Tyramine

Food sources and biomolecular targets of tyramine

Tyramine is a biogenic trace amine that is generated via the decarboxylation of the amino acid tyrosine. At pico- to nanomolar concentrations, it can influence a multitude of physiological mechanisms, exhibiting neuromodulatory properties as well as cardiovascular and immunological effects. In humans, the diet is the primary source of physiologically relevant tyramine concentrations, which are influenced by a large number of intrinsic and extrinsic factors. Among these factors are the availability of tyrosine in food, the presence of tyramine-producing bacteria, the environmental pH, and the salt content of food. The process of fermentation provides a particularly good source of tyramine in human nutrition. Here, the potential impact of dietary tyramine on human health was assessed by compiling quantitative data on the tyramine content in a variety of foods and then conducting a brief review of the literature on the physiological, cellular, and systemic effects of tyramine. Together, the data sets presented here may allow both the assessment of tyramine concentrations in food and the extrapolation of these concentrations to gauge the physiological and systemic effects in the context of human nutrition.

The Prescriber's Guide to the MAOI Diet-Thinking Through Tyramine Troubles

This review article features comprehensive discussions on the dietary restrictions issued to patients taking a classic monoamine oxidase inhibitor (phenelzine, tranylcypromine, isocarboxazid), or high-dose (oral or transdermal) selegiline. It equips doctors with the knowledge to explain to their patients which dietary precautions are necessary, and why that is so: MAOIs alter the capacity to metabolize certain monoamines, like tyramine, which causes dose-related blood pressure elevations. Modern food production and hygiene standards have resulted in large reductions of tyramine concentrations in most foodstuffs and beverages, including many cheeses. Thus, the risk of consequential blood pressure increases is considerably reduced-but some caution remains warranted. The effects of other relevant biogenic amines (histamine, dopamine), and of the amino acids L-dopa and L-tryptophan are also discussed. The tables of tyramine data usually presented in MAOI diet guides are by nature unhelpful and imprecise, because tyramine levels vary widely within foods of the same category. For this reason, it is vital that doctors understand the general principles outlined in this guide; that way, they can tailor their instructions and advice to the individual, to his/her lifestyle and situation. This is important because the pressor response is characterized by significant interpatient variability. When all factors are weighed and balanced, the conclusion is that the MAOI diet is not all that difficult. Minimizing the intake of the small number of risky foods is all that is required. Many patients may hardly need to change their diet at all.

Tyramine: from octopamine precursor to neuroactive chemical in insects

It is well acknowledged that tyramine acts as the biosynthetic intermediate precursor for octopamine. This fact has biased the interpretation of biological effects of tyramine towards an artifact of it being a partial agonist on octopamine receptors. Over recent years there has been an accumulation of evidence to show that tyramine is in fact a neuroactive chemical in its own right, with diverse physiological/behavioral roles. In addition, tyramine plays a unique role in a non-neuronal tissue, namely the Malpighian tubules. This review examines this evidence, taking into account the criteria that need to be satisfied in order to claim neuroactive chemical status. Thus, the evidence points to tyramine being synthesized by, and present in, neurons; capable of being released from neurons; removed by high affinity plasma membrane transporters; acting upon specific tyramine receptors; and producing physiological/behavioral effects that can be blocked by antagonists. This composite evidence is strong, although the final proof still awaits analysis on a uniquely identifiable tyraminergic neuron as has been possible with octopamine.

The control of metabolic traits by octopamine and tyramine in invertebrates

Octopamine (OA) and tyramine (TA) are closely related biogenic monoamines that act as signalling compounds in invertebrates, where they fulfil the roles played by adrenaline and noradrenaline in vertebrates. Just like adrenaline and noradrenaline, OA and TA are extremely pleiotropic substances that regulate a wide variety of processes, including metabolic pathways. However, the role of OA and TA in metabolism has been largely neglected. The principal aim of this Review is to discuss the roles of OA and TA in the control of metabolic processes in invertebrate species. OA and TA regulate essential aspects of invertebrate energy homeostasis by having substantial effects on both energy uptake and energy expenditure. These two monoamines regulate several different factors, such as metabolic rate, physical activity, feeding rate or food choice that have a considerable influence on effective energy intake and all the principal contributors to energy consumption. Thereby, OA and TA regulate both metabolic rate and physical activity. These effects should not be seen as isolated actions of these neuroactive compounds but as part of a comprehensive regulatory system that allows the organism to switch from one physiological state to another.

Tyramine and octopamine: ruling behavior and metabolism

Octopamine (OA) and tyramine (TA) are the invertebrate counterparts of the vertebrate adrenergic transmitters. They are decarboxylation products of the amino acid tyrosine, with TA as the biological precursor of OA. Nevertheless, both compounds are independent neurotransmitters that act through G protein-coupled receptors. OA modulates a plethora of behaviors and peripheral and sense organs, enabling the insect to respond correctly to external stimuli. Because these two phenolamines are the only biogenic amines whose physiological significance is presumably restricted to invertebrates, pharmacologists have focused their attention on the corresponding receptors, which are still believed to represent promising targets for new insecticides. Recent progress made on all levels of OA and TA research has enabled researchers to understand better the molecular events underlying the control of complex behaviors.