Elusive proatherothrombotic role of Lp(a): a new direction?

Association of D-dimer with Plaque Characteristics and Plasma Biomarkers of Oxidation-Specific Epitopes in Stable Subjects with Coronary Artery Disease

D-dimer has emerged as a biomarker of cardiovascular event risk, yet pathophysiological factors associated with plasma D-dimer levels in stable coronary artery disease (CAD) subjects are poorly understood. In 106 stable CAD subjects undergoing intravascular ultrasound with virtual histology (IVUS-VH), we measured D-dimer, lipoprotein(a) (Lp(a)), plasminogen, biomarkers reflecting oxidation-specific epitopes (OSE) such as oxidized phospholipids on apolipoprotein B-100 (OxPL-apoB), OxPL on plasminogen (OxPL-PLG), and autoantibodies to phosphorylcholine-BSA [PC-BSA] and a malondialdehyde [MDA] mimotope. In univariate analysis, D-dimer was positively associated with Lp(a), OxPL-apoB, OxPL-PLG, and coronary artery calcium, and inversely associated with autoantibodies to OSE and plaque fibrosis. D-dimer levels > 500 ng/ml also showed positive association with plaque necrosis. After multivariate analysis, D-dimer remained significantly associated with Lp(a) and plaque calcium. While further studies are needed, results provide evidence that plasma D-dimer levels are associated with levels of OxPLs and IVUS-VH indices linked to plaque erosion and rupture.

Lipoprotein (a) and atherogenic indices in Sudanese patients with type 2 diabetes

BACKGROUND & AIMS

Type 2 diabetes is associated with significant cardiac morbidity and mortality with a more than threefold increased risk of coronary artery disease (CAD). We aimed to assess the serum concentrations of lipoprotein (a) and lipid profile indexes as predictors for CAD in Sudanese type 2 diabetics compared to healthy subjects.

MATERIALS & METHODS

This case-control study was conducted at Jabir Abu-Aliz Specialized Center, Khartoum State, Sudan. After overnight fasting, 4 ml blood samples were collected in plain vials through venous puncture from each subject. Lipid profile parameters were estimated by standard laboratory procedures. Serum lipoprotein (a) was measured by immunoturbidimetric method. Statistical analyses were performed using SPSS software (version 17).

RESULTS

Compared to healthy controls, type 2 diabetics showed significantly higher serum lipids and lipoprotein fractions. The mean values of lipoprotein (a), TC: HDL-C (5.55±.8 vs. 3.89±.6) and LDL-C: HDL-C (3.80±0.7 vs. 2.32±0.5) were significantly increased in patients. Lipoprotein (a) was significantly correlated with TG (p=.025), HDL-C (inversely, p<.001), VLDL-C (p= .025), and TC: HDL-C ratio (p= 016). Moreover, LDL-C: HDL-C ratio and TC were the most common risk factors distributed among the study patients (80% and 71.4% respectively).

CONCLUSION

Diabetic patients characterized by higher ratios of TC: HDL -C and LDL: HDL and Lipoprotein (a) compared to healthy controls. The evaluation of these lipid indices in diabetics, beside the routine lipid profile analysis, may be a crucial helpful step in the prevention of coronary artery disease since these atherogenic factors can be reduced by lifestyle modifications.

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.

Lipoprotein (a) as an acute phase reactant in patients on chronic hemodialysis

Lipoprotein (a) [Lp(a)], is an independent risk factor for atherosclerotic cardiovascular disease in patients on chronic hemodialysis. A low concentration of high density lipoprotein cholesterol (HDL-C) and serum albumin are another potential risk factors. The purpose of this study was to explore in patients on chronic hemodialysis, whether Lp(a) elevated levels are influenced by activated acute phase response (APR) and the correlation of Lp(a) with HDL-C and serum albumin. In 69 hemodialysis patients with C-reactive protein (CRP) levels over than 10 mg/L and 101 hemodialysis patients with CRP levels in the normal range, Lp(a), HDL-C and serum albumin were determined in relation to CRP, as a sensitive marker of an APR. Results showed that serum concentration of CRP in 69 hemodialysis patients was significantly higher than in controls (44,62 mg/L versus 8,75 mg/L, p<0,01).Patients with elevated CRP had significantly higher serum levels of Lp(a) and lower serum levels of HDL-C and albumin, than patients with CRP in the normal range ( 35,39 mg/dl versus 28,6 mg/dl, p<0,01, 0,91 mmol/L versus 1,29 mmol/L, p<0,01 and 33,56 g/L versus 35,86 g/L, p<0,01). Lp(a) levels correlated positively with CRP and negatively with HDL-C and serum albumin, in patients with elevated CRP, but not in healthy controls. According to the results Lp(a) reacts as an acute phase protein, in patients with APR.