Influence of selenium on glutathione and some associated enzymes in rats with mammary tumor induced by 7,12-Dimethylbenz(a)anthracene

Biologic and pharmacologic regulation of mammalian glutathione synthesis.

Abstract: Glutathione (L-gamma-glutamyl-L-cysteinylglycine, GSH) is synthesized from its constituent amino acids by the sequential action of gamma-glutamylcysteine synthetase (gamma-GCS) and GSH synthetase. The intracellular GSH concentration, typically 1-8 mM, reflects a dynamic balance between the rate of GSH synthesis and the combined rate of GSH consumption within the cell and loss through efflux. The gamma-GCS reaction is rate limiting for GSH synthesis, and regulation of gamma-GCS expression and activity is critical for GSH homeostasis. Transcription of the gamma-GCS subunit genes is controlled by a variety of factors through mechanisms that are not yet fully elucidated. Glutathione synthesis is also modulated by the availability of gamma-GCS substrates, primarily L-cysteine, by feedback inhibition of gamma-GCS by GSH, and by covalent inhibition of gamma-GCS by phosphorylation or nitrosation. Because GSH plays a critical role in cellular defenses against electrophiles, oxidative stress and nitrosating species, pharmacologic manipulation of GSH synthesis has received much attention. Administration of L-cysteine precursors and other strategies allow GSH levels to be maintained under conditions that would otherwise result in GSH depletion and cytotoxicity. Conversely, inhibitors of gamma-GCS have been used to deplete GSH as a strategy for increasing the sensitivity of tumors and parasites to certain therapeutic interventions.

Estrogen receptor-mediated regulation of oxidative stress and DNA damage in breast cancer

Abstract: Estrogens have been implicated to be complete carcinogens in breast and gynecologic tissues. Possible mechanisms may include differential metabolism with subsequent formation of reactive oxygen species and/or a receptor-mediated pathway, which may also involve indirect modulation of intracellular redox state. Estrogen-mediated oxidative DNA damage in mammary gland epithelia includes the induction of 8-oxo-2'-deoxyguanosine, both in vitro and in vivo, thereby suggesting a role for oxidative stress in the initiation and/or progression of breast neoplasia. In order to study this phenomenon, we have treated estrogen receptor alpha (ER-alpha)-positive MCF-7 cells and ER-alpha-negative MDA-MB-231 cells with 10 nM 17beta-estradiol (E2), while measuring changes in antioxidant status and sensitivity to DNA damage by peroxide. Treatment of MCF-7 cells with E2 resulted in a marked decrease in the ability for these cells to metabolize peroxide, which paralleled a decrease in catalase activity and total glutathione levels. These observations also correlated with an increased sensitivity to peroxide-induced DNA damage. The estrogen-induced effects were all opposed by the anti-estrogen tamoxifen. In addition, the estrogen-mediated down regulation of peroxide metabolism, catalase activity, and sensitivity to DNA damage were not observed in the MDA-MB-231 cell line. Treatment of MCF-7 cells with E2 also resulted in increased glutathione peroxidase, superoxide dismutases (I) and (II) and glucose-6-phosphate dehydrogenase activities. Therefore, in this breast cancer model antioxidant status is modulated through the actions of the ER. The data may explain some of the estrogen-induced pro-oxidant effects previously reported in vivo. In addition, this is the first report indicating that E2 is capable of inducing an increase in sensitivity to oxidative DNA damage through an ER-mediated mechanism.

Toxicological profile for selenium

Abstract: SELENIUM ii DISCLAIMER The use of company or product name(s) is for identification only and does not imply endorsement by the Agency for Toxic Substances and Disease Registry. A Toxicological Profile for selenium, Draft for Public Comment was released in September, 2001. This edition supersedes any previously released draft or final profile. Toxicological profiles are revised and republished as necessary, but no less than once every three years. For information regarding the update status of previously released profiles, contact ATSDR at: Toxicological Profiles are a unique compilation of toxicological information on a given hazardous substance. Each profile reflects a comprehensive and extensive evaluation, summary, and interpretation of available toxicologic and epidemiologic information on a substance. Health care providers treating patients potentially exposed to hazardous substances will find the following information helpful for fast answers to often-asked questions. Chapter 1: Public Health Statement: The Public Health Statement can be a useful tool for educating patients about possible exposure to a hazardous substance. It explains a substance's relevant toxicologic properties in a nontechnical, question-and-answer format, and it includes a review of the general health effects observed following exposure. Chapter 3: Health Effects: Specific health effects of a given hazardous compound are reported by type of health effect (death, systemic, immunologic, reproductive), by route of exposure, and by length of exposure (acute, intermediate, and chronic). In addition, both human and animal studies are reported in this section. NOTE: Not all health effects reported in this section are necessarily observed in the clinical setting. Please refer to the Public Health Statement to identify general health effects observed following exposure. The following additional material can be ordered through the ATSDR Information Center: Case Studies in Environmental Medicine: Taking an Exposure History—The importance of taking an exposure history and how to conduct one are described, and an example of a thorough exposure history is provided. Other case studies of interest include Reproductive and Developmental Hazards; Skin Lesions and Environmental Exposures; Cholinesterase-Inhibiting Pesticide Toxicity; and numerous chemical-specific case studies. SELENIUM viii Managing Hazardous Materials Incidents is a three-volume set of recommendations for on-scene (prehospital) and hospital medical management of patients exposed during a hazardous materials incident. Volumes I and II are planning guides to assist first responders and hospital emergency department personnel in planning for incidents that involve hazardous materials. Volume III— Medical Management Guidelines for Acute Chemical Exposures—is a guide for health care professionals treating patients …

Oxidant and antioxidant activity changes in patients with oral cancer and treated with radiotherapy

Abstract: Of all the clinical disciplines, radiotherapy probably has the most secure and scientific foundations. In oral cancer, radiotherapy may be used as the sole treatment or in combination with other modalities of treatment. Blood samples were collected from stage III oral cancer patients attending the Oncology Department, Bernard Institute of Radiation and Oncology, Chennai Medical College, Chennai, India, before initiating radiotherapy and after the sixth week of radiotherapy. The effect of radiation on oral cancer patients has been studied using activities of superoxide dismutase (SOD), catalase, glutathione peroxidase (GPX), glutathione reductase (GR), glutathione-S-transferase (GST), glucose-6-phosphate dehydrogenase (G6PDH) and levels of malondialdehyde (MDA). The levels of MDA showed a significant increase in untreated and radiation oral cancer patients when compared with normal subjects. The activities of red blood cell (RBC) hemolysate antioxidant enzymes such as SOD, catalase, GPX, GR, GST and G6PDH showed a significant decrease, representing the lack of antioxidant defense. Radiation induces lipid peroxidation by inactivating the antioxidant enzymes, thereby rendering the system inefficient in management of the free radical attack. Thus, the degree of radiation affects the extent of the depression of the antioxidant enzyme activities and increases lipid peroxidation.

Protein Measurement with the Folin Phenol Reagent

Abstract: Since 1922 when Wu proposed the use of the Folin phenol reagent for the measurement of proteins, a number of modified analytical procedures utilizing this reagent have been reported for the determination of proteins in serum, in antigen-antibody precipitates, and in insulin. Although the reagent would seem to be recommended by its great sensitivity and the simplicity of procedure possible with its use, it has not found great favor for general biochemical purposes. In the belief that this reagent, nevertheless, has considerable merit for certain application, but that its peculiarities and limitations need to be understood for its fullest exploitation, it has been studied with regard to effects of variations in pH, time of reaction, and concentration of reactants, permissible levels of reagents commonly used in handling proteins, and interfering substances. Procedures are described for measuring protein in solution or after precipitation with acids or other agents, and for the determination of as little as 0.2 gamma of protein.

Selenium: Biochemical Role as a Component of Glutathione Peroxidase

Abstract: When hemolyzates from erythrocytes of selenium-deficient rats were incubated in vitro in the presence of ascorbate or H(2)O(2), added glutathione failed to protect the hemoglobin from oxidative damage. This occurred because the erythrocytes were practically devoid of glutathione-peroxidase activity. Extensively purified preparations of glutathione peroxidase contained a large part of the (75)Se of erythrocytes labeled in vivo. Many of the nutritional effects of selenium can be explained by its role in glutathione peroxidase.

Enzymic method for quantitative determination of nanogram amounts of total and oxidized glutathione: Applications to mammalian blood and other tissues

Abstract: A method for the analysis of nanogram quantities of glutathione has been developed which is based on the catalytic action of GSH or GSSG in the reduction of Ellman reagent (DTNB) by a mixture of TPNH and yeast glutathione reductase. Unlike previous methods of analysis the procedure described here effectively measures the total glutathione (GSH + GSSG) content of unknown mixtures and is not subject to appreciable interference by the presence of other thiol components. It is suggested that the catalytic action of glutathione in this system resides in the continual enzymic regeneration of GSH, present initially or formed enzymically from GSSG, following its interaction with the sulfhydryl reagent. The sensitivity of the method is such as to permit the determination of total glutathione in extracellular tissue fluids such as plasma, saliva, and urine normally containing very low levels of this material, essentially without pretreatment of the sample. The same is true for glutathione determinations of whole blood, in which the preliminary procedure is confined to the preparation of a 1:100 hemolyzate from as little as 10 μl of sample. Following published procedures, the pretreatment of tissue extracts with NEM to form an enzymically inactive complex with free GSH allowed the determination of the low levels of oxidized glutathione normally present therein. The use of the foregoing analytical method in the determination of total and oxidized glutathione contents of rat blood, kidney, and liver gave values in good agreement with those obtained by previous investigators.