Serum S100A8/A9 as a Potentially Sensitive Biomarker for Inflammatory Bowel Disease

Kohki Okada, PhD, (ASCPi) MLS; Makoto Okabe, MD; Yuto Kimura, MD; Hiroshi Itoh, PhD; Masaki Ikemoto, PhD

Disclosures

Lab Med. 2019;50(4):370-380. 

In This Article

Abstract and Introduction

Abstract

Background: The clinical significance of human S100A8/A9 (h-S100A8/A9) in patients with inflammatory bowel disease (IBD) is poorly understood.

Objective: To clarify whether serum S100A8/A9 is a sensitive biomarker for IBD.

Methods: Serum specimens from outpatients with IBD (n = 101) and healthy volunteers (HVs) (n = 101) were used in this study. Enzyme-linked immunosorbent assays for h-S100A8/A9 and inflammatory cytokines were performed using these specimens. Further, correlation analysis was performed to investigate the significance of h-S100A8/A9 fluctuation in patients with IBD.

Results: The average of serum h-S100A8/A9 concentration in outpatients with IBD was significantly higher than that in HVs. The concentration of h-S100A8/A9 in patients with IBD was barely correlated with that of CRP and inflammatory cytokines. Despite that finding, the serum level of h-S100A8/A9 in patients with ulcerative colitis (UC) was correlated with the severity of IBD, compared with other inflammatory proteins.

Conclusion: Serum h-S100A8/A9 is superior to CRP as a sensitive biomarker for IBD.

Introduction

S100A8, S100A9, and S100A8/A9 (S100 proteins) were originally found in the synovial fluid of patients with rheumatoid arthritis (RA)[1] as risk factors for many inflammatory diseases, such as RA, hepatitis, and inflammatory bowel disease (IBD).[2–4] S100A8/A9 is involved in immune regulation in the human body and in the onset of and remission from IBD.[1,5] S100 proteins activate cell-signaling pathways via receptors, such as toll-like receptor (TLR)4 and the receptor for advanced glycation end-products (RAGE), which contribute to internal homeostasis in the body.[6,7] The onset of IBD causes inflammatory cytokines to be secreted from immune cells of myeloid origin, such as neutrophils and macrophages, in which S100 proteins serve as ligands for receptors in the nuclear factor kappa B (NF-κB) pathway.[8]

Although S100 proteins may have important roles in the immune system, their immunological functions are poorly understood. To investigate the immune function of S100A8, we established S100A8 transgenic rats (Tg-S100A8).[9] Expression of interleukin (IL)–6 and tumor necrosis factor–α (TNF-α) messenger RNAs (mRNAs) were significantly lower in colon tissue of Tg-S100A8 animals than in healthy rats, even if Tg-S100A8 rats were treated with 5% dextran sulfate sodium (DSS). This finding suggests that S100A8 negatively regulates the expression of inflammatory cytokine mRNAs.

Ulcerative colitis (UC) and Crohn disease are representative IBDs characterized by recurrent and sometimes severe inflammation in the intestinal tract.[10] It is still unclear how IBD is formed in a limited region of the large colon and rectal tissue. Also, dysregulation of innate and adaptive immunity is a risk factor for the onset of IBD. Excessive activation of macrophages or neutrophils in large colon tissue may result in the onset of IBD.[11] Previously, we showed[12] that rat S100A9 (r-S100A9) was expressed more in macrophages in the rectal region of the large intestine of rats with UC, compared with r-S100A8 expression, but r-S100A8 and r-S100A9 were coexpressed at similar levels in most macrophages in the rectal tissues of rats treated with an immunosuppressant (tacrolimus). Further, we discovered that S100 proteins tightly bound cluster of differentiation (CD)68 on macrophages, which activated cells and produced inflammatory cytokines such as IL-6 and TNF-α.[13] These results strongly suggest that the immune functions of macrophages can be regulated by S100 proteins through certain cell-signaling pathways, such as the NF-κB and mitogen-activated protein kinase (MAPK) pathways.

S100 proteins are proinflammatory proteins in inflammatory diseases[1–4] and have various immune functions.[9,12,13] Human S100A8/A9 (h-S100A8/A9) is markedly increased in the serum and synovial fluid in the joints of patients with RA during the active period of RA.[14] The increase in serum S100 proteins is highly correlated with the pathological stage of different cancers, such as renal-cell carcinoma and prostate cancer.[15] The concentration of fecal h-S100A8/A9 is generally measured to evaluate the severity of IBD;[16,17] however, it is difficult to collect stool specimens from patients with IBD because of diarrhea and melena.

To overcome these problems, we used blood specimens from patients with IBD because blood specimens can be obtained easily from patients with IBD. Histological significance of serum r-S100A8/A9 concentration in IBD has been previously revealed using experimental rats with colitis.[18] To measure serum h-S100A8/A9 concentration, we originally developed a preparative enzyme-linked immunosorbent assay (ELISA) system for the heterodimer and applied it to clinical specimens.

In this study, we measured the concentration of h-S100A8/A9 using this ELISA method and evaluated the clinical significance of h-S100A8/A9, compared with other inflammatory biomarkers. We evaluated serum h-S100A8/A9 as a sensitive biomarker for IBD and examined whether the serum level of h-S100A8/A9 corresponded to the severity of IBD.

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