Genetics and irritable bowel syndrome: from genomics to intermediate phenotype and pharmacogenetics

Genetics of irritable bowel syndrome: shifting gear via biobank-scale studies

The pathophysiology of irritable bowel syndrome (IBS) is multifactorial and probably involves genetic predisposition and the effect of environmental factors. Unlike other gastrointestinal diseases with a heritable component, genetic research in IBS has been scarce and mostly characterized by small underpowered studies, leading to inconclusive results. The availability of genomic and health-related data from large international cohorts and population-based biobanks offers unprecedented opportunities for long-awaited, well-powered genetic studies in IBS. This Review focuses on the latest advances that provide compelling evidence for the importance of genes involved in the digestion of carbohydrates, ion channel function, neurotransmitters and their receptors, neuronal pathways and the control of gut motility. These discoveries have generated novel information that might be further refined for the identification of predisposed individuals and selection of management strategies for patients. This Review presents a conceptual framework, the advantages and potential limitations of modern genetic research in IBS, and a summary of available evidence.

A Swedish national adoption study of risk of irritable bowel syndrome (IBS)

Objectives

Irritable bowel syndrome (IBS) clusters in families, but the familial risk of IBS has not been determined in adoptees. Studying adoptees and their biological and adoptive parents is a strong study design for separating genetic from environmental causes of familial clustering. This nationwide study aimed to separate the biological (genetic) and familial environmental contribution to the familial transmission of IBS.

Methods

We performed a family study for Swedish-born adoptees born from 1951 until 1995, and their biological and adoptive parents. The Swedish Multigeneration Register was linked to the Hospital Register (inpatients and outpatients) for the period 1964-2012 and the Swedish Outpatient Care Register for 2001-2012, and the Swedish Primary Healthcare register for 1989-2012. ORs for IBS were calculated for adoptees with an affected biological parent with IBS compared with adoptees without a biological parent with IBS. The OR for IBS was also determined in adoptees with an adoptive parent with IBS compared with adoptees without an adoptive parent with IBS. Heritability h² (±SE) was also determined.

Results

The ORs for IBS were 1.67 in adoptees (95% CI 1.06 to 2.62) of biological parents diagnosed with IBS. The ORs for IBS were 0.88 in adoptees (95% CI 0.48 to 1.63) of adoptive parents diagnosed with IBS. The heritability was 19.5%±8.5%.

Conclusions

The present study indicates that biological (genetic) factors are important for the familial clustering of IBS. The heritability calculated is in the range from twin studies and suggests that heritability may be estimated in adoptees.

Systematic review with meta-analysis: post-infectious irritable bowel syndrome after travellers' diarrhoea

BACKGROUND

Gastrointestinal infection is known as a risk factor for the development of the irritable bowel syndrome (post-infectious irritable bowel syndrome, PI-IBS). The incidence of PI-IBS ranges between 3% and over 30% of people after infectious gastroenteritis.

AIM

To perform a meta-analysis pools and report data concerning the relative risk (RR) of PI-IBS after TD.

METHODS

Database search using Medline through PubMed, Scopus, EBM Reviews (Cochrane Database of Systematic Reviews) and PsycINFO was performed to identify relevant studies. Those that met the inclusion criteria were pooled. A random effects model (Mantel-Haenszel) was performed.

RESULTS

Six eligible studies were found. In three of six studies, the authors reported a statistically significant association of TD and PI-IBS. The pooled RR was 3.35 (95% CI: 2.22-5.05) with a significant overall effect (P < 0.00001). Overall PI-IBS incidence was 5.4% in TD subjects and 1.4% in healthy subjects. There was no significant heterogeneity within the pooled studies (I(2)  = 5%). Self-reported TD alone resulted in an over 1.5-fold RR for PI-IBS compared to laboratory-confirmed TD [RR 3.90 (95% CI: 2.35-6.49) vs. RR 2.42 (95% CI: 1.22-4.78)].

CONCLUSIONS

There is a strong association between travellers' diarrhoea and post-infectious irritable bowel syndrome. Self-reports of exposure seem to result in a higher post-infectious irritable bowel syndrome occurrence than laboratory-confirmed cases of travellers' diarrhoea, but further studies are needed to confirm this finding. Finally, potential influences of the selection of an appropriate study population on post-infectious irritable bowel syndrome epidemiology are discussed.

Risk of irritable bowel syndrome in first-degree, second-degree and third-degree relatives of affected individuals: a nationwide family study in Sweden

OBJECTIVES

IBS aggregates in families, but the familial risk of IBS has only been determined in first-degree relatives and spouses. This nationwide study aimed to determine the familial risk of IBS in first-degree, second-degree, and third-degree relatives and spouses of affected individuals in order to estimate the relative influences of genes and shared family environment.

METHODS

We performed a case-cohort study. The Swedish Multigeneration Register was linked to the Hospital Discharge Register for the period 1987-2010 and the Swedish Outpatient Care Register for 2001-2010. ORs for IBS were calculated for relatives of individuals who had been diagnosed with IBS compared with relatives of individuals unaffected by IBS as the reference group. ORs were also determined for IBS cases diagnosed in primary healthcare in four Swedish counties (2001-2007).

RESULTS

The ORs for IBS were 1.75 in siblings (95% CI 1.63 to 1.89), 1.82 in offspring (1.67 to 1.97), 1.90 in parents (1.76 to 2.05), 1.10 in maternal half-siblings (0.88 to 1.39), 1.78 in paternal half-siblings (1.48 to 2.15), 1.27 in nieces/nephews (1.18 to 1.38), 1.11 in cousins (1.04 to 1.18), and 1.51 in spouses (1.24 to 1.84) of probands diagnosed with IBS. The OR for probands diagnosed in primary healthcare was 1.82 in siblings (1.52 to 2.18), and 1.82 in offspring (1.49 to 2.21).

CONCLUSIONS

The increased IBS risk among first-degree relatives and also second-degree and third-degree relatives indicates a genetic component of the familial clustering of IBS. However, a non-genetic contribution is also suggested by the increased risk among spouses.

Stress-induced visceral pain: toward animal models of irritable-bowel syndrome and associated comorbidities

Visceral pain is a global term used to describe pain originating from the internal organs, which is distinct from somatic pain. It is a hallmark of functional gastrointestinal disorders such as irritable-bowel syndrome (IBS). Currently, the treatment strategies targeting visceral pain are unsatisfactory, with development of novel therapeutics hindered by a lack of detailed knowledge of the underlying mechanisms. Stress has long been implicated in the pathophysiology of visceral pain in both preclinical and clinical studies. Here, we discuss the complex etiology of visceral pain reviewing our current understanding in the context of the role of stress, gender, gut microbiota alterations, and immune functioning. Furthermore, we review the role of glutamate, GABA, and epigenetic mechanisms as possible therapeutic strategies for the treatment of visceral pain for which there is an unmet medical need. Moreover, we discuss the most widely described rodent models used to model visceral pain in the preclinical setting. The theory behind, and application of, animal models is key for both the understanding of underlying mechanisms and design of future therapeutic interventions. Taken together, it is apparent that stress-induced visceral pain and its psychiatric comorbidities, as typified by IBS, has a multifaceted etiology. Moreover, treatment strategies still lag far behind when compared to other pain modalities. The development of novel, effective, and specific therapeutics for the treatment of visceral pain has never been more pertinent.

Relationship between IL-10 promoter gene polymorphisms and plasma level and susceptibility to overlap syndrome of diarrhea irritable bowel syndrome and functional dyspepsia

AIM: To investigate the relationship between interleukin-10 (IL-10) promoter gene polymorphisms and plasma levels and susceptibility to overlap syndrome of diarrhea irritable bowel syndrome (D-IBS) and functional dyspepsia (FD).

METHODS: Blood samples were collected from 164 patients and 200 healthy controls and genomic DNA was extracted. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was used to determine the genotypes in the -592A/C site, and amplification refractory mutation system polymerase chain reactions (ARMS-PCR) and DNA sequencing were performed to detect the polymorphism of the -1082G/A site. IL-10 plasma levels were determined by enzyme-linked immunosorbent assay (ELISA).

RESULTS: The -592A/C site in the IL-10 gene showed no significant differences in genotypes or allele frequency between the D-IBS-FD overlap syndrome group and control group, but the frequency of -592 CC genotype was significantly decreased in the D-IBS-FD overlap syndrome group. Compared with the CC genotype, the AA genotype and the AA+AC genotypes increased the risk of D-IBS-FD overlap syndrome 1.989 and 1.808 times, respectively. There were no significant differences in the distribution or the allele frequency of -1082 genotypes, the genotypes of the combination of -592 and -1082, and the distribution of the genotypes of different IL-10 levels between the D-IBS-FD overlap syndrome and healthy control groups. The average plasma IL-10 levels were significantly lower in patients with D-IBS-FD overlap syndrome than in healthy controls (14.60 pg/mL ± 7.14 pg/mL vs 22.86 pg/mL ± 10.62 pg/mL, P < 0.001). Among patients with D-IBS-FD overlap syndrome, the average plasma IL-10 levels in patients with -592 AA, -592 AC, -592 CC, and -592 AA+AC genotypes were 14.50 pg/mL ± 6.37 pg/mL, 14.85 pg/mL ± 7.75 pg/mL, 13.92 pg/mL ± 7.63 pg/mL, 14.68 pg/mL ± 7.10 pg/mL, respectively, which showed no significant differences. Plasma IL-10 levels showed no significant difference between the carriers of A allele and non-carriers.

CONCLUSION: The -592A site in IL-10 gene promoter and lower IL-10 plasma level may be associated with susceptibility to overlap syndrome of D-IBS and FD, but there is no association between them.

Genetic variants in CDC42 and NXPH1 as susceptibility factors for constipation and diarrhoea predominant irritable bowel syndrome

OBJECTIVE

The complex genetic aetiology underlying irritable bowel syndrome (IBS) needs to be assessed in large-scale genetic studies. Two independent IBS cohorts were genotyped to assess whether genetic variability in immune, neuronal and barrier integrity genes is associated with IBS.

DESIGN

384 single nucleotide polymorphisms (SNPs) covering 270 genes were genotyped in an exploratory cohort (935 IBS patients, 639 controls). 33 SNPs with Puncorrected<0.05 were validated in an independent set of 497 patients and 887 controls. Genotype distributions of single SNPs were assessed using an additive genetic model in IBS and clinical subtypes, IBS-C and IBS-D, both in individual and combined cohorts. Trait anxiety (N=614 patients, 533 controls), lifetime depression (N=654 patients, 533 controls) and mRNA expression in rectal biopsies (N=22 patients, 29 controls) were correlated with SNP genotypes.

RESULTS

Two SNPs associated independently in the exploratory and validation cohort: rs17837965-CDC42 with IBS-C (ORexploratory=1.59 (1.05 to 1.76); ORvalidation=1.76 (1.03 to 3.01)) and rs2349775-NXPH1 with IBS-D (ORexploratory=1.28 (1.06 to 1.56); ORvalidation=1.42 (1.08 to 1.88)). When combining both cohorts, the association of rs2349775 withstood post hoc correction for multiple testing in the IBS-D subgroup. Additionally, three SNPs in immune-related genes (rs1464510-LPP, rs1881457-IL13, rs2104286-IL2RA), one SNP in a neuronal gene (rs2349775-NXPH1) and two SNPs in epithelial genes (rs245051-SLC26A2, rs17837965-CDC42) were weakly associated with total-IBS (Puncorrected<0.05). At the functional level, rs1881457 increased IL13 mRNA levels, whereas anxiety and depression scores did not correlate with rs2349775-NXPH1.

CONCLUSIONS

Rs2349775 (NXPH1) and rs17837965 (CDC42) were associated with IBS-D and IBS-C, respectively, in two independent cohorts. Further studies are warranted to validate our findings and to determine the mechanisms underlying IBS pathophysiology.

Irritable bowel syndrome: The evolution of multi-dimensional looking and multidisciplinary treatments

Irritable bowel syndrome (IBS) is common in the society. Among the putative pathogeneses, gut dysmotility results in pain and disturbed defecation. The latter is probably caused by the effect of abnormal gut water secretion. The interaction between abnormal gas accumulation, abdominal pain and bloating remains controversial. Visceral hypersensitivity and its modification along with the central transmission are the characteristics of IBS patients. The identification of biologic markers based on genetic polymorphisms is undetermined. Imbalanced gut microbiota may alter epithelial permeability to activate nociceptive sensory pathways which in turn lead to IBS. Certain food constituents may exacerbate bowel symptoms. The impact of adult and childhood abuses on IBS is underestimated. Using the concept of biopsychosocial dysfunction can integrate multidimensional pathogeneses. Antispasmodics plus stool consistency modifiers to treat the major symptoms and defecation are the first-line drug treatment. New drugs targeting receptors governing bowel motility, sensation and secretion can be considered, but clinicians must be aware of their potential serious side effects. Psychiatric drugs and modalities may be the final options for treating intractable subjects. Probiotics of multi-species preparations are safe and worth to be considered for the treatment. Antibiotics are promising but their long-term safety and effectiveness are unknown. Diet therapy including exclusion of certain food constituents is an economic measure. Using relatively safe complementary and alternative medicines (CAMs) may be optional to those patients who failed classical treatment. In conclusion, IBS is a heterogeneous disorder with multidimensional pathogeneses. Personalized medicines with multidisciplinary approaches using different classes of drugs, psychiatric measures, probiotics and antibiotics, dietary therapy, and finally CAMs, can be considered.

Irritable bowel syndrome-diarrhea: characterization of genotype by exome sequencing, and phenotypes of bile acid synthesis and colonic transit

The study objectives were: to mine the complete exome to identify putative rare single nucleotide variants (SNVs) associated with irritable bowel syndrome (IBS)-diarrhea (IBS-D) phenotype, to assess genes that regulate bile acids in IBS-D, and to explore univariate associations of SNVs with symptom phenotype and quantitative traits in an independent IBS cohort. Using principal components analysis, we identified two groups of IBS-D (n = 16) with increased fecal bile acids: rapid colonic transit or high bile acids synthesis. DNA was sequenced in depth, analyzing SNVs in bile acid genes (ASBT, FXR, OSTα/β, FGF19, FGFR4, KLB, SHP, CYP7A1, LRH-1, and FABP6). Exome findings were compared with those of 50 similar ethnicity controls. We assessed univariate associations of each SNV with quantitative traits and a principal components analysis and associations between SNVs in KLB and FGFR4 and symptom phenotype in 405 IBS, 228 controls and colonic transit in 70 IBS-D, 71 IBS-constipation. Mining the complete exome did not reveal significant associations with IBS-D over controls. There were 54 SNVs in 10 of 11 bile acid-regulating genes, with no SNVs in FGF19; 15 nonsynonymous SNVs were identified in similar proportions of IBS-D and controls. Variations in KLB (rs1015450, downstream) and FGFR4 [rs434434 (intronic), rs1966265, and rs351855 (nonsynonymous)] were associated with colonic transit (rs1966265; P = 0.043), fecal bile acids (rs1015450; P = 0.064), and principal components analysis groups (all 3 FGFR4 SNVs; P < 0.05). In the 633-person cohort, FGFR4 rs434434 was associated with symptom phenotype (P = 0.027) and rs1966265 with 24-h colonic transit (P = 0.066). Thus exome sequencing identified additional variants in KLB and FGFR4 associated with bile acids or colonic transit in IBS-D.

Relationship between expression of TPRV1 and TPRV2 and visceral hypersensitivity in rats with irritable bowel syndrome

AIM: To analyze the pathogenesis of irritable bowel syndrome (IBS) by observing the expression of TPRV1 and TPRV2 in the hypothalamus-pituitary-colon and visceral hypersensitivity in rats.

METHODS: Forty rats were divided into two groups randomly: a normal group and an IBS group. Diarrhea-predominate IBS was induced by intragastrical administration of folium sennae and bondage stress. At the end of the fourth week, all rats were sacrificed by intraperitoneal anesthesia. Histopathological changes were detected by HE staining. The expression of mast cells was detected by toluidine blue staining. The protein and mRNA expression of VR1 and VR2 was assayed by Western blot and real-time PCR. Visceral hypersensitivity was evaluated by colorectal distension and abdominal wall tension.

RESULTS: IBS was characterized by visceral hypersensitivity and mast cell activation. The expression of VR1 and VR2 in the hypothalamus-pituitary-colon was significantly increased in the IBS group compared with the normal group (all P < 0.05).

CONCLUSION: High expression of VR1 and VR2 may mediate visceral hypersensitivity and plays an important role in the development of IBS.

IBS and the role of otilonium bromide

INTRODUCTION

Awareness of the seriousness of irritable bowel disorder (IBS) remains low among clinicians. In this review, we summarize the current knowledge of IBS and highlight the major personal, economic, and social burden of the disease, and the importance of adequate treatment of what is still often viewed as a trivial disorder. In fact, IBS is a major reason for referral.

PATHOPHYSIOLOGY

It is crucial that the varied pathophysiologies of this complex heterogeneous disease are understood in order to be able to treat both the presenting symptoms (pain, bloating, flatulence, abnormal defecation, diarrhea, constipation) and the underlying disorder effectively. Low-grade inflammatory and immune activation has been observed, but the precise triggers and mechanisms, and the relevance to symptom generation, remain to be established.

TREATMENT

IBS patients require different treatment strategies according to the pattern, severity, frequency, and symptoms. While initial therapy traditionally targets the most bothersome symptom, long-term therapy aims at maintaining symptom control and preventing recurrence. In addition to dietary/lifestyle interventions and psychosocial strategies, a wide range of pharmacologic therapies are approved for use in IBS depending on the symptoms reported. Musculotropic spasmolytics, which act directly on intestinal smooth muscle contractility, such as otilonium bromide, are effective, particularly in the relief of abdominal pain and bloating, and are well tolerated in IBS. THE OBIS TRIAL: The recent large placebo-controlled Otilonium Bromide in Irritable Bowel Syndrome study demonstrated the superiority of otilonium bromide versus placebo not only in the reduction of pain and bloating, but also in protection from relapse due to the long-lasting effect.

Lower serum IL-10 is an independent predictor of IBS among volunteers in Mexico

OBJECTIVES

Studies suggest that altered immune activation, manifested by an imbalance in anti- and pro-inflammatory cytokine levels, exists in a subgroup of irritable bowel syndrome (IBS) patients. However, similar studies have not been conducted in Latin populations. The objective of this study was to measure serum levels of interleukin (IL)-10 and tumor necrosis factor (TNF)-α in subjects fulfilling symptom criteria for IBS and controls.

METHODS

Volunteers (n=178) from a university population in Mexico City, participated in the study. Of the sample, 34.8% met Rome II criteria for IBS and 65.2% were designated as controls. Serum cytokines were measured by enzyme-linked immunoabsorbent assay. Analysis of covariance models were used to test main effects between gender, IBS symptoms, and bowel habit subtype to explain the cytokine serum levels. Statistical models were tested using body mass index as a covariate.

RESULTS

IL-10 levels were significantly lower in IBS vs. controls (mean (95% confidence interval): 15.6 (14.8, 16.3) vs. 18.6 (17.9, 19.4) pg/ml, P<0.001), while TNF-α levels were higher in IBS (20.9 (19.1, 23.0) vs. 17.9 (16.7, 19.3) pg/ml, P=0.010). IBS and female gender were independent predictors for IL-10 (P<0.05). In contrast, female gender was an independent predictor for TNF-α. In addition, women with IBS-D had the lowest IL-10 (P<0.001) and highest TNF-α (P=0.021) vs. other subtypes.

CONCLUSIONS

The lower serum IL-10 in our subjects fulfilling IBS Rome II symptom criteria suggests an altered immune regulation. Further studies are needed to elucidate if a lower serum IL-10 may be useful as a biomarker for IBS in the Mexican population, especially for women with IBS-D.

Psychosocial determinants of irritable bowel syndrome

From a pure motor disorder of the bowel, in the past few years, irritable bowel syndrome (IBS) has become a multifactorial disease that implies visceral hypersensitivity, alterations at the level of nervous and humoral communications between the enteric nervous system and the central nervous system, alteration of the gut microflora, an increased intestinal permeability and minimum intestinal inflammation. Psychological and social factors can interfere with the communication between the central and enteric nervous systems, and there is proof that they are involved in the onset of IBS and influence the response to treatment and outcome. There is evidence that abuse history and stressful life events are involved in the onset of functional gastrointestinal disorders. In order to explain clustering of IBS in families, genetic factors and social learning mechanisms have been proposed. The psychological features, such as anxiety, depression as well as the comorbid psychiatric disorders, health beliefs and coping of patients with IBS are discussed in relation to the symptoms and outcome.

Stress-related alterations of visceral sensation: animal models for irritable bowel syndrome study

Stressors of different psychological, physical or immune origin play a critical role in the pathophysiology of irritable bowel syndrome participating in symptoms onset, clinical presentation as well as treatment outcome. Experimental stress models applying a variety of acute and chronic exteroceptive or interoceptive stressors have been developed to target different periods throughout the lifespan of animals to assess the vulnerability, the trigger and perpetuating factors determining stress influence on visceral sensitivity and interactions within the brain-gut axis. Recent evidence points towards adequate construct and face validity of experimental models developed with respect to animals' age, sex, strain differences and specific methodological aspects such as non-invasive monitoring of visceromotor response to colorectal distension as being essential in successful identification and evaluation of novel therapeutic targets aimed at reducing stress-related alterations in visceral sensitivity. Underlying mechanisms of stress-induced modulation of visceral pain involve a combination of peripheral, spinal and supraspinal sensitization based on the nature of the stressors and dysregulation of descending pathways that modulate nociceptive transmission or stress-related analgesic response.

A Klothoβ variant mediates protein stability and associates with colon transit in irritable bowel syndrome with diarrhea

BACKGROUND & AIMS

Bile acid (BA) malabsorption of moderate severity is reported in 32% of patients with chronic unexplained diarrhea, including diarrhea-predominant irritable bowel syndrome (IBS-D). We hypothesized that variants of genes regulating hepatic BA synthesis play a role in IBS-D.

METHODS

In 435 IBS and 279 healthy subjects, we tested individual associations of 15 common single nucleotide polymorphisms (SNPs) from 7 genes critical to BA homeostasis with symptom-based subgroups using dominant genetic models. In a subset of 238 participants, we tested association with colonic transit. SNP-SNP interactions were investigated based on known protein interactions in BA homeostasis. The function of SNP rs17618244 in Klothoβ (KLB) was evaluated using a protein stability assay in HEK293 cells.

RESULTS

SNP rs17618244 (Arg728Gln in KLB) is associated with colonic transit at 24 hours. G allele (Arg728) compared with A allele (Gln728) is associated with accelerated colonic transit (P=.0007) in the overall cohort; this association was restricted to IBS-D (P=.0018). Interaction tests of KLB rs17618244 with 3 nonsynonymous SNPs of fibroblast growth factor receptor 4 (FGFR4) revealed that rs1966265 (Val10Ile) and rs351855 (Gly388Arg) modulate rs1768244's association with colonic transit in IBS-D (P=.0025 and P=.0023, respectively). KLB Arg728 significantly reduced protein stability compared with KLB Gln728, demonstrating KLB rs17618244's functional significance. No significant associations with symptom-based subgroups of IBS were detected.

CONCLUSIONS

A functional KLB gene variant mediating protein stability associates with colonic transit in IBS-D. This association is modulated by 2 genetic variants in FGFR4. The FGF19-FGFR4-KLB pathway links regulation of BA synthesis to colonic transit in IBS-D.

Gene, environment, and brain-gut interactions in irritable bowel syndrome

The genetic predisposition and influence of environment may underlie in the pathogenesis and/or pathophysiology of irritable bowel syndrome (IBS). This phenomenon, gene x environment interaction together with brain-gut interactions is emerging area to be clarified in IBS research. Earlier studies focused on candidate genes of neurotransmitters, cytokines, and growth factors. Among them, some studies but not all studies revealed association between phenotypes of IBS and 5-hydroxytryptamine (5-HT)-related genes, noradrenaline-related genes, and cytokine genes. Recent prospective cohort study showed that genes encoding immune and adhesion molecules were associated with post-infectious etiology of IBS. Psychosocial stressors and intraluminal factors especially microbiota are keys to develop IBS. IBS patients may have abnormal gut microbiota as well as increased organic acids. IBS is disorder that relates to brain-gut interactions, emotional dysregulation, and illness behaviors. Brain imaging with or without combination of visceral stimulation enables us to depict the detailed information of brain-gut interactions. In IBS patients, thalamus, insula, anterior cingulate cortex, amygdala, and brainstem were more activated in response to visceral stimulation than controls. Corticotropin-releasing hormone and 5-HT are the candidate substances which regulate exaggerated brain-gut response. In conclusion, gene x environment interaction together with brain-gut interactions may play crucial roles in IBS development. Further fundamental research on this issue is warranted.

MicroRNA in the regulation and expression of serotonergic transmission in the brain and other tissues

In addition to transcriptional regulation, the translation of protein-coding genes is modulated by MicroRNA-binding miRNAs (miRNAs), which have emerged to fulfil important roles in the control and expression of serotonergic transmission. Thus, miR-96 and miR-510 inhibit the translation of serotonin (5-HT)(1B) receptors and 5-HT(3E) receptor subunits respectively, and their susceptibility to repression is modified by polymorphisms in the 3'-UTR (miRNA-binding) regions of their mRNAs. Contrasting susceptibility of human subjects to miRNA-induced alterations in the translation of cerebral 5-HT(1B) receptors and intestinal 5-HT(3E) receptor subunits is related to differential aggressive behaviour and incidence of irritable bowel syndrome, respectively. Fluoxetine promotes the biogenesis of miR-16, leading to translational repression of 5-HT transporters in mouse serotonergic neurones. While the precise mechanism of action of fluoxetine is uncertain, studies of Aplysia have shown that 5-HT inhibits the generation of miR-124, thereby promoting de-repression of CREB and facilitation of synaptic plasticity. Interestingly, 5-HT(2C) receptors harbour a miRNA (miR-448) in their 4th intron that - oppositely to 5-HT(2C) sites - reduces adipocyte differentiation. Finally, interactions amongst 5-HT and miRNAs control processes of bone formation, as well as growth, motility and survival of tumours. The present article discusses the functionally and clinically important interplay amongst miRNAs and serotoninergic mechanisms in the brain, peripheral organs and cancerous tissue.

Human serotonin transporter gene (SLC6A4) variants: their contributions to understanding pharmacogenomic and other functional G×G and G×E differences in health and disease

Recent major findings from studies of SLC6A4 and its corresponding protein, the serotonin (5-HT) transporter (SERT) in humans, rodents and non-human primates indicate that combinations of SLC6A4 non-coding 5', 3' UTRs and intronic regions plus coding variants acting together can change 5HT transport as much as 40-fold in vitro. In vivo, SLC6A4 variants in humans and other species lead to marked physiological changes, despite mitigating neurodevelopmental adaptations in 5-HT receptors plus compensatory alterations in 5-HT synthesis and metabolism. Polymorphisms in SLC6A4 are associated with differences in emotional, endocrine, and personality characteristics as well as many diseases. This gene, in combinations with gene×gene (G×G) and gene×environment (G×E) interactions nonetheless remains incompletely understood, with some association findings remaining controversial. Considering its primary importance in the regulation and function of the entire serotonergic system (as evidenced by the consequences of SERT-mediated reuptake inhibition by SRIs like fluoxetine in humans and of genetically engineered changes in mice and rats), it seems likely that SLC6A4 and SERT will remain areas of high interest in our field's attempts to better understand and treat 5-HT-related disorders.

From cytokines to toll-like receptors and beyond - current knowledge and future research needs in irritable bowel syndrome

The irritable bowel syndrome (IBS) is a complex disorder in which psychosocial, cultural and biological factors, interact. Recent knowledge in the pathophysiology of IBS, seem to combine issues such as a low grade inflammation or immune activation and dysbiosis that can trigger or exacerbate IBS. On the other hand, stress mediated through the hypothalamic-pituitary-adrenal axis can produce motility abnormalities that can modify the microbiota as well, with the subsequent immune activation in the mucosa and stimulation of nerve terminals, generating symptoms of IBS. Also, we speculate that, stress, dysbiosis or an underlying genetic predisposition, may increase the epithelial permeability leading to a contact between pathogens-associated molecular patterns and toll-like receptors in the deeper layers of the gut, developing a host immunity response and IBS generation. We believe that the role of toll-like receptors in IBS and elucidating the communication processes between the immune and the nervous system, warrant future research.

Irritable bowel syndrome: a review article

Irritable bowel syndrome (IBS) is the most prevalent functional gastrointestinal disorder noted in the general population worldwide. Its chronic nature, signs and symptoms which vary periodically from mild to severe have many negative effects on the quality of life for the sufferer; therefore the appropriate treatment of these patients is highly important. Patients should be informed by their doctors that the nature of the disease is benign, and educated on how to deal with and control symptoms of the disease. This article sets out a review of recent studies on the prevalence of IBS in Iran and appropriate methods for management of patients affected by IBS.

Challenges and prospects for pharmacotherapy in functional gastrointestinal disorders

Functional gastrointestinal disorders, such as irritable bowel syndrome and functional dyspepsia, are complex conditions with multiple factors contributing to their pathophysiology. As a consequence they are difficult to treat and have posed significant challenges to the pharmaceutical industry when trying to develop new and effective treatments. This review provides an overview of these difficulties and how the industry is reshaping its drug developmental strategies. It describes some of the more significant and encouraging advances that have occurred, and discusses how future research might embrace the opportunities provided by advances in genetic and in particular, epigenetic research.

IBS: An epigenetic perspective

IBS is a common and debilitating disorder. The pathophysiology of IBS is poorly understood and is currently viewed as a biopsychosocial disorder with symptoms mediated via the brain-gut axis. Epidemiological studies of IBS point to risk factors such as familial clustering, sexual abuse and other forms of childhood trauma, low birth weight and gastrointestinal infection. Epigenetics focuses on the complex and dynamic interaction between the DNA sequence, DNA modifications and environmental factors, all of which combine to produce the phenotype. Studies in animal models of early stress and in humans who have experienced childhood trauma or abuse suggest that these events can lead to long-lasting epigenetic changes in the glucocorticoid receptor gene brought about by hypermethylation of a key regulatory component. Animal studies also indicate that the microbiota has a pivotal role in programming the core stress system, the hypothalamic-pituitary-adrenal axis and the immune system through epigenetic mechanisms. In this Perspectives, an epigenetic model of IBS is presented that incorporates many of the current findings regarding IBS, including proinflammatory markers, neuroendocrine alterations and links with both psychosocial stress and stress related to infection. We conclude that applying epigenetic methodology to this common and disabling disorder may help unravel its complex pathophysiology and lead to more effective treatments.

Bacteria, genetics and irritable bowel syndrome

EVALUATION OF: Villani AC, Lemire M, Thabane M et al. Genetic risk factors for post-infectious irritable bowel syndrome following a waterborne outbreak of gastroenteritis. Gastroenterology 138, 1502-1513 (2010). While the pathogenesis of irritable bowel syndrome (IBS) remains to be fully defined, two clinical observations - the occurrence, de novo, of IBS following bacterial gastroenteritis and the history, commonly obtained from IBS patients, of other instances of the syndrome within their families - have instigated investigations, in IBS, of the potential roles, on the one hand, of the gut microbiota and the host response and, on the other hand, of genetic factors. The study reviewed here relates to both of these factors by studying genetic predisposition to postinfective IBS in a large population of individuals who were exposed to a multimicrobial enteric infection, which resulted in a severe outbreak of gastroenteritis and was followed by the development of IBS in over a third. In this detailed study, the investigators identified a number of genes that were linked significantly to the development of postinfectious-IBS in the Toll-like receptor 9, IL-6 and cadherin 1 regions. These genes play important roles in bacterial recognition, the inflammatory response and epithelial integrity, respectively, and provide considerable support for the hypothesis that links IBS onset to disturbances in the microbiota and the host response.

The future of neuroscientific research in functional gastrointestinal disorders: integration towards multidimensional (visceral) pain endophenotypes?

The growing evidence for a key role of psychophysiological processes in the etiopathogenesis of functional gastrointestinal disorders (FGID) originates from various sources, including epidemiological, psychometric, physiological, and behavioural studies. Functional neuroimaging has improved our knowledge about central processing of visceral pain, a defining feature of FGID. However, results have been disappointingly inconsistent, often due to psychosocial factors not being controlled for. In this paper, we aim to show that using integrated research strategies, encompassing a number of scientific disciplines, is critical to advancing our understanding of FGID. We will illustrate this by describing recent integrative studies that may serve as good examples. More specifically, future FGID neuroimaging studies should control for psychosocial factors and incorporate methods from other branches of neuroscience outside this field, especially cognitive, affective and autonomic neuroscience. We therefore propose a framework for the development of an integrative cross-disciplinary research strategy based on advancing our understanding of visceral nociceptive physiology in health as well as vulnerability and susceptibility factors for FGID. This approach will allow the identification of factors responsible for the inter-individual differences in visceral pain perception and susceptibility to chronic visceral pain, leading to the description of multidimensional (visceral) pain "endophenotypes." These may represent the critical steps needed towards a pathophysiological, rather than symptom-based, classification of FGID, which may be more suitable for genetic association studies. This approach may ultimately culminate in individual tailoring of treatment, in addition to disease prevention, thereby improving outcomes for the patient and researcher alike.

Irritable bowel syndrome symptoms and health related quality of life in female veterans

BACKGROUND

The status and determinants of health-related quality of life (HRQOL) in female veterans with and without irritable bowel syndrome (IBS) are unknown.

AIM

To compare HRQOL in female veterans with and without IBS symptoms and examine the contribution of post-traumatic stress disorder, depression and anxiety to HRQOL.

METHODS

A cross-sectional study of 339 female veterans. Self-report questionnaires were used to evaluate IBS symptoms, post-traumatic stress disorder, depression, anxiety and HRQOL.

RESULTS

Symptoms consistent with IBS were present in 33.5% of participants. Female veterans with IBS symptoms had significant reductions in physical component score and 5 of 8 Health Related Quality of Life subscales and on 7 of 8 Irritable Bowel Syndrome Quality Of Life subscales than female veterans without IBS symptoms. Compared with the US general female population, female veterans had significantly lower Health Related Quality of Life physical component score and mental component scores (MCS) irrespective of IBS symptom status. Differences in the MCS score were most explained by depression, while those in the physical component score were most explained by anxiety.

CONCLUSIONS

Irritable bowel syndrome symptoms in female veterans are associated with considerable reduction in HRQOL. However, female veterans, regardless of IBS symptom status, have lower HRQOL compared with the general US female population.