Penumbra is the viable tissue around the irreversibly damaged ischemic core. The purpose of acute stroke treatment is to salvage penumbral tissue and to improve brain function. However, the majority of acute stroke patients who have treatable penumbra are left untreated.

Therefore, developing an effective non-recanalizational therapeutics, such as neuroprotective agents, has significant clinical applications. Part I of this serial review on “targeting penumbra” puts special emphases on penumbral pathophysiology and the development of therapeutic strategies. Bioenergetic intervention by massive metabolic suppression and direct energy delivery would be a promising future direction.

An effective drug delivery system for this purpose should be able to penetrate BBB and achieve high local tissue drug levels while non-ischemic region being largely unaffected. Selective drug delivery to ischemic stroke penumbra is feasible and deserves intensive research. IntroductionEach year, approximately 795 000 people experience a new or recurrent stroke. On average, every 40 seconds, someone in the United States has a stroke. Overall stroke prevalence during 2003 to 2006 is around 2.9%. Of all strokes, 87% are ischemic.

(Lloyd-Jones et al.) Due to stroke's high incidence and prevalence rates and the lack of effective treatment, stroke remains one of the major diseases causing most mortality and disability. Stroke is the third leading cause of death, behind diseases of the heart and cancer, and is a leading cause of serious, long-term disability in the United States. Although treatments for ischemic stroke have been rigorously investigated for two decades, up to now there is only one FDA-approved pharmacological treatment for ischemic stroke, the intravenous thrombolytic treatment using recombinant tissue plasminogen activator (r-tPA)., which can only be available to a very limited number of patients.Acute stroke causes an irreversibly damaged ischemic core and salvageable surrounding tissue. “Penumbra” is the term used for the reversibly injured brain tissue around ischemic core; which is the pharmacological target for acute ischemic stroke treatment.

Background: Identifying tissue at risk for infarction is important in deciding which patients would benefit most from potentially harmful therapies and provides a way to evaluate newer therapies with regard to the amount of ischemic tissue salvaged. Objective: To operationally define and characterize cerebral tissue at risk for stroke progression. Penumbra, Inc. Is a global healthcare company focused on innovative therapies that address challenging medical conditions and significant clinical needs.

The goal to treat ischemic stroke is to salvage the penumbra as much and early as possible. It has been reported that roughly half of all acute ischemic patients show penumbra on MRI and are potentially treatable. However, only 8% of all ischemic stroke patients eligible for treatment with recombinant tissue plasminogen activator (r-tPA).

Effective pharmacological treatment with or without recanalization could be used for the majority of stroke patients, having invaluable clinical significance. The development of neuroprotective treatment for ischemic stroke is obstructed by the blood-brain barrier and reduced blood supply to ischemic brain tissue, facing repeated translational failure in recent 20 years. Drug delivery to brain tissue, especially the ischemic brain tissue has long been the technical bottleneck limiting acute stroke treatments. A breakthrough in this area will possibly bring in numerous related applications. The technology to be developed in this field may also be extended to other fields, such as traumatic brain injury, brain tumor, and CNS inflammatory diseases. This review summarizes advances for ischemic stroke penumbra, and puts special emphases on strategy development from a metabolic point of view for effective drug delivery to ischemic penumbra. Penumbra and infarct expansion: the “time is brain” conceptIn animal studies, the dynamic changes of penumbra area and infarct expansion can be better illustrated based on the data obtained from experimental strokes, in which the timing of occlusion and reperfusion was precisely controlled.

After middle cerebral artery (MCA) occlusion, the infarct evolves rapidly in the first few hours, supporting the interventional concept that “time is brain”. For an example, in a 300 g rat, 2-h MCA occlusion (MCAO) produces a big infarct of 400-450 mm 3 that is close to the infarct caused by 24-h permanent MCAO (; ). Ninety minute transient MCAO results in a smaller infarct about 250–380 mm 3 (; ) whilst 60-min MCAO only produces approximately 170 mm 3 infarct.

Therefore, in a 300g rat, at 1-h post-MCA occlusion approximately 170 mm 3 brain tissue has already been irreversibly injured. At this moment the occlusion has caused approximately 230 mm 3 tissue in danger. Roughly 140 mm 3 of this 230 mm 3 in-danger brain tissue will die in 30 min, and the left 90 mm 3 will die in 60 min. If we assume the specific gravity of rat brain is 1.0 mg/mm 3, the average speed of infarct expansion for a 300g rat is approximately 3.3 mg/min after MCA occlusion. Imaging penumbraFor identifying the salvageable brain tissue in acute stroke, the direct method is to image penumbra. In acute ischemic stroke, the viability and size of penumbra change dynamically (; ) in response to regional cerebral blood flow, pathophysiological environment and treatment. Penumbra can be imaged using different technologies, such as MRI, CT (Kumar et al.), PET, and SPECT.

For targeting penumbra in stroke patients, imaging penumbra is necessary for monitoring treatment response as well as for patient screening. The “mismatch” of perfusion-weighted and diffusion-weighted images (PWI-DWI mismatch) is the most commonly used method for imaging penumbra and may serve for this purpose (; ). The diffusion-weighted image may represent reversibly injured tissue in the early hours after stroke (; ) whereas the perfusion-weighted image may include area of benign oligemia. The mismatched tissue represents “tissue-at-risk”, not “tissue-doomed-to die”; therefore it does not identify lesion growth by itself. (For infarct expansion see the following paragraph.) Penumbra may resolve spontaneously , either by merging with the ischemic core, or becoming normal tissue. When recanalizational therapy started early enough, the mismatched tissue, the penumbra, may be salvaged, which has been observed using both CT and MRI methods.

Penumbra in stroke patients: the majority of potentially treatable patients are not treatedThe use of imaging modalities detecting the existence of penumbra in stroke patients brought in new lights in patient management. Theoretically, all patients having penumbra zone should be treated. However, the number of patients treated by recanalizational intervention is only a small portion of all acute stroke patients who have a salvageable penumbra. When further looking into the subtypes according to the Trial of Org 10172 in Acute Stroke Treatment (TOAST) classification , the existence of penumbral tissue significantly correlates to stroke subtypes. The majority (about 94%)of intracranial large artery atherosclerotic (IC-LAA) stroke patients had perfusion-diffusion mismatch, whereas in cargioembolic strokes the penumbra existed in 35.7% patients.

Although the initial penumbral volume is similar among large-vessel stroke, cardioembolic stroke and cryptogenic embolic stroke, the mean perfusion defect in IC-LAA stroke was less severe than in other groups. This finding may indicate that the penumbral tissue in intracranial large artery atherosclerotic stroke may be more responsive to acute treatment. When an infarct involves white matter, it is associated with a relatively greater penumbral zone than in gray matter because white matter is more resistant to cerebral ischemia (;; ) possibly due to the difference in constituent cell population and NMDA receptor dexpression‥ Lacunar infarction is caused by occlusion of perforating artery, which is end-artery without collateral circulation; and its occlusion is thought not to result in a penumbral zone. Because of the small volume of lacunar infarcts, the finding of a perfusion-diffusion mismatch in lacunar stroke is affected by MRI technical issue.

Studies using a 1.5-T scanner (; ), or CT perfusion imaging and CT angiography , found no PWI abnormality in patients with a final diagnosis of lacunar infarct. In a most recent study of lacunar infarcts using a 3-T scanner that provide a higher spatial resolution, only 68.2% patients was found having abnormal PWI at the site of the diffusion-weighted imaging lesion.

The fate of penumbra: role of energy stateWhile cerebral blood flow determines both the metabolic process (; ) and the fate of ischemic tissue (;; ), energy state of an ischemic cell determines the pathway (;; ) (; ) and the destination of a cell to die or to survive. For detailed discussion please refer to our previous publication. Cerebral ischemia causes a disturbance of energy metabolism. In global ischemia, brain ATP levels decrease to approximately 60% of baseline in one minute. In focal cerebral ischemia, the ischemic core is depleted with ATP whilst the penumbra has decreased ATP level, see. Theoretically, intervention that maintains cell energy state may provide robust neuroprotection. Such examples can be found in some classic neuroprotectants.

Bioenergetic intervention could be equally important and effective as recanalizational intervention for acute stroke treatment. From pathophysiology to therapeutic strategy. Salvaging penumbra is the goal for acute stroke treatment. Neuroprotection for acute ischemic stroke should target the upper stream event that determines the fate of ischemic penumbra. Bioenergetic intervention could be the therapeutic modality equivalent to recanalizational therapies at metabolic levels because the disturbance of energy metabolism after acute brain ischemia differentiates the ischemic cascades. C1-C9: pathological cycles between major events that are supported by literature; Q1-Q3: suspected pathological cycles between major events that need more literature support. Potential of neuroprotection: view from metabolic suppressionNeuroprotection can be achieved through metabolic suppression that decreases energy demand, therefore, maintains energy state.

The human brain is metabolically highly active, and the majority of its metabolism is for functional purposes and can be suppressed. The human brain constitutes only about 2% of the body weight, yet the energy-consuming processes that ensure proper brain function account for approximately 25% of total body glucose utilization. The average ATP concentration of normal rat brain tissue is between 2.38 to 2.75 nmole/mg wet weight (;; ). The main energy-consuming process of the brain is the maintenance of ionic gradients across the plasma membrane and function-related activities. About 87% of total energy consumed reflects function-related activities , which could be suppressed to decrease energy consumption. Metabolic suppression happens naturally in hibernating animals without causing tissue injury.

Hibernation and torpid state can reduce basal metabolic rate to 1-5% of resting normothermic metabolic rate below ischemic threshold for causing irreversible injury. Decreasing energy demand by metabolic suppression is the classic method for achieving neuroprotection.

Metabolic rate could be drastically reduced by hypothermia (;; ), anesthetics and sedatives (; ); but hypothermia-related (; ) and drug-related systemic complications have limited their use in acute strokes. Recent advances in CNS drug delivery system may provide a solution for these problems. Direct energy deliveryATP molecules are negatively charged and cannot freely pass membrane barriers entering intracellular space. Because extracellular ATP are rapidly degraded by ectonucleotidases , investigators have tried using nanoliposome-entrapped ATP to deliver energy to ischemic tissue. Nanoliposome-encapsulated ATP has shown protective effects in intestinal injury from hemorrhagic shock , forebrain ischemia (; ), myocardial ischemia.(;; ), and skin wound healing. ATP blood levels can be increased drastically after the administration of ATP-loaded nanoliposomes; a similar administration of carboxyfluorescein-loaded nanoliposomes showed that nanoliposomes can reach the ischemic cerebral parenchyma in rats.

Direct energy delivery for brain ischemiaATP molecules are highly recycled in living cells. It is not practical and neither necessary to provide the total consumption amount of exogenous ATP because injured cells still have, although limited, ability to regenerate ATP. Because ATP is released into, and degraded in, extracellular space, theoretically, it could also be beneficial for ischemic cells if such loss of intracellular ATP can be replenished through exogenous resources by targeted intracellular ATP delivery. Administration of liposomal ATP has been shown to be promising in a forebrain ischemia model.The liposomal ATP solution for in vivo experiments could reach a high concentration about 12 mg/ml (21.8 μmole/ml).

With a bolus injection of serum stable pH-sensitive liposomes, 50%, 24%, and 15% of injected dose could remain in the blood at 1-h, 10-h, and 24-h post-injection, respectively. Considering the regional cerebral blood flow (rCBF) in the inner penumbra being approximately 15 ml/100g/min (0.00015 ml/mg/min), (; ) therefore, an injection of 1 ml such ATP-loaded liposomes (12 mg/ml) into a 300g rat could deliver ATP to the inner boundary of penumbra with a speed of 0.079 nmole/mg/min (21.8.0.5/21.0.) at 1-h post-injection, assuming the total blood volume being 21 ml. At this delivery speed, it will only need about 30-min (2.38/0.079) to replenish the total ATP base pool (2.38 nmole/mg wet weight) in the inner penumbra through the residue blood flow.In a forebrain ischemia model, it has been observed that when being entrapped into nanoliposomes and administered intracarotidally, ATP greatly increased the number of ischemic episodes that can be tolerated before brain electrical silence and death appeared (; ) because of improvement in energy metabolism.

Direct energy delivery remains an attractive treatment for ischemic stroke, yet it still needs extensive research before its successful translation to clinic settings. Efforts need to be put on aspects such as giving synergistic adjunctive treatments, improving the bioavailability of ATP-loaded nanoliposomes, and minimizing the interaction of exogenous ATP purinergic receptors (;; ). A non-selective P2 receptor antagonist, such as suramin (; ), can be used for minimizing these compounding effects. Suramin can be encapsulated into liposomes (; ). Delivery of a metabolic suppressorNanoliposomes have been used as a carrier for CNS drug delivery and can be tissue selective. Selective delivery of a metabolic suppressor to a specific brain region makes it possible to reach a desired regional drug concentration with minimized drug-related systemic adverse effects (CNS depression, hypotension, etc.), therefore, having its application in acute stroke treatments.

Some local anesthetics and sedatives have been reported of their liposomal formulation for topical application and controlled release, such as lidocaine , benzocaine , diazepam (; ). Because the amphiphilic drug diazepam, which binds to the same GABA A receptor as pentobarbital does, can be used in liposomal formulation, the more water-soluble pentobarbital will theoretically be better encapsulated in nanoliposomes and be bioactive. Penumbral drug delivery strategyConventional drug delivery methods cause unwanted drug exposure to other tissue or brain regions, leading to severe side effects and toxicity, especially when high dose is being used for reaching therapeutic drug levels in ischemic tissue. For examples, the classic metabolic suppressor pentobarbital could reduce metabolic rate by 56%having a proven neuroprotective effect; but it cannot be used with a sufficient dose to achieve the desired maximal metabolic suppression because of its drug-related respiratory suppression.

Neuroprotection by providing exogenous energy has also been facing problems of adverse effects and low bioavailability. With the advancement of CNS drug delivery, those problems can be tackled through innovative approaches (see following paragraph).Brain ischemia causes a serial of pathological changes that affect drug delivery. In the ischemic local region there is limited blood supply while the blood-brain barrier and the shrunk extracellular space further limit drug access to ischemic brain tissue. However, there are also some pathological changes that may be utilized for facilitating drug delivery to local ischemic tissue. For example, brain ischemia causes a metabolic shift towards anaerobic glycolysis, resulting in a lower intracellular pH value in the ischemic brain tissue. Targeting at this property of ischemic brain tissue, liposomal nanocarrier may be optimized to release their cargos under acidic condition similar to the intracellular environment of ischemic brain tissue(pH.

SummaryIt is of great clinical significance to develop a neuroprotective treatment that can be made available to most acute stroke patients. Bioenergetic intervention by massive metabolic suppression and direct energy delivery would be a promising future direction. An effective drug delivery system for this purpose should be able to penetrate BBB and achieve high local tissue drug levels while non-ischemic region being largely unaffected. Selective drug delivery to ischemic stroke penumbra is feasible and deserves intensive research. Adams HP, Jr, Bendixen BH, Kappelle LJ, Biller J, Love BB, Gordon DL, Marsh EE., 3rd Classification of subtype of acute ischemic stroke. Definitions for use in a multicenter clinical trial. Trial of Org 10172 in Acute Stroke Treatment.

1993; 24:35–41. Ames A., 3rd CNS energy metabolism as related to function. Brain Res Brain Res Rev.

2000; 34:42–68. Anderson RE, Tan WK, Meyer FB. Brain acidosis, cerebral blood flow, capillary bed density, and mitochondrial function in the ischemic penumbra.

J Stroke Cerebrovasc Dis. 1999; 8:368–379. Arakawa A, Ishiguro S, Ohki K, Tamai M.

Preparation of liposome-encapsulating adenosine triphosphate. Tohoku J Exp Med.

1998; 184:39–47. Arakawa S, Wright PM, Koga M, Phan TG, Reutens DC, Lim I, Gunawan MR, Ma H, Perera N, Ly J, Zavala J, Fitt G, Donnan GA. Ischemic thresholds for gray and white matter: a diffusion and perfusion magnetic resonance study. 2006; 37:1211–1216. Astrup J, Siesjo BK, Symon L. Thresholds in cerebral ischemia - the ischemic penumbra. 1981a; 12:723–725.

Astrup J, Sorensen PM, Sorensen HR. Inhibition of cerebral oxygen and glucose consumption in the dog by hypothermia, pentobarbital, and lidocaine. 1981b; 55:263–268. Avila CM, Martinez F.

Thermodynamics of partitioning of benzocaine in some organic solvent/buffer and liposome systems. Chem Pharm Bull (Tokyo) 2003; 51:237–240. Bardutzky J, Shen Q, Henninger N, Schwab S, Duong TQ, Fisher M. Characterizing tissue fate after transient cerebral ischemia of varying duration using quantitative diffusion and perfusion imaging. 2007; 38:1336–1344. Berger R, Jensen A, Hossmann KA, Paschen W. Effect of mild hypothermia during and after transient in vitro ischemia on metabolic disturbances in hippocampal slices at different stages of development.

Brain Res Dev Brain Res. 1998; 105:67–77. Boomer JA, Qualls MM, Inerowicz HD, Haynes RH, Patri VS, Kim JM, Thompson DH. Cytoplasmic delivery of liposomal contents mediated by an acid-labile cholesterol-vinyl ether-PEG conjugate.

Bioconjug Chem. 2009; 20:47–59. Boucsein C, Zacharias R, Farber K, Pavlovic S, Hanisch UK, Kettenmann H. Purinergic receptors on microglial cells: functional expression in acute brain slices and modulation of microglial activation in vitro. Eur J Neurosci.

2003; 17:2267–2276. Bristow MS, Simon JE, Brown RA, Eliasziw M, Hill MD, Coutts SB, Frayne R, Demchuk AM, Mitchell JR.

MR perfusion and diffusion in acute ischemic stroke: human gray and white matter have different thresholds for infarction. J Cereb Blood Flow Metab. 2005; 25:1280–1287.

Chang HC, Flanagan DR. Liposomal entrapment of suramin. 1994; 83:1043–1046. Chang HC, Flanagan DR. Liposomal entrapment of suramin(II): interaction of suramin with phospholipids of various chain lengths. 1995; 84:1078–1082. Chapat S, Frey V, Claperon N, Bouchaud C, Puisieux F, Couvreur P, Rossignol P, Delattre J.

Efficiency of liposomal ATP in cerebral ischemia: bioavailability features. Brain Res Bull. 1991; 26:339–342. Chen HH, Schock SC, Xu J, Safarpour F, Thompson CS, Stewart AF.

Extracellular ATP-dependent upregulation of the transcription cofactor LMO4 promotes neuron survival from hypoxia. Exp Cell Res. 2007; 313:3106–3116. Chiang B, Essick E, Ehringer W, Murphree S, Hauck MA, Li M, Chien S. Enhancing skin wound healing by direct delivery of intracellular adenosine triphosphate. 2007; 193:213–218.

Collins D, Maxfield F, Huang L. Immunoliposomes with different acid sensitivities as probes for the cellular endocytic pathway. Biochim Biophys Acta. 1989; 987:47–55. Coupey SM.

1997; 18:260–264. Ebinger M, De Silva DA, Christensen S, Parsons MW, Markus R, Donnan GA, Davis SM. Imaging the penumbra - strategies to detect tissue at risk after ischemic stroke. J Clin Neurosci. 2009; 16:178–187. Eguchi Y, Shimizu S, Tsujimoto Y. Intracellular ATP levels determine cell death fate by apoptosis or necrosis.

1997; 57:1835–1840. Eschenfelder CC, Krug R, Yusofi AF, Meyne JK, Herdegen T, Koch A, Zhao Y, Carl UM, Deuschl G. Neuroprotection by oxygen in acute transient focal cerebral ischemia is dose dependent and shows superiority of hyperbaric oxygenation. Cerebrovasc Dis. 2008; 25:193–201. Fatouros DG, Antimisiaris SG. Effect of amphiphilic drugs on the stability and zeta-potential of their liposome formulations: a study with prednisolone, diazepam, and griseofulvin.

J Colloid Interface Sci. 2002; 251:271–277.

Fransson BA, Peck KE, Smith JK, Anthony JA, Mealey KL. Transdermal absorption of a liposome-encapsulated formulation of lidocaine following topical administration in cats. Am J Vet Res. 2002; 63:1309–1312.

Galeffi F, Sinnar S, Schwartz-Bloom RD. Diazepam promotes ATP recovery and prevents cytochrome c release in hippocampal slices after in vitro ischemia.

2000; 75:1242–1249. Geiser F. Metabolic rate and body temperature reduction during hibernation and daily torpor. Annu Rev Physiol. 2004; 66:239–274. Gerraty RP, Parsons MW, Barber PA, Darby DG, Desmond PM, Tress BM, Davis SM.

Examining the lacunar hypothesis with diffusion and perfusion magnetic resonance imaging. 2002; 33:2019–2024.

Gordon JL. Extracellular ATP: effects, sources and fate. 1986; 233:309–319. Greco R, Amantea D, Blandini F, Nappi G, Bagetta G, Corasaniti MT, Tassorelli C. Neuroprotective effect of nitroglycerin in a rodent model of ischemic stroke: evaluation of Bcl-2 expression. Int Rev Neurobiol. 2007; 82:423–435.

Han JL, Kollmar R, Tobyas B, Schwab S. Inhibited glutamate release by granulocyte-colony stimulating factor after experimental stroke. Neurosci Lett. 2008; 432:167–169. Hata R, Maeda K, Hermann D, Mies G, Hossmann KA. Evolution of brain infarction after transient focal cerebral ischemia in mice. J Cereb Blood Flow Metab.

2000; 20:937–946. Hong HY, Choi JS, Kim YJ, Lee HY, Kwak W, Yoo J, Lee JT, Kwon TH, Kim IS, Han HS, Lee BH. Detection of apoptosis in a rat model of focal cerebral ischemia using a homing peptide selected from in vivo phage display. J Control Release. 2008; 131:167–172.

Hossmann KA. Viability thresholds and the penumbra of focal ischemia. 1994; 36:557–565. Hsu SS, Meno JR, Zhou JG, Gordon EL, Winn HR.

Influence of hyperglycemia on cerebral adenosine production during ischemia and reperfusion. Am J Physiol. 1991; 261:H398–403. Jahan R, Vinuela F.

Treatment of acute ischemic stroke: intravenous and endovascular therapies. Expert Rev Cardiovasc Ther. 2009; 7:375–387.

Jian S, Yongming Q, Zhihua C, Yan C. Feasibility and safety of moderate hypothermia after acute ischemic stroke. Int J Dev Neurosci.

2003; 21:353–356. Kharlamov A, Jones SC, Kim DK.

Suramin reduces infarct volume in a model of focal brain ischemia in rats. Exp Brain Res.

2002; 147:353–359. Kleindorfer D, Kissela B, Schneider A, Woo D, Khoury J, Miller R, Alwell K, Gebel J, Szaflarski J, Pancioli A, Jauch E, Moomaw C, Shukla R, Broderick JP. Eligibility for recombinant tissue plasminogen activator in acute ischemic stroke: a population-based study. 2004; 35:e27–29. Koga M, Reutens DC, Wright P, Phan T, Markus R, Pedreira B, Fitt G, Lim I, Donnan GA. The existence and evolution of diffusion-perfusion mismatched tissue in white and gray matter after acute stroke. 2005; 36:2132–2137.

Kuge Y, Yokota C, Tagaya M, Hasegawa Y, Nishimura A, Kito G, Tamaki N, Hashimoto N, Yamaguchi T, Minematsu K. Serial changes in cerebral blood flow and flow-metabolism uncoupling in primates with acute thromboembolic stroke. J Cereb Blood Flow Metab. 2001; 21:202–210. Kumar G, Goyal MK, Sahota PK, Jain R.

Penumbra, the basis of neuroimaging in acute stroke treatment: current evidence. J Neurol Sci. Laham A, Claperon N, Durussel JJ, Fattal E, Delattre J, Puisieux F, Couvreur P, Rossignol P. Intracarotidal administration of liposomally-entrapped ATP: improved efficiency against experimental brain ischemia.

Pharmacol Res Commun. 1988; 20:699–705. Leist M, Single B, Castoldi AF, Kuhnle S, Nicotera P. Intracellular adenosine triphosphate (ATP) concentration: a switch in the decision between apoptosis and necrosis. 1997; 185:1481–1486.

Dream chronicles. Dream Chronicles is the first of a three part well-acclaimed series.You wend your way through stunning environments, removing the obstacles that the wicked fairy Lilith has put in your path. You are trying to rescue your husband from the clutches of Lilith who has kidnapped him and put a sleeping spell on your little daughter.

Lieberthal W, Menza SA, Levine JS. Graded ATP depletion can cause necrosis or apoptosis of cultured mouse proximal tubular cells. Am J Physiol.

1998; 274:F315–327. Liu S, Levine SR. The continued promise of neuroprotection for acute stroke treatment. Journal of Experimental Stroke & Translational Medicine. Liu S, Liu W, Ding W, Miyake M, Rosenberg GA, Liu KJ. Electron paramagnetic resonance-guided normobaric hyperoxia treatment protects the brain by maintaining penumbral oxygenation in a rat model of transient focal cerebral ischemia. J Cereb Blood Flow Metab.

2006; 26:1274–1284. Lloyd-Jones D, Adams RJ, Brown TM, Carnethon M, Dai S, De Simone G, Ferguson TB, Ford E, Furie K, Gillespie C, Go A, Greenlund K, Haase N, Hailpern S, Ho PM, Howard V, Kissela B, Kittner S, Lackland D, Lisabeth L, Marelli A, McDermott MM, Meigs J, Mozaffarian D, Mussolino M, Nichol G, Roger VL, Rosamond W, Sacco R, Sorlie P, Stafford R, Thom T, Wasserthiel-Smoller S, Wong ND, Wylie-Rosett J. Heart disease and stroke statistics-2010 update: a report from the american heart association; pp. Magistretti P. Brain Energy Metabolism. In: Squire L, Roberts J, Spitzer N, et al., editors.

Fundamental Neuroscience. Elsevier Science & Technology Books; 2002. Masada T, Hua Y, Xi G, Ennis SR, Keep RF.

Attenuation of ischemic brain edema and cerebrovascular injury after ischemic preconditioning in the rat. J Cereb Blood Flow Metab. 2001; 21:22–33. Meerwaldt R, Slart RH, van Dam GM, Luijckx GJ, Tio RA, Zeebregts CJ. PET/SPECT imaging: From carotid vulnerability to brain viability.

Eur J Radiol 2009. Millart H, Alouane L, Oszust F, Chevallier S, Robinet A. Involvement of P2Y receptors in pyridoxal-5′-phosphate-induced cardiac preconditioning. Fundam Clin Pharmacol. 2009; 23:279–292. Mori K, Maeda M, Miyazaki M, Iwase H. Effects of mild (33 degrees C) and moderate (29 degrees C) hypothermia on cerebral blood flow and metabolism, lactate, and extracellular glutamate in experimental head injury.

1998; 20:719–726. Muller TB, Haraldseth O, Jones RA, Sebastiani G, Godtliebsen F, Lindboe CF, Unsgard G. Combined perfusion and diffusion-weighted magnetic resonance imaging in a rat model of reversible middle cerebral artery occlusion.

1995; 26:451–457. Discussion 457-458. Murphy BD, Fox AJ, Lee DH, Sahlas DJ, Black SE, Hogan MJ, Coutts SB, Demchuk AM, Goyal M, Aviv RI, Symons S, Gulka IB, Beletsky V, Pelz D, Hachinski V, Chan R, Lee TY. Identification of penumbra and infarct in acute ischemic stroke using computed tomography perfusion-derived blood flow and blood volume measurements. 2006; 37:1771–1777. Nicotera P, Leist M.

As a Druid, you can harness the power of the Deck of Nature to weave your spells. Avalon legends solitaire full free download. Description:The magical realm of Avalon needs your help!

Energy supply and the shape of death in neurons and lymphoid cells. Cell Death Differ. 1997; 4:435–442. Nicotera P, Leist M, Ferrando-May E. Intracellular ATP, a switch in the decision between apoptosis and necrosis. Toxicol Lett. 1998; 102-103:139–142.

Ohashi M, Tsuji A, Kaneko M, Matsuda M. Threshold of regional cerebral blood flow for infarction in patients with acute cerebral ischemia. J Neuroradiol. 2005; 32:337–341. Olivot JM, Mlynash M, Thijs VN, Kemp S, Lansberg MG, Wechsler L, Schlaug G, Bammer R, Marks MP, Albers GW.

Relationships between infarct growth, clinical outcome, and early recanalization in diffusion and perfusion imaging for understanding stroke evolution (DEFUSE) Stroke. 2008; 39:2257–2263. Plaschke K, Bardenheuer HJ, Weigand MA, Martin E, Hoyer S. Increased ATP production during long-term brain ischemia in rats in the presence of propentofylline. Eur J Pharmacol. 1998; 349:33–40. Poppe AY, Coutts SB, Kosior J, Hill MD, O'Reilly CM, Demchuk AM.

Normal Magnetic Resonance Perfusion-Weighted Imaging in Lacunar Infarcts Predicts a Low Risk of Early Deterioration. Cerebrovasc Dis. 2009; 28:151–156. Puisieux F, Fattal E, Lahiani M, Auger J, Jouannet P, Couvreur P, Delattre J.

Liposomes, an interesting tool to deliver a bioenergetic substrate (ATP). In vitro and in vivo studies. J Drug Target. 1994; 2:443–448.

Rivers CS, Wardlaw JM, Armitage PA, Bastin ME, Carpenter TK, Cvoro V, Hand PJ, Dennis MS. Do acute diffusion- and perfusion-weighted MRI lesions identify final infarct volume in ischemic stroke? 2006; 37:98–104.

Sakoh M, Ostergaard L, Gjedde A, Rohl L, Vestergaard-Poulsen P, Smith DF, Le Bihan D, Sakaki S, Gyldensted C. Prediction of tissue survival after middle cerebral artery occlusion based on changes in the apparent diffusion of water. 2001; 95:450–458. Saver JL. Time is brain-quantified.

2006; 37:263–266. Schwab S, Georgiadis D, Berrouschot J, Schellinger PD, Graffagnino C, Mayer SA. Feasibility and safety of moderate hypothermia after massive hemispheric infarction.

2001; 32:2033–2035. Shimosegawa E, Hatazawa J, Ibaraki M, Toyoshima H, Suzuki A. Metabolic penumbra of acute brain infarction: a correlation with infarct growth. 2005; 57:495–504. Siow NL, Xie HQ, Choi RC, Tsim KW.

ATP induces the post-synaptic gene expression in neuron-neuron synapses: Transcriptional regulation of AChE catalytic subunit. Chem Biol Interact. 2005; 157-158:423–426. Slepushkin VA, Simoes S, Dazin P, Newman MS, Guo LS, Pedroso de Lima MC, Duzgunes N. Sterically stabilized pH-sensitive liposomes. Intracellular delivery of aqueous contents and prolonged circulation in vivo. 1997; 272:2382–2388.

Sobesky J, Zaro Weber O, Lehnhardt FG, Hesselmann V, Neveling M, Jacobs A, Heiss WD. Does the mismatch match the penumbra? Magnetic resonance imaging and positron emission tomography in early ischemic stroke. 2005; 36:980–985. Sznitowska M, Janicki S, Gajewska M, Kulik M.

Investigation of diazepam lipospheres based on Witepsol and lecithin intended for oral or rectal delivery. Acta Pol Pharm. 2000; 57:61–64.

Vergoni AV, Ottani A, Botticelli AR, Zaffe D, Guano L, Loche A, Genedani S, Gessa GL, Bertolini A. Neuroprotective effect of gamma-hydroxybutyrate in transient global cerebral ischemia in the rat. Eur J Pharmacol.

2000; 397:75–84. Verma DD, Hartner WC, Levchenko TS, Bernstein EA, Torchilin VP. ATP-loaded liposomes effectively protect the myocardium in rabbits with an acute experimental myocardial infarction. 2005a; 22:2115–2120.

Verma DD, Levchenko TS, Bernstein EA, Mongayt D, Torchilin VP. ATP-loaded immunoliposomes specific for cardiac myosin provide improved protection of the mechanical functions of myocardium from global ischemia in an isolated rat heart model. J Drug Target. 2006; 14:273–280.

Verma DD, Levchenko TS, Bernstein EA, Torchilin VP. ATP-loaded liposomes effectively protect mechanical functions of the myocardium from global ischemia in an isolated rat heart model. J Control Release. 2005b; 108:460–471. Wang J, Chambers G, Cottrell JE, Kass IS.

Differential fall in ATP accounts for effects of temperature on hypoxic damage in rat hippocampal slices. J Neurophysiol. 2000; 83:3462–3472. Warner DS, Takaoka S, Wu B, Ludwig PS, Pearlstein RD, Brinkhous AD, Dexter F. Electroencephalographic burst suppression is not required to elicit maximal neuroprotection from pentobarbital in a rat model of focal cerebral ischemia.

1996; 84:1475–1484. Winn HR, Rubio R, Berne RM.

Brain adenosine production in the rat during 60 seconds of ischemia. 1979; 45:486–492. Zakaria el R, Ehringer WD, Tsakadze N, Li N, Garrison RN. Direct energy delivery improves tissue perfusion after resuscitated shock. 2005; 138:195–203.