In a small study of Hirschsprung’s disease (HSCR) patients, those with a low-fiber colonic mucosal acetylcholinesterase-positive (AChE+) innervation phenotype were more likely to suffer from postoperative enterocolitis, which can be life-threatening.
The study lends insight into crosstalk between the human enteric nervous and immune systems. It suggests a role for acetylcholine-secreting (cholinergic) nerve fibers in aganglionic sections of colon in patients with HSCR, which is a congenital disorder marked by the absence of enteric neuronal cells in the distal part of the gut.
There are also potential clinical implications. “These observations suggest that HSCR patients with low-fiber phenotype might have a higher risk of developing postoperative enterocolitis and that the fiber phenotype could serve as a predictive marker for development of prophylactic therapy,” wrote Simone Keck of the University of Basel (Switzerland) and colleagues in apublished in Cellular and Molecular Gastroenterology and Hepatology.
HSCR is a multigenetic congenital condition that includes a lack of enteric ganglia cells (aganglionosis) in the distal part of the colon, leading to intestinal obstruction and prestenotic megacolon. Treatment consists of pull-through surgery to remove the aganglionic portion of the bowel, but 20%-50% of patients develop life-threatening HSCR-associated enterocolitis before or after surgery. Although the mechanism of the complication is uncertain, immune cells, intestinal barrier function, and the microbiome may play a role.
Mouse models have shown connections between the immune and nervous system, but it has been challenging to study the effects of specific neurotransmitters in humans. There are more than 30 separate neurotransmitters in the enteric nervous system, making it difficult to tease apart individual functions. But there are comparatively few enteric nervous system neurotransmitters in patients with HSCR and the aganglionic colon in these patients contains enlarged AChE+ nerve fibers, “neuronal cholinergic function can be examined particularly well” among these patients. .
The researchers of the current study from analyzed tissue from 44 pediatric HSCR patients who underwent pull-through surgery, along with 6 non-HSCR controls who had surgery for various other reasons. Tissue samples were semiquantitatively categorized according to the extent of colonic mucosal AChE+ innervation: Low-fiber rectosigmoid tissue lacked intrinsic nerve cell bodies and mucosal ACHe+ innervation, while high-fiber tissue lacked nerve cell bodies but had mucosal AChE+ innervation. The researchers also determined tissue cytokine profile and immune cell frequencies, and used confocal immunofluorescence microscopy to determine proximity of macrophages to nerve fibers and 16S-rDNA sequencing to determine microbial populations.
They found that aganglionic low-fiber samples had higher levels of inflammatory cytokines such as interleukin-17, IL-1-beta, and IL6. Levels of these cytokines were lower in both ganglionic sections of the colon and in high-fiber samples with mucosal AChE+ nerve fibers. Low-fiber samples also had elevated Th17 T cells, compared with high-fiber, aganglionic, and ganglionic distal colon samples. Regulatory T cells were highest in cholinergic high-fiber segments.
Out of 42 patients, 9 developed enterocolitis within 1 year of surgery; 7 had a low-fiber phenotype, while 2 were high-fiber. This difference was not statistically significant, but the researchers then performed a retrospective analysis of 29 HSCR patients to validate the findings. Of these, 14 developed enterocolitis after surgery, with 12 of the cases occurring among children with the low-fiber phenotype, and 2 cases occurred among those with the high-fiber phenotype.
The findings could help guide postsurgical management of HSCR by allowing clinicians to employ preventive measures against enterocolitis, such as high-volume enemas, antibiotics, prebiotics, probiotics, or dietary changes. Th17 cells are known to migrate to nearby mesenteric lymph nodes, where they may promote enterocolitis, and this site is usually not removed during HSCR surgery. Fiber phenotype could prompt a surgeon to also remove mesenteric lymph nodes to reduce enterocolitis risk. A potential therapeutic strategy is to target IL-17 or IL-23.
The study was funded by the University of Basel. The authors have no relevant financial disclosures.