Assessment of the Oral Delivery of a Myelin Basic
Protein Gene Promoter with Antiapoptotic bcl‑xL (pMBP-bcl‑xL) DNA by Cyclic Peptide Nanotubes with Two Aspect Ratios and
Its Biodistribution in the Brain and Spinal Cord
Cyclo-(D-Trp-Tyr)
peptide nanotubes (PNTs) were reported to be
potential carriers for oral gene delivery in our previous study; however,
the effect of the aspect ratio (AR) of these PNTs on gene delivery in vivo could affect penetration or interception in biological
environments. The aim of this study was to assess the feasibility
of cyclo-(D-Trp-Tyr) PNTs with two ARs as carriers for oral pMBP-bcl-xL-hRluc delivery to the spinal cord to treat
spinal cord injury (SCI). We evaluated the biodistribution of oligodendrocyte
(OLG)-specific myelin basic protein gene promoter-driven antiapoptotic
DNA (pMBP-bcl-xL) to the brain and spinal cord delivered
with cyclo-(D-Trp-Tyr) PNTs with large (L) and small (S) PNTs with
two ARs. After complex formation, the length, width, and AR of the
L-PNTs/DNA were 77.86 ± 3.30, 6.51 ± 0.28, and 13.75 ±
7.29 μm, respectively, and the length and width of the S-PNTs/DNA
were 1.17 ± 0.52 and 0.17 ± 0.05 μm, respectively,
giving an AR of 7.12 ± 3.17 as detected by scanning electron
microscopy. Each of these three parameters exhibited significant differences
(p < 0.05) between L-PNTs/DNA and S-PNTs/DNA.
However, there were no significant differences (p > 0.05) between the L-PNTs and S-PNTs for either their DNA encapsulation
efficiency (29.72 ± 14.19 and 34.31 ± 16.78%, respectively)
or loading efficiency (5.15 ± 2.58 and 5.95 ± 2.91%). The
results of the in vitro analysis showed that the
S-PNT/DNA complexes had a significantly higher DNA release rate and
DNA permeation in the duodenum than the L-PNT/DNA complexes. Using
Cy5 and TM-rhodamine to individually and chemically conjugate the
PNTs with plasmid DNA, we observed, using laser confocal microscopy,
that the PNTs and DNA colocalized in complexes. We further confirmed
the complexation between DNA and the PNTs using fluorescence resonance
energy transfer (FRET). Data from an in vivo imaging
system (IVIS) showed that there was no significant difference (p > 0.05) in PNT distribution between L-PNTs/DNA and
S-PNTs/DNA
within 4 h. However, the S-PNT/DNA group had a significantly higher
DNA distribution (p < 0.05) in several organs,
including the ilium, heart, lungs, spleen, kidneys, testes, brain,
and spinal cord. Finally, we determined the bcl-xL protein
expression levels in the brain and spinal cord regions for the L-PNT/DNA
and S-PNT/DNA complex formulations. These results suggested that either
L-PNTs or S-PNTs may be used as potential carriers for oral gene delivery
to treat SCI.