Purified tumour angiogenesis factor enhances proliferation of capillary, but not aortic, endothelial cells in vitro

The Functional Implications of Endothelial Gap Junctions and Cellular Mechanics in Vascular Angiogenesis

Angiogenesis—the sprouting and growth of new blood vessels from the existing vasculature—is an important contributor to tumor development, since it facilitates the supply of oxygen and nutrients to cancer cells. Endothelial cells are critically affected during the angiogenic process as their proliferation, motility, and morphology are modulated by pro-angiogenic and environmental factors associated with tumor tissues and cancer cells. Recent in vivo and in vitro studies have revealed that the gap junctions of endothelial cells also participate in the promotion of angiogenesis. Pro-angiogenic factors modulate gap junction function and connexin expression in endothelial cells, whereas endothelial connexins are involved in angiogenic tube formation and in the cell migration of endothelial cells. Several mechanisms, including gap junction function-dependent or -independent pathways, have been proposed. In particular, connexins might have the potential to regulate cell mechanics such as cell morphology, cell migration, and cellular stiffness that are dynamically changed during the angiogenic processes. Here, we review the implication for endothelial gap junctions and cellular mechanics in vascular angiogenesis.

Circulating endothelial cells and tumor blood volume as predictors in lung cancer

The current criteria for evaluating antiangiogenic efficacy is insufficient as tumor shrinkage occurs after blood perfusion decreases. Tumor blood volume (BV) in computed tomography perfusion imaging and circulating endothelial cells (CEC) might predict the status of angiogenesis. The present study aimed to validate their representation as feasible predictors in non-small-cell lung carcinoma (NSCLC). A total of 74 patients was categorized randomly into two arms undergoing regimens of vinorelbine and cisplatin (Navelbine and platinum [NP]) with rh-endostatin or single NP. The response rate, perfusion imaging indexes and activated CEC (aCEC) during treatment were recorded. Progression-free survival (PFS) was determined through follow up. Correlations among the above indicators, response and PFS were analyzed: aCEC increased significantly in cases of progressive disease after single NP chemotherapy (P = 0.024). Tumor BV decreased significantly in cases with a clinical benefit in the combined arm (P = 0.026), whereas inverse correlations existed between ∆aCEC (post-therapeutic value minus the pre-therapeutic value) and PFS (P = 0.005) and between ∆BV and PFS (P = 0.044); a positive correlation existed between ∆aCEC and ∆BV. Therefore, both aCEC and tumor BV can serve as predictors, and detection of both indicators can help evaluate the chemo-antiangiogenic efficacy in NSCLC more accurately.

Physical factors and angiogenesis

Angiogenesis consists of migration and mitosis of blood vessels and lymphatic endothelium. The control of angiogenesis is multifactorial, being determined by physical as well as chemical factors. The physical factors include contact, binding, scaffolds and barriers, attachment, spreading, lining and even phagocytosis. The vascular pattern in the skin suggests that epithelium is a principal influence on angiogenesis and that it may guide or obstruct the growth of its blood supply, using fibrin, collagen, elastin and ground substance as a means of exerting control. The hamster cheek pouch and the chorioallantoic membrane have been used to demonstrate that epithelium exerts both chemical and physical effects. There is a need for further investigation of mechanisms underlying the conversion of physical factors into chemical signals. They probably include the release of proteases or their inhibitors during the distortion of fibrillar material.

Role of mast cells in experimental tumour angiogenesis

Although the morphological features of angiogenesis are well documented and many promoting factors are known, the pharmacological mechanisms for the development of new vessels are not understood. Compounds found in platelets and/or mast cells--adenosine diphosphate, 5-hydroxytryptamine, histamine and heparin--caused endothelial cell growth stimulation in vitro: tumour angiogenesis factor did not. These same vasoactive compounds, as well as tumour angiogenesis factor, induced neovascularization on the chick chorioallantoic membrane. The increased vascularity produced by tumour angiogenesis factor was associated with considerable numbers of mast cells. These findings, together with an appreciation of the biochemical armoury of the mast cell and how its products could relate to the morphological steps of angiogenesis, and a realization that known anti-angiogenesis factors could all act through inhibition of mast cell products, strongly implicate the mast cell in the inductive mechanisms of neovascularization.

Human microvascular endothelial cells from different fetal organs demonstrate organ-specific CAM expression

In this work, we isolated and produced long-term cultures of human fetal endothelial cells (fECs) deriving from different organs of the same 12-week-old embryos. Highly pure endothelium cultures were obtained from specimens of brain, heart, lung, liver, aorta and kidney by using magnetic microspheres coated with CD31 or CD34 specific endothelial antibodies. The endothelial nature of these cells was confirmed by the presence of von Willebrand Factor (vWf), Flk-1/VEGFR2 and CD31. The fECs cultures showed organ-specific differences as regards to the morphological appearance, the growth rate and the expression of cellular adhesion molecules (CAMs) before or after stimulation by the inflammatory cytokines IL-1beta and TNF-alpha. For instance, TNF-alpha showed a specific effect on fetal heart ECs by stimulating E-selectin expression. Our findings indicate that fECs may represent an innovative tool to study differences among ECs of different vascular districts of the same individual, thus increasing the possibility to compare many pathological aspects of human adult and fetal microvasculature.

Effects of cyclophilin A on cell proliferation and gene expressions in human vascular smooth muscle cells and endothelial cells

BACKGROUND

Cyclophilin A (CypA) is a cytosolic protein which involves many biological functions including immune modulation, cell growth, tumorigenesis, and vascular disease. The objective of this study was to determine the effect of CypA on cell proliferation and several gene expressions in human endothelial cells and vascular smooth muscle cells.

METHODS

Human coronary artery endothelial cells (HCAEC), human lung microvascular endothelial cells (HMVEC-L), and human aorta smooth muscle cells (HAoSMC) were used in this study. Cells were treated with 10 nM CypA for 24 h. The cell proliferation was determined by [3H]thymidine incorporation. The mRNA levels of 13 genes including CD147 (receptor for CypA), PDGF-BB, endothelin-1 (ET-1), vascular endothelial growth factor receptor-1 (VEGFR-1), VEGFR-2, VEGFR-3, neuropilin-1 (NRP-1), NRP-2, eNOS, iNOS, nNOS, ICAM-1, and PECAM-1 were semiquantitatively determined by real time RT-PCR as standardized with a house keeping gene beta-actin.

RESULTS

CypA significantly increased cell proliferation of HAoSMC and HMVEC-L by 31% and 45%, respectively, as compared to controls, but had no effect on HCAEC. Blocking CD147 did not affect the mitogenic action of CypA. In addition, CypA also significantly increased the mRNA expression of CD147 by 43% and VEGFR-2 by 65% in HAoSMCs (P < 0.05, t test). HAoSMCs expressed much higher CD147 and neuropilin-1 (NRP-1) mRNA than HMVECs-L and HCAECs (P < 0.017, ANOVA). Furthermore, CypA increased ET-1 mRNA by 22% and VEGFR-1 mRNA by 23% in HMVECs-L, but had limited effects on HCAECs. HMVECs-L had much higher expressions of PDGF-BB, ET-1, VEGFR-2, VEGFR-1, VEGFR-3, and NRP-2 than HAoSMCs and HCAECs (P < 0.017, ANOVA). By contrast, HCAECs had much higher ICAM-1 mRNA levels than HMVECs-L and HAoSMCs (P < 0.017, ANOVA).

CONCLUSIONS

These data demonstrate that CypA has a mitogenic effect on HAoSMCs and HMVECs-L, but not HCAECs. CD147 may not mediate the action of CypA. In addition, CypA substantially alters the mRNA levels of several key genes in human vascular cells, indicating potential multifunctional roles of CypA in vascular system. Furthermore, this study provides several new aspects of gene expressions in vascular cells.

Human microvascular endothelial cells immortalized with human telomerase catalytic protein: a model for the study of in vitro angiogenesis

Human microvascular endothelial cell-1 (HMEC-1) generated by transfection with SV40 large T antigen has been the prevailing model for in vitro studies on endothelium. However, the transduction of SV40 may lead to unwanted cell behaviors which are absent in primary cells. Thus, establishing a new microvascular endothelial cell line, which is capable of maintaining inherent features of primary endothelial cells, appears to be extremely important. Here, we immortalized primary human microvascular endothelial cells (pHMECs) by engineering the human telomerase catalytic protein (hTERT) into the cells. Endothelial cell-specific markers were examined and the angiogenic responses were characterized in these cells (termed as HMVECs, for human microvascular endothelial cells). We found that VEGF receptor 2 (Flk-1/KDR), tie1, and tie2 expression is preserved in HMVEC, whereas Flk-1/KDR is absent in HMEC-1. In addition, HMVEC showed similar angiogenic responses to VEGF as HMEC-1. Furthermore, the HMVEC line was found to generate a prominent angiogenic response to periostin, a potent angiogenic factor identified recently. The data indicate that HMVEC may serve as a suitable in vitro endothelium model.

Differences in hyaluronic acid-mediated functions and signaling in arterial, microvessel, and vein-derived human endothelial cells

Hyaluronic acid (HA), a nonsulfated glycosaminoglycan, regulates cell adhesion and migration. Small HA fragments (3-25 disaccharide units) induce neovascularization. We investigated the effect of HA and a HA fragment (10-15 disaccharide units, F1) on primary human endothelial cells (ECs). Human pulmonary ECs (HPAEC) and lung microvessel ECs (HMVEC-L) bound HA (K(d) approximately 1 and 2.3 nm, respectively) and expressed 17,780 and 16,690 HA binding sites, respectively. Both ECs showed HA-mediated cell adhesion; however, HMVEC-L was 1.5-fold better. Human umbilical vein ECs neither bound HA nor showed HA-mediated adhesion. All three ECs expressed CD44 ( approximately 110 kDa). The expression of receptor for HA-mediated motility (RHAMM) (approximately 80 kDa) was the highest in HMVEC-L, followed by HPAEC and human umbilical vein ECs. RHAMM, not CD44, bound HA in all three ECs. F1 was better than HA and stimulated a 2. 5- and 1.8-fold mitogenic response in HMVEC-L and HPAEC, respectively. Both HA and F1 induced tyrosine phosphorylation of p125(FAK), paxillin, and p42/44 ERK in HMVEC-L and HPAEC, which was blocked by an anti-RHAMM antibody. These results demonstrate that RHAMM is the functional HA receptor in primary human ECs. Heterogeneity exists among primary human ECs of different vascular origins, with respect to functional HA receptor expression and function.

Levels of endothelial cell stimulating angiogenesis factor and vascular endothelial growth factor are elevated in psoriasis

Neovascularization appears to play an early and important part in the evolution of psoriatic plaques. We studied the distribution and production of two known angiogenesis factors, endothelial cell stimulating angiogenesis factor (ESAF) and vascular endothelial growth factor (VEGF), in the skin of patients with chronic plaque psoriasis and normal control subjects. Our results showed that tissue levels of ESAF and VEGF were significantly elevated in involved as compared with normal control skin (P = 0.006 and P < 0. 0001, respectively). Tissue levels of ESAF and VEGF were also raised in involved skin as compared with uninvolved skin in patients with psoriasis (P = 0.001 and P < 0.0001, respectively). Tissue levels of ESAF and VEGF in plaques of psoriasis correlated closely with the clinical severity of psoriasis (r = 0.6 and r = 0.9, respectively). Serum levels of ESAF and VEGF were significantly raised in patients with psoriasis as compared with control subjects (P = 0.001 and P = 0.02, respectively). In vitro culture studies revealed that ESAF is produced by both keratinocytes and fibroblasts in approximately equal quantities in normal skin, whereas VEGF is secreted predominately by keratinocytes. A similar pattern is seen in both involved and uninvolved skin of patients with psoriasis. However, there is increased secretion of both factors in keratinocytes and fibroblasts from involved and uninvolved skin as compared with normal control skin (P < 0.001). The increased levels and secretion in plaques of psoriasis of two molecules, ESAF and VEGF, known to promote new blood vessel formation, suggest a pathogenetic role for them in this disease.

Isolation and culture of human neuromicrovascular endothelial cells for the study of angiogenesis in vitro

Neovascularization in the adult central nervous system occurs as a response to several pathophysiological conditions such as ischemia, wound repair, or neoplasia. Endothelial cells from different blood vessel types, different organs, and different species are heterogeneous; therefore, the appropriate cell type should be used to study specific aspects of vascular pathology. We have developed a method to isolate human cerebral microvascular endothelial cells (CMECs) from small, freshly obtained specimens of normal brain adherent to human arteriovenous malformations (AVMs). The isolation procedure involves enzymatic digestions and gradient centrifugations, yielding over 95% pure primary cultures. Alternative isolation methods using magnetic beads, panning, or cloning were not superior with regard to cell purity or yield. CMECs were identified by their immunoreactivity for vWF, CD34, EN4, binding of Ulex europeus lectin, and uptake of DiI-Ac-LDL. They displayed ultrastructural features characteristic of blood-brain barrier endothelial cells and expressed GLUT-1. CMECs were subcultured; however, prolonged culture led to reduced culture purity. Vascular endothelial growth factor, basic fibroblast growth factor and hepatocyte growth factor/scatter factor stimulated the directional motility of CMECs, with dose-response profiles similar to human umbilical vein endothelial cells (HUVECs). In contrast, to stimulate proliferation, lower concentrations of growth factors tended to be necessary for CMECs than for the large vessel endothelial cells. CMECs formed capillary tube-like structures in an in vitro angiogenesis assay using matrigel. This study expands the spectrum of available tissue sources for the isolation of human neuromicrovascular endothelial cells, which are essential for the in vitro study of blood-brain barrier function and cerebral angiogenesis.

The effect of ALA and radiation on porphyrin/heme biosynthesis in endothelial cells

To study porphyrin biosynthesis in human microvascular endothelial cells, HMEC-1 cells, a transformed human microvascular endothelial cell line, were incubated with 5-aminolevulinic acid (ALA), the precursor of endogenous porphyrins, and porphyrin accumulation was measured spectro-fluorometrically. The HMEC-1 cells accumulated porphyrin in a concentration-related and a time-dependent fashion. Protoporphyrin was the predominant porphyrin accumulated in the cells. The effect of light on protoporphyrin accumulation was evaluated by exposing the ALA-loaded HMEC-1 cells to ultraviolet-A (UVA) and blue light, followed by another incubation with ALA for 2-24 h. Enhancement of protoporphyrin accumulation in irradiated HMEC-1 cells was observed 2-24 h after irradiation, which was associated with a decrease in ferrochelatase protein and activity. Porphyrin accumulation from ALA after irradiation was significantly decreased when catalase (750-3000 U/mL, 29.3-44.3% suppression) or superoxide dismutase (270 U/mL, 36.4% suppression) was present during irradiation. These data demonstrate that HMEC-1 cells were capable of porphyrin biosynthesis, and that exposure of protoporphyrin-containing HMEC-1 cells to UVA and blue light, which includes the Soret band spectrum, decreased the ferrochelatase activity and its protein. These changes were mediated, at least in part, by reactive oxygen species.

Characterization of expression and modulation of cell adhesion molecules on an immortalized human dermal microvascular endothelial cell line (HMEC-1)

We have recently reported the creation of the first immortalized cell line derived from human dermal microvascular endothelial cells (HMEC-1). In preliminary studies this line was found to closely resemble microvascular endothelial cells in regard to many phenotypic characteristics. Because two key functional features of endothelial cells are their ability to bind to peripheral blood leukocytes and extracellular matrix proteins via cell adhesion molecules, we have now characterized HMEC-1 in terms of expression and regulation of cell adhesion molecules of the integrin, immunoglobulin gene superfamily, and selectin families. HMEC-1 can either constitutively express or can be induced to express key integrins, including alpha-1, -2, -3, -4, -5, -6, and -V, as well as beta-1, -3, -4, and -5. They also express or are capable of expressing immunoglobulin gene superfamily molecules, such as intercellular adhesion molecule-1 and vascular cell adhesion molecule-1, and a member of the selectin family, E-selectin. A number of important cell adhesion molecules that are either constitutively expressed or that must be induced are regulated in a time- and dose-dependent fashion by selected cytokines. Experiments comparing the phenotypic characteristics of HMEC-1 with human dermal microvascular endothelial cells or human umbilical vein endothelial cells reveal HMEC-1 to have features of both small- and large-vessel endothelial cells.

Effects of media conditioned by a non-metastasizing human salivary gland adenocarcinoma cell clone and metastasizing clones from salivary gland and various other tissues on the proliferation, migration and protease production of bovine aortic endothelial cells in vitro

We demonstrate the role in tumor-associated angiogenesis of factors released into conditioned medium (CM) from in vitro human salivary gland cell clones with biological phenotypes ranging from non-metastasizing to metastasizing. A non-metastasizing human salivary gland adenocarcinoma cell clone HSGc and its subclone with metastatic potential (Gc2-100 cl-1) were employed. We also used metastasizing cell clones obtained by explant cultures of organs of Gc2-100 cl-1 tumor-bearing nude mouse. The proliferation and migration of bovine aortic endothelial (BAE) cells were significantly stimulated by the addition of CM obtained from Gc2-100 cl-1 and metastasizing cell clones, while CM from HSGc was ineffective. When the effect on protease secretion by BAE cells was examined, CM from Gc2-100 cl-1 and metastasizing cell clones inhibited the secretion of type IV collagenases by BAE cells much more than did CM from HSGc. These findings, therefore, may imply that Gc2-100 cl-1 and metastasizing cell clones secrete angiogenic factors that stimulate not only the proliferation and migration of endothelial cells but also the formation of basement membrane components necessary for the reconstruction of new blood vessels at migrated sites of endothelial cells by preventing the degradation of basement membrane component, type IV collagen.

HMEC-1: Establishment of an Immortalized Human Microvascular Endothelial Cell Line

The study of human microvascular endothelial cells has been limited, because these cells are difficult to isolate in pure culture, are fastidious in their in vitro growth requirements, and have a very limited lifespan. In order to overcome these difficulties, we have transfected human dermal microvascular endothelial cells (HMEC) with a PBR-322-based plasmid containing the coding region for the simian virus 40 A gene product, large T antigen, and succeeded in immortalizing them. These cells, termed CDC/EU.HMEC-1 (HMEC-1), have been passaged 95 times to date and show no signs of senescence, whereas normal microvascular endothelial cells undergo senescence at passages 8-10. HMEC-1 exhibit typical cobblestone morphology when grown in monolayer culture, express and secrete von Willebrand's Factor, take up acteylated low-density lipoprotein, and rapidly form tubes when cultured on matrigel. HMEC-1 grow to densities three to seven times higher than microvascular endothelial cells and require much less stringent growth medium. HMEC-1 will grow in the absence of human serum, whereas microvascular endothelial cells require culture medium supplemented with 30% human serum. These cells express other cell-surface molecules typically associated with endothelial cells, including CD31 and CD36 and epitopes identified by monoclonal antibodies EN4 and PAL-E. They also express the cell adhesion molecules ICAM-1 and CD44 and following stimulation with interferon-gamma express major histocompatibility complex class II antigens. HMEC-1 specifically bind lymphocytes in cell adhesion assays. Thus HMEC-1 is the first immortalized human microvascular endothelial cell line that retains the morphologic, phenotypic, and functional characteristics of normal human microvascular endothelial cells.

Characterization of angiogenin receptors on bovine brain capillary endothelial cells

The mitogenic effect of bovine milk angiogenin was studied on bovine brain capillary and aortic endothelial cells, smooth muscle cells and fibroblasts. The proliferation of only bovine brain capillary endothelial cells was detected at concentrations ranging from 10 to 1,000 ng/ml, with a maximum effect at 100 ng/ml. This mitogenic activity may be correlated with a specific binding of angiogenin which was demonstrated only to bovine brain capillary endothelial cells. [125I]-labeled angiogenin binding was time and concentration dependent and saturable. Scatchard analyses of binding data showed evidence of a single class of binding sites with an apparent dissociation constant of 5.10(-10)M. The molecular mass of the angiogenin receptor (49 kDa) was determined by ligand blotting.

Myointimal hyperplasia: pathogenesis and implications. 1. In vitro characteristics

Myointimal hyperplasia (MIH) is an arterial wall smooth muscle cell (SMC) proliferative disorder. This process is responsible for a significant number of early and long-term arterial reconstructive and graft failures. Histopathologically, this process is characterized by a proliferation of SMC in the intima of traumatized arteries resulting in arterial and/or anastomatic stenosis with secondary thrombosis. In vitro studies of cultured SMC have allowed the evaluation of SMC response to factors suspected of being clinically associated with MIH. Principal among these is platelet derived growth factor (PDGF), which is known to be secreted by several cell types including endothelial cells (ECs) and monocytes as well as being stored and secreted by platelets. PDGF, somatomedin-C, epithelial growth factor, insulin, and other factors have been found to significantly increase SMC replication in vitro. Lipoproteins may be important substrates for SMC proliferation in contrast to heparin, which may directly inhibit SMC protein synthesis. Unlike SMCs, whose continued growth in culture is dependent on various growth factors and nutrients, ECs essentially cease to proliferate after the cells have formed a monolayer over the available surface. Extracellular matrix proteins, polypeptide mitogens, and heparin have been shown to modify EC migration and proliferation in vitro. Wounding of EC monolayers by scratching results in increased replication and migration, processes which require plasma factors that remain poorly defined. However, two general forms of EC growth factor have been isolated from many body tissues, are potent stimulators of capillary endothelial growth, and appear important both for normal EC monolayer homeostasis and for the response to injury. Cultured ECs produce mitogens for SMC. Production of the principal mitogen, PDGF, is significantly increased in sparse versus confluent cell cultures as well as by toxic agents such as endotoxin and phorbol esters. Acetyl low density lipoprotein as well as omega-3 fatty acids may significantly and selectively inhibit EC PDGF production, a finding with potentially profound implications for the clinical control of MIH in vivo.

Low molecular weight angiogenesis factors

A number of substances have been proposed for the role of angiogenesis factors. Many of these are of protein origin and are therefore amenable to the tools of the molecular biologist. However a number of low molecular weight angiogenesis factors are emerging as important initiators and/or cofactors of neovascularization. Of these a number are known to stimulate angiogenesis indirectly, possibly through an inflammatory response. Some putative angiogenic factors stimulate microvessel endothelial cells nonspecifically, also causing migration and proliferation of large vessel cells. Others are specific for microvessel cells either for stimulating migration, proliferation or both. The nature and action of the low molecular weight factors in vivo and in vitro are reviewed.

Gangliosides, copper ions and angiogenic capacity of adult tissues

The report summarizes the work of our laboratory aimed at improving the understanding of the angiogenic response of adult tissues, an event that transforms a micro-embolus of neoplastic cells into a growing metastasis. Attention has been focused on tumor-induced angiogenesis. The following aspects of the subject are discussed: (a) relationship between size of vascular network and tumor growth rate or tumor cell population; (b) angiogenic capacity of tumors and role that prostaglandin E1 may have as an angiogenesis factor; (c) relationship between acquisition of angiogenic capacity and neoplastic transformation of a cell population; (d) modification of tissue composition at the onset of angiogenesis; (e) behaviour of copper ions and copper carriers in the course of the angiogenic response; (f) the influence of gangliosides on endothelial cell motility, survival and growth in vitro; (g) modulation of the angiogenic response by gangliosides (GM1, GT1b) in vivo.

Identification of hypoxanthine and inosine in brain dialyzable fraction as stimulators for growth of porcine aortic endothelial cells in response to fibroblast growth factor in either dialyzed serum media or low serum media

The rate of proliferation of porcine aortic endothelial cells (PAEC) in response to fibroblast growth factor (FGF) was largely retarded when incubated in Dulbecco's modified Eagle's medium (DMEM) supplemented with either 1% fetal bovine serum (FBS) or 10% dialyzed FBS in place of 10% FBS. Proliferation of endothelial cells in low serum media in response to FGF was enhanced to the level of media containing FGF plus 10% FBS by the addition of the dialyzable fraction from bovine brain homogenates. From the bovine brain dialyzable fraction, two active components were purified and identified as hypoxanthine and inosine. Either hypoxanthine or inosine, at a dose of 5 microM in DMEM with 1% FBS, maximally increased the incorporation of [3H]thymidine into DNA of PAEC in low serum media in the presence of FGF. However, no additive effect was observed when hypoxanthine and inosine were added simultaneously. The present data indicate that the proliferative action of FGF on PAEC can be potentiated by hypoxanthine and inosine.

Fibroblast growth factor-stimulated growth of porcine aortic endothelial cells depends on hypoxanthine in fetal bovine serum in culture media

The rate of proliferation of porcine aortic endothelial cells (PAEC) in response to stimulation of fibroblast growth factors (FGFs) was largely retarded in media supplemented with 10% dialyzed fetal bovine serum (FBS) in place of nondialyzed FBS. This inhibition was overcome by supplement of dialyzable fraction, and hypoxanthine was purified from the dialyzable fraction as the active compound which stimulated the basal and FGF-dependent growth rates of dialyzed FBS-treated PAEC. Addition of hypoxanthine (5 microM) to media with 10% dialyzed FBS containing FGFs (10 ng/ml) markedly increased the rate of both cell proliferation and DNA synthesis of PAEC, and their maximal levels were comparable to those attained by cells in media with 10% nondialyzed FBS. Hypoxanthine changed the spindle-like morphology of dialyzed FBS-treated PAEC even in the presence of FGFs into the cobblestone-like morphology of regular PAEC in media with 10% FBS.

Establishment of human mucosal microvascular endothelial cells from inferior turbinate in culture

Human microvascular endothelial cells were isolated and cultured from the mucosa of inferior turbinates. Using dish-coated collagen and a medium composed of a 1:1 mixture of sarcoma 180-conditioned medium and Dulbecco's modified Eagle's medium (containing 10% fetal bovine serum and 75 micrograms/mL endothelial cell growth factors prepared from bovine pituitary glands), these cells grew rapidly to confluence and survived serial passages until the 16th population doubling level. The cells were identified as endothelial cells by their morphology, immunostaining of factor VIII antigen, and cytochemical staining with Ulex europeus agglutinin. Furthermore, Weibel-Palade bodies and numerous pinocytotic vesicles were confirmed by electron microscopy. Proliferation experiments demonstrated the need for either endothelial cell growth factor or tumor-conditioned medium. An exogenous matrix was also required for these cells in tissue culture. A tubule-like morphology appeared in the original monolayer of human microvascular endothelial cells after 1 month in the same plate, indicating that these cells have the ability to form tubules in the presence of sarcoma 180-conditioned medium.

The effect of a native collagen gel substratum on the synthesis of collagen by bovine brain capillary endothelial cells

Cultured capillary endothelial cells, derived from bovine brain, and maintained on a plastic substratum synthesized predominantly interstitial collagens of which approximately 75 per cent were secreted into the medium. When grown on a native hydrated collagen type I gel, although no marked alteration in the 'collagen synthetic pattern' was observed, the overall level of collagen synthesis was increased by approximately 100 per cent. More dramatic, however, was the alteration in the distribution of these molecules between medium and cell layer. Interstitial collagens produced by cells grown on collagen gels were almost exclusively associated with the cell layer or collagenous gel. These studies, thus, demonstrate that an extracellular matrix may exert a considerable influence on the cellular synthetic activities and possibly cellular polarity of capillary endothelial cells.

Induction of endothelial cell migration by proline analogs and its relevance to angiogenesis

The proline analogs cis-4-hydroxy-L-proline, 3,4-dehydro-L-proline, and 2-azetidinecarboxylic acid induced increases in the migration rate of retinal capillary endothelial cells, aortal endothelial cells, corneal endothelial cells, aortal smooth muscle cells, and retinal pericytes. cis-4-hydroxy-D-proline did not. The optimal concentration for migration induction by any of the active agents was approximately 10(-5) M. At higher concentrations (5 x 10(-4) M) migration was not induced or was inhibited. When tested by subcutaneous implant assays in rabbits, cis-4-hydroxy-L-proline and 2-azetidinecarboxylic acid consistently elicited a marked angiogenic response. Whereas these compounds are known to modulate collagen synthesis and secretion, the concentrations at which they are effective inducers of migration suggest that they may have a more specific target than general collagen synthesis.

Retinal capillary endothelial cells prefer different substrates for growth and migration

Recent studies have shown that the extracellular matrix modifies the behaviour of endothelial cells. We have studied the effects of extracellular matrix components on retinal capillary endothelial cell migration and proliferation. Bovine retinal capillary endothelial cells were selectively cultured from collagenase-digested microvessel fragments. In a filter system for the assessment of migration, endothelial cells responded to substrate-bound fibronectin but not to soluble fibronectin. Cell migration on collagen- or gelatin-coated filters was minimal, and these cells failed to adopt a spread morphology, remaining instead as round cells. Cell replication was quantified using a protein dye binding assay for adherent cells in 96 well plates. Serum was essential for growth irrespective of the substrate. Cells harvested from microvessel cultures proliferated more rapidly on collagen- and gelatin-coated plastic than on fibronectin and were unaffected by additions to the medium such as endothelial cell conditioned medium, whereas cells proliferating directly from the microvessels grew at a faster rate on fibronectin and also responded to conditioned medium supplement. When cultured on collagen gels, initial microvessel cells and harvested cells required surface fibronectin in order to adopt a cobblestone morphology. These results show that fibronectin is a requirement for bovine retinal capillary endothelial cell migration, but proliferation of these cells can be supported, with slight differences, by both fibronectin and collagen provided serum growth factors are present. These findings are relevant to the early phase of angiogenesis in which migration and proliferation of endothelial cells occurs.

Heterogeneity in endothelial cells from large vessels and microvessels

The successful isolation and culture of vascular endothelial cells has led to an upsurge of interest in their role in such diverse processes as thrombogenesis, atherosclerosis and tumour growth. In this article we have outlined methods for the culture and characterization of endothelial cells from large vessels, capillary and post-capillary venules of lymph nodes. Comparison of their immunological and metabolic properties illustrates the heterogeneity within the vasculature. The effect of growth and angiogenic factors on these cells and the efficacy of their use in culture medium is considered.

A synergistic effect on microvessel cell proliferation between basic fibroblast growth factor (FGFb) and endothelial cell stimulating angiogenesis factor (ESAF)

Stimulation of microvessel endothelial cells grown on collagen gels by endothelial cell stimulating angiogenesis factor was confirmed (1). The potent endothelial cell growth stimulating activity of basic fibroblast growth factor has also been demonstrated for cells grown on collagen gels. However, the growth factor activity of basic fibroblast growth factor towards microvessel endothelial cells was almost eliminated when experiments were carried out in the presence of diafiltered foetal calf serum, but was partially restored by the addition of endothelial cell stimulating angiogenesis factor to medium containing the diafiltered serum. In contrast to these observations, foetal skin fibroblasts were stimulated by basic fibroblast growth factor when grown in medium with diafiltered serum, and this stimulation was not modified by the presence of endothelial cell stimulating angiogenesis factor.

Phorbol esters induce angiogenesis in vitro from large-vessel endothelial cells

We have shown previously that the tumor promoter phorbol myristate acetate (PMA) induces capillary endothelial cells grown on the surface of three-dimensional collagen gels to invade the underlying matrix as capillary-like tubular structures, a phenomenon mimicking angiogenic processes that occur in vivo (Montesano and Orci: Cell 42:469, 1985). To establish whether the potential to invade the extracellular matrix as capillary-like sprouts is restricted to microvascular endothelial cells or is also shared by large vessel endothelium, we have examined the response to PMA of endothelial cells isolated from the human umbilical vein and the calf pulmonary artery. The results of these experiments show that both types of macrovascular endothelial cells are able to penetrate into collagen gels as vessel-like tubes following treatment with PMA. This demonstrates that endothelial cells derived from large vessels can, in response to appropriate signals, express invasive properties thought to be associated specifically with capillary endothelial cells in vivo.

Therapy of spontaneously metastatic HSV-2 induced hamster tumours with cortisone acetate administered with or without heparin

Subcutaneous injection of cortisone acetate administered with or without oral heparin retarded the growth of two HSV-2 induced hamster fibrosarcomas. Histological sections showed no obvious difference between the vasculature of treated and untreated tumours although there were fewer infiltrating lymphocytes in treated tumours. Treatment was, however, found to be ineffective against metastatic development following resection of primary tumours. Natural killer cell activity was found to be greatly reduced in animals receiving heparin and/or cortisone acetate treatment and this may influence the effectiveness of treatment on the metastatic process. We conclude that treatment of tumours with cortisone plus heparin is no different from the response to cortisone used alone.

The isolation and culture of endothelial cells and pericytes from the bovine retinal microvasculature: a comparative study with large vessel vascular cells

Endothelial cells (BREC) and pericytes (BRP) were isolated from the bovine retinal microvasculature. These cells were first identified by morphological criteria and by their differential staining for Factor VIII related antigen. BREC and BRP responded differently to a number of experimental parameters in vitro; for example, the plating efficiency of BREC was enhanced by the use of a gelatin substratum and medium conditioned by either endothelial cells or pericytes; oxygen tension had no effect. In contrast, the plating efficiency of BRP was only enhanced by low oxygen tension. Conditioned media also stimulated the proliferation of BREC, but not that of BRP. The saturation density reached by BREC was dependent on the initial plating density while BRP plated at different initial densities reached the same final density. The in vitro behavior of the retinal microvascular cells was also compared to that of large vessel (aorta) endothelial cells (BAEC) and smooth muscle cells (SMC). Aortic and retinal endothelial cells showed similar morphology and behavior. When initially plated as a homogeneous cell suspension within a collagen matrix, both BREC and BAEC self-associated to form three-dimensional meshworks; this morphogenesis was accomplished by cell migration and did not involve cell proliferation. By contrast, BRP and SMC divided and remained homogeneously distributed when plated within a collagen gel matrix. BRP and SMC did, however, behave differently when plated on the surface of a collagen gel; SMC migrated extensively into the gel while BRP remained confined to the gel surface. BRP grown on any substratum began to retract upon themselves shortly after confluence, producing characteristic nodules interconnected by cellular strands. BRP and SMC were able to contract a collagen gel substratum, while retinal and aortic endothelial cells were unable to do so. These results provide new means for the in vitro characterization of endothelial cells, smooth muscle cells and pericytes.

Expression of organ-specific antigens on capillary endothelial cells

Our central thesis is that the endothelial cells which line capillaries of various organs are not all alike. Using monoclonal and conventional antibodies we demonstrate that capillary endothelial cells express on their cell surface an array of antigens that manifest organ selectivity. Brain-derived endothelial cells possess brain-associated antigens, ovary-derived endothelial cells share antigenic markers with other ovarian cells, and lung-derived endothelium possesses antigens that are primarily expressed on cells of the lung. Our experiments lead us to suggest that organ-associated determinants on the endothelial cell surface may play a role in the selective adhesion of tumor cells during metastasis, in site-limited vascular pathology, and in the regionally limited release of angiogenesis-induced factors.

Tumor-derived angiogenesis factors from rat Walker 256 carcinoma: an experimental investigation and review

Angiogenesis, the process of developing a hemovascular network, is an essential feature of the growth of solid tumors, and is induced by factors secreted by tumor cells. Assay procedures suitable for the investigation of angiogenesis, and for the screening of angiogenesis factors during purification are reviewed; and a number of reports describing the purification of angiogenesis factors, primarily from the rat Walker 256 carcinoma as starting material, are discussed. Work from the authors' laboratory is also presented. Walker 256 cells grown in large-scale culture were the source of a reproducible and homogeneous source of angiogenic material. Factors secreted by these cells were isolated by a series of chromatographic steps. Ion exchange chromatography on carboxymethyl-Sephadex produced two active fractions, one of which was fractionated into several macromolecular species by lectin affinity and hydrophobic adsorption chromatography. The other gave a high mol.wt, active fraction that was resolved into a low mol.wt, active component and a non-angiogenic but possibly carrier molecule with a mol.wt of 140,000. While none of the angiogenic factors were identified chemically, the results demonstrate the existence of both high and low mol.wt tumor-secreted angiogenic substances, confirming the hypothesis for tumor-induced angiogenesis and predicting potential means to interfere with the process of tumor growth.

A study of angiogenesis factors from five different sources using a radioimmunoassay

The use of a radioimmunoassay (RIA) demonstrated that angiogenic factors from human and animal tumours, normal bovine retinas, myocardial infarcts, synovial fluid from patients with joint diseases and wound fluid shared common antigenic determinants. Values for angiogenesis factors expressed as microgram Walker tumour TAF/mg protein varied from 0.8 (wound fluid) to 207 (myocardial infarct). Activated macrophages produced an angiogenic factor which did not cross-react. Normal tissue extracts which were non-angiogenic by the chicken chorioallantoic membrane assay also failed to cross-react in the RIA. The antigenic similarity of angiogenic factors from such a wide variety of sources suggests that, in order to minimize therapeutic side effects, it would be best to use angiogenic agonists and antagonists locally.

Tumor angiogenesis

The hypothesis that tumors are angiogenesis dependent has, in the past decade, generated new investigations designed to elucidate the mechanism of angiogenesis itself. Many laboratories are now engaged in this pursuit. Some are studying angiogenesis that occurs in physiological situations, whereas others are interested in angiogenesis that dominates pathological conditions. These efforts have led to (1) the development of bioassays for angiogenesis; (2) the partial purification and, in one case, the complete purification of angiogenic factors from neoplastic and non-neoplastic cells; (3) the development of new polymer technology for the sustained release of these factors and other macromolecules in vivo; (4) the cloning and long-term culture of capillary endothelial cells; (5) the demonstration of the role of nonendothelial cells, such as mast cells in modulating angiogenesis; (6) the discovery of angiogenesis inhibitors; and (7) the demonstration that certain animal tumors will regress when angiogenesis is inhibited. The effects of angiogenesis inhibitors provide perhaps the most compelling evidence for the role of angiogenesis in tumor growth. It is conceivable that the original effort to understand the role of angiogenesis in tumor growth will also lead to the use of angiogenesis inhibitors as a new class of pharmacologic agents in a variety of non-neoplastic diseases such as arthritis, psoriasis, and ocular neovascularization. However, much work remains to be done before it will be possible to understand (1) the regulatory systems that govern capillary density in normal tissues; (2) the factors that maintain the viability of microvascular endothelium; (3) the development of the vascular system itself; and (4) the mechanism by which vascular regression occurs, both in the embryo and in the postnatal organism. A knowledge of the mechanisms which underlie these normal processes may help to enlarge our comprehension of tumor angiogenesis.

Heparin affinity: purification of a tumor-derived capillary endothelial cell growth factor

A tumor-derived growth factor that stimulates the proliferation of capillary endothelial cells has a very strong affinity for heparin. This heparin affinity makes it possible to purify the growth factor to a single-band preparation in a rapid two-step procedure. The purified growth factor is a cationic polypeptide, has a molecular weight of about 18,000, and stimulates capillary endothelial cell proliferation at a concentration of about 1 nanogram per milliliter.

Angiogenesis of cultured endothelial cells of bovine coronary artery

Endothelial cells of bovine coronary artery were isolated and cultivated and bovine clots were placed in the cultured endothelial cells (42 generations), followed by observation on the 14th day. Cultured endothelial cells not only covered the surface of each clot but also migrated in it to form oval or irregularly shaped intracytoplasmic vacuoles or sometimes intercellular vacuoles surrounded by 2 or 3 cells. Some of these vacuoles contained membranous materials. This vacuolization was considered to represent angiogenetic activity peculiar to endothelial cells.

Angiogenic factors and their assay: activity of formyl methionyl leucyl phenylalanine, adenosine diphosphate, heparin, copper, and bovine endothelium stimulating factor

A number of chemically unrelated substances have been compared for their neovasculogenic activity by two different in vivo tests, and for their ability to induce cultured endothelial cell migration and proliferation. Formyl methionyl leucyl phenylalanine, copper ions, heparin, adenosine diphosphate, and low-molecular-weight bovine endothelium stimulating factor were all neovasculogenic by the corneal pocket assay. By the chorioallantoic membrane assay, copper ions and formyl methionyl leucyl phenylalanine were not detectably neovasculogenic. By the same assay it has been possible to demonstrate angiogenic activity in bovine endothelium stimulating factor that is distinguishable from copper ions. This bovine factor, in contrast to the other agents, induced marked endothelial cell migration and also proliferation and may belong to a special class of agents which represents direct acting angiogenic activity.

Tumour angiogenesis

A variety of different factors has been implicated in inducing angiogenesis. Their identity and precise mechanisms of action remain elusive. The present treatise summarises the state of our knowledge not only in relation to tumour-induced capillary growth but also for non-neoplastic situations and mechanisms.

Human lung tumour cell line adapted to grow in serum-free medium secretes angiogenesis factor

A human lung tumour cell line has been grown in serum-free medium for 12 months and during this period cells were subcultured every 4 days. The culture medium contained an angiogenesis factor which has been purified and shown to be similar to that isolated from other sources including solid tumours. This is the first report that demonstrates de novo synthesis and secretion of angiogenesis factor by a cell line adapted to grow in a serum-free medium.

Angiogenesis factor from human myocardial infarcts

5 of 8 infarcted human myocardial tissues were shown to contain an angiogenesis factor which resembles that obtained from solid tumours. The concentration of angiogenesis factor, measured by radioimmunoassay, was similar to that in tumours. It is suggested that the myocardial-infarct angiogenesis factor modulates collateral enlargement or ingrowth of new blood vessels in the infarcted tissues.

Activation of a procollagenase by low-molecular-weight angiogenesis factor

Avascular tumours have the ability to establish a blood supply for themselves by secreting a humoral factor which stimulates their host's endothelial cells to proliferate and to migrate towards the tumour source. The mechanism of action of such a humoral angiogenesis factor is more than that of an endothelial-cell growth factor since it requires an oriented migration of cells towards the tumour. We report here the activation of pure skin-fibroblast procollagenase by a low-molecular-weight angiogenesis factor capable of stimulating endothelial-cell growth in vitro. The activation was observed when either Type I or III collagen was used as substrate. It is suggested that at least one function of angiogenesis factor is to promote limited degradation of the connective tissue through which it passes causing channeling in the matrix along which stimulated endothelial cells may migrate.