Introduction
Irritable Bowel Syndrome (IBS) is a complex gastrointestinal functional disorder characterized by abdominal pain or discomfort and altered bowel habits. Despite its prevalence, and often chronic relapsing nature, the underlying pathophysiology of IBS remains incompletely understood. The etiology is likely multifactorial. Chronic low-grade subclinical inflammation has been implicated in the disease process and thought to perpetuate the symptoms of IBS.
Through previous studies on the serum proteomic profiles of IBS patients, it was seen that some inflammatory proteins are overexpressed in IBS, giving rise to a different serum proteome signature in IBS compared to healthy controls. [1,2] Systemic inflammatory protein profiles have also been used to distinguish patients with ulcerative colitis from IBS patients. [3] This suggests that proteomic profiling can potentially give us more insight into understanding the inflammatory mechanisms driving IBS.
Aims & Methods
This study aims to determine if systemic inflammatory protein profiles differ between patients with IBS and healthy controls.
Serum inflammatory proteins from 42 asymptomatic healthy controls undergoing screening colonoscopy with no colonic pathology, and 41 IBS patients fulfilling ROME IV criteria were analyzed using the Olink Target 96 Inflammation Panel. A partial-least square discriminant analysis was undertaken to identify additional discriminative inflammatory proteins. Univariate t-test analyses, with false discovery rate correction, were also performed to identify proteins unique to varying subtypes of IBS.
Results
Among IBS patients, the mean age was 48.6 years (SD +/- 15.5), while 31.7% were male. Among the controls, the mean age was 61.6 years (SD +/- 7) and 50% were male. There were 18 (43.9%), 14 (34.1%), 8 (19.5%) and 1 (2.4%) IBS patients with IBS-D, IBS-M, IBS-C and IBS-U respectively. 73.2% of IBS patients and 90.5% of controls were Chinese, with the rest being Indians, Malays or others.
Majority of the proteins (n=88, 96%) were prevalent in >40% of the study participants. Of which, 6 proteins (AXIN1, CCL19, CCL28, CD8A, EN-RAGE, MMP10) were differentially abundant (p<0.05) in IBS patients. Participants with IBS-C displayed higher levels of CD8A, while participants with IBS-D showed higher levels of AXIN1 and EN-RAGE (Table 1).
Interestingly, a recent study showed that CCL28 is elevated in IBS patients, which is consistent with our findings. [4] EN-RAGE has also been studied to be elevated in several digestive diseases including IBS, inflammatory bowel disease, digestive tract cancers, necrotizing enterocolitis and gastroenteritis. [5]
Table 1: Differentially abundant immunoproteins in IBS
Immunoprotein Marker | Molecular function | Biological Processes | Selectively differentially abundant IBS subtypes (p<0.05) |
Axin-1 (AXIN1) | Developmental protein | Apoptosis WNT signaling pathway | IBS-D, IBS-M |
C-C motif chemokine 19 (CCL19) | Cytokine | Chemotaxis Inflammatory response |
|
C-C motif chemokine 28 (CCL28) | Cytokine | Chemotaxis |
|
T-cell surface glycoprotein CD8 alpha chain (CD8A) | Glycoprotein | Adaptive immunity | IBS-C, IBS-M |
S100A12 (EN-RAGE) | Antibiotic Antimicrobial Fungicide | Innate immunity Inflammatory response | IBS-D, IBS-M |
Stromelysin-2 (MMP-10) | Hydrolase Metalloprotease Protease | Collagen degradation |
|
Conclusion
We conclude that the serum cytokine profiles of IBS patients differ from that of healthy controls. We identified 6 immunoproteins that distinguish IBS from controls, and found that the levels of these immunoproteins also differ amongst the IBS subtypes. As this was a pilot study, the data collected was preliminary and limited by a small sample size. Future larger scale studies on proteomic profiling can potentially help with understanding the immune dysregulatory mechanisms driving IBS, and guide the diagnosis of and differentiation between subtypes.
References
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[2] Darkoh C, Comer L, Zewdie G, Harold S, Snyder N, Dupont HL. Chemotactic chemokines are important in the pathogenesis of irritable bowel syndrome. PLoS One. 2014 Mar 25;9(3):e93144.
[3] Moraes L, Magnusson MK, Mavroudis G, Polster A, Jonefjäll B, Törnblom H, Sundin J, Simrén M, Strid H, Öhman L. Systemic Inflammatory Protein Profiles Distinguish Irritable Bowel Syndrome (IBS) and Ulcerative Colitis, Irrespective of Inflammation or IBS-Like Symptoms. Inflamm Bowel Dis. 2020 May 12;26(6):874-884.
[4] Sheikhesmaili F, Jalili A, Taghizadeh E, Fakhari S, Jalili K, Ghaderi E, Rahimi E. The CCL28 levels are elevated in the serum of patients with irritable bowel syndrome and associated with the clinical symptoms. Am J Clin Exp Immunol. 2021 Feb15;10(1):23-29.
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