bluuebunny/crossref_metadata_2025 huggingface dataset:
Glucose transport rate and glycogen synthase activity both limit skeletal muscle glycogen accumulation
Authors: Fisher Jonathan S. , Nolte Lorraine A. , Kawanaka Kentaro , Han Dong-Ho , Jones Terry E. , Holloszy John O.
Published: February 2015

We varied rates of glucose transport and glycogen synthase I (GS-I) activity (%GS-I) in isolated rat epitrochlearis muscle to examine the role of each process in determining the rate of glycogen accumulation. %GS-I was maintained at or above the fasting basal range during 3 h of incubation with 36 mM glucose and 60 μU/ml insulin. Lithium (2 mM LiCl) added to insulin increased glucose transport rate and muscle glycogen content compared with insulin alone. The glycogen synthase kinase-3β inhibitor GF-109203x (GF; 10 μM) maintained %GS-I about twofold higher than insulin with or without lithium but did not increase glycogen accumulation. When %GS-I was lowered below the fasting range by prolonged incubation with 36 mM glucose and 2 mU/ml insulin, raising rates of glucose transport with bpV(phen) or of %GS-I with GF produced additive increases in glycogen concentration. Phosphorylase activity was unaffected by GF or bpV(phen). In muscles of fed animals, %GS-I was ∼30% lower than in those of fasted rats, and insulin-stimulated glycogen accumulation did not occur unless %GS-I was raised with GF. We conclude that the rate of glucose transport is rate limiting for glycogen accumulation unless %GS-I is below the fasting range, in which case both glucose transport rate and GS activity can limit glycogen accumulation.
AMP-activated protein kinase activates transcription of the UCP3 and HKII genes in rat skeletal muscle
Authors: Stoppani James , Hildebrandt Audrey L. , Sakamoto Kei , Cameron-Smith David , Goodyear Laurie J. , Neufer P. Darrell
Published: February 2015

AMP-activated protein kinase (AMPK) has recently emerged as a key signaling protein in skeletal muscle, coordinating the activation of both glucose and fatty acid metabolism in response to increased cellular energy demand. To determine whether AMPK signaling may also regulate gene transcription in muscle, rats were given a single subcutaneous injection (1 mg/g) of the AMP analog 5-aminoimidazole-4-carboxamide-1-β-d-ribonucleoside (AICAR). AICAR injection activated ( P < 0.05) AMPK-α2 (∼2.5-fold) and transcription of the uncoupling protein-3 (UCP3, ∼4-fold) and hexokinase II (HKII, ∼10-fold) genes in both red and white skeletal muscle. However, AICAR injection also elicited ( P < 0.05) an acute drop (60%) in blood glucose and a sustained (2-h) increase in blood lactate, prompting concern regarding the specificity of AICAR on transcription. To maximize AMPK activation in muscle while minimizing potential systemic counterregulatory responses, a single-leg arterial infusion technique was employed in fully conscious rats. Relative to saline-infused controls, single-leg arterial infusion of AICAR (0.125, 0.5, and 2.5 μg · g−1 · min−1for 60 min) induced a dose-dependent increase (2- to 4-fold, P < 0.05) in UCP3 and HKII transcription in both red and white skeletal muscle. Importantly, AICAR infusion activated transcription only in muscle from the infused leg and had no effect on blood glucose or lactate levels. These data provide evidence that AMPK signaling is linked to the transcriptional regulation of select metabolic genes in skeletal muscle.
Functional consequences of thyroid hormone-induced changes in the mitochondrial protein import pathway
Authors: Colavecchia Marco , Christie Loraine N. , Kanwar Yashpal S. , Hood David A.
Published: February 2015

Thyroid hormone [3,5,3′-triiodo-l-thyronine (T3)] induces phenotypic alterations in cardiac mitochondria, in part by influencing protein import and the expression of the import motor mitochondrial heat shock protein (mtHsp70). Here we examined the adaptability of translocases of the inner membrane (Tim) proteins, as well as the outer membrane receptor Tom34, to T3. Administration of T3to rats for 5 days increased cardiac Tim23 and Tim44 mRNA levels by 55 and 50%, respectively, but had no effect on Tim17. T3treatment also induced a 45% increase in Tom34 mRNA, with no accompanying changes at the protein level, suggesting regulation at the posttranscriptional level. In H9c2 cardiac cells, Tim17 mRNA was elevated by 114% by 9 days of differentiation, whereas Tim23 and Tim44 declined by 25 and 29%, respectively. To determine the functional consequences of these T3-induced changes, malate dehydrogenase (MDH) import rates were measured in H9c2 cells stably overexpressing Tim44 and mtHsp70, either alone or in combination. MDH import remained unaltered in cells overexpressing Tim44 or in cells overexpressing both Tim44 and mtHsp70. However, when mtHsp70 was overexpressed alone, a 13% ( P < 0.05) increase in MDH import rate was observed. These findings indicate that import machinery components are differentially regulated in response to stimuli that induce mitochondrial biogenesis, like T3and differentiation. In addition, the induction of an import machinery component in response to T3may not necessarily result in functional changes in protein import during mitochondrial biogenesis. Finally, mtHsp70 may play a regulatory role in the import process that is independent of its interaction with Tim44.
Physical exercise prevents the development of type 2 diabetes mellitus inPsammomys obesus
Authors: Heled Yuval , Shapiro Yair , Shani Yoav , Moran Dani S. , Langzam Lea , Braiman Liora , Sampson Sanford R. , Meyerovitch Joseph
Published: February 2015

We hypothesized that exercise training might prevent diabetes mellitus in Psammomys obesus. Animals were assigned to three groups: high-energy diet (CH), high-energy diet and exercise (EH), and low-energy diet (CL). The EH group ran on a treadmill 5 days/wk, twice a day. After 4 wk, 93% of the CH group were diabetic compared with only 20% of the EH group. There was no difference in weight gain among the groups. Both EH and CH groups were hyperinsulinemic. Epididymal fat (% of body weight) was higher in the CH group than in either the EH and or the CL group. Protein kinase C (PKC)-δ activity and serine phosphorylation were higher in the EH group. No differences were found in tyrosine phosphorylation of the insulin receptor, insulin receptor substrate-1, and phosphatidylinositol 3-kinase among the groups. We demonstrate for the first time that exercise training effectively prevents the progression of diabetes mellitus type 2 in Psammomys obesus. PKC-δ may be involved in the adaptive effects of exercise in skeletal muscles that lead to the prevention of type 2 diabetes mellitus.
The calcium endocrine system of adolescent rhesus monkeys and controls before and after spaceflight
Authors: Arnaud Sara B. , Navidi Meena , Deftos Leonard , Thierry-Palmer Myrtle , Dotsenko Rita , Bigbee Allison , Grindeland Richard E.
Published: February 2015

The calcium endocrine system of nonhuman primates can be influenced by chairing for safety and the weightless environment of spaceflight. The serum of two rhesus monkeys flown on the Bion 11 mission was assayed pre- and postflight for vitamin D metabolites, parathyroid hormone, calcitonin, parameters of calcium homeostasis, cortisol, and indexes of renal function. Results were compared with the same measures from five monkeys before and after chairing for a flight simulation study. Concentrations of 1,25-dihydroxyvitamin D were 72% lower after the flight than before, and more than after chairing on the ground (57%, P < 0.05). Decreases in parathyroid hormone did not reach significance. Calcitonin showed modest decreases postflight ( P < 0.02). Overall, effects of spaceflight on the calcium endocrine system were similar to the effects of chairing on the ground, but were more pronounced. Reduced intestinal calcium absorption, losses in body weight, increases in cortisol, and higher postflight blood urea nitrogen were the changes in flight monkeys that distinguished them from the flight simulation study animals.
ATP-sensitive potassium channels participate in glucose uptake in skeletal muscle and adipose tissue
Authors: Miki Takashi , Minami Kohtaro , Zhang Li , Morita Mizuo , Gonoi Tohru , Shiuchi Tetsuya , Minokoshi Yasuhiko , Renaud Jean-Marc , Seino Susumu
Published: February 2015

ATP-sensitive potassium (KATP) channels are known to be critical in the control of both insulin and glucagon secretion, the major hormones in the maintenance of glucose homeostasis. The involvement of KATPchannels in glucose uptake in the target tissues of insulin, however, is not known. We show here that Kir6.2(−/−) mice lacking Kir6.2, the pore-forming subunit of these channels, have no KATPchannel activity in their skeletal muscles. A 2-deoxy-[3H]glucose uptake experiment in vivo showed that the basal and insulin-stimulated glucose uptake in skeletal muscles and adipose tissues of Kir6.2(−/−) mice is enhanced compared with that in wild-type (WT) mice. In addition, in vitro measurement of glucose uptake indicates that disruption of the channel increases the basal glucose uptake in Kir6.2(−/−) extensor digitorum longus and the insulin-stimulated glucose uptake in Kir6.2(−/−) soleus muscle. In contrast, glucose uptake in adipose tissue, measured in vitro, was similar in Kir6.2(−/−) and WT mice, suggesting that the increase in glucose uptake in Kir6.2(−/−) adipocytes is mediated by altered extracellular hormonal or neuronal signals altered by disruption of the KATPchannels.
Exercise induces an increase in muscle UCP3 as a component of the increase in mitochondrial biogenesis
Authors: Jones Terry E. , Baar Keith , Ojuka Edward , Chen May , Holloszy John O.
Published: February 2015

Previous studies have indicated that exercise acutely induces large increases in uncoupling protein-3 (UCP3) in skeletal muscle, whereas endurance training results in marked decreases in muscle UCP3. Because UCP3 expression appears to be regulated by the same mechanism as other mitochondrial constituents, it seemed unlikely that exercise would result in such large and divergent changes in mitochondrial composition. The purpose of this study was to test the hypothesis that major changes in UCP3 protein concentration do not occur independently of mitochondrial biogenesis and that UCP3 increases as a component of the exercise-induced increase in mitochondria. We found a large increase in UCP3 mRNA immediately and 3 h after a bout of swimming. UCP3 protein concentration was increased ∼35% 18 h after a single exercise bout, ∼63% after 3 days, and ∼84% after 10 days of exercise. These increases in UCP3 roughly paralleled those of other mitochondrial marker proteins. Our results are consistent with the interpretation that endurance exercise induces an adaptive increase in mitochondria that have a normal content of UCP3.
Gastrointestinal absorption and plasma kinetics of soy Δ5-phytosterols and phytostanols in humans
Authors: Ostlund Richard E. , McGill Janet B. , Zeng Chun-Min , Covey Douglas F. , Stearns Jay , Stenson William F. , Spilburg Curtis A.
Published: February 2015

Our objective was to measure the systemic absorption of lecithin-emulsified Δ5-phytosterols and phytostanols during test meals by use of dual stable isotopic tracers. Ten healthy subjects underwent two single-meal absorption tests in random order 2 wk apart, one with intravenous dideuterated Δ5-phytosterols and oral pentadeuterated Δ5-phytosterols and the other with the corresponding labeled stanols. The oral-to-intravenous tracer ratio in plasma, a reflection of absorption, was measured by a sensitive negative ion mass spectroscopic technique and became constant after 2 days. Absorption from 600 mg of Δ5-soy sterols given with a standard test breakfast was 0.512 ± 0.038% for sitosterol and 1.89 ± 0.27% for campesterol. The absorption from 600 mg of soy stanols was 0.0441 ± 0.004% for sitostanol and 0.155 ± 0.017% for campestanol. Reduction of the double bond at position 5 decreased absorption by 90%. Plasma t½for stanols was significantly shorter than that for Δ5-sterols. We conclude that the efficiency of phytosterol absorption is lower than what was reported previously and is critically dependent on the structure of both sterol nucleus and side chain.
IGF-I and IGFBP-3 transport in the rat heart
Authors: Boes Mary , Dake Brian L. , Booth Barbara A. , Sandra Alexander , Bateman Mathew , Knudtson Kevin L. , Bar Robert S.
Published: February 2015

Specific binding of IGF-binding protein (IGFBP)-3 was shown to be present in the isolated, beating rat heart. The uptake of perfused 125I-labeled IGF-I in the beating heart was decreased to 9% by blocking IGF-I binding sites with the IGF-I analog Long R3 (LR3) IGF-I. When LR3 was perfused with complexes of125I-IGF-I · IGFBP-3, uptake of125I-IGF-I was decreased to 41%, which was significantly greater than LR3 and 125I-IGF-I (41 vs. 9%). These data suggest that both microvessel IGF-I and IGFBP-3 binding sites contribute to the transport of IGF-I in the perfused rat heart. This also suggests a novel and plausible mechanism whereby circulating IGFs reach sites of IGF bioactivity.
Skeletal muscle metabolism is unaffected by DCA infusion and hyperoxia after onset of intense aerobic exercise
Authors: Savasi Ingrid , Evans Melissa K. , Heigenhauser George J. F. , Spriet Lawrence L.
Published: February 2015

This study investigated whether hyperoxic breathing (100% O2) or increasing oxidative substrate supply [dichloroacetate (DCA) infusion] would increase oxidative phosphorylation and reduce the reliance on substrate phosphorylation at the onset of high-intensity aerobic exercise. Eight male subjects cycled at 90% maximal O2uptake (V˙o2 max) for 90 s in three randomized conditions: 1) normoxic breathing and saline infusion over 1 h immediately before exercise (CON), 2) normoxic breathing and saline infusion with DCA (100 mg/kg body wt), and 3) hyperoxic breathing for 20 min at rest and during exercise and saline infusion (HYP). Muscle biopsies from the vastus lateralis were sampled at rest and after 30 and 90 s of exercise. DCA infusion increased pyruvate dehydrogenase (PDH) activation above CON and HYP (3.10 ± 0.23, 0.56 ± 0.08, 0.69 ± 0.05 mmol · kg wet muscle−1· min−1, respectively) and significantly increased both acetyl-CoA and acetylcarnitine (11.0 ± 0.7, 2.0 ± 0.5, 2.2 ± 0.5 mmol/kg dry muscle, respectively) at rest. However, DCA and HYP did not alter phosphocreatine degradation and lactate accumulation and, therefore, the reliance on substrate phosphorylation during 30 s (CON, 51.2 ± 5.4; DCA, 56.5 ± 7.1; HYP, 69.5 ± 6.3 mmol ATP/kg dry muscle) and 90 s of exercise (CON, 90.6 ± 9.5; DCA, 107.2 ± 13.0; HYP, 101.2 ± 15.2 mmol ATP/kg dry muscle). These data suggest that the rate of oxidative phosphorylation at the onset of exercise at 90% V˙o2 maxis not limited by oxygen availability to the active muscle or by substrate availability (metabolic inertia) at the level of PDH in aerobically trained subjects.
Contribution of the endoplasmic reticulum to the glucose-induced [Ca2+]cresponse in mouse pancreatic islets
Authors: Arredouani Abdelilah , Henquin Jean-Claude , Gilon Patrick
Published: February 2015

Thapsigargin (TG), a blocker of Ca2+uptake by the endoplasmic reticulum (ER), was used to evaluate the contribution of the organelle to the oscillations of cytosolic Ca2+concentration ([Ca2+]c) induced by repetitive Ca2+influx in mouse pancreatic β-cells. Because TG depolarized the plasma membrane in the presence of glucose alone, extracellular K+was alternated between 10 and 30 mM in the presence of diazoxide to impose membrane potential (MP) oscillations. In control islets, pulses of K+, mimicking regular MP oscillations elicited by 10 mM glucose, induced [Ca2+]coscillations whose nadir remained higher than basal [Ca2+]c. Increasing the depolarization phase of the pulses while keeping their frequency constant (to mimic the effects of a further rise of the glucose concentration on MP) caused an upward shift of the nadir of [Ca2+]coscillations that was reproduced by raising extracellular Ca2+(to increase Ca2+influx) without changing the pulse protocol. In TG-pretreated islets, the imposed [Ca2+]coscillations were of much larger amplitude than in control islets and occurred on basal levels. During intermittent trains of depolarizations, control islets displayed mixed [Ca2+]coscillations characterized by a summation of fast oscillations on top of slow ones, whereas no progressive summation of the fast oscillations was observed in TG-pretreated islets. In conclusion, the buffering capacity of the ER in pancreatic β-cells limits the amplitude of [Ca2+]coscillations and may explain how the nadir between oscillations remains above baseline during regular oscillations or gradually increases during mixed [Ca2+]coscillations, two types of response observed during glucose stimulation.
Acute glucocorticoid treatment increases urinary biotin excretion and serum biotin
Authors: Rathman Sara C. , Lewis Brandon , McMahon Robert J.
Published: February 2015

Previous studies have demonstrated that glucocorticoids alter biotin metabolism. To extend these studies, the effect of dexamethasone on biotin pools was analyzed in rats consuming a purified diet containing a more physiological level of dietary biotin intake (0.06 mg/kg). Acute (5 h) dexamethasone administration (0.5 mg/kg) elicited elevated urinary glucose output as well as elevated urinary biotin excretion and serum biotin. Renal and hepatic free biotin was also significantly elevated by acute dexamethasone administration. Chow-fed rats treated with an acute administration of dexamethasone demonstrated significantly elevated urinary glucose excretion, urinary biotin excretion, and serum biotin, but no change in tissue associated biotin was detected. Chronic administration of dexamethasone (0.5 mg/kg ip) over 4 days significantly elevated urinary glucose excretion 42% but had no effect on urinary biotin excretion, serum biotin, or hepatic- or renal-associated free biotin. These results demonstrate the existence of potentially novel regulatory pathways for total biotin pools and the possibility that experimental models with high initial biotin status may mask potentially important regulatory mechanisms.
Testosterone administration to older men improves muscle function: molecular and physiological mechanisms
Authors: Ferrando Arny A. , Sheffield-Moore Melinda , Yeckel Catherine W. , Gilkison Charles , Jiang Jie , Achacosa Alison , Lieberman Steven A. , Tipton Kevin , Wolfe Robert R. , Urban Randall J.
Published: February 2015

We investigated the effects of 6 mo of near-physiological testosterone administration to older men on skeletal muscle function and muscle protein metabolism. Twelve older men (≥60 yr) with serum total testosterone concentrations <17 nmol/l (480 ng/dl) were randomly assigned in double-blind manner to receive either placebo ( n = 5) or testosterone enanthate (TE; n = 7) injections. Weekly intramuscular injections were given for the 1st mo to establish increased blood testosterone concentrations at 1 mo and then changed to biweekly injections until the 6-mo time point. TE doses were adjusted to maintain nadir serum testosterone concentrations between 17 and 28 nmol/l. Lean body mass (LBM), muscle volume, prostate size, and urinary flow were measured at baseline and at 6 mo. Protein expression of androgen receptor (AR) and insulin-like growth factor I, along with muscle strength and muscle protein metabolism, were measured at baseline and at 1 and 6 mo of treatment. Hematological parameters were followed monthly throughout the study. Older men receiving testosterone increased total and leg LBM, muscle volume, and leg and arm muscle strength after 6 mo. LBM accretion resulted from an increase in muscle protein net balance, due to a decrease in muscle protein breakdown. TE treatment increased expression of AR protein at 1 mo, but expression returned to pre-TE treatment levels by 6 mo. IGF-I protein expression increased at 1 mo and remained increased throughout TE administration. We conclude that physiological and near-physiological increases of testosterone in older men will increase muscle protein anabolism and muscle strength.
Bone as an ion exchange system: evidence for a link between mechanotransduction and metabolic needs
Authors: Rubinacci A. , Covini M. , Bisogni C. , Villa I. , Galli M. , Palumbo C. , Ferretti M. , Muglia M. A. , Marotti G.
Published: February 2015

To detect whether the mutual interaction occurring between the osteocytes-bone lining cells system (OBLCS) and the bone extracellular fluid (BECF) is affected by load through a modification of the BECF-extracellular fluid (ECF; systemic extracellular fluid) gradient, mice metatarsal bones immersed in ECF were subjected ex vivo to a 2-min cyclic axial load of different amplitudes and frequencies. The electric (ionic) currents at the bone surface were measured by a vibrating probe after having exposed BECF to ECF through a transcortical hole. The application of different loads and different frequencies increased the ionic current in a dose-dependent manner. The postload current density subsequently decayed following an exponential pattern. Postload increment's amplitude and decay were dependent on bone viability. Dummy and static loads did not induce current density modifications. Because BECF is perturbed by loading, it is conceivable that OBLCS tends to restore BECF preload conditions by controlling ion fluxes at the bone-plasma interface to fulfill metabolic needs. Because the electric current reflects the integrated activity of OBLCS, its evaluation in transgenic mice engineered to possess genetic lesions in channels or matrix constituents could be helpful in the characterization of the mechanical and metabolic functions of bone.
Prior exercise and the response to insulin-induced hypoglycemia in the dog
Authors: Koyama Yoshiharu , Galassetti Pietro , Coker Robert H. , Pencek R. Richard , Lacy D. Brooks , Davis Stephen N. , Wasserman David H.
Published: February 2015

To test whether hepatic insulin action and the response to an insulin-induced decrement in blood glucose are enhanced in the immediate postexercise state as they are during exercise, dogs had sampling (artery, portal vein, and hepatic vein) catheters and flow probes (portal vein and hepatic artery) implanted 16 days before a study. After 150 min of moderate treadmill exercise or rest, dogs were studied during a 150-min hyperinsulinemic (1 mU · kg−1· min−1) euglycemic ( n = 5 exercised and n = 9 sedentary) or hypoglycemic (65 mg/dl; n = 8 exercised and n = 9 sedentary) clamp. Net hepatic glucose output (NHGO) and endogenous glucose appearance (Ra) and utilization (Rd) were assessed with arteriovenous and isotopic ([3-3H]glucose) methods. Results show that, immediately after prolonged, moderate exercise, in relation to sedentary controls: 1) the glucose infusion rate required to maintain euglycemia, but not hypoglycemia, was higher; 2) Rdwas greater under euglycemic, but not hypoglycemic conditions; 3) NHGO, but not Ra, was suppressed more by a hyperinsulinemic euglycemic clamp, suggesting that hepatic glucose uptake was increased; 4) a decrement in glucose completely reversed the enhanced suppression of NHGO by insulin that followed exercise; and 5) arterial glucagon and cortisol were transiently higher in the presence of a decrement in glucose. In summary, an increase in insulin action that was readily evident under euglycemic conditions after exercise was abolished by moderate hypoglycemia. The means by which the glucoregulatory system is able to overcome the increase in insulin action during moderate hypoglycemia is related not to an increase in Rabut to a reduction in insulin-stimulated Rd. The primary site of this reduction is the liver.
Muscle fiber type is associated with obesity and weight loss
Authors: Tanner Charles J. , Barakat Hisham A. , Dohm G. Lynis , Pories Walter J. , MacDonald Kenneth G. , Cunningham Paul R. G. , Swanson Melvin S. , Houmard Joseph A.
Published: February 2015

The purpose of this study was to test the hypothesis that muscle fiber type is related to obesity. Fiber type was compared 1) in lean and obese women, 2) in Caucasian (C) and African-American (AA) women, and 3) in obese individuals who lost weight after gastric bypass surgery. When lean (body mass index 24.0 ± 0.9 kg/m2, n = 28) and obese (34.8 ± 0.9 kg/m2, n = 25) women were compared, there were significant ( P < 0.05) differences in muscle fiber type. The obese women possessed fewer type I (41.5 ± 1.8 vs. 54.6 ± 1.8%) and more type IIb (25.1 ± 1.5 vs. 14.4 ± 1.5%) fibers than the lean women. When ethnicity was accounted for, the percentage of type IIb fibers in obese AA was significantly higher than in obese C (31.0 ± 2.4% vs. 19.2 ± 1.9%); fewer type I fibers were also found in obese AA (34.5 ± 2.8% vs. 48.6 ± 2.2%). These data are consistent with the higher incidence of obesity and greater weight gain reported in AA women. With weight loss intervention, there was a positive relationship ( r = 0.72, P < 0.005) between the percentage of excess weight loss and the percentage of type I fibers in morbidly obese patients. These findings indicate that there is a relationship between muscle fiber type and obesity.
The role of protein kinase C-δ in PTH stimulation of IGF-binding protein-5 mRNA in UMR-106–01 cells
Authors: Erclik Mary S. , Mitchell Jane
Published: February 2015

We have investigated the role of protein kinase C (PKC) signal transduction pathways in parathyroid hormone (PTH) regulation of insulin-like growth factor-binding protein-5 (IGFBP-5) gene expression in the rat osteoblast-like cell line UMR-106–01. Involvement of the PKC pathway was determined by the findings that bisindolylmaleimide I inhibited 40% of the PTH effect, and 1 μM bovine PTH-(3–34) stimulated a 10-fold induction of IGFBP-5 mRNA. PTH-(1–34) and PTH-(3–34) (100 nM) both stimulated PKC-δ translocation from the membrane to the nuclear fraction. Rottlerin, a PKC-δ-specific inhibitor, and a dominant negative mutant of PKC-δ were both able to significantly inhibit PTH-(1–34) and PTH-(3–34) induction of IGFBP-5 mRNA, suggesting a stimulatory role for PKC-δ in the effects of PTH. Phorbol 12-myristate 13-acetate (PMA) stimulated PKC-α translocation from the cytosol to the membrane and inhibited ∼50% of the PTH-(1–34), forskolin, and 8-bromoadenosine 3′,5′-cyclic monophosphate-stimulated IGFBP-5 mRNA levels, suggesting that PKC-α negatively regulates protein kinase A (PKA)-mediated induction of IGFBP-5 mRNA. These results suggest that the induction of IGFBP-5 by PTH is both PKA and PKC dependent and PKC-δ is the primary mediator of the effects of PTH via the PKC pathway.
Regulation of endogenous glucose production after a mixed meal in type 2 diabetes
Authors: Singhal Parag , Caumo Andrea , Carey Peter E. , Cobelli Claudio , Taylor Roy
Published: February 2015

The extent and time course of suppression of endogenous glucose production (EGP) in type 2 diabetes after a mixed meal have been determined using a new tracer methodology. Groups of age-, sex-, and weight-matched normal controls ( n = 8) and diet-controlled type 2 diabetic subjects ( n = 8) were studied after ingesting a standard mixed meal (550 kcal; 67% carbohydrate, 19% fat, 14% protein). There was an early insulin increment in both groups such that, by 20 min, plasma insulin levels were 266 ± 54 and 190 ± 53 pmol/l, respectively. EGP was similar basally [2.55 ± 0.12 mg · kg−1· min−1in control subjects vs. 2.92 ± 0.16 mg · kg−1· min−1in the patients ( P = 0.09)]. After glucose ingestion, EGP declined rapidly in both groups to ∼50% of basal within 30 min of the meal. Despite the initial rapid decrease, the EGP was significantly greater in the diabetic group at 60 min (1.75 ± 0.12 vs. 1.05 ± 0.14 mg · kg−1· min−1; P < 0.01) and did not reach nadir until 210 min (0.96 ± 0.17 mg · kg−1· min−1). Between 60 and 240 min, EGP was 47% higher in the diabetic group (0.89 ± 0.09 vs. 1.31 ± 0.13 mg · kg−1· min−1, P < 0.02). These data quantitate the initial rapid suppression of EGP after a mixed meal in type 2 diabetes and the contribution of continuing excess glucose production to subsequent hyperglycemia.
FFA cause hepatic insulin resistance by inhibiting insulin suppression of glycogenolysis
Authors: Boden Guenther , Cheung Peter , Stein T. Peter , Kresge Karen , Mozzoli Maria
Published: February 2015

Free fatty acids (FFA) have been shown to inhibit insulin suppression of endogenous glucose production (EGP). To determine whether this is the result of stimulation by FFA of gluconeogenesis (GNG) or glycogenolysis (GL) or a combination of both, we have determined rates of GNG and GL (with2H2O) and EGP in 16 healthy nondiabetic volunteers (11 males, 5 females) during euglycemic-hyperinsulinemic (∼450 pM) clamping performed either with or without simultaneous intravenous infusion of lipid plus heparin. During insulin infusion, FFA decreased from 571 to 30 μmol/l ( P < 0.001), EGP from 15.7 to 2.0 μmol · kg−1· min−1( P < 0.01), GNG from 8.2 to 3.7 μmol · kg−1· min−1( P < 0.05), and GL from 7.4 to −1.7 μmol · kg−1· min−1( P < 0.02). During insulin plus lipid/heparin infusion, FFA increased from 499 to 1,247 μmol/l ( P< 0.001). EGP decreased 64% less than during insulin alone (−5.1 ± 0.7 vs. −13.7 ± 3.4 μmol · kg−1· min−1). The decrease in GNG was not significantly different from the decrease of GNG during insulin alone (−2.6 vs. −4.5 μmol · kg−1· min−1, not significant). In contrast, GL decreased 66% less than during insulin alone (−3.1 vs. −9.2 μmol · kg−1· min−1, P < 0.05). We conclude that insulin suppressed EGP by inhibiting GL more than GNG and that elevated plasma FFA levels attenuated the suppression of EGP by interfering with insulin suppression of GL.
Activation of AMPK is essential for AICAR-induced glucose uptake by skeletal muscle but not adipocytes
Authors: Sakoda Hideyuki , Ogihara Takehide , Anai Motonobu , Fujishiro Midori , Ono Hiraku , Onishi Yukiko , Katagiri Hideki , Abe Miho , Fukushima Yasushi , Shojima Nobuhiro , Inukai Kouichi , Kikuchi Masatoshi , Oka Yoshitomo , Asano Tomoichiro
Published: February 2015

5-Aminoimidazole-4-carboxamide ribonucleoside (AICAR) reportedly activates AMP-activated protein kinase (AMPK) and stimulates glucose uptake by skeletal muscle cells. In this study, we investigated the role of AMPK in AICAR-induced glucose uptake by 3T3-L1 adipocytes and rat soleus muscle cells by overexpressing wild-type and dominant negative forms of the AMPKα2 subunit by use of adenovirus-mediated gene transfer. Overexpression of the dominant negative mutant had no effect on AICAR-induced glucose transport in adipocytes, although AMPK activation was almost completely abolished. This suggests that AICAR-induced glucose uptake by 3T3-L1 adipocytes is independent of AMPK activation. By contrast, overexpression of the dominant negative AMPKα2 mutant in muscle markedly suppressed both AICAR-induced glucose uptake and AMPK activation, although insulin-induced uptake was unaffected. Overexpression of the wild-type AMPKα2 subunit significantly increased AMPK activity in muscle but did not enhance glucose uptake. Thus, although AMPK activation may not, by itself, be sufficient to increase glucose transport, it appears essential for AICAR-induced glucose uptake in muscle.
Effect of IGF-I therapy on VLDL apolipoprotein B100 metabolism in type 1 diabetes mellitus
Authors: Christ Emanuel R. , Carroll Paul V. , Albany Elaine , Umpleby A. Margot , Lumb Peter J. , Wierzbicki Anthony S. , Sönksen Peter H. , Russell-Jones David L.
Published: February 2015

Abnormal lipid metabolism may be related to the increased cardiovascular risk in type 1 diabetes. Secretion and clearance rates of very low density lipoprotein (VLDL) apolipoprotein B100 (apoB) determine plasma lipid concentrations. Type 1 diabetes is characterized by increased growth hormone (GH) secretion and decreased insulin-like growth factor (IGF) I concentrations. High-dose IGF-I therapy improves the lipid profile in type 1 diabetes. This study examined the effect of low-dose (40 μg · kg−1· day−1) IGF-I therapy on VLDL apoB metabolism, VLDL composition, and the GH-IGF-I axis during euglycemia in type 1 diabetes. Using a stable isotope technique, VLDL apoB kinetics were estimated before and after 1 wk of IGF-I therapy in 12 patients with type 1 diabetes in a double-blind, placebo-controlled trial. Fasting plasma triglyceride ( P < 0.03), VLDL-triglyceride concentrations ( P < 0.05), and the VLDL-triglyceride-to-VLDL apoB ratio ( P < 0.002) significantly decreased after IGF-I therapy, whereas VLDL apoB kinetics were not significantly affected by IGF-I therapy. IGF-I therapy resulted in a significant increase in IGF-I and a significant reduction in GH concentrations. The mean overnight insulin concentrations during euglycemia decreased by 25% after IGF-I therapy. These results indicate that low-dose IGF-I therapy restores the GH-IGF-I axis in type 1 diabetes. IGF-I therapy changes fasting triglyceride concentrations and VLDL composition probably because of an increase in insulin sensitivity.
Role of PDK1 in insulin-signaling pathway for glucose metabolism in 3T3-L1 adipocytes
Authors: Yamada Tetsuya , Katagiri Hideki , Asano Tomoichiro , Tsuru Masatoshi , Inukai Kouichi , Ono Hiraku , Kodama Tatsuhiko , Kikuchi Masatoshi , Oka Yoshitomo
Published: February 2015

To investigate the role of 3-phosphoinositide-dependent protein kinase 1 (PDK1) in the insulin-signaling pathway for glucose metabolism, wild-type (wt), the kinase-dead (kd), or the plecstrin homology (PH) domain deletion (ΔPH) mutant of PDK1 was expressed using an adenovirus gene transduction system in 3T3-L1 adipocytes. wt-PDK1 and kd-PDK1 were found in both membrane and cytosol fractions, whereas ΔPH-PDK1, which exhibited PDK1 activity similar to that of wt-PDK1, was detected exclusively in the cytosol fraction. Insulin dose dependently activated protein kinase B (PKB) but did not change atypical protein kinase C (aPKC) activity in control cells. aPKC activity was not affected by expression of wt-, kd-, or ΔPH-PDK1 in either the presence or the absence of insulin. Overexpression of wt-PDK1 enhanced insulin-induced activation of PKB as well as insulin-induced phosphorylation of glycogen synthase kinase (GSK)3α/β, a direct downstream target of PKB, although insulin-induced glycogen synthesis was not significantly enhanced by wt-PDK1 expression. Neither ΔPH-PDK1 nor kd-PDK1 expression affected PKB activity, GSK3 phosphorylation, or glycogen synthesis. Thus membrane localization of PDK1 via its PH domain is essential for insulin signaling through the PDK1-PKB-GSK3α/β pathway. Glucose transport activity was unaffected by expression of wt-PDK1, kd-PDK1, or ΔPH-PDK1 in either the presence or the absence of insulin. These findings suggest the presence of a signaling pathway for insulin-stimulated glucose transport in which PDK1 to PKB or aPKC is not involved.
Cr supplementation decreases tyrosine phosphorylation of the CreaT in skeletal muscle during sepsis
Authors: Wang Weiyang , Jobst Michael A. , Bell Brian , Zhao Chun-Rui , Shang Li-Hong , Jacobs Danny O.
Published: February 2015

Myocellular creatine (Cr) uptake is predominantly governed by a sodium-dependent Cr transporter (CreaT) and plays a pivotal role in skeletal muscle energy metabolism. The CreaT belongs to a neurotransmitter transporter family that can be functionally regulated by protein tyrosine kinase-induced tyrosine phosphorylation. The association between myocellular Cr and c-Src-related tyrosine phosphorylation of the CreaT and the influence of oral Cr supplementation on this association were investigated during sepsis. Animals were randomized to receive standard rat chow or standard rat chow with oral Cr supplementation for 4 days followed by cecal ligation and puncture (CLP) or sham operation. Fast-twitch gastrocnemius muscles were harvested 24 h after operation. Myocellular free Cr levels were 70% higher after CLP. Western blotting of the immunoprecipitated CreaT with an anti-phosphotyrosine or anti-phospho-c-Src (Y-416) antibody revealed that tyrosine phosphorylation of the CreaT and tyrosine-phosphorylated c-Src (Tyr416) expression in the CreaT-c-Src complex were significantly increased after CLP compared with sham operation. These changes were observed in homogenates and plasma membrane fractions of gastrocnemius muscles. Although oral Cr supplementation increased myocellular free Cr levels equivalently in CLP and sham-operated animals, c-Src-related tyrosine phosphorylation of the CreaT in homogenates and plasma membrane fractions of gastrocnemius muscles was, however, downregulated in Cr-supplemented CLP animals compared with Cr-supplemented sham-operated rats. During sepsis, increased myocellular free Cr levels are associated with enhanced tyrosine phosphorylation of the CreaT, which is likely induced by active c-Src. Oral Cr supplementation downregulates c-Src-related tyrosine phosphorylation of the CreaT. The data suggest that myocellular Cr homeostasis and CreaT activity are tightly regulated and closely related during sepsis.
Overexpression of CRIP in transgenic mice alters cytokine patterns and the immune response
Authors: Lanningham-Foster Lorraine , Green Calvert L. , Langkamp-Henken Bobbi , Davis Barbara A. , Nguyen Khanh T. , Bender Bradley S. , Cousins Robert J.
Published: February 2015

Cysteine-rich intestinal protein (CRIP), which contains a double zinc finger motif, is a member of the Group 2 LIM protein family. Our results showed that the developmental regulation of CRIP in neonates was not influenced by conventional vs. specific pathogen-free housing conditions. Thymic and splenic CRIP expression was not developmentally regulated. A line of transgenic (Tg) mice that overexpress the rat CRIP gene was created. When challenged with lipopolysaccharide, the Tg mice lost more weight, exhibited increased mortality, experienced greater diarrhea incidence, and had less serum interferon-γ (IFN-γ) and more interleukin (IL)-6 and IL-10. Similarly, splenocytes from the Tg mice produced less IFN-γ and IL-2 and more IL-10 and IL-6 upon mitogen stimulation. Delayed-type hypersensitivity response was less in the Tg mice. Influenza virus infection produced greater weight loss in the Tg mice, which also showed delayed viral clearance. The observed responses to overexpression of the CRIP gene are consistent with a role for this LIM protein in a cellular pathway that produces an imbalance in cytokine pattern favoring Th2 cytokines.
Human insulin release processes measured by intraportal sampling
Authors: Pørksen Niels , Grøfte Thorbjørn , Greisen Jacob , Mengel Anette , Juhl Claus , Veldhuis Johannes D. , Schmitz Ole , Rössle Martin , Vilstrup Hendrik
Published: February 2015

Insulin is secreted as a series of punctuated secretory bursts superimposed on variable basal insulin release. The contribution of these secretory bursts to overall insulin secretion has been estimated on the basis of peripheral vein sampling in humans to encompass ≥75% of overall insulin release. A similar contribution of the pulsatile mode of release was inferred in a canine model by use of portal vein sampling. The primary regulation of insulin secretion is through perturbation of the mass and frequency of these secretory bursts. The mode of delivery of insulin into the circulation seems important for insulin action; therefore, physiological conditions that alter the pattern of insulin release may affect insulin action through this mechanism. Transhepatic intraportal shunt in humans may provide access to portal vein samples, thus potentially improving the sensitivity of detecting and quantitating the frequency, mass, and amplitude of secretory bursts along with basal release and the regularity of these variables. To establish the insulin-secretory mechanism in nondiabetic humans by the use of portal vein sampling, we here assessed the mass, frequency, amplitude, and overall contribution of pulsatile insulin secretion by deconvolution analysis of portal vein insulin profiles. We find that, in nondiabetic humans fasted overnight, the portal vein insulin concentration oscillates at a periodicity of 4.1 ± 0.2 min/pulse and with secretory peak amplitudes averaging 660% of basal (interpulse) release. The frequency was confirmed by spectral and autocorrelation analyses. The punctuated insulin-secretory bursts partially overlap and are responsible for the majority (70 ± 4%) of insulin release. After ingestion of a mixed meal, the insulin release was increased through amplification of the secretory burst mass (507 ± 104 vs. 1,343 ± 211 pmol · l−1· min−1, P < 0.001), whereas frequency (4.4 ± 0.2 vs. 4.3 ± 0.2, P = 0.86) and basal secretion (62 ± 14 vs. 91 ± 22 pmol · l−1· min−1, P = 0.33) were unaffected. One subject with diabetes and cirrhosis had a similar insulin-secretory pattern, whereas a subject with insulin-dependent diabetes mellitus and minimal insulin release had preserved pulsatile release. A single subject was entrained to show agreement between entrained frequency and portal vein insulin oscillations. We conclude that insulin release in the human portal vein occurs at a mean periodicity of 4.4 ± 0.2 min with a high signal-to-noise ratio (pulse amplitude 660% of basal). The impact of noise on the detected high frequency cannot be excluded.
Contrasting effects of exercise and NOS inhibition on tissue-specific fatty acid and glucose uptake in mice
Authors: Rottman Jeffrey N. , Bracy Deanna , Malabanan Carlo , Yue Zou , Clanton Jeff , Wasserman David H.
Published: February 2015

Isotopic techniques were used to test the hypothesis that exercise and nitric oxide synthase (NOS) inhibition have distinct effects on tissue-specific fatty acid and glucose uptakes in a conscious, chronically catheterized mouse model. Uptakes were measured using the radioactive tracers125I-labeled β-methyl- p-iodophenylpentadecanoic acid (BMIPP) and deoxy-[2-3H]glucose (DG) during treadmill exercise with and without inhibition of NOS. [125I]BMIPP uptake at rest differed substantially among tissues with the highest levels in heart. With exercise, [125I]BMIPP uptake increased in both heart and skeletal muscles. In sedentary mice, NOS inhibition induced by nitro-l-arginine methyl ester (l-NAME) feeding increased heart and soleus [125I]BMIPP uptake. In contrast, exercise, but not l-NAME feeding, resulted in increased heart and skeletal muscle [2-3H]DG uptake. Significant interactions were not observed in the effects of combined exercise and l-NAME feeding on [125I]BMIPP and [2-3H]DG uptakes. In the conscious mouse, exercise and NOS inhibition produce distinct patterns of tissue-specific fatty acid and glucose uptake; NOS is not required for important components of exercise-associated metabolic signaling, or other mechanisms compensate for the absence of this regulatory mechanism.
Impact of high-fat diet and antioxidant supplement on mitochondrial functions and gene transcripts in rat muscle
Authors: Sreekumar R. , Unnikrishnan J. , Fu A. , Nygren J. , Short K. R. , Schimke J. , Barazzoni R. , Nair K. Sreekumaran
Published: February 2015

High-fat diets are reported to increase oxidative stress in a variety of tissues, whereas antioxidant supplementation prevents many diseases attributed to high-fat diet. Rodent skeletal muscle mitochondrial DNA has been shown to be a potential site of oxidative damage. We hypothesized that the effects of a high-fat diet on skeletal muscle DNA functions would be attenuated or partially reversed by antioxidant supplementation. Gene expression profiling and measurement of mitochondrial ATP production capacity were performed in skeletal muscle from male rats after feeding one of three diets (control, high-fat diet with or without antioxidants) for 36 wk. The high-fat diet altered transcript levels of 18 genes of 800 surveyed compared with the control-fed rats. Alterations included reduced expression of genes involved in free-radical scavenging and tissue development and increased expression of stress response and signal transduction genes. The magnitude of these alterations due to high-fat diet was reduced by antioxidant supplementation. Real-time PCR measurements confirmed the changes in transcript levels of cytochrome c oxidase subunit III and superoxide dismutase-1 and -2 noted by microarray approach. Mitochondrial ATP production was unaltered by dietary changes or antioxidant supplemention. It is concluded that the high-fat diet increases the transcription of genes involved in stress response but reduces those of free-radical scavenger enzymes, resulting in reduced DNA repair/metabolism (increased DNA damage). Antioxidants partially prevent these changes. Mitochondrial functions in skeletal muscle remain unaltered by the dietary intervention due to many adaptive changes in gene transcription.
Mild streptozotocin diabetes in the Göttingen minipig. A novel model of moderate insulin deficiency and diabetes
Authors: Larsen Marianne O. , Wilken Michael , Gotfredsen Carsten F. , Carr Richard D. , Svendsen Ove , Rolin Bidda
Published: February 2015

Nonrodent models of diabetes are needed for practical and physiological reasons. Induction of mild insulin-deficient diabetes was investigated in male Göttingen minipigs by use of streptozotocin (STZ) alone (75, 100, and 125 mg/kg) or 125 mg/kg combined with pretreatment with nicotinamide (NIA; 0, 20, 67, 100, 150, and 230 mg/kg). Use of NIA resulted in a less steep slope of the regression line between fasting plasma glucose and changing doses compared with STZ [−7.0 ± 1.4 vs. 29.7 ± 7.0 mM · mg−1· kg−1, P < 0.0001]. Intermediate NIA doses induced moderate changes of glucose tolerance [glucose area under the curve increased from 940 ± 175 to 1,598 ± 462 mM · min, P < 0.001 (100 mg/kg) and from 890 ± 109 to 1,669 ± 691 mM · min, P = 0.003 (67 mg/kg)] with reduced insulin secretion [1,248 ± 602 pM · min after 16 days and 1,566 ± 190 pM · min after 60 days vs. 3,251 ± 804 pM · min in normal animals ( P < 0.001)] and β-cell mass [5.5 ± 1.4 mg/kg after 27 days and 7.9 ± 4.1 mg/kg after 60 days vs. 17.7 ± 4.7 mg/kg in normal animals ( P = 0.009)]. The combination of NIA and STZ provided a model characterized by fasting and especially postprandial hyperglycemia and reduced, but maintained, insulin secretion and β-cell mass. This model holds promise as an important tool for studying the pathophysiology of diabetes and development of new pharmacological agents for treatment of the disease.
Minimal model SI=0 problem in NIDDM subjects: nonzero Bayesian estimates with credible confidence intervals
Authors: Pillonetto Gianluigi , Sparacino Giovanni , Magni Paolo , Bellazzi Riccardo , Cobelli Claudio
Published: February 2015

The minimal model of glucose kinetics, in conjunction with an insulin-modified intravenous glucose tolerance test, is widely used to estimate insulin sensitivity (SI). Parameter estimation usually resorts to nonlinear least squares (NLS), which provides a point estimate, and its precision is expressed as a standard deviation. Applied to type 2 diabetic subjects, NLS implemented in MINMOD software often predicts SI=0 (the so-called “zero” SI problem), whereas general purpose modeling software systems, e.g., SAAM II, provide a very small SI but with a very large uncertainty, which produces unrealistic negative values in the confidence interval. To overcome these difficulties, in this article we resort to Bayesian parameter estimation implemented by a Markov chain Monte Carlo (MCMC) method. This approach provides in each individual the SI a posteriori probability density function, from which a point estimate and its confidence interval can be determined. Although NLS results are not acceptable in four out of the ten studied subjects, Bayes estimation implemented by MCMC is always able to determine a nonzero point estimate of SI together with a credible confidence interval. This Bayesian approach should prove useful in reanalyzing large databases of epidemiological studies.