Stress protein expression in the Alzheimer-diseased choroid plexusAnthony, Shawn G.; Schipper, Hyman M.; Tavares, Rosemarie; Hovanesian, Virginia; Cortez, Selina C.; Stopa, Edward G.; Johanson, Conrad E.
doi: 10.3233/jad-2003-5301pmid: 12897402
Abnormal patterns of stress protein expression are found in the cerebral cortex and hippocampus of Alzheimer (AD) subjects. In this study, expression of various stress proteins in the Alzheimer-diseased choroid plexus (CP) was assessed immunohistochemically. We observed decreased HO-1 immunoreactivity in the AD CP, commensurate with our earlier report of suppressed HO-1 protein levels in AD cerebrospinal fluid (Schipper et al., Neurology 54:1297–1304, 2000). Heat shock protein (HSP) 90 was up-regulated in the AD CP relative to controls. There was a trend towards increased expression of HSP60, a mitochondrial stress protein; this is compatible with mitochondrial pathology recently documented in AD CP. Up-regulation of HSP90, a steroid receptor chaperone, in the AD CP may indicate abnormal hormone receptor expression in this secretory tissue. Glucose-regulated protein (GRP) 78 and 94 immunostaining was diminished in AD CP, implicating possible derangements in glucose or calcium homeostasis. Oxidative stress, per se, is probably not responsible for our observations because: i) there were no noticeable differences in the expression of HSP 70, ubiquitin, and alpha-B crystallin in the AD CP; and ii) augmentation, rather than the noted suppression, of HO-1 immunoreactivity would have been expected.
The incorporation and metabolism of amyloid-β into chylomicron-like lipid emulsionsJames, Anthony P.; Pal, Sebely; Gennat, Hanni C.; Vine, Donna F.; Mamo, John C.L.
doi: 10.3233/jad-2003-5302pmid: 12897403
The aggregation and deposition of amyloid-β (Aβ) in the brain is thought to be an early event in the pathology of Alzheimer's disease (AD). Many studies have reported the association of Aβ with lipoproteins from plasma suggesting an involvement of lipoprotein particles in Aβ transport. Chylomicron-like lipid emulsions, resembling chylomicrons in composition, size and metabolism were prepared in the presence of [125I]Aβ1-40. Aβ was found to associate significantly with these lipid emulsions during their preparation. The chylomicron-like emulsions containing Aβ were then injected into a lateral ear vein of conscious rabbits and blood sampled at regular intervals up to 30 mins. It was observed that there was no difference in the plasma clearance of [125I]Aβ and that of the 3H-cholesteryl ester, a marker of the emulsion particles, demonstrating that Aβ remains associated with these particles throughout both their lipolysis and tissue uptake. Our results show that Aβ can be metabolised in association with triglyceride rich lipoproteins (TRLs). In addition we report the presence of specific markers of TRLs of hepatic and intestinal origin in human CSF thus suggesting a potential means of cerebral Aβ delivery.
Apolipoprotein E genotyping as a potential biomarker for mercury neurotoxicityGodfrey, Michael E.; Wojcik, Damian P.; Krone, Cheryl A.
doi: 10.3233/jad-2003-5303pmid: 12897404
Apolipoprotein-E (apo-E) genotyping has been investigated as an indicator of susceptibility to heavy metal (i.e., lead) neurotoxicity. Moreover, the apo-E epsilon (ε)4 allele is a major risk factor for neurodegenerative conditions, including Alzheimer's disease (AD). A theoretical biochemical basis for this risk factor is discussed herein, supported by data from 400 patients with presumptive mercury-related neuro-psychiatric symptoms and in whom apo-E determinations were made. A statistically relevant shift toward the at-risk apo-E ε4 groups was found in the patients p<0.001). The patients possessed a mean of 13.7 dental amalgam fillings and 31.5 amalgam surfaces. This far exceeds the number capable of producing the maximum identified tolerable daily intake of mercury from amalgam.The clinical diagnosis and proof of chronic low-level mercury toxicity has been difficult due to the non-specific nature of the symptoms and signs. Dental amalgam is the greatest source of mercury in the general population and brain, blood and urine mercury levels increase correspondingly with the number of amalgams and amalgam surfaces in the mouth. Confirmation of an elevated body burden of mercury can be made by measuring urinary mercury, after provocation with 2,3,-dimercapto-propane sulfonate (DMPS) and this was measured in 150 patients.Apo-E genotyping warrants investigation as a clinically useful biomarker for those at increased risk of neuropathology, including AD, when subjected to long-term mercury exposures. Additionally, when clinical findings suggest adverse effects of chronic mercury exposure, a DMPS urine mercury challenge appears to be a simple, inexpensive procedure that provides objective confirmatory evidence. An opportunity could now exist for primary health practitioners to help identify those at greater risk and possibly forestall subsequent neurological deterioration.
Muscarinic receptor subtype determines vulnerability to amyloid β toxicity in transfected cos-7 cellsJoseph, J.A.; Fisher, D.R.
doi: 10.3233/jad-2003-5304pmid: 12897405
Research has suggested that there are age-related increases in neuronal sensitivity to insult from oxidative stress (OS) and that the CNS alterations seen in Alzheimer disease (AD) and vascular dementia (VaD) are superimposed upon declining nervous and vascular systems. Since muscarinic receptors (mAChR) may be important in regional sensitivity, regulation of micro- circulation, and in various aspects of both neuronal (AβPP processing) and vascular functioning, we postulated that the various mAChR subtypes may show differential sensitivity to OS. Indeed, recent findings indicated that M1, M2, or M4 AChR-transfected COS-7 cells showed greater OS sensitivity [as reflected in Ca2+ buffering (i.e., the ability to extrude or sequester Ca2+ following oxotremorine-induced depolarization)] than those transfected with M3 or M5 AChR when exposed to dopamine. Interestingly, the results from the present study indicate that similar findings were also observed when the cells were exposed to Aβ 25-35 and Aβ 1-40 showed similar effects on1 and M3 AChR. No effects were seen with Aβ35-25 or Aβ 40-1. Thus, cells transfected with M1, M2 or M4 AChR showed greater disruptions in calcium regulation (as assessed via fluorescent imaging analysis prior to and following 750 μm oxotremorine) than those transfected with M3 or M5 AChR. We also examined the effects of calcium channel antagonists (e.g., Nifedipine) or antioxidants (vitamin E) in protecting against the deleterious effects of Aβ. Results are discussed in terms of differences in MAChR structure that could lead to selective Aβ effects and the possible implications on memory and AβPP processing.
Transient hypoxia causes Alzheimer-type molecular and biochemical abnormalities in cortical neurons: Potential strategies for neuroprotection1Chen, Guo-Jun; Xu, Julia; Lahousse, Stephanie A.; Caggiano, Niki L.; de la Monte, Suzanne M.
doi: 10.3233/jad-2003-5305pmid: 12897406
Familial Alzheimer's Disease (AD) has been linked to amyloid β protein precursor (AβPP) and presenilin gene mutations. In sporadic AD, which accounts for the vast majority of cases, the pathogenesis of neurodegeneration is unknown; however, recent evidence suggests a role for oxidative stress. The present study demonstrates that transient hypoxic injury to cortical neurons causes several of the molecular and biochemical abnormalities that occur in AD including, mitochondrial dysfunction, impaired membrane integrity, increased levels of DNA damage, reactive oxygen species, phospho-tau, phospho-MAP-1B, and ubiquitin immunoreactivity, and AβPP cleavage with accumulation of Aβ-immunoreactive products. These abnormalities were associated with activation of kinases that phosphorylate tau, including glycogen synthase kinase 3β (GSK-3β), mitogen-activated protein kinase (MAPK), and cyclin-dependent kinase 5 (Cdk-5). Further studies showed that significant neuro-protection with sparing of mitochondrial function and membrane integrity could be achieved by pre-treating the cortical neurons with N-acetyl cysteine, glutathione, or inhibitors of GSK-3β, MAP kinase, or AβPPγ-secretase. Therefore, in the absence of underlying gene mutations, oxidative stress can cause AD-type abnormalities, including aberrant post-translational processing of neuronal cytoskeletal proteins and APP. Our results also suggest that pre-treatment with agents that block specific components of the AD neurodegeneration cascade may provide neuroprotection against oxidative stress-induced impairments in membrane integrity, mitochondrial function, and viability.
Protection against amyloid beta peptide and iron/hydrogen peroxide toxicity by alpha lipoic acidLovell, Mark A.; Xie, Chengsong; Xiong, Shuling; Markesbery, William R.
doi: 10.3233/jad-2003-5306pmid: 12897407
Current evidence supports the role of oxidative stress in the pathogenesis of neuron degeneration in Alzheimer's disease (AD). α-Lipoic acid (LA), an essential cofactor in mitochondrial dehydrogenase reactions, functions as an antioxidant and reduces oxidative stress in aged animals. Here, we describe the effects of LA and its reduced form, dihydrolipoic acid (DHLA), in neuron cultures treated with amyloid β-peptide (Aβ 25-35) and iron/hydrogen peroxide (Fe/H2O2). Pretreatment of dissociated primary hippocampal cultures with LA significantly protected against Aβ and Fe/H2O2toxicity. In contrast, concomitant treatment of cultures with LA and Fe/H2O2 significantly potentiated the toxicity. Decreased cell survival in cultures treated concomitantly with LA and Fe/H2O2correlated with increased free radical production measured by dichlorofluorescein fluorescence. Treatment of cortical neurons with DHLA significantly protected glucose-transport against Fe/H2O2 or β-mediated decreases although treatment with LA did not provide protection. These data suggest that DHLA, the reduced form of LA, significantly protects against both Aβ and Fe/H2O2 mediated toxicity. The data also suggest that concomitant exposure to LA and Fe/H2O2significantly potentiates the oxidative stress. Overall, these data suggest that the oxidation state of LA is critical to its function and that in the absence of studies of LA/DHLA equilibria in human brain the use of LA as an antioxidant in disorders where there is increased Fe such as AD is of questionable efficacy.
Does proteasome inhibition play a role in mediating neuropathology and neuron death in Alzheimer's disease?Ding, Qunxing; Keller, Jeffrey N.
doi: 10.3233/jad-2003-5307pmid: 12897408
An increasing number of studies have demonstrated evidence that inhibition of proteasome activity may play a causal role in mediating the neuropathology and neuron death observed in Alzheimer's disease (AD). These reports have clearly demonstrated that proteasome inhibition occurs in the AD brain, with numerous in vitro and in vivo studies elucidating the ability of proteasome inhibitors to induce AD-like neuropathology and even neuron death. In spite of these clear and significant findings, several important questions regarding the role of proteasome inhibition in AD remain unanswered. We propose that chronic low-level proteasome inhibition, but not severe and acutely toxic levels of proteasome inhibition, likely plays a role in mediating specific aspects of AD neuropathology. Experimental evidence supporting this hypothesis, as well as the scientific implications of this hypothesis are discussed.