Inorganic nitrate prevents the loss of tight junction proteins and modulates inflammatory events induced by broad-spectrum antibiotics: A role for intestinal microbiota?

Abstract

Upon consumption, dietary nitrate is reduced to nitrite in the oral cavity and to nitric oxide (^•NO) in the stomach. Here, ^•NO increases mucosal blood flow, mucus thickness and prevents microbial infections. However, the impact of nitrate on gut microbiota, a pleiotropic organism essential to maintain gastrointestinal and systemic welfare, remains elusive. This study investigates the impact of nitrate on gut microbiota profile and ensued mucosal effects during dysbiosis. Male Wistar rats were randomly distributed in 4 groups and the drinking water was supplemented for 7 days as follows: 1) antibiotic cocktail (neomycin, bacitracin and imipenem), 2) antibiotic cocktail + sodium nitrate, 3) sodium nitrate and 4) regular drinking water. Animals were weighted daily and feces were collected before and after the treatment. The stomach was isolated and the expression of occludin, claudin-5 as well as myeloperoxidase and iNOS was studied. Bacterial DNA was analyzed in fecal samples by PCR-DGGE genetic fingerprinting. Nitrate prevented antibiotic-induced body weight loss (1.9 ± 1.8% vs 8.9 ± 1.8%, p < 0.05) and cecamegalia (7.1 ± 0.5% vs 5.6 ± 0.4%, p < 0.05). Gastric expression of occludin and claudin-5 tended to decrease during dysbiosis but both protein levels were recovered following nitrate consumption (p < 0.05). Similarly, nitrate inhibited the overexpression of myeloperoxidase and iNOS observed under dysbiosis (p < 0.05). Broad spectrum antibiotics significantly decreased microbiota richness and diversity in comparison to controls (p = 0.0016). After 7 days of treatment, whereas antibiotics reduced microbiota richness by 56%, it was observed that nitrate was able to prevent such microbial loss to only 48%, although without statistical differences (p = 0.068). This data suggests that dietary nitrate may be envisaged as a key component of functional foods with beneficial impact on gastric mucosal integrity during antibiotherapy but further studies are mandatory to better ascertain as to whether it modulates intestinal microbiota in terms of taxonomic and functional levels.

Keywords: Antibiotics; Inflammation; Microbiome; Nitrate; Tight junctions; gut.