The inhibition of tissue type plasminogen activator by plasminogen activator inhibitor-1. The effects of fibrinogen, heparin, vitronectin, and lipoprotein(a)

Serum Lipoprotein(a) as Predictive Factor for Early Neurological Deterioration of Acute Ischemic Stroke After Thrombolysis

Objective

This study aimed to explore the relationship between serum lipoprotein(a) (LP(a)) levels and early neurological deterioration (END) in patients with acute ischemic stroke (AIS) after thrombolysis.

Methods

In total, 236 patients with AIS after thrombolysis were enrolled in this study. Serum LP(a) levels were measured on admission after thrombolysis. END was defined as an increase of at least two points in the NIHSS score within 48 hours after thrombolysis. Binary logistic regression analysis was used to assess the association between serum LP(a) levels and END.

Results

Overall, patients with END had higher LP(a) than those without END (high LP(a): 38.3% vs 22.2%, intermediate LP(a): 40.3% vs 41.8%, low LP(a): 21.3% vs 36.0%, p<0.005). In the multivariate analysis, high LP(a) (defined as LP(a) level≥ 300 mg/L) was an independent risk factor for END post-thrombolysis (OR=3.154, 95% CI=1.067-9.322, p=0.038).

Conclusion

Our findings demonstrated that LP(a) was an independent risk factor for END post-thrombolysis and that LP(a) level≥ 300 mg/L could be associated with END post-thrombolysis in this study population.

B-vitamin treatment modifies the mortality risk associated with calcium channel blockers in patients with suspected stable angina pectoris: A prospective cohort study

BACKGROUND

Calcium channel blockers (CCBs) are used for the treatment of cardiovascular disease (CVD), including angina pectoris, and hypertension; however, the effect on survival remains uncertain. CCBs impair fibrinolysis and have been linked to elevated plasma homocysteine (Hcy), a CVD risk marker.

OBJECTIVE

We explored the association between CCB use and mortality in a large prospective cohort of patients with suspected stable angina pectoris (SAP), and potential effect modifications by Hcy-lowering B-vitamin treatment (folic acid, B₁₂ and/or B₆) as 61.8% of the patients participated in a randomized placebo-controlled B-vitamin intervention trial.

METHODS

Patient baseline continuous characteristics according to CCB treatment were tested by linear regression. Hazard ratios (HRs) for mortality associated with CCB treatment, also according to B-vitamin intervention, were examined using Cox regression analysis. The multivariable model included cardiovascular risk factors, medical histories, and use of CVD medications.

RESULTS

A total of 3991 patients (71.5 % men) were included, of whom 907 were prescribed CCBs at discharge. During 10.3 years of median follow-up, 20.6% died and 8.9% from cardiovascular- and 11.6% from non-cardiovascular causes. Patients treated with CCBs had higher plasma Hcy, fibrinogen levels and erythrocyte sedimentation rate (all P<0.001). Further, CCB use was positively associated with mortality, also after multivariable adjustments (HRs [95% CIs]: 1.34 [1.15-1.57], 1.35 [1.08-1.70] and 1.33 [1.09-1.64] for total, CVD and non-CVD death, respectively). Numerically stronger associations were observed among patients not treated with B-vitamins (HR [95% CI]: 1.54 [1.25-1.88], 1.69 [1.25-2.30] and 1.41 [1.06- 1.86] for total, CVD and non-CVD death, respectively), whereas, no association was seen in patients treated with B-vitamins (HR [95% CI]: 1.15 [0.91-1.46], 1.09 [0.76-1.57] and 1.20 [0.88-1.65]).

CONCLUSIONS

In patients with suspected SAP, CCB treatment was associated with increased mortality risk primarily among patients not treated with B-vitamins.

CLINICAL TRIAL REGISTRATION-URL

https://clinicaltrials.gov/ct2/show/NCT00354081?term=NCT00354081&draw=2&rank=1. Clinical Trial Registration-Unique identifier (NCT number): NCT00354081.

Lipoprotein(a) as an Old and New Causal Risk Factor of Atherosclerotic Cardiovascular Disease

Lipoprotein(a) [Lp(a)], discovered in 1963, has been associated with atherosclerotic cardiovascular disease (ASCVD) independent of other traditional risk factors, including LDL cholesterol. Lp(a) is an apolipoprotein B (apoB)-containing lipoprotein, which contains an LDL-like particle. Unlike LDL, which is a primary therapeutic target to decrease ASCVD, current guidelines recommend measuring Lp(a) for risk assessments because there is no clear evidence demonstrating the clinical benefit of decreasing Lp(a) using classical drugs such as niacin. However, recent Mendelian randomization studies indicate that Lp(a) causally correlates with ASCVD. In addition, novel drugs, including PCSK9 inhibitors, as well as antisense oligonucleotide for apo(a), have exhibited efficacy in decreasing Lp(a) substantially, invigorating a discussion whether Lp(a) could be a novel therapeutic target for further ASCVD risk reduction. This review aims to provide current understanding, and future perspectives, of Lp(a), which is currently considered a mere biomarker but may emerge as a novel therapeutic target in future clinical settings.

Lipoprotein(a) in cardiovascular diseases

Lipoprotein(a) (Lp(a)) is an LDL-like molecule consisting of an apolipoprotein B-100 (apo(B-100)) particle attached by a disulphide bridge to apo(a). Many observations have pointed out that Lp(a) levels may be a risk factor for cardiovascular diseases. Lp(a) inhibits the activation of transforming growth factor (TGF) and contributes to the growth of arterial atherosclerotic lesions by promoting the proliferation of vascular smooth muscle cells and the migration of smooth muscle cells to endothelial cells. Moreover Lp(a) inhibits plasminogen binding to the surfaces of endothelial cells and decreases the activity of fibrin-dependent tissue-type plasminogen activator. Lp(a) may act as a proinflammatory mediator that augments the lesion formation in atherosclerotic plaques. Elevated serum Lp(a) is an independent predictor of coronary artery disease and myocardial infarction. Furthermore, Lp(a) levels should be a marker of restenosis after percutaneous transluminal coronary angioplasty, saphenous vein bypass graft atherosclerosis, and accelerated coronary atherosclerosis of cardiac transplantation. Finally, the possibility that Lp(a) may be a risk factor for ischemic stroke has been assessed in several studies. Recent findings suggest that Lp(a)-lowering therapy might be beneficial in patients with high Lp(a) levels. A future therapeutic approach could include apheresis in high-risk patients in order to reduce major coronary events.

Recombinant C1-inhibitor: effects on coagulation and fibrinolysis in patients with hereditary angioedema

BACKGROUND

Recombinant human C1-inhibitor (rhC1INH; Ruconest®) has been developed for treatment of acute angioedema attacks in patients with hereditary angioedema (HAE) due to heterozygous deficiency of C1INH. Previous reports suggest that administration of plasma-derived C1INH products may be associated with an increased risk for thromboembolic complications.

OBJECTIVES

Our aim is to evaluate the effects of rhC1INH on coagulation and fibrinolysis in symptomatic HAE patients.

METHODS

Levels of various coagulation and fibrinolytic parameters were determined in pre- and post-exposure plasma samples from HAE patients included in a randomized clinical trial. Patients were treated with either saline, or 50 or 100 U/kg rhC1INH for an acute angioedema attack.

RESULTS

Prior to rhC1INH treatment, the majority of patients had low to normal activated partial thromboplastin times (aPTT) and increased levels of prothrombin fragment 1+2, thrombin-antithrombin complexes, D-dimers and plasmin-antiplasmin complexes, all of which indicate activation of both coagulation and fibrinolysis. Infusion of rhC1INH at doses up to 100 U/kg did not affect these parameters except for a dose-dependent prolongation of aPTT, confirming that rhC1INH is an inhibitor of the contact system, and that F1+2 levels decreased.

CONCLUSION

Coagulation and fibrinolytic systems are activated in HAE patients suffering from an acute angioedema attack. Treatment with rhC1INH at 50 or 100 U/kg had no effect on parameters reflecting activation of these systems except for a significant effect on aPTT, which likely reflects a pharmacodynamic effect of rhC1INH, and a reduction on plasma levels of the prothrombin activation fragment F1+2. We conclude that these results argue against a prothrombotic effect of treatment with this rhC1INH product in HAE patients.

Mutants of plasminogen activator inhibitor-1 designed to inhibit neutrophil elastase and cathepsin G are more effective in vivo than their endogenous inhibitors

Neutrophil elastase and cathepsin G are abundant intracellular neutrophil proteinases that have an important role in destroying ingested particles. However, when neutrophils degranulate, these proteinases are released and can cause irreparable damage by degrading host connective tissue proteins. Despite abundant endogenous inhibitors, these proteinases are protected from inhibition because of their ability to bind to anionic surfaces. Plasminogen activator inhibitor type-1 (PAI-1), which is not an inhibitor of these proteinases, possesses properties that could make it an effective inhibitor of neutrophil proteinases if its specificity could be redirected. PAI-1 efficiently inhibits surface-sequestered proteinases, and it efficiently mediates rapid cellular clearance of PAI-1-proteinase complexes. Therefore, we examined whether PAI-1 could be engineered to inhibit and clear neutrophil elastase and cathepsin G. By introducing specific mutations in the reactive center loop of wild-type PAI-1, we generated PAI-1 mutants that are effective inhibitors of both proteinases. Kinetic analysis shows that the inhibition of neutrophil proteinases by these PAI-1 mutants is not affected by the sequestration of neutrophil elastase and cathepsin G onto surfaces. In addition, complexes of these proteinases and PAI-1 mutants are endocytosed and degraded by lung epithelial cells more efficiently than either the neutrophil proteinases alone or in complex with their physiological inhibitors, alpha1-proteinase inhibitor and alpha1-antichymotrypsin. Finally, the PAI-1 mutants were more effective in reducing the neutrophil elastase and cathepsin G activities in an in vivo model of lung inflammation than were their physiological inhibitors.

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.

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.

A simple method for determining kinetic constants of complexing inactivation at identical enzyme and inhibitor concentrations

The kinetics of complexing inactivation at identical enzyme and inhibitor concentrations were analyzed and the equations of product generation were derived when the free enzyme concentration is great, larger or smaller than the dissociation constant of inhibitor, K(I). The kinetic constants can be obtained by fitting the derived equations to the progress curve. Numerical examples show that this method is valid and gives satisfactory results.

The inhibition of human factor Xa by plasminogen activator inhibitor type 1 in the presence of calcium ion, and its enhancement by heparin and vitronectin

Plasminogen activator inhibitor type 1 (PAI-1), a member of serine proteinase inhibitor superfamily, is known to inhibit thrombin in the presence of either heparin or vitronectin. We analyzed possible inhibitory activity of PAI-1 on human factor Xa. PAI-1 inhibited factor Xa in the presence of calcium ion (Ca2+), whereas no inhibition was observed in the absence of Ca2+. Half maximal enhancement by Ca2+ was obtained at 0.8 mM. An equimolar complex formation between factor Xa and PAI-1 in the presence of Ca2+ was observed by SDS polyacrylamide gel electrophoresis. Both unfractionated heparin and vitronectin enhanced the inhibition only in the presence of Ca2+. Apparent second-order rate constant (ki) for the inhibition of factor Xa by PAI-1 at 5 mM Ca2+ was 1.6 x 10(4) M-1 s-1, and was enhanced 3-fold by 2 u/ml of heparin (4.6 x 10(4) M-1 s-1) and 10-fold by 100 nM vitronectin (1.6 x 10(5) M-1 s-1), respectively. The interaction between Ca(2+)-bound factor Xa and PAI-1 could be important from the view of PAI-1 neutralization and enhancement of fibrinolysis.

Plasminogen activators and plasminogen activator inhibitors: biochemical aspects

Although this chapter does not represent a historical review, it will be clear how the biochemistry of t-PA, u-PA, PAI-1 and PAI-2 has evolved and where we stand in 1994. While the functional activities of the proteins were recognized at least three to four decades ago, highly purified preparations became available around 1980. In the mid-eighties the cDNAs of the proteins were cloned, representing a major breakthrough in the biochemistry of the four proteins. Amino acid sequences were derived from the nucleotide sequences, homologies with other proteins were recognized and larger amounts of (recombinant) proteins became available for research. In addition, mutant proteins were prepared by recombinant DNA technology, enabling investigation of structure-function relationships. This report is mainly based on the latter studies. Detailed information about three-dimensional structures of the proteins and the mode of interaction with other macromolecules is still lacking. To obtain this information will be the goal for biochemists in the coming years.

Association of fibrinolytic parameters with early atherosclerosis. The ARIC Study. Atherosclerosis Risk in Communities Study

BACKGROUND

Thrombosis, provoked by a rupture of an atherosclerotic plaque, plays a crucial role in precipitating a coronary heart disease event. Its role at the early stage of atherosclerosis has, however, been unclear, but it has been hypothesized that thrombosis or defective fibrinolysis contributes to the progression of atherosclerotic lesions.

METHODS AND RESULTS

We studied the association of plasminogen activator inhibitor antigen (PAI-1), tissue-type plasminogen activator antigen (TPA), and D-dimer with early atherosclerosis in a cross-sectional case-control study involving 457 pairs chosen from the biracial cohort of the Atherosclerosis Risk in Communities (ARIC) Study. As examined by B-mode ultrasound, patients (cases) had intima-media thickness of carotid arteries above the 90th percentile and control subjects had thickness below the 75th percentile of the ARIC cohort. Persons with a history of heart disease, stroke, or claudication were excluded from the case-control selection. PAI-1, TPA, and D-dimer were higher in patients than in control subjects (P < or = .001, Wilcoxon signed rank statistic). In conditional logistic regression analyses, the odds ratios of carotid atherosclerosis were, for PAI-1, for example, 1.22, 1.54, and 1.60 in the second, third, and fourth quartiles compared with the first quartile (P < .0001, test of linear trend, adjusting for age, systolic blood pressure, total cholesterol, acetylsalicylic acid use, and time of blood draw). Corresponding tests for D-dimer and TPA also showed an increasing trend (P < .0001).

CONCLUSIONS

The findings support the hypothesis that thrombosis and fibrinolysis play a role at the early stage of the atherosclerotic process.

Lipoprotein (a) in the regulation of fibrinolysis

Elevated plasma levels of lipoprotein(a) [LP(a)] are associated with increased an risk of developing atherosclerosis. This increased risk may be due to an Lp(a)-mediated depression of fibrinolytic activity. Lp(a) regulates fibrinolysis by controlling the activity of plasminogen activators. Lp(a) is a low density lipoprotein with an apoprotein(a) subunit which has a high degree of homology with the fibrinolytic zymogen plasminogen. The apoprotein(a) subunit contains up to thirty seven copies of a domain homologous to the plasminogen kringle 4 domain, which enables Lp(a) to bind to fibrin. The subunit also has a zymogen domain, but it is not activated by plasminogen activators. Lp(a) inhibits plasminogen activation by competing with plasminogen for access to plasminogen activators bound to vascular surfaces. Lp(a) also competes with the irreversible inhibitor of plasminogen activators, plasminogen activator inhibitor-1. Therefore increases in Lp(a) concentration may decrease fibrinolytic activity by preventing activation of plasminogen, but Lp(a) may also prolong plasminogen activation by preventing the irreversible inhibition of the activators. At elevated levels of Lp(a) the decreased rate of plasmin generation may not be offset by the prolongation in plasminogen activation, and fibrinolysis will be inhibited.

Tissue plasminogen activator, plasminogen activator inhibitor-1, and fibrin as indexes of clinical course in cardiac allograft recipients. An immunocytochemical study

BACKGROUND

Tissue-type plasminogen activator (TPA) is the principal activator of plasminogen. Since hemostasis in the microcirculation of allografts is a well-recognized complication of transplantation, we asked (1) whether the distribution and amount of cellular TPA in biopsies of transplanted human hearts are associated with fibrin deposits in and around the microcirculation, (2) whether such changes involve the physiological inhibitors of TPA and plasmin, and (3) whether the presence of these activators and inhibitors of fibrinolysis in tissue is correlated with clinical outcome.

METHODS AND RESULTS

We immunocytochemically quantified the presence of fibrin, plasmin, TPA, and the TPA inhibitor PAI-1 in 938 biopsies from 68 consecutive cardiac allografts over a 54-month period. The localization, distribution, and quantification of TPA in arteriolar smooth muscle cells revealed that 35 of the 68 allografts maintained vascular TPA reactivity consistent with time-zero biopsies of autologous donor hearts: this was designated as the normal TPA group. In contrast, 33 of the 68 allografts significantly lost vascular TPA reactivity compared with time-zero biopsies of autologous donor hearts: this was designated as the depleted TPA group. Analysis of sequential biopsies from both groups during 54 months revealed that the mean cumulative quantitative TPA value for the normal TPA group was 1.0 +/- 0.01, whereas the depleted TPA group value was 1.9 +/- 0.02 (P = .0001), and the mean cumulative quantitative fibrin value for the normal TPA group was 1.0 +/- 0.01, whereas the depleted TPA group value was 1.5 +/- 0.05 (P = .0001). Biopsies of allografts in the depleted TPA group contained endothelial reactivity for TPA-PAI-1 complexes, whereas biopsies from the normal TPA group did not. Plasmin-associated molecules were rarely identified in biopsies of the normal TPA group but were present in the depleted TPA group, and the fibrin-to-plasmin ratio in the normal TPA group always was less than the fibrin-to-plasmin ratio in biopsies from the depleted TPA group. Analysis of demographic and risk factors revealed no significant differences between patients in the normal and depleted TPA groups, but none of the 35 patients in the normal TPA group died or were retransplanted, and 13 of the 33 patients in the depleted TPA group died or required retransplantation (P = .0001).

CONCLUSIONS

Time-zero hearts (n = 68) and 34 of 38 stable allografts contained immunocytochemically detectable TPA only in vascular smooth muscle cells. Twenty-nine of 30 patients with normal TPA in their time-zero biopsies who subsequently developed a poor clinical outcome were found to have depleted TPA in biopsies evaluated during their first postoperative month and remained depleted throughout the study. Of 33 patients with depleted TPA, 39% died or required retransplantation. Depleted arteriolar TPA associated significantly with vascular and interstitial deposits of fibrin, plasmin, and endothelial TPA-PAI-1 complexes. These findings indicate that hemostatic and fibrinolytic pathways are activated in falling allografts, and they reveal evidence of depleted TPA before clinical or histopathological signs of failure. Patients with such allografts were found to be at high risk of death independently of other widely used clinical/laboratory parameters of prediction.

Lipoprotein (a) regulates plasmin generation and inhibition

The relationship between lipoprotein (a) (Lp(a)) and atherosclerosis has been appreciated for a number of years. Only in recent years, however, has the structural relationship of Lp(a) to plasminogen resulted in studies of the effect of this lipoprotein on fibrinolysis. Lp(a) inhibits activation of plasminogen by tissue-type (t-PA) and urinary-type (u-PA) plasminogen activators. These inhibitory reactions are surface-dependent. When Lp(a) binds to fibrin, fibrinogen, heparin or cells it blocks activation of plasminogen by t-PA. u-PA-mediated activation of plasminogen is blocked on surfaces including heparin and chondroitin sulfate. Lp(a) also favors inhibition of plasmin by alpha 2-antiplasmin (alpha 2-AP). The ability of Lp(a) to compete with plasmin for fibrin binding displaces plasmin into solution where alpha 2-AP rapidly inhibits this proteinase. These effects are all antifibrinolytic. Lp(a) also exhibits one profibrinolytic effect, since it blocks inhibition of t-PA by plasminogen activator type 1 in the presence of fibrinogen or heparin. Thus, Lp(a) modulates most of the reactions involved in plasmin generation and inhibition. Its overall effect will depend primarily on the concentrations of Lp(a), PAI-1 and t-PA in vivo.

Tumor invasion, proteolysis, and angiogenesis

In this review, some of the current literature on the regulation of proteolysis and angiogenesis during tumor invasion is discussed. Due to the critical location of brain tumors, an understanding of tumor cell interactions with the local environment is particularly relevant. Tissue breakdown during tumor invasion is associated with proteolytic activity, mediated by tumor cells, and surrounding host cells. This review covers two classes of proteinases and inhibitors that have commonly been associated with tumor invasion i.e., plasminogen activator (PA)/plasmin and matrix metalloproteinases (MMP) with special emphasis on the MMP inhibitors, TIMP-1 and TIMP-2. At different steps of the metastatic process, tumor cells interact with endothelial cells. Tumor cells also stimulate the formation of new vessels through the expression of specific angiogenic molecules. At least eight angiogenic molecules have been purified, sequenced and cloned, four of which are discussed here. Regulation of angiogenic activity has been the focus of intense studies recently, and a wide range of synthetic and natural angiogenesis inhibitors have been discovered. Targeting of angiogenic molecules and tumor vasculature may prove useful in future cancer therapeutic strategies.

Immunohistochemical localization of plasminogen activator inhibitor-1 in human coronary atherosclerotic lesions involved in acute myocardial infarction

Immunohistochemical localization of plasminogen activator inhibitor-1 (PAI-1) was studied using the streptavidin-biotin method in human atherosclerotic coronary arteries. The patients (one male and two females), whose ages ranged from 61 to 78 years, died of anteroseptal acute myocardial infarction without having received any thrombolytic therapy. PAI-1 immunoreactivities (IRs) were mainly detected in the endothelial cells, smooth muscle cells, and collagen fibers of the coronary arterial intima and not in thrombi. Remarkable immunohistochemical staining was seen in intimal collagen fibers. In one patient, intimal PAI-1 IRs partly bordered a thrombus and surrounded a large atheroma rich in cholesterol crystals. Our results suggest that PAI-1 is present in both cellular and extracellular components of human coronary atherosclerotic lesions.

Occlusive arterial thrombosis in cynomolgus monkeys with varying plasma concentrations of lipoprotein(a)

Lipoprotein(a) (Lp[a]) is a newly recognized risk factor for the development of coronary heart disease and stroke in human beings; however, the mechanisms by which Lp(a) increases the risk of coronary heart disease remain unclear. The purpose of this study was to examine the effects of Lp(a) on the occurrence of occlusive arterial thrombosis. Occlusive arterial thrombus formation was examined in 18 cynomolgus monkeys with high plasma Lp(a) concentrations (> 35 mg/dL, n = 6), intermediate Lp(a) concentrations (20-25 mg/dL, n = 6), and low Lp(a) concentrations (< 12 mg/dL, n = 6). A Goldblatt clamp was positioned around the left common carotid artery to produce a stenotic segment, and the artery was pinch-injured with needle holders. A 20-MHz Doppler velocity crystal, placed distal to the stenosis/injury site, was used to detect cyclic flow reductions (indicative of transient thrombosis) or permanent cessation of flow velocity (indicative of more stable occlusive thrombosis). All monkeys with high Lp(a) concentrations developed permanent cessation of flow, whereas only one of six arteries from low-Lp(a) monkeys developed permanent cessation of flow (p < 0.05). Arteries from monkeys with intermediate Lp(a) concentrations developed pronounced cyclic reductions of flow but did not progress to permanent cessation of flow. There were no differences in plasma von Willebrand factor activity among the three groups. Immunohistochemical analysis of the damaged arterial segments indicated incorporation of Lp(a) into the adventitia, media, and intima of arteries from monkeys with low and high plasma Lp(a) concentrations, as well as the presence of an occlusive thrombus in arteries that developed permanent cessation of flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutamine/histidine polymorphism in apo A-IV affects plasma concentrations of lipoprotein(a) and fibrin split products in coronary heart disease patients

A glutamine/histidine polymorphism at residue 360 in apolipoprotein (apo) A-IV that generates two electrophoretically detectable isoforms, apo A-IV-1 and apo A-IV-2, affects the plasma concentration of lipoprotein(a) (Lp[a]) in a healthy population. To verify this unexpected association we analyzed the effect of the apo A-IV polymorphism on Lp(a) serum concentrations in 275 male coronary heart disease patients. Allele frequencies of apo A-IV-1 and apo A-IV-2 were 0.917 and 0.083, respectively. In addition, apo A-IV-1/2 heterozygotes showed a 30% lower geometric mean concentration of Lp(a) than apo A-IV-1/1 homozygotes in this study. The relative frequency of Lp(a) concentrations > 20 mg/dl was significantly increased by a factor of 2.25 in apo A-IV-1/1 homozygotes. Other lipid parameters were not significantly affected by this apo A-IV polymorphism. Because of the relations between Lp(a) and the fibrinolytic system, we also analyzed the effect of the apo A-IV polymorphism on hemostatic variables. Apo A-IV-1/2 heterozygosity was associated with a 70% higher geometric mean plasma concentration of D-dimer, i.e., proteolytic fragments of cross-linked fibrin. Plasma concentrations of prothrombin fragments F1 + F2, fibrinogen, plasminogen, and plasminogen activator inhibitor-1 were unaffected. In conclusion, our results indicate a hitherto unappreciated role of the apo A-IV gene or a closely linked locus for the regulation of Lp(a) metabolism and hemostasis and also possibly for atherosclerosis and thrombosis.

Ionic modulation of the effects of heparin on plasminogen activation by tissue plasminogen activator: the effects of ionic strength, divalent cations, and chloride

Ionic strength, divalent cations, and Cl- modulate the ability of the glycosaminoglycan heparin to stimulate the activation of human plasminogen (Pg) by tissue-type Pg activator. Kinetic analysis of Pg activation indicates that heparin is inhibitory, stimulatory, or nonstimulatory as a function of ionic strength. While increasing ionic strength inhibits Pg activation in the absence of heparin, in it presence an activation phase followed by an inhibitory phase is observed. Divalent cations, inhibitors of activation in the absence of heparin, increase the rate of activation in its presence. Kinetic analysis demonstrates that divalent cations augment the heparin stimulatory effect a maximum of 60-fold due to increases in kcat without changes in Km of the reaction. This effect is heparin-specific, since activation is not affected by Ca2+ in the presence of heparan sulfate or de-N-sulfated heparin. Also, Cl- inhibits Pg activation in the presence of heparin by acting as a competitive inhibitor (Kic of 100 mM). Furthermore, inhibition by Cl- reduces the overall magnitude of heparin stimulation of Pg activation. These results suggest that physiologic ions in combination with heparin may be significant effectors of Pg activation in the vascular microenvironment.

Extracellular matrix regulation of growth factor and protease activity

Extracellular matrices bind many growth factors, proteases, and protease inhibitors. These interactions not only localize these molecules to the pericellular environment, but also modulate their biological activities. Recent evidence suggests that some growth factors may be active in vivo primarily in complexes with extracellular matrix molecules and that this interaction may be essential to their activity.