Plasma phenylethylamine in schizophrenic patients.

Plasma samples were collected from 41 patients who met DSM-III criteria for schizophrenia and from 34 healthy controls. Phenylethylamine (PE) levels were determined using a gas chromatography-mass spectrometry negative chemical ionization method. PE was significantly higher in the schizophrenic patients compared with controls. There were no differences in PE between paranoid and nonparanoid patients. Plasma PE did not appear to be influenced by the severity of schizophrenic symptoms (rated by BPRS, SANS, and SAPS) or by the amount of dietary phenylalanine ingested within 24 hr of testing. Plasma PE did not correlate with current or past exposure to neuroleptic medication. It was not possible, however, to test individual patients during two periods when they were taking and not taking medication. Thus it is possible that neuroleptic exposure may have confounded the results. This study provides further evidence that PE excess may play a role in the etiology of schizophrenia but does not support previous studies which suggest that such an abnormality is limited to the paranoid subgroup.

Longitudinal effect of amitriptyline and fluoxetine treatment on plasma phenylacetic acid concentrations in depression.

Unconjugated (U-PAA), conjugated (C-PAA), and total phenylacetic acid (T-PAA) concentrations in blood plasma and monoamine oxidase (MAO) activity in platelets towards phenylethylamine (PE) were determined in 40 drug-free, depressed patients (23 melancholic, 17 nonmelancholic) from five psychiatric treatment centers, and in 34 normal healthy volunteers. No significant differences were found between controls and all depressed patients or between melancholic and nonmelancholic depressed patients. Treatment of the depressed patients with amitriptyline or fluoxetine over a 6-week period resulted in clinical improvement and in a significant increase in plasma PAA concentrations. A decline in the Beck and Hamilton rating scores during treatment correlated significantly with increases in the concentrations of unconjugated, conjugated, and total phenylacetic acid but not with MAO activity, which did not change during treatment. At each of the three assessment times, however, plasma PAA concentrations and psychiatric rating scores were not significantly correlated. Except for higher end-of-study T-PAA concentrations in the amitriptyline-treated subjects, no significant differences were found between the effects of the two drugs with regard to plasma phenylacetic acid levels, MAO activity, or rating scores.

Formation of beta-phenylethylamine from the antidepressant, beta-phenylethylhydrazine.

To determine whether the monoamine oxidase inhibitor phenelzine was metabolized in vivo to produce beta-phenylethylamine (PE) and p-hydroxy-beta-phenylethylamine [p-tyramine (pTA)], a deuterated analogue, alpha, alpha,, beta, beta-2H-phenelzine (d4-phenelzine) was synthesized and injected i.p. into rats. In the first experiment, rat striata from d4-phenelzine-treated rats were analyzed for the presence of d4-PE and d4-pTA at a time at which phenelzine was known to cause particularly large increases in striatal pTA. While d4-PE was found to be present in these rat striata at a concentration equivalent to the endogenous PE, no d4-pTA was present. The amounts of d4-PE produced at various times after the i.p. injection of 50 mg/kg d4-phenelzine were measured; at 1 hr post-injection, 371 +/- 60, 1295 +/- 682 and 1242 +/- 394 ng/g (mean +/- S.E.M.) d4-PE were present in whole brain, liver and kidney. Rat urine collected for a 24-hr period after this treatment contained (mean +/- S.E.M.) 88.5 +/- 14.0 micrograms d4-PE. These results clearly indicate that the antidepressant phenelzine was metabolized in vivo to produce the trace amine PE.

Effects of monoamine oxidase inhibitors on the acid metabolites of some trace amines and of dopamine in the rat striatum.

The effects of the administration of selective and non-selective inhibitors of monoamine oxidase (MAO) on the concentrations of three trace acid metabolites [phenylacetic acid (PAA); m-hydroxyphenylacetic acid (mHPAA); and p-hydroxyphenylacetic acid (pHPAA)] and of an acid metabolite of dopamine [3,4-dihydroxyphenylacetic acid (DOPAC)] in the rat striatum were determined. Administration of brofaromine (1-100 mg/kg, s.c.) a type AMAO inhibitor, dose-dependently decreased DOPAC and mHPAA levels. pHPAA levels were decreased by 100 mg/kg brofaromine, but PAA levels were unaffected. Doses of deprenyl of less than 100 mg/kg, i.p., had no effect on any of the acids, while 100 mg/kg decreased DOPAC, mHPAA and pHPAA but not PAA levels. Clorgyline, pargyline and tranylcypromine treatment decreased the levels of DOPAC, mHPAA and pHPAA but not PAA. Administration of alpha-monofluoromethyldopa, an inhibitor of aromatic amino acid decarboxylase, decreased the levels of all four acids. It was concluded that deamination of the respective parent amine by type A MAO is primarily responsible for the synthesis of DOPAC and mHPAA, but that another pathway contributes to pHPAA synthesis. It appears that either PAA arises predominantly independently from the actions of MAO or that is removal via transport or further metabolism regulates its concentration.

Interaction of biogenic amines with components of cigarette smoke. Formation of cyanomethylamine derivatives.

A reaction of the biogenic amines 5-hydroxytryptamine, dopamine, histamine, p-tyramine, beta-phenylethylamine and tryptamine with components of cigarette smoke was observed. The adducts formed from 5-hydroxytryptamine and beta-phenylethylamine were purified by chromatographic procedures and identified by high resolution mass spectrometry. The structures of some of these compounds were established as cyanomethylamine derivatives, i.e. RCH2CH2NHCH2CN. In the case of 5-hydroxytryptamine, a cyanomethyl-beta-1,2,3,4-tetrahydrocarboline product formed via a Pictet-Spengler condensation reaction was isolated. The mass spectra of such adducts and their fragment ions were observed to be identical to those of chemically synthesized cyanomethylamines. Both formaldehyde and cyanide, which are known to be present in cigarette smoke, were involved in the reaction with the primary amines. The reaction was time dependent and was enhanced by an increase in temperature or by incubation under alkaline conditions. Cyanomethyl adduct formation was increased when smoke from cigarettes with higher tar and nicotine content was used. When the amines were incubated with human saliva obtained after cigarette smoking, cyanomethylamine products were readily detected.

Potentiation of the biochemical effects of beta-phenylethylhydrazine by deuterium substitution.

The concentrations of dopamine (DA), m-tyramine (mTA), p-tyramine (pTA) and serotonin (5-HT) in the striata of rats 18 hr after the administration of three different doses (5, 50, or 100 mg/kg) of beta-phenylethylhydrazine (phenelzine, PEH) were measured. These concentrations were compared to those following the administration of the same doses of 1,1,2,2-tetradeutero-PEH (d4PEH). In general, PEH and d4PEH caused dose-dependent increases in the levels of mTA, pTA and 5-HT. The lowest dose of d4PEH caused greater increases than PEH in the levels of all four monoamines. The concentration of 5-HT was increased more by d4PEH than PEH at all three doses. The inhibition of mitochondrial MAO obtained from rat striatum by PEH or d4PEH in vitro revealed no differences. However, the inhibition of striatal MAO obtained from rats injected with d4PEH was found to be greater than that from rats injected with PEH. It was concluded that deuteration of PEH potentiates its ability to inhibit MAO following its administration to the rat by slowing its degradation in vivo.

Stereospecific deuterium substitution at the alpha-carbon position of dopamine and its effect on oxidative deamination catalyzed by MAO-A and MAO-B from different tissues.

Stereospecific replacement of deuterium in the alpha-carbon side chain position of dopamine (DA) was achieved by decarboxylation of L-3,4-dihydroxyphenylalanine (L-dopa) using hog kidney aromatic aminoacid decarboxylase. The S[alpha-2H1]DA enantiomer was obtained by decarboxylation of L-[alpha-2H1]dopa in H2O, while the R[alpha-2H1]DA enantiomer was obtained by decarboxylation of unsubstituted L-dopa in 2H2O. An inverse solvent isotope effect of L-dopa decarboxylation was observed in 2H2O. The deaminated aldehyde products of the four DA analogues, i.e. undeuterated DA, [alpha, alpha-2H2] DA, R[alpha-2H1]DA and S[alpha-2H1]DA, have been analyzed by the gas chromatography-mass spectrometry (GC-MS) method. It is evident that monoamine oxidase (MAO) catalyzes the stereochemical removal of only R-deuterium and that S-deuterium was maintained at the alpha-carbon atom of 3,4-dihydroxyphenylacetaldehyde. The steady-state kinetics of the oxidative deamination of undeuterated, [alpha, alpha-2H2], R[alpha-2H1], and S[alpha-2H1] dopamine were assessed by determination of the aldehyde products directly by high performance liquid chromatography (HPLC) using electrochemical detection (ECD). MAO-A from rat liver mitochondria (deprenyl-treated) and from human placenta, as well as MAO-B from rat liver (clorgyline-treated) and from human platelet were used in this study. The apparent isotope effects, i.e. (V/K)H/(V/K)D ratios of [alpha, alpha-2H2]DA and R[alpha-2H1]DA, were quite similar (2.34 and 3.13) with respect to both MAO-A and MAO-B. S[alpha-2H1]DA exhibited a slight secondary isotope effect. Formula: see text.

Determination of meta- and para-hydroxyphenylacetic acid levels in single caudate nuclei by selected metastable peak monitoring: a new sensitive gas chromatographic--mass spectrometric procedure.

The levels of meta- and para-hydroxyphenylacetic acids in rat brain caudate nuclei have been determined by a new gas chromatography-mass spectrometric (GC-MS) procedure in which metastable transitions specific to the derivatized acids are observed. The method is more sensitive than previous procedures and allows determination of the acid concentrations using single caudate nuclei. The levels of the meta- and para-isomers were found to be 9.2 +/- 1.5 and 43 +/- 3.7 ng/g, respectively.

Enzymatic N-methylation of phenelzine catalyzed by phenylethanolamine N-methyltransferase.

1. Phenelzine has been found to be methylated by enzymes obtained from bovine adrenal and some rat tissues in the presence of S-adenosylmethionine (SAM) as methyl group donor. 2. The methylated product was chromatographically (TLC and HPLC) identical with chemically synthesized N-methylphenelzine. The structure of this methylated phenelzine has been confirmed by a GC-MS procedure. 3. The phenelzine methyltransferase in the bovine adrenal has a molecular weight and isoelectric point identical with that of bovine adrenal phenylethanolamine N-methyl-transferase (PNMT). 4. Methylated phenelzine possesses much reduced inhibitory activity towards monoamine oxidase (MAO). It can, however, be deaminated by MAO to produce phenylacetaldehyde, and subsequently phenylacetic acid. 5. Other hydrazine compounds, such as hydralazine, have also been found to be methylated by the adrenal enzyme. 6. Our finding of enzymatic methylation of hydrazine compounds is novel, and it may play a role in the metabolism of hydrazine drugs.

The effect of age, sex, weight and height on the plasma concentrations in healthy subjects of the acidic metabolites of some biogenic monoamines involved in psychiatric and neurological disorders.

1. The plasma concentrations of unconjugated phenylacetic acid and m-hydroxyphenylacetic acid are lower in male than in female subjects. 2. The plasma concentrations of unconjugated phenylacetic acid and mandelic acid decrease with increasing weight and height for all subjects combined. The same relationships apply for both males and females but are significant only for males. 3. Homovanillic and vanillylmandelic acid concentrations in plasma increase with age. 4. The importance of using age, sex, weight and height matched groups in studies involving the plasma concentrations of some of the trace amine metabolites in psychiatric disorders has been demonstrated. This is particularly the case for phenylacetic acid, the major metabolite of phenylethylamine which is now thought to be a neuromodulator of catecholaminergic neurotransmission.

Changes in brain catecholamine levels following DL-dopa are not potentiated by deuterium substitution.

Adult male Wistar rats were treated with either DL-dopa, D3-DL-dopa or vehicle and sacrificed at various time intervals after treatment. Brain dopamine and noradrenaline concentrations were measured using quantitative mass spectrometric analysis. After treatment with DL-dopa or D3-DL-dopa, total dopamine levels increased above control values; however, no differences were observed between the two drug treatments. Total noradrenaline levels were not significantly altered by treatment with either DL-dopa or D3-DL-dopa. Deuterium substitution did not appear to affect catecholamine deamination or beta-hydroxylation in vivo.

The effect of the MAO-A selective inhibitor brofaromine on the plasma and urine concentrations of some biogenic amines and their acidic metabolites in bulimia nervosa.

1. Brofaromine or placebo were administered to female bulimia nervosa patients over a period of eight weeks. Plasma and urinary trace amines, their acidic metabolites and the acidic metabolites of the catecholamines and serotonin were assessed prior to treatment and at four and eight weeks after commencement of treatment. 2. The levels of both plasma and urinary homovanillic and vanilmandelic acids declined significantly during the first four weeks of treatment with brofaromine and then partially recovered to pre-drug levels by the eighth week. 5-Hydroxyindoleacetic acid levels were not affected by drug treatment at the times assessments were made. Urinary tryptamine increased significantly during the first four weeks of brofaromine treatment then partially recovered towards pre-drug levels by the eighth week. No effect from placebo treatment was observed.

A longitudinal study of the relationships between psychometric test scores, offence history and the plasma concentrations of phenylacetic and 5-hydroxyindoleacetic acids in seven inmates of a prison for the psychiatrically disturbed.

1. The plasma concentrations of phenylacetic (PAA) and 5-hydroxyindoleacetic (5HIAA) acids in seven inmates incarcerated in the Regional Psychiatric Centre (Prairies), Correctional Service of Canada, were assessed each weekday for four weeks (i.e., 20 samples each). Psychometric assessments for hostility, anger, depression and anxiety were also performed daily. Mean differences between subjects in psychometric and biochemical measures were subjected to tests of statistical significance. 2. The subject who was clearly most aggressive by offence history/institutional behavior scored significantly highest on scales of anger and hostility and significantly lowest with respect to PAA concentration. It was concluded that PAA may be a trait marker for aggression. 3. Plasma 5HIAA concentrations were invariant between subjects. 4. The psychometric measures were intercorrelated, thus confounding the variables of interest. They also varied little, proving insensitive to subtle mood changes.

Effect of dietary phenylalanine on the plasma concentrations of phenylalanine, phenylethylamine and phenylacetic acid in healthy volunteers.

1. Phenylethylamine has been proposed as a neuromodulator in several psychiatric and other brain disorders, and its concentration and that of its major metabolite, phenylacetic acid, in plasma may prove useful as state or trait markers in diagnosis, treatment or in the elucidation of biochemical mechanisms of these disorders. 2. The effect of dietary phenylalanine intake and changes in dietary phenylalanine intake on the plasma concentrations and changes in plasma concentrations, respectively, of phenylalanine, phenylethylamine and unconjugated and conjugated phenylacetic acid have been investigated. 3. Dietary phenylalanine affects the concentration of plasma phenylalanine on the following day, but has no effect on phenylethylamine or phenylacetic acid concentrations. Thus single measurements per subject of phenylethylamine or phenylacetic acid do not need to take dietary factors into account. 4. Changes in dietary phenylalanine (whether in absolute amount or in the proportion of phenylalanine in the diet) are significantly correlated with changes in unconjugated phenylacetic acid. Therefore, in longitudinal studies, dietary factors should be taken into account.

Phenylacetic acid in CSF and serum in Indian schizophrenic patients.

1. It has been proposed that an increase in the concentration of the neuromodulator phenylethylamine at the post-synaptic dopamine receptor may be involved in the etiology of schizophrenia. If this increase is the case, a reduction in the CSF and/or serum concentrations of phenylacetic acid, its major metabolite, might be anticipated. 2. The authors have found in hospitalized Indian schizophrenic patients ingesting antipsychotic drugs, that the paranoid subgroup did indeed exhibit lower levels of unconjugated, conjugated and total phenylacetic acid in both serum and CSF.

Deuterium-labelled p-tyramine challenge test and phenolsulfotransferase activity in depressed patients--failure to replicate decreased p-tyramine conjugation in depression.

1. Depressed and normal subjects were challenged with deuterium-labelled p-tyramine and urine was collected for 3 h. 2. Urinary excretion of conjugated p-tyramine was not significantly different between normal, melancholic and non-melancholic depressed subjects. 3. Platelet phenolsulfotransferase activity to p-tyramine (p less than 0.05) and to phenol (p less than 0.005) were significantly lower in the depressed patients.

Effect of chronic deuterated and non-deuterated phenelzine on rat brain monoamines and monoamine oxidase.

The effects of phenelzine and 1,1-dideuterophenelzine (0.5 or 2.5 mg/kg/day) administered s.c. via miniosmotic pumps for 13 days were compared. Striatal levels of p-tryrosine and tryptophan were unaffected by either treatment. The concentrations of DOPAC, HVA and 5-HIAA were dose-dependently decreased by phenelzine and deuterated phenelzine; furthermore, the deuterated compound decreased the amounts of these acids more than the same dose of phenelzine. Dopamine levels were increased by a rather small amount by all drug treatments; no effects of drug dose or drug type (deuterated or nondeuterated) were observed. With the exception of phenylethylamine, qualitatively similar effects were found with all other amines measured; their amounts were increased dose-dependently and the effects of deuterated phenelzine were greater than those of phenelzine. Rat cerebral MAO activity was inhibited dose-dependently by phenelzine and by deuterated phenelzine. Type A MAO was inhibited more than type B, and deuterated phenelzine inhibited both types more than did phenelzine. The present study shows that the efficacy of phenelzine was increased about 5-fold by deuteration, that deuterated phenelzine increased tryptamine, m-tyramine and p-tyramine levels much more than it did the other monoamines, that phenylethylamine levels were least affected by the drug treatments, and that deuterated phenelzine inhibited MAO more than did phenelzine.

Conjugation of phenylacetic acid and m- and p-hydroxyphenylacetic acids in the rat striatum.

Two factors that might regulate the levels of the trace acids, phenylacetic acid (PAA), m-hydroxyphenylacetic acid (mHPAA) and p-hydroxyphenylacetic acid (pHPAA) in the rat striatum were investigated: first, formation of conjugates of these acids and second, transport out of the brain by a probenecid-sensitive system. The presence of conjugates of these acids was investigated by subjecting homogenates of rat striatum to hydrolysis. The concentrations of PAA were increased ten-fold by hydrolysis, pHPAA increased two-fold, and mHPAA was unaffected. These findings coupled with the failure of parglyline to decrease free or total PAA levels suggest that conjugation of PAA is an important factor regulating free PAA levels. The transport inhibitor, probenecid, increased the concentrations of free mHPAA, free pHPAA and the total concentrations of all three acids indicating that all three trace acids can be removed from the rat brain by a transport system.

Longitudinal study of inmates of a prison for the psychiatrically disturbed: plasma concentrations of biogenic amine metabolites and amino acids.

Plasma concentrations of eight large and neutral amino acids and 10 acidic metabolites of biogenic amines in seven inmates incarcerated in the Regional Psychiatric Centre (Praries), Correctional Service of Canada, were assessed each week day for 4 weeks (i.e., 20 samples each). Measures of central tendency and dispersion of the variables were calculated. The measures are distinctively different in their variability and their normality of distribution. The large and neutral amino acid (LNAA) measures are somewhat less variable, but also less likely to be normally distributed than most acid metabolites. Acid metabolites tend to show consistent interindividual differences that persist over time, with the notable exception of 5-hydroxyindoleacetic acid. LNAA measures tend to show differences across time but not between individuals. The distributional properties of LNAA measures are largely accounted for by the observation of a downward convergence of values of these variables over the 4 weeks of the study.

Effects of chronic oral administration of L-deprenyl in the dog.

Dogs were administered capsules containing L-deprenyl daily over 3 weeks at dose levels of 0, 0.1, 0.5, and 1.0 mg/kg. Spontaneous behavior was measured using a canine open field test, and was not significantly affected by L-deprenyl. Plasma levels of amphetamine showed a clear dose-dependent elevation 2 h and was not significantly affected by L-deprenyl. Plasma levels of amphetamine showed a clear dose-dependent elevation 2 h following treatment, but were markedly lower after 24 h, and were undetectable 5 days following the last treatment. Plasma levels of phenylethylamine were increased, but were highly variable. Animals sacrificed 1 day following the last treatment showed a dose-dependent inhibition of monoamine oxidase B in the brain, liver, and kidney, whereas monoamine oxidase A was unaffected in these tissues. L-Deprenyl also caused an increase in phenylethylamine in the striatum and hypothalamus, but not in the neocortex. Brain levels of DA, DOPAC, 3-MT, HVA, 5-HT, and 5-HIAA were unaffected. The pharmacological profile for the dog is distinct from that of other species in that long-term treatment did not produce any significant inhibition of MAO-A activity. The absence of an effect on biogenic amines or metabolites suggests that the metabolism of dopamine is mediated at least in part through pathways other than MAO-B in the normal adult dog.