Nitric oxide reduces tumor cell adhesion to isolated rat postcapillary venules

Quantification of Nitric Oxide Concentration Using Single-Walled Carbon Nanotube Sensors

Nitric oxide (NO), a free radical present in biological systems, can have many detrimental effects on the body, from inflammation to cancer. Due to NO's short half-life, detection and quantification is difficult. The inability to quantify NO has hindered researchers' understanding of its impact in healthy and diseased conditions. Single-walled carbon nanotubes (SWNTs), when wrapped in a specific single-stranded DNA chain, becomes selective to NO, creating a fluorescence sensor. Unfortunately, the correlation between NO concentration and the SWNT's fluorescence intensity has been difficult to determine due to an inability to immobilize the sensor without altering its properties. Through the use of a recently developed sensor platform, systematic studies can now be conducted to determine the correlation between SWNT fluorescence and NO concentration. This paper explains the methods used to determine the equations that can be used to convert SWNT fluorescence into NO concentration. Through the use of the equations developed in this paper, an easy method for NO quantification is provided. The methods outlined in this paper will also enable researchers to develop equations to determine the concentration of other reactive species through the use of SWNT sensors.

Role of NO and S-nitrosylation in the Expression of Endothelial Adhesion Proteins That Regulate Leukocyte and Tumor Cell Adhesion

Leukocyte recruitment is one of the most important cellular responses to tissue damage. Leukocyte extravasation is exquisitely regulated by mechanisms of selective leukocyte-endothelium recognition through adhesion proteins in the endothelial cell surface that recognize specific integrins in the activated leukocytes. A similar mechanism is used by tumor cells during metastasis to extravasate and form a secondary tumor. Nitric oxide (NO) has been classically described as an anti-inflammatory molecule that inhibits leukocyte adhesion. However, the evidence available shows also a positive role of NO in leukocyte adhesion. These apparent discrepancies might be explained by the different NO concentrations reached during the inflammatory response, which are highly modulated by the expression of different nitric oxide synthases, along the inflammatory response and by changes in their subcellular locations.

Tumor Metastasis in the Microcirculation

Tumor cell metastasis through blood circulation is a complex process and is one of the great challenges in cancer research as metastatic spread is responsible for ∼90% of cancer-related mortality. Tumor cell intravasation into, arrest and adhesion at, and extravasation from the microvessel walls are critical steps in metastatic spread. Understanding these steps may lead to new therapeutic concepts for tumor metastasis. Vascular endothelium forming the microvessel wall and the glycocalyx layer at its surface are the principal barriers to and regulators of the material exchange between circulating blood and body tissues. The cleft between adjacent endothelial cells is the principal pathway for water and solute transport through the microvessel wall in health. Recently, this cleft has been found to be the location for tumor cell adhesion and extravasation. The blood-flow-induced hydrodynamic factors such as shear rates and stresses, shear rate and stress gradients, as well as vorticities, especially at the branches and turns of microvasculatures, also play important roles in tumor cell arrest and adhesion. This chapter therefore reports the current advances from in vivo animal studies and in vitro culture cell studies to demonstrate how the endothelial integrity or microvascular permeability, hydrodynamic factors, microvascular geometry, cell adhesion molecules, and surrounding extracellular matrix affect critical steps of tumor metastasis in the microcirculation.

Inhibition of endothelial nitric oxide synthase decreases breast cancer cell MDA-MB-231 adhesion to intact microvessels under physiological flows

Nitric oxide (NO) at different concentrations may promote or inhibit tumor growth and metastasis under various conditions. To test the hypothesis that tumor cells prefer to adhere to the locations with a higher endothelial NO production in intact microvessels under physiological flows and to further test that inhibiting NO production decreases tumor cell adhesion, we used intravital fluorescence microscopy to measure NO production and tumor cell adhesion in postcapillary venules of rat mesentery under normal and reduced flow conditions, and in the presence of an endothelial nitric oxide synthase (eNOS) inhibitor, N(G)-monomethyl-l-arginine (l-NMMA). Rats (SD, 250-300 g) were anesthetized. A midline incision (∼2 inch) was made in the abdominal wall, and the mesentery was taken out from the abdominal cavity and spread over a coverslip for the measurement. An individual postcapillary venule (35-50 μm) was first loaded with 4,5-diaminofluorescein diacetate (DAF-2 DA), a fluorescent indictor for NO. Then the DAF-2 intensity was measured for 30 min under a normal or reduced flow velocity, with and without perfusion with MDA-MB-231 breast cancer cells, and in the presence of l-NMMA. We found that tumor cells prefer to adhere to the microvessel locations with a higher NO production such as curved portions. Inhibition of eNOS by l-NMMA attenuated the flow-induced NO production and reduced tumor cell adhesion. We also found that l-NMMA treatment for ∼40 min reduced microvessel permeability to albumin. Our results suggest that inhibition of eNOS is a good approach to preventing tumor cell adhesion to intact microvessels under physiological flows.

G894T and 4a/b polymorphisms of NOS3 gene are not associated with cancer risk: a meta-analysis

Endothelial nitric oxide synthase (eNOS or NOS3) produces nitric oxide and genetic polymorphisms of NOS3 gene play significant roles in various processes of carcinogenesis. The results from published studies on the association between NOS3 G894T and NOS3 intron 4 (4a/b) polymorphisms and cancer risk are conflicting and inconclusive. However, i n order to assess this relationship more precisely, a meta-analysis was performed with PubMed (Medline), EMBASE and Google web searches until February 2014 to select all published case- control and cohort studies. Genotype distribution data were collected to calculate the pooled odd ratios (ORs) and 95% confidence intervals (CIs) to evaluate the strength of association. A total of 10,546 cancer cases and 10,550 controls were included from twenty four case-control studies for the NOS3 G894T polymorphism. The results indicated no significant association with cancer risk as observed in allelic (T vs G: OR=1.024, 95%CI=0.954 to 1.099, p=0.508), homozygous (TT vs GG: OR=1.137, 95%CI=0.944 to 1.370, p=0.176), heterozygous (GT vs GG: OR=0.993, 95%CI=0.932 to 1.059, p=0.835), recessive (TT vs GG+GT: OR=1.100, 95%CI=0.936 to 1.293, p=0.249) and dominant (TT+GT vs GG: OR=1.012, 95%CI=0.927 to 1.105, p=0.789) genetic models. Similarly, a total of 3,449 cancer cases and 3,691 controls were recruited from fourteen case-control studies for NOS3 4a/b polymorphism. Pooled results indicated no significant association under allelic (A vs B: OR=0.981, 95%CI=0.725 to 1.329, p=0.902), homozygous (AA vs BB: OR=1.166, 95%CI=0.524 to 2.593, p=0.707), heterozygous (BA vs BB: OR=1.129, 95%CI=0.896 to 1.422, p=0.305), dominant (AA+BA vs BB: OR=1.046, 95%CI=0.779 to 1.405, p=0.763) and recessive (AA vs BB+BA: OR=1.196, 95%CI=0.587 to 2.439, p=0.622) genetic contrast models. This meta-analysis suggests that G894T and 4a/b polymorphisms of NOS3 gene are not associated with increased or decreased risk of overall cancer.

Relation between Endothelial Nitric Oxide Synthase Genotypes and Oxidative Stress Markers in Larynx Cancer

Nitric oxide synthase (eNOS/NOS3) is responsible for the endothelial synthesis of nitric oxide (NO(•)). G894T polymorphism leads to the amino acid substitution from Glu298Asp that causes lower NOS3 activity and basal NO(•) production in NOS3 894T (298Asp) allele carriers compared with the GG homozygotes. NO(•) acts as an antioxidant protecting against Fenton's reaction which generates highly reactive hydroxyl radicals. Allelic variation of NOS3 may influence an individual's risk of laryngeal cancer (LC). In the current study we have examined the possible relationship between NOS3 G894T genotypes and various systemic oxidative damage markers such as protein carbonyl, advanced oxidation protein products, Cu, Zn-superoxide dismutase, thiol group fractions, and lipid hydroperoxides in LC patients. Genotyping was carried out by PCR-RFLP. In LC patients with TT genotype, Cu, Zn-superoxide dismutase activities and nonprotein thiol levels were significantly higher than the controls. In patients with GT and GG genotype, high levels of lipid hydroperoxides showed statistical significance when compared to controls. Our results indicate a potential relationship among G894T polymorphism of NOS3, and impaired redox homeostasis. Further studies are required to determine the role of NOS3 gene polymorphism and impaired plasma redox homeostasis.

Intravital microscopic methods to evaluate anti-inflammatory effects and signaling mechanisms evoked by hydrogen sulfide

Hydrogen sulfide (H2S) is an endogenous gaseous signaling molecule with potent anti-inflammatory properties. Exogenous application of H2S donors, administered either acutely during an inflammatory response or as an antecedent preconditioning intervention that invokes the activation of anti-inflammatory cell survival programs, effectively limits leukocyte rolling, adhesion and emigration, generation of reactive oxygen species, chemokine and cell adhesion molecule expression, endothelial barrier disruption, capillary perfusion deficits, and parenchymal cell dysfunction and injury. This chapter focuses on intravital microscopic methods that can be used to assess the anti-inflammatory effects exerted by H2S, as well as to explore the cellular signaling mechanisms by which this gaseous molecule limits the aforementioned inflammatory responses. Recent advances include use of intravital multiphoton microscopy and optical biosensor technology to explore signaling mechanisms in vivo.

Possible relation between the NOS3 gene GLU298ASP polymorphism and bladder cancer in Turkey

Endothelial nitric oxide synthase (eNOS), encoded by the NOS3 gene, has been suggested to play an important role in uncontrolled cell growth in several cancer types. The objective of this study was to evaluate the role of the NOS3 Glu298Asp polymorphism in bladder cancer susceptibility in a Turkish population. We determined the genotypes of 66 bladder cancer cases and 88 healthy controls. Genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism analysis. A significant association for NOS3 Glu298Asp heterozygotes genotypes and T allely were found between healthy controls and bladder cancer, respectively (p<0.001: p=0.002). There were no significant associations between any genotypes and the stage, grade, and histological type of bladder cancer. Our study suggested an increased risk role of NOS3 GT genotype in bladder cancer susceptibility in our Turkish population.

Role of coagulation in the recruitment of colon adenocarcinoma cells to thrombus under shear

Colorectal cancer metastases can appear on the peritoneum and in lymph nodes, liver, and lungs, suggesting both hematogenous and lymphatic spreading of the primary tumor. While antithrombotic agents have been shown to reduce both long-term incidence and metastasis, the role of coagulation in facilitating metastasis is ill defined. We investigated the kinetics and molecular mechanisms of metastatic colon adenocarcinoma cell recruitment to thrombi under shear flow, ex vivo. Platelet aggregates were formed by perfusing citrated anticoagulated whole blood over immobilized fibrinogen or fibrillar collagen. Thrombi were formed by perfusing recalcified whole blood over fibrinogen or fibrillar collagen in the presence of coagulation. Cultured colon adenocarcinoma cells (SW620) were perfused either during or following platelet aggregate or thrombus formation. The degree of transient tumor cell interactions (recruitment, rolling, and release) and the number of firmly adhered tumor cells were quantified using fluorescence microscopy. Platelet aggregates and thrombi formed on either fibrinogen- or fibrillar-collagen supported SW620 cell interactions and adhesion under shear. Thrombi or fibrin supported a greater degree of SW620 cell interactions and adhesion compared with platelet aggregates or fibrinogen, respectively, demonstrating that coagulation promoted SW620 cell recruitment under shear. Interestingly, in the absence of anticoagulation, we observed SW620 preferentially binding to thrombus-bound polymorphonuclear leukocytes (PMNs). The addition of purified PMNs to thrombi resulted in a doubling of the number of interacting and bound SW620 cells. Since thrombi often accumulate and activate leukocytes, our findings suggest that leukocytes may play a role in localizing metastases to sites of thrombogenesis.

Association of eNOS polymorphisms (-786T>C, 4a4b, 894G>T) with colorectal cancer susceptibility in the Korean population

BACKGROUND

Polymorphisms of endothelial nitric oxide synthases (eNOS) have been shown to be associated with cancer susceptibility. However, the results of such studies are conflicting to date. We investigated whether polymorphisms of the eNOS gene correlated with patients with colorectal cancer (CRC), relative to healthy individuals.

PATIENTS AND METHODS

In the present study, we analyzed three polymorphisms of eNOS (-786T>C, 4a4b, and 894G>T) in 509 healthy controls and 528 patients with CRC. The genotyping of eNOS polymorphisms was performed using polymerase chain reaction or polymerase chain reaction-restriction fragment length polymorphism assays.

RESULTS

We found that the TC+CC genotype of the -786T>C polymorphism was significantly associated with an increased risk of CRC compared with the TT genotype. Similarly, the GT+TT genotype of the 894G>T polymorphism was associated with an increased susceptibility to CRC. However, no evidence was found for any association between the 4a4b polymorphism and CRC risk. In addition, the C/4b/G (-786T>C/4a4b/894G>T) haplotype was significantly associated with increased risk of CRC and C/4b/T (-786T>C/4a4b/894G>T) haplotype was only detected in CRC patients.

CONCLUSIONS

Our study suggests that the eNOS -786T>C and 894G>T polymorphisms may be associated with the development of CRC in the Korean population.

Effects of the T-786C, G894T, and Intron 4 VNTR (4a/b) polymorphisms of the endothelial nitric oxide synthase gene on the risk of prostate cancer

Several studies have shown that nitric oxide (NO) and nitric oxide synthase (NOS) system plays an important role in carcinogenesis. Endothelial nitric oxide synthase (eNOS) gene polymorphisms significantly affects serum NO concentrations. Studies addressing the relationship between eNOS gene polymorphisms and prostate cancer (CaP) are very scarce. We examined the association between the 3 eNOS gene polymorphisms (T-786C, G894T, and 4a/b) with risk and clinical features of CaP. One hundred seventy patients with CaP (mean age 63.6 ± 12.4 years) and 340 age-matched healthy controls (mean age 64.9 ± 12.9 years) were recruited in this case-control study. Genotyping was performed by polymerase chain reaction restriction fragment length polymorphism (PCR-RLFP) technique. For T-786C polymorphism, we found that CC genotype was associated to CaP risk [odds ratio (OR) = 3.62, 95% confidence interval (CI): 1.89-7.74, P = 0.002), high grade tumor (OR = 2.46, 95% CI:1.78-4.72; P = 0.006), and advanced disease (OR = 4.67, 95% CI: 2.64-8.61; P = 0.002). Neither the CaP risk nor clinical features of CaP were associated with the G894T polymorphism. It was found that, compared with 4a/b bb genotype, the 4a/b "a" variant genotypes were associated with an increased risk of CaP in an allele dose dependent manner (OR = 2.12, 95% CI: 1.68-3.44; P = 0.031 for 4a/b ab genotype, and OR = 4.32, 95% CI: 2.21-6.08; P = 0.001 for 4a/b aa genotype). In addition, genotypes with the "a" allele of the eNOS 4a/b polymorphism predispose the patients to high grade (OR = 4.76, 95% CI: 2.74-8.62; P = 0.001) and advanced CaP (OR = 5.28, 95% CI: 3.64-8.72; P = 0.001). Furthermore, the T-Asp-b and C-Asp-b haplotypes were associated with a significantly decreased risk of CaP (OR = 0.44, 95% CI: 0.33-0.77; P = 0.004, and OR = 0.39, 95% CI: 0.26-0.61; P = 0.001, respectively). We found significant differences in genotype distribution and allelic frequencies between CaP patients and controls for the T-786C, and 4a/b eNOS polymorphisms.

Biochemistry of nitric oxide

Nitric oxide (NO) a free radical having both cytoprotective as well as tumor promoting agent is formed from l-arginine by converting it to l-citrulline via nitric oxide synthase enzymes. The reaction product of nitric oxide with superoxide generates potent oxidizing agent, peroxynitrite which is the main mediator of tissue and cellular injury. Peroxynitrite is reactive towards many biomolecules which includes amino acids, nucleic acid bases; metal containing compounds, etc. NO metabolites may play a key role in mediating many of the genotoxic/carcinogenic effects as DNA damage, protein or lipid modification, etc. The basic reactions of nitric oxide can be divided as direct effect of the radical where it alone plays a role in either damaging or protecting the cell milieu and an indirect effect in which the byproducts of nitric oxide formed by convergence of two independent radical generating pathways play the role in biological reactions which mainly involve oxidative and nitrosative stress. Nitric oxide is also capable of directly interacting with mitochondria through inhibition of respiration or by permeability transition. Reaction of nitric oxide with metal ions include its direct interaction with the metals or with oxo complexes thereby reducing them to lower valent state. Excessive production of nitric oxide can be studied by inhibiting the synthetic pathway of nitric oxide using both selective or specific nitric oxide synthase inhibitor or non-selective nitric oxide synthase inhibitor with respect to isoforms of nitric oxide.

Genetic polymorphisms in the endothelial nitric oxide synthase gene correlate with overall survival in advanced non-small-cell lung cancer patients treated with platinum-based doublet chemotherapy

Background

Nitric oxide (NO) is a free radical that is involved in carcinogenesis. Endothelial NO, synthesized from L-arginine by endothelial NO synthase (eNOS), inhibits apoptosis and promotes angiogenesis, tumor cell proliferation and metastasis. The aim of this study was to evaluate the influence of polymorphisms in the eNOS gene on prognosis of patients with advanced stage non-small-cell lung cancer (NSCLC).

Methods

Unresectable, chemotherapy naïve stage III or IV NSCLC patients who were treated with standard platinum-containing doublet regimens were analyzed. All individuals were genotyped for the single-nucleotide polymorphism G894T in exon 7 of the eNOS gene and for a variable number of tandem repeats (VNTR) polymorphism in intron 4 that results in a rare smaller allele (a) and a common larger allele (b), to investigate the association between these polymorphisms and clinical outcomes. The primary endpoint was correlation with overall survival.

Results

From October 2004 to December 2007, 108 patients (male/female, 66/42; Stage IIIA/IIIB/IV, 6/30/72) aged 29-77 years (median 63) with good performance status were consecutively enrolled in this study. Using Kaplan-Meier estimates, we showed that 5-year overall survival was significantly increased in patients carrying the VNTR a-allele compared with VNTR b/b patients (P = 0.015). In multivariate Cox proportional hazard analysis, the VNTR polymorphism was an independent prognostic factor for survival.

Conclusions

The results support the role of the VNTR polymorphism in intron 4 as a marker for survival in patients with advanced stage NSCLC who are candidates for standard chemotherapy.

An intron 4 VNTR polymorphism of the endothelial nitric oxide synthase gene is associated with early-onset colorectal cancer

Endothelial-derived nitric oxide, which is produced by endothelial nitric oxide synthase (eNOS), may play an important role in colorectal carcinogenesis. However, the putative contribution of common eNOS genetic polymorphisms to colorectal cancer risk remains unknown. We genotyped 3 polymorphisms of eNOS (T-786C, G894T, and intron4b/a) in 727 colorectal adenocarcinoma cases and 736 age- and sex-matched healthy controls in Taiwan. Genotypes of the T-786C and G894T polymorphisms were determined by fluorescence polarization assays and the 27-bp variable number of tandem repeat (VNTR) polymorphism in intron 4 (intron4b/a) was analyzed by PCR. Logistic regression was used to calculate odds ratios (ORs) and 95% confidence intervals (CIs). Among younger participants (< or =60 yrs), the intron4a variant genotype was associated with a significantly increased risk of colorectal cancer, compared with the intron4bb genotype (OR = 1.60, 95% CI = 1.04-2.46). In addition, those young individuals bearing a greater number of high-risk genotypes (OR > 1, i.e., CT+TT for T-786C, ba+aa for intron4b/a, and GG for G894T) of eNOS had a higher colorectal cancer risk (p(trend) = 0.039). Compared with younger individuals without any putative high-risk genotypes, those with 3 high-risk genotypes had a significantly greater cancer risk (OR = 1.89, 95% CI = 1.04-3.43). Our results suggest that the eNOS intron4b/a polymorphism may contribute to early-onset colorectal cancer risk in the Taiwanese population.

Role of nitric oxide in the development of distant metastasis from squamous cell carcinoma

BACKGROUND

Metastasis, the dissemination of malignant cells to distant sites, remains one of the most significant factors responsible for death from cancer. Recent studies have shown some improvement in the rate of distant metastasis (DM) with the addition of chemotherapy to surgery and radiation for treatment of head and neck squamous cell carcinoma (HNSCC). However, diagnosis and treatment at an early stage ultimately leads to a better prognosis. The prediction of which patients will develop metastasis and the selection of treatment most effective at preventing and treating metastasis remains dependent on an incomplete understanding of prognostic factors and the biological and molecular basis for metastatic development. This study was undertaken using an in vivo model to investigate the possible role of nitric oxide (NO) in the development of metastasis from HNSCC. The findings will result in better understanding of the metastatic process for HNSCC, with the potential to develop and implement therapies that could prevent and treat metastasis in patients.

OBJECTIVES/HYPOTHESIS

1) To analyze whether in vivo videomicroscopy (IVVM) is useful for the study of DM from squamous cell carcinoma of the head and neck; 2) with use of IVVM, investigate the effect of the biological mediators NO and interleukin (IL)-1 on the adhesion of circulating human HNSCC cells in the hepatic microcirculation.

STUDY DESIGN

Prospective study using an animal model.

METHODS

Phase 1: athymic nude rats and mice were used for IVVM experiments. The cremaster muscle and liver, used as arterial and venous flow models, were tested to determine whether IVVM was useful for the study of human HNSCC interactions with the microcirculation. A human squamous cell carcinoma cell line (FaDu) labeled with the intracytoplasmic fluorescent marker BCECF-am. was used for all experiments. Videomicroscopic images of FaDu cells in the microcirculation were analyzed for cell adhesion, morphology, deformation, circulation, location of adhesion within the microcirculation, and alteration of microvascular circulation. Phase 2: the effect of IL-1, NO, and NO inhibitors on HNSCC cell adhesion in the hepatic microcirculation of nude mice was analyzed by IVVM. This was followed by histologic determination of the ratio of FaDu cells present for liver area analyzed. Nude mice were treated with 1) IL-1; 2) L-arginine (an NO substrate); or 3) L-N-monomethyl-L-arginine (an NO synthase inhibitor) alone or in combination. These data were analyzed statistically to determine the effect on cell adhesion in the liver.

RESULTS

IVVM provided a method for the study of circulating HNSCC with the microcirculation in both the cremaster and liver models. FaDu cells were arrested at the inflow side of the circulation, with maintenance of cell integrity. L-arginine and IL-1 both increased FaDu cell arrest in the liver above baseline (P = .00008 and P = .03), and the combination of these agents potentiated the effect (P = .000009).

CONCLUSIONS

IVVM allows direct assessment of circulating HNSCC with the microcirculation and is a powerful model for the study of DM. NO and IL-1 play a role in increasing the arrest of HNSCC in the liver and are important in the generation of DM in patients with HNSCC.

Cancer relapse under chemotherapy: why TLR2/4 receptor agonists can help

Liver or lung metastases usually relapse under chemotherapy. Such life-threatening condition urgently needs new, systemic anticancer compounds, with original and efficient mechanisms of action. In B16 melanoma mice treated with cyclophosphamide, D'Agostini et al. [D'Agostini, C., Pica, F., Febbraro, G., Grelli, S., Chiavaroli, C., Garaci, E., 2005. Antitumour effect of OM-174 and Cyclophosphamide on murine B16 melanoma in different experimental conditions. Int. Immunopharmacol. 5, 1205-1212.] recently found that OM-174, a chemically defined Toll-like receptor(TLR)2/4 agonist, reduces tumor progression and prolongs survival. Here we review 149 articles concerning molecular mechanisms of TLR2/4 agonists, alone or in combination with chemotherapy. It appears that TLR2/4 agonists induce a well controlled tumor necrosis factor-alpha (TNF-alpha) secretion, at plasma levels known to permeabilize neoangiogenic tumor vessels to the passage of cytotoxic drugs. Moreover, TLR2/4 agonists induce inducible nitric oxide synthase (iNOS) expression, and nitric oxide is able to induce apoptosis of chemotherapy-resistant tumor cell clones. Finally, TLR2/4-stimulation activates dendritic cell traffic and its associated tumor-specific, cytotoxic T-cell responses. Therefore, parenteral TLR2/4 agonists seem promising molecules to prolong survival in cancer patients who relapse under chemotherapy.

Promoter polymorphism (-786t>C) in the endothelial nitric oxide synthase gene is associated with risk of sporadic breast cancer in non-Hispanic white women age younger than 55 years

BACKGROUND

Nitric oxide (NO) is constitutively synthesized in the endothelium by endothelial nitric oxide synthase (eNOS) and acts as a pleiotropic regulator involved in carcinogenesis. Most breast cancers develop from mammary epithelial cells; therefore, NO may play a role in their development. It was hypothesized that eNOS polymorphisms are associated with risk of breast cancer.

METHODS

In the current hospital-based case-control study of 421 non-Hispanic white women with sporadic breast cancer and 423 frequency-matched control subjects, we genotyped 3 polymorphisms of eNOS (i.e., -786T>C, the 27-base pair [bp] variable number of tandem repeats [VNTR] in intron 4, and 894G>T [Glu298Asp]) and assessed their associations with risk of breast cancer.

RESULTS

It was found that, compared with -786TT, the -786C variant genotypes were associated with a significantly increased risk of breast cancer in an allele dose-dependent manner (adjusted odds ratio [OR], 1.33 [95% confidence interval (95% CI)], 0.99-1.77 for -786TC; and OR, 1.79 [95% CI, 1.11-2.87] for -786CC; P(trend) = .007), but 27-bp VNTR and 894G>T genotypes were not. Stratification analysis demonstrated that the risk associated with -786C variant genotypes (-786TC/CC) was more pronounced in smokers and in those 50 years or older (OR, 1.82 [95% CI, 1.19-2.80] and OR, 2.08 [95% CI, 1.25-3.45], respectively), and in the estrogen and progesterone receptor-negative cases (OR, 1.70 [95% CI, 1.10-2.62] and OR, 1.57 [95% CI, 1.07-2.32], respectively). Furthermore, the C4G haplotype derived from the observed genotypes was also associated with a significantly increased risk of breast cancer (OR, 2.16; 95% CI, 1.07-4.36).

CONCLUSIONS

The results suggest that eNOS polymorphisms (especially -786T>C) may play a role in the development of sporadic breast cancer.

Current views concerning the influences of murine hepatic endothelial adhesive and cytotoxic properties on interactions between metastatic tumor cells and the liver

Substantial recent experimental evidence has demonstrated the existence of reciprocal interactions between the microvascular bed of a specific organ and intravascular metastatic tumor cells through expression of adhesion molecules and nitric oxide release, resulting in a significant impact upon metastatic outcomes.

This review summarizes the current findings of adhesive and cytotoxic endothelial-tumor cell interactions in the liver, the inducibility, zonal distribution and sinusoidal structural influences on the hepatic endothelial regulatory functions, and the effects of these functions on the formation of liver cancer metastases. New insights into the traditional cancer metastatic cascade are also discussed.

Inducible nitric oxide synthase (iNOS) in tumor biology: the two sides of the same coin

Inducible nitric oxide synthase (iNOS) is one of three key enzymes generating nitric oxide (NO) from the amino acid l-arginine. iNOS-derived NO plays an important role in numerous physiological (e.g. blood pressure regulation, wound repair and host defence mechanisms) and pathophysiological (inflammation, infection, neoplastic diseases, liver cirrhosis, diabetes) conditions. iNOS is the synthase isoform most commonly associated with malignant disease. Nevertheless, the role of iNOS during tumor development is highly complex, and incompletely understood. Both promoting and deterring actions have been described, presumably depending upon the local concentration of iNOS within the tumor microenvironment. In particular, pivotal effects such as malingnant transformation, angiogenesis, and metastasis are modulated by iNOS. On the other hand, NO derived from macrophages has a potentially cytotoxic/cytostatic effect upon tumor cells. Hence, therapeutical interference with iNOS activity is of considerable interest, especially in tumors where metastatic activity, host defence mechanisms and the level of differentiation seem to be correlated to iNOS expression. This review will aim to summarize the dual actions of iNOS as simultaneous tumor promoter and suppressor.

Immunohistochemical evaluation of endothelial nitric oxide synthase expression in primary breast cancer

To evaluate the clinical potential of endothelial nitric oxide synthase (e-NOS) in human breast cancer, we performed immunohistochemical (IHC) staining of paraffin-embedded primary breast cancer tissue of 163 patients for e-NOS using a monoclonal antibody. A correlation was found between e-NOS expression and both the classic prognostic factors and survival rates. Under half the patients were premenopausal (38.5%), 61.5% being postmenopausal. The median tumour size was 2 cm; in 41.7% of the patients there was involvement of the axillary lymph nodes. Most (84.1%) of the tumours were hormone receptor positive. e-NOS staining was positive in 62%, most of the positive tumours having weak (32.5%) or medium (21.5%) staining for e-NOS. The median follow-up time was 42 months, during which 46 (28%) patients had a local recurrence or metastatic disease. A positive correlation of e-NOS with the hormone receptor status was found (P=0.031). However, no impact on survival rates was observed.

Evaluation of the Interaction Between TGF β and Nitric Oxide in the Mechanisms of Progression of Colon Carcinoma

It is recognised that stromal cells determine cancer progression. We have previously shown that active TGFbeta produced by rat colon carcinoma cells modulated NO production in rat endothelial cells. To elucidate the role of TGFbeta and NO in the mechanisms of interaction of colon carcinoma cells with stromal cells and in cancer progression, we transfected REGb cells, a regressive colon carcinoma clone secreting latent TGFbeta, with a cDNA encoding for a constitutively-secreted active TGFbeta. Out of 20 injected rats only one tumour progressed, which was resected and sub-cultured (ReBeta cells). ReBeta cells secreted high levels of active TGFbeta. The adhesive properties of REGb and Rebeta cells to endothelial cells were similar, showing that the secretion of active TGFbeta is not involved in tumour cell adhesion to endothelial cells. ReBeta, but not REGb, cell culture supernatants inhibited cytokine-dependent NO secretion by endothelial cells, but inhibition of NO production was similar in co-cultures of REGb or ReBeta cells with endothelial cells. Therefore, secretion of active TGFbeta regulated endothelial NO synthase activity when tumour cells were distant from, but not in direct contact with, endothelial cells. However, only ReBeta cells inhibited cytokine-dependent secretion of NO in coculture with macrophages, indicating that the active-TGFbeta-NO axis confers an advantage for tumour cells in their interaction with macrophages rather than endothelial cells in cancer progression.

The role of early expression of inducible nitric oxide synthase in human breast cancer

Nitric oxide synthases are expressed in breast cancer. To elucidate the clinical role of the inducible NOS (i-NOS) in human breast cancer, 161 primary breast cancer tissues were stained immunohistochemically. Staining patterns for i-NOS were correlated with classical prognostic factors such as lymph node status, age, hormonal receptor status, tumour size and tumour differentiation. With classical prognostic factors such as lymph node status, age, hormonal receptor status, tumour size and tumour differentiation. Patients survival was also analysed. Sixty-one percent of the tumours stained positively for i-NOS. Detection of i-NOS was positively correlated with increasing tumour size and decreasing tumour differentiation (P=0.018 and P=0.039, respectively). However, in the 50 year age group, i-NOS staining also correlated with lymph node status. Patients with i-NOS-positive breast carcinomas had a significantly worse overall survival rate versus those with negative stains (5-year survival rate 84.8% versus 67.1%; P=0.049; log-rank test). To date, this is the largest analysis of i-NOS expression in breast cancer patients and the only study to assess survival.

High expression of endothelial cell nitric oxide synthase in peritumoral microvessels predicts increased disease-free survival in colorectal cancer

We have previously shown that a high frequency of microvessels expressing endothelial cell nitric oxide synthase (ecNOS) in the area surrounding the primary tumor (peritumoral ecNOS-expressing microvessel density: PEMVD) is a favorable prognostic indicator in breast cancer. Studies of a retrospective material of 186 colorectal tumors (Duke's stage B) now show that PEMVD is a significant and independent prognostic indicator for disease-free survival also in these patients. These data reinforce our hypothesis that a high level of expression of ecNOS in microvessels in the tumor-adjacent area protects against tumor metastasis.

Nitric oxide in health and disease of the respiratory system

During the past decade a plethora of studies have unravelled the multiple roles of nitric oxide (NO) in airway physiology and pathophysiology. In the respiratory tract, NO is produced by a wide variety of cell types and is generated via oxidation of l-arginine that is catalyzed by the enzyme NO synthase (NOS). NOS exists in three distinct isoforms: neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS). NO derived from the constitutive isoforms of NOS (nNOS and eNOS) and other NO-adduct molecules (nitrosothiols) have been shown to be modulators of bronchomotor tone. On the other hand, NO derived from iNOS seems to be a proinflammatory mediator with immunomodulatory effects. The concentration of this molecule in exhaled air is abnormal in activated states of different inflammatory airway diseases, and its monitoring is potentially a major advance in the management of, e.g., asthma. Finally, the production of NO under oxidative stress conditions secondarily generates strong oxidizing agents (reactive nitrogen species) that may modulate the development of chronic inflammatory airway diseases and/or amplify the inflammatory response. The fundamental mechanisms driving the altered NO bioactivity under pathological conditions still need to be fully clarified, because their regulation provides a novel target in the prevention and treatment of chronic inflammatory diseases of the airways.

Vascular invasion in human breast cancer is correlated to T-->786C polymorphism of NOS3 gene

BACKGROUND

Nitric oxide (NO) is a free radical known to be a major regulator of vascular tonus, to inhibit cell proliferation, induce apoptosis, and be a mediator of macrophage cytostatic and cytotoxic effects. Recently, NO synthesis has been reported to be elevated in different cancers and is expected to promote metastasis by maintaining a vasodilator tone in blood vessels in and around the tumour. Two different common genetic polymorphisms were found on endothelial NO synthase (NOS3) gene: Glu298Asp on exon 7 and T-->786C in the promoter region.

PURPOSE

To evaluate the impact of the NOS3 polymorphisms on vascular invasion and metastasis in breast cancer patients.

DESIGN

Two NOS3 gene polymorphisms (Glu298Asp and T-->786C) were genotyped in 71 patients operated for breast cancer and followed for 6-30 months (median 21). A control population of 91 age and sex matched tumour-free subjects was also genotyped for the same polymorphisms.

RESULTS

The distribution of both polymorphisms was not different between cases and controls. In patients without vascular invasion, T allele frequency was significantly lower than in patients with vascular invasion (p=0.033). At the end of the follow-up, T allele frequency was found to be less frequent in the metastasis free group than normal population (0.51 vs 0.64; p=0.047).

CONCLUSION

Our results suggest that T allele reduction at the NOS3 promoter region may reduce vascular invasion in breast cancer and consequently reduce metastatic spread and be a favorable prognostic factor. These results need further validation in larger studies.

Lovastatin inhibits Rho-regulated expression of E-selectin by TNFalpha and attenuates tumor cell adhesion

E-selectin mediated cell-cell adhesion plays an important role in inflammatory processes and extravasation of tumor cells. Tumor necrosis factor-alpha (TNF-alpha) induces E-selectin gene and protein expression in primary human endothelial cells (HUVEC) and in an endothelial cell line (EA.hy-926). As shown by ELISA and FACS analyses, HMG-CoA reductase inhibitors (e.g., lovastatin) impair the TNF-alpha stimulated increase in E-selectin protein expression. Similar results were obtained for E-selectin mRNA expression and promoter activity, indicating that the effect of lovastatin is based on inhibition of gene expression. The effective inhibitory concentration of lovastatin was in a physiologically relevant range (IC50<0.1 microM). Lovastatin-mediated block of TNF-alpha induced E-selectin expression is due to inhibition of protein geranylgeranylation rather than farnesylation. Down-regulation of Rho signaling by coexpression of dominant-negative Rho mutants (i.e RhoA, RhoB and Rac) impaired TNF-alpha driven E-selectin gene expression, indicating Rho signaling to be essential for transcriptional activation of the E-selectin gene. Inhibition of E-selectin expression by lovastatin gives rise to a significant reduction in TNF-alpha stimulated adhesion of colon carcinoma cells to HUVEC. Furthermore, low concentration of lovastatin (i.e., < or =1 microM) attenuated TNF-alpha induced tumor cell invasion in vitro. The data support the view that statins might be clinically useful in protection against E-selectin mediated metastasis.

Different effects of constitutive nitric oxide synthase and heme oxygenase on pulmonary or liver metastasis of colon cancer in mice

It has recently been reported that not only endogenous nitric oxide (NO) but also carbon monoxide (CO) produced by heme oxygenase (HO) have many physiological functions. The objective of the present study was to determine whether endogenous NO or CO is involved in the experimental pulmonary or liver metastasis of colon cancer in mice. Intravenous or intrasplenic injection of colon 26 cells from a mouse colon adenocarcinoma cell line resulted in multiple pulmonary or liver metastases. NG-nitro-L-arginine methyl ester (L-NAME), a competitive inhibitor of NO synthase (NOS), or zinc deuteroporphyrin 2, 4-bis glycol (ZnDPBG), a competitive inhibitor of HO, was administered to the mice only on the day of tumor inoculation. We assessed the number of tumor cells 24 h later and the outcome of metastases of the target organ. In the pulmonary metastasis model, L-NAME increased both the number of tumor cells 24 h later and outcome of metastases 18 days later, but did not have a significant effect on liver metastasis. On the other hand, metastasis to the liver, but not that to the lung, increased following administration of ZnDPBG. These results suggest that the activities of NOS and HO could influence experimental metastasis in an organ-specific manner.

Effect of sildenafil citrate on an orthotopic prostate cancer growth and metastasis model

PURPOSE

We characterized the effects of sildenafil citrate on the growth and metastasis of human prostate cancer cells in nude mice.

MATERIALS AND METHODS

The androgen independent human prostate cancer cell line PC-3 was inoculated into the prostate of nude mice to produce orthotopic primary prostate cancers and metastases. Sildenafil citrate gavage was started on day 31 after tumor cell inoculation and given every other day 15 times (30 days). The 7 mice in the low dose group received 25 mg/kg body weight sildenafil citrate per gavage, while the 7 in the high dose group received 50 mg/kg body weight sildenafil citrate and the 9 in the control group received water. Autopsy was performed on day 75 to evaluate primary tumor growth and metastasis. Plasma cyclic guanosine monophosphate concentrations were measured after the single dose of 50 mg/kg sildenafil citrate in the mice.

RESULTS

Plasma cyclic guanosine monophosphate concentration increased 4-fold 1 hour after sildenafil citrate administration. The plasma concentration decreased rapidly and returned to normal after 8 hours. There was no significant difference in tumor weight between any of the 3 groups. The number of metastatic lymph nodes correlated significantly with primary tumor weight (p = 0.03) with a correlation coefficient of 0.454 but there was no significant correlation between the number of involved lymph nodes and sildenafil administration. Distant metastases were not significantly promoted by sildenafil administration.

CONCLUSIONS

Incontinuous oral administration of sildenafil citrate did not promote primary tumor growth and metastasis in an orthotopic prostate cancer model.

Arrest of B16 melanoma cells in the mouse pulmonary microcirculation induces endothelial nitric oxide synthase-dependent nitric oxide release that is cytotoxic to the tumor cells

Metastatic cancer cells seed the lung via blood vessels. Because endothelial cells generate nitric oxide (NO) in response to shear stress, we postulated that the arrest of cancer cells in the pulmonary microcirculation causes the release of NO in the lung. After intravenous injection of B16F1 melanoma cells, pulmonary NO increased sevenfold throughout 20 minutes and approached basal levels by 4 hours. NO induction was blocked by N(G)-nitro-L-arginine methyl ester (L-NAME) and was not observed in endothelial nitric oxide synthase (eNOS)-deficient mice. NO production, visualized ex vivo with the fluorescent NO probe diaminofluorescein diacetate, increased rapidly at the site of tumor cell arrest, and continued to increase throughout 20 minutes. Arrested tumor cells underwent apoptosis with apoptotic counts more than threefold over baseline at 8 and 48 hours. Neither the NO signals nor increased apoptosis were seen in eNOS knockout mice or mice pretreated with L-NAME. At 48 hours, 83% of the arrested cells had cleared from the lungs of wild-type mice but only approximately 55% of the cells cleared from eNOS-deficient or L-NAME pretreated mice. eNOS knockout and L-NAME-treated mice had twofold to fivefold more metastases than wild-type mice, measured by the number of surface nodules or by histomorphometry. We conclude that tumor cell arrest in the pulmonary microcirculation induces eNOS-dependent NO release by the endothelium adjacent to the arrested tumor cells and that NO is one factor that causes tumor cell apoptosis, clearance from the lung, and inhibition of metastasis.

Regulation of B16F1 melanoma cell metastasis by inducible functions of the hepatic microvasculature

We have previously shown that circulating intravascular cells generally arrest by mechanical restriction in the hepatic sinusoids, causing rapid release of nitric oxide (NO) which is cytotoxic to these cells and inhibits their growth into metastatic tumours. Here, we present evidence that these NO-dependent cytotoxic mechanisms are susceptible to upregulation by lipopolysaccharide (LPS). Five x 10(5) fluorescently labelled melanoma cells were injected into the mesenteric vein of C57BL/6 mice to effect their localisation in the hepatic microvasculature. Test mice were then given 1 mg/kg LPS intraperitoneally (i.p.) to activate the microvascular cells. By electron paramagnetic resonance (EPR) spectroscopy, the expression of NO in the liver was significantly increased by 8 h in the LPS-treated mice. The non-selective NO synthase inhibitor L-NAME inhibited the induction of NO by LPS, while its inactive enantiomer D-NAME had no significant effect. Using immunohistochemistry (IHC), iNOS-positive microvascular cells were detected in the terminal portal venule (TPV) region of the liver 8 h after LPS stimulation. LPS treatment also increased the retention of melanoma cells in the liver between 8 and 24 h, especially in the TPV region. Eight hours after cell injection, local expression of VCAM-1 and ICAM-1 was detected by double-label immunohistochemistry at the sites of tumour cell arrest. Expression of these adhesion molecules was enhanced in mice treated with LPS. Using flow cytometry, 98% of the B16F1 melanoma cells expressed VLA-4, the counter receptor of VCAM-1, and approximately 1.5% expressed LFA-1, the counter receptor of ICAM-1. LPS did not significantly alter the expression of either counter receptor on melanoma cells in vitro or in vivo. By DNA end-labelling, the rates of melanoma cell apoptosis were significantly increased from 8 to 24 h in the TPV region (but not in the sinusoids) of LPS-treated mice. Fourteen days after tumour cell injection, the LPS-treated mice had a significantly smaller hepatic metastatic tumour burden than the control mice. These data suggest that LPS can inhibit the metastasis of melanoma cells in the liver by inducing the expression of NO and adhesion molecules by the hepatic endothelium. The induction of iNOS and the inducible cytotoxic effect of LPS appear to be primarily located within the TPV region of the liver acinus.

Interactions between cancer cells and the endothelium in metastasis

The haematogenous phase of cancer metastasis facilitates the transport of metastatic cells within the blood and incorporates a sequence of interactions between circulating intravascular cancer cells and the endothelium of blood vessels at the sites of tumour cell arrest. Initial interactions involve mechanical contact and transient adhesion, mediated by endothelial selectins and their ligands on the neoplastic cells. This contact initiates a sequence of activation pathways that involves cytokines, growth factors, bioactive lipids, and reactive oxygen species produced by either the cancer cell or the endothelium. These molecules elicit expression of integrin adhesion molecules in cancer cells and the endothelium, matrix metalloproteinases, and chemotactic factors that promote the attachment of tumour cells to the vessel wall and/or transvascular penetration. Induction of endothelial free radicals can be cytotoxic to cancer cells. Collectively, the sum of these interactions constitutes an interdependent relationship, the outcome of which determines the fate of the metastatic process.

Mu3 opiate receptor expression in lung and lung carcinoma: ligand binding and coupling to nitric oxide release

The mu3 opiate receptor subtype is expressed in human surgical specimens of both normal lung and non-small-cell lung carcinoma. Nitric oxide (NO) release is mediated through the mu3 receptor, and in lung carcinoma, morphine-stimulated NO release is significantly higher and prolonged than in normal lung. Using reverse transcriptase-polymerase chain reaction (RT-PCR) and Southern blot analysis we show that specific mu opioid receptor transcripts are present in lung carcinoma and other cells with the mu3 profile. Our findings identify a unique role for the mu3 opiate receptor in opiate-mediated NO release and suggest that endogenous opiates, through their release of NO, may play a role in cancer progression.

Targeting nitric oxide to cancer cells: cytotoxicity studies of glyco-S-nitrosothiols

Glyco-S-nitrosothiols, fructose-2-SNAP and glucose-2-SNAP, were synthesized and found to be much more cytotoxic than SNAP in killing DU-145 human prostate cancer cells in vitro.

Increase in experimental pulmonary metastasis in mice by L-arginine under inhibition of nitric oxide production by NG-nitro-L-arginine methyl ester

As we have previously reported, intraperitoneal injections of NG-nitro-L-arginine methyl ester [L-NAME; a competitive inhibitor of nitric oxide (NO) synthase] before and after the injection of B16 melanoma cells through a tail vein increased experimental pulmonary metastasis, while simultaneous injections of L-arginine (a substrate of NO synthase) at a 20-fold higher dose synergistically increased pulmonary metastasis. Our present study was intended to elucidate the mechanisms by which L-NAME alone or together with L-arginine increases metastasis. Injections of L-NAME decreased the serum concentration of nitrite plus nitrate (metabolites of NO) by about 50%, which was not reversed by simultaneous injections of L-arginine. Injections of L-NAME also decreased the diameter of arterioles and venules by 20-30%, while simultaneous injections of L-arginine did not show any significant effect. When collagen- or ADP-induced platelet aggregation was examined using platelet-rich plasma, injections of L-NAME showed little effects on platelet aggregation, while simultaneous injections of L-arginine rather suppressed platelet aggregation. B16 melanoma cells produced NO in culture, and L-NAME (0.2 mM) decreased NO production without effects on viability. Our results suggest that the increased experimental pulmonary metastasis induced by L-NAME can be ascribed partly to the contraction of arterioles and venules, which is induced by the inhibition of endogenous NO production by L-NAME, and that the synergistic effect of L-arginine on metastasis is related to the inhibition of endogenous NO production through unknown mechanisms.

Nitric oxide induced by tumor cells activates tumor cell adhesion to endothelial cells and permeability of the endothelium in vitro

Human fibrosarcoma HT1080 cell surface phenotype analysis revealed the expression of "cluster of differentiation 15" (CD15) antigen and to a lesser extent, of "very late antigen-4" (VLA-4). Expression of "endothelial-leukocyte adhesion molecule-1" (ELAM-1) was negligible on resting human umbilical vascular endothelial cells (HUVECs), but its expression could be induced by HT1080 conditioned medium. HT1080 cell adhesion to HUVECs was partially dependent on CD15/ELAM-1 adhesion molecules. HT1080 cell adhesion to HUVECs induced the enhancement of nitric oxide (NO) production from HUVECs. Exogenous NO and NO from HUVECs enhanced ELAM-1 expression on HUVECs, HT1080 cell adhesion to HUVECs, permeability of the HUVEC monolayer, and HT1080 cell invasion through the HUVEC monolayer. These enhancements were not induced by NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME). These results suggest that NO expression induced by tumor cells via the CD15/ELAM-1 adhesion system may contribute to enhancement of tumor cell adhesion to endothelial cells and hyperpermeability of the endothelium, facilitating tumor cell invasion.

Melanoma cell adhesion to injured arterioles: mechanisms of stabilized tethering

An isolated perfused vessel model was used to examine the mechanisms underlying the adhesive interactions between circulating tumor cells and subendothelial matrix in denuded arterioles. Arterioles ranging from 70 to 100 microm in diameter were isolated from rat mesentery, transferred to an isolated vessel chamber, cannulated on both ends with glass micropipettes, and perfused with media containing 10(6) hamster melanoma (RPMI 1856) cells/ml. In a second group of arterioles, the endothelium was denuded by running 2 ml of air through the vessel lumen. Since the tumor cells did not adhere to the vessel wall when perfused at physiologically relevant shear rates, perfusate flow was stopped and the tumor cells were allowed to settle onto the vessel wall for 20 min. After counting the number of tumor cells that settled onto the arteriolar wall, perfusate flow was re-initiated and unattached cells were washed away. The number of cells remaining adherent were counted and the percentage of adherent cells (relative to the total number of cells that settled on to the vessel wall during the period of no-flow) were calculated and compared among different groups. We observed that tumor cells are much more adhesive to denuded arterioles than to intact arterioles. To determine the mechanisms responsible for the adhesive interactions that become established and stabilized during the period of flow reduction, denuded arterioles were treated with fibronectin antiserum or Arg-Gly-Asp (RGD) peptides. Both treatments significantly reduced tumor cell adhesion to denuded arterioles. In subsequent studies, melanoma cells were treated with a transglutaminase inhibitor, monodansylcadaverine (MDC), which reduced the ability of adherent tumor cells to withstand the anti-adhesive effects of a subsequent increase in perfusate flow rate after the period of no-flow. Our data suggest that tumor cells adhere to fibronectin in the subendothelial matrix in denuded arterioles by an RGD-dependent mechanism. Moreover, our observations are consistent with the concept that a transglutaminase-catalysed reaction acts to stabilize the adhesive interactions between subendothelial matrix components and melanoma cells during the period of flow stasis such that the cells are able to withstand subsequent substantial increases in wall shear rate and remain adherent.

Quantification of diazeniumdiolate mutagenicity in four different in vitro assays

Diazeniumdiolates are under investigation as possible prodrugs of the multifaceted bioregulatory agent nitric oxide. This study was undertaken to assess further the mutagenic potential of two diazeniumdiolates, DEA/NO (Et2N[N(O)NO]Na) and SPER/NO ([H2N(CH2)3NH(CH2)4N[N(O)NO-](CH2)3 NH3+]), which generate NO spontaneously with half-lives at 37 degrees C and pH 7.4 of 2 and 39 min, respectively. The genotoxic potential of these compounds was investigated with the Ames bacterial reverse mutation assay, two mammalian cell gene mutation assays (CHO/HGPRT and L5178Y TK+/-), and an assay for sister chromatid exchange (SCE) using Chinese hamster ovary (CHO) cells. Both diazeniumdiolates had previously been shown to be mutagenic in the Ames Salmonella plate assay. In the experiments reported here, Salmonella typhimurium strain TA1535 was exposed to the compounds in a liquid incubation assay for either 15 min or 48 h without an S-9 fraction. With the 15-min exposure, DEA/NO was mutagenic at concentrations of 0.625 mM (3.5 x control) and greater, while SPER/NO was mutagenic at 0.5 mM (2.7 x control) and above. In the CHO/HGPRT assay, DEA/NO was weakly mutagenic only at the highest concentration used, 20 mM, inducing a mutant frequency per survivor that was 2.5 x control, while SPER/NO was mutagenic at 0.5 mM with a mutant frequency of 2.5 x control. When the CHO cells were given 10 repetitive 20 mM DEA/NO exposures (3 min each), HGPRT mutant frequency was 4.1 x control. In the L5178Y mouse lymphoma cell TK+/- assay, DEA/NO doubled the mutation rate at 1.82 mM, while SPER/NO's mutation frequency was more than twice that of control at 0.63 mM. DEA/NO was positive in the SCE assay without metabolic activation, yielding significant SCE at 1.25, 2.5, and 5 mM that was 1.8, 2.2, and 2.6 times control, respectively. SPER/NO increased the SCE by 1.2, 1.4, and 1.3 times at 1.5, 2.0, and 2.5 mM. The results suggest that the two diazeniumdiolates, although mutagenic in the bacteria, are much weaker mutagens in mammalian cells.