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Objective To test the hypothesis that HIV infection impairs the beneficial effects of weight loss on insulin sensitivity, adipose tissue inflammation, and endoplasmic reticulum (ER) stress. Methods A prospective clinical trial evaluated the effects of moderate diet-induced weight loss on body composition, metabolic function, and adipose tissue biology in women with obesity who were HIV-seronegative (HIV−) or HIV-positive (HIV+). Body composition, multiorgan insulin sensitivity (assessed by using a two-stage hyperinsulinemic-euglycemic clamp procedure with stable isotopically labeled tracer infusions), and adipose tissue expression of markers of inflammation, autophagy, and ER stress were evaluated in 8 HIV− and 20 HIV+ women with obesity before and after diet-induced weight loss of 6% to 8%. Results Although weight loss was not different between groups (∼7.5%), the decrease in fat-free mass was greater in HIV+ than HIV− subjects (−4.4 ± 0.7% vs. −1.7 ± 1.0%, P

Summary Anabolic resistance and impaired myocellular quality contribute to age-related sarcopenia, which exacerbates with obesity. Diet-induced muscle mass loss is attenuated by resistance or aerobic plus resistance exercise compared to aerobic exercise in obese elderly. We assessed chronic effects of weight loss plus different exercise modalities on muscle protein synthesis response to feeding and myocellular quality. Obese older adults were randomized to a weight-management program plus aerobic, resistance, or combined aerobic and resistance exercise or to control. Participants underwent vastus lateralis biopsies at baseline and 6 months. Muscle protein synthesis rate increased more in resistance and combined than in control. Autophagy mediators’ expression decreased more in combined than in aerobic, which experienced a higher increase in inflammation and mitochondrial regulators’ expression. In obese elderly, combined aerobic and resistance exercise is superior to either mode independently for improving muscle protein synthesis and myocellular quality, thereby maintaining muscle mass during weight-loss therapy.

Objective Age is the single greatest risk factor for Alzheimer's disease (AD), with the incidence doubling every 5 years after age 65. However, our understanding of the mechanistic relationship between increasing age and the risk for AD is currently limited. We therefore sought to determine the relationship between age, amyloidosis, and amyloid-beta (Aβ) kinetics in the central nervous system (CNS) of humans. Methods Aβ kinetics were analyzed in 112 participants and compared to the ages of participants and the amount of amyloid deposition. Results We found a highly significant correlation between increasing age and slowed Aβ turnover rates (2.5-fold longer half-life over five decades of age). In addition, we found independent effects on Aβ42 kinetics specifically in participants with amyloid deposition. Amyloidosis was associated with a higher (>50%) irreversible loss of soluble Aβ42 and a 10-fold higher Aβ42 reversible exchange rate. Interpretation These findings reveal a mechanistic link between human aging and the risk of amyloidosis, which may be owing to a dramatic slowing of Aβ turnover, increasing the likelihood of protein misfolding that leads to deposition. Alterations in Aβ kinetics associated with aging and amyloidosis suggest opportunities for diagnostic and therapeutic strategies. More generally, this study provides an example of how changes in protein turnover kinetics can be used to detect physiological and pathophysiological changes and may be applicable to other proteinopathies. Ann Neurol 2015;78:439–453

HIV infection is associated with a greater risk for fasting hyperinsulinemia, impaired glucose tolerance, and higher incidence rates for vascular disease, myocardial infarction, or stroke despite effective combination antiretroviral therapy (cART). The underlying mechanism(s) may involve chronic low-grade systemic inflammation and immune cell activation. Dipeptidyl peptidase-4 inhibitors (sitagliptin) improve glucose tolerance and may possess immunomodulatory effects because leukocyte CD26 cell surface receptors express dipeptidyl peptidase-4 activity.Sitagliptin will reduce inflammatory and immune cell activation markers known to be elevated in cART-treated HIV-infected (HIV+) adults with impaired glucose tolerance.This was designed as a prospective, randomized, placebo-controlled, double-blind trial of sitagliptin in HIV+ adults.The setting was an academic medical center.Patients were cART-treated HIV+ men and women (n = 36) with stable HIV disease and impaired glucose tolerance.Interventions included sitagliptin 100 mg/d or placebo for 8 weeks.At baseline and week 8, plasma high-sensitivity C-reactive protein and C-X-C motif chemokine 10 concentrations (ELISA), oral glucose tolerance, and abdominal sc adipose mRNA expression for M1 macrophage markers (monocyte chemotactic protein-1, EGF-like module-containing, mucin-like hormone receptor 1).Sitagliptin reduced glucose area under the curve (P = .002) and improved oral glucose insulin sensitivity index (P = .04) more than placebo. Sitagliptin reduced plasma high-sensitivity C-reactive protein and C-X-C motif chemokine 10 levels more than placebo (P.009). Adipose tissue monocyte chemotactic protein-1 mRNA abundance declined significantly more (P = .01), and adipose EGF-like module-containing, mucin-like hormone receptor 1 mRNA expression tended to decline more (P = .19) in sitagliptin than placebo.Sitagliptin had beneficial systemic and adipose anti-inflammatory effects in cART-treated HIV+ adults with impaired glucose tolerance. Large-scale, long-term studies should determine whether sitagliptin reduces cardiovascular risk and events in HIV+ adults.

Individuals with HIV infection and peripheral metabolic complications have impaired basal myocardial insulin sensitivity that is related to left ventricular (LV) diastolic dysfunction. It is unknown whether interventions shown to be effective in improving peripheral insulin sensitivity can improve basal myocardial insulin sensitivity and diastolic function in people with HIV and peripheral metabolic complications.In a pilot study, we evaluated whether the peroxisome proliferator-activated receptor-gamma (PPAR-γ) agonist pioglitazone or combined endurance and resistance exercise training improves basal myocardial insulin sensitivity and diastolic function in HIV+ adults with peripheral metabolic complications.Twenty-four HIV+ adults with metabolic complications including peripheral insulin resistance were randomly assigned to 4 months of pioglitazone (PIO; 30 mg/d) or supervised, progressive endurance and resistance exercise training (EXS; 90-120 min/d, 3 d/wk). Basal myocardial substrate metabolism was quantified by radioisotope tracer methodology and positron emission tomography (PET) imaging, and LV function was measured by echocardiography.Twenty participants completed the study. Neither PIO nor EXS resulted in a detectable improvement in basal myocardial insulin sensitivity or diastolic function. Post hoc analyses revealed sample sizes of more than 100 participants are needed to detect significant effects of these interventions on basal myocardial insulin sensitivity and function.PIO or EXS alone did not significantly increase basal myocardial insulin sensitivity or LV diastolic function in HIV+ individuals with peripheral metabolic complications.

Our objective was to determine if the presence of metabolic complications (MC) conveyed an additional risk for left ventricular (LV) dysfunction in people with HIV. HIV+ and HIV− men and women were categorized into four groups: (1) HIV+ with MC (43±7 years, n=64), (2) HIV+ without MC (42±7 years, n=59), (3) HIV− with MC (44±8 years, n=37), or (4) HIV− controls without MC (42±8 years, n=41). All participants underwent two-dimensional (2-D), Doppler, and tissue Doppler echocardiography. Overall, the prevalence of systolic dysfunction (15 vs. 4%, p=0.02) and LV hypertrophy (9 vs. 1%, p=0.03) was greater in HIV+ than in HIV− participants. Participants with MC had a greater prevalence of LV hypertrophy (10% vs. 1%). Early mitral annular velocity during diastole was significantly (p

There is little prospective information on the cardiometabolic risks of testosterone and growth hormone (GH) replacement therapy to youthful levels during aging. We conducted a double-masked, partially placebo controlled study in 112 men 65–90 years-old. Transdermal testosterone (5g-vs-10g/day) using a Leydig Cell Clamp and subcutaneous recombinant GH (rhGH) (0-vs-3-vs-5ug/kg/day) were administered for 16-weeks. Measurements included testosterone and IGF-1 levels, body composition by DEXA, and cardiometabolic risk factors (upper body fat, blood pressure, insulin sensitivity, fasting triglycerides, HDL-cholesterol, and serum adiponectin) at baseline and after 16 weeks of treatment. Some cardiometabolic factors improved (total and trunk fat, triglycerides, HDL-cholesterol) and others worsened (systolic blood pressure, insulin sensitivity index [QUICKI], adiponectin). Cardiometabolic risk composite scores (CRCS) improved (−0.69±1.55, p

Background: Gastric cancer is increasingly recognized in Zambia. Although nutritional factors contribute to gastric cancer risk, their effect in Zambia is unknown. Objective: The objective was to investigate the association between intake of dietary antioxidants, urinary 8-iso prostaglandin F2α (8-iso PGF2α) as a marker of oxidative stress, and gastric cancer. Design: This was a case-control study at the University Teaching Hospital in Zambia. Gastric cancer cases were compared with age- and sex-matched controls. Urine 8-iso PGF2α was measured primarily by ELISA, and by gas chromatography–mass spectrometry in a subset, expressed as a ratio to creatinine. Blood was collected for Helicobacter pylori, HIV serology, gastrin-17, and pepsinogen 1 and 2 concentrations. Clinical and dietary data were collected by using questionnaires. Food items were broadly classified into 7 major categories (fruit, vegetables, fish, meat, insects, cereals, and starches). Results: Fifty cases with gastric cancer (mean age: 61 y; n = 31 males) and 90 controls (mean age: 54 y; n = 41 males) were enrolled. Median urinary 8-iso PGF2α excretion was higher in cases (0.014; IQR: 0.008–0.021) than in controls (0.011; IQR: 0.006–0.018; P = 0.039). On univariate analysis, habitual fruit intake was lower in cases than in controls during the dry season (P = 0.02). On multivariate analysis, smoking (OR: 7.22; IQR: 1.38–37.9) and gastric atrophy (OR: 2.43; IQR: 1.12–5.13) were independently associated with cancer, and higher fruit intake was protective (OR: 0.44; IQR: 0.20–0.95). Isoprostane excretion was inversely correlated with total fruit intake (ρ = −0.23; n = 140; P = 0.006). Conclusion: Urinary 8-iso PGF2α excretion was associated with the risk of gastric cancer, as were smoking and gastric atrophy, but increased fruit intake conferred protection. This trial was registered at www.pactr.org as ISRCTN52971746.

People infected with HIV have a higher risk for developing insulin resistance, diabetes, and cardiovascular disease than the general population. Dipeptidyl peptidase IV (DPP4) inhibitors are glucose-lowering medications with pleiotropic actions that may particularly benefit people with HIV, but the immune and virological safety of DPP4 inhibition in HIV is unknown.DPP4 inhibition will not reduce CD4+ T lymphocyte number or increase HIV viremia in HIV-positive adults.This was a randomized, placebo-controlled, double-blind safety trial of sitagliptin in HIV-positive adults.The study was conducted at an academic medical center.Twenty nondiabetic HIV-positive men and women (9.8 ± 5.5 years of known HIV) taking antiretroviral therapy and with stable immune (625 ± 134 CD4+ T cells per microliter) and virological (48 copies HIV RNA per milliliter) status.The intervention included sitagliptin (100 mg/d) vs matching placebo for up to 24 weeks.CD4+ T cell number and plasma HIV RNA were measured every 4 weeks; fasting serum regulated upon activation normal T-cell expressed and secreted (RANTES), stromal derived factor (SDF)-1α, Soluble TNF receptor II, and oral glucose tolerance were measured at baseline, week 8, and the end of study. ANOVA was used for between-group comparisons; P.05 was considered significant.Compared with placebo, sitagliptin did not reduce CD4+ T cell count, plasma HIV RNA remained less than 48 copies/mL, RANTES and soluble TNF receptor II concentrations did not increase. SDF1α concentrations declined (P.0002) in the sitagliptin group. The oral glucose tolerance levels improved in the sitagliptin group at week 8.Despite lowering SDF1α levels, sitagliptin did not adversely affect immune or virological status, or increase immune activation, but did improve glycemia in healthy, nondiabetic HIV-positive adults. These safety data allow future efficacy studies of sitagliptin in HIV-positive people with cardiometabolic complications.

Aging may alter protein metabolism during periods of metabolic and physiologic challenge. The purpose of this study was to assess the effects of age on whole-body amino acid turnover in response to eccentric exercise and hyperglycemia-induced hyperinsulinemia. 16 healthy men were divided into young (N = 8) and older (N = 8) groups. Protein metabolism was assessed using a [1-13C]-leucine isotopic tracer approach. Measures were obtained under fasted basal conditions and during 3-h hyperglycemic clamps that were performed without (control) and 48 h after eccentric exercise. Exercise reduced leucine oxidation in the younger men (P < 0.05), but not in older men. Insulin sensitivity was inversely correlated with leucine oxidation (P < 0.05), and was lower in older men (P < 0.05). Healthy aging is associated with an impaired capacity to adjust protein oxidation in response to eccentric exercise. The decreased efficiency of protein utilization in older men may contribute to impaired maintenance, growth, and repair of body tissues with advancing age.

Summary Objectives To determine the durability of anabolic effects and adverse events (AEs) after stopping testosterone and growth hormone supplementation in older men. Design Secondary analysis of a double-masked, randomized controlled trial of testosterone gel (5 or 10 g/daily) plus rhGH (0, 3 or 5 μg/kg/day) with follow-up of outcomes 3 months later. Participants A total of 108 community-dwelling 65- to 90-year-old men. Measurements Testosterone and IGF-1 levels, body composition (DEXA), 1-repetition maximum (1-RM) strength, stair-climbing power, quality-of-life (QOL) and activity questionnaires, AEs. Results Despite improvements in body composition during treatment, residual benefits 3 months later (week 28) were variable. For participants with improvements exceeding their week-17 median changes, benefits were sustained at week 28 for lean body mass (1·45 ± 1·63 kg, 45% of week-17 values, P

The prevalence and incidence of insulin resistance and type 2 diabetes mellitus (DM) are higher in people treated for human immunodeficiency virus-1 (HIV) infection than in the general population. Identifying safe and effective interventions is a high priority. We evaluated whether the peroxisome proliferator-activated receptor-γ agonist pioglitazone with exercise training improves central and peripheral insulin sensitivity more than pioglitazone alone in HIV-infected adults with insulin resistance and central adiposity. Forty-four HIV-infected adults with baseline insulin resistance and central adiposity were randomly assigned to 4 mo of pioglitazone (30 mg/day) with or without supervised, progressive aerobic, and resistance exercise training (1.5–2 h/day, 3 days/wk). The hyperinsulinemic euglycemic clamp was used to evaluate alterations in central and peripheral insulin sensitivity. Thirty-nine participants completed the study. Hepatic insulin sensitivity improved similarly in both groups. Exercise training augmented the beneficial effects of pioglitazone on peripheral insulin sensitivity. Greater improvements in peripheral insulin sensitivity were associated with reductions in total body and limb adipose content rather than increases in limb adiposity or pioglitazone-induced increases in adiponectin concentration. We conclude that supplementing pioglitazone with increased physical activity improved insulin sensitivity more effectively than pioglitazone alone in HIV-infected adults with insulin resistance and central adiposity. Pioglitazone alone did not significantly increase limb adipose content. Potential cardiovascular benefits of these interventions in HIV need investigation.

LOSS of skeletal muscle mass (sarcopenia) contributes to declines in muscle performance and physical function during aging. Substantial losses in muscle strength may result in difficulty rising from a chair, climbing stairs, generating gait speed, maintaining balance, and frailty (1,2). The levels of endogenous anabolic hormones also decline during the aging process (3). Indeed, 25%–30% of men aged older than 60 years have low levels of serum testosterone levels (4) that may be associated with sarcopenia and muscle weakness (3,5). Restoring testosterone to youthful levels increases synthesis of myofibrillar proteins, total body cell mass, and muscle strength (6,7). Declines in growth hormone (GH) and insulin-like growth factor 1 (IGF-1) may also contribute to comorbidities in older men with normal testosterone levels (3,8). To better understand the relative contributions of testosterone and GH/IGF-1 axes in older persons at risk for sarcopenia, we conducted the HORMA (Hormonal Regulators of Muscle and Metabolism in Aging) Trial to test our hypothesis that endogenous testosterone and GH are important independent but complementary regulators of skeletal muscle mass and function even into advanced age (9). Total lean body mass (LBM), appendicular skeletal muscle mass (ASMM), muscle performance, and stair climbing power increased significantly with testosterone and changes appeared to be enhanced by recombinant human growth hormone (rhGH) (9). However, there was considerable variability in anabolic responses as well as in changes in testosterone and IGF-1 levels during treatment. This provided the opportunity to examine relationships of a broad range of hormone changes, including declines in levels as may occur in clinical practice, and their effects on changes in lean tissue mass, muscle strength, performance, and physical function. We used pathway analysis to test the hypothesis that testosterone and rhGH affected muscle mass directly and that a threshold change in lean tissue mass was needed to generate significant improvements in muscle performance and physical function. Additionally, we used bootstrap analysis to determine target hormone levels associated with threshold changes in whole-body and appendicular lean mass that would be necessary for improving muscle performance and functional outcomes.

Insulin-like growth factor I (IGF-I) is a potent myogenic factor that plays a critical role in muscle regeneration and muscle hypertrophy. The purpose of this study was to evaluate the effect of IGF-I overexpression on the recovery of muscle size and function during reloading/reambulation after a period of cast immobilization in predominantly fast twitch muscles. In addition, we investigated concomitant molecular responses in IGF-I receptor and binding proteins (BPs). Recombinant adeno-associated virus vector for IGF-I (rAAV-IGF-IA) was injected into the anterior compartment of one of the hindlimbs of young (3 wk) C57BL6 female mice. At 20 wk of age, both hindlimbs were cast immobilized in a shortened position for 2 wk to unload the tibialis anterior (TA) and extensor longus digitorum (EDL) muscles. The TA and EDL muscles were removed bilaterally after 2 wk of cast immobilization and after 1 and 3 wk of free cage reambulation. Increases in IGF-I mRNA and protein levels with IGF-I overexpression were associated with significant increases in muscle wet weight, fiber size, and tetanic force, although overexpression did not protect against cast immobilization-induced muscle atrophy. After 1 wk of reambulation, evidence of enhanced muscle regeneration was noted in IGF-I-overexpressing muscles with an increased prevalence of central nuclei, embryonic myosin, and Pax7 positive fibers. We also observed larger relative gains in muscle size (wet weight and fiber area), but not force, during the 3-wk reambulation period in hindlimb muscles overexpressing IGF-I compared with contralateral control legs. Changes in IGFBP-5 mRNA expression during cast immobilization and reambulation paralleled those of IGF-I, whereas IGFBP-3 expression changed inversely to IGFBP-5.

Metabolic complications associated with HIV infection and treatment frequently present as a relative lack of peripheral adipose tissue associated with dyslipidemia and insulin resistance. In this review we explain the connection between abnormalities of intermediary metabolism, observed either in vitro or in vivo, and this group of metabolic effects. We review molecular mechanisms by which the HIV protease inhibitor (PI) class of drugs may affect the normal stimulatory effect of insulin on glucose and fat storage. We then propose that both chronic inflammation from HIV infection and treatment with some drugs in this class trigger cellular homeostatic stress responses with adverse effects on intermediary metabolism. The physiologic outcome is such that total adipocyte storage capacity is decreased, and the remaining adipocytes resist further fat storage. The excess circulating and dietary lipid metabolites, normally “absorbed” by adipose tissue, are deposited ectopically in lean (muscle and liver) tissue, where they impair insulin action. This process leads to a pathologic cycle of lipotoxicity and lipoatrophy and a clinical phenotype of body fat distribution with elevated waist-to-hip ratio similar to the metabolic syndrome.

Resistance (RE) and endurance (EE) exercise stimulate mixed skeletal muscle protein synthesis. The phenotypes induced by RE (myofibrillar protein accretion) and EE (mitochondrial expansion) training must result from differential stimulation of myofibrillar and mitochondrial protein synthesis. We measured the synthetic rates of myofibrillar and mitochondrial proteins and the activation of signalling proteins (Akt-mTOR-p70S6K) at rest and after an acute bout of RE or EE in the untrained state and after 10 weeks of RE or EE training in young healthy men. While untrained, RE stimulated both myofibrillar and mitochondrial protein synthesis, 67% and 69% (P < 0.02), respectively. After training, only myofibrillar protein synthesis increased with RE (36%, P = 0.05). EE stimulated mitochondrial protein synthesis in both the untrained, 154%, and trained, 105% (both P < 0.05), but not myofibrillar protein synthesis. Acute RE and EE increased the phosphorylation of proteins in the Akt-mTOR-p70S6K pathway with comparatively minor differences between two exercise stimuli. Phosphorylation of Akt-mTOR-p70S6K proteins was increased after 10 weeks of RE training but not by EE training. Chronic RE or EE training modifies the protein synthetic response of functional protein fractions, with a shift toward exercise phenotype-specific responses, without an obvious explanatory change in the phosphorylation of regulatory signalling pathway proteins.

Fatty acids are a major fuel for many tissues, and abnormal utilization is implicated in diseases. However, tissue fatty acid oxidation has not been determined reliably in vivo. Furthermore, fatty acid oxidation has not been partitioned into intracellular and extracellular components. In this report, a one-pool model is described that enables direct quantitation of fluxes of intracellular and plasma fatty acids to mitochondria in skeletal muscle using dual stable isotopes and liquid chromatography/electrospray ionization ion-trap tandem mass spectrometry technology. It is validated by the determination of palmitate oxidation by skeletal muscle in lean and obese rats and the regulation by insulin. Resting postabsorptive intramyocellular and plasma palmitate oxidation by the gastrocnemius muscle was determined to be 3.47 6 0.8 and 2.06 6 0.5 nmol/g/min in lean and 6.96 6 1.8 and 1.34 6 0.2 nmol/g/min in obese rats, respectively. In obese rats, hyperinsulinemia (1 nmol/L) suppressed intramyocellular (by 59 6 5% to 2.88 6 0.3 nmol/g/ min; p ,0.05) but not plasma (1.41 6 0.14 nmol/g/min; p .0.05) palmitate oxidation. The fractional turnover rate of palmitoylcarnitine (0.34 6 0.1/min vs. 0.83 6 0.2/min; p ,0.05) was also suppressed by insulin in obese rats. In obese and lean rats, 83 and 51%, respectively (p = 0.08), of plasma fatty acids traverse the triacylglycerol pool before being oxidized. The results demonstrated that the methodology is feasible and sensitive to metabolic alterations and thus can be used to study fatty acid utilization at tissue level in vivo in a compartmentalized manner for the first time.

The aim of this study was to assess the effects of nutrient ingestion, dietary protein intake, age, and sex on the fractional synthesis rate (FSR) of albumin. Thirty-six healthy free-living individuals (8 females and 10 males aged 21-43 y and 9 females and 9 males aged 63-79 y) completed three 18-d periods of controlled feeding with protein intakes of 125% (P125, 1.00 g protein x kg(-1) x d(-1)), 94% (P94, 0.75 g protein x kg(-1) x d(-1)), and 63% (P63, 0.50 g protein x kg(-1) x d(-1)) of the recommended dietary allowance. On d 12 of each trial, postabsorptive (PA) serum albumin concentration was determined and PA and postprandial (PP) albumin FSR were estimated from the rate of l-[1- 13C] leucine incorporation into plasma albumin during an 8-h infusion. There were no age-related differences in PA and PP albumin FSR. Albumin FSR was higher PP than PA (P < 0.0001), and the increase in albumin FSR from PA to PP was smaller as dietary protein intake decreased from P125 to P94 and P63 (P < 0.05). Independent of protein intake, males had a higher albumin FSR (P < 0.05) and a greater increase in albumin FSR with feeding (P < 0.05). There was no age or dietary protein effect on serum albumin concentrations, but males had higher albumin concentrations than females (P < 0.0001). These results show that older persons are responsive to nutrient ingestion and dietary protein-related changes in albumin FSR. The greater albumin synthesis rate in males might contribute to a higher albumin concentration set point.

The impressive success of antiretroviral therapy (ART) in reducing the morbidity and mortality associated with HIV disease has been tempered by frequent toxicities associated with chronic ART use. Lipid abnormalities, insulin resistance, increased cardiovascular risk, and lipodystrophy have been reported.1 Lipodystrophy refers to body fat distribution changes that occur after the initiation of ART. Two distinct components have been described: limb fat atrophy (lipo-atrophy) and trunk and visceral fat accumulation. Limb lipoatrophy has become a common distinguishing characteristic associated with HIV and its treatment.2,3 This complication can profoundly affect the well-being of the patient, can be stigmatizing, and can be coincident with a cluster of metabolic complications. Longitudinal studies evaluating the effect of ART initiation have demonstrated that within weeks of initiating ART, lean body mass and limb and trunk fat mass increase.4,5 With continued treatment for more than a year, limb fat mass slowly and progressively declines, whereas the gain in trunk fat mass is maintained.4,6,7 Patient-related factors that are associated with progressive limb fat mass loss include age,8,9 white race, female gender,7 low nadir CD4+ cell count, hepatitis C virus (HCV) coinfection,9–12 and specific polymorphisms in the tumor necrosis factor-α (TNFα) and ApoC3 genes.13 Treatment-related factors that may also contribute include exposure to stavudine (d4T)14 and, potentially, zidovudine (ZDV). Protease inhibitors (PIs) were initially thought to play a significant role in the development of lipoatrophy,15 but subsequent data have also implicated the nucleoside reverse transcriptase inhibitors (NRTIs).16,17 Some authors have suggested that PIs may contribute to the development of osteopenia or osteoporosis associated with HIV or its treatment,18 fat accumulation and lipid abnormalities,19 and glucose intolerance or diabetes.20 Effective interventions for managing HIV lipoatrophy have not been identified. Several studies report that substituting the PI component of ART does not improve or reverse limb lipoatrophy.21 Treatment with the peroxisome proliferator-activated receptor-γ (PPARγ) agonist rosiglitazone seemed to increase limb fat mass in patients with HIV-associated lipoatrophy,22 but these findings were not confirmed in a large prospective randomized trial.23 Pioglitazone was only modestly active in improving subcutaneous fat in the extremities.24 Switching d4T or ZDV to abacavir (ABC) or tenofovir (TDF) has been reported to increase limb fat mass,25–28 however, with a decrease of limb lean mass in a study by Boyd et al.28 Switching to regimens without NRTIs increased mitochondrial DNA content in fat and peripheral blood mononuclear cells,28 a potential mechanism implicated in the development of lipoatrophy.29 If osteopenia or osteoporosis, fat accumulation, lipid abnormalities, and insulin resistance are linked to PI use, the expectation would be that clinical improvements should occur after switching to alternative regimens that do not include these drugs. In the AIDS Clinical Trials Group (ACTG) A5125s, we examined the effects of PI-containing NRTI-sparing and NRTI-containing PI-sparing regimens on fat distribution, changes in bone mineral density (BMD), and metabolic parameters in patients who switched their currently successful antiretroviral regimen to a PI-sparing or NRTI-sparing regimen. The primary objective was to quantify the changes in limb fat mass (using regional dual-energy x-ray absorptiometry [DEXA]) within and between each of the 2 treatment arms. The secondary objectives were to quantify changes in fasting lipids (high-density lipoproteins [HDLs], low-density lipoproteins [LDLs], total cholesterol, and triglycerides), fasting glucose, insulin, the homeostasis model assessment of insulin resistance (HOMA-IR), hip and spine BMD, and serum markers of bone metabolism after switching ART; to examine relations between changes in regional fat, lipids, and insulin resistance; and to examine relations between baseline demographic variables, CD4+ lymphocyte cell counts, body mass index (BMI), limb fat mass, and changes in indices of glucose metabolism, lipids, and bone metabolism after switching ART.

The protease inhibitor (PI) ritonavir (RTV) has been associated with elevated resting lipolytic rate, hyperlipidemia, and insulin resistance/glucose intolerance. The purpose of this study was to examine relationships between lipolysis and fatty acid (FA) oxidation during rest, moderate exercise and recovery, and measures of insulin sensitivity/glucose tolerance and fat redistribution in HIV-positive subjects taking RTV ( n = 12), HAART but no PI ( n = 10), and HIV-seronegative controls ( n = 10). Stable isotope tracers [1-13C]palmitate and [1,1,2,3,3-2H5]glycerol were continuously infused with blood and breath collection during 1-h rest, 70-min submaximal exercise (50% V̇o2 peak), and 1-h recovery. Body composition was evaluated using DEXA, MRI, and MRS, and 2-h oral glucose tolerance tests with insulin monitoring were used to evaluate glucose tolerance and insulin resistance. Lipolytic and FA oxidation rates were similar during rest and recovery in all groups; however, they were lower during moderate exercise in both HIV-infected groups [glycerol Ra: HIV + RTV 5.1 ± 1.2 vs. HIV + no PI 5.9 ± 2.8 vs. Control 7.4 ± 2.2 μmol·kg fat-free mass (FFM)−1·min−1; palmitate oxidation: HIV + RTV 1.6 ± 0.8 vs. HIV + no PI 1.6 ± 0.8 vs. Control 2.5 ± 1.7 μmol·kg FFM·min, P < 0.01]. Fasting and orally-challenged glucose and insulin values were similar among groups. Lipolytic and FA oxidation rates were blunted during moderate exercise in HIV-positive subjects taking HAART. Lower FA oxidation during exercise was primarily due to impaired plasma FA oxidation, with a minor contribution from lower nonplasma FA oxidation. Regional differences in adipose tissue lipolysis during rest and moderate exercise may be important in HIV and warrant further study.

Fibrates, activators of the nuclear receptor PPARα, improve dyslipidemia, but their effects on insulin resistance and vascular disease are unresolved. To test the hypothesis that PPARα activation improves insulin resistance and vascular function, we determined the effects of fenofibrate in healthy adults with insulin resistance induced by short-term glucocorticoid administration. Eighteen normal-weight subjects were studied in four stages: at baseline, after 21 days of fenofibrate (160 mg/day) alone, after 3 days of dexamethasone (8 mg/day) added to fenofibrate, and after 3 days of dexamethasone added to placebo (dexamethasone alone). Dexamethasone alone caused hyperinsulinemia, increased glucose, decreased glucose disposal, and reduced insulin-induced suppression of hepatic glucose production as determined by hyperinsulinemic euglycemic clamp and increased systolic blood pressure as determined by ambulatory monitoring, features associated with an insulin-resistant state. Fenofibrate improved fasting LDL and total cholesterol in the setting of dexamethasone treatment but had no significant effect on levels of insulin or glucose, insulin-stimulated glucose disposal, or insulin suppression of glucose production during clamps, or ambulatory monitored blood pressure. In the absence of dexamethasone, fenofibrate lowered fasting triglycerides and cholesterol but unexpectedly increased systolic blood pressure by ambulatory monitoring. These data suggest that PPARα activation in humans does not correct insulin resistance induced by glucocorticoids and may adversely affect blood pressure.

Type 2 diabetes (T2DM) is characterized by impaired glucose tolerance (IGT) and insulin resistance with respect to glucose metabolism, but not amino acid metabolism. We examined whether whole body leucine and protein metabolism are dysregulated in HIV-infected people with IGT. Glucose and leucine kinetics were measured under fasting insulin conditions and during euglycemic-hyperinsulinemia using primed constant infusions of 2H2-glucose and 13C-leucine in 10 HIV-seronegative control subjects, 16 HIV+ with normal glucose tolerance, and 21 HIV+IGT. Glucose disposal rate during hyperinsulinemia was lower in HIV+IGT than the other two groups. Absolute plasma leucine levels and rate of appearance (whole body proteolysis) were higher in HIV+IGT at all insulin levels, but declined in response to hyperinsulinemia in parallel to those in the other two groups. HIV+IGT had greater visceral adiposity, fasting serum IL-8 and FFA levels, and higher lipid oxidation rates during the clamp than the other two groups. The findings implicate several factors in the insulin-signaling pathway that may be further dysregulated in HIV+IGT, and support the notion that insulin-signaling pathways for glucose and leucine metabolism may be disrupted by increased proinflammatory adipocytokines (IL-8) and increased lipid oxidation. Increased proteolysis may provide amino acids for gluconeogenesis; exacerbating hyperglycemia in HIV.

Dyslipidemia is common in patients with HIV infection. In this study, a two-stage euglycemic hyperinsulinemic clamp, with infusion of stable isotopically labeled tracers, was used to evaluate insulin action in skeletal muscle, liver, and adipose tissue in HIV-infected men with dyslipidemia (HIV-DL; plasma triglyceride >250 mg/dl and HDL a), glucose disposal (glucose Rd), and lipolysis (palmitate Ra) were similar between groups. The relative suppression of glucose Ra(63 ± 4, 77 ± 2, and 78 ± 3%, P = 0.008) and palmitate Ra(49 ± 4, 63 ± 3, and 68 ± 3%, P = 0.005) during low-dose insulin infusion (plasma insulin ∼30 μU/ml), and the relative stimulation of glucose Rd(214 ± 21, 390 ± 25, and 393 ± 46%, P = 0.001) during high-dose insulin infusion (plasma insulin ∼75 μU/ml) were lower in HIV-DL than in HIV w/o DL and healthy volunteers, respectively. Suppression of basal glucose Racorrelated with plasma adiponectin ( r = 0.44, P = 0.02) and inversely with plasma IL-6 ( r = −0.49, P < 0.001). Stimulation of glucose Rdcorrelated directly with adiponectin ( r = 0.48, P < 0.01) and inversely with IL-6 ( r = −0.49, P = 0.02). We conclude that dyslipidemia in HIV-infected men is indicative of multiorgan insulin resistance, and circulating adipokines may be important in the pathogenesis of impaired insulin action.

Use of protease inhibitor (PI)–based highly active antiretroviral therapy (HAART) has been associated with altered regional fat distribution, insulin resistance, and dyslipidemias. To assess how PI-based HAART affects adipocyte gene expression in male HIV-1–infected patients, reverse transcription–polymerase chain reaction was used to quantify messenger RNA expression of adipocyte transcription factors and adipocytokines in thigh and abdominal subcutaneous adipose tissue from male (1) HIV-1 seronegative subjects (control, n = 9), (2) asymptomatic treatment-naive HIV-1–infected patients (naive, n = 6), (3) HIV-1–infected patients who were receiving antiretroviral agents but never received PIs (PI naive, n = 5), (4) HIV-1–infected patients who were receiving PI-based HAART (PI, n = 7), and (5) HIV-1–infected patients who discontinued the PI component of their antiviral therapy more than 6 months before enrollment (past PI, n =7). In the PI group, the messenger RNA expression levels of the CCAAT/enhancer–binding protein α, leptin, and adiponectin (18%, P < .01; 23%, P < .05; and 13%, P < .05, respectively) were significantly lower than the levels measured in the PI-naive group. These results are consistent with previous studies on the effects of PIs on cultured adipocytes. Prospective longitudinal studies of thigh fat adipose tissue gene expression could provide further insights on the pathogenesis of metabolic complications associated with PI-based HAART.

We have developed an animal model of diabetic sympathetic autonomic neuropathy which is characterized by neuroaxonal dystrophy (NAD), an ultrastructurally distinctive axonopathy, in chronic streptozotocin (STZ)-diabetic rats. Diabetes-induced alterations in the sorbitol pathway occur in sympathetic ganglia and therapeutic agents which inhibit aldose reductase or sorbitol dehydrogenase improve or exacerbate, respectively, diabetes-induced NAD. The sorbitol dehydrogenase inhibitor SDI-711 (CP-470711, Pfizer) is approximately 50-fold more potent than the structurally related compound SDI-158 (CP 166,572) used in our earlier studies. Treatment with SDI-711 (5 mg/kg/day) for 3 months increased ganglionic sorbitol (26-40 fold) and decreased fructose content (20-75%) in control and diabetic rats compared to untreated animals. SDI-711 treatment of diabetic rats produced a 2.5- and 4-5-fold increase in NAD in the SMG and ileal mesenteric nerves, respectively, in comparison to untreated diabetics. Although SDI-711 treatment of non-diabetic control rat ganglia increased ganglionic sorbitol 40-fold (a value 8-fold higher than untreated diabetics), the frequency of NAD remained at control levels. Levels of ganglionic sorbitol pathway intermediates in STZ-treated rats (a model of type 1 diabetes) and Zucker Diabetic Fatty rats (ZDF, a genetic model of type 2 diabetes) were comparable, although STZ-diabetic rats develop NAD and ZDF-diabetic rats do not. SDI failed to increase diabetes-related ganglionic NGF above levels seen in untreated diabetics. Initiation of Sorbinil treatment for the last 4 months of a 9 month course of diabetes, substantially reversed the frequency of established NAD in the diabetic rat SMG without affecting the metabolic severity of diabetes. These findings indicate that sorbitol pathway-linked metabolic alterations play an important role in the development of NAD, but sorbitol pathway activity, not absolute levels of sorbitol or fructose per se, may be most critical to its pathogenesis.

Age-associated alterations in muscle protein quantity and quality that adversely affect muscle structure, composition, and function have been referred to as sarcopenia. Muscle protein is metabolically active, and the age-associated loss of muscle protein mass is related to a loss of physical function and an inability to perform activities of daily living (physical frailty). It is important to maintain adequate reserves of muscle protein and amino acids as we age. As in all cachectic conditions, sarcopenia can be explained by an imbalance between the rates of muscle protein synthesis and muscle proteolysis, in which net muscle protein balance is negative. This review summarizes evidence that supports the notion that: (a). advancing age and physical frailty are associated with a reduction in the fasting rate of mixed and myosin heavy chain protein synthesis, which contributes to muscle protein wasting in advancing age; (b). this impairment can be corrected because resistance exercise acutely and dramatically increases the rate of muscle protein synthesis in men and women aged 76 years and older; and (c). resistance exercise training maintains a modest increment in the rate of muscle protein synthesis and contributes to muscle hypertrophy and improved muscle strength in frail elderly men and women. The cellular mechanisms responsible for these adaptations, as well as the role of nutrition and hormone replacement in reversing sarcopenia, require further investigation.

Possible reasons for why a new study could not replicate our finding that the serotonin reuptake inhibitor citalopram decreased amyloid β concentrations in the cerebrospinal fluid of healthy volunteers.

Serotonin signaling suppresses generation of amyloid-β (Aβ) in vitro and in animal models of Alzheimer’s disease (AD). We show that in an aged transgenic AD mouse model (APP/PS1 plaque-bearing mice), the antidepressant citalopram, a selective serotonin reuptake inhibitor (SSRI), decreased Aβ in brain interstitial fluid (ISF) in a dose-dependent manner. Growth of individual amyloid plaques was assessed in plaque-bearing mice that were chronically administered citalopram. Citalopram arrested the growth of pre-existing plaques and reduced the appearance of new plaques by 78%. In healthy human volunteers, citalopram’s effects on Aβ production and Aβ concentrations in cerebrospinal fluid (CSF) were measured prospectively using stable-isotope labeling kinetics (SILK), with CSF sampling during acute dosing of citalopram. Aβ production in CSF was slowed by 37% in the citalopram group compared to placebo. This change was associated with a 38% decrease in total CSF Aβ concentrations in the drug-treated group. The ability to safely decrease Aβ concentrations is potentially important as a preventive strategy for AD. This study demonstrates key target engagement for future AD prevention trials.

Advancing age is associated with a reduction in skeletal muscle protein, muscle strength, muscle quality, and chemical modifications that may impair protein function. Sarcopenia has been coupled with physical disability, frailty, and a loss of independent function (5, 19). Using stable isotope tracer methodologies and mass spectrometric detection, we observed: (a) 76–92-year-old physically frail and 62–74-year-old middle-age adults have lower mixed muscle protein synthetic rates than 20–32-year-old men and women; (b) 2 weeks and 3 months of weightlifting exercise increased the synthetic rate of myosin heavy chain (MHC) and mixed muscle proteins to a similar magnitude in frail, middle-age, and young women and men; (c) Serum myostatin-immunoreactive protein levels were elevated in physically frail women and were inversely correlated with lean mass. This suggests that the protein synthetic machinery adapts rapidly to increased contractile activity and that the adaptive response(s) are maintained even in frail elders.

Testosterone increases muscle mass and strength and regulates other physiological processes, but we do not know whether testosterone effects are dose dependent and whether dose requirements for maintaining various androgen-dependent processes are similar. To determine the effects of graded doses of testosterone on body composition, muscle size, strength, power, sexual and cognitive functions, prostate-specific antigen (PSA), plasma lipids, hemoglobin, and insulin-like growth factor I (IGF-I) levels, 61 eugonadal men, 18–35 yr, were randomized to one of five groups to receive monthly injections of a long-acting gonadotropin-releasing hormone (GnRH) agonist, to suppress endogenous testosterone secretion, and weekly injections of 25, 50, 125, 300, or 600 mg of testosterone enanthate for 20 wk. Energy and protein intakes were standardized. The administration of the GnRH agonist plus graded doses of testosterone resulted in mean nadir testosterone concentrations of 253, 306, 542, 1,345, and 2,370 ng/dl at the 25-, 50-, 125-, 300-, and 600-mg doses, respectively. Fat-free mass increased dose dependently in men receiving 125, 300, or 600 mg of testosterone weekly (change +3.4, 5.2, and 7.9 kg, respectively). The changes in fat-free mass were highly dependent on testosterone dose ( P = 0.0001) and correlated with log testosterone concentrations ( r = 0.73, P = 0.0001). Changes in leg press strength, leg power, thigh and quadriceps muscle volumes, hemoglobin, and IGF-I were positively correlated with testosterone concentrations, whereas changes in fat mass and plasma high-density lipoprotein (HDL) cholesterol were negatively correlated. Sexual function, visual-spatial cognition and mood, and PSA levels did not change significantly at any dose. We conclude that changes in circulating testosterone concentrations, induced by GnRH agonist and testosterone administration, are associated with testosterone dose- and concentration-dependent changes in fat-free mass, muscle size, strength and power, fat mass, hemoglobin, HDL cholesterol, and IGF-I levels, in conformity with a single linear dose-response relationship. However, different androgen-dependent processes have different testosterone dose-response relationships.

OBJECTIVES—Moderate weight loss and exercise have been proposed as important tools in the treatment and prevention of type 2 diabetes. Therefore, we tested the hypothesis that short-term (4 weeks) moderate energy restriction (−750 kcal/day) would result in a significant increase in insulin-stimulated glucose disposal (40 mU · m−2 · min−1 hyperinsulinemic-euglycemic clamp) in moderately overweight postmenopausal women and that when combined with resistance training (RT) an even greater effect would be seen. RESEARCH DESIGN AND METHODS—Older women were randomly assigned to energy restriction (WLoss group; n = 9) or energy restriction plus RT (RT + WLoss group; n = 10). RESULTS—For the WLoss versus the RT + WLoss groups, changes in body weight (−3.0 ± 0.2 kg vs. −3.2 ± 0.3 kg), fat mass (FM) (−3.0 ± 0.3 kg vs. −3.2 ± 0.3 kg), and percent body fat (BF) (−2.1 ± 0.4 vs. −2.4 ± 0.3%) were not different between groups. Muscle mass (group-by-time interaction, P = 0.04) was preserved in RT + WLoss (0.40 ± 0.40 kg) and reduced in WLoss (−0.64 ± 0.18 kg). There were no changes in fat-free mass (FFM) and waist-to-hip ratio in either group. Whole body glucose disposal (WLoss 6.14 ± 0.57 vs. 6.03 ± 0.53, RT + WLoss 5.85 ± 0.60 vs. 6.09 ± 0.56 mg/kg of FFM/min) did not change in either group. CONCLUSIONS—The results of this study demonstrate that short-term energy restriction resulting in moderate decreases in body weight (4.0 ± 0.3%) and FM (8.2 ± 0.7%) did not improve insulin-stimulated glucose disposal. The addition of RT to the hypoenergetic diet preserved muscle mass but provided no synergistic effect on insulin action. These results suggest that a greater change in body weight or FM may be necessary to observe a significant improvement in insulin action.

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.

We investigated the effects of a glutamine-supplemented amino acid mixture on vastus lateralis muscle protein synthesis rate in healthy young men and women. Three men and 3 women (27.8 +/- 2.0 yr, 22.2 +/- 1.0 body mass index [BMI], 56.1 +/- 4.5 kg lean body mass [LBM]) received a 14-hour primed, constant intravenous infusion of L[1-13C]leucine to evaluate the fractional rate of mixed muscle protein synthesis. In addition to tracer administration, a clinically relevant amino acid mixture supplemented with either glutamine or glycine in amounts isonitrogenous to glutamine, was infused. Amino acid mixtures were infused on separate occasions in random order at a rate of 0.04 g/kg/h (glutamine at approximately 0.01 g/kg/h) with at least 2 weeks between treatment. For 2 days before and on the day of an infusion, dietary intake was controlled so that each subject received 1.5 g protein/kg/d. Compared with our previous report in the postabsorptive state, amino acid infusion increased the fractional rate of mixed muscle protein synthesis by 48% (P < .05); however, the addition of glutamine to the amino acid mixture did not further elevate muscle protein synthesis rate (ie, 0.071% +/- 0.008%/h for amino acids + glutamine v 0.060% +/- 0.008%/h for amino acids + glycine; P = .316). Plasma glutamine concentrations were higher (P < .05) during the glutamine-supplemented infusion, but free intramuscular glutamine levels were not increased (P = .363). Both plasma and free intramuscular glycine levels were increased when extra glycine was included in the infused amino acid mixture (both P < .0001). We conclude that intravenous infusion of amino acids increases the fractional rate of mixed muscle protein synthesis, but addition of glutamine to the amino acid mixture does not further stimulate muscle protein synthesis rate in healthy young men and women.

In Rabson-Mendenhall syndrome, severe insulin resistance is caused by defective insulin receptors. The patient studied lacks insulin receptor binding due to a truncation mutation of one allele and a point mutation of the other allele of the insulin receptor alpha-subunit. He developed pulmonary hypertension and cor pulmonale, and was considered for organ transplantation. A trial of prednisone 1.2 mg/kg/d was initiated to determine if he could tolerate immunosuppressive therapy without deterioration of his pre-existing, difficult to control diabetes mellitus. Insulin responsiveness was measured prior to and after 4 d of glucocorticoid administration ('Before GC' and 'After GC') using the hyperinsulinemic glucose clamp and stable isotope tracer dilution techniques. After a 12-h fast and 24 h of intravenous insulin, a primed continuous infusion of 6,6-(2)H(2)-glucose was administered during a 2-h tracer equilibration period followed by a 2-h insulin-deficient period, and a 2-h hyperinsulinemic glucose clamp period during which insulin was infused at 7 u/kg/h. Blood glucose concentrations during the basal periods, while no insulin was infused, were 245+/-7 and 138+/-8 mg/dL in the studies Before GC and After GC, respectively. During both hyperinsulinemic glucose clamp periods, the blood glucose was 171+/-1 and 167+/-5 mg/dL, respectively. Hepatic glucose production (HGP) was higher during the basal period Before GC than during the same period After GC (7.86+/-0.23 vs. 5.31+/-0.19 mg/kg/min). HGP rate was suppressed by insulin to 1.48+/-0.45 mg/kg/min Before GC, but was not suppressed After GC (4.19+/-0.81 mg/kg/min). The hyperinsulinemic glucose clamp did not increase the glucose utilization rate nor the glucose clearance rate over basal in either Before GC or After GC, indicating complete peripheral insulin resistance. In summary, the liver showed some response to insulin in the absence of insulin receptors but the peripheral tissues had no response to insulin. Glucocorticoids worsened insulin resistance in the liver in this patient.

We determined whether short-term weight-lifting exercise increases the synthesis rate of the major contractile proteins, myosin heavy chain (MHC), actin, and mixed muscle proteins in nonfrail elders and younger women and men. Fractional synthesis rates of mixed, MHC, and actin proteins were determined in seven healthy sedentary 23- to 32-yr-old and seven healthy 78- to 84-yr-old participants in paired studies done before and at the end of a 2-wk weight-lifting program. The in vivo rate of incorporation of 1-[13C]leucine into vastus lateralis MHC, actin, and mixed proteins was determined using a 14-h constant intravenous infusion of 1-[13C]leucine. Before exercise, the mixed and MHC fractional synthetic rates were lower in the older than in the younger participants ( P ≤ 0.04). Baseline actin protein synthesis rates were similar in the two groups ( P = not significant). Over a 2-wk period, participants completed ten 1- to 1.5-h weight-lifting exercise sessions: 2–3 sets per day of 9 exercises, 8–12 repetitions per set, at 60–90% of maximum voluntary muscle strength. At the end of exercise, MHC and mixed protein synthetic rates increased in the younger (88 and 121%) and older participants (105 and 182%; P < 0.001 vs. baseline). These findings indicate that MHC and mixed protein synthesis rates are reduced more than actin in advanced age. Similar to that of 23–32 yr olds, the vastus lateralis muscle in 78–84 yr olds retains the capacity to increase MHC and mixed protein synthesis rates in response to short-term resistance exercise.

In kwashiorkor, there is less endogenous proteolysis in response to acute infection than in a well-nourished state. Thus the amino acid composition of dietary protein may be more important in facilitating the acute phase response in kwashiorkor. This study tested the hypothesis that during the treatment of kwashiorkor with infection, there is a lower rate of urea appearance when the dietary intake of amino acids more closely resembles the amino acid composition of acute phase proteins. Thirty children in Malawi with kwashiorkor and acute infection were fed isoenergetic, isonitrogenous meals containing either egg white-tryptophan or milk as a protein source. After 24 h, the rates of urea appearance and whole-body protein breakdown and synthesis were measured with the use of 1-13C-leucine and 15N2-urea tracers. Plasma concentrations of seven acute phase proteins, interleukin 6 and tumor necrosis factor-alpha were measured on admission, and at 24 and 48 h. The 16 children who received egg white-tryptophan had lower rates of urea appearance than those who received milk [57+/-30 vs. 87+/-36 micromol/(kg x h), mean +/- SD, P

Advancing age is associated with a reduction in skeletal muscle protein and muscle force production, a syndrome referred to as sarcopenia . This process occurs during normal aging, but it is accelerated by physical inactivity and degenerative or other disease conditions.1 Decreased muscle mass and force production are associated with an increased risk of falling2 and, therefore, an increased risk for hip fracture.3 Reduced muscle force production with aging can also result in physical disability and frailty1 and in a loss of independent function,4 and it contributes to escalating health care costs.5 Our understanding of the mechanisms responsible for sarcopenia is limited. The most obvious intervention is exercise, but the feasibility and effectiveness of exercise in this population are still under investigation. Pharmacological and nutritional interventions for sarcopenia have been proposed,6–8 but preliminary evidence is not encouraging.6–15 Efficacious interventions for elderly people need to enhance both muscle protein mass and force production. The biological consequences of advancing age and the progressive decline in physical activity with age contribute to sarcopenia. Exercise, especially resistance exercise training, has the potential to improve overall fitness and quality of life. The physiological and functional benefits of increased muscle activity, even into the ninth decade of life, have been reported.16 Thus, human skeletal muscle protein maintains the ability to respond to, and adapt favorably to, exercise-induced increases in contractile activity throughout the life span. The ability to adapt with advancing age, however, may be somewhat limited by other biological processes. For example, circulating concentrations and the pulsatile release patterns of several hormones that regulate metabolism are reduced with advancing age.7–9,12,17–21 By virtue of their anabolic actions on body proteins, low serum growth hormone …

Background Uraemia and dialysis are viewed as catabolic processes resulting in malnutrition in chronic renal failure (CRF) patients. To sort out the effects of uraemia, acidosis, and dialysis on protein metabolism, we measured leucine flux in CRF patients before and after initiation of maintenance dialysis. Subjects and methods Whole-body leucine flux was measured by primed-constant infusion of L[1-(13)C] leucine in nine CRF patients longitudinally; twice before and once after initiation of maintenance dialysis (D). Before dialysis, one leucine flux was measured when the patients were acidotic (A), and the other, when acidosis was corrected with NaHCO, (NA). Five normal subjects underwent one single leucine flux measurement to serve as control (N). Both patients and normal subjects consumed a constant diet for 6 days and leucine flux was measured on the 7th day 12 h post-absorption. Diet for the CRF patients was identical during the three periods. Plasma L[1-(13)C] leucine and L[1-(13)C]KIC were measured by gas chromatography/mass spectrometry and expired 13CO2 by isotope ratio spectrometry. Leucine kinetics were calculated using standard equations. Results Plasma CO2 levels were 19, 26 and 31 mmol/l in A, NA and D periods respectively. All kinetic results (micromol/kg/h) are presented as means +/- SD in the order of A, NA, D, and N, and CRF values that are statistically different from N are identified (*). The amounts of leucine release from endogenous protein breakdown (Ra or Q) were 101 +/- 12* 95 +/- 9* 113 +/- 22 and 117 +/- 6. Leucine oxidation (C), quantities of leucine irreversibly oxidized to CO2, were 16.5 +/- 5.4, 9.7 +/- 3.7*, 12.3 +/- 3.0*, and 23.2 +/- 3.1. Leucine protein incorporation levels (S) were 85 +/- 10, 85 +/- 8, 101 +/- 19 and 94 +/- 6. The S of 101 in CRF patients at period D was statistically higher than those during A and NA periods. Conclusions These data indicate that when acidosis was corrected, CRF patients adapted to lower protein intake by reducing amino-acid oxidation and protein degradation, and maintained protein synthesis at normal levels. Metabolic acidosis impaired the downregulation of amino-acid oxidation. Maintenance dialysis treatment longitudinally restored protein flux to normal and increased protein synthesis. The general notion that uraemia and dialysis are protein catabolic is not supported by this work.

OBJECTIVE The purpose of this study was to evaluate whether 16 weeks of heavy resistance exercise training combined with daily growth hormone administration (GH) increases bone mineral density in 64–75-year-old men greater than resistance exercise training without GH supplementation. DESIGN Eighteen healthy, elderly men (67 ± 1 year) followed a 16-week progressive resistance training programme (75–90% maximum strength, 5–10 repetitions/set, 4 sets/day, 4 days/week) after double-blind, random assignment to either a GH (12.5 or 18 μg/kg/day, equivalent to 25 or 36 mU/kg/day, n = 7) or placebo (n = 11) group. MEASUREMENTS Before and at the end of 16 weeks of resistance exercise with or without GH administration, body composition, whole body and regional bone mineral density (BMD) were determined by dual-energy X-ray absorptiometry. Serum osteocalcin and IGF-I were determined by radioimmunoassay before, during and at the end of treatment. RESULTS Increments in fat-free mass and training-specific maximum voluntary muscle strength were similar in both groups after training. Serum insulin-like growth factor-I (IGF-I) and osteocalcin levels were increased (P

Roy, B. D., M. A. Tarnopolsky, J. D. MacDougall, J. Fowles, and K. E. Yarasheski. Effect of glucose supplement timing on protein metabolism after resistance training. J. Appl. Physiol. 82(6): 1882–1888, 1997.—We determined the effect of the timing of glucose supplementation on fractional muscle protein synthetic rate (FSR), urinary urea excretion, and whole body and myofibrillar protein degradation after resistance exercise. Eight healthy men performed unilateral knee extensor exercise (8 sets/∼10 repetitions/∼85% of 1 single maximal repetition). They received a carbohydrate (CHO) supplement (1 g/kg) or placebo (Pl) immediately ( t = 0 h) and 1 h ( t = +1 h) postexercise. FSR was determined for exercised (Ex) and control (Con) limbs by incrementall-[1-13C]leucine enrichment into the vastus lateralis over ∼10 h postexercise. Insulin was greater ( P < 0.01) at 0.5, 0.75, 1.25, 1.5, 1.75, and 2 h, and glucose was greater ( P < 0.05) at 0.5 and 0.75 h for CHO compared with Pl condition. FSR was 36.1% greater in the CHO/Ex leg than in the CHO/Con leg ( P = not significant) and 6.3% greater in the Pl/Ex leg than in the Pl/Con leg ( P = not significant). 3-Methylhistidine excretion was lower in the CHO (110.43 ± 3.62 μmol/g creatinine) than Pl condition (120.14 ± 5.82, P < 0.05) as was urinary urea nitrogen (8.60 ± 0.66 vs. 12.28 ± 1.84 g/g creatinine, P < 0.05). This suggests that CHO supplementation (1 g/kg) immediately and 1 h after resistance exercise can decrease myofibrillar protein breakdown and urinary urea excretion, resulting in a more positive body protein balance.

This study tested the hypothesis that whole- body protein kinetics remain low in children with edematous malnutrition and acute infection. Thirteen children with edematous malnutrition and acute infection (subjects) were compared with 14 uninfected children with edematous malnutrition early in recovery (control children). Protein kinetics were determined by using a primed, constant intravenous infusion of (13C)leucine and ('5N,)urea in the postabsorptive state. Calculations of rates of whole-body protein synthesis and breakdown were based on the rate of leucine appearance; the rate of leucine oxidation was estimated from the rate of urea appearance. Protein synthesis and breakdown rates were lower in subjects than in control children (97 ± 30 compared with 153 ± 67, P < 0.01, and 103 ± 30 compared with 160 ± 67 �mol leucine ' kg � . h �, P < 0.01). No difference was found between the two groups in the rate of urea appearance, but this analysis only had a statistical power of 54%. The absence of the expected increase in the rate of protein turnover during acute infection in edematous malnutrition implies that acute phase proteins are made with a corresponding depletion of muscle, hepatic, and other body proteins such as albumin, and that there may also be a blunting of the acute phase response. Am J C/in Nut,' 1997;65:lOOS-l0.

Testosterone-induced nitrogen retention in castrated male animals and sex-related differences in the size of the muscles in male and female animals have been cited as evidence that testosterone has anabolic effects. However, the effects of testosterone on body composition and muscle size have not been rigorously studied. The objective of this study was to determine the effects of replacement doses of testosterone on fat-free mass and muscle size in healthy hypogonadal men in the setting of controlled nutritional intake and exercise level. Seven hypogonadal men, 19-47 yr of age, after at least a 12-week washout from previous androgen therapy, were treated for 10 weeks with testosterone enanthate (100 mg/week) by im injections. Body weight, fat-free mass measured by underwater weighing and deuterated water dilution, and muscle size measured by magnetic resonance imaging were assessed before and after treatment. Energy and protein intake were standardized at 35 Cal/kg.day and 1.5 g/kg.day, respectively. Body weight increased significantly from 79.2 +/- 5.6 to 83.7 +/- 5.7 kg after 10 weeks of testosterone replacement therapy (weight gain, 4.5 +/- 0.6 kg; P = 0.0064). Fat-free mass, measured by underwater weighing, increased from 56.0 +/- 2.5 to 60.9 +/- 2.2 kg (change, +5.0 +/- 0.7 kg; P = 0.0004), but percent fat did not significantly change. Similar increases in fat-free mass were observed with the deuterated water method. The cross-sectional area of the triceps arm muscle increased from 2421 +/- 317 to 2721 +/- 239 mm2 (P = 0.045), and that of the quadriceps leg muscle increased from 7173 +/- 464 to 7720 +/- 454 mm2 (P = 0.0427), measured by magnetic resonance imaging. Muscle strength, assessed by one repetition maximum of weight-lifting exercises increased significantly after testosterone treatment. L-[1-13C]Leucine turnover, leucine oxidation, and nonoxidative disappearance of leucine did not significantly change after 10 weeks of treatment. There was no significant change in hemoglobin, hematocrit, creatinine, and transaminase levels. Replacement doses of testosterone increase fat-free mass and muscle size and strength in hypogonadal men. Whether androgen replacement in wasting states characterized by low testosterone levels will have similar anabolic effects remains to be studied.

Alzheimer’s disease is hypothesized to be caused by an over-production or reduced clearance of amyloid-beta (Aβ) peptide. Autosomal Dominant Alzheimer’s Disease (ADAD) caused by mutations in the presenilin (PSEN) gene have been postulated to result from increased production of Aβ42 compared to Aβ40 in the central nervous system (CNS). This has been demonstrated in rodent models of ADAD but not in human mutation carriers We used compartmental modeling of stable isotope labeling kinetic (SILK) studies in human carriers of PSEN mutations and related non-carriers to evaluate the pathophysiological effects of PSEN1 and PSEN2 mutations on the production and turnover of Aβ isoforms. We compared these findings by mutation status and amount of fibrillar amyloid deposition as measured by positron emission tomography (PET) using the amyloid tracer, Pittsburgh compound B (PiB). CNS Aβ42 to Aβ40 production rates were 24% higher in mutation carriers compared to non-carriers and this was independent of fibrillar amyloid deposits quantified by PET PiB imaging. The fractional turnover rate of soluble Aβ42 relative to Aβ40 was 65% faster in mutation carriers and correlated with amyloid deposition, consistent with increased deposition of Aβ42 into plaques leading to reduced recovery of Aβ42 in cerebrospinal fluid (CSF). Reversible exchange of Aβ42 peptides with pre-existing unlabeled peptide was observed in the presence of plaques. These findings support the hypothesis that Aβ42 is overproduced in the CNS of humans with presenilin mutations that cause AD, and demonstrate that soluble Aβ42 turnover and exchange processes are altered in the presence of amyloid plaques, causing a reduction in Aβ42 concentrations in the CSF.

The purpose of this study was to determine whether growth hormone (GH) administration enhances the muscle protein anabolism associated with heavy-resistance exercise training in older men. Twenty-three healthy, sedentary men (67 +/- 1 yr) with low serum insulin-like growth factor I levels followed a 16-wk progressive resistance exercise program (75-90% max strength, 4 days/wk) after random assignment to either a GH (12.5-24 micrograms.kg-1.day-1; n = 8) or placebo (n = 15) group. Fat-free mass (FFM) and total body water increased more in the GH group. Whole body protein synthesis and breakdown rates increased in the GH group after treatment. However, increments in vastus lateralis muscle protein synthesis rate, urinary creatinine excretion, and training-specific isotonic and isokinetic muscle strength were similar in both groups, while 24-h urinary 3-methylhistidine excretion was unchanged after treatment. These observations suggest that resistance exercise training improved muscle strength and anabolism in older men, but these improvements were not enhanced when exercise was combined with daily GH administration. The greater increase in FFM with GH treatment may have been due to an increase in noncontractile protein and fluid retention.

Apolipoprotein E (ApoE) is the strongest genetic risk factor for Alzheimer's disease and has been implicated in the risk for other neurological disorders. The three common ApoE isoforms (ApoE2, E3, and E4) each differ by a single amino acid, with ApoE4 increasing and ApoE2 decreasing the risk of Alzheimer's disease (AD). Both the isoform and amount of ApoE in the brain modulate AD pathology by altering the extent of amyloid beta (Aβ) peptide deposition. Therefore, quantifying ApoE isoform production and clearance rates may advance our understanding of the role of ApoE in health and disease. To measure the kinetics of ApoE in the central nervous system (CNS), we applied in vivo stable isotope labeling to quantify the fractional turnover rates of ApoE isoforms in 18 cognitively-normal adults and in ApoE3 and ApoE4 targeted-replacement mice. No isoform-specific differences in CNS ApoE3 and ApoE4 turnover rates were observed when measured in human CSF or mouse brain. However, CNS and peripheral ApoE isoform turnover rates differed substantially, which is consistent with previous reports and suggests that the pathways responsible for ApoE metabolism are different in the CNS and the periphery. We also demonstrate a slower turnover rate for CSF ApoE than that for amyloid beta, another molecule critically important in AD pathogenesis.

It is clear that the anthropometric ramifications, especially with respect to muscle mass, of the metabolic actions of GH and IGF-I treatment in intact and GH-deficient adults require further study. At present, it appears that daily GH or IGF-I treatment modestly increases nitrogen retention in most normal adults, probably by separate but permissive mechanisms, but only for a short period of time (approximately 1 month). During prolonged GH administration, resistance to the anabolic actions of GH seems to occur, and optimizing the anabolic effects of GH or IGF-I treatment will require a better understanding of the interactions among GH, GHBP, IGF-I production, IGFBPs, the GH dose regimen, and other unidentified regulatory factors. On the basis of the similar increases in muscle protein synthesis, muscle cross-sectional area, and muscle strength observed in placebo and GH-treated exercising young adults, it is doubtful that the nitrogen retention associated with daily GH treatment results in an increase in contractile protein, improved muscle function, strength and athletic performance. Even in catabolic or GH-deficient populations, GH treatment provides only modest increments in nitrogen retention, muscle size, strength, and exercise capacity. Further, the side effects of GH treatment (water retention, carpal tunnel compression, insulin resistance) would be a detriment, rather than an aid, to athletic performance. In addition, whether prolonged (> 6 months) GH treatment alone or in combination with other agents used by athletes (e.g., anabolic steroids, beta-agonists) is associated with other adverse side effects (e.g., cancer, diabetes) has not been evaluated. Therefore, health professionals should continue to discourage the use of GH by exercise enthusiasts.

Acute deviations in protein intake before the quantification of protein kinetics in older humans may explain the controversy over the effects of older age on muscle protein synthesis and proteolysis rates.We hypothesized that an acute decrease in protein intake from the habitual intake is associated with lower muscle protein synthesis and higher proteolysis rates, whereas an acute increase in protein intake from the habitual intake is associated with higher muscle protein synthesis and lower proteolysis rates.In 112 community-dwelling healthy men aged 65-90 y, we quantified resting whole-body [1,2-(13)C(2)]leucine kinetics, muscle mixed protein fractional synthesis rates (FSRs), and muscle proteasome proteolytic enzyme activities after participants consumed for 3 d controlled research meals (0.9-1.1 g protein · kg(-1) · d(-1)) that contained more or less protein than that habitually consumed and that induced alterations in nitrogen balance.Protein kinetic parameters were not significantly different between the groups, despite controlled research protein intakes that were lower (-0.2 to -0.3 g · kg(-1) · d(-1)) or higher (+0.2 g · kg(-1) · d(-1)) than habitual intakes and that induced negative (-22 to -25 mg · kg(-1) · d(-1)) or positive (22-25 mg · kg(-1) · d(-1)) nitrogen balance. Within these acutely altered protein intake and nitrogen balance boundaries, a reduction in protein intake from habitual intake and induction of negative nitrogen balance were not associated with higher proteolysis or lower muscle FSR, and an acute increase in protein intake from habitual intake and induction of positive nitrogen balance were not associated with lower proteolysis or higher muscle FSR. A higher quantitative insulin sensitivity check index was associated with lower whole-body proteolysis rates.The practice of acutely controlling protein intake, even at intakes lower than habitual intakes that induce negative nitrogen balance, before quantifying human protein kinetics does not significantly reduce muscle protein synthesis or increase proteolysis. Factors other than protein intake explain lower muscle protein synthesis rates with advanced age. This trial is registered at clinicaltrials.gov as NCT00183040.