Alterations of the enteric smooth musculature in diverticular disease

From diverticulosis to complicated diverticular disease: Progression of myogenic alterations and oxidative imbalance

BACKGROUND

The natural history and pathophysiology of diverticular disease (DD) are still uncertain. An ex-vivo human complicated DD (cDD) model has recently shown a predominant transmural oxidative imbalance. The present study aims to evaluate whether the previously described alterations may precede the symptomatic form of the disease.

METHODS

Colonic surgical samples obtained from patients with asymptomatic diverticulosis (DIV), complicated DD, and controls were systematically and detailed morphologically and molecularly analyzed. Therefore, histologic, histomorphometric, immunohistochemical evaluation, and gene and protein expression analysis were performed to characterize colonic muscle changes and evaluate chronic inflammation, oxidative imbalance, and hypoxia. Functional muscle activity was tested on strips and isolated cells in response to contractile and relaxant agents.

KEY RESULTS

Compared with controls, DD showed a marketed increase in muscle layer thickness, smooth muscle cell syncytium disarray, and increased interstitial fibrosis; moreover, the observed features were more evident in the cDD group. These changes mainly affected longitudinal muscle and were associated with altered contraction-relaxation dynamics and fibrogenic switch of smooth muscle cells. Chronic lymphoplasmacytic inflammation was primarily evident in the mucosa and spared the muscle. A transmural increase in carbonylated and nitrated proteins, with loss of antioxidant molecules, characterized both stages of DD, suggesting early oxidative stress probably triggered by recurrent ischemic events, more pronounced in cDD, where HIF-1 was detected in both muscle and mucosa.

CONCLUSION & INFERENCES

The different DD clinical scenarios are part of a progressive process, with oxidative imbalance representing a new target in the management of DD.

Genetic, epigenetic and environmental factors in diverticular disease: systematic review

BACKGROUND

Diverticulosis is a normal anatomical variant of the colon present in more than 70% of the westernized population over the age of 80. Approximately 3% will develop diverticulitis in their lifetime. Many patients present emergently, suffer high morbidity rates and require substantial healthcare resources. Diverticulosis is the most common finding at colonoscopy and has the potential for causing a significant morbidity rate and burden on healthcare. There is a need to better understand the aetiology and pathogenesis of diverticular disease. Research suggests a genetic susceptibility of 40-50% in the formation of diverticular disease. The aim of this review is to present the hypothesized functional effects of the identified gene loci and environmental factors.

METHODS

A systematic literature review was performed using PubMed, MEDLINE and Embase. Medical subject headings terms used were: 'diverticular disease, diverticulosis, diverticulitis, genomics, genetics and epigenetics'. A review of grey literature identified environmental factors.

RESULTS

Of 995 articles identified, 59 articles met the inclusion criteria. Age, obesity and smoking are strongly associated environmental risk factors. Intrinsic factors of the colonic wall are associated with the presence of diverticula. Genetic pathways of interest and environmental risk factors were identified. The COLQ, FAM155A, PHGR1, ARHGAP15, S100A10, and TNFSF15 genes are the strongest candidates for further research.

CONCLUSION

There is increasing evidence to support the role of genomics in the spectrum of diverticular disease. Genomic, epigenetic and omic research with demographic context will help improve the understanding and management of this complex disease.

Immunoglobulin superfamily member 3 is required for the vagal neural crest cell migration and enteric neuronal network organization

The immunoglobulin (Ig) superfamily members are involved in cell adhesion and migration, complex multistep processes that play critical roles in embryogenesis, wound healing, tissue formation, and many other processes, but their specific functions during embryonic development remain unclear. Here, we have studied the function of the immunoglobulin superfamily member 3 (IGSF3) by generating an Igsf3 knockout (KO) mouse model with CRISPR/Cas9-mediated genome engineering. By combining RNA and protein detection methodology, we show that during development, IGSF3 localizes to the neural crest and a subset of its derivatives, suggesting a role in normal embryonic and early postnatal development. Indeed, inactivation of Igsf3 impairs the ability of the vagal neural crest cells to migrate and normally innervate the intestine. The small intestine of Igsf3 KO mice shows reduced thickness of the muscularis externa and diminished number of enteric neurons. Also, misalignment of neurons and smooth muscle cells in the developing intestinal villi is detected. Taken together, our results suggest that IGSF3 functions contribute to the formation of the enteric nervous system. Given the essential role of the enteric nervous system in maintaining normal gastrointestinal function, our study adds to the pool of information required for further understanding the mechanisms of gut innervation and etiology behind bowel motility disorders.

150 risk variants for diverticular disease of intestine prioritize cell types and enable polygenic prediction of disease susceptibility

We conducted a genome-wide association study (GWAS) analysis of diverticular disease (DivD) of intestine within 724,372 individuals and identified 150 independent genome-wide significant DNA variants. Integration of the GWAS results with human gut single-cell RNA sequencing data implicated gut myocyte, mesothelial and stromal cells, and enteric neurons and glia in DivD development. Ninety-five genes were prioritized based on multiple lines of evidence, including SLC9A3, a drug target gene of tenapanor used for the treatment of the constipation subtype of irritable bowel syndrome. A DivD polygenic score (PGS) enables effective risk prediction (area under the curve [AUC], 0.688; 95% confidence interval [CI], 0.645-0.732) and the top 20% PGS was associated with ∼3.6-fold increased DivD risk relative to the remaining population. Our statistical and bioinformatic analyses suggest that the mechanism of DivD is through colon structure, gut motility, gastrointestinal mucus, and ionic homeostasis. Our analyses reinforce the link between gastrointestinal disorders and the enteric nervous system through genetics.

Ultrasonographic and Functional Features of Symptomatic Uncomplicated Diverticular Disease

INTRODUCTION

To evaluate the ability of intestinal ultrasound (IUS) in discriminating symptomatic uncomplicated diverticular disease (SUDD) among patients with abdominal symptoms including irritable bowel syndrome (IBS).

METHODS

This observational, prospective study included consecutive patients classified into the following categories: (i) SUDD; (ii) IBS; (iii) unclassifiable abdominal symptoms; and (iv) controls, including asymptomatic healthy subjects and diverticulosis. The IUS evaluation of the sigmoid: assessed the presence of diverticula, thickness of the muscularis propria, and IUS-evoked pain, namely the intensity of pain evoked by compression with the ultrasound probe on sigmoid colon compared with an area of the left lower abdominal quadrant without underlying sigmoid colon.

RESULTS

We enrolled 40 patients with SUDD, 20 patients with IBS, 28 patients with unclassifiable abdominal symptoms, 10 healthy controls, and 20 patients with diverticulosis. Patients with SUDD displayed significantly ( P < 0.001) greater muscle thickness (2.25 ± 0.73 mm) compared with patients with IBS (1.66 ± 0.32 mm), patients with unclassifiable abdominal pain, and healthy subjects, but comparable with that of patients with diverticulosis (2.35 ± 0.71 mm). Patients with SUDD showed a greater (not significant) differential pain score than other patients. There was a significant correlation between the thickness of the muscularis propria and the differential pain score only for patients with SUDD ( r = 0.460; P : 0.01). Sigmoid diverticula were detected by colonoscopy in 40 patients (42.4%) and by IUS with a sensitivity of 96.0% and a specificity of 98.5%.

DISCUSSION

IUS could represent a useful diagnostic tool for SUDD, potentially useful in characterizing the disease and appropriately address the therapeutic approach.

Oxidative imbalance and muscular alterations in diverticular disease

BACKGROUND

It is still a matter of debate if neuromuscular alterations reflect a primary event in diverticular disease (DD).

AIMS

This study aimed to assess colonic wall layers from both stenotic and non-stenotic complicated DD, bio-phenotypic alterations, inflammatory and oxidative status.

METHODS

A systematic analysis of colonic specimens obtained from stenotic and non-stenotic DD specimens was conducted and compared with controls. Biological activity and qPCR analysis were performed on longitudinal and circular muscles. Western blot analysis was performed throughout colonic wall layers to quantify oxidative and inflammatory markers.

RESULTS

A homogenous increase in oxidative stress was observed through all the layers, which were more sharpened in the longitudinal muscle for a loss in antioxidant defenses. In both stenotic and non-stenotic colon, the longitudinal muscle presented an impaired relaxation and a cellular phenotypic switch driven by transforming growth factor-β with an increase in mRNA expression of collagen Iα and a decrease in myosin heavy chain. The circular muscle, as the mucosa, was less affected by molecular alterations. No peculiar increase in inflammatory markers was observed.

CONCLUSION

A longitudinal colonic myopathy is present in DD, independently from the disease stage associated with an oxidative imbalance that could suggest new therapeutic strategies.

Pathophysiology of Diverticular Disease: From Diverticula Formation to Symptom Generation

Diverticular disease is a common clinical problem, particularly in industrialized countries. In most cases, colonic diverticula remain asymptomatic throughout life and sometimes are found incidentally during colonic imaging in colorectal cancer screening programs in otherwise healthy subjects. Nonetheless, roughly 25% of patients bearing colonic diverticula develop clinical manifestations. Abdominal symptoms associated with diverticula in the absence of inflammation or complications are termed symptomatic uncomplicated diverticular disease (SUDD). The pathophysiology of diverticular disease as well as the mechanisms involved in the shift from an asymptomatic condition to a symptomatic one is still poorly understood. It is accepted that both genetic factors and environment, as well as intestinal microenvironment alterations, have a role in diverticula development and in the different phenotypic expressions of diverticular disease. In the present review, we will summarize the up-to-date knowledge on the pathophysiology of diverticula and their different clinical setting, including diverticulosis and SUDD.

Right sided diverticulitis in western countries: A review

BACKGROUND

Although the treatment guidelines for left sided diverticulitis are clear, the management of right colonic diverticulitis is not well established. This disease can no longer be ignored due to significant spread throughout Asia.

AIM

To analyse epidemiology, diagnosis and treatment of right-sided diverticulitis in western countries.

METHODS

MEDLINE and PubMed searches were performed using the key words “right-sided diverticulitis’’, ‘‘right colon diverticulitis’’, ‘‘caecal diverticulitis’’, ‘‘ascending colon diverticulitis’’ and ‘‘caecum diverticula’’ in order to find relevant articles published until 2021.

RESULTS

A total of 18 studies with 422 patients were found. Correct diagnosis was made only in 32.2%, mostly intraoperatively or via CT scan. The main reason for misdiagnosis was a suspected acute appendicitis (56.8%). The treatment was a non-operative management (NOM) in 184 patients (43.6%) and surgical in 238 patients (56.4%), seven of which after NOM failure. Recurrence rate was low (5.45%), similar to eastern studies and inferior to left -sided diverticulitis. Recurrent patients were successfully conservatively retreated in most cases.

CONCLUSION

The management of right- sided diverticulitis is not well clarified in the western world and no selective guidelines have been considered even if principles are similar to those with left- sided diverticulitis. Wrong diagnosis is one of the most important problems and CT scan seems to be the best imaging modality. NOM offers a safe and effective treatment; surgery should be considered only in cases of complicated diverticulitis or if malignancy cannot be excluded. Further studies are needed to clarify the correct treatment.

Impaired Colonic Contractility and Intestinal Permeability in Symptomatic Uncomplicated Diverticular Disease

Background/Aims

Impaired intestinal motility seems to play a crucial role in symptomatic uncomplicated diverticular disease (SUDD), although the mechanism is not clear. The aim of the present study is to explore the contractility patterns of colonic smooth muscle strips (MS) and smooth muscle cells (SMCs) and to assess mucosal integrity in SUDD patients.

Methods

MS or SMCs were isolated from specimens of human distal colon of 18 patients undergoing surgery for non-obstructive colonic cancer, among them 9 with SUDD. Spontaneous phasic contractions on strips and morpho-functional parameters on cells were evaluated in basal conditions and in response to acetylcholine (ACh). Mucosal integrity of SUDD colonic biopsies was evaluated by the Ussing Chamber system. Immunohistochemical staining for tight junction protein complex and for Toll-like receptor 4 (TLR4) was performed.

Results

Colonic MS of SUDD group showed a significant reduced basal tone and ACh-elicited contraction, compared to the control group (9.5 g and 47.0% in the SUDD group; 14.16 g and 69.0% in the control group; P < 0.05). SMCs of SUDD group showed a maximal contractile response to ACh significantly reduced compared to control group (8.8% vs 16.5%, P < 0.05). SUDD patients displayed lower transepithelial electrical resistance and increased paracellular permeability compared to control group. Immunohistochemical expression of TLR4 was not different in both groups, while tight junction protein complex expression was lower in SUDD patients compared to control group patients.

Conclusion

It could be hypothesized that in SUDD, in absence of severe inflammation, an increased intestinal mucosal permeability is related to altered colonic motility probably responsible for symptoms genesis.

Sex and Race Disparities in Diverticulosis Prevalence

BACKGROUND & AIMS

The prevalence of diverticulosis differs with demographic features of patients, but evidence is limited. Well-defined demographic studies are necessary to understand diverticulosis biology. We estimated the prevalence of diverticulosis among patients of different ages, sexes, and races and ethnicities and calculated odds ratios.

DESIGN

Using data from an endoscopic database, we identified 271,181 colonoscopy procedures performed from 2000 through 2012 at 107 sites in the United States. Our analysis included individuals 40 years and older who underwent colonoscopy examination for average-risk screening. The outcome was any reported diverticulosis on colonoscopy. Multivariate analyses were performed using logistic regression to estimate odds ratios (ORs) and 95% CI values, adjusting for confounding variables.

RESULTS

The prevalence of diverticulosis increased with age in men and women of all races and ethnicities. Women 40-49 years old had significantly lower odds of any diverticulosis (OR, 0.71; 95% CI, 0.63-0.80) compared with men 40-49 years old, after adjustment. The strength of this association decreased with age. Compared with non-Hispanic white individuals, non-Hispanic black individuals (OR, 0.80; 95% CI, 0.77-0.83) and Asian/Pacific Islanders (OR, 0.38; 95% CI, 0.35-0.41) had lower odds of any diverticulosis. However, non-Hispanic black individuals (OR, 1.53, 95% CI, 1.44-1.62) had increased odds of any proximal diverticulosis, whereas Asian/Pacific Islanders (OR, 3.12; 95% CI, 2.67-3.66) had increased odds of only proximal diverticulosis.

CONCLUSIONS

In an analysis of data from 271,181 colonoscopy procedures, diverticulosis was less prevalent in women compared with men in the same age groups, indicating that sex hormones might affect pathogenesis. Differences in the odds of diverticulosis by race and ethnicity indicate a genetic contribution to risk.

Diverticular disease epidemiology: acute hospitalisations are growing fastest in young men

BACKGROUND

Older age has long been linked to risk of diverticulitis, but the epidemiology is seldom described for a national population. The aim of this study was to investigate age- and gender differences in incidence, temporal trends, lifetime risk and prevalence related to acute diverticulitis hospitalisations in New Zealand.

METHODS

Records of all hospitalisations with diverticulitis the primary diagnosis were obtained from the Ministry of Health for the period 2000-2015. The first acute diverticulitis admission recorded for an individual was taken as an incident event; all others were classified as recurrent. Trends in age- and sex-specific and age-standardised incidence rates are described, and lifetime risk and prevalence estimated.

RESULTS

Over the 16 years from 2000 to 2015, 37,234 acute hospitalisations for diverticulitis were recorded in 28,329 people aged 30 + years (median = 66 years). Rates of incident hospitalisations rose with age, from 5/10,000 person-years at age 50-54 years to 19/10,000py by age 80-84 years. Rates for women were lower than men before age 55 years, but higher thereafter. Age-standardised rates rose 0.2/10,000py annually, but approximately doubled among men aged < 50 years. Lifetime risk was estimated at over 5%, with the prevalence pool rising to over 1.5% of the population aged 30+ in 2030.

CONCLUSIONS

Rapid increases in diverticulitis admissions among young men since 2000 correspond with increases reported elsewhere but remain unexplained; notably young women follow similar trends 5-10 years later. Increasing incidence, combined with population ageing, adds urgency to explain diverticular formation, to understand factors that trigger or provoke their inflammation/infection, and to clarify treatment and (self-)management pathways.

Etiopathogenetic Mechanisms in Diverticular Disease of the Colon

This article reviews epidemiological evidence of heritability and putative mechanisms in diverticular disease, with greatest attention to 3 recent studies of genetic associations with diverticular disease based on genome-wide or whole-genome sequencing studies in large patient cohorts. We provide an analysis of the biological plausibility of the significant associations with gene variants reported and highlight the relevance of ANO1, CPI-17 (aka PPP1R14A), COLQ6, COL6A1, CALCB or CALCA, COL6A1, ARHGAP15, and S100A10 to colonic neuromuscular function and tissue properties that may result in altered compliance and predispose to the development of diverticular disease. Such studies also identify candidate genes for future studies.

Diverticulosis and nine connective tissue disorders: epidemiological support for an association

Purpose: An underlying connective tissue disorder (CTD) may predispose to formation of intestinal diverticula. We assess the association of diverticulosis with nine selected CTDs, to inform the pathophysiology of diverticula. Methods: A population-based period-prevalence study. Individuals (3.5 million New Zealand residents born 1901-1986) with a health system record 1999-2016 were grouped into those with a hospital diagnosis of diverticulosis or diverticulitis (ICD-10-AM K57), and those without. Also recorded were any hospital diagnoses of nine selected CTDs. The association of exposure to diverticulosis and each CTD was assessed using logistic regressions adjusted for age, gender, ethnicity and region. Results: In all, 85,958 (2.4%) people had a hospital diagnosis of diverticulosis. Hospitalisation with diverticulosis was highly significantly associated with rectal prolapse (adjusted odds ratio [OR] = 3.9), polycystic kidney disease (OR = 3.8), heritable syndromes (Marfan or Ehlers-Danlos) (OR = 2.4), female genital prolapse (OR = 2.3), non-aortic aneurysm (OR = 2.3), aortic aneurysm (OR = 2.2), inguinal hernia (OR = 1.9) and dislocations of shoulder and other joints (OR = 1.7), but not subarachnoid haemorrhage (OR = 1.0). Conclusion: People with diverticulosis are more likely to have colonic extracellular matrix (ECM)/connective tissue alterations in anatomical areas other than the bowel, suggesting linked ECM/connective tissue pathology. Although biases may exist, the results indicate large-scale integrated studies are needed to investigate underlying genetic pathophysiology of colonic diverticula, together with fundamental biological studies to investigate cellular phenotypes and ECM changes.

Ultrastructural changes of the human enteric nervous system and interstitial cells of Cajal in diverticular disease

BACKGROUND

In spite of numerous advances in understanding diverticular disease, its pathogenesis remains one of the main problems to be solved. We aimed to investigate the ultrastructural changes of the enteric nervous system in unaffected individuals, in asymptomatic patients with diverticulosis and in patients with diverticular disease.

METHODS

Transmission electron microscopy was used to analyse samples of the myenteric, outer submucosal and inner submucosal plexuses from patients without diverticula (n=9), asymptomatic patients with diverticulosis (n=7) and in patients with complicated diverticular disease (n=9). We described the structure of ganglia, interstitial cells of Cajal and enteric nerves, as well as their relationship with each other. The distribution and size of nerve processes were analysed quantitatively.

RESULTS

In complicated diverticular disease, neurons exhibited larger lipofuscin-like inclusions, their membranous organelles had larger cisterns and the nucleus showed deeper indentations. Nerve remodeling occurred in every plexus, characterised by an increased percentage of swollen and fine neurites. Interstitial cells of Cajal had looser contacts with the surrounding cells and showed cytoplasmic depletion and proliferation of the rough endoplasmic reticulum. In asymptomatic patients with diverticulosis, alterations of enteric nerves and ICC were less pronounced.

CONCLUSIONS

In conclusion, the present findings suggest that most ultrastructural changes of the enteric nervous system occur in complicated diverticular disease. The changes are compatible with damage to the enteric nervous system and reactive remodeling of enteric ganglia, nerves and interstitial cells of Cajal. Disrupted architecture of enteric plexuses might explain clinical and pathophysiological changes associated with diverticular disease.

Changing theories on the pathogenesis and risk factors for diverticulitis

Diverticulitis was thought to be a simple complication of an even simpler disease (diverticulosis), but may in fact result from an entirely new set of complex pathologies. Considering diverticulitis is increasing in annual incidence and becoming more prevalent in younger populations, the implications of appropriate management become more vital than ever. This article reviews old and new understandings of diverticulitis and current recommendations for prevention and clinical management.

Altered enteric expression of the homeobox transcription factor Phox2b in patients with diverticular disease

Background

Diverticular disease, a major gastrointestinal disorder, is associated with modifications of the enteric nervous system, encompassing alterations of neurochemical coding and of the tyrosine receptor kinase Ret/GDNF pathway. However, molecular factors underlying these changes remain to be determined.

Objectives

We aimed to characterise the expression of Phox2b, an essential regulator of Ret and of neuronal subtype development, in the adult human enteric nervous system, and to evaluate its potential involvement in acute diverticulitis.

Methods

Site-specific gene expression of Phox2b in the adult colon was analysed by quantitative polymerase chain reaction. Colonic specimens of adult controls and patients with diverticulitis were subjected to quantitative polymerase chain reaction for Phox2b and dual-label immunochemistry for Phox2b and the neuronal markers RET and tyrosine hydroxylase or the glial marker S100β.

Results

The results indicate that Phox2b is physiologically expressed in myenteric neuronal and glial subpopulations in the adult enteric nervous system. Messenger RNA expression of Phox2b was increased in patients with diverticulitis and both neuronal, and glial protein expression of Phox2b were altered in these patients.

Conclusions

Alterations of Phox2b expression may contribute to the enteric neuropathy observed in diverticular disease. Future studies are required to characterise the functions of Phox2b in the adult enteric nervous system and to determine its potential as a therapeutic target in gastrointestinal disorders.

Alterations in enteric calcitonin gene-related peptide in patients with colonic diverticular disease: CGRP in diverticular disease

Diverticular disease (DD) is one of the most prevalent diseases of the large bowel. Lately, imbalance of neuro-muscular transmission has been recognized as a major etiological factor for DD. Neuronal calcitonin gene-related peptide (CGRP) is a potent gastrointestinal smooth muscle relaxant shown to have a widespread effect within the alimentary tract. Nevertheless, CGRPergic innervation of the enteric ganglia has never been considered in the context of motility impairment observed in DD patients. Changes in CGRP and calcitonin receptor-like receptor (CRLR) abundance within enteric ganglia were investigated in sigmoid samples from symptomatic and asymptomatic DD patients using quantitative fluorescence microscopy. CGRP effect on gastrointestinal smooth muscle was investigated using organ bath technique. We found CGRP levels within the enteric ganglia to be declined by up to 52% in symptomatic DD patients. Conversely, CRLR within the enteric ganglia was upregulated by 41% in symptomatic DD. Longitudinal smooth muscle displayed an elevated (+10.5%) relaxant effect to the exogenous application of CGRP in colonic strips from symptomatic DD patients. Samples from asymptomatic DD patients consistently showed intermediate values across different experiments. In conclusion, the present study demonstrates that CGRPergic signaling is subject to alteration in DD. Our results suggest that a hypersensitization mechanism to gradually decreasing levels of CGRP-IR nerve fibers takes place during DD progression. Alterations to CGRPergic signaling in DD disease may have implications for physiological abnormalities associated with colonic DD.

Pathophysiology of diverticular disease

Inflammation of diverticula, or outpouchings of the colonic mucosa and submucosa through the muscularis layer, leads to diverticulitis. The development of diverticular disease, encompassing both diverticulosis and diverticulitis, is a result of genetic predisposition, lifestyle, and environmental factors, including the microbiome. Areas covered: Previous reports implicated genetic predisposition, environmental factors, and colonic dysmotility in diverticular disease. Recent studies have associated specific host immune responses and the microbiome as contributors to diverticulitis. To review pertinent literature describing pathophysiological factors associated with diverticulosis or diverticulitis, we searched the PubMed database (March 2018) for articles considering the role of colonic architecture, genetic predisposition, environment, colonic motility, immune response, and the microbiome. Expert commentary: In the recent years, research into the molecular underpinnings of diverticular disease has enhanced our understanding of diverticular disease pathogenesis. Although acute uncomplicated diverticulitis is treated with broad spectrum antibiotics, evaluation of the microbiome has been limited and requires further comprehensive studies. Evidence suggests that a deregulation of the host immune response is associated with both diverticulosis and diverticulitis. Further examining these pathways may reveal proteins that can be therapeutic targets or aid in identifying biological determinants of clinical or surgical decision making.

Animal Models of Diverticulosis: Review and Recommendations

Diverticulosis is a structural alteration of the colon tissue characterized by the development of pouch-like structures called diverticula. It afflicts a significant portion of the population in Western countries, with a higher prevalence among the elderly. Diverticulosis is believed to be the result of a synergetic interaction between inherent tissue weakness, diet, colonic microstructure, motility, and genetic factors. A validated etiology has, however, not yet been established. Non-surgical treatment is currently lacking due to this poor understanding, and surgical colon resection is the only long-term solution following recurrent complications. With rising prevalence, the burden of diverticulosis on patients and hospital resources has increased over the past several years. More efficient and less invasive treatment approaches are, thus, urgently needed. Animal models of diverticulosis are crucial to enable a preclinical assessment and evaluation of such novel approaches. This review discusses the animal models of diverticulosis that have been proposed to date. The current models require either a significant amount of time to develop diverticulosis, present a relatively low success rate, or seriously deteriorate the animals' systemic health. Recommendations are thus provided to address these pitfalls through the selection of a suitable animal and the combination of multiple risk factors for diverticulosis.

Recent advances in understanding and managing diverticulitis

In the past few decades, the increasing socioeconomic burden of acute diverticulitis (AD) has become evident, and with the growth of the population age, this significant economic impact will likely continue to rise. Furthermore, recent evidence showed an increased rate of hospital admissions especially evident among women and younger individuals. The natural history and pathophysiology of this clinical condition is still to be fully defined, and efforts continue to be made in the identification of risk factors and the establishment of relative preventive strategies. The actual therapeutic strategies aimed to modulate gut microbiota, such as rifaximin or probiotics, or to reduce mucosal inflammation, such as mesalazine, present a relatively poor efficacy for both the prevention of the first AD episode (primary prevention) and its recurrence (secondary prevention). In the last few years, the main goal achieved has been in the management of AD in that uncomplicated AD can, to a larger extent, be managed in an outpatient setting with no or little supportive therapy, a strategy that will certainly impact on the health costs of this disease. The problem of AD recurrence remains a topic of debate. The aim of this review is to present updated evidence on AD epidemiology and relative open clinical questions and to analyze in detail predisposing and protective factors with an attempt to integrate their possible modes of action into the several pathogenic mechanisms that have been suggested to contribute to this multifactorial disease. A unifying hypothesis dealing with the colonic luminal and extra-luminal microenvironments separately is provided. Finally, evidence-based changes in therapeutic management will be summarized. Because of an ascertained multifactorial pathogenesis of uncomplicated and complicated AD, it is probable that a single 'causa prima' will not be identifiable, and a better stratification of patients could allow one to pursue tailored therapeutic algorithm strategies.

Diverticular Disease of the Colon: Neuromuscular Function Abnormalities

Colonic diverticular disease is a frequent finding in daily clinical practice. However, its pathophysiological mechanisms are largely unknown. This condition is likely the result of several concomitant factors occurring together to cause anatomic and functional abnormalities, leading as a result to the outpouching of the colonic mucosa. A pivotal role seems to be played by an abnormal colonic neuromuscular function, as shown repeatedly in these patients, and by an altered visceral perception. There is recent evidence that these abnormalities might be related to the derangement of the enteric innervation, to an abnormal distribution of mucosal neuropeptides, and to low-grade mucosal inflammation. The latter might be responsible for the development of visceral hypersensitivity, often causing abdominal pain in a subset of these patients.

Myenteric plexitis: A frequent feature in patients undergoing surgery for colonic diverticular disease

BACKGROUND

Diverticular disease of the colon is frequent in clinical practice, and a large number of patients each year undergo surgical procedures worldwide for their symptoms. Thus, there is a need for better knowledge of the basic pathophysiologic mechanisms of this disease entity.

OBJECTIVES

Because patients with colonic diverticular disease have been shown to display abnormalities of the enteric nervous system, we assessed the frequency of myenteric plexitis (i.e. the infiltration of myenteric ganglions by inflammatory cells) in patients undergoing surgery for this condition.

METHODS

We analyzed archival resection samples from the proximal resection margins of 165 patients undergoing left hemicolectomy (60 emergency and 105 elective surgeries) for colonic diverticulitis, by histology and immunochemistry.

RESULTS

Overall, plexitis was present in almost 40% of patients. It was subdivided into an eosinophilic (48%) and a lymphocytic (52%) subtype. Plexitis was more frequent in younger patients; and it was more frequent in those undergoing emergency surgery (50%), compared to elective (28%) surgery (p = 0.007). All the severe cases of plexitis displayed the lymphocytic subtype.

CONCLUSIONS

In conclusion, myenteric plexitis is frequent in patients with colonic diverticular disease needing surgery, and it might be implicated in the pathogenesis of the disease.

Morphologic Basis for Developing Diverticular Disease, Diverticulitis, and Diverticular Bleeding

Diverticula of the colon are pseudodiverticula defined by multiple outpouchings of the mucosal and submucosal layers penetrating through weak spots of the muscle coat along intramural blood vessels. A complete prolapse consists of a diverticular opening, a narrowed neck, and a thinned diverticular dome underneath the serosal covering. The susceptibility of diverticula to inflammation is explained by local ischemia, translocation of pathogens due to retained stool, stercoral trauma by fecaliths, and microperforations. Local inflammation may lead to phlegmonous diverticulitis, paracolic/mesocolic abscess, bowel perforation, peritonitis, fistula formation, and stenotic strictures. Diverticular bleeding is due to an asymmetric rupture of distended vasa recta at the diverticular dome and not primarily linked to inflammation. Structural and functional changes of the bowel wall in diverticular disease comprise: i) Altered amount, composition, and metabolism of connective tissue; ii) Enteric myopathy with muscular thickening, deranged architecture, and altered myofilament composition; iii) Enteric neuropathy with hypoganglionosis, neurotransmitter imbalance, deficiency of neurotrophic factors and nerve fiber remodeling; and iv) Disturbed intestinal motility both in vivo (increased intraluminal pressure, motility index, high-amplitude propagated contractions) and in vitro (altered spontaneous and pharmacologically triggered contractility). Besides established etiologic factors, recent studies suggest that novel pathophysiologic concepts should be considered in the pathogenesis of diverticular disease.

[Anatomy and pathogenesis of diverticular disease]

BACKGROUND

Although diverticular disease is one of the most frequent gastrointestinal disorders the pathogenesis is not yet sufficiently clarified.

OBJECTIVES

The aim is to define the anatomy and pathogenesis of diverticular disease considering the risk factors and description of structural and functional alterations of the bowel wall.

METHODS

This article gives an appraisal of the literature, presentation and evaluation of classical etiological factors, analysis and discussion of novel pathogenetic concepts.

RESULTS

Colonic diverticulosis is defined as an acquired out-pouching of multiple and initially asymptomatic pseudodiverticula through muscular gaps in the colon wall. Diverticular disease is characterized by diverticular bleeding and/or inflammatory processes (diverticulitis) with corresponding complications (e.g. abscess formation, fistula, covered and open perforation, peritonitis and stenosis). Risk factors for diverticular disease include increasing age, genetic predisposition, congenital connective tissue diseases, low fiber diet, high meat consumption and pronounced overweight. Alterations of connective tissue cause a weakening of preformed exit sites of diverticula and rigidity of the bowel wall with reduced flexibility. It is assumed that intestinal innervation disorders and structural alterations of the musculature induce abnormal contractile patterns with increased intraluminal pressure, thereby promoting the development of diverticula. Moreover, an increased release of pain-mediating neurotransmitters is considered to be responsible for persistent pain in chronic diverticular disease.

CONCLUSIONS

According to the present data the pathogenesis of diverticular disease cannot be attributed to a single factor but should be considered as a multifactorial event.