Effects of methionine on selenium embryotoxicity in cultured rat embryos

Effects of methionine, an essential amino acid, on the embryotoxicity of selenium (Se) were examined using the rat embryo culture. Rat embryos at day 9.5 of gestation were cultured for 48 h in the presence of sodium selenite at 10 and 20 microM or sodium selenate at 30 and 100 microM with or without the addition of 1 mM DL-methionine. Selenite at 20 microM or selenate at 100 microM alone increased the incidence of embryonic malformation and inhibited the embryonic growth. The addition of methionine increased the incidence of embryonic malformation at 10 microM of selenite but decreased the incidence of embryonic malformation at 100 microM of selenate. On the other hand, the addition of methionine partially restored the inhibited embryonic growth at 20 microM of selenite or at 100 microM of selenate. It was considered from these results that the methionine availability in the embryonic environment and the oxidation state of Se are critical in Se embryotoxicity.     

Speciation and metabolism of selenium injected with 82Se-enriched selenite and selenate in rats

Selenate and selenite injected intravenously into rats were speciated by the HPLC-ICP MS method with use of an enriched stable isotope as the tracer. In dose-relation experiments, 82Se-enriched selenate or selenite was injected intravenously into male Wistar rats of 8 weeks of age (three rats/group) at single doses of 10, 25, 50, 100 and 200 microg/kg body weight for the selenate group, and 2, 5, 10, 25 and 50 microg/kg body weight for the selenite group. The animals were sacrificed 1 or 24 h later, and the concentrations and distributions of 82Se in the liver, kidneys, serum, and urine remaining in the bladder or 24-h urine were determined. In time-course experiments, 82Se-enriched selenate and selenite were injected at doses of 50 and 10 microg/kg body weight, respectively, and the animals were sacrificed 5, 15, 30, 60 and 180 min later. It was suggested that selenate is directly taken up by the liver with an efficiency of approximately 1/2 compared with selenite, the latter being taken up by the liver after being metabolized to selenide in red blood cells. Although selenate and selenite were metabolized differently in the bloodstream, and also a part of only selenate was excreted directly into the urine, the 82Se taken up by the liver was shown to be metabolized in a manner indistinguishable between selenate and selenite. 82Se of selenite origin but not of selenate origin was suggested to undergo redox reaction in the bloodstream. These results suggest that although parenteral selenate is utilized less efficiently by the body, it is utilized in the liver in a similar manner to selenite much more safely.     

Depression of glutathione in male reproductive tissues and potentiation of EMS-induced germ cell mutagenesis by L-buthionine sulfoximine

Buthionine sulfoximine (BSO) treatment significantly reduced testicular epididymal and vas deferens glutathione (GSH) levels in rats. Testicular levels of GSH were reduced by 20%, while epididymal GSH levels were reduced by more than 50%. BSO treatment correspondingly enhanced ethyl methanesulfonate (EMS)-induced dominant lethal mutations. EMS-induced resorption rates were doubled following BSO treatment. This effect was observed in mating wk 2 and 3 (d 8-19 following treatment), indicating effects on those germ cells which were in late testicular stages or were caput epididymal spermatozoa at the time of EMS treatment. The enhancement of the mutagenic action of EMS by BSO is restricted to the same time period (spermatid-spermatozoa transition, early epididymal maturation) as maximum sensitivity to the clastogenic action of EMS on male germ cells. The temporal pattern of EMS alkylation of rat spermatozoa correlated with the incidence of EMS-induced dominant lethal mutations. BSO depresses GSH in the male reproductive tract in a dose- and time-dependent manner. Perturbation of GSH in the male reproductive tract appears to influence chemical-induced germ cell mutations.     

The effect of N-acetylcysteine on ifosfamide-induced nephrotoxicity: in vitro studies in renal tubular cells

Ifosfamide (IF) nephrotoxicity is a serious adverse effect in children undergoing chemotherapy. Previous studies have shown that, in addition to the renal production of chloroacetaldehyde, a toxic metabolite of IF, lower levels of glutathione (GSH) may predispose the kidney to damage. The antioxidant N-acetylcysteine (NAC) is used extensively as an antidote for acetaminophen poisoning in children by replenishing GSH levels. As it has been safely and effectively used clinically, the objective of this study was to test whether the reversal of ifosfamide-induced nephrotoxicity can be achieved by administering NAC. Supplementation with NAC may reduce or prevent the degree of cellular cytotoxicity induced by IF. Porcine renal proximal tubular (LLCPK-1) cells were treated with NAC (0.4 mM or 2.5 mM) concurrently with 1 mM IF and 50 microM L-buthionine sulfoximine (BSO). Cellular viability was assessed by alamarBlue assay at 96 h. Intracellular GSH and oxidized GSH (GSSG) levels were determined using a GSH/GSSG colorimetric detection kit. A significant 60% decrease in cellular viability occurred when cells were treated daily with BSO and IF for 96 h. This decrease was significantly reduced when cells were concurrently treated with NAC in a concentration-dependent manner. Intracellular and total GSH levels in cells receiving concurrent treatment of NAC were significantly higher than those without NAC treatment. NAC protects renal tubular cells from IF-induced cytotoxicity. It is likely that NAC is protecting the cells by partially acting as a precursor for GSH synthesis. This mode of therapy may allow for protecting children from life-threatening nephrotoxicity induced by IF.     

Bacterial growth,morphology, and cell component changes in Herbaspirillum sp. WT00C exposed to high concentration of selenate

Selenium (Se) is a nonmetallic element of the chalcogens. It is primarily available in natural environments as selenate and selenite oxoanions. Although selenate/selenite reduction in many microbes is widely studied at low concentrations (<50 mM), the effects of high selenate stress on bacterial growth, morphology, and cell components have not yet been studied. In this study, the response of Herbaspirillum sp. WT00C to selenate stress at high concentration is investigated by microbiological and scanning electron microscopy (SEM) techniques as well as proteomic analysis. Bacterial growth was seriously inhibited under high selenate concentrations and its growth-inhibitory phase was prolonged with the increase of selenate concentrations. More interestingly, this bacterium was able to recover its growth even if the selenate concentration was up to 400 mM. Its growth inhibition period shortened to 6 h when the bacterium growing in 200 mM selenate for 28 h was reinoculated to the Luria-Bertani medium containing 200 mM selenate. The high concentration of selenate also induces marked changes in the cell dimension and surface roughness, as revealed by SEM, along with compositional changes in the cell wall shown by proteomic analysis. The bacterial growth inhibition results from the marked downregulation of the α-subunit of DNA polymerase III and RNA helicase, whereas its growth recovery is related to its high antioxidative activities. More NADPH synthesis and the upregulation of thioredoxin reductase and GPx are beneficial for Herbaspirillum sp. WT00C to establish and maintain a balance between oxidant and antioxidant intracellular systems for defending selenate toxicity. This study is an important contribution to understanding why Herbaspirillum sp. WT00C survives in a high concentration of selenate and how the bacterial cells respond physiologically to selenate stress at high concentration.     

Differential effects of L-buthionine sulfoximine and ethacrynic acid on glutathione levels and mitochondrial function in PC12 cells.

We investigated the effect of glutathione (GSH) depletion on mitochondrial function and generation of reactive oxygen intermediates (ROI) in PC12 cells in vitro. Direct depletion of cellular GSH using ethacrynic acid (EA, 500 mM) resulted in a concentration-dependent generation of ROI and cell death within 24 h. Treatment with 500 microM L-buthionine sulfoximine (BSO), which inhibits GSH synthesis, reduced cellular GSH but did not lead to generation of ROI. Furthermore, cells remained viable up to 72 h. Analysis of subcellular fractions revealed complete loss of cytosolic and mitochondrial GSH within 4 h of EA treatment. In contrast, BSO-treated cells still maintained 100% GSH in the mitochondrial fraction for 4 h and 6% for 48 h. Mitochondrial complex II/IIi and IV activities were not significantly decreased up to 48 h of BSO treatment while EA treatment resulted in a complete loss of complex II/III activity and a 70% reduction of complex IV activity within 4 h. These findings suggest that mitochondrial GSH is critical for the maintenance of mitochondrial function and cellular viability.     

Hepatoprotective role and antioxidant capacity of selenium on arsenic-induced liver injury in rats

The present study was undertaken to evaluate the protective effect of selenium against arsenic-induced oxidative damage in experimental rats. Males were randomly divided into four groups where the first was served as a control, whereas the remaining groups were respectively treated with sodium selenite (3 mg/kg b.w.), sodium arsenite (5.55 mg/kg b.w.) and a combination of sodium arsenite and sodium selenite. Changes in liver enzyme activities, thiobarbituric acid reactive substances (TBARS) level, antioxidants and reduced glutathione (GSH) contents were determined after 3 weeks experimental period.Exposure of rats to As caused a significant increase in liver TBARS compared to control, but the co-administration of Se was effective in reducing its level. The activities of glutathione peroxidase (GPx) and glutathione-S-transferase (GST) of As-treated group were found lower compared to the control and the Se-treated group. The co-administration of Se had an additive protective effect on liver enzyme activities compared to As-treated animals. On the other hand, a significant increase in plasmatic activities of AST, ALT and ALP was observed in As-treated group. The latter was also exhibited a decrease in body weight and an increase in liver weight compared to the control. The co-administration of Se has decreased the activities of AST, AST and ALP and improved the antioxidant status as well. Liver histological studies have confirmed the changes observed in biochemical parameters and proved the beneficial role of Se. To conclude, results suggest that As exposure enhanced an oxidative stress by disturbing the tissue antioxidant defense system, but the Se co-administration protected liver tissues against As intoxication probably owing to its antioxidant properties.     

Embryotoxicity of magainin-2-amide and its enhancement by cyclodextrin, albumin, hydrogen peroxide and acidification.

BACKGROUND: The channel-forming antimicrobial peptide, magainin-2-amide, interacts preferentially with negatively charged, non cholesterol-containing membranes, including those of sperm, oocytes and cells of pre-implantation embryos. Cyclodextrin and albumin remove membrane cholesterol and together with hydrogen peroxide (H2O2) are potential enhancers of embryotoxicity. METHODS: Two-cell murine embryos were cultured in vitro with magainin-2-amide at a high effective concentration (250 microg/ml) and at subthreshold concentrations (166 and 200 microg/ml). Embryos treated with sub-threshold concentrations of magainin were additionally treated with cyclodextrin, bovine serum albumin or H2O2 or were cultured under acidified conditions. Cell viability was verified with propidium iodide and fluorescein diacetate. RESULTS: The embryotoxic effect of magainin and H2O2 was dose- and time-dependent. Cyclodextrin, H2O2, acidification of the medium, and to a lesser extent albumin, enhanced the embryotoxicity of magainin at sub-threshold concentrations. CONCLUSION: Magainin on its own is highly embryotoxic. Its embryotoxicity is enhanced by cyclodextrin, albumin, H2O2 and acidification. Thus, magainin which has antibacterial, antifungal and antiprotozoal activity may also have a potential role as a contraceptive agent. The harmful effects of various concentrations of the exogenous H2O2 on 2-cell stage mouse embryos are reported here, to the best of our knowledge, for the first time.     

Quantitative analysis of cellular glutathione in early preimplantation mouse embryos developing in vivo and in vitro.

The relative levels of reduced glutathione (GSH) have been measured fluorimetrically in individual eggs and early embryos from two mouse strains, one of which shows developmental arrest in vitro. GSH levels fell by approximately 20-25% at fertilization and by approximately 45% by the late 2-cell and early 4-cell stages. No differences were observed between strains or between embryos cultured in vitro or in vivo. Addition of exogenous H2O2 or diethylmaleate depleted GSH. GSH levels were not affected significantly after inhibition of GSH-peroxidase by mercaptosuccinate nor of catalase by aminotriazole. Mercaptosuccinate did not inhibit development but catalase inhibition caused arrest at the 2-cell stage. Addition of exogenous GSH or thioredoxin did not promote development of 'blocking' embryos through the 2-cell block. It is concluded that early embryos lack a mercaptosuccinate sensitive peroxidase activity for removing H2O2, which may be removed by catalase or the glutathione-S-transferase system. It is suggested that GSH may have a role in detoxifying peroxidated lipids. The results are consistent with a role for reactive oxygen species in the 2-cell block.     

Effects of 2-mercaptoethanol and buthionine sulfoximine on cystine metabolism by and proliferation of mitogen-stimulated human and mouse lymphocytes.

Cysteine is an essential amino acid for lymphocytes and its anabolic products are intimately involved in lymphocyte activation. The purpose of this study was to assess the uptake and subsequent utilization of cyst(e)ine by mitogen-stimulated human peripheral blood mononuclear cells (PBMC), to evaluate the effect of an exogenous thiol, 2-mercaptoethanol (2ME), on these processes, and to compare human and mouse lymphocyte reactivities. Unlike mouse lymphocytes, the proliferation of human T-cells was inhibited by addition of 2ME although 2ME enhanced cystine uptake. Optimal responses to T-cell mitogens (Con A and PHA) were obtained with a cystine concentration of greater than or equal to 25 and 200 microM for human and mouse cells, respectively, and 2ME enhanced DNA synthesis of Con A-stimulated mouse cells regardless of the cystine dose; however, 2ME enhanced the response of human cells only in the presence of suboptimal doses of cystine. To assess whether 2ME's inability to enhance human PBMC responses was related to their glutathione (GSH) content, the human PBMC were pretreated with buthionine sulfoximine (BSO, an inhibitor of GSH synthesis). Even when the initial intracellular GSH concentration was lowered to below that of mouse lymphocytes, 2ME still inhibited proliferation. In contrast, addition of 2ME to human PBMC maintained in the presence of BSO enhanced the proliferative response suggesting that a critical level of thiols is needed for proliferation. The ability of 2ME to enhance proliferative responses in cystine deficient medium supports this contention. Consistent with thiol involvement in activation, Con A increased [35S]cystine uptake 2-fold within 4 h of incubation and enhanced subsequent conversion of cystine into cysteine and GSH. Interestingly, BSO treatment only slightly inhibited Con A-induced protein synthesis (5%), but it significantly suppressed conversion of cystine into cysteine or GSH (80-95%) and blocked DNA synthesis (90%). Overall, the results indicate that various differential thiol characteristics must exist between human and mouse lymphocytes and that a reducing equivalent is necessary for DNA synthesis but not lymphocyte activation.     

The selenium link: the missing link in our understanding of biochemical trigger reactions?

'Inorganic' selenium (Se), e.g. selenite and selenate, is assumed to be transformed into selenide and to be incorporated into selenoproteins, but this has never been proved. There is evidence, however, that vitamin C reduces selenite to elemental Se. Elemental sulphur (S) and Se bind easily to sulphides and selenides, forming links containing two or more S or Se atoms. Such links exist in natural minerals and have been found in proteins in living organisms. There are many indications that selenocysteine in special proteins combines with elemental Se to form Se links that transfer electrons from redoxable agents to oxygen (O2). This implies a reduction to hydrogen peroxide (H2O2) or H2O, while gaining energy and achieving trigger effects. H2O2 supplies anaerobic reactions with energy eventually via adenosine 5'-triphosphate (ATP) or guanosine 5'-triphosphate (GTP). Without Se links, redoxable agents can be oxidized by oxygen, which leads to the formation of oxygen products and inhibition of further electron transference. Nitrous oxide (NO) is one product of oxidation that, firmly binding to heme structures, may result in a system of protection. NO can prevent O2 from binding to them and thereby stop destroying oxidations.     

Effects of buthionine sulfoximine on the development of ozone-induced pulmonary fibrosis

The capacity of reduced glutathione (GSH) to protect lung tissue against ozone-induced pulmonary fibrosis was investigated. Male B6C3F1 mice were exposed to 0, 0.2, 0.5, and 1.0 ppm ozone for 23 hr/day for 14 days. During exposures and/or for a period of 90 days after exposures, subgroups of mice at each exposure level were given drinking water containing 30 mM L-buthionine-S,R-sulfoximine (BSO) to lower in vivo levels of GSH. These BSO treatments reduced blood glutamylcysteine synthetase (GCS) activity (regulatory enzyme for GSH biosynthesis) and lung nonprotein sulfhydryl (NPSH) levels in nonexposed animals by approximately half. In contrast, ozone exposures increased blood GCS activity and lung NPSH levels in a concentration-dependent manner, with smaller increases in the BSO-treated mice. Immediately after exposures, an ozone-related inflammatory response was seen in lungs, but no histopathological signs of developing fibrosis were evident. Ninety days later, mice exposed to 1 ppm ozone and not treated with BSO had modest evidence of pulmonary fibrosis. Mice exposed to 1 ppm ozone and treated with BSO during this post-exposure period (regardless of BSO treatment during exposures) showed histopathological evidence of exacerbated pulmonary fibrosis, compared to similarly exposed mice not treated with BSO postexposure. These results indicated that interference with the body's normal defense mechanisms against oxidant damage, including suppression of GSH biosynthesis, exacerbates the subsequent development of pulmonary fibrosis.     

丁硫氨酸硫酸亚胺早期处理抑制单核细胞向树突状细胞的分化

 目的 研究细胞氧化-还原态对树突状细胞（DC）分化和功能的影响。 方法 细胞氧化-还原态的调控应用特异性谷胱甘肽（GSH）合成抑制剂丁硫氨酸硫酸亚胺（BSO）。自健康人外周血单个核细胞（PBMC）分离单核细胞，在含重组人粒细胞-巨噬细胞集落刺激因子和 IL-4的RPMI 1640 培养液中诱导分化 DC。将单核细胞分为 BSO 早期（培养第 1 天）用药组、BSO 晚期（培养第 5 天）用药组和不予 BSO 处理的对照组。BSO 用药剂量为终浓度 1 mmol/L，换液时补加相应剂量的 BSO。培养第 5 天，分别给予加入脂多糖（LPS）100 ng/ml（LPS刺激组）或重组人干扰素 （rhIFN- ）20 U/ml（IFN- 刺激组）或不予刺激（无刺激组）的处理；培养第 7 天收集各组悬浮细胞进行表型分析和功能检测，并在倒置显微镜下观察 BSO 早期用药组和对照组贴壁细胞。表型分析采用特异性荧光标记单抗及流式细胞仪。功能检测采用混合淋巴细胞反应试验，将经丝裂霉素C 处理的 DC（刺激细胞）与异基因非贴壁 PBMC（反应细胞）混合（刺激细胞:反应细胞分别为 1:25、1:50、1:100）培养 5 d 后，用3H-胸腺嘧啶核苷法检测淋巴细胞增殖情况。 结果 培养第 7 天，镜下观察显示 BSO早期用药组贴壁细胞明显多于对照组；流式细胞仪检测显示 BSO 早期用药组 CD86 和CD1a表达明显低于对照组，CD86 平均荧光强度（MFI）分别为311.3 ± 97.3、552.0 ± 97.9（P = 0.01），CD1a 分别为52.2 ± 22.2、121.2 ± 4.2（P = 0.03）；BSO早期用药组及对照组3H-胸腺嘧啶核苷掺入量（cpm）在刺激细胞:反应细胞＝1:25时分别为 1587 ± 1458 和9336 ± 1333（P=0.015）；加入rhIFN- 20 U/ml 刺激后二组 CD86 MFI 分别为 495.9 ± 143.9 和 800.4 ± 27.7（P = 0.06），而加入 LPS 100 ng/ml 刺激后二组CD86 MFI 分别为 1736.7 ± 375.7 和 1960.8 ± 494.5（P > 0.05）。表明单核细胞分化早期加入 BSO 对 DC 的分化和功能有抑制作用，并对 IFN- 诱导DC成熟有抑制作用。BSO 晚期用药组 DC 抗原提呈功能分子的表达及与对照组比较均无明显差异，对 LPS 或 rhIFN- 刺激的 DC成熟也无明显影响。 结论 BSO 早期持续处理能抑制单核细胞向 DC 细胞的分化，细胞内氧化-还原态水平可能是影响 DC 分化成熟的关键因子。     

Subcellular compartmentalization of glutathione: correlations with parameters of oxidative stress related to genotoxicity

Glutathione (GSH) is a major component of the antioxidant defence system of mammalian cells and is found in subcellular pools within the cytoplasm, nucleus and mitochondria. To evaluate the relationships between these pools and parameters of oxidative stress related to genotoxicity, wild type (WT) and 8-oxo-2'-deoxyguanosine glycosylase 1 (OGG1)-null (mOGG1(-/-)) mouse embryonic fibroblasts (MEF) were treated with buthionine sulphoximine (BSO; 0-1000 microM, 24 h), an inhibitor of GSH biosynthesis. BSO treatment resulted in a concentration-dependent depletion of GSH from the cytoplasm, but depletion of mitochondrial and nuclear GSH occurred only at concentrations > or =100 microM. GSH levels were correlated with reactive oxygen species (ROS), lipid peroxidation (measured as the increase in the genotoxic end-product malondialdehyde (MDA)) and oxidative DNA modifications, measured as both frank DNA strand-breaks (FSB) and oxidized purine lesions (OxP) using the alkaline comet assay with formamidopyrimidine DNA glycosylase (FPG) modification; this system allowed for the identification of BSO-induced DNA modifications as primarily mutagenic 8-oxo-2'-deoxyguanosine lesions. A number of significant correlations were observed. First, negative linear correlations were observed between mitochondrial GSH and ROS (r = -0.985 and r = -0.961 for WT and mOGG1(-/-) MEF, respectively), and mitochondrial GSH and MDA (r = -0.967 and r = -0.963 for WT and mOGG1(-/-) MEF, respectively). Second, positive linear correlations were observed between ROS and MDA (r = 0.996 and r = 0.935 for WT and mOGG1(-/-) MEF, respectively), and ROS and OxP (r = 0.938 and r = 0.981 for WT and mOGG1(-/-) MEF, respectively). Finally, oxidative DNA modifications displayed a negative linear correlation with nuclear GSH (r = -0.963 and -0.951 between nuclear GSH and FSB and OxP, respectively, for WT MEF and r = -0.960 between nuclear GSH and OxP in mOGG1(-/-) MEF), thus, demonstrating the genotoxic potential of compounds that deplete GSH. The findings highlight the critical roles of the mitochondrial and nuclear GSH pools in protecting cellular components, particularly DNA, from oxidative modification.     

Inhibitory effects of cadmium on peripheral blood mononuclear cell proliferation and cytokine release are reversed by zinc and selenium salts

Zinc (Zn) and selenium (Se) exert regulatory activities on immune functions, while cadmium (Cd) is an immunotoxic agent. The object of this study was to detect effects of 10(-4), 10(-5), and 10(-6) M Cd sulphate, Zn sulphate, and sodium selenite, and their combinations on human peripheral blood mononuclear cell (PBMC) proliferation and IFN-gamma and TNF-alpha production. Only 10(-5) M Zn sulphate significantly enhanced spontaneous PBMC proliferation, which was unaffected by the other salts. At 10(-4) and 10(-5) M, Cd sulphate exerted a dose-response inhibitory action on phytohemagglutinin- (PHA-) stimulated PBMC proliferation and cytokine release, while 10(-4) M and 10(-5) M Zn sulphate and 10(-5) M sodium selenite induced a stimulatory effect on both proliferation and cytokine release; 10(-4) M sodium selenite enhanced only the PBMC proliferation; at 10(-6) M, none of the salts changed the PHA-stimulated immune activity. Moreover, 10(-4) and 10(-5) M Zn and 10(-5) M Se strongly upregulated IFN-gamma (a Th1 cytokine) release, even in presence of 10(-5) M Cd, and reduced the inhibitory effects of Cd on PBMC proliferation and TNF-alpha release. This study confirms that Zn and Se both strongly enhance cytokine release induced by mitogenic stimulation, showing also that Zn acts with a broader range of concentrations than Se. This suggests that dietary excess of Se may not have beneficial effects.     

Anticonvulsant effects of four neuropeptides in the rat hippocampus during self-sustaining status epilepticus

The plaques in multiple sclerosis (MS) autopsy tissue contain tumor necrosis factor-alpha (TNF-alpha) at high concentrations. Moreover, microglia are able to convert L-tryptophan to quinolinic acid. Thus, TNF-alpha and quinolinic acid are endogenous compounds which may compromise oligodendrocytes during inflammatory demyelination. It is also known that cellular functions depend on adequate concentrations of glutathione (GSH). As some apoptotic oligodendrocytes have been observed in MS plaques, it was therefore logical to determine whether oligodendrocyte apoptosis would occur in response to TNF-alpha, quinolinic acid or GSH depletion. Oligodendrocytes were treated in vitro with TNF-alpha, quinolinic acid and the GSH-depleting agent, buthionine sulfoximine (BSO), respectively, and the numbers of intact and apoptotic cells were counted. TNF-alpha reduced the numbers of mature oligodendrocytes, but not immature oligodendrocytes, without producing apoptosis. Quinolinic acid and BSO each caused oligodendrocyte loss via apoptosis, and GSH ethyl ester partly protected the cells against BSO. The data suggest that oligodendrocytes undergo apoptosis under adverse conditions that result from an endogenous toxicant or depletion of GSH.     

Glutathione deficiency intensifies ischaemia-reperfusion induced cardiac dysfunction and oxidative stress.

The efficacy of glutathione (GSH) in protecting ischaemia-reperfusion (I-R) induced cardiac dysfunction and myocardial oxidative stress was studied in open-chest, stunned rat heart model. Female Sprague-Dawley rats were randomly divided into three experimental groups: (1) GSH-depletion, by injection of buthionine sulphoxamine (BSO, 4 mmol kg(-1), i.p.) 24 h prior to I-R, (2) BSO injection (4 mmol kg(-1), i.p.) in conjunction with acivicin (AT125, 0.05 mmol kg(-1), i.v.) infusion 1 h prior to I-R, and (3) control (C), receiving saline treatment. Each group was further divided into I-R, with surgical occlusion of the main left coronary artery (LCA) for 30 min followed by 20 min reperfusion, and sham. Myocardial GSH content and GSH : glutathione disulphide (GSSG) ratio were decreased by approximately 50% (P < 0.01) in both BSO and BSO + AT125 vs. C. Ischaemia-reperfusion suppressed GSH in both left and right ventricles of C (P < 0.01) and left ventricles of BSO and BSO + AT125 (P < 0.05). Contractility (+dP/dt and -dP/dt) in C heart decreased 55% (P < 0.01) after I and recovered 90% after I-R, whereas +/-dP/dt in BSO decreased 57% (P < 0.01) with ischaemia and recovered 76 and 84% (P < 0.05), respectively, after I-R. For BSO + AT125, +/-dP/dt were 64 and 76% (P < 0.01) lower after ischaemia, and recovered only 67 and 61% (P < 0.01) after I-R. Left ventricular systolic pressure in C, BSO and BSO + AT125 reached 95 (P > 0.05) 87 and 82% (P < 0.05) of their respective sham values after I-R. Rate-pressure double product was 11% (P > 0.05) and 25% (P < 0.05) lower in BSO and BSO + AT125, compared with Saline, respectively. BSO and BSO + AT125 rats demonstrated significantly lower liver GSH and heart Mn superoxide dismutase activity than C rats after I-R. These data indicate that GSH depletion by inhibition of its synthesis and transport can exacerbate cardiac dysfunction inflicted by in vivo I-R. Part of the aetiology may involve impaired myocardial antioxidant defenses and whole-body GSH homeostasis.     

Rationale for the treatment of cancer with sodium selenite

Epidemiological studies conducted during several decades of the last century have demonstrated the importance of sufficient nutritional supply of selenium (Se) for human health. More importantly, low blood Se levels were found to be associated with an increased incidence and mortality from various types of cancers. Recently, attention of researchers was drawn to the relationship between free radical generation, known otherwise as oxidative stress, and carcinogenesis. It was therefore thought that antioxidants should be beneficial for prevention and inhibition of different malignancies. However, there appeared to be a paradox, because tumor growth is associated with tissue hypoxia that is accompanied by the formation of reductive rather than oxidative free radicals. Various organic and inorganic Se compounds, generally considered to be antioxidants, produced mixed results when tested in animal models and human subjects. Amongst them, sodium selenite has been shown to be the most effective in an in vitro and in vivo carcinogenesis studies. As recently demonstrated, selenite is not an antioxidant, but possesses oxidizing properties in the presence of specific substrates. Thus selenite is capable of oxidizing polythiols to corresponding disulfides, but does not react with monothiols. Such polythiols associated with cancer membrane-bound proteins appear under the reducing conditions of hypoxic tumor tissue. These thiol groups can, in turn, initiate a disulfide exchange reaction with plasma proteins, predominantly with fibrinogen, to form an insoluble and protease-resistant fibrin-like polymer. As the result, tumor cells become surrounded by a coat which masks specific tumor antigens thus allowing cancer cells to escape immune recognition and elimination by natural killer (NK) cells. Selenite by virtue of oxidizing cell membrane thiols, can prevent the formation of the coat and consequently makes cancer cells vulnerable to the immune surveillance and destruction. In addition, selenite may directly activate NK cells, as well as inhibit angiogenesis without undesirable decrease in the oxidative potential of cellular environment. It is, therefore, postulated that sodium selenite, in view of its relative low toxicity, might become a drug of choice for many types of cancer including leukemia.     

Protective effects of the glutathione redox cycle and vitamin E on cultured fibroblasts infected by Mycoplasma pneumoniae.

The role of the glutathione (GSH) redox cycle and vitamin E as antioxidant defense systems was studied in normal human cultured skin fibroblasts infected by virulent Mycoplasma pneumoniae. In cells infected for 20 h, catalase activity was inhibited by 75% and the intracellular GSH decreased to 32% of its normal values. GSH peroxidase and oxidized glutathione (reductase activities in the infected cells were unaffected.) GSSG glutathione in the medium of the infected cells rose in accordance with the intracellular GSH decrease. The observed elevation in GSSG/GSH ratio was attributed to the increase in intracellular H2O2 content in M. pneumoniae-infected cells due to the marked inhibition in their catalase activity. The protective effect of the GSH redox cycle in infected cells was studied by depletion of cellular GSH, prior to their infection with M. pneumoniae, using buthionine sulfoximine (BSO), a selective inhibitor of gamma-glutamyl cysteine synthetase. After 16 h of incubation with BSO, the GSH levels were reduced to 38% of their normal value and recovered to 55% during 24 h after removal of the inhibitor. BSO had no effect on GSH peroxidase and catalase activities in either infected or noninfected cells. The level of malonyldialdehyde (an indicator of membrane lipid peroxidation) in BSO-treated cells infected by M. pneumoniae was 1.8 times higher than in infected controls. Cells enriched with 0.25 and 2.25 micrograms of vitamin E per mg of protein prior to their infection by M. pneumoniae revealed the following: a lesser degree of catalase inhibition, 46 and 30%, respectively, versus 64% in infected control cells that were not supplemented with vitamin E; lower levels of malonyldialdehyde, 55 and 20% increments, respectively, versus a 140% increment in infected controls; higher residual activity of lactate dehydrogenase, 76 and 96%, respectively, versus 58% in infected controls. Our data indicate that the oxidative damage induced in M. pneumoniae-infected cells due to the increase in intracellular levels of H2O2 and O2- is limited by the host cell GSH redox cycle and by supplementation with vitamin E.     

亚硒酸钠抑制人胃癌SGC-7901细胞系增殖和hTERT的表达

目的 探讨亚硒酸钠对人胃癌SGC-7901细胞系增殖和hTERT表达的作用及其机制.方法用含亚硒酸钠(0μmol/L、0.5μmol/L、2.5μmol/L、5μmol/L、8μmol/L)的培养液培养SGC-7901细胞24h、48h、72h、96h,通过四甲基偶氮唑盐(MTT)比色法检测亚硒酸钠对SGC-7901的...