Altered expression of ATP-sensitive K(+) channels in Hirschsprung's disease

Update on the Pathogenesis of the Hirschsprung-Associated Enterocolitis

Despite the significant progress that has been made in terms of understanding the pathophysiology and risk factors of Hirschsprung-associated enterocolitis (HAEC), the morbidity rate has remained unsatisfactorily stable, and clinical management of the condition continues to be challenging. Therefore, in the present literature review, we summarized the up-to-date advances that have been made regarding basic research on the pathogenesis of HAEC. Original articles published between August 2013 and October 2022 were searched in a number of databases, including PubMed, Web of Science, and Scopus. The keywords "Hirschsprung enterocolitis", "Hirschsprung's enterocolitis", "Hirschsprung's-associated enterocolitis", and "Hirschsprung-associated enterocolitis" were selected and reviewed. A total of 50 eligible articles were obtained. The latest findings of these research articles were grouped into gene, microbiome, barrier function, enteric nervous system, and immune state categories. The present review concludes that HAEC is shown to be a multifactorial clinical syndrome. Only deep insights into this syndrome, with an accrual of knowledge in terms of understanding its pathogenesis, will elicit the necessary changes that are required for managing this disease.

Translational research in Hirschprung's disease at the National Children's Research Centre in Dublin

Hirschsprung's disease (HD) is a congenital condition characterised by aganglionosis in the distal bowel. Over the years, at the National Children's Research Centre (NCRC), HD has been one of the most prominent and successful research areas for Prof. Prem Puri's research team. Research fellows from around the world came to the NCRC to work on both animal and human studies of HD and, cumulatively, made important discoveries in this field, publishing a total of 144 HD articles in peer-reviewed journals. Through their published work, the NCRC has been recognised as the leading international centre for the investigation of HD and its allied disorders. In this review, I will summarise the main findings from this work.

The short form of the SUR1 and its functional implications in the damaged brain

Sulfonylurea receptor (SUR) belongs to the adenosine 5′-triphosphate (ATP)-binding cassette (ABC) transporter family; however, SUR is associated with ion channels and acts as a regulatory subunit determining the opening or closing of the pore. Abcc8 and Abcc9 genes code for the proteins SUR1 and SUR2, respectively. The SUR1 transcript encodes a protein of 1582 amino acids with a mass around 140–177 kDa expressed in the pancreas, brain, heart, and other tissues. It is well known that SUR1 assembles with Kir6.2 and TRPM4 to establish K_ATP channels and non-selective cation channels, respectively. Abbc8 and 9 are alternatively spliced, and the resulting transcripts encode different isoforms of SUR1 and SUR2, which have been detected by different experimental strategies. Interestingly, the use of binding assays to sulfonylureas and Western blotting has allowed the detection of shorter forms of SUR (~65 kDa). Identity of the SUR1 variants has not been clarified, and some authors have suggested that the shorter forms are unspecific. However, immunoprecipitation assays have shown that SUR2 short forms are part of a functional channel even coexisting with the typical forms of the receptor in the heart. This evidence confirms that the structure of the short forms of the SURs is fully functional and does not lose the ability to interact with the channels. Since structural changes in short forms of SUR modify its affinity to ATP, regulation of its expression might represent an advantage in pathologies where ATP concentrations decrease and a therapeutic target to induce neuroprotection. Remarkably, the expression of SUR1 variants might be induced by conditions associated to the decrease of energetic substrates in the brain (e.g. during stroke and epilepsy). In this review, we want to contribute to the knowledge of SUR1 complexity by analyzing evidence that shows the existence of short SUR1 variants and its possible implications in brain function.

Roles of Key Ion Channels and Transport Proteins in Age-Related Hearing Loss

The auditory system is a fascinating sensory organ that overall, converts sound signals to electrical signals of the nervous system. Initially, sound energy is converted to mechanical energy via amplification processes in the middle ear, followed by transduction of mechanical movements of the oval window into electrochemical signals in the cochlear hair cells, and finally, neural signals travel to the central auditory system, via the auditory division of the 8th cranial nerve. The majority of people above 60 years have some form of age-related hearing loss, also known as presbycusis. However, the biological mechanisms of presbycusis are complex and not yet fully delineated. In the present article, we highlight ion channels and transport proteins, which are integral for the proper functioning of the auditory system, facilitating the diffusion of various ions across auditory structures for signal transduction and processing. Like most other physiological systems, hearing abilities decline with age, hence, it is imperative to fully understand inner ear aging changes, so ion channel functions should be further investigated in the aging cochlea. In this review article, we discuss key various ion channels in the auditory system and how their functions change with age. Understanding the roles of ion channels in auditory processing could enhance the development of potential biotherapies for age-related hearing loss.

Increased protease activated receptors in the colon of patients with Hirschsprung's disease

PURPOSE

The pathophysiology of Hirschsprung's associated enterocolitis (HAEC) is not understood. Abnormal intestinal motility and altered intestinal epithelial barrier function have been suggested to play a key role in the causation of HAEC. Protease-activated receptors (PARs) 1 and 2, have been implicated in inflammatory reactions, intestinal permeability and modulation of motility in the gut.

METHODS

We investigated PAR-1 and PAR-2 protein expression in aganglionic and ganglionic regions of patients with Hirschsprung's Disease (HSCR) (n = 10) versus normal control colon (n = 10). Protein distribution was assessed by using immunofluorescence and confocal microscopy. Gene and protein expression were quantified using quantitative real-time polymerase chain reaction (qPCR), western blot analysis, and densitometry.

RESULTS

qPCR and Western blot analysis revealed that PAR-1 and PAR-2 expression was significantly increased in ganglionic and aganglionic bowel in HSCR compared to controls (p < 0.003). Confocal microscopy revealed strong PAR-1 and PAR-2 expression in smooth muscles, interstitial cells of Cajal (ICCs), platelet-derived growth factor-alpha receptor-positive (PDGFRα⁺) cells, enteric neurons and epithelium in the ganglionic and aganglionic bowel compared to controls.

CONCLUSION

Increased PAR-1 and PAR-2 expression in the colon of patients with HSCR suggests that excessive local release of PAR activating proteases may trigger inflammatory responses leading to HAEC.

Postoperative Pullthrough Obstruction in Hirschsprung Disease: Etiologies and Diagnosis

Some patients continue to have obstructive symptoms and/or incontinence after pullthrough surgery for Hirschsprung disease. Incontinence can be due to injury to the anal sphincter and/or dentate line, abnormal colonic motility (nonretentive), or a chronic large stool burden (retentive). A diagnostic algorithm based on clinical and pathological evaluations can be applied to distinguish potential etiologies for obstructive symptoms, which segregate into anatomic (mechanical or histopathological) or physiologic subgroups. Valuable clinical information may be obtained by anorectal examination under anesthesia, radiographic studies, and anorectal or colonic manometry. In addition, histopathological review of a patient's original resection specimen(s) as well as postoperative biopsies of the neorectum usually are an important component of the diagnostic workup. Goals for the surgical pathologist are to exclude incomplete resection of the aganglionic segment or transition zone and to identify other neuromuscular pathology that might explain the patient's dysmotility. Diagnoses established from a combination of clinical and pathological data dramatically alter management strategies. In rare instances, reoperative pullthrough surgery is required, in which case the pathologist must be aware of histopathological features specific to redo pullthrough resection specimens.

Surgery, Surgical Pathology, and Postoperative Management of Patients With Hirschsprung Disease

Endorectal pullthrough surgery is integral in the treatment of patients with Hirschsprung disease. Several different surgical procedures exist, which share as common goals to excise the aganglionic segment and upstream transition zone and attach ganglionic bowel just proximal to the anal canal. The operation requires collaboration between surgeon and pathologist to localize ganglionic bowel and prevent retention of transition zone. Intraoperative frozen sections are extremely important, first to establish that ganglion cells are present and subsequently to exclude features of transition zone (partial circumferential aganglionosis, myenteric hypoganglionosis, and submucosal nerve hypertrophy) at the proximal surgical (anastomotic) margin. Postoperative histopathological analysis of resection specimens should be tailored to document distal aganglionosis, document the length of the aganglionic segment and its proximity to the anastomotic margin, and confirm that transition zone has been resected completely. Adherence to the recommendations described in this review will reduce the likelihood of transition zone pullthrough and should decrease the incidence of persistent postoperative obstructive symptoms.

Laparoscopic-assisted Duhamel procedure with ex-anal rectal transection for total colonic aganglionosis

PURPOSE

Laparoscopic-assisted Duhamel procedure has a larger anastomosis and a reservoir which allows early recovery of defecation frequency, but concerns have been raised regarding the long operative time, high incidence of pouchitis and Hirschsprung associated enterocolitis (HAEC). The purpose of this study was to evaluate the postoperative complications and functional outcomes for patients with TCA undergoing modified laparoscopic-assisted Duhamel procedure (MLDP) with ex-abdominal partial colectomy and ex-anal rectal transection.

METHODS

From 2011 to 2014, 16 patients with TCA who underwent MLDP were reviewed at our institution. Main modified techniques were to mobilize partial bowel through abdominal stoma opening, mobilize remaining colon, and dissect the retro-rectal space using laparoscopy, pull out and transect rectum ex-anally using a linear stapling device for creation of a short rectal pouch of 35~45mm. Seven patients who underwent classical laparoscopic Duhamel procedure (CLDP) with a long rectal pouch of 50-60mm between 2009 and 2011 were used as control group. Data were collected including demographics, laparoscopic technique, operative time, stool frequency, complications and continence outcomes.

RESULTS

The operative time in MLDP group was significantly shorter than control group (3.0h vs. 4.7h, p=0.02). The incidence of postoperative HAEC in MLDP group was lower than control group (12.5% versus 42.9%; p=0.03) within the second postoperative year. Two patients (28.6%) experienced episodes of pouchitis in CLDP group and none was found in MLDP group. There was no significant difference in overall functional outcome between two groups, but the performance of MLDP group was better in terms of diapers required than CLDP group (1.80±0.45 vs. 1.00±0.64; p=0.02). All patients after 4years of age had a normal defecation frequency in both groups.

CONCLUSIONS

MLDP is a safe, simple, and reliable technique for TCA. It has fewer postoperative complications due to the short rectal pouch. However, longer follow-up and a larger sample size are necessary to prove the efficacy in the treatment of TCA.

LEVEL OF EVIDENCE

Level 3.

Reduction of hydrogen sulfide synthesis enzymes cystathionine-β-synthase and cystathionine-γ-lyase in the colon of patients with Hirschsprungs disease

PURPOSE

Hirschsprung associated enterocolitis (HAEC) is the most common cause of morbidity and mortality in Hirschsprung Disease (HSCR). The pathogenesis of HAEC is poorly understood. In recent years, there is increasing evidence that a compromised intestinal barrier function plays a major role in the pathogenesis of HAEC. Hydrogen sulfide, synthesized from L-cysteine by two key enzymes, cystathionine-β-synthase (CBS) and cystathionine-γ-lysase (CSE) is reported to play a key role in regulating gastrointestinal motility and promoting resolution of inflammation. We designed this study to test the hypothesis that CBS and CSE expression is altered in the colon of patients with HSCR.

METHODS

We investigated CBS and CSE protein expression in both the aganglionic and ganglionic regions of HSCR patients (n=10) versus healthy control colon (n=10). Protein distribution was assessed by using immunofluorescence and confocal microscopy. Gene and protein expression was quantified using quantitative real-time polymerase chain reaction (qPCR), Western blot analysis, and densitometry.

MAIN RESULTS

qPCR and Western blot analysis revealed that CBS and CSE are expressed in the normal human colon. CBS and CSE expression was significantly decreased (p<0.003) in the ganglionic and aganglionic bowel in HSCR compared to controls. Confocal microscopy revealed that CBS and CSE expression in smooth muscles, interstitial cells of Cajal, platelet-derived growth factor-alpha receptor-positive cells, enteric neurons and colonic epithelium was markedly decreased in HSCR specimens compared to controls.

CONCLUSION

We demonstrate for the first time the expression and distribution of CBS/CSE in patients with HSCR. The observed decreased expression of CBS and CSE may affect mucosal integrity and colonic contractility and thus render HSCR patients more susceptible to develop HAEC.

Altered expression of a two-pore domain (K2P) mechano-gated potassium channel TREK-1 in Hirschsprung's disease

BACKGROUND

The pathophysiology of Hirschsprung's disease (HSCR) is not fully understood. A significant proportion of patients have persisting bowel symptoms such as constipation, soiling, and enterocolitis despite correctly performed operations. Animal data suggest that stretch-activated 2-pore domain K⁺ channels play a critical role in the maintenance of intestinal barrier integrity.

METHODS

We investigated TREK-1 protein expression in ganglionic and aganglionic regions of HSCR patients (n = 10) vs. normal control colon (n = 10). Protein distribution was assessed by using immunofluorescence and confocal microscopy. Gene and protein expression were quantified using quantitative real-time polymerase chain reaction, western blot analysis, and densitometry.

RESULTS

Confocal microscopy of the normal colon revealed strong TREK-1 channel expression in the epithelium. TREK-1-positive cells were decreased in aganglionic and ganglionic bowel compared to controls. TREK-1 gene expression levels were significantly decreased in aganglionic and ganglionic bowel compared to controls (P < 0.05). Western blotting revealed decreased TREK-1 protein expression in aganglionic and ganglionic bowel compared to controls.

CONCLUSION

We demonstrate, for the first time, the expression and distribution of TREK-1 channels in the human colon. The decreased TREK-1 expression in the aganglionic and ganglionic bowel observed in HSCR may alter intestinal epithelial barrier function leading to the development of enterocolitis.

Laparoscopic-assisted pull-through operation for Hirschsprung's disease: a systematic review and meta-analysis

PURPOSE

In the last two decades, laparoscopic-assisted pull-through (LAPT) has gained much popularity in the treatment of Hirschsprung's disease. The aim of this meta-analysis was to determine the long-term outcome of patients treated laparoscopically.

METHODS

A systematic literature-based search for relevant cohorts was performed using the terms "Hirschsprung's disease and Laparoscopy", "Laparoscopic-assisted pull-through outcome", "Laparoscopic-assisted Soave pull-through" "Laparoscopic-assisted Swenson pull-through" and Laparoscopic-assisted Duhamel pull-through. The relevant cohorts of laparoscopic operated HD were systematically searched for outcome regarding continence, constipation, secondary surgery related to the laparoscopic approach and enterocolitis. Pooled incidence rates and odds ratios (ORs) with 95 % confidence intervals (CI) were calculated using standardized statistical methodology.

RESULTS

Sixteen studies met defined inclusion criteria, reporting a total of 820 patients. All studies were retrospective case series, with variability in outcome assessment quality and length of follow-up. The median cohort size consisted of 28 patients (range 15-218). In the long-term follow-up, 97 patients (11.14 %) experienced constipation (OR 0.06, 95 % CI 0.05-0.08, p < 0.00001), 53 (6.46 %) incontinence/soiling (OR 0.01 95 % CI 0.01-0.01, p < 0.00001), 75 (9.14 %) recurrent enterocolitis (OR 0.02 95 % CI 0.01-0.02, p < 0.00001) and 69 (8.4 %) developed complications requiring secondary surgery (OR 0.01 95 % CI 0.01-0.02, p < 0.00001). Overall events in long-term follow-up occurred in 225 (27.5 %) patients (OR 0.24 95 % CI 0.20-0.30, p < 0.00001).

CONCLUSIONS

This meta-analysis shows that nearly one-third of the patients continue to have long-term bowel problems, such as constipation, soiling and recurrent enterocolitis following LAPT. Many patients treated by LAPT require secondary surgery. Large randomized studies with long-term follow-up are necessary to determine the difference in outcome between LAPT and completely transanal pull-through operation.