Discovery of novel biomarkers associated with myocardial fibrosis in chimpanzees (Pan troglodytes)

Background: Idiopathic myocardial fibrosis (IMF) is a prevalent and life-threatening condition in captive chimpanzees (Pan troglodytes). Ante-mortem diagnosis remains challenging due to the limitations of current veterinary diagnostics. This study aimed to identify and validate circulating serum protein biomarkers for the detection of IMF. Methods: Serum samples collected from zoo-housed chimpanzees with post-mortem confirmed cardiac phenotypes were utilised. An initial discovery phase using a Proximity Extension Assay (PEA) screened 92 cardiovascular proteins in a subset of 10 chimpanzees. Three candidate biomarkers (ICAM-2, AXL, and PECAM-1) were subsequently selected for Enzyme-Linked Immunosorbent Assay (ELISA) validation in a broader cohort (N=25). Final biomarker efficacy was assessed alongside Receiver Operating Characteristic (ROC) curve analysis. Results: In the discovery phase, ICAM-2, AXL, and PECAM-1 were significantly elevated in IMF-affected animals. During ELISA validation, circulating ICAM-2 remained significantly elevated in the IMF cohort (p=0.010, Cohen's d=0.91). No significant association was detected with subject age or the time interval between sampling and death. AXL and PECAM-1 did not reach statistical significance in the validation cohort. ROC analysis for ICAM-2 established an optimal diagnostic cut-off of >1.535 ng/mL (AUC = 0.672), which demonstrated 100% specificity and a 100% positive predictive value. Conclusion: ICAM-2 is a highly specific, putative "rule-in" biomarker for moderate-to-severe IMF in chimpanzees. Implementing this biomarker into routine health assessments could enhance the early, non-invasive detection and clinical management of cardiovascular disease in this endangered species, though further validation is required before wider clinical use.