A comparative study on effect of dietary selenium and vitamin E on some antioxidant enzyme activities of liver and brain tissues

Since selenium and vitamin E have been increasingly recognized as an essential element in biology and medicine, current research activities in the field of human medicine and nutrition are devoted to the possibilities of using these antioxidants for the prevention or treatment of many diseases. The present study was aimed at investigating and comparing the effects of dietary antioxidants on glutathione reductase and glutathione peroxidase activities as well as free and protein-bound sulfhydryl contents of rat liver and brain tissues. For 12–14 wk, both sex of weanling rats were fed a standardized selenium-deficient and vitamin E-deficient diet, a selenium-excess diet, or a control diet. It is observed that glutathione reductase and glutathione peroxidase activities of both tissues of the rats fed with a selenium-deficient or excess diet were significantly lower than the values of the control group. It is also shown that free and bound sulfhydryl concentrations of these tissues of both experimental groups were significantly lower than the control group. The percentage of glutathione reductase and glutathione peroxidase activities of the deficient group with respect to the control were 50% and 47% in liver and 66% and 61% in the brain, respectively; while these values in excess group were 51% and 69% in liver and 55% and 80% in brain, respectively. Free sulfhydryl contents of the tissues in both experimental groups showed a parallel decrease. Furthermore, the decrease in protein-bound sulfhydryl values of brain tissues were more pronounced than the values found for liver. It seems that not only liver but also the brain is an important target organ to the alteration in antioxidant system through either a deficiency of both selenium and vitamin E or an excess of selenium alone in the diet.     

Inhibition Kinetics of Sheep Brain Glutathione Reductase by Cadmium Ion

Glutathione reductase participates in preventing lipid peroxidation by oxygen radicals which results in cellular damage. The brain is among the organs most susceptible to cadmium-induced lipid peroxidation. The mechanism of free radical generation by Cd²⁺ is not well understood, but it is known that Cd²⁺ is an inhibitor of glutathione reductase. In this study, inhibition kinetics of the brain glutathione reductase by Cd²⁺ was investigated. Sheep brain enzyme (11,000-fold purified) was used for this purpose. The data were analyzed by a nonlinear curve fitting program. It was found that the inhibition was competitive with respect to oxidized glutathione and uncompetitive with respect to NADPH. Inhibition constants were found as 12.3 and 9.4 μM, respectively. These findings might contribute to the understanding of the mechanism of lipid peroxidation by Cd²⁺ in brain.     

Selenium and hepatic microsomal hemoproteins

The microsomal share of liver homogenate ⁷⁵Se after injection of a tracer dose of ⁷⁵SeO₃^2? was three times greater in rats fed a selenium-deficient diet than in rats fed a selenium-adequate diet. Basal levels of microsomal cytochromes P-450 and b₅ were unaffected by selenium deficiency. However, induction of these cytochromes by phenobarbital was markedly inpaired in selenium-deficient rats, whereas liver weight increase and NADPH cytochrome $\text{c}$ reductase induction were not impaired. These data indicate that selenium is essential for phenobarbital induction of microsomal hemoproteins.     

Effect of manganese on some bioantioxidants in various organs of protein-deficient rats

The effect of manganese exposure (Mn2+ 4 mg Mn/kg intraperitoneally) on certain bioantioxidants in brain, liver, kidney and testes in growing rats maintained on 21% and 8% casein diet were investigated. Manganese administration for 30 days caused significant reduction in the level of GSH (reduced glutathione) in liver and testes and GR (glutathione reductase) and G-6-PDH (glucose-6-phosphate dehydrogenase) in brain, liver and testes. The magnitude of alteration was greater in 8% casein diet fed animals compared to rats maintained on 21% casein diet. These results indicate that protein deficient animals are more susceptible to the manganese induced biochemical changes in various tissues. The mechanism of such changes is discussed.     

Stress response in two strains of the aquatic hyphomycete <Emphasis Type="BoldItalic">Heliscus lugdunensis</Emphasis> after exposure to cadmium and copper ions

Biochemical responses to cadmium (Cd²⁺) and copper (Cu²⁺) exposure were compared in two strains of the aquatic hyphomycete (AQH) Heliscus lugdunensis. One strain (H4-2-4) had been isolated from a heavy metal polluted site, the other (H8-2-1) from a moderately polluted habitat. Conidia of the two strains differed in shape and size. Intracellular accumulation of Cd²⁺ and Cu²⁺ was lower in H4-2-4 than in H8-2-1. Both␣strains synthesized significantly more glutathione (GSH), cysteine (Cys) and γ-glutamylcysteine (γ-EC) in the presence of 25 and 50 μM Cd²⁺, but quantities and rates of synthesis were different. In H4-2-4, exposure to 50 μM Cd²⁺ increased GSH levels to 262% of the control; in H8-2-1 it increased to 156%. Mycelia of the two strains were analysed for peroxidase, dehydroascorbate reductase, glutathione reductase and glucose-6-phosphate dehydrogenase. With Cd²⁺ exposure, peroxidase activity increased in both strains. Cu²⁺ stress increased dehydroascorbate reductase activity in H4-2-4 but not in H8-2-1. Dehydroascorbate reductase and glucose-6-phosphate dehydrogenase activities progressively declined in the presence of Cd²⁺, indicating a correlation with Cd²⁺ accumulation in both strains. Cd²⁺ and Cu²⁺ exposure decreased glutathione reductase activity.     

低硒小鼠模型的建立及低硒对心肌的影响

目的建立低硒实验动物模型,观察低硒对心肌的影响。方法利用黑龙江地产酵母配制低硒小鼠饲料,使用配制的小鼠饲料喂养BALB/c幼鼠,经过4个月的喂养,测定血清、肝脏、心肌细胞的硒含量,观察心肌超微结构的变化,测定血清心肌酶的变化。结果利用黑龙江地产酵母配制的低硒饲料,硒含量为0.016 mg/kg,符合低硒标准。BALB/c鼠用该饲料喂养4个月,心肌、肝脏、血清硒含量分别为0.187 mg/kg、0.219 mg/kg、0.241mg/kg,符合低硒诊断标准。观察低硒鼠心肌超微结构,可见心肌细胞线粒体肿胀,细胞核出现了异型性,血清心肌酶较常硒鼠升高。结论利用黑龙江地产酵母成功配制了低硒饲料。经过低硒饲料饲养可建立低硒鼠模型。低硒可以引起BALB/c鼠心肌细胞损伤。     

Increased sister-chromatid exchange in bone-marrow cells of mice exposed to whole cigarette smoke

Male Wistar rats were fed diets of varying selenium content in order to obtain selenium-deficient and selenium-supplemented rats. After 5-6 weeks on the respective diet, the rats were used to investigate how selenium influences the effect of dimethylnitrosamine (DMN) on some liver enzymes and related reactions. The selenium-dependent glutathione peroxidase activity in postmicrosomal supernatant from liver was about 1% in selenium-deficient rats as compared to selenium-supplemented rats or rats fed a standard diet. The highest DMN-demethylase activity was observed in postmitochondrial supernatant from selenium-deficient rat liver, and the lowest in selenium-supplemented rats. No dietary effect was observed on hepatic microsomal cytochrome P450 levels. C-Oxygenation of N,N-dimethylaniline (DMA) was not affected by the selenium level. On the other hand, selenium deficiency seemed to reduce N-oxygenation of DMA. The mutagenicity of DMN in Chinese hamster V79 cells after metabolic activation by the isolated perfused rat liver, was approximately doubled when selenium-deficient livers were used as compared to selenium-supplemented livers and livers from rats fed a standard diet. A negative correlation between DMA-N-oxygenation and mutagenicity from DMN was observed, whereas no correlation between DMA-C-oxygenation and mutagenicity from DMN was found.     

Iodothyronine deiodinase activity in methionine-deficient rats fed selenium-deficient or selenium-sufficient diets

We examined the effect of methionine deficiency on iodothyronine 5’-deiodinase activity in selenium-deficient rats or selenium-sufficient rats fed sodium selenate or selenomethionine. Forty-two weanling male Wistar rats were divided into six groups and pair fed the respective purifiedl-amino acid-based diets for 4 wk.l-methionine concentrations in the diet were 8.0 g/kg for sufficient rats, and 2.0 g/kg for deficient rats. Selenium concentrations in the diet were 0.5 mg/kg (as sodium selenate or selenomethionine) for selenium-sufficient rats and less than 0.005 mg/kg for selenium-deficient rats. Type I 5’-deiodinase activities were significantly lower in liver and higher in kidney of methionine-deficient rats than in those of methionine-sufficient rats fed either the selenium-sufficient or the selenium-deficient diets. The type I 5’-deiodinase activity in brain was significantly lower in the methionine-deficient rats than in the methionine-sufficient rats fed the selenium-deficient diet. Type II 5’-deiodinase activity in brain was significantly higher in the methionine-deficient rats than in the methionine-sufficient rats fed selenium-sufficient diet as sodium selenate. Both thyroxine and 3,3’,5-triiodothyronine concentrations in plasma were significantly higher in the methionine-deficient rats than in the methionine-sufficient rats. It is suggested that the methionine deficiency affects the 5’-deiodinase activity and thyroid hormones level in the rats.     

Effect of cadmium on antioxidative enzymes,glutathione content,and glutathionylation in tall fescue

The aim of this work was to assess the effect of different Cd2+concentrations on some antioxidant enzymes in Festuca arundinacea. Increased activities of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione S-transferase, and glutathione reductase were ascertained in response to low Cd²⁺ concentrations (0–20 μM), whereas the enzyme activities were less increased or decreased at a higher Cd²⁺ dosage (50 μM) and a longer exposure. The content of reduced glutathione (GSH) decreased significantly with increasing Cd²⁺ concentrations, whereas the content of oxidized glutathione (GSSG) increased proportionally to the amount of Cd²⁺ applied. Further experiments, performed by incubating the enzyme extracts with oxidized glutathione, evidenced that the addition of GSSG to the incubation mixtures caused significant decreases of some enzymatic activities. Finally, the effect of glutathione S-transferase, FaGST I, extracted from fescue seedlings and purified till homogeneity, on these enzyme activities was investigated. It was found that FaGST I enhanced the decreased enzymatic activities caused by GSSG.     

The effects of in vitro lipid peroxidation on the activity of rat liver microsomal glutathione S-transferase from rats supplemented or deficient in antioxidants

Glutathione S-transferases are a group of multifunctional isozymes that play a central role in the detoxification of hydrophobic xenobiotics with electrophilic centers (1). In this study we investigated the effects of in vitro lipid peroxidation on the activity of liver microsomal glutathione S-transferases from rats either supplemented or deficient in both vitamin E and selenium. Increased formation of malondialdehyde (MDA), a by-product of lipid peroxidation, was associated with a decreased activity of rat liver microsomal glutathione S-transferase. The inhibition of glutathione S-transferase occurred rapidly in microsomes from rats fed a diet deficient in both vitamin E and selenium (the B diet) but was delayed for 15 minutes in microsomes from rats fed the same diet but supplemented with these micro-nutrients (B+E+Se diet). Lipid peroxidation inhibits microsomal glutathione S-transferase and this inhibition is modulated by dietary antioxidants.     

The effect of selenium-deficiency on rat fat-cell glucose oxidation.

When rats are fed a selenium-deficient diet, the glutathione peroxidase activity of epididymal fat-cells decreases to 5-9% of that of control rats fed the same diet supplemented with 0.5 p.p.m. of selenium as sodium selenite. [1-14C]Glucose oxidation in fat-cells from rats fed a selenium-deficient diet is unresponsive to the action of t-butyl hydroperoxide, which stimulates 14CO2 formation from [1-14C]glucose 4-fold in control rats. Insulin enhances [1-14C]glucose oxidation and incorporation into lipids in fat-cells from both groups of rats; however, the response elicited is reduced in fat-cells prepared from selenium-deficient animals. The 'C-1/C-6 ratio' (ratio of glucose C-1 to glucose C-6 oxidized) is enhanced by insulin to a similar degree in fat-cells from both groups of animals. The stimulatory action of Zn2+ and dithiothreitol on [1-14C]glucose oxidation observed in fat-cells from selenium-supplemented rats is greatly reduced in fat-cells from selenium-deficient rats. [1-14C]Glucose oxidation in fat-cells from both groups of animals is highly sensitive to the stimulatory action of adenosine. It is concluded that the enhanced formation and glutathione-linked destruction of H2O2 plays, at the most, only a minor role in the stimulation of the flux of glucose through the pentose phosphate pathway elicited by insulin, although elimination of glutathione peroxidase activity may influence the action of insulin on glucose oxidation. Production and subsequent destruction of H2O2 may play an important role in the stimulatory action of Zn2+ and dithiothreitol on fat-cell [1-14C]glucose oxidation.     

Cadmium is a catalytic inhibitor of DNA topoisomerase II

Cadmium (Cd²⁺) is a highly toxic and carcinogenic metal that is an environmental and occupational hazard. DNA topoisomerase II is an essential nuclear enzyme and its inhibition can result in the formation of genotoxic and recombinogenic DNA double strand breaks. In this study we showed that cadmium chloride strongly inhibited the DNA decatenation activity of human topoisomerase IIα in the low micromolar concentration range and that its inhibitory effects were reduced by glutathione. Because the activity of topoisomerase II is strongly inhibited by thiol-reactive compounds this result suggested that cadmium may be binding to critical topoisomerase II cysteine thiols. Cadmium, however, did not stabilize DNA-topoisomerase II covalent complexes, as measured by the lack of formation of DNA double strand breaks. Hence, it is not likely to be a topoisomerase II poison. Consistent with the idea that cadmium cytotoxicity may be modulated by glutathione levels, buthionine sulfoximine pretreatment to decrease glutathione levels resulted in a greatly increased cadmium-induced cytotoxicity in K562 cells. The results of this study suggest that cadmium may exert some of its cell growth inhibitory, and possibly its toxicity and carcinogenicity, by inhibiting topoisomerase IIα through reaction with critical cysteine thiols.     

Comparative study of effects of cadmium cations in free and chelated forms on activity of glutathione S-transferase, growth, and endocytosis in culture of the infusoriumTetrahymena pyriformis

Effects of cadmium cations in free (Cd²⁺) and chelated with EDTA (Cd²⁺-EDTA) forms were studied on growth, endocytosis, and activity of glutathione S-transferase (GT) in the free-living infusoriaTetrahymena pyriformis. It is shown that the cytotoxicity of Cd²⁺ in the free form at a concentration of 10 μM is much higher than of the Cd²⁺-EDTA complex at the equimolar concentration. Even at a low concentration (2 μM), Cd²⁺ produces an inhibition of the growth rate and endocytosis in theT. pyriformis culture, while the Cd²⁺-EDTA complex suppresses these functions insignificantly. Cd²⁺ in the free form at concentrations of 10 and 100 μM reduced activity of glutathione S-transferase by 39 and 61%. The chelated Cd²⁺-EDTA complex at these concentrations inhibited the GT activity by 5 and 55%, respectively.     

The inhibition kinetics of yeast glutathione reductase by some metal ions

Glutathione reductase (GR, type IV, Baker's yeast, E.C 1.6.4.2) is a flavoprotein that catalyzes the NADPH-dependent reduction of oxidized glutathione (GSSG) to reduced glutathione (GSH). In this study some metal ions have been tested on GR; lithium, manganese, molybdate, aluminium, barium, zinc, calcium, cadmium and nickel. Cadmium, nickel and calcium showed a good to moderate inhibitory effect on yeast GR. GR is inhibited non-competitively by Zn^{2 +} (up to 2 mM) and activated above this concentration. Ca^{2 +} inhibition was non-competitive with respect to GSSG and uncompetitive with respect to NADPH. Nickel inhibition was competitive with respect to GSSG and uncompetitive with respect to NADPH. The inhibition constants for these metals on GR were determined. The chelating agent EDTA recovered 90% of the GR activity inhibited by these metals.     

Expression of merA,trxA, amoA,and hao in continuously cultured Nitrosomonas europaea cells exposed to cadmium sulfate additions

The effects of CdSO₄ additions on the gene expressions of a mercury reductase, merA, an oxidative stress protein, trxA, the ammonia‐monooxygenase enzyme (AMO), amoA, and the hydroxylamine oxidoreductase enzyme (HAO), hao, were examined in continuously cultured N. europaea cells. The reactor was fed 50 mM NH₄+ and was operated for 78 days with a 6.9 days hydraulic retention time. Over this period, six successive batch additions of CdSO₄ were made with increasing maximum concentrations ranging from 1 to 60 µM Cd²⁺. The expression of merA was highly correlated with the level of Cd²⁺ within the reactor (Rs = 0.90) with significant up‐regulation measured at non‐inhibitory Cd²⁺ concentrations. Cd²⁺ appears to target AMO specifically at lower concentrations and caused oxidative stress at higher concentrations, as indicated by the SOURs (specific oxygen uptake rates) and the up‐regulation of trxA. Since Cd²⁺ inhibition is irreversible and amoA was up‐regulated in response to Cd²⁺ inhibition, it is hypothesized that de novo synthesis of the AMO enzyme occurred and was responsible for the observed recovery in activity. Continuously cultured N. europaea cells were more resistant to Cd²⁺ inhibition than previously examined batch cultured cells due to the presence of Mg²⁺ and Ca²⁺ in the growth media, suggesting that Cd²⁺ enters the cell through Mg²⁺ and Ca²⁺ import channels. The up‐regulation of merA during exposure to non‐inhibitory Cd²⁺ levels indicates that merA is an excellent early warning signal for Cd²⁺ inhibition. Biotechnol. Bioeng. 2009; 104: 1004–1011. © 2009 Wiley Periodicals, Inc.     

The effect of cadmium on potato (Solanum tuberosum L.) shoot culture growth

The uptake of cadmium and its effect on the growth of potato shoot tips grownin vitro were followed in dependence on cadmium concentration in nutrient medium. Concentration of 10 ⁻⁶ M Cd ²⁺ did not substantially affect potato plantlet growth dynamics; but the concentration of 10⁻³ M Cd²⁺ showed a strong growth inhibitory effect accompanied with increased cadmium accumulation in both root and shoot tissues.     

Evidence of hepatic endogenous hydrogen peroxide in bile of selenium-deficient rats

Hepatic endogenous hydrogen peroxide (H(2)O(2)) in bile of selenium-deficient rats (SeD) was for the first time found using the electron spin resonance (ESR) spin-trap technique, and the relationship between glutathione peroxidase (GPX) activity and H(2)O(2) amount is discussed. Normal rats and four groups of rats fed a selenium-deficient diet with different feeding periods were examined. The results showed that the GPX activity decreased depending on the feeding period with the selenium-deficient diet and that the hepatic endogenous H(2)O(2) amount in the bile of the rats fed the selenium-deficient diet for the longest period (a week before birth to 8 weeks old) was drastically higher than those in other groups of rats (P < 0.005). We found that generation of H(2)O(2) due to the decrease in the GPX activity has a threshold value. The results suggest that an exposure to selenium deficiency for long term will cause oxidative stress.     

Lipid peroxidation and glutathione system in hyperlipemic rabbits: influence of olive oil administration

We studied the effect of supplementation (10% w/w) of a hyperlipemic diet (1% cholesterol) with olive oil (OLIV) for 6 weeks in four groups of 10 rabbits each. At the end of this period, we determined lipid peroxidation, glutathione content, and glutathione peroxidase, reductase and transferase activities in liver, brain, heart, aorta and platelets. The atherogenic diet increased tissue lipid peroxidation and decreased the protective antioxidant effect of glutathione. Dietary supplementation with olive oil reduced tissue lipid peroxidation by 71.6% in liver, 20.3% in brain, 84.5% in heart, 63.6% in aorta, 72% in platelets. The ratios total/oxidized glutathione were increased in all tissues (49% in liver, 48% in brain, 45% in heart, 83% in aorta, 70% in platelets). Olive oil increased glutathione peroxidase and transferase activities in all tissues. We conclude that in rabbits made hyperlipemic with a diet rich in saturated fatty acids, olive oil decreased tissue oxidative stress.     

Cd~(2+)胁迫对小桐子幼苗叶片抗氧化系统的影响

以小桐子幼苗为材料,设置不同浓度CdCl_2处理,测定Cd~(2+)胁迫对小桐子幼苗叶片中可溶性蛋白、丙二醛(MDA)含量,以及5种抗氧化酶活性和2种抗氧化剂含量的变化,探讨镉胁迫对小桐子幼苗抗氧化系统的影响。结果表明:(1)Cd~(2+)胁迫导致小桐子幼苗叶片中可溶性蛋白含量降低、MDA含量增加;(2)随着镉胁迫时间的延长,幼苗叶片中愈创木酚过氧化物酶(POD)、过氧化氢酶(CAT)、超氧化物歧化酶(SOD)、抗坏血酸专一性过氧化酶(APX)、谷胱甘肽还原酶(GR)等抗氧化酶活性表现出先升高然后降低的变化趋势;(3)幼苗叶片中还原型抗坏血酸(ASA)和还原型谷胱甘肽(GSH)含量随着胁迫时间延长而降低,但其中氧化型抗坏血酸(DHA)和氧化型谷胱甘肽(GSSG)含量则升高。研究表明,镉胁迫初期能诱导小桐子幼苗抗氧化系统活性显著增强,提高其抗氧化能力,但随着胁迫时间的延长,致使其抗氧化酶的活性和抗氧物质含量下降,植株遭受明显氧化胁迫,幼苗生长受到镉的严重毒害。     

Antioxidant potential of evening primrose oil administration in hyperlipemic rabbits.

The dietary intake of saturated fatty acids affects arteriosclerosis. We studied the effect of supplementation (15% wt/wt) of a hyperlipemic diet (1.33% cholesterol) with evening primrose oil (EPO) (Oenothera biennis) for 6 weeks in four groups of 10 rabbits each. At the end of this period we determined lipid peroxidation, glutathione content, and glutathione peroxidase, reductase and transferase activities in liver, brain, heart, aorta and platelets. The atherogenic diet increased tissue lipid peroxidation and decreased the protective antioxidant effect of glutathione. Dietary supplementation with EPO reduced tissue lipid peroxidation (61% in liver, 57% in brain, 42% in heart, 24% in aorta, 33% in platelets). Total glutathione was increased, especially in the aorta (90%) and platelets (200%); however, in all tissues the percentage of oxidised glutathione decreased. Evening primrose oil reduced glutathione peroxidase activity and increased the activities of glutathione reductase and transferase. We conclude that in rabbits made hyperlipemic with a diet rich in saturated fatty acids, EPO decreased tissue oxidative stress.