Neuroprotective effects of GYKI 52466 on experimental spinal cord injury in rats

De novo expression of Trpm4 initiates secondary hemorrhage in spinal cord injury

The role of transient receptor potential M4 (Trpm4), an unusual member of the Trp family of ion channels, is poorly understood. Using rodent models of spinal cord injury, we studied involvement of Trpm4 in the progressive expansion of secondary hemorrhage associated with capillary fragmentation, the most destructive mechanism of secondary injury in the central nervous system. Trpm4 mRNA and protein were abundantly upregulated in capillaries preceding their fragmentation and formation of petechial hemorrhages. Trpm4 expression in vitro rendered COS-7 cells highly susceptible to oncotic swelling and oncotic death following ATP depletion. After spinal cord injury, in vivo gene suppression in rats treated with Trpm4 antisense or in Trpm4(-/-) mice preserved capillary structural integrity, eliminated secondary hemorrhage, yielded a threefold to fivefold reduction in lesion volume and produced a substantial improvement in neurological function. To our knowledge, this is the first example of a Trp channel that must undergo de novo expression for manifestation of central nervous system pathology.

Endothelial sulfonylurea receptor 1-regulated NC Ca-ATP channels mediate progressive hemorrhagic necrosis following spinal cord injury

Acute spinal cord injury (SCI) causes progressive hemorrhagic necrosis (PHN), a poorly understood pathological process characterized by hemorrhage and necrosis that leads to devastating loss of spinal cord tissue, cystic cavitation of the cord, and debilitating neurological dysfunction. Using a rodent model of severe cervical SCI, we tested the hypothesis that sulfonylurea receptor 1-regulated (SUR1-regulated) Ca(2+)-activated, [ATP](i)-sensitive nonspecific cation (NC(Ca-ATP)) channels are involved in PHN. In control rats, SCI caused a progressively expansive lesion with fragmentation of capillaries, hemorrhage that doubled in volume over 12 hours, tissue necrosis, and severe neurological dysfunction. SUR1 expression was upregulated in capillaries and neurons surrounding necrotic lesions. Patch clamp of cultured endothelial cells exposed to hypoxia showed that upregulation of SUR1 was associated with expression of functional SUR1-regulated NC(Ca-ATP) channels. Following SCI, block of SUR1 by glibenclamide or repaglinide or suppression of Abcc8, which encodes for SUR1 by phosphorothioated antisense oligodeoxynucleotide essentially eliminated capillary fragmentation and progressive accumulation of blood, was associated with significant sparing of white matter tracts and a 3-fold reduction in lesion volume, and resulted in marked neurobehavioral functional improvement compared with controls. We conclude that SUR1-regulated NC(Ca-ATP) channels in capillary endothelium are critical to development of PHN and constitute a major target for therapy in SCI.

Stretch-induced injury in organotypic hippocampal slice cultures reproduces in vivo post-traumatic neurodegeneration: role of glutamate receptors and voltage-dependent calcium channels

The relationship between an initial mechanical event causing brain tissue deformation and delayed neurodegeneration in vivo is complex because of the multiplicity of factors involved. We have used a simplified brain surrogate based on rat hippocampal slices grown on deformable silicone membranes to study stretch-induced traumatic brain injury. Traumatic injury was induced by stretching the culture substrate, and the biological response characterized after 4 days. Morphological abnormalities consistent with traumatic injury in humans were widely observed in injured cultures. Synaptic function was significantly reduced after a severe injury. The N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 attenuated neuronal damage, prevented loss of microtubule-associated protein 2 immunoreactivity and attenuated reduction of synaptic function. In contrast, the NMDA receptor antagonists 3-[(R)-2-carboxypiperazin-4-yl]-propyl-1-phosphonic acid (CPP) and GYKI53655, were neuroprotective in a moderate but not a severe injury paradigm. Nifedipine, an L-type voltage-dependent calcium channel antagonist was protective only after a moderate injury, whereas omega-conotoxin attenuated damage following severe injury. These results indicate that the mechanism of damage following stretch injury is complex and varies depending on the severity of the insult. In conclusion, the pharmacological, morphological and electrophysiological responses of organotypic hippocampal slice cultures to stretch injury were similar to those observed in vivo. Our model provides an alternative to animal testing for understanding the mechanisms of post-traumatic delayed cell death and could be used as a high-content screen to discover neuroprotective compounds before advancing to in vivo models.