Development of an in vitro system combining aqueous and lipid phases as a tool to understand gastric nitrosation

Effect of carnosine on nitrosamine formation in gastric-simulated aqueous and lipid environments

BACKGROUND

Nitrite salts are frequently utilized as meat additives to improve the quality and safety of processed meat products. However, these salts are associated with the formation of carcinogenic nitrosamines. Given its potential regulating effect on the formation of intermediate molecules, such as nitric oxide, it is hypothesized that carnosine, a meat constituent possessing antioxidant activity and other multiple health benefits, could dampen the formation of nitrosamines. The current study therefore assessed the effect of carnosine on nitrosamine formation in both a monophasic aqueous system and a biphasic water-lipid system simulating a gastric environment.

RESULTS

In the monophasic system, relatively high levels of carnosine were required to significantly reduce the formation of different species of nitrosamine compared with the control (no carnosine). While higher levels of some nitrosamines were generated in both phases of the biphasic system, low carnosine concentrations significantly suppressed nitrosamine formation in the aqueous phase, while in the lipid phase, intermediate levels of carnosine were required. At higher carnosine levels, further reduction in nitrosamines was observed in the lipid phase.

CONCLUSIONS

This study demonstrates the capacity of carnosine to reduce nitrosamine formation in aqueous and lipid environments and suggests the potential of dietary carnosine to lower the risks associated with the consumption of processed meat products. © 2024 His Majesty the King in Right of Canada and The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. Reproduced with the permission of the Minister of Agriculture and Agri-Food Canada.

Genetic and epigenetic instability induced by betel quid associated chemicals

Over the years, betel quid chewing and tobacco use have attracted considerable interest as they are implicated as the most likely causative risk factors of oral and esophageal cancers. Although areca nut use and betel quid chewing may lead to apoptosis, chronic exposure to areca nut and slaked lime may promote pre-malignant and malignant transformation of oral cells. The putative mutagenic and carcinogenic mechanisms may involve endogenous nitrosation of areca and tobacco alkaloids as well as the presence of direct alkylating agents in betel quid and smokeless tobacco. Metabolic activation of carcinogenic N-nitrosamines by phase-I enzymes is required not only to elicit the genotoxicity via the reactive intermediates but also to potentiate the mutagenicity with the sporadic alkylations of nucleotide bases, resulting in the formation of diverse DNA adducts. Persistent DNA adducts provides the impetus for genetic and epigenetic lesions. The genetic and epigenetic factors cumulatively influence the development and progression of disorders such as cancer. Accumulation of numerous genetic and epigenetic aberrations due to long-term betel quid (with or without tobacco) chewing and tobacco use culminates into the development of head and neck cancers. We review recent evidence that supports putative mechanisms for mutagenicity and carcinogenicity of betel quid chewing along with tobacco (smoking and smokeless) use. The detailed molecular mechanisms of the extent of accumulation and patterns of genetic alterations, indicative of the prior exposure to carcinogens and alkylating agents because of BQ chewing and tobacco use, have not yet been elucidated.

Exogenous asymmetric dimethylarginine (ADMA) in pathogenesis of ischemia-reperfusion-induced gastric lesions: interaction with protective nitric oxide (NO) and calcitonin gene-related peptide (CGRP)

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide (NO) synthesis inhibitor and pro-inflammatory factor. We investigated the role of ADMA in rat gastric mucosa compromised through 30 min of gastric ischemia (I) and 3 h of reperfusion (R). These I/R animals were pretreated with ADMA with or without the combination of l-arginine, calcitonin gene-related peptide (CGRP) or a small dose of capsaicin, all of which are known to afford protection against gastric lesions, or with a farnesoid X receptor (FXR) agonist, GW 4064, to increase the metabolism of ADMA. In the second series, ADMA was administered to capsaicin-denervated rats. The area of gastric damage was measured with planimetry, gastric blood flow (GBF) was determined by H₂-gas clearance, and plasma ADMA and CGRP levels were determined using ELISA and RIA. ADMA significantly increased I/R-induced gastric injury while significantly decreasing GBF, the luminal NO content, and the plasma level of CGRP. This effect of ADMA was significantly attenuated by pretreatment with CGRP, l-arginine, capsaicin, or a PGE₂ analogue. In GW4064 pretreated animals, the I/R injury was significantly reduced and this effect was abolished by co-treatment with ADMA. I/R damage potentiated by ADMA was exacerbated in capsaicin-denervated animals with a further reduction of CGRP. Plasma levels of IL-10 were significantly decreased while malonylodialdehyde (MDA) and plasma TNF-α contents were significantly increased by ADMA. In conclusion, ADMA aggravates I/R-induced gastric lesions due to a decrease of GBF, which is mediated by a fall in NO and CGRP release, and the enhancement of lipid peroxidation and its pro-inflammatory properties.