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Biomedical subjects

J O Holloszy

Publications and source records attributed to J O Holloszy.

At least 19 recordsLinked to original sources
PubMed2001

Development of glucose-induced insulin resistance in muscle requires protein synthesis.

Muscles and fat cells develop insulin resistance when exposed to high concentrations of glucose and insulin. We used an isolated muscle preparation incubated with high levels of glucose and insulin to further evaluate how glucose-induced insulin resistance (GIIR) is mediated. Incubation with 2 milliunits/ml insulin and 36 mm glucose for 5 h resulted in an approximately 50% decrease in insulin-stimulated muscle glucose transport. The decrease in insulin responsiveness of glucose transport induced by glucose was not due to impaired insulin signaling, as insulin-stimulated phosphatidylinositol 3-kinase activity and protein kinase B phosphorylation were not reduced. It has been hypothesized that entry of glucose into the hexosamine biosynthetic pathway with accumulation of UDP-N-acetylhexosamines (UDP-HexNAcs) mediates GIIR. However, inhibition of the rate-limiting enzyme GFAT (glutamine:fructose-6-phosphate amidotransferase) did not protect against GIIR despite a marked reduction of UDP-HexNAcs. The mRNA synthesis inhibitor actinomycin D and the protein synthesis inhibitor cycloheximide both completely protected against GIIR despite the massive increases in UDP-HexNAcs and glycogen that resulted from increased glucose entry. Activation of AMP-activated protein kinase also protected against GIIR. These results provide evidence that GIIR can occur in muscle without increased accumulation of hexosamine pathway end products, that neither high glycogen concentration nor impaired insulin signaling is responsible for GIIR, and that synthesis of a protein with a short half-life mediates GIIR. They also suggest that dephosphorylation of a transcription factor may be involved in the induction of GIIR.

Animals↗
PubMed2001

Modest lifestyle intervention and glucose tolerance in obese African Americans.

OBJECTIVE: Previous studies have demonstrated the benefit of short-term diets on glucose tolerance in obese individuals. The purpose of this study was to evaluate the effectiveness of modest lifestyle changes in maintaining improvements in glucose tolerance induced by short-term energy restriction in obese African Americans with impaired glucose tolerance or type 2 diabetes mellitus. RESEARCH METHODS AND PROCEDURES: An intervention group (n = 45; 47 +/- 1 year [mean +/- SE]), 105 +/- 4 kg; body mass index: 39 +/- 1 kg/m(2)) received an energy-restricted diet (943 +/- 26 kcal/d) for 1 week, followed by a lifestyle program of reduced dietary fat (-125 kcal/d) and increased physical activity (+125 kcal/d) for 1 year. Body weight and plasma concentrations of glucose, insulin, and C-peptide during an oral glucose tolerance test were measured at baseline, 1-week, and 4-month intervals. A control group (n = 24; 48 +/- 1 year; 110 +/- 5 kg; body mass index: 41 +/- 2 kg/m(2)) underwent these measurements at 4-month intervals. RESULTS: No changes in weight or glucose tolerance were observed in the control group. The intervention group had significant (p < 0.05) improvements in body weight and glucose tolerance in response to the 1-week diet, which persisted for 4 months (p < 0.001 vs. control for change in weight). A total of 19 subjects (42%) continued the intervention program for 1 year, with sustained improvements (weight: -4.6 +/- 1.0 kg; p < 0.001 vs. control; oral glucose tolerance test glucose area: -103 +/- 44 mM. min; p < 0.05 vs. control). DISCUSSION: A modest lifestyle program facilitates weight loss and enables improvements in glucose tolerance to be maintained in obese individuals with abnormal glucose tolerance. However, attrition was high, despite the mild nature of the program.

Adult↗
PubMed2001

The HIV protease inhibitor indinavir decreases insulin- and contraction-stimulated glucose transport in skeletal muscle.

In many patients with human immunodeficiency virus (HIV) treated with HIV protease inhibitors, a complication develops that resembles abdominal obesity syndrome, with insulin resistance and glucose intolerance that, in some cases, progresses to diabetes. In this study, we tested the hypothesis that indinavir, an HIV-protease inhibitor, directly induces insulin resistance of glucose transport in skeletal muscle. Rat epitrochlearis muscles were incubated with a maximally effective insulin concentration (12 nmol/l) and 0, 1, 5, 20, or 40 micromol/l indinavir for 4 h. In control muscles, insulin increased 3-O-[(3)H]methyl-D-glucose (3MG) transport from 0.15 +/- 0.03 to 1.10 +/- 0.05 micromol. ml(-)(1). 10 min(-)(1). Incubation of muscles with 5 micromol/l indinavir reduced the insulin-stimulated increase in 3MG transport by 40%, whereas 20 micromol/l indinavir reduced the insulin-stimulated increase in 3MG transport by 58%. Indinavir induced a similar reduction in maximally insulin-stimulated 3MG transport in the soleus muscle. The increase in glucose transport activity induced by stimulating epitrochlearis muscles to contract was also markedly reduced by indinavir. The insulin-stimulated increase in cell-surface GLUT4, assessed using the 2-N-4-(1-azi-2,2,2-trifluoroethyl)benzoyl-1,3-bis-[2-(3)H] (D-mannose-4-yloxy)-2-propylamine exofacial photolabeling technique, was reduced by approximately 70% in the presence of 20 micromol/l indinavir. Insulin stimulation of phosphatidylinositol 3-kinase activity and phosphorylation of protein kinase B were not decreased by indinavir. These results provide evidence that indinavir inhibits the translocation or intrinsic activity of GLUT4 rather than insulin signaling.

Animals↗
PubMed2000

Transgenic overexpression of hexokinase II in skeletal muscle does not increase glucose disposal in wild-type or Glut1-overexpressing mice.

Glut1 transgenic mice were bred with transgenic mice that overexpress hexokinase II in skeletal muscle in order to determine whether whole-body glucose disposal could be further augmented in mice overexpressing glucose transporters. Overexpression of hexokinase alone in skeletal muscle had no effect on glucose transport or metabolism in isolated muscles, nor did it alter blood glucose levels or the rate of whole-body glucose disposal. Expression of the hexokinase transgene in the context of the Glut1 transgenic background did not alter glucose transport in isolated muscles but did cause additional increases in steady-state glucose 6-phosphate (3.2-fold) and glycogen (7.5-fold) levels compared with muscles that overexpress the Glut1 transporter alone. Surprisingly, however, these increases were not accompanied by a change in basal or insulin-stimulated whole-body glucose disposal in the doubly transgenic mice compared with Glut1 transgenic mice, probably due to an inhibition of de novo glycogen synthesis as a result of the high levels of steady-state glycogen in the muscles of doubly transgenic mice (430 micromol/g versus 10 micromol/g in wild-type mice). We conclude that the hexokinase gene may not be a good target for therapies designed to counteract insulin resistance or hyperglycemia.

Animals↗
PubMed2000

Skeletal muscle respiratory uncoupling prevents diet-induced obesity and insulin resistance in mice.

To determine whether uncoupling respiration from oxidative phosphorylation in skeletal muscle is a suitable treatment for obesity and type 2 diabetes, we generated transgenic mice expressing the mitochondrial uncoupling protein (Ucp) in skeletal muscle. Skeletal muscle oxygen consumption was 98% higher in Ucp-L mice (with low expression) and 246% higher in Ucp-H mice (with high expression) than in wild-type mice. Ucp mice fed a chow diet had the same food intake as wild-type mice, but weighed less and had lower levels of glucose and triglycerides and better glucose tolerance than did control mice. Ucp-L mice were resistant to obesity induced by two different high-fat diets. Ucp-L mice fed a high-fat diet had less adiposity, lower levels of glucose, insulin and cholesterol, and an increased metabolic rate at rest and with exercise. They were also more responsive to insulin, and had enhanced glucose transport in skeletal muscle in the setting of increased muscle triglyceride content. These data suggest that manipulating respiratory uncoupling in muscle is a viable treatment for obesity and its metabolic sequelae.

Animals↗
PubMed2000

Effects of DHEA replacement on bone mineral density and body composition in elderly women and men.

OBJECTIVE: Dehydroepiandrosterone (DHEA) is a precursor for both oestrogens and androgens. Its marked decline with ageing may influence age-related changes in tissues influenced by sex hormones. The aim of this study was to determine the effects of DHEA replacement on bone mineral density (BMD) and body composition in elderly women and men with low serum DHEA sulphate (DHEAS) levels. DESIGN: Prospective 6 month trial of oral DHEA replacement, 50 mg/day. PATIENTS: Experimental subjects were 10 women and eight men, aged 73 +/- 1 years. Control subjects were 10 women and eight men, aged 74 +/- 1 years. MEASUREMENTS: BMD, body composition, serum markers of bone turnover, serum lipids and lipoproteins, oral glucose tolerance, serum IGF-I, total serum oestrogens and testosterone. RESULTS: BMD of the total body and lumbar spine increased (mean +/- SEM; 1.6 +/- 0.6% and 2.5 +/- 0.8%, respectively; both P < or = 0.05), fat mass decreased (- 1.3 +/- 0.4 kg; P < 0.01) and fat-free mass increased (0.9 +/- 0.4 kg; P < or = 0. 05) in response to DHEA replacement. DHEA replacement also resulted in increases in serum IGF-I (from 108 +/- 8 to 143 +/- 7 microg/l; P < 0.01) and total serum testosterone concentrations (from 10.7 +/- 1.2 to 15.6 +/- 1.8 nmol/l in the men and from 2.1 +/- 0.2 to 4.5 +/- 0.4 nmol/l in the women; both P < or = 0.05). CONCLUSIONS: The results provide preliminary evidence that DHEA replacement in those elderly women and men who have very low serum DHEAS levels can partially reverse age-related changes in fat mass, fat-free mass, and BMD, and raise the possibility that increases in IGF-I and/or testosterone play a role in mediating these effects of DHEA.

Adjuvants, Immunologic↗
PubMed2000

Low-intensity exercise as a modifier of physical frailty in older adults.

OBJECTIVE: To examine the effects of a 3-month low-intensity exercise program on physical frailty. DESIGN: Randomized clinical trial. SETTING: Regional tertiary-care hospital and academic medical center with an outpatient rehabilitation fitness center. PARTICIPANTS: Eighty-four physically frail older adults (mean age, 83 +/- 4 yrs). INTERVENTION: Three-month low-intensity supervised exercise (n = 48) versus unsupervised home-based flexibility activities (n = 36). MAIN OUTCOME MEASURES: Physical performance test, measures of balance, strength, flexibility, coordination, speed of reaction, peripheral sensation. RESULTS: Significant improvement was made by the exercise group on our primary indicator of frailty, a physical performance test (PPT) (29 +/- 4 vs 31 +/- 4 out of a possible 36 points), as well as many of the risk factors previously identified as contributors to frailty; eg, reductions in flexibility, strength, gait speed, and poor balance. Although the home exercise control group showed increases in range of motion, the improvements in flexibility did not translate into improvements in physical performance capacity as assessed by the PPT. CONCLUSIONS: Our results suggest that physical frailty is modifiable with a program of modest activities that can be performed by virtually all older adults. They also indicate that exercise programs consisting primarily of flexibility activities are not likely to reverse or attenuate physical frailty. Although results suggest that frailty is modifiable, it is not likely to be eliminated with exercise, and efforts should be directed toward preventing the condition.

Aged↗
PubMed2000

Mechanisms underlying impaired GLUT-4 translocation in glycogen-supercompensated muscles of exercised rats.

Exercise training induces an increase in GLUT-4 in muscle. We previously found that feeding rats a high-carbohydrate diet after exercise, with muscle glycogen supercompensation, results in a decrease in insulin responsiveness so severe that it masks the effect of a training-induced twofold increase in GLUT-4 on insulin-stimulated muscle glucose transport. One purpose of this study was to determine whether insulin signaling is impaired. Maximally insulin-stimulated phosphatidylinositol (PI) 3-kinase activity was not significantly reduced, whereas protein kinase B (PKB) phosphorylation was approximately 50% lower (P < 0.01) in muscles of chow-fed, than in those of fasted, exercise-trained rats. Our second purpose was to determine whether contraction-stimulated glucose transport is also impaired. The stimulation of glucose transport and the increase in cell surface GLUT-4 induced by contractions were both decreased by approximately 65% in glycogen-supercompensated muscles of trained rats. The contraction-stimulated increase in AMP kinase activity, which has been implicated in the activation of glucose transport by contractions, was approximately 80% lower in the muscles of the fed compared with the fasted rats 18 h after exercise. These results show that both the insulin- and contraction-stimulated pathways for muscle glucose transport activation are impaired in glycogen-supercompensated muscles and provide insight regarding possible mechanisms.

3-O-Methylglucose↗
PubMed2000

High-fat diet-induced muscle insulin resistance: relationship to visceral fat mass.

It has been variously hypothesized that the insulin resistance induced in rodents by a high-fat diet is due to increased visceral fat accumulation, to an increase in muscle triglyceride (TG) content, or to an effect of diet composition. In this study we used a number of interventions: fish oil, leptin, caloric restriction, and shorter duration of fat feeding, to try to disassociate an increase in visceral fat from muscle insulin resistance. Substituting fish oil (18% of calories) for corn oil in the high-fat diet partially protected against both the increase in visceral fat and muscle insulin resistance without affecting muscle TG content. Injections of leptin during the last 4 days of a 4-wk period on the high-fat diet partially reversed the increase in visceral fat and the muscle insulin resistance, while completely normalizing muscle TG. Restricting intake of the high-fat diet to 75% of ad libitum completely prevented the increase in visceral fat and muscle insulin resistance. Maximally insulin-stimulated glucose transport was negatively correlated with visceral fat mass (P < 0.001) in both the soleus and epitrochlearis muscles and with muscle TG concentration in the soleus (P < 0.05) but not in the epitrochlearis. Thus we were unable to dissociate the increase in visceral fat from muscle insulin resistance using a variety of approaches. These results support the hypothesis that an increase in visceral fat is associated with development of muscle insulin resistance.

Adipose Tissue↗
PubMed2000

Increased expression of GLUT-4 and hexokinase in rat epitrochlearis muscles exposed to AICAR in vitro.

Exercise acutely stimulates muscle glucose transport and also brings about an adaptive increase in the capacity of muscle for glucose uptake by inducing increases in GLUT-4 and hexokinase.(1) Recent studies have provided evidence that activation of AMP protein kinase (AMPK) is involved in the stimulation of glucose transport by exercise. The purpose of this study was to determine whether activation of AMPK is also involved in mediating the adaptive increases in GLUT-4 and hexokinase. To this end, we examined the effect of incubating rat epitrochlearis muscles in culture medium for 18 h in the presence or absence of 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), which enters cells and is converted to the AMP analog ZMP, thus activating AMPK. Exposure of muscles to 0.5 mM AICAR in vitro for 18 h resulted in an approximately 50% increase in GLUT-4 protein and an approximately 80% increase in hexokinase. This finding provides strong evidence in support of the hypothesis that the activation of AMPK that occurs in muscle during exercise is involved in mediating the adaptive increases in GLUT-4 and hexokinase.

Adenylate Kinase↗
PubMed2000

Activation of AMP-activated protein kinase increases mitochondrial enzymes in skeletal muscle.

Muscle contraction causes an increase in activity of 5'-AMP-activated protein kinase (AMPK). This study was designed to determine whether chronic chemical activation of AMPK will increase mitochondrial enzymes, GLUT-4, and hexokinase in different types of skeletal muscle of resting rats. In acute studies, rats were subcutaneously injected with either 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR; 1 mg/g body wt) in 0.9% NaCl or with 0.9% NaCl alone and were then anesthetized for collection and freezing of tissues. AMPK activity increased in the superficial, white region of the quadriceps and in soleus muscles but not in the deep, red region of the quadriceps muscle. Acetyl-CoA carboxylase (ACC) activity, a target for AMPK, decreased in all three muscle types in response to AICAR injection but was lowest in the white quadriceps. In rats given daily, 1 mg/g body wt, subcutaneous injections of AICAR for 4 wk, activities of citrate synthase, succinate dehydrogenase, and malate dehydrogenase were increased in white quadriceps and soleus but not in red quadriceps. Cytochrome c and delta-aminolevulinic acid synthase levels were increased in white, but not red, quadriceps. Carnitine palmitoyl-transferase and hydroxy-acyl-CoA dehydrogenase were not significantly increased. Hexokinase was markedly increased in all three muscles, and GLUT-4 was increased in red and white quadriceps. These results suggest that chronic AMPK activation may mediate the effects of muscle contraction on some, but not all, biochemical adaptations of muscle to endurance exercise training.

Adaptation, Physiological↗
PubMed2000

Exercise induces lipoprotein lipase and GLUT-4 protein in muscle independent of adrenergic-receptor signaling.

Exercise increases the expression of lipoprotein lipase (LPL) and GLUT-4 in skeletal muscle. Intense exercise increases catecholamines, and catecholamines without exercise can affect the expression of both LPL and GLUT-4. To test the hypothesis that adrenergic-receptor signaling is central to the induction of LPL and GLUT-4 by exercise, six untrained individuals [age 28 +/- 4 (SD) yr, peak oxygen uptake 3.6 +/- 0.3 l/min] performed two exercise bouts within 12 days. Exercise consisted of cycling at approximately 65% peak oxygen uptake for 60 min with (block trial) and without (control trial) adrenergic-receptor blockade. Exercise intensity was the same during the block and control trials. Plasma catecholamine concentrations were significantly higher and heart rates were significantly lower during the block trial compared with the control trial, consistent with known effects of adrenergic-receptor blockade. However, blockade did not prevent the induction of either LPL or GLUT-4 proteins assayed in biopsies of skeletal muscle. LPL was significantly increased by 170-240% and GLUT-4 was significantly increased by 32-51% at 22 h after exercise compared with before exercise during both the control and block trials. These findings provide evidence that exercise increases muscle LPL and GLUT-4 protein content via signals generated by alterations in cellular homeostasis and not by adrenergic-receptor stimulation.

Adrenergic alpha-Antagonists↗
PubMed2000

The biology of aging.

Nothing has been demonstrated to slow or reverse the primary aging process in humans; instead, the factors that are known to affect longevity do so by their influence on disease development, which is part of secondary aging. Preventive strategies against secondary aging are aimed at maintaining health and functional capacity and rectangularizing, rather than extending, the survival curve. Interventions for preventive geriatrics and successful aging include a low-fat, low-energy diet with a high content of fruits and vegetables; exercise; and hormone replacement.

Aged↗
PubMed1999

Respiratory uncoupling induces delta-aminolevulinate synthase expression through a nuclear respiratory factor-1-dependent mechanism in HeLa cells.

Nuclear respiratory factor (NRF)-1 appears to be important for the expression of several respiratory genes, but there is no direct evidence that NRF-1 transduces a physiological signal into the production of an enzyme critical for mitochondrial biogenesis. We generated HeLa cells containing plasmids allowing doxycycline-inducible expression of uncoupling protein (UCP)-1. In the absence of doxycycline, UCP-1 mRNA and protein were undetectable. In the presence of doxycycline, UCP-1 was expressed and oxygen consumption doubled. This rise in oxygen consumption was associated with an increase in NRF-1 mRNA. It was also associated with an increase in NRF-1 protein binding activity as determined by electrophoretic mobility shift assay using a functional NRF-1 binding site from the delta-aminolevulinate (ALA) synthase promoter. Respiratory uncoupling also caused a time-dependent increase in protein levels of ALA synthase, an early marker for mitochondrial biogenesis. ALA synthase induction by respiratory uncoupling was prevented by transfecting cells with an oligonucleotide antisense to the region of the NRF-1 initiation codon; a scrambled oligonucleotide with the same base composition had no effect. Respiratory uncoupling increases oxygen consumption and lowers energy reserves. In HeLa cells, uncoupling also increases ALA synthase, an enzyme critical for mitochondrial respiration, but only if translatable mRNA for NRF-1 is available. These data suggest that the transcription factor NRF-1 plays a key role in cellular adaptation to energy demands by translating physiological signals into an increased capacity for generating energy.

5-Aminolevulinate Synthetase↗
PubMed1999

Hydroxyl radical generation during exercise increases mitochondrial protein oxidation and levels of urinary dityrosine.

Isolated mitochondria are well-established sources of oxidants in vitro. There is little direct evidence that mitochondria promote oxidative stress in vivo, however. Model system studies demonstrate that ortho-tyrosine, meta-tyrosine, and o,o'-dityrosine increase in proteins oxidized by hydroxyl radical. To determine whether mitochondria generate oxidants in vivo, we used isotope dilution gas chromatography mass spectrometry to quantify levels of these markers in the heart muscle of control and exercised rats. Exercise led to a 50% increase in ortho-tyrosine, metatyrosine, and o,o'-dityrosine in the mitochondrial proteins but not cytosolic proteins of heart muscle. This increase was transient, and levels returned to normal when exercised animals were allowed to rest. There also was a transient increase in the level of o,o'-dityrosine in the urine of exercised rats. This relationship between mitochondrial and urine levels of o,o'-dityrosine suggests that urine assays of this oxidized amino acid may serve as noninvasive measures of oxidative stress. These observations also provide direct evidence that heart muscle mitochondria produce an intermediate resembling the hydroxyl radical that promotes protein oxidation in vivo.

Animals↗
PubMed1999

Decreased insulin-stimulated GLUT-4 translocation in glycogen-supercompensated muscles of exercised rats.

It was recently found that the effect of an exercise-induced increase in muscle GLUT-4 on insulin-stimulated glucose transport is masked by a decreased responsiveness to insulin in glycogen-supercompensated muscle. We evaluated the role of hexosamines in this decrease in insulin responsiveness and found that UDP-N-acetyl hexosamine concentrations were not higher in glycogen-supercompensated muscles than in control muscles with a low glycogen content. We determined whether the smaller increase in glucose transport is due to translocation of fewer GLUT-4 to the cell surface with the 2-N-4-(1-azi-2,2,2-trifluroethyl)-benzoyl-1, 3-bis(D-mannose-4-yloxy)-2-propylamine (ATB-[2-3H]BMPA) photolabeling technique. The insulin-induced increase in GLUT-4 at the cell surface was no greater in glycogen-supercompensated exercised muscle than in muscles of sedentary controls and only 50% as great as in exercised muscles with a low glycogen content. We conclude that the decreased insulin responsiveness of glucose transport in glycogen-supercompensated muscle is not due to increased accumulation of hexosamine biosynthetic pathway end products and that the smaller increase in glucose transport is mediated by translocation of fewer GLUT-4 to the cell surface.

Animals↗