Thrombin induces neoangiogenesis in the chick chorioallantoic membrane

Do coagulation or fibrinolysis reflect the disease condition in patients with soft tissue sarcoma?

BACKGROUND

Coagulation and fibrinolysis are distinct processes that are highly correlated. Cells control coagulation and fibrinolysis by expression of tissue factor and urokinase-type plasminogen activator receptor on their surface. Tumor cells express these proteins, adjust their microenvironment and induce tumor exacerbation. We hypothesized that the expression of plasma markers for coagulation and fibrinolysis in patients with soft tissue sarcomas (STSs) was dependent on the level of tumor malignancy. To elucidate which markers are predictive of recurrence, metastasis and prognosis, coagulation or fibrinolysis, we analyzed the correlation between plasma levels of thrombin-antithrombin III complex (TAT), soluble fibrin (SF), plasmin-α2 plasmin inhibitor complex (PIC), D-dimer (DD) and clinical parameters in patients with STSs.

METHODS

TAT, SF, PIC or DD were measured in pre-treatment blood samples from 64 patients with primary STSs and analyzed with clinicopathological parameters, and 5-year recurrence free survival (RFS), 5-year metastasis free survival (MFS) and 5-year overall survival (OS) were evaluated.

RESULTS

The metastasis group had significantly higher DD (p = 0.0394), PIC (p = 0.00532) and SF (p = 0.00249) concentrations than the group without metastasis. The group that died of disease showed significantly higher DD (p = 0.00105), PIC (p = 0.000542), SF (p = 0.000126) and TAT (p = 0.0373) than surviving patients. By dividing the patients into low and high groups, the group with high DD, PIC, SF and TAT showed significantly lower 5-year MFS and 5-year OS than the corresponding low group. Furthermore, in multivariate COX proportional hazard analysis of continuous variables for 5-year MFS, only PIC was found to be a significant factor (HR: 2.14).

CONCLUSION

Fibrinolysis was better than coagulation at reflecting the disease condition of patients with STS. Notably, PIC levels ≥ 1.1 can not only predict the risk of metastasis and poor prognosis, but also increasing PIC levels correspond to further increases in risks of metastasis and poor prognosis.

A new classification of cardio-oncology syndromes

Increasing evidence suggests a multifaceted relationship exists between cancer and cardiovascular disease (CVD). Here, we introduce a 5-tier classification system to categorize cardio-oncology syndromes (COS) that represent the aspects of the relationship between cancer and CVD. COS Type I is characterized by mechanisms whereby the abrupt onset or progression of cancer can lead to cardiovascular dysfunction. COS Type II includes the mechanisms by which cancer therapies can result in acute or chronic CVD. COS Type III is characterized by the pro-oncogenic environment created by the release of cardiokines and high oxidative stress in patients with cardiovascular dysfunction. COS Type IV is comprised of CVD therapies and diagnostic procedures which have been associated with promoting or unmasking cancer. COS Type V is characterized by factors causing systemic and genetic predisposition to both CVD and cancer. The development of this framework may allow for an increased facilitation of cancer care while optimizing cardiovascular health through focused treatment targeting the COS type.

Transcriptional Regulation of Thrombin-Induced Endothelial VEGF Induction and Proangiogenic Response

Thrombin, the ligand of the protease-activated receptor 1 (PAR1), is a well-known stimulator of proangiogenic responses in vascular endothelial cells (ECs), which are mediated through the induction of vascular endothelial growth factor (VEGF). However, the transcriptional events underlying this thrombin-induced VEGF induction and angiogenic response are less well understood at present. As reported here, we conducted detailed promotor activation and signal transduction pathway studies in human microvascular ECs, to decipher the transcription factors and the intracellular signaling events underlying the thrombin and PAR-1-induced endothelial VEGF induction. We found that c-FOS is a key transcription factor controlling thrombin-induced EC VEGF synthesis and angiogenesis. Upon the binding and internalization of its G-protein-coupled PAR-1 receptor, thrombin triggers ERK1/2 signaling and activation of the nuclear AP-1/c-FOS transcription factor complex, which then leads to VEGF transcription, extracellular secretion, and concomitant proangiogenic responses of ECs. In conclusion, exposure of human microvascular ECs to thrombin triggers signaling through the PAR-1–ERK1/2–AP-1/c-FOS axis to control VEGF gene transcription and VEGF-induced angiogenesis. These observations offer a greater understanding of endothelial responses to thromboinflammation, which may help to interpret the results of clinical trials tackling the conditions associated with endothelial injury and thrombosis.

Targeting hemostasis-related moieties for tumor treatment

Under normal conditions, the hemostatic system, that includes the involvement of the coagulation response and platelets, is anatomically and functionally inseparable from the vasculature. However, the hemostatic response always occurs in a wide range of tumors because of the high expression of coagulation initiator tissue factor (TF) in many tumor tissues, and due to the leakage of coagulation factors and platelets from the circulation system into the tumor interstitium through abnormal tumor vessels. Therefore, in addition to TF, these coagulation factors, platelets, the central moiety thrombin, the final product fibrin, and fibronectin, which is capable of stabilizing coagulation clots, are also abundant in tumors. These hemostasis-related moieties (HRMs), including TF, thrombin, fibrin, fibronectin, and platelets, are also closely associated with tumor progression, e.g., primary tumor growth and distal metastasis. The hemostatic response only occurs under pathological conditions, such as tumors, thrombosis, and atherosclerosis other than in normal tissues. The HRMs within tumors are also highly specific, establishing functional and therapeutic targets for tumor treatment. Therefore, strategies including active targeting to these moieties, modulation of HRMs deposited in the tumor microenvironment to improve tumor drug delivery, activation of prodrug by the coagulation complex formed during coagulation response, and direct inhibition of the tumor-promoting activity of HRMs could be designed for tumor therapy. In this review, we summarize various strategies that target HRMs for tumor treatment.

G Protein-Coupled Receptors at the Crossroad between Physiologic and Pathologic Angiogenesis: Old Paradigms and Emerging Concepts

G protein-coupled receptors (GPCRs) have been implicated in transmitting signals across the extra- and intra-cellular compartments, thus allowing environmental stimuli to elicit critical biological responses. As GPCRs can be activated by an extensive range of factors including hormones, neurotransmitters, phospholipids and other stimuli, their involvement in a plethora of physiological functions is not surprising. Aberrant GPCR signaling has been regarded as a major contributor to diverse pathologic conditions, such as inflammatory, cardiovascular and neoplastic diseases. In this regard, solid tumors have been demonstrated to activate an angiogenic program that relies on GPCR action to support cancer growth and metastatic dissemination. Therefore, the manipulation of aberrant GPCR signaling could represent a promising target in anticancer therapy. Here, we highlight the GPCR-mediated angiogenic function focusing on the molecular mechanisms and transduction effectors driving the patho-physiological vasculogenesis. Specifically, we describe evidence for the role of heptahelic receptors and associated G proteins in promoting angiogenic responses in pathologic conditions, especially tumor angiogenesis and progression. Likewise, we discuss opportunities to manipulate aberrant GPCR-mediated angiogenic signaling for therapeutic benefit using innovative GPCR-targeted and patient-tailored pharmacological strategies.

Associated Risk of Malignancy in Patients with Cardiovascular Disease: Evidence and Possible Mechanism

Cardiovascular disease and malignancy are leading causes of morbidity and mortality. Increased risk of malignancy was identified in patients with cardiovascular disease, including patients with heart failure, heart failure after myocardial infarction, patients undergoing cardiac intervention, and patients after a thrombotic event. Common risk factors and biological pathways can explain this association and are explored in this review. Further research is needed to establish the causes of malignancy in this population and direct possible intervention.

Proinflammatory signaling functions of thrombin in cancer

Thrombin-induced activation of protease-activated receptors (PARs) represents a link between inflammation and cancer. Proinflammatory signaling functions of thrombin are associated with several inflammatory diseases including neurodegenerative, cardiovascular, and of special interest in this review cancer. Thrombin-induced inflammatory responses up-regulates expression of cytokines, adhesion molecules, angiogenic factors, and matrix-degrading proteases that facilitate tumor cells proliferation, angiogenesis, invasion, and metastasis. This review summarizes the current knowledge about the mechanisms of thrombin-mediated proinflammatory responses in cancer pathology for a better understanding and hence a better management of this disease.

Tissue factor expressed by circulating cancer cell-derived microparticles drastically increases the incidence of deep vein thrombosis in mice

BACKGROUND

The risk of thrombotic complications such as deep vein thrombosis (DVT) during tumor development is well known. Tumors release into the circulation procoagulant microparticles (MPs) that can participate in thrombus formation following vessel injury. The importance of this MP tissue factor (TF) in the initiation of cancer-associated DVT remains uncertain.

OBJECTIVE

To investigate how pancreatic cancer MPs promote DVT in vivo.

METHODS

We combined a DVT mouse model in which thrombosis is induced by flow restriction in the inferior vena cava with one of subcutaneous pancreatic cancer in C57BL/6J mice. We infused high-TF and low-TF tumor MPs to determine the importance of TF in experimental cancer-associated DVT.

RESULTS

Both tumor-bearing mice and mice infused with tumor MPs subjected to 3 h of partial flow restriction developed an occlusive thrombus; fewer than one-third of the control mice did. We observed that MPs adhered to neutrophil extracellular traps (NETs), which are functionally important players during DVT, whereas neither P-selectin nor glycoprotein Ib were required for MP recruitment in DVT. The thrombotic phenotype induced by MP infusion was suppressed by hirudin, suggesting the importance of thrombin generation. TF carried by tumor MPs was essential to promote DVT, as mice infused with low-TF tumor MPs had less thrombosis than mice infused with high-TF tumor MPs.

CONCLUSIONS

TF expressed on tumor MPs contributes to the increased incidence of cancer-associated venous thrombosis in mice in vivo. These MPs may adhere to NETs formed at the site of thrombosis.

Endothelial Angiogenesis and Barrier Function in Response to Thrombin Require Ca2+ Influx through the Na+/Ca2+ Exchanger

Thrombin acts on the endothelium by activating protease-activated receptors (PARs). The endothelial thrombin-PAR system becomes deregulated during pathological conditions resulting in loss of barrier function and a pro-inflammatory and pro-angiogenic endothelial phenotype. We reported recently that the ion transporter Na(+)/Ca(2+) exchanger (NCX) operating in the Ca(2+)-influx (reverse) mode promoted ERK1/2 activation and angiogenesis in vascular endothelial growth factor-stimulated primary human vascular endothelial cells. Here, we investigated whether Ca(2+) influx through NCX was involved in ERK1/2 activation, angiogenesis, and endothelial barrier dysfunction in response to thrombin. Reverse-mode NCX inhibitors and RNAi-mediated NCX1 knockdown attenuated ERK1/2 phosphorylation in response to thrombin or an agonist of PAR-1, the main endothelial thrombin receptor. Conversely, promoting reverse-mode NCX by suppressing Na(+)-K(+)-ATPase activity enhanced ERK1/2 activation. Reverse-mode NCX inhibitors and NCX1 siRNA suppressed thrombin-induced primary human vascular endothelial cell angiogenesis, quantified as proliferation and tubular differentiation. Reverse-mode NCX inhibitors or NCX1 knockdown preserved barrier integrity upon thrombin stimulation in vitro. Moreover, the reverse-mode NCX inhibitor SEA0400 suppressed Evans' blue albumin extravasation to the lung and kidneys and attenuated edema formation and ERK1/2 activation in the lungs of mice challenged with a peptide activator of PAR-1. Mechanistically, thrombin-induced ERK1/2 activation required NADPH oxidase 2-mediated reactive oxygen species (ROS) production, and reverse-mode NCX inhibitors and NCX1 siRNA suppressed thrombin-induced ROS production. We propose that reverse-mode NCX is a novel mechanism contributing to thrombin-induced angiogenesis and hyperpermeability by mediating ERK1/2 activation in a ROS-dependent manner. Targeting reverse-mode NCX could be beneficial in pathological conditions involving unregulated thrombin signaling.

Recombinant hirudin suppresses the viability, adhesion, migration and invasion of Hep-2 human laryngeal cancer cells

Recombinant hirudin (rH) is a highly potent and specific inhibitor of thrombin, and has been shown to inhibit the growth and metastasis of several types of cancers in experimental tumor models. The objective of this study was to evaluate the antitumor effects and explore the underlying mechanisms of rH in Hep-2 human laryngeal carcinoma (LC) cells. Hep-2 cells were treated with various concentrations of rH for 24 h. The cell viability was evaluated by a water-soluble tetrazolium salt (WST) assay. The adhesion ability of the cells was evaluated by cell adhesion to fibronectin. Cell migration and invasion were measured with the Boyden chamber assay. Cell apoptosis was detected by Hoechst 33324 fluorescence staining. A chicken chorioallantoic membrane (CAM) assay was used to assess the effects of rH on angiogenesis in vivo. Western blotting was used to detect the expression levels of vascular endothelial growth factor receptor (VEGF-R), focal adhesion kinase (FAK), Bcl-2-associated agonist of cell death (Bad) and B-cell CLL/lymphoma 2 (Bcl-2) proteins. rH significantly inhibited the cell viability and induced apoptosis in LC Hep-2 cells in a dose-dependent manner, as compared with phosphate-buffered saline (PBS) as control. These results were accompanied by a decrease in the anti-apoptotic protein Bcl-2 and an increase in the pro-apoptotic protein Bad. Moreover, rH dose-dependently inhibited the adhesion, migration and invasion of the Hep-2 cells, compared to the vehicle PBS. In addition, rH robustly suppressed angiogenesis in the CAM assay. Importantly, the expression of adhesion and angiogenesis-associated proteins FAK and VEGF-R was significantly downregulated by rH in a dose-dependent manner. The present findings demonstrate that rH exerts antitumor effects in Hep-2 human laryngeal cancer cells via multiple mechanisms and suggests that targeting thrombin by rH is a potential strategy for the treatment of LC.

Biochemistry and biology: heart-to-heart to investigate cardiac progenitor cells

BACKGROUND

Cardiac regenerative medicine is a rapidly evolving field, with promising future developments for effective personalized treatments. Several stem/progenitor cells are candidates for cardiac cell therapy, and emerging evidence suggests how multiple metabolic and biochemical pathways strictly regulate their fate and renewal.

SCOPE OF REVIEW

In this review, we will explore a selection of areas of common interest for biology and biochemistry concerning stem/progenitor cells, and in particular cardiac progenitor cells. Numerous regulatory mechanisms have been identified that link stem cell signaling and functions to the modulation of metabolic pathways, and vice versa. Pharmacological treatments and culture requirements may be exploited to modulate stem cell pluripotency and self-renewal, possibly boosting their regenerative potential for cell therapy.

MAJOR CONCLUSIONS

Mitochondria and their many related metabolites and messengers, such as oxygen, ROS, calcium and glucose, have a crucial role in regulating stem cell fate and the balance of their functions, together with many metabolic enzymes. Furthermore, protein biochemistry and proteomics can provide precious clues on the definition of different progenitor cell populations, their physiology and their autocrine/paracrine regulatory/signaling networks.

GENERAL SIGNIFICANCE

Interdisciplinary approaches between biology and biochemistry can provide productive insights on stem/progenitor cells, allowing the development of novel strategies and protocols for effective cardiac cell therapy clinical translation. This article is part of a Special Issue entitled Biochemistry of Stem Cells.

Tissue factor, blood coagulation, and beyond: an overview

Emerging evidence shows a broad spectrum of biological functions of tissue factor (TF). TF classical role in initiating the extrinsic blood coagulation and its direct thrombotic action in close relation to cardiovascular risks have long been established. TF overexpression/hypercoagulability often observed in many clinical conditions certainly expands its role in proinflammation, diabetes, obesity, cardiovascular diseases, angiogenesis, tumor metastasis, wound repairs, embryonic development, cell adhesion/migration, innate immunity, infection, pregnancy loss, and many others. This paper broadly covers seminal observations to discuss TF pathogenic roles in relation to diverse disease development or manifestation. Biochemically, extracellular TF signaling interfaced through protease-activated receptors (PARs) elicits cellular activation and inflammatory responses. TF diverse biological roles are associated with either coagulation-dependent or noncoagulation-mediated actions. Apparently, TF hypercoagulability refuels a coagulation-inflammation-thrombosis circuit in “autocrine” or “paracrine” fashions, which triggers a wide spectrum of pathophysiology. Accordingly, TF suppression, anticoagulation, PAR blockade, or general anti-inflammation offers an array of therapeutical benefits for easing diverse pathological conditions.

The development of inflammatory joint disease is attenuated in mice expressing the anticoagulant prothrombin mutant W215A/E217A

Thrombin is a positive mediator of thrombus formation through the proteolytic activation of protease-activated receptors (PARs), fibrinogen, factor XI (fXI), and other substrates, and a negative regulator through activation of protein C, a natural anticoagulant with anti-inflammatory/cytoprotective properties. Protease-engineering studies have established that 2 active-site substitutions, W215A and E217A (fII(WE)), result in dramatically reduced catalytic efficiency with procoagulant substrates while largely preserving thrombomodulin (TM)-dependent protein C activation. To explore the hypothesis that a prothrombin variant favoring antithrombotic pathways would be compatible with development but limit inflammatory processes in vivo, we generated mice carrying the fII(WE) mutations within the endogenous prothrombin gene. Unlike fII-null embryos, fII(WE/WE) mice uniformly developed to term. Nevertheless, these mice ultimately succumbed to spontaneous bleeding events shortly after birth. Heterozygous fII(WT/WE) mice were viable and fertile despite a shift toward an antithrombotic phenotype exemplified by prolonged tail-bleeding times and times-to-occlusion after FeCl₃ vessel injury. More interestingly, prothrombin(WE) expression significantly ameliorated the development of inflammatory joint disease in mice challenged with collagen-induced arthritis (CIA). The administration of active recombinant thrombin(WE) also suppressed the development of CIA in wild-type mice. These studies provide a proof-of-principle that pro/thrombin variants engineered with altered substrate specificity may offer therapeutic opportunities for limiting inflammatory disease processes.

Identification of a metalloprotease-chemokine signaling system in the ovarian cancer microenvironment: implications for antiangiogenic therapy

Ovarian cancer is a lethal gynecologic malignancy that may benefit from new therapies that block key paracrine pathways involved in tumor-stromal interactions and tumor vascularity. It was recently shown that matrix metalloprotease-1 (MMP1) activation of the G protein-coupled receptor protease-activated receptor-1 (PAR1) is an important stimulator of angiogenesis and metastasis in peritoneal mouse models of ovarian cancer. In the present study, we tested the hypothesis that MMP1-PAR1 promotes angiogenesis through its paracrine control of angiogenic chemokine receptors. We found that MMP1-PAR1 activation induces the secretion of several angiogenic factors from ovarian carcinoma cells, most prominently interleukin (IL)-8, growth-regulated oncogene-alpha (GRO-alpha), and monocyte chemoattractant protein-1. The secreted IL-8 and GRO-alpha acts on endothelial CXCR1/2 receptors in a paracrine manner to cause robust endothelial cell proliferation, tube formation, and migration. A cell-penetrating pepducin, X1/2pal-i3, which targets the conserved third intracellular loop of both CXCR1 and CXCR2 receptors, significantly inhibited endothelial cell proliferation, tube formation, angiogenesis, and ovarian tumor growth in mice. Matrigel plugs mixed with MMP1-stimulated, OVCAR-4-conditioned media showed a dramatic 33-fold increase in blood vessel formation in mice. The X1/2pal-i3 pepducin completely inhibited MMP1-dependent angiogenesis compared with a negative control pepducin or vehicle. Conversely, a vascular endothelial growth factor-directed antibody, Avastin, suppressed angiogenesis in mice but, as expected, was unable to inhibit IL-8 and GRO-alpha-dependent endothelial tube formation in vitro. These studies identify a critical MMP1-PAR1-CXCR1/2 paracrine pathway that might be therapeutically targeted for ovarian cancer treatment.

Protease-activated receptors, cyclo-oxygenases and pro-angiogenic signalling in endothelial cells

COX (cyclo-oxygenase)-2 and members of the PAR (protease-activated receptor) family (PARs 1–4) are highly overexpressed in a number of angiogenesis-dependent pathologies, including advanced atherosclerosis and cancer. An appreciation of the potential role(s) of PARs and COX enzymes in physiological angiogenesis is, however, currently lacking. Exposure of human endothelial cells to serine proteases (e.g. thrombin) or to PAR-selective agonist peptides leads to a wide range of cellular responses, including enhanced expression of COX-2, and we have shown that this induction depends on activation of classic pro-inflammatory signalling elements [e.g. MAPKs (mitogen-activated protein kinases) and NF-κB (nuclear factor κB)]. Our current studies suggest that COX-2-derived mediators are important autocrine regulators of PAR-stimulated angiogenesis. This mechanism could help us to explain how this novel family of receptors couple vascular inflammation with repair and angiogenesis in health and disease.

[Characterization of endothelial progenitor cells and putative strategies to improve their expansion]

Injection of endothelial progenitor cells (EPC) expanded ex vivo has been shown to increase neovascularization in preclinical models of ischemia and in adult patients, but the precise origin and identity of the cell population responsible for these clinical benefits are controversial. Given the potential usefulness of EPC as a cell therapy product, their thorough characterization is of major importance. This review describes the two cell populations currently called EPC and the means to find differential phenotypic markers. We have shown that BMP2/4 are specific markers of late EPC and play a key role in EPC commitment and outgrowth during neovascularization. Several authors have attempted to expand EPC ex vivo in order to obtain a homogeneous cell therapy product. One possible mean of expanding EPC ex vivo is to activate the thrombin receptor PAR-1 with the specific peptide SFLLRN. Indeed, PAR-1 activation increases angiogenic properties of EPC through activation of SDF-1, angiopoietin and IL-8 pathways. This review summarizes the characterization of EPC and different methods of ex vivo expansion.

Thrombin induces tumor cell cycle activation and spontaneous growth by down-regulation of p27Kip1, in association with the up-regulation of Skp2 and MiR-222

The effect of thrombin on tumor cell cycle activation and spontaneous growth was examined in synchronized serum-starved tumor cell lines and a model of spontaneous prostate cancer development in TRAMP mice. BrdUrd incorporation and propidium iodide staining of prostate LNCaP cells arrested in G(0) and treated with thrombin or serum revealed a 48- and 29-fold increase in S phase cells, respectively, at 8 hours. Similar results were obtained with TRAMP cells and a glioblastoma cell line, T98G. Cell cycle kinases and inhibitors in synchronized tumor cells revealed high levels of p27(Kip1) and low levels of Skp2 and cyclins D1 and A. Addition of thrombin, TFLLRN, or serum down-regulated p27(Kip1) with concomitant induction of Skp2, Cyclin D1, and Cyclin A with similar kinetics. LNCaP p27(Kip1)-transfected cells or Skp2 knockdown cells were refractory to thrombin-induced cell cycle activation. MicroRNA 222, an inhibitor of p27(Kip1), was robustly up-regulated by thrombin. The in vitro observations were tested in vivo with transgenic TRAMP mice. Repetitive thrombin injection enhanced prostate tumor volume 6- to 8-fold (P < 0.04). Repetitive hirudin, a specific potent antithrombin, decreased tumor volume 13- to 24-fold (P < 0.04). Thus, thrombin stimulates tumor cell growth in vivo by down-regulation of p27(Kip1).

Is thrombin a key player in the 'coagulation-atherogenesis' maze?

In addition to its established roles in the haemostatic system, thrombin is an intriguing coagulation protease demonstrating an array of effects on endothelial cells, vascular smooth muscle cells (VSMC), monocytes, and platelets, all of which are involved in the pathophysiology of atherosclerosis. There is mounting evidence that thrombin acts as a powerful modulator of many processes like regulation of vascular tone, permeability, migration and proliferation of VSMC, recruitment of monocytes into the atherosclerotic lesions, induction of diverse pro-inflammatory markers, and all of these are related to the progression of cardiovascular disease. Recent studies in transgenic mice models indicate that the deletion of the natural thrombin inhibitor heparin cofactor II promotes an accelerated atherogenic state. Moreover, the reduction of thrombin activity levels in apolipoprotein E-deficient mice, because of the administration of the direct thrombin inhibitor melagatran, attenuates plaque progression and promotes stability in advanced atherosclerotic lesions. The combined evidence points to thrombin as a pivotal contributor to vascular pathophysiology. Considering the clinical development of selective anticoagulants including direct thrombin inhibitors, it is a relevant moment to review the different thrombin-induced mechanisms that contribute to the initiation, formation, progression, and destabilization of atherosclerotic plaques.

Thrombin promotes arteriogenesis and hemodynamic recovery in a rabbit hindlimb ischemia model

BACKGROUND

Compared with angiogenesis, arteriogenesis is a distinct process based on the remodeling and maturation of pre-existing arterioles into large conductance arteries. Therapeutic angiogenesis has been proposed as a potential treatment for ischemic atherosclerotic diseases. Since a variety of angiogenic factors have been tested with inconsistent so far clinical results, the challenge remains in identifying the factor(s) that will stimulate functional neovascularization. Thrombin has been reported to play a pivotal role in the initiation of angiogenesis by regulating and organizing a network of angiogenic mediators. Also, it was recently demonstrated that thrombin is a potent anti-apoptotic factor for endothelial cells, providing evidence on a potential role of thrombin in vascular protection and maintenance of vessel integrity. Based on these observations, we hypothesized that thrombin may promote the development of mature functional blood vessels.

METHODS

Seventy-four (n=74) rabbits underwent bilateral femoral artery surgical excision. On the 20th postsurgical day increasing doses of VEGF or bFGF or thrombin were injected in one ischemic limb per rabbit and an equal volume of normal saline to the contralateral control limbs. Quantification of newly developed collateral vessels (diameter >500 mum) was performed by transauricular intra-arterial subtraction angiography. Computerized quantitative analysis of collateral vessels in angiography images was based on the concept of multiscale structural tensor. Perfusion analysis of an in vivo dynamic computed tomography study was performed to investigate hemodynamic recovery of the distal ischemic limbs. Tissue perfusion analysis was performed with the semiquantitative slope methodology, which focuses on the first-pass arterial phase.

RESULTS

A single administration of thrombin exhibited a dose-dependent increase of arteriogenic outcome. Thrombin at 5000 IU induced a 30.2 +/- 7.4% (P < 0.05) increase of total collateral area and length. Both VEGF and bFGF were without any significant effect at the concentrations used. Functional estimation of limb perfusion showed a statistically significant increase of blood flow recovery only for thrombin. The semiquantitative slope method perfusion score differed significantly in the 5000 IU thrombin treated limbs (5.7 +/- 0.3 vs 5.0 +/- 0.3 in control ischemic limbs; P < .05), and was not significantly inferior from the score of normal nonoperated limbs (6.5 +/- 0.3) suggesting a trend towards hemodynamic recovery of distal limb perfusion.

CONCLUSIONS

In a rabbit hindlimb ischemia model, thrombin promoted the formation of large collateral vessels and improved the perfusion of distal ischemic tissue. These results provide new insights in understanding the involvement of thrombin in vascular formation and point to a novel role of thrombin in arteriogenesis.

FXa-induced intracellular signaling links coagulation to neoangiogenesis: potential implications for fibrosis

Fibrosis represents the end-stage of a broad range of disorders affecting organ function. These disorders are often associated with aberrant angiogenesis, but whether vascular abnormalities during fibrosis are characterized by excessive or diminished neo-vascularization remains questionable. Strikingly, activation of the coagulation cascade is frequently observed in association with the progression of fibroproliferative disorders. As we recently showed that coagulation factor (F)Xa induced fibrotic responses in fibroblasts, we hypothesized that FXa might indirectly induce angiogenesis by triggering fibroblasts to secrete proangiogenic factors. In the present study, we show that although FXa induces p42/44 MAP Kinase phosphorylation in endothelial cells, it has no direct effect on endothelial cell proliferation, protein synthesis and tube formation. In contrast, conditioned medium of fibroblasts stimulated with FXa enhanced endothelial cell proliferation, extra cellular matrix synthesis, wound healing and endothelial tube formation. FXa induced VEGF production by fibroblasts and a VEGF neutralizing antibody blocked the indirect effect of FXa on proliferation and realignment of endothelial cells identifying VEGF as a crucial player in angiogenesis during coagulation factor-induced fibrosis. Overall, our results establish a link between the coagulation cascade and angiogenesis during fibrosis.

Thrombin up-regulates cathepsin D which enhances angiogenesis, growth, and metastasis

Cathepsin D (CD) up-regulation has been associated with human malignancy and poor prognosis. Thrombin up-regulated CD mRNA and protein in eight tumor cell lines as well as in human umbilical vascular endothelial cells (HUVEC). Thrombin increased the secretion of CD by 3- to 8-fold and enhanced chemotaxis ( approximately 2-fold) in 4T1 murine mammary CA cells, which was completely inhibited with the knockdown of CD. Secreted 4T1 CD induced neoangiogenesis by 2.4-fold on a chick chorioallantoic membrane, which was blocked in CD-KD cells. The addition of pure CD (2 ng) to the chick chorioallantoic membrane increased angiogenesis by 2.1-fold, which was completely inhibited by Pepstatin A (Pep A). CD enhanced human HUVEC chemotaxis and Matrigel tube formation by 2-fold, which was then blocked by Pep A. CD enhanced HUVEC matrix metalloproteinase 9 (MMP-9) activity by approximately 2-fold, which was completely inhibited by Pep A as well as a generic MMP inhibitor, GM6001. The injection of CD-KD 4T1 cells into syngeneic mice inhibited tumor growth by 3- to 4-fold compared with empty vector (EV) cells. Hirudin, a specific thrombin inhibitor, inhibited the growth of wild-type and EV cells by 2- to 3-fold, compatible with thrombin up-regulation of CD. CD and thrombin also contributed to spontaneous pulmonary metastasis; 4-fold nodule inhibition with CD versus EV and 4.6-fold inhibition with hirudin versus EV (P < 0.02). Thus, thrombin-induced CD contributes to the malignant phenotype by inducing tumor cell migration, nodule growth, metastasis, and angiogenesis. CD-induced angiogenesis requires the proteolytic activation of MMP-9.

Twist is required for thrombin-induced tumor angiogenesis and growth

Twist, a master regulator of embryonic morphogenesis, induces functions that are also required for tumor invasion and metastasis. Because thrombin contributes to the malignant phenotype by up-regulating tumor metastasis, we examined its effect on Twist in five different tumor cell lines and two different endothelial cell lines. Thrombin up-regulated Twist mRNA and protein in all seven cell lines. Down-regulation of Twist in B16F10 tumor cell lines led to a approximately 3-fold decrease in tumor growth on a chorioallantoic membrane assay and approximately 2-fold decrease in syngeneic mice. Angiogenesis was decreased approximately 45% and 36%, respectively. The effect of Twist on angiogenesis was further examined and compared with the effect of thrombin. In studies using a Twist-inducible plasmid, several identical vascular growth factors and receptors were up-regulated approximately 2- to 3-fold in tumor cells as well as human umbilical vascular endothelial cells by both Twist as well as thrombin (vascular endothelial growth factor, KDR, Ang-2, matrix metalloproteinase 1, GRO-alpha, and CD31). Thrombin-induced endothelial cell chemotaxis and Matrigel endothelial cell tubule formation were similarly regulated by Twist. Thus, thrombin up-regulates Twist, which is required for thrombin-induced angiogenesis as measured by endothelial cell migration, Matrigel tubule formation, and tumor angiogenesis.

Thrombin mediates mitogenesis and survival of human endothelial cells through distinct mechanisms

Thrombin has been reported to play a pivotal role in the initiation of angiogenesis by indirectly regulating and organizing a network of angiogenic molecules. In addition, it has been proposed that thrombin can directly activate endothelial cell proliferation. However, in this report it was shown that thrombin is a poor growth factor for human endothelial cells, and its modest mitogenic activity is mediated indirectly by the release of heparin-binding epidermal growth factor, subsequent to proteinase-activated receptor 1 (PAR1) activation. On the other hand, it was demonstrated that thrombin is a potent anti-apoptotic factor for endothelial cells, pointing to a novel role of thrombin in vascular protection. Analysis by annexin V-propidium iodide double staining revealed that thrombin, specifically, promoted survival of serum-starved endothelial cells in a concentration-dependent manner. In contrast to its mitogenic effect, the anti-apoptotic effect of thrombin was largely independent of its catalytic activity and was mediated through interaction with alphanubeta3 and alpha5beta1 integrins, whereas the involvement of PAR1 was limited. These results provide new insights in understanding the role of thrombin in endothelial cell signaling and vascular biology.

Protease signaling in tumor progression

Protease-activated receptors (PARs) constitute a family four of G-protein coupled receptors that mediate cellular responses to serine proteases. Best known as receptors for the coagulation protease thrombin, PARs can also be activated by other coagulation proteases, intestinal proteases and proteases released by epithelial cells and granulocytes. Many tumor cells express PARs, and protease agonists are often either co-expressed by the tumor cells or present in the tumor stroma. Tumors and their microenvironment should thus provide fertile ground for protease signaling, raising the question of whether this mechanism contributes to tumor progression. Cellular responses to PAR activation defined in vitro are consistent with possible roles in promoting proliferation, survival and/or malignant transformation of the tumor cells themselves and with activation of host endothelial cells and platelets to promote angiogenesis and metastasis. Indeed, expression of PARs and their potential agonists correlates with malignancy in several types of human cancer, and mouse models have pointed to a possible role in invasion and hematogenous metastasis. Whether PARs make important contributions to the biology of human tumors and/or whether they will provide useful markers of the malignant phenotype remains to be determined.

Tissue factor and PAR signaling in tumor progression

Tumor development depends on multiple reciprocal interactions of tumor cells with the host cell compartment. Tumor cells initiate TF-dependent crosstalks with the tumor microenvironment by releasing procoagulant microparticles, soluble cytokines and angiogenic growth factors. Conversely, the hemostatic system in the host compartment provides multiple circuits that regulate tumor growth and sustain angiogenesis. A combination of experimental models of spontaneous and transplanted tumor development and metastasis start to delineate the role of TF in tumor progression and identified potential therapeutic approaches to target the TF pathway.

'Role reversal' for the receptor PAR1 in sepsis-induced vascular damage

Sepsis is a deadly disease characterized by considerable derangement of the proinflammatory, anti-inflammatory and coagulation responses. Protease-activated receptor 1 (PAR1), an important regulator of endothelial barrier function and blood coagulation, has been proposed to be involved in the lethal sequelae of sepsis, but it is unknown whether activation of PAR1 is beneficial or harmful. Using a cell-penetrating peptide (pepducin) approach, we provide evidence that PAR1 switched from being a vascular-disruptive receptor to a vascular-protective receptor during the progression of sepsis in mice. Unexpectedly, we found that the protective effects of PAR1 required transactivation of PAR2 signaling pathways. Our results suggest therapeutics that selectively activate PAR1-PAR2 complexes may be beneficial in the treatment of sepsis.

Vascular density is highest in the proximal region of the mouse prostate

BACKGROUND

The proximal region of the prostatic ducts harbor the prostatic epithelial stem cells. As stem cell niches in other organs are highly vascularized, we determined if the proximal region is more highly vascularized than the remaining regions of the prostate. The effect of androgen on vascular density in the different prostatic regions was also examined.

METHODS

Sections from prostates were immunostained with antibodies to CD31, and the vascular density in proximal, intermediate, and distal regions was calculated by image analysis software. Vascular density was compared in prostates from castrated mice that received daily inoculations of testosterone or vehicle alone for 3 days. To examine the role of angiogenic factors in the response to androgen, some animals were also treated with soluble VEGF receptor-2-Fc or Tie-2--Fc fusion proteins, which inhibit the activities of VEGF and angiopoietins, respectively. The endothelial proliferative response to androgen was determined by double staining sections with antibodies to CD31 and Ki-67.

RESULTS

In prostates from intact mice, vascular density was highest in the proximal region and lowest in the distal region. Administration of testosterone to castrated mice increased vascular density to the greatest extent in the distal and intermediate regions. The increase in vascular density required VEGF and the angiopoietins. Endothelial cell proliferation was less sensitive to androgen in the proximal region than the remainder of the prostate.

CONCLUSIONS

Vascular density is highest in the proximal region of the prostate, but the proximal vessels are less responsive to testosterone.

Vascular endothelial growth factor and angiopoietin are required for prostate regeneration

BACKGROUND

The regulation of the prostate size by androgens may be partly the result of androgen effects on the prostatic vasculature. We examined the effect of changes in androgen levels on the expression of a variety of angiogenic factors in the mouse prostate and determined if vascular endothelial growth factor (VEGF)-A and the angiopoietins are involved in the vascular response to androgens.

METHODS

Expression of angiogenic factors in prostate was quantitated using real-time PCR at different times after castration and after administration of testosterone to castrated mice. Angiopoietins were localized in prostate by immunohistochemistry and in situ hybridization. The roles of VEGF and the angiopoietins in regeneration of the prostate were examined in mice inoculated with cells expressing soluble VEGF receptor-2 or soluble Tie-2.

RESULTS

Castration resulted in a decrease in VEGF-A, VEGF-B, VEGF-C, placenta growth factor, FGF-2, and FGF-8 expression after 1 day. In contrast, VEGF-D mRNA levels increased. No changes in angiopoietin-1 (Ang-1), angiopoietin-2 (Ang-2), hepatocyte growth factor, VEGF receptor-1, VEGF receptor-2, or tie-2 mRNA levels were observed. Administration of testosterone to castrated mice had the opposite effect on expression of these angiogenic factors. Ang-2 was expressed predominantly in prostate epithelial cells whereas Ang-1 was expressed in epithelium and smooth muscle. Inoculation of mice with cells expressing soluble VEGF receptor-2 or Tie-2 blocked the increase in vascular density normally observed after administration of testosterone to castrated mice. The soluble receptors also blocked the increase in prostate weight and proliferation of prostatic epithelial cells.

CONCLUSION

VEGF-A and angiopoietins are required for the vascular response to androgens and for the ability of the prostate to regenerate in response to androgens.

Endothelial progenitor cells: characterization, in vitro expansion, and prospects for autologous cell therapy

Injection of hematopoietic stem cells or endothelial progenitor cells (EPCs) expanded ex vivo has been shown to augment neovascularization in adult patients, but the precise origin and identity of the cell population responsible for these clinical benefits are controversial. The limited quantity of EPCs in the circulation has been the main obstacle to clinical trials. Several authors have therefore attempted to expand these cells ex vivo in order to obtain a homogeneous cell therapy product. One possible means of expanding EPCs ex vivo is to activate the thrombin receptor PAR-1 with the specific peptide SFLLRN. Indeed, PAR-1 activation promotes cell proliferation and C-X-C chemokine receptor type 4 (CXCR4) dependent migration and differentiation, with an overall angiogenic effect. This review summarizes the results and rationale of clinical trials of angiogenic therapy, the nature of EPCs, the different methods of ex vivo expansion, and current methods of quantification.

Role of protease activated receptor 1 and 2 signaling in hypoxia-induced angiogenesis

OBJECTIVE

Tissue factor (TF) initiates coagulation and indirectly triggers thrombin-dependent protease activated receptor (PAR) signaling. The TF-VIIa complex also directly cleaves PAR2 and promotes angiogenesis in vitro in TF cytoplasmic domain-deleted (TF(deltaCT)) mice. Here we address the effect of PAR1 and PAR2 deficiency on angiogenesis in vivo.

METHODS AND RESULTS

In hypoxia-driven angiogenesis of oxygen induced retinopathy (OIR), wild-type, PAR1-/-, PAR2-/-, and TF(deltaCT) mice showed a comparable regression of the superficial vascular plexus during the initial exposure of mice to hyperoxia. However, TF(deltaCT) mice revascularized areas of central vaso-obliteration significantly faster than wild-type animals. Pharmacological inhibition of the TF-VIIa complex, but not of Xa, and blockade of tyrosine kinase receptor pathways with Gleevec reversed accelerated angiogenesis of TF(deltaCT) mice to revascularization rates observed in wild-type mice. Genetic deletion of PAR2, but not of PAR1, abolished enhanced revascularization of TF(deltaCT) mice. PAR1 knock-out animals were indistinguishable from wild-type mice in the model of retinal neoangiogenesis and angiogenesis-dependent subcutaneous tumor growth was unaltered in PAR1- and PAR2-deficient animals.

CONCLUSION

Loss of the TF cytoplasmic domain results in accelerated hypoxia-induced angiogenesis mediated by TF-VIIa signaling. PAR2 signaling is sufficient for this proangiogenic effect without apparent contributions of mouse host cell PAR1.

Retrospective analysis of coagulation factor II receptor (F2R) sequence variation and coronary heart disease in hypertensive patients

OBJECTIVES

The purpose of this study was to evaluate the role of genetic variants within the coagulation factor II receptor (F2R) in the occurrence of coronary heart disease (CHD).

METHODS AND RESULTS

Four SNPs (-1738 G/A, 2860 G/A, 2930 T/C, and 9113 C/A) and an ins/del polymorphism -506-/GGCCGCGGGAAGC (D/I), replicating a consensus sequence for Ets-1 transcription factor, and their related haplotypes were tested for association to CHD in 1600 hypertensive patients divided in 2 groups according to presence (cases, n=559) and absence (controls, n=1041) of CHD. Allele I at -506 locus was associated with increased risk of CHD under additive, dominant, and recessive models of inheritance (all P<0.01). Three haplotypes carrying I allele were consistently associated with an increased risk of CHD (all P<0.05). Patients homozygous for the C allele at the 2930 locus also showed an increased risk of CHD (P<0.05). To test the functionality of -506 locus, nuclear extracts were incubated with -506D and -506I sequences by EMSA and F2R promoter activity (F2R-A) were assessed in HUVECs transfected with vectors carrying -506D and -506I sequences and exposed to hypoxia. Presence of the -506I sequence was associated with a 26% reduction of affinity binding to nuclear proteins and to blunted F2R-A in response to hypoxia as compared with the -506D sequence (all P<0.05).

CONCLUSIONS

F2R genetic variants may influence the natural history of CHD in patients at high risk of cardiovascular events.

Posttransplant Kaposi's sarcoma restricted to the site of a previous deep venous thrombosis: abrupt onset after withdrawal of sirolimus

Kaposi's sarcoma (KS) is an angioproliferative neoplasia associated with human herpesvirus 8 (HHV-8) infection. HHV-8 generates KS by means of the secretion of vascular endothelial growth factor (VEGF) andup-regulation of VEGF receptor, KDR, in endothelial cells. We report a case of KS in a 72-year-old male with a renal transplant who had received immunosuppressant drugs including sirolimus, mycophenolate mofetil, tacrolimus and steroids. KS developed 11 months after transplantation, in relation to deep venous thrombosis and withdrawal of sirolimus due to toxicity. Multiple purple papules and nodules were observed exclusively in the limb affected by thrombosis. Diagnosis of KS was confirmed by biopsy. Progressive withdrawal of prednisone was accompanied by full remission of the tumour. The thrombosis and withdrawal of sirolimus may have acted as cofactors in the development of KS, favouring the activation of the VEGF/KDR autocrine loop. Our experience contributes to further evidence that sirolimus may protect against KS.

Thrombin induces tumor growth, metastasis, and angiogenesis: Evidence for a thrombin-regulated dormant tumor phenotype

The association of idiopathic venous thrombosis with occult cancer is generally recognized. However, it has not been fully appreciated that thrombin generated during thrombosis can augment the malignant phenotype. Thrombin activates tumor cell adhesion to platelets, endothelial cells, and subendothelial matrix proteins; enhances tumor cell growth; increases tumor cell seeding and spontaneous metastasis; and stimulates tumor cell angiogenesis. These mechanisms are reviewed. Evidence is also presented to support the hypothesis that thrombin serves to preserve dormant tumor cells in individuals, preventing host eradication. It is proposed that tumor malignancy may be regulated by a procoagulant/anticoagulant axis.

Toward a core nutraceutical program for cancer management

As previously suggested, it may be feasible to impede tumorevoked angiogenesis with a nutraceutical program composed of glycine, fish oil, epigallocatechin-3-gallate, selenium, and silymarin, complemented by a low-fat vegan diet, exercise training, and, if feasible, a salicylate and the drug tetrathiomolybdate. It is now proposed that the scope of this program be expanded to address additional common needs of cancer patients: blocking the process of metastasis; boosting the cytotoxic capacity of innate immune defenses (natural killer [NK] cells); preventing cachexia, thromboembolism, and tumor-induced osteolysis; and maintaining optimal micronutrient status. Modified citrus pectin, a galectin-3 antagonist, has impressive antimetastatic potential. Mushroombeta-glucans and probiotic lactobacilli can amplify NK activity via stimulatory effects on macrophages. Selenium, beta-carotene, and glutamine can also increase the number and/or cytotoxic activity of NK cells. Cachectic loss of muscle mass can be opposed by fish oil, glutamine, and beta-hydroxy-beta-methylbutyrate. Fish oil, policosanol, and vitamin D may have potential for control of osteolysis. High-dose aspirin or salicylates, by preventing NF-B activation, can be expected to aid prevention of metastasis and cachexia while down-regulating osteolysis, but their impacts on innate immune defenses will not be entirely favorable. A nutritional insurance formula crafted for the special needs of cancer patients can be included in this regimen. To minimize patient inconvenience, this complex core nutraceutical program could be configured as an oil product, a powder, and a capsule product, with the nutritional insurance formula provided in tablets. It would be of interest to test this program in nude mouse xenograft models.

The angiopoietin pathway is modulated by PAR-1 activation on human endothelial progenitor cells

OBJECTIVES

The importance of protease-activated receptor-1 (PAR-1) in blood vessel development has been shown in knock-out mice. As endothelial progenitor cells (EPCs) express functional PAR-1, we examined whether PAR-1 stimulation by the peptide SFLLRN interfered with the angiopoietin pathway, that is EPC commitment, proliferation and migration.

METHODS AND RESULTS

Given the strong PAR-1 expression on CD34+ cells, we tested the effect of SFLLRN 75 micromol L(-1) on the emergence of EPCs from cord blood. PAR-1 activation did not modify the number of colonies or the day of emergence, in keeping with the lack of induction of angiopoietin 1 gene expression. Conversely, SFLLRN treatment of EPCs induced angiopoietin 2 gene expression and protein synthesis. Experiments with polyclonal blocking antibodies showed that angiopoietin 2 was involved in the proliferative effect of PAR-1 activation. PAR-1 activation also enhanced migration toward angiopoietin 1 in a Boyden chamber assay.

CONCLUSIONS

Our study demonstrates that PAR-1-induced proliferation of EPCs involves angiopoietin 2. PAR-1 also enhances EPC migration toward angiopoietin 1. These findings might explain the role of thrombin in neovascularization via the angiopoietin pathway.

Growth-regulated oncogene is pivotal in thrombin-induced angiogenesis

The mechanism of thrombin-induced angiogenesis is poorly understood. Using a gene chip array to investigate the pro-malignant phenotype of thrombin-stimulated cells, we observed that thrombin markedly up-regulates growth-regulated oncogene-alpha (GRO-alpha) in several tumor cell lines as well as endothelial cells by mRNA and protein analysis. Thrombin enhanced the secretion of GRO-alpha from tumor cells 25- to 64-fold. GRO-alpha is a CXC chemokine with tumor-associated angiogenic as well as oncogenic activation following ligation of its CXCR2 receptor. GRO-alpha enhanced angiogenesis in the chick chorioallantoic membrane assay 2.2-fold, providing direct evidence for GRO-alpha as an angiogenic growth factor. Anti-GRO-alpha antibody completely inhibited the 2.7-fold thrombin-induced up-regulation of angiogenesis, as well as the 1.5-fold thrombin-induced up-regulation of both endothelial cell cord formation in Matrigel and growth in vitro. Thrombin as well as its PAR-1 receptor activation peptide [thrombin receptor activation peptide (TRAP)] as well as GRO-alpha all markedly increased vascular regulatory proteins and growth factors: matrix metalloproteinase (MMP)-1, MMP-2, vascular endothelial growth factor (VEGF), angiopoietin-2 (Ang-2), CD31, and receptors KDR and CXCR2 in human umbilical vein endothelial cells. All of the thrombin/TRAP gene up-regulations were completely inhibited by anti-GRO-alpha antibody and unaffected by irrelevant antibody. Similar inhibition of gene up-regulation as well as thrombin-induced chemotaxis was noted with small interfering RNA (shRNA) GRO-alpha KD 4T1 breast tumor and B16F10 melanoma cells. In vivo tumor growth studies in wild-type mice with shRNA GRO-alpha KD cells revealed 2- to 4-fold impaired tumor growth, metastasis, and angiogenesis, which was not affected by endogenous thrombin. Thus, thrombin-induced angiogenesis requires the up-regulation of GRO-alpha. Thrombin up-regulation of GRO-alpha in tumor cells as well as endothelial cells contributes to tumor angiogenesis.

Tissue factor upregulation drives a thrombosis-inflammation circuit in relation to cardiovascular complications

The extrinsic coagulation is recognized as an 'inducible' signalling cascade resulting from tissue factor (TF) upregulation by exposure to clotting zymogen FVII upon inflammation or tissue injury. Following the substantial initiation, an array of proteolytic activation generates mediating signals (active serine proteases: FVIIa, FXa and FIIa) that lead to hypercoagulation with fibrin overproduction manifesting thrombosis. In addition, TF upregulation plays a central role in driving a thrombosis-inflammation circuit. Coagulant mediators (FVIIa, FXa and FIIa) and endproduct (fibrin) are proinflammatory, eliciting tissue necrosis factor, interleukins, adhesion molecules and many other intracellular signals in different cell types. Such resulting inflammation could ensure 'fibrin' thrombosis via feedback upregulation of TF. Alternatively, the resulting inflammation triggers platelet/leukocyte/polymononuclear cell activation thus contributing to 'cellular' thrombosis. TF is very vulnerable to upregulation resulting in hypercoagulability and subsequent thrombosis and inflammation, either of which presents cardiovascular risks. The prevention and intervention of TF hypercoagulability are of importance in cardioprotection. Blockade of inflammation reception and its intracellular signalling prevents TF expression from upregulation. Natural (activated protein C, tissue factor pathway inhibitor, or antithrombin III) or pharmacological anticoagulants readily offset the extrinsic hypercoagulation mainly through FVIIa, FXa or FIIa inhibition. Therefore, anticoagulants turn off the thrombosis-inflammation circuit, offering not only antithrombotic but anti-inflammatory significance in the prevention of cardiovascular complications.

Low-molecular-weight heparins and angiogenesis

The involvement of the vascular system in malignancy encompasses not only angiogenesis, but also systemic hypercoagulability and a pro-thrombotic state, and there is increasing evidence that pathways of blood coagulation and angiogenesis are reciprocally linked. In fact, cancer atients often display hypercoagulability resulting in markedly increased thromboembolism, which requires anti-coagulant treatment using heparins, for example. Clinical trials reveal that treatment with various low-molecular-weight heparins (LMWHs) improves the survival time in cancer patients receiving chemotherapy compared with those receiving unfractionated standard heparin (UFH) or no heparin treatment, as well as in cancer patients receiving LMWH as thrombosis prophylaxis during primary surgery. This anti-tumor effect of the heparins appears to be unrelated to their anti-coagulant activity, but the mechanisms involved are not fully understood. Tumor growth and spread are dependent on angiogenesis and it is noteworthy that the most potent endogenous pro- and anti-angiogenic factors are heparin-binding proteins that may be affected by systemic treatment with heparins. Heparin and other glycosaminoglycans play a role in vascular endothelial cell function, as they are able to modulate the activities of angiogenic growth factors by facilitating the interaction with their receptor and promoting receptor activation. To date, preclinical studies have demonstrated that only LMWH fragments produced by the heparinase digestion of UFH, i.e. tinzaparin, exert anti-angiogenic effects in any type of tissue in vivo. These effects are fragment-mass-specific and angiogenesis-type-specific. Data on the effect of various LMWHs and UFH on endothelial cell capillary tube formation and proliferation in vitro are also presented. We hope that this paper will stimulate and facilitate future research designed to elucidate whether the anti-angiogenic or anti-tumor effects of commercial LMWHs in their own right are agent specific and whether anti-angiogenic properties increase the anti-tumor properties of the LMWHs in the clinic.

PAR-1 Activation on Human Late Endothelial Progenitor Cells Enhances Angiogenesis In Vitro With Upregulation of the SDF-1/CXCR4 System

Objectives— The importance of PAR-1 in blood vessel development has been demonstrated in knockout mice. As endothelial progenitor cells (EPCs) are involved in postnatal vasculogenesis, we examined whether they express PAR-1 and whether stimulation by the peptide SFLLRN modulates their angiogenic properties.

Methods and Results— EPC expanded from human CD34+ cord blood cells expressed PAR-1. PAR-1 activation induced EPC proliferation in a concentration-dependent manner far more potently than that of human umbilical vein endothelial cells. PAR-1 activation also enhanced actin reorganization, promoting both spontaneous migration in a Boyden chamber assay and migration toward SDF-1 and VEGF. As shown by real-time quantitative reverse-transcription polymerase chain reaction (RT-PCR), EPC stimulation by SFLLRN significantly enhanced the mRNA expression of SDF-1 and its receptor CXCR-4. PAR-1 activation also increased CXCR4 expression on EPC and induced SDF-1 secretion, leading to autocrine stimulation. PAR-1 stimulation by SFLLRN also increased the formation of capillary-like structures by EPC in Matrigel, and this effect was abrogated by anti-CXCR-4, anti-SDF-1, and MEK inhibitor pretreatment.

Conclusions— Human EPCs express functional PAR-1. PAR-1 activation promotes cell proliferation and CXCR4-dependent migration and differentiation, leading to a proangiogenic effect.