Acute Neuronal Injury and Blood Genomic Profiles in a Nonhuman Primate Model for Ischemic Stroke

The goal of this study was to characterize acute neuronal injury in a novel nonhuman primate (NHP) ischemic stroke model by using multiple outcome measures. Silk sutures were inserted into the M1 segment of the middle cerebral artery of rhesus macaques to achieve permanent occlusion of the vessel. The sutures were introduced via the femoral artery by using endovascular microcatheterization techniques. Within hours after middle cerebral artery occlusion (MCAO), infarction was detectable by using diffusion-weighted MRI imaging. The infarcts expanded by 24 h after MCAO and then were detectable on T2-weighted images. The infarcts seen by MRI were consistent with neuronal injury demonstrated histologically. Neurobehavioral function after MCAO was determined by using 2 neurologic testing scales. Neurologic assessments indicated that impairment after ischemia was limited to motor function in the contralateral arm; other neurologic and behavioral parameters were largely unaffected. We also used microarrays to examine gene expression profiles in peripheral blood mononuclear cells after MCAO-induced ischemia. Several genes were altered in a time-dependent manner after MCAO, suggesting that this ischemia model may be suitable for identifying blood biomarkers associated with the presence and severity of ischemia. This NHP stroke model likely will facilitate the elucidation of mechanisms associated with acute neuronal injury after ischemia. In addition, the ability to identify candidate blood biomarkers in NHP after ischemia may prompt the development of new strategies for the diagnosis and treatment of ischemic stroke in humans.Abbreviations: MCAO, middle cerebral artery occlusion; NHP, nonhuman primate; PBMC, peripheral blood mononuclear cellsStroke is a debilitating neurologic condition, and little progress has been made in the development of neuroprotective treatments for acute stroke. The Stroke Therapy Academic Industry Roundtable (STAIR) report suggested that preclinical candidates for stroke therapy should be validated by testing in large animals with similarities to humans, such as nonhuman primates (NHP).²⁶ NHP stroke models have been developed in several species, including rhesus monkeys, marmosets, and baboons, by using a variety of techniques for middle cerebral artery occlusion (MCAO).^{4,10,12,13,14,25,32} The rhesus macaque is ideal for stroke studies because of its structural similarities to human brain. The rhesus brain is gyrencephalic, which makes it preferable to those of lissencephalic primates (for example, marmosets) and is functionally similar to human brain.⁶ In addition, the immunologic profile of rhesus macaques is similar to that of humans; therefore these animals are the preferred model for the study of immune responses to infectious diseases such as HIV/SIV, Dengue virus, and others.^17,23,30In addition to their use for neuroprotection assessment, NHP stroke models can facilitate efforts to develop diagnostic tools for identifying and treating stroke symptoms. The use of genomics in peripheral blood cells has been shown to be an excellent method to identify candidate biomarkers and cellular mechanisms associated with stroke.^28,29 Blood biomarkers can be used to rapidly determine the occurrence, timing, subtype, and severity of stroke.^11,15 One possible reason for the lack of viable stroke biomarkers may be the research models used to search for these markers. Although rodent stroke models have yielded a wealth of information on the mechanisms associated with brain ischemia, the findings have not translated well to human clinical trials.²⁶ Recent studies in human patients showed promising results when genomic tools have been used to screen for novel stroke biomarkers.^3,16,27 However, validation of human studies is limited by the need for large data sets in light of heterogeneity in stroke onset, subtype, comorbidities, and other factors. In addition, it is also impossible to know the exact time of stroke onset in most patients.Here we characterized acute neuronal injury in a novel, minimally invasive permanent ischemic stroke model involving rhesus macaques. Using endovascular catheterization techniques, we introduced silk sutures into the M1 segment of the middle cerebral artery and permanently occluded it. This procedure reliably produced infarcts that could be measured by MRI of the macaque brains during the acute phase period. The procedure resulted in discrete and limited neurobehavioral deficits, indicating the potential of this stroke model for chronic neuroprotection studies in the future. In addition, we used microarrays to identify blood genomic profiles that were altered in a time-dependent manner after ischemia. These studies characterize a preclinical model that is suitable for elucidating the mechanisms associated with cerebral ischemia and that may aid in identifying strategies for the diagnosis and treatment of stroke in humans.