Changes in neuromuscular structure and functions of human colon during ageing are region-dependent

Overall and Regional Colonic Transit Abnormalities in Elderly Patients with Constipation

OBJECTIVE

Chronic constipation (CC) more frequently affects the elderly; pelvic floor dysfunction (PFD) may confuse the appraisal of the pathophysiology of CC. The aim was to characterize colonic transit (CT) in elderly with CC with/without PFD.

DESIGN

We conducted retrospective medical records review of 191 patients ≥ 65 years who underwent scintigraphic CT for assessing CC. Overall CT and distribution of isotopes in 4 colonic regions and stool were compared with 179 healthy controls < 65 years and 183 CC < 66 years. Presence of PFD, comorbidities, and concomitant medications were documented. Data shown are median (IQR).

RESULTS

Elderly CC patients were predominantly female (69.3%), aged 70 (67,74) years, with PFD in 56.9%. Elderly CC had overall slower CT (geometric center) at 48 h [2.5 (2.0,3.48)] compared to controls [3.79 (2.69,4.69)], but overall and proximal CT were not different compared to CC < 66 years. Combined ascending and transverse colon (AC + TC) at 48 h was lower in elderly CC [51.1 (14.4,76.5)] % compared to healthy controls [86.5 (53.6, 100)% p < 0.001]. There was no difference in overall CT among elderly CC with and without PFD. Among groups with PFD, the elderly CC (compared to CC < 66y) had higher AC + TC emptying at 24 h (8.6% [IQR 0.0-30.2] vs 0.3% [0.0-20.6] p = 0.042), but not at 48 h.

CONCLUSION

Overall and proximal CT of elderly with CC was slower to healthy controls, but similar to adults < 66 years with CC. In the 56.9% elderly CC with PFD, overall CT and AC + TC emptying were similar to those without PFD.

Multi-omics revealed that the postbiotic of hawthorn-probiotic alleviated constipation caused by loperamide in elderly mice

Background

Constipation is a prevalent and recurrent gastrointestinal disorder causing significant discomfort. However, current treatments often prove ineffective. Previous research indicates that the postbiotic derived from a combination of hawthorn and probiotics can alleviate constipation. This study aimed to investigate its mechanisms using loperamide-induced constipation in aged KM mice.

Methods

Constipated mice were divided into groups receiving 10% lactulose (Y), hawthorn extract (S), probiotics (F), and the postbiotic of hawthorn-probiotic (FS). UPLC–MS metabolomics identified constituents of F, S, and FS. Network pharmacological analysis identified targets affected by FS. RT-qPCR assessed target expression in mouse colons, along with IL-6 and IL-17A levels. Molecular docking with AutoDock Tools1.5.6 evaluated interactions between FS components and targets. ex vivo colonic organ culture and RT-qPCR assessed target changes. Molecular dynamics analysis further scrutinized interactions. Targeted metabolomics measured short-chain fatty acid levels in mouse stool.

Results

UPLC–MS metabolomics revealed distinct profiles for F, S, and FS, with FS showing decreased toxic substances and increased beneficial ones compared to S. Network pharmacology identified 20 cross-targets of FS in constipation. RT-qPCR showed decreased NR1I2 and SULT1A1 and increased GLP-2r in FS-treated mice. Inflammatory cytokines IL-6 and IL-17A were also reduced. ex vivo colonic organ culture and molecular docking identified effective combinations such as TNF-Baicalin and AQP3-Quinacridone. RMSD, RMSF, and RG analyses indicated favorable interactions between small molecules and targets. Targeted metabolomics revealed differing short-chain fatty acid contents in feces among groups.

Conclusion

The postbiotic of hawthorn-probiotic alleviates constipation by regulating intestinal water and sodium metabolism, maintaining the intestinal barrier and gut flora, promoting epithelial cell proliferation, reducing inflammatory responses, and improving short-chain fatty acid metabolism.

Leaky gut in systemic inflammation: exploring the link between gastrointestinal disorders and age-related diseases

Global average life expectancy has steadily increased over the last several decades and is projected to reach ~ 77 years by 2050. As it stands, the number of people > 60 years currently outnumbers children younger than 5 years, and by 2050, it is anticipated that the global population of people aged > 60 years will double, surpassing 2.1 billion. This demographic shift in our population is expected to have substantial consequences on health services globally due to the disease burden associated with aging. Osteoarthritis, chronic obstructive pulmonary disease, diabetes, cardiovascular disease, and cognitive decline associated with dementia are among the most common age-related diseases and contribute significantly to morbidity and mortality in the aged population. Many of these age-related diseases have been linked to chronic low-grade systemic inflammation which often accompanies aging. Gastrointestinal barrier dysfunction, also known as "leaky gut," has been shown to contribute to systemic inflammation in several diseases including inflammatory bowel disease and irritable bowel syndrome, but its role in the development and/or progression of chronic low-grade systemic inflammation during aging is unclear. This review outlines current literature on the leaky gut in aging, how leaky gut might contribute to systemic inflammation, and the links between gastrointestinal inflammatory diseases and common age-related diseases to provide insight into a potential relationship between the intestinal barrier and inflammation.

Decreases in mucosally-evoked tachykinin signaling pathways can explain age-related reductions in murine colonic motility patterns

BACKGROUND

Increasing age increases the incidence of chronic constipation and fecal impaction. The contribution of the natural aging process to this phenotype is unclear. This study explored the effects of age on key motility patterns in the murine colon and determined the contribution that altered neurokinin 2 (NK2) -mediated signaling made to the aging phenotype.

METHODS

Mucosal reflexes, colonic migrating motor complexes (CMMCs) and colonic motility assays were explored in isolated ex vivo colons from 3, 12-14, 18- and 24-months old mice and the NK2-mediated response determined. Electrical field stimulation (EFS) or exogenous drug application were used to explore the role of the mucosa in colonic segments.

KEY RESULTS

Aging reduced the force of contraction of the distal colon mucosal reflex, the frequency and force of contraction of CMMCs and the NK2-mediated component of both motility patterns. Ondansetron, a 5-HT3 receptor antagonist, blocked a component of both motility patterns in full thickness but not in mucosa-free segments of the distal colon. 5, hydroxytryptamine (5-HT) and EFS-evoked NK2-dependent contractions were reduced with increasing age. Smooth muscle sensitivity to 5-HT or neurokinin A (NKA) was not altered with age. In isolated colon motility assays application of NKA decreased transit time in 24-months colon and the NK2 antagonist GR159897 increased transit times in both 3- and 24-months old colons.

CONCLUSIONS AND INFERENCES

Aging impairs key motility patterns in the murine colon. These changes involve a decrease in mucosally-evoked NK2-mediated signaling. Targeting NK2-mediated signaling may provide a novel approach to treating age-related motility disorders in the lower bowel.

Slow gut transit increases the risk of Alzheimer's disease: An integrated study of the bi-national cohort in South Korea and Japan and Alzheimer's disease model mice

INTRODUCTION

Although the association between Alzheimer's disease (AD) and constipation is controversial, its causality and underlying mechanisms remain unknown.

OBJECTIVES

To investigate the potential association between slow gut transit and AD using epidemiological data and a murine model.

METHODS

We conducted a bi-national cohort study in South Korea (discovery cohort, N=3,130,193) and Japan (validation cohort, N=4,379,285) during the pre-observation period to determine the previous diagnostic history (2009-2010) and the follow-up period (2011-2021). To evaluate the causality, we induced slow gut transit using loperamide in 5xFAD transgenic mice. Changes in amyloid-beta (Aβ) and other markers were examined using ELISA, qRT-PCR, RNA-seq, and behavioral tests.

RESULTS

Constipation was associated with an increased risk of AD in the discovery cohort (hazard ratio, 2.04; 95% confidence interval [CI], 2.01-2.07) and the validation cohort (hazard ratio; 2.82; 95% CI, 2.61-3.05). We found that loperamide induced slower gut transit in 5xFAD mice, increased Aβ and microglia levels in the brain, increased transcription of genes related to norepinephrine secretion and immune responses, and decreased the transcription of defense against bacteria in the colonic tissue.

CONCLUSION

Impaired gut transit may contribute to AD pathogenesis via the gut-brain axis, thus suggesting a cyclical relationship between intestinal barrier disruption and Aβ accumulation in the brain. We propose that gut transit or motility may be a modifiable lifestyle factor in the prevention of AD, and further clinical investigations are warranted.

Age-related decline in goblet cell numbers and mucin content of the human colon: Implications for lower bowel functions in the elderly

BACKGROUND & AIMS

Older people experience a greater incidence of lower bowel disorders, including constipation. Causes can include factors associated with growing older, such as use of medications or disease, but compounded by degenerative changes within the bowel wall. It has been suggested that the latter is exacerbated by loss of an effective mucosal barrier to luminal contents. In human colon, little is known about the impact of ageing on key components of this barrier, namely the goblet cells and mucin content.

METHODS

Changes in the number of goblet cells and density of mucin content were investigated in macroscopically normal human ascending (AC; n = 13) and descending (DC; n = 14) colon from elderly (≥ 67 years) and younger adults (60 years and below). Samples were serially sectioned and stained for haematoxylin and eosin to assess tissue morphology, and alcian blue periodic acid Schiff (ABPAS) and MUC-2 antibody to identify goblet cells producing mucins. New procedures in visualization and identification of goblet cells and mucin contents were employed to ensure unbiased counting and densitometric analysis.

RESULTS

Compared with the younger adults, the numbers of goblet cells per crypt were significantly lower in the elderly AC (72 ± 1.2 vs 51 ± 0.5) and DC (75 ± 2.6 vs. 54 ± 1.9), although this reduction did not reach statistical significance when assessed per mucosal area (AC: P = 0.068; DC: P = 0.096). In both regions from the elderly, numerous empty vesicles (normally containing mucins) were observed, and some areas of epithelium were devoid of goblet cells. Thus, the density of mucin content per unit mucosal area were significantly reduced with age.

CONCLUSIONS

Ageing could result in a reduced number of goblet cells and development of degenerative changes in mucin production. Together, these have implications for the mucus barrier function in the colon of elderly individuals.

Functional and Structural Investigation of Myenteric Neurons in the Human Colon

Background and Aims

The enteric nervous system independently controls gastrointestinal function including motility, which is primarily mediated by the myenteric plexus, therefore also playing a crucial role in functional intestinal disorders. Live recordings from human myenteric neurons proved to be challenging due to technical difficulties. Using the neuroimaging technique, we are able to record human colonic myenteric neuronal activity and investigate their functional properties in a large cohort of patients.

Methods

Activity from myenteric neurons in wholemount preparations of different sampling sites of fresh, human colonic tissue was recorded using neuroimaging with the voltage sensitive dye 1-(3-sulfanatopropyl)-4-[beta[2-(di-n-octylamino)-6-naphthyl]vinyl]pyridinium betaine. Neuronal responses were analyzed following stimulation with nicotine and serotonin (5-HT) for differences based on the donor's age, the disorder indicative for surgery and the colonic region. Immunohistochemistry was performed to calculate the total neuronal numbers.

Results

Stimulation with nicotine and 5-HT elicited reproducible action potential discharge in a proportion of human myenteric neurons. The responses to 5-HT were significantly greater in tissues from older patients and from those with inflammatory disorders, while neuronal activity to nicotinergic stimulation was comparable in all patients. Neuronal numbers declined with rising patient's age and was highest in the sigmoid colon.

Conclusion

Neuroimaging with 1-(3-sulfanatopropyl)-4-[beta[2-(di-n-octylamino)-6-naphthyl]vinyl]pyridinium betaine was successfully adapted to record reproducible responses from human colonic myenteric neurons upon pharmacological stimulation. Evidence exists for an impact of age and inflammation on the serotonergic neuronal signaling and for differences in neuronal numbers in the distinct colonic regions as well as a neuronal decrease with age.

Ex Vivo Study of Colon Health, Contractility and Innervation in Male and Female Rats after Regular Exposure to Instant Cascara Beverage

Instant Cascara (IC) is a sustainable beverage made from dried coffee cherry pulp, a by-product of coffee processing. It is rich in nutrients and bioactive compounds and has a high concentration of antioxidants. This study explored the impact of regular IC consumption on colonic motor function and innervation. Over a period of 4 weeks, male and female healthy rats were given drinking water containing 10 mg/mL of IC. Thereafter, colon samples were obtained to evaluate the longitudinal (LM) and circular (CM) smooth muscle contractile response to acetylcholine (ACh) and electrical field stimulation (EFS) in an organ bath, before and after atropine administration (10-6 M). Histological and immunohistochemical analyses assessed colon damage, muscle thickness, and immunoreactivity to substance P (SP) and neuronal nitric oxide synthase (nNOS). ACh and EFS induced similar responses across groups, but the CM response to EFS was greater in females compared with males, despite their lower body weight. Atropine completely blocked the response to ACh but only partially antagonized the neural response to EFS, particularly that of CM in females treated with IC, which had a greater liquid intake than those exposed to water. However, in the myenteric ganglia, no statistically significant differences were observed in SP or nNOS. Our results suggest that regular IC exposure may enhance specific neural pathway functions, particularly in females, possibly due to their increased IC consumption.

Evaluation of the mechanism of action of paracetamol, drotaverine, and peppermint oil and their effects in combination with hyoscine butylbromide on colonic motility: human ex-vivo study

Introduction

Drotaverine, paracetamol, and peppermint oil are often prescribed for the treatment of gastrointestinal spasm and pain. This study aimed to evaluate the effect of these drugs alone and combined with the well-known antispasmodic hyoscine butylbromide on the human colon.

Methods

Colon samples were obtained from macroscopically normal regions of 68 patients undergoing surgery and studied in muscle bath. Drotaverine, paracetamol, and peppermint oil were tested alone and in combination with hyoscine butylbromide on (1) spontaneous contractility induced by isometric stretch (in the presence of 1 µM tetrodotoxin) and (2) contractility induced by 10-5 M carbachol and after (3) electrical field stimulation-induced selective stimulation of excitatory (in the presence of 1 mM Nω-nitro-L-arginine and 10 µM MRS2179) and (4) inhibitory (under non-adrenergic, non-cholinergic conditions) pathways. (5) Drotaverine alone was also tested on cAMP-dependent pathway activated by forskolin.

Results

Compared with the vehicle, drotaverine and paracetamol (10-9-10-5 M) did not modify spontaneous contractions, carbachol-induced contractions, and responses attributed to selective activation of excitatory pathways. The addition of hyoscine butylbromide (10-7-10-5 M), concentration-dependently reduced myogenic contractions and carbachol- and electrical field stimulation-induced contractile responses. The association of paracetamol (10-4 M) and hyoscine butylbromide (10-7-10-5 M) was not different from hyoscine butylbromide alone (10-7-10-5 M). At higher concentrations (10-3M-3*10-3 M), paracetamol decreased myogenic and carbachol-induced contractions. The adenylate cyclase activator, forskolin, concentration-dependently reduced contractility, leading to smooth muscle relaxation. The effect of forskolin 10-7 M was concentration-dependently enhanced by drotaverine (10-6M-10-5M).

Discussion

Peppermint oil reduced myogenic activity and carbachol- and electrical field stimulation-induced contractions. The association of hyoscine butylbromide and peppermint oil was synergistic since the interaction index measured with the isobologram was lower than 1. No effect was seen on the neural-mediated inhibitory responses with any of the drugs studied although peppermint oil reduced the subsequent off-contraction. Drotaverine and hyoscine butylbromide have a complementary effect on human colon motility as one stimulates the cAMP inhibitory pathway and the other inhibits the excitatory pathway. Peppermint oil is synergic with hyoscine butylbromide suggesting that a combination therapy may be more effective in treating patients. In contrast, at therapeutic concentrations, paracetamol does not modify colonic contractility, suggesting that the association of paracetamol and hyoscine butylbromide has independent analgesic and antispasmodic properties.

Therapeutic potential of allosteric modulators for the treatment of gastrointestinal motility disorders

Gastrointestinal motility is tightly regulated by the enteric nervous system (ENS). Disruption of coordinated enteric nervous system activity can result in dysmotility. Pharmacological treatment options for dysmotility include targeting of G protein-coupled receptors (GPCRs) expressed by neurons of the enteric nervous system. Current GPCR-targeting drugs for motility disorders bind to the highly conserved endogenous ligand-binding site and promote indiscriminate activation or inhibition of the target receptor throughout the body. This can be associated with significant side-effect liability and a loss of physiological tone. Allosteric modulators of GPCRs bind to a distinct site from the endogenous ligand, which is typically less conserved across multiple receptor subtypes and can modulate endogenous ligand signalling. Allosteric modulation of GPCRs that are important for enteric nervous system function may provide effective relief from motility disorders while limiting side-effects. This review will focus on how allosteric modulators of GPCRs may influence gastrointestinal motility, using 5-hydroxytryptamine (5-HT), acetylcholine (ACh) and opioid receptors as examples. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

The human colon: Evidence for degenerative changes during aging and the physiological consequences

BACKGROUND

The incidence of constipation increases among the elderly (>65 years), while abdominal pain decreases. Causes include changes in lifestyle (e.g., diet and reduced exercise), disease and medications affecting gastrointestinal functions. Degenerative changes may also occur within the colo-rectum. However, most evidence is from rodents, animals with relatively high rates of metabolism and accelerated aging, with considerable variation in time course. In humans, cellular and non-cellular changes in the aging intestine are poorly investigated.

PURPOSE

To examine all available studies which reported the effects of aging on cellular and tissue functions of human isolated colon, noting the region studied, sex and age of tissue donors and study size. The focus on human colon reflects the ability to access full-thickness tissue over a wide age range, compared with other gastrointestinal regions. Details are important because of natural human variability. We found age-related changes within the muscle, in the enteric and nociceptor innervation, and in the submucosa. Some involve all regions of colon, but the ascending colon appears more vulnerable. Changes can be cell- and sublayer-dependent. Mechanisms are unclear but may include development of "senescent-like" and associated inflammaging, perhaps associated with increased mucosal permeability to harmful luminal contents. In summary, reduced nociceptor innervation can explain diminished abdominal pain among the elderly. Degenerative changes within the colon wall may have little impact on symptoms and colonic functions, because of high "functional reserve," but are likely to facilitate the development of constipation during age-related challenges (e.g., lifestyle, disease, and medications), now operating against a reduced functional reserve.

Contractility of isolated colonic smooth muscle strips from rats treated with cancer chemotherapy: differential effects of cisplatin and vincristine

Background

Certain antineoplastic drugs cause gastrointestinal disorders even after the end of treatment. Enteric neuropathy has been associated with some of these alterations. Our goal was to assess the impact of repeated treatment with cisplatin and vincristine on the contractility of circular and longitudinal muscle strips isolated from the rat colon.

Methods

Two cohorts of male rats were used: in cohort 1, rats received one intraperitoneal (ip) injection of saline or cisplatin (2 mg kg-1 week-1) on the first day of weeks 1-5; in cohort 2, rats received two cycles of five daily ip injections (Monday to Friday, weeks 1-2) of saline or vincristine (0.1 mg kg-1 day-1). Body weight and food and water intake were monitored throughout the study. One week after treatment, responses of colonic smooth muscle strips to acetylcholine (10-9-10-5 M) and electrical field stimulation (EFS, 0.1-20 Hz), before and after atropine (10-6 M), were evaluated in an organ bath.

Results

Both drugs decreased body weight gain. Compared to saline, cisplatin significantly decreased responses of both longitudinal and circular smooth muscle strips to EFS, whereas vincristine tended to increase them, although in a non-significant manner. No differences were observed in the muscle response to acetylcholine. Atropine abolished the contractile responses induced by acetylcholine, although those induced by EFS were only partially reduced in the presence of atropine.

Conclusion

The findings suggest that although both drugs cause the development of enteric neuropathy, this seems to have a functional impact only in cisplatin-treated animals. Understanding the effects of chemotherapy on gastrointestinal motor function is vital for enhancing the quality of life of cancer patients.

The Crucial Role of the Interstitial Cells of Cajal in Neurointestinal Diseases

Neurointestinal diseases result from dysregulated interactions between the nervous system and the gastrointestinal (GI) tract, leading to conditions such as Hirschsprung's disease and irritable bowel syndrome. These disorders affect many people, significantly diminishing their quality of life and overall health. Central to GI motility are the interstitial cells of Cajal (ICC), which play a key role in muscle contractions and neuromuscular transmission. This review highlights the role of ICC in neurointestinal diseases, revealing their association with various GI ailments. Understanding the functions of the ICC could lead to innovative perspectives on the modulation of GI motility and introduce new therapeutic paradigms. These insights have the potential to enhance efforts to combat neurointestinal diseases and may lead to interventions that could alleviate or even reverse these conditions.

Types of Neurons in the Human Colonic Myenteric Plexus Identified by Multilayer Immunohistochemical Coding

BACKGROUND AND AIMS

Gut functions including motility, secretion, and blood flow are largely controlled by the enteric nervous system. Characterizing the different classes of enteric neurons in the human gut is an important step to understand how its circuitry is organized and how it is affected by disease.

METHODS

Using multiplexed immunohistochemistry, 12 discriminating antisera were applied to distinguish different classes of myenteric neurons in the human colon (2596 neurons, 12 patients) according to their chemical coding. All antisera were applied to every neuron, in multiple layers, separated by elutions.

RESULTS

A total of 164 combinations of immunohistochemical markers were present among the 2596 neurons, which could be divided into 20 classes, with statistical validation. Putative functions were ascribed for 4 classes of putative excitatory motor neurons (EMN1-4), 4 inhibitory motor neurons (IMN1-4), 3 ascending interneurons (AIN1-3), 6 descending interneurons (DIN1-6), 2 classes of multiaxonal sensory neurons (SN1-2), and a small, miscellaneous group (1.8% of total). Soma-dendritic morphology was analyzed, revealing 5 common shapes distributed differentially between the 20 classes. Distinctive baskets of axonal varicosities surrounded 45% of myenteric nerve cell bodies and were associated with close appositions, suggesting possible connectivity. Baskets of cholinergic terminals and several other types of baskets selectively targeted ascending interneurons and excitatory motor neurons but were significantly sparser around inhibitory motor neurons.

CONCLUSIONS

Using a simple immunohistochemical method, human myenteric neurons were shown to comprise multiple classes based on chemical coding and morphology and dense clusters of axonal varicosities were selectively associated with some classes.

Effect of old age on the subpopulations of enteric glial cells in human descending colon

Old age is associated with a higher incidence of lower bowel conditions such as constipation. Recent evidence suggest that colonic motility may be influenced by enteric glial cells (EGCs). Little is known about the effect of aging on the subpopulation of EGCs in the human colon. We assessed and compared the pattern of distribution of EGCs in adult and elderly human colon. Human descending colon were obtained from 23 cancer patients comprising of adults (23-63 years; 6 male, 7 female) and elderly (66-81 year; 6 male, 4 female). Specimens were serially-sectioned and immunolabeled with anti-Sox-10, anti-S100 and anti-GFAP for morphometric analysis. Standardized procedures were utilized to ensure unbiased counting and densitometric evaluation of EGCs. The number of Sox-10 immunoreactive (IR) EGCs were unaltered with age in both the myenteric plexus (MP) (respectively, in adult and elderly patients, 1939 ± 82 and 1760 ± 44/mm length; p > .05) and submucosal plexus; there were no apparent differences between adult males and females. The density of S100-IR EGCs declined among the elderly in the circular muscle and within the MP per ganglionic area. In the adult colon, there were more S100-IR EGCs distributed in the circular muscle per unit area than the Taenia coli. There was little or no GFAP-IR EGCs in both adult and elderly colon. We concluded that aging of the human descending colon does not result in a loss of Sox-10-IR EGCs in the MP and SMP but reduces S100-IR EGCs density within the musculature. This alteration in myenteric EGCs density with age may contribute to colonic dysfunction.

Ageing and the Autonomic Nervous System

The vertebrate nervous system is divided into central (CNS) and peripheral (PNS) components. In turn, the PNS is divided into the autonomic (ANS) and enteric (ENS) nervous systems. Ageing implicates time-related changes to anatomy and physiology in reducing organismal fitness. In the case of the CNS, there exists substantial experimental evidence of the effects of age on individual neuronal and glial function. Although many such changes have yet to be experimentally observed in the PNS, there is considerable evidence of the role of ageing in the decline of ANS function over time. As such, this chapter will argue that the ANS constitutes a paradigm for the physiological consequences of ageing, as well as for their clinical implications.

Total collagen content and distribution is increased in human colon during advancing age

Background

The effect of ageing on total collagen content of human colon has been poorly investigated. The aim of this study was to determine if ageing altered total collagen content and distribution in the human colon.

Methods

Macroscopically normal ascending colon was obtained at surgery from cancer patients (n = 31) without diagnosis of diverticular disease or inflammatory bowel disease. Masson’s trichrome and Picrosirius red stains were employed to identify the total collagen content and distribution within the sublayers of the colonic wall for adult (22–60 years; 6 males, 6 females) and elderly (70 – 91years; 6 males, 4 female) patients. A hydroxyproline assay evaluated the total collagen concentration for adult (30–64 years; 9 male, 6 female) and elderly (66–91 years; 8 male, 8 female) patients.

Key results

Histological studies showed that the percentage mean intensity of total collagen staining in the mucosa, submucosa and muscularis externa was, respectively, 14(1.9) %, 74(3.2) % and 12(1.5) % in the adult ascending colon. Compared with the adults, the total collagen fibres content was increased in the submucosa (mean intensity; 163.1 ± 11.1 vs. 124.5 ± 7.8; P < 0.05) and muscularis externa (42.5 ± 8.0 vs. 20.6 ± 2.8; P < 0.01) of the elderly patients. There was no change in collagen content of the mucosa. The total collagen concentration was increased in the elderly by 16%. Sex-related differences were not found, and data were combined for analysis.

Conclusions

Greater total collagen content was found in the submucosa and muscularis externa of the elderly human male and female colon. These changes may contribute to a possible loss of function with ageing.

Transduction of Systemically Administered Adeno-Associated Virus in the Colonic Enteric Nervous System and c-Kit Cells of Adult Mice

Systemic delivery of adeno-associated virus (AAV) vectors transduces the enteric nervous system. However, less is known on the mapping and morphological and neurochemical characterization in the adult mouse colon. We used AAV9-CAG-GFP (AAV9) and AAV-PHP.S-hSyn1-tdTomato farnesylated (PHP.S-tdTf) to investigate the segmental distribution, morphologies and neurochemical coding of the transduction. The vectors were retro-orbitally injected in male and female adult mice, and 3 weeks later, the colon was prepared for microcopy with or without immunohistochemistry for neuronal and non-neuronal markers. In contrast to the distributions in neonatal and juvenile rodents, the AAV transduction in neurons and/or nerve fibers was the highest in the proximal colon, decreased gradually in the transverse, and was sparse in the distal colon without difference between sexes. In the proximal colon, the AAV9-transduced myenteric neurons were unevenly distributed. The majority of enteric neurons did not have AAV9 expression in their processes, except those with big soma with or without variously shaped dendrites, and a long axon. Immunolabeling demonstrated that about 31% neurons were transduced by AAV9, and the transduction was in 50, 28, and 31% of cholinergic, nitrergic, and calbindin-positive myenteric neurons, respectively. The nerve fiber markers, calcitonin gene-related peptide alpha, tyrosine hydroxylase or vasoactive intestinal polypeptide co-localized with AAV9 or PHP.S-tdTf in the mucosa, and rarely in the myenteric plexus. Unexpectedly, AAV9 expression appeared also in a few c-Kit immunoreactive cells among the heavily populated interstitial cells of Cajal (ICC). In the distal colon, the AAV transduction appeared in a few nerve fibers mostly the interganglionic strands. Other types of AAV9 and AAV-PHP vectors induced a similar colonic segmental difference which is not colon specific since neurons were transduced in the small intestine and gastric antrum, while little in the gastric corpus and none in the lower esophagus.

Conclusion

These findings demonstrate that in adult mice colon that there is a rostro-caudal decrease in the transduction of systemic delivery of AAV9 and its variants independent of sex. The characterization of AAV transduction in the proximal colon in cholinergic and nitrergic myenteric neurons along with a few ICC suggests implications in circuitries regulating motility.

Aging of enteric neuromuscular systems in gastrointestinal tract

BACKGROUND

Aging is a complex biological process and associated with a progressive decline in functions of most organs including the gastrointestinal (GI) tract. Age-related GI motor disorders/dysfunctions include esophageal reflux, dysphagia, constipation, fecal incontinence, reduced compliance, and accommodation. Although the incidence and severity of these diseases and conditions increase with age, they are often underestimated due in part to nonspecific and variable symptoms and lack of sufficient medical attention. They negatively affect quality of life and predispose the elderly to other diseases, sarcopenia, and frailty. The mechanisms underlying aging-associated GI dysfunctions remain unclear, and there is limited data examining the effect of aging on GI motor functions. Many studies on aging-associated changes to cells within the tunica muscularis including enteric neurons, smooth muscles, and interstitial cells have proposed that cell loss and/or molecular changes may be involved in the pathogenesis of age-related GI motor disorders/dysfunctions. There is also evidence that the aging contributes to phenotypic changes in innate immune cells, which are physically and functionally linked to other cells in the tunica muscularis and can alter GI (patho) physiology. However, various patterns of changes have been reported, some of which are contradictory, indicating a need for additional work in this area.

PURPOSE

Although GI infection due to intestinal bacterial overgrowth, bleeding, and cancers are also important and common problems in the elderly patients, this mini-review focuses on data obtained from enteric neuromuscular aging research with the goal of better understanding the cellular and molecular mechanisms of enteric neuromuscular aging to enhance future therapy.

The Involvement of the Endogenous Opioid System in the Gastrointestinal Aging in Mice and Humans

Nearly 20% of elderly patients suffer from constipation, but the age-related changes in the gastrointestinal (GI) tract remain insufficiently elucidated. In this study, the alterations within the endogenous opioid system (EOS) as a potential cause of constipation in the elderly were evaluated. The GI functions were assessed in vitro and in vivo and compared between 6-, 12- and 18-month old mice. Moreover, the effect of opioid receptor (MOP, DOP, KOP) agonists on the mouse GI tract functions and the EOS components expression in mouse tissues and colonic biopsies from patients with functional constipation were determined. In the oldest mice, the GI peristalsis was significantly impaired as compared to the younger groups. The tissue response to MOP and DOP, but not KOP, agonists weakened with age in vitro; for DOP, it was confirmed in vivo. In the mouse upper GI tract, Oprm1, Oprd1, Oprk1 expression decreased with age; in the colon, Oprm1 expression increased. There were no differences in the expression of these genes in the colonic biopsies from patients >50 years old as compared to the younger group. In conclusion, the age-related impairment of the GI peristalsis may result from reduced MOP and DOP response to the activation with opioid agonists or the alterations in the EOS expression.

Age-related differences of γ-aminobutyric acid (GABA)ergic transmission in human colonic smooth muscle

BACKGROUND

Enteric neurons undergo to functional changes during aging. We investigated the possible age-associated differences in enteric γ-aminobutyric acid (GABA)ergic transmission evaluating function and distribution of GABAergic receptors in human colon.

METHODS

Mechanical responses to GABA and GABA receptor agonists on slow phasic contractions were examined in vitro as changes in isometric tension in colonic muscle strips from young (<65 years old) and aged patients (>65 years old). GABAergic receptor expression was assessed by quantitative RT-PCR.

KEY RESULTS

In both preparations GABA induced an excitatory effect, consisting in an increase in the basal tone, antagonized by the GABAA receptor antagonist, bicuculline, and potentiated by phaclofen, GABAB receptor antagonist.Tetrodotoxin (TTX) and atropine-sensitive contractile responses to GABA and GABAA receptor agonist, muscimol, were more pronounced in old compared to young subjects. Baclofen, GABAB receptor agonist, induced a TTX-sensitive reduction of the amplitude of the spontaneous. Nω-nitro-l-arginine methyl ester (L-NAME), nitric oxide (NO) synthase inhibitor abolished the inhibitory responses in old preparations, but a residual responses persisted in young preparations, which in turn was abolished by suramin, purinergic receptor antagonist. α3-GABAA receptor subunit expression tends to change in an age-dependent manner.

CONCLUSIONS AND INFERENCES

Our results reveal age-related differences in GABAergic transmission in human colon. At all the age tested GABA regulates muscular contractility modulating the activity of the intrinsic neurons. Activation of GABAA receptor, through acetylcholine release, induces contraction, which increases in amplitude with age. GABAB receptor activation leads to neural release of NO and purines, being a loss of purinergic-component in aged group.

Analyzing fecal loading and retention patterns by abdominal X-rays of hospitalized older adults: A retrospective study

Background

Aging may affect ascending colon (AC) differently from descending colon (DC) and increase the risk of fecal loading (FL) in AC.

Methods

Patients aged ≥65 years admitted to a community hospital were analyzed by abdominal x-ray for fecal loads and stool retention patterns. FL was scored between 0 and 5 (severe) on each segment of colon with a possible total score 20. Mean segment scores ≥3.5 were designated as high scores for both AC and DC. Logistic regression was performed between groups to identify factors associated with FL patterns.

Results

Groups identified were high FL in both AC and DC (N = 21, 17.2%), FL predominantly in AC (N = 38, 31.1%), low FL in both AC and DC (N=60, 49.2%), and FL low in AC and high in DC (N = 3, 2.5%). Among 71 patients with total FL scores ≥13 (indicating significant stool retention), 37 (52.1%) had the FL predominantly in AC. Patients prescribed antibiotic(s) prior to hospitalization had lower odds of FL predominantly in AC (adjusted odds ratio = 0.18, 95% confidence interval = 0.04-0.84) compared to the group of low FL in both AC and DC with the adjustment of confounders.

Conclusion

This study found that 52.1% of those with significant stool retention on x-ray had the FL predominantly in AC. Antibiotic use was associated with lower odds of having FL predominately in AC. This study provided insights of FL distribution in colon and AC could be an area for significant stool burden in older adults with stool retention.

Understanding the physiology of human defaecation and disorders of continence and evacuation

The act of defaecation, although a ubiquitous human experience, requires the coordinated actions of the anorectum and colon, pelvic floor musculature, and the enteric, peripheral and central nervous systems. Defaecation is best appreciated through the description of four phases, which are, temporally and physiologically, reasonably discrete. However, given the complexity of this process, it is unsurprising that disorders of defaecation are both common and problematic; almost everyone will experience constipation at some time in their life and many will develop faecal incontinence. A detailed understanding of the normal physiology of defaecation and continence is critical to inform management of disorders of defaecation. During the past decade, there have been major advances in the investigative tools used to assess colonic and anorectal function. This Review details the current understanding of defaecation and continence. This includes an overview of the relevant anatomy and physiology, a description of the four phases of defaecation, and factors influencing defaecation (demographics, stool frequency/consistency, psychobehavioural factors, posture, circadian rhythm, dietary intake and medications). A summary of the known pathophysiology of defaecation disorders including constipation, faecal incontinence and irritable bowel syndrome is also included, as well as considerations for further research in this field.

Expression of p16 Within Myenteric Neurons of the Aged Colon: A Potential Marker of Declining Function

Human colonic neuromuscular functions decline among the elderly. The aim was to explore the involvement of senescence. A preliminary PCR study looked for age-dependent differences in expression of CDKN1A (encoding the senescence-related p21 protein) and CDKN2A (encoding p16 and p14) in human ascending and descending colon (without mucosa) from 39 (approximately 50: 50 male: female) adult (aged 27–60 years) and elderly donors (70–89 years). Other genes from different aging pathways (e.g., inflammation, oxidative stress, autophagy) and cell-types (e.g., neurons, neuron axonal transport) were also examined. Unlike CDKN1A, CDKN2A (using primers for p16 and p14 but not when using p14-specific primers) was upregulated in both regions of colon. Compared with the number of genes appearing to upregulate in association with temporal age, more genes positively associated with increased CDKN2A expression (respectively, 16 and five of 44 genes studied for ascending and descending colon). Confirmation of increased expression of CDKN2A was sought by immunostaining for p16 in the myenteric plexus of colon from 52 patients, using a semi-automated software protocol. The results showed increased staining not within the glial cells (S100 stained), but in the cytoplasm of myenteric nerve cell bodies (MAP2 stained, with identified nucleus) of ascending, but not descending colon of the elderly, and not in the cell nucleus of either region or age group (5,710 neurons analyzed: n = 12–14 for each group). It was concluded that increased p16 staining within the cytoplasm of myenteric nerve cell bodies of elderly ascending (but not descending) colon, suggests a region-dependent, post-mitotic cellular senescence-like activity, perhaps involved with aging of enteric neurons within the colon.

Disorders of the enteric nervous system - a holistic view

The enteric nervous system (ENS) is the largest division of the peripheral nervous system and closely resembles components and functions of the central nervous system. Although the central role of the ENS in congenital enteric neuropathic disorders, including Hirschsprung disease and inflammatory and functional bowel diseases, is well acknowledged, its role in systemic diseases is less understood. Evidence of a disordered ENS has accumulated in neurodegenerative diseases ranging from amyotrophic lateral sclerosis, Alzheimer disease and multiple sclerosis to Parkinson disease as well as neurodevelopmental disorders such as autism. The ENS is a key modulator of gut barrier function and a regulator of enteric homeostasis. A 'leaky gut' represents the gateway for bacterial and toxin translocation that might initiate downstream processes. Data indicate that changes in the gut microbiome acting in concert with the individual genetic background can modify the ENS, central nervous system and the immune system, impair barrier function, and contribute to various disorders such as irritable bowel syndrome, inflammatory bowel disease or neurodegeneration. Here, we summarize the current knowledge on the role of the ENS in gastrointestinal and systemic diseases, highlighting its interaction with various key players involved in shaping the phenotypes. Finally, current flaws and pitfalls related to ENS research in addition to future perspectives are also addressed.

Constipation and Fecal Incontinence in the Elderly

PURPOSE OF REVIEW

To review the epidemiology, pathogenesis, clinical features, and management of primary constipation and fecal incontinence in the elderly.

RECENT FINDINGS

Among elderly people, 6.5%, 1.7%, and 1.1% have functional constipation, constipation-predominant IBS, and opioid-induced constipation. In elderly people, the number of colonic enteric neurons and smooth muscle functions is preserved; decreased cholinergic function with unopposed nitrergic relaxation may explain colonic motor dysfunction. Less physical activity or dietary fiber intake and postmenopausal hormonal therapy are risk factors for fecal incontinence in elderly people. Two thirds of patients with fecal incontinence respond to biofeedback therapy. Used in combination, loperamide and biofeedback therapy are more effective than placebo, education, and biofeedback therapy. Vaginal or anal insert devices are another option. In the elderly, constipation and fecal incontinence are common and often distressing symptoms that can often be managed by addressing bowel disturbances. Selected diagnostic tests, prescription medications, and, infrequently, surgical options should be considered when necessary.

Wnt-induced, TRP53-mediated Cell Cycle Arrest of Precursors Underlies Interstitial Cell of Cajal Depletion During Aging

BACKGROUND & AIMS

Gastric dysfunction in the elderly may cause reduced food intake, frailty, and increased mortality. The pacemaker and neuromodulator cells interstitial cells of Cajal (ICC) decline with age in humans, and their loss contributes to gastric dysfunction in progeric klotho mice hypomorphic for the anti-aging Klotho protein. The mechanisms of ICC depletion remain unclear. Klotho attenuates Wnt (wingless-type MMTV integration site) signaling. Here, we examined whether unopposed Wnt signaling could underlie aging-associated ICC loss by up-regulating transformation related protein TRP53 in ICC stem cells (ICC-SC).

METHODS

Mice aged 1-107 weeks, klotho mice, APC^Δ468 mice with overactive Wnt signaling, mouse ICC-SC, and human gastric smooth muscles were studied by RNA sequencing, reverse transcription-polymerase chain reaction, immunoblots, immunofluorescence, histochemistry, flow cytometry, and methyltetrazolium, ethynyl/bromodeoxyuridine incorporation, and ex-vivo gastric compliance assays. Cells were manipulated pharmacologically and by gene overexpression and RNA interference.

RESULTS

The klotho and aged mice showed similar ICC loss and impaired gastric compliance. ICC-SC decline preceded ICC depletion. Canonical Wnt signaling and TRP53 increased in gastric muscles of klotho and aged mice and middle-aged humans. Overstimulated canonical Wnt signaling increased DNA damage response and TRP53 and reduced ICC-SC self-renewal and gastric ICC. TRP53 induction persistently inhibited G₁/S and G₂/M cell cycle phase transitions without activating apoptosis, autophagy, cellular quiescence, or canonical markers/mediators of senescence. G₁/S block reflected increased cyclin-dependent kinase inhibitor 1B and reduced cyclin D1 from reduced extracellular signal-regulated kinase activity.

CONCLUSIONS

Increased Wnt signaling causes age-related ICC loss by up-regulating TRP53, which induces persistent ICC-SC cell cycle arrest without up-regulating canonical senescence markers.

Proton pump inhibitors act with unprecedented potencies as inhibitors of the acetylcholine biosynthesizing enzyme-A plausible missing link for their association with incidence of dementia

INTRODUCTION

Several pharmacoepidemiological studies indicate that proton pump inhibitors (PPIs) significantly increase the risk of dementia. Yet, the underlying mechanism is not known. Here, we report the discovery of an unprecedented mode of action of PPIs that explains how PPIs may increase the risk of dementia.

METHODS

Advanced in silico docking analyses and detailed enzymological assessments were performed on PPIs against the core-cholinergic enzyme, choline-acetyltransferase (ChAT), responsible for biosynthesis of acetylcholine (ACh).

RESULTS

This report shows compelling evidence that PPIs act as inhibitors of ChAT, with high selectivity and unprecedented potencies that lie far below their in vivo plasma and brain concentrations.

DISCUSSION

Given that accumulating evidence points at cholinergic dysfunction as a driving force of major dementia disorders, our findings mechanistically explain how prolonged use of PPIs may increase incidence of dementia. This call for restrictions for prolonged use of PPIs in elderly, and in patients with dementia or amyotrophic lateral sclerosis.

The asymmetric innervation of the circular and longitudinal muscle of the mouse colon differently modulates myogenic slow phasic contractions

BACKGROUND

Neuromuscular transmission has been extensively studied in the circular layer of the mouse colon where a co-transmission of purines acting on P2Y₁ receptors and NO has been previously described. However, the corresponding mechanisms in the longitudinal layer are less known.

METHODS

Electrophysiological and myography techniques were used to evaluate spontaneous phasic contractions (SPC) and neural-mediated responses in the proximal, mid, and distal colon devoid of CD1 mice. Immunohistochemistry against c-kit and PDGFRα was performed in each colonic segment.

KEY RESULTS

SPC were recorded in both muscle layers at a similar frequency being about four contractions per minute (c.p.m.) in the proximal and distal colon compared to the mid colon (2 c.p.m.). In non-adrenergic, non-cholinergic conditions, L-NNA (1 mmol/L) increased contractility in the circular but not in the longitudinal layer. In the longitudinal muscle, both electrophysiological and mechanical neural-mediated inhibitory responses were L-NNA and ODQ (10 µmol/L) sensitive. NaNP (1 µmol/L) caused cessation of SPC and the response was blocked by ODQ. Neither ADPßS (10 µmol/L) nor CYPPA (10 µmol/L), which both targeted the purinergic pathway, altered longitudinal contractions. PDGFRα + cells were located in both muscle layers and were more numerous compared with cKit + cells, which both formed a heterologous cellular network. A decreasing gradient of the PDGFRα labeling was observed along the colon.

CONCLUSION

An inhibitory neural tone was absent in the longitudinal layer and neuronal inhibitory responses were mainly nitrergic. Despite the presence of PDGFRα + cells, purinergic responses were absent. Post-junctional pathways located in different cell types might be responsible for neurotransmitter transduction.

Normative values for region-specific colonic and gastrointestinal transit times in 111 healthy volunteers using the 3D-Transit electromagnet tracking system: Influence of age, gender, and body mass index

BACKGROUND

The 3D-Transit electromagnet tracking system (Motilis Medica, SA, Lausanne, Switzerland) is an emerging tool for the ambulatory assessment of gastrointestinal (GI) transit and motility. Using this tool, we aimed to derive normative values for region-specific colonic and GI transit times and to assess the influence of age, gender, and body mass index (BMI).

METHODS

Regional and total colonic transit times (CTT), gastric emptying (GET), small intestinal (SITT), and whole gut (WGTT) transit times were extracted from 111 healthy volunteers from the United Kingdom and Denmark (58 female; median age: 40 years [range: 21-88]). The effects of age, gender, and BMI were assessed using standard statistical methods.

KEY RESULTS

The ascending, transverse, descending, and rectosigmoid colon transit times accounted for 32%, 34%, 17%, and 17% of total CTT in females, and 33%, 25%, 14%, and 28% of total CTT in males. CTT and WGTT were seen to cluster at intervals separated by approximately 24 hours, providing further evidence of the non-continuous nature of these measurements. Increasing age was associated with longer CTT (P = .021), WGTT (P < .001) ascending (P = .004), transverse (P < .001), and total right (P < .001) colon transit times, but shorter rectosigmoid (P = .004) transit time. Female gender was significantly associated with longer transverse (P = .049) and descending (P < .001) colon transit times, but shorter rectosigmoid (P < .001) transit time. Increasing BMI was significantly associated with shorter WGTT (P = .012).

CONCLUSIONS AND INFERENCES

For the first time, normative reference values for region-specific colonic transit have been presented. Age, gender, and BMI were seen to have an effect on transit times.

Management of functional constipation in children and adults

Functional constipation is common in children and adults worldwide. Functional constipation shows similarities in children and adults, but important differences also exist regarding epidemiology, symptomatology, pathophysiology, diagnostic workup and therapeutic management. In children, the approach focuses on the behavioural nature of the disorder and the initial therapeutic steps involve toilet training and laxatives. In adults, management focuses on excluding an underlying cause and differentiating between different subtypes of functional constipation - normal transit, slow transit or an evacuation disorder - which has important therapeutic consequences. Treatment of adult functional constipation involves lifestyle interventions, pelvic floor interventions (in the presence of a rectal evacuation disorder) and pharmacological therapy. When conventional treatments fail, children and adults are considered to have intractable functional constipation, a troublesome and distressing condition. Intractable constipation is managed with a stepwise approach and in rare cases requires surgical interventions such as antegrade continence enemas in children or colectomy procedures for adults. New drugs, including prokinetic and prosecretory agents, and surgical strategies, such as sacral nerve stimulation, have the potential to improve the management of children and adults with intractable functional constipation.