Combination Therapy With Insulin-like Growth Factor-1 and Hypothermia Synergistically Improves Outcome After Transient Global Brain Ischemia in the Rat

Objectives Hypothermia has a well-established neuroprotective effect and offers a foundation for combination therapy for brain ischemia. The authors evaluated the effect of combination therapy with insulin-like growth factor-1 (IGF-1) and hypothermia on brain structure and function in the setting of global brain ischemia and reperfusion in rats. Methods Male Sprague-Dawley rats were randomly assigned to groups by a registrar. Animals were subjected to 8minutes of global brain ischemia using bilateral carotid occlusion and systemic hypotension, followed by 7days (Stage I dose studies) or 28days (Stage II outcome studies) of reperfusion. Sham controls were subjected to surgery, but not ischemia. Stage II animals were randomized to no treatment, IGF-1 at the dose determined in Stage I, hypothermia (32 degrees C for 4hours), or a combination of IGF-1 and hypothermia. Stage II animals underwent 21days of spatial memory testing. At 7days (Stage I) or 28days (Stage II), brains were harvested for counting of CA1 neurons. The primary Stage II outcome was a neurologic outcome index computed as the ratio of viable CA1 neurons per 300-m field to the number ofdays to reach success criteria on the memory task. Results Stage I experiments confirmed the neuroprotective effect of the hypothermia protocol and IGF-1 at a dose of 0.6 U/kg. Stage II studies suggested that early neuroprotection with hypothermia and IGF-1 was not well maintained to 28days and that combination therapy was more beneficial than either IGF-1 or hypothermia alone. Median and interquartile ranges (IQRs) of viable neurons per 300-m field were 114 (IQR= 99.5 to 136) for sham, three (IQR= 2 to 4.8) for untreated ischemia, four (IQR= 3 to 70.25) for ischemia treated with IGF-1 alone, 25 (IQR= 3 to 70) for ischemia treated with hypothermia alone, and 78 (IQR 47.3 to 97.5) for ischemia treated with combination therapy. Days to memory success criteria were 13.6 (IQR= 11.5 to 15.5days) for sham, 23.5 (IQR= 20 to 25.5days) for untreated ischemia, 17.5 (IQR= 15.5 to 25.5days) for ischemia treated with IGF-1, 15 (IQR= 14.5 to 21days) for ischemia treated with hypothermia, and 13.5 (IQR= 12.25 to 18.5days) for ischemia treated with combination therapy. Neurologic outcome indices were 8.5 (IQR= 7.4 to 9.5) for sham, 0.14 (IQR= 0.08 to 0.2) for untreated ischemia, 0.18 (IQR= 0.17 to 4.6) for ischemia treated with IGF-1, 0.7 (IQR= 0.2 to 4.8) for ischemia treated with hypothermia, and 5.7 (IQR= 3.3 to 6.2) for ischemia treated with combination therapy. Statistically significant differences in neuron counts,days to memory test criteria, and outcome index were found between sham and untreated ischemic animals. Of the three treatment regimens, only combination therapy showed a statistically significant difference from the untreated ischemic group for neuronal salvage (p=0.02),days to criteria (p=0.043), and outcome index (p=0.014). Conclusions Combination therapy with IGF-1 (0.6 U/kg) and therapeutic hypothermia (32 degrees C for 4hours) at the onset of reperfusion synergistically preserves CA1 structure and function at 28days after 8minutes of global brain ischemia in healthy male rats. ACADEMIC EMERGENCY MEDICINE 2013; 20: 344-351 (C) 2013 by the Society for Academic Emergen cy Medicine