IBS Patients Less Affected by Pain Treatments

Pain treatments are less effective in patients with irritable bowel syndrome (IBS), according to research published in Brain, Behavior, and Immunity.

Though there are many types of IBS — affecting up to 10 percent of the community — each impacts the patients’ quality of life. Researchers from the University of Adelaide in Australia determined the mechanisms behind IBS in their Nerve-Guy Research Laboratory. Over 100 patients were studied, of which half were suffering from IBS. The researchers’ objective was to examine which cells in the immune system, if any, were responsible for opioid secretion in patients with IBS.

For the study, β-endorphin content of specific immune cell lineages in peripheral blood and colonic mucosal biopsies from healthy and IBS patients were compared. The cells were then applied to mice with post-inflammatory chronic visceral hypersensitivity. β-endorphin was primarily identified in monocyte/macrophages relative to T or B cells in human peripheral blood mononuclear cells (PBMCs) and colonic lamina propria.

The researchers also found monocyte-derived β-endorphin levels and colonic macrophage were higher in healthy patients when compared to their IBS counterparts. The investigators also noted PBMC supernatants from healthy subjects showed significantly more inhibitory effects on colorectal afferent mechanosensitivity than their IBS counterparts.

“IBS patients have lower monocyte derived β-endorphin levels than healthy subjects, causing less inhibition of colonic afferent endings,” the researchers concluded in their report. “Consequently, altered immune function contributes toward visceral hypersensitivity in IBS.

In healthy mice, the inhibitory effects of PBMC supernatants were more prominent than chronic visceral hypersensitivity (CVH) mice, which researchers attributed to an increase in μ-opioid receptor expression in dorsal root ganglia neurons in the CVH mice.

“This study is the first to give us a real understanding of the interaction between the immune system and pain symptoms in IBS patients,” the study’s lead author Patrick Hughes, PhD, NHMRC Peter Doherty Fellow with the University's School of Medicine, said in a press release. “The gut contains specialized immune cells, known as monocytes and macrophages. Our research has shown that in healthy people, these immune cells normally secrete opioid chemicals, like morphine, that block pain. But in people with IBS, the opioid production by these cells is defective. So it’s no wonder that people with IBS are experiencing ongoing periods of unexplained pain. And if the immune system is defective, it may also mean that painkilling medications taken by the patient to relieve their symptoms are not being adequately converted to pain relief.”

Hughes and his team hope that their research can contribute to more developments in targeted IBS treatment plans, or treatments to prevent the long-term pain IBS patients experience.