A review of the possible mechanisms of action of tocotrienol - a potential antiosteoporotic agent.

Osteoporosis is posing a tremendous healthcare problem globally. Much effort has been invested in finding novel antiosteoporotic agents to stop the progression of this disease. Tocotrienol, one of the isoforms of vitamin E, is poised as a potential antiosteoporotic agent. Previous studies showed that tocotrienol as a single isomer or as a mixture demonstrated both anabolic and antiresorptive effects in various rodent models of osteoporosis. In vitro experiments further demonstrated that tocotrienol could up-regulate genes related to osteoblastogenesis and modify receptor activator of nuclear factor kappa B signaling against osteoclastogenesis. Additionally, tocotrienol was also shown to be a strong 3- hydroxy-3-methyl-glutaryl-CoA reductase down-regulator with a mechanism different from that of statins. Inhibition of the mevalonate pathway affects both osteoblast and osteoclast formation in favor of the former. Tocopherol, a more commonly used isoform of vitamin E does not possess similar effects. Tocotrienol is also a potent antioxidant. It can scavenge free radicals and prevent oxidative damage on osteoblast thus promoting its survival. It may also up-regulate the antioxidant defense network in osteoclast and indirectly act against free radical signaling essential in osteoclastogenesis. The effects of tocotrienol on Wnt/β-catenin signaling essential in osteoblastogenesis have not been determined. More mechanistic studies need to be conducted to illustrate the antiosteoporotic effects of tocotrienol. Clinical trials are also required to confirm its effects in humans. In conclusion, tocotrienol demonstrates great potential as an antiosteoporotic agent and much research effort should be invested to develop it as an agent to curb osteoporosis.