Evidence for decreased transport of PNMT protein in advanced Alzheimer's disease.

Phenylethanolamine N-methyltransferase (PNMT) is the rate-limiting enzyme in the synthesis of epinephrine and a specific marker for adrenergic neurons. PNMT protein is decreased in axon terminals in brains from patients with Alzheimer's disease due to retrograde degeneration of epinephrine neurons. To determine the subcellular mechanism underlying retrograde degeneration, the distribution of PNMT between axon terminal and cell body was calculated in early and advanced Alzheimer cases compared with age-matched controls. In early Alzheimer's disease there is a decrease in PNMT in axon terminals and in total PNMT in epinephrine cell bodies and terminals compared with control values. There is no difference in the ratio of PNMT in cell body/axon terminal compared with controls. In contrast, in advanced Alzheimer's disease, PNMT activity increases by 124% in epinephrine neuronal cell bodies compared with controls. Immunochemical titration shows that this increased enzyme activity is due to an increase in PNMT protein. The cell body/axon terminal ratio of PNMT is increased 2.5-fold in advanced Alzheimer's disease compared with controls. These findings are consistent with the hypothesis that in early Alzheimer's disease there is a decreased synthesis or increased degradation of PNMT. However, in advanced Alzheimer's disease we propose that the accumulation of this enzyme in the perikarya results from a diminished transport of PNMT to axon terminals. We further postulate that epinephrine, the product of PNMT, and its further metabolites are endogenous neurotoxins. Therefore, the accumulation of PNMT in epinephrine cell bodies may contribute to the degeneration of these neurons in Alzheimer's disease.

Evidence for decreased transport of tryptophan hydroxylase in Alzheimer's disease.

Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the synthesis of serotonin and a specific marker for serotonergic neurons. These neurons are affected in Alzheimer's disease (AD) in several ways: serotonin is decreased in axon terminals, serotonin neurons accumulate neurofibrillary protein, and these neurons are lost in AD brains. One subcellular mechanism which may underlie degeneration of neurons in AD is decreased axonal transport with accumulation of enzymes and their potentially toxic metabolites in the cell body. To determine whether there is a defect in axonal transport in serotonin neurons in AD we measured TPH activity, serotonin and its oxidative metabolite 5-hydroxyindoleacetic acid (5-HIAA) in dorsal raphe cell bodies from Alzheimer and control cases. TPH activity is increased 4.7-fold in raphe neuron cell bodies in Alzheimer brains. Serotonin and 5-HIAA are increased by 4.0- and 2.0-fold, respectively in Alzheimer compared to control raphe cell bodies. In contrast, in synaptic terminals of the amygdala 5-HT and 5-HIAA were decreased by 41% and 50%, respectively in the same AD cases. We propose that the accumulation of TPH and its products in the raphe perikarya in AD results from a diminished transport of TPH to axon terminals. The accumulation of oxidative metabolites of serotonin may contribute to the degeneration of serotonergic neurons in AD.

Detection of 3,4-dihydroxyphenylglycolaldehyde in human brain by high-performance liquid chromatography.

The monoamine oxidase A metabolite of noradrenaline, 3,4-dihydroxyphenylglycolaldehyde, is the precursor of 3,4-dihydroxymandelic acid, and 3,4-dihydroxyphenylglycol, metabolites of noradrenaline. Owing to difficulties in purifying this aldehyde, it has not been previously characterized or identified in biological sources. This paper describes an enzymatic synthesis, purification, and characterization of 3,4-dihydroxyphenylglycolaldehyde. The aldehyde metabolite is identified in postmortem human brain using high-performance liquid chromatography and electrochemical detection. We estimate the concentration in human hippocampus to be 0.164 +/- 0.05 nmol/g. The importance of this aldehyde metabolite of noradrenaline is discussed.

Evidence for retrograde degeneration of epinephrine neurons in Alzheimer's disease.

Alzheimer's disease (AD) is associated with a progressive loss of locus ceruleus neurons. These noradrenergic neurons receive a major afferent projection from epinephrine neurons in epinephrine cell groups in the brainstem. The epinephrine neurons have a specific enzymatic marker, phenylethanolamine N-methyltransferase (PNMT), which allows them to be identified chemically and immunohistochemically. We have previously reported a decrease in PNMT in brains of patients with AD. We now report that the decrease in PNMT activity in projections to the locus ceruleus is not due to the loss of epinephrine neurons, although up to 33% of these neurons are atrophic. The decrease in presynaptic PNMT does, however, correlate with the loss of postsynaptic locus ceruleus neurons in brains from AD patients. The percentage of degenerating neurons in the epinephrine nuclei also correlates significantly with the amount of loss of locus ceruleus neurons in AD. In addition, there is a 55% decrease in mitogen activity, a nonspecific measure of growth or maintenance factors, in dialysed locus ceruleus extracts from the AD patients compared to those from control subjects. The mitogen activity in the locus ceruleus was significantly correlated with PNMT activity and with the density of locus ceruleus neurons in all cases examined. These findings provide evidence for the hypothesis that retrograde degeneration is a mechanism of neuronal degeneration in AD and suggest that trophic factors may play a role in this process.

Fluorinated phenytoin anticonvulsant analogs.

Six ring-fluorinated phenytoin analogs were synthesized, and their anticonvulsant activity in the maximal electroshock seizure and subcutaneous pentylenetetrazol assays was determined. 5-(4-Fluorophenyl)-5-phenylhydantoin, 5-(3-fluorophenyl)-5-phenylhydantoin, and 5,5-bis(4-fluorophenyl)hydantoin were active in the maximal electroshock seizure assay. The compounds were much less potent than phenytoin but showed an extremely long duration of action.

Short-term consumption effects of a lower minimum alcohol-purchasing age.

Multiple-regression analysis revealed that apparent short-term increases in consumption of distilled spirits after reductions in minimum legal purchasing ages were not statistically significant.