Effect of Antibiotics on Enteric Neurons and Glia

Overview

The interactions between bacteria and their products with the intestinal tissue are important for maintaining a healthy and balanced system. Alterations in gut bacteria communities have been associated with various human pathologies. The investigators have found that mice treated with short and long-term antibiotics exhibit a transient yet profound loss of neurons in the more superficial submucosal and deeper muscularis plexi in the intestine accompanied by slow motility. Glia cells also depend on microbiota for their maintenance. In humans, antibiotic use has been associated with disorders of gut-brain interactions (DGBI) such as irritable bowel syndrome however whether there are changes in the enteric neurons and glia cells remain unknown. Therefore, the investigators propose to further characterize the neurons and glia populations in the human distal colon after a single antibiotic course. This study will reveal glia and neuronal subtypes that are susceptible to changes in the bacteria populations and depend on microbial products for their maintenance. These findings will guide future DGBI studies to ascertain the physiological effects that such loss has on intestinal healthy balance.

The enteric nervous system (ENS) has been recognized as the "second brain" as it can regulate enteric physiology without central nervous system input. Similar to the central nervous system, it is composed of multiple neuron populations whose main functions are gut motility, secretion, and absorption. In addition to the neurons, the ENS contains glia cells whose main role is neuroprotection but also contribute to normal gut motility. Several studies have demonstrated that the microbiota and the ENS have an intimate relationship that begins in utero, and it is critical for its normal development. Neurons can recognize bacteria and their products. Several investigators have shown neuronal loss after enteric infections and antibiotic (Ampicillin) treatment in the muscularis layer, that results in delayed transit time in animal models. Hence, communication between the microbiota and the ENS is important to maintain normal gut motility. Disorders of Gut-Brain Interactions (DGBIs) are quite common, among these are Irritable Bowel Syndrome (IBS) defined by Rome IV criteria as abdominal pain associated with a change in consistency and frequency of bowel movements and the constipation predominant subtype (less than 3 bowel movements per week) is the most prevalent, which is also the most common motility disorder that mouse models of infection and antibiotics treatment exhibit. IBS has been associated with dysbiosis and a recent study demonstrated that antibiotic use immediately before or after screening colonoscopy increased the risk of developing IBS. In addition, dysfunction of submucosal neurons in IBS has been previously reported but whether there are changes in neuron numbers or neuron characteristics has not been explored. While there have been prospective studies that have explored the effects of antibiotics in patients treated for Helicobacter Pylori, there have been other investigators who have focused on the long term effects of antibiotics in healthy volunteers. Therefore, similar to animal models, investigators propose that humans experience a profound and transient loss/alteration of neurons in the setting of antimicrobial use associated dysbiosis that manifest as DGBIs, most notably the constipation subtypes. This proposal will address whether antimicrobial use leads to quantitative and qualitative changes in the populations of submucosal neurons and glia cells in human subjects. This hypothesis will be tested in a prospective study in which healthy participants will be asked to take the commonly used antibiotic amoxicillin twice a day for 7 days, and colon tissue biopsies will be obtained before and after treatment. Human tissue will be processed and analyzed to visualize structural changes, and changes in gene expression, bacteria, metabolites will be determined through single nuclei RNA sequencing, 16S ribosomal bacteria RNA sequencing and metabolomics analysis respectively.