Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: DrugBank:EXPT00568 (ascorbate)
 23,072 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ascorbate was found to inhibit oxidation of oxyhaemoglobin and Heinz body formation in glucose-6-phosphate dehydrogenase deficient red cells incubated with acetylphenylhydrazine. It is proposed that ascorbate can substitute for the glutathione which is depleted and act as a scavenger for drug free radicals generated during the reaction. Ascorbate was protective at concentrations only a little higher than that in normal blood, and the possibility that administration of ascorbate could protect GSH deficient cells against the action of oxidative drugs such as APH is considered. A simple method of quantitatively assessing Heinz body formation by measuring the turbidity of the lysed cells is described.
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PMID:Protection by ascorbate against acetylphenylhydrazine-induced Heinz body formation in glucose-6-phosphate dehydrogenase deficient erythrocytes. 42 33

Patients receiving BCNU [1,3-bis(2 chloroethyl)-1-nitrosourea] acquire a profound deficiency of erythrocytic oxidized glutathione reductase (GSSG-R) within minutes after the first intravenous injection of a single therapeutic dose (75 mg/M.2) of the drug. This effect is not accompanied by changes in the activites of 19 additional erythrocytic enzymes tested, is reproducible in vitro in a dose-related manner, and is not caused by the antitumor agents administered concurrently with the nitrosourea. The inactivation of erythrocytic GSSG-R results in decreased levels of reduced glutathione (GSH), marked GSH instability and disturbed hydrogen peroxide removal with a positibe ascorbate cyanide test and leads to increased susceptibility to oxidative hemolysis, particularly in glucose-6-phosphate dehydrogenase (G-6-D)-deficient patients. BCNU inhibits GSSG-R irreversibly, probably through alkylation rather than carbamylation, and the reappearance of enzyme activity in vivo after each chemotherapy pulse depends on the capacity of the marrow to release erythrocytes with normal activity formed during the drug-free interval. BCNU inhibits GSSG-R not only in erythrocytes but also in human leukocytes and platelets, as well as in yeast, monkey erythrocytes, and all the organs tested in the mouse. This generalized, severe, and specific GSSG-R deficiency caused by therapeutic doses of BCNU may enhance or mediate the toxic and antitumor effects of the nitrosourea and provides a simple yet sensitive biochemical means of monitoring bone marrow reserve in patients receiving multiple courses of chemotherapy with this agent.
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PMID:Severe generalized glutathione reductase deficiency after antitumor chemotherapy with BCNU" [1,3-bis(chloroethyl)-1-nitrosourea]. 87 May 69

Human spermatozoa contain appreciable amounts of intracellular glutathione, which has a protective function against peroxidative degradation of spermatozoal polyunsaturated fatty acids by the NADPH-dependent glutathione peroxidase/reductase enzymatic system. The glutathione system provides a basic defense against peroxidative damage, without which the superoxide dismutase system would dominate. Since oxidative damage is said to include enzyme leakage and changes in metabolism, cytochrome oxidase and lactate dehydrogenase activities were used as indicators of the energy metabolism in unwashed and washed human spermatozoa during lipid peroxidation. Lipid peroxidation was induced by aerobic incubation of sperms in the presence of sodium ascorbate and ferrous sulphate. In addition, since NADPH concentrations influence the concentration of reduced glutathione, we studied glucose-6-phosphate dehydrogenase activity as an indicator of pentose phosphate shunt activity, the main source of NADPH. Microdensitometric measurements of the three enzymes were made by a Vickers M85a scanning microdensitometer. We found that the lipid peroxidation process greatly affects the 3 enzymatic activities examined and that seminal plasma protects against the extensive deleterious effects of lipid peroxidation.
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PMID:Cytophotometric assay of cytochrome oxidase, lactate dehydrogenase and glucose-6-phosphate dehydrogenase activities in human peroxidized spermatozoa. 133 42

We treated leaves of winter wheat (Triticum aestivum L.) with cold, paraquat, or 3-amino-1,2,4-triazole and compared the responses. We assayed the activities of glucose-6-phosphate dehydrogenase, catalase, dehydroascorbate reductase and ascorbate free radical reductase and levels of hydrogen peroxide, glucose-6-phosphate, fructose-6-phosphate, ascorbate, dehydroascorbate, reduced and oxidized glutathione. With any of the three treatments, contents of cellular peroxides and hexose phosphates were raised. The content of ascorbate was lowered markedly by paraquat treatment, which produces active oxygen species, whereas such a decrease did not occur in other two treatments. When the plants were treated with 3-amino-1,2,4-triazole, which is a specific inhibitor of catalase, the content of oxidized glutathione increased severalfold. The glucose-6-phosphate dehydrogenase activity increased with all three treatments, but it decreased after glyphosate treatment, which does not stimulate the formation of peroxides. The activities of catalase and dehydroascorbate reductase were increased by the treatment of cold and paraquat, while 3-amino-1,2,4-triazole did not affect the dehydroascorbate reductase activity. The activity of ascorbate free radical reductase increased after treatment by paraquat only.
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PMID:Metabolic response to treatment with cold, paraquat, or 3-amino-1,2,4-triazole in leaves of winter wheat. 136 90

The effect of methionine or citrate on antioxidant defense system has been studied in urolithic rat. Liver weight and its protein concentration did not change in the rats fed with calculi producing diet (CPD) when compared to normal diet fed rats. Feeding rats along with citrate (c-CPD) or methionine (m-CPD) improved their body weight gain. Liver microsomes and mitochondria fractions of CPD and c-CPD fed groups showed increased susceptibility for lipid peroxidation in presence of ascorbate and t-butyl hydroperoxide when compared to either control or m-CPD fed groups. Increased superoxide dismutase and xanthine oxidase activities, decreased catalase, glutathione peroxidase and glucose-6-phosphate dehydrogenase activities, decreased concentrations of reduced glutathione, total thiols, ascorbic acid and vitamin-E and increased formation of hydroxyl radical, hydroperoxides and diene conjugates were observed in the liver of both CPD fed group as well as c-CPD fed group. Except SOD and xanthine oxidase, all other parameters were normalized in m-CPD fed group. This suggested that feeding methionine reduced the susceptibility for lipid peroxidation by restoration of the level of free radical scavengers.
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PMID:Restoration of antioxidants in liver by methionine feeding in experimental rat urolithiasis. 142 65

Correlation between rates of oxidative and non-oxidative steps of the pentose phosphate pathway and vitamin C concentration was studied in experimental diffuse impairment of connective tissue. As compared with transketolase, activity of glucose-6-phosphate dehydrogenase was more closely dependent on concentration of ascorbic acid. Content of vitamin C was considerably altered in tissues thus demonstrating profound deterioration of vitamin C metabolism under these conditions. Simultaneous impairment of the pentose phosphate pathway primary steps and of vitamin C metabolism appear to be responsible for initiation of the diffuse injury of the connective tissue.
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PMID:[Dependence of the initial stages of the pentose phosphate cycle on vitamin C metabolism in connective tissue pathology]. 149 96

Oxidative inactivation of various key enzymes and alpha-1-proteinase inhibitor (alpha-1-PI) was studied by treatment with N-chloramines and the metal-catalyzed oxidation (MCO)-systems ascorbate/Fe(III) and ascorbate/Cu(II). Chlorinated amines completely inhibited alpha-1-PI, fructose-1,6-bis phosphatase (Fru-P2ase) and glyceraldehyde phosphate dehydrogenase (GAPD) at a low molar excess, and glucose-6-phosphate dehydrogenase (G6PD) at a high molar excess, but did not impair beta-N-acetylglucosaminidase (beta-NAG), alkaline phosphatase (AP) or lactate dehydrogenase (LDH). MCO-systems affected the activities of Fru-P2ase, GAPD, AP, LDH and G6PD, but not those of beta-NAG or alpha-1-PI. EDTA prevented inactivation of Fru-P2ase, G6PD and LDH by ascorbate/Cu(II) and of Fru-P2ase by ascorbate/Fe(III) suggesting a site-specific oxidation catalyzed by a protein-bound metal ion. In conclusion, N-chloramines and MCO-systems exhibited different properties with regard to oxidative inactivation, sulfhydryl-enzymes were susceptible to both systems, but other enzymes were only susceptible to one or neither system.
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PMID:Inactivation of enzymes and an enzyme inhibitor by oxidative modification with chlorinated amines and metal-catalyzed oxidation systems. 183 66

We have used 1,3-bis(2-chloroethyl)-1-nitrosourea, a selective inhibitor of oxidized glutathione reductase (GSSG-R), to examine the role of this enzyme in regulating the hexose monophosphate shunt (HMS) and to explore how a variety of agents influence glucose decarboxylation in intact human red blood cells (RBCs). Substances tested included primaquine and several other drugs that are specially hemolytic and methemoglobinemic in glucose-6-phosphate dehydrogenase (G6PD) deficiency and related disorders. The results allowed us to distinguish and quantitate contrasting modes of HMS stimulation and to clarify how RBCs respond to different classes of oxidants. Some agents like methylene blue (MB), phenazine methosulfate, and pyrroline carboxylate do not require GSSG-R to increase CO2 production; they activate G6PD and 6-phosphogluconic dehydrogenase by directly oxidizing reduced nicotinamide adenine dinucleotide phosphate (NADPH) to oxidized nicotinamide adenine dinucleotide phosphate (NADP). Other compounds, like ascorbate, nitrofurantoin, and doxorubicin, oxidize GSH primarily; CO2 increases indirectly only when GSSG-R, activated by glutathione disulfide (GSSG), raises the level of NADP. Chemicals like primaquine, daunorubicin, and methylphenylazoformate trigger the HMS by independently oxidizing both NADPH and GSH. Unlike MB, most drugs that are hemolytic in G6PD deficiency activate the HMS in a manner that depends to a variable extent on GSSG-R. This variability may explain hitherto puzzling clinical and pharmacogenetic differences between primaquine and diaminodiphenylsulfone-induced hemolysis.
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PMID:Defenses against oxidation in human erythrocytes: role of glutathione reductase in the activation of glucose decarboxylation by hemolytic drugs. 190 43

Nitroxides were used as models of persistent free radicals to study the antioxidant function of ascorbic acid in the human erythrocyte. It was concluded that: 1) ascorbate and other reductant(s) derived from dehydroascorbic acid (DHA) in the presence of thiols are the only significant reducing agents for nitroxides, 2) glutathione and DHA reduce nitroxides by a process that cannot be inhibited by ascorbic acid oxidase, 3) erythrocytes can be depleted of ascorbic acid by exhaustive washing in the presence of membrane-permeable cationic nitroxides such as N,N-dimethylamino-Tempo, 4) ascorbate-depleted cells do not reduce nitroxides; however, nitroxide reduction is restored when the cells are incubated with DHA, 5) reduction of nitroxides in ascorbate-depleted, DHA-treated cells is significantly faster than in buffered solutions of DHA and glutathione, 6) several equivalents of nitroxide are reduced relative to the intracellular ascorbate pool, 7) sustained nitroxide reduction is observed even when most of the intracellular ascorbate is oxidized, 8) spin trapping of oxyradicals in tert-butyl hydroperoxide-treated cells is accelerated with ascorbate depletion and inhibited with ascorbate loading, 9) ascorbate can be quantified within intact cells by analyzing the initial reduction rates of membrane-permeable cationic nitroxides, and 10) DHA-stimulated reduction of cationic nitroxides is slower and less extensive in erythrocytes deficient in glucose-6-phosphate dehydrogenase than in normal erythrocytes.
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PMID:Ascorbate- and dehydroascorbic acid-mediated reduction of free radicals in the human erythrocyte. 199 52

Despite similar vitamin E contents, erythrocytes of smokers have an increased tendency (P less than 0.01) to peroxidize in vitro compared with those of nonsmokers. This difference is abolished by vitamin E supplementation (1000 mg alpha-tocopherol acetate/d for 14 d). The increased susceptibility to erythrocyte peroxidation in the smokers may reflect lower glucose-6-phosphate dehydrogenase (P less than 0.02) and glutathione peroxidase (P less than 0.05) activities. Smokers seem to be under a sustained oxidant stress with increased plasma-conjugated dienes (P less than 0.01) and dehydroascorbate (P less than 0.05) and decreased ascorbate (P less than 0.06) concentrations. Additionally, plasma ceruloplasmin in smokers is elevated (P less than 0.01), consistent with an acute-stress response. Plasma total cholesterol is similar in smokers and nonsmokers and is unaffected by vitamin E supplementation. Indices of sustained oxidant stress in smokers are partially ameliorated by vitamin E supplementation.
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PMID:Effects of smoking and vitamin E on blood antioxidant status. 201 19


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