Linaclotide, through activation of guanylate cyclase C, acts locally in the gastrointestinal tract to elicit enhanced intestinal secretion and transit

A Simple Approach to Assign Disulfide Connectivity for Ziconotide via Partial Reduction Without Alkylation

RATIONALE

Disulfide bond, an important post-translational modification in peptides or proteins, is of great significance for stabilizing the three-dimensional spatial structure of peptides and proteins, maintaining correct folding conformation, and regulating biological activity. The medicinal peptide with unexpected disulfide connectivity might not have efficacy, even induce immunogenicity. Therefore, it is of importance to assign disulfide connectivity for a peptide.

METHODS

A relatively simple method based on partial reduction without alkylation was developed. For demonstration, ziconotide was chosen as a model establishing the method. After a partial reduction reaction by using tris(2-carboxyethyl)phosphine, the partially reduced ziconotide products containing one disulfide bond were analyzed by liquid chromatography tandem mass spectrometry. The information about the sequence uninvolved in the cyclic structure was obtained by tandem mass spectrometry, which reveals the connectivity of the disulfide bridges forming the cyclic structure.

RESULTS

Based on the results of only two partially reduced products, accurate connectivity of all disulfide bridges in ziconotide was obtained. Six cysteine moieties present in a ziconotide molecule form three disulfide bonds, which could produce 15 possible disulfide isoforms with different disulfide connectivities. The actual disulfide connectivity was easily identified using this novel method.

CONCLUSIONS

A relatively simple method based on partial reduction without alkylation, followed by analysis with liquid chromatography-tandem mass spectrometry, was developed, assigning disulfide connectivity for a disulfide-rich peptide. This method is useful in the quality control of medicinal peptides with an extensive disulfide network.

Interferon-responsive intestinal BEST4/CA7+ cells are targets of bacterial diarrheal toxins

BEST4/CA7+ cells of the human intestine were recently identified by single-cell RNA sequencing. While their gene expression profile predicts a role in electrolyte balance, BEST4/CA7+ cell function has not been explored experimentally owing to the absence of BEST4/CA7+ cells in mice and the paucity of human in vitro models. Here, we establish a protocol that allows the emergence of BEST4/CA7+ cells in human intestinal organoids. Differentiation of BEST4/CA7+ cells requires activation of Notch signaling and the transcription factor SPIB. BEST4/CA7+ cell numbers strongly increase in response to the cytokine interferon-γ, supporting a role in immunity. Indeed, we demonstrate that BEST4/CA7+ cells generate robust CFTR-mediated fluid efflux when stimulated with bacterial diarrhea-causing toxins and find the norepinephrine-ADRA2A axis as a potential mechanism in blocking BEST4/CA7+ cell-mediated fluid secretion. Our observations identify a central role of BEST4/CA7+ cells in fluid homeostasis in response to bacterial infections.

The structural integrity of human TFF1 under reducing conditions

The trefoil factor family (TFF) comprises three secretory peptides (TFF1, TFF2, TFF3) that regulate diverse physiological processes to maintain gastrointestinal mucosal integrity and homeostasis. The TFF domain is stabilized by six conserved cysteine residues forming three intramolecular disulfide bonds. In this work, we investigated human TFF1 domain stability against increasing concentrations of the reducing agent tris(2-carboxyethyl)phosphine (TCEP). Experiments revealed high resistance of the disulfide bonds within the TFF1 domain to reduction compared to two reference peptides with similar three-disulfide frameworks, namely the bovine pancreatic trypsin inhibitor (BPTI) and the peptide drug linaclotide. Full reduction of TFF1 was only achieved with a large excess of TCEP (150-fold), and no partially reduced intermediates were observed, supporting a compact TFF1 domain. This TFF1 domain stability was supported by extensive all-atom molecular dynamics simulations for a total of 24 μs of all possible combinatorial states of disulfide bond reduction. Despite minor structural and conformational changes observed upon reduction, the domain substantially retained its overall compactness and solvent exposure when only one or two disulfide bonds were removed. The reduced cysteine residues did not undergo large structural rearrangements and remained buried. The loss of covalent disulfide bonds upon reduction was counterbalanced through persistent non-covalent interactions. These molecular simulations explained why TFF1 could not be partially reduced and alkylated during the experiments despite titrating different TCEP concentrations in the presence of alkylating agents. Our findings provide the first insights into the remarkable stability of the human TFF domain under reducing conditions, supporting its functional resilience upon expression and secretion throughout the human body.

Aging-related impairment of neurogenic chloride secretion in human colon mucosa

Background

lderly individuals are more susceptible to chronic constipation, which may be linked to imbalanced mucosa secretion and absorption. Our research aims to explore the age-related alterations in epithelial chloride secretion within the human colon.

Methods

Colonic mucosal tissues were obtained from 9 young patients (aged 28-35 years), 10 middle-aged patients (aged 48-56 years), 10 elderly patients without constipation (aged 66-75 years), and 12 elderly patients with constipation (aged 65-78 years) who underwent surgery for colonic carcinoma. The epithelial chloride (Cl-) secretion was assessed using the short-circuit current (Isc) method. Comparative analysis was conducted on Cl- secretion induced by spontaneous activity, bethanechol, forskolin, veratridine, and electrical field stimulation (EFS) in the four groups. Additionally, investigations were carried out on changes in cholinergic and VIPergic Cl- secretion.

Results

The spontaneous Cl- secretion was not affected by aging. The increase in Isc induced by bethanechol and forskolin remained unaltered in aged colon. However, the veratridine-induced neurogenic Isc increment were significantly reduced with aging and constipation. The EFS-evoked Isc rising, which typically exhibiting a biphasic pattern, was inhibited by aging in a frequency-dependent manner. Administration of scopolamine and VIP6-28 to block cholinergic and vasoactive intestinal peptide (VIP) receptors led to smaller increases in the first and second phases of the EFS-evoked response in aged colons compared to young colons.

Conclusion

Significant impairments in neurogenic Cl- secretion occur in the aged colon, correlating with the degeneration of cholinergic and VIPergic nerves in the mucosa. This study could enhance our understanding of the pathophysiology of elderly constipation.

Beyond Conventional Drug Design: Exploring the Broad-Spectrum Efficacy of Antimicrobial Peptides

In the fight against pathogenic infections, antimicrobial peptides (AMPs) constitute a novel and promising class of compounds that defies accepted drug development conventions like Lipinski's rule. AMPs are remarkably effective against a variety of pathogens, including viruses, bacteria, parasites, and fungi. Their effectiveness, despite differing from traditional drug-like properties defies accepted standards. This review investigates the complex world of AMPs with an emphasis on their structural and physicochemical properties, which include size, sequence, structure, charge, and half-life. These distinguishing characteristics set AMPs apart from conventional therapeutics that adhere to Lipinski's rules and greatly contribute to their selective targeting, reduction of resistance, multifunctionality, and broad-spectrum efficacy. In contrast to traditional drugs that follow Lipinski's guidelines, AMPs have special qualities that play a big role in their ability to target specific targets, lower resistance, and work across a wide range of conditions. Our work is unique because of this nuanced investigation, which offers a new viewpoint on the potential of AMPs in tackling the worldwide problem of antibiotic resistance. In the face of the escalating global challenge of antibiotic resistance, antimicrobial peptides (AMPs) are innovative antimicrobial agents with unique mechanisms of action that challenge traditional Lipinski's Rule. They can withstand various microbial threats through membrane disruption, intracellular targeting, and immunomodulation. AMP versatility sets them apart from other antibiotics and their potential to address microbial infections and antibiotic resistance is growing. To fully unlock their potential, traditional drug development approaches need to be reconsidered. AMPs have revolutionary potential, paving the way for innovative solutions to health issues and transforming the antimicrobial therapy landscape.

Partially differentiated enterocytes in ileal and distal-colonic human F508del-CF-enteroids secrete fluid in response to forskolin and linaclotide

Constipation causes significant morbidity in Cystic Fibrosis (CF) patients. Using CF patient (F508del) derived ex vivo ileal and distal colonic/rectal enteroids as a model and the Forskolin Induced Swelling Assay (FIS), we compared CFTR mediated fluid secretion in human enterocytes across the crypt-villus axis. CFTR expression and FIS decreased as enterocytes differentiated from crypt to become partially differentiated and then mature villus cells . While there was no FIS response in undifferentiated (crypt enterocytes) F508del-CF enteroids, partially differentiated F508del-CF enteroids had a swelling response to forskolin (cAMP) and linaclotide (cGMP) which was ∼48%, and ∼67% of the response in healthy enteroids, respectively and was prevented by a CFTR inhibitor. Also, linaclotide and a general PDE inhibitor independently enhanced combined CFTR-modulator-induced FIS response from partially differentiated F508del-CF enteroids. These findings demonstrate that partially differentiated ileal and distal colonic F508del-CFTR enteroids can be stimulated to secrete fluid by cAMP and cGMP.

cDNA Display Selection of Interacting Peptide Ligands of the Guanylate Cyclase C Receptor

Guanylate cyclase C (GC-C), a receptor expressed on the apical membrane of intestinal mucosal cells, is activated by heat-stable enterotoxin (STa) produced by enterotoxigenic Escherichia coli, as well as the endogenous ligands guanylin and uroguanylin. In this study, novel peptides that interact with GC-C were generated using the cDNA display method, and their binding affinity and biological activity were evaluated. While the linear peptide library did not yield peptides with sufficient affinity for GC-C, three cyclic peptides (GCC-P1, GCC-P2, and GCC-P3), each containing two cysteine residues within a 15-residue sequence, were obtained from a cyclic peptide library containing nine-residue random sequences. GC-P2 exhibited significant binding affinity in Biacore assays, although the affinity was lower than those reported for known ligands. Notably, GCC-P2 and GCC-P3 demonstrated enhanced cGMP activity when used in combination with linaclotide. However, the agonist activity of these peptides was minimal, indicating that further modifications may be necessary to develop them for clinical applications. This study successfully extracted consensus sequences of peptide motifs that bind to GC-C from a highly diverse nine-residue random sequence library, which provides fundamental insights for the discovery and optimization of novel GC-C ligands.

Oxytocin Analogues for the Oral Treatment of Abdominal Pain

Abdominal pain presents an onerous reality for millions of people affected by gastrointestinal disorders such as irritable bowel syndrome (IBS) and inflammatory bowel diseases (IBD). The oxytocin receptor (OTR) has emerged as a new analgesic drug target with OTR expression upregulated on colon-innervating nociceptors in chronic visceral hypersensitivity states, accessible via luminal delivery. However, the low gastrointestinal stability of OTR's endogenous peptide ligand oxytocin (OT) is a bottleneck for therapeutic development. Here, we report the development of potent and fully gut-stable OT analogues, laying the foundation for a new area of oral gut-specific peptide therapeutics. Ligand optimisation guided by structure-gut-stability-activity relationships yielded highly stable analogues (t1/2>24 h, compared to t1/2<10 min of OT in intestinal fluid) equipotent to OT (~3 nM) and with enhanced OTR selectivity. Intra-colonic administration of the lead ligand significantly reduced colonic mechanical hypersensitivity in a concentration-dependent manner in a mouse model of chronic abdominal pain. Moreover, oral administration of the lead ligand also displayed significant analgesia in this abdominal pain mouse model. The generated ligands and employed strategies could pave the way to a new class of oral gut-specific peptides to study and combat chronic gastrointestinal disorders, an area with substantial unmet medical needs.

Application of linaclotide in bowel preparation for colonoscopy in patients with constipation: A prospective randomized controlled study

BACKGROUND AND AIM

Colonoscopy plays a crucial role in the early diagnosis and treatment of colorectal cancer. Adequate bowel preparation is essential for clear visualization of the colonic mucosa and lesion detection. However, inadequate bowel preparation is common in patients with constipation, and there is no standardized preparation protocol for these patients. This study aimed to explore the effectiveness and tolerability of a pre-colonoscopy combination regimen of linaclotide and polyethylene glycol (PEG).

METHODS

In this prospective, single-center, randomized controlled trial, 322 participants were divided into two groups: a 3-L PEG + 870-μg linaclotide group (administered as a single dose for 3 days) and a 4-L PEG group. The primary endpoints were the Boston Bowel Preparation Scale (BBPS) score and the rate of adequate and excellent bowel preparation. Secondary endpoints were the rates of detection of colonic adenomas and polyps, cecal intubation rates, colonoscopy time, adverse reactions, patient satisfaction, and physician satisfaction.

RESULTS

The study included 319 patients. The 3-L PEG + linaclotide group showed significantly higher rates of adequate and excellent bowel preparation than the 4-L PEG group (89.4% vs 73.6% and 37.5% vs 25.3%, respectively; P < 0.05). The mean BBPS score for the right colon in the 3-L PEG + linaclotide group was significantly higher than that in the 4-L PEG group. There were no significant between-group differences regarding the detection rates of colonic polyps and adenomas (44.4% vs 37.7% and 23.1% vs 20.1%, respectively; P > 0.05). There were no significant between-group differences regarding cecal intubation rates, colonoscopy operation, and withdrawal times. However, patient tolerance and sleep quality were better in the 3-L PEG + linaclotide group.

CONCLUSION

The combination of 3-L PEG and 870-μg linaclotide, because of its lower volume of intake, can be considered as an alternative bowel preparation regimen for constipated patients undergoing colonoscopy, especially for the elderly.

Bowel preparation efficacy and discomfort of 2 L polyethylene glycol combined with linaclotide versus 3 L polyethylene glycol: a noninferiority, prospective, multicenter, randomized controlled trial

Background

Three liters of polyethylene glycol administered in a split dose is a commonly recommended regimen for bowel preparation before colonoscopy.

Objectives

The aim of this study was to compare the quality and tolerability of low-dose (2 L) polyethylene glycol combined with linaclotide (2 L+L) versus the 3 L polyethylene glycol (PEG) bowel preparation regimen.

Design

A noninferiority, prospective, multicenter, randomized controlled trial.

Methods

In this noninferiority, prospective, multicenter, randomized controlled study, patients scheduled for colonoscopy were enrolled and randomized to receive a 3 L PEG or 2L PEG+L regimen. The quality of bowel preparation and patients' discomfort was assessed.

Results

Over 12 months, 458 patients were randomized into 3 L PEG and 2 L+L groups. The primary endpoints showed that the 2 L+L regimen was superior to the 3L PEG regimen in overall bowel cleansing scores (Ottawa Bowel Preparation Scale: 3.3 ± 2.1 vs 3.7 ± 2.1, p = 0.021), but no significant difference in adequate bowel preparation rate between the two groups according to the OBPS score (97% vs 97.4%, p = 0.791). Before colonoscopy, patients in the 2 L +L regimen group had lower bloating scores (0.5 (0, 2) vs 1 (0, 3), p = 0.013), discomfort scores (1 (0, 2) vs 1 (0, 3), p = 0.006), and intolerability scores (1 (0, 3) vs 2 (0, 4), p = 0.016) than did those in the 3L PEG group.

Conclusion

Two liters of polyethylene glycol combined with linaclotide may be an alternative regimen to 3 L of PEG taken in split doses for bowel preparation before colonoscopy.

Trial registration

ChiCTR2100041992.

Recent Progress on Transition Metal Catalyzed Macrocyclizations Based on C-H Bond Activation at Heterocyclic Scaffolds

Macrocycles are essential in protein-protein interactions and the preferential intake of bioactive scaffolds. Macrocycles are commonly synthesized by late-stage macrolactonizations, macrolactamizations, transition metal-catalyzed ring-closing metathesis, S-S bond-forming reactions, and copper-catalyzed alkyne-azide cycloaddition. Recently, transition metal-catalyzed C-H activation strategies have gained significant interest among chemists to synthesize macrocycles. This article provides a comprehensive overview of the transition metal-catalyzed macrocyclization via C-H bond functionalization of heterocycle-containing peptides, annulations, and heterocycle-ring construction through direct C-H bond functionalization. In the first part, palladium salt catalyzed coupling with indolyl C(sp3)-H and C(sp2)-H bonds for macrocyclization is reported. The second part summarizes rhodium-catalyzed macrocyclizations via site-selective C-H bond functionalization. Earth-abundant, less toxic 3d metal salt Mn-catalyzed cyclizations are reported in the latter part. This summary is expected to spark interest in emerging methods of macrocycle production among organic synthesis and chemical biology practitioners, helping to develop the discipline. We hope that this mini-review will also inspire synthetic chemists to explore new and broadly applicable C-C bond-forming strategies for macrocyclization via intramolecular C-H activation.

Review of the Patient Burden and Therapeutic Landscape of Irritable Bowel Syndrome with Constipation in the United States

Irritable bowel syndrome (IBS) is a common disorder of the gut-brain axis. IBS with constipation (IBS-C) accounts for approximately one-third of IBS cases and is associated with substantial burden of illness and decreased quality of life. This narrative review provides an overview of the current and upcoming treatment options and disease management for IBS-C from a US perspective and discusses the importance of the relationship between patient and health care provider in diagnosis and treatment. A positive diagnostic strategy for IBS-C is recommended, based on clinical history, physical examination, and minimal laboratory tests. An effective communication strategy between patients and health care professionals is essential to ensure early diagnosis and reduce both health care costs and overall disease burden. Treatment typically begins with lifestyle interventions and nonpharmacologic options, such as dietary interventions, fiber supplements, and osmotic laxatives. In patients with inadequate response to these therapies, 4 currently available therapies (lubiprostone, linaclotide, plecanatide, and tenapanor) approved by the US Food and Drug Administration may relieve IBS-C symptoms. These agents are generally well tolerated and efficacious in improving IBS-C symptoms, including constipation and abdominal pain. In patients with persistent abdominal pain and/or psychological symptoms, brain-gut behavioral therapy or neuromodulator therapy may be beneficial.

Examining linaclotide for the treatment of chronic idiopathic constipation

INTRODUCTION

Chronic idiopathic constipation (CIC) is characterized by infrequent bowel movements and hard stools lasting for at least three months or longer. This disease affects 8-12% of the US population and 10-17% of the world population. Treatment and management involve identifying the primary cause, changing dietary habits, and adequate physical activity. Linaclotide is a guanylate cyclase-agonist acting locally in the luminal surface of the intestinal enterocyte leading to a signal transduction cascade, activation of the cystic fibrosis transmembrane conductance regulator (CFTR), thus increasing secretion of chloride and bicarbonate into the intestinal lumen with eventual increased intestinal fluid and faster transit time.

AREAS COVERED

We reviewed multiple studies and did a thorough literature review on CIC including its pathophysiology. Through this literature review, we were able to discuss and give the context and rationale for drug regimens indicated for CIC.

EXPERT OPINION

The era we live in right now is akin to nutrient-rich and fertilized soil as knowledge and resources are abundant. The opportunities and potential are endless. Constipation being more extensively studied, our understanding of medications and diseases broadens, leading to novel medications being discovered. Linaclotide is a pioneer in this aspect and can pave the way for future generations.

DRA involvement in linaclotide-stimulated bicarbonate secretion during loss of CFTR function

Duodenal bicarbonate secretion is critical to epithelial protection, as well as nutrient digestion and absorption, and is impaired in cystic fibrosis (CF). We examined if linaclotide, typically used to treat constipation, may also stimulate duodenal bicarbonate secretion. Bicarbonate secretion was measured in vivo and in vitro using mouse and human duodenum (biopsies and enteroids). Ion transporter localization was identified with confocal microscopy, and de novo analysis of human duodenal single-cell RNA sequencing (scRNA-Seq) data sets was performed. Linaclotide increased bicarbonate secretion in mouse and human duodenum in the absence of cystic fibrosis transmembrane conductance regulator (CFTR) expression (Cftr-knockout mice) or function (CFTRinh-172). Na+/H+ exchanger 3 inhibition contributed to a portion of this response. Linaclotide-stimulated bicarbonate secretion was eliminated by down-regulated in adenoma (DRA, SLC26A3) inhibition during loss of CFTR activity. ScRNA-Seq identified that 70% of villus cells expressed SLC26A3, but not CFTR, mRNA. Loss of CFTR activity and linaclotide increased apical brush border expression of DRA in non-CF and CF differentiated enteroids. These data provide further insights into the action of linaclotide and how DRA may compensate for loss of CFTR in regulating luminal pH. Linaclotide may be a useful therapy for CF individuals with impaired bicarbonate secretion.

Key role of down-regulated in adenoma (SLC26A3) chloride/bicarbonate exchanger in linaclotide-stimulated intestinal bicarbonate secretion upon loss of CFTR function

Duodenal bicarbonate secretion is critical to epithelial protection, nutrient digestion/absorption and is impaired in cystic fibrosis (CF). We examined if linaclotide, typically used to treat constipation, may also stimulate duodenal bicarbonate secretion. Bicarbonate secretion was measured in vivo and in vitro using mouse and human duodenum (biopsies and enteroids). Ion transporter localization was identified with confocal microscopy and de novo analysis of human duodenal single cell RNA sequencing (sc-RNAseq) datasets was performed. Linaclotide increased bicarbonate secretion in mouse and human duodenum in the absence of CFTR expression (Cftr knockout mice) or function (CFTRinh-172). NHE3 inhibition contributed to a portion of this response. Linaclotide-stimulated bicarbonate secretion was eliminated by down-regulated in adenoma (DRA, SLC26A3) inhibition during loss of CFTR activity. Sc-RNAseq identified that 70% of villus cells expressed SLC26A3, but not CFTR, mRNA. Loss of CFTR activity and linaclotide increased apical brush border expression of DRA in non-CF and CF differentiated enteroids. These data provide further insights into the action of linaclotide and how DRA may compensate for loss of CFTR in regulating luminal pH. Linaclotide may be a useful therapy for CF individuals with impaired bicarbonate secretion.

The gut microbiota participates in the effect of linaclotide in patients with irritable bowel syndrome with constipation (IBS-C): a multicenter, prospective, pre-post study

BACKGROUND

Interindividual variation characterizes the relief experienced by constipation-predominant irritable bowel syndrome (IBS-C) patients following linaclotide treatment. Complex bidirectional interactions occur between the gut microbiota and various clinical drugs. To date, no established evidence has elucidated the interactions between the gut microbiota and linaclotide. We aimed to explore the impact of linaclotide on the gut microbiota and identify critical bacterial genera that might participate in linaclotide efficacy.

METHODS

IBS-C patients were administered a daily linaclotide dose of 290 µg over six weeks, and their symptoms were then recorded during a four-week posttreatment observational period. Pre- and posttreatment fecal samples were collected for 16S rRNA sequencing to assess alterations in the gut microbiota composition. Additionally, targeted metabolomics analysis was performed for the measurement of short-chain fatty acid (SCFA) concentrations.

RESULTS

Approximately 43.3% of patients met the FDA responder endpoint after taking linaclotide for 6 weeks, and 85% of patients reported some relief from abdominal pain and constipation. Linaclotide considerably modified the gut microbiome and SCFA metabolism. Notably, the higher efficacy of linaclotide was associated with enrichment of the Blautia genus, and the abundance of Blautia after linaclotide treatment was higher than that in healthy volunteers. Intriguingly, a positive correlation was found for the Blautia abundance and SCFA concentrations with improvements in clinical symptoms among IBS-C patients.

CONCLUSION

The gut microbiota, especially the genus Blautia, may serve as a significant predictive microbe for symptom relief in IBS-C patients receiving linaclotide treatment.

TRIAL REGISTRATION

This trial was registered with the Chinese Clinical Trial Registry (Chictr.org.cn, ChiCTR1900027934).

The evolutionary divergence of receptor guanylyl cyclase C has implications for preclinical models for receptor-directed therapeutics

Mutations in receptor guanylyl cyclase C (GC-C) cause severe gastrointestinal disease, including meconium ileus, early onset acute diarrhea, and pediatric inflammatory bowel disease that continues into adulthood. Agonists of GC-C are US Food and Drug Administration-approved drugs for the treatment of constipation and irritable bowel syndrome. Therapeutic strategies targeting GC-C are tested in preclinical mouse models, assuming that murine GC-C mimics human GC-C in its biochemical properties and downstream signaling events. Here, we reveal important differences in ligand-binding affinity and GC activity between mouse GC-C and human GC-C. We generated a series of chimeric constructs of various domains of human and mouse GC-C to show that the extracellular domain of mouse GC-C contributed to log-orders lower affinity of mouse GC-C for ligands than human GC-C. Further, the Vmax of the murine GC domain was lower than that of human GC-C, and allosteric regulation of the receptor by ATP binding to the intracellular kinase-homology domain also differed. These altered properties are reflected in the high concentrations of ligands required to elicit signaling responses in the mouse gut in preclinical models and the specificity of a GC inhibitor towards human GC-C. Therefore, our studies identify considerations in using the murine model to test molecules for therapeutic purposes that work as either agonists or antagonists of GC-C, and vaccines for the bacterial heat-stable enterotoxin that causes watery diarrhea in humans.

Microbiota-derived butyrate dampens linaclotide stimulation of the guanylate cyclase C pathway in patient-derived colonoids

BACKGROUND & AIMS

Disorders of gut-brain interaction (DGBI) are complex conditions that result in decreased quality of life and a significant cost burden. Linaclotide, a guanylin cyclase C (GCC) receptor agonist, is approved as a DGBI treatment. However, its efficacy has been limited and variable across DGBI patients. Microbiota and metabolomic alterations are noted in DGBI patients, provoking the hypothesis that the microbiota may impact the GCC response to current therapeutics.

METHODS

Human-derived intestinal organoids were grown from pediatric DGBI, non-IBD colon biopsies (colonoids). Colonoids were treated with 250 nM linaclotide and assayed for cGMP to develop a model of GCC activity. Butyrate was administered to human colonoids overnight at a concentration of 1 mM. Colonoid lysates were analyzed for cGMP levels by ELISA. For the swelling assay, colonoids were photographed pre- and post-treatment and volume was measured using ImageJ. Principal coordinate analyses (PCoA) were performed on the Bray-Curtis dissimilarity and Jaccard distance to assess differences in the community composition of short-chain fatty acid (SCFA) producing microbial species in the intestinal microbiota from pediatric patients with IBS and healthy control samples.

KEY RESULTS

Linaclotide treatment induced a significant increase in [cGMP] and swelling of patient-derived colonoids, demonstrating a human in vitro model of linaclotide-induced GCC activation. Shotgun sequencing analysis of pediatric IBS patients and healthy controls showed differences in the composition of commensal SCFA-producing bacteria. Butyrate exposure significantly dampened linaclotide-induced cGMP levels and swelling in patient-derived colonoids.

CONCLUSIONS & INFERENCES

Patient-derived colonoids demonstrate that microbiota-derived butyrate can dampen human colonic responses to linaclotide. This study supports incorporation of microbiota and metabolomic assessment to improve precision medicine for DGBI patients.

Fundamental Neurochemistry Review: The role of enteroendocrine cells in visceral pain

While visceral pain is commonly associated with disorders of the gut-brain axis, underlying mechanisms are not fully understood. Dorsal root ganglion (DRG) neurons innervate visceral structures and undergo hypersensitization in inflammatory models. The characterization of peripheral DRG neuron terminals is an active area of research, but recent work suggests that they communicate with enteroendocrine cells (EECs) in the gut. EECs sense stimuli in the intestinal lumen and communicate information to the brain through hormonal and electrical signaling. In that context, EECs are a target for developing therapeutics to treat visceral pain. Linaclotide is an FDA-approved treatment for chronic constipation that activates the intestinal membrane receptor guanylyl cyclase C (GUCY2C). Clinical trials revealed that linaclotide relieves both constipation and visceral pain. We recently demonstrated that the analgesic effect of linaclotide reflects the overexpression of GUCY2C on neuropod cells, a specialized subtype of EECs. While this brings some clarity to the relationship between linaclotide and visceral analgesia, questions remain about the intracellular signaling mechanisms and neurotransmitters mediating this communication. In this Fundamental Neurochemistry Review, we discuss what is currently known about visceral nociceptors, enteroendocrine cells, and the gut-brain axis, and ongoing areas of research regarding that axis and visceral pain.

Bowel preparation efficacy and safety of compound polyethylene glycol electrolyte powder combined with linaclotide for colonoscopy: A randomized controlled trial

Background and Aim

Adequate bowel preparation is essential for colonoscopy, which is important for detecting colon polyps and preventing colorectal cancer. Linaclotide is approved for irritable bowel syndrome with predominant constipation (IBS-C) symptoms. The main objective of this study was to explore the quality of bowel preparation by low-volume compound polyethylene glycol (PEG) combined with linaclotide.

Methods

A total of 266 patients who underwent colonoscopy in Shangrao People's Hospital from June 2021 to June 2022 were randomized to 1 of 3 split PEG regimens: 4LPEG, 2LPEG, and 2LPEG + L (linaclotide). The primary end point was adequate bowel preparation (Boston Bowel Preparation Scale [BBPS] total score of ≥6, with each of three colonic segments subscores ≥2). Secondary outcomes were polyp detection rates and the incidence of adverse reactions.

Results

Over 12 months, 266 subjects were randomized into 2LPEG (n = 12), 4LPEG (n = 112), or 2LPEG + L (n = 142). There were no significant differences between the 4LPEG and 2LPEG + L groups in achieving adequate bowel preparation (P > 0.05). The mean BBPS score of the total colon, left hemi-colon, right hemi-colon, and transverse in the 2LPEG + L group was higher than that in the 2LPEG group (P < 0.001). Patient's sleeping quality and the incidence of adverse reactions of 2LPEG + L group were compatible with 2LPEG group, but it was significantly lower than that in 4LPEG group. There was no statistically significant difference in the detection rate of colon polyps between each group.

Conclusion

The quality of bowel preparation of the compound polyethylene glycol electrolyte powder combined with linaclotide is approximately the same as that of 4LPEG, and it can reduce the adverse reactions in the process of bowel preparation, and its intestinal cleansing effect is also better than that of 2LPEG.

A New Regioselective Synthesis of the Cysteine-Rich Peptide Linaclotide

Linaclotide is a 14-amino acid residue peptide approved by the FDA for the treatment of irritable bowel syndrome with constipation (IBS-C), which activates guanylate cyclase C to accelerate intestinal transit. Here we show a new method for the synthesis of linaclotide through the completely selective formation of three disulfide bonds in satisfactory overall yields via mild oxidation reactions of the solid phase and liquid phase, using 4-methoxytrityl (Mmt), diphenylmethyl (Dpm) and 2-nitrobenzyl (O-NBn) protecting groups of cysteine as substrate, respectively.

Involvement of Intestinal Enteroendocrine Cells in Neurological and Psychiatric Disorders

Neurological and psychiatric patients have increased dramatically in number in the past few decades. However, effective treatments for these diseases and disorders are limited due to heterogeneous and unclear pathogenic mechanisms. Therefore, further exploration of the biological aspects of the disease, and the identification of novel targets to develop alternative treatment strategies, is urgently required. Systems-level investigations have indicated the potential involvement of the brain–gut axis and intestinal microbiota in the pathogenesis and regulation of neurological and psychiatric disorders. While intestinal microbiota is crucial for maintaining host physiology, some important sensory and regulatory cells in the host should not be overlooked. Intestinal epithelial enteroendocrine cells (EECs) residing in the epithelium throughout intestine are the key regulators orchestrating the communication along the brain-gut-microbiota axis. On one hand, EECs sense changes in luminal microorganisms via microbial metabolites; on the other hand, they communicate with host body systems via neuroendocrine molecules. Therefore, EECs are believed to play important roles in neurological and psychiatric disorders. This review highlights the involvement of EECs and subtype cells, via secretion of endocrine molecules, in the development and regulation of neurological and psychiatric disorders, including Parkinson’s disease (PD), schizophrenia, visceral pain, neuropathic pain, and depression. Moreover, the current paper summarizes the potential mechanism of EECs in contributing to disease pathogenesis. Examination of these mechanisms may inspire and lead to the development of new aspects of treatment strategies for neurological and psychiatric disorders in the future.

On the Utility of Chemical Strategies to Improve Peptide Gut Stability

Inherent susceptibility of peptides to enzymatic degradation in the gastrointestinal tract is a key bottleneck in oral peptide drug development. Here, we present a systematic analysis of (i) the gut stability of disulfide-rich peptide scaffolds, orally administered peptide therapeutics, and well-known neuropeptides and (ii) medicinal chemistry strategies to improve peptide gut stability. Among a broad range of studied peptides, cyclotides were the only scaffold class to resist gastrointestinal degradation, even when grafted with non-native sequences. Backbone cyclization, a frequently applied strategy, failed to improve stability in intestinal fluid, but several site-specific alterations proved efficient. This work furthermore highlights the importance of standardized gut stability test conditions and suggests defined protocols to facilitate cross-study comparison. Together, our results provide a comparative overview and framework for the chemical engineering of gut-stable peptides, which should be valuable for the development of orally administered peptide therapeutics and molecular probes targeting receptors within the gastrointestinal tract.

Foundations of gastrointestinal-based drug delivery and future developments

Gastrointestinal-based drug delivery is considered the preferred mode of drug administration owing to its convenience for patients, which improves adherence. However, unique characteristics of the gastrointestinal tract (such as the digestive environment and constraints on transport across the gastrointestinal mucosa) limit the absorption of drugs. As a result, many medications, in particular biologics, still exist only or predominantly in injectable form. In this Review, we examine the fundamentals of gastrointestinal drug delivery to inform clinicians and pharmaceutical scientists. We discuss general principles, including the challenges that need to be overcome for successful drug formulation, and describe the unique features to consider for each gastrointestinal compartment when designing drug formulations for topical and systemic applications. We then discuss emerging technologies that seek to address remaining obstacles to successful gastrointestinal-based drug delivery.

Nutrition management in adults with cystic fibrosis

Cystic fibrosis (CF) is a lethal, monogenic, autosomal recessive disease with manifestations in multiple organ systems, including the lungs and gastrointestinal tract, that impact adequate nutrition. This review discusses important aspects of nutrition in adults with CF with a focus on exocrine pancreatic insufficiency, CF-related diabetes, and gastrointestinal motility, as well as how advanced lung disease, CF transmembrane conductance regulator modulators, and aging impact nutrition in CF.

Guanylate cyclase-C agonists as peripherally acting treatments of chronic visceral pain

Irritable bowel syndrome (IBS) is a chronic gastrointestinal disorder characterized by abdominal pain and altered bowel habit that affects ~11% of the global population. Over the past decade, preclinical and clinical studies have revealed a variety of novel mechanisms relating to the visceral analgesic effects of guanylate cyclase-C (GC-C) agonists. Here we discuss the mechanisms by which GC-C agonists target the GC-C/cyclic guanosine-3',5'-monophosphate (cGMP) pathway, resulting in visceral analgesia as well as clinically relevant relief of abdominal pain and other sensations in IBS patients. Due to the preponderance of evidence we focus on linaclotide, a 14-amino acid GC-C agonist with very low oral bioavailability that acts within the gut. Collectively, the weight of experimental and clinical evidence supports the concept that GC-C agonists act as peripherally acting visceral analgesics.

Pain in irritable bowel syndrome: Does anything really help?

Pain relief remains a significant challenge in the management of irritable bowel syndrome (IBS): "Does anything really help relieve the pain in patients with IBS?". Interventions aimed at pain relief in patients with IBS include diet, probiotics or antibiotics, antidepressants, antispasmodics, and drugs targeting specific gastrointestinal receptors such as opioid or histamine receptors. In the systematic review and meta-analysis published in this journal, Lambarth et al. examined the literature on the role of oral and parenteral anti-neuropathic agents in the management of pain in patients with IBS. This review article appraises their assessment of the efficacy of the anti-neuropathic agents amitriptyline, pregabalin, gabapentin, and duloxetine in the relief of abdominal pain or discomfort, and impact on overall IBS severity and quality of life. This commentary provides an update of current evidence on the efficacy of the dietary and pharmacological treatments that are available or in development, as well psychological and cognitive behavioral therapy for pain in IBS. Advances in recent years augur well for efficacious treatments that may expand the therapeutic arsenal for pain in IBS.

Diarrhea-Predominant and Constipation-Predominant Irritable Bowel Syndrome: Current Prescription Drug Treatment Options

Irritable bowel syndrome (IBS) is a heterogenous disease with a variety of therapeutic options, including eight prescription drugs approved for use in IBS in the USA. Choosing among the myriad treatment options requires attention to patient preferences both on clinical outcomes and costs associated with treatment. We performed a narrative review of the literature to summarize these important determinants of treatment choice including: labeled indications; clinical profiles of efficacy, safety, and tolerability of prescription drugs; and cost-effectiveness for diarrhea-predominant IBS drugs (IBS-D: alosetron, eluxadoline, and rifaximin) and constipation-predominant IBS drugs (IBS-C: linaclotide, lubiprostone, plecanatide, tegaserod, and tenapanor). We then review the standard model of shared decision-making aimed at guiding an informed, patient-centered discussion to integrate comparative clinical and cost outcomes toward choosing an IBS treatment in practice.

Phase I double-blind, placebo-controlled trial of dolcanatide (SP-333) 27 mg to explore colorectal bioactivity in healthy volunteers

Guanylyl cyclase C (GUCY2C) is a tumor-suppressing receptor silenced by loss of expression of the luminocrine hormones guanylin and uroguanylin early in colorectal carcinogenesis. This observation suggests oral replacement with a GUCY2C agonist may be an effective targeted chemoprevention agent. Previous studies revealed that linaclotide, an oral GUCY2C agonist formulated for gastric release, did not persist to activate guanylyl cyclase signaling in the distal rectum. Dolcanatide is an investigational oral uroguanylin analog, substituted with select D amino acids, for enhanced stability and extended persistence to activate GUCY2C in small and large intestine. However, the ability of oral dolcanatide to induce a pharmacodynamic (PD) response by activating GUCY2C in epithelial cells of the colorectum in humans remains undefined. Here, we demonstrate that administration of oral dolcanatide 27 mg daily for 7 d to healthy volunteers did not activate GUCY2C, quantified as accumulation of its product cyclic GMP, in epithelial cells of the distal rectum. These data reveal that the enhanced stability of dolcanatide, with persistence along the rostral-caudal axis of the small and large intestine, is inadequate to regulate GUCY2C across the colorectum to prevent tumorigenesis. These results highlight the importance of developing a GUCY2C agonist for cancer prevention formulated for release and activity targeted to the colorectum.

Comparative transcriptome analysis revealed omnivorous adaptation of the small intestine of Melinae

As the main digestive organ, the small intestine plays a vital role in the digestion of animals. At present, most of the research on animal feeding habits focuses on carnivores and herbivores. However, the mechanism of feeding and digestion in omnivores remains unclear. This study aims to reveal the molecular basis of the omnivorous adaptive evolution of Melinae by comparing the transcriptome of the small intestines of Asian Badgers (Meles leucurus) and Northern Hog Badgers (Arctonyx albogularis). We obtained high-quality small intestinal transcriptome data from these two species. Key genes and signalling pathways were analysed through Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) and other databases. Research has mainly found that orthologous genes related to six enzymes have undergone adaptive evolution. In addition, the study also found three digestion-related pathways (cGMP-PKG, cAMP, and Hippo). They are related to the digestion and absorption of nutrients, the secretion of intestinal fluids, and the transport of food through the small intestine, which may help omnivorous animals adapt to an omnivorous diet. Our study provides insight into the adaptation of Melinae to omnivores and affords a valuable transcriptome resource for future research.

Efficacy of Linaclotide in Reducing Abdominal Symptoms of Bloating, Discomfort, and Pain: A Phase 3B Trial Using a Novel Abdominal Scoring System

INTRODUCTION

Linaclotide improves abdominal pain and constipation in patients with constipation-predominant irritable bowel syndrome (IBS-C). Patients report additional bothersome abdominal symptoms of bloating and discomfort. The intention of this study was to evaluate linaclotide's efficacy in relieving IBS-C-related abdominal symptoms (bloating, discomfort, and pain) using a novel multi-item Abdominal Score (AS).

METHODS

Patients with IBS-C with abdominal pain ≥3 (0-10 scale) were randomized to linaclotide 290 μg or placebo daily for 12 weeks. The AS, derived from the Diary for IBS Symptoms-Constipation, is the average of abdominal bloating, discomfort, and pain at their worst (0 = none, 10 = worst possible). The primary end point was overall change from baseline (CFB) in AS. Secondary end points included CFB in 12-week AS evaluated using cumulative distribution function and 6-week/12-week AS responder (AS improvement ≥2 points for ≥6-week/12-week).

RESULTS

Overall, 614 patients (mean age 46.7 years; 81% female) were randomized. All prespecified end points showed significant benefit of linaclotide vs placebo. The mean overall CFB AS reduction for linaclotide was -1.9 vs -1.2 for placebo (P < 0.0001); the 6-week/12-week AS responder rate was 40.5% for linaclotide vs 23.4% for placebo (odds ratio = 2.2 [95% confidence interval, 1.55-3.12; P < 0.0001]). Diarrhea was the most common treatment-emergent adverse event (linaclotide = 4.6%, placebo = 1.6%).

DISCUSSION

Linaclotide significantly reduced multiple abdominal symptoms important to patients with IBS-C (bloating, discomfort, and pain) compared with placebo, as measured by a novel multi-item AS. The AS, derived from the Diary for IBS Symptoms-Constipation, should be considered for use in future IBS-C clinical studies to measure clinically meaningful improvements beyond traditional end points.

Oral delivery of proteins and peptides: Challenges, status quo and future perspectives

Proteins and peptides (PPs) have gradually become more attractive therapeutic molecules than small molecular drugs due to their high selectivity and efficacy, but fewer side effects. Owing to the poor stability and limited permeability through gastrointestinal (GI) tract and epithelia, the therapeutic PPs are usually administered by parenteral route. Given the big demand for oral administration in clinical use, a variety of researches focused on developing new technologies to overcome GI barriers of PPs, such as enteric coating, enzyme inhibitors, permeation enhancers, nanoparticles, as well as intestinal microdevices. Some new technologies have been developed under clinical trials and even on the market. This review summarizes the history, the physiological barriers and the overcoming approaches, current clinical and preclinical technologies, and future prospects of oral delivery of PPs.

The α isoform of cGMP-dependent protein kinase 1 (PKG1α) is expressed and functionally important in intrinsic primary afferent neurons of the guinea pig enteric nervous system

BACKGROUND

Intrinsic primary afferent neurons (IPANs) enable the gut to manifest reflexes in the absence of CNS input. PKG1α is selectively expressed in a subset of neurons in dorsal root ganglia (DRG) and has been linked to nociception and long-term hyperexcitability.

METHODS

We used immunoblotting, immunocytochemistry, and in vitro assays of IPAN-dependent enteric functions to test hypotheses that subsets of primary neurons of the ENS and DRG share a reliance on PKG1α expression.

KEY RESULTS

PKG1α immunoreactivity was demonstrated in immunoblots from isolated myenteric ganglia. PKG1α, but not PKG1β, immunoreactivity, was coincident with that of neuronal markers (HuC/D; β3-tubulin) in both enteric plexuses. PKG1α immunoreactivity also co-localized with the immunoreactivities of the IPAN markers, calbindin (100%; myenteric plexus) and cytoplasmic NeuN (98 ± 1% submucosal plexus). CGRP-immunoreactive DRG neurons, identified as visceral afferents by retrograde transport, were PKG1α-immunoreactive. We used intraluminal cholera toxin to determine whether PKG1α was necessary to enable stimulation of the mucosa to activate Fos in enteric neurons. Tetrodotoxin (1.0 µM), low Ca2+ /high Mg2+ media, and the PKG inhibitor, N46 (100 µM), all inhibited Fos activation in myenteric neurons. N46 also concentration dependently inhibited peristaltic reflexes in isolated preparations of distal colon (IC50  = 83.3 ± 1.3 µM).

CONCLUSIONS & INFERENCES

These data suggest that PKG1α is present and functionally important in IPANs and visceral afferent nociceptive neurons.

Action Mode of Gut Motility, Fluid and Electrolyte Transport in Chronic Constipation

Chronic constipation is a common gastrointestinal disorder, with a worldwide incidence of 14–30%. It negatively affects quality of life and is associated with a considerable economic burden. As a disease with multiple etiologies and risk factors, it is important to understand the pathophysiology of chronic constipation. The purpose of this review is to discuss latest findings on the roles of gut motility, fluid, and electrolyte transport that contribute to chronic constipation, and the main drugs available for treating patients. We conducted searches on PubMed and Google Scholar up to 9 February 2021. MeSH keywords “constipation”, “gastrointestinal motility”, “peristalsis”, “electrolytes”, “fluid”, “aquaporins”, and “medicine” were included. The reference lists of searched articles were reviewed to identify further eligible articles. Studies focusing on opioid-induced constipation, evaluation, and clinic management of constipation were excluded. The occurrence of constipation is inherently connected to disorders of gut motility as well as fluid and electrolyte transport, which involve the nervous system, endocrine signaling, the gastrointestinal microbiota, ion channels, and aquaporins. The mechanisms of action and application of the main drugs are summarized; a better understanding of ion channels and aquaporins may be helpful for new drug development. This review aims to provide a scientific basis that can guide future research on the etiology and treatment of constipation.

British Society of Gastroenterology guidelines on the management of irritable bowel syndrome

Irritable bowel syndrome (IBS) remains one of the most common gastrointestinal disorders seen by clinicians in both primary and secondary care. Since publication of the last British Society of Gastroenterology (BSG) guideline in 2007, substantial advances have been made in understanding its complex pathophysiology, resulting in its re-classification as a disorder of gut-brain interaction, rather than a functional gastrointestinal disorder. Moreover, there has been a considerable amount of new evidence published concerning the diagnosis, investigation and management of IBS. The primary aim of this guideline, commissioned by the BSG, is to review and summarise the current evidence to inform and guide clinical practice, by providing a practical framework for evidence-based management of patients. One of the strengths of this guideline is that the recommendations for treatment are based on evidence derived from a comprehensive search of the medical literature, which was used to inform an update of a series of trial-based and network meta-analyses assessing the efficacy of dietary, pharmacological and psychological therapies in treating IBS. Specific recommendations have been made according to the Grading of Recommendations Assessment, Development and Evaluation system, summarising both the strength of the recommendations and the overall quality of evidence. Finally, this guideline identifies novel treatments that are in development, as well as highlighting areas of unmet need for future research.

Improving the Gastrointestinal Stability of Linaclotide

High susceptibility to proteolytic degradation in the gastrointestinal tract limits the therapeutic application of peptide drugs in gastrointestinal disorders. Linaclotide is an orally administered peptide drug for the treatment of irritable bowel syndrome with constipation (IBS-C) and abdominal pain. Linaclotide is however degraded in the intestinal environment within 1 h, and improvements in gastrointestinal stability might enhance its therapeutic application. We therefore designed and synthesized a series of linaclotide analogues employing a variety of strategic modifications and evaluated their gastrointestinal stability and pharmacological activity at its target receptor guanylate cyclase-C. All analogues had substantial improvements in gastrointestinal half-lives (>8 h vs linaclotide 48 min), and most remained active at low nanomolar concentrations. This work highlights strategic approaches for the development of gut-stable peptides toward the next generation of orally administered peptide drugs for the treatment of gastrointestinal disorders.

Randomized Trial of 2 Delayed-Release Formulations of Linaclotide in Patients With Irritable Bowel Syndrome With Constipation

INTRODUCTION

Immediate-release (IR) formulation of linaclotide 290 μg improves abdominal pain and constipation (APC) in patients with irritable bowel syndrome (IBS) with constipation. Delayed-release (DR) formulations were developed on the premise that targeting the ileum (delayed-release formulation 1 [DR1]) or ileocecal junction and cecum (MD-7246, formerly DR2) would modulate linaclotide's secretory effects while preserving pain relief effects.

METHODS

This phase 2b study randomized patients with IBS with constipation to placebo or 1 of 7 once-daily linaclotide doses (DR1 30, 100, or 300 μg; MD-7246 30, 100, or 300 μg; or IR 290 μg) for 12 weeks. Key efficacy endpoints were change from baseline in abdominal pain and complete spontaneous bowel movement frequency, and 6/12-week combined APC+1 responder rate.

RESULTS

Overall, 532 patients were randomized; mean age was 45.1 years, and most were women (83.3%) and White (64.7%). All linaclotide DR1 and MD-7246 groups experienced greater improvements in abdominal pain from baseline and vs placebo throughout treatment. Linaclotide DR1 and IR led to numerically greater improvements from baseline in complete spontaneous bowel movement frequency and higher APC+1 responder rates compared with placebo; MD-7246 results were similar to placebo. Diarrhea was the most common adverse event with DR1 and IR; rates were similar between MD-7246 and placebo.

DISCUSSION

Altering the site of drug delivery in the intestine might uncouple linaclotide's pain relief from secretory effects. Persistent, modest abdominal pain improvement with limited impact on bowel symptom parameters, as seen across MD-7246 doses, warrants further study of MD-7246 as a novel treatment for abdominal pain, regardless of IBS subtype.

Importance of Non-pharmacological Approaches for Treating Irritable Bowel Syndrome: Mechanisms and Clinical Relevance

Chronic visceral pain represents a major unmet clinical need with the severity of pain ranging from mild to so severe as to prevent individuals from participating in day-to-day activities and detrimentally affecting their quality of life. Although chronic visceral pain can be multifactorial with many different biological and psychological systems contributing to the onset and severity of symptoms, one of the major triggers for visceral pain is the exposure to emotional and physical stress. Chronic visceral pain that is worsened by stress is a hallmark feature of functional gastrointestinal disorders such as irritable bowel syndrome (IBS). Current pharmacological interventions for patients with chronic visceral pain generally lack efficacy and many are fraught with unwanted side effects. Cognitive behavioral therapy (CBT) has emerged as a psychotherapy that shows efficacy at ameliorating stress-induced chronic visceral pain; however, the molecular mechanisms underlying CBT remain incompletely understood. Preclinical studies in experimental models of stress-induced visceral pain employing environmental enrichment (EE) as an animal model surrogate for CBT are unraveling the mechanism by which environmental signals can lead to long-lasting changes in gene expression and behavior. Evidence suggests that EE signaling interacts with stress and nociceptive signaling. This review will (1) critically evaluate the behavioral and molecular changes that lead to chronic pain in IBS, (2) summarize the pharmacological and non-pharmacological approaches used to treat IBS patients, and (3) provide experimental evidence supporting the potential mechanisms by which CBT ameliorates stress-induced visceral pain.

Comparative Efficacy of Drugs for the Treatment of Chronic Constipation: Quantitative Information for Medication Guidelines

BACKGROUND

Quantitative information is scarce with regard to guidelines for currently prescribed medications for constipation. Furthermore, these guidelines do not reflect the differences in the number of bowel movements caused by each drug.

GOALS

In this study, we used a model-based meta-analysis to quantitatively estimate the deviations from the baseline number of spontaneous bowel movements (SBMs) and complete spontaneous bowel movements (CSBMs) associated with pharmacotherapy for chronic constipation to bridge the knowledge gap in the guidelines for current medications.

STUDY

A comprehensive survey was conducted using literature databases. In this study, we also included randomized placebo-controlled trials on chronic constipation. Pharmacodynamic models were established to describe the time course of the numbers of SBMs and CSBMs produced by each drug.

RESULTS

Data from 20 studies (comprising 9998 participants and 8 drugs) were used to build this model. The results showed that bisacodyl had the greatest effect on increasing the frequency of bowel movements, whereas plecanatide yielded the lowest increase in the number of SBMs and CSBMs. After eliminating the placebo effect, the maximal increase in bowel movement frequency associated with bisacodyl was 6.8 for SBMs (95% confidence interval: 6.1-7.6) and 4.7 for CSBMs (95% confidence interval: 4.3-5.1) per week. These numbers are ∼4 times higher than the number of bowel movements produced by plecanatide. The change in the frequency of SBMs and CSBMs for other drugs, such as sodium picosulfate, velusetrag, linaclotide, elobixibat, lubiprostone, and prucalopride, was similar. The highest increases in the frequency of SBM and CSBM were 2.5 to 4 and 1 to 2.1 per week, respectively. Bisacodyl had the most noticeable loss of efficacy between week 1 and week 4; it reduced the frequencies of SBMs and CSBMs by 2.3 and 2.2, respectively. By contrast, the changes in the frequencies of SBMs and CSBMs were not as great with other drugs.

CONCLUSIONS

The data provided in this study may be a valuable supplement to the medication guidelines for the treatment of chronic constipation.

An overview of interventions for constipation in adults

INTRODUCTION

The increasing global prevalence of the symptoms of constipation adversely affects the quality of life (QOL) of symptomatic patients. An acceptable universal definition of constipation does not exist and a detailed history taking form each patient with various complaints including stool consistency, sensing of incomplete evacuation or a manual need to assist evacuation is required. Complexity of obtaining etiologic diagnosis and the wide range of therapeutic options can mislead physicians in choosing correct treatment.

AREAS COVERED

This review, considers the pathophysiology of constipation and the diagnostic approach to identify the etiology of constipation. Available interventions including non-pharmacological, pharmacological, and invasive methods such as acupuncture and surgical management are discussed. This review utilized on PubMed, Google Scholar, Scopus, and clinicaltrials.gov to search for studies and reviews published between 2000 and 2020.

EXPERT COMMENTARY

Constipation necessitates careful considerations to detect the exact pathophysiology. Medical history, focused physical assessments, and selected diagnostic tests help choosing the right management. Non-pharmacological methods are beneficial in most of the cases. If a satisfactory response is not achieved, over the counter or prescribed medications are available. Options for patients who failed to respond to available medications are addressed in this review.

Recent Advances and Computational Approaches in Peptide Drug Discovery

BACKGROUND

Drug design and development is a vast field that requires huge investment along with a long duration for providing approval to suitable drug candidates. With the advancement in the field of genomics, the information about druggable targets is being updated at a fast rate which is helpful in finding a cure for various diseases.

METHODS

There are certain biochemicals as well as physiological advantages of using peptide-based therapeutics. Additionally, the limitations of peptide-based drugs can be overcome by modulating the properties of peptide molecules through various biomolecular engineering techniques. Recent advances in computational approaches have been helpful in studying the effect of peptide drugs on the biomolecular targets. Receptor - ligand-based molecular docking studies have made it easy to screen compatible inhibitors against a target.Furthermore, there are simulation tools available to evaluate stability of complexes at the molecular level. Machine learning methods have added a new edge by enabling accurate prediction of therapeutic peptides.

RESULTS

Peptide-based drugs are expected to take over many popular drugs in the near future due to their biosafety, lower off-target binding chances and multifunctional properties.

CONCLUSION

This article summarises the latest developments in the field of peptide-based therapeutics related to their usage, tools, and databases.

Tadalafil versus linaclotide in gastrointestinal dysfunction and depressive behavior in constipation-predominant irritable bowel syndrome

BACKGROUND

Intestinal GC-C/cGMP pathway may be involved in visceral hypersensitivity and fluid secretion in irritable bowel syndrome (IBS). The guanylcyclase C agonist linaclotide, approved for IBS- constipation, is contraindicated in children as it may cause severe diarrhea. In contrast, drugs increasing cGMP by inhibiting phosphodiesterase 5 (PDE-5) are well tolerated in children with pulmonary hypertension. Accordingly, we investigated whether beneficial effects of linaclotide in IBS might be shared by PDE-5inhibitor tadalafil without the severe diarrhea reported for linaclotide. Since depression is commonly comorbid with IBS and is implicated in its pathophysiology; and since tadalafil is absorbed systemically and crosses blood brain barrier, whereas linaclotide does not, impact of both drugs on behavioral changes in IBS was also investigated.

METHODS

72 rats were divided into 6groups (control naive, control tadalafil, control linaclotide, untreated IBS, IBS tadalafil, and IBS linaclotide-treated). IBS was induced by 0 to 4 °C intragastric saline for 14 days.

RESULTS

Both drugs reduced visceral hypersensitivity and colonic C fos. Tadalafil, and to a greater extent, linaclotide increased colonic cGMP, fecal pellets (8.66 ± 4.6 (IBS),versus14.8 ± 3.3(tadalafil), 20 ± 1.2(linaclotide), fecal water content (29.8 ± 5.5 (IBS), versus 47.83 ± 12.6 (tadalafil), 63.58 ± 11.6 (linaclotide) and reduced intestinal transit time (% distance travelled: 29 ± 6.1(IBS), versus 40.58 + 7.5(tadalafil), 51.83 ± 8.3(linaclotide). Tadalafil, but not linaclotide, increased hippocampal cGMP, and improved behavioral tests scores compared to linaclotide (immobility time: 97.3 ± 12.5 s (IBS) versus 68 ± 12.8(tadalafil), 80 ± 17.06 (linaclotide).

CONCLUSION

Systemic PDE-5 inhibitors might be alternatives to locally acting guanyl cyclase agonists in IBS, inducing less severe diarrhea and more beneficial effects on the associated behavioral changes.

Efficacy and safety of linaclotide for opioid-induced constipation in patients with chronic noncancer pain syndromes from a phase 2 randomized study

Constipation is the most common adverse event (AE) of opioid therapy. This multicenter, phase 2 study evaluated the efficacy and safety of linaclotide in treating opioid-induced constipation (OIC) in patients with chronic noncancer pain syndromes (NCT02270983). Adults with OIC (<3 spontaneous bowel movements [SBMs]/week) related to chronic noncancer pain were randomized 1:1:1 to receive linaclotide 145 µg, linaclotide 290 µg, or placebo once daily for 8 weeks. The primary endpoint was change from baseline in 8-week SBM frequency rate (SBMs/week). Secondary efficacy endpoints included 6/8-week SBM 3 + 1 responders, time to first SBM, and changes from baseline in 8-week stool consistency, abdominal bloating, and straining. Additional endpoints included treatment satisfaction and adequate relief responders. In total, 254 patients were randomized: 87, 88, and 79 received linaclotide 145 µg, linaclotide 290 µg, and placebo, respectively. The mean changes from baseline in SBMs/week during the treatment period were 2.9 and 3.5 in the linaclotide 145 and 290 µg groups (P < 0.01 for both doses), respectively, vs 1.6 in the placebo group. Diarrhea, the most common AE, was generally mild, resulting in 1.1%, 5.7%, and 1.3% of patients discontinuing in the linaclotide 145 μg, linaclotide 290 μg, and placebo groups, respectively. No serious AEs related to diarrhea were reported in any treatment group. Compared with placebo, linaclotide-treated patients had significant improvements in stool consistency, straining, abdominal bloating, and treatment satisfaction scores (P < 0.05). Linaclotide significantly improved OIC symptoms and was well tolerated in patients with chronic noncancer pain.

Epithelial-Neuronal Communication in the Colon: Implications for Visceral Pain

Visceral hypersensitivity and pain result, at least in part, from increased excitability of primary afferents that innervate the colon. In addition to intrinsic changes in these neurons, emerging evidence indicates that changes in lining epithelial cells may also contribute to increased excitability. Here we review recent studies on how colon epithelial cells communicate directly with colon afferents. Specifically, anatomical studies revealed specialized synaptic connections between epithelial cells and nerve fibers and studies using optogenetic activation of the epithelium showed initiation of pain-like responses. We review the possible mechanisms of epithelial-neuronal communication and provide an overview of the possible neurotransmitters and receptors involved. Understanding the biology of this interface and how it changes in pathological conditions may provide new treatments for visceral pain conditions.

Postprandial regulation of prouroguanylin in humans of a healthy weight and those who are overweight or with obesity

Uroguanylin is a peptide gut hormone proposed to have a role in signalling post meal satiety. Uroguanylin circulates as its pro-hormone, prouroguanylin. There has been limited investigation of the regulation of prouroguanylin by food; therefore we investigated prouroguanylin regulation following meals. In separate experiments we investigated the effects of high calorie (1451 kcal) and medium calorie (725 kcal), high fat meals, on plasma prouroguanylin concentrations. We then examined the effect of a 722.5 kcal high carbohydrate breakfast on prouroguanylin concentrations, comparing the response in healthy weight adults versus those who are overweight/ with obesity. The 1451 kcal meal increased prouroguanylin concentrations, versus fasting at 60 (P < 0.05), 90 (P < 0.01) and 120 (P < 0.001) minutes. After the 725 kcal meal hormone concentrations rose more slowly and were significant versus fasting concentrations at 120 min (P < 0.01). The high carbohydrate breakfast 722.5 kcal, led to an initial suppression of hormone concentrations at 30 min. post meal (P < 0.05) followed by an increase in concentrations until they were significant versus fasting at 120 min. (P < 0.01). Participants overweight/ with obesity had lower fasting prouroguanylin concentrations (P < 0.05), but post meal concentrations did not differ between the groups. Our results suggest there is a delayed increase in prouroguanylin concentrations following, large and regular sized mixed macronutrient meals rich in fat or carbohydrate. Fasting levels are suppressed in people who are overweight/ with obesity, but the post meal response remains intact. There may be potential to target post meal release of prouroguanylin in obesity.

Multicentre, non-interventional study of the efficacy and tolerability of linaclotide in the treatment of irritable bowel syndrome with constipation in primary, secondary and tertiary centres: the Alpine study

OBJECTIVES

We evaluated the effectiveness and tolerability of linaclotide, a minimally absorbed guanylate cyclase-C agonist, in patients with irritable bowel syndrome with constipation (IBS-C) in routine clinical practice.

SETTING

A multicentre, non-interventional study conducted between December 2013 and November 2015 across 31 primary, secondary and tertiary centres in Austria and Switzerland.

PARTICIPANTS

The study enrolled 138 patients aged ≥18 years with moderate-to-severe IBS-C. Treatment decision was at the physician's discretion. Patients with known hypersensitivity to the study drug or suspected mechanical obstruction were excluded. The mean age of participants was 50 years, and >75% of the patients were women. 128 patients completed the study.

PRIMARY AND SECONDARY OUTCOME MEASURES

Data were collected at weeks 0 and 4 in Austria and weeks 0, 4 and 16 in Switzerland. The primary effectiveness endpoints included severity of abdominal pain and bloating (11-point numerical rating scale [0=no pain/bloating to 10=worst possible pain/bloating]), frequency of bowel movements and physicians' global effectiveness of linaclotide. Treatment-related adverse events (AEs) were recorded.

RESULTS

Following a 4-week treatment period, the mean intensity score of abdominal pain was reduced from 5.8 at baseline to 2.7, while the bloating intensity score was reduced from 5.8 at baseline to 3.1e (both indices p<0.001). The frequency of mean weekly bowel movements increased from 2.1 at baseline to 4.5 at week 4 (p<0.001). Global effectiveness and tolerability of linaclotide were assessed by the treating physicians as 'good' or 'excellent' in >70% of patients. In total, 31 AEs were reported in 22 patients, the most common being diarrhoea, reported by 6 (7%) and 8 (15.4%) patients in Austria and Switzerland, respectively.

CONCLUSIONS

Patients with IBS-C receiving linaclotide experienced effective treatment of moderate-to-severe symptoms in routine clinical practice. Linaclotide was safe and well tolerated and no new safety concerns were raised, supporting results from previous clinical trials.

What's in the pipeline for lower functional gastrointestinal disorders in the next 5 years?

The overall objectives of this review are to summarize actionable biomarkers for organic etiology of lower functional gastrointestinal disorders (FGIDs) that lead to individualized treatment for their FGIDs and to assess the pipeline for novel approaches to the management of constipation, diarrhea, and chronic abdominal pain in lower FGIDs. The new approaches to therapy include ion exchangers/transporters for functional constipation (sodium-glucose cotransporter 1, Na+/H+ exchanger 3, and solute carrier family 26 member 3 inhibitors), bile acid modulators for constipation such as ileal bile acid transporter inhibitors and fibroblast growth factor 19 analog for functional constipation, and bile acid sequestrants or farnesoid X receptor agonists for functional diarrhea. Treatment for chronic abdominal pain remains an unmet need in patients with lower FGIDs, and promising novel approaches include delayed-release linaclotide, nonclassical opioid visceral analgesics, and selective cannabinoid receptor agonists. The role of probiotics, fecal microbial transplantation, and possible future microbiome therapies is discussed.