Nitrate partially inhibits lipopolysaccharide-induced inflammation by maintaining mitochondrial function.

OBJECTIVE

Nitrate has been reported to protect cells the nitrate-nitrite-nitric oxide (NO) pathway. Most studies tend to use nitrite to investigate the mechanisms of this pathway. However, the latest studies have confirmed that mammals can directly degrade nitrate xanthine oxidoreductase (XOR). The hypothesis is that nitrate could play a protective role in inflammatory responses independent of bacterial nitrate reductases.

METHODS

Mouse RAW264.7 macrophages were pre-incubated with sodium nitrate (10, 100, and 500 µM) for 2 hours, and then treated with lipopolysaccharide (LPS) for 2 hours to induce inflammation. The Quantikine Immunoassay was used to measure interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) concentrations in the supernatant. The fluorescence intensity ratio of red/green from JC-1 was used to assay mitochondrial membrane potential. The fluorescence intensity of MitoSOX Red was used to indicate the generation of mitochondrial reactive oxygen species.

RESULTS

Nitrate partially reduced IL-6 and TNF-α secretion reducing NF-κB signaling in LPS-induced macrophages. Nitrate also reduced the generation of mitochondrial reactive oxygen species by regulating mitochondrial function. These effects depended on XOR-derived NO but were independent of inducible nitric oxide synthase-derived NO.

CONCLUSION

Nitrate regulates mitochondrial function XOR-derived NO to partially inhibit LPS-induced inflammation.