Plasma Aβ42/40 and cognitive variability are associated with cognitive function in Black Americans: Findings from the AA-FAIM cohort

Introduction

It is critical to develop more inclusive Alzheimer's disease (AD) research protocols to ensure that historically excluded groups are included in preclinical research and have access to timely diagnosis and treatment. If validated in racialized groups, plasma AD biomarkers and measures of subtle cognitive dysfunction could provide avenues to expand diversity in preclinical AD research. We sought to evaluate the utility of two easily obtained, low-burden disease markers, plasma amyloid beta (Aβ)42/40, and intra-individual cognitive variability (IICV), to predict concurrent and longitudinal cognitive performance in a sample of Black adults.

Methods

Two hundred fifty-seven Black participants enrolled in the African Americans Fighting Alzheimer's in Midlife (AA-FAIM) study underwent at least one cognitive assessment visit; a subset of n = 235 had plasma samples. Baseline IICV was calculated as the standard deviation across participants' z scores on five cognitive measures: Rey Auditory Verbal Learning Test Delayed Recall, Trail Making Test Parts A and B (Trails A and B), and Boston Naming Test. Using mixed effects regression models, we compared concurrent and longitudinal models to baseline plasma Aβ42/40 or IICV by age interactions. PrecivityAD assays quantified baseline plasma Aβ42/40.

Results

IICV was associated with concurrent/baseline performance on several outcomes but did not modify associations between age and cognitive decline. In contrast, plasma Aβ42/40 was unrelated to baseline cognitive performance, but a pattern emerged in interactions with age in longitudinal models of Trails A and B and Rey Auditory Verbal Learning Test total learning trials. Although not significant after correcting for multiple comparisons, low Aβ42/40 was associated with faster cognitive declines over time.

Discussion

Our results are promising as they extend existing findings to an Black American sample using low-cost, low-burden methods that can be implemented outside of a research center, thus supporting efforts for inclusive AD biomarker research.

Evaluation of Blood-Based Plasma Biomarkers as Potential Markers of Amyloid Burden in Preclinical Alzheimer's Disease

BACKGROUND

Participant eligibility for the A4 Study was determined by amyloid PET imaging. Given the disadvantages of amyloid PET imaging in accessibility and cost, blood-based biomarkers may serve as a sufficient biomarker and more cost-effective screening tool for patient enrollment into preclinical AD trials.

OBJECTIVE

To determine if a blood-based screening test can adequately identify amyloid burden in participants screened into a preclinical AD trial.

METHODS

In this cross-sectional study, 224 participants from the A4 Study received an amyloid PET scan (18Florbetapir) within 90 days of blood sample collection. Blood samples from all study participants were processed within 2 h after phlebotomy. Plasma amyloid measures were quantified by Shimazdu and C2 N Diagnostics using mass spectrometry-based platforms. A corresponding subset of blood samples (n = 100) was processed within 24 h after phlebotomy and analyzed by C2 N.

RESULTS

Plasma Aβ42/Aβ40 demonstrated the highest association for Aβ accumulation in the brain with an AUC 0.76 (95%CI = 0.69, 0.82) at C2 N and 0.80 (95%CI = 0.75, 0.86) at Shimadzu. Blood samples processed to plasma within 2 h after phlebotomy provided a better prediction of amyloid PET status than blood samples processed within 24 h (AUC 0.80 versus 0.64; p < 0.001). Age, sex, and APOE ɛ4 carrier status did not the diagnostic performance of plasma Aβ42/Aβ40 to predict amyloid PET positivity in A4 Study participants.

CONCLUSION

Plasma Aβ42/Aβ40 may serve as a potential biomarker for predicting elevated amyloid in the brain. Utilizing blood testing over PET imaging may improve screening efficiency into clinical trials.

SILK studies - capturing the turnover of proteins linked to neurodegenerative diseases

Alzheimer disease (AD) is one of several neurodegenerative diseases characterized by dysregulation, misfolding and accumulation of specific proteins in the CNS. The stable isotope labelling kinetics (SILK) technique is based on generating amino acids labelled with naturally occurring stable (that is, nonradioactive) isotopes of carbon and/or nitrogen. These labelled amino acids can then be incorporated into proteins, enabling rates of protein production and clearance to be determined in vivo and in vitro without the use of radioactive or chemical labels. Over the past decade, SILK studies have been used to determine the turnover of key pathogenic proteins amyloid-β (Aβ), tau and superoxide dismutase 1 (SOD1) in the cerebrospinal fluid of healthy individuals, patients with AD and those with other neurodegenerative diseases. These studies led to the identification of several factors that alter the production and/or clearance of these proteins, including age, sleep and disease-causing genetic mutations. SILK studies have also been used to measure Aβ turnover in blood and within brain tissue. SILK studies offer the potential to elucidate the mechanisms underlying various neurodegenerative disease mechanisms, including neuroinflammation and synaptic dysfunction, and to demonstrate target engagement of novel disease-modifying therapies.

Dissemination and Implementation Program in Hypertension in Rwanda: Report on Initial Training and Evaluation

BACKGROUND

Cardiovascular disease (CVD) is the leading cause of morbidity and mortality worldwide and in low- and middle-income countries, and hypertension (HTN) is a major risk factor for CVD. Although effective evidence-based interventions for control of HTN in high-income countries exist, implementation of these in low- and middle-income countries has been challenging due to limited capacity and infrastructure for late-phase translational research. In Rwanda, the 2015 STEPS NCD (STEPwise Approach to Surveillance of Noncommunicable Diseases) risk survey reported an overall prevalence of HTN of 15% (95% confidence interval [CI]: 13.8 to 16.3) for those ages 15 to 64 years; prevalence increased with increasing age to 39% (95% CI: 35.7 to 43.1) for those ages 55 to 64 years; CVD was the third most common cause of mortality (7%). Suboptimal infrastructure and capacity in Rwanda hinders research and community knowledge for HTN control.

OBJECTIVES

To address the issue of suboptimal capacity to implement evidence-based interventions in HTN, this project was designed with the following objectives: 1) to develop a regional needs assessment of infrastructure for dissemination and implementation (D & I) strategies for HTN-CVD control; 2) to develop HTN-CVD research capacity through creation of countrywide resources such as core research facilities and training in the fields of HTN-CVD, D & I, and biostatistics; and 3) to engage and train multiple stakeholders in D & I and HTN-CVD evidence-based interventions.

METHODS

A weeklong training program in HTN-CVD, biostatistics, and D & I was conducted in Rwanda in August 2018, and pre- and post-D & I training competency questionnaires were administered.

RESULTS

Questionnaire results show a statistically significant increase in D & I knowledge and skills as a result of training (full scale pre- to post-test scores: 2.12 ± 0.78 vs. 3.94 ± 0.42; p < 0.0001).

CONCLUSIONS

Using principles of community engagement and train-the-trainer methods, we will continue to adapt guidelines and treatments for HTN-CVD developed in high-income countries to the context of Rwanda with the goal of establishing a sustainable platform to address the burden of disease from HTN-CVD.

Age and amyloid effects on human central nervous system amyloid-beta kinetics

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.

An antidepressant decreases CSF Aβ production in healthy individuals and in transgenic AD mice

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, decreased Aβ in brain interstitial fluid 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 preexisting 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, 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.

Gastric cancer in Zambian adults: a prospective case-control study that assessed dietary intake and antioxidant status by using urinary isoprostane excretion

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.

Testosterone threshold levels and lean tissue mass targets needed to enhance skeletal muscle strength and function: the HORMA trial

BACKGROUND

In the HORMA (Hormonal Regulators of Muscle and Metabolism in Aging) Trial, supplemental testosterone and recombinant human growth hormone (rhGH) enhanced lean body mass, appendicular skeletal muscle mass, muscle performance, and physical function, but there was substantial interindividual variability in outcomes.

METHODS

One hundred and twelve men aged 65-90 years received testosterone gel (5 g/d vs 10 g/d via Leydig cell clamp) and rhGH (0 vs 3 vs 5 μg/kg/d) in a double-masked 2 × 3 factorial design for 16 weeks. Outcomes included lean tissue mass by dual energy x-ray absorptiometry, one-repetition maximum strength, Margaria stair power, and activity questionnaires. We used pathway analysis to determine the relationship between changes in hormone levels, muscle mass, strength, and function.

RESULTS

Increases in total testosterone of 1046 ng/dL (95% confidence interval = 1040-1051) and 898 ng/dL (95% confidence interval = 892-904) were necessary to achieve median increases in lean body mass of 1.5 kg and appendicular skeletal muscle mass of 0.8 kg, respectively, which were required to significantly enhance one-repetition maximum strength (≥ 30%). Co-treatment with rhGH lowered the testosterone levels (quantified using liquid chromatography-tandem mass spectrometry) necessary to reach these lean mass thresholds. Changes in one-repetition maximum strength were associated with increases in stair climbing power (r = .26, p = .01). Pathway analysis supported the model that changes in testosterone and insulin-like growth factor 1 levels are related to changes in lean body mass needed to enhance muscle performance and physical function. Testosterone's effects on physical activity were mediated through a different pathway because testosterone directly affected Physical Activity Score of the Elderly.

CONCLUSIONS

To enhance muscle strength and physical function, threshold improvements in lean body mass and appendicular skeletal muscle mass are necessary and these can be achieved by targeting changes in testosterone levels. rhGH augments the effects of testosterone. To maximize functional improvements, the doses of anabolic hormones should be titrated to achieve target blood levels.

N-terminal propeptide of type III procollagen as a biomarker of anabolic response to recombinant human GH and testosterone

CONTEXT

Biomarkers that predict musculoskeletal response to anabolic therapies should expedite drug development. During collagen synthesis in soft lean tissue, N-terminal propeptide of type III procollagen (P3NP) is released into circulation. We investigated P3NP as a biomarker of lean body mass (LBM) and muscle strength gains in response to testosterone and GH.

DESIGN

Community-dwelling older men received GnRH agonist plus 5 or 10 g testosterone gel plus 0, 3, or 5 microg recombinant human GH daily. P3NP levels were measured at baseline and wk 4, 8, 12, and 16. LBM and appendicular skeletal muscle mass (ASM) were measured by dual-energy x-ray absorptiometry.

RESULTS

One hundred twelve men completed treatment; 106 underwent serum P3NP measurements. P3NP levels were higher at wk 4 than baseline (6.61 +/- 2.14 vs. 4.51 +/- 1.05, P < 0.0001) and reached plateau by wk 4 in men receiving testosterone alone. However, wk 8 P3NP levels were higher than wk 4 levels in men receiving testosterone plus recombinant human GH. Increases in P3NP from baseline to wk 4 and 16 were significantly associated with gains in LBM (r = 0.26, P = 0.007; r = 0.53, P < 0.001) and ASM (r = 0.17, P = 0.07; r = 0.40, P < 0.0001). Importantly, for participants receiving only testosterone, P3NP increases at wk 4 and 16 were related to muscle strength gains (r = 0.20, P = 0.056 and r = 0.36, P = 0.04). In stepwise regression, change in P3NP explained 28 and 30% of the change in ASM and LBM, respectively, whereas change in testosterone but not IGF-I and age provided only small improvements in the models.

CONCLUSION

Early changes in serum P3NP levels are associated with subsequent changes in LBM and ASM during testosterone and GH administration. Serum P3NP may be a useful early predictive biomarker of anabolic response to GH and testosterone.

Peripheral and visceral fat changes following a treatment switch to a non-thymidine analogue or a nucleoside-sparing regimen in HIV-infected subjects with peripheral lipoatrophy: results of ACTG A5110

BACKGROUND

Switching a thymidine analogue to a non-thymidine analogue or changing to a nucleoside-sparing regimen has been shown to partially reverse peripheral lipoatrophy. The current study evaluated both approaches.

METHODS

Subjects at 15 AIDS Clinical Trial Group sites receiving thymidine analogue stavudine- or zidovudine-containing regimens with plasma HIV RNA < or =500 copies/mL and lipoatrophy were prospectively randomized to: (i) switch the thymidine analogue to abacavir; (ii) discontinue all antiretrovirals and switch to lopinavir/ritonavir plus nevirapine (LPV/r+NVP); or (iii) delay switching for 24 weeks (ClinicalTrials.gov identifier: NCT00028314). Single-slice computer tomography of mid-thigh and abdominal fat and metabolic and virological/immunological parameters were measured at baseline and weeks 24 and 48.

RESULTS

Among the 101 patients enrolled, there were significant subcutaneous thigh fat and subcutaneous abdominal tissue (SAT) increases over time and decreases in visceral adipose tissue to total adipose tissue (VAT:TAT) ratios for both interventions, and a decrease in VAT for abacavir. CD4 increased in the LPV/r+NVP arm. LPV/r+NVP had a significantly shorter time to grade 3 or higher toxicity (P = 0.007), but discontinuation rates were similar. Glucose levels did not change, but insulin decreased in the LPV/r+NVP arm. Lipids tended to increase in the LPV/r+NVP arm.

CONCLUSIONS

Switching stavudine or zidovudine to a non-thymidine analogue or changing to a nucleoside reverse transcriptase inhibitor-sparing regimen is associated with qualitatively similar improvements in thigh fat, SAT and VAT:TAT ratio at 48 weeks. Abacavir also resulted in VAT reductions and LPV/r+NVP resulted in CD4 count increases.

The role of protease inhibitors in the pathogenesis of HIV-associated lipodystrophy: cellular mechanisms and clinical implications

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.

Switching to a protease inhibitor-containing, nucleoside-sparing regimen (lopinavir/ritonavir plus efavirenz) increases limb fat but raises serum lipid levels: results of a prospective randomized trial (AIDS clinical trial group 5125s)

BACKGROUND

Subcutaneous limb fat loss continues to be one the most troubling side effects of long-term antiretroviral regimens. Nucleoside analogues and protease inhibitors (PIs) have been linked to the development of this complication.

METHODS

We evaluated the effects of nucleoside-sparing and PI-sparing regimens on fat distribution, bone mineral density, and metabolic parameters in 62 subjects, who were not selected for lipoatrophy, with advanced HIV (nadir CD4 count <or=200 cells/mm or HIV RNA level >or=80,000 copies/mL) and an undetectable HIV viral load. Participants were randomized to switch their initial successful antiretroviral regimen to open-label lopinavir/ritonavir (LPV/r) at a dose of 533/133 mg twice a day and efavirenz (EFV) at a dose of 600 mg/d (the nucleoside-sparing arm) versus EFV and 2 nucleoside analogues (the PI-sparing arm).

FINDINGS

At week 48, the median change in limb fat in the nucleoside-sparing arm was 562 g (6%, interquartile range [IQR]: -218-1186 g) versus a loss of -242 g (-4%, IQR: -539-452 g) in the nucleoside-containing PI-sparing arm (P = 0.086). At the time of last observation (median = 102 weeks, IQR: 73-152 weeks), a median gain of 782 g (10%, IQR: -380-1168 g) of limb fat was noted in the nonnucleoside arm (n = 22) versus a loss of 850 g (-15%, IQR: -1270 to -526 g) in the nucleoside-containing arm (n = 25; P = 0.002).

INTERPRETATION

The switch to a nucleoside-sparing combination antiretroviral regimen (LPV/r + EFV) was associated with significant improvement in limb fat. These results provide additional evidence that nucleoside analogues are important in the progressive limb fat loss that characterizes antiretroviral treatment and that switching medications can significantly improve this complication. This option has to be carefully balanced with the potential to increase serum lipid levels and the trend to increase virologic failure.

Metabolic syndrome in HIV-infected patients from an urban, midwestern US outpatient population

BACKGROUND

The association between the use of highly active antiretroviral therapy (HAART) and an increased risk of metabolic syndrome and cardiovascular disease remains unclear.

METHODS

We conducted a prospective, cross-sectional study of the risk factors associated with metabolic syndrome and cardiovascular disease among patients from an urban outpatient human immunodeficiency virus (HIV) clinic. Evaluation included laboratory data that were obtained after an overnight fast and a health survey that assessed traditional risk factors associated with cardiovascular disease, HIV-related factors, and comorbidities. Data collected were compared with data files from a cohort from the National Health and Nutrition Examination Survey (NHANES; 2001-2002) of persons who were seronegative for HIV infection who were matched for age, sex, race, and tobacco use.

RESULTS

Four hundred seventy-one HIV-infected subjects provided complete data. The overall prevalence of metabolic syndrome was similar between the group HIV-infected patients and the group of persons who were seronegative for HIV infection (25.5% vs. 26.5%, respectively), although the HIV-infected patients had a significantly smaller waist circumference, lower body mass index, lower high-density lipoprotein cholesterol levels, higher triglyceride levels, and lower glucose levels, compared with the subjects from the NHANES cohort. Framingham 10-year risk scores were also similar between the 2 groups. HIV-infected patients with metabolic syndrome were more likely to be diabetic, older, and white and have a high CD4 cell count and body mass index, compared with patients without metabolic syndrome (P<.05 for all). The type or duration of antiretroviral therapy was not an independent risk factor for metabolic syndrome.

CONCLUSIONS

The prevalence of metabolic syndrome is high among HIV-infected persons, but not higher than the prevalence among HIV-uninfected persons. Traditional risk factors play a more significant role in the development of metabolic syndrome than do HIV treatment-associated factors.

High-precision isotopic analysis of palmitoylcarnitine by liquid chromatography/electrospray ionization ion-trap tandem mass spectrometry

Single quadrupole gas chromatography/mass spectrometry (GC/MS) has been widely used for isotopic analysis in metabolic investigations using stable isotopes as tracers. However, its inherent shortcomings prohibit it from broader use, including low isotopic precision and the need for chemical derivatization of the analyte. In order to improve isotopic detection power, liquid chromatography/electrospray ionization ion-trap tandem mass spectrometry (LC/ESI-itMS2) has been evaluated for its isotopic precision and chemical sensitivity for the analysis of [13C]palmitoylcarnitine. Over the enrichment range of 0.4-10 MPE (molar % excess), the isotopic response of LC/ESI-itMS2 to [13C]palmitoylcarnitine was linear (r = 1.00) and the average isotopic precision (standard deviation, SD) was 0.11 MPE with an average coefficient of variation (CV) of 5.6%. At the lower end of isotopic enrichments (0.4-0.9 MPE), the isotopic precision was 0.05 MPE (CV = 8%). Routine analysis of rat skeletal muscle [13C4]palmitoylcarnitine demonstrated an isotopic precision of 0.03 MPE for gastrocnemius (n = 16) and of 0.02 MPE for tibialis anterior (n = 16). The high precision enabled the detection of a small (0.08 MPE) but significant (P = 0.01) difference in [13C4]palmitoylcarnitine enrichments between the two muscles, 0.51 MPE (CV = 5.8%) and 0.43 MPE (CV = 4.6%), respectively. Therefore, the system demonstrated an isotopic lower detection limit (LDL) of < or =0.1 MPE (2 x SD) that has been impossible previously with other organic mass spectrometry instruments. LC/ESI-itMS2 systems have the potential to advance metabolic investigations using stable isotopes to a new level by significantly increasing the isotopic solving power.

Evaluation of the virological and metabolic effects of switching protease inhibitor combination antiretroviral therapy to nevirapine-based therapy for the treatment of HIV infection

In spite of indisputable benefits, the use of antiretroviral therapy is associated with multiple metabolic complications. Switching to simpler regimens might maintain viral suppression, improve metabolic side effects, and provide insight into the pathogenesis of these complications. Our objective was to carefully characterize the virological and metabolic effects of switching from a successful protease inhibitor (PI)-based antiretroviral regimen to a nonnucleoside reverse transcriptase inhibitor (NNRTI)-based regimen with nevirapine (NVP). Forty patients, taking their first successful (less than 40 HIV RNA copies/ml) PI-based regimen, switched their PI to NVP. If patients did not tolerate NVP, substitution with efavirenz was allowed. The duration of the study was 48 weeks. At 12 weeks intervals subjects had multiple virological and metabolic parameters including glucose, insulin, C-peptide, glucagon, proinsulin, blood lipids, and lipoproteins. A subgroup of 18 patients also had body composition evaluations with DEXA scans and MRIs of the abdomen and the thighs as well as insulin tolerance tests. Ninety-five percent of the patients maintained viral suppression (95% CI 88-100%); only one patient failed and another developed hepatitis. There were improvements in glucose (decreased fasting glucose, insulin, and improved insulin tolerance) and lipid metabolism (decreased triglycerides and increased HDL), but no changes in body composition and bone mineral density. Our study supports a pathogenic role for PIs in the development of hypertriglyceridemia and insulin resistance, but a more limited role in the fat redistribution syndrome.

Longitudinal evolution of bone mineral density and bone markers in human immunodeficiency virus-infected individuals

The underlying mechanisms of several bone disorders in human immunodeficiency virus (HIV)-infected persons and any relation to antiretroviral therapy have yet to be defined. A longitudinal study was conducted to estimate the prevalence of osteopenia or osteoporosis in HIV-infected persons; to assess bone mineralization, metabolism, and histomorphometry over time; and to evaluate predisposing factors. A total of 128 patients enrolled the study, and 93 were observed for 72 weeks. "Classic" risk factors (low body mass index, history of weight loss, steroid use, and smoking) for low bone mineral density (BMD) and duration of HIV infection were strongly associated with osteopenia. There was a weak association between low BMD and receipt of treatment with protease inhibitors; this association disappeared after controlling for the above factors. Markers of bone turnover tended to be elevated in the whole cohort but were not associated with low BMD. BMD increased slightly during follow-up. Traditional risk factors and advanced HIV infection play a more significant pathogenic role in the development of osteopenia and osteoporosis associated with HIV infection than do treatment-associated factors.

Electrospray ionization mass spectrometric analyses of changes in tissue phospholipid molecular species during the evolution of hyperlipidemia and hyperglycemia in Zucker diabetic fatty rats

The Zucker diabetic fatty (ZDF) rat is a genetic model of type II diabetes mellitus in which males homozygous for nonfunctional leptin receptors (fa/fa) develop obesity, hyperlipidemia, and hyperglycemia, but rats homozygous for normal receptors (+/+) remain lean and normoglycemic. Insulin resistance develops in young fa/fa rats and is followed by evolution of an insulin secretory defect that triggers hyperglycemia. Because insulin secretion and insulin sensitivity are affected by membrane phospholipid fatty acid composition, we have determined whether metabolic abnormalities in fa/fa rats are associated with changes in tissue phospholipids. Electrospray ionization mass spectrometric analyses of glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE) molecular species from tissues of prediabetic (6 wk of age) and overtly diabetic (12 wk) fa/fa rats and from +/+ rats of the same ages indicate that arachidonate-containing species from heart, aorta, and liver of prediabetic fa/fa rats made a smaller contribution to GPC total ion current than was the case for +/+ rats. There was a correspondingly larger contribution from species with sn-2 oleate or linoleate substituents in fa/fa heart and aorta. The relative contributions of arachidonate-containing GPC species increased in these tissues as fa/fa rats aged and were equal to or greater than those for +/+ rats by 12 wk. For heart and aorta, relative contributions from GPE species with sn-2 arachidonate or docosahexaenoate substituents to the total ion current increased and those from species with sn-2 oleate or linoleate substituents fell as fa/fa rats aged, but these tissue lipid profiles changed little with age in +/+ rats. GPC and GPE profiles for brain, kidney, sciatic nerve, and red blood cells were similar among fa/fa and +/+ rats at 6 and 12 wk of age, and pancreatic islets from fa/fa and +/+ rats exhibited similar GPC and GPE profiles at 12 wk of age. Under-representation of arachidonate-containing GPC and GPE species in some fa/fa rat tissues at 6 wk could contribute to insulin resistance, but depletion of islet arachidonate-containing GPC and GPE species is unlikely to explain the evolution of the insulin secretory defect that is well-developed by 12 wk of age.

Undermodeling affects minimal model indexes: insights from a two-compartment model

The classic (hereafter cold) and the labeled (hereafter hot) minimal models are powerful tools to investigate glucose metabolism. The cold model provides, from intravenous glucose tolerance test (IVGTT) data, indexes of glucose effectiveness (SG) and insulin sensitivity (SI) that measure the effect of glucose and insulin, respectively, to enhance glucose disappearance and inhibit endogenous glucose production. The hot model provides, from hot IVGTT data, indexes of glucose effectiveness (SG*) and insulin sensitivity (SI*) that, respectively, measure the effects of glucose and insulin on glucose disappearance only. Recent reports call for a reexamination of some of the assumptions of the minimal models. We have previously pointed out the criticality of the single-compartment description of glucose kinetics on which both the minimal models are founded. In this paper we evaluate the impact of single-compartment undermodeling on SG, SI*, and by using a two-compartment model to describe the glucose system. The relationships of the minimal model indexes to the analogous indexes measured with the glucose clamp technique are also examined. Theoretical analysis and simulation studies indicate that cold indexes are more affected than hot indexes by undermodeling. In particular, care must be exercised in the physiological interpretation of SG, because this index is a local descriptor of events taking place in the initial portion of the IVGTT. As a consequence, SG not only reflects glucose effect on glucose uptake and production but also the rapid exchange of glucose between the accessible and nonaccessible glucose pools that occurs in the early part of the test.

Organization of the human myostatin gene and expression in healthy men and HIV-infected men with muscle wasting

Myostatin, a member of the transforming growth factor-beta superfamily, is a genetic determinant of skeletal muscle growth. Mice and cattle with inactivating mutations of myostatin have marked muscle hypertrophy. However, it is not known whether myostatin regulates skeletal muscle growth in adult men and whether increased myostatin expression contributes to wasting in chronic illness. We examined the hypothesis that myostatin expression correlates inversely with fat-free mass in humans and that increased expression of the myostatin gene is associated with weight loss in men with AIDS wasting syndrome. We therefore cloned the human myostatin gene and cDNA and examined the gene's expression in the skeletal muscle and serum of healthy and HIV-infected men. The myostatin gene comprises three exons and two introns, maps to chromosomal region 2q33.2, has three putative transcription initiation sites, and is transcribed as a 3.1-kb mRNA species that encodes a 375-aa precursor protein. Myostatin is expressed uniquely in the human skeletal muscle as a 26-kDa mature glycoprotein (myostatin-immunoreactive protein) and secreted into the plasma. Myostatin immunoreactivity is detectable in human skeletal muscle in both type 1 and 2 fibers. The serum and intramuscular concentrations of myostatin-immunoreactive protein are increased in HIV-infected men with weight loss compared with healthy men and correlate inversely with fat-free mass index. These data support the hypothesis that myostatin is an attenuator of skeletal muscle growth in adult men and contributes to muscle wasting in HIV-infected men.

Isotope dilution mass spectrometric quantification of 3-nitrotyrosine in proteins and tissues is facilitated by reduction to 3-aminotyrosine

Oxidative damage by reactive nitrogen species has been implicated in the pathogenesis of atherosclerosis and other inflammatory diseases. The mechanisms of tissue damage are poorly understood, however, because the toxic intermediates are short-lived. Previous in vitro studies have suggested that 3-nitrotyrosine represents a specific marker of protein oxidation by reactive nitrogen species. The detection of this nitrated aromatic amino acid may thus serve as an indicator of tissue injury by nitrogen species in vivo. Here we describe a highly sensitive and specific analytical method for quantifying free and protein-bound 3-nitrotyrosine. The assay involves acid hydrolysis of proteins, isolation of 3-nitrotyrosine by ion exchange chromatography, and reduction of 3-nitrotyrosine to 3-aminotyrosine with dithionite. The reduced amino acid is then converted to its n-propyl, per-heptafluorobutyryl derivative and quantified by isotope dilution gas chromatography negative-ion chemical ionization mass spectrometry. Attomole levels of 3-nitrotyrosine can be reproducibly measured in this manner. Quantifying 3-nitrotyrosine levels of tissues by stable isotope dilution gas chromatography/mass spectrometry should provide a powerful tool for exploring the impact of reactive nitrogen species on oxidative reactions in vivo.