Platelet monamine oxidase in Alzheimer's disease

Platelets, a reliable source for peripheral Alzheimer's disease biomarkers?

Peripheral biomarkers play an indispensable role in quick and reliable diagnoses of any kind of disease. With the population ageing, the number of people suffering from age-related diseases is expected to rise dramatically over the coming decades. In particular, all types of cognitive deficits, such as Alzheimer's disease, will increase. Alzheimer's disease is characterised mainly by coexistence of amyloid plaques and neurofibrillary tangles in brain. Reliable identification of such molecular characteristics antemortem, however, is problematic due to restricted availability of appropriate sample material and definitive diagnosis is only possible postmortem. Currently, the best molecular biomarkers available for antemortem diagnosis originate from cerebrospinal fluid. Though, this is not convenient for routine diagnosis because of the required invasive lumbar puncture. As a consequence, there is a growing demand for additional peripheral biomarkers in a more readily accessible sample material. Blood platelets, due to shared biochemical properties with neurons, can constitute an attractive alternative as discussed here. This review summarises potential platelet Alzheimer's disease biomarkers, their role, implication, and alteration in the disease. For easy comparison of their performance, the Hedge effect size was calculated whenever data were available.

Consensus paper of the WFSBP Task Force on Biological Markers of Dementia: the role of CSF and blood analysis in the early and differential diagnosis of dementia

Aging of population, and increasing life expectancy result in an increasing number of patients with dementia. This symptom can be a part of a completely curable disease of the central nervous system (e.g, neuroinflammation), or a disease currently considered irreversible (e.g, Alzheimer's disease, AD). In the latter case, several potentially successful treatment approaches are being tested now, demanding reasonable standards of pre-mortem diagnosis. Cerebrospinal fluid and serum analysis (CSF/serum analysis), whereas routinely performed in neuroinflammatory diseases, still requires standardization to be used as an aid to the clinically based diagnosis of AD. Several AD-related CSF parameters (total tau, phosphorylated forms of tau, Abeta peptides, ApoE genotype, p97, etc.) tested separately or in a combination provide sensitivity and specificity in the range of 85%, the figure commonly expected from a good diagnostic tool. In this review, recently published reports regarding progress in neurochemical pre-mortem diagnosis of dementias are discussed with a focus on an early and differential diagnosis of AD. Novel perspectives offered by recently introduced technologies, e.g, fluorescence correlation spectroscopy (FCS) and surface enhanced laser desorption/ionization time-of-flight mass spectrometry (SELDI-TOF MS) are briefly discussed.

Oxidative stress related markers in the “VITA” and the centenarian projects

Oxidative stress seems to play an important role in the pathophysiology of Alzheimer's disease (AD). At present there are no easily accessible biochemical markers for AD. We performed activity assays for platelet MAO-B and erythrocyte Cu/Zn-SOD as well as Western blotting for these two proteins. Moreover, we assessed plasma lactoferrin and performed RFLP-analysis for the MAO-B-intron-13-polymorphism in patients from the Vienna-Transdanube Aging (VITA) and from the so called centenarian project. The first one, VITA, is a community-based cohort study of all 75 years old inhabitants of a geographical region of Vienna. The centenarian project investigates chronic care in-old patients suffering from AD. In both sexes platelet MAO-B activity increased significantly in the AD group, and Cu/Zn-SOD activity decreased, but the latter effect was significant only in females. No significant difference was found regarding plasma lactoferrin. No correlation was found between MAO-Bi13 and MAO-B platelet activity or allele MAO-Bi13 and disease frequency. These results point to the possibility that a combination of MAO-B and SOD activity levels might be useful tools for an early diagnosis of AD.

Platelet phenolsulphotransferase activity, monoamine oxidase activity and peripheral-type benzodiazepine binding in demented patients

Blood platelet phenolsulphotransferase and monoamine oxidase activities, as well as platelet peripheral-type benzodiazepine binding have been studied in several neuropsychiatric disorders, in order to identify biochemical markers for altered brain functioning. In the present work, we determined platelet phenolsulphotransferase and monoamine oxidase activities in demented patients: they showed significantly higher phenolsulphotransferase and monoamine oxidase activities than controls. A significant positive correlation was found between enzyme activities and severity of illness. In the same subjects, we evaluated platelet peripheral-type benzodiazepine binding: a significant reduction of Bmax values was observed in demented patients, whereas Kd values did not substantially differ between the two subject groups. These findings are discussed with reference to central nervous system biochemical abnormalities of demented subjects: it may be that in Dementia of Alzheimer type either some central biochemical changes are reflected in certain peripheral tissues (such as platelets), or a systemic derangement occurs together with a cerebral involvement.

Platelet monoamine oxidase molecular activity in demented patients

Blood platelet monoamine oxidase activity, as well as other platelet enzyme activities, have been studied in several neuropsychiatric disorders in an attempt to identify biochemical markers of altered brain function. In this study, we determined both total and molecular monoamine oxidase activity in platelets derived from demented patients, which showed significantly greater enzyme activity than those of the controls. It therefore seems that the high degree of monoamine oxidase activity depends on the increased intrinsic activity of individual enzyme molecules. A significant positive correlation was found between monoamine oxidase activity and the severity of illness, which suggests that monoamine oxidase activity may be a state-dependent marker of neurodegeneration. These findings are discussed with reference to the central nervous system biochemical abnormalities of demented subjects: it may be that Alzheimer-type dementia involves some central biochemical changes that are reflected in certain peripheral tissues (e.g. platelets), or a systemic derangement that also affects the brain.

Selegiline in treatment of behavioral and cognitive symptoms of Alzheimer disease

OBJECTIVE

To evaluate the effects of selegiline on behavioral and cognitive symptoms of patients with Alzheimer disease.

DATA SOURCES

An English-language MEDLINE search (1982-1995) was used to identify the review articles and human clinical trials discussed in this article.

STUDY SELECTION

Double- and single-blind and open-label trials were reviewed. Studies were also reviewed if selegiline was evaluated comparatively with other agents. Review articles were used for background information.

DATA EXTRACTION

Data were evaluated from human studies. Studies were critiqued on the basis of design, methodology, duration, sample size, and the degree to which neuropsychological tests used in each study were compared.

DATA SYNTHESIS

Selegiline is a selective, irreversible inhibitor of monoamine oxidase type B. Eight of 11 controlled trials showed selegiline had a positive effect on cognition (e.g., word fluency, delayed recall, total recall). Two of 5 controlled trials evaluating selegiline's effect on behavior (e.g., anxiety, tension, excitement, depression) showed a positive effect.

CONCLUSIONS

The role of selegiline remains to be determined by large well-controlled long-term clinical trials. Selegiline may be a useful agent in managing behavioral and cognitive symptomatology associated with Alzheimer disease. Given that the management of Alzheimer disease is symptomatic and no standard treatment exists, selegiline should be considered among the various options.

Increased platelet 3H-imipramine binding and monoamine oxidase B activity in Alzheimer's disease

Several biochemical abnormalities in peripheral tissues have been reported in Alzheimer's disease (AD). With this in mind we studied platelet monoamine oxidase B (MAO B) activity and 3H-imipramine (IMI) binding in both AD patients and healthy subjects and found a significantly higher level of platelet MAO B activity and 3H-IMI Bmax values in the AD patients. In view of the part that MAO B plays in metabolizing serotonin (5HT) and of the relationship which exists between 3H-IMI binding and 5HT uptake, our results would suggest that with AD there occurs a complex dysfunction in the 5HT system, at least at a peripheral level.

Monoamine oxidase (MAO), 5-hydroxyindole acetic acid (5 HIAA) and homovanillic acid (HVA) in motor neuron disease

Thrombocyte monoamine oxidase (MAO) activity and concentrations of 5-hydroxyindole acetic acid (5-HIAA) and homovanillic acid (HVA) in the cerebrospinal fluid (CSF) were studied in patients with motor neuron disease (MND) and healthy controls. The MAO activity in MND (n = 32) did not differ from age and sex-matched controls (n = 27) or from healthy relatives (n = 9) and no difference was found between advanced and mild cases. In an attempt to explain divergent results from other studies, the effect of storage time on analysis of platelet concentration was studied in three healthy subjects and in three patients with MND. No difference was observed between the groups. No differences were found between the MND group (n = 28) and healthy controls (n = 18) with regard to CSF levels of 5-HIAA and HVA, except for an increase of 5-HIAA among males with MND. The results of this study do not confirm earlier studies that have reported extensive changes in the variables analyzed in patients with MND.

Brain and brain monoamine oxidase in aging and in dementia of Alzheimer's type

Brain MAO-B activity increases with age. The rate of increase varies in different brain regions. Brain MAO-A activity does not change with age in man and is decreased in the rat. Brain MAO-B activity in AD/SDAT is higher than in age-matched controls. The increased MAO-B activity in aging is due to an increased concentration of otherwise unchanged extrasynaptosomal MAO-B. The increase in brain MAO-B activity with age and in AD/SDAT is more pronounced in white matter than in gray matter. Platelet MAO is increased in patients with AD/SDAT.

A double-blind, placebo controlled trial of high-dose lecithin in Alzheimer's disease

The first long-term double-blind placebo controlled trial of high dose lecithin in senile dementia of the Alzheimer type is reported. Fifty one subjects were given 20-25 g/day of purified soya lecithin (containing 90% phosphatidyl plus lysophosphatidyl choline) for six months and followed up for at least a further six months. Plasma choline levels were monitored throughout the treatment period. There were no differences between the placebo group and the lecithin group but there was an improvement in a subgroup of relatively poor compliers. These were older and had intermediate levels of plasma choline. It is suggested that the effects of lecithin are complex but that there may be a "therapeutic window" for the effects of lecithin in the condition and that this may be more evident in older patients.

Evidence for an increased rate of choline efflux across erythrocyte membranes in Alzheimer's disease

Alzheimer's disease (AD), the major dementing disorder of the elderly, is associated with cholinergic neuronal loss and decreased activity of choline acetyltransferase (CAT). Previous biophysical studies had suggested an altered conformation of membrane proteins in AD erythrocyte ghosts. Since erythrocytes have a choline transport system and cholinergic neurons are implicated in AD, the present experiments were undertaken to determine if the efflux rate of [14C]choline was altered in AD erythrocytes. The mean efflux rate constant was highly significantly increased (P less than 0.01) by greater than 25% in 9 drug-free AD patients compared to 9 sex-matched, drug-free controls of similar age. These results are discussed in terms of potential molecular mechanisms to account for cholinergic neuronal loss in AD.

Red blood cell abnormalities in Alzheimer disease

In a prospective, double-blind study of 84 unselected persons in a dementia clinic, the red blood cell/plasma choline ratios were found to be significantly higher in 47 subjects with clinically defined Alzheimer disease (DAT) than in 37 non-DAT, nondepressed subjects (3.54 +/- 0.48 versus 2.04 +/- 0.34, p less than 0.02). The latter group included intellectually intact subjects as well as patients with other dementias who were comparable to the Alzheimer patients in age, sex, and degree of cognitive impairment. The elevated mean ratio reflected the greater proportion of Alzheimer patients with high red blood cell plasma choline ratios. These elevated ratios appeared to be related to both increases in red cell content and decreases in plasma choline. The authors conclude that the results confirm and extend those previously reported in short series of patients and agree with other evidence that Alzheimer disease has systemic manifestations in nonneural cells, which may be useful in further investigations of the disease's cellular pathophysiology.

Peripheral catecholamine enzyme function and cognitive impairment of elderly schizophrenics and controls

Alterations of peripheral and central catecholamine systems are found in both schizophrenic and demented subjects. Reported here are the results of bivariate and multivariate analyses of cognitive function and peripheral catecholamine enzyme activities in a group of elderly schizophrenic patients and controls. The entire sample shows an inverse relationship of platelet monoamine oxidase (MAO) activity with cognitive impairment after controlling for the effects of age, race, and gender. Schizophrenic subjects also demonstrated an inverse relationship of plasma dopamine beta hydroxylase (DBH) activity with cognitive impairment. Demented subjects were characterized in both groups as having increments in platelet MAO activity. Demented schizophrenic subjects also were characterized by increments in plasma DBH activity. Results from this sample are discussed with respect to findings from other studies and future research.