Vitamin E Analogs as Radiation Response Modifiers

Table 1

Salient structural and physiobiological properties of tocopherols and tocotrienols.

Attributes	Tocopherol	Tocotrienol
Abundance	Corn, wheat, and soybeans	Barley, oats, palm, and rice bran
Number of analogs	Four analogs (α, β, γ, and δ)	Four analogs (α, β, γ, and δ)
Presence of chromanol ring and a 15-carbon tail at the C-2 position	Yes	Yes
Type of hydrocarbon tail	Saturated hydrocarbon tail	Unsaturated hydrocarbon tail (three transdouble bonds present in the hydrocarbon tail)
Interaction of the chromanol ring with the lipid bilayer	Not very efficient	Very efficient
Metabolism	Through ω-hydroxylation followed by five cycles of β-oxidation	Through ω-hydroxylation followed by five cycles of β-oxidation
Distribution in lipid bilayer	Not in uniform	Uniformly distributed
Recycling efficiency	Lower	Higher
Cellular uptake rate	Lower	Higher
Antioxidant activity	Very high	High
Effect on serum level of cholesterol	Induce the serum levels of both total and low-density lipoprotein cholesterol	Reduce the serum levels of lipoprotein cholesterol
Effect on 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase	Either inhibits or stimulates	Always inhibits
Effect on c-Src kinase	Does not inhibit the early activation of c-Src kinase	Inhibits the early activation of c-Src kinase
Effect on tumor-induced angiogenesis	Does not inhibit tumor-induced angiogenesis	Inhibits tumor-induced angiogenesis
Effect on mobilization of progenitor cells	Mobilizes progenitor cells from bone marrow to peripheral blood	Mobilizes progenitors cells from bone marrow to peripheral blood