beta-Carotene inhibits inflammatory gene expression in lipopolysaccharide-stimulated macrophages by suppressing redox-based NF-kappaB activation.

beta-Carotene has shown antioxidant and anti-inflammatory activities; however, its molecular mechanism has not been clearly defined. We examined in vitro and in vivo regulatory function of beta-carotene on the production of nitric oxide (NO) and PGE(2) as well as expression of inducible NO synthase (iNOS), cyclooxygenase-2, TNF-alpha, and IL-1beta. beta-Carotene inhibited the expression and production of these inflammatory mediators in both LPS-stimulated RAW264.7 cells and primary macrophages in a dose-dependent fashion as well as in LPS-administrated mice. Furthermore, this compound suppressed NF-kappaB activation and iNOS promoter activity in RAW264.7 cells stimulated with LPS. beta-Carotene blocked nuclear translocation of NF-kappaB p65 subunit, which correlated with its inhibitory effect on IkappaBalpha phosphorylation and degradation. This compound directly blocked the intracellular accumulation of reactive oxygen species in RAW264.7 cells stimulated with LPS as both the NADPH oxidase inhibitor diphenylene iodonium and antioxidant pyrrolidine dithiocarbamate did. The inhibition of NADPH oxidase also inhibited NO production, iNOS expression, and iNOS promoter activity. These results suggest that beta-carotene possesses anti-inflammatory activity by functioning as a potential inhibitor for redox-based NF-kappaB activation, probably due to its antioxidant activity.