• The Effect of Mineralocorticoid Receptor Antagonism on Ischemic Infarct Size

      Rigsby, Christiné Spring; Department of Physiology (2006-12)
      Stroke is the third leading cause of death and the leading cause of long-term disability in the United States, where approximately 88% of stroke occurrences are ischemic in origin. Hypertension is a primary risk factor for stroke. Elevated aldosterone levels have also been identified as a risk factor for stroke, as patients with primary aldosteronism incur increased incidences of cardiovascularrelated pathologies than do patients with essential hypertension. Previous studies from our laboratory have shown that mineralocorticoid (aldosterone) receptor (MR) activation can induce deleterious vascular remodeling and, conversely, blockade of the MR with spironolactone reduces cerebral infarct size in male spontaneously hypertensive stroke-prone rats (SHRSP). It is known from studies in SHRSP that cerebral vessel structure is directly related to infarct size. We hypothesized that chronic spironolactone treatment would alter cerebral vessel structure. Six-week-old male SHRSP were treated with spironolactone for six weeks and passive vessel structure was analyzed using a pressurized arteriograph. Spironolactone treatment prevented cerebral vessel remodeling. From a clinical standpoint, many patients present with pre-existing vascular damage; therefore, we hypothesized that chronic MR antagonism would reverse existing vascular damage. Twelve-week-old male SHRSP were treated as described above. Interestingly, spironolactone treatment partially reversed existing cerebral vessel remodeling. Recent analysis of data from the Framingham Heart Study show that females may be more sensitive to the effects of aldosterone, but few studies looking at MR blockade have been performed in females. Similar ischemic stroke and vascular analysis studies were performed in 12-week-old female SHRSP. Contrary to the male studies, MR antagonism, using spironolactone or eplerenone, did not reduce damage from ischemic stroke or improve vessel structure. MR protein expression was evaluated in cerebral arteries collected from 12-week-old male and female SHRSP using Western blot analysis. Surprisingly, female SHRSP had increased MR expression, compared to male SHRSP. These novel studies uncover an apparent sexual dimorphism in the actions of MR antagonists and expression of the MR in SHRSP. The action of the MR antagonists may be influenced by differential MR expression and this could help to explain the sex difference observed.
    • Mechanisms of Diabetes-Mediated Cerebrovascular Injury in Ischemic Stroke

      Cobbs, Aisha Imani; Department of Physiology (2012-08)
      Diabetes increases the risk of cerebrovascular disease and is a reliable predictor of increased morbidity and mortality following acute ischemic stroke. The objective of the current study was to investigate the underlying mechanisms by which diabetes-mediated vascular dysregulation contributes to greater injury and poor stroke outcomes. We hypothesized that peroxynitrite mediates vascular dysfunction in diabetes by destabilizing the vascular smooth muscle actin cytoskeleton. In addition, we proposed that excess peroxynitrite formation and inflammation during ischemia/reperfusion injury in pre-existing diabetes amplifies the proteolytic activity of matrix metalloproteinases (MMPs), thereby contributing to greater vascular injury (i.e., edema and hemorrhagic transformation) and neurological deficit. Using a modified oxygen-glucose deprivation protocol, we examined the effects of hypoxia on cerebral macrovascular reactivity. We found that peroxynitrite mediates hypoxia-induced loss of myogenic tone and medial thickening in cerebral resistance vessels isolated from type 2 diabetic rats. Furthermore, we demonstrated that reductions in polymerized actin cytoskeletal filaments following hypoxia exposure in these vessels cannot be attributed to peroxynitrite nitration, suggesting that an alternate target or different type of peroxynitrite-mediated protein modification may be involved. Targeting mediators of stroke-induced vascular injury at reperfusion was more beneficial in diabetic animals compared to controls. Acute administration of FeTPPs, curcumin, and minocycline at reperfusion in experimental stroke successfully reduced hemorrhagic transformation in all diabetic animals. This reduction in bleeding was associated with decreased MMP-9 activity in cerebral macrovessels. Administration of curcumin and minocycline attenuated edema formation in these animals. Functional outcomes were also improved in varying degrees by these therapies. Based on the findings of these studies, we concluded that oxidative stress, inflammation, and MMP activity in the cerebrovasculature of diabetic animals play a significant role in stroke pathologies that contribute to worse outcomes. Therefore, the following dissertation research has the potential to reduce the gap in knowledge of how pre-existing diabetes contributes to stroke pathophysiology and will potentially aid in the development of novel therapeutic strategies tailored to the diabetic population.
    • Vascular Protection by Angiotensin Receptor Antagonism Involves Differential VEGF Expression in Both Hemispheres after Experimental Stroke

      Guan, Weihua; Somanath, Payaningal R.; Kozak, Anna; Goc, Anna; El-Remessy, Azza B.; Ergul, Adviye; Johnson, Maribeth H.; Alhusban, Ahmed; Soliman, Sahar; Fagan, Susan C.; et al. (2011-09-1)
      We identified that the angiotensin receptor antagonist, candesartan, has profound neurovascular protective properties when administered after ischemic stroke and was associated with a proangiogenic state at least partly explained by vascular endothelial growth factor A (VEGFA). However, the spatial distribution of vascular endothelial growth factor (VEGF) isoforms and their receptors remained unknown. Protein analysis identified a significant increase in vascular endothelial grow factor B (VEGFB) in the cerebrospinal fluid (CSF) and the ischemic hemispheres (with increased VEGF receptor 1 activation) of treated animals (p<0.05) which was co-occurring with an increase in protein kinase B (Akt) phosphorylation (p<0.05). An increase in VEGFA protein in the contralesional hemisphere corresponded to a significant increase in vascular density at seven days (p<0.01) after stroke onset