INVESTIGATIONS ON THE LIGHT-EMITTING SPECIES IN THE REACTION OF METMYOGLOBIN AND METHEMOGLOBIN WITH HYDROGEN PEROXIDE

Stochastic light concentration from 3D to 2D reveals ultraweak chemi- and bioluminescence

For countless applications in science and technology, light must be concentrated, and concentration is classically achieved with reflective and refractive elements. However, there is so far no efficient way, with a 2D detector, to detect photons produced inside an extended volume with a broad or isotropic angular distribution. Here, with theory and experiment, we propose to stochastically transform and concentrate a volume into a smaller surface, using a high-albedo Ulbricht cavity and a small exit orifice through cavity walls. A 3D gas of photons produced inside the cavity is transformed with a 50% number efficiency into a 2D Lambertian emitting orifice with maximal radiance and a much smaller size. With high-albedo quartz-powder cavity walls (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\rho =99.94\%$$\end{document}ρ=99.94%), the orifice area is \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$1/(1-\rho )\approx 1600$$\end{document}1/(1-ρ)≈1600 times smaller than the walls’ area. When coupled to a detectivity-optimized photon-counter (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\mathcal{D}=0.015\,{\text{photon}}^{-1}\,{\text{s}}^{1/2}\text{ cm}$$\end{document}D=0.015photon-1s1/2cm) the detection limit is \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$110\;{\text{photon}}\;{\text{s}}^{ - 1} \;{\text{L}}^{ - 1}$$\end{document}110photons-1L-1. Thanks to this unprecedented sensitivity, we could detect the luminescence produced by the non-catalytic disproportionation of hydrogen peroxide in pure water, which has not been observed so far. We could also detect the ultraweak bioluminescence produced by yeast cells at the onset of their growth. Our work opens new perspectives for studying ultraweak luminescence, and the concept of stochastic 3D/2D conjugation should help design novel light detection methods for large samples or diluted emitters.

Chemiluminescence of Hemoglobin and Identification of Related Compounds with the Hemoglobin Chemiluminescence in Plasma¶

A low level of chemiluminescence by hemoglobin (Hb) was detected in the reaction with H2O2 and hydrogen donors such as gallic acid and catechins. The photon intensity was affected by the ferric state of Hb (methemoglobin > oxyhemoglobin), and was roughly correlated with the radical-scavenging potential of catechins. We hypothesized the reversible activation reaction of Hb as the chemiluminescence mechanism of the H2O2/gallic acid/Hb system. It is indicated that the oxidized-Hb (Hb-OOH) formation was a chemiluminescence-rate-determining step and one-electron reduction by a hydrogen donor of the compound-I-type intermediate ([.XFeIV] = O) proved a chemiluminescence-specificity-determining step. Spectral analysis showed that the photon emission from the H2O2/gallic acid/Hb system was produced without singlet oxygen generation. The concentration dependence of photon intensity suggests a high consumption ratio of H2O2 leading to protection from H2O2 toxicity. Albumin was defined as a hydrogen donor by the isolation of chemiluminescent substance in plasma using this chemiluminescence system.

Effects of glutathione peroxidase and catalase on hemolysis and methemoglobin modifications induced by photooxidized psoralen

Psoralen photooxidation products (POP products) were obtained by UVA irradiation (365 nm, 180-640 W/m2) of an aqueous psoralen solution with fluences of 0-800 kJ/m2. Preincubation of POP products with glutathione peroxidase (GSHPer) or catalase, as well as presence of catalase during UVA irradiation of the aqueous psoralen solution did not influence their hemolytic activity. However, both GSHPer and catalase inhibited POP-induced conversion of methemoglobin. This indicates that hydrogen peroxide and psoralen peroxides destructible by GSHPer, which are being produced during psoralen photooxidation, do not possess hemolytic activity. Furthermore, hydrogen peroxide does not appear to serve as an intermediate in the process of hemolysin formation. Hydrogen peroxide generated during psoralen photooxidation is apparently the main POP product responsible for MetHb conversion.

Detection of free radicals generated from hydrogen peroxide, gallic acid and haemoprotein chemiluminescence system by electron spin resonance spectroscopy

Low-level chemiluminescence is produced in a hydrogen peroxide (H(2)O(2))/gallic acid/haemoprotein system with single broad peaks around 520 nm, regardless of the biological role of the haemoprotein. The free haem iron systems (haemin and haematin systems) gave a higher photon intensity (1.5 x 10(4) and 2.0 x 10(4) cps) than that of the H(2)O(2)/gallic acid/haematoporphyrin system. These results indicated that haem iron plays a significant role in the photon emission of haemoprotein systems. A free radical with a g value of 2. 0058 was detected through a direct electron spin resonance (ESR) method. The photon intensity of the H(2)O(2)/gallic acid/haemoprotein system decreased in the order: HRP > cytochrome c > myoglobin > haemoglobin, and this corresponded to the decrease in radical intensity. These results indicated that the formation of the free radical with a g value of 2.0058 may be the key step for chemiluminescence in the H(2)O(2)/gallic acid/haemoprotein system. A quartet line similar to DMPO-OH adducts and uncomplexed free radicals (g = 2.0058) was detected using the ESR spin-trapping method in the H(2)O(2)/gallic acid/cytochrome c system.

Free radical formation and erythrocyte membrane alterations during MetHb formation induced by the BHA metabolite, tert-butylhydroquinone

Erythrocyte membranes are altered as a consequence of oxidative stress following the incubation of intact erythrocytes with one of the major metabolites of the antioxidant butylated hydroxyanisole (BHA), tertbutylhydroquinone(tBHQ). Arather persistent semiquinone radical was observed by electron spin resonance (ESR) spectroscopy when tBHQ was incubated with either homogeneous oxyhemoglobin solutions or suspensions of intact erythrocytes. Erythrocyte ghosts prepared from fresh control erythrocytes and ghosts from erythrocytes preincubated with BHA and its metabolite, tBHQ, were subjected to polyacrylamide gel electrophoresis (SDS-PAGE). Only minor changes of the electrophoresis pattern relative to the control was observed in the BHA incubations whereas tBHQ significantly increased the amount of high molecular weight degradation products of erythrocyte membrane constituents. These changes were only observed when incubations were performed in the presence of oxygen. In control experiments where heme oxygen was replaced by carbon monoxide, no membrane degradation products appeared. These observations can be interpreted in terms of metabolic activation of the antioxidant BHAvia tBHQ to the tert-butylsemiquinone free radical and finally to the corresponding quinone, thereby leading to harmful effects on erythrocyte membrane structures. Moreover, deleterious effects on other biological membranes are also likely to occur.

The effects of xenobiotics on erythrocytes

1. Methemoglobin formation was observed when erythrocytes were incubated with xenobiotics such as hydroxylamines or phenols, other metabolites resulting from the interaction of these compounds with erythrocytes being reactive free radicals derived from the respective xenobiotic, and a ferryl-heme oxo-complex. 2. Steady-state levels of these reaction products depended on the permeability of the erythrocyte membrane for the various methemoglobin (MetHb) generators and the presence of antioxidants that downregulate the radicals formed. 3. Electron spin resonance (ESR) spectra of xenobiotic-derived free radicals could be obtained only from the readily water soluble hydroxylamines, whereas the poorly water soluble phenolic compounds did not allow the use of concentrations required for the generation of detectable amounts of ESR-sensitive metabolites in erythrocytes. 4. Previous investigations with oxyhemoglobin solutions and with the MetHb/H2O2 model systems have shown that, apart from ESR-sensitive radical species, excited reaction intermediates such as compound 1 ferryl hemoglobin can be detected as well by using chemiluminescence measurements. 5. A strong correlation was found between the intensity of the emitted light and the MetHb formation rate, indicating that the production of compound 1 ferryl hemoglobin is closely related to the MetHb formation step. 6. The sensitivity of the photon-counting method allowed measurements of excited species in intact erythrocytes not only with the readily soluble hydroxylamines, but also with the less soluble phenolic compounds. 7. In addition, parameters indicative of xenobiotic-induced oxidative alterations were found: a significant decrease in intraerythrocytic thiol levels was a result of all compounds that initiate MetHb formation, as also described for slowly reacting xenobiotics. 8. With the most reactive compound investigated, unsubstituted hydroxylamine, a significant release of iron from the oxidatively modified hemoglobin was detected, facilitated by binding of this transition metal to hydroxylamine and its final oxidation product, nitric oxide. 9. The use of the ESR spin-labeling technique revealed membrane alterations of erythrocytes exposed to the reducing MetHb generators presented in this study. 10. A direct action of BHA and BHT on the integrity of the erythrocyte membrane was observed, leading to hemolysis independent of the formation of prooxidant species. 11. The presence of strong prooxidants (radicals) was indicated both by fluidity changes in the membrane and by an oxidative decrease in cytosolic thiol levels.

Light emission resulting from hydroxylamine-induced singlet oxygen formation of oxidizing LDL particles

Oxidation of low-density lipoprotein (LDL) by low amounts of cupric ions resulted in the formation of singlet oxygen (1O2, 1 delta g) when hydroxylamine (NH2OH) was added. Direct evidence on this excited species came from partial spectral resolution of the emitted light in the red spectral region (634 nm and 703 nm), which can be attributed to the dimol decay of singlet oxygen. Additional evidence for the existence of singlet oxygen came from the enhancing effect of deuterium oxide buffer (D2O) on chemiluminescence intensity and the quenching effect of sodium azide. A linear correlation between NH2OH-dependent chemiluminescence intensity and the amount of diene conjugates (DC) formed in this reaction was observed. Removal of adventitious transition metals by adequate chelators prevented chemiluminescence in this system; NH2OH was also found to efficiently decrease metabolites of lipid peroxidation (LPO). Our findings are consistent with a sequence of reactions in which NH2OH first converts transition metals to their reduced state, thereby stimulating the formation of alkoxy- and peroxyradicals. Peroxyradicals decompose in a bimolecular Russel reaction to hydroxyl compounds and singlet oxygen while the majority of alkoxy radicals are eliminated by a secondary reaction with NH2OH. Identical effects were observed when reducing antioxidants such as ascorbic acid or trolox C were used instead of hydroxylamine.

Hydroxylamine and phenol-induced formation of methemoglobin and free radical intermediates in erythrocytes

As previously shown with isolated oxyhemoglobin, methemoglobin formation can also be induced in intact erythrocytes by hydroxylamine compounds and substituted phenols such as butylated hydroxyanisole (BHA). Electron spin resonance investigations revealed that, accordingly, free radical intermediates were formed in erythrocytes from hydroxylamine, N,N-dimethylhydroxylamine, and N-hydroxyurea. Due to the low stability of the dihydronitroxyl radicals, their detection required the use of a continuous flow system and relatively high amounts of the reactants. As has already been demonstrated with the solubilized hemoglobin system, hemoglobin of intact erythrocytes also reacts with the more hydrophilic xenobiotics such as hydroxylamine. However, the reaction rate was slightly reduced, indicating the existence of an incomplete permeability barrier for these compounds. The limited solubility of phenolic compounds in the aqueous buffer of suspended erythrocytes (in combination with the strict requirement of osmolarity in order to prevent hemolysis) impeded the direct detection of the respective phenoxyl radicals previously reported in hemoglobin solutions. However, in accordance with earlier findings in homogeneous reaction systems, chemiluminescence was observed as well, indicating the existence of a further reaction intermediate, which was also obtained in pure hemoglobin solutions when mixed with the respective reactants. As has recently been demonstrated, this light emission is indicative of the existence of highly prooxidative compound I intermediates during methemoglobin formation. Prooxidant formation in erythrocytes is reflected by a significant decrease in thiol levels even with those compounds where free radical formation was not directly detectable by ESR spectroscopy. The use of the spin-labeling technique revealed membrane effects as a result of oxidative stress. Oxidative metabolism of hemoglobin with hydroxylamine caused a release of low molecular weight iron. The marked hemolysis observed in the presence of BHA results from a direct membrane effect of this compound rather than a consequence of free radical-induced oxidative stress. A correlation of the different results is discussed in terms of possible toxicological consequences.

Chemiluminescence and EPR studies on the excitation site of ferric-heme-oxo complexes of natural and model heme systems

Chemiluminescence was detected both in the reaction system of H2O2 plus heme proteins such as methemo- and metmyoglobin and ferric-protoheme complexes used as a model system. The intensity of chemiluminescence was found to be mediated by ligand binding to the sixth coordination site of the ferric-protoheme compounds, e.g. chemiluminescence was not observed with the bisimidazole ferric-protoheme complex. On the other hand the pentacoordinated histidine ferric-protoheme complex exhibited strong light emission. Comparative studies with various ligand-heme compounds elucidated that light emission was inversely correlated with the binding strength of the respective ligand at the sixth coordination site. The basic reaction mechanism causing the establishment of an excited state was studied by monitoring chemiluminescence and EPR signal formation of ligand-modified heme proteins in the presence of different electron donors. External electron donors such as Trolox C, TMPD and ascorbic acid affected a strong reduction in the development of chemiluminescence suggesting the essential involvement of an inner-molecular electron transfer process. Our results allow the conclusion that chemiluminescence is generated from the decay of an excited state of oxo-heme compounds established as a result of a one electron transfer step from a ligand group to heme iron.

Reactions of reducing xenobiotics with oxymyoglobin. Formation of metmyoglobin, ferryl myoglobin and free radicals: an electron spin resonance and chemiluminescence study

The oxygen-haem centre of oxymyoglobin reacts with reducing xenobiotics such as hydroxylamines and phenols with the concomitant formation of metmyoglobin and oxidation of the respective xenobiotic. Metmyoglobin formation rates were measured by visible spectroscopy with xenobiotic concentrations ranging from 100 microM to 30 mM. Analogous to previous results obtained with oxyhaemoglobin, the first step in the reaction of hydroxylamines with oxymyoglobin leads to the formation of the one-electron oxidation product of hydroxylamine, a nitroxyl radical detectable by electron spin resonance. A variety of paramagnetic secondary products were also found. The terminal oxidation product of hydroxylamine and hydroxyurea was the myoglobin-nitric oxide complex, one showing similar spectral characteristics to the analogous haemoglobin-nitric oxide adduct found in our previous experiments. On the other hand, the amount of low-spin ferric complexes obtained from metmyoglobin and an excess of the respective hydroxylamine was considerably lower than the corresponding results with methaemoglobin. A second important reaction intermediate was the compound I-type ferryl haem-species detected by a recently-published chemiluminescence assay. Partial spectral resolution of the emitted light using a set of cut-off filters indicated that maximum light emission occurred above 600 nm, most probably involving excited porphyrin states. The intensity of oxymyoglobin-related light emission was considerably higher than that reported earlier with oxyhaemoglobin. This indicates a difference in the excitation mechanism which leads to the formation of the compound I-type ferry haem species.