It has recently been demonstrated by biochemical means (12,14,17) that ethylcholine aziridinium i... more It has recently been demonstrated by biochemical means (12,14,17) that ethylcholine aziridinium ion, AF64A (1,12,17), injected intracerebro- ventricularly (i.e.v.), (12), intrastriatally (i.s.) (18,19,20) or intra- hippocampally (i.h.), (14) reduces high affinity choline transport (HAChT), choline acetyltransferase (ChAT) activity, and acetylcholine (ACh) levels in the hippocampus, and to a lesser extent in the striatum, but it does not affect the number of muscarinic acetylcholine-receptors (mAChR-s) (1,2). It has been suggested that AF64A is a neurotoxin which destroys the cholinergic axon terminals and can therefore be considered a “cholinotoxin1”. However, Levy et al. (11) and Jarrard et al. (6) injected AF64A into the substantia nigra or i.e.v., and concluded that AF64A affects other axons besides the cholinergic ones: They thus have cast doubt on the usefulness of AF64A for the specific destruction of cholinergic axon terminals. Since neither Fisher et al. (2) nor Levy et al. (11) presented detailed morphological evidence to support their views, we have decided to conduct our own histochemical and histological studies, including detailed electronmicroscopic investigations. In this paper evidence is given that AF64A is a neurotoxin, and that it can be used as a cholino- toxin if it is administered in the appropriate dose and concentration, at a suitable site of application. Some of these findings have been presented earlier (8,22).
Current Drug Target -CNS & Neurological Disorders, 2003
Potentiation of central cholinergic activity has been proposed as a therapeutic approach for impr... more Potentiation of central cholinergic activity has been proposed as a therapeutic approach for improving the cognitive function in patients with Alzheimer's disease (AD). Increasing the acetylcholine concentration in the brain by modulating acetylcholine-sterase (AChE) activity is among the most promising therapeutic strategies. Efforts to treat the underlying pathology based on the modulation of amyloid precursor protein (APP) processing in order to decrease the accumulation of beta-amyloid are also very important. Alterations in APP metabolism have recently been proposed to play a key role in the long-lasting effects of AChE inhibitors. This review surveys recent data from in vivo and in vitro studies that have contributed to our understanding of the role of AChE inhibitors in APP processing. The regulatory mechanisms relating to the muscarinic agonist effect, protein kinase C activation and mitogen-activated protein kinase phosphorylation, involving the alpha-secretase or the 5 -UTR region of the APP gene, are also discussed. Further work is warranted to elucidate the exact roles in APP metabolism of the AChE inhibitors used in AD therapy at present.
Earlier post-mortem histological and autoradiographic studies have indicated a reduction of cell ... more Earlier post-mortem histological and autoradiographic studies have indicated a reduction of cell numbers in the locus coeruleus (LC) and a corresponding decrease in norepinephrine transporter (NET) in brains obtained from Alzheimer's disease (AD) patients as compared to age-matched healthy controls. In order to test the hypothesis that the regional decrease of NET is a disease specific biomarker in AD and as such, it can be used in PET imaging studies for diagnostic considerations, regional differences in the density of NET in various anatomical structures were measured in whole hemisphere human brain slices obtained from AD patients and age-matched control subjects in a series of autoradiographic experiments using the novel selective PET radioligand for NET (S,S)-[18F]FMeNER-D2. (S,S)-[18F]FMeNER-D2 appears to be a useful imaging biomarker for quantifying the density of NET in various brain structures, including the LC and the thalamus wherein the highest densities are found in physiological conditions. In AD significant decreases of NET densities can be demonstrated with the radioligand in both structures as compared to age-matched controls. The decreases in AD correlate with the progress of the disease as indicated by Braak grades. As the size of the LC is below the spatial resolution of the PET scanners, but the size of the thalamus can be detected with appropriate spatial accuracy in advanced scanners, the present findings confirm our earlier observations with PET that the in vivo imaging of NET with (S,S)-[18F]FMeNER-D2 in the thalamus is viable. Nevertheless, further studies are warranted to assess the usefulness of such an imaging approach for the early detection of changes in thalamic NET densities as a disease-specific biomarker and the possible use of (S,S)-[18F]FMeNER-D2 as a molecular imaging biomarker in AD.
ABSTRACT Earlier in vivo PET experiments have demonstrated the binding of the neuroprotective alk... more ABSTRACT Earlier in vivo PET experiments have demonstrated the binding of the neuroprotective alkaloid vinpocetine to the peripheral benzodiazepine receptor (PBR) or, with other terminology, the TSPO (18kDa translocator protein). With the aim of demonstrating the direct binding of vinpocetine to TSPO in vitro, two different ionidated versions of the novel TSPO ligand DAA1106 were used in autoradiographic experiments on human postmortem whole hemisphere brain slices. Vinpocetine effectively blocked the binding of both [125I]desmethoxy-DAA1106 and [125I]desfluoro-DAA1106 to TSPO, the decrease in binding reaching 30 % to 64 % in various brain structures. This present findings yield further evidence to vinpocetine's direct binding to the TSPO in the human brain in vitro as well as to the possible use of its radiolabelled versions as imaging biomarkers. The results also support the usefulness of two ionidated versions of DAA1106 as biomarkers of TSPO for in vitro and in vivo studies in neurological diseases accompanied with microglia activation.
A cholinotoxin, ethylcholine mustard aziridinium ion, (AF64A) specifically and irreversibly block... more A cholinotoxin, ethylcholine mustard aziridinium ion, (AF64A) specifically and irreversibly blocks the intraaxonal transport of acetylcholinesterase in the rat. Impairment of the transport of this enzyme in the septo-hippocampal cholinergic fibres and in the sciatic nerve has been studied, using different doses of AF64A. It is demonstrated that the effect on the axonal transport is dose-dependent, but is not related to the mode of drug application. AF64A thus may exert its neurotoxic effects on cholinergic neurons at several target sites of action. In addition to the localized presynaptic mechanisms, it may also be compromising cholinergic function by inhibiting axonal transport in vivo.
It has recently been demonstrated by biochemical means (12,14,17) that ethylcholine aziridinium i... more It has recently been demonstrated by biochemical means (12,14,17) that ethylcholine aziridinium ion, AF64A (1,12,17), injected intracerebro- ventricularly (i.e.v.), (12), intrastriatally (i.s.) (18,19,20) or intra- hippocampally (i.h.), (14) reduces high affinity choline transport (HAChT), choline acetyltransferase (ChAT) activity, and acetylcholine (ACh) levels in the hippocampus, and to a lesser extent in the striatum, but it does not affect the number of muscarinic acetylcholine-receptors (mAChR-s) (1,2). It has been suggested that AF64A is a neurotoxin which destroys the cholinergic axon terminals and can therefore be considered a “cholinotoxin1”. However, Levy et al. (11) and Jarrard et al. (6) injected AF64A into the substantia nigra or i.e.v., and concluded that AF64A affects other axons besides the cholinergic ones: They thus have cast doubt on the usefulness of AF64A for the specific destruction of cholinergic axon terminals. Since neither Fisher et al. (2) nor Levy et al. (11) presented detailed morphological evidence to support their views, we have decided to conduct our own histochemical and histological studies, including detailed electronmicroscopic investigations. In this paper evidence is given that AF64A is a neurotoxin, and that it can be used as a cholino- toxin if it is administered in the appropriate dose and concentration, at a suitable site of application. Some of these findings have been presented earlier (8,22).
Current Drug Target -CNS & Neurological Disorders, 2003
Potentiation of central cholinergic activity has been proposed as a therapeutic approach for impr... more Potentiation of central cholinergic activity has been proposed as a therapeutic approach for improving the cognitive function in patients with Alzheimer's disease (AD). Increasing the acetylcholine concentration in the brain by modulating acetylcholine-sterase (AChE) activity is among the most promising therapeutic strategies. Efforts to treat the underlying pathology based on the modulation of amyloid precursor protein (APP) processing in order to decrease the accumulation of beta-amyloid are also very important. Alterations in APP metabolism have recently been proposed to play a key role in the long-lasting effects of AChE inhibitors. This review surveys recent data from in vivo and in vitro studies that have contributed to our understanding of the role of AChE inhibitors in APP processing. The regulatory mechanisms relating to the muscarinic agonist effect, protein kinase C activation and mitogen-activated protein kinase phosphorylation, involving the alpha-secretase or the 5 -UTR region of the APP gene, are also discussed. Further work is warranted to elucidate the exact roles in APP metabolism of the AChE inhibitors used in AD therapy at present.
Earlier post-mortem histological and autoradiographic studies have indicated a reduction of cell ... more Earlier post-mortem histological and autoradiographic studies have indicated a reduction of cell numbers in the locus coeruleus (LC) and a corresponding decrease in norepinephrine transporter (NET) in brains obtained from Alzheimer's disease (AD) patients as compared to age-matched healthy controls. In order to test the hypothesis that the regional decrease of NET is a disease specific biomarker in AD and as such, it can be used in PET imaging studies for diagnostic considerations, regional differences in the density of NET in various anatomical structures were measured in whole hemisphere human brain slices obtained from AD patients and age-matched control subjects in a series of autoradiographic experiments using the novel selective PET radioligand for NET (S,S)-[18F]FMeNER-D2. (S,S)-[18F]FMeNER-D2 appears to be a useful imaging biomarker for quantifying the density of NET in various brain structures, including the LC and the thalamus wherein the highest densities are found in physiological conditions. In AD significant decreases of NET densities can be demonstrated with the radioligand in both structures as compared to age-matched controls. The decreases in AD correlate with the progress of the disease as indicated by Braak grades. As the size of the LC is below the spatial resolution of the PET scanners, but the size of the thalamus can be detected with appropriate spatial accuracy in advanced scanners, the present findings confirm our earlier observations with PET that the in vivo imaging of NET with (S,S)-[18F]FMeNER-D2 in the thalamus is viable. Nevertheless, further studies are warranted to assess the usefulness of such an imaging approach for the early detection of changes in thalamic NET densities as a disease-specific biomarker and the possible use of (S,S)-[18F]FMeNER-D2 as a molecular imaging biomarker in AD.
ABSTRACT Earlier in vivo PET experiments have demonstrated the binding of the neuroprotective alk... more ABSTRACT Earlier in vivo PET experiments have demonstrated the binding of the neuroprotective alkaloid vinpocetine to the peripheral benzodiazepine receptor (PBR) or, with other terminology, the TSPO (18kDa translocator protein). With the aim of demonstrating the direct binding of vinpocetine to TSPO in vitro, two different ionidated versions of the novel TSPO ligand DAA1106 were used in autoradiographic experiments on human postmortem whole hemisphere brain slices. Vinpocetine effectively blocked the binding of both [125I]desmethoxy-DAA1106 and [125I]desfluoro-DAA1106 to TSPO, the decrease in binding reaching 30 % to 64 % in various brain structures. This present findings yield further evidence to vinpocetine's direct binding to the TSPO in the human brain in vitro as well as to the possible use of its radiolabelled versions as imaging biomarkers. The results also support the usefulness of two ionidated versions of DAA1106 as biomarkers of TSPO for in vitro and in vivo studies in neurological diseases accompanied with microglia activation.
A cholinotoxin, ethylcholine mustard aziridinium ion, (AF64A) specifically and irreversibly block... more A cholinotoxin, ethylcholine mustard aziridinium ion, (AF64A) specifically and irreversibly blocks the intraaxonal transport of acetylcholinesterase in the rat. Impairment of the transport of this enzyme in the septo-hippocampal cholinergic fibres and in the sciatic nerve has been studied, using different doses of AF64A. It is demonstrated that the effect on the axonal transport is dose-dependent, but is not related to the mode of drug application. AF64A thus may exert its neurotoxic effects on cholinergic neurons at several target sites of action. In addition to the localized presynaptic mechanisms, it may also be compromising cholinergic function by inhibiting axonal transport in vivo.
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