Biomedical Engineering Reference
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a
HO
NHR
NHR
HO
HO
O
O
O
O
O
O
HO
O
NH2
OH
n
OH
R = H or COCH
3
c
O
O
HO
b
O
OH
HO
O
OH
O
O
n
O
HN
OH
O
OH
n
OH
O
HN
N
N
H
NH
2
Fig. 6
Gene vectors based on natural polymers: (
a
) chitosan, (
b
) diethylaminoethyl-dextran
(DEAE-dextran), and (
c
) spermine-conjugated dextran (DEX-SP)
amine (CS) to phosphate (DNA), and cell type (Ishii et al.
2001
; Sato et al.
2001
;
Corsi et al.
2003
).
The effect of CS molecular mass, plasmid concentration, N/P ratio, serum, and
medium pH on the transfection efficiency of CS/pGL3-Luc(encoding luciferase)
was systematically studied by Sato and coworkers. The optimized formulation by
adjusting each of these factors showed the highest transfection in SOJ cells (Ishii
et al.
2001
). For different cell types, however, the optimized conditions were found
to be different (Sato et al.
2001
). Based on the study using mesenchymal stem cells,
MG63 and HEK293, Corsi et al. have found that the transfection activity of
CS-DNA polyplexes is cell type dependent (Corsi et al.
2003
).
To improve transfection efficiency, numerous chemical modifications on CS have
been carried out, which include quaternization, ligand conjugation, and hydrophobic
modification. By methylation using methyl iodide in an alkaline environment, trim-
ethylated CS oligomers (TM-CS) were prepared (Thanou et al.
2002
). The quater-
nized chitosan oligomers were able to effectively condense DNA to form
nano-polyplexes (200-500 nm).
In vitro
transfection in COS-1 and Caco-2 cells
revealed that the quaternized derivatives were superior to unmodified CS. In the trans-
fection of Caco-2 cells, TM-CS was more effective than DOTAP. The presence of
fetal calf serum did not affect the transfection efficiency of the DNA/TM-CS
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