Soluble amyloid precursor proteins in the cerebrospinal fluid as novel potential biomarkers of Alzheimer's disease: a multicenter study

In this report, we present the results of a multicenter study to test analytic and diagnostic performance of soluble forms of amyloid precursor proteins alpha and beta (sAPP alpha and sAPP beta) in the cerebrospinal fluid (CSF) of patients with different forms of dementing conditions. CSF samples were collected from 188 patients with early dementia (mini-mental state examination >or=20 in majority of cases) and mild cognitive impairment (MCI) in 12 gerontopsychiatric centers, and the clinical diagnoses were supported by neurochemical dementia diagnostic (NDD) tools: CSF amyloid beta peptides, Tau and phospho-Tau. sAPP alpha and sAPP beta were measured with multiplexing method based on electrochemiluminescence. sAPP alpha and sAPP beta CSF concentrations correlated with each other with very high correlation ratio (R=0.96, P<0.001). We observed highly significantly increased sAPP alpha and sAPP beta CSF concentrations in patients with NDD characteristic for Alzheimer's disease (AD) compared to those with NDD negative results. sAPP alpha and sAPP beta highly significantly separated patients with AD, whose diagnosis was supported by NDD findings (sAPP alpha: cutoff, 117.4 ng ml(-1), sensitivity, 68%, specificity, 85%, P<0.001; sAPP beta: cutoff, 181.8 ng ml(-1), sensitivity, 75%, specificity, 85%, P<0.001), from the patients clinically assessed as having other dementias and supported by NDD untypical for AD. We conclude sAPP alpha and sAPP beta might be regarded as novel promising biomarkers supporting the clinical diagnosis of AD.

Decreased circulating CD34+ stem cells in early Alzheimer's disease: Evidence for a deficient hematopoietic brain support?

Hematopoietic stem cells contribute to mammalian brain tissue regeneration by transdifferentiation processes. We found decreased counts of circulating CD34+ cells in early Alzheimer's dementia (AD; P = 0.01), which significantly correlated with age (r = -0.661; P = 0.001), cerebrospinal fluid beta-amyloid (Abeta)1-42 (r = -0.467; P = 0.025) and most pronounced the Abeta42/40 ratio (r = -0.688; P = 0.005). Our data suggest a deficient regenerative hematopoietic support for the central nervous system in early AD.

Lithium decreases secretion of Abeta1-42 and C-truncated species Abeta1-37/38/39/40 in chicken telencephalic cultures but specifically increases intracellular Abeta1-38

We studied endogenous amyloid precursor protein (APP) processing and amyloid beta (Abeta) peptide formation in primary chicken telencephalic neurons, because their Abeta peptide sequence is identical to humans. As detected by quantitative Abeta-SDS-PAGE/immunoblot, Abeta peptides 1-40/42 and three additional C-truncated species, namely Abeta1-37/38/39 were regularly released into the supernatant. The highly conserved Abeta quintet strongly resembles the pattern of Abeta peptides found in human cerebrospinal fluid. Furthermore, the C-terminally shorter Abeta peptides 1-33/34 could be readily detected. Recent evidence indicates that lithium specifically inhibits secretion of the amyloidogenic Abeta1-42 peptide in cultured permanent cells transfected with human APP. We therefore investigated the effect of lithium on Abeta peptide secretion as well as intracellular Abeta peptides in our untransfected primary cell culture system. Our data shows that lithium leads to a dose-dependent reduction of Abeta1-37/38/39/40/42 secretion. Surprisingly, intracellular analysis revealed that lithium specifically increases a band comigrating with synthetic Abeta1-38 while Abeta1-40 and Abeta1-42 remained almost unaffected. These results demonstrate for the first time that lithium treatment decreases Abeta peptide secretion in primary chicken neuronal cells but specifically elevates intracellular Abeta1-38. Therefore, we conclude that there are two independent mechanisms of lithium in intra- and extracellular Abeta peptide production.

Homocysteine induces cell death of rat astrocytes in vitro

From several disease states as well as from animal models homocysteine is known to be toxic to the central nervous system. Homocysteine is an excitatory amino acid which markedly enhances the vulnerability of neuronal cells to excitotoxic, apoptotic, and oxidative injury in vitro and in vivo. Both beneficent and deleterious effects of astrocytes in the pathogenesis of different neurodegenerative disorders have been described. However, data about the neurotoxic effect of homocysteine on astrocytes are lacking. The present study therefore was undertaken to investigate a possible cytotoxic effect of homocysteine on cortical astrocytes in vitro. Exposure to D,L-homocysteine resulted in a time and dose-dependent gliotoxic effect at doses of 2 mM and above (P<0.001). This is comparable to homocysteine toxicity observed in other cell culture models and implies that a participation of astrocytes in homocysteine-induced neurodegeneration may be considered. The results of the present in vitro studies may therefore have implications for understanding the pathogenesis of neurotoxicity linked to neurodegenerative disorders (e.g. Alzheimer's disease, glaucomatous optic neuropathy). This is the first study to report that homocysteine induces cell death of astrocytes. The mechanisms by which homocysteine induces cell death of astrocytes warrant further study.

[Excitatory neurotransmission in alcoholism]

Glutamate is the neurotransmitter at the majority of excitatory synapses in the mammalian CNS. It has been proposed that neurotoxicity linked to chronic alcoholism is mediated primarily by activation of glutamate N-methyl-D-aspartate (NMDA) receptors. Since ethanol stabilizes the membrane potential of NMDA receptors a persistent attenuation of glutamatergic neurotransmission occurs in chronic alcoholism resulting in a compensatory up-regulation of NMDA receptors. Thus, delayed neurotoxicity can be triggered by rebound activation of NMDA receptor-mediated neurotransmission during the withdrawal state. Besides glutamate, homocysteine and excitatory amino acids (EAA) have been shown to act as endogenous agonists at the NMDA receptor and increase excitatory postsynaptic potentials. There is evidence that chronic alcoholism is associated with a derangement in this sulfur amino acid metabolism. These findings indicate the role of hyperhomocysteinemia for withdrawal symptoms, the withdrawal state, and alcoholism-associated brain atrophy. The role of alcoholism-associated hyperhomocysteinemia in respect to NMDA-receptor mediated neurotoxicity and excitotoxicity is discussed.

[Glutamatergic neurotransmission in schizophrenics]

Glutamate is the most abundant amino acid in the brain, where it plays an important role as a well-established major excitatory neurotransmitter in the central nervous system. It has been suggested that reduced glutamate neurotransmission may be involved in the pathophysiology of schizophrenia. The glutamate hypothesis of schizophrenia postulates alterations in the glutamatergic system as an important neurobiochemical event in the pathophysiology of this group of psychotic disorders. An altered glutamate release from synaptosomes including a hypofunction of different glutamate receptors (i.e. NMDA receptors) from different brain areas have previously been reported. Furthermore, partial agonists at the glycine co-agonist site of the NMDA receptor might be a new approach in the treatment of schizophrenic symptoms but further studies are necessary to clarify the role and efficacy of these substances in schizophrenia. Changes in the glutamatergic cortico-striatal connections in schizophrenia could precipitate a potential perceptive overstimulation of the neocortex from thalamic input and an inhibiting influence of the striatum on the thalamus would modulate the information input of the cortex, thereby possibly counteracting the disturbed information processing which is relatively characteristic for schizophrenic psychoses.

Molecular biology of Alzheimer's dementia and its clinical relevance to early diagnosis and new therapeutic strategies

Over the past few years, molecular biological research has considerably deepened our understanding of the pathophysiological basis of Alzheimer's dementia (AD). Although different genetic origins of the disease have been identified, all of the findings point to a common terminal sequence in familial AD. This consists of an increased production of beta-amyloid peptides from beta-amyloid precursor protein. For the cases of sporadic AD, which far outweigh the number of cases of familial AD, an impaired catabolism of the beta-amyloid peptides may also be pathophysiologically decisive according to the latest findings. Research into the molecular level of AD makes it possible to identify points of attack for rational drug treatment of the disease, while molecular markers of AD are increasingly being used as a part of early and differential neurochemical diagnostics.

Elevated homocysteine levels in alcohol withdrawal

Ethanol exerts its behavioural effects largely by interacting with receptors for brain neurotransmitters. However, the molecular mechanisms involving these interactions and the pathogenesis of alcohol-withdrawal symptomatology are still not well understood. Until recently, no data were available about homocysteine (Hcy) levels in acute alcohol intoxication of chronic alcoholics and in patients undergoing withdrawal from alcohol. Hcy, blood-alcohol concentrations, vitamins B6, B12, and folate concentrations were assessed in 29 chronic alcoholics, who underwent withdrawal from alcohol. We observed increased Hcy levels in most patients. Hcy levels steadily decreased during the observation period. We postulate that hyperhomocysteinaemia and excitatory amino acid neurotransmitters, by their agonism at the N-methyl-D-aspartate receptor, may partly mediate alcohol-associated withdrawal symptomatology. The importance of assessing serum Hcy levels in order to detect methylation deficiency in patients with chronic alcoholism and for possible therapeutic strategies is discussed.