The discovery that mammalian cells have the ability to synthesize the free radical nitric oxide (NO) has stimulated an extraordinary impetus for scientific research in all the fields of biology and medicine. Since its early description as an endothelial-derived relaxing factor, NO has emerged as a fundamental signaling device regulating virtually every critical cellular function, as well as a potent mediator of cellular damage in a wide range of conditions. Recent evidence indicates that most of the cytotoxicity attributed to NO is rather due to peroxynitrite, produced from the diffusion-controlled reaction between NO and another free radical, the superoxide anion. Peroxynitrite interacts with lipids, DNA, and proteins via direct oxidative reactions or via indirect, radical-mediated mechanisms. These reactions trigger cellular responses ranging from subtle modulations of cell signaling to overwhelming oxidative injury, committing cells to necrosis or apoptosis. In vivo, peroxynitrite generation represents a crucial pathogenic mechanism in conditions such as stroke, myocardial infarction, chronic heart failure, diabetes, circulatory shock, chronic inflammatory diseases, cancer, and neurodegenerative disorders. Hence, novel pharmacological strategies aimed at removing peroxynitrite might represent powerful therapeutic tools in the future. Evidence supporting these novel roles of NO and peroxynitrite is presented in detail in this review.

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Nitric Oxide and Peroxynitrite in Health and Disease

Evolution has resorted to nitric oxide (NO), a tiny, reactive radical gas, to mediate both servoregulatory and cytotoxic functions. This article reviews how different forms of nitric oxide synthase help confer specificity and diversity on the effects of this remarkable signaling molecule.

https://faseb.onlinelibrary.wiley.com/doi/pdf/10.1096/fasebj.6.12.1381691

Nitric oxide as a secretory product of mammalian cells.

▪ Abstract At the interface between the innate and adaptive immune systems lies the high-output isoform of nitric oxide synthase (NOS2 or iNOS). This remarkable molecular machine requires at least 17 binding reactions to assemble a functional dimer. Sustained catalysis results from the ability of NOS2 to attach calmodulin without dependence on elevated Ca2+. Expression of NOS2 in macrophages is controlled by cytokines and microbial products, primarily by transcriptional induction. NOS2 has been documented in macrophages from human, horse, cow, goat, sheep, rat, mouse, and chicken. Human NOS2 is most readily observed in monocytes or macrophages from patients with infectious or inflammatory diseases. Sustained production of NO endows macrophages with cytostatic or cytotoxic activity against viruses, bacteria, fungi, protozoa, helminths, and tumor cells. The antimicrobial and cytotoxic actions of NO are enhanced by other macrophage products such as acid, glutathione, cysteine, hydrogen peroxide, or superoxid...

Nitric oxide and macrophage function

A rapid, simple spectrophotometric method for simultaneous detection of nitrate and nitrite.

The production of natural antibiotic peptides has emerged as an important mechanism of innate immunity in plants and animals. Defensins are diverse members of a large family of antimicrobial peptides, contributing to the antimicrobial action of granulocytes, mucosal host defence in the small intestine and epithelial host defence in the skin and elsewhere. This review, inspired by a spate of recent studies of defensins in human diseases and animal models, focuses on the biological function of defensins.

Defensins: antimicrobial peptides of innate immunity.

Rat ameboid microglia are able to lyse rat oligodendrocytes in vitro. The lysis is inhibited by transforming growth factor-beta, antagonists of nitric oxide (NO) production, as well as antibodies to TNF-alpha, intercellular adhesion molecule-1 (ICAM-1), and leukocyte functional Ag-1. Ameboid microglial cells spontaneously produce detectable levels of the NO metabolite nitrite (NO2-). Stimuli such as PMA, LPS, and/or IFN-gamma induce micromolar concentrations of NO2- within 24 h. TNF-alpha increases IFN gamma but not LPS-induced NO2- production. Incubation with target oligodendrocytes also increases NO2- production in a contact-dependent manner. NO2- production is inhibited by NO synthase antagonists, transforming growth factor-beta, and anti TNF-alpha. Neither antileukocyte functional Ag-1 nor anti-ICAM-1 inhibit NO2- production by microglia in the presence or absence of oligodendrocytes. Indeed, anti-ICAM-1 treatment increases NO2- production. There is a correlation between ameboid microglial cell killing of oligodendrocytes and NO2- production suggesting NO may be a mechanism of death of the oligodendrocyte and possibly play a role in lesion formation in multiple sclerosis.

Microglial cell cytotoxicity of oligodendrocytes is mediated through nitric oxide.

Amniotic fluid (AF) is a complex substance essential to fetal well-being. This article reviews recent discoveries and the current understanding of the origin and circulation of AF and its nutritive, protective, and diagnostic functions. Future directions for AF research are also discussed.

Amniotic fluid: not just fetal urine anymore.

In view of the recent findings that NO reacts with superoxide anion to generate hydroxyl radical, the present study was conducted to ascertain the role of endogenous NO in mediating myocardial reoxygenation injury in the hypoxic piglet on cardiopulmonary bypass. Anesthetized piglets were made hypoxic (PaO2 = 20-30 mmHg) for up to 120 min, followed by reoxygenation on cardiopulmonary bypass for 30 min. Reoxygenation caused rapidly developing myocardial injury characterized by decreased contractility (expressed as end-systolic elastance) and increased lipid peroxidation (measured as conjugated dienes). Systemic venous and coronary sinus blood content of NO decreased significantly during hypoxia and increased substantially above prehypoxic levels during reoxygenation on cardiopulmonary bypass. Administration of either the antioxidants mercaptopropionyl glycine and catalase or the NO synthase inhibitor, NG-nitro-L-arginine methyl ester, to the extracorporeal circuit afforded similar and nearly complete protection against myocardial reoxygenation injury. The protective effects of NG-nitro-L-arginine methyl ester were nullified by adding an excess of L-arginine to the pump circuit, suggesting that the L-arginine-NO pathway is involved in myocardial reoxygenation injury.

Role of L-arginine-nitric oxide pathway in myocardial reoxygenation injury

When cultured in vitro, peritoneal macrophages, obtained from mice previously inoculated with bacillus Calmette-Guerin, release nitric oxide, which is cytostatic and/or cytolytic for tumor cells. However, it is not known whether nitric oxide has antitumor effects in vivo. Here we demonstrate that nitric oxide is an important mediator of host resistance to syngeneic and xenogeneic ovarian tumor grafts in C3HeB/FeJ mice. A murine ovarian teratocarcinoma cell line, utilized to study the mechanism of bacillus Calmette-Guerin-induced host resistance to a syngeneic ovarian tumor, proliferated when transplanted intraperitoneally. Marked tumoricidal activity was observed, however, when these murine ovarian teratocarcinoma cells were transplanted 8 days after intraperitoneal bacillus Calmette-Guerin inoculation. In studies related to xenogeneic ovarian tumor grafts, tumoricidal activity was observed after intraperitoneal transplantation of a human epithelial ovarian cancer cell line, NIH:OVCAR-3. This cell line proliferates only in athymic nude (immunologically incompetent) mice. In both sets of experiments, tumoricidal activity was reduced by inhibition of nitric oxide synthesis. These results demonstrate the tumoricidal action of nitric oxide in vivo.

Michael P. Sherman

Papers

Microglial cell cytotoxicity of oligodendrocytes is mediated through nitric oxide.

Amniotic fluid: not just fetal urine anymore.

Role of L-arginine-nitric oxide pathway in myocardial reoxygenation injury

Nitric oxide is an important mediator for tumoricidal activity in vivo

Pyrrolidine Dithiocarbamate Inhibits Induction of Nitric Oxide Synthase Activity in Rat Alveolar Macrophages