Continuous monitoring of in vivo nitric oxide formation using EPR analysis in biliary flow

Detection of Nitric Oxide by Electron Paramagnetic Resonance Spectroscopy: Spin-Trapping with Iron-Dithiocarbamates

Electron paramagnetic resonance (EPR) spectroscopy is the ideal methodology to identify radicals (detection and characterization of molecular structure) and to study their kinetics, in both simple and complex biological systems. The very low concentration and short life-time of NO and of many other radicals do not favor its direct detection and spin-traps are needed to produce a new and persistent radical that can be subsequently detected by EPR spectroscopy.In this chapter, we present the basic concepts of EPR spectroscopy and of some spin-trapping methodologies to study NO. The "strengths and weaknesses" of iron-dithiocarbamates utilization, the NO traps of choice for the authors, are thoroughly discussed and a detailed description of the method to quantify the NO formation by molybdoenzymes is provided.

Spinnokinetic Analyses of Blood Disposition and Biliary Excretion of Nitric Oxide (NO)-Fe(II)-N-(Dithiocarboxy)sarcosine Complex in Rats: BCM-ESR and BEM-ESR Studies

Nitric oxide (NO) is well known to have a wide variety of biological and physiological functions in animals. On the basis of the fact that Fe(II)-dithiocarbamates react with NO, a Fe(II)-N-(dithiocarboxy)sarcosine complex (Fe(II)-DTCS) was proposed as a trapping agent for endogenous NO. However, quantitative pharmacokinetic investigation for NO-Fe(II)-dithiocarbamate complexes in experimental animals has been quite limited. This paper describes the results on the quantitative pharmacokinetic features of a NO-Fe(II)-N-DTCS in both the blood and bile of rats following intravenous (i.v.) administration of the complex. For this purpose, we applied two in vivo methods, i.e. (1) in vivo blood circulation monitoring-electron spin resonance (BCM-ESR) which previously developed, and (2) in vivo biliary excretion monitoring-electron spin resonance (BEM-ESR). We monitored real-time ESR signals due to nitrosyl-iron species in the circulating blood and bile flow. The ESR signal due to NO-Fe(II)-DTCS was stable in biological systems such as the fresh blood and bile. In in vivo BCM- and BEM-ESR, the pharmacokinetic parameters were calculated on the basis of the two-compartment and hepatobiliary transport models. The studies also revealed that the compound is widely distributed in the peripheral organs and partially excreted into the bile. We named a kinetic method to follow spin concentrations as spinnokinetics and this method will be useful for detecting and quantifying the endogenously generated NO in Fe(II)-DTCS administered animals.

Quinoid radio-toxin (QRT) induced metabolic changes in mice: an ex vivo and in vivo EPR investigation

Radio-toxins are toxic metabolites produced by ionizing irradiation and have toxic effects similar to those caused by direct irradiation. We have investigated the effect of a quinoid radio-toxin (QRT) obtained from gamma-irradiated potato tuber on various organs in mice using ex vivo and in vivo EPR spectroscopy. Results indicate a decrease in the activity of ribonucleotide reductase enzyme in spleen of mice treated with 0.2mg QRT. A dose of 2mg QRT was fatal to mice within 45-60 min of treatment. Nitrosyl hemoglobin complexes alpha-(Fe(2+)-NO)alpha-(Fe(2+))beta-(Fe(2+))(2) were detected from spleen, blood, liver, kidney, heart, and lung tissue samples of mice treated with lethal doses of QRT. A significant decrease of pO(2) in liver and brain was observed after administration of QRT at the lethal dose. The time of the appearance of the nitrosyl hemoglobin complex and its intensity varied with the dose of QRT and the type of tissue. These results indicate that the effect of the QRT is more prominent in spleen and to a lesser extent in liver and blood. The QRT action at the lethal doses resulted in an increased hypoxia over time with disruption of compensatory adaptive response. The results indicate similar outcome of QRT as observed with gamma-irradiation.

Nitrones as therapeutics in age-related diseases

Age-related diseases deprive individuals of a higher quality of life and therefore therapeutics for their treatment provide significant potential. An overview of the observations of nitrones as potential therapeutics in several age-related diseases is presented. Treatment of acute ischemic stroke is one condition where a nitrone (NXY-059) is in late phase 3 clinical trials now. Also presented is a summary of the most recent work we have accomplished on the anticancer activity of the nitrones in a hepatocellular carcinoma. The mechanistic basis of action of these compounds in several animal models is not yet understood at the molecular levels; however, it does appear clear that their anti-inflammatory properties are central to their action, which is based on their ability to down-regulate exacerbated signal transduction processes.

Spin trapping of nitric oxide with the iron-dithiocarbamate complex: chemistry and biology

This brief review describes chemical and biological aspects concerning spin trapping of nitric oxide (NO) with the iron-dithiocarbamate (Fe-DTC) complex as a spin trap. Knowledge on basic properties of the Fe-DTC complex would help in understanding the applicability and limitation of the Fe-DTC-based NO spin-trapping method when it is employed in viable biological systems.

The role of thiol and nitrosothiol compounds in the nitric oxide-forming reactions of the iron-N-methyl-d-glucamine dithiocarbamate complex

The object of the present study is to investigate whether the physiologically dominant thiol compounds such as GSH and cysteine or their nitrosothiol compounds affect the formation of the iron- N -methyl-D-glucamine dithiocarbamate [(MGD)(2)Fe(2+)]-nitric oxide complex. The present study provided experimental evidence that physiological concentrations of GSH (approx. 5 mM) and L-cysteine (approx. 0.5 mM) accelerated the formation of the (MGD)(2)Fe(2+)-NO complex from nitrite by two and three times respectively. The rate constants for the reduction of (MGD)(3)Fe(3+) to (MGD)(2)Fe(2+) by GSH and cysteine were calculated as 1.3 and 2.0x10(2) M(-1).s(-1) respectively. Furthermore, depletion of GSH was demonstrated in PC12 cells, and thiol compounds enhanced the formation of reactive oxygen species by the (MGD)(2)Fe(2+) complex by accelerating its redox turnover. The main effect of the physiological concentration of thiols was the reduction of (MGD)(3)Fe(3+). S -nitrosoglutathione spontaneously reacted with (MGD)(2)Fe(2+) to produce the (MGD)(2)Fe(2+)-NO complex with a 1:2 stoichiometry. In fact, (MGD)(2)Fe(2+) was as good an indicator of nitrosothiols as it was of NO itself. The present study elucidates the difficulties of utilizing the (MGD)(2)Fe(2+) complex for the quantification of NO in biological samples, especially in vivo.

Interleukin-10 overexpression mediates phenyl-N-tert-butyl nitrone protection from endotoxemia

The free radical trapping compound phenyl N-tert-butylnitrone (PBN) provides potent protection against lethal endotoxemia in rodents, but the mechanism of this protection is not well understood. The objective of this study was to show that PBN administration in lipopolysaccharide- (LPS) induced endotoxemia promotes enhanced production of endogenous interleukin 10 (IL-10), and the expressed IL-10 is a causal factor in the protection from endotoxemia. We show the amplified expression of IL-10 in liver and plasma in PBN- (150 mg/kg) plus LPS- (4 mg/kg) treated rats using ribonuclease protection assay (RPA) and ELISA. In situ hybridization was utilized to visualize the overexpression of the IL-10 gene, and ELISA was used to determine plasma IL-10 and TNFalpha levels. Plasma IL-10 showed a 3-fold increase in PBN/LPS- treated rats compared to those treated with LPS alone, and in contrast, TNFalpha level decreased by more than 90%. However, the administration of PBN alone induced no IL-10 production. Immunoneutralization of IL-10 through anti-IL-10 antibody administration to PBN/LPS-treated rats abrogated PBN's suppression of systemic nitric oxide (NO) formation, a surrogate marker for the severity of endotoxemia, indicating that IL-10 is a causal factor for the protection. In these experiments, systemic NO level was quantified using an in vivo electron paramagnetic resonance (EPR) NO-trapping technique. Gel-shift and immunohistochemical analyses indicated that the transcription factor NF-kappaB was deactivated after PBN treatment, suggesting that NF-kappaB deactivation is closely involved in IL-10 overexpression.

Dose- and time-dependence of radiation-induced nitric oxide formation in mice as quantified with electron paramagnetic resonance

In vivo nitric oxide (NO) formation was quantified in mice after exposure to high-dose whole-body X-ray irradiation. NO produced and accumulated in the livers of irradiated mice was determined using NO trapping method with iron-dithiocarbamate complex combined with electron paramagnetic resonance (EPR) spectroscopy. When mice were irradiated with 50 Gy X-ray, NO formation peaked in approximately 3 h after the irradiation was terminated. Dose-dependence study indicated that NO formation measured 5 h after irradiation was leveled off at the dose higher than 50 Gy. Administration of NO synthase inhibitor, N(G)-monomethyl L-arginine (L-NMMA) shortly after irradiation completely abolished the NO signal, indicating that radiation-induced NO is produced through L-arginine-dependent NO synthase pathways. These results suggest that irradiation of X-ray initiates inflammation processes, resulting in delayed NO synthase expression and NO formation.

Redox properties of iron-dithiocarbamates and their nitrosyl derivatives: implications for their use as traps of nitric oxide in biological systems

While the Fe(2+)-dithiocarbamate complexes have been commonly used as NO traps to estimate NO production in biological systems, these complexes can undergo complex redox chemistry. Characterization of this redox chemistry is of critical importance for the use of this method as a quantitative assay of NO generation. We observe that the commonly used Fe(2+) complexes of N-methyl-D-glucamine dithiocarbamate (MGD) or diethyldithiocarbamate (DETC) are rapidly oxidized under aerobic conditions to form Fe(3+) complexes. Following exposure to NO, diamagnetic NO-Fe(3+) complexes are formed as demonstrated by the optical, electron paramagnetic resonance and gamma-resonance spectroscopy, chemiluminescence and electrochemical methods. Under anaerobic conditions the aqueous NO-Fe(3+)-MGD and lipid soluble NO-Fe(2+)-DETC complexes gradually self transform by reductive nitrosylation into paramagnetic NO-Fe(2+)-MGD complexes with yield of up to 50% and the balance is converted to Fe(3+)-MGD and nitrite. In dimethylsulfoxide this process is greatly accelerated. More efficient transformation of NO-Fe(3+)-MGD into NO-Fe(2+)-MGD (60-90% levels) was observed after addition of reducing equivalents such as ascorbate, hydroquinone or cysteine or with addition of excess Fe(2+)-MGD. With isotope labeling of the NO-Fe(3+)-MGD with (57)Fe, it was shown that these complexes donate NO to Fe(2+)-MGD. NO-Fe(3+)-MGD complexes were also formed by reversible oxidation of NO-Fe(2+)-MGD in air. The stability of NO-Fe(3+)-MGD and NO-Fe(2+)-MGD complexes increased with increasing the ratio of MGD to Fe. Thus, the iron-dithiocarbamate complexes and their NO derivatives exhibit complex redox chemistry that should be considered in their application for detection of NO in biological systems.

Nitric oxide-forming reaction between the iron-N-methyl-D-glucamine dithiocarbamate complex and nitrite

The objective of this study was to elucidate the origin of the nitric oxide-forming reactions from nitrite in the presence of the iron-N-methyl-D-glucamine dithiocarbamate complex ((MGD)(2)Fe(2+)). The (MGD)(2)Fe(2+) complex is commonly used in electron paramagnetic resonance (EPR) spectroscopic detection of NO both in vivo and in vitro. Although it is widely believed that only NO can react with (MGD)(2)Fe(2+) complex to form the (MGD)(2)Fe(2+).NO complex, a recent article reported that the (MGD)(2)Fe(2+) complex can react not only with NO, but also with nitrite to produce the characteristic triplet EPR signal of (MGD)(2)Fe(2+).NO (Hiramoto, K., Tomiyama, S., and Kikugawa, K. (1997) Free Radical Res. 27, 505-509). However, no detailed reaction mechanisms were given. Alternatively, nitrite is considered to be a spontaneous NO donor, especially at acidic pH values (Samouilov, A., Kuppusamy, P., and Zweier, J. L. (1998) Arch Biochem. Biophys. 357, 1-7). However, its production of nitric oxide at physiological pH is unclear. In this report, we demonstrate that the (MGD)(2)Fe(2+) complex and nitrite reacted to form NO as follows: 1) (MGD)(2)Fe(2).NO complex was produced at pH 7.4; 2) concomitantly, the (MGD)(3)Fe(3+) complex, which is the oxidized form of (MGD)(2)Fe(2+), was formed; 3) the rate of formation of the (MGD)(2)Fe(2+).NO complex was a function of the concentration of [Fe(2+)](2), [MGD], [H(+)] and [nitrite].

Pharmacologic properties of phenyl N-tert-butylnitrone

Phenyl N-tert-butylnitrone (PBN) is the parent of a family of nitrones used as spin-trapping agents to trap free radicals. PBN's pharmacological effects in animal models are extensive, ranging from protection against death after endotoxin shock, protection from ischemia-reperfusion injury, to increasing the life span of mice. Recent additions to the list include protection from bacterial meningitis, thalidomide-induced teratogenicity, drug-induced diabetogenesis, and choline-deficient hepatocarcinogenesis. Because PBN reacts with oxygen radicals to produce less reactive species, it has been suggested that this is the basis of its pharmacological effects. However, there has been no hard evidence for this notation. Nevertheless, many investigators have used the presence of PBN's pharmacologic effect as evidence for free radical involvement in their models. Mechanistic studies on the PBN's antisepsis action revealed that PBN inhibits expression of various pro-inflammatory genes, suggesting that the protective action involves more than a straightforward free radical-scavenging mechanism. Previous and recent developments in the investigations on the pharmacologic properties of PBN are described in this review.