Beta2-Adrenoceptor Agonists in Parkinson's Disease and Other Synucleinopathies.

Evidence supporting the use of β2AR agonists in synucleinopathies is rapidly growing. Findings come from different scientific approaches. Molecular and immunological data suggest that adrenergic stimulation may decrease both α-synuclein (α-syn) deposition and pro-inflammatory/neurotoxic molecules release. Small open label clinical trials including a total number of 25 Parkinson's disease (PD) patients, in which the β2AR agonist salbutamol was added to levodopa, suggest a promising symptomatic benefit. In line with these findings, epidemiological studies investigating the risk of PD development suggest that long term exposure to the agonist salbutamol might be protective, while the antagonist propranolol possibly detrimental. Nonetheless, in both lines of investigation the studies performed so far present important limitations. On the clinical side, large randomized controlled trials are lacking, whereas on the epidemiological side the presence of co-morbid conditions (i.e. smoking and essential tremor) potentially influencing PD risk should taken into consideration. In summary, it is our opinion that β2AR stimulation in synucleinopathies has a rationale and therefore merits further investigation. Graphical Abstract.