Activation of platelet monoamine oxidase by plasma in the human.

A pronounced activation of platelet monoamine oxidase (MAO) by human plasma has been observed. The activation was substrate selective, since serotonin, $\text{p}$-tyramine, dopamine and benzylamine were much more effective than β-phenylethylamine or tryptamine. The activator(s) in the plasma was heat stable but labile to acid hydrolysis and treatment with lipase and protease. The plasma was also found to be capable of activating partially purified MAO obtained from rat liver mitochondria. Phospholipids such as phosphatidylethanolamine were shown to activate MAO.     

Influence of selective, reversible inhibitors of monoamine oxidase on the prolonged depletion of striatal dopamine by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mice

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) hydrochloride injected s.c. at 20 mg/kg once daily for four days resulted in marked depletion of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in mouse striatum one week after the last dose. Pretreatment with MD 240928, (R)-[4-((3-chlorophenyl)-methoxy)phenyl]-5-[(methylamino)methyl]-2- oxazolidinone methanesulfonate, prevented the depletion of striatal dopamine, DOPAC and HVA, whereas pretreatment with harmaline did not. MD 240928 selectively inhibited type B not type A monoamine oxidase (MAO), whereas harmaline selectively inhibited type A MAO in mouse striatum. Acutely after injection of harmaline, DOPAC and HVA concentrations were decreased in mouse striatum; these changes were not produced by MD 240928. The acute changes in dopamine metabolites reveal that MAO-A not MAO-B is responsible for the oxidation of dopamine in mouse striatum. Protection against the neurotoxic effects of MPTP by MD 240928 but not by harmaline indicates that prevention of dopamine oxidation is not the mechanism of the protective effect; instead the protection probably is due to prevention of MPTP metabolism by MAO-B, this metabolism having been shown to occur by other workers. The results with these reversible, competitive inhibitors of the two types of MAO are in agreement with previously reported results from studies using irreversible inhibitors of MAO.     

N-Acetylcysteine Prevents the Increase in Spontaneous Oxidation of Dopamine During Monoamine Oxidase Inhibition in PC12 Cells

The catecholaldehyde hypothesis for the pathogenesis of Parkinson’s disease proposes that the deaminated dopamine metabolite 3,4-dihydroxyphenylacetaldehyde (DOPAL) is toxic to nigrostriatal dopaminergic neurons. Inhibiting monoamine oxidase (MAO) should therefore slow the disease progression; however, MAO inhibition increases spontaneous oxidation of dopamine, as indicated by increased 5-S-cysteinyl-dopamine (Cys-DA) levels, and the oxidation products may also be toxic. This study examined whether N-acetylcysteine (NAC), a precursor of the anti-oxidant glutathione, attenuates the increase in Cys-DA production during MAO inhibition. Rat pheochromocytoma PC12 cells were incubated with NAC, the MAO-B inhibitor selegiline, or both. Selegiline decreased DOPAL and increased Cys-DA levels (p?<?0.0001 each). Co-incubation of NAC at pharmacologically relevant concentrations (1–10 µM) with selegiline (1 µM) attenuated or prevented the Cys-DA response to selegiline, without interfering with the selegiline-induced decrease in DOPAL production or inhibiting tyrosine hydroxylation. NAC therefore mitigates the increase in spontaneous oxidation of dopamine during MAO inhibition.

     

Reversal of subcellular remodelling by losartan in heart failure due to myocardial infarction

This study tested the reversal of subcellular remodelling in heart failure due to myocardial infarction (MI) upon treatment with losartan, an angiotensin II receptor antagonist. Twelve weeks after inducing MI, rats were treated with or without losartan (20 mg/kg; daily) for 8 weeks and assessed for cardiac function, cardiac remodelling, subcellular alterations and plasma catecholamines. Cardiac hypertrophy and lung congestion in 20 weeks MI‐induced heart failure were associated with increases in plasma catecholamine levels. Haemodynamic examination revealed depressed cardiac function, whereas echocardiographic analysis showed impaired cardiac performance and marked increases in left ventricle wall thickness and chamber dilatation at 20 weeks of inducing MI. These changes in cardiac function, cardiac remodelling and plasma dopamine levels in heart failure were partially or fully reversed by losartan. Sarcoplasmic reticular (SR) Ca²⁺‐pump activity and protein expression, protein and gene expression for phospholamban, as well as myofibrillar (MF) Ca²⁺‐stimulated ATPase activity and α‐myosin heavy chain mRNA levels were depressed, whereas β‐myosin heavy chain expression was increased in failing hearts; these alterations were partially reversed by losartan. Although SR Ca²⁺‐release activity and mRNA levels for SR Ca²⁺‐pump were decreased in failing heart, these changes were not reversed upon losartan treatment; no changes in mRNA levels for SR Ca²⁺‐release channels were observed in untreated or treated heart failure. These results suggest that the partial improvement of cardiac performance in heart failure due to MI by losartan treatment is associated with partial reversal of cardiac remodelling as well as partial recovery of SR and MF functions.     

Adaptive Changes in Postsynaptic Dopamine Receptors Despite Unaltered Dopamine Dynamics in Mice Lacking Monoamine Oxidase B

Monoamine oxidase (MAO) B is considered a key enzyme in dopamine metabolism. The present studies, conducted in MAO B knockout mice, show that lack of MAO B does not alter extracellular levels of dopamine in striatum. Similarly, the synthesis, storage, uptake, and release of dopamine are also unaltered. However, autoradiography revealed a significant up-regulation of the D2-like dopamine receptors in the striatum of MAO B knockout mice. Mutant mice also exhibit a functional supersensitivity of D1-dopamine receptors in the nucleus accumbens. Thus, the agonist SKF 38,393-induced c-Fos immunoreactivity was significantly increased in knockout mice as compared with wild-type controls. In view of the apparently normal basal dopamine dynamics observed in MAO B knockout mice, we hypothesize that a dopamine-independent mechanism underlies adaptations in dopamine receptor function that occur as a consequence of MAO B depletion. Finally, these findings suggest that chronic administration of MAO inhibitors, as occurs in the treatment of Parkinson's disease and depression, may be associated with an increased responsiveness of CNS neurons to dopamine receptor ligands.     

Marked Amine and Amine Metabolite Changes in Norrie Disease Patients with an X-Chromosomal Deletion Affecting Monoamine Oxidase

Urinary and plasma amines and amine metabolites were quantified in two individuals with Norrie disease resulting from a deletion in chromosomal region Xp11.3, recently reported to be associated with absence of the gene encoding monoamine oxidase (MAO)-A and nondetectable MAO-A activity in fibroblasts and MAO-B activity in platelets. Marked (four-to 100-fold) elevations in levels of urinary phenylethylamine, o-tyramine, and m-tyramine (which are preferential substrates for MAO-B) and marked reductions (90%) in levels of 3-methoxy-4-hydroxyphenylglycol (a deaminated metabolite of norepinephrine, a preferential substrate for MAO-A) in urine and plasma confirmed the presence of a systemic, functionally significant reduction in the activities of both MAO isozymes. The magnitude of these changes, which are equivalent to those found in subjects taking MAO-inhibiting antidepressants, suggests that early initiation of dietary and drug restrictions may be clinically important in these and other patients with X-chromosomal mutations involving MAO. These findings further support the proposition that the MAOA and MAOB genes are located in close proximity on the X chromosome. Negligible changes in the metabolites of dopamine and serotonin raise the possibility that other metabolic pathways are of importance for their production, that dietary or intestinal bacterial sources contribute substantially to the presence of these amine metabolites in urine, or both.     

Red cell ouabain binding sites, Na+K+-ATPase, and intracellular Na+ as individual characteristics

Healthy male volunteers were infused for three hours with either a dopamine hydrochloride solution at a rate of 4 ug/kg/min or with normal saline. Plasma amine oxidase and platelet MAO activity towards benzylamine both increased in response to intravenous dopamine. There was no increase in enzyme activity when dopamine was added to the platelet and plasma enzymes in vitro. This heretofore unreported increase in the oxidative deaminating capacity of the human organism may represent an adaptive physiologic response to the high circulating levels of dopamine and provides further evidence for a possible functional significance of these enzymes in man.     

Plasma amine oxidases in Wilson's disease

Plasma Mono- and Diamine-Oxidase activities (MAO and DAO), two copper containing enzymes, were estimated in 5 patients with Wilson's disease, without treatment and during D-Penicillamine treatment. Ceruloplasmin and “free” copper plasma levels were simultaneously measured. MAO was elevated in all cases, while DAO was within normal limits.D-Penicillamine administration did not result in significant reductions of these enzyme activities. It is likely that alterations of copper metabolism induced by Wilson's disease and by D-Penicillamine administration do not affect the activity of MAO or DAO. The increase in MAO activity in Wilson's disease probably results from the hepatic fibrosis.     

Lactating and nonlactating rats differ to renal toxicity induced by mercuric chloride: the preventive effect of zinc chloride

This study evaluated the effects of HgCl₂ on renal parameters in nonlactating and lactating rats and their pups, as well as the preventive role of ZnCl₂. Rats received 27 mg kg^?1 ZnCl₂ for five consecutive days and 5 mg kg^?1 HgCl₂ for five subsequent days (s.c.). A decrease in δ‐aminolevulinic acid dehydratase (δ‐ALA‐D) activity in the blood and an increase in urine protein content in renal weight as well as in blood and urine Hg levels were observed in lactating and nonlactating rats from Sal―Hg and Zn―Hg groups. ZnCl₂ prevented partially the δ‐ALA‐D inhibition and the proteinuria in nonlactating rats. Renal Hg levels were increased in all HgCl₂ groups, and the ZnCl₂ exposure potentiated this effect in lactating rats. Nonlactating rats exposed to HgCl₂ exhibited an increase in plasma urea and creatinine levels, δ‐ALA‐D activity inhibition and histopathological alterations (necrosis, atrophic tubules and collagen deposition) in the kidneys. ZnCl₂ exposure prevented the biochemical alterations. Hg‐exposed pups showed lower body and renal weight and an increase in the renal Hg levels. In conclusion, mercury‐induced nephrotoxicity differs considerably between lactating and nonlactating rats. Moreover, prior exposure with ZnCl₂ may provide protection to individuals who get exposed to mercury occupationally or accidentally. Copyright © 2014 John Wiley & Sons, Ltd.     

Scale dependent drivers of wild bee diversity in tropical heterogeneous agricultural landscapes

Factors associated with agricultural intensification, for example, loss of seminatural vegetation and pesticide use has been shown to adversely affect the bee community. These factors may impact the bee community differently at different landscape scales. The scale dependency is expected to be more pronounced in heterogeneous landscapes. However, the scale‐dependent response of the bee community to drivers of its decline is relatively understudied, especially in the tropics where the agricultural landscape is often heterogeneous. This study looked at effects of agricultural intensification on bee diversity at patch and landscape scales in a tropical agricultural landscape. Wild bees were sampled using 12 permanent pan trap stations. Patch and landscape characteristics were measured within a 100 m (patch scale) and a 500 m (landscape scale) radius of pan trap stations. Information on pesticide input was obtained from farmer surveys. Data on vegetation cover, productivity, and percentage of agricultural and fallow land (FL) were collected using satellite imagery. Intensive areas in a bee‐site network were less specialized in terms of resources to attract rare bee species while the less intensive areas, which supported more rare species, were more vulnerable to disturbance. A combination of patch quality and diversity as well as pesticide use regulates species diversity at the landscape scale (500 m), whereas pesticide quantity drove diversity at the patch scale (100 m). At the landscape scale, specialization of each site in terms of resources for bees increased with increasing patch diversity and FL while at the patch scale specialization declined with increased pesticide use. Bee functional groups responded differentially to landscape characteristics as well as pesticide use. Wood nesting bees were negatively affected by the number of pesticides used but other bee functional groups were not sensitive to pesticides. Synthesis and Applications: Different factors affect wild bee diversity at the scale of landscape and patch in heterogeneous tropical agricultural systems. The differential response of bee functional groups to agricultural intensification underpins the need for guild‐specific management strategies for wild bee conservation. Less intensively farmed areas support more rare species and are vulnerable to disturbance; consequently, these areas should be prioritized for conservation to maintain heterogeneity in the landscape. It is important to conserve and restore seminatural habitats to maintain complexity in the landscapes through participatory processes and to regulate synthetic chemical pesticides in farm operations to conserve the species and functional diversity of wild bees.     

A physiological dose of estradiol with progesterone affects striatum biogenic amines

The acute effect of estradiol and progesterone on dopamine and serotonin metabolism in rat striatum was studied. One subcutaneous injection of 17 beta-estradiol (300 ng) and progesterone (150 micrograms) into intact male rats increased plasma levels of these steroids, while testosterone, corticosterone, and estrone remained unchanged. Dehydroepiandrosterone, androstane-3 beta, 17 beta-diol and dihydrotestosterone remained undetectably low. Prolactin decreased and androstane-3 alpha, 17 beta-diol, and 17-OH progesterone increased, but less than estradiol and progesterone. Peak levels of striatal dopamine, dihydroxyphenylacetic acid, and homovanillic acid were observed 15-45 min after steroid injection with a return to control values after 45-60 min, while serotonin and 5-hydroxyindoleacetic acid levels were slightly decreased. An injection of estradiol (70 ng) with progesterone (70 micrograms) to ovariectomized female rats left plasma prolactin levels unchanged, while striatum dopamine and serotonin as well as their metabolite concentrations peaked 15-60 min after steroid injection and returned to control values after 45-75 min. To allow for a better comparison of the action of these steroids, the effect of estradiol or progesterone alone and in combination on the brain of ovariectomized rats was compared in the same experiment. A similar increase in metabolites of dopamine levels was observed after these steroids alone or in combination, while dopamine levels were increased only after progesterone alone or in combination with estradiol. An injection of estradiol or progesterone to ovariectomized rats led to peak steroid concentrations at approximately the same time in the brain and plasma. In addition, plasma and brain steroid levels were significantly correlated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of intrastriatal kainic acid injection on [3H]dopamine metabolism in rat striatal slices: evidence for postsynaptic glial cell metabolism by both the type A and B forms of monoamine oxidase

Abstract: Intrastriatal injections of kainic acid (KA) were utilized to investigate the cellular localization of postsynaptic dopamine (DA) metabolism by type A and B monoamine oxidase (MAO) in rat striatum. At 2 days postinjection, maximal degeneration of cholinergic and γ-aminobutyric acid (GABA)ergic neurons was observed and found to be associated with a significant decrease in both type A and B MAO activity. However, over the next 8-day period, when only the process of gliosis appeared to be occurring, a selective return to control of type B MAO activity was seen. When the metabolism of [³H]DA (10^?7 M) was examined in 8-day KA-lesioned rat striatal slices, an increase in [³H]dihydroxyphenylacetic acid (DOPAC) and [³H]homovanillic acid (HVA) formation was observed. The KA-induced elevation of [³H]DOPAC formation (but not [³H]HVA) was abolished by the DA neuronal uptake inhibitor nomifensine. This is consistent with earlier findings suggesting that HVA is formed exclusively within sites external to DA neurons. Experiments with clorgyline and/or deprenyl revealed that the relative roles of type A and B MAO in striatal DA deamination remained unchanged following KA (90% deamination by type A MAO) even though total deamination was substantially enhanced. At high concentrations of [³H]DA (10^?5 M), deamination by type B MAO could be increased to 30% of the total MAO activity; however, this was observed in both control and KA-lesioned striata. These results suggest that KA-sensitive neurons contain type A and/or type B MAO. Moreover, whereas these neurons may metabolize DA, a major portion of postsynaptic DA deamination appears to occur within glial sites of rat striatal tissue. Furthermore, glial cells would appear to contain functionally important quantities of both type A and B MAO.     

Neuromediator mechanisms of the effect of the antihistamine agent dimebone on the brain

Dimebone was shown to inhibit monoamine oxidase (MAO) deaminating dopamine and serotonin, decrease dopamine metabolism in the basal ganglia of the rat brain, increase noradrenaline level and depress dopamine deamination in the hypothalamus. Dimebone first increased and then diminished the release of dopamine in the cortex, with the concomitant MAO activation and the increase in dopamine and noradrenaline levels. The in vitro experiments have demonstrated that dimebone (10(-4)) preferentially inhibited MAO activity, type B and dopamine deamination in homogenates of different rat brain structures. The role of MAO inhibition in the mechanism of dimebone action on the catecholamine metabolism in the brain structures and its stimulating effect on CNS are discussed.     

Consequences of renal mass reduction on amino acid and biogenic amine levels in nephrectomized mice

Summary. Amino acid and biogenic amine changes were investigated in nephrectomized mice ten days postsurgery. Uremic mice exhibited changes in amino acid concentrations in plasma, urine and brain. Particularly plasma methionine, citrulline and arginine levels were significantly enhanced in nephrectomized mice compared to controls whereas serine was decreased. Urinary excretion of methionine, citrulline and alanine was higher in nephrectomized mice compared to controls whereas many amino acids were increased in brain of nephrectomized mice. Brain and urinary amino acid changes were more pronounced in the 75% than in the 50% nephrectomized mice. Brain norepinephrine and dopamine and its metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid were significantly increased whereas serotonin was decreased comparing the 75% nephrectomized mice to the sham-operated mice. This study demonstrates that at very early stages of renal insufficiency, specific amino acid and biogenic amine changes occur in plasma, urine and brain. These alterations might depend qualitatively and quantitatively on the degree of functional renal mass reduction. Received April 5, 1999     

THE EFFECTS OF CHRONIC REGIMENS OF CLORGYLINE AND PARGYLINE ON MONOAMINE METABOLISM IN THE RAT BRAIN

The effects of chronic administration of clorgyline and pargyline on rat brain monoamine metabolism have been examined. The inhibitory selectivity of these drugs towards serotonin deamina-tion (MAO type A) and phenylethylamine deamination (MAO type B) can be maintained over a 21-day period by proper selection of low doses of these drugs (0.5-1.0 mg/kg/24h). The results are consistent with MAO type A catalyzing the deamination of serotonin and norepinephrine and with MAO type B having little effect on these monoamines. Dopamine appears to be dcaminated in vivo principally by MAO type A. Clorgyline administration during a 3-week period was accompanied by persistent elevations in brain norepinephrine concentrations; serotonin levels were also increased during the first 2 weeks, but returned towards control levels by the third week of treatment. Low doses of pargyline did not increase brain monoamine concentrations, but treatment with higher doses for 3 weeks led to elevations in brain norepinephrine and 5-hydroxytryptamine; at this time significant MAO-A inhibition had developed. The changes in monoamine metabolism seen at the end of the chronic clorgyline regimen are not due to alterations in tryptophan hydroxylase activity. At this time tyrosine hydroxylase activity was also unaffected.     

Testosterone replacement therapy in insulin‐sensitive hypogonadal men restores phosphatidylcholine levels by regulation of arachidonic acid metabolism

Male hypogonadism is notoriously associated with altered lipid metabolism. In this study, we performed an untargeted mass spectrometry–based profiling of plasma lipids from twenty healthy and twenty hypogonadal men before and after testosterone replacement therapy (TRT) for 60 days. Results demonstrated that hypogonadism was associated with a significant increase in sphingomyelin (SM), whereas phosphatidylcholine (PC) was mainly cleaved by activated phospholipase‐A2 into lysophosphatidylcholine (LPC). In hypogonadal patients, arachidonic acid (AA), also produced through the latter cleavage, was prevalently bio‐transformed into leukotriene B4 (LTB4) and not into endoperoxides from which prostaglandins and thromboxanes are derived. Interestingly, upon testosterone treatment SM, PC and LPC returned to levels similar to controls. Also, AA was newly converted into prostaglandin‐A2, thromboxane‐A2 and 5(S)‐hydroxyeicosatetraenoic acid (HETE), suggesting that testosterone probably plays a role in controlling hypogonadal alterations above reported.     

Effects of tobacco smoke constituents on MPTP-induced toxicity and monoamine oxidase activity in the mouse brain

Exposure to cigarette smoke has been found to attenuate the reduction in striatal dopamine levels caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in mice and to inhibit monoamine oxidase (MAO) activity in brain tissue. To confirm whether specific smoke constituents which have been reported to protect against MPTP toxicity were responsible for these effects, mice were treated chronically with nicotine, 4-phenylpyridine and hydrazine. Although all three compounds prevented the decrease in dopamine metabolite levels induced by MPTP, there was no significant effect on dopamine levels. None of the three compounds inhibited MAO activity in cerebral tissue following treatment in vivo. However, an extract of tobacco smoke particulate matter caused a marked inhibition of MAO A and MAO B activity when added in vitro. The results suggest that one or more unidentified substances in tobacco smoke are capable of inhibiting brain MAO and perhaps altering the formation of the active metabolite of MPTP.     

Highly sensitive HPLC method for the determination of galantamine in human plasma and urine through derivatization with dansyl chloride using fluorescence detector

A new method based on fluorescence derivatization with 5‐(dimethylamino) naphthalene‐1‐sulfonyl chloride (dansyl chloride) was developed for the quantitative determination of galantamine in human plasma and urine using high‐performance liquid chromatography. The reaction between galantamine and dansyl chloride was optimally realized in 30 min at room temperature and pH 10.5, with a reagent to galantamine molar ratio of 2.13. The derivative was extracted with dichloromethane, and the extract was dried under a nitrogen stream and dissolved in the mobile phase. Chromatographic analysis was performed with an Inertsil C₁₈ column and a mobile phase comprising 40% acetonitrile and 60% 10 mM o‐phosphoric acid, 1.2 ml/min. The injection volume was 20 μl. The derivatives were detected with a fluorescence detector (excitation 375 nm/emission 537 nm). The retention time for the dansyl derivative of galantamine was 16.8 min. Linearity was observed between 125 and 2000 ng/ml in water, urine and plasma. The limit of detection and limit of quantification for the developed method were 6.27–70.99 and 18.81–212.97 ng/ml, respectively. Per cent recovery was calculated as 95.15 for urine and 95.78 for plasma. Interday repeatability values for urine and plasma samples (n = 6) at three different concentrations were calculated as a per cent relative standard deviation of 0.24–0.59 and 0.35–0.56. The corresponding per cent relative standard deviation values for intraday repeatability were 0.13–0.51 and 0.04–0.15, respectively.     

3,4-Dihydroxyphenylethanol (Hydroxytyrosol) Mitigates the Increase in Spontaneous Oxidation of Dopamine During Monoamine Oxidase Inhibition in PC12 Cells

The catecholaldehyde hypothesis predicts that monoamine oxidase (MAO) inhibition should slow the progression of Parkinson’s disease, by decreasing production of the autotoxic dopamine metabolite 3,4-dihydroxyphenylacetaldehyde (DOPAL). Inhibiting MAO, however, diverts the fate of cytoplasmic dopamine toward potentially harmful spontaneous oxidation products, indicated by increased 5-S-cysteinyl-dopamine (Cys-DA) levels. 3,4-Dihydroxyphenylethanol (hydroxytyrosol) is an abundant anti-oxidant phenol in constituents of the Mediterranean diet. Whether hydroxytyrosol alters enzymatic or spontaneous oxidation of dopamine has been unknown. Rat pheochromocytoma PC12 cells were incubated with hydroxytyrosol (10 µM, 180 min) alone or with the MAO-A inhibitor clorgyline (1 nM) or the MAO-B inhibitors rasagiline or selegiline (0.5 µM). Hydroxytyrosol decreased levels of DOPAL by 30 % and Cys-DA by 49 % (p < 0.0001 each). Co-incubation with hydroxytyrosol prevented the increases in Cys-DA seen with all 3 MAO inhibitors. Hydroxytyrosol therefore inhibits both enzymatic and spontaneous oxidation of endogenous dopamine and mitigates the increase in spontaneous oxidation during MAO inhibition.