Differential angiogenic regulation of experimental colitis

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.

Thrombospondin 1 and its mimetic peptide ABT-510 decrease angiogenesis and inflammation in a murine model of inflammatory bowel disease

OBJECTIVE

Vascular abnormalities and expression of proangiogenic factors have been repeatedly reported in inflammatory bowel disease (IBD). Thrombospondin 1 (TSP-1) is a protein well known for its antiangiogenic and anti-inflammatory properties. Using the dextran sulfate sodium (DSS) model, the role of TSP-1 in IBD has been investigated in vivo.

METHODS

TSP-1-deficient mice (TSP-1-/-) and WT mice were treated with DSS for 7 days. Disease activity indices, myeloperoxidase activity (MPO) and histology were analyzed. Microvascular density (MVD) was quantified using immunohistochemistry (IMH) with CD31 antibody. TGF-beta(1), basic FGF, VEGF, TNF-alpha and MMPs protein levels were evaluated by IMH and enzyme-linked immunoabsorbent assay (ELISA). Mice were treated with ABT-510 (Abbott Laboratories), an antiangiogenic TSP peptide, using miniosmotic pumps for 7 days.

RESULTS

TSP-1(-/-) mice had a worse clinical outcome and exhibited severe signs of rectal bleeding compared to the WT controls. The TSP-1-/- mice showed a higher level of crypt damage and deeper lesions. The grade of inflammation and the levels of MPO activity were also significantly higher in colons of TSP-1-/- mice. TSP-1-/- mice displayed higher MVD in focal areas of the colon after only 3 days of DSS treatment. Furthermore, clinical severity of the colitis and angiogenesis was significantly diminished when mice was treated with ABT-510.

CONCLUSIONS

These findings directly link TSP-1 as a protective factor in IBD and suggest antiangiogenesis treatment, including compounds such as ABT-510 as an adjuvant therapy for IBD.

Negative regulators of angiogenesis in inflammatory bowel disease: thrombospondin in the spotlight

Angiogenesis is the growth of new blood vessels. In the two major forms of inflammatory bowel disease (IBD), Crohn's disease and ulcerative colitis, robust angiogenesis exists, and its blockade may have therapeutic potential, as shown in animal models of experimental intestinal inflammation. While abundant literature is available on the positive regulators of intestinal pathological angiogenesis, e.g. VEGF, b-FGF, IL-8, CD40 and CD40L, almost no data exist on negative regulators. Thrombospondin-1 is a negative regulator of angiogenesis, and it plays a new role in IBD-associated angiogenesis. In addition, recombinant thrombospondin-1 may inhibit pathological angiogenesis and may offer a new therapeutic approach to intestinal inflammation.

Sildenafil Promotes Ischemia-Induced Angiogenesis Through a PKG-Dependent Pathway

BACKGROUND

Peripheral artery disease (PAD) is a prevalent cardiovascular disorder that results in tissue ischemia which can progress to critical limb ischemia. Restoration of tissue perfusion in the setting of chronic ischemia through stimulation of arteriogenesis and angiogenesis remains a key therapeutic target for PAD. However, experimental therapeutics, including growth factor and gene therapy, have had little clinical success indicating the need for a better understanding of molecular pathways required for therapeutic angiogenesis.

METHODS AND RESULTS

Here we report that phosphodiesterase-5 inhibition by sildenafil significantly increases vascular perfusion, tissue blood flow, and vascular density during chronic ischemia of the mouse hind limb. Importantly, sildenafil therapy did not alter any of these parameters in nonischemic limbs. Sildenafil increased tissue cGMP levels independently of increases in nitric oxide production, and sildenafil therapy stimulated angiogenesis in ischemic limbs of eNOS-/- and iNOS-/- mice. Lastly, sildenafil-mediated angiogenic activity was blocked by inhibition of protein kinase G using the PKG antagonist DT-3.

CONCLUSIONS

These data demonstrate that sildenafil therapy results in increased angiogenic activity through a PKG-dependent pathway that is independent of nitric oxide production or NOS activity and identify the angiogenic therapeutic potential of sildenafil for critical limb ischemia.

Pathogenic angiogenesis in IBD and experimental colitis: new ideas and therapeutic avenues

Angiogenesis is now understood to play a major role in the pathology of chronic inflammatory diseases and is indicated to exacerbate disease pathology. Recent evidence shows that angiogenesis is crucial during inflammatory bowel disease (IBD) and in experimental models of colitis. Examination of the relationship between angiogenesis and inflammation in experimental colitis shows that initiating factors for these responses simultaneously increase as disease progresses and correlate in magnitude. Recent studies show that inhibition of the inflammatory response attenuates angiogenesis to a similar degree and, importantly, that inhibition of angiogenesis does the same to inflammation. Recent data provide evidence that differential regulation of the angiogenic mediators involved in IBD-associated chronic inflammation is the root of this pathological angiogenesis. Many factors are involved in this phenomenon, including growth factors/cytokines, chemokines, adhesion molecules, integrins, matrix-associated molecules, and signaling targets. These factors are produced by various vascular, inflammatory, and immune cell types that are involved in IBD pathology. Moreover, recent studies provide evidence that antiangiogenic therapy is a novel and effective approach for IBD treatment. Here we review the role of pathological angiogenesis during IBD and experimental colitis and discuss the therapeutic avenues this recent knowledge has revealed.

Inflammation and the mucosal microcirculation in inflammatory bowel disease: the ebb and flow

PURPOSE OF REVIEW

Inflammatory bowel disease pathogenesis involves the interplay of multiple biological factors, among which nonimmune cells, including the endothelium, represent a crucial component of disease pathogenesis.

RECENT FINDINGS

Endothelial cells play a key role in chronic inflammation through multiple and disparate activities. The mucosal microvasculature in inflammatory bowel disease is dysfunctional, overexpresses inflammatory molecules and undergoes intense angiogenesis, failing to exert its physiological antiinflammatory and anticoagulant activities.

SUMMARY

The mucosal microcirculation is abnormal in inflammatory bowel disease and represents a novel component of disease pathogenesis; targeting the various abnormalities of the inflammatory bowel disease microcirculation may lead to new forms of therapeutic intervention.

Angiogenesis blockade as a new therapeutic approach to experimental colitis

BACKGROUND

Neoangiogenesis is a critical component of chronic inflammatory disorders. Inhibition of angiogenesis is an effective treatment in animal models of inflammation, but has not been tested in experimental colitis.

AIM

To investigate the effect of ATN-161, an anti-angiogenic compound, on the course of experimental murine colitis.

METHOD

Interleukin 10-deficient (IL10(-/-)) mice and wild-type mice were kept in ultra-barrier facilities (UBF) or conventional housing, and used for experimental conditions. Dextran sodium sulphate (DSS)-treated mice were used as a model of acute colitis. Mice were treated with ATN-161 or its scrambled peptide ATN-163. Mucosal neoangiogenesis and mean vascular density (MVD) were assessed by CD31 staining. A Disease Activity Index (DAI) was determined, and the severity of colitis was determined by a histological score. Colonic cytokine production was measured by ELISA, and lamina propria mononuclear cell proliferation by thymidine incorporation.

RESULT

MVD increased in parallel with disease progression in IL10(-/-) mice kept in conventional housing, but not in IL10(-/-) mice kept in UBF. Angiogenesis also occurred in DSS-treated animals. IL10(-/-) mice with established disease treated with ATN-161, but not with ATN-163, showed a significant and progressive decrease in DAI. The histological colitis score was significantly lower in ATN-161-treated mice than in scrambled peptide-treated mice. Inhibition of angiogenesis was confirmed by a significant decrease of MVD in ATN-161-treated mice than in ATN-163-treated mice. No therapeutic effects were observed in the DSS model of colitis. ATN-161 showed no direct immunomodulatory activity in vitro.

CONCLUSION

Active angiogenesis occurs in the gut of IL10(-/-) and DSS-treated colitic mice and parallels disease progression. ATN-161 effectively decreases angiogenesis as well as clinical severity and histological inflammation in IL10(-/-) mice but not in the DDS model of inflammatory bowel disease (IBD). The results provide the rational basis for considering anti-angiogenic strategies in the treatment of IBD in humans.