Association of lipoprotein(a) with atherothrombotic events and fibrinolytic variables. A case-control study

Lipoprotein(a) is related to the extent of lesions in the coronary vasculature and to unstable coronary syndromes

BACKGROUND

Lp(a) is a highly atherogenic particle with a prothrombotic effect. Until now its relation to the extent and severity of the atheromatic lesions had not been established by standard procedures.

HYPOTHESIS

This study examined the correlation of Lp(a) to the extent and severity of coronary artery disease (CAD) and its relation to unstable clinical events (not including sudden death).

METHODS

In 202 patients undergoing coronary angiography, plasma lipids were measured with the usual procedures and Lp(a) with the enzyme-linked immunosorbent assay. The extent of CAD was expressed in the number of diseased vessels and its severity in terms of the severity coefficient and the obstruction coefficient.

RESULTS

A very strong relationship between LP(a) and the number of diseased vessels (p = 0.0007) signifying diffuse atherosclerosis, but no relation with the severity of the lesions. was found. However, it was the only lipid that correlated significantly with the number of totally occluded vessels (p = 0.0003). The thrombogenic ability of Lp(a) was manifested by increased incidence of myocardial infarction and unstable angina episodes in patients with elevated Lp(a) (p = 0.0157).

CONCLUSION

Elevated Lp(a) predisposes to the extent of CAD and total occlusions but not to the severity of lesions. Patients with increased Lp(a) levels and unstable angina are at increased danger of suffering myocardial infarction. Thus, Lp(a) may predispose to plaque destabilization and thrombosis of noncritical lesions.

Arginyl-glycyl-aspartyl (RGD) epitope of human apolipoprotein (a) inhibits platelet aggregation by antagonizing the IIb subunit of the fibrinogen (GPIIb/IIIa) receptor

An unknown epitope of apolipoprotein (a) antagonizes fibrinogen binding to agonist-stimulated platelet's fibrinogen (GPIIb/IIIa) receptor yielding lipoprotein (a) mediated decreased platelet aggregation. The purpose of this study was to test the hypothesis that human apolipoprotein (a)'s single arginyl-glycyl-aspartyl (RGD) epitope, unique to apolipoprotein (a) in lipoprotein (a) binds to the RGD binding motif on the IIb subunit of the GPIIb/IIIa receptor thus reducing platelet-bound fibrinogen and consequently decreasing agonist-stimulated platelet aggregation. Platelets (N=30 subjects) were prepared from fresh plasma, washed three times in Tyrode's buffer and stimulated using 10 microM ADP or 2 microg/ml collagen. Lipoprotein (a) was isolated from plasma using lectin affinity chromatography followed by ultracentrifugation. The peptide RGDS inhibited (125)I-labelled lipoprotein (a) binding to autologous platelets with IC-50's of 25.1+/-2.2 (mean+/-SEM) and 15.4+/-1.3 microM for collagen- and ADP-stimulation respectively. Further, RGDS reduced platelet binding of (125)I-labelled fibrinogen IC-50's of 35.5+/-3.2 (mean+/-SEM) and 20.7+/-2.2 microM for collagen- and ADP-stimulation respectively. The monoclonal antibody PAC-1, uniquely directed at the RGD binding motif on the IIb subunit on collagen- and ADP-stimulated platelets, inhibited binding of (125)I-labelled lipoprotein (a) with IC-50's of 6.4+/-0.7 and 2.5+/-2.2 microg/10(8) platelets for collagen- and ADP-stimulation respectively. Additionally, PAC-1 reduced platelet bound of (125)I-labelled fibrinogen with IC-50's of 9.0+/-1.4 and 4.1+/-2.2 microg/10(8) platelets for collagen- and ADP-stimulation respectively. In a dose-related fashion, a polyclonal antibody, specific for the RGD epitope on apolipoprotein (a), restored platelet aggregation to control levels, inhibited (125)I-labelled lipoprotein (a) binding, and increased (125)I-labelled fibrinogen by displacing lipoprotein (a) from the GPIIb/IIIa receptor. Thus a never before demonstrated aspect of the mechanism of lipoprotein (a)'s suggested novel role as an endogenous regulator of fibrinogen binding to collagen- and ADP-stimulated platelets has been shown. In conclusion, lipoprotein (a), via apolipoprotein (a)'s RGD epitope, binds to the RGD binding motif on the IIb protein of the GPIIb/IIIa receptor consequently reducing platelet-bound fibrinogen which results in decreased platelet aggregation.

Does smoking status influence the effect of physical exercise on fibrinolytic function in healthy volunteers?

Exercise has been reported to simultaneously trigger and protect against sudden death, the so-called "The Paradox of Exercise". Differences in fibrinolytic function appear to exist between chronic and acute exercise. The aim of the present study was to assess the fibrinolytic system after strenuous exercise in healthy people and explored the influence of smoking habit.

METHODS

23 healthy male volunteers were studied (14 non-smokers; 9 current smokers). Citrated plasma blood samples were taken before and 30 minutes after a maximal exercise treadmill test, and levels of tissue type plasminogen activator (t-PA) antigen, plasminogen activator inhibitor (PAI-1) antigen and lipoprotein-a, Lp(a), [all ELISA] were measured as indices of fibrinolytic function.

RESULTS

Smokers had higher body mass index and higher heart rate at baseline than non smokers (p = 0.046 and p = 0.001, respectively). At baseline, smokers showed increased plasma Lp(a) levels than non smokers (p = 0.04), with no differences in t-PA and PAI-1 antigen levels. Following the exercise treadmill test, smokers had a shorter exercise duration and lower exercise capacity than non smokers (p = 0.008 and p = 0.004, respectively). This was associated with a reduction in t-PA antigen levels in the whole study population, (p = 0.048) without differences in PAI-1 levels, with no significant differences between smokers and non smokers. Lp(a) levels were also significantly reduced (p = 0.0001).

CONCLUSIONS

Acute exercise alters plasma tPA antigen and Lp(a) levels, but there was no significant effect of smoking status in healthy subjects.

Interrelationships between the fibrinolytic system and lipoproteins in the pathogenesis of coronary atherosclerosis

The fibrinolytic system is comprised of a series of serine proteases and serine protease inhibitors which are involved in the dissolution of fibrin in the vascular lumen, but also in the migration of cells and in the remodeling of the extracellular matrix of the vascular wall. The transcription, expression and degradation of the various fibrinolytic enzymes by cells in the vascular wall is influenced by lipoproteins and this interrelationship may play a significant role in the development of the atherosclerotic plaque: the transcription of plasminogen activator inhibitor-1 is influenced by very low-density lipoproteins, the expression of both tissue plasminogen activator and plasminogen activator inhibitor-1 is influenced by low-density lipoproteins and lipoprotein(a) (Lp(a)) and the internalization of the urokinase: plasminogen activator inhibitor-1 complex occurs via the low-density lipoprotein related protein. Several clinical studies have shown correlations between fibrinolytic parameters and lipoproteins in healthy populations and in patients with dyslipidemia, but the correlation between single plasma fibrinolytic enzymes and the severity of coronary atherosclerosis is less well documented. The reduction of plasma lipids with lipid-lowering drugs also affects the concentration of fibrinolytic enzymes, although this may also be due to direct effects of the drugs on the expression of the various fibrinolytic enzymes. The reduction of fibrinolytic and proteolytic activity in the atherosclerotic plaque by their lipid-lowering effect and by their direct action on the fibrinolytic system may be one of the mechanisms by which some lipid-lowering drugs achieve plaque stabilization.

Prothrombotic determinants of coronary atherothrombosis

An acute coronary syndrome (ACS) is the clinical manifestation of a thrombotic event occurring within a coronary artery narrowed by atherosclerosis. This atherothrombotic event is thought to occur following destabilizing changes within the atherosclerotic plaque, rendering it a surface on which thrombus can develop. The development and progression of this thrombus are determined by deleterious perturbations in the hemostatic equilibrium within the local environment of the plaque that favor thrombosis. Major risk factors for the development of atherosclerotic disease have been clearly established and are targets of aggressive modification in an effort to impede the development or slow the progression of disease. While conferring an increased risk for plaque development, these and other risk factors also establish a prothrombotic milieu within the microenvironment of the atherosclerotic plaque that favors thrombosis. This review seeks to address these traditional and emerging risk factors from the context of their pathologic effects on local hemostatic balance. Aggressive risk factor modification not only reduces atherosclerotic disease development and progression, but also ameliorates the prothrombotic state, and ultimately serves to reduce atherothrombotic events.

[Predictive value of changes in the hemostasis system in patients with ischemic brain diseases]

The aim of this research was to determine the importance of tracking the dynamics of changes of the hemostatic system factors (aggregation of thrombocytes, D-dimer, PAI-1, antithrombin III, protein C and protein S, factor VII and factor VIII, fibrin degradation products, euglobulin test and th activated partial thromboplastin time--aPTPV) in relation to the level of the severity of ischaemic brain disorders (IBD) and the level of neurological and functional deficiency in the beginning of IBD manifestation from 7 to 10 days, 19 to 21 day, and after 3 to 6 months. The research results confirmed significant predictive value of changes of hemostatic system with the predomination of procoagulant factors, together with the insufficiency of fibrinolisys. Concerning the IBD severity and it's outcome, the significant predictive value was shown in the higher levels of PAI-1 and the lower level of antithrombin III, and borderline significant value was shown in the accelerated aggregation of thrombocytes and the increased concentration of D-dimer. It could be concluded that the tracking of the dynamics of changes in parameters of hemostatic system proved to be an easily accessible method with the significant predictive value regarding the development of more severe. IBD cases and the outcome of the disease itself.

[Atherosclerosis of the aortic arch--a possible etiopathogenic factor in cerebral ischemic disease]

Ishemijska bolest mozga je po slozenosti patofizioloskih procesa svakako najslozeniji klinicki entitet savremene medicine. Ovo, takodje, vazi i za etiopatogenetske procese vezane za njen nastanak i razvoj. Pored znacajnog napretka u razumijevanju etiopatogeneze i patofiziologije IBM, a takodje i razvoja visokosofistikovanih dijagnostickih procedura ukljucenih u algoritam etioloskog razjasnjenja i potvrde IBM, svjedoci smo velikog ucesca nerazjasnjenih uzroka IBM. Ateroskleroza aortnog luka, posebno tezeg stepena izrazenosti, uz postojanje ulceracija i tromboticnih mobilnih naslaga na ateromskim plakovima, etiopatogentski i patofizioloski, a rezultatima brojnih klinickih studija potvrdjeno, predstavlja novi nezavisni faktor rizika za nastanak ishemijske bolesti mozga. Ovo je posebno nacajno kod bolesnika starijih od 60 godina.

Lipoprotein(a) concentration and molecular weight of apolipoprotein(a) in patients with cerebrovascular disease and diabetes mellitus

Plasma lipoprotein(a) [Lp(a)] concentrations are genetically determined, and hyper-Lp(a)-emia is an independent risk factor for atherosclerosis and thrombosis. To study the implications of Lp(a) in cerebrovascular disease (CVD) and diabetes mellitus (DM), we examined plasma Lp(a) levels and molecular weights of apolipoprotein(a) [apo(a)] in 118 patients with CVD, and 125 cases with DM. Although mean Lp(a) concentrations were higher in those cases with atherothrombotic brain infarction than in those with brain hemorrhage and lacunar infarction, the difference was not statistically significant. Lp(a) levels were significantly higher in the DM cases treated with insulin and in those treated with oral hypoglycemic agents than in those on diet therapy alone, suggesting that insulin and oral agents modulate apo(a) expression. Lp(a) concentrations correlated significantly with the low-molecular-weight isoforms of apo(a) in all CVD and DM groups.