Brain Regions In Alzheimer's Disease Research Articles

Phospholipid mass is increased in fibroblasts bearing the Swedish amyloid precursor mutation

Phospholipid changes occur in brain regions affected by Alzheimer disease (AD), including a marked reduction in plasmalogens, which could diminish brain function either by directly altering signaling events or by bulk membrane effects. However, model systems for studying the dynamics of lipid biosynthesis in AD are lacking. To determine if fibroblasts bearing the Swedish amyloid precursor protein (swAPP) mutation are a useful model to study the mechanism(s) associated with altered phospholipid biosynthesis in AD, we examined the steady-state phospholipid mass and composition of fibroblasts, including plasmalogens. We found a 15% increase in total phospholipid mass, accounted for by a 24% increase in the combined total of phosphatidylethanolamine and plasmanylethanolamine mass and a 19% increase in the combined total of phosphatidylcholine (PtdCho) and plasmanycholine (PakCho) mass in the swAPP mutant bearing fibroblasts. Cholesterol mass was unchanged in these cells. The changes in phospholipid mass did not alter the cellular molar composition of the phospholipids nor the cholesterol to phospholipid ratio. While plasmalogen mass was not altered, the ratio of choline plasmalogen (PlsCho) mass to PtdCho + PakCho mass was decreased 16% and there was a 14% reduction in the proportion of PlsCho as a percent of total phospholipids in the swAPP mutant bearing fibroblasts. This change in choline plasmalogen is consistent with the reported decreases in plasmalogen proportions in affected regions of AD brain, suggesting that these cells may serve as a useful model to determine the mechanism underlying changes in plasmalogen biosynthesis in AD brain.

Redox proteomics identification of oxidized proteins in Alzheimer's disease hippocampus and cerebellum: An approach to understand pathological and biochemical alterations in AD

Alzheimer's disease (AD) is characterized by the presence of neurofibrillary tangles, senile plaques and loss of synapses. There is accumulating evidence that oxidative stress plays an important role in AD pathophysiology. Previous redox proteomics studies from our laboratory on AD inferior parietal lobule led to the identification of oxidatively modified proteins that were consistent with biochemical or pathological alterations in AD. The present study was focused on the identification of specific targets of protein oxidation in AD and control hippocampus and cerebellum using a redox proteomics approach. In AD hippocampus, peptidyl prolyl cis– trans isomerase, phosphoglycerate mutase 1, ubiquitin carboxyl terminal hydrolase 1, dihydropyrimidinase related protein-2 (DRP-2), carbonic anhydrase II, triose phosphate isomerase, α-enolase, and γ-SNAP were identified as significantly oxidized protein with reduced enzyme activities relative to control hippocampus. In addition, no significant excessively oxidized protein spots were identified in cerebellum compared to control, consistent with the lack of pathology in this brain region in AD. The identification of oxidatively modified proteins in AD hippocampus was verified by immunochemical means. The identification of common oxidized proteins in different brain regions of AD brain suggests a potential role for these oxidized proteins and thereby oxidative stress in the pathogenesis of Alzheimer's disease.

Cellular distribution of insulin-like growth factor-II/mannose-6-phosphate receptor in normal human brain and its alteration in Alzheimer's disease pathology

The insulin-like growth factor-II/mannose-6-phosphate (IGF-II/M6P) receptor is a multifunctional membrane glycoprotein, which binds different classes of ligands including IGF-II and M6P-bearing lysosomal enzymes. Besides participating in the process of endocytosis this receptor functions in the trafficking of lysosomal enzymes from the trans-Glogi network (TGN) or the cell surface to lysosomes. In Alzheimer's disease (AD) brain, marked overexpression of certain lysosomal enzymes in vulnerable neuronal populations and their association to β-amyloid (Aβ) containing neuritic plaques has been correlated to altered metabolic functions. In the present study, we measured the levels of IGF-II/M6P receptor and characterized its distribution profile in selected regions of AD and age-matched normal postmortem brains. Western blot analysis revealed no significant alteration in the levels of IGF-II/M6P receptor either in the hippocampus, frontal cortex or cerebellum between AD and age-matched control brains. However, a significant gene dose effect of apolipoprotein E (APOE) ɛ4 allele on IGF-II/M6P receptor levels was evident in the hippocampus of the AD brain. At the cellular level, immunoreactive IGF-II/M6P receptors were localized in the neurons of the frontal cortex, hippocampus and cerebellum of control brains. In AD brains, the labeling of the neurons was less intense in the frontal cortex and hippocampus than in the age-matched control brains. Additionally, IGF-II/M6P receptor immunoreactivity was observed in association with a subpopulation of Aβ-containing neuritic plaques as well as tau-positive neurofibrillary tangles both in the frontal cortex and the hippocampus. Reactive glial cells localized adjacent to the plaques also occasionally exhibited IGF-II/M6P receptor immunoreactivity. These results, when analyzed in context of the established role of the IGF-II/M6P receptor in the regulation of the intracellular trafficking of lysosomal enzymes, suggest that alterations in IGF-II/M6P receptor levels/distribution are possibly associated with altered functioning of the lysosomal enzymes and/or loss of neurons observed in AD brains, especially in patients carrying APOE ɛ4 alleles.

Age- and region-dependent alterations in Aβ-degrading enzymes: implications for Aβ-induced disorders

Accumulation of amyloid β-protein (Aβ) is a fundamental feature of certain human brain disorders such as Alzheimer's disease (AD) and Down syndrome and also of the skeletal muscle disorder inclusion body myositis (IBM). Emerging evidence suggests that the steady-state levels of Aβ are determined by the balance between production and degradation. Although the proteolytic processes leading to Aβ formation have been extensively studied, less is known about the proteases that degrade Aβ, which include insulin-degrading enzyme (IDE) and neprilysin (NEP). Here we measured the steady-state levels of these proteases as a function of age and brain/muscle region in mice and humans. In the hippocampus, which is vulnerable to AD pathology, IDE and NEP steady-state levels diminish as function of age. By contrast, in the cerebellum, a brain region not marked by significant Aβ accumulation, NEP and IDE levels either increase or remain unaltered during aging. Moreover, the steady-state levels of IDE and NEP are significantly higher in the cerebellum compared to the cortex and hippocampus. We further show that IDE is more oxidized in the hippocampus compared to the cerebellum of AD patients. In muscle, we find differential levels of IDE and NEP in fast versus slow twitch muscle fibers that varies with aging. These findings suggest that age- and region-specific changes in the proteolytic clearance of Aβ represent a critical pathogenic mechanism that may account for the susceptibility of particular brain or muscle regions in AD and IBM.

Binding of two potential imaging agents targeting amyloid plaques in postmortem brain tissues of patients with Alzheimer's disease

In vivo imaging of amyloid plaques may be useful for evaluation and diagnosis of Alzheimer's disease (AD) patients. Towards that end, we have developed 6-iodo-2-(4′-dimethylamino-)phenyl-imidazo[1,2]pyridine (IMPY), and 4- N-methylamino-4′-hydroxystilbene (SB-13) as ligands for specifically targeting amyloid plaques. These ligands can be readily radiolabeled with I-123 or C-11, for in vivo imaging using single photon emission computerized tomography (SPECT) or positron emission tomography (PET), respectively. However, in order to be useful in vivo, probes must show selective high affinity binding to a sufficiently abundant binding site on amyloid plaques. Therefore, as a prelude to in vivo imaging studies, we evaluated the binding properties of these two potential imaging agents to amyloid plaques present in human brain tissues. In vitro binding studies were carried out with [ 125I]IMPY and [ 3H]SB-13 in homogenates prepared from postmortem samples of affected cortex and cerebellum of pathologically confirmed AD patients and age-matched controls. Binding parameters such as K d and B max were estimated. Competition study was designed to evaluate the amyloid plaque binding specificity using human brain tissues. Plaque binding was confirmed by thioflavin-S staining. Specific [ 125I]IMPY or [ 3H]SB-13 binding can be clearly measured in the cortical gray matter, but not in the white matter of AD cases. There was a very low specific binding in cortical tissue homogenates of control brains. Cerebellar homogenates prepared from either AD or control brains did not show any specific [ 125I]IMPY or [ 3H]SB-13 binding. The K d values of AD cortical homogenates were 5.3±1.0 and 2.4±0.2 nM for [ 125I]IMPY and [ 3H]SB-13, respectively. High binding capacity and comparable values were observed for both ligands (14–45 pmol/mg protein). The location and density of specific signal detected by [ 125I]IMPY or [ 3H]SB-13 correlated with the distribution of amyloid plaques in these brain specimens, as confirmed by thioflavin-S staining. Competition profiles of known ligands suggest that the binding is highly selective and comparable to that reported by using preformed Aβ peptide aggregates. [ 125I]IMPY and [ 3H]SB-13 show an abundant binding capacity with high binding affinities for amyloid plaques in affected cortical regions of AD brains. These properties suggest that when labeled with I-123 or C-11, these two ligands may be useful to quantitate amyloid plaque burdens in the living AD patients.

Differential expression of N-methyl-D-aspartate receptor NR2 isoforms in Alzheimer's disease.

We have previously shown that the expression of NMDA receptor NR1 subunit mRNA splice variants in Alzheimer's disease (AD) brain varies according to regional susceptibility to pathological damage. Here we investigated the expression of the modulatory NR2 subunits of the NMDA receptor using quantitative RT-PCR to assay all NR2 isoforms. Significantly lower expression of NR2A and NR2B transcripts was found in susceptible regions of AD brain, whereas expression of NR2C and NR2D transcripts did not differ from that in controls. Western blot analysis confirmed a lower expression of the NR2A and NR2B isoforms at the protein level. The results suggest that NR2 subunit composition may modulate NMDA receptor-mediated excitotoxicity. NMDA receptor dysfunction might give rise to the regionally selective pattern of neuronal loss that is characteristic of AD.

12/15-Lipoxygenase Is Increased in Alzheimer's Disease: Possible Involvement in Brain Oxidative Stress

Alzheimer's disease (AD) is a chronic neurodegenerative disorder that impairs cognition and behavior. Although the initiating molecular events are not known, increasing evidence suggests that oxidative stress could play a functional role in its pathogenesis. Lipoxygenase (LOX) enzymes by oxidizing polyunsaturated fatty acids synthesize hydroperoxyacids, which are potent pro-oxidant mediators. Because circumstantial evidence suggests that 12/15-LOX is a major source of oxidative stress, we investigated the protein levels and activity of this enzyme in different brain regions of histopathologically confirmed AD and control cases. Using quantitative Western blot analysis we demonstrated that in affected frontal and temporal regions of AD brains the amount of 12/15-LOX was higher compared with controls, whereas no difference between the two groups was detected in the cerebellum. This observation was confirmed by immunohistochemical studies. Levels of 12/15-hydroxyeicosatetraenoic acids, metabolic products of 12/15-LOX, were also markedly elevated in AD brains compared to controls. This increase directly correlated with brain lipid peroxidation, and inversely with vitamin E levels. Finally, genetic deletion of this enzyme in vitro resulted in a reduction of the cellular oxidative stress response after incubation with H2O2 or amyloid beta. These data show that the 12/15-LOX metabolic pathway is increased and correlates with an oxidative imbalance in the AD brain, implying that this enzyme might contribute to the pathogenesis of this neurodegenerative disorder.

N-methyl- d-aspartate receptor subunit NR2A and NR2B messenger RNA levels are altered in the hippocampus and entorhinal cortex in Alzheimer's disease

The N-methyl- d-aspartate (NMDA) receptor is a subtype of ionotropic glutamate receptor that is involved in synaptic mechanisms of learning and memory, and mediates excitotoxic neuronal injury. In this study, we tested the hypothesis that NMDA receptor subunit gene expression is altered in Alzheimer's disease (AD), especially in brain regions known to be important in memory. Quantitative reverse transcriptase–polymerase chain reaction (RT–PCR) was used to determine the messenger RNA (mRNA) levels of the NMDA receptor subunits NR1, NR2A, and NR2B in the hippocampus and entorhinal cortex of postmortem brain samples from nine clinically well-characterized AD patients and nine aged controls. Cerebellum, a site minimally affected by AD, was also chosen for comparison assessment. Results showed decreased levels of the NR2 mRNAs in AD brains compared to controls. Reductions of NR2A (46.2%, p<0.01) and NR2B (43.2%, p<0.0001) mRNA levels were identified in the entorhinal cortex. Reductions of NR2A (41.4%, p<0.05) and NR2B (40.6%, p=0.058) mRNA levels were found in the hippocampus. NR1 mRNA levels were similar in all three brain regions in both AD and controls. No significant changes of subunit NR2A and NR2B mRNA levels were identified in the cerebellum. Postmortem delay (PMD), tissue storage time, brain weight, or age of the subjects did not affect these changes. These data suggest that alterations in NMDA receptor subunits, especially the NR2A and NR2B, may be important in AD, particularly in neuronal populations that underlie impaired learning and memory.

The pentraxins: possible role in Alzheimer's disease and other innate inflammatory diseases

Two short pentraxins, C-reactive protein and amyloid P, are found in association with the senile plaques and neurofibrillary tangles of Alzheimer disease (AD). Formerly thought to be made primarily if not solely in liver, recent work has shown that they are made not only in the brain but in other tissues such as heart and arteries. Their synthesis is markedly upregulated in affected brain regions in AD. Since they are known to activate the complement cascade in an antibody-independent fashion and chronic activation can cause destruction of host tissue, these pentraxins may be important initiators of an autodestructive process. As such, they may be prime targets for therapeutic intervention.

Neurofilament proteins NF-L, NF-M and NF-H in brain of patients with Down syndrome and Alzheimer's disease.

Neurofilaments (NFs) are integral constituents of the neuron playing a major role in brain development, maintenance, regeneration and the pattern of expression for NFs suggests their contribution to plasticity of the neuronal cytoskeleton and creating and maintaining neuronal architecture. Using immune-histochemical techniques the altered expression of NFs in Down syndrome (DS) and Alzheimer's disease (AD) has been already published but as no corresponding systematic immune-chemical study has been reported yet, we decided to determine proteins levels of three NFs in several brain regions of DS and AD brain. We evaluated immunoreactive NF-H, NF-M and NF-L levels using Western blotting in brain regions temporal, occipital cortex and thalamus of patients with DS (n = 9), AD (n = 9) and controls (n = 12). We found significantly increased NF-H in temporal cortex (controls: means 0.74+/-0.39 SD; DS: means 3.01+/-2.18 SD) of DS patients and a significant decrease of NF-L in occipital cortex of DS and AD patients (controls: means 1.19+/-0.86 SD; DS: means 0.35+/-0.20; AD: 0.20+/-0.11 SD). We propose that the increase of NF-H in temporal cortex of DS brain is due to neuritic sprouting as observed in immune-histochemical studies. The increase may not be caused by the known accumulation of NFs in plaques, tangles or Lewy bodies due to our solubilization protocol. The decrease of NF-L in occipital cortex of DS and AD patients may well be reflecting neuronal loss. Altogether, however, we suggest that NFs are not reliable markers for neuronal death, a hallmark of both neurodegenerative diseases, in DS or AD. The increase of NF-H in DS or the decrease of NF-L in DS and AD leaves the other NFs unchanged, which points to dysregulation in DS and AD and raises the question of impaired structural assembly of neurofilaments.

Neurons in Alzheimer disease emerge from senescence

A number of cell cycle markers are associated with the selective neuronal pathology found in Alzheimer disease. However, the significance of such cell cycle markers is clouded by duplicity of function in that many such proteins are also involved in apoptosis and/or DNA repair following oxidative damage. To clarify whether or not neurons in Alzheimer disease do in fact emerge from a quiescent status, with subsequent entry into the G 1 phase of the cell cycle, in this study we focused on a family of MORF4-related proteins that are associated with emergence from senescence. Our results show that many neurons in vulnerable regions of Alzheimer disease brain, but not in control brain, have increased MORF4-related proteins indicating re-entry into the cell cycle. Immunoblot analysis showed a specific disease-related increase in a 52 kDa protein that is likely the human homologue of the MORF4-related transcription factor. The novel localization of such a transcriptional activating protein to selectively vulnerable neurons in Alzheimer disease provides compelling evidence for mitotic re-entry as part of the pathogenesis of neuronal dysfunction and death in Alzheimer disease.

A novel fluorescent method for direct visualization of neurofibrillary pathology in Alzheimer's disease

Methods currently available for detecting neurofibrillary pathology are indirect and depend on staining with exogenous chemicals or antibodies. In the present study, we report a novel method named intrinsic fluorescence induction (IFI), which allows direct visualization of neurofibrillary tangles (NFTs), neuropil threads (NTs), and neuritic plaques (NPs) in tissue sections of Alzheimer's disease (AD) brain. The IFI method is based on both induction of a red intrinsic fluorescence and quenching red background autofluorescence. The IFI procedure includes sustained hydrophobic treatment, protein secondary structure enhancement and incubation in high concentration of phosphate buffer. Following this procedure, a unique red fluorescence is generated from the structures of NFTs, NTs, and NPs in brain sections from AD patients. Sequential application of mild permanganate oxidation and 1% sodium borohydride selectively removes the red background autofluorescence, while the latter enhances the intrinsic fluorescence of neurofibrillary pathology. Comparative studies reveal that the IFI method is as sensitive as Gallyas silver staining, and more sensitive than Bielschowsky silver staining or PHF-1 immunostaining in detecting NFTs in the pre-α layer of entorhinal cortex and the pri-α layer of the entorhinal/transentorhinal cortex. Furthermore, the IFI method is sensitive in displaying plaque neurites and threads, but not NFTs in the hippocampus. This novel finding provides a direct method for detecting neurofibrillary pathology in particular regions of AD brain and a novel tool for AD research.

Evidence that neurones accumulating amyloid can undergo lysis to form amyloid plaques in Alzheimer's disease.

Amyloid has recently been shown to accumulate intracellularly in the brains of patients with Alzheimer's disease (AD), yet amyloid plaques are generally thought to arise from gradual extracellular amyloid deposition. We have investigated the possibility of a link between these two apparently conflicting observations. Immunohistochemistry and digital image analysis was used to examine the detailed localization of beta-amyloid(42) (A beta 42), a major component of amyloid plaques, in the entorhinal cortex and hippocampus of AD brains. A beta 42 first selectively accumulates in the perikaryon of pyramidal cells as discrete, granules that appear to be cathepsin D-positive, suggesting that they may represent lysosomes or lysosome-derived structures. AD brain regions abundantly populated with pyramidal neurones exhibiting excessive A beta 42 accumulations also contained evidence of neuronal lysis. Lysis of these A beta 42-burdened neurones apparently resulted in a local, radial dispersion of their cytoplasmic contents, including A beta 42 and lysosomal enzymes, into the surrounding extracellular space. A nuclear remnant was found at the dense core of many amyloid plaques, strengthening the idea that each amyloid plaque represents the end product of a single neuronal cell lysis. The inverse relationship between the amyloid plaque density and pyramidal cell density in the AD brain regions also supports this possibility, as does the close correlation between plaque size and the size of local pyramidal cells. Our findings suggest that excessive intracellular accumulation of A beta 42-positive material in pyramidal cells can result in cell lysis, and that cell lysis is an important source of amyloid plaques and neuronal loss in AD brains.

Deranged Expression of Molecular Chaperones in Brains of Patients with Alzheimer's Disease

Alzheimer's disease (AD) is one of the disorders caused by protein conformational changes and recent studies have shown that several chaperone proteins are involved in this process. As information of chaperone expression in AD brain is limited, we aimed to study the expressional pattern of chaperones in several brain regions, as this may be essential to understand how folding defects can lead to disease. We studied the concomitant expressional patterns of molecular chaperones in seven brain regions of adults with AD using two-dimensional polyacrylamide gel electrophoresis (2-DE) and matrix-associated laser desorption ionization mass spectroscopy (MALDI-MS). We unambiguously identified and quantified nine different chaperone proteins. Six chaperone proteins, heat shock protein 60 (HSP 60), HSP 70 RY, heat shock cognate (HSC) 71, alpha crystallin B chain, glucose regulated protein (GRP) 75, and GRP 94 showed aberrant expressional patterns depending on brain region. HSP 70.1, GRP 78 and T-complex 1 (TCP-1) epsilon subunit did not show any significant expressional change. These findings are compatible with neuropathological and biochemical abnormalities in AD brain and this report presents the first approach to quantify nine different chaperones simultaneously at the protein level in individual AD brain regions providing evidence for the relevance of aberrant chaperone expression to AD neuropathology.

Decreased base excision repair and increased helicase activity in Alzheimer's disease brain

Recent studies show an increase in DNA oxidation in brain and cerebrospinal fluid (CSF), and decreased levels of the free repair product in CSF in Alzheimer's disease (AD). This is a study of the activity of the base excision repair enzyme, 8-oxoguanine glycosylase (responsible for the excision of 8-oxoguanine), and DNA helicase activity in nuclear protein samples from four brain regions of 10 AD and eight age-matched control subjects. Statistically significant ( p<0.05) decreases in 8-oxoguanine glycosylase activity were observed in the nuclear fraction of AD hippocampal and parahippocampal gyri (HPG), superior and middle temporal gyri (SMTG), and inferior parietal lobule (IPL). DNA helicase activity was elevated in all nuclear samples except the IPL with statistically significant elevations in the HPG and CER. Statistically significant depletion of helicase activity was observed in the nuclear fraction in AD IPL. Our results demonstrate that the repair capabilities for 8-oxoguanine are decreased in AD. The modest increase in DNA helicase activity in some brain regions in AD may interfere with base excision repair mechanisms. Overall, the decreased repair of DNA damage could be involved in the pathogenesis of neurodegeneration in AD.

Alzheimer's disease and inflammation: a review of cellular and therapeutic mechanisms.

1. Of the neurodegenerative diseases that cause dementia, Alzheimer's disease (AD) is the most common. Three major pathologies characterize the disease: senile plaques, neurofibrillary tangles and inflammation. We review the literature on events contributing to the inflammation and the treatments thought to target this pathology. 2. The senile plaques of AD consist primarily of complexes of the beta-amyloid protein. This protein is central to the pathogenesis of the disease. 3. Inflammatory microglia are consistently associated with senile plaques in AD, although the classic inflammatory response (immunoglobulin and leucocyte infiltration) is absent. beta-Amyloid fragments appear to mediate such inflammatory mechanisms by activating the complement pathway in a similar fashion to immunoglobulin. 4. Epidemiological studies have identified a reduced risk of AD in patients with arthritis and in leprosy patients treated with anti-inflammatory drugs. Longitudinal studies have shown that the consumption of anti-inflammatory medications reduces the risk of AD only in younger patients (< 75 years). 5. There is a considerable body of in vitro evidence indicating that the inflammatory response of microglial cells is reduced by non-steroidal anti-inflammatory drugs (NSAID). However, no published data are available concerning the effects of these medications on brain pathology in AD. 6. Cyclo-oxygenase 2 enzyme is constitutively expressed in neurons and is up-regulated in degenerative brain regions in AD. Non-steroidal anti-inflammatory drugs may reduce this expression. 7. Platelets are a source of beta-amyloid and increased platelet activation and increased circulating beta-amyloid have been identified in AD. Anti-platelet medication (including NSAID) would prevent such activation and its potentially harmful consequences. 8. Increased levels of luminal beta-amyloid permeabilizes the blood-brain barrier (BBB) and increases vasoconstriction of arterial vessels, paralleling the alterations observed with infection and inflammation. Cerebral amyloidosis is highly prevalent in AD, compromising the BBB and vasoactivity. Anti-inflammatory medications may alleviate these problems.

Serum amyloid A in Alzheimer's disease brain is predominantly localized to myelin sheaths and axonal membrane

Immunohistochemical localization of the injury specific apolipoprotein, acute phase serum amyloid A (A-apoSAA), was compared in brains of patients with neuropathologically confirmed Alzheimer's disease (AD), multiple sclerosis (MS), Parkinson's disease (PD), Pick's disease (Pick's), dementia with Lewy bodies (DLB), coronary artery disease (CAD), and schizophrenia. Affected regions of both AD and MS brains showed intense staining for A-apoSAA in comparison to an unaffected region and non-AD/MS brains. The major site of A-apoSAA staining in both diseases was the myelin sheaths of axons in layers V and VI of affected cortex. A-apoSAA contains a cholesterol binding site near its amino terminus and is likely to have a high affinity for cholesterol-rich myelin. These findings, along with our recent evidence that A-apoSAA can inhibit lipid synthesis in vascular smooth muscle cells suggest that A-apoSAA plays a role in the neuronal loss and white matter damage occurring in AD and MS.

Kynurenine metabolism in Alzheimer's disease.

L-kynurenine (L-KYN) serves as a substrate for the synthesis of neurotoxic 3-OH-kynurenine (3-OH-KYN) and neuroprotective kynurenic acid (KYNA). KYNA is able to interact with ionotropic excitatory amino acid receptors that are involved in a variety of neurodegenerative disorders. The purpose of the present study was to investigate the biosynthetic machinery of KYNA in several regions of Alzheimer's disease (AD) brain. The endogenous levels of L-KYN, 3-OH-KYN and KYNA in frontal cortex, caudate nucleus, putamen, hippocampus, and cerebellum of 11 autopsy confirmed cases of AD and 13 age-matched controls were analyzed. Subsequently, the activity of two proteins responsible for the production of KYNA, kynurenine aminotransferases I and II (KAT I and KAT II), was investigated. There was a trend for a decrease of L-KYN and 3-OH-KYN in all examined regions of AD brain, as compared to controls. However, KYNA was increased significantly in the putamen and caudate nucleus of AD, by 192 and 177%, respectively. In other areas of AD brain only a minor increase of KYNA was present. Elevated KYNA in the caudate nucleus and putamen correlated with a significant increase of KAT I activities in both nuclei-157 and 147%, respectively. A minor increase of KAT II was measured only in the caudate nucleus of AD subjects. Kinetic analysis of KAT I and II performed in the caudate nucleus of AD patients revealed a marked increase of Vmax, by 207 and 274% of controls, respectively. Km value for L-KYN using pyruvate as amino acceptor was significantly higher for KAT II (247% of controls). The present data indicate an elevated kynurenine metabolism in AD brain. A marked increase of KYNA in the caudate nucleus and putamen may compensate the hyperactivity of the striato-frontal loop in AD brains. Blockade of NMDA receptors by KYNA may be responsible for impaired memory, learning and cognition in AD patients.

Increased glyceraldehyde 3-phosphate dehydrogenase levels in the brain of patients with Down's syndrome

Impaired glucose metabolism in Down's syndrome (DS) has been well-documented in vivo, although information on the underlying biochemical defect is limited and no biochemical studies on glucose handling enzymes have been carried out in the brain. In a previous study, we found by gene hunting in DS brain an overexpressed sequence homologous to the glyceraldehyde 3-phosphate dehydrogenase (G3PD) gene. Here we studied G3PD activity and expression levels, using two-dimensional gel analysis, in five brain regions of patients with DS and Alzheimer's disease (AD). The protein expression levels in four brain areas were approximately 1.5-fold higher in patients with DS in comparison with the controls. G3PD activity was significantly elevated in the frontal, parietal, occipital and temporal lobe of DS as well, but not in the corresponding AD brain regions. We conclude that our biochemical findings complement previously published data of impaired brain glucose metabolism in DS evaluated by positron emission tomography in clinical studies.

Expression of differential immune factors in temporal cortex and cerebellum: The role of ?-1-antichymotrypsin, apolipoprotein E, and reactive glia in the progression of Alzheimer's disease

A variety of factors and processes have been implicated in the development and progression of the pathology of Alzheimer's Disease (AD), including amyloid fragment deposition, reactive gliosis, alpha-1-antichymotrypsin (ACT), and apolipoprotein E (APOE). Carriers of the APOE 4 allele have been shown to have an enhanced risk of developing AD, and the ACT signal peptide A/A genotype may modify the APOEepsilon4 risk. The protein products of these genes have been shown to enhance conversion of diffuse beta amyloid (Abeta) fibrils, which are found in diffuse plaques, to the fibrillar form found in neuritic plaques. In affected regions of AD brain, ACT and APOE colocalize with Abeta deposits and reactive microglia and astrocytes. We examined the regional distribution of ACT, APOE, and reactive glia in temporal cortex, where neuritic plaques are abundant, and cerebellum (in areas where diffuse plaques but not neuritic plaques accumulate) to examine the relationship of these markers to the deposition of Abeta. In temporal cortex, ACT and APOE staining was localized to plaque-like profiles, reactive astrocytes, and blood vessels; human leukocyte antigen-DR (HLA-DR) and glial fibrillary acidic protein (GFAP) staining revealed focal clusters of reactive microglia and astrocytes. In cerebellum, ACT and APOE immunoreactivity was never localized to plaque-like profiles but was weakly localized to unreactive astrocytes; weak HLA-DR and GFAP immunoreactivity was present on quiescent microglia throughout the cerebellum. The lack of fibrillar amyloid deposits in cerebellum, despite the presence of well-characterized markers thought to mediate the production of Abeta, suggests that this brain region may be lacking certain factors necessary for fibril formation or that the cerebellum responds differently to stimuli that successfully mediate inflammation in affected cortex.