ABSTRACT
A multi-species nitrifying biofilm model (MSNBM) is developed to describe nitrite accumulation by simultaneous free ammonia (FA) and free nitrous acid (FNA) inhibition, direct pH inhibition, and oxygen limitation in a biofilm. The MSNBM addresses the spatial gradient of pH with biofilm depth and how it induces changes of FA and FNA speciation and inhibition. Simulations using the MSNBM in a completely mixed biofilm reactor show that influent total ammonia nitrogen (TAN) concentration, bulk dissolved oxygen (DO) concentration, and buffer concentration exert significant control on the suppression of nitrite-oxidizing bacteria (NOB) and shortcut biological nitrogen removal (SBNR), but the pH in the bulk liquid has a weaker influence. Ammonium oxidation increases the nitrite concentration and decreases the pH, which together can increase FNA inhibition of NOB in the biofilm. Thus, a low buffer concentration can accentuate SBNR. DO and influent TAN concentrations are efficient means to enhance DO limitation, which affects NOB more than ammonia-oxidizing bacteria (AOB) inside the biofilm. With high influent TAN concentration, FA inhibition is dominant at an early phase, but finally DO limitation becomes more important as TAN degradation and biofilm growth proceed. MSNBM results indicate that oxygen depletion and FNA inhibition throughout the biofilm continuously suppress the growth of NOB, which helps achieve SBNR with a lower TAN concentration than in systems without concentration gradients.
Subject(s)
Ammonia/metabolism , Biofilms , Models, Biological , Nitrites/metabolism , Nitrous Acid/antagonists & inhibitors , Oxygen/metabolism , Algorithms , Biomass , Buffers , Computer Simulation , Hydrogen-Ion Concentration , Kinetics , Nitrous Acid/metabolism , Oxidation-Reduction , Systems Biology/methodsABSTRACT
Studies have suggested that diets rich in polyphenols such as flavonoids may lead to a reduced risk of gastrointestinal cancers. We demonstrate the ability of monomeric and dimeric flavanols to scavenge reactive nitrogen species derived from nitrous acid. Both epicatechin and dimer B2 (epicatechin dimer) inhibited nitrous acid-induced formation of 3-nitrotyrosine and the formation of the carcinogenic N-nitrosamine, N-nitrosodimethylamine. The reaction of monomeric and dimeric epicatechin with nitrous acid led to the formation of mono- and di-nitroso flavanols, whereas the reaction with hesperetin resulted primarily in the formation of nitrated products. Although, epicatechin was transferred across the jejunum of the small intestine yielding metabolites, its nitroso form was not absorbed. Dimer B2 but not epicatechin monomer inhibited the proliferation of, and triggered apoptosis in, Caco-2 cells. The latter was accompanied by caspase-3 activation and reductions in Akt phosphorylation, suggesting activation of apoptosis via inhibition of prosurvival signaling. Furthermore, the dinitroso derivative of dimer B2, and to a lesser extent the dinitroso-epicatechin, also induced significant toxic effects in Caco-2 cells. The inhibitory effects on cellular proliferation were paralleled by early inhibition of ERK 1/2 phosphorylation and later reductions in cyclin D1 levels, indicating modulation of cell cycle regulation in Caco-2 cells. These effects highlight multiple routes in which dietary derived flavanols may exert beneficial effects in the gastrointestinal tract.
Subject(s)
Colonic Neoplasms/drug therapy , Flavonoids/chemistry , Flavonoids/pharmacology , Nitroso Compounds/metabolism , Nitroso Compounds/pharmacology , Nitrous Acid/chemistry , Absorption , Animals , Apoptosis/drug effects , Apoptosis/physiology , Caco-2 Cells , Caspase 3 , Caspases/drug effects , Caspases/metabolism , Catechin/analogs & derivatives , Catechin/chemistry , Catechin/pharmacology , Cell Cycle/drug effects , Cell Cycle/physiology , Cell Proliferation/drug effects , Colonic Neoplasms/metabolism , Cyclin D1/drug effects , Cyclin D1/metabolism , Dimethylnitrosamine , Dose-Response Relationship, Drug , Drug Screening Assays, Antitumor , Gastrointestinal Tract/drug effects , Humans , In Vitro Techniques , Mitogen-Activated Protein Kinase Kinases/drug effects , Mitogen-Activated Protein Kinase Kinases/metabolism , Nitrosamines/antagonists & inhibitors , Nitrosamines/chemistry , Nitrosamines/metabolism , Nitroso Compounds/chemistry , Nitrous Acid/antagonists & inhibitors , Phenols/chemistry , Phenols/pharmacology , Phosphorylation , Proto-Oncogene Proteins c-akt/drug effects , Proto-Oncogene Proteins c-akt/metabolism , Rats , Reactive Nitrogen Species/antagonists & inhibitors , Reactive Nitrogen Species/pharmacology , Time Factors , Tyrosine/analogs & derivatives , Tyrosine/antagonists & inhibitors , Tyrosine/metabolismABSTRACT
Peroxynitrous acid synthesized by reaction of hydrogen peroxide and nitrite and generated from 3-morpholinosydononimine (SIN-1) induced cellular DNA breaking of human promyelocytic leukemia HL-60 cells in phosphate buffer (pH 7.5) as assessed by alkaline single cell gel electrophoresis (comet) assay and quantification of comet types. Ascorbate and Trolox inhibited cellular DNA breaking induced by peroxynitrous acid, but the concentrations of these antioxidants required for effective inhibition was about 50-fold higher than that of peroxynitrous acid. beta-Carotene protected DNA breaking by peroxynitrous acid in 20% tetrahydrofuran-phosphate buffer (pH 7.5) much more effectively than ascorbate and Trolox. The concentrations of beta-carotene required for effective inhibition was lower than the concentration of peroxynitrous acid.
