Catalase: its role in xenobiotic detoxification

Chronic inflammation, neuroglial dysfunction, and plasmalogen deficiency as a new pathobiological hypothesis addressing the overlap between post-COVID-19 symptoms and myalgic encephalomyelitis/chronic fatigue syndrome

After five waves of coronavirus disease 2019 (COVID-19) outbreaks, it has been recognized that a significant portion of the affected individuals developed long-term debilitating symptoms marked by chronic fatigue, cognitive difficulties ("brain fog"), post-exertional malaise, and autonomic dysfunction. The onset, progression, and clinical presentation of this condition, generically named post-COVID-19 syndrome, overlap significantly with another enigmatic condition, referred to as myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Several pathobiological mechanisms have been proposed for ME/CFS, including redox imbalance, systemic and central nervous system inflammation, and mitochondrial dysfunction. Chronic inflammation and glial pathological reactivity are common hallmarks of several neurodegenerative and neuropsychiatric disorders and have been consistently associated with reduced central and peripheral levels of plasmalogens, one of the major phospholipid components of cell membranes with several homeostatic functions. Of great interest, recent evidence revealed a significant reduction of plasmalogen contents, biosynthesis, and metabolism in ME/CFS and acute COVID-19, with a strong association to symptom severity and other relevant clinical outcomes. These bioactive lipids have increasingly attracted attention due to their reduced levels representing a common pathophysiological manifestation between several disorders associated with aging and chronic inflammation. However, alterations in plasmalogen levels or their lipidic metabolism have not yet been examined in individuals suffering from post-COVID-19 symptoms. Here, we proposed a pathobiological model for post-COVID-19 and ME/CFS based on their common inflammation and dysfunctional glial reactivity, and highlighted the emerging implications of plasmalogen deficiency in the underlying mechanisms. Along with the promising outcomes of plasmalogen replacement therapy (PRT) for various neurodegenerative/neuropsychiatric disorders, we sought to propose PRT as a simple, effective, and safe strategy for the potential relief of the debilitating symptoms associated with ME/CFS and post-COVID-19 syndrome.

Effects of Zinc Supplementation in Mitigating the Harmful Effects of Chronic Cadmium Exposure in a Zebrafish Model

Cadmium (Cd) is a heavy metal that is highly toxic to living organisms, including humans. But the dietary zinc (Zn) supplements play critical role in minimizing or preventing Cd poisoning, without any side effects. The underlying mechanisms, however, have not been thoroughly investigated. Therefore, in this study, we investigated the use of Zn as a protection against Cd toxicity in zebrafish models. The obtained results confirmed the levels of antioxidant enzymes and supported the synergistic effects of Zn in reducing Cd toxicity. The lipid, carbohydrate, and protein concentrations in the liver tissue have also been negatively impacted by Cd; however, treatment with Zn has lessened these adverse effects. Furthermore, the level of 8-hydroxy-2' -deoxyguanosine (8-OHdG), caspase-3 also confirms the protective effects of Zn in reducing DNA damage caused by Cd. The results of this study demonstrate that a Zn supplement can lessen the harmful effects of Cd in zebrafish model.

Ginkgo biloba extracts (GBE) protect human RPE cells from t-BHP-induced oxidative stress and necrosis by activating the Nrf2-mediated antioxidant defence

OBJECTIVES

Age-related macular degeneration (AMD) is a prevalent ocular disease. Dry AMD accounts for most cases of blindness associated with AMD but there are no treatments. Oxidative stress-induced damage to retinal pigment epithelial (RPE) cells is a major contributor to the pathogenesis of dry AMD. This study investigated the protective actions of Ginkgo biloba extracts (GBE) in human RPE cells subjected to tert-butyl hydroperoxide (t-BHP)-mediated oxidative stress.

METHODS

The human ARPE-19 cells were pre-treated with or without GBE before the exposure to t-BHP. Cell viability, cell death profile and lipid peroxidation were assessed. The findings were verified using human primary RPE cultures.

KEY FINDINGS

GBE pre-treatment prevented the increase in lipid peroxidation and necrosis/ferroptosis, and the concurrent viability decrease in RPE cells exposed to t-BHP. It enabled the pronounced activation of Nrf2 and its downstream genes. We found that ERK1/2 phosphorylation was increased to a similar extent by t-BHP and GBE.

CONCLUSION

This study revealed that GBE pre-treatment attenuates pro-oxidant stress and protects human RPE cells from oxidative injury by modulating ERK1/2-Nrf2 axis. These findings suggest that GBE has the potential to be developed as a agent that may be valuable in decreasing AMD progression.

A riboswitch gives rise to multi-generational phenotypic heterogeneity in an auxotrophic bacterium

Auxotrophy, the inability to produce an organic compound essential for growth, is widespread among bacteria. Auxotrophic bacteria rely on transporters to acquire these compounds from their environment. Here, we study the expression of both low- and high-affinity transporters of the costly amino acid methionine in an auxotrophic lactic acid bacterium, Lactococcus lactis. We show that the high-affinity transporter (Met-transporter) is heterogeneously expressed at low methionine concentrations, resulting in two isogenic subpopulations that sequester methionine in different ways: one subpopulation primarily relies on the high-affinity transporter (high expression of the Met-transporter) and the other subpopulation primarily relies on the low-affinity transporter (low expression of the Met-transporter). The phenotypic heterogeneity is remarkably stable, inherited for tens of generations, and apparent at the colony level. This heterogeneity results from a T-box riboswitch in the promoter region of the met operon encoding the high-affinity Met-transporter. We hypothesize that T-box riboswitches, which are commonly found in the Lactobacillales, may play as-yet unexplored roles in the predominantly auxotrophic lifestyle of these bacteria.

Influence of chronic exposure to thiamethoxam and chronic bee paralysis virus on winter honey bees

Co-exposure to pesticides and viruses is likely to occur in honey bee colonies. Pesticides can be present in pollen, nectar, and persist in stored food (honey and bee bread), and viruses can be highly prevalent in honey bee colonies. Therefore, the present study describes the influence of chronic co-exposure to thiamethoxam and Chronic bee paralysis virus (CBPV) on bee survival, virus loads, expression level of immune and detoxication genes, and pesticide metabolism Experiments were performed on honey bees collected from a winter apiary with reduced viral contaminations. No synergistic effect of co-exposure was observed on bee survival, nor on the ability of bees to metabolise the pesticide into clothianidin. However, we found that co-exposure caused an increase in CBPV loads that reached the viral levels usually found in overt infections. The effect of co-exposure on CBPV replication was associated with down-regulation of vitellogenin and dorsal-1a gene transcription. Nevertheless, the observed effects might be different to those occurring in spring or summer bees, which are more likelyco-exposed to thiamethoxam and CBPV and exhibit a different physiology.

Lactate-stimulated ethanol oxidation: Revisiting an old hypothesis

Liver slices from starved rats and incubated without other substrates oxidized ethanol at a rate of 4.1 µmols • h^-1 • g^-1. Addition of 10 mmols • L^-1 lactate increased this rate 2-fold. 4-methylpyrazole (4-MP), an alcohol dehydrogenase (ADH) inhibitor, drastically decreased the rate of ethanol oxidation, but did not inhibit the stimulation due to lactate. In the same context, liver acetaldehyde production, as the main by-product of ethanol oxidation, appeared to be much less inhibited by 4-MP in the presence of lactate. Aminotriazole (a catalase inhibitor), however, completely inhibited the stimulation. Furthermore, 2-hydroxybut-3-ynoate, an alpha-hydroxy acid oxidase inhibitor, completely abolished the stimulated ethanol oxidation promoted by lactate. Moreover, to determine the origin of the H₂O₂ produced, we did liver subcellular fractionation and then analyzed their content in peroxisomes, mitochondria and catalase. We observed that cytoplasm and peroxisomes appears to be the main producers of H₂O₂, and that the acceleration of ethanol oxidation by lactate is completely dependent on catalase. In conclusion, the H₂O₂ necessary to boost the catalase-dependent oxidation of ethanol appears to come from cytoplasm and peroxisomes, and is produced by the enzyme lactate oxidase.

Formate: The Neglected Member of One-Carbon Metabolism

Formate, the only non-tetrahydrofolate (THF)-linked intermediate in one-carbon metabolism, is produced in mammals from a variety of metabolic sources. It occurs in serum of adults at a concentration of approximately 30 μM. Its principal function lies as a source of one-carbon groups for the synthesis of 10-formyl-THF and other one-carbon intermediates; these are primarily used for purine synthesis, thymidylate synthesis, and the provision of methyl groups for synthetic, regulatory, and epigenetic methylation reactions. Although formate is largely produced in mitochondria, these functions mostly occur in the cytoplasm and nucleus. Formate plays a significant role in embryonic development, as evidenced by the effectiveness of formate in the pregnant dam's drinking water on the incidence of neural tube defects in some genetic models. High formate concentrations in fetal lambs may indicate a role in fetal development and suggest that extracellular formate may play a role in the interorgan distribution of one-carbon groups.

Division of labour: how does folate metabolism partition between one-carbon metabolism and amino acid oxidation?

One-carbon metabolism is usually represented as having three canonical functions: purine synthesis, thymidylate synthesis and methylation reactions. There is however a fourth major function: the metabolism of some amino acids (serine, glycine, tryptophan and histidine), as well as choline. These substrates can provide cells with more one-carbon groups than they need for these three canonical functions. Therefore, there must be mechanisms for the disposal of these one-carbon groups (when in excess) which maintain the complement of these groups required for the canonical functions. The key enzyme for these mechanisms is 10-formyl-THF (tetrahydrofolate) dehydrogenase (both mitochondrial and cytoplasmic isoforms) which oxidizes the formyl group to CO2 with the attendant reduction of NADP(+) to NADPH and release of THF. In addition to oxidizing the excess of these compounds, this process can reduce substantial quantities of NADP(+) to NADPH.

Alleviation of Dimethylnitrosamine-Induced Liver Injury and Fibrosis by Supplementation of Anabasis articulata Extract in Rats

Anabasis articulata (Forssk) Moq. (Chenopodiaceae) is an herb, grows in Egypt, and used in folk medicine to treat diabetes, fever, and kidney infections. The protective and therapeutic effects of the ethanol extract of A. articulata aerial parts were evaluated against dimethylnitrosamine (DMN)-induced liver fibrosis, compared with the standard drug, silymarin. Hepatic hydroxyproline content, serum transforming growth factor-β1 (TGF-β1), interleukin 10 (IL-10) and fructosamine were measured as liver fibrosis markers. Hepatic malondialdehyde (MDA), nitric oxide (NO), catalase (CAT), glutathione reductase (GR) and glutathione content (GSH) were measured as oxidant/antioxidant markers. Parallel histopathological investigations were also performed. Protective and therapeutic administration of A. articulata (100 mg/kg daily for 4 weeks), markedly prevented DMN-induced loss in body and liver weights. The extract significantly inhibited the elevation of hepatic hydroxyproline, NO and MDA (P < 0.05), as well as serum fructosamine, and TGF-β1 (P < 0.05) induced by DMN while it restored IL-10 to normal level in both protective and therapeutic groups. Furthermore, A. articulata prevented the depletion in CAT, GR, and GSH levels (P ≤ 0.05). In addition, oral administration of A. articulata extract and silymarin to both protective and therapeutic groups reduced the increase in liver function enzyme activities; alanine and aspartate amintransferases, gamma-glutamyl transferase in addition to alkaline phosphatase, and caused significant increase in serum albumin concentration as compared to DMN group. These data corresponded closely with those obtained for the drug silymarin. Histopathological studies confirmed the biochemical data and revealed remarkable improvement in liver architecture. Thus, it could be concluded that, A. articulata extract exhibited in vivo hepatoprotective and therapeutic effects against DMN-induced liver injury and may act as a useful agent in controlling the progression of hepatic fibrosis through reduction of oxidative stress and improving liver function.

Oxidant stress, mitochondria, and cell death mechanisms in drug-induced liver injury: lessons learned from acetaminophen hepatotoxicity

Hepatotoxicity is a serious problem during drug development and for the use of many established drugs. For example, acetaminophen overdose is currently the most frequent cause of acute liver failure in the United States and Great Britain. Evaluation of the mechanisms of drug-induced liver injury indicates that mitochondria are critical targets for drug toxicity, either directly or indirectly through the formation of reactive metabolites. The consequence of these modifications is generally a mitochondrial oxidant stress and peroxynitrite formation, which leads to structural alterations of proteins and mitochondrial DNA and, eventually, to the opening of mitochondrial membrane permeability transition (MPT) pores. MPT pore formation results in a collapse of mitochondrial membrane potential and cessation of adenosine triphosphate synthesis. In addition, the release of intermembrane proteins, such as apoptosis-inducing factor and endonuclease G, and their translocation to the nucleus, leads to nuclear DNA fragmentation. Together, these events trigger necrotic cell death. Alternatively, the release of cytochrome c and other proapoptotic factors from mitochondria can promote caspase activation and apoptotic cell death. Drug toxicity can also induce an inflammatory response with the formation of reactive oxygen species by Kupffer cells and neutrophils. If not properly detoxified, these extracellularly generated oxidants can diffuse into hepatocytes and trigger mitochondrial dysfunction and oxidant stress, which then induces MPT and necrotic cell death. This review addresses the formation of oxidants and the defense mechanisms available for cells and applies this knowledge to better understand mechanisms of drug hepatotoxicity, especially acetaminophen-induced liver injury.

Hepatic antioxidant responses related to levels of PCBs and metals in chicks of three Arctic seabird species

The efficiency of antioxidant defenses and relationship with body burden of metal and organic contaminants has not been previously investigated in arctic seabirds, neither in chicks nor in adults. The objective of this study was to compare such defenses in chicks from three species, Black-legged kittiwake (Rissa tridactyla), Northern fulmar (Fulmarus glacialis), and Herring gull (Larus argentatus), and the relationship with tissue concentrations of essential metals such as selenium and iron and halogenated organic compounds, represented by polychlorinated biphenyl (PCB). The results showed significant species-specific differences in the antioxidant responses which also corresponded with metal and PCB levels in different ways. The capability to neutralize hydroxyl radicals (TOSC-HO•) and the activities of catalase and Se-dependent glutathione peroxidases (GPX) clearly increased in species with the higher levels of metals and PCBs, while the opposite trend was observed for Se-independent GPX, TOSC against peroxyl radicals (ROO•) and peroxynitrite (ONOOH). Less clear relationships were obtained for glutathione levels, GSH/GSSG ratio, glutathione reductase and superoxide dismutase. The results showed differences in antioxidant efficiency between the species, and some of these defenses exhibited dose-response-like relationships with measured levels of selenium, iron and ΣPCBs. PCBs, selenium and iron levels were positively related to the responses of antioxidants with potential to reduce HO•/H₂O₂ (Se-dependent GPX, CAT and TOSC against HO•). However, direct causal relationships between antioxidant responses and contaminant concentrations could not be shown on individual level. Varying levels of metals and contaminants due to different diet and age were probably the main explanations for the species differences in antioxidant defense.

Extract of Xylopia aethiopica (Annonaceae) protects against gamma-radiation induced testicular damage in Wistar rats

Ionizing radiation is an important environmental risk factor and, a major therapeutic agent for cancer treatment. This study was designed to evaluate the protective effect of extract of Xylopia aethiopica (XA) on gamma-radiation-induced testicular damage in rats. Vitamin C (VC) served as the reference antioxidant during the study. The study consists of 4 groups of 11 rats each. Group I received corn oil (vehicle), groups II and IV were pretreated with XA (250 mg/kg) and VC (250mg/kg) for 6 weeks before and 8 weeks after exposure to gamma-radiation; group III was exposed to a single dose of gamma-radiation (5 Gy). Biochemical analysis revealed that gamma-irradiation caused a significant increase (p < .05) in serum and testicular lipid peroxidation (LPO) levels by 217% and 221%, respectively. Irradiated rats had markedly decreased testicular catalase (CAT), superoxide dismutase (SOD), glutathione-S-transferase (GST), and reduced glutathione (GSH) levels. Irradiation resulted in 59% and 40% decreases in spermatozoa motility and live/dead sperm count, respectively, and a 161% increase in total sperm abnormalities. Histologically, testes of the irradiated rats showed extensive degenerative changes in the seminiferous tubules and defoliation of spermatocytes. Supplementation of XA and VC reversed the adverse effects of gamma-radiation on biochemical and histological indices of the rats. These findings demonstrated that Xylopia aethiopica has a protective effect by inhibiting oxidative damage in testes of irradiated rats.

Radiation protection by 6-palmitoyl ascorbic acid-2-glucoside: studies on DNA damage in vitro, ex vivo, in vivo and oxidative stress in vivo

A palmitoyl derivative of ascorbic acid 2-glucoside, 6-palmitoyl ascorbic acid-2-glucoside (PAsAG), which possess good antioxidant properties, is examined for radioprotection in vitro, ex vivo and in vivo models. PAsAG protected plasmid DNA from gamma-radiation induced damages under in vitro conditions. Presence of 1.6 mM PAsAG inhibited the disappearance of ccc (covalently closed circular) form of plasmid pBR322 with a dose modifying factor of 1.5. Comet assay studies on mouse spleen cells exposed to 6 Gy gamma-radiation (ex vivo) in presence and absence of PAsAG revealed that cellular DNA was effectively protected by this compound from radiation induced damages. Oral administration of 80 mg/kg body weight of PAsAG to mice 1 hour prior to 6 Gy whole body gamma-radiation exposure, efficiently protected cellular DNA in tissues such as spleen, bone marrow and blood, from radiation induced damages as indicated by alkaline comet assay. Oxidative stress in tissues such as liver and brain of mice, following whole body exposure to various doses of gamma-radiation (2-8 Gy), monitored as levels of GSH and peroxidation of lipids, were found considerably reduced when PAsAG was orally administered (80 mg/kg body weight) to the mice one hour prior to the radiation exposure. PAsAG administration improved the per cent survival of mice following exposure to 10 Gy whole body gamma-radiation. Thus PAsAG could act as a radioprotector under in vitro, ex vivo and in vivo conditions of ionizing-radiation exposure.

Protein oxidation and cellular homeostasis: Emphasis on metabolism

Reactive oxygen species (ROS) are generated as the result of a number of physiological and pathological processes. Once formed ROS can promote multiple forms of oxidative damage, including protein oxidation, and thereby influence the function of a diverse array of cellular processes. This review summarizes the mechanisms by which ROS are generated in a variety of cell types, outlines the mechanisms which control the levels of ROS, and describes specific proteins which are common targets of ROS. Additionally, this review outlines cellular processes which can degrade or repair oxidized proteins, and ultimately describes the potential outcomes of protein oxidation on cellular homeostasis. In particular, this review focuses on the relationship between elevations in protein oxidation and multiple aspects of cellular metabolism. Together, this review describes a potential role for elevated levels of protein oxidation contributing to cellular dysfunction and oxidative stress via impacts on cellular metabolism.

Modulation of radiation-induced disturbances of antioxidant defense systems by ginsan

There are numerous studies to indicate that irradiation induces reactive oxygen species (ROS), which play an important causative role in radiation damage of the cell. We evaluated the effects of ginsan, a polysaccharide fraction extracted from Panax ginseng, on the γ-radiation induced alterations of some antioxidant systems in the spleen of Balb/c mice. On the 5th day after sublethal whole-body irradiation, homogenized spleen tissues of the irradiated mice expressed only marginally increased mRNA levels of Mn-SOD (superoxide dimutase) in contrast to Cu/Zn-SOD, however, catalase mRNA was decreased by ∼50% of the control. In vivo treatment of non-irradiated mice with ginsan (100 mg kg⁻¹, intraperitoneal administration) had no significant effect, except for glutathione peroxidase (GPx) mRNA, which increased to 144% from the control. However, the combination of irradiation with ginsan effectively increased the SODs and GPx transcription as well as their protein expressions and enzyme activities. In addition, the expression of heme oxygenase-1 and non-protein thiol induced by irradiation was normalized by the treatment of ginsan. Evidence indicated that transforming growth factor-β and other important cytokines such as IL-1, TNF and IFN-γ might be involved in evoking the antioxidant enzymes. Therefore, we propose that the modulation of antioxidant enzymes by ginsan was partly responsible for protecting the animal from radiation, and could be applied as a therapeutic remedy for various ROS-related diseases.

p53-induced up-regulation of MnSOD and GPx but not catalase increases oxidative stress and apoptosis

p53-mediated apoptosis may involve the induction of redox-controlling genes, resulting in the production of reactive oxygen species. Microarray expression analysis of doxorubicin exposed, related human lymphoblasts, p53 wild-type (WT) Tk6, and p53 mutant WTK1 identified the p53-dependent up-regulation of manganese superoxide dismutase (MnSOD) and glutathione peroxidase 1 (GPx). Consensus p53 binding sequences were identified in human MnSOD and GPx promoter regions. A 3-fold increase in the MnSOD promoter activity was observed after the induction of p53 in Li-Fraumeni syndrome (LFS) fibroblast, TR9-7, expressing p53 under the control of a tetracycline-regulated promoter. An increased protein expression of endogenous MnSOD and GPx also positively correlated with the level of p53 induction in TR9-7 cells. However, catalase (CAT) protein expression remained unaltered after p53 induction. We also examined the expression of MnSOD, GPx, and CAT in a panel of normal or LFS fibroblasts, containing either WT or mutant p53. We found increased MnSOD enzymatic activity, MnSOD mRNA expression, and MnSOD and GPx protein in LFS fibroblasts carrying a WT p53 allele when compared with homozygous mutant p53 isogenic cells. The CAT protein level was unchanged in these cells. We observed both the release of cytochrome C and Ca(2+) from the mitochondria into the cytoplasm and an increased frequency of apoptotic cells after p53 induction in the TR9-7 cells that coincided with an increased expression of MnSOD and GPx, and the level of reactive oxygen species. The increase in apoptosis was reduced by the antioxidant N-acetylcysteine. These results identify a novel mechanism of p53-dependent apoptosis in which p53-mediated up-regulation of MnSOD and GPx, but not CAT, produces an imbalance in antioxidant enzymes and oxidative stress.

The changes of superoxide dismutase, catalase and glutathione peroxidase activities in erythrocytes of active and passive smokers

Cigarette smoking has been implicated in the pathogenesis of ischemic heart disease, emphysema, obstructive lung disease and neoplastic disorders. More than 1000 constituents of smoke, including many oxidants, pro-oxidants, free radicals and reducing agents, have been identified. The activities of erythrocyte superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px), which are the important components of antioxidant defense system, were measured in 100 healthy volunteers. This study included heavy smokers (consuming cigarettes > or = 20 per day; n=30, group I), light smokers (consuming cigarettes<20 per day; n=30, group II), passive smokers (exposed to cigarette smoke in the indoor environment; n=20, group III), and non-smokers (n=20, the control group). While activities of SOD and CAT in erythro cytes were significantly lower in groups I, II and III than in the control group (p<0.01 for all), mean erythrocyte GSH-Px activity in group III was higher than that in groups l, II and in controls. These results suggest that the increased oxidative stress occurs in smokers, owing to the free radicals present in smoke. It might cause a decrease in antioxidant enzyme activities and oxidant/antioxidant imbalance. We also observed that passive smokers were affected by the environmental smoke to the same extent as active smokers.

Auto-protective redox buffering systems in stimulated macrophages

BACKGROUND

Macrophages, upon encounter with micro-organisms or stimulated by cytokines, produce various effector molecules aimed at destroying the foreign agents and protecting the organism. Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are front line molecules exerting strong cytotoxic activities against micro-organisms and many cells, including macrophages themselves. Using cells of the murine macrophage cell line (RAW 264.7) stimulated in vitro with lipopolysaccharide (LPS) and/or interferon (IFN-gamma), which induce strong endogenous NO production, we examined by which mechanisms a fraction of activated macrophages protect themselves from nitrosative stress and manage to escape destruction?

RESULTS

We observed that survivors (10-50% depending on the experiments) had acquired a resistant phenotype being capable to survive when further exposed in vitro to an apoptosis inducing dose of the NO donor compound DETA-NO. These cells expressed an increased steady-state levels of Mn SOD, CuZn SOD and catalase mRNA (130-200%), together with an increased activity of the corresponding enzymes. Intracellular concentration of glutathione was also increased (x 3.5 fold at 6 hours, still maintained x 5.2 fold at 48 hours). Neither mRNA for glutathione peroxydase, gamma-glutamylcysteine synthase and glutathione reductase, nor thioredoxine and thioredoxine reductase, were significantly modified. Additional experiments in which RAW 264.7 cells were stimulated with LPS and/or IFN-gamma in the presence of relatively specific inhibitors of both Mn and Cu/Zn SOD, aminotriazol (ATZ) catalase inhibitor and buthionine sulfoximine (BSO) glutathione inhibitor, showed that inhibiting LPS-induced up-regulation of intracellular redox buffering systems also prevented acquisition of the resistant phenotype.

CONCLUSIONS

Our data suggest a direct causal relationship between survival of a fraction of macrophages and a up-regulation of key sets of auto-protective intracellular redox buffering systems, occurring simultaneously with modulation of expression of apoptotic molecules of the Bcl2-Bcl-XL/Bax-Bad family.

Plasma pharmacokinetics, nervous system biodistribution and biostability, and spinal cord permeability at the blood-brain barrier of putrescine-modified catalase in the adult rat

Free radical-mediated oxidative damage has been proposed to be an underlying mechanism in several neurodegenerative disorders. Previous investigations in our laboratory have shown that putrescine-modified catalase (PUT-CAT) has increased permeability at the blood-brain (BBB) and blood-nerve barriers with retained enzymatic activity after parenteral administration when compared to native catalase (CAT). The goals of the present study were to examine the plasma stability, spinal cord BBB permeability, nervous system biodistribution, and spinal cord enzyme activity of CAT and PUT-CAT after parenteral administration in the adult rat. TCA precipitation and chromatographic analyses revealed that CAT and PUT-CAT were found intact in the plasma and in the central nervous system (CNS) after iv, ip, or sc bolus injections. The highest percentages of intact CAT or PUT-CAT proteins were found in the plasma after iv administration, and similar percentages of intact CAT or PUT-CAT were found in the CNS following all three types of administration. Increases of 2.4- to 4.7-fold in permeability at the BBB and similar increases in the levels of intact PUT-CAT were found in different brain regions compared to the levels of CAT. A 2.4-fold higher level of intact PUT-CAT compared to that of CAT (P < 0.05) was found in the spinal cord 60 min after a sc bolus injection. CAT enzyme activity in the spinal cord was 50% higher (P < 0.05) in rats treated with PUT-CAT continuously for 1 week by subcutaneously implanted, osmotic pumps than the activity found in rats treated with PBS. These results provide evidence that intact, enzymatically active PUT-CAT is efficiently delivered to the nervous system following iv, ip, and sc administration and suggest that sc administration of PUT-CAT may be effective in treating neurodegenerative disorders in which the underlying mechanisms involve the action of free radicals and oxidative damage.

Bacterial gene products in response to near-ultraviolet radiation

Our research has focused on bacterial gene products that protect cells from damage by near-ultraviolet radiation (near-UV) including gene products involved in the subsequent recovery process. Protective gene products include such anti-oxidants as catalases, superoxide dismutases and glutathione reductase. Near-UV damage recovery products include exonuclease III and DNA-glycosylases. Perhaps more critical than the products of structural genes are certain regulatory gene products that are triggered upon excess near-UV oxidation and lead to synthesis of entire batteries of anti-oxidant enzymes, DNA repair enzymes, and DNA-integrity proteins. Our recent experiments have focused on RpoS and its interaction with OxyR, two proteins that regulate the synthesis of molecules that protect cells from near-UV and other oxidative stresses.

Vulnerability of the human airway epithelium to hyperoxia. Constitutive expression of the catalase gene in human bronchial epithelial cells despite oxidant stress

Although catalase is a major intracellular antioxidant, the expression of the human catalase gene appears to be limited in the airway epithelium, making these cells vulnerable to oxidant stress. The basis for this limited gene expression was examined by evaluation of the expression of the endogenous gene in human bronchial epithelial cells in response to hyperoxia. Hyperoxia failed to upregulate endogenous catalase gene expression, in contrast to a marked increase in expression of the heat shock protein gene. Sequence analysis of 1.7 kb of the 5'-flanking region of the human catalase gene showed features of a "house-keeping" gene (no TATA box, high GC content, multiple CCAAT boxes, and transcription start sites). Transfection of human bronchial epithelial cells with fusion genes composed of various lengths of the catalase 5'-flanking region and luciferase as a reporter gene showed low level constitutive promoter activity that did not change after exposure to hyperoxia. Importantly, using a replication-deficient recombinant adenoviral vector containing the human catalase cDNA, levels of catalase were significantly increased in human airway epithelial cells and this was associated with increased survival of the cells when exposed to hyperoxia. These observations provide a basis for understanding the sensitivity of the human airway epithelium to oxidant stress and a strategy for protecting the epithelium from such injury.

Effect of subchronic administration of antioxidants against cigarette smoke exposure in rats

Effects of subchronic administration of antioxidants against pulmonary damage mediated by cigarette smoke were investigated in rats. Rats were continuously received ascorbic acid, N-acetylcysteine and ginseng extract together drinking water from day 25 after birth. After 30 days of antioxidant supplementation, rats were exposed to cigarette smoke generated from six cigarettes (11 mg tar) for 20 min per day throughout 30 days, and then several biochemical markers related to the redox status in vivo were analyzed in the respiratory system. The cigarette smoke induced mild histological changes in trachea and lungs. The activity of superoxide dismutase (SOD) in the lung was significantly increased, and catalase and glutathione peroxidase activities were increased less than SOD, but total sulfhydryl compounds (Total-SH) content was decreased by cigarette smoking. In spite of the increase in activities of antioxidant enzymes, the inhibitory capacity of lung preparations on in vitro lipid peroxidation using ox brain homogenates was decreased and the change in the capacity was not related to the changes of these intracellular enzymes activities, but with the content of Total-SH. On the other hand, the content of thiobarbituric acid reactive substances and the ratio of elastase to anti-protease in the lung homogenates were significantly increased. Supplementation of antioxidants, however, effectively attenuated all of such alterations induced by cigarette smoke. These results indicate that although cigarette smoking induces antioxidant enzymes in the lung as a self defense mechanism, it seems to be not sufficient to protect the pulmonary system, and that chronic antioxidant feeding could be effective to reduce pulmonary damage induced by free radicals.

Hydrogen peroxide-induced oxidative stress to the mammalian heart-muscle cell (cardiomyocyte): nonperoxidative purine and pyrimidine nucleotide depletion

Hydrogen peroxide (H2O2) overload may contribute to cardiac ischemia-reperfusion injury. We report utilization of a previously described cardiomyocyte model (J. Cell. Physiol., 149:347, 1991) to assess the effect of H2O2-induced oxidative stress on heart-muscle purine and pyrimidine nucleotides and high-energy phosphates (ATP, phosphocreatine). Oxidative stress induced by bolus H2O2 elicited the loss of cardiomyocyte purine and pyrimidine nucleotides, leading to eventual de-energization upon total ATP and phosphocreatine depletion. The rate and extent of ATP and phosphocreatine loss were dependent on the degree of oxidative stress within the range of 50 microM to 1.0 mM H2O2. At the highest H2O2 concentration, 5 min was sufficient to elicit appreciable cardiomyocyte high-energy phosphate loss, the extent of which could be limited by prompt elimination of H2O2 from the culture medium. Only H2O2 dismutation completely prevented ATP loss during H2O2-induced oxidative stress, whereas various free-radical scavengers and metal chelators afforded no significant ATP preservation. Exogenously-supplied catabolic substrates and glycolytic or tricarboxylic acid-cycle intermediates did not ameliorate the observed ATP and phosphocreatine depletion, suggesting that cardiomyocyte de-energization during H2O2-induced oxidative stress reflected defects in substrate utilization/energy conservation. Compromise of cardiomyocyte nucleotide and phosphocreatine pools during H2O2-induced oxidative stress was completely dissociated from membrane peroxidative damage and maintenance of cell integrity. Cardiomyocyte de-energization in response to H2O2 overload may constitute a distinct nonperoxidative mode of injury by which cardiomyocyte energy balance could be chronically compromised in the post-ischemic heart.

Protection of human endothelial cells from oxidant injury by adenovirus-mediated transfer of the human catalase cDNA

In a variety of disorders, endothelial cells are exposed to high levels of oxidants, generated within the cells and/or consequent to local inflammation. In the context of the sensitivity of endothelial cells to oxidant stress, particularly related to H2O2, we have designed a replication deficient recombinant adenovirus containing the human catalase cDNA (AdCL) to transfer the catalase cDNA to the endothelial cells, in order to augment intracellular anti-H2O2 protection. Human umbilical vein endothelial cells that were not infected or infected with control adenovirus maintained low levels of catalase mRNA. Endothelial cells infected with AdCL expressed AdCL-driven exogenous catalase mRNA, as early as 24 hr and at least for 7 days. Catalase protein levels were increased significantly over controls in cells infected with AdCL, as were catalase activity levels, with catalase activity correlated closely with levels of catalase protein. Importantly, when the endothelial cells were exposed to 500 microM H2O2, all the AdCL infected endothelial cells survived, compared to only 37% of the control cells. Thus, a recombinant adenovirus containing the human catalase cDNA is able to infect human endothelial cells in vitro and express high levels of functional intracellular catalase, protecting the cells against H2O2-mediated oxidant stress. These observations support the feasibility of the transfer of catalase cDNA to human endothelium to protect against oxidant injury.

Hydrogen peroxide-induced oxidative stress to the mammalian heart-muscle cell (cardiomyocyte): lethal peroxidative membrane injury

Oxidative stress induced by hydrogen peroxide (H2O2) may contribute to the pathogenesis of ischemic-reperfusion injury in the heart. For the purpose of investigating directly the injury potential of H2O2 on heart muscle, a cellular model of H2O2-induced myocardial oxidative stress was developed. This model employed primary monolayer cultures of intact, beating neonatal-rat cardiomyocytes and discrete concentrations of reagent H2O2 in defined, supplement-free culture medium. Cardiomyocytes challenged with H2O2 readily metabolized it such that the culture content of H2O2 diminished over time, but was not depleted. The consequent H2O2-induced oxidative stress caused lethal sarcolemmal disruption (as measured by lactate dehydrogenase release), and cardiomyocyte integrity could be preserved by catalase. During oxidative stress, a spectrum of cellular derangements developed, including membrane phospholipid peroxidation, thiol oxidation, consumption of the major chain-breaking membrane antiperoxidant (alpha-tocopherol), and ATP loss. No net change in the protein or phospholipid contents of cardiomyocyte membranes accompanied H2O2-induced oxidative stress, but an increased turnover of these membrane constituents occurred in response to H2O2. Development of lethal cardiomyocyte injury during H2O2-induced oxidative stress did not require the presence of H2O2 itself; a brief "pulse" exposure of the cardiomyocytes to H2O2 was sufficient to incite the pathogenic mechanism leading to cell disruption. Cardiomyocyte disruption was dependent upon an intracellular source of redox-active iron and the iron-dependent transformation of internalized H2O2 into products (e.g., the hydroxyl radical) capable of initiating lipid peroxidation, since iron chelators and hydroxyl-radical scavengers were cytoprotective. The accelerated turnover of cardiomyocyte-membrane protein and phospholipid was inhibited by antiperoxidants, suggesting that the turnover reflected molecular repair of oxidized membrane constitutents. Likewise, the consumption of alpha-tocopherol and the oxidation of cellular thiols appeared to be epiphenomena of peroxidation. Antiperoxidant interventions coordinately abolished both H2O2-induced lipid peroxidation and sarcolemmal disruption, demonstrating that an intimate pathogenic relationship exists between sarcolemmal peroxidation and lethal compromise of cardiomyocyte integrity in response to H2O2-induced oxidative stress. Although sarcolemmal peroxidation was causally related to cardiomyocyte disruption during H2O2-induced oxidative stress, a nonperoxidative route of H2O2 cytotoxicity was also identified, which was expressed in the complete absence of cardiomyocyte-membrane peroxidation. The latter mode of H2O2-induced cardiomyocyte injury involved ATP loss such that membrane peroxidation and cardiomyocyte disruption on the one hand and cellular de-energization on the other could be completely dissociated.(ABSTRACT TRUNCATED AT 400 WORDS)