Serum disease-associated proteins of ankylosing spondylitis: results of a preliminary study by comparative proteomics

Ankylosing spondylitis (AS) is difficult to diagnose at the early stage since it lacks simple and specific diagnostic indicators. Proteomics is a new enabling technology to screen disease-associated proteins which can be used in diagnostics or therapeutics. This study was performed by using two-dimensional electrophoresis (2-DE) in combination with mass spectrometry to search for disease-associated proteins in the sera of AS patients.

Sera from 6 AS patients and 6 healthy volunteers (HVs) were mixed respectively and high-abundance proteins were depleted by Plasma 7 Multiple Affinity Removal System. The protein expression profiles of the sera between the two groups were compared by 2-DE and proteins over/under-expressed in the AS group were identified by mass spectrometry. Two of the identified proteins were then chosen to be verified by using ELISA in the individual sera of 32 AS patients and 32 HVs.

Serum amyloid A, apolipoprotein A (ApoA)-IV, ApoA-IV precursor, haptoglobin 2, ceruloplasmin (Cp) and immunoglobulin superfamily 22 were over-expressed by more than 3-fold in the sera of AS patients compared with HVs. Plasma glutathione peroxidase, similar to complement component 3 and chain A of transthyretin (TTR) were under-expressed in the sera of the AS patients. ELISA experiments showed the same trends in the expression levels of Cp and TTR with 2-DE.

There were 9 differentially expressed proteins in the sera of the AS group compared with the HV group, which might be candidate AS-associated proteins and might be promising diagnostic indicators or therapeutic targets for AS.