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PubMed2003

The role of iron and the factors affecting off-color development of polyphenols.

Iron deficiency affects over two billion people worldwide (Lotfi, M.; Venkatesh Mannar, M. G.; Merx, R. J.; Naber-van den Heuvel, P. Micronutrient Fortification of Foods: Current Practices, Research,and Opportunities; Micronutrient Initiative: Ottawa, Ontario, Canada, 1996). However, fortifying foods with highly bioavailable iron is technically challenging because of off-color and off-flavor development, catalytic degradation of vitamins, and oxidation of lipids. The role of highly bioavailable iron in the off-color development of foods and beverages is not well-understood. The goal of this research was to examine the interaction of iron with simple phenolics and polyphenols. Factors that may affect off-color development, such as pH, oxygen, temperature, and reducing and chelating agents, were evaluated as a model for food products. Our results demonstrated that the iron that reacts with the simple phenolic, catechol, to develop off-color must be in the oxidized state, and the iron is reduced in the presence of catechol. Because this is an oxidation/reduction reaction, the redox potential of all of the components is critical to the color development. Ferrous iron sources with low redox potentials and ferric iron sources with high redox potentials caused off-color development with catechol. Only polyphenols that contain ortho-hydroxyl groups cause off-color development with iron. All of the factors tested affect off-color development and redox potential of the system. Low pH, low oxygen, high temperature, and the presence of reducing and chelating agents inhibited off-color development. To confirm the model, foods that contained these polyphenols were evaluated for off-color development when iron was added. The foods tested reacted similarly to the models of polyphenols with iron. Off-color development was caused by oxidation-reduction interactions between ferric iron and polyphenols that contained ortho-dihydroxyl groups. Ferrous iron needed to be oxidized to participate in off-color development. In addition, methods identified in the models to prevent off-color development were effective in most of the food products examined. Using the ferrous form of iron and maintaining it in its reduced form by lowering pH, removing oxygen, and including reducing agents, it was possible to fortify foods with highly bioavailable iron.

Catechols↗
PubMed2002

Dications of fluorenylidenes. Relationship between electrochemical oxidation potentials and antiaromaticity in diphenyl-substituted fluorenyl cations.

The antiaromaticity of a series of dications of p-substituted diphenylmethylidene fluorenes was explored using three criteria attributed to aromaticity/antiaromaticity. The relative stability of the dications (energetic criterion) was measured via the redox potentials obtained by electrochemical oxidation under very fast sweep rates with microelectrodes. Comparison of redox potentials with those of a model system, p-substituted tetraphenylethylenes, shows relatively small destabilization of the potentially antiaromatic fluorenylidene dication. However, the amount of destabilization is comparable with the limited electrochemical data available for other antiaromatic systems. Nucleus independent chemical shifts (NICS) were calculated for these dications (magnetic criterion) and indicated their antiaromaticity. A good linear relationship between experimental and calculated (B3LYP/6-31G(d)) (1)H and (13)C NMR shifts for the three dications, 3c, 3e, and 3f, for which NMR data has been reported, validated the accuracy of the NICS values. Bond length alternation/elongation (structural criterion) was explored via the harmonic oscillator model of aromaticity (HOMA) using the geometries calculated with density functional theory, but there was insufficient variation to evaluate relative antiaromaticity. In addition, the presence of benzannulation appears to restrict bond length alternation to such an extent that the magnitude of the HOMA index is of little use in evaluating the antiaromaticity of many polycyclic hydrocarbons. Both NICS values and redox potentials for formation of the dication in these systems show a strong linear correlation with sigma(p)(+) values, with the more antiaromatic fluorenylidene dication possessing the more electron-withdrawing substituent. The correlation between NICS values and redox potentials is also good, as might be expected, suggesting a strong relationship between magnetic and energetic characteristics of antiaromaticity. However, magnetic characteristics appear to be a more sensitive probe than energetic characteristics evaluated through redox potentials or structural characteristics evaluated through HOMA calculations.

Journal Article↗
PubMed2000

NADH/NAD redox state of cytoplasmic glycolytic compartments in vascular smooth muscle.

The cytoplasmic NADH/NAD redox potential affects energy metabolism and contractile reactivity of vascular smooth muscle. NADH/NAD redox state in the cytosol is predominately determined by glycolysis, which in smooth muscle is separated into two functionally independent cytoplasmic compartments, one of which fuels the activity of Na(+)-K(+)-ATPase. We examined the effect of varying the glycolytic compartments on cystosolic NADH/NAD redox state. Inhibition of Na(+)-K(+)-ATPase by 10 microM ouabain resulted in decreased glycolysis and lactate production. Despite this, intracellular concentrations of the glycolytic metabolite redox couples of lactate/pyruvate and glycerol-3-phosphate/dihydroxyacetone phosphate (thus NADH/NAD) and the cytoplasmic redox state were unchanged. The constant concentration of the metabolite redox couples and redox potential was attributed to 1) decreased efflux of lactate and pyruvate due to decreased activity of monocarboxylate B-H(+) transporter secondary to decreased availability of H(+) for cotransport and 2) increased uptake of lactate (and perhaps pyruvate) from the extracellular space, probably mediated by the monocarboxylate-H(+) transporter, which was specifically linked to reduced activity of Na(+)-K(+)-ATPase. We concluded that redox potentials of the two glycolytic compartments of the cytosol maintain equilibrium and that the cytoplasmic NADH/NAD redox potential remains constant in the steady state despite varying glycolytic flux in the cytosolic compartment for Na(+)-K(+)-ATPase.

Animals↗
PubMed1991

Functional modulation of ANF-sensitive particulate guanylate cyclase by redox mechanisms.

We examined the effects of sulfhydryl-reactive redox agents and of the apparent oxidation-reduction (redox) potential of the assay medium on enzyme activity and atrial natriuretic factor (ANF) binding properties of particular guanylate cyclase from bovine adrenal cortex. Redox potential was varied by addition of redox-reactive agents and quantified by electrochemical measurement. The modification of free SH groups by thiol-reactive agents had only a minor effect on ANF binding or on the extent of ANF-dependent enzyme stimulation whereas free thiol groups were essential for basal enzyme activity of ANF-sensitive particulate guanylate cyclase. Basal and ANF-stimulated particulate guanylate cyclase activity was modulated by exposure to different redox potential states. This modulation was different for the substrates Mg.GTP and Mn.GTP. The apparent redox potential had no influence on the extent of guanylate cyclase activation by ANF. Our results suggest that critical free thiol groups, which are sensitive to thiol-reactive redox agents, are involved in the catalytic, but not in the receptor function of ANF-sensitive particulate guanylate cyclase. These thiol groups could be the structural basis for the effects of redox events which modulate basal enzyme activity, but not activation by ANF.

Adrenal Cortex↗
PubMed1996

Regulation of the redox order of four hemes by pH in cytochrome c3 from D. vulgaris Miyazaki F.

The assignment of 1H-NMR signals of the heme methyl and propionate groups of cytochrome c3 of D. vulgaris Miyazaki F was performed. The heme assignment was revised for hemes 2 and 3 (sequential heme numbering). Namely, heme 4 is mainly reduced at first with hemes 1, 2 and 3 following it in this order. The p2H titration of heme methyl signals in four macroscopic oxidation states was performed in the p2H range of 5.2 to 9.0. While the heme methyl resonances in the fully oxidized state showed just small changes with p2H, most resonances in the intermediate oxidation states revealed clear p2H dependence. In particular, the methyl resonances of heme 1 shifted significantly in the acidic region. Then, the chemical shifts of beta-CH2 (next to the carboxyl group) of all propionate groups in the fully oxidized state were observed at various p2H in the range of 4.5 to 9.0. Only the propionate group at C-13 (IUPAC-IUB nomenclature) of heme 1 showed a clear change in this p2H range, its titration curve being similar to those of the methyl resonances of heme 1 in the intermediate oxidation states. pKa of the propionate group was 5.95 +/- 0.05. Analysis of the microscopic formal redox potentials was carried out for the observations at p2H 5.2, 7.1 and 9.0. The redox potentials of heme 1 showed the most remarkable p2H dependence, resulting in the change of the order of the redox potentials of four hemes. A significant change was also found in the interacting potential between hemes 1 and 2. In the light of the p2H-titration experiments, the propionate at C-13 of heme 1 was identified as the most plausible ionizable group responsible for the p2H dependence of microscopic redox potentials of heme 1 in the acidic region.

Cytochrome c Group↗
PubMed2005

Electrochemical characterisation of the human cytochrome P450 CYP2C9.

The electrochemistry of human cytochrome P4502C9 (CYP2C9) was characterised using purified His-tagged enzyme. The His-tagged enzyme was shown to have similar functional characteristics to native CYP2C9 heterologously expressed in Escherichia coli and to the CYP2C9 activity of human liver microsomes. Evidence was observed for a reversible one-electron transfer between the P450 heme and the electrode. Both pH and ionic strength influenced the electrochemical behaviour of CYP2C9. A range of substrates was investigated to determine the effect of the heme-substrate interaction on CYP2C9 redox potential. In the absence of oxygen, tolbutamide, diclofenac, warfarin and sulfaphenazole did not alter the redox potential of the iron heme. In contrast, torsemide, carbon monoxide and oxygen led to an anodic shift in redox potential. These results suggest alternative mechanisms by which CYP2C9 (and by inference other P450 enzymes) may alter redox potential to facilitate electron delivery from physiological donors.

Aryl Hydrocarbon Hydroxylases↗
PubMed2004

Separation of heavy metals from water solutions at the laboratory scale.

Separation of heavy metals from water may be done by sulphide precipitation. In order to make the metal sulphides more valuable for reuse, they should be as pure as possible. To separate the metals from each other during the precipitation process different parameters as pH, sulphide concentration and redox potential may be controlled. Adjustment of the redox potential to specific values results in separation of copper from cadmium even at the same pH. In the copper precipitation step 98.7 +/- 0.5% was precipitated and the remaining part was transferred to the cadmium precipitation step where 0.7 +/- 0.5% of the copper precipitated. The main part of cadmium (95.6 +/- 1.3%) was precipitated in the second step. These results show that it is possible to separate copper from cadmium by the use of redox potential control.

Cadmium↗
PubMed2005

Cytochrome c and bioenergetic hypothetical model for alkaliphilic Bacillus spp.

Although a bioenergetic parameter is unfavorable for production of ATP (DeltapH<0), the growth rate and yield of alkaliphilic Bacillus strains are higher than those of neutralophilic Bacillus subtilis. This finding suggests that alkaliphiles possess a unique energy-producing machinery taking advantage of the alkaline environment. Expected bioenergetic parameters for the production of ATP (DeltapH and DeltaPsi) do not reflect the actual parameters for energy production. Certain strains of alkaliphilic Bacillus spp. possess large amounts of cytochrome c when grown at a high pH. The growth rate and yield are higher at pH 10 than at pH 7 in facultative alkaliphiles. These findings suggest that a large amount of cytochrome c at high pHs (e.g., pH 10) may be advantageous for sustaining growth. To date, isolated cytochromes c of alkaliphiles have a very low midpoint redox potential (less than +100 mV) compared with those of neutralophiles (approximately +220 mV). On the other hand, the redox potential of the electron acceptor from cytochrome c, that is, cytochrome c oxidase, seems to be normal (redox potential of cytochrome a=+250 mV). This large difference in midpoint redox potential between cytochrome c and cytochrome a concomitant with the configuration (e.g., a larger negative ion capacity at the inner surface membrane than at the outer surface for the attraction of H+ to the intracellular membrane and a large amount of cyrochrome c) supporting H+-coupled electron transfer of cytochrome c may have an important meaning in the adaptation of alkaliphiles at high pHs. This respiratory system includes a more rapid and efficient H+ and e- flow across the membrane in alkaliphiles than in neutralophiles.

Bacillus↗
PubMed1984

Variation of transition-state structure as a function of the nucleotide in reactions catalyzed by dehydrogenases. 2. Formate dehydrogenase.

Since hydride transfer is completely rate limiting for yeast formate dehydrogenase [Blanchard, J.S., & Cleland, W. W. (1980) Biochemistry 19, 3543], the intrinsic isotope effects on this reaction are fully expressed. Primary deuterium, 13C, and 18O isotope effects in formate and the alpha-secondary deuterium isotope effect at C-4 of the nucleotide have been measured for nucleotide substrates with redox potentials varying from -0.320 (NAD) to -0.258 V (acetylpyridine-NAD). As the redox potential gets more positive, the primary deuterium isotope effect increases from 2.2 to 3.1, the primary 13C isotope effect decreases from 1.042 to 1.036, the alpha-secondary deuterium isotope effect drops from 1.23 to 1.06, and Vmax decreases. The 18O isotope effects increase from 1.005 to 1.008 per single 18O substitution in formate (these values are dominated by the normal isotope effect on the dehydration of formate during binding; pyridinealdehyde-NAD gives an inverse value, possibly because it is not fully dehydrated during binding). These isotope effects suggest a progression toward earlier transition states as the redox potential of the nucleotide becomes more positive, with NAD having a late and acetyl-pyridine-NAD a nearly symmetrical transition state. By contrast, the I2 oxidation of formate in dimethyl sulfoxide has a very early transition state (13k = 1.0154; Dk = 2.2; 18k = 0.9938), which becomes later as the proportion of water in the solvent increases (13k = 1.0265 in 40% dimethyl sulfoxide and 1.0362 in water). alpha-secondary deuterium isotope effects with formate dehydrogenase are decreased halfway to the equilibrium isotope effect when deuterated formate is the substrate, showing that the bending motion of the secondary hydrogen is coupled to hydride transfer in the transition state and that tunneling of the two hydrogens is involved. The 15N isotope effect of 1.07 for NAD labeled at N-1 of the nicotinamide ring suggests that N-1 becomes pyramidal during the reaction. 18O fractionation factors for formate ion relative to aqueous solution are 1.0016 in sodium formate crystal, 1.0042 bound to Dowex-1, and 1.0040 as an ion pair (probably hydrated) in CHCl3. The CO2 analogue azide binds about 10(4) times better than the formate analogue nitrate to enzyme-nucleotide complexes (even though the Ki values for both and the affinity for formate vary by 2 orders of magnitude among the various nucleotides), but the ratio is not sensitive to the redox potential of the nucleotide. Thus, not the nature of the transition state but rather the shape of the initial binding pocket for formate is determining the relative affinity.(ABSTRACT TRUNCATED AT 400 WORDS)

Aldehyde Oxidoreductases↗
PubMed1981

The potential span of photoredox reactions of porphyrins and chlorophyll at the lipid bilayer-water interface.

Lipid bilayers containing chlorophyll (Chl) or magnesium octaethylporphyrin (MgOEP) and separating solutions containing varying amounts of differing acceptors are illuminated by a dye laser pulse (FWHM 0.3 microseconds) at 590 mm. Interfacial charge transfer is measured at the first current peak in a voltage clamp circuit. The constants describing the hyperbolic saturations of the charge transferred by differing acceptors are only weakly related to the redox potential of the acceptors. An assymetric molecule, anthraquinone-2-sulfonate, is over 20 times as effective in accepting the electron as is the symmetrical anthraquinone-2,6-disulfonate. In contrast to this variable effectiveness, the maximum amount of charge transferred as a function of acceptor redox potential is constant up to a cut-off value: -0.6 V (vs. standard hydrogen electrode) for MgOEP and -0.5 V for Chl. The reversible redox potential of MgOEP in the bilayer was determined by following both the decrease in photoactivity and the transmembrane potential as a function of aqueous redox potential. It is +0.77 V for MgOEP and approximately 0.7 V for Chl (limited by stability). Thus, a total of 1.4 V of reversible redox potential (free energy) is obtained from 1.8 eV (internal energy) of the triplet excited state of MgOEP.

Chlorophyll↗
PubMed1990

Rapid reduction of iron in horse spleen ferritin by thioglycolic acid measured by dispersive X-ray absorption spectroscopy.

The release of iron from ferritin is important in the formation of iron proteins and for the management of diseases in both animals and plants associated with abnormal accumulations of ferritin iron. Much more iron can be released experimentally by reduction of the ferric hydrous oxide core than by chelation of Fe3+ which has led to the notion that reduction is also the major aspect of iron release in vivo. Variations in the kinetics of reduction of the mineral core of ferritin have been attributed to the redox potential of the reductant, redox properties of the iron core, the structure of the protein coat, the analytical method used to detect Fe2+ and reactions at the surface of the mineral. Direct measurements of the oxidation state of the iron during reduction has never been used to analyze the kinetics of reduction, although Mössbauer spectroscopy has been used to confirm the extent of reduction after electrochemical reduction using dispersive X-ray absorption spectroscopy (DXAS). We show that the near edge of X-ray absorption spectra (XANES) can be used to quantify the relative amounts of Fe2+ and Fe3+ in mixtures of the hydrated ions. Since the nearest neighbors of iron in the ferritin iron core do not change during reduction, XANES can be used to monitor directly the reduction of the ferritin iron core. Previous studies of iron core reduction which measured by Fe2+.bipyridyl formation, or coulometric reduction with different mediators, suggested that rates depended mainly on the redox potential of the electron donor.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Correlation of metal ion toxicities to mice.

Recently reported correlations of acute ip LD50 metal ion toxicities to mice by Turner et al. (1983), have been re-investigated using the ion-specific parameters reported by Kaiser (1980) for sublethal metal ion toxicities to Daphnia magna. For the 15 ions with partially or completely filled d-shells, Rh(III), Fe(III), Cr(III), Mn(II), Co(II), Pd(II), Ni(II), Au(III), Zn(II), Pt(II), Ag(I), Cu(II), In(III), Hg(II), and Cd(II), a correlation coefficient of r2 = 0.76 is found. This is a significant improvement over the value of r2 = 0.36 observed for the 14 divalent metal ions by Turner et al. with the softness parameter sigma as the independent variable. This re-investigation proves the applicability of the ionization potential and redox potential derived parameters for the quantitative correlation of metal ion toxicities to both aquatic and terrestrial biota.

Animals↗
PubMed2000

Electrochemical studies of corrphycenes and metallocorrphycenes.

Corrphycene 3 (Cn) is a structural isomer of porphyrin 1 that was synthesized for the first time 5 years ago. This paper reports on the redox properties of free-base octaethylcorrphycene H2OECn and 16 metal complexes derived therefrom. In CH2Cl2 solution, the free base and the metallo(II) octaethylcorrphycenes, M(II)OECn, typically undergo four distinct one-electron redox steps involving the tetrapyrrolic macrocycle, of which two are reduction steps and two are oxidations. One exception to this general pattern is displayed by the Co(II)OECn complex. In this instance, the first one-electron reduction is metal-centered and produces Co(I)OECn. A comparison of the redox potentials of corrphycenes with those of porphyrins and porphycenes indicates that the first reduction potentials of the free base and of the metallo-octaethylcorrphycenes are between those of the porphycenes-the easiest to reduce molecules in this set of isomeric tetrapyrrolic systems-and those of the porphyrins. The oxidation potentials of corrphycenes and porphyrins are found to be quite similar. On the other hand, porphycenes are oxidized at less positive potentials. The redox gap deltaE1/2 = E1/2Ox1 - E1/2Red1 is equal to 2.15 +/- 0.08 V for the free base corrphycene and the various metallocorrphycenes that were subjected to study. This redox gap is not much different from that observed in porphyrins (deltaE1/2 = 2.25 +/- 0.1 V), whereas if differs significantly from that observed in porphycenes (deltaE1/2 = 1.85 +/- 0.15 V). The sequence of these deltaE1/2 values parallels the lowest energy absorption maxima observed in the UV-vis spectra of these three isomers.

Journal Article↗
PubMed2006

Studies on photoinduced H-atom and electron transfer reactions of o-naphthoquinones by laser flash photolysis.

The quenching of the triplets of 1,2-naphthoquinone (NQ) and 1,2-naphthoquinone-4-sulfonic acid sodium salt (NQS) by various electron and H-atom donors was investigated by laser flash photolysis measurement in acetonitrile and benzene. The results showed that the reactivities and configurations of 3NQ* (3NQS*) are governed by solvent polarity. All the quenching rate constants (kq) measured in benzene are larger than those in acetonitrile. The SO3Na substituent at the C-4 position of NQS makes 3NQS* more reactive than 3NQ* in electron/H-atom transfer reactions. Large differences of kq values were discovered in H-atom transfer reactions for alcohols and phenols, which can be explained by different H-abstraction mechanisms. Detection of radical cations of amines/anilines in time-resolved transient absorption spectra confirms an electron transfer mechanism. Triplets are identified as precursors of formed radical anions of NQ and NQS in photoinduced reactions. The dependence of electron transfer rate constants on the free energy changes (DeltaG) was treated by using the Rehm-Weller equation. For the four anilines with different substituents on the para or meta position of amidocyanogen, good correlation between log kq values with Hammett sigma constants testifies the correctness of empirical Hammett equation. Charge density distributions, adiabatic ionization/affinity potentials and redox potentials of NQ (NQS) and some quenchers were studied by quantum chemistry calculation.

Electrons↗
PubMed1981

Thermodynamic and electron paramagnetic resonance characterization of flavin in succinate dehydrogenase.

Thermodynamic parameters of succinate dehydrogenase flavin were determined potentiometrically from the analysis of free radical signal levels as a function of the oxidation-reduction potential. Midpoint redox potentials of consecutive 1-electron transfer steps are -127 and -31 mV at pH 7.0. This corresponds to a stability constant of intermediate stability, 2.5 x 10(-2), which suggests flavin itself may be a converter from n = 2 to n = 1 electron transfer steps. The pK values of the free radical (FlH . in equilibrium Fl . -) and the fully reduced form (FlH2 in equilibrium FlH-) were estimated as 8.0 +/- 0.2 and 7.7 +/- 0.2, respectively. Succinate dehydrogenase flavosemiquinone elicits an EPR spectrum at g = 2.00 with a peak to peak width of 1.2 mT even in the protonated form, suggesting the delocalization in the unpaired electron density. A close proximity of succinate dehydrogenase flavin and iron-sulfur cluster S-1 was demonstrated based on the enhancement of flavin spin relaxation by Center S-1.

Anaerobiosis↗
PubMed1979

[Reaction of the cerebral cortical neurons to complete ischemia].

Changes of morphological and neurophysiological characteristics of pyramidal neurons in response to complete ischemia have been studied by means of vital microscopy of cat and rabbit cortex neurons in addition to some other cytological methods. These responses were found to be complex involving phasic changes in the neuron size, membrane potential and redox potential. Neurons of particular types responded to normo- and hypothermic ischemia differently. Pyramidal neurons retained their vital ability for the whole prolonged period of the complete ischemia (up to 40--60 min).

Animals↗
PubMed1991

Oxidation-reduction properties of trimethylamine dehydrogenase: effect of inhibitor binding.

The redox potentials of trimethylamine dehydrogenase from the bacterium W3A1 have been determined by means of uv-visible spectroelectrochemistry. In the presence of the inhibitor tetramethylammonium chloride a shift of +0.2 V was observed in the midpoint redox potential for conversion of the oxidized 6-S-cysteinyl-FMN to the flavin radical form. The pH-independent value was +0.23 V vs the standard hydrogen electrode. The pH-dependent conversion of this radical to fully reduced flavin was shifted negative by 0.1 V in the presence of the inhibitor to -0.05 V at pH 7.0 and -0.15 V at pH 8.4. Tetramethylammonium chloride also caused moderate negative shifts (0.03-0.05 V) in the midpoint redox potential for the Fe4S(+2)4/Fe4S(+1)4 couple of trimethylamine dehydrogenase. The midpoint potentials are +0.06 V at pH 7.0 and +0.04 V at pH 8.4. Therefore, in the presence of tetramethylammonium chloride, electron transfer from the flavin radical to the Fe4S(+2)4 group is energetically unfavorable and trimethylamine dehydrogenase is trapped in the flavin radical state. The redox potential changes provide a thermodynamic basis for inhibition by tetramethylammonium chloride. Spectroelectrochemical titrations of trimethylamine dehydrogenase which had been inactivated by phenylhydrazine revealed heterogeneity in the redox behavior which had not been observed in other laboratories. The reason for this heterogeneity was not determined, but the midpoint redox potential for the Fe4S(+2)4/Fe4S(+1)4 couple of the main fraction of the inactivated enzyme was the same as that of active trimethylamine dehydrogenase.

Bacteria↗
PubMed2004

Effects of hyperbaric oxygen therapy on cerebral oxygenation and mitochondrial function following moderate lateral fluid-percussion injury in rats.

OBJECT: In the current study, the authors examined the effects of hyperbaric O2 (HBO) following fluid-percussion brain injury and its implications on brain tissue oxygenation (PO2) and O2 consumption (VO2) and mitochondrial function (redox potential). METHODS: Cerebral tissue PO2 was measured following induction of a lateral fluid-percussion brain injury in rats. Hyperbaric O2 treatment (100% O2 at 1.5 ata) significantly increased brain tissue PO2 in both injured and sham-injured animals. For VO2 and redox potential experiments, animals were treated using 30% O2 or HBO therapy for 1 or 4 hours (that is, 4 hours 30% O2 or 1 hour HBO and 3 hours 100% O2). Microrespirometer measurements of VO2 demonstrated significant increases following HBO treatment in both injured and sham-injured animals when compared with animals that underwent 30% O2 treatment. Mitochondrial redox potential, as measured by Alamar blue fluorescence, demonstrated injury-induced reductions at 1 hour postinjury. These reductions were partially reversed at 4 hours postinjury in animals treated with 30% O2 and completely reversed at 4 hours postinjury in animals on HBO therapy when compared with animals treated for only 1 hour. CONCLUSIONS: Analysis of data in the current study demonstrates that HBO significantly increases brain tissue PO2 after injury. Nonetheless, treatment with HBO was insufficient to overcome injury-induced reductions in mitochondrial redox potential at 1 hour postinjury but was able to restore redox potential by 4 hours postinjury. Furthermore, HBO induced an increase in VO2 in both injured and sham-injured animals. Taken together, these data demonstrate that mitochondrial function is depressed by injury and that the recovery of aerobic metabolic function may be enhanced by treatment with HBO.

Animals↗