Coffee ingredients, hydroquinone, pyrocatechol, and 4-ethylcatechol exhibit anti-inflammatory activity through inhibiting NF-κB and activating Nrf2

Pyrocatechol is a coffee ingredient that exhibits anti-inflammatory activity. We herein identified hydroquinone and 4-ethylcatechol as novel coffee ingredients inhibiting LPS-induced inflammatory responses. Similar to pyrocatechol, hydroquinone and 4-ethylcatechol significantly inhibited LPS-induced nitric oxide (NO) production and CCL2 secretion by suppressing the mRNA expression of iNOS and CCL2 in murine macrophage-like RAW264.7 cells. These ingredients also inhibited the LPS-induced activation of NF-κB, a pivotal transcription factor in inflammation, by preventing its nuclear localization, and induced the expression of Nrf2, a transcription factor negatively regulating LPS-induced inflammation. By utilizing Keap1^−/−MEFs reconstituted with Keap1 mutants in which major cysteine residues were substituted, we found that Cys151 in Keap1 was a critical sensor for pyrocatechol, hydroquinone, and 4-ethylcatechol to induce Nrf2 expression. However, the amounts of hydroquinone and 4-ethylcatechol in the coffee decoction were markedly lower than that of pyrocatechol, suggesting that pyrocatechol is the main coffee ingredient exhibiting anti-inflammatory activity.