Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.5.1.5 (urease)
 7,257 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The role of neutrophil and its chlorinated oxidant were investigated in Helicobacter pylori-induced gastric mucosal injury in vitro. Luminol-dependent chemiluminescence (ChL) was used to detect neutrophil-derived oxidants. ChL activity was significantly elevated when neutrophils were incubated in H. pylori, indicating that H. pylori actually elicits oxidative burst of neutrophils. To assess whether H. pylori-activated neutrophils exert the cytotoxicity for gastric mucosal cells, rabbit gastric mucosal cell was monolayered in culture wells and labeled with a fluorescence dye, 2',7'-bis(2-carboxyethyl)-5(6)carboxy-fluorescein, which is retained in the intracellular space as long as the cell membrane is intact. Labeled cells were coincubated with neutrophils and H. pylori. We inferred from the cytotoxicity index (specific %cytotoxicity), which was calculated from fluorometrical measurements of supernatant and lysate, that the mucosal cells were significantly damaged by H. pylori-activated neutrophils. This injury was largely attenuated by eliminating urea from the incubation mixture or by acetohydroxamic acid, a potent urease inhibitor. Additionally, the scavengers of neutrophil-derived oxidants, including taurine, methionine, and catalase, also attenuated this injury. Cultured mucosal cells that were exposed to the solution containing monochloramine (an oxidant yielded by reaction of hypochlorous acid and ammonia) were highly damaged compared with cells exposed to hypochlorous acid or hydrogen peroxide at physiological concentrations. These data suggest that H. pylori-activated neutrophils promote gastric mucosal cell injury and that monochloramine plays a unique and important role in this process.
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PMID:Helicobacter pylori-associated ammonia production enhances neutrophil-dependent gastric mucosal cell injury. 144 47

Hydrolysis of arginine into urea and ornithine (Orn) was observed to take place in several segments of the rat nephron including cortical and medullary pars recta of the proximal tubule (PST) and collecting duct (CD). This work was now extended to the adult mouse and rabbit. Representative nephron segments, obtained by microdissection of collagenase-treated kidneys, were incubated with L-[guanido-14C]arginine (216 microM). Addition of urease produced 14CO2 + 2 NH3 from the newly formed urea released in the incubate. 14CO2 was trapped in KOH and counted. In both species, as well as in the rat, the PST was the site of the highest urea + Orn production, with an intensity increasing from cortex to medulla. For other nephron segments, the pattern was not similar in all species. Significant production of urea + Orn was observed in the proximal convoluted tubule and the medullary thick ascending limb in the rabbit, but not in the CD of either the rabbit or the mouse. The functional significance of this urea + Orn production remains unclear. The total amount of urea generated intrarenally by this reaction does not seem sufficient to play a significant role in the urinary concentrating mechanism. It may be assumed that Orn could be further metabolized to polyamines and play a role in maintaining cell integrity and function in the PST, especially in its medullary part, exposed to hypertonicity and poor oxygen supply.
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PMID:Localization of urea and ornithine production along mouse and rabbit nephrons: functional significance. 144 76

Neomycin (700 mg/8 h), ampicillin (500/6 h) and metronidazole (400 mg/8 h), were compared for their effect, on oral administration for 4 days, in reducing blood ammonia in 27 patients with stable chronic liver disease. It was found that there was 38.2, 38.5 and 8.7 m mol/litre mean reduction in blood ammonia in the neomycin, ampicillin and metronidazole treated groups respectively. The difference in blood ammonia was statistically significant for both neomycin (P = 0.01) and ampicillin (P = 0.03) but there was no significant change after metronidazole treatment (P = 0.6). The total stool enzyme activity at optimum pH was maximally reduced by ampicillin and minimally with metronidazole. The reduction was noted to be 3.51 m mol/1 (P = 0.01), 3.87 m mol/1 (P = 0.08) and 2.8 m mol/1 (P = 0.02) of NH3/g dry weight of stool for neomycin, ampicillin and metronidazole respectively. The main bacterial gut enzymes responsible for ammonia production, urease and protease, were found to be very sensitive to stool pH. At pH 6 their activity was around 20 per cent of what was found in optimum pH of 7.4 and at pH 5 it is only about 8 per cent of optimum activity. None of the three antibacterial agents changed the stool pH significantly. It can be concluded that oral neomycin and ampicillin are superior to oral metronidazole in lowering blood ammonia.
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PMID:Effect of three antibacterial drugs in lowering blood & stool ammonia production in hepatic encephalopathy. 145 72

The high plasma level of citrulline (Cit) is one of a number of abnormalities in the plasma amino acid pattern in chronic renal failure (CRF). Synthesis of arginine (Arg) from citrulline in the kidney is the major source of Arg for the body. In order to evaluate the renal activity of Arg synthesis in CRF, we studied arginine production in proximal convoluted tubules (PCT) isolated from male Sprague-Dawley rats 1 month after 5/6 nephrectomy and from sham-operated rats (n = 6 of each). PCT segments were incubated in a sealed chamber with 50 or 200 microM of [L-ureido 14C]-Cit (simulating in vivo plasma concentrations in healthy rats or rats with CRF, respectively). Arginase and urease were added to the medium to hydrolyze Arg into 14CO2 + NH3. 14CO2 was trapped in KOH and counted. Results showed that: (1) in CRF, Arg production per unit tubular length is increased in proportion to hypertrophy of PCT (x 1.5); (2) in CRF, as in the healthy kidney, Arg production increases with Cit concentration (x 2.5 from Cit 50 to 200 microM). Taking into account the hypertrophy and the elevation in Cit concentration, the increase in Arg production per unit length (x 3.6) is not sufficient to compensate for the reduction in nephron number. Most likely, a greater length of maximal tubule is recruited for renal Arg synthesis in CRF.
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PMID:Arginine synthesis by the proximal convoluted tubule in rats with chronic renal failure. 146 41

The presence of ammonium in gastric contents was described in 1852; urease activity in the stomach was identified 70 years later. The discovery of gastric urease resulted in intense research activity to discover its origin, function, and relation to the gastric levels of ammonium and urea. Interest in urease waned in the 1960s as most pertinent questions appeared to have been addressed and there was strong evidence that gastric urease was not a property of the stomach but was of microbial origin. Identification of Helicobacter pylori as the source of urease in the stomach in the last decade has resulted in a rebirth of interest in gastric urease and its products. There is little actual evidence to support a role for toxicity of ammonia in relation to H. pylori and the bulk of the evidence suggests that the products of urease activity are not toxic and may even be beneficial. The purpose of this review is to examine the older literature and to examine new findings in the perspective of what is already known and to suggest areas remaining to be examined. We ask, 'What is old, what is new, and what needs to be done?'
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PMID:Review article: urease, gastric ammonium/ammonia, and Helicobacter pylori--the past, the present, and recommendations for future research. 148 53

A modified end-point enzymatic method for the measurement of ammonia in stool water is presented. A protein precipitation step was included in order to inactivate urease and faecal enzymes, which oxidise NADH. The modified method is reliable, with acceptable precision and accuracy, and is linear up to a concentration of 1.5 mmol/l.
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PMID:Measurement of faecal ammonia. 148 77

Helicobacter pylori (HP) has been shown to possibly be a pathogen of gastric carcinoma. HP has urease activity and produces ammonia in the stomach. In this study, the role of ammonia on gastric carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) were investigated in rats. After 24 weeks pretreatment with MNNG (83 mg/l), 0.01% ammonia or tap water as a drinking water was administered for 24 weeks. The ammonia-treated rats showed a significantly higher incidence of gastric cancer (percent of animals with tumors and number of tumors per rat). Ammonia would thus appear to have an important role in HP-related human gastric carcinogenesis.
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PMID:Ammonia: a possible promotor in Helicobacter pylori-related gastric carcinogenesis. 151 5

To evaluate partial or total replacement of renal function using gut, we measured in vivo transport of nitrogen metabolites, electrolytes, and water into a jejunal segment configured as a continent reservoir in the dog. Reservoir contents were sampled and analyzed at serial time intervals during a 3-h period after instillation of solution containing (in mM) 40 NaCl, 10 NaHCO3, 220 mannitol, pH 8.5, without or with added urease. At 10 min postinstillation, the amount of urea in the solution without added urease was 3-5 times greater than in the presence of added urease, but accumulation of NH4+ was 14-21 times greater in the solution containing added urease, giving a luminal NH4+ concentration up to 10,000 times that of plasma. In the absence of urease, HCO3- concentration fell to 0, and pH declined to 6 at 3 h; in the presence of urease, HCO3- concentration was 4.5 mM, and pH was 7.8 at 3 h. We conclude 1) urea is secreted by the reservoir; 2) H+ is secreted and/or formed in the reservoir; 3) in the presence of urease, urea hydrolyzed to NH3 is converted to NH4+ by H+ and trapped in the lumen; and 4) in the urease solution, H+ binding by NH3 preserves luminal HCO3-, maintaining the initial pH. Thus the continent jejunal reservoir may supplement or replace impaired renal function.
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PMID:Transport properties of an in situ jejunal reservoir in dogs. 155 68

Former studies have shown that Helicobacter pylori can induce vacuolation of vacuolation of epithelial cells in vitro and possibly in vivo, either by direct action of a cytotoxin or by the action of its strong urease, which breaks down the urea physiologically present in the stomach into cytotoxic ammonia. We have developed a test using HEp2 cells with adherent H. pylori bacteria in order to compare the effects of an H. pylori urease-negative variant with those of its urease-positive parent strain in the presence of 10 mM urea. The level of ammonia production as well as cell vacuolation and viability were monitored for 72 h. The ammonia produced (20 mM) was found to be the essential determinant of the degree of cell vacuolation and viability of HEp2 cells. However, the addition of acetohydroxamic acid (200 mg/liter), a potent urease inhibitor which inhibits ammonia production, did not completely restore cell growth, suggesting the difficulty of neutralizing the ammonia in the vicinity of the cells. Antibodies directed against H. pylori did not neutralize the urease activity. When H. mustelae was tested in the same manner, the detrimental effects were not observed because a lower quantity of ammonia (5 mM) was generated. This was due to a lower urease activity, although the adherence properties of H. mustelae were different from those of H. pylori both quantitatively (greater adherence) and qualitatively (localized instead of diffuse adherence). We conclude that H. pylori-induced ammonia is an essential determinant of its cell toxicity as well as its adherence properties, which allow a high concentration of ammonia at the cellular level.
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PMID:Further evidence of the toxic effect of ammonia produced by Helicobacter pylori urease on human epithelial cells. 156 74

In this method for serum and urinary urea determination, the same reagent is used without predilution of urine samples. The method is based on the pH increase resulting from the ammonia released by urease hydrolysis of urea. o-Cresolphthalein complexone is used to monitor the pH change colorimetrically. Urea concentration and absorbance at 570 nm are linearly related for concentrations as great as 600 mmol/L for urine samples and 100 mmol/L for serum. There are no clinically significant interferences from physiological substances or drugs, and precision and accuracy are excellent (CV approximately 2%, except at very low concentrations in serum; analytical recovery was 99% in urine, 100% in serum). Results by this method (y) and by the Astra method (x) for urine correlated well (y = 0.991x - 2.87, Sy/x = 9.21, r = 0.994), as did the results by this method and by the total enzymatic method (x') for serum (y = 1.002x' + 0.192, Sy/x' = 0.598, r = 0.997). This method is applicable to automated as well as manual instruments, and one-reagent or two-reagent formats can be used.
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PMID:Simple and sensitive determination of urea in serum and urine. 158 10


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