Assessment of angiogenesis and tumor growth in conscious mice by a fluorimetric method

Glucocorticoid-mediated effects on angiogenesis in solid tumors

Angiogenesis is essential in tumor development to maintain the oxygen and nutrient supply. Glucocorticoids have shown both direct and indirect angiostatic properties in various types of solid cancers. In most of the reported cases glucocorticoid-mediated actions involved suppression of multiple pro-angiogenic factors expression by cancer cells. The anti-angiogenic properties of glucocorticoids correlated with diminished tumor vasculature and reduced tumor growth in multiple in vivo studies. However, when glucocorticoid treatment is considered, possible adverse events should be taken into account. Additional research is needed to further test the use of these steroidal drugs in cancer therapy.

The Sponge Implant Model of Angiogenesis

The host response observed after the application of an appropriate stimulus, such as mechanical injury or injection of neoplastic or normal tissue implants, has allowed the cataloging of a number of molecules and cells involved in the vascularization of normal repair or neoplastic tissue. Implantation of sponge matrices has been adopted as a model for the accurate quantification of angiogenic and fibrogenic responses, as they may occur during wound healing, in vivo. Such implants are particularly useful because they offer scope for modulating the environment within which angiogenesis occurs. Sponge implantation model has been optimized and adapted to characterize essential components and their roles in blood vessels formation in a variety of physiological and pathological conditions. As a direct consequence of advances in genetic manipulation, mouse models (i.e., knockouts, SCID, nude) have provided resources to delineate the mechanisms regulating the healing associated with implants. Here we outline the usefulness of the sponge implant model of angiogenesis and detailed description of the methodology.

Differential Contribution of Acute and Chronic Inflammation to the Development of Murine Mammary 4T1 Tumors

Based on the notion that inflammation favors tumorigenesis, our experiments comparatively assessed the influence of acute and chronic inflammation on the development of a murine mammary tumor (4T1). In addition, we characterized angiogenic and inflammatory markers in the tumor tissue and systemically. Subcutaneous implantation of polyether-polyurethane sponge discs in Balb/c mice was used to host 4T1 tumor cells (1x10(6)), which were inoculated intraimplant 24 h or 10 days post implantation. Flow cytometric analysis of enzyme-digested implants revealed that, after 24 hours, the population of leukocytes was primarily characterized by neutrophils (42.53% +/- 8.45) and monocytes (37.53% +/- 7.48), with some lymphocytes (16.27% +/- 4.0) and a few dendritic cells (1.82% +/- 0.36). At 10 days, macrophages were predominant (37.10% +/- 4.54), followed by lymphocytes (28.1% +/- 4.77), and monocytes (22.33% +/- 3.05), with some dendritic cells (13.60% +/- 0.55) and neutrophils (11.07% +/- 2.27). A mammary tumor grown in a chronic inflammatory environment was 2-fold when compared with one grown in acute inflammation and 5-fold when compared with tumor alone. The levels of pro-angiogenic cytokine (VEGF-Vascular Endothelial Growth Factor) were higher in implant-bearing tumor when 4T1 cells were grown in 10-day old implants as compared to the VEGF levels of the two other groups. Overall, the levels of the inflammatory markers evaluated (NAG -N-acetylglucosaminidase, TNF-α-Tumor Necrosis Factor-α) were higher in both groups of implant-bearing tumors and in serum from those animals when compared with the tumor alone levels. This inflammation-related difference in tumor growth may provide new insights into the contribution of different inflammatory cell populations to cancer progression.

Combining collagen and bioactive glasses for bone tissue engineering: a review

Collagen (COL), the most abundant protein in mammals, offers a wide range of attractive properties for biomedical applications which are the result of its biocompatibility and high affinity to water. However, due to the relative low mechanical properties of COL its applications are still limited. To tackle this disadvantage of COL, especially in the field of bone tissue engineering, COL can be combined with bioactive inorganic materials in a variety of composite systems. One of such systems is the collagen-bioactive glass (COL-BG) composite family, which is the theme of this Review. BG fillers can increase compressive strength and stiffness of COL-based structures. This article reviews the relevant literature published in the last 15 years discussing the fabrication of a variety of COL-BG composites. In vitro cell studies have demonstrated the osteogenic, odontogenic, and angiogenic potential of these composite systems, which has been confirmed by stimulating specific biochemical indicators of relevant cells. Bony integration and connective tissue vessel formation have also been studied by implantation of the composites in vivo. Areas of future research in the field of COL-BG systems, based on current challenges, and gaps in knowledge are highlighted.

Camel milk inhibits inflammatory angiogenesis via downregulation of proangiogenic and proinflammatory cytokines in mice

Camel milk has traditionally been used to treat cancer, but this practice awaits scientific scrutiny, in particular its role in tumor angiogenesis, the key step involved in tumor growth and metastasis. We aimed to investigate the effects of camel milk on key components of inflammatory angiogenesis in sponge implant angiogenesis model. Polyester-polyurethane sponges, used as a framework for fibrovascular tissue growth, were implanted in Swiss albino mice and camel milk (25, 50 and 100 mg/kg/day) was administered for 14 days through installed cannula. The implants collected at day 14 post-implantation were processed for the assessment of hemoglobin (Hb), myeloperoxidase (MPO), N-acetylglucosaminidase (NAG), and collagen, which were used as indices for angiogenesis, neutrophil, and macrophage accumulation and extracellular matrix deposition, respectively. Relevant inflammatory, angiogenic, and fibrogenic cytokines were also determined. Camel milk treatment attenuated the main components of the fibrovascular tissue, wet weight, vascularization (Hb content), macrophage recruitment (NAG activity), collagen deposition and the levels of vascular endothelial growth factor (VEGF), interleukin (IL)-1β, IL-6, IL-17, tumor necrosis factor-α, and transforming growth factor-β. A regulatory function of camel milk on multiple parameters of the main components of inflammatory angiogenesis has been revealed, giving insight into the potential therapeutic benefit underlying the anti-cancer actions of camel milk.

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.

Strychnine inhibits inflammatory angiogenesis in mice via down regulation of VEGF, TNF-α and TGF-β

Strychnine is known to possess anti-inflammatory and antitumour activity, but its roles in tumour angiogenesis, the key step involved in tumour growth and metastasis, and the involved molecular mechanism are still unknown. We aimed to investigate the effects of strychnine on key components of inflammatory angiogenesis in the murine cannulated sponge implant angiogenesis model. Polyester-polyurethane sponges, used as a framework for fibrovascular tissue growth, were implanted in Swiss albino mice and strychnine (0.25, and 0.5 mg/kg/day) was given through installed cannulas for 9 days. The implants collected at day 9 postimplantation were processed for the assessment of haemoglobin (Hb), myeloperoxidase (MPO), N-acetylglucosaminidase (NAG) and collagen used as indexes for angiogenesis, neutrophil and macrophage accumulation and extracellular matrix deposition, respectively. Relevant inflammatory, angiogenic and fibrogenic cytokines were also determined. Strychnine treatment attenuated the main components of the fibrovascular tissue, wet weight, vascularization (Hb content), macrophage recruitment (NAG activity), collagen deposition and the levels of vascular endothelial growth factor (VEGF), tumour necrosis factor (TNF)-α and transforming growth factor (TGF-β). A regulatory function of strychnine on multiple parameters of main components of inflammatory angiogenesis has been revealed giving insight into the potential therapeutic underlying the actions of strychnine.

Anti-tumor therapy with macroencapsulated endostatin producer cells

Background

Theracyte is a polytetrafluoroethylene membrane macroencapsulation system designed to induce neovascularization at the tissue interface, protecting the cells from host's immune rejection, thereby circumventing the problem of limited half-life and variation in circulating levels. Endostatin is a potent inhibitor of angiogenesis and tumor growth. Continuous delivery of endostatin improves the efficacy and potency of the antitumoral therapy. The purpose of this study was to determine whether recombinant fibroblasts expressing endostatin encapsulated in Theracyte immunoisolation devices can be used for delivery of this therapeutic protein for treatment of mice bearing B16F10 melanoma and Ehrlich tumors.

Results

Mice were inoculated subcutaneously with melanoma (B16F10 cells) or Ehrlich tumor cells at the foot pads. Treatment began when tumor thickness had reached 0.5 mm, by subcutaneous implantation of 10⁷ recombinant encapsulated or non-encapsulated endostatin producer cells. Similar melanoma growth inhibition was obtained for mice treated with encapsulated or non-encapsulated endostatin-expressing cells. The treatment of mice bearing melanoma tumor with encapsulated endostatin-expressing cells was decreased by 50.0%, whereas a decrease of 56.7% in tumor thickness was obtained for mice treated with non-encapsulated cells. Treatment of Ehrlich tumor-bearing mice with non-encapsulated endostatin-expressing cells reduced tumor thickness by 52.4%, whereas lower tumor growth inhibition was obtained for mice treated with encapsulated endostatin-expressing cells: 24.2%. Encapsulated endostatin-secreting fibroblasts failed to survive until the end of the treatment. However, endostatin release from the devices to the surrounding tissues was confirmed by immunostaining. Decrease in vascular structures, functional vessels and extension of the vascular area were observed in melanoma microenvironments.

Conclusions

This study indicates that immunoisolation devices containing endostatin-expressing cells are effective for the inhibition of the growth of melanoma and Ehrlich tumors.

Macroencapsulation of engineered cells is therefore a reliable platform for the refinement of innovative therapeutic strategies against tumors.

Angiostatic activity of human plasminogen fragments is highly dependent on glycosylation

To assess the importance of carbohydrate moieties to the anti-angiogenic activity of plasminogen fragments, we cloned the fragment corresponding to amino acids Val(79) to Thr(346) (Kint3-4) that presents the three glycosylation sites. The activity of glycosylated and unglycosylated Kint3-4 was tested in murine sponge implant model. We observed a significant decrease in the neovascularization on the sponge after treatment with Kint3-4 by histological examination and determination of the hemoglobin levels. The effects were more intense with the glycosylated than the unglycosylated protein. (99m)Technecium-labeled red blood cells confirmed the inhibition of cell infiltration in the implanted sponge. Studies using melanoma B16F1 implanted in a mouse demonstrated that treatment with glycosylated Kint3-4 (0.15 nmol/48 h) during 14 days suppresses tumor growth by 80%. The vascular endothelial growth factor mRNA levels on the tumor were reduced after treatment. Kint3-4 is a potent plasminogen fragment that has been found to inhibit tumor growth.

Differential effects of rolipram on chronic subcutaneous inflammatory angiogenesis and on peritoneal adhesion in mice

The specific PDE4 inhibitor (rolipram) has been shown to attenuate excessive accumulation/activation of inflammatory cells and fibroblasts and cytokine production in several pathological conditions through cyclic nucleotide modulation. Here, using the murine sponge model to induce chronic subcutaneous inflammatory response and to elicit the formation of intraperitoneal adhesions we explored the hypothesis that rolipram would exert beneficial effects on decreasing key components of both processes (inflammatory cell recruitment, angiogenesis, and deposition of extracellular matrix component). Two doses of rolipram (0.2 or 2 mg/kg/day) were administered orally for 7 days in groups of mice bearing either subcutaneous or intraperitoneal polyether-polyurethane implants. Rolipram was effective in inhibiting angiogenesis as assessed by hemoglobin content and VEGF levels in subcutaneous implants (about 40% with both doses) but failed to exert this activity in intraperitoneal implants. Conversely, accumulation of neutrophils and macrophages determined by measuring myeloperoxidase (MPO) and N-acetylglucosaminidase (NAG) activities intraimplant, respectively, was attenuated only in intraperitoneal implants by the treatment. Levels of TNF-alpha and MCP-1 were also determined and rolipram at both doses decreased the production of both cytokines in intraperitoneal implants. The levels of MCP-1 in the subcutaneous implants were not affected by the treatment. Fibrosis was evaluated by determining the amount of collagen and production of TGF-beta1 intraimplant. Both parameters were attenuated by rolipram. These results have shown differential sensitivity of proliferating tissues to PDE4 inhibitor indicating that this agent may be used to target inflammatory angiogenesis selectively.

A critical analysis of current in vitro and in vivo angiogenesis assays

The study of angiogenesis has grown exponentially over the past 40 years with the recognition that angiogenesis is essential for numerous pathologies and, more recently, with the advent of successful drugs to inhibit angiogenesis in tumours. The main problem with angiogenesis research remains the choice of appropriate assays to evaluate the efficacy of potential new drugs and to identify potential targets within the angiogenic process. This selection is made more complex by the recognition that heterogeneity occurs, not only within the endothelial cells themselves, but also within the specific microenvironment to be studied. Thus, it is essential to choose the assay conditions and cell types that most closely resemble the angiogenic disease being studied. This is especially important when aiming to translate data from in vitro to in vivo and from preclinical to the clinic. Here we critically review and highlight recent advances in the principle assays in common use including those for endothelial cell proliferation, migration, differentiation and co-culture with fibroblasts and mural cells in vitro, vessel outgrowth from organ cultures and in vivo assays such as chick chorioallantoic membrane (CAM), zebrafish, sponge implantation, corneal, dorsal air sac, chamber and tumour angiogenesis models. Finally, we briefly discuss the direction likely to be taken in future studies, which include the use of increasingly sophisticated imaging analysis systems for data acquisition.

The sponge implant model of angiogenesis

The host response observed after the application of an appropriate stimulus, such as mechanical injury or injection of neoplastic or normal tissue implants, has allowed the cataloguing of a number of molecules and cells involved in the vascularization of normal repair or neoplastic tissue. Implantation of sponge matrices has been adopted as a model for the accurate quantification of angiogenic and fibrogenic responses as they may occur during wound healing in vivo. Such implants are particularly useful because they offer scope for modulating the environment within which angiogenesis occurs. A sponge implantation model has been optimised and adapted to characterise essential components and their roles in blood vessel formation in a variety of physiological and pathological conditions. As a direct consequence of advances in genetic manipulation, mouse models (i.e., knockouts, severe combined immunodeficient [SCID], nude) have provided resources to delineate the mechanisms regulating the healing associated with implants. Here, we outline the usefulness of the cannulated sponge implant model of angiogenesis and provide a detailed description of the methodology.

Cannabinoids reduce granuloma-associated angiogenesis in rats by controlling transcription and expression of mast cell protease-5

BACKGROUND AND PURPOSE

Chronic inflammatory conditions, such as granulomas, are associated with angiogenesis. Mast cells represent the main cell type orchestrating angiogenesis, through the release of their granule content. Therefore, compounds able to modulate mast cell behaviour may be considered as a new pharmacological approach to treat angiogenesis-dependent events. Here, we tested the effect of selective cannabinoid (CB) receptor agonists in a model of angiogenesis-dependent granuloma formation induced by lambda-carrageenin in rats.

EXPERIMENTAL APPROACH

Granulomas were induced by lambda-carrageenin-soaked sponges implanted subcutaneously on the back of male Wistar rats. After 96 h, implants were removed and granuloma formation was measured (wet weight); angiogenesis was evaluated by histological analysis and by the measurement of haemoglobin content. Mast cells in the granulomas were evaluated histologically and by RT-PCR and immunoblotting analysis for mast cell-derived proteins (rat mast cell protease-5 (rMCP-5) and nerve growth factor). Selective CB1 and CB2 receptor agonists(,) ACEA and JWH-015 (0.001-0.1 mg mL(-1)), were given locally only once, at the time of implantation.

KEY RESULTS

The CB1 and CB2 receptor agonists decreased the weight and vascularization of granulomas after 96 h. This treatment also reduced mast cell number and activation in granulomatous tissue. Specifically, these compounds prevented the transcription and expression of rMCP-5, a protein involved in sprouting and advance of new blood vessels.

CONCLUSION AND IMPLICATIONS

Modulation of mast cell function by cannabinoids reduced granuloma formation and associated angiogenesis. Therefore cannabinoid-related drugs may be useful in the management of granulomatous diseases accompanied by angiogenesis.

In vivo performance of a sol-gel glass-coated collagen

Synthetic bioactive materials offer possibilities to repair large tissue defects. It is well known that bioactivity, angiogenesis, and inflammation are key events in implant incorporation. Using glass-coated and glass-free collagen as potential bone graft substitutes, we carried out in vitro bioactivity and an in vivo angiogenesis and inflammation studies. The in vitro study showed bioactivity when the glass-coated samples were left in SBF for 5 days. This was confirmed by FTIR results, which presented P--O vibration bands characteristic of hydroxyapatite close to 1060 cm(-1) and 600 cm(-1). The in vivo response was evaluated following subcutaneous implantation of the biomaterial in the mouse dorsa. Angiogenesis, as determined by hemoglobin content extracted from implants 7 and 14 days after implantation, increased progressively in both glass-coated and glass-free collagen implants. However, vascularization was higher in the glass-coated collagen implants 14 days after implantation (mug Hb per mg wet tissue 6.0 +/- 0.3) compared with the glass-free group (1.6 +/- 0.1). The inflammatory process, determined by the levels of myeloperoxidase and N-acetylglucosaminidase, was similar for both implants. This study shows that glass-coated collagen implants hold osteogenic and angiogenic potential and may be used in clinical conditions requiring improvement of these biological processes.

Differential Effects of Antiangiogenic Compounds in Neovascularization, Leukocyte Recruitment, VEGF Production, and Tumor Growth in Mice

Angiogenesis and inflammation play critical roles in tumor growth. Using an in vivo tumor model, we report that thalidomide (100 mg kg(-1)day(-1)) or clotrimazole (120 mg kg(-1) day(-1)), inhibit blood vessel formation (determined by hemoglobin content), leukocyte recruitment [myeloperoxidase (MPO) activity; N-acetylglucosa-minidase (NAG) activity], and vascular endothelial growth factor production. Inhibition of angiogenesis ranged from 35% to 65%. Clotrimazole was the most potent antiangiogenic compound and the agent capable of inhibiting tumor growth. Thalidomide was able to reduce the inflammatory reaction (MPO and NAG activities) by 50% to 70%, but was unable to delay tumor development. These results suggest that for this type of solid tumor the degree of neovascularization, rather than inhibition of inflammatory cell recruitment, is a determinant factor in tumor development. As the contribution of angiogenesis and inflammation to cancer progression vary markedly among different tumor types, it may be relevant to consider these factors in cancer therapy using antiangiogenesis/antiinflammatory approaches.

Inhibition of inflammatory angiogenesis by distant subcutaneous tumor in mice

We investigated angiogenesis, inflammatory cells accumulation and endogenous production of cytokines in sponge implants of tumor-bearing mice. Seven days after inoculation of Ehrlich tumor cells (2.5 x 10(6)), sponge discs were implanted subcutaneously in the dorsa of mice to induce the formation of fibrovascular tissue. The implants of tumor-bearing and non tumor-bearing animals were assessed for neovascularization and leukocyte accumulation, together with levels of relevant cytokines, vascular endothelial growth factor VEGF), tumor necrosis factor alpha (TNF-alpha), CXCL1-3/KC and CCL2/JE. In the implants of tumor-bearing animals angiogenesis (assessed by hemoglobin content and VEGF levels in the implants) and leukocyte accumulation (assessed by myeloperoxidase -MPO- and N- acetylglucosaminidase-NAG-enzyme activities) were all significantly less than those in the implants of non tumor-bearing animals. Although the chemokine CXCL1-3/KC was lower in the implants of tumor-bearing animals, the chemokine CCL2/JE was increased in this group. The production of TNF-alpha in the implants was not modified by the presence of the subcutaneous tumor. The combination of the methodologies used in this study has provided a novel approach to investigate the interaction between two distinct proliferating tissues that share common features (angiogenesis, cell recruitment, inflammation) and has shown that the predominant inhibitory effect of a tumor mass over repair process is associated with altered cytokine production.

Sponge-induced angiogenesis and inflammation in PAF receptor-deficient mice (PAFR-KO)

1. To determine biological functions of platelet-activating factor (PAF) in chronic inflammation, we have investigated the kinetics of angiogenesis, inflammatory cells recruitment and cytokine production in sponge-induced granuloma in wild type and PAF receptor-deficient mice (PAFR-KO). 2. Angiogenesis as determined by morphometric analysis and hemoglobin content was significantly higher in the implants of PAFR-KO mice at all time points. Treatment with PAF receptor antagonist UK74505 (30 mg kg(-1)) also increased angiogenesis in sponge implants. 3. Neutrophils and macrophages accumulation, as determined by myeloperoxidase and N-acetylglucosaminidase activities in the supernatant of implanted sponges were markedly decreased in PAFR-KO mice. Surprisingly, the levels of the proinflammatory chemokines, keratinocyte-derived chemokine and chemokine monocyte chemoattractant protein 1 were higher in the implants of the transgenic animals. 4. We have shown that angiogenesis was stimulated in PAFR-KO mice whereas inflammation was decreased, indicating that PAF is an endogenous regulator of new blood vessels formation in the inflammatory microenvironment induced by the sponge implant.

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

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