Novel hypothesis and therapeutic interventions for irritable bowel syndrome: interplay between metal dyshomeostasis, gastrointestinal dysfunction, and neuropsychiatric symptoms.

Irritable bowel syndrome is a gastrointestinal disorder due to multiple pathologies. While patients with this condition experience anxiety and depressed mood more frequently than healthy individuals, it is unclear how gastrointestinal dysfunction interacts with such neuropsychiatric symptoms. Data suggest that irritable bowel syndrome patients predominantly display a lower zinc intake, which presumably impairs enterochromaffin cells producing 5-hydroxytryptamine, gut bacteria fermenting short-chain fatty acids, and barrier system in the intestine, with the accompanying constipation, diarrhea, low-grade mucosal inflammation, and visceral pain. Dyshomeostasis of copper and zinc concentrations as well as elevated pro-inflammatory cytokine levels in the blood can disrupt blood-cerebrospinal fluid barrier function, leading to locus coeruleus neuroinflammation and hyperactivation with resultant amygdalar overactivation and dorsolateral prefrontal cortex hypoactivation as found in neuropsychiatric disorders. The dysregulation between the dorsolateral prefrontal cortex and amygdala is likely responsible for visceral pain-related anxiety, depressed mood caused by anticipatory anxiety, and visceral pain catastrophizing due to catastrophic thinking or cognitive distortion. Collectively, these events can result in a spiral of gastrointestinal symptoms and neuropsychiatric signs, prompting the progression of irritable bowel syndrome. Given that the negative feedback mechanism in regulation of the hypothalamic-pituitary-adrenal axis is preserved in a subset of neuropsychiatric cases, dorsolateral prefrontal cortex abnormality accompanied by neuropsychiatric symptoms may be a more significant contributing factor in brain-gut axis malfunction than activation of the hypothalamic corticotropin-releasing hormone system. The proposed mechanistic model could predict novel therapeutic interventions for comorbid irritable bowel syndrome and neuropsychiatric disorders.