Changes in the fibrinolytic components of cultured human umbilical vein endothelial cells induced by endotoxin, tumor necrosis factor-alpha and interleukin-1alpha.
(17/1717)
BACKGROUND AND OBJECTIVE: Vascular fibrinolysis, a major natural defense mechanism against thrombosis, is a highly regulated process. The aim of this study was to evaluate the effect of endotoxin, tumor necrosis factor-alpha (TNFalpha) and interleukin-1alpha (IL-1alpha), on the fibrinolytic potential of cultured human umbilical vein endothelial cells (HUVEC). DESIGN AND METHODS: Samples of stimulated conditioned media were collected over a period of 24 hours to determine: plasminogen activator (PA) and plasminogen activator inhibitor (PAI) activity, PAI-1 mRNA, tissue-type plasminogen activator (t-PA) antigen and urokinase-type plasminogen activator (u-PA) antigen. RESULTS: Similar changes were observed after endotoxin and cytokine stimulation: there was a significant increase of PAI activity (p<0.01), starting at 6 hours, which remained 24 hours after stimulation. PAI-1 mRNA also showed an important rise with these agents, although cytokines induced an earlier and more intense inhibitor response (up to 6-fold increase). PA activity increased significantly at 6 hours (p<0.01) to drop at 24 hours and was mainly related to the presence of u-PA. INTERPRETATION AND CONCLUSIONS: We conclude that endotoxin,+TNFalpha and IL-1alpha induce profound alterations in the fibrinolytic potential of HUVEC, characterized by an initial rise of activators (u-PA) followed by a strong increase of PAI-1. These changes may be of pathophysiologic significance for thrombosis and inflammatory reactions. (+info)
Alzheimer's beta-amyloid peptides can activate the early components of complement classical pathway in a C1q-independent manner.
(18/1717)
beta-Amyloid (beta-A) accumulates in the brain of patients with Alzheimer's disease (AD) and is presumably involved in the pathogenesis of this disease, on account of its neurotoxicity and complement-activating ability. Although assembly of beta-A in particular aggregates seems to be crucial, soluble non-fibrillar beta-A may also be involved. Non-fibrillar beta-A does not bind C1q, so we investigated alternative mechanisms of beta-A-dependent complement activation in vitro. On incubation with normal human plasma, non-fibrillar beta-A 1-42, and truncated peptide 1-28, induced dose-dependent activation of C1s and C4, sparing C3, as assessed by densitometric analysis of immunostained membrane after SDS-PAGE and Western blotting. The mechanism of C4 activation was not dependent on C1q, because non-fibrillar beta-A can still activate C1s and C4 in plasma genetically deficient in C1q (C1qd). In Factor XII-deficient plasma (F.XIId) the amount of cleaved C4 was about 5-10% less that in C1qd and in normal EDTA plasma; the reconstitution of F.XIId plasma with physiologic concentrations of F.XII resulted in an increased (8-15%) beta-A-dependent cleavage of C4. Thus our results indicate that the C1q-independent activation of C1 and C4 can be partially mediated by the activation products of contact system. Since the activation of contact system and of C4 leads to generation of several humoral inflammatory peptides, non-fibrillar beta-A might play a role in initiating the early inflammatory reactions leading to a multistep cascade contributing to neuronal and clinical dysfunction of AD brain. (+info)
Recent insight into therapy of congestive heart failure: focus on ACE inhibition and angiotensin-II antagonism.
(19/1717)
One possible intervention to interrupt the deleterious effects of the renin-angiotensin system is suppression of angiotensin II (Ang II) formation by inhibition of angiotensin-converting enzyme (ACE). However, ACE inhibition incompletely suppresses Ang II formation and also leads to accumulation of bradykinin. Angiotensin II type 1 (AT1) receptors are believed to promote the known deleterious effects of Ang II. Therefore, AT1 receptor antagonists have been recently introduced into therapy for hypertension and congestive heart failure (CHF). Although there are significant differences between the effects of AT1 receptor antagonists and ACE inhibitors including the unopposed stimulation of angiotensin II type 2 (AT2) receptors by AT1 receptor antagonists, the discussion of whether ACE inhibitors, AT1 receptor antagonists or the combination of both are superior in the pharmacotherapy of CHF is still largely theoretical. Accordingly, AT1 receptor antagonists are still investigational. Angiotensin-converting enzyme inhibitors remain first line therapy in patients with CHF due to systolic dysfunction. However, in patients not able to tolerate ACE inhibitor induced side effects, in particular cough, AT1 receptor antagonism is a good alternative. In clinical practice, emphasis should be placed on increasing the utilization of ACE inhibitors, as more than 50% of patients with CHF do not receive ACE inhibitors. In addition, the majority of those on ACE inhibitors receive doses lower than the dosage used in the large clinical trials. Although not yet completely proved, it is likely that high doses of ACE inhibition are superior to low doses with respect to prognosis and symptoms. (+info)
The presence of infection-related antiphospholipid antibodies in infective endocarditis determines a major risk factor for embolic events.
(20/1717)
OBJECTIVES: The impact of infection-associated antiphospholipid antibodies (APA) on endothelial cell activation, blood coagulation and fibrinolysis was evaluated in patients with infective endocarditis with and without major embolic events. BACKGROUND: An embolic event is a common and severe complication of infective endocarditis. Despite the fact that APAs are known to be associated with infectious diseases, their pathogenic role in infective endocarditis has not been clearly defined. METHODS: The relationship among the occurrence of major embolic events, echocardiographic vegetation size, endothelial cell activation, thrombin generation, fibrinolysis and APA was examined in 91 patients with definite infective endocarditis, including 26 patients with embolic events and 65 control subjects without embolic events. RESULTS: Overall, 14.3% of patients exhibited elevated APA levels. Embolic events occurred more frequently in patients with elevated levels of APA than in patients without (61.5% vs. 23.1%; p = 0.008). Patients with elevated levels of APA showed higher levels of prothrombin-fragment F1 +2 (p = 0.005), plasminogen-activator inhibitor 1 (p = 0.0002), von Willebrand factor (p = 0.002) and lower levels of activated protein C (p = 0.001) than patients with normal levels of APA. Thrombin generation and endothelial cell activation were both positively correlated with levels of APA. The occurrence of elevated APA levels was frequently associated with structural valve abnormalities (p = 0.01) and vegetations >1.3 cm (p = 0.002). CONCLUSIONS: Infection-associated elevated APA levels in patients with infective endocarditis are related to endothelial cell activation, thrombin generation and impairment of fibrinolysis. This may contribute to the increased risk for major embolic events in these patients. (+info)
Hyperhomocysteinemia and hypofibrinolysis in young adults with ischemic stroke.
(21/1717)
BACKGROUND AND PURPOSE: Data from epidemiological and case-control studies suggest that increased total homocysteine (tHcy) levels are associated with increased risk for thromboembolic disease. The mechanisms by which hyperhomocysteinemia contributes to thrombogenesis are incompletely understood. The main objectives of this study of young ischemic stroke patients were (1) to examine fasting and post-methionine load levels of tHcy, (2) to ascertain the genotype frequency of the C677CT mutation in the methylenetetrahydrofolate reductase gene (TT genotype), and (3) to study the possible interaction between plasma tHcy levels and fibrinolytic factors. METHODS: This case-control study was based on 80 consecutive patients aged 18 to 44 years admitted between January 1992 and May 1996 as a result of a first-ever ischemic stroke. Forty-one healthy control subjects were recruited. Measurement of fasting tHcy and post-methionine load levels and evaluation of the fibrinolytic system were undertaken at least 3 months (mean, 5.1+/-1. 9 months) after admission. Genotyping of the methylenetetrahydrofolate reductase gene was performed. RESULTS: Although the increase after methionine loading (ie, postload tHcy minus fasting-level tHcy) was significantly higher among patients, there was no difference in fasting and postload tHcy levels. After adjustment for conventional risk factors, elevated postload increase tHcy levels were associated with a 4.8-fold increased risk of ischemic stroke. There was no difference between patients and control subjects in either TT genotype frequency or T allele frequency. Abnormal response to methionine loading was associated with higher tissue plasminogen activator (tPA) mass concentration, higher plasminogen activator inhibitor-1 levels, and lower tPA activity. After adjustment for age, sex, body mass index, serum cholesterol, and triglycerides, an abnormal increase in postload tHcy levels remained significantly associated with tPA mass concentration levels (P=0.03). CONCLUSIONS: A moderately elevated increase in tHcy levels after methionine loading was associated with an increased risk for ischemic stroke in young adults. In contrast, fasting tHcy levels did not differ between patients and controls. A moderately elevated increase in tHcy after methionine loading may provide a additional thrombogenic risk mediated in part by interactions with the fibrinolytic system. In young stroke patients, a methionine loading test to detect hyperhomocysteinemia should always be considered in the convalescent phase of the disease. (+info)
Role of plasminogen system components in focal cerebral ischemic infarction: a gene targeting and gene transfer study in mice.
(22/1717)
BACKGROUND: The role of plasminogen system components in focal cerebral ischemic infarction (FCI) was studied in mice deficient in plasminogen (Plg-/-), in tissue or urokinase plasminogen activator (tPA-/- or uPA-/-), or in plasminogen activator inhibitor-1 or alpha2-antiplasmin (PAI-1(-/-) or alpha2-AP-/-). METHODS AND RESULTS: FCI was produced by ligation of the left middle cerebral artery and measured after 24 hours by planimetry of stained brain slices. In control (wild-type) mice, infarct size was 7.6+/-1.1 mm3 (mean+/-SEM), uPA-/- mice had similar infarcts (7.8+/-1.0 mm3, P=NS), tPA-/- mice smaller (2.6+/-0.80 mm3, P<0.0001), PAI-1(-/-) mice larger (16+/-0.52 mm3, P<0.0001), and Plg-/- mice larger (12+/-1.2 mm3, P=0.037) infarcts. alpha2-AP-/- mice had smaller infarcts (2. 2+/-1.1 mm3, P<0.0001 versus wild-type), which increased to 13+/-2.5 mm3 (P<0.005 versus alpha2-AP-/-) after intravenous injection of human alpha2-AP. Injection into alpha2-AP-/- mice of Fab fragments of affinospecific rabbit IgG against human alpha2-AP, after injection of 200 microg human alpha2-AP, reduced FCI from 11+/-1.5 to 5.1+/-1.1 mm3 (P=0.004). CONCLUSIONS: Plg system components affect FCI at 2 different levels: (1) reduction of tPA activity (tPA gene inactivation) reduces whereas its augmentation (PAI-1 gene inactivation) increases infarct size, and (2) reduction of Plg activity (Plg gene inactivation or alpha2-AP injection) increases whereas its augmentation (alpha2-AP gene inactivation or alpha2-AP neutralization) reduces infarct size. Inhibition of alpha2-AP may constitute a potential avenue to treatment of FCI. (+info)
Proteoglycans contribution to association of Lp(a) and LDL with smooth muscle cell extracellular matrix.
(23/1717)
Lp(a) interference with fibrinolysis could contribute to atherothrombosis. Additionally, accumulation of Lp(a) and LDLs, could lead to cholesterol deposition and foam cell formation in atherogenesis. The interactions between Lp(a) and LDL could cause their entrapment in the extracellular matrix of lesions. We found that association of Lp(a) with matrix secreted by cultured human arterial smooth muscle cells increased 2 to 3 times the subsequent specific binding of radioactive LDL. Chondroitin sulfate proteoglycans seem responsible for formation of the specific matrix-Lp(a) and matrix-LDL aggregates. The proteoglycans appeared also to participate in a cooperative increase of radioactive LDL binding to matrix pretreated with Lp(a). In the matrix preincubated with LDL, approximately 50% of the additional lipoprotein was bound by ionic interactions. In the matrix preincubated with Lp(a), 20% of the additional LDL was held by ionic bonds, and the rest was held by strong nonionic associations. Binding analysis in physiological solutions confirmed that chondroitin sulfate-rich proteoglycans from the smooth muscle cell matrix have a high affinity for Lp(a) and LDL. The results provide an explanation to the observed localization of Lp(a) and LDL in the extracellular matrix of arterial lesions and suggest a mechanism for their cooperative accumulation there. (+info)
Assay of procarboxypeptidase U, a novel determinant of the fibrinolytic cascade, in human plasma.
(24/1717)
BACKGROUND: Procarboxypeptidase U (proCPU) is a novel proenzyme found in human plasma. The active form, carboxypeptidase U (CPU; EC 3.4.17.20), retards the rate of fibrinolysis through its ability to cleave C-terminal lysine residues on fibrin partially degraded by plasmin. This reduces the number of high-affinity plasminogen-binding sites on fibrin. METHODS: We developed an assay to determine the proCPU concentration in human plasma. The assay involved quantitative conversion of proCPU to active CPU by thrombin-thrombomodulin, a very efficient activator of proCPU, followed by determination of the enzymatic activity of CPU with the substrate hippuryl-L-arginine, using an HPLC-assisted determination of the released hippuric acid. Using this method, we established a reference interval based on 490 healthy individuals. RESULTS: The mean proCPU concentration, determined after activation of the zymogen in diluted plasma and expressed as CPU activity, was 964 U/L, with a SD of 155 U/L. The population showed a gaussian distribution. However, we noticed important differences related to age and the use of hormone preparations. CONCLUSIONS: The sensitivity and precision of the method make it suitable for routine clinical determinations and as a reference procedure. (+info)