Caffeoylglycolic acid methyl ester, a major constituent of sorghum, exhibits anti-inflammatory activity via the Nrf2/heme oxygenase-1 pathway

Abstract

Sorghum contains diverse pharmacologically active phytochemicals including tannins, phenolic acids and anthocyanins. In the present study, we show that caffeoylglycolic acid methyl ester (CGME), a major constituent of the grains of Sorghum bicolor, exerted anti-inflammatory effects by inducing HO-1 expression. Treatment of RAW264.7 cells with CGME induced HO-1 protein and mRNA expression. CGME increased nuclear translocation of nuclear factor-E2-related factor 2 (Nrf2) and knockdown of Nrf2 by siRNA blocked CGME-mediated HO-1 induction. SP600125 (a JNK inhibitor) or LY294002 (a PI3K inhibitor) blocked CGME-induced HO-1 expression and nuclear translocation of Nrf2, suggesting that CGME induces HO-1 expression via activating Nrf2 through a PI3K and JNK pathway. Consistent with the notion that HO-1 has anti-inflammatory properties, CGME inhibited the production of nitric oxide (NO), prostaglandin E₂ (PGE₂) and interleukin-6 (IL-6) as well as the expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2) and IL-6 in lipopolysaccharide (LPS)-stimulated RAW264.7 cells. CGME also protected C57BL/6 mice from LPS-induced mortality. However, inhibition of HO-1 abrogated the inhibitory effects of CGME on the production of NO, COX-2 and IL-6 in LPS-stimulated RAW264.7 cells. Taken together, these findings suggest that CGME exerts an anti-inflammatory effect through the Nrf2/HO-1 pathway, and may be a potential HO-1 inducer for preventing or treating inflammatory diseases.