Analysis of biogenic amines in plasma of hypertensive patients and a control group

Quantitative Determination of Endogenous Tetrahydroisoquinolines, Potential Parkinson's Disease Biomarkers, in Mammals

Current diagnostic options for Parkinson's disease are very limited and primarily based on characteristic clinical symptoms. Thus, there are urgent needs for reliable biomarkers that enable us to diagnose the disease in the early stages, differentiate it from other atypical Parkinsonian syndromes, monitor its progression, increase knowledge of its pathogenesis, and improve the development of potent therapies. A promising group of potential biomarkers are endogenous tetrahydroisoquinoline metabolites, which are thought to contribute to the multifactorial etiology of Parkinson's disease. The aim of this critical review is to highlight trends and limitations of available traditional and modern analytical techniques for sample pretreatment (extraction and derivatization procedures) and quantitative determination of tetrahydroisoquinoline derivatives in various types of mammalian fluids and tissues (urine, plasma, cerebrospinal fluid, brain tissue, liver tissue). Particular attention is paid to the most sensitive and specific analytical techniques, involving immunochemistry and gas or liquid chromatography coupled with mass spectrometric, fluorescence, or electrochemical detection. The review also includes a discussion of other relevant agents proposed and tested in Parkinson's disease.

The safety of Citrus aurantium (bitter orange) and its primary protoalkaloid p-synephrine

Citrus aurantium (bitter orange) extract and its principal protoalkaloidal constituent p-synephrine are widely used in weight loss and weight management as well as in sports performance products. However, questions are raised frequently regarding the safety of these ingredients. The potential inherent dangers associated with the use of products containing C. aurantium extract are frequently touted, while conversely, millions of doses of dietary supplements have been consumed by possibly millions of individuals in recent years. Furthermore, millions of people consume on a daily basis various juices and food products from Citrus species that contain p-synephrine. This review summarizes current information regarding the safety of C. aurantium (bitter orange) extract and p-synephrine based on human, animal and in vitro assessments as well as receptor binding and mechanistic studies. The data indicate that based on current knowledge, the use of bitter orange extract and p-synephrine appears to be exceedingly safe with no serious adverse effects being directly attributable to these ingredients.

Effects of dietary amines on the gut and its vasculature

Trace amines, including tyramine and β-phenylethylamine (β-PEA), are constituents of many foods including chocolate, cheeses and wines and are generated by so-called ‘friendly’ bacteria such as Lactobacillus, Lactococcus and Enterococcus species, which are found in probiotics. We therefore examined whether these dietary amines could exert pharmacological effects on the gut and its vasculature. In the present study we examined the effects of tyramine and β-PEA on the contractile activity of guinea-pig and rat ileum and upon the isolated mesenteric vasculature and other blood vessels. Traditionally, these amines are regarded as sympathomimetic amines, exerting effects through the release of noradrenaline from sympathetic nerve endings, which should relax the gut. A secondary aim was therefore to confirm this mechanism of action. However, contractile effects were observed in the gut and these were independent of noradrenaline, acetylcholine, histamine and serotonin receptors. They were therefore probably due to the recently described trace amine-associated receptors. These amines relaxed the mesenteric vasculature. In contrast, the aorta and coronary arteries were constricted, a response that was also independent of a sympathomimetic action. From these results, we propose that after ingestion, trace amines could stimulate the gut and improve intestinal blood flow. Restriction of blood flow elsewhere diverts blood to the gut to aid digestion. Thus, trace amines in the diet may promote the digestive process through stimulation of the gut and improved gastrointestinal circulation.

Trace amine-associated receptor 1-Family archetype or iconoclast?

Interest has recently been rekindled in receptors that are activated by low molecular weight, noncatecholic, biogenic amines that are typically found as trace constituents of various vertebrate and invertebrate tissues and fluids. The timing of this resurgent focus on receptors activated by the "trace amines" (TA) beta-phenylethylamine (PEA), tyramine (TYR), octopamine (OCT), synephrine (SYN), and tryptamine (TRYP) is the direct result of 2 publications that appeared in 2001 describing the cloning of a novel G protein-coupled receptor (GPCR) referred to by their discoverers Borowsky et al. as TA1 and Bunzow et al. as TA receptor 1 (TAR1). When heterologously expressed in Xenopus laevis oocytes and various eukaryotic cell lines, recombinant rodent and human TAR dose-dependently couple to the stimulation of adenosine 3',5'-monophosphate (cAMP) production. Structure-activity profiling based on this functional response has revealed that in addition to the TA, other biologically active compounds containing a 2-carbon aliphatic side chain linking an amino group to at least 1 benzene ring are potent and efficacious TA receptor agonists with amphetamine (AMPH), methamphetamine, 3-iodothyronamine, thyronamine, and dopamine (DA) among the most notable. Almost 100 years after the search for TAR began, numerous TA1/TAR1-related sequences, now called TA-associated receptors (TAAR), have been identified in the genome of every species of vertebrate examined to date. Consequently, even though heterologously expressed TAAR1 fits the pharmacological criteria established for a bona fide TAR, a major challenge for those working in the field is to discern the in vivo pharmacology and physiology of each purported member of this extended family of GPCR. Only then will it be possible to establish whether TAAR1 is the family archetype or an iconoclast.

Acute effects of 6-hydroxydopamine on dopaminergic neurons of the rat substantia nigra pars compacta in vitro

6-Hydroxydopamine (6-OHDA) is a neurotoxin which has been implicated in the degeneration of dopaminergic neurons of the substantia nigra pars compacta (SNc) in Parkinson's disease (PD), and is frequently used to produce animal models of the disease. The aim of our study, conducted on midbrain slices obtained from young Wistar rats, was to determine the little known acute effects of this toxin (0.2-2.0 mM; 10-20 min exposure; 34 degrees C) on electrophysiological properties, intracellular Ca2+ levels and dendritic morphology of SNc neurons. Four experimental approaches were used: extracellular recording of firing frequency, whole-cell patch-clamping, ratiometric fura-2 imaging, and cell labeling with lucifer yellow (LY) or dextran-rhodamine. Extracellular recording revealed a concentration-dependent decrease in the tonic, pacemaker-like firing. In whole-cell recordings in voltage-clamp (V(hold) -60 mV), smaller doses (0.2-0.5 mM) induced an outward current (or cell membrane hyperpolarization in current-clamp), which could in some cells be reversed with tolbutamide (blocker of ATP-dependent K+ channels). A higher dose (1.0-2.0 mM) caused rapid reductions of cell membrane capacitance and membrane resistance. Toxin exposure gradually increased the intracellular Ca2+ level, which did not subsequently return to control. The increase in Ca2+ signal was not prevented by depletion of intracellular Ca2+ stores with thapsigargin (10 microM) or cyclopiazonic acid (30 microM), nor by removing extracellular Ca2+. Cell membrane current and Ca2+ responses were not prevented by blocking dopamine transporter (DAT). Cells loaded with LY or dextran-rhodamine showed signs of damage (cell membrane blebbing) in dendrites following toxin exposure (1 mM; 10-20 min). These results demonstrate that the oxidative and metabolic stress induced in SNc neurons by 6-OHDA results in rapid dose-dependent changes of cell membrane properties with morphological evidence of dendritic damage, as well as in disturbance of intracellular Ca2+ homeostasis.

Assessment of O-methylated catecholamine levels in plasma and urine for diagnosis of autonomic disorders

The term 'metanephrines' is used to indicate the two catechol 3-O-methylated metabolites of epinephrine (E) and norepinephrine (NE): metanephrine and normetanephrine (NMN). The corresponding 3-O-methylated metabolite of dopamine is usually referred to as 3-methoxytyramine rather than 3-methoxydopamine and is not generally considered a "metanephrine". O-Methylation occurs outside the sympathetic neuron and neuroeffector junction. Metanephrines are products of the enzyme catechol-O-methyltransferase (COMT). Subsequent conjugation with sulfate or deamination by monoamine oxidase (MAO) followed by reduction to vanilmandelic acid (VMA) facilitates urinary excretion. For the clinician, measurement of normetanephrine provides an index of norepinephrine released during sympathetic nervous system activity, whereas metanephrine concentration provides an indication of adrenal medullary metabolism of epinephrine prior to its discharge into the circulation. Plasma epinephrine concentration is the preferable index of adrenal medullary epinephrine discharge. Pheochromocytomas, with their protean clinical manifestations, may be diagnostic challenges, but assay of metanephrines, especially plasma metanephrine, can be particularly helpful in diagnosis. These COMT metabolites may also help in elucidation of still undiscovered genetic and acquired disorders of catecholamine metabolism.

HPLC electrochemical detection of trace amines in human plasma and platelets and expression of mRNA transcripts of trace amine receptors in circulating leukocytes

We evaluated, using a multi-channel electrochemical HPLC system, whether trace amines are detectable in plasma and platelets of healthy control subjects. To this end, levels of tyramine, octopamine and synephrine were assessed in samples obtained from eight males and eight females, age matched and free from drugs. In plasma, octopamine was detectable in all subjects, synephrine in 15 and tyramine in six out of 16 subjects. Likewise, detectable levels of octopamine together with synephrine were, in contrast to tyramine, found within platelets of most individuals. Intracellular levels of the amines significantly diminished following platelet activation (ADP or collagen). In addition, circulating leukocytes from these same subjects are herein shown to express mRNA transcripts for the recently discovered 'trace amine receptors' (TAR-1, -3, -4 and -5). Thus, although baseline plasma levels of octopamine tyramine or synephrine may vary among healthy individuals, the observation that platelets store and actively release these trace amines suggests that they may be effectors involved in platelet-mediated signaling events in the bloodstream.

Catecholamines and methods for their identification and quantitation in biological tissues and fluids

Catecholamines act via dopaminergic-, and adrenergic receptors, and are involved in a variety of regulatory systems. They take part in regulation of the response to stress, psychomotor activity, emotional processes, learning, sleep and memory. Due to many catecholaminergic pathways, and a wide range of functions they are involved in, both in the central nervous system and in periphery, a development of the reliable techniques for their extraction and quantitation is essential. This paper presents an overview of the currently applied methodologies for catecholamines detection and identification in various biological samples.

Dopamine formation from tyramine by CYP2D6

Dopamine is formed form L-tyrosine by tyrosine hydroxylase and aromatic L-amino acid decarboxylase. In addition to this pathway, however, the formation of catecholamines, including dopamine, from trace amines such as tyramine by hepatic microsomes has been demonstrated. In this study, we investigated the formation of dopamine from trace amines, using human hepatic microsomes and human cytochrome P450 (CYP) isoforms expressed in yeast. Among the 11 isoforms of human CYP expressed in yeast, CYP2D6 was the only isoform exhibiting strong ability to convert p-tyramine and m-tyramine to dopamine. In studies with human hepatic microsomes, the hydroxylation of tyramine to dopamine was inhibited by bufuralol, a typical substrate for CYP2D isoforms, and anti-CYP2D1 antiserum. This is the first report showing that CYP2D is capable of converting tyramine to dopamine. The Km values of CYP2D6, expressed in yeast, for p-tyramine and m-tyramine were 190.1 +/- 19.5 microM and 58.2 +/- 13.8 microM, respectively. Tyramine is an endogenous compound which exists in the brain as a trace amine but is also an exogenous compound which is found in foods such as cheese and wine. Our results suggest that dopamine is formed from endogenous and/or exogenous tyramine by this CYP2D isoform.

Analysis of 5-methoxytryptamine at the femtomole level in the rat and quail brain by gas chromatography-electron-capture negative-ion chemical ionization mass spectrometry

A sensitive method for the measurement of endogenous 5-methoxytryptamine in brain tissue has been developed using capillary column gas chromatography-electron-capture negative-ion chemical ionization mass spectrometry. 5-Methoxytryptamine was first converted to N-[2H3]acetyl-5-methoxytryptamine by reaction with hexa-deuterated acetic anhydride, followed by reaction with pentafluoropropionic anhydride to yield the highly electron-capturing 3,3'-spirocyclic pentafluoro-propionyl indolenine derivative. Quantitative analysis was carried out by selected-ion monitoring of the [M-HF].- and [M-HF-DF].- ion intensity of the 3.3'-spirocyclic pentafluoropropionyl indolenine derivative, using 5-methoxy-[alpha, alpha, beta, beta-2H4]tryptamine as the internal standard. The presence of 5-methoxytryptamine in the brain tissue was demonstrated. In the absence of a monoamine oxidase inhibitor, the mean +/- S.D. levels of 5-methoxytryptamine in the rat and quail whole brain were found to be 30 +/- 6 and 347 +/- 52 pg/g, respectively. The possible physiological functions of 5-methoxytryptamine as a neuromodulator and/or neurotransmitter have to be considered.

The determination of hydroxydopamines and other trace amines in the urine of parkinsonian patients and normal controls

5- and 6-Hydroxydopamine, which we had earlier identified as naturally occurring amines in human urine, were quantified in Parkinson's patients treated with L-DOPA, Parkinson's patients whose treatment did not include L-DOPA and in age matched controls. Analysis was carried out by GC-MS of the ditrifluoromethylbenzoyl-trimethylsilyl (DTFMB-TMS) derivatives of the compounds. The concentrations of 5- and 6-hydroxydopamine in the urine of DOPA treated Parkinson's patients were significantly higher than the concentrations from patients not treated and from normal controls. Urinary dopamine levels were greatly elevated in DOPA treated Parkinson's patients while p-tyramine levels were suppressed. No marked differences were seen between the three groups in terms of the urinary concentrations of any of the other amines measured.