Abstract WP216: Intraperitoneal Delivery Of Capsinoids (Non-pungent TRPV1 Agonists) Promotes Mild Hypothermia And Improved Long-term Outcome Following Stroke

Abstract

Intro: Mild hypothermia has been shown to improve outcomes in cardiac arrest and experimental stroke models. Unfortunately, hypothermia protocols in awake subjects are hampered by inconsistent temperature management due to incomplete suppression of cold defense mechanisms (e.g. shiver response). To address a need for better strategies for cooling conscious subjects, we sought to promote mild hypothermia by pharmacological activation of heat-sensing nerve fibers in the thermoregulatory system. We hypothesize that capsinoids - non-pungent agonists of the transient receptor potential vanilloid 1 (TRPV1) channel - activate vagal afferents, triggering thermoregulatory regions of the brain to induce mechanisms of whole-body cooling, protecting the brain and preventing injury progression after a stroke. Methods: C57BL6 male mice of 11wks underwent permanent distal middle cerebral artery occlusion (pdMCAO) or sham. Mice recovered for 2hrs in warming cages to maintain normal body temperatures during post-stroke recovery before being administered capsinoids or vehicle (4 IP injections, 90 min interval) to produce 6 hours of mild hypothermia (or normothermic control). After 1 month, mice underwent functional tests and brains were collected for histological analysis. Results: Capsinoids provided a significant and consistent hypothermia whereas vehicle maintained a baseline temperature (two-way ANOVA, n=7, p=0.0036). Capsinoid-treated mice showed ~50% infarct volume reduction 1 month after stroke, measured by cresyl-violet staining (0.7% ± 0.1% SEM vs 1.5% ± 0.2% SEM, n=7, two-tailed unpaired t-test: p=0.0046). Additionally, a stroke-induced breathing dysfunction (decrease in tidal volume by plethysmography) was significantly restored toward normal in the capsinoid-treated group (7.7e-3 ± 5.6e-4 SEM vs 5.8e-3 ± 2.4e-4 SEM, n=8, one-way ANOVA: p=0.033). Conclusion: Capsinoids delivered to TRPV1-containing visceral afferents promotes reversible mild hypothermia in freely moving conscious mice. Application of this form of cooling in the pdMCAO model provides significant reduction of stroke injury volume and long-term improvement in functional outcome.