Figure 1: Redox antioxidant cycles
Cell membrane is an important site for cellular respiration process and lipid bilayer is a universal component of all cell membranes. Free radicals (eg: O2, H2O2 and OH-) can be generated from respiration process and excess production of free radicals will lead to oxidative stress and eventually cell damage. Hence, the balance between free radicals and antioxidants such as vitamin E are crucial for maintaining healthy cells.
Vitamin E does not work alone, it works with other antioxidants to form an interlinking set of redox antioxidant cycles (Figure 1). Vitamin E acts catalytically (forming reduced state after scavenging free radicals and return back to its native state) between water- and lipid soluble substances via non-enzymatic and enzymatic reactions. Act as a reducing agent, vitamin C reacts with vitamin E radicals (α-tocopheroxyl and α- tocotrienoxyl) to yield vitamin C radical (semi-ascorbyl radical) while regenerating vitamin E. Conversely, vitamin C can regenerate vitamin E directly while thiol antioxidants such as glutathione and lipoate are able to regenerate vitamin E indirectly via vitamin C. Hence, diet-derived antioxidants such as Tocotrienol ( a form of vitamin E) is very important in preserving health as tocotrienol is one of the most effective lipophilic antioxidant.
A study by Serbinova et.al showed that d-α-tocotrienol exhibits 40-60 times higher antioxidant activity against NADPH-induced lipid peroxidation, and 6.5 times better protection against oxidative damage when compared to d- α-tocopherol. Additionally, d-α-tocotrienol shows
- Higher recycling efficiency from chromanoxyl radicals;
- More uniform distribution in membrane bilayer;
- Stronger disordering of membrane lipids
All these three factors contribute to the higher antioxidant potency of make d-α-tocotrienol as opposed to d- α-tocopherol.
References:
Serbinova EA, Packer L. Antioxidant properties of alpha-tocopherol and alpha-tocotrienol. Methods Enzymol 1994;234:354–66.