A simplified method for the determination of nitric oxide in biological solutions

Neuroprotective potential of lignan-rich fraction of Piper cubeba L. by improving antioxidant capacity in the rat's brain

Piper cubeba contains various types of lignans. These compounds have been found to have potential pharmacological activities, one being a neuroprotector through an antioxidant mechanism, especially in the brain. This study examined the antioxidant activity of the lignan-rich fraction of P. cubeba (LF) in rat brains. The rats were given LF (200 and 400 mg/kg), Vitamin C (200 mg/kg), and a carrier as the control group for one-week p.o. The following day, rat brains were collected for antioxidant tests, including examining lipid peroxide inhibition, superoxide dismutase and catalase activity, and determination of nitric oxide (NO) concentration. The phytochemical compounds were analyzed with thin-layer chromatography (TLC), ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS), and gas chromatography-mass spectrometry (GC-MS). Test results show that the LF of both doses of 200 and 400 mg/kg could significantly increase antioxidant activity in the brain by inhibiting lipid peroxidation. LF could also increase catalase, despite the decrease in superoxide dismutase activity. Reduction in NO only occurred in the LF-200 group, while LF-400 showed insignificant results compared to the control group. In conclusion, LF showed potential as an antioxidant in the brain and could be beneficial for treating neurological diseases.

Influence of nitric oxide donors and peroxynitrite on the contractile effect and concentration of norepinephrine

Nitric oxide (NO) and peroxynitrite (ONOO) are said to destroy norepinephrine (NE). We studied the role of NE decomposition by NO donors and ONOO as they affect the contractile activity of NE in rat denuded thoracic aorta. First, we determined the relaxing effect of NO donors (SNAP, PROLI/NO, Sodium nitrite, SIN-1) and ONOO after precontraction by NE (1 microM). SNAP and SIN-1 (EC(50) 50-110 nM) were more active than PROLI/NO, Sodium nitrite or ONOO (EC(50) 19-30 microM). The relaxing effect of NO donors and ONOO were decreased by ODQ (10 microM), a guanylate cyclase inhibitor. Second, we compared the contractile activity of NE before and after preincubation with NO donors or ONOO in presence of ODQ. NE (1 microM) was incubated with NO donors or ONOO at the concentrations of 0.1 mM in both Krebs solution or phosphate buffer (pH 7.4; 0.1 M) for 10 minutes at 37 degrees C. NE evoked the aorta contraction in the same concentrations before and after preincubation with NO donors. In contrast, ONOO decreased effect of NE, EC(50) was measured at 4.3+/-0.3 nM and 13.4+/-1.6 nM, before and after preincubation of NE with ONOO respectively. Third, we measured the NE concentration using the HPLC method. We revealed that the concentration of NE after preincubation with NO donors was unaltered. However HPLC measurement revealed that NE concentration after preincubation with ONOO was reduced 2-3-fold. Therefore, under these experimental conditions ONOO, but not NO donors, was capable of destroying NE.

Downregulation of nitric oxide in the brain of mice during their hypoxic preconditioning

An animal model of hypoxic preconditioning was produced in mice by repeated exposure to autohypoxic condition. The animals' tolerance times to hypoxia were 1.7, 1.8, 2.1, and 2.3 times longer in runs 2, 3, 4, and 5, respectively, than that in run 1, and their oxygen consumption and heart and respiration rates were progressively and significantly slowed down during the repetitive exposure to hypoxia. L-Arginine concentration, nitric oxide (NO) synthase-positive cells, NO synthase activity, and NO content in the whole brain and the subregions telencephalon, diencephalon, and brain stem were significantly increased during the first exposure and were, instead of continuing to increase, significantly decreased in run 4 after the second and third exposure. Tolerance times under the hypoxic condition were significantly shortened and prolonged when preadministration of L-arginine and its analog, respectively, was made. These results indicate that NO in the brain is downregulated under condition of hypoxic preconditioning and negatively involved in increased tolerance to hypoxia.

Effect of cyclooxygenase-2 inhibitor (celecoxib) on the infarcted heart in situ

Several attempts have been made to replace aspirin with compounds without gastric toxicity; a cyclooxygenase-2 (COX-2) inhibitor, celecoxib, and a nitric oxide-aspirin, NCX-4016, have been developed for this purpose. This paper compares effects of celecoxib, NCX-4016 and aspirin on production of prostacyclin (PGI2) and thromboxane A2 (TXA2) and activation of the inducible form of nitric oxide synthase (iNOS) in infarcted heart in situ. Aspirin was most effective in reducing myocardial PGI2 synthesis and formation of TXA2. Myocardial effects of celecoxib resemble those of NCX-4016, although the two compounds have different modes of action.

The pharmacology of a new nitric oxide donor: B-NOD

We describe here a new compound, B-NOD, which, in vitro and in situ, releases nitric oxide (NO). Its activity in situ persists for more than 7 h, it does not cause a fall in blood pressure or an increase in heart rate and can be orally administered. It increases cyclic guanosine monophosphate (cGMP) and prevents platelet aggregation. In vitro, its release of NO is augmented by the presence of living cells (blood platelets). B-NOD may be useful in a number of clinical conditions in which prolonged release of NO without hemodynamic effects are desirable. A combination of aspirin with B-NOD could be formulated in which the individual concentrations of aspirin and B-NOD may be useful in the long-term treatment of coronary artery disease and in clinical situations in which long-term release of NO may be beneficial.

Biomonitoring of n-nitroso compounds, nitrite and nitrate in the urine of Egyptian bladder cancer patients with or without Schistosoma haematobium infection

The excretion of nitrate, nitrite, apparent total N-nitroso compounds and volatile nitrosamines was measured in 24 hr urine from 61 Egyptians, divided into 4 groups: controls, Schistosoma haematobium-infected patients and bladder cancer patients with and without a history of schistosomal infection. Urinary nitrate in S. haematobium-infected patients was significantly higher than in the other 3 groups. Nitrite was below the detection limit of the method (</=0.015 microgram/mg creatinine) in all but one of the control samples. S. haematobium infection significantly increased urinary nitrite to 0.9 +/- 1.16 microgram/mg creatinine (mean +/- SD, p = 0. 001). In both bladder cancer groups, nitrite was about 20 times that in S. haematobium-infected patients without bladder cancer. Excretion of apparent total N-nitroso compounds paralleled that of nitrite. Overall, a good correlation was observed between these 2 variables (r = 0.71, p = 0.0001). N-nitrosodimethylamine was present in all the samples analyzed. S. haematobium infection significantly increased urinary N-nitrosodimethylamine level compared with that of controls (4.02 +/- 1.61 and 2.04 +/- 2.97 ng/mg creatinine, respectively, p = 0.01). Among cancer patients, N-nitrosodimethylamine was higher than in controls only in those with schistosomal infection. The presence of N-nitroso compounds and N-nitrosodimethylamine in the urine of S. haematobium-infected patients both before and after the development of cancer, and the observation that these compounds also occur in bladder cancer patients with no history of schistosomal infection, suggest that these compounds might have a role not only in the initiation of the carcinogenic process, but also in its progression.

Production of prostanoids and nitric oxide by infarcted heart in situ and the effect of aspirin

The production of prostacyclin (PGI2) and thromboxane A2 (TXA2) in infarcted and noninfarcted portions of the rabbit heart was studied prior to and following administration of acetylsalicylic acid (aspirin). Aspirin was administered intravenously (iv) as water-soluble Aspisol, d-lysinmono (acetylsalicylate) (Bayer, Leverkusen, Germany) into an ear vein. A branch of the left circumflex coronary artery was ligated. The animals were divided into three groups. The first group received 150 mg/kg/day of aspirin (75 mg/kg of aspirin every 12 h, n = 10). The first administration of aspirin was 1 h after ligation of the coronary artery and the last injection was 1 h before euthanasia. The second group received 5 mg/kg/day of aspirin (every 24 h, n = 10). A separate group of rabbits not receiving aspirin served as controls (n = 12). Two days following onset of ischemia, inducible form of nitric oxide synthase (iNOS) was measured in heart muscle and the oxidation products of nitric oxide (nitrite, NO-2 plus nitrate, NO-3: their sum referred to as NOx) were determined in arterial and coronary venous blood. Concentrations of both PGI2 and TXA2 were elevated in the infarcted portions of the heart compared to the noninfarcted regions. Formation of prostanoids was accompanied by increased activation of iNOS. Both doses of aspirin diminished the concentrations of PGI2 and TXA2 in infarcted heart muscle; in contrast, small doses of aspirin failed to influence myocardial iNOS activity. Apparently small doses of aspirin changed the relationship of iNOS to cyclooxygenase (COX). Coronary arterial-venous difference of NOx and myocardial iNOS activity showed parallel increases. Diminution of prostacyclin by aspirin can damage gastric mucosa and interfere with vasodilatation. Since NO counters these deficiencies, a combination of aspirin with a nitric oxide donor may be advantageous.

Effect of acetylsalicylic acid on nitric oxide production in infarcted heart in situ

The effect of Acetylsalicylic Acid (ASA, Aspirin) on the myocardial production of the inducible form of nitric oxide synthase (iNOS) and the oxidation products of nitric oxide (nitrite, NO-2 and nitrate, NO-3: NOx) were studied in the rabbit heart two days after ligation of a branch of the left circumflex coronary artery. ASA was administered intravenously as AspisolR, DL-Lysinmono(acetylsalicylate) which is soluble in water. Animals received a total dose of 250, 375, or 500 mg/kg of ASA in five divided doses intravenously. Significant inhibition of iNOS was noted in the infarcted portion of the myocardium at 375 and 500 mg/kg of ASA. The reduction in myocardial nitric oxide (NO) production was paralleled by a diminution in coronary arterial-venous difference of NOx, demonstrating that ASA inhibition extended also to the oxidation products of NO. ASA is an inhibitor of cyclooxygenase (COX). The inhibition of iNOS by ASA demonstrates the close relationship between COX and iNOS activity in the heart in situ. Whether activity of the infarcted heart is influenced by the diminution in the production of NO by ASA is not known.

Production of oxidative products of nitric oxide in infarcted human heart

OBJECTIVES

We sought to assess whether oxidation products of nitric oxide (NO), nitrite (NO2-) and nitrate (NO3-), referred to as NOx, are released by the heart of patients after acute myocardial infarction (AMI) and whether NOx can be determined in peripheral blood of these patients.

BACKGROUND

Previously we reported that in experimental myocardial infarction (rabbits) NOx is released mainly by inflammatory cells (macrophages) in the myocardium 3 days after onset of ischemia. NOx is formed in heart muscle from NO; NO originates through the activity of the inducible form of nitric oxide synthase (iNOS).

METHODS

Eight patients with acute anterior MI and an equal number of controls were studied. Coronary venous blood was obtained by coronary sinus catheterization; NOx concentrations in coronary sinus, in arterial and peripheral venous plasma were measured. Left ventricular end-diastolic pressure was determined. Measurements were carried out 24, 48 and 72 h after onset of symptoms. The type and location of coronary arterial lesions were determined by coronary angiography. Plasma NO3- was reduced to NO2- by nitrate reductase before determination of NO2- concentration by chemiluminescence.

RESULTS

The results provided evidence that in patients with acute anterior MI, the myocardial production of nitrite and nitrate (NOx) was increased, as well as the coronary arterial-venous difference. Increased NOx production by the infarcted heart accounted for the increase of NOx concentration in arterial and the peripheral venous plasma. The peak elevation of NOx occurred on days 2 and 3 after onset of the symptoms, suggesting that NOx production was at least in part the result of production of NO by inflammatory cells (macrophages) in the heart.

CONCLUSIONS

The appearance of oxidative products of NO (NO2- and NO3-) in peripheral blood of patients with acute MI is the result of their increased release from infarcted heart during the inflammatory phase of myocardial ischemia. Further studies are needed to define the clinical value of these observations.

Chemiluminescence detection of nitric oxide production from rat cerebral cortical endothelial cells in culture

Cultured brain microvascular endothelial cells have been used to study blood-brain barrier properties in vitro. Among several endothelial derived factors the gaseous free radical nitric oxide (NO) has been shown to regulate both vascular tone and blood-brain barrier permeability. Due to its short half-life and high reactivity with many other molecules, effects of NO have preferentially been investigated using NO synthase inhibitors, NO donors or, more recently, in NO synthase knock-out animals. In the present study we describe a rapid, sensitive and reliable protocol for chemiluminescence detection of NO2-, the stable oxydation product of NO, from the supernatant of rat cortical endothelial cells in culture. After suppression of inducible NOS activity brain endothelial cells showed low basal NO levels. After stimulation with calcium ionophore NO levels increased and were attenuated again by NOS blockade. NO release was also elicited by bradykinin or acetylcholine, albeit to a lesser extent. This protocol might prove useful to investigate calcium-dependent NO formation in cerebral endothelial cells and blood-brain barrier models in vitro. In principle, the same protocol can be applied to virtually any cell type in culture.

The production of nitric oxide in endothelial cells by amphiphiles

Lysophosphatidylcholine, an endogenous detergent is an endothelium-dependent smooth muscle relaxant, which acts through the release of nitric oxide. It is known to activate a number of membrane-bound enzymes. Because of the relationship between detergent action, relaxation of endothelium-intact rabbit aortic strips and the release of nitric oxide, we considered the possibility that other amphiphiles also produce nitric oxide from endothelial cells. We therefore investigated the effect of digitonin on relaxation of precontracted rabbit aortic strips and the release of nitric oxide from freshly harvested bovine endothelial cells as determined by chemiluminescence. We found that both digitonin and LPC release nitric oxide and that this process is inhibited by the NO synthase inhibitor N omega-Nitro-L-Arginine Methyl Ester (L-NNAME).