APO(a) variants and lipoprotein(a) in men with or without myocardial infarction

Lipoprotein(a) and risk of myocardial infarction--genetic epidemiologic evidence of causality

Elevated levels of lipoprotein(a) are associated with an increased risk of myocardial infarction. Our study aimed to test whether genetic data are consistent with this association being causal. Accordingly, we developed a high-throughput realtime PCR assay to genotype for the lipoprotein(a) kringle IV type 2 (KIV-2) repeat polymorphism in the LPA gene in > 40,000 individuals. The LPA KIV-2 genotype associated with plasma levels of lipoprotein(a) (trend p < 0.001), and the LPA KIV-2 genotype associated with risk of myocardial infarction (trend p < 0.001 to 0.03) in a manner consistent with its effect on plasma levels of lipoprotein(a). The association of LPA KIV-2 genotypes raising plasma levels of lipoprotein(a) with increased risk of myocardial infarction strongly supports a causal association of lipoprotein(a) with risk of myocardial infarction.

Apolipoprotein(a) inhibits lipopolysaccharide-induced IL-6 secretion in human astrocytoma cell line by interfering with lipopolysaccharide signaling

OBJECTIVE

To examine the role of lipoprotein(a) [Lp(a)] on the inflammatory response of cells in the nervous system by investigating its effect on lipopolysaccharide (LPS)-induced interleukin-6 (IL-6) secretion.

MATERIALS AND METHODS

Human astrocytoma U373 cells were treated with recombinant apolipoprotein(a) [r-apo(a)] A10K (175-11 nM), alone or in combination with LPS (100 and 10 ng/ml). IL-6 levels were evaluated by immunoblotting. Statistical analysis was performed by one-way ANOVA.

RESULTS

r-apo(a) caused dose-dependent inhibition of LPS-induced IL-6 secretion (100 ng/ml LPS, p = 0.0205; 10 ng/ml LPS, p = 0.0005). Pre-treatment of cells with 88 nM r-apo(a), rinsing, and activation with 10 ng/ml LPS did not reverse the inhibition (p = 0.0048), which could be reversed by supplementation with excess serum (5-20%) (p = 0.0454) or recombinant CD14 (2.0-0.05 μg/ml) (p = 0.0230).

CONCLUSIONS

Our data indicate that apo(a) plays a natural anti-endotoxin role which relies on its interference with cell-associated and serum components of LPS signaling.

Lipoprotein(a) and ischemic heart disease--a causal association? A review

The aim of this review is to summarize present evidence of a causal association of lipoprotein(a) with risk of ischemic heart disease (IHD). Evidence for causality includes reproducible associations of a proposed risk factor with risk of disease in epidemiological studies, evidence from in vitro and animal studies in support of pathophysiological effects of the risk factor, and preferably evidence from randomized clinical trials documenting reduced morbidity in response to interventions targeting the risk factor. Elevated and in particular extreme lipoprotein(a) levels have in prospective studies repeatedly been associated with increased risk of IHD, although results from early studies are inconsistent. Data from in vitro and animal studies implicate lipoprotein(a), consisting of a low density lipoprotein particle covalently bound to the plasminogen-like glycoprotein apolipoprotein(a), in both atherosclerosis and thrombosis, including accumulation of lipoprotein(a) in atherosclerotic plaques and attenuation of t-PA mediated plasminogen activation. No randomized clinical trial of the effect of lowering lipoprotein(a) levels on IHD prevention has ever been conducted. Lacking evidence from randomized clinical trials, genetic studies, such as Mendelian randomization studies, can also support claims of causality. Levels of lipoprotein(a) are primarily determined by variation in the LPA gene coding for the apolipoprotein(a) moiety of lipoprotein(a), and genetic epidemiologic studies have documented association of LPA copy number variants, influencing levels of lipoprotein(a), with risk of IHD. In conclusion, results from epidemiologic, in vitro, animal, and genetic epidemiologic studies support a causal association of lipoprotein(a) with risk of IHD, while results from randomized clinical trials are presently lacking.

Apolipoprotein gene polymorphisms and plasma levels in healthy Tunisians and patients with coronary artery disease

Aim

To analyze apolipoprotein gene polymorphisms in the Tunisian population and to check the relation of these polymorphisms and homocysteine, lipid and apolipoprotein levels to the coronary artery disease (CAD).

Methods

In healthy blood donors and in patients with CAD complicated by myocardial infarction (MI) four apolipoprotein gene polymorphisms [APO (a) PNR, APO E, APO CI and APO CII] were determined and plasma levels of total homocysteine, total cholesterol (TC), triglycerides (TG), HDL-cholesterol (HLD-C) and apolipoproteins (apo A-I, Apo B, Apo E) were measured.

Results

Analysis of the four apolipoprotein gene polymorphisms shows a relative genetic homogeneity between Tunisian population and those on the other side of Mediterranean basin. Compared to controls, CAD patients have significantly higher main concentrations of TC, TG, LDL-C, apo B and homocysteine, and significantly lower ones of HDL-C, apo A-I and apo E. The four apolipoprotein gene polymorphisms have not showed any significant differences between patients and controls. However, the APO E4 allele appears to be associated to the severity of CAD and to high levels of atherogenic parameters and low level of apo E, which has very likely an anti-atherogenic role.

Conclusion

Although APO (a) PNR, APO CI and APO CII genes are analyzed in only few populations, they show a frequency distribution, which is not at variance with that of APO E gene and other widely studied genetic markers. In the Tunisian population the APO E 4 appears to be only indirectly involved in the severity of CAD. In the routine practice, in addition of classic parameters, it will be useful to measure the concentration of apo E and that of Homocysteine and if possible to determine the APO E gene polymorphism.

Lipoprotein(a) in the cerebrospinal fluid of neurological patients with blood-cerebrospinal fluid barrier dysfunction

BACKGROUND

Lipoprotein(a) [Lp(a)] is a recognized pathogenic particle in human plasma, but its presence in the cerebrospinal fluid and its possible role in the central nervous system have not been documented. We tested the hypothesis that apolipoprotein(a) [apo(a)], free or as a component of the Lp(a) particle, can cross the blood-cerebrospinal fluid barrier and be found in the cerebrospinal fluid of patients affected by neurologic pathologies.

METHODS

We studied paired cerebrospinal fluid/serum samples from 77 patients with inflammatory (n=20) or noninflammatory (n=34) blood-cerebrospinal fluid barrier dysfunction and without blood-cerebrospinal fluid barrier dysfunction (n=23). We used ELISA to measure Lp(a) concentrations and Western blot and immunodetection to analyze apo(a) isoforms in native and reducing conditions.

RESULTS

Entire Lp(a) with either small or large apo(a) isoforms was present in the cerebrospinal fluid of patients with blood-cerebrospinal fluid barrier dysfunction, regardless of its pathogenesis. Multiple linear regression analysis showed that both serum Lp(a) concentration (P=0.003) and cerebrospinal fluid/serum albumin ratio (P<0.001) were predictors of the Lp(a) concentration in cerebrospinal fluid.

CONCLUSIONS

Our results demonstrate that Lp(a) can cross a dysfunctional blood-cerebrospinal fluid barrier. The unusual presence of Lp(a) in the cerebrospinal fluid could extend some of its known pathogenic effects to the central nervous system.

Lipoprotein(a), lipids and proinflammatory cytokines in patients undergoing major abdominal surgery

Background

The aims were to investigate whether surgical stress can induce a positive or negative lipoprotein(a) acute response, to determine any association with apolipoprotein(a) phenotypes, and to establish whether any such response is dependent on changes in lipids and proinflammatory cytokines. In addition, the impact of interleukin (IL) 6 genetic variability on the cytokine response to surgery was examined.

Methods

This prospective, observational study included 41 patients with cancer referred for abdominal surgery. Preoperative (T0) plasma concentrations of lipoprotein(a), IL-6, tumour necrosis factor α, and serum concentrations of transforming growth factor β1 and lipids, were compared with values obtained 5 h (T1), 24 h (T2) and 5 days (T3) after surgery. Apolipoprotein(a) Kringle IV (KIV)-VNTR (variable-number tandem repeat) and IL-6 − 174 G/C polymorphisms were analysed.

Results

Lipoprotein(a) was found to act as a negative acute-phase reactant (30·0 per cent reduction at T2) (P = 0·009). Surgery had a more profound impact on subjects with low KIV-VNTR. After surgery, lipoprotein(a) correlated significantly with corrected low-density lipoprotein (LDL)-cholesterol (r = 0·408 at T2). IL-6 inversely correlated with lipoprotein(a) (r = −0·321 at T1) and LDL-cholesterol (r = −0·418 at T1). The IL-6 response could be predicted from a combination of the surgical severity and −174 G/C genotype.

Conclusion

Although temporal associations did not indicate causality, these data provide a hypothesis to explain the inverse relationship between lipoprotein(a) and IL-6.

[New aspects of normolipidemic dyslipoproteinemias]

INTRODUCTION

Normolipidemic dislipoproteinemias include various disorders of different lipoproteins, of their subfractions or some apolipo-proteins, of primary or secondary origin, which are widespread among general population and, like hyperlipoproteinemias, they are associated with the risk for premature atherosclerosis.

DECREASED LEVEL OF HDL CHOLESTEROL

It is a primary, familial hypoalphalipoproteinemia, which is commonly associated with obesity, diet rich in carbohydrates, decreased physical activity and excessive use of coffee and some drugs.

HYPERAPOBETALIPOPROTEINEMIA

It is characterized by increase of apo B-100 in LDL particles, most probably as a consequence of increased hepatic synthesis. Apolipoprotein E isoforms ApoE4 isoform is associated with elevated LDL-cholesterol concentration due to rapid IDL to LDL conversion.

ELECTROPHORETIC DISORDERS

The most important is the latent type IV (pre-beta) or IVb (pre-beta1) with decreased VLDL clearance.

PROLONGED POSTPRANDIAL LIPEMIA

It is common in obesity, NIDDM and coronary heart disease, as an independent risk factor for premature atherosclerosis.

INCREASED OXIDATIVE MODIFICATION OF THE LDL AND HDL PARTICLES

Oxidatively modified LDL may have a key role in the pathogenesis of atherosclerosis and oxidative modification of HDL reduces its transport capacity and its inhibition of LDL oxidation. INCREASED LEVEL OF LP(A) Lp(a) is an independent risk factor for premature atherosclerosis, primarily in young and middle-aged men, in persons with elevated global cardiovascular risk factor profile, decreased HDL-cholesterol, and hypertension. The risk is smaller in persons taking hypocholesterolemic drugs. Also, it is elevated in NIDDM, hypothyroidism and kidney disease.

Helicobacter pylori is associated with modified lipid profile: impact on Lipoprotein(a)

OBJECTIVES

Helicobacter pylori is a controversial risk factor for atherosclerosis. We investigated whether the bacterium persistent inflammation or the expression of the cytotoxin-associated gene A (CagA) may affect serum lipids as well as Lipoprotein(a).

DESIGN AND METHODS

Two hundred-eleven healthy volunteers were evaluated for lipids and Lipoprotein(a). Helicobacter pylori was characterized by Urea Breath Test and IgG-anti-CagA. apo(a) Kringle-IV polymorphism was genotyped.

RESULTS

Prevalence of the infection was 72%; 43% of subjects expressed CagA reactivity. Infected subjects showed increased levels of cholesterol, LDL-cholesterol, and cholesterol/HDL-cholesterol atherogenic index. Association with the Helicobacter pylori CagA(-) strains persisted after the adjustment for covariates. Significant difference between infected and uninfected subjects was found in Lipoprotein(a) levels. This difference did not arise from the Kringle-IV genotype.

CONCLUSIONS

The infection per se significantly modified serum lipid and Lipoprotein(a) concentrations. CagA does not seem to be a reliable marker of pathogenicity for the atherogenic complications of H. pylori infection.