Significant Angiogenic Effects Research Articles

Horse serum or equine platelet lysate increases total vascular endothelial growth factor A concentrations and correlates with vascular growth in an equine facial arterial ring assay.

To evaluate ex vivo angiogenesis of equine arterial rings in response to various growth media. Facial arteries were dissected from 11 horses post-euthanasia. Equine platelet lysate (ePL) was harvested from 6 horses. Arteries were exposed to endothelial growth media (EGM) + horse serum (HS) for first sprout (FS), vascular regression (VR), and (basement membrane matrix [Matrigel]) lysis (ML) evaluation. Additional rings supplemented with (1) EGM, (2) EGM + EDTA, (3) endothelial basal media (EBM), (4) EBM + HS, or (5) EBM + human VEGF were compared for vascular network area (VNA) and maximum network growth (MNG). Additional rings exposed to EGM + ePL at 10-(10xePL), 5-(5xePL), or 2-fold (2xePL) increases from baseline platelet concentration, EGM + HS, EGM + platelet-poor plasma (PPP), EBM + PPP and EBM were analyzed for branch number, density, VNA, and VEGF-A concentration from days 0-3. Arteries demonstrated sprouting in Matrigel supplemented with EBM alone. EGM + HS exposure resulted in no differences in FS (P = .3934), VR (P = .0607), or ML (P = .2364) between horses. VNA in EGM + HS was greater than EBM (P = .0015). MNG was greater in EGM + HS, EBM + HS, and EBM + hVEGF compared with EBM (P = .0001). ePL treatment did not have an overall significant angiogenic effect compared with supplementation with HS, PPP, or EBM alone; however, VEGF-A concentrations were higher for EGM + 10xePL, EGM + 5xePL, and EGM-HS compared with EBM and positively correlated with VNA (P = .0243). Equine arterial rings serve as an ex vivo model for angiogenesis but have a high degree of variability. HS, PPP, or ePL support vascular growth, and HS and ePL may stimulate the secretion and be sources of VEGF-A.

Glucose withdrawal induces Endothelin 1 release with significant angiogenic effect from first trimester (FTM), but not term human umbilical cord perivascular cells (HUCPVC).

Perivascular cells (PVC) and their "progeny," mesenchymal stromal cells (MSC), have high therapeutic potential for ischemic diseases. While hypoxia can increase their angiogenic properties, the other aspect of ischemic conditions-glucose shortage-is deleterious for MSC and limits their therapeutic applicability. Regenerative cells in developing vascular tissues, however, can adapt to varying glucose environment and react in a tissue-protective manner. Placental development and fetal insulin production generate different glucose fluxes in early and late extraembryonic tissues. We hypothesized that FTM HUCPVC, which are isolated from a developing vascular tissue with varying glucose availability react to low-glucose conditions in a pro-angiogenic manner in vitro. Xeno-free (Human Platelet Lysate 2.5%) expanded FTM (n = 3) and term (n = 3) HUCPVC lines were cultured in low (2mM) and regular (4mM) glucose conditions. After 72h, the expression (Next Generation Sequencing) and secretion (Proteome Profiler) of angiogenic factors and the functional angiogenic effect (rat aortic ring assay and Matrigel™ plug) of the conditioned media were quantified and statistically compared between all cultures. Low-glucose conditions had a significant post-transcriptional inductive effect on FTM HUCPVC angiogenic factor secretion, resulting in significantly higher VEGFc and Endothelin 1 release in 3days compared to term counterparts. Conditioned media from low-glucose FTM HUCPVC cultures had a significantly higher endothelial network enhancing effect compared to all other experimental groups both in vitro aortic ring assay and in subcutan Matrigel™ plugs. Endothelin 1 depletion of the low-glucose FTM HUCPVC conditioned media significantly diminished its angiogenic effect CONCLUSIONS: FTM HUCPVC isolated from an early extraembryonic tissue show significant pro-angiogenic paracrine reaction in low-glucose conditions at least in part through the excess release of Endothelin 1. This can be a substantial advantage in cell therapy applications for ischemic injuries.

Neurohormonal Regulation of Tumor Growth

Neurohormones vasopressin and oxytocin are synthesized in the hypothalamus and are transported along the axons to the neurohypophysis as a part of equimolar complexes with hormone-specific neurophysins. The tumors of epithelial origin synthesize ectopic vasopressin and have an ability to express all types of receptors of neurohypophysis hormones. Vasopressin and oxytocin receptors provide the transduction of signals to protein kinases A, B, and C and activate intracellular cascades of the CREB, MDM2, and TORC1/2 proteins and mitogen-activated protein kinases. Central endocrine and autocrine neurohormonal contours are involved in the regulation of proliferative, migration, and angiogenic processes accompanied by tumor progression. Tumor growth and development occur in close cooperation with the supporting stroma. The interstitial tissue is involved in signal communication of tumor cells by integrins and integral CD44 glycoproteins formulating hyaluronic acid. Hyaluronic acid metabolites modulate the effect of neurohormones and peptide growth factors; intermediate hyaluronan fragments with molecular weight of approximately 20 kDa elicit the most significant angiogenic effect. Platelets expressing AVPR1 vasopressin receptors are an important source of hyaluronidase 2 hydrolyzing macromolecular hyaluronan to fragments of intermediate length. The AVPR2 receptors localized in endothelium and AVPR1-AVPR2 vasopressin receptors expressing themselves in the tumor cells are involved in the mechanisms controlling local hemostasis. Neurohormonal regulatory contours are involved in optimization of the balance of inducing and inhibiting signals generated by the tumor and stroma in the process of progressive growth.

Hirudin promotes angiogenesis by modulating the cross-talk between p38 MAPK and ERK in rat ischemic skin flap tissue.

Hirudin's ability to increase angiogenesis in ischemic flap tissue and improve the flaps survival has been demonstrated in our previous studies. However, the knowledge about hirudin functional role in angiogenesis is still limited. In the present study, we investigate the effects of locally injected hirudin on the expression of VEGF, endostatin and thrombospondin-1 (TSP-1) using rat model. Caudally based dorsal skin flaps were created and were treated with hirudin or normal saline. Result showed that the flap survival was improved by hirudin treatment relative to the control. Treatment of flaps with hirudin exerted significant angiogenic effect as evidenced by increased VEGF expression and reduced endostatin and TSP-1 production (p<0.01), and promoted neovascularization (microvascular density, p<0.01). Moreover, hirudin treatment increased the ERK1/2 phosphorylation, while attenuated the phosphorylation of p38 MAPK, and the addition of thrombin could reverse these effects of hirudin on ERK1/2 and p38 MAPK activity. The MEK inhibitor blocked the hirudin-induced VEGF expression, and the p38 MAPK inhibitor attenuated the thrombin-induced TSP-1 expression. Furthermore, a specific inhibitor of p38 MAPK activates ERK1/2 in ischemic flaps, suggesting that cross-talk between p38 MAPK and ERK might exist in rat ischemic flap tissue. Moreover, either the hirudin or SCH79797 (PAR1 antagonist) could attenuate the p38 MAPK phosphorylation and increases the ERK1/2 phosphorylation, indicating that the cross-talk between p38 MAPK and ERK1/2 modulated by thrombin/PAR1 signaling may participate in the process of hirudin-stimulated ERK1/2 signaling. In conclusion, these observations suggest that hirudin exerts its angiogenesis effect by regulating the expression of angiogenic and antiangiogenic factors via a cross-talk of p38 MAPK-ERK pathway.

Dual gene transfer of bFGF and PDGF in a single plasmid for the treatment of myocardial infarction

Basic fibroblast growth factor (bFGF) and platelet-derived growth factor (PDGF) have been shown to be involved in a spectrum of cellular processes. In a previous study, we constructed a novel multigenic vector that contained two separate transcription units, each consisting of a strong promoter and an efficient polyadenylation signal. The two promoters were chosen for their ability to work simultaneously. Dual gene transfer of bFGF and PDGF in a single plasmid resulted in a significant increase in collateral blood vessel formation in a rabbit model of hind limb ischemia. The aim of the present study was to investigate the effect of this dual gene transfer strategy in a rat model of acute myocardial infarction (AMI). AMI was induced in rats by ligation of the left anterior descending coronary artery. The animals were randomly divided into four groups and treated with the following therapeutic strategies: Empty plasmid (control), plasmid encoding bFGF (PL-bFGF), plasmid encoding PDGF (PL-PDGF) or plasmid encoding bFGF and PDGF (PL-F-P). Echocardiography and histological examinations were performed 28 days subsequent to gene transfer. Dual gene therapy with bFGF and PDGF resulted in a significant angiogenic effect accompanied by vessel maturation, along with a significant reduction in infarct size and improvement in cardiac function. In a rat model of AMI, single plasmid-mediated dual gene therapy with bFGF and PDGF decreased infarct size and improved cardiac function due to the formation of functionally and morphologically mature vasculature. These results are relevant to the ongoing clinical trials involving the use of single plasmid-mediated angiogenic factors for the treatment of myocardial ischemic disease.

Phenotypic modulation of human cardiospheres between stemness and paracrine activity, and implications for combined transplantation in cardiovascular regeneration

As the search for new cell types for cardiovascular regeneration continues, it has become increasingly important to optimize ex vivo cell processing. We aimed to develop an optimal processing strategy for human cardiac progenitor cells. We hypothesized that enhancing the stemness potential and promoting the secretory activity for paracrine effects are mutually exclusive routes. Therefore, we investigated the two divergent cell processing methods to enhance cellular potency and humoral activity, respectively. We obtained human right ventricular tissues and sequentially generated primary cardiosphere (CS), primary CS-derived cells (PCDC) and secondary CSs. During secondary CS formation, inhibiting the ERK pathway, using selective RTK1 and TGF-β inhibitors, Oct4 increased 20 fold and VEGF was decreased. When the ERK pathway was stimulated by addition of EGF and TGF-β, VEGF expression was upregulated and Oct4 was downregulated, indicating that the ERK pathway serves a directional role for cellular potency versus paracrine capacity. Transplantation of PCDCs or secondary CSs into the infarcted heart of immunocompromised mouse showed significant angiogenic effects compared with PBS injection. Interestingly, combined transplantation of the two differently-processed, dual-purpose secondary CSs resulted in an additional increase in neovascularization. Human VEGF was primarily produced from secondary CSs under ERK stimulating conditions. Cardiomyocyte-like cells were produced from secondary CSs under ERK inhibitory conditions. These findings indicate that combined transplantation of specifically-processed human secondary CSs enhances infarct repair through the complementary enhancement of cardiopoietic regenerative and paracrine protective effect. Furthermore, these results underscore the fact that optimal cell processing methods have the potential to maximize the therapeutic benefits.

The effects of bosentan on thrombin‐activated fibroblasts and endothelial cells

Endothelin‐1 and thrombin are elevated during lung injury and repair, as seen in scleroderma and other interstitial lung diseases, and each plays important roles in remodeling epithelium, blood vessels and connective tissue. Both factors promote myofibroblast differentiation, the hallmark of pulmonary fibrosis. Here we show that thrombin significantly induces endothelin‐1 expression in human lung fibroblasts. Bosentan, the dual, specific and competitive inhibitor of endothelin, significantly decreases α‐SMA, collagen gel contraction, and proliferation of human lung fibroblasts stimulated by thrombin, suggesting that thrombin‐induced differentiation of fibroblasts to the myofibroblast phenotype is at least in part regulated by endothelin‐1. Moreover, bosentan inhibits the basal level of fibroblast proliferation suggesting that endogenous endothelin may be in part responsible for fibroblast proliferation. The effect of bosentan on endothelial cells is concentration dependent. At concentrations of 10μM and 100μM bosentan inhibits thrombin‐induced endothelial cell migration and angiogenesis, whereas low‐dose (10nM) bosentan demonstrates a significant angiogenic effect. Bosentan rapidly phosphorylates Akt in endothelial cells and promotes cell survival. Our results demonstrate that low‐dose bosentan protects endothelial cells from apoptosis and increases their functionality. We conclude that bosentan may be a promising therapeutic agent in the treatment of microvascular injury as seen in scleroderma and other interstitial lung diseases.Study sponsor: Actelion Pharmaceuticals

ERYTHROPOIETIN ENHANCES ANGIOGENESIS IN AN EXPERIMENTAL CYCLOSPORINE A‐INDUCED NEPHROTOXICITY MODEL IN THE RAT

1. Erythropoietin (EPO) is a hormone regulating the proliferation and differentiation of erythroid precursor cells. The hypothesis that haematopoietic and endothelial cells share a common haemanglioblast progenitor among others is based on the finding that both cell lineages express cell surface antigens, such as CD31 and CD34. 2. In the present study, we investigated the angiogenic potential of recombinant human erythropoietin on cyclosporine A (CsA)-induced nephrotoxicity in the rat kidney and compared it with the effect of basic fibroblast growth factor (bFGF), a well-known angiogenic factor. 3. Rats were divided into five groups: A (control), B (EPO treated), C (CsA treated), D (CsA + EPO treated) and E (CsA + bFGF treated). Mouse anti-human CD31 and CD34 antibodies were used to evaluate the kidney vessels present in histological preparations. 4. Glomerular and peritubular capillaries in Group B (EPO) were increased compared with the control (Group A; P < 0.05). Reduction of the same kidney vessels (glomerular and peritubular capillaries) in Group C (CsA; P < 0.05) compared with controls was observed, whereas in Groups D (CsA + EPO treated) and E (CsA + bFGF treated), capillaries were increased compared with Group C (CsA; P < 0.05). 5. Erythropoietin has a significant angiogenic effect in rat kidney with CsA-induced nephrotoxicity, similar to the effect of the other angiogenic factor bFGF.

Estrogen induces angiogenesis of the female rabbit bladder

Postmenopausal bladder dysfunction has been speculated to involve decreased circulating estrogen levels. It is our hypothesis that estrogen induces bladder dysfunctions by modulating blood flow to the bladder, i.e. low estrogen reduces blood flow to the bladder, whereas high estrogen increases blood flow. Our previous studies have demonstrated that estrogen administration in female rabbits induces a 'functional hypertrophy' of the urinary bladder smooth muscle represented by increased smooth muscle mass, which corresponds to increased contractile responses to all forms of stimulation. The present study investigates the effect of estrogen on vasculature density and distribution. Twenty-four female New Zealand white rabbits were separated into six groups of four rabbits each. Group 1 served as controls. Groups 2-6 were ovariectomized. Two weeks after ovariectomy (Ovx), groups 3-6 were given 17-beta estradiol (1 mg/kg per day) by s.c. implant for 1, 3, 7, and 14 days respectively. Blood vessel density and distribution were evaluated by immunohistochemistry and quantitative image analyses. Ovx resulted in significant vascular degeneration and decreased density, whereas estradiol administration mediated a significant angiogenic effect characterized by increased vascular density, and distribution of new vasculature within the smooth muscle bundles of the detrusor. Estradiol-induced vasculogenesis corresponds with our previously demonstrated increase in blood flow to the bladder and increased contractility. The most interesting aspect of these studies is the increased vascularization localized within the muscle bundles rather than between the muscle bundles, which may be important in the link between estrogen and increased incidence of cancers.

Aggretin, a snake venom–derived endothelial integrin α2β1 agonist, induces angiogenesis via expression of vascular endothelial growth factor

AbstractAggretin, a collagen-like α2β1 agonist purified from Calloselasma rhodostoma venom, was shown to increase human umbilical vein endothelial cell (HUVEC) proliferation and HUVEC migration toward immobilized aggretin was also increased. These effects were blocked by A2-IIE10, an antibody raised against integrin α2. Aggretin bound to HUVECs in a dose-dependent and saturable manner, which was specifically inhibited by A2-IIE10, as examined by flow cytometry. Aggretin elicited significant angiogenic effects in both in vivo and in vitro angiogenesis assays, and incubation of HUVECs with aggretin activated phosphatidylinositol 3-kinase (PI3K), Akt, and extracellular-regulated kinase 1/2 (ERK1/2); these effects were blocked by A2-IIE10 or vascular endothelial growth factor (VEGF) monoclonal antibody (mAb). The angiogenic effect induced by aggretin may be via the production of VEGF because the VEGF level was elevated and VEGF mAb pretreatment inhibited Akt/ERK1/2 activation as well as the in vivo angiogenesis induced by aggretin. The VEGF production induced by aggretin can be blocked by A2-IIE10 mAb pretreatment. In conclusion, aggretin induces endothelial cell proliferation, migration, and angiogenesis by interacting with integrin α2β1, leading to activation of PI3K, Akt, and ERK1/2 pathways, and the increased expression of VEGF may be responsible for its angiogenic activity.

The angiogenic response to skeletal injury is preserved in the elderly

Angiogenesis is essential for normal bone formation and repair. Avascularity characterizes aberrant fracture union in the elderly, while angiogenic mechanisms during cutaneous wound repair are attenuated in aged humans. We hypothesized that skeletal injury results in local (circulating) and systemic (fracture site) `angiogenic' responses and that these reparative mechanisms are attenuated with advanced patient age. This prospective study examined peripheral blood and fracture hematoma from 32 patients, 16 under 40 years and 16 over the age of 75, undergoing emergent surgery for isolated fracture. The angiogenic cytokines vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) were assayed. Endothelial cell cultures were supplemented with patient plasma and fracture hematoma and angiogenesis determined in vitro by measuring cell proliferation and blood vessel tube formation. Angiogenesis was determined in vivo using a murine dorsal wound pocket model and quantification of new blood vessel formation after 7 days. We found that all injured patients, irrespective of age, have elevated plasma and fracture hematoma levels of VEGF and PDGF. These elevated cytokine concentrations translate into biologically significant angiogenic effects, in vitro and in vivo. These effects are primarily VEGF mediated and are not dependent on patient age. The biological activity of these growth factors does not diminish with advanced age. Thus skeletal injury does result in local and systemic angiogenic responses whereby angiogenic cytokine availability and activity is preserved in the aged suggesting alternative mechanisms for the development of avascularity in delayed and fracture non-union in the elderly.

Patterns of brain angiogenesis after vascular endothelial growth factor administration in vitro and in vivo.

Vascular endothelial growth factor (VEGF) is a secreted endothelial cell mitogen that has been shown to induce vasculogenesis and angiogenesis in many organ systems and tumors. Considering the importance of VEGF to embryonic vascularization and survival, the effects of administered VEGF on developing or adult cerebrovasculature are unknown: can VEGF alter brain angiogenesis or mature cerebrovascular patterns? To examine these questions we exposed fetal, newborn, and adult rat cortical slice explants to graduated doses of recombinant VEGF. The effects of another known angiogenic factor, basic fibroblast growth factor (bFGF), were evaluated in a comparable manner. In addition, we infused VEGF via minipump into the adult cortex. Significant angiogenic effects were found in all VEGF experiments in a dose-responsive manner that were abolished by the addition of VEGF neutralizing antibody. Fetal and newborn explants had a highly complex network of branched vessels that immunoexpressed the flt-1 VEGF receptor, and flk-1 VEGF receptor expression was determined by reverse transcription-PCR. Adult explants had enlarged, dilated vessels that appeared to be an expansion of the existing network. All bFGF-treated explants had substantially fewer vascular profiles. VEGF infusions produced both a remarkable localized neovascularization and, unexpectedly, the expression of flt-1 on reactive astrocytes but not on endothelial cells. The preponderance of neovascularization in vitro and in vivo, however, lacked the blood-brain barrier (BBB) phenotype marker, GLUT-1, suggesting that in brain the angiogenic role of VEGF may differ from a potential BBB functional role, i.e., transport and permeability. VEGF may serve an important capacity in neovascularization or BBB alterations after brain injury.

Effect of Basic Fibroblast Growth Factor on Angiogenesis in Rabbit Flexor Digitorum Profundus Tendons Lacerated and Repaired in The Avascular Area

Prompt angiogenesis has been hypothesised as beneficial for successful surgical repair of the flexor digitorum profundus (FDP) tendon, especially in the avascular area known as zone II. After the tendon has been lacerated and sutured, we analysed the angiogenic effects of the basic fibroblast growth factor (bFGF) on the suture site of zone II and the normal vasculature of rabbit FDP tendons, using the silicon vascular casting method in combination with microscopy. Intratendinous angiogenesis was accelerated at two weeks in the bFGF group. Capillaries formed well-developed vascular networks in the layer of the epitenon and invaded the tendon internally in the suture site along the connective tissue sheath. Three weeks after laceration and repair, the suture only group approved the same as the bFGF group at two weeks following treatment. These results suggest that bFGF has a significant angiogenic effect on a lacerated and sutured avascular area of an FDP tendon, along with development of the connective tissue sheath which may promote intratendinous vascular invasion and favourably influence the tendon repair process.

Interleukin-8 and de novo mammalian angiogenesis.

In the rat mesenteric-window angiogenesis assay (MWAA), the test tissue is natively vascularized, lacks significant physiological angiogenesis and its homeostasis is unperturbed by surgical intervention. Using the rat MWAA, it is shown here that interleukin-8 (IL-8), administered at approximately physiological doses, is able to induce de novo angiogenesis. Human recombinant IL-8 was administered intraperitoneally at two daily doses of 25 pM, 250 pM and 2.5 nM for 5 consecutive days (days 0-4). Using microscopic, computer-aided techniques including image analysis, the de novo angiogenic response was quantified in groups of animals on days 7, 14 and 21 in terms of the relative vascularized area (VA), a measure of the microvascular spatial extension, and the microvascular length (MVL), a measure of microvascular density or length. The total microvascular length (TMVL) was computed from VA x MVL. A statistically significant angiogenic effect was found in terms of MVL on day 7 and in terms of VA and TMVL on day 14 following the treatment with 2.5 nM, whereas MVL was significantly increased in statistical terms on day 14 following the treatment with IL-8 at the low dose of 25 pM. Notably, IL-8 at the intermediate dose of 250 pM did not induce a statistically significant angiogenic effect in terms of VA, MVL or TMVL on any observation occasion, thereby suggesting that the dose-related angiogenic effect of IL-8 may be nonlinear. This appears to be the first paper showing that IL-8 is able to induce de novo angiogenesis in normally vascularized mammalian tissue.

Studies on tumor induced angiogenesis.

Methods were developed to test angiogenic response to human tumor implants and various biologic agents in the cornea of rabbits and non-human primates (Macaca arctoides). Crude PDGF preparations were found to have significant angiogenic effect. Purified, recombinant PDGF preparations were also effective inhibitors (e.g. pentoxifylline (Px) (which also were found to release PgI2 and t-PA) inhibited human tumor implant induced angiogenesis and reduced spontaneous metastases in 3 transplantable murine tumors (Furth-Columbia Wilms' tumor in Furth-Wistar rats, C-1300 neuroblastoma in A/J mice and HM-Kim mammary carcinoma in Wistar rats) but not in the NIH adenocarcinoma in Balb/c mice. Sodium diethyldithiocarbamate (DDTC), a metal complexing agent with special affinity to copper and anti-thyroid as well as, immune stimulating activity was shown to be anti-angiogenic and to potentiate the effect of Px. The anti-fibrinolytic agents epsilon amino caproic acid (EACA) and tranaxamic acid (t-AMCHA) were anti-angiogenic. DDTC and Px were synergistic from this point of view.