Lipoprotein(a): intrigues and insights

Serum lipids, lipoproteins and apolipoproteins levels in patients with nonalcoholic steatohepatitis

GOALS/BACKGROUND

Nonalcoholic steatohepatitis (NASH) is a form of liver disease that is histologically indistinguishable from alcoholic hepatitis but occurs in persons who do not consume alcohol in excess. The objectives of this study are to measure serum levels of lipids, lipoproteins and apolipoproteins (apo AI, apo B), lipoprotein (a) [Lp (a)] in patients with nonalcoholic steatohepatitis (NASH), and to investigate the relationship with liver histology.

STUDY

The scope of this study is composed of 36 patients (27 males, 9 females) with NASH, diagnosed by biochemical liver function tests, sonographic examination of liver and liver biopsy and 32 healthy adults as a control group (22 males, 10 females). Serum lipids, lipoproteins and apo AI, apo B, and Lp (a) measurements were taken in the study group and controls, and a correlation with histopathologic findings was searched for.

RESULTS

Serum mean levels (+/- SD as mg/dl) of total cholesterol (201.05 +/- 34.48), triglyceride (225.94 +/- 156.50), and LDL-cholesterol (111.77 +/- 19.85) in patients with NASH were significantly higher than those of the control group (170.68 +/- 31.06; 138.81 +/- 49.96; 100.68 +/- 17.98; respectively) and serum HDL-cholesterol level (41.22 +/- 2.47) was less than that of the control group (45.06 +/- 8.32) (P = 0.017). The serum mean level of apo AI (151.54 +/- 30.90) in the study group was lower than that of the controls (160.62 +/- 22.11), but the difference was not significant (P = 0.17). However, the serum apo AI level in patients with liver fibrosis (140.62 +/- 35.62) was significantly lower than that of patients without liver fibrosis (164.57 +/- 25.47) (P = 0.01). The serum mean level of apo B (89.80 +/- 20.62) in the patients was significantly higher than the control group (73.25 +/- 25.39) (P = 0.004), but not correlate with liver histopathology. The serum Lp (a) levels in both the patients (13.09 +/- 9.61) and the controls (12.01 +/- 7.50) were not different (P = 0.61). Hypertriglyceridemia (above 220 mg/dL) had a positive correlation with steatosis of the liver (r = 0.333, P = 0.04) and a negative correlation with liver fibrosis (r = -0.438, P = 0.008). There was a significant negative correlation between apo AI and steatosis (r = -0.360, P = 0.03), inflammation (r = -0.364, P = 0.03) and fibrosis of liver (r = -0.418, P = 0.01). A positive correlation of serum LDL-cholesterol (r = 0.507, P = 0.002) and Lp(a) (r = 0.394, P = 0.01) concentrations with liver fibrosis was also noted.

CONCLUSIONS

Abnormalities of lipid metabolism such as the increase of serum triglyceride, cholesterol and LDL-cholesterol level and decrease of HDL-cholesterol may be the contributing factors in the development of NASH. The decrease in apo AI and the increase in LDL and Lp (a) in patients were correlated with liver fibrosis. Apo AI may be a serum marker for liver fibrosis in patients with NASH.

Long term statin treatment reduces lipoprotein(a) concentrations in heterozygous familial hypercholesterolaemia

BACKGROUND

Raised plasma lipoprotein(a) (Lp(a)) is associated with increased risk of cardiovascular disease. It is unknown whether increased Lp(a) is an additional risk factor for coronary artery disease in familial hypercholesterolaemia (FH) or whether statin treatment can reduce Lp(a) concentrations in the long term.

OBJECTIVE

To investigate Lp(a) concentrations in relation to statin treatment and the progression of atherosclerosis in a large cohort of FH patients.

DESIGN

A two year, randomised, double blind trial (the ASAP trial).

PATIENTS

325 heterozygous FH patients.

INTERVENTION

Treatment with 80 mg atorvastatin or 40 mg simvastatin.

MAIN OUTCOME MEASURE

Change in Lp(a) concentrations and intima-media thickness of carotid artery segments at one year and two years.

RESULTS

At baseline, median Lp(a) concentrations were 327 mg/l and 531 mg/l in the atorvastatin and simvastatin arms, respectively (p = 0.03). In the atorvastatin arm, Lp(a) concentrations decreased to 243 mg/l after one year (p < 0.001) and to 263 mg/l after two years (p < 0.001). In the simvastatin arm, Lp(a) concentrations decreased to 437 mg/l after one year (p < 0.001) and to 417 mg/l after two years (p < 0.001). The difference in Lp(a) reduction between the two treatment arms was significant after one year (p = 0.004), but not after two years (p = 0.086). Lp(a) concentrations at baseline were not related to cardiovascular events at baseline. There was no correlation between baseline Lp(a) concentrations and low density lipoprotein cholesterol concentrations or intima-media thickness at baseline. Change in Lp(a) concentrations was not correlated with change in intima-media thickness after one or two years.

CONCLUSIONS

Long term statin treatment significantly lowers Lp(a) in FH patients. However, this reduction was unrelated to changes in intima-media thickness and casts doubt on the importance of Lp(a) in the progression of atherosclerotic disease in these patients.

Study of apo(a) length polymorphism and lipoprotein(a) concentrations in subjects with single or double apo(a) isoforms

Cardiovascular risk is associated with high lipoprotein(a) (Lp(a)) concentrations and low molecular weight apolipoprotein(a) (apo(a)) isoforms. We studied the relationship between these two biological parameters, particularly in subjects expressing two apo(a) isoforms. Plasma Lp(a) was measured by immunonephelometry in 530 unrelated Caucasian patients at high cardiovascular risk, and apo(a) size determined by immunoblotting using a recombinant standard. Two, one, or no apo(a) isoforms were detected in 258, 270, and 2 subjects, respectively. Lp(a) concentrations showed a non-Gaussian distribution, being higher in the 'double band' than in the 'single band' group (median 0.42 vs. 0.11 g/l, p < 0.0005). Apo(a) size distribution was bimodal, with two frequency peaks at 18 kringles (K) and 27 K. Small size apo(a) isoforms were more frequently found in the 'double band' group, where major isoforms were of lower size than minor isoforms (median 20 vs. 27 K). Regression analysis showed that apo(a) gene length accounted for 33% of Lp(a) variation, with a threshold effect at 20 K, no correlation being found over this value. The minor apo(a) isoform did not significantly influence Lp(a) concentration. These data confirm the relationship between apo(a) size and Lp(a) concentration and suggest that the assessment of cardiovascular risk should take into account the threshold effect at 20 K and the absence of influence of the minor apo(a) isoform.

Androgens and coronary artery disease

A significant and independent association between endogenous testosterone (T) levels and coronary events in men and women has not been confirmed in large prospective studies, although cross-sectional data have suggested coronary heart disease can be associated with low T in men. Hypoandrogenemia in men and hyperandrogenemia in women are associated with visceral obesity; insulin resistance; low high-density lipoprotein (HDL) cholesterol (HDL-C); and elevated triglycerides, low-density lipoprotein cholesterol, and plasminogen activator type 1. These gender differences and confounders render the precise role of endogenous T in atherosclerosis unclear. Observational studies do not support the hypothesis that dehydroepiandrosterone sulfate deficiency is a risk factor for coronary artery disease. The effects of exogenous T on cardiovascular mortality or morbidity have not been extensively investigated in prospective controlled studies; preliminary data suggest there may be short-term improvements in electrocardiographic changes in men with coronary artery disease. In the majority of animal experiments, exogenous T exerts either neutral or beneficial effects on the development of atherosclerosis. Exogenous androgens induce both apparently beneficial and deleterious effects on cardiovascular risk factors by decreasing serum levels of HDL-C, plasminogen activator type 1 (apparently deleterious), lipoprotein (a), fibrinogen, insulin, leptin, and visceral fat mass (apparently beneficial) in men as well as women. However, androgen-induced declines in circulating HDL-C should not automatically be assumed to be proatherogenic, because these declines may instead reflect accelerated reverse cholesterol transport. Supraphysiological concentrations of T stimulate vasorelaxation; but at physiological concentrations, beneficial, neutral, and detrimental effects on vascular reactivity have been observed. T exerts proatherogenic effects on macrophage function by facilitating the uptake of modified lipoproteins and an antiatherogenic effect by stimulating efflux of cellular cholesterol to HDL. In conclusion, the inconsistent data, which can only be partly explained by differences in dose and source of androgens, militate against a meaningful assessment of the net effect of T on atherosclerosis. Based on current evidence, the therapeutic use of T in men need not be restricted by concerns regarding cardiovascular side effects. Available data also do not justify the uncontrolled use of T or dehydroepiandrosterone for the prevention or treatment of coronary heart disease.

Apolipoprotein[a] secretion from hepatoma cells is regulated in a size-dependent manner by alterations in disulfide bond formation

Apolipoprotein[a] (apo[a]) is a large disulfide linked glycoprotein synthesized by hepatocytes. We have examined the role of disulfide bond formation in the processing of apo[a] using human and rat hepatoma cells expressing apo[a] isoforms containing varying numbers of kringle 4 (K4) domains, following treatment with DTT. Hepatoma cells expressing 6- or 9-K4 isoforms revealed approximately 90% inhibition of apo[a] secretion following DTT treatment, although larger isoforms containing 13- or 17-K4 domains demonstrated continued secretion (up to 30% of control values), suggesting that a fraction of the larger isoforms is at least partially DTT resistant. Wash-out experiments demonstrated that these effects were completely reversible for all isoforms studied, with no enhanced degradation associated with prolonged intracellular retention. DTT treatment was associated with enhanced binding of apo[a] with the endoplasmic reticulum-associated chaperone proteins calnexin, calreticulin, and BiP, which was reversible upon DTT removal. The chemical chaperone 6-aminohexanoic acid, previously demonstrated by others to rescue defective apo[a] secretion associated with alterations in glycosylation, failed to alter the secretion of apo[a] following DTT treatment. The demonstration that DTT modulates apo[a] secretion in a manner influenced by both the type and number of K4 repeats extends understanding of the mechanisms that regulate its exit from the endoplasmic reticulum.

Lipoprotein (a) levels and apolipoprotein (a) isoform size in patients with subclinical hypothyroidism: effect of treatment with levothyroxine

The increased risk for ischemic heart disease (IHD) associated with subclinical hypothyroidism (SH) has been partly attributed to dyslipidemia. There is limited information on the effect of SH on lipoprotein (a) [Lp(a)], which is considered a significant predictor of IHD. Serum Lp(a) levels are predominantly regulated by apolipoprotein [apo(a)] gene polymorphisms. The aim of our study was to evaluate the Lp(a) levels and apo(a) phenotypes in patients with SH compared to healthy controls as well as the influence of levothyroxine substitution therapy on Lp(a) values in relation to the apo(a) isoform size. Lp(a) levels were measured in 69 patients with SH before and after restoration of a euthyroid state and in 83 age- and gender-matched healthy controls. Apo(a) isoform size was determined by sodium dodecyl sulfate (SDS) agarose gel electrophoresis followed by immunoblotting and development via chemiluminescence. Patients with SH exhibited increased Lp(a) levels compared to controls (median value 10.6 mg/dL vs. 6.0 mg/dL, p = 0.003]), but this was not because of differences in the frequencies of apo(a) phenotypes. There was no association between thyrotropin (TSH) and Lp(a) levels in patients with SH. In subjects with either low (LMW; 25 patients and 28 controls) or high (HMW; 44 patients and 55 controls) molecular weight apo(a) isoforms, Lp(a) concentrations were higher in patients than in the control group (median values 26.9 mg/dL vs. 21.8 mg/dL, p = 0.02 for LMW, and 6.0 mg/dL versus 3.3 mg/dL, p < 0.001 for HMW). Levothyroxine treatment resulted in an overall reduction of Lp(a) levels (10.6 mg/dL baseline vs. 8.9 mg/dL posttreatment, p = 0.008]). This effect was mainly evident in patients with LMW apo(a) isoforms associated with high baseline Lp(a) concentrations (median values 26.9 mg/dL vs. 23.2 mg/dL pretreatment and posttreatment, respectively; p = 0.03). In conclusion, even though a causal effect of thyroid dysfunction on Lp(a) was not clearly demonstrated in patients with SH, levothyroxine treatment is beneficial, especially in patients with increased baseline Lp(a) levels and LMW apo(a) isoforms.

The susceptibility of lipoprotein(a) to copper oxidation is correlated with the susceptibility of autologous low density lipoprotein to oxidation

OBJECTIVES

Lipoprotein(a) [Lp(a)] can be oxidized by copper in vitro in a way comparable to low-density lipoprotein (LDL). We sought to determine whether the susceptibility of Lp(a) to oxidation is correlated with the susceptibility of autologous heterogeneous LDL, with apolipoprotein(a) [apo(a)] molecular size, or with both factors.

DESIGN AND METHODS

We examined shifts in electrophoretic mobility of Lp(a) and LDL caused by copper oxidation in plasma samples from 81 healthy men. The effect of copper oxidation on different-sized apo(a) was also evaluated.

RESULTS

There was a close correlation between the relative electrophoretic mobilities of oxidized Lp(a) and oxidized LDL in subjects, especially with small-sized apo(a) (n = 25, r = 0.72, p < 0.0001). Oxidative processes in Lp(a) resulted in the degradation of large-, but not small-sized apo(a).

CONCLUSIONS

The susceptibility of Lp(a) to oxidation is correlated with that of autologous LDL. Large-sized apo(a) may be involved in the Lp(a) oxidation.

Diabetes mellitus and coronary artery disease: therapeutic considerations

Diabetes mellitus affects about 6% of the U.S. population and represents a significant public health challenge, with numbers of those affected increasing every year. The most common cause of death in these patients is macrovascular disease, with coronary disease being the predominant form. The pathophysiology of coronary disease in patients with diabetes is complex and involves elements of hyperglycemia, dyslipidemia, hyperinsulinemia, as well as a procoagulant vascular milieu. First-generation trials looking at revascularization of multivessel disease in patients with diabetes have had long clinical follow-up periods and seem to consistently favor coronary bypass grafting over percutaneous interventions; however, newer trials that include the use of stents and glycoprotein IIb/IIIa inhibitor therapy as part of the latter strategy have raised some interesting questions, so that the issue remains controversial and by no means settled.

Lipoprotein(a) and the atherothrombotic process: mechanistic insights and clinical implications

Although many epidemiologic studies have pointed at an association between plasma levels of lipoprotein(a) (Lp(a)) and cardiovascular risk, the data obtained have been conflicting because of a number of factors, particularly those dealing with plasma storage, lack of assay standardization, population sample size, age, gender, ethnic variations, and variable disease endpoints. Moreover, the attention has been primarily focused on whole Lp(a), with relatively less emphasis on its constituent apolipoprotein(a) and on the apolipoprotein B100-containing lipoprotein, mainly low-density lipoprotein (LDL), to which apolipoprotein(a) is linked. According to recent studies, small-size apolipoprotein(a) isoforms may represent a cardiovascular risk factor either by themselves or synergistically with plasma Lp(a) concentration. Moreover, the density properties of the LDL moiety may have an impact on Lp(a) pathogenicity. It has also become apparent that Lp(a) can be modified by oxidative events and by the action of lipolytic and proteolytic enzymes with the generation of products that exhibit atherothrombogenic potential. The role of the O-glycans linked to the inter-kringle linkers of apolipoprotein(a) is also emerging. This information is raising the awareness of the pleiotropic functions of Lp(a) and is opening new vistas on pathogenetic mechanisms whose knowledge is essential for developing rational therapies against this complex cardiovascular pathogen.

Temporal increases in plasma markers of oxidized low-density lipoprotein strongly reflect the presence of acute coronary syndromes

OBJECTIVES

This study was conducted to test the hypothesis that plasma markers of oxidized low-density lipoprotein (OxLDL) reflect acute coronary syndromes (ACS).

BACKGROUND

Oxidized LDL contributes to the pathogenesis of atherosclerosis, but its role in ACS is not established.

METHODS

Serial plasma samples were prospectively obtained from patients with an acute myocardial infarction (MI) (n = 8), unstable angina (UA) (n = 15), stable coronary artery disease (CAD) (n = 17), angiographically normal coronary arteries (n = 8), and from healthy subjects (n = 18), at entry into the study, hospital discharge (MI group only), and at 30, 120, and 210 days. Chemiluminescent enzyme-linked immunosorbent assay was used to quantitate plasma levels of: 1) immunoglobulin (Ig)M and IgG OxLDL autoantibody titers (presented as a mean OxLDL autoantibody titer by averaging the results of four distinct epitopes); 2) LDL-autoantibody immune complexes (LDL-IC); and 3) minimally OxLDL measured by antibody E06 (OxLDL-E06), as determined by the content of oxidized phospholipids (OxPL) per apolipoprotein B-100.

RESULTS

Baseline OxLDL IgG autoantibody levels were higher in the MI group (p < 0.0001). At 30-day follow-up, the mean IgM OxLDL titers increased by 48% (p < 0.001) and 20% (p < 0.001), and IgM LDL-IC increased by 60% (p < 0.01) and 26% (p < 0.01) in the MI and UA groups, respectively. The OxLDL-E06 levels increased by 54% (p < 0.01) in the MI group at hospital discharge and by 36% at 30 days. No significant changes in any OxLDL markers were noted in the other groups. The OxLDL-E06 levels strongly paralleled the acute rise in lipoprotein(a), or Lp(a), in the MI group, suggesting that toxic OxPL are preferentially bound to Lp(a). Oxidized LDL-E06 also correlated extremely well with Lp(a) in the entire cohort of patients (r = 0.91, p < 0.0001).

CONCLUSIONS

Circulating OxLDL-specific markers strongly reflect the presence of ACS, implying immune awareness to newly exposed oxidation-specific epitopes and possible release of OxLDL in the circulation. The OxLDL-E06 measurements provide novel insights into plaque rupture and the potential atherogenicity of Lp(a).

Impact of genetic defects on coronary atherosclerosis in patients suspected of having familial hypercholesterolaemia

BACKGROUND

In the present study we assessed whether the presence of genetic mutations typical of familial hypercholesterolaemia (FH) was associated with greater atherosclerosis in the coronary vessels in patients with severe hypercholesterolaemia and a family history of early cardiovascular disease.

MATERIALS AND METHODS

Two hundred and thirty-five patients selected for having severe hypercholesterolaemia and a family history of cardiovascular disease were classified as FH (57 men and 38 women) or non-FH (84 men and 56 women) according to a genetic analysis of the LDL-R or ApoB genes. Coronary atherosclerosis was evaluated by performing a thoracic CT scan and exercise stress testing.

RESULTS

Familial hypercholesterolaemia individuals had a significantly higher prevalence of coronary calcification than the non-FH patients from among both the men (OR = 3.90; 95% CI 1.86-8.19; P < 0.001) and the women (OR = 2.34; 95% CI 1.01-5.48; P = 0.05). In exercise stress testing, ECG abnormalities suggestive of cardiac ischaemia were found with a higher prevalence in the FH patients than the non-FH patients from among both the men (OR 6.15; 95% CI 2.16-17.5; P < 0.001) and the women (OR 4.76; 95% CI 0.91-24.6; P = 0.06). All differences were statistically significant after adjusting for age and cholesterol and for most classical risk factors that differed between the FH and non-FH groups.

CONCLUSION

Among patients with severe hypercholesterolaemia and a family history of early cardiovascular disease, the presence of a genetically ascertained FH is associated with a higher prevalence of coronary artery calcifications and a positive exercise stress test. These results suggest that despite a similar phenotype, patients carrying mutations suggestive of FH may have a greater cardiovascular risk than patients without these mutations.

Possible association between genetic variability at the apolipoprotein(a) locus and Alzheimer's disease in apolipoprotein E2 carriers

Apolipoprotein(a) (Apo(a)) is a glycoprotein that is linked by a disulfide bond to apolipoprotein B on low density lipoprotein particles to form lipoprotein(a) (Lp(a)). High plasma levels of Lp(a) are thought to contribute directly to the development of atherosclerosis. We tested a variant (T3888P) located in the Kringle-IV region of Apo(a) in a case-control series. Overall, there were no differences between case and controls. However, in the apoE2 positive subgroup, we noticed that the mutant allele is over-represented in the cases (P=0.005). We suggest that this polymorphism and others at the Apo(a) locus be further studied in relation to Alzheimer's disease.

National differences in lipid response to postmenopausal hormone replacement therapy

OBJECTIVE

To compare the response of serum lipids and lipoproteins to the transdermal hormone replacement therapy (HRT) in five European countries.

METHODS

Five-hundred and sixty-seven healthy postmenopausal women from Belgium, Finland, the Netherlands, Sweden, and the UK received transdermal estradiol 50 microg daily for 12 months. In addition, two groups received transdermally norethisterone acetate (NETA) continuously, two groups sequentially (170 or 350 microg/day); one group received sequentially oral NETA (1 mg/day), and one group dydrogestrone (20 mg/day). Serum total cholesterol, HDL-, HDL2-, LDL-cholesterol, lipoprotein(a) (Lp(a)), and triglycerides were assessed before and at the end of treatment.

RESULTS

No significant national differences existed in the pretreatment levels of lipids and lipoproteins. Mean cholesterol, LDL, Lp(a), and triglycerides decreased during HRT, and HDL and HDL2 increased. Individual changes in responses to HRT were strongly dependent on pretreatment values. In this regard, British women differed from the others: their cholesterol, HDL, HDL2, and Lp(a) responses, when related to the pretreatment levels, were smaller than those of the others.

CONCLUSION

A national difference discovered in response of serum lipids to HRT calls for caution in generalization of lipid data from one nation to another during HRT.

Serum apolipoprotein AI levels in atherosclerotic and diabetic patients

OBJECTIVE

To evaluate the association between Apolipoprotein AI (ApoAI), Apolipoprotein B100 (ApoB) and the presence of lower limb atherosclerotic occlusive disease.

MATERIALS AND METHODS

Serum lipids, lipoprotein fractions, ApoAI, ApoB and Lp(a) were measured in 52 patients (28 diabetics and 24 non-diabetics) with lower limb occlusive disease. They were evaluated according to patients' glucose and compared with those in 75 healthy controls.

RESULTS

There was a significant decrease in HDL-cholesterol and ApoAI serum levels (p = 0.000001) and an increase in Lp(a) (p = 0.000001) in patients as compared to controls. No difference was observed in total cholesterol, non HDL-cholesterol or triglycerides. Multiple regression analysis revealed a significant association between low ApoAI (or HDL) levels and the disease as well as between high Lp(a) levels and the disease. ApoAI (p = 0.0003), HDL-cholesterol (p = 0.00005) and total cholesterol (p = 0.01) levels were significantly lower in diabetic patients compared to non-diabetic patients. Lp(a) levels did not correlate with fasting glucose concentration. Multiple regression analysis revealed a significant association between low ApoAI (or HDL) levels and diabetes.

CONCLUSION

Decreased ApoAI appears to be a main component of the dyslipidaemic serum profile observed in patients with atherosclerotic occlusive disease of the lower extremities. Increased Lp(a) levels is an independent risk factor. Decreased HDL-cholesterol is also involved in the dyslipidaemic profile.

Impact of genetic defects on atherosclerosis in patients suspected of familial hypercholesterolaemia

BACKGROUND

Among patients with severe hypercholesterolaemia and a family history of early cardiovascular disease, we assessed whether patients with mutations of low-density lipoprotein (LDL) receptor and apolipoprotein B genes related to familial hypercholesterolaemia (FH) have a different degree of atherosclerosis than those without such mutations.

METHOD

In our lipid clinics, 273 patients were selected on the basis of a severe hypercholesterolaemia (cholesterol above 95th percentile) and a family history of early cardiovascular disease. By molecular genetic test, 122 patients were classified as FH. Atherosclerosis was evaluated by the ultrasonographic measurement of intima-media thickness (IMT) in the carotid and femoral arteries.

RESULT

Despite the fact that non-FH individuals had a higher prevalence of obesity, hypertension, diabetes and hypertriglyceridaemia, FH individuals had significantly greater carotid and femoral IMT than non-FH patients: difference between carotid and femoral IMT, respectively, 0.19 mm (95% CI, 0.08-0.29; P < 0.001) and 0.20 mm (95% CI, 0.09-0.35; P = 0.001), respectively. These differences remained statistically significant after adjustment for the various risk factors as well as in sub-analysis restricted to the patients with LDL-cholesterol between 240 and 300 mg dL-1 (range with similar distribution in the two groups). When classified according to the severity of their mutations, FH individuals with null LDL receptor allele tended to have thicker carotid IMT than FH individuals carrying the LDL receptor-defective allele.

CONCLUSION

Among patients with severe hypercholesterolaemia and a family history of early cardiovascular disease, the presence of a genetically ascertained FH is associated with a higher degree of atherosclerosis. This suggests that molecular genetic identification of FH may be helpful to evaluate better the coronary heart disease risk in these patients.

The role of lipoprotein(a) in the pathogenesis of atherosclerotic cardiovascular disease and its utility as predictor of coronary heart disease events

Lipoprotein(a), is a highly heterogeneous lipoprotein, due to variations in the size of apolipoprotein(a), and the density of the apoB100-containing particles to which apo(a) is linked. Although high plasma levels of Lp(a) have been associated with an increased risk for atherosclerotic cardiovascular disease, the mechanism underlying this association is still largely undetermined, as is the potential role played by the particle's heterogeneity. Lp(a) pathogenicity may also be influenced by the action of environmental factors and post-translational events relating to oxidative processes, and the action of lipolytic and proteolytic enzymes. Complicating the study of Lp(a) are the competing methods for its quantification due to its complex structure, and the lack of standardized methodologies. The recognition that Lp(a) particles may not all be alike in atherogenic potential should encourage studies to identify genetic and nongenetic factors underlying its heterogeneity, in order to reach a better understanding of its actual impact on atherosclerotic cardiovascular disease.

Effect of Antiepileptic drugs on plasma lipoprotein (a) and other lipid levels in childhood

Antiepileptic drugs may alter plasma lipid status in epileptic patients. We conducted a study to assess the effect of phenobarbital, carbamazepine, and valproate on plasma levels of lipoprotein (a), total cholesterol, triglycerides, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, apolipoprotein A, and apolipoprotein B in 22 epileptic children. The children were separated as group 1, seven children, mean age 1.6+/-0.2 years, treated with phenobarbital, 5 mg/kg/day, twice daily; group 2, seven children, mean age 9.8+/-1.2 years, treated with carbamazepine, 20 mg/kg/day, twice daily; and group 3, eight children, mean age 6.8+/-0.6 years, treated with valproate, 20 mg/kg/day, twice daily. Plasma lipoprotein (a) and other lipid levels were studied before (pretreatment) and at 3 and 6 months of treatment. Friedman two-way analysis of variance and Wilcoxon's signed-rank test were used for statistical analysis, and the results were expressed as the mean and standard error of the mean. The mean age of children in group 1 was significantly low, compared with groups 2 and, 3 (P < .001). The mean pretreatment lipid levels between the groups were not significant. The increase in lipoprotein (a) at 3 and 6 months and high-density lipoprotein cholesterol at 6 months was statistically significant in group 1 (P < .025). We suggest a careful monitoring of plasma levels of lipoprotein (a) and other lipids in epileptic children treated with antiepileptic drugs.

[Subclinical carotid atherosclerosis in patients with coronary disease]

BACKGROUND

B-mode ultrasonography is a simple and valid method to evaluate subclinical atherosclerosis of the major superficial arteries. The aim of this study was toknow by this technique the prevalence of carotid atherosclerosisin patients with coronary disease and related factors.

PATIENTS AND METHOD

In 232patients (205 men and 27 women; age: mean [standard deviation]59 [8] years) with coronary disease, intima-media thickness (IMT),presence and number of atheroma plaques in carotid arteries wereevaluated by B-mode ultrasonography. Controls were 50 healthy subjects whose age was not different from patients. Carotid atherosclerosis was considered when IMT was higher than mean plus two standarddeviations of control values, and/or existence of atheroma plaques.

RESULTS

Carotid IMT wasincreased in patients compared to controls 0.82 [0.22] vs 0.62[0.12] mm; p < 0.001) and there were more patients with plaques(67 vs 20%; p < 0.001). Carotid atherosclerosis was found in170 patients and 11 controls (73 vs 22%; p < 0.001). By multivariate analysis, carotid atherosclerosis was associated with age (oddsratio: 1.05; 95% confidence interval [CI], 1.01-1.09) and smoking(odds ratio, 2.11; 95% CI: 1.04-4.26). The presence of more thanone plaque was associated with levels of low-density-lipoprotein(LDL)-cholesterol (odds ratio, 1.01; 95% CI, 1.00-1.02).

CONCLUSIONS

In the patients with coronary disease, prevalence of subclinical carotid atherosclerosisis very high (73%), and it is associated with age and smoking. The advanced stage of atherosclerosis, evaluated by the existence of more than one plaque, is correlated with LDL-cholesterol levels.

Genetics of lipoprotein abnormalities associated with coronary artery disease susceptibility

Coronary heart disease is a complex genetic disease with many genes involved, environmental influences, and important gene-environment interactions. This review discusses the genetic basis of the principal lipoprotein abnormalities associated with coronary heart disease susceptibility in the general population. Individual sections discuss genes regulating LDL cholesterol, HDL cholesterol, and triglyceride levels. A section is included on the effects of the common apo E genetic variation on lipoprotein levels, as well as sections on the genetic regulation of lipoprotein(a) levels, genes regulating the inverse relationship between triglyceride-rich lipoproteins and HDL cholesterol levels, and our current understanding of the genetic basis of familial combined hyperlipidemia. It is clear that the field has progressed, with early studies focused mainly on the association of candidate gene RFLPs with phenotypes, later studies of candidate genes in both parametric and nonparametric linkage studies, and now more and more studies combining linkage analysis with genome scans to identify new loci that influence lipoprotein phenotypes. The future should provide us with the capability to perform reasonable genetic profiling for lipoprotein abnormalities associated with coronary heart disease susceptibility.

Lipoprotein(a), Friedewald formula, and NCEP guidelines. National Cholesterol Education Program

The Friedewald low-density lipoprotein cholesterol formula, which is commonly used in clinical chemistry laboratories, comprises both low-density lipoprotein and lipoprotein(a) cholesterol. This confounder must be recognized and appropriately corrected when dealing with subjects with high plasma lipoprotein(a) levels.

Lipoprotein (a) up-regulates the expression of the plasminogen activator inhibitor 2 in human blood monocytes

Elevated plasma lipoprotein (a) (Lp[a]) and cardiac events show a modest but significant association in various clinical studies. However, the influence of high Lp(a) on the gene expression in blood monocytes as a major cell involved in atherogenesis is poorly described. To identify genes influenced by elevated serum Lp(a), the gene expression was analyzed on a complementary DNA microarray comparing monocytes from a patient with isolated Lp(a) hyperlipidemia and coronary heart disease with monocytes from a healthy blood donor with low Lp(a). By using this approach, numerous genes were found differentially expressed in patient-versus-control monocytes. Verification of these candidates by Northern blot analysis or semiquantitative polymerase chain reaction in monocytes from additional patients with Lp(a) hyperlipidemia and healthy blood donors with elevated Lp(a) confirmed a significant induction of plasminogen activator inhibitor type 2 (PAI-2) messenger RNA (mRNA) in monocytes from male, but not from female, individuals with high Lp(a), indicating that this observation is gender specific. This led also to increased intracellular and secreted PAI-2 protein in monocytes from male probands with Lp(a) hyperlipidemia. Plasminogen activator inhibitor type 1 (PAI-1) mRNA was found suppressed only in the patients' monocytes and not in healthy probands with high Lp(a) levels. Purified Lp(a) induced PAI-2 mRNA and protein and reduced PAI-1 expression in monocytes isolated from various controls. The finding that PAI-2 is elevated in monocytes from male patients with isolated Lp(a) hyperlipidemia and male healthy probands with high Lp(a) and that purified Lp(a) up-regulates PAI-2 in control monocytes in vitro indicate a direct, but gender-specific, effect of Lp(a) for the induction of PAI-2 expression.

Lipoprotein(a) further increases the risk of coronary events in men with high global cardiovascular risk

OBJECTIVES

This prospective population study was conducted to assess the role of elevated lipoprotein(a) [Lp(a)] as a coronary risk factor.

BACKGROUND

The role of elevated Lp(a) as a risk factor for coronary heart disease is controversial. In addition, little attention has been paid to the interaction of Lp(a) with other risk factors.

METHODS

A total of 788 male participants of the Prospective Cardiovascular Münster (PROCAM) study aged 35 to 65 years were followed for 10 years. Both Lp(a) and traditional cardiovascular risk factors (e.g., age, low density lipoprotein [LDL] cholesterol, high density lipoprotein [HDL] cholesterol, triglycerides, systolic blood pressure, cigarette smoking, diabetes mellitus, angina pectoris, and family history of myocardial infarction) were evaluated in 44 men who suffered from myocardial infarction, and in 744 men who survived without major coronary events or stroke. A multiple logistic function algorithm was used to estimate global cardiovascular risk by the combined effects of traditional risk factors.

RESULTS

Overall, the risk of a coronary event in men with an Lp(a) > or =0.2 g/liter was 2.7 times that of men with lower levels (95% confidence interval [CI]: 1.4 to 5.2). This increase in risk was most prominent in men with LDL cholesterol level > or =4.1 mmol/liter (relative risk [RR]: 2.6; 95% CI: 1.2 to 5.7), with HDL cholesterol < or =0.9 mmol/liter (RR 8.3; 95% CI: 2.0 to 35.5), with hypertension (RR 3.2; 95% CI: 1.4 to 7.2), or within the two highest global risk quintiles (relative risk: 2.7; 95% CI: 1.3 to 5.7).

CONCLUSIONS

Lp(a) increases the coronary risk, especially in men with high LDL cholesterol, low HDL cholesterol, hypertension and/or high global cardiovascular risk.

Mapping of a minimal apolipoprotein(a) interaction motif conserved in fibrin(ogen) beta - and gamma -chains

Lipoprotein(a) (Lp(a)) is a major independent risk factor for atherothrombotic disease in humans. The physiological function(s) of Lp(a) as well as the precise mechanism(s) by which high plasma levels of Lp(a) increase risk are unknown. Binding of apolipoprotein(a) (apo(a)) to fibrin(ogen) and other components of the blood clotting cascade has been demonstrated in vitro, but the domains in fibrin(ogen) critical for interaction are undefined. We used apo(a) kringle IV subtypes to screen a human liver cDNA library by the yeast GAL4 two-hybrid interaction trap system. Among positive clones that emerged from the screen, clones were identified as fibrinogen beta- and gamma-chains. Peptide-based pull-down experiments confirmed that the emerging peptide motif, conserved in the carboxyl-terminal globular domains of the fibrinogen beta and gamma modules specifically interacts with apo(a)/Lp(a) in human plasma as well as in cell culture supernatants of HepG2 and Chinese hamster ovary cells, ectopically expressing apo(a)/Lp(a). The influence of lysine in the fibrinogen peptides and of lysine binding sites in apo(a) for the interaction was evaluated by binding experiments with apo(a) mutants and a mutated fibrin(ogen) peptid. This confirmed the lysine binding sites in kringle IV type 10 of apo(a) as the major fibrin(ogen) binding site but also demonstrated lysine-independent interactions.

Changes in lipoprotein(a) levels in overt and subclinical hypothyroidism before and during treatment

The aim of this prospective, follow-up study was to examine the influence of overt hypothyroidism (OHP) and subclinical (SHP), before and during thyroxine (T4) treatment, on lipoprotein(a) [Lp(a)], other lipoproteins, and apolipoproteins. Twenty-four patients (17 females, 7 males) with OHP, aged 54 +/- 11.1 years (group A) and 23 patients (females) with SHP aged 50.1 +/- 13.2 years (group B) were evaluated and compared to 34 and 38 controls, respectively. All patients received T4 therapy in a stepwise fashion until euthyroidism was reached. Thyrotropin (TSH), free thyroxine (FT4), and total triiodothyronine (TT3) levels were measured before T4 therapy and repeatedly every 4 weeks after the initiation of treatment until the euthyroid state was reached. Levels of Lp(a), total cholesterol (TC), triglycerides (TG), low-density lipoprotein cholesterol (LDLc), high-density lipoprotein cholesterol (HDLc), apolipoprotein A1 (apoA1) and apolipoprotein B (apoB) were measured before and 4 months after the achievement of euthyroidism. Additionally, body mass index (BMI) was also evaluated. We found that in OHP patients, levels of TC, LDLc, and apoB were elevated before treatment and decreased significantly after the return to the euthyroid state. BMI and levels of triglycerides also decreased significantly; Lp(a) was higher in OHP patients in comparison with controls and decreased significantly by 14.56% (25.29% in men and 10.34% in women) during T4 treatment. In SHP patients, levels of all common lipoproteins, apolipoproteins, and Lp(a) did not differ significantly from controls before treatment and did not change after the euthyroid stage was reached. It is concluded that in overt hypothyroidism, Lp(a) levels and most of the lipoproteins were elevated before treatment and decreased significantly. In subclinical hypothyroidism, lipoproteins and Lp(a) levels were normal at baseline and did not change during treatment.

Lipoprotein (a) and stroke

Strokes are one of the most common causes of mortality and long term severe disability. There is evidence that lipoprotein (a) (Lp(a)) is a predictor of many forms of vascular disease, including premature coronary artery disease. Several studies have also evaluated the association between Lp(a) and ischaemic (thrombotic) stroke. Several cross sectional (and a few prospective) studies provide contradictory findings regarding Lp(a) as a predictor of ischaemic stroke. Several factors might contribute to the existing confusion--for example, small sample sizes, different ethnic groups, the influence of oestrogens in women participating in the studies, plasma storage before Lp(a) determination, statistical errors, and selection bias. This review focuses on the Lp(a) related mechanisms that might contribute to the pathogenesis of ischaemic stroke. The association between Lp(a) and other cardiovascular risk factors is discussed. Therapeutic interventions that can lower the circulating concentrations of Lp(a) and thus possibly reduce the risk of stroke are also considered.

Interactions between apolipoprotein E and apolipoprotein(a) in patients with late-onset Alzheimer disease

BACKGROUND

Apolipoprotein(a) [apo(a)], the distinctive, highly polymorphic glycoprotein of lipoprotein(a), shares a series of common features with apolipoprotein E (apoE), which is implicated in the development of Alzheimer disease.

OBJECTIVE

To determine whether apo(a) is associated with Alzheimer disease.

DESIGN

Case-control study.

SETTING

University hospitals in Europe.

PARTICIPANTS

285 patients with Alzheimer disease and 296 controls.

MEASUREMENTS

Plasma lipoprotein(a) levels, size of the apo(a) isoforms, and apoE and apo(a) genotyping.

RESULTS

Among carriers of the apoE epsilon4 allele, lipoprotein(a) was associated with a progressive, age-dependent increased risk for late-onset Alzheimer disease (odds ratio for patients >80 years of age, 6.0 [95% CI, 1.2 to 30.8]; P<0.01). Among noncarriers older than 80 years of age, lipoprotein(a) was associated with a reduced risk for Alzheimer disease (odds ratio, 0.4 [CI, 0.2 to 0.91; P<0.05).

CONCLUSIONS

In this convenience sample, lipoprotein(a) was an additional risk factor for late-onset Alzheimer disease in carriers of the apoE epsilon4 allele. However, lipoprotein(a) may protect against late-onset Alzheimer disease in noncarriers.

Twenty-four hours of insulin infusion does not lower plasma lipoprotein(a) in healthy men

The effect of 24-h exogenous hyperinsulinaemia on the plasma level of the atherogenic lipoprotein(a) (Lp(a)) is unknown. We evaluated the responses of plasma cholesterol, triglycerides, apolipoprotein (apo) B and Lp(a) during 24-h insulin infusion (180 pmol/kg/h) in 6 healthy men. Plasma total cholesterol (p < 0.01) and triglycerides (p < 0.05) decreased after 24 h of hyperinsulinaemia. Apo B was unchanged after 8 h (-2.4 +/- 3.0%, n.s.) and decreased by 10.9 +/- 4.8% (p<0.025) after 24 h of insulin. In contrast, Lp(a) did not decrease (+28.4 +/- 18.4%, n.s., and +/- 49.1 +/- 22.0%, n.s., after 8 and 24 h of insulin, respectively). This experiment supports the hypothesis that moderate hyperinsulinaemia has a different effect on the plasma level of triglyceride-rich lipoproteins compared to Lp(a).