Valproic acid prevents brain injury in a canine model of hypothermic circulatory arrest: a promising new approach to neuroprotection during cardiac surgery.

BACKGROUND: The anticonvulsant valproic acid (sodium valproate, Depacon) acts as a neuroprotectant in rodents, but has never been tested in larger animals. We used valproate in our canine model of hypothermic circulatory arrest to evaluate its neuroprotective benefit in complex cardiac surgical cases.
METHODS: Thirteen dogs pretreated with valproate before 2 hours of hypothermic circulatory arrest survived for 24 hours (n = 7) or 72 hours (n = 6). Thirteen control animals (placebo only) also survived for 24 hours (n = 7) or 72 hours (n = 6) after hypothermic circulatory arrest. Blinded clinical neurologic evaluation was performed daily until sacrifice using the Pittsburgh Canine Neurologic Scoring System. Brains were harvested for blinded histopathologic analysis by a neuropathologist to determine the extent of apoptosis and necrosis in 11 brain regions (Total Brain Cell Death Score: 0 = normal, 99 = extensive neuronal death in all regions). Quantification of N-acetyl-aspartate, an established marker for brain injury, was performed with mass spectrometry.
RESULTS: Valproate dogs scored significantly better than control animals on clinical neurologic evaluation. Histopathologic examination revealed that valproate animals demonstrated less neuronal damage (by Total Brain Cell Death Score) than control animals at both 24 hours (16.4 versus 11.4; p = 0.03) and 72 hours (21.7 versus 17.7; p = 0.07). At 72 hours, the entorhinal cortex, an area involved with learning and memory, was significantly protected in valproate dogs (p < 0.05). Furthermore, the cortex, hippocampus, and cerebellum demonstrated preservation of near-normal N-acetyl-aspartate levels after valproate pretreatment.
CONCLUSIONS: These data demonstrate clinical, histologic, and biochemical improvements in dogs pretreated with valproate before hypothermic circulatory arrest. This commonly used drug may offer a promising new approach to neuroprotection during cardiac surgery.