Nonneural markers in Alzheimer disease

Morphometric and Nanomechanical Screening of Peripheral Blood Cells with Atomic Force Microscopy for Label-Free Assessment of Alzheimer's Disease, Parkinson's Disease, and Amyotrophic Lateral Sclerosis

Neurodegenerative disorders (NDDs) are complex, multifactorial disorders with significant social and economic impact in today's society. NDDs are predicted to become the second-most common cause of death in the next few decades due to an increase in life expectancy but also to a lack of early diagnosis and mainly symptomatic treatment. Despite recent advances in diagnostic and therapeutic methods, there are yet no reliable biomarkers identifying the complex pathways contributing to these pathologies. The development of new approaches for early diagnosis and new therapies, together with the identification of non-invasive and more cost-effective diagnostic biomarkers, is one of the main trends in NDD biomedical research. Here we summarize data on peripheral biomarkers, biofluids (cerebrospinal fluid and blood plasma), and peripheral blood cells (platelets (PLTs) and red blood cells (RBCs)), reported so far for the three most common NDDs-Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS). PLTs and RBCs, beyond their primary physiological functions, are increasingly recognized as valuable sources of biomarkers for NDDs. Special attention is given to the morphological and nanomechanical signatures of PLTs and RBCs as biophysical markers for the three pathologies. Modifications of the surface nanostructure and morphometric and nanomechanical signatures of PLTs and RBCs from patients with AD, PD, and ALS have been revealed by atomic force microscopy (AFM). AFM is currently experiencing rapid and widespread adoption in biomedicine and clinical medicine, in particular for early diagnostics of various medical conditions. AFM is a unique instrument without an analog, allowing the generation of three-dimensional cell images with extremely high spatial resolution at near-atomic scale, which are complemented by insights into the mechanical properties of cells and subcellular structures. Data demonstrate that AFM can distinguish between the three pathologies and the normal, healthy state. The specific PLT and RBC signatures can serve as biomarkers in combination with the currently used diagnostic tools. We highlight the strong correlation of the morphological and nanomechanical signatures between RBCs and PLTs in PD, ALS, and AD.

Cross-species metabolomic analysis of tau- and DDT-related toxicity

Exposure to the pesticide dichlorodiphenyltrichloroethane (DDT) has been associated with increased risk of Alzheimer's disease (AD), a disease also associated with hyperphosphorylated tau (p-tau) protein aggregation. We investigated whether exposure to DDT can exacerbate tau protein toxicity in Caenorhabditiselegans using a transgenic strain that expresses human tau protein prone to aggregation by measuring changes in size, swim behavior, respiration, lifespan, learning, and metabolism. In addition, we examined the association between cerebrospinal fluid (CSF) p-tau protein-as a marker of postmortem tau burden-and global metabolism in both a human population study and in C. elegans, using the same p-tau transgenic strain. From the human population study, plasma and CSF-derived metabolic features associated with p-tau levels were related to drug, amino acid, fatty acid, and mitochondrial metabolism pathways. A total of five metabolites overlapped between plasma and C. elegans, and four between CSF and C. elegans. DDT exacerbated the inhibitory effect of p-tau protein on growth and basal respiration. In the presence of p-tau protein, DDT induced more curling and was associated with reduced levels of amino acids but increased levels of uric acid and adenosylselenohomocysteine. Our findings in C. elegans indicate that DDT exposure and p-tau aggregation both inhibit mitochondrial function and DDT exposure can exacerbate the mitochondrial inhibitory effects of p-tau aggregation. Further, biological pathways associated with exposure to DDT and p-tau protein appear to be conserved between species.

Metabolic stress is a primary pathogenic event in transgenic Caenorhabditis elegans expressing pan-neuronal human amyloid beta

Alzheimer’s disease (AD) is the most common neurodegenerative disease affecting the elderly worldwide. Mitochondrial dysfunction has been proposed as a key event in the etiology of AD. We have previously modeled amyloid-beta (Aβ)-induced mitochondrial dysfunction in a transgenic Caenorhabditis elegans strain by expressing human Aβ peptide specifically in neurons (GRU102). Here, we focus on the deeper metabolic changes associated with this Aβ-induced mitochondrial dysfunction. Integrating metabolomics, transcriptomics and computational modeling, we identify alterations in Tricarboxylic Acid (TCA) cycle metabolism following even low-level Aβ expression. In particular, GRU102 showed reduced activity of a rate-limiting TCA cycle enzyme, alpha-ketoglutarate dehydrogenase. These defects were associated with elevation of protein carbonyl content specifically in mitochondria. Importantly, metabolic failure occurred before any significant increase in global protein aggregate was detectable. Treatment with an anti-diabetes drug, Metformin, reversed Aβ-induced metabolic defects, reduced protein aggregation and normalized lifespan of GRU102. Our results point to metabolic dysfunction as an early and causative event in Aβ-induced pathology and a promising target for intervention.

Mitochondria and cell bioenergetics: increasingly recognized components and a possible etiologic cause of Alzheimer's disease

SIGNIFICANCE

Mitochondria and brain bioenergetics are increasingly thought to play an important role in Alzheimer's disease (AD).

RECENT ADVANCES

Data that support this view are discussed from the perspective of the amyloid cascade hypothesis, which assumes beta-amyloid perturbs mitochondrial function, and from an opposite perspective that assumes mitochondrial dysfunction promotes brain amyloidosis. A detailed review of cytoplasmic hybrid (cybrid) studies, which argue mitochondrial DNA (mtDNA) contributes to sporadic AD, is provided. Recent AD endophenotype data that further suggest an mtDNA contribution are also summarized.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Biochemical, molecular, cybrid, biomarker, and clinical data pertinent to the mitochondria-bioenergetics-AD nexus are synthesized and the mitochondrial cascade hypothesis, which represents a mitochondria-centric attempt to conceptualize sporadic AD, is discussed.

Systemic and brain metabolic dysfunction as a new paradigm for approaching Alzheimer's dementia

Since its definition Alzheimer's disease has been at the centre of consideration for neurologists, psychiatrists, and pathologists. With John P. Blass it has been disclosed a different approach Alzheimer's disease neurodegeneration understanding not only by the means of neurochemistry but also biochemistry opening new scenarios in the direction of a metabolic system degeneration. Nowadays, the understanding of the role of cholesterol, insulin, and adipokines among the others in Alzheimer's disease etiopathogenesis is clarifying approaches valuable not only in preventing the disease but also for its therapy.

Predicting Alzheimer dementia in mild cognitive impairment patients. Are biomarkers useful?

A correct clinical diagnosis in the early stage of Alzheimer disease is not only of importance given the current available treatment with acetylcholine esterase inhibitors, but would be the basis for disease-modifying therapy slowing down or arresting the degenerative process. Moreover, in the last years, several efforts have been made to determine if a patient with mild cognitive impairment has incipient Alzheimer disease, i.e. will progress to Alzheimer disease with dementia, or have a benign form of mild cognitive impairment. In this review, the recent published reports regarding progress in early and preclinical Alzheimer disease diagnosis are discussed and the role of peripheral and cerebrospinal fluid biomarkers highlighted. Approaches combining panels of different biomarkers show promise for discovering profiles that are characteristic of Alzheimer disease, even in the pre-symptomatic stage. More work is needed but available novel perspectives offered by recent introduced technologies shed some lights in identifying incipient Alzheimer disease in mild cognitive impairment subjects.

Polymorphisms of the CHRNA4 gene encoding the alpha4 subunit of nicotinic acetylcholine receptor as related to the oxidative DNA damage and the level of apoptotic proteins in lymphocytes of the patients with Alzheimer's disease

The study aimed at the analysis of polymorphisms in the gene coding for the nicotinic acetylcholine receptor alpha4 subunit (CHRNA4) and the evaluation of the extent of the oxidative damage to DNA (8-oxo2dG), as well as the level of proteins participating in DNA repair (p53, PARP) and DNA degradation (Bax:Bcl-2, 85-kDa fragment) in the peripheral blood lymphocytes of the patients suffering from Alzheimer's disease (AD) and in the healthy individuals of the control group. In the AD patients the increased levels of oxidized guanine were demonstrated in DNA, accompanied by the elevated expression of p53, Bax, PARP, and of a 85-kDa protein subunit as well as an augmented ratio of Bax:Bcl-2. Also, the level of Bcl-2 protein was decreased. In the AD patients with the CHRNA4 polymorphisms the highest level of 8-oxo2dG and of proteins involved in DNA repair were documented in patients with polymorphisms in exon 5, in contrast to the patients with polymorphisms in intron 5. In the former patients, levels of pro- and antiapoptotic proteins remained at the same level. Both CHRNA4 polymorphisms and the extent of dementia seem to affect the levels of DNA oxidative damage as well as to activate factors that participate in the DNA degradation and its repair.

Platelets provide human tissue to unravel pathogenic mechanisms of Alzheimer disease

Alzheimer disease (AD) is a progressive neurodegenerative disorder characterised by a progressive cognitive and memory decline. From a neuropathological point of view, Alzheimer disease is defined by the presence of characteristic lesions, i.e. mature senile plaques, neurofibrillary tangles and amyloid angiopathy. In particular, accumulation of the amyloid beta-peptide in the brain parenchyma and vasculature is an invariant event in the pathogenesis of both sporadic and familial Alzheimer cases. Amyloid beta-peptide originates from a larger precursor, the Amyloid Precursor Protein (APP) ubiquitously expressed. Among the different peripheral cells expressing APP forms, platelets are particularly interesting since they show concentrations of its isoforms equivalent to those found in brain. Moreover, a number of laboratories independently described alterations in APP metabolism/concentration in platelets of Alzheimer patients when compared to control subjects matched for demographic characteristics. These observations defined the frame of our work aimed to investigate if a correlation between levels of platelet APP forms and Alzheimer disease could be detected. We have reported that patients affected by Alzheimer disease show a differential level of platelet APP forms. This observation has several implications: APP processing abnormalities, believed to be a very early change in Alzheimer disease in neuronal compartment, does occur in extraneuronal tissues, such as platelets, thus suggesting that Alzheimer disease is a systemic disorder; further, our data strongly indicate that a differential level of platelet APP forms can be considered a potential peripheral marker of Alzheimer disease allowing for discrimination between Alzheimer and other types of dementia with good sensitivity and specificity.

Neural cell adhesion molecule in human serum. Increased levels in dementia of the Alzheimer type

Memory impairment is a process associated with alterations in neuronal plasticity, synapses formation, and stabilization. As the neural cell adhesion molecule (NCAM) plays a key role in synaptic bond stabilization, we analyzed the usefulness of soluble NCAM isoforms in the diagnosis of patients with dementia of the Alzheimer type (DAT). NCAM was measured in the sera of 70 control subjects and 43 DAT patients (with different severity of cognitive impairment, GDS), employing Western blot and densitometric quantification. LMW-NCAM bands (100-130 kDa) decreased significantly with age independently of sex. DAT patients presented values of LMW-NCAM and HMW-NCAM significantly higher than healthy controls of similar age (higher than 130 kDa). Only LMW-NCAM was associated with GDS. Our results suggest that NCAM could be involved in the pathogenesis of DAT disorder and that serum NCAM levels could be useful as differential diagnostic markers of the disease.

Cerebrometabolic abnormalities in Alzheimer's disease

Extensive, replicated evidence in patients in vivo and in Alzheimer (AD) tissues in vitro indicates that impaired brain metabolism is one of the cardinal and essentially invariable events in AD. The degree of impairment in brain metabolism is proportional to the degree of clinical disability, both in vivo and in vitro. The 'cerebrometabolic lesion' cannot be attributed to 'slower thinking' or 'brain atrophy', because of quantitative considerations and because the metabolic lesion precedes the development of neuropsychological abnormalities or decreases in brain mass detectable by modern imaging techniques. The causes of the cerebrometabolic lesion in AD are not well defined. Free radicals seem likely to be involved, including free radicals generated from Alzheimer amyloid. Thus, the importance of the cerebrometabolic lesion is entirely compatible with most versions of the widely accepted 'amyloid cascade hypothesis' of AD. A variety of plausible, redundantly documented mechanisms are compatible with the proposal that the cerebrometabolic lesion is a proximate cause of the clinical disability in AD. In agreement with these findings, recent attempts to treat the cerebrometabolic lesion in AD have given encouraging preliminary results. The cerebrometabolic lesion in AD deserves further study.

Glucose/mitochondria in neurological conditions

Impairments of glucose and mitochondrial function are important causes of brain dysfunction and therefore of brain disease. Abnormalities have been found in association with disease of the nervous system in most of the components of glucose/mitochondrial metabolism. In many, molecular genetic abnormalities have been defined. Brain glucose oxidation is abnormal in common diseases of the nervous system, including Alzheimer disease and other dementias, Parkinson disease, delirium, probably schizophrenia and other psychoses, and of course cerebrovascular disease. Defects in a single component and even a single mutation can be associated with different clinical phenotypes. The same clinical phenotype can result from different genotypes. The complex relationship between biological abnormality in brain glucose utilization and clinical disorder is similar to that in other disorders that have been intensively studied at the genetic level. Genes for components of the pathways of brain glucose oxidation are good candidate genes for disease of the brain. Preliminary data support the proposal that treatments to normalize abnormalities in brain glucose oxidation may benefit many patients with common brain diseases.

ApoE genotype influences the biological effect of donepezil on APP metabolism in Alzheimer disease: evidence from a peripheral model

Three major amyloid precursor protein (APP) forms with apparent molecular weight ranging from 106 to 130 kDa are present in human platelets. Alzheimer disease (AD) is associated with a decreased APP forms ratio (APPr) between the three major forms. A total of 25 mild to moderate AD patients were investigated. Platelet APPr was studied before and after 30 days of acetylcholinesterase-inhibitor treatment (donepezil, 5 mg daily). Patients were grouped into non-epsilon4 carriers and epsilon4 carriers according to apolipoprotein E (ApoE) genotype. At baseline, all patients showed low APPr levels and no significant difference was found between the two ApoE subgroups. After treatment, although a marked improvement in APPr was observed in most patients, non-epsilon4 carriers displayed a higher increase compared to epsilon4 carriers (P<0.0001). The present study provides evidence that donepezil influences APP metabolism in platelets, and suggests that ApoE genotype might be an important modulating factor for drug responsiveness in AD.

A unifying hypothesis of Alzheimer's disease. IV. Causation and sequence of events

Contrary to common concepts, the brain in Alzheimer's disease (AD) does not follow a suicide but a rescue program. Widely shared features of metabolism in starvation, hibernation and various conditions of energy deprivation, e.g. ischemia, allow the definition of a deprivation syndrome which is a phylogenetically conserved adaptive response to energetic stress. It is characterized by hypometabolism, oxidative stress and adjustments of the glucose-fatty acid cycle. Cumulative evidence suggests that the brain in aging and AD actively adapts to the progressive fuel deprivation. The counterregulatory mechanisms aim to preserve glucose for anabolic needs and promote the oxidative utilization of ketone bodies. The agent mediating the metabolic switch is soluble Abeta which inhibits glucose utilization and stimulates ketone body utilization at various levels. These processes, which are initiated during normal aging, include inhibition of pro-glycolytic neurohormones, cholinergic transmission, and pyruvate dehydrogenase, the key transmitter and effector systems regulating glucose metabolism. Hormonal and effector systems which promote ketone body utilization, such as glucocorticosteroid and galanin activity, GABAergic transmission, nitric oxide, lipid transport, Ca2+ elevation, and ketone body metabolizing enzymes, are enhanced. A multitude of risk factors feed into this pathophysiological cascade at a variety of levels. Taking into account its pleiotropic regulatory actions in the deprivation response, a new name for Abeta is suggested: deprivin. On the other hand, cumulative evidence, taken together compelling, suggests that senile plaques are the dump rather than the driving force of AD. Moreover, the neurotoxic action of fibrillar Abeta is a likely in vitro artifact but does not contribute significantly to the in vivo pathophysiological events. This archaic program, conserved from bacteria to man, aims to ensure the survival of a deprived organism and controls such divergent processes as sporulation, hibernation, aging and aging-related diseases. In contrast to the immature brain, ketone body utilization of the aged brain is no longer sufficient to meet the energetic demands and is later supplemented by lactate, thus recapitulating in reverse order the sequential fuel utilization of the immature brain. The transduction pathways which operate to switch metabolism also convey the programming and balancing of the de-/redifferentiation/apoptosis cell cycle decisions. This encompasses the reiteration of developmental processes such as transcription factor activation, tau hyperphosphorylation, and establishment of growth factor independence by means of Ca2+ set point shift. Thus, the increasing energetic insufficiency results in the progressive centralization of metabolic activity to the neuronal soma, leading to pruning of the axonal/dendritic trees, loss of neuronal polarity, downregulation of neuronal plasticity and, eventually, depending on the Ca2+ -energy-redox homeostasis, degeneration of vulnerable neurons. Finally, it is outlined that genetic (e.g. Down's syndrome, APP and presenilin mutations and apoE4) and environmental risk factors represent progeroid factors which accelerate the aging process and precipitate the manifestation of AD as a progeroid systemic disease. Aging and AD are related to each other by threshold phenomena, corresponding to stage 2, the stage of resistance, and stage 3, exhaustion, of a metabolic stress response.

Differential alterations in antioxidant capacity in cells from Alzheimer patients

Oxidative stress occurs in brains of Alzheimer's disease (AD) patients. A major question in AD research is whether the oxidative stress is just secondary to neurodegeneration. To test whether oxidative stress is an inherent property of AD tissues, the ability of cultured fibroblasts bearing the AD Presenilin-1 246 Ala-->Glu mutation to handle reactive oxygen species (ROS) was compared to controls. Although ROS in cells from AD subjects were only slightly less than cells from controls under basal conditions (-10%) or after exposure to H(2)O(2) (-16%), treatment with antioxidants revealed clear differences. Pretreatment with DMSO, a hydroxyl radical scavenger, reduced basal and H(2)O(2)-induced ROS levels significantly more in cells from controls (-22%, -22%) than in those from AD subjects (-4%, +14%). On the other hand, pretreatment with Trolox diminished H(2)O(2)-induced ROS significantly more in cells from AD (-60%) than control subjects (-39%). In summary, cells from AD patients have greater Trolox sensitive ROS and less DMSO sensitive ROS than controls. The results demonstrate that fibroblasts bearing this PS-1 mutation have altered means of handling oxidative stress and appear useful for determining the mechanism underlying the altered redox metabolism.

Platelets as a peripheral district where to study pathogenetic mechanisms of alzheimer disease: the case of amyloid precursor protein

Alzheimer disease is a progressive neurodegenerative disease, characterised by a progressive cognitive and memory decline. From a neuropathological point of view, Alzheimer disease is defined by the presence of characteristic lesions, i.e. mature senile plaques, neurofibrillary tangles (NFTs) and amyloid angiopathy. In particular, accumulation of the amyloid beta-peptide in the brain parenchyma and vasculature is an invariant event in the pathogenesis of both sporadic and familial Alzheimer cases. Amyloid beta-peptide originates from a larger precursor, the amyloid precursor protein (APP) ubiquitously expressed. Among the different peripheral cells expressing APP forms, platelets are particularly interesting since they show concentrations of its isoforms equivalent to those found in brain. Moreover, a number of laboratories independently described alterations in APP metabolism/concentration in platelets of Alzheimer patients when compared to control subjects matched for demographic characteristics. These observations defined the frame of our work aimed to investigate if a correlation between levels of platelet APP forms and Alzheimer disease could be detected. We have reported that patients affected by Alzheimer disease show a differential level of platelet APP forms. This observation has several implications: APP processing abnormalities, believed to be a very early change in Alzheimer disease in neuronal compartment, do occur in extraneuronal tissues, such as platelets, thus, suggesting that Alzheimer disease is a systemic disorder; further, our data strongly indicate that a differential level of platelet APP isoforms can be considered a potential peripheral marker of Alzheimer disease allowing for discrimination between Alzheimer and other types of dementia.

The frequency of point mutations in mitochondrial DNA is elevated in the Alzheimer's brain

Using a PCR-based strategy, we found that point mutation frequencies in mitochondrial DNA (mtDNA) were 2- to 3-fold higher in the parietal gyrus, hippocampus, and cerebellum from subjects with Alzheimer's disease (AD) compared to normal controls. In contrast, levels of a commonly studied deletion mutation, mtDNA(4977), were not elevated in AD. The frequency of point mutations did not vary significantly among the three brain areas, whereas the frequency of mtDNA(4977) was 15- to 25-fold lower in the cerebellum in comparison to the cortex; this regional variation was seen in both the normal and Alzheimer's brain. In blood mtDNA, point mutation frequencies were not elevated in AD patients. The elevated frequency of point mutations in all three brain regions is consistent with the idea that increased oxidant stress is associated with AD.

Mitotic index and Alzheimer's disease

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is diagnosed definitively by increased numbers of beta-amyloid plaques and neurofibrillary tangles in brain biopsy or autopsy specimens. There are no simple straightforward laboratory tests currently available for clinical diagnosis. We have found consistent reduction in mitotic index levels in skin fibroblast cultures from AD individuals compared with age- and sex-matched controls. These differences were enhanced by overnight exposure to colcemid (p = 0.04). Results suggest that mitotic index in skin fibroblasts cultures should be further investigated as a potential diagnostic indicator for AD.

Brain endothelial cell enzymes cleave platelet-retained amyloid precursor protein

We have previously demonstrated that thrombin-activated platelets from patients with advanced Alzheimer's disease (AD) retain significantly more surface membrane-bound amyloid precursor protein (mAPP) than platelets from non-demented age-matched individuals (AM). We have studied interactions between these platelets and the cerebrovascular endothelium to which activated platelets adhere in a model system, investigating their involvement in the formation of amyloid beta peptide (Abeta) deposits in AD patients. We report here that there appear to be alpha and beta secretase-like activities in primary human blood brain barrier endothelial cell (BEC) cultures from both AD patients and AM control subjects (AD-BEC and AM-BEC, respectively) as well as a gamma secretase-like activity that appears only in AD-BEC. No such activities were observed in human umbilical vein endothelial cells (HUVECs). Furthermore, there is more penetration of the platelet-released products platelet factor 4 and soluble APP through the BEC layer grown from AD patients than that grown from AM individuals, whereas none penetrate through a HUVEC layer. Thus the interaction between platelets, the APP they have retained or released, and cerebral vascular endothelial cells may be at least partially responsible for amyloidogenic deposits around the cerebral vasculature of AD patients.

Moderate and advanced Alzheimer's patients exhibit platelet activation differences

We previously reported that platelets from advanced sporadic Alzheimer's disease (AD) patients exhibit two defects: first, an aberrant signal transduction presenting as a thrombin-induced hyperacidification, which is more severe for donors with the apolipoprotein E4 allele (apoE4), and second, an AD-specific Amyloid Precursor Protein (APP) processing defect that presents as retention of APP on the activated platelets' surface and in independent of the apo E allele. This retention of membrane APP correlates with decreased release of soluble APP. To determine at what stage in the disease progression these defects appear, we performed signal transduction and secretion studies on moderate AD patients. Thrombin-activated platelets from these patients do not exhibit either hyperacidification or APP retention; their APP processing and secretion are normal by Western blotting, suggesting that the two platelet defects appear in the advanced stages of AD.

Binding of platelet-activating factor to platelets of Alzheimer's disease and multiinfarct dementia patients

The binding of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine (platelet-activating factor, PAF) to platelets was studied in 22 patients with probable Alzheimer's disease (AD), 11 with multi-infarct dementia (MID), 22 age-matched normal old controls, and 20 young subjects. The results showed a significantly lower degree of PAF binding to platelets of AD and MID patients than in those of the old controls and young subjects (133.3 +/- 8.5, and 123.4 +/- 16.5 vs. 202.3 +/- 11.6 and 206.7 +/- 17.3 receptors/cell, respectively; p < 0.01). These differences were due to reduced Bmax, while Kd remained unchanged. No significant difference was observed between the PAF binding to platelets of AD and MID patients nor between that of old and young controls. No correlation was found between age and binding in the various elderly groups. However, a significant correlation was found between PAF binding and degree of cognitive impairment in the AD patients. This is the first evidence to support a possible involvement of PAF in dementing disorders.

Pupillary response to tropicamide in patients with Alzheimer disease

PURPOSE

To determine whether pupillary responses to dilute tropicamide could be used as a diagnostic test for Alzheimer disease (AD). The authors also investigated whether concurrent use of an oral acetylcholinesterase inhibitor (tacrine) alters the pupillary response to dilute tropicamide in patients with AD, and whether pupillary responses to dilute tropicamide differ in young versus older control subjects.

METHODS

Pupillary diameter and area of both eyes were measured in light and darkness, at 10-minute intervals for 40 minutes after random instillation of 0.01% tropicamide to one eye. Four groups of subjects were studied: 9 patients with AD, 10 who were treated with tacrine, 11 older control subjects, and 10 young control subjects.

RESULTS

Mean change in anisocoria was not significantly different among groups at any of the measurement time points. Mean percent change in diameter of the treated eyes showed a trend toward faster maximum dilatation in the AD groups, but change in pupillary measurements did not identify individuals with AD.

CONCLUSION

Pupillary response to dilute tropicamide did not effectively distinguish individual patients with AD from young or older control subjects.

Changes in platelet phospholipase C protein level and activity in Alzheimer's disease

We have previously demonstrated that PLC-delta was abnormally accumulated in autopsied brains with Alzheimer's disease (AD). As nonneuronal tissue involvement in AD is also suggested and PLC activity is reduced in AD platelets, we examined the changes of the protein level of PLC-delta and its enzyme activity in platelets taken from patients with AD and age-matched controls. PLC-delta in human platelets was detected as a 72 kDa protein using a specific antibody against PLC-delta. Western blots revealed that the protein level of PLC-delta was significantly higher in the cytosolic fraction prepared from AD platelets compared to controls. We investigated the activity of PLC-delta which hydrolyzes phosphatidylinositol and found that the PLC-delta activity in the cytosolic fraction from AD platelets was significantly reduced compared to the control. This finding that the enzyme activity per PLC-delta molecule is reduced in AD platelets is consistent with the study using Alzheimer brains. These results suggest that aberrant phosphoinositide metabolism is present in nonneuronal tissues as well as the brains of patients with AD.

Increased cerebrospinal fluid pyruvate levels in Alzheimer's disease

Impaired energy metabolism is an early, predominant feature in Alzheimer's disease. In order to find out simple, reliable 'in vivo' markers for the clinical-biological typization of the disorder, we measured cerebrospinal fluid (CSF) glucose, lactate and pyruvate levels in patients suffering from dementia of Alzheimer type (DAT) and in healthy elderly controls. DAT group showed remarkably higher levels of pyruvate (P = 0.01), with no overlap with the values obtained in controls. CSF pyruvate levels were also significantly associated with the severity of dementia. Therefore, CSF pyruvate levels neatly separate DAT patients from controls, having also pathogenetic value.

Tau-like immunoreactivity in Alzheimer and control skin fibroblasts

The presence of the microtubule-associated protein tau in skin fibroblasts derived from Alzheimer patients and normal controls was investigated using a panel of well-characterized anti-tau antibodies against epitopes spanning the tau protein from the amino to the carboxyl end. The antibodies immunolabeled a fine, fibrillar cytoplasmic network in all skin fibroblasts. Disruption of the microtubule network with colchicine did not affect the immunolabeling of the fibrillar network nor did treatment with cytochalasin B known to disrupt the microfilament network. Immunoelectron microscopy with the anti-tau antibodies revealed colocalization of the label with the 10 nm intermediate filaments. Furthermore, immunoblots found no reactivity against purified vimentin, suggesting that the antibodies recognize an intermediate filament-associated protein. The findings indicate the presence of tau or a protein with considerable homology to tau in fibroblasts associated with intermediate filaments and not microtubules.

Platelet protein kinase C levels in Alzheimer's disease

Alzheimer's disease (AD) has been suggested to be a systemic disease, and signal transduction abnormalities have been reported in non-neuronal AD cells. We have previously quantified the protein kinase C (PKC) subtypes in AD and control brains using a two-site enzyme immunoassay (EIA), and have shown that type II PKC levels were significantly reduced in the temporal cortex of AD patients. In this study, we used this EIA to assess the platelet levels of type II PKC in age-matched groups of AD patients and normal controls. The cytosolic level of type II PKC was significantly higher in AD platelets than in control platelets but was unchanged in the membranous fraction. Platelet proteins showed no differences between the AD and control groups. Therefore, the type II PKC content of the cytosolic fraction was increased in AD platelets. These results suggest that type II PKC may be altered in both the brain and platelets of AD patients and support the hypothesis that AD is a systemic disease.

Peripheral markers and diagnostic criteria in Alzheimer's disease: critical evaluations

This review analyzes recent developments in diagnostic criteria and peripheral markers used clinically in the definitive diagnosis of Alzheimer's disease (AD), comparing past and current views, together with a discussion of their shortcoming and difficulties of implementation. Consideration is given to studies on the presence of amyloid substances outside the central nervous system: in cerebrospinal fluid, in plasma, in primary cultures, and in continuous cultures of cell lines of neuronal and glial origin. We discuss alterations of cholinesterases and noradrenaline in red blood cells (RBC) in AD and, with relation to the infectious theory, the presence of spirochaetes in patients. The activities of the enzymes leading to the formation of amyloid substances and those reflecting more general alterations of metabolic processes are considered, both in respect to their role in the pathogenesis of the neurodegenerative disorders of AD and of their potential use as markers. Enzymatic changes have been studied comparing AD patients with non AD controls as well as with AD relatives: proteases and their inhibitors; plasminogen activators; transketolases; increases in the activity of Cu-Zn superoxide dismutase in AD patients' RBC, serum, fibroblasts and cortical neurons, pointing to alterations in oxidative processes; and apolipoprotein E epsilon 4 allele, linked to late-onset AD and familial cases. This review presents reasons why the involvement of peripheral markers in AD should advance from hypothesis to accepted fact.

Alterations of intracellular calcium regulation during aging and Alzheimer's disease in nonneuronal cells

Because of its function as an intracellular messenger in many cells, calcium plays an important role in signal transduction. Changes in intracellular free calcium concentration occur in central neurons during aging and Alzheimer's disease (AD). It is possible that similar changes in peripheral cells could mirror or, at least parallel, similar abnormalities in the brain. Assuming that manifestations of the aging process and AD are also present outside the central nervous system, nonneuronal tissues like lymphocytes could be used to search directly for abnormalities in cellular calcium regulation in man. Consistent with observations of reduced depolarization-induced Ca2+ rises in dissociated neurons of aged mice, corresponding age-related changes of reduced mitogen-induced Ca2+ responses were observed both in mouse lymphocytes and, more importantly, in circulating human lymphocytes. With respect to AD, Ca2+ responses after stimulation were unaltered (compared to normal controls). In addition, freshly prepared human lymphocytes showed elevated mitogen-induced Ca2+ responses after exposure to beta-amyloid, the main component of senile plaques in AD. These findings again parallel our observations that this peptide amplifies the K(+)-induced Ca2+ rise in acutely dissociated mouse brain cells. Thus, the lymphocyte seems to be a valuable model to study the effects of beta-amyloid in man. In a preliminary study with AD-patients, sensitivity of the lymphocytes to beta-amyloid's effects on Ca2+ rise was reduced, an observation which was entirely unexpected. Nevertheless, such studies indicate lymphocytes may represent a promising candidate for a peripheral marker of AD and can contribute to the understanding of the disease process.