effect of leptin on T3production is mediated by brown adipose tissue type II deiodinase
Authors: Cettour-Rose Philippe , Burger Albert G. , Meier Christoph A. , Visser Theo J. , Rohner-Jeanrenaud Françoise
Published: March 2015

To assess whether intracerebroventricular leptin administration affects monodeiodinase type II (D2) activity in the tissues where it is expressed [cerebral cortex, hypothalamus, pituitary, and brown adipose tissue (BAT)], hepatic monodeiodinase type I (D1) activity was inhibited with propylthiouracil (PTU), and small doses of thyroxine (T4; 0.6 nmol · 100 g body wt−1· day−1) were supplemented to compensate for the PTU-induced hypothyroidism. Two groups of rats were infused with leptin for 6 days, one of them being additionally treated with reverse triiodothyronine (rT3), an inhibitor of D2. Control rats were infused with vehicle and pair-fed the amount of food consumed by leptin-infused animals. Central leptin administration produced marked increases in D2 mRNA expression and activity in BAT, changes that were likely responsible for increased plasma T3and decreased plasma T4levels. Indeed, plasma T3and T4concentrations were unaltered by central leptin administration in the presence of rT3. The additional observation of a leptin-induced increased mRNA expression of BAT uncoupling protein-1 suggested that the effect on BAT D2 may be mediated by the sympathetic nervous system.
Regulatory roles for small G proteins in the pancreatic β-cell: lessons from models of impaired insulin secretion
Authors: Kowluru Anjaneyulu
Published: March 2015

Emerging evidence suggests that GTP-binding proteins (G proteins) play important regulatory roles in physiological insulin secretion from the islet β-cell. Such conclusions were drawn primarily from experimental data derived through the use of specific inhibitors of G protein function. Data from gene depletion experiments appear to further substantiate key roles for these signaling proteins in the islet metabolism. The first part of this review will focus on findings supporting the hypothesis that activation of specific G proteins is essential for insulin secretion, including regulation of their function by posttranslational modifications at their COOH-terminal cysteines (e.g., isoprenylation). The second part will overview novel, non-receptor-dependent mechanism(s) whereby glucose might activate specific G proteins via protein histidine phosphorylation. The third section will review findings that appear to link abnormalities in the expression and/or functional activation of these key signaling proteins to impaired insulin secretion. It is hoped that this review will establish a basis for future research in this area of islet signal transduction, which presents a significant potential, not only in identifying key signaling proteins that are involved in physiological insulin secretion, but also in examining potential abnormalities in this signaling cascade that lead to islet dysfunction and onset of diabetes.
Novel concepts in insulin regulation of hepatic gluconeogenesis
Authors: Barthel Andreas , Schmoll Dieter
Published: March 2015

The regulation of hepatic gluconeogenesis is an important process in the adjustment of the blood glucose level, and pathological changes in the glucose production of the liver are a central characteristic in type 2 diabetes. The pharmacological intervention in signaling events that regulate the expression of the key gluconeogenic enzymes phospho enolpyruvate carboxykinase (PEPCK) and the catalytic subunit glucose-6-phosphatase (G-6-Pase) is regarded as a potential strategy for the treatment of metabolic aberrations associated with this disease. However, such intervention requires a detailed understanding of the molecular mechanisms involved in the regulation of this process. Glucagon and glucocorticoids are known to increase hepatic gluconeogenesis by inducing the expression of PEPCK and G-6-Pase. The coactivator protein PGC-1 has been identified as an important mediator of this regulation. In contrast, insulin is known to suppress both PEPCK and G-6-Pase gene expression by the activation of PI 3-kinase. However, PI 3-kinase-independent pathways can also lead to the inhibition of gluconeogenic enzymes. This review focuses on signaling mechanisms and nuclear events that transduce the regulation of gluconeogenic enzymes.
Greater replication and differentiation of preadipocytes in inherited corticosteroid-binding globulin deficiency
Authors: Joyner J. M. , Hutley L. J. , Bachmann A. W. , Torpy D. J. , Prins J. B.
Published: March 2015

Glucocorticoids are pivotal for adipose tissue development. Rodent studies suggest that corticosteroid-binding globulin (CBG) modulates glucocorticoid action in adipose tissue. In humans, both genetic CBG deficiency and suppressed CBG concentrations in hyperinsulinemic states are associated with obesity. We hypothesized that CBG deficiency in humans modulates the response of human preadipocytes to glucocorticoids, predisposing them to obesity. We compared normal preadipocytes with subcultured preadipocytes from an individual with the first ever described complete deficiency of CBG due to a homozygous null mutation. CBG-negative preadipocytes proliferated more rapidly and showed greater peroxisome proliferator-activated receptor-γ-mediated differentiation than normal preadipocytes. CBG was not expressed in normal human preadipocytes. Glucocorticoid receptor number and binding characteristics and 11β-hydroxysteroid dehydrogenase activity were similar for CBG-negative and normal preadipocytes. We propose that the increased proliferation and enhanced differentiation of CBG-negative preadipocytes may promote adipose tissue deposition and explain the obesity seen in individuals with genetic CBG deficiency. Furthermore, these observations may be relevant to obesity occurring with suppressed CBG concentrations associated with hyperinsulinemia.
Splanchnic free fatty acid kinetics
Authors: Jensen Michael D. , Cardin Sylvain , Edgerton Dale , Cherrington Alan
Published: March 2015

These studies were conducted to assess the relationship between visceral adipose tissue free fatty acid (FFA) release and splanchnic FFA release. Steady-state splanchnic bed palmitate ([9,10-3H]palmitate) kinetics were determined from 14 sampling intervals from eight dogs with chronic indwelling arterial, portal vein, and hepatic vein catheters. We tested a model designed to predict the proportion of FFAs delivered to the liver from visceral fat by use of hepatic vein data. The model predicted that 15 ± 2% of hepatic palmitate delivery originated from visceral lipolysis, which was greater ( P = 0.004) than the 11 ± 2% actually observed. There was a good relationship ( r 2 = 0.63) between the predicted and observed hepatic palmitate delivery values, but the model overestimated visceral FFA release more at lower than at higher palmitate concentrations. The discrepancy could be due to differential uptake of FFAs arriving from the arterial vs. the portal vein or to release of FFAs in the hepatic circulatory bed. Splanchnic FFA release measured using hepatic vein samples was strongly related to visceral adipose tissue FFA release into the portal vein. This finding suggests that splanchnic FFA release is a good indicator of visceral adipose tissue lipolysis.
Glucose-dependent insulinotropic polypeptide receptor null mice exhibit compensatory changes in the enteroinsular axis
Authors: Pamir Nathalie , Lynn Francis C. , Buchan Alison M. J. , Ehses Jan , Hinke Simon A. , Pospisilik J. Andrew , Miyawaki Kazumasa , Yamada Yuichiro , Seino Yutaka , McIntosh Christopher H. S. , Pederson Raymond A.
Published: March 2015

The incretins glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are gut hormones that act via the enteroinsular axis to potentiate insulin secretion from the pancreas in a glucose-dependent manner. Both GLP-1 receptor and GIP receptor knockout mice ( GLP-1R−/−and GIPR−/−, respectively) have been generated to investigate the physiological importance of this axis. Although reduced GIP action is a component of type 2 diabetes, GIPR-deficient mice exhibit only moderately impaired glucose tolerance. The present study was directed at investigating possible compensatory mechanisms that take place within the enteroinsular axis in the absence of GIP action. Although serum total GLP-1 levels in GIPR knockout mice were unaltered, insulin responses to GLP-1 from pancreas perfusions and static islet incubations were significantly greater (40–60%) in GIPR−/−than in wild-type ( GIPR+/+) mice. Furthermore, GLP-1-induced cAMP production was also elevated twofold in the islets of the knockout animals. Pancreatic insulin content and gene expression were reduced in GIPR−/−mice compared with GIPR+/+mice. Paradoxically, immunocytochemical studies showed a significant increase in β-cell area in the GIPR-null mice but with less intense staining for insulin. In conclusion, GIPR−/−mice exhibit altered islet structure and topography and increased islet sensitivity to GLP-1 despite a decrease in pancreatic insulin content and gene expression.
AMPK expression and phosphorylation are increased in rodent muscle after chronic leptin treatment
Authors: Steinberg Gregory R. , Rush James W. E. , Dyck David J.
Published: March 2015

We have previously reported that chronic leptin administration (2 wk) increases fatty acid (FA) oxidation and triacylglycerol hydrolysis in rodent soleus muscle. Acute stimulation of AMP-activated protein kinase (AMPK) results in a repartitioning of FA toward oxidation and away from esterification in rodent soleus muscle and has recently been shown to be responsible, at least in part, for the acute stimulatory effect of leptin on FA oxidation. Therefore, we hypothesized that the effects of chronic leptin treatment on muscle FA metabolism are mediated in part through an increased expression and/or activation of AMPK and a subsequent phosphorylation of acetyl-CoA carboxylase and a decrease in malonyl-CoA content. Female Sprague-Dawley rats were infused for 2 wk with leptin (0.5 mg · kg−1· day−1) using subcutaneously implanted mini-osmotic pumps. Control and pair-fed animals received saline-filled implants. Leptin levels were elevated approximately fourfold ( P < 0.001) in treated animals, relative to controls. Chronic leptin treatment resulted in an ∼2- to 3-fold greater protein expression of AMPK catalytic (α2) and regulatory (β2) units as well as a 1.5- to 2-fold increase in Thr172phosphorylation of AMPK in both soleus and white gastrocnemius muscles. The increased expression/phosphorylation of AMPK was not the result of an altered energy status of the muscle. Correspondingly, there was also a 1.5- to 2-fold increase in acetyl-CoA carboxylase (ACC) phosphorylation after leptin treatment in soleus and white gastrocnemius. In spite of the measured increase in ACC phosphorylation after leptin treatment, we were unable to detect a decrease in resting malonyl-CoA content in either muscle. However, taken as a whole, our data support recent evidence in rodent muscle that leptin stimulates FA oxidation through stimulation of AMPK and a subsequent downregulation of ACC activity.
Effects of fatty acids on hepatic amino acid catabolism and fibrinogen synthesis in young healthy volunteers
Authors: Freyse Ernst-Joachim , Giessmann Thomas , Petzke Klaus Jürgen , Knospe Siegfried , Engel Georg , Heinke Peter , Metges Cornelia C. , Siegmund Werner
Published: March 2015

Increased synthesis rate of fibrinogen, an independent risk factor for cardiovascular disease, was recently reported in obese insulin-resistant female adolescents with chronic elevated nonesterified fatty acids (NEFA). It is unknown whether a short-term change of NEFA concentrations controls hepatic fibrinogen synthesis. Therefore, 10 healthy male volunteers (24.5 ± 3.3 yr, body mass index 23.5 ± 2.9 kg/m2) were investigated in random order under basal and elevated NEFA for 8 h. Leucine metabolism, the fractional synthesis rates (FSR) of plasma fibrinogen, and endogenous urea production rates were measured during primed, continuous infusion of [1-13C]leucine and [15N2]urea, respectively. Plasma α-[13C]ketoisocaproic acid and [15N2]urea enrichment values were measured with GC-MS. Plasma fibrinogen was isolated with the β-alanine method, and fibrinogen-related [13C]leucine enrichment was analyzed by GC-CIRMS. Lipofundin infusion and subcutaneous heparin tripled NEFA and triglycerides in the tests. Plasma glucose, circulating insulin, human C-peptide, and plasma glucagon were not changed by the study procedure. Fibrinogen FSR were significantly lower in tests with NEFA elevation (18.44 ± 4.67%) than in control tests (21.48 ± 4.32%; P < 0.05). Plasma fibrinogen concentrations measured were not significantly different (NEFA test subjects: 1.85 ± 0.33, controls: 1.97 ± 0.54 g/l). Parameters of leucine metabolism, such as leucine rate of appearance, leucine oxidation, and nonoxidative leucine disposal, were not influenced by NEFA elevation, and endogenous urea production remained unchanged. NEFA contributes to short-term regulation of fibrinogen FSR in healthy volunteers under unchanged hormonal status, leucine metabolism, and overall amino acid catabolism. Its contribution might be of relevance at least after fat-rich meals, counteracting by reduction of FSR the blood viscosity increase implied by hyperlipidemia.
Role of caveolin and caveolae in insulin signaling and diabetes
Authors: Cohen Alex W. , Combs Terry P. , Scherer Philipp E. , Lisanti Michael P.
Published: March 2015

Caveolae are specialized membrane microdomains present within the plasma membrane of the vast majority of cell types. They have a unique composition in that they are highly enriched in cholesterol, sphingolipids, and their coat proteins the caveolins (-1, -2, and -3). In recent years it has been recognized that caveolae act as signaling platforms, serving as a concentrating point for numerous signaling molecules, as well as regulating flux through many distinct signaling cascades. Although caveolae are found in a variety of cell types, they are most abundant in adipose tissue. This fact has led to the intense study of the function of these organelles in adipocytes. It has now become apparent that effective insulin signaling in the adipocyte may be strictly dependent on localization of at least two insulin-responsive elements to caveolae (insulin receptor and GLUT4), as well as on a direct functional interaction between caveolin-1 and the insulin receptor. We present a critical discussion of these recent findings.
Creatine supplementation has no effect on human muscle protein turnover at rest in the postabsorptive or fed states
Authors: Louis Magali , Poortmans Jacques R. , Francaux Marc , Hultman Eric , Berré Jacques , Boisseau Nathalie , Young Vernon R. , Smith Kenneth , Meier-Augenstein Wolfram , Babraj John A. , Waddell Tom , Rennie Michael J.
Published: March 2015

Dietary creatine supplementation is associated with increases in muscle mass, but the mechanism is unknown. We tested the hypothesis that creatine supplementation enhanced myofibrillar protein synthesis (MPS) and diminished muscle protein breakdown (MPB) in the fed state. Six healthy men (26 ± 7 yr, body mass index 22 ± 4 kg/m2) were studied twice, 2–4 wk apart, before and after ingestion of creatine (21 g/day, 5 days). We carried out two sets of measurements within 5.5 h of both MPS (by incorporation of [1-13C]leucine in quadriceps muscle) and MPB (as dilution of [1-13C]leucine or [2H5]phenylalanine across the forearm); for the first 3 h, the subjects were postabsorptive but thereafter were fed orally (0.3 g maltodextrin and 0.083 g protein · kg body wt−1 · h−1). Creatine supplementation increased muscle total creatine by ∼30% ( P < 0.01). Feeding had significant effects, doubling MPS ( P < 0.001) and depressing MPB by ∼40% ( P < 0.026), but creatine had no effect on turnover in the postabsorptive or fed states. Thus any increase in muscle mass accompanying creatine supplementation must be associated with increased physical activity.
Dual PPARα/γ activation provides enhanced improvement of insulin sensitivity and glycemic control in ZDF rats
Authors: Brand Christian L. , Sturis Jeppe , Gotfredsen Carsten F. , Fleckner Jan , Fledelius Christian , Hansen Bo F. , Andersen Birgitte , Ye Ji-Ming , Sauerberg Per , Wassermann Karsten
Published: March 2015

Improvement of insulin sensitivity and lipid and glucose metabolism by coactivation of both nuclear peroxisome proliferator-activated receptor (PPAR)γ and PPARα potentially provides beneficial effects over existing PPARγ and α preferential drugs, respectively, in treatment of type 2 diabetes. We examined the effects of the dual PPARα/γ agonist ragaglitazar on hyperglycemia and whole body insulin sensitivity in early and late diabetes stages in Zucker diabetic fatty (ZDF) rats and compared them with treatment with the PPARγ preferential agonist rosiglitazone. Despite normalization of hyperglycemia and Hb A1cand reduction of plasma triglycerides by both compounds in both prevention and early intervention studies, ragaglitazar treatment resulted in overall reduced circulating insulin and improved insulin sensitivity to a greater extent than after treatment with rosiglitazone. In late-intervention therapy, ragaglitazar reduced Hb A1cby 2.3% compared with 1.1% by rosiglitazone. Improvement of insulin sensitivity caused by the dual PPARα/γ agonist ragaglitazar seemed to have beneficial impact over that of the PPARγ-preferential activator rosiglitazone on glycemic control in frankly diabetic ZDF rats.
Assessment of transcapillary glucose exchange in human skeletal muscle and adipose tissue
Authors: Regittnig Werner , Ellmerer Martin , Fauler Günter , Sendlhofer Gerald , Trajanoski Zlatko , Leis Hans-Jörg , Schaupp Lukas , Wach Paul , Pieber Thomas R.
Published: March 2015

We studied the kinetics of glucose exchange between plasma and interstitial fluid (ISF) in human skeletal muscle and adipose tissue under fasting conditions. Five normal human subjects received an intravenous [6,6-2H2]glucose infusion in a prime-continuous fashion. During the tracer infusion, the open-flow microperfusion technique was employed to frequently sample ISF from quadriceps muscle and subcutaneous adipose tissue. The tracer glucose kinetics observed in muscle and adipose tissue ISF were found to be well described by a capillary-tissue exchange model. As a measure of transcapillary glucose exchange efficiency, the 95% equilibrium time was calculated from the identified model parameters. This time constant was similar for skeletal muscle and adipose tissue (28.6 ± 3.2 vs. 26.8 ± 3.6 min; P = 0.60). Furthermore, we found that the (total) interstitial glucose concentration was significantly lower ( P < 0.01) in muscle (3.32 ± 0.46 mmol/l) and adipose tissue (3.51 ± 0.17 mmol/l) compared with arterialized plasma levels (5.56 ± 0.13 mmol/l). Thus the observed gradients and dynamic relationships between plasma and ISF glucose in muscle and adipose tissue provide evidence that transcapillary exchange of glucose is limited in these two tissues under fasting conditions.
N-acetylcysteine and taurine prevent hyperglycemia-induced insulin resistance in vivo: possible role of oxidative stress
Authors: Haber C. Andrew , Lam Tony K. T. , Yu Zhiwen , Gupta Neehar , Goh Tracy , Bogdanovic Elena , Giacca Adria , Fantus I. George
Published: March 2015

Exposure to high concentrations of glucose and insulin results in insulin resistance of metabolic target tissues, a characteristic feature of type 2 diabetes. High glucose has also been associated with oxidative stress, and increased levels of reactive oxygen species have been proposed to cause insulin resistance. To determine whether oxidative stress contributes to insulin resistance induced by hyperglycemia in vivo, nondiabetic rats were infused with glucose for 6 h to maintain a circulating glucose concentration of 15 mM with and without coinfusion of the antioxidant N-acetylcysteine (NAC), followed by a 2-h hyperinsulinemic-euglycemic clamp. High glucose (HG) induced a significant decrease in insulin-stimulated glucose uptake [tracer-determined disappearance rate (Rd), control 41.2 ± 1.7 vs. HG 32.4 ± 1.9 mg · kg–1· min–1, P < 0.05], which was prevented by NAC (HG + NAC 45.9 ± 3.5 mg · kg–1· min–1). Similar results were obtained with the antioxidant taurine. Neither NAC nor taurine alone altered Rd. HG caused a significant (5-fold) increase in soleus muscle protein carbonyl content, a marker of oxidative stress that was blocked by NAC, as well as elevated levels of malondialdehyde and 4-hydroxynonenal, markers of lipid peroxidation, which were reduced by taurine. In contrast to findings after long-term hyperglycemia, there was no membrane translocation of novel isoforms of protein kinase C in skeletal muscle after 6 h. These data support the concept that oxidative stress contributes to the pathogenesis of hyperglycemia-induced insulin resistance.
Adipose tissue sensitization to insulin induced by troglitazone and MEDICA 16 in obese Zucker rats in vivo
Authors: Kalderon Bella , Mayorek Nina , Ben-Yaacov Limor , Bar-Tana Jacob
Published: March 2015

The putative role played by insulin sensitizers in modulating adipose tissue lipolysis in the fasting state was evaluated in obese conscious Zucker rats treated with troglitazone or β,β′-tetramethylhexadecanedioic acid (MEDICA 16) and compared with nontreated lean and obese animals. The rates of appearance (Ra) of glycerol and free fatty acid (FFA), primary intra-adipose reesterification, and secondary reuptake of plasma FFA in adipose fat were measured using constant infusion of stable isotope-labeled [2H5]glycerol, [2,2-2H2]palmitate, and radioactive [3H]palmitate. The overall lipolytic flux (Raglycerol) was increased 1.7- and 1.4-fold in obese animals treated with troglitazone or MEDICA 16, respectively, resulting in increased FFA export (Ra FFA) in the troglitazone-treated rats. Primary intra-adipose reesterification of lipolysis-derived fatty acids was enhanced twofold by insulin sensitizers, whereas reesterification of plasma fatty acids was unaffected by either treatment. Despite the unchanged Ra FFA in MEDICA 16 or the increased Ra FFA induced by troglitazone, very low density lipoprotein production rates were robustly curtailed. Total adipose tissue reesterification, used as an estimate of glucose conversion to glyceride-glycerol, was increased 1.9-fold by treatment with the insulin sensitizers. Our results indicate that, in the fasting state, insulin sensitizers induce, in vivo, a significant activation rather than suppression of adipose tissue lipolysis together with stimulation of glucose conversion to glyceride-glycerol.
Testosterone-induced muscle hypertrophy is associated with an increase in satellite cell number in healthy, young men
Authors: Sinha-Hikim Indrani , Roth Stephen M. , Lee Martin I. , Bhasin Shalender
Published: March 2015

Testosterone (T) supplementation in men induces muscle fiber hypertrophy. We hypothesized that T-induced increase in muscle fiber size is associated with a dose-dependent increase in satellite cell number. We quantitated satellite cell and myonuclear number by using direct counting and spatial orientation methods in biopsies of vastus lateralis obtained at baseline and after 20 wk of treatment with a gonadotropin-releasing hormone agonist and a 125-, 300-, or 600-mg weekly dose of T enanthate. T administration was associated with a significant increase in myonuclear number in men receiving 300- and 600-mg doses. The posttreatment percent satellite cell number, obtained by direct counting, differed significantly among the three groups (ANCOVA P < 0.000001); the mean posttreatment values (5.0 and 15.0%) in men treated with 300- and 600-mg doses were greater than baseline (2.5 and 2.5%, respectively, P < 0.05 vs. baseline). The absolute satellite cell number measured by spatial orientation at 20 wk (1.5 and 4.0/mm) was significantly greater than baseline (0.3 and 0.6/mm) in men receiving the 300- and 600-mg doses ( P < 0.05). The change in percent satellite cell number correlated with changes in total ( r = 0.548) and free T concentrations ( r = 0.468). Satellite cell and mitochondrial areas were significantly higher and the nuclear-to-cytoplasmic ratio lower after treatment with 300- and 600-mg doses. We conclude that T-induced muscle fiber hypertrophy is associated with an increase in satellite cell number, a proportionate increase in myonuclear number, and changes in satellite cell ultrastructure.