Allopurinol Reprograms Uric Acid Self-Assembly by Disrupting Cytotoxic Fibrils and Redirecting Crystal Growth

The supramolecular self-assembly of uric acid (UA), the end product of purine metabolism, underlies crystal deposition in gout and kidney diseases. However, the intermediate states linking soluble UA to crystalline phases remain poorly defined. Here, we report that UA self-assembles into amyloid-like fibrils that coexist with crystalline forms and exhibit cytotoxicity. Native ion mobility spectrometry-mass spectrometry (IMS-MS) reveals discrete UA oligomers up to 60-mers, suggesting a stepwise assembly process. Optical and electron microscopy distinguish between fibrous and crystalline morphologies, with the fibrillar network acting as a potential scaffold for nucleation. We demonstrate that allopurinol, beyond its known function as a xanthine oxidase inhibitor, directly perturbs UA aggregation. Allopurinol alters the thermodynamics of self-assembly, suppressing fibril formation and promoting crystallization into a more stable anhydrous polymorph. In contrast, epigallocatechin gallate (EGCG) suppresses both fibrillation and crystallization. X-ray diffraction confirms the formation of a distinct anhydrous crystal phase in the presence of allopurinol, analogous to that found in patient-derived deposits. These findings expand the chemical understanding of UA phase behavior and polymorphism and establish cytotoxic UA fibrils as drug-modifiable intermediates. Modulating small-molecule-driven metabolite self-assembly provides a mechanistic basis for rational intervention in gout and other disorders characterized by metabolite aggregation.