Antioxidant defence mechanisms: from the beginning to the end (of the beginning)

Role of beta-carotene in ameliorating the cadmium-induced oxidative stress in rat brain and testis

The role of oxidative stress in chronic cadmium (Cd) toxicity and its prevention by cotreatment with beta-carotene was investigated. Adult male rats were intragastrically administered 2 mg CdCl2/kg body weight three times a week intragastrically for 3 and 6 weeks. Brain and testicular thiobarbituric acid reactive substances (TBARS) was elevated after 3 and 6 weeks of Cd administration, indicating increased lipid peroxidation (LPO) and oxidative stress. Cellular damage was indicated by inhibition of adenosine triphosphatase (ATPase) activity and increased lactate dehydrogenase (LDH) activity in brain and testicular tissues. Chronic Cd administration resulted in a decline in glutathione (GSH) content and a decrease of superoxide dismutase (SOD) and glutathione S-transferase (GST) activity in both organs. Administration of beta-carotene (250 IU/kg i.g.) concurrent with Cd ameliorated Cd-induced LPO. The brain and testicular antioxidants, SOD, GST, and GSH, decreased by Cd alone, were restored by beta-carotene cotreatment. Concurrent treatment with beta-carotene also ameliorated the decrease in ATPase activity and the increase in LDH activity in brain and testis of Cd-treated rats, indicating a prophylactic action of beta-carotene on Cd toxicity. Therefore, the results indicate that the nutritional antioxidant beta-carotene ameliorated oxidative stress and the loss of cellular antioxidants and suggest that beta-carotene may control Cd-induced brain and testicular toxicity.

Effect of graded hypoxia on the high-affinity CPP binding site of the NMDA receptor in the cerebral cortex of newborn piglets

Previous studies have shown that the N-methyl-D-aspartate (NMDA) receptor is modified during hypoxia in the cerebral cortex of newborn piglets. The present study tests the hypothesis that the NMDA receptor 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) high-affinity binding site is modified during hypoxia and that the degree of modification correlates with the progressive decrease in cerebral cellular energy metabolism and increase in lipid peroxidation induced by hypoxia. Studies were conducted in twelve anesthetized, ventilated newborn piglets, five normoxic and seven hypoxic which were exposed to decreased fraction of inspired oxygen (FiO2) to achieve varying phosphocreatine (PCr) levels. 3[H]-CPP binding was performed with CPP concentrations ranging from 0.5 to 1500 nM at 23 degrees C for 40 min in P2 membrane fractions. Brain tissue PCr levels were determined biochemically. Conjugated dienes (CDs) were measured as an index of lipid peroxidation. In the normoxic group, B(max) (receptor number) for the CPP binding site was 329+/-93 fmol/mg protein and Kd (dissociation constant) 137+/-44 nM, the mean PCr value was 2.5+/-0.4 micromol/g brain and the CD level was 0.0 nmol/g brain. As tissue hypoxia worsened, there was a gradual decline in tissue PCr as well as receptor B(max) and K(d) values, and there was an increase in conjugated dienes. Both the receptor B(max) (r=0.90) and Kd (r=0.72) decreased in a linear relationship as PCr decreased. As the levels of CDs increased both the receptor B(max) (r=0.88) and Kd (r=0.68) decreased in a linear fashion. The data show that there is not a critical hypoxic threshold for modification of the CPP binding site of the NMDA receptor, but that modification is coupled to a gradual decrease in brain cell energy metabolism and increase in lipid peroxidation. We speculate that hypoxia-induced modification of the NMDA receptor is mediated not only by changes in the receptor recognition site but also by an alteration of brain cell membrane structure secondary to conjugated diene formation.

Heterogeneity within animal thioredoxin reductases. Evidence for alternative first exon splicing

Animal thioredoxin reductases (TRs) are selenocysteine-containing flavoenzymes that utilize NADPH for reduction of thioredoxins and other protein and nonprotein substrates. Three types of mammalian TRs are known, with TR1 being a cytosolic enzyme, and TR3, a mitochondrial enzyme. Previously characterized TR1 and TR3 occurred as homodimers of 55-57-kDa subunits. We report here that TR1 isolated from mouse liver, mouse liver tumor, and a human T-cell line exhibited extensive heterogeneity as detected by electrophoretic, immunoblot, and mass spectrometry analyses. In particular, a 67-kDa band of TR1 was detected. Furthermore, a novel form of mouse TR1 cDNA encoding a 67-kDa selenoprotein subunit with an additional N-terminal sequence was identified. Subsequent homology analyses revealed three distinct isoforms of mouse and rat TR1 mRNA. These forms differed in 5' sequences that resulted from the alternative use of the first three exons but had common downstream sequences. Similarly, expression of multiple mRNA forms was observed for human TR3 and Drosophila TR. In these genes, alternative first exon splicing resulted in the formation of predicted mitochondrial and cytosolic proteins. In addition, a human TR3 gene overlapped with the gene for catechol-O-methyltransferase (COMT) on a complementary DNA strand, such that mitochondrial TR3 and membrane-bound COMT mRNAs had common first exon sequences; however, transcription start sites for predicted cytosolic TR3 and soluble COMT forms were separated by approximately 30 kilobases. Thus, this study demonstrates a remarkable heterogeneity within TRs, which, at least in part, results from evolutionary conserved genetic mechanisms employing alternative first exon splicing. Multiple transcription start sites within TR genes may be relevant to complex regulation of expression and/or organelle- and cell type-specific location of animal thioredoxin reductases.

Why and how should we measure oxidative DNA damage in nutritional studies? How far have we come?

Free radicals and other reactive species are constantly generated in vivo and cause oxidative damage to DNA at a rate that is probably a significant contributor to the age-related development of cancer. Agents that decrease oxidative DNA damage should thus decrease the risk of cancer development. That is, oxidative DNA damage is a "biomarker" for identifying persons at risk (for dietary or genetic reasons, or both) of developing cancer and for suggesting how the diets of these persons could be modified to decrease that risk. This biomarker concept presupposes that we can measure oxidative damage accurately in DNA from relevant tissues. Little information is available on whether oxidative DNA damage in blood cells mirrors such damage in tissues at risk of cancer development. Measurement of 8-hydroxylated guanine (eg, as 8-hydroxy-2'-deoxyguanosine; 8OHdG) is the commonest method of assessing DNA damage, but there is no consensus on what the true levels are in human DNA. If the lowest levels reported are correct, 8OHdG may be only a minor product of oxidative DNA damage. Indeed, 8OHdG may be difficult to measure because of the ease with which it is formed artifactually during isolation, hydrolysis, and analysis of DNA. Mass spectrometry can accurately measure a wide spectrum of DNA base damage products, but the development of liquid chromatography-mass spectrometry techniques and improved DNA hydrolysis procedures is urgently required. The available evidence suggests that in Western populations, intake of certain fruit and vegetables can decrease oxidative DNA damage, whereas ascorbate, vitamin E, and beta-carotene cannot.

Distinct mechanisms of DNA damage in apoptosis induced by quercetin and luteolin

Quercetin has been reported to have carcinogenic effects. However, both quercetin and luteolin have anti-cancer activity. To clarify the mechanism underlying the carcinogenic effects of quercetin, we compared DNA damage occurring during apoptosis induced by quercetin with that occuring during apoptosis induced by luteolin. Both quercetin and luteolin similarly induced DNA cleavage with subsequent DNA ladder formation, characteristics of apoptosis, in HL-60 cells. In HP 100 cells, an H2O2-resistant clone of HL-60 cells, the extent of DNA cleavage and DNA ladder formation induced by quercetin was less than that in HL-60 cells, whereas differences between the two cell types were minimal after treatment with luteolin. In addition, quercetin increased the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG), an indicator of oxidative DNA damage, in HL-60 cells but not in HP 100 cells. Luteolin did not increase 8-oxodG formation, but inhibited topoisomerase II (topo II) activity of nuclear extract more strongly than quercetin and cleaved DNA by forming a luteolin-topo II-DNA ternary complex. These results suggest that quercetin induces H2O2-mediated DNA damage, resulting in apoptosis or mutations, whereas luteolin induces apoptosis via topo II-mediated DNA cleavage. The H2O2-mediated DNA damage may be related to the carcinogenic effects of quercetin.

Metabolic age modelling: the lesson from centenarians

Evolutionary theories of ageing, and data emerging from cellular and molecular biology of ageing, suggested that animals and humans capable of reaching an age close to the extreme limit of the life span should be equipped with a very efficient network of anti-ageing mechanisms. Indeed several evidences have demonstrated that starting from young to very old subjects, ageing is associated with a progressive remodelling. Thus, a new paradigm, the remodelling theory of age, was proposed. This theory, focusing on the human immune system, suggested that immunosenescence is the net result of the continuous adaptation of the body to the deteriorative changes occurring over time. According to this hypothesis, body resources are continuously optimized, and immunosenescence must be considered a very dynamic process including both loss and gain. Whether the metabolic pathways and the endocrine functions are also part of the age remodelling is not investigated. The aim of this review is to focus on the age-related changes in metabolic pathways and endocrine functions and to demonstrate that healthy centenarians (HC) represent the best living example of successful age-remodelling in whom the age remodelling has occurred without problems. In order to design the clinical picture of such successful ageing, anthropometric, endocrine and metabolic characteristics of healthy centenarians (HC), compared with aged subject, have been outlined.

NO synthase and NO-dependent signal pathways in brain aging and neurodegenerative disorders: the role of oxidant/antioxidant balance

Nitric oxide and other reactive nitrogen species appear to play several crucial roles in the brain. These include physiological processes such as neuromodulation, neurotransmission and synaptic plasticity, and pathological processes such as neurodegeneration and neuroinflammation. There is increasing evidence that glial cells in the central nervous system can produce nitric oxide in vivo in response to stimulation by cytokines and that this production is mediated by the inducible isoform of nitric oxide synthase. Although the etiology and pathogenesis of the major neurodegenerative and neuroinflammatory disorders (Alzheimer's disease, amyothrophic lateral sclerosis, Parkinson's disease, Huntington's disease and multiple sclerosis) are unknown, numerous recent studies strongly suggest that reactive nitrogen species play an important role. Furthermore, these species are probably involved in brain damage following ischemia and reperfusion, Down's syndrome and mitochondrial encephalopathies. Recent evidence also indicates the importance of cytoprotective proteins such as heat shock proteins (HSPs) which appear to be critically involved in protection from nitrosative and oxidative stress. In this review, evidence for the involvement of nitrosative stress in the pathogenesis of the major neurodegenerative/ neuroinflammatory diseases and the mechanisms operating in brain as a response to imbalance in the oxidant/antioxidant status are discussed.

Phenotype determination of a common Pro-Leu polymorphism in human glutathione peroxidase 1

Oxidative stress has been implicated in human illness such as cardiovascular and neurodegenerative disease. The genetic mechanisms involved are only poorly understood. Here we describe the determination of the allelic frequency and phenotype of a common polymorphism in Se-dependent glutathione peroxidase 1 (GPX1) in Finnish/Swedish populations. A proline/leucine variant occurs at position 197 close to the C-terminus of the protein. The more common allele encoding the Pro variant is present at 59% in a Finnish/Swedish population (n = 66) and at 73% in a Swedish population (n = 315). The genotypes encoding Pro/Pro, Pro/Leu, and Leu/Leu are distributed according to the Hardy-Weinberg relationship. The Swedish population consisted of 101 stroke cases and 214 controls. No significant association between allele frequency and risk to suffer from stroke was evident. Erythrocyte GPX activity was determined in the Finnish/Swedish population and no significant differences were obtained between the genotypes. It can be concluded that the Pro/Leu genetic variation does not appear to compromise the defense against oxidative stress in red blood cells nor to be associated with stroke.

Regulation of protein function by S-glutathiolation in response to oxidative and nitrosative stress

Protein S-glutathiolation, the reversible covalent addition of glutathione to cysteine residues on target proteins, is emerging as a candidate mechanism by which both changes in the intracellular redox state and the generation of reactive oxygen and nitrogen species may be transduced into a functional response. This review will provide an introduction to the concepts of oxidative and nitrosative stress and outline the molecular mechanisms of protein regulation by oxidative and nitrosative thiol-group modifications. Special attention will be paid to recently published work supporting a role for S-glutathiolation in stress signalling pathways and in the adaptive cellular response to oxidative and nitrosative stress. Finally, novel insights into the molecular mechanisms of S-glutathiolation as well as methodological problems related to the interpretation of the biological relevance of this post-translational protein modification will be discussed.

Secretion of 10-kDa and 12-kDa thioredoxin species from blood monocytes and transformed leukocytes

Thioredoxins (TRX) are ubiquitous, small redox-active proteins with multiple functions, including antioxidant, cytoprotective, and chemoattractant activities. In addition to a 12-kDa intracellular form, extracellular 10-kDa and 12-kDa TRX have been defined. The biological activities of the 10-kDa TRX were previously measured as eosinophil cytotoxicity enhancing activity or B-cell stimulatory activity. Cytotrophoblastic cell lines also release a 10-kDa TRX form. To study the biological role of 10-kDa TRX, we established two highly sensitive enzyme-linked immuno-spot assays (ELISPOT), which detect secreted truncated 10-kDa and full-length 12-kDa TRX at the single cell level. TRX secretion was investigated in several cell lines including the T-helper cell hybridoma MP6, the Jurkat T-cell leukemia, the U-937 myelomonocytic leukemia, and the 3B6, EBV-transformed, lymphoblastoid B-cell line. The highest number of secreting cells was found in 3B6 cultures, median = 34 (quartiles, 27-39) per well (10(5) cells). Peripheral blood monocytes isolated from healthy donors secreted significantly more TRX after stimulation with ionomycin, phorbol myristate acetate (PMA), fMLP, and lipopolysaccharide (LPS), compared to unstimulated cells. Oxidative stress induced by thioloxidant diamide also induced the secretion of both truncated and full-length TRX measured in ELISPOT (p = 0.047 and p = 0.031, respectively). The biological activity of the truncated and full-length forms was tested in a cell migration assay. Truncated TRX was devoid of protein disulfide reductase activity, but retained strong chemoattractant activity for human monocytes, in the same range as full-length TRX, as previously reported (Bertini et al., 1999).

Thioredoxin blood level increases after severe burn injury

We have investigated the thioredoxin (TRX) levels in severely burned patients and the possible origin of TRX, based on the recent understanding that TRX is a potent antioxidant with cytoprotective functions. Serum and plasma samples from burns patients and healthy blood donors were collected during the first 10 post-burn days and analyzed in a sandwich TRX enzyme-linked immunosorbent assay (ELISA). The TRX levels found were correlated to a panel of blood tests. The presence of TRX in platelets was investigated by immunoelectron microscopy and Western blotting. TRX serum levels of the severely burned patients showed a significant increase, with a mean serum TRX concentration on the day of injury of 76.5 +/- 19.5 ng/ml (mean +/- SD) and on post-burn day one 122.6 +/- 66.9 ng/ml, compared to control blood donor levels of 22.7 +/- 12.2 ng/ml (p = 0.0041 and 0.0117, respectively). A second peak of increase was found on post-burn days 7 to 9 with a four- to five-fold rise in concentration compared to controls. TRX elevation correlated well with increased platelet (p = 0.007) and leukocyte counts (p = 0.002). We also demonstrated by immunoelectron microscopy and Western blotting the presence of TRX in platelets. In conclusion, our demonstration of TRX release in burn injuries indicates that the TRX system is involved in a rapid antioxidant defense, coagulation processes, cell growth, and control of the extracellular peroxide tone intimately linked to cytoprotection and wound healing in burns. One of the cell types that delivers TRX promptly and efficiently into the blood may be the platelet.