A High-Throughput NMR Method for Lipoprotein-X Quantification

Lipoprotein X (LP-X) is an abnormal cholesterol-rich lipoprotein particle that accumulates in patients with cholestatic liver disease and familial lecithin-cholesterol acyltransferase deficiency (FLD). Because there are no high-throughput diagnostic tests for its detection, a proton nuclear magnetic resonance (NMR) spectroscopy-based method was developed for use on a clinical NMR analyzer commonly used for the quantification of lipoproteins and other cardiovascular biomarkers. The LP-X assay was linear from 89 to 1615 mg/dL (cholesterol units) and had a functional sensitivity of 44 mg/dL. The intra-assay coefficient of variation (CV) varied between 1.8 and 11.8%, depending on the value of LP-X, whereas the inter-assay CV varied between 1.5 and 15.4%. The assay showed no interference with bilirubin levels up to 317 mg/dL and was also unaffected by hemolysis for hemoglobin values up to 216 mg/dL. Samples were stable when stored for up to 6 days at 4 °C but were not stable when frozen. In a large general population cohort (n = 277,000), LP-X was detected in only 50 subjects. The majority of LP-X positive cases had liver disease (64%), and in seven cases, had genetic FLD (14%). In summary, we describe a new NMR-based assay for LP-X, which can be readily implemented for routine clinical laboratory testing.

Triglyceride/HDL cholesterol ratio and lipoprotein insulin resistance Score: Associations with subclinical atherosclerosis and incident cardiovascular disease

BACKGROUND

The triglyceride/HDL cholesterol (TG/HDL-C) ratio and the Lipoprotein Insulin Resistance (LP-IR) score are lipid markers of insulin resistance. Their associations with carotid intima media thickness (cIMT; subclinical atherosclerosis) and incident cardiovascular disease (CVD) have not been thoroughly investigated.

METHODS

In a cross-sectional cohort (89 subjects without type 2 diabetes (T2D) and 81 subjects with T2D we determined cIMT (ultrasound), homeostasis model assessment of insulin resistance (HOMA-IR) and the TG/HDL-C ratio. The LP-IR score, based on 6 lipoprotein characteristics determined by nuclear magnetic resonance spectroscopy, was measured in 123 participants. A prospective study was carried out among 6232 participants (Prevention of REnal and Vascular ENd-stage Disease study).

RESULTS

Cross-sectionally, the adjusted associations of HOMA-IR, the TG/HDL-C ratio and the LP-IR score with cIMT were approximately similar (standardized β = 0.34 (95 % CI 0.19-0.48), 0.24 (95 % CI 0.09-039) and 0.41 (95 % CI 0.23--0.59), respectively). Prospectively, 507 new cases of CVD were observed after a median follow-up of 8.2 (interquartile range 7.5-8.8) years. HOMA-IR, the TG/HDL-C ratio and LP-IR were each associated with incident CVD independent of potential confounders (HR 1.12, 95 % CI 1.02-1.24;1.22, 95 % CI 1.11-1.35 and 1.15. 95 % CI 1.01-1.31, respectively). The association of the TG/HDL-C ratio with incident CVD was somewhat stronger than that of HOMA-IR.

CONCLUSION

Lipoprotein-based markers of insulin resistance are at least as strongly associated with subclinical atherosclerosis and clinical atherosclerosis development as HOMA-IR, obviating the need to measure insulin to determine the impact of insulin resistance. For practical purposes, the easily obtainable TG/HDL-C ratio may suffice.

Circulating Citrate Is Associated with Liver Fibrosis in Nonalcoholic Fatty Liver Disease and Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease (NAFLD) is associated with mitochondrial damage. Circulating mitochondrial metabolites may be elevated in NAFLD but their associations with liver damage is not known. This study aimed to assess the association of key mitochondrial metabolites with the degree of liver fibrosis in the context of NAFLD and nonalcoholic steatohepatitis (NASH). Cross-sectional analyses were performed on two cohorts of biopsy-proven NAFLD and/or NASH subjects. The association of circulating mitochondrial metabolite concentrations with liver fibrosis was assessed using linear regression analysis. In the single-center cohort of NAFLD subjects (n = 187), the mean age was 54.9 ±13.0 years, 40.1% were female and 86.1% were White. Type 2 diabetes (51.3%), hypertension (43.9%) and obesity (72.2%) were prevalent. Those with high citrate had a higher proportion of moderate/significant liver fibrosis (stage F ≥ 2) (68.4 vs. 39.6%, p = 0.001) and advanced fibrosis (stage F ≥ 3) (31.6 vs. 13.6%, p = 0.01). Citrate was associated with liver fibrosis independent of age, sex, NAFLD activity score and metabolic syndrome (per 1 SD increase: β = 0.19, 95% CI: 0.03-0.35, p = 0.02). This association was also observed in a cohort of NASH subjects (n = 176) (β = 0.21, 95% CI: 0.07-0.36, p = 0.005). The association of citrate with liver fibrosis was observed in males (p = 0.005) but not females (p = 0.41). In conclusion, circulating citrate is elevated and associated with liver fibrosis, particularly in male subjects with NAFLD and NASH. Mitochondrial function may be a target to consider for reducing the progression of liver fibrosis and NASH.

Creatine and creatinine quantified using nuclear magnetic resonance: A method validation study and clinical associations between circulating creatine and fatigue in kidney transplant recipients

BACKGROUND

A potential contributor to fatigue in kidney transplant recipients (KTR) may be impaired creatine homeostasis. We developed and validated a high-throughput NMR assay allowing for simultaneous measurement of circulating creatine and creatinine, and determined plasma creatine and estimated intramuscular creatine concentrations in KTRs, delineated their determinants and explored their associations with self-reported fatigue.

METHODS

An NMR assay was developed and validated for measurement of circulating creatinine and creatine concentrations. Plasma creatine and creatinine concentrations were measured in 618 KTR. Fatigue was assessed using the checklist individual strength. Associations of creatine parameters with fatigue was assessed using linear mixed effect models.

RESULTS

The NMR-based assay had good sensitivity, precision and demonstrated linearity across a large range of values. Among KTR, the mean age was 56 ± 13 years, 62% were men and eGFR was 54 ± 18 ml/min/1.73 m2. Plasma creatine concentration was 27 [19-39] µmol/L. Estimated intramuscular creatine concentration was 27 ± 7 mmol/kg. Higher plasma creatine concentration and higher estimated intramuscular creatine concentration were independently associated with a lower total fatigue score and less motivation problems.

CONCLUSION

An NMR method for measurement of circulating creatine and creatinine which offers the potential for accurate and efficient quantification was developed. The found associations suggest that improving creatine status may play a beneficial role in mitigating fatigue.

Multimarkers of metabolic malnutrition and inflammation and their association with mortality risk in cardiac catheterisation patients: a prospective, longitudinal, observational, cohort study

BACKGROUND

Complex and incompletely understood metabolic dysfunction associated with inflammation and protein-energy wasting contribute to the increased mortality risk of older patients and those with chronic organ diseases affected by cachexia, sarcopenia, malnutrition, and frailty. However, these wasting syndromes have uncertain relevance for patients with cardiovascular disease or people at lower risk. Studies are hampered by imperfect objective clinical assessment tools for these intertwined metabolic malnutrition and inflammation syndromes. We aimed to assess, in two independent cohorts of patients who underwent cardiac catheterisation, the mortality risk associated with the metabolic vulnerability index (MVX), a multimarker derived from six simultaneously measured serum biomarkers plausibly linked to these dysmetabolic syndromes.

METHODS

In this prospective, longitudinal, observational study, we included patients aged ≥18 years recruited into the CATHGEN biorepository (Jan 2, 2001, to Dec 30, 2011) and the Intermountain Heart Collaborative Study (Sept 12, 2000, to Sept 21, 2006) who underwent coronary angiography and had clinical nuclear magnetic resonance metabolomic profiling done on frozen plasma obtained at catheterisation. We aggregated six mortality risk biomarkers (GlycA, small HDL, valine, leucine, isoleucine, and citrate concentrations) into sex-specific MVX multimarker scores using coefficients from predictive models for all-cause mortality in the CATHGEN cohort. We assessed associations of biomarkers and MVX with mortality in both cohorts using Cox proportional hazards models adjusted for 15 clinical covariates.

FINDINGS

We included 5876 participants from the CATHGEN biorepository and 2888 from the Intermountain Heart study. Median follow-up was 6·2 years (IQR 4·4-8·9) in CATHGEN and 8·2 years (6·9-9·2) in the Intermountain Heart study. The six nuclear magnetic resonance biomarkers and MVX made strong, independent contributions to 5-year mortality risk prediction in both cohorts (hazard ratio 2·18 [95% CI 2·03-2·34] in the CATHGEN cohort and 1·67 [1·50-1·87] in the Intermountain Heart cohort). CATHGEN subgroup analyses showed similar MVX associations in men and women, older and younger individuals, for death from cardiovascular or non-cardiovascular causes, and in patients with or without multiple comorbidities.

INTERPRETATION

MVX made a dominant contribution to mortality prediction in patients with cardiovascular disease and in low-risk subgroups without pre-existing disease, suggesting that metabolic malnutrition-inflammation syndromes might have a more universal role in survival than previously thought.

FUNDING

Labcorp.

Nuclear Magnetic Resonance-Measured Ionized Magnesium Is Inversely Associated with Type 2 Diabetes in the Insulin Resistance Atherosclerosis Study

The aims were to optimize a nuclear magnetic resonance (NMR)-based assay for quantifying ionized or free magnesium and investigate its association with type 2 diabetes (T2D). A high-throughput, ionized magnesium assay was optimized and evaluated. Plasma magnesium was quantified, and associations with T2D were ascertained in Insulin Resistance Atherosclerosis Study (IRAS) participants. Coefficients of variation for the ionized magnesium assay ranged from 0.7−1.5% for intra-assay and 4.2−4.7% for inter-assay precision. In IRAS (n = 1342), ionized magnesium was significantly lower in subjects with prediabetes and T2D than in normoglycemic subjects, and lower in participants with T2D than those with prediabetes (p < 0.0001). Cross-sectional regression analyses revealed that magnesium was associated with T2D at baseline in models adjusted for multiple clinical risk factors (p = 0.032). This association appeared to be modified by sex, in such a way that the associations were present in women (OR = 0.54 (95% CI 0.37−0.79), p = 0.0015) and not in men (OR = 0.98 (95% CI 0.71−1.35), p = 0.90). Longitudinal regression analyses revealed an inverse association between magnesium and future T2D in the total population (p = 0.035) that was attenuated by LP-IR (p = 0.22). No interactions were detected between magnesium and age, race, BMI, glucose, insulin, triglycerides, or LPIR for the prospective association with future T2D. However, a significant interaction between magnesium and sex was present, now with a trend for an association in men (OR = 0.75 (95% CI 0.55−1.02), p = 0.065 and absence of an association in women (OR = 1.01 (0.76−1.33), p = 0.97). Conclusions: lower ionized magnesium, as measured by an NMR-based assay optimized for accuracy and precision, was associated cross-sectionally with T2D at baseline and longitudinally with incident T2D in IRAS.

Lipoprotein Z, a hepatotoxic lipoprotein, predicts outcome in alcohol-associated hepatitis

BACKGROUND AND AIMS

Lipoprotein Z (LP-Z) is an abnormal free cholesterol (FC)-enriched LDL-like particle discovered from patients with cholestatic liver disease. This study aims to define the diagnostic value of LP-Z in alcohol-associated hepatitis (AH) and interrogate the biology behind its formation.

APPROACH AND RESULTS

We measured serum levels of LP-Z using nuclear magnetic resonance spectroscopy, a well-established clinical assay. Serum levels of LP-Z were significantly elevated in four AH cohorts compared with control groups, including heavy drinkers and patients with cirrhosis. We defined a Z-index, calculated by the ratio of LP-Z to total apolipoprotein B-containing lipoproteins, representing the degree of deviation from normal VLDL metabolism. A high Z-index was associated with 90-day mortality independent from the Model for End-Stage Liver Disease (MELD) and provided added prognosticative value. Both a Z-index ≤ 0.6 and a decline of Z-index by ≥0.1 in 2 weeks predicted 90-day survival. RNA-sequencing analyses of liver tissues demonstrated an inverse association in the expression of enzymes responsible for the extrahepatic conversion of VLDL to LDL and AH disease severity, which was further confirmed by the measurement of serum enzyme activity. To evaluate whether the FC in LP-Z could contribute to the pathogenesis of AH, we found significantly altered FC levels in liver explant of patients with AH. Furthermore, FC in reconstituted LP-Z particles caused direct toxicity to human hepatocytes in a concentration-dependent manner, supporting a pathogenic role of FC in LP-Z.

CONCLUSIONS

Impaired lipoprotein metabolism in AH leads to the accumulation of LP-Z in the circulation, which is hepatotoxic from excessive FC. A Z-index ≤ 0.6 predicts 90-day survival independent from conventional biomarkers for disease prognostication.

Calorie restriction improves lipid-related emerging cardiometabolic risk factors in healthy adults without obesity: Distinct influences of BMI and sex from CALERIE™ a multicentre, phase 2, randomised controlled trial

BACKGROUND

For many cardiovascular risk factors there is no lower limit to which further reduction will result in decreased disease risk; this includes values within ranges considered normal for healthy adults. This seems to be true for new emerging metabolic risk factors identified by innovative technological advances. Further, there seems to be ever evolving evidence of differential responses to lifestyle interventions by sex and body compositions in the normal range. In this secondary analysis, we had the opportunity to test these principles for newly identified molecular biomarkers of cardiometabolic risk in a young (21-50 years), normal weight healthy population undergoing calorie restriction for two years.

METHODS

The Comprehensive Assessment of Long-term Effects of Reducing Intake of Energy (CALERIE™) was a 24-month, multicenter, randomized controlled trial (May 2007-November 2012) in healthy, adults without obesity to evaluate the potential for calorie restriction (CR) to promote anti-aging adaptations, including those associated with disease risk. 218 participants (age 37.9 ± 7.2 years and body mass index (BMI) 25.1 ± 1.7 kg/m², mean±SD) were randomized 2:1 to 24 months of CR (prescribed as 25% reduction from baseline calorie intake) versus ad libitum (AL). Fasting plasma from baseline, 12, and 24 months was used for assessments of lipoproteins, metabolites, and inflammatory markers using nuclear magnetic resonance spectroscopy.

FINDINGS

Averaging 11.9% CR, the CR group had reductions at 12 and 24 months in the cardiovascular disease risk markers, apolipoprotein B and GlycA, and risks for insulin resistance and type 2 diabetes-Lipoprotein Insulin Resistance Index and Diabetes Risk Index (all P_CRvsAL ≤0.0009). Insulin resistance and diabetes risk improvements resulted from CR-induced alterations in lipoproteins, specifically reductions in triglyceride-rich lipoprotein particles and low-density lipoprotein particles, a shift to larger high-density lipoprotein particles (more effective cholesterol transporters), and reductions in branched chain amino acids (BCAAs) (all P_CRvsAL ≤0.004). These CR responses were more pronounced in overweight than normal weight participants and greater in men than women.

INTERPRETATION

In normal to slightly overweight adults without overt risk factors or disease, 12 months of ∼12% CR improved newly identified risk markers for atherosclerotic cardiovascular disease, insulin resistance and type 2 diabetes. These markers suggest that CR improves risks by reducing inflammation and BCAAs and shifting lipoproteins from atherogenic to cholesterol transporting. Additionally, these improvements are greater for men and for those with greater BMIs indicating sex and BMI-influences merit attention in future investigations of lifestyle-mediated improvements in disease risk factors.

FUNDING

The CALERIE™ trial design and implementation were supported by a National Institutes of Health (NIH) U-grant provided to four institutions, the three intervention sites and a coordinating center (U01 AG022132, U01 AG020478, U01 AG020487 U01 AG020480). For this secondary analysis including sample acquisition and processing, data analysis and interpretation, additional funding was provided by the NIH to authors as follows: R01 AG054840 (MO, VBK); R33 AG070455 (KMH, DCP, MB, SBR, CKM, LMR, SKD, CFP, CJR, WEK); P30 DK072476 (CKM, LMR); and U54 GM104940 (CKM, LMR).

A metabolomic index based on lipoprotein subfractions and branched chain amino acids is associated with incident hypertension

OBJECTIVE

The present study aims to evaluate the performance of the Diabetes Risk Index (DRI), a metabolomic index based on lipoprotein particles and branched chain amino acids, on the incidence of newly developed hypertension in a large community dwelling cohort.

METHODS

The DRI was calculated by combining 6 lipoprotein parameters [sizes of very-low-density lipoprotein (VLDL), low-density lipoprotein (LDL) and high-density lipoprotein (HDL), concentrations of large VLDL, small LDL, and large HDL particles], and the concentrations of valine and leucine. DRI scores were estimated in 4169 participants from the PREVEND prospective cohort. Cox proportional hazards regression was used to evaluate the association of DRI scores with incident hypertension.

RESULTS

During a median follow-up of 8.6 years, 924 new hypertension cases were ascertained. In analyses adjusted for age and sex, there was a significant association between DRI and incident hypertension with a hazard ratio (HR) per 1 SD increase of 1.45 (95% CI 1.36,1.54; p < 0.001). After additional adjustment for traditional risk factors, the HR remained significant (HR_adj 1.21, 95% CI 1.10, 1.33, p <0.001). Likewise, subjects in the top quartile of DRI presented with a higher risk of hypertension (HR_adj 1.64, 95% CI 1.28, 2.10, p <0.001). Furthermore, the net reclassification improvement assessment improved after the addition of DRI to a traditional risk model (p <0.001), allowing proper reclassification of 34% of the participants.

CONCLUSION

Higher DRI scores were associated with an increased risk of incident hypertension. Such association was independent of traditional clinical risk factors for hypertension.

Association of beta-hydroxybutyrate with development of heart failure: Sex differences in a Dutch population cohort

BACKGROUND

In the failing heart, energy metabolism is shifted towards increased ketone body oxidation. Nevertheless, the association of beta-hydroxybutyrate (β-OHB) with development of heart failure (HF) remains unclear. We investigated the association between plasma β-OHB and the risk of HF in a prospective population-based cohort.

DESIGN

Plasma β-OHB concentrations were measured in 6134 participants of the PREVEND study. Risk of incident HF with reduced (HFrEF) or preserved (HFpEF) ejection fraction was estimated using multivariable-adjusted Cox regression models.

RESULTS

During median follow-up for 8.2 years, 227 subjects were diagnosed with HF (137 with HFrEF; 90 with HFpEF). Cox regression analyses revealed a significant association of higher β-OHB concentrations with incident HF (HR per 1 standard deviation increase, 1.40 (95% CI: 1.21-1.63; P < .001), which was largely attributable to HFrEF. In women, the hazard ratio (HR) for HFrEF per 1 standard deviation increase in β-OHB was 1.73 (95% confidence interval (CI): 1.17-2.56, P = .005) in age, BMI, type 2 diabetes, hypertension, myocardial infarction, smoking, alcohol consumption, total cholesterol, HDL-C, triglycerides, glucose, eGFR and UAE adjusted analysis. In men, in the same fully adjusted analysis, the HR was 1.14 (CI: 0.86-1.53, P = .36) (P < .01 for sex interaction). In N-terminal pro-brain natriuretic peptide (NT-proBNP)-stratified analysis, the age-adjusted association with HF was significant in women with higher NT-proBNP levels (P = .008).

CONCLUSIONS

This prospective study suggests that high plasma concentrations of β-OHB are associated with an increased risk of HFrEF, particularly in women. The mechanisms responsible for the sex differences of this association warrant further study.

High-throughput nuclear magnetic resonance measurement of citrate in serum and plasma in the clinical laboratory

Objectives

Despite reports highlighting citrate association with different diseases, serum citrate is scarcely used for diagnosis. Existing methods to quantify citrate are limited by their complexity and practicality of implementation. A simple and rapid NMR-based method to measure circulating citrate is described here, and its analytical performance evaluated.

Design

and Methods: Citrate was quantified from NMR spectra using a non-negative linear least squares deconvolution algorithm. The analytical characteristics of the assay were evaluated using CLSI guidelines. To determine if the assay has adequate sensitivity to measure clinically relevant concentrations of citrate, the assay was used to quantify citrate in apparently healthy adults (n ​= ​553), and in the general population (n ​= ​133,576).

Results

The LOQ for the assay was determined to be 1.48 ​mg/dL. Linearity was demonstrated over a wide range of concentrations (1.40–4.46 ​mg/dL). Coefficients of variation (%CV) for intra- and inter-assay precision ranged from 5.8–9.3 and 5.2–9.6%, respectively. Substances tested did not elicit interference with assay results. Specimen type comparison revealed <1% bias between serum and plasma samples, except for heparin plasma (3% bias). Stability was demonstrated up to 8 days at room temperature and longer at lower temperatures. In a cohort of apparently healthy adults, the reference interval was <1.48–2.97 ​mg/dL. Slightly higher values were observed in the general population.

Conclusions

The newly developed NMR-based assay exhibits analytical characteristics that allow the accurate quantification of clinically relevant citrate concentrations. The assay provides a simple and fast means to analyze samples for research and clinical studies.

Effects of Amount, Intensity, and Mode of Exercise Training on Insulin Resistance and Type 2 Diabetes Risk in the STRRIDE Randomized Trials

Background

Lipoprotein Insulin Resistance Index (LP-IR) and Diabetes Risk Index are novel spectroscopic multimarkers of insulin resistance and type 2 diabetes risk. As the Studies of a Targeted Risk Reduction Intervention through Defined Exercise (STRRIDE) randomized trials have previously demonstrated the ability of exercise training to improve traditional markers of insulin action, the aim of this study was to examine the effects of exercise amount, intensity, and mode on LP-IR and the Diabetes Risk Index.

Methods

A total of 503 adults with dyslipidemia [STRRIDE I (n = 194), STRRIDE AT/RT (n = 139)] or prediabetes [STRRIDE-PD (n = 170)] were randomized to control or one of 10 exercise interventions, ranging from doses of 8–23 kcal/kg/week; intensities of 50–75% V̇O_2peak; and durations of 6–8 months. Two groups included resistance training and one included dietary intervention (7% weight loss goal). Fasting plasma samples were obtained at baseline and 16–24 h after the final exercise bout. LP-IR, the Diabetes Risk Index, and concentrations of the branched chain amino acids valine and leucine were determined using nuclear magnetic resonance spectroscopy. LP-IR and the Diabetes Risk Index scores range from 0–100 and 1–100, respectively (greater scores indicate greater risk). Paired t-tests determined significance within groups (p < 0.05).

Results

After training, six exercise groups significantly improved LP-IR (ranging from −4.4 ± 8.2 to −12.4 ± 14.1), and four exercise groups significantly improved the Diabetes Risk Index (ranging from −2.8 ± 8.2 to −8.3 ± 10.4). The most beneficial interventions for both LP-IR and the Diabetes Risk Index were low amount/moderate intensity aerobic, aerobic plus resistance, and aerobic plus diet.

Summary

Multiple exercise interventions improved LP-IR and the Diabetes Risk Index. In those with dyslipidemia, adding resistance to aerobic training elicited a synergistic effect on insulin resistance and type 2 diabetes risk. In individuals with prediabetes, combining a dietary intervention and weight loss with aerobic training resulted in the most robust type 2 diabetes risk improvement.

The extended lipid panel assay: a clinically-deployed high-throughput nuclear magnetic resonance method for the simultaneous measurement of lipids and Apolipoprotein B

Background

Standard lipid panel assays employing chemical/enzymatic methods measure total cholesterol (TC), triglycerides (TG), and high-density lipoprotein cholesterol (HDL-C), from which are calculated estimates of low-density lipoprotein cholesterol (LDL-C). These lipid measures are used universally to guide management of atherosclerotic cardiovascular disease risk. Apolipoprotein B (apoB) is generally acknowledged to be superior to LDL-C for lipid-lowering therapeutic decision-making, but apoB immunoassays are performed relatively infrequently due to the added analytic cost. The aim of this study was to develop and validate the performance of a rapid, high-throughput, reagent-less assay producing an “Extended Lipid Panel” (ELP) that includes apoB, using the Vantera® nuclear magnetic resonance (NMR) analyzer platform already deployed clinically for lipoprotein particle and other testing.

Methods

Partial least squares regression models, using as input a defined region of proton NMR spectra of plasma or serum, were created to simultaneously quantify TC, TG, HDL-C, and apoB. Large training sets (n > ~ 1000) of patient sera analyzed independently for lipids and apoB by chemical methods were employed to ensure prediction models reflect the wide lipid compositional diversity of the population. The analytical performance of the NMR ELP assay was comprehensively evaluated.

Results

Excellent agreement was demonstrated between chemically-measured and ELP assay values of TC, TG, HDL-C and apoB with correlation coefficients ranging from 0.980 to 0.997. Within-run precision studies measured using low, medium, and high level serum pools gave coefficients of variation for the 4 analytes ranging from 1.0 to 3.8% for the low, 1.0 to 1.7% for the medium, and 0.9 to 1.3% for the high pools. Corresponding values for within-lab precision over 20 days were 1.4 to 3.6%, 1.2 to 2.3%, and 1.0 to 1.9%, respectively. Independent testing at three sites over 5 days produced highly consistent assay results. No major interference was observed from 38 endogenous or exogenous substances tested.

Conclusions

Extensive assay performance evaluations validate that the NMR ELP assay is efficient, robust, and substantially equivalent to standard chemistry assays for the clinical measurement of lipids and apoB. Routine reporting of apoB alongside standard lipid measures could facilitate more widespread utilization of apoB for clinical decision-making.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12944-020-01424-2.

Characterization of LP-Z Lipoprotein Particles and Quantification in Subjects with Liver Disease Using a Newly Developed NMR-Based Assay

Background: Lipoprotein particles with abnormal compositions, such as lipoprotein X (LP-X) and lipoprotein Z (LP-Z), have been described in cases of obstructive jaundice and cholestasis. The study objectives were to: (1) develop an NMR-based assay for quantification of plasma/serum LP-Z particles, (2) evaluate the assay performance, (3) isolate LP-Z particles and characterize them by lipidomic and proteomic analysis, and (4) quantify LP-Z in subjects with various liver diseases. Methods: Assay performance was assessed for linearity, sensitivity, and precision. Mass spectroscopy was used to characterize the protein and lipid content of isolated LP-Z particles. Results: The assay showed good linearity and precision (2.5–6.3%). Lipid analyses revealed that LP-Z particles exhibit lower cholesteryl esters and higher free cholesterol, bile acids, acylcarnitines, diacylglycerides, dihexosylceramides, lysophosphatidylcholines, phosphatidylcholines, triacylglycerides, and fatty acids than low-density lipoprotein (LDL) particles. A proteomic analysis revealed that LP-Z have one copy of apolipoprotein B per particle such as LDL, but less apolipoprotein (apo)A-I, apoC3, apoA-IV and apoC2 and more complement C3. LP-Z were not detected in healthy volunteers or subjects with primary biliary cholangitis, primary sclerosing cholangitis, autoimmune hepatitis, or type 2 diabetes. LP-Z were detected in some, but not all, subjects with hypertriglyceridemia, and were high in some subjects with alcoholic liver disease. Conclusions: LP-Z differ significantly in their lipid and protein content from LDL. Further studies are needed to fully understand the pathophysiological reason for the enhanced presence of LP-Z particles in patients with cholestasis and alcoholic liver disease.

Ketone Bodies Are Mildly Elevated in Subjects with Type 2 Diabetes Mellitus and Are Inversely Associated with Insulin Resistance as Measured by the Lipoprotein Insulin Resistance Index

Background: Quantifying mildly elevated ketone bodies is clinically and pathophysiologically relevant, especially in the context of disease states as well as for monitoring of various diets and exercise regimens. As an alternative assay for measuring ketone bodies in the clinical laboratory, a nuclear magnetic resonance (NMR) spectroscopy-based test was developed for quantification of β-hydroxybutyrate (β-HB), acetoacetate (AcAc) and acetone. Methods: The ketone body assay was evaluated for precision, linearity and stability and method comparisons were performed. In addition, plasma ketone bodies were measured in the Insulin Resistance Atherosclerosis Study (IRAS, n = 1198; 373 type 2 diabetes mellitus (T2DM) subjects). Results: β-HB and AcAc quantified using NMR and mass spectrometry and acetone quantified using NMR and gas chromatography/mass spectrometry were highly correlated (R² = 0.996, 0.994, and 0.994 for β-HB, AcAc, acetone, respectively). Coefficients of variation (%CVs) for intra- and inter-assay precision ranged from 1.3% to 9.3%, 3.1% to 7.7%, and 3.8% to 9.1%, for β-HB, AcAc and acetone, respectively. In the IRAS, ketone bodies were elevated in subjects with T2DM versus non-diabetic individuals (p = 0.011 to ≤0.001). Age- and sex-adjusted multivariable linear regression analysis revealed that total ketone bodies and β-HB were associated directly with free fatty acids (FFAs) and T2DM and inversely with triglycerides and insulin resistance as measured by the Lipoprotein Insulin Resistance Index. Conclusions: Concentrations of the three main ketone bodies can be determined by NMR with good clinical performance, are elevated in T2DM and are inversely associated with triglycerides and insulin resistance.

Lipoprotein insulin resistance index, a high-throughput measure of insulin resistance, is associated with incident type II diabetes mellitus in the Prevention of Renal and Vascular End-Stage Disease study

BACKGROUND

Early assessment of insulin resistance may be a way of identifying patients at risk as well as monitoring treatments that increase insulin sensitivity and reduce the risk of developing type II diabetes mellitus (T2DM).

OBJECTIVE

The objective of the study was to evaluate the ability of the Lipoprotein Insulin Resistance Index (LP-IR) to predict incident T2DM in a large cohort.

METHODS

LP-IR scores were calculated using 6 lipoprotein particle concentrations and sizes measured by nuclear magnetic resonance spectroscopy. In total, 5977 nondiabetic men and women were included. Cox proportional hazards regression was used to evaluate the association of LP-IR scores with incident T2DM.

RESULTS

LP-IR scores were closely associated with insulin resistance, assessed by homeostatic model assessment of insulin resistance (r = 0.51; P < .0001). During a median follow-up for 7.5 years, 278 new T2DM cases were ascertained. The Kaplan-Meier plot with log-rank test (P < .001) demonstrated that elevated LP-IR levels are associated with an increased T2DM risk. In analyses adjusted for age and sex, LP-IR was associated with incident T2DM; hazard ratio (HR) for the highest versus lowest quartile was 10.18 (95% confidence interval: 6.24-16.61), P < .0001. After adjustment for clinical risk factors, the HR was attenuated but remained significant (HR 3.02 [1.73-5.25], P < .0001). LP-IR scores added significantly to the performance of the Framingham Offspring prediction algorithm; C-index (95% confidence interval) for the Framingham Offspring score without and with LP-IR (0.863 [0.863-0.864] and 0.868 [0.867-0.86], P < .0001). Similar results were observed when LP-IR was analyzed as a categorical variable with a clinical cut-point of 68.

CONCLUSION

LP-IR may be a convenient way to assess insulin resistance and T2DM risk, as well as to monitor preventative treatments.

A Pathophysiologic Approach Combining Genetics and Insulin Resistance to Predict the Severity of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a complex disease dictated by both genetic and environmental factors. While insulin resistance (IR) is a key pathogenic driver, two common genetic variants in patatin‐like phospholipase domain containing 3 (PNPLA3) and transmembrane 6 superfamily member 2 (TM6SF2) also impart significant risk for disease progression. Traditional approaches to NAFLD risk stratification rely on biomarkers of fibrosis, an end result of disease progression. We hypothesized that by combining genetics and a novel measurement for IR we could predict disease progression by the NAFLD activity score (NAS) and histologic presence of significant fibrosis. A total of 177 patients with biopsy‐proven NAFLD were enrolled in this cross‐sectional study. PNPLA3 I148M and TM6SF2 E167K genotypes were determined by TaqMan assays. The enhanced lipoprotein IR index (eLP‐IR) was calculated from serum biomarkers using nuclear magnetic resonance (NMR) spectroscopy. Multivariate regression models were used to study the relationships between genetics, IR, and histologic features of NAFLD. In the multivariate analysis, the eLP‐IR was strongly associated with histologic features of NAFLD activity and hepatic fibrosis (P < 0.001 to 0.02) after adjustment for potential confounders. PNPLA3 148M and TM6SF2 E167K genotypes were significantly associated with steatosis (P = 0.003 and P = 0.02, respectively). A combination of the eLP‐IR and genetic score was able to predict the presence of NAS ≥3 with an area under the receiver operating characteristic curve (AUROC) of 0.74. Adding age to this model predicted stages 3‐4 liver fibrosis with an AUROC of 0.82. Conclusion: This proof‐of‐concept study supports the hypothesis that genetics and IR are major determinants of NAFLD severity and demonstrates the feasibility of a new risk stratification paradigm using exclusively pathogenic factors.

A novel NMR-based assay to measure circulating concentrations of branched-chain amino acids: Elevation in subjects with type 2 diabetes mellitus and association with carotid intima media thickness

OBJECTIVES

Plasma branched-chain amino acid (BCAA) levels, measured on nuclear magnetic resonance (NMR) metabolomics research platforms or by mass spectrometry, have been shown to be associated with type 2 diabetes mellitus (T2DM) and cardiovascular disease (CVD). We developed a new test for quantification of BCAA on a clinical NMR analyzer and used this test to determine the clinical correlates of BCAA in 2 independent cohorts.

DESIGN AND METHODS

The performance of the NMR-based BCAA assay was evaluated. A method comparison study was performed with mass spectrometry (LC-MS/MS). Plasma BCAA were measured in the Insulin Resistance Atherosclerosis Study (IRAS, n = 1209; 376 T2DM subjects) and in a Groningen cohort (n = 123; 67 T2DM subjects). In addition, carotid intima media thickness (cIMT) was measured successfully in 119 subjects from the Groningen cohort.

RESULTS

NMR-based BCAA assay results were linear over a range of concentrations. Coefficients of variation for inter- and intra-assay precision ranged from 1.8-6.0, 1.7-5.4, 4.4-9.1, and 8.8-21.3%, for total BCAA, valine, leucine, and isoleucine, respectively. BCAA quantified from the same samples using NMR and LC-MS/MS were highly correlated (R² = 0.97, 0.95 and 0.90 for valine, leucine and isoleucine). In both cohorts total and individual BCAA were elevated in T2DM (P = 0.01 to ≤0.001). Moreover, cIMT was associated with BCAA independent of age, sex, T2DM and metabolic syndrome (MetS) categorization or alternatively of individual MetS components.

CONCLUSIONS

BCAA levels, measured by NMR in the clinical laboratory, are elevated in T2DM and may be associated with cIMT, a proxy of subclinical atherosclerosis.

GlycA, a novel biomarker of systemic inflammation and cardiovascular disease risk

Background

GlycA is a novel spectroscopic marker of systemic inflammation with low intra-individual variability and other attributes favoring its clinical use in patients with chronic inflammatory and autoimmune diseases. GlycA is unique in its composite nature, reflecting both increased glycan complexity and circulating acute phase protein levels during local and systemic inflammation. Recent studies of GlycA from cross-sectional, observational and interventional studies have been highly informative, demonstrating that GlycA is elevated in acute and chronic inflammation, predicts death in healthy individuals and is associated with disease severity in patients with chronic inflammatory diseases such as rheumatoid arthritis, psoriasis and lupus. Moreover, following treatment with biological therapy in psoriasis, reduction in skin disease severity was accompanied by a decrease in GlycA levels and improvement in vascular inflammation.

Conclusions

Collectively, these findings suggest GlycA is a marker that tracks systemic inflammation and subclinical vascular inflammation. However, larger prospective studies and randomized trials are necessary in order to assess the impact of novel therapies on GlycA in patients with chronic inflammatory conditions, which may be concomitant with cardiovascular benefits.

Genome- and CD4+ T-cell methylome-wide association study of circulating trimethylamine-N-oxide in the Genetics of Lipid Lowering Drugs and Diet Network (GOLDN)

BACKGROUND

Trimethylamine-N-oxide (TMAO), an atherogenic metabolite species, has emerged as a possible new risk factor for cardiovascular disease. Animal studies have shown that circulating TMAO levels are regulated by genetic and environmental factors. However, large-scale human studies have failed to replicate the observed genetic associations, and epigenetic factors such as DNA methylation have never been examined in relation to TMAO levels.

METHODS AND RESULTS

We used data from the family-based Genetics of Lipid Lowering Drugs and Diet Network (GOLDN) to investigate the heritable determinants of plasma TMAO in humans. TMAO was not associated with other plasma markers of cardiovascular disease, e.g. lipids or inflammatory cytokines. We first estimated TMAO heritability at 27%, indicating a moderate genetic influence. We used 1000 Genomes imputed data (n=626) to estimate genome-wide associations with TMAO levels, adjusting for age, sex, family relationships, and study site. The genome-wide study yielded one significant hit at the genome-wide level, located in an intergenic region on chromosome 4. We subsequently quantified epigenome-wide DNA methylation using the Illumina Infinium array on CD4+ T-cells. We tested for association of methylation loci with circulating TMAO (n=847), adjusting for age, sex, family relationships, and study site as the genome-wide study plus principal components capturing CD4+ T-cell purity. Upon adjusting for multiple testing, none of the epigenetic findings were statistically significant.

CONCLUSIONS

Our findings contribute to the growing body of evidence suggesting that neither genetic nor epigenetic factors play a critical role in establishing circulating TMAO levels in humans.

Differences in GlycA and lipoprotein particle parameters may help distinguish acute kawasaki disease from other febrile illnesses in children

Background

Glycosylation patterns of serum proteins, such as α1-acid glycoprotein, are modified during an acute phase reaction. The response of acute Kawasaki disease (KD) patients to IVIG treatment has been linked to sialic acid levels on native IgG, suggesting that protein glycosylation patterns vary during the immune response in acute KD. Additionally, the distribution and function of lipoprotein particles are altered during inflammation. Therefore, the aim of this study was to explore the potential for GlycA, a marker of protein glycosylation, and the lipoprotein particle profile to distinguish pediatric patients with acute KD from those with other febrile illnesses.

Methods

Nuclear magnetic resonance was used to quantify GlycA and lipoprotein particle classes and subclasses in pediatric subjects with acute KD (n = 75), post-treatment subacute (n = 36) and convalescent (n = 63) KD, as well as febrile controls (n = 48), and age-similar healthy controls (n = 48).

Results

GlycA was elevated in acute KD subjects compared to febrile controls with bacterial or viral infections, IVIG-treated subacute and convalescent KD subjects, and healthy children (P <0.0001). Acute KD subjects had increased total and small low density lipoprotein particle numbers (LDL-P) (P <0.0001) and decreased total high density lipoprotein particle number (HDL-P) (P <0.0001) compared to febrile controls. Consequently, the ratio of LDL-P to HDL-P was higher in acute KD subjects than all groups tested (P <0.0001). While GlycA, CRP, erythrocyte sedimentation rate, LDL-P and LDL-P/HDL-P ratio were able to distinguish patients with KD from those with other febrile illnesses (AUC = 0.789–0.884), the combinations of GlycA and LDL-P (AUC = 0.909) or GlycA and the LDL-P/HDL-P ratio (AUC = 0.910) were best at discerning KD in patients 6–10 days after illness onset.

Conclusions

High levels of GlycA confirm enhanced protein glycosylation as part of the acute phase response in KD patients. When combined with common laboratory tests and clinical characteristics, GlycA and NMR-measured lipoprotein particle parameters may be useful for distinguishing acute KD from bacterial or viral illnesses in pediatric patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s12887-016-0688-5) contains supplementary material, which is available to authorized users.

High-density lipoprotein and inflammation in cardiovascular disease

Great advances are being made at the mechanistic level in the understanding of the structural and functional diversity of high-density lipoprotein (HDL). HDL particle subspecies of different sizes are now known to differ in the protein and lipid cargo they transport, conferring on them the ability to perform different functions that in aggregate would be expected to provide protection against the development of atherosclerosis and its downstream clinical consequences. Exacerbating what is already a very complex system is the finding that inflammation, via alteration of the proteomic and lipidomic composition of HDL subspecies, can modulate at least some of their functional activities. In contrast to the progress being made at the mechanistic level, HDL epidemiologic research has lagged behind, largely because the simple HDL biomarkers used (mainly just HDL cholesterol) lack the needed complexity. To address this deficiency, analyses will need to use multiple HDL subspecies and be conducted in such a way as to eliminate potential sources of confounding. To help account for the modulating influence of inflammation, effective use must also be made of inflammatory biomarkers including searching systematically for HDL-inflammation interactions. Using nuclear magnetic resonance (NMR)-measured HDL subclass data and a novel NMR-derived inflammatory biomarker, GlycA, we offer a case study example of the type of analytic approach considered necessary to advance HDL epidemiologic understanding.

GlycA: A Composite Nuclear Magnetic Resonance Biomarker of Systemic Inflammation

BACKGROUND

Nuclear magnetic resonance (NMR) spectra of serum obtained under quantitative conditions for lipoprotein particle analyses contain additional signals that could potentially serve as useful clinical biomarkers. One of these signals that we named GlycA originates from a subset of glycan N-acetylglucosamine residues on enzymatically glycosylated acute-phase proteins. We hypothesized that the amplitude of the GlycA signal might provide a unique and convenient measure of systemic inflammation.

METHODS

We developed a spectral deconvolution algorithm to quantify GlycA signal amplitudes from automated NMR LipoProfile® test spectra and assessed analytic precision and biological variability. Spectra of acute-phase glycoproteins and serum fractions were analyzed to probe the origins of the GlycA signal. GlycA concentrations obtained from archived NMR LipoProfile spectra of baseline plasma from 5537 participants in the Multi-Ethnic Study of Atherosclerosis (MESA) were used to assess associations with demographic and laboratory parameters including measures of inflammation.

RESULTS

Major acute-phase protein contributors to the serum GlycA signal are α1-acid glycoprotein, haptoglobin, α1-antitrypsin, α1-antichymotrypsin, and transferrin. GlycA concentrations were correlated with high-sensitivity C-reactive protein (hsCRP) (r = 0.56), fibrinogen (r = 0.46), and interleukin-6 (IL-6) (r = 0.35) (all P &lt; 0.0001). Analytic imprecision was low (intra- and interassay CVs 1.9% and 2.6%, respectively) and intraindividual variability, assessed weekly for 5 weeks in 23 healthy volunteers, was 4.3%, lower than for hsCRP (29.2%), cholesterol (5.7%), and triglycerides (18.0%).

CONCLUSIONS

GlycA is a unique inflammatory biomarker with analytic and clinical attributes that may complement or provide advantages over existing clinical markers of systemic inflammation.

HDL particle number measured on the Vantera®, the first clinical NMR analyzer

OBJECTIVES

Nuclear magnetic resonance (NMR) spectroscopy has been successfully applied to the measurement of high-density lipoprotein (HDL) particles, providing particle concentrations for total HDL particle number (HDL-P), HDL subclasses (small, medium, large) and weighted, average HDL size for many years. Key clinical studies have demonstrated that NMR-measured HDL-P was more strongly associated with measures of coronary artery disease and a better predictor of incident cardiovascular disease (CVD) events than HDL-cholesterol (HDL-C). Recently, an NMR-based clinical analyzer, the Vantera(®), was developed to allow lipoprotein measurements to be performed in the routine, clinical laboratory setting. The aim of this study was to evaluate and report the performance characteristics for HDL-P quantified on the Vantera(®) Clinical Analyzer.

DESIGN AND METHODS

Assay performance was evaluated according to Clinical and Laboratory Standards Institute (CLSI) guidelines. In order to ensure that quantification of HDL-P on the Vantera(®) Clinical Analyzer was similar to the well-characterized HDL-P assay on the NMR profiler, a method comparison was performed.

RESULTS

The within-run and within-lab imprecision ranged from 2.0% to 3.9%. Linearity was established within the range of 10.0 to 65.0 μmol/L. The reference intervals were different between men (22.0 to 46.0 μmol/L) and women (26.7 to 52.9 μmol/L). HDL-P concentrations between two NMR platforms, Vantera(®) Clinical Analyzer and NMR Profiler, demonstrated excellent correlation (R(2) = 0.98).

CONCLUSIONS

The performance characteristics, as well as the primary tube sampling procedure for specimen analysis on the Vantera(®) Clinical Analyzer, suggest that the HDL-P assay is suitable for routine clinical applications.

NMR measurement of LDL particle number using the Vantera Clinical Analyzer

BACKGROUND

The Vantera Clinical Analyzer was developed to enable fully-automated, high-throughput nuclear magnetic resonance (NMR) spectroscopy measurements in a clinical laboratory setting. NMR-measured low-density lipoprotein particle number (LDL-P) has been shown to be more strongly associated with cardiovascular disease outcomes than LDL cholesterol (LDL-C) in individuals for whom these alternate measures of LDL are discordant.

OBJECTIVE

The aim of this study was to assess the analytical performance of the LDL-P assay on the Vantera Clinical Analyzer as per Clinical Laboratory Standards Institute (CLSI) guidelines.

RESULTS

Sensitivity and linearity were established within the range of 300-3500 nmol/L. For serum pools containing low, medium and high levels of LDL-P, the inter-assay, intra-assay precision and repeatability gave coefficients of variation (CVs) between 2.6 and 5.8%. The reference interval was determined to be 457-2282 nmol/L and the assay was compatible with multiple specimen collection tubes. Of 30 substances tested, only 2 exhibited the potential for assay interference. Moreover, the LDL-P results from samples run on two NMR platforms, Vantera Clinical Analyzer and NMR Profiler, showed excellent correlation (R(2)=0.96).

CONCLUSIONS

The performance characteristics suggest that the LDL-P assay is suitable for routine testing in the clinical laboratory on the Vantera Clinical Analyzer, the first automated NMR platform that supports NMR-based clinical assays.

Lipoprotein insulin resistance index: a lipoprotein particle-derived measure of insulin resistance

Abstract Background: Lipoprotein particle sizes and concentrations are characteristically altered in patients with insulin resistance (IR) or type 2 diabetes mellitus (T2DM). This study assessed the ability of an IR score, based on nuclear magnetic resonance (NMR)-derived lipoprotein information, to detect IR in otherwise healthy individuals.

METHODS

Lipoprotein subclass and size information were evaluated for strength of association with IR, as measured by homeostasis model assessment of insulin resistance (HOMA-IR) in the Multi-Ethnic Study of Atherosclerosis (MESA). To increase the likelihood of identifying subjects with IR, six lipoprotein measures were combined into a single algorithm. The resulting assay [Lipoprotein Insulin Resistance Index (LP-IR)] was developed using HOMA-IR in 4972 nondiabetic subjects from MESA and verified independently using glucose disposal rates (GDRs) measured during hyperinsulinemic-euglycemic clamps in 56 insulin-sensitive, 46 insulin-resistant, and 46 untreated subjects with T2DM.

RESULTS

LP-IR exhibited stronger associations with HOMA-IR (r=0.51) and GDR (r=-0.53) than each of the individual lipoprotein parameters as well as the triglycerides/high-density lipoprotein cholesterol (TGs/HDL-C) ratio (r=0.41 and -0.44, respectively). In MESA, associations between the LP-IR score and HOMA-IR were strong in men (r=0.51), women (r=0.52), European Americans (r=0.58), African Americans (r=0.48), Chinese Americans (r=0.49), and Hispanic Americans (r=0.45). When LP-IR was categorized by HOMA-IR and either body mass index (BMI) or fasting plasma glucose (FPG), subgroups were revealed whose LP-IR scores were high (≥ 50), despite having normal BMIs (<24 kg/m(2)) or FPG (<100 mg/dL).

CONCLUSIONS

LP-IR scores had strong associations with multiple measures, HOMA-IR, and GDR, the former being more reflective of hepatic and the latter of peripheral insulin sensitivity, and may represent a simple means to identify individuals with IR.

Clinical implications of discordance between low-density lipoprotein cholesterol and particle number

BACKGROUND

The amount of cholesterol per low-density lipoprotein (LDL) particle is variable and related in part to particle size, with smaller particles carrying less cholesterol. This variability causes concentrations of LDL cholesterol (LDL-C) and LDL particles (LDL-P) to be discordant in many individuals.

METHODS

LDL-P measured by nuclear magnetic resonance spectroscopy, calculated LDL-C, and carotid intima-media thickness (IMT) were assessed at baseline in the Multi-Ethnic Study of Atherosclerosis, a community-based cohort of 6814 persons free of clinical cardiovascular disease (CVD) at entry and followed for CVD events (n = 319 during 5.5-year follow-up). Discordance, defined as values of LDL-P and LDL-C differing by ≥ 12 percentile units to give equal-sized concordant and discordant subgroups, was related to CVD events and to carotid IMT in models predicting outcomes for a 1 SD difference in LDL-C or LDL-P, adjusted for age, gender, and race.

RESULTS

LDL-C and LDL-P were associated with incident CVD overall: hazard ratios (HR 1.20, 95% CI [CI] 1.08-1.34; and 1.32, 95% CI 1.19-1.47, respectively, but for those with discordant levels, only LDL-P was associated with incident CVD (HR 1.45, 95% CI 1.19-1.78; LDL-C HR 1.07, 95% CI 0.88-1.30). IMT also tracked with LDL-P rather than LDL-C, ie, adjusted mean IMT of 958, 932, and 917 microm in the LDL-P > LDL-C discordant, concordant, and LDL-P < LDL-C discordant subgroups, respectively, with the difference persisting after adjustment for LDL-C (P = .002) but not LDL-P (P = .60).

CONCLUSIONS

For individuals with discordant LDL-C and LDL-P levels, the LDL-attributable atherosclerotic risk is better indicated by LDL-P.

Low-density lipoprotein and high-density lipoprotein particle subclasses predict coronary events and are favorably changed by gemfibrozil therapy in the Veterans Affairs High-Density Lipoprotein Intervention Trial

BACKGROUND

Changes in conventional lipid risk factors with gemfibrozil treatment only partially explain the reductions in coronary heart disease (CHD) events experienced by men in the Veterans Affairs High-Density Lipoprotein Intervention Trial (VA-HIT). We examined whether measurement of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) particle subclasses provides additional information relative to CHD risk reduction.

METHODS AND RESULTS

This is a prospective nested case-control study of 364 men with a new CHD event (nonfatal myocardial infarction or cardiac death) during a 5.1-year (median) follow-up and 697 age-matched controls. Nuclear magnetic resonance (NMR) spectroscopy was used to quantify levels of LDL and HDL particle subclasses and mean particle sizes in plasma obtained at baseline and after 7 months of treatment with gemfibrozil or placebo. Odds ratios for a 1-SD increment of each lipoprotein variable were calculated with adjusted logistic regression models. Gemfibrozil treatment increased LDL size and lowered numbers of LDL particles (-5%) while raising numbers of HDL particles (10%) and small HDL subclass particles (21%). Concentrations of these LDL and HDL particles achieved with gemfibrozil were significant, independent predictors of new CHD events. For total LDL and HDL particles, odds ratios predicting CHD benefit were 1.28 (95% CI, 1.12 to 1.47) and 0.71 (95% CI, 0.61 to 0.81), respectively. Mean LDL and HDL particle sizes were not associated with CHD events.

CONCLUSIONS

The effects of gemfibrozil on NMR-measured LDL and HDL particle subclasses, which are not reflected by conventional lipoprotein cholesterol measures, help to explain the demonstrated benefit of this therapy in patients with low HDL cholesterol.

Sex and age differences in lipoprotein subclasses measured by nuclear magnetic resonance spectroscopy: the Framingham Study

BACKGROUND

The sex differential in coronary heart disease (CHD) risk, which is not explained by male/female differences in lipid and lipoprotein concentrations, narrows with age. We examined whether this differential CHD risk might, in part, be attributable to the sizes of lipoprotein particles or concentrations of lipoprotein subclasses.

METHODS

We analyzed frozen plasma samples from 1574 men and 1692 women from exam cycle 4 (1988-1990) of the Framingham Offspring Study. Nuclear magnetic resonance (NMR) spectroscopy was used to determine the subclass concentrations and mean sizes of VLDL, LDL, and HDL particles. Concentrations of lipids and apolipoproteins were measured by standard chemical methods.

RESULTS

In addition to the expected sex differences in concentrations of triglycerides, LDL-cholesterol, and HDL-cholesterol, women also had a lower-risk subclass profile consisting of larger LDL (0.4 nm) and HDL (0.5 nm) particles. The sex difference was most pronounced for HDL, with women having a twofold higher (8 vs 4 micromol/L) concentration of large HDL particles than men. Furthermore, similar to the narrowing of the sex difference in CHD risk with age, the observed male/female difference in HDL particle size also decreased with age. Although lipoprotein particle sizes were highly correlated with lipid and lipoprotein concentrations, the sex differences in the mean sizes of lipoprotein particles persisted (P <0.001) even after adjustment for lipid and lipoprotein concentrations.

CONCLUSIONS

Women have a less atherogenic subclass profile than men, even after accounting for differences in lipid concentrations.

Effects of pravastatin treatment on lipoprotein subclass profiles and particle size in the PLAC-I trial

Lipoprotein subclass analyses may facilitate coronary heart disease (CHD) risk stratification and provide insight into the cardioprotective benefits of statins (3-hydroxymethylglutaryl-coenzyme A reductase inhibitors). This study evaluated the influence of pravastatin on lipoprotein subclass profiles to determine whether subjects with predominantly large LDL (LDL size >20.5 nm) or small LDL (LDL size < or =20.5 nm) at baseline differ in responsiveness to drug treatment. Frozen plasma specimens were analyzed from a subset of participants in the Pravastatin Limitation of Atherosclerosis in the Coronaries (PLAC-I) trial at baseline and after treatment for 6 months with pravastatin (n=154) or placebo (n=138). Lipids were measured by standard chemical methods and lipoprotein subclasses by nuclear magnetic resonance (NMR) spectroscopy. Pravastatin-induced changes in lipid levels were similar in subjects with large or small LDL at baseline. Levels of the most abundant LDL subclass were preferentially lowered by pravastatin, resulting in an increase in average LDL size for those with a predominance of small LDL. High-risk CHD subjects with small LDL particles gain at least as much pharmacological benefit from pravastatin as those with large LDL, as evidenced by reductions in the numbers of total and small LDL particles, and increases in average LDL and HDL particle size.