Oxygen free radical involvement in ischemia and reperfusion injury to brain

Evidence is presented which implicates increased oxygen free radicals during ischemia reperfusion of gerbil brain. Salicylate, which reacts with hydroxyl free radicals to yield dihydroxybenzoic acid (DHBA), was used as an in vivo trap. Brain ischemia for at least 5 min followed by reperfusion yielded significantly increased brain DHBA. Without reperfusion or with only 2 min of ischemia and then reperfusion, the production of DHBA was not increased. Increased levels of DHBA in brain correlated with ischemia reperfusion-mediated behavioral modification of gerbils, but salicylate administration did not protect against the behavior changes.

Renal work, glutathione and susceptibility to free radical-mediated postischemic injury

Studies were performed to determine whether renal glutathione (GSH) is an important free-radical scavenger following ischemia and reperfusion, whether alterations in renal transport work affect renal GSH levels, and whether a decrease in renal work decreases susceptibility to postischemic renal injury via the first two effects. Following administration of either intravenous GSH to increase renal GSH or intraperitoneal diethylmaleate to decrease renal GSH, Sprague-Dawley rats underwent 60 minutes of renal ischemia. In animals with high renal GSH following GSH infusion, GFR 24 hours after ischemia was 0.43 +/- 0.08 ml/min compared to 0.15 +/- 0.02 ml/min in saline-infused control animals (P less than 0.01). When renal GSH was decreased by the administration of diethylmaleate postischemic renal dysfunction was accentuated. Twenty-four hours after ischemia GFR was 0.05 +/- 0.02 ml/min in diethylmaleate-treated animals and 0.28 +/- 0.06 ml/min in control animals (P less than 0.005). To test whether a decrease in renal transport work alters renal GSH the filtered load of sodium was reduced by producing unilateral renal artery stenosis. Alternatively, renal work was lessened when sodium reabsorption was interfered with by the infusion of a combination of natriuretic agents. Renal artery stenosis produced a 37% decrease in GFR. Renal GSH was 0.435 +/- 0.089 nmol/mg protein in intact kidneys and 0.804 +/- 0.239 nmol/mg protein in stenotic kidneys (P less than 0.05). The infusion of natriuretic agents produced no change in GFR or renal plasma flow but resulted in a striking elevation in renal GSH.(ABSTRACT TRUNCATED AT 250 WORDS)

Free radicals. Formation, function and potential relevance in anaesthesia

Free radical species are ubiquitous in plant and animal life. This article describes briefly the formation of certain oxygen-centred free radicals which are essential for aerobic metabolism and host defences in humans. The mechanism of cytotoxicity of excess or inappropriate free radical production is described. The potential relevance of free radical tissue injury to the anaesthetist is illustrated using oxygen toxicity, adult respiratory distress syndrome and halothane hepatitis as examples.

Oxygen metabolism of the HL-60 cell line: comparison of the effects of monocytoid and neutrophilic differentiation

HL-60 cells are promyelocytic leukemia cells that respond to culture conditions with differentiation into granulocytelike or macrophagelike phagocytes. O2 metabolism is critical to the microbicidal function of phagocytic cells. O2 metabolism was studied in HL-60 cells differentiated with dimethylsulfoxide (Me2SO) and 1,25(OH)2D3, with the objective of 1) determining the validity of these cells as models for human neutrophils and monocytes, respectively, and 2) determining whether these cells are capable of forming hydroxyl radical. Me2SO-treated cells had morphology consistent with human neutrophils. O2 consumption by these cells in response to phorbol myristate acetate (PMA; 100 ng/ml) or opsonized zymosan (3 mg/ml) was less than that by neutrophils, as was superoxide formation. O2 metabolism was not inhibited by KCN or antimycin A. Myeloperoxidase (MPO) activity decreased during differentiation but remained greater than that of human neutrophils. Cytochalasin B enhanced recovery of superoxide secreted in response to zymosan, implying its release from the phagosome. 1,25(OH)2D3-treated cells had morphology consistent with monocytes. O2 consumption and superoxide release were less than with Me2SO-treated cells. Unlike the case with human monocytes, O2 consumption was not inhibited by KCN or antimycin A. MPO activity was minimally reduced by differentiation. Cytochalasin B inhibited recovery of superoxide. Luminol-dependent luminescence was greater among 1,25(OH)2D3-treated cells than among Me2SO-treated cells. Free radicals were also measured with a spin trapping technique using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Spin trapping allows direct, simultaneous detection of superoxide and hydroxyl radicals. Regardless of the mechanism of differentiation, only superoxide was formed by HL-60 cells. These results show that Me2SO-treated HL-60 cells represent an excellent model for the study of human neutrophil oxidative function. However, 1,25(OH)2D3-treated cells are quite different in their O2 metabolism from peripheral blood monocytes.

Specificity of oxygen radical scavengers and assessment of free radical scavenger efficiency using luminol enhanced chemiluminescence

The selective scavenging capacities of 19 important oxygen radical scavengers were determined by adding them individually to each of the four oxy radical standards, (superoxide, hydroxy, alkoxy and hydroperoxy, and singlet O2), calculating the percent chemiluminescence inhibited, and extrapolating O2 equivalents neutralized from baseline. The sensitivity (0.01 nm/ml) and selectivity of this method not only allows identification of individual oxygen free radical species but also quantitates the efficiency of free radical scavengers.

The influence of dietary history on the production of free radicals in rat liver microsomes

Free radicals have been trapped in microsomal fractions from rat livers by the use of alpha-(4-pyridyl-l-oxide)-N-tert-butylnitrone (4-POBN) and detected by ESR spectroscopy. Using this technique we have investigated the effects of low dietary concentrations of vitamin E and selenium (Se) on free radical production. When the microsomal fractions were incubated with Fe, ADP and NADPH significantly greater amounts of radicals were initially trapped when rats were deficient in vitamin E (whether combined with Se deficiency or not) than from Se-deficient animals or Se- and vitamin E-supplemented controls. After prolonged incubation (ca. 30-45 mins) the free radicals trapped from the microsomes from the Se-deficient animals rose to amounts comparable to those seen in the vitamin E-deficient microsomes. Over the same period of incubation approximately half this quantity of radicals were trapped in liver microsomes from Se- and vitamin E-supplemented rats. The effects of 4-POBN on the levels of peroxidation in the various microsomal fractions were assessed by measuring the thiobarbituric acid reactive substances (TBARS). The presence of 4-POBN significantly reduced the amounts of TBARS formed on incubation and there was a clear distinction between the groups on the basis of the vitamin E status of their diets.

The case for oxygen free radicals in the pathogenesis of ischemic acute renal failure

One of the more glaring paradoxes of ischemic acute renal failure is that such injury appears to be worse in the kidney as opposed to other organs, even though the kidney is the best oxygenated. An answer can be deduced from the anatomical and physiological background, together with a reappraisal of the role of medullary vascular damage and recent evidence of the importance of the postischemic component of ischemic injury, which is mediated by oxygen free radicals. As far as oxygenation is concerned, the kidney's Achilles heel is the tubules of the outer strip of the outer medulla, which are also those that have the most metabolic activity. It is here that ischemic injury begins, and is maintained and exacerbated in the postischemic stage by the free radicals. These are produced by the kidney in large quantities, since it has all the necessary chemical ingredients available. It is therefore readily understandable why the kidney, being the best oxygenated organ, is so sensitive to an ischemic insult, since the damage caused in the postischemic stage is increased the greater the amount of oxygen brought in by reperfusion.

Granulocytes cause reperfusion ventricular dysfunction after 15-minute ischemia in the dog

Regional ventricular dysfunction (the stunned myocardium) persists for several hours after 15 minutes of ischemia and reperfusion in the dog. Superoxide-radical-induced damage appears to be one of the mechanisms of this injury. We tested whether granulocytes were a direct source of injury in the stunned myocardium in the 15-minute ischemia dog model. Regional function during agranulocytic extracorporeal coronary perfusion (using Leukopak filters) with ischemia and reperfusion was compared with function during a second period of ischemia and reperfusion after removal of the filters (granulocytopenia). Flow reduction and reperfusion flow, preload, afterload, and inotropic stimulation were the same during agranulocytic and granulocytopenic perfusion. During agranulocytic perfusion, stunning did not occur (greater than 100% of preischemic function during reperfusion), but when the filters were removed and about 10% of the normal granulocyte count was present, stunning occurred with only 76% return of function at 60 minutes of reperfusion (p less than 0.01). A second series of studied animals with extracorporeal perfusion and granulocyte replete perfusion all had less than 75% return of regional function, indicating that the agranulocytic perfusion and not the extracorporeal aspects of the experiment prevented stunning. We conclude that granulocytes are the direct source of the injury in stunned myocardium and apparently the main source of superoxide in the 15-minute ischemia dog model. Other possible granulocyte-related mechanisms of reperfusion injury include capillary no-reflow, causing microvascular ischemia and degranulation leading to enzyme-induced damage.

Free radical scavengers in myocardial ischemia

Reperfusion of ischemic myocardium is recognized as potentially beneficial because mortality is directly related to infarct size, and the latter is related to the severity and duration of ischemia. However, reperfusion is associated with extension of the injury that is additive to that produced by ischemia alone. The phenomenon of reperfusion injury is caused in large part by oxygen-derived free radicals from both extracellular and intracellular sources. The loci of oxygen-free radical formation include: myocardial sources (mitochondria), vascular endothelial sources (xanthine oxidase and other oxidases), or the inflammatory cellular infiltrate (neutrophils). Experimental studies have shown that free radical scavengers and agents that prevent free radical production can reduce myocardial infarct size in dogs subjected to temporary regional ischemia followed by reperfusion. Superoxide dismutase and catalase, which catalyze the breakdown of superoxide anion and hydrogen peroxide, respectively, limit experimental myocardial infarct size. The free radical scavenging agent N-(2-mercaptopropionyl)glycine (MPG) is reported to be effective in limiting infarct size. The ischemic-reperfused myocardium derives significant protection when experimental animals are pretreated with the xanthine oxidase inhibitor allopurinol. Neutrophils also serve as a significant source of oxygen-derived free radicals at the site of tissue injury. A number of agents have been shown to directly inhibit neutrophil-derived oxygen free radical formation and neutrophil accumulation within the reperfused myocardium. These agents include ibuprofen, nafazatrom, BW755C, prostacyclin, and iloprost. Thus, free radical scavengers and agents that prevent free radical formation can provide significant protection to the ischemic-reperfused myocardium.

Lipid peroxidation is not a major factor involved in the edema formation in perfused lungs

Perfusion of isolated rat lungs was previously found to induce edema formation, which was considered to be mediated by oxygen-free radicals as scavengers reduced the edema. In the present study we elaborated upon these findings by measuring products found by O2-radical generation. We measured reduced and oxidized glutathione as well as conjugated dienes as an estimate of lipid peroxidation. Amount of water was also measured. Perfusion with oxygenated dextran/Tyrode solution increased edema as compared to nonoxygenated dextran/Tyrode and to nonperfused control lungs. Induction of oxygen radical formation by addition of xanthine and xanthine oxidase to the nonoxygenated dextran/Tyrode perfusate significantly increased the amount of edema as measured by the percentage of water in the lung to 87.0% as compared to the control value of 78.2%. Addition of the radical scavenger superoxide dismutase and catalase to this perfusate prevented edema accumulation. Levels of conjugated dienes as well as those of reduced and oxidized glutathione in lung tissue were measured before the start of perfusion and after 5 and 30 min of perfusion. No significant changes were seen in any of these parameters, indicating that lipid peroxidation may not be a major factor contributing to the edema formation during perfusion of isolated lungs.

Detection of free radicals as a consequence of rat intestinal cellular drug metabolism

Because the intestine is the first pass organ for orally administered drugs and because some of these drugs are known to undergo oxidative metabolism leading to the formation of free radicals, we investigated the potential for this to occur in cell suspensions of rat enterocytes. As part of our study, the effect of intracellularly produced superoxide on cellular metabolism was investigated. The drugs chosen were the quinone, menadione and the aromatic nitro-containing compound, nitrazepam. On incubation of both drugs with isolated enterocytes and the spin trap, 5,5-dimethyl-1-pyrroline N-oxide (DMPO), rapid appearance of an electron paramagnetic resonance (EPR) spectrum was recorded which was characteristic of hydroxyl radicals being spin trapped by DMPO giving 2,2-dimethyl-5-hydroxy-1-pyrrolidenyloxyl (DMPO-OH). Experiments were conducted which determined that the EPR spectrum of DMPO-OH resulted from the initial spin trapping of superoxide by DMPO to yield the corresponding nitroxide, 2,2-dimethyl-5-hydroxyl-1-pyrrolidenyloxyl (DMPO-OOH). Bioreduction of DMPO-OOH by glutathione peroxidase led to the rapid formation of DMPO-OH. We believe this enzymic pathway accounted for the EPR spectrum noted in incubations with either drug in the presence of the spin trap, DMPO. The incubation of enterocytes with both drugs did not mediate release of 51Cr nor lactate dehydrogenase. However, production of 14CO2 from [14C]glucose was severely inhibited (4-5-fold) in the presence of both drugs, while the incorporation of [14C]leucine into trichloroacetic acid precipitable protein was antagonized by menadione only. We conclude that superoxide can be demonstrated to arise as the result of enterocyte metabolism of menadione or nitrazepam. The consequence of oxidative metabolism of these drugs results in cellular dysfunction.

Corynebacterium parvum-elicited hepatic macrophages demonstrate enhanced respiratory burst activity compared with resident Kupffer cells in the rat

We have recently demonstrated that release of oxygen-derived free radicals by activated hepatic macrophages may be involved in the pathogenesis of a rat model of liver injury induced by Corynebacterium parvum and endotoxin. In the present study we have compared the respiratory burst activity of isolated normal rat Kupffer cells with that of hepatic macrophages elicited by C. parvum. Superoxide production (O2-.) and glucose oxidation via the hexose monophosphate shunt (HMPS) were low in normal Kupffer cells, but were significantly increased (O2-. 2.1-fold, HMPS 1.7-fold) by phorbol myristate acetate, a stimulant of the respiratory burst. Corynebacterium parvum-elicited hepatic macrophages demonstrated significantly enhanced superoxide production and HMPS activity compared with normal Kupffer cells, both in the absence of specific stimuli (O2-. 3.3-fold, HMPS 5.3-fold) and after exposure to phorbol myristate acetate (O2-. 4.5-fold, HMPS 5.3-fold). These results demonstrate that normal Kupffer cells are capable of exhibiting respiratory burst activity, but this is markedly increased for hepatic macrophages elicited by an inflammatory stimulus.

Superoxide production in experimental brain injury

The appearance of superoxide anion radicals in cerebral extracellular space during and after experimental fluid-percussion brain injury was investigated in anesthetized cats equipped with cranial windows. Superoxide was detected by demonstrating the presence of superoxide dismutase (SOD)-inhibitable reduction of nitroblue tetrazolium (NBT). The SOD-inhibitable rate of reduction of NBT was 3.52 +/- 0.72 nM/min/sq cm during brain injury and 4.11 +/- 0.74 nM/min/sq cm 1 hour after injury. No significant superoxide production was detected in control animals. The sustained arteriolar dilation and reduced responsiveness to the vasoconstrictor effects of arterial hypocapnia observed 30 minutes after brain injury were eliminated by after-treatment with topical SOD (60 U/ml) and catalase (40 U/ml). The results show that experimental brain injury causes the generation and appearance in extracellular fluid space of superoxide. Superoxide production continues for at least 1 hour following injury. The sustained dilation and abnormal responsiveness of cerebral arterioles after injury are due to the continued generation of superoxide and other radicals derived from it. These functional changes can be reversed by after-treatment with appropriate scavenging agents.

Studies on the activity of Bendalina (bendazac L-lysine salt) as a scavenger of hydroxyl and superoxide radicals

Bendalina (bendazac L-lysine salt) strongly inhibits the depolymerization of hyaluronic acid solutions by OH. or O2.- radicals. By viscometric determinations of these reactions the activity of Bendalina as a free radical scavenger was demonstrated.

Influence of acidosis on lipid peroxidation in brain tissues in vitro

To study the influence of acidosis on free radical formation and lipid peroxidation in brain tissues, homogenates fortified with ferrous ions and, in some experiments, with ascorbic acid were equilibrated with 5-15% O2 at pH values of 7.0, 6.5, 6.0, and 5.0, with subsequent measurements of thiobarbituric acid-reactive (TBAR) material, as well as of water- and lipid-soluble antioxidants (glutathione, ascorbate, and alpha-tocopherol) and phospholipid-bound fatty acids (FAs). Moderate to marked acidosis (pH 6.5-6.0) was found to grossly exaggerate the formation of TBAR material and the decrease in alpha-tocopherol content and to enhance degradation of phospholipid-bound, polyenoic FAs. These effects were reversed at pH 5.0, suggesting a pH optimum at pH 6.0-6.5. It is concluded that acidosis of a degree encountered in ischemic brain tissues has the potential of triggering increased free radical formation. This effect may involve increased formation of the protonated form of superoxide radicals, which is strongly prooxidant and lipid soluble, and/or the decompartmentalization of iron bound to cellular macromolecules like ferritin.

Increased luminol enhanced chemiluminescence from peripheral granulocytes in juvenile periodontitis

The granulocyte function in patients with juvenile periodontitis (JP) (eight men and six women, aged 13-33 yr) and sex and age matched controls was determined by the luminol enhanced chemiluminescence (CL) induced by opsonized and unopsonized bacteria or latex beads. Maximal CL induced by latex beads with or without autologus serum did not differ between the two groups. However, bacteria with or without autologous serum seemed to induce a higher maximal CL in the JP group. The difference was statistically significant for the results obtained with opsonized bacteria. Serum opsonized bacteria induced a much higher maximal CL than the unopsonized. The opsonin dependent reaction indicates a close association with the process of phagocytosis. The increased CL of granulocytes in JP could indicate the formation of extracellularly free oxygen radicals with the potential to damage tissue. These observations support a possible involvement of the granulocytes in the pathogenesis of JP.

In vitro cross-linking of bovine lens proteins photosensitized by promazines

Promazine derivatives induce cross-linking of bovine lens crystallins in vitro by irradiation with near-ultraviolet (UV) light in the presence of O2, as revealed by electrophoresis after denaturation. With the five derivatives tested (promazine [PZ], chlorpromazine [CPZ], triflupromazine [ TFPZ ], methoxypromazine [ MTPZ ], and acepromazine [ ACPZ ] ), single-hit kinetics are observed. Evidence implicating the cation radicals of the PZ derivatives as the causative agent of this in vitro effect is presented. Hydroxyl radicals do not appear to be involved in the photo-cross-linking reaction. Sodium ascorbate protects against damage induced either by PZ derivatives plus light or by PZ cation radicals in the dark. These findings are discussed with respect to development of cataracts induced by these drugs in vivo.

Evidence that N-acetoxy-N-acetyl-2-aminofluorene crosslinks DNA to protein by a free radical mechanism

A method was devised to quantitate N-acetoxy-N-acetyl-2-aminofluorene (N-AcO-AAF) induced crosslinking of the ionic complex between [methyl-3H]thymidine labeled pBR322 DNA and lysozyme. This involved chromatography of the modified complex on Sephadex CM 25 with a high salt buffer that dissociated the non-covalently bound complex and permitted early elution of unbound [3H]DNA. The crosslinked complex was then eluted with buffer at pH 10.5. The amount of crosslinking was a function of the carcinogen concentration in the reaction mixture containing the complex. Addition of the spin trap nitrosobenzene or the radical trap 2,2-diphenyl-1-picrylhydrazyl to the complex prior to the addition of N-AcO-AAF decreased crosslinking. Reaction of the carcinogen with a solution of [methyl-3H]thymidine labeled Escherichia coli DNA led to the formation of tritiated water that was azeotropically distilled from the mixture. If nitrosobenzene was added prior to the carcinogen, the amount of tritium water released was depressed. Addition of N-AcO-AAF to a mixture of acrylamide and bisacrylamide increased its relative viscosity. Far u.v. irradiation of the complex or reacting it with ammonium persulfate that dissociates to the sulfate anion radical, SO(4), induced crosslinking. While these observations support a free radical mechanism for crosslinking, whether the free radicals arise from heterolytic or homolytic cleavage of N-AcO-AAF remains undetermined.

[Mechanism of action of non-steroidal antirheumatic agents]

Non-steroidal antirheumatic drugs permit a nonspecific, symptomatic therapy of inflammatory rheumatic processes and may also be given for a limited period of time in patients with so-called activated osteoarthrosis. Their mode of action is a complex one. More recent knowledge on mediators in inflammation such as prostaglandins, leukotriens and oxygen radicals have brought new insights on the mode of action of non-steroidal antirheumatic drugs.

Reduction, oxidation, and addition reactions between free radicals and flavins

Flavins and reduced flavins were reacted with a variety of free radicals produced in dilute aqueous solution at pH 7 +/- 0.1 by radiation chemical methods. The radical .CH2C(CH3)2OH and the aliphatic beta, gamma, and delta radicals of ethanol, 2-propanol, and 1-butanol added to the radical form of flavin adenine dinucleotide (FAD) (FH.) to yield products that could not be reoxidized to flavin by oxygen. The first radical also added to FAD but with a much lower efficiency. In contrast, the alpha-carbon radicals .CH(OH)CH2OH, CH3(-3) CHOH, and (CH3)2COH appeared to undergo two reactions: FH. + RR'COH leads to FH- + RR'C==O FH. + RR'COH leads to FH- + RR'C==O + H+ The formate radical anion .CO2(-) reacted similarly, producing stoichiometric two-electron reduction of riboflavin and lumiflavin as well as FAD. While eaq- also seemed capable of this, it was found to react irreversibly with FADH2, which makes it a poor reagent for producing the dihydroflavin. The dihydro form of FAD was reoxidized to FAD by the species RS. and .BR2(-). In contrast to FAD, the alloxazine lumichrome underwent only one-electron reduction and oxidation by .CO2(-) and .Br2(-), respectively.

Laser flash photolysis studies of electron transfer between semiquinone and fully reduced free flavins and horse heart cytochrome c

Laser flash photolysis has been used to determine the second-order rate constants for the reduction of horse heart cytochrome c by the semiquinone and fully reduced forms of various flavin analogs. We find that substitution in the dimethylbenzene ring of the flavin causes appreciable changes in the rate constants, whereas substitutions at the N-10 position do not. Placing a charged phosphate group in the N-10 ribityl side chain leads to only small ionic strength effects on the rate constants, whereas a charged group attached to the dimethylbenzene ring produces a large ionic strength effect. These results can be accounted for by assuming that a productive collision between flavin and cytochrome involves an orientation that positions the aromatic ring--N-5 region of the flavin toward the heme crevice and the N-10--pyrimidine ring region away from it. Our observations have implications for mechanistic understanding of biological electron transfer reactions and are discussed in this context.

The kinetics and thermodynamics of the reduction of cytochrome c by substituted p-benzoquinols in solution

1. The mechanisms by which p-benzoquinol and its derivatives reduce cytochrome c in solution have been investigated. 2. The two major reductants are the species QH- (anionic quinol) and Q.- (anionic semiquinone). A minor route of electron transfer from the fully protonated QH2 species can also occur. 3. The relative contributions of these routes to the overall reduction rate are governed by pH, ionic strength and relative reactant concentrations. 4. For a series of substituted p-benzoquinols, the forward rate constant, k1, of the anionic quinol-mediatd reaction is related to the midpoint potential of the QH-/QH. couple involved in the rate-limiting step, as predicted by the theory of Marcus for outer-sphere electron transfer reactions in a bimolecular collision process. 5. A mechanism for the biological quinol oxidation reactions in mitochondria and chloroplasts is proposed based upon the findings with these reactions in solution.

Effect of oxygen-derived free radicals on hyaluronic acid

To investigate possible mechanisms of hyaluronic acid depolymerization, superoxide anion and other secondary oxygen-derived free radicals were generated in vitro and allowed to act upon a hyaluronate substrate. Superoxide, generated either enzymatically with xanthine oxidase or by stimulation of polymorphonuclear leukocytes, reduced the viscosity of hyaluronate solutions dramatically while the chromatographic profiles of the glycosaminoglycan shifted toward lower molecular weights. Superoxide-treated hyaluronate also became susceptible to further degradation by beta-N-acetylglucosaminidase A. Experiments with scavengers of various toxic oxygen-derived free radicals clearly implicated these reactants as mediators of hyaluronate depolymerization. Generation of superoxide by leukocytes in vivo may account for the loss of synovial fluid viscosity that accompanies inflammatory joint disease.

Aspects of free radical reactions in biological systems: aging

The role of free radicals and lipid peroxidation is reviewed with regard to the aging process. Free radicals are produced during mitochondrial respiration, during the autooxidation of a variety of biological molecules and chemicals, during irradiation damage, and are found as environmental pollutants. Free radicals induce lipid peroxidation which results in membrane damage, increased disulfide/sulfhydryl ratios, and accumulation of aging pigments. Superoxide dismutase, glutathione peroxidase, vitamin E, vitamin C, and selenium are of importance with respect to free radical and lipid peroxide quenching. During aging, the levels of vitamin C appear to decline in the human, guinea pig, and the mouse. Synthetic antioxidants, added to the diets of mice, have been noted to extend the lifespan and mean half-survivale times.

Production of hydroxyl radical by human alveolar macrophages

Stimulated human alveolar macrophages were demonstrated to oxidize B-methyl proprionaldehyde (methional) or 2-keto-4-thiomethylbutyric acid to ethylene (C2H4). Agents which are believed to scavenge the hydroxyl radical (.OH), sodium benzoate, and mannitol, as well as scavengers of superoxide anion (O2-) or hydrogen peroxide, decreased C2H4 production, implicaing .OH as the oxidizing radical. Differences in C2H4 rpoduction, as well as oxygen uptake and O2- release between human alveolar macrophages and polymorphonuclear leukocytes, were also documented.

Effect of ischemic anoxia and barbiturate anesthesia on free radical oxidation of mitochondrial phospholipids

The mitochondrial fraction obtained from brains of animals submitted to ischemia shows a decrease of phospholipid level, especially plasmalogens in the fraction of ethanolamine phospholipids and choline phospholipids. There appears simultaneously an increase of free radical oxidation processes of unsaturated fatty acids from these phospholipids. The peroxidation processes of mitochondrial lipids are stimulated by calcium ions and, to a smaller extent, by magnesium ions. Barbiturate anesthesia inhibits the peroxidation of fatty acids and increases the antioxidant abilities of the nervous tissue. Nembutal added in vitro remains without effect on the above processes. The effect of acetylcholine and the antioxidant ability of nervous tissue under barbiturate anesthesia with respect to ischemia are discussed.

Free radical theory of aging: effect of age, sex and dietary precursors on rat-brain docosahexanoic acid

Increasing the peroxidizability of dietary fat has an adverse effect on the function of the central nervous system (CNS) in the rat. This effect may be influenced by the level of docosahexanoic acid, a highly unsaturated fatty acid, selectively concentrated in the phospholipids of brain membranes. This study was aimed at determining the influence of age, sex, and the nature of a dietary lipid supplement - linolenic acid (18:3w3), docosahexanoic acid (22:6w3), or the same amount of 22:6w3 in the form of menhaden oil triglycerides - on the rate of increase in the percentage of 22:6w3 in the whole-brain fatty acids of rats between the ages of 1 and 12 months. The dietary lipid supplements were reflected in linear increases in the brain 22:6w3 of female rats throughout the study. Between 6 and 12 months of age, the rate of incorporation of dietary 22:6w3 and its precursors into the brain 22:6w3 of male rats dropped. At 12 months it was about half that for females in the case of 22:6w3 and menhaden oil, and about zero for 18:3w3. It is suggested that dietary 22:6w3 and its precursors may modify CNS function by altering membrane function and peroxidizability through changes in the concentration of 22:6w3 in membrane phospholipids.

Involvement of the superoxide free radical ion in photosynthetic oxygen reduction

Photosynthetic oxygen reduction by isolated chloroplast lamellar systems has been studied with the aid of superoxide dismutase. Two mechanisms of oxygen reduction by illuminated chloroplast lamellar systems can be differentiated:

1. In the presence of low potential electron acceptors like AQ or MV the superoxide free radical ion is the product of autooxidation of the reduced acceptor. Addition of superoxide dismutase has no influence on the initial rates of oxygen reduction.

2. Stimulation of photosynthetic oxygen reduction by o-diphenols is only observed in the absence of superoxide dismutase and ascorbate; apparently the superoxide free radical ions is involved in both initiation and propagation of a chain reaction.

If the ferredoxin-stimulated photosynthetic oxygen reduction is measured, both ascorbate and superoxide dismutase are active as inhibitors. By heating suspensions of chloroplast lamellar systems, a substance is released into the supernatant which exhibits the activity of an oxygen reducing factor (ORF) with properties similar to o-diphenols: The stimulation of photosynthetic oxygen reduction is reversed by addition of either SDM or ascorbate. A reaction sequence for photosynthetic oxygen reduction in the presence of ferredoxin is considered, which is initiated by the superoxide free radical ion produced by autooxidation of reduced ferredoxin; the superoxide free radical ion "activates" an endogenous oxygen reducing factor, which in this "active" state can reduce oxygen to O2·-. The presence of either superoxide dismutase or ascorbate yields in chain termination by scavenging the superoxide free radical ion