Hypothalamic-Pituitary-Gut Axis Dysregulation in Irritable Bowel Syndrome: Plasma Cytokines as a Potential Biomarker?

Background & Aims: Irritable bowel syndrome (IBS) is a functional disorder with an etiology that has been linked to both psychological stress and infection. The primary aim of this study was to examine the hypothalamic-pituitary-adrenal axis in patients with IBS and to relate such response to plasma cytokine profiles. Methods: A total of 151 subjects, 76 patients and 75 controls, were recruited. The patients with IBS were diagnosed according to Rome II criteria. Forty-nine patients and 48 matched controls had cytokine levels measured, and a subset of 21 patients and 21 controls also underwent a corticotropin-releasing hormone (CRH) stimulation test with plasma levels of adrenocorticotropic hormone (ACTH) and cortisol measured. The remaining 27 patients and 27 controls underwent a dexamethasone (1 mg) challenge. Results: Cortisol and the proinflammatory cytokines interleukin (IL)-6 (together with its soluble receptor) and IL-8 were elevated in all IBS subgroups (diarrhea predominant, constipated, and alternators), although the elevation was most marked in the constipated subgroup. There was no alteration in the anti-inflammatory cytokine IL-10. Following CRH infusion, an exaggerated release of both ACTH and cortisol was observed in patients with IBS. There was a significant correlation between the ACTH response (δACTH) and the IL-6 levels. A similar relationship existed between the δACTH/δcortisol ratio and the IL-6 levels. Dexamethasone suppression of cortisol was similar in patients and controls. Conclusions: IBS is characterized by an overactivation of the hypothalamic-pituitary-adrenal axis and a proinflammatory cytokine increase.