Recent evidence suggests that trace
amines such as
tyramine and
octopamine, alternative products of
tyrosine metabolism (an aminoacid parent of
dopamine and
noradrenaline), play a role in the homeostasis of the extrapyramidal system. However, the relevance of these trace
amines in the pathogenesis of
Parkinson's disease is still largely unknown. Here, we assessed the plasma levels of
octopamine and
noradrenaline in three sub-groups of PD patients, namely de novo, non-fluctuating and fluctuating patients, versus age-matched control subjects. We show that
octopamine is detectable in plasma of all subjects, the mean levels of which are significantly lower in PD patients, including de novo patients, when compared to controls (p<0.001). Unlike this, no changes in plasmatic
noradrenaline levels were found in the de novo patients, but only in plasma of fluctuating and non-fluctuating PD patients. These findings raise the possibility that
Parkinson's disease is firstly characterized by abnormalities of
tyrosine decarboxylase, rather than
tyrosine hydroxylase,
enzyme activity. Given the role of this
enzyme in the production of trace
amines, circulating
octopamine levels may hold promise as a
biomarker of early
Parkinson's disease.