To identify protein biomarkers associated with proinflammatory high-density lipoprotein (HDL) in patients with active rheumatoid arthritis (RA) by proteomic analysis.
Liquid chromatography tandem mass spectrometry (LC-MS/MS) was used to analyze proteins associated with immunoaffinity-purified HDL from plasma obtained from 2 sets of RA patients, 1 with antiinflammatory HDL and 1 with proinflammatory HDL. Proteins were fractionated by Offgel electrophoresis and analyzed using an LC-MS/MS system equipped with a high-capacity high-performance liquid chromatography chip incorporating C18 reverse-phase trapping and analytical columns. Sandwich enzyme-linked immunosorbent assays were used to validate the association between select proteins and proinflammatory HDL in a second cohort of RA patients.
Seventy-eight proteins were identified in the HDL complexes. The levels of 12 proteins were significantly increased in RA patients with proinflammatory HDL compared to RA patients with antiinflammatory HDL. These proteins included the acute-phase proteins apolipoprotein J, fibrinogen, haptoglobin, serum amyloid A, and complement factors (B, C3, and C9). The associations between proinflammatory HDL and 4 of the proteins were validated in a second RA cohort.
Our findings indicate that proinflammatory HDL in patients with RA contains a significantly altered proteome, including increased amounts of acute-phase proteins and proteins involved in the complement cascade. These findings suggest that HDL is significantly altered in the setting of chronic inflammation in active RA, with resultant loss of its antiinflammatory function. The characterization of the biomarkers described herein may identify novel molecular connections that contribute to the higher risk of cardiovascular disease in RA patients.