Plasma Protein Levels Analysis in Multiple Sclerosis Sardinian Families Identified C9 and CYP24A1 as Candidate Biomarkers

Abstract

Here we investigate protein levels in 69 multiple sclerosis (MS) cases and 143 healthy controls (HC) from twenty Sardinian families to search for promising biomarkers in plasma. Using antibody suspension bead array technology, the plasma levels of 56 MS-related proteins were obtained. Differences between MS cases and HC were estimated using Linear Mixed Models or Linear Quantile Mixed Models. The proportion of proteins level variability, explained by a set of 119 MS-risk SNPs as to the literature, was also quantified. Higher plasma C9 and CYP24A1 levels were found in MS cases compared to HC (p < 0.05 after Holm multiple testing correction), with protein level differences estimated as, respectively, 0.53 (95% CI: 0.25, 0.81) and 0.42 (95% CI: 0.19, 0.65) times plasma level standard deviation measured in HC. Furthermore, C9 resulted in both statistically significantly higher relapsing-remitting MS (RRMS) and secondary-progressive MS (SPMS) compared to HC, with SPMS showing the highest differences. Instead, CYP24A1 was statistically significantly higher only in RRMS as compared to HC. Respectively, 26% (95% CI: 10%, 44%) and 16% (95% CI: 9%, 39%) of CYP24A1 and C9 plasma level variability was explained by known MS-risk SNPs. Our results highlight C9 and CYP24A1 as potential biomarkers in plasma for MS and allow us to gain insight into molecular disease mechanisms.

Biomarkers in Multiple Sclerosis

“…Proteomic studies have shown a decrease in alpha-1-antichymotrypsin in the CSF of patients with RRMS compared with samples collected from patients with other inflammatory diseases of the CNS. This is supported by the results obtained in the validation of studies using ELISA in both sexes [14,21].…”

“…However, the availability of leakage or release of products from different tissues or blood cells in the plasma may correspond with pathological and physiological condition of the specific tissues. Since that plasma is easy to be received in noninvasive way, it can be proposed as a useful fluid for deriving promising diagnostic biomarkers [14].…”

Heritability Estimation of Multiple Sclerosis Related Plasma Protein Levels in Sardinian Families with Immunochip Genotyping Data

“…Specifically, as reported in [ 15 ], a bead-based antibody array format, containing human platelet antigen antibodies immobilized into microspheres in suspension, was used to profile proteins via direct labeling of whole and unfractionated samples with biotin. Antibody-conjugated bead arrays were analyzed in a multiplexed manner with immediate data acquisition from the flow cytometer-like Flexmap 3D instrument, to determine relative signal intensities from the binding of antibodies to their target antigens.…”

“… and were assumed to be independent. Sex and MS status were included in the model as fixed effects to avoid potential confounding [ 15 , 28 ]. Variance component decomposition was performed according to the total trait variance ( ) decomposition provided by the formula: …”

“…Many studies aimed at focusing on MS-related proteins, for example, studying their role during the onset of the disease by comparing their levels in patients and controls, such as the one proposed by Lovett-Racke et al [ 14 ]. Many efforts have been made also in the field of biomarker discovery [ 15 , 16 ] to identify candidate molecular biomarkers for MS, gaining more insight into the pathogenetic aspects of the disease.…”