beta A4 amyloid protein deposition in brain after head trauma

Amyloid beta accumulation in axons after traumatic brain injury in humans

OBJECT

Although plaques composed of amyloid beta (AD) have been found shortly after traumatic brain injury (TBI) in humans, the source for this Abeta has not been identified. In the present study, the authors explored the potential relationship between Abeta accumulation in damaged axons and associated Abeta plaque formation.

METHODS

The authors performed an immunohistochemical analysis of paraffin-embedded sections of brain from 12 patients who died after TBI and from two control patients by using antibodies selective for Abeta peptides, amyloid precursor protein (APP), and neurofilament (NF) proteins. In nine brain-injured patients, extensive colocalizations of Abeta, APP, and NF protein were found in swollen axons. Many of these immunoreactive axonal profiles were present close to Abeta plaques or were surrounded by Abeta staining, which spread out into the tissue. Immunoreactive profiles were not found in the brains of the control patients.

CONCLUSIONS

The results of this study indicate that damaged axons can serve as a large reservoir of Abeta, which may contribute to Abeta plaque formation after TBI in humans.

Expanding the association between the APOE gene and the risk of Alzheimer's disease: possible roles for APOE promoter polymorphisms and alterations in APOE transcription

Alzheimer's disease (AD) is the most commonly diagnosed form of dementia in the elderly. Predominantly this disease is sporadic in nature with only a small percentage of patients exhibiting a familial trait. Early-onset AD may be explained by single gene defects; however, most AD cases are late onset (> 65 years) and, although there is no known definite cause for this form of the disease, there are several known risk factors. Of these, the epsilon4 allele of the apolipoprotein E (apoE) gene (APOE) is a major risk factor. The epsilon4 allele of APOE is one of three (epsilon2 epsilon3 and epsilon4) common alleles generated by cysteine/arginine substitutions at two polymorphic sites. The possession of the epsilon 4 allele is recognized as the most common identifiable genetic risk factor for late-onset AD across most populations. Unlike the pathogenic mutations in the amyloid precursor or those in the presenilins, APOE epsilon4 alleles increase the risk for AD but do not guarantee disease, even when present in homozygosity. In addition to the cysteine/arginine polymorphisms at the epsilon2/epsilon3/epsilon4 locus, polymorphisms within the proximal promoter of the APOE gene may lead to increased apoE levels by altering transcription of the APOE gene. Here we review the genetic and biochemical evidence supporting the hypothesis that regulation of apoE protein levels may contribute to the risk of AD, distinct from the well known polymorphisms at the epsilon2/epsilon3/epsilon4 locus.

Apolipoprotein E4 influences amyloid deposition but not cell loss after traumatic brain injury in a mouse model of Alzheimer's disease

The epsilon4 allele of apolipoprotein E (APOE) and traumatic brain injury (TBI) are both risk factors for the development of Alzheimer's disease (AD). These factors may act synergistically, in that APOE4+ individuals are more likely to develop dementia after TBI. Because the mechanism underlying these effects is unclear, we questioned whether APOE4 and TBI interact either through effects on amyloid-beta (Abeta) or by enhancing cell death/tissue injury. We assessed the effects of TBI in PDAPP mice (transgenic mice that develop AD-like pathology) expressing human APOE3 (PDAPP:E3), human APOE4 (PDAPP:E4), or no APOE (PDAPP:E-/-). Mice were subjected to a unilateral cortical impact injury at 9-10 months of age and allowed to survive for 3 months. Abeta load, hippocampal/cortical volumes, and hippocampal CA3 cell loss were quantified using stereological methods. All of the groups contained mice with Abeta-immunoreactive deposits (56% PDAPP:E4, 20% PDAPP:E3, 75% PDAPP:E-/-), but thioflavine-S-positive Abeta (amyloid) was present only in the molecular layer of the dentate gyrus in the PDAPP:E4 mice (44%). In contrast, our previous studies showed that in the absence of TBI, PDAPP:E3 and PDAPP:E4 mice have little to no Abeta deposition at this age. After TBI, all of the Abeta deposits present in PDAPP:E3 and PDAPP:E-/- mice were diffuse plaques. In contrast to the effect of APOE4 on amyloid, PDAPP:E3, PDAPP:E4, and PDAPP:E-/- mice did not differ in the amount of brain tissue or cell loss. These data support the hypothesis that APOE4 influences the neurodegenerative cascade after TBI via an effect on Abeta.

Changes in expression of amyloid precursor protein and interleukin-1beta after experimental traumatic brain injury in rats

There is increasing evidence linking neurodegenerative mechanisms in Alzheimer's disease (AD) and traumatic brain injury (TBI), including increased production of amyloid precursor protein (APP), and amyloid-beta (Abeta) peptide. In vitro data indicate that expression of APP may be regulated in part by the inflammatory cytokine IL-1beta. To further investigate the mechanisms involved, we measured APP and IL-1beta protein levels and examined immunohistochemical localization of APP in brain tissue from rats subjected to controlled cortical impact (CCI) injury. Animals were examined at time intervals ranging from 3 h to 4 weeks after TBI. The 24-h time point revealed a dramatic increase in APP immunoreactivity, detected with both N- and C-terminal antibodies, in the hippocampus and cortex ipsilateral to injury. This finding was sustained up to 3 days post-injury. At these early time points, APP increase was particularly robust in the white matter axonal tracts. By 14 days after injury, APP immunoreactivity was not significantly different from sham controls in cortex, but remained slightly elevated in hippocampus. Western blot data corroborated early increases in hippocampal and cortical APP in injured versus control animals. Despite profound APP changes, no Abeta deposits were observed at any time after injury. Hippocampal and cortical IL-1beta increases were even more robust, with IL-1beta levels peaking by 6 h post-injury and returning to baseline by 24-72 h. Our results demonstrate that both APP and IL-1beta are rapidly elevated after injury. Because of the rapidity in the IL-1beta peak increase, it may serve a role in regulation of APP expression after TBI.

Long-term accumulation of amyloid-beta in axons following brain trauma without persistent upregulation of amyloid precursor protein genes

Brain trauma has been shown to be a risk factor for developing Alzheimer disease (AD), and AD-like plaques containing amyloid-beta (Abeta) peptides have been found in the brain shortly following trauma. Here, we evaluated the effects of brain trauma on the accumulation of Abeta and expression of amyloid precursor protein (APP) genes (APP695 and APP751/ 770) over 1 yr in a non-transgenic rodent model. Anesthetized male Sprague-Dawley rats were subjected to parasagittal fluid percussion brain injury of moderate severity (2.5-2.9 atm) or sham treatment and their brains were evaluated at 2, 4, 7, 14 days, and 1, 2, 6, 12 months following injury. Immunohistochemical analysis detected only weak Abeta staining by 2 wk following injury. However, by 1 month to 1 yr following injury, strong immunoreactivity for Abeta was found in damaged axons throughout the thalamus and white matter. Western blot analysis confirmed the accumulation of Abeta peptides in tissue from injured brains. Although in situ hybridization demonstrated an increased gene expression of APP751/770 surrounding the cortical lesion at 2 to 7 days following injury, this expression returned to baseline levels at all subsequent time points and no increase in the expression of APP695 was detected at any time point. These results demonstrate that long-termAbeta accumulation in damaged axons can be induced in a non-transgenic rodent model of brain trauma. Surprisingly, the extent of this Abeta production appeared to be dependent on the maturity of the injury, but uncoupled from the gene expression of APP. Together, these data suggest a mechanism that may contribute to long-term neurodegeneration following brain trauma.

Neuroinflammation in Alzheimer's disease and prion disease

Alzheimer's disease (AD) and prion disease are characterized neuropathologically by extracellular deposits of Abeta and PrP amyloid fibrils, respectively. In both disorders, these cerebral amyloid deposits are co-localized with a broad variety of inflammation-related proteins (complement factors, acute-phase protein, pro-inflammatory cytokines) and clusters of activated microglia. The present data suggest that the cerebral Abeta and PrP deposits are closely associated with a locally induced, non-immune-mediated chronic inflammatory response. Epidemiological studies indicate that polymorphisms of certain cytokines and acute-phase proteins, which are associated with Abeta plaques, are genetic risk factors for AD. Transgenic mice studies have established the role of amyloid associated acute-phase proteins in Alzheimer amyloid formation. In contrast to AD, there is a lack of evidence that cytokines and acute-phase proteins can influence disease progression in prion disease. Clinicopathological and neuroradiological studies have shown that activation of microglia is a relatively early pathogenetic event that precedes the process of neuropil destruction in AD patients. It has also been found that the onset of microglial activation coincided in mouse models of prion disease with the earliest changes in neuronal morphology, many weeks before neuronal loss and subsequent clinical signs of disease. In the present work, we review the similarities and differences between the involvement of inflammatory mechanisms in AD and prion disease. We also discuss the concept that the demonstration of a chronic inflammatory-like process relatively early in the pathological cascade of both diseases suggests potential therapeutic strategies to prevent or to retard these chronic neurodegenerative disorders.

Intraneuronal amyloid precursor protein (APP) and appearance of extracellular beta-amyloid peptide (abeta) in the brain of aging kokanee salmon

Antibodies to human amyloid precursor protein (APP(695)) and beta-amyloid peptide (A beta(1-42)) were used to determine timing of amyloidosis in the brain of kokanee salmon (Oncorhynchus nerka kennerlyi) in one of four reproductive stages: immature (IM), maturing (MA), sexually mature (SM), and spawning (SP), representing a range of aging from somatically mature but sexually immature to spawning and somatic senescence. In IM fish, immunoreactive (ir) intracellular APP occurred in 18 of 23 brain regions. During sexual maturation and aging, the number of neurons expressing APP increased in 11 of these APP-ir regions. A beta-ir was absent in IM fish, present in seven regions in MA fish, moderately abundant in 15 regions in SM fish, and was most abundant in all brain regions of SP fish exhibiting A beta-ir. Intracellular APP-ir was observed in brain regions involved in sensory integration, olfaction, vision, stress responses, reproduction, and coordination. Intra- and extracellular A beta(1-42) immunoreactivity (A beta-ir) was present in all APP-ir regions except the nucleus lateralis tuberis (hypothalamus) and Purkinje cells (cerebellum). APP-ir and A beta deposition increase during aging. APP-ir is present in IM fish; A beta-ir usually appears first in MA or SM fish and increases in SM fish as does APP-ir. Extracellular A beta deposition dramatically increases between SM and SP stages (1-2 weeks) in all fish, indicating an extremely rapid and synchronized process. Rapid senescence observed in pacific salmon could make them a useful model to investigate timing of amyloidosis and neurodegeneration during brain aging.

Timing of neurodegeneration and beta-amyloid (Abeta) peptide deposition in the brain of aging kokanee salmon

Brains of kokanee salmon (Oncorhynchus nerka kennerlyi) in one of four reproductive stages (sexually immature, maturing, sexually mature, and spawning) were stained with cresyl violet and silver stain to visualize neurodegeneration. These reproductive stages correlate with increasing somatic aging of kokanee salmon, which die after spawning. Twenty-four regions of each brain were examined. Brains of sexually immature fish exhibited low levels of neurodegeneration, whereas neurodegeneration was more marked in maturing fish and greatest in spawning fish. Neurodegeneration was present in specific regions of the telencephalon, diencephalon, mesencephalon, and rhombencephalon. Pyknotic neurons were observed in all regions previously reported to be immunopositive for A beta. Regions that did not exhibit neurodegeneration during aging included the magnocellular vestibular nucleus, the nucleus lateralis tuberis of the hypothalamus, and Purkinje cells of the cerebellum, all of which also lack A beta; perhaps these regions are neuroprotected. In 14 of 16 brain areas for which data were available on both the increase in A beta deposition and pyknosis, neurodegeneration preceded or appeared more or less simultaneously with A beta production, whereas in only two regions did A beta deposition precede neurodegeneration. This information supports the hypothesis that A beta deposition is a downstream product of neurodegeneration in most brain regions. Other conclusions are that the degree of neurodegeneration varies among brain regions, neurodegeneration begins in maturing fish and peaks in spawning fish, the timing of neurodegeneration varies among brain regions, and some regions do not exhibit accelerated neurodegeneration during aging.

Senile plaque composition and posttranslational modification of amyloid-beta peptide and associated proteins

Amyloid deposits are primarily composed of the amyloid-beta protein, although other proteins (and metal ions) also have been colocalized to these lesions. The pattern of oxidative modifications in amyloid plaques is very different to that associated with neurofibrillary tangles and neuronal cell bodies, likely reflecting the different composition of these structures, accessibility of oxidants, the generation of oxidants in and around these structures and the intrinsic antioxidant defense systems to protect these structures. Future studies directed at understanding Abeta interactions with other amyloid components, the role of oxidative modifications in stabilizing amyloid deposits and the determination of protease cleavage sites on Abeta may provide mechanistic insights regarding both amyloid formation and removal.

Advances in the cellular and molecular biology of the beta-amyloid protein in Alzheimer's disease

Alzheimer's disease (AD) is a progressive senile dementia characterized by deposition of a 4 kDa peptide of 39-42 residues known as amyloid beta-peptide (Abeta) in the form of senile plaques and the microtubule associated protein tau as paired helical filaments. Genetic studies have identified mutations in the Abeta precursor protein (APP) as the key triggers for the pathogenesis of AD. Other genes such as presenilins 1 and 2 (PS1/2) and apolipoprotein E (APOE) also play a critical role in increased Abeta deposition. Several biochemical and molecular studies using transfected cells and transgenic animals point to mechanisms by which Abeta is generated and aggregated to trigger the neurodegeneration that may cause AD. Three important enzymes collectively known as "secretases" participate in APP processing. An enzymatic activity, beta-secretase, cleaves APP on the amino side of Abeta producing a large secreted derivative, sAPPbeta, and an Abeta-bearing membrane-associated C-terminal derivative, CTFbeta, which is subsequently cleaved by the second activity, gamma-secretase, to release Abeta. Alternatively, a third activity, alpha-secretase, cleaves APP within Abeta to the secreted derivative sAPPalpha and membrane-associated CTFalpha. The predominant secreted APP derivative is sAPPalpha in most cell-types. Most of the secreted Abeta is 40 residues long (Abeta40) although a small percentage is 42 residues in length (Abeta42). However, the longer Abeta42 aggregates more readily and was therefore considered to be the pathologically important form. Advances in our understanding of APP processing, trafficking, and turnover will pave the way for better drug discovery for the eventual treatment of AD. In addition, APP gene regulation and its interaction with other proteins may provide useful drug targets for AD. The emerging knowledge related to the normal function of APP will help in determining whether or not the AD associated changes in APP metabolism affect its function. The present review summarizes our current understanding of APP metabolism and function and their relationship to other proteins involved in AD.

Caspase-3-mediated cleavage of amyloid precursor protein and formation of amyloid Beta peptide in traumatic axonal injury

Immunohistochemical studies demonstrate accumulation of the beta-amyloid precursor protein (APP) within injured axons following traumatic brain injury (TBI). Despite such descriptions, little is known about the ultimate fate of accumulating APP at sites of traumatic axonal injury (TAI). Recently, caspase-3-mediated cleavage of APP and subsequent Abeta deposition was linked to apoptotic neuronal death pathways in hippocampal neurons following ischemic and excitotoxic brain injury. Given that (1) APP is known to accumulate within traumatically injured axons, (2) caspase-3 activation has been demonstrated in traumatic axonal injury (TAI), and (3) recent studies have identified a caspase-3 cleavage site within APP, we initiated the current investigation to determine whether caspase-3-mediated cleavage of APP occurs in TAI. We further assessed whether these events were found in relation to Abeta peptide formation. To this end, we employed antibodies targeting APP, the caspase-3-mediated breakdown product of APP proteolysis, and the Abeta peptide. Rats were subjected to impact acceleration TBI (6 h to 10 days survival), and their brains were processed for single-label bright field and multiple double-label immunofluorescent paradigms using the above antibodies. By 12 h postinjury, caspase-3-mediated APP proteolysis (CMAP) was demonstrated within the medial lemniscus (ML) and medial longitudinal fasciculus (MLF) in axons undergoing TAI, identified by their concomitant APP accumulation. Immunoreactivity for CMAP persisted up to 48 h postinjury in the ML and MLF, but was notably reduced by 10 days following injury. Further, CMAP was colocalized with Abeta formation in foci of TAI. The current study demonstrates that caspase-3 cleavage of APP occurs in TAI and is associated with formation of Abeta peptide. These findings are of interest given recent epidemiological studies supporting an association between TBI and later risk for AD development.

Alzheimer's disease: role of aging in pathogenesis

Alzheimer's disease (AD) is characterized by intraneuronal fibrillary tangles, plaques, and cell loss. Brain lesions in both sporadic AD (SAD) and familial AD (FAD) are the same, and in the same distribution pattern, as those in individuals with Down syndrome (DS) and in smaller numbers in nondemented older individuals. Dementia onset is around 40 years for DS, 40-60 years for FAD, and usually over 60 years for SAD. The different categories of AD may be due to processes that augment to different degrees the innate cellular aging rate, that is, mitochondrial superoxide radical (SO) formation. Thus, they increase the rate of accumulation of AD lesions. This lowers the age of onset into the dementia ranges associated with DS, FAD, and SAD, and concomitantly shortens life spans. Faster aging lowers AD onset age by decreasing the onset age for neurofibrillary tangle formation and neuronal loss, and the age when brain intercellular H2O2 can activate microglial cells. The early AD onset in DS is attributed to a defective mitochondrial complex 1. The proteins associated with FAD and their normal counterparts undergo proteolytic processing in the endoplasmic reticulum (ER). The mutated compounds increase the ratio of betaA42 to betaA40 and likely also down-regulate the ER calcium (Ca2+) buffering activity. Decreases in ER Ca2+ content should increase the mitochondrial Ca2+ pool, thus enhancing SO formation. SAD may be due to increased SO formation caused by mutations in the approximately 1000 genes involved in mitochondrial biogenesis and function. The hypothesis suggests measures to prevent and treat.

Low cerebrospinal fluid beta-amyloid 42 in patients with acute bacterial meningitis and normalization after treatment

CSF-A beta 42 may be a marker of Alzheimer's disease (AD). A decreased level of CSF-A beta 42 is consistently found in AD and has been suggested to be related to the deposition of amyloid plaques in the brain. However, low CSF-A beta 42 levels have also been found in disorders devoid of plaques, for instance Creutzfeldt-Jakob disease. To examine if the level of A beta 42 in CSF is related to inflammatory processes, we studied CSF-A beta 42 levels in eight patients with acute purulent bacterial meningitis, 10 patients with acute viral meningitis and 18 age-matched controls. In acute purulent bacterial meningitis, the CSF-A beta 42 level was markedly reduced (28% of that in controls, P<0.0001), whereas no change was found in viral meningitis. After successful treatment of bacterial meningitis, the CSF-A beta 42 level increased (P<0.05 compared to baseline) and did no longer differ from that in controls (ns). The decrease could not be explained by interference with high protein levels, since addition of increasing volumes of serum did not influence the CSF-A beta 42 levels. Our findings suggest that the reduction in CSF-A beta 42 found in bacterial meningitis is not a direct consequence of the inflammatory process. The cause may be disturbance of the clearance of A beta 42 from the brain.

Delayed hemispheric neuronal loss in severely head-injured patients

Recent experimental studies have revealed that traumatic brain injury as well as ischemic brain injury can cause chronic progressive neuronal damage. In the present study, we demonstrate previously unreported delayed cerebral atrophy on computerized tomography (CT) scans in severely head-injured patients. Seventeen severely head-injured patients who required mild hypothermia to control intracranial hypertension after the failure of conventional therapies were retrospectively analyzed. All 17 patients survived more than 1 year. Delayed neuronal loss (DNL) was observed in only eight of the 17 patients. Eight patients with DNL required longer durations of mild hypothermia to control intracranial hypertension than nine patients without DNL. Six of these eight patients with DNL achieved functional recovery despite progressive atrophic changes demonstrated on CT scans. On CT scans, DNL was characterized by (1) the sudden appearance at several months postinjury of a low-density area in the hemisphere ipsilateral to the injury; (2) the preservation of essential cortical structure although related white matter structures showed severe atrophic changes; and (3) no spread of the low-density area to the contiguous territory of the other main cerebral artery. It is concluded that focal primary injury to underlying brain, if severe enough, can result in delayed hemispheric atrophy.

Upregulation of neuronal amyloid precursor protein (APP) and APP mRNA following magnesium sulphate (MgSO4) therapy in traumatic brain injury

The aim of this study was to assess and quantitate topographically the effects of posttraumatic intravenous magnesium sulphate (MgSO4) on neuronal perikaryal APP antigen and messenger RNA (mRNA) expression in sheep brains 2 h after a controlled focal head impact. The percentage brain area with APP immunoreactive neuronal perikarya was 71, 56, 27.5 and 5.5%, respectively, in MgSO4-treated head-injured animals, head-injured animals without any treatment, MgSO4 treated nonimpacted animals, and nontreated nonimpacted control sheep. Although there was no statistically significant difference in APP immunoreactive neuronal perikarya in the MgSO4-treated HI group (mean 71%) compared to the HI group without any treatment (mean 56%), northern analysis showed that there was a 2.3-+/-0.2-fold increase in APP mRNA in the thalamus of treated impacted animals compared to untreated impacted animals (p < 0.005). However, MgSO4 treated nonimpacted control animals also showed a 1.6-+/-0.1-fold increase in APP mRNA compared to untreated nonimpacted controls (p < 0.005). MgSO4 therapy results in upregulation of neuronal APP mRNA and APP expression that is quantitatively greater following a focal head impact.

Lower cognitive performance of older football players possessing apolipoprotein E epsilon4

OBJECTIVE

To determine whether the cognitive status of professional football players varies as a function of age and apolipoprotein E (APOE) genotype.

METHODS

Fifty-three active players underwent APOE and neuropsychological assessments. Players were grouped according to age (proxy indicator of high/low exposure to contact) and the presence/absence of at least one copy of the epsilon4 allele. Outcome measures were overall cognitive performance and scores in cognitive domains.

RESULTS

As a group, older players possessing APOE epsilon4 exhibited significantly lower cognitive test scores than did all other players studied, including non-epsilon4-possessing players and younger epsilon4-carriers. Measures of general cognitive functioning, information-processing speed and accuracy, and attention were related to poorer performance among the epsilon4-carrying players. In an analysis of variance model, the interaction between APOE genotype and age was significant (P = 0.004). As determined using linear regression, age accounted for 34% of the variance in the memory index among APOE epsilon4-possessing players but did not contribute significantly to variance among the non-epsilon4-possessing players. Older APOE epsilon4-carriers were significantly overrepresented among players whose scores indicated possible cognitive impairment, with the criterion of performing two or more standard deviations below the general normal values in a summary index of general cognitive functioning.

CONCLUSION

Older professional football players who possessed the APOE epsilon4 allele scored lower on cognitive tests than did players without this allele or less experienced players of any genotype. The cognitive status of professional athletes with repeated exposure to head trauma may therefore be influenced by age, inherited factors such as APOE genotype, and cumulative exposure to contact.

Alzheimer's disease: A hypothesis on pathogenesis

Alzheimer's disease (AD) is the major cause of dementia. It is a systemic disorder whose major manifestations are in the brain. AD cases can be categorized into two groups on the basis of the age of onset-before or after about age 60. The majority of cases, 90-95 percent, are in the late onset category. Early onset cases are largely, if not all, familial (FAD). These are caused by mutations in the genes for the amyloid precursor protein (APP), presenilin 1 (PS1), and presenilin 2 (PS2). In contrast late onset cases are mainly sporadic. The disorder is characterized by intraneuronal fibrillary tangles, plaques, and cell loss. The brain lesions in both early and late-onset AD are the same, and in the same distribution pattern, as those seen in individuals with Down's syndrome (DS) and in smaller numbers in normal older individuals. Extensive studies of AD have yet to result in a generally accepted hypothesis on the pathogenesis of the disorder. Major emphasis has been placed on the role of amyloid, the neurotoxin formed by the action of free radicals on preamyloid. The observation that AD lesions are frequently present in normal older individuals prompted the hypothesis that AD is the result of faster than normal aging of the neurons associated with it. This hypothesis provides plausible explanations for FAD and AD. FAD is associated with mutations in APP, PS1, and PS2. These substances, along with their normal counterparts, undergo proteolytic processing in the endoplasmic reticulum (ER). The mutated compounds, aside from increasing the ratio of βA42 to βA40, may down-regulate the calcium buffering activity of the ER in a manner akin to one or more of the many compounds known to do so. Decreases in the ER calcium pool would cause compensatory increases in other calcium pools, particularly in mitochondria. Increases in mitochondrial calcium levels are associated with enhanced formation of superoxide radical formation, and hence of the rate of aging. SAD may be caused by nuclear and/or mitochondrial DNA mutations beginning early in life that enhance mitochondrial superoxide radical formation in the neurons associated with the disorder. The above explanations for FAD and AD are suggestive of measures to prevent and for treatment.

Does human betaA4 exert a protective function against oxidative stress in Alzheimer's disease?

The hypothesis is advanced that human betaA4--as opposed to rodent betaA4--may exert a protective function against the iron-induced oxidative stress associated with neurological diseases (notably Alzheimer's disease). Subsequent to its release by the host in response to oxidative injury, human betaA4 would interact with Cu(2+)ions whose level is correlatively elevated, adopting the 'aggregated' structure recently characterized by Atwood et al.(15). Then, depending on the oxidative state--hence the pH--of the medium, it might either return to its original structure if physiological pH is restored, or undergo site-specific copper-mediated oxidation and, finally, degradation. In this context, betaA4 pathogenicity could be due to an interfering mechanism preventing the degradation of the oxidized peptide, making its aggregation irreversible and inducing its final deposition. Coordination of side group oxygen donors of the oxidized peptide with 'hard' metal ions occurring in the physiological medium (notably Al(3+)) might be at the origin of this interference.

The role of apolipoprotein E in Alzheimer's disease, acute brain injury and cerebrovascular disease: evidence of common mechanisms and utility of animal models

The epsilon 4 allele of apolipoprotein E (APOE denotes gene; apoE denotes protein) is a major risk factor for Alzheimer's disease (AD). More recent evidence indicates an association with a poor outcome after acute brain injury including that due to head trauma and intracerebral hemorrhage. APOE gene polymorphism also influences the risk of hemorrhage in cerebral amyloid angiopathy. These diverse brain disorders seem to have some mechanisms in common. The multiplicity of the roles of apoE within the central nervous system is currently being unraveled. For example, apoE can interact with amyloid beta-protein and tau, proteins central to the pathogenesis of AD. In addition to these effects, it is proposed that one of the major functions of apoE is to mediate neuronal protection, repair and remodeling. In all of the different roles proposed, there are marked apoE-isoform specific differences. Although it remains to be clarified which is the most important mechanism(s) in each disorder in which apoE is involved, these isoform specific differences seem to underly a genetically determined susceptibility to outcome from acute brain injury and to AD with APOE epsilon 4 conferring relative vulnerability. This review focuses on apoE research, from clinical studies to animal models, in AD, acute brain injury and cerebrovascular disease and explores the common mechanisms that may explain some of the complex underlying neurobiology.

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.

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.

A unifying hypothesis of Alzheimer's disease. III. Risk factors

Normal ageing and Alzheimer's disease (AD) have many features in common and, in many respects, both conditions only differ by quantitative criteria. A variety of genetic, medical and environmental factors modulate the ageing-related processes leading the brain into the devastation of AD. In accordance with the concept that AD is a metabolic disease, these risk factors deteriorate the homeostasis of the Ca(2+)-energy-redox triangle and disrupt the cerebral reserve capacity under metabolic stress. The major genetic risk factors (APP and presenilin mutations, Down's syndrome, apolipoprotein E4) are associated with a compromise of the homeostatic triangle. The pathophysiological processes leading to this vulnerability remain elusive at present, while mitochondrial mutations can be plausibly integrated into the metabolic scenario. The metabolic leitmotif is particularly evident with medical risk factors which are associated with an impaired cerebral perfusion, such as cerebrovascular diseases including stroke, cardiovascular diseases, hypo- and hypertension. Traumatic brain injury represents another example due to the persistent metabolic stress following the acute event. Thyroid diseases have detrimental sequela for cerebral metabolism as well. Furthermore, major depression and presumably chronic stress endanger susceptible brain areas mediated by a host of hormonal imbalances, particularly the HPA-axis dysregulation. Sociocultural and lifestyle factors like education, physical activity, diet and smoking may also modulate the individual risk affecting both reserve capacity and vulnerability. The pathophysiological relevance of trace metals, including aluminum and iron, is highly controversial; at any rate, they may adversely affect cellular defences, antioxidant competence in particular. The relative contribution of these factors, however, is as individual as the pattern of the factors. In familial AD, the genetic factors clearly drive the sequence of events. A strong interaction of fat metabolism and apoE polymorphism is suggested by intercultural epidemiological findings. In cultures, less plagued by the 'blessings' of the 'cafeteria diet-sedentary' Western lifestyle, apoE4 appears to be not a risk factor for AD. This intriguing evidence suggests that, analogous to cardiovascular diseases, apoE4 requires a hyperlipidaemic lifestyle to manifest as AD risk factor. Overall, the etiology of AD is a key paradigm for a gene-environment interaction. Copyright 2000 John Wiley & Sons, Ltd.

Prolonged activation of NF-kappaB following traumatic brain injury in rats

Activation of transcription factor, nuclear factor kappa B (NF-kappaB), has been shown to play a key role in inflammatory response, neuronal survival and signaling. We investigated the regional and temporal distribution of activated NF-kappaB in rats at 1 h, 2 h, 24 h, 48 h, 1 week, 2 weeks, 1 month, 2 months, 6 months, and 1 year following brain injury in rats. Early after trauma (1-2 h), activated NF-kappaB was detected in axons, and subsequently found in the cytoplasm and nucleus of neurons by 24 h and lasting up to 1 week. In addition, by 24 h posttrauma, activated NF-kappaB was detected in microglia/macrophages and astrocytes in injured cortex. Surprisingly, this activation persisted for at least 1 year following injury in the cortex, primarily at the margins of progressively enlarging ventricle. Activated NF-kappaB was also detected in endothelial cells, as early as 1 h, and persisted for up to 1 year. These results suggest that a neuronal response to brain trauma includes the activation of NF-kappaB first in the axon with subsequent translocation to the nucleus. Furthermore, these results demonstrate that remarkably prolonged activation of NF-kappaB in glia is found in the same regions undergoing persistent atrophy, suggesting NF-kappaB activation may play a role in long-term inflammatory processes following brain trauma.

Upregulation of amyloid precursor protein messenger RNA in response to traumatic brain injury: an ovine head impact model

There is evidence that the amyloid precursor protein (APP) plays an important role in neuronal growth and synaptic plasticity and that its increased expression following traumatic brain injury represents an acute phase response to trauma. We hypothesized that the previously described increased APP expression in response to injury (Van den Heuvel et al., Acta Neurochir. Suppl. 71, 209-211) is due to increased mRNA expression and addressed this by examining the expression of APP mRNA and APP within neuronal cell bodies over time in an ovine head impact model. Twenty-five anesthetized and ventilated 2-year-old Merino ewes sustained a left temporal head impact using a humane stunner and 9 normal sheep were used as nonimpact controls. Following postimpact survival periods of 15, 30, 45, 60, and 120 min, brains were perfusion fixed in 4% paraformaldehyde and examined according to standard neuropathological protocol. APP mRNA and antigen expression were examined in 5-microm sections by nonisotopic in situ hybridization and APP immunocytochemistry. The percentage of brain area with APP immunoreactivity within neuronal cell bodies in the impacted animals increased with time from a mean of 7.5% at 15 min to 54.5% at 2 h. Control brains showed only very small numbers of weakly APP-positive neuronal cell bodies ranging from 2 to 14% (mean 7%). Increased expression of APP mRNA was first evident in impacted hemispheres at 30 min after impact and progressively increased over time to involve neurons in all sampled regions of the brain, suggesting increased transcription of APP. In contrast, APP mRNA was undetectable in tissue from nonimpacted sheep. These data show that APP mRNA and antigen expression are sensitive early indicators of neuronal injury with widespread upregulation occurring as early as 30 min after head impact.

Herpes simplex virus type 1 and Alzheimer's disease

Until recently, the only risk factors implicated in noninherited cases of Alzheimer's disease were increasing age, Down's syndrome, and probably, head injury. Having found that herpes simplex type 1 virus (HSV1) is present in the brain of many elderly people, we discovered that it is a risk factor for Alzheimer's disease when in the central nervous system of APOE-epsilon4 allele carriers. On the basis of this result and our finding that apoE-epsilon4 is a risk factor for herpes labialis, we suggested that the combination of virus and genetic factor is particularly damaging in the nervous system. The present review describes 1) the search for HSV1 in human brain; 2) HSV1 infection of the peripheral nervous system; 3) HSV1 infection of the central nervous system; 4) how APOE genotype might influence HSV1 infection; 5) possible APOE genotype effect on viral latency and its reactivation; 6) interactions of viruses with lipoproteins, their components, and lipoprotein receptors; 7) the role of APOE in repair; 8) pathological processes in AD and their relationship to prior damage; and 9) implications for the prevention or treatment of Alzheimer's disease.

Translation of the alzheimer amyloid precursor protein mRNA is up-regulated by interleukin-1 through 5'-untranslated region sequences

The amyloid precursor protein (APP) has been associated with Alzheimer's disease (AD) because APP is processed into the beta-peptide that accumulates in amyloid plaques, and APP gene mutations can cause early onset AD. Inflammation is also associated with AD as exemplified by increased expression of interleukin-1 (IL-1) in microglia in affected areas of the AD brain. Here we demonstrate that IL-1alpha and IL-1beta increase APP synthesis by up to 6-fold in primary human astrocytes and by 15-fold in human astrocytoma cells without changing the steady-state levels of APP mRNA. A 90-nucleotide sequence in the APP gene 5'-untranslated region (5'-UTR) conferred translational regulation by IL-1alpha and IL-1beta to a chloramphenicol acetyltransferase (CAT) reporter gene. Steady-state levels of transfected APP(5'-UTR)/CAT mRNAs were unchanged, whereas both base-line and IL-1-dependent CAT protein synthesis were increased. This APP mRNA translational enhancer maps from +55 to +144 nucleotides from the 5'-cap site and is homologous to related translational control elements in the 5'-UTR of the light and and heavy ferritin genes. Enhanced translation of APP mRNA provides a mechanism by which IL-1 influences the pathogenesis of AD.

Is there a genetic basis for the deposition of beta-amyloid after fatal head injury?

1. Alzheimer's disease is a heterogeneous disorder that may be caused by genetic or environmental factors or by a combination of both. Abnormalities in chromosomes 1, 14, and 21 have all been implicated in the pathogenesis of the early-onset form of the disease, while the epsilon 4 allele of the apolipoprotein E gene (on chromosome 19) is now recognized as a risk factor for early- and late-onset sporadic and familial Alzheimer's disease. 2. The best-established environmental trigger for the disease is a head injury, based on epidemiological and neuropathological evidence. Approximately 30% of patients who die after a single episode of severe head injury show intracerebral deposition of beta-amyloid protein (A beta), a protein that is thought to be central to the pathogenesis of Alzheimer's disease. 3. Recent studies have revealed an over-representation of the apoE epsilon 4 allele in those head-injured patients displaying A beta pathology, thus providing the first evidence for a link between a genetic susceptibility (apoE epsilon 4) and an environmental trigger (head injury) in the development of Alzheimer-type pathology.

Increased interleukin-6 expression by microglia from brain of aged mice

Over expression of inflammatory cytokines in the brain may establish a state that is permissive to the onset of neurodegenerative disease. Because the occurrence of certain neurodegenerative diseases increases with age, in the present study we examined the expression of the inflammatory cytokine, interleukin-6 (IL-6), in the brain of aged mice. In an initial experiment, IL-6 was measured in crude protein extracts from brains of juvenile (1-month-old), adult (3-month-old), and aged (24-month-old) male BALB/c mice. The concentration of IL-6 in crude protein extracts from the cerebellum, cerebral cortex, and hippocampus increased with age. The increase in IL-6 was discrete, as levels in the hypothalamus were not age-dependent. To begin evaluating spontaneous IL-6 production in aging, glial cells were cultured from brains of neonate, adult, and aged mice. An age-associated increase in IL-6 mRNA and supernatant IL-6 concentration was evident, indicating glia from aged mice spontaneously express high levels of IL-6 relative to glia from adult and neonate mice. Flow cytometric analysis revealed that cultures established from aged brain compared to either adult or neonate brain comprised more microglia (i.e., MAC-1-positive cells). Furthermore, the proportion of microglia that was positive for IL-6 increased with age, whereas the proportion of astrocytes that were positive for IL-6 was not age-dependent. The present results suggest that IL-6 increases in the mouse brain with age, and that microglia cultured from aged mice spontaneously produce more IL-6 than those from neonate or adult mice. Therefore, microglia may contribute to the increased level of IL-6 present in aged brain.

What are the facts and artifacts of the pathogenesis and etiology of Alzheimer disease?

Over the past decade, an increased clinical awareness, together with advances in biochemical, cellular, and molecular analyses, have catapulted the study of Alzheimer disease to the forefront of biomedical research. During this time, a great number of theories, regarding disease pathogenesis, have come and gone but several have persisted. Here, we critically evaluate these theories in an attempt to delineate the facts from the artifacts.

Genetics and the central nervous system: apolipoprotein E and brain injury

Apolipoprotein E (apoE), a protein produced by glial cells, is responsible for maintenance of the structural integrity of the microtubules within the axon of the neuron. The gene associated with apolipoprotein E, APOE, influences the construction and regeneration of the microtubules in an APOE allele-specific manner: APOE 2/2 may be neuroprotective, whereas APOE 4/4 may be neurodestructive. Thus, APOE appears to be one genetic factor that modifies the brain's response to insult, and therefore may modify the severity of neuropsychologic deficits. This article presents an overview of the genetic relation between APOE and neuropsychological function in Alzheimer disease and proposes a relation between APOE and recovery after head injury.

Inflammation and Alzheimer's disease: relationships between pathogenic mechanisms and clinical expression

During the past 15 years a variety of inflammatory proteins has been identified in the brains of patients with Alzheimer's disease (AD) postmortem. There is now considerable evidence that in AD the deposition of amyloid-beta (A beta) protein precedes a cascade of events that ultimately leads to a local "brain inflammatory response." Here we reviewed the evidence (i) that inflammatory mechanisms can be a part of the relevant etiological factors for AD in patients with head trauma, ischemia, and Down's syndrome; (ii) that in cerebral A beta disorders the clinical symptoms are determined to a great extent by the site of inflammation; and (iii) that a brain inflammatory response can explain some poorly understood characteristics of the clinical picture, among others the susceptibility of AD patients to delirium. The present data indicate that inflammatory processes in the brain contribute to the etiology, the pathogenesis, and the clinical expression of AD.

Enduring cognitive, neurobehavioral and histopathological changes persist for up to one year following severe experimental brain injury in rats

Clinical studies have demonstrated that patients sustain prolonged behavioral deficits following traumatic brain injury, in some cases culminating in the cognitive and histopathological hallmarks of Alzheimer's disease. However, few studies have examined the long-term consequences of experimental traumatic brain injury. In the present study, anesthetized male Sprague-Dawley rats (n = 185) were subjected to severe lateral fluid-percussion brain injury (n = 115) or sham injury (n = 70) and evaluated up to one year post-injury for cognitive and neurological deficits and histopathological changes. Compared with sham-injured controls, brain-injured animals showed a spatial learning impairment that persisted up to one year post-injury. In addition, deficits in specific neurologic motor function tasks also persisted up to one year post-injury. Immunohistochemistry using multiple antibodies to the amyloid precursor protein and/or amyloid precursor protein-like proteins revealed novel axonal degeneration in the striatum, corpus callosum and injured cortex up to one year post-injury and in the thalamus up to six months post-injury. Histologic evaluation of injured brains demonstrated a progressive expansion of the cortical cavity, enlargement of the lateral ventricles, deformation of the hippocampus, and thalamic calcifications. Taken together, these findings indicate that experimental traumatic brain injury can cause long-term cognitive and neurologic motor dysfunction accompanied by continuing neurodegeneration.

Experimental brain injury induces expression of amyloid precursor protein, which may be related to neuronal loss in the hippocampus

Previous reports have demonstrated that some focal brain injuries increase amyloid precursor protein (APP) immunoreactivity in the region surrounding the injury where it was localized, in damaged axons and in pre-alpha 2 cells of the entorhinal cortex. However, to date, APP expression in the hippocampus remote from the impact site has not been comprehensively studied. Therefore, we have evaluated APP expression not only in the locally injured cerebral cortex but also in the hippocampus remote from the impact site. In the present paper, diffuse axonal injury was induced in rats in midline fluid percussion injury. APP expression was examined post injury using Western blot analysis and immunohistochemistry. Western blot analysis demonstrated that the expression of 100-kd APP was increased in both the cerebral cortex and hippocampus 24 h after injury. It then decreased in the hippocampus, but did not change in the cerebral cortex, 7 days after injury. Immunohistochemical studies showed increased immunoreactivity of APP in the neuronal perikarya and reactive astrocytes near the region of injury in the cerebral cortex 24 h to 7 days after injury. In the hippocampus, APP accumulated in the CA3 neurons 24 h and 3 days after injury, although no hemorrhagic lesions were seen at that site. The APP positive neurons in CA3 showed shrunken cell bodies and pyknotic nuclei 3 days after injury, and some of the neurons in CA3 had disappeared by 7 days postinjury. The results of present study suggest that traumatic brain injury induces overexpression and accumulation of APP in neuronal perikarya and that these events are followed by degeneration of CA3 neurons. Further, the decline in APP expression in the hippocampus is thought to be due to neuronal loss in CA3 subsector.

Brain trauma induces massive hippocampal neuron death linked to a surge in beta-amyloid levels in mice overexpressing mutant amyloid precursor protein

Although brain trauma is a risk factor for Alzheimer's disease, no experimental model has been generated to explore this relationship. We developed a model of brain trauma in transgenic mice that overexpress mutant human amyloid precursor protein (PDAPP) leading to the appearance of Alzheimer's disease-like beta-amyloid (Abeta) plaques beginning at 6 months of age. We induced cortical impact brain injury in the PDAPP animals and their wild-type littermates at 4 months of age, ie, before Abeta plaque formation, and evaluated changes in posttraumatic memory function, histopathology, and regional tissue levels of the Abeta peptides Abeta1-40 and Abeta1-42. We found that noninjured PDAPP mice had impaired memory function compared to noninjured wild-type littermates (P < 0.01) and that brain-injured PDAPP mice had more profound memory dysfunction than brain-injured wild-type littermates (P < 0.001). Although no augmentation of Abeta plaque formation was observed in brain-injured PDAPP mice, a substantial exacerbation of neuron death was found in the hippocampus (P < 0.001) in association with an acute threefold increase in Abeta1-40 and sevenfold increase in Abeta1-42 levels selectively in the hippocampus (P < 0.01). These data suggest a mechanistic link between brain trauma and Abeta levels and the death of neurons.

The Dorothy Russell Memorial Lecture. The molecular and cellular sequelae of experimental traumatic brain injury: pathogenetic mechanisms

The mechanisms underlying secondary or delayed cell death following traumatic brain injury (TBI) are poorly understood. Recent evidence from experimental models of TBI suggest that diffuse and widespread neuronal damage and loss is progressive and prolonged for months to years after the initial insult in selectively vulnerable regions of the cortex, hippocampus, thalamus, striatum, and subcortical nuclei. The development of new neuropathological and molecular techniques has generated new insights into the cellular and molecular sequelae of brain trauma. This paper will review the literature suggesting that alterations in intracellular calcium with resulting changes in gene expression, activation of reactive oxygen species (ROS), activation of intracellular proteases (calpains), expression of neurotrophic factors, and activation of cell death genes (apoptosis) may play a role in mediating delayed cell death after trauma. Recent data suggesting that TBI should be considered as both an inflammatory and/or a neurodegenerative disease is also presented. Further research concerning the complex molecular and neuropathological cascades following brain trauma should be conducted, as novel therapeutic strategies continue to be developed.

The role of the complement system in traumatic brain injury

A traumatic impact to the brain induces an intracranial inflammatory response, which consequently leads to the development of brain edema and delayed neuronal death. Evidence from experimental, clinical, and in vitro studies highlight an important role for the complement system in contributing to inflammation within the injured brain. The present review summarizes the current understanding of the mechanisms of complement-mediated secondary brain injury after head trauma.

An region upstream of the gene promoter for the beta-amyloid precursor protein interacts with proteins from nuclear extracts of the human brain and PC12 cells

The amyloid beta-protein (Abeta) is the major proteinaceous component of the amyloid deposits that accumulate extracellularly in the brain of Alzheimer's disease (AD). Abeta is generated proteolytically from a larger beta-amyloid precursor protein (betaAPP). The apparent overexpression of the betaAPP gene in certain areas of AD brains indicate that abnormalities in gene regulation might be an important factor in AD. Here, I report that an upstream regulatory element (URE) located between -2257 to -2234 base pair (bp) of the human betaAPP promoter may interact with a novel protein(s) as determined by a gel shift assay. To determine whether this novel protein is related to an already characterized transcription factor, a gel shift assay was performed using various specific competitors in human neuroblastoma and rat pheochromocytoma (PC12) cells. The labeled URE probe could interact with a distinct nuclear factor which was not competed by the oligonucleotides specific for the different transcription factors, AP1, AP2, AP3, GRE, Oct1, NF1 and NF-kappaB. Alternatively the specific protein band(s) detected with either the labeled NF-kappaB or NF1 probe could not be competed out with an excess of unlabeled URE. To determine if such a band could be detected in human brain tissue samples, a gel shift assay from the nuclear extracts of the human brain was performed. A distinct URE-specific nuclear factor was detected in different regions of the brain as well. To determine the size of the protein(s) that were specifically bound in the DNA-protein complexes, Southwestern blotting was performed. Using the URE probe, two major protein bands of approximately 53 and 116 kDa were detected in PC12 nuclear extracts. These results suggest that the protein factor(s) interacting with URE is not related to the known transcription factors tested, and that the protein is expressed in certain cell types and different regions of the human brain.

Prevalence of Alzheimer plaques in AIDS

OBJECTIVES

Both genetic and environmental risk factors for Alzheimer's disease have been identified. The best established environmental risk factor, head trauma, is thought to act through the triggering of an inflammatory response. Another stimulus to an inflammatory response in the brain is AIDS. Whether there is an increased prevalence of beta/A4 amyloid deposits in the form of argyrophilic plaques in the brains of patients with AIDS has therefore been investigated.

METHODS

The prevalence of argyrophilic amyloid plaques in the cerebral cortex of frontal and temporal lobes was compared in 97 cases of AIDS dying at ages 30-69 years with that in 125 age matched, non-HIV infected controls.

RESULTS

In the control group, and in AIDS, the prevalence of plaques increased with age (p=0.005 and 0.048 respectively). There was a significantly greater prevalence of argyrophilic plaques in the AIDS group as a whole (29%) (p < 0.004) and in those in the fourth decade (18%) (p < 0.014) than in control subjects (13% and 0% respectively).

CONCLUSION

There is a predisposition to argyrophilic plaque formation in the brain in AIDS. The findings support the view that a stimulus to an inflammatory response in the brain favours argyrophilic plaque formation. The clinical relevance of our findings is, as yet, unclear.

Dramatic aggregation of Alzheimer abeta by Cu(II) is induced by conditions representing physiological acidosis

The cortical deposition of Abeta is an event that occurs in Alzheimer's disease, Down's syndrome, head injury, and normal aging. Previously, in appraising the effects of different neurochemical factors that impact upon the solubility of Abeta, we observed that Zn2+ was the predominant bioessential metal to induce the aggregation of soluble Abeta at pH 7.4 in vitro and that this reaction is totally reversible with chelation. We now report that unlike other biometals tested at maximal biological concentrations, marked Cu2+-induced aggregation of Abeta1-40 emerged as the solution pH was lowered from 7.4 to 6.8 and that the reaction was completely reversible with either chelation or alkalinization. This interaction was comparable to the pH-dependent effect of Cu2+ on insulin aggregation but was not seen for aprotinin or albumin. Abeta1-40 bound three to four Cu2+ ions when precipitated at pH 7.0. Rapid, pH-sensitive aggregation occurred at low nanomolar concentrations of both Abeta1-40 and Abeta1-42 with submicromolar concentrations of Cu2+. Unlike Abeta1-40, Abeta1-42 was precipitated by submicromolar Cu2+ concentrations at pH 7.4. Rat Abeta1-40 and histidine-modified human Abeta1-40 were not aggregated by Zn2+, Cu2+, or Fe3+, indicating that histidine residues are essential for metal-mediated Abeta assembly. These results indicate that H+-induced conformational changes unmask a metal-binding site on Abeta that mediates reversible assembly of the peptide. Since a mildly acidic environment together with increased Zn2+ and Cu2+ are common features of inflammation, we propose that Abeta aggregation by these factors may be a response to local injury. Cu2+, Zn2+, and Fe3+ association with Abeta explains the recently reported enrichment of these metal ions in amyloid plaques in Alzheimer's disease.

Brain injury and growth inhibitory factor (GIF)--a minireview

Growth inhibitory factor (GIF) is a small (7 kDa), heat-stable, acidic, hydrophilic metallothionein (MT)-like protein. GIF inhibits the neurotrophic activity in Alzheimer's disease (AD) brain extracts on neonatal rat cortical neurons in culture. GIF has been shown to be drastically reduced and down-regulated in AD brains. In neurodegenerative diseases in humans, GIF expression levels are reduced whereas GFAP expression levels are markedly induced in reactive astrocytes. Both GIF and GIF mRNA are present at high levels in reactive astrocytes following acute experimental brain injury. In chronological observations the level of GIF was found to increase more slowly and remain elevated for longer periods than that of glial fibrillary acidic protein (GFAP). These differential patterns and distribution of GIF and GFAP seem to be important in understanding the mechanism of brain tissue repair. The most important point concerning GIF in AD is not simply the decrease in the level of expression throughout the brain, but the drastic decrease in the level of expression in reactive astrocytes around senile plaques in AD. Although what makes the level of GIF decrease drastically in reactive astrocytes in AD is still unknown, supplements of GIF may be effective for AD, based on a review of current evidence. The processes of tissue repair following acute brain injury are considered to be different from those in AD from the viewpoint of reactive astrocytes.

Intracerebral inflammation after human brain contusion

OBJECTIVE

This study was undertaken to analyze the inflammatory components in contused human brain tissue to compare the findings with previous experimental data regarding the pathogenesis of brain contusions.

METHODS

Contused brain tissue biopsies were obtained from 12 consecutive patients undergoing surgery for brain contusions 3 hours to 5 days after trauma. Inflammatory and immunological components were analyzed by immunohistochemistry.

RESULTS

In patients undergoing surgery less than 24 hours after trauma, the inflammatory response was limited to vascular margination of polymorphonuclear cells. In patients undergoing surgery 3 to 5 days after trauma, however, a massive inflammatory response consisting of monocytes/macrophages, reactive microglia, polymorphonuclear cells, and CD4- and CD8-positive T lymphocytes was detected. Human lymphocyte antigen-DQ was expressed on reactive microglia and infiltrating leukocytes in the late patient group. In addition, CD1a, which is a marker for antigen-presenting dendritic cells, was detected in a subgroup of microglial cells.

CONCLUSION

The results corroborated hypotheses derived from experimental data. In the early phase after contusional trauma, inflammation is mainly intravascular and dominated by polymorphonuclear cells. The inflammation was parenchymal in patients undergoing surgery 3 to 5 days after trauma. The brain swelling seemed to be biphasic, the delayed phase correlating with a parenchymal inflammation. The inflammatory cells may produce several potentially harmful effects, such as acute cellular degeneration; they may also lead to degenerative long-term effects.