Bioactivities of Chitosan and Its Derivatives - Chitosan Based Hydrogels: Functions and Applications - page 154

acidic steroids were performed. 5α-Cholestane and 5β-cholanic acid were used as an inter-
nal calibration standard. Serum lipoprotein fractions were separated by sequential ultra-
centrifugation in the 40.3 rotor of a Beckman ultracentrifuge.
3.4.4 Antitumor
Anticancer drugs are almost nonselective on tumor tissue and normal cells and pose wide-
spread problems such as low efficacy, high toxicity, difficult-to-control metastasis, and so
on. Therefore, the anticancer drug delivery system has become the focus of research in the
field of pharmacy. The targeted delivery system and sustained-release and controlled-
release delivery systems have been proved to reduce the adverse effects of antitumor drugs
effectively, improving clinical efficacy and patient medication compliance. Chitosan, as an
anticancer drug carrier, can be made of microballs, microcapsules, nanoparticles, water,
gels, implants, polymer micelles, and other formulations to achieve the role of targeting
and sustained release in vivo .
3.4.4.1 Antitumor Activity of an LMWC
The functions of chitosan have been shown to be dependent not only on chemical struc-
ture but also on molecular size. In medicine and food industry applications, native poly-
saccharide is limited by its high MW, which results in its low solubility in acid-free aqueous
media. Some chitosan applications require a low-molecular-weight (LMW) chitosan, which
has high solubility in acid-free water and low viscosity. To be effectively absorbed in the
human body, it should be converted to LMWC. LMWC is known to have biological activi-
ties such as antitumor activity [174-177], immuno-enhancing effects [174,178,179], enhanc-
ing protective effects against infection with certain pathogens in mice [180], antifungal
activity, and antimicrobial activity [181].
LMWC can be prepared by enzymatic and chemical degradation of the chitosan poly-
mer chain. Various acids have always been used for hydrolysis of chitosan to obtain
LMWCs, but it seemed to be difficult to obtain water-soluble COS with a higher polym-
erization degree. In particular, the downstream procedure is tedious. Many oxidizing
agents have also been used for the degradations, but most of them are toxic reagents
such as chrome compounds, which are not desirable for application in medicine. The
enzymic process of LMWC preparation seems to be generally preferable to chemical
reactions, because the course under gentle conditions and product distribution can be
controlled more readily, in spite of the faster rate of chemical reaction. The enzymatic
method also minimizes alteration in the chemical nature of the product. However, the
high cost of specific enzymes such as chitosanase and chitinase inhibits their use in
industrial scale.
Recently, several hydrolytic enzymes, such as lysozyme, cellulase, papain, and pecti-
nases, were found to catalyze the cleavage of glycosidic linkage in chitosan [182-185]. In an
article on the enzymic preparation of water-soluble chitosan and its antitumor activity,
cheap, commercially available hemicellulase was used to prepare water-soluble LMWC
[186]. The method is suitable for scale-up manufacture of LMWC.
Preparation of samples by enzymatic hydrolysis : Crude hemicellulase solution was from
Yufeng Company (Wuhan, China). Crude enzyme solution obtained was the fraction of
culture supernatants that passed out of 100 kDa membrane but did not pass out of 5 kDa
membrane. Further purified chitosan was obtained by the following procedure: Solid
ammonium sulfate was added to the enzyme solution to 80% saturation; the solid enzyme