Background: Thai medicine plants used for Osteoarthritis of knee (OA) treatment consist of twelve plants such as Crinum asiaticum, Cleome viscosa, Drypetes roxburghii, Piper longum, Piper nigrum, Plumbago indica, Alpinia galanga, Curcuma aromatica, Globba malaccensis, Zingiber montanum, Zingiber officinale and Zingiber zerumbet. They showed high frequency in OA formula.
Objective: To investigate inhibitory effect on LPS-induced nitric oxide (NO) release from RAW 264.7 cell and free radical scavenging activity using DPPH assay of these ethanolic plant extracts.
Material and Method: Plant materials were extracted by maceration in 95% ethanol. Anti-inflammatory activity were tested on LPS-induced NO production. Free radical scavenging activity was performed by DPPH assay.
Results: All of ethanolic extracts exhibited potent inhibitory effect on NO release. The ethanolic extract of Z. zerumbet
exhibited the highest inhibitory effect followed by Z. montanum and G. malaccensis, respectively. Except A. galanga and C. viscosa, all extracts possessed more influential than indomethacin (IC50 = 20.32+3.23 μg/ml), a positive control. The investigation on antioxidant activity suggested that the ethanolic extracts of D. roxburghii, Z. officinale, Z. montanum, C. aromatic, A. galanga, P. indica, G. malaccensis, P. nigrum exhibited antioxidant activity. By means of D. roxburghii had the highest electron donating activity, followed by Z. officinale. Moreover, both extracts were more effective than BHT, a positive control (EC50 = 14.04+1.95 μg/ml).
Conclusion: Thai medicinal plants had anti-inflammatory activity and could inhibit destruction of articular cartilage that corresponded to the traditional medicine and supported using these medicinal plants for OA treatment.

Keywords: Osteoarthritis of knee, Thai medicinal plants, Inhibitory effect on nitric oxide release, Antioxidant activity