Improved group determination of total N-nitroso compounds in human gastric juice by chemical denitrosation and thermal energy analysis

Abstract

A procedure for the determination of total N-nitroso compounds (NOC) in human gastric juice was developed by modifying earlier methods. The gastric juice sample, treated with sulphamic acid to remove nitrite, is injected directly into refluxing ethyl acetate containing either acetic acid for determining thermo-and acetic acid labile thermal energy analyser (TEA) responsive compounds (TAC), or into hydrogen bromide for the determination of TAC and NOC. The nitric oxide (NO) levels released are measured using thermal energy analysis with chemiluminescence detection, and the difference between the two determinations represents the concentrations of NOC in gastric juice. This method is not affected by nitrate concentrations of up to 1000 pmol I-'.The method was found to be rapid, reproducible and sensitive (detection limit 0.02 ymol I-' NOC), requiring only small volumes of gastric juice and no prior extraction. Because the difficulties arising from the system response to the denitrosating agent and variability of NO release by acetic acid from nitrite were eliminated, this improved method can more accurately distinguish NOC from most other TEA-responsive species. Suitable techniques for stabilising gastric juice samples from duodenal ulcer and atrophic gastritis patients and the influence of the time and storage conditions on NOC concentrations have been studied.

N-Nitroso compounds in the gastrointestinal tract of rats and in the feces of mice with induced colitis or fed hot dogs or beef

“…The results in Exp. 3 (Figure 2) extend the sections of the GIT known to contain NOC from the previously studied stomach (33) and colon (7) to the entire GIT, and suggest that at least some fecal NOC arise from dietary NOC that pass unabsorbed through the GIT. Most likely, NOC concentration increases on descending the GIT because the GIT mucosa absorbs water and digested food components, but not some of the NOC.…”

“…To determine NOC (8), 850 µl of supernatant A was mixed with 50 µl of 2 N HCl and 100 µl of a freshly prepared saturated solution of sulfamic acid in water to destroy any nitrite present. After the mixture was kept for 15 min at room temperature and up to 4 h on ice, 100-200 µl samples were injected into a modified Walters' system for determining total NOC, in which NOC are decomposed to NO by an HBr/HCl/HOAc/EtOAc mixture refluxing under reduced pressure at 28°C (8,33,34). The NO is swept in a stream of argon through seven wash bottles to dry and remove acid from the gas stream, and is then passed into a Thermal Energy Analyzer to determine the NO.…”

Meat Processing and Colon Carcinogenesis: Cooked, Nitrite-Treated, and Oxidized High-Heme Cured Meat Promotes Mucin-Depleted Foci in Rats

“…Fecal samples were stored at −20°C before they were transported on dry ice to Pollock and Pool Ltd. for apparent total N-nitroso compound (ATNC) determination (38). Fecal samples were prepared for analysis by macerating feces with 10 times their weight of water and centrifuging.…”

Dietary meat, endogenous nitrosation and colorectal cancer

“…The analytical method used relies on chemical denitrosation using HBr and/or HCl [20][21][22] and NO detection by chemiluminescence [23]. Although this method has been developed and refined for the analysis of NOCs [21,[24][25][26], the chemical denitrosation with HBr can also release NO from other compounds such as nitroso thiols (SNO) [24,27], nitriolic acid [26], O-nitroso compounds and nitrosyl iron (FeNO) [28]. Owing to this lack in specificity, the term ATNC (apparent total N-nitroso compound) is used to describe substances measured by this technique [19].…”