Author ORCID Identifier

0000-0001-9064-4149

Date of Graduation

8-2018

Document Type

Thesis (MS)

Program Affiliation

Biomedical Sciences

Degree Name

Masters of Science (MS)

Advisor/Committee Chair

Louise McCullough

Committee Member

Jaroslaw Aronowski

Committee Member

Dorothy Lewis

Committee Member

Sean Marrelli

Committee Member

Venugopal Venna

Abstract

Introduction:

Stroke is the leading cause of serious long-term disability and is the 5th leading cause of death causing approximately 130,000 deaths in the United States every year {1}. Stroke is also the 2nd leading cause of death in American women {2}. Women are 33% more likely to require nursing home care then men, have a higher lifetime risk of stroke and are 13% less likely to receive thrombolytic (clot busting) treatment than men {2}. Interleukin 6 (IL-6) is a pro-inflammatory cytokine involved in the regulation of the immune system in multiple disease states such as rheumatoid arthritis and contributes to increased inflammation. In stroke patients, higher plasma IL-6 levels correlate with increased stroke severity and poor long-term prognosis {3}. Preliminary work in our lab has shown that tocilizumab, an FDA approved immunosuppressive drug that blocks IL-6 receptors to inhibit the pro-inflammatory effects of IL-6, reduced infarct size in young male mice following ischemic stroke. Based on this promising preliminary data, we now hypothesize that tocilizumab will reduce injury in aged male and female mice.

Methods:

Experiments utilized aged (18-20 month) C57BL/6J male and female mice and examined neuroprotection and behavioral outcome after tocilizumab treatment. Mice were randomly assigned to the stroke or sham surgery group and then further subdivided into tocilizumab or IgG control treatment groups. Stroke was induced by 1 hour of transient right middle cerebral artery occlusion (MCAO) {6} under isoflurane anesthesia followed by reperfusion and then studied for 35 days. Four hours after the onset of ischemia, mice were given an intraperitoneal injection of either tocilizumab (20mg/1kg) or an IgG control antibody. Behavior tests evaluated sensorimotor deficits, locomotor activity, working memory, gait and spatial learning {6, 9}. Mice were sacrificed and brain atrophy assessed using cresyl violet staining.

Results:

Tocilizumab treatment reduced stroke damage by decreasing brain atrophy. In addition mortality and behavioral deficits were lessened in aged males on multiple behavior tests (P< 0.05). Females did not show similar benefits with tocilizumab at a dose of 20mg/kg. However, tocilizumab did show acute neuroprotection in aged females at a dose of 100mg/kg three-days post-stroke, which is likely the result of higher levels of soluble IL-6 receptor in females post-stroke. The results support our hypothesis that inhibition of the IL-6 receptor is a potential therapeutic approach for stroke treatment.

Summary and Conclusions:

Together, these results support our hypothesis that inhibition of the IL-6 receptor can be a novel therapeutic approach for stroke treatment. Interestingly, the neuroprotective dose of tocilizumab was different in males and females. This effect appears to be due to significantly higher soluble IL-6 receptor levels in females in the post-stroke phase and emphasizes the importance of determining efficacy in a sex-specific manner.

Keywords

Ischemic stroke, interleukin-6, sex differences, aging

Available for download on Thursday, August 15, 2019

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