## 4 Discussion  
The current study compared the anti-osteoarthritis effects of palm TRF, glucosamine sulphate, and both agents in combination in a rat model of osteoarthritis induced by MIA. It revealed that all treatment regimens halted the cartilage deterioration process in the rat joints induced with MIA, as illustrated via the serum COMP level. However, the joint lesions caused by MIA might not have healed completely, as demonstrated by the joint histology. From the functional aspect, the combination of palm TRF and glucosamine significantly increased the grip strength of rats with OA, and the effects were better than each agent used alone. The improved joint function might enable the rats to reach for food and maintain their body weight. MIA inhibits glyceraldehyde-3-phosphate dehydrogenase involved in the glycolysis. Treating chondrocytes with MIA has been shown to cause mitochondrial dysfunction and, subsequently, cell death [26, 27]. In another study, MIA arrested chondrocyte proliferation due to S-phase arrest [28]. MIA has been commonly used to induce cartilage damage in animals to mimic osteoarthritis in humans [29, 30, 31]. In this study, MIA induced apparent cartilage damage, as similarly observed in previous studies [19, 32]. However, quantifying the damage using a modified Mankin's score revealed no statistically significant changes between the N and O group in the structural, matrix, and cellular scores. This observation was probably due to the narrow range of scores of each component between these two groups (all 0 in the N group, 0-2 in the O group). The total [PERSON]'s score for the O group was significantly higher than for the N group, indicating more degenerative features in rats induced with MIA. On the other hand, all treatment groups showed varying degrees of cartilage damage compared to the N group. The [PERSON]'s score for each joint component was inconsistent between the treatment groups and the control groups. The total [PERSON]'s score revealed that the overall joint damage in the treatment groups was similar to the O group. In contrast, a previous study showed that anantatto locotrienol (100-150 mg/kg for one month) suppressed joint damage in a rat model of osteoarthritis induced by MIA [19]. The distinction in the composition between palm TRF and anantatto locotrienol might be responsible for the difference. In the inflammatory/rheumatoid arthritis model, \(\gamma\)-tocotrienol (5 mg/kg for 25 days) [16], \(\delta\)-tocotrienol (10 mg/kg for 25 days) [17] and palm TRF (30 mg/kg for 25 days) [18] were shown to reduce degenerative joint changes in rats. Based on the dosage used in these studies, palm TRF may not be as potent as pure \(\gamma\) and \(\delta\)-tocotrienol in preventing joint damage due to arthritis, thus necessitating a higher dose to achieve the same protective effects. Meanwhile, in a previous study, supplementation of glucosamine sulphate (250 mg/kg) was shown to attenuate but not completely prevent cartilage damage in a rat model of osteoarthritis induced by anterior cruciate ligament transection [22]. In contrast, cartilage lesions were still present in the current study in rats supplemented with the same dose of glucosamine sulphate. The MIA-induced osteoarthritis model used in this study could induced more intense cartilage damage than other models, thus requiring more time to heal even with glucosamine sulphate supplementation. COMP is a pentameric extracellular matrix glycoprotein found in the cartilage and other joint tissues (synovium, ligaments, tendons and fibroblasts) [33]. It is a sensitive marker of cartilage degradation in osteoarthritis and rheumatoid arthritis [33]. Its level increases in the early stage of osteoarthritis and subsequently decreases in late-stage disease [34]. In the present study, the rats with osteoarthritis showed a significantly higher COMP than the normal rats, indicating an ongoing damage process in the joint. All treatment regimens suppressed COMP levels, but no significant difference was observed among them.