Plasma lipoprotein(a) distribution in the Framingham Offspring Study as determined with a commercially available immunoturbidimetric assay

Lipid Parameters and Proprotein Convertase Subtilisin/Kexin Type 9 in Healthy Lebanese Adults

Background: High levels of non-HDL cholesterol (non-HDL-C), triglycerides (TG), lipoprotein (a) (Lp(a)), and Proprotein convertase subtilisin/kexin type 9 (PCSK9) as well as low levels of HDL-C are strongly associated with cardiovascular disease (CVD). Our study aims to estimate the prevalence of dyslipidemia and high Lp(a) in the Lebanese population and to study the relationship of these variables with gender, age, body mass index (BMI), and PCSK9. Methods: This cross-sectional study was carried out on a sample of healthy volunteers aged 18 to 65. Blood samples were drawn from volunteers for total cholesterol (TC), HDL-C, TG, PCSK9, and Lp(a) measurements. Non-HDL-C was calculated by subtracting HDL-C from TC. Results: In total, 303 volunteer subjects with an average age of 38.9 years were included in the study. Respectively, 44%, 29.8%, and 44% of men had high non-HDL-C and TG with low HDL-C versus 23.5%, 8%, and 37% in women. Non-HDL-C and TG were significantly higher in men than in women, while the reverse was observed for HDL-C (p < 0.0001 for the three comparisons). Non-HDL-C and TG were significantly correlated with age and BMI (p< 0.0001 for all correlations), while HDL-C was inversely correlated with BMI (p < 0.0001) but not with age. Abnormal Lp(a) levels (≥75 nmol/L) were found in 19.1% of the population, predominantly in women (24.1% versus 13.4% in men, p = 0.004). The median PCSK9 and its interquartile was 300 (254−382) ng/L with no gender difference (p = 0.18). None of the following factors: gender, age, BMI, non-HDL-C, HDL-C, or TG, were independently associated with Lp(a), while PCSK9 was significantly correlated with age, non-HDL-C, and TG in both men and women and inversely correlated with HDL-C in men. Dyslipidemia is very common in the Lebanese population and is associated with age, high BMI, and male sex. Lp(a) is higher in women without any correlation with the lipid profile, whereas PCSK9 is associated with non-HDL-C and TG. Further studies are needed to evaluate the potential role of Lp(a) and PCSK9 in predicting CVD in healthy populations.

Lipoprotein(a) Concentration and Risks of Cardiovascular Disease and Diabetes

BACKGROUND

Lipoprotein(a) [Lp(a)] is a causal risk factor for cardiovascular diseases that has no established therapy. The attribute of Lp(a) that affects cardiovascular risk is not established. Low levels of Lp(a) have been associated with type 2 diabetes (T2D).

OBJECTIVES

This study investigated whether cardiovascular risk is conferred by Lp(a) molar concentration or apolipoprotein(a) [apo(a)] size, and whether the relationship between Lp(a) and T2D risk is causal.

METHODS

This was a case-control study of 143,087 Icelanders with genetic information, including 17,715 with coronary artery disease (CAD) and 8,734 with T2D. This study used measured and genetically imputed Lp(a) molar concentration, kringle IV type 2 (KIV-2) repeats (which determine apo(a) size), and a splice variant in LPA associated with small apo(a) but low Lp(a) molar concentration to disentangle the relationship between Lp(a) and cardiovascular risk. Loss-of-function homozygotes and other subjects genetically predicted to have low Lp(a) levels were evaluated to assess the relationship between Lp(a) and T2D.

RESULTS

Lp(a) molar concentration was associated dose-dependently with CAD risk, peripheral artery disease, aortic valve stenosis, heart failure, and lifespan. Lp(a) molar concentration fully explained the Lp(a) association with CAD, and there was no residual association with apo(a) size. Homozygous carriers of loss-of-function mutations had little or no Lp(a) and increased the risk of T2D.

CONCLUSIONS

Molar concentration is the attribute of Lp(a) that affects risk of cardiovascular diseases. Low Lp(a) concentration (bottom 10%) increases T2D risk. Pharmacologic reduction of Lp(a) concentration in the 20% of individuals with the greatest concentration down to the population median is predicted to decrease CAD risk without increasing T2D risk.

PCSK9 Association With Lipoprotein(a)

RATIONALE

Lipoprotein(a) [Lp(a)] is a highly atherogenic low-density lipoprotein-like particle characterized by the presence of apoprotein(a) [apo(a)] bound to apolipoprotein B. Proprotein convertase subtilisin/kexin type 9 (PCSK9) selectively binds low-density lipoprotein; we hypothesized that it can also be associated with Lp(a) in plasma.

OBJECTIVE

Characterize the association of PCSK9 and Lp(a) in 39 subjects with high Lp(a) levels (range 39-320 mg/dL) and in transgenic mice expressing either human apo(a) only or human Lp(a) (via coexpression of human apo(a) and human apolipoprotein B).

METHODS AND RESULTS

We show that PCSK9 is physically associated with Lp(a) in vivo using 3 different approaches: (1) analysis of Lp(a) fractions isolated by ultracentrifugation; (2) immunoprecipitation of plasma using antibodies to PCSK9 and immunodetection of apo(a); (3) ELISA quantification of Lp(a)-associated PCSK9. Plasma PCSK9 levels correlated with Lp(a) levels, but not with the number of kringle IV-2 repeats. PCSK9 did not bind to apo(a) only, and the association of PCSK9 with Lp(a) was not affected by the loss of the apo(a) region responsible for binding oxidized phospholipids. Preferential association of PCSK9 with Lp(a) versus low-density lipoprotein (1.7-fold increase) was seen in subjects with high Lp(a) and normal low-density lipoprotein. Finally, Lp(a)-associated PCSK9 levels directly correlated with plasma Lp(a) levels but not with total plasma PCSK9 levels.

CONCLUSIONS

Our results show, for the first time, that plasma PCSK9 is found in association with Lp(a) particles in humans with high Lp(a) levels and in mice carrying human Lp(a). Lp(a)-bound PCSK9 may be pursued as a biomarker for cardiovascular risk.

Significant associations between lipoprotein(a) and corrected apolipoprotein B-100 levels in African-Americans

OBJECTIVES

Lipoprotein(a), Lp(a), represents an apolipoprotein (apo) B-carrying lipoprotein, yet the relationship between Lp(a) and apoB levels has not been fully explored.

METHODS

We addressed the relationship between Lp(a) and apoB-containing lipoprotein levels in 336 Caucasians and 224 African-Americans. Our approach takes unique molecular properties of Lp(a) as well as contribution of Lp(a) to the levels of these lipoproteins into account.

RESULTS

Levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), apoB and apoB/apoA-1 did not differ across ethnicity. African-Americans had higher levels of Lp(a) and high-density lipoprotein cholesterol and lower triglyceride levels compared to Caucasians. Lp(a) levels were correlated with levels of TC (p < 0.005), LDL-C (p < 0.001), apoB (p < 0.05) or apoB/apoA-1 (p < 0.05) in both ethnic groups. These associations remained significant only in African-Americans after adjustments for the contribution of Lp(a)-cholesterol or Lp(a)-apoB. Furthermore, taking Lp(a)-apoB into account, allele-specific apo(a) levels were significantly associated with apoB levels and the apoB/apoA-1 ratio in African-Americans. The latter associations in African-Americans remained significant for allele-specific apo(a) levels for smaller apo(a) sizes (<26 K4 repeats), after controlling for the effects of age, sex, and BMI.

CONCLUSIONS

Although TC, LDL-C, and apoB levels were comparable between African-Americans and Caucasians, the associations of these parameters with Lp(a) and allele specific apo(a) levels differed between these two ethnic groups. In African-Americans, apoB and apoB/apoA-1 remained consistently and positively associated with both Lp(a) and allele-specific apo(a) levels after adjustments for the contribution of Lp(a)-apoB. The findings suggest an interethnic difference with a closer relationship between Lp(a) and apoB among African-Americans.

Prehypertension in dyslipidemic individuals; relationship to metabolic parameters and intima-media thickness

INTRODUCTION

Like hypertension, prehypertension is associated with cardiovascular disease.

AIMS

The aim of this study was to evaluate: a) the prevalence of prehypertension/hypertension in individuals with various dyslipidemic phenotypes; b) the relation between blood pressure (BP) and other risk factors for atherosclerosis; c) atherogenic potential of prehypertension by the assessment of intima-media thickness of the arteria carotis communis (IMT).

METHODS

667 clinically asymptomatic subjects were divided into four dyslipidemic phenotypes (DLP) according to apolipoprotein B (apoB) and triglycerides (TG): DLP1 (n=198, normo-apoB/normo-TG), DLP2 (n=179, normo-apoB/hyper-TG), DLP3 (n=87, hyper-apoB/normo-TG), DLP4 (n=203, hyper-apoB/hyper-TG). DLP1 served as a control group.

RESULTS

There was significantly higher prevalence of prehypertension and hypertension in subjects with dyslipidemia (DLP2 43.0%, 41.3%; DLP3 42.5%, 29.9%; DLP4 42.4%, 47.8%) than in normolipidemic individuals (DLP1 32.8%, 20.2%). Systolic and diastolic blood pressure (SBP + DBP) correlated with age, total cholesterol, TG, non-HDL-cholesterol, body mass index and waist circumference; SBP additionally with C-peptide, fasting glycemia; DBP additionally with apoB, homeostasis model assessment (HOMA) and plasminogen activator inhibitor-1. The IMT of hypertensive and of prehypertensive subjects was higher than that of subjects with normal BP in all DLPs.

CONCLUSIONS

The prevalence of prehypertension was higher in all dyslipidemic patients. The common prevalence of prehypertension/hypertension was highest in the hypertriglyceridemic subjects. Prehypertensive and hypertensive patients had higher IMT than normotensive individuals in all DLPs.

Cord blood ASP is predicted by maternal lipids and correlates with fetal birth weight

BACKGROUND

The acylation stimulating protein (ASP) is a potent lipogenic adipokine that correlates with postprandial triglyceride (TG) clearance and is linked to the pathophysiology of obesity and related disorders.

OBJECTIVE

To investigate ASP levels in cord blood and its relation to maternal and cord blood lipid parameters and fetal birth weight.

METHODS AND PROCEDURES

Thirty nondiabetic pregnant women, their newborns, and thirty-three nonpregnant controls were included in this study. Fasting maternal and cord blood ASP, TGs, nonesterified fatty acids (NEFAs), cholesterol, glucose levels, in addition to maternal BMI and fetal birth weight were measured.

RESULTS

No significant difference was found between cord blood ASP (16.3 +/- 0.96 nmol/l) and ASP levels in the adult controls (15.7 +/- 1.0 nmol/l). Cord blood ASP, however, was lower than maternal plasma ASP levels (25.4 +/- 1.6 nmol/l, P < 0.001). Yet, lipid levels in cord blood, particularly TGs were markedly decreased compared to control and maternal TG levels (threefold and 7.4-fold, P < 0.001 respectively). Maternal TGs significantly correlated with fetal birth weight (r = 0.54, P = 0.002). Multiple regression analysis showed that maternal TGs (beta = 0.57, P = 0.01) and NEFAs (beta = 0.43, P = 0.024) predicted 45% variation in cord blood ASP levels, independent of all measured maternal and cord blood parameters. Cord blood ASP showed a positive correlation with fetal birth weight (r = 0.524, P = 0.037) in neonates above average fetal birth weight of the studied population.

DISCUSSION

This is the first study investigating ASP in cord blood. We suggest that maternal hypertriglyceridemia is associated with increased fetal ASP production, thus enhancing fetal fat storage independent of maternal glucose variations in nondiabetic women.

Increased plasma acylation-stimulating protein correlates with hyperlipidemia at late gestation

OBJECTIVES

Obesity is often associated with negative consequences, including hyperlipidemia and insulin resistance. Weight gain during pregnancy is also associated with major lipid alterations. Fat storage is enhanced in early pregnancy. At late gestation, hyperlipidemia becomes a major manifestation. The acylation-stimulating protein (ASP) is a potent lipogenic adipocytokine that correlates with postprandial triglyceride (TG) clearance in vivo and has been linked to hyperlipidemic disorders. The role of ASP during a normal pregnancy is unknown. The objective of this study was to investigate plasma ASP levels in correlation with the lipid profile during late gestation.

RESEARCH METHODS AND PROCEDURES

Seventy healthy women at late gestation and 60 non-pregnant controls of similar age and prepregnancy BMI were included in a cross-sectional study. Fasting plasma ASP levels and the lipid profile of all of the women were measured.

RESULTS

ASP levels were markedly elevated in the pregnant women (66%, p < 0.001). ASP levels correlated strongly with the elevated levels of TGs (r = 0.608, p < 0.000), apolipoprotein B (0.519, p < 0.000), and low-density lipoprotein-cholesterol (r = 0.405, p < 0.000). Multivariate analysis adjusting for BMI and age showed that changes in ASP levels at late gestation were best predicted by TG and apoB levels, accounting for 53.8% of plasma ASP variation. For the controls, ASP strongly correlated with BMI, which was the only significant predictor of ASP levels.

DISCUSSION

Gestational hormone alterations during pregnancy may affect ASP function as a lipogenic factor. Increased plasma ASP levels at late gestation and their strong correlation with parameters reflecting very low-density lipoprotein accumulation are suggestive of ASP resistance, which may further contribute to the hyperlipidemic state, shifting energy in the form of TGs to the rapidly growing fetus.

Coagulation and inflammatory markers in Alzheimer's and vascular dementia

Alzheimer's disease is classified as a degenerative dementia while vascular dementia is known to be associated with atherothrombosis and classical vascular risk factors. However, over the last decade, there is increasing evidence of the role of haemostatic factors and inflammatory mechanisms in the pathogenesis of Alzheimer's disease. Serum markers of hypercoagulability and markers of inflammation could lead to thrombosis, accelerated atherogenesis and resulting dementia of both Alzheimer's and vascular dementia. In this case control study, we studied these serum markers of coagulation and inflammation in patients suffering from dementia.

Fasting acylation-stimulating protein is predictive of postprandial triglyceride clearance

Postprandial plasma triglyceride (ppTG) and NEFA clearance were stratified by plasma acylation-stimulating protein (ASP) and gender to determine the contribution of fasting ASP in a normal population (70 men; 71 women). In the highest ASP tertile only, ASP decreased over 8 h (90 +/- 9.7 nM to 70 +/- 5.9 nM, P<0.05 males; 61.9 +/- 4.0 nM to 45.6 +/- 6.2 nM, P<0.01 females). Fasting ASP correlated positively with ppTG response. ppTG (P<0.0001, 2-way ANOVA, both genders) and NEFA levels progressively increased from lowest to highest ASP tertile, with the greatest differences in males. By stepwise multiple regression, the best prediction of ppTG was: (fasting ASP + apolipoprotein B + insulin + TG; r=0.806) for men and (fasting ASP + total cholesterol; r=0.574) for women. Leptin, body mass index, and other fasting variables did not improve the prediction. Thus, in men and women, ASP significantly predicted ppTG and NEFA clearance and, based on lower ASP, women may be more ASP sensitive than men. Plasma ASP may be useful as a fasting variable that will provide additional information regarding ppTG and NEFA clearance.

Reference intervals for serum apolipoproteins A-I, A-II, B, C-II, C-III, and E in healthy Japanese determined with a commercial immunoturbidimetric assay and effects of sex, age, smoking, drinking, and Lp(a) level

BACKGROUND

Apolipoproteins, which are contained in lipoprotein particles, play important roles in the transport of lipids.

METHODS

Serum levels of apolipoproteins (apo) A-I, A-II, B, C-II, C-III, and E were determined by immunoturbidimetry in a healthy Japanese study population (1018 men and 1167 women, age 20-69 years) to establish reference intervals.

RESULTS

Among the 2185 subjects examined, the mean serum value for apoA-I was 1.42 +/- 0.20 g/l, for apoA-II was 0.30 +/- 0.05 g/l, for apoB was 0.87 +/- 0.18 g/l, for apoC-II was 29 +/- 13 mg/l, for apoC-III was 75 +/- 20 mg/l, and for apoE was 36 +/- 9 mg/l. A sex difference was detected in the mean serum concentrations of all six apolipoproteins. Alcohol consumption and cigarette use had a slight effect on serum apolipoprotein concentrations. Age effects were observed among women in apoB, apoC-II, and apoC-III concentrations. Moreover, individuals with elevated serum lipoprotein (a) [Lp(a), >300 mg/l] also displayed increased serum apoB and apoC-II levels and an increased apoB/apoA-I ratio.

CONCLUSION

The reference intervals for apolipoproteins in Japanese adults that we established, using commercially available reagents for automated analyzers, will be helpful for assessing risk of coronary heart disease and pathological conditions of patients with hyperlipidemia. We recommend use of these reference intervals for the clinical interpretation of serum apolipoprotein concentrations.

Differential influence of LDL cholesterol and triglycerides on lipoprotein(a) concentrations in diabetic patients

OBJECTIVE

To evaluate the relationship between plasma lipid profiles and lipoprotein(a) [Lp(a)] concentrations in diabetic patients, taking into account the Lp(a) phenotype.

RESEARCH DESIGN AND METHODS

We included 191 consecutive diabetic outpatients (69 type 1 and 122 type 2 diabetic patients) in a cross-sectional study Serum Lp(a) was determined by enzyme-linked immunosorbent assay, and Lp(a) phenotypes were assessed by SDS-PAGE followed by immunoblotting. The statistical methods included a stepwise multiple regression analysis using the Lp(a) serum concentration as the dependent variable. The lipid profile consisted of total cholesterol, HDL cholesterol, LDL cholesterol, corrected LDL cholesterol, triglycerides, and apolipoproteins AI and B.

RESULTS

In the multiple regression analysis, LDL cholesterol (positively) and triglycerides (negatively) were independently related to the Lp(a) concentration, and they explained the 6.6 and 7.8% of the Lp(a) variation, respectively. After correcting LDL cholesterol, the two variables explained 3.8 and 6.4% of the Lp(a) variation, respectively. In addition, we observed that serum Lp(a) concentrations were significantly lower in patients with type IV hyperlipidemia (mean 1.0 mg/dl [range 0.5-17], n = 16) than in normolipidemic patients (6.5 mg/dl [0.5-33.5], n = 117) and in type II hyperlipidemic patients (IIa 15.5 mg/dl [3.5-75], n = 13; IIb 9 mg/dl [1-80], n = 45); P < 0.001 by analysis of variance.

CONCLUSIONS

Lp(a) concentrations were directly correlated with LDL cholesterol and negatively correlated with triglyceride levels in diabetic patients. Therefore, our results suggest that the treatment of diabetic dyslipemia may indirectly affect Lp(a) concentrations.

Quantitative determination of cholesterol in lipoprotein fractions by electrophoresis

The Helena REP cholesterol profile system (Helena Laboratories, Beaumont, TX) separates VLDL, LDL, HDL and Lp(a) by agarose gel electrophoresis, and quantitates cholesterol by enzymatic staining and densitometry. We compared results by electrophoresis to combined ultracentrifugation/precipitation (beta-quantification, BQ) for VLDL, LDL, and HDL cholesterol and to immunonephelometry for Lp(a) mass (Behring Diagnostics, Westwood, MA) in serum from 64 patients with a variety of lipid disorders. There was good agreement between methods, with a mean bias of -0.19 (-7.3), 0.09 (3.5), and 0.09 (3.4) mmol/l (mg/dl) for VLDL, HDL, and LDL cholesterol for electrophoresis vs. BQ. These differences were significant for HDL and VLDL cholesterol (P < 0.001), but not for LDL cholesterol measurement (P > 0.05). There was also good correlation between methods with coefficients of 0.83, 0.92, 0.91, and 0.97 for VLDL, HDL, Lp(a), and LDL, respectively. Our data indicate that this method can accurately and precisely measure LDL cholesterol directly in fresh serum from patients with a wide range of triglyceride values. However, HDL cholesterol measurement did not meet NCEP guidelines for precision and accuracy. Also, the poor resolution of VLDL and LDL in some specimens is a concern.

Family history of early cardiovascular disease in children with moderate to severe hypercholesterolemia: relationship to lipoprotein (a) and low-density lipoprotein cholesterol levels

Lipoprotein (a) (Lp(a)) is an established cardiovascular risk factor in adults. We sought to evaluate whether raised Lp(a) levels were predictive of a family history of early cardiovascular disease (CVD) in children already at increased risk for premature atherosclerosis because of elevated low-density lipoprotein (LDL) cholesterol levels. Lp(a) and serum lipid levels were measured in 69 children and offspring with established moderate to severe hypercholesterolemia (serum cholesterol > 170 mg/dL) who were aged 10.7 +/- 4.3 years (range 1.5 to 21 years) and had been referred to a pediatric lipid center. The children represented families with a positive (n = 27) or negative (n = 42) history for premature CVD (<55 years of age in parent or grandparent). In all children, Lp(a) levels ranged from 1 to 140 mg/dL, with a median of 29 mg/dL. Mean total cholesterol, LDL cholesterol, and high-density lipoprotein (HDL) cholesterol levels were 234 mg/dL, 166 mg/dL, and 45 mg/dL, respectively. There was no difference in median Lp(a) levels between the children with a positive family history and those with a negative family history (29.9 mg/dL vs 29.0 mg/dL, respectively). In contrast, children with a positive family history showed significantly higher LDL cholesterol levels (186 +/- 61 mg/dL vs 153 +/- 52 mg/dL, P = .02). Thus, in this group of hypercholesterolemic children, LDL cholesterol but not Lp(a) levels were associated with a family history of premature CVD. Further studies are needed to identify additional specific risk factors associated with the development of CVD in this population.

Biochemical risk factors and patient's outcome: the case of lipoprotein(a)

Lipoprotein(a) (Lp(a)) is a genetic variant of low density lipoproteins and consists of the covalent association of the unique and enigmatic apolipoprotein(a) to apoliprotein B100. Despite the high degree of homology with low density lipoproteins, Lp(a) displays distinctive physico-chemical properties, function and metabolism. The present article reviews the main biological and clinical evidences about the association between raised concentration of Lp(a) and atherothrombotic diseases and provides tentative guidelines to improve the clinical usefulness of Lp(a) measurements.

Mechanized lipoprotein(a) assay as a marker for coronary artery disease illustrates the usefulness of high lipoprotein(a) levels

Only a few simple lipoprotein(a) [Lp(a)] assays are available in kit form for use in clinical laboratories. The present study compares the analytical and clinical performance of a mechanized immunonephelometric method to enzyme-linked immunosorbent assay. Clinical performance was evaluated by measuring lipoprotein markers in 191 patients, with the extent of stenosis defined by angiography. Analytically, both methods showed little or no correlation with cholesterol, high density lipoprotein cholesterol, elevated triglycerides, apo A-I and apo B, while they showed good agreement with one another (r = 0.88). The methods showed comparable well known differences between black and white persons. Logistic regression indicated that Lp(a) was a weak but independent marker for coronary artery disease (CAD). Receiver operator characteristic curve analysis showed an association with CAD only at higher Lp(a) concentrations. We conclude that Lp(a) at higher concentrations may be a contributory marker for CAD and that mechanized nephelometric assays for it can be used in the clinical laboratory.