Expression of Endothelial Cell Adhesion Molecules in Neovascularized Tissue

Immunological insights of selectins in human disease mechanism

Selectin enzymes are glycoproteins and are an important adhesion molecule in the mammalian immune system, especially in the inflammatory response and the healing process of tissues. Selectins play an important role in a variety of biological processes, including the rolling of leukocytes in endothelial cells, a process known as the adhesion cascade. It has recently been discovered and reported that the selectin mechanism plays a role in cancer and thrombosis disease. This process begins with non-covalent interactions-based selectin-ligand binding and the glycans play a role as a connector between cancer cells and the endothelium in this process. The selectin mechanism is critical for the immune system, but it is also involved in disease mechanisms, earning the selectins the nickname "Selectins-The Two Dr. Jekyll and Mr. Hyde Faces". As a result, the drug for selectins should have a multifaceted role and be a dynamic molecule that targets the disease mechanism specifically. This chapter explores the role of selectins in the disease mechanism at the mechanism level that provides the impact for identifying the selectin inhibitors. Overall, this chapter provides the molecular level insights on selectins, their ligands, involvement in normal and disease mechanisms.

Treatment with Uncaria tomentosa Promotes Apoptosis in B16-BL6 Mouse Melanoma Cells and Inhibits the Growth of B16-BL6 Tumours

Uncaria tomentosa is a medicinal plant native to Peru that has been traditionally used in the treatment of various inflammatory disorders. In this study, the effectiveness of U. tomentosa as an anti-cancer agent was assessed using the growth and survival of B16-BL6 mouse melanoma cells. B16-BL6 cell cultures treated with both ethanol and phosphate-buffered saline (PBS) extracts of U. tomentosa displayed up to 80% lower levels of growth and increased apoptosis compared to vehicle controls. Treatment with ethanolic extracts of Uncaria tomentosa were much more effective than treatment with aqueous extracts. U. tomentosa was also shown to inhibit B16-BL6 cell growth in C57/bl mice in vivo. Mice injected with both the ethanolic and aqueous extracts of U. tomentosa showed a 59 ± 13% decrease in B16-BL6 tumour weight and a 40 ± 9% decrease in tumour size. Histochemical analysis of the B16-BL6 tumours showed a strong reduction in the Ki-67 cell proliferation marker in U. tomentosa-treated mice and a small, but insignificant increase in terminal transferase dUTP nick labelling (TUNEL) staining. Furthermore, U. tomentosa extracts reduced angiogenic markers and reduced the infiltration of T cells into the tumours. Collectively, the results in this study concluded that U. tomentosa has potent anti-cancer activity that significantly inhibited cancer cells in vitro and in vivo.

Neutrophil crawling in capillaries; a novel immune response to Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA), particularly the USA300 strain, is a highly virulent pathogen responsible for an increasing number of skin and soft tissue infections globally. Furthermore, MRSA-induced soft tissue infections can rapidly progress into life-threatening conditions, such as sepsis and necrotizing fasciitis. The importance of neutrophils in these devastating soft tissue infections remains ambiguous, partly because of our incomplete understanding of their behaviour. Spinning disk confocal microscopy was used to visualize the behaviour of GR1-labelled neutrophils in subcutaneous tissue in response to GFP-expressing MRSA attached to a foreign particle (agarose bead). We observed significant directional neutrophil recruitment towards the S. aureus agarose bead but not a control agarose bead. A significant increase in neutrophil crawling within the capillaries surrounding the infectious nidus was noted, with impaired capillary perfusion in these vessels and increased parenchymal cell death. No neutrophils were able to emigrate from capillaries. The crawling within these capillaries was mediated by the β(2) and α(4) integrins and blocking these integrins 2 hours post infection eliminated neutrophil crawling, improved capillary perfusion, reduced cell death and reduced lesion size. Blocking prior to infection increased pathology. Neutrophil crawling within capillaries during MRSA soft tissue infections, while potentially contributing to walling off or preventing early dissemination of the pathogen, resulted in impaired perfusion and increased tissue injury with time.

Blockade of cannabinoid receptors reduces inflammation, leukocyte accumulation and neovascularization in a model of sponge-induced inflammatory angiogenesis

OBJECTIVE

Angiogenesis depends on a complex interaction between cellular networks and mediators. The endocannabinoid system and its receptors have been shown to play a role in models of inflammation. Here, we investigated whether blockade of cannabinoid receptors may interfere with inflammatory angiogenesis.

MATERIALS AND METHODS

Polyester-polyurethane sponges were implanted in C57Bl/6j mice. Animals received doses (3 and 10 mg/kg/daily, s.c.) of the cannabinoid receptor antagonists SR141716A (CB1) or SR144528 (CB2). Implants were collected at days 7 and 14 for cytokines, hemoglobin, myeloperoxidase, and N-acetylglucosaminidase measurements, as indices of inflammation, angiogenesis, neutrophil and macrophage accumulation, respectively. Histological and morphometric analysis were also performed.

RESULTS

Cannabinoid receptors expression in implants was detected from day 4 after implantation. Treatment with CB1 or CB2 receptor antagonists reduced cellular influx into sponges at days 7 and 14 after implantation, although CB1 receptor antagonist were more effective at blocking leukocyte accumulation. There was a reduction in TNF-α, VEGF, CXCL1/KC, CCL2/JE, and CCL3/MIP-1α levels, with increase in CCL5/RANTES. Both treatments reduced neovascularization. Dual blockade of cannabinoid receptors resulted in maximum inhibition of inflammatory angiogenesis.

CONCLUSIONS

Blockade of cannabinoid receptors reduced leukocyte accumulation, inflammation and neovascularization, suggesting an important role of endocannabinoids in sponge-induced inflammatory angiogenesis both via CB1 and CB2 receptors.

The vascular endothelial growth factor (VEGF)-E encoded by orf virus regulates keratinocyte proliferation and migration and promotes epidermal regeneration

Vascular endothelial growth factor (VEGF)-A, a key regulator of cutaneous blood vessel formation, appears to have an additional role during wound healing, enhancing re-epithelialization. Orf virus, a zoonotic parapoxvirus, induces proliferative skin lesions that initiate in wounds and are characterized by extensive blood vessel formation, epidermal hyperplasia and rete ridge formation. The vascular changes beneath the lesion are largely due to viral-expressed VEGF-E. This study investigated using mouse skin models whether VEGF-E can induce epidermal changes such as that seen in the viral lesion. Injection of VEGF-E into normal skin increased the number of endothelial cells and blood vessels within the dermis and increased epidermal thickening and keratinocyte number. Injection of VEGF-E into wounded skin, which more closely mimics orf virus lesions, increased neo-epidermal thickness and area, promoted rete ridge formation, and enhanced wound re-epithelialization. Quantitative RT-PCR analysis showed that VEGF-E did not induce expression of epidermal-specific growth factors within the wound, but did increase matrix metalloproteinase (MMP)-2 and MMP-9 expression. In cell-based assays, VEGF-E induced keratinocyte migration and proliferation, responses that were inhibited by a neutralizing antibody against VEGF receptor (VEGFR)-2. These findings demonstrate that VEGF-E, both directly and indirectly, regulates keratinocyte function, thereby promoting epidermal regeneration.

Inosculation: connecting the life-sustaining pipelines

Recent progress in engineering microvascular networks in vitro and in vivo offers exciting opportunities to create tissue constructs with preformed blood vessels, which are rapidly blood perfused by developing interconnections to the preexisting blood vessels of the host tissue after implantation. This process, termed as inosculation, is well known from the revascularization of various tissue grafts, such as transplanted skin, nerves, or bone. It is characterized by the close interaction of the implant's preformed microvascular network and the host microvasculature. The sprouting angiogenic activity of both counterparts determines whether inosculation takes place internally within the implant or externally within the surrounding host tissue. Successful inosculation involves vascular remodeling as well as infiltration of inflammatory cells and stem cells. With the use of sophisticated in vitro and in vivo models, more detailed analysis of regulatory mechanisms of inosculation will help to develop novel strategies, aiming at further accelerating the establishment of a life-sustaining blood supply to implanted tissue constructs.

Advances in imaging the blood and aqueous vessels of the ocular limbus

The vessels of the limbus play a pivotal role in the drainage of the major portion of aqueous humour from the anterior chamber. Aberrations in the limbal architecture can lead to raised intraocular pressure, which in turn can lead to blinding conditions such as glaucoma. Imaging these vessels in the normal eye, in development, and in conditions where there is anterior segment dysgenesis remains a challenge. Here we review the progress in limbal vessel imaging in the past 50 years and provide key information on their strengths and limitations. Included is an analysis of serial histological sectioning, ultrathin sections, microvascular perfusion with plastics and corrosion casting, X-ray microcomputed tomography, in vivo imaging including analysis of transgenic mice expressing GFP-vascular endothelium fusion proteins, in vivo microscopy imaging using fluorescent-labelled antibodies, slit-lamp microscopy and gonioscopy, fluorescein angiography, optical coherence tomography, and various labelling procedures for the vascular endothelium and the various forms of microscopy used to view these.

Prolene-Monocryl-composite meshes do not increase microvascular Staphylococcus aureus adherence and do not sensitize for leukocytic inflammation

BACKGROUND AND AIMS

Mesh implantation for hernia repair bears the risk of bacterial mesh infection. In this study, we analyzed whether this complication is supported by an increased interaction of bacteria and leukocytes with the microvascular endothelium at the implantation site.

MATERIALS AND METHODS

Ultrapro meshes were implanted into the dorsal skinfold chamber of Syrian golden hamsters. After 12 days, fluorescein isothiocyanate (FITC)-labeled staphylococci were injected in the animals. Subsequently, we analyzed bacterial adherence, leukocyte-endothelial cell interaction, and microhemodynamics in venules of the mesh border zone and of distant control tissue under baseline conditions and during TNF-alpha-induced inflammation using intravital fluorescence microscopy. The results were compared to animals which did not receive any bacteria.

RESULTS

Under baseline conditions, leukocyte-endothelial cell interaction and bacterial adherence were not affected by the implanted biomaterial. TNF-alpha-induced inflammation significantly increased numbers of adherent leukocytes and bacteria in venules located in direct vicinity to the mesh however without any differences to control tissue. Comparable results were found for the leukocyte-endothelial cell interaction when animals were not exposed to bacteria.

CONCLUSION

Implanted Ultrapro meshes do neither increase microvascular Staphylococcus aureus adherence nor sensitize for leukocytic inflammation. Thus, we suggest that a mesh-induced increase of bacterial adherence in vessels of the implantation site cannot be considered as a primary cause for the development of mesh infection.

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.

Impaired inflammatory angiogenesis, but not leukocyte influx, in mice lacking TNFR1

The majority of biological responses classically attributed to tumor necrosis factor alpha (TNF-alpha) is mediated by p55 receptor (TNFR1). Here, we aimed to clarify the biological role of TNFR1-mediated signals in an in vivo inflammatory angiogenesis model. Polyester-polyurethane sponges, used as a framework for tissue growth, were implanted in C57Bl/6 mice. These implants were collected at days 1, 7, and 14 post-implant for enzyme-linked immunosorbent assay or at days 7 and 14 for hemoglobin, myeloperoxidase, and N-acetylglucosaminidase measurements, used as indexes for angiogenesis, neutrophil, and macrophage accumulation, respectively. In TNFR1-deficient C57Bl/6 mice, there was a significant decrease in sponge vascularization but not in late inflammatory cell influx. It is interesting that levels of vascular endothelial growth factor were significantly lower in TNFR1-deficient than in wild-type mice at days 1 and 7. Levels of angiogenic chemokines, CC chemokine ligand 2/murine homologue of monocyte chemoattractant protein-1 and CXC chemokine ligand 1-3/keratinocyte-derived chemokine, were significantly lower in TNFR1-deficient mice at days 1 and 7 after implantation, respectively. These observations suggest that TNFR1-mediated signals have a critical role in sponge-induced angiogenesis, possibly by influencing the effector state of inflammatory cells and hence, modulating the angiogenic molecular network.

Leukocyte behavior in angiogenic vessels is affected by tumor-derived nitric oxide

Recent studies indicate a possible role of nitric oxide (NO) in regulating leukocyte-endothelial cell interactions, which plays a key role in the tumor immunity. The purpose of the present study is aimed to observe the tumor hemodynamics intravitally and to clarify the effect of NO on tumor microcirculation by means of a real-time confocal laser-scanning microscope using NO-reactive indicators. Visualization of localization of NO and the leukocyte behavior was made in the mesenteric microvessels of an experimental tumor model rat. Production of NO was clearly visualized along the endothelium of the tumor-free rats, but scarcely found in the newly formed tumor microvessels. A higher level of NO production was observed in a solid tumor region, where a more marked decrease in the leukocyte-endothelial cell interactions was observed. Local administration of a NO synthase (NOS) inhibitor increased leukocyte adhesion. This indicates that tumor-derived NOS creates the tumor specific microenvironment of the immature angiogenic tumor vessels, thereby modulating leukocyte behavior.

Leukocyte recruitment in colon cancer: role of cell adhesion molecules, nitric oxide, and transforming growth factor beta1

BACKGROUND & AIMS

A deficient leukocyte recruitment has been suggested in tumor vasculature, but little is known about the underlying molecular mechanism. To characterize leukocyte-endothelium interaction in experimental colon cancer, quantify the main endothelial cell adhesion molecules (CAMs), and evaluate the effect of tumor-derived products.

METHODS

Leukocyte recruitment was assessed by intravital videomicroscopy in mice bearing HT29-derived tumors. Endothelial CAMs were measured using the dual-radiolabeled antibody technique. The role of molecules mediating leukocyte rolling (P-, E-, and L-selectin) or adhesion (intercellular adhesion molecule 1 [ICAM-1] and vascular cell adhesion molecule 1 [VCAM-1]) carcinoembryonic antigen (CEA), and transforming growth factor (TGF) beta1 was assessed through immunoblockade, whereas participation of nitric oxide (NO) and cyclooxygenase (COX) metabolites were evaluated by means of nonselective and selective inhibition.

RESULTS

Basal and lipopolysaccharide-stimulated leukocyte rolling and adhesion were markedly reduced in tumor vasculature. ICAM-1 immunoblockade prevented leukocyte adhesion in both tumor and nontumor microvessels. Neither baseline nor LPS-induced endothelial ICAM-1, P-, and E-selectin expression in tumors were reduced with respect to nontumor vasculature. Although VCAM-1 expression was reduced in tumor endothelium, immunoneutralization of VCAM-1 failed to reverse LPS-induced leukocyte recruitment in this setting. CEA immunoblockade and COX inhibition did not modify the deficient leukocyte rolling. Nonselective NO inhibition partially reversed the defective adhesion response in tumor microvessels. Finally, TGF-beta1 immunoblockade partially and selectively restored impaired leukocyte rolling and adhesion in tumor microvessels.

CONCLUSIONS

Impaired leukocyte recruitment in tumor vasculature cannot be attributed to a depressed expression of the main CAMs. Selective restoration after NO inhibition and TGF-beta1 immunoblockade suggests involvement of both molecules in this phenomenon.

Lung uptake of antibodies to endothelial antigens: key determinants of vascular immunotargeting

Vascular immunotargeting is a mean for a site-selective delivery of drugs and genes to endothelium. In this study, we compared recognition of pulmonary and systemic vessels in rats by candidate carrier monoclonal antibodies (MAbs) to endothelial antigens platelet endothelial cell adhesion molecule (PECAM)-1 (CD31), intercellular adhesion molecule (ICAM)-1 (CD54), Thy-1.1 (CD90.1), angiotensin-converting enzyme (ACE; CD143), and OX-43. Tissue immunostaining showed that endothelial cells were Thy-1.1 positive in capillaries but negative in large vessels. In the lung, anti-ACE MAb provided a positive staining in 100% capillaries vs. 5–20% capillaries in other organs. Other MAbs did not discriminate between pulmonary and systemic vessels. We determined tissue uptake after infusion of 1 μg of 125I-labeled MAbs in isolated perfused lungs (IPL) or intravenously in intact rats. Uptake in IPL attained 46% of the injected dose (ID) of anti-Thy-1.1 and 20–25% ID of anti-ACE, anti-ICAM-1, and anti-OX-43 (vs. 0.5% ID of control IgG). However, after systemic injection at this dose, only anti-ACE MAb 9B9 displayed selective pulmonary uptake (16 vs. 1% ID/g in other organs). Anti-OX-43 displayed low pulmonary (0.5% ID/g) but significant splenic and cardiac uptake (7 and 2% ID/g). Anti-Thy-1.1 and anti-ICAM-1 displayed moderate pulmonary (4 and 6% ID/g, respectively) and high splenic and hepatic uptake (e.g., 18% ID/g of anti-Thy-1.1 in spleen). The lung-to-blood ratio was 5, 10, and 15 for anti-Thy-1.1, anti-ACE, and anti-ICAM-1, respectively. PECAM antibodies displayed low pulmonary uptake in perfusion (2% ID) and in vivo (3–4% ID/g). However, conjugation with streptavidin (SA) markedly augmented pulmonary uptake of anti-PECAM in perfusion (10–54% ID, depending on an antibody clone) and in vivo (up to 15% ID/g). Therefore, ACE-, Thy-1.1-, ICAM-1-, and SA-conjugated PECAM MAbs are candidate carriers for pulmonary targeting. ACE MAb offers a high selectivity of pulmonary targeting in vivo, likely because of a high content of ACE-positive capillaries in the lungs.