P049 The lipidome of creeping fat in Crohn’s disease points towards a harmful microenvironment

Abstract

Abstract Background A pathognomonic observation in Crohn’s disease (CD) is the existence of mesenteric adipose tissue (MAT) wrapping around the inflamed and fibrotic intestine, so-called creeping fat. The etiology of this phenomenon is unclear, and both a protective and harmful role in disease pathogenesis and progression have been proposed. Given this conflicting evidence, we aimed to further unravel the role of creeping fat by extensive profiling of its lipidome. Methods We prospectively included 22 CD patients who underwent an ileocecal resection with ileocolonic anastomosis (Table 1). Perioperatively paired adipose tissue samples were collected from 3 locations: (1) creeping fat, (2) MAT close to the proximal unaffected ileum, and (3) MAT far from the diseased ileum, defined as near the base of the ileocecal artery (Fig. 1A). The lipidome of all 66 samples was profiled by quantitative mass spectrometry (targeted C18 LC-MS/MS and HILIC LC-MS/MS; Lipometrix core KU Leuven). This approach enables the detection of mediator lipids, and membrane and storage lipids, of which the latter group represents more complex chemical structures and thus a higher diversity in classification and number of species. Data analysis and paired Wilcoxon rank- sum tests were performed with Python and R 4.3.2. Results Across all CD adipose tissue samples, we detected 38 mediator lipid species, and 456 membrane and storage lipid species . When paired-wise comparing creeping fat with MAT far from the diseased ileum, we observed a significant decrease in 16 lipid mediators (p<0.05), namely arachidonic acid (AA), docosahexaenoic acid (DHA), 4 epoxy and 10 hydroxy mediator lipids; with hydroxy mediator X being the top downregulated in creeping fat (fold change (FC)=-2.11, p=0.0003) (Fig. 1B). While AA and DHA are (semi)-essential fatty acids and function as precursors, the other 8 decreased lipids in creeping fat are known to be anti-inflammatory, and 3 (incl. mediator X) are also anti-fibrotic. The lipid mediator profile of MAT close to the proximal unaffected ileum was similar to that of creeping fat, except for a pro-inflammatory lipid being increased in creeping fat (FC=2.30, p=0.004) (Fig. 1B). Lastly, when evaluating the membrane and storage lipid abundances both at species level (sum notation; fatty acyl composition) and at class level, no paired-wise differences among the three adipose tissue locations were found (p>0.05). Conclusion In this pilot lipidomics study, we did not observe any changes in storage or membrane lipids in creeping fat as compared to paired unaffected MAT. In contrast, a decrease in anti-inflammatory and anti-fibrotic lipid species along with an increase in a pro-inflammatory species points towards a harmful microenvironment within creeping fat.