Astaxanthin, Cell Membrane Nutrient with Diverse Clinical Benefits ...

amr
in peer-reviewed journals and some were published
only in Japanese. However, the English-language,
peer-reviewed publications sufficiently establish
astaxanthin as a nutrient with broad-ranging
efficacy and safety.
Biochemistry
The Unique Molecular Layout of Astaxanthin
Astaxanthin (3,3’-dihydroxy-beta,beta-carotene-
4,4’-dione) belongs to the xanthophyll subclass of
carotenoids. It has oxygen in its molecular structure,
which sets it apart from beta-carotene and
other molecules of the carotene subclass. 5 The
astaxanthin molecule has an extended shape, with
a polar structure at either end of the molecule and
a nonpolar zone in the middle (Figure 1). The polar
structures are ionone rings that have potent
capacity for quenching free radicals or other
oxidants, primarily in an aqueous environment,
but possibly also in the absence of water. 8,9
The nonpolar middle segment of the astaxanthin
molecule is a series of carbon-carbon double bonds,
which alternate with carbon-carbon single bonds
– termed “conjugated.” This series of conjugated
double bonds gives the molecule a further antioxidant
dimension, with a capacity to remove highenergy
electrons from free radicals and “delocalize”
their electronic energy via the carbon-carbon chain
– analogous to a lightning rod on the molecular
level (Figure 2). 10 This polar-nonpolar-polar layout
also allows the astaxanthin molecule to take a
transmembrane orientation, making a precise fit
into the polar-nonpolar-polar span of the cell
membrane.
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Complex Three-Dimensional Chemistry
The bonding patterns of natural astaxanthin
generate many different molecular forms (isomers),
each with its unique three-dimensional shape. The
intricacies of astaxanthin’s isomer array are beyond
the scope of this review. Pertaining to its use as a
dietary supplement, virtually all commercially
available natural astaxanthin is predominantly in
the all-trans geometric form 3S,3S’ Astaxanthin, as
occurs in H. pluvialis and as illustrated in Figure 1.
This is the predominant natural astaxanthin used
in all clinical trials to date.
Another complication in the chemistry of natural
astaxanthin is that the molecule in its free form is
relatively uncommon within the various organisms
that produce it. Instead, most of this astaxanthin is
either conjugated with proteins or esterified with
one or two fatty acids (as astaxanthin acyl monoesters
or diesters). 11 Acyl esters make up more than
99 percent of the astaxanthin from H. pluvialis and
Figure 1. Molecular Layout of All-trans Astaxanthin, the Major Molecular Species in Natural Foods and Dietary
Supplements
HO
O
approximately 80 percent of astaxanthin in
krill. 11,12 Thus, acyl monoester and diester forms
make up virtually all the astaxanthin currently
available in dietary supplements.
Metabolism: Absorption and Tissue
Distribution
In pharmacokinetic studies, after ingestion of
esterified natural astaxanthin, only unesterified
astaxanthin appears in the blood. 13 This is most
likely due to breaking the ester bonds by digestive
enzymes via their hydrolytic activity. Absorption
into the intestinal lining cells (enterocytes) is
thought to occur by passive diffusion and is
O
all-trans astaxanthin
Note the polar ionone rings at the ends and the non-polar zone of conjugated carbon-carbon bonds in the middle.
OH
Monograph
Key words: astaxanthin,
antioxidant, carotenoid,
cardiovascular, cell membranes,
cognition, CRP, DNA
damage, eye accommodation,
free radicals, H. pylori,
inflammation, immunity,
male fertility, mitochondria,
oxidative stress, redox, vision,
xanthophyll
Volume 16, Number 4 Alternative Medicine Review 356