From Wikipedia,
the free encyclopedia.
Chitosan is a linear
polysaccharide composed of
randomly distributed
ß-(1-4)-linked D-glucosamine (deacetylated
unit) and N-acetyl-D-glucosamine
(acetylated unit). Chitosan is
produced commercially by
deacetylation of chitin (can be
produced from
chitin also), which is the
structural
element in the
exoskeleton of
crustaceans (crabs, shrimp,
etc.). The degree of deacetylation
(%DA) can be determined by NMR
spectroscopy, and the %DA in
commercial chitosans is in the
range 60-100 %. The
amino group in chitosan has a
pKa value of ~6.5, thus, chitosan
is positively charged and soluble
in acidic to neutral solution with
a charge density dependent on pH
and the %DA-value. In other words,
chitosan is bioadhesive and
readily binds to negatively
charged surfaces such as mucosal
membranes. Chitosan enhance the
transport of polar
drugs across epithelial
surfaces, and is
biocompatible and
biodegradable. Purified
qualities of chitosans are
available for
biomedical applications.
Chitosan and its derivatives such
as trimethylchitosan (where the
amino group has been trimethylated)
have been used in non-viral gene
delivery. Trimethylchitosan, or
quaternised chitosan, has been
shown to transfect breast cancer
cells (1). As the degree of
trimethylation increases the
cytotoxicity of the derivative
increases (1). At approximately
50% trimethylation the derivative
is the most efficient at gene
delivery (1). Oligomeric
derivatives (3-6 kDa) are
relatively non-toxic and have good
gene delivery properties (1).
Chitosan is frequently sold in
tablet form at health stores as a
'fat attractor': It is supposed to
have the capability of attracting
fat from the digestive system and
expelling it from the body so that
users can, it is claimed, lose
weight without eating less.
However, scientific research
suggests that these claims are
entirely without substance. In
fact, using chitosan can have the
deleterious effect of rendering
ineffective certain minerals found
in foodstuffs and required by the
body in order to remain healthy.
The use of chitosan in a
bandage has been approved in the
USA (2).
