Biomedical Engineering Reference
In-Depth Information
pathologies of viral origin. Since chitosan can be degraded in living cell
media, the question remains whether the biological activity is due to the
monomer and oligomer or directly due to the polymer. It seems that both
kinds of involvements must be considered.
Immune-stimulating function of chitosan oligosaccharide is condi-
tioned by the similarity of its molecular structure to that of cell membrane.
On the basis of this hypothesis, the immune stimulatory activity of chi-
tin and chitin derivatives was extensively explored in the middle to late
1980s especially with the oligomers. h e water of soluble hexa-N-acetyl-
chitohexaose, the hexamer of N-acetylglucosamine, and chitohexaose, the
hexamer of glucosamine, at 100×5 mg/kg dosage, gave complete regres-
sion of solid tumors in all mice observed [107]. Besides growth inhibitory
ef ect against solid Meth-A tumors N-acetylchitohexose was also found to
display antimetastatic ef ects against Lewis lung carcinoma transplanted
into mice, giving rise to 40-50 % inhibition ratio of pulmonary metasta-
sis when administered intravenously (1mg/g) on day 6 at er implantation
[108]. h is oligosaccharide was also shown to enhance the tumorocidal
ef ect of splenic T-lymphocytes against mastocytoma cells and to increase
the NK activity of splenic T-lymphocytes [109]. Protection against infec-
tion by
Pseudomonas aeruginosa
,
Listeria monocytogenes
, and
Candida
albicans
was also noticed in tumor-bearing mice [110-112]. h e triggering
of the defense functions of macrophages, polymorphonuclear leukocytes,
cytotoxic and NK cells activity was proposed and evidenced as mode of
action [113].
Immunological activities of higher chitin derivatives were evaluated
where, deacetylated chitin derivatives such as 70 % deacetylated chitin and
30 % deacetylated chitin among the test derivatives were potent immuno-
logical activators of murine peritoneal macrophages and NK cells
in vivo,
suppression of Meth-A tumour cells in syngeneic BALB/c mice and stimu-
lation of host resistance against
Escherichia coli
infection in mice [114].
h e immunomodulating ef ect was mainly by stimulation of production of
cytokines [115].
Shibata,
et al.
, evaluated the immunological ef ects of chitin
in vivo
and
in vitro
using phagocytosable small (1-10 mm) chitin particles. h ese
studies demonstrated that intravenous administration of fractionated chi-
tin particles into the lung activated alveolar macrophages to express cyto-
kines such as IL-12, tumor necrosis factor (TNF)-α, and IL-18, leading to
INF-γ production mainly by NK cells [116]. Subsequent studies by the
same group of investigators demonstrated that cytokine production was
mediated by a mannose-receptor-dependent phagocytic process [117]. h e
mannose receptors also mediated the internalisation of the chitin particles
