Biomedical Engineering Reference
In-Depth Information
However, there may be some drawbacks to using nanoceria particles. Synthesis of nanoceria
particles through the use of hexamethylenetetramine (HMT) may induce cytotoxic effects in the
ocular tissue [6]. In addition, some cell culture studies with nanoceria have yielded results of par-
ticle aggregation, which may negatively affect the ocular tissue [10]. Given these possible negative
effects of nanoceria particles, there are no negative effects on healthy retinal cells with enhanced
redox nanoceria capacity [6]. The minimal cytotoxic effects of nanoceria particles on the retinal tis-
sue make it a great candidate for the possible widespread of ocular drug therapies.
16.1.2 ck30peg
Recombinant adeno-associated viruses (AAVs) have been extensively used in the ocular tissue as
a gene therapeutic method by which long-term gene expression can be induced, thereby offering
therapeutic intervention for defects in large genes [11,12]. Plasmid DNA (deoxyribonucleic acid)
compacted with polyethylene glycol (PEG)-substituted polylysine (CK30PEG) nanoparticles
offers a promising alternative to AAV gene therapies [13,14]. Subretinal injections of CK30PEG
nanoparticles were able to induce persistent gene expression in mice for up to a year, opening up
doors to efficiently deliver up to 20 kbp plasmid vectors efficiently to dividing and postmitotic cells
[11,13,15]. These nanoparticles have been shown to be safe and effective in human clinical trials,
thereby allowing for the direct targeting of molecular markers in photoreceptors and retinal pig-
ment epithelium cells for gene therapies [11]. Similar therapeutic results have been shown in mouse
models expressing the retinitis pigmentosa phenotype [16].
Histological examination showed that the subretinal delivery of CK30PEG nanoparticles did not
induce infiltration of inflammatory cells in the eye [13]. Injected eyes did not show the prolifera-
tion of polymorphonuclear leukocytes (PMN), an early response to toxicity [13]. Myeloperoxidase
(MPO) immunoreactivity, an activator of inflammatory signaling cascades, was not detected in
injected eyes, nor was F4/80 microglia/macrophage marker, a response to ischemia-induced reti-
nopathy [13]. PMN, MPO, and F4/80 markers were histologically expressed in positive experi-
mental controls [13]. The lack of such expression in CK30PEG-injected eyes suggests that these
nanoparticles do not cause an inflammatory cascade in injected eyes [13].
Enzyme-linked immunosorbent assay (ELISA) and real-time reverse-transcription PCR (qRT-PCR)
were used to detect the presence of interleukin-8 (IL-8), monocyte chemotactic protein-1 (MCP-1),
and tumor necrosis factor-α (TNF-α) proteins and mRNA, respectively, in CK30PEG-injected eyes,
saline-injected eyes, and
Bacillus cereus
endophthalmitis eyes as a positive control [13]. IL-8 can be
produced in response to inflammatory stimuli and is involved in the initiation and amplification of
acute inflammatory response processes [13].
B. cereus
eyes expressed elevated levels of IL-8 protein
and mRNA, with lack of elevation of either, expressed by the nanoparticle and saline-injected eyes
[13]. MCP-1 is a member of the chemokine family and recruits monocytes to sites of injury and infec-
tion [13]. Eyes injected with CK30PEG nanoparticles showed transient elevations in MCP-1 mRNA
and protein that returned to saline-injected control levels after 1 day [13].
B. cereus
positive control eye
samples markedly expressed elevated levels of MCP-1 protein and mRNA [13]. TNF-α is produced by
macrophages and monocytes as a part of the inflammation cascade pathway and apoptotic cell death
[13]. There was no detectable increase in TNF-α levels following subretinal injection of CK30PEG,
compared to the significantly increased TNF-α levels in endophthalmitis positive control eyes.
The lack in expression of inflammatory cascade proteins in eyes with subretinally injected
CK30PEG suggests that this gene therapy model is nontoxic in the ocular tissue, thereby safely
inducing sustained gene expression in necessary tissues [13].
16.1.3 M
agNetIc
N
aNopartIcles
DNA-tethered magnetic nanoparticles (MNPs) are Food and Drug Administration (FDA)-approved
MRI (magnetic resonance imaging) contrast agents able to successfully deliver genes to targeted
ocular tissues [2,4,5]. These nanoparticles are nontoxic to the retinal tissue; apart from successfully
