5-Hydroxytryptophan Acts on the Mitogen-Activated Protein Kinase Extracellular-Signal Regulated Protein Kinase Pathway to Modulate Cyclooxygenase-2 and Inducible Nitric Oxide Synthase Expression in RAW 264.7 Cells

In this study, we evaluated the effect of 5-hydroxytryptophan on anti-inflammatory and analgesic activity in RAW 264.7 cells. Cells were treated with different concentrations of 5-hydroxytryptophan for either 1 h or for 24 h. The anti-inflammatory effect was then analyzed by enzyme-linked immunosorbent assay (ELISA), Western blotting and reverse transcription polymerase chain reaction (RT-PCR). In addition, the analgesic activity was evaluated by measuring the acetic acid-induced writhing response. We found that 5-hydroxytryptophan significantly reduced the acetic acid-induced writhing response. Moreover we evaluated the effects of 5-hydroxytryptophan on the release of several inflammatory mediators including nitric oxide (NO) and interleukin-6 (IL-6). Our results demonstrated that 5-hydroxytryptophan inhibited the lipopolysaccharide (LPS)-induced expression of NO and IL-6. Furthermore, we found that 5-hydroxytryptophan played a role in LPS induced inducible nitric oxide synthase (iNOS), cyclo oxygenase-2 (COX-2) and extracellular-signal regulated protein kinase (ERK) activation. Taken together, these results indicate that 5-hydroxytryptophan has the potential for use in the treatment of inflammatory disease and as an analgesic.