Biochanin A ameliorates the cytokine secretion profile of lipopolysaccharide-stimulated macrophages by a PPARγ-dependent pathway

The role of peroxisome proliferator-activated receptors (PPARs) as anti-inflammatory mediators has been established, and the fact that some isoflavones are dual agonists of PPARc/gamma indicates the involvement of PPAR alpha and/or PPAR gamma in the anti-inflammatory action of certain isoflavones. However, the dependency of isoflavones on PPARs in their anti-inflammatory action has not been demonstrated. Here, we report the dependency of an isoflavone biochanin A and the independency of another isoflavone genistein in relation to PPAR gamma to ameliorate the cytokine secretion profile of lipopolysaccharide (LPS)-simulated mouse RAW264.7 macrophages. A total amount of 10 mu mol/l of biochanin A or genistein significantly suppressed the secretion of tumor necrosis factor alpha (TNF alpha) and interleukin-6 (IL-6) in LPS-induced RAW264.7 cells, whereas another two isoflavones, formononectin and daidzein, only significantly suppressed the secretion of IL-6. Their anti-inflammatory efficiencies were not in correspondence with their PPAR alpha/gamma agonist activities. Inhibition of PPAR gamma activity by its antagonist GW9662 significantly reversed the anti-inflammatory effect of biochanin A but not genistein, which demons sated the dependency of biochanin A and the independency of genistein on PPAR gamma in their anti-inflammatory actions. Meanwhile, the PPAR gamma-dependency of biochanin A was further confirmed by the result that the suppression of LPS-induced NF-kappa B activation by biochanin A was reversed following GW9662 co-treatment. Moreover, inhibition of PPARa activity by its antagonist MK886 did not significantly reverse the anti-inflammatory effects of biochanin A and genistein, indicating that their anti-inflammatory properties were PPAR alpha-independent.