Inhibited Nitrite Production Research Articles

Suppression of nitric oxide production by cyclosporin A and FK506A in rat vascular smooth muscle cells.

1. The effects of the immunosuppressants cyclosporin A (CsA) and FK506 on nitric oxide (NO) synthesis induced by lipopolysaccharide (LPS) or cytokines were examined in rat vascular smooth muscle cells (VSMC) in culture. 2. CsA inhibited by up to 90% the accumulation of nitrite induced by LPS, but FK506 had a weaker effect on nitrite accumulation induced by LPS in these cells. Both CsA and FK506 (at 1 mumol/L) significantly inhibited nitrite production induced by recombinant murine interleukin-1 beta (rIL-1 beta). 3. Given their differing potency, it is likely that CsA and FK506 suppress induction of NO synthase through different intracellular mechanisms. This action could contribute to the side effects of CsA therapy.

Inhibition of macrophage nitric oxide production by arachidonate-cascade inhibitors.

We examined whether inhibitors of the arachidonic acid cascade inhibited nitric oxide (NO) production, as measured by nitrite concentration, either in macrophages or by their cytosolic fractions. Nitrite production by peritoneal macrophages from mice receiving OK-432 treatment was significantly inhibited by phospholipase A2 inhibitors [dexamethasone and 4-bromophenacyl bromide (4-BPB)], lipoxygenase inhibitors [nordihydroguaiaretic acid (NDGA) and ketoconazole] and a glutathione S-transferase (leukotrienes LTA4-LTC4) inhibitor (ethacrynic acid). However, caffeic acid and esculetin, inhibitors of 5- and 12-lipoxygenase respectively, were not inhibitory. On the other hand, indomethacin, a cyclooxygenase inhibitor, slightly inhibited whereas another inhibitor, ibuprofen, did not. Inhibition of the nitrite production by dexamethasone, 4-BPB, NDGA and ethacrynic acid was also demonstrated when the macrophages were restimulated ex vivo with OK-432 or with lipopolysaccharide. The inhibitory activity of dexamethasone, NDGA and ethacrynic acid was significantly reduced by ex vivo restimulation with OK-432, whereas that of 4-BPB was hardly affected. Furthermore, the inhibitory activity of dexamethasone, NDGA and ethacrynic acid was much higher when the macrophages were continuously exposed to the agents than when they were pulsed. Meanwhile, inhibition by 4-BPB was almost the same with either treatment. In addition, the inhibitory activity of these agents was not blocked with L-arginine, a substrate of NO synthases, or with arachidonate metabolites (LTB4, LTC4 and LTE4). Ethacrynic acid and 4-BPB, but not dexamethasone and NDGA, also inhibited nitrite production by the cytosolic fractions from OK-432-restimulated peritoneal macrophages, and the inhibitory activity of 4-BPB was superior to that of ethacrynic acid. These agents, however, did not inhibit nitrite production from sodium nitroprusside, a spontaneous NO-releasing compound. These results indicate that dexamethasone, 4-BPB, NDGA and ethacrynic acid inhibited the production of NO by macrophages through at least two different mechanisms: one was inhibited by dexamethasone, NDGA and ethacrynic acid and the other by 4-BPB. Furthermore, 4-BPB and ethacrynic acid directly inhibited the activity of the NO synthase in macrophages, suggesting that the agents work by binding to the active site(s) of the enzyme.

Neutrophil-mediated nitrosamine formation: Role of nitric oxide in rats

It is well known that chronic inflammation of the colon and rectum is associated with an increased risk of colorectal cancer, but the mechanisms by which inflammation promotes neoplasia remain undefined. The authors propose that inflammatory neutrophils may produce carcinogenic nitrosamines via the l-arginine-dependent formation of nitrogen oxides such as nitric oxide. Therefore, the objectives of the study were to characterize the l-arginine-dependent formation of nitrogen oxides by inflammatory (elicited) neutrophils using conditions that more closely mimic the extravascular (i.e., interstitial) compartment of the gut and to characterize the neutrophil-dependent N-nitrosation of a model amine to yield its nitrosamine derivative. In the absence of any metabolic activation, adherent, inflammatory neutrophils (2 × 106 cells) produced 12.8 ± 1.4 μmol/L of nitrite during a 4-hour incubation period. Omission of l-arginine and/or inhibition of nitric oxide synthase by the addition of 1 mmol/L NG-nitro-l-arginine methyl ester (l-NAME) resulted in 35%–78% inhibition of nitrite production, suggesting that nitrite was derived from nitric oxide. By comparison, neither circulating rat neutrophils nor elicited rat macrophages produced significant amounts of nitrite under the same conditions. Furthermore, elicited neutrophils (2 × 106 cells) were capable of N-nitrosating 2,3-diaminonapthalene to yield its nitrosamine derivative 1-naptho-2,3-triazole (282 ± 12 nmol/L) in a time- and cell-dependent pattern similar to that of nitrite production. Addition of a variety of antioxidants (e.g., ascorbic acid, reduced glutathione, α-tocopherol analog), 5-aminosalicylic acid, or l-NAME resulted in 80%–85% inhibition of neutrophil-mediated nitrosamine formation. Taken together, these data suggest that inflammatory neutrophils may represent an important metabolic source of endogenous carcinogens during times of active intestinal inflammation.

Effects of phenolic acids on ammonia oxidation by terrestrial autotrophic nitrifying microorganisms

Abstract It has been hypothesized that vegetation in certain ecosystems inhibits nitrification in soil by producing phenolic compounds that inhibit oxidation of ammonia by nitrifying microorganisms. This hypothesis is based largely on a report that very low concentrations (10 −6 M–10 −8 M) of several phenolic acids (notably ferulic acid) completely inhibited NO 2 − production in an aqueous suspension of soil treated with (NH 4 ) 2 SO 4 and a nutrient solution suitable for growth of Nitrosomonas and other autotrophic nitrifying microorganisms. To evaluate this hypothesis, we determined the effects of three ohenolic acids (ferulic acid, caffeic acid, and p -coumaric on nitrite production by representatives of three genera of terrestrial autotrophic nitrifying microorganisms ( Nitrosospira, Nitrosomonas, or Nitrosolubos ) grown on a defined medium containing NH 4 + . We found that nitrite production by the Nitrososspira was not inhibited by ferulic acid, caffeic acid, or p -coumaric acid at concentrations of 10 −6 or 10 −5 M and was only slightly inhibited when these acids were at a concentration of 10 −4 M. We also found that ferulic acid did not markedly inhibit nitrite production by the three genera of nitrifying microorganisms studied, even when its concentration was as high as 10 −3 M. These observations invalidate the hypothesis tested because the phenolic acids studied did not significantly retard ammonia oxidation by autotrophic microorganisms even when their concentration in cultures of these microorganisms greatly exceeded their concentrations in soils.

The effect of nitrapyrin and chloropicolinic acid on ammonium oxidation byNitrosomonas europaea

Both nitrapyrin and 6-chloropicolinic acid inhibited nitrite production when added to stationary-phase and exponentially growing cells of Nitrosomonas europaea at a concentration of 2.17 μM. Nitrapyrin inhibited growth immediately, but there was a lag before inhibition by chloropicolinic acid added to growing cells, and induction of a lag phase when this was added to stationary phase cells. There was no effect on the subsequent specific oxidation rate.

Effect of Parthenium hysterophorus on nitrogen-fixing and nitrifying bacteria

Root or leaf extract of Parthenium hysterophorus L. inhibited the growth of Rhizobium phaseoli and Azotobacter vinelandii. Similar inhibition was caused by parthenin, caffeic acid, and anisic acid, the important inhibitors isolated from the weed. Leghaemoglobin content in the root nodules of the bean plants grown in soil mixed with Parthenium leaf was reduced significantly as compared with the control. Nitrosomonas activity was progressively lowered with decreasing distance from the plant and also in leaf- or root-mixed soil. Leaf and root leachate, parthenin, anisic acid, vanillic acid, and fumaric acid inhibited nitrite production to varying degrees.

Role of the central nervous system in hepatic steroid and ammonia metabolism — studies on the cerebro-hepatic relationship

Effects of guanidino and uremic compounds on nitric oxide pathways. Aminoguanidine, NG-monomethyl-L-arginine (L-NMMA), NGNGdimethyl-L-arginine (asymmetric dimethylarginine; ADMA), creatinine, guanidinosuccinic acid, guanidinoproprionic acid and methylguanidine were added to cultures of activated murine macrophages. Only aminoguanidine, ADMA, L-NMMA and methylguanidine inhibited nitrite production in a dose-dependent manner. In the presence of 100 µM arginine, nitrite production was inhibited by 31.8 ± 7.1% by ADMA (100 µM; P < 0.01) but the same dose of methylguanidine was without effect. A higher dose of methylguanidine (1000 µM) inhibited nitrite production by 47.6 ± 5.6% (P < 0.001). The effects of these compounds were also tested on relaxation of human saphenous veins. L-NMMA and ADMA inhibited endothelium-dependent relaxations (EC50 = 4.7 ± 1.1 µM and 17.9 ± 4.9 µM, respectively); methylguanidine caused endothelium-independent contractions and reversed the relaxations to bradykinin and sodium nitroprusside (EC50 > 100 µM); aminoguanidine was without effect. The results of this study suggest that of the guanidino compounds which accumulate in renal failure, only ADMA is a potent inhibitor of nitric oxide (NO) synthesis. Methylguanidine is a weak inhibitor of nitric oxide synthesis, whereas the closely related compound aminoguanidine appears to inhibit selectively the inducible isoform of nitric oxide synthase and has no effect on constitutive NO synthase in human veins.