Thrombin as a multifunctional protein: induction of cell adhesion and proliferation

Inflammation and coagulation abnormalities via the activation of the HMGB1‑RAGE/NF‑κB and F2/Rho pathways in lung injury induced by acute hypoxia

High‑altitude acute hypoxia is commonly associated with respiratory cardiovascular diseases. The inability to adapt to acute hypoxia may lead to cardiovascular dysfunction, lung injury and even death. Therefore, understanding the molecular basis of the adaptation to high‑altitude acute hypoxia may reveal novel therapeutic approaches with which to counteract the detrimental consequences of hypoxia. In the present study, a high‑altitude environment was simulated in a rat model in order to investigate the role of the high mobility group protein‑1 (HMGB1)/receptor for advanced glycation end products (RAGE)/NF‑κB and F2/Rho signaling pathways in lung injury induced by acute hypoxia. It was found that acute hypoxia caused inflammation through the HMGB1/RAGE/NF‑κB pathway and coagulation dysfunction through the F2/Rho pathway, both of which may be key processes in acute hypoxia‑induced lung injury. The present study provides new insight into the molecular basis of lung injury induced by acute hypoxia. The simultaneous activation of the HMGB1/RAGE/NF‑κB and F2/Rho signaling pathways plays a critical role in hypoxia‑induced inflammatory responses and coagulation abnormalities, and provides a theoretical basis for the development of potential therapeutic strategies.

Positive Effects of UV-Photofunctionalization of Titanium Oxide Surfaces on the Survival and Differentiation of Osteogenic Precursor Cells-An In Vitro Study

INTRODUCTION

The UVC-irradiation ("UV-photofunctionalization") of titanium dental implants has proved to be capable of removing carbon contamination and restoring the ability of titanium surfaces to attract cells involved in the process of osteointegration, thus significantly enhancing the biocompatibility of implants and favoring the post-operative healing process. To what extent the effect of UVC irradiation is dependent on the type or the topography of titanium used, is still not sufficiently established.

OBJECTIVE

The present study was aimed at analyzing the effects of UV-photofunctionalization on the TiO₂ topography, as well as on the gene expression patterns and the biological activity of osteogenic cells, i.e., osteogenic precursors cultured in vitro in the presence of different titanium specimens.

METHODOLOGY

The analysis of the surface roughness was performed by atomic force microscopy (AFM) on machined surface grade 2, and sand-blasted/acid-etched surface grades 2 and 4 titanium specimens. The expression of the genes related with the process of healing and osteogenesis was studied in the MC3T3-E1 pre-osteoblastic murine cells, as well as in MSC murine stem cells, before and after exposure to differently treated TiO₂ surfaces.

RESULTS

The AFM determinations showed that the surface topographies of titanium after the sand-blasting and acid-etching procedures, look very similar, independently of the grade of titanium. The UVC-irradiation of the TiO₂ surface was found to induce an increase in the cell survival, attachment and proliferation, which was positively correlated with an increased expression of the osteogenesis-related genes Runx2 and alkaline phosphatase (ALP).

CONCLUSION

Overall, our findings expand and further support the current view that UV-photofunctionalization can indeed restore biocompatibility and osteointegration of TiO₂ implants, and suggest that this at least in part occurs through a stimulation of the osteogenic differentiation of the precursor cells.

Expression/Activation of PAR-1 in Airway Epithelial Cells of COPD Patients: Ex Vivo/In Vitro Study

The role of PAR-1 expression and activation was described in epithelial cells from the central and distal airways of COPD patients using an ex vivo/in vitro model. PAR-1 immunoreactivity was studied in epithelial cells from surgical specimens of the central and distal airways of COPD patients and healthy control (HC). Furthermore, PAR-1 expression and activation were measured in both the human bronchial epithelial cell line (16HBE) and normal human bronchial epithelial cells (NHBEs) exposed to cigarette smoke extract (CSE) (10%) or thrombin. Finally, cell proliferation, apoptosis, and IL-8 release were detected in stimulated NHBEs. We identified higher levels of PAR-1 expression/activation in epithelial cells from the central airways of COPD patients than in HC. Active PAR-1 increased in epithelial cells from central and distal airways of COPD, with higher levels in COPD smokers (correlated with pack-years) than in COPD ex-smokers. 16HBE and NHBEs exposed to CSE or thrombin showed increased levels of active PAR-1 (localized in the cytoplasm) than baseline conditions, while NHBEs treated with thrombin or CSE showed increased levels of IL-8 proteins, with an additional effect when used in combination. Smoking habits generate the upregulation of PAR-1 expression/activation in airway epithelial cells, and promoting IL-8 release might affect the recruitment of infiltrating cells in the airways of COPD patients.

Photofunctionalization of dental zirconia oxide: Surface modification to improve bio-integration preserving crystal stability

The use of zirconium oxide in dental implantology is rapidly increasing as it is regarded as being more aesthetical and biologically friendly than titanium oxide. The interaction of titanium oxide with cells and proteins has proven to be significantly affected by the inevitable atmospheric hydrocarbon contamination, defined as biological ageing. The latter has proven to be effectively reversed by UVC irradiation. Crystal structures of both Zr and Ti oxides are very similar, thus also ZrO₂ is prone to contamination by hydrocarbons. In the present study we have characterized the chemical-physical changes occurring to ZrO₂ after UVC irradiation. Firstly a reduction by 3-fold of carbon present on its surface. XRD analysis has indicated that UVC irradiation treatment does not affect the crystalline structure of ZrO₂, suggesting that it is possible to improve cell attachment on the surface without sacrificing the mechanical strength of the material. In addition a chemical model of interaction of cell surface proteins with the almost carbon free ZrO₂ surface obtainable after UVC irradiation is proposed, pointing to the important role likely played by integrins and RGD sequences originating in soluble proteins adsorbed at the cell/ZrO₂ interface. Hence in clinical practice UVC photofunctionalization could improve the soft tissue seal around dental implants functioning as a valid barrier between implant and peri-implant bone, thereby improving the long-term success of implants.

Thrombin-induced IL-8/CXCL8 release is mediated by CK2, MSK1, and NF-κB pathways in human lung epithelial cells

Airway inflammation plays a major role in the pathophysiology of lung inflammatory diseases such as asthma. Thrombin, a serine protease, is known to mediate central functions in thrombosis and hemostasis and also plays a critical role in lung inflammation via producing chemokine release including interleukin (IL)-8/CXCL8. Our previous studies showed that c-Src- and Rac-dependent nuclear factor (NF)-κB signaling pathways participate in thrombin-induced IL-8/CXCL8 release in human lung epithelial cells. In this study, we further investigated the role of casein kinase 2 (CK2)/mitogen stress-activated protein kinase 1 (MSK1)-dependent p65 phosphorylation in thrombin-induced NF-κB activation and IL-8/CXCL8 release. Thrombin-induced IL-8/CXCL8 release was inhibited by CK2 inhibitors (apigenin and tetrabromobenzotriazole, TBB), small interfering RNA of CK2β (CK2β siRNA), and MSK1 siRNA. Treatment of cells with thrombin caused increases in CK2β phosphorylation at Ser209, which was inhibited by a protein kinase C α (PKCα) inhibitor (Ro-32-0432). Thrombin-induced MSK1 phosphorylation at Ser581 and Akt phosphorylation at Ser473 were inhibited by apigenin. Moreover, the thrombin-induced increase in IL-8/CXCL8 release was attenuated by p65 siRNA. Stimulation of cells with thrombin resulted in an increase in p65 phosphorylation at Ser276, which was inhibited by apigenin and MSK1 siRNA. Thrombin-induced κB-luciferase activity was also inhibited by apigenin and MSK1 siRNA. Taken together, these results show that thrombin activates the PKCα/CK2/MSK1 signaling pathways, which in turn initiates p65 phosphorylation and NF-κB activation, and ultimately induces IL-8/CXCL8 release in human lung epithelial cells.

Screening of phytochemicals against protease activated receptor 1 (PAR1), a promising target for cancer

CONTEXT

Drug resistance and drug-associated toxicity are the primary causes for withdrawal of many drugs, although patient recovery is satisfactory in many instances. Interestingly, the use of phytochemicals in the treatment of cancer as an alternative to synthetic drugs comes with a host of advantages; minimum side effects, good human absorption and low toxicity to normal cells. Protease activated receptor 1 (PAR1) has been established as a promising target in many diseases including various cancers. Strong evidences suggest its role in metastasis also.

OBJECTIVE

There are no natural compounds known to inhibit its activity, so we aimed to identify phytochemicals with antagonist activity against PAR1.

METHODS

We screened phytochemicals from Naturally Occurring Plant-based Anticancer Compound-Activity-Target database (NPACT, http://crdd.osdd.net/raghava/npact/ ) against PAR1 using virtual screening workflow of Schrödinger software. It analyzes pharmaceutically relevant properties using Qikprop and calculates binding energy using Glide at three accuracy levels (high-throughput virtual screening, standard precision and extra precision).

RESULTS AND CONCLUSION

Our study led to the identification of phytochemicals, which showed interaction with at least one experimentally determined active site residue of PAR1, showed no violations to Lipinski's rule of five along with predicted high human absorption. Furthermore, structural interaction fingerprint analysis indicated that the residues H255, D256, E260, S344, V257, L258, L262, Y337 and S344 may play an important role in the hydrogen bond interactions of the phytochemicals screened. Of these residues, H255 and L258 residues were experimentally proved to be important for antagonist binding. The residues Y183, L237, L258, L262, F271, L332, L333, Y337, L340, A349, Y350, A352, and Y353 showed maximum hydrophobic interactions with the phytochemicals screened. The results of this work suggest that phytochemicals Reissantins D, 24,25-dihydro-27-desoxywithaferin A, Isoguaiacin, 20-hydroxy-12-deoxyphorbol angelate, etc. could be potential antagonist of PAR1. However, further experimental studies are necessary to validate their antagonistic activity against PAR1.

Thrombin-induced NF-κB activation and IL-8/CXCL8 release is mediated by c-Src-dependent Shc, Raf-1, and ERK pathways in lung epithelial cells

In addition to its functions in thrombosis and hemostasis, thrombin also plays an important role in lung inflammation. Our previous report showed that thrombin activates the protein kinase C (PKC)α/c-Src and Gβγ/Rac1/PI3K/Akt signaling pathways to induce IκB kinase α/β (IKKα/β) activation, NF-κB transactivation, and IL-8/CXCL8 expressions in human lung epithelial cells (ECs). In this study, we further investigated the mechanism of c-Src-dependent Shc, Raf-1, and extracellular signal-regulated kinase (ERK) signaling pathways involved in thrombin-induced NF-κB activation and IL-8/CXCL8 release. Thrombin-induced increases in IL-8/CXCL8 release and κB-luciferase activity were inhibited by the Shc small interfering RNA (siRNA), p66Shc siRNA, GW 5074 (a Raf-1 inhibitor), and PD98059 (a mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitor). Treatment of A549 cells with thrombin increased p66Shc and p46/p52Shc phosphorylation at Tyr239/240 and Tyr317, which was inhibited by cell transfection with the dominant negative mutant of c-Src (c-Src DN). Thrombin caused time-dependent phosphorylation of Raf-1 and ERK, which was attenuated by the c-Src DN. Thrombin-induced IKKα/β phosphorylation was inhibited by GW 5074 and PD98059. Treatment of cells with thrombin induced Gβγ, c-Src, and p66Shc complex formation in a time-dependent manner. Taken together, these results show for the first time that thrombin activates Shc, Raf-1, and ERK through Gβγ, c-Src, and Shc complex formation to induce IKKα/β phosphorylation, NF-κB activation, and IL-8/CXCL8 release in human lung ECs.

PAR1 is selectively over expressed in high grade breast cancer patients: a cohort study

Background

The protease-activated receptor (PAR1) expression is correlated with the degree of invasiveness in cell lines. Nevertheless it has never been directed involved in breast cancer patients progression. The aim of this study was to determine whether PAR1 expression could be used as predictor of metastases and mortality.

Methods

In a cohort of patients with infiltrating ductal carcinoma studied longitudinally since 1996 and until 2007, PAR1 over-expression was assessed by immunoblotting, immunohistochemistry, and flow citometry. Chi-square and log rank tests were used to determine whether there was a statistical association between PAR1 overexpression and metastases, mortality, and survival. Multivariate analysis was performed including HER1, stage, ER and nodes status to evaluate PAR1 as an independent prognostic factor.

Results

Follow up was 95 months (range: 2–130 months). We assayed PAR1 in a cohort of patients composed of 136 patients; we found PAR1 expression assayed by immunoblotting was selectively associated with high grade patients (50 cases of the study cohort; P = 0.001). Twenty-nine of 50 (58%) patients overexpressed PAR1, and 23 of these (46%) developed metastases. HER1, stage, ER and PAR1 overexpression were robustly correlated (Cox regression, P = 0.002, P = 0.024 and P = 0.002 respectively). Twenty-one of the 50 patients (42%) expressed both receptors (PAR1 and HER1 P = 0.0004). We also found a statistically significant correlation between PAR1 overexpression and increased mortality (P = 0.0001) and development of metastases (P = 0.0009).

Conclusion

Our data suggest PAR1 overexpression may be involved in the development of metastases in breast cancer patient and is associated with undifferentiated cellular progression of the tumor. Further studies are needed to understand PAR1 mechanism of action and in a near future assay its potential use as risk factor for metastasis development in high grade breast cancer patients.

Up-regulation of thrombin activity induced by vascular endothelial growth factor in asthmatic airways

BACKGROUND

High expression of vascular endothelial growth factor (VEGF) induces subepithelial fibrosis associated with angiogenesis in patients with asthma. Thrombin is recognized as a new candidate mediating airway remodeling. Therefore, this study was designed to determine the role of up-regulated thrombin activity induced by VEGF on airway remodeling in patients with asthma.

METHODS

Levels of biochemical parameters in induced sputum were examined in 21 asthmatic patients and 11 normal control subjects.

RESULTS

Thrombin activity in induced sputum was significantly higher in asthmatic patients than in normal control subjects: median, 3.67 U/mL; range, 1.15 to 10.2 U/mL; vs median, 1.26 U/mL; range, 0.93 to 2.42 U/mL (p < 0.0001). In contrast, protein C activity in induced sputum was lower in asthmatic patients than in normal control subjects: median, 20%; range, 5 to 30%; vs 41%; range, 30 to 59% (p < 0.0001). VEGF level in induced sputum was positively correlated with thrombin activity in asthmatic patients (r = 0.55, p = 0.02), while inversely correlated with protein C activity (r = - 0.57, p = 0.01). Levels of basic fibroblast growth factor (bFGF), a major profibrotic factor, were also significantly higher in asthmatic patients than in normal control subjects. Moreover, thrombin activity was significantly correlated with bFGF level in asthmatic patients (r = 0.67, p = 0.003).

CONCLUSIONS

Increase in VEGF level leads to up-regulation of thrombin activity in asthmatic airways, and this elevated thrombin activity induces elevation of bFGF level. It will become to be a new strategy of asthma therapy to attenuate thrombin activity for the regulation of airway remodeling.

Significance of endothelial dysfunction in the pathogenesis of early and delayed radiation enteropathy

This review summarizes the current state of knowledge regarding the role of endothelial dysfunction in the pathogenesis of early and delayed intestinal radiation toxicity and discusses various endothelial-oriented interventions aimed at reducing the risk of radiation enteropathy. Studies published in the biomedical literature during the past four decades and cited in PubMed, as well as clinical and laboratory data from our own research program are reviewed. The risk of injury to normal tissues limits the cancer cure rates that can be achieved with radiation therapy. During treatment of abdominal and pelvic tumors, the intestine is frequently a major dose-limiting factor. Microvascular injury is a prominent feature of both early (inflammatory), as well as delayed (fibroproliferative) radiation injuries in the intestine and in many other normal tissues. Evidence from our and other laboratories suggests that endothelial dysfunction, notably a deficiency of endothelial thrombomodulin, plays a key role in the pathogenesis of these radiation responses. Deficient levels of thrombomodulin cause loss of vascular thromboresistance, excessive activation of cellular thrombin receptors by thrombin, and insufficient activation of protein C, a plasma protein with anticoagulant, anti-inflammatory, and cytoprotective properties. These changes are presumed to be critically involved in many aspects of early intestinal radiation toxicity and may sustain the fibroproliferative processes that lead to delayed intestinal dysfunction, fibrosis, and clinical complications. In conclusion, injury of vascular endothelium is important in the pathogenesis of the intestinal radiation response. Endothelial-oriented interventions are appealing strategies to prevent or treat normal tissue toxicity associated with radiation treatment of cancer.

c-Src Mediates Thrombin-Induced NF-κB Activation and IL-8/CXCL8 Expression in Lung Epithelial Cells

In this study, we examined the regulation of NF-kappaB activation and IL-8/CXCL8 expression by thrombin in human lung epithelial cells (EC). Thrombin caused a concentration-dependent increase in IL-8/CXCL8 release in a human lung EC line (A549) and primary normal human bronchial EC. In A549 cells, thrombin, SFLLRN-NH2 (a protease-activated receptor 1 (PAR1) agonist peptide), and GYPGQV-NH2 (a PAR4 agonist peptide), but not TFRGAP-NH2 (a PAR3 agonist peptide), induced an increase in IL-8/CXCL8-luciferase (Luc) activity. The thrombin-induced IL-8/CXCL8 release was attenuated by D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone (a thrombin inhibitor), U73122 (a phosphoinositide-phospholipase C inhibitor), Ro-32-0432 (a protein kinsase C alpha (PKC alpha) inhibitor), an NF-kappaB inhibitor peptide, and Bay 117082 (an IkappaB phosphorylation inhibitor). Thrombin-induced increase in IL-8/CXCL8-Luc activity was inhibited by the dominant-negative mutant of c-Src and the cells transfected with the kappaB site mutation of the IL-8/CXCL8 construct. Thrombin caused time-dependent increases in phosphorylation of c-Src at tyrosine 416 and c-Src activity. Thrombin-elicited c-Src activity was inhibited by Ro-32-0432. Stimulation of cells with thrombin activated IkappaB kinase alphabeta (IKK alphabeta), IkappaB alpha phosphorylation, IkappaB alpha degradation, p50 and p65 translocation from the cytosol to the nucleus, NF-kappaB-specific DNA-protein complex formation, and kappaB-Luc activity. Pretreatment of A549 cells with Ro-32-4032 and the dominant-negative mutant of c-Src DN inhibited thrombin-induced IKK alphabeta activity, kappaB-Luc activity, and NF-kappaB-specific DNA-protein complex formation. Further studies revealed that thrombin induced PKC alpha, c-Src, and IKK alphabeta complex formation. These results show for the first time that thrombin, acting through PAR1 and PAR4, activates the phosphoinositide-phospholipase C/PKC alpha/c-Src/IKK alphabeta signaling pathway to induce NF-kappaB activation, which in turn induces IL-8/CXCL8 expression and release in human lung EC.

Thrombin and TNF-alpha/IL-1beta synergistically induce fibroblast-mediated collagen gel degradation

Degradation of preexisting and newly synthesized extracellular matrix is thought to play an important role in tissue remodeling. The current study evaluated whether thrombin and TNF-alpha/IL-1beta could collaboratively induce collagen degradation by human fetal lung fibroblasts (HFL-1) and adult bronchial fibroblasts cultured in three-dimensional collagen gels. TNF-alpha/IL-1beta alone induced production of matrix metalloproteinases (MMPs)-1, -3, and -9, which were released in latent form. With the addition of thrombin, the latent MMPs were converted into active forms and this resulted in collagen gel degradation. Part of the activation of MMPs by thrombin resulted from direct activation of MMP-1, MMP-2, MMP-3, and MMP-9 in the absence of cells. In addition, tissue inhibitor of metalloproteinase-1 production was inhibited by the combination of thrombin and TNF-alpha/IL-1beta. These results suggest that thrombin and TNF-alpha/IL-1beta synergize to induce degradation of three-dimensional collagen gels through increasing the production and activation of MMPs, and that this effect is mediated through both direct activation of MMPs by thrombin and indirectly by thrombin activation of fibroblasts. Through such mechanisms, thrombin could contribute to many chronic lung disorders characterized by tissue remodeling.

Thrombin mediated migration of osteogenic cells

Given that thrombin is ubiquitously expressed at sites of vascular injury, and that osteogenic cells express receptors for thrombin, we questioned whether thrombin could attract osteogenic cells to a bony wound. Using a scratch wound assay, thrombin stimulated a significant increase in migration of osteogenic cultures of primary marrow cells. This effect was dependent on thrombin proteolytic activity; however, thrombin was unable to stimulate the migration of a more differentiated marrow-derived osteogenic cell line. To better understand the role of thrombin in osteoprogenitor migration, we developed an osteoprogenitor migration assay that combines a modified Boyden chamber with a bone nodule assay. Primary cells that migrated through the transwell filter in the presence of thrombin formed significantly more bone nodules compared to the condition without thrombin. This was not due to proliferation or differentiation effects of thrombin. In contrast, thrombin was unable to stimulate an increase in the number of nodules for the more differentiated osteogenic cell line. Thus, our results suggest that thrombin exhibits differential motogenic effects on osteogenic cells depending on their differentiation state. The cell migration/bone nodule assay described here is the first assay that can be specifically used to examine the effects of factors on the migration of osteoprogenitor cells, particularly those derived from primary populations.

Thrombin and Its Protease-Activated Receptor-1 (PAR1) Participate in the Endothelial–Mesenchymal Transdifferentiation Process

The serine protease thrombin, independently of its participation in hemostasis and thrombosis, has been involved in tissue repair and remodeling, embryogenesis, angiogenesis, and development and progression of atherosclerosis. Many of these functions appear to be mediated by specific thrombin receptors, particularly the protease-activated receptor-1 (PAR1). In this study, we investigated whether both thrombin and PAR1 were present in the aortic wall of chicken embryos at days 11 and 12 of development. We found that PAR1 was limited to some cells of the intimal thickening and the inner media, whereas thrombin appeared distributed across the aortic wall. We also investigated whether PAR1 was present during endothelial-mesenchymal transdifferentiation (EMT) in vitro. A moderate immunoreactivity was detected in the monolayer of endothelial cells. In contrast, a strong cytoplasmic immunoreactivity was observed in the detaching and migrating cells and those that had acquired mesenchymal characteristics. This PAR1 expression was confirmed by flow cytometry. In this study, the addition of thrombin to arrested endothelial cell cultures was assessed. We found that thrombin stimulated endothelial cell spreading and migration, as no migrating cells were observed in serum-free medium (SFM) condition. Immunolocalization of PAR1 in the thrombin-treated cultures showed strong cytoplasmic immunoreactivity in the monolayers and in spreading and migrating cells, whereas in the SFM condition undetectable PAR1 immunoreactivity was observed. Flow cytometry of these cultures revealed an elevated expression of PAR1 in the presence of thrombin, in contrast to that detected in SFM and complete medium. These data indicate that both thrombin and PAR1 are involved in the remodeling of the aortic wall and intimal thickening formation, and in the endothelial-mesenchymal transdifferentiation process.

Increased Thrombin Activity after Allergen Challenge

In addition to its central role in hemostasis, thrombin may play a role in inflammation and remodeling. To investigate the contribution of thrombin to allergic airway inflammation in asthma, we used an enzymatic assay to determine thrombin activity in bronchoalveolar lavage fluid obtained from 19 subjects with atopic asthma before (Day 0) and 48 hours after (Day 2) segmental bronchoprovocation with antigen. Thrombin activity increased from 0 (0, 2.9) on Day 1 to 41.1 (0.3, 75.6) U x 10(-3)/ml on Day 2 (p = 0.002) and correlated with total protein levels in lavage fluid on Day 2 (r = 0.885, p < 0.001). After antigen challenge, thrombin activity also showed significant correlations with interleukin-5 (r = 0.66, p = 0.002), transforming growth factor beta1 (r = 0.70, p < 0.001), fibronectin (r = 0.85, p < 0.001) and tissue factor (r = 0.55, p = 0.03) levels in lavage fluid. Furthermore, Day 2, but not Day 0 lavage fluid, induced proliferation of human airway fibroblasts. This mitogenic effect was significantly reduced with hirudin, a specific thrombin inhibitor. Taken together, our findings suggest that allergen-driven airway inflammation in asthma is associated with enhanced potential for fibroblast proliferation that is related, at least in part, to increased thrombin activity. We propose that enhanced thrombin activity provides a potential link between allergic inflammation and initiation of airway remodeling.

Factor Xa induces mitogenesis of vascular smooth muscle cells via autocrine production of epiregulin

Factor Xa has been reported to elicit smooth muscle cell proliferation via autocrine release of platelet-derived growth factor. However, this study has shown that factor Xa-induced mitogenesis of rat aortic smooth muscle cell is independent of platelet-derived growth factor. We also could not observe any platelet-derived growth factor isoforms in the cultured medium of factor Xa-stimulated cells. Our finding that the cultured medium of factor Xa-stimulated cells strongly induces rat aortic smooth muscle cell mitogenesis in the absence of factor Xa activity led us to explore the existence of a novel autocrine pathway. The autocrine growth factor was purified from the cultured medium and was identified to be epiregulin. Recombinant epiregulin was also able to induce the mitogenesis. The secretion of epiregulin from factor Xa-stimulated rat aortic smooth muscle cell required mRNA expression and protein synthesis of the growth factor. The mitogenic effect of factor Xa on rat aortic smooth muscle cell was significantly reduced by anti-epiregulin antibody or by antisense oligodeoxynucleotide to epiregulin. Several lines of experimental evidence clearly indicate that the autocrine production of epiregulin, an epidermal growth factor-related ligand, is induced in the factor Xa-stimulated mitogenic process of rat aortic smooth muscle cell.

Role of thrombin in CNS damage associated with intracerebral haemorrhage: opportunity for pharmacological intervention?

Intracerebral haemorrhage (ICH) results in high mortality and morbidity. The most important causes of neurological deterioration after ICH are progression of oedema and injury to nerve cells and axons surrounding the haematoma, as well as haematoma enlargement. Recent studies have indicated that thrombin, formed upon clotting of the haematoma, plays an important role in these processes. As opposed to conventional therapeutic approaches, administration of a thrombin inhibitor could effectively limit oedema formation and neuronal damage, improving survival and functional outcome. A small, preliminary clinical trial has suggested that antithrombin therapy with intravenously administered argatroban may be useful in treatment of ICH. Randomised, controlled studies are needed to confirm these initial findings.

Impact of thrombophilic gene mutations on thrombosis risk in patients with gastrointestinal carcinoma

BACKGROUND

Patients with malignancies have an increased risk for thromboembolic events due to the release of tissue factor by the tumor, damage to the vessel wall, and immobilization. Moreover, tumors may improve their growth and metastatic spread by utilizing the coagulation system. To date, no information is available on the additional role of prothrombotic mutations in these patients.

METHODS

The prevalence of the factor V Leiden mutation (FVL) and the prothrombin G20210A mutation and of homozygosity for the methylenetetrahydrofolate reductase (MTHFR) C677T substitution has been analyzed in a cohort of 175 patients with gastrointestinal adenocarcinoma by the polymerase chain reaction-restriction fragment length polymorphism technique.

RESULTS

6.9% of the patients were heterozygous for FVL, 5.7% were heterozygous for the prothrombin mutation, and 9.7% were homozygous for the MTHFR C677T mutation was detected in 9.7% of patients. Compared with the normal population, we found an increased prevalence of the prothrombin G20210A substitution (5.7% vs. 0.8%, P = 0.028). Thromboses were absent in 147 patients (Group A), whereas 28 of the patients suffered from thromboses during the period following tumor diagnosis (Group B). In Group A, 6.8% of the patients and 21.4% of the patients in Group B had a thrombosis before the diagnosis of cancer (P = 0.025, odds ratio [OR] 3.7). Heterozygous FVL was present in 4.8% of the patients in Group A and in 17.9% of the patients in Group B (P = 0.026, OR 4.4). In patients with thromboses before the detection of the tumor, the risk was elevated 6.3-fold (25.0% vs 5.0%, P = 0.015). Heterozygosity for the prothrombin mutation and homozygosity for the MTHFR C677T substitution did not increase the incidence of thromboses.

CONCLUSIONS

We demonstrated a significant effect of FVL on thrombosis in patients with malignant disease. Most thromboses occurred during the first months after tumor diagnosis, implicating diagnostic and therapeutic procedures as important nongenetic risk factors for venous thromboembolism. Our data also indicate that the prothrombin G20210A mutation may be a possible cofactor in cancer pathogenesis.

Thrombin upregulates tissue transglutaminase in endothelial cells: a potential role for tissue transglutaminase in stability of atherosclerotic plaque

Atherosclerosis is characterized by thickening of the vessel wall, smooth muscle cell proliferation, macrophage infiltration, and deposition of a fibrin network. Transglutaminases are a family of enzymes catalyzing the formation of stable covalent cross-links between proteins. Here, we show that tissue transglutaminase (tTG) synthesis by human umbilical vein endothelial cells is upregulated by thrombin, the serine protease that causes fibrin formation and many cellular inflammatory effects. Thrombin upregulated tTG 2-fold at the mRNA and protein level. Cellular cross-linking activity was increased to an even greater extent; antibody to tTG neutralized the increased activity. The effect on tTG expression required active thrombin and was mediated mainly through protease-activated receptor-1, a thrombin receptor. Increased tTG antigen and activity were evident in human umbilical vein endothelial cells and extracellular matrix in situ. Thrombin treatment also led to a cellular redistribution of tTG. Normal vessel wall stained positively for tTG in the smooth muscle cells and in the subendothelium. The intensity of staining increased in vessel walls with plaque, where there was a striking increase in tTG in the smooth muscle cells immediately below the plaque. These studies indicate a role for tTG in the stabilization of atherosclerotic plaques and suggest that its local expression can be controlled by thrombin.

Hypopyon uveitis

Hypopyon uveitis has inflammatory, infective, and neoplastic causes and a high association with systemic disease. Careful questioning of the patient and detailed examination of the eye for other signs is necessary to guide the differential diagnosis and relevant investigations. Because the underlying causes require very different types of investigation and, if missed, can have serious sequelae for the patient, a rational approach based on the understanding of the causes of hypopyon uveitis is imperative. In this review, hypopyon uveitis is considered in the context of the associated ocular and systemic diseases that cause it.

Depletion of protein kinase Cepsilon in normal and scleroderma lung fibroblasts has opposite effects on tenascin expression

OBJECTIVE

To determine whether the extracellular matrix protein tenascin-C (TN-C) is overexpressed in lung fibroblasts from systemic sclerosis (SSc) patients, the molecular mechanisms regulating TN-C secretion in SSc and normal lung fibroblasts, and how these processes might contribute to lung fibrosis in SSc patients.

METHODS

TN-C secretion by SSc and normal fibroblasts was compared in vivo (in bronchoalveolar lavage [BAL] fluid) and in vitro (in culture medium). The ability of thrombin to induce TN-C was confirmed at both the protein and the messenger RNA (mRNA) level. The role of protein kinase Cepsilon (PKCepsilon) in the expression of TN-C was evaluated by determining the effects of thrombin on PKCepsilon levels and by directly manipulating PKCepsilon levels via the use of antisense oligonucleotides.

RESULTS

BAL fluid from SSc patients contained high levels of TN-C, whereas that from normal subjects contained little or no TN-C. In vitro, SSc lung fibroblasts expressed much higher amounts of TN-C than did normal lung fibroblasts. Consistent with the idea that thrombin is a physiologic inducer of TN-C, thrombin stimulated TN-C mRNA and protein expression in both SSc and normal lung fibroblasts by a mechanism that required proteolytic cleavage of the thrombin receptor. Surprisingly, thrombin treatment and antisense oligonucleotide-mediated depletion of PKCepsilon indicated that TN-C expression is regulated via opposite signaling mechanisms in SSc and normal cells. In SSc lung fibroblasts, thrombin decreased PKCepsilon levels, and the decreased PKCepsilon induced TN-C secretion; in normal fibroblasts, thrombin increased PKCepsilon levels, and the increased PKCepsilon induced TN-C secretion. Normal and SSc lung fibroblasts also differed in the subcellular localization of PKCepsilon, both before and after thrombin treatment.

CONCLUSION

These studies are the first to demonstrate that thrombin is a potent simulator of TN-C in lung fibroblasts and that PKCepsilon is a critical regulator of TN-C protein levels in these cells. Furthermore, our results indicate that both the regulation of PKCepsilon levels by thrombin and the regulation of TN-C levels by PKCepsilon are defective in SSc lung fibroblasts.

Intratracheal administration of activated protein C inhibits bleomycin-induced lung fibrosis in the mouse

It is well recognized that activation of the coagulation system plays an important role in bleomycin (BLM)-induced lung injury and fibrosis. The protein C (PC) pathway is an important regulator of the coagulation system. In this study, we evaluated the bronchoalveolar lavage fluid (BALF) concentration of activated PC (APC) and the therapeutic effect of the intratracheal administration of APC on BLM-induced lung fibrosis in mice. APC levels in BALF were significantly lower in BLM-treated animals than in the saline-treated group. Fibrotic changes were progressive in mice treated with BLM and intratracheal instillation of vehicle (BLM/Veh) after 14 and 21 d of BLM infusion. Compared with the BLM/Veh group, histologic findings on Days 14 and 21 in mice treated with BLM and intratracheal instillation of APC (BLM/APC) showed less fibrotic lesions in the subpleural and central areas of the lung. The mean Aschcroft's fibrosis score in the BLM/Veh group was significantly (p < 0.05) higher than in the BLM/APC group. The lung hydroxyproline content on Day 21 was significantly higher (p < 0.05) in the BLM/Veh group (1.78 +/- 0.07 micromol/lung weight) than in the BLM/APC (1.30 +/- 0.06 micromol/lung weight) group. The ratio of plasminogen activator activity to thrombin level in BALF was significantly increased in the BLM/APC group compared with the BLM/ Veh group on Day 21. The expression of tumor necrosis factor-alpha and interleukin-1beta was significantly decreased in the lungs of the BLM/APC group compared with the BLM/Veh group on Day 14 after BLM infusion. These results showed that intratracheal APC administration inhibits the development of lung fibrosis in BLM-induced lung injury, giving further support to the important role that the PC pathway plays in the mechanism of lung fibrosis.

Effects of hypothermia on thrombin-induced brain edema formation

Recent studies have shown that thrombin plays an important role in brain edema formation after intracerebral hemorrhage (ICH). The possible mechanisms of thrombin-induced brain edema formation include blood-brain barrier (BBB) disruption and inflammatory response involving polymorphonuclear (PMN) leukocyte. Animal experiments have revealed that moderate therapeutic hypothermia improves pathological and functional outcome in various models of brain injury. In this study, we examined the effect of hypothermia on thrombin-induced brain edema formation. Effects of hypothermia on BBB permeability and the accumulation of PMN leukocytes were also determined to clarify the protective mechanism of hypothermia in this model. Anesthetized adult rats received an injection of 10 Units of thrombin into the basal ganglia. Animals were separated into the normothermic and hypothermic groups, which were housed in a room maintained at 25 degrees C and in a cold room maintained at 5 degrees C, respectively, for 24 h after the thrombin injection. The brain temperature in rats housed in a cold room reduced temporarily to approximately 30 degrees C and then gradually recovered to 35 degrees C by the end of the observation. Brain water content in the basal ganglia was significantly reduced in rats treated with hypothermia compared to the normothermic rats (84.3+/-0.2 vs. 82.4+/-0.1%; P<0.01). The decrease of brain water content was accompanied with a significant reduction in BBB permeability to Evan's blue dye and in accumulation of PMN leukocytes. This study indicates that hypothermic treatment significantly reduces thrombin-induced brain edema formation in the rat. Inhibition of thrombin-induced BBB breakdown and inflammatory response by hypothermia appear to contribute to brain protection in this model. Hypothermic treatment may provide an approach to potentially reduce ongoing edema after ICH.

Thrombin inhibits apoptosis of monocytes and plasminogen activator inhibitor 2 (PAI-2) is not responsible for this inhibition

Plasminogen activator inhibitor 2 (PAI-2) has been shown to inhibit apoptosis in transfected cells. We have investigated this phenomenon in activated human monocytes, which are a physiological source of intracellular PAI-2. Apoptosis of monocytes was rapidly induced by removal of serum, addition of hydrogen peroxide, or binding of a monoclonal antibody to Fas. Treatment of monocytes with thrombin or lipopolysaccharide (LPS) inhibited apoptosis of monocytes and also up-regulated intracellular PAI-2. Increased apoptosis was accompanied with increased activity of caspases 3 and 8. Thrombin or LPS treatment of monocytes decreased the activity of both caspases, which correlated with protection from apoptosis. The role for PAI-2 in protection of monocytes from apoptosis was studied. Monocytes were transfected with antisense oligonucleotides that blocked PAI-2 antigen, and antisense for PAI-2 had no effect on apoptosis of monocytes. No interaction was evident between PAI-2 and recombinant caspases 3 and 8 in vitro. PAI-2 was not a substrate for caspases during apoptosis of monocytes, although some cleavage of recombinant PAI-2 by caspase 3 was evident in vitro. This study shows that thrombin or LPS protected monocytes from apoptosis and that PAI-2 did not mediate this inhibitory effect.

Thrombin stimulates the expression of PDGF in lung epithelial cells

Several growth factors, including platelet-derived growth factor (PDGF), have been implicated in the mechanism of lung and airway remodeling. In the present study, we evaluated whether thrombin may promote lung and airway remodeling by increasing PDGF production from lung and airway epithelial cells. Conditioned medium (CM) was prepared by treating epithelial cells with increasing concentrations of thrombin; before use in the assays, CM was treated with hirudin until complete inhibition of thrombin activity. CM from epithelial cells stimulated the proliferation of lung fibroblasts and bronchial smooth muscle cells. Anti-PDGF antibody significantly inhibited this CM proliferative activity, implicating PDGF in this effect. Enzyme immunoassay and RT-PCR demonstrated that thrombin induced the secretion and expression of PDGF from bronchial and alveolar epithelial cells. RT-PCR showed that epithelial cells express the thrombin receptors protease-activated receptor (PAR)-1, PAR-3, and PAR-4. The PAR-1 agonist peptide was also found to induce PDGF secretion from epithelial cells, suggesting that the cellular effect of thrombin occurs via a PAR-1-mediated mechanism. Overall, this study showed for the first time that thrombin may play an important role in the process of lung and airway remodeling by stimulating the expression of PDGF via its cellular receptor, PAR-1.

Review article: proteinase-activated receptors - novel signals for gastrointestinal pathophysiology

Proteinase-activated receptors (PARs) have the common property of being activated by the proteolytic cleavage of their extracellular N-terminal domain. The new NH2-terminus acts as a 'tethered ligand' binding and activating the receptor itself. Four members of this family have been cloned, three of which are activated by thrombin (PAR-1, PAR-3 and PAR-4) while the fourth (PAR-2) is activated by trypsin or mast cell tryptase. In physiological or pathophysiological conditions, the gastrointestinal tract is exposed more than other tissues to proteinases (digestive enzymes, proteinases from pathogens or proteinases from inflammatory cells) that can activate PARs. Since PARs are highly expressed throughout the gastrointestinal tract, the study of the role of PARs in these tissues appears to be particularly important. It has already been shown that PAR-2 activation induces calcium mobilization and eicosanoid production in enterocytes as well as changes in ion transport in jejunal tissue segments. PAR-2 activation also causes calcium mobilization and stimulates amylase release from pancreatic acini. Moreover, both PAR-1 and PAR-2 activation can alter the gastrointestinal motility. In inflammatory or allergic conditions, the proteinases that constitute the major agonists for PARs (thrombin, trypsin and mast cell tryptase) are usually released. The activation of PARs by these proteinases might contribute to the gastrointestinal disorders associated with these pathologies. A complete understanding of the role of PARs in the gastrointestinal tract will require the development of selective receptor antagonists that are not yet available. Nonetheless, the use of PAR agonists has already highlighted new potential functions for proteinases in the gastrointestinal tract, thus the control of PAR activation might represent a promising therapeutic target.

Role of clot-associated (-derived) thrombin in cell proliferation induced by fibrin clots in vitro

Thrombin is a potent mitogenic agent. Clot-associated thrombin retains its amidolytic and pro-aggregant activity. We therefore studied the ability of fibrin clots to induce proliferation in CCL39 cells (Chinese hamster lung fibroblasts), in the absence and presence of the thrombin inhibitors PPACK, recombinant hirudin (rHV2 Lys47) and heparin:antithrombin III. Fibrin clots incubated for 48 h with CCL39 cells led to significant cell proliferation, which was dependent on the concentration of thrombin used to prepare the clots. Thus, clots prepared with 91 nmol l(-1) thrombin produced a similar proliferation (231+/-21%) to that obtained with 50 nmol l(-1) thrombin in solution (213+/-29%). Rabbit plasma clots led to a 499+/-41% increase in cell number under identical conditions. Fibrin clot-induced cell proliferation was inhibited by all three thrombin inhibitors with no difference in IC(50) values compared to those obtained against thrombin in solution, suggesting that cell proliferation be due to thrombin leaching from the clots. We found a time-dependent increase in thrombin release from the clots attaining a plateau at 24 h (approximately 61% of the total thrombin used in clot formation). Clots separated from the cells using porous cell culture chamber inserts led to similar proliferation to that of clots in contact with the cells. Thus fibrin-clot induced CCL39 proliferation is due to thrombin released from the clots.

Thrombin upregulates interleukin-8 in lung fibroblasts via cleavage of proteolytically activated receptor-I and protein kinase C-gamma activation

Acute and chronic interstitial lung diseases are accompanied by evidence of inflammation and vascular injury. Thrombin activity in bronchoalveolar lavage fluid from such conditions is often increased, as well as interleukin (IL)-8. We observed that conditioned medium from lung fibroblasts exposed to thrombin has chemotactic activity for polymorphonuclear cells, and that this activity can be abolished by antibody to IL-8. We report that thrombin stimulates expression of IL-8 in human lung fibroblasts on both the messenger RNA and protein levels in a time- and dose-dependent manner. Stimulation of IL-8 expression by thrombin is inhibited by specific thrombin inhibitors. Synthetic thrombin receptor agonist peptide-14 mimics thrombin's stimulation of IL-8 expression in a dose-dependent manner consistent with the idea that upregulation of IL-8 by thrombin in human lung fibroblasts requires cleavage of proteolytically activated receptor-I. We demonstrate further that thrombin-induced IL-8 synthesis is regulated by protein kinase (PK) C. PKC-gamma may be involved in the upregulation of lung fibroblast IL-8 by thrombin because stimulation of lung fibroblasts with thrombin caused significant upregulation of PKC-gamma and because PKC-gamma antisense oligonucleotides inhibited the accumulation of PKC-gamma protein and IL-8 protein. Our data suggest that the PKC-gamma isoform increase observed after thrombin stimulation is required for thrombin-induced IL-8 formation by human lung fibroblasts.

Evidence that thrombin present in lungs of patients with pulmonary metastasis may contribute to the development of the disease

Early cellular events in the lung which may lead to the development of pulmonary metastases (PM) are still poorly understood. Thrombin, a key component of the coagulation cascade, may be involved in the development of PM as it has been shown to be an enhancer of platelet-tumor interaction in vitro and metastasis in vivo, and because it has been found in high levels in lungs from patients with PM. In this study, we assessed the potential role of thrombin in promoting PM by inducing an enhancement of tumor cell adhesion to platelets and tumor cell chemoinvasion and proliferation. We used bronchoalveolar lavage fluid (BALF) from 20 patients with PM. Results were compared with those from healthy controls. We found an enhancement of adhesion of PM-BALF-treated tumor cells to untreated platelets. BALF from patients with PM significantly increased chemoinvasion and proliferation in three human tumor cell lines. These activities were attenuated significantly by a thrombin inhibitor: hirudin. These results indicate that the thrombin present in the lungs of patients with PM is, at least in part, responsible for their adhesive, invasive and mitogenic activity on three different tumor cell lines. They also suggest that thrombin may be involved in the development of PM.

Effects of alpha-thrombin on superoxide dismutase levels in human cerebral microvascular endothelial cells

BACKGROUND

Sequelae of traumatic brain injury include generation of oxygen-free radicals and fibrin deposition, which worsen the initial injury. Superoxide dismutases (SODs) scavenge and bind to the free-radical superoxide anion (O2-), potentially defending against oxidative stress. In the present study, we investigated the production of SOD within human cerebral microvascular endothelial (HCME) cells after exposure to alpha-thrombin, hypothesizing that manganese SOD (MnSOD) expression is increased. Our aims were to determine whether alterations in SOD are observed at the mRNA level, to examine whether a particular species is preferentially expressed, and to determine the requirement of the active site of alpha-thrombin.

METHODS

HCME cells were characterized and grown to confluence. Control cells and cells exposed to 10 nmol/L alpha-thrombin were harvested for mRNA isolation using reverse transcriptase-polymerase chain reaction. Quantitation of mRNA production determined the levels of copper-zinc SOD and MnSOD. Active site blocked alpha-thrombin was used as a negative control and determined the specificity of the response.

RESULTS

The cells in culture were identified as endothelial after fulfilling criteria, such as positive immunocytochemical staining for factor VIII/von Willebrand factor antigen and binding of Ulex europaeus agglutinin-1 lectin. Levels of MnSOD mRNA were elevated at all time points in response to alpha-thrombin, whereas the cytosolic form was undetectable. HCME cells that were exposed to active site-blocked alpha-thrombin produced mRNA levels of MnSOD that were increased above those of controls, but this increase was half that of mRNA levels of MnSOD produced by HCME cells that were exposed to alpha-thrombin.

CONCLUSION

Our study showed for the first time that alpha-thrombin partially modulates SOD in HCME cells, causing a preferential increase in MnSOD. Further investigation into secondary brain injury will provide insights into the role of alpha-thrombin in the mechanism of free radical-induced alterations, potentially improving the outcome of patients with head injury.

A model of in vivo human venous thrombosis that confirms changes in the release of specific soluble cell adhesion molecules in experimental venous thrombogenesis

PURPOSE

The mechanisms of venous thrombogenesis have been studied by using animal models and cells in culture. The results from these systems may not, however, be relevant to the human condition. The aim of this study was to develop a method by which thrombus could be safely produced in a human vein in vivo. The model that was developed was used as a means of studying the changes in soluble adhesion molecule expression in human venous thrombogenesis.

METHODS

An autologous thrombin extract was used to generate experimental thrombi in the disconnected portion of the long saphenous veins of 30 patients who were undergoing routine bilateral varicose vein surgery. The contralateral vein was perfused with thrombin extract diluent buffer to act as the control. The concentration of soluble P-, E- and L-selectin, intercellular adhesion molecule 1 (ICAM-1), and vascular cell adhesion molecule-1 were measured by means of specific enzyme-linked immunosorbent assays in samples of blood taken from veins in which thrombus had formed and in contralateral control veins.

RESULTS

Thrombosis invariably formed when at least 100 IU of thrombin activity was administered. Thrombus formation was independent of the time that the thrombin extract was allowed to remain within the emptied vessel. Thrombosis never developed in control vessels that were similarly treated with the buffer used to dilute the thrombin extract. Experimental thrombi were composed mainly of red cells, with layers of fibrin next to platelet and leukocyte packages. These findings are similar to those observed in samples of established human venous thrombi. There were small but significantly higher levels of the adhesion molecules, soluble P-selectin, and vascular cell adhesion molecule-1 in blood taken from veins in which experimental thrombi had formed, compared with controls (P =.015 and.007, respectively; Wilcoxon signed rank test). Serum levels of soluble L-selectin, E-selectin, and ICAM-1 were not affected by thrombosis.

CONCLUSION

This model is safe and reproducible. It produces thrombi with a morphology similar to that described for established human deep venous thrombi. The model may be appropriate for the study of the early changes that occur during human venous thrombogenesis and may also be of value in testing the efficacy of novel antithrombotic agents.

Thrombin induces production of growth factors from aortic smooth muscle cells

BACKGROUND

Myointimal hyperplasia is a common complication of arterial recontructive surgery. The serine protease thrombin has a major role in vessel wall healing and eventual myointimal hyperplasia formation. The aim of this study was to determine the effect of thrombin on the production of PDGF AA and bFGF by arterial smooth muscle cells.

MATERIALS AND METHODS

Bovine smooth muscle cells were stimulated with thrombin in a serum-free culture. The release of PDGF AA and bFGF was assessed by ELISA. The effect of thrombin on the proliferation of confluent monolayers of bovine smooth muscle cells was determined by tritiated thymidine uptake.

RESULTS

Smooth muscle cells stimulated with thrombin released more PDGF AA (P < 0.001) and bFGF (P < 0.001) than the control. Addition of anti-PDGF AA and anti-bFGF antibodies to the medium of smooth muscle cell cultures neutralized the mitogenic effect of thrombin (P < 0.001).

CONCLUSIONS

The findings of our study suggest that thrombin may lead to myointimal hyperplasia formation through induction of PDGF and bFGF production by smooth muscle cells.

Enhanced Adherence of Sickle Erythrocytes to Thrombin-Treated Endothelial Cells Involves Interendothelial Cell Gap Formation

The adherence of sickle erythrocytes to vascular endothelium has the capacity to initiate vasoocclusion. The known effects of thrombin on endothelial cell function and the increased activity of thrombin in sickle cell disease led us to examine the effect of thrombin on the adhesivity of cultured endothelial cells for sickle erythrocytes. In particular, we studied whether the effect of thrombin on interendothelial cell gap formation (ICGF) was involved in endothelial cell adhesivity for sickle erythrocytes. Those endothelial cell monolayers stimulated by thrombin to maximal levels of static sickle erythrocyte adherence also underwent striking cell contraction and enlargement of interendothelial cell gaps. Adhesivity also increased when gaps were induced with antilaminin antibodies or EDTA. Maximally adhesogenic thrombin conditions failed to increase adhesivity when gap formation was prevented by pretreatment of the monolayers with 8-bromo-cyclic adenosine monophosphate (bromo-cAMP) or glutaraldehyde, agents that respectively inhibit actin-myosin–dependent cell contraction or cross-link adjacent cells in the monolayer. The influence of these two agents on EDTA-enhanced adhesivity was linked to their ability to prevent gap formation. Glutaraldehyde prevented both increased adherence and gap formation; bromo-cAMP prevented neither. Interendothelial cell gap formation may contribute to vasoocclusion by facilitating sickle erythrocyte adherence.

© 1998 by The American Society of Hematology.

Enhanced Adherence of Sickle Erythrocytes to Thrombin-Treated Endothelial Cells Involves Interendothelial Cell Gap Formation

The adherence of sickle erythrocytes to vascular endothelium has the capacity to initiate vasoocclusion. The known effects of thrombin on endothelial cell function and the increased activity of thrombin in sickle cell disease led us to examine the effect of thrombin on the adhesivity of cultured endothelial cells for sickle erythrocytes. In particular, we studied whether the effect of thrombin on interendothelial cell gap formation (ICGF) was involved in endothelial cell adhesivity for sickle erythrocytes. Those endothelial cell monolayers stimulated by thrombin to maximal levels of static sickle erythrocyte adherence also underwent striking cell contraction and enlargement of interendothelial cell gaps. Adhesivity also increased when gaps were induced with antilaminin antibodies or EDTA. Maximally adhesogenic thrombin conditions failed to increase adhesivity when gap formation was prevented by pretreatment of the monolayers with 8-bromo-cyclic adenosine monophosphate (bromo-cAMP) or glutaraldehyde, agents that respectively inhibit actin-myosin–dependent cell contraction or cross-link adjacent cells in the monolayer. The influence of these two agents on EDTA-enhanced adhesivity was linked to their ability to prevent gap formation. Glutaraldehyde prevented both increased adherence and gap formation; bromo-cAMP prevented neither. Interendothelial cell gap formation may contribute to vasoocclusion by facilitating sickle erythrocyte adherence.

© 1998 by The American Society of Hematology.

Tissue inhibitors of metalloproteinases and metalloproteinases in atherosclerosis

The ability of the metalloproteinases to degrade extracellular matrix proteins is essential for the matrix remodelling that occurs during infiltration of inflammatory cells, intimal thickening, angiogenesis and plaque rupture which are a result of atherosclerosis. Increased metalloproteinase activity therefore requires stimulation of metalloproteinase expression by cytokines and growth factors, activation of metalloproteinases, and downregulation of tissue inhibitors of metalloproteinases. In addition, metalloproteinases may influence atherosclerosis by processing of proteins involved in inflammation and cell growth and death and the tissue inhibitors of metalloproteinases may also play a less inhibitory role by influencing cell growth and apoptosis.

Proteinase-activated receptors: novel mechanisms of signaling by serine proteases

Although serine proteases are usually considered to act principally as degradative enzymes, certain proteases are signaling molecules that specifically regulate cells by cleaving and triggering members of a new family of proteinase-activated receptors (PARs). There are three members of this family, PAR-1 and PAR-3, which are receptors for thrombin, and PAR-2, a receptor for trypsin and mast cell tryptase. Proteases cleave within the extracellular NH2-terminus of their receptors to expose a new NH2-terminus. Specific residues within this tethered ligand domain interact with extracellular domains of the cleaved receptor, resulting in activation. In common with many G protein-coupled receptors, PARs couple to multiple G proteins and thereby activate many parallel mechanisms of signal transduction. PARs are expressed in multiple tissues by a wide variety of cells, where they are involved in several pathophysiological processes, including growth and development, mitogenesis, and inflammation. Because the cleaved receptor is physically coupled to its agonist, efficient mechanisms exist to terminate signaling and prevent uncontrolled stimulation. These include cleavage of the tethered ligand, receptor phosphorylation and uncoupling from G proteins, and endocytosis and lysosomal degradation of activated receptors.

Protein C anticoagulant system in patients with interstitial lung disease

Excessive procoagulant activity in the alveolar space may play a relevant role in the pathogenesis of pulmonary fibrosis. Hypercoagulability results from the disruption of the balance between the procoagulant and anticoagulant factors. The aim of this study was to assess the levels of molecular markers of the anticoagulant protein C (PC) pathway in the bronchoalveolar lavage fluid (BALF) and plasma of 11 patients with idiopathic pulmonary fibrosis (IPF), 14 with sarcoidosis and 16 with collagen vascular disease (CVD)-associated interstitial lung disease (CVD-ILD). Six healthy nonsmoking volunteers served as control subjects. BALF concentrations of the marker of clotting activation, thrombin- antithrombin III complex (TAT), in patients with sarcoidosis and CVD-ILD were significantly greater than those in control subjects. PC levels in BALF were markedly higher in patients with IPF (610 +/- 150 ng/ml), sarcoidosis (680 +/- 170 ng/ml), and CVD-ILD (1,580 +/- 600 ng/ml) than in control subjects (230 +/- 140 ng/ml). BALF concentrations of activated PC-PC inhibitor (APC-PCI) complex were significantly decreased in IPF (0.46 +/- 0.16 ng/ml), sarcoidosis (0. 43 +/- 0.11 ng/ml), and CVD-ILD (0.50 +/- 0.15 ng/ml) patients as compared with control subjects (1.08 +/- 0.23 ng/ml). APC-PCI/PC ratios were significantly lower in patients with IPF (2.70 +/- 1.74 ng/microg), sarcoidosis (1.94 +/- 0.82 ng/microg), and CVD-ILD (1.89 +/- 0.68 ng/microg) than in control subjects (15.91 +/- 8.45 ng/microg). Plasma levels of APC- PCI and the APC-PCI/PC ratio were also significantly decreased in patients with CVD-ILD as compared with control subjects. Overall, these findings suggest that decreased PC activation with increased procoagulant activity occurs in patients with ILD.

The response of smooth muscle cells to alpha-thrombin depends on its arterial origin: comparison among different species

BACKGROUND

Thrombin plays a pivotal role in the pathogenesis of arterial thrombosis and exerts a wide spectrum of effects on the cells of vessel walls.

METHODS

In this paper we focus on the direct role of thrombin as a mitogen for smooth muscle cells (SMCs) derived from different vessels from the vascular tree (coronary artery, aorta, carotid artery and pulmonary artery) of different species (human and pig). All cell populations examined responded mitogenically to alpha-thrombin, however the extent of this response was dependent on both vascular origin and the species from which vessels were derived.

RESULTS

Thrombin (1-100 nmol L-1) induced DNA synthesis ranging from 1.5- to 4-fold baseline depending on cell type. Porcine coronary SMCs showed the highest response to thrombin (100 nmol L-1) in terms of protein and DNA synthesis (4.0 +/- 0.2-fold) and cell division (53.4 +/- 8.8%) among the tested cells. In these cells recombinant (r)-hirudin, a specific thrombin inhibitor, exhibited maximal effectiveness to block the mitogenic effect of thrombin. Human SMC response ([3H]-thymidine incorporation) to either sera or thrombin was lower than that of porcine cells. In contrast, c-fos mRNA levels induced by thrombin in human SMCs were higher than those induced in porcine cells. In human cells, thrombin elicited an overexpression of c-fos and a lower rate of [3H]-thymidine incorporation than in porcine cells. Insulin-like growth factor I but not insulin showed additive mitogenic effects with thrombin in human coronary SMCs. The response of these cells to thrombin from different sources was a function of thrombin specific activity.

CONCLUSION

These results suggest that the cell system chosen to check thrombin mitogenicity not only determines thrombin quantitative effects but also may affect the effectiveness of an inhibitor to block its biological activity.

Expression of thrombin receptors in human atherosclerotic coronary arteries leads to an exaggerated vasoconstrictory response in vitro

Alpha-thrombin can alter vascular tone by proteolytic cleavage of its cell-surface receptor, which exposes a tethered peptide sequence, Ser-Phe-Leu-Leu-Arg-Asn (SFLLRN) that activates the receptor. We investigated the effects of increasing severity of coronary atherosclerosis on SFLLRN-induced responses on 165 human coronary artery rings isolated fresh from 15 patients who underwent cardiac transplantation. In 40 coronary rings with minimal intimal proliferation, addition of 0.001-5 microM SFLLRN resulted in a dose- and endothelium-dependent relaxation reaching a maximum of -87.0 +/- 2.3% (mean +/- SEM) and median inhibitory concentration (IC50) of 0.1 microM. Increasing severity of atherosclerotic lesion, as determined by morphometric quantification of intimal thickening under light microscopy, resulted in graded decreases in both sensitivity and magnitude of the observed relaxation. The maximal relaxations in coronary arteries with mild and moderate intimal proliferation were -76.7 +/- 3.5% (mean +/- SEM of 41 rings) and -63.6 +/- 6.4% (mean +/- SEM of 22 rings), respectively. In the 21 coronary rings with severe intimal proliferation, no significant SFLLRN-induced relaxation was noted. Mechanical disruption of intimal endothelium abolished the SFLLRN-induced relaxation observed in the minimal to mild intimally thickened arteries, whereas in arteries with moderate and severe intimal thickening, a significant SFLLRN-induced contraction (19 +/- 10% and 43 +/- 7%, respectively) was observed. Similar endothelium-dependent relaxations in minimal atherosclerotic and endothelium-independent contraction in severe atherosclerotic coronary arteries were also observed with alpha-thrombin. These findings confirm a recent in situ hybridization and immunohistochemistry study reporting localization of cloned thrombin receptors only in endothelium of "normal appearing" human abdominal aortae and induced expression of thrombin receptors in intimal/medial regions of the atherosclerotic vessels and further demonstrate that similar expression of thrombin receptors in human atherosclerotic coronary arteries leads to an unmasking of a marked vasoconstrictory response.

Thrombin promotes activation of matrix metalloproteinase-2 produced by cultured vascular smooth muscle cells

Thrombin generated at sites of vascular injury not only participates in the coagulation cascade but can signal other events related to development and complication of atherosclerotic plaques. We investigated here a novel non-thrombotic action of thrombin: the possibility that this protease influences the expression or activation of matrix metalloproteinases (MMPs) produced by vascular smooth muscle cells (SMCs). Matrix-degrading proteinases likely contribute to several aspects of vascular lesion development. Vascular SMCs constitutively elaborate the zymogen form of gelatinase A (MMP-2), found in cell supernatants complexed with its inhibitor, the tissue inhibitor of metalloproteinases (TIMP)-2. When activated, MMP-2 digests collagens and elastin and may thus promote cell migration and vascular remodeling. Analysis of culture supernatants harvested from either human or rabbit vascular SMCs by gelatin zymography revealed that compared with supernatants of unstimulated SMCs, media conditioned by thrombin-stimulated cells contained increased amounts of proteolytically processed MMP-2, suggesting activation of this MMP. Further experiments tested whether thrombin directly activates MMP-2. In cell-free experiments, when added to medium harvested from unstimulated SMCs, alpha-thrombin increased in a dose- and time-dependent manner the amount of proteolytically processed MMP-2, as shown by zymography and by Western blotting with specific antibodies. Thrombin cleaved pro-MMP-2 within 4 hours, even when the gelatinase was bound with its inhibitor, TIMP-2. Thrombin treatment rendered culture media of unstimulated SMCs able to degrade collagen type IV, consistent with generation of active MMP-2. Addition of inhibitors of either thrombin or MMPs decreased this type IV collagenolytic activity, but thrombin in the absence of SMC-conditioned medium containing pro-MMP-2 exhibited only minimal collagenolysis. Our results suggest that at sites of vascular injury, thrombin may activate locally produced MMP-2 and thereby facilitate cell migration and proliferation. In the case of complicated atherosclerotic plaques, episodes of intraplaque hemorrhage or plaque disruption with thrombosis may promote plaque instability by increasing local matrix-degrading activity.

Specific involvement of glypican in thrombin adhesive properties

We have previously demonstrated that thrombin possesses an active yet cryptic Arg-Gly-Asp (RGD) site which upon exposure induces endothelial cell (EC) adhesion via alpha nu beta 3 integrin [Bar-Shavit et al. (1991): J Cell Biol 112:335]. This was achieved in the presence of cell surface-associated heparan sulfate proteoglycans (HSPG) and exceedingly low concentrations of plasmin [Bar-Shavit et al. (1993): J Cell Biol 123:1279]. A portion of the cell surface-associated HSPG (glypican) is anchored via a covalently linked glycosyl-phosphatidylinositol (PI) residue, which can be released by treatment with glycosyl-PI-specific phospholipase C (PI-PLC). We report here that exposure of either bovine aortic EC, smooth muscle cells (SMC), or wild-type CHO cells to PI-PLC released HSPG involved in the conversion of thrombin to an adhesive molecule. The adhesion-promoting activity of the released HSPG was abolished following treatment with heparinase but not chondroitinase ABC. Incubation of thrombin with heparan sulfate-deficient CHO cells or cells that were pretreated with PI-PLC failed to induce its conversion to an adhesive molecule, indicating that glypican was playing a major role in this conversion. Moreover, affinity-purified glypican, but not syndecan or fibroglycan, elicited efficient conversion of plasmin-treated thrombin into an adhesive molecule. Antibodies raised against the RGD site in thrombin failed to interact with native thrombin, prothrombin, or the RGD site in other adhesive proteins such as vitronectin, fibrinogen, or fibronectin. Anti-thrombin-RGD antibodies which blocked the adhesion-promoting activity of thrombin were also capable of recognizing thrombin that was first incubated with a suboptimal concentration of plasm in in the presence of PI-PLC-released HSPG. Heparin, heparan sulfate, and PI-PLC-released HSPG had no effect on other cellular properties of thrombin such as receptor binding and growth-promoting activity. Altogether we have demonstrated that the heparin binding domain in thrombin plays a specific role in promoting thrombin adhesive properties and that membrane-associated glypican is likely to be the major physiological inducer of this property.

The role of the coagulation cascade in brain edema formation after intracerebral hemorrhage

The coagulation cascade has a potential role in brain edema formation due to intracerebral hemorrhage. In this study blood and other solutions were injected stereotactically into the right basal ganglia in rats. Twenty-four hours following injection, brain water and ion contents were measured to determine the amount of brain edema. Intracerebral blood resulted in an increase in brain water content. The amount of brain edema surrounding the intracerebral hematoma was reduced by a thrombin inhibitor N alpha-(2-Naphthalenesulfonylglycyl)-4-amidino-DL-phenylalaninep iperidide, (alpha-NAPAP) infused into the hematoma after the clot had been allowed to solidify. The inhibitor did not alter the actual size of the clot mass. An artificial clot composed of fibrinogen, thrombin, and styrene microspheres also produced brain edema. A fibrin clot led to edema formation even in the absence of mass effect provided by the microspheres. The single component responsible for production of brain edema in all these models was thrombin. The edema was formed in response to a fibrinogen-independent pathway. These results indicate that the coagulation cascade is involved in brain edema that develops adjacent to an intracerebral hematoma.

Edema from intracerebral hemorrhage: the role of thrombin

The mechanism by which intracerebral hemorrhage leads to the formation of brain edema is unknown. This study assesses the components of blood to determine if any are toxic to surrounding brain. Various solutions were infused stereotactically into the right basal ganglia of rats. The animals were sacrificed 24 hours later; brain edema and ion contents were measured. Whole blood caused an increase in brain water content and ion changes consistent with brain edema. Concentrated blood cells, serum from clotted blood, and plasma from unclotted blood all failed to provoke edema formation when infused directly into the brain. On the other hand, activation of the coagulation cascade by adding prothrombinase to plasma did produce brain edema. The edema response to whole blood could be prevented by adding a specific thrombin inhibitor, hirudin, to the injected blood. This study indicates that thrombin plays an important role in edema formation from an intracerebral blood clot.

Intracerebral infusion of thrombin as a cause of brain edema

Purified thrombin from an exogenous source is a hemostatic agent commonly used in neurosurgical procedures. The toxicity of thrombin in the brain, however, has not been examined. This study was performed to assess the effect of thrombin on brain parenchyma, using the formation of brain edema as an indicator of injury. Ten microliters of test solution was infused stereotactically into the right basal ganglia of rats. The animals were sacrificed 24 hours later, and the extent of brain edema and ion content were measured. Concentrations of human thrombin as low as 1 U/microliter resulted in a significant increase in brain water content. Rats receiving 10 U/microliters had a mortality rate of 33% compared to no mortality in the groups receiving smaller doses. Thrombin-induced brain edema was inhibited by a specific and potent thrombin inhibitor, hirudin. A medical grade of bovine thrombin commonly used in surgery also caused brain edema when injected at a concentration of 2 U/microliters. Edema formation was prevented by another highly specific thrombin inhibitor, N alpha-(2-Naphthalenesulfonylglycyl)-4-DL-phenylalaninepiperidid e (alpha-NAPAP). Thrombin-induced brain edema was accompanied by increases in brain sodium and chloride contents and a decrease in brain potassium content. Changes in brain ions were inhibited by both hirudin and alpha-NAPAP, corresponding to the inhibition of brain water accumulation. This study shows that thrombin causes brain edema when infused into the brain at concentrations as low as 1 U/microliter, an amount within the range of concentrations used for topical hemostasis in neurosurgery.