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internal element of the 2-4 mm particles contained a tRNA-core coated with con-
secutive layers of PEI and siRNA. Daily particle administration (~0.4 m g siRNA/
dose) by oral gavage over an 8-day period resulted in reduced mRNA levels of
Map4k4 (~60-70%) or TNF-a (~40-60%) in peritoneal exudate cells (PECs) com-
pared to animals receiving scrambled-siRNA containing particles. Map4k4 down-
regulation elicited a concomitant reduction in TNF-a expression that suggests a role
for Map4k4-mediated control of TNF-a. In addition extended knockdown duration
of ~8 days was observed after the final dose. Interestingly, the authors proposed that
siRNA release from the glucan shell was triggered by the acidic environment in
phagosomes; this, however, could compromise particle integrity at low pH within
the GI tract. Notably, no unspecific interferon-g response was detected even though
non-modified siRNA was used. Map4k4 and TNF-a silencing in macrophage-
enriched cells isolated from spleen, liver and lung tissues was observed ascribed to
particle uptake across GALT and subsequent dissemination in migrating mac-
rophages. No direct evidence for M-cell uptake or adsorption levels was provided;
however, this study does suggest the possibility for systemic silencing via the oral
route.
In certain pathologies, such as IBD, a localised rather than systemic effect is
more desirable. IBD encompass a group of complex autoimmune diseases, which
are broadly categorised as Crohn's disease or ulcerative colitis found in the small
intestine and colon respectively. An attractive pathological condition that could be
exploited for improved siRNA-based therapeutic delivery is mucosa integrity loss in
IBD. Despite the numerous targets investigated that includes IL-12, IL-23, IL-17
and IL6 [ 127 ], the current biologic treatment of IBD is based on anti-TNF-a
molecules [ 128 ] . TNF- a has been the preferred target for oral-based siRNA thera-
pies in two recent studies employing orally delivered siRNA for the prevention/
treatment of dextran sodium sulphate (DSS)-induced ulcerative colitis in mice. In the
first of these studies, Wilson et al. [ 89 ] used thioketal (poly-1, 4-phenyleneacetone
dimethylene thioketal) nanoparticles (TKNs) designed for triggered anti-TNF-a
siRNA release in response to raised levels of reactive oxygen species (ROS) com-
mon to inflamed regions. A tenfold specific decrease in colonic mRNA levels of
TNF-a and other proinflammatory cytokines (IFN-g, IL-6 and IL-1) was detected
after oral administration of anti-TNF-a TKNs (~46 mg siRNA/dose) over 5 con-
secutive days during colitis induction. Furthermore, the authors also demonstrated
by histological and weight analysis that a ten times lower siRNA dose (~4.6 m g
siRNA/dose) was sufficient to protect mice from DSS-induced colitis.
An alternative approach for site-specific delivery was reported by Kriegel et al.
[ 90 ]. The nanoparticles-in-microsphere oral system (NiMOS) is based on lipase-
mediated intestinal degradation of poly epsilon-caprolactone microspheres for trig-
gered release of gelatin nanoparticles containing TNF-a -speci fi c siRNA.
Administration by oral gavage at days 2, 4 and 6 after DSS treatment of anti-TNF-a
siRNA-loaded NiMOS (~24 mg siRNA/dose) resulted in reduced intestinal mRNA
and protein levels compared with controls. In addition, ELISA showed decreased
levels of several proinflammatory cytokines (IFN-g, IL-1b, IL-2, IL-5, IL-6 and
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