Inhibition of lipopolysaccharide-induced pro-inflammatory cytokine expression via suppression of nuclear factor-κB activation by Mallotus japonicus phloroglucinol derivatives

An aqueous acetone extract obtained from the pericarps of Mallotus japonicus (MJE) was observed to inhibit pro-inflammatory cytokine (tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) production in a lipopolysaccharide (LPS)-activated murine macrophage-like cell line, RAW 264.7, or human blood monocytes. Several phloroglucinol derivatives were isolated from the pericarps as active compounds. Among these compounds, isomallotochromanol and isomallotochromene were the most potent in inhibiting cytokine production. WE and the phloroglucinol derivatives significantly reduced these cytokine rnRNA expressions. Gel shift analysis revealed that stimulation of macrophages with LPS caused an increase in the DNA binding activity of nuclear factor-kappaB (NF-kappaB), which was inhibited by isomallotochromanol and isomallotochromene. Western blot analysis showed that LPS reduced the IkappaB-alpha level in macrophages, while 10 muM isomallotochromanol and 10 muM isomallotochromene attenuated the LPS-induced decrease in IkappaB-alpha protein. We conclude that these phloroglucinol derivatives inhibit pro-inflammatory cytokine production and mRNA expression via suppression of NF-kappaB activation in activated macrophages. (C) 2003 Published by Elsevier Science B.V