Citations

Objective— To determine whether serum levels of N-terminal (NT) pro–B-type natriuretic peptide (pro-BNP) are higher in patients with poorly compressible arteries (PCA) than in patients with peripheral artery disease (PAD) and control subjects without PCA or PAD. Methods and Results— Medial arterial calcification in the lower extremities results in PCA and may be associated with increased arterial stiffness and hemodynamic/myocardial stress. PCA was defined as having an ankle-brachial index >1.4 or an ankle blood pressure >255 mm Hg, whereas PAD was defined as having an ankle-brachial index ≤0.9. Study participants with PCA (n=100; aged 71±10 years; 70% men) and age- and sex-matched patients with PAD (n=300) were recruited from the noninvasive vascular laboratory. Age- and sex-matched controls (n=300) were identified from a community-based cohort and had no history of PAD. NT pro-BNP levels were approximately 2.5-fold higher in patients with PCA than in patients with PAD and approximately 4-fold higher than in age- and sex-matched controls. In multivariable regression analyses that adjusted for age, sex, smoking, hypertension, history of coronary heart disease/stroke, systolic blood pressure, and serum creatinine, NT pro-BNP levels remained significantly higher in patients with PCA than in patients with PAD and controls ( P <0.001). Conclusion— Patients with medial arterial calcification and PCA have higher serum levels of NT pro-BNP than patients with PAD and controls, which is suggestive of an adverse hemodynamic milieu and increased risk for adverse cardiovascular outcomes.

Objective— Osteocalcin has been reported to influence insulin secretion in experimental animals. We investigated whether serum osteocalcin was associated with measures of insulin resistance, circulating adipokine levels, and the presence of metabolic syndrome (MetSyn). Methods and Results— Serum osteocalcin was measured by solid-phase sandwich immunoassay in 1284 blacks (64±9 years; 71% women) and 1209 non-Hispanic whites (59±10 years; 57% women) belonging to hypertensive sibships. MetSyn was defined per Adult Treatment Panel III criteria. The prevalence of MetSyn was 50% in blacks and 49% in non-Hispanic whites. In each ethnic group, after adjustment for age and gender, osteocalcin levels were inversely correlated with body mass index, fasting glucose and insulin, homeostasis model assessment of insulin resistance, triglycerides, and leptin, and positively correlated with adiponectin ( P <0.001 for each variable). In multivariable regression analyses that adjusted for age, gender, smoking, serum creatinine, and statin and estrogen use, osteocalcin levels in the highest quartile (compared with the lowest quartile) were associated with a lower odds ratio (OR) of having MetSyn: OR (95% CI) in blacks, 0.33 (0.23 to 0.46); OR in non-Hispanic whites, 0.43 (0.31 to 0.63). Conclusion— Serum osteocalcin is associated with measures of insulin resistance, adipokine levels, and the presence of MetSyn, suggesting a novel cross-talk between bone and adipose tissue.

Abstract Background: The measurement of multiple protein biomarkers may refine risk stratification in clinical settings. This concept has stimulated development of multiplexed immunoassay platforms that provide multiple, parallel protein measurements on the same specimen. Content: We provide an overview of antibody-based multiplexed immunoassay platforms and discuss technical and operational challenges. Multiplexed immunoassays use traditional immunoassay principles in which high-affinity capture ligands are immobilized in parallel arrays in either planar format or on microspheres in suspension. Development of multiplexed immunoassays requires rigorous validation of assay configuration and analytical performance to minimize assay imprecision and inaccuracy. Challenges associated with multiplex configuration include selection and immobilization of capture ligands, calibration, interference between antibodies and proteins and assay diluents, and compatibility of assay limits of quantification. We discuss potential solutions to these challenges. Criteria for assessing analytical multiplex assay performance include the range of linearity, analytical specificity, recovery, and comparison to a quality reference method. Quality control materials are not well developed for multiplexed protein immunoassays, and algorithms for interpreting multiplex quality control data are needed. Summary: Technical and operational challenges have hindered implementation of multiplexed assays in clinical settings. Formal procedures that guide multiplex assay configuration, analytical validation, and quality control are needed before broad application of multiplexed arrays can occur in the in vitro diagnostic market.

Abstract Peripheral arterial disease (PAD), a relatively common manifestation of atherosclerotic vascular disease, is associated with significant morbidity and mortality. Although conventional risk factors contribute to the onset and progression of PAD, the role of ‘novel’ biomarkers in pathways of inflammation, thrombosis, lipoprotein metabolism, and oxidative stress in determining susceptibility to PAD is being increasingly recognized. Validation of novel risk factors for PAD may allow earlier detection, an improved understanding of disease etiology and progression, and the development of new therapies. In this review, we discuss available evidence for associations between novel circulating markers and several aspects of PAD including disease susceptibility, progression, functional limitation, and adverse outcomes.

Background Inflammation is proposed to play a role in the development of Alzheimer's disease, and may also be involved in the pathogenesis of mild cognitive impairment (MCI). This study examined the association of inflammatory markers in serum or plasma with prevalent MCI and MCI subtypes in a population‐based sample. Methods Olmsted County, MN, residents aged 70–89 years on October 1, 2004, were evaluated using the Clinical Dementia Rating Scale, a neurological evaluation, and neuropsychological testing. Information ascertained for each participant was reviewed by an expert panel of neuropsychologists, physicians, and nurses, and a diagnosis of normal cognition, MCI, or dementia was made by consensus. C‐reactive protein (CRP), interleukin‐6 (IL‐6), tumor necrosis alpha (TNFα), and adiponectin were measured at baseline. Results Among 313 subjects with MCI and 1570 cognitively normal subjects, a CRP level in the upper quartile (>3.3 mg/L) was significantly associated with MCI (odds ratio [OR], 1.42; 95% confidence interval [CI], 1.00–2.01) and with nonamnestic MCI (OR, 2.05; 95% CI, 1.12–3.78) after adjusting for age, sex, and years of education. However, there was no association with amnestic MCI (OR, 1.21; 95% CI, 0.81–1.82). No association was observed with the other inflammatory markers. Conclusions Plasma CRP is associated with prevalent MCI and with nonamnestic MCI in elderly, nondemented persons in a population‐based setting. These findings suggest the involvement of inflammation in the pathogenesis of MCI.

Abstract Myeloperoxidase (MPO) is an enzymatic mediator of several inflammatory cascades and higher serum levels have been associated with increased risk of adverse cardiovascular events. We investigated the association of serum MPO with the ankle–brachial index (ABI) and peripheral arterial disease (PAD) in a bi-ethnic cohort of African-Americans and non-Hispanic white individuals. Participants included 1324 African-Americans (mean age 64 years, 71% women) and 1237 non-Hispanic white individuals (mean age 59 years, 57% women) belonging to hypertensive sibships. Serum levels of MPO were measured by solid phase sandwich immunoassay. ABI was measured using a standard protocol and PAD was defined as an ABI < 0.90. Multivariable regression analysis using generalized estimating equations were performed to assess whether serum MPO levels were associated with ABI and the presence of PAD. After adjustment for age and sex, higher MPO levels were significantly associated with lower ABI and the presence of PAD in African-Americans ( p = 0.004 and p = 0.005, respectively) and in non-Hispanic white individuals ( p = 0.001 and p = 0.016, respectively). After additional adjustment for conventional risk factors (diabetes, smoking status, total and high-density lipoprotein cholesterol, waist circumference, hypertension), prior history of myocardial infarction or stroke, and medication use (statins, aspirin, estrogen), higher MPO levels remained significantly associated with lower ABI and the presence of PAD in both African-Americans ( p = 0.008 and p = 0.010, respectively) and non-Hispanic white individuals ( p = 0.001 and p = 0.018, respectively). We conclude that higher MPO levels are associated with lower ABI and the presence of PAD in African-Americans and non-Hispanic white individuals.

Abstract Background: Multiplex arrays are increasingly used for measuring protein biomarkers. Advantages of this approach include specimen conservation, limited sample handling, and decreased time and cost, but the challenges of optimizing assay format for each protein, selecting common dilution factors, and establishing robust quality control algorithms are substantial. Here, we use measurements of 15 protein biomarkers from a large study to illustrate processing, analytic, and quality control issues with multiplexed immunoassays. Methods: We contracted with ThermoScientific for duplicate measurements of 15 proteins in 2322 participants from a community-based cohort, a plasma control, and recombinant protein controls using 2 custom planar microarrays with 6 (panel A) or 9 (panel B) capture antibodies printed in each well. We selected constituent analytes in each panel based on endogenous concentrations and assay availability. Protocols were standardized for sample processing, storage, and freeze-thaw exposures. We analyzed data for effects of deviations from processing protocols, precision, and bias. Results: Measurements were within reportable ranges for each of the assays; however, concentrations for 7 of the 15 proteins were not centered on the dose–response curves. An additional freeze-thaw cycle and erroneous sample dilution for a subset of samples produced significantly different results. Measurements with large differences between duplicates were seen to cluster by analyte, plate, and participant. Conventional univariate quality control algorithms rejected many plates. Plate-specific medians of cohort and plasma control data significantly covaried, an observation important for development of alternative quality control algorithms. Conclusions: Multiplex measurements present difficult challenges that require further analytical and statistical developments.

Context: Stress-mediated hypothalamic-pituitary-adrenal axis activation, regulated by arginine vasopressin (AVP), may have a role in the pathophysiology of metabolic syndrome (MetSyn). Objective: The objective of the study was to investigate whether plasma C-terminal provasopressin fragment (copeptin), a surrogate for circulating AVP, was associated with measures of insulin resistance and presence of MetSyn. Design, Setting, and Participants: This was a multicenter, community-based study, investigating novel biomarkers for vascular disease. Participants included 1293 African-Americans (AA) (64 ± 9 yr) and 1197 non-Hispanic whites (NHW) (59 ± 10 yr) belonging to hypertensive sibships. Main Outcome Measures: Plasma copeptin levels were measured by an immunoluminometric assay. MetSyn was defined per Adult Treatment Panel III criteria. Generalized estimating equations were used to assess whether plasma copeptin was associated with measures of insulin resistance and MetSyn. Results: The prevalence of MetSyn was 50% in AA and 49% in NHW. In each group, after adjustment for age and sex, plasma copeptin levels significantly correlated with body mass index, fasting plasma glucose and insulin, homeostasis model assessment of insulin resistance, triglycerides, and (inversely) high-density lipoprotein cholesterol (P &lt; 0.05 for each variable). In multivariable logistic regression models that adjusted for age, sex, smoking, statin use, serum creatinine, education, physical activity, and diuretic use, plasma copeptin levels in the highest quartile were associated with an increased odds ratio of having MetSyn compared with bottom quartile: odds ratio (95% confidence interval) in AA, 2.07 (1.45–2.95); in NHW, 1.74 (1.21–2.5). Conclusions: Our findings indicate a novel cross-sectional association between plasma copeptin and measures of insulin resistance and MetSyn.