β2-Microglobulin as a biomarker in peripheral arterial disease: Proteomic profiling and clinical studies

BACKGROUND - Peripheral arterial disease (PAD) is common but commonly unrecognized. Improved recognition of PAD is needed. We used high-throughput proteomic profiling to find PAD-associated biomarkers. METHODS AND RESULTS - Plasma was collected from PAD patients (ankle brachial index of <0.90; n=45) and subjects with risk factors but without PAD (n=43). Plasma was analyzed with surface-enhanced laser desorption/ionization time-of-flight mass spectrometry to quantify 1619 protein peaks. The peak intensity of a 12-kDa protein was higher in PAD patients. Western blot analyses and immunoaffinity studies confirmed that this protein was β2-microglobulin (B2M). In a validation study, B2M was measured by ELISA in plasma in age- and gender-matched PAD (n=20) and non-PAD (n=20) subjects. Finally, we studied a larger cohort of subjects (n=237) referred for coronary angiography but without known PAD. Plasma B2M levels were higher in PAD patients than in non-PAD patients with coronary artery disease. Plasma B2M correlated with ankle brachial index and functional capacity. Independent predictors of PAD were diabetes mellitus, age, and the combination of B2M and C-reactive protein level. CONCLUSIONS - In PAD patients, circulating B2M is elevated and correlates with the severity of disease independent of other risk factors. These findings might provide a needed biomarker for PAD and new insight into its pathophysiology. Further studies in other populations are needed to confirm the utility of measuring B2M in cardiovascular disease risk assessment.