The formation of free radicals by cardiac myocytes under oxidative stress and the effects of electron-donating drugs

The Cellular and Organismal Effects of Nitroxides and Nitroxide-Containing Nanoparticles

Nitroxides are stable free radicals that have antioxidant properties. They react with many types of radicals, including alkyl and peroxyl radicals. They act as mimics of superoxide dismutase and stimulate the catalase activity of hemoproteins. In some situations, they may exhibit pro-oxidant activity, mainly due to the formation of oxoammonium cations as products of their oxidation. In this review, the cellular effects of nitroxides and their effects in animal experiments and clinical trials are discussed, including the beneficial effects in various pathological situations involving oxidative stress, protective effects against UV and ionizing radiation, and prolongation of the life span of cancer-prone mice. Nitroxides were used as active components of various types of nanoparticles. The application of these nanoparticles in cellular and animal experiments is also discussed.

Thiol-induced hemoglobin oxidation

Addition of cysteine in the mM range to purified oxyhemoglobin, red blood cell lysate or red blood cell suspensions leads to oxidation of the hemoprotein. The rate and extent of the process depend on the initial hemoglobin and cysteine concentrations, and the reaction is limited by the total destruction of the sulfhydryl groups. Similar results are obtained employing glutathione, but the rate of the process is considerably slower. Oxidation of the purified hemoprotein is faster than in the red blood cell lysate. This difference is mainly due to the inhibitory effect of catalase present in the lysate. Addition of sodium azide increases the rate of oxyhemoglobin oxidation in the lysate, while addition of catalase reduces the rate of oxidation of the purified hemoprotein. The results are interpreted in terms of a mechanism comprising the oxidation of the oxyhemoglobin by the -SH group, with concomitant formation of superoxide anion and hydrogen peroxide. These species further contribute to the oxyhemoglobin oxidation. A chain oxidation of the thiol, catalyzed by the hemoprotein, explains the extensive cysteine destruction.

Altered iron homeostasis in an animal model of hypertensive nephropathy: stroke-prone rats

BACKGROUND AND AIM

Iron is the most abundant metal in mammalian cells, and plays a pivotal role in many metabolic processes. Dysregulated iron homeostasis is involved in the cause of a number of pathological processes including renal diseases.

METHODS AND RESULTS

Longitudinal MRI scans of salt-loaded spontaneously hypertensive stroke-prone rats (SHRSP), an animal model that spontaneously develops hypertensive nephropathy, showed a decrease in renal and hepatic T2 SI (a sign of iron accumulation) of, respectively, 42.3 ± 2.5% (P < 0.01) and 60.4 ± 15.1% (P < 0.01) in comparison with SHRSP fed a standard diet. This was accompanied by the development of renal inflammation and oxidative stress (as evaluated by immunohistochemical and proteomic analyses), mitochondrial dysfunction, massive proteinuria and sustained intravascular hemolysis with the subsequent depletion of plasma haptoglobin, which was responsible for the renal uptake of hemoglobin and iron accumulation. In order to investigate the role of iron in these pathological processes, we subcutaneously treated the salt-loaded rats with the iron chelator deferoxamine (200 mg/kg per day). The pharmacological treatment prevented iron tissue accumulation, as indicated by the increase in renal and hepatic T2 SI of, respectively, 120.0 ± 10.1% (P < 0.01) and 73.9 ± 4.4% (P < 0.01) in comparison with salt-loaded rats treated with vehicle alone. Deferoxamine also preserved renal morphology and function, the renal infiltration of ED-1-positive macrophages/monocytes, and the expression of MCP-1 and TGF-β mRNA, reduced the level of reactive oxygen species, and improved the activity of mitochondrial cytochrome c oxidase.

CONCLUSION

These findings suggest that iron dysmetabolism is involved in the development of hypertensive nephropathy in SHRSP.

The mechanism underlying nitroxyl and nitric oxide formation from hydroxamic acids

BACKGROUND

The pharmacological effects of hydroxamic acids (RC(O)NHOH, HX) are partially attributed to their ability to serve as HNO and/or NO donors under oxidative stress. Given the development and use of HXs as therapeutic agents, elucidation of the oxidation mechanism is needed for more educated selection of HX-based drugs.

METHODS

Acetohydroxamic and glycine-hydroxamic acids were oxidized at pH 7.0 by a continuous flux of radiolytically generated (·)OH or by metmyoglobin and H(2)O(2) reactions system. Gas chromatography and spectroscopic methods were used to monitor the accumulation of N(2)O, N(2), nitrite and hydroxylamine.

RESULTS

Oxidation of HXs by (·)OH under anoxia yields N(2)O, but not nitrite, N(2) or hydroxylamine. Upon the addition of H(2)O(2) to solutions containing HX and metmyoglobin, which is instantaneously and continuously converted into compound II, nitrite and, to a lesser extent, N(2)O are accumulated under both anoxia and normoxia.

CONCLUSIONS

Oxidation of HXs under anoxia by a continuous flux of (·)OH, which solely oxidizes the hydroxamate moiety to RC(O)NHO(·), forms HNO. This observation implies that bimolecular decomposition of RC(O)NHO(·) competes efficiently with unimolecular decomposition processes such as internal disproportionation, hydrolysis or homolysis. Oxidation by metmyoglobin/H(2)O(2) involves relatively mild oxidants (compounds I and II). Compound I reacts with HX forming RC(O)NHO(·) and compound II, which oxidizes HX, RC(O)NHO(·), HNO and NO. The latter reaction is the main source of nitrite.

GENERAL SIGNIFICANCE

HXs under oxidative stress release HNO, but can be considered as NO-donors provided that HNO oxidation is more efficient than its reaction with other biological targets.

Oxidative modulation of marcaine and lekoptin in H9C2 rat myoblasts

AIM

The cytotoxicity of marcaine was estimated in combination with a calcium channel blocker. In addition, the influence of marcaine and marcaine plus lekoptin on a model system using the H9C2 cardiac cell line was investigated.

METHODS

Cells were incubated for five hours with marcaine, lekoptin, or with both drugs simultaneously. Apoptotic cells were detected using the TUNEL assay and the alkaline comet assay. Mitochondrial cell function after drug uptake was examined using the MTT assay. The concentration of MDA (malondialdehyde) -- the final product of fatty-acid peroxidation, was quantified spectrophotometrically. The expression of glutathione S-transferase pi (GST-pi) was detected by immunofluorescence (IF) and Western blotting (WB) and inducible nitric oxide synthase (iNOS) was assessed by immunocytochemical staining (ABC).

RESULTS

Incubation with marcaine resulted in the highest number of apoptotic cells. After incubation with both marcaine and lekoptin, moderate damage to cells (54.2%+/-1.775% of DNA destruction) was observed. The highest levels of iNOS and GST-pi expression were observed in cells treated with marcaine and marcaine plus lekoptin. The characteristic nuclear GST-pi expression was observed in cells treated with both drugs.

CONCLUSION

Lekoptin stimulated cells to proliferate. Marcaine caused membrane damage and ultimately cell death.

Potential role and mechanisms of subcellular remodeling in cardiac dysfunction due to ischemic heart disease

Several studies have revealed varying degrees of changes in sarcoplasmic reticular and myofibrillar activities, protein content, gene expression and intracellular Ca-handling during cardiac dysfunction due to ischemia-reperfusion (I/R); however, relatively little is known about the sarcolemmal and mitochondrial alterations, as well as their mechanisms in the I/R hearts. Because I/R is associated with oxidative stress and intracellular Ca-overload, it has been indicated that changes in subcellular activities, protein content and gene expression due to I/R are related to both oxidative stress and Ca-overload. Intracellular Ca-overload appears to induce changes in subcellular activities, protein contents and gene expression (subcellular remodeling) by activation of proteases and phospholipases, as well as by affecting the genetic apparatus, whereas oxidative stress is considered to cause oxidation of functional groups of different subcellular proteins in addition to modifying the genetic machinery. Ischemic preconditioning, which is known to depress the development of both intracellular Ca-overload and oxidative stress due to I/R, was observed to attenuate the I/R-induced subcellular remodeling and improve cardiac performance. It is suggested that a combination therapy with antioxidants and interventions, which reduce the development of intracellular Ca-overload, may improve cardiac function by preventing or attenuating the occurrence of subcellular remodeling due to ischemic heart disease. It is proposed that defects in the activities of subcellular organelles may serve as underlying mechanisms for I/R-induced cardiac dysfunction under acute conditions, whereas subcellular remodeling due to alterations in gene expression may explain the impaired cardiac performance under chronic conditions of I/R.

Deferoxamine lowers tissue damage after 80% exchange transfusion with polymerized hemoglobin

Hemoglobin (Hb) solutions have been proposed as potential substitutes for erythrocytes to maintain oxygen-carrying capacity in situations in which blood is not available. This study investigated systemic and microvascular hemodynamics as well as tissue oxygenation and viability after an 80% exchange transfusion with an oxygen-carrying blood substitute based on polymerized bovine hemoglobin (PBH). Studies were carried in unanesthetized hamsters prepared with a window-chamber model for microcirculation evaluation. Heme iron-mediated injury to the tissue was analyzed by using deferoxamine (an iron chelator), which reduces free iron toxicity. Exchange transfusion led to a significant decrease in hematocrit (Hct) and an increase in plasma Hb, in addition to a significant decrease of arteriolar and venular diameters, flow velocity, and, therefore, microvascular blood flow. Capillary perfusion was severely compromised after exchange, but tissue pO2 increased above baseline, and oxygen extraction was reduced. Apoptotic and necrotic cells increased significantly after the exchange; however, this effect was only partially due to the toxicity of free iron. Iron therapy decreased the microvascular and oxygenation changes but did not fully reverse the adverse effects. Assessment of tissue viability after exchange suggests that chelation treatment in cases of large exchange transfusions with acellular Hb could be potentially beneficial.

A new sensitive assay reveals that hemoglobin is oxidatively modified in vivo

Free radical formation in heme proteins is recognised as a factor in mediating the toxicity of peroxides in oxidative stress. As well as initiating free radical damage, heme proteins damage themselves. Under extreme conditions, where oxidative stress and low pH coincide (e.g., myoglobin in the kidney following rhabdomyolysis and hemoglobin in the CSF subsequent to subarachnoid hemorrhage), peroxide can induce covalent heme to protein cross-linking. In this paper we show that, even at neutral pH, the heme in hemoglobin is covalently modified by oxidation. The product, which we term OxHm, is a "green heme" iron chlorin with a distinct optical spectrum. OxHm formation can be quantitatively prevented by reductants of ferryl iron, e.g., ascorbate. We have developed a simple, robust, and reproducible HPLC assay to study the extent of OxHm formation in the red cell in vivo. We show that hemoglobin is oxidatively damaged even in normal blood; approximately 1 in 2,000 heme groups exist as OxHm in the steady state. We used a simple model (physical exercise) to demonstrate that OxHm increases significantly during acute oxidative stress. The exercise-induced increase is short-lived, suggesting the existence of an active mechanism for repairing or removing the damaged heme proteins.

Regio- and stereo-chemical oxidation of linoleic acid by human myoglobin and hydrogen peroxide: Tyr(103) affects rate and product distribution

Mb (myoglobin) plus H2O2 catalyses the oxidation of various substrates via a peroxidase-like activity. A Y103F (Tyr103-->Phe) variant of human Mb has been constructed to assess the effect of exchanging an electron-rich oxidizable amino acid on the peroxidase activity of human Mb. Steady-state analyses of reaction mixtures containing Y103F Mb, purified linoleic acid and H2O2 revealed a lower total yield of lipid oxidation products than mixtures containing the wild-type protein, consistent with the reported decrease in the rate constant for reaction of Y103F Mb with H2O2 [Witting, Mauk and Lay (2002) Biochemistry 41, 11495-11503]. Irrespective of the Mb employed, lipid oxidation yielded 9(R/S)-HODE [9(R,S)-hydroxy-10E,12Z-octadecadienoic acid] in preference to 13(R/S)-HODE [13(R,S)-hydroxy-9Z,11E-octadecadienoic acid], while 9- and 13-keto-octadecadienoic acid were formed in trace amounts. However, lipid oxidation by the Y103F variant of Mb proceeded with a lower V(max) value and an increased K(m) value relative to the wild-type control. Consistent with the increased K(m), the product distribution from reactions with Y103F Mb showed decreased selectivity compared with the wild-type protein, as judged by the decreased yield of 9(S)-relative to 9(R)-HODE. Together, these data verify that Tyr103 plays a significant role in substrate binding and orientation in the haem pocket of human Mb. Also, the midpoint potential for the Fe(III)/(II) one-electron reduction was shifted slightly, but significantly, to a higher potential, confirming the importance of Tyr103 to the hydrogen-bonding network involving residues that line the haem crevice of human Mb.

The radical and redox chemistry of myoglobin and hemoglobin: from in vitro studies to human pathology

Recent research has shown that myoglobin and hemoglobin play important roles in the pathology of certain disease states, such as renal dysfunction following rhabdomyolysis and vasospasm following subarachnoid hemorrhages. These pathologies are linked to the interaction of peroxides with heme proteins to initiate oxidative reactions, including generation of powerful vasoactive molecules (the isoprostanes) from free and membrane- bound lipids. This review focuses on the peroxide-induced formation of radicals, their assignment to specific protein residues, and the pseudoperoxidase and prooxidant activities of the heme proteins. The discovery of heme to protein cross-linked forms of myoglobin and hemoglobin in vivo, definitive markers of the participation of these heme proteins in oxidative reactions, and the recent results from heme oxygenase knockout/knockin animal model studies, indicate that higher oxidation states (ferryl) of heme proteins and their associated radicals play a major role in the mechanisms of pathology.

Role of tyrosine-103 in myoglobin peroxidase activity: kinetic and steady-state studies on the reaction of wild-type and variant recombinant human myoglobins with H(2)O(2)

Myoglobin (Mb) catalyzes a range of oxidation reactions in the presence of hydrogen peroxide (H(2)O(2)) through a peroxidase-like cycle. C110A and Y103F variants of human Mb have been constructed to assess the effects of removing electron-rich oxidizable amino acids from the protein on the peroxidase activity of Mb: a point mutation at W14 failed to yield a viable protein. Point mutations at C110 and Y103 did not result in significant changes to structural elements of the heme pocket, as judged by low-temperature electron paramagnetic spectroscopy (EPR) studies on the ground-state ferric proteins. However, compared to the native protein, the yield of globin radical (globin*) was significantly decreased for the Y103F but not the C110A variant Mb upon reaction of the respective proteins with H(2)O(2). In contrast with our expectation that inhibiting pathways of intramolecular electron transfer may lead to enhanced Mb peroxidase activity, mutation of Y103 marginally decreased the rate constant for reaction of Mb with H(2)O(2) (1.4-fold) as judged by stopped-flow kinetic analyses. Consistent with this decrease in rate constant, steady-state analyses of Y103F Mb-derived thioanisole sulfoxidation indicated decreased V(max) and increased K(m) relative to the wild-type control. Additionally, thioanisole sulfoxidation proceeded with lower stereoselectivity, suggesting that Y103 plays a significant role in substrate binding and orientation in the heme pocket of Mb. Together, these results show that electron transfer within the globin portion of the protein is an important modulator of its stability and catalytic activity. Furthermore, the hydrogen-bonding network involving the residues that line the heme pocket of Mb is crucial to both efficient peroxidase activity and stereospecificity.

Oxidation of tetrahydrobiopterin by peroxynitrite or oxoferryl species occurs by a radical pathway

The molecular mechanisms of tetrahydrobiopterin (BH4) oxidation by peroxynitrite (ONOO-) was studied using ultra-weak chemiluminescence, electron paramagnetic resonance (EPR) and UV-visible diode-array spectrophotometry, and compared to BH4 oxidation by oxoferryl species produced by the myoglobin/hydrogen peroxide (Mb/H2O2) system. The oxidation of BH4 by ONOO- produced a weak chemiluminescence, which was altered by addition of 50 mM of the spin trap alpha-(4-pyridyl-1-oxide)-N-tert butylnitrone (POBN). EPR spin trapping demonstrated that the reaction occurred at least in part by a radical pathway. A mixture of two spectra composed by an intense six-line spectrum and a fleeting weak nine-line one was observed when using ONOO-. Mb/H2O2 produced a short-living light emission that was suppressed by the addition of BH4. Simultaneous addition of POBN, BH4 and Mb/H2O2 produced the same six-line EPR spectrum, with a signal intensity depending on BH4 concentration. Spectrophotometric studies confirmed the rapid disappearance of the characteristic peak of ONOO- (302 nm) as well as substantial modifications of the initial BH4 spectrum with both oxidant systems. These data demonstrated that BH4 oxidation, either by ONOO- or by Mb/H2O2, occurred with the production of activated species and by radical pathways.

Attenuation of the acute adriamycin-induced cardiac and hepatic oxidative toxicity by N-(2-mercaptopropionyl) glycine in rats

The protective effect of the synthetic aminothiol, N-(2-mercaptopropionyl) glycine (MPG) on adriamycin (ADR) induced acute cardiac and hepatic oxidative toxicity was evaluated in rats. ADR toxicity, induced by a single intraperitoneal injection (15 mg/kg), was indicated by an elevation in the level of serum glutamic pyruvic transaminase (GPT), glutamic oxaloacetic transaminase (GOT), creatine kinase isoenzyme (CK-MB), and lactic dehydrogenase (LDH). ADR produced significant elevation in thiobarbituric acid reactive substances (TBARS), indicating lipid peroxidation, and significantly inhibited the activity of superoxide dismutase (SOD) in heart and liver tissues. In contrast, a single injection of ADR did not affect the cardiac or hepatic glutathione (GSH) content and cardiac catalase (CAT) activity but elevated hepatic CAT. Pretreatment with MPG, (2.5 mg/kg) intragastrically, significantly reduced TBARS concentration in both heart and liver and ameliorated the inhibition of cardiac and hepatic SOD activity. In addition, MPG significantly decreased the serum level of GOT, GPT, CK-MB, and LDH of ADR treated rats. These results suggest that MPG exhibited antioxidative potentials that may protect heart and liver against ADR-induced acute oxidative toxicity. This protective effect might be mediated, at least in part, by the high redox potential of sulfhydryl groups that limit the activity of free radicals generated by ADR.

Free radical-induced protein degradation of erythrocyte membrane is influenced by the localization of radical generation

We have investigated the role of the localization of free radical generation in erythrocyte membrane proteins degradation. The extracellular radical producer 2,2'-azobis(2-amidinopropane) hydrochloride induced a greater loss of band-3 protein in comparison with spectrin whereas the intracellular radical initiator cysteine induced the reverse effect. However, a large extent of main-chain fragmentation was observed for both proteins under the action of cysteine-derived radicals. The results show that the relative localization of the radical generation has an important influence on the degradation of specific proteins of the erythrocyte membrane.

The effects of pH on the mechanism of hydrogen peroxide and lipid hydroperoxide consumption by myoglobin: a role for the protonated ferryl species

Myoglobin catalyses the breakdown of lipid hydroperoxides (e.g., HPODE) during which the absorption band of the lipid conjugated diene (234 nm) is partially bleached. The constant for this process is strongly pH-dependent (k = 9.5 x 10(-3)s(-1), pH 7: k = 2.3 x 10(-1)s(-1), pH 5). This rate enhancement is not due to acid-induced changes in protein conformation or the involvement of protein-based radical species, as demonstrated by an almost identical pH dependence of the same reaction catalyzed by ferric haemin. The rate constants for ferryl formation and auto-reduction show different pH dependencies, with a pK of 8.3 for ferryl formation and a projected pK of 3.5 for ferryl auto-reduction. The pH dependence for the auto-reduction of the ferryl species is the same as that of the myoblobin catalyzed breakdown of HPODE. We propose that the protonated form of ferryl myoglobin (Fe(4+) - OH(-)) is the reactive species regulating the peroxidatic activity of myoglobin. The protonated ferryl species abstracts an electron from either the protein or porphyrin, allowing fast regeneration of the ferric species. Alkaline conditions stabilize the ferryl species, making myoglobin considerably less reactive towards lipids and lipid hydroperoxides. These findings are significant for understanding myoglobin-induced oxidative stress in vivo and the development of therapies.

Reaction of human myoglobin and H2O2. Electron transfer between tyrosine 103 phenoxyl radical and cysteine 110 yields a protein-thiyl radical

The sequence of human myoglobin (Mb) is similar to that of other species except for a unique cysteine at position 110 (Cys(110)). Adding hydrogen peroxide (H(2)O(2)) to human Mb affords Trp(14)-peroxyl, Tyr(103)-phenoxyl, and Cys(110)-thiyl radicals and coupling of Cys(110)-thiyl radicals yields a homodimer through intermolecular disulfide bond formation (Witting, P. K., Douglas, D. J., and Mauk, A. G. (2000) J. Biol. Chem. 275, 20391-20398). Treating a solution of wild type Mb and H(2)O(2) with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) at DMPO:protein </= 10 mol/mol yields DMPO-Cys(110) adducts as determined by EPR. At DMPO:protein ratios (25-50 mol/mol), both DMPO-Tyr(103) and DMPO-Cys(110) adducts were detected, whereas at DMPO:protein >/= 100 mol/mol only DMPO-Tyr(103) radicals were present. The DMPO-dependent decrease in DMPO-Cys(110) was matched by a near 1:1 stoichiometric increase in DMPO-Tyr(103). In contrast, reaction of the Y103F human Mb with H(2)O(2) gave no DMPO-Cys(110) at DMPO:protein </= 10 mol/mol, and only trace DMPO-Cys(110) at DMPO:protein >/= 100 mol/mol (i.e. conditions that consistently gave DMPO-Tyr(103) in the case of wild type Mb). No detectable homodimer was formed by incubation of the Y103F variant with H(2)O(2). However, the homodimer was detected in a mixture of both the Y103F and C110A variants of human Mb upon treatment with H(2)O(2) (C110A:Y103F:H(2)O(2) 2:1:5 mol/mol/mol); the yield of this homodimer increased with increasing ratios of C110A:Y103F. Together, these data suggest that addition of H(2)O(2) to human Mb can produce Cys(110)-thiyl radicals through an intermolecular electron transfer reaction from Cys(110) to a Tyr(103)-phenoxyl radical.

Reaction of hydrogen peroxide with ferrylhemoglobin: superoxide production and heme degradation

The reaction of Fe(II) hemoglobin (Hb) but not Fe(III) hemoglobin (metHb) with hydrogen peroxide results in degradation of the heme moiety. The observation that heme degradation was inhibited by compounds, which react with ferrylHb such as sodium sulfide, and peroxidase substrates (ABTS and o-dianisidine), demonstrates that ferrylHb formation is required for heme degradation. A reaction involving hydrogen peroxide and ferrylHb was demonstrated by the finding that heme degradation was inihibited by the addition of catalase which removed hydrogen peroxide even after the maximal level of ferrylHb was reached. The reaction of hydrogen peroxide with ferrylHb to produce heme degradation products was shown by electron paramagnetic resonance to involve the one-electron oxidation of hydrogen peroxide to the oxygen free radical, superoxide. The inhibition by sodium sulfide of both superoxide production and the formation of fluorescent heme degradation products links superoxide production with heme degradation. The inability to produce heme degradation products by the reaction of metHb with hydrogen peroxide was explained by the fact that hydrogen peroxide reacting with oxoferrylHb undergoes a two-electron oxidation, producing oxygen instead of superoxide. This reaction does not produce heme degradation, but is responsible for the catalytic removal of hydrogen peroxide. The rapid consumption of hydrogen peroxide as a result of the metHb formed as an intermediate during the reaction of reduced hemoglobin with hydrogen peroxide was shown to limit the extent of heme degradation.

Reaction of human myoglobin and H2O2. Involvement of a thiyl radical produced at cysteine 110

The human myoglobin (Mb) sequence is similar to other mammalian Mb sequences, except for a unique cysteine at position 110. Reaction of wild-type recombinant human Mb, the C110A variant of human Mb, or horse heart Mb with H(2)O(2) (protein/H(2)O(2) = 1:1.2 mol/mol) resulted in formation of tryptophan peroxyl (Trp-OO( small middle dot)) and tyrosine phenoxyl radicals as detected by EPR spectroscopy at 77 K. For wild-type human Mb, a second radical (g approximately 2. 036) was detected after decay of Trp-OO( small middle dot) that was not observed for the C110A variant or horse heart Mb. When the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) was included in the reaction mixture at protein/DMPO ratios </=1:10 mol/mol, a DMPO adduct exhibiting broad absorptions was detected. Hyperfine couplings of this radical indicated a DMPO-thiyl radical. Incubation of wild-type human Mb with thiol-blocking reagents prior to reaction with peroxide inhibited DMPO adduct formation, whereas at protein/DMPO ratios >/=1:25 mol/mol, DMPO-tyrosyl radical adducts were detected. Mass spectrometry of wild-type human Mb following reaction with H(2)O(2) demonstrated the formation of a homodimer (mass of 34,107 +/- 5 atomic mass units) sensitive to reducing conditions. The human Mb C110A variant afforded no dimer under identical conditions. Together, these data indicate that reaction of wild-type human Mb and H(2)O(2) differs from the corresponding reaction of other myoglobin species by formation of thiyl radicals that lead to a homodimer through intermolecular disulfide bond formation.

Peroxidation of linoleate at physiological pH: hemichrome formation by substrate binding protects against metmyoglobin activation by hydrogen peroxide

Peroxidation by metmyoglobin, MbFe(III), by metmyoglobin/hydrogen peroxide, MbFe(III)/H(2)O(2), to yield the myoglobin ferryl radical (*MbFe(IV)=O), or by ferrylmyoglobin, MbFe(IV)=O, was investigated at physiological pH (7.4) in oil-in-water linoleate emulsions. Linoleate peroxidation was followed using second derivative ultraviolet (UV)-spectroscopy for monitoring formation of conjugated dienes and quantitative determination of specific linoleate hydroperoxides by liquid chromatography with photodiode absorption detection. Modifications of myoglobins during lipid peroxidation were followed simultaneously by changes in the Soret absorption band (410 or 424 nm), and in the visible absorption region (from 450 to 700 nm), combined with electron spin resonance (ESR) spectroscopy for direct detection of changes in the spin state of the iron center. In contrast to MbFe(IV)=O, MbFe(III) and MbFe(III)/H(2)O(2) were not able to initiate linoleate peroxidation in oil-in-water emulsions, and MbFe(III) was converted, by binding of linoleate (but not methyl linoleate), to a low-spin hemichrome derivate, HMbFe(III), with the distal histidine reversibly bound to the iron center. HMbFe(III) is ineffective in initiating lipid peroxidation and cannot be activated to *MbFe(IV)=O or MbFe(IV)=O by addition of moderate amounts of H(2)O(2). Addition of MbFe(III) to linoleate emulsions containing H(2)O(2) results in the competitive formation of *MbFe(IV)=O and HMbFe(III) in favor of HMbFe(III), and little linoleate peroxidation is detected, demonstrating the inherent protection, at physiologic pH, against peroxidation by reversible binding of the substrate to the potential myoglobin catalyst.

Lipid oxidation in human low-density lipoprotein induced by metmyoglobin/H2O2: involvement of alpha-tocopheroxyl and phosphatidylcholine alkoxyl radicals

Metmyoglobin (metMb) and H(2)O(2) can oxidize low-density lipoprotein (LDL) in vitro, and oxidized LDL may be atherogenic. The role of alpha-tocopherol (alpha-TOH) in LDL oxidation by peroxidases such as metMb is unclear. Herein, we show that during metMb/H(2)O(2)-induced oxidation of native LDL, alpha-tocopheroxyl radical (alpha-TO(*)) and hydroperoxides and alcohols of cholesteryl esters [CE-O(O)H] and phosphatidylcholine [PC-O(O)H] accumulate concomitantly with alpha-TOH consumption. The ratio of accumulating CE-O(O)H to PC-O(O)H remains constant as long as alpha-TOH is present. Accumulation of CE-O(O)H is dependent on, and correlates with, LDL's alpha-TOH content, yet does not require preformed lipid hydroperoxides or H(2)O(2). This indicates that in native LDL alpha-TOH can act as a phase-transfer agent and alpha-TO(*) as a chain-transfer agent propagating LDL lipid peroxidation via tocopherol-mediated peroxidation (TMP). After alpha-TOH depletion, CE-O(O)H continues to accumulate, albeit at a slower rate than in the presence of alpha-TOH. This second phase of LDL oxidation is accompanied by depletion of PC-OOH, a rapid increase in the CE-O(O)H/PC-O(O)H ratio, formation of lipid-derived alkoxyl radicals and phosphatidylcholine hydroxides (PC-OH), and accumulation of a second organic radical, characterized by a broad singlet EPR signal. The latter persists for several hours at 37 degrees C. We conclude that metMb/H(2)O(2)-induced peroxidation of LDL lipids occurs initially via TMP. After alpha-TOH depletion, cholesteryl esters peroxidize at higher fractional rates than surface phospholipids, and this appears to be mediated at least in part via reactions involving alkoxyl radicals derived from the peroxidatic activity of metMb on PC-OOH.

Electrochemical generation of ferrylmyoglobin during oxidation of styrene with films of DNA and a poly (ester sulfonic acid) ionomer

The chemistry of electrochemically-driven myoglobin-catalyzed oxidation of styrene was investigated in films of DNA or Eastman AQ ionomer on optically transparent electrodes. Conversion of styrene to styrene oxide proceeded via a ferrylmyoglobin radical intermediate. Ferrylmyoglobins were clearly detected by spectroelectrochemistry in films of 1-4 mm thick. The ferrylmyoglobin radical is produced by reaction of metmyoglobin (Mb) in the films with hydrogen peroxide formed by electrochemical catalytic reduction of oxygen catalyzed by Mb. Thus, electrochemically-driven styrene oxidation with these films proceeds by a 'doubly catalytic' electrode-driven reduction-oxidation pathway. Ferrylmyoglobin formation during electrolysis of Mb-DNA films in aerobic solutions was much faster, and styrene oxidation occurred with less Mb decomposition compared to the Mb-AQ films. The better performance of Mb-DNA films is correlated with a larger fraction of electroactive Mb and better stability than for the Mb-AQ films.

Myoglobin-induced oxidative damage: evidence for radical transfer from oxidized myoglobin to other proteins and antioxidants

Reaction of equine Fe(III) myoglobin with H2O2 gives rise to an Fe(IV)-oxo species at the heme center and protein (globin)-derived radicals. Studies have shown that there are two (or more) sites for the protein-derived radical: at tyrosine (Tyr-103) or tryptophan (Trp-14). The latter radical reacts rapidly with oxygen to give a Trp-derived peroxyl radical. The formation of both the tyrosine phenoxyl radical and the tryptophan-derived peroxyl species have been confirmed in the present study; the latter appears to be the major initial radical, with the phenoxyl radical appearing at longer reaction times, possibly via secondary reactions. We have investigated, by EPR spectroscopy, the reactivity of the Trp-14 peroxyl radical with amino acids, peptides, proteins, and antioxidants, with the aim of determining whether this species can damage other targets, i.e., whether intermolecular protein-to-protein radical transfer and hence chain-oxidation occurs, and the factors that control these reactions. Three amino acids show significant reactivity: Tyr, Trp, and Cys, with Cys the least efficient. Evidence has also been obtained for (inefficient) hydrogen abstraction at peptide alpha-carbon sites; this may result in backbone cleavage in the presence of oxygen. The myoglobin Trp-14 peroxyl radical has been shown to react rapidly with a wide range of proteins to give long-lived secondary radicals on the target protein. These reactions appear to mainly involve Tyr residues on the target protein, although evidence for reaction at Trp has also been obtained. Antioxidants (GSH, ascorbate, Trolox C, vitamin E, and urate) react with the myoglobin-derived peroxyl radical; in some cases antioxidant-derived radicals are detected. These reactions are only efficient at high antioxidant concentrations, suggesting that protein-to-protein damage transfer and protein chain-oxidation may occur readily in biological systems.

A causative role for redox cycling of myoglobin and its inhibition by alkalinization in the pathogenesis and treatment of rhabdomyolysis-induced renal failure

Muscle injury (rhabdomyolysis) and subsequent deposition of myoglobin in the kidney causes renal vasoconstriction and renal failure. We tested the hypothesis that myoglobin induces oxidant injury to the kidney and the formation of F2-isoprostanes, potent renal vasoconstrictors formed during lipid peroxidation. In low density lipoprotein (LDL), myoglobin induced a 30-fold increase in the formation of F2-isoprostanes by a mechanism involving redox cycling between ferric and ferryl forms of myoglobin. In an animal model of rhabdomyolysis, urinary excretion of F2-isoprostanes increased by 7.3-fold compared with controls. Administration of alkali, a treatment for rhabdomyolysis, improved renal function and significantly reduced the urinary excretion of F2-isoprostanes by approximately 80%. EPR and UV spectroscopy demonstrated that myoglobin was deposited in the kidneys as the redox competent ferric myoglobin and that it's concentration was not decreased by alkalinization. Kinetic studies demonstrated that the reactivity of ferryl myoglobin, which is responsible for inducing lipid peroxidation, is markedly attenuated at alkaline pH. This was further supported by demonstrating that myoglobin-induced oxidation of LDL was inhibited at alkaline pH. These data strongly support a causative role for oxidative injury in the renal failure of rhabdomyolysis and suggest that the protective effect of alkalinization may be attributed to inhibition of myoglobin-induced lipid peroxidation.

Oxidation of adrenaline by ferrylmyoglobin

The oxidation of adrenaline by ferrylmyoglobin, the product formed by the oxidation of myoglobin with H2O2, was examined by absorption, fluorescence, and EPR spectroscopy in terms of the formation of intermediate free radicals and stable molecular products and the binding of adrenaline oxidation products to the apoprotein. The reaction of adrenaline with ferrylmyoglobin resulted in reduction of the hemoprotein to metmyoglobin and consumption of adrenaline. Quantification of metmyoglobin formed per adrenaline yielded a ratio of 1.66. The reaction was found first order on adrenaline concentration and second order on ferrylmyoglobin concentration. This, together with the above ratio, suggested a mechanism by which two oxoferryl moieties (ferrylmyoglobin) were reduced by adrenaline yielding metmyoglobin and the o-semiquinone state of adrenaline. The decay of the o-semiquinone to adrenochrome was confirmed by an increase in absorbance at 485 nm. The product was nonfluorescent; alkalinization of the reaction mixture resulted in a strong fluorescence at 540 nm ascribed to 3,5,6-trihydroxyindol or adrenolutin. Hence, adrenochrome and its alkali-catalyzed product, adrenolutin, are the major molecular products formed during the oxidation of adrenaline by ferrylmyoglobin. Semiquinones formed during the adrenaline/ferrylmyoglobin interaction were detected by EPR, spin stabilizing these species with Mg2+. The six-line EPR spectrum observed (aN=4.5 G, aN(CH3)=5.1, and a2H=0.91; g=2.0040) may be assigned to the semiquinone forms of adrenochrome and/or adrenolutin or a composite of these species. The intensity of the EPR signal increased with time and its subsequent decay followed a second-order kinetics as inferred by the proportionality of the square of the EPR line intensity with H2O2 concentration. Heme destruction and lysine loss, inherent in the reaction of metmyoglobin with H2O2, were prevented 80 and 34% by adrenaline, respectively. The low protection exerted by adrenaline against lysine loss was possibly due to the formation of Schiff bases between the epsilon-NH2 group of lysine and the o-quinone oxidation product(s) of adrenaline. The yield of Schiff base formation was 20-25%. The autoxidation of adrenaline at physiological pH is extremely slow or nonexistent. These data provide a rationale for the primary oxidation of adrenaline by the pseudoperoxidatic activity of ferrylmyoglobin and suggest implications of the free radicals thereby formed for the oxidative damage in reperfusion injury.

Nitric oxide protects cardiomyocytes against tert-butyl hydroperoxide-induced formation of alkoxyl and peroxyl radicals and peroxidation of phosphatidylserine

We studied protective effects of nitric oxide against tert-butyl hydroperoxide-induced oxidative damage to cardiac myocytes. Two distinct free radicals species--alkoxyl radicals associated with non-heme iron catalytic sites and myoglobin protein-centered peroxyl radicals--were found in low-temperature EPR spectra of cardiac myocytes exposed to t-BuOOH. The t-BuOOH-induced radical formation was accompanied by site-specific oxidative stress in membrane phospholipids (peroxidation of phosphatidylserine) assayed by fluorescence HPLC after metabolic labeling of cell phospholipids with oxidation-sensitive cis-parinaric acid. An NO-donor, (Z)-1-[N-(3-ammonio-propyl)-N-(n-propyl) amino]-diazen-1-ium-1,2-diolate], protected cardiac myocytes against tert-butyl hydroperoxide-induced: (i) formation of non-protein- and protein-centered free radical species and (ii) concomitant peroxidation of phosphatidylserine. Thus nitric oxide can act as an effective antioxidant in live cardiomyocytes.

Site-specific spin trapping of tyrosine radicals in the oxidation of metmyoglobin by hydrogen peroxide

The reaction between metmyoglobin and hydrogen peroxide produces both a ferryl-oxo heme and a globin-centred radical(s) from the two oxidizing equivalents of the hydrogen peroxide. Evidence has been presented for localization of the globin-centred radical on one tryptophan residue and tyrosines 103 and 151. When the spin-trapping agent 5,5-dimethyl-1-pyrroline N-oxide (DMPO) is included in the reaction mixture, a radical adduct has been detected, but the residue at which that adduct is formed has not been determined. Replacement of either tryptophans 7 and 14 or tyrosines 146 and 151 with phenylalanine has no effect on the formation of DMPO adduct in the reaction with hydrogen peroxide. When tyrosine 103 is replaced with phenylalanine, however, only DMPOX, a product of the oxidation of the spin-trap, is detected. Tyrosine-103 is, therefore, the site of radical adduct formation with DMPO. The spin trap 2-methyl-2-nitrosopropane (MNP), however, forms radical adducts with any recombinant sperm whale metmyoglobin that contains either tyrosine 103 or 151. Detailed spectral analysis of the DMPO and MNP radical adducts of isotopically substituted tyrosine radical yield complete structural determinations. The multiple sites of trapping support a model in which the unpaired electron density is spread over a number of residues in the population of metmyoglobin molecules, at least some of which are in equilibrium with each other.

Non-oxidative modification of low density lipoprotein by ruptured myocytes

In this study, the interaction of ruptured cardiac myocytes with low density lipoprotein (LDL) has been investigated and the consequent extent of uptake by macrophages. The results show that lysate released from ruptured myocytes is capable of inducing LDL oxidation and that the resulting modified form is recognised and degraded by macrophages. Peroxyl radical scavengers inhibit the LDL oxidation but not the macrophage uptake suggesting that LDL can be modified by mechanisms that are independent of oxidative processes by intracellular constituents of cardiac myocytes.

On the molecular mechanism of metmyoglobin-catalyzed reduction of hydrogen peroxide by ascorbate

Hydrogen peroxide induces rapid oxidation of metmyoglobin with an apparent second order rate constant, k1 = 3.4 x 10(4) M-1 min-1. The product of this interaction is ferrylmyoglobin with an unstable free radical on the globin moiety. This activated form of myoglobin is able: (a) to initiate the peroxidation of erythrocyte membranes and (b) to form intra- and intermolecular covalent crosslinkings. The presence of ascorbic acid in amounts stoichiometric to H2O2 efficiently prevents all the above processes. Moreover, in the presence of ascorbic acid a cyclic process is taking place leading to H2O2 reduction, ascorbic acid oxidation, and unmodified metmyoglobin formation (reaction 1).

Stimulation by nitroxides of catalase-like activity of hemeproteins. Kinetics and mechanism

The ability of stable nitroxide radicals to detoxify hypervalent heme proteins such as ferrylmyoglobin (MbFeIV) produced in the reaction of metmyoglobin (MbFeIII) and H2O2 was evaluated by monitoring O2 evolution, H2O2 depletion, and redox changes of the heme prosthetic group. The rate of H2O2 depletion and O2 evolution catalyzed by MbFeIII was enhanced by stable nitroxides such as 4-OH-2,2,6,6-tetramethyl-piperidinoxyl (TPL) in a catalytic fashion. The reduction of MbFeIV to MbFeIII was the rate-limiting step. Excess TPL over MbFeIII enhanced catalase-like activity more than 4-fold. During dismutation of H2O2, [TPL] and [MbFeIV] remained constant. NADH caused: (a) inhibition of H2O2 decay; (b) progressive reduction of TPL to its respective hydroxylamine TPL-H; and (c) arrest/inhibition of oxygen evolution or elicit consumption of O2. Following depletion of NADH the evolution of O2 resumed, and the initial concentration of TPL was restored. Kinetic analysis showed that two distinct forms of MbFeIV might be involved in the process. In summary, by shuttling between two oxidation states, namely nitroxide and oxoammonium cation, stable nitroxides enhance the catalase mimic activity of MbFeIII, thus facilitating H2O2 dismutation accompanied by O2 evolution and providing protection against hypervalent heme proteins.

Practical approaches to low density lipoprotein oxidation: whys, wherefores and pitfalls

The purpose of this review is to bring together the different approaches for studying the oxidation of low density lipoproteins and try to identify some critical factors which will permit greater comparability between laboratories. These issues are discussed both in terms of the variety of exogenous mediators of oxidation applied (transition metal ions, haem proteins, azo initiators, peroxynitrite, cells etc.) and their raisons d'être, as well as the methodologies (formation of conjugated dienes, hydroperoxides, decomposition products of lipid peroxidation, altered surface charge, macrophage uptake) applicable to the different stages of the oxidation and the factors underlying their accurate execution and interpretation.

L-Arginine infusion after ischaemia-reperfusion of rat kidney enhances lipid peroxidation

To assess the role of superoxide (O2-) and nitric oxide (NO) in ischaemic-reperfusion-induced acute renal failure, we investigated whether an activation of the L-arginine-NO pathway contributes to ischaemia-reperfusion-induced kidney membrane peroxidation by measurement of 4-hydroxynonenal (HNE) content in anaesthetized rats submitted to acute renal ischaemia. Following ischaemia-reperfusion injury, renal blood flow (RBF) was significantly reduced, while renal vascular resistance was significantly increased. Infusion of neither L-arginine nor D-arginine led to a recovery of RBF. L-Arginine, but not D-arginine, caused a significant increase in HNE accumulation in the ischaemic kidney. L-Arginine infusion enhanced the degree of lipid peroxidation afforded by ischaemia-reperfusion injury in the kidney suggesting that products of the endogenous L-arginine-NO pathway may react with O2- to initiate lipid peroxidation.

Antioxidant potential of intermediates in phenylpropanoid metabolism in higher plants

In this study the antioxidant activities of the hydroxycinnamic acids, chlorogenic, caffeic, ferulic and p-coumaric, have been investigated in peroxidising lipid systems mediated by metmyoglobin. The results show that the order of effectiveness in increasing the resistance of LDL to peroxidation, in protecting LDL cholesterol from oxidation and preventing the oxidative modification of the LDL apoprotein B100 is caffeic = chlorogenic > ferulic > p-coumaric acid. Assessment of the rates of reaction of the hydroxycinnamates with ferrylmyoglobin, a product of the reductive decomposition of lipid hydroperoxides, reveals that the compounds are more effective as peroxyl radical scavengers than reductants of ferryl myoglobin in peroxidising LDL systems mediated by haem proteins.

Self-peroxidation of metmyoglobin results in formation of an oxygen-reactive tryptophan-centered radical

In the reaction between hydrogen peroxide and metmyoglobin, the heme iron is oxidized to its ferryl-oxo form and the globin to protein radicals, at least one of which reacts with dioxygen to form a peroxyl radical. To identify the residue(s) that forms the oxygen-reactive radical, we utilized electron spin resonance (ESR) spectroscopy and the spin traps 2-methyl-2-nitrosopropane and 3,5-dibromo-4-nitrosobenzenesulfonic acid (DB-NBS). Metmyoglobin radical adducts had spectra typical of immobilized nitroxides that provided little structural information, but subsequent nonspecific protease treatment resulted in the detection of isotropic three-line spectra, indicative of a radical adduct centered on a tertiary carbon with no bonds to nitrogen or hydrogen. Similar isotropic three-line ESR spectra were obtained by spin trapping the oxidation product of tryptophan reacting with catalytic metmyoglobin and hydrogen peroxide. High resolution ESR spectra of DBNBS/.trp and of the protease-treated DBNBS/.metMb were simulated using superhyperfine coupling to a nitrogen and three non-equivalent hydrogens, consistent with a radical adduct formed at C-3 of the indole ring. Oxidation of tryptophan by catalytic metMb and hydrogen peroxide resulted in spin trap-inhibitable oxygen consumption, consistent with formation of a peroxyl radical. The above results support self-peroxidation of a tryptophan residue in the reaction between metMb and hydrogen peroxide.

The reactivity of thiol compounds with different redox states of leghaemoglobin: evidence for competing reduction and addition pathways

Reaction of the ferric form of leghaemoglobin with hydrogen peroxide has been previously shown to give rise to an iron(IV)-oxo (ferryl) species, and a protein radical. Inclusion of a variety of thiol compounds in this system is shown to lead to rapid loss of the iron(IV)-oxo species and the regeneration of the ferric form and/or the formation of novel sulf species formed by nucleophilic attack of the thiol group on the tetrapyrrole ring. The reduction process also results in the generation of thiyl radicals which have been detected by EPR spin trapping. The relative yields of the products produced by these two competing pathways is shown to be highly dependent on the steric and electronic characteristics of the thiol compound. Evidence has also been obtained, in the absence of hydrogen peroxide, for both the reduction of the ferric form of the protein to the oxy-ferrous form, via a process believed to involve the deoxy-ferrous species, and the formation of sulf-leghaemoglobin species. Both of these pathways are again highly dependent on the structure of the thiol, and the former also results in the generation of thiyl radicals. Inclusion of the sulfide anion in place of the organic thiols results in somewhat different behaviour, in that this species appears to both reduce the iron centre and form a complex with the iron atom. This ligation process is reversible, and the sulfide complex is shown to react readily with both strong oxidizing and reducing agents. The behaviour of this protein, which is structurally related to myoglobin, is dramatically different to that demonstrated by myoglobin; this is rationalized in terms of the much more open heme site of leghaemoglobins, and the presence of an electronic gate which hinders access by negatively charged molecules. The contribution of these processes to the maintenance of the leghaemoglobin proteins in the oxy-ferrous form in vivo and the binding of oxygen is discussed.

Promotion of oxidative damage to arachidonic acid and alpha 1-antiproteinase by anti-inflammatory drugs in the presence of the haem proteins myoglobin and cytochrome C

A mixture of myoglobin and hydrogen peroxide (H2O2) causes peroxidation of arachidonic acid. This peroxidation is greatly accelerated by adding phenylbutazone, which is effective even in the absence of H2O2. A wide range of other drugs was examined for their ability to exert similar pro-oxidant effects. We found that meclofenamic acid and flufenamic acid stimulated myoglobin-dependent lipid peroxidation, but only in the presence of H2O2. Ascorbic acid inhibited peroxidation both in the presence and in the absence of these drugs. Phenylbutazone, meclofenamic acid and flufenamic acid could also cause damage to proteins (as measured by inactivation of alpha 1-antiproteinase) in the presence of myoglobin and H2O2. The mitochondrial protein cytochrome c can also stimulate lipid peroxidation in the presence of H2O2. Phenylbutazone and meclofenamic acid, but not flufenamic acid, enhanced the peroxidation, which was again inhibited by ascorbic acid. However, only phenylbutazone caused inactivation of alpha 1-antiproteinase in the presence of cytochrome c and H2O2. Since respiring mitochondria generate superoxide radicals and H2O2, catalysis of lipid peroxidation and of the formation of drug-derived radicals by cytochrome c could be a mechanism contributing to mitochondrial damage by drugs.

Reactivity of metmyoglobin towards phospholipid hydroperoxides

Ferrylmyoglobin, the high oxidation state of myoglobin analogous to compound II of peroxidases, promotes the peroxidation of palmitoyl-linoleyl-phosphatidylcholine (PLPC) large unilamellar vesicles. This was associated with oxygen consumption and a slow conversion of ferrylmyoglobin to metmyoglobin. The time course of oxygen consumption was characterized by the occurrence of a lag phase, which could be overcome by the addition of sodium deoxycholate to the reaction mixture. The rate of conversion of ferrylmyoglobin to metmyoglobin was slower than that of oxygen consumption, and there was not stoichiometric correlation between both events. These findings suggest that the observed oxygen consumption linked to lipid peroxidation is supported by a peroxidatic activity encompassed by the ferrylmyoglobin<==>metmyoglobin transition as well as free radical propagation reactions. Incubation of metmyoglobin with PLPC vesicles containing 3% hydroperoxide resulted in oxygen consumption, the time course of which was devoid of the lag phase observed with hydroperoxide-free unilamellar lipid vesicles. The incubation of metmyoglobin with peroxide-containing PLPC vesicles or with equimolar amounts of lipid hydroperoxide was not associated with Soret or visible absorption spectral changes of metmyoglobin, which could be ascribed to its conversion to ferrylmyoglobin. Treatment of the metmyoglobin/lipid hydroperoxide mixtures with Na2S did not lead to the formation of the sulfheme protein derivative, which can be considered as a fingerprint for the occurrence of ferrylmyoglobin.(ABSTRACT TRUNCATED AT 250 WORDS)

A hydrogen-donating monohydroxamate scavenges ferryl myoglobin radicals

The addition of 25 microM hydrogen peroxide to 20 microM metmyoglobin produces ferryl (FeIV = O) myoglobin. Optical spectroscopy shows that the ferryl species reaches a maximum concentration (60-70% of total haem) after 10 minutes and decays slowly (hours). Low temperature EPR spectroscopy of the high spin metmyoglobin (g = 6) signal is consistent with these findings. At this low peroxide concentration there is no evidence for iron release from the haem. At least two free radicals are detectable by EPR immediately after H2O2 addition, but decay completely after ten minutes. However, a longer-lived radical is observed at lower concentrations that is still present after 90 minutes. The monohydroxamate N-methylbutyro-hydroxamic acid (NMBH) increases the rate of decay of the fenyl species. In the presence of NMBH, none of the protein-bound free radicals are detectable; instead nitroxide radicals produced by oxidation of the hydroxamate group are observed. Similar results are observed with the trihydroxamate, desferrioxamine. "Ferryl myoglobin" is still able to initiate lipid peroxidation even after the short-lived protein free radicals are no longer detectable (E.S.R. Newman, C.A. Rice-Evans and M.J. Davies (1991) Biochemical and Biophysical Research Communications 179, 1414-1419). It is suggested that the longer-lived protein radicals described here may be partly responsible for this effect. The mechanism of inhibition of initiation of lipid peroxidation by hydroxyamate drugs, such as NMBH, may therefore be due to reduction of the protein-derived radicals, rather than reduction of ferryl haem.

Lipoic and dihydrolipoic acids as antioxidants. A critical evaluation

A detailed evaluation of the antioxidant and pro-oxidant properties of lipoic acid (LA) and dihydrolipoic acid (DHLA) was performed. Both compounds are powerful scavengers of hypochlorous acid, able to protect alpha 1-antiproteinase against inactivation by HOCl. LA was a powerful scavenger of hydroxyl radicals (OH.) and could inhibit both iron-dependent OH. generation and peroxidation of ox-brain phospholipid liposomes in the presence of FeCl3-ascorbate, presumably by binding iron ions and rendering them redox-inactive. By contrast, DHLA accelerated iron-dependent OH. generation and lipid peroxidation, probably by reducing Fe3+ to Fe2+. LA inhibited this pro-oxidant action of DHLA. However, DHLA did not accelerate DNA degradation by a ferric bleomycin complex and slightly inhibited peroxidation of arachidonic acid by the myoglobin-H2O2 system. Under certain circumstances, DHLA accelerated the loss of activity of alpha-antiproteinase exposed to ionizing radiation under a N2O/O2 atmosphere and also the loss of creatine kinase activity in human plasma exposed to gas-phase cigarette smoke. Neither LA nor DHLA reacted with superoxide radical (O.2-) or H2O2 at significant rates, but both were good scavengers of trichloromethylperoxyl radical (CCl3O2.). We conclude that LA and DHLA have powerful antioxidant properties. However, DHLA can also exert pro-oxidant properties, both by its iron ion-reducing ability and probably by its ability to generate reactive sulphur-containing radicals that can damage certain proteins, such as alpha 1-antiproteinase and creatine kinase.

Ferrylmyoglobin formation induced by acute magnesium deficiency in perfused rat heart causes cardiac failure

The oxidation states of intracellular myoglobin and cytochrome oxidase aa3 were monitored by reflectance spectrophotometry in isolated perfused rat hearts subjected to an acutely magnesium deficient environment. After exposure to low extracellular [Mg2+]o (i.e., 0.3 mM) for 30 min, more than 80% of the oxymyoglobin converted to its deoxygenated form. The level of reduced cytochrome oxidase aa3 also increased about 80% in low [Mg2+]o. The deoxymyoglobin was converted further to a species identified as ferrylmyoglobin by its reaction with Na2S to form ferrous sulfmyoglobin which was optically visible. This process, set into motion by acute Mg deficiency, resulted from a direct accessibility of the exogenous peroxide to the cytosolic protein. The results suggest that a pathway leading to cardiac tissue damage, induced by magnesium deficiency, is probably involved in the generation of a ferrylmyoglobin radical which could be prevented by addition of ascorbate, which is known to be a one-electron reductant of this hypervalent form of myoglobin. In further studies, we also investigated whether addition of different concentrations of ascorbic acid (AA) to the perfusate could enhance myocardial function after exposure to low [Mg2+]o perfusion. Four concentrations of AA (0.5, 1, 5, 10 mM) were tested, and the results indicate that they exert their effects in a concentration-dependent manner; 1 mM AA was the most effective dose in improving aortic output in a Mg-deficient heart. Ferrylmyoglobin formation was found to be formed considerably before intracellular release of either creatine phosphokinase or lactic dehydrogenase. These studies may have wide implications as a new mechanism by which low extracellular Mg2+ can induce myocardial injury and subsequent cardiac failure.

Free radical production by activated haem proteins: protective effect of coenzyme Q

The interaction of hydrogen peroxide with haem proteins leads readily to the formation of myoglobin and/or haemoglobin higher oxidation states (MbIV and/or HbIV), which are capable of promoting the oxidation of cellular costituents and are probably to blame for myocardic tissue damage in ischaemia/reperfusion. This study supports the evidence that the reduced form of Coenzyme Q, like other reducing agents, has an antioxidant activity exerted through the progressive reduction of ferryl forms (MbIV and/or HbIV) back to met and oxy forms (Mb and/or HbIIO2). Furthermore, the strong inactivation afforded by ferryl states of myoglobin on several enzymes, especially creatine kinase (CK), can be prevented by the addition of ubiquinol which protects the enzyme from the oxidative modifications. The ability of ubiquinol to recycle ferryl states of haem proteins provides a novel antioxidant mechanism for Coenzyme Q, besides its direct or indirect antiperoxidative activity, and may represent an important defense mechanism against oxidative tissue injury.