Biomedical Engineering Reference
In-Depth Information
adsorption, particle aggregation, and polycation-protein exchange. The
transfection efficiency of PEI-g-EHDO was 30-fold higher than 25 kDa PEI
in the presence of serum.
Peptide-modified PEIs are also advantageous because they are easily
metabolized and nontoxic to cells, making different combinations possible.
Dey et al. designed histidine-based peptide-linked PEI polymers for trans-
fection studies.
19
The results demonstrated that these peptide-linked PEI
complexes significantly reduced the toxic effects of the 25 kDa PEI.
L
-
Carnosine derivatives of PEI showed significantly higher transfection
efficiency in primary human cells with respect to the widely used transfection
agent, Lipofectamine. PEI linked with the dipeptides
L
-carnosine or Boc-
L
-
carnosine appeared to be the most promising gene delivery agents among all
the complexes tested, based on their reduced production of reactive oxygen
species and markedly high transfection efficiency.
Generally, based on different degradation mechanisms, crosslinked PEIs
could be divided into three types: reduction, hydrolysis, and acidic hydrolysis.
As for reduction type, the disulfide bond-containing PEIs (SS-PEIs) can be
synthesized by crosslinking LMW PEI with reducible disulfide crosslinkers.
Glutathione as a water-soluble reducing agent, found within cells at millimolar
concentrations, can degrade disulfide bonds to the corresponding thiols. In
consequence, under the reducing conditions of the cytoplasm, SS-PEI could be
fragmentized into small PEIs, so that the condensed DNA would release from
the
d
n
4
y
3
n
g
|
3
complexes
easily
and
rapidly,
reducing
cytotoxicity
and
enhancing
transgene expression.
Peng and co-workers synthesized a series of disulfide-crosslinked PEIs by
the reaction between 800 Da PEI and methylthiirane or thiirane at different
molar ratios (Scheme 4.3A).
20,21
The results showed that transfection
efficiency was dependent on disulfide content and molecular weight. The
compounds with an adequate thiolation degree between 2.6 and 4.5 have
relatively lower cytotoxicity and higher gene transfection efficiency than 25
KDa PEI. Wei et al. synthesized bioreducible SS-PEIs by chemical coupling of
39-dithiobispropanoic acid (DTPA) and LMW PEI (800 Da) via an EDC/NHS
activation reaction (Scheme 4.3B).
22
This compound was employed to transfer
hTERT siRNA into HepG2 cells and revealed relatively low cytotoxicity in
vitro and at an appropriate dose had no adverse effect on liver and kidney
functions in vivo. Sun et al. synthesized the SS-PEIs by Michael addition
between cystamine bisacrylamide and LMW branched 800 Da PEI
(Scheme 4.3C).
23
In vitro transfection experiments showed that SS-PEI/DNA
binary complexes demonstrated comparable transfection efficiency, but lower
cytotoxicity, in comparison with that of 25 kDa PEI. Deng et al. synthesized
disulfide-containing poly(b-amino amine)s and then used them to crosslink
LMW PEI (1800 Da) through Michael addition to obtain SS-PBAA-PEIs as
the final gene carriers.
24
In vitro transfection showed that the SS-PBAA-PEIs
had comparable transfection efficiencies and lower cytotoxicities compared
with 25 kDa PEI. Confocal laser scanning microscopy confirmed that these
