The Potential of Trace Amines and Their Receptors for Treating Neurological and Psychiatric Diseases

Mining of the human genome has revealed approximately 7000 novel proteins, which could serve as potential targets for the development of novel therapeutics. Of these, approximately 2000 are predicted to be G-protein coupled receptors. Within this group of proteins, a family of 18 mammalian receptors has recently been identified that appear to exhibit selectivity toward the so-called trace amines. The trace amines are a family of endogenous compounds with strong structural similarity to classical monoamine neurotransmitters, consisting primarily of 2-phenylethylamine, m-and p-tyramine, tryptamine, m-and p-octopamine and the synephrines. The endogenous levels of these compounds are at least two orders of magnitude below those of neurotransmitters such as dopamine, noradrenaline and 5-HT. The effects of these low physiological concentrations have been difficult to demonstrate but it has been suggested that they may serve to maintain the neuronal activity of monoamine neurotransmitters within defined physiological limits. Such an effect of trace amines would make them ideal candidates for the development of novel therapeutics for a wide range of human disorders. Although the demonstration of a trace amine family of receptors has seen a resurgence of interest in these endogenous compounds, with recent articles reviewing trace amine pharmacological and physiological responses, the potential clinical utility of the trace amine receptors has not been specifically addressed. Historically, trace amines have been implicated in a diverse array of human pathologies ranging from schizophrenia to affective disorders to migraine. Recent studies have strengthened some of this historical data by linking trace amine receptor polymorphisms and mutations to distinct clinical conditions. The aim of the current article is to review the previous studies linking trace amines to human pathology in the context of the recently discovered trace amine receptors and evidence of the existence of trace amine receptor polymorphisms and mutations associated with such disorders. In addition, recent evidence linking trace amines to the development of drug dependence will be discussed.