Molecular basis of Brucella pathogenicity: an update

Microorganisms belonging to the genus Brucella can infect humans and many species of animals. Virulence of the brucellae is thought to be essentially due to their capacity to survive and replicate within the phagocytic cells. However, many gaps remain in our understanding of this ability of brucellae to elude the bactericidal effects of host phagocytes, and basic questions remain unanswered. Identification of Brucella gene products which are related to intracellular survival, as well as those which contribute to the induction of protective immunity, is critical to elucidate the molecular mechanisms of the pathogenesis of the organism. The present article summarizes the current status of the research on gene products and other structural or metabolic factors associated with virulence of the brucellae.

Beta-cell defence and repair mechanisms in human pancreatic islets

In vivo and in vitro data obtained in rodents indicate that beta-cells can trigger efficient repair mechanisms following non-lethal injury. Recent observations suggest that human pancreatic islets are more resistant than rodent islets to damage by alkylating agents, free oxygen radicals, nitric oxide and cytokines. This increased resistance to injury is associated with higher expression of heat shock protein 70, catalase and superoxide dismutase. These findings emphasise the potential relevance of beta-cell repair and/or defence mechanisms in the development of human IDDM.

Human hepatic alcohol dehydrogenase and human erythrocyte catalase do not metabolize the cytochrome P-4502E1 substrate, chlorzoxazone

Studies of cytochrome P-4502E1 (CYP2E1)-mediated oxidation of ethanol have been hampered by the lack of a suitable probe for in vivo human studies. Chlorzoxazone, a prescribed skeletal muscle relaxant, is metabolized to 6-hydroxychlorzoxazone by CYP2E1 and has been advocated as a specific probe of this enzyme on the basis of microsomal studies. The applications of this probe may include delineating the contribution of CYP2E1 to in vivo human ethanol metabolism. However, the activity of nonmicrosomal enzymes in metabolizing chlorzoxazone is unknown. Alcohol dehydrogenase (ADH), predominantly a hepatic cytosolic enzyme, may be more important than CYP2E1 in the oxidation of ethanol to acetaldehyde. The contribution of catalase in the in vivo oxidation of ethanol to acetaldehyde is controversial. To determine if either of these enzymes metabolizes chlorzoxazone and whether ethanol oxidation by either enzyme is inhibited by chlorzoxazone or its metabolite, multiple in vitro studies were performed. ADH enzyme kinetics were performed with human recombinant beta 1 beta 1 and beta 3 beta 3 ADH with ethanol and chlorzoxazone (0.5 to 2.5 mM). Neither ADH isoenzyme exhibited NAD(+) -dependent oxidation of chlorzoxazone, but displayed Michaelis-Menten kinetics for ethanol with K(m) values of 89 microM and 34 mM, for beta 1 beta 1 and beta 3 beta 3, respectively. Typical in vivo concentrations of chlorzoxazone and its metabolite, 6-hydroxychlorzoxazone, did not alter beta 1 beta 1 or beta 3 beta 3 ADH-mediated oxidation of ethanol to acetaldehyde. Studies of human hepatic nonmicrosomal enzyme activity were expanded to include all nonmicrosomal NAD(+) -dependent hepatic enzymes by starch gel electrophoresis assessment. Human hepatic enzymatic activity in the presence of chlorzoxazone was similar to that observed in the control sample (no added substrate), suggesting a lack of metabolism by NAD(+)-dependent enzymes. Similarly, human erythrocyte catalase, in the presence of a hydrogen peroxide generating system, did not metabolize chlorzoxazone. Furthermore, neither chlorzoxazone nor 6-hydroxychlorzoxazone altered the catalase-induced formation of acetaldehyde from ethanol. These data are consistent with chlorzoxazone as a specific probe of CYP2E1 that may be useful to alcohol researchers.

Variation in cellular glutathione peroxidase activity in lens epithelial cells, transgenics and knockouts does not significantly change the response to H2O2 stress

This investigation examines the contribution of glutathione peroxidase (GSHPx-1) in degrading H2O2 in lens preparations. Rabbit (N/N1003A) and normal and GSHPx-1 transfected mouse (alpha TN4-1) lens epithelial cell lines and normal and GSHPx-1 transgenic and knockout mouse lenses were utilized. GSHPx-1 activity in the cell lines was increased from two-fold to about four-fold, in the lenses from transgenics more than four-fold and the lenses from knockouts had less than 3% of normal GSHPx-1 activity. The transgenic and knockout mice as well as their lenses appeared normal for up to 3 to 4 months, the longest period of observation. The preparations were subjected to oxidative stress by placing them either in a medium containing 120 or 300 microM H2O2 or utilizing photochemical stress where the H2O2 levels normally rise to about 100 microM over a few hours in the presence of a normal lens. With all preparations, it was found that either markedly increasing or eliminating GSHPx-1 activity had only a small effect on the system's ability to metabolize H2O2, 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), an inhibitor of GSSG reductase (GSSG Red) and 3-aminotriazole (3-AT), an inhibitor of catalase, also had little effect. However, the addition of both inhibitors caused a marked decrease in H2O2 degradation. Examination of the distribution of GSHPx-1 in the lens indicated that the activity per milligram of protein was evenly distributed between the epithelium and the remainder of the lens in the normal lens and was about 1.7-fold greater in the epithelium of transgenic lenses than in the remainder of the lens. Surprisingly, the distribution of GSSG Red was quite different with eight- to ten-fold more activity in the epithelium. Catalase was also found to be concentrated in the epithelium. With H2O2 exposure, a rapid loss of non-protein thiol (NP-thiol) was found in cell cultures and in the epithelia of cultured lenses. However, the remainder of the lens showed little change in NP-thiol. The variation of GSHPx-1 activity did not influence the NP-thiol changes which occurred more rapidly and to a greater extent in the presence of BCNU. The addition of BCNU also caused a decrease in total lens NP-thiol. Examination of thymidine incorporation and choline transport, indicators of nuclear and membrane function, also reflects the H2O2 degradation data, showing little difference in the degree to which H2O2 effects these parameters in lenses from normal and transgenic animals. Catalase activity is four- to six-fold greater than GSHPX-1 activity in the alpha TN4-1 cell lines, about three-fold lower in the rabbit cell line and, remarkably, about 18-fold lower than the peroxidase in the normal mouse lens. In spite of such observations, the consistent overall conclusion is that GSHPx-1 and catalase function together but when GSHPx-1 is knocked out or GSSG Red is inhibited, catalase is able to protect the system from H2O2 stress. Indeed, the young mouse does not appear to require GSH Px-1 for normal function.

Helicobacter pylori enzymes

Helicobacter pylori exhibits a complex system of enzymes which serve a range of functions, such as colonization, damage of the host epithelium and provision of essential metabolic substrates. Colonization is favoured by urease and by the action on mucus and the mucosal barrier exerted by phospholipases and proteases, although this latter mechanism is controversial. Toxic effects are effected by urease, alcohol dehydrogenase (ADH), phospholipases and proteolytic enzymes. ADH produces acetaldehyde that is toxic to the mucosal cells, while phospholipases induce generation of products such as lysolecithin, which damage the gastric epithelium. Catalase and sodium dismutase of H. pylori are mainly involved in transforming toxic oxygen metabolites to harmless water; they protect the bacterium from the killing effect of neutrophils. Metabolic enzymes (for example, phosphatases, ATPases) are essential for the generation of energy, for synthesis and transport of cell products and for ion fluxes. In addition, they influence cell growth and the expression of virulence factors.

[The role of catalase in histologic changes of acute experimental pancreatitis]

We produced acute biliary reflux pancreatitis by an injection of auto-bile in 31 young mongrel dogs. We divided into control group (n = 10), catalase administration group (B1 group, n = 17) and no-administration group (B2 group, n = 14). We studied the histologic changes of the brain tissue in those groups. There was no significant difference in the survival rate between group B1 and B2. In the histologic findings, ischemic cell changes were dominant in both groups within one month, but after 3 or 6 months after operation in group B2, satellitosis and/or neuronophagia was recognized as the irreversible changes. The lipid peroxides level was significant high in group B2. Consequentially, it is natural to think that the production of free radicals have been inhibited by catalase and the histologic changes in the brain in group B1 have been light.

Ethanol-induced oxidative stress in the liver

Oxygen stress is well recognized to be a key step in the pathogenesis of ethanol-associated liver injury. Ethanol administration induces an increase in lipid peroxidation either by enhancing the production of oxygen-reactive species and/or by decreasing the level of endogenous antioxidants. Numerous experimental studies have emphasized the role of the ethanol-inducible cytochrome P-450 in the microsomes, as well as the molybdo-flavoenzymes xanthine oxidase in the cytosol. This review shows the putative role of ethanol-induced disturbances in iron metabolism in relation to iron as a prooxidant factor. Ethanol administration also affects the mitochondrial free radical generation. Although many previous studies suggest a role for active oxygens in ethanol-induced mitochondrial dysfunction in hepatocytes, the detailed mechanism of ethanol-induced oxidative stress on mitochondria remains to be clarified further. Studies of our laboratory using a confocal laser scanning microscopic system strongly suggest that active oxidants produced during ethanol metabolism modulate mitochondrial energy synthesis in isolated and cultured hepatocytes. In addition, our investigations implicate endogenous glutathione-glutathione peroxidase system and catalase as important antioxidants and cytoprotective machinery in the hepatocyte mitochondria exposed to ethanol. The fluorographic investigations using the confocal laser scanning microscopy may be useful to extend our knowledge and provide a new view about ethanol-associated oxidative stress and metabolic changes in hepatocytes.

Role of catalase in retinal antioxidant defence system: its comparative study among rabbits, guinea pigs, and rats

The role of catalase in the retinal antioxidant defence system was examined in rabbits, guinea pigs, and rats with and without prolonged administration of a diet containing 0.4% 3-aminotriazole (3-AT), a catalase inhibitor. When weanling rabbits, guinea pigs, and rats we administered 3-AT for 8, 7, and 10 weeks, respectively, retinal catalase activity was reduced by approximately 50% in all these animals. In the retina of rabbits with 3-AT administration, a decrease in superoxide dismutase (SOD) activity and an increase in lipid peroxide (LPO) concentration occurred. while glutathione peroxidase (GSH-px) activity did not change. In the retina of guinea pigs with 3-AT administration, an increase in LPO concentration occurred, while SOD and GSH-px activities did not change. In the retina of rats with 3-AT administration, a decrease in GSH-px activity and an increase in LPO concentration occurred, while SOD activity did not change. An increase in serum LPO concentration was found in rats with 3-AT administration, while the concentration did not change in rabbits and guinea pigs. These results indicate that catalase plays an important role in the retinal antioxidant defence system, but that the way catalase contributes to the maintenance of the retinal antioxidant defence system is different among these animals. The present results suggest that under the prolonged inhibition of catalase, the retina of rats, but not of rabbits and guinea pigs, may suffer from the influence of systemic oxidative stress.

Biochemical aspects of cellular antioxidant systems

Aerobic life is characterized by a steady generation of reactive oxygen species balanced by a similar rate of their consumption by antioxidants. To maintain homeostasis, there is a requirement for the continuous regeneration of antioxidant capacity, and if this is not met, oxidative stress occurs, resulting in pathophysiological events. Cellular protection against oxidative stress is organized at multiple levels. Defense strategies include prevention, interception, replacement, and repair. These mechanisms are coupled to the intermediary metabolism for a continuous supply of energy, reducing equivalents, and precursors, and depend on the dietary supply of metabolic fuels and essential molecules to allow an optimal cellular functioning.

Cloning and characterization of the katB gene of Pseudomonas aeruginosa encoding a hydrogen peroxide-inducible catalase: purification of KatB, cellular localization, and demonstration that it is essential for optimal resistance to hydrogen peroxide

Pseudomonas aeruginosa is an obligate aerobe that is virtually ubiquitous in the environment. During aerobic respiration, the metabolism of dioxygen can lead to the production of reactive oxygen intermediates, one of which includes hydrogen peroxide. To counteract the potentially toxic effects of this compound, P. aeruginosa possesses two heme-containing catalases which detoxify hydrogen peroxide. In this study, we have cloned katB, encoding one catalase gene of P. aeruginosa. The gene was cloned on a 5.4-kb EcoRI fragment and is composed of 1,539 bp, encoding 513 amino acids. The amino acid sequence of the P. aeruginosa katB was approximately 65% identical to that of a catalase from a related species, Pseudomonas syringae. The katB gene was mapped to the 71- to 75-min region of the P. aeruginosa chromosome, the identical region which harbors both sodA and sodB genes encoding both manganese and iron superoxide dismutases. When cloned into a catalase-deficient mutant of Escherichia coli (UM255), the recombinant P. aeruginosa KatB was expressed (229 U/mg) and afforded this strain resistance to hydrogen peroxide nearly equivalent to that of the wild-type E. coli strain (HB101). The KatB protein was purified to homogeneity and determined to be a tetramer of approximately 228 kDa, which was in good agreement with the predicted protein size derived from the translated katB gene. Interestingly, KatB was not produced during the normal P. aeruginosa growth cycle, and catalase activity was greater in nonmucoid than in mucoid, alginate-producing organisms. When exposed to hydrogen peroxide and, to a greater extent, paraquat, total catalase activity was elevated 7- to 16-fold, respectively. In addition, an increase in KatB activity caused a marked increase in resistance to hydrogen peroxide. KatB was localized to the cytoplasm, while KatA, the "housekeeping" enzyme, was detected in both cytoplasmic and periplasmic extracts. A P. aeruginosa katB mutant demonstrated 50% greater sensitivity to hydrogen peroxide than wild-type bacteria, suggesting that KatB is essential for optimal resistance of P. aeroginosa to exogenous hydrogen peroxide.

[Reactive oxygen species and arachidonic acid metabolites of polymorphonuclear leukocytes]

The activation of polymorphonuclear leukocytes by stimulants from host or parasites leads to various metabolic processes and to enhanced oxygen uptake. Oxygen is enzymatically processed to from reactive oxygen compounds and metabolites of arachidonic acid which are involved in killing of microbial pathogens and influence many processes in inflammation. Their activities are regulated intracellularly by antioxidants. A lack or exhaustion of these systems may lead to cell and organ damage in which DNA, proteins, lipids and sugars may be involved. Antioxidants and inhibitors of the arachidonic acid metabolism are applied to reduce these pathological changes. An essential aspect of microbial pathogenicity is the multifold modification of the formation of reactive oxygen compounds and arachidonic acid metabolites.

Function and stationary-phase induction of periplasmic copper-zinc superoxide dismutase and catalase/peroxidase in Caulobacter crescentus

Although cytosolic superoxide dismutases (SODs) are widely distributed among bacteria, only a small number of species contain a periplasmic SOD. One of these is Caulobacter crescentus, which has a copper-zinc SOD (CuZnSOD) in the periplasm and an iron SOD (FeSOD) in the cytosol. The function of periplasmic CuZnSOD was studied by characterizing a mutant of C. crescentus with an insertionally inactivated CuZnSOD gene. Wild-type and mutant strains showed identical tolerance to intracellular superoxide. However, in response to extracellular superoxide, the presence of periplasmic CuZnSOD increased survival by as much as 20-fold. This is the first demonstration that periplasmic SOD defends against external superoxide of environmental origin. This result has implications for those bacterial pathogens that contain a CuZnSOD. C. crescentus was shown to contain a single catalase/peroxidase which, like Escherichia coli KatG catalase/peroxidase, is present in both the periplasmic and cytoplasmic fractions. The growth stage dependence of C. crescentus catalase/peroxidase and SOD activity was studied. Although FeSOD activity was identical in exponential- and stationary-phase cultures, CuZnSOD was induced nearly 4-fold in stationary phase and the catalase/peroxidase was induced nearly 100-fold. Induction of antioxidant enzymes in the periplasm of C. crescentus appears to be an important attribute of the stationary-phase response and may be a useful tool for studying its regulation.

Catalase and glutathione reductase protection of human alveolar macrophages during oxidant exposure in vitro

Because alveolar macrophages generate and release reactive oxygen metabolites but also contain antioxidative enzymes, they have the potential of either damaging or protecting tissues. We investigated the relative role of the hydrogen peroxide (H2O2)-scavenging antioxidative enzymes in H2O2 disposal and cell protection using freshly isolated (5 h ex vivo) and overnight (24 h ex vivo) cultured human alveolar macrophages. Cell protection was assessed on the basis of maintenance of cellular high-energy phosphates, leakage of intact nucleotides into the extracellular medium, and appearance of the nucleotide catabolic products xanthine, hypoxanthine, and uric acid. To investigate the relative importance of catalase and the glutathione redox cycle, the experiments were conducted in cells pretreated with amino-triazole (ATZ) to inactivate catalase or with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) to inactivate glutathione reductase. Catalase, glutathione peroxidase, and glutathione reductase activities did not change significantly during overnight culture of the cells. Both freshly isolated and cultured cells consumed exogenous H2O2 mainly by the catalase-dependent pathway. When the cells were exposed to H2O2 (100 microM), catalase and the glutathione redox cycle equally participated in maintaining cellular high-energy nucleotides. However, when cultured cells were exposed to formylated peptide (FMLP) (10(-7) M), the glutathione redox cycle was responsible for the maintenance of high-energy nucleotides. Furthermore, in both exposures, the glutathione redox cycle was more important in maintaining cell membrane integrity and preventing nucleotide leakage from the cells. Immunocytochemical labeling showed that catalase was primarily localized in the peroxisomal compartment of these cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Transient overexpression of catalase does not inhibit TNF- or PMA-induced NF-kappa B activation

H2O2 has been proposed as a second messenger involved in cell signaling for NF-kappa B activation. In the present study, this hypothesis was tested by transiently overexpressing catalase, a specific scavenger of H2O2, in COS-1 cells. A mammalian expression vector was constructed by incorporating catalase gene from pCAT10 clone into the unique EcoRI site of the pSG5 vector which contains the SV-40 promoter. Transient transfection of the catalase expression vector by the DEAE-dextran method led to a four-fold increase in catalase activity and catalase content as detected by immunoblot analysis. This level of increase was detected in both nuclear/mitochondrial- and cytosolic/microsomal fractions. Overexpression of catalase, however, did not block TNF- or PMA-induced NF-kappa B activation. These results weaken the hypothesis that H2O2 is a second messenger for TNF- and PMA-signaling for NF-kappa B activation.

The cysteines of catalase HPII of Escherichia coli, including Cys438 which is blocked, do not have a catalytic role

Site-directed mutagenesis of the katE gene of Escherichia coli was used to change, individually and in combination, Cys438 and Cys669 to serine in catalase HPII. The Cys438-->Ser mutation caused a 30% reduction in the specific activity of the enzyme, whereas the Cys669-->Ser mutation did not affect enzyme activity. The titration of free sulfhydryl groups in HPII revealed that Cys669 was reactive whereas Cys438 was unreactive. Properties of the modification on Cys438 included alkali lability, insensitivity to methylamine, hydroxylamine or reducing agents, and a mass determined by mass spectrometry to be approximately 43 +/- 2 Da. A hemithioacetal structure is consistent with these properties. Although free sulfhydryl groups do not play a significant role in the stability or catalytic mechanism of HPII, the sulfhydryl agent 2-mercaptoethanol caused a 50% inactivation of HPII along with an irreversible change in the absorption spectrum of the protein. Other sulfhydryl agents, including dithiothreitol, cysteine and glutathione, and the organic peroxide, t-butylhydroperoxide, which cannot directly access the active site, do not affect HPII activity, but they do cause a small reversible change in the absorption spectrum, possibly by a mechanism involving superoxide.

Antioxidant therapy in critical care medicine

Antioxidant therapies are currently undergoing clinical trials to determine their benefit in a number of diseases seen in the critical care unit. It is particularly likely that their use will become standard therapy in a number of situations in which there is reperfusion injury following an ischemic episode. During the lag time from the conception of antioxidant interventions to their introduction into clinical practice, our understanding of how oxidant injuries are mediated has changed considerably. This understanding has allowed the development of more rational approaches to antioxidant therapy while exposing the limitations of some of the approaches currently being evaluated in a clinical setting. In addition, some existing therapeutic agents have previously unrecognized antioxidant and pro-oxidant effects. An inherent requirement of an effective antioxidant therapy is that such therapy is effective against the radicals being generated, and that sufficient quantities of the antioxidants used reach all sites of radical generation in time to limit tissue injury. Recent observations suggest that few, if any, of the currently known individual antioxidants can adequately meet these goals. However, combination therapy, or the development of synthetic compounds that can combine the properties of current antioxidants, may come close.

Activities of antioxidant enzymes in various tissues of male Fischer 344 rats are altered by food restriction

The objective of this study was to determine how food restriction (40% restriction of food intake) altered the age-related changes in the activities of Cu,Zn superoxide dismutase, catalase and glutathione peroxidase in liver, brain cortex, heart, kidney and intestinal mucosa obtained from 6-, 16- and 26-mo-old male Fischer 344 rats. Food restriction increased the activity of one or more of the antioxidant enzymes in the liver, brain cortex, heart and kidney of the rats. However, the magnitude of the effect and the antioxidant enzyme(s) affected by food restriction varied from tissue to tissue, and food restriction had no significant effect on the activities of these enzymes in intestinal mucosa. Interestingly, the four tissues in which food restriction increased the activity of one or more of the antioxidant enzymes showed reduced lipid peroxidation as measured by thiobarbituric acid-reactive material. These data suggest that food restriction might enhance the survival of rodents by altering the levels of the antioxidant enzymes and hence reducing free radical damage.

Antioxidant defence mechanism of the skin against UV irradiation: study of the role of catalase using acatalasaemia fibroblasts

To clarify the role of catalase, an antioxidant enzyme, in response to UV irradiation, we compared the effects of irradiation on cytotoxicity, activities of antioxidant enzymes, total glutathione concentrations, lipid peroxidation and the rate of collagen synthesis in skin fibroblasts from a patient with acatalasaemia and in those from a normal individual. The cells were irradiated with UVA (6 and 12 J/cm2 or UVB (0.5 and 1 J/cm2). Cell survival curves after UV irradiation were similar in cells from both subjects. Although superoxide dismutase activity in acatalasaemia cells was higher than in the control cells before irradiation, after irradiation the activity decreased in acatalasaemia cells (76% with 12 J/cm2 UVA, 47% with 1 J/cm2 UVB), but remained unchanged in control cells. Total glutathione concentrations also decreased in acatalasaemia cells (60% with 12 J/cm2) in response to UVA irradiation, but remained unchanged in control cells. Lipid peroxidation did not increase significantly in either cell type. The rate of collagen synthesis decreased to a similar extent in response to UV exposure in the two cell types (60-80% with 8.2 J/cm2 UVA, 40-50% with 10 mJ/cm2 UVB). We conclude from the results of cytotoxicity and lipid peroxidation that although acatalasaemia cells were killed by hydrogen peroxide at low concentrations with a single UV exposure, catalase functions only to a small degree as an antioxidant enzyme. There remains the possibility, however, that a deficiency of catalase may chronically damage the skin resulting in a reduced defence function of superoxide dismutase and glutathione with repeated exposures to UV, which is becoming more common in our daily life.

Apparent antibacterial activity of catalase: role of lipid hydroperoxide contamination

Escherichia coli was killed by catalase in dose-, time-, and pH-dependent manners. Dialyzed catalase had bactericidal activity, but enzyme which had been heat-denatured or inactivated by pretreatment with 3-aminotriazole plus hydrogen peroxide did not. Cytochrome c and hemoglobin also had bactericidal activity. Thiobarbituric acid-reactive substances were detected in commercial hemoproteins except for horseradish peroxidase and the relationship between the contents of these substances and bactericidal activity was demonstrated. Without the addition of hydroperoxide, hemoproteins except for horseradish peroxidase initiated the oxidation of 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and catalase caused the peroxidation of linoleic acid. The pH patterns of bactericidal activity, lipid peroxidation, and the oxidation of ABTS were similar. The results indicate that hemoprotein preparations are contaminated with lipid hydroperoxides and it is the decomposition of these contaminants catalyzed by the hemoprotein into alkoxyl/peroxyl radicals that causes bacterial killing.

Time-dependent effect of chronic UV irradiation on superoxide dismutase and catalase activity in hairless mice skin

Reactive oxygen species are produced by ultraviolet (UV) exposure and cause oxidative damage. Enzymic antioxidants such as superoxide dismutase (SOD) and catalase (CAT) may play important defensive roles in vivo. The previous studies have focused on the acute effects after single UV irradiation on those enzyme activities. In this study, we investigated the chronic effects of ultraviolet-A (UVA) or ultraviolet-B (UVB) exposure on the skin SOD and CAT activities using hairless mice. Accumulated doses of UVA and UVB after 36-week irradiation conducted 3 times a week were 3240 J/cm2 and 4320 mJ/cm2, respectively. SOD activity was increased by UVB irradiation and gradually returned to control levels, but was unaffected by UVA irradiation. In contrast, CAT activity was suppressed by UVA irradiation, indicating that the skin SOD and CAT activities are not coordinately regulated by long-term UV irradiation. These findings suggest that SOD activity is induced by repeated exposures to UVB in response to chronic photooxidative stress. However, continual cumulative stress may overwhelm the capacity of this system. These time-dependent changes of the cutaneous antioxidant system by chronic UV irradiation should provide us with important information on photooxidative events in cutaneous photoaging.

Free oxygen radicals contribute to platelet aggregation and cyclic flow variations in stenosed and endothelium-injured canine coronary arteries

OBJECTIVES

The purpose of this study was to test the hypothesis that free oxygen radicals contribute to platelet aggregation and cyclic flow variations in stenosed and endothelium-injured coronary arteries.

BACKGROUND

Although free oxygen radicals, such as superoxide anion and hydrogen peroxide, have been shown to alter platelet function in vitro, the potential role of free oxygen radicals has not been fully described in an in vivo model of coronary artery thrombosis.

METHODS

Cyclic flow variations were produced in dogs by an external constrictor placed at the site of the left anterior descending coronary artery with injured endothelium. Blood flow in this artery was monitored by a pulsed Doppler flow probe. If cyclic flow variations were observed during postoperative days, dogs intravenously received superoxide dismutase plus catalase. In anesthetized dogs that did not develop an episode of cyclic flow variations, the effect of intracoronary infusion of xanthine plus xanthine oxidase or hydrogen peroxide on arterial blood flow velocity was studied. In platelet studies, the effect of free oxygen radicals and radical scavengers on platelet aggregation was examined.

RESULTS

In conscious dogs with cyclic flow variations, superoxide dismutase plus catalase significantly reduced cyclic flow variations (n = 7), whereas saline infusion had no effect (n = 7). The infusion of xanthine plus xanthine oxidase or hydrogen peroxide significantly induced cyclic flow variations in four of six dogs or in five of seven dogs, respectively. In vitro platelet studies showed that xanthine plus xanthine oxidase or hydrogen peroxide significantly enhanced platelet aggregation, and superoxide dismutase or catalase significantly inhibited such aggregation.

CONCLUSIONS

Reduction of free radical formation decreases platelet aggregation and may eliminate cyclic flow variations, whereas promotion of free radical generation enhances platelet aggregation and may induce cyclic flow variations. Thus, free oxygen radicals are an important mediator in this model.

Characterization and virulence analysis of catalase mutants of Haemophilus influenzae

In addition to detoxifying peroxides generated by aerobic metabolism, the catalases of pathogenic bacteria have also been hypothesized to serve as virulence factors by enabling microorganisms to resist the oxidative bursts of host inflammatory cells. Using transposon mutagenesis of the hktE gene, encoding the Haemophilus influenzae structural gene for catalase, we constructed defined catalase mutants of H. influenzae strains Rd- and Eagan b+. These mutants show no detectable catalase production during exponential or stationary phases or following induction with hydrogen peroxide or ascorbic acid, indicating that hktE is the only functional hydroperoxidase gene present in these two strains of H. influenzae. Exponential-phase cultures of hktE mutants are 8- to 25-fold more sensitive to hydrogen peroxide than the wild type. Using the infant rat model, hktE mutants of strain Eagan b+ were 2.3-fold less virulent than the wild type following intraperitoneal inoculation (P = 0.07). When administered intranasally, the Eagan b+ hktE mutant produced wild-type levels of bacteremia and nasal colonization. The results of this study show that while the H. influenzae hktE gene is important for survival in the presence of peroxides, deletion of the gene produces only a modest reduction in ability to cause lethal sepsis following parenteral challenge and no change in ability to colonize following intranasal inoculation in the infant rat model of infection.

Different influence of superoxide anions and hydrogen peroxide on endothelial function of isolated cat cerebral and pulmonary arteries

1. Exogenous superoxide dismutase (SOD) or catalase did not modify isolated cat middle cerebral arterial basal tone. Catalase but not SOD reduced ACh relaxation. 2. H2O2 induced endothelium-independent relaxation which was abolished by catalase. 3. 3-Amino-1,2,4-triazole (AT) evoked endothelium-dependent contractions and diminished ACh relaxation. 4. Diethyldithio carbamic acid (DETC) induced endothelium-independent relaxation and did not modify ACh vasodilatation. 5. ACh relaxation of cat isolated pulmonary arteries was unaffected by SOD, catalase or AT, and diminished by DETC. 6. Endothelial catalase but neither SOD nor superoxide anions is involved in EDRF cerebral vasodilatation and H2O2 participates in ACh relaxation. In pulmonary arteries, only endothelial SOD activity plays a role.

Effects of ethanol treatment upon sources of reactive oxygen species in brain and liver

Sources of reactive oxygen species (ROS) generation have been compared in microsomal and mitochondrial fractions of brain and liver from ethanol-treated and control rats. Rates of ROS generation were quantitated with the fluorescent probe precursor, 2'7'-dihydrochloroflurescin diacetate, whose validity has been previously established. The production of active pro-oxidant species was measured in the presence of various selective inhibitors of enzymes potentially able to contribute to oxidative events. Several steps in the arachidonic acid cascade appeared to constitute a large fraction of total ROS generating capacity. Chelation of intrinsic iron with desferoxamine greatly reduced such capacity, especially in cerebral tissue. Aldehyde oxidases were active in generating ROS in both tissues. Inhibition of catalase dramatically enhanced ROS in liver but not in brain microsomes. While no ethanol-treatment effects were found in brain, there was evidence that ethanol consumption decreased hepatic levels of catalase, aldehyde oxidases and cyclooxygenase. However, despite these reductions, total basal ROS production was elevated in liver but not brain fractions from treated animals. The addition of an exogenous iron salt enhanced ROS formation to a lesser extent in ethanol-consuming rats than in controls. The elevation of basal hepatic ROS levels in ethanol-treated rats may thus be compatible with the release of cytosolic low molecular weight free iron compounds into the cytosol.

Adaptation of a Saccharomyces cerevisiae strain to high copper concentrations

A strain of Saccharomyces cerevisiae has been adapted to increasing concentrations of copper at two different pH values. The growth curve at pH 5.5 is characterized by a time generation increasing with the amount of added copper. A significant decrease of cell volume as compared with the control is also observed. At pH 3 the cells grow faster than at pH 5.5 and resist higher copper concentrations (3.8 against 1.2 mM). Experimental evidence indicates that, after copper treatment, the metal is not bound to the cell wall, but is localized intracellularly. A significant precipitation of copper salts in the medium was observed only at pH 5.5. Increased levels of superoxide dismutase (SOD) activity were observed in copper-treated cells and which persisted after 20 subsequent inocula in a medium without added metal. On the contrary, catalase activity was not stimulated by copper treatment and, hence, not correlated with SOD levels. The mechanism of copper resistance, therefore, probably involves a persistent induction of SOD, but not of catalase, and it is strongly pH-dependent.