Biology Reference
In-Depth Information
BBB score (
Monnier, Mueller, & Schwab, 2002
). The most reliable testing
has been to demonstrate efficacy of Cethrin, a recombinant protein fully
characterized by Good Manufacturing Practice guidelines and now being
investigated in clinical trials (see below). The potency and purity of Cethrin
is rigorously controlled to conform to regulatory guidelines. Functional test-
ing in rats and mice showed small, but robust, results when tested by BBB or
by grid walking when studied in fully double-blind experiments (
Lord-
Fontaine et al., 2008
). These results contrast with an earlier study of BBB
scores in rats where 500
g of C3 transferase without a transport sequence
was applied by Alzet minipump (
Fournier et al., 2003
). The current studies
with Cethrin help us understand the differences between these studies. More
recently, during translational studies, a full set of dose ranging toxicology
studies with Cethrin in over 400 rats was completed to show adverse effects
of high doses, and we now know that 500
m
g exceeds the tolerable level in
rats. The no observed adverse effect level in rats for extradural application is
10
m
g, which corresponds to a dose of approximately 1-5 mg in humans
(
Fehlings et al., 2011
). The lack of effect of C3 at high dose is not surprising
because it is not uncommon for biologic drugs to show a bell-shaped curve
(hormetic dose-responses) (
Reynolds, 2010
). These studies with Rho inhib-
itors highlight the need for careful dose-response testing as early as possible
in SCI studies.
Further support for theRho signaling pathway as a target topromote func-
tional recovery after SCI comes from numerous independent studies with
ROCK inhibitors. The ROCK inhibitor Fasudil was evaluated after contu-
sion injury at T3 in rats by an aneurysm clip (
Hara et al., 2000
). Fasudil was
applied intraperitoneally immediately after injury in combinationwithmeth-
ylprednisolone, and the motor recovery was compared to control animals
treatedwith phosphate-buffered saline ormethlyprednisolone alone. The rats
were tested for reflex responses (toe spread, contact placing) and coordinated
motor activity. Rats treated with Fasudil showed better hindlimb reflex
movements compared to control groups and exhibited statistically significant
motor recovery, as measured by open field locomotion, inclined plane, and
swimming. After Fasudil treatment, some tissue was spared caudal to the
lesion site, as evaluated in histological studies. A second study with intraper-
itoneal Fasudil treatment after contusion injury in rats at T9/T10 reported a
three-point improvement in BBB score (
Sung et al., 2003
). Control rats
regained weight support, and treated rats regained coordinated movements.
The ROCK inhibitor Y-27632 has been studied in rat and mouse
models of SCI as well. In mice, Y-27632 given by local application at the
m
