Background: Considering the anti-inflammatory properties of the Japanese traditional Kampo medicine Boiogito (BO), we aimed to investigate the therapeutic effect of BO to prevent the development of knee osteoarthritis (KOA) in rats with surgically induced KOA. Methods: Destabilization of the medial meniscus (DMM) was performed to induce osteoarthritis in the right knees of 12-week-old Wistar rats under general anesthesia. The rats were orally administered 3% BO in standard powder chow for 4 weeks after surgery (controls: n = 6; sham group: n = 6; DMM group: n = 5; DMM + BO group: n = 5). During this period, the rotarod test was performed to monitor locomotive function. After 4 weeks, histological assessment was performed on the right knee. Results: Oral administration of BO improved locomotive function in the rotarod test. Walking time on postoperative days 1, 14, or later was significantly longer in the DMM + BO group than in the DMM group. Histologically, the DMM group showed significant progression of KOA, which, in the DMM + BO group, was strongly suppressed, as assessed by the Osteoarthritis Research Society International score. Conclusions: Our results showed that oral administration of BO had a clinically preventive effect on early stage posttraumatic KOA.

Boiogito (BO), a Japanese traditional herbal medicine, has been proven to be clinically effective against knee osteoarthritis (KOA)-associated pain. However, the therapeutic mechanism of BO remains unclear. Thus, we investigated the analgesic mechanism of BO using a rat KOA model. KOA was induced by destabilization of the medial meniscus (DMM). Rats were allocated into the following four groups: control, sham, DMM, and DMM + BO groups. Rotarod test was performed to evaluate the pain-related locomotive dysfunction. Expression of phosphorylated extracellular signal-regulated kinase1/2 (pERK1/2) in the spinal dorsal horn was examined using immunofluorescence staining and Western blotting on days 1 and 28 after DMM surgery. A mitogen-activated protein kinase inhibitor, U0126, was intrathecally injected and rotarod test and Western blotting were performed. The rotarod test revealed hampered locomotive function in the DMM group, which was significantly improved upon BO administration. The number of pERK1/2-positive cells was increased in the DMM group, whereas it was significantly decreased in the DMM + BO group. U0126 significantly inhibited ERK1/2 phosphorylation and increased walking time in the rotarod test, suggesting that the DMM-related pain was associated with ERK1/2 phosphorylation in the spinal dorsal horn. In conclusion, BO administration improved the pain-related locomotive dysfunction by suppressing ERK1/2 phosphorylation.