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 μg/mL. At 10 μg/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 E₂ (PGE₂) levels were significantly inhibited by over 50% in the presence of 10 μg/mL of the extract. The protein expression of cyclooxygenase-2 (COX-2), which generates PGE₂, decreased with increasing concentrations of the extract. Proinflammatory cytokines, such as tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and IL-1β, were detected in RAW 264.7 cells after lipopolysaccharide (LPS) treatment. The extract did not affect the levels of TNF-α and IL-6, but it significantly inhibited the level of IL-1β. It also completely inhibited the transcription of nuclear factor-kappaB (NF-κB). These results indicate that the PDR extract reduces inflammatory response-related proteins, such as NO, PGE₂, iNOS, and COX-2, in LPS-induced RAW 264.7 cells via the regulation of NF-κB. 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-κB. The PDR extract can therefore be considered as an effective anti-inflammatory agent.