Degenerative changes in epinephrine tonic vasomotor neurons in Alzheimer's disease

A simple and highly sensitive flexible sensor with extended-gate field-effect transistor for epinephrine detection utilizing InZnSnO sensing films

This study introduces a straightforward method for depositing InZnSnO films onto flexible polyimide substrates at room temperature, enabling their application in electrochemical pH sensing and the detection of epinephrine. A comprehensive analysis of these sensing films, spanning structural, morphological, compositional, and profiling characteristics, was conducted using diverse techniques, including X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectroscopy. The investigation into the influence of oxygen flow rates on the performance of InZnSnO sensitive films revealed a significant correlation between their structural properties and sensing capabilities. Notably, exposure to an oxygen flow rate of 30/2 (Ar/O2) the ratio of resulted in the InZnSnO sensitive film demonstrating outstanding pH sensitivity at 59.58 mV/pH within a broad pH range of 2-12, surpassing the performance observed with other oxygen flow rates. Moreover, under this specific condition, the film exhibited excellent stability, with a minimal drift rate of 0.14 mV/h at pH 7 and a low hysteresis voltage of 1.8 mV during a pH cycle of 7 → 4→7 → 10→7. Given the critical role of epinephrine in mammalian central nervous and hormone systems, monitoring its levels is essential for assessing human health. To facilitate the detection of epinephrine, we utilized the carboxyl group of 4-formylphenylboronic acid to enable a reaction with the amino group of the 3-aminopropyltriethoxysilane-coated InZnSnO film. Through optimization, the resulting InZnSnO-based flexible sensor displayed a broad and well-defined linear relationship within the concentration range of 10-7 to 0.1 μM. In practical applications, this sensor proved effective in analyzing epinephrine in human serum, showcasing notable selectivity, stability, and reproducibility. The promising outcomes of this study underscore the potential for future applications, leveraging the advantages of electrochemical sensors, including affordability, rapid response, and user-friendly operation.

Chromogranin A (CgA) Deficiency Attenuates Tauopathy by Altering Epinephrine-Alpha-Adrenergic Receptor Signaling

Our previous studies have indicated that insulin resistance, hyperglycemia, and hypertension in aged wild-type (WT) mice can be reversed in mice lacking chromogranin-A (CgA-KO mice). These health conditions are associated with a higher risk of Alzheimer's disease (AD). CgA, a neuroendocrine secretory protein has been detected in protein aggregates in the brains of AD patients. Here, we determined the role of CgA in tauopathies, including AD (secondary tauopathy) and corticobasal degeneration (CBD, primary tauopathy). We found elevated levels of CgA in both AD and CBD brains, which were positively correlated with increased phosphorylated tau in the frontal cortex. Furthermore, CgA ablation in a human P301S tau (hTau) transgenic mice (CgA-KO/hTau) exhibited reduced tau aggregation, resistance to tau spreading, and an extended lifespan, coupled with improved cognitive function. Transcriptomic analysis of mice cortices highlighted altered levels of alpha-adrenergic receptors (Adra) in hTau mice compared to WT mice, akin to AD patients. Since CgA regulates the release of the Adra ligands epinephrine (EPI) and norepinephrine (NE), we determined their levels and found elevated EPI levels in the cortices of hTau mice, AD and CBD patients. CgA-KO/hTau mice exhibited reversal of EPI levels in the cortex and the expression of several affected genes, including Adra1 and 2, nearly returning them to WT levels. Treatment of hippocampal slice cultures with EPI or an Adra1 agonist intensified, while an Adra1 antagonist inhibited, tau hyperphosphorylation and aggregation. These findings reveal a critical role of CgA in regulation of tau pathogenesis via the EPI-Adra signaling axis.

Hypotension with neurovascular changes and cognitive dysfunction: An epidemiological, pathobiological, and treatment review

ABSTRACT

Hypotension is a leading cause of age-related cognitive impairment. The available literature evidences that vascular factors are associated with dementia and that hypotension alters cerebral perfusion flow and can aggravate the neurodegeneration of Alzheimer's disease (AD). Despite the discovery of biomarkers and the recent progress made in neurovascular biology, epidemiology, and brain imaging, some key issues remain largely unresolved: the potential mechanisms underlying the neural deterioration observed in AD, the effect of cerebrovascular alterations on cognitive deficits, and the positive effects of hypotension treatment on cognition. Therefore, further well-designed studies are needed to unravel the potential association between hypotension and cognitive dysfunction and reveal the potential benefits of hypotension treatment for AD patients. Here, we review the current epidemiological, pathobiological, and treatment-related literature on neurovascular changes and hypotension-related cognitive dysfunction and highlight the unsettled but imminent issues that warrant future research endeavors.

Insights into S-adenosyl-l-methionine (SAM)-dependent methyltransferase related diseases and genetic polymorphisms

Enzymatic methylation catalyzed by methyltransferases has a significant impact on many human biochemical reactions. As the second most ubiquitous cofactor in humans, S-adenosyl-l-methionine (SAM or AdoMet) serves as a methyl donor for SAM-dependent methyltransferases (MTases), which transfer a methyl group to a nucleophilic acceptor such as O, As, N, S, or C as the byproduct. SAM-dependent methyltransferases can be grouped into different types based on the substrates. Here we systematically reviewed eight types of methyltransferases associated with human diseases. Catechol O-methyltransferase (COMT), As(III) S-adenosylmethionine methyltransferase (AS3MT), indolethylamine N-methyltransferase (INMT), phenylethanolamine N-methyltransferase (PNMT), histamine N-methyltransferase (HNMT), nicotinamide N-methyltransferase (NNMT), thiopurine S-methyltransferase (TPMT) and DNA methyltansferase (DNMT) are classic SAM-dependent MTases. Correlations between genotypes and disease susceptibility can be partially explained by genetic polymorphisms. The physiological function, substrate specificity, genetic variants and disease susceptibility associated with these eight SAM-dependent methyltransferases are discussed in this review.

Hypertension in patients with Alzheimer's disease--prevalence, characteristics, and impact on clinical outcome. Experience of one neurology center in Poland

The aim of the study was to evaluate hypertension (HT) prevalence, characteristics, and impact on clinical outcome in patients with Alzheimer's disease (AD). We evaluated 701 patients with AD (249 males, 452 females, and mean age 74.9 ± 7.5 years). As a group representing general population matched with regard to age, education level, and place of residence, we included 762 subjects (438 males, 324 females, and mean age 74.7 ± 4.4 years) from the Polish National Multicenter Health Survey (WOBASZ) studies. The patients with AD were characterized by lower systolic blood pressure (BP) and diastolic BP values (134 ± 21 vs. 151 ± 23 mm Hg, P < .001 and 77 ± 11 vs. 86 ± 12 mm Hg, P < .001, respectively) as well as lower HT prevalence (66% vs. 78.6%, P < .001) compared with the WOBASZ group. In long-term follow-up of AD group, HT and BP levels were not associated with the decline in cognitive functions nor the increased risk of death. Patients with AD were characterized by lower prevalence of HT and other vascular risk factors. BP levels and HT had no impact on clinical outcome.

Kinetic and pH studies on human phenylethanolamine N-methyltransferase

Phenylethanolamine N-methyltransferase (PNMT) catalyzes the conversion of norepinephrine (noradrenaline) to epinephrine (adrenaline) while, concomitantly, S-adenosyl-L-methionine (AdoMet) is converted to S-adenosyl-L-homocysteine. This reaction represents the terminal step in catecholamine biosynthesis and inhibitors of PNMT have been investigated, inter alia, as potential antihypertensive agents. At various times the kinetic mechanism of PNMT has been reported to operate by a random mechanism, an ordered mechanism in which norepinephrine binds first, and an ordered mechanism in which AdoMet binds first. Here we report the results of initial velocity studies on human PNMT in the absence and presence of product and dead end inhibitors. These, coupled with isothermal titration calorimetry and fluorescence binding experiments, clearly shown that hPNMT operates by an ordered sequential mechanism in which AdoMet binds first. Although the logV pH-profile was not well defined, plots of logV/K versus pH for AdoMet and phenylethanolamine, as well as the pKi versus pH for the inhibitor, SK&F 29661, were all bell-shaped indicating that a protonated and an unprotonated group are required for catalysis.

Alzheimer's disease is associated with a low prevalence of hypertension

BACKGROUND/AIM

Dementia is one of the most common health problems in the world. Alzheimer's disease (AD) is the most common form of dementia. The relation between blood pressure (BP) and dementia has been the subject of numerous epidemiological studies, and midlife hypertension (HT) is a risk factor for AD. The association between BP and risk of dementia is lower in the older population. The aim of this study was to examine the association between the prevalence of HT and AD in elderly individuals.

METHODS

In this cross-sectional study, 193 patients with AD and 1,860 patients with normal cognitive function were evaluated.

RESULTS

The prevalence of HT was lower in the AD group (60.6 vs. 70.5%; p = 0.005). In multivariate analysis, AD was found to be negatively correlated with HT (OR = 0.649; 95% CI 0.461-0.916).

CONCLUSION

The prevalence of HT was lower in patients with AD compared to subjects without AD. Physicians who deal with AD patients must keep in mind that the need for antihypertensive medication may decline during the dementia process.

The reaction mechanism of phenylethanolamine N-methyltransferase: a density functional theory study

Hybrid density functional theory methods were used to investigate the reaction mechanism of human phenylethanolamine N-methyltransferase (hPNMT). This enzyme catalyzes the S-adenosyl-L-methionine-dependent conversion of norepinephrine to epinephrine, which constitutes the terminal step in the catecholamine biosynthesis. Several models of the active site were constructed based on the X-ray structure. Geometries of the stationary points along the reaction path were optimized and the reaction barrier and energy were calculated and compared to the experimental values. The calculations demonstrate that the reaction takes place via an SN2 mechanism with methyl transfer being rate-limiting, a suggestion supported by mutagenesis studies. Optimal agreement with experimental data is reached using a model in which both active site glutamates are protonated. Overall, the mechanism of hPNMT is more similar to those of catechol O-methyltransferase and glycine N-methyltransferase than to that of guanidinoacetate N-methyltransferase in which methyl transfer is coupled to proton transfer.

How much does hypertension affect cognition?: explained variance in cross-sectional analysis of non-demented community-dwelling individuals in the SEARCH study

Vascular pathology impairs cognition and impaired cognition increases the risk of dementia. Hypertension is arguably the vascular risk factor that can be reverted best. Here we estimated the effect magnitude of hypertension by determining the variance in cognition explained by systolic blood pressure (sBP) in non-demented community-dwelling individuals. We recruited 525 individuals (mean age 65, range 40-85) selected from the city registry of Muenster, Germany, measured cognitive performance with a comprehensive test battery and assessed vascular risk based on glycosylated hemoglobin, serum cholesterol, high sensitive C-reactive protein, body mass index, smoking pack years, and blood pressure. Including gender and education as well as the vascular risk factors, multiple linear regression analysis for different age groups showed that in midlife age groups systolic blood pressure explained up to 11% of the variance in cognitive performance. These findings suggest that in non-demented community-dwelling individuals hypertension may account for one tenth of cognitive impairment and thus for an increased risk for dementia.

Time-dependent inactivation of human phenylethanolamine N-methyltransferase by 7-isothiocyanatotetrahydroisoquinoline

Inhibitors of phenylethanolamine N-methyltransferase [PNMT, the enzyme that catalyzes the final step in the biosynthesis of epinephrine (Epi)] may be of use in determining the role of Epi in the central nervous system. Here we describe the synthesis and characterization of 7-SCN tetrahydroisoquinoline as an affinity label for human PNMT.

Hypertension and cerebrovascular dysfunction

Essential hypertension has devastating effects on the brain, being the major cause of stroke and a leading cause of dementia. Hypertension alters the structure of cerebral blood vessels and disrupts intricate vasoregulatory mechanisms that assure an adequate blood supply to the brain. These alterations threaten the cerebral blood supply and increase the susceptibility of the brain to ischemic injury as well as Alzheimer's disease. This review focuses on the mechanisms by which hypertension disrupts cerebral blood vessels, highlighting recent advances and outstanding issues.

High-Normal Blood Pressure Is Associated With Poor Cognitive Performance

While the relation between systolic blood pressure (SBP) and vascular events is linear down to the high-normal range, the relation between SBP and cognition is less clear. We cross-sectionally assessed the relation between SBP and cognition in a cohort extending from mid- to late-life. From a total of 2200 community-dwelling individuals we recruited 377 aged 44 to 82 years (median: 64 years, 171 male) in the SEARCH-Health study (Systematic evaluation and alteration of risk factors for cognitive health). Participants were studied with a comprehensive neuropsychological test battery that provided, based on principal component analysis, 5 composite scores for cognition (learning and memory, attention and executive function, spatial skills, working memory, and verbal skills). Global cognition was calculated from the sum of the composite scores. SBP (corrected R 2 =0.007), education (corrected R 2 =0.203), age (corrected R 2 =0.102), and gender (corrected R 2 =0.011) explained one third of variance in global cognitive performance ( P <0.001) on multivariate analyses. Moreover, the relation between SBP (based on 10 mm Hg-categories from <120 mm Hg to >170 mm Hg) and global cognitive performance was linear in this range of SBP-values, ie, even in the normotensive range (β=−0.110, P <0.05). Subgroup analysis showed that the association of SBP and cognition was driven by results in midlife (<60 years) individuals (β=−0.291, P <0.005). Thus, even in the normotensive range increasing systolic blood pressure is inversely related to cognition.

Dopaminergic and adrenergic toxicities on SK-N-MC human neuroblastoma cells are mediated through G protein signaling and oxidative stress

Dopamine and norepinephrine are neurotransmitters which participate in various regulatory functions of the human brain. These functions are lost in neurodegenerative diseases including Parkinson's disease and Alzheimer's disease. In this study, we used SK-N-MC neuroblastoma cells to investigate the cytotoxicities of high concentrations of dopamine and norepinephrine on neuronal cells. Dopamine, norepinephrine, as well as their corresponding synthetic agonists (SKF38393 and isoproterenol, respectively) triggered SK-N-MC cell death when applied at 50-100 muM persistently for 2 days. This catecholamine-induced cell death appears to be neuronal specific, as demonstrated by their inabilities of triggering apoptosis of A549 lung carcinoma cells and Cos-7 kidney fibroblasts. By pretreating SK-N-MC cells with target-specific inhibitors before administration of catecholamine, components of G protein signaling (i.e. G( s )/cAMP/PKA), monoamine oxidases, nitric oxide synthase, c-Jun N-terminal kinase and oxidative stress were found to be involved in this dopamine/norepinephrine-induced cytotoxicity, which subsequently led to caspase-dependent and -independent apoptotic responses as well as DNA degradation. In contrast, agonists of G( i )-coupled dopamine receptors and adrenergic receptors (quinpirole and UK14,304, respectively) were incapable of triggering apoptosis of SK-N-MC cells. Our results suggest that both G protein (G( s ))-mediated signaling cascade and oxidative stress participate in the dopamine/norepinephrine-induced neuronal apoptosis.

Neurotoxicity and metabolism of the catecholamine-derived 3,4-dihydroxyphenylacetaldehyde and 3,4-dihydroxyphenylglycolaldehyde: the role of aldehyde dehydrogenase

Aldehydes are highly reactive molecules formed during the biotransformation of numerous endogenous and exogenous compounds, including biogenic amines. 3,4-Dihydroxyphenylacetaldehyde is the aldehyde metabolite of dopamine, and 3,4-dihydroxyphenylglycolaldehyde is the aldehyde metabolite of both norepinephrine and epinephrine. There is an increasing body of evidence suggesting that these compounds are neurotoxic, and it has been recently hypothesized that neurodegenerative disorders may be associated with increased levels of these biogenic aldehydes. Aldehyde dehydrogenases are a group of NAD(P)+ -dependent enzymes that catalyze the oxidation of aldehydes, such as those derived from catecholamines, to their corresponding carboxylic acids. To date, 19 aldehyde dehydrogenase genes have been identified in the human genome. Mutations in these genes and subsequent inborn errors in aldehyde metabolism are the molecular basis of several diseases, including Sjögren-Larsson syndrome, type II hyperprolinemia, gamma-hydroxybutyric aciduria, and pyridoxine-dependent seizures, most of which are characterized by neurological abnormalities. Several pharmaceutical agents and environmental toxins are also known to disrupt or inhibit aldehyde dehydrogenase function. It is, therefore, possible to speculate that reduced detoxification of 3,4-dihydroxyphenylacetaldehyde and 3,4-dihydroxyphenylglycolaldehyde from impaired or deficient aldehyde dehydrogenase function may be a contributing factor in the suggested neurotoxicity of these compounds. This article presents a comprehensive review of what is currently known of both the neurotoxicity and respective metabolism pathways of 3,4-dihydroxyphenylacetaldehyde and 3,4-dihydroxyphenylglycolaldehyde with an emphasis on the role that aldehyde dehydrogenase enzymes play in the detoxification of these two aldehydes.

Exploring the active site of phenylethanolamine N-methyltransferase with 1,2,3,4-tetrahydrobenz[h]isoquinoline inhibitors

1,2,3,4-Tetrahydrobenz[h]isoquinoline (THBQ, 11) is a potent, inhibitor of phenylethanolamine N-methyltransferase (PNMT). Docking studies indicated that the enhanced PNMT inhibitory potency of 11 (hPNMT K(i)=0.49microM) versus 1,2,3,4-tetrahydroisoquinoline (5, hPNMT K(i)=5.8microM) was likely due to hydrophobic interactions with Val53, Met258, Val272, and Val269 in the PNMT active site. These studies also suggested that the addition of substituents to the 7-position of 11 that are capable of forming hydrogen bonds to the enzyme could lead to compounds (14-18) having enhanced PNMT inhibitory potency. However, these compounds are in fact less potent at PNMT than 11. Furthermore, 7-bromo-THBQ (19, hPNMT K(i)=0.22mM), which has a lipophilic 7-substituent that cannot hydrogen bond to the enzyme, is twice as potent at PNMT than 11. This once again illustrates the limitations of docking studies for lead optimization.

Comparison of the Binding of 3-Fluoromethyl-7-sulfonyl-1,2,3,4-tetrahydroisoquinolines with Their Isosteric Sulfonamides to the Active Site of Phenylethanolamine N-Methyltransferase

3-Fluoromethyl-7-(N-substituted aminosulfonyl)-1,2,3,4-tetrahydroisoquinolines (14, 16, and 18-22) are highly potent and selective inhibitors of phenylethanolamine N-methyltransferase (PNMT). Molecular modeling studies with 3-fluoromethyl-7-(N-alkyl aminosulfonyl)-1,2,3,4-tetrahydroisoquinolines, such as 16, suggested that the sulfonamide -NH- could form a hydrogen bond with the side chain of Lys57. However, SAR studies and analysis of the crystal structure of human PNMT (hPNMT) in complex with 7 indicated that the sulfonamide oxygens, and not the sulfonamide -NH-, formed favorable interactions with the enzyme. Thus, we hypothesized that replacement of the sulfonamide -NH- with a methylene group could result in compounds that would retain potency at PNMT and that would have increased lipophilicity, thus increasing the likelihood they will cross the blood brain barrier. A series of 3-fluoromethyl-7-sulfonyl-1,2,3,4-tetrahydroisoquinolines (23-30) were synthesized and evaluated for their PNMT inhibitory potency and affinity for the alpha2-adrenoceptor. A comparison of these compounds with their isosteric sulfonamides (14, 16, and 18-22) showed that the sulfones were more lipophilic but less potent than their corresponding sulfonamides. Sulfone 24 (hPNMT Ki = 1.3 microM) is the most potent compound in this series and is quite selective for PNMT versus the alpha2-adrenoceptor, but 24 is less potent than the corresponding sulfonamide, 16 (hPNMT Ki = 0.13 microM). We also report the crystal structure of hPNMT in complex with sulfonamide 15, from which a potential hydrogen bond acceptor within the hPNMT active site has been identified, the main chain carbonyl oxygen of Asn39. The interaction of this residue with the sulfonamide -NH- is likely responsible for much of the enhanced inhibitory potency of the sulfonamides versus the sulfones.

Synthesis and evaluation of 4-fluoro-8-substituted-2,3,4,5-tetrahydro-1H-2-benzazapines as selective inhibitors of phenylethanolamine N-methyltransferase versus the alpha(2)-adrenoceptor

A small series of 4-fluoro-8-substituted-2,3,4,5-tetrahydro-1H-2-benzazapines (4-fluoro-THBAs; 12-15) were synthesized and evaluated as inhibitors of phenylethanolamine N-methyltransferase (PNMT; EC 2.1.1.28) and as inhibitors of the binding of clonidine at the alpha(2)-adrenoceptor. 4-Fluoro-THBAs 13-15 displayed selectivity ratios (alpha(2) K(i)/PNMT K(i)) greater than 75 and 4-fluoro-8-nitro-THBA (13) was found to be one of the most selective inhibitors of PNMT known, with a selectivity ratio of greater than 900. These compounds are also quite lipophilic and according to previous results from this laboratory should be able to penetrate the blood-brain barrier. These 4-fluoro-THBAs represent important leads in the development of new, more selective, CNS-active inhibitors of PNMT.

Phenylethanolamine N-methyltransferase (PNMT) gene and early-onset Alzheimer disease

The activity of human phenylethanolamine N-methyltransferase (PNMT) is reduced in the neurons of those cells in many subcortical areas of the brain that are known to undergo neurodegeneration in Alzheimer disease (AD). Others have reported that PNMT is decreased in brains of persons with AD and that the decrease in enzymatic activity is due to a reduced amount of the enzyme protein. We have previously described two polymorphisms, G-353A and G-148A, in the promoter region of the gene coding for PNMT. These markers were tested for their association with the occurrence of sporadic AD. Genotyping of 131 necropsy confirmed AD cases, and 947 adult nondemented controls were completed. We observed a significant association between both of the PNMT gene polymorphisms and early-onset AD (EOAD) (P < or = 0.007), but not in late-onset AD (LOAD). These data suggest that genetic variation in the promoter of the PNMT gene is associated with increased susceptibility to the sporadic form of EOAD.

Differential expression of catecholamine biosynthetic enzymes in the rat ventrolateral medulla

Adrenergic (C1) neurons located in the rostral ventrolateral medulla are considered a key component in the control of arterial blood pressure. Classically, C1 cells have been identified by their immunoreactivity for the catecholamine biosynthetic enzymes tyrosine hydroxylase (TH) and/or phenylethanolamine N-methyltransferase (PNMT). However, no studies have simultaneously demonstrated the expression of aromatic L-amino acid decarboxylase (AADC) and dopamine beta-hydroxylase (DBH) in these neurons. We examined the expression and colocalization of all four enzymes in the rat ventrolateral medulla using immunohistochemistry and reverse transcription-polymerase chain reaction (RT-PCR) analysis. Retrograde tracer injected into thoracic spinal segments T2-T4 was used to identify bulbospinal neurons. Using fluorescence and confocal microscopy, most cells of the C1 group were shown to be double or triple labeled with TH, DBH, and PNMT, whereas only 65-78% were immunoreactive for AADC. Cells that lacked detectable immunoreactivity for AADC were located in the rostral C1 region, and approximately 50% were spinally projecting. Some cells in this area lacked DBH immunoreactivity (6.5-8.3%) but were positive for TH and/or PNMT. Small numbers of cells were immunoreactive for only one of the four enzymes. Numerous fibres that were immunoreactive for DBH but not for TH or PNMT were noted in the rostral C1 region. Single-cell RT-PCR analysis conducted on spinally projecting C1 neurons indicated that only 76.5% of cells that contained mRNA for TH, DBH, and PNMT contained detectable message for AADC. These experiments suggest that a proportion of C1 cells may not express all of the enzymes necessary for adrenaline synthesis.

Catecholamine monoamine oxidase a metabolite in adrenergic neurons is cytotoxic in vivo

3,4-Dihydroxyphenylglycolaldehyde is the monoamine oxidase-A metabolite of two catecholamine neurotransmitters, epinephrine and norepinephrine. This aldehyde metabolite and its synthesizing enzymes increase in cell bodies of catecholamine neurons in Alzheimer's disease. To test the hypothesis that 3,4-dihydroxyphenylglycolaldehyde, but not epinephrine or its major metabolite 4-hydroxy-3-methoxyphenylglycol, is a neurotoxin, we injected 3,4-dihydroxyphenylglycolaldehyde onto adrenergic neurons in the rostral ventrolateral medulla. Injections of epinephrine or 4-hydroxy-3-methoxyphenylglycol were made into the same area of controls. A dose response and time study were performed. Adrenergic neurons were identified by their content of the epinephrine synthesizing enzyme, phenylethanolamine N-methyltransferase, immunohistochemically. Apoptosis was evaluated by in situ terminal deoxynucleotidyl-transferase mediated dUTP nick end label staining. Injection of 3,4-dihydroxyphenylglycolaldehyde in amounts as low as 50 ng results in loss of adrenergic neurons and apoptosis after 18 h. The degree of neurotoxicity is dose and time dependent. Doses of 3,4-dihydroxyphenylglycolaldehyde 10-fold higher produce necrosis. Neither epinephrine nor 4-hydroxy-3-methoxyphenylglycol are toxic. A 2.5 microg injection of 3,4-dihydroxyphenylglycolaldehyde is toxic to cortical neurons but not glia. Active uptake of the catecholamine-derived aldehyde into differentiated PC-12 cells is demonstrated. Implications of these findings for catecholamine neuron death in neurodegenerative diseases are discussed.

Enantiospecific synthesis of 3-fluoromethyl-, 3-hydroxymethyl-, and 3-chloromethyl-1,2,3,4-tetrahydroisoquinolines as selective inhibitors of phenylethanolamine N-methyltransferase versus the alpha(2)-adrenoceptor

An enantiospecific method was developed for the synthesis of 3-fluoromethyl-, 3-hydroxymethyl-, and 3-chloromethyl-7-substituted-1,2,3,4-tetrahydroisoquinolines (THIQs) from phenylalanine. Biochemical evaluation of the enantiomers of these compounds at both PNMT and the alpha(2)-adrenoceptor indicates that both sites display similar stereoselectivity. Overall the R-enantiomer was usually the more potent enantiomer at both PNMT and the alpha(2)-adrenoceptor for these 3-fluoromethyl-, 3-hydroxymethyl-, and 3-chloromethyl-THIQs. The one exception is 3-hydroxymethyl-7-nitro-THIQ (9), which was found to display the opposite stereoselectivity at the alpha(2)-adrenoceptor. A comparison of the PNMT inhibitory potency of the enantiomers of these 3-fluoromethyl-, 3-hydroxymethyl-, and 3-chloromethyl-THIQs indicates that all of the 3-substituted-THIQs displayed similar inhibitory potency for PNMT. However, the nature of the 3-substituent was found to have a major effect on the alpha(2)-adrenoceptor affinity of these compounds with the 3-hydroxymethyl- and 3-fluoromethyl-THIQs having the highest affinity and THIQs containing the 3-chloromethyl moiety the least. Compounds R-3-fluoromethyl-7-cyano-THIQ (R-12) and R-3-fluoromethyl-7-N-(4-chlorophenyl)aminosulfonyl-THIQ (R-13) and both enantiomers of 3-chloromethyl-7-nitro-THIQ (R- and S-30) are the most selective inhibitors in this study and display selectivities (alpha(2)-adrenoceptor K(i)/PNMT K(i)) greater than 200. These compounds give important insight into the steric and stereochemical preferences of both PNMT and the alpha(2)-adrenoceptor, which should assist in the development of new PNMT inhibitors.

Synthesis and biochemical evaluation of 3-fluoromethyl-1,2,3, 4-tetrahydroisoquinolines as selective inhibitors of phenylethanolamine N-methyltransferase versus the alpha(2)-adrenoceptor

A series of 3-fluoromethyl-1,2,3,4-tetrahydroisoquinolines (3-fluoromethyl-THIQs) was proposed, and their phenylethanolamine N-methyltransferase (PNMT) and alpha(2)-adrenoceptor affinities were predicted through the use of comparative molecular field analysis (CoMFA) models. These compounds were synthesized and evaluated for affinity at PNMT and the alpha(2)-adrenoceptor. It was discovered that these compounds are some of the most selective inhibitors of PNMT versus the alpha(2)-adrenoceptor known. To determine the ability of these compounds to penetrate the blood-brain barrier (BBB), a series of THIQs possessing a variety of calculated partition coefficients (Clog P) were assayed using an in vitro BBB model. This study found a good correlation between lipophilicity (Clog P) and BBB permeability, which indicated that THIQs possessing Clog P values of at least 0.13-0.57 should have some penetration into the brain. Two compounds [3-fluoromethyl-7-N-(4-chlorophenyl)aminosulfonyl-THIQ (18) and 3-fluoromethyl-7-cyano-THIQ (20)] possess calculated partition coefficients greater than 0.57 and display selectivities (alpha(2)-adrenoceptor K(i)/PNMT K(i)) greater than 200 and thus represent promising leads in the development of highly selective inhibitors of PNMT with the ability to penetrate the BBB.

Synthesis and evaluation of 3-trifluoromethyl-7-substituted-1,2,3, 4-tetrahydroisoquinolines as selective inhibitors of phenylethanolamine N-methyltransferase versus the alpha(2)-adrenoceptor

A series of 3-trifluoromethyl-1,2,3,4-tetrahydroisoquinolines was synthesized and evaluated as inhibitors of phenylethanolamine N-methyltransferase (PNMT) and as inhibitors of the binding of clonidine at the alpha(2)-adrenoceptor. These compounds were found to be selective inhibitors of PNMT due to their decreased affinity for the alpha(2)-adrenoceptor, which was attributed to steric bulk intolerance around the 3-position of 1,2,3,4-tetrahydroisoquinoline (THIQ) at the alpha(2)-adrenoceptor and to the decreased pK(a) of the THIQ amine due to the 3-trifluoromethyl moiety. Overall, these compounds displayed less affinity for PNMT compared to previously studied THIQ-type inhibitors, except for 16 which was found to have good affinity for PNMT (PNMT K(i) = 0.52 microM). Compounds 14 and 16 proved to be the most selective inhibitors in this small series of compounds and are some of the most selective inhibitors of PNMT known (14, selectivity alpha(2) K(i)/PNMT K(i) = 700; 16, selectivity alpha(2) K(i)/PNMT K(i) > 1900). Compounds 14 and 16 are also quite lipophilic due to the 3-trifluoromethyl moiety and represent promising new leads for the development of new highly selective inhibitors of PNMT, which should be sufficiently lipophilic to penetrate the blood-brain barrier.

1,3-Dimethyl-7-substituted-1,2,3,4-tetrahydroisoquinolines as probes for the binding orientation of tetrahydroisoquinoline at the active site of phenylethanolamine N-methyltransferase

In order to determine the function of epinephrine (Epi) in the central nervous system, we have targeted the enzyme that catalyzes the final step in the biosynthesis of Epi, phenylethanolamine N-methyltransferase (PNMT; EC 2.1.1.28). 1,2,3,4-Tetrahydroisoquinolines (THIQs) are inhibitors of this enzyme, but also display affinity for the alpha2-adrenoceptor. To gain further understanding about how THIQs bind at the PNMT active site and in an attempt to further increase the selectivity of THIQ-type inhibitors versus the alpha2-adrenoceptor, a series of cis- and trans-1,3-dimethyl-7-substituted-THIQs were synthesized. Evaluation of these compounds suggests that THIQs bind in two different orientations at the PNMT active site, based on the lipophilicity of the 7-substituent. However, no significant increases in selectivity versus the alpha2-adrenoceptor were observed for these compounds.

Accumulation of 3,4-dihydroxyphenylglycolaldehyde, the neurotoxic monoamine oxidase A metabolite of norepinephrine, in locus ceruleus cell bodies in Alzheimer's disease: mechanism of neuron death

3,4-Dihydroxyphenylglycolaldehyde (DOPEGAL) is the neurotoxic monoamine oxidase A (MAO-A) metabolite of norepinephrine (NE). NE neurons in the locus ceruleus (LC) die in Alzheimer's disease (AD). To determine if DOPEGAL could contribute to NE neuron death in AD we measured levels of DOPEGAL, NE and their synthesizing enzymes in LC from AD and matched controls. We found 2.8- and 3.6-fold increases in DOPEGAL and MAO-A in AD LC neuronal cell bodies compared to controls. NE and dopamine beta-hydroxylase were increased by 3.8- and 10.7-fold, respectively. Implications for the mechanism of neuron death in AD are discussed.

Noradrenaline transporter expression in the pons and medulla oblongata of the rat: localisation to noradrenergic and some C1 adrenergic neurones

Catecholaminergic neurotransmission is normally terminated by rapid re-uptake of the neurotransmitter by a high-affinity Na+/Cl--dependent plasma membrane transporter. Specific transporters have been cloned for both dopamine (DAT) and noradrenaline (NAT) in the rat. While DAT has been studied extensively, NAT expression has received less attention, particularly at the protein level. We used an antibody generated against a 49 residue segment of an extracellular loop region of NAT to study expression of the transporter protein throughout the rat pons and medulla oblongata. NAT was expressed in over 95% of noradrenergic neurones in the A1, A2/area postrema, A5, A6/locus subcoeruleus, and A7 noradrenergic groups. Approximately 10% of C1 adrenergic neurones located in the rostral ventrolateral medulla (RVL) also expressed NAT. Expression of NAT mRNA in bulbospinal C1 cells was confirmed using single-cell reverse transcription polymerase chain reaction (RT-PCR) of acutely isolated RVL neurones. Spinally projecting neurones were identified by retrograde labelling with rhodamine beads, and C1 neurones were identified by RT-PCR using primers specific for tyrosine hydroxylase (TH) or phenylethanolamine N-methyltransferase (PNMT) mRNAs. Thirteen percent of adrenergic bulbospinal neurones tested expressed NAT mRNA. C1 neurones are potentially important in cardiovascular control and blood pressure regulation, and the identification of NAT expression in a sub-population of these neurones provides further evidence for the heterogeneity of this neuronal population.

Norepinephrine transmitter metabolite generates free radicals and activates mitochondrial permeability transition: a mechanism for DOPEGAL-induced apoptosis

3,4-Dihydroxyphenylglycolaldehyde (DOPEGAL) is the monoamine oxidase A metabolite of norepinephrine (NE) and epinephrine. DOPEGAL, but neither NE nor its other metabolites induces apoptosis in differentiated PC-12 cells by an unknown mechanism. To study the mechanism of DOPEGAL-induced apoptosis, we tested DOPEGAL and NE for their capacity to generate free radicals and to induce mitochondrial permeability transition (PT). Results show that DOPEGAL but not NE forms reactive free radical intermediates under oxidative stress and enhances Ca2+-mediated induction of the mitochondrial PT. Linkage of these events to apoptosis is described. Implications for degenerative diseases are discussed.

Norepinephrine transmitter metabolite induces apoptosis in differentiated rat pheochromocytoma cells

3,4-Dihydroxyphenylglycolaldehyde (DOPEGAL) is the monoamine oxidase A metabolite of norepinephrine and epinephrine. DOPEGAL, but not other metabolites, kills differentiated PC-12 cells. However, the type of DOPEGAL induced cell death, whether necrosis or apoptosis, is not known. To determine the type of cell death triggered by DOPEGAL, PC-12 cells cultured in the presence or absence of 30 microM DOPEGAL were examined by electron microscopy and DNA agarose gel electrophoresis for characteristic features of apoptosis. Results indicate that DOPEGAL induces apoptosis in these cells. Implications for degenerative diseases are discussed.

Molecular cloning and characterization of an L-epinephrine transporter from sympathetic ganglia of the bullfrog, Rana catesbiana

Chemical signaling by dopamine (DA) and L-norepinephrine (L-NE) at synapses is terminated by uptake via specialized presynaptic transport proteins encoded by the DA transporter (DAT) and L-NE transporter (NET) genes, respectively. In some vertebrate neurons, particularly the sympathetic neurons of amphibians, L-NE is converted to L-epinephrine (L-Epi, adrenaline) and released as the primary neurotransmitter. Although evidence exists for a molecularly distinct L-Epi transporter (ET) in the vertebrate brain and peripheral nervous system, a transporter specialized for extracellular L-Epi clearance has yet to be identified. To pursue this issue, we cloned transporter cDNAs from bullfrog (Rana catesbiana) paravertebral sympathetic ganglia and characterized functional properties via heterologous expression in non-neuronal cells. A cDNA of 2514 bp (fET) was identified for which the cognate 3.1 kb mRNA is highly enriched in frog sympathetic ganglia. Sequence analysis of the fET cDNA reveals an open reading frame coding for a protein of 630 amino acids. Inferred fET protein sequence bears 75, 66, and 48% amino acid identity with human NET, DAT, and the 5-hydroxytryptamine transporter (SERT), respectively. Transfection of fET confers Na+- and Cl--dependent catecholamine uptake in HeLa cells. Uptake of [3H]-L-NE by fET is inhibited by catecholamines in a stereospecific manner. L-Epi and DA inhibit fET-mediated [3H]-L-NE uptake more potently than they inhibit [3H]-L-NE uptake by human NET (hNET), whereas L-NE exhibits equivalent potency between the two carriers. Moreover, fET exhibits a greater maximal velocity (Vmax) for the terminal products of catecholamine biosynthesis (L-Epi > L-NE >> DA), unlike hNET, in which a Vmax rank order of L-NE > DA > L-Epi is observed. fET-mediated transport of catecholamines is sensitive to cocaine and tricyclic antidepressants, with antagonist potencies significantly correlated with hNET inhibitor sensitivity. Amino acid conservation and divergence of fET with mammalian catecholamine transporters help define residues likely to be involved in catecholamine recognition and translocation as well as blockade by selective reuptake inhibitors.

Norepinephrine transmitter metabolite is a selective cell death messenger in differentiated rat pheochromocytoma cells

3,4-Dihydroxyphenylglycolaldehyde (DOPEGAL) is the monoamine oxidase A (MAO-A) metabolite of norepinephrine (NE) and epinephrine (Epi). Oxidative metabolites of amines are predicted toxins. In this study we determine the toxicity of DOPEGAL, its tautomer 2',3,4-trihydroxyacetophenone (THAP) as well as NE, Epi and their oxidative and methylated metabolites in cultures of differentiated PC-12 cells. At 59.5 microM DOPEGAL, THAP and Epi, but not NE or other NE or Epi metabolites decreased PC-12 cells by 43.8%, 26.7% and 16.8% respectively. DOPEGAL toxicity was concentration and time dependent. Possible implications for degenerative diseases are discussed.