Cerebrospinal fluid levels of amyloid precursor protein and amyloid beta-peptide in Alzheimer's disease and major depression - inverse correlation with dementia severity

Highly conserved and disease-specific patterns of carboxyterminally truncated Abeta peptides 1-37/38/39 in addition to 1-40/42 in Alzheimer's disease and in patients with chronic neuroinflammation

Human lumbar CSF patterns of Abeta peptides were analysed by urea-based beta-amyloid sodium dodecyl sulphate polyacrylamide gel electrophoresis with western immunoblot (Abeta-SDS-PAGE/immunoblot). A highly conserved pattern of carboxyterminally truncated Abeta1-37/38/39 was found in addition to Abeta1-40 and Abeta1-42. Remarkably, Abeta1-38 was present at a higher concentration than Abeta1-42, being the second prominent Abeta peptide species in CSF. Patients with Alzheimer's disease (AD, n = 12) and patients with chronic inflammatory CNS disease (CID, n = 10) were differentiated by unique CSF Abeta peptide patterns from patients with other neuropsychiatric diseases (OND, n = 37). This became evident only when we investigated the amount of Abeta peptides relative to their total Abeta peptide concentration (Abeta1-x%, fractional Abeta peptide pattern), which may reflect disease-specific gamma-secretase activities. Remarkably, patients with AD and CID shared elevated Abeta1-38% values, whereas otherwise the patterns were distinct, allowing separation of AD from CID or OND patients without overlap. The presence of one or two ApoE epsilon4 alleles resulted in an overall reduction of CSF Abeta peptides, which was pronounced for Abeta1-42. The severity of dementia was significantly correlated to the fractional Abeta peptide pattern but not to the absolute Abeta peptide concentrations.

Cortico-hippocampal APP and NGF levels are dynamically altered by cholinergic muscarinic antagonist or M1 agonist treatment in normal mice

To determine whether altered cholinergic neurotransmission can modify the long-term secretion of amyloid precursor protein (APP), endogenous levels of APP and nerve growth factor (NGF), we administered a selective M1 muscarinic receptor agonist (RS86) or the muscarinic antagonist, atropine, for 7 days in vivo into young adult mice (C57BL/6j). The levels of NGF and total APP in the hippocampus, frontal cortex, striatum, parietal cortex and cerebrospinal fluid (CSF) were examined by ELISA and Western blot. We found that this repeated i.m. administration of M1 receptor agonist resulted in decreased total APP levels in the hippocampus, frontal cortex and parietal cortex, and increased secreted alpha-APPs levels in the CSF. M1 agonist treatment also resulted in decreased NGF levels in the hippocampus and CSF. These effects of the M1 muscarinic agonist could be blocked by atropine, which by itself elevated tissue levels of total APP. Interestingly, we found that the decrease of total APP in the hippocampus and striatum after M1 agonist treatment inversely correlated with the change in NGF levels. These data suggest that a sustained increased cholinergic, M1-mediated neurotransmission will enhance secretion of alpha-APPs in CSF and adaptively reduce the levels of total APP and NGF in the corticohippocampal regions of normal mice. The dynamic and adaptive regulation linking total APP and NGF levels in normal adult mice is relevant for understanding the pathophysiology of conditions with cholinergic and APP related pathologies, like Alzheimer's disease and Down's syndrome.

The cerebrospinal fluid levels of tau, growth-associated protein-43 and soluble amyloid precursor protein correlate in Alzheimer's disease, reflecting a common pathophysiological process

Cerebrospinal fluid (CSF) levels of tau (total tau), growth-associated protein-43 (GAP-43), soluble amyloid precursor protein (sAPP; i.e. total sAPP), and beta-amyloid(42) (Abeta(42)) were studied in patients with frontotemporal dementia (FTD; n = 14), Alzheimer's disease (AD; n = 47) and vascular dementia (VAD; n = 16), and in age-matched controls (n = 12). CSF-tau was increased in AD compared to controls and FTD (p < 0.001 for both). CSF-GAP-43 was increased in AD compared to controls (p < 0.05), and both CSF-GAP-43 and CSF-sAPP were increased in AD compared to FTD (p < 0.01). Positive and highly significant correlations were found between CSF-tau and CSF-GAP-43 in all groups and between CSF-tau, CSF-GAP-43 and CSF-sAPP in AD. The correlations found may reflect a common pathophysiologic process such as axonal degeneration.

Tau and transgenic animal models

Advances in genetics and transgenic approaches have a continuous impact on our understanding of Alzheimer's disease (AD) and related disorders, especially as aspects of the histopathology and neurodegeneration can be reproduced in animal models. AD is characterized by extracellular Abeta peptide-containing plaques and neurofibrillary aggregates of hyperphosphorylated isoforms of microtubule-associated protein tau. A causal link between Abeta production, neurodegeneration and dementia has been established with the identification of familial forms of AD which are linked to mutations in the amyloid precursor protein APP, from which the Abeta peptide is derived by proteolysis. No mutations have been identified in the tau gene in AD until today. Tau filament formation, in the absence of Abeta production, is also a feature of several additional neurodegenerative diseases including progressive supranuclear palsy, corticobasal degeneration, Pick's disease, and frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17). The identification of mutations in the tau gene which are linked to FTDP-17 established that dysfunction of tau can, as well as Abeta formation, lead to neurodegeneration and dementia. In this review, newly recognized cellular functions of tau, and the neuropathology and clinical syndrome of FTDP-17 will be presented, as well as recent advances that have been achieved in studies of transgenic mice expressing tau and AD-related kinases and phosphatases. These models link neurofibrillary lesion formation to neuronal loss, provide an in vivo model in which therapies can be assessed, and may contribute to determine the relationship between Abeta production and tau pathology.

Reduction of cerebrospinal fluid amyloid beta after systemic administration of M1 muscarinic agonists

Overproduction of the peptide amyloid beta (A beta) is a critical event in Alzheimer's disease (AD). Systemic administration of 3 M1-selective muscarinic agonists, AF102B, AF150S and AF267B, decreased cerebrospinal fluid (CSF) A beta concentrations; levels of CSF secreted beta-APP were not significantly altered. Rabbits treated for 5 days with s.c. injections of each drug (2 mg/kg/day) had levels of CSF A beta which were between 55 and 71% of control for A beta 1-40 and between 59 and 84% of control for A beta 1--42.

Treatment with the selective muscarinic agonist talsaclidine decreases cerebrospinal fluid levels of total amyloid beta-peptide in patients with Alzheimer's disease

Brain amyloid load in Alzheimer's disease (AD) is, at least in genetic forms, associated with overproduction of amyloid beta-peptides (A beta). Thus, lowering A beta production is a central therapeutic target in AD and may be achieved by modulating such key enzymes of amyloid precursor protein (APP) processing as beta-, gamma-, and alpha-secretase activities. Talsaclidine is a selective muscarinic M1 agonist that stimulates the nonamyloidogenic alpha-secretase pathway in model systems. Talsaclidine was administered double-blind, placebo-controlled, and randomized to 24 AD patients and cerebrospinal fluid (CSF) levels of total A beta were quantitated before and after 4 weeks of drug treatment. We observed that talsaclidine decreases CSF levels of A beta significantly over time within the treatment group (n = 20) by a median of 16% as well as compared to placebo (n = 4) by a median of 27%. We conclude that treatment with selective M1 agonists may reduce A beta production and may thus be further evaluated as a potential amyloid-lowering therapy of AD.

Proteomics in molecular medicine: applications in central nervous systems disorders

Bodily fluids such as cerebrospinal fluid (CSF) and serum can be analysed at the time of presentation and throughout the course of the disease. Changes in the protein composition of CSF may be indicative of altered CNS protein expression pattern with a causative or diagnostic disease link. These findings can be strengthened through subsequent proteomic analysis of specific brain areas implicated in the pathology. New isolation strategies of clinically relevant cellular material such as laser capture microdissection, protein enrichment procedures and proteomic approaches to neuropeptide and neurotransmitter analysis give us the opportunity to map out complex cellular interaction at an unprecedented level of detail. In neurological disorders multiple underlying pathogenic mechanisms as well as an acute and a chronic CNS disease components may require a selective repertoire of molecular targets and biomarkers rather than an individual protein to better define a complex disease. The resulting proteome database bypasses many ambiguities of experimental models and may facilitate pre- and clinical development of more specific disease markers and new selective fast acting therapeutics.

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.

Prediction of deterioration in mild cognitive disorder in old age--neuropsychological and neurochemical parameters of dementia diseases

In normal senescence, an age-related impairment of cognitive function is observed. The difficult clinical question is in which cases of mild cognitive impairment (MCI) will there be a rapid cognitive decline to a dementia syndrome. Two ways to improve prognosis are discussed: neuropsychological tests and analysis of neurochemical markers. First, the question is asked as to whether there are clusters of MCI. Longitudinal neuropsychological data from the Berlin Aging Study (BASE) are presented, a population-based sample of 516 subjects aged 70 to 103 years. There are clusters found that in part match those clusters, which have been identified by a study from Ritchie et al. in 1996. Especially, a cluster of 13.8% of the nondemented participants with a decline in memory performance is observed. The validation of clusters of cognitive performance and decline opens up the possibility of diagnosing distinctive subgroups of MCI to improve prognosis in old age. Second, the existing data concerning the diagnostic laboratory analysis for Alzheimer's disease (AD) are reviewed. Especially, data regarding nerve growth factor (NGF) are reported. In MCI, preliminary data show a correlation between the NGF serum level and cognitive performance. It can be concluded that the combined investigation of neuropsychological functions and cognitive decline, as well as laboratory measurement of neurochemical markers, might allow an improved prognosis for mental health in very old age.

Age-related cognitive decline, mild cognitive impairment or preclinical Alzheimer's disease?

With the promising development of effective treatment, significant improvement in the very early diagnosis of Alzheimer's disease (AD) is required. There is vast agreement that a decline in memory, especially in verbal episodic memory, is the earliest and perhaps the most sensitive sign of incipient AD at the preclinical stage. However, this review offers evidence that impairment in episodic memory can be observed in normal elderly people as well as in aged subjects with mild cognitive impairment (MCI), a large proportion of whom will, however, not convert to dementia. Quantitative measurement of atrophy and brain activation in the hippocampal-parahippocampal formation by using structural and functional magnetic resonance imaging may help to distinguish the MCI decliners from the nondecliners. Cerebrospinal fluid levels of tau protein and Abet1-42 peptide, together with the presence of an apolipoprotein (apo)E epsilon4 allele may also increase our confidence in the early positive diagnosis of AD. This review concludes, however, that while adequate for constituting groups of patients in a research perspective, the extensive diagnostic procedure based on specific cognitive testing, neuroimaging and biological investigations is still out of reach for the practitioner.

Neuronal overexpression of mutant amyloid precursor protein results in prominent deposition of cerebrovascular amyloid

Transgenic mice that overexpress mutant human amyloid precursor protein (APP) exhibit one hallmark of Alzheimer's disease pathology, namely the extracellular deposition of amyloid plaques. Here, we describe significant deposition of amyloid beta (Abeta) in the cerebral vasculature [cerebral amyloid angiopathy (CAA)] in aging APP23 mice that had striking similarities to that observed in human aging and Alzheimer's disease. Amyloid deposition occurred preferentially in arterioles and capillaries and within individual vessels showed a wide heterogeneity (ranging from a thin ring of amyloid in the vessel wall to large plaque-like extrusions into the neuropil). CAA was associated with local neuron loss, synaptic abnormalities, microglial activation, and microhemorrhage. Although several factors may contribute to CAA in humans, the neuronal origin of transgenic APP, high levels of Abeta in cerebrospinal fluid, and regional localization of CAA in APP23 mice suggest transport and drainage pathways rather than local production or blood uptake of Abeta as a primary mechanism underlying cerebrovascular amyloid formation. APP23 mice on an App-null background developed a similar degree of both plaques and CAA, providing further evidence that a neuronal source of APP/Abeta is sufficient to induce cerebrovascular amyloid and associated neurodegeneration.

Regulation of amyloid precursor protein cleavage

Multiple lines of evidence suggest that increased production and/or deposition of the beta-amyloid peptide, derived from the amyloid precursor protein, contributes to Alzheimer's disease. A growing list of neurotransmitters, growth factors, cytokines, and hormones have been shown to regulate amyloid precursor protein processing. Although traditionally thought to be mediated by activation of protein kinase C, recent data have implicated other signaling mechanisms in the regulation of this process. Moreover, novel mechanisms of regulation involving cholesterol-, apolipoprotein E-, and stress-activated pathways have been identified. As the phenotypic changes associated with Alzheimer's disease encompass many of these signaling systems, it is relevant to determine how altered cell signaling may be contributing to increasing brain amyloid burden. We review the myriad ways in which first messengers regulate amyloid precursor protein catabolism as well as the signal transduction cascades that give rise to these effects.