Inhibition of production of monocyte/macrophage-derived angiogenic activity by oxygen free-radical scavengers

Natural Herbal Medicine as a Treatment Strategy for Myocardial Infarction through the Regulation of Angiogenesis

Methods

We conducted a literature search on the bioactive components of medicinal plants and their effects on angiogenesis after MI. We searched for articles in Web of Science, MEDLINE, PubMed, Scopus, Google Scholar, and China National Knowledge Infrastructure databases before April 2021.

Results

In this article, we summarized the mechanisms by which copper ions, microRNA, Akt1, inflammation, oxidative stress, mitochondria, and pericytes are involved in angiogenesis after myocardial infarction. In addition, we reviewed the angiogenic effects of natural herbal medicines such as Salvia miltiorrhiza Bunge Bunge, Carthamus tinctorius L., Pueraria lobata, Astragalus, Panax ginseng C.A. Mey., Panax notoginseng (Burkill) F.H. Chen, Cinnamomum cassia (L.) J. Presl, Rehmannia glutinosa (Gaertn.) DC., Leonurus japonicus Houtt, Scutellaria baicalensis Georgi., and Geum macrophyllum Willd.

Conclusions

Some herbs have the effect of promoting angiogenesis. In the future, natural proangiogenic drugs may become candidates for the treatment of cardiovascular diseases.

Calcium Dobesilate Modulates PKCδ-NADPH Oxidase- MAPK-NF-κB Signaling Pathway to Reduce CD14, TLR4, and MMP9 Expression during Monocyte-to-Macrophage Differentiation: Potential Therapeutic Implications for Atherosclerosis

Monocyte-to-macrophage differentiation results in the secretion of various inflammatory mediators and oxidative stress molecules necessary for atherosclerosis pathogenesis. Consequently, this differentiation represents a potential clinical target in atherosclerosis. Calcium dobesilate (CaD), an established vasoactive and angioprotective drug in experimental models of diabetic microvascular complications reduces oxidative stress and inhibits inflammation via diverse molecular targets; however, its effect on monocytes/macrophages is poorly understood. In this study, we investigated the anti-inflammatory mechanism of CaD during phorbol 12-myristate 13-acetate (PMA)-induced monocyte-to-macrophage differentiation in in vitro models of sepsis (LPS) and hyperglycemia, using THP-1 monocytic cell line. CaD significantly suppressed CD14, TLR4, and MMP9 expression and activity, lowering pro-inflammatory mediators, such as IL1β, TNFα, and MCP-1. The effects of CaD translated through to studies on primary human macrophages. CaD inhibited reactive oxygen species (ROS) generation, PKCδ, MAPK (ERK1/2 and p38) phosphorylation, NOX2/p47phox expression, and membrane translocation. We used hydrogen peroxide (H2O2) to mimic oxidative stress, demonstrating that CaD suppressed PKCδ activation via its ROS-scavenging properties. Taken together, we demonstrate for the first time that CaD suppresses CD14, TLR4, MMP9, and signature pro-inflammatory cytokines, in human macrophages, via the downregulation of PKCδ/NADPH oxidase/ROS/MAPK/NF-κB-dependent signaling pathways. Our data present novel mechanisms of how CaD alleviates metabolic and infectious inflammation.

Skeletal muscle-derived exosomes regulate endothelial cell functions via reactive oxygen species-activated nuclear factor-κB signalling

NEW FINDINGS

What is the central question of this study? Capillary rarefaction is found in diabetic and aged muscle, whereas exercise increases skeletal muscle angiogenesis. The association implies a crosstalk between muscle cells and endothelial cells. The underlying mechanisms mediating the crosstalk between these cells remains to be elucidated fully. What is the main finding and its importance? Endothelial cell functions are regulated by skeletal muscle cell-derived exosomes via a vascular endothelial growth factor-independent pathway. This study reveals a new mechanism mediating the crosstalk between skeletal muscle cells and endothelial cells.

ABSTRACT

Loss of skeletal muscle capillarization, known as capillary rarefaction, is found in type 2 diabetes, chronic heart failure and healthy ageing and is associated with impaired delivery of substrates to the muscle. However, the interaction and communication of skeletal muscle with endothelial cells in the regulation of capillaries surrounding the muscle remains elusive. Exosomes are a type of secreted extracellular vesicle containing mRNAs, proteins and, especially, microRNAs that exert paracrine and endocrine effects. In this study, we investigated whether skeletal muscle-derived exosomes (SkM-Exo) regulate the endothelial cell functions of angiogenesis. We demonstrated that C2C12 myotube-derived exosomes improved endothelial cell functions, assessed by the proliferation, migration and tube formation of human umbilical vein endothelial cells (HUVECs), which were increased by 20, 23 and 40%, respectively, after SkM-Exo exposure. The SkM-Exo failed to activate HUVEC vascular endothelial growth factor (VEGF) signalling. The SkM-Exo increased HUVEC reactive oxygen species and activated the nuclear factor-κB pathway, suggesting that SkM-Exo-induced angiogenesis was mediated by a VEGF-independent pathway. In addition, several angiogenic microRNAs were packaged in SkM-Exo, with miR-130a being particularly enriched and successfully transferred from SkM-Exo to HUVECs. Delivery of miRNAs into endothelial cells might explain the enhancement of reactive oxygen species production and angiogenesis by SkM-Exo. The potential angiogenic effect of SkM-Exo could provide an effective therapy for promoting skeletal muscle angiogenesis in diseases characterized by capillary rarefaction or inadequate angiogenesis.

Interaction of endothelial cells with macrophages-linking molecular and metabolic signaling

Angiogenesis and inflammation go hand in hand in various (patho-)physiological conditions. Several studies have highlighted the interconnection between endothelial cells (ECs) and macrophages in these conditions at the level of growth factor and cytokine signaling, yet the importance of metabolism and metabolic signaling has been largely overlooked. Modulating macrophage and/or endothelial functions by interfering with metabolic pathways offers new perspectives for therapeutic strategies. In this review, we highlight the complexity of the interrelationship between the inflammatory response and angiogenesis. More in particular, the interaction between macrophages and ECs will be discussed with a special focus on how their metabolism can contribute to (patho-)physiological conditions.

Review : Angiogenesis: A new target for antineoplastic therapy

Objective. To review the pathophysiologic rationale and therapeutic applications of inhibiting angiogenesis in solid tumor growth.

Data Sources. A MEDLINE search of articles published from 1985 to 1995 and a CancerLit search of articles published from 1988 to 1995, using the MESH heading "neovascularization" and text words "angiogenesis" and "antiangiogenesis." References listed in identified publications were reviewed for additional pertinent literature.

Study Selection. All human trials evaluating angiogenesis inhibitors in malignant disease and pre- clinical trials that illustrate potential mechanisms of action of such agents were included.

Data Synthesis. Angiogenesis, the formation of new blood vessels, is necessary for the development of significant solid tumor growth. Inhibition of angio genesis is a unique mechanism of antineoplastic ther apy that does not use traditional cytotoxic actions. Four investigational antiangiogenic agents are cur rently being evaluated in phase I and II trials. Poten tially beneficial applications of angiogenesis inhibitors include suppression of occult and premalignant le sions, symptomatic control of angiogenesis-depen dent malignancies, and combination therapy with traditional antineoplastic agents.

Conclusion. Inhibition of angiogenesis is a new pharmacologic strategy that may prove useful in controlling malignant growth. A number of agents with antiangiogenic activity have been developed, and further study of these drugs will define their role in antineoplastic therapy.

The twisted survivin connection to angiogenesis

Survivin, a member of the inhibitor of apoptosis family of proteins (IAPs) that controls cell division, apoptosis, metastasis and angiogenesis, is overexpressed in essentially all human cancers. As a consequence, the gene/protein is considered an attractive target for cancer treatment. Here, we discuss recent findings related to the regulation of survivin expression and its role in angiogenesis, particularly in the context of hypoxia. We propose a novel role for survivin in cancer, whereby expression of the protein in tumor cells promotes VEGF synthesis, secretion and angiogenesis. Mechanistically, we propose the existence of a positive feed-back loop involving PI3-kinase/Akt activation and enhanced β-Catenin-TCF/LEF-dependent VEGF expression followed by secretion. Finally, we elaborate on the possibility that this mechanism operating in cancer cells may contribute to enhanced tumor vascularization by vasculogenic mimicry together with conventional angiogenesis.

Functional role of inorganic trace elements in angiogenesis part III: (Ti, Li, Ce, As, Hg, Va, Nb and Pb)

Many essential elements exist in nature with significant influence on human health. Angiogenesis is vital in developmental, repair, and regenerative processes, and its aberrant regulation contributes to pathogenesis of many diseases including cancer. Thus, it is of great importance to explore the role of these elements in such a vital process. This is third in a series of reviews that serve as an overview of the role of inorganic elements in regulation of angiogenesis and vascular function. Here we will review the roles of titanium, lithium, cerium, arsenic, mercury, vanadium, niobium, and lead in these processes. The roles of other inorganic elements in angiogenesis were discussed in part I (N, Fe, Se, P, Au, and Ca) and part II (Cr, Si, Zn, Cu, and S) of these series. The methods of exposure, structure, mechanisms, and potential activities of these elements are briefly discussed. An electronic search was performed on the role of these elements in angiogenesis from January 2005 to April 2014. These elements can promote and/or inhibit angiogenesis through different mechanisms. The anti-angiogenic effect of titanium dioxide nanoparticles comes from the inhibition of angiogenic processes, and not from its toxicity. Lithium affects vasculogenesis but not angiogenesis. Nanoceria treatment inhibited tumor growth by inhibiting angiogenesis. Vanadium treatment inhibited cell proliferation and induced cytotoxic effects through interactions with DNA. The negative impact of mercury on endothelial cell migration and tube formation activities was dose and time dependent. Lead induced IL-8 production, which is known to promote tumor angiogenesis. Thus, understanding the impact of these elements on angiogenesis will help in development of new modalities to modulate angiogenesis under various conditions.

Reactive oxygen species in endothelial function - from disease to adaptation -

Endothelial function is largely dictated by its ability to rapidly sense environmental cues and adapt to these stimuli through changes in vascular tone, inflammation/immune recruitment, and angiogenesis. When any one of these abilities is compromised, the endothelium becomes dysfunctional, which ultimately leads to disease. Reactive oxygen species (ROS) have been established at the forefront of endothelial dysfunction; however, more careful examination has demonstrated that ROS are fundamental to each of the sensing/signaling roles of the endothelium. The purpose of this review is to document endothelial ROS production in both disease and physiological adaptation. Through understanding new endothelial signaling paradigms, we will gain insight into more targeted therapeutic strategies for vascular diseases.

Oxidative stress in angiogenesis and vascular disease

Despite the damaging effect on tissues at a high concentration, it has been gradually established that oxidative stress plays a positive role during angiogenesis. In adults, physiological or pathological angiogenesis is initiated by tissue demands for oxygen and nutrients, resulting in a hypoxia/reoxygenation cycle, which, in turn promotes the formation of reactive oxygen species (ROS). The ROS can be generated either endogenously, through mitochondrial electron transport chain reactions and nicotinamide adenine dinucleotide phosphate oxidase, or exogenously, resulting from exposure to environmental agents, such as ultraviolet or ionizing radiation. In many conditions, ROS promotes angiogenesis, either directly or via the generation of active oxidation products, including peroxidized lipids. The latter lipid metabolites are generated in excess during atherosclerosis, thereby linking atherogenic processes and pathological angiogenesis. Although the main mechanism of oxidative stress-induced angiogenesis involves hypoxia-inducible factor/vascular endothelial growth factor (VEGF) signaling, recent studies have identified several pathways that are VEGF-independent. This review aims to provide a summary of the past and present views on the role of oxidative stress as a mediator and modulator of angiogenesis, and to highlight newly identified mechanisms.

Inhibitory effects of topical thymoquinone on corneal neovascularization

PURPOSE

Thymoquinone, one of the biologically active components of black seed oil, has anti-inflammatory and antioxidant properties. We aimed to study the effect of thymoquinone on corneal neovascularization in rats and to compare its efficacy with that of triamcinolone acetonide.

METHODS

Chemical cauterization of the cornea was performed with silver nitrate/potassium nitrate sticks in 40 eyes in 40 rats. An examiner blinded to the experiments scored the intensity of the cauterization. Topical instillation of thymoquinone 0.1%, thymoquinone 0.4%, and triamcinolone acetonide was continued for 7 days. The inhibitory effects of the drugs on corneal neovascularization were tested and compared with each other and with controls with a computer program that evaluates percent areas of cornea covered by neovascularization.

RESULTS

The means of percent area of corneal neovascularization in the thymoquinone 0.1%, thymoquinone 0.4%, triamcinolone acetonide, and control groups were 60.1%, 45%, 46%, and 72%, respectively. The inhibitory effect of thymoquinone 0.4% was found to be equal to that of triamcinolone acetonide (P = 0.87). The thymoquinone 0.4% and triamcinolone groups were different from the thymoquinone 0.1% and control groups (P < 0.05). There was also a significant difference between the percent area of corneal neovascularization in the thymoquinone 0.1% group and that of the controls (P < 0.05). The mean burn stimulus intensities were not different among the groups (P = 0.54).

CONCLUSIONS

Thymoquinone was shown to have an inhibitory effect, comparable with that of triamcinolone, on corneal neovascularization in this rat model. However, thymoquinone decreased corneal neovascularization in a dose-dependent manner.

Angiogenic signal during cardiac repair

Despite significant advances in myocardial revascularization and reperfusion, coronary artery disease and subsequently myocardial infarction, are the leading causes of morbidity and mortality in the United States. Strategies which improve the myocardial substrate during and following a myocardial infarction-such as the regrowth of functional blood vessels to the ischemic myocardium would be of great clinical importance. This review article attempts to address this important clinical issue through identifying potential signalling mechanisms by various mode of preconditioning that cause angiogenesis.

A key angiogenic role of monocyte chemoattractant protein-1 in hemangioendothelioma proliferation

Angiomatous lesions are common in infants and children. Hemangioendotheliomas (HE) represent one type of these lesions. Endothelial cell proliferation and the development of vascular/blood cell-filled spaces are inherent in the growth of HE. Therefore, understanding mechanisms that regulate the proliferation of these lesions should provide key insight into mechanisms regulating angiogenesis. A murine model was used to test the significance of monocyte chemoattractant protein (MCP)-1 in HE proliferation. EOMA cells, a cell line derived from a spontaneously arising murine HE, generate these lesions with 100% efficiency when injected subcutaneously into syngeneic mice. MCP-1 produced by EOMA cells recruit macrophages, which were shown to induce angiogenic behavior in EOMA cells by stimulating transwell migration and inducing sprout formation on type I collagen gels. When EOMA cells were injected into MCP-1(-/-) mice, only 50% of the mice developed tumors, presumably because the low levels of MCP-1 expressed by the injected EOMA cells were enough to overcome any host deficits of this chemokine. When EOMA cells were coinjected with a neutralizing antibody to MCP-1, tumors failed to develop in any of the treated mice, including syngeneic 129P3, C57Bl/6 (wild type), and MCP-1(-/-). These results present the first evidence that MCP-1 is required for HE proliferation and may promote the growth of these lesions by stimulating angiogenic behavior of endothelial cells. This study has produced the first in vivo evidence of a complete response for any neoplasm, specifically a vascular proliferative lesion, to anti-MCP-1 therapy in animals with intact immune systems.

Redox signaling in vascular angiogenesis

Angiogenesis is thought to be regulated by several growth factors (EGF, TGF-alpha, beta-FGF, VEGF). Induction of these angiogenic factors is triggered by various stresses. For instance, tissue hypoxia exerts its pro-angiogenic action through various angiogenic factors, the most notable being vascular endothelial growth factor, which has been mainly associated with initiating the process of angiogenesis through the recruitment and proliferation of endothelial cells. Recently, reactive oxygen species (ROS) have been found to stimulate angiogenic response in the ischemic reperfused hearts. Short exposure to hypoxia/reoxygenation, either directly or indirectly, produces ROS that induce oxidative stress which is associated with angiogenesis or neovascularization. ROS can cause tissue injury in one hand and promote tissue repair in another hand by promoting angiogenesis. It thus appears that after causing injury to the cells, ROS promptly initiate the tissue repair process by triggering angiogenic response.

MCP-1 expression in CNS-1 astrocytoma cells: implications for macrophage infiltration into tumors in vivo

Gliomas are among the most resistant tumors to conventional anti-tumor therapy, and are typified by their highly infiltrative nature and ill-defined borders. Macrophages constitute a major proportion of the tumor cell mass in both primary human gliomas and as shown here, a CNS-1 glioma model. The objective of this study was to identify tumor-cell-derived chemotactic factor(s) which participate in macrophage recruitment into tumors in vivo. This study demonstrates the constitutive expression of monocyte chemoattractant protein-1 (MCP-1), a potent monocyte chemoattractant, by the rat astrocytoma cell line CNS-1. Characterization of cytokine expression by CNS-1 cells in vitro revealed the constitutive expression of TGF-beta but not other proinflammatory cytokines. However, numerous cytokines were detected in CNS-I tumors in vivo including Ltbeta, IL-1alpha, IL-1beta, TNF-alpha, TNF-beta, IL-10, and IFN-gamma. Attenuation of MCP- I release from CNS-1 cells using an anti-sense approach revealed no significant alterations in macrophage infiltration into tumors in vivo, suggesting redundancy in the signal(s) involved in macrophage recruitment. Depletion of peripheral macrophages using liposome-encapsulated clodronate revealed no significant differences in tumor growth or in the degree of macrophage infiltration into CNS-1 tumors in vivo. These results indicate that CNS-1 cells produce chemotactic factors which likely participate in macrophage recruitment into tumors in vivo. Whether or not macrophage recruitment confers a growth advantage for the tumor remains to be determined.

Human endothelial cells express CCR2 and respond to MCP-1: direct role of MCP-1 in angiogenesis and tumor progression

Although several CXC chemokines have been shown to induce angiogenesis and play roles in tumor growth, to date, no member of the CC chemokine family has been reported to play a direct role in angiogenesis. Here we report that the CC chemokine, monocyte chemotactic protein 1 (MCP-1), induced chemotaxis of human endothelial cells at nanomolar concentrations. This chemotactic response was inhibited by a monoclonal antibody to MCP-1. MCP-1 also induced the formation of blood vessels in vivo as assessed by the chick chorioallantoic membrane and the matrigel plug assays. As expected, the angiogenic response induced by MCP-1 was accompanied by an inflammatory response. With the use of a rat aortic sprouting assay in the absence of leukocytic infiltrates, we ruled out the possibility that the angiogenic effect of MCP-1 depended on leukocyte products. Moreover, the direct effect of MCP-1 on angiogenesis was consistent with the expression of CCR2, the receptor for MCP-1, on endothelial cells. Assessment of supernatant from a human breast carcinoma cell line demonstrated the production of MCP-1. Treatment of immunodeficient mice bearing human breast carcinoma cells with a neutralizing antibody to MCP-1 resulted in significant increases in survival and inhibition of the growth of lung micrometastases. Taken together, our data indicate that MCP-1 can act as a direct mediator of angiogenesis. As a chemokine that is abundantly produced by some tumors, it can also directly contribute to tumor progression. Therefore, therapy employing antagonists of MCP-1 in combination with other inhibitors of angiogenesis may achieve more comprehensive inhibition of tumor growth.

Human endothelial cells express CCR2 and respond to MCP-1: direct role of MCP-1 in angiogenesis and tumor progression

Although several CXC chemokines have been shown to induce angiogenesis and play roles in tumor growth, to date, no member of the CC chemokine family has been reported to play a direct role in angiogenesis. Here we report that the CC chemokine, monocyte chemotactic protein 1 (MCP-1), induced chemotaxis of human endothelial cells at nanomolar concentrations. This chemotactic response was inhibited by a monoclonal antibody to MCP-1. MCP-1 also induced the formation of blood vessels in vivo as assessed by the chick chorioallantoic membrane and the matrigel plug assays. As expected, the angiogenic response induced by MCP-1 was accompanied by an inflammatory response. With the use of a rat aortic sprouting assay in the absence of leukocytic infiltrates, we ruled out the possibility that the angiogenic effect of MCP-1 depended on leukocyte products. Moreover, the direct effect of MCP-1 on angiogenesis was consistent with the expression of CCR2, the receptor for MCP-1, on endothelial cells. Assessment of supernatant from a human breast carcinoma cell line demonstrated the production of MCP-1. Treatment of immunodeficient mice bearing human breast carcinoma cells with a neutralizing antibody to MCP-1 resulted in significant increases in survival and inhibition of the growth of lung micrometastases. Taken together, our data indicate that MCP-1 can act as a direct mediator of angiogenesis. As a chemokine that is abundantly produced by some tumors, it can also directly contribute to tumor progression. Therefore, therapy employing antagonists of MCP-1 in combination with other inhibitors of angiogenesis may achieve more comprehensive inhibition of tumor growth.

Production of vascular endothelial growth factor by murine macrophages: regulation by hypoxia, lactate, and the inducible nitric oxide synthase pathway

Murine thioglycolate-induced peritoneal macrophages (MPMs) and the murine RAW264.7 macrophage-like cell line (RAW cells) constitutively produce vascular endothelial growth factor (VEGF). VEGF production is increased under hypoxic conditions or after cell activation with interferon-gamma (IFNgamma) and endotoxin (lipopolysaccharide, LPS). In contrast, tumor necrosis factor-alpha is produced only by IFNgamma/LPS-activated cells. Lactate (25 mmol/L) does not increase VEGF production by these cells. However, hypoxia, lactate, and IFNgamma/LPS-activated MPMs express angiogenic activity, whereas normoxic, nonactivated MPMs do not. Lack of angiogenic activity is not due to an antiangiogenic factor(s) in the medium of these cells. Angiogenic activity produced by hypoxia and lactate-treated MPMs is neutralized by anti-VEGF antibody, which also neutralizes most of the angiogenic activity produced by IFNgamma/LPS-activated MPMs. The inducible nitric oxide synthase inhibitors Ng-nitro-L-arginine-methyl ester (1.5 mmol/L) and aminoguanidine (1 mmol/L) block production of angiogenic activity by MPMs and RAW cells. In RAW cells, Ng-nitro-L-arginine-methyl ester and AG block IFNgamma/LPS-activated, but not constitutive, VEGF production, whereas in MPMs, neither constitutive nor IFNgamma/LPS-activated VEGF synthesis is affected. Synthesis of tumor necrosis factor-alpha is also unaffected. In contrast to normoxic, nonactivated MPMs, inducible nitric oxide synthase-inhibited, IFNgamma/LPS-activated MPMs produce an antiangiogenic factor(s). We conclude that VEGF is a major contributor to macrophage-derived angiogenic activity, and that activation by hypoxia, lactate, or IFNgamma/LPS switches macrophage-derived VEGF from a nonangiogenic to an angiogenic state. This switch may involve a posttranslational modification of VEGF, possibly by the process of ADP-ribosylation. ADP-ribosylation by MPM cytosolic extracts or by cholera toxin switches rVEGF165 from an angiogenic to a nonangiogenic state. In IFNgamma/LPS-activated MPMs, the inducible nitric oxide synthase-dependent pathway also regulates the expression of an antiangiogenic factor(s) that antagonizes the bioactivity of VEGF and provides an additional regulatory pathway controlling the angiogenic phenotype of macrophages.

Arterial wall neovascularization--potential role in atherosclerosis and restenosis

Neointimal formation and arterial wall remodeling are pivotal causes of luminal narrowing in atherogenesis and restenosis. Arterial remodeling refers to a series of dynamic structural changes that arteries may undergo in response to various stimuli, including changes in blood flow and pressure, and acute injury. The biological mechanisms involved in arterial remodeling are poorly understood and are currently a main target for research. We have recently focused on the role of the arterial wall microcirculation (ie, vasa vasorum) in arterial remodeling after injury. In the past, a correlation between arterial wall neovascularization and the accumulation of arterial plaque has been documented; however, the dynamic role of these microvessels in arterial repair and luminal narrowing has not been examined. The type of arterial injury, the nature of the lesion that develops, and the arterial compartment in which angiogenesis occurs may determine the role of the vasa vasorum in arterial narrowing. In this review, we highlight the data that link arterial wall neovascularization with lesion formation and the process of arterial remodeling.

Angiogenesis as a biologic and prognostic indicator in human breast carcinoma

In this review we describe angiogenesis pathways involved in the development of breast carcinoma. Different assessment techniques for angiogenesis and their optimisation are discussed. Angiogenesis is an important factor for prognosis and will be increasingly important in therapeutic decisions.

Cellular proliferation and infiltration following interstitial irradiation of normal dog brain is altered by an inhibitor of polyamine synthesis

PURPOSE

The objectives of this study were to quantitatively define proliferative and infiltrative cell responses after focal 125I irradiation of normal brain, and to determine the effects of an intravenous infusion of alpha-difluoromethylornithine (DFMO) on those responses.

METHODS AND MATERIALS

Adult beagle dogs were irradiated using high activity 125I sources. Saline (control) or DFMO (150 mg/kg/day) was infused for 18 days starting 2 days before irradiation. At varying times up to 8 weeks after irradiation, brain tissues were collected and the cell responses in and around the focal lesion were quantified. Immunohistochemical stains were used to label astrocytes (GFAP), vascular endothelial cells (Factor VIII), polymorphonuclear leukocytes (PMNs; MAC 387) and cells synthesizing deoxyribonucleic acid (DNA) (BrdU). Cellular responses were quantified using a histomorphometric analysis.

RESULTS

After radiation alone, cellular events included a substantial acute inflammatory response followed by increased BrdU labeling and progressive increases in numbers of capillaries and astrocytes. alpha-Difluoromethylornithine treatment significantly affected the measured cell responses. As in controls, an early inflammatory response was measured, but after 2 weeks there were more PMNs/unit area than in controls. The onset of measurable BrdU labeling was delayed in DFMO-treated animals, and the magnitude of labeling was significantly reduced. Increases in astrocyte and vessel numbers/mm2 were observed after a 2-week delay. At the site of implant, astrocytes from DFMO-treated dogs were significantly smaller than those from controls.

CONCLUSIONS

There is substantial cell proliferation and infiltration in response to interstitial irradiation of normal brain, and these responses are significantly altered by DFMO treatment. Although the precise mechanisms by which DFMO exerts its effects in this model are not known, the results from this study suggest that modification of radiation injury may be possible by manipulating the response of normal cells to injury.

Production of angiogenic activity by human monocytes requires an L-arginine/nitric oxide-synthase-dependent effector mechanism

Human monocytes (M phi) require stimulation with substances such as bacterial endotoxin [LPS (lipopolysaccharide)] to produce angiogenic activity. In this study, we report that stimulation of M phi with LPS (5 micrograms/ml) in the absence of L-arginine greatly reduced their production of angiogenic activity, as assessed in vivo in rat corneas and in vitro by chemotaxis of human umbilical vein endothelial cells (HU-VECs). D-Arginine did not substitute for L-arginine in the production of angiogenic activity. The nitric oxide synthase (NO synthase, EC 1.14-13.39) inhibitors NG-monomethyl-L-arginine (L-NMMA) and NG-nitro-L-arginine methyl ester (L-NAME) both inhibited the production of angiogenic activity by LPS-stimulated M phi in the presence of L-arginine, suggesting the involvement of this enzyme in the pathway that generates angiogenic activity. Neither of these substances directly inhibited the M phi-derived angiogenic activity. LPS-induced production of the cytokines tumor necrosis factor alpha (TNF-alpha) and interleukin 8 (IL-8) was not significantly reduced when M phi were incubated in the absence of L-arginine. Similarly, L-NMMA and L-NAME did not significantly reduce the LPS-induced production of these cytokines by M phi in the presence of L-arginine. These results suggest that the LPS-stimulation-dependent generation of angiogenic activity by M phi requires an L-arginine-dependent NO-synthase effector mechanism that may be independent of the generation of TNF-alpha and IL-8.

Tumour angiogenesis

The progressive emergence of a close relationship between the formation of blood vessels in the vicinity of tumour cells and the development and spreading of tumours, strongly suggests that angiogenesis might be a prerequisite for tumour development. Angiogenesis starts and develops in response to two sets of extracellular signals: soluble angiogenic factors and extracellular matrix. Different experimental models have been used to study angiogenesis in vivo, but they have numerous limitations. Three-dimensional culture systems reconstitute normal interactions between endothelial cells and the surrounding extracellular matrix. Numerous parameters including angiogenic growth factors and cytokines, cell-to-cell interactions and cell-to-extracellular matrix adhesion influence the growth and differentiation of endothelial cells in vitro as well as in vivo. Angiogenesis plays a major role not only in tumour growth but also in metastasis development. Mechanisms of switching to angiogenic phenotype have been recently described and onset of angiogenic activity is now recognized as another discrete step in tumorigenesis. Tumour cells can induce b-FGF expression and exportation, VEGF and VEGF receptor expression and inactivation of the cancer suppressor gene encoding for a fragment of thrombospondin. A controlled net proteolytic balance produced by tumour cells or endothelial cells is required to favour migration and invasion of endothelial cells and angiogenesis. The hypothesis that assessment of tumour angiogenesis might predict tumour aggressiveness in human cancer has recently gained support from several clinical studies. This has been shown for cutaneous melanoma, breast carcinoma, and non-small-cell lung cancer by quantitation of microvessels in human biopsies using von Willebrand factor or CD3 antigen labelling with specific antibodies. However, more specific and sensitive markers are needed to improve this approach for predicting tumour aggressiveness. Folkman proposed twenty years ago that inhibition of angiogenesis might represent a suitable complementary strategy for the treatment of various forms of cancer. Since then numerous angiostatic compounds have been identified but very few of them fit the required criteria of a potential drug. Fumagillin and particularly its synthetic analogue AGM 1470 might be developed for use in humans in the near future.