Fe-S cluster proteins are intracellular targets for nitric oxide generated luminally at the gastro-oesophageal junction

Abstract

In human, high concentrations of nitric oxide are generated at the gastro-oesophageal junction through entero-salivary recirculation of dietary nitrate. Nitric oxide is known to have a high affinity for Fe-S cluster proteins. The aim of this study is to investigate whether nitric oxide arising from the lumen diffuses into the adjacent tissue where it can interact with Fe-S proteins both in a rat animal model and human. An electron paramagnetic resonance detectable complex, dinitrosyl dithiolato iron complex (DNIC), was used as a biomarker for the interaction between Fe-S proteins and nitric oxide. The generation of the complex was evaluated in resected gastric tissue of nitrite-administered rat or biopsy specimens from human after nitrate ingestion. The activity of aconitase, one of the Fe-S cluster proteins, was also determined. The signal of the complex was observed at the rat gastro-oesophageal junction where luminal generation of nitric oxide from nitrite was maximal, and the intensity increased in a dose- and time-dependent manner. The appearance of the complex was accompanied by a significant inhibition of the aconitase activity at that site. The complex appeared in biopsy specimens from the gastro-oesophageal junction in three of five men after nitrate ingestion. Since DNIC is considered to be a decomposition product when Fe-S cluster proteins interact with nitric oxide, the appearance of the signal provides direct evidence that nitric oxide arising from the lumen can destroy such proteins. DNIC formation may represent the cellular mechanism responsible for the high prevalence of disease at the gastro-oesophageal junction.