Caffeic acid phenethyl ester and caffeic acid ethyl ester activate transcription of heme oxygenase-1 gene in RAW 264.7 mouse monocyte-macrophage cell line independently of redox-regulated pathway
Activation of the transcription of HO-1 gene by elements from foods was examined in a mouse monocyte-macrophage cell line RAW264.7 by measuring relative levels of HO-1 mRNA by real-time reverse transcription-polymerase chain reaction, and it was confirmed that caffeic acid phenethyl ester (CAPE), a component of propolis, had a distinguished potential to induce HO-1 gene expression in the macrophage tumor cell. When RAW cells were incubated with 2 mM of CAPE, the level of the mRNA of HO-1 gene was enhanced significantly even at 1 h, and reached a peak at 4 h leading to an drastic increase of 25 times, then was down-regulated at 6 h. A similar induction was observed in another mouse macrophage cell line, J774.1, but not in the human hepatocarcinoma cell line HepG2, indicating that the activation is common and specific to macrophages. Caffeic acid ethyl ester (CAEE) also induced transcription of HO-1 mRNA in RAW 264.7 cells, leading to 20 times activation. However, chlorogenic acid exhibited a little activation of HO-1 as 1.3 times although it is also an ester of caffeic acid. 2 mM of curcumin and ethyl ferulate increased HO-1 mRNA by 6.4 and 7.2 times, respectively. Resveratrol also elevated HO-1 mRNA 3.4 times, though at a 66 mM. When a non-phenolic antioxidant, cysteamine, was used, 10 mM of cysteamine was required to activate HO-1 gene as 2.3 times. To investigate whether this activation is dependent upon the reductive capacity of the chemicals, the one-electron oxidation potentials of these phenolic compounds were determined by the second-harmonic alternative current voltammetry. The E0ox values of CAPE (0.48), CAEE (0.49), and chlorogenic acid (0.48) determined from the intersection of the voltammograms were almost the same. However, the value of curcumin (0.42) was smaller than those three caffeic acid esters. Thus, the reductive capacity of curcumin was the most potent, and those of CAPE, CAEE, and chlorogenic acid were almost the same and were lower than that of curcumin. However, chlorogenic acid exhibited a very little activation of HO-1 gene, and curcumin was less potent than CAPE. From these results we suggest that the transcriptional activation of HO-1 gene by CAPE and CAEE is not dependent on a redox-regulated mechanism, but on a structure-specific interaction mediated by receptors.HO Conference 2005. 4th International Congress