Neurovascular Protection by Ischemic Tolerance: Role of Nitric Oxide and Reactive Oxygen Species

Abstract

Cerebral ischemic preconditioning or tolerance is a powerful neuroprotective phenomenon by which a sublethal injurious stimulus renders the brain resistant to a subsequent damaging ischemic insult. We used lipopolysaccharide (LPS) as a preconditioning stimulus in a mouse model of middle cerebral artery occlusion (MCAO) to examine whether improvements in cerebrovascular function contribute to the protective effect. Administration of LPS 24 h before MCAO reduced the infarct by 68% and improved ischemic cerebral blood flow (CBF) by 114% in brain areas spared from infarction. In addition, LPS prevented the dysfunction in cerebrovascular regulation induced by MCAO, as demonstrated by normalization of the increase in CBF produced by neural activity, hypercapnia, or by the endotheliumdependent vasodilator acetylcholine. These beneficial effects of LPS were not observed in mice lacking inducible nitric oxide synthase (iNOS) or the nox2 subunit of the superoxide-producing enzyme NADPH oxidase. LPS increased reactive oxygen species and the peroxynitrite marker 3-nitrotyrosine in wild-type mice but not in nox2 nulls. The peroxynitrite decomposition catalyst 5,10,15, 20-tetrakis(4-sulfonatophenyl)porphyrinato iron (III) attenuated LPS-induced nitration and counteracted the beneficial effects of LPS on infarct volume, ischemic CBF, and vascular reactivity. Thus, LPS preserves neurovascular function and ameliorates CBF in regions of the ischemic territory at risk for infarction. This effect is mediated by peroxynitrite formed from iNOS-derived NO and nox2-derived superoxide. The data indicate that preservation of cerebrovascular function is an essential component of ischemic tolerance and suggest that combining neuroprotection and vasoprotection may be a valuable strategy for treating ischemic brain injury.

Nitric Oxide: Considerations for the Treatment of Ischemic Stroke

“…Among the stimuli investigated for induction of tolerance are sublethal ischemia and proinflammatory mediators (Stagliano et al, 1999;Dawson and Dawson, 2000;Dirnagl et al, 2003;Kunz et al, 2007). Nitric oxide seems to have a major role in mediating ischemic tolerance induced by preconditioning.…”

Bilateral Common Carotid Artery Occlusion as an Adequate Preconditioning Stimulus to Induce Early Ischemic Tolerance to Focal Cerebral Ischemia

“…Furthermore, we have demonstrated that the preconditioning protocol used is a safe and minor invasive procedure with no noteworthy postoperative morbidity, no signs of apoptosis in brain and no mortality. Several different preconditioning protocols have been described previously [6][7]12 . Others have used 6 min of BCCAO as a preconditioning stimulus [13][14] .…”

“…Additionally, after removal of monofilaments CBF recovered to >90% of the respective baseline values after CCA occlusion. These LDF criteria are established in the literature and result in consistent infarct volumes 7 . We only included animals which had a Bederson score of at least of 1 after recovery from anesthesia after MCAO.…”

“…MCAO is a widely established model for induction of focal cerebral ischemia in rodents [5][6][7] . The surgical procedures were carried out using standardized operating procedures (SOP) 8 .…”

3-Nitropropionic Acid-Induced Ischemia Tolerance in the Rat Brain is Mediated by Reduced Metabolic Activity and Cerebral Blood Flow

“…Only few studies have investigated changes in CBF because of preconditioning before and at the time of subsequent ischemia. After preconditioning, some groups have found an increase in relative CBF, as determined from laser Doppler flowmetry, during or in the hours after subsequent ischemia, [32][33][34] whereas others observed neuroprotection without CBF effects during MCAO. [35][36][37] Dawson et al used autoradiography to show that 15 minutes after the onset of MCAO, CBF was unchanged in animals subjected to lipopolysaccharide preconditioning; however, 4 and 24 hours later, microvascular perfusion as assessed by an intravascular fluorescent tracer technique was preserved at higher levels in preconditioned animals compared with controls.…”