Bioactivities of Chitosan and Its Derivatives - Chitosan Based Hydrogels: Functions and Applications - page 151

Figure 3.20
Confocal micrograph of gelatin microparticles in a chitosan scaffold.
gut [166]. Several other related studies showed that chitosan has the unique ability of
absorbing fat from the body: that is, chitosan can absorb fat up to five times its weight.
Chitosan was also shown to lower the level of low-density lipoprotein (LDL) cholesterol
while boosting the high-density lipoprotein (HDL) cholesterol level. Some studies have
shown that chitosan can decrease blood cholesterol levels by more than 50%, and it was
considered to be an effective hypocholesterolemic agent. Further, in a preliminary
human study, intake of 3-6 g of chitosan in a day for 2 weeks could decrease the blood
cholesterol level by 6% and increase the HDL level by 10% [167]. In addition to chitosan,
the chitosan oligosaccharides (COSs) also lead to control of blood cholesterol level. COSs
are capable of decreasing the cholesterol level in the liver. Unlike HMW chitosan, COS
application does not lead to an increase in compensatory cholesterol synthesis and a
decrease in essential fatty acids, fat-soluble vitamins, and microelements from the organ-
isms [168]. In particular, COSs prevent the development of fatty liver caused by the action
of hepatotrope poisons.
Despite some research carried out to search for the ability of chitosan and COSs to
bind with bile salts and lipids, the exact mechanism by which they lower blood choles-
terol level has not been completely elucidated. However, several hypotheses have been
suggested to explain the possible action of COS in reducing blood cholesterol levels. One
hypothesis suggests that ionic binding of COS with bile salts and bile acids may inhibit
micelle formation during lipid digestion in the digestive track [169]. Another hypothesis
suggests that chitosan and its oligomers can directly trap lipids and fatty acids [170].
However, contradictory results have been observed with regard to ionic interactions of
COS, and thus the fat-binding and cholesterol-lowering effects of chitosan cannot be
explained using only the ion binding hypothesis [171]. Moreover, some other evidence
from animal studies suggests that the effective lowering of cholesterol level can be
explained in relation to the ability of COSs to increase the excretion of neutral sterol and
indigestion of dietary fats. Sugano et al. [172] employed a series of experiments with
male rats that clearly demonstrated the hypocholesterolemic activity of dietary chitosan.
On feeding a high-cholesterol diet for 20 days, the addition of 2-5% chitosan resulted in
a significant reduction, by 25-30%, of plasma cholesterol without influencing food intake