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)

A cell fraction containing small hepatocytes and nonparenchymal cells was isolated from the adult rat liver and was cultured in the presence of vitamin C. epidermal growth factor, nicotinamide, and dimethylsulfoxide. All of the small hepatocytes that had attached to a dish expressed hepatocytic phenotypes such as albumin, transferrin, and cytokeratin (CK)8 and CK18 but not biliary markers such as BD1, CK7, and CK19. Single hepatocytes started to proliferate and grew into colonies. The growth potential was variable among the cells, the highest case being that a single cell produced a colony containing over 100 cells in 10 days. The hepatocytes in the colony developed through a proliferation phase and then a differentiation phase. They showed very high bromodeoxyuridine labeling indexes during the first 7 days (proliferation phase), which gradually decreased thereafter. Phenotypic alterations took place at 7 to 10 days, and some hepatocytes started to express mature hepatocyte markers and biliary markers (differentiation phase). The presence of cells that coexpress albumin and biliary markers (CK7 and CK19) was demonstrated by double immunocytochemistry. In addition, cells were identified that ceased to express albumin and in turn were positive for CK19 or CK7. Therefore, the colony was considered to contain liver progenitor-like cells that can differentiate during culture into cells expressing phenotypes of mature hepatocytes or biliary epithelial cells.
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PMID:Growth and differentiation in culture of clonogenic hepatocytes that express both phenotypes of hepatocytes and biliary epithelial cells. 890 49

Cytochrome P450 (CYP) 2E1 was the most efficient CYP enzyme that oxidized benzene to soluble and covalently bound metabolites in rat and human liver microsomes. The covalent binding was due mostly to the formation of benzoquinone (BQ), the oxidation product of hydroquinone (HQ), and was inversely related to the formation of soluble metabolites. In rats, inhalation of benzene (4 mg/liter of air) caused a rapid destruction of CYP2B1 previously induced by phenobarbital. The ability of benzene metabolites to destroy liver microsomal CYP in vitro decreased in the order BQ > HQ > catechol > phenol. The destruction was reversed by ascorbate and diminished by alpha-tocopherol, suggesting that HQ was not toxic, whereas BQ and semiquinone radical (SQ) caused the effect. In the presence of nicotinamide adenine dinucleotide phosphate, reduced (NADPH) the microsomes did not oxidize HQ to BQ, while the formation of superoxide anion radical from both HQ and BQ was markedly quenched. Destruction of CYP in vitro caused by HQ or BQ was not mediated by hydroxyl radical formation or by lipid peroxidation. On the contrary, HQ and BQ inhibited NADPH-mediated lipid peroxidation. Ascorbate induced high levels of hydroxyl radical formation and lipid peroxidation, which were differentially affected by quinones, indicating different mechanisms. Despite reducing the toxicity of HQ and BQ, ascorbate appeared to induce its own toxicity, reflected in high levels of lipid peroxidation. Iron redox cycling played a significant role in the NADPH-induced hydroxyl radical formation but not in that caused by ascorbate; however, lipid peroxidation induced by NADPH or ascorbate was suppressed by ethylenediaminetraacetate, indicating a crucial role of iron. Thus, the data indicate that the quinones destroyed CYP directly and not via oxygen activation or lipid peroxidation.
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PMID:Cytochromes P450 in benzene metabolism and involvement of their metabolites and reactive oxygen species in toxicity. 911 95

Streptozotocin (STZ) is widely used as a strong inducer of insulin-dependent diabetes in experimental animals. Although nitric oxide (NO) generation from STZ has been proposed to be responsible for the toxicity of pancreatic B-cells, the mechanism is yet unknown. We found that STZ generates NO in the presence of Cu(II) plus ascorbate. In addition, nicotinamide, which is an antidiabetic agent against STZ, has been found to inhibit NO generation from STZ during the reaction with Cu(II) plus ascorbate. Since rat pancreatic islets contain both ascorbate and Cu at the concentrations of 3.5 mM and 1. 0 nmol/mg protein, respectively, our present results indicate that (1>) NO generation is responsible for the development of STZ-induced diabetes and (2) mechanism for the protection of diabetes by nicotinamide is due to the inhibition of NO generation from STZ through complex formation between nicotinamide and Cu (I), which is reduced by ascorbate.
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PMID:Generation of nitric oxide from streptozotocin (STZ) in the presence of copper(II) plus ascorbate: implication for the development of STZ-induced diabetes. 953 74

Because mitochondrial inner membrane respiratory complexes are important targets of iron toxicity, we used iron-loaded rat heart cells in culture to study the beneficial effect on mitochondrial enzymes of the iron chelators deferoxamine (DFO) and deferiprone (L1) and of antioxidants and reducing agents (ascorbate and alpha-tocopherol). Reduced nicotinamide adenine dinucleotide-cytochrome c oxidoreductase (complex I-III) and succinate dehydrogenase were the most-sensitive indicators of iron toxicity and cardioprotective effect. Although at concentrations below 0.3 mmol/L the iron-mobilizing effect of L1 was less than that of DFO, both were equally effective in protecting or restoring mitochondrial respiratory enzyme activity. At 1.0 mmol/L, L1 toxicity was manifested in respiratory enzyme inhibition, whereas DFO had no such effect. Ascorbate (0.057 to 5.7 mmol/L) had a mild cardioprotective effect at the highest concentration only, in association with decreased cellular iron uptake. By contrast, alpha-tocopherol (0.023 mmol/L) completely inhibited mitochondrial iron toxicity without affecting iron uptake or release, and irrespective of whether it was used before, during, or after in vitro iron loading. These observations illustrate the usefulness and limitations of iron chelators and other agents used for preventing iron toxicity to the heart and other vital organs, and they underline the need for exploring in more detail the effects of these agents in the clinical setting.
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PMID:Cardioprotective effect of alpha-tocopherol, ascorbate, deferoxamine, and deferiprone: mitochondrial function in cultured, iron-loaded heart cells. 998 70

Vitamins are essential for the growth and normal function of human body. There are very few reports on vitamin A deficiency in pregnant women and newborn. Vitamin B complex includes various fractions essential to proper nutrition. The absence of vitamin C results Barlow disease in newborn. Vitamin D, the antirachitic Vitamin, is of great importance in safeguarding the mother and fetus from its relation to calcium and phosphorus metabolism. Vitamin E is also useful for the treatment of toxemia of pregnancy, intra-uterine growth retardation (IUGR), and neonatal jaundice. Vitamin K is well known for the protection of neonatal hemorrhage. The 6th recommended dietary allowances for Japanese in 1999 is shown in the table.
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PMID:[Vitamins in pregnancy]. 1054 Aug 91

Nicotinamide (vitamin B3) an endogenous metabolite, showed significant inhibition of oxidative damage induced by reactive oxygen species (ROS) generated by ascorbate-Fe2+ and photosensitization systems in rat brain mitochondria. It protected against both protein oxidation and lipid peroxidation, at millimolar concentrations. Inhibition was more pronounced against oxidation of proteins than peroxidation of lipids. Chemically related endogenous compounds, tryptophan and isonicotinic acid, showed comparable inhibitory properties. The protective effect observed, at biologically relevant concentrations, with nicotinamide was more than that of the endogenous antioxidants ascorbic acid and alpha-tocopherol. Hence our studies suggest that nicotinamide (vitamin B3) can be considered as a potent antioxidant capable of protecting the cellular membranes in brain, which is highly susceptible to prooxidants, against oxidative damage induced by ROS.
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PMID:Nicotinamide (vitamin B3) as an effective antioxidant against oxidative damage in rat brain mitochondria. 1065 23

Bifunctional peptidylglycine alpha-amidating monooxygenase (PAM) catalyzes the copper-, ascorbate-, and O(2)-dependent cleavage of C-terminal glycine-extended peptides and N-acylglycines to the corresponding amides and glyoxylate. The alpha-amidated peptides and the long-chain acylamides are hormones in humans and other mammals. Bile acid glycine conjugates are also substrates for PAM leading to the formation of bile acid amides. The (V(MAX)/K(m))(app) values for the bile acid glycine conjugates are comparable to other known PAM substrates. The highest (V(MAX)/K(m))(app) value, 3.1 +/- 0.12 x 10(5) M(-1) s(-1) for 3-sulfolithocholylglycine, is 6.7-fold higher than that for d-Tyr-Val-Gly, a representative peptide substrate. The time course for O(2) consumption and glyoxylate production indicates that bile acid glycine conjugate amidation is a two-step reaction. The bile acid glycine conjugate is first converted to an N-bile acyl-alpha-hydroxyglycine intermediate which is ultimately dealkylated to the bile acid amide and glyoxylate. The enzymatically produced bile acid amides and the carbinolamide intermediates were characterized by mass spectrometry and two-dimensional (1)H-(13)C heteronuclear multiple quantum coherence NMR.
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PMID:The enzymatic formation of novel bile acid primary amides. 1066 88

The effect of different oxygen radical-generating systems on NAD(P)H was determined by incubating the reduced forms of the pyridine coenzymes with either Fe2+-H2O2 or Fe3+-ascorbate and by analyzing the reaction mixtures using a HPLC separation of adenine nucleotide derivatives. The effect of the azo-initiator 2,2'-azobis(2-methylpropionamidine)dihydrochloride was also tested. Results showed that, whilst all the three free radical-producing systems induced, with different extent, the oxidation of NAD(P)H to NAD(P)+, only Fe2+-H2O2 also caused the formation of equimolar amounts of ADP-ribose(P) and nicotinamide. Dose-dependent experiments, with increasing Fe2+ iron (concentration range 3-180 microM) or H2O2 (concentration range 50-1000 microM), were carried out at pH 6.5 in 50 mM ammonium acetate. NAD(P)+, ADP-ribose(P) and nicotinamide formation increased by increasing the amount of hydroxyl radicals produced in the medium. Under such incubation conditions NAD(P)+/ADP-ribose(P) ratio was about 4 at any Fe2+ or H2O2 concentration. By varying pH to 2.0, 3.0, 4.0, 4.5, 5.0, 5.5, 6.0, 7.0 and 7.4, NAD(P)+/ADP-ribose(P) ratio changed to 5.5, 3.2, 1.8, 1.6, 2.0, 2.5, 3.0, 5.4 and 6.5, respectively. Kinetic experiments indicated that 90-95% of all compounds were generated within 5s from the beginning of the Fenton reaction. Inhibition of ADP-ribose(P), nicotinamide and NAD(P)+ production of Fe2+-H2O2-treated NAD(P)H samples, was achieved by adding mannitol (10-50 mM) to the reaction mixture. Differently, selective and total inhibition of ADP-ribose(P) and nicotinamide formation was obtained by performing the Fenton reaction in an almost completely anhydrous medium, i.e. in HPLC-grade methanol. Experiments carried out in isolated postischemic rat hearts perfused with 50 mM mannitol, showed that, with respect to values of control hearts, this hydroxyl radical scavenger prevented reperfusion-associated pyridine coenzyme depletion and ADP-ribose formation. On the basis of these results, a possible mechanism of action of ADP-ribose(P) and nicotinamide generation through the interaction between NAD(P)H and hydroxyl radical (which does not involve the C-center where "conventional" oxidation occurs) is presented. The implication of this phenomenon in the pyridine coenzyme depletion observed in postischemic tissues is also discussed.
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PMID:Direct NAD(P)H hydrolysis into ADP-ribose(P) and nicotinamide induced by reactive oxygen species: a new mechanism of oxygen radical toxicity. 1082 16

In a prospective, randomized, double-blind therapeutic trial, 191 patients with non-alcoholic steatohepatitis were treated for 8 weeks daily b.i.d. orally either with betaine glucuronate combined with diethanolamine glucuronate and nicotinamide ascorbate (Ietepar) (96 patients) or with undistinguishable placebo capsules (95 patients). The verum treatment effectively reduced by 25% hepatic steatosis (p < 0.01) and by 6% hepatomegaly (p < 0.05), while placebo did not significantly reduce the disorders. Verum was also more effective than placebo on discomfort in abdominal upper right quadrant. The global efficacy of treatment was rated by the doctor "very good" or "good" in 48% of verum treated patients and only in 17% after placcbo (P of difference = 9 x 10(-6)). 52% of patients self-rated efficacy as "very good" or "good" after verum and only 34% after placebo (P of difference = 0.017). The verum treatment provoked a significant reduction of the increased liver transaminases (ALT, AST and gamma-GT) while placebo was ineffective. Adverse events were recorded in 10% of verum-treated patients and in 7% under placebo (no significant difference). In both groups the adverse events were mild and transient, did not require treatment discontinuation and were undistinguishable from common symptoms of liver disorders. In conclusion, the 8-week treatment with betaine glucuronate combined with diethanolamine glucuronate and nicotinamide ascorbate was found effective in non-alcoholic steatohepatitis, a disorder for which the hitherto pharmacological interventions were poorly and inconsistently effective.
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PMID:Efficacy and safety of oral betaine glucuronate in non-alcoholic steatohepatitis. A double-blind, randomized, parallel-group, placebo-controlled prospective clinical study. 1099 56

The present studies were designed to investigate the susceptibility of LLC-PK1 cells to cytotoxicity induced by para-aminophenol (PAP) and the ability of antioxidants to prevent PAP-induced cytotoxicity. LLC-PK1 cells were incubated for 4 h with varying concentrations of PAP (0-0.2 mM). Incubation was continued for 20 h and viability was monitored at 24 h after initial exposure to PAP. For coincubation experiments, cells were incubated for 4 h with various antioxidants [including ascorbate, glutathione (GSH), butylated hydroxytoluene (BHT), beta-nicotinamide adenine dinucleotide (NADH), or beta-nicotinamide adenine dinucleotide phosphate (NADPH)] in the absence or presence of 0.1 mM PAP. For preincubation experiments, cells were incubated for 1 h with ascorbate, GSH or NADPH. Antioxidants were removed and cells were exposed to 0 or 0.1 mM PAP for 4 h. Viability was determined 24 h following PAP exposure. LLC-PK1 cells displayed a steep concentration-response relationship for PAP; 0.1 mM PAP caused approximately 50% loss of viability. Coincubation with ascorbate, GSH and NADPH was without effect on cell viability in the absence of PAP and attenuated PAP-induced losses in viability. In contrast, NADH was ineffective in preventing PAP-induced cytotoxicity. BHT alone produced a significant loss of cell viability and was ineffective in preventing PAP cytotoxicity. Inability of NADH to prevent PAP-induced cytotoxicity was related to rapid degradation of NADH in aqueous solution. Preincubation of cells with ascorbate or GSH but not NADPH was associated with attenuation of PAP-induced cytotoxicity. These data suggest that (1) PAP is cytotoxic to LLC-PK1 cells, (2) a portion of PAP cytotoxicity is due to nonenzymatic oxidation that occurs in the incubation medium, and (3) a portion of PAP cytotoxicity is due to enzymatic or nonenzymatic oxidation that occurs within cells.
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PMID:Effect of antioxidants on para-aminophenol-induced toxicity in LLC-PK1 cells. 1116 74


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