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Abstract

This study aimed at determining the effect of drug therapy, age and type of dementia on biological markers. Both platelet monoamine oxidase type B (MAO-B) activity and serotonin content of 57 demented patients and 20 control subjects were determined. Platelet MAO-B activity was measured using [14C]tyramine as substrate. Serotonin content was determined by HPLC-EC method. Increased platelet serotonin content and platelet count was found in patients with dementia compared to controls. A positive correlation was experienced between platelet MAO-B activity, platelet serotonin content and age. Platelet MAO-B activity was higher in the haloperidol treated group, compared with patients treated with anxyolitics. The main original finding of the present study is that platelet serotonin content is increased in demented patients with delusions compared to dementia without complications (p = 0.006). It seems, that platelet MAO-B activity is influenced mainly by drug therapy, while serotonin content rather reflects clinical characteristics in dementia.

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

“…These AD-related findings were subsequently confirmed in at least 12 clinical studies from different research groups [57, 59, 73, 112–120]. Five other studies, however, reported no AD-related activity increase [58, 61, 73, 99, 121]. Importantly, instead of phenethylamine, three of these studies used the substrates tyramine or kynuramine [61, 73, 99], both converted by Mao-A and Mao-B [122].…”

“…Higher Mao-B activity in patient samples could only be detected with the Mao-B-specific substrate phenethylamine. These AD-related findings were subsequently confirmed in at least 12 clinical studies from different research groups [57, 59, 73, 112–120]. Five other studies, however, reported no AD-related activity increase [58, 61, 73, 99, 121].…”

“…In strong contrast, another study even showed increased accumulation of the neurotransmitter in platelets of female AD patients [97]. Intraplatelet serotonin concentrations reported in literature are also quite inconsistent as reduced [72, 98, 99], as well as increased [73] values in AD patients with delusions have been measured. In the latter observation, there might be a weak parallel to findings of higher serotonin level in AD patients with psychotic features than in inconspicuous subjects [98].…”

“…In the latter observation, there might be a weak parallel to findings of higher serotonin level in AD patients with psychotic features than in inconspicuous subjects [98]. Similarly, in demented patients concentrations of platelet serotonin were higher as compared to controls [73]. Further details about the role of serotonin in depression, ageing, and AD can be found in the review by Meltzer et al [100] which also compares results from platelets and neurons.…”

“…Five other studies, however, reported no AD-related activity increase [58, 61, 73, 99, 121]. Importantly, instead of phenethylamine, three of these studies used the substrates tyramine or kynuramine [61, 73, 99], both converted by Mao-A and Mao-B [122]. In a recent study, Mao-B activity quantified by kynuramine has been found to be significantly lower in late stage AD patients as compared to healthy controls, whereas in early and middle stage AD Mao-B activity was not changed significantly [99].…”