Glutathione Deficiency and Alterations in the Sulfur Amino Acid Homeostasis during Early Postnatal Development as Potential Triggering Factors for Schizophrenia-Like Behavior in Adult Rats

Impaired glutathione (GSH) synthesis and dopaminergic transmission are important factors in the pathophysiology of schizophrenia. Our research aimed to assess the effects of l-buthionine-(S,R)-sulfoximine (BSO), a GSH synthesis inhibitor, and GBR 12909, a dopamine reuptake inhibitor, administered alone or in combination, to Sprague–Dawley rats during early postnatal development (p5–p16), on the levels of GSH, sulfur amino acids, global DNA methylation, and schizophrenia-like behavior. GSH, methionine (Met), homocysteine (Hcy), and cysteine (Cys) contents were determined in the liver, kidney, and in the prefrontal cortex (PFC) and hippocampus (HIP) of 16-day-old rats. DNA methylation in the PFC and HIP and schizophrenia-like behavior were assessed in adulthood (p90–p93). BSO caused the tissue-dependent decreases in GSH content and alterations in Met, Hcy, and Cys levels in the peripheral tissues and in the PFC and HIP. The changes in these parameters were accompanied by alterations in the global DNA methylation in the studied brain structures. Parallel to changes in the global DNA methylation, deficits in the social behaviors and cognitive functions were observed in adulthood. Only BSO + GBR 12909-treated rats exhibited behavioral alterations resembling positive symptoms in schizophrenia patients. Our results suggest the usefulness of this neurodevelopmental model for research on the pathomechanism of schizophrenia.

Putative Role of Nuclear Factor-Kappa B But Not Hypoxia-Inducible Factor-1α in Hypoxia-Dependent Regulation of Oxidative Stress in Hematopoietic Stem and Progenitor Cells

Aims: Adaptation to low oxygen of hematopoietic stem cells (HSCs) in the bone marrow has been demonstrated to depend on the activation of hypoxia-inducible factor (HIF)-1α as well as the limited production of reactive oxygen species (ROS). In this study, we aimed at determining whether HIF-1α is involved in protecting HSCs from ROS. Results: Oxidative stress was induced by DL-buthionine-(S,R)-sulfoximine (BSO)-treatment, which increases the mitochondrial ROS level. Hypoxia rescued Lineage-Sca-1+c-kit+ (LSK) cells from BSO-induced apoptosis, whereas cells succumbed to apoptosis in normoxia. Apoptosis in normoxia was inhibited with the antioxidant N-acetyl-L-cysteine or by overexpression of anti-apoptotic BCL-2. Moreover, stabilized expression of oxygen-insensitive HIFs could not protect LSK cells from oxidative stress-induced apoptosis at normoxia, neither could short hairpin RNA to Hif-1α inhibit the protective effects by hypoxia in LSK cells. Likewise, BSO treatment of LSK cells from Hif-1α knockout mice did not suppress the effects seen in hypoxia. Microarray analysis identified the nuclear factor-kappa B (NF-κB) pathway as a pathway induced by hypoxia. By using NF-κB lentiviral construct and DNA-binding assay, we found increased NF-κB activity in cells cultured in hypoxia compared with normoxia. Using an inhibitor against NF-κB activation, we could confirm the involvement of NF-κB signaling as BSO-mediated cell death was significantly increased in hypoxia after adding the inhibitor. Innovation: HIF-1α is not involved in protecting HSCs and progenitors to elevated levels of ROS on glutathione depletion during hypoxic conditions. Conclusion: The study proposes a putative role of NF-κB signaling as a hypoxia-induced regulator in early hematopoietic cells.

Synergistic activation of the Nrf2-signaling pathway by glyceollins under oxidative stress induced by glutathione depletion

Oxidative stress state such as depletion of the intracellular glutathione (GSH) is associated with the development of cancer. Some dietary phytochemicals have been shown to possess a cancer preventive effect, although the understanding of the involved mechanisms is still limited. Recent study has shown that glyceollins, phytoalexins derived from soybean by biotic elicitor, might have a cancer preventive effect through induction of detoxifying/antioxidant enzymes. The objective of this study was to investigate the effects of glyceollins on the Nrf2 signaling pathway under excessive oxidative stress induced by GSH depletion. In mouse hepatoma cells (Hepa1c1c7) subjected to the buthionine sulfoximine (BSO), an inhibitor of γ-glutamylcysteine synthetase (γGCS), the intracellular GSH content was significantly lowered. On the other hand, incubation with glyceollins in the presence of BSO increased the level of GSH, expression of γGCS, and nuclear translocation of NF-E2-related factor-2 (Nrf2), compared to the cells treated with BSO only. Nrf2-antioxidant responsive element (ARE)-reporter activity assay in HepG2-C8 showed that BSO increased the ARE-reporter activity in a dose-dependent manner, compared to vehicle-treated cells, whereas cotreatment with glyceollins caused further increase in reporter luciferase activity relative to BSO alone. Taken together, glyceollins synergistically activated the Nrf2 signaling pathway and subsequently the expression of phase 2/antioxidant enzymes in the presence of BSO, suggesting that BSO-induced oxidative stress and that glyceollins regulate the expression of phase 2/antioxidant enzymes through different mechanisms from each other.

Genomic instability induced by mutant succinate dehydrogenase subunit D (SDHD) is mediated by O2(-•) and H2O2

SDHD mutations are associated with human cancers but the mechanisms that may contribute to transformation are unknown. The hypothesis that mutations in SDHD increase levels of superoxide leading to genomic instability was tested using site-directed mutagenesis to generate a truncated SDHD cDNA that was expressed in Chinese hamster fibroblasts. Stable expression of mutant SDHD resulted in 2-fold increases in steady-state levels of superoxide that were accompanied by a significantly increased mutation rate as well as a 70-fold increase in mutation frequency at the hprt locus. Overexpression of MnSOD or treatment with polyethylene glycol conjugated (PEG)-catalase suppressed mutation frequency in SDHD mutant cells by 50% (P<0.05). Simultaneous treatment with PEG-catalase and PEG-SOD suppressed mutation frequency in SDHD mutant cells by 90% (P<0.0005). Finally, 95% depletion of glutathione using l-buthionine-[S,R]-sulfoximine (BSO) in SDHD mutant cells caused a 4-fold increase in mutation frequency (P<0.05). These results demonstrate that mutations in SDHD cause increased steady-state levels of superoxide which significantly contributed to increases in mutation rates and frequency mediated by superoxide and hydrogen peroxide. These results support the hypothesis that mutations in SDHD may contribute to carcinogenesis by increasing genomic instability mediated by increased steady-state levels of reactive oxygen species.

Potential contribution of oxidative stress and inflammation to anxiety and hypertension

Previously, we have published that pharmacological induction of oxidative stress causes anxiety-like behavior in rats and also is associated with hypertension in these animals. Here, we report that sub-chronic induction of oxidative stress via pharmacological induction leads to i) reduction in glyoxalase (GLO)-1 and glutathione reductase (GSR)-1 expression; ii) calpain mediated reduction of brain derived neurotrophic factor (BDNF) levels; iii) NFκB mediated upregulation of proinflammatory factors interleukin (IL)-6 and tumor necrosis factor (TNF)-α and elevated angiotensin (AT)-1 receptor levels in hippocampus, amygdala and locus coeruleus regions of the brain. Acute oxidative stress has opposite effects. We speculate that regulation of GLO1, GSR1, BDNF, NFκB and AT-1 receptor may contribute to anxiety-like behavior and hypertension in rats.

Vitamin E prevents buthionine sulfoximine-induced biochemical disorders in the rat

Antioxidant therapy can improve the protection and metabolic activity of cells and tissues. In this study, the effect of vitamin E administration on buthionine sulfoximine (BSO)-induced glutathione (GSH) depletion in the rat lung and liver was investigated. Hepatic GSH was depleted by intraperitoneal administration of BSO (4 mmol kg−1), twice a day, for 30 days to rats. We also investigated whether the lung and liver mitochondrial GSH contents were influenced by BSO administration and whether an extracellular supply of vitamin E could prevent the changes caused by BSO-mediated GSH depletion. Glutathione levels in lung and liver tissues were depleted by 47% and 60%, respectively. Depletion of hepatic and pulmonary GSH in turn causes decline in the levels of mitochondrial GSH, leading to impaired antioxidant defence function of mitochondria. Both the cytosolic and mitochondrial glutathione disulfides (GSSG) were altered during BSO treatment, and led to drastic increase in GSSG/GSH redox status. One of the experimental groups was given vitamin E (65 mg (kg diet)−1) mixed with rat feed. The rats fed with vitamin E were found to have partially restored GSH levels in liver and lung, diminished levels of TBARS and minimized tissue damage. The current findings suggest that the impaired glutathione and glutathione-dependent enzyme status may be correlated with the elevated lipid peroxidation and mitochondrial membrane damage and that vitamin E therapy to the BSO-administered rats prevents the above changes. However, vitamin E did not have any effect on the activity of γ-glutamyl cysteine synthetase (γ-GCS).

[Oxidative stress on idiopathic osteonecrosis]

The increasing incidence of steroid-induced osteonecrosis of the femoral head is a recent and emerging problem. In-depth pathogenesis, however, has not been well understood. We focused on oxidative stress, which was reported to be involved in many diseases, and conducted animal studies to investigate it. Our results from the rabbit model of steroid-induced osteonecrosis demonstrated that administration of steroids caused oxidative damage in bones, and the administration of glutathione reduced the incidence of osteonecrosis. We were also the first to have successfully induced osteonecrosis in rats by administering buthionine sulfoximine (BSO) . The results indicated the involvement of oxidative stress in the development of osteonecrosis and may contribute to elucidating the underlying mechanisms and prevention of the pathogenesis of steroid-induced osteonecrosis.

Glutathione depletion induces differential apoptosis in cells of mouse retina, in vivo

Oxidative stress affects numerous intracellular macromolecules, and may result in cell death unless precisely regulated. Unregulated oxidative stress can be controlled by various cellular defense mechanisms such as glutathione (GSH) which can critically counteract the damaging effects of oxidative stress in mammalian cells. We determined the effects of unregulated oxidative stress induced by GSH depletion on cells in mouse retina. Mice were intraperitoneally injected with buthionine sulphoximine (BSO) at 1.5 g/kg. After 0, 1, 4, and 7 days of BSO administration, retinas were excised and sections were subjected to GSH assay and terminal uridine deoxynucleotidyl nick end labeling (TUNEL) analysis. After 4 days of BSO administration, the number of TUNEL positive cells was significantly increased. However, after 7 days, TUNEL positive cells returned to the basal level. The retinal region most affected by the BSO treatment appeared to be the outer nuclear layer where the photoreceptor cells reside. Different from cells in other regions, retinal cells in the inner nuclear layer increased in their apoptosis even after the first day of BSO injection, and the increase was further potentiated after 4 days. Taken together, our studies suggested that GSH depletion may cause unregulated oxidative stress to the cells in the retina and indeed increased cell death in the retina. The cells in the inner nuclear layer seemed to be affected earlier than the cells in other layers of the retina. The GSH level in the retina may be a crucial therapeutic target in preventing blindness.

Glutathione depletion with L-buthionine-(S,R)-sulfoximine demonstrates deleterious effects in acute pancreatitis of the rat

A common pathway in the pathogenesis of acute pancreatitis is the generation of free oxygen radicals. The most important defense mechanisms are free radical scavengers, especially glutathione. This study evaluates the influence of the inhibition of glutathione synthesis with L-buthionine-(S,R)-sulfoximine (BSO) on the course of experimentally induced acute pancreatitis in rats and the effects on isolated pancreatic acini and their secretion pattern. Thus acute necrotizing pancreatitis was induced with intraductal infusion of low-dose glycodeoxycholic acid and subsequent hyperstimulation with cerulein with and without pretreatment with BSO. In vitro pancreatic acini were isolated and stimulated with different concentrations of cerulein with and without BSO. The BSO-treated group showed a significantly reduced survival, more necrosis, and a decreased secretion of amylase in vivo. No effect on secretion pattern in either groups was seen in vitro and BSO did not exert toxic effects. Based on the data presented, this study demonstrates deleterious effects of scavenger depletion on the course of experimental pancreatitis. This is due to the systemic effects of free oxygen radicals rather than to local effects.

Neuroprotective effect of cyclic GMP against radical-induced toxicity in cultured spinal motor neurons

We have previously reported that nitric oxide-related cyclic guanosine-3',5'-monophosphate (GMP) protected spinal nonmotor neurons, but not motor neurons against chronic glutamate-induced toxicity, which is associated with selective motor neuronal death after glutamate stress. In this report, we investigated the effect of cyclic GMP against reactive oxygen species (ROS)-induced toxicity in cultured neurons from embryonic rat spinal cords. Pretreatment with a cGMP analogue, 8-bromoguanosine monophosphate (8br-cGMP), for 12-24 hours protected both spinal motor neurons and nonmotor neurons against injury induced by either hydrogen peroxide (H(2)O(2)), or a glutathione depletor, L-buthionine-[S,R]-sulfoximine (BSO). This protective effect was reversed by coadministration with the cGMP-dependent protein kinase (PKG) inhibitor Arg-Lys-Arg-Ala-Arg-Lys-Glu. Interestingly, when cultures were exposed to BSO for 24 hours to allow irreversible inhibition of glutathione synthesis, 8br-cGMP protected only nonmotor neurons. Our results indicate that cGMP attenuates oxidative injury to cultured spinal neurons, in a mechanism associated with glutathione synthesis.

Did consumption of flour bleached by the agene process contribute to the incidence of neurological disease?

The present report proposes the hypothesis that increased levels of neurodegenerative disorders in humans may have arisen due to inclusion in the diet of methionine sulfoximine (MSO), a byproduct of the bleaching of flour by nitrogen trichloride. This method of bleaching, the 'agene process' was in use from early in the century and continued until at least 1949/1950. Estimates indicate that, at least in the UK, as much as 80% of all flour during this period was produced by this process. MSO acts directly to inhibit the production of two crucial molecules, glutathione (GSH) and glutamine. Decreases in GSH, a key antioxidant and free radical scavenger, diminish the body's antioxidant defenses and may lead to increased oxidative stress. Decreases in glutamine synthesis may act to increase free glutamate and give rise to increased levels of ammonia. Cells in the nervous system are particularly sensitive to a decline in either GSH or glutamine. The combined effects of decreases in these molecules, particularly with long-term exposure to MSO in bleached flour, may have had quite drastic effects on neuronal health and survival. The present hypothesis may provide clues to the etiology of neurological disorders such as Alzheimer's disease (AD), Parkinson's disease (PD) and amyotrophic lateral sclerosis (ALS), suggesting that such disorders may arise in part due to toxic actions of some compounds in processed human foods.

Progression of mouse buthionine sulfoximine cataracts in vitro is inhibited by thiols or ascorbate

Mouse lens cultures were employed to study the progression of cataracts initiated by injection of buthionine sulfoximine, an inhibitor of glutathione (GSH) biosynthesis. Culture of lenses removed from untreated mice on postnatal day 7, for 48 hr in the presence of 4 mm BSO, resulted in only limited cataractous changes. To enable substantial progression of cataracts in vitro, it was therefore necessary to pretreat the mice with BSO prior to lens culture. A single injection of BSO (4 nmol mg-1 lens), administered on day 7, resulted in >90% depletion of lens GSH within 3 days, but no visible cataractous changes. The clear lenses were incubated for 29+/-1 hr at 37 degrees C in Medium HL-1, supplemented with EGF, insulin and Ca2+, in the presence or absence of BSO, and were scored for cataract development by previously described criteria. In the absence of BSO, only 4 of 10 lenses developed large opacities. However, in the presence of 4 mm BSO, 40 out of 45 experimental lenses developed opacities affecting at least 50% of the lens visual field and were scored as stages 1C-4, depending upon the extent and density of the cataracts. In addition, three lenses had opacities involving 20-50% of the field (stage 1B). By contrast, less than 10% of lenses from untreated mice incubated in the absence of BSO developed opacities. The cataracts developed in 4 mm BSO were accompanied by reduction of lens glutathione levels to <0.010 nmol mg-1 lens. They were almost completely prevented by 1 mm ascorbate, 2 mm GSH, 2 mm GSH monoethyl ester and 2 mm cysteamine. GSH and GSH ester maintained lens glutathione content between 0.1 and 0.2 nmol mg-1 in the presence of BSO, whereas ascorbate did not prevent near-total GSH depletion. The prevention of cataracts by thiols and ascorbate was confirmed by lens Na/K ratios not significantly different from those in control lenses. The above combination of GSH depletion in vivo by a single injection of BSO, followed 3 days later with lens culture in the presence of BSO, may yield a useful system to elucidate and control the biochemical mechanisms involved in oxidative cataract induction by this GSH-depleting agent.