Fecal Arachidonic Acid: A Potential Biomarker for Inflammatory Bowel Disease Severity

Abstract

Arachidonic acid levels are elevated in the colonic mucosa of patients with inflammatory bowel disease (IBD). Fecal metabolites are emerging as valuable diagnostic tools for IBD. This study aimed to investigate associations between 31 fecal fatty acids, including arachidonic acid, to identify potential correlations with disease severity. Among the 31 fatty acids analyzed in feces, dihomo-γ-linolenic acid, arachidonic acid, and adrenic acid were significantly increased in patients with IBD compared to controls. In contrast, levels of linoleic acid and γ-linolenic acid, the precursors of arachidonic acid, were similar between both groups. No significant differences in fatty acid levels were observed between patients with Crohn's disease and ulcerative colitis. Arachidonic acid and adrenic acid levels positively correlated with fecal calprotectin, a clinically established marker of IBD severity, but showed no association with stool consistency or the Gastrointestinal Symptom Rating Scale. This suggests that these fatty acids are linked to disease severity rather than disease-related symptoms. Current IBD-specific medications had no significant impact on the fecal levels of any of the 31 fatty acids. In summary, this study demonstrates elevated fecal levels of dihomo-γ-linolenic acid, arachidonic acid, and adrenic acid in IBD patients. Normal levels of precursor fatty acids suggest that impaired downstream metabolism may contribute to the accumulation of these n-6 polyunsaturated fatty acids.

Keywords: biomarker; calprotectin; fatty acids; feces; inflammatory bowel disease; stool consistency.

Figure 1

Fecal fatty acid levels (µmol/g dry weight) of controls, patients with Crohn’s Disease (CD), and patients with ulcerative colitis (UC). (a) Total levels of fecal fatty acids were similar between the groups; (b) Concentrations of saturated, monounsaturated, di-unsaturated, and polyunsaturated fatty acids in stool of controls and patients were similar between the groups. Boxplots highlight outliers with circles and asterisks.

Figure 2

Receiver operating characteristic curve for the discrimination of patients and controls by fecal arachidonic acid, adrenic acid, and dihomo-γ-linolenic acid. The other fatty acids measured in feces were similar between patients and controls.

Figure 3

Connection between fecal fatty acid and fecal calprotectin levels. Concentrations (µmol/g dry weight) of (a) arachidonic acid and (b) adrenic acid in stool of IBD patients classified by fecal calprotectin levels. * p < 0.05. Boxplots highlight outliers with circles and asterisks. Arachidonic acid and adrenic acid, but none of the other fecal fatty acids measured, increased with higher fecal calprotectin levels.

Figure 4

Levels of fecal arachidonic acid (µmol/g dry weight) according to stool consistency. Patients with diarrhea have higher fecal levels of arachidonic acid compared to patients with normal stool consistency * p < 0.05. All of the other fatty acids did not differ between the groups. Boxplots highlight outliers with circles and asterisks.