Proteomic analysis of intra-arterial thrombus secretions reveals a negative association of clusterin and thrombospondin-1 with abdominal aortic aneurysm

Objective: Abdominal aortic aneurysm (AAA) is usually accompanied by the formation of a large volume of intra-luminal thrombus (ILT). ILT-derived proteins have been suggested as circulating markers for AAA. We conducted a proteomic study screening whole and hexapeptide ligand library (HLL) treated ILT explant secretions to identify potential ILT-derived markers for AAA. Methods: Unfractionated and HLL-treated ILT secretions from 3 AAA patients were analysed in parallel using liquid chromatography tandem mass spectrometry (LC-MS/MS). In silico analyses were employed to identify proteins with biomarker potential. Proteomic findings were validated by measuring serum concentrations of 2 representative ILT proteins in 313 AAA patients and 690 controls. Results: A total of 150 proteins were identified from thrombus conditioned media; HLL treatment enabled the detection of 53 previously unseen polypeptides. Gene ontology analysis revealed high representation of platelet-secreted proteins. Thrombospondin-1 (TSP-1) and clusterin were selected for further assessment. Serum TSP-1 and clusterin were negatively associated with AAA after adjusting for other risk factors. Odds ratio and 95% confidence intervals were 0.62, 0.41-0.94, and 0.50, 0.33-0.75, for men with serum TSP-1 and clusterin in the fourth compared to first quartiles, respectively. Conclusion: This proteomic analysis has identified a group of proteins concentrated in AAA ILT. Assessment of circulating concentrations of two representative polypeptides suggests for the first time that the ILT selectively sequesters proteins rather than actively releasing them. Further work is required to assess the mechanisms underpinning this observation and the associated clinical implications.8 page(s