Lipoprotein(a): From Molecules to Therapeutics

Sex, age, and ethnic dependency of lipoprotein variants as the risk factors of ischemic heart disease: a detailed study on the different age-classes and genders in Tehran Cardiometabolic Genetic Study (TCGS)

Biological processes involving environmental and genetic factors drive the interplay between age- and sex-regulating lipid profile. The relation between variations in the LPA gene with increasing the risk of coronary heart disease is dependent on population differences, sex, and age. The present study tried to do a gene candidate association analysis in people with myocardial infarction (MI) in a 22 year cohort family-based longitudinal cohort study, Tehran Cardiometabolic Genetic Study (TCGS). After adjusting p value by the FDR method, only the association of rs6415084 with the MI probability and the age-of-CHD-onset was significant in males in their middle age (p < 0.005). Surprisingly, a lack of association was observed for the rest of the markers (16 SNPs). These results revealed the moderator effects of age and sex on the association between the genetic variants (SNPs) of LPA and heart disease risk. Our observations may provide new insights into the biology that underlies lipid profile with age or the sexual dimorphism of Lp(a) metabolism. Finally, Lp(a) appears to be an independent risk factor; however, the role of sex and ethnicity is important.

Effect of Ezetimibe Monotherapy on Plasma Lipoprotein(a) Concentrations in Patients with Primary Hypercholesterolemia: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

BACKGROUND AND AIMS

Ezetimibe reduces plasma low-density lipoprotein cholesterol (LDL-C) levels by up to 20%. However, its effect on plasma lipoprotein(a) [Lp(a)] concentrations in patients with primary hypercholesterolemia has not been defined.

OBJECTIVE

Therefore, we performed a systematic review and meta-analysis to assess this effect based on the available randomized controlled trials (RCTs).

METHODS

We searched the PubMed and SCOPUS databases from inception until 28 February 2017 to identify RCTs that investigated the effect of ezetimibe monotherapy on plasma Lp(a) concentrations in patients with primary hypercholesterolemia. We pooled mean percentage changes in plasma Lp(a) concentrations as a mean difference (MD) with a 95% confidence interval (CI).

RESULTS

Seven RCTs with 2337 patients met the selection criteria and were included in the analysis. Overall pooled analysis suggested that ezetimibe 10 mg significantly reduced plasma Lp(a) concentrations in patients with primary hypercholesterolemia by - 7.06% (95% CI - 11.95 to - 2.18; p = 0.005) compared with placebo. No significant heterogeneity was observed (χ² = 5.34; p = 0.5). Excluding one study from the analysis resulted in insignificant differences between the two groups (p = 0.2). Meta-regression did not find a significant association between the mean percentage changes in Lp(a) and other potential moderator variables, which included the mean percentage changes of LDL-C concentrations (p = 0.06) and baseline Lp(a) mean values (p = 0.46).

CONCLUSIONS

Ezetimibe monotherapy (10 mg/day) showed a small (7.06%) but statistically significant reduction in the plasma levels of Lp(a) in patients with primary hypercholesterolemia. According to current literature, this magnitude of reduction seems to have no clinical relevance. However, further studies are warranted to clarify the mechanism mediating this effect of ezetimibe and to investigate its efficacy in combination with other drugs that have shown promise in lowering Lp(a) levels.

The Effects of Tamoxifen on Plasma Lipoprotein(a) Concentrations: Systematic Review and Meta-Analysis

Introduction

Tamoxifen is a selective estrogen receptor modulator widely used in the treatment of breast cancer. Tamoxifen therapy is associated with lower circulating low-density lipoprotein cholesterol and increased triglycerides, but its effects on other lipids are less well studied.

Aims

We aimed to investigate the effect of tamoxifen on circulating concentrations of lipoprotein(a) [Lp(a)] through a meta-analysis of available randomized controlled trials (RCTs) and observational studies.

Methods

This study was registered in the PROSPERO database (CRD42016036890). Scopus, MEDLINE and EMBASE were searched from inception until 22 March 2016 to identify studies investigating the effect of tamoxifen on Lp(a) values in humans. Meta-analysis was performed using an inverse variance-weighted, random-effects model with standardized mean difference (SMD) as the effect size estimate.

Results

Meta-analysis of five studies with 215 participants suggested a statistically significant reduction of Lp(a) levels following tamoxifen treatment (SMD −0.41, 95% confidence interval −0.68 to −0.14, p = 0.003). This effect was robust in the sensitivity analysis.

Conclusions

Meta-analysis suggested a statistically significant reduction of Lp(a) levels following tamoxifen treatment. Further well-designed trials are required to validate these results.

Pilot study of vascular health in survivors of osteosarcoma

BACKGROUND

Cardiovascular-related toxicities have been reported among survivors of osteosarcoma.

METHODS

Fasting blood samples from 24 osteosarcoma survivors were analyzed for high-sensitivity C-reactive protein (hsCRP), triglycerides, total cholesterol, high-density lipoprotein (HDL), apolipoprotein-ß, lipoprotein (a), fibrinogen, circulating endothelial cells (CECs), and surface expression of vascular cell adhesion molecule-1 (VCAM-1). Values were compared to subjects in the natural history Coronary Artery Risk Development in Young Adults (CARDIA) cohort study except for CECs and VCAM-1 expression, which were compared to controls studied at the University of Minnesota Lillehei clinical trials unit.

PROCEDURE

Survivors (54.2% male), median age 18 years (9-32) at diagnosis, 36.5 years (20-56) at evaluation were treated with a variety of chemotherapeutic exposures, all but one were exposed to doxorubicin (median dose 450 mg/m(2) ; range: 90-645 mg/m(2)), 14 (58.3%) received cisplatin, and 3 (12.5%) were exposed to carboplatin. Two survivors (8.3%) received radiation therapy for disease relapse. Compared to CARDIA subjects, mean hsCRP (3.0 mg/L ± 2.0 vs. 1.6 ± 2.3), triglycerides (151 mg/dl ± 81.7 vs. 95.4 ± 101.3), lipoprotein (a) (34.9 mg/dl ± 17.7 vs. 13.8 ± 22.0), and fibrinogen (315.0 mg/dl ± 49.3 vs. 252.4 ± 61.7) were significantly elevated. The number of CECs (0.47 cells/ml ± 2.5 vs. 0.92 ± 2.5) did not differ while surface expression of VCAM-1 (86.4% ± 34.0 vs. 42.1 ± 33.8) was significantly elevated compared to controls.

CONCLUSIONS

Among survivors of osteosarcoma, assessed a median of 14 years from diagnosis, there is evidence of vascular inflammation, dyslipidemia, and early atherogenesis.

When should we measure lipoprotein (a)?

Recently published epidemiological and genetic studies strongly suggest a causal relationship of elevated concentrations of lipoprotein (a) [Lp(a)] with cardiovascular disease (CVD), independent of low-density lipoproteins (LDLs), reduced high density lipoproteins (HDL), and other traditional CVD risk factors. The atherogenicity of Lp(a) at a molecular and cellular level is caused by interference with the fibrinolytic system, the affinity to secretory phospholipase A2, the interaction with extracellular matrix glycoproteins, and the binding to scavenger receptors on macrophages. Lipoprotein (a) plasma concentrations correlate significantly with the synthetic rate of apo(a) and recent studies demonstrate that apo(a) expression is inhibited by ligands for farnesoid X receptor. Numerous gaps in our knowledge on Lp(a) function, biosynthesis, and the site of catabolism still exist. Nevertheless, new classes of therapeutic agents that have a significant Lp(a)-lowering effect such as apoB antisense oligonucleotides, microsomal triglyceride transfer protein inhibitors, cholesterol ester transfer protein inhibitors, and PCSK-9 inhibitors are currently in trials. Consensus reports of scientific societies are still prudent in recommending the measurement of Lp(a) routinely for assessing CVD risk. This is mainly caused by the lack of definite intervention studies demonstrating that lowering Lp(a) reduces hard CVD endpoints, a lack of effective medications for lowering Lp(a), the highly variable Lp(a) concentrations among different ethnic groups and the challenges associated with Lp(a) measurement. Here, we present our view on when to measure Lp(a) and how to deal with elevated Lp(a) levels in moderate and high-risk individuals.

Lipoprotein(a) metabolism: potential sites for therapeutic targets

Lipoprotein(a) [Lp(a)] resembles low-density lipoprotein (LDL), with an LDL lipid core and apolipoprotein B (apoB), but contains a unique apolipoprotein, apo(a). Elevated Lp(a) is an independent risk factor for coronary and peripheral vascular diseases. The size and concentration of plasma Lp(a) are related to the synthetic rate, not the catabolic rate, and are highly variable with small isoforms associated with high concentrations and pathogenic risk. Apo(a) is synthesized in the liver, although assembly of apo(a) and LDL may occur in the hepatocytes or plasma. While the uptake and clearance site of Lp(a) is poorly delineated, the kidney is the site of apo(a) fragment excretion. The structure of apo(a) has high homology to plasminogen, the zymogen for plasmin and the primary clot lysis enzyme. Apo(a) interferes with plasminogen binding to C-terminal lysines of cell surface and extracellular matrix proteins. Lp(a) and apo(a) inhibit fibrinolysis and accumulate in the vascular wall in atherosclerotic lesions. The pathogenic role of Lp(a) is not known. Small isoforms and high concentrations of Lp(a) are found in healthy octogenarians that suggest Lp(a) may also have a physiological role. Studies of Lp(a) function have been limited since it is not found in commonly studied small mammals. An important aspect of Lp(a) metabolism is the modification of circulating Lp(a), which has the potential to alter the functions of Lp(a). There are no therapeutic drugs that selectively target elevated Lp(a), but a number of possible agents are being considered. Recently, new modifiers of apo(a) synthesis have been identified. This review reports the regulation of Lp(a) metabolism and potential sites for therapeutic targets.

Variations of lipoprotein(a) levels in the metabolic syndrome: a report from the Maracaibo City Metabolic Syndrome Prevalence Study

BACKGROUND

Lipoprotein(a) [Lp(a)] is a known risk factor for cardiovascular disease, yet its influence on metabolic syndrome (MS) is still controversial. The purpose of this study was to assess the impact generated by this diagnosis in serum Lp(a) concentrations.

MATERIALS AND METHODS

A total of 1807 subjects of both genders (55.3% women and 44.7% men) belonging to the Maracaibo City Metabolic Syndrome Prevalence Study were evaluated. Results were expressed as Mean ± SD, determining differences through Student's t-test and One-Way ANOVA test. Multiple logistic regression models were utilized for analyzing factors associated with elevated serum Lp(a) levels and MS. Total cholesterol and LDL-C were corrected according to Lp(a)-Cholesterol when necessary.

RESULTS

No differences were found in Lp(a) values between genders; P = 0,292. The association between MS and the classification of Lp(a) was statistically significant (χ (2) = 28.33; P < 0,0001), with greater levels in subjects with this diagnosis. In the univariate analysis, subjects with each of the separate diagnostic criteria showed higher serum Lp(a) concentrations, except for hyperglycemia.

CONCLUSIONS

Lp(a) values exhibit important variations regarding MS and each of its components. Impaired fasting glucose appeared as a protecting factor against elevated Lp(a) concentrations, whereas its association with LDL-C and hs-CRP suggests a potential pro-inflammatory role.

Characteristics of Himalayan marmots and their response to an atherogenic diet

The purpose of the present study was to characterize Himalayan marmot lipoprotein profiles and investigate their response to an atherogenic diet. Sixteen marmots were randomly divided into two groups. The control group was fed with a standard chow diet, and the other group was fed with a chow diet containing 0.3% cholesterol, 6.7% lard, and 3.3% corn oil (designated as HFCD) for 16 weeks. The plasma lipids were measured, and lipoprotein profiles were analyzed. With the chow diet, the major lipoproteins were high density lipoproteins. HFCD feeding increased not only plasma total cholesterol levels but also body weight compared with the control group (P<0.05). Plasma lipoprotein (a) was detected in marmots, and the plasma lipoprotein (a) levels were 4.5-fold higher after being fed HFCD for 16 weeks. However, atherosclerotic lesions were not found in the aorta of HFCD-fed marmots. This study suggested that marmots are HDL-rich mammals and resistant to HFCD-induced atherosclerosis.

Pilot study of vascular health in survivors of Hodgkin lymphoma

BACKGROUND

Vascular-related toxicities have been reported among survivors of Hodgkin lymphoma (HL), but their genesis is not well understood.

PROCEDURE

Fasting blood samples from 25 previously irradiated HL survivors were analyzed for biomarkers that can reveal underlying inflammation and/or endothelial cell activation: high-sensitivity C-reactive protein (hsCRP), triglycerides, total cholesterol, high-density lipoprotein (HDL), apolipoprotein ß, lipoprotein (a), fibrinogen, circulating endothelial cells (CECs), and vascular cell adhesion molecule-1 (VCAM-1) expression. Values were compared to subjects in the Coronary Artery Risk Development in Young Adults (CARDIA) study. CECs and VCAM-1 were compared to healthy controls.

RESULTS

Survivors (76% male), median age 17.6 years (5-33) at diagnosis, 33.0 years (19-55) at follow-up, included stages IA (n = 6), IIA (n = 10), IIB (n = 2), IIIA (n = 4), and IVA (n = 3) patients. Twenty-four received at least chest radiation therapy (RT) (median dose 3,150 cGy; range: 175-4,650 cGy), one received neck only; 14 (56%) had a history of anthracycline exposure (median dose: 124 mg/m(2) range: 63-200 mg/m2). Compared to CARDIA subjects, mean hsCRP (3.0 mg/L ± 2.0 vs. 1.6 ± 1.9), total cholesterol (194.1 mg/dl ± 33.2 vs. 179.4 ± 32.9), lipoprotein (a) (34.2 mg/dl ± 17.5 vs. 13.8 ± 17.5), and fibrinogen (342.0 mg/dl ± 49.1 vs. 252.6 ± 48.4) were significantly elevated. CECs (2.3 cells/ml ± 1.5 vs. 0.34 ± 1.4) were significantly elevated compared to controls. No difference in VCAM-1 expression (51.1% ± 36.8 vs. 42.3 ± 35.6) was detected.

CONCLUSION

HL survivors exposed to RT have evidence of vascular inflammation, dyslipidemia, and injury suggestive of early atherogenesis.

A Mediterranean-style, low-glycemic-load diet decreases atherogenic lipoproteins and reduces lipoprotein (a) and oxidized low-density lipoprotein in women with metabolic syndrome

The objective was to assess the impact of a Mediterranean-style, low-glycemic-load diet (control group, n = 41) and the same diet plus a medical food (MF) containing phytosterols, soy protein, and extracts from hops and Acacia (MF group, n = 42) on lipoprotein atherogenicity in women with metabolic syndrome. Plasma lipids, apolipoproteins (apos), lipoprotein subfractions and particle size, low-density lipoprotein (LDL) oxidation, and lipoprotein (a) were measured at baseline, week 8, and week 12 of the intervention. Three-day dietary records were collected at the same time points to assess compliance. Compared with baseline, women decreased energy intake from carbohydrate (P < .001) and fat (P < .001), whereas they increased energy intake from protein (P < .001). A significant increase in energy from monounsaturated fatty acids was also observed as well as increases in eicosapentaenoic acid and docosahexaenoic acid, whereas trans-fatty acid intake was reduced (P < .00001). The atherogenic lipoproteins, large very low-density lipoprotein (P < .0001) and small LDL (P < .0001), were reduced, whereas the ratio of large high-density lipoprotein to smaller high-density lipoprotein particles was increased (P < .0001). Apolipoprotein B was reduced for all women (P < .0001), with a greater reduction in the MF group (P < .025). Oxidized LDL (P < .05) and lipoprotein (a) (P < .001) were reduced in both groups at the end of the intervention. Consumption of a Mediterranean-style diet reduces the risk for cardiovascular disease by decreasing atherogenic lipoproteins, oxidized LDL, and apo B. Inclusion of an MF may have an additional effect in reducing apo B.

Biomarker analysis of Morquio syndrome: identification of disease state and drug responsive markers

Background

This study was conducted to identify potential biomarkers that could be used to evaluate disease progression and monitor responses to enzyme replacement therapy (ERT) in patients with mucopolysaccharidosis (MPS) IVA.

Methods

Levels of 88 candidate biomarkers were compared in plasma samples from 50 healthy controls and 78 MPSIVA patients not receiving ERT to test for significant correlations to the presence of MPSIVA. MPSIVA samples were also tested for correlations between candidate biomarkers and age, endurance, or urinary keratin sulfate (KS) levels. Then, levels of the same 88 analytes were followed over 36 weeks in 20 MPSIVA patients receiving ERT to test for significant correlations related to ERT, age, or endurance.

Results

Nineteen candidate biomarkers were significantly different between MPSIVA and unaffected individuals. Of these, five also changed significantly in response to ERT: alpha-1-antitrypsin, eotaxin, lipoprotein(a), matrix metalloprotein (MMP)-2, and serum amyloid P. Three of these were significantly lower in MPSIVA individuals versus unaffected controls and were increased during ERT: alpha-1-antitrypsin, lipoprotein(a), and serum amyloid P.

Conclusions

Candidate biomarkers alpha-1-antitrypsin, lipoprotein(a), and serum amyloid P may be suitable markers, in addition to urinary KS, to follow the response to ERT in MPSIVA patients.