bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of an organic anion transport system in a placental cell line
Authors: Zhou Fanfan , Tanaka Kunihiko , Soares Michael J. , You Guofeng
Published: March 2015

Transporters within the placenta play a crucial role in the distribution of nutrients and xenobiotics across the maternal-fetal interface. An organic anion transport system was identified on the apical membrane of the rat placenta cell line HRP-1, a model for the placenta barrier. The apical uptake of 3H-labeled organic anion estrone sulfate in HRP-1 cells was saturable ( Km = 4.67 μM), temperature and Na+ dependent, Li+ tolerant, and pH sensitive. The substrate specificity of the transport system includes various steroid sulfates, such as β-estradiol 3,17-disulfate, 17β-estradiol 3-sulfate, and dehydroepiandrosterone 3-sulfate (DHEAS) but does not include taurocholate, p-aminohippuric acid (PAH), and tetraethylammonium. Preincubation of HRP-1 cells with 8-bromo-cAMP (a cAMP analog) and forskolin (an adenylyl cyclase activator) acutely stimulated the apical transport activity. This stimulation was further enhanced in the presence of IBMX (a phosphodiesterase inhibitor). Together these data show that the apical membrane of HRP-1 cells expresses an organic anion transport system that is regulated by cellular cAMP levels. This transport system appears to be different from the known taurocholate-transporting organic anion-transporting polypeptides and PAH-transporting organic anion transporters, both of which also mediate the transport of estrone sulfate and DHEAS.
Body composition assessment in extreme obesity and after massive weight loss induced by gastric bypass surgery
Authors: Das Sai Krupa , Roberts Susan B. , Kehayias Joseph J. , Wang Jack , Hsu L. K. George , Shikora Scott A. , Saltzman Edward , McCrory Megan A
Published: March 2015

Body composition methods were examined in 20 women [body mass index (BMI) 48.7 ± 8.8 kg/m2] before and after weight loss [−44.8 ± 14.6 (SD) kg] after gastric bypass (GBP) surgery. The reference method, a three-compartment (3C) model using body density by air displacement plethysmography and total body water (TBW) by H2 18O dilution (3C-H2 18O), showed a decrease in percent body fat (%BF) from 51.4 to 34.6%. Fat-free mass hydration was significantly higher than the reference value (0.738) in extreme obesity (0.756; P < 0.001) but not after weight reduction (0.747; P = 0.16). %BF by H2 18O dilution and air displacement plethysmography differed significantly from %BF by 3C-H2 18O in extreme obesity ( P< 0.05) and 3C models using 2H2O or bioelectrical impedance analysis (BIA) to determine TBW improved mean %BF estimates over most other methods at both time points. BIA results varied with the equation used, but BIA better predicted %BF than did BMI at both time points. All methods except BIA using the Segal equation were comparable to the reference method for determining changes over time. A simple 3C model utilizing air displacement plethysmography and BIA is useful for clinical evaluation in this population.
Modeling of Ca2+flux in pancreatic β-cells: role of the plasma membrane and intracellular stores
Authors: Fridlyand Leonid E. , Tamarina Natalia , Philipson Louis H.
Published: March 2015

We have developed a detailed mathematical model of ionic flux in β-cells that includes the most essential channels and pumps in the plasma membrane. This model is coupled to equations describing Ca2+, inositol 1,4,5-trisphosphate (IP3), ATP, and Na+homeostasis, including the uptake and release of Ca2+by the endoplasmic reticulum (ER). In our model, metabolically derived ATP activates inward Ca2+flux by regulation of ATP-sensitive K+channels and depolarization of the plasma membrane. Results from the simulations support the hypothesis that intracellular Na+and Ca2+in the ER can be the main variables driving both fast (2–7 osc/min) and slow intracellular Ca2+concentration oscillations (0.3–0.9 osc/min) and that the effect of IP3on Ca2+leak from the ER contributes to the pattern of slow calcium oscillations. Simulations also show that filling the ER Ca2+stores leads to faster electrical bursting and Ca2+oscillations. Specific Ca2+oscillations in isolated β-cell lines can also be simulated.
White adipose tissue contributes to UCP1-independent thermogenesis
Authors: Granneman J. G. , Burnazi M. , Zhu Z. , Schwamb L. A.
Published: March 2015

β3-Adrenergic receptors (AR) are nearly exclusively expressed in brown and white adipose tissues, and chronic activation of these receptors by selective agonists has profound anti-diabetes and anti-obesity effects. This study examined metabolic responses to acute and chronic β3-AR activation in wild-type C57Bl/6 mice and congenic mice lacking functional uncoupling protein (UCP)1, the molecular effector of brown adipose tissue (BAT) thermogenesis. Acute activation of β3-AR doubled metabolic rate in wild-type mice and sharply elevated body temperature and BAT blood flow, as determined by laser Doppler flowmetry. In contrast, β3-AR activation did not increase BAT blood flow in mice lacking UCP1 (UCP1 KO). Nonetheless, β3-AR activation significantly increased metabolic rate and body temperature in UCP1 KO mice, demonstrating the presence of UCP1-independent thermogenesis. Daily treatment with the β3-AR agonist CL-316243 (CL) for 6 days increased basal and CL-induced thermogenesis compared with naive mice. This expansion of basal and CL-induced metabolic rate did not require UCP1 expression. Chronic CL treatment of UCP1 KO mice increased basal and CL-stimulated metabolic rate of epididymal white adipose tissue (EWAT) fourfold but did not alter BAT thermogenesis. After chronic CL treatment, CL-stimulated thermogenesis of EWAT equaled that of interscapular BAT per tissue mass. The elevation of EWAT metabolism was accompanied by mitochondrial biogenesis and the induction of genes involved in lipid oxidation. These observations indicate that chronic β3-AR activation induces metabolic adaptation in WAT that contributes to β3-AR-mediated thermogenesis. This adaptation involves lipid oxidation in situ and does not require UCP1 expression.
Aging is associated with elevated muscle triglyceride content and increased insulin-stimulated fatty acid uptake
Authors: Tucker Michelle Z. , Turcotte Lorraine P.
Published: March 2015

The purpose of the present study was to examine the utilization of fatty acids (FA) and muscle substrates by skeletal muscle in young, middle-aged, and old adult rats under hyperglycemic and hyperinsulinemic conditions. Male Fischer 344 × Brown Norway rats aged 5, 15, or 24 mo underwent hindlimb perfusion with a medium of 20 mM glucose, 1 mM palmitate, 1,000 μU/ml insulin, [1-14C]palmitate, and [3-3H]glucose. Glucose uptake and palmitate delivery were similar among age groups. Palmitate uptake and oxidation as well as muscle protein concentration of fatty acid translocase (FAT/CD36) and plasma membrane fatty acid-binding protein (FABPPM) were significantly increased ( P ≤ 0.05) in 24- vs. 5- and 15-mo-old animals. Compared with 5- and 15-mo-old animals, pre- and postperfusion muscle triglyceride (TG) levels were significantly ( P < 0.05) elevated 72–145% in red and 112–129% in white muscles of 24-mo-old animals. Palmitate uptake was associated with total preperfusion TG concentration ( r2= 0.27, P < 0.05) and total TG synthesis rate ( r2= 0.68, P < 0.05). These results indicate that, under insulin-stimulated conditions, FA uptake is significantly increased in old animals, which is associated with increased rates of TG synthesis and may contribute to the accumulation of TG in muscle of old animals.
Akt signaling in skeletal muscle: regulation by exercise and passive stretch
Authors: Sakamoto Kei , Aschenbach William G. , Hirshman Michael F. , Goodyear Laurie J.
Published: March 2015

Akt/protein kinase B is a serine/threonine kinase that has emerged as a critical signaling component for mediating numerous cellular responses. Contractile activity has recently been demonstrated to stimulate Akt signaling in skeletal muscle. Whether physiological exercise in vivo activates Akt is controversial, and the initiating factors that result in the stimulation of Akt during contractile activity are unknown. In the current study, we demonstrate that treadmill running exercise of rats using two different protocols (intermediate high or high-intensity exhaustive exercise) significantly increases Akt activity and phosphorylation in skeletal muscle composed of various fiber types. To determine if Akt activation during contractile activity is triggered by mechanical forces applied to the skeletal muscle, isolated skeletal muscles were incubated and passively stretched. Passive stretch for 10 min significantly increased Akt activity (2-fold) in the fast-twitch extensor digitorum longus (EDL) muscle. However, stretch had no effect on Akt in the slow-twitch soleus muscle, although there was a robust phosphorylation of the stress-activated protein kinase p38. Similar to contraction, stretch-induced Akt activation in the EDL was fully inhibited in the presence of the phosphatidylinositol 3-kinase inhibitor wortmannin, whereas glycogen synthase kinase-3 (GSK3) phosphorylation was only partially inhibited. Stretch did not cause dephosphorylation of glycogen synthase on GSK3-targeted sites in the absence or presence of wortmannin. We conclude that physiological exercise in vivo activates Akt in multiple skeletal muscle fiber types and that mechanical tension may be a part of the mechanism by which contraction activates Akt in fast-twitch muscles.
Disruption of microtubules in rat skeletal muscle does not inhibit insulin- or contraction-stimulated glucose transport
Authors: Ai Hua , Ralston Evelyn , Lauritzen Hans P. M. M. , Galbo Henrik , Ploug Thorkil
Published: March 2015

Insulin and muscle contractions stimulate glucose transport in skeletal muscle through a translocation of intracellular GLUT4 glucose transporters to the cell surface. Judged by immunofluorescence microscopy, part of the GLUT4 storage sites is associated with the extensive microtubule cytoskeleton found in all muscle fibers. Here, we test whether microtubules are required mediators of the effect of insulin and contractions. In three different incubated rat muscles with distinct fiber type composition, depolymerization of microtubules with colchicine for ≤8 h did not inhibit insulin- or contraction-stimulated 2-deoxyglucose transport or force production. On the contrary, colchicine at least partially prevented the ∼30% decrease in insulin-stimulated transport that specifically developed during 8 h of incubation in soleus muscle but not in flexor digitorum brevis or epitrochlearis muscles. In contrast, nocodazole, another microtubule-disrupting drug, rapidly and dose dependently blocked insulin- and contraction-stimulated glucose transport. A similar discrepancy between colchicine and nocodazole was also found in their ability to block glucose transport in muscle giant “ghost” vesicles. This suggests that the ability of insulin and contractions to stimulate glucose transport in muscle does not require an intact microtubule network and that nocodazole inhibits glucose transport independently of its microtubule-disrupting effect.
Melanotrope secretory cycle is regulated by physiological inputs via the hypothalamus
Authors: Vazquez-Martinez Rafael , Castaño Justo P. , Tonon Marie Christine , Vaudry Hubert , Gracia-Navarro Francisco , Malagon Maria M.
Published: March 2015

Previously, it has been shown that background color conditions regulate the overall activity of the frog intermediate lobe by varying the proportions of the two subtypes of melanotropes existing in the gland, the highly active or secretory melanotropes and hormone storage melanotropes, depending on melanocyte-stimulating hormone requirements. However, the factors and mechanisms underlying these background-induced changes are still unknown. In the present study, we investigated whether hypothalamic factors known to regulate melanotrope cell function can induce changes in vitro similar to those caused by background adaptation in vivo. We found that the inhibitors apomorphine (a dopamine receptor agonist) and neuropeptide Y decreased the number of active melanotropes and increased simultaneously that of storage melanotropes. On the other hand, the stimulator TRH increased the number of active cells and concomitantly reduced that of storage cells. Inasmuch as none of these treatments modified the apoptotic and proliferation rates in melanotrope cells, it appears that these hypothalamic factors caused actual interconversions of cells from a subpopulation to its counterpart. Taken together, these findings suggest that the hypothalamus would control melanotrope activity not only through short-term regulation of hormone synthesis and release, but also through a long-term regulation of the secretory phenotype of these cells whereby the activity of the intermediate lobe would be adjusted to fulfill the hormonal requirements imposed by background conditions.
Glucosamine and glucose induce insulin resistance by different mechanisms in rat skeletal muscle
Authors: Han Dong-Ho , Chen May M. , Holloszy John O.
Published: March 2015

It has been hypothesized that glucose-induced insulin resistance is mediated by accumulation of UDP- N-acetylhexosamines (UDP-HexNAcs). In a previous study on rat epitrochlearis muscles incubated with high concentrations of glucose and insulin (Kawanaka K, D-H Han, J Gao, LA Nolte, and JO Holloszy. J Biol Chem 276: 20101–20107, 2001), we found that insulin resistance developed even when the increase in UDP-Hex-NAcs was prevented. Furthermore, actinomycin D completely prevented glucose-induced insulin resistance despite a greater accumulation of UDP-HexNAcs. In the present study, we used the same epitrochlearis muscle preparation, as well as the rat hemidiaphragm, to determine whether, like glucose, glucosamine causes insulin resistance by an actinomycin D-inhibitable process. Incubation of diaphragm muscles with 10 mM glucosamine for 3 h resulted in an approximately fivefold increase in UDP-HexNAcs, an ∼50% reduction in insulin responsiveness of glucose transport, and a 58% reduction in ATP concentration. These effects of glucosamine were not prevented by actinomycin D. Incubation of epitrochlearis muscles with 20 mM glucosamine for 3 h or with 10 mM glucosamine for 5 h also caused large decreases in insulin responsiveness of glucose transport but with no reduction in ATP concentration. Actinomycin D did not prevent the glucosamine-induced insulin resistance. The insulin-induced increases in tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and the binding of PI 3-kinase to IRS-1 were decreased ∼60% in epitrochlearis muscles exposed to glucosamine. This is in contrast to glucose-induced insulin resistance, which was not associated with impaired insulin signaling. These results provide evidence that glucosamine and glucose induce insulin resistance by different mechanisms.
Characterization and identification of steroid sulfate transporters of human placenta
Authors: Ugele Bernhard , St-Pierre Marie V. , Pihusch Monika , Bahn Andrew , Hantschmann Peer
Published: March 2015

Human trophoblasts depend on the supply of external precursors, such as dehydroepiandrosterone-3-sulfate (DHEA-S) and 16α-OH-DHEA-S, for synthesis of estrogens. The aim of the present study was to characterize the uptake of DHEA-S by isolated mononucleated trophoblasts (MT) and to identify the involved transporter polypeptides. The kinetic analysis of DHEA-35S uptake by MT revealed a saturable uptake mechanism ( Km= 26 μM, Vmax= 428 pmol · mg protein−1· min−1), which was superimposed by a nonsaturable uptake mechanism (diffusion constant = 1.2 μl · mg protein−1· min−1). Uptake of [3H]DHEA-S by MT was Na+dependent and inhibited by sulfobromophthalein (BSP), steroid sulfates, and probenecid, but not by steroid glucuronides, unconjugated steroids, conjugated bile acids, ouabain, p-aminohippurate (PAH), and bumetanide. MT took up [35S]BSP, [3H]estrone-sulfate, but not3H-labeled ouabain, estradiol-17β-glucuronide, taurocholate, and PAH. RT-PCR revealed that the organic anion-transporting polypeptides OATP-B, -D, -E, and the organic anion transporter OAT-4 are highly expressed, and that OATP-A, -C, -8, OAT-3, and Na+-taurocholate cotransporting polypeptide (NTCP) are not or are only lowly expressed in term placental tissue and freshly isolated and cultured trophoblasts. Immunohistochemistry of first- and third-trimester placenta detected OAT-4 on cytotrophoblast membranes and at the basal surface of the syncytiotrophoblast. Our results indicate that uptake of steroid sulfates by isolated MT is mediated by OATP-B and OAT-4 and suggest a physiological role of both carrier proteins in placental uptake of fetal-derived steroid sulfates.
Resistance to high-fat diet-induced obesity and altered expression of adipose-specific genes in HSL-deficient mice
Authors: Harada Kenji , Shen Wen-Jun , Patel Shailja , Natu Vanita , Wang Jining , Osuga Jun-ichi , Ishibashi Shun , Kraemer Fredric B.
Published: March 2015

To elucidate the role of hormone-sensitive lipase (HSL) in diet-induced obesity, HSL-deficient ( HSL–/–) and wild-type mice were fed normal chow or high-fat diets. HSL–/–mice were resistant to diet-induced obesity showing higher core body temperatures. Weight and triacylglycerol contents were decreased in white adipose tissue (WAT) but increased in both brown adipose tissue (BAT) and liver of HSL–/–mice. Serum insulin levels in the fed state and tumor necrosis factor-α mRNA levels in adipose tissues were higher, whereas serum levels of adipocyte complement-related protein of 30 kDa (ACRP30)/adiponectin and leptin, as well as mRNA levels of ACRP30/adiponectin, leptin, resistin, and adipsin in WAT, were lower in HSL–/–mice than in controls. Expression of transcription factors associated with adipogenesis (peroxisome proliferator-activated receptor-γ, CAAT/enhancer-binding protein-α) and lipogenesis (carbohydrate response element-binding protein, adipocyte determination- and differentiation-dependent factor-1/sterol regulatory element-binding protein-1c), as well as of adipose differentiation markers (adipocyte lipid-binding protein, perilipin, lipoprotein lipase), lipogenic enzymes (glycerol-3-phosphate acyltransferase, acyl-CoA:diacylglycerol acyltransferase-1 and -2, fatty acid synthase, ATP citrate lyase) and insulin signaling proteins (insulin receptor, insulin receptor substrate-1, GLUT4), was suppressed in WAT but not in BAT of HSL–/–mice. In contrast, expression of genes associated with cholesterol metabolism (sterol-regulatory element-binding protein-2, 3-hydroxy-3-methylglutaryl-CoA reductase, acyl-CoA:cholesterol acyltransferase-1) and thermogenesis (uncoupling protein-2) was upregulated in both WAT and BAT of HSL–/–mice. Our results suggest that impaired lipolysis in HSL deficiency affects lipid metabolism through alterations of adipose differentiation and adipose-derived hormone levels.
ATP-sensitive K+ channel-mediated glucose uptake is independent of IRS-1/phosphatidylinositol 3-kinase signaling
Authors: Minami Kohtaro , Morita Mizuo , Saraya Atsunori , Yano Hideki , Terauchi Yasuo , Miki Takashi , Kuriyama Takayuki , Kadowaki Takashi , Seino Susumu
Published: March 2015

We previously found that disruption of Kir6.2-containing ATP-sensitive K+ (Katp) channels increases glucose uptake in skeletal muscle, but the mechanism is not clear. In the present study, we generated knockout mice lacking both Kir6.2 and insulin receptor substrate-1 (IRS-1). Because IRS-1 is the major substrate of insulin receptor kinase, we expected disruption of the IRS-1 gene to reduce glucose uptake in Kir6.2 knockout mice. However, the double-knockout mice do not develop insulin resistance or glucose intolerance. An insulin tolerance test reveals the glucose-lowering effect of exogenous insulin in double-knockout mice and in Kir6.2 knockout mice to be similarly enhanced compared with wild-type mice. The basal 2-deoxyglucose uptake rate in skeletal muscle of double-knockout mice is increased similarly to the rate in Kir6.2 knockout mice. Accordingly, disruption of the IRS-1 gene affects neither systemic insulin sensitivity nor glucose uptake in skeletal muscles of Kir6.2-deficient mice. In addition, no significant changes were observed in phosphatidylinositol 3-kinase (PI3K) activity and its downstream signal in skeletal muscle due to lack of the Kir6.2 gene. Disruption of Kir6.2-containing Katp channels clearly protects against IRS-1-associated insulin resistance by increasing glucose uptake in skeletal muscles by a mechanism separate from the IRS-1/PI3K pathway.
Sexual dimorphism is associated with decreased expression of processed myostatin in males
Authors: McMahon Christopher D. , Popovic Ljiljana , Jeanplong Ferenc , Oldham Jenny M. , Kirk Sonnie P. , Osepchook Claire C. , Wong Karen W. Y. , Sharma Mridula , Kambadur Ravi , Bass John J.
Published: March 2015

Myostatin inhibits skeletal muscle development. Therefore, we sought to determine whether larger body and muscle mass in male mice was associated with lower mRNA and protein expression of myostatin compared with females. Ten male and ten female mice of the C57 strain were killed at 16–18 wk of age, and their biceps femoris, gastrocnemius, and quadriceps femoris muscles were collected. Body and muscle masses were 40% heavier ( P < 0.001) in males than in females. Northern analysis showed no difference in mRNA between males and females. In contrast, Western analysis showed that processed myostatin (26 kDa) was 40–60% lower ( P < 0.001) in males compared with females. These data show first that decreased processed myostatin is a posttranscriptional and posttranslational event and, second, that decreased abundance of processed myostatin is associated with increased body mass and skeletal muscle mass in male compared with female mice.
Vasodilator effects of l-arginine are stereospecific and augmented by insulin in humans
Authors: Dallinger Susanne , Sieder Anna , Strametz Jeanette , Bayerle-Eder Michaela , Wolzt Michael , Schmetterer Leopold
Published: March 2015

The amino acid l-arginine, the precursor of nitric oxide (NO) synthesis, induces vasodilation in vivo, but the mechanism behind this effect is unclear. There is, however, some evidence to assume that the l-arginine membrane transport capacity is dependent on insulin plasma levels. We hypothesized that vasodilator effects of l-arginine may be dependent on insulin plasma levels. Accordingly, we performed two randomized, double-blind crossover studies in healthy male subjects. In protocol 1 ( n = 15), subjects received an infusion of insulin (6 mU · kg−1 · min−1for 120 min) or placebo and, during the last 30 min,l-arginine or d-arginine (1 g/min for 30 min). In protocol 2 ( n = 8), subjects receivedl-arginine in stepwise increasing doses in the presence (1.5 mU · kg−1 · min−1) or absence of insulin. Renal plasma flow and glomerular filtration rate were assessed by the para-aminohippurate and inulin plasma clearance methods, respectively. Pulsatile choroidal blood flow was assessed with laser interferometric measurement of fundus pulsation, and mean flow velocity in the ophthalmic artery was measured with Doppler sonography.l-arginine, but not d-arginine, significantly increased renal and ocular hemodynamic parameters. Coinfusion ofl-arginine with insulin caused a dose-dependent leftward shift of the vasodilator effect of l-arginine. This stereospecific renal and ocular vasodilator potency ofl-arginine is enhanced by insulin, which may result from facilitated l-arginine membrane transport, enhanced intracellular NO formation, or increased NO bioavailability.
Routes of FA delivery to cardiac muscle: modulation of lipoprotein lipolysis alters uptake of TG-derived FA
Authors: Augustus Ayanna S. , Kako Yuko , Yagyu Hiroaki , Goldberg Ira J.
Published: March 2015

Long-chain fatty acids (FA) supply 70–80% of the energy needs for normal cardiac muscle. To determine the sources of FA that supply the heart, [14C]palmitate complexed to bovine serum albumin and [3H]triolein [triglyceride (TG)] incorporated into Intralipid were simultaneously injected into fasted male C57BL/6 mice. The ratio of TG to FA uptake was much greater for hearts than livers. Using double-labeled Intralipid with [3H]cholesteryl oleoyl ether (CE) and [14C]TG, we observed that hearts also internalize intact core lipid. Inhibition of lipoprotein lipase (LPL) with tetrahydrolipstatin or dissociation of LPL from the heart with heparin reduced cardiac uptake of TG by 82 and 64%, respectively ( P < 0.01). Palmitate uptake by the heart was not changed by either treatment. Uptake of TG was 88% less in hearts from LPL knockout mice that were rescued via LPL expression in the liver. Our data suggest that the heart is especially effective in removal of circulating TG and core lipids and that this is due to LPL hydrolysis and not its bridging function.
PPARα/γ ragaglitazar eliminates fatty liver and enhances insulin action in fat-fed rats in the absence of hepatomegaly
Authors: Ye Ji-Ming , Iglesias Miguel A. , Watson David G. , Ellis Bronwyn , Wood Leonie , Jensen Per Bo , Sørensen Rikke Veggerby , Larsen Philip Just , Cooney Gregory J. , Wassermann Karsten , Kraegen Edward W.
Published: March 2015

Peroxisome proliferator-activated receptor (PPAR)α and PPARγ agonists lower lipid accumulation in muscle and liver by different mechanisms. We investigated whether benefits could be achieved on insulin sensitivity and lipid metabolism by the dual PPARα/γ agonist ragaglitazar in high fat-fed rats. Ragaglitazar completely eliminated high-fat feeding-induced liver triglyceride accumulation and visceral adiposity, like the PPARα agonist Wy-14643 but without causing hepatomegaly. In contrast, the PPARγ agonist rosiglitazone only slightly lessened liver triglyceride without affecting visceral adiposity. Compared with rosiglitazone or Wy-14643, ragaglitazar showed a much greater effect (79%, P< 0.05) to enhance insulin's suppression of hepatic glucose output. Whereas all three PPAR agonists lowered plasma triglyceride levels and lessened muscle long-chain acyl-CoAs, ragaglitazar and rosiglitazone had greater insulin-sensitizing action in muscle than Wy-14643, associated with a threefold increase in plasma adiponectin levels. There was a significant correlation of lipid content and insulin action in liver and particularly muscle with adiponectin levels ( P < 0.01). We conclude that the PPARα/γ agonist ragaglitazar has a therapeutic potential for insulin-resistant states as a PPARγ ligand, with possible involvement of adiponectin. Additionally, it can counteract fatty liver, hepatic insulin resistance, and visceral adiposity generally associated with PPARα activation, but without hepatomegaly.
Leptin response to short-term fasting in sympathectomized men: role of the SNS
Authors: Jeon Justin Y. , Harber Vicki J. , Steadward Robert D.
Published: March 2015

We studied plasma leptin levels in six people with high-lesion spinal cord injury [SCI; body mass index (BMI) 25.9 ± 1.5 kg/m2, age 37 ± 3.0 yr] and six able-bodied (AB) controls (BMI 29.1 ± 1.9 kg/m2, age 35 ± 3.5 yr) before and after 12, 24, and 36 h of fasting. The plasma leptin levels significantly decreased during 36 h fasting by 48.8 ± 4.5% (pre: 11.3 ± 2.3, post: 6.2 ± 1.5 ng/ml) and 38.6 ± 7.9% (pre: 7.6 ± 5.0, post: 4.2 ± 1.0 ng/ml) in SCI and AB, respectively. Plasma leptin started to decrease at 24 h of fasting in the SCI group, whereas plasma leptin started to decrease at 12 h of fasting in the AB group. The current study demonstrated that plasma leptin decreased with fasting in both SCI and AB groups, with the leptin decrease being delayed in the SCI group. The delayed leptin response to fasting in the SCI group may be because of increased fat mass (%body fat, SCI: 33.8 ± 3.0, AB: 24.1 ± 2.9) and sympathetic nervous system dysfunction.
Somatotropin-induced protein anabolism in hindquarters and portal-drained viscera of growing pigs
Authors: Bush Jill A. , Burrin Douglas G. , Suryawan Agus , O'Connor Pamela M. J. , Nguyen Hanh V. , Reeds Peter J. , Steele Norman C. , Van Goudoever Johannes B. , Davis Teresa A.
Published: March 2015

To differentiate the effect of somatotropin (ST) treatment on protein metabolism in the hindquarter (HQ) and portal-drained viscera (PDV), growing swine ( n = 20) treated with ST (0 or 150 μg · kg−1 · day−1) for 7 days were infused intravenously with NaH13CO3 and [2H5]phenylalanine and enterally with [1-13C]phenylalanine while in the fed state. Arterial, portal venous, and vena cava whole blood samples, breath samples, and blood flow measurements were obtained for determination of tissue and whole body phenylalanine kinetics under steady-state conditions. In the fed state, ST treatment decreased whole body phenylalanine flux, oxidation, and protein degradation without altering protein synthesis, resulting in an improvement in whole body net protein balance. Blood flow to the HQ (+80%), but not to the PDV, was increased with ST treatment. In the HQ and PDV, ST increased phenylalanine uptake (+44 and +23%, respectively) and protein synthesis (+43 and +41%, respectively), with no effect on protein degradation. In ST-treated and control pigs, phenylalanine was oxidized in the PDV (34–43% of enteral and arterial sources) but not the HQ. In both treatment groups, dietary (40%) rather than arterial (10%) extraction of phenylalanine predominated in gut amino acid metabolism, whereas localized blood flow influenced HQ amino acid metabolism. The results indicate that ST increases protein anabolism in young, growing swine by increasing protein synthesis in the HQ and PDV, with no effect on protein degradation. Differing results between the whole body and the HQ and PDV suggest that the effect of ST treatment on protein metabolism is tissue specific.
Effect of heterozygous PPARγ deficiency and TZD treatment on insulin resistance associated with age and high-fat feeding
Authors: Miles Philip D. G. , Barak Yaacov , Evans Ronald M. , Olefsky Jerrold M.
Published: March 2015

Peroxisome proliferator-activated receptor-γ (PPARγ) is the target receptor for thiazolidinedione (TZD) compounds, which are a class of insulin-sensitizing drugs used in the treatment of type 2 diabetes. Paradoxically, however, mice deficient in PPARγ ( PPARγ+/−) are more insulin sensitive than their wild-type (WT) littermates, not less, as would be predicted. To determine whether PPARγ deficiency could prevent the development of the insulin resistance associated with increasing age or high-fat (HF) feeding, insulin sensitivity was assessed in PPARγ+/−and WT mice at 2, 4, and 8 mo of age and in animals fed an HF diet. Because TZDs elicit their effect through PPARγ receptor, we also examined the effect of troglitazone (a TZD) in these mice. Glucose metabolism was assessed by hyperinsulinemic euglycemic clamp and oral glucose tolerance test. Insulin sensitivity declined with age for both groups. However, the decline in the PPARγ+/−animals was substantially less than that of the WT animals, such that, by 8 mo of age, the PPARγ+/−mice were markedly more insulin sensitive than the WT mice. This greater sensitivity in PPARγ+/−mice was lost with TZD treatment. HF feeding led to marked adipocyte hypertrophy and peripheral tissue and hepatic insulin resistance in WT mice but also in PPARγ+/−mice. Treatment of these mice with troglitazone completely prevented the adipocyte hypertrophy and normalized insulin action. In conclusion, PPARγ deficiency partially protects against age-related insulin resistance but does not protect against HF diet-induced insulin resistance.
Myogenic and nonmyogenic cells differentially express proteinases, Hsc/Hsp70, and BAG-1 during skeletal muscle regeneration
Authors: Duguez Stéphanie , Bihan Marie-Catherine Le , Gouttefangeas Dominique , Féasson Léonard , Freyssenet Damien
Published: March 2015

Skeletal muscle has a remarkable capacity to regenerate after injury. To determine whether changes in the expression of proteinases, 73-kDa constitutive heat shock cognate protein (Hsc70) and stress-inducible 72-kDa heat shock protein (Hsp70) (Hsc/Hsp70), and Bcl-2-associated gene product-1 (BAG-1) contribute to the remodeling response of muscle tissue, tibialis anterior muscles of male Sprague-Dawley rats were injected with 0.75% bupivacaine and removed at 3, 5, 7, 10, 14, 21, or 35 days postinjection ( n = 5–7/group). The immunohistochemical analysis of desmin, α-actin, and developmental/neonatal myosin heavy chain expressions indicated the presence of myoblasts ( days 3–7), inflammatory cells ( days 3–7), degenerating myofibers ( days 3–7), regenerating myofibers ( days 5–10), and growing mature myofibers ( days 10–21) in regenerating muscles. Our biochemical analysis documented profound adaptations in proteolytic metabolism characterized by significant increases in the enzyme activities of matrix metalloproteinases 2 and 9 and plasminogen activators ( days 3–14), calpains 1 and 2 ( days 3–7), cathepsins B and L( days 3–10), and proteasome ( days 3–14). Proteasome activity was strongly correlated with proliferating cell nuclear antigen protein level, suggesting that proteasome played a key role in myoblast proliferation. The expression pattern of BAG-1, a regulatory cofactor of Hsc/Hsp70 at the interface between protein folding and proteasomal proteolysis, did not corroborate the changes in proteasome enzyme activity, suggesting that BAG-1 may promote other functions, such as the folding capacity of Hsc/Hsp70. Altogether, the diversity of functions attributed to proteinases in the present study was strongly supported by the relative changes in the proportion of myogenic and nonmyogenic cells over the time course of regeneration.
Endotoxin induces differential regulation of mTOR-dependent signaling in skeletal muscle and liver of neonatal pigs
Authors: Kimball Scot R. , Orellana Renán A. , O'Connor Pamela M. J. , Suryawan Agus , Bush Jill A. , Nguyen Hanh V. , Thivierge M. Carole , Jefferson Leonard S. , Davis Teresa A.
Published: March 2015

In the present study, differential responses of regulatory proteins involved in translation initiation in skeletal muscle and liver during sepsis were studied in neonatal pigs treated with lipopolysaccharide (LPS). LPS did not alter eukaryotic initiation factor (eIF) 2B activity in either tissue. In contrast, binding of eIF4G to eIF4E to form the active mRNA-binding complex was repressed in muscle and enhanced in liver. Phosphorylation of eIF4E-binding protein, 4E-BP1, and ribosomal protein S6 kinase, S6K1, was reduced in muscle during sepsis but increased in liver. Finally, changes in 4E-BP1 and S6K1 phosphorylation were associated with altered phosphorylation of the protein kinase mammalian target of rapamycin (mTOR). Overall, the results suggest that translation initiation in both skeletal muscle and liver is altered during neonatal sepsis by modulation of the mRNA-binding step through changes in mTOR activation. Moreover, the LPS-induced changes in factors that regulate translation initiation are more profound than previously reported changes in global rates of protein synthesis in the neonate. This finding suggests that the initiator methionyl-tRNA-rather than the mRNA-binding step in translation initiation may play a more critical role in maintaining protein synthesis rates in the neonate during sepsis.
Obesity in transgenic female mice with constitutively elevated luteinizing hormone secretion
Authors: Kero Jukka T. , Savontaus Eriika , Mikola Maarit , Pesonen Ullamari , Koulu Markku , Keri Ruth A. , Nilson John H. , Poutanen Matti , Huhtaniemi Ilpo T.
Published: March 2015

Transgenic (TG) female mice, expressing a chimeric bovine luteinizing hormone (LH) β-subunit/human chorionic gonadotropin β-subunit COOH-terminal extension (bLHβ-CTP) gene, produce high levels of circulating LH and serve as a model for functional ovarian hyperandrogenism and follicular cysts. We report here that obesity is a typical feature of these female mice. The mean body weight of the bLHβ-CTP females was significantly higher than in controls at, and beyond 5 wk of age, and at 5 mo, it was 32% increased. At this age, the amount of white adipose tissue in the bLHβ-CTP females was significantly increased, as reflected by the weight difference of the retroperitoneal fat pad. In addition, the expression of leptin mRNA in white adipose tissue of the TG females was elevated about twofold. Serum leptin and insulin levels, and food intake, were also increased significantly in the TG females. Brown adipose tissue (BAT) thermogenic activity, as measured by GDP binding to BAT mitochondria, was reduced ( P < 0.05). Ovariectomy at the age of 3 wk totally prevented the development of obesity. In summary, the present results show that intact female bLHβ-CTP mice are obese, have increased food consumption, and reduced BAT thermogenic activity. The weight gain can be explained partly by elevated androgens but is probably also contributed to the increased adrenal steroidogeneisis. Hence, the bLHβ-CTP mice provide a useful model for studying obesity related to elevated LH secretion, with consequent alterations in ovarian and adrenal function.
Effect of weight loss on muscle lipid content in morbidly obese subjects
Authors: Gray Robert E. , Tanner Charles J. , Pories Walter J. , MacDonald Kenneth G. , Houmard Joseph A.
Published: March 2015

The purpose of this study was to test the hypothesis that weight loss results in a reduction in intramuscular lipid (IMCL) content that is concomitant with enhanced insulin action. Muscle biopsies were obtained from morbidly obese individuals [body mass index (BMI) 52.2 ± 2.5 kg/m2; n= 6] before and after gastric bypass surgery, an intervention that improves insulin action. With intervention, there was a 47% reduction ( P < 0.01) in BMI and a 93% decrease in homeostasis model assessment, or HOMA (7.0 ± 1.9 vs. 0.5 ± 0.1). Histochemically determined IMCL content decreased ( P < 0.05) by ∼30%. In relation to fiber type, IMCL was significantly higher in type I vs. type II fibers. In both fiber types, there were reductions in IMCL and trends for muscle atrophy. Despite these two negating factors, the IMCL-to-fiber area ratio still decreased by ∼44% with weight loss. In conclusion, despite differing initial levels and possible atrophy, weight loss appears to decrease IMCL deposition to a similar relative extent in type I and II muscle fibers. This reduction in intramuscular triglyceride may contribute to enhanced insulin action seen with weight loss.
Chylomicron and palmitate metabolism by perfused hearts from diabetic mice
Authors: Neitzel Andrew S. , Carley Andrew N. , Severson David L.
Published: March 2015

Hydrolysis of triacylglycerols (TG) in circulating chylomicrons by endothelium-bound lipoprotein lipase (LPL) provides a source of fatty acids (FA) for cardiac metabolism. The effect of diabetes on the metabolism of chylomicrons by perfused mouse hearts was investigated with db/db (type 2) and streptozotocin (STZ)-treated (type 1) diabetic mice. Endothelium-bound heparin-releasable LPL activity was unchanged in both type 1 and type 2 diabetic hearts. The metabolism of LPL-derived FA was examined by perfusing hearts with chylomicrons containing radiolabeled TG and by measuring3H2O accumulation in the perfusate (oxidation) and incorporation of radioactivity into tissue TG (esterification). Rates of LPL-derived FA oxidation and esterification were increased 2.3-fold and 1.7-fold in db/db hearts. Similarly, LPL-derived FA oxidation and esterification were increased 3.4-fold and 2.5-fold, respectively, in perfused hearts from STZ-treated mice. The oxidation and esterification of [3H]palmitate complexed to albumin were also increased in type 1 and type 2 diabetic hearts. Therefore, diabetes may not influence the supply of LPL-derived FA, but total FA utilization (oxidation and esterification) was enhanced.
Intramyocellular lipid accumulation and reduced whole body lipid oxidation in HIV lipodystrophy
Authors: Luzi Livio , Perseghin Gianluca , Tambussi Giuseppe , Meneghini Elena , Scifo Paola , Pagliato Emanuela , Del Maschio Alessandro , Testolin Giulio , Lazzarin Adriano
Published: March 2015

Antiretroviral therapy in human immunodeficiency virus (HIV)-positive patients can induce a lipodystrophy syndrome of peripheral fat wasting and central adiposity, dyslipidemia, and insulin resistance. To test whether in this syndrome insulin resistance is associated with abnormal muscle handling of fatty acids, 12 HIV-1 patients (8 females/4 males , age = 26 ± 2 yr, HIV duratio n = 8 ± 1 yr, body mass index = 22.0 ± 1.0 kg/m2, on protease inhibitors and nucleoside analog RT inhibitors) and 12 healthy subjects were studied. HIV-1 patients had a total body fat content (assessed by dual-energy X-ray absorptiometry) similar to that of controls (22 ± 1 vs. 23 ± 2%; P = 0.56), with a topographic fat redistribution characterized by reduced fat content in the legs (18 ± 2 vs. 32 ± 3%; P < 0.01) and increased fat content in the trunk (25 ± 2 vs. 19 ± 2%; P = 0.03). In HIV-positive patients, insulin sensitivity (assessed by QUICKI) was markedly impaired (0.341 ± 0.011 vs. 0.376 ± 0.007; P = 0.012). HIV-positive patients also had increased total plasma cholesterol (216 ± 20 vs. 174 ± 9 mg/dl; P = 0.05) and triglyceride (298 ± 96 vs. 87 ± 11 mg/dl; P = 0.03) concentrations. Muscular triglyceride content assessed by means of1H NMR spectroscopy was higher in HIV patients in soleus [92 ± 12 vs. 42 ± 5 arbitrary units (AU); P < 0.01] and tibialis anterior (26 ± 6 vs. 11 ± 3 AU; P = 0.04) muscles; in a stepwise regression analysis, it was strongly associated with QUICKI ( R 2 = 0.27; P < 0.0093). Even if the basal metabolic rate (assessed by indirect calorimetry) was comparable to that of normal subjects, postabsorptive lipid oxidation was significantly impaired (0.30 ± 0.07 vs. 0.88 ± 0.09 mg · kg−1 · min−1; P < 0.01). In conclusion, lipodystrophy in HIV-1 patients in antiretroviral treatment is associated with intramuscular fat accumulation, which may mediate the development of the insulin resistance syndrome.
Soy protein, casein, and zein regulate histidase gene expression by modulating serum glucagon
Authors: Tovar Armando R. , Ascencio Claudia , Torres Nimbe
Published: March 2015

Glucagon has been postulated as an important physiological regulator of histidase (Hal) gene expression; however, it has not been demonstrated whether serum glucagon concentration is associated with the type and amount of protein ingested. The purpose of the present work was to study the association between hepatic Hal activity and mRNA concentration in rats fed 18 or 50% casein, isolated soy protein, or zein diets in a restricted schedule of 6 h for 10 days, and plasma glucagon and insulin concentrations. On day 10, five rats of each group were killed at 0900 (fasting), and then five rats were killed after being given the experimental diet for 1 h (1000). Rats fed 50% casein or soy diets showed higher Hal activity than the other groups studied. Rats fed 50% zein diets had higher Hal activity than rats fed 18% casein, soy, or zein diets, but lower activity than rats fed 50% casein or soy diets. Hal mRNA concentration followed a similar pattern. Hal activity showed a significant association with serum concentrations of glucagon. Serum glucagon concentration was significantly correlated with protein intake. Thus the type and amount of protein consumed affect Hal activity and expression through changes in serum glucagon concentrations.
Protein anabolic effects of insulin and IGF-I in the ovine fetus
Authors: Shen Weihua , Wisniowski Paul , Ahmed Lasker , Boyle David W. , Denne Scott C. , Liechty Edward A.
Published: March 2015

We determined the effect of insulin and/or recombinant human (rh)IGF-I infusion on ovine fetal phenylalanine kinetics, protein synthesis, and phenylalanine accretion. The chronically catheterized fetal lamb model was used at 130 days gestation. All studies were performed while fetal glucose and amino acid concentrations were held constant. Experimental infusates were 1) saline, 2) rhIGF-I plus a replacement dose of insulin (40 nmol), 3) insulin (890 mIU/h), and 4) IGF-I plus insulin (40 nmol IGF-I/h and 890 mIU insulin/h). Both hormones increased glucose and amino acid utilization, with insulin having a greater effect. The major effect on phenylalanine kinetics was a pronounced fall in phenylalanine hydroxylation, again with insulin having the greatest effect. Whole body protein breakdown was not significantly altered by either hormone; whole body protein synthesis was significantly increased during the combined infusion. Protein accretion was increased by both hormones, with the greatest increase during combined infusion. The fractional synthetic rate (FSR) of circulating albumin was increased by IGF-I but not by insulin. Both hormones significantly increased skeletal muscle FSR without a synergistic effect. The anabolic effects of insulin and IGF-I were more pronounced in these studies than in previous studies where amino acid concentrations were not maintained. The present data also suggest that insulin and IGF-I promote fetal growth through distinct, organ-specific mechanisms.
Interorgan exchange of aminothiols in humans
Authors: Garibotto Giacomo , Sofia Antonella , Saffioti Stefano , Russo Rodolfo , Deferrari Giacomo , Rossi Daniela , Verzola Daniela , Gandolfo Maria Teresa , Sala Maria Rita
Published: March 2015

In the present study, we used organ balance across the kidney, splanchnic organs, and lower limb in subjects undergoing diagnostic central venous catheterizations to gain insight into the renal and extrarenal exchange of aminothiols in humans. Although Hcy was released only in low amounts from leg tissues, Cys-Gly (a peptide derived from GSH hydrolysis) was released by both the leg and splanchnic organs, whereas Cys was released by the kidney and taken up by splanchnic organs. The kidney removed ∼90% of the Cys-Gly released into the circulation. Removal of Cys-Gly by the kidney depended on Cys-Gly arterial levels and showed a high fractional extraction (∼26%), with clearance rates slightly higher than the glomerular filtration rate (GFR). Although the average kidney removal of Hcy was not statistically significant, the fractional extraction of Hcy across the kidney varied directly with renal plasma flow. Our data show that thiol metabolism in humans is a compartmentalized interorgan process involving fluxes of individual aminothiols that are parallel and of opposite sign among peripheral tissues, splanchnic organs, and kidney. Cys-Gly is released by peripheral tissue and splanchnic organs from GSH hydrolysis and is taken up by the kidney by GFR; the kidney returns Cys to the circulation to preserve substrate availability for GSH synthesis. On the other hand, Hcy is released by peripheral tissues in low amounts, and its removal by the kidney seems to depend on blood supply. These findings may help explain several alterations in aminothiol metabolism observed in patients with chronic diseases.