Application of Chitosan-Based Gels in Pharmaceuticals - Chitosan Based Hydrogels: Functions and Applications - page 322

protect incorporated DNA against degradation by DNase. As physiological concentra-
tions of the enzyme can merely be estimated, protection against DNase is routinely
checked by incubation of the chitosan-DNA complexes or nanoparticles with DNase I or
II as a model enzyme at different concentrations [47], followed by gel electrophoresis.
Complexation of DNA with highly purified chitosan fractions (molecular weights of
<5000, 5000-10,000, and >10,000 Da) at a charge ratio of 1:1 resulted in almost complete
inhibition of degradation by DNase II. Leong's studies have shown that cross-linked chi-
tosan/DNA nanoparticles stored in water remained stable for more than 3 months,
whereas uncross-linked nanoparticles stored in PBS remained stable for only a few hours
[39]. Lyophilized chitosan/DNA nanoparticles retained their transfection potency for
more than 4 weeks [48].
In summary, chitosan and chitosan derivatives effectively condense plasmid DNA, pro-
tecting it from DNase degradation. These gene delivery systems based on chitosans can also
be equipped with ligands for specific cell interaction, such as transferrin or galactose. A
number of in vitro and in vivo studies showed that chitosan is a suitable material for efficient
nonviral gene delivery.
7.4.1.4 Vaccine Delivery
Immunization has been the most effective way to protect individuals and the community
against debilitating infectious diseases, thereby preventing economic losses and morbid-
ity. The use of vaccines has achieved great success in the last two decades, contributing
significantly to an increase in life expectancy and improving the quality of life, especially
in children, both locally and globally. Today most vaccines are given by parenteral injec-
tion, which stimulates the immune system to produce antibodies in the serum but fails to
generate a mucosal antibody response.
Chitosan and chitosan derivatives have been developed and studied recently for various
vaccines, such as influenza, pertussis, and diphtheria antigens [49]. The immune-stimulat-
ing factor of Bordetella bronchiseptica dermonecrotoxin, a major virulence factor of a caus-
ative agent of atropic rhinitis, has been loaded in CMs. In vivo activity of immune induction
was investigated by intranasal administration of the loaded CMs into mice. Bordetella bron-
chiseptica dermonecrotoxin-specific IgA titers in the nasal cavity were time- and dose-
dependently increased by this administration. Similar phenomena were observed with
the analysis of systemic IgA and IgG in sera that suggest that direct vaccination via the
nasal cavity is effective for targeting nasal-associated lymphoid tissues, and that CMs are
an efficient adjuvant in nasal mucosal immunity for atropic rhinitis vaccine [50]. CMs pre-
pared by an ionic gelation process with TPP were also used for loading Bordetella bron-
chiseptica dermonecrotoxin. TNF-α and nitric oxide from RAW264.7 cells that were exposed
to the loaded CMs were gradually secreted with time, suggesting that the antigen released
from the CMs had the immune-stimulating activity [51].
A single injection of PLGA or CM containing tetanus toxoid could maintain the antibody
response from days to over months at a level comparable to the booster injections of conven-
tional aluminum hydroxide-adsorbed vaccines. Hence, CMs have potential application in
replacing the expensive polymer PLGA in vaccine delivery [52].
Porous CMs suitable for the delivery of antigen have been prepared using a wet phase-
inversion method, and were chemically modified with 3-chloro-2-hydroxypropyltrimeth-
ylammonium chloride. The antigen of the Newcastle disease vaccine was immobilized
into the pores of CMs. Sustained release of the Newcastle disease vaccine's antigen was
achieved through an adsorption-desorption release test [53].