Liver selenium and testis phospholipid hydroperoxide glutathione peroxidase are associated with growth during selenium repletion of second-generation Se-deficient male rats

We have previously shown that changes in glutathione peroxidase-1 (GPX1; H2O2:oxidoreductase, EC 1.11.1.9), plasma thyroid hormone and glutathione-S-transferase were not associated with changes in growth observed in second-generation (F2) severely Se-deficient rats; we also found that liver phospholipid hydroperoxide glutathione peroxidase (GPX4; EC 1.11.1.12) activity falls in first-generation (F1) Se-deficient rats to 41% of levels in Se-adequate rats. The purposes of this study were to determine the effect of F2 Se deficiency on GPX4 and to detect early changes in Se parameters associated with growth after single, small Se injections. Se-deficient male F2 weanling rats were randomly divided into two groups and fed a Se-deficient crystalline amino acid (0.003 microg Se/g diet; -Se) diet or that diet supplemented for 14 d with 0.2 microg Se/g diet (+Se) as Na2SeO3. Growth of -Se rats was 55% of the rate of +Se rats. Liver Se, GPX1 activity, GPX4 activity and testis GPX4 activity in -Se rats at 14 d were 1, 2, 23 and 13%, respectively, of levels in +Se rats. In a series of experiments, additional F2 male weanling rats were fed the -Se diet for 14 d and then were given an intraperitoneal single saline injection of 0, 1 or 5 microg Se/100 g body weight (BW) as Na2SeO3 and killed 1 or 7 d later. Rats injected with 1 or 5 microg Se/100 g BW grew 36 or 48%, respectively, above the rate of saline-injected rats. Liver Se concentration increased 367% and testis GPX4 activity doubled in rats 1 d after injection of 1 microg Se/100 g BW compared with saline-injected rats; these parameters were further elevated with 5 microg Se/100 g BW injections. Increases in liver Se and testis GPX4 activity were the parameters best associated with improved growth after Se injection, but the molecular role for Se in growth remains unclear.     

Selenium regulation of classical glutathione peroxidase expression requires the 3' untranslated region in Chinese hamster ovary cells

Classical glutathione peroxidase (GPX) mRNA levels fall dramatically in selenium (Se)-deficient animals, but it is not known whether this mechanism is related to the mRNA 3' untranslated region (3'UTR) sequences that have been shown to direct Se incorporation. In this study, we used recombinant GPX constructs to investigate the role of the GPX 3'UTR in Se regulation of GPX mRNA levels in Chinese hamster ovary (CHO) cells. The CHO cells were transfected with GPX (pRc/GPX), GPX lacking the 3'UTR (pRc/Delta3'UTR) or the pRc/CMV vector alone, and GPX activity and GPX mRNA levels were determined in stable transfectants grown in low Se basal medium with a range of added Se concentrations. We identified two pRc/GPX transfectants with significantly elevated GPX activity levels compared with pRc/CMV transfectants. The elevated GPX expression did not dramatically shift the amount of Se that was sufficient for GPX activity to reach the Se-adequate plateau level (100 nmol/L added Se). As expected, GPX activity was not significantly different when pRc/Delta3'UTR transfectants were compared with pRc/CMV control transfectants. Among the wild type and transfected CHO cells, Se-deficient GPX activity levels averaged 35 +/- 5% of Se-adequate levels. Selenium-deficient levels of endogenous GPX mRNA as well as recombinant pRc/GPX mRNA averaged 54-58% of Se-adequate levels; 3-4 nmol/L added Se was sufficient for maximal GPX mRNA levels. In contrast, pRc/Delta3'UTR mRNA levels in the unsupplemented cells remained at Se-adequate levels and showed no distinct Se regulation. These studies demonstrate that the GPX 3'UTR is necessary for Se regulation of GPX mRNA levels in addition to its role in Se incorporation.     

A novel glutathione peroxidase in bovine eye. Sequence analysis, mRNA level, and translation

Bovine ciliary body contains a selenium-independent glutathione peroxidase (GPX) with a molecular mass of about 100 kDa that is composed of four identical subunits and exhibits no glutathione S-transferase activity. In this study, we isolated cDNA clones and determined the nucleotide sequence to deduce the primary structure of the enzyme. The cDNA contained 672 base pairs encoding a polypeptide with an estimated molecular mass of 25,064 Da. Translation of bovine ciliary mRNA produced a protein which was immunologically indistinguishable from GPX and showed high enzyme activity. The encoded amino acid sequence of the protein was 95% identical with that of a human keratinocyte gene product expressed in response to keratinocyte growth factor. It also showed sequence identity to bacterial alkyl hydroperoxide reductases and thiol specific antioxidant enzymes. GPX mRNA level was highest in the ciliary body, followed by the retina and iris. In various rat organs, the level of GPX mRNA was highest in the lung, followed by the muscle, liver, eye, heart, testis, thymus, kidney, and spleen. A very low level of mRNA was detected in the brain. Enzyme-linked immunosorbent assay with an antibody raised against the NH2-terminal sequence of GPX detected GPX protein in all rat tissues examined.     

Cis-acting elements are required for selenium regulation of glutathione peroxidase-1 mRNA levels

Classical glutathione peroxidase (GPX1) mRNA levels can decrease to less than 10% in selenium (Se)-deficient rat liver. The cis-acting nucleic acid sequence requirements for Se regulation of GPX1 mRNA levels were studied by transfecting Chinese hamster ovary (CHO) cells with GPX1 DNA constructs in which specific regions of the GPX1 gene were mutated, deleted, or replaced by comparable regions from unregulated genes such as phospholipid hydroperoxide glutathione peroxidase (GPX4). For each construct, stable transfectants were pooled two weeks after transfection, divided into Se-deficient (2 nM Se) or Se-adequate (200 nM Se) medium, and grown for an additional four days. On day of harvest, Se-deficient GPX1 and GPX4 activities averaged 13 +/- 2% and 15 +/- 2% of Se adequate levels, confirming that cellular Se status was dramatically altered by Se supplementation. RNA was isolated from replicate plates of cells and transfected mRNA levels were specifically determined by RNase protection assay. Analysis of chimeric GPX1/GPX4 constructs showed that the GPX4 3'-UTR can completely replace the GPX1 3'-UTR in Se regulation of GPX1 mRNA. We did not find any GPX1 coding regions that could be replaced by the corresponding GPX4 coding regions without diminishing or eliminating Se regulation of the transfected GPX1 mRNA. Further analysis of the GPX1 coding region demonstrated that the GPX1 Sec codon (UGA) and the GPX1 intron sequences are required for full Se regulation of transfected GPX1 mRNA levels. Mutations that moved the GPX1 Sec codon to three different positions within the GPX1 coding region suggest that the mechanism for Se regulation of GPX1 mRNA requires a Sec codon within exon 1. Lastly, we found that addition of the GPX1 3'-UTR to beta-globin mRNA can convey significant Se regulation to beta-globin mRNA levels when a UGA codon is placed within exon 1. We conclude that Se regulation of GPX1 mRNA requires a functional selenocysteine insertion sequence (SECIS) in the 3'-UTR and a Sec codon followed by an intron.     

Selenium regulation of selenium-dependent glutathione peroxidases in animals and transfected CHO cells

Glutathione peroxidase (GPX1) was the first identified selenium-dependent enzyme, and this enzyme has been most useful as a biochemical indicator of selenium (Se) status and the parameter of choice for determining Se requirements. We have continued to study Se regulation of GPX1 to better understand the underlying mechanism and to gain insight into how cells themselves regulate nutrient status. In progressive Se deficiency in rats, GPX1 activity, protein and mRNA all decrease in a dramatic, coordinated and exponential fashion such that Se-deficient GPX1 mRNA levels are 6-15% of Se-adequate levels. mRNA levels for other Se-dependent proteins are far less decreased in the same animals. The mRNA levels for a second Se-dependent peroxidase, phospholipid hydroperoxide glutathione peroxidase (GPX4), are little affected by Se deficiency, demonstrating that Se regulation of GPX1 is unique. Se regulation of GPX1 activity in growing male and female rats shows that the Se requirement is 100 ng/g diet, based on liver GPX1 activity; use of GPX1 mRNA as the parameter indicates that the Se requirement is nearer to 50 ng Se/g diet in both male and female rats. This approach will readily detect an altered dietary Se requirement, as shown by the incremental increases in dietary Se requirement by 150, 100 or 50 ng Se/g diet in Se-deficient rat pups repleted with Se for 3, 7 or 14 d, respectively. Studies with CHO cells stably transfected with recombinant GPX1 also show that overexpression of GPX1 does not alter the minimum level of media Se necessary for Se-adequate levels of GPX1 activity or mRNA. We hypothesize that classical GPX1 has an integral biological role in the mechanism used by cells to regulate Se status, making GPX1 an especially useful and effective parameter for determining Se requirements in animals.     

Translational selection and molecular evolution

Fourteen commercial antibodies against human antioxidant enzymes were tested on whole cell lysates by Western analysis for specificity and species crossreactivity. All antibodies, except one, recognized pure protein antigen. All four catalase antibodies were of high quality, and they could also recognize the catalases from rat, mouse, dog, and hamster cells. Two CuZnSOD antibodies were very specific for CuZnSOD protein. They could also crossreact with CuZnSOD from rat, mouse, and hamster cells, but not from dog cells. All five MnSOD antibodies detected only very high levels of MnSOD. We believe that they could not properly be used in immunohistochemistry. Three GPX antibodies could not detect the specific GPX band from cell lysates. We believe that it is difficult to use these GPX antibodies in both Western blotting and immunohistochemistry.     

Molecular cDNA cloning and tissue distribution of mRNA encoding a novel ATP-binding cassette (ABC) half-transporter

After feeding a commercial rodent chow for 8 weeks, tissues from male and female rats were collected and examined for selenium content, glutathione peroxidase (GPX) activities and selenoprotein W (Se-W) levels. There were no differences (P > 0.05) between plasma selenium content, plasma GPX activity, whole blood selenium content, or whole blood GPX activity between male and female rats. There was also no gender effect on selenium concentration in muscle, brain, spleen, and skin, but selenium concentration in liver was higher (P < 0.05) in female than in male rats. Western blots indicated that the tissue distribution of Se-W was similar in male and female rats. Se-W protein level was high in testes of male rats but very low in ovaries of female rats. Muscle and skin from female rats had significantly higher (P < 0.05) Se-W levels than from male rats. Consistent with Se-W content, the Se-W mRNA levels from female skins were significantly higher (P < 0.05) than from male rats. The expression of Se-W was different in various tissues and gender influenced this regulation in some tissues.     

Contrasting patterns of regulation of the antioxidant selenoproteins, thioredoxin reductase, and glutathione peroxidase, in cancer cells

There is strong evidence that selenium protects against certain human cancers, but the underlying mechanism is unknown. Glutathione peroxidase (GPX1) and thioredoxin reductase (TR), the most abundant antioxidant selenium-containing proteins in mammals, have been implicated in this protection. We analyzed the expression of TR and GPX1 in the following model cancer systems: (1) liver tumors in TGFalpha/c-myc transgenic mice; (2) human prostate cell lines from normal and cancer tissues; and (3) p53-induced apoptosis in a human colon cancer cell line. TR was induced while GPX1 was repressed in malignancies relative to controls in transgenic mice and prostate cell lines. In the colon cell line, p53 expression resulted in elevated GPX1, but repressed TR. The data indicate that TR and GPX1 are regulated in a contrasting manner in the cancer systems tested and reveal the p53-dependent regulation of selenoprotein expression. The data suggest that additional studies on selenoprotein regulation in different cancers are required to evaluate future implementation of selenium as a dietary supplement in individuals at risk for developing certain cancers.     

Glutathione, glutathione-related enzymes, and catalase activities in the earthworm Eisenia fetida andrei

The aim of this work was to provide basic data on the antioxidant defences in the annelid Eisenia fetida andrei (E. f. a.). Methods for measurement of three antioxidant enzymes-catalase (CAT), glutathione peroxidase (GPX), and glutathione reductase (GR)-and of glutathione-S-transferase (GST) were optimized. GPX activity differed according to the substrate used: cumene hydroperoxide (CUOOH) or hydrogen peroxide (H2O2). The effects on the enzyme activities of storage up to 2 months at -80 degrees C, -20 degrees C, and +4 degrees C were evaluated. The subcellular distribution (in cytosol, mitochondrial, and microsomal fractions) was examined. The properties and subcellular distribution of the enzymes and glutathione were also characterized in dissected tissues and body fluids. The GR activity decreased at -80 degrees C and was the only one not stable at this temperature. The four enzymes were localized mainly in the cytosolic fraction. CAT distribution was unusual as it was not associated with peroxisomes, its properties being consistent with a catalase-peroxidase, rather than a true catalase. However, this result could also be an artifact linked to the use of an inappropriate method to obtain the fractions. Our observations indicate the presence of a distinct cytosolic selenium-dependent GPX (Se-GPX), and of a possible microsomal Se-GPX. A strong non-Se-GPX activity was measured in the CF and CL, which could be linked to the peroxidase activity of fetidins secreted by coelomocytes and with the ROS production of these cells. This study seems to indicate that E. f. a. is well equipped for the metabolism of electrophilic and pro-oxidants through glutathione.     

Overexpression of glutathione S-transferase/glutathione peroxidase enhances the growth of transgenic tobacco seedlings during stress

Transgenic tobacco seedlings that overexpress a cDNA encoding an enzyme with both glutathione S-transferase (GST) and glutathione peroxidase (GPX) activity had GST- and GPX-specific activities approximately twofold higher than wild-type seedlings. These GST/GPX overexpressing seedlings grew significantly faster than control seedlings when exposed to chilling or salt stress. During chilling stress, levels of oxidized glutathione (GSSG) were significantly higher in transgenic seedlings than in wild-types. Growth of wild-type seedlings was accelerated by treatment with GSSG, while treatment with reduced glutathione or other sulfhydryl-reducing agents inhibited growth. Therefore, overexpression of GST/GPX can stimulate seedling growth under chilling and salt stress, and this effect could be caused by oxidation of the glutathione pool.     

Some physicochemical and enzymic properties of selenium-containing abzyme

We successfully prepared the Se-containing abzyme (Se-abzyme) with glutathione peroxidase (GPX) activity and further studied its physicochemical and enzymic properties and stabilities. Data showed that the isoelectric point of the abzyme was 6.95-7.08, and its molecular weight was 158 KD. The ranges of optimum pH and temperature of the Se-abzyme were wider than the native GPX. The store stability of the abzyme was higher than the native GPX. The Se content in the abzyme was found to be 5 mol Se/mol abzyme by X-ray photoelectron spectrum, and binding constant 1.11 x 10(7)M-1 by using ELISA method. The Se-abzyme was inhibited competitively by dithiobis(2-nitrobenzoic acid) (DTNB), and inhibition constant was determined to be 1.25 x 10(-3)M-1.     

Precursor B cells of mouse bone marrow express two different complexes with the surrogate light chain on the surface

Two monoclonal antibodies raised against the complex of mu heavy (H) chain and Vpre-B/lambda 5 surrogate light (L) chains recognize surrogate L chain in different conformations on normal pre-B cells. One, LM34 recognizes free lambda 5 protein and free lambda 5/Vpre-B surrogate L chains and binds to surrogate L chains on the surface of early, pro-B and pre-B-I cells where the surrogate L chain is associated with a gp130/gp35-65 complex of proteins. It also recognizes the surrogate L chain associated with the mu H chain on pre-B-II cells. The other monoclonal antibody, SL156, does not recognize free surrogate L chain or its components, nor its complex with gp130/gp35-65 on pro-B and pre-B-I cells. However, it does bind to a conformational epitope on the surrogate light chain/mu H chain complex on a subpopulation of pre-B-II cells and on mu H chain-positive pre-B cell lines. On mouse precursor B cells prepared ex vivo on ice, expression of the surrogate L chain is very low and almost undetectable. Incubation of the precursor cells for 1 h at 37 degrees C up-regulates the surface expression of surrogate L chain associated with gp130/gp35-65 (early complex) as well as the mu H chain/surrogate L chain complex. These results reconcile some of the apparently discrepant results on surface expression of the surrogate L chain obtained with human and mouse bone marrow pre-B cells, and show that a surrogate L chain/mu H chain-containing pre-B cell receptor can be expressed also on the surface of mouse pre-B-II cells.     

Studying low-density lipoprotein-monoclonal antibody complexes using dynamic laser light scattering and analytical ultracentrifugation

Monoclonal antibody complexes have proven very useful in the study of low-density lipoproteins (LDLs). Thus, complexes composed of two different monoclonal antibodies, selected from a panel of 11 different antibodies, and LDL have been employed to map apolipoprotein B (apoB) on the surface of the LDL. In this way, apoB was found to surround the LDL as a ribbon with a bow [Chatterton, J. E., et al. (1995) J. Lipid Res. 36, 2027-2037]. Moreover, monoclonal MB19, which recognizes a polymorphic site, has been employed to quantitate the two different allelic forms of apoB found on LDL in human sera, and in this way, we assessed the effect of most of the known common polymorphisms of this protein as well as detected the depletion of the normal allele product in two forms of familial defective apoB-100 [Chatterton, J. E., et al. (1995) Biochemistry 34, 9571-9580; Pullinger, C. R., et al. (1995) J. Clin. Invest. 95, 1225-1234]. In this paper, these studies have been extended by examining by dynamic light scattering and sedimentation velocity techniques the complexes formed with only one antibody, and complexes formed using two antibodies. Our data show that the largest complex formed with a single monoclonal antibody was that of an LDL dimer; no larger, nonspecific complexes were present. With two antibodies, a variety of complexes were seen. Thus, monoclonal antibodies MB47 and 4G3, which bound about 55 degrees apart, formed a very stable dimer. Monoclonal antibodies MB47 and 2D8, which bound 136 degrees apart, formed a very stable tetramer, with four LDLs held together in probably a circular structure with four monoclonal antibodies. Finally, monoclonal antibodies 2D8 and 1D1, which bound 86 degrees apart, probably formed a less stable LDL tetramer, held together by three to four monoclonal antibodies. A rationale for these structures is discussed, as well as the biological relevance of these complexes.     

Increase in resting levels of superoxide anion in the whole blood of uremic patients on chronic hemodialysis

Recently, we developed a new method to measure the resting level of superoxide anion in whole blood using an ultrasensitive chemiluminescence analyzer and lucigenin amplification. The advantage of this method is that the assay system can be performed in the absence of leukocyte isolation and stimulant administration. In this study, we applied this method to measure the blood resting levels of superoxide anion in 104 uremic patients on chronic hemodialysis (CHD) and 98 sex- and age-matched healthy controls to clarify the influence of HD on blood levels of superoxide anion. Simultaneously, the plasma levels of copper, zinc superoxide dismutase (Cu,Zn-SOD), glutathion peroxidase (GPX), myeloperoxidase (MPO) and lactoferrin (Lacto-F) were measured. The results showed that the basal blood levels of superoxide anion, Cu,Zn-SOD, and MPO in CHD patients were significantly greater than those of healthy controls. However, there was no difference in the basal plasma levels of Lacto-F and GPX between CHD patients and healthy controls. One session of HD further increased the blood levels of superoxide anion, MPO, Lacto-F and Cu,Zn-SOD but not GPX. These results suggest that the blood levels of superoxide anion are higher in CHD patients and further increase after one session of HD. This mechanism should be studied further.     

Two-site enzyme immunometric assays for determination of native and denatured beta-lactoglobulin

Two enzyme immunometric assays suitable for measuring native and denatured beta-lactoglobulin (BLg) have been developed. The assays were performed in 96-well microtitre plates and were based on the use of pairs of monoclonal antibodies specific to either the native form or the reduced and carboxymethylated form of BLg (RCM-BLg). Detection limits of 30 and 200 pg/ml were obtained for the native BLg and the RCM-BLg assay, respectively, with very low or negligible cross-reactivity of the other milk proteins and tryptic fragments of BLg. The validity of the assays in different media such as cow's milk and cow's milk products, saline buffer or serum was supported by recovery experiments. The assays were first applied to the determination of BLg and RCM-BLg in PBS and in raw skimmed milk. The ability of the RCM-BLg assay to detect heat-denatured BLg was confirmed by a kinetic study of BLg heat-denaturation in the two media. During heat treatment, the decrease in the concentration of native BLg was associated with an increase in denatured BLg specifically detected by the RCM-BLg assay. By selecting an appropriate monoclonal antibody which failed to recognize caprine BLg, we were able to establish a modified sandwich immunoassay permitting very sensitive detection of cow's milk in goat's milk.     

Humanization of an anti-vascular endothelial growth factor monoclonal antibody for the therapy of solid tumors and other disorders

Vascular endothelial growth factor (VEGF) is a major mediator of angiogenesis associated with tumors and other pathological conditions, including proliferative diabetic retinopathy and age-related macular degeneration. The murine anti-human VEGF monoclonal antibody (muMAb VEGF) A.4.6.1 has been shown to potently suppress angiogenesis and growth in a variety of human tumor cells lines transplanted in nude mice and also to inhibit neovascularization in a primate model of ischemic retinal disease. In this report, we describe the humanization of muMAb VEGF A.4.6.1. by site-directed mutagenesis of a human framework. Not only the residues involved in the six complementarity-determining regions but also several framework residues were changed from human to murine. Humanized anti-VEGF F(ab) and IgG1 variants bind VEGF with affinity very similar to that of the original murine antibody. Furthermore, recombinant humanized MAb VEGF inhibits VEGF-induced proliferation of endothelial cells in vitro and tumor growth in vivo with potency and efficacy very similar to those of muMAb VEGF A.4.6.1. Therefore, recombinant humanized MAb VEGF is suitable to test the hypothesis that inhibition of VEGF-induced angiogenesis is a valid strategy for the treatment of solid tumors and other disorders in humans.     

Biological characteristics of esophageal squamous cell carcinoma associated with contiguous intraepithelial carcinoma

To evaluate the biological significance of esophageal squamous cell carcinoma that is associated with contiguous intraepithelial carcinoma, we analyzed 95 patients with operated esophageal carcinoma. Of these 95 patients, eight had in situ carcinoma. Among 87 cases in which the tumo had invaded more deeply than the lamina propria, there were 42 cases (48.3%) of contiguous intraepithelial carcinoma associated with the main tumor. The biological characteristics (proliferative activity of cells, as revealed by immunostaining with the Ki-67 monoclonal antibody) of 45 tumors without contiguous intraepithelial carcinoma (group A) were compared with those of 42 tumors with contiguous intraepithelial carcinoma (group B). The more advanced was the main lesion, the lower was the incidence of contiguous intraepithelial carcinoma. The mean Ki-67 score of the main tumors in group A was 51.6% and that of the main tumors in group B was 45.9%. The mean Ki-67 score of the main tumors in group B was very similar to that of the contiguous intraepithelial carcinomas that were associated with the main tumors (44.4%, P = 0.682). Furthermore, the mean Ki-67 score of contiguous intraepithelial carcinomas associated with main tumors was very similar to that of carcinomas in situ (41.2%, P = 0.529). From our results, it is suggested that tumors with high proliferative activity may be assumed to grow rapidly and, as a result, the region of intraepithelial carcinoma may develop into an invasive tumor. By contrast, tumors with low proliferative activity may grow slowly and, in such cases, the carcinoma may remain in the epithelium around the invasive tumor.