Systemic alterations in plasma proteins from women with chronic widespread pain compared to healthy controls: a proteomic study

Abstract

Chronic widespread pain (CWP) is a complex pain condition that is difficult to treat. The prevalence of CWP approximates ~10% of the general population, with higher prevalence in women. Lack of understanding of molecular mechanisms has been a challenge for diagnosis and treatment of chronic pain. The aim of this study was to explore the systemic protein changes in CWP compared to those in healthy controls (CON). By applying 2-dimensional gel electrophoresis, we analyzed the protein pattern of plasma samples from women with CWP (n=16) and healthy women (n=23). The proteomic data were analyzed using multivariate statistical models, and altered proteins were identified using mass spectrometry. The proteome analysis was further validated by gel-free Western blot. Multivariate statistical data analysis of quantified proteins revealed 22 altered proteins in women with CWP, compared to CON group. Many of the identified proteins are previously known to be involved in different parts of the complement system and metabolic and inflammatory processes, e.g., complement factor B, vitamin D-binding protein, ceruloplasmin, transthyretin and alpha-2-HS-glycoprotein. These results indicate that important systemic protein differences exist between women with CWP and healthy women. Further, this study illustrates the potential use of proteomics to detect biomarkers that may provide new insights into the molecular mechanism(s) of chronic pain. However, further larger investigations are required in order to confirm these findings before it will be possible to identify proteins as potential pain biomarkers for clinical use.

Keywords: GC protein; biomarker; complement system; inflammation; painomics.

Figure 1

OPLS-DA model of quantified proteins from plasma. Notes: (A) A score plot of CWP compared to CON, visualizing clear separation between the 2 included groups. (B) Loading plot corresponding to significant proteins, with a VIP value >1 (triangles), between CWP and CON. The parameters for the models were R²=0.84, Q²=0.60, CV-ANOVA, p-value=2.31e⁻⁰⁶ Abbreviations: OPLS-DA, orthogonal partial least square discriminant analysis; CWP, chronic widespread pain; CON, controls; VIP, variable influence of projection; CV-ANOVA, cross-validated analysis of variance.

Figure 2

A representative SYPRO Ruby^® stained 2-DE gel of the plasma proteome from one woman with CWP (right) and one healthy CON (left). Notes: A total of 22 proteins (marked, numbered spots), including different isoforms, had a VIP value >1, were highly significant for the model, and were further identified. Abbreviations: 2-DE, 2-dimensional gel electrophoresis; CWP, chronic widespread pain; CON, controls; VIP, variable influence of projection; MW, molecular weight; pI, isoelectric point.

Figure 3

Concentration of VDBP in plasma for the 2 groups of subjects. Note: Significantly elevated concentration of VDBP was found in CWP compared to CON (*p=0.0343). Abbreviations: VDBP, vitamin D-binding protein; CWP, chronic widespread pain; CON, controls.