A reflectance spectrophotometer-surface fluorometer suitable for monitoring changes in hemoprotein spectra and fluorescence of flavins and nicotinamide nucleotides in intact tissues

Mitochondrial function and brain Metabolic Score (BMS) in ischemic Stroke: Evaluation of "neuroprotectants" safety and efficacy

The initial and significant event developed in ischemic stroke is the sudden decrease in blood flow and oxygen supply to brain tissue, leading to dysfunction of the mitochondria. Many attempts were and are being made to develop new drugs and treatments that will save the ischemic brain, but the efficacy is not optimal and in many patients, irreversible damage to the brain will persist. We review a unique approach to evaluate mitochondrial function and microcirculatory hemodynamic in real time in vivo. Three out of four monitored physiological parameters are integrated into a new Brain Metabolic Score (BMS) calculated in real time and is correlated to Brain Oxygen Balance. The technology was adapted to various experimental as well as clinical situations for monitoring the brain in real time. The developed protocols could be used in testing the efficacy and safety of new drugs in experimental animals. Few models of brain monitoring during partial or complete ischemia were developed and used in naive animals or under brain activation protocols. It was found that mitochondrial function/dysfunction is the major and dominant parameter affecting the calculated Brain Metabolic Score. Using our monitoring system and protocols will provide direct information regarding the ability of the tested brain to provide enough oxygen consumed by the mitochondria in the "resting" or in the "activated" brain in vivo and in real-time. Preliminary studies, indicated that testing the efficacy and safety of new neuroprotectant drugs provided significant results to the R&D studies of ischemic stroke related to mitochondrial function.

Conformational changes of bovine serum albumin upon its adsorption in dodecane-in-water emulsions as revealed by front-face steady-state fluorescence

Front-face fluorescence spectroscopy was used to characterise dodecane-in-buffer (0.1 M phosphate buffer; pH = 7.6) emulsions stabilised by bovine serum albumin (BSA). A 15-nm blue-shift of the emission maximum of the adsorbed protein and a significant increase of its fluorescence quantum yield were observed. The contribution of tyrosyl residues to total fluorescence was tentatively evaluated from different spectra and an R ratio taking into account the stray-light interference; R increased upon BSA absorption but the Tyrosine contribution remained weak in all cases. Thus, conformational changes of the protein take place upon BSA adsorption onto the dodecane-water interface. They involve modifications in the environment of the protein aromatic amino acids especially of the tryptophanyl residues which are displaced to a more hydrophobic location. Moreover, the proportions of absorbed and non-adsorbed BSA in emulsions can be estimated from the position of the emission maximum.

Peroxisomes and beta-oxidation of long-chain unsaturated carboxylic acids

Degradation of unsaturated long-chain carboxylic acids by beta-oxidation, which is a compartmentalized process occurring in both mitochondria and peroxisomes in mammalian cells, was studied using rat liver as a model tissue. Inclusion of (poly)unsaturated fatty acids in the perfusion medium resulted in an increased concentration of catalase-H2O2 complex indicating on-going peroxisomal beta-oxidation. For this to occur, an active peroxisomal delta 3, delta 2-enoyl-CoA isomerase was required for metabolism of the double bonds at odd-numbered positions in acyl-CoA. Experiments with isolated subcellular organelles from rat liver confirmed the presence of isomerase in the peroxisomes, and the enzyme was subsequently isolated with apparent homogeneity. Comparison of amino acid sequences from the enzyme with a published sequence for a bifunctional protein from rat liver identified them representing the same molecule. The peroxisomal bifunctional protein can thus act as a multifunctional hydratase-dehydrogenase-isomerase enzyme. Examination of the mitochondrial isomerase revealed that rat liver mitochondria possess two isoenzymes: a long-chain isomerase not induced by clofibrate-treatment and showing a preference for C10-C12 substrates, and a clofibrate-inducible short-chain isomerase which gave the highest catalytic activity with C6 substrates. Experiments with isolated peroxisomes and unsaturated acyl-CoAs demonstrated that the beta-oxidation of fatty acids having double bonds at even-numbered positions was dependent on 2,4-dienoyl-CoA reductase in peroxisomes, as in mitochondria. Immunocytochemical experiments using the protein A-gold labelling technique, and comparison of their physicochemical properties indicated that all the mammalian reductases purified so far are mitochondrial isoenzymes. It turned out during the isolation of 3-hydroxyacyl-CoA epimerase that there was no monofunctional epimerase at all in the rat liver. Instead, the epimerization reaction occurred via dehydration-hydration catalyzed by two distinct stereospecific hydratases, 2-enoyl-CoA hydratase 1 (the classic hydratase) and 2-enoyl-CoA hydratase 2 (a novel hydratase). The present data demonstrate that peroxisomes contain all the enzymes required for the beta-oxidation of unsaturated fatty acids and support the notion that one of the physiological functions of peroxisomal beta-oxidation is to metabolize long-chain hydrophobic carboxylic acids to shorter, more polar metabolites which are then either metabolized further in the body or excreted.

Fluoroscopic determination of NAD(P)H/NAD(P)+ ratios in brain slices under perifusion conditions

The adaptation of a commercially available fluorescence microscope for continuous monitoring of endogenous NAD(P)H levels in brain slices is described. A specially designed self-stirring perifusion chamber was used to monitor a stable fluorescence signal for hours, indicating sufficient oxygen and substrate supply under measuring conditions. Profiles and reversibility of the fluorescence signals following changes in NAD(P)H levels in the picomolar range are demonstrated in slices of rat hippocampus. The degree of reduction obtained under normal metabolic conditions in the presence of 10 mM glucose was 29.9% +/- 1.3 (mean +/- S.D.; n = 12). The present technique allows convenient monitoring of the influence of various exogenous factors on metabolic conditions which are accompanied by changes in the redox state of brain nicotinamide nucleotides.

Sensitivity to NN'-dicyclohexylcarbodi-imide of proton translocation by mitochondrial NADH:ubiquinone oxidoreductase

Proton extrusion during ferricyanide reduction by NADH-generating substrates or succinate was studied in isolated rat liver mitochondria with the use of optical indicators. NN'-Dicyclohexylcarbodi-imide (DCCD) caused a decrease of 84% in the H+/e- ratio of NADH:cytochrome c reduction, but a decrease of only 49% in that of succinate:cytochrome c reduction, even though electron transfer was decreased equally in both spans. The data indicate that a DCCD-sensitive channel operates in the NADH:ubiquinone oxidoreductase region of the respiratory chain.

Dependence of ethanol-induced redox shift on hepatic oxygen tensions prevailing in vivo

Since many metabolic derangements induced by ethanol have been linked to the redox shift, we studied the effects of oxygen in the range of tensions prevailing in vivo along the sinusoids on both the basal redox state and the shift induced by ethanol. The redox state of nicotinamide nucleotides was assessed by surface NADH fluorescence and that of cytochrome oxidase by transmittance dual-wavelength spectrophotometry in the hemoglobin-free, perfused rat liver. In the absence of ethanol, varying the oxygen tensions within the physiological range produced a redox gradient of both cytochrome oxidase and NAD+, with a more reduced state at tensions normally prevailing in perivenular zones. The degree of reduction of cytochrome oxidase at these physiological oxygen tensions was associated with no impairment in the ability of the liver to consume oxygen and to produce ATP, suggesting lack of cellular anoxia. 25 mM ethanol increased hepatic oxygen consumption, but had no direct effect on the state of reduction of cytochrome oxidase. The effects of ethanol and oxygen tensions on NADH fluorescence were additive, indicating that a greater redox shift should occur when ethanol is oxidized at oxygen tensions similar to those normally prevailing in prievenular zones than at those in periportal zones. This dependence of the ethanol-induced redox shift on oxygen tensions may contribute to the selective perivenular hepatotoxicity of alcohol.

Subcellular origin of the surface fluorescence of reduced nicotinamide nucleotides in the isolated perfused rat heart

Surface fluorometric measurements and indicator metabolite determinations in the isolated perfused rat heart showed that the NADH + NADPH fluorescence of the intact tissue originates largely from the mitochondria. The redox potential of the lactate dehydrogenase system calculated from the endogenous lactate/pyruvate ratios was closely similar to that of the glycerol-3-phosphate dehydrogenase system calculated from the concentrations of glycerol-3-phosphate and dihydroxyacetone phosphate in the tissue. Thus, in contrast to the liver, the cytosolic redox state of the NADH/NAD+ system in isolated perfused heart oxidizing external glucose or fatty acid is not amenable to optical monitoring, but can be assessed from the state of the lactate dehydrogenase or glycerol-3-phosphate dehydrogenase systems.

Regulation of fatty acid oxidation in heart muscle. Effects of pyruvate and dichloroacetate

The possibility of a mutual regulation between carbohydrate and fatty acid oxidation was studied in isolated perfused rat hearts. Infusions of pyruvate and/or dichloroacetate were employed to convert fully the pyruvate dehydrogenase complex into its active form during [1-14C]octanoate oxidation, the rate of which was measured by the production of 14CO2. It was found that 5 mM dichloroacetate suppressed the oxidation of 0.1 mM octanoate by 58%, but 10 mM external pyruvate was without effect. Dichloroacetate reduced the tissue malate concentration by 41% and the citrate concentration by 76% at a 0.1 mM octanoate concentration, but had no effect on the metabolite concentrations or fatty acid oxidation rate in perfusions with 1 mM octanoate. Metabolite depletion was probably partly due to inhibition of the carboxylation of pyruvate, as verified by determination of the metabolite labelling kinetics from [1-14C]pyruvate. It is, therefore, possible that the dichloroacetate-induced inhibition of octanoate oxidation could also be partly due to inhibition of tricarboxylic acid cycle secondary to metabolite depletion. Since both dichloroacetate and pyruvate converted pyruvate dehydrogenase to its active form, but only dichloroacetate inhibited fatty acid oxidation, the latter effect could not be due to oxidation of a competing substrate, but instead may result from an inhibition of fatty acid uptake, activation or transport, as also indicated by the observed decrease in the acid-soluble acyl-CoA concentration. This interpretation is also supported by the mitochondrial redox effects of dichloroacetate observed during octanoate oxidation in the perfused heart.

Role of acetaldehyde and acetate in the development of ethanol-induced cardiac lipidosis, studied in isolated perfused rat hearts

Isolated perfused rat hearts were used to study the effects of ethanol, acetaldehyde, and acetate on the cellular redox state and fatty acid metabolism in the myocardium. Ethanol had negligible effects on the cellular redox state but at high concentrations depressed the contractile activity and thereby secondarily the oxygen consumption. Acetaldehyde in concentrations below 50 microM had negligible effects on the redox state of the mitochondrial free NAD+/NADH couple, as studied by surface fluorometry of flavins and nicotinamide nucleotides. A reduction of NAD+ was observed with concentrations between 50 and 500 microM, while in the range of 0.5-1 mM the effect was biphasic, i.e., an initial reduction was followed by oxidation concomitantly with an increase in heart rate and peak systolic pressure. Acetate in millimolar concentrations caused in the coronary flow. A mitochondrial acetaldehyde dehydrogenase was revealed in the myocardium, having an apparent Km of 1.1 microM for acetaldehyde. Acetaldehyde in 50-microM concentration had no major effects on the uptake, oxidation, or lipid incorporation of oleate in the myocardium. Acetate in concentrations less than 2 mM did not affect the uptake of oleate into the myocardium, but did inhibit is oxidation and enhance its incorporation into tissue lipids in a dose-dependent manner. 2 mM acetate caused a 91% increase in oleate incorporation into tissue lipids over 30 min. The data can be interpreted as showing that acetaldehyde and acetate, the metabolites of ethanol, have metabolic effects on the myocardium, but only those of acetate are significant in concentrations encountered during ethanol oxidation in vivo. It is probable that acetate is involved in the development of ethanol-induced myocardial lipidosis, inhibiting the oxidation of fatty acids, and channelling them into the esterification pathway.