Generation of ammonia and mucosal lesion formation following hydrolysis of urea by urease in the rat stomach

X-ray Structures and Computational Studies of Two Bioactive 2-(Adamantane-1-carbonyl)-N-substituted Hydrazine-1-carbothioamides

Two biologically active adamantane-linked hydrazine-1-carbothioamide derivatives, namely 2-(adamantane-1-carbonyl)-N-(tert-butyl)hydrazine-1-carbothioamide) 1 and 2-(adamantane-1-carbonyl)-N-cyclohexylhydrazine-1-carbothioamide 2, have been synthesized. X-ray analysis was conducted to study the effect of the t-butyl and cyclohexyl moieties on the intermolecular interactions and conformation of the molecules in the solid state. X-ray analysis reveals that compound 1 exhibits folded conformation, whereas compound 2 adopts extended conformation. The Hirshfeld surface analysis indicates that the contributions of the major intercontacts involved in the stabilization of the crystal structures do not change much as a result of the t-butyl and cyclohexyl moieties. However, the presence and absence of these contacts is revealed by the 2D-fingerprint plots. The CLP-Pixel method was used to identify the energetically significant molecular dimers. These dimers are stabilized by different types of intermolecular interactions such as N-H···S, N-H···O, C-H···S, C-H···O, H-H bonding and C-H···π interactions. The strength of these interactions was quantified by using the QTAIM approach. The results suggest that N-H···O interaction is found to be stronger among other interactions. The in vitro assay suggests that both compounds 1 and 2 exhibit urease inhibition potential, and these compounds also display moderate antiproliferative activities. Molecular docking analysis shows the key interaction between urease enzyme and title compounds.

Ureases in the gastrointestinal tracts of ruminant and monogastric animals and their implication in urea-N/ammonia metabolism: A review

Urea in diets of ruminants has been investigated to substitute expensive animal and vegetable protein sources for more than a century, and has been widely incorporated in diets of ruminants for many years. Urea is also recycled to the fermentative parts of the gastrointestinal (GI) tracts through saliva or direct secretory flux from blood depending upon the dietary situations. Within the GI tracts, urea is hydrolyzed to ammonia by urease enzymes produced by GI microorganisms and subsequent ammonia utilization serves the synthesis of microbial protein. In ruminants, excessive urease activity in the rumen may lead to urea/ammonia toxicity when high amounts of urea are fed to animals; and in non-ruminants, ammonia concentrations in the GI content and milieu may cause damage to the GI mucosa, resulting in impaired nutrient absorption, futile energy and protein spillage and decreased growth performance. Relatively little attention has been directed to this area by researchers. Therefore, the present review intends to discuss current knowledge in ureolytic bacterial populations, urease activities and factors affecting them, urea metabolism by microorganisms, and the application of inhibitors of urease activity in livestock animals. The information related to the ureolytic bacteria and urease activity could be useful for improving protein utilization efficiency in ruminants and for the reduction of the ammonia concentration in GI tracts of monogastric animals. Application of recent molecular methods can be expected to provide rationales for improved strategies to modulate urease and urea dynamics in the GI tract. This would lead to improved GI health, production performance and environmental compatibility of livestock production.

Nickel trafficking system responsible for urease maturation in Helicobacter pylori

Helicobacter pylori (H. pylori) is a common human pathogen responsible for various gastric diseases. This bacterium relies on the production of urease and hydrogenase to inhabit the acidic environment of the stomach. Nickel is an essential cofactor for urease and hydrogenase. H. pylori has to uptake sufficient nickel ions for the maturation of urease, and on the other way, to prevent the toxic effects of excessive nickel ions. Therefore, H. pylori has to strike a delicate balance between the import of nickel ions, its efficient intracellular storage, and delivery to nickel-dependent metalloenzymes when required. The assembly and maturation of the urease enzyme is a complex and timely ordered process, requiring various regulatory, uptake, chaperone and accessory proteins. In this review, we focus on several nickel trafficking proteins involved in urease maturation: NikR, NixA, HypAB, UreEFGH, HspA, Hpn and Hpnl. The work will deepen our understanding of how this pathogenic bacterium adapts to severe habitant environments in the host.

A proteomic approach for the identification of bismuth-binding proteins in Helicobacter pylori

Helicobacter pylori is a major human pathogen that can cause peptic ulcers and chronic gastritis. Bismuth-based triple or quadruple therapies are commonly recommended for the treatment of H. pylori infections. However, the molecular mechanisms underlying treatment with bismuth are currently not fully understood. We have conducted a detailed comparative proteomic analysis of H. pylori cells both before and after treatment with colloidal bismuth subcitrate (CBS). Eight proteins were found to be significantly upregulated or downregulated in the presence of CBS (20 microg mL(-1)). Bismuth-induced oxidative stress was confirmed by detecting higher levels of lipid hydroperoxide (approximately 1.8 times) and hemin (approximately 3.4 times), in whole cell extracts of bismuth-treated H. pylori cells, compared with those from untreated cells. The presence of bismuth also led to an approximately eightfold decrease in cellular protease activities. Using immobilized-bismuth affinity chromatography, we isolated and subsequently identified seven bismuth-binding proteins from H. pylori cell extracts. The intracellular levels of four of these proteins (HspA, HspB, NapA and TsaA) were influenced by the addition of CBS, which strongly suggests that they interact directly with bismuth. The other bismuth-interacting proteins identified were two enzymes (fumarase and the urease subunit UreB), and a translational factor (Ef-Tu). Our data suggest that the inhibition of proteases, modulation of cellular oxidative stress and interference with nickel homeostasis may be key processes underlying the molecular mechanism of bismuth's actions against H. pylori.

Histological alterations of intestinal villi in chickens fed dried Bacillus subtilis var. natto

Two experiments were conducted. In experiment 1, chickens were fed dried Bacillus subtilis var. natto for 3 or 28 days. Growth performance and internal organs were not different from controls, but feed efficiency tended to be improved in the 28-day feeding. In these birds, blood ammonia concentration was decreased (P<0.05). Blood glucose concentration, and amylase and lipase activity in the intestinal content were not significantly different among dietary groups. These results suggest that the B. subtilis natto depressed ammonia concentration. In experiment 2, chickens were fed dietary B. subtilis natto for 28 days. These birds had a tendency to display greater growth performance and intestinal histologies, such as villus height, cell area and cell mitosis, than the controls. Flat cell outline on the duodenal villus surface in controls developed large, protruded cell clusters and cell protuberances after feeding of dietary B. subtilis natto. These results indicate that intestinal function was activated by the depressed blood ammonia concentration in the body of the chicken. The present results may suggest that the B. subtilis natto has the potential to be a beneficial microorganism in chickens.

Feeding diets containing high levels of milk products or cellulose decrease urease activity and ammonia production in rat intestine

Three studies were done to determine the effect of feeding diets containing high levels of a readily fermentable carbohydrate (lactose in milk or yogurt, or pure lactose) or an undigestible, unfermentable diluent (alpha-cellulose) on urease (EC 3.5.1.5) activity and net ammonia production in the rat gastrointestinal (GI) contents. Rats (170-200 g) were fed a control diet or diets containing 55% dried milk or 55% dried yogurt, 25% lactose or 10% alpha-cellulose. Feeding diets containing milk or yogurt decreased urease activity to approximately 11% of the control value in the small intestine (on the basis of grams of collected contents or total contents), and to 50% in the large intestine (only on the basis of grams of collected contents). Feeding the diet containing 25% lactose also decreased urease activity (on the basis of grams of collected contents or total contents) to about 20% of the control value in the small intestine, but not (P > 0.05) in the large intestine. Net ammonia production rate was correlated (r2 = 0.98) with urease activity in the large intestinal contents, and the rate of ammonia production from ureolysis represented about two thirds of the total. Feeding the cellulose diet decreased (P < 0.05) both urease activity and net ammonia production in the large intestine to approximately 30% of the control value. Weights of tissue and contents of the large intestine were much higher (P < 0.01) in rats fed diets containing milk products or lactose than in the control rats, but were not affected by consumption of the cellulose diet. Results of our studies indicate that feeding diets containing high levels of milk products (lactose) or cellulose reduces urease activity and net ammonia production in the rat intestine, and thus may be beneficial for improving animal and human health.

Helicobacter pylori-dependent intragastric urea biodegradation in children: diagnostic and pathogenetic importance

The objective of the present work was to study the relationship between intragastric urea hydrolysis generated by Helicobacter pylori urease and acid-peptic disease in childhood. Intragastric urease activity was examined by urea and ammonia concentration measurement in gastric juice in 91 children with upper abdominal complaints. Helicobacter pylori infection was detected from 70 (76.9%) of 91 patients, including all of the 15 subjects with peptic ulcer disease. Helicobacter pylori-related gastritis in children was associated with a decrease of urea and an increase of ammonia in gastric juice (P < 0.001) in comparison with H. pylori-negative children. The gastritis score was correlated with the concentrations of urea and ammonia in the gastric juice of patients infected with H. pylori. There was a significant correlation between the histologically detected dissemination of organisms and gastric ammonia levels. Similar results were obtained concerning correlation between gastric juice ammonia and anti-H. pylori specific immunoglobulin G versus highly purified antigen of H. pylori containing urease. Present findings prove that H. pylori plays an essential role in the pathogenesis of gastritis and that ammonia is one of the main pathogenic factors of acid-peptic disease.

Studies on gastric mucosal cell injury induced by Helicobacter pylori

The cause of gastric cell injury induced by Helicobacter pylori was investigated in vitro using gastric mucosal cells derived from male Japanese white rabbits. To evaluate the contribution of the potent urease activity of H. pylori to gastric mucosal cell injury, the supernatant of the H. pylori bacterial pellet, solubilized with N-octyl-glucoside, was added to the gastric mucosal cell suspension. Cell injury was assessed by lactate dehydrogenase (LDH) release into the extracellular fluid. Treatment of cells with H. pylori extracts together with urea resulted in high levels of LDH release, suggesting definite gastric mucosal cell injury, and elevation of ammonia concentration was also observed. In contrast, incubation with H. pylori extracts alone or urea solution alone did not result in increased LDH release or elevated ammonia concentrations. The degree of LDH release from gastric mucosal cells due to H. pylori extracts in the presence of urea was similar to that induced by administration of the same amount of exogenous ammonia. The addition of acetohydroxamic acid, a potent specific urease inhibitor, remarkably inhibited ammonia production, the elevation of pH of extracellular fluid, and LDH release in a dose-dependent manner. These results suggest that ammonia produced by potent urease activity of H. pylori in the presence of urea plays an important role in the pathogenesis of gastric mucosal cell injury.

Effect of feeding diets containing an antibiotic, a probiotic, or yucca extract on growth and intestinal urease activity in broiler chicks

A 6-wk study was conducted to determine the effect of feeding diets containing an antibiotic, a probiotic, or yucca extract on daily gain, feed conversion ratio, and urease activity and ammonia production in intestinal contents of broiler chicks. Four replicates of 10 broiler chicks (average body weight, 48 g) each were assigned to a control or diets containing 0.1% chloroxytetracycline (antibiotic), 0.1% Lactobacillus casei (probiotic), or 0.2% yucca extract. Feeding a diet containing the probiotic significantly (P < 0.05) increased average daily gain during the first 3-wk period compared to the control (30.7 vs 28.7 g). This increase was partly accounted for by increased feed intake. During the first 3 wk, feeding the diet containing probiotic significantly (P < 0.05) decreased urease activity (per gram of collected contents) in small intestinal contents but not in large intestinal contents, compared with the control. Urease activity determined at 6 wk of age was not significantly affected by diet. Our studies indicate that dietary probiotic decreases urease activity in the small intestinal contents of young chicks and thus may be beneficial for improving animal health and growth, especially during early life.

Awakenings to the pathogenicity of urease and the requirement for continuous long term therapy

Urease is an enzyme found in plants and bacteria, but not mammals. It catalyzes the conversion of urea to carbon dioxide and ammonia. Ammonia shortens the life span of cells; and higher concentrations cause tissue necrosis and cytolysis. Twenty percent of total body urea is converted to ammonia by bacterial urease in the colon. Small injections of urease immunize animals by producing antiurease, a gamma globulin, which inactivates urease. Immunization eliminates the colonic conversion of urea to ammonia. Injection of urease produces ammonia intoxication making immunization hazardous. Although previously impossible, a non enzymatic urease antigen was synthesized by covalently bonding jack bean urease with glutaraldehyde. This antigen stimulated the production of antiurease that inactivates native urease. Helicobacter pylori, a potent urease producer, has been implicated in peptic ulcer, gastritis and other inflammatory bowel lesions. The pathogenicity of H pylori is dependent on its urease production. Immunization to urease can render H pylori non pathogenic. Cirrhotics develop encephalopathy and hyperammonemia because their livers fail to convert all the ammonia in portal venous blood to urea and collaterals develop by passing the liver. Colonic ammonia increases the turnover rate of colonic mucosa. Ammonia absorbed into the portal venous system is transported to the liver where it is reconverted to urea. Absorbed ammonia adversely influences liver function. Infections with urease producing organisms destroy the renal parenchyma and produce struvite stones. Urease immunization aids colonic healing and prevents uremic colitis. Absorbed ammonia is a noxious influence on the liver. Animals immunized to urease regenerate the liver faster and are less susceptible to hepatotoxins. Immunization to urease ameliorates cirrhosis. Proteus and other urease producers become non toxic and do not damage the renal parenchyma. Urease is responsible for the pathogenicity of infections with urease producing organisms. Immunization to urease renders urease producing organisms non pathogenic.

Phospholipase activity of Helicobacter pylori and its inhibition by bismuth salts. Biochemical and biophysical studies

In this study we measured phospholipase A (PLA) and C (PLC) activity of media filtrates and French Press lysates of the gastritis-inducing bacteria Helicobacter pylori. We report here that both H. pylori lysates and filtrates contain PLA1, PLA2, and C enzymes, which readily hydrolyze a radiolabeled dipalmitoylphosphatidylcholine (DPPC) and phosphorylcholine substrates, respectively. The specific activity of both PLA and C enzymes were greatest in the 6.5-7.0 and 8.4-8.8 pH ranges, respectively. Colloidal bismuth subcitrate (CBS) induced a dose-dependent inhibition of PLA2 and C activity of both H. pylori lysates and filtrates. This inhibitory effect of CBS on PLA2 was antagonized in a dose-dependent fashion by the addition of CaCl2 to the incubation mixture, suggesting that calcium and bismuth may be competing for the same site on the enzyme. In contrast, the ability of bismuth salts to inhibit PLC activity of H. pylori lysates was not antagonized by CaCl2. Employing a biophysical assay system for surface wettability, it was determined that H. pylori lysates had the capacity to remove a synthetic phospholipid monolayer off a glass in a dose-dependent fashion. This ability of the bacterial lysates to catalyze the transformation of a hydrophobic surface to a wettable state was significantly attenuated in the presence of bismuth salts. Our experimental results are, therefore, consistent with the possibility that H. pylori colonization compromises the stomach's barrier to acid by eroding a phospholipid lining, possibly a monolayer, on the surface of the gastric mucus gel and that this process is blocked in response to bismuth therapy.

Reduced incidence of stress ulcer in germ-free Sprague Dawley rats

Recent findings with respect to the role of spiral gram-negative bacteria in peptic ulcer disease have stimulated interest in discerning the role of these agents in stress ulcer disease. We tested the hypothesis that a standard restraint-cold ulcerogenic procedure would fail to produce ulcers in axenic rats. Axenic, as well as normal Sprague Dawley rats, were exposed to a cold-restraint procedure. The germ-free condition was maintained throughout the study in the axenic rats. Axenic rats had significantly fewer ulcers as compared to normal rats exposed to the standard cold-restraint procedure, as well as handling control rats. The data represent the first report suggesting a microbiologic component in the development of stress ulcer using the rat model.

Is there a place for antacids in the treatment of Helicobacter pylori infection?

Two pilot studies were performed to determine whether aluminium-containing antacids may have a place in the treatment of Helicobacter pylori infection. The urease activity of H. pylori is cytopathic to gastric epithelium, and inhibition of this enzyme may have therapeutic potential. In the first study 24 subjects, 12 of which were infected with H. pylori, were given 1 tablet of chewable aluminium hydroxide-containing antacids 10 min before a 14C-urea breath test. Gastric urease activity was suppressed by 33.3% (p = 0.02) in the H. pylori-positive subjects (none became negative) within 40 min after administration of the tablet. Gastric H. pylori infection can be effectively eradicated by triple regimens containing bismuth salts, tetracycline, and metronidazole. Owing to adverse effects of this treatment and concern for possible neurotoxicity of bismuth, a bismuth substitute is warranted. Hence, in the second study, 20 subjects infected with H. pylori were treated with 1 antacid tablet 4 times daily between meals, plus 500 mg oxytetracycline and 200 mg metronidazole 4 times daily with meals for 2 weeks. Individual H. pylori status was assessed by the 14C-urea breath test. Four weeks after cessation of treatment, H. pylori was eradicated in 45% (9 of 20) of the subjects (95% confidence interval, 23.1-68.5%). Thirty per cent (6 of 20) observed one or more adverse effect regarded as moderate or severe, of which loose stools and headache were the most common.(ABSTRACT TRUNCATED AT 250 WORDS)