Fig 3.

Therapeutic targets along the purine metabolic pathway. Adenosine A_2A antagonists (including caffeine) and urate have emerged as realistic candidate neuroprotectants. In humans the enzymatic metabolism of purines such as adenosine ends with urate due to multiple mutations within the urate oxidase gene during primate evolution (see text). The schematic suggests a possible homeostatic mechanism linking an adenosinergic neurodegenerative influence with an offsetting neuroprotective influence of urate.