The combination of efavirenz with HIV-1 protease inhibitors (PI) results in complex interactions secondary to mixed induction and inhibition of oxidative metabolism. ACTG A5043 was a prospective, open-label, controlled, two-period, multiple-dose study with 55 healthy volunteers. The objective of the present study was to evaluate the potential pharmacokinetic interaction between efavirenz and dual PIs. The subjects received a daily dose of 600 mg efavirenz for 10 days with amprenavir 600 mg twice daily added at day 11 and were randomized to receive nelfinavir, indinavir, ritonavir, saquinavir, or no second PI on days 15–21. Intensive pharmacokinetic studies were conducted on day 14 and 21. Efavirenz plasma concentrations were fit to candidate models using weighted non-linear regression. The disposition of efavirenz was described by a linear two-compartment model with first order absorption following a fitted lag time. Apparent clearance (CLt/F), volume of distribution at steady state (Vss/F), inter-compartmental clearance, and the central and peripheral volume of distribution were estimated. The mean CLt/F and Vss/F of efavirenz were 0.126 l/h/kg and 4.412 l/kg, respectively. Both AUC and CLt/F of efavirenz remained unchanged after 7 days of dual PI dosing. The mean Vss/F of efavirenz increased an average of 89% across arms, ranging from 52% (nelfinavir) to 115% (indinavir) relative to efavirenz with amprenavir alone. Increases were also observed in Vp/F after the addition of nelfinavir, indinavir, ritonavir and saquinavir by 85%, 170%, 162% and 111%, respectively. In conclusion, concomitant administration of dual PIs is unlikely to have any clinically significant effect on the pharmacokinetics of CYP2B6 substrates in general or oral efavirenz specifically.
pharmacokinetic modeling; drug interactions; non-nucleoside reverse transcriptase inhibitor; efavirenz; HIV-1 protease inhibitors
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.
peroxisome proliferator-activated receptor-α; dexamethasone; insulin sensitivity; metabolic syndrome
Older persons often lose muscle mass, strength, and physical function. This report describes the challenges of conducting a complex clinical investigation assessing the effects of anabolic hormones on body composition, physical function, and metabolism during aging.
HORMA is a multicenter, randomized double masked study of 65–90-year-old community dwelling men with testosterone levels of 150–550 ng/dL and IGF-1 < 167 ng/dL. Subjects were randomized to transdermal testosterone (5 or 10 g/day) and rhGH (0, 3, or 5 μg/kg/day) for 16 weeks. Outcome measures included body composition by DEXA, MRI, and 2H2O dilution; muscle performance (strength, power, and fatigability), VO2peak, measures of physical function, synthesis/breakdown of myofibrillar proteins, other measures of metabolism, and quality of life.
Major challenges included delay in startup caused by need for 7 institutional contracts, creating a 142-page manual of operations, orientation and training, creating a 121-page CRF; enrollment inefficiencies; scheduling 16 evaluations/subject; overnight admissions for invasive procedures and isotope infusions; large data and image management and transfer; quality control at multiples sites; staff turnover; and replacement of a clinical testing site. Impediments were largely solved by implementation of a web-based data entry and eligibility verification; electronic scheduling for multiple study visits; availability of research team members to educate and reassure subjects; more frequent site visits to validate all source documents and reliability of data entry; and intensifying quality control in testing and imaging. The study exceeded the target goal of 108 (n =112) completely evaluable cases. Two interim DSMB meetings confirmed the lack of excessive adverse events, lack of center effects, comparability of subjects, and that distribution of subjects and enrollment will not jeopardize outcomes or generalizability of results.
Flexibility and rapidly solving evolving problems is critical when conducting highly complex multicenter metabolic studies.
BACE, a β-secretase, is an attractive potential disease-modifying therapeutic strategy for Alzheimer's disease (AD) as it results directly in the decrease of amyloid precursor protein (APP) processing through the β-secretase pathway and a lowering of CNS amyloid-β (Aβ) levels. The interaction of the β-secretase and α-secretase pathway-mediated processing of APP in the rhesus monkey (nonhuman primate; NHP) CNS is not understood. We hypothesized that CNS inhibition of BACE would result in decreased newly generated Aβ and soluble APPβ (sAPPβ), with increased newly generated sAPPα.
A stable isotope labeling kinetics experiment in NHPs was performed with a 13C6-leucine infusion protocol to evaluate effects of BACE inhibition on CNS APP processing by measuring the kinetics of sAPPα, sAPPβ, and Aβ in CSF. Each NHP received a low, medium, or high dose of MBI-5 (BACE inhibitor) or vehicle in a four-way crossover design. CSF sAPPα, sAPPβ, and Aβ were measured by ELISA and newly incorporated label following immunoprecipitation and liquid chromatography-mass spectrometry. Concentrations, kinetics, and amount of newly generated APP fragments were calculated.
sAPPβ and sAPPα kinetics were similar, but both significantly slower than Aβ. BACE inhibition resulted in decreased labeled sAPPβ and Aβ in CSF, without observable changes in labeled CSF sAPPα. ELISA concentrations of sAPPβ and Aβ both decreased and sAPPα increased. sAPPα increased by ELISA, with no difference by labeled sAPPα kinetics indicating increases in product may be due to APP shunting from the β-secretase to the α-secretase pathway. These results provide a quantitative understanding of pharmacodynamic effects of BACE inhibition on NHP CNS, which can inform about target development.
amyloid beta; amyloid precursor protein; BACE inhibitor; sAPPα; sAPPβ; SILK
Fasting hyperglycemia has been associated with HIV protease inhibitor (PI) therapy.
To determine whether absolute insulin deficiency or insulin resistance with relative insulin deficiency and an elevated body mass index (BMI) contribute to HIV PI–associated diabetes.
8 healthy seronegative men, 10 nondiabetic HIV-positive patients naive to PI, 15 nondiabetic HIV-positive patients receiving PI (BMI = 26 kg/m2), 6 nondiabetic HIV-positive patients receiving PI (BMI = 31 kg/m2), and 8 HIV-positive patients with diabetes receiving PI (BMI = 34 kg/m2). All patients on PI received indinavir.
Fasting concentrations of glucoregulatory hormones. Direct effects of indinavir (20 μM) on rat pancreatic [beta]-cell function in vitro.
In hyperglycemic HIV-positive subjects, circulating concentrations of insulin, C-peptide, proinsulin, glucagon, and the proinsulin/insulin ratio were increased when compared with those of the other 4 groups (p < .05). Morning fasting serum cortisol concentrations were not different among the 5 groups. Glutamic acid decarboxylase (GAD) antibody titers were uncommon in all groups. High BMI was not always associated with diabetes. In vitro, indinavir did not inhibit proinsulin to insulin conversion or impair glucose-induced secretion of insulin and C-peptide from rat [beta]-cells.
The pathogenesis of HIV PI–associated diabetes involves peripheral insulin resistance with insulin deficiency relative to hyperglucagonemia and a high BMI. Pancreatic [beta]-cell function was not impaired by indinavir. HIV PI–associated diabetes mirrors that of non–insulin-dependent diabetes mellitus and impaired insulin action in the periphery.
AIDS; Metabolic complications; Glucose metabolism; Pancreatic [beta]-cells; Insulin release
The product of the obese gene (ob) is the protein leptin, which is synthesized in and secreted from adipocytes. Fasting serum leptin concentrations are closely related to body fat content and are higher in obese than in normal-weight individuals. Leptin may contribute to body weight regulation. Overproduction of leptin in certain pathologic conditions such as acquired immunodeficiency syndrome (AIDS) might in principle contribute to the low body fat content associated with body wasting. We measured fasting serum leptin levels by radioimmunoassay in individuals infected with the human immunodeficiency virus (HIV) and in a group of healthy lean men to determine whether HIV infection increases leptin levels. Thirteen HIV-infected men aged 26 to 50 years with a body mass index (BMI) of 15 to 26 kg/m2 and 4 to 24 kg body fat (7% to 29% body fat) had serum leptin levels (3.4 ± 1.6 ng/mL) that were not elevated compared with the levels in 17 healthy men (4.0 ± 1.4 ng/mL) matched for age (23 to 47 years), BMI (18 to 26 kg/m2), and body fat (5 to 21 kg; 9% to 28%). In both groups of men, serum leptin concentrations were correlated with percent body fat and body fat content (P < .001), and these relationships were not different between the two groups. In both groups, leptin concentrations were not correlated with lean body mass (P ≥ .24). Energy intake in the HIV-infected men, assessed from 3-day intake records, was within the normal range. These findings extend the hypothesis that circulating leptin concentrations directly reflect adipose tissue mass, even in HIV-infected men with low body fat content. These findings do not support the hypothesis that HIV infection is associated with high circulating leptin concentrations, and suggest that low leptin levels do not stimulate food intake in HIV-infected individuals.
Anaerobic digesters rely on the diversity and distribution of parallel metabolic pathways mediated by complex syntrophic microbial communities to maintain robust and optimal performance. Using mesophilic swine waste digesters, we experimented with increased ammonia loading to induce a shift from aceticlastic methanogenesis to an alternative acetate-consuming pathway of syntrophic acetate oxidation. In comparison with control digesters, we observed shifts in bacterial 16S rRNA gene content and in functional gene repertoires over the course of the digesters' 3-year operating period. During the first year, under identical startup conditions, all bioreactors mirrored each other closely in terms of bacterial phylotype content, phylogenetic structure, and evenness. When we perturbed the digesters by increasing the ammonia concentration or temperature, the distribution of bacterial phylotypes became more uneven, followed by a return to more even communities once syntrophic acetate oxidation had allowed the experimental bioreactors to regain stable operation. The emergence of syntrophic acetate oxidation coincided with a partial shift from aceticlastic to hydrogenotrophic methanogens. Our 16S rRNA gene analysis also revealed that acetate-fed enrichment experiments resulted in communities that did not represent the bioreactor community. Analysis of shotgun sequencing of community DNA suggests that syntrophic acetate oxidation was carried out by a heterogeneous community rather than by a specific keystone population with representatives of enriched cultures with this metabolic capacity.
People living with human immunodeficiency virus infection (HIV) are at increased risk for developing cardiovascular disease (CVD). Safe and effective interventions for lowering CVD risk in HIV are high priorities.
We conducted a prospective, randomized, controlled study to evaluate whether a yoga lifestyle intervention improves CVD risk factors, virologic or immunologic status, or quality of life in HIV-infected adults more than in a matched control group.
Sixty HIV-infected adults with mild-moderate CVD risk were assigned to 20 wks of supervised yoga practice or standard of care treatment. Baseline and week 20 measures were; 2hr-oral glucose tolerance test with insulin monitoring, body composition, fasting serum lipid/lipoprotein profile, resting blood pressures, CD4+ T-cell number and plasma HIV RNA, and the Medical Outcomes Study SF-36 health-related quality of life inventory.
Resting systolic and diastolic blood pressures were reduced more (p=0.04) in the yoga group (−5±2 and −3±1 mmHg) than in the standard of care group (+1±2 and +2±2 mmHg), despite no greater reduction in body weight, fat mass, proatherogenic lipids, or improvements in glucose tolerance or overall quality of life after yoga. Immune and virologic status was not adversely affected.
Among traditional lifestyle modifications, yoga is a low cost, simple to administer, non-pharmacological, popular behavioral intervention that can lower blood pressure in pre-hypertensive HIV-infected adults with mild-moderate CVD risk factors.
complementary or alternative therapy; physical activity; cardiometabolic complications; hypertension
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<0.005) lower in groups with MC (HIV+/MC+: 11.6±2.3, HIV−/MC+: 12.0±2.3 vs. HIV+/MC−: 12.4±2.3, HIV−/MC−: 13.1±2.4 cm/s) and tended to be lower in groups with HIV (p=0.10). However, there was no interaction effect of HIV and MC for any systolic or diastolic variable. Regardless of HIV status, participants with MC had reduced LV diastolic function. Although both the presence of MC and HIV infection were associated with lower diastolic function, there was no additive negative effect of HIV on diastolic function beyond the effect of MC. Also, HIV was independently associated with lower systolic function. Clinical monitoring of LV function in individuals with metabolic risk factors, regardless of HIV status, is warranted.
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.
muscle amino acid metabolism; insulin signaling; adipocytokine; lipotoxicity; substrate partitioning; mass spectrometry; stable isotope tracer methods; HIV=human immunodeficiency virus; AIDS=acquired immunodeficiency syndrome; HAART=highly active antiretroviral therapy; FFM=fat-free mass; T2DM=type 2 diabetes mellitus; BCAA=branched chain amino acids; Rd=rate of disposal; Ra=rate of appearance; IGT=impaired glucose tolerance; FFA=serum free fatty acids; VAT=visceral adipose tissue content; SAT=subcutaneous adipose tissue content; TAT=total adipose tissue content; HOMA=homeostasis model assessment of insulin resistance; RIA=radioimmunoassay; NRTI= nucleoside analog reverse transcriptase inhibitors; NNRTI= non-nucleoside analog reverse transcriptase inhibitor; PI= protease inhibitor
The measurement of skeletal muscle protein fractional synthetic rate using an infusion of (1-13C)leucine and measuring the isotopic abundance of the tracer in skeletal muscle protein by preparative gas chromatography (GC)/ninhydrin isotope ratio mass spectrometry (IRMS) is laborious and subject to errors owing to contamination by 12C. The purpose of this study was to compare muscle (13C)leucine enrichment measured with the conventional preparative GC/ninhydrin IRMS approach to a new, continuous-flow technique using capillary GC/combustion IRMS. Quadriceps muscles were removed from four Sprague–Dawley rats after each was infused at a different rate with (1-13C)leucine for 6–8 h. Muscle leucine enrichment (at.% excess) measured by both methods differed by less than 4%, except at low (13C)leucine enrichments (<0.03 at.% excess). In addition, capillary GC/combustion IRMS was used to assess muscle (13C)leucine enrichment and fractional muscle protein synthesis rate in ten normal young men and women infused with (1,2-13C2)leucine for 12–14 h. This approach reduced the variability of the isotope abundance measure and gave estimates of muscle protein synthesis rate (0.050 ± 0.011% h−1 (mean ± SEM); range = 0.023–0.147% h−1) that agree with published values determined using the standard analytical approach. The measurement of (13C)leucine enrichment from skeletal muscle protein by capillary GC/combustion IRMS provides a simple, acceptable and practical alternative to preparative GC/ninhydrin IRMS.
Research suggests that changes in leucine oxidation (leuox) with feeding may reflect adult protein requirements. We evaluated this possibility by assessing the effects of age, sex, and different protein intakes on whole-body leucine kinetics and nitrogen balance. Thirty-four young (n = 18, 22–46 years) and old (n= 16, 63–81 years) men and women completed three 18-day trials with protein intakes of 0.50, 0.75 and 1.00 g protein·kg body weight−1·d−1. Fasting and fed-state leucine kinetics were quantified on day 12 of each trial using a primed, constant infusion of L-[1-13C]leucine. Protein requirement was estimated using classical nitrogen balance measurements and calculations. Leucine kinetics parameters were influenced by age and sex across all protein intakes. With feeding, leuox increased more in old vs. young adults. Independent of age, fasting and fed-state leuox were lower, and net leucine balance (fasting+fed-state) was higher in women vs. men. Among all subjects and protein intakes, nitrogen balance was correlated with fed-state leuox (r=0.39), fed-state leucine balance (r=0.60), net leucine balance (r=0.49) and the change in leuox from the fasting to fed state (r=0.49) (P<.05 for all results). At the highest protein intake, the change in leuox with feeding was inversely correlated with protein requirement (r=−0.39). These findings indicate that leucine kinetics, especially leuox, reflect nitrogen balance-based estimates of the need for dietary protein and generally support the view that protein requirement is comparable between young and old adults.
Dietary protein; Protein adequacy; Protein metabolism
As HAART becomes more accessible in sub-Saharan Africa, metabolic syndromes, body fat redistribution (BFR), and cardiovascular disease may become more prevalent. We conducted a 6-month, randomized controlled trial to test whether cardiorespiratory exercise training (CET), improves metabolic, body composition and cardiorespiratory fitness parameters in HAART-treated HIV+ African subjects with BFR. Six months of CET reduced waist circumference (−7.13 ± 4.4 cm, p < 0.0001), WHR (−0.10 ± 0.1, p < 0.0001), sum skinfold thickness (−6.15 ± 8.2 mm, p < 0.0001) and % body fat mass (−1.5 ± 3.3, p < 0.0001) in HIV+BFR+EXS. Hip circumference was unchanged in non-exercise control groups. CET reduced fasting total cholesterol (−0.03 ± 1.11 mM, p < 0.05), triglycerides (−0.22 ± 0.48 mM, p < 0.05) and glucose levels (−0.21 ± 0.71 mM, p < 0.05) (p < 0.0001). HDL-, LDL-cholesterol and HOMA values were unchanged after CET. Interestingly, HIV+ subjects randomized to non-exercising groups experienced increases in fasting plasma glucose levels, whereas HIV seronegative controls did not (p < 0.001). Predicted VO2 peak increased more in the HIV+BFR+EXS than in all other groups (4.7 ± 3.9 ml/kg/min, p < 0.0001). Exercise training positively modulated body composition and metabolic profiles, and improved cardiorespiratory fitness in HAART-treated HIV+ Africans. These beneficial adaptations imply that exercise training is a safe, inexpensive, practical, and effective treatment for evolving metabolic and cardiovascular syndromes associated with HIV and HAART exposure in resource-limited sub-Saharan countries, where treatment is improving, morbidity and mortality rates are declining, but where minimal resources are available to manage HIV- and HAART-associated cardiovascular and metabolic syndromes.
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%V̇ O2 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.
human immunodeficiency virus; highly active antiretroviral therapy; ritonavir; lipodystrophy; insulin resistance; metabolic syndrome; mass spectrometry
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.
exercise; HIV; insulin resistance; left ventricular dysfunction; metabolic syndrome
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 · kg−1 · d−1), 94% (P94, 0.75 g protein · kg−1 · d−1), and 63% (P63, 0.50 g protein · kg−1 · 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.
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.
Insulin resistance, hyperglycemia, and type 2 diabetes are among the sequelae of metabolic syndromes that occur in 60–80% of human immunodeficiency virus (HIV)-positive patients treated with HIV-protease inhibitors (PIs). Studies to elucidate the molecular mechanism(s) contributing to these changes, however, have mainly focused on acute, in vitro actions of PIs. Here, we examined the chronic (7 wk) in vivo effects of the PI indinavir (IDV) in male Zucker diabetic fatty (fa/fa) (ZDF) rats. IDV exposure accelerated the diabetic state and dramatically exacerbated hyperglycemia and oral glucose intolerance in the ZDF rats, compared with vehicle-treated ZDF rats. Oligonucleotide gene array analyses revealed upregulation of suppressor of cytokine signaling-1 (SOCS-1) expression in insulin-sensitive tissues of IDV rats. SOCS-1 is a known inducer of insulin resistance and diabetes, and immunoblotting analyses revealed increases in SOCS-1 protein expression in adipose, skeletal muscle, and liver tissues of IDV-administered ZDF rats. This was associated with increases in the upstream regulator TNF-α and downstream effector sterol regulatory element-binding protein-1 and a decrease in IRS-2. IDV and other PIs currently in clinical use induced the SOCS-1 signaling cascade also in L6 myotubes and 3T3-L1 adipocytes exposed acutely to PIs under normal culturing conditions and in tissues from Zucker wild-type lean control rats administered PIs for 3 wk, suggesting an effect of these drugs even in the absence of background hyperglycemia/hyperlipidemia. Our findings therefore indicate that induction of the SOCS-1 signaling cascade by PIs could be an important contributing factor in the development of metabolic dysregulation associated with long-term exposures to HIV-PIs.
metabolic syndrome; insulin-signaling pathways; human immunodeficiency virus
We hypothesized that treatment with testosterone (T) and recombinant human growth hormone (rhGH) would increase lean mass (LM) and muscle strength proportionally and an in a linear manner over 16 weeks. This was a multicenter, randomized, controlled, double-masked investigation of T and rhGH supplementation in older (71 ± 4 years) community-dwelling men. Participants received transdermal T at either 5 or 10 g/day as well as rhGH at 0, 3.0 or 5.0 µg/kg/day for 16 weeks. Body composition was determined by dual-energy X-ray absorptiometry (DEXA) and muscle performance by composite one-repetition maximum (1-RM) strength and strength per unit of lean mass (muscle quality, MQ) for five major muscle groups (upper and lower body) at baseline, week 8 and 17. The average change in total LM at study week 8 compared with baseline was 1.50 ± 1.54 kg (P < 0.0001) in the T only group and 2.64 ± 1.7 (P < 0.0001) in the T + rhGH group and at week 17 was 1.46 ± 1.48 kg (P < 0.0001) in the T only group and 2.14 ± 1.96 kg (P < 0.0001) in the T + rhGH group. 1-RM strength improved modestly in both groups combined (12.0 ± 23.9%, P < 0.0001) at week 8 but at week 17 these changes were twofold greater (24.7 ± 31.0%, P < 0.0001). MQ did not significantly change from baseline to week 8 but increased for the entire cohort, T only, and T + rhGH groups by week 17 (P < 0.001). Despite sizeable increases in LM measurements at week 8, tests of muscle performance did not show substantive improvements at this time point.
Anabolic hormones; Androgen supplementation; Muscle quality; HORMA study
Persistent vascular inflammation has been implicated as an important cause for a higher prevalence of cardiovascular disease (CVD) in HIV-infected adults. In several populations at high risk for CVD, vascular 18Fluorodeoxyglucose (18FDG) uptake quantified using 3D-positron emission-computed tomography (PET-CT) has been used as a molecular level biomarker for the presence of metabolically active proinflammatory macrophages in rupture-prone early atherosclerotic plaques. We hypothesized that 18FDG PET-CT imaging would detect arterial inflammation and early atherosclerosis in HIV-infected adults with modest CVD risk.
We studied 9 HIV-infected participants with fully suppressed HIV viremia on antiretroviral therapy (8 men, median age 52 yrs, median BMI 29 kg/m2, median CD4 count 655 cells/μL, 33% current smokers) and 5 HIV-negative participants (4 men, median age 44 yrs, median BMI 25 kg/m2, no current smokers). Mean Framingham Risk Scores were higher for HIV-infected persons (9% vs. 2%, p < 0.01). 18FDG (370 MBq) was administered intravenously. 3D-PET-CT images were obtained 3.5 hrs later. 18FDG uptake into both carotid arteries and the aorta was compared between the two groups.
Right and left carotid 18FDG uptake was greater (P < 0.03) in the HIV group (1.77 ±0.26, 1.33 ±0.09 target to background ratio (TBR)) than the control group (1.05 ± 0.10, 1.03 ± 0.05 TBR). 18FDG uptake in the aorta was greater in HIV (1.50 ±0.16 TBR) vs control group (1.24 ± 0.05 TBR), but did not reach statistical significance (P = 0.18).
Carotid artery 18FDG PET-CT imaging detected differences in vascular inflammation and early atherosclerosis between HIV-infected adults with CVD risk factors and healthy HIV-seronegative controls. These findings confirm the utility of this molecular level imaging approach for detecting and quantifying glucose uptake into inflammatory macrophages present in metabolically active, rupture-prone atherosclerotic plaques in HIV infected adults; a population with increased CVD risk.
Pathophysiologic molecular-level biomarker; Atherogenesis; Non-invasive imaging; Infectious disease
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.
Skeletal muscle (SM) mass decreases with advanced age and with disease in HIV infection. It is unknown whether age-related muscle loss is accelerated in the current era of antiretroviral therapy and which factors might contribute to muscle loss among HIV-infected adults. We hypothesized that muscle mass would be lower and decline faster in HIV-infected adults than in similar-aged controls.
Whole-body 1H-magnetic resonance imaging was used to quantify regional and total SM in 399 HIV-infected and 204 control men and women at baseline and 5 years later. Multivariable regression identified associated factors.
At baseline and Year 5, total SM was lower in HIV-infected than control men. HIV-infected women were similar to control women at both time points. After adjusting for demographics, lifestyle factors, and total adipose tissue, HIV infection was associated with lower Year 5 SM in men and higher SM in women compared with controls. Average overall 5-year change in total SM was small and age related, but rate of change was similar in HIV-infected and control men and women. CD4 count and efavirenz use in HIV-infected participants were associated with increasing SM, whereas age and stavudine use were associated with decreasing SM.
Muscle mass was lower in HIV-infected men compared with controls, whereas HIV-infected women had slightly higher SM than control women after multivariable adjustment. We found evidence against substantially faster SM decline in HIV infected versus similar-aged controls. SM gain was associated with increasing CD4 count, whereas stavudine use may contribute to SM loss.
Sarcopenia; Lipoatrophy; Fat redistribution; Body composition
Alzheimer’s disease is thought to be caused by an imbalance between amyloid-β (Aβ) production and clearance leading to Aβ accumulation in the Central Nervous System (CNS). Aβ production and clearance are key targets in the development of disease modifying therapeutic agents for Alzheimer’s disease. However, there has not been direct evidence of altered Aβ production or clearance in Alzheimer’s disease. Using metabolic labeling, we measured Aβ42 and Aβ40 production and clearance rates in the CNS of patients with Alzheimer’s disease and cognitively normal controls. Clearance rates for both Aβ42 and Aβ40 were impaired in Alzheimer’s disease compared to controls. On average, there were no differences in Aβ42 or Aβ40 production rates. Thus, the common late-onset form of Alzheimer’s disease may involve an overall impairment of Aβ clearance.