A Selenium-deficient Caco-2 Cell Model for Assessing Differential Incorporation of Chemical or Food Selenium into Glutathione Peroxidase

Assessing the ability of a selenium (Se) sample to induce cellular glutathione peroxidase (GPx) activity in Se-deficient animals is the most commonly used method to determine Se bioavailability. Our goal is to establish a Se-deficient cell culture model with differential incorporation of Se chemical forms into GPx, which may complement the in vivo studies. In the present study, we developed a Se-deficient Caco-2 cell model with a serum gradual reduction method. It is well recognized that selenomethionine (SeMet) is the major nutritional source of Se; therefore, SeMet, selenite, or methylselenocysteine (SeMSC) was added to cell culture media with different concentrations and treatment time points. We found that selenite and SeMSC induced GPx more rapidly than SeMet. However, SeMet was better retained as it is incorporated into proteins in place of methionine; compared with 8-, 24-, or 48-h treatment, 72-h Se treatment was a more sensitive time point to measure the potential of GPx induction in all tested concentrations. Based on induction of GPx activity, the cellular bioavailability of Se from an extract of selenobroccoli after a simulated gastrointestinal digestion was comparable with that of SeMSC and SeMet. These in vitro data are, for the first time, consistent with previous published data regarding selenite and SeMet bioavailability in animal models and Se chemical speciation studies with broccoli. Thus, Se-deficient Caco-2 cell model with differential incorporation of chemical or food forms of Se into GPx provides a new tool to study the cellular mechanisms of Se bioavailability.     

Modulation of glutathione peroxidase expression by selenium: effect on human MCF-7 breast cancer cell transfectants expressing a cellular glutathione peroxidase cDNA and doxorubicin-resistant MCF-7 cells.

We have studied the effect of selenium on the expression of a cellular glutathione peroxidase, GSHPx-1, in transfected MCF-7 cells and in doxorubicin-resistant (Adrr) MCF-7 cells. A GSHPx-1 cDNA with a Rous Sarcoma virus promoter was transfected into a human mammary carcinoma cell line, MCF-7, which has very low endogenous cytosolic glutathione (GSH) peroxidase activity and no detectable message. The transfectant with the highest GSH peroxidase activity among the isolates, MCF-7H6, was characterized. Adrr MCF-7 cells, a subline of MCF-7 cells, also has elevated GSH peroxidase activity. GSH peroxidase expressed by MCF-7H6 and Adrr MCF-7 cells is similar to the endogenous GSHPx-1 based on molecular weight, immunoreactivity, and metabolic labeling with 75Se. MCF-7H6 and Adrr MCF-7 cells grown in Se-deficient media had 2.6 +/- 2.4 (mean +/- S.D.) and 4.2 +/- 3.6 units/mg protein of GSH peroxidase specific activity, respectively. Se supplementation increased GSH peroxidase activity in a concentration- and time-dependent fashion. Enzymatic activity reached a level of 164 +/- 62 in MCF-7H6 cells and 114 +/- 27 in Adrr MCF-7 cells within 5 days of growth in media supplemented with 30 nM Se. Northern analysis revealed that Se-deficient MCF-7H6 cells expressed 2.1 +/- 0.4-fold less GSHPx-1 mRNA than their Se-sufficient counterparts. Similarly, Se-deficient Adrr MCF-7 cells expressed 3.3 +/- 1.8-fold less GSHPx-1 mRNA than their Se-supplemented counterparts after the quantity of mRNA was normalized with beta-actin. These studies suggest that modulation of GSH peroxidase activity by Se in both MCF-7H6 transfectants expressing pRSV-GSHPx-1 and Adrr MCF-7 cells expressing endogenous GSHPx-1 occurs largely at the translational level, and to a lesser degree at the level of mRNA, possibly by stabilizing GSHPx-1 mRNA since the transfected cDNA in MCF-7H6 cells has only 5 nucleotides 5' to the AUG initiation codon.     

Minimum Selenium Requirements Increase When Repleting Second-Generation Selenium-Deficient Rats but Are Not Further Altered by Vitamin E Deficiency

Second-generation selenium-deficient weanling rats fed graded levels of dietary Se were used (a) to study the impact of initial Se deficiency on dietary Se requirements; (b) to determine if further decreases in selenoperoxidase expression, especially glutathione peroxidase 4 (Gpx4), affect growth or gross disease; and (c) to examine the impact of vitamin E deficiency on biochemical and molecular biomarkers of Se status. Rats were fed a vitamin E-deficient and Se-deficient crystalline amino acid diet (3 ng Se/g diet) or that diet supplemented with 100 μg/g all-rac-α-tocopheryl acetate and/or 0, 0.02, 0.05, 0.075, 0.1, or 0.2 μg Se/g diet as Na₂SeO₃ for 28 days. Se-supplemented rats grew 6.91 g/day as compared to 2.17 and 3.87 g/day for vitamin E-deficient/Se-deficient and vitamin E-supplemented/Se-deficient groups, respectively. In Se-deficient rats, liver Se, plasma Gpx3, red blood cell Gpx1, liver Gpx1 and Gpx4 activities, and liver Gpx1 mRNA levels decreased to <1, <1, 21, 1.6, 49, and 11 %, respectively, of levels in rats fed 0.2 μg Se/g diet. For all biomarkers, ANOVA indicated significant effects of dietary Se, but no significant effects of vitamin E or vitamin E × Se interaction, showing that vitamin E deficiency, even in severely Se-deficient rat pups, does not result in compensatory changes in these biochemical and molecular biomarkers of selenoprotein expression. Se requirements determined in this study, however, were >50 % higher than in previous studies that started with Se-adequate rats, demonstrating that dietary Se requirements determined using initially Se-deficient animals can result in overestimation of Se requirements.     

High Dietary Intake of Sodium Selenite Does Not Affect Gene Mutation Frequency in Rat Colon and Liver

Our previous studies have shown that selenium (Se) is protective against dimethylhydrazine (DMH)-induced preneoplastic colon cancer lesions, and protection against DNA damage has been hypothesized to be one mechanism for the anticancer effect of Se. The present study was designed to determine whether dietary selenite affects somatic mutation frequency in vivo. We used the Big Blue transgenic model to evaluate the in vivo mutation frequency of the cII gene in rats fed either a Se-deficient (0 μg Se/g diet) or Se-supplemented diet (0.2 or 2 μg Se/g diet; n = 3 rats/diet in experiment 1 and n = 5 rats/group in experiment 2) and injected with DMH (25 mg/kg body weight, i.p.). There were no significant differences in body weight between the Se-deficient and Se-supplemented (0.2 or 2 μg Se/g diet) rats, but the activities of liver glutathione peroxidase and thioredoxin reductase and concentration of liver Se were significantly lower (p < 0.0001) in Se-deficient rats compared to rats supplemented with Se. We found no effect of dietary Se on liver 8-hydroxy-2′-deoxyguanosine. Gene mutation frequency was significantly lower in liver (p < 0.001) than that of colon regardless of dietary Se. However, there were no differences in gene mutation frequency in DNA from colon mucosa or liver from rats fed the Se-deficient diet compared to those fed the Se-supplemented (0.2 or 2 μg Se/g diet) diet. Although gene mutations have been implicated in the etiology of cancer, our data suggest that decreasing gene mutation is not likely a key mechanism through which dietary selenite exerts its anticancer action against DMH-induced preneoplastic colon cancer lesions in a Big Blue transgenic rat model. The US Department of Agriculture, Agricultural Research Service, Northern Plains Area, is an equal opportunity/affirmative action employer and all agency services are available without discrimination. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the US Department of Agriculture and does not imply its approval to the exclusion of other products that may also be suitable. This work was supported by the US Department of Agriculture and National Cancer Institute.     

Microbial products from probiotic bacteria inhibit Salmonella enteritidis 857-induced IL-8 synthesis in Caco-2 cells

Oral administration of Lactobacillus spp. as probiotics is gaining importance in the treatment of intestinal inflammations. However, their mechanism of action is unknown. We investigated whether nonspecific binding Lactobacillus casei Shirota (LcS) and mannose-specific Lactobacillus plantarum 299v (Lp) and their spent culture supernatant (SCS) affect Salmonella enteritidis 857 (Se) growth, IL-8 and Hsp70 syntheses. In one set of experiments human enterocyte-like Caco-2 cells were infected with LcS, Lp or Se at 1–500 bacteria per cell for 1 h. In another set, cells were exposed to Se (0–200 per cell, 1 h) after exposure to lactobacilli (LB) (500 per cell, 30 min) or by co-incubation of Se and LB (1 h). The third set of experiments involved exposure of cells for 1 h to SCS or Se (100 per cell) pretreated (1 h) in SCS. The effect of LB SCS on Se growth was evaluated by agar plate diffusion test. IL-8 and Hsp70 were assessed over 2–24 h using ELISA and Western blotting, respectively. Neither LcS nor Lp affected the Se growth and IL-8 production. In addition, they did not induce Hsp70 expression by Caco-2 cells. Instead, their SCS inhibited the Se growth and IL-8 production and induced the expression of Hsp70 by both crypt- and villus-like cells. The beneficial effect of Lactobacillus spp. to the intestinal inflammations might be associated with a decrease in IL-8 levels. This effect could be mediated, at least in part, via a secreted antimicrobial product(s) either directly against the pathogens or indirectly through the synthesis of Hsp70.     

Influence of selenium deficiency on the acute cardiotoxicity of adriamycin in rats

The influence of selenium (Se) deficiency on the acute cardiotoxicity induced by the anticancer drug adriamycin (ADR) has been studied in rats by electrocardiography. Two categories were formed by feeding groups of rats a Se-supplemented and a Se-deficient diet. The supplemented animals were taken as normals. The two categories were treated with iv injections of saline solution containing ADR at doses of 0, 7.5, and 15 mg/kg body wt. The cardiac Se concentration and glutathione peroxidase (GSH-Px) activity in the Se-deficient groups were <2% lower than in the normals. The normal groups showed significant widening of the SaT and QaT durations when given 15 mg/kg ADR. The Se-deficient groups exhibited a dose-dependent widening of the SaT and QaT duration at 7.5 and 15 mg/kg and narrowing of the PQ duration at 15 mg/kg ADR. No heart rate or QRS duration changes were detected in both categories. Our results suggest that an imbalance of the antioxidant system is associated with Se deficiency and that Se plays a role in preventing the cardiac functional disorder attributable to oxygen free radical formation induced by ADR.     

Effects of Selenium Supplementation on Expression of Endothelin-1 and Its Receptors in Pulmonary Microvascular Endothelial Cells from Chick Embryos

The objective of this study was to evaluate the effects of supplemental selenium (Se) on expression of endothelin-1 (ET-1) and its receptors in cultured chick embryos pulmonary microvascular endothelial cells (PMVECs). To accomplish this, PMVECs were treated in Se-deficient or Se-supplement (12, 24, 50, 100?ng/ml) culture medium for 48?h. Low Se medium was achieved by reducing serum concentrations and the essential growth factors were added. After the incubation, the effects of supplemental Se on ET-1 and its receptors gene expression were assessed by quantitative real-time PCR (qRT-PCR). Compared with the control group, our results showed that among the different concentrations of Se supplement, the levels of ET-1 gene expression treated with both the moderate Se doses (24, 50?ng/ml, P?<?0.01, P?<?0.01, respectively) and the high doses (100?ng/ml, P?<?0.05) were noticeably decreased, the low-dose group (12?ng/ml), which showed no changes. Meanwhile, Se supplement (24, 50, 100?ng/ml) was found to be effective in reducing the expression levels of ETA (P?<?0.01, P?<?0.05, P?<?0.05, respectively) in cultured PMVECs grown in low Se medium. However, there were no significant changes (P?>?0.05) in ETB mRNA levels during the cell proliferation. These observations indicated that Se may play both direct and indirect role in the regulation of ET-1 and its receptors gene expression and their production in avian PMVECs. Se supplement decreases in ET-1 and ETA production in Se-deficient PMVECs may partly explain the mechanism of the protective effects of the Se on the cardiovascular system.     

In vitro anti-proliferative activities of ellagic acid

The potential cytotoxic and anti-proliferative activities of ellagic acid (a naturally occurring bioactive compound in berries, grapes, and nuts) was evaluated using human umbilical vein endothelial cells (HUVEC), normal human lung fibroblast cells HEL 299, Caco-2 colon, MCF-7 breast, Hs 578T breast, and DU 145 human prostatic cancer cells. Ellagic acid at concentration in the range 10-100 micromol/L did not affect the viability of normal fibroblast cells during a 24-hour incubation. An increase in adenosine triphosphate (ATP) bioluminescence of approximately 18-21% was observed in normal cells incubated with ellagic acid. In contrast, ellagic acid at 1-100 micromol/L dose-dependently inhibited HUVEC tube formation and proliferation on a reconstituted extracellular matrix and showed strong anti-proliferative activity against the colon, breast, and prostatic cancer cell lines investigated. The most sensitive cells were the Caco-2, and the most resistant were the breast cancer cells. Ellagic acid induced cancer cell death by apoptosis as shown by the microscopic examination of cell gross morphology. Ellagic acid induced reduced cancer cell viability as shown by decreased ATP levels of the cancer cells. After 24 hours incubation of 100 micromol/L of ellagic acid with Caco-2, MCF-7, Hs 578T, and DU 145 cancer cells, ellagic acid suppressed fetal bovine serum (FBS) stimulation of cell migration. The apoptosis induction was accompanied by a decreased in the levels of pro-matrix metalloproteinase-2 (pro-MMP-2 or gelatinase A), pro-matrix metalloproteinase-9 (pro-MMP-9 or gelatinase B), and vascular endothelial growth factor (VEGF(165)) in conditioned media. The results suggest that ellagic acid expressed a selective cytotoxicity and anti-proliferative activity, and induced apoptosis in Caco-2, MCF-7, Hs 578T, and DU 145 cancer cells without any toxic effect on the viability of normal human lung fibroblast cells. It was also observed that the mechanism of apoptosis induction in ellagic acid-treated cancer cells was associated with decreased ATP production, which is crucial for the viability of cancer cells.     

Effect of selenium compounds on the damage induced by oxysterol on rat arterial walls

Wistar rats were fed Se-deficient (0.017±0.002 mg Se/kg) and Seadequate (0.32±0.045 Se mg/kg) diets for 12 mo and then were given 5 mg/kg of cholestane-3β,tα,6β-triol (3-triol), intravenously. Se compounds (Na₂SeO₃ and ebselen) were supplemented in different doses and times to the Se-deficient rats. Twenty-four hours after 3-triol infusion, the changes in ultrastructures of rat aorta were examined by scanning electron micrography (SEM) and transmission electron micrography (TEM). SEM examinations showed that 3-triol induced diffused injuries on arterial endothelial urfaces of long-term Se-deficient rat, and a large number of holes or craterlike defects were observed. TEM examinations further showed that 3-triol induced swelling, necrosis, and shedding of endothelial cells, which resulted in the destruction of endothelial integrity. Mean-while, smooth muscle cells proliferated and migrated toward intimae; the breakage of internal elastic lamina benefited the migration of smooth muscle cells. Supplemented with Na₂SeO₃ (40 μg/kg, 10 d per continuum) and ebselen (20 mg/kg), respectively, exhibited significant protection from damages induced by 3-triol. It seems that protecting mechanisms were different between Na₂SeO₃ and ebselen. The present investigation gave visual evidence that both injuries induced by cholesterol oxides and the Se nutritional status contributed to the development of atherosclerosis.     

Selenium Regulates Gene Expression for Estrogen Sulfotransferase and Alpha 2U-globulin in Rat Liver

Dietary intake of the essential trace element selenium (Se) regulates expression of genes for seleno-proteins and certain non-Se-containing proteins. However, these proteins do not account for all of Se's biological effects. The objective of this work was to identify additional genes whose expression is regulated by Se. Identification of these genes may reveal new functions for Se or define mechanisms for its biological effects. Weanling male Sprague-Dawley rats were fed a Torula yeast-based Se-deficient basal diet or the same diet supplemented with 0.5 mg Se/kg diet as sodium selenite for 13 weeks. Total RNA was used as template for RNA fingerprinting. Two differentially expressed cDNA fragments were identified and cloned. The first had 99% nucleotide identity with rat liver estrogen sulfotransferase (EST) isoform-6. The second had 99% nucleotide sequence identity with rat liver 2u-globulin. The mRNA levels for both were markedly reduced in Se deficiency. Laser densitometry showed that EST mRNA in Se deficiency was 7.3% of that in Se-adequate rat liver. The level of 2u-globulin mRNA in Se-deficient rat liver was only 12.6% of that in Se-adequate rat liver. These results indicate that dietary Se may play a role in steroid hormone metabolism in rat liver.     

Biological effects of a nano red elemental selenium.

A novel selenium form, nano red elemental selenium (Nano-Se) was prepared by adding bovine serum albumin to the redox system of selenite and glutathione. Nano-Se has a 7-fold lower acute toxicity than sodium selenite in mice (LD(50) 113 and 15 mg Se/kg body weight respectively). In Se-deficient rat, both Nano-Se and selenite can increase tissue selenium and GPx activity. The biological activities of Nano-Se and selenite were compared in terms of cell proliferation, enzyme induction and protection against free racial-mediated damage in human hepatoma HepG2 cells. Nano-Se and selenite are similarly cell growth inhibited and stimulated synthesis of glutathione peroxidase (GPx), phospholipid hydroperoxide glutathione peroxidase (PHGPx) and thioredoxin reductase (TR). When HepG2 cells were co-treated with selenium and glutathione, Nano-Se showed less pro-oxidative effects than selenite, as measured by cell growth. These results demonstrate that Nano-Se has a similar bioavailability in the rat and antioxidant effects on cells.     

Evidence that a polymorphism within the 3′UTR of glutathione peroxidase 4 is functional and is associated with susceptibility to colorectal cancer

Low selenium (Se) status has been associated with increased risk of colorectal cancer (CRC). Se is present as the amino acid selenocysteine in selenoproteins, such as the glutathione peroxidases. Se incorporation requires specific RNA structures in the 3' untranslated region (3'UTR) of the selenoprotein mRNAs. A single nucleotide polymorphism (SNP) occurs at nucleotide 718 (within the 3'UTR) in the glutathione peroxidase 4 gene. In the present study, Caco-2 cells were transfected with constructs in which type 1 iodothyronine deiodinase coding region was linked to the GPx4 3'UTR with either C or T variant at position 718. Higher reporter activity was observed in cells expressing the C variant compared to those expressing the T variant, under either Se-adequate or Se-deficient conditions. In addition, a disease association study was carried out in cohorts of patients with either adenomatous polyps, colorectal adenocarcinomas and in healthy controls. A higher proportion of individuals with CC genotype at the GPx4 T/C 718 SNP was present in the cancer group, but not in the polyp group, compared with the control group (P < 0.05). The present data demonstrate the functionality of the GPx4 T/C 718 SNP and suggest that T genotype is associated with lower risk of CRC.     

Effect of Dietary Selenium and Cancer Cell Xenograft on Peripheral T and B Lymphocytes in Adult Nude Mice

Selenium (Se) is known to regulate tumorigenesis and immunity at the nutritional and supranutritional levels. Because the immune system provides critical defenses against cancer and the athymic, immune-deficient NU/J nude mice are known to gradually develop CD8⁺ and CD4⁺ T cells, we investigated whether B and T cell maturation could be modulated by dietary Se and by tumorigenesis in nude mice. Fifteen homozygous nude mice were fed a Se-deficient, Torula yeast basal diet alone (Se−) or supplemented with 0.15 (Se+) or 1.0 (Se++) mg Se/kg (as Na₂SeO₄) for 6 months, followed by a 7-week time course of PC-3 prostate cancer cell xenograft (2 × 10⁶ cells/site, 2 sites/mouse). Here, we show that peripheral B cell levels decreased in nude mice fed the Se −  or Se++ diet and the CD4⁺ T cell levels increased in mice fed the Se++ diet. During the PC-3 cell tumorigenesis, dietary Se status did not affect peripheral CD4⁺ or CD8⁺ T cells in nude mice whereas mice fed with the Se++ diet appeared to exhibit greater peripheral CD25⁺CD4⁺ T cells on day 9. Dietary Se status did not affect spleen weight in nude mice 7 weeks after the xenograft. Spleen weight was associated with frequency of peripheral CD4⁺, but not CD8⁺ T cells. Taken together, dietary Se at the nutritional and supranutritional levels regulates peripheral B and T cells in adult nude mice before and after xenograft with PC-3 prostate cancer cells.     

Disruption of endoplasmic reticulum is the primary ultrastructural lesion of the pancreas in the selenium-deficient chick

Severe uncomplicated selenium (Se) deficiency was produced in chicks by feeding, from 1 day of age, a purified diet that contained 0.010 ppm Se but was adequate with respect to all other known nutrients. The deficiency was characterized by depressions in rate of growth and efficiency of feed utilization and by reductions in the plasma activity of Se-dependent glutathione peroxidase (SeGSHpx) by 85-97% from levels in chicks fed the basal diet supplemented with 0.20 ppm Se as Na2SeO3. Histological observations of the target organ of Se deficiency in the chick, i.e., the pancreas, using transmission electron microscopy, showed severe losses of endoplasmic reticulum (ER) and absence of secretory granules in acinar cells of Se-deficient animals. These effects were not uniform within individuals, as Se-deficient pancreases also showed areas of unaffected acini. By 14 days of age, Se-deficient pancreases contained many apparently undifferentiated cells, which were absent from pancreases of Se-fed chicks. It is noteworthy that abnormal mitochondria were not observed in any pancreas sections. It is concluded that the metabolic consequences of severe uncomplicated Se deficiency in the chick result from the disruption of ER and loss of functional acinar cells, rather than to damage to mitochondria as previously suggested.     

Dietary selenium effects on milk eicosanoid concentration in dairy cows during coliform mastitis.

The effect of selenium deficiency on the product profile of arachidonic acid oxidation by enzymatic pathways in Holstein cows with experimentally-induced coliform mastitis was investigated. The animals were fed dairy rations containing 0.05 mg Se/kg dry matter, with the supplemented group receiving additional Se to increase the dietary concentration to approximately 0.35 mg Se/kg dry matter. Cows were inoculated intracisternally with 30 colony-forming-units of Escherichia coli at 14-16 weeks of lactation. Eicosanoids and bacteria numbers were recorded at various intervals of time for 60 h postinoculation. Milk from cows fed the Se-depleted diet had significantly higher (p less than 0.05) concentrations of TXB2 between 24 and 48 h and 6-keto-PGF1 alpha between 24 and 60 h postinoculation. Milk PGE2 concentration was significantly higher in the Se-deficient group at 24 h, whereas LTB4 was higher between 36 and 60 h postinoculation in the Se-deficient cows (p less than 0.05). Milk bacteria numbers were significantly higher between 16 and 24 h postinoculation in the Se-deficient group and three of the four cows in this group required euthanasia, whereas all four cows in the Se-supplemented group recovered without therapeutic intervention. These data indicate marked effects of dietary Se on milk eicosanoid concentrations in response to an E. coli infection. The changes in eicosanoid concentrations may be associated with the altered pathogenesis and outcome of mastitis in a Se-deficient state.     

Impacts of glutathione peroxidase-1 knockout on the protection by injected selenium against the pro-oxidant-induced liver aponecrosis and signaling in selenium-deficient mice

Previous research has suggested that repletion of cellular glutathione peroxidase (GPX1) activity by a single injection of Se was dissociated from the Se protection against the pro-oxidant-induced liver necrosis in Se-deficient rodents. Using the GPX1 knockout (GPX1-/-) mice, TUNEL assay, and apoptosis gene expression microarray, we have demonstrated strikingly different impacts of GPX1 knockout on hepatotoxicity and the related signaling induced by an intraperitoneal injection of 12.5 mg paraquat/kg body weight (b.wt.). In both Se-deficient GPX1-/- and wild-type (WT) mice, the paraquat did not induce typical liver necrosis, rather aponecrosis or necrapoptosis, a syncretic process of cell death sharing characteristics of both apoptosis and necrosis. The severity of liver aponecrosis and the associated mortality were reduced to a much greater extent by an injection of Se (ip, 50 microg/kg b.wt. as Na2SeO3) prior to paraquat stress in the WT mice, compared with the GPX1-/- mice. The induced liver aponecrosis seemed to be more apoptotic in the GPX1-/- mice but more necrotic in the WT mice. The paraquat-mediated gene or protein expression of proapoptotic Bax, Bcl-w, and Bcl-X(S), cell survival/death factors GADD45, MDM2, c-Myc, and caspase-3 was upregulated, but that of antiapoptotic Bcl-2 was downregulated in the GPX1-/- mice vs. the WT mice. Overall, these differences between the two groups of mice were related to a low level of liver GPX1 activity in the WT mice that represented < 4% of the normal physiological level. Therefore, the low level of GPX1 activity in the Se-deficient mice can exert a potent role in defending against liver aponecrosis induced by moderate oxidative stress.     

表达肌醇甲基转移酶基因载体的构建及转基因烟草的耐盐性研究

构建了肌醇甲基转移酶（Imtl）基因的植物表达载体pDH5．通过农杆菌（Agrobacterium）介导,获得了转基因烟草（NicotianatabacumLev．SR1）植株,在附加1．2％－1．5％NaCl的生根培养基MSr（MSO＋3g／L蔗糖＋7g／L葡萄糖）上可生根。生化分析表明,不具有芒柄醇（D－ononitol）合成途径的烟草鲜叶片积累了100－654nmol／g的芒柄醇,新产生了一个代谢分支。Western杂交分析证明Imtl基因在烟草中的表达,从而为植物耐盐的基因工程育种提供了一条新途径。