Blood-brain barrier leakage after transient cerebral ischemia

Acute ischemic stroke is a devastating disease leaving more than half of its victims disabled and causing nearly 5% of all deaths worldwide. In large ischemic strokes, a major cause of death is brain edema, which follows blood-brain barrier (BBB) leakage. The BBB ensures brain homeostasis in health and disease by limiting the entry of harmful blood-borne substances into the brain parenchyma. With a leaky BBB, the brain becomes devoid of protection from detrimental components of the circulating blood. The BBB leakage in animal models of ischemia reperfusion has long been considered to be biphasic; however, a considerable amount of discrepancies exist among the studies. Knowing exact temporal changes of the BBB permeability (BBBP) is important for the management of stroke patients. When the BBB is open, BBBP alleviating therapies would be effective, neuroprotective or neurorestorative drugs would be introduced, and if the BBB is closed these drugs would not enter the brain. Practical and reliable biomarkers of BBBP status are needed. Stanniocalcins (STCs) are widely expressed in the brain and STC-1 expression is elevated in pathologies, such as hypoxia and focal ischemia. Recent data suggest a neuroprotective role for STC-1 especially trough hypoxic preconditioning (HPC). No previous data associate STC-1 and the BBB. We systematically evaluated disruption of the BBB following ischemia-reperfusion in a rat model of transient focal ischemia via suture occlusion of the middle cerebral artery for 90 min. Firstly (I, II), animals were allocated to 15 groups after reperfusion (25 min to 5 weeks). Secondly (III), a group of animals were evaluated repeatedly from 2 h to 1 week after reperfusion. BBBP to both small (gadolinium) (I, II, III), and large (Evans blue) (I) molecules were quantified by magnetic resonance imaging and fluorescence, respectively. Lastly, the contribution of STC-1 to HPC and the BBB was explored using STC-1 deficient mice (STC-/-). (I, II, III) After transient ischemia, the BBB leakage was continuous. Leakage to Evans Blue persisted up to 3 weeks and to gadolinium up to 5 weeks. Evans blue leakage slightly decreased at 36 and 72 h, gadolinium leakage was lesser at 25 min, 3 and 4 weeks. (IV) In STC-/- mice, HPC was effective in reducing lesion size, but these mice scored worse than wild type littermates. BBBP to Evans blue was not increased in STC-/- mice; neither under normal conditions, nor after hypoxia. To conclude, transient focal ischemia in rats triggers a continuous BBB leakage lasting for several weeks. Until the final closure of the BBB, no earlier transient closure occurs. This finding indicates a long therapeutic window opportunity in respect to BBB passage of drugs to treat stroke. BBBP imaging method used in these studies may be easily translated to clinics. STC-1 is not obligatory for hypoxic preconditioning and is not a determining component of the BBB. Yet, STC-1 is important for preservation of neurological function after transient ischemia.Aivoinfarkti on vakava tauti jonka seurauksena yli puolet potilaista vammautuu ja tarvitsevat ulkopuolista apua. Maailmassa kaikesta kuolemista 5% johtuu aivoinfarktista. Kun kyseessä on laaja-alainen aivoinfarkti, tärkein kuoleman syy on veri-aivoesteen häiriö, joka johtaa nesteen siirtymiseen suonista aivokudokseen ja siten aivoturvotukseen. Aivoinfarktin eläinmalleissa aivoinfarktin jälkeinen veri-aivoesteenhäiriö on toistetusti osoitettu bifaasiseksi ilmiöksi, määrittäen että, este ensin avautuu, sitten sulkeutuu ja uudestaan avautuu. Kuitenkin, tutkimustuloksissa on merkittäviä eroja, lähinnä esteen avautumisen ajankohdat suuresti vaihtelevat. Väitöskirjatyössäni olen tutkinut aivoiskemian aiheuttamaa veri-aivoesteen vauriota systemaattisesti histologisin menetelmin ja magneettikuvausta käyttäen. Osatöissäni I-III rotille aiheutettiin aivoinfarkti ja veri-aivoesteen läpäisevyys tutkittiin 5-15 eri aikapisteessä. Menetelminä käytettiin eläinten ollessa elossa varjoaine (gadolinium, pieni molekyyli) -magneettikuvaus ja kokeiden lopetusvaiheessa Evans blue värjäys (iso molekyyli). Osajulkaisussa IV tutkittiin stanniokalsiini-1 (STC-1):n roolia veri-aivoesteen läpäisevyydessä ja hypoksia-esikäsittelyn jälkeen aivoinfarktista suojaamisessa (hypoxic preconditioning). Tätä varten käytettiin STC-1 poistogeenisiä hiiriä ja aivoinfarktimallia. Tutkimuksessa I-III todettiin veri-aivoesteen olevan jatkuvasti avoimena, toisin sanoen osoitimme häiriön olevan monofaasinen. Veri-aivoesteen lisääntynyt Evans blue-läpäisevyys on normalisoitunut 3 vko aivoinfarktin aiheuttamisen jälkeen ja gadolinium-läpäisevyys 5 vko jälkeen. Evans blue-läpäisevyys hieman väheni 36 ja 72 t infarktista, gadolinium läpäisi vähemmän 25 min sekä 3 ja 4 vko infarktista. STC-1 poistogeeniset hiiret pystyivät suojautumaan infarktista hypoksia-esikäsittelyn jälkeen, mutta olivat huonommassa neurologisessa tilassa kuin villityypin hiiret. Veri-aivoesteen vaurioitumisessa ei todettu eroja. Yhteenvetona, aivoinfarkti johtaa veri-aivoesteen jatkuvaan avautumiseen, joka kestää useita viikkoja. Ei paljastunut merkittäviä eroja läpäisevyydessä kunnes aivo-veriesteen toiminta lopulta korjaantui. Tulokset tulevat auttamaan veri-aivoesteen toimintahäiriön patofysiologian syvällisemmässä ymmärtämisessä ja siten saattavat auttaa kehittämään täsmähoitoja tähän vakavaan, aivohalvauspotilaiden henkeä uhkaavaan aivoturvotukseen. Väitöskirjani magneettikuvaukseen perustuva tutkimusmenetelmä voisi siirtää sellaisenaan kliiniseen käyttöön veri-aivoesteen läpäisevyyden tutkimiseksi aivoinfarkti potilailla

Preconditioning-induced ischemic tolerance: a window into endogenous gearing for cerebroprotection

Ischemic tolerance defines transient resistance to lethal ischemia gained by a prior sublethal noxious stimulus (i.e., preconditioning). This adaptive response is thought to be an evolutionarily conserved defense mechanism, observed in a wide variety of species. Preconditioning confers ischemic tolerance if not in all, in most organ systems, including the heart, kidney, liver, and small intestine. Since the first landmark experimental demonstration of ischemic tolerance in the gerbil brain in early 1990's, basic scientific knowledge on the mechanisms of cerebral ischemic tolerance increased substantially. Various noxious stimuli can precondition the brain, presumably through a common mechanism, genomic reprogramming. Ischemic tolerance occurs in two temporally distinct windows. Early tolerance can be achieved within minutes, but wanes also rapidly, within hours. Delayed tolerance develops in hours and lasts for days. The main mechanism involved in early tolerance is adaptation of membrane receptors, whereas gene activation with subsequent de novo protein synthesis dominates delayed tolerance. Ischemic preconditioning is associated with robust cerebroprotection in animals. In humans, transient ischemic attacks may be the clinical correlate of preconditioning leading to ischemic tolerance. Mimicking the mechanisms of this unique endogenous protection process is therefore a potential strategy for stroke prevention. Perhaps new remedies for stroke are very close, right in our cells

Demographic and Geographic Vascular Risk Factor Differences in European Young Adults With Ischemic Stroke The 15 Cities Young Stroke Study

Background and Purpose-We compared among young patients with ischemic stroke the distribution of vascular risk factors among sex, age groups, and 3 distinct geographic regions in Europe. Methods-We included patients with first-ever ischemic stroke aged 15 to 49 years from existing hospital-or population-based prospective or consecutive young stroke registries involving 15 cities in 12 countries. Geographic regions were defined as northern (Finland, Norway), central (Austria, Belgium, France, Germany, Hungary, The Netherlands, Switzerland), and southern (Greece, Italy, Turkey) Europe. Hierarchical regression models were used for comparisons. Results-In the study cohort (n=3944), the 3 most frequent risk factors were current smoking (48.7%), dyslipidemia (45.8%), and hypertension (35.9%). Compared with central (n=1868; median age, 43 years) and northern (n=1330; median age, 44 years) European patients, southern Europeans (n=746; median age, 41 years) were younger. No sex difference emerged between the regions, male: female ratio being 0.7 in those aged <34 years and reaching 1.7 in those aged 45 to 49 years. After accounting for confounders, no risk-factor differences emerged at the region level. Compared with females, males were older and they more frequently had dyslipidemia or coronary heart disease, or were smokers, irrespective of region. In both sexes, prevalence of family history of stroke, dyslipidemia, smoking, hypertension, diabetes mellitus, coronary heart disease, peripheral arterial disease, and atrial fibrillation positively correlated with age across all regions. Conclusions-Primary preventive strategies for ischemic stroke in young adults-having high rate of modifiable risk factors-should be targeted according to sex and age at continental level. (Stroke. 2012; 43:2624-2630.