Abstract WP353: Post-stroke infusion of metformin achieves pharmacological levels in the brain and ameliorates stroke outcomes in e-cigarette exposed mice

Introduction: Stroke is a leading cause of death and disability, and its outcomes can be worsened by lifestyle risk factors such as smoking. There is increasing interest in repurposing metformin, a medication used for diabetes, to meet the urgent need for new treatments for stroke. However, the conclusions regarding its effectiveness in stroke treatment from preclinical studies are mixed. This is largely due to the challenges in achieving and maintaining sufficient levels of metformin in the brain using traditional delivery methods. In this study, we introduce a novel subcutaneous infusion method to improve the brain level of metformin and evaluate its neuroprotective effects in a rodent model of stroke. Methods: Male C57BL/6 mice were subjected to a 14-day session of e-cigarette vaping and then underwent transient middle cerebral artery occlusion to simulate ischemic stroke in smokers. During the reperfusion phase, a subcutaneous infusion of metformin (200 mg/mL, 8 μL/hr) was administered. LC-MS/MS was used to quantify the levels of metformin. Behavioral tests, TTC stain, and untargeted metabolomics were employed to evaluate the stroke outcomes. Results: After 24 hours of infusion, the brain concentration of metformin in the ischemic hemispheres reached and maintained a level of 25.6 ± 3.1 µM, which was sustained above the reported pharmacological threshold (10 - 20 µM) needed to mitigate ischemia-induced injury to brain cells. The ischemic hemispheres showed a higher concentration of metformin compared to the contralateral hemispheres (4.2 ± 0.5 vs. 2.2 ± 0.5 µg/g, p < 0.05), possibly due to changes in blood-brain barrier integrity and transport mechanisms under stroke conditions. Additionally, compared to the vehicle alone, post-stroke infusion of metformin improved stroke outcomes, as indicated by reduced infarct sizes (p < 0.01) and increased locomotor activity (p < 0.05). Furthermore, we observed no significant difference in plasma glucose levels between the vehicle and metformin groups (p > 0.05), indicating that a short-term metformin infusion did not affect systemic glucose levels. Metabolomics analysis studies are underway to investigate the possible protective mechanisms associated with metformin on the metabolic state in the ischemic brain. Conclusion: This study shows that post-stroke infusion of metformin achieves pharmacological levels in the brain and improves stroke outcomes, supporting its potential as a neuroprotective agent for stroke.