The antioxidant vitamins C and E

Acknowledgment
The Oxygen Club of California (OCC) symposium on the antioxidant vitamins C and
E and this book were made possible through support from BASF Aktiengesellschaft.
Preface
Early in the last century, vitamins C and E were identified as essential micronutrients
for humans. Subsequent studies established the important roles of these vitamins as the
body’s major dietary antioxidants. Vitamin C (ascorbic acid) and the various forms of
vitamin E react with many different free radicals and reactive oxygen and nitrogen
species. When scavenging free radicals, vitamin E in cell membranes and lipoproteins
and vitamin C in aqueous intra- and extracellular fluids form one- and two-electron oxidation
products. Initially, demonstrations in chemical systems and later in biochemical
systems showed that vitamin E radicals formed by oxidant or free radical exposure
were reduced by ascorbic acid, resulting in regeneration of vitamin E. Vitamin E, which
is usually present only in relatively low concentrations in the body, may thus be spared
by this vitamin C action. Both vitamins appear to interact in a network of redox-active
antioxidants including thiols, NADH- and NADPH-dependent enzymes, and
bioflavonoids.
In addition to their antioxidant functions as electron or hydrogen donors in free
radical reactions, vitamins C and E exhibit many other activities in biological systems.
Ascorbic acid is a coenzyme (or more accurately, a cosubstrate) in hydroxylation reactions
during collagen biosynthesis and also functions in various metabolic reactions.
Most studies with the various members of the vitamin E family of molecules have
focused on α-tocopherol, which is maintained in the circulation and tissues by the αtocopherol
transfer protein(s). Interestingly, other vitamin E forms, such as γ-tocopherol
and α-tocotrienol, exhibit unique properties in various cell and in vitro systems
and are the subject of emerging interest.
Both vitamins C and E by virtue of regulating oxidative processes through their
antioxidant actions have important effects on regulating cell signaling and gene expression.
Although oxidants and oxidative stress conditions affect many of the essential
pathways involved in gene transcription and protein synthesis, these antioxidants may
themselves be involved in redox regulation of cell signaling. Hence, vitamins C and E
affect cell growth and proliferation and also participate in some of the cell death pathways
involving apoptosis or necrosis. Importantly, α-tocopherol specifically inhibits
certain cell signaling pathways dependent upon protein kinase C and interacts with a
number of binding proteins.
Copyright © 2002 AOCS Press