Formation of hemoprotein-alkylperoxide complexes demonstrated by ESR and optical absorption spectroscopy

Saccharated colloidal iron enhances lipopolysaccharide-induced nitric oxide production in vivo

We investigated the effects of iron on the production of nitric oxide (NO), inducible NO synthase (iNOS), and plasma cytokines induced by lipopolysaccharide (LPS) in vivo. Male Wistar rats were preloaded with a single intravenous injection of saccharated colloidal iron (Fesin, 70 mg iron/kg body weight) or normal saline as a control, and then given an intraperitoneal injection of LPS (5.0 mg/kg body weight). Rats, preloaded with iron, had evidence of both iron deposition and strong iNOS induction in liver Kupffer cells upon injection of LPS; phagocytic cells in the spleen and lung had similar findings. LPS-induced NO production in iron-preloaded rats was significantly higher than control rats as accessed by NO-hemoglobin levels measured by ESR (electron spin resonance) and NOx (nitrate plus nitrite) levels. Western blot analysis showed that iron preloading significantly enhanced LPS-induced iNOS induction in the liver, but not in the spleen or lung. LPS-induced plasma levels of IL-6, IL-1beta, and TNF-alpha were also significantly higher in iron-preloaded rats as shown by ELISA, but IFN-gamma levels were unchanged. We conclude that colloidal-iron phagocytosed by liver Kupffer cells enhanced LPS-induced NO production in vivo, iNOS induction in the liver, and release of IL-6, IL-1beta, and TNF-alpha.

Models of the low-spin iron(III) hydroperoxide intermediate of heme oxygenase: magnetic resonance evidence for thermodynamic stabilization of the d(xy) electronic state at ambient temperatures

The (13)C pulsed ENDOR and NMR study of [meso-(13)C-TPPFe(OCH(3))(OO(t)Bu)](-) performed in this work shows that although the unpaired electron in low-spin ferrihemes containing a ROO(-) ligand resides in a d(pi) orbital at 8 K, the d(xy) electron configuration is favored at physiological temperatures. The variable temperature NMR spectra indicate a dynamic situation in which a heme with a d(pi) electron configuration and planar porphyrinate ring is in equilibrium with a d(xy) electron configuration that has a ruffled porphyrin ring. Because of the similarity in the EPR spectra of the hydroperoxide complexes of heme oxygenase, cytochrome P450, and the model heme complex reported herein, it is possible that these two electron configurations and ring conformations may also exist in equilibrium in the enzymatic systems. The ruffled porphyrinate ring would aid the attack of the terminal oxygen of the hydroperoxide intermediate of heme oxygenase (HO) on the meso-carbon, and the large spin density at the meso-carbons of a d(xy) electron configuration heme suggests the possibility of a radical mechanism for HO. The dynamic equilibrium between the ruffled (d(xy)) and planar (d(pi)) conformers observed in the model complexes also suggests that a flexible heme binding cavity may be an important structural motif for heme oxygenase activity.

Ex vivo demonstration of nitric oxide in the rat brain: effects of intrastriatal endothelin-1 injection

Nitric oxide (NO) is a novel transmitter with multiple functions in endothelium and neuronal tissue. In particular, it has been implicated in the pathogenesis of neurodegenerative diseases. The aim of the present study was to demonstrate the ex vivo detection of NO in basal conditions and after ET-1 intrastriatal injection by means of electron paramagnetic resonance (EPR) spectroscopy using locally injected hemoglobin (Hb) as a NO trapping agent. The extent of neostriatal damage after Hb and ET-1 injections was assessed by means of immunocytochemistry with a monoclonal antibody against dopamine and cAMP-phosphoprotein M(r) 32 (DARPP-32), which is considered a marker of striatal intrinsic neurons. In the absence of local Hb injection, no signal related to endogenous NO was detected in the neostriatum, suggesting that endogenous NO trapping agents are not sufficiently concentrated to allow NO detection with the present technique. Instead, 1 h after Hb injection, a clear nitrosyl-Hb signal can be detected in neostriatal homogenates. ET-1, a powerful vasoconstrictor agent, was used to cause neuronal loss in the neostriatum. No change in nitrosyl-Hb signal was observed in neostriatal 1 h after ET-1 injection, whereas an almost 3-fold increase in the signal intensity was present 24 h after ET-1 injection. The analysis of neostriatal damage showed that Hb injection did not cause either significant damage of striatal tissue or potentiation of ET-1-induced lesions. In conclusion, the present technique allows ex vivo detection of NO in the brain. The delayed increase in NO observed after ET-1 injection indicates that this molecule may participate in the development of slowly progressive neuronal damage occurring at late post-ischemic times.

ESR demonstration of nitric oxide production from nitroglycerin and sodium nitrite in the blood of rats

Electron spin resonance (ESR) spectra of iron-metal complexes formed by the reaction between nitric oxide (NO) and hemoglobin (Hb), referred to as nitrosylhemoglobin (HB-NO), were observed in rat blood treated in vitro and in vivo with nitroglycerin (GTN) at 77K. The same types of spectra were also detected in rats treated with sodium nitrite (NaNO2). Two types of Hb-NO, which were identified by ESR parameters of g values and superhyperfine coupling constants (shfcc), were the 6- and 5-coordinated complexes. These two types of Hb-NO were generated in a dose-dependent manner in the blood after intraperitoneal administration of 1.5-6 mg of GTN. At the higher dose of GTN (6 mg), the 6-coordinated complex was the major species generated initially, but within 10 min, the 5-coordinated complex increased time-dependently. Quantitative analysis of Hb-NO revealed that when GTN 0.3 mg and 0.6 mg was administered sublingually in rats, the concentration of Hb-NO observed in rat blood was 30% higher than the estimated concentration of GTN. The methemoglobin and peroxide complex of hemoglobin were observed in the blood incubated with GTN at 37 degrees C. These results suggest that the function of GTN was related to oxidative stress with the generation of Hb-NO. Therefore, monitoring of Hb-NO levels may be useful as an indicator of the function of various vasodilators.

Coordination structure and chemical reactivity of hemoprotein-butyl peroxide complex

ESR and optical spectra ascribed to be the hemoprotein-butylperoxide complex were detected for the frozen aqueous solution containing whale met-Mb and t- or n-butylhydroperoxide at pH 10. The observed ESR and optical parameters of the complex were characteristic to those of six coordinate ferric low-spin complexes, having the butylperoxide anion at the axial position of heme. pH dependent ESR measurements demonstrated the formation of the complex in the biological pH regions (7.0). Time dependent ESR and optical measurements indicated that the complex may be one of the intermediate species in the processes of heme degradation reaction induced by butylperoxide.