Protective Effects of Annatto Tocotrienol and Palm Doctorrienol-Rich Fraction on Chondrocytes Exposed to Monosodium Iodoacetate  
[PERSON]  
1 Department of Pharmacology, Faculty of Medicine, Universiti Kebangsaan Malaysia, Cheras,  
Kuala Lumpur 56000, Malaysia; [EMAIL_ADDRESS] (K-L.P.); [EMAIL_ADDRESS] (I.N.S.) 2 Newcastle University Medicine Malaysia, Iskandar Puteri 79200, Malaysia 2  
[PERSON]  
3 Department of Anatomy, Faculty of Medicine, University Kebangsaan Malaysia, Jalan Yaacob Latif,  
Bandar Tun Razak, Cheras, Kuala Lumpur 56000, Malaysia; [EMAIL_ADDRESS] (Correspondence: [EMAIL_ADDRESS]; Tel. +60-39-91459573  
of cartilage or chondrocyte cell death in OA initiation [6; 7; 8]. Chondrocytes with mechanical, oxidative or inflammation-induced damage have poor recovery capacity due to the lymphatic and avascular condition in the cartilage [9; 10]. The function and metabolism of damaged chondrocytes will be compromised. Ultimately, the chondrocytes will die off via apoptosis and lead to hypocellularity, matrix depletion and degradation of cartilage [7; 11]. Additionally, the leaked or degraded cellular content from dead chondrocytes, as well as the cartilage debris, could activate the inflammatory cascades and the release of pro-inflammatory mediators by joint tissues and immune cells, leading to synovitis [12]. In turn, these mediators induce the release of metalloproteinase by chondrocytes and pro-voke further cartilage damage [13; 14]. Inflammation and oxidative stress are two intricately linked process in OA. Pro-inflammatory cytokines such as interleukin-1 \(\beta\) and tumour necrosis factor-alpha induce nitric oxide production and mitochondrial dysfunction, which contribute to chondrocyte malfunction and apoptosis [15]. A previous study showed that monosodium iodoacetate (MIA), a glycolysis inhibitor, induced proliferation arrest and oxidative stress in chondrocytes in vitro [16]. Therefore, the MIA model may represent a suitable model to study early chondrocyte damage. The primary pharmacological treatment of OA aims to relieve its symptoms, e.g., nonsteroidal anti-inflammatory agents and paracetamol relieve joint pain in OA patients [17]. Intra-articular corticosteroid injection is effective against joint pain, but it may cause local and systemic side effects [18]. Besides, evidence for the efficacy of several common supplements for OA, such as glucosamine, chondroitin and avocado or soybean unsaponifiables for OA management, has not been conclusive according to meta-analysis [19]. The failure of pharmacological interventions allows the condition to progress to end-stage OA, necessitating joint replacement or arthroplasty. Arthroplasty is a costly procedure and introduces the risk of infection, loosening of prosthetics and periprosthetic fractures [20; 21]. Therefore, the search for novel agents with better efficacy to treat OA is ongoing. Tocotrienol, a subfamily of vitamin E found in botanical oil, has been reported to protect chondrocytes and joint health. Palm tocotrienol (30 mg/kg), \(\gamma\)-tocotrienol (5 mg/kg) and \(\delta\)-tocotrienol (10 mg/kg) isomers have been tested in rat models of rheumatoid arthritis (RA) induced by collagen II [22; 23; 24]. They were reported to prevent paw oedema, joint deterioration and oxidative stress in rats with RA [22; 23; 24]. In addition, annatto locotrienol (AnTT; 100 mg/kg/day) has been shown to reduce cartilage damage and its associated cartilage degradation markers in rats administered intraarticularly with MIA [25]. Another study on the effects of palm tocotrienol-rich (PT3, 100 mg/kg) combined with glucosamine sulphate (250 mg/kg) using a similar animal model demonstrated reduced circulating degradation markers and improved grip strength [26]. However, the currently available studies on vitamin E and cartilage damage are predominantly on \(\alpha\)-tocopherol, the major isoform of vitamin in the human diet and body [27]. Thus, evidence on the direct action of tocotrienol on chondrocytes is very limited.