Abstract
Background
Treatment of spinal cord injury (SCI) induced neuropathic pain (NP) proves to
be extremely clinically challenging as the mechanism behind SCINP is poorly
understood. Matrix metalloproteinase (MMP) is largely responsible for the
early disruption of the blood spinal cord barrier. This system initiates
macrophage infiltration and degradation of myelin, which plays a pivotal
role in how NP occurs. In a recent study, we demonstrated that folic acid
(FA) treatment to cSCI rats reduced NP and improved functional recovery by
repressing MMP-2 expression. We hypothesize that MMP-2 expression is
suppressed because FA actively methylates the DNA sequence that encodes for
the MMP-2 protein. However, modulation of MMP-2 expression for alleviation
of NP is only pertinent to the mid- to late-phase of injury. Therefore, we
need to explore alternate therapeutic methods to target the early- to
mid-phase of injury to wholly alleviate NP.
Purpose
Furthering our previous findings on inhibiting MMP-2 expression by FA in mid-
and late- phase following cSCI in rats, we hypothesized that FA will
methylate and suppress MMP-9 expression during the early- phase, day 1, 3, 7
post cSCI and mid- phase (day 18 post cSCI), in comparison with MMP-2
expression during mid- and the late-phase of cSCI.
Methods
Adult male Sprague Dawley rats (250–270g) underwent cSCI, using a NYU
impactor, with 12.5 gm/cm injury. The spinal cord-injured animals were
treated intraperitoneally (i.p.) with a standardized dose of FA (80 μg/kg
body weight) on day 1, 2, 3, prior to cSCI, followed by daily injection up
to 14 or 17 days post-cSCI in different experiments. Animals were euthanized
on day 1, 3, 7 post cSCI (early- phase), day 18 post cSCI (mid- phase), and
day 42 post cSCI (late-phase) and the epicenter region of injured spinal
cord were harvested for MMP-9 and MMP-2 expression analysis by Western blots
technique.
Results
i) During early-phase on day 1, 3, and 7, the quantitation displayed no
statistical significance in MMP-9 expression, between water- and FA-
injected rats. ii) On day 18 post-cSCI, FA significantly modulates the
expression of MMP-9 (p = 0.043) iii) Comparing results with MMP-2 expression
and inhibition, FA significantly modulates the expression of MMP-2 on day 18
post cSCI (FA- and water-injected rats (p = 0.003). iv) In addition, FA
significantly modulates the expression of MMP-2 on day 42 post-cSCI
comparing FA- and water- injected rat groups (p = 0.034).
Conclusion
We report that FA administration results in alleviating cSCI-induced NP by
inhibiting MMP-9 in the proposed mid- phase of cSCI. However, FA
administration resulted in MMP-2 decline during both mid- through late-
phase following cSCI. Our study elucidates a new phase of cSCI, the
mid-phase. We conclude that further investigation on discovering and
quantifying the nature of the mid- phase of SCI injury is needed.
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