Prostaglandin E(2) modulation of vascular endothelial growth factor production in murine macrophages

IL-4 regulates specific Arg-1(+) macrophage sFlt-1-mediated inhibition of angiogenesis

One of the main drivers for neovascularization in age-related macular degeneration is activation of innate immunity in the presence of macrophages. Here, we demonstrate that T helper cell type 2 cytokines and, in particular, IL-4 condition human and murine monocyte phenotype toward Arg-1(+), and their subsequent behavior limits angiogenesis by increasing soluble fms-like tyrosine kinase 1 (sFlt-1) gene expression. We document that T helper cell type 2 cytokine-conditioned murine macrophages neutralize vascular endothelial growth factor-mediated endothelial cell proliferation (human umbilical vein endothelial cell and choroidal vasculature) in a sFlt-1-dependent manner. We demonstrate that in vivo intravitreal administration of IL-4 attenuates laser-induced choroidal neovascularization (L-CNV) due to specific IL-4 conditioning of macrophages. IL-4 induces the expression of sFlt-1 by resident CD11b(+) retinal microglia and infiltrating myeloid cells but not from retinal pigment epithelium. IL-4-induced suppression of L-CNV is not prevented when sFlt-1 expression is attenuated in retinal pigment epithelium. IL-4-mediated suppression of L-CNV was abrogated in IL-4R-deficient mice and in bone marrow chimeras reconstituted with myeloid cells that had undergone lentiviral-mediated shRNA silencing of sFlt-1, demonstrating the critical role of this cell population. Together, these data establish how lL-4 directly drives macrophage sFlt-1 production expressing an Arg-1(+) phenotype and support the therapeutic potential of targeted IL-4 conditioning within the tissue to regulate disease conditions such as neovascular age-related macular degeneration.

Novel mechanisms and signaling pathways of esophageal ulcer healing: the role of prostaglandin EP2 receptors, cAMP, and pCREB

Clinical studies indicate that prostaglandins of E class (PGEs) may promote healing of tissue injury e.g., gastroduodenal and dermal ulcers. However, the precise roles of PGEs, their E-prostanoid (EP) receptors, signaling pathways including cAMP and cAMP response element-binding protein (CREB), and their relation to VEGF and angiogenesis in the tissue injury healing process remain unknown, forming the rationale for this study. Using an esophageal ulcer model in rats, we demonstrated that esophageal mucosa expresses predominantly EP2 receptors and that esophageal ulceration triggers an increase in expression of the EP2 receptor, activation of CREB (the downstream target of the cAMP signaling), and enhanced VEGF gene expression. Treatment of rats with misoprostol, a PGE1 analog capable of activating EP receptors, enhanced phosphorylation of CREB, stimulated VEGF expression and angiogenesis, and accelerated esophageal ulcer healing. In cultured human esophageal epithelial (HET-1A) cells, misoprostol increased intracellular cAMP levels (by 163-fold), induced phosphorylation of CREB, and stimulated VEGF expression. A cAMP analog (Sp-cAMP) mimicked, whereas an inhibitor of cAMP-dependent protein kinase A (Rp-cAMP) blocked, these effects of misoprostol. These results indicate that the EP2/cAMP/protein kinase A pathway mediates the stimulatory effect of PGEs on angiogenesis essential for tissue injury healing via the induction of CREB activity and VEGF expression.

MK886 inhibits the proliferation of HL-60 leukemia cells by suppressing the expression of mPGES-1 and reducing prostaglandin E2 synthesis

Microsomal prostaglandin E synthase-1 (mPGES-1), an inducible enzyme that specifically catalyzes the conversion of prostaglandin H2 (PGH2) to prostaglandin E2 (PGE2), has been reported to be over-expressed in a variety of solid tumor cells and tissues, but not in normal tissues. Its association with leukemia, however, has not been fully investigated. Our study revealed, for the first time, that mPGES-1 is over-expressed in human acute myeloid leukemia HL-60 cells. Cytotoxicity assays and flow cytometry showed that MK886, an inhibitor of mPGES-1, inhibits proliferation of HL-60 cells and induces apoptosis in a dose- and time-dependent manner, which may result from down-regulation of mPGES-1 expression and PGE2 synthesis. Evaluation of mediators of apoptotic signaling revealed up-regulation of BAX expression and caspase-3 activity, as well as significant decreases in Bcl2 and P-Akt. We conclude that MK886 reduces the viability of leukemia HL-60 cells by reducing mPGES-1 expression and PGE2 synthesis in a dose-dependent manner, which strongly suggests that mPGES-1 inhibitors should be considered as promising candidates for leukemia treatment.

IL-10 regulation of macrophage VEGF production is dependent on macrophage polarisation and hypoxia

Vascular endothelial growth factor A (VEGF) is critical for vascular remodelling during tissue repair subsequent to inflammation or injury, but under pathological conditions, VEGF induces tissue damaging angiogenesis. Macrophages generate VEGF that supports angiogenesis, when they adapt to their environment and respond with a co-ordinated set of signals to promote or resolve inflammation. Depending on the stimulus, the phenotype of macrophage activation is broadly classified into M1 (NOS2(+)) and M2 (arginase-1(+)). In recent studies, IL-10, an anti-inflammatory cytokine that suppresses the M1 phenotype, has been shown to dampen the angiogenic switch and subsequent neovascularisation. However, as we show here, these effects are context dependent. In this study, we have demonstrated that IL-10 inhibits M1 bone marrow-derived macrophages (BMDMs) VEGF, stimulated by LPS/CGS21680 (adenosine A2A receptor agonist), but does not prevent VEGF production from M2 macrophages stimulated with prostaglandin E2 (PGE2). Furthermore, we show that hypoxic-conditioned BMDM generated VEGF was maintained in the presence of IL-10, but was suppressed when concomitantly stimulated with IFN-gamma. Finally, LPS/PGE2 generated an arginase-1(+) M2 macrophage that in addition to generating VEGF produced significant quantities of IL-10. Under these conditions, neither in IL-10 deficient macrophages nor following IL-10 neutralization was VEGF production affected. Our results indicate IL-10 suppressed M1 but not M2 derived VEGF, and that activation signals determined the influence of IL-10 on VEGF production. Consequently, therapies to suppress macrophage activation that as a result generate IL-10, or utilising IL-10 as a potential anti-angiogenic therapy, may result in a paradoxical support of neovascularisation and thus on-going tissue damage or aberrant repair.

Role of cyclooxygenase-2 induction by transcription factor Sp1 and Sp3 in neuronal oxidative and DNA damage response

Cyclooxygenase-2 (COX-2) has been implicated in neuronal survival and death. However, the precise regulatory mechanisms involved in COX-2 function are unclear. In the present study we found that COX-2 is induced in response to glutathione depletion-induced oxidative stress in primary cortical neurons. Two proximal specific Sp1 and Sp3 binding sites are responsible for the COX-2 promoter activity under normal as well as oxidative stress conditions through enhanced Sp1 and Sp3 DNA binding activity. Site-directed mutagenesis confirmed that -268/-267 positions serve as specific Sp1 and Sp3 recognition sites under oxidative stress. Enforced expression of Sp1 and Sp3 using HSV vectors increased the promoter activity, transcription, and protein level of COX-2 in cortical neurons. The dominant negative form of Sp1 abrogated the oxidative stress-induced promoter activity and expression of COX-2. We also demonstrated that adenovirus-mediated COX-2 gene delivery protected neurons from DNA damage induced by oxidative, genotoxic, and excitotoxic stresses and by ischemic injury. Moreover, COX-2(-/-) cortical neurons were more susceptible to DNA damage-induced cell death. These results indicate that in primary neurons Sp1 and Sp3 play an essential role in the modulation of COX-2 transcription, which mediates neuronal homeostasis and survival by preventing DNA damage in response to neuronal stress.

The inhibition of lung colonization of B16-F10 melanoma cells in EFA-deficient animals is related to enhanced apoptosis and reduced angiogenesis

Previous studies conducted in our laboratory showed that the reproduction of spontaneous and experimental metastases was reduced in host animals deprived of essential fatty acids (EFA). In the present study, we have explored the possibility whether apoptosis, proliferation, and angiogenesis might be involved in the antimetastatic effect of EFA deficiency. To this aim, in pulmonary colonies developed from B16-F10 cells in EFA-deficient animals or in animals fed a 5% corn oil diet, we performed an immunohistochemical analysis of bcl-2/bax proteins, PCNA, and VEGF and von Willebrand Factor (vWF), typical markers of apoptosis, proliferation, and angiogenesis, respectively. Apoptosis was also evaluated by detecting DNA fragments in metastatic cells. We found that the reduction of pulmonary colonies grown in EFA-deficient animals was associated with a high expression of apoptotic activity as revealed by the presence of apoptotic nuclei and a high immunoreactivity for bax. Cell proliferation seemed not to be influenced by EFA deficiency in view of the observation that PCNA was highly expressed in pulmonary colonies of control as well as EFA-deficient animals. Pulmonary colonies developed in EFA- deficient animals showed a lower expression of VEGF and a decreased microvessel density, indicating that a reduced angiogenesis contributes to the antimetastatic effects of EFA deficiency. Our analysis of the results invokes the possibility that a relationship between angiogenesis and apoptosis may account for the diminution of the development of experimental metastases in the lungs of EFA-deficient animals.

Effects of prostaglandin E2 on expression of vascular endothelial growth factor in human gastric cancer cell line MKN28

AIM: To investigate the expression of vascular endothelial growth factor (VEGF) in human gastric cell line MKN28 in vitro, and identify whether exogenous prostaglandin E₂ (PGE₂) can increase the expression of VEGF.

METHODS: Human gastric cell line MKN28 was culture in vitro and then treated with 0.1, 1, 5, and 10 μmol/L PGE₂ for 3 h. Real-time polymerase chain reaction (PCR) and Western blot were used to detect the expression of VEGF mRNA and protein, respectively.

RESULTS: The transcription of VEGF mRNA increased in a dose-dependent manner after PGE₂ treatment, and the difference between the groups of 0.1, 1, 5, 10 μmol/L PGE₂ treatment and the control group had statistical significances (0.67 ± 0.093, 0.74 ± 0.13, 0.87 ± 0.07, 1.49 ± 0.15 vs 0.42 ± 0.10, P < 0.05 or P < 0.01). PGE₂ also up-regulated the expression of VEGF protein in a dose-dependent manner, and except 0.1 μmol/L PGE₂ treatment group, the difference between the groups of 1, 5, 10 μmol/L PGE₂ treatment and the control group had statistical significances (51.02 ± 2.16, 66.69 ± 9.85, 136.49 ± 6.89 vs 26.87 ± 3.98, P < 0.05 or P < 0.01).

CONCLUSION: PGE₂ can promote VEGF mRNA transcription and protein expression in human gastric cancer cell line MKN28.

COX-2 expression in ampullary carcinoma: correlation with angiogenesis process and clinicopathological variables

BACKGROUND

There is evidence that the anti-neoplastic effect of non-steroidal anti-inflammatory drugs is attributable to cyclooxygenase-2 (COX-2) inhibition, but the exact mechanisms whereby COX-2 can promote tumour cell growth remain unclear. One hypothesis is the stimulation of tumour angiogenesis by the products of COX-2 activity. To data, there have been few clinicopathological studies on COX-2 expression in human ampullary carcinoma and no data have been reported about its relation with tumour angiogenesis.

OBJECTIVE

To investigate by immunohistochemistry the expression of COX-2 and the angiogenesis process in a series of primary untreated ampullary carcinomas.

METHODS

Tissue samples from 40 archival ampullary carcinomas were analysed for COX-2, vascular endothelial growth factor (VEGF), and an endothelial cell marker von Willebrand factor (vWF) by immunohistochemistry, using specific antibodies.

RESULTS

COX-2 expression was detected in 39 tissue samples (97.5%), of which two (5%) were graded as weak, 26 (65%) as moderate, and 11 (27.5%) as strong. Only one lesion (2.5%) was negative for COX-2 expression. VEGF expression was detected in 36 tissue samples (90%). A significant positive correlation was found between COX-2 and VEGF expression. No statistic correlation was found between COX-2 expression and microvessel density.

CONCLUSIONS

COX-2 is highly expressed in ampullary carcinomas. This suggests an involvement of the COX-2 pathway in ampullary tumour associated angiogenesis, providing a rationale for targeting COX-2 in the treatment of ampullary cancer.

Expression and regulation of murine macrophage angiopoietin-2

Our understanding of angiogenesis has increased significantly in the past few years with the discovery of angiopoietins (Ang). Specifically, Ang2 has been associated with pathologic as well as normal vascularization. While previous studies have shown that a major source of Ang2 has been endothelial cells and tumor cells, we reasoned that macrophages would also have the ability to express angiopoietins, specifically Ang2, due to that cell's role in wound healing, tumor angiogenesis, and a number of non-oncological diseases, such as rheumatoid arthritis and psoriasis. In this study, murine macrophages constitutively expressed both transcripts and protein for Ang2 but not Ang1 or Ang3. The secretion of Ang2 was enhanced by treatment with lipopolysaccharide, interferon-gamma, prostaglandin E2 and other cyclic AMP-elevating agents, as well as vascular endothelial growth factor (VEGF). Cyclic AMP-dependent protein kinase (PKA) played a major role in this enhancement since the PKA inhibitor, H89, blocked secretion of Ang2. Since stimulation of the PKA pathway can lead to macrophage production of VEGF, it is possible that enhancement of Ang2 production by macrophages may be due to autocrine responsiveness to VEGF. Adding anti-VEGF antibodies to the supernatants of stimulated macrophages blocked secretion of Ang2. This study is the first to show murine macrophage production of Ang2 and to provide evidence that it can be regulated. Understanding the regulation of macrophage Ang2 production is especially important in an effort to target the pathologic role of macrophages while preserving their role in immunity and homeostasis.

Beta-adrenergic receptor agonists induce the release of granulocyte chemotactic protein-2, oncostatin M, and vascular endothelial growth factor from macrophages

Vascular endothelial growth factor (VEGF), oncostatin M (OSM), and granulocyte chemotactic protein-2 (GCP-2/CXCL6) are up-regulated in U937 macrophages and peripheral blood macrophages exposed to LPS, beta-adrenergic receptor (beta2-AR) agonists (e.g. zilpaterol, and clenbuterol) and some other agents that induce intracellular cAMP (prostaglandin E2, forskolin, and butyryl cAMP). LPS in combination with beta2-agonists and cAMP elevating agents had an additional effect on the release of VEGF, OSM, and CXCL6. These proteins are up-regulated after 16-24 h of exposure and this is mediated by the beta2-AR, as determined by time course experiments and the use of a specific beta2-AR antagonist (ICI 118551). Beta2-AR agonists are used as bronchodilators in the treatment of asthma, but appear to have no effect on the chronic inflammation of the disease. However, the up-regulation of VEGF, OSM, and CXCL6 may have adverse effects on the inflammatory process of asthma. These mediators are involved in the recruitment of neutrophils, airway remodelling and angiogenesis, known features of chronic inflammatory diseases. We propose that the up-regulation of these proteins could play a role in the adverse effects of prolonged excessive usage of beta2-AR agonists on the airways besides the desensitization of the beta2-AR.

The role of omega-3 long-chain polyunsaturated fatty acids in health and disease of the retina

In this work we advance the hypothesis that omega-3 (omega-3) long-chain polyunsaturated fatty acids (LCPUFAs) exhibit cytoprotective and cytotherapeutic actions contributing to a number of anti-angiogenic and neuroprotective mechanisms within the retina. omega-3 LCPUFAs may modulate metabolic processes and attenuate effects of environmental exposures that activate molecules implicated in pathogenesis of vasoproliferative and neurodegenerative retinal diseases. These processes and exposures include ischemia, chronic light exposure, oxidative stress, inflammation, cellular signaling mechanisms, and aging. A number of bioactive molecules within the retina affect, and are effected by such conditions. These molecules operate within complex systems and include compounds classified as eicosanoids, angiogenic factors, matrix metalloproteinases, reactive oxygen species, cyclic nucleotides, neurotransmitters and neuromodulators, pro-inflammatory and immunoregulatory cytokines, and inflammatory phospholipids. We discuss the relationship of LCPUFAs with these bioactivators and bioactive compounds in the context of three blinding retinal diseases of public health significance that exhibit both vascular and neural pathology. How is omega-3 LCPUFA status related to retinal structure and function? Docosahexaenoic acid (DHA), a major dietary omega-3 LCPUFA, is also a major structural lipid of retinal photoreceptor outer segment membranes. Biophysical and biochemical properties of DHA may affect photoreceptor membrane function by altering permeability, fluidity, thickness, and lipid phase properties. Tissue DHA status affects retinal cell signaling mechanisms involved in phototransduction. DHA may operate in signaling cascades to enhance activation of membrane-bound retinal proteins and may also be involved in rhodopsin regeneration. Tissue DHA insufficiency is associated with alterations in retinal function. Visual processing deficits have been ameliorated with DHA supplementation in some cases. What evidence exists to suggest that LCPUFAs modulate factors and processes implicated in diseases of the vascular and neural retina? Tissue status of LCPUFAs is modifiable by and dependent upon dietary intake. Certain LCPUFAs are selectively accreted and efficiently conserved within the neural retina. On the most basic level, omega-3 LCPUFAs influence retinal cell gene expression, cellular differentiation, and cellular survival. DHA activates a number of nuclear hormone receptors that operate as transcription factors for molecules that modulate reduction-oxidation-sensitive and proinflammatory genes; these include the peroxisome proliferator-activated receptor-alpha (PPAR-alpha) and the retinoid X receptor. In the case of PPAR-alpha, this action is thought to prevent endothelial cell dysfunction and vascular remodeling through inhibition of: vascular smooth muscle cell proliferation, inducible nitric oxide synthase production, interleukin-1 induced cyclooxygenase (COX)-2 production, and thrombin-induced endothelin 1 production. Research on model systems demonstrates that omega-3 LCPUFAs also have the capacity to affect production and activation of angiogenic growth factors, arachidonic acid (AA)-based vasoregulatory eicosanoids, and MMPs. Eicosapentaenoic acid (EPA), a substrate for DHA, is the parent fatty acid for a family of eicosanoids that have the potential to affect AA-derived eicosanoids implicated in abnormal retinal neovascularization, vascular permeability, and inflammation. EPA depresses vascular endothelial growth factor (VEGF)-specific tyrosine kinase receptor activation and expression. VEGF plays an essential role in induction of: endothelial cell migration and proliferation, microvascular permeability, endothelial cell release of metalloproteinases and interstitial collagenases, and endothelial cell tube formation. The mechanism of VEGF receptor down-regulation is believed to occur at the tyrosine kinase nuclear factor-kappa B (NFkappaB). NFkappaB is a nuclear transcription factor that up-regulates COX-2 expression, intracellular adhesion molecule, thrombin, and nitric oxide synthase. All four factors are associated with vascular instability. COX-2 drives conversion of AA to a number angiogenic and proinflammatory eicosanoids. Our general conclusion is that there is consistent evidence to suggest that omega-3 LCPUFAs may act in a protective role against ischemia-, light-, oxygen-, inflammatory-, and age-associated pathology of the vascular and neural retina.

Growth Stimulation of COX-2–Negative Pancreatic Cancer by a Selective COX-2 Inhibitor

Cyclooxygenase 2 (COX-2) inhibitors are promising antiangiogenic agents in several preclinical models. The aim of the present study was to evaluate the effect of selective COX-2 inhibitors on vascular endothelial growth factor (VEGF) production in vitro and angiogenesis and growth of pancreatic cancer in vivo, focusing on putative differences between COX-2–negative and COX-2–positive tumors. VEGF production and angiogenesis in vitro were determined by ELISA and endothelial cell migration assay. To determine whether the effect of COX-2 inhibitors was mediated by peroxisome proliferator–activated receptor γ (PPAR-γ), we used a dominant-negative PPAR-γ and a pharmacologic inhibitor. In vitro findings were validated in a pancreatic cancer animal model. Microvessel density was assessed by CD31 immunostaining. Intratumoral prostaglandin and VEGF levels were measured by mass spectroscopy and ELISA. Selective COX-2 inhibitors had a concentration-dependent effect on VEGF production in vitro. Higher concentrations increased VEGF levels and stimulated angiogenesis by activating PPAR-γ. In vivo, nimesulide increased VEGF production by cancer cells in COX-2–positive and COX-2–negative pancreatic tumors. In COX-2–negative pancreatic cancer, this effect was associated with an increase in angiogenesis and growth. In COX-2–positive pancreatic cancer, the nimesulide-induced increase of VEGF production by the cancer cells was offset by a decrease in VEGF production by the nonmalignant cell types leading to reduced tumor angiogenesis and growth. Selective COX-2 inhibitors had opposite effects on growth and angiogenesis in pancreatic cancer depending on COX-2 expression. These findings imply that assessing the COX-2 profile of the pancreatic tumor is mandatory before initiating therapy with a selective COX-2 inhibitor.

The role of antioxidants in models of inflammation: Emphasis on l-arginine and arachidonic acid metabolism

Inflammatory processes are made up of a multitude of complex cascades. Under physiological conditions these processes aid in tissue repair. However, under pathophysiological environments, such as wound healing and hypoxia-ischaemia (HI), inflammatory mediators become imbalanced, resulting in tissue destruction. This review addresses the changes in reactive oxygen species (ROS), L-arginine and arachidonic acid metabolism in wound healing and HI and subsequent treatments with promising anti-oxidants. Even though these models may appear divergent, anti-oxidant treatments are nevertheless still having favourable effects. On the basis of recent findings, it is apparent that protection with anti-oxidants is not solely attributed to scavenging of ROS. In addition, the actions of anti-oxidants must be considered in light of the inflammatory process being assessed. To this end, there does not appear to be any universally applicable single mechanism to explain the actions of anti-oxidants.

Prostaglandin E(2) modulation of gene expression in an Atlantic salmon (Salmo salar) macrophage-like cell line (SHK-1)

Following lipopolysaccharide (LPS)-stimulation of Atlantic salmon (Salmo salar) macrophage-like SHK-1 cells, prostaglandin E(2) (PGE(2)) exhibited dose-dependent inhibition of the antigen presenting molecules major histocompatability class I and II and the pro-inflammatory cytokine interleukin-1 beta gene expression. Prostaglandin E(2) was found to be stimulatory towards cyclooxygenase-2 (COX-2) expression at higher concentrations (1 x 10(-6) and 1 x 10(-8)M) and inhibitory at lower concentrations (1 x 10(-10) and 1 x 10(-12)M) after 4h exposure. After 24h exposure, however, LPS-induced COX-2 expression decreased and was completely inhibited by all PGE(2) concentrations (1 x 10(-6)-1 x 10(-10)M). Incubation of SHK-1 cells with LPS alone had no effect on tumour necrosis factor alpha (TNFalpha)-like gene or transforming growth factor beta-like gene expression after 4h, however, LPS and PGE(2) showed a synergistic effect on TNFalpha-like gene expression after 24h. This study provides evidence for the existence of a PGE(2)-mediated negative feedback mechanism in the control of PGs through down-regulation of COX-2, as well as for inflammatory responses by the down-regulation of both COX-2 and IL-1 beta. The differential regulation of immune-related genes under these conditions further demonstrates the usefulness of the SHK-1 cell line for studying aspects of salmonid immunology.

Prostaglandin E2 induces degranulation-independent production of vascular endothelial growth factor by human mast cells

Mast cells accumulate in large numbers at angiogenic sites, where they have been shown to express a number of proangiogenic factors, including vascular endothelial growth factor (VEGF-A). PGE(2) is known to strongly promote angiogenesis and is found in increased levels at sites of chronic inflammation and around solid tumors. The expression pattern of VEGF and the regulation of VEGF-A by PGE(2) were examined in cord blood-derived human mast cells (CBMC). CBMC expressed mRNA for five isoforms of VEGF-A and other members of the VEGF family (VEGF-B, VEGF-C, and VEGF-D) with strong expression of the most potent secretory isoforms. PGE(2) was a very strong inducer of VEGF-A(121/165) production by CBMC and also elevated VEGF-A mRNA expression. The amount of VEGF-A(121/165) protein production induced by PGE(2) was 4-fold greater than that induced by IgE-mediated activation of CBMC. Moreover, the response to PGE(2) as well as to other cAMP-elevating agents such as forskolin and salbutamol was observed under conditions that were not associated with mast cell degranulation. CBMC expressed substantial levels of the EP(2) receptor, but not the EP(4) receptor, when examined by flow cytometry. In contrast to other reported PGE(2)-mediated effects on mast cells, VEGF-A(121/165) production occurred via activation of the EP(2) receptor. These data suggest a role for human mast cells as a potent source of VEGF(121/165) in the absence of degranulation, and may provide new opportunities to regulate angiogenesis at mast cell-rich sites.

Homocysteine induces vascular endothelial growth factor expression in differentiated THP-1 macrophages

Hyperhomocysteinemia has been reported to be an independent risk factor for atherosclerosis and atherothrombosis. However, the molecular mechanism by which hyperhomocysteinemia can lead to atherosclerosis and atherothrombosis has not been completely described. Vascular endothelial growth factor (VEGF) has been proposed to play an important role in the progression of atherosclerosis. In the present study, we hypothesized that hyperhomocysteinemia might be associated with VEGF expression in atherosclerotic lesions. We investigated VEGF mRNA expression and VEGF secretion by homocysteine (Hcy) in differentiated THP-1 macrophages. As a result, it has been revealed that VEGF mRNA was upregulated by Hcy in a dose- and time-dependent manner in THP-1 macrophages with the increase in VEGF secretion. Importantly, other sulfur compounds, such as methionine and cysteine, showed no effect on VEGF expression, indicating that homocysteine specifically induced VEGF. Our findings suggest that hyperhomocysteinemia could promote the development of atherosclerotic lesions through VEGF induction in macrophages.

Cancer-associated immunodeficiency and dendritic cell abnormalities mediated by the prostaglandin EP2 receptor

Prostaglandin E(2) (PGE(2)), a major COX metabolite, plays important roles in several facets of tumor biology. We characterized the contribution of the PGE(2) EP2 receptor to cancer-associated immune deficiency using EP2(-/-) mice. EP2(-/-) mice exhibited significantly attenuated tumor growth and longer survival times when challenged with MC26 or Lewis lung carcinoma cell lines as compared with their wild-type littermates. While no differences in T cell function were observed, PGE(2) suppressed differentiation of DCs from wild-type bone marrow progenitors, whereas EP2-null cells were refractory to this effect. Stimulation of cells in mixed lymphocyte reactions by wild-type DCs was suppressed by treatment with PGE(2), while EP2(-/-)-derived DCs were resistant to this effect. In vivo, DCs, CD4(+), and CD8(+) T cells were significantly more abundant in draining lymph nodes of tumor-bearing EP2(-/-) mice than in tumor-bearing wild-type mice, and a significant antitumor cytotoxic T lymphocyte response could be observed only in the EP2(-/-) animals. Our data demonstrate an important role for the EP2 receptor in PGE(2)-induced inhibition of DC differentiation and function and the diminished antitumor cellular immune responses in vivo.

Omega-3 Fatty Acids: Implications for the Treatment of Tumor-Associated Inflammation

Our in vivo and in vitro studies using ω-3 fatty acids (FA) have provided insight into the biological effects and mechanisms of their anti-inflammatory action(s). The implications for this research are profound because there are few nutritional therapies available that have the potential to be clinically effective in malignancies and other chronic inflammatory conditions as ω-3 FA. In this summary of experiments the biological effects of ω-3 FA are discussed and the potential mechanisms of action presented.

Induction of a potential paracrine angiogenic loop between human THP-1 macrophages and human microvascular endothelial cells during Bartonella henselae infection

Bartonella henselae is responsible for various disease syndromes that loosely correlate with the immune status of the host. In the immunocompromised individual, B. henselae-induced angiogenesis, or bacillary angiomatosis, is characterized by vascular proliferative lesions similar to those in Kaposi's sarcoma. We hypothesize that B. henselae-mediated interaction with immune cells, namely, macrophages, induces potential angiogenic growth factors and cytokines which contribute in a paracrine manner to the proliferation of endothelial cells. Vascular endothelial growth factor (VEGF), a direct inducer of angiogenesis, and interleukin-1beta (IL-1beta), a potentiator of VEGF, were detected within 12 and 6 h, respectively, in supernatants from phorbol 12-myristate 13-acetate-differentiated human THP-1 macrophages exposed to live B. henselae. Pretreatment of macrophages with cytochalasin D, a phagocytosis inhibitor, yielded comparable results, suggesting that bacterium-cell attachment is sufficient for VEGF and IL-1beta induction. IL-8, an angiogenic cytokine with chemotactic properties, was induced in human microvascular endothelial cells (HMEC-1) within 6 h of infection, whereas no IL-8 induction was observed in infected THP-1 cells. In addition, conditioned medium from infected macrophages induced the proliferation of HMEC-1, thus demonstrating angiogenic potential. These data suggest that Bartonella modulation of host or target cell cytokines and growth factors, rather than a direct role of the bacterium as an endothelial cell mitogen, is the predominant mechanism responsible for angiogenesis. B. henselae induction of VEGF, IL-1beta, and IL-8 outlines a broader potential paracrine angiogenic loop whereby macrophages play the predominant role as the effector cell and endothelial cells are the final target cell, resulting in their proliferation.