Differential angiogenic regulation of experimental colitis

Angiopoietins in inflammation and their implication in the development of inflammatory bowel disease. A review

BACKGROUND

Angiopoietins are essential angiogenic mediators. Since inflammatory bowel disease (IBD) involves inflammation, ulceration and regeneration of the intestinal mucosa, the angiopoietin system has been proposed as a factor to maintain pathological angiogenesis during the development of the IBD.

AIM

To review the potential role of angiopoietins in the inflammation driven by angiogenesis during the course of the IBD.

METHODS

Publications were identified by PubMed searches using the following key words: angiopoietin; Tie-2 receptor; angiogenesis; inflammatory bowel disease and inflammation, in various combinations.

RESULTS

Angiopoietin-1 acts as a regulator of blood vessel maturation and has anti-inflammatory properties, whereas angiopoietin-2 marks the onset of angiogenesis and is required for normal formation of lymph vessels. Both angiopoietins make use of their angiogenic regulatory effects via the angiopoietin tyrosine-kinase receptor (Tie-2). While angiogenesis has been shown to promote and sustain many events of inflammation, the involvement of the angiopoietin system in IBD has been reported in few studies. It is not clear whether the angiopoietins' role in the development of intestinal inflammation is due to an imbalance in the levels of these proteins or this system exerts its pro-angiogenic properties through a different mechanism during the close-loop relationship between angiogenesis and inflammation.

CONCLUSIONS

Angiopoietins have key functions in the angiogenic process, and their abnormal activation might depend on their surrounding inflamed environment. The determination of these angiogenic factors in serum and tissue could be useful for monitoring IBD progression.

Anti-VEGF therapy reduces intestinal inflammation in Endoglin heterozygous mice subjected to experimental colitis

Chronic intestinal inflammation is associated with pathological angiogenesis that further amplifies the inflammatory response. Vascular endothelial growth factor (VEGF), is a major angiogenic cytokine that has been implicated in chronic colitis and inflammatory bowel diseases. Endoglin (CD105), a transforming growth factor-β superfamily co-receptor expressed on endothelial and some myeloid cells, is a modulator of angiogenesis involved in wound healing and potentially in resolution of inflammation. We showed previously that Endoglin heterozygous (Eng (+/-)) mice subjected to dextran sodium sulfate developed severe colitis, abnormal colonic vessels and high tissue VEGF. We therefore tested in the current study if treatment with a monoclonal antibody to VEGF could ameliorate chronic colitis in Eng (+/-) mice. Tissue inflammation and microvessel density (MVD) were quantified on histological slides. Colonic wall thickness, microvascular hemodynamics and targeted MAdCAM-1(+) inflamed vessels were assessed in vivo by ultrasound. Mediators of angiogenesis and inflammation were measured by Milliplex and ELISA assays. Colitic Eng (+/-) mice showed an increase in intestinal inflammation, MVD, colonic wall thickness, microvascular hemodynamics and the number of MAdCAM-1(+) microvessels relative to colitic Eng (+/+) mice; these parameters were all attenuated by anti-VEGF treatment. Of all factors up-regulated in the inflamed gut, granulocyte colony-stimulating factor (G-CSF) and amphiregulin were further increased in colitic Eng (+/-) versus Eng (+/+) mice. Anti-VEGF therapy decreased tissue VEGF and inflammation-induced endoglin, IL-1β and G-CSF in colitic Eng (+/-) mice. Our results suggest that endoglin modulates intestinal angiogenic and inflammatory responses in colitis. Furthermore, contrast-enhanced ultrasound provides an excellent non-invasive imaging modality to monitor gut angiogenesis, inflammation and responses to anti-angiogenic treatment.

Relationship between levels of angiogenic and lymphangiogenic factors and the endoscopic, histological and clinical activity, and acute-phase reactants in patients with inflammatory bowel disease

BACKGROUND

Angiogenic and lymphangiogenic factors (ALFs) may play an important role in inflammatory bowel disease (IBD). Our aims were to evaluate levels of ALFs in serum and the colonic mucosa culture supernatant (MCS) of patients with active and quiescent IBD and healthy subjects and to correlate them with the endoscopic, clinical and histological activity and with acute-phase reactants.

METHODS

This is a prospective study of 28 controls and 72 IBD patients. Serum and MCS concentration of VEGFA, VEGFC, VEGFD, VEGFR1, VEGFR2, VEGFR3, PlGF, Ang1, Ang2 and Tie2 were measured by ELISA. Activity was established by specific indexes (CDAI, Mayo score, SES-CD, D'Haens scale and Riley index). Acute-phase reactants were routinely measured.

RESULTS

MCS levels of all ALFs except VEGFR3 were higher in patients with endoscopic (p<0.05), clinical (p<0.05) and histological (p<0.01) activity than in those without it. In serum, VEGFA, VEGFC and Ang1 and VEGFA and Ang1 levels were lower in patients in remission than in patients with clinical and histological activity, respectively (p<0.05). There was a correlation between serum and MCS concentrations for VEGFD, VEGFR3, PlGF and Tie2 (r=0.25, r=0.48, r=-0.45 and r=0.36; p<0.05). Ang2 in MCS was the best predictor for the diagnosis of endoscopic, histological and clinical activity (area under ROC curve>0.8).

CONCLUSIONS

MCS determination suggests a local increase in ALFs that correlates with IBD activity. Although the correlation between ALFs in serum and MCS was not good, the study of some of these factors as possible targets of new drugs for IBD constitutes a key new line of research.

Advances in therapeutic interventions targeting the vascular and lymphatic endothelium in inflammatory bowel disease

PURPOSE OF REVIEW

The review summarizes the current knowledge of the roles played by the vascular and lymphatic endothelium throughout the gut in the pathogenesis of inflammatory bowel disease (IBD) and gives an update on emerging strategies targeting both vasculatures.

RECENT FINDINGS

Enormous efforts have been made to understand the mechanisms underlining the origin, development and maintenance of intestinal chronic inflammation. In particular, new studies focused their attention on the role played by the microvascular and lymphatic endothelium in the pathogenesis of IBD. During inflammation, whereas the microvasculature is responsible for the entry and distribution of immune cells in the mucosa, the lymphatic system controls leukocyte exit, bacterial clearance and edema absorption. The study of these events, which are aberrant during chronic inflammation, has resulted in the identification and validation of several targets for the treatment of experimental colitis, some of which have translated into effective treatments for patients with IBD.

SUMMARY

Although much attention has been paid to the microvascular endothelium and to antiangiogenic therapies, specific studies on the lymphatic vasculature and its functions in IBD are still at the initial stage, and other molecular mechanisms, genes, molecules and new pathways must definitely be explored.

VEGF-A isoform modulation in an preclinical TNBS model of ulcerative colitis: protective effects of a VEGF164b therapy

BACKGROUND

Ulcerative colitis (UC) is the most common form of inflammatory bowel disease in the USA. A key component of UC is the increase in inflammatory angiogenesis of the colon during active disease. This increase is driven to a great extent by the over expression of VEGF-A. Recently, VEGF165(b) (VEGF164(b) in mouse), an anti-angiogenic form of VEGF-A was described and its regulation was determined to be disturbed in many pathologies such as cancer and pre-eclampsia.

RESULTS

The aims of this study were to examine the role of this inhibitory VEGF by expressing this molecule in a model of intestinal inflammation, and to evaluate its expression as a potential new therapeutic approach for treating UC. A modified model of TNBS colitis was used to determine the effects of rVEGF164(b) expression on colon inflammation. Expansion of the vascular system was assessed by immunhistochemical methods and macro- and microscopic measurements of inflammation in the colon were measured. Leukocyte invasion of the tissue was measured by myeloperoxidase assay and identification and counting of lymphoid follicles. Both angio- and lymphangiogenesis were reduced by expression of rVEGF164(b), which correlated with reduction in both gross and microscopic inflammatory scores. Leukocyte invasion of the tissue was also reduced by rVEGF164(b) expression.

CONCLUSIONS

This is the first report using an endogenous inhibitory VEGF-A isoform for therapy in a model of experimental colitis. Inhibitory VEGF molecules play an important role in maintenance of gut homeostasis and may be dysregulated in UC. The results of this study suggest that restoration of rVEGF164(b) expression has anti-inflammatory activity in a TNBS model and warrants further examination as a possible therapeutic for UC.

Protective effects of hydrogen-rich saline on ulcerative colitis rat model

BACKGROUND

Ulcerative colitis (UC) is associated with enhanced production of reactive oxygen species and altered angiogenesis. Molecular hydrogen has been documented as a novel antioxidant to treat various reactive oxygen species-related diseases. The present study aimed to investigate the effects of hydrogen on UC using a rat model.

MATERIALS AND METHODS

UC in rats was induced with intracolonically administrated acetic acid. Hydrogen was supplied through intraperitoneal injection of 10 or 20 mL/kg hydrogen-rich saline. The hydrogen treatment was performed once every 2 d and lasted 2 wk. The stool consistency and weight loss were used to evaluate UC development. Colonic mucosal damage at the end of the experiment was scored using the macroscopic and microscopic observations. Vascular endothelial growth factor expression in the colonic mucosa was determined using immunohistochemistry.

RESULTS

The administration of acetic acid induced acute rat UC, as indicated by diarrhea, weight loss, and colonic mucosal damage. Treatment with hydrogen-rich saline reduced the weight loss and diarrhea and alleviated the colonic mucosal damage in the UC rats. In addition, the expression of vascular endothelial growth factor in the UC rats increased and could be inhibited by hydrogen treatment.

CONCLUSIONS

Antioxidative hydrogen-rich saline effectively protected the rats from UC, which might be, at least in part, because of inhibition of vascular endothelial growth factor.

Therapeutic DNA vaccination and RNA interference in inflammatory bowel disease

Angiogenesis plays a significant role in numerous diseases. Recently, dysbalanced angiogenesis was found to be a component of pathogenesis of inflammatory bowel disease (IBD). Therefore, inhibition of angiogenesis is a novel therapeutic strategy that alleviates the inflammation and clinical outcomes of IBD. Bacteria act as vectors for the delivery of therapeutic sequences, a process that is particularly suitable in IBD, due to the natural occurrence of bacteria in gut. The main focus of the present study was the application of bacterial gene therapy in the modulation of angiogenesis in IBD. As a target molecule we used the main proangiogenic factor, vascular endothelial growth factor (VEGF). Bacterial strain Salmonella typhimurium SL7207 was used as a gene delivery vector for oral application. DNA vaccination and RNA interference were examined and their efficiency in improving the course of the disease in dextran sulfate sodium-induced colitis in mice was compared. The two approaches yielded similar beneficial results in evaluation of the disease activity parameters (stool consistency, weight loss and colon length) as well as VEGF expression and tumor necrosis factor-α (TNF-α). Improvement in all of the parameters compared with the control groups not treated by therapeutic bacterial strains was also observed. All the bacterial groups showed similar improvement in histopathological scoring. Results of this study are consistent with the literature and provide a basis for additional studies on the modulation of angiogenesis in IBD.

Poly-γ-glutamic acid attenuates angiogenesis and inflammation in experimental colitis

Poly-γ-glutamic acid (γ-PGA), naturally secreted from various strains of Bacillus, has anti-inflammatory activity. In inflammatory bowel disease (IBD), inflammation is promoted and sustained by angiogenesis; however, the role played by γ-PGA in this condition is unclear. Therefore, we evaluated γ-PGA effects on angiogenesis and inflammation in a dextran sulfate sodium- (DSS-) induced mouse colitis model. Experimental colitis was induced in male C57BL/6 mice by administering 3% DSS. Disease activity index (DAI), histopathological scores, microvascular density, myeloperoxidase activity, and VEGF-A and VEGFR2 expression were compared among control mice, DSS-treated mice, and mice receiving 3% DSS along with γ-PGA at 50 mg/kg body weight per day or 3% DSS with γ-PGA at 200 mg/kg body weight per day. We found that γ-PGA significantly attenuated weight loss, DAI, and colon shortening. γ-PGA also significantly reduced histopathological evidence of injury. Moreover, γ-PGA significantly attenuated DSS-induced blood vessel densities. Furthermore, γ-PGA attenuated DSS-induced expression of VEGF-A and its receptor, VEGFR2. In addition, γ-PGA treatment led to reduced recruitment of leukocytes to the inflamed colon. Therefore, our results indicate that γ-PGA has potential application in conditions marked by inflammatory-driven angiogenesis and mucosal inflammation.

Probiotic yeast inhibits VEGFR signaling and angiogenesis in intestinal inflammation

Background and Aims

Saccharomyces boulardii (Sb) can protect against intestinal injury and tumor formation, but how this probiotic yeast controls protective mucosal host responses is unclear. Angiogenesis is an integral process of inflammatory responses in inflammatory bowel diseases (IBD) and required for mucosal remodeling during restitution. The aim of this study was to determine whether Sb alters VEGFR (vascular endothelial growth factor receptor) signaling, a central regulator of angiogenesis.

Methods

HUVEC were used to examine the effects of Sb on signaling and on capillary tube formation (using the ECMatrix™ system). The effects of Sb on VEGF-mediated angiogenesis were examined in vivo using an adenovirus expressing VEGF-A(164) in the ears of adult nude mice (NuNu). The effects of Sb on blood vessel volume branching and density in DSS-induced colitis was quantified using VESsel GENeration (VESGEN) software.

Results

1) Sb treatment attenuated weight-loss (p<0.01) and histological damage (p<0.01) in DSS colitis. VESGEN analysis of angiogenesis showed significantly increased blood vessel density and volume in DSS-treated mice compared to control. Sb treatment significantly reduced the neo-vascularization associated with acute DSS colitis and accelerated mucosal recovery restoration of the lamina propria capillary network to a normal morphology. 2) Sb inhibited VEGF-induced angiogenesis in vivo in the mouse ear model. 3) Sb also significantly inhibited angiogenesis in vitro in the capillary tube assay in a dose-dependent manner (p<0.01). 4) In HUVEC, Sb reduced basal VEGFR-2 phosphorylation, VEGFR-2 phosphorylation in response to VEGF as well as activation of the downstream kinases PLCγ and Erk1/2.

Conclusions

Our findings indicate that the probiotic yeast S boulardii can modulate angiogenesis to limit intestinal inflammation and promote mucosal tissue repair by regulating VEGFR signaling.

Increased expression of VEGF and CD31 in postradiation rectal tissue: implications for radiation proctitis

Background. Inflammation mediators related to radiation proctitis are partially elucidated, and neovascularization is thought to play a key role. Objectives. To investigate the expression of vascular endothelial growth factor (VEGF) and CD31 as angiogenetic markers in postradiation rectal tissue. Methods. Rectal mucosa biopsies from 11 patients who underwent irradiation for prostate cancer were examined immunohistochemically for the expression of VEGF and CD31 at three time settings—before, at the completion of, and 6 months after radiotherapy. VEGF expressing vascular endothelial cells and CD31 expressing microvessels were counted separately in 10 high-power fields (HPFs). VEGF vascular index (VEGF-VI) and microvascular density (MVD) were calculated as the mean number of VEGF positive cells per vessel or the mean number of vessels per HPF, respectively. Histological features were also evaluated. Results. VEGF-VI was significantly higher at the completion of radiotherapy (0.17 ± 0.15 versus 0.41 ± 0.24, P = 0.001) declining 6 months after. MVD increased significantly only 6 months after radiotherapy (7.3 ± 3.2 versus 10.5 ± 3.1, P < 0.005). The histopathological examination revealed inflammatory changes at the completion of radiotherapy regressing in the majority of cases 6 months after. Conclusions. Our results showed that in postradiation rectal biopsy specimens neoangiogenesis seems to be inflammation-related and constitutes a significant postradiation component of the tissue injury.

Vascular endothelial growth factor receptor-2 inhibition in experimental murine colitis

BACKGROUND

In the setting of inflammatory bowel disease, inflammation is associated with a simultaneous increase in angiogenesis; moreover, elevated vascular endothelial growth factor (VEGF) levels implicate angiogenesis as a pathologic contributor to disease severity. We hypothesize that selectively inhibiting vascular endothelial growth factor receptor-2 (VEGFR2) in a model of murine colitis will reduce angiogenesis, resulting in decreased inflammation and disease severity, providing mechanistic insight into the role of pathologic angiogenesis in IBD.

MATERIALS AND METHODS

In a dextran sodium sulfate model of murine colitis, anti-VEGFR2 monoclonal antibody (DC101) or placebo was administered. Clinical assessments followed by histologic and molecular tissue analysis were performed to quantify inflammation, microvessel density (MVD), VEGF and VEGFR2 gene expression, and phosphorylated mitogen-activated protein kinase protein expression.

RESULTS

Weight loss began after d 6 with the treatment group demonstrating a more favorable percent weight change. Inflammation and MVD were similar between cohorts, both increasing in parallel toward a plateau. VEGF and VEGFR2 messenger RNA expression were not significantly different, but phosphorylated mitogen-activated protein kinase was elevated in the DC101 cohort (P = 0.03).

CONCLUSIONS

Despite a more favorable weight change profile in the treated group, no difference was observed between cohorts regarding clinical disease severity. However, a parallel rise in inflammation and MVD was observed coinciding with weight loss, suggesting their relationship in IBD. VEGFR2 downstream signaling was significantly elevated in the treated cohort, possibly by VEGF-independent signal transduction. Early and effective inhibition of angiogenesis by limiting downstream VEGF signaling or targeting multiple angiogenic pathways may block angiogenesis, thereby reducing disease severity and provide evidence toward the mechanism and clinical benefit of antiangiogenics in the setting of IBD.

Effect of vascular endothelial cells on the pathogenesis of inflammatory bowel disease

Inflammatory bowel disease (IBD), including Crohn's disease (CD) and ulcerative colitis (UC), are a group of chronic recurrent intestinal autoimmune diseases characterized by intestinal chronic intestinal inflammation. The important characteristics of persistent intestinal inflammation in IBD are the aggregation of inflammatory cells and the release of inflammatory factors in the intestinal mucosa. Functional alternations of immune cells and intestinal microvascular endothelial cells play an important role in the mucosal immunity and intestinal function. Moreover, alternation of the structure and function of microvascular endothelial cells can regulate the migration of immune cells, blood supply and homeostasis of intestinal tissue. Endothelial cells in newly formed vessels can induce tissue injury by regulating the recruitment of blood cells and inflammatory mediators to maintain the inflammatory reaction.

S1P₁ localizes to the colonic vasculature in ulcerative colitis and maintains blood vessel integrity

Signaling through sphingosine-1-phosphate receptor₁ (S1P₁) promotes blood vessel barrier function. Degradation of S1P₁ results in increased vascular permeability in the lung and may explain side effects associated with administration of FTY720, a functional antagonist of the S1P₁ receptor that is currently used to treat multiple sclerosis. Ulcerative colitis (UC) is characterized by an increased density of abnormal vessels. The expression or role of S1P₁ in blood vessels in the colon has not been investigated. In the present study, we show that S1P₁ is overexpressed in the colonic mucosa of UC patients. This increase in S1P₁ levels reflects increased vascular density in the inflamed mucosa. Genetic deletion of S1pr1 in mice increases colonic vascular permeability under basal conditions and increases bleeding in experimental colitis. In contrast, neither FTY720 nor AUY954, two S1P receptor-targeting agents, increases bleeding in experimental colitis. Taken together, our findings demonstrate that S1P₁ is critical to maintaining colonic vascular integrity and may play a role in UC pathogenesis.

Effect of treatment with safflower solution on expression of VEGF and bFGF in ulcerative colitis in rats

AIM: To evaluate the therapeutic effect of safflower solution on 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced ulcerative colitis in rats and to explore the underlying mechanisms by observing the expression of vascular endothelial growth factor (VEGF) and basal fibroblast growth factor (bFGF).

METHODS: Thirty Wistar rats were randomly divided into normal control group, model group and safflower group. Ulcerative colitis was induced in the safflower group and model group with TNBS by enema. Rats of the safflower group were intraperitoneally injected with safflower solution. After ten days, all rats were killed. Disease activity index (DAI), colon macroscopic damage score (CMDS) and histological damage score were evaluated. Pathological changes in the colonic mucosa were examined by HE staining. The expression of VEGF and bFGF in the colonic mucosa was detected by real time-polymerase chain reaction (RT-PCR) and immunohistochemistry (IHC).

RESULTS: Compared to normal controls, the DAI, CMDS and histological damage scores in model rats were significantly increased (all P < 0.01). Compared to the model group, the above parameters were significantly improved in the safflower group (all P < 0.05). Compared to normal controls, the expression levels of VEGF and bFGF in model rats were increased significantly (all P < 0.01). Treatment with safflower solution significantly decreased the expression levels of VEGF mRNA and protein in ulcerative colitis (both P < 0.05).

CONCLUSION: Treatment with safflower solution could reduce inflammatory injury in a rat model of ulcerative colitis possibly by reducing the expression of VEGF and inhibiting pathologic angiogenesis in the colonic mucosa.

For Application to Human Spaceflight and ISS Experiments: VESGEN Mapping of Microvascular Network Remodeling during Intestinal Inflammation

Challenges to long-duration space exploration and colonization in microgravity and cosmic radiation environments by humans include poorly understood risks for gastrointestinal function and cancer. Nonetheless, constant remodeling of the intestinal microvasculature is critical for tissue viability, healthy wound healing, and successful prevention or recovery from vascular-mediated inflammatory or ischemic diseases such as cancer. Currently no automated image analysis programs provide quantitative assessments of the complex structure of the mucosal vascular system that are necessary for tracking disease development and tissue recovery. Increasing abnormalities to the microvascular network geometry were therefore mapped with VESsel GENeration Analysis (VESGEN) software from 3D tissue reconstructions of developing intestinal inflammation in a dextran sulfate sodium (DSS) mouse model. By several VESGEN parameters and a novel vascular network linking analysis, inflammation strongly disrupted the regular, lattice-like geometry that defines the normal microvascular network, correlating positively with the increased recruitment of dendritic cells during mucosal defense responses.

Temporal genome expression profile analysis during t-cell-mediated colitis: identification of novel targets and pathways

BACKGROUND

T cells critically regulate inflammatory bowel disease (IBD), with T-cell-dependent experimental colitis models gaining favor in identifying potential pathogenic mechanisms; yet limited understanding of specific pathogenic molecules or pathways still exists.

METHODS

In this study we sought to identify changes in whole genome expression profiles using the CD4CD45Rbhi T-cell transfer colitis model compared to genome expression differences from Crohn's disease (CD) tissue specimens. Colon tissue was used for histopathological and genome expression profiling analysis at 0, 2, 4, or 6 weeks after adoptive T-cell transfer.

RESULTS

We identified 1775 genes that were significantly altered during disease progression, with 361 being progressively downregulated and 341 progressively upregulated. Gene expression changes were validated by quantitative real-time polymerase chain reaction (qRT-PCR), confirming genome expression analysis data. Differentially expressed genes were clearly related to inflammation/immune responses but also strongly associated with metabolic, chemokine signaling, Jak-STAT signaling, and angiogenesis pathways. Ingenuity network analysis revealed 25 unique network associations that were associated with functions such as antigen presentation, cell morphology, cell-to-cell signaling and interaction, as well as nervous system development and function. Moreover, many of these genes and pathways were similarly identified in CD specimens.

CONCLUSIONS

These findings reveal novel, complex, and dynamic changes in gene expression that may provide useful targets for future therapeutic approaches.

The role of thrombospondin 1 on intestinal inflammation and carcinogenesis

Crohn’s disease and ulcerative colitis are inflammatory bowel diseases (IBD) quite common in the United States and other Western countries. Patients suffering IBD are at greater risk of developing colorectal adenocarcinoma than the general population. Both, the adenomacarcinoma and the inflammation-carcinogenesis processes are characterized by active angiogenesis. Recent studies also have shown that anti-angiogenesis might be a novel therapeutic approach for IBD. Thrombospondin 1 (TSP1) is an extracellular protein well known for its anti-angiogenic properties. TSP1 also has key functions in inflammation, which is assumed to be the primary cause for carcinogenesis in IBD. This review is focused on the role of TSP1 in colorectal carcinogenesis. The therapeutic effects of TSP derived-peptides on inhibiting the inflammation-carcinogenesis progression are also discussed.

VEGF₁₆₄ isoform specific regulation of T-cell-dependent experimental colitis in mice

BACKGROUND

Inflammatory bowel disease (IBD) consists of Crohn's disease (CD) and ulcerative colitis (UC), two widespread diseases of unknown, multifactorial etiology. Colitis pathology involves a pathological angiogenic response where increases in vascular density participate in colitis histopathology. Vascular endothelial growth factor-A (VEGF-A) is a potent angiogenesis stimulator known to be involved in pathological angiogenesis in several diseases including colitis. However, the pathogenic importance of specific VEGF-A isoforms during T-cell-mediated experimental colitis remains largely unknown.

METHODS

The CD4⁺ CD45RB(high) T-cell transfer model of experimental colitis was used for these studies. The VEGF lac-Z transgenic reporter mouse was used to examine specific cellular sources of VEGF-A production. The VEGF₁₆₄ aptamer (Macugen), adenoviral VEGF₁₆₄, and the VEGF Trap were used to evaluate pathological importance.

RESULTS

VEGF lac-Z reporter mice experiments showed that both infiltrating T cells and local tissue cells produce VEGF-A in the colon during disease. Inhibition of VEGF₁₆₄ using a highly selective RNA aptamer significantly attenuated CD4⁺ CD45RB(high) T-cell-dependent experimental colitis by reducing pathological angiogenesis and inflammatory pathology. Conversely, broad-spectrum VEGF inhibition with VEGF Trap did not attenuate disease, nor did adenoviral VEGF₁₆₄ overexpression significantly alter colitis pathology.

CONCLUSIONS

VEGF₁₆₄ is actively produced by multiple cell types during T-cell-mediated colitis. Importantly, specific inhibition of the VEGF₁₆₄ isoform during T-cell-mediated colitis dose-dependently attenuated disease progression, while broad-scale inhibition of all VEGF-A isoforms was not therapeutically beneficial.

Relationship among circulating leukocytes, platelets, and microvascular responses during induction of chronic colitis

The mechanisms by which microvascular alterations contribute to the pathogenesis of the inflammatory bowel diseases (IBDs; Crohn's disease, ulcerative colitis) have not been clearly delineated. The purpose of the current study was to characterize the inflammatory events, microvascular alterations, and blood cell changes that occur in a mouse model of IBD. In this model, CD4(+) T-lymphocytes obtained from interleukin-10-deficient mice were injected intraperitoneally into lymphopenic, recombinase-activating gene-1 deficient (RAG(-/-)) mice. Two groups of control mice were also included: RAG(-/-) mice and C57BL/6 mice that were injected with phosphate-buffered saline but did not receive the T-cells. Four weeks later, the RAG(-/-) mice that had received the T-cell transfer showed significant signs of colonic inflammation, but without significant decreases in either body weight or mean arterial blood pressure. T-cell transfer increased the volume % of circulating platelets, while decreasing the number of circulating red blood cells. Additionally, the T-cell transfer tended to increase the circulating numbers of both lymphocytes and neutrophils when compared to unmanipulated RAG(-/-) mice. First-order colonic arterioles and venules tended to dilate in the colitic mice; however, the dilation was considerably more substantial with higher numbers of circulating leukocytes. The possibility that circulating inflammatory cells initiate the microvascular alterations in colitis warrants further investigation.

Pharmacological intervention studies using mouse models of the inflammatory bowel diseases: translating preclinical data into new drug therapies

Most therapeutic agents used in clinical practice today were originally developed and tested in animal models so that drug toxicity and safety, dose-responses, and efficacy could be determined. Retrospective analyses of preclinical intervention studies using animal models of different diseases demonstrate that only a small percentage of the interventions reporting promising effects translate to clinical efficacy. The failure to translate therapeutic efficacy from bench to bedside may be due, in part, to shortcomings in the design of the clinical studies; however, it is becoming clear that much of the problem resides within the preclinical studies. One potential strategy for improving our ability to identify new therapeutics that may have a reasonable chance of success in clinical trials is to identify the most immunologically-relevant mouse models of IBD and pharmacologic strategies that most closely mimic the clinical situation. This review presents a critical evaluation of the different mouse models and pharmacological approaches that may be used in intervention studies as well as discuss emerging issues related to study design and data interpretation of preclinical studies.

Corticosteroids modulate angiogenic soluble factors in ulcerative colitis patients

AIMS

The aim of this study was to compare angiogenic factors in serum levels of active ulcerative colitis (UC) patients and in healthy controls, and to analyze these angiogenic levels depending on the achievement of remission after oral corticosteroid treatment throughout treatment, and according to the Truelove-Witts activity index.

METHODS

Blood samples were collected from 13 patients receiving oral corticosteroids for treatment of UC flares at three different intervals--baseline, during, and after treatment--and from 26 healthy controls. Vascular endothelial growth factor (VEGF), placental growth factor (PlGF), VEGF receptor 1 (VEGFR1), angiopoietins (Ang) 1 and 2, and its receptor Tie2 were assayed by ELISA.

RESULTS

While VEGF and Ang2 levels in UC patients were higher than in healthy controls (P < 0.05), UC patients showed lower levels of Ang1 than healthy individuals (P < 0.05). In UC patients who achieved clinical remission after corticosteroid treatment, a statistically significant higher baseline serum level of PlGF was observed (22 ± 5 vs. 18 ± 2; P < 0.05). Angiogenic factor levels varied during treatment; however, they did not show a statistically significant correlation to the activity of the disease.

CONCLUSIONS

VEGF, Ang1, and Ang2 levels showed statistically significant differences between UC patients and healthy controls. Although determination of PlGF serum levels before corticosteroid treatment might be helpful to anticipate the response by UC patients, no angiogenic pattern that could accurately predict "a priori" this response to corticosteroid treatment was observed. Corticosteroids altered temporarily circulating levels of VEGF, angiopoietins and Tie2. No correlation was found between systemic levels of angiogenic factors and the clinical activity of UC.

Role of the endothelium in inflammatory bowel diseases

Inflammatory bowel diseases (IBD) are a complex group of diseases involving alterations in mucosal immunity and gastrointestinal physiology during both initiation and progressive phases of the disease. At the core of these alterations are endothelial cells, whose continual adjustments in structure and function coordinate vascular supply, immune cell emigration, and regulation of the tissue environment. Expansion of the endothelium in IBD (angiogenesis), mediated by inflammatory growth factors, cytokines and chemokines, is a hallmark of active gut disease and is closely related to disease severity. The endothelium in newly formed or inflamed vessels differs from that in normal vessels in the production of and response to inflammatory cytokines, growth factors, and adhesion molecules, altering coagulant capacity, barrier function and blood cell recruitment in injury. This review examines the roles of the endothelium in the initiation and propagation of IBD pathology and distinctive features of the intestinal endothelium contributing to these conditions.

Quantitative analysis of intravenously administered contrast media reveals changes in vascular barrier functions in a murine colitis model

Inflammatory bowel disease is a chronic inflammatory disorder of the gastrointestinal tract associated with alterations and dysfunction of the intestinal microvasculature. The goal of this work was to develop a preclinical protocol for quantitative functional characterization of the colonic microvasculature in a murine colitis model. Experimental colitis was induced in mice by addition of dextran sodium sulfate to the drinking water. Histopathologic analysis revealed severe multifocal colitis. Dynamics of intravenously injected macromolecular dextran-FITC and biotin-BSA-GdDTPA in the colonic microvasculature were imaged using fluorescent confocal endomicroscopy and MRI (9.4 T), respectively. Both MRI and fluorescent confocal endomicroscopy revealed a substantial increase in the permeability of the colonic microvasculature associated with colitis, resulting in extravascular accumulation of the macromolecular contrast agent in the lumen of the colon. MRI data were validated by immunohistochemical staining of the contrast agent and leakage of fluorescently labeled BSA-FAM coinjected with the MRI contrast agent. Leakage of plasma proteins and deposition of a provisional matrix can support inflammation and stimulate remodeling of the colonic vasculature. Thus, the plasma protein leakage from the colonic microvasculature at the focal inflammatory patches could be quantified by MRI, providing a biomarker for assessment of disease progression.

VEGF₁₆₄ differentially regulates neutrophil and T cell adhesion through ItgaL- and ItgaM-dependent mechanisms

Leukocyte recruitment to inflamed tissues is the cornerstone of inflammatory responses and the driving force behind the establishment of inflammatory bowel disease, consisting of Crohn's disease and ulcerative colitis. It has been reported that angiogenic cytokines contribute to this inflammatory response that facilitates the chronic nature of disease. We have previously reported (Goebel S, Huang M, Davis WC, Jennings M, Siahaan TJ, Alexander JS, Kevil CG. Am J Physiol Gastrointest Liver Physiol 290: G648-G654, 2006) that vascular endothelial growth factor (VEGF)-A can stimulate neutrophil adhesion to colon microvascular endothelial cells in a β₂-integrin (Itgb2)-dependent manner. However, it is not known which of the specific leukocyte integrins are critical for VEGF-A-dependent neutrophil and T cell recruitment. Here we examine the differential importance of either α-integrin (Itga)L or ItgaM in governing neutrophil and T cell adhesion to VEGF-A-activated colonic endothelium. Using an in vitro parallel-plate flow chamber model, we found that genetic deficiency of ItgaM completely blunted neutrophil adhesion to VEGF-A-stimulated endothelium, whereas ItgaL deficiency only partly blocked neutrophil adhesion. Deficiency of ItgaM did significantly decrease neutrophil rolling, whereas deficiency of ItgaL did not. We found that genetic deficiency of either ItgaL or ItgaM did significantly blunt T cell adhesion to VEGF-A-stimulated colon endothelium. We also found that genetic deficiency of these Itgas significantly attenuated T cell rolling behavior. Lastly, we examined whether VEGF-A-mediated leukocyte recruitment occurred through different VEGF receptor (VEGFR) pathways and found that VEGFR2 activation regulates neutrophil recruitment, whereas both VEGFR1 and VEGFR2 modulate T cell recruitment. Together, these data identify differential molecular mechanisms of VEGF-A-mediated leukocyte recruitment.

Role of anti-angiogenic factor endostatin in the pathogenesis of experimental ulcerative colitis

AIMS

Vascular endothelial growth factor (VEGF) and pathologic angiogenesis have been demonstrated to play a pathogenic role in the development and progression of inflammatory bowel disease. Thus, we hypothesized that the potent anti-angiogenic factor endostatin might play a beneficial role in experimental ulcerative colitis (UC).

MAIN METHODS

We used three animal models of UC: (1) induced by 6% iodoacetamide (IA) in rats, or (2) by 3% dextran sulfate sodium (DSS) in matrix metalloproteinase-9 (MMP-9) knockout (KO) and wild-type mice, and (3) interleukin-10 (IL-10) KO mice. Groups of MMP-9 KO mice with DSS-induced UC were treated with endostatin or water for 5days.

KEY FINDINGS

We found concomitant upregulation of VEGF, PDGF, MMP-9 and endostatin in both rat and mouse models of UC. A positive correlation between the levels of endostatin or VEGF and the sizes of colonic lesions was seen in IA-induced UC. The levels and activities of MMP-9 were also significantly increased during UC induced by IA and IL-10 KO. Deletion of MMP-9 decreased the levels of endostatin in both water- and DSS-treated MMP-9 KO mice. Treatment with endostatin significantly improved DSS-induced UC in MMP-9 KO mice.

SIGNIFICANCE

1) Concomitantly increased endostatin is a defensive response to the increased VEGF in UC, 2) MMP-9 is a key enzyme to generate endostatin which may modulate the balance between VEGF and endostatin during experimental UC, and 3) endostatin treatment plays a beneficial role in UC. Thus, anti-angiogenesis seems to be a new therapeutic option for UC.

Dextran sulfate sodium leads to chronic colitis and pathological angiogenesis in Endoglin heterozygous mice

BACKGROUND

Pathological angiogenesis is an intrinsic component of chronic intestinal inflammation, which results in remodeling and expansion of the gut microvascular bed. Endoglin is essential for endothelial cell function and physiological angiogenesis. In this study we investigated its potential role in the regulation of inflammation by testing the response of Endoglin heterozygous (Eng(+/-)) mice to experimental colitis.

METHODS

C57BL/6 Eng(+/-) and littermate control mice drank water supplemented with 3% dextran sulfate sodium (DSS) for 5 days and were monitored for up to 26 days for clinical signs of colitis. Inflammation, crypt damage, and angiogenic index were scored on histological sections of distal colon. Levels of the vascular endothelial growth factor (VEGF) and angiopoietins were measured by real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and/or Western blots. Vascular permeability was assessed using Evans Blue.

RESULTS

Eng(+/-) and control mice developed acute colitis, which peaked at day 9. While control mice recovered by days 19-26, Eng(+/-) mice progressed to chronic colitis and showed numerous vascular protrusions penetrating into the serosa of the inflamed distal colon. Prior to DSS induction, VEGF levels and vascular permeability were higher in the distal colon of Eng(+/-) mice, while angiopoietin 1 and 2 levels were unchanged. In the chronic phase of colitis, VEGF levels were increased in both groups of mice and remained significantly higher in the Eng(+/-) mice.

CONCLUSIONS

Higher VEGF levels and increased vascular permeability in the distal colon may predispose Eng(+/-) mice to progress to chronic and persistent bowel inflammation, associated with pathological angiogenesis.

Temporal genomewide expression profiling of DSS colitis reveals novel inflammatory and angiogenesis genes similar to ulcerative colitis

Dextran sodium sulfate (DSS)-induced colitis is widely used to study pathological mechanisms and potential treatments of inflammatory bowel disease. Because temporal changes in genome expression profiles remain unknown in this model, we performed whole genome expression profile analysis during the development of DSS colitis in comparison with ulcerative colitis (UC) specimens to identify novel and common responses during disease. Colon tissue from DSS-treated mice was collected at days 0, 2, 4, and 6. Half of each specimen was used for histopathological analysis and half for Affymetrix whole genome expression profiling and qRT-PCR validation. Genesifter and Ingenuity software analysis was used to identify differentially expressed genes and perform interactive network analysis. Identified DSS-associated genes in mice were also compared with UC patient data. We identified 1,609 genes that were significantly altered during DSS colitis; the majority were functionally related to inflammation, angiogenesis, metabolism, biological adhesion, cellular growth and proliferation, and cell-to-cell signaling responses. Five hundred and one genes were progressively upregulated, while one hundred seventy-three genes were progressively downregulated. Changes in gene expression were validated in a subset of 33 genes by qRT-PCR, with r(2) = 0.925. Ingenuity gene interaction network analysis revealed novel relationships among antigen presentation, cell morphology, and other biological functions in the DSS mouse. Finally, DSS colitis gene array data were compared with UC patient array data: 152 genes were similarly upregulated, and 22 genes were downregulated. Temporal genomewide expression profile analysis of DSS-induced colitis revealed novel associations with various immune responses and tissue remodeling events such as angiogenesis similar to those in UC patients. This study provides a comprehensive view of DSS colitis changes in colon gene expression and identifies common molecules with clinical specimens that are interesting targets for further investigation.

Angiopoietin-2 in experimental colitis

BACKGROUND

The pathophysiology of inflammatory bowel disease (IBD) includes leukocyte infiltration, blood and lymphatic remodeling, weight loss and protein enteropathy. The roles of angiopoietin-2 (Ang-2) in initiating gut inflammation, leukocyte infiltration and angiogenesis are not well understood.

METHODS

Disease activity index, histopathological scoring, myeloperoxidase assay, immunohistochemistry and sodium dodecyl sulphate- polyacrylamide gel electrophoretic methods were employed in the present study to address the roles of Ang-2 in experimental colitis.

RESULTS

Several important differences were seen in the development of experimental IBD in Ang-2(-/-) mice. Although weight change and disease activity differ only slightly in WT and Ang-2(-/-) + DSS treated mice, leukocyte infiltration, inflammation and blood and lymphatic vessel density is significantly attenuated compared to WT + DSS mice. Gut capillary fragility and water export (stool blood and form) appear significantly earlier in Ang-2(-/-) + DSS mice vs. WT. Colon lengths were also significantly reduced in Ang-2(-/-) and gut histopathology was less severe in Ang-2(-/-) compared to WT + DSS. Lastly, the decrease in serum protein content in WT + DSS was less severe in Ang-2(-/-) + DSS, thus protein losing enteropathy (PLE) a feature of IBD is relieved by Ang-2(-/-).

CONCLUSION

These data demonstrate that in DSS colitis, Ang-2 mediates inflammatory hemangiogenesis, lymphangiogenesis and neutrophil infiltration to reduce some, but not all clinical features of IBD. The implications for Ang-2 manipulation in the development of IBD and other inflammatory diseases and treatments involving Ang-2 are discussed.

Caveolae, caveolins, and cavins: complex control of cellular signalling and inflammation

Caveolae are specialized lipid rafts that form flask-shaped invaginations of the plasma membrane. They are involved in cell signalling and transport and have been shown critically regulate vascular reactivity and blood pressure. The organization and functions of caveolae are mediated by coat proteins (caveolins) and support or adapter proteins (cavins). The caveolins, caveolin-1, -2, and -3, form the structural backbone of caveolae. These proteins are also highly integrated into caveolae function and have their own activity independent of caveolae. The cavins, cavins 1-4, are involved in regulation of caveolae and modulate the function of caveolins by promoting the membrane remodelling and trafficking of caveolin-derived structures. The relationships between these different proteins are complex and intersect with many aspects of cell function. Caveolae have also been implicated in chronic inflammatory conditions and other pathologies including atherosclerosis, inflammatory bowel disease, muscular dystrophy, and generalized dyslipidaemia. The pathogenic role of the caveolins is an emerging area, however, the roles of cavins in disease is just beginning to be explored. This review will examine the relationship between caveolins and cavins and explore the role of caveolae in inflammatory signalling mechanisms.

Association between blood flow and inflammatory state in a T-cell transfer model of inflammatory bowel disease in mice

BACKGROUND

Adoptive transfer of naive T-lymphocyte subsets into lymphopenic mice initiates chronic gut inflammation that mimics several aspects of inflammatory bowel disease (IBD). Patients with IBD can have profound alterations in intestinal blood flow, but whether the same is true in the T-cell transfer model has yet to be determined.

METHODS

In the current study, chronic intestinal inflammation was induced in recombinase-activating gene-1-deficient (RAG(-/-)) mice by adoptive transfer of CD4(+) T-lymphocytes obtained from interleukin-10 deficient (IL-10(-/-)) mice.

RESULTS

Four weeks later, widespread colonic inflammation was observed in the reconstituted recipients, in contrast to 2 control sets of mice injected with a different subset of lymphocytes or with vehicle alone. We observed that the resulting pathology induced in the reconstituted RAG(-/-) mice was divided distinctly into 2 subsets: 1 with blood flow near normal with very high inflammation scores, and the other with severely attenuated blood flow but with much lower signs of inflammation. Colonic and ileal blood flow rates in the latter subset of CD4(+) mice averaged only approximately 30% compared to the mice with higher inflammation scores. The lower blood flow rates were associated with greatly reduced red blood cell concentrations in the tissue, suggesting a possible loss of vascular density.

CONCLUSIONS

In this model of chronic intestinal inflammation, mild inflammation was associated with significant decreases in blood flow.

On the role of ischemia in the pathogenesis of IBD: a review

Inflammatory bowel disease (IBD) is a chronic intestinal disorder comprising 2 distinct but often overlapping diseases: Crohn's disease and ulcerative colitis. Although much research to identify the etiology of IBD has focused on genetic constitution, infectious causes, and immune dysregulation, its exact cause and pathogenesis remain incompletely understood. Mesenteric blood flow, the intestinal microcirculation, and intestinal ischemia also have been proposed as etiologic, although they remain less-explored themes despite evidence suggesting a contributory role in IBD pathogenesis. The anatomy, architecture, and function of the splanchnic microcirculation will be reviewed here with regard to the development of intestinal microvascular ischemia, a pathologic process that appears to precede the classic changes that characterize IBD.

Absence of placental growth factor blocks dextran sodium sulfate-induced colonic mucosal angiogenesis, increases mucosal hypoxia and aggravates acute colonic injury

Angiogenesis has recently been described as a component of inflammatory bowel disease. Placental growth factor (PlGF), a vascular endothelial growth factor (VEGF) homologue, establishes its angiogenic capacity under pathophysiological conditions. We investigated the function of PlGF in experimental models of acute colitis. Acute colonic damage was induced in PlGF knock-out ((-/-)) mice and PlGF wild-type ((+/+)) mice by dextran sodium sulfate (DSS) and trinitrobenzenesulfonic acid (TNBS). The concentrations of PlGF and VEGF were measured in distal colonic lysates using an enzyme-linked immunosorbent assay. Colonic injury was evaluated by assessing colon length, colonocyte apoptosis (by terminal dUTP nick-end labeling), colonic cytokine production and histological score. Infiltration of polymorphonuclear cells was determined by assaying myeloperoxidase (MPO) activity. In a separate experiment, recombinant PlGF was administered to PlGF(-/-) mice by adenoviral transfer before DSS administration. Mucosal vascularization was quantified by computerized morphometric analysis of CD31-stained distal colonic sections. Colonic mucosal hypoxia was visualized by pimonidazole staining. Both VEGF and PlGF were upregulated during acute colitis. In addition, compared with PlGF(+/+) controls, PlGF(-/-) mice showed a significant increase in weight loss and colonic shortening during both DSS and TNBS colitis. This correlated with enhanced colonocyte apoptosis, elevated colonic cytokine levels and increased histological damage score, but not with enhanced inflammatory cell infiltration (MPO activity). The increased morbidity of PlGF(-/-) mice during DSS colitis was preventable by adenovirus (Ad)-mediated overexpression of PlGF. After the administration of DSS, strongly reduced mucosal angiogenesis was observed in PlGF(-/-) mice compared with PlGF(+/+) mice. This was associated with an early increase in intestinal epithelial pimonidazole accumulation in PlGF(-/-) mice, suggesting a function of enhanced epithelial hypoxia in the observed differences between the two groups. In summary, our data show that the absence of PlGF strongly inhibits mucosal intestinal angiogenesis in acute colitis, which is associated with an early increase in intestinal epithelial hypoxia and aggravation of the course of the disease.

Quantitative lymphatic vessel trait analysis suggests Vcam1 as candidate modifier gene of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic debilitating disease resulting from a complex interaction of multiple genetic factors with the environment. To identify modifier genes of IBD, we used an F2 intercross of IBD-resistant C57BL/6J-Il10(-/-) mice and IBD-susceptible C3H/HeJBir-Il10(-/-) (C3Bir-Il10(-/-)) mice. We found a prominent involvement of lymphatic vessels in IBD and applied a scoring system to quantify lymphatic vascular changes. Quantitative trait locus (QTL) analyses revealed a large-effect QTL on chromosome 3, mapping to an interval of 43.6 Mbp. This candidate interval was narrowed by fine mapping to 22 Mbp, and candidate genes were analyzed by a systems genetics approach that included quantitative gene expression profiling, search for functional polymorphisms, and haplotype block analysis. We identified vascular adhesion molecule 1 (Vcam1) as a candidate modifier gene in the interleukin 10-deficient mouse model of IBD. Importantly, VCAM1 protein levels were increased in susceptible C3H/HeJ mice, compared with C57BL/6J mice; systemic blockade of VCAM1 in C3Bir-Il10(-/-) mice reduced their inflammatory lymphatic vessel changes. These results indicate that genetically determined expression differences of VCAM1 are associated with susceptibility to colon inflammation, which is accompanied by extensive lymphatic vessel changes. VCAM1 is, therefore, a promising therapeutic target for IBD.

Endogenous IGF-I and alphaVbeta3 integrin ligands regulate increased smooth muscle hyperplasia in stricturing Crohn's disease

BACKGROUND & AIMS

Insulin-like growth factor-I (IGF-I) regulates human intestinal smooth muscle growth by stimulating proliferation and inhibiting apoptosis. IGF-I-stimulated growth is augmented when alphaVbeta3 integrin is occupied by its ligands, fibronectin and vitronectin. Increased IGF-I expression and muscle cell hyperplasia are features of stricturing Crohn's disease (CD); however, the role of IGF-I in stricture formation is unknown. The aim was to identify the functional role of endogenous IGF-I and alphaVbeta3 integrin ligands in regulating muscle cell hyperplasia in stricturing CD.

METHODS

Smooth muscle cells were isolated from muscularis propria of stricturing CD or normal margins. Quantitative polymerase chain reaction, immunoblot analysis, and enzyme-linked immunosorbent assay were used to measure fibronectin, vitronectin, alphaVbeta3 integrin, and IGF-I levels. Activation of the IGF-I receptor, Erk1/2, p70S6 kinase, and GSK-3beta was measured by immunoblot. Proliferation was quantified by Ki67 immunostaining and [(3)H]thymidine incorporation. Apoptosis was measured from caspase-3 cleavage and nucleosome accumulation.

RESULTS

IGF-I, vitronectin, and fibronectin RNA and protein levels were increased 1.8- to 3.4-fold in muscle cells from strictures over normal margins. Basal IGF-I receptor phosphorylation was increased 320% in strictured over normal muscle, and basal Erk1/2, p70S6 kinase, and GSK-3beta phosphorylation were increased 205%-292% in strictures. In muscle cells from strictures, Ki67 immunoreactivity and [(3)H]thymidine incorporation were increased and apoptosis was decreased compared with normal margins. Antagonists of the IGF-I receptor or alphaVbeta3 integrin reversed these changes.

CONCLUSIONS

Smooth muscle cell hyperplasia in stricturing CD is regulated by increased endogenous IGF-I and alphaVbeta3 integrin ligands that regulate augmented proliferation and diminished apoptosis.

Effects of the endothelin-converting enzyme inhibitor SM-19712 in a mouse model of dextran sodium sulfate-induced colitis

BACKGROUND

Ingestion by mice of dextran sodium sulfate (DSS) induces colonic vasoconstriction and inflammation, with some of the effects potentially mediated by the vasoconstrictor endothelin-1 (ET-1).

METHODS

In this study, mice given 5% 40 kD DSS for 5-6 days had elevated colonic immunostaining for ET-1 and platelet endothelial cell adhesion molecule-1 (PECAM-1). Increased ET-1 can induce microvascular constriction; however, the increase in PECAM-1 is consistent with angiogenesis that could decrease flow resistance.

RESULTS

Our measurements of intestinal blood flow, via infused microspheres, suggests that these 2 factors may offset each other, with only a nonsignificant tendency for a DSS-induced decrease in flow. Daily administration of the endothelin converting enzyme inhibitor SM-19712 (15 mg/kg) attenuated DSS-induced increases in colonic immunostaining of ET-1 and PECAM-1.

CONCLUSIONS

SM-19712 attenuated histologic signs of tissue injury and inflammation induced by DSS, and decreased the extent of loose stools and fecal blood. However, the inhibitor did not significantly decrease DSS-induced colon shortening or tissue levels of myeloperoxidase (an indicator of neutrophil infiltration).

Altered microvascular hemodynamics during the induction and perpetuation of chronic gut inflammation

Adoptive transfer of naïve CD4+ T cells into lymphopenic mice induces chronic small and large bowel inflammation similar to Crohn's disease. Although much is now known regarding the immunopathology in this model of inflammatory bowel disease, virtually nothing is known about the microvascular hemodynamic changes during the induction and perpetuation of chronic gut inflammation. In this study, CD4+CD45RBhigh T cells obtained from healthy C57BL/6 donor mice were transferred into lymphopenic recombinase-activating gene-1-deficient (RAG knockout) mice, which induced small and large bowel inflammation. At various time points following reconstitution (3 days-9 wk), intravital microscopy was used to examine the microvessels in the submucosa of the ileum and proximal colon following infusion of fluorescently labeled platelets and injection of rhodamine 6G (to label leukocytes). Hemodynamic measurements and the extent of blood cell adhesion to the venular wall were compared with measurements in unreconstituted RAG knockout controls. In <1 wk following reconstitution, velocity and wall shear rate of the arterioles decreased by >50% compared with controls, with this decrease also observed at 4-5 and 7-9 wk postreconstitution. At 7-9 wk, arteriolar diameters were found to be approximately 15% larger than in controls, but, despite this dilation, flow rates in the individual vessels were decreased by approximately 30%. Venular platelet and leukocyte adherence were not significantly elevated above controls; however, an association was found between platelet adherence and venular shear rate. In summary, significant decreases in arteriolar velocity and shear rates are observed in this model of chronic gut inflammation.

Neutralizing anti-vascular endothelial growth factor (VEGF) antibody reduces severity of experimental ulcerative colitis in rats: direct evidence for the pathogenic role of VEGF

In ulcerative colitis (UC), an increased expression of vascular endothelial growth factor (VEGF) correlates with disease activity, but a causal relationship is unknown. We tested the hypothesis that VEGF plays a mechanistic role in the pathogenesis of experimental UC and that VEGF neutralization may exert therapeutic effect. UC was induced in Sprague-Dawley rats by 6% iodoacetamide given intracolonically. Neutralizing anti-VEGF antibody (50 microg/rat), nonspecific IgG, or saline (0.1 ml/rat) was injected intramuscularly on the 3rd and 5th days after iodoacetamide enema. Rats were euthanized on the 7th day. We examined the extent of macroscopic, histologic, and clinical features of colitis and colonic vascular permeability. Colonic VEGF mRNA and protein expressions increased as early as 0.5 h after iodoacetamide enema and remained elevated in the active phase of colitis. Treatment with anti-VEGF antibody markedly improved the clinical and morphologic features of UC. Colonic lesion area was significantly reduced from 370 +/- 140 or 311 +/- 170 mm(2) in saline- or IgG-treated groups to 122 +/- 57 mm(2) in the anti-VEGF-group (p < 0.05). Increased colonic vascular permeability was decreased by the anti-VEGF antibody (p < 0.05) and the Src inhibitor PP1 [pyrazolopyrimidine, 4-amino-5-(4-methylphenyl)-7-(t-butyl)pyrazolo[3,4-d]-pyrimidine] (p < 0.01). The number of acute and chronic inflammatory cells in the lesion area was significantly reduced in anti-VEGF-treated rats. In the anti-VEGF-treated group, mucosal levels of VEGF, platelet-derived growth factor, and basic fibroblast growth factor were also reduced.

IN CONCLUSION

1) Neutralizing anti-VEGF antibody significantly ameliorates experimental UC in rats in part by reducing excessive vascular permeability and decreasing inflammatory cells infiltration; and 2) VEGF seems to mediate increased colonic vascular permeability in experimental UC via the Src-dependent mechanism.

Loss of purinergic vascular regulation in the colon during colitis is associated with upregulation of CD39

Evidence from patients with inflammatory bowel disease (IBD) and animal models suggests that inflammation alters blood flow to the mucosa, which precipitates mucosal barrier dysfunction. Impaired purinergic sympathetic regulation of submucosal arterioles, the resistance vessels of the splanchnic vasculature, is one of the defects identified during IBD and in mouse models of IBD. We hypothesized that this may be a consequence of upregulated catabolism of ATP during colitis. In vivo and in vitro video microscopy techniques were employed to measure the effects of purinergic agonists and inhibitors of CD39, an enzyme responsible for extracellular ATP catabolism, on the diameter of colonic submucosal arterioles from control mice and mice with dextran sodium sulfate [DSS, 5% (wt/vol)] colitis. Using a luciferase-based ATP assay, we examined the degradation of ATP and utilized real-time PCR, Western blotting, and immunohistochemistry to examine the expression and localization of CD39 during colitis. Arterioles from mice with DSS colitis did not constrict in response to ATP (10 microM) but did constrict in the presence of its nonhydrolyzable analog alpha,beta-methylene ATP (1 microM). alpha,beta-Methylene ADP (100 microM), an inhibitor of CD39, restored ATP-induced vasoconstriction in arterioles from mice with DSS-induced colitis. CD39 protein and mRNA expression was markedly increased during colitis. Immunohistochemical analysis demonstrated that, in addition to vascular CD39, F4/80-immunoreactive macrophages accounted for a large proportion of submucosal CD39 staining during colitis. These data implicate upregulation of CD39 in impaired sympathetic regulation of gastrointestinal blood flow during colitis.

VEGF-A links angiogenesis and inflammation in inflammatory bowel disease pathogenesis

BACKGROUND & AIMS

Vascular endothelial growth factor A (VEGF-A) mediates angiogenesis and might also have a role in inflammation and immunity. We examined whether VEGF-A signaling has a role in inflammatory bowel disease (IBD).

METHODS

Expression levels of VEGF-A, and its receptors VEGFR-1 and VEGFR-2, were examined in samples from patients with IBD and compared with those of controls. The capacity of VEGF-A to induce angiogenesis was tested in human intestinal microvascular endothelial cells using cell-migration and matrigel tubule-formation assays. Levels of vascular cellular adhesion molecule-1 and intercellular adhesion molecule were measured by flow cytometry to determine induction of inflammation; neutrophil adhesion was also assayed. Expression patterns were determined in tissues from mice with dextran sulfate sodium (DSS)-induced colitis; the effects of VEGF-A overexpression and blockade were assessed in these mice by adenoviral transfer of VEGF-A and soluble VEGFR-1. Intestinal angiogenesis was measured by quantitative CD31 staining and leukocyte adhesion in vivo by intravital microscopy.

RESULTS

Levels of VEGF-A and VEGFR-2 increased in samples from patients with IBD and colitic mice. VEGF-A induced angiogenesis of human intestinal microvascular endothelial cells in vitro as well as an inflammatory phenotype and adherence of neutrophils to intestinal endothelium. Overexpression of VEGF-A in mice with DSS-induced colitis worsened their condition, whereas overexpression of soluble VEGFR-1 had the opposite effect. Furthermore, overexpression of VEGF-A increased mucosal angiogenesis and stimulated leukocyte adhesion in vivo.

CONCLUSIONS

VEGF-A appears to be a novel mediator of IBD by promoting intestinal angiogenesis and inflammation. Agents that block VEGF-A signaling might reduce intestinal inflammation in patients with IBD.

Endothelial caveolin-1 regulates pathologic angiogenesis in a mouse model of colitis

BACKGROUND & AIMS

Increased vascular density has been associated with progression of human inflammatory bowel diseases (IBDs) and animal models of colitis. Pathologic angiogenesis in chronically inflamed tissues is mediated by several factors that are regulated at specialized lipid rafts known as caveolae. Caveolin-1 (Cav-1), the major structural protein of caveolae in endothelial cells, is involved in the regulation of angiogenesis, so we investigated its role in experimental colitis.

METHODS

Colitis was induced by administration of dextran sodium sulfate to wild-type and Cav-1(-/-) mice, as well as Cav-1(-/-) mice that overexpress Cav-1 only in the endothelium. Colon tissues were analyzed by histologic analyses. Leukocyte recruitment was analyzed by intravital microscopy; angiogenesis was evaluated by immunohistochemistry and in vivo disk assays.

RESULTS

Cav-1 protein levels increased after the induction of colitis in wild-type mice. In Cav-1(-/-) mice or mice given a Cav-1 inhibitory peptide, the colitis histopathology scores, vascular densities, and levels of inflammatory infiltrates decreased significantly compared with controls. Lower levels of leukocyte and platelet rolling and adhesion colitis also were observed in Cav-1(-/-) mice and mice given a Cav-1 inhibitory peptide, compared with controls. Cav-1(-/-) mice that received transplants of wild-type bone marrow had a lower colitis score than wild-type mice. Data from mice that overexpress Cav-1 only in the endothelium indicated that endothelial Cav-1 is the critical regulator of colitis. Genetic deletion or pharmacologic inhibition of endothelial Cav-1 also significantly decreased vascular densities and angiogenesis scores, compared with controls.

CONCLUSIONS

Endothelial Cav-1 mediates angiogenesis in experimental colitis. Modulation of Cav-1 could provide a novel therapeutic target for IBD.

Thalidomide effect in endothelial cell of acute radiation proctitis

AIM: To determine whether thalidomide prevents microvascular injury in acute radiation proctitis in white rats.

METHODS: Fourteen female Wistar rats were used: six in the radiation group, six in the thalidomide group, and two in normal controls. The radiation and thalidomide groups were irradiated at the pelvic area using a single 30 Gy exposure. The thalidomide (150 mg/kg) was injected into the peritoneum for 7 d from the day of irradiation. All animals were sacrificed and the rectums were removed on day 8 after irradiation. The microvessels of resected specimens were immunohistochemically stained with thrombomodulin (TM), von Willebrand Factor (vWF), and vascular endothelial growth factor (VEGF).

RESULTS: The microscopic scores did not differ significantly between the radiation and thalidomide groups, but both were higher than in the control group. Expression of TM was significantly lower in the endothelial cells (EC) of the radiation group than in the control and thalidomide groups (P < 0.001). The number of capillaries expressing vWF in the EC was higher in the radiation group (15.3 ± 6.8) than in the control group (3.7 ± 1.7), and the number of capillaries expressing vWF was attenuated by thalidomide (10.8 ± 3.5, P < 0.001). The intensity of VEGF expression in capillaries was greater in the radiation group than in the control group and was also attenuated by thalidomide (P = 0.003).

CONCLUSION: The mechanisms of acute radiation-induced proctitis in the rats are related to endothelial cell injury of microvessel, which may be attenuated with thalidomide.

Increased expression of VEGF and CD146 in patients with inflammatory bowel disease

BACKGROUND

Angiogenesis has been suggested as an integral part of inflammatory bowel disease pathology. Vascular endothelial growth factor has long been considered to play a central, specific role in angiogenesis. Endothelial junction adhesion molecules, such as CD146, have recently been suggested to play a potent role in angiogenesis. CD34 is expressed on vascular endothelium, and it has been reported to be upregulated on endothelium in IBD. We investigated the expression of tissue vascular endothelial growth factor, CD34 and CD146 in the inflamed mucosa of patients with active inflammatory bowel disease compared with no inflamed mucosa of healthy controls.

METHODS

Forty-two IBD patients [23 ulcerative colitis, 19 Crohn's disease] and ten healthy controls were included in the study. In colonoscopically obtained biopsies, CD34, CD146 and vascular endothelial growth factor expression were evaluated by immunohistochemistry.

RESULTS

Vascular endothelial growth factor was detected in the mucosa of all groups, and its expression was significantly higher in both Crohn's disease and ulcerative colitis compared with controls (p<0.05). Immunohistochemical staining for CD146 in the inflamed mucosa was significantly higher in both Crohn's disease and ulcerative colitis compared with controls (p=0.002). A trend of higher CD34 expression in Crohn's disease and ulcerative colitis compared with controls was also found, but the difference among the three groups was not statistically significant (p=0.09).

CONCLUSIONS

Inflamed mucosa of patients with active Crohn's disease and ulcerative colitis showed a markedly enhanced expression of VEGF and CD146, than normal mucosa of controls, indicating a possible role of angiogenesis in the pathogenesis of inflammatory bowel disease.

SNO-hemoglobin is not essential for red blood cell-dependent hypoxic vasodilation

The coupling of hemoglobin sensing of physiological oxygen gradients to stimulation of nitric oxide (NO) bioactivity is an established principle of hypoxic blood flow. One mechanism proposed to explain this oxygen-sensing-NO bioactivity linkage postulates an essential role for the conserved Cys93 residue of the hemoglobin beta-chain (betaCys93) and, specifically, for S-nitrosation of betaCys93 to form S-nitrosohemoglobin (SNO-Hb). The SNO-Hb hypothesis, which conceptually links hemoglobin and NO biology, has been debated intensely in recent years. This debate has precluded a consensus on physiological mechanisms and on assessment of the potential role of SNO-Hb in pathology. Here we describe new mouse models that exclusively express either human wild-type hemoglobin or human hemoglobin in which the betaCys93 residue is replaced with alanine to assess the role of SNO-Hb in red blood cell-mediated hypoxic vasodilation. Substitution of this residue, precluding hemoglobin S-nitrosation, did not change total red blood cell S-nitrosothiol abundance but did shift S-nitrosothiol distribution to lower molecular weight species, consistent with the loss of SNO-Hb. Loss of betaCys93 resulted in no deficits in systemic or pulmonary hemodynamics under basal conditions and, notably, did not affect isolated red blood cell-dependent hypoxic vasodilation. These results demonstrate that SNO-Hb is not essential for the physiologic coupling of erythrocyte deoxygenation with increased NO bioactivity in vivo.

Multiple pathogenic roles of microvasculature in inflammatory bowel disease: a Jack of all trades

The etiology of Crohn's disease and ulcerative colitis, the two major forms of inflammatory bowel disease (IBD), is still largely unknown. However, it is now clear that the abnormalities underlying pathogenesis of intestinal inflammation are not restricted to those mediated by classic immune cells but also involve nonimmune cells. In particular, advances in vascular biology have outlined a central and multifaceted pathogenic role for the microcirculation in the initiation and perpetuation of IBD. The microcirculation and its endothelial lining play a crucial role in mucosal immune homeostasis through tight regulation of the nature and magnitude of leukocyte migration from the intravascular to the interstitial space. Chronically inflamed IBD microvessels display significant alterations in microvascular physiology and function compared with vessels from healthy and uninvolved IBD intestine. The investigation into human IBD has demonstrated how endothelial activation present in chronically inflamed IBD microvessels results in a functional phenotype that also includes leakiness, chemokine and cytokine expression, procoagulant activity, and angiogenesis. This review contemplates the newly uncovered contribution of intestinal microcirculation to pathogenesis and maintenance of chronic intestinal inflammation. In particular, we assess the multiple roles of the microvascular endothelium in innate immunity, leukocyte recruitment, coagulation and perfusion, and immune-driven angiogenesis in IBD.