Biomedical Engineering Reference
In-Depth Information
chitosan copolymer through this unique structural design (Scheme 4.6B).
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A
series of well-defined PEG brush-like PMPEG living chains with dithioester
residues was prepared by employing the reversible addition-fragmentation
chain transfer (RAFT) method, which then was grafted onto the allyl-chitosan
via the radical coupling method. The resulting conjugate as a novel gene
delivery vector showed excellent transfection efficiency and less cytotoxicity in
mouse embryonic fibroblast cells (NIH3T3) compared to pristine chitosan.
N,N,N-Trimethylated-chitosan (TMC) is a partially quaternized chitosan
derivative which, compared to chitosan, has improved solubility in aqueous
solution at neutral pH, safety, and effectiveness. Varkouhi et al. reported that
the gene-silencing activity of the siRNA complexes based on thiolated TMC
was substantially higher compared to the non-thiolated TMC and
Lipofectamine-based complexes (Scheme 4.6C).
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Zhao et al. synthesized a
TMC-cysteine conjugate by conjugating
L
-cysteine hydrochloride onto TMC,
which
d
n
4
y
3
n
g
|
3
exhibited
significant
higher
in
vivo
transfection
efficiency
than
Lipofectamine 2000 (Scheme 4.6D).
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Polypeptides can bind the negatively charged backbone of a DNA chain,
not only promoting its condensation but also favoring the interaction of the
nanoparticle with the cell membrane and the consequent internalizations.
Therefore, combining chitosan with polypeptides would allow higher
transfection efficiency and low cytotoxicity. To assist the intracellular
release of siRNA and enhance its effectiveness in gene silencing, Liao et al.
reported an approach for the enhancement of the efficiencies of cellular
uptake and gene silencing through the inclusion of a negatively charged
poly(c-glutamic acid) (c-PGA) into the formulation of chitosan/siRNA
complexes.
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c-PGA is a water-soluble, biodegradable, and nontoxic
naturally occurring peptide. The results demonstrated that c-PGA played
an important role in improving the cellular uptake of chitosan/siRNA
complexes, expediting their intracellular unpackaging, and the release of
siRNA, thus significantly enhancing the efficiency of gene silencing and
prolonging the duration of its action. Opanasopit and co-workers demon-
strated that ternary complexes, resulting from association of chitosan with
poly-
L
-arginine/DNA complexes, were significantly more efficient in medi-
ating transfection than the corresponding chitosan/DNA complexes and had
low cytotoxicity.
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NOVAFECT chitosans are ultrapure chitosan oligomers that were recently
marketed as carriers for nonviral gene therapy. Klausner et al. designed
chitosan-DNA nanoparticles based on NOVAFECT.
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In vitro transfection
studies demonstrated the ability of oligomeric chitosan-DNA nanoparticles to
effectively transfect COS-7 cells. In rat corneas, injection of a select
formulation of oligomeric chitosan-DNA nanoparticles into the stroma
showed that gene expression was 5.4 times greater than PEI/DNA complexes.
It was a promising approach for the treatment of acquired and inherited
corneal diseases that otherwise lead to blindness.
