Carnosine modulates nitric oxide in stimulated murine RAW 264.7 macrophages

Excess nitric oxide (NO) production occurs in several pathological states, including neurodegeneration, ischemia, and inflammation. Carnosine has been reported to decrease oxidative/nitrosative stress-associated cell damage by reducing the amount of NO produced. In this study, we evaluated the effect of carnosine on NO production by macrophages stimulated with LPS + IFN-γ. Intracellular NO and intracellular and extracellular nitrite were measured by microchip electrophoresis with laser-induced fluorescence and by the Griess assay, respectively. Results showed that carnosine causes an apparent suppression of total NO production by stimulated macrophages accompanied by an unexpected simultaneous drastic increase in its intracellular low toxicity endproduct, nitrite, with no inhibition of inducible nitric oxide synthase (iNOS).
ESI-MS and NMR spectroscopy in a cell-free system showed the formation of multiple adducts (at different
ratios) of carnosine-NO and carnosine-nitrite, involving both constituent amino acids (β-Ala and His) of carnosine, thus providing a possible mechanism for the changes in free NO and nitrite in the presence of carnosine. In stimulated macrophages, the addition of carnosine was also characterized by changes in the expression of macrophage activation markers and a decrease in the release of the pro-inflammatory cytokine IL-6, suggesting that carnosine might alter M1/M2 macrophage ratio.