Silybin
/ ß-cyclodextrin Inclusion
Complex
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| Dextrins
& cyclodextrins : |
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Dextrins
and cyclodextrins are natural
nutritional products, which
are widely produced for
the food industry. Cyclodextrins
are produced through enzymatic
degradation of starch by
glucosyltransferase enzyme
(CGT) and subsequent separation
of the mixture.
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Cyclodextrins
are crystalline homogenous
non-hygroscopic substances
which have a cylindrical
macro-ring shape, built
up from glucopyranose units.
A ß-cyclodextrin molecule
is made up of 7 such units.
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Functional
Structure of Cyclodextrins
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Cyclodextrins
(CD) can be considered as
empty capsules of molecular
size (host). When the cavity
of CD molecule is filled
with a molecule of another
substance (guest), such
as a silybin molecule, it
is called an inclusion
complex. Only
physical forces (no covalent
bonding) are involved in
the process. The included
molecules are oriented in
the host in such a position
as to achieve the maximum
contact between the hydrophobic
part of the guest and the
non-polar CD cavity. The
hydrophilic part of the
guest molecule remains at
the outer face of the complex.
This ensures maximum contact
with both the solvent and
the hydroxyl groups of the
host.
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Pharmacokinetics of Cyclodextrins
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Upon rapid dissociation
of the inclusion complex in
the stomach, absorption of
the guest drug, such as silybin,
and of the CD are separate
processes. While the absorption
of the (hydrophobic) guest
is strongly accelerated, only
an insignificant amount of
CD is absorbed. Cyclodextrins
are completely resistant to
human amylases. They cannot
be fermented and cannot be
utilized by yeasts. Some hydrolysis
takes place in the human colon
by the bacterial flora which
produce specific cyclodextrinase
enzymes. Metabolism of cyclodextrins
takes place only in the colon
by the microflora. The primary
metabolites (maltose, glucose
& maltotriose) are then
rapidly further metabolized
and finally excreted as carbon
dioxide and water. Cyclodextrins
have no effect on the glucose
level of diabetic patients.
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