Singlet molecular oxygen in biological systems: non-quenching of singlet oxygen-mediated chemiluminescence by superoxide dismutase

Propofol prevents endothelial dysfunction induced by glucose overload

Surgical operations often induce acute hyperglycemia, which is known to affect endothelial functions. In this study, we examined the effects of propofol, a commonly used general anaesthetic, on bovine aortic endothelial cell (BAEC) dysfunction induced by glucose overload. 2 D-glucose overload (23 mM) induced an accumulation of superoxide anion (O2-), assessed by MCLA chemiluminescence, to a similar extent as that generated by 233 microU ml(-1) xanthine oxidase (XO) and 100 micro M xanthine. Propofol inhibited this accumulation with an IC50 of 0.21 micro M, whereas much higher concentrations of propofol were required to scavenge O2- generated by 250 microU ml(-1) XO and 100 microM xanthine (IC50: 13.5 micro M). 3 D-glucose overload attenuated ATP-induced NO production which was detected using diaminofluorescence-2 (DAF-2). The inhibition was reversed by propofol with an EC50 of 0.60 microM. In contrast, inhibitions caused by xanthine/XO were not altered by propofol (1 microM). 4 D-glucose overload suppressed ATP-induced Ca2+ oscillations and capacitative Ca2+ entry (CCE), which were both restored by superoxide dismutase, indicating that O2- was responsible. Propofol restored these attenuated Ca2+ oscillations and CCE with EC50 of 0.31 and 1.0 microM, respectively. 5 D-glucose overload (23 mM) increased the intracellular glucose concentration 4 fold, compared with cells exposed to 5.75 mM glucose, and 1 micro M propofol reduced this increase to 2.8 fold. 6 We conclude from these results that anaesthetic concentrations of propofol prevent the impairment of Ca2+-dependent NO production in BAEC induced by glucose overload. This effect is mainly due to the reduction of O2- accumulation, and involves, at least in part, the inhibition of cellular glucose uptake.

Superoxide anion impairs contractility in cultured aortic smooth muscle cells

We examined the effects of superoxide anion (O) generated by xanthine plus xanthine oxidase (X/XO) on the intracellular Ca(2+) concentration ([Ca(2+)](i)) and muscle contractility in cultured bovine aortic smooth muscle cells (BASMC). Cells were grown on collagen-coated dish for the measurement of [Ca(2+)](i). Pretreatment with X/XO inhibited ATP-induced Ca(2+) transient and Ca(2+) release-activated Ca(2+) entry (CRAC) after thapsigargin-induced store depletion, both of which were reversed by superoxide dismutase (SOD). In contrast, Ca(2+) transients induced by high-K(+) solution and Ca(2+) ionophore A-23187 were not affected by X/XO. BASMC-embedded collagen gel lattice, which was pretreated with xanthine alone, showed contraction in response to ATP, thapsigargin, high-K(+) solution, and A-23187. Pretreatment of the gel with X/XO impaired gel contraction not only by ATP and thapsigargin, but also by high-K(+) solution and A-23187. The X/XO-treated gel showed normal contraction; however, when SOD was present during the pretreatment period. These results indicate that O(2)(-) attenuates smooth muscle contraction by impairing CRAC, ATP-induced Ca(2+) transient, and Ca(2+) sensitivity in BASMC.

Impairment of endothelial nitric oxide production by acute glucose overload

We examined the effects of acute glucose overload (pretreatment for 3 h with 23 mM D-glucose) on the cellular productivity of nitric oxide (NO) in bovine aortic endothelial cells (BAEC). We had previously reported (Kimura C, Oike M, and Ito Y. Circ Res, 82: 677-685, 1998) that glucose overload impairs Ca(2+) mobilization due to an accumulation of superoxide anions (O(2)(-)) in BAEC. In control cells, ATP induced an increase in NO production, assessed by diaminofluorescein 2 (DAF-2), an NO-sensitive fluorescent dye, mainly due to Ca(2+) entry. In contrast, ATP-induced increase in DAF-2 fluorescence was impaired by glucose overload, which was restored by superoxide dismutase, but not by catalase or deferoxamine. Furthermore, pyrogallol, an O(2)(-) donor, also attenuated ATP-induced increase in DAF-2 fluorescence. In contrast, a nonspecific intracellular Ca(2+) concentration increase induced by the Ca(2+) ionophore A-23187, which depletes the intracellular store sites, elevated DAF-2 fluorescence in both control and high D-glucose-treated cells in Ca(2+)-free solution. These results indicate that glucose overload impairs NO production by the O(2)(-)-mediated attenuation of Ca(2+) entry.

SP-22 is a thioredoxin-dependent peroxide reductase in mitochondria

SP-22 is a mitochondrial antioxidant protein in bovine adrenal cortex. The protein is homologous to thioredoxin peroxidase and other antioxidant proteins. It protects radical-sensitive enzymes from oxidative damage by a radical-generating system (Fe2+/dithiothreitol) in the presence of a small amount of serum. In this study we purified a second mitochondrial protein with Mr 11,777, which cooperates with SP-22 to protect glutamine synthetase and other proteins from Fe2+/dithiothreitol-mediated damage. Without SP-22, the protein had no protecting activity. We determined amino acid and nucleotide sequences of the protein and its cDNA, respectively, and found that it was a protein of the thioredoxin family. The protein, designated as mt-Trx (mitochondrial thioredoxin), had a presequence composed of 59 amino acids that seemed to be a mitochondrial targeting signal. Mitochondrial extract prepared from adrenal cortex contained NADPH-dependent 5,5'dithiobis(2-nitrobenzoic acid) (Nbs2) reductase activity. The enzyme was thought to have thioredoxin reductase activity, since the Nbs2-reducing activity was stimulated by mt-Trx. We partially purified the Nbs2 reductase from bovine adrenocortical mitochondria. In the presence of the partially purified reductase, mt-Trx, and NADPH, SP-22 showed the activity to protect oxyhemoglobin against ascorbate-induced damage. Furthermore, with the three protein components (Nbs2 reductase, mt-Trx, and SP-22) NADPH was oxidized in the presence of hydrogen peroxide or tert-butyl hydroperoxide. The oxidation of NADPH was concomitant with the disappearance of an equimolar amount of hydrogen peroxide. Without any one of the protein components no hemoglobin-protecting and peroxide-dependent NADPH-oxidizing activities were observed. From these results we concluded that SP-22 is thioredoxin-dependent peroxide reductase or so-called thioredoxin peroxidase in mitochondria from the adrenal cortex.

Initiation of oxidative changes in foods

Initiation of lipid peroxidation in foods may be accomplished by a variety of mechanisms. Two principal initiation reactions involve homolytic scission of preformed peroxides as catalyzed by metal ions and heme proteins and the reaction of activated oxygen species with the lipid substrate to yield peroxides and free radicals. Copper and cytochromes in the milk fat globule membrane may serve as focal points for initiation of lipid peroxidation by catalyzing homolytic scission of peroxides. Activated oxygen species which may be important in initiating oxidative changes in foods include singlet oxygen, hydroxyl radical, ozone, superoxide anion (perhydroxyl radical at low pH), and hydrogen peroxide. Chemical and enzymic reactions in biological materials can generate singlet oxygen, hydroxyl radical, superoxide anion, and hydrogen peroxide. Ozone is primarily a product of photoreactions in polluted air. Reactions involving singlet oxygen, hydroxyl radical, and ozone with food constituents ultimately can yield peroxides which decompose to initiate oxidative chain reactions. Superoxide anion and hydrogen peroxide are relatively inert toward organic molecules but can decompose to produce the more reactive singlet oxygen and hydroxyl radical. Inhibition of reactions initiated by reactive oxygen species in foods should be very important in preserving the oxidative stability of foods. This paper presents a brief review of possible initiation reactions for lipid peroxidation and inhibition of reactions of activated oxygen species that are of importance in food systems.

Catalysis of the disproportionation of superoxide by metalloporphyrins

The efficiencies of several metalloporphyrin complexes at catalyzing the disproportionation of superoxide have been determined at pH 10 in both carbonate and borate buffer systems. Catalytic rate constants were obtained for the iron(III) and cobalt(III) derivatives of tetrakis(4-N-methylpyridyl) porphine, for tetraphenylporphinesulfonatoferrate(III) and for hemin. In addition, the effects of added bovine serum albumin and imidazole were studied. The order of catalytic efficiency is FeTMpyP greater than FeTMpyP(Im)2 greater than FeTPPS(Im)2 approximately FeTPPS approximately FeTPPS.BSA approximately Fe(EDTA) greater than or approximately CoTMpyP greater than hemin(Im)2 greater than or approximately hemin.

Activated oxygen species and oxidation of food constituents

Activated oxygen species which may be important in initiating oxidative changes in foods include singlet oxygen, hydroxyl radical, ozone, superoxide anion (perhydroxyl radical at low pH), and hydrogen peroxide. Chemical and enzymic reactions known to occur in biological materials can generate singlet oxygen, hydroxyl radical, superoxide anion, and hydrogen peroxide. Ozone is primarily a product of photoreactions in polluted air. Reactions involving singlet oxygen, hydroxyl radical, and ozone with food constituents can ultimately yield peroxides which decompose to initiate oxidative chain reactions. Superoxide anion and hydrogen peroxide are relatively inert toward organic molecules but can decompose to produce the more reactive singlet oxygen and hydroxyl radical. Inhibition of reactions initiated by reactive oxygen species in foods should be very important in preserving the oxidative stability of foods. The generation, detection, measurement, reaction, and inhibition of reactions of active oxygen species are surveyed in this review.

Superoxide dismutases: defence against endogenous superoxide radical

Attempts to measure the rate of O2- production, in whole cells or in intact subcellular organelles, are frustrated by the endogenous superoxide dismutase (SOD). Streptococcus faecalis contains a single manganese-SOD which was isolated and used as an antigen in the rabbit. A precipitating and inhibiting antibody was obtained and used to suppress the SOD in crude lysates of S. faecalis. It allowed the demonstration that 17% of the total oxygen uptake by such lysates, in the presence of NADH, was associated with O2- production. O2- attacks unsaturated lipids and breaches the integrity of membranes. When the membranes are free of lipid hydroperoxides, then both O2- and H2O2 are required and singlet oxygen appears to be the proximal attacking species. When the membrane contains some lipid hydroperoxide, then O2- is itself sufficient and seems to generate an alkoxy radical, by reacting with the lipid hydroperoxide. It appears likely that attack on membranes is one of the reasons for the cytotoxicity of O2-. In Escherichia coli the manganese-SOD is derepressed by O2-. This enzyme is not made in the absence of oxygen and in aerobic conditions any change which results in enhanced production of O2- calls forth an increased synthesis of this enzyme. Increased levels of SOD, however achieved, correlate with greater resistance towards oxygen toxicity. It is generally true that respiring cells contain more SOD than non-respiring cells. Among obligate anaerobes there is a correlation between SOD-content and tolerance towards oxygen. It is not known whether the SOD in obligate anaerobes is a retained primitive characteristic or one recently acquired by plasmid transfer. There is an exception to the rule that copper-zinc-SOD is found in eukaryotes but not in prokaryotes, and that is the symbiotic bacterium Photobacterium leiognathi. This symbiont may have obtained the Cu-ZnSOD gene from the host fish.

Sterol metabolism. XL. On the failure of superoxide radical anion to react with cholesterol

Superoxide radical anion (O-2) failed to react with cholesterol under a variety of conditions. In some instances products indicative of free radical oxidation by molecular oxygen (O2) were found, but no products of electronically excited (singlet) molecular oxygen (1O2) attack on cholesterol were detected. These results do not support a direct role of O-2 in lipid peroxidation of cholesterol-rich membranes or of the formation of 1O2 from O-2 dismutation.

Formation of lipid peroxides in isolated rat liver microsomes by singlet molecular oxygen

Rat liver microsomes were incubated in neutral aqueous solution of potassium peroxychromate, a system which generates singlet molecular oxygen. Such incubation resulted both in a rapid decline in NADPH-cytochrome c reductase activity, and in an increase in formation of lipid peroxides. These reactions were not inhibited by either superoxide dismutase (SOD) or mannitol, nor were they entirely duplicated by incubating microsomes with hydrogen peroxide. However, a high concentration of 1,4-diazabicyclo-[2,2,2]octane (DABCO), a known scavenger of singlet oxygen, prevented both decline in reductase activity and formation of lipid peroxides. These results suggest that the observed effects are, in fact, attributable to singlet oxygen, and not to hydrogen peroxide, superoxide radical, or hydroxyl radical.

Induction of benzo[a]pyrene Mono-oxygenase in liver cell culture by the photochemical generation of active oxygen species. Evidence for the involvement of singlet oxygen and the formation of a stable inducing intermediate

1. The photochemical generation of excited states of oxygen in liver cell culture by the mild ilumination of culture medium containing riboflavin, results in stimulation of benzo[a]pyrene 3-mono-oxygenase, a cytochrome P-450-linked mono-oxygenase. 2. The same large increase in mono-oxygenase activity was found when medium containing riboflavin was illuminated in the absence of cells and then stored in the dark for 24h before contact with the cells. From this it may be inferred that stimulation is due to the formation of a stable inducer in the culture medium. Further experiments indicate that the stable inducer is due to the photo-oxidation of an amino acid. 3. Evidence that singlet oxygen is responsible for initiating the stimulation of the mono-oxygenase is based on the use of molecules that scavenge particular active oxygen species. Of all the scavengers tested, only those that scavenge single oxygen inhibited the stimulation. 4. A hypothesis is developed to relate the stimulation of the mono-oxygenase by singlet oxygen in cultured cells to the regulation of the cytochrome P-450 enzyme system in vivo. It is suggested that single oxygen generation within cells may be a common factor linking the many structurally diverse inducers of the enzyme system.

Radioprotective effect of superoxide dismutase on model phospholipid membranes

1. Hydroperoxide formation in model membranes was measured via the net increase in absorbance at 232 nm after exposure to X-rays or 137Cs gamma rays in the presence and absence of bovine superoxide dismutase and other radical scavengers. 2. Membranes X-irradiated in air to 4200 rad at 210 rad/min exhibited a large increase in absorbance, a major portion of which was O2--mediated since active superoxide dismutase at 1 mug/ml reduced it by more than 80% to the level observed in N2O. In N2 the change in absorbance was smaller than in N2O but not in proportion to the halving in OH production. 3. The net absorbance of membranes exposed to a constant dose from 137Cs increased with decreasing dose rate. A minor component of this effect was due to exposure protraction with decreasing dose rates while the major component was attributed to long chain reactions initiated by ionizing radiation. A corollary effect was also observed, namely, that with reducing dose rate the dose required to elicit a constant absorbance change decreased. Both aspects were abolished by superoxide dismutase at 1 mug/ml. 4. The enzyme protected membranes after an acute exposure and from low level radiation at natural background while its inactivated form sensitized.

Inactivation of biologically active DNA by gamma-ray-induced superoxide radicals and their dismutation products singlet molecular oxygen and hydrogen peroxide

Since superoxide radicals are involved in many metabolically important as well as in some other, detrimental cellular processes, the reactivity of gamma-ray-induced superoxide radicals and its dismutation products singlet molecular oxygen and hydrogen peroxide with DNA have been studied. Superoxide dismutase which removes superoxide radicals and inhibits the formation of singlet oxygen in the solution protects the biologically active replicative form of DNA (from bacteriophage theta X174) against inactivation by ionizing radiation. Catalase which removes hydrogen peroxide also protects the DNA. Attempts with various chemical sources of singlet oxygen to determine whether this species inactivates DNA did not give an unequivocal answer. It is concluded from the presented experiments that a combination of the protonated form of the superoxide radical (HO-2) and H2O2 do inactivate DNA.

Lamellar superoxide dismutase of isolated chloroplasts

Photooxidation of hydroxylamine to nitrite by spinach (Spinacia oleracea L. and sugarbeet (Beta vulgaris L.) chloroplast lamellae in the presence of autoxidable electron acceptors is inhibited by either solubilized or membrane-bound superoxide dismutase (SOD). This inhibition is reversed by KCN. The rates of hydroxylamine photooxidation by chloroplast lamellae, a reaction which is apparently driven by the superoxide free-radical ion, was used for quantitating the amount of SOD bound to chloroplast lamellae, as compared to a soluble enzyme of defined concentration. After digitonin fragmentation of chloroplast lamellae, ca. 80% of the SOD activity is associated with subchloroplast particles sedimenting after 2 h centrifugation at 200 000 x g. Less than 10% of the SOD activity is associated with particles sedimenting after centrifugation for 30 min at 20 000 x g. 5-10% of the cyanide-sensitive SOD is recovered in the soluble fraction of the subchloroplast-free supernatant after centrifugation at 200 000 x g for 2 h.