There are at least 600 known carotenoid compounds, of which about 20 are found in the human diet. Beta-carotene is one of the most abundant of these compounds and is the best known because it is a major source of vitamin A, which is obtained by a very specific, enzyme-catalyzed symmetric cleavage by oxidation of the central carbon-carbon double bond. However, beta-carotene and the several other carotenoids that also are sources of vitamin A are known to show other, non-vitamin A, biological activities, i.e., activities that cannot be reproduced by replacing the carotenoid with vitamin A. Furthermore, many of the carotenoid compounds that are not sources of vitamin A have biological activities that, obviously, cannot be attributed to vitamin A.
Our premise is that non-vitamin A carotenoid bioactivities in vertebrates derive from one or more oxidation products formed by asymmetric oxidative cleavage of the carotenoid compound, not from the carotenoid compound itself. This idea stems from the strong propensity of carotenoids to undergo spontaneous, autocatalytic asymmetric oxidation with oxygen to form a slew of products. This provides a much more plausible and useful explanation for the non-vitamin A activity of carotenoids, in distinct contrast to the conventional wisdom that non-vitamin A behaviour results from a non-specific antioxidant action of the carotenoid itself.
Oxidized carotenoid compounds and, in particular, oxidized beta-carotene (OxBC) are mixtures that are formed by spontaneous oxidative cleavage of the parent carotenoid and contain many compounds of both small molecule and polymeric nature. We propose that certain of these oxidation products appear to be responsible for most, if not all, of the diverse biological activities of carotenoids.
Figure. Oxidation of beta-carotene. Traditionally,
beta-carotene is recognized as a major source of vitamin A,
a single oxidation product. Spontaneous reaction with
oxygen, however, leads to a very complex mixture (OxBC) of
very low molecular weight compounds and a complex polymeric
product mixture, both of which have counterparts in
nature.
Oxidized carotenoids represent
a new, proprietary class of product that Chemaphor has
developed by adapting the oxidation reaction that
carotenoids naturally and spontaneously undergo using a
simple process that results in the complete conversion of
the carotenoid into a complex mixture of oxidation
products.
The product derived from beta-carotene, OxBC, may be viewed
as providing a concentrated source of a cross section of
the products that are formed naturally when carotenoids are
metabolically transformed by oxidation, often in
association with certain stages of the plant life cycle
(e.g., flowering, fruit ripening). At least some of the
carotenoid oxidation compounds, acting alone or in
combination, may contribute to the epidemiologically
well-documented protective effect of fruit and vegetables
against cancer and cardiovascular disease in humans.
OxBC shows a wide range of non-toxic bioactivities,
including inhibition of cell proliferation in vitro and
tumour growth in vivo, and promotion of cell
differentiation.