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

A hospital-based case-control study of gastric cancer precursor lesions was conducted in a high-risk black population in southern Louisiana. Ninety-three subjects with biopsy-proved advanced chronic atrophic gastritis were compared to two control series: a gastroscopy clinic series and a general hospital-admission series. Dietary case-control differences indicated a protective effect associated with fruit and vegetable intake and with dietary vitamin C and a risk elevation associated with milk consumption. The protective effect associated with consumption of fruits, vegetables, and vitamin C is consistent with findings for gastric cancer and with the etiologic hypothesis of intragastric nitrosation. A twofold increased risk was associated with cigarette smoking. Gastric juice pH, NO3-, and NO2- were determined for subjects undergoing gastroscopy, and comparisons were made between this high-risk U.S. group and a Colombian population with a much greater magnitude of risk; the latter had higher NO3- and NO2- levels. An increase in pH was associated with increasing severity of gastric lesions. Levels of pH and NO2- concentration were significantly correlated (P less than .0005); however, in Louisiana the large difference in NO2- concentration associated with pH elevation is not associated with histopathologic severity. Divergent trends with severity of lesions for NO3- concentration were seen in the two populations.
 ...
PMID:Diet and chronic atrophic gastritis: a case-control study. 345 99

The transfer of various Np(IV) and Np(V) chemical forms across the small intestine of rats was measured in instilled and perfused jejunum. Instillation of Np(V) nitrate together with citrate or DTPA resulted in the same absorption of Np as after instillation of Np(V) nitrate alone (3 per cent per hour). Perfusion of Np(V) nitrate with bicarbonate or DTPA resulted in a similar transfer (2 per cent) but added citrate or ascorbate resulted in reduced transfer (0.8 per cent). Addition of phytate reduced Np transfer in both instilled and perfused jejunum (0.4 per cent). Np(IV) transfer was usually the same as, or less than that of, the corresponding Np(V) forms. Np(IV) transfer was similar in perfused and instilled jejunum, increasing from 0.2 per cent in the presence of citrate and phytate, to 1 per cent with EDTA and DTPA. Except for phytate, all the forms of Np(V) tested behaved like Np(V) nitrate after transfer from the intestine or after intravenous injection. By contrast, the behaviour of Np(IV) varied for all the forms tested and, for a given form, varied as a function of the experimental procedure used, i.e. jejunal instillation, perfusion, or intravenous injection. These findings suggest that the intestinal transfer of Np might occur via the intercellular pathway, and that it is controlled by both the molecular weight of the Np compound and its stability constant.
 ...
PMID:Effects of the chemical forms and valency states of neptunium on its jejunal transfer in the rat. 349 5

Although no absolute certainty exists about the role of nutrition in the etiology of cancer, many facts in favor of the relationship became available during the last decades. Correlation studies, experimental work and to a lesser extent case-control studies made it possible to clarify the role of certain nutrients and foods in carcinogenesis. The most important cancer sites where nutrition could play a role are esophagus, stomach, colon, rectum, prostate and breast. Esophageal cancer is of a very complex etiology, in which alcohol intake plays an important role, at least in western countries. The cancer-promoting properties of alcohol intake are enhanced by smoking. Three factors from nutrition are probably related to stomach cancer, namely salt, nitrate/nitrite and vitamin C. Salt is caustic to the stomach mucosa, resulting in atrophic gastritis. Salt is also co-carcinogenic and stomach cancer-promoting in experimental animals. Nitrate is probably important at the stage of atrophic gastritis, where bacterial overgrowth, due to the high pH, converts nitrates in nitrites, making the loco synthesis possible of potent nitrosocarcinogens. Vitamin C inhibits the latter step. The epidemiological evidence for the role of those factors is provided. The most important among them is the strong and consistent association of stomach cancer mortality with stroke. Rectum, colon, prostate and breast cancer are related in some way to fat intake. They all seem positively related to saturated fat intake, whereas breast cancer is probably also promoted by polyunsaturated fat intake. However, polyunsaturated fat seems to be without effect on rectum cancer. Colon and prostate cancer are probably also influenced by polyunsaturated fat but to a lesser degree than breast cancer. An important argument for this are the positive ecological correlations between changes in rectum, colon and breast cancer mortality from 1968 on, and changes occurring in coronary heart diseases, stroke and diabetes mortality. Those six types of mortality are decreasing, or only slightly increasing in the USA, Belgium, France, the Netherlands, etc. They are strongly increasing in East European countries. The intake of saturated fat has generally decreased in the first group of countries, and has markedly increased in the second group.(ABSTRACT TRUNCATED AT 400 WORDS)
 ...
PMID:Nutrition and cancer. 353 16

Values of about 0.005-0.01 per cent were obtained for the absorption in fed hamsters of plutonium ingested as Pu4+ citrate, isocitrate, phytate and malate complexes and Pu3+ ascorbate compared with about 0.003-0.004 per cent for Pu4+ nitrate. Replacing drinking water with tea did not affect the result for Pu4+ nitrate. Fasting hamsters for 8 h before the administration of plutonium citrate increased absorption to 0.1-0.2 per cent. An extra period of fasting for 4 h after administration did not lead to a further increase in absorption. Similar values were also obtained when plutonium citrate was administered after a 24 h fast, followed either by immediate access to food or a further 4 h fast. In hamsters fasted for 24 h before administration of either Pu3+ ascorbate or Pu4+ nitrate, about 6-7 per cent of the ingested plutonium was retained in the gastrointestinal tract after one week. At three weeks after ingestion of Pu3+ ascorbate, gastrointestinal retention had fallen 100-fold without an increase in absorption.
 ...
PMID:The gastrointestinal absorption of organically bound forms of plutonium in fed and fasted hamsters. 353 44

Pseudomonas aureofaciens truncates the respiratory reduction of nitrate (denitrification) at the level of N2O. The nitrite reductase from this organism was purified to apparent electrophoretic homogeneity and found to be a blue copper protein. The enzyme contained 2 atoms of copper/85 kDa, both detectable by electron paramagnetic resonance (EPR) spectroscopy. The protein was dimeric, with subunits of identical size (40 +/- 3 kDa). Its pI was 6.05. The EPR spectrum showed an axial signal g at 2.21(8) and g at 2.04(5). The magnitude of the hyperfine splitting (A parallel = 6.36 mT) indicated the presence of type 1 copper only. The electronic spectrum had maxima at 280 nm, 474 nm and 595 nm (epsilon = 7.0 mM-1 cm-1), and a broad shoulder around 780 nm. A copper protein of low molecular mass (15 kDa), with properties similar to azurin, was also isolated from P. aureofaciens. The electronic spectrum of this protein showed a maximum at 624 nm in the visible range (epsilon = 2.5 mM-1 cm-1) and pronounced structures in the ultraviolet region. The EPR parameters were g parallel = 2.26(6) and g perpendicular = 2.05(6), with A parallel = 5.8 mT. The reduced azurin transferred electrons efficiently to nitrite reductase; the product of nitrite reduction was nitric oxide. The specific nitrite-reducing activity with ascorbate-reduced phenazine methosulfate as electron donor was 1 mumol substrate min-1 mg protein-1. The reaction product again was nitric oxide. Nitrous oxide was the reaction product from hydroxylamine and nitrite and from dithionite-reduced methyl viologen and nitrite. No 'oxidase' activity could be demonstrated for the enzyme. Our data disprove the presumed exclusiveness of cytochrome cd1 as nitrite reductase within the genus Pseudomonas.
 ...
PMID:Type 1, blue copper proteins constitute a respiratory nitrite-reducing system in Pseudomonas aureofaciens. 366 26

It has been hypothesized that dietary nitrate and nitrite are converted in the stomach to nitrous acid, which reacts with secondary amines and amides to form nitrosamines and nitrosamides, compounds frequently demonstrated to be carcinogenic in animals, and that vitamins C and E inhibit N-nitroso product formation by chemically reducing nitrous acid. This hypothesis and others were tested in a case-control study (controls were individually matched by age, sex and area of residence), utilizing a standardized, quantitative, dietary history questionnaire interview. Daily nutrient consumption values were calculated from interview responses, and continuous conditional logistic regression was used for the data analysis. Significant findings are as follows: (1) Average daily consumption of nitrite, chocolate and carbohydrate was associated with increasing trends in risk. (2) While citrus fruit intake appeared to be somewhat protective, any protective effect of vitamin C intake was less apparent, and of vitamin E, not at all apparent. (3) Consumption of dietary fibre was negatively associated with gastric cancer risk. These findings appear to implicate a number of dietary components, including nitrite consumption, in the genesis of gastric cancer in humans.
 ...
PMID:Consumption of precursors of N-nitroso compounds and human gastric cancer. 367 29

Three samples of 24-h urine were collected from each of 104 inhabitants of high-risk (Akita) and low-risk (Iwate) areas for stomach cancer in northern Japan, according to the following protocols: (i) when they were undosed, (ii) after ingestion of proline three times a day and (iii) after ingestion of proline together with vitamin C three times a day. These samples were analysed for N-nitrosamino acids, nitrate and chloride ion as indices of the exposure. The median values of N-nitrosoproline (NPRO) and N-nitroso-2-methylthiazolidine 4-carboxylic acid (NMTCA) excreted in the urine of undosed subjects were not different between the two areas; however, that of N-nitrosothiazolidine 4-carboxylic acid (NTCA) was significantly higher in subjects of the high-risk area. Salt intake, estimated from the level of chloride ion in the urine, did not differ in two areas. After intake of proline, the NPRO level increased significantly only in subjects of the high-risk area, but not in those of the low-risk area; intake of vitamin C inhibited this increase of NPRO and lowered the levels of other nitrosamino acids only in the high-risk subjects. In contrast, the urinary level of nitrate was higher in subjects of the low-risk area than in those of the high-risk area; nitrate levels were found to correlate well with the amounts of vegetables consumed.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Urinary excretion of N-nitrosamino acids and nitrate by inhabitants in high- and low-risk areas for stomach cancer in northern Japan. 367 30

Samples of 12-h overnight urine were collected from approximately 40 male adults in each of the 26 counties of China. Two urine specimens were collected from each subject--one after a loading dose of proline and ascorbic acid and another after a loading dose of proline only. Levels of N-nitrosamino acids, nitrite and nitrate were measured in urine samples and correlated with cancer mortality per 100,000 male subjects in the truncated age range 35-64 years. Preliminary results show no clear correlation between presence of stomach cancer or liver cancer and nitrosation potential [as measured by the urinary level of N-nitrosoproline (NPRO) after the proline load test or of nitrate]. There was a moderate, although not clearly significant, tendency for oesophageal cancer mortality rates to be associated positively with nitrosation potential and negatively with background ascorbate levels in plasma. This result was due chiefly to the inclusion of one county (Song Xian) in which there is a fairly high oesophageal mortality rate, an average nitrosation potential three times greater than that of any other county, and the lowest ascorbate index of any county. Further study of this county is planned.
 ...
PMID:A correlation study on urinary excretion of N-nitroso compounds and cancer mortality in China: interim results. 367 31

Urinary excretion of N-nitrosoproline (NPRO) following ingestion of a high-nitrate salad meal, without then with an oral dose of 500 mg L-proline, was investigated in 16 healthy volunteers. The mean excretion rate following consumption of the high-nitrate meal alone was significantly lower than that measured after ingestion of the salad plus proline. Supplementation of the same meal (plus proline) with vitamin C from dietary sources resulted in a significant decrease in mean urinary NPRO levels in healthy subjects. The nitrosation-inhibiting effect of vitamin C was not affected by an increase in the fat content of the meal. Supplementation of the high-nitrate salad with alcohol or coffee did not affect subsequent urinary NPRO levels. No significant difference was observed in the urinary NPRO concentrations of smokers and nonsmokers after ingestion of high-nitrate salad (with or without vitamin C) plus proline.
 ...
PMID:The availability of dietary nitrate for the endogenous nitrosation of L-proline. 367 34

The participation of distinct formate dehydrogenases and cytochrome components in nitrate reduction by Escherichia coli was studied. The formate dehydrogenase activity present in extracts prepared from nitrate-induced cells of strain HfrH was active with various electron acceptors, including methylene blue, phenazine methosulfate, and benzyl viologen. Certain mutants which are unable to reduce nitrate had low or undetectable levels of formate dehydrogenase activity assayed with methylene blue or phenazine methosulfate as electron acceptor. Of nine such mutants, five produced gas when grown anaerobically without nitrate and possessed a benzyl viologen-linked formate dehydrogenase activity, suggesting that distinct formate dehydrogenases participate in the nitrate reductase and formic hydrogenlyase systems. The other four mutants formed little gas when grown anaerobically in the absence of nitrate and lacked the benzyl viologen-linked formate dehydrogenase as well as the methylene blue or phenazine methosulfate-linked activity. The cytochrome b(1) present in nitrate-induced cells was distinguished by its spectral properties and its genetic control from the major cytochrome b(1) components of aerobic cells and of cells grown anaerobically in the absence of nitrate. The nitrate-specific cytochrome b(1) was completely and rapidly reduced by 1 mm formate but was not reduced by 1 mm reduced nicotinamide adenine dinucleotide; ascorbate reduced only part of the cytochrome b(1) which was reduced by formate. When nitrate was added, the formate-reduced cytochrome b(1) was oxidized with biphasic kinetics, but the ascorbate-reduced cytochrome b(1) was oxidized with monophasic kinetics. The inhibitory effects of n-heptyl hydroxyquinoline-N-oxide on the oxidation of cytochrome b(1) by nitrate provided evidence that the nitrate-specific cytochrome is composed of two components which have different redox potentials but identical spectral properties. We conclude from these studies that nitrate reduction in E. coli is mediated by the sequential operation of a specific formate dehydrogenase, two specific cytochrome b(1) components, and nitrate reductase.
 ...
PMID:Nitrate reductase complex of Escherichia coli K-12: participation of specific formate dehydrogenase and cytochrome b1 components in nitrate reduction. 490 36


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>