The role of thrombin activatable fibrinolysis inhibitor and factor XI in platelet-mediated fibrinolysis resistance: a thromboelastographic study in whole blood

BACKGROUND

The resistance of platelet-rich thrombi to fibrinolysis is generally attributed to clot retraction and platelet PAI-1 release. The role of TAFI in platelet-mediated resistance to lysis is unclear.

OBJECTIVE

We investigated the contribution of TAFI to the antifibrinolytic effect of platelets in whole blood by thromboelastography.

METHODS

Platelet-poor (PP-WB, < 40 × 10(3) μL(-1) ) and platelet-rich (PR-WB, > 400 × 10(3) μL(-1) ) blood samples were obtained from normal human blood (N-WB, 150-220 × 10(3) μL(-1) ). Clot lysis time was measured by thromboelastography in recalcified blood supplemented with t-PA (100 ng mL(-1) ) and tissue factor (1:1000 Recombiplastin).

RESULTS

t-PA-induced lysis time increased in parallel with platelet concentration (up to 3-fold). Neutralization of TAFI, but not of PAI-1, shortened the lysis time by ∼ 50% in PR-WB and by < 10% in PP-WB. Accordingly, prothrombin F1+2 and TAFIa accumulation was greater in PR-WB than in PP-WB. A similar TAFI-dependent inhibition of fibrinolysis was observed when clot retraction was prevented by cytochalasin D or abciximab, or when platelet membranes were tested. Moreover, in blood with an intact contact system, platelet-mediated fibrinolysis resistance was attenuated by an anti-FXI but not by an anti F-XII antibody. Finally, platelets made the clots resistant to the profibrinolytic effect of heparin concentrations displaying a strong anticoagulant activity.

CONCLUSIONS

Our data indicate that TAFI activation is one major mechanism whereby platelets make clots resistant to fibrinolysis and underscore the importance of TAFI inhibitors as new antithrombotic agents.

Dabigatran enhances clot susceptibility to fibrinolysis by mechanisms dependent on and independent of thrombin-activatable fibrinolysis inhibitor

BACKGROUND

Anticoagulants are expected to promote fibrinolysis by counteracting the antifibrinolytic effects of thrombin, which include thrombin-activatable fibrinolysis inhibitor (TAFI) activation and clot structure enhancement. However, the efficiency of anticoagulants may vary remarkably, and the ability of direct thrombin inhibitors to facilitate clot lysis remains controversial.

OBJECTIVE

To evaluate the profibrinolytic effect of dabigatran, a new, direct thrombin inhibitor, using different in vitro models.

METHODS AND RESULTS

The resistance of tissue factor-induced plasma clots to fibrinolysis by exogenous tissue-type plasminogen activator (t-PA) (turbidimetric method) was reduced by dabigatran in a concentration-dependent manner, with > or = 50% shortening of lysis time at clinically relevant concentrations (1-2 microm). A similar effect was observed in the presence of low (0.1 and 1 nm) but not high (10 nm) concentrations of thrombomodulin. Acceleration of clot lysis by dabigatran was associated with a reduction in TAFI activation and thrombin generation, and was largely, although not completely, negated by an inhibitor of activated TAFI, potato tuber carboxypeptidase inhibitor. The assessment of the viscoelastic properties of clots showed that those generated in the presence of dabigatran were more permeable, were less rigid, and consisted of thicker fibers. The impact of these physical changes on fibrinolysis was investigated using a model under flow conditions, which demonstrated that dabigatran made the clots markedly more susceptible to flowing t-PA, by a mechanism that was largely TAFI-independent.

CONCLUSIONS

Dabigatran, at clinically relevant concentrations, enhances the susceptibility of plasma clots to t-PA-induced lysis by reducing TAFI activation and by altering the clot structure. These mechanisms might contribute to the antithrombotic activity of the drug.

Comprehensive exercise training improves ventilatory muscle function and reduces dyspnea perception in patients with COPD

BACKGROUND

Comprehensive exercise training (CET) is an efficient strategy to decrease dyspnea perception in chronic obstructive pulmonary disease (COPD) and may result in significant improvement in ventilatory muscles function. Our aim was to evaluate the effects of general exercise training on dyspnea perception and on respiratory muscles strength in COPD patients.

METHODS

Consecutive COPD patients were enrolled to complete a CET programme. The patients underwent a routine that included a global warm up, upper and lower limbs endurance exercise as well as stretching and relaxation. Before and after the CET programme, patients completed maximal inspiratory (PImax) and expiratory (PEmax) pressures measurements, maximal incremental test, endurance test, and 6-min walk distance (6MWD).

RESULTS

71 patients (52 male). Mean age 67.6 +/- 8.6 years, FEV1 (%) 44.2 +/- 16.2 and Mahler dyspnea scale 6.4 +/- 1.8. The results before and after the exercise programme were: PImax 64.7 +/- 22.9 vs. 75.5 +/- 23.7 cmH2O (p=0.001), PEmax 110.8 +/- 28.1 vs. 120.4 +/- 28.1 cmH2O (p=0.004), 6MWD 510.6 +/- 90.3 vs. 528.2 +/- 99.7 metres (p=0.88), time of incremental test 672 +/- 135 vs. 856 +/- 226 sec (p<0.0001). Compared with the pre exercise programme, we observed a significant reduction on Borg dyspnea scale (6.1 +/- 2.8 to 3.6 +/- 2.3, p<0.0001) as well as a longer test time (504 +/- 218 to 1.038 +/- 841, p<0.0001) at the end of the endurance test after CET programme. Improvement of PImax correlated negatively with dyspnea perception at iso-time during the endurance test (r = -0.33, p=0.03).

CONCLUSIONS

Our results confirm that CET is associated with significant improvement in PImax, PEmax and provide evidence demonstrating that CET reduces dyspnea perception in patients with COPD.

Inhaled ammonium persulphate inhibits non-adrenergic, non-cholinergic relaxations in the guinea pig isolated trachea

BACKGROUND

Persulphates can act both as irritants and sensitizers in inducing occupational asthma. A dysfunction of nervous control regulating the airway tone has been hypothesized as a mechanism underlying bronchoconstriction in asthma.

OBJECTIVES

It was the aim of this study to investigate whether inhaled ammonium persulphate affects the non-adrenergic, non-cholinergic (NANC) inhibitory innervation, the cholinergic nerve-mediated contraction or the muscular response to the spasmogens, carbachol or histamine, in the guinea pig epithelium-free, isolated trachea.

METHODS

Male guinea pigs inhaled aerosols containing ammonium persulphate (10 mg/m(3) for 30 min for 5 days during 3 weeks). Control animals inhaled saline aerosol. NANC relaxations to electrical field stimulation at 3 Hz were evaluated in whole tracheal segments as intraluminal pressure changes. Drugs inactivating peptide transmission, nitric oxide synthase, carbon monoxide production by haem oxygenase-2 and soluble guanylyl cyclase were used to assess the involvement of various inhibitory neurotransmitters. Carbachol and histamine cumulative concentration-response curves were obtained.

RESULTS

In both groups, nitric oxide and carbon monoxide participated to the same extent as inhibitory neurotransmitters. In exposed animals, the tracheal NANC relaxations were reduced to 45.9 +/- 12.1% (p < 0.01). The cholinergic nerve-mediated contractions to electrical field stimulation and the muscular response to histamine were not modified by ammonium persulphate exposure. The muscular response to carbachol was unaffected up to 1 microM. Conversely, the response to the maximal concentration of carbachol (3 microM) was increased (p < 0.01).

CONCLUSION

Ammonium persulphate inhalation at high concentrations impairs the nervous NANC inhibitory control in the guinea pig airways. This may represent a novel mechanism contributing to persulphate-induced asthma.

Functional and neurochemical changes of the gastrointestinal tract in a rodent model of Parkinson's disease

Patients with Parkinson's disease develop motor disturbances often accompanied by peripheral autonomic dysfunctions, including gastrointestinal disorders, such as dysphagia, gastric stasis and constipation. While the mechanisms subserving enteric autonomic dysfunctions are not clearly understood, they may involve the enteric dopaminergic and/or nitrergic systems. In the present study, we demonstrate that rats with unilateral 6-hydroxydopamine lesion of nigrostriatal dopaminergic neurons develop a marked inhibition of propulsive activity compared to sham-operated controls, as indicated by a 60% reduction of daily fecal output at the 4th week of observation. Immunohistochemical data revealed that 6-hydroxydopamine treatment did not affect the total number of HuC/D-positive myenteric neurons in both the proximal and distal segments of ileum and colon. Conversely, in the distal ileum and proximal colon the number of nitrergic neurons was significantly reduced. These results suggest that a disturbed distal gut transit, reminiscent of constipation in the clinical setting, may occur as a consequence of a reduced propulsive motility, likely due to an impairment of a nitric oxide-mediated descending inhibition during peristalsis.

Mild hyperhomocysteinemia is associated with increased TAFI levels and reduced plasma fibrinolytic potential

BACKGROUND

Mild hyperhomocysteinemia (HHcy) has been shown to be associated with impaired fibrinolysis, but some aspects of this association are unclear.

OBJECTIVE

Using an in vitro model of physiological relevance, we investigated whether and how HHcy influences plasma fibrinolytic potential.

PATIENTS/METHODS

We studied 176 patients with previous venous thromboembolism, 58 with HHcy, 118 with normal total homocysteine (tHcy) levels (NHcy), at least 3 months after withdrawal of anticoagulant therapy. Plasma fibrinolytic potential was measured as the fibrinolysis time of tissue factor (TF)-induced clots exposed to 15 ng mL(-1) t-PA.

RESULTS

Fibrinolysis time was longer in HHcy than in NHcy patients, but this difference disappeared when the assay was performed in the presence of the TAFIa inhibitor, PTCI. Plasma levels of thrombin activatable fibrinolysis inhibitor (TAFI) and factor VIII (FVIII) were higher in HHcy than NHcy, whereas PAI-1, fibrinogen and endogenous thrombin potential were similar. Using multivariate analysis, plasma tHcy was identified as an independent predictor of fibrinolysis time. Experiments in which native fibrinogen was replaced by purified fibrinogen suggested that alterations of fibrinogen structure did not contribute appreciably to the hypofibrinolysis of HHcy plasma samples. The acute increase of tHcy either in vivo (after an oral methionine load) or in vitro (after incubation of normal plasma with 0.5 mm DL-Hcy) had no effects on fibrinolysis or TAFI levels.

CONCLUSIONS

We describe an enhanced TAFI-related antifibrinolytic activity in mild HHcy, which might account for the reported heightened thrombosis risk; however, it is unknown whether HHcy is causally related to hypofibrinolysis or an associated bystander.

Cholera toxin B subunit promotes the induction of regulatory T cells by preventing human dendritic cell maturation

Cholera toxin B subunit (CTB) is an efficient mucosal carrier molecule for the generation of immune responses to linked antigens. There is also good evidence that CTB acts as an immunosuppressant, as it is able to down-modulate human monocyte/macrophage cell line activation and to suppress Th1-type responses. In the present study, we examined the possibility that recombinant CTB (rCTB) may affect human dendritic cell (DC) functions in response to LPS stimulation and may induce the generation of DC with the capacity to generate CD4(+) regulatory T cells (Tregs). Our findings show that rCTB partially prevents the LPS-induced maturation process of monocyte-derived DC (MDDC) and decreases their IL-12 production with no relevant effect on IL-10 production. LPS-stimulated MDDC pretreated with rCTB are able to promote the induction of low proliferating T cells, which show an enhanced IL-10 production associated with a reduced IFN-gamma production and the same high levels of TGF-beta as the control. These T cells suppress proliferation of activated autologous T cells. Transwell experiments and blockade of IL-10R and TGF-beta showed that the immunomodulatory effect is mediated by soluble factors. Thus, T cells induced by rCTB-conditioned MDDC acquire a regulatory phenotype and activity similar to those described for type 1 Tregs.

Tissue factor and vascular endothelial growth factor expression in colorectal cancer: relation with cancer recurrence

OBJECTIVE

This study was undertaken to quantify tissue factor (TF) and vascular endothelial growth factor (VEGF) in colorectal cancer and to evaluate their possible relationship with recurrence.

METHOD

TF and VEGF were measured by enzyme-linked immunosorbent assay in surgical tumour specimens and normal mucosa from 50 consecutive patients with colorectal cancer who were followed up for 3 years for the assessment of disease recurrence.

RESULTS

TF and VEGF antigens were detected in all tumour samples. VEGF, but not TF, was much higher in tumour than in normal mucosa (P < 0.0001), as also confirmed by measurement of specific mRNAs. There was a strong correlation between TF and VEGF antigens (P < 0.0005) in tumour tissue but not in normal mucosa. Neither protein was related to tumour stage, grade or size. Local or distant recurrence was statistically related to pTNM stage. High VEGF, but not TF, levels in tumour extracts were associated with an increased risk of recurrence both by univariate (RR, 4.00, 95% CI: 1.45-11.0) and multivariate analyses (RR, 3.65, 95% CI: 1.33-10.0).

CONCLUSION

These findings suggest that VEGF content in colorectal cancer is an independent risk factor for tumour recurrence and might help select patients who might benefit from adjuvant therapy.

The number of pregnancies is a risk factor for Alzheimer's disease

Epidemiological data show a higher prevalence of late-onset Alzheimer's disease (AD) in women. The estrogenic deficiency in the post-menopausal period is suspected to be the cause of the gender-related risk of the disease, but studies on the estrogenic therapy and occurrence of AD were not consistent and sometimes contradicting. The aim of this study is to investigate whether a higher exposure to endogenous estrogens is associated with lower risk of dementia or not. Two hundred and four AD patients and 201 control women were considered. By interviews, we evaluated different variables, indirectly correlated to estrogenic natural exposure, as well as educational level and head trauma. These data were correlated in the AD group with the disease progression, as well as with the age at onset. Unexpectedly, we found a significant higher number of pregnancies in the AD than in the control group. Within the AD cases, the number of lifetime pregnancies is related to an earlier onset of the disease. As previously reported, we confirmed that the educational level is a protective factor and that major head trauma represents a risk factor in developing AD. The higher number of pregnancies and a less frequency of nulliparous women, indirectly relate the AD group to a higher estro-progestinic exposure. These findings suggest that it is the increase of progesterone or estrogens level--and not the estrogens decrease, as previously indicated by other authors--that could play a role in the Alzheimer's pathology.

Variability among polysulphone calibration curves

Within an epidemiological study regarding the correlation between skin pathologies and personal ultraviolet (UV) exposure due to solar radiation, 14 field campaigns using polysulphone (PS) dosemeters were carried out at three different Italian sites (urban, semi-rural and rural) in every season of the year. A polysulphone calibration curve for each field experiment was obtained by measuring the ambient UV dose under almost clear sky conditions and the corresponding change in the PS film absorbance, prior and post exposure. Ambient UV doses were measured by well-calibrated broad-band radiometers and by electronic dosemeters. The dose-response relation was represented by the typical best fit to a third-degree polynomial and it was parameterized by a coefficient multiplying a cubic polynomial function. It was observed that the fit curves differed from each other in the coefficient only. It was assessed that the multiplying coefficient was affected by the solar UV spectrum at the Earth's surface whilst the polynomial factor depended on the photoinduced reaction of the polysulphone film. The mismatch between the polysulphone spectral curve and the CIE erythemal action spectrum was responsible for the variability among polysulphone calibration curves. The variability of the coefficient was related to the total ozone amount and the solar zenith angle. A mathematical explanation of such a parameterization was also discussed.

Changes in coagulation-fibrinolysis balance in blood mononuclear cells and in gastric mucosa from patients with Helicobacter pylori infection

INTRODUCTION

Helicobacter pylori and some of its virulence factors stimulate human blood mononuclear cells (MNC) in vitro to produce tissue factor (TF) and plasminogen activator inhibitor-2 (PAI-2). In this study we investigated the procoagulant-fibrinolytic potential of blood MNC in patients with H. pylori infection. In the same patients we also evaluated the coagulation-fibrinolysis profile in gastric tissue and in plasma.

METHODS AND RESULTS

The production of TF and PAI-2 was evaluated in 61 patients with dyspepsia, 31 positive and 30 negative for H. pylori infection. TF expressed by MNC and PAI-2 accumulation in cell culture medium after incubation for 20 h at 37 degrees C were significantly higher in H. pylori(+) than in H. pylori(-) patients and were significantly correlated. TF and PAI-2 content in extracts of gastric mucosa was similar in the two groups whereas lower levels of tissue plasminogen activator (t-PA) and thrombomodulin (TM) antigens were found in the antrum of H. pylori(+) patients. No difference between the groups was observed in plasma thrombus precursor protein, prothrombin fragment 1+2, D-dimer, t-PA, PAI-1, TM and thrombin activatable fibrinolysis inhibitor.

CONCLUSIONS

H. pylori infection is associated with functional abnormalities of blood MNC resulting in the coordinate expression of TF and antifibrinolytic activity. Changes in cell coagulation-fibrinolysis balance may represent a link between H. pylori infection and ischemic heart disease.

A novel nitric oxide-releasing statin derivative exerts an antiplatelet/antithrombotic activity and inhibits tissue factor expression

BACKGROUND

NO-releasing statins are new chemical entities, combining HMG-CoA reductase inhibition and slow NO release, that possess stronger anti-inflammatory and antiproliferative activities than the native statins.

OBJECTIVE

We evaluated the antithrombotic effects of nitropravastatin (NCX-6550) by assessing its activity on platelet activation and tissue factor (TF) expression by mononuclear cells in vitro and in vivo.

METHODS AND RESULTS

In vitro, NCX-6550 inhibited (1) U46619- and collagen-induced platelet aggregation in buffer and plasma; (2) collagen-induced P-selectin expression in whole blood and (3) platelet adhesion to collagen-coated coverslips under high shear stress. These effects were displayed at concentrations of NCX-6550 ranging from 25 to 100 mum, and were totally reverted by the guanylylcyclase inhibitor ODQ (10 microm). Equimolar concentrations of pravastatin had no influence on these parameters of platelet function. LPS- and PMA-induced TF expression by blood mononuclear cells was also inhibited by NCX-6550 (IC50 13 microm), but not by pravastatin, as assessed by functional and immunological assays and by real-time PCR. In a mouse model of platelet pulmonary thromboembolism, induced by the i.v. injection of collagen plus epinephrine, pretreatment with NCX-6550 (24-48 mg kg(-1)) significantly reduced platelet consumption, lung vessel occlusion and mortality. Moreover, nitropravastatin markedly inhibited the generation of procoagulant activity by spleen mononuclear cells and peritoneal macrophages in mice treated with LPS. In these in vivo models too, pravastatin failed to affect platelet activation and monocyte/macrophage procoagulant activity.

CONCLUSIONS

Our results show that nitropravastatin exerts strong antithrombotic effects in vitro and in vivo, and may represent an interesting antiatherothrombotic agent for testing in acute coronary syndromes.

Plasma levels of amyloid -protein 42 are increased in women with mild cognitive impairment

BACKGROUND

Accumulation in the brain of small aggregates of amyloid beta-protein 42 (Abeta42) is the major pathogenic event of Alzheimer disease (AD). In familial early-onset AD this event is likely the result of Abeta42 overproduction; in the most common sporadic late-onset form of the disease the mechanisms of Abeta42 accumulation are unknown.

METHODS

To address this issue the authors analyzed plasma levels of Abeta42 in 88 elderly patients with amnestic mild cognitive impairment (MCI), chosen as paradigm of preclinical sporadic AD.

RESULTS

The authors found a significant increase of Abeta42 plasma levels in women with MCI, in comparison to the affected men and 72 cognitively normal age-matched subjects. The levels were independent of variables in education, apolipoprotein E genotype, cholesterol, and creatinine plasma concentrations, as well as hemoglobin content.

CONCLUSIONS

The elevation of Abeta42 plasma levels in women with MCI may represent a biologic explanation for the sex-dependent increased incidence of late-onset AD in women identified by epidemiologic studies.

Sensitivity of 14-3-3 protein test varies in subtypes of sporadic Creutzfeldt-Jakob disease

BACKGROUND

The increase of the 14-3-3 protein in CSF is used as a diagnostic test in Creutzfeldt-Jakob disease (CJD), but the sensitivity and specificity of the 14-3-3 test are disputed. One reason for the dispute may be the recently established heterogeneity of sporadic CJD. The relationship between CSF 14-3-3 protein and sporadic CJD subtypes, distinguished by electrophoretic mobility of proteinase K-resistant prion protein (PrP(Sc)) and genotype at codon 129 of the prion protein gene, has not been elucidated.

METHODS

The authors examined the 14-3-3 protein test in 90 patients with sporadic CJD. PrP(Sc) type (type 1 or type 2) and the genotype at polymorphic codon 129 were determined in each patient. Mutations were excluded by prion gene sequencing.

RESULTS

The authors' findings indicate that the sensitivity of the 14-3-3 test is higher in patients with molecular features of the classic sporadic CJD than in patients with the nonclassic CJD subtypes. The difference appears to be related to the PrP(Sc) type and not to the codon 129 genotype. Disease duration before 14-3-3 testing might also have an influence because it was shorter in classic sporadic CJD.

CONCLUSION

The Creutzfeldt-Jakob disease clinical subtype should be considered when interpreting results of the 14-3-3 test.

[Expression of tissue factor and vascular endothelial growth factor in colorectal carcinoma]

Tissue factor (TF) and vascular endothelial growth factor (VEGF) play an important role in tumor progression and metastasis. We analyzed their expression in the carcinoma and normal mucosa of 53 colorectal cancer patients. VEGF levels were significantly higher in the tumor and correlated with TF expression. No correlation was found with tumor stage. TF may influence tumor growth and metastasis by modulating VEGF expression and neoangiogenesis.

Novel differences between two human prion strains revealed by two-dimensional gel electrophoresis

The phenotype of human sporadic prion diseases is affected by patient genotype at codon 129 of the prion protein (PrP) gene, the site of a common methionine/valine polymorphism, and by the type of the scrapie PrP (PrP(Sc)), which likely reflects the prion strain. However, two distinct disease phenotypes, identified as sporadic Creutzfeldt-Jakob disease (M/M2 sCJD) and sporadic fatal insomnia (sFI), share methionine homozygosity at codon 129 and PrP(Sc) type 2. One-dimensional gel electrophoresis and immunoblotting reveal no difference between the M/M2 sCJD and sFI species of PrP(Sc) in gel mobility and glycoform ratio. In contrast, the two-dimensional immunoblot demonstrates that in M/M2 sCJD the full-length PrP(Sc) form is overrepresented and carries glycans that are different from those present in the PrP(Sc) of sFI. Because the altered glycans are detectable only in the PrP(Sc) and not in the normal or cellular PrP (PrP(C)), they are likely to result from preferential conversion to PrP(Sc) of rare PrP(C) glycoforms. This is the first evidence that a qualitative difference in glycans contributes to prion diversity.

Effectiveness of hepatitis B vaccination in babies born to hepatitis B surface antigen-positive mothers in Italy

This study examined 522 children born to hepatitis B surface antigen (HBsAg)-positive mothers from 1985 through 1994 and evaluated the protection provided by anti-hepatitis B virus (HBV) immunization at birth. Babies were given hepatitis B immunoglobulin and hepatitis B vaccine at birth. At 5-14 years after immunization, 17 children (3.3%) were anti-HB core antigen positive, and 3 also were HBsAg positive. One carrier child had a double mutation, with substitution of proline-->serine at codons 120 (P120S) and 127 (P127S) within the a determinant of HBsAg. Of the 522 children, 400 (79.2%) of 505 still had protective anti-HBsAg titers > or =10 mIU/mL. Thus, HBV vaccination of children born to HBsAg-positive mothers is effective and confers long-term immunity. There is no evidence that the emergence of HBV escape mutants secondary to the immune pressure against wild-type HBV is of concern.

Aberrant metal binding by prion protein in human prion disease

Human prion diseases are characterized by the conversion of the normal prion protein (PrP(C)) into a pathogenic isomer (PrP(Sc)). Distinct PrP(Sc) conformers are associated with different subtypes of prion diseases. PrP(C) binds copper and has antioxidation activity. Changes in metal-ion occupancy can lead to significant decline of the antioxidation activity and changes in conformation of the protein. We studied the trace element status of brains from patients with sporadic Creutzfeldt-Jakob disease (sCJD). We found a decrease of up to 50% of copper and an increase in manganese of approximately 10-fold in the brain tissues from sCJD subjects. We have also studied the metal occupancy of PrP in sCJD patients. We observed striking elevation of manganese and, to a lesser extent, of zinc accompanied by significant reduction of copper bound to purified PrP in all sCJD variants, determined by the PrP genotype and PrP(Sc) type, combined. Both zinc and manganese were undetectable in PrP(C) preparations from controls. Copper and manganese changes were pronounced in sCJD subjects homozygous for methionine at codon 129 and carrying PrP(Sc) type-1. Anti-oxidation activity of purified PrP was dramatically reduced by up to 85% in the sCJD variants, and correlated with increased in oxidative stress markers in sCJD brains. These results suggest that altered metal-ion occupancy of PrP plays a pivotal role in the pathogenesis of prion diseases. Since the metal changes differed in each sCJD variants, they may contribute to the diversity of PrP(Sc) and disease phenotype in sCJD. Finally, this study also presented two potential approaches in the diagnosis of CJD; the significant increase in brain manganese makes it potentially detectable by MRI, and the binding of manganese by PrP in sCJD might represent a novel diagnostic marker.

Helicobacter pylori neutrophil-activating protein stimulates tissue factor and plasminogen activator inhibitor-2 production by human blood mononuclear cells

Helicobacter pylori neutrophil-activating protein (HP-NAP) is a virulence factor that activates phagocytic NADPH-oxidase. The effect of HP-NAP on the production of tissue factor (TF), plasminogen activator inhibitor-2 (PAI-2), and urokinase-type plasminogen activator (u-PA) by human blood mononuclear cells (MNC) was evaluated by using functional and immunological assays and mRNA analysis. HP-NAP induced time- and dose-dependent increases in TF and PAI-2, with a maximal effect at 300 nmol/L (>15-fold increase in antigens). No changes in u-PA were observed. When whole bacteria were used, an H. pylori mutant lacking HP-NAP was significantly less active than the wild-type strain. MNC from a patient with chronic granulomatous disease behaved as do normal cells, which indicates that HP-NAP effects can occur independently of NADPH-oxidase. HP-NAP, by inducing the coordinate expression of cell procoagulant and antifibrinolytic activities, might favor fibrin deposition and contribute to the inflammatory reaction of gastric mucosa elicited by H. pylori.

Human immunodeficiency virus type 1 Tat protein decreases cyclic AMP synthesis in rat microglia cultures

We have studied the modulation of cyclic AMP (cAMP) accumulation by the human immunodeficiency virus type 1 (HIV 1) protein Tat in microglia and astrocyte cultures obtained from neonatal rat brain. Pretreatment of microglia with recombinant Tat resulted in a dose- and time-dependent decrease of cAMP accumulation induced by subsequent exposure to isoproterenol (1 microM). The inhibitory action of 100 ng/mL Tat approached 50% after 4 h of preincubation and reached a maximum of 70% after 24 h. The Tat-induced time- and dose-dependent decrease of cAMP accumulation was observed also when microglial cultures were stimulated with the adenylyl cyclase activator forskolin (100 microM). In both cases, Tat inhibitory action was 70% reverted by a specific monoclonal anti-Tat antibody, but was not prevented either by the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xantine (100 microM) or by a 16-h pretreatment of microglial cultures with the Gi protein inhibitor pertussis toxin (10 ng/mL). All these results suggested that the viral protein acts at a step of the cAMP transduction pathway other than receptors, G proteins and phosphodiesterases. The target of Tat appeared to be adenylyl cyclase, whose activity was markedly reduced (up to 60%) in membranes prepared from Tat-treated microglial cells, both in basal conditions and after stimulation with isoproterenol and forskolin. The inability of the competitive inhibitor of nitric oxide synthase N(G)-monometyl- L-arginine (20 and 200 microM) to revert Tat action on forskolin-induced cAMP accumulation, and of two potent nitric oxide donors, PAPA and DETA (0.1-2 m M), to alter forskolin-induced cAMP accumulation, excluded an involvement of nitric oxide in Tat-induced adenylyl cyclase inhibition. On the contrary, two inhibitors of nuclear factor kappaB activation, N-tosyl-( L)-phenylalanine chloromethyl ketone (10 microM) and SN50 (25 microM), markedly prevented the reduction of forskolin-evoked cAMP accumulation by Tat, suggesting a possible role for this nuclear transcriptional factor in the regulation of adenylyl cyclase by Tat in microglia. This assumption was strengthened by the ability of lipopolysaccharide (100 ng/mL, 4 h) to mimic the inhibitory effect of the viral protein. Conversely, astrocyte cAMP accumulation was unaffected by the viral protein, as tested at various concentrations and time points. Finally, Tat inhibition of microglial adenylyl cyclase was not due to non-specific cytotoxicity. As cAMP has been reported to exert a neuroprotective role in several in vivo and in vitro models of brain pathologies, and microglia is believed to mediate Tat-induced neurotoxicity, these results suggest that the ability of Tat to inhibit cAMP synthesis in microglia may contribute to neuronal degeneration and cell death associated with HIV infection.

Thrombin activatable fibrinolysis inhibitor (TAFI) does not inhibit in vitro thrombolysis by pharmacological concentrations of t-PA

TAFI (thrombin activatable fibrinolysis inhibitor) is a plasma procarboxypeptidase that upon activation inhibits the fibrinolytic process by removing the C-terminal lysines from partially degraded fibrin. The generation of activated TAFI (TAFIa) has been suggested to represent a mechanism of thrombus resistance to thrombolytic therapy. However, the ability of TAFI to inhibit fibrinolysis by pharmacological concentrations of t-PA has not been properly investigated. We used an in vitro model consisting of 125I-fibrin blood clots submerged in autologous defibrinated plasma. Upon addition of t-PA (125-5,000 ng/ml) and CaCl2 (25 mM), samples were incubated at 37 degrees C, and clot lysis was measured at intervals from the radioactivity released into solution. The role of TAFI was assessed either by neutralizing the generated TAFIa with the specific inhibitor PTI (50 microg/ml) or by enhancing TAFI activation through the addition of recombinant soluble thrombomodulin (solulin, 1 microg/ml). In our clot lysis model, activation of TAFI amounted to about 20% of inducible carboxypeptidase activity. Addition of PTI, however, produced a significant increase in the extent of lysis only at concentrations of t-PA equal to or lower than 250 ng/ml. When solulin was added to the plasma surrounding the clot, about 70% of TAFI was activated within 15 min. Under these conditions, inhibition of clot lysis was very marked in samples containing 125 or 250 ng/ml of t-PA, but negligible in those containing pharmacological concentrations of the activator (1,000 and 5,000 ng/ml). Additional experiments suggest that loss of fibrin-dependence by elevated concentrations of t-PA may be one of the mechanisms explaining the lack of effect of TAFIa. Our data indicate that, under our experimental conditions, clot lysis by pharmacological concentrations of t-PA is not influenced by TAFIa even after maximal activation of this procarboxy-peptidase.

Low molecular weight heparins prevent thrombin-induced thrombo-embolism in mice despite low anti-thrombin activity. Evidence that the inhibition of feed-back activation of thrombin generation confers safety advantages over direct thrombin inhibition

BACKGROUND AND OBJECTIVES

Thrombin-induced thromboembolism in mice is a model in which the feed-back clotting activation produced by the injected enzyme greatly contributes to fibrin accumulation in lungs and to mortality. Using this model we have previously shown that activated human protein C (aPC), by interrupting endogenous clotting activation at a high level (factors Va and VIIIa), prevents mortality inducing only a minor hemostatic impairment. With the same model we have now compared the antithrombotic and prohemorrhagic effects of two low molecular weight heparins (LMWHs), reviparin and tinzaparin, which are expected to inhibit preferentially the positive feed-back triggered by thrombin (anti Xa activity), with those of unfractionated heparin (UFH) and PEG-hirudin, which inhibit mainly or exclusively thrombin activity (anti IIa activity).

DESIGN AND METHODS

Pulmonary thromboembolism was induced in mice by i.v. injection of bovine thrombin (1,000U/kg). Drugs (from 0.12 to 1.2 mg/kg) were given as bolus injection 2 min prior to thrombin challenge and mortality was assessed within 15 min. The bleeding time was assessed by a tail tip transection model. Activated partial thromboplastin time (aPTT), thrombin clotting time (TcT), fibrinogen assay and anti Xa activity determination were performed in citrated plasma from saline- or drug-treated animals.

RESULTS

All drugs protected mice from thrombin-induced mortality in a dose-dependent way. At comparable antithrombotic dosages, the anti IIa activity generated in plasma (assessed by TcT) was highest with UFH, intermediate with tinzaparin and very low with reviparin. Accordingly, the fibrinogen drop, which is caused mainly by the injected thrombin, was prevented by the heparins to an extent that was fairly well related to their anti IIa activity. aPTT and bleeding time, used as measures of hemorrhagic risk, were markedly more prolonged by UFH than by reviparin. Tinzaparin, instead, had an intermediate effect. Interestingly, PEG-hirudin, at equipotent antithrombotic dosages, caused a prolongation of bleeding time comparable to that observed with UFH.

INTERPRETATIONS AND CONCLUSIONS

Our data show that, in our model, drugs acting at a high level of the blood clotting cascade, like LMWHs with a high anti Xa/anti IIa ratio, display a better antithrombotic/prohemorrhagic profile than drugs acting prevalently on thrombin.

Monocytes, but not endothelial cells, downregulate the anticoagulant activity of activated protein C

Activated protein C (APC) is a natural anticoagulant and inhibits thrombin generation by degrading factors Va and VIIIa. We evaluated the ability of APC to inhibit blood coagulation triggered by lipopolysaccharide (LPS)-stimulated [tissue factor (TF)-expressing] human mononuclear cells (MNCs) or umbilical vein endothelial cells (HUVECs). Using a plasma recalcification assay, we found that APC (up to 53.3 nmol/l final concentration) had a poor anticoagulant effect in the presence of LPS-stimulated MNCs, whereas it caused a marked prolongation of clotting time in the presence of LPS-stimulated HUVECs. A poor response to APC was also observed when platelet-free MNCs, monocyte-enriched preparations or the monocytoid cell line U937 were tested. Using a TF-independent (FXa-induced) thrombin generation assay, we demonstrated that both LPS-stimulated and unstimulated MNCs negated the inhibitory activity of APC. Direct determination of FVa activity indicated that MNCs were less efficient than HUVECs in promoting FVa inactivation by APC. Together, our results suggest that MNCs, at variance with HUVECs, protect factor Va from inactivation by APC, probably through the expression of a membrane component not present on endothelial cells. These strengthen the importance of monocytes in fibrin deposition associated with pathological conditions characterized by monocyte recruitment and activation.

Fibrin down-regulates LPS- and PMA-induced tissue factor expression by blood mononuclear cells

Several studies indicate that fibrin may play a functional role in inflammation by modulating a variety of cellular functions. We investigated the effect of fibrin on tissue factor (TF) production by blood mononuclear cells (MNC). Citrated human blood was recalcified and incubated at 37 degrees C for 1-4 h. The resulting clot was lysed by the addition of tissue plasminogen activator (t-PA) and MNC were isolated by density gradient centrifugation. A control blood sample was processed in the same way but omitting calcium addition and clot formation. Clot- and blood-derived MNC did not express detectable TF activity and antigen whatever the incubation time. Clot-derived MNC, however, generated on average 5 fold less TF (activity and antigen) than control cells, when stimulated with lipopolysaccharide (LPS, I microg/ml) for 3 h at 37 degrees C. A reduced TF response of clot-derived cells was also observed at mRNA level as indicated by RT-PCR and in situ hybridization. The effect was dependent on the incubation time within the clot, could not be reversed by enhancing LPS concentration or by adding serum, and was maintained if LPS was replaced by the tumor promoter PMA. A reduced TF response was also found when washed MNC were incorporated for 1 h at 37 degrees C within purified fibrin but not when the cells were incubated with fibrinogen, thrombin or fibrin split products alone. indicating that contact with fibrin was responsible for the inhibition of TF production. Fibrin-induced down-regulation of TF response to LPS and PMA by MNC may represent a negative feed-back aimed at limiting excessive blood clotting activation in immunoinflammatory diseases.

Absence of hemispheric dominance for mental rotation ability: a transcranial Doppler study

Mean blood flow velocity (MFV) of the middle cerebral arteries was monitored in 19 healthy, adult, right-handed subjects during the resting phase and the execution of a series of neuropsychological tests: two right/left discrimination tasks, two mental rotation paradigms (the Ratcliff's test and a cube comparison test) and a phonemic fluency task, which was utilised as an internal control. In the group as a whole, the Ratcliff's test was associated with a significant bilateral increase in MFV versus both the resting state (right: p < .000001, left: p < .000001) and right/left discrimination tasks (task 1: right: p = .003, left: p = .005; task 2: right: p = .001, left: p = .001). The cube comparison in turn produced a significant increase in MFV versus both the baseline conditions (right: p < .000001, left: p < .000001) and the Ratcliff's test (right: p = .01, left: p = .002). As expected, the fluency task was associated with a significant asymmetric increase in cerebral perfusion (left > right: p = .0001). Increasing task difficulty (right/left discrimination < Ratcliffs test < cube comparison) was paralleled by a roughly proportional rise in MFV values (right: r = .424, p < .01; left: r = .331, p = .01). In conclusion, we were able to demonstrate that (1) in addition to the amount of MFV variation due to right/left discrimination (when required), mental rotation per se causes a bihemispheric activation irrespective of the experimental paradigm; (2) the MFV variation is proportional to the difficulty of the tasks.

Protein kinase C activation reduces microglial cyclic AMP response to prostaglandin E2 by interfering with EP2 receptors

We studied the modulation by protein kinase C (PKC) of the cyclic AMP (cAMP) accumulation induced by prostaglandin (PG) E2 in rat neonatal microglial cultures. Short pretreatment of microglia with phorbol 12-myristate 13-acetate (PMA) or 4beta-phorbol 12,13-didecanoate, which activate PKC, but not with the inactive 4alpha-phorbol 12,13-didecanoate, substantially reduced cAMP accumulation induced by 1 microM PGE2. The action of PMA was dose and time dependent, and the maximal inhibition (approximately 85%) was obtained after 10-min preincubation with 100 nM PMA. The inhibitory effect of PMA was mimicked by diacylglycerol and was prevented by the PKC inhibitor calphostin C. As PMA did not affect isoproterenol- or forskolin-stimulated cAMP accumulation, we investigated whether activation of PKC decreased cAMP production by acting directly at PGE2 EP receptors. Neither sulprostone (10(-9)-10(-5) M), a potent agonist at EP3 receptors (coupled to adenylyl cyclase inhibition), nor 17-phenyl-PGE2 (10(-6)-10(-5) M), an agonist of EP1 receptors, modified cAMP accumulation induced by forskolin. On the contrary, 11-deoxy-16,16-dimethyl PGE2, which does not discriminate between EP2 and EP4 receptors, both coupled to the activation of adenylyl cyclase, and butaprost, a selective EP2 agonist, induced a dose-dependent elevation of cAMP that was largely reduced by PMA pretreatment, as in the case of PGE2. These results indicated EP2 receptors as a possible target of PKC and suggest that PKC-activating agents present in the pathological brain may prevent the cAMP-mediated microglia-deactivating function of PGE2.

Retinoic acid stimulates plasminogen activator inhibitor 2 production by blood mononuclear cells and inhibits urokinase-induced extracellular proteolysis

Retinoids have been shown to modulate several functions of mononuclear phagocytes. We investigated the in vitro effect of all-trans-retinoic acid (ATRA) on the production of two major fibrinolytic components, urokinase-type plasminogen activator (u-PA) and PA inhibitor 2 (PAI-2), by human blood mononuclear cells (MNC). ATRA caused a dose-dependent (range 0.01-10 microM) accumulation of PAI-2 antigen and activity into the cell culture medium, with a maximal increase (about 5-fold over control) at a concentration of 1-10 microM. Similarly, a dose-dependent increase in PAI-2 antigen was observed in cell extracts upon ATRA stimulation. Northern blot analysis showed a parallel increase in the amount of PAI-2 mRNA in ATRA-treated cells. Time-course experiments with 1 microM ATRA showed enhanced PAI-2 mRNA expression as early as 2 h, reaching a maximum at 4-6 h and then declining at 18-24 h, and a time-dependent increase in PAI-2 antigen in the cell culture medium. At variance with PAI-2, u-PA was not influenced by the drug. To establish whether ATRA-induced changes influenced the fibrinolytic process, we evaluated the effect of MNC stimulated with ATRA on u-PA-induced degradation of diluted plasma clots. ATRA-treated cells markedly inhibited clot lysis induced by low concentrations of u-PA. The effect was due to enhanced extracellular PAI-2 accumulation since it was observed with conditioned medium from ATRA-treated cells; it was abolished by the addition of neutralizing anti-PAI-2 antibodies and was negligible when single-chain t-PA was used instead of u-PA. Since monocyte/macrophage-mediated, plasminogen-dependent extracellular proteolysis has been proposed as an important mechanism of tissue damage in several inflammatory states, our findings might contribute to better explain the anti-inflammatory properties of retinoids.

Angiotensin IV stimulates plasminogen activator inhibitor-1 expression in proximal tubular epithelial cells

BACKGROUND

Angiotensin II (Ang II) has been shown to be implicated in the development of renal fibrosis in several forms of chronic glomerulonephritides, but the precise mechanisms of its effects remain unclear. It has recently been reported that Ang II stimulates the expression of plasminogen activator inhibitor-1 (PAI-1) in several cell lines. PAI-1 is a major physiological inhibitor of the plasminogen activator/plasmin system, a key regulator of fibrinolysis and extracellular matrix (ECM) turnover. PAI-1 induction by Ang II in endothelial cells seems to be mediated by Ang IV via a receptor that is different from Ang II type 1 and 2 receptors (AT1 and AT2).

METHODS

In this study, we sought to evaluate the effects of Ang IV on PAI-1 gene and protein expression in a well-characterized and immortalized human proximal tubular cell line (HK2) by Northern blot and enzyme-linked immunosorbent assay.

RESULTS

Ang IV stimulated PAI-1 mRNA expression, whereas it did not induce a significant increase in tritiated thymidine uptake after 24 hours of incubation. This effect was dose and time dependent. Ang IV (10 nM) induced a 7.8 +/- 3.3-fold increase in PAI-1 mRNA expression. The PAI-1 antigen level was significantly higher in conditioned media and the ECM of cells treated with Ang II and Ang IV than in control cells (both P < 0.02). Although Ang II induced a 4.2 +/- 2. 1-fold increase in PAI-1 mRNA expression, its effect underwent a dose-dependent reduction when amastatin, a potent inhibitor of the endopeptidases that catalyzes the conversion of Ang II to Ang IV, was added. In contrast, amastatin was not able to prevent the expression of PAI-1 mRNA induced by Ang IV. Finally, pretreatment of HK2 cells with losartan and N-Nicotinoyl-Tyr-N3-(Nalpha-CBZ-Arg)-Lys-His-Pro-Ile, the specific antagonists of AT1 and AT2 receptors, failed to modify PAI-1 mRNA expression as induced by Ang II.

CONCLUSIONS

Our results demonstrate that Ang II stimulates PAI-1 mRNA expression and the production of its protein in human proximal tubular cells. This is mainly-if not exclusively-due to Ang IV, which acts on a receptor that is different than AT1 or AT2. Therefore, it can be hypothesized that the induction of PAI-1 by Ang IV may be implicated in the pathogenesis of renal interstitial fibrosis in several forms of chronic glomerulonephritides.

Prevention and therapy of experimental venous thrombosis in rabbits by desmin 370

Desmin 370 (D370), a low molecular weight dermatan sulfate, has been shown to reduce the size of preformed thrombi in rats, via a mechanism largely independent of its anticoagulant activity. In the present study we investigated the therapeutic efficacy of D370 in rabbits with experimental jugular vein thrombosis. Experiments performed to evaluate the antithrombotic dosages in rabbits indicated that D370 prevented the formation of venous thrombi (Wessler model) in a dose-dependent manner with complete inhibition at 20 mg/kg. When injected to rabbits bearing a 30 min aged thrombus, D370 caused a time- and dose-dependent reduction in thrombus weight. Thrombi harvested 2 h after injection of 50 mg/kg of D370 were 71% smaller than thrombi from saline-treated rabbits and 50% smaller than pretreatment thrombi, suggesting a double effect of the drug: inhibition of thrombus accretion and reduction of the existing thrombus. Interestingly, pretreatment with the fibrinolytic inhibitor EACA (1 g/kg), significantly attenuated the therapeutic efficacy of D370, suggesting a possible involvement of the fibrinolytic system. Heparin (50 and 200 U/kg) was less active as therapeutic agent, the maximal decrease in thrombus weight, as compared to untreated rabbits, amounting to 38%. Heparin, moreover, caused a more pronounced prolongation of APTT than comparable antithrombotic dosages of D370. Our present data extend previous results on the therapeutic efficacy of D370 and underscore its potential as an alternative antithrombotic drug.

Activated human protein C prevents thrombin-induced thromboembolism in mice. Evidence that activated protein c reduces intravascular fibrin accumulation through the inhibition of additional thrombin generation

Activated protein C (APC) is a potent physiologic anticoagulant with profibrinolytic properties, and has been shown to prevent thrombosis in different experimental models. We investigated the effect of human APC on thrombin-induced thromboembolism in mice, a model of acute intravascular fibrin deposition leading to death within minutes. APC given intravenously (i.v.) as a bolus 2 min before thrombin challenge (1,250 U/kg) reduced mortality in a dose-dependent manner despite the lack of thrombin inhibitor activity. Significant inhibition of thrombin-induced death was observed at the dose of 0.05 mg/kg, and maximal protection was obtained with 2 mg/kg (> 85% reduction in mortality rate). Histology of lung tissue revealed that APC treatment (2 mg/kg) reduced significantly vascular occlusion rate (from 89.2 to 46.6%, P < 0.01). The protective effect of APC was due to the inhibition of endogenous thrombin formation as indicated by the fact that (a) the injection of human thrombin caused a marked decrease in the coagulation factors of the intrinsic and common pathways (but not of Factor VII), suggesting the activation of blood clotting via the contact system; (b) APC pretreatment reduced markedly prothrombin consumption; (c) the lethal effect of thrombin was almost abolished when the animals were made deficient in vitamin K-dependent factors by warfarin treatment, and could be restored only by doubling the dose of thrombin, indicating that the generation of endogenous thrombin contributes significantly to death; and (d) APC failed to protect warfarin-treated animals, in which mortality is entirely due to injected thrombin, even after protein S supplementation. Other results suggest that APC protects from thrombin-induced thromboembolism by rendering the formed fibrin more susceptible to plasmin degradation rather than by reducing fibrin formation: in thrombin-treated mice, fibrinogen consumption was not inhibited by APC; and inhibition of endogenous fibrinolysis by epsilon-aminocaproic or tranexamic acid resulted in a significant reduction of the protective effect of APC. Since APC did not enhance plasma fibrinolytic activity, as assessed by the measurement of plasminogen activator (PA) or PA inhibitor (PAI) activities, PAI-1 antigen, or 125I-fibrin degrading activity, we speculate that the inhibition of additional (endogenous) thrombin formation by APC interrupts thrombin-dependent mechanisms that make fibrin clots more resistant to lysis, so that the intravascular deposited fibrin can be removed more rapidly by the endogenous fibrinolytic system.

Thrombolysis enhancing activity of a low molecular weight dermatan sulfate (Desmin 370) in experimental pulmonary embolism in rats

The effect of Desmin 370 (D370), a low molecular weight dermatan sulfate, on the extent of lysis of radiolabelled pulmonary emboli in rats was evaluated. 125I-fibrin labelled blood clots were embolized into the lungs via a jugular vein, and the degree of lysis was calculated, at predetermined intervals, by the residual radioactivity in the lungs. A single i.v. injection of D370 (50 mg/kg) caused a significant increase in the rate of lysis, which was visible at 30 min and persisted for the whole experimental period (2 h). This effect was prevented by epsilon-aminocaproic acid (1 g/kg). At comparable antithrombotic dosages, heparin (2 mg/kg) also produced a significant enhancement of thrombolysis while hirudin (2 mg/kg) was totally ineffective. Heparin, however, produced a much more pronounced anticoagulant effect than D370. No changes in the plasma levels of plasminogen activator and plasminogen activator inhibitor activities were observed after treatment with D370. Moreover, the dermatan sulfate failed to enhance the blood fibrinolytic activity measured by a solid phase 125I-fibrin assay. These results extend previous data indicating that D370 may be efficient also in the therapy of thrombosis and provide direct evidence that this effect occurs, at least in part, via degradation of thrombus associated fibrin.

Tissue factor in health and disease

Over the last years numerous studies have focussed on the in vivo expression of tissue factor (TF) in health and disease. The selective perivascular distribution of TF and the lethal effects of TF knockouts have added strong support to the widely accepted view that TF plays a pivotal role in the initiation of blood coagulation during physiological hemostasis. Inappropriate in vivo expression of TF, particularly by cells that do not express this protein under normal conditions (mainly monocyte-macrophages and endothelial cells), has been documented and is likely responsible for fibrin deposition in a variety of pathological conditions, among which sepsis-associated disseminated intravascular coagulation (DIC) and thromboembolic disease. In malignancy, in vivo expression of TF by tumor cells and/or by host cells has been implicated not only in intratumoral and systemic activation of blood coagulation but also in tumor growth and dissemination.

In vitro clot lysis as a potential indicator of thrombus resistance to fibrinolysis--study in healthy subjects and correlation with blood fibrinolytic parameters

Using an in vitro model of clot lysis, the individual response to a pharmacological concentration of recombinant tissue plasminogen activator (rt-PA) and the influence on this response of the physiological variations of blood parameters known to interfere with the fibrinolytic/thrombolytic process were investigated in 103 healthy donors. 125I-fibrin labelled blood clots were submersed in autologous plasma, supplemented with 500 ng/ml of rt-PA or solvent, and the degree of lysis was determined after 3 h of incubation at 37 degrees C. Baseline plasma levels of t-PA, plasminogen activator inhibitor 1 (PAI-1), plasminogen, alpha 2-antiplasmin, fibrinogen, lipoprotein (a), thrombomodulin and von Willebrand factor as well as platelet and leukocyte count and clot retraction were also determined in each donor. rt-PA-induced clot lysis varied over a wide range (28-75%) and was significantly related to endogenous t-PA, PAI-1, plasminogen (p < 0.001) and age (p < 0.01). Multivariate analysis indicated that both PAI-1 antigen and plasminogen independently predicted low response to rt-PA. Surprisingly, however, not only PAI-1 but also plasminogen was negatively correlated with rt-PA-induced clot lysis. The observation that neutralization of PAI-1 by specific antibodies, both in plasma and within the clot, did not potentiate clot lysis indicates that the inhibitor, including the platelet-derived form, is insufficient to attenuate the thrombolytic activity of a pharmacological concentration of rt-PA and that its elevation, similarly to the elevation of plasminogen, is not the cause of clot resistance but rather a coincident finding. It is concluded that the in vitro response of blood clots to rt-PA is poorly influenced by the physiological variations of the examined parameters and that factors other than those evaluated in this study interfere with clot dissolution by rt-PA. In vitro clot lysis test might help to identify patients who may be resistant to thrombolytic therapy.

Effect of Helicobacter pylori lipopolysaccharide (LPS) and LPS derivatives on the production of tissue factor and plasminogen activator inhibitor type 2 by human blood mononuclear cells

Different Helicobacter pylori lipopolysaccharides (LPSs) and LPS-derivatives were studied for their ability to induce the production of procoagulant activity (PCA) and plasminogen activator inhibitor type 2 (PAI-2) by human blood mononuclear leukocytes. Smooth (S)- and rough (R)-form LPSs caused a similar increase in cell-associated PCA (tissue factor) and PAI-2 antigen release. Both effects were potentiated by fetal bovine serum via a CD14-mediated mechanism. The potency of H. pylori LPSs was approximately 1000-fold lower than that of Salmonella typhimurium LPSs. When H. pylori LPS derivatives (dephosphorylated R-LPS, S-lipid A, and R-lipid A) were used, PCA and PAI-2 production were markedly reduced. R-lipid A was approximately 4-fold less efficient than S-lipid A. These findings suggest that the induction of monocyte tissue factor and PAI-2 by H. pylori LPS is influenced by the lipid A structure and modulated by the core oligosaccharide and that phosphate groups present in both regions may play an important role.

Non neutralizing antibodies to tissue type plasminogen activator in the serum of acute myocardial infarction patients treated with the recombinant protein

Recombinant tissue-type plasminogen activator (rt PA) is currently used as a thrombolytic agent in the management of acute myocardial infarction (AMI). Since it is known that other recombinant proteins induce antibody formation when administered to humans, we determined the presence of anti-rt-PA antibodies in serial blood samples from 60 AMI patients (43 treated with and 17 without rt-PA). Blood samples were taken upon hospital admission, 15 days and 1, 3, 6 months thereafter. A blood sample was also collected from 200 healthy subjects. Using an ELISA, anti-rt-PA antibodies were detected as serum immunoglobulins specifically binding immobilized rt-PA, AMI patients before treatment and normal subjects exhibited negligible levels of anti-rt-PA antibodies; both groups had only one outlier value. Fifteen days after rt-PA treatment, 2 AMI patients showed an increase in antibody titer beyond the highest normal value. This titer progressively decreased during the following 6 months. The antibodies from these two patients bound rt-PA both in a solid and fluid phase. They bound melanoma t-PA to a lower degree and did not bind urokinase type plasminogen activator at all, indicating specificity for t-PA. The marked temporal relationship between rt-PA infusion and antibody appearance indicated that antibody formation had been elicited by the infusion of rt-PA. Nevertheless, the lack of anti-rt-PA antibody interference with rt-PA function in vitro, along with the favourable clinical outcome of those patients having such antibodies would indicate that the appearance of anti-rt-PA antibodies does not interfere with the physiological fibrinolytic activity.

Cultured human mesangial cells produce both type 1 and type 2 plasminogen activator inhibitors

Cultured human mesangial cells (HMC) derived from normal kidneys have been shown to synthesize tissue-type plasminogen activator (t-PA) and excess amounts of PA inhibitor type 1 (PAI-1). Conflicting results have been obtained concerning the production of urokinase-type PA (u-PA) and efforts to show PA inhibitor 2 (PAI-2) met with failure. We evaluated the fibrinolytic profile of cultured HMC lines obtained from 12 patients with renal carcinoma and one cadaveric kidney donor. Subconfluent cells (third passage) were incubated overnight in serum-free medium. t-PA, u-PA, PAI-1 and PAI-2 antigens were assayed by ELISA methods and PA and PAI activities by amidolytic methods both in conditioned medium (CM) and cell extracts (CE). Besides PAI-1, PAI-2 antigen was detected in all but one HMC lines. At variance with the former, which was largely released in the culture medium, PAI-2 was mainly cell-associated. t-PA antigen was found in all but two cell lines while u-PA antigen was detected in relatively high concentrations in 8 cell lines. PA activity, identified as u-PA by functional and immunological criteria, was measured in CM of six of the eight u-PA producing cell lines, whereas PAI activity was undetectable or very low in CM of all cell lines, suggesting that PAI-1 was largely inactive. Functional assays of cell extracts demonstrated the presence of PA activity, again identified as u-PA, only in samples (five lines) containing u-PA antigen in excess over PAI-2. PAI activity was found instead in the extracts in which the inhibitor was higher than the activator (six lines) and was identified as PAI-2, as it inhibited u-PA but not single-chain t-PA and was neutralized by a polyclonal anti-PAI-2 antibody. The heterogeneous fibrinolytic pattern of HMC lines was confirmed by mRNA analysis of three representative lines. Results were similar when HMC lines at passage five were used, except that the u-PA content was significantly reduced both in CM and CE. These findings indicate that the fibrinolytic profile of cultured HMC is more complex than previously reported. The production of large amounts of PAI-2 may represent an additional control mechanism of proteinase activity.

Blood and tissue fibrinolytic profiles in patients with colorectal carcinoma

In patients with colorectal cancer, profound alterations of the plasminogen activator system have been described at the tumor level, but conflicting results have been obtained for fibrinolytic parameters in plasma. Components of the fibrinolytic system, including tissue-type and urokinase-type plasminogen activators and their inhibitors type 1 and 2, were measured in tissue and/or plasma from 41 patients with colorectal cancer and in 40 controls. Procoagulant activity of freshly isolated mononuclear cells (basal activity) and the procoagulant activity and fibrinolytic proteins produced by the cells after incubation for 18 h without exogenous stimulation were also evaluated. Malignant tissue extracts had significantly higher levels of urokinase-type plasminogen activator and plasminogen activator inhibitor-1, but lower levels of tissue-type plasminogen activator than normal mucosa. Plasminogen activator inhibitor-1 alone was higher in advanced (Dukes' stages C + D) than limited (B) tumors. Plasminogen activator inhibitor-2 was not different in malignant tissue and normal mucosa. Plasma levels of plasminogen activator inhibitor-1 antigen were significantly increased in cancer patients compared with controls, but there were no differences in tissue-type and urokinase-type plasminogen activator, in plasminogen activator inhibitor-2, and D-dimer levels. Intra-patient analysis revealed no significant correlation between tumor and plasma levels of plasminogen activators or type 1 inhibitor. Tissue-type plasminogen activator, but not the urokinase type or inhibitor type 1, was higher in venous than in arterial blood collected at the tumor site during surgery. Basal procoagulant activity of mononuclear cells and the procoagulant activity and inhibitor type-2 produced by the cells after short-term culture were comparable in patients and controls. These findings indicate that, at least in our patients with colorectal cancer, the profound changes occurring at tumor level are barely detectable in the blood. Thus, the clinical relevance of plasma fibrinolytic parameters, especially urokinase-type plasminogen activator antigen, as tumor markers in colorectal cancer remains to be established.

Desmin 370, a low molecular weight dermatan sulfate, reduces the weight of preformed thrombi in rats made afibrinogenemic by ancrod

Desmin 370 (D370), a low molecular weight dermatan sulfate, has been shown to induce a marked reduction of the weight of preformed venous thrombi in rats and rabbits by mechanisms that appeared largely independent of inhibition of thrombus accretion. In order to provide further support for such a mechanism, we exploited the defibrinating capacity of ancrod to obtain a thrombosis model characterized by the lack of thrombus growth and thus sensitive only to agents promoting thrombus lysis. Thrombus formation in anesthetized rats was induced by vena cava ligature. Injection of ancrod (5 U/kg) 5 h after induction of venous stasis caused a more than 95% reduction in plasma fibrinogen and prevented thrombus accretion as indicated by the lack of thrombus weight increase during the 3 h experimental period (12.2 +/- 0.6 vs 14.5 +/- 1 as compared to 12.6 +/- 0.6 vs 19.6 +/- 0.8, p < 0.01, in control rats) and by the almost complete (> 90%) inhibition of 125I-fibrin(ogen) binding to thrombi. Moreover, when ancrod was given 1 h before vena cava ligature, no thrombi were formed within 2 h whereas at the same time interval visible thrombi were present in all control rats. Administration of D370 (10 mg/kg) to thrombus bearing rats, 1 h after induction of afibrinogenemia, resulted in a significant reduction in thrombus weight (43% after 2 h, p < 0.01) which was only slightly lower than that recorded in normofibrinogenemic rats (54%). Enhancement of plasma fibrinolytic activity by ancrod had no influence on thrombus lysis and was not all affected by administration of D370.(ABSTRACT TRUNCATED AT 250 WORDS)