Fatal Visceral Gout in Three Crocodilian Species (Crocodylus Palustris, Caiman Yacare, and Crocodylus Suchus): A Multi-Omics Cohort Study Revealing Purine Metabolic Collapse and Mitochondrial Injury

Visceral gout is a fatal metabolic disorder in captive crocodilians, yet its molecular pathogenesis remains poorly understood. This cohort study integrates clinical, pathologic, quantitative proteomic, targeted metabolomic, and transmission electron microscopic findings from 18 crocodilians (Crocodylus palustris n = 9, Caiman yacare n = 3, Crocodylus suchus n = 6) with fatal visceral gout, compared with 48 controls (18 tissue + 30 serum) from 11 Iranian zoological institutions over 5 year. Renal tissue and antemortem serum were comprehensively analyzed using histopathology, transmission electron microscopy, label-free LC-MS/MS proteomics, and targeted metabolomics with longitudinal sampling (6–7 time points) in five cases—constituting the first temporal metabolomic dataset in reptilian gout research. All cases exhibited diffuse urate deposition on visceral and musculoskeletal surfaces. Histopathologically, extensive tubular necrosis with characteristic radial "starburst" urate crystallization and granulomatous inflammation was consistently observed. Ultrastructurally, transmission electron microscopy confirmed severe, irreversible mitochondrial degeneration in all cases, characterized by organellar swelling, complete cristolysis, and outer membrane rupture. Proteomic profiling identified 347 differentially expressed proteins (fold change ≥ 2, adjusted P < 0.05): purine catabolic enzymes were markedly upregulated (xanthine dehydrogenase 4.9-fold, adenosine deaminase 3.4-fold, guanase 2.9-fold), whereas antioxidant defenses were profoundly suppressed (superoxide dismutase 1 0.29-fold, glutathione peroxidase 1 0.39-fold, catalase 0.31-fold, glutathione peroxidase 4 0.20-fold). Longitudinal metabolomics demonstrated that xanthine accumulation and glutathione depletion (GSH/GSSG decline from 8.2 to 1.2) preceded exponential uric acid elevation by 30–60 d. KEGG enrichment confirmed involvement of purine metabolism (P = 1.6×10⁻⁴) and reactive oxygen species pathways (P = 0.006). Notably, species-specific variability was observed: C. suchus exhibited the most pronounced purine metabolic upregulation and antioxidant suppression, while C. yacare showed relatively mild alterations. Collectively, these findings establish the first quantitative multi-omic reference for reptilian gout and demonstrate that fatal visceral gout is consistently associated with purine metabolic collapse, antioxidant defense failure, and irreversible mitochondrial injury, with species-specific variability suggesting differential genetic susceptibility. These results provide a quantitative framework for early biomarker-based diagnosis and species-specific risk assessment in captive crocodilian populations.