Adenosine, adenosine A 2A antagonists, and Parkinson's disease.

Adenosine derived from the degradation of ATP/AMP functions as a signalling molecule in the nervous system through the occupation of A1, A2, and A3 adenosine receptors. Adenosine A(2A) receptors have a selective localization to the basal ganglia and specifically to the indirect output pathway, and as a consequence offer a unique opportunity to modulate the output from the striatum that is believed critical to the occurrence of motor components of PD. Indeed, the ability of A(2A) antagonists to modulate basal ganglia neurotransmission has been shown to be associated with improved motor function in experimental models of PD. This suggests that A(2A) antagonists would be effective as a symptomatic treatment in humans without provoking marked dyskinesia. Indeed, the A(2A) antagonist istradefylline reduces OFF time in moderate- to late-stage patients with PD already receiving dopaminergic therapy, with an increase in non-troublesome dyskinesia. Adenosine and adenosine receptors also exert actions relevant to pathogenesis in PD, raising the possibility of their use as neuroprotective agents. Both epidemiologic evidence and the current preclinical data strongly support a role for A(2A) antagonists in protecting dopaminergic neurons and influencing the onset and progression of PD.