Effects of preischemic hyperglycemia on brain damage incurred by rats subjected to 2.5 or 5 minutes of forebrain ischemia

Neuroprotective effects of lactate and ketone bodies in acute brain injury

The goal of neurocritical care is to prevent and reverse the pathologic cascades of secondary brain injury by optimizing cerebral blood flow, oxygen supply and substrate delivery. While glucose is an essential energetic substrate for the brain, we frequently observe a strong decrease in glucose delivery and/or a glucose metabolic dysregulation following acute brain injury. In parallel, during the last decades, lactate and ketone bodies have been identified as potential alternative fuels to provide energy to the brain, both under physiological conditions and in case of glucose shortage. They are now viewed as integral parts of brain metabolism. In addition to their energetic role, experimental evidence also supports their neuroprotective properties after acute brain injury, regulating in particular intracranial pressure control, decreasing ischemic volume, and leading to an improvement in cognitive functions as well as survival. In this review, we present preclinical and clinical evidence exploring the mechanisms underlying their neuroprotective effects and identify research priorities for promoting lactate and ketone bodies use in brain injury.

Long-Term Neurobehavioral and Quality of Life Outcomes of Critically Ill Children after Glycemic Control

OBJECTIVES

To investigate adaptive skills, behavior, and quality health-related quality of life in children from 32 centers enrolling in the Heart And Lung Failure-Pediatric INsulin Titration randomized controlled trial.

STUDY DESIGN

This prospective longitudinal cohort study compared the effect of 2 tight glycemic control ranges (lower target, 80-100 mg/dL vs higher target, 150-180 mg/dL) 1-year neurobehavioral and health-related quality of life outcomes. Subjects had confirmed hyperglycemia and cardiac and/or respiratory failure. Patients aged 2-16 years old enrolled between April 2012 and September 2016 were studied at 1 year after intensive care discharge. The primary outcome, adaptive skills, was assessed using the Vineland Adaptive Behavior Scale. Behavior and health-related quality of life outcomes were assessed as secondary outcomes using the Pediatric Quality of Life and Child Behavior Checklist at baseline and 1-year follow-up. Group differences were evaluated using regression models adjusting for age category, baseline overall performance, and risk of mortality.

RESULTS

Of 369 eligible children, 358 survived after hospital discharge and 214 (60%) completed follow-up. One-year Vineland Adaptive Behavior Scale-II composite scores were not different (mean ± SD, 79.9 ± 25.5 vs 79.4 ± 26.9, lower vs higher target; P = .20). Improvement in Pediatric Quality of Life total health from baseline was greater in the higher target group (adjusted mean difference, 8.2; 95% CI, 1.1-15.3; P = .02).

CONCLUSIONS

One-year adaptive behavior in critically ill children with lower vs higher target glycemic control did not differ. The higher target group demonstrated improvement from baseline in overall health. This study affirms the lack of benefit of lower glucose targeting.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01565941.

Cerebrovascular Reactivity during Prolonged Breath-Hold in Experienced Freedivers

BACKGROUND AND PURPOSE

Experienced freedivers can endure prolonged breath-holds despite severe hypoxemia and are therefore ideal subjects to study apnea-induced cerebrovascular reactivity. This multiparametric study investigated CBF, the spatial coefficient of variation as a correlate of arterial transit time and brain metabolism, dynamics during prolonged apnea.

MATERIALS AND METHODS

Fifteen male freedivers (age range, 20-64 years; cumulative previous prolonged breath-holds >2 minutes and 30 seconds: 4-79,200) underwent repetitive 3T pseudocontinuous arterial spin-labeling and ³¹P-/¹H-MR spectroscopy before, during, and after a 5-minute breath-hold (split into early and late phases) and gave temporally matching venous blood gas samples. Correlation of temporal and regional cerebrovascular reactivity to blood gases and cumulative previous breath-holds of >2 minutes and 30 seconds in a lifetime was assessed.

RESULTS

The spatial coefficient of variation of CBF (by arterial spin-labeling) decreased during the early breath-hold phase (-30.0%, P = .002), whereas CBF remained almost stable during this phase and increased in the late phase (+51.8%, P = .001). CBF differed between the anterior and the posterior circulation during all phases (eg, during late breath-hold: MCA, 57.3 ± 14.2 versus posterior cerebral artery, 42.7 ± 10.8 mL/100 g/min; P = .001). There was an association between breath-hold experience and lower CBF (1000 previous breath-holds reduced WM CBF by 0.6 mL/100 g/min; 95% CI, 0.15-1.1 mL/100 g/min; P = .01). While breath-hold caused peripheral lactate rise (+18.5%) and hypoxemia (oxygen saturation, -24.0%), cerebral lactate and adenosine diphosphate remained within physiologic ranges despite early signs of oxidative stress [-6.4% phosphocreatine / (adenosine triphosphate + adenosine diphosphate); P = .02].

CONCLUSIONS

This study revealed that the cerebral energy metabolism of trained freedivers withstands severe hypoxic hypercarbia in prolonged breath-hold due to a complex cerebrovascular hemodynamic response.

Cerebrovascular Safety of Sulfonylureas: The Role of KATP Channels in Neuroprotection and the Risk of Stroke in Patients With Type 2 Diabetes

Sulfonylureas are ATP-sensitive potassium (KATP) channel blockers commonly used in the treatment of type 2 diabetes mellitus (T2DM). Activation of KATP channels plays a neuroprotective role in ischemia; thus, whether sulfonylureas affect the outcomes of stroke in patients with T2DM needs to be further studied. In our study, streptozotocin (STZ)-induced diabetic mice subjected to transient middle cerebral artery occlusion (MCAO) showed larger areas of brain damage and poorer behavioral outcomes. Blocking the KATP channel by tolbutamide increased neuronal injury induced by oxygen-glucose deprivation (OGD) in vitro and permanent MCAO (pMCAO) in vivo. Activating the KATP channel by diazoxide reduced the effects of both the OGD and pMCAO. Western blot analysis in STZ mouse brains indicated an early increase in protein levels of N-methyl-d-aspartate receptor 2B and postsynaptic density protein-95, followed by a decrease in phosphorylation of glycogen synthase kinase 3β. Our systematic meta-analysis indicated that patients with T2DM treated with sulfonylureas had a higher odds ratio for stroke morbidity than those who received comparator drugs. Taken together, these results suggest that sulfonylurea treatment in patients with T2DM may inhibit the neuroprotective effects of KATP channels and increase the risk of stroke.

Anti-inflammatory properties of lipoxin A4 protect against diabetes mellitus complicated by focal cerebral ischemia/reperfusion injury

Lipoxin A4 can alleviate cerebral ischemia/reperfusion injury by reducing the inflammatory reaction, but it is currently unclear whether it has a protective effect on diabetes mellitus complicated by focal cerebral ischemia/reperfusion injury. In this study, we established rat models of diabetes mellitus using an intraperitoneal injection of streptozotocin. We then induced focal cerebral ischemia/reperfusion injury by occlusion of the middle cerebral artery for 2 hours and reperfusion for 24 hours. After administration of lipoxin A4 via the lateral ventricle, infarction volume was reduced, the expression levels of pro-inflammatory factors tumor necrosis factor alpha and nuclear factor-kappa B in the cerebral cortex were decreased, and neurological functioning was improved. These findings suggest that lipoxin A4 has strong neuroprotective effects in diabetes mellitus complicated by focal cerebral ischemia/reperfusion injury and that the underlying mechanism is related to the anti-inflammatory action of lipoxin A4.

Protocol for the induction of subarachnoid hemorrhage in mice by perforation of the Circle of Willis with an endovascular filament

Genetically engineered mice are a valuable tool to investigate the molecular and cellular mechanisms leading to brain damage following subarachnoid hemorrhage (SAH). Therefore, several murine SAH models were developed during the last 15 years. Among those models, the perforation of the Circle of Willis by an endovascular filament or “filament model” turned out to become the most popular one, since it is believed to reproduce some of the most prominent pathophysiological features observed after human SAH. Despite the importance of the endovascular filament model for SAH research, relatively few studies were published using this technique during the past years and a number of laboratories reported problems establishing the technique. This triggered discussions about the standardization, reproducibility, and the reliability of the model. In order to improve this situation, the current paper aims to provide a comprehensive hands-on protocol of the murine endovascular filament model. The protocol proved to result in induction of SAH in mice with high intrapersonal and interpersonal reproducibility and is based on our experience with this technique for more than 10 years. By sharing our experience with this valuable model, we aim to initiate a constantly ongoing discussion process on the improvement of standards and techniques in the field of experimental SAH research.

Intraoperative maintenance of normoglycemia with insulin and glucose preserves verbal learning after cardiac surgery

Objective

The hyperglycemic response to surgery may be a risk factor for cognitive dysfunction. We hypothesize that strict maintenance of normoglycemia during cardiac surgery preserves postoperative cognitive function.

Methods

As part of a larger randomized, single-blind, interventional efficacy study on the effects of hyperinsulinemic glucose control in cardiac surgery (NCT00524472), consenting patients were randomly assigned to receive combined administration of insulin and glucose, titrated to preserve normoglycemia (3.5–6.1 mmol L⁻¹; experimental group), or standard metabolic care (blood glucose 3.5–10 mmol L⁻¹; control group), during open heart surgery. The patients’ cognitive function was assessed during three home visits, approximately two weeks before the operation, and two months and seven months after surgery. The following tests were performed: Rey Auditory Verbal Learning Task (RAVLT for verbal learning and memory), Digit Span Task (working memory), Trail Making A & B (visuomotor tracking and attention), and the Word Pair Task (implicit memory). Questionnaires measuring specific traits known to affect cognitive performance, such as self-esteem, depression, chronic stress and social support, were also administered. The primary outcome was to assess the effect of hyperinsulinemic-normoglycemic clamp therapy versus standard therapy on specific cognitive parameters in patients receiving normoglycemic clamp, or standard metabolic care.

Results

Twenty-six patients completed the study with 14 patients in the normoglycemia and 12 patients in the control group. Multiple analysis of covariance (MANCOVA) for the RAVLT showed a significant effect for the interaction of group by visit (F = 4.07, p = 0.035), and group by visit by recall (F = 2.21, p = 0.04). The differences occurred at the second and third visit. MANCOVA for the digit span task, trail making and word pair association test showed no significant effect.

Conclusions

Preserving intraoperative normoglycemia by intravenous insulin and glucose may prevent the impairment of memory function, both short and long-term, after cardiac surgery.

Hyperglycaemia increases S100β after short experimental cardiac arrest

BACKGROUND

Hyperglycaemia is associated with aggravated ischaemic brain injury. The main objective of this study was to investigate the effects on cerebral perfusion of 5 min of cardiac arrest during hyperglycaemia and normoglycaemia.

METHODS

Twenty triple-breed pigs (weight: 22-29 kg) were randomised and clamped at blood glucose levels of 8.5-10 mM [high (H)] or 4-5.5 mM [normal (N)] and thereafter subjected to alternating current-induced 5 min-cardiac arrest followed by 8 min of cardiopulmonary resuscitation and direct current shock to restore spontaneous circulation.

RESULTS

Haemodynamics, laser Doppler measurements and regional venous oxygen saturation (HbO2) were monitored, and biochemical markers in blood [S100β, interleukin (IL)-6 and tumour necrosis factor (TNF)] quantified throughout an observation period of 3 h. The haemodynamics and physiological measurements were similar in the two groups. S100β increased over the experiment in the H compared with the N group (P < 0.05). IL-6 and TNF levels increased across the experiment, but no differences were seen between the groups.

CONCLUSIONS

The enhanced S100β response is compatible with increased cerebral injury by hyperglycaemic compared with normoglycaemic 5 min of cardiac arrest and resuscitation. The inflammatory cytokines were similar between groups.

Structural and ultrastructural analysis of cerebral cortex, cerebellum, and hypothalamus from diabetic rats

Autonomic and peripheral neuropathies are well-described complications in diabetes. Diabetes mellitus is also associated to central nervous system damage. This little-known complication is characterized by impairment of brain functions and electrophysiological changes associated with neurochemical and structural abnormalities. The purpose of this study was to investigate brain structural and ultrastructural changes in rats with streptozotocin-induced diabetes. Cerebral cortex, hypothalamus, and cerebellum were obtained from controls and 8 weeks diabetic rats. Light and electron microscope studies showed degenerative changes of neurons and glia, perivascular and mitochondrial swelling, disarrangement of myelin sheath, increased area of myelinated axons, presynaptic vesicle dispersion in swollen axonal boutoms, fragmentation of neurofilaments, and oligodendrocyte abnormalities. In addition, depressive mood was observed in diabetic animals. The brain morphological alterations observed in diabetic animals could be related to brain pathologic process leading to abnormal function, cellular death, and depressive behavioral.

Protein kinase C epsilon activation delays neuronal depolarization during cardiac arrest in the euthermic arctic ground squirrel

During the pre-hibernation season, arctic ground squirrels (AGS) can tolerate 8 min of asphyxial cardiac arrest (CA) without detectable brain pathology. Better understanding of the mechanisms regulating innate ischemia tolerance in AGS has the potential to facilitate the development of novel prophylactic agents to induce ischemic tolerance in patients at risk of stroke or CA. We hypothesized that neuroprotection in AGS involves robust maintenance of ion homeostasis similar to anoxia-tolerant turtles. Ion homeostasis was assessed by monitoring ischemic depolarization (ID) in cerebral cortex during CA in vivo and during oxygen glucose deprivation in vitro in acutely prepared hippocampal slices. In both models, the onset of ID was significantly delayed in AGS compared with rats. The epsilon protein kinase C (epsilonPKC) is a key mediator of neuroprotection and inhibits both Na+/K+-ATPase and voltage-gated sodium channels, primary mediators of the collapse of ion homeostasis during ischemia. The selective peptide inhibitor of epsilonPKC (epsilonV1-2) shortened the time to ID in brain slices from AGS but not in rats despite evidence that epsilonV1-2 decreased activation of epsilonPKC in brain slices from both rats and AGS. These results support the hypothesis that epsilonPKC activation delays the collapse of ion homeostasis during ischemia in AGS.

Neuroprotection during cardiac surgery

Cardiac surgery continues to be associated with significant adverse cerebral outcomes, ranging from stroke to cognitive decline. The underlying mechanism of the associated cerebral injury is incompletely understood but is believed to be primarily caused by cerebral embolism and hypoperfusion, exacerbated by ischemia/reperfusion injury. Extensive research has been undertaken in an attempt to minimize the incidence of perioperative cerebral injury, and both pharmacological and nonpharmacological strategies have been investigated. Although many agents demonstrated promise in preclinical studies, there is currently insufficient evidence from clinical trials to recommend the routine administration of any pharmacological agents for neuroprotection during cardiac surgery. The nonpharmacological strategies that can be recommended on the basis of evidence include transesophageal echocardiography and epiaortic ultrasound-guided assessment of the atheromatous ascending aorta with appropriate modification of cannulation, clamping or anastomotic technique and optimal temperature management. Large-scale randomized controlled trials are still required to address further the issues of optimal pH management, glycemic control, blood pressure management and hematocrit during cardiopulmonary bypass. Past, present and future directions in the field of neuroprotection in cardiac surgery will be discussed.

Intraoperative hyperglycemia and cognitive decline after CABG

BACKGROUND

Neurocognitive dysfunction (NCD) continues to occur in a significant number of patients after cardiac procedures. The factors influencing its incidence and severity are not completely known. We hypothesized that hyperglycemia, which is known to exacerbate other forms of cerebral injury, may exacerbate NCD after cardiac operations.

METHODS

A total of 525 patients having on-pump coronary artery bypass graft (CABG) procedures underwent cognitive testing at baseline and 6 weeks postoperatively. Multivariable linear regression was used to determine the relationship between NCD and intraoperative hyperglycemia (glucose > or = 200 mg/dL). Diabetic and nondiabetic patients were analyzed separately to eliminate a possible confounding effects between diabetes and hyperglycemia.

RESULTS

In the nondiabetic patients, even after controlling for age, years of education, and baseline cognitive function, hyperglycemia was associated with a decrease in cognitive function at 6 weeks (p = 0.0351). Hyperglycemia had no effect on cognitive function in diabetic patients, however.

CONCLUSIONS

These findings suggest that in nondiabetic patients undergoing CABG operations, intraoperative hyperglycemia is associated with an increased risk of NCD.

Neuroprotection during cardiac surgery

Cerebral injury following cardiac surgery continues to be a significant source of morbidity and mortality after cardiac surgery. A spectrum of injuries ranging from subtle neurocognitive dysfunction to fatal strokes are caused by a complex series of multifactorial mechanisms. Protecting the brain from these injuries has focused on intervening on each of the various etiologic factors. Although numerous studies have focused on a pharmacologic solution, more success has been found with nonpharmacologic strategies, including optimal temperature management and reducing emboli generation.

Streptozotocin-induced diabetes causes astrocyte death after ischemia and reperfusion injury

Diabetes exacerbates neuronal cell death induced by cerebral ischemia. One contributing factor is enhanced acidosis during ischemia. Astrocytes are vulnerable to hypoxia under acidic conditions in vitro and may be targets of ischemia under diabetic conditions. The objective of this study was to determine whether diabetes would cause damage to astrocytes after an ischemic brain injury in vivo. Diabetic and nondiabetic rats were subjected to 5 min of forebrain ischemia and followed by 30 min, 6 h, or 1 or 3 days of recovery. The results showed that ischemia caused activation of astrocytes in nondiabetic rats. In contrast, diabetes caused astrocyte activation in early stage of reperfusion and astrocyte death in late stage of reperfusion. Remarkable astrocyte death was preceded by increased DNA oxidation. Further studies revealed that increased astrocyte damage coincided with enhanced production of free radicals. These data suggest that hyperglycemic ischemia worsens outcome in astrocytes, as it does in neurons.

The effect of clonidine on cell survival, glutamate, and aspartate release in normo- and hyperglycemic rats after near complete forebrain ischemia

The present study was undertaken to investigate the effects of the alpha2 adrenergic agonist, clonidine, on the near complete cerebral ischemia (NCFI) evoked release of glutamate and aspartate from normo- and hyperglycemic rodent brain tissue using microdialysis tissue techniques. Hemodynamic variables, blood lactate, and glucose levels were monitored throughout the 40 min NCFI occlusion period. After 48 h, rats were killed and the extent of neuronal injury was determined in the cortex, striatum, and hippocampus. Hemodynamic variables recorded during ischemia improved with clonidine treatment in both normo- and hyperglycemic groups. Glutamate and aspartate levels were greatly increased over control values during normo- and hyperglycemic NCFI treatment. Clonidine pretreatment suppressed the release of both glutamate and aspartate during NCFI in normo- and hyperglycemic rodents when compared with NCFI-treated normo- and hyperglycemic rats without the drug. Significant neuroprotection of cells in the cortex, striatum, and hippocampus was also observed in drug-treated animals 48 h postischemia. The combined effects of diminished glutamate release after NCFI and reduced neuronal injury in both normo- and hyperglycemic states suggests that clonidine treatment during NCFI is neuroprotective. The neuroprotective effect of clonidine during ischemia may be ascribed to both a sensitization of central sympathetic activity and a reduced release of glutamate thereby reducing NMDA receptor activation and neuronal damage.

Lactate and glucose as energy substrates during, and after, oxygen deprivation in rat hippocampal acute and cultured slices

The effects of raised brain lactate levels on neuronal survival following hypoxia or ischemia is still a source of controversy among basic and clinical scientists. We have sought to address this controversy by studying the effects of glucose and lactate on neuronal survival in acute and cultured hippocampal slices. Following a 1-h hypoxic episode, neuronal survival in cultured hippocampal slices was significantly higher if glucose was present in the medium compared with lactate. However, when the energy substrate during the hypoxic period was glucose and then switched to lactate during the normoxic recovery period, the level of cell damage in the CA1 region of organotypic cultures was significantly improved from 64.3 +/- 2.1 to 74.6 +/- 2.1% compared with cultures receiving glucose during and after hypoxia. Extracellular field potentials recorded from the CA1 region of acute slices were abolished during oxygen deprivation for 20 min, but recovered almost fully to baseline levels with either glucose (82.6 +/- 10.0%) or lactate present in the reperfusion medium (108.1 +/- 8.3%). These results suggest that lactate alone cannot support neuronal survival during oxygen deprivation, but a combination of glucose followed by lactate provides for better neuroprotection than either substrate alone.

Perioperative infusions in paediatric patients: rationale for using Ringer-lactate solution with low dextrose concentration

To assess the usefulness of Ringer-lactate solution with 0.9% dextrose, fluid therapy during surgery in paediatric patients was reviewed. From the literature, the need for intravenous (i.v.) infusion and water could be established. The need for sodium was also evident and use of normonatraemic i.v. solutions should be recommended to avoid hyponatraemia. Little data were found about the value of the other electrolytes. Dextrose requirements have been the subject of debate for the last two decades. The choice of dextrose concentration is a compromise between avoiding hypoglycaemia and hyperglycaemia. Four clinical trials assessing the use of Ringer-lactate solution with 0.9 or 1% dextrose in paediatric patients suggest that it is appropriate for routine infusion in paediatric patients during the perioperative period. However, fluid therapy during surgery has rarely been studied, probably because it is inexpensive, rarely leads to problems and is used in very different clinical settings. Development of consensus clinical guidelines on the use of electrolyte infusions in paediatric surgery would be helpful.

Initial hyperglycemia as an indicator of severity of the ictus in poor-grade patients with spontaneous subarachnoid hemorrhage

An association between hyperglycemia and outcome in spontaneous subarachnoid hemorrhage (SAH) has been sporadically reported. Our hypothesis was that hyperglycemia is a sign of central metabolic disturbance linked with specific appearances on computerized tomography (CT) scans reflecting different degrees of corresponding brain injury. The admission plasma glucose level, initial CT findings, and outcome after 6 months were analysed in a cohort of 99 patients with SAH in Hunt & Hess Grade IV or V. The CT scans were quantitatively assessed for subarachnoid blood, intracerebral hematoma, intraventricular hemorrhage, hydrocephalus, midline shift and compression of the perimesencephalic cisterns. These findings were combined to determine a three-point CT severity score. All patients showed elevated (>5.8 mmol/l) plasma glucose levels on admission. Mortality among 33 patients with glucose concentration below 9.0 mmol/l was 33.3%, 71.1% for the 45 patients with glucose level between 9.0 and 13.0 mmol/l, and 95.2% for the 21 patients with concentration above 13.0 mmol/l (P<0.0001). Glucose level was higher in Grade V than in Grade IV patients (mean+/-SD) (11.8+/-3.2 vs 9.8+/-2.9 mmol/l; P=0.0012). Patients with mild CT findings (n=10) had the lowest glucose level (8.9+/-1.8 mmol/l; P=0.0082), whereas patients with severe findings (n=56) had the highest glucose (11.4+/-3.5 mmol/l; P=0.011). Despite association with clinical grade and extent of CT findings, logistic multiple regression revealed the admission plasma glucose level to be an independent prognosticator of outcome. The prognostic potential of the initial plasma glucose level may be beneficial in management protocols of poor-grade SAH patients.

Survival- and death-promoting events after transient cerebral ischemia: phosphorylation of Akt, release of cytochrome C and Activation of caspase-like proteases

Release of cytochrome c (cyt c) into cytoplasm initiates caspase-mediated apoptosis, whereas activation of Akt kinase by phosphorylation at serine-473 prevents apoptosis in several cell systems. To investigate cell death and cell survival pathways, the authors studied release of cyt c, activation of caspase, and changes in Akt phosphorylation in rat brains subjected to 15 minutes of ischemia followed by varying periods of reperfusion. The authors found by electron microscopic study that a portion of mitochondria was swollen and structurally altered, whereas the cell membrane and nuclei were intact in hippocampal CA1 neurons after 36 hours of reperfusion. In some neurons, the pattern of immunostaining for cyt c changed from a punctuate pattern, likely representing mitochondria, to a more diffuse cytoplasmic localization at 36 and 48 hours of reperfusion as examined by laser-scanning confocal microscopic study. Western blot analysis showed that cyt c was increased in the cytosolic fraction in the hippocampus after 36 and 48 hours of reperfusion. Consistently, caspase-3-like activity was increased in these hippocampal samples. As demonstrated by Western blot using phosphospecific Akt antibody, phosphorylation of Akt at serine-473 in the hippocampal region was highly increased during the first 24 hours but not at 48 hours of reperfusion. The authors conclude that transient cerebral ischemia activates both cell death and cell survival pathways after ischemia. The activation of Akt during the first 24 hours conceivably may be one of the factors responsible for the delay in neuronal death after global ischemia.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

Hyperglycemia and focal brain ischemia

The influence of hyperglycemic ischemia on tissue damage and cerebral blood flow was studied in rats subjected to short-lasting transient middle cerebral artery (MCA) occlusion. Rats were made hyperglycemic by intravenous infusion of glucose to a blood glucose level of about 20 mmol/L, and MCA occlusion was performed with the intraluminar filament technique for 15, 30, or 60 minutes, followed by 7 days of recovery. Normoglycemic animals received saline infusion. Perfusion-fixed brains were examined microscopically, and the volumes of selective neuronal necrosis and infarctions were calculated. Cerebral blood flow was measured autoradiographically at the end of 30 minutes of MCA occlusion and after 1 hour of recirculation in normoglycemic and hyperglycemic animals. In two additional groups with 30 minutes of MCA occlusion, CO2 was added to the inhaled gases to create a similar tissue acidosis as in hyperglycemic animals. In one group CBF was measured, and the second group was examined for tissue damage after 7 days. Fifteen and 30 minutes of MCA occlusion in combination with hyperglycemia produced larger infarcts and smaller amounts of selective neuronal necrosis than in rats with normal blood glucose levels, a significant difference in the total volume of ischemic damage being found after 30 minutes of MCA occlusion. After 60 minutes of occlusion, when the volume of infarction was larger, only minor differences between normoglycemic and hyperglycemic animals were found. Hypercapnic animals showed volumes of both selective neuronal necrosis and infarction that were almost identical with those observed in normoglycemic, normocapnic animals. When local CBF was measured in the ischemic core after 30 minutes of occlusion, neither the hyperglycemic nor the hypercapnic animals were found to be significantly different from the normoglycemic group. Brief focal cerebral ischemia combined with hyperglycemia leads to larger and more severe tissue damage. Our results do not support the hypothesis that the aggravated injury is caused by any disturbances in CBF.

Hyperglycemia-exaggerated ischemic brain damage following 30 min of middle cerebral artery occlusion is not due to capillary obstruction

Transient focal ischemia of brief duration (15-30 min) gives rise to brain damage. In normoglycemic animals this damage usually consists of selective neuronal necrosis (SNN), and is largely confined to the lateral caudoputamen. In hyperglycemic subjects damage occurs more rapidly, involves also neocortical areas, and is often of the pan-necrotic type ('infarction'). Since experiments on forebrain ischemia of 30 min duration suggest that microcirculatory compromise develops during recirculation, we studied whether focal ischemia of the same duration, followed by reperfusion for 1, 2 or 4 h, leads to microcirculatory dysfunction. To test this possibility, we fixed the tissue by perfusion and counted the number of formed elements (leukocytes, macrophages and erythrocytes) in capillaries and postcapillary venules. Furthermore, capillary patency was evaluated following in vivo injection of Evan's blue. Histopathological examination of tissue fixed by perfusion after 1, 2 and 4 h of recirculation showed an increasing density of SNN in the caudoputamen of normoglycemic animals. Hyperglycemic, but not normoglycemic, animals showed pan-necrotic lesions ('infarction') after 4 h of recirculation. As a result, the total volume of tissue damage (SNN plus infarction) was larger in hyper- than in normoglycemic animals at 2 and 4 h of recirculation. In addition, hyperglycemic animals showed involvement of neocortex which increased with the time of reperfusion. In the ischemic hemisphere, between 5 and 10% of counted capillaries contained formed elements. However, since hyperglycemic animals contained an equal (or smaller) amount of cells the results did not suggest that capillary 'plugging' could explain the aggravated damage. Moreover, both normo- and hyperglycemic animals showed close to 100% capillary patency. The results thus fail to support the notion that the aggravation of focal ischemic damage by hyperglycemia is due to obstruction of microvessel by swelling or leukocyte adherence.

Preischemic hyperglycemia leads to rapidly developing brain damage with no change in capillary patency

The present experiments were undertaken to explore whether exaggeration of ischemic brain damage by preischemic hyperglycemia is due to lack of capillary patency in the postischemic period. Normo- and hyperglycemic rats were exposed to 10 min of forebrain ischemia. Histopathological changes were evaluated after 6 and 16-18 h of recovery by light microscopy, and capillary patency was assessed at the same time points by a double-staining technique, depicting perfused and morphologically identifiable capillaries. The results demonstrate that some neuronal damage was detectable after 6 h of recirculation which was aggravated after 16-18 h of recirculation in hyperglycemic rats. In contrast, the degree of capillary patency was similar in normo- and hyperglycemic rats. In both groups the perfusion marker, Evans blue, perfused about 95% of all capillaries when injected 10 s before decapitation. Since preischemic hyperglycemia exaggerates brain damage without cessation of capillary perfusion the primary targets of hyperglycemic brain damage may not be capillaries but neurons or glial cells.

Role of protein kinase C in acidosis induced glial swelling--current understanding

A major factor in secondary brain injury following cerebral trauma is accumulation of lactic acid resulting in glial swelling. Further, evidence obtained in this context demonstrates activation of protein kinase C (PKC) under these circumstances. Glial swelling from acidosis is attributable to activation of the Na+/H(+)-exchanger, mediating influx of Na(+)-ions in exchange for the extrusion of H+ ions. The antiporter is activated following phosphorylation by PKC. The current study was made to elucidate the role of PKC activation in acidosis-induced glial swelling. For that purpose, suspended C6 glioma cells were used to examine changes of the cell volume and intracellular pH (pHi). Acidosis was induced by administration of isotonic lactic acid. Stimulation of PKC by the phorbol-ester PMA was significantly enhancing glial swelling from severe acidosis (pH 6.2), whereas the decrease of pHi was somewhat attenuated. On the other side, inhibition of PKC by staurosporine did not affect cell swelling nor the decrease of pHi from acidosis. The results indicate that activation of PKC in cerebral trauma or ischemia may enhance glial swelling from lactacidosis.

Hyperglycemia and hypercapnia suppress BDNF gene expression in vulnerable regions after transient forebrain ischemia in the rat

Preischemic hyperglycemia or superimposed hypercapnia exaggerates brain damage caused by transient forebrain ischemia. Because high regional levels of brain-derived neurotrophic factor (BDNF) protein correlate with resistance to ischemic damage, we studied the expression of BDNF mRNA using in situ hybridization in rats subjected to 10 minutes of forebrain ischemia under normoglycemic, hyperglycemic, or hypercapnic conditions. Compared with normoglycemic animals, the increase of BDNF mRNA using in situ hybridization in rats subjected to 10 minutes of forebrain ischemia under normoglycemic, or hypercapnic conditions. Compared with normoglycemic animals, the increase of BDNF mRNA in dentate granule cells was attenuated and that in CA3 pyramidal neurons completely prevented in hyperglycemic rats. No ischemia-induced increases of BDNF mRNA levels in the hippocampal formation were detected in hypercapnic animals. Hyperglycemic and hypercapnic rats showed transiently decreased expression of BDNF mRNA levels in the cingulate cortex, which was not observed in normoglycemic animals. The results suggest that suppression of the BDNF gene might contribute to the increased vulnerability of the CA3 region and cingulate cortex in hyperglycemic and hypercapnic animals.