Primary bile acid shapes peripheral immunity in inflammatory bowel disease-associated primary sclerosing cholangitis

Abstract

Primary sclerosing cholangitis (PSC) is a chronic cholestatic liver disease often associated with underlying inflammatory bowel disease (IBD). This study investigates how PSC predisposes individuals to altered inflammatory immune responses compared with IBD alone. A case-control study was conducted with a cohort of 75 patients, including 16 with PSC (14 with concomitant IBD), 39 with IBD alone, and 20 controls. Serum bile acid profile, proteomic analysis, and immune-related gene expression in the colon tissue were examined. Colonic tissue from PSC patients exhibited up-regulation of immune regulation and inflammatory signaling mRNA markers, including LGR5, IL-8, CCL2, COX2, TWIST1, and SNAIL. Additionally, PSC patients displayed a distinct proinflammatory serum proteomic signature and moderate elevation of some bile acids, such as glycochenodeoxycholic acid (GCDCA). Co-incubation of human-derived monocytes with GCDCA partially replicated the inflammatory profile observed in PSC. These findings suggest that circulating bile acids modulate the peripheral immune system proinflammatory response, contributing to the unique PSC phenotype.

Keywords: GCDCA; IBD; PSC; bile acids; immune response.

Figure 1. Patients with PSC have increased conjugated primary bile acids and inflammatory factors when compared with IBD alone.

(A) Serum total bile acid profile. (B) Percentage of unconjugated bile acids and ratio between primary and secondary bile acids in serum. (C) Serum 7α-hydroxy-4-cholesten-3-one (C4) and C-reactive protein quantification. (D) Serum levels of IL-6, IL-8, IL-10, IL-17, IL-33, and IFN-γ. Results are expressed in fold change as mean values with error bars ± SEM.

Figure 2. Serum proteomic analysis reveals an increase in peripheral pro-inflammatory markers in PSC patients.

(A) Serum proteomic analysis after albumin depletion of IBD vs. control, PSC vs. control, and IBD vs. PSC. (B) String analysis of the 112 significant proteins increased in PSC serum samples; orange – immune receptor activity; yellow – PPAR signaling pathway; magenta – PI3K-Akt signaling pathway; light green – cell–cell adhesion via plasma-membrane adhesion molecules; maroon – acute inflammatory response; purple – vasodilation; pink – inflammatory response; gray – leukocyte cell–cell adhesion; light blue – immune system process; black – acute-phase response; dark green – neutrophil degranulation; red – innate immune system; blue – immune system; lime green – signaling by Interleukins; cyan – immunoregulatory interactions between a lymphoid and a non-lymphoid cell. Proteomic data are log₂ fold change and log₁₀ adjusted P values.

Figure 3. Effect of GCDCA on monocytes in vitro.

(A) Percentage of differentiated monocytes expressing CD14, CD16, CD80, CD163, CD204, CD206, and HLA-DR, differentiated with 50 µM of GCDCA and exposed to LPS (100 ng/ml) or recombinant human TNF-α (20 ng/ml) for 24 h. (B) Mean fluorescence intensity (MFI) of differentiated monocytes expressing CD16, CD14, CD80, CD206, and CD163, differentiated with 50 µM of GCDCA and exposed to LPS (100 ng/ml) or recombinant human TNF-α (20 ng/ml) for 24 h. Results are expressed in fold change as mean values with error bars ± SEM.

Figure 4. Altered colon immune system response in PSC patients.

(A) Fecal calprotectin quantification. (B) Right colon mRNA expression of intestinal stem cell and regeneration mRNA marker LGR5. (C) Right colon mRNA expression of intestinal epithelial–mesenchymal transition markers SNAIL and TWIST1. (D) Right colon mRNA expression of pro-inflammatory tumor microenvironment markers IL-8, CCL2, and COX2. qPCR results are expressed in fold change as mean values with error bars ± SEM. Proteomic data are log₂ fold change and log₁₀ adjusted P values.