Dietary nitrite induces occludin nitration in the stomach

Abstract

The clinical implications of the nitrate–nitrite–nitric oxide pathway have been extensively studied in recent years. However, the physiological impact of bioactive nitrogen oxides produced from dietary nitrate has remained largely elusive. Here, we report a hitherto unrecognized nitrite-dependent nitrating pathway that targets tight junction proteins in the stomach. Inorganic nitrate, nitrite or saliva obtained after the consumption of lettuce were administered by oral gavage to Wistar rats. The enterosalivary circulation of nitrate was allowed to occur for 4 h after which the animals were euthanized and the stomach collected. Nitrated occludin was detected by immunoprecipitation in the gastric epithelium upon inorganic nitrite administration (p < .05) but was not observed in the case of inorganic nitrate or human saliva administration. This observation, along with differences in ^•NO production rates from inorganic and salivary nitrite under simulated gastric conditions, suggests that competing reactions at acidic pH determine the production of nitrating agents (^•NO₂) or other, more stable, oxides. Accordingly, it is shown in vitro that salivary nitrite yields higher steady state concentrations of ^•NO (0.37 ± 0.01 μM) than sodium nitrite (0.12 ± 0.03 μM). Dietary-dependent reactions involving the production of nitrogen oxides should be further investigated as, in the context of occludin nitration, the consumption of green leafy vegetables (with high nitrate content), if able to modulate gut barrier function, may have important implications in the context of leaky gut disorders.

Keywords:

• Dietary nitrite
• occludin
• nitration
• gut

Acknowledgements

We would like to thank Dr. Rui M. Barbosa for helpful discussions and critically reviewing the manuscript.

Disclosure statement

The authors report no conflict of interest.

Funding

This work was supported by FCT – Funda¸ão para a Ciência e Tecnologia, Portugal, by grant [PTDC/BBB-BQB/3217/2012]. This work was supported by FCT – Fundação para a Ciência e Tecnologia, Portugal, by grant [UID/NEU/04539/2013]. BSR acknowledges the grant [SFRH/BPD/84438/2012] from FCT, Portugal.