Selenium deficiency in cultured adrenocortical cells: restoration of glutathione peroxidase and resistance to hydroperoxides on addition of selenium

The beginning of GPX2 and 30 years later

We published the first paper to characterize GPX2 (aka GSHPx-GI) as a selenoenzyme with glutathione peroxidase activity in 1993. Among the four Se-GPX isozymes, GPX1-4, GPX1 and GPX2 are closely related in terms of structure, substrate specificities, and subcellular localization. What sets them apart are distinct patterns of gene regulation, tissue distribution and response to selenium. While we identified the digestive tract epithelium as the main site of GPX2 expression, later work has shown GPX2 is found more widely in epithelial tissues with concentration of expression in stem cell and proliferative compartments. GPX2 expression is regulated over a wide range of levels by many pathways, including NRF2, WNT, p53, RARE and this often results in attaching undue significance to GPX2 as GPX2 is only a part of a system of hydroperoxidase activities, including GPX1, peroxiredoxins and catalase. These other activities may play equal or greater roles, particularly in cell lines cultured without selenium supplementation and often with very low GPX2 levels. This could be assessed by examining levels of mRNA and protein among these various peroxidases at the outset of studies. As an example, it was found that GPX1 responds to the absence of GPX2 in mouse ileum and colon epithelium with higher expression. As such, both Gpx1 and Gpx2 had to be knocked out in mice to produce ileocolitis. However, we note that the actual role of GPX1 and GPX2 in relation to peroxiredoxin function is unclear. There may be an interdependence that requires only low amounts of GPX1 and/or GPX2 in a supporting role to maintain proper peroxiredoxin function. GPX2 levels may be prognostic for cancer progression in colon, breast, prostate and liver, however, there is no consistent trend for higher or lower levels to be favorable.

Selenium-deficient diet induces inflammatory response in the pig adrenal glands by activating TLR4/NF-κB pathway via miR-30d-R_1

Selenium (Se) is an important trace element to maintain the body's dynamic balance. Lack of Se can cause inflammation. Studies have shown that inflammation often leads to disorders of the hypothalamic-pituitary-adrenal axis, but the mechanism by which Se deficiency causes inflammation of the porcine adrenal glands is still unclear. In order to study the effect of Se deficiency on the adrenal glands of pigs, we obtained Se-deficient pig adrenal glands through a low-Se diet. The results of mass spectrometry showed that the Se content in the Se-deficient group was only one-tenth of the control group. We detected the expression of the toll-like receptor 4 (TLR4) and downstream factors by qRT-PCR and Western blotting, and found that the lack of Se affected the TLR4/NF-κB pathway. It is known that miR-155-3p, miR-30d-R_1, and miR-146b have all been verified for targeting relationship with TLR4. We confirmed by qRT-PCR that miR-30d-R_1 decreased most significantly in the Se-deficient pig model. Then we tested 25 selenoproteins and some indicators of oxidative stress. It is confirmed that Se deficiency reduces the antioxidant capacity and induces oxidative stress in pig adrenal tissue. In short, a diet lacking Se induces oxidative stress in pig adrenal tissues and leads to inflammation through the miR-30d-R_1/TLR4 pathway. This study provides a reference for the prevention of adrenal inflammation in pigs from a nutritional point of view.

Effect of selenium supplementation on glutathione peroxidase and catalase activities in senescent cultured human fibroblasts

AIMS

To investigate the effect of senescence and selenium supplementation on glutathione peroxidase (cGPx) and catalase (CAT) activities, and concurrent hydrogen peroxide (H(2)O(2)) generation in subcultured human fibroblasts.

METHODS

cGPx and CAT activities and H(2)O(2) levels were assayed in presenescent passage 5 and 10 cells, and in senescent passage 20, 25, 30 and 35 cells cultured in routine medium (MEM1) and supplemented media MEM2 and MEM3 containing normal and triple human plasma levels of Se, respectively. Senescent cells were identified by studying their growth and replication states, and by monitoring their activity of key glucose and glycogen degradative enzymes.

RESULTS

cGPx activity showed moderate increases in senescent cells at passages 20-35 subcultured in MEM1 or MEM2. This activity underwent highly significant progressive increases in the same senescent cells subcultured in MEM3. In contrast, CAT activity showed progressive, highly significant increases in senescent cells at passages 20-35 regardless of the culture medium type. Concurrent H(2)O(2) generation was significantly increased in passage 15-25 cells and peaked to higher levels in passage 30 and 35 cells cultured in MEM1 or MEM2. These rates, however, were significantly reduced in senescent passage 20-35 cells cultured in MEM3.

CONCLUSIONS

The highest cGPx activity and coupled lower H(2)O(2) generation were achieved in senescent cells cultured in MEM3.

Structural organization of the murine microsomal glutathione S-transferase gene (MGST1) from the 129/SvJ strain: identification of the promoter region and a comprehensive examination of tissue expression

The structure and regulation of the murine microsomal glutathione transferase gene (MGST1) from the 129/SvJ strain is described and demonstrates considerable difference in nucleotide sequence and consequently in restriction enzyme sites as compared to other mouse strains. A comparison of the amino acid sequence for MGST1 revealed one difference in exon 2 between the 129/SvJ strain (arginine at position 5) and the sequence previously reported for the Balb/c strain (lysine). The promoter region immediately upstream of the dominant first exon is functional, transcriptionally responds to oxidative stress, and is highly homologous to the human region. Oxidative stress also induced the production of endogenous MGST1 mRNA. The tissue-specific expression of MGST1 mRNA was studied, and as anticipated, was indeed highest in liver. There was, however, marked mRNA expression in several tissues not previously studied including smooth muscle, epidymus, ovaries, and endocrine glands in which the expression of various peroxidases is also very high (salivary and thyroid). Overall, there was a good agreement between the mRNA content detected and previous reports of MGST1 activity with the exception of brain tissue.

Selenium deficiency impairs corticosterone and leptin responses to adrenocorticotropin in the rat

Selenium deficiency causes oxidative stress and impairs steroidogenesis in vitro. Leptin is closely related to the hypothalamo-pituitary-adrenal (HPA) axis. Leptin inhibits the HPA axis at the central level while corticosteroids have been shown to stimulate leptin secretion in most studies. We hypothesized that oxidative stress impairs adrenal steroidogenesis and decreases leptin production in vivo. The goal of this study was to investigate in rats the effects of selenium deficiency and oxidative stress on adrenal function and on leptin concentrations. Weanling rats were fed a selenium-deficient (Se-) or selenium-sufficient (Se+) diet for 4-10 weeks. Selenium deficiency caused a marked decrease in liver (> or = 99%) and adrenal (> or = 81%) glutathione peroxidase (GPx) activities. Selenium deficiency did not affect basal and short-term adrenocorticotropin (ACTH) stimulated corticosterone or leptin concentrations. In contrast, after long-term ACTH stimulation, selenium deficiency caused a doubling in adrenal isoprostane content and blunted the increase in corticosterone and leptin concentrations observed in Se+ animals. Plasma leptin concentrations were 50% lower in Se- compared to Se+ animals following long-term ACTH. Our results suggest that oxidative stress causes a decrease in circulating corticosterone in response to ACTH, and, as a consequence, a decrease in plasma leptin concentrations.

Identification of selenoprotein P fragments as a cell-death inhibitory factor

Megakaryoblastoma (Dami cells) cultured in a serum-free medium containing albumin, proliferated for three days but died on the fourth day. This cell death was not observed when human plasma was added, suggesting that human plasma contains a cell-death inhibitory factor. In order to identify this factor, we purified it from human plasma. N-terminal amino acid sequence analysis revealed that this factor is a mixture of C-terminal fragments of selenoprotein P, a major selenocysteine-containing protein in plasma. The specific activity (unit per pmol of selenium) of selenoprotein P fragments protein was 15-fold and 1900-fold higher than that of the full-length SeP and sodium selenite, respectively.

Purification and characterization of recombinant microsomal prostaglandin E synthase-1

Recombinant human microsomal prostaglandin E(2) synthase-1 (mPGES-1) was expressed in a baculovirus-Sf9 cell system. The mPGES-1 was solubilized from Sf9 cell membranes with diheptanoylphosphatidylcholine and purified in the presence of octylglucoside using hydroxyapatite column chromatography. The K(m) values of the substrates PGH(2) and GSH were 14 microM and 0.75 mM, respectively, with the purified enzyme. The specific activity (4 micromol/min/mg) was increased 3-5-fold by non-ionic and zwitterionic detergents. Kinetic analysis showed that dodecylmaltoside increases V(max) but does not affect the K(m) values of either substrate. Several other thiol-containing compounds were tested as glutathione replacements, none of which yielded detectable enzyme activity. During enzyme catalysis, glutathione was not oxidized and therefore can be considered an enzyme cofactor. No glutathione transferase or peroxidase activity could be determined with a range of potential substrates. The results show that purified mPGES-1 has a specific activity similar to Cox-2, consistent with its postulated role in Cox-2 mediated PGE(2) formation.

Selenium spares ascorbate and alpha-tocopherol in cultured liver cell lines under oxidant stress

The selenoenzyme thioredoxin reductase (TR) can recycle ascorbic acid, which in turn can recycle alpha-tocopherol. Therefore, we evaluated the role of selenium in ascorbic acid recycling and in protection against oxidant-induced loss of alpha-tocopherol in cultured liver cells. Treatment of HepG2 or H4IIE cultured liver cells for 48 h with sodium selenite (0-116 nmol/l) tripled the activity of the selenoenzyme TR, measured as aurothioglucose-sensitive dehydroascorbic acid (DHA) reduction. However, selenium did not increase the ability of H4IIE cells to take up and reduce 2 mM DHA, despite a 25% increase in ascorbate-dependent ferricyanide reduction (which reflects cellular ascorbate recycling). Nonetheless, selenium supplements both spared ascorbate in overnight cultures of H4IIE cells, and prevented loss of cellular alpha-tocopherol in response to an oxidant stress induced by either ferricyanide or diazobenzene sulfonate. Whereas TR contributes little to ascorbate recycling in H4IIE cells, selenium spares ascorbate in culture and alpha-tocopherol in response to an oxidant stress.

Modulation of steroidogenesis by selenium in a novel adrenal cell line developed using targeted tumorigenesis

Glutathione peroxidase (GPx-1) is a selenoenzyme that metabolizes H(2)O(2), a source of potentially toxic free radicals. Steroidogenesis is markedly inhibited by H(2)O(2) in vitro.

OBJECTIVE

to study the effects of selenium deficiency on GPx activity and adrenal steroidogenesis in a novel adrenal cell line developed using targeted tumorigenesis.

METHODS

AN4Rppc7 cells were grown for 7 days in serum-free medium. 8-Br-cAMP-stimulated concentrations of steroid hormones were measured by RIA. StAR (Steroid Acute Reactive Protein) mRNA was measured by Northern blot.

RESULTS

selenium deficiency caused a 99% There was a 51%, progesterone, corticosterone and aldosterone production, respectively (p<0.05 by ANOVA). StAR mRNA was not affected by selenium.

CONCLUSIONS

selenium deficiency causes a marked decrease in GPx activity. Decreased steroid hormone production occurs for selenium concentrations equal or lower than 5 nM. The absence of changes in StAR mRNA content suggests that selenium deficiency does not affect cholesterol access to the mitochondria.

Structural organization of the human gastrointestinal glutathione peroxidase (GPX2) promoter and 3'-nontranscribed region: transcriptional response to exogenous redox agents

The flanking upstream and downstream regions of the human GPX270%). The human GPX2 promoter region was not G-C rich (<50% G+C) and classical TATA/CCAAT elements were not present. The ubiquitous SP1 and AP elements were present. Several GATA elements as well as liver-specific sites (HNF series) were present. Despite the unique intestinal specific expression of GPX2, classical intestine-specific sites were not detected in the flanking 5' or 3' regions. The ability of the GPX2 promoter to direct transcription was confirmed. Exogenous agents capable of producing oxidative stress, such as paraquat, could induce the transcriptional activity of the GPX2 promoter. Analysis of three previously reported polymorphism sites revealed that they represented the most common polymorphisms. Surprisingly, the human GPX2 promoter could direct transcription and respond to oxidative stress in the murine NIH3T3 fibroblast cell line, which is devoid of the ability to bind to a variety of intestinal specific elements. This finding suggests that the unique intestinal specific expression of GPX2 may be due to elements in the intron, the flanking 3'-nontranslated region, or to elements existing even farther upstream. The ability of GPX2 to respond transcriptionally to redox stress is likely to be more physiologically relevant than post-transcriptional regulation which is dependent upon selenium availability.

Structural organization of the microsomal glutathione S-transferase gene (MGST1) on chromosome 12p13.1-13.2. Identification of the correct promoter region and demonstration of transcriptional regulation in response to oxidative stress

The structure and regulation of the microsomal glutathione S-transferase gene (MGST1) are considerably more complex than originally perceived to be. The MGST1 gene has two alternative first exons and is located in the 12p13.1-13.2 region. Two other potential first exons were determined to be nonfunctional. The region between the functional first exons cannot direct transcription. Thus, one common promoter element directing transcription exists, and RNA splicing occurs such that only one of the first exons (containing only untranslated mRNA) is incorporated into each mRNA species with common downstream exons. MGST1 expression and regulation are therefore similar to those of other hepatic xenobiotic handling enzymes, which also produce mRNA species differing only in the 5'-untranslated regions to yield identical proteins. MGST1 was previously considered a "housekeeping" gene, as non-oxidant inducers had little effect on activity. However, the promoter region immediately upstream of the dominant first exon transcriptionally responds to oxidative stress. In this respect, MGST1 is similar to glutathione peroxidases that also transcriptionally respond to oxidative stress. The discovery that MGST1 utilizes alternative first exon splicing eliminates a problem with the first description of MGST1 cDNA in that it appeared that MGST1 expression was in violation of the ribosomal scanning model. The identification that the first exon originally noted is in fact a minor alternative first exon far downstream of the primary first exon eliminates this conundrum.

Mice with a homozygous null mutation for the most abundant glutathione peroxidase, Gpx1, show increased susceptibility to the oxidative stress-inducing agents paraquat and hydrogen peroxide

Glutathione peroxidases have been thought to function in cellular antioxidant defense. However, some recent studies on Gpx1 knockout (-/-) mice have failed to show a role for Gpx1 under conditions of oxidative stress such as hyperbaric oxygen and the exposure of eye lenses to high levels of H2O2. These findings have, unexpectedly, raised the issue of the role of Gpx1, especially under conditions of oxidative stress. Here we demonstrate a role for Gpx1 in protection against oxidative stress by showing that Gpx1 (-/-) mice are highly sensitive to the oxidant paraquat. Lethality was already detected within 24 h in mice exposed to paraquat at 10 mg.kg-1 (approximately (1)/(7) the LD50 of wild-type controls). The effects of paraquat were dose-related. In the 30 mg.kg-1-treated group, 100% of mice died within 5 h, whereas the controls showed no evidence of toxicity. We further demonstrate that paraquat transcriptionally up-regulates Gpx1 in normal cells, reinforcing a role for Gpx1 in protection against paraquat toxicity. Finally, we show that cortical neurons from Gpx1 (-/-) mice are more susceptible to H2O2; 30% of neurons from Gpx1 (-/-) mice were killed when exposed to 65 microM H2O2, whereas the wild-type controls were unaffected. These data establish a function for Gpx1 in protection against some oxidative stressors and in protection of neurons against H2O2. Further, they emphasize the need to elucidate the role of Gpx1 in protection against different oxidative stressors and in different disease states and suggest that Gpx1 (-/-) mice may be valuable for studying the role of H2O2 in neurodegenerative disorders.

Effect of dietary antioxidants on puromycin aminonucleoside nephrotic syndrome

Several studies indicate the pathophysiological importance of reactive oxygen species in rats with nephrotic syndrome induced by puromycin aminonucleoside, an experimental model of the human minimal change disease. The role of reactive oxygen species in these rats was further evaluated, examining the effect of dietary deficiency and supplementation of antioxidants (vitamin E and selenium) on biochemical and renal ultrastructural alterations induced by puromycin aminonucleoside. Male Wistar rats, weaned at 3 weeks, were placed on diets normal, deficient or supplemented in vitamin E and selenium for 4 weeks. At the end of this period, rats were divided in two groups: control (sacrificed without any further treatment) and nephrotic (injected with puromycin aminonucleoside and sacrificed 7 and 22 days later). In control rats, the dietary deficiency or supplementation of antioxidants resulted in no significative differences in renal function, proteinuria or kidney ultrastructure. However, kidney lipoperoxidation, kidney glutathione peroxidase activity and circulating levels of vitamin E changed according to the amount of antioxidants in the diet. Seven days after the injection of puromycin aminonucleoside, rats fed normal, deficient or supplemented diets, developed nephrotic syndrome. However, proteinuria, hypoproteinemia, renal dysfunction and ultrastructural alterations were higher in rats fed a deficient diet. In contrast, proteinuria and kidney ultrastructural alterations were lower in rats fed a supplemented diet. Kidney lipoperoxidation and glutathione peroxidase activity increased on day 7 in rats fed a normal or a deficient diet, but not in rats fed a supplemented diet. This study shows that nephrotic syndrome induced by puromycin aminonucleoside in rats is modified by dietary antioxidants (vitamin E and selenium). Dietary supplementation ameliorates it and dietary deficiency exacerbates it.(ABSTRACT TRUNCATED AT 250 WORDS)

Transfection with human copper-zinc superoxide dismutase induces bidirectional alterations in other antioxidant enzymes, proteins, growth factor response, and paraquat resistance

Transfection of a pSV2 human copper-zinc superoxide dismutase expression vector into murine fibroblasts resulted in stable transgenic clones producing increased amounts of copper-zinc superoxide dismutase. Two classes of transfectants were observed and were characterized by the presence or absence of an increase in endogenous glutathione peroxidase activity. In addition, increases and decreases in individual clones in the activities of manganese superoxide dismutase, glutathione reductase, and NADPH-reductase were detected. In general, these alterations in enzyme activity correlated to the cellular glutathione peroxidase/copper-zinc superoxide dismutase ratio. Parameters of cellular physiological functions were also altered, including cell division time, FGF and EGF response, fibronectin content, paraquat resistance, hydrogen peroxide release into media, and sensitivity to radiation. Some of these cellular parameters were also bidirectional and reflected the cellular glutathione peroxidase/copper-zinc superoxide dismutase ratio. Our results indicate that small deviations from the normal physiological copper-zinc superoxide dismutase/seleno-glutathione peroxidase ratios can have pronounced effects on other antioxidant enzymes, growth rate, growth factor response, and expression of proteins normally not associated with oxygen metabolism.

Oxidative stress in a clonal cell line of neuronal origin: effects of antioxidant enzyme modulation

The effects of intracellularly generated H2O2 on cell viability, morphology, and biochemical markers of injury have been investigated in a clonal cell line of neuronal origin (140-3, mouse neuroblastoma X rat glioma) as a cell culture model for the role of oxidative stress in the long-term loss of neurons in the brain. The H2O2 was generated from the redox cycling of menadione, or by the oxidation of serotonin catalyzed by monoamine oxidase, to simulate the effect of amine neurotransmitter turnover. Incubation with menadione at concentrations as low as 10 microM for several hours resulted in significant losses of cell viability and altered morphology. Similar effects were evident in the presence of serotonin only after incubation overnight with concentrations > 1 mM. The cytotoxicity of either agent was potentiated by preincubation with specific inhibitors of two enzymes important to cellular antioxidant defenses, 3-amino-1,2,4-triazole for catalase and 1,3-bis(chloromethyl)-1-nitrosourea for glutathione reductase. Activity of another antioxidant enzyme of particular importance to antioxidant defenses in brain, the selenoprotein glutathione peroxidase, was stimulated fourfold by growth of cultures in the presence of sodium selenite as a source of active-site Se for the enzyme. The only effect of the selenite on other functionally coupled antioxidant enzymes was a decrease in activity of superoxide dismutase at concentrations > 200 nM. The selenite substantially protected cells against oxidative stress induced by combinations of menadione, 3-amino-1,2,4-triazole, and 1,3-bis(chloromethyl)-1-nitrosourea, but was only marginally effective with serotonin as a source of oxidative stress. The monoamine oxidase inhibitor pargyline increased cell survival in the presence of serotonin, demonstrating the role of this enzyme in its cytotoxicity. DNA damage (single strand breaks), but not lipid peroxidation, correlated with the cytotoxic effects of menadione.

The effects of vitamin E on tissue oxidation in nephrotoxic (anti-glomerular basement membrane) nephritis

The effects of vitamin E on tissue oxidation, kidney function and morphology were studied in rats with nephrotoxic nephritis (NTN). Thirty-six nephritic animals received no treatment (group 1), while 36 were treated with vitamin E (group 2). Twenty-four hours after the administration of anti-glomerular basement membrane antibody, sulfhydryl-containing renal protein was significantly lower in group 1 than in group 2 (0.70 +/- 0.16 and 1.08 +/- 0.06 mmol/100 g kidney tissue, respectively), suggesting a free oxygen radical scavenging effect of vitamin E in group 2. The difference was similar on day 14. The creatinine clearance was significantly lower in group 1 than in group 2 on day 1 (40 +/- 30 and 204 +/- 60 microliter/min per 100 g body weight, respectively). The protein excretion was initially high in both groups, but a significant decrease was detected in group 2 relative to group 1 on day 14 (25 +/- 18 and 92 +/- 38 mg/24 h, respectively). The morphological changes were less severe in group 2. Vitamin E treatment did not alter any of the above values significantly in healthy animals. The release of oxygen free radicals in NTN might play an important role in the pathogenesis, which can be influenced by free radical scavengers through changes in kidney function and morphology.

Cytotoxic effects of expression of human superoxide dismutase in bovine adrenocortical cells

Oxygen radicals and the cellular antioxidant enzymes may play a role in cellular senescence. We studied the feasibility of altering oxygen radical metabolism in a normal differentiated cell that undergoes senescence in culture by transfection of an expression vector containing human CuZn-SOD cDNA. Plasmid pRSV2-cSOD was constructed to contain the cDNA for human CuZn-SOD under the regulation of the Rous sarcoma virus long terminal repeat. Early passage cultures of bovine adrenocortical cells were cotransfected with pRSV2-cSOD and a plasmid (pSV3neo) allowing initial selection and continued growth of transfectants. Three passages after isolation of the polyclonal population, as cells grew to confluence, cultures showed focal cell death that spread outward to affect neighboring cells, so that by 72 h most cells had detached from the culture dish. Long term growth of the polyclonal population of transfectants without extensive cell death was achieved by continuous maintenance of low cell density during growth. Southern blot analysis of DNA from the pooled polyclonal population of transfected cells showed the presence of the expected 625 bp band from human CuZn-SOD. However, the intensity of this band indicated that only a minority of cells in the population had integrated the SOD plasmid, and DNA isolated from cells after 25 passages at low cell density showed plasmid sequences only of an altered form, suggesting that cells containing intact human SOD cDNA had been selectively lost from the population. When early passage low density transfectants were allowed to grow back to high cell density, cell death foci were again observed. Additionally, cell fusion with the formation of giant cells with massive multinucleation was observed by fluorescence microscopy after staining cultures with a DNA binding dye. In later stages of this process, the large nuclear mass in such a giant cell became fragmented as the cell detached from the dish and formed the center of a focus of cell death in the surrounding cells. Because cell death prevented the growth of large numbers of transfected cells, it was not possible to demonstrate the involvement of CuZn-SOD in the cytotoxic effect by direct means, but the control plasmid without the CuZn-SOD cDNA insert had no cytotoxic effect. Thus, the introduction of a vector for human CuZn-SOD in a normal differentiated cell caused a cytotoxic effect involving cell death, cell fusion, and nuclear fragmentation.

Cyclic AMP-mediated cytoskeletal effects in adrenal cells are modified by serum, insulin, insulin-like growth factor-I, and an antibody against urokinase plasminogen activator

In adrenocortical cells in culture, increased intracellular cyclic AMP resulting from exposure to agents such as ACTH and cholera toxin causes a change in cell morphology termed 'retraction' or 'rounding'. The breakdown of actin-containing stress fibers in rounding suggested a role for microfilaments in steroidogenesis. Previously, we showed that cultured bovine adrenal cells under standard conditions (medium with 10% fetal bovine serum) do not round in response to intracellular cyclic AMP. Here, we show that these cells do round in defined, serum-free medium. Rounding was maximal within 1 h of addition of 1 nM cholera toxin and after 10 h most cells remained rounded. Cycloheximide at 100 micrograms/ml did not inhibit the response to cholera toxin. The rounding response was abolished when 10% fetal bovine serum, horse serum, or ether-extracted fetal bovine serum was included in the medium. The inhibitory effect of serum was not mimicked by growth factors with the exception that insulin and insulin-like growth factor-I (IGF-I), while not preventing rounding, accelerated the return of cells to a flattened morphology. A monoclonal antibody against urokinase plasminogen activator completely prevented rounding whereas a monoclonal antibody against tissue plasminogen activator had only a slight effect. Fluorescence visualization of F-actin with N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)-phallacidin showed that rounding in cultured bovine adrenocortical cells resembles that defined earlier for human and rat adrenocortical cells and includes depolymerization of actin microfilaments. These cytoskeletal changes in adrenal cells are unlikely to play a role in steroidogenesis; however, they may be involved in tissue remodeling occurring as part of the indirect mitogenic effects of ACTH.

Antioxidant enzymatic activities and resistance to oxidative stress in primary and subcultured rat astroglial cells

The survival of neural tissues depends in part on the balance between the formation of free radicals due to oxidative metabolism and the transformation of the free radicals to non-toxic compounds. Serial subculture of rat glial cells as described here resulted in a decrease of the specific activities of several antioxidant enzymes and a glial specific marker for astrocytes. Thus, there was an increased susceptibility to oxidative stress in cultures by the third passage. These subcultured glial cell cultures may represent a useful model for the study of free radical induced neural damage that may be relevant to CNS trauma and aging.

Replicative senescence and differentiated gene expression in cultured adrenocortical cells

We have used a differentiated endocrine cell type, the adrenocortical cell, to investigate the interrelationship of senescence and differentiation, the effects of the environment on differentiated gene expression, and the interrelationship of differentiated gene expression and proliferation. In bovine adrenocortical cells, expression of some differentiated functions is maintained to very late points in the replicative life span, whereas expression of others is lost at various times prior to senescence. There is clonal variation in the rate and extent of loss of functions. For steroid 17 alpha-hydroxylase, in situ hybridization shows that the observed decline in induction of 17 alpha-hydroxylase mRNA during senescence results from a decline in the fraction of cells expression the gene. Descendants of expressing cells in the primary cell population randomly become nonexpressing. Among clones there is a correlation between the fraction of cells expressing the gene and remaining replicative potential, although several experiments show no direct mechanism linking replicative senescence and 17 alpha-hydroxylase expression. Transfection with SV40 early region genes also dissociates the decline in growth and the change in 17 alpha-hydroxylase expression. SV40 T antigen selectively affects growth; expression of 17 alpha-hydroxylase is stabilized either in the on state, when cells are transfected early in the culture life span, or in the off state, when senescent cells are transfected. Thus, although the switching off of 17 alpha-hydroxylase expression and the loss of replicative potential are independent events, the switching process requires DNA replication. Because the switch is irreversible, changes in replicative potential occurring after the switch-off event do not affect the state of expression of the switched-off gene. Changes in differentiated cell properties and changes in replicative potential may be two facets of a general phenomenon of stochastic changes in gene expression in normal cells during senescence.

Role of superoxide in endothelial-cell modification of low-density lipoproteins

Cultured endothelial cells and arterial smooth muscle cells have been shown to modify LDL in a way that leads to rapid uptake by macrophages. Previous studies have demonstrated that this modification involves free radical peroxidation of LDL, and that the role of the cells was to accelerate oxidation under conditions where it otherwise would occur slowly. The objective of the present study was to determine whether the modification was mediated by oxygen-derived free radicals, and whether the ability of a given cell type of line to modify LDL was related to its secretion rate of O2- or H2O2. The results showed that modification required the presence of oxygen, and could be specifically inhibited by superoxide dismutase but not by catalase or by mannitol, a hydroxyl radical scavenger. Rabbit aortic endothelial cells, rabbit arterial smooth muscle cells, monkey arterial smooth muscle cells and human skin fibroblasts were all found to modify LDL, and all of these cell types generated more O2- (superoxide dismutase-inhibitable cytochrome c reduction) than a line of bovine aortic endothelial cells that did not modify LDL. The content of superoxide dismutase and catalase was higher in bovine aortic endothelial cells than in the cell lines that modified LDL, but glutathione peroxidase levels were not different. It was concluded that cells that were capable of modifying LDL produced superoxide or a substance that could be converted to superoxide in the medium, and that superoxide was an important, though possibly indirect, mediator of the modification of LDL by cells.

Strategies and criteria for the development of molecular biomarkers of senescence

While it may be possible to employ panels of molecular parameters which correlate with senescence in vivo or in vitro, in a manner analogous to the use of mutagenesis assays for economic carcinogen screening, such an endeavor would at present be impeded by the absence of a clear mechanistic rationale for focusing on particular biomarkers, and by the complexity of the senescent phenotype and its multilevel interactions. Nevertheless, insight into the mechanism(s) of senescence may derive indirectly from correlative studies, or directly from strategies of molecular intervention, provided that such studies meet reasonable criteria for relevance and functionality. Even the control of expression of a single gene may be quite complex, with multigenic interactions and the potential to produce a cascade affecting many downstream genes. In order to understand such processes, functional assays and selective systems will need to be developed.

Clonal growth and culture life span of bovine adrenocortical cells in a serum-free medium

The life span and growth from clonal density of bovine adrenocortical cell cultures were studied in serum-supplemented medium and a serum-free defined medium, which supported sustained cell proliferation and steroid production. The total culture life span was 79 population doublings in serum-supplemented medium with fibroblast growth factor (FGF) and 36 population doublings in the defined medium without serum. Older passage cell cultures grown in the defined medium progressively lost the ability to produce 11 beta- and 21-hydroxylated steroids, which was observed previously for cultures in serum-supplemented medium, and also had a decline of 17 alpha-hydroxylated steroid production. The cloning efficiency in the defined medium was 12.2% as compared to 24% in serum-supplemented medium with FGF. Five isolated clonal cell lines grown in the defined medium were characterized for steroid function in response to steroidogenic agents. All five clonal cell lines had stimulated steroid production with 8-bromo-cAMP, but only four of the clonal lines were stimulated also by adrenocorticotropin. None of the clonal cell lines produced 11 beta-, 21- or 17 alpha-hydroxylated steroids in response to treatment with either steroidogenic agent, results that were similar to data obtained from older mass cultures. The apparent deficiency of the defined medium as compared to serum-supplemented medium for maximum support of the culture life span and cloning efficiency may be useful in studies of cellular aging and its relation to differentiated function for this cell culture system.

Oxidative damage to DNA and replicative lifespan in cultured adrenocortical cells

Oxidative damage to DNA in cultured bovine adrenocortical cells was investigated by exposing cells to a sublethal concentration (10 microM) of cumene hydroperoxide under conditions previously shown to be deficient in the biological antioxidants selenium and alpha-tocopherol (vitamin E). DNA prepared from cells incubated for 4 h with 10 microM cumene hydroperoxide had a greater fraction showing resistance to S1 nuclease after denaturation and reassociation to a log C0t of -3. Cross-linking by cumene hydroperoxide was abolished in cells that had been grown in the presence of 20 nM selenite or 1 microM alpha-tocopherol for 96 h prior to peroxide addition, whereas such cells remained susceptible to cross-linking by nitrogen mustard. Extensive strand breaks in DNA from peroxide-treated cells as assessed by alkaline sucrose gradient centrifugation were greatly reduced in cells grown in selenite or alpha-tocopherol. Despite the evidence of damage to DNA, cumene hydroperoxide was not detectably mutagenic, in contrast to 5 microM methylnitronitrosoguanidine (MNNG), when assessed as the incidence of resistance to 25 microM ouabain. We confirmed that cumene hydroperoxide at greater than 10 microM lowers cloning efficiency and that this is largely prevented by selenite or alpha-tocopherol. Additionally, selenite or alpha-tocopherol produced increased clonogenicity in cells not incubated with peroxide. To examine effects of the biological antioxidants on replicative lifespan, cells were grown continuously in fetal bovine serum (FBS), fibroblast growth factor (FGF), and selenite or alpha-tocopherol. Selenium increased replicative lifespan by 10-20% and alpha-tocopherol by 22-30%. Levels of DNA cross-links and strand breaks did not differ under any circumstances between early (second) passage and late (30th) passage cells. The experiments on replicative potential were all performed in the presence of FGF. When FGF was omitted from the culture medium, replicative lifespan was reduced by 85%. We conclude that types of damage to DNA resulting from peroxide exposure are not present in cells under standard culture conditions at early or late stages of the lifespan. Other work has noted a relationship between clonogenicity and replicative lifespan; thus, the increase in cloning efficiency seen with selenium and alpha-tocopherol may cause the observed slight increase in replicative lifespan. Oxidative damage does not appear to be a major determinant of cellular senescence in adrenocortical cells.

Kidney glomerular explants in serum-free media: role of individual medium components in cell outgrowth

Guinea pig glomeruli were grown for 22 days in a serum-free medium composed of Waymouth's MB 752/1 supplemented with sodium pyruvate, nonessential amino acids, and antibiotics. To this basic medium was added insulin, transferrin, selenium (Se), tri-iodothyronine, or fibronectin (FN) - either singly, or in various combinations - and sequential quantitative studies of the glomerular outgrowths were performed. Total cells in glomerular outgrowths, mitotic index, and glomerular attachment rate were determined and compared with values for glomerular outgrowths in media containing either no additions or all of the above components. FN was required for whole glomerular attachment, while transferrin plus FN was required for mitosis in glomerular cell outgrowths. Insulin and tri-iodothyronine slightly increased glomerular cell outgrowth by slightly increasing whole glomerular attachment, but had little effect on mitosis in glomerular outgrowths. The effect of Se was complex. Se did not affect whole glomerular attachment or mitosis in the presence of transferrin plus FN. However, in a medium containing transferrin, FN, and 3-amino-1,2,4-triazole (AT) (an inhibitor of catalase and glutathione peroxidase), Se increased total cell number but had little effect on the glomerular attachment rate or the mitotic index. Morphologic analysis of glomeruli early in culture suggested that Se may act by decreasing the amount of or delaying the time of cell death. In all of the media tested, total DNA was relatively constant over the course of 22 days, suggesting the possibility that glomerular cells cultured in a serum-free medium are part of a cell renewal system.

Interaction of bovine renal mitochondrial cytochrome P-450 with antioxidants

The antioxidants butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), nordihydroguiaretic acid (NDGA), benzyl sulfoxide (BS), ferulic acid (FA), caffeic acid (CA), dimethyl sulfoxide (Me2SO), protocatechuic acid (PCA), and P-450 inhibitor metyrapone all acted to slow the previously noted loss of vitamin D3 1 alpha-and 24-hydroxylase activities in cultured bovine proximal tubule cells. The slowing of the loss of hydroxylase activities by antioxidants was increased by culturing cells in 5% O2 vs 19% O2. These same antioxidants also directly inhibited 1 alpha- and 24-hydroxylase activities. For a single antioxidant, or metyrapone, Ki's for inhibition of both hydroxylases were equal, ED50's for stabilization of both hydroxylase activities were equal, and Ki's and ED50's were not significantly different. These antioxidants prevented tert-butylhydroperoxide (tert-BOOH)-mediated proximal tubule cell death at concentrations, i.e., 0.1 mM, which were effective in stabilizing hydroxylase activities. When added together, the antioxidants H2SeO3, uric acid, and trolox c gave slight stabilization of hydroxylase activities without inhibiting hydroxylase activities. Singly, these antioxidants did not stabilize or directly inhibit hydroxylase activities. This antioxidant combination augmented BHA- or BHT-mediated stabilization of both hydroxylase activities independent of any effects on inhibition. But the most potent antioxidants which acted to stabilize hydroxylase activities in culture also directly acted to inhibit hydroxylase activities. Antioxidant effects were additive for both inhibition and stabilization of hydroxylase activities. Stabilization of hydroxylase activities was dissociated from inhibition in the presence of maximal FA, CA, and BHA or FA, CA, and BHT combinations. Bovine renal mitochondrial cytochrome P-450 levels decreased in cultured bovine proximal tubule cells to nondetectable levels by 8 days in culture. When cultures were treated with BHA and BS, mitochondrial P-450 levels were almost twofold greater than in untreated controls. Percentage changes in mitochondrial P-450 levels closely paralleled percentage changes in hydroxylase activities elicited by antioxidant treatment regimes. Antioxidants which were effective inhibitors of hydroxylase activities in cultured bovine proximal tubule cells were also effective in inhibiting hydroxylase activities in isolated proximal tubule mitochondria, supplemented with a NADPH-generating source. Ki's for inhibition of hydroxylase activities were very similar in cultured cells and in isolated mitochondria.(ABSTRACT TRUNCATED AT 400 WORDS)

Cytochrome P-450/pseudosubstrate interactions and the role of antioxidants in the adrenal cortex

The adrenal cortex is the site of the synthesis of the steroid hormones such as the glucocorticoid cortisol and the mineralocorticoid aldosterone. The pathway of biosynthesis of these steroids from cholesterol involves a sequence of transformations using cytochrome P-450 enzymes. The hypothesis presented here is that damage to cytochrome P-450 enzymes on interaction with certain steroids, synthesized by the adrenal cortex itself, may be of pathological and perhaps physiological importance. The interaction between cytochrome P-450 enzymes and these steroids, which act as pseudosubstrates, may form part of the pathogenesis of some steroidogenic enzyme deficiencies, with consequent overproduction of precursor steroids, leading to mineralocorticoid or androgen excess. This interaction is dependent on achieving high concentrations of the pseudosubstrate steroids in the adrenal cortex, which probably occurs as a result of the arrangement of the vasculature in the adrenal gland. High concentrations of steroids may be expected to accumulate in steroidogenic cells, both in culture and in vivo, and may have autoregulating effects. The high content of antioxidant compounds in the adrenal cortex, principally ascorbate, may serve to protect cytochrome P-450 enzymes from the damaging effects of oxygen radical species formed as a result of cytochrome P-450/pseudosubstrate interactions.

Antioxidant enzyme content of pulmonary artery endothelial cells: effects of subculture

The activities of glutathione peroxidase, superoxide dismutase and catalase, enzymes which play a critical role in protection of the vascular endothelium from oxygen free-radical injury, were determined in large vessel endothelial cells obtained under three different growth conditions: from freshly isolated from bovine pulmonary arteries, in the first (primary) subculture and after six serial subcultures (6.5 population doublings). The endothelium was obtained by mechanically scraping the vascular lumen. Endothelial cell monolayers were detached mechanically from the substratum prior to passage. No proteolytic enzymes were used in either procedure. The activities of catalase, superoxide dismutase and glutathione peroxidase determined in freshly isolated endothelial cells were, respectively, 39.9 +/- 10.3, 2.2 +/- 0.8 and 3.0 +/- 0.5 X 10(2) units per mg protein. After primary culture there was no change in superoxide dismutase activity, but a significant decrease in glutathione peroxidase activity to 1.4 +/- 0.4 X 10(2) was observed, and catalase activity dropped significantly to 18.6 +/- 5.0 units per mg protein. After 6.5 population doublings, the activity of all three enzymes returned to values similar to those of the freshly isolated cells. A fourfold increase in the protein to DNA ratio occurred in cells in primary culture and was maintained in sixth-passage cells. This increase in endothelial cell size upon culture was reflected in the electron microscopic evidence of cellular hypertrophy. Measurement of the rate of transport of 5-hydroxytryptamine by endothelial cell monolayers revealed a substantial loss upon multiple passage. Transport in the sixth-passage cells was decreased to one-half the rate of primary cells.(ABSTRACT TRUNCATED AT 250 WORDS)