Phenylethylamine excretion in depression

The mysterious trace amines: protean neuromodulators of synaptic transmission in mammalian brain

The trace amines are a structurally related group of amines and their isomers synthesized in mammalian brain and peripheral nervous tissues. They are closely associated metabolically with the dopamine, noradrenaline and serotonin neurotransmitter systems in mammalian brain. Like dopamine, noradrenaline and serotonin the trace amines have been implicated in a vast array of human disorders of affect and cognition. The trace amines are unique as they are present in trace concentrations, exhibit high rates of metabolism and are distributed heterogeneously in mammalian brain. While some are synthesized in their parent amine neurotransmitter systems, there is also evidence to suggest other trace amines may comprise their own independent neurotransmitter systems. A substantial body of evidence suggests that the trace amines may play very significant roles in the coordination of biogenic amine-based synaptic physiology. At high concentrations, they have well-characterized presynaptic "amphetamine-like" effects on catecholamine and indolamine release, reuptake and biosynthesis; at lower concentrations, they possess postsynaptic modulatory effects that potentiate the activity of other neurotransmitters, particularly dopamine and serotonin. The trace amines also possess electrophysiological effects that are in opposition to these neurotransmitters, indicating to some researchers the existence of receptors specific for the trace amines. While binding sites or receptors for a few of the trace amines have been advanced, the absence of cloned receptor protein has impeded significant development of their detailed mechanistic roles in the coordination of catecholamine and indolamine synaptic physiology. The recent discovery and characterization of a family of mammalian G protein-coupled receptors responsive to trace amines such as beta-phenylethylamine, tyramine, and octopamine, including socially ingested psychotropic drugs such as amphetamine, 3,4-methylenedioxymethamphetamine, N,N-dimethyltryptamine, and lysergic acid diethylamide, have revitalized the field of scientific studies investigating trace amine synaptic physiology, and its association with major human disorders of affect and cognition.

Urinary phenylacetate and response to methylphenidate

Phenylacetate (PAA) is the metabolic end-product of phenylalanine, a catecholamine precursor, and of phenylethylamine, a centrally active neurochemical substance which has been implicated in the actions of stimulant medications. PAA has been reported to be low in unipolar depression. We measured 24-h urinary PAA in normal controls (N = 21) and in-patients with unipolar depression (N = 33; 12 drug-free) and did subsequent dexamethasome suppression tests (DST). We also gave patients methylphenidate challenges, examining mood response. There were no significant differences between depressed patients and controls in 24-h urinary PAA excretion (P greater than 0.9). However, the variance in PAA excretion was higher in patients than normals and 5 patients had values at or above the 99% confidence limits for the normal control group. There was no association of DST results with PAA excretion (P greater than 0.4). Patients with a worsened mood after taking methylphenidate excreted less PAA than those with an improved mood, however (P less than 0.025). The clinical and theoretical significance of these results is discussed.

The trace amines and their acidic metabolites in depression--an overview

1. Investigations of the role of the trace amines (phenylethylamine, tryptamine, m- and p-tyramine) and their acidic metabolites (phenylacetic, indoleacetic, m- and p-hydroxyphenylacetic acids) in depression are reviewed. 2. The evidence for the phenylethylamine hypothesis of depression is mixed. 3. Reduced phenylacetic acid levels in urine, plasma and CSF and changes in those levels during treatment with antidepressants show potential as state markers for depression. 4. Impaired p-tyramine conjugation following a tyramine challenge may be a good trait marker for depression.

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.

Beta-phenylethylamine and noradrenergic function in depression

1. The relationship between plasma levels of beta-phenylethylamine (PEA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) was investigated in depressive patients. 2. The mean PEA level in plasma in healthy subjects was 1.19 ng/ml (N = 32). No clearly age-related difference was found. The plasma levels of PEA were measured in major depression, but no significant difference was found between healthy and depressive subjects. 3. Plasma levels of MHPG correlated positively with age in healthy subjects (N = 22, R = 0.71, p less than 0.01). There was no significant difference in MHPG levels between healthy subjects and depressive patients. 4. There was no significant correlation between PEA and MHPG levels in healthy subjects; however, in depressive patients, there was a significant negative correlation between plasma PEA levels and plasma MHPG levels (N = 14, R = -0.73, p less than 0.05). These results suggested that PEA may regulate noradrenergic function in depression.

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.

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.

Phenylethylaminergic modulation of catecholaminergic neurotransmission

1. PE is present in the brain in tiny quantities; it is heterogeneously distributed and present in synaptosomes. 2. It is synthesised from phenylalanine by L-AADC and oxidatively deaminated by MAO-B. Its turnover is remarkably fast. 3. Its concentration, particularly in the caudate nucleus, is affected by MAO inhibition (increased), lesion of the Substantia nigra (decreased), amine depletion (increased) and antipsychotic drugs (increased). 4. When iontophoresed (or injected) it amplifies the effects of DA and NA (and their agonists) but is without effect on other neurotransmitters. 5. It is suggested that it acts postsynaptically as a neuromodulator of catecholaminergic neurotransmission and that it is involved in the mechanism of action of Deprenyl; it is also suggested that it, or its principal metabolite PAA, may be involved in the aetiology of schizophrenia, depression and aggression as well as perhaps in other neuropsychiatric conditions.

Phenylethylaminergic mechanisms in attention-deficit disorder

Urinary excretion (24-hr) of beta-phenylethylamine (PEA), phenylacetic acid (PAA), phenylalanine (Phe), and p-tyrosine (Tyr), and plasma levels of PAA, Phe, and Tyr were examined in 18 normal children and 26 children diagnosed as having attention-deficit hyperactivity disorder (ADHD). The results indicated that urinary excretion (expressed per g of creatinine) of free and total PEA was significantly lower in the ADHD patients, and plasma levels of Phe and Tyr were also decreased in the ADHD subjects compared with the normal controls.

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.

Urinary phenylacetic acid in panic disorder with and without depression

Phenylacetic acid (PAA) excretion was measured in 39 patients who met criteria for panic disorder; 9 of these also had major depression, and 30 did not. Patients with panic and depression excreted 66 +/- 23 mg/day of PAA, an amount significantly lower than in normal controls; patients with panic disorder but without depression excreted 104 +/- 23 mg/day of PAA (not significantly lower than controls). The results support previous studies indicating that PAA excretion is a marker for depressive disorder.

Urinary amines in Tourette's syndrome patients with and without phenylethylamine abnormality

Previous data indicated a subgroup of Tourette's syndrome patients with a beta-phenylethylamine (PEA) level that was lower than all subjects in a control group matched for age and education. The current study compared the subgroups of Tourette's syndrome patients (n = 28) from the previous study with 20 control subjects in regard to other amines and metabolites. Patients with low levels of PEA were also found to have lower levels of 3-methoxy-4-hydroxy-phenylglycol, normetanephrine, serotonin, m-tyramine, and p-tyramine. There was also some evidence of dopaminergic abnormalities in the low-PEA subgroup. These data provide suggest a role of PEA in the pathophysiology of some patients with Tourette's syndrome. This effect may be mediated through other neurotransmitter systems.

Effect of trimipramine, an atypical tricyclic antidepressant, on the activities of various enzymes involved in the metabolism of biogenic amines

1. The mechanism of action of trimipramine, a clinically efficacious tricyclic antidepressant, is not well understood. In order to investigate whether it might affect the activities of different enzymes involved in biogenic amine metabolism we have undertaken a comparative study of it along with amitriptyline. 2. Neither trimipramine nor amitriptyline, at concentrations up to 1 mM, exhibited any significant effect on phenylalanine hydroxylase, tyrosine hydroxylase, L-aromatic amino acid decarboxylase, dopamine-beta-hydroxylase, phenylethanolamine-N-methyltransferase, catechol-O-methyltransferase, phenylsulfotransferase or tyrosine aminotransferase. 3. Monoamine oxidase, however, was inhibited by both drugs with the greatest effect being on MAO-B. The inhibition was reversible, non-competitive and relatively weak.

Biogenic amines and their metabolites in body fluids of normal, psychiatric and neurological subjects

The biogenic monoamines and their metabolites have been isolated, identified and quantified in human body fluids over the past forty years using a wide variety of chromatographic separation and detection techniques. This review summarizes the results of those studies on normal, psychiatric and neurological subjects. Tables of normal values and the methods used to obtain them should prove to be useful as a reference source for benchmark amine and metabolite concentrations and for successful analytical procedures for their chromatographic separation, detection and quantification. Summaries of the often contradictory results of the application of these methods to psychiatric and neurological problems are presented and may assist in the assessment of the validity of the results of experiments in this field. Finally, the individual, environmental and the methodological factors affecting the concentrations of the amines and their metabolites are discussed.

Plasma phenylethylamine and phenylalanine in chronic schizophrenic patients

The hypothesis that phenylethylamine (PEA) is an endogenous psychotogen in schizophrenics, particularly those with the paranoid subtype, has been previously studied by measuring PEA levels in urine and cerebrospinal fluid (CSF) of schizophrenic patients. However, plasma PEA may more accurately reflect simultaneous alterations of PEA in many organ systems, as might occur in a genetic disorder of PEA metabolism. No study to date has examined phenylalanine (Phe), which is thought to be a precursor of PEA, in the same patients who had PEA measured. In this study, we measure both plasma PEA and Phe in 17 drug-free schizophrenic patients and 17 matched controls. Plasma PEA in normal controls was found to be lower by three orders of magnitude compared to normal controls from previous studies--a finding that has not previously been reported. PEA was significantly lower in those schizophrenic patients who had a Research Diagnostic Criteria diagnosis of paranoid schizophrenia. PEA did not differ between patients and controls, and the correlation between plasma Phe and PEA was not significant.