Temporal profiles of accumulation of amyloid beta/A4 protein precursor in the gerbil after graded ischemic stress

Histopathological study of encephalomalacia in neonatal calves and application of neuronal and axonal degeneration marker

Five calves that had shown neurological symptoms within 9 days after birth were histopathologically diagnosed as encephalomalacia. Two calves showed bilateral laminar cerebrocortical necrosis and neuronal necrosis in the corpus striatum and hippocampus. Since the distributional pattern of the lesions was consistent with that of global ischemia in other species, the lesions were probably hypoxic/ischemic encephalopathy consistent with the history of dystocia and perinatal asphyxia. One calf also showed bilateral laminar cerebrocortical necrosis. However, the lesions were chronic ones, because the calf had survived for long time and necropsied at postnatal day 118. Additionally, the lesions did not involve the corpus striatum and hippocampus. The other two calves showed multifocal necrosis with vascular lesions characterized by fibrin thrombi, perivascular edema and perivascular hyaline droplets in the cerebral cortex, corpus striatum, thalamus, brain stem and cerebellum. Considering the age of onsets and histopathological appearance, it was possible that latter three calves were also hypoxic/ischemic encephalopathy, however, exact cause of them was not revealed. In all calves, degenerated/necrotic neurons showed positive reactions for Fluoro-Jade C and degenerated axons showed immunoreactivity for Alzheimer precursor protein A4. Therefore, these markers were applicable to examination of brain injury in neonatal calves.

Bilateral Common Carotid Artery Occlusion in the Rat as a Model of Retinal Ischaemia

Ocular ischaemic syndrome is a devastating eye disease caused by severe carotid artery stenosis. The purpose of the study was to develop a reliable rat model for this syndrome by means of common carotid artery occlusion and a controllable needle suture method. Adult Wistar rats were subjected to common carotid artery occlusion and sham surgery. The common carotid artery was ligated unilaterally or bilaterally with needles of different diameters, and ocular arterial filling time was examined by fluorescein fundus angiography at different time points. Haematoxylin-eosin staining of vessels and degree of stenosis were considered outcome measures. The ocular blood flow was monitored and measured by laser doppler flowmetry. Needles with a diameter of 0.4 mm were more effective in developing severe stenosis of the common carotid arteries compared with needles of other diameters. Bilateral common carotid artery occlusion was a more effective model than unilateral occlusion. The arterial filling time was significantly increased at 14 and 21 days after ligation (5.75 ± 0.45 and 6.27 ± 0.95 s, respectively) compared with arterial filling time before surgery (5.22 ± 0.64 s). The total blood flow in the sham surgery group was significantly higher than in the bilateral common carotid artery occlusion group. The fundus blood flow was statistically different between the two groups, whereas that of the anterior segment was not. In conclusion, the authors have established a rat model of ocular ischaemic syndrome via a controllable needle suture method, which was reliable up to 2-3 weeks after surgery.

Non-psychiatric comorbidity associated with Alzheimer's disease

The burden of medical comorbidity in individuals with Alzheimer's disease is greater than that observed in matched individuals without dementia. This has important implications for all clinicians and healthcare providers who deal with this common condition. The prevalence of vascular risk factors and vascular disease is particularly high. Additionally, associations with a number of other chronic medical conditions have been described, including thyroid disorders, sleep apnoea, osteoporosis and glaucoma. This review gives an overview of evidenced medical (non-psychiatric) comorbidity associated with Alzheimer's disease and briefly explores the underlying mechanisms that may account for these associations.

Synergistic memory impairment through the interaction of chronic cerebral hypoperfusion and amlyloid toxicity in a rat model

BACKGROUND AND PURPOSE

Vascular pathology and Alzheimer disease (AD) pathology have been shown to coexist in the brains of dementia patients. We investigated how cognitive impairment could be exacerbated in a rat model of combined injury through the interaction of chronic cerebral hypoperfusion and amyloid beta (Aβ) toxicity.

METHODS

In Wistar rats, chronic cerebral hypoperfusion was modeled by permanent occlusion of bilateral common carotid arteries (BCCAo). Further, AD pathology was modeled by bilateral intracerebroventricular Aβ (Aβ toxicity) using a nonphysiological Aβ peptide (Aβ 25 to 35). The experimental animals were divided into 4 groups, including sham, single injury (Aβ toxicity or BCCAo), and combined injury (BCCAo-Aβ toxicity) groups (n=7 per group) . Cerebral blood flow and metabolism were measured using small animal positron emission tomography. A Morris water maze task, novel object location and recognition tests, and histological investigation, including neuronal cell death, apoptosis, neuroinflammation, and AD-related pathology, were performed.

RESULTS

Spatial memory impairment was synergistically exacerbated in the BCCAo-Aβ toxicity group as compared to the BCCAo or Aβ toxicity groups (P<0.05). Compared to the sham group, neuroinflammation with microglial or astroglial activation was increased both in multiple white matter lesions and the hippocampus in other experimental groups. AD-related pathology was enhanced in the BCCAo-Aβ toxicity group compared to the Aβ toxicity group.

CONCLUSIONS

Our experimental results support a clinical hypothesis of the deleterious interaction between chronic cerebral hypoperfusion and Aβ toxicity. Chronic cerebral hypoperfusion-induced perturbation in the equilibrium of AD-related pathology may exacerbate cognitive impairment in a rat model of combined injury.

Chronic hypoxia in the human neuroblastoma SH-SY5Y causes reduced expression of the putative alpha-secretases, ADAM10 and TACE, without altering their mRNA levels

Alzheimer's disease is more frequent following an ischemic or hypoxic episode, with levels of beta-amyloid peptides elevated in brains from patients. Similar increases are found after experimental ischemia in animals. It is possible that increased beta-amyloid deposition arises from alterations in amyloid precursor protein (APP) metabolism, indeed, we have shown that exposing cells of neuronal origin to chronic hypoxia decreased the secretion of soluble APP (sAPPalpha) derived by action of alpha-secretase on APP, coinciding with a decrease in protein levels of ADAM10, a disintegrin metalloprotease which is thought to be the major alpha-secretase. In the current study, we extended those observations to determine whether the expression of ADAM10 and another putative alpha-secretase, TACE, as well as the beta-secretase, BACE1 were regulated by chronic hypoxia at the level of protein and mRNA. Using Western blotting and RT-PCR, we demonstrate that after 48 h chronic hypoxia, such that sAPPalpha secretion is decreased by over 50%, protein levels of ADAM10 and TACE and by approximately 60% and 40% respectively with no significant decrease in BACE1 levels. In contrast, no change in the expression of the mRNA for these proteins could be detected. Thus, we conclude that under CH the level of the putative alpha-secretases, ADAM10 and TACE are regulated by post-translational mechanisms, most probably proteolysis, rather than at the level of transcription.

Alzheimer's disease and post-operative cognitive dysfunction

Alzheimer's disease (AD), an insidious and progressive neurodegenerative disorder accounting for the vast majority of dementia, is characterized by global cognitive decline and the robust accumulation of amyloid deposits and neurofibrillary tangles in the brain. This review article is based on the currently published literature regarding molecular studies of AD and the potential involvement of AD neuropathogenesis in post-operative cognitive dysfunction (POCD). Genetic evidence, confirmed by neuropathological and biochemical studies, indicates that excessive beta-amyloid protein (Abeta) generated from amyloidogenic processing of the beta-amyloid precursor protein (APP) plays a fundamental role in the AD neuropathogenesis. Abeta is produced from APP by beta-secretase, and then gamma-secretase complex, consisting of presenilins, nicastrin (NCSTN), APH-1 and PEN-2. Additionally, Abeta clearance and APP adaptor proteins can contribute to AD neuropathogenesis via affecting Abeta levels. Finally, cellular apoptosis may also be involved in AD neuropathogenesis. Surgery and anesthesia can cause cognitive disorders, especially in elderly patients. Even the molecular mechanisms underlying these disorders are largely unknown; several perioperative factors such as hypoxia, hypocapnia and anesthetics may be associated with AD and render POCD via trigging AD neuropathogenesis. More studies to assess the potential relationship between anesthesia/surgery and AD dementia are, therefore, urgently needed.

Altered processing of the amyloid precursor protein and decreased expression of ADAM 10 by chronic hypoxia in SH-SY5Y: no role for the stress-activated JNK and p38 signalling pathways

Clinical studies suggest that the incidence of Alzheimer's disease (AD) is increased following an ischaemic or hypoxic episode, such as stroke. Furthermore, levels of the AD-associated amyloid beta-peptides (Abeta) and the amyloid precursor protein (APP) are enhanced in experimental ischaemia. In our previous study [Webster, N.J., Green, K.N., Peers, C., Vaughan, P.F., Altered processing of amyloid precursor protein in the human neuroblastoma SH-SY5Y by chronic hypoxia, J. Neurochem., 83 (2002) 1262-1271] we reported that exposing cells of neuronal origin to a period of chronic hypoxia (CH; 2.5% O(2), 24 h) led to a decrease in processing of the amyloid precursor protein (APP) by the alternative and neuroprotective alpha-secretase pathway. In SH-SY5Y cells, the most likely mechanism was that CH inhibits the protein level of ADAM 10, a disintegrin metalloprotease widely believed to be the alpha-secretase. One effect of CH is to alter the activity of the stress-activated protein kinases (SAPKs) c-Jun amino terminal kinase (JNK) and p38. Thus, the main aims of this study were to investigate the effect of CH on (1) the activity of these SAPKs in SH-SY5Y and (2) whether changes in the activity of these kinases may account for the CH-induced decreases in ADAM 10 expression and sAPPalpha secretion. We demonstrated that the phosphorylation (activity) of JNK was decreased approximately 50% following a period of CH. An inhibitor of JNK did not mimic the effects of CH on either ADAM 10 expression or sAPPalpha secretion under conditions in which the phosphorylation of c-Jun was inhibited by approximately 80%. Thus the loss of JNK activity does not appear to be linked to the decrease in expression of ADAM 10 and secretion of sAPPalpha. In contrast, phosphorylation (activity) of p38 was enhanced approximately 300% following a period of CH. However, inhibitors of p38 were unable to reverse the loss of sAPPalpha in CH cells, indicating that this increase in activity was not linked to the altered processing of APP.

Relationship between flow-metabolism uncoupling and evolving axonal injury after experimental traumatic brain injury

Blood flow-metabolism uncoupling is a well-documented phenomenon after traumatic brain injury, but little is known about the direct consequences for white matter. The aim of this study was to quantitatively assess the topographic interrelationship between local cerebral blood flow (LCBF) and glucose metabolism (LCMRglc) after controlled cortical impact injury and to determine the degree of correspondence with the evolving axonal injury. LCMRglc and LCBF measurements were obtained at 3 hours in the same rat from 18F-fluorodeoxyglucose and 14C-iodoantipyrine coregistered autoradiographic images, and compared to the density of damaged axonal profiles in adjacent sections and in an additional group at 24 hours using beta-amyloid precursor protein (beta-APP) immunohistochemistry. LCBF was significantly reduced over the ipsilateral hemisphere by 48 +/- 15% compared with sham-controls, whereas LCMRglc was unaffected, apart from foci of elevated LCMRglc in the contusion margin. Flow-metabolism was uncoupled, indicated by a significant 2-fold elevation in the LCMRglc/LCBF ratio within most ipsilateral structures. There was a significant increase in beta-APP-stained axons from 3 to 24 hours, which was negatively correlated with LCBF and positively correlated with the LCMRglc/LCBF ratio at 3 hours in the cingulum and corpus callosum. Our study indicates a possible dependence of axonal outcome on flow-metabolism in the acute injury stage.

Altered processing of amyloid precursor protein in the human neuroblastoma SH-SY5Y by chronic hypoxia

Alzheimer's disease (AD) is more prevalent following an ischemic or hypoxic episode, such as stroke. Indeed, brain levels of amyloid precursor protein (APP) and the cytotoxic amyloid beta peptide (Abeta) fragment are enhanced in these patients and in animal models following experimental ischaemia. We have investigated the effect of chronic hypoxia (CH; 2.5% O2, 24 h) on processing of APP in the human neuroblastoma, SH-SY5Y. We demonstrate that constitutive and muscarinic-receptor-enhanced secretion of the alpha-secretase cleaved fragment of APP, sAPPalpha, was reduced by approximately 60% in CH cells. The caspase inhibitor BOC-D(Ome)FMK did not reverse this effect of CH, and CH cells were as viable as controls, based on MTT assays. Thus, loss of sAPPalpha is not related to cell death or caspase processing of APP. Pre-incubation with antioxidants did not reverse the effect of CH, and the effect could not be mimicked by H2O2, discounting the involvement of reactive oxygen species in hypoxic loss of sAPPalpha. CH did not affect muscarinic activation of extracellular-signal regulated kinase. However, expression of ADAM 10 (widely believed to be alpha-secretase) was decreased approximately 50% following CH. Thus, CH selectively decreases processing of APP by the alpha-secretase pathway, most likely by decreasing levels of ADAM 10.

Axonal damage and demyelination in the white matter after chronic cerebral hypoperfusion in the rat

Cerebral white matter (WM) lesions are observed frequently in human ischemic cerebrovascular disease and have been thought to contribute to cognitive impairment. This type of lesion can be experimentally induced in rat brains under chronic cerebral hypoperfusion by the permanent occlusion of both common carotid arteries. However, it remains uncertain whether chronic ischemia can damage both the gray and white matter, and whether it can induce demyelination with or without axonal damage. Therefore, we examined axonal damage using immunohistochemistry for the amyloid beta/A4 precursor protein (APP), chromogranin A (CgA) and demyelination using immunohistochemistry for the encephalitogenic peptide (EP) in this model. Severe WM lesions such as vacuolation and the loss of nerve fibers appeared in the optic nerve and optic tract after 3 days of ligation, and less intense changes were observed in the corpus callosum, internal capsule, and fiber bundles of the caudoputamen after 7 days with Klüver-Barrera and Bielschowsky staining. These WM lesions persisted even after 30 days. The APP, CgA, and EP-immunopositive fibers increased in number from 1 to 30 days after the ligation in the following WM regions: the optic nerve, optic tract, corpus callosum, internal capsule, and fiber bundles of the caudoputamen. In contrast, only a few APP, CgA, or EP-immunopositive fibers were detected in the gray matter regions, including the cerebral cortex and hippocampus. These results indicate that the WM is more susceptible to chronic cerebral hypoperfusion than the gray matter, with an involvement of both axonal and myelin components. Furthermore, immunohistochemistry for APP, CgA, and EP is far superior to routine histological staining in sensitivity and may become a useful tool to investigate WM lesions caused by various pathoetiologies.

The functions of the amyloid precursor protein gene

The amyloid precursor protein (APP) gene and its protein products have multiple functions in the central nervous system and fulfil criteria as neuractive peptides: presence, release and identity of action. There is increased understanding of the role of secretases (proteases) in the metabolism of APP and the production of its peptide fragments. The APP gene and its products have physiological roles in synaptic action, development of the brain, and in the response to stress and injury. These functions reveal the strategic importance of APP in the workings of the brain and point to its evolutionary significance.

Hyperglycemic but not normoglycemic global ischemia induces marked early intraneuronal expression of beta-amyloid precursor protein

Preischemic hyperglycemia is known to accentuate acute ischemic injury to neurons, microglia, and endothelia. In the present study, we used a monoclonal antibody to the N-terminal portion of beta-APP to examine how the immunoreactivity of this normal membrane glycoprotein is differentially influenced by transient cerebral ischemia when carried out under normoglycemic vs. hyperglycemic conditions. Anesthetized, physiologically regulated rats received 12.5 min of global forebrain ischemia by bilateral carotid artery occlusions plus systemic hypotension. Hyperglycemia was induced by intraperitoneal dextrose administration prior to ischemia. One or three days later, brains were examined by beta-APP immunohistochemistry. Ischemia under hyperglycemic conditions led to the robust, widespread intraneuronal expression of beta-APP immunoreactivity in neocortex, hippocampus, thalamus, and striatum of all 11 rats; this was most prominent at 24 h postischemia. Compared to rats with normoglycemic ischemia, numbers of beta-APP-immunopositive neurons in the parietal cortex of hyperglycemic rats were increased by 5.9 fold at 24 h, and by 10.6 fold at 3 days postischemia. beta-APP-immunopositive neurons in hyperglycemic rats often exhibited striking morphological alterations typical of ischemic necrosis; however, no beta-APP immunoreaction was observed in zones of frank infarction. Brains of normoglycemic rats (n=11), by contrast, showed only weak beta-APP immunostaining in occasional non-necrotic pyramidal neurons of parietal neocortex; no necrosis was present in thalamus. In sham-operated hyperglycemic rats, beta-APP immunostaining of thalamic neurons was somewhat increased at 24 h. Western analysis revealed that the hyperglycemia-induced intraneuronal overexpression of beta-APP was not associated with an overall increase in tissue levels. The results of this study demonstrate that transient forebrain ischemia under hyperglycemic conditions leads to the early intraneuronal expression of beta-APP within neuronal populations showing a heightened susceptibility to hyperglycemia-induced accentuation of ischemic injury. Our data suggest that beta-APP or its metabolites may be involved in the injury process.

Alzheimer's disease: a review concerning immune response and microischemia

Alzheimer's disease (AD), as we think of it today, is the idiopathic progressive loss of cognitive function over a period of several years. The risk of late onset dementia increases significantly with each decade of life such that half of the population over the age of 80 is vulnerable to this disease (1). We know that proper functioning of the central nervous system is dependent on adequate blood flow to remove harmful metabolic products and supply nutrients such as glucose and oxygen to the brain. It has been suggested that cerebral hypoperfusion causes AD (2). Mean cerebral blood flow decreases with age and with sclerosis of cerebral blood vessels. Blood flow appears to increase in stimulated areas of the brain during different activities. However, there is a derangement of blood flow in disease states; this has been documented in the temporal lobes of AD patients, (3,4). English language journal articles located by a MEDLINE search (1960-1999) were reviewed with consideration to the hypothesis that Alzheimer's disease is an autoimmune disease initiated by low oxygen tension and microischemia. Inflammation is thought to be a known contributor to the pathology of AD (5,6). Recent reports support the concept of autoimmunity as a final common pathway of neuron death, particularly for cholinergic in Alzheimer's disease (6). A model of Alzheimer's disease is proposed and related research and treatment modalities are discussed.

beta-amyloid (Abeta)42(43), abeta42, abeta40 and apoE immunostaining of plaques in fatal head injury

beta-Amyloid (Abeta) deposits are found in the brains of approximately one-third of patients who die within days after a severe head injury; their presence correlating strongly with possession of an apolipoprotein E (apoE)-epsilon4 allele. The aim of the study was to investigate the relationship between Abeta42, Abeta40 and apoE immunostaining of Abeta plaques in the cerebral cortex and the relevance of apoE genotype in 23 fatally head-injured patients. These cases were known to have Abeta deposits from a previous study in which they were examined and semiquantified and related to apoE genotype. In the present study, the temporal cortex was probed using four different antibodies that recognize Abeta42(43), Abeta40 and an antibody to apoE. Abeta42(43)-positive plaques were observed in all of the 23 cases and Abeta40 immunoreactivity in only 11 of the 23 cases. In addition, semiquantitative analysis showed that relatively fewer plaques were detected with anti-Abeta40 than anti-Abeta42(43). ApoE-immunoreactive plaques were identified in 18 of the 23 cases. The number of plaques stained for apoE was relatively less than for Abeta42(43) but greater than for Abeta40. Furthermore, the density of Abeta plaques detected using either Abeta42(43), Abeta40 or apoE antibodies was associated with possession of apoE-epsilon4 in an allele dose-dependent manner. The results are consistent with Abeta42(43) as the initially deposited species in brain parenchyma and provide evidence that apoE is involved in the early stages of amyloid deposition. Further, the findings may be of relevance to the role of apoE genotype in influencing outcome after acute brain injury.

The role of cerebral ischemia in Alzheimer's disease

The Alzheimer type of dementia and stroke are known to increase at comparable rates with age. Recent advances suggest that vascular risk factors linked to cerebrovascular disease and stroke in the elderly significantly increase the risk of developing Alzheimer's disease (AD). These include atherosclerosis, atrial fibrillation, coronary artery disease, hypertension, and diabetes mellitus. Moreover, review of various autopsy series shows that 60-90% of AD cases exhibit variable cerebrovascular pathology. Although some vascular lesions such as cerebral amyloid angiopathy, endothelial degeneration, and periventricular white matter lesions are evident in most cases of AD, a third will exhibit cerebral infarction. Despite the interpretation of pathological evidence, longitudinal clinical studies suggest that the co-existence of stroke and AD occurs more than by chance alone. Strokes known to occur in patients with Alzheimer syndrome and most frequently in the oldest old substantially worsen cognitive decline and outcome, implicating some interaction between the disorders. Nevertheless, the nature of a true relationship between the two disorders seems little explored. What predisposes to strokes in underlying cognitive decline or AD? Is it possible that cerebral ischemia is a causal factor for AD? I examined several vascular factors and the vascular pathophysiology implicated in stroke and AD, and propose that cerebral ischemia or oligemia may promote Alzheimer type of changes in the aging brain. Irrespective of the ultimate pathogenetic mechanism, these approaches implicate that management of peripheral vascular disease is important in the treatment or prevention of Alzheimer's disease or mixed dementia.

β -amyloid precursor protein positive axonal bulbs may form in non-head-injured patients

Since the early 1980s axonal bulbs staining positively for beta-amyloid precursor protein (betaAPP) have been used as a marker of diffuse axonal injury (DAI), bulb formation been attributed to shearing forces generated during rotational acceleration/deceleration head injury. This study draws attention to the observation that they may form in the absence of a head injury and, thus, axonal injury cannot be assumed to result from mechanical injury alone. Out of 20 cases with no history of head injury studied, which only showed evidence of neuronal hypoxic change, 11 (55%) showed variable positive staining for betaAPP in a similar anatomical distribution to that previously described for DAI. The role of hypoxia in the formation of axonal bulbs, as well as the possible role of betaAPP as an acute phase protein, are discussed. These observations further clarify the pattern and relationship between neuronal and axonal staining observed following a brain insult and emphasize the possible role of betaAPP as a neuroprotective protein.

Altered expression of amyloid precursors proteins after traumatic brain injury in rats: in situ hybridization and immunohistochemical study

The expression of alternatively spliced mRNAs for amyloid precursor protein (APP) isoforms and their translation products were examined in the rat cerebral cortex 1, 3, 6, and 12 h and 1, 3, and 7 days (n = 4-5 in each group) after fluid-percussion brain injury. In situ hybridization studies demonstrated that the expression of APP695 mRNA decreased in and around the damaged area of the cerebral cortex exposed to fluid-percussion injury 1 h after the insult. On the other hand, APP751/770 mRNAs were increased in the regions surrounding the damaged cortical areas 1 day after the injury. An increase of immunoreactive APP was detected in the regions around the damaged cortical areas 3 h after traumatic injury and maintained for the following 3 days. The APP immunoreactivity in the damaged cortices declined to the level of sham-operated animals by post-experimental day 7. Using an anti-amyloid beta (Abeta) protein (17-24) antibody, no deposits of immunoreactive Abeta (17-24) were observed in any of the samples examined in these experiments. These results suggest that the induction of Kunitz-type protease inhibitor (KPI) domain-containing APP mRNAs and the increased accumulation of APP are involved in the physiological and neuropathological responses of brains under various neurodegenerative conditions, including head trauma.

Histochemically-reactive zinc in amyloid plaques, angiopathy, and degenerating neurons of Alzheimer's diseased brains

Excess brain zinc has been implicated in Alzheimer's neuropathology. Here we evaluated that hypothesis by searching the brains of Alzheimer's patients for abnormal zinc deposits. Using histochemical methods, we found vivid Zn2+ staining in the amyloid deposits of dense-core (senile) plaques, in the amyloid angiopathy surrounding diseased blood vessels, and in the somata and dendrites of neurons showing the characteristic neurofibrillary tangles (NFT) of Alzheimer's. In contrast, brains from age-matched, non-demented subjects showed only occasional staining for Zn2+ in scattered neurons and possible plaques. A role of abnormal zinc metabolism in Alzheimer's neuropathology is suggested.

Alteration of phosphoinositide degradation by cytosolic and membrane-bound phospholipases after forebrain ischemia-reperfusion in gerbil: effects of amyloid beta peptide

The reperfusion of previously ischemic brain is associated with exacerbation of cellular injury. Reperfusion occasionally potentates release of intracellular enzymes, influx of Ca2+, breakdown of membrane phospholipids, accumulation of amyloid precursor protein or amyloid beta-(like) proteins, and apolipoprotein E. In this study, the effect of reperfusion injury on the activity of cerebral cortex enzymes acting on phosphatidyl [3H] inositol (PI) and [14C-arachidonoyl] PI was investigated. Moreover the effect of amyloid beta25-35 on PI degradation by phospholipase(s) of normoxic brain and subjected to ischemia-reperfusion injury was determined. Brain ischemia in gerbils (Meriones unguiculatus) was induced by ligation of both common carotid arteries for 5 min and then brains were perfused for 15 min, 2 h and 7 days. Statistically significant activation of enzyme(s) involved in phosphatidylinositol degradation in gerbils subjected to ischemia-reperfusion injury was observed. Nearly all gerbils showed a higher activity of cytosolic PI phospholipase C (PLC) at 15 min after ischemia. Concomitantly, the significant enhancement of the level of DAG and AA radioactivity at this short reperfusion time confirmed the active PI degradation by phospholipase(s) in cerebral cortex and hippocampus. After a prolonged reperfusion time of 7 days after ischemia, both cytosolic and membrane-bound forms of PI-PLC were activated. The question arises if alteration of membranes by the degradation of phospholipids occurring after an ischemic episode potentiates the effect of Abeta on membrane-bound enzymes. A neurotoxic fragment of amyloid, Abeta 25-35, incubated in the presence of endogenous Ca2+, increased significantly the PI-PLC activity of normoxic brain. In its non-aggregated form, Abeta 25-35 activates PI-PLC but in the aggregated form the enzymatic activity decreased. Thus, Abeta 25-35 exerts a similar effect on the membrane-bound PI-PLC from normoxic brain or subjected to ischemia reperfusion injury. We conclude that the degradation of phosphatidylinositol by cytosolic phosphoinositide-phospholipase C may contribute to the pathophysiology of delayed neuronal death following cerebral ischemia. Thus, a specific inhibitor of this enzyme(s) may offer therapeutic strategies to protect the brain from damage triggered by ischemia. Ischemia-reperfusion injury had no effect on Abeta-evoked alterations of synaptic plasma membrane-bound PI-PLC.

Expression of amyloid precursor protein (beta-APP) in the neonatal brain following hypoxic ischaemic injury

Perinatal hypoxic ischaemic brain injury (HII) is a major cause of neonatal mortality and long-term neurological morbidity. An understanding of the molecular events which follow HII may lead to novel treatments to improve the final outcome for affected infants. The beta-amyloid precursor protein (beta-APP) is a widely expressed transmembrane protein whose proposed functions include stabilization of neuronal calcium fluxes, inhibition of the clotting cascade and cell-cell or cell-matrix adhesion. Normally present at low levels in neurons its expression is induced as part of the acute response of the adult brain to HII. This study aimed to determine whether beta-APP is also part of the acute adaptive response of the infant brain to HII. Immunohistochemistry and Western blotting were used to assess cerebral beta-APP expression in 14-day-old rat pups subjected to unilateral HII, and in 10 term human infants, who died between 12 h and 16 months after severe perinatal HII. In the rat pups beta-APP expression was increased by 2 h post-injury, peaked, fourfold above control levels, at 24 h and gradually declined over the following 4 days. Expression was induced bilaterally, but was greater on the side of injury. In the human infants, increased, predominantly neuronal expression of beta-APP, was detectable immunohistochemically within 24 h of injury and was greatest in those infants dying within 3 days. Expression was particularly strong in the areas showing histological evidence of injury, but was also seen in apparently undamaged areas. We conclude that beta-APP induction is part of the the acute adaptive response of the neonatal brain to HII.

Ribonuclease improves the state of hippocampal sections in the post-ischemic period

Living hippocampal slices from Wistar rats were used to study the dynamics of changes in population electrical responses in field CA1 to electrical stimulation of Shaffer collaterals during the development of ischemia (imposed by exclusion of oxygen and glucose from the perfusion solution). These studies showed that during ischemia, addition of ribonuclease (a blocker of protein synthesis) to the perfusion solution resulted in a significantly smaller increase in the latent period of the response and slowed the onset of the reduction in the amplitude of the evoked potential, and promoted faster recovery of the response after the ischemia session ended. It is suggested that the reduction in protein synthesis due to ribonuclease preserved energy reserves in the nerve tissue, which in turn promoted more complete recovery of neuron function in the post-ischemic period.

The amyloid precursor protein gene: a neuropeptide gene with diverse functions in the central nervous system

The amyloid precursor protein (APP) is a member of a family of proteins found in the central nervous system with a fundamental role in the pathogenesis of Alzheimer's disease. This review describes the experimental evidence that has provided functional insights into this protein and emphasizes the importance of APP in many neurobiological processes.

Pathogenesis of decreased glucose turnover and oxidative phosphorylation in ischemic and trauma-induced dementia of the Alzheimer type

The pathogenetic mechanisms causing a dementing brain disease after temporary ischemia, heat shock, or brain trauma are surveyed. These lesions increase beta amyloid precursor protein (beta APP) synthesis. This process is potentiated by an ischemic glutamate release that opens cellular Ca2+ channels, inhibiting glucose turnover and ATP production, which is, under these conditions, accompanied by the generation of beta amyloid (beta A), even in young persons. Beta amyloid starts a vicious circle by inactivating the glycolytic key enzyme, phosphofructokinase, which, with age, exhausts the functional reserve capacity of the brain. This demonstrates that beta A is an epiphenomenon of a dementing brain disease, triggered by the disturbance of glucose turnover and oxidative phosphorylation. Clinical studies have shown that a dementing brain disease can be clearly objectified and monitored by 18F-2-deoxyglucose PET studies. This paper looks briefly at pharmacologic approaches to this disease using models of temporary ischemia, the testing of 14C-deoxyglucose turnover, or examination with 31P magnetic resonance spectroscopy techniques. In conclusion, the key process of all dementing brain diseases of the Alzheimer type is a decreased glucose turnover and subsequently decreased oxidative phosphorylation, linked directly to a secondary amyloid formation and nerve cell atrophy.

Changes in amyloid precursor protein and apolipoprotein E immunoreactivity following ischemic brain injury in rat with long-term survival: influence of idebenone treatment

We observed in extra- and intracellular space accumulation of different fragments of amyloid precursor protein (APP) and apolipoprotein E (Apo E) in rat brain after cardiac arrest with long-term survival. Idebenone treatment did not affect APP and Apo E alterations in this condition.

Intracortical glutamate perfusion in vivo induces cellular alterations in specific protein kinase C isoforms and amyloid precursor protein

This study investigated the immunostaining of protein kinase C (PKC) isoforms and amyloid precursor protein (APP) in rat brain cortex and determined alterations following an excitotoxic challenge in vivo. Cellular alterations in APP and PKC isoforms (alpha, beta, gamma, delta, epsilon, and zeta) following glutamate perfusion in the rat parietal cortex were compared with NaCl perfusion. In all animals, two histological zones could be defined consistently, a necrotic core and a boundary zone immediately adjacent to the core. Following glutamate and NaCl perfusion, cellular immunoreactivity to PKC isoforms and amino-terminal APP was significantly reduced within the necrotic core. Striking carboxy-terminal APP immunoreactivity was observed in some neurons remaining within the necrotic core. In the boundary of the glutamate lesion, the perikarya of most neurons were intensely immunoreactive to PKC alpha and beta. Furthermore, within the boundary zone, enhanced immunoreactivity within neuronal perikarya was observed to amino-terminal APP and, to a lesser extent, carboxy-terminal APP. Increased immunostaining of PKC alpha and beta and APP at the boundary zone was a consistent feature of intracortical glutamate perfusion and was not observed following NaCl perfusion. There were minimal alterations in PKC isoforms gamma, delta, epsilon, and zeta, in the boundary region following intracortical glutamate or NaCl perfusion. There was no astrocytic response, as detected by GFAP immunoreactivity, at the boundary zone. These findings indicate that there is a topographical relationship between cellular alterations of specific PKC isoforms and APP following an excitotoxic challenge in vivo.

Delayed decrease of excitatory amino acid neurotransmitters in parietotemporal cortex and hippocampus after complete cerebral ischemia in aged rats

A 15-min period of complete cerebral ischemia (CCI) was used in aged rats to investigate changes in tissue contents of the amino acid neurotransmitters (AANT) glutamate (glu), aspartate (asp), gamma aminobutyric acid (gaba) and glycine (gly) in parietotemporal cortex and hippocampus during ischemia and up to 96 h of postischemic recirculation. The AANT were determined by HPLC. The excitatory AANT glu and asp showed a first decrease at the end of CCI in hippocampus and after 1 h of postischemic recirculation in parietotemporal cortex, reflecting a release of these AANT into the extracellular space with a further loss into the blood. A second decrease in glu and asp was seen after 24 h of postischemic recirculation in hippocampus and after 48 h in parietotemporal cortex. This coincides with previously described disturbances in energy metabolism from 24 h to 96 h in hippocampus and from 48 h to 72 h in parietotemporal cortex in the same experimental model in aged rats. This might be a causal factor in delayed postischemic neuronal damage. A comparison with investigations in young animals reveals an enhanced decrease of glutamate and aspartate tissue contents during the postischemic recirculation period in old rats indicating an enhanced release of these amino acid neurotransmitters. A significant decrease of gaba tissue content seen in hippocampus at 48 h and 72 h of postischemic recirculation with subsequent disproportion of inhibitory AANT (lower) to excitatory AANT (higher) might reflect a greater vulnerability of hippocampus than of parietotemporal cortex to ischemia. A significant decrease in the NMDA-receptor coactivator gly in parietotemporal cortex at the end of CCI and at 48 h, 72 h, and 96 h of postischemic recirculation, which was not seen in hippocampus, might be another reason for higher vulnerability of hippocampus to ischemia.

Cytotoxic fragment of amyloid precursor protein accumulates in hippocampus after global forebrain ischemia

We developed an antibody specific to beta-amyloid precursor protein (beta APP) fragments possessing the exact amino terminus of the beta-amyloid peptide and examined its induction in postischemic hippocampus. In control hippocampus, this APP fragment was lightly observed in pyramidal neurons of CA sectors and dentate granule cells. Transient forebrain ischemia enhanced accumulation of the APP fragment in CA1 pyramidal neurons. Seven days after the ischemia, while the APP fragment was still observed in dentate granule cells and CA3 neurons, it disappeared in dead CA1 neurons. While astrocytes did not show in any immunoreactivity throughout the experiment, those in the CA1 sector showed moderate immunoreactivity 7 days after the ischemia. The APP fragment has a cytotoxic effect on cultured neurons. These results suggest that the accumulation of the cytotoxic APP fragment in CA1 neurons may play a role in the development of delayed neuronal death after the ischemic insult.

Selective alterations in the cellular distribution of apolipoprotein E immunoreactivity following transient cerebral ischaemia in the rat

The aim of this study was to examine the cellular localization and alterations of apolipoprotein E (apoE) following a transient ischaemic insult using immunohistochemistry. Transient cerebral ischaemia was induced in Wistar rats by occlusion of both carotid arteries with hypotension followed by reperfusion for 4 h (n = 5), 24 h (n = 5) or 72 h (n = 6). In sham-operated animals (n = 9), the carotids were not occluded. In this model, ischaemia for 15 min results in selective neuronal damage in the caudate nucleus and neocortex (24 h after reperfusion) and the hippocampal CA1 pyramidal cells (72 h after reperfusion) while there is minimal damage in other areas such as the CA3 hippocampal region. In sham animals apoE immunoreactivity was confined to astrocytes and their processes. ApoE immunoreactivity was not altered at 4 h post-ischemic reperfusion. At 24 h reperfusion, intense apoE staining of the cytoplasm of astrocytes and neuropil within the caudate and neocortex was observed and at 72 h reperfusion apoE stained neuronal cell bodies within these regions. Within the CA1 region at 24 h reperfusion, there was increased immunoreactivity of the cytoplasm of astrocytes and the neuropil was more intensely stained compared with sham animals. At 72 h reperfusion, intense apoE staining of pyramidal cell bodies and dendrites was consistently observed in the CA1 region of the hippocampus. In contrast, at 72 h reperfusion, apoE staining of astrocytic processes was dramatically reduced in the CA1 region although GFAP staining indicated their preservation. The results demonstrate that following an ischaemic insult apoE is localized to degenerating neurons and their processes. This may indicate an inherent protective response of cells to injury. Alternatively, the results are consistent with the hypothesis that apoE is synthesized and released by astrocytes and taken up by neurons following injury.

Altered beta-APP metabolism after head injury and its relationship to the aetiology of Alzheimer's disease

There is increasing evidence of a link between head injury and the subsequent onset of Alzheimer's disease. Deposits of amyloid beta-protein (A beta) are found not only in cases of dementia pugilistica but in some 30% of patients dying after a single episode of severe head injury. Detailed clinicopathological studies have shown that A beta deposition is most likely, but not exclusively, to occur, the older the patient at the time of injury, and if the injury is the result of a fall. Distribution studies have shown that the A beta is widely deposited in the neocortex and there is no apparent association with any of the multiple primary or secondary pathologies of traumatic brain injury. There is an increased expression of beta-APP particularly in the pre-alpha cells of the entorhinal cortex and in areas of axonal damage. Recent molecular genetic studies have shown that there is a strong association between deposits of A beta and the apolipoprotein E genotype of the individual.

Immunohistochemical study of apolipoprotein E in human cerebrovascular white matter lesions

In the brains of ine cases with cerebrovascular disease, one with mixed dementia, one with amyloid angiopathy and two non-neurological controls, we found three cases with focal accumulation of apolipoprotein E (apo-E) in dystrophic axons and accompanying macrophages. Since amyloid precursor protein (APP) and chromogranin A (CgA) accumulate after axonal damages, and are sensitive markers of the white matter lesions, the regional distribution of apo-E was compared to that of APP and CgA. apo-E-immunoreactive axons were present in the periphery of an infarction with neighboring macrophages, but not in mild white matter lesions that contained APP- or CgA-immunoreactive fiber bundles. The results suggest a role of apo-E in recycling cholesterol and other membrane components via macrophages into remodeling neurites in the brain, but this phenomenon is restricted to the periphery of infarction and may be less prominent than in the peripheral nervous system.

Ischemic stress induces deposition of amyloid beta immunoreactivity in human brain

The histoblot immunostaining technique for locating and characterizing amyloidogenic proteins was used to obtain information about the relationship of cerebral ischemia/hypoxia to the accumulation of amyloid beta protein (A beta). We investigated brains of 131 subjects (ages 25-94 years, mean 72 years). Three distribution patterns of A beta immunoreactivity were identified: (1) colocalization with diffuse and neuritic plaques of Alzheimer's disease (AD) and aging; (2) diffuse punctuate deposits in the cerebral cortex in association with small vessel cerebral vascular disease ; and (3) cerebral cortical accumulation localized to arterial boundary zones and other regions susceptible to ischemic/hypoxic injury designated "stress-induced deposits" (SID). SID were not identified in tissue sections by immunohistochemical, Congo red or Bielschowsky silver techniques; no histological abnormalities were present in adjacent formalin-fixed tissue sections, SID occurred in subjects with histories of cerebral ischemia, and severe orthostatic hypotension. There was also an association with aging in general and with the incidence of neuritic plaques specifically. These latter findings are consistent with the hypothesis that brain ischemia/hypoxia plays a role in the pathogenesis of AD.

Accumulation of amyloid precursor protein-like immunoreactivity in rat brain in response to thiamine deficiency

Thiamine deficiency (TD) is a classical model of impaired cerebral oxidation. As in Alzheimer's disease (AD), TD is characterized by selective neuronal loss, decreased activities of thiamine pyrophosphate-dependent enzymes, cholinergic deficits and memory loss. Amyloid beta-protein (A beta), a approximately 4 kDa fragment of the beta-amyloid precursor protein (APP), accumulates in the brains of patients with AD or Down's syndrome. In the current study, we examined APP and A beta immunoreactivity in the brains of thiamine-deficient rats. Animals received thiamine-deficient diet ad libitum and daily injections of the thiamine antagonist, pyrithiamine. Immunocytochemical staining and immunoblotting utilized a rabbit polyclonal antiserum against human APP645-694 (numbering according to APP695 isoform). Three, 6 and 9 days of TD did not appear to damage any brain region nor change APP-like immunoreactivity. However, 13 days of TD led to pathological lesions mainly in the thalamus, mammillary body, inferior colliculus and some periventricular areas. While immunocytochemistry and thioflavine S histochemistry failed to show fibrillar beta-amyloid, APP-like immunoreactivity accumulated in aggregates of swollen, abnormal neurites and perikarya along the periphery of the infarct-like lesion in the thalamus and medial geniculate nucleus. Immunoblotting of the thalamic region around the lesion revealed increased APP-like holoprotein immunoreactivity. APP-like immunoreactive neurites were scattered in the mammillary body and medial vestibular nuclei where the lesion did not resemble infarcts. In the inferior colliculus, increased perikaryal APP-like immunostaining occurred in neurons surrounding necrotic areas. Regions without apparent pathological lesions showed no alteration in APP-like immunoreactivity. Thus, the oxidative insult associated with cell loss, hemorrhage and infarct-like lesions during TD leads to altered APP metabolism. This is the first report to show a relationship between changes in APP expression, oxidative metabolism and selective cell damage caused by nutritional/cofactor deficiency. This model appears useful in defining the role of APP in the reponse to central nervous system injury, and may also be relevant to the pathophysiology of Wernicke-Korsakoff syndrome and AD.

Ultrastructural localization of amyloid protein precursor in the normal and postischemic gerbil brain

Intracellular localization of amyloid protein precursor (APP) in the normal and postischemic gerbil brain was examined by immunoelectron microscopy. In the normal brain, APP immunoreactivity was localized to the multivesicular body, the nuclear membrane, Golgi apparatus and rough endoplasmic reticulum. After ischemia for 5 min and reperfusion for 24 h, some neurons became intensely immunoreactive for APP in the subiculum and CA3 region of the hippocampus and layers III and V/VI of the cerebral cortex. No intense labeling occurred in glial cells. Intensely labeled neurons were characterized by eccentric nuclei and accumulation of cellular organelles in the center of the neuronal perikarya, as well as a strongly immunoreactive nuclear membrane and cisternal structures, which were presumed to be dispersed Golgi apparatus and/or fragmented rough ER. APP immunoreactivity in the multivesicular body suggests re-internalization of APP and its degradation in the endosomal-lysosomal pathway. The ultrastructural features of neurons with intense APP immunoreactivity suggested mild neuronal damage, similar to those found in central chromatolysis. This indicates that accumulation of APP in these neurons is caused by disturbance of axonal transport, although the information does not allow us to exclude the possibility of an increase in APP production.