Carnosol, an antioxidant in rosemary, suppresses inducible nitric oxide synthase through down-regulating nuclear factor-κB in mouse macrophages

Carnosol is a naturally occurring phytopolyphenol found in rosemary. Carnosol functions as antioxidant and anticarcinogen. In the present study, we compared the antioxidant activity of carnosol and other compounds extracted from rosemary. Carnosol showed potent antioxidative activity in α,α-diphenyl-β-picrylhydrazyl (DPPH) free radicals scavenge and DNA protection from Fenton reaction. High concentrations of nitric oxide (NO) are produced by inducible NO synthase (iNOS) in inflammation and multiple stages of carcinogenesis. Treatment of mouse macrophage RAW 264.7 cell line with carnosol markly reduced lipopolysaccharide (LPS)-stimulated NO production in a concentration-related manner with an IC₅₀ of 9.4 μM; but other tested compounds had slight effects. Western blot, reverse transcription-polymerase chain reaction, and northern blot analyses demonstrated that carnosol decreased LPS-induced iNOS mRNA and protein expression. Carnosol treatment showed reduction of nuclear factor-κB (NF-κB) subunits translocation and NF-κB DNA binding activity in activated macrophages. Carnosol also showed inhibition of iNOS and NF-κB promoter activity in transient transfection assay. These activities were referred to down-regulation of inhibitor κB (IκB) kinase (IKK) activity by carnosol (5 μM), thus inhibited LPS-induced phosphorylation as well as degradation of IκBα. Carnosol also inhibited LPS-induced p38 and p44/42 mitogen-activated protein kinase (MAPK) activation at a higher concentration (20 μM). These results suggest that carnosol suppresses the NO production and iNOS gene expression by inhibiting NF-κB activation, and provide possible mechanisms for its anti-inflammatory and chemopreventive action.