Comparative studies of the angiogenic activity of vasoactive intestinal peptide, endothelins-1 and -3 and angiotensin II in a rat sponge model

Modular, Vascularized Hypertrophic Cartilage Constructs for Bone Tissue Engineering Applications

Insufficient vascularization is a main barrier to creating engineered bone grafts for treating large and ischemic defects. Modular tissue engineering approaches have promise in this application because of the ability to combine tissue types and to localize microenvironmental cues to drive desired cell function. In direct bone formation approaches, it is challenging to maintain sustained osteogenic activity, since vasculogenic cues can inhibit tissue mineralization. This study harnessed the physiological process of endochondral ossification to create multiphase tissues that allowed concomitant mineralization and vessel formation. Mesenchymal stromal cells in pellet culture were differentiated toward a cartilage phenotype, followed by induction to chondrocyte hypertrophy. Hypertrophic pellets exhibited increased alkaline phosphatase activity, calcium deposition, and osteogenic gene expression relative to chondrogenic pellets. In addition, hypertrophic pellets secreted and sequestered angiogenic factors, and supported new blood vessel formation by co-cultured endothelial cells and undifferentiated stromal cells. Multiphase constructs created by combining hypertrophic pellets and vascularizing microtissues and maintained in unsupplemented basal culture medium were shown to support robust vascularization and sustained tissue mineralization. These results demonstrate a new in vitro strategy to produce multiphase engineered constructs that concomitantly support the generation of mineralize and vascularized tissue in the absence of exogenous osteogenic or vasculogenic medium supplements.

Protection of Vasoactive Intestinal Peptide on the Blood-Brain Barrier Dysfunction Induced by Focal Cerebral Ischemia in Rats

OBJECTIVE

To investigate the effects of vasoactive intestinal peptide on the blood brain barrier function after focal cerebral ischemia in rats.

MATERIALS AND METHODS

Rats were intracerebroventricular injected with vasoactive intestinal peptide after a two hours middle cerebral artery occlusion. Functional outcome was studied with the neurological severity score. The brain edema and the infarction were evaluated via histology. The blood brain barrier permeability was assessed using Evans Blue dye injection method. We also measure the apoptosis of brain microvascular endothelial cells and brain levels of B-cell leukemia-2 protein by immunohistochemical analysis and western blotting, respectively.

RESULTS

In contrast to the cases treated with vehicle at 72 h after middle cerebral artery occlusion, the treatment with vasoactive intestinal peptide significantly (P < 0.05) reduced the neurological severity score, the brain edema and infarct volume. The Evans Blue leakage and brain water content were obviously reduced (P < 0.05) in vasoactive intestinal peptide-treated rats compared with those of control rats at 72 and 96 h after stroke. In addition, vasoactive intestinal peptide decreased the numbers of terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling positive endothelial cells and increased the protein levels of B-cell leukemia-2 in the ischemic hemisphere at 72 h after ischemia.

CONCLUSIONS

Our data suggest that treatment with vasoactive intestinal peptide ameliorates the blood brain barrier function, contributing to reduce in brain damage both morphologically and functionally in the ischemic rat. This amelioration may be associated with attenuation in apoptosis of brain microvascular endothelial cells by increased B-cell leukemia-2 expression.

Vasoactive intestinal peptide is upregulated in women with endometriosis and chronic pelvic pain

PROBLEM

Chronic pelvic pain (CPP) causes compromised the quality of life in women with endometriosis and is often attributed to local inflammation and ingrowth of nerve fibers. In this pilot study, we aimed to investigate whether the inflammation-related vasoactive intestinal peptide (VIP) and interleukin (IL)-6 were increased in affected patients.

METHOD OF STUDY

Endometrial and endometriotic tissue biopsy specimens, and serum and peritoneal fluid (PF) samples, were obtained from 85 endometriosis patients and 53 controls. VIP and IL-6 analysis and measurement of microvessel density in tissue were performed using immunohistochemistry, Western blotting, RT-qPCR, and ELISA.

RESULTS

Compared with controls, VIP transcript and protein levels were increased in endometrium from endometriosis patients and further elevated in patients with CPP. In addition, microvessel density, a measurement of angiogenic activity, was increased in the endometrium and in endometriosis lesions in the same subset of patients. Serum and PF levels of VIP and IL-6 were higher in women with endometriosis and CPP compared with endometriosis patients who reported no chronic pain.

CONCLUSION

Vasoactive intestinal peptide is upregulated in endometriosis patients reporting chronic pain. Increased microvessel density in tissue and peritoneal fluid concentrations of IL-6 indicate an elevated inflammation in the pelvic microenvironment of these patients.

Erythropoietin and Its Angiogenic Activity

Erythropoietin (EPO) is the main hematopoietic hormone acting on progenitor red blood cells via stimulation of cell growth, differentiation, and anti-apoptosis. However, its receptor (EPOR) is also expressed in various non-hematopoietic tissues, including endothelium. EPO is a pleiotropic growth factor that exhibits growth stimulation and cell/tissue protection on numerous cells and tissues. In this article we review the angiogenesis potential of EPO on endothelial cells in heart, brain, and leg ischemia, as well as its role in retinopathy protection and tumor promotion. Furthermore, the effect of EPO on bone marrow and adipose tissue is also discussed.

Vasoactive intestinal peptide administration after stroke in rats enhances neurogenesis and improves neurological function

The aim of this study was to investigate the effects of vasoactive intestinal peptide (VIP) on neurogenesis and neurological function after cerebral ischemia. Rats were intracerebroventricular administered with VIP after a 2h middle cerebral artery occlusion (MCAO) and sacrificed at 7, 14 and 28 days after MCAO. Functional outcome was studied with the modified neurological severity score. The infarct volume was evaluated via histology. Neurogenesis, angiogenesis and the protein expression of vascular endothelial growth factor (VEGF) were measured by immunohistochemistry and Western blotting analysis, respectively. The treatment with VIP significantly reduced the neurological severity score and the infarc volume, and increased the numbers of bromodeoxyuridine (BrdU) immunoreactive cells and doublecortin immunoreactive area in the subventricular zone (SVZ) at 7, 14 and 28 days after ischemia. The cerebral protein levels of VEGF and VEGF expression in the SVZ were also enhanced in VIP-treated rats at 7 days after stroke. VIP treatment obviously increased the number of BrdU positive endothelial cells in the SVZ and density of cerebral microvessels in the ischemic boundary at 28 days after ischemia. Our study suggests that in the ischemic rat brain VIP reduces brain damage and promotes neurogenesis by increasing VEGF. VIP-enhanced neurogenesis is associated with angiogenesis. These changes may contribute to improvement in functional outcome.

Vasoactive intestinal peptide increases VEGF expression to promote proliferation of brain vascular endothelial cells via the cAMP/PKA pathway after ischemic insult in vitro

Vasoactive intestinal peptide (VIP) enhances angiogenesis in rats with focal cerebral ischemia. In the present study, we investigated the molecular mechanism of the proangiogenic action of VIP using an in vitro ischemic model, in which rat brain microvascular endothelial cells (RBMECs) are subjected to oxygen and glucose deprivation (OGD). Western blotting and immunocytochemistry were carried out to examine the expression of VIP receptors and vascular endothelial growth factor (VEGF) in cultured RBMECs. The cell proliferation was assessed by the MTT assay. Cyclic adenosine monophosphate (cAMP) and VEGF levels were measured by using the enzyme-linked immunosorbent assay. The cultured RBMECs expressed VPAC1, VPAC2 and PAC1 receptors. Treatment with VIP significantly promoted the proliferation of RBMECs and increased OGD-induced expression of VEGF, and this effect was antagonized by the VPAC receptor antagonist VIP6-28 and VEGF antibody. VIP significantly increased contents of cAMP in RBMECs and VEGF in the culture medium. The VIP-induced VEGF production was blocked by H89, a protein kinase A (PKA) inhibitor. These data suggest that treatment with VIP promotes VEGF-mediated endothelial cell proliferation after ischemic insult in vitro, and this effect appears to be initiated by the VPAC receptors leading to activation of the cAMP/PKA pathway.

VIP and growth factors in the infected cornea

PURPOSE

Vasoactive intestinal peptide (VIP) is an anti-inflammatory neuropeptide that downregulates proinflammatory cytokines and promotes healing in a susceptible model of P. aeruginosa keratitis. Growth factors also play a role in corneal healing and restoration of tissue homeostasis after wounding. However, whether VIP treatment modulates growth factors to promote healing in the infected cornea remains untested and is the purpose of this study.

METHODS

C57BL/6 (B6) mice were injected with VIP and mRNA and protein levels, and immunostaining for EGF, FGF, HGF, and VEGF-A were done. Exogenous treatment with a mixture of the growth factors also was tested and levels of cytokines, defensins, and bacterial counts were determined.

RESULTS

Real-time RT-PCR, immunostaining, and ELISA data demonstrated that treatment with VIP enhanced levels of EGF, FGF, and HGF during disease, and that VEGF-A, and associated angiogenic molecules also were increased by VIP. Moreover, immunohistochemical studies confirmed that both epithelial and stromal cells participated in growth factor production. Most notably, treatment with a mixture of EGF, FGF, and HGF after disease onset, prevented corneal perforation when compared with controls. This outcome was associated with downregulation of proinflammatory cytokines such as macrophage inflammatory protein-2 (MIP-2), upregulation of anti-inflammatory cytokines such as TGF-β, and antimicrobials β-defensins 2 and 3, as well as decreased plate counts at 1 day postinfection (p.i.) (P = 0.0001).

CONCLUSIONS

Collectively, the data provide evidence that VIP treatment modulates growth factors, angiogenic molecules, and defensins in the infected cornea and that this in turn promotes healing and restoration of tissue homeostasis.

The renin-angiotensin system and cancer: old dog, new tricks

For cancers to develop, sustain and spread, the appropriation of key homeostatic physiological systems that influence cell growth, migration and death, as well as inflammation and the expansion of vascular networks are required. There is accumulating molecular and in vivo evidence to indicate that the expression and actions of the renin-angiotensin system (RAS) influence malignancy and also predict that RAS inhibitors, which are currently used to treat hypertension and cardiovascular disease, might augment cancer therapies. To appreciate this potential hegemony of the RAS in cancer, an expanded comprehension of the cellular actions of this system is needed, as well as a greater focus on translational and in vivo research.

Role of the renin angiotensin system on bone marrow-derived stem cell function and its impact on skeletal muscle angiogenesis

Autologous bone marrow cell (BMC) transplantation has been shown as a potential approach to treat various ischemic diseases. However, under many conditions BMC dysfunction has been reported, leading to poor cell engraftment and a failure of tissue revascularization. We have previously shown that skeletal muscle angiogenesis induced by electrical stimulation (ES) is impaired in the SS/Mcwi rats and that this effect is related to a dysregulation of the renin angiotensin system (RAS) that is normalized by the replacement of chromosome 13 derived from the Brown Norway rat (SS-13(BN)/Mcwi consomic rats). The present study explored bone marrow-derived endothelial cell (BM-EC) function in the SS/Mcwi rat and its impact on skeletal muscle angiogenesis induced by ES. SS/Mcwi rats were randomized to receive BMC from: SS/Mcwi; SS-13(BN)/Mcwi; SS/Mcwi rats infused with saline or ANG II (3 ng kg(-1) min(-1)). BMC were injected in the stimulated tibialis anterior muscle of SS/Mcwi rats. Vessel density was evaluated in unstimulated and stimulated muscles after 7 days of ES. BMC isolated from SS/Mcwi or SS/Mcwi rats infused with saline failed to restore angiogenesis induced by ES. However, BMC isolated from SS-13(BN)/Mcwi and SS/Mcwi rats infused with ANG II effectively restored the angiogenesis response in the SS/Mcwi recipient. Furthermore, ANG II infusion increased the capacity of BM-EC to induce endothelial cell tube formation in vitro and slightly increased VEGF protein expression. This study suggests that dysregulation of the RAS in the SS/Mcwi rat contributes to impaired BM-EC function and could impact the angiogenic therapeutic potential of BMC.

Vasoactive intestinal peptide in rats with focal cerebral ischemia enhances angiogenesis

We studied the effect of vasoactive intestinal peptide (VIP) on angiogenesis in the ischemic boundary area after focal cerebral ischemia. Adult male Sprague-Dawley rats underwent middle cerebral artery occlusion for 2 h. A single dose of VIP was given via i.c.v. injection at the beginning of reperfusion. Immunohistochemistry and Western blotting were performed to assay angiogenesis and brain levels of vascular endothelial growth factor (VEGF) protein, respectively. In addition, the expression of VEGF and its receptors (flt-1 and flk-1), as well as endothelial proliferation, was measured using rat brain microvascular endothelial cells. Immunohistochemical analyses revealed significant (P<0.05) increases in the numbers of bromodeoxyuridine (BrdU) positive endothelial cells and microvessels at the boundary of the ischemic lesion in rats treated with VIP compared with rats treated with saline. Western blotting analysis showed that treatment with VIP significantly (P<0.05) raised VEGF levels in the ischemic hemisphere. In addition, treatment with VIP increased flt-1 and flk-1 immunoreactivity in endothelial cells. In vitro, incubation with VIP significantly (P<0.01) increased the proliferation of endothelial cells and induced the expression of VEGF, flt-1 and flk-1 in endothelial cells. The stimulatory effect of VIP on the proliferation of endothelial cells was significantly (P<0.01) inhibited by SU5416, a selective inhibitor of VEGF receptor tyrosine kinase. Our data suggest that treatment with VIP enhances angiogenesis in the ischemic brain, and this effect may be mediated by increases in levels of VEGF and its receptors.

Self-sustaining pathological processes in skin psoriasis

Clinical findings suggest that an etiological factor of skin psoriasis (SPs) is of nervous origin. Vasoactive intestinal peptide (VIP) is the most probable candidate for such a factor since VIP is the only neurotransmitter the extracellular level of which increases during SPs exacerbation and decreases in remission. VIP released from skin nerves induces keratinocyte hyperproliferation, angiogenesis, vasodilation, and other SPs-associated cutaneous pathological processes. These can go on over a prolonged period since (1) once released, VIP induces its own further secretion; (2) VIP induces release of interleukin-6 (IL6) that evokes both its own further release and release of VIP. Thereby, a vicious circle-type mechanism perpetuating and amplifying VIP secretion can function in the focuses of psoriatic damage. The mechanism described operates still more intensively under the effects of parathyroid hormone, aldosterone, and enkephalin, the blood levels of which are elevated in patients with SPs. The above explains such features of SPs as its association with human immunodeficiency virus infection, mental stress, alcohol consumption, smoking, and dependence of SPs on skin pigmentation.

Trophic factors in the carotid body

The aim of the present study is to provide a review of the expression and action of trophic factors in the carotid body. In glomic type I cells, the following factors have been identified: brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor, artemin, ciliary neurotrophic factor, insulin-like growth factors-I and -II, basic fibroblast growth factor, epidermal growth factor, transforming growth factor-alpha and -beta1, interleukin-1beta and -6, tumour necrosis factor-alpha, vascular endothelial growth factor, and endothelin-1 (ET-1). Growth factor receptors in the above cells include p75LNGFR, TrkA, TrkB, RET, GDNF family receptors alpha1-3, gp130, IL-6Ralpha, EGFR, FGFR1, IL1-RI, TNF-RI, VEGFR-1 and -2, ETA and ETB receptors, and PDGFR-alpha. Differential local expression of growth factors and corresponding receptors plays a role in pre- and postnatal development of the carotid body. Their local actions contribute toward producing the morphologic and molecular changes associated with chronic hypoxia and/or hypertension, such as cellular hyperplasia, extracellular matrix expansion, changes in channel densities, and neurotransmitter patterns. Neurotrophic factor production is also considered to play a key role in the therapeutic effects of intracerebral carotid body grafts in Parkinson's disease. Future research should also focus on trophic actions on carotid body type I cells by peptide neuromodulators, which are known to be present in the carotid body and to show trophic effects on other cell populations, that is, angiotensin II, adrenomedullin, bombesin, calcitonin, calcitonin gene-related peptide, cholecystokinin, erythropoietin, galanin, opioids, pituitary adenylate cyclase-activating polypeptide, atrial natriuretic peptide, somatostatin, tachykinins, neuropeptide Y, neurotensin, and vasoactive intestinal peptide.

Vasoactive intestinal peptide (VIP) increases vascular endothelial growth factor (VEGF) expression and secretion in human breast cancer cells

Previous studies have shown that vasoactive intestinal peptide (VIP) and its receptors (VPAC(1) and VPAC(2) receptors) are involved in promotion and growth of many human tumours including breast cancer. Here we investigated whether VIP regulates the expression of the main angiogenic factor, vascular endothelial cell growth factor (VEGF) in human oestrogen-dependent (T47D) and oestrogen-independent (MDA-MB-4687) breast cancer cells. Semiquantitative and quantitative real-time RT-PCRs were used at mRNA level whereas enzyme immunoanalysis was performed at protein level. Both cancer cell lines expressed VIP and VPAC(1) (but not VPAC(2)) receptors that were functional as shown by VIP stimulation of adenylate cyclase activity. VIP induced VEGF expression at both mRNA and protein levels following a time-dependent pattern. The responses were faster in T47D than in MDA-MB-468 cells. The observed VIP regulation of VEGF expression appears to be modulated at least by the cAMP/protein kinase A (PKA) and the phosphoinositide 3-kinase (PI3-K) signalling systems as shown by studies of adenylate cyclase stimulation and using specific kinase inhibitors such as H89 and wortmannin. These actions suggest a proangiogenic potential of VIP in breast cancer.

Nonclassic Endogenous Novel Regulators of Angiogenesis

Angiogenesis, the process through which new blood vessels arise from preexisting ones, is regulated by several "classic" factors, among which the most studied are vascular endothelial growth factor (VEGF) and fibroblast growth factor-2 (FGF-2). In recent years, investigations showed that, in addition to the classic factors, numerous endogenous peptides play a relevant regulatory role in angiogenesis. Such regulatory peptides, each of which exerts well-known specific biological activities, are present, along with their receptors, in the blood vessels and may take part in the control of the "angiogenic switch." An in vivo and in vitro proangiogenic effect has been demonstrated for erythropoietin, angiotensin II (ANG-II), endothelins (ETs), adrenomedullin (AM), proadrenomedullin N-terminal 20 peptide (PAMP), urotensin-II, leptin, adiponectin, resistin, neuropeptide-Y, vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating polypeptide (PACAP), and substance P. There is evidence that the angiogenic action of some of these peptides is at least partly mediated by their stimulating effect on VEGF (ANG-II, ETs, PAMP, resistin, VIP and PACAP) and/or FGF-2 systems (PAMP and leptin). AM raises the expression of VEGF in endothelial cells, but VEGF blockade does not affect the proangiogenic action of AM. Other endogenous peptides have been reported to exert an in vivo and in vitro antiangiogenic action. These include somatostatin and natriuretic peptides, which suppress the VEGF system, and ghrelin, that antagonizes FGF-2 effects. Investigations on "nonclassic" regulators of angiogenesis could open new perspectives in the therapy of diseases coupled to dysregulation of angiogenesis.

Angiotensin II Captopril Cotreatment Augments Angiogenesis in Abdominal Skin Flap in Rats

The effect of captopril, angiotensin-converting enzyme inhibitor, on angiogenesis in several reports remained unclear. Its effect on neovascularization in rat abdominal skin flaps was investigated. Flap elevation, based on the right superficial inferior epigastric artery was performed with or without the administration of captopril (10 mg/kg/d), Ang II (100 microg/kg/d), or captopril and Ang II cotreatment. Mean arterial pressure (MAP), microangiography, capillary density measurement, necrosis area determination, laser Doppler flowmetry (LDF), AT1 and vascular endothelial growth factor (VEGF) immunostaining were used to evaluate the effects of captopril and the interaction between captopril and Ang II on the angiogenesis. Ang II and captopril cotreatment improved angiogenesis more than Ang II or captopril alone. The reduction of necrosis, enhancement of vascular network formation, capillary density, VEGF immunostaining, and local blood flow were evident in the cotreated group. We suggest that Ang II and captopril cotreatment improves ischemia-induced angiogenesis and increased viability and vascularity of skin flap in rats.

Roles for host and tumor angiotensin II type 1 receptor in tumor growth and tumor-associated angiogenesis

Angiotensin II (AII) is a multifunctional bioactive peptide, and host renin-angiotensin system (RAS) is closely associated with tumor growth. Recent reports have described that AII is a proangiogenic growth factor, and that Angiotensin II type 1 (AT1) receptor antagonists reduce tumor growth and tumor-associated angiogenesis. In this paper, we investigated the participation of AT1 receptor-signaling in cancer progression using murine Lewis lung carcinoma (LLC) cells, which express AT1 receptor, and AT1a receptor gene-deficient (AT1a-/-) mice. When LLC cells were implanted subcutaneously into wild-type (WT) mice, developed tumors showed intensive angiogenesis with an induction of vascular endothelial growth factor (VEGF) a. Compared with WT mice, tumor growth and tumor-associated angiogenesis was reduced in AT1a-/- mice with reduced expression of VEGFa. In AT1a-/- mice, administration of the AT1 receptor antagonist, TCV-116, showed further reductions of tumor growth, tumor-associated angiogenesis, and VEGFa expression. In vitro study, the expression of VEGFa mRNA and the production of VEGFa protein in LLC cells were significantly increased by AII, which were cancelled by AT1 receptor antagonist, CV-11974. Although the expression of other angiogenic factors, such as angiopoietin-1, angiopoietin-2, epidermal growth factor, and VEGF receptor 2 mRNA, was also investigated in tumor tissues, the expression of VEGFa was most correlated with tumor size among those other angiogenic factors. VEGFa induction by AT1 receptor-signaling in both host and tumor tissues is one of key regulators of tumor growth and tumor-associated angiogenesis. In conclusion, tumor tissue RAS as well as host tissue RAS were found to have an important role in tumor growth. AT1 receptor-signaling blockade may be a novel and effective target in the treatment of cancer.

Role of endothelial cell apoptosis in regulation of skeletal muscle angiogenesis during high and low salt intake

Angiogenesis, under normal conditions, is a tightly regulated balance between pro- and antiangiogenic factors. The goal of this study was to investigate the mechanisms involved in the control of the skeletal muscle angiogenic response induced by electrical stimulation during the suppression of plasma renin activity (PRA) with a high-salt diet. Rats fed 0.4% or 4% salt diets were exposed to electrical stimulation for 7 days. The tibialis anterior (TA) muscles from stimulated and unstimulated hindlimbs were removed and prepared for gene expression analysis, CD31-terminal deoxynucleotide transferase-mediated dUTP nick-end labeling (TUNEL) double-staining assay, and Bcl-2 and Bax protein expression by Western blot. Rats fed a low-salt diet showed a dramatic angiogenesis response in the stimulated limb compared with the unstimulated limb. This angiogenesis response was significantly attenuated when rats were placed on a high-salt diet. Microarray analysis showed that in the stimulated limb of rats fed a low-salt diet many genes related to angiogenesis were upregulated. In contrast, in rats fed a high-salt diet most of the genes upregulated in the stimulated limb function in apoptosis and cell cycle arrest. Endothelial cell apoptosis, as analyzed by CD31-TUNEL staining, increased by fourfold in the stimulated limb compared with the unstimulated limb. There was also a 48% decrease in the Bcl-2-to-Bax ratio in stimulated compared with unstimulated limbs of rats fed a high-salt diet, confirming severe apoptosis. This study suggests that the increase in endothelial cell apoptosis in TA muscle might contribute to the attenuation of angiogenesis response observed in rats fed a high-salt diet.

Angiotensin II type 2 receptor gene deficiency attenuates susceptibility to tobacco-specific nitrosamine-induced lung tumorigenesis: involvement of transforming growth factor-beta-dependent cell growth attenuation

To clarify an involvement of angiotensin II signaling in lung neoplasia, we have examined the effect of angiotensin II receptor deficiency on 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumorigenesis. Male angiotensin II type 2 receptor (AT2)-null mice with an SWR/J genetic background and control wild-type mice were treated with NNK (100 mg/kg, i.p.) or saline vehicle. NNK treatment caused the development of lung tumors in all wild-type control mice (100 % tumor prevalence), but only 85% of AT2-null mice developed tumors. The tumor multiplicity in AT2-null mice (1.9 +/- 0.3) was significantly smaller than that in wild-type mice (4.1 +/- 0.9). Primary cultured lung fibroblasts prepared from both AT2-null and wild-type mice markedly increased the colony counts of A549 lung cancer cells in soft agar, but a consistently higher colony count was observed with the wild-type fibroblasts (fold increase in colony number, 5.6 +/- 0.5) than with the AT2-null fibroblasts (3.5 +/- 0.8). The underlying mechanism by which angiotensin II regulates cancer cell growth is due to the regulation of active transforming growth factor-beta (TGF-beta) production. Although the total level of TGF-beta was significantly stimulated when A549 cells were cocultured with either type of fibroblasts, the level of active TGF-beta in the conditioned medium was consistently higher with AT2-null fibroblasts than with wild-type fibroblasts. These results imply that the AT2 receptor negatively regulates the level of active TGF-beta and thus increases NNK-induced lung tumorigenesis. The AT2 receptor function in lung stromal fibroblasts may be a potential modulator of tumor susceptibility in chemical carcinogen-induced lung tumorigenesis.

Sensory but not parasympathetic nerves are required for ocular vascular remodeling following chronic sympathectomy in rat

Choroidal vascularity increases following chronic sympathetic denervation in rats. The mechanisms of this remodeling are unclear. Since both nitric oxide and substance P/CGRP have been suggested as angiogenic factors in other targets, we hypothesized that sensory or parasympathetic nerves may also participate in ocular vascular remodeling. To test this hypothesis, sympathetic denervation was accomplished by superior cervical ganglionectomy. Sensory denervation was induced by subcutaneous injections of capsaicin on postnatal days 2 and 9, and ocular parasympathetic innervation was ablated by pterygopalatine ganglion excision on postnatal day 60. Eyes were processed and sectioned for light microscopic histomorphometry. Sympathetic denervation for 6 weeks resulted in increased choroidal thickness, vascular luminal area, numbers of large venules and large arterioles, and capillaries in the outer nuclear layer. Capsaicin pretreatment prevented sympathectomy-induced increases in choroidal thickness, vascular luminal area and large venules and large arterioles, whereas pterygopalatine ganglionectomy was without effect. Both sensory and parasympathetic denervation attenuated increases in outer nuclear layer capillaries. These studies indicate that increased choroidal vascularity noted after chronic sympathectomy requires intact sensory innervation.

Retinal angiogenesis is mediated by an interaction between the angiotensin type 2 receptor, VEGF, and angiopoietin

There is evidence that angiotensin II, vascular endothelial growth factor (VEGF), angiopoietins, and their cognate receptors participate in retinal angiogenesis. We investigated whether angiotensin type 2-receptor blockade (AT2-RB) reduces retinal angiogenesis and alters the expression of VEGF/VEGF-R2 and angiopoietin-Tie2. Retinopathy of prematurity (ROP) was induced in Sprague Dawley (SD) rats by exposure to 80% oxygen from postnatal (P) days 0 to 11, followed by 7 days in room air. ROP shams were in room air from P0-18. A group of ROP rats received the AT2-RB, PD123319, by mini-osmotic pump (5 mg/kg/day) from P11-18 (angiogenesis period). Evaluation of the retinal status of the AT2 receptor indicated that this receptor, as assessed by real-time PCR, immunohistochemistry, and in vitro autoradiography, was present in the retina, was more abundant than the AT1 receptor in the neonatal retina, and was increased in the ROP model. AT2-RB reduced retinal angiogenesis. VEGF and VEGF-R2 mRNA were increased in ROP and localized to blood vessels, ganglion cells, and the inner nuclear layer, and were decreased by PD123319. Angiopoietin2 and Tie2, but not angiopoietin1 mRNA were increased with ROP, and angiopoietin2 was reduced with PD123319. This study has identified a potential retinoprotective role for AT2-RB possibly mediated via interactions with VEGF- and angiopoietin-dependent pathways.

Emerging role of endothelin-1 in tumor angiogenesis

Tumor vessels express distinct molecular markers that are functionally relevant in the angiogenic process. Although tyrosine kinase receptor agonists are the major mediators of angiogenesis, several G-protein-coupled receptor agonists have also been shown to have a role. Among these, endothelin-1 (ET-1), by acting directly on endothelial cells via the ET(B) receptor, modulates different stages of neovascularization, including proliferation, migration, invasion, protease production and morphogenesis, and also stimulates neovascularization in vivo. ET-1 can also modulate tumor angiogenesis indirectly through the induction of vascular endothelial growth factor (VEGF). Engagement of the ET(A) receptor by ET-1 induces VEGF production by increasing levels of hypoxia-inducible factor 1 alpha. Moreover, tumor cells themselves, predominantly expressing the ET(A) receptor, might form vessel-like channels within the tumors. The role of ET-1 and its signaling network in tumor angiogenesis suggests that new therapeutic strategies using specific ET(A)-receptor antagonists could improve antitumor treatment by inhibiting both neovascularization and tumor cell growth.

Significance of vascular endothelial cell growth factor up-regulation mediated via a chymase-angiotensin-dependent pathway during angiogenesis in hamster sponge granulomas

Chymase is a serine protease responsible for local production of angiotensin (Ang) II from its precursor Ang I in several species, including humans, dogs, and hamsters. We have previously reported that chymase facilitates angiogenesis in sponge granulation tissues via local production of Ang II. Herein, we report the significance of vascular endothelial growth factor (VEGF) up-regulation mediated by Ang II during angiogenesis in hamster sponge granulomas. Treatment of granulation tissues with an anti-VEGF neutralizing antibody or antisense oligomers against VEGF mRNA significantly reduced Ang II-induced angiogenesis, supporting a significant role for VEGF during angiogenesis. In cultured fibroblasts prepared from granulation tissues, VEGF mRNA was up-regulated in response to Ang II within 2 h and this enhanced expression was abolished in the presence of an Ang II type 1 receptor-selective antagonist, an inhibitor of nuclear factor-kappaB activation, or an activator protein-1 inhibitor. To study the significance of local production of Ang II by chymase, we examined the effects of chymostatin on in vivo angiogenesis. We found that chymostatin markedly inhibited both up-regulation of VEGF mRNA and angiogenesis in granulation tissues treated by compound 48/80 or basic fibroblast growth factor. Our results suggest that Ang II directly acts on fibroblasts in granulation tissue to up-regulate VEGF mRNA and thereby induce angiogenesis. Furthermore, a chymase-Ang II-VEGF pathway may operate in granulation tissue as the primary mediator of angiogenesis.

Vasodilator effect of angiotensin-(1-7) in mature and sponge-induced neovasculature

Angiotensin-(1-7) (Ang-(1-7)), a peptide constituent of the renin-angiotensin system, has been shown to act as a vasodilator mediator in pre-existing (skin) and newly formed vasculatures (14-day-old sponge implants). Blood flow was determined by the outflow rate of sodium fluorescein applied intradermally or intraimplant and the results were expressed in t(1/2) values (time taken for the fluorescence to reach 50% of the peak in the systemic circulation). We showed that the t(1/2) value was significantly lower (4.1+/-0.46) in the implants compared with the cutaneous vasculature (5.7+/-0.5). Ang-(1-7) 20 ng was able to decrease t(1/2) values in both vasculatures. The specific receptor antagonist, D-Ala7-Ang-(1-7) (A-779), prevented Ang-(1-7)-induced vasodilation and altered the basal vascular tone of the implants. The vasodilator effect was also abolished by nitric oxide (NO) synthase inhibitors in both vasculatures and by indomethacin in the implant. Selective AT(1) and AT(2) receptor antagonists did not alter the vasodilation induced by the peptide. These results establish the vasodilator effect of Ang-(1-7) in the cutaneous and implant vasculature and that the peptide is produced endogenously by the fibrovascular tissue, and suggest that this peptide contributes for the vasodilation found in newly formed vascular beds (wound healing, chronic inflammatory processes and tumors).

Angiotensin and calcium signaling in the pituitary and hypothalamus

1) In the rat pituitary, angiotensin type 1B receptors (AT1B) are located in lactotrophs and corticotrophs. 2) Activation of AT1B receptors are coupled to Gq/11 (Guanine protein coupled receptor, or GPCR); they increase phospholipase beta C (PLC) activity resulting in inositol 1,4,5 triphosphate (InsP3) and diacylglycerol (DAG) formation. A biphasic increase in [Ca2+]i triggered by InsP3 and DAG ensues. 3) As many GPCRs, AT1B pituitary receptors rapidly desensitize. 4) This was observed in the generation of InsP3, the mobilization of intracellular Ca(2+), and in prolactin release. Both homologous and heterologous desensitization was evidenced. 5) Desensitization of the angiotensin II type 1 (AT1) receptor in the pituitary shares similarities and differences with endogenously expressed or transfected AT1 receptors in different cell types. 6) In the pituitary hyperplasia generated by chronic estrogen treatment there was desensitization or alteration in angiotensin II (Ang II) evoked intracellular Ca2+ increase, InsP3 generation, and prolactin release. This correlates with a downregulation of AT1 receptors. 7) In particular, in hyperplastic cells Ang II failed to evoke a transient acute peak in [Ca2+]i, which was replaced by a persistent plateau phase of [Ca2+]i increase. 8) Different calcium channels participate in Ang II induced [Ca2+]i increase in control and hyperplastic cells. While spike phase in control cells is dependent on intracellular stores sensitive to thapsigargin, in hyperplastic cells plateau increase is dependent on extracellular calcium influx. 9) Signal transduction of the AT1 pituitary receptor is greatly modified by hyperplasia, and it may be an important mechanism in the control of the hyperplastic process. 10) In the hypothalamus and brain stem there is a predominant expression of AT1A and AT2 mRNA. 11) Ang II acts at specific receptors located on neurons in the hypothalamus and brain stem to elicit alterations in blood pressure, fluid intake, and hormone secretion. 12) Calcium channels play important roles in the Ang II induced behavioral and endocrine responses. 13) Ang II, in physiological concentrations, can activate AT1 receptors to stimulate both Ca2+ release from intracellular stores and Ca2+ influx from the extracellular space to increase [Ca2+]i in polygonal and stellate astroglia of the hypothalamus and brain stem. 14) In primary cell culture of neurons from newborn rat hypothalamus and brain stem, it has also been determined that Ang II elicits an AT1 receptor mediated inhibition of delayed rectifier K(+) current and a stimulation of Ca2+ current. 15) In primary cell cultures derived from the subfornical organ or the organum vasculosum laminae terminalis of newborn rat pups, Ang II produced a pronounced desensitization of the [Ca2+]i response. 16) Hypothalamic and pituitary Ang II systems are involved in different functions, some of which are related. At both levels Ang II signals through [Ca2+]i in a characteristic way.

Local administration of vasoactive intestinal peptide after nerve transection accelerates early myelination and growth of regenerating axons

Our goal was to determine whether local injections of vasoactive intestinal peptide (VIP) promote early stages of regeneration after nerve transection. Sciatic nerves were transected bilaterally in 2 groups of 10 adult mice. In the first group, 15 microg (20 microL) of VIP were injected twice daily into the gap between transected ends of the right sciatic nerve for 7 days (4 mice) or 14 days (6 mice). The same number of mice in the second group received placebo injections (20 microL of 0.9% sterile saline) in the same site, twice daily, for the same periods. After 7 days, axon sizes, relationships with Schwann cells and degree of myelination were compared in electron micrographs of transversely sectioned distal ends of proximal stumps. Fourteen days after transection, light and electron microscopy were used to compare and measure axons and myelin sheaths in the transection gap, 2-mm distal to the ends of proximal stumps. Distal ends of VIP-treated proximal stumps contained larger axons 7 days after transection. More axons were in 1:1 relationships with Schwann cells and some of them were surrounded by thin myelin sheaths. In placebo-treated proximal stumps, axons were smaller, few were in 1:1 relationships with Schwann cells and no myelin sheaths were observed. In VIP-treated transection gaps, measurements 14 days after transection showed that larger axons were more numerous and their myelin sheaths were thicker. Our results suggest that in this nerve transection model, local administration of VIP promotes and accelerates early myelination and growth of regenerating axons.

Antiangiogenic effect of angiotensin II type 2 receptor in ischemia-induced angiogenesis in mice hindlimb

This study examined the potential role of angiotensin type 2 (AT(2)) receptor on angiogenesis in a model of surgically induced hindlimb ischemia. Ischemia was produced by femoral artery ligature in both wild-type and AT(2) gene-deleted mice (Agtr2(-)/Y). After 28 days, angiogenesis was quantitated by microangiography, capillary density measurement, and laser Doppler perfusion imaging. Protein levels of vascular endothelial growth factor (VEGF), endothelial nitric oxide synthase (eNOS), Bax, and Bcl-2 were determined by Western blot analysis in hindlimbs. The AT(2) mRNA level (assessed by semiquantitative RT-PCR) was increased in the ischemic hindlimb of wild-type mice. Angiographic vessel density and laser Doppler perfusion data showed significant improvement in ischemic/nonischemic leg ratio, 1.9- and 1.7-fold, respectively, in Agtr2(-)/Y mice compared with controls. In ischemic leg of Agtr2(-)/Y mice, revascularization was associated with an increase in the antiapoptotic protein content, Bcl-2 (211% of basal), and a decrease (60% of basal) in the number of cell death, determined by TUNEL method. Angiotensin II treatment (0.3 mg/kg per day) raised angiogenic score, blood perfusion, and both VEGF and eNOS protein content in ischemic leg of wild-type control but did not modulate the enhanced angiogenic response observed in untreated Agtr2(-)/Y mice. Finally, immunohistochemistry analysis revealed that VEGF was mainly localized to myocyte, whereas eNOS-positive staining was mainly observed in the capillary of ischemic leg of both wild-type and AT(2)-deficient mice. This study demonstrates for the first time that the AT(2) receptor subtype may negatively modulate ischemia-induced angiogenesis through an activation of the apoptotic process.

Angiotensin AT(1) receptor signalling modulates reparative angiogenesis induced by limb ischaemia

1. The concept that angiotensin II exerts pro-angiogenic activity is not universally accepted. We evaluated whether inhibition of the renin-angiotensin system (RAS) would influence reparative angiogenesis in a murine model of limb ischaemia. 2. Perfusion recovery following surgical removal of the left femoral artery was analysed by laser Doppler flowmetry in mice given the ACE inhibitor ramipril (1 mg kg(-1) per day), the AT(1) antagonist losartan (15 mg kg(-1) per day), or vehicle. Muscular capillarity was examined at necroscopy. Ramipril-induced effects were also studied under combined blockade of kinin B(1) and B(2) receptors. Furthermore, the effects of ischaemia on AT(1) gene expression and ACE activity were determined. 3. In untreated mice, muscular AT(1a) gene expression was transiently decreased early after induction of limb ischaemia, whereas AT(1b) mRNA was up-regulated. ACE activity was reduced in ischaemic muscles at 1 and 3 days. Gene expression of AT(1) isoforms as well as ACE activity returned to basal values by day 14. Spontaneous neovascularization allowed for complete perfusion recovery of the ischaemic limb after 21 days. 4. Reparative angiogenesis was negatively influenced by either ramipril (P<0.02) or losartan (P<0.01), leading to delayed and impaired post-ischaemic recovery (50 - 70% less compared with controls). Ramipril-induced effects remained unaltered under kinin receptor blockade. 5. The present study indicates that (a) expression of angiotensin II AT(1) receptors and ACE activity are modulated by ischaemia, (b) ACE-inhibition or AT(1) antagonism impairs reparative angiogenesis, and (c) intact AT(1) receptor signalling is essential for post-ischaemic recovery. These results provide new insights into the role of the RAS in vascular biology and suggest cautionary use of ACE inhibitors and AT(1) antagonists in patients at risk for developing peripheral ischaemia.

Intraluteal release of angiotensin II and progesterone in vivo during corpora lutea development in the cow: effect of vasoactive peptides

The newly formed corpus luteum (CL) develops rapidly and has the features of active vascularization and mitosis of steroidogenic cells. Such local mechanisms must be strictly regulated by the complex relationship between angiogenic growth factors and vasoactive peptides such as angiotensin (Ang) II, atrial natriuretic peptide (ANP), and endothelin (ET)-1. Thus, the objective of the present study was to determine 1) the changes in vasoactive peptides and progesterone (P) concentrations within the developing CL, along with the changes in concentration in ovarian venous plasma (OVP) and jugular venous plasma (JVP) in the cow, 2) the effects of CL exposure to vasoactive peptides on Ang II and P secretion, and 3) the expression of mRNA for ANP type C receptor in the bovine CL and endothelial cells (ETC) from bovine developing CL. A microdialysis system (MDS) was surgically implanted into multiple CL of six cows on Day 3 after a GnRH injection that induced superovulation, and a catheter was simultaneously inserted into the ovarian vein. The Ang II concentration in OVP was higher than that in JVP throughout the experiment, while the intraluteal release of Ang II was stable. During the experimental period, the concentrations of other vasoactive peptides (ANP and ET-1) showed no clear changes in plasma and were below detectable levels in the MDS perfusate. Exposure of CL to Ang II using the MDS stimulated P release, while exposure to ANP enhanced Ang II release within the developing CL. However, ET-1 had no effect on either P or Ang II release. The expression of mRNA for ANP type C receptor was mainly observed in early CL and ETC. The results suggest that the ET-Ang-ANP system in the preovulatory follicle switches to an Ang-ANP system to enhance both the angiogenesis and steroidogenesis that are actively occurring in developing CL.

Angiotensin II in cardiac pressure-overload hypertrophy in fetal sheep

We previously demonstrated in fetal sheep that blockade of ANG II type 1 (AT(1)) receptors did not attenuate an increase in right ventricle (RV) mass resulting from partial occlusion of the pulmonary artery (PA). We have now determined the effects of AT(2)-receptor blockade (PD-123319, 10 mg. kg(-1). day(-1) continuous iv) on the response of the fetal RV to PA banding for 7 days. Four groups of fetuses (each n = 7) were studied beginning at 126 +/- 1 days gestation (term 145 days). RV weight-to-body weight ratio (RV wt/body wt) increased (P < 0.05) in PA-banded (6.00 +/- 0.09 g/kg) and PA-banded + PD-123319 (6.19 +/- 0.27 g/kg) compared with control (5.17 +/- 0.17 g/kg) and PD-123319-infused (5.27 +/- 0.35 g/kg) fetuses (means +/- SE). Blood pressure and heart rate were similar in all groups. PD-123319 produced a decrease (P < 0.05) in AT(1) but not AT(2) mRNA levels in both fetal ventricles. To examine the effect of ANG II on fetal heart growth, twin fetal sheep were infused with either ANG II (twin received vehicle) or phenylephrine (Phe) (twin received vehicle) continuously for 7 days. Mean arterial blood pressure was 20-25 mmHg higher in ANG II and Phe fetuses compared with controls. The rate-pressure product was similar in ANG II and Phe fetuses and 40-50% greater than controls. Phe resulted in no change in RV wt/body wt or left ventricle-to-body weight ratio (LV wt/body wt) compared with controls. In contrast, ANG II produced a selective increase (27 +/- 5%, P < 0.05) in LV wt/body wt; no effect was seen on the RV. ANG II produced a decrease (P < 0.05) in LV but not RV AT(1) mRNA levels compared with controls; no effect was seen with Phe. The data demonstrate that in the ovine fetus, AT(2) receptors do not contribute to the maintenance of blood pressure or the development of pressure-overload RV hypertrophy. Elevated ANG II levels produce a selective increase in LV mass in the fetal sheep that is, in part, independent of increased systolic load.

Bone reinnervation after fracture: a study in the rat

Reinnervation after tibial fracture in the rat was studied by analyzing the occurrence of growth-associated protein 43 (GAP-43), a marker for regenerating nerve fibers, and protein gene product 9.5 (PGP-9.5), a marker for mature nerve fibers, by immunohistochemistry. At 3 days postfracture, GAP-43--immunoreactive nerve fibers were first observed in the fracture hematoma and periosteum. At 7 days postfracture, abundant sprouting of GAP-43--positive fibers was seen in the callus, hyperplastic periosteum, and edge of fibrocartilage. In the latter region, the nerve fibers were nonvascular, showing dense ramifications and terminal sprouting close to chondroid cells. At 14 days and 21 days postfracture, many GAP-43--positive fibers were still sprouting into the fibrocartilage and new woven bone. Fine varicose GAP-43--positive fibers also were present in the bone marrow. In contrast to GAP-43, PGP-9.5-positive nerve fibers were observed only occasionally at 3 days postfracture but gradually increased in number from day 14 to 21. Our study shows that intense nerve regeneration occurs in early fracture healing partly unrelated to neovascularization. Considering that neuronal mediators have been shown to participate in local bone formation and resorption, the nerve regeneration observed may prove to be essential for delivery of neuronal mediators required for normal callus formation and/or neovascularization.

Mechanisms of angiotensin-(1-7)-induced inhibition of angiogenesis

Angiotensin-(1-7) [ANG-(1-7)], an endogenous bioactive peptide constituent of the renin-angiotensin system, acts as an inhibitory growth factor in vitro and in vivo. In this study, we evaluated whether the antiangiogenic effect of ANG-(1-7) in the mouse sponge model of angiogenesis might be receptor mediated and involved in the release of nitric oxide (NO). The hemoglobin content (microg/mg wet tissue) of 7-day-old sponge implants was used as an index of the vascularization and showed that daily injections of ANG-(1-7) (20 ng) inhibited significantly the angiogenesis in the implants relative to the saline-treated group. The specific receptor antagonist D-Ala(7)-ANG-(1-7); A-779 prevented ANG-(1-7)-induced inhibition of angiogenesis. The antiangiogenic effect was also abolished by pretreatment with NO synthase inhibitors aminoguanidine (1 mg/ml) or N(G)-nitro-L-arginine methyl ester (0.3 mg/ml). Selective AT1 and AT2 angiotensin-receptor antagonists and an angiotensin-converting enzyme inhibitor, in combination with ANG-(1-7) or alone, did not alter angiogenesis in the implants. These results establish that the regulation of the vascular tissue growth by ANG-(1-7) is associated with NO release by activation of an angiotensin receptor distinct from AT1 and AT2.

Endothelin-1 induces an angiogenic phenotype in cultured endothelial cells and stimulates neovascularization in vivo

The endothelial cell-derived endothelin-1 (ET-1) is a potent mitogen for endothelial cells, vascular smooth muscle cells, and tumor cells. In this study, we analyzed the role of ET-1 on human umbilical vein endothelial cell (HUVEC) phenotype related to different stages of angiogenesis. ET-1 promoted HUVEC proliferation, migration, and invasion in a dose-dependent manner. The ET(B) receptor (ET(B)R) antagonist, BQ 788, blocked the angiogenic effects induced by ET-1, whereas the ET(A)R antagonist was less effective. ET-1 stimulated matrix metalloproteinase-2 mRNA expression and metalloproteinase-2 production, as determined by reverse transcriptase-polymerase chain reaction and gelatin zymography. Furthermore ET-1 was able to enhance HUVEC differentiation into cord vascular-like structures on Matrigel. When tested in combination with vascular endothelial growth factor (VEGF), ET-1 enhanced VEGF-induced angiogenic-related effects on endothelial cells in vitro. Finally, using the Matrigel plug neovascularization assay in vivo, ET-1 in combination with VEGF stimulated an angiogenic response comparable to that elicited by basic fibroblast growth factor. These findings demonstrated that ET-1 induces angiogenic responses in cultured endothelial cells through ET(B)R and that stimulates neovascularization in vivo in concert with VEGF. ET-1 and its receptors acting as angiogenic regulators might represent new targets for anti-angiogenic therapy.

Wound healing: captopril, an angiogenesis inhibitor, and Staphylococcus aureus peptidoglycan

BACKGROUND

Captopril, an angiotensin-converting enzyme inhibitor, used for treating hypertension and heart failure, inhibits angiogenesis in the corneas of rats in response to basic fibroblast growth factor, slows the growth of experimental tumors in rats, and leads to the regression of Kaposi's sarcoma. Because angiogenesis is key to wound healing, we hypothesized that captopril would impair wound healing. We hypothesized also that because local application at operation of Staphylococcus aureus peptidoglycan (SaPG) increases angiogenesis and accelerates wound healing in rats, SaPG would prevent or ameliorate the postulated captopril-impaired wound healing.

MATERIALS AND METHODS

In each experiment, rats were divided randomly into two groups: one drinking tap water, and the other, tap water containing 0.5 mg captopril/ml. All ate chow and drank ad libitum, pre-operatively (4-12 days) and postoperatively (7 days). In experiments 1 and 2, bilateral paravertebral 5.5-cm skin incisions were made aseptically (intraperitoneal sodium pentobarbital), and closed with interrupted No. 35 stainless-steel sutures. On one side, the wound was immediately inoculated with 157 microliter pyrogen-free isotonic saline and on the other side the wound was inoculated with 157 microliter saline containing 4.7 mg SaPG (860 microgram SaPG/cm incision). In the third experiment, polyvinyl alcohol (PVA) sponges (16-17 mg dry wt each) containing either 50 microliter saline or 0.5 mg SaPG in 50 microliter saline were implanted subcutaneously, two on each side, via 1-cm incisions closed with a single suture. In the fourth experiment, 5.5-cm bilateral skin incisions and subcutaneous implantation of PVA sponges were done as described but all sites were instilled with saline only. All rats were euthanized (CO(2) asphyxia) 7 days postoperatively.

RESULTS

Wound breaking strength (WBS) of the saline-treated incisions was significantly higher (P < 0.001) in captopril-treated rats than in controls (172 +/- 13 g vs 105 +/- 6 g) in experiment 1 and higher, but not significantly in captopril-treated rats in experiment 2 (153 +/- 8 g vs 114 +/- 6 g) (PNS). SaPG inoculation of the incisions increased WBS significantly in both control and captopril-treated rats: 187 +/- 11 g vs 105 +/- 6 g (P < 0.001) and 283 +/- 16 g vs 172 +/- 13 g (P < 0.001), respectively, in experiment 1, and 217 +/- 13 g vs 114 +/- 6 g (P < 0.0001) (controls) and 266 +/- 17 g vs 153 +/- 8 g (captopril-treated rats) (P < 0.0001) in experiment 2. In experiment 3, subcutaneous PVA saline-inoculated sponge reparative tissue hydroxyproline (OHP) content was similar in control and captopril-treated rats, and SaPG inoculation increased reparative tissue OHP significantly in both groups: 2458 +/- 218 microgram/100 mg dry sponge vs 3869 +/- 230 microgram/100 mg (P < 0.001) (controls) and 2489 +/- 166 microgram/100 mg vs 4176 +/- 418 microgram/100 mg (P < 0.001) (captopril-treated rats). Histologically, angiogenesis and reparative tissue collagen were similar in control and captopril-treated rats, in both saline-inoculated and SaPG-inoculated sponges. In experiment 4 (all incisions and subcutaneous PVA sponges were saline-inoculated), there was no significant difference in WBS between control and captopril-treated rats (107 +/- 6 g vs 96 +/- 5 g, NS). PVA sponge reparative tissue OHP was significantly higher in captopril-treated rats: 3698 +/- 170 microgram/100 mg dry sponge vs 2534 +/- 100 microgram/100 mg (P < 0.0001).

CONCLUSION

Unexpectedly, in four experiments, captopril did not inhibit WBS or PVA sponge reparative tissue angiogenesis or collagen accumulation; in fact, WBS was increased significantly in one of three experiments, and PVA sponge reparative tissue OHP was increased significantly in one of two experiments. Also, captopril did not interfere with the wound healing-accelerating effect of SaPG.

Angiotensin-(1-7): an update

The renin-angiotensin system is a major physiological regulator of arterial pressure and hydro-electrolyte balance. Evidence has now been accumulated that in addition to angiotensin (Ang) II other Ang peptides [Ang III, Ang IV and Ang-(1-7)], formed in the limited proteolysis processing of angiotensinogen, are importantly involved in mediating several actions of the RAS. In this article we will review our knowledge of the biological actions of Ang-(1-7) with focus on the puzzling aspects of the mediation of its effects and the interaction Ang-(1-7)-kinins. In addition, we will attempt to summarize the evidence that Ang-(1-7) takes an important part of the mechanisms aimed to counteract the vasoconstrictor and proliferative effects of Ang II.

Opposing actions of angiotensins on angiogenesis

Using the murine sponge model of angiogenesis, associated to functional and morphological parameters we have demonstrated opposing actions of angiotensin II (Ang II) and angiotensin-(1-7;Ang-1-7) in modulating fibrovascular tissue growth. Angiogenesis in the implants was assessed at day 7 postimplantation by extracting the hemoglobin content, by determining the outflow rate of sodium fluorescein applied intraimplant and by histological analysis. Furthermore, the proliferative activity of control and angiotensin-treated implants was established using the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2(4 -sulfonyl)2H-tetrazolium)assay. The hemoglobin content in the control implants was 2.4 +/- 0.14 (microg/mg wet weight) versus 3.6 +/- 0.27(Ang II;100 ng) and 0.86 +/- 0.07 Ang-(1-7); 20 ng. Blood flow in the implants as determined by t1/2 values (time taken for the fluorescence to reach 50% of the peak in the systemic circulation) showed that Ang II stimulated angiogenesis, whereas Ang-(1-7) inhibited it. The proliferative activity of the sponge-induced fibrovascular tissue was enhanced by Ang II and diminished by Ang-(1-7). These results show the pro-versus anti-angiogenic effects of these angiotensin molecules, providing evidence for their opposing effects on vascular tissue growth and wound healing in vivo.

Chymase as a proangiogenic factor. A possible involvement of chymase-angiotensin-dependent pathway in the hamster sponge angiogenesis model

We investigated the profound involvement of chymase, an alternative angiotensin II-generating enzyme, in angiogenesis using a hamster sponge implant model. In vivo transfection of human pro-chymase cDNA or a direct injection of purified chymase into the sponges implanted resulted in marked increment of hemoglobin contents in the sponge granuloma tissues, demonstrating that chymase has an ability to elicit angiogenesis and is a potent angiogenic factor. Daily injection of basic fibroblast growth factor into the sponges implanted also induced angiogenesis, which was suppressed by the treatment with chymostatin, an inhibitor of chymase, or TCV-116, an antagonist of angiotensin II (Ang II) type 1 receptor. Expression of chymase mRNA and production of Ang II in the granuloma tissues were enhanced by the stimulation with basic fibroblast growth factor. Chymase activity in the sponge granulomas increased in parallel with the rise in hemoglobin contents, and mast cells observed in the granuloma tissues were positively stained with anti-chymase antibody. Exogenous administration not only of Ang II but of angiotensin I (Ang I) directly into the sponges could enhance angiogenesis. Chymostatin inhibited the angiogenesis induced by Ang I but not Ang II, suggesting the presence of a chymase-like Ang II-generating activity in the sponge granulomas. Our results may suggest a potential ability of chymase to promote angiogenesis through the local chymase-dependent and angiotensin-converting enzyme-dependent Ang II generating system in pathophysiological angiogenesis.

Human Erythropoietin Induces a Pro-Angiogenic Phenotype in Cultured Endothelial Cells and Stimulates Neovascularization In Vivo

Hematopoietic and endothelial cell lineages share common progenitors. Accordingly, cytokines formerly thought to be specific for the hematopoietic system have been shown to affect several functions in endothelial cells, including angiogenesis. In this study, we investigated the angiogenic potential of erythropoietin (Epo), the main hormone regulating proliferation, differentiation, and survival of erythroid cells. Epo receptors (EpoRs) have been identified in the human EA.hy926 endothelial cell line by Western blot analysis. Also, recombinant human Epo (rHuEpo) stimulates Janus Kinase-2 (JAK-2) phosphorylation, cell proliferation, and matrix metalloproteinase-2 (MMP-2) production in EA.hy926 cells and significantly enhances their differentiation into vascular structures when seeded on Matrigel. In vivo, rHuEpo induces a potent angiogenic response in the chick embryo chorioallantoic membrane (CAM). Accordingly, endothelial cells of the CAM vasculature express EpoRs, as shown by immunostaining with an anti-EpoR antibody. The angiogenic response of CAM blood vessels to rHuEpo was comparable to that elicited by the prototypic angiogenic cytokine basic fibroblast growth factor (FGF2), it occurred in the absence of a significant mononuclear cell infiltrate, and it was not mimicked by endothelin-1 (ET-1) treatment. Taken together, these data demonstrate the ability of Epo to interact directly with endothelial cells and to elicit an angiogenic response in vitro and in vivo and thus act as a bona fide direct angiogenic factor.

Human Erythropoietin Induces a Pro-Angiogenic Phenotype in Cultured Endothelial Cells and Stimulates Neovascularization In Vivo

Hematopoietic and endothelial cell lineages share common progenitors. Accordingly, cytokines formerly thought to be specific for the hematopoietic system have been shown to affect several functions in endothelial cells, including angiogenesis. In this study, we investigated the angiogenic potential of erythropoietin (Epo), the main hormone regulating proliferation, differentiation, and survival of erythroid cells. Epo receptors (EpoRs) have been identified in the human EA.hy926 endothelial cell line by Western blot analysis. Also, recombinant human Epo (rHuEpo) stimulates Janus Kinase-2 (JAK-2) phosphorylation, cell proliferation, and matrix metalloproteinase-2 (MMP-2) production in EA.hy926 cells and significantly enhances their differentiation into vascular structures when seeded on Matrigel. In vivo, rHuEpo induces a potent angiogenic response in the chick embryo chorioallantoic membrane (CAM). Accordingly, endothelial cells of the CAM vasculature express EpoRs, as shown by immunostaining with an anti-EpoR antibody. The angiogenic response of CAM blood vessels to rHuEpo was comparable to that elicited by the prototypic angiogenic cytokine basic fibroblast growth factor (FGF2), it occurred in the absence of a significant mononuclear cell infiltrate, and it was not mimicked by endothelin-1 (ET-1) treatment. Taken together, these data demonstrate the ability of Epo to interact directly with endothelial cells and to elicit an angiogenic response in vitro and in vivo and thus act as a bona fide direct angiogenic factor.

Pharmacological reactivity of neoplastic and non-neoplastic associated neovasculature to vasoconstrictors

Angiogenesis and the pharmacological responses of the tumour and non-tumour associated neovasculature have been investigated. Cannulated sponge discs in mice were used to host the angiogenic stimulators, while 133Xe washout was employed to assess local blood flow. Enhancement of blood flow was detected in implants bearing B16 cells, 3T3 cells and angiotensin II (AII)-treated at day 7. The responses of non-neoplastic associated neovasculature at day 14 post sponge implantation to the vasoconstrictors used endothelin-1 (Et-1), AII, platelet activating factor (PAF) and 5-hydroxytryptamine (5-HT) were dose-dependent. By contrast, the newly formed blood vessels induced by tumour cells were markedly insensitive to the vasoconstrictors agonists Et-1 and AII, while fully responsive to PAF and 5-HT. The vessels resulting from neoplastic stimulus exhibited altered pharmacological reactivity, suggesting that the characteristics of the neovasculature are dependent on the nature of the angiogenic stimuli.

Angiotensin II-induced Ca2+ mobilization and prolactin release in normal and hyperplastic pituitary cells

We evaluated the effects of angiotensin II (ANG II) and its antagonists on prolactin release, intracellular calcium ([Ca2+]i) mobilization, and [3H]thymidine uptake in cells from normal rat pituitaries and from estrogen-induced pituitary tumors. ANG II (10(-7) to 10(-9) M) increased prolactin release significantly in control and not in tumoral cells. In control cells, ANG II (10(-6) to 10(-9) M) produced an immediate spike of [Ca2+]i followed by a plateau. Spike levels rose significantly between 10(-10) and 10(-8) M ANG II, whereas the onset of the spike was retarded with decreasing concentrations. In tumoral cells, ANG II did not produce a spike phase even at 10(-6) M. ANG II-induced prolactin release and calcium mobilization were blocked by losartan (AT1 receptor antagonist) and not by PD-123319 (AT2 antagonist). Finally, [3H]thymidine uptake was not modified by ANG II (10(-7) to 10(-10) M) or its antagonists in either group. Our results suggest that chronic in vivo estrogenic treatment alters in vitro pituitary response to ANG II. Alterations might function to limit excessive prolactin secretion of hypersecreting tumors. Besides, ANG II does not modify DNA synthesis in vitro of cells from normal or tumor-derived hypophyses.

Sequential development of angiotensin receptors and angiotensin I converting enzyme during angiogenesis in the rat subcutaneous sponge granuloma

1. The vasoconstrictor peptide antiotensin II (AII) can stimulate angiogenesis, an important process in wound healing, tumour growth and chronic inflammation. To elucidate mechanisms underlying AII-enhanced angiogenesis, we have studied a subcutaneous sponge granuloma model in the rat by use of 133Xe clearance, morphometry and quantitative in vitro autoradiography. 2. When injected directly into the sponge, AII (1 nmol day-1) increased 133Xe clearance from, and fibrovascular growth in sponge granulomas, indicating enhanced angiogenesis 6 to 12 days after implantation. This AII-enhanced angiogenesis was inhibited by daily doses (100 nmol/sponge) of the specific but subtype non-selective AII receptor antagonist (Sar1, Ile8)AII, and by the selective non-peptide AT1 receptor antagonists losartan and DuP 532. In contrast, AII-enhanced neovascularization was not inhibited by the AT2 receptor antagonist PD123319, nor was it mimicked by the AT2 receptor agonist CGP42112A (each at 100 nmol/sponge day-1). 3. AI (1 nmol/sponge day-1), the angiotensin converting enzyme (ACE) inhibitors captopril (up to 100 micrograms/sponge day-1) and lisinopril (40 micrograms/sponge day-1), or AII receptor antagonists did not affect angiogenesis in the absence of exogenous AII. 4. [125I]-(Sar1, Ile8)AII binding sites with characteristics of AT1 receptors were localized to microvessels and to non-vascular cells within the sponge stroma from 4 days after implantation, and were at higher density than in skin throughout the study. 5. [125I]-(Sar1, Ile8)AII binding sites with characteristics of AT2 receptors were localized to non-vascular stromal cells, were of lower density and appeared later than did AT1 sites. 6. The ACE inhibitor [125I]-351A bound to sites with characteristics of ACE, 14 days after sponge implantation. [125I]-351A bound less densely to sponge stroma than to skin. 7. We propose that AII can stimulate angiogenesis, acting via AT1 receptors within the sponge granuloma. AT1 and AT2 receptors and ACE develop sequentially during microvascular maturation, and the role of the endogenous angiotensin system in angiogenesis will depend on the balanced local expression of its various components. Pharmacological modulation of this balance may provide novel therapeutic approaches in angiogenesis-dependent diseases.