(Fig. 4c,d).
As DSASP polymer did not show any cytotoxicity, cell proliferation was
reported in some weight ratio like 10 w/w compared to control.
Additionally, by increasing the polymer mass ratio, except 100 w/w, no
significant cytotoxicity was observed for any DSA8SP and
DSA6SP magnetic complexes (Fig. 5a,b ). It is
noticeable that the iron oxide nanoparticles, even after amphiphilic
surface modification, sustained their low cytotoxicity in presence and
absence of MFs (Fig. 5c ). The polyamines like spermine are
fundamental factors in the cell proliferation cycle which naturally
exist in cells [19, 46]. Indeed, although spermine’s increasing rate
provides grounds to accelerate cell proliferation and restrict apoptosis
by inhibiting cytochrome c release, its intracellular depletion leads
cellular growth to be arrested [46].
Decrease in time association of nucleic acids with enzymatic conditions
in cells and/or serum by the aim of accelerating DNA agglomeration to
targeted cells and intensifying its rapid physical transportation, is
demonstrated as another impressive factor in DNA protection which is
studied through magnetofection [32]. Magnetofection through applying
the external MF is considered as a non-invasive therapeutic approach,
leading to cell viability without disrupting plasma membranes [23].
It is clearly shown that incubation with the application of a magnetic
field in cell culture media remarkably reinforces cellular efficiency of
complex for all DSASP–pDNA/MNPs, especially at weight ratio of 50 and
10 w/w in DSA6SP and also 50 and 20 in
DSA8SP (Fig. 6) . However,
DSA6SP–pDNA/Fe3O4nanoparticles show a preferable transfection efficacy presumably based
on higher stearic acid residues which result in better condensation of
complexes (Fig. 6b). DSA6SP with higher grafted
rate of stearic acid (20%), gradually restricted more spermine
conjugation with dextran chain which its amine content was evaluated at
0.26 µmol/mg as well as 0.35 µmol/mg and also 15% stearic acid in
DSA8SP.
Spermine residues conjugated on dextran make it a more appropriate
biodegradable polycations for gene delivery applications [47].
Moreover, based on our obtained results, the addition of both spermine
and stearic acid conjugations along the dextran chain, affect the
DNA-binding complex transfection efficiency and density, significantly.
Hosseinkhani et al., considered stable interactions with various
cationic polysaccharide derivatives and different grafts of oligoamines,
only dextran-spermine polycations found active in transfection assay
[47]. Additionally, the emphasis of grafted spermine moieties in
transfection efficiency was represented properly by the study of Azzam
et al., to point out the spermine residues high buffering capacity.
Therefore, the more spermine incorporation in dextran-spermine compound,
the more luciferase expression [14]. Furthermore, spermine could
promote DNA condensation and simplify endo-lysosomal escape of
oligonucleotide with two primary and two secondary amino groups
respectively which results in an efficient transfection rate [19].
In conclusion, conjugation of fatty acids to polycations are utilized to
protect the coated DNA-polymer complex from enzymes and ease the
cellular uptake of amphiphilic complex into lipophilic plasma membrane
based on hydrophobic surface [14]. Particle size in amphiphilic
polymers, was directly affected by hydrophobic to hydrophilic chain
ratios. So, the enhancement of stearic acid conjugation degree in
amphiphilic structure simultaneously leads to increase in polymer
hydrophobic properties, closer polymeric interactions in aqueous medium
and assembly of smaller particles. Indeed, decreasing the size will
subsequently increase the surface/volume ratio of particles. These
phenomena lead more particles to communicate and destabilized the
aqueous medium [22]. Therefore, through higher association of
stearic acid with dextran in
DSASP-pDNA/Fe3O4 complexes, the
surface/volume ratio increases alongside decreasing complex size which
consequent more hydrophobic interaction with plasma membrane.
Considering DSA8SP with more amine content and also the
efficient role of positive charges, the lower transfection efficacy was
represented for this carrier compared to DSA6SP.
Finally, the importance of hydrophilic content in transfection assay is
explained based on the efficient effects on total size of complexes and
enhancement of their cellular attachment due to plasma cell membranes.