Inhibition of inflammatory responses in lipopolysaccharide-induced RAW 264.7 cells by Pinus densiflora root extract

Pinus densiflora root (PDR) is used as a medicinal plant. In this study, we investigated whether the PDR extract has anti-inflammatory activities. Cell viability assays showed that the extract was not toxic toward RAW 264.7 cells at concentrations up to $10{\mu}g/mL$. At $10{\mu}g/mL$, the extract decreased nitric oxide (NO) content to 40% of the control level. The protein expression of inducible nitric oxide synthase (iNOS), which generates NO, decreased with increasing concentrations of the extract. Prostaglandin $E_2$ ($PGE_2$) levels were significantly inhibited by over 50% in the presence of $10{\mu}g/mL$ of the extract. The protein expression of cyclooxygenase-2 (COX-2), which generates $PGE_2$, decreased with increasing concentrations of the extract. Proinflammatory cytokines, such as tumor necrosis factor-alpha ($TNF-{\alpha}$), interleukin-6 (IL-6), and $IL-1{\beta}$, were detected in RAW 264.7 cells after lipopolysaccharide (LPS) treatment. The extract did not affect the levels of $TNF-{\alpha}$ and IL-6, but it significantly inhibited the level of $IL-1{\beta}$. It also completely inhibited the transcription of nuclear factor-kappaB ($NF-{\kappa}B$). These results indicate that the PDR extract reduces inflammatory response-related proteins, such as NO, $PGE_2$, iNOS, and COX-2, in LPS-induced RAW 264.7 cells via the regulation of $NF-{\kappa}B$. Consequently, we have provided a mechanism to explain the anti-inflammatory effect of the PDR extract; that is, it exerts such an effect by regulating $NF-{\kappa}B$. The PDR extract can therefore be considered as an effective anti-inflammatory agent.