Production of vascular endothelial growth factor by murine macrophages: regulation by hypoxia, lactate, and the inducible nitric oxide synthase pathway

Dextran sodium sulfate strongly promotes colorectal carcinogenesis in Apc(Min/+) mice: inflammatory stimuli by dextran sodium sulfate results in development of multiple colonic neoplasms

The mouse model for familial adenomatous polyposis, Apc(Min/+) mouse, contains a truncating mutation in the Apc gene and spontaneously develops numerous adenomas in the small intestine but few in the large bowel. Our study investigated whether dextran sodium sulfate (DSS) treatment promotes the development of colonic neoplasms in Apc(Min/+) mice. Apc(Min/+) and Apc+/+ mice of both sexes were exposed to 2% dextran sodium sulfate in drinking water for 7 days, followed by no further treatment for 4 weeks. Immunohistochemistry for cyclooxygenase-2, inducible nitric oxide synthase, beta-catenin, p53, and nitrotyrosine, and mutations of beta-catenin and K-ras and loss of wild-type allele of the Apc gene in the colonic lesions were examined. Sequential observation of female Apc(Min/+) mice that received DSS was also performed up to week 5. At week 5, numerous colonic neoplasms developed in male and female Apc(Min/+) mice but did not develop in Apc+/+ mice. Adenocarcinomas developed in Apc(Min/+) mice that received DSS showed loss of heterozygosity of Apc and no mutations in the beta-catenin and K-ras genes. The treatment also significantly increased the number of small intestinal polyps. Sequential observation revealed increase in the incidences of colonic neoplasms and dysplastic crypts in female Apc(Min/+) mice given DSS. DSS treatment increased inflammation scores, associated with high intensity staining of beta-catenin, cyclooxygenase-2, inducible nitric oxide synthase and nitrotyrosine. Interestingly, strong nuclear staining of p53 was specifically observed in colonic lesions of Apc(Min/+) mice treated with DSS. Our results suggest a strong promotion effect of DSS in the intestinal carcinogenesis of Apc(Min/+) mice. The findings also suggest that strong oxidative/nitrosative stress caused by DSS-induced inflammation may contribute to the colonic neoplasms development.

Expression of developmentally regulated endothelial cell locus 1 was induced by tumor-derived factors including VEGF

Developmentally regulated endothelial cell locus 1 (Del1) is a new angiogenic molecules expressed specifically in early embryonic endothelial cells. We investigated the relationship between Del1 and tumor cell-derived vascular endothelial growth factor (VEGF). Dunn osteosarcoma cells and high- and low-metastatic murine sarcoma cells did not express Del1. However, the expression of Del1 was observed in these primary tumor tissues and the pulmonary metastatic tissues after subcutaneous inoculation in vivo. Every tumor cell-conditioned medium containing VEGF induced the expression of Del1 in murine lung microvascular endothelial (MLE) cells, although control MLE cells did not express Del1. The anti-mouse VEGF monoclonal antibody inhibited the induction of the Del1 expression. In addition, mouse recombinant interleukin-1alpha and tumor necrosis factor-alpha also induced Del1 in MLE cells. Del1 may play an important role in tumor angiogenesis through the effects of tumor-derived factors including VEGF.

Macrophage responses to hypoxia: implications for tumor progression and anti-cancer therapies

The presence of multiple areas of hypoxia (low oxygen tension) is a hallmark feature of human and experimental tumors. Monocytes are continually recruited into tumors, differentiate into tumor-associated macrophages (TAMs), and then accumulate in these hypoxic areas. A number of recent studies have shown that macrophages respond to the levels of hypoxia found in tumors by up-regulating such transcription factors as hypoxia-inducible factors 1 and 2, which in turn activate a broad array of mitogenic, pro-invasive, pro-angiogenic, and pro-metastatic genes. This could explain why high numbers of TAMs correlate with poor prognosis in various forms of cancer. In this review, we assess the evidence for hypoxia activating a distinct, pro-tumor phenotype in macrophages and the possible effect of this on the growth, invasion, angiogenesis, and immune evasion of tumors. We also discuss current attempts to selectively target TAMs for destruction or to use them to deliver gene therapy specifically to hypoxic tumor sites.

Ovarian carcinoma cells and IL-1beta-activated human peritoneal mesothelial cells are possible sources of vascular endothelial growth factor in inflammatory and malignant peritoneal effusions

OBJECTIVE

Inflammatory or malignant peritoneal diseases are associated with high levels of ascitic vascular endothelial growth factor (VEGF). We compared the VEGF secretion by human peritoneal mesothelial cells (HPMC) and ovarian carcinoma (OVCA) cells and its regulation by pro-inflammatory cytokines.

MATERIALS AND METHODS

VEGF secretion in cultured HPMC, established human OVCA cell lines, and inflammatory or OVCA-associated ascites was determined by enzyme linked immunosorbent assay.

RESULTS

HPMC constitutively produced VEGF at median levels of 43 +/- 7 pg/10(5) cells. Treatment of HPMC with 1 ng/ml IL-1beta (567 +/- 213 pg/10(5) cells) or TNF-alpha (89 +/- 1 pg/10(5) cells) resulted in a 13-fold (P < 0.01) or 2-fold (P < 0.05) elevation of the VEGF secretion. In OVCA, the constitutive VEGF expression was 8-fold higher than VEGF levels in HPMC (364 +/- 185 pg/10(5) cells; P < 0.001). VEGF secretion in OVCA cells was also increased by IL-1beta (514 +/- 105 pg/10(5) cells; P < 0.01) or TNF-alpha (458 +/- 168 pg/10(5) cells; P < 0.01) reaching similar levels as in IL-1beta-activated HPMC. Median VEGF levels in malignant ascites (2761 +/- 1549 pg/ml) were 11-fold higher compared with levels in inflammatory fluids (244 +/- 170 pg/ml; P < 0.01). VEGF levels in both inflammatory- and OVCA-associated fluids correlated with ascitic IL-1beta levels (P < 0.05).

CONCLUSION

We identified ovarian cancer cells and/or IL-1beta-activated peritoneal mesothelial cells as important sources of ascitic VEGF. The present data indicate that IL-1beta-triggered VEGF production by neoplastic and normal cells is a common pathomechanism for ascites formation in both inflammatory and malignant conditions.

Essential roles of angiotensin II in vascular endothelial growth factor expression in sleep apnea syndrome

BACKGROUND

Hypoxia-induced endothelial cell dysfunction has been implicated in increased cardiovascular disease associated with obstructive sleep apnea syndrome (OSAS). OSAS mediates hypertension by stimulating angiotensin II (Ang II) production. Hypoxia and Ang II are the major stimuli of vascular endothelial growth factor (VEGF), which is a potent angiogenic cytokine and also contributes to the atherogenic process itself.

METHODS AND RESULTS

We observed serum Ang II and VEGF levels and peripheral blood mononuclear cell (PBMC) and neutrophil VEGF expression. Compared to controls, subjects with OSAS had significantly increased levels of serum Ang II and VEGF and VEGF mRNA expression in their leukocytes. To examine whether Ang II stimulates VEGF expression in OSAS, we treated PBMCs obtained from control subjects with Ang II and with an Ang II receptor type 1 (AT(1)) blocker, olmesartan. We observed an increased expression of VEGF in the Ang II-stimulated PBMCs and decreased in VEGF mRNA and protein expression in the PBMCs treated with olmesartan.

CONCLUSIONS

These findings suggest that the Ang II-AT(1) receptors pathway potentially are involved in OSAS and VEGF-induced vascularity and that endothelial dysfunction might be linked to this change in Ang II activity within leukocytes of OSAS patients.

Vascular endothelial growth factor expression and cyclosporine toxicity in renal allograft rejection

The aim of this study was to evaluate the influence of vascular endothelial growth factor (VEGF) on renal function and on development of interstitial fibrosis (IF) in renal allografts. Tubular and interstitial expressions of VEGF and TNF-alpha, and density of macrophages in the interstitium were examined in 92 patients with nonrejected kidneys, acute rejection (AR), chronic allograft nephropathy (CAN), borderline changes (BC) and acute cyclosporin A (CsA) toxicity. Follow-up biopsy specimens from patients with AR and BC were evaluated for development of IF. A significant difference in tubular and interstitial VEGF expressions was found between patients with AR, BC, CAN and CsA toxicity (p < 0.001). Macrophage infiltration was positively correlated with VEGF and TNF-alpha expressions (p < 0.001). VEGF expression increased with increasing expression of TNF-alpha (p < 0.001). Renal function in first 6 months after initial biopsy was better in patients with marked tubular VEGF expression (p < 0.01); however, in follow-up, development of IF and graft loss was found earlier in these patients (p < 0.01 and p < 0.05, respectively). Increased renal VEGF expression has protective properties immediately following renal allograft but allows for increased risk of early IF, and therefore poor graft outcome in the long term.

Constitutive and inducible expression and regulation of vascular endothelial growth factor

Vascular endothelial growth factor (VEGF), which was originally discovered as vascular permeability factor, is critical to human cancer angiogenesis through its potent functions as a stimulator of endothelial cell survival, mitogenesis, migration, differentiation and self-assembly, as well as vascular permeability, immunosuppression and mobilization of endothelial progenitor cells from the bone marrow into the peripheral circulation. Genetic alterations and a chaotic tumor microenvironment, such as hypoxia, acidosis, free radicals, and cytokines, are clearly attributed to numerous abnormalities in the expression and signaling of VEGF and its receptors. These perturbations confer a tremendous survival and growth advantage to vascular endothelial cells as manifested by exuberant tumor angiogenesis and a consequent malignant phenotype. Understanding the regulatory mechanisms of both inducible and constitutive VEGF expression will be crucial in designing effective therapeutic strategies targeting VEGF to control tumor growth and metastasis. In this review, molecular regulation of VEGF expression in tumor cells is discussed.

Gene transfer of CuZn superoxide dismutase enhances the synthesis of vascular endothelial growth factor

Nitric oxide (NO) and reactive oxygen species (ROS) are emerging as important regulators of angiogenesis. NO enhances VEGF synthesis in several cell types and is required for execution of VEGF angiogenic effect in endothelial cells. Similarly, hydrogen peroxide induces VEGF synthesis and recent studies indicate the involvement of ROS in signaling downstream of VEGF stimulation. VEGF synthesis can not only be enhanced by gene transfer of VEGF but also by overexpression of NO synthase genes. Here, we examined the possibility of augmentation of VEGF production by gene transfer of copper/zinc superoxide dismutase (CuZnSOD, SOD1). Overexpression of human SOD1 in mouse NIH 3T3 fibroblasts increased SOD activity, enhanced intracellular generation of H2O2 and significantly stimulated VEGF production as determined by increase in VEGF promoter activity, VEGF mRNA expression and VEGF protein synthesis. The stimulatory effect on VEGF synthesis induced by SOD1 gene transfer was reverted by overexpression of human catalase. The effect of H2O2 produced by engineered cells is mediated by activation of hypoxia-inducible factor response element (HRE) as well as Sp1 recognition site of VEGF promoter. This data suggest the feasibility of stimulation of angiogenesis by overexpression of SOD1.

Gene transfer of CuZn superoxide dismutase enhances the synthesis of vascular endothelial growth factor

Nitric oxide (NO) and reactive oxygen species (ROS) are emerging as important regulators of angiogenesis. NO enhances VEGF synthesis in several cell types and is required for execution of VEGF angiogenic effect in endothelial cells. Similarly, hydrogen peroxide induces VEGF synthesis and recent studies indicate the involvement of ROS in signaling downstream of VEGF stimulation. VEGF synthesis can not only be enhanced by gene transfer of VEGF but also by overexpression of NO synthase genes. Here, we examined the possibility of augmentation of VEGF production by gene transfer of copper/zinc superoxide dismutase (CuZnSOD, SOD1). Overexpression of human SOD1 in mouse NIH 3T3 fibroblasts increased SOD activity, enhanced intracellular generation of H2O2 and significantly stimulated VEGF production as determined by increase in VEGF promoter activity, VEGF mRNA expression and VEGF protein synthesis. The stimulatory effect on VEGF synthesis induced by SOD1 gene transfer was reverted by overexpression of human catalase. The effect of H2O2 produced by engineered cells is mediated by activation of hypoxia-inducible factor response element (HRE) as well as Sp1 recognition site of VEGF promoter. This data suggest the feasibility of stimulation of angiogenesis by overexpression of SOD1.

Nitric oxide: a newly discovered function on wound healing

Wound healing impairment represents a particularly challenging clinical problem to which no efficacious treatment regimens currently exist. The factors ensuring appropriate intercellular communication during wound repair are not completely understood. Although protein-type mediators are well-established players in this process, emerging evidence from both animal and human studies indicates that nitric oxide (NO) plays a key role in wound repair. The beneficial effects of NO on wound repair may be attributed to its functional influences on angiogenesis, inflammation, cell proliferation, matrix deposition, and remodeling. Recent findings from in vitro and in vivo studies of NO on wound repair are summarized in this review. The unveiled novel mechanisms support the use of NO-containing agents and/or NO synthase gene therapy as new therapeutic regimens for impaired wound healing.

Nitric oxide, VEGF, and VEGFR-2: interactions in activity-induced angiogenesis in rat skeletal muscle

Vascular endothelial growth factor (VEGF) is considered to be important in promotion of capillary growth in skeletal muscles exposed to increased activity. We studied its interactions with nitric oxide (NO) by examining the expression of endothelial NO synthase (NOS), VEGF, and VEGF receptor-2 (VEGFR-2) proteins in relation to capillary growth in rat extensor digitorum longus muscles electrically stimulated for 2, 4, or 7 days with and without NOS inhibition by N(omega)-nitro-L-arginine (L-NNA, 3 mg/day). Stimulation increased all proteins from 2 days onward, concomitantly with capillary proliferation (labeling for proliferating cell nuclear antigen). Capillary-to-fiber ratio was elevated by 25% after 7 days. Concurrent oral administration of L-NNA did not affect the increase in endothelial NOS but depressed its activity, as shown by increased blood pressure and decreased arteriolar diameters in 2-day-stimulated muscles. NOS inhibition eliminated the increased expression of VEGFR-2 and VEGF proteins in muscles stimulated for 2 and 4 days but not for 7 days. However, it depressed capillary proliferation and the increase in C/F at all time points. We conclude that, in stimulated muscles, NO, generated by activation of neuronal NOS by muscle activity or endothelial NOS by increased blood flow and capillary shear stress, may increase capillary proliferation in the early stages of stimulation through upregulation of VEGFR-2 and VEGF. With longer stimulation, capillary growth appears to require NO, and high levels of VEGF and VEGFR-2 may be contributing to maintenance of the increased capillary bed.

Progressive loss of endothelial P-selectin expression with increasing malignancy in colorectal cancer

Adhesion of inflammatory cells to vascular endothelium is mediated by specific cell adhesion receptors on both leukocytes and endothelial cells. One of the adhesion molecules on the endothelium is P-selectin. Decreased vascular P-selectin expression has been associated with tumor progression in melanoma patients. We now report on the expression of endothelial P-selectin in colorectal cancer (CRC). We studied a colorectal tissue specimen series ranging from normal colorectal tissue via unmetastasized primary tumors to tumors with the same depth of invasion at the primary site but with liver metastases. Moreover, P-selectin expression levels in liver metastases were determined. The number of P-selectin positive vessels as a fraction of the total number of vessels, both intra- and peritumorally, was determined by staining for CD62P and CD34, respectively. Furthermore, by immunostaining for leukocytes (CD45) and macrophages (CD68), it was evaluated whether levels of P-selectin expression influenced infiltrate density and composition. The results showed that levels of peritumoral P-selectin expression were reciprocal to the degree of progression in CRC. This relation was even more pronounced intratumorally: in metastasized primary tumors and in the metastatic lesions, P-selectin expression was virtually absent. This distribution pattern was reflected in the numbers of leukocytes that accumulated in the various tissues, since in the primary tumors with metastases, and in the metastatic lesions, hardly any infiltrating cells were observed. In these lesions, leukocytes were present in the peritumoral zone, but seemed unable to enter the tumor tissue. In primary tumors without metastasis, the intratumoral leukocyte infiltration density was significantly higher. Recruitment levels of macrophages remained constant throughout the different tissues. We suggest that downregulation of endothelial P-selectin expression is a mechanism by which CRC lesions evade inflammatory regression and, thereby, progress to a more advanced stage of malignancy.

Nitric oxide in inflammatory bowel disease: a universal messenger in an unsolved puzzle

In recent years, nitric oxide (NO), a gas previously considered to be a potentially toxic chemical, has been established as a diffusible universal messenger that mediates cell-cell communication throughout the body. Constitutive and inducible NO production regulate numerous essential functions of the gastrointestinal mucosa, such as maintenance of adequate perfusion, regulation of microvascular and epithelial permeability, and regulation of the immune response. Up-regulation of the production of NO via expression of inducible nitric oxide synthase (iNOS) represents part of a prompt intestinal antibacterial response; however, NO has also been associated with the initiation and maintenance of inflammation in human inflammatory bowel disease (IBD). Recent studies on animal models of experimental IBD have shown that constitutive and inducible NO production seems to be beneficial during acute colitis, but sustained up-regulation of NO is detrimental. This fact is also supported by studies on mice genetically deficient in various NOS isoforms. However, the mechanism by which NO proceeds from being an indispensable homeostatic regulator to a harmful destructor remains unknown. Furthermore, extrapolation of data from animal colitis models to human IBD is questionable. The purpose of this review is to update our knowledge about the role of this universal mediator and the enzymes that generate it in the pathogenesis of IBD.

Prenylflavonoids and phloroglucinol derivatives from hops (Humulus lupulus)

The ethyl acetate soluble fraction of hops (Humulus lupulus) showed potent inhibitory activity on the production of nitric oxide (NO) induced by a combination of LPS and IFN-gamma. Four known prenylflavonoids (1-4) and a new prenylflavonoid (5), hulupinic acid (6), lupulone (7), and its six new derivatives (8-13) were isolated from the active fraction. The structures were determined on the basis of physiochemical properties and spectroscopic analysis. Their inhibitory activities on the production of NO in macrophage RAW 264.7 cells were examined.

Complex role of heme oxygenase-1 in angiogenesis

Angiogenesis occurring during reparative or pathological processes is driven by various inflammatory mediators that influence the synthesis of growth factors. It has been recognized recently that reactive oxygen species (ROS) and nitric oxide (NO) are important modulators of the synthesis and activity of vascular endothelial growth factor (VEGF), a major angiogenic molecule. Moreover, heme oxygenase-1 (HO-1), a ubiquitous stress-inducible enzyme that is induced by ROS and NO, was recently discovered to be involved in angiogenesis. Genetic overexpression of HO-1 enhanced VEGF synthesis and augmented formation of vascular capillaries, improving the blood flow in ischemic tissues. In addition, by-products of HO-1 exert numerous effects that can also influence angiogenesis in both positive and negative ways. Therefore, the antiinflammatory effects of HO-1 can attenuate the excess formation of blood vessels in inflammatory angiogenesis. In this review, the recent data on the role of HO-1 in angiogenesis are critically discussed. It is suggested that further studies using potent and specific augmentation of HO-1 gene expression by viral vectors, as well as targeted, specific inhibition of HO-1 expression, are required to elucidate fully the complex role of this enzymatic pathway in angiogenesis.

Carbon dioxide pneumoperitoneum causes severe peritoneal acidosis, unaltered by heating, humidification, or bicarbonate in a porcine model

BACKGROUND

Carbon dioxide (CO(2)) is the most common gas used for insufflation in laparoscopy, but its effects on peritoneal physiology are poorly understood. This study looks at the changes in peritoneal and bowel serosal pH during CO(2) pneumoperitoneum, and whether heating and humidification with or without bicarbonate alters the outcomes.

METHODS

Twenty-one pigs divided into four groups as follows: (1) standard (STD) laparoscopy (n = 5); (2) heated and humidified (HH) laparoscopy (n = 6); (3) heated and humidified with bicarbonate (HHBI) laparoscopy (n = 5); and (4) laparotomy (n = 5). Peritoneal pH, bowel serosal pH, and arterial blood gas (ABG) were obtained at 15-min intervals for 3 h.

RESULTS

Severe peritoneal acidosis (pH range 6.59-6.74) was observed in all laparoscopy groups, and this was unaltered by heating and humidification or the addition of bicarbonate. Bowel serosal acidosis was observed in all laparoscopy groups with onset of pneumoperitoneum, but it recovered after 45 minutes. No significant changes in peritoneal or bowel serosal pH were observed in the laparotomy group.

CONCLUSION

CO(2) pneumoperitoneum resulted in severe peritoneal acidosis that was unaltered by heating and humidification with or without bicarbonate. Alteration in peritoneal pH may conceivably be responsible for providing an environment favorable for tumor-cell implantation during laparoscopy.

Role of infiltrated leucocytes in tumour growth and spread

Leucocytes are a major component of the tumour microenvironment. Recent studies have indicated that the infiltration and activity of these host cells are regulated by the tumour to promote its survival and progression. Through the production of an array of growth factors, proteases and angiogenic mediators, leucocytes in the tumour microenvironment promote tumour growth, angiogenesis and metastasis.

Association of presence of Aspergillus antibodies with hemoptysis in patients with old tuberculosis or bronchiectasis but no radiologically visible mycetoma

Old tuberculosis and bronchiectasis are the two most important causes of chronic structural changes of lungs in our locality. In the absence of radiologically visible mycetoma, the cause of hemoptysis in these two groups of patients is largely unknown. A 17-month prospective study was carried out to compare the prevalence of Aspergillus fumigatus and Aspergillus flavus antibodies in hemoptysis patients with old tuberculosis or bronchiectasis but no radiologically visible mycetoma (cases, n = 38), hemoptysis patients with other diagnosis (control group 1, n = 29), and patients with old tuberculosis or bronchiectasis but no hemoptysis (control group 2, n = 47) by a recently developed sensitive and specific A. fumigatus and A. flavus antibody assay. There were a significantly larger number of patients with antibody against A. fumigatus or A. flavus among the cases than among the patients in control groups 1 and 2 (P < 0.05 in both comparisons). Molds were not recovered from any of the patients. Among the 10 cases with Aspergillus antibody, eight and two had antibody against A. flavus and A. fumigatus, respectively. We conclude that there was an association between the presence of Aspergillus antibodies and hemoptysis in patients with old tuberculosis or bronchiectasis, suggesting that these patients probably had occult infections caused by the corresponding fungi. Development of serological tests against other Aspergillus species as well as other causes of mycetoma will probably increase the detection of occult mold infections in patients with existing parenchymal lung diseases, and treatment of fungal microinvasion may help to alleviate hemoptysis in these patients with bronchiectasis or old tuberculosis who have Aspergillus antibodies.

Lactate and oxygen constitute a fundamental regulatory mechanism in wound healing

For many years, lactate has been known to accelerate collagen deposition in cultured fibroblasts and, without detailed explanation, has been presumed to stimulate angiogenesis. Similarly, hypoxia has been linked to angiogenic effects and collagen deposition from cultured cells. Paradoxically, however, wound angiogenesis and collagen deposition are increased by breathing oxygen and decreased by hypoxia. Lactate accumulates to 4-12 mM in wounds for several reasons, only one of which is the result of hypoxia. Oxygen in wounds is usually low but can be increased by breathing oxygen (without change in lactate). We have reported that lactate elicits vascular endothelial growth factor (VECF) from macrophages, as well as collagen, some heat shock proteins, and VECF from endothelial cells, and collagen from fibroblasts, even in the presence of normal amounts of oxygen. Hypoxia exerts many of these same effects in cultured cells. In this study, we elevated extracellular lactate in wounds by implanting purified solid-state, hydrolysable polyglycolide. A steady-state 2-3 mM additional elevation of lactate resulted. With it, there was a significant short-term elevation of interleukin-1beta, a long-term elevation of VECF (2x) and transforming growth factor-beta1 (2-3x), a 50% elevation in collagen deposition, and a large reduction of insulin-like growth factor-1 (- 90%). We propose that lactate induces a biochemical "perception" of hypoxia and instigates several signals that activate growth factor/cytokine signals while the continued presence of molecular oxygen allows endothelial cells and fibroblasts to reproduce and deposit collagen. The data are consistent with ADP-ribosylation effects and oxidant signaling. (WOUND REP REG 2003;11:504-509)

Transcription of the Vascular Endothelial Growth Factor Gene in Macrophages Is Regulated by Liver X Receptors

Macrophages are an important source of angiogenic activity in wound healing, cancer, and chronic inflammation. Vascular endothelial growth factor (VEGF), a cytokine produced by macrophages, is a primary inducer of angiogenesis and neovascularization in these contexts. VEGF expression by macrophages is known to be stimulated by low oxygen tension as well as by inflammatory signals. In this study, we provide evidence that Vegfa gene expression is also regulated by activation of liver X receptors (LXRs). VEGF mRNA was induced in response to synthetic LXR agonists in murine and human primary macrophages as well as in murine adipose tissue in vivo. The effects of LXR ligands on VEGF expression were independent of hypoxia-inducible factor HIF-1alpha activation and did not require the previously characterized hypoxia response element in the VEGF promoter. Rather, LXR/retinoid X receptor heterodimers bound directly to a conserved hormone response element (LXRE) in the promoter of the murine and human Vegfa genes. Both LXRalpha and LXRbeta transactivated the VEGF promoter in transient transfection assays. Finally, we show that induction of VEGF expression by inflammatory stimuli was independent of LXRs, because these effects were preserved in LXR null macrophages. These observations identify VEGF as an LXR target gene and point to a previously unrecognized role for LXRs in vascular biology.

Expression of HIF-2α/EPAS1 in hepatocellular carcinoma

AIM: To investigate the expression of hypoxia-inducible factor (HIF)-2α/endothelial PAS domain protein1 (EPAS1) in hepatocellular carcinoma (HCC).

METHODS: Expression of HIF-2α/EPAS1 was investigated immunohistochemically on paraffin-embedded sections from 97 patients with HCC. To further confirm that HIF-2α/EPAS1 in HCC tissues also correlated with angiogenesis, a parallel immunohistchemistry study of vascular endothelial growth factor (VEGF) was performed on these 97 cases.

RESULTS: HIF-2α/EPAS1 could be detected in 50 of 97 cases (51.6%), including 19 weakly positive (19.8%), and 31 strongly positive (31.1%), the other 47 cases were negative (48.4%). The expression of HIF-2α/EPAS1was significantly correlated with tumor size, capsule infiltration, portal vein invasion, and necrosis. A parallel immunohistochemical analysis of VEGF demonstrated its positive correlation with capsule infiltration, portal vein invasion, and HIF-2α/EPAS1 overexpression, which supported the correlation of HIF-2α/ EPAS1up-regulation with tumor angiogenesis. No apparent correlation was observed between HIF-2α/EPAS1 and capsular formation, presence of cirrhosis, and histological grade.

CONCLUSION: HIF-2α/EPAS1 is expressed in most of HCC with capsular infiltration and portal vein invasion, which indicates a possible role of HIF-2α/EPAS1 in HCC metastasis.

Role of ADP-ribosylation in wound repair. The contributions of Thomas K. Hunt, MD

Nearly 36 years ago Thomas K. Hunt, with Patrick Twomey, was the first to report that the level of lactate significantly increases in healing wounds. This observation convinced him that lactate, besides being the by-product of glycolysis, must have a regulatory role in the healing process. He set out to investigate this observation and found it to be so. This article is written in recognition of his foresight. It summarizes the salient findings emanating from this fundamental observation and describes the biochemical principles by which most of the lactate action may be explained. Down-regulation of the ubiquitous protein modification reaction called ADP-ribosylation turned out to be a basic signal behind the role of lactate in wound healing.

Vascular endothelial growth factor levels are increased and associated with disease activity in patients with Behçet's syndrome

BACKGROUND/AIMS

Vascular endothelial growth factor (VEGF) is a cytokine participating in inflammation with potent endothelial cell effects. It is produced by macrophages, neutrophils and vascular endothelial cells and can alter vessel permeability. Behçet's syndrome is a systemic inflammatory disorder with unknown etiology. Vascular endothelial dysfunction is one of the prominent features of the disease. We previously demonstrated the possible involvement of proinflammatory cytokines [tumor necrosis factor (TNF)-alpha, soluble interleukin-2 receptor (sIL-2R), interleukin (IL)-6 and IL-8], nitric oxide (NO) and adrenomedullin in the etiopathogenesis of Behçet's syndrome. Since VEGF expression is induced by these cytokines and VEGF itself is a potent stimulator of NO production with endothelial cell effects, this study aimed to investigate whether VEGF was affected during the course of Behçet's syndrome. We also assessed the possible involvement of VEGF in ocular Behçet's syndrome or in disease activity.

METHODS

This multicenter case-control study included a total of 39 patients with active (n = 22) or inactive (n = 17) Behçet's syndrome (mean age, 38.1 +/- 10.4 years; 21 men and 18 women) satisfying International Study Group criteria, and 15 healthy hospital-based control volunteers (mean age, 39.2 +/- 9.3 years; eight men and seven women) matched for age and gender from a similar ethnic background. Patients were examined by a dermatologist and an ophthalmologist with an interest in Behçet's syndrome. Plasma VEGF concentrations were measured using a newly established enzyme-linked immunosorbent assay. Clinical findings and acute-phase reactant parameters such as erythrocyte sedimentation rate, alpha1-antitrypsin, alpha2-macroglobulin, and neutrophil count were used to classify the disease in Behçet's patients as active or inactive. The Wilcoxon test or the Mann-Whitney U-test was used for statistical analysis as indicated and the results were expressed as mean +/- SD, with range.

RESULTS

The mean plasma VEGF level in patients with Behçet's syndrome (291.9 +/- 97.1 pg/mL; range 121-532 pg/mL) was higher than that in control subjects (103.0 +/- 43.6 pg/mL; range 25-187 pg/mL) and the difference was significant (P < 0.001). Patients with active disease had significantly (P < 0.001) higher VEGF levels than patients with inactive disease (347.6 +/- 87.1 vs. 219.9 +/- 51.6 pg/mL). In addition, ocular Behçet's patients (n = 23) had higher VEGF levels (315.7 +/- 92.1 pg/mL) than nonocular patients (n = 16, 257.8 +/- 96.6 pg/mL) and the difference was of borderline significance (P = 0.041). The levels of all acute-phase reactant parameters were significantly higher in the active stage than in the inactive stage (for each, P < 0.01) or in control subjects (for each, P < 0.001).

CONCLUSIONS

VEGF may participate in the course of Behçet's syndrome, especially in the active stage, and elevated levels of VEGF may be an additional risk factor for the development of ocular disease, contributing to poor visual outcome.

Hypoxic gene activation by lipopolysaccharide in macrophages: implication of hypoxia-inducible factor 1alpha

Hypoxia-inducible factor 1 (HIF-1) regulates many genes induced by low oxygen conditions. The expression of important hypoxic genes such as glucose transporter 1 and vascular endothelial growth factor are increased in macrophages during wound healing and in the presence of the endotoxin, lipopolysaccharide (LPS). Recent studies have demonstrated that nonhypoxic stimuli can also activate HIF-1 in a cell-specific manner. Here, we demonstrate that in macrophages, LPS can control the activation of hypoxia-regulated genes through the HIF-1 pathway. We show that in these cells, protein expression levels of HIF-1alpha are strongly increased to levels comparable to hypoxic induction. HIF-1alpha mRNA levels are markedly increased following LPS stimulation, suggesting a transcriptional induction. In functional studies, the LPS-induced HIF-1 complex could specifically bind to the HIF-1 DNA-binding motif. Additionally, when cells were transfected with an HIF-1-specific reporter construct, LPS could strongly activate the expression of the reporter to levels that surpassed those observed after hypoxic induction. This induction was blocked by the cotransfection of a dominant-negative form of HIF-1alpha. These results indicate that the HIF-1 complex is involved in macrophage gene activation following LPS exposure and identify a novel pathway that could play a determinant role during inflammation and wound healing.

Marked increase in vascular endothelial growth factor concentrations during Escherichia coli endotoxin-induced acute inflammation in humans

BACKGROUND

Bacterial endotoxins can induce the synthesis and release of vascular endothelial growth factor (VEGF), which may alter vascular permeability and cause vascular leakage.

MATERIALS AND METHODS

The effect of acute systemic inflammation on VEGF concentration was measured in healthy males after an intravenous bolus infusion of Escherichia coli endotoxin (lipopolysaccharide, LPS, 20 IU kg-1) in a double-blind, placebo-controlled parallel group study. LPS administration was followed by an infusion of lepirudin (bolus 0.1 mg kg-1, continuous infusion of 0.1 mg kg-1 h-1, n = 12) or saline (n = 12).

RESULTS

Plasma VEGF increased from a mean of 15.1 pg mL-1 to 74.6 pg mL-1 5 h after LPS (P < 0.003). Body temperature, pulse rate, leukcytes, prothrombin fragment 1 + 2 (F1 + 2) and lactoferrin increased and platelets decreased after LPS (P < 0.05). The LPS-induced increase in VEGF was paralleled by the neutrophil cell degranulation marker lactoferrin but not by F1 + 2, and was not affected by lepirudin, which blunted F1 + 2 formation (P < 0.05).

CONCLUSIONS

Inflammation-induced activation of leukcytes rather than platelets plays a role in the marked increase in VEGF, which cannot be abrogated by antithrombotic therapy.

Oxidized low-density lipoprotein (oxLDL) triggers hypoxia-inducible factor-1alpha (HIF-1alpha) accumulation via redox-dependent mechanisms

Oxidized low-density lipoprotein (oxLDL) and macrophages play a central role in atherosclerosis. Here, we obtained evidence that oxLDL induced hypoxia-inducible factor-1alpha (HIF-1alpha) protein accumulation in human macrophages (Mono-Mac-6) under normoxia. HIF-1alpha accumulation was attenuated by pretreatment with the antioxidant N-acetyl-L-cysteine (NAC), the nitric oxide (NO) donor S-nitrosoglutathione (GSNO), and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitors such as diphenyleniodonium (DPI) or 4-(2-aminoethyl)-benzenesulfonyl fluoride (AEBSF), thus implicating the contribution of oxLDL-generated reactive oxygen species (ROS). Whereas oxLDL did not modulate HIF-1alpha mRNA levels, experiments with cycloheximide pointed to a translational mechanism in oxLDL action. HIF-1-dependent luciferase reporter gene analysis underscored HIF-1 transactivation. Our results indicate that oxLDL induced HIF-1alpha accumulation and HIF-1-dependent reporter gene activation in human macrophages via a redox-mediated pathway. This finding may suggest a role of HIF-1 in atherosclerosis and oxLDL-induced pathogenesis.

Regulation of vascular endothelial growth factor gene expression in murine macrophages by nitric oxide and hypoxia

Vascular endothelial growth factor (VEGF) expression in murine peritoneal macrophages is strongly upregulated by hypoxia via transcriptional and posttranscriptional mechanisms. Interferon-gamma (IFN-gamma) with Escherichia coli lipopolysaccharide (LPS) also upregulates expression of VEGF, as well as of the inducible nitric oxide synthase (iNOS). Hypoxia (1% O(2)) upregulates VEGF expression in macrophages from both wild-type and iNOS knockout mice, indicating that hypoxic upregulation of VEGF is independent of iNOS. However, the iNOS inhibitor aminoguanidine (AG) decreases the VEGF expression induced by LPS/IFN-gamma, indicating an important role for NO. NO-dependent induction of VEGF is strongly dependent on cell density. LPS/IFN-gamma treatment induces minimal VEGF protein expression in macrophages cultured at low cell densities (<0.25 x 10(6) cells/cm(2)); at higher cell densities (>0.25 x 10(6) cells/cm(2)) that lead to conditions of pericellular hypoxia, however, induction of VEGF expression was strong. Transient transfection of RAW 264.7 cells with luciferase reporter constructs of the murine VEGF promoter indicates that both hypoxia and LPS/IFN-gamma independently induce VEGF promoter activity, irrespective of cell density. Although LPS/IFN-gamma treatment induces transcriptional activation of the VEGF promoter, significant levels of VEGF protein are only expressed by cells at high density under conditions of pericellular hypoxia. This suggests an important regulatory role for hypoxia at the posttranscriptional level. Deletion analysis of the VEGF promoter shows that the hypoxia response element region and its immediate flanking sequences are essential for both hypoxia and LPS/IFN-gamma-induced VEGF promoter activation.

Nitric oxide and wound repair

NO produced by both iNOS and eNOS plays many important roles in wound healing, from the inflammatory phase through to scar remodeling. NO has cytostatic, chemotactic, and vasodilatory effects during early wound repair, regulates proliferation and differentiation of several cell types, modulates collagen deposition and angiogenesis, and affects wound contraction. The data accumulated thus far indicates that the timing, level, and site of NO production are highly coordinated in normal wound repair. Defining states resulting from either inadequate substrate or depressed enzyme expression appear to contribute to impaired wound repair; however, NO represents only one factor in the complex process of wound healing. Approaches to improve NO availability may be of therapeutic value.

Effect of lipopolysaccharides on vascular endothelial growth factor expression in mouse pulp cells and macrophages

Vascular endothelial growth factor (VEGF), a potent pro-angiogenic factor, might regulate the neovascularization observed in the pulp of teeth with deep caries. The purpose of this in vitro study was to evaluate the effect of bacterial lipopolysaccharides (LPS) on VEGF expression in dental pulp cells. Mouse odontoblast-like cells (MDPC-23) or undifferentiated pulp cells (OD-21) were exposed to 0-20 microg ml-1Escherichia coli LPS or 0-80 microg ml-1Prevotella intermedia LPS. As controls, mouse macrophages or gingival fibroblasts were exposed to LPS, since these cells are known to secrete VEGF. The VEGF expression was evaluated by reverse transcriptase polymerase chain reaction or enzyme-linked immunosorbent assay. The baseline expression levels of VEGF protein were higher in MDPC-23 and OD-21 than in fibroblasts or macrophages. Vascular endothelial growth factor protein expression was upregulated in MDPC-23 and macrophages exposed to E. coli LPS, but not in OD-21 cells or fibroblasts. Higher concentrations of P. intermedia LPS were required to induce VEGF expression in MDPC-23 cells. Treatment with LPS did not affect VEGF expression at the mRNA level in any of the cells evaluated. These results demonstrate that bacterial LPS upregulates VEGF expression in odontoblast-like cells and macrophages, and suggest that the regulation of VEGF expression occurs primarily at a post-transcriptional level.

Association between macrophage activation and function of micro-encapsulated rat islets

AIMS/HYPOTHESIS

Survival of microencapsulated islet grafts is limited, even when inflammatory reactions against the capsules are restricted to a small portion of less than 10%.

METHODS

This study investigates both in vivo in rat recipients and in vitro whether cellular overgrowth on this minority of the capsules contributes to limitations in the functional survival of the 90% of the encapsulated islets which remain free of any cellular overgrowth.

RESULTS

In successful rat recipients of an allogenic microencapsulated islet graft we found that the vast majority of cells in the capsular overgrowth were activated ED-1 and ED-2 positive macrophages which were found in numbers of approximately 1500 per capsule. Co-culture of encapsulated islets with 1500 (nr8383) rat-macrophages per capsule showed that the activation of macrophages was caused by islet-derived bioactive factors since TNF-alpha and IL-1beta secretion by macrophages was induced by islet-containing capsules and not by empty capsules. This activation of macrophages was associated with a decrease in function of the encapsulated islets as evidenced by a quantitatively reduced (35%) insulin response in static incubation and a slower response in perifusion.

CONCLUSION/INTERPRETATION

Present research aims to design strategies for the temporary inhibition of macrophage activation since macrophages are predominantly present in the first two months after implantation. These strategies will serve as a pertinent basis for future clinical application of microencapsulated islets.

Regulation of vascular endothelial growth factor synthesis by nitric oxide: facts and controversies

Vascular endothelial growth factor (VEGF) is the major molecule governing angiogenesis, defined as the growth of blood vessels from vascular structure. There is abundant evidence that nitric oxide (NO) is an effector molecule mediating the activity of VEGF. By binding to its receptors, VEGF initiates the signaling cascades leading to NO production and angiogenic activation of endothelial cells. Recent data show that NO induces VEGF synthesis in numerous cell types, including vascular smooth muscle cells, macrophages, keratinocytes, and tumor cells. NO enhances VEGF production by augmenting its expression through activation of Akt kinase, followed by induction of several transcription factors, of which stabilization of hypoxia-inducible factor (HIF-1) is the critical step. With respect to its effect on VEGF expression, NO mimics hypoxia, the classical activator of HIF-1 and VEGF synthesis. The effect of NO on VEGF production is also mediated by heme oxygenase, an enzyme generating carbon monoxide, which appears to stimulate VEGF release. In this review, we attempt to elucidate the molecular mechanisms underlying the effects of NO on VEGF synthesis. We also discuss some discrepant data and suggest explanations for various aspects of the NO-VEGF relationship.

Host microenvironment in breast cancer development: inflammatory and immune cells in tumour angiogenesis and arteriogenesis

Breast cancer progression is associated with and dependent upon robust neovascularization. It is becoming clear that tumour-associated 'normal' cells, such as immune/inflammatory cells, endothelial cells and stromal cells, conspire with cancer cells in promoting this process. In particular, infiltrating immune/inflammatory cells secrete a diverse repertoire of growth factors and proteases that enable them to enhance tumour growth by stimulating angiogenesis and, as we suggest here, by promoting 'tumour arteriogenesis' - enlargement of feeding vessels supplying the expanding tumour capillary bed. Macrophages and their chemoattractants (e.g. macrophage chemoattractant protein-1) are critical for the arteriogenic process in ischaemia, and probably also in breast neoplasia. A better understanding of these various cellular and molecular constituents of breast cancer neovascularization may be useful in designing more effective therapies.

Inhibitors of nitric oxide production from hops (Humulus lupulus L.)

Nitric oxide (NO) plays an important role in many inflammatory responses and is also involved in carcinogenesis. In the present study, we investigated the inhibitory effect of extracts from Humulus lupulus L. on both the production of NO and the expression of inducible NO synthase (iNOS) in mouse macrophage RAW 264.7 cells. The production of NO was induced by a combination of lipopolysaccharide (LPS) and IFN-gamma, and determined by Griess assay. The expression of iNOS was detected by Western blotting. The LPS/IFN-gamma-induced production of NO and expression of iNOS were significantly inhibited by the ethyl acetate soluble fraction of Humulus lupulus L. Through bioactivity guided fractionation, humulene, five chalcones, 2,2-di-(3-methyl-2-butyleyl)-4,5-dihydoxy-cyclopent-4-en-1,3-dione, lupulone and three of its derivatives were isolated from the ethyl acetate soluble fraction. The chalcones, including xanthohumol, significantly inhibited the production of NO by suppressing the expression of iNOS.

Hypoxia is an inducer of vasodilator agents in peritoneal macrophages of cirrhotic patients

The aim of the investigation was to assess whether hypoxia induces the production of endogenous vasoactive peptides in macrophages of cirrhotic patients with ascites because low tissue oxygenation is a relatively frequent event in these patients. Peritoneal macrophages were isolated from ascites, seeded on well plates, and cultured at different times under hypoxic (5% O(2)) or normoxic conditions (21% O(2)). Then, accumulation of vasoactive peptides sensitive to hypoxia including endothelin-1 (ET-1), vascular endothelial growth factor (VEGF), and adrenomedullin (ADM) was measured. Only VEGF and ADM were constitutively secreted, and hypoxia further stimulated the release of these vasodilator peptides. In concordance, increased messenger RNA (mRNA) levels of VEGF and ADM were found at culturing macrophages in hypoxia. This characteristic response was not observed in circulating monocytes of either cirrhotic patients or healthy subjects. Next the expression of the transcription factor, hypoxia inducible factor 1 (HIF-1), was analyzed. Expression of HIF-1alpha and HIF-1beta messengers and HIF-1beta protein subunit remained unchanged regardless of O(2) tension, whereas HIF-1alpha protein subunit was overexpressed under hypoxic conditions. Moreover, conditioned medium from macrophages cultured under hypoxic conditions promoted a larger nitric oxide (NO) release in endothelial cells than that of normoxic macrophages. In conclusion, these data indicate that hypoxia induces the synthesis of VEGF and ADM in macrophages of cirrhotic patients, likely through HIF-1-enhanced transcriptional activity. These data suggest that a local reduction in O(2) tension could enhance the synthesis of macrophage-derived vasodilators, thus aggravating the circulatory disturbance of these patients.

Effects of nitric oxide releasing poly(vinyl alcohol) hydrogel dressings on dermal wound healing in diabetic mice

Healing of chronic wounds such as diabetic foot ulcers is a significant clinical problem. Methods of accelerating healing in these difficult lower extremity sites include use of growth factor-loaded gels, hyperbaric oxygen, grafts, and artificial skin replacements. Nitric oxide (NO) has been proposed as a possible active agent for enhancing wound healing. This study examines the in vitro and in vivo responses to a novel hydrogel that produces therapeutic levels of NO. A hydrogel wound dressing was fabricated using ultraviolet light-initiated polymerization from poly(vinyl alcohol) with a NO donor covalently coupled to the polymer backbone. NO release from the NO-modified hydrogel was shown to occur over a time period of up to 48 hours, and there was no associated decrease in fibroblast growth or viability in vitro associated with NO hydrogels. Fibroblasts in culture with NO hydrogels had an increased production of extracellular matrix compared with cells cultured without the NO hydrogels. Preliminary animal studies in a diabetic mouse, impaired wound healing model were conducted comparing low (0.5 mM) and high (5 mM) doses of NO. Time to complete closure was similar in control wounds and NO-treated wounds; however, at 8 days control wounds were significantly smaller than NO-treated wounds. By days 10 to 13 this delay was no longer apparent. Granulation tissue thickness within the wounds at days 8 and 15 and scar tissue thickness after wound closure were increased in animals exposed to higher dose NO hydrogels. The results of this study suggest that exogenous NO released from a hydrogel wound dressing has potential to modulate wound healing.

Nitric oxide and wound repair: role of cytokines?

Wound healing involves platelets, inflammatory cells, fibroblasts, and epithelial cells. All of these cell types are capable of producing nitric oxide (NO), either constitutively or in response to inflammatory cytokines, through the activity of nitric oxide synthases (NOSs): eNOS (NOS3; endothelial NOS) and iNOS (NOS2; inducible NOS), respectively. Indeed, pharmacological inhibition or gene deletion of these enzymes impairs wound healing. The wound healing mechanisms that are triggered by NO appear to be diverse, involving inflammation, angiogenesis, and cell proliferation. All of these processes are controlled by defined cytokine cascades; in many cases, NO appears to modulate these cytokines. In this review, we summarize the history and present state of research on the role of NO in wound healing within the framework of modulation of cytokines.

Improved angiogenic potency by implantation of ex vivo hypoxia prestimulated bone marrow cells in rats

Therapeutic angiogenesis can be induced by local implantation of bone marrow cells. We tried to enhance the angiogenic potential of this treatment by ex vivo hypoxia stimulation of bone marrow cells before implantation. Bone marrow cells were collected and cultured at 33 degrees C under 2% O(2)-5% CO(2)-90% N(2) (hypoxia) or 95% air-5% CO(2) (normoxia). Cells were also injected into the ischemic hindlimb of rats after 24 h of culture. Hypoxia culture increased the mRNA expression of vascular endothelial growth factor (VEGF), vascular endothelial (VE)-cadherin, and fetal liver kinase-1 (Flk-1) from 2.5- to fivefold in bone marrow cells. The levels of VEGF protein in the ischemic hindlimb were significantly higher 1 and 3 days after implantation with hypoxia-cultured cells than with normoxia-cultured or noncultured cells. The microvessel density and blood flow rate in the ischemic hindlimbs were also significantly (P < 0.001) higher 2 wk after implantation with hypoxia-cultured cells (89.7 +/- 5.5%) than with normoxia-cultured cells (67.0 +/- 9.6%) or noncultured cells (70.4 +/- 7.7%). Ex vivo hypoxia stimulation increased the VEGF mRNA expression and endothelial differentiation of bone marrow cells, which together contributed to improved therapeutic angiogenesis in the ischemic hindlimb after implantation.

Plasma vascular endothelial growth factor in sleep apnea syndrome: effects of nasal continuous positive air pressure treatment

Sleep apnea syndrome is associated with recurrent episodic hypoxia during sleep, which has been implicated in the development of cardiovascular morbidity. Hypoxia is the major stimulus of vascular endothelial growth factor (VEGF), which is a potent angiogenic cytokine. In the present article we describe the results of three experiments in which plasma concentrations of VEGF were measured in patients with sleep apnea. In Experiment 1, apnea-hypopnea index was found to be a significant independent predictor of morning VEGF concentrations in 85 male subjects investigated in the sleep laboratory, of whom 47 had an apnea-hypopnea index greater than 20. In Experiment 2, VEGF concentrations measured hourly during the sleep period were found to be significantly higher in a group of five sleep apnea patients compared with six age-similar snorers and six normal young adults (129.1 +/- 43.4 versus 74.6 +/- 11.5 and 32.5 +/- 12.8 pg/ml, respectively [p < 0.007]). In Experiment 3, VEGF concentrations were compared in patients with sleep apnea before and 1 year after nasal continuous positive airway pressure treatment. A significant decrease in VEGF concentrations was found only in patients in whom nocturnal hypoxia improved after treatment (57.1 +/- 62.5 versus 39.6 +/- 46.9 pg/ml, p < 0.01). There was no comparable improvement in patients who did not accept treatment (53.9 +/- 23.6 versus 54.0 +/- 21.5 pg/ml, ns). These results raise the possibility that VEGF may contribute to the long-term adaptation of sleep apnea syndrome to recurrent nocturnal hypoxia.

Synergistic up-regulation of vascular endothelial growth factor expression in murine macrophages by adenosine A(2A) receptor agonists and endotoxin

Under normoxic conditions, macrophages from C57BL mice produce low levels of vascular endothelial growth factor (VEGF). Hypoxia stimulates VEGF expression by approximately 500%; interferon-gamma (IFN-gamma) with endotoxin [lipopolysaccharide (LPS)] also stimulates VEGF expression by approximately 50 to 150% in an inducible nitric oxide synthase (iNOS)-dependent manner. Treatment of normoxic macrophages with 5'-N-ethyl-carboxamido-adenosine (NECA), a nonselective adenosine A(2) receptor agonist, or with 2-[p-(2-carboxyethyl)-phenylethyl amino]-5'-N-ethyl-carboxamido-adenosine (CGS21680), a specific adenosine A(2A) receptor agonist, modestly increases VEGF expression, whereas 2-chloro-N(6)-cyclopentyl adenosine (CCPA), an adenosine A(1) agonist, does not. Treatment with LPS (0 to 1000 ng/ml), or with IFN-gamma (0 to 300 U/ml), does not affect VEGF expression. In the presence of LPS (EC(50) < 10 ng/ml), but not of IFN-gamma, both NECA and CGS21680 synergistically up-regulate VEGF expression by as much as 10-fold. This VEGF is biologically active in vivo in the rat corneal bioassay of angiogenesis. Inhibitors of iNOS do not affect this synergistic induction of VEGF, and macrophages from iNOS-/- mice produce similar levels of VEGF as wild-type mice, indicating that NO does not play a role in this induction. Under hypoxic conditions, VEGF expression is slightly increased by adenosine receptor agonists but adenosine A(2) or A(1) receptor antagonists 3,7-dimethyl-1-propargyl xanthine (DMPX), ZM241385, and 8-cyclopentyl-1,3-dipropylxanthine (DCPCX) do not modulate VEGF expression. VEGF expression is also not reduced in hypoxic macrophages from A(3)-/- and A(2A)-/- mice. Thus, VEGF expression by hypoxic macrophages does not seem to depend on endogenously released or exogenous adenosine. VEGF expression is strongly up-regulated by LPS/NECA in macrophages from A(3)-/- but not A(2A)-/- mice, confirming the role of adenosine A(2A) receptors in this pathway. LPS with NECA strongly up-regulates VEGF expression by macrophages from C(3)H/HeN mice (with intact Tlr4 receptors), but not by macrophages from C(3)H/HeJ mice (with mutated, functionally inactive Tlr4 receptors), implicating signaling through the Tlr4 pathway in this synergistic up-regulation. Finally, Western blot analysis of adenosine A(2A) receptor expression indicated that the synergistic interaction of LPS with A(2A) receptor agonists does not involve up-regulation of A(2A) receptors by LPS. These results indicate that in murine macrophages there is a novel pathway regulating VEGF production, that involves the synergistic interaction of adenosine A(2A) receptor agonists through A(2A) receptors with LPS through the Tlr4 pathway, resulting in the strong up-regulation of VEGF expression by macrophages in a hypoxia- and NO-independent manner.

Red wine and black tea polyphenols modulate the expression of cycloxygenase-2, inducible nitric oxide synthase and glutathione-related enzymes in azoxymethane-induced f344 rat colon tumors

Polyphenolic compounds extracted from red wine (WE) and black tea (BT), 50 mg/(kg. d), inhibit the promotion phase of the colon carcinogenesis process induced by azoxymethane (AOM) in rodents. To investigate possible mechanisms of this protective activity, we evaluated by RT-PCR the gene expression of cycloxygenase-2 (COX-2), inducible NO synthase (iNOS), gamma-glutamylcysteine synthetase (gamma-GCS) and two isoforms of glutathione S-transferase (GST), GST-P and GST-M2, in 30 AOM-induced tumors and in the corresponding normal colon mucosa. AOM-induced colon tumors had significantly greater GST-P, GST-M2, COX-2 and iNOS gene expression than the corresponding normal mucosa. However, tumors harvested from rats treated with BT (P < 0.05) and WE (P < 0.01) polyphenols had a lower GST-P mRNA level than tumors from controls. Treatment with WE polyphenols induced a similar inhibitory effect on the colon tumor overexpression of GST-M2 (P < 0.01), COX-2 (P < 0.05) and iNOS (P < 0.05). In the normal mucosa, rats treated with BT polyphenols had greater gamma-GCS expression than controls (P < 0.01). Our results provide evidence that WE and BT polyphenols modulate COX-2, iNOS and glutathione-related gene expression in tumors, suggesting that these compounds have possible chemotherapeutic activity.

Induction of endothelial cell proliferation by angiogenic factors released by activated monocytes

INTRODUCTION

Cell-cell interaction is an essential component of atherosclerotic plaque development. Activated monocytes appear to play a central role in the development of atherosclerosis, not only through foam cell formation but also via the production of various growth factors that induce proliferation of different cell types that are involved in the plaque development. Using serum free co-culture method, we determined the effect of monocytes on endothelial cell proliferation.

METHODS

Endothelial cell proliferation is determined by the amount of [3H]thymidine incorporated in to the DNA. Basic fibroblast growth factor (b-FGF), vascular endothelial growth factor (VEGF) and interleukin-8 (IL-8) levels in the conditioned medium were determined by ELISA.

RESULTS

Conditioned medium from unactivated monocytes partially inhibited endothelial cell proliferation, whereas conditioned medium from activated monocytes promoted endothelial cell proliferation. The mitogenic effect of conditioned medium derived from activated monocytes is due to the presence of b-FGF, VEGF and IL-8. Neutralizing antibodies against b-FGF, VEGF and IL-8 partially reversed the mitogenic effect of conditioned medium derived from activated monocytes. When b-FGF, VEGF and IL-8 were immunoprecipitated from conditioned medium derived from activated monocytes, it is less mitogenic to endothelial cells.

CONCLUSION

Activated monocytes may play an important role in the development of atherosclerotic plaque by producing endothelial cell growth factors.

Effects of pH-neutral, bicarbonate-buffered dialysis fluid on peritoneal transport kinetics in children

BACKGROUND

Due to their superior biocompatibility, pH-neutral solutions are beginning to replace acidic lactate-buffered peritoneal dialysis (PD) fluids. We hypothesized that pH-neutral and acidic solutions might differentially affect peritoneal transport in the early dwell phase, due to differences in ionic shifts and initial peritoneal vasodilation. Such differences may become clinically relevant in patients with frequent short cycles on automated PD (APD).

METHODS

Twenty-five children were treated with a lactate-buffered (35 mmol/L, pH 5.5) or a bicarbonate-buffered PD solution (34 mmol/L, pH 7.4) in randomized order on two sequential days. Each day a four-hour Standardized Permeability Analysis (SPA) was performed, followed by overnight APD (7 cycles, fill volume 1000 mL/m2, dwell time 75 min). Functional peritoneal surface area was dynamically assessed using the three-pore model.

RESULTS

While intraperitoneal pH was constant at 7.41 +/- 0.03 throughout the SPA with bicarbonate fluid, the dialysate remained acidic for more than one hour with lactate solution (pH 7.12 +/- 0.08 at 1 h). Total pore area was 60% higher during the first 30 minutes of the dwell than under steady-state conditions, without a difference between acidic and pH-neutral fluid. Net base gain, intraperitoneal volume kinetics, glucose absorption, ultrafiltration rate, effective lymphatic absorption and the transport of urea, potassium, beta2-microglobulin and albumin were similar with both fluids. However, phosphate and creatinine elimination were 10% lower with bicarbonate PD fluid, resulting in corresponding significant decreases in the 24-hour clearances of these solutes.

CONCLUSION

The peritoneal surface area is not measurably influenced by pH-neutral PD fluid. Creatinine and phosphate elimination appears to be slightly reduced with bicarbonate fluid; this observation awaits clarification in extended therapeutical trials.

Heme oxygenase activity modulates vascular endothelial growth factor synthesis in vascular smooth muscle cells

Hypoxia, cytokines, and nitric oxide (NO) stimulate the generation of vascular endothelial growth factor (VEGF) and induce heme oxygenase-1 (HO-1) expression in vascular tissue. HO-1 degrades heme to carbon monoxide (CO), iron, and biliverdin, the latter being reduced to bilirubin by biliverdin reductase. In the present study, we investigated the role of HO-1 in the modulation of VEGF synthesis in rat vascular smooth muscle cells (VSMC). In VSMC stimulated with cytokines, inhibition of NO production significantly, but not completely, reduced VEGF release. In contrast, inhibition of HO activity by tin protoporphyrin IX (SnPPIX) totally prevented cytokine-induced increase in VEGF, despite an augmented synthesis of intracellular NO. Stimulation of HO-1 activity by hemin enhanced VEGF production; this effect was abrogated by blockade of the HO pathway. Similarly, VEGF synthesis induced by hypoxia was down-regulated by SnPPIX, but not by inhibitors of NO synthase. To elucidate further a direct involvement of HO-1 in the observed effects, we generated transfected cells that overexpressed the HO-1 gene. Notably, these cells synthesized significantly more VEGF protein than cells transfected with a control gene. Among the products of HO-1, biliverdin and bilirubin showed no effect, whereas iron ions inhibited VEGF synthesis. Exposure of cells to 1% CO resulted in a marked accumulation of VEGF (20-fold increase) over the basal level. Our data indicate that HO-1 activity influences the generation of VEGF in VSMC in both normoxic and hypoxic conditions. As CO and iron, respectively the inducer and the inhibitor of VEGF synthesis, are concomitantly produced during the degradation of heme, these data indicate that HO by-products may differentially modulate VEGF production.

Physiologically low oxygen concentrations in fetal skin regulate hypoxia-inducible factor 1 and transforming growth factor-beta3

In the first-trimester mammalian fetus, skin wounds heal with perfect reconstitution of the dermal architecture without scar formation. Understanding environmental molecular regulation in fetal wound healing may reveal scar-limiting therapeutical strategies for the prevention of postnatal scarring wound repair. Therefore, we performed studies on fetal skin oxygenation and skin and wound expression of hypoxia-inducible factor 1alpha (HIF-1alpha) in the sheep model in vivo and performed studies on the potential relevance of HIF-1alpha during wound healing in vitro. Skin oxygen partial pressure levels were hypoxic throughout normal development. In nonscarring fetal skin at gestation day (GD)60, HIF-1alpha could be detected neither in healthy nor in wounded tissue. At GD100, in wounds with minimal scar formation, HIF-1alpha was expressed in fibroblasts and was markedly up-regulated at the wound edge. In scarring fetal wounds at GD120, HIF-1alpha was predominantly expressed in inflammatory cells. Expression of transforming growth factor beta3 (TGF-beta3), a potent antiscarring cytokine, overlapped with HIF-1a expression at GD100. HIF-1alpha-deficient mouse embryonic fibroblasts showed impaired migratory capabilities and demonstrated that TGF-beta3, but not proscarring TGF-beta1, manifests hypoxia- and HIF-1alpha-dependent regulation. In conclusion, HIF-1alpha-dependent regulation of a potent antiscarring cytokine may provide new strategies for antiscarring manipulation of wound healing.

Role of macrophages and lymphocytes in the induction of neovascularization in renal allograft rejection

The aim of this study was to clarify the relationship between angiogenesis and mononuclear cell infiltration in renal allografts. Kidney biopsies from 70 renal transplant recipients were evaluated. The density of CD68, CD3, and HLA-DR-positive infiltrating cells were semiquantitatively assessed by immunohistochemistry. Microvessels were highlighted by immunostaining endothelial cells for factor VIII-RA. Of the 70 patients, 38 showed acute rejection (AR), and 32 showed chronic rejection (CR). The mean microvessel density (MVD) in the AR cases was 931.6 +/- 82 and 481.6 +/- 43.6 in the CR cases. MVD in the controls was 210.4 +/- 21.7. A significant difference was found between the 3 groups (P < 0.001). There were significant positive correlations between MVD and the proportions of the various types of mononuclear cells in the interstitial tissue in both the AR (P < 0.001) and CR (P < 0.001) groups. In the CR group, mean MVD increased in parallel with increasing interstitial fibrosis (P < 0.001). In follow-up biopsies, 23 of 38 patients with AR showed variable degrees of interstitial fibrosis. The mean MVD in the initial biopsy was 537.2 +/- 46.8 in cases that showed no fibrosis in follow-up biopsies, whereas mean MVD in the initial biopsy was 1,196 +/- 98.7 in 23 patients who showed interstitial fibrosis in follow-up biopsies. The difference between these values was significant (P < 0.001). Patients with AR whose initial biopsies showed high MVD developed interstitial fibrosis earlier and had poorer graft outcome than those whose initial biopsies showed low MVD. The results suggest that advanced tubulointerstitial injury and mononuclear cell infiltration may play an important role in the induction of angiogenesis. Mononuclear cells may potentiate interstitial fibrosis in vivo by stimulating neovascularization, which leads to early fibrotic changes and poor outcome.

Vascular endothelial growth factor synthesis in vascular smooth muscle cells is enhanced by 7-ketocholesterol and lysophosphatidylcholine independently of their effect on nitric oxide generation

Nitric oxide (NO) generated by inducible NO synthase (iNOS) enhances vascular endothelial growth factor (VEGF) synthesis in vascular smooth muscle cells (VSMC) and both NO and modified low density lipoprotein (LDL) augment VEGF production in macrophages. Oxidized LDL (oxLDL) are known inhibitors of NO generation in the cells of vascular wall. As the relationship between VEGF, iNOS and oxLDL has not been well elucidated, we studied the effect of two main components of oxLDL, 7-ketocholesterol (7-Kchol) and lysophosphatidylcholine (LPC), on VEGF and NO synthesis in rat VSMC and on VEGF synthesis in human VSMC. Both LPC and 7-Kchol significantly augmented VEGF production in rat and human VSMC. Increase in VEGF generation was related to the activation of VEGF promoter by both 7-Kchol and LPC and enhancement of VEGF mRNA transcription. In rat, VSMC IL-1beta-induced NO generation and enhanced VEGF synthesis. 7-Kchol decreased rat iNOS promoter activity, iNOS expression and NO generation, but it did not impair IL-1beta-induced VEGF synthesis. LPC did not significantly influence IL-1beta-induced NO production in rat VSMC and VEGF synthesis was significantly enhanced by combined treatment with IL-1beta and LPC in comparison to the effect of either compound alone. The results indicate that VEGF and NO synthesis in VSMC can be modulated by oxLDL. Those interactions might have an effect on the plaque growth and might be of relevance for the physiology of vascular wall cells.

Vascular endothelial growth factor expression by activated synovial leukocytes in rheumatoid arthritis: critical involvement of the interaction with synovial fibroblasts

OBJECTIVE

To examine the expression and regulation of the angiogenic factor, vascular endothelial growth factor (VEGF), by fibroblast-like synoviocytes (FLS), monocytes, and polymorphonuclear neutrophils (PMNs) isolated from the synovial fluid (SF) of rheumatoid arthritis (RA) patients.

METHODS

Monocytes or PMNs obtained from RA SF were cocultured with unstimulated, semiconfluent RA FLS. Culture supernatants were assayed for the proliferation and in vitro tube formation of endothelial cells, and for the production of VEGF, by enzyme-linked immunosorbent assay. The expression of VEGF messenger RNA and protein was also determined by reverse transcription-polymerase chain reaction and immunohistochemistry, respectively.

RESULTS

We found that the interaction of inflammatory, activated leukocytes with FLS resulted in synergistic increases in VEGF expression and secretion, which contributed to the proliferation of endothelial cells and to in vitro endothelial tube formation. The induction of VEGF was mediated via specific adhesion molecules, as indicated by the finding that anti-integrin antibodies significantly inhibited VEGF. Furthermore, the levels of VEGF secretion correlated with the expression of cell surface integrin (CD11b and CD18) on both monocytes and PMNs in the SF.

CONCLUSION

VEGF expression within inflamed joints thus appears to be regulated not only by inflammatory cytokines, but also by the physical interaction of activated leukocytes and FLS. Once expressed, VEGF likely plays a crucial role in the neovascularization of the pannus and the progressive joint destruction associated with the synovial inflammation of RA.

Effects of maitake (Grifola frondosa) D-Fraction on the carcinoma angiogenesis

We have reported that D-Fraction extracted from maitake (Grifola frondosa), activates immune competent cells, and indicates anti-tumor activities. The D-Fraction was observed to induce angiogenesis in vivo and to enhance the proliferation capability and migration capability of human vascular endothelial cell in vitro. The D-Fraction also increased plasma vascular endothelial growth factor (VEGF) concentration significantly. Also VEGF and TNF-alpha production by the activated peritoneal macrophages were enhanced. These results suggest that the anti-tumor activity of the D-Fraction is not only associated with the activation of the immuno-competent cells but also possibly related to the carcinoma angiogenesis induction.