Lipoprotein(a), a clinically elusive lipoprotein particle

A Molecular Troika of Angiogenesis, Coagulopathy and Endothelial Dysfunction in the Pathology of Avascular Necrosis of Femoral Head: A Comprehensive Review

Avascular necrosis of the femoral head (ANFH) is a painful disorder characterized by the cessation of blood supply to the femoral head, leading to its death and subsequent joint collapse. Influenced by several risk factors, including corticosteroid use, excessive alcohol intake, hypercholesterolemia, smoking and some inflammatory disorders, along with cancer, its clinical consequences are thrombus formation due to underlying inflammation and endothelial dysfunction, which collaborates with coagulopathy and impaired angiogenesis. Nonetheless, angiogenesis resolves the obstructed free flow of the blood by providing alternative routes. Clinical manifestations of early stage of ANFH mimic cysts or lesions in subchondral bone, vasculitis and transient osteoporosis of the hip, rendering it difficult to diagnose, complex to understand and complicated to cure. To date, the treatment methods for ANFH are controversial as no foolproof curative strategy is available, and these depend upon different severity levels of the ANFH. From an in-depth understanding of the pathological determinants of ANFH, it is clear that impaired angiogenesis, coagulopathy and endothelial dysfunction contribute significantly. The present review has set two aims, firstly to examine the role and relevance of this molecular triad (impaired angiogenesis, coagulopathy and endothelial dysfunction) in ANFH pathology and secondly to propose some putative therapeutic strategies, delineating the fact that, for the better management of ANFH, a combined strategy to curtail this molecular triangle must be composed rather than focusing on individual contributions.

[C reactive protein in women with coronary heart disease and its association with depression]

OBJECTIVES

Depression is associated with increased risk and poor outcome of coronary heart disease (CHD), though the mechanisms are largely unknown. Low-grade inflammation offers a possible biological pathway, which has been confirmed in men but not in women.

METHODS

We studied the association of C reactive protein (CRP), a biomarker of inflammation, with depressive symptoms in 292 women with CHD and 300 healthy age-matched controls, considering confounder variables (BMI, age, HDL cholesterol, triglycerides, menopausal status). CRP was measured by a high sensitivity assay.

RESULTS

In the overall sample no significant association was found between depressive symptoms and CRP, whereas in the control group women with 2 or more versus 0-1 depressive symptoms showed heightened CRP (p = 0.005); there was no significant difference in CRP levels between CHD patients with 0-1 versus 2 or more depressive symptoms. Women with CHD had higher serum levels of CRP and more depressive symptoms than did controls.

CONCLUSIONS

Contrary to men and healthy controls there was no link between CRP and depressive symptoms in women with CHD. More research is needed on how the harmful effects of depression are mediated, especially in women.

The role of hypercoagulability in the development of osteonecrosis of the femoral head

Despite the large number of the outstanding researches, pathogenesis of osteonecrosis remains unknown. During the last decades the hypothesis that increased intravascular coagulation may be the pathogenetic mechanism which leads to osteonecrosis is gaining constantly support. Both primary factors of hyper-coagulability, such as resistance to activated protein C, protein C and protein S deficiency, low levels of tissue plasminogen activator, high levels of plasminogen activator inhibitor, von Willebrand factor, lipoprotein (a), and secondary factors of hypercoagulability with factors potentially activating intravascular coagulation, such as pregnancy, antiphospholipid antibodies, systemic lupus erythematosus, hemoglobinopathies and sickle cell disease, and hemato-oncologic diseases are discussed in this article. Although coagulation abnormalities in patients with hip osteonecrosis might represent increased risk factors for the development of bone necrosis by predisposing the patient to thromboembolic phenomena, further investigation is needed to indicate the definite correlation between factors leading to increased intravascular coagulation and pathogenesis of osteonecrosis.

Gemfibrozil treatment in patients with elevated lipoprotein a: a pilot study

OBJECTIVE

This pilot study investigated the efficacy of high-dose gemfibrozil (2400 mg/day) in treating patients with elevated lipoprotein (a) [Lp(a)]. Lp(a) has been shown to be an independent risk factor for the development of coronary heart disease (CHD).

PATIENTS

Eleven patients with serum Lp(a) >/=45 mg/dl participated in this 12-week study. Initially, all patients received oral gemfibrozil 600mg twice daily. At 4-week intervals, the dose was increased by 600mg for patients able to tolerate the increase up to a maximum of 2400 mg/day.

RESULTS

Eight patients completed the study. Three of these patients met the predetermined criterion of a clinically meaningful Lp(a) reduction of 33%. The mean percentage change in Lp(a) was not statistically significant with values of -18.3 +/- 15.4% (p = 0.14, 1-tailed). All patients demonstrated a significant decrease in plasma triglycerides. The mean percentage change was -62.5 +/- 1.8% (p < 0.001, 1-tailed). The mean percentage change in total cholesterol was -12.4 +/- 3.8% (p = 0.007, 1-tailed). Gemfibrozil was considered suspect in five of 16 adverse events reported, but only one of these (dyspepsia) caused withdrawal from the study. For all patients participating in the study no adverse event was characterised as severe.

CONCLUSION

While the small number of patients does not allow any definitive conclusion on effectiveness to be drawn, the results suggest that further randomised studies utilising larger patient numbers appear warranted.

Thrombotic and fibrinolytic alterations in the aseptic necrosis of femoral head

Recent reports seem to support the role of the thrombophilia and decreased fibrinolysis in the aetiopathogenesis of aseptic necrosis of bone. In the present study, haemostatic disturbances were analysed in adults (n = 49) and patients in childhood (Perthes disease) (n = 47) with aseptic necrosis of the femoral head. Fibrinolytic parameters (in vitro clot lysis, plasminogen, plasmatic plasminogen activator inhibitor-1 activity, D-dimer) along with lipoprotein (a) [Lp(a)] and fibrinogen were measured. von Willebrand factor, platelet activation and some thrombophilic factors (activated protein C resistance and factor V Leiden mutation, protein C, protein S activity) were also determined. Impaired fibrinolysis, an increased Lp(a) level along with slow clot lysis and increased platelet activation were found in adult cases. We detected five cases of factor V Leiden mutations (one heterozygotic and four homozygotic) among patients with Perthes disease. The clinical course of the heterozygous case was similar to the usual form of Perthes disease. The most severe form of Perthes disease has been observed in homozygous factor V Leiden mutation cases. The mutation of factor V Leiden per se probably does not induce the development of aseptic necrosis of bone tissue in childhood, but it does play a role in its acceleration. Homozygous factor V Leiden mutation definitely runs a more severe course. On the other hand, in adult cases, the disturbances of haemostasis, impaired fibrinolysis, elevated Lp(a) level, increased platelet activation and slight elevation of fibrinogen might have clinical relevance. Further studies should focus on proving the role of the haemostatic alterations in the pathogenesis of severe forms of aseptic bone necrosis. The use of antithrombotic drugs in order to slow the process of aseptic necrosis also has to be addressed in future surveys.

Evaluation of a fully-automated particle-enhanced turbidimetric immunoassay for the measurement of plasma lipoprotein(a). population-based reference values in an area with low incidence of cardiovascular disease

OBJECTIVES

Lipoprotein(a) has been proposed as an independent risk factor for cardiovascular disease. This lipoprotein possesses a marked size polymorphism that makes difficult to measure accurately its concentration in plasma. The International Federation of Clinical Chemistry recently recommended to carefully evaluate new commercial methods for lipoprotein(a) measurement to discard the possible influence of lipoprotein(a) isoforms on immunoreactivity. They also recommended to perform population-based studies for different ethnic and geographic groups. Therefore, in the evaluation of a fully automated, particle-enhanced turbidimetric immunoassay for the measurement of lipoprotein(a) we have determined its reference interval in the Spanish population, an area with the lowest incidence of cardiovascular disease in Europe.

DESIGN AND METHOD

We evaluated a commercial kit of reagents calibrated against the Proposed Reference Material and determined the effect of lipoprotein(a) size polymorphism on the measurements. A population-based study was carried out in two different villages on the Mediterranean coast of Spain.

RESULTS

Imprecision at different lipoprotein(a) concentrations ranged between 3.0 and 15.4%. Recovery was 98.5 +/- 2.1. Detection limit was 4.8 nmol/L. There were no significant interferences from lipemia, jaundice, hemolysis, paraproteinemia, apolipoprotein B or plasminogen. We did not observe any effect of the lipoprotein(a) size polymorphism on the measurements. Mean (and SD) values for plasma lipoprotein(a) (n = 369) were 53.6 (65.3) nmol/L, the median was = 25.3 nmol/L and range varied between <4.8 and 356.0 nmol/L.

CONCLUSION

The present article presents an accurate and practical assay for measuring plasma lipoprotein(a) concentrations and describes its reference values in a population of Spanish Caucasians. Our results are similar to those obtained in other Caucasian populations (between 10 and 25% higher than in participants of the CARDIA study).

Lipoprotein(a): an emerging cardiovascular risk factor

Lipoprotein(a) is a cholesterol-enriched lipoprotein, consisting of a covalent linkage joining the unique and highly polymorphic apolipoprotein(a) to apolipoprotein B100, the main protein moiety of low-density lipoproteins. Although the concentration of lipoprotein(a) in humans is mostly genetically determined, acquired disorders might influence synthesis and catabolism of the particle. Raised concentration of lipoprotein(a) has been acknowledged as a leading inherited risk factor for both premature and advanced atherosclerosis at different vascular sites. The strong structural homologies with plasminogen and low-density lipoproteins suggest that lipoprotein(a) might represent the ideal bridge between the fields of atherosclerosis and thrombosis in the pathogenesis of vascular occlusive disorders. Unfortunately, the exact mechanisms by which lipoprotein(a) promotes, accelerates, and complicates atherosclerosis are only partially understood. In some clinical settings, such as in patients at exceptionally low risk for cardiovascular disease, the potential regenerative and antineoplastic properties of lipoprotein(a) might paradoxically counterbalance its athero-thrombogenicity, as attested by the compatibility between raised plasma lipoprotein(a) levels and longevity.

Lipoprotein (a), thrombophilia and inflammatory bowel disease

Thrombophilia in inflammatory bowel disease may be due to several risk factors, such as a dysbalanced haemostasis with a hypercoagulative state, thrombocytosis, hyperfibrinogenaemia and hyperhomocysteinaemia. In addition, increased concentrations of lipoprotein (a), a modified form of low-density lipoprotein particles, have been associated with a higher risk of thrombotic vascular disease, probably due to inhibition of (local and endothelial) fibrinolysis. The mechanisms regulating the plasma concentration of lipoprotein (a) have not yet been elucidated completely, but genetic factors are involved. Dietary factors seem to play a minor role. In this issue of the journal, Koutroubakis et al. report that lipoprotein (a) concentration is elevated in patients with Crohn's disease, but not in patients with ulcerative colitis. Several other (apo)lipoproteins have a different pattern in patients with inflammatory bowel disease than in a control population of healthy subjects from Crete. These findings add up to the multifactorial nature of thrombophilia in inflammatory bowel disease patients, especially in patients with Crohn's disease, and give rise to speculations about the clinical significance of the observed different lipoprotein metabolism in patients with inflammatory bowel disease.

Cardiovascular reactivity to mental stress in the Stockholm Female Coronary Risk Study

OBJECTIVE

This study evaluated the ability of mental stress testing to discriminate between women with and without CHD, and among women with different disease manifestations, taking into account history of hypertension and beta-blocker use.

METHODS

Analyses were based on data from a community-based case-control study of women aged 65 years or younger. The study group consisted of 292 women who were hospitalized for an acute event of CHD, either AMI or unstable AP in Stockholm between 1991 and 1994. Controls were matched to cases by age and catchment area. Cardiovascular reactivity and emotional response to an anagram task solved under time pressure were measured 3 to 6 months after hospitalization.

RESULTS

Patients reacted with smaller increases in heart rate (4 bpm) than their controls (7 bpm). Results for the rate-pressure product were similar. Cardiovascular reactions did not distinguish patients with AP from those with AMI. History of hypertension (present in 50% of patients and 11% of controls) was related to enhanced diastolic blood pressure reactivity. Patients on beta-blockers (66%) had lower heart-rate levels throughout testing, but did not differ in their cardiovascular stress reactions when compared with the remaining participants.

CONCLUSIONS

Women with heart disease have somewhat lower heart-rate responses to stress than healthy age-matched controls. History of hypertension is related to enhanced diastolic blood pressure reactivity to mental stress in both patients and controls.

Changes in lipoprotein(a) levels measured by six kit methods during growth hormone treatment of growth hormone-deficient adults

Lipoprotein(a) [Lp(a)], an independent risk factor for cardiovascular disease, has previously been reported to increase, decrease or show no change in growth hormone (GH)-deficient individuals receiving GH replacement. To assess whether these inconsistencies could be attributed to differences in immunoassay methods, Lp(a) was measured by six commercial kits at 0, 3, 6 and 9 months in nine GH-deficient individuals (median age 68.3 years, six male) during 9 months GH therapy. There was a significant rise in Lp(a) with the INCStar immunoturbidimetric (IT) method and the Mercodia enzyme linked immunosorbent assay (ELISA) (P</=0.05, two-tailed Wilcoxon signed rank test), a non-significant rise with the Pharmacia immuno-radiometric assay and the Biopool ELISA methods (P =0.06), and no change with the Immuno ELISA and WAKO IT kits. There was also considerable variation in the values reported within each individual. These results suggest that the previously reported inconsistencies may in part be due to methodological differences, and that the effect of GH on Lp(a) remains unknown. This study highlights the need for a more common approach to the standardization of Lp(a) methods and the selection of antibodies used in them. Better performing methods may allow a more reliable interpretation of the effects of GH on Lp(a)

Contribution of apolipoprotein(a) size, pentanucleotide TTTTA repeat and C/T(+93) polymorphisms of the apo(a) gene to regulation of lipoprotein(a) plasma levels in a population of young European Caucasians

Several studies indicate that the inter-individual variation in plasma concentrations of lipoprotein(a) (Lp(a)) is mainly under genetic control. To define the effect of three DNA polymorphisms on apolipoprotein(a) (apo(a)) expression, we have determined plasma Lp(a) concentrations, apo(a) isoform size, KpnI allele size, the TTTTA pentanucleotide repeat number in the 5' control region of the apo(a) gene and the +93 C/T polymorphism in a European Caucasian population. The simultaneous determination of the kringle 4 (K4) number by genotyping and by phenotyping revealed that the size distribution of non-expressed apo(a) alleles was markedly skewed towards alleles with greater than 25 K4 repeats. This is consistent with the inverse relationship frequently described between the kringle 4 number and the plasma Lp(a) level. Apportioning the Lp(a) concentration from the surface of the peaks on apo(a) phenotyping blots, we have observed that the Lp(a) plasma concentration associated with alleles having more than 25 K4 units does not exceed 400 mg/l, whereas the range of Lp(a) concentrations associated with smaller alleles was broad, from 0 to more than 1000 mg/l. It can thus be concluded that the number of K4 repeats is the main determinant of Lp(a) concentration when this number is more than 25, whereas other polymorphisms may be involved in the alleles with fewer than 26 K4. Analyses of the TTTTA repeat number and of the +93 C/T polymorphism were performed in subjects with KpnI alleles of the same length: low Lp(a) concentrations were shown to be preferentially associated with the presence of apo(a) alleles with more than eight pentanucleotide repeats while no association was revealed between Lp(a) plasma levels and the C/T polymorphism. These results demonstrate that the (TTTTA)(n) polymorphism affects the Lp(a) expression independently of apo(a) size polymorphism.

Lipoprotein(a) and coronary thrombosis and restenosis after stent placement

OBJECTIVES

The objective of this prospective study was to evaluate the relation between high lipoprotein(a) levels and thrombotic and restenotic events after coronary stent implantation.

BACKGROUND

Lipoprotein(a) may promote atherogenesis, coronary thrombosis and restenosis after balloon angioplasty, but the clinical significance remains unclear.

METHODS

The study included 2,223 consecutive patients with successful coronary stent placement. According to the serum level of lipoprotein(a), patients were divided in two groups: 457 patients of the highest quintile formed the high lipoprotein(a) group, and 1,766 patients of the lower four quintiles formed the low lipoprotein(a) group. Primary end points were the incidence of angiographic restenosis at six months and the event-free survival at one year. Secondary end point was the incidence of angiographic stent occlusion.

RESULTS

Early stent occlusion occurred in four of the 457 patients (0.9%) with high and 37 of the 1,766 patients (2.1%) with low lipoprotein(a) levels, odds ratio of 0.41 (95% confidence interval, 0.15 to 1.16). Angiographic restenosis occurred in 173 of the 523 lesions (33.2%) in the high lipoprotein(a) group and 636 of the 1,943 lesions (32.7%) in the low lipoprotein(a) group, odds ratio of 1.02 (0.83 to 1.25). The probability of event-free survival was 73.0% in the high lipoprotein(a) group and 74.8% in the low lipoprotein(a) group (p = 0.45). On the basis of the findings in the low lipoprotein(a) group, the power of this study to detect a 25% increase in the incidence of restenosis and adverse events in the group with elevated lipoprotein(a) was 90% and 75%, respectively.

CONCLUSIONS

Elevated lipoprotein(a) levels did not influence the one-year clinical and angiographic outcome after stent placement. Thrombotic events and measures of restenosis were not adversely affected by the presence of high lipoprotein(a) levels.

Metabolic risk factors for coronary heart disease: current and future prospects

In this review, data are reviewed concerning various metabolic risk factors that have been associated with coronary heart disease, drawing upon the experience of observational studies and clinical trials. Topics include lipids, glycemia, secular trends, hematologic factors, homocysteine, estrogen replacement, and familial and genetic factors. Using combinations of these types of factors in multivariate risk profiles is discussed, along with the opportunity to incorporate some of these factors into the prediction of coronary heart disease in the future.

Serum concentration of lipoprotein(a) decreases on treatment with hydrosoluble coenzyme Q10 in patients with coronary artery disease: discovery of a new role

OBJECTIVE

To examine the effect of coenzyme Q10 supplementation on serum lipoprotein(a) in patients with acute coronary disease.

STUDY DESIGN

Randomized double blind placebo controlled trial.

SUBJECTS AND METHODS

Subjects with clinical diagnosis of acute myocardial infarction, unstable angina, angina pectoris (based on WHO criteria) with moderately raised lipoprotein(a) were randomized to either coenzyme Q10 as Q-Gel (60 mg twice daily) (coenzyme Q10 group, n=25) or placebo (placebo group, n=22) for a period of 28 days.

RESULTS

Serum lipoprotein(a) showed significant reduction in the coenzyme Q10 group compared with the placebo group (31.0% vs 8.2% P<0.001) with a net reduction of 22.6% attributed to coenzyme Q10. HDL cholesterol showed a significant increase in the intervention group without affecting total cholesterol, LDL cholesterol, and blood glucose showed a significant reduction in the coenzyme Q10 group. Coenzyme Q10 supplementation was also associated with significant reductions in thiobarbituric acid reactive substances, malon/dialdehyde and diene conjugates, indicating an overall decrease in oxidative stress.

CONCLUSION

Supplementation with hydrosoluble coenzyme Q10 (Q-Gel) decreases lipoprotein(a) concentration in patients with acute coronary disease.

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.

Elevated plasma levels of soluble P-selectin in patients with acute myocardial infarction and unstable angina. An inverse link to lipoprotein(a)

P-selectin in platelets and endothelial cells mediates adhesive interactions between platelet, leukocyte and endothelium to form thrombi. The purpose of the present study was to investigate the plasma level of soluble P-selectin (sP-selectin) in patients with coronary heart disease and the relationship between sP-selectin and plasma concentration of lipoprotein(a) [Lp(a)]. Levels of sP-selectin and Lp(a) were determined by enzyme-linked immunoabsorbent assay on plasma taken from patients with acute myocardial infarction (AMI), old myocardial infarction (OMI), unstable angina (UA), stable angina (SA) and the controls. In patients with AMI and UA, sP-selectin levels (79.62+/-3.82 ng/ml, 43.75+/-2.97 ng/ml, respectively) were significantly higher (P<0.01) than those in patients with OMI (15.92+/-1.34 ng/ml), SA (15.31+/-1.51 ng/ml), and the controls (14.93+/-1.33 ng/ml), but there was no difference between AMI and UA groups. Among all subjects studied, there was an inverse correlation between Lp(a) and sP-selectin (r=-0.315 P<0.001). These findings indicate that plasma levels of sP-selectin are increased in patients with AMI and UA, and high levels of soluble P-selectin may play a role in the pathogenesis of acute coronary events.

Elevated lipoprotein(a) levels in South Asians in North America

This report demonstrates that South Asians living in North America have elevated levels of Lp(a) compared with North American whites. Elevated Lp(a) levels may account, in part, for the tendency of South Asians to develop premature coronary heart disease (CHD).

Standardization and clinical management of lipoprotein(a) measurements

The present article proposes personal suggestions to improve determinations and clinical interpretation of results of lipoprotein(a) assays. Methods and procedures for sampling and quantification of the various isoforms of lipoprotein(a) in serum, plasma and urine are reviewed with the aim of improving the reliability and reproducibility of results and reinforcing the clinical utility of lipoprotein(a) measurements.