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.     

Elevation of rat liver mRNA for selenium-dependent glutathione peroxidase by selenium deficiency.

Selenium-dependent glutathione peroxidase (Se-GSH-Px, GSH-H2O2 oxidoreductase EC 1.11.1.9) is the best characterized selenoprotein in higher animals, but the mechanism whereby selenium becomes incorporated into the enzyme protein remains under investigation. To elucidate the mechanism of insertion of selenium into Ge-GSH-Px further, we have systematically analyzed and compared the results of Western blot, in vitro translation immunoprecipitation, and Northern blot experiments conducted with liver proteins and RNAs obtained from rats fed on selenium-deficient and selenium-supplemented diets. The anti-serum employed in this study was raised against an electrophoretically pure Se-GSH-Px preparation obtained from rat livers by a simplified purification procedure involving separation by high performance liquid chromatography on a hydrophobic interaction column. Different forms of Se-GSH-Px, including apo-protein, cross-reacted with this antiserum and Western blot analysis found no Se-GSH-Px protein present in livers from rats fed on selenium-deficient diets. By contrast, a distinct protein band corresponding to purified Se-GSH-Px was detected in livers from selenium-supplemented animals, a result consistent with the finding that the Se-GSH-Px activity was reduced to undetectable levels in livers of selenium-deficient rats. The in vitro translation experiments, however, indicated not only that mRNA for Se-GSH-Px was present during selenium deficiency but also that its translation products contained 2-3-fold as much immunoprecipitable protein as the products of poly(A) RNA from livers of selenium-supplemented rats. This result suggests that the Se-GSH-Px mRNA may be increased in the selenium-deficient state. Elevated levels of Se-GSH-Px mRNA were directly demonstrated in Northern blot experiments employing cDNA clone pGPX1211 as a probe. A similar increase in Se-GSH-Px mRNA was observed in such other tissues as kidney, testis, brain, and lung tissue, in selenium-deficient states. The present data support the co-translational mechanism for the incorporation of selenium into Se-GSH-Px in rat liver.     

Gene expression profiling reveals differential effects of sodium selenite, selenomethionine, and yeast-derived selenium in the mouse

The essential trace mineral selenium is an important determinant of oxidative stress susceptibility, with several studies showing an inverse relationship between selenium intake and cancer. Because different chemical forms of selenium have been reported to have varying bioactivity, there is a need for nutrigenomic studies that can comprehensively assess whether there are divergent effects at the molecular level. We examined the gene expression profiles associated with selenomethionine (SM), sodium selenite (SS), and yeast-derived selenium (YS) in the intestine, gastrocnemius, cerebral cortex, and liver of mice. Weanling mice were fed either a selenium-deficient (SD) diet (<0.01 mg/kg diet) or a diet supplemented with one of three selenium sources (1 mg/kg diet, as either SM, SS or YS) for 100 days. All forms of selenium were equally effective in activating standard measures of selenium status, including tissue selenium levels, expression of genes encoding selenoproteins (Gpx1 and Txnrd2), and increasing GPX1 enzyme activity. However, gene expression profiling revealed that SS and YS were similar (and distinct from SM) in both the expression pattern of individual genes and gene functional categories. Furthermore, only YS significantly reduced the expression of Gadd45b in all four tissues and also reduced GADD45B protein levels in liver. Taken together, these results show that gene expression profiling is a powerful technique capable of elucidating differences in the bioactivity of different forms of selenium.

Electronic supplementary material

The online version of this article (doi:10.1007/s12263-011-0243-9) contains supplementary material, which is available to authorized users.     

Inhibition of glutathione reductase by cadmium ion in some rabbit tissues and the protective role of dietary selenium

This study is aimed at investigating the inhibitory effect of cadmium ion on glutathione reductase activity of rabbit brain and liver and the relationship of this effect with dietary selenium. For this purpose, one group of New Zealand rabbits were fed a selenium-deficient diet, another group was fed a selenium-rich diet, and the control group was fed a normal diet. The brain and liver tissues of these groups were investigated for the in vitro inhibitory effects of Cd²⁺ on glutathione reductase activity. For liver, the percentage inhibition of glutathione reductase by 40 nmol/mg protein of Cd²⁺ was similar for selenium-deficient and control groups, but significantly lower in the selenium-rich group. For brain tissues, there was no difference with respect to cadmium inhibition of glutathione reductase in all three groups.     

Influence of dietary selenium on the mutagenic activity of perfusate and bile from rat liver, perfused with 1,1-dimethylhydrazine

The mutagenic effect of 1,1-dimethylhydrazine (UDMH) was studied in the liver perfusion/cell culture system. Male Wistar rats, fed a selenium-deficient diet with or without selenium supplementation in the drinking water, were used as liver donors. UDMH caused an increased mutation frequency in Chinese hamster V79 cells exposed in the perfusate. The effect was statistically significant with both selenium-deficient and selenium-supplemented livers. With selenium-deficient livers, a significant mutagenic effect was also obtained when V79 cells were treated with bile collected after the administration of UDMH. Bile flow and bile acid excretion were not affected by UDMH treatment of selenium-deficient or selenium-supplemented livers. There was a tendency towards reduced C-oxygenation of N,N-dimethylaniline in microsomes from selenium-deficient livers perfused with UDMH. The lactate/pyruvate ratio in the perfusate was increased by UDMH, the effect being more pronounced with selenium-deficient than selenium-supplemented livers.     

The effects of selenium depletion and repletion on the metabolism of thyroid hormones in the rat

Rats were fed selenium-deficient (less than 0.005 mg selenium/kg) or selenium-supplemented diets (0.1 mg selenium/kg, as Na2SeO2) for up to five wks from weaning to assess the effects of developing selenium deficiency on the metabolism of thyroid hormones. Within two wks 3:5,3'-triiodothyronine (T3) production from thyroxine (T4) in liver homogenates from selenium-deficient rats was significantly lower compared with the activity in liver homogenates from selenium-supplemented rats. This decreased activity was probably responsible, in part, for the higher T4 and lower T3 concentrations in plasma from the selenium-deficient rats after 3, 4, and 5 weeks of experiment. Repletion of selenium-deficient rats with single intra-peritoneal injections of 200 micrograms selenium/kg body wt. (as Na2SeO3) 5 days before sampling reversed the effects of the deficiency on thyroid hormone metabolism and significantly increased liver and plasma glutathione peroxidase activities. However a dose of 10 micrograms selenium/kg body wt given to rats of similar low selenium status had no effect on thyroid hormone metabolism or glutathione peroxidase activity but did reverse the increase in hepatic glutathione S-transferase activity characteristic of severe selenium deficiency. Imbalances in thyroid hormone metabolism are an early consequence of selenium deficiency and are probably not related to changes in hepatic xenobiotic metabolizing enzymes associated with severe deficiency.     

The Effect of Level and Source of Dietary Selenium Supplementation on Eggshell Quality

A 16-week-long experiment was performed to compare the effect of sodium selenite (SS) and selenium-enriched yeast (SY) supplementation on eggshell quality and also to evaluate breaking force correlation with other parameters of shell quality originating from hens fed with selenium supplementation. One hundred Shaver 579 hens (27 weeks old) with similar body size were randomly divided for five dietary treatments: basal diet without selenium supplementation and basal diets with two levels of selenium supplementation (0.4 or 0.8 mg/kg) via SS or SY. No adverse effect of Se inclusion in hen's feed, regardless of its source, on shell breaking force, shell deformation, shape index, shell thickness and shell percentage, were observed throughout the current study (P > 0.05). Moderate correlations were found between breaking force and nondestructive shell deformation for all diets (P < 0.05). There was no significant overall correlation between egg breaking force and shell thickness or/and percentage shell in the presence of selenium supplemention (P > 0.05). Shape index in all four selenium-supplemented groups was not related to the breaking force (P > 0.05). Selenium supplementation of up to 0.8 mg/kg, regardless of its source, in the diet of laying hens in their first phase of laying does not adversely affect eggshell quality.     

Long-term Selenium Deficiency Increases the Pathogenicity of a Citrobacter rodentium Infection in Mice

Citrobacter rodentium is a mouse pathogen that causes infectious colitis and shares characteristics with human enteropathogenic (EPEC) and enterohemorrhagic (EHEC) Escherichia coli, including the ability to cause attaching and effacing lesions in the colon and serves as a useful model to study the pathogenicity of these bacteria. In this study, mice were fed a selenium-deficient diet for 5 or 20?weeks and then infected with C. rodentium. Colonization of the colon by C. rodentium was similar in mice fed adequate or selenium-deficient diets, but total bacterial colonization of the spleen was elevated in mice fed selenium-deficient diet for 20?weeks. Infection-induced changes to the colon included inflammatory cell infiltration, gross changes in crypt architecture, and ulceration and denuding of the epithelial layer that were greatest in mice fed a selenium-deficient diet for 20?weeks. Expression of pro-inflammatory genes was significantly higher 12-days post-infection in mice fed the selenium-deficient diet for 20?weeks compared to mice fed a selenium-adequate diet or selenium-deficient diet for 5?weeks. Diarrhea was prevalent in mice fed the selenium-deficient diet for 20?weeks but not 5?weeks, and this was associated with decreased expression of solute carrier family 26a3 and carbonic anhydrase IV, genes involved in ion transport. These results indicated that selenium played an important role in resistance to the pathological effects of a C. rodentium infection, and therefore, selenium status may be important in the expression of human disease caused by common food-borne bacteria.     

Differential effects of dietary selenium (Se) and folate on methyl metabolism in liver and colon of rats

A previous study compared the effects of folate on methyl metabolism in colon and liver of rats fed a selenium-deficient die (<3 μg Se/kg) to those of rats fed a diet containing supranutritional Se (2 mg selenite/kg). The purpose of this study was to investigate the effects of folate and adequate Se (0.2 mg/kg) on methyl metabolism in colon and liver. Weanling, Fischer-344 rats (n=8/diet) were fed diets containing 0 or 0.2 mg selenium (as selenite)/kg and 0 or 2 mg folic acid/kg in a 2×2 design. After 70 d, plasma homocysteine was increased (p<0.0001) by folate deficiency; this increase was markedly, attenuated (p<0.0001) in rats fed the selenium-deficient diet compared to those fed 0.2 mg Se/kg. The activity of hepatic glycine N-methyltransferase (GNMT), an enzyme involved in the regulation of tissue S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH), was increased by folate deficiency (p<0.006) and decreased by selenium deprivation, (p<0.0003). Colon and liver SAH were highest (p<0.006) in rats fed deficient folate and adequate selenium. Although folate deficiency decreased liver SAM (p<0.001), it had no effect on colon SAM. Global DNA methylation was decreased (p<0.04) by selenium deficiency in colon but not liver; folate had no effect. Selenium, deficiency did not affect DNA methyltransferase (Dnmt) activity in liver but tended to decrease (p<0.06) the activity of the enzyme in the colon. Dietary folate did not affect liver or colon Dnmt. These results in rats fed adequate selenium are similar to previous results found in rats fed supranutritional selenium. This suggests that selenium deficiency appears to be a more important modifier of methyl metabolism than either adequate or supplemental selenium. The U.S. Department of Agriculture, Agriculture Research Service, Northern Plains Area, is an equal opportunity/affirmative action employer and all agency services are available without discrimination.     

Microarray analysis of differential gene expression in sensitive and resistant pig to Escherichia coli F18

In this study, Agilent two‐colour microarray‐based gene expression profiling was used to detect differential gene expression in duodenal tissues collected from eight full‐sib pairs of Sutai pigs differing in adhesion phenotype (sensitivity and resistance to Escherichia coli F18). Using a two‐fold change minimum threshold, we found 18 genes that were differentially expressed (10 up‐regulated and eight down‐regulated) between the sensitive and resistant animal groups. Our gene ontology analysis revealed that these differentially expressed genes are involved in a variety of biological processes, including immune responses, extracellular modification (e.g. glycosylation), cell adhesion and signal transduction, all of which are related to the anabolic metabolism of glycolipids, as well as to inflammation‐ and immune‐related pathways. Based on the genes identified in the screen and the pathway analysis results, real‐time PCR was used to test the involvement of ST3GAL1 and A genes (of glycolipid‐related pathways), SLA‐1 and SLA‐3 genes (of inflammation‐ and immune‐related pathways), as well as the differential genes FUT1, TAP1 and SLA‐DQA. Subsequently, real‐time PCR was performed to validate seven differentially expressed genes screened out by the microarray approach, and sufficient consistency was observed between the two methods. The results support the conclusion that these genes are related to the E. coli F18 receptor and susceptibility to E. coli F18.     

森林草莓SUN基因家族的鉴定及其对逆境的响应

SUN基因是调控植物生长发育的关键基因。本研究鉴定了二倍体森林草莓(Fragaria vesca)的SUN基因家族,并对各成员的理化性质、基因结构、系统进化以及基因表达进行了分析。结果表明,森林草莓有31个FvSUN基因,其编码蛋白可聚类为7个组,同一组内成员具有高度相似的基因结构与编码蛋白保守域;FvSUNs蛋白的亚细胞定位主要在细胞核中。共线性分析表明森林草莓FvSUNs基因家族主要通过染色体片段复制产生,拟南芥与森林草莓存在23对直系同源基因。利用森林草莓的转录组数据,对FvSUNs基因的组织表达特征进行分析,发现主要可归为3类：各组织均表达、组织中几乎不表达、组织特异性表达,并通过实时荧光定量PCR (quantitative real-time polymerase chain reaction, qRT-PCR)进一步验证结果。此外,还对森林草莓进行不同的逆境胁迫处理,qRT-PCR分析了31个FvSUNs基因的表达情况,发现大部分基因均在不同程度上受低温、高盐或干旱胁迫的诱导表达。这些研究结果为深入揭示草莓SUN基因的生物学功能及其分子机制奠定了基础。     

Selenoprotein Expression in Macrophages Is Critical for Optimal Clearance of Parasitic Helminth Nippostrongylus brasiliensis

The plasticity of macrophages is evident in helminthic parasite infections, providing protection from inflammation. Previously we demonstrated that the micronutrient selenium induces a phenotypic switch in macrophage activation from a classically activated (pro-inflammatory; M1/CAM) toward an alternatively activated (anti-inflammatory; M2/AAM) phenotype, where cyclooxygenase (COX)-dependent cyclopentenone prostaglandin J₂ (15d-PGJ₂) plays a key role. Here, we hypothesize that dietary selenium modulates macrophage polarization toward an AAM phenotype to assist in the increasing clearance of adult Nippostrongylus brasiliensis, a gastrointestinal nematode parasite. Mice on a selenium-adequate (0.08 ppm) diet significantly augmented intestinal AAM presence while decreasing adult worms and fecal egg production when compared with infection of mice on selenium-deficient (<0.01 ppm) diet. Further increase in dietary selenium to supraphysiological levels (0.4 ppm) had very little or no impact on worm expulsion. Normal adult worm clearance and enhanced AAM marker expression were observed in the selenium-supplemented Trsp^fl/flCre^WT mice that express selenoproteins driven by tRNA^Sec (Trsp), whereas N. brasiliensis-infected Trsp^fl/flCre^LysM selenium-supplemented mice showed a decreased clearance, with lowered intestinal expression of several AAM markers. Inhibition of the COX pathway with indomethacin resulted in delayed worm expulsion in selenium-adequate mice. This was rescued with 15d-PGJ₂, which partially recapitulated the effect of selenium supplementation on fecal egg output in addition to increasing markers of AAMs in the small intestine. Antagonism of PPARγ blocked the effect of selenium. These results suggest that optimal expression of selenoproteins and selenium-dependent production of COX-derived endogenous prostanoids, such as Δ¹²-PGJ₂ and 15d-PGJ₂, may regulate AAM activation to enhance anti-helminthic parasite responses.     

Effects of vitamin E and selenium deficiency on the fatty acid composition of rat retinal tissues.

The fatty acid composition of retinal tissues was measured in rats maintained for 26--32 weeks on each of the following diets: a purified basal diet deficient in alpha-tocopherol and selenium, an identical control diet supplemented with alpha-tocopherol and selenium, and a commerical laboratory rat chow. Dietary deficiencies of antioxidant nutrients were found to cause a large decrease in total polyunsaturated fatty acids in the retinal pigment epithelium, a small decrease in the retinal rod outer segments, but no change in the whole retina or liver when compared to tissues from animals fed the vitamin E- and selenium-supplemented control diet. The polyunsaturated fatty acid content which we have observed for the retinal pigment epithelium from rats fed commerical lab chow is similar to that which we observed for bovine retinal pigment epithelium. Our results indicate that changes in fatty acid composition are not generalized to all tissues in severely antioxidant-deficient animals, but that changes do occur in some tissues, such as the retinal pigment epithelium, which appears to be particularly sensitive to in vivo lipid peroxidation.