Growth factor-induced angiogenesis in vivo requires specific cleavage of fibrillar type I collagen

The contribution of specific type I collagen remodeling in angiogenesis was studied in vivo using a quantitative chick embryo assay that measures new blood vessel growth into well-defined fibrillar collagen implants. In response to a combination of basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF), a strong angiogenic response was observed, coincident with invasion into the collagen implants of activated fibroblasts, monocytes, heterophils, and endothelial cells. The angiogenic effect was highly dependent on matrix metalloproteinase (MMP) activity, because new vessel growth was inhibited by both a synthetic MMP inhibitor, BB3103, and a natural MMP inhibitor, TIMP-1. Multiple MMPs were detected in the angiogenic tissue including MMP-2, MMP-13, MMP-16, and a recently cloned MMP-9-like gelatinase. Using this assay system, wild-type collagen was compared to a unique collagenase-resistant collagen (r/r), with regard to the ability of the respective collagen implants to support cell invasion and angiogenesis. It was found that collagenase-resistant collagen constitutes a defective substratum for angiogenesis. In implants made with r/r collagen there was a substantial reduction in the number of endothelial cells and newly formed vessels. The presence of the r/r collagen, however, did not reduce the entry into the implants of other cell types, that is, activated fibroblasts and leukocytes. These results indicate that fibrillar collagen cleavage at collagenase-specific sites is a rate-limiting event in growth factor-stimulated angiogenesis in vivo.     

Membrane-type matrix metalloproteinase-mediated angiogenesis in a fibrin-collagen matrix

Adult angiogenesis, associated with pathologic conditions, is often accompanied by the formation of a fibrinous exudate. This temporary matrix consists mainly of fibrin but is intermingled with plasma proteins and collagen fibers. The formation of capillary structures in a fibrinous matrix in vivo was mimicked by an in vitro model, in which human microvascular endothelial cells (hMVECs) seeded on top of a fibrin-10% collagen matrix form capillarylike tubular structures after stimulation with basic fibroblast growth factor/tumor necrosis factor alpha (bFGF/TNF-alpha) or vascular endothelial growth factor (VEGF)/TNF-alpha. In the fibrin-collagen matrix the metalloproteinase inhibitor BB94 inhibited tubule formation by 70% to 80%. Simultaneous inhibition of plasmin and metalloproteinases by aprotinin and BB94 caused a nearly complete inhibition of tubule formation. Adenoviral transduction of tissue inhibitor of metalloproteinases 1 (TIMP-1) and TIMP-3 into endothelial cells revealed that TIMP-3 markedly inhibited angiogenesis, whereas TIMP-1 had only a minor effect. Immunohistochemical analysis showed the presence of matrix metalloproteinase 1 (MMP-1), MMP-2, and membrane-type 1 (MT1)-MMP, whereas MMP-9 was absent. The endothelial production of these MMPs was confirmed by antigen assays and real-time polymerase chain reaction (PCR). MT1-MMP mRNA was markedly increased in endothelial cells under conditions that induced tubular structures. The presence of MMP-1, MMP-2, and MT1-MMP was also demonstrated in vivo in the newly formed vessels of a recanalized arterial mural thrombus. These data suggest that MMPs, in particular MT-MMPs, play a pivotal role in the formation of capillarylike tubular structures in a collagen-containing fibrin matrix in vitro and may be involved in angiogenesis in a fibrinous exudate in vivo.     

Involvement of membrane-type matrix metalloproteinases (MT-MMPs) in capillary tube formation by human endometrial microvascular endothelial cells: role of MT3-MMP

In the endometrium, angiogenesis is a physiological process, whereas in most adult tissues neovascularization is initiated only during tissue repair or pathological conditions. Pericellular proteolysis plays an important role in angiogenesis being required for endothelial cell migration, invasion, and tube formation. We studied the expression of proteases by human endometrial microvascular endothelial cells (hEMVECs) and their involvement in the formation of capillary tubes and compared these requirements with those of foreskin MVECs (hFMVECs). Inhibition of urokinase and matrix metalloproteinase (MMP) both reduced tube formation in a fibrin or fibrin/collagen matrix. hEMVECs expressed various MMP mRNAs and proteins; in particular MMP-1, MMP-2, and membrane-type (MT)1-, MT3-, and MT4-MMPs. MT3- and MT4-MMP mRNA expressions were significantly higher in hEMVECs than in hFMVECs. Other MT-MMP mRNAs and MMP-9 were hardly detectable. Immunohistochemistry confirmed the presence of MT3-MMP in endothelial cells of endometrial tissue. Overexpression of tissue inhibitor of MMP (TIMP)-1 or TIMP-3 by adenoviral transduction of hEMVECs reduced tube formation to the same extent, whereas only TIMP-3 was able to inhibit tube formation by hFMVECs. Tube formation by hEMVECs was partly inhibited by the presence of anti-MT3-MMP IgG. Thus, in contrast to tube formation by hFMVECs, which largely depends on MT1-MMP, capillary-like tube formation by hEMVECs is, at least in part, regulated by MT3-MMP.     

Dynamics of collagen, MMP and TIMP gene expression during the granulomatous, fibrotic process induced by Schistosoma mansoni eggs

In schistosomiasis mansoni, granulomatous inflammation and fibrotic resolution are the major pathogenetic factors. The outcome of fibrosis is influenced by the deposition of collagen and degradation mediated by matrix metalloproteinases (MMP). There is a dearth of data on the expression of MMP and the tissue inhibitors of metalloproteinase (TIMP) during the fibrosis associated with schistosomiasis. In this study, the dynamics of collagen, MMP and TIMP gene expression were analysed during murine Schistosoma mansoni infection. Expression within the granulomatous liver tissue of the genes coding for collagen of types I, III and IV was up-regulated at the onset of granuloma development, and the dominant type-I expression peaked at the chronic, fibrotic stage. The amount of deposited hepatic collagen increased with the chronicity of the infection, indicating cumulative fibrosis. Collagenase, gelatinase, stromelysin, matrilysin-specific gene activities were similarly up-regulated, but only MMP-8 (collagenase-2) expression peaked at the height of fibrosis. TIMP-1 gene expression gradually increased during the course of the disease and, along with TIMP-2, peaked at the chronic, fibrotic stage. Granuloma myofibroblasts expressed both MMP and TIMP-1 genes. In ELISA of the splenic cytokines, high levels of fibrogenic interleukin-13 and moderate production of transforming growth factor-beta were found to be concurrent with fibrosis. These data indicate that an imbalance in MMP:TIMP expression and fibrogenic cytokine production are associated with cumulative fibrosis.     

Melatonin promotes angiogenesis during protection and healing of indomethacin‐induced gastric ulcer: role of matrix metaloproteinase‐2

Abstract: Matrix metalloproteinase (MMP)‐2 is considered as a crucial regulator of angiogenesis, a process of new blood vessel formation. We reported previously that melatonin (N‐acetyl‐5‐methoxy tryptamine), an antioxidant and anti‐inflammatory agent, prevents indomethacin‐induced gastric ulcers. Herein, we investigated the effect of melatonin on MMP‐2‐mediated angiogenesis during gastroprotection. Angiogenic properties of melatonin were tested in both rat corneal micropocket assay and in mouse model of indomethacin‐induced gastric lesions. Melatonin augmented angiogenesis that was associated with amelioration of MMP‐2 expression and activity and, upregulation of vascular endothelial growth factor (VEGF) in rat cornea. Melatonin prevented gastric lesions by promoting angiogenesis via upregulation of VEGF followed by over‐expression of MMP‐2. Similarly, healing of gastric lesions was associated with early expression of VEGF followed by MMP‐2. In addition, upregulation of MMP‐2 was parallel to MMP‐14 and inverse to tissue inhibitor of metalloprotease (TIMP)‐2 expression during gastroprotection. Our data demonstrated that melatonin exerts angiogenesis through MMP‐2 and VEGF over‐expression during protection and healing of gastric ulcers. This study highlights for the first time a phase‐associated regulation of MMP‐2 activity in gastric mucosa and an angiogenic action of melatonin to rescue indomethacin‐induced gastropathy.     

Stromal-derived factor 1-induced megakaryocyte migration and platelet production is dependent on matrix metalloproteinases

Despite the discovery of thrombopoietin (TPO) and its contribution to megakaryocytopoiesis, the exact mechanisms and sites of platelet production are unknown. It has been shown that mature megakaryocytes (MKs) functionally express the stromal-derived factor 1 (SDF-1) receptor, CXCR4. SDF-1-induced migration of mature MKs through endothelial cell layers results in increased platelet production. Because the migration of polyploid MKs from the bone marrow microenvironment requires remodeling of the perivascular extracellular matrix, it was hypothesized that mature polyploid MKs may express matrix metalloproteinases (MMPs), facilitating their exit into the bone marrow extravascular space. In this report, it is demonstrated that SDF-1 induces the expression and release of gelatinase B (MMP-9) by purified mature polyploid human MKs and an adeno-CXCR4-infected megakaryocytic cell line. Neutralizing antibody to MMP-9, but not MMP-2, blocked SDF-1-induced migration of MKs through reconstituted basement membrane, suggesting that expression of MMP-9 is critical for MK migration. Incubation of mature MKs with a synthetic MMP inhibitor, 5-phenyl-1,10-phenanthrolene, resulted in the inhibition of platelet formation, suggesting that the expression of MMPs is not only critical for megakaryocyte migration but also for subsequent platelet release. Confirming these results, adeno-SDF-1 injection into normal mice resulted in increased platelet counts, a process that could be blocked by a synthetic MMP inhibitor. These results suggest mobilization of MKs involves sequential expression and activation of chemokine receptors such as CXCR4, MMP-9, followed by transendothelial migration. MMP inhibitors may have potential use in the treatment of thrombotic and myeloproliferative disorders. (Blood. 2000;96:4152-4159)     

Matrix metalloproteinases and the thyroid.

Matrix metalloproteinases (MMPs) are proteolytic enzymes that degrade components of the extracellular matrix (ECM) and basement membrane. They play a critical role in many physiological and pathological processes, such as tumor metastasis. The original concept-that MMP activity during metastasis is restricted solely to invasion of the basement membrane and destruction of ECM components-has been modified to encompass multiple aspects of tumor progression: tumor establishment, growth, angiogenesis, intravasation, extravasation, and almost all metastatic steps. Moreover, the role of tissue inhibitors of matrix metalloproteinases (TIMPs), originally believed to exhibit anti-invasion properties solely by virtue of their inhibition of MMPs, has been extended to include their multiple biological effects, such as growth promotion. In thyroid neoplasia as well, MMPs, in particular MMP-2, seem to be associated with metastatic potential. It would seem that similar and divergent patterns regulate MMP and TIMP gene expression in benign and malignant human thyrocytes, in many instances in agreement with the concept of MMPs playing the role of stimulating, and TIMPs inhibiting cell invasion.     

Matrix metalloproteinase inhibition after myocardial infarction: a new approach to prevent heart failure?

Increased activity of matrix metalloproteinases (MMPs) has been implicated in numerous disease processes, including tumor growth and metastasis, arthritis, and periodontal disease. It is now becoming increasingly clear that extracellular matrix degradation by MMPs is also involved in the pathogenesis of cardiovascular disease, including atherosclerosis, restenosis, dilated cardiomyopathy, and myocardial infarction. Administration of synthetic MMP inhibitors in experimental animal models of these cardiovascular diseases significantly inhibits the progression of, respectively, atherosclerotic lesion formation, neointima formation, left ventricular remodeling, pump dysfunction, and infarct healing. This review focuses on the role of MMPs in cardiovascular disease, in particular myocardial infarction and the subsequent progression to heart failure. MMPs, which are present in the myocardium and capable of degrading all the matrix components of the heart, are the driving force behind myocardial matrix remodeling. The recent finding that acute pharmacological inhibition of MMPs or deficiency in MMP-9 attenuates left ventricular dilatation in the infarcted mouse heart led to the proposal that MMP inhibitors could be used as a potential therapy for patients at risk for the development of heart failure after myocardial infarction. Although these promising results encourage the design of clinical trials with MMP inhibitors, there are still several unresolved issues. This review describes the biology of MMPs and discusses new insights into the role of MMPs in several cardiovascular diseases. Attention will be paid to the central role of the plasminogen system as an important activator of MMPs in the remodeling process after myocardial infarction. Finally, we speculate on the use of MMP inhibitors as potential therapy for heart failure.     

Host metalloproteinases in Lyme arthritis.

OBJECTIVE: To assess the role of matrix metalloproteinases (MMPs) in cartilage and bone erosions in Lyme arthritis METHODS: We examined synovial fluid from 10 patients with Lyme arthritis for the presence of MMP-2, MMP-3, MMP-9, and "aggrecanase" activity using gelatinolytic zymography and immunoblot analysis. We developed an in vitro model of Lyme arthritis using cartilage explants and observed changes in cartilage degradation in the presence of Borrelia burgdorferi and/or various protease inhibitors. RESULTS: Synovial fluid from patients with Lyme arthritis was found to contain at least 3 MMPs: gelatinase A (MMP-2), stromelysin (MMP-3), and gelatinase B (MMP-9). In addition, there was evidence in 2 patients of "aggrecanase" activity not accounted for by the above enzymes. Infection of cartilage explants with B. burgdorferi resulted in induction of MMP-3, MMP-9, and "aggrecanase" activity. Increased induction of these enzymes by B. burgdorferi alone was not sufficient to cause cartilage destruction in the explants as measured by glycosaminoglycan (GAG) and hydroxyproline release. However, addition of plasminogen, which can act as an MMP activator, to cultures resulted in significant GAG and hydroxyproline release in the presence of B. burgdorferi. The MMP inhibitor batimastat significantly reduced the GAG release and completely inhibited the collagen degradation. CONCLUSION: MMPs are found in synovial fluids from patients with Lyme arthritis and are induced from cartilage tissue by the presence of B. burgdorferi. Inhibition of MMP activity prevents B. burgdorferi-induced cartilage degradation in vitro.     

Downregulation of vascular matrix metalloproteinase inducer and activator proteins in hypertensive patients

BACKGROUND: Peripheral vasculature undergoes extensive vascular remodeling in the hypertensive state. Regulation of extracellular matrix turnover by the matrix metalloproteinase (MMP) system is an important step in the vascular remodeling process. However, the expression pattern of the vascular MMP system in human hypertension remained unknown. METHODS AND RESULTS: Internal mammary artery specimens were obtained from normotensive (n = 13) and hypertensive (n = 19) patients undergoing coronary artery bypass grafting surgery. Zymographic analysis indicated a threefold decrease in total gelatinolytic activity of MMP-2 and MMP-9 in hypertension. MMP-1 activity was also decreased by fourfold without a significant change in protein levels. Tissue levels of extracellular matrix inducer protein (EMMPRIN), MMP activator protein (MT1-MMP), MMP-1, MMP-2, and MMP-9, as well as tissue inhibitors of MMPs (TIMP-1 and TIMP-2) were assessed by immunoblotting and yielded a significant decrease in MMP-9, EMMPRIN, and MT1-MMP levels in hypertension. In addition, measurement of plasma markers of collagen synthesis (procollagen type I amino-terminal propeptide [PINP]) and collagen degradation (carboxy-terminal telopeptide of collagen type I [ICTP]) indicated no difference in PINP levels but suppressed degradation of collagen in hypertension. Evaluation of profibrotic growth factors demonstrated higher levels of fibroblast growth factor (FGF)-2 in tissue preparations from hypertensive patients but no difference in transforming growth factor-beta1 levels. CONCLUSIONS: These findings demonstrate that not only MMP-1 and MMP-9, but MMP inducer and activator proteins are also downregulated in the hypertensive state. Augmented FGF-2 levels may contribute to parallel decreases in MMP activity and MMP induction system resulting in enhanced collagen deposition in hypertension.     

Myocardial matrix degradation and metalloproteinase activation in the failing heart: a potential therapeutic target

A fundamental structural event in the progression of heart failure due to dilated cardiomyopathy is left ventricular (LV) myocardial remodeling. The matrix metalloproteinases (MMPs) are an endogenous family of enzymes which contribute to matrix remodeling in several disease states. The goal of this report is to summarize recent findings regarding the myocardial MMP system and the relation to matrix remodeling in the failing heart. In both experimental and clinical forms of dilated cardiomyopathy (DCM), increased expression of certain species of myocardial MMPs have been demonstrated. Specifically, increased myocardial levels of the gelatinase, MMP-9 has been identified in both ischemic and non-ischemic forms of human DCM. In addition, stromelysin or MMP-3 increased by over four-fold in DCM. The increased levels of MMP-3 in DCM may have particular importance since this MMP degrades a wide range of extracellular proteins and can activate other MMPs. In normal human LV myocardium, the membrane type 1 MMP (MT1-MMP) was detected. These MT-MMPs may provide important sites for local MMP activation within the myocardium. In a pacing model of LV failure, MMP expression and activity increased early and were temporally associated with LV myocardial matrix remodeling. Using a broad-spectrum pharmacological MMP inhibitor in this pacing model, the degree of LV dilation was attenuated and associated with an improvement in LV pump function. Thus, increased LV myocardial MMP expression and activity are contributory factors in the LV remodeling process in cardiomyopathic disease states. Regulation of myocardial MMP expression and activity may be an important therapeutic target for controlling myocardial matrix remodeling in the setting of developing heart failure.     

Visfatin induces human endothelial VEGF and MMP-2/9 production via MAPK and PI3K/Akt signalling pathways: novel insights into visfatin-induced angiogenesis

AIMS: Visfatin is a novel adipokine whose plasma concentrations are altered in obesity and obesity-related disorders; these states are associated with an increased incidence of cardiovascular disease. We therefore investigated the effect of visfatin on vascular endothelial growth factor (VEGF) and matrix metalloproteinases (MMP-2, MMP-9) production and the potential signalling cascades. METHODS AND RESULTS: In human umbilical vein endothelial cells (HUVECs), visfatin significantly and dose-dependently up-regulated gene expression and protein production of VEGF and MMPs and down-regulated expression of tissue inhibitors of MMPs (TIMP-1 and TIMP-2). The gelatinolytic activity of MMPs (analysed by zymography) correlated with mRNA and western blot findings. Interestingly, visfatin significantly up-regulated VEGF receptor 2 expression. Inhibition of VEGFR2 and VEGF [by soluble FMS-like tyrosine kinase-1 (sFlt1)] down-regulated visfatin-induced MMP induction. Visfatin induced dose- and time-dependent proliferation and capillary-like tube formation. Importantly, visfatin was noted to have anti-apoptotic effects. In HUVECs, visfatin dose-dependently activated PI3K/Akt (phosphatidylinositol 3-kinase/Akt) and ERK(1/2) (extracellular signal-regulated kinase) pathways. The functional effects and MMP/VEGF induction were shown to be dependent on the MAPK/PI3K-Akt/VEGF signalling pathways. Inhibition of PI3K/Akt and ERK(1/2) pathways led to significant decrease of visfatin-induced MMP and VEGF production and activation, along with significant reduction in endothelial proliferation and capillary tube formation. CONCLUSION: Our data provide the first evidence of visfatin-induced endothelial VEGF and MMP production and activity. Further, we show for the first time the involvement of the MAPK and PI3K/Akt signalling pathways in mediating these actions, as well as endothelial cell proliferation. Collectively, our findings provide novel insights into visfatin-induced endothelial angiogenesis.     

Enforced expression of tissue inhibitor of matrix metalloproteinase-3 affects functional capillary morphogenesis and inhibits tumor growth in a murine tumor model

Homeostasis of the extracellular matrix is a delicate balance between degradation and remodeling, the balance being maintained by the interaction of activated matrix metalloproteinases (MMPs) and specific tissue inhibitors of matrix metalloproteinases (TIMPs). Up-regulation of MMP activity, favoring proteolytic degradation of the basement membrane and extracellular matrix, has been linked to tumor growth and metastasis, as well as tumor-associated angiogenesis, whereas inhibition of MMP activity appears to restrict these processes. We have used retroviral-mediated gene delivery to effect sustained autocrine expression of TIMP-3 in murine neuroblastoma and melanoma tumor cells in order to further examine the ability of TIMPs to inhibit angiogenesis in vivo. Growth of both histologic types of gene-modified tumor cells in severe combined immunodeficiency (SCID) mice was significantly restricted when compared with controls. Grossly, these tumors were small and had few feeding vessels. Histologic evaluation revealed that although tumors overexpressing TIMP-3 had an increased number of CD31(+) endothelial cells, these endothelial cells had not formed functional tubules, as evidenced by decreased vessel continuity and minimal pericyte recruitment. This effect appears to be mediated, in part, by decreased expression of vascular endothelial (VE)-cadherin by endothelial cells in the presence of TIMP-3 as seen both in an in vitro assay and in TIMP-3-overexpressing tumors. Taken together, these results demonstrate that overexpression of TIMP-3 can inhibit angiogenesis and associated tumor growth, and that the antiangiogenic effects of TIMP-3 appear to be mediated through the inhibition of functional capillary morphogenesis.     

Fibroblasts potentiate blood vessel formation partially through secreted factor TIMP-1

During wound repair, new blood vessels form in response to angiogenic signals emanating from injured tissues. Dermal fibroblasts are known to play an important role in wound healing, and have been linked to angiogenesis; therefore, we sought to understand the mechanisms through which these cells control blood vessel formation. Using a three-dimensional angiogenesis assay we demonstrate that dermal fibroblasts enhance the tube-forming potential of endothelial cells, and this augmentation is partially due to secreted factors present in conditioned media. Interestingly, we identified tissue inhibitor of metalloproteinase-1 (TIMP-1) as a factor uniquely secreted by fibroblasts, and addition of exogenous TIMP-1 increased vessel assembly. The enhancing activity of TIMP-1 was matrix metalloproteinase (MMP)-dependent, since a mutant version of TIMP-1 was unable to promote angiogenesis. Consistent with this, chemical inhibition of MMP-2/9 showed a similar increase in angiogenesis, and addition of exogenous MMP-9 blocked the enhancing effect of TIMP-1. We further demonstrated that TIMP-1 inhibits the production of tumstatin, an anti-angiogenic fragment of collagen IV that is produced by MMP-9 cleavage. Our results support the notion that dermal fibroblasts regulate blood vessel formation through multiple mediators, and provide novel evidence that fibroblast-derived TIMP-1 acts on endothelial cells in a pro-angiogenic capacity.     

Lymphoid tissue collagen deposition in HIV-infected patients correlates with the imbalance between matrix metalloproteinases and their inhibitors

We studied the lymphoid tissue biopsies of 20 patients with chronic human immunodeficiency virus (HIV) infection by analyzing collagen deposition, CD4+ cell number, and gene expression of metalloproteinases (MMPs; MMP-2, MMP-9) and tissue inhibitors of MMPs (TIMPs; TIMP-1, TIMP-2). HIV-infected patients had significantly increased collagen deposition (P = .001), fewer CD4+ T cells (P = .05), and decreased MMP-9/TIMP-1 and MMP-2/TIMP-2 ratios (P = .01), compared with HIV-negative control patients. Moreover, we found a significant negative correlation between collagen deposition and the MMP-9/TIMP-1 ratio (ρ = -0.50; P = .047). To our knowledge, this is the first time that MMP/TIMP imbalance has been correlated with lymphoid tissue collagen deposition and incomplete immune recovery in HIV-infected patients, even after long-term antiretroviral treatment.     

Matrix metalloproteinases, tissue inhibitors of matrix metalloproteinases and angiogenic cytokines in peripheral blood of patients with thyroid cancer.

Stimulation of growth of endothelial cells from preexisting blood vessels, i.e., angiogenesis, is one of the essential elements necessary to create a permissive environment in which a tumor can grow. During angiogenesis, the matrix metalloproteinase (MMP) family of tissue enzymes contributes to normal (embriogenesis or wound repair) and pathologic tissue remodeling (chronic inflammation and tumor genesis). The proposed pathogenic roles of MMPs in cancer are tissue breakdown and remodeling during invasive tumor growth and tumor angiogenesis. Tissue inhibitors of metalloproteinases (TIMPs) form a complex with MMPs, which in turn inhibits active MMPs. Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) are unique among mediators of angiogenesis with synergistic effect, and both can also be secreted by thyroid cancer cells. The goal of the study was to evaluate the plasma blood concentration of VEGF, bFGF, MMP-1, MMP-2, MMP-3, MMP-8, MMP-9, TIMP-1, and TIMP-2 in patients with cancer and in normal subjects. Twenty-two patients with thyroid cancers (papillary cancer, 11; partly papillary and partly follicular cancer, 3; anaplastic cancer, 5; medullary cancer, 3) and 16 healthy subjects (controls) were included in the study. VEGF, bFGF MMPs, and TIMPs were evaluated by enzyme-linked immunosorbent assay (ELISA). In patients with thyroid cancer, normal VEGF concentrations (74.29 +/- 13.38 vs. 84.85 +/- 21.71 pg/mL; p > 0.05) and increased bFGF (29.52 +/- 4.99 vs. 6.05 +/- 1.43 pg/mL; p < 0.001), MMP-2 (605.95 +/- 81.83 vs. 148.75 +/- 43.53 ng/mL; p < 0.001), TIMP-2 (114.19 +/- 6.62 vs. 60.75 +/- 9.18 ng/mL; p < 0.001), as well as lower MMP-1 (0.70 +/- 0.42 vs. 3.87 +/- 0.53; p < 0.001) levels have been noted. Increased plasma levels of MMP-3 and MMP-9 were also found in patients with medullary carcinoma. In conclusion, predominance of MMP-2 over TIMP-2 and TIMP-1 over MMP-1 as well as increased concentration of bFGF in peripheral blood are common features in patients with thyroid cancer.     

Generation and role of angiostatin in human platelets

Platelets regulate new blood vessel growth, because they contain a number of angiogenesis promoters and inhibitors. Additionally, platelets contain matrix metalloproteinases (MMPs), which when released mediate platelet adhesion and aggregation, and plasminogen, a fibrinolytic system enzyme that serves to limit blood clot formation. Enzymatic cleavage of plasminogen by MMPs generates angiostatin, an angiogenesis inhibitor. Therefore, we examined whether platelets generate angiostatin during aggregation in vitro. Platelets were isolated from healthy human donors and then aggregated with collagen, thrombin, or HT-1080 fibrosarcoma cells. Angiostatin was detected by Western blot analysis in the platelet releasates of all blood donors irrespective of the aggregating agent used. Platelet pellet homogenates showed the presence of angiostatin in all donors, which was released upon aggregation. Furthermore, platelet-derived angiostatin was isolated and purified by lysine-Sepharose affinity chromatography from collagen-aggregated platelet releasates. Bioassay of platelet-derived angiostatin showed that it inhibited the formation of capillary structures by human umbilical vein endothelial cells (HUV-EC-Cs) in an in vitro angiogenesis model. Inhibition of angiostatin in platelet releasates promoted the formation of capillary structures by HUV-EC-Cs. We conclude that healthy human platelets contain angiostatin, which is released in active form during platelet aggregation, and platelet-derived angiostatin has the capacity to inhibit angiogenesis.