Hydroxyl and alkoxyl radical production by oxidation products of metmyoglobin

Protein oxidation mediated by heme-induced active site conversion specific for heme-regulated transcription factor, iron response regulator

The Bradyrhizobium japonicum transcriptional regulator Irr (iron response regulator) is a key regulator of the iron homeostasis, which is degraded in response to heme binding via a mechanism that involves oxidative modification of the protein. Here, we show that heme-bound Irr activates O2 to form highly reactive oxygen species (ROS) with the "active site conversion" from heme iron to non-heme iron to degrade itself. In the presence of heme and reductant, the ROS scavenging experiments show that Irr generates H2O2 from O2 as found for other hemoproteins, but H2O2 is less effective in oxidizing the peptide, and further activation of H2O2 is suggested. Interestingly, we find a time-dependent decrease of the intensity of the Soret band and appearance of the characteristic EPR signal at g = 4.3 during the oxidation, showing the heme degradation and the successive formation of a non-heme iron site. Together with the mutational studies, we here propose a novel "two-step self-oxidative modification" mechanism, during which O2 is activated to form H2O2 at the heme regulatory motif (HRM) site and the generated H2O2 is further converted into more reactive species such as ·OH at the non-heme iron site in the His-cluster region formed by the active site conversion.

Antioxidant mechanisms of nitric oxide against iron-catalyzed oxidative stress in cells

Three distinct antioxidant pathways are considered through which iron-catalyzed oxidative stress may be regulated by nitric oxide (NO). The first two pathways involve direct redox interactions of NO with iron catalytic sites and represent a fast response that may be considered an emergency mechanism to protect cells from the consequences of acute and intensive oxidative stress. These are (i) NO-induced nitrosylation at heme and non-heme iron catalytic sites that is capable of directly reducing oxoferryl-associated radicals, (ii) formation of nitrosyl complexes with intracellular "loosely" bound redox-active iron, and (iii) an indirect regulatory pathway that may function as an adaptive mechanism that becomes operational upon long-term exposure of cells to NO. In the latter pathway, NO down-regulates expression of iron-containing proteins to prevent their catalytic prooxidant reactions.

Pretreatment of whole blood for use in immunochromatographic assays for hepatitis B virus surface antigen

Immunochromatographic assays (ICAs) are also referred to as rapid tests, since they are simple and the results can be obtained within minutes after manually loading a few drops of a sample into each sample well of the test device. However, whole blood cannot be tested with ICA kits due to the visual hindrance caused by the color of red blood cells (RBCs), unless a cell-removing device such as a filter is mounted on the kits. Thus, when testing with blood, the advantage of the ICA kit is lost because of the additional time and machines required to coagulate and separate whole blood before preparing the serum. To overcome this limitation, whole-blood samples were added to a pretreatment solution to decolor the RBCs; the resulting mixtures were then loaded into the sample wells of the test device. The pretreating solution was composed of hydrogen peroxide (H(2)O(2)) to decolor the RBCs, Sag 471 (Osi Specialties) to restrain the mixture from vigorous foaming, sodium azide (NaN(3)) to inhibit the enzyme, which generates excessive foam at the beginning of decolorization, and EDTA as a chelating agent. As a result of this pretreatment, whole blood could be used with the ICA kit without reducing its simplicity and rapidity.

Lag-time measurement of antioxidant capacity using myoglobin and 2, 2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid): rationale, application, and limitation

The application of a simple lag-time assay for antioxidant capacity using myoglobin and 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) or ABTS has been studied for its general application conditions. In the presence of an antioxidant, the ABTS(*+) radical-cation-forming chromogenic reaction, catalyzed by myoglobin and initiated by hydrogen peroxide (H(2)O(2)), has a lag period, and its duration is linearly correlated to the concentration of that antioxidant. The high linearity between the lag time and the antioxidant concentration remained unchanged regardless of the assay conditions. It was also found that the linearity was better for antioxidants at lower concentrations. The change of assay condition could significantly affect the relative antioxidant value of a chemical to the standard (ascorbic acid), although not to a large extent. Most of antioxidants investigated were found suitable to be assayed using this method. Some antioxidants, e.g., genistein, however, were not, probably due to their low reactivity toward ferrylmyoglobin or ABTS(*+). In conclusion, the lag-time assay is a reliable method for measuring the antioxidant capacity, provided caution is taken for antioxidants that mainly act through lowering the rate of the chromogenic reaction.

Induction of heme oxygenase produces load-independent cardioprotective effects in hypertensive rats

Although heme oxygenase (HO) has been suggested to be involved in the regulation of cardiovascular function through production of carbon monoxide (CO), the pathophysiological significance of HO in hypertensive organ damage remains unknown. We examined the effects of inducing HO-1 mRNA by stannous chloride (SnCl2) on cardiac hypertrophy in stroke-prone spontaneously hypertensive rats (SHR-SP/Izm). Chronic administration of SnCl2 resulted in a significant decrease in left ventricular (LV) weight/body weight ratio and LV brain natriuretic peptide (BNP) mRNA levels as a marker of cardiac hypertrophy and a significant increase in LV HO-1 mRNA levels and LV cGMP contents in SHR-SP/Izm, while there was no significant change in systemic blood pressure. These results provide the first evidence that induction of HO in the heart attenuates cardiac hypertrophy in load-independent mechanism in genetically hypertensive rats.

Effect of the heme/heme oxygenase pathway on the relationship between salt consumption and blood pressure

OBJECTIVE

Some studies have shown that heme oxygenase inhibition increases blood pressure in rats. This effect may be due to the consequent lower levels of the heme degradation products (carbon monoxide, biliverdin, and Fe3+) or due to heme accumulation. However, it is not yet known if the variable effect of NaCl on blood pressure levels is influenced by the heme/heme oxygenase pathway activity. This enzymatic system may be studied by blocking its activity with zinc protoporphyrin IX (ZnPP IX), a heme oxygenase inhibitor.

DESIGN AND METHODS

Male Wistar rats were fed from weaning with low (LSD--0.15% NaCl), normal (NSD--1.3% NaCl), or high (HSD--8% NaCl) salt diet On the 12th week of age, assessment of the tail-cuff blood pressure (tc-BP) response to acute inhibition of heme oxygenase with ZnPP IX or after vehicle (Na2CO3) was performed.

RESULTS

A higher tc-BP was observed on HSD both before ZnPP IX (P< 0.001) and vehicle (P = 0.003). After ZnPP IX, tc-BP decreased on HSD (P < 0.001) and increased on NSD (P = 0.003) and on LSD (P < 0.001). The area under the curve (AUC) of the percentage change in the blood pressure response was calculated. On putting all the rats from the three dietary groups together, an inverse correlation was observed between individual AUC after ZnPP IX and control tc-BP (r = -0.71; P< 0.001) but not after vehicle (r = 0.34; P < 0.05).

CONCLUSIONS

Chronic salt overload increases blood pressure in Wistar rats and the pressure response to heme oxygenase is modulated by the effect of NaCl consumption on blood pressure levels.

Visible chemiluminescence associated with the reaction between methemoglobin or oxyhemoglobin with hydrogen peroxide

Visible chemiluminescence is emitted in the irreversible deactivation of hemoglobin or methemoglobin with excess H2O2. The emission takes place in two phases. The most intense one lasts a few seconds and is followed by a second phase of lower intensity that remains for longer periods. This second phase presents chaotic or sustained oscillations. Free radicals are implicated in the luminescent process since the emission can be reduced by free radical scavengers such as 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox) or ascorbic acid. These additives lead to a delay in reaching the maximum intensity, which can be related to their consumption, implying substantial recycling of the hemoprotein. Chemiluminescence is also observed in the oxidation of hemin by H2O2, suggesting a role for the heme group in the processes leading to the excited state production. The lower intensity observed in the presence of hemin can be related to the contribution of the globin chains.