We recently documented the progressive nature of
mitochondrial dysfunction over 24 hr after
contusion spinal cord injury (SCI), but the underlying mechanism has not been elucidated. We investigated the effects of targeting two distinct possible mechanisms of
mitochondrial dysfunction by using the mitochondrial uncoupler
2,4-dinitrophenol (2,4-DNP) or the
nitroxide antioxidant Tempol after
contusion SCI in rats. A novel aspect of this study was that all assessments were made in both synaptosomal (neuronal)- and nonsynaptosomal (glial and neuronal
soma)-derived mitochondria 24 hr after injury. Mitochondrial uncouplers target Ca(2+) cycling and subsequent
reactive oxygen species production in mitochondria after injury. When
2,4-DNP was injected 15 and 30 min after injury, mitochondrial function was preserved in both populations compared with vehicle-treated rats, whereas 1 hr postinjury treatment was ineffective. Conversely, targeting
peroxynitrite with
Tempol failed to maintain normal bioenergetics in synaptic mitochondria, but was effective in nonsynaptic mitochondria when administered 15 min after injury. When administered at 15 and 30 min after injury, increased hydroxynonenal, 3-NT, and
protein carbonyl levels were significantly reduced by
2,4-DNP, whereas
Tempol only reduced 3-NT and
protein carbonyls after SCI. Despite such
antioxidant effects, only
2,4-DNP was effective in preventing
mitochondrial dysfunction, indicating that mitochondrial Ca(2+) overload may be the key mechanism involved in acute mitochondrial damage after SCI. Collectively, our observations demonstrate the significant role that
mitochondrial dysfunction plays in SCI neuropathology. Moreover, they indicate that combinatorial therapeutic approaches targeting different populations of mitochondria holds great potential in fostering neuroprotection after acute SCI.