Glutathione in human plasma: decline in association with aging, age-related macular degeneration, and diabetes

Increased protein glycation in non-diabetic pediatric nephrotic syndrome: possible role of lipid peroxidation

BACKGROUND

Malondialdehyde (MDA), ascorbic acid and reduced glutathione (GSH) have been reported to play a possible role in glycation of proteins. This study was performed to evaluate this correlation in nephrotic syndrome patients by comparing the levels of fructosamine with MDA, ascorbic acid and GSH.

METHODS

Fifteen children with nephrotic syndrome during relapse and 10 age- and sex-matched healthy controls were enrolled for this study. Whole blood GSH, plasma MDA, total ascorbic acid and fasting glucose were analyzed in both the groups. Partial correlation analysis was performed to predict the independent association of MDA, ascorbic acid and GSH on fructosamine.

RESULTS

Plasma MDA and fructosamine levels were found to be increased in nephrotic syndrome patients when compared with controls. Plasma ascorbic acid and whole blood GSH were decreased in nephrotic group vs. healthy controls. Partial correlation analysis showed a significant positive correlation between fructosamine and MDA.

CONCLUSIONS

Present data point to a possible involvement of MDA in the glycation of protein in non-diabetic nephrotic syndrome patients, and provide support for the potential use of an antioxidant therapy in these patients.

Advancing age and other factors influencing the balance between amino acid requirements and toxicity

As the average human lifespan increases, so does the recognition that advancing age is associated with changes in nutrient intake and requirements as a consequence of biological, social, and pathological factors. Studies show that whereas protein requirements may not differ significantly between younger and older adults, the adaptive mechanisms and responses to nutritional or pathological stressors may differ and alter the balance between requirement and toxicity of specific amino acids (AAs). As an individual gets older, cardiovascular disease and cancer become the leading causes of morbidity and mortality. Advancing age is also associated with changes in appetite, food intake, and physical activity, all of which can influence protein and AA metabolism. The sulfur amino acids (SAAs) methionine and cysteine recently attracted attention because of their pivotal roles in methyl group metabolism and maintenance of the cellular redox state. Methionine, an indispensable AA, is important for methylation reactions and as a precursor for cysteine, which is the rate-limiting AA for glutathione (GSH) synthesis. On one hand, high intake levels or blood concentrations of methionine are associated with adverse consequences such as hyperhomocysteinemia and endothelial dysfunction, which are risk factors for cardiovascular disease. On the other hand, methionine deficiency is reported to lower the threshold of chemical-induced toxicity and play a role in carcinogenesis. Therefore, it is evident that understanding the biological significance of the interrelationship between SAAs, GSH, and methyl group metabolism is key to determining optimal dietary intakes of SAAs in older individuals.

Oxidative stress in Alzheimer's and vascular dementias: masking of the antioxidant profiles by a concomitant Type II diabetes mellitus condition

Oxidative stress is associated with Alzheimer's (DAT) and vascular (VD) dementias, as well as Type II diabetes mellitus (DIAB) and affected by hypoglycemic therapy. The population (n = 122; males = 60; mean age = 72.57 +/- 7.06) consisted of controls (CTR), DAT and VD patients, with (DAT + DIAB, VD + DIAB) and without concomitant DIAB, resulting in six groups where the antioxidant profile was determined: copper-zinc superoxide dismutase (SOD), thiobarbituric acid reactive substances (TBARS), and total antioxidant capacity (TRAP). The results were analyzed using a two-way ANOVA design and Bonferroni statistic. The ANOVAs yielded significant differences between groups for all components of the profile: SOD, p = 0.00000006; TBARS, p = 0.0000012; TRAP, p = 0.0000003. The significance level for comparisons between groups was set at alpha = 0.05. The comparisons DIAB vs. CTR, DAT+DIAB vs. DAT, and DIAB demented vs. DIAB non-demented resulted significant for all variables. VD + DIAB vs. VD resulted significant for all variables except TRAP. The antioxidant profiles of DIAB and CTR are different. The differences cannot be directly related with what is observed in dementias. The differences in profiles of demented and non-demented are somewhat hidden when demented patients are affected by a concomitant DIAB condition and/or hypoglycemic treatment, thus conditioning the diagnostic value for dementias of the profiles.

An improved HPLC measurement for GSH and GSSG in human blood

The pathophysiological sequelae of oxidative/nitrosative stress are notoriously difficult to quantify. Despite these impediments, the medical significance of oxidative/nitrosative stress has become increasingly recognized to the point that it is now considered to be a component of virtually every disease. The level of oxidative stress can be quantified in blood by the measurement of the increase in glutathione disulfide (GSSG) and the decrease in the GSH/GSSG ratio, which has been shown to be altered in a variety of human diseases such as lung inflammation, amyotrophic lateral sclerosis, chronic renal failure, malignant disorders, and diabetes. Among the proposed methods for GSH/GSSG detection, the amino group derivatization with 2,4-dinitrofluorobenzene followed by HPLC separation has the advantage of allowing evaluation of both parameters within a single run contemporaneously. However, it has been shown that the application of this method on blood samples is not reproducible. In this report, we offer an explanation for these experimental limits and suggest some modifications that allow the application of this method to blood samples. The modified method has a low detection limit (0.5 microM, i.e., 1.4 pmoles) and a high reproducibility with a within-run imprecision of less than 2%. It could have a wide application as it is simple, virtually artifact-free, and not time-consuming, especially for large-scale screening studies.

Analysis of glutathione: implication in redox and detoxification

BACKGROUND

Glutathione is a ubiquitous thiol-containing tripeptide, which plays a central role in cell biology. It is implicated in the cellular defence against xenobiotics and naturally occurring deleterious compounds, such as free radicals and hydroperoxides. Glutathione status is a highly sensitive indicator of cell functionality and viability. Its levels in human tissues normally range from 0.1 to 10 mM, being most concentrated in liver (up to 10 mM) and in the spleen, kidney, lens, erythrocytes and leukocytes. In humans, GSH depletion is linked to a number of disease states including cancer, neurodegenerative and cardiovascular diseases. The present review proposes an analysis of the current knowledge about the methodologies for measuring glutathione in human biological samples and their feasibility as routine methods in clinical chemistry. Furthermore, it elucidates the fundamental role of glutathione in pathophysiological conditions and its implication in redox and detoxification process.

TESTS AVAILABLE

Several methods have been optimised in order to identify and quantify glutathione forms in human biological samples. They include spectrophotometric, fluorometric and bioluminometric assays, often applied to HPLC analysis. Recently, a liquid chromatography-mass spectrometry technique for glutathione determination has been developed that, however, suffers from the lack of total automation and the high cost of the equipment.

CONCLUSION

Glutathione is a critical factor in protecting organisms against toxicity and disease. This review may turn useful for analysing the glutathione homeostasis, whose impairment represents an indicator of tissue oxidative status in human subjects.

Relationship between gluconeogenesis and glutathione redox state in rabbit kidney-cortex tubules

The intracellular glutathione redox state and the rate of glucose formation were studied in rabbit kidney-cortex tubules. In the presence of substrates effectively utilized for glucose formation, ie, aspartate + glycerol + octanoate, alanine + glycerol + octanoate, malate, or pyruvate, the intracellular reduced glutathione/oxidized glutathione (GSH/GSSG) ratios were significantly higher than those under conditions of negligible glucose production. Changes in the intracellular GSH/GSSG ratio corresponded to those in glucose-6-phosphate content and reduced nicotinamide adenine dinucleotide phosphate/oxidized nicotinamide adenine dinucleotide phosphate (NADPH/NADP(+)) ratio obtained from malate/pyruvate measurements. Gluconeogenesis stimulation by extracellular adenosine triphosphate (ATP) or inosine caused an elevation of the intracellular GSH/GSSG and NADPH/NADP(+) ratios, as well as glucose-6-phosphate level. Surprisingly, in the presence of 5 mmol/L glucose, both the intracellular GSH/GSSG and NADPH/NADP(+) ratios and glucose-6-phosphate content were almost as low as under conditions of negligible glucose synthesis. L-buthionine sulfoximine (BSO)-induced decline in both the intracellular glutathione level and redox state resulted in inhibition of gluconeogenesis accompanied by accumulation of phosphotrioses and a decrease in fructose-1,6-bisphosphate content, while cysteine precursors altered neither GSH redox state nor the rate of glucose formation. In view of the data, it seems likely that: (1) intensive gluconeogenesis rather than extracellular glucose is responsible for maintaining a high intracellular GSH/GSSG ratio due to effective glucose-6-phosphate delivery for NADPH generation via the pentose phosphate pathway; (2) a decline in the intracellular glutathione level and/or redox state causes a decrease in glucose synthesis resulting from a diminished flux through aldolase; (3) induced by cysteine precursors, elevation of the intracellular GSH level does not affect the rate of glucose formation, probably due to no changes in the intracellular GSH/GSSG ratio.

Hepatic glutathione and nitric oxide are critical for hepatic insulin-sensitizing substance action

We tested the hypothesis that hepatic nitric oxide (NO) and glutathione (GSH) are involved in the synthesis of a putative hormone referred to as hepatic insulin-sensitizing substance HISS. Insulin action was assessed in Wistar rats using the rapid insulin sensitivity test (RIST). Blockade of hepatic NO synthesis with N(G)-nitro-l-arginine methyl ester (l-NAME, 1.0 mg/kg intraportal) decreased insulin sensitivity by 45.1 +/- 2.1% compared with control (from 287.3 +/- 18.1 to 155.3 +/- 10.1 mg glucose/kg, P < 0.05). Insulin sensitivity was restored to 321.7 +/- 44.7 mg glucose/kg after administration of an NO donor, intraportal SIN-1 (5 mg/kg), which promotes GSH nitrosation, but not after intraportal sodium nitroprusside (20 nmol x kg(-1) x min(-1)), which does not nitrosate GSH. We depleted hepatic GSH using the GSH synthesis inhibitor l-buthionine-[S,R]-sulfoximine (BSO, 2 mmol/kg body wt ip for 20 days), which reduced insulin sensitivity by 39.1%. Insulin sensitivity after l-NAME was not significantly different between BSO- and sham-treated animals. SIN-1 did not reverse the insulin resistance induced by l-NAME in the BSO-treated group. These results support our hypothesis that NO and GSH are essential for insulin action.

Improvement in muscular performance and decrease in tumor necrosis factor level in old age after antioxidant treatment

Aging-related loss of muscle function is a predictor of mortality and a surrogate parameter of the aging process. Its consequences include a high risk for falls, hip fractures, and loss of autonomy. Aging is associated with changes in the oxidant/antioxidant balance including a decrease in plasma thiol (cysteine) concentration. To assess the importance of cysteine, we determined in a double-blind study the effects of N-acetylcysteine on the functional capacity of frail geriatric patients and their response to physical exercise. The subjects on placebo showed only a relatively weak response, and 31% showed even a decrease in more than one parameter during the observation period. Low plasma arginine levels were correlated with a weak overall performance before exercise and a poor response to exercise. N-Acetylcysteine strongly enhanced the increase in knee extensor strength and significantly increased the sum of all strength parameters if adjusted for baseline arginine level as a confounding parameter. N-acetylcysteine had no significant effect on growth hormone and IGF-1 levels but caused a significant decrease in plasma TNF-alpha. These findings may provide a basis for therapeutic intervention and suggest that the loss of function involves limitations in cysteine and one or more other amino acids which may compromise muscular protein synthesis.

Aging-related changes in the thiol/disulfide redox state: implications for the use of thiol antioxidants

Genetic and biochemical studies suggest that free radical-derived reactive oxygen species play a key role in a common mechanism of aging in many or all animal species. This led to the hypothesis that the quality of life in old age may be improved by pharmacological or dietary thiol antioxidants. This review describes important details about how the organism deals with its own thiol antioxidants. Aging was found to be associated with an oxidative shift in the thiol/disulfide redox state (REDST) of the intracellular glutathione pool and of the plasma cyst(e)ine and albumin pools. There is also a decrease in plasma thiol (mainly cysteine) concentration. The oxidative shift in intracellular REDST was found to be typically associated with cellular dysfunctions. Studies in humans related to plasma REDST revealed correlations with aging-related pathophysiological processes, suggesting that oxidative changes in REDST play a key role in processes and diseases which limit the human life span. The age-related shift in plasma REDST is mediated, at least partly, by the decreasing capacity to remove dietary cysteine from the oxidative environment of the blood. Thiol antioxidants were found to ameliorate various aging-related processes but obviously ought to be used with caution in consideration of the oxidative environment of the blood.

Glutathione and thioredoxin redox during differentiation in human colon epithelial (Caco-2) cells

Cellular redox, maintained by the glutathione (GSH)- and thioredoxin (Trx)-dependent systems, has been implicated in the regulation of a variety of biological processes. The redox state of the GSH system becomes oxidized when cells are induced to differentiate by chemical agents. The aim of this study was to determine the redox state of cellular GSH/glutathione disulfide (GSH/GSSG) and Trx as a consequence of progression from proliferation to contact inhibition and spontaneous differentiation in colon carcinoma (Caco-2) cells. Results showed a significant decrease in GSH concentration, accompanied by a 40-mV oxidation of the cellular GSH/GSSG redox state and a 28-mV oxidation of the extracellular cysteine/cystine redox state in association with confluency and increase in differentiation markers. The redox state of Trx did not change. Thus the two central cellular antioxidant and redox-regulating systems (GSH and Trx) were independently controlled. According to the Nernst equation, a 30-mV oxidation is associated with a 10-fold change in the reduced/oxidized ratio of a redox-sensitive dithiol motif. Therefore, the measured 40-mV oxidation of the cellular GSH/GSSG couple or the 28-mV oxidation of the extracellular cysteine/cystine couple should be sufficient to function in signaling or regulation of differentiation in Caco-2 cells.

Extracellular thiol/disulfide redox state affects proliferation rate in a human colon carcinoma (Caco2) cell line

Redox mechanisms function in regulation of cell growth, and variation in redox state of plasma thiol/disulfide couples occurs in various physiologic conditions, including diabetes, chemotherapy, and aging. The present study was designed to determine whether a systematic variation in extracellular thiol/disulfide redox state (E(h)) over a range (0 mV to -150 mV) that occurs in human plasma altered proliferation of cultured cells. Experiments were performed with a human colon carcinoma cell line (Caco2), which grows slowly in the absence of serum and responds to peptide growth factors with increased rate of cell division. The extracellular redox states were established by varying concentrations of cysteine and cystine, maintaining constant pool size in terms of cysteine equivalents. Incorporation of 5-bromo-2-deoxyuridine (BrdU) was used to measure DNA synthesis and was lowest at the most oxidized extracellular E(h) (0 mV). Incorporation increased as a function of redox state, attaining a 100% higher value at the most reduced condition (-150 mV). Addition of insulin-like growth factor-1 (IGF-1) or epidermal growth factor (EGF) increased the rate of BrdU incorporation at more oxidizing redox conditions (0 to -80 mV) but had no effect at -150 mV. Cellular GSH was not significantly affected by variation in extracellular E(h). In the absence of growth factors, extracellular E(h) values were largely maintained for 24 h. However, IGF-1 or EGF stimulated a change in extracellular redox to values similar to that for cysteine/cystine redox in plasma of young, healthy individuals. The results show that extracellular thiol/disulfide redox state modulates cell proliferation rate and that this control interacts with growth factor signaling apparently independently of cellular glutathione.

Screening for ocular phototoxicity

Normally light transmission through the eye is benign and serves to direct vision and circadian rhythm. However, with very intense light exposure, or with ambient light exposure to the aged eye and/or young or adult eye in the presence of light-activated (photosensitizing) drugs or dietary supplements, cosmetics, or diagnostic dyes, light can be hazardous, leading to blinding disorders. Light damage to the human eye is avoided because the eye is protected by a very efficient antioxidant system and the chromophores present absorb light and dissipate its energy. After middle age, there is a decrease in the production of antioxidants and antioxidant enzymes and an accumulation of endogenous chromophores that are phototoxic. The extent to which a particular exogenous photosensitizing substance is capable of producing phototoxic side effects in the eye depends on several parameters, including (1) the chemical structure; (2) the absorption spectra of the drug; (3) binding of the drug to ocular tissue (lens proteins, melanin, DNA); and (4) the ability to cross blood-ocular barriers (amphiphilic or lipophilic). For instance, compounds that have either a tricyclic, heterocyclic, or porphyrin ring structure and are incorporated into ocular tissues are potentially phototoxic agents in the eye. The extent to which these substances might damage the eye (photoefficiency) can be predicted using in vitro and photophysical techniques. With simple, inexpensive testing, compounds can be screened for their potential ocular phototoxicity at the developmental stage. It may be that a portion of the molecule can be modified to reduce phototoxicity while leaving the primary drug effect intact. Preclinical safety testing may prevent ocular side effects that can range from mild, reversible blurred vision to permanent blindness.

Redox analysis of human plasma allows separation of pro-oxidant events of aging from decline in antioxidant defenses

Oxidative stress is a component of diseases and degenerative processes associated with aging. However, no means are available to assess causative oxidative events separately from decline in function of protective antioxidant systems. Previous studies show that ongoing oxidative processes maintain plasma cysteine/cystine redox at a value that is more oxidized than the antioxidant glutathione/glutathione disulfide (GSH/GSSG) system, suggesting that redox analysis of these plasma thiols could allow separate evaluation of an increase in oxidative events from a decline in antioxidant function. The present study uses measurement of cysteine/cystine and GSH/GSSG redox in plasma of 122 healthy individuals aged 19-85 years to determine whether thiol-disulfide redox changes occur with age. The results show a linear oxidation of cysteine/cystine redox state with age at a rate of 0.16 mV/year over the entire age span. In contrast, GSH/GSSG redox was not oxidized prior to 45 years and subsequently was oxidized at a nearly linear rate of 0.7 mV/year. These data suggest that there is a continuous, linear increase in oxidative events throughout adult life but that the capacity of the GSH antioxidant system is maintained until 45 years and then declines rapidly. The data further suggest that redox states of cysteine/cystine and GSH/GSSG provide an approach to clinically distinguish between increased causative oxidative events and decreased GSH antioxidant function. In principle, such analyses can be used to assess efficacy of intervention strategies against oxidative stress prior to or early after onset of clinical symptoms in aging and age-related disease.

Induction of vascular endothelial growth factor by 4-hydroxynonenal and its prevention by glutathione precursors in retinal pigment epithelial cells

Although 4-hydroxynonenal, a highly reactive lipid peroxidation product, is implicated in several age-related disorders such as Alzheimer's and Parkinson's diseases, its role in age-related macular degeneration is not known. The purpose of this study was to determine whether 4-hydroxynonenal increases vascular endothelial growth factor (VEGF) expression in human retinal pigment epithelial cells (ARPE-19), a source of VEGF in choroidal neovascularization observed in age-related macular degeneration. In addition, it was the purpose of this study to assess whether glutathione (GSH) and GSH precursors can inhibit the effects of 4-hydroxynonenal. At 1 micro M, 4-hydroxynonenal did not alter cell viability, but elevated VEGF secretion and mRNA expression by 35% (p<0.05) and 1.9-fold (p<0.05), respectively. However, at concentrations 5 microM and above, 4-hydroxynonenal reduced VEGF secretion as well as cell viability. At 1 and 10 microM, 4-hydroxynonenal did not induce apoptosis in ARPE-19 cells. 4-Hydroxynonenal (1 microM) reduced intracellular GSH by 25% (p<0.05) and increased oxidative stress by 50% (p<0.05). GSH precursor pretreatment for 1 h, which increased intracellular GSH levels by 50% (p<0.05), as well as GSH co-treatment, inhibited the VEGF-inductive and cytotoxic effects of 4-hydroxynonenal. Thus, 4-hydroxynonenal (1 microM) induces VEGF expression and secretion in ARPE-19 cells. This effect is likely due to GSH depletion and an associated increase in intracellular oxidative stress, resulting in increased VEGF mRNA levels. 4-Hydroxynonenal-mediated VEGF secretion as well as cytotoxicity can be reversed with GSH precursor pretreatment or GSH co-treatment.

Oxidation of the glutathione/glutathione disulfide redox state is induced by cysteine deficiency in human colon carcinoma HT29 cells

Glutathione (GSH) has a central role in the maintenance of the thiol-disulfide redox state in mammalian cells. GSH synthesis can be physiologically limited by the availability of cysteine (Cys), and Cys and its precursors are variable in the human diet. The purpose of this study was to determine the effect of severe Cys deficiency and readdition of Cys on the redox state of the GSH/glutathione disulfide (GSSG) pool in human colon carcinoma HT29 cells. Cells were cultured in Cys- (and cystine-)limiting medium for 48 h followed by culture in medium containing either Cys or cystine for 24 h. GSH and GSSG were measured by HPLC. Cys limitation decreased cellular GSH and GSSG concentrations with an associated >80 mV oxidation of the GSH/GSSG redox state. Upon addition of either Cys or its disulfide cystine (CySS), redox of GSH/GSSG recovered in 4 h, whereas GSH concentration continued to increase over 12 h. Maximal GSH concentrations attained were 200% of control cell values. These results show that severe Cys deficiency can have marked effects on cellular redox state but that redox recovers rapidly upon resupply. The magnitude of oxidation during Cys limitation in this cell model is sufficient to result in a >100-fold change in the reduced/oxidized ratio of redox-sensitive dithiol/disulfide motifs in proteins. If redox changes occur in vivo in association with variations in dietary Cys and its precursors, these changes could have important physiologic effects through altered redox signaling and control of cell proliferation and apoptosis.

Oxidative damage increases with age in a canine model of human brain aging

We assayed levels of lipid peroxidation, protein carbonyl formation, glutamine synthetase (GS) activity and both oxidized and reduced glutathione to study the link between oxidative damage, aging and beta-amyloid (Abeta) in the canine brain. The aged canine brain, a model of human brain aging, naturally develops extensive diffuse deposits of human-type Abeta. Abeta was measured in immunostained prefrontal cortex from 19 beagle dogs (4-15 years). Increased malondialdehyde (MDA), which indicates increased lipid peroxidation, was observed in the prefrontal cortex and serum but not in cerebrospinal fluid (CSF). Oxidative damage to proteins (carbonyl formation) also increased in brain. An age-dependent decline in GS activity, an enzyme vulnerable to oxidative damage, and in the level of glutathione (GSH) was observed in the prefrontal cortex. MDA level in serum correlated with MDA accumulation in the prefrontal cortex. Although 11/19 animals exhibited Abeta, the extent of deposition did not correlate with any of the oxidative damage measures, suggesting that each form of neuropathology accumulates in parallel with age. This evidence of widespread oxidative damage and Abeta deposition is further justification for using the canine model for studying human brain aging and neurodegenerative diseases.

Rats with a glucocorticoid-induced catabolic state show symptoms of oxidative stress and spleen atrophy: the effects of age and recovery

In this study we wanted to determine whether changes in antioxidant profile could follow the catabolic effects of glucocorticoids. We also wanted to compare resistance to glucocorticoid overload in young and old rats. To address these questions, whole body catabolism was induced by the administration of dexamethasone (Dex) at either 2 mg/kg bodyweight/day to young (6 weeks old) or 0.5 mg/kg body-weight/day to old (94 weeks old) rats. Bodyweight loss of pair-fed rats not given Dex was only 2% in the young rats and 8% in the old rats, whereas in Dex-treated rats the decrease in bodyweight was 22% in the young rats and 13% in the old rats after 5 days of treatment. Spleen weight decreased by 65% in the young rats and by 52% in the old rats. Additionally, in the young rats there was a 46% reduction in glutathione (GSH) in erythrocytes as well as a 36% reduction in GSH/tissue wet weight in the soleus muscle. The corresponding figures for the old rats were 35 and 26%, respectively. Taken together, these results suggest that Dex directly and/or indirectly impaired the antioxidant reactions. This was further confirmed by a significant (50%) decline in Cu-Zn superoxide dismutase (SOD-1) activity in erythrocytes isolated from the young rats treated with Dex but not the old rats as they showed a significant elevation in SOD-1 activity (by 101%). Thiobarbituric acid reactant substances were significantly higher in both young and old rats. Activity of blood plasma creatine kinase increased by 73% in the young rats and by 307% in the old rats treated with Dex. Although both the young and the old rats could recover from oxidative stress, the old rats in contrast to the young rats remained catabolic until the end of the experiment. In conclusion, we suggest that old rats are more vulnerable to the catabolic action of Dex, whereas young rats are more susceptible to the oxidative stress induced by Dex.

Blood Glutathione Disulfide: In Vivo Factor or in Vitro Artifact?

Background: The reported mean concentration of glutathione disulfide (GSSG) in human blood/erythrocytes varies widely (1 to &gt;500 μmol/L), as does that of reduced glutathione (GSH) to a lesser extent. We have identified and investigated possible pitfalls in measurement of both GSH and GSSG.

Methods: We measured GSH and GSSG using a spectrophotometer with a modification of the GSH recycling method; the same samples were also measured by reversed-phase HPLC after derivatization of thiols (dithiothreitol was used to reduce disulfides) with monobromobimane. The thiol-bimane adduct was measured by a fluorescence detector.

Results: Measured GSH/GSSG concentrations were affected by the following: (a) oxidation of thiols in acidified samples; (b) oxidation after restoring neutral-alkaline pH; (c) oxidation during acid deproteinization; (d) shift in the GSH/GSSG equilibrium because of irreversible blocking of free thiols; and (e) reaction of electrophiles with amino groups. In particular, oxidation during sample deproteinization with acid influenced and produced artifacts (30–150 μmol/L GSSG was produced by this procedure); this phenomenon was directly correlated with the presence of oxygenated hemoglobin, being minimized by both oxygen deprivation and incubation in an atmosphere of 5% carbon monoxide.

Conclusions: GSSG is present in healthy human blood at low concentrations (2–6 μmol/L), and most published data on GSSG may be affected by artifacts.

Down-regulation of gamma-glutamylcysteine synthetase regulatory subunit gene expression in rat brain tissue during aging

The mechanism underlying age-related neurodegenerative diseases is still an area of significant controversy. Increased evidence suggests that oxidative stress contributes importantly to neuronal damage observed in the brains of aged animals and in neurodegenerative diseases. Glutathione (GSH), the most abundant intracellular nonprotein thiol, plays an important role in antioxidant defense. The concentration of this important antioxidant decreases with age in the brain, which is accompanied by an increase in oxidative damage to macromolecules. The mechanism underlying the age-associated decline in GSH content in the brain, however, is not clear. In this study, we demonstrate for the first time that the expression of the regulatory subunit of gamma-glutamylcysteine synthetase (GCS), the rate-limiting enzyme in de novo GSH synthesis, decreases with age in cerebellum, cerebral cortex, and hippocampus of Fisher 344 rats. This was accompanied by a decline in GCS activity and GSH content. There were no significant differences in either the concentrations of cysteine and glutathione disulfide (GSSG) or the activities of glutathione synthetase (GS), gamma-glutamyl traspeptidase (GGT), and glutathione reductase (GR) in the brains from different age groups. Our results suggest that the age-associated decrease in GSH in the brain may result from the down-regulation of GCS regulatory subunit and consequently a decrease in the activity of GCS.

The thiol sensitivity of glutathione transport in sidedness-sorted basolateral liver plasma membrane and in Oatp1-expressing HeLa cell membrane

Sinusoidal efflux of hepatic reduced glutathione (GSH) is a key step in interorgan GSH/cysteine homeostasis and extracellular detoxification. Rat organic anion transporter polypeptide1 (Oatp1) is known to transport GSH but several features of sinusoidal GSH uptake, such as electrogenic property and asymmetric effects of uncharged thiols (increased efflux, decreased uptake), either cannot be accounted for by Oatp1 or have not been studied. The asymmetric effect of thiols has only been studied in intact cells and not directly in membrane vesicles. To accomplish the latter, we studied GSH uptake in inside-out-(IO) and rightside-out-(RO) oriented basolateral plasma membrane vesicles (bLPM). We also studied the kinetics and effect of thiols on GSH transport by Oatp1 stably expressed in HeLa cells. GSH uptake was approximately 2- to 3-fold higher in IO than RO bLPM. Dithiothreitol-stimulated GSH uptake in IO but inhibited uptake in RO bLPM, demonstrating that thiols exert direct asymmetric side-specific effects on GSH transport. Uptake in IO and RO bLPM was sigmoid (K(m) approximately 13 mM) with a 2-fold higher capacity in IO compared with RO bLPM. In both IO and RO bLPM, a component with a high affinity but low capacity for GSH (K(m) approximately 100 microM) was also present. Endogenous GSH transporter in HeLa cells was thiol-sensitive, electrogenic, and described by a single Michaelis-Menten component (K(m) approximately 15 mM). In contrast, GSH transport mediated by Oatp1 was insensitive to thiols and membrane potential, inhibited by cystine, and stimulated by an inward H(+) gradient. These findings identify novel functional asymmetries in sinusoidal efflux and uptake of GSH and further clarify the role of Oatp1 in GSH transport.

The role of A2E in prevention or enhancement of light damage in human retinal pigment epithelial cells

The process of sight (photostasis) produces, as a by-product, a chromophore called 2-[2,6-dimethyl-8-(2,6,6-trimethyl-1-cyclohexen-1-yl)-1E,3E, 5E,7E-octatetraenyl]-1-(2-hydroxyethyl)-4-[4-methyl-6-(2,6,6-trimethyl-1-cyclohexen-1-yl)-1E, 3E, 5E-hexatrienyl]-pyridinium (A2E), whose function in the eye has not been defined as yet. In youth and adulthood, A2E is removed from human retinal pigment epithelial (h-RPE) cells as it is made, and so it is present in very low concentrations, but with advanced age, it accumulates to concentrations reaching 20 microM. In the present study we have used photophysical techniques and in vitro cellular measurements to explore the role of A2E in h-RPE cells. We have found that A2E has both pro- and antioxidant properties. It generated singlet oxygen (phiso = 0.004) much less efficiently than its precursor trans-retinal (phiso = 0.24). It also quenched singlet oxygen at a rate (10(8) M(-1) s(-1)) equivalent to two other endogenous quenchers of reactive oxygen species in the eye: alpha-tocopherol (vitamin E) and ascorbic acid (vitamin C). The endogenous singlet oxygen quencher lutein, whose quenching rate is two orders of magnitude greater than that of A2E, completely prevented light damage in vitro, suggesting that singlet oxygen does indeed play a role in light-induced damage to aged human retinas. We have used multiphoton confocal microscopy and the comet assay to measure the toxic, phototoxic and protective capacity of A2E in h-RPE cells. At 1-5 microM, A2E protected these cells from UV-induced breaks in DNA; at 20 microM, A2E no longer exerted this protective effect. These results imply that the role of A2E is not simple and may change over the course of a lifetime. A2E itself may play a protective role in the young eye but a toxic role in older eyes.

Intracellular glutathione deficiency is associated with enhanced nuclear factor-kappaB activation in older non-insulin dependent diabetic patients

Diabetes mellitus may be associated with intracellular glutathione (GSH) deficiency. Since in vivo studies have shown that plasma intracellular GSH plays a key role in regulating the activation of nuclear factor kappaB (NF-kappaB), we have investigated the relationship between intracellular thiols (GSH, homocysteine, cysteine and cysteinyglycine) and NF-kappaB activity in the peripheral blood mononuclear cells (PBMC) of 63 elderly non-insulin dependent diabetes mellitus (NIDDM) patients (28 microalbuminurics and 35 normoalbuminurics) and 30 healthy age- and sex-matched subjects. In addition, we have measured plasma concentrations of these thiol compounds, serum concentrations of interleukin-6 (IL-6) and vascular cell adhesion molecule-1 (sVCAM-1), that are partly dependent on the NF-kappaB activation, as well as the serum levels of thiobarbituric acid reacting substances (TBARS), as index of lipid peroxidation. Diabetic patients with microalbuminuria (MAB) and normoalbuminuria had NF-kappaB activity 2.1- and 1.5-fold greater, respectively, than the control group. As compared to normoalbuminuric patients, patients with MAB had significantly higher levels of glycemia, plasma homocysteine, and serum concentrations of TBARS, IL-6 and sVCAM-1 (in all cases, p < 0.01), and significantly lower GSH content in the PBMC (p < 0.05). The intracellular GSH in PBMC correlated with NF-kappaB activation (r = -0.82; p < 0.0001), serum TBARS (r = -0.60; p < 0.001), and with fasting glycemia (r = -0.56; p < 0.001) in patients with MAB, whereas a weaker association between GSH levels in PBMC and NF-kappaB activation (r = -0.504, p < 0.001) was seen in patients without MAB. These results suggest that the decrease of intracellular GSH content in elderly NIDDM patients with MAB is strongly associated with enhanced NF-kappaB activation, which could contribute to the development of increased glomerular capillary permeability and its rapid progression.

Ocular phototoxicity

The human eye is constantly exposed to sunlight and artificial lighting. Therefore the eye is exposed to UV-B (295-320 nm), UV-A (320-400 nm), and visible light (400-700 nm). Light is transmitted through the eye and then signals the brain directing both sight and circadian rhythm. Therefore light absorbed by the eye must be benign. Damage to the young and adult eye by intense ambient light is avoided because the eye is protected by a very efficient antioxidant system. In addition, there are protective pigments such as the kynurenines, located in the human lens, and melanin, in the uvea and retina, which absorb ambient radiation and dissipate its energy without causing damage. After middle age there is a decrease in the production of antioxidants and antioxidant enzymes. At the same time, the protective pigments are chemically modified (lenticular 3-hydroxy kynurenine pigment is enzymatically converted into the phototoxic chromophore xanthurenic acid; melanin is altered from an antioxidant to pro-oxidant) and fluorescent chromophores (lipofuscin) accumulate to concentrations high enough to produce reactive oxygen species. We have known for some time that exposure to intense artificial light and sunlight either causes or exacerbates age-related ocular diseases. We now know many of the reasons for these effects, and with this knowledge methods are being developed to interfere with these damaging processes.

Enalapril attenuates oxidative stress in diabetic rats

Oxidative stress is involved in both the pathogenesis and complications of diabetes. ACE inhibitors can slow the progression of cardiac and renal impairments related to diabetes. The effect of enalapril treatment on oxidative stress and tissue injury was studied in hearts, kidneys, and livers from streptozotocin-induced diabetic rats. Twenty-four rats were divided into the following groups: streptozotocin (65 mg/kg, single intraperitoneal dose), streptozotocin+enalapril (20 mg enalapril/L drinking water), and control (intraperitoneal saline). Seven months after streptozotocin injection, organs were studied by light microscopy and collagen III immunolabeling. Tissue lesions and collagen labeling were graded by a semiquantitative score (0 to 4). Total glutathione content, glutathione redox status (reduced/oxidized glutathione), antioxidant enzyme activities, protein-associated sulfhydryls, thiobarbituric acid-reactive substances, and fluorescent chromolipids were determined in tissue homogenates. Glycemia was higher in both the streptozotocin and streptozotocin+enalapril groups relative to the control group. In the streptozotocin group, creatinine clearance and body weight were lower, and systolic blood pressure and urinary albumin excretion were higher than in the streptozotocin+enalapril and control groups. Heart, kidney, and liver lesion/labeling scores were significantly higher in the streptozotocin group compared with the streptozotocin+enalapril and control groups. Kidney and liver total glutathione was lower in the streptozotocin group relative to the control group (P<0.05). Enalapril treatment significantly attenuated the reduction of total glutathione. In the heart, kidney, and liver, both glutathione and proteins were relatively more oxidized in the streptozotocin group relative to the control group (P<0.05). Protein and glutathione oxidation were attenuated in the streptozotocin+enalapril group in the 3 tissues studied (P<0.05). Enalapril treatment attenuated the oxidation of lipids in the heart and kidney (P<0.05). Tissue fibrosis scores were inversely correlated with (1) both total glutathione and reduced/oxidized glutathione in heart, kidney, and liver and (2) glutathione reductase activity in the kidney. These results suggest that in streptozotocin-induced diabetic rats, the protective action of enalapril might be mediated, at least in part, by its effect on tissue oxidant/antioxidant status.

Influence of plasma glutathione levels on radiation mucositis

PURPOSE

To test the hypothesis that there is a link between plasma glutathione (GSH) or other antioxidants (uric acid, ascorbate) and the severity of radiation mucositis following radiation treatment of tumors of the head and neck.

PATIENTS AND METHODS

Patients with carcinomas of the head-and-neck region were treated with the continuous hyperfractionated accelerated radiotherapy (CHART) regimen (54 Gy in 36 fractions over 12 days). Samples of blood plasma were analyzed for GSH, cysteine, urate, and ascorbate by high-pressure liquid chromatography. Patients were graded for dysphagia and requirement for analgesics. The areas under the curves of scores over 2-6 weeks following treatment were computed, and Spearman's rank-correlation coefficient was used to test for an association between plasma GSH levels (or those of other antioxidants) and mucositis.

RESULTS

The pretreatment plasma GSH level in 18 patients scored in the study was 1.0 +/- 0.7 M. Analysis of these and the dysphagia scores produced a correlation coefficient of 0.22 (confidence interval -0.28, 0.61; p = 0.39). No correlation was seen between mucositis severity and other measures of plasma antioxidants: cysteine (7.6 +/- 1.7 M), cysteine + GSH (8.6 +/- 1.9 M), uric acid (317 +/- 86 M), ascorbate (29 +/- 20 M), or whole-blood GSH concentrations (1,010 +/- 239 M).

CONCLUSION

The measurements of approximately micromolar levels of plasma GSH, or about 10 M cysteine + GSH (almost all of the total nonprotein thiols), are consistent with most other published data for either healthy adults or cancer patients; however, the values reported in an earlier study, suggesting a link between GSH and mucositis, are much higher. The hypothesis of a possible link between radiation mucositis and plasma-free (nonprotein) thiols was not supported.

Effect of inhibition of glutathione synthesis on insulin action: in vivo and in vitro studies using buthionine sulfoximine

Decreased cellular GSH content is a common finding in experimental and human diabetes, in which increased oxidative stress appears to occur. Oxidative stress has been suggested to play a causative role in the development of impaired insulin action on adipose tissue and skeletal muscle. In this study we undertook to investigate the potential of GSH depletion to induce insulin resistance, by utilizing the GSH synthesis inhibitor, L-buthionine-[S,R]-sulfoximine (BSO). GSH depletion (20-80% in various tissues), was achieved in vivo by treating rats for 20 days with BSO, and in vitro (80%) by treating 3T3-L1 adipocytes with BSO for 18 h. No demonstrable change in the GSH/GSSG ratio was observed following BSO treatment. GSH depletion was progressively associated with abnormal glucose tolerance test, which could not be attributed to impaired insulin secretion. Skeletal muscle insulin responsiveness was unaffected by GSH depletion, based on normal glucose response to exogenous insulin, 2-deoxyglucose uptake measurements in isolated soleus muscle, and on normal skeletal muscle expression of GLUT4 protein. Adipocyte insulin responsiveness in vitro was assessed in 3T3-L1 adipocytes, which displayed decreased insulin-stimulated tyrosine phosphorylation of insulin-receptor-substrate proteins and of the insulin receptor, but exaggerated protein kinase B phosphorylation. However, insulin-stimulated glucose uptake was unaffected by GSH depletion. In accordance, normal adipose tissue insulin sensitivity was observed in BSO-treated rats in vivo, as demonstrated by normal inhibition of circulating non-esterified fatty acid levels by endogenous insulin secretion. In conclusion, GSH depletion by BSO results in impaired glucose tolerance, but preserved adipocyte and skeletal muscle insulin responsiveness. This suggests that alternative oxidation-borne factors mediate the induction of peripheral insulin resistance by oxidative stress.

Oxidative stress indices in IDDM subjects with and without long-term diabetic complications

BACKGROUND

Numerous animal and population studies of diabetes have identified markers of oxidative stress. However, for most markers that have been measured the results are not consistent. In addition, it is less clear whether oxidative stress is related to the development of diabetic complications. The objective of this study was to evaluate a series of plasma markers and leukocyte markers to test the hypothesis that type 1 Insulin Dependent Diabetes Mellitus (IDDM) subjects experience oxidative stress. A related question was whether markers of oxidative stress are higher in IDDM subjects who have developed long-term complications.

METHODS

The study population consisted of 22 IDDM subjects with diabetic complications and 22 IDDM subjects without complications, both groups matched by age and gender and with similar HbA1c levels, and 16 nondiabetic control subjects. Plasma levels of organoperoxides were determined by the ferrous oxidation/xylenol orange (FOX) assay, malondialdehyde by the thiobarbituric acid (TBARS) assay, and vitamin E by HPLC. Mononuclear cells and polymorphonuclear cells were analyzed for ascorbic acid by HPLC and for glutathione (GSH) by enzymatic recycling. In addition, GSH peroxidase, GSH transferase and glucose-6-phosphate dehydrogenase levels were determined in both cell fractions.

RESULTS

Plasma organoperoxides were significantly elevated in the IDDM subjects compared to controls (p = 0.02) while TBARS and vitamin E levels were not significantly different. In the IDDM subjects, mononuclear cell levels of ascorbic acid were significantly lower (p < 0.02) and levels of GSH were lower, approaching significance (p = 0.07), compared to controls. Ascorbic acid and GSH levels in polymorphonuclear cells were not significantly different between IDDM subjects and controls, nor were enzyme levels different. In addition, the plasma and intracellular indices of oxidative status in IDDM subjects were not different when IDDM subjects with complications were compared to IDDM subjects without complications.

CONCLUSION

Demonstration of oxidative stress in IDDM subjects depends upon which markers are measured. This is in agreement with previous studies of oxidative stress in various disease states including diabetes. Plasma levels of organoperoxides may be the most reliable indicators of oxidative stress. However, it is unclear whether elevated plasma organoperoxides indicate a generalized systemic stress or are produced in localized areas. By comparison, oxidative stress indices determined with isolated blood cells may provide a clearer picture. Depressed levels of ascorbic acid and GSH were observed only in mononuclear cells, which are mainly long-lived T lymphocytes. Mononuclear cells antioxidant status may reflect systemic oxidative stress. In this study, neither plasma markers nor intracellular markers of oxidative stress were different in IDDM subjects with long-term diabetic complications compared to subjects without complications.

Methods for monitoring oxidative stress, lipid peroxidation and oxidation resistance of lipoproteins

After a brief discussion of lipid peroxidation mechanism and the action of antioxidants and their potential to exhibit prooxidant effects, we give an overview on the clinical relevance of oxidative stress parameters. Many diseases are associated with oxidative stress e.g. by radical damage, among them atherosclerosis, diabetes mellitus, chronic renal failure, rheumatoid arthritis, and neurodegenerative diseases, and in many cases the investigation of parameters of oxidative stress has brought substantial insights into their pathogenesis. We then briefly review methods for the continuous monitoring of lipid peroxidation processes in vitro, which has helped in elucidating their mechanism and in some more detail cover such methods which have been proposed more recently to assess oxidative status and antioxidant activity in biological samples.

Oxidative stress during hemodialysis: effect of heparin

BACKGROUND

Patients on chronic hemodialysis (HD) are exposed to oxidative stress. An HD session is used in this study as an in vivo model for studying the influence of heparin on oxidative stress caused partially by activated peripheral blood polymorphonuclear leukocytes (PMNLs) during a HD session.

METHODS

Each patient underwent HD once with and once without heparin. Oxidative stress was determined by evaluating both the rate of superoxide release from phorbol 12-myristate 13-acetate (PMA)-stimulated PMNLs and plasma levels of oxidized glutathione (GSSG), both measured before and after the dialysis session.

RESULTS

In vitro, heparin reduced the rate of superoxide release from separated PMA-stimulated PMNLs. In vivo, the rate of superoxide release from PMNLs was always increased after the dialysis session, regardless of the presence of heparin. However, in the presence of heparin, this increase was significantly smaller. The augmentation in the rate of superoxide release after the dialysis session without heparin was accompanied by a significant elevation of GSSG, reflecting a preceding oxidation of plasma glutathione.

CONCLUSIONS

The increase in both parameters, the rate of superoxide release, and the plasma GSSG concentration after HD treatment suggest that heparin in vivo alleviates the oxidative stress induced by the dialysis process. Based on our results, heparin should be the anticoagulant of choice because of its suppressant action on HD-induced oxidative stress.

N-acetylcysteine replenishes glutathione in HIV infection

BACKGROUND

Glutathione (GSH) deficiency is common in HIV-infected individuals and is associated with impaired T cell function and impaired survival. N-acetylcysteine (NAC) is used to replenish GSH that has been depleted by acetaminophen overdose. Studies here test oral administration of NAC for safe and effective GSH replenishment in HIV infection.

DESIGN

Oral NAC administration in a randomized, 8-week double-blind, placebo-controlled trial followed by optional open-label drug for up to 24 weeks.

SUBJECTS

HIV-infected, low GSH, CD4 T cells < 500 micro L(-1), no active opportunistic infections or other debilitation; n = 81. Study conducted prior to introduction of protease inhibitors.

RESULTS

Whole blood GSH levels in NAC arm subjects significantly increased from 0.88 mM to 0.98 mM, bringing GSH levels in NAC-treated subjects to 89% of uninfected controls (P = 0.03). Baseline GSH levels in the placebo group (0.91) remained essentially the same during the 8 week placebo-controlled trial. T cell GSH, adjusted for CD4 T cell count and beta2-microglobulin levels, also increased in the NAC-treated subjects (P = 0.04). Adverse effects were minimal and not significantly associated with NAC ingestion.

CONCLUSION

NAC treatment for 8 weeks safely replenishes whole blood GSH and T cell GSH in HIV-infected individuals. Thus, NAC offers useful adjunct therapy to increase protection against oxidative stress, improve immune system function and increase detoxification of acetaminophen and other drugs. These findings suggest that NAC therapy could be valuable in other clinical situations in which GSH deficiency or oxidative stress plays a role in disease pathology, e.g. rheumatoid arthritis, Parkinson's disease, hepatitis, liver cirrhosis, septic shock and diabetes.

Plasma antioxidant status after high-dose chemotherapy: a randomized trial of parenteral nutrition in bone marrow transplantation patients

BACKGROUND

Chemotherapy and radiation therapy result in increased free radical formation and depletion of tissue antioxidants. It is not known whether parenteral nutrition (PN) administered during bone marrow transplantation (BMT) supports systemic antioxidant status.

OBJECTIVE

The aims of the study were to determine 1) whether high-dose chemotherapy decreases concentrations of major circulating antioxidants in patients undergoing BMT and 2) whether administration of standard PN maintains systemic antioxidant concentrations compared with PN containing micronutrients and minimal lipids alone.

DESIGN

Twenty-four BMT patients were randomly assigned to receive either standard PN containing conventional amounts of dextrose, amino acids, micronutrients, and lipid (120 kJ/d) or a solution containing only micronutrients (identical to those in standard PN) and a small amount of lipid (12 kJ/d). Plasma antioxidant status was measured before conditioning therapy and serially at days 1, 3, 7, 10, and 14 after BMT.

RESULTS

Plasma glutathione (GSH) and alpha- and gamma-tocopherol concentrations decreased and the GSH redox state became more oxidized after conditioning chemotherapy. Plasma cysteine concentrations were unchanged, whereas cystine concentrations increased. Plasma vitamin C and zinc concentrations and GSH peroxidase activity increased over time. Plasma alpha-tocopherol concentrations were lower in patients given standard PN. There were no differences in other plasma antioxidants between groups.

CONCLUSIONS

A significant decline in GSH-glutathione disulfide, cysteine-cystine, and vitamin E status occurs after chemotherapy and BMT. Standard PN does not improve antioxidant status compared with administration of micronutrients alone. Further evaluation of PN formulations to support patients undergoing high-dose chemotherapy and BMT are needed.

Status of glutathione and other thiols and disulfides in human plasma

While plasma thiols, including homocysteine (HCys), glutathione (GSH), and cysteine (Cys), are being investigated as potential indicators of disease risk and health status, low levels, poor stability, and the lack of comprehensive methodologies have hampered their accurate assessment. Using our previously described HPLC with electrochemical detection method, our goal was to assess levels, stability, and distribution of biologically relevant thiols and disulfides in human plasma. In fresh plasma, processed immediately after collection, low levels of Cys, cystine, Cys-Gly, and the mixed disulfide Cys-GSH (CSSG) were consistently observed, whereas the levels of GSH and Cys-Gly disulfide were often below the limits of detection. These profiles were a consequence of poor thiol stability, as thiol standards added to human plasma were lost rapidly due to autoxidation or formation of mixed disulfides. A 75% loss of added GSH observed after 30 min was accounted for completely by the formation of GSH disulfide (24%) and CSSG (74%). Similar changes were found with other thiols when added to plasma. Thiols lost to oxidation were recovered quantitatively by reducing samples with potassium borohydride (KBH(4)) prior to analysis. In a study of 106 healthy adults, mean total thiol levels in plasma were: Cys (201 microM) > Cys-Gly (101 microM) > HCys (7 microM) > gamma-Glu-Cys (5 microM) > GSH (4 microM). All together, these results account for the poor stability of thiols in plasma and provide a method for their comprehensive and accurate determination.

Oxidative stress, acute and regular exercise: are they really harmful in the diabetic patient?

Oxidative stress has been involved in the pathogenic process of a variety of diseases including diabetes mellitus. The production of oxidative reactive products has been involved in biochemical changes in bio-molecules that might produce tissue damage directly related to some of the main vascular complications in the diabetic patient. On the other hand, exercise, paradoxically, is a well-recognized model of oxidative stress and also an important therapeutic tool in diabetes management. Therefore, the relationship between oxidative stress and exercise in diabetic patients implies an interesting biochemical paradox due to some of the negative effects of exercise principally by the increase of oxidative species in plasma. The effect of oxidative stress during an acute exercise and after an aerobic training period on those patients remains unknown and needs to be studied.

Radiation inactivation studies of hepatic sinusoidal reduced glutathione transport system

Sinusoidal transport of reduced glutathione (GSH) is a carrier-mediated process. Perfused liver and isolated hepatocyte models revealed a low-affinity transporter with sigmoidal kinetics (K(m) approximately 3.2-12 mM), while studies with sinusoidal membrane vesicles (SMV) revealed a high-affinity unit (K(m) approximately 0.34 mM) besides a low-affinity one (K(m) approximately 3.5-7 mM). However, in SMV, both the high- and low-affinity units manifested Michaelis-Menten kinetics of GSH transport. We have now established the sigmoidicity of the low-affinity unit (K(m) approximately 9) in SMV, consistent with other models, while the high-affinity unit has been retained intact with Michaelis-Menten kinetics (K(m) approximately 0.13 mM). We capitalized on the negligible cross-contributions of the two units to total transport at the low and high ends of GSH concentrations and investigated their characteristics separately, using radiation inactivation, as we did in canalicular GSH transport (Am. J. Physiol. 274 (1998) G923-G930). We studied the functional sizes of the proteins that mediate high- and low-affinity GSH transport in SMV by inactivation of transport at low (trace and 0.02 mM) and high (25 and 50 mM) concentrations of GSH. The low-affinity unit in SMV was much less affected by radiation than in canalicular membrane vesicles (CMV). The target size of the low-affinity sinusoidal GSH transporter appeared to be considerably smaller than both the canalicular low- and high-affinity transporters. The high-affinity unit in SMV was markedly inactivated upon irradiation, revealing a single protein structure with a functional size of approximately 70 kDa. This size is indistinguishable from that of the high-affinity GSH transporter in CMV reported earlier.

Thyroid-specific gene expression is differentially influenced by intracellular glutathione level in FRTL-5 cells

Alteration of the redox potential has been proposed as a mechanism influencing gene expression. Reduced glutathione (GSH) is one of the cellular scavengers involved in the regulation of the redox potential. To test the role that GSH may play in thyroid cells, we cultured a differentiated rat thyroid cell strain (FRTL-5) in the presence of L-buthionine-(S,R)-sulfoximine (BSO). BSO affects GSH synthesis by irreversibly inhibiting gamma-glutamylcysteine synthetase (EC 6.3.2.2), a specific enzyme involved in GSH synthesis. BSO-treated FRTL-5 cells show a great decrease in the GSH level, whereas malondialdehyde increases in the cell culture medium as a sign of lipid peroxidation. In these conditions the activity of two thyroid-specific promoters, thyroglobulin (Tg) and thyroperoxidase (TPO), is strongly reduced in transient transfection experiments. As both Tg and TPO promoters depend upon the thyroid-specific transcription factors, thyroid-specific transcription factor-1 (TTF-1) and Pax-8 for full transcriptional activity, we tested whether reduction of GSH concentration impairs the activity of these transcription factors. After BSO treatment of FRTL-5 cells, both transcription factors fail to trans-activate the respective chimerical targets, C5 and B-cell specific activating protein promoters, containing, respectively, multimerized TTF-1- or Pax-8-binding sites only as well as the Tg and TPO natural promoters. Northern analysis revealed that endogenous Tg messenger RNA (mRNA) expression is also reduced by BSO treatment, whereas endogenous TPO expression is not modified. Furthermore, the Pax-8 mRNA steady state concentration does not change in BSO-treated cells, whereas TTF-1 mRNA slightly decreases. Immunoblotting analysis of FRTL-5 nuclear extracts does not show significant modification of the Pax-8 concentration in BSO-treated cells, whereas a decrease of 25% in TTF-1 protein is revealed. Furthermore, BSO treatment decreases the DNA-binding activity to the respective consensus sequence of both transcription factors. Finally, different mechanisms seem to act on TTF-1 and Pax-8 functional impairment in BSO-treated cells. Indeed, with a lowered GSH concentration, the overexpressed Pax-8 still activates transcription efficiently, whereas, on the contrary, the overexpressed TTF-1 does not recover its transactivation capability when the respective chimerical target sequences are used (C5 and BSAP). When the natural Tg and TPO promoter sequences are used, overexpression of Pax-8 parallels the effect on both promoters observed using the chimeric target sequences, whereas overexpression of TTF-1 increases TPO promoter transcriptional activity only.

Oxidative damage and protection of the RPE

This review provides a model for the role of oxidative stress in the etiology of age-related macular degeneration (AMD). Epidemiological studies of diet, environmental and behavioral risk factors suggest that oxidative stress is a contributing factor of AMD. Pathological studies indicate that damage to the retinal pigment epithelium (RPE) is an early event in AMD. In vitro studies show that oxidant treated RPE cells undergo apoptosis, a possible mechanism by which RPE cells are lost during early phase of AMD. The main target of oxidative injury seems to be mitochondria, an organelle known to accumulate genomic damages in other postmitotic tissues during aging. The thiol antioxidant GSH and its amino acid precursors protect RPE cells from oxidant-induced apoptosis. Similar protection occurs with dietary enzyme inducers which increase GSH synthesis. These results indicate that therapeutic or nutritional intervention to enhance the GSH antioxidant capacity of RPE may provide an effective way to prevent or treat AMD.

Redox state of glutathione in human plasma

Thiol and disulfide forms of glutathione (GSH) and cysteine (Cys) were measured in plasma from 24 healthy individuals aged 25-35 and redox potential values (E(h)) for thiol/disulfide couples were calculated using the Nernst equation. Although the concentration of GSH (2.8 +/- 0.9 microM) was much greater than that of GSSG (0.14 +/- 0.04 microM), the redox potential of the GSSG/2GSH pool (-137 +/- 9 mV) was considerably more oxidized than values for tissues and cultured cells (-185 to -258 mV). This indicates that a rapid oxidation of GSH occurs upon release into plasma. The difference in values between individuals was remarkably small, suggesting that the rates of reduction and oxidation in the plasma are closely balanced to maintain this redox potential. The redox potential for the Cys and cystine (CySS) pool (-80 +/- 9 mV) was 57 mV more oxidized, showing that the GSSG/2GSH and the CySS/2Cys pools are not in redox equilibrium in the plasma. Potentials for thiol/disulfide couples involving CysGly were intermediate between the values for these couples. Regression analyses showed that the redox potentials for the different thiol/disulfide couples within individuals were correlated, with the E(h) for CySS-mono-Gly/(Cys. CysGly) providing the best correlation with other low molecular weight pools as well as protein disulfides of GSH, CysGly and Cys. These results suggest that E(h) values for GSSG/2GSH and CySS-mono-Gly/(Cys. CysGly) may provide useful means to quantitatively express the oxidant/antioxidant balance in clinical and epidemiologic studies.

Glutathione redox potential in response to differentiation and enzyme inducers

The reduced glutathione (GSH)/oxidized glutathione (GSSG) redox state is thought to function in signaling of detoxification gene expression, but also appears to be tightly regulated in cells under normal conditions. Thus it is not clear that the magnitude of change in response to physiologic stimuli is sufficient for a role in redox signaling under nontoxicologic conditions. The purpose of this study was to determine the change in 2GSH/GSSG redox during signaling of differentiation and increased detoxification enzyme activity in HT29 cells. We measured GSH, GSSG, cell volume, and cell pH, and we used the Nernst equation to determine the changes in redox potential Eh of the 2GSH/GSSG pool in response to the differentiating agent, sodium butyrate, and the detoxification enzyme inducer, benzyl isothiocyanate. Sodium butyrate caused a 60-mV oxidation (from -260 to -200 mV), an oxidation sufficient for a 100-fold change in protein dithiols:disulfide ratio. Benzyl isothiocyanate caused a 16-mV oxidation in control cells but a 40-mV oxidation (to -160 mV) in differentiated cells. Changes in GSH and mRNA for glutamate:cysteine ligase did not correlate with Eh; however, correlations were seen between Eh and glutathione S-transferase (GST) and nicotinamide adenine dinucleotide phosphate (NADPH):quinone reductase activities (N:QR). These results show that 2GSH/GSSG redox changes in response to physiologic stimuli such as differentiation and enzyme inducers are of a sufficient magnitude to control the activity of redox-sensitive proteins. This suggests that physiologic modulation of the 2GSH/GSSG redox poise could provide a fundamental parameter for the control of cell phenotype.

Management of oxidative stress in the CNS: the many roles of glutathione

An outline is given of mechanisms that generate oxidative stress and inflammation. Considered are the metabolic mechanisms that give rise to peroxides, the source of strong oxidants; the production of dicarbonyls that interact with macromolecules to form advanced glycation endproducts; and the role that activation of the transcription factor NF(Kappa)B has in the expression of pro-inflammatory genes. Management of oxidative stress is considered by outlining the central role of reduced glutathione (GSH) in peroxide scavenging, dicarbonyl scavenging and activation of NF(Kappa)B. Cellular GSH levels are dictated by the balance between consumption, oxidation of GSH, reduction of oxidized-glutathione, and synthesis. The rate-limiting enzyme in GSH synthesis is L-gamma-glutamyl-L-cysteine synthase, a phase II enzyme. Phase II enzyme inducers are found in many fruits and vegetables. It is suggested that dietary phase II enzyme inducers be investigated for their potential for preventing or retarding the development of degenerative diseases that have an underlying oxidative stress and inflammatory component.

Constitutive differences in antioxidant defense status distinguish alloxan-resistant and alloxan-susceptible mice

Alloxan (AL), a potent generator of superoxide and hydroxyl radicals, selectively destroys rodent pancreatic beta-cells. Alloxan-susceptible (ALS/Lt) and AL-resistant (ALR/Lt) are inbred mouse strains derived in Japan by inbreeding CD-1 (ICR) mice with concomitant selection for high or low sensitivity to a relatively low AL dose. The present study was undertaken to examine whether resistance was mediated by differences in either systemic or beta-cell antioxidant defense status. Superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and glutathione peroxidase (GPX) activities were determined in tissues of AL-untreated ALR/Lt and ALS/Lt male mice at 7 weeks of age. Specific activities of pancreatic SOD1, GR, and GPX were significantly increased in ALR/Lt mice compared with ALS/Lt mice. ALR/Lt mice further exhibited higher levels of glutathione in plasma, blood, pancreas, and liver combined with lower constitutive lipid peroxides in serum, liver, and pancreas. These results support the hypothesis that the selection process leading to the development of an AL-resistant mouse strain entailed accumulation of a gene or genes contributing to upregulated antioxidant status.

Age-related changes in vascular responses

Aging causes changes in the structure and function of the vessels that leads to an increase in the incidence of certain cardiovascular diseases, such as hypertension, coronary artery disease, heart failure, and postural hypotension with enhancement of both morbidity and mortality. When aging is associated with hypertension, these changes are increased. Aging alters endothelial cells, and so the vascular tone regulation, reducing the endothelium-dependent relaxations, probably by a decrease in endothelial synthesis or release of nitric oxide. In addition, endothelium-independent relaxations are essentially unaltered, those elicited by beta-adrenoceptor agonists being usually reduced. Aging scarcely modifies the contractions induced by different agents, such as 5-hydroxytryptamine, histamine, high potassium, and angiotensin, whereas reduces those elicited by noradrenaline or endothelin. Vascular Ca(2+) homeostasis appears to be altered in aging. The extracellular Ca(2+) dependence of contractile responses elicited by agonists is enhanced, which explains the increased sensitivity to Ca(2+) antagonists in elderly. Finally, Na(+) pump activity, that controls cellular ionic homeostasis, seems to be reduced in aging. The contractions elicited by Na(+) pump inhibition with ouabain are negatively modulated by the release of a diffusible endothelial factor, an effect lost in aging, being replaced by an endothelium-dependent contracting factor that facilitates ouabain responses.