Abstract
Abstract only Introduction: Menopause increases the risk and severity of ischemic stroke (IS), while endogenous 17β-estradiol (E2) naturally protects premenopausal women against IS. The female sex hormone E2 is a potent neuro- and cognitive-protective agent. Studies have shown that periodic E2 or estrogen receptor subtype-beta (ER-β) agonist pre-treatments every 48 hours before an ischemic episode ameliorated ischemic brain damage in young ovariectomized or reproductively senescent (RS) aged female rats. The current study investigates the underlying mechanism of ER-β agonist-mediated neuroprotection. Methods: Retired breeder (9–10 months) Sprague–Dawley female rats were considered RS after remaining in constant diestrus phase for more than a month. The RS rats were exposed to transient middle cerebral artery occlusion (tMCAO; 90 mins) and treated with either ER-β agonist (beta 2, 3-bis(4-hydroxyphenyl) propionitrile; DPN; 1 mg/kg; s.c.) or DMSO vehicle at 4.5 hours after induction of tMCAO. Subsequently, rats were treated with either ER-β agonist or DMSO vehicle every 48 hours (48-h) for ten injections. Forty-eight hours after the last treatment, animals were tested for cognitive deficits via the Morris water maze. At 1-month post-tMCAO, brains were collected for histopathological analysis. A second cohort of RS rats underwent DPN or DMSO treatment for a month; 48-h after last injection, brains were collected for unbiased global metabolomic analysis (conducted by Metabolon Inc.). The metabolomic study was complemented with western blot analysis and enzyme activity measurements of key altered pathways. Results: Data showed significant (p<0.05) decreases in glucose-6-phosphate and increases in 5-phosphyribosyl diphosphate, UDP-galactose, and N-acetylglucoseamine-6-phosphate in the brain of DPN-treated RS female rats as compared to DMSO-treated controls. DPN treatment also changes the enzymatic activity of glycolytic rate limiting enzyme hexokinase. Metabolomics data also showed significant increase in choline and arginine levels in the brain of DPN-treated RS female rats as compared to DMSO-treated controls. Conclusion: The observed changes in glycolytic and amino acid pathway metabolites could enhance brain energy metabolism and increase choline availability, potentially contributing to the improved post-stroke cognitive outcomes in RS rats.