Association between a functional polymorphism in the serotonin transporter gene and diarrhoea predominant irritable bowel syndrome in women

Alosetron, cilansetron and tegaserod modify mesenteric but not colonic blood flow in rats

BACKGROUND AND PURPOSE

As the use of the 5-HT(3) receptor antagonist alosetron (GlaxoSmithKline) and the 5-HT(4) receptor agonist tegaserod (Novartis) in patients with irritable bowel syndrome has been associated with cases of ischaemic colitis, the effects of alosetron, cilansetron (Solvay) and tegaserod on the rat splanchnic circulation were evaluated.

EXPERIMENTAL APPROACH

Phenobarbital-anaesthetised rats were instrumented to record blood flow in the superior mesenteric artery and transverse colon and to calculate mesenteric and colonic vascular conductance.

KEY RESULTS

Intravenous alosetron (0.03-0.3 mg.kg(-1)) did not alter blood pressure or heart rate but reduced mesenteric blood flow and vascular conductance by 15-20%. This activity profile was also seen after intraduodenal alosetron and shared by the 5-HT(3) receptor antagonist cilansetron. In contrast, blood flow, vascular conductance and intraluminal pressure in the colon were not modified by alosetron and cilansetron. Intravenous or intraduodenal tegaserod (0.3-1.0 mg.kg(-1)) had no inhibitory effect on mesenteric and colonic blood flow. Peroral treatment of rats with alosetron or tegaserod for 7 days did not modify mesenteric haemodynamics at baseline and after blockade of nitric oxide synthesis. Mild inflammation induced by dextran sulphate sodium failed to provoke a vasoconstrictor effect of cilansetron in the colon.

CONCLUSIONS AND IMPLICATIONS

Alosetron and cilansetron, not tegaserod, caused a small and transient constriction of the rat mesenteric vascular bed, whereas blood flow in the colon remained unaltered. The relevance of these findings to the treatment-associated occurrence of ischaemic colitis in patients with irritable bowel syndrome remains open.

Serotonin release and uptake in the gastrointestinal tract

The afferent innervation of the gastrointestinal (GI) tract consists of intrinsic and extrinsic sensory neurons that respond to nutrients, chemicals or mechanical stimuli within the gut lumen. Most stimuli do not interact directly with the afferent nerves but instead activate specialised cells in the epithelium in a process of sensory transduction. It is thought that one of the first steps in this process is the release of serotonin (5-HT) from the enterochromaffin (EC) cells. The EC cells are a sub-type of enteroendocrine (EE) cells which are found among the enterocytes of the intestinal epithelium. The EC cells are responsible for the production and storage of the largest pool of 5 HT in the body. Released 5-HT can act on the intrinsic nerves and vagal endings. This review will focus on the role of 5-HT in sensory transduction and examine how the EC cell produces and releases 5-HT. We will explore recent developments that have helped to elucidate some of the proteins that allow EC cells to sense the luminal environment. Finally, we will highlight some of the findings from new studies using electrochemical techniques which allow the real-time recording of 5-HT concentrations near to the EC cell.

Genetic variation in the serotonin transporter gene (5-HTTLPR, rs25531) influences the analgesic response to the short acting opioid Remifentanil in humans

Background

There is evidence from animal studies that serotonin (5-HT) can influence the antinociceptive effects of opioids at the spinal cord level. Therefore, there could be an influence of genetic polymorphisms in the serotonin system on individual variability in response to opioid treatment of pain. The serotonin transporter (5-HTT) is a key regulator of serotonin metabolism and availability and its gene harbors several known polymorphisms that are known to affect 5-HTT expression (e.g. 5-HTTLPR, rs25531). The aim of this study was to investigate if the triallelic 5-HTTLPR influences pain sensitivity or the analgesic effect of opioids in humans. 43 healthy volunteers (12 men, 31 women, mean age 26 years) underwent heat pain stimulations before and after intravenous injection of Remifentanil; a rapid and potent opioid drug acting on μ-type receptors. Subjects rated their perceived pain on a visual analogue scale (VAS). All participants were genotyped for the 5-HTTLPR and the rs25531 polymorphism. We recruited by advertising, with no history of drug abuse, chronic pain or psychiatric disorders.

Results

At baseline, there was no difference in pain ratings for the different triallelic 5-HTTLPR genotype groups. However, the opiod drug had a differential analgesic effect depending on the triallelic 5-HTTLPR genotype. Remifentanil had a significantly better analgesic effect in individuals with a genotype coding for low 5-HTT expression (S_A/S_A and S_A/L_G) as compared to those with high expression(L_A/L_A), p < 0.02. The analgesic effect for the three different genotype groups was linear to degree of 5-HTT expression.

Conclusion

This is the first report showing an influence of the triallelic 5-HTTLPR on pain sensitivity or the analgesic effect of opioids in humans. Previously the 5-HTTLPR s-allele has been associated with higher risk of developing chronic pain conditions but in this study we show that the genotype coding for low 5-HTT expression is associated with a better analgesic effect of an opioid. The s-allele has been associated with downregulation of 5-HT1 receptors and we suggest that individuals with a desensitization of 5-HT1 receptors have an increased analgesic response to opioids during acute pain stimuli, but may still be at increased risk of developing chronic pain conditions.

Public health significance of neuroticism

The personality trait of neuroticism refers to relatively stable tendencies to respond with negative emotions to threat, frustration, or loss. Individuals in the population vary markedly on this trait, ranging from frequent and intense emotional reactions to minor challenges to little emotional reaction even in the face of significant difficulties. Although not widely appreciated, there is growing evidence that neuroticism is a psychological trait of profound public health significance. Neuroticism is a robust correlate and predictor of many different mental and physical disorders, comorbidity among them, and the frequency of mental and general health service use. Indeed, neuroticism apparently is a predictor of the quality and longevity of our lives. Achieving a full understanding of the nature and origins of neuroticism, and the mechanisms through which neuroticism is linked to mental and physical disorders, should be a top priority for research. Knowing why neuroticism predicts such a wide variety of seemingly diverse outcomes should lead to improved understanding of commonalities among those outcomes and improved strategies for preventing them.

Serotonin transporter gene variation and refractory mesial temporal epilepsy with hippocampal sclerosis

We performed a molecular epidemiology study in a population of 105 mesial temporal lobe epilepsy with hippocampal sclerosis (MTE-HS) patients in order to investigate the role of a polymorphism in the serotonin transporter gene (SLC6A4) in the prediction of antiepileptic drug (AED) treatment response. Homozygous carriers of the 12-repeat allele had an almost fourfold increase in risk for a MTE-HS not responding to medical treatment (OR 3.88; CI 95% 1.40-10.7; p=0.006) compared to carriers of the 10-repeat allele. Therefore, a polymorphism of SLC6A4 might be a genetic marker of pharmacoresistance in MTE-HS patients.

Role of serotonin in intestinal inflammation: knockout of serotonin reuptake transporter exacerbates 2,4,6-trinitrobenzene sulfonic acid colitis in mice

Serotonin (5-HT) regulates peristaltic and secretory reflexes in the gut. The serotonin reuptake transporter (SERT; SLC6A4), which inactivates 5-HT, is expressed in the intestinal mucosa and the enteric nervous system. Stool water content is increased and colonic motility is irregular in mice with a targeted deletion of SERT. We tested the hypotheses that 5-HT plays a role in regulating intestinal inflammation and that the potentiation of serotonergic signaling that results from SERT deletion is proinflammatory. Rectal installation of 2,4,6-trinitrobenzene sulfonic acid (TNBS) was used to induce an immune-mediated colitis, which was compared in SERT knockout mice and littermate controls. Intestinal myeloperoxidase and histamine levels were significantly increased, whereas the survival rate and state of health were significantly decreased in TNBS-treated mice that lacked SERT. Deletion of SERT thus increases the severity of TNBS colitis. These data suggest that 5-HT and its SERT-mediated termination play roles in intestinal immune/inflammatory responses in mice.

A randomized, double-blind, placebo-controlled clinical trial of the effectiveness of the novel serotonin type 3 receptor antagonist ramosetron in both male and female Japanese patients with diarrhea-predominant irritable bowel syndrome

OBJECTIVE

Irritable bowel syndrome is characterized by abdominal discomfort and/or pain associated with altered bowel habits. The neurotransmitter serotonin and serotonin type 3 receptors that are extensively distributed on enteric neurons in the human gastrointestinal tract play a role in increasing the sensation of pain and affecting bowel habits in patients with irritable bowel syndrome. The aim of this study was to evaluate the efficacy and safety of the serotonin type 3 receptor antagonist ramosetron hydrochloride in Japanese patients with diarrhea-predominant irritable bowel syndrome.

MATERIAL AND METHODS

In a double-blind, placebo-controlled, parallel group-comparative study with a 1-week run-in period, 539 patients with diarrhea-predominant irritable bowel syndrome meeting the Rome II diagnostic criteria received either 5 microg ramosetron hydrochloride (n=270) or placebo (n=269) once daily for 12 weeks.

RESULTS

Forty-seven percent of ramosetron hydrochloride-treated patients were monthly responders in the primary end-point, "Patient-reported global assessment of relief of irritable bowel syndrome symptoms", compared with 27% for placebos (p<0.001). The most frequently reported adverse event in the ramosetron hydrochloride-treated group compared with the placebo group was hard stool.

CONCLUSIONS

Ramosetron hydrochloride 5 microg once daily is effective and well tolerated in the treatment of abdominal pain, discomfort and bowel habits in patients with diarrhea-predominant irritable bowel syndrome.

Non-invasive brain stimulation approaches to fibromyalgia pain

Fibromyalgia is a poorly understood disorder that likely involves central nervous system sensory hypersensitivity. There are a host of genetic, neuroendocrine and environmental abnormalities associated with the disease, and recent research findings suggest enhanced sensory processing, and abnormalities in central monoamines and cytokines expression in patients with fibromyalgia. The morbidity and financial costs associated with fibromyalgia are quite high despite conventional treatments with antidepressants, anticonvulsants, low-impact aerobic exercise and psychotherapy. Noninvasive brain stimulation techniques, such as transcranial direct current stimulation, transcranial magnetic stimulation, and electroconvulsive therapy are beginning to be studied as possible treatments for fibromyalgia pain. Early studies appear promising but more work is needed. Future directions in clinical care may include innovative combinations of noninvasive brain stimulation, pharmacological augmentation, and behavior therapies.

Serotonin (5-HT) release and uptake measured by real-time electrochemical techniques in the rat ileum

Serotonin (5-HT) is released from the enterochromaffin cells and plays an important role in regulating intestinal function. Although the release of 5-HT is well documented, the contribution of the serotonin reuptake transporter (SERT) to the levels and actions of 5-HT in the intestine is unclear. This study aimed to demonstrate real-time SERT activity in ileal mucosa and to assess the effects of SERT inhibition using fluoxetine. Electrochemical recordings were made from the mucosa in full-thickness preparations of rat ileum using a carbon fiber electrode to measure 5-HT oxidation current and a force transducer to record circular muscle (CM) tension. Compression of the mucosa stimulated a peak 5-HT release of 12 +/- 6 microM, which decayed to 7 +/- 4 microM. Blockade of SERT with fluoxetine (1 microM) increased the peak compression-evoked release to 19 +/- 9 microM, and the background levels of 5-HT increased to 11 +/- 7 microM (P < 0.05, n = 7). When 5-HT was exogenously applied to the mucosa, fluoxetine caused a significant increase in the time to 50% and 80% decay of the oxidation current. Fluoxetine also increased the spontaneous CM motility (P < 0.05; n = 7) but did not increase the CM contraction-evoked 5-HT release (P > 0.05, n = 5). In conclusion, this is the first characterization of the real-time uptake of 5-HT into the rat intestine. These data suggest that SERT plays an important role in the modulation of 5-HT concentrations that reach intestinal 5-HT receptors.

Genetic determination of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common functional gastrointestinal disorder. According to the Rome III criteria, IBS is defined as recurrent abdominal pain or discomfort for at least 3 d per month during the previous 3 mo associated with two or more of the following symptoms: improvement with defecation, onset associated with a change in the frequency of stool and/or onset associated with a change in form or appearance of stool. There is growing evidence regarding the genetic contribution in IBS, however the precise etiology of IBS is still unknown. The evaluation of the genetic influence is based on twin studies, familial aggregation and genetic epidemiological investigations. Most studies showed a concordance for IBS significantly greater in monozygotic than in dizygotic twins. The majority of the studies have shown that familial aggregation may represent exposures to a similar environment, as well as the influence of genetic factors. Whereas no specific gene has been identified in association with IBS, recent studies have noticed the importance of polymorphisms in the promoter region of the serotonin reuptake transporter gene, G-protein beta 3 subunit gene (C825T), cholecystokinin receptor (CCKAR gene 779T>C), and high-producer tumor necrosis factor genotype. Further studies are necessary to determine how genetic factors influence the clinical manifestations and therapeutical response in IBS patients.

How the serotonin story is being rewritten by new gene-based discoveries principally related to SLC6A4, the serotonin transporter gene, which functions to influence all cellular serotonin systems

Discovered and crystallized over sixty years ago, serotonin's important functions in the brain and body were identified over the ensuing years by neurochemical, physiological and pharmacological investigations. This 2008 M. Rapport Memorial Serotonin Review focuses on some of the most recent discoveries involving serotonin that are based on genetic methodologies. These include examples of the consequences that result from direct serotonergic gene manipulation (gene deletion or overexpression) in mice and other species; an evaluation of some phenotypes related to functional human serotonergic gene variants, particularly in SLC6A4, the serotonin transporter gene; and finally, a consideration of the pharmacogenomics of serotonergic drugs with respect to both their therapeutic actions and side effects. The serotonin transporter (SERT) has been the most comprehensively studied of the serotonin system molecular components, and will be the primary focus of this review. We provide in-depth examples of gene-based discoveries primarily related to SLC6A4 that have clarified serotonin's many important homeostatic functions in humans, non-human primates, mice and other species.

The role of serotonin in irritable bowel syndrome: implications for management

Irritable bowel syndrome (IBS) is a poorly understood, common, chronic condition characterized by -abdominal discomfort associated with altered bowel habits in the absence of structural or biochemical abnormalities. Despite the significant economic and personal burden associated with IBS, treatment options remain limited. Serotonin is recognized as a key neurotransmitter in intestinal secretory, sensory, and motor function. Although the pathophysiology of IBS is incompletely understood, there is evidence that abnormalities in brain-gut signaling and serotonin metabolism play a role. This article reviews the evidence that serotonin, one of the better-understood neurotransmitters with respect to its role in human central and intestinal physiology, plays a role in IBS. Serotonin signaling is discussed, with a focus on receptor subtypes and the therapeutic agents that target these receptors. Evidence that IBS is associated with perturbations in serotonin metabolism at various steps in the signaling pathway is also addressed, along with the limitations on alteration in serotonin metabolism as the sole explanation for the constellation of symptoms observed in patients with IBS.

Genes and irritable bowel syndrome: is there a link?

Advances in genetics and genomics during the past decade, including sequencing of the human genome and DNA sequencing technologies, have made it possible to discover the genetic basis for many diseases. With the discovery of multiple genetic loci for gastrointestinal diseases such as Crohn's disease, some have begun to wonder-Could there be a genetic basis for irritable bowel syndrome (IBS)? This article summarizes the evidence for and against a link between genes and IBS. In addition, a gene-environment paradigm is presented to combine the two opposing hypotheses, as IBS may represent a complex genetic disorder that results from the interaction of several genes and environmental risk factors.

Impact of serotonin transporter and catechol-O-methyl transferase genes polymorphism on gastrointestinal dysfunction in Swedish and Japanese familial amyloidotic polyneuropathy patients

BACKGROUND

Differences in the gastrointestinal manifestations have emerged between Swedish and Japanese familial amyloidotic polyneuropathy amyloidogenic transthyretin Valine30Methionine (FAP ATTR Val30Met) patients. To elucidate the cause of the differences, we investigated the associations between serotonin transporter gene-linked polymorphic region (5-HTTLPR) and/or catechol-O-methyl transferase (COMT) gene polymorphism and their gastrointestinal in these patients.

METHODS

Twenty-six Swedish and 24 Japanese patients with gastrointestinal disturbances, in whom genetic material was available, were included in the study. The initial gastrointestinal manifestations of the disease were classified as constipation, constipation alternating with diarrhoea, continuous diarrhoea, and nausea/vomiting. 5-HTTLPR and COMT gene polymorphism were assessed by polymerase chain reaction and enzymatic digestion.

RESULTS

A significantly higher LA allele frequency of 5-HTTLPR was noted in the Swedish population compared with that of the Japanese. Moreover, the LA allele frequency tended to be lower in the continuous diarrhoea group than in that of the remaining groups of both Swedish and Japanese patients. No association between COMT genotype and initial gastrointestinal symptoms was noted.

CONCLUSION

A high expression of serotonin transporter induced by LA allele of 5-HTTLPR may be one of the factors implicated with the inhibition of severe diarrhoea in early stages of Swedish FAP ATTR Val30Met patients.

Genetics of irritable bowel syndrome

Irritable bowel syndrome (IBS) is one of the most common diagnoses made by gastroenterologists and primary care providers alike, and yet the underlying mechanism remains poorly understood. Family and twin studies suggest that IBS may have a genetic basis. Several candidate gene association studies have been performed, but thus far, they have failed to clearly identify an "IBS gene." Epidemiological studies are needed to facilitate phenotype definition and identify relevant environment risk factors that will need to factor in gene and environment interactions in all future genetic studies. As genetic research in IBS is relatively nascent, much opportunity, as well as many challenges, exists in identifying the genes responsible for IBS.

The genetics of the serotonin transporter and irritable bowel syndrome

Serotonin transporter (SERT) mediates the intracellular reuptake of released serotonin, thus regulating its biological functions. Abnormalities in serotonin reuptake can alter enteric serotonergic signalling, leading to sensory, motor and secretory gut dysfunctions, which contribute to the pathophysiology of irritable bowel syndrome (IBS). This relationship has fostered the use of selective serotonin reuptake inhibitors (SSRIs) in the treatment of IBS. Current data on the efficacy of SSRIs in IBS, association of the SERT gene promoter polymorphism 5-HTTLPR with IBS and the expression pattern of SERT in the intestinal mucosa of IBS patients are conflicting. Recent molecular studies have raised critical questions about multiple SERT mRNA transcripts in the human gut, the role of polymorphic SERT promoter in the regulation of enteric SERT expression and the ability of 5-HTTLPR to affect human SERT gene transcription. The present review highlights recent advances in SERT genetics, discusses their implications for potential therapeutic applications of SSRIs in IBS and presents original suggestions for future investigations.

Candidate genotypes associated with functional dyspepsia

There is accumulating evidence of a genetic predisposition for developing a functional gastrointestinal (GI) disorder. Identification of the genetic factors may improve understanding of underlying pathophysiological mechanisms. We aimed to test the association of functional polymorphisms in genes involved in serotonergic signalling and G-protein-mediated signal transduction, both affecting gastroduodenal sensory and motor function, with functional dyspepsia (FD). FD patients, send to our tertiary referral centre, were studied (n = 112). Healthy controls (n = 336) free of GI symptoms were matched 1 : 3 for age and gender. Polymorphisms in genes encoding the serotonin receptor type three A subunit (HTR3A), the serotonin transporter (SERT) and the G-protein beta3 subunit (GNB3) were analysed. The FD patients displayed a higher prevalence of the T allele of the GNB3 C825T polymorphism compared to healthy controls (OR = 1.60, 95% CI: 1.03-2.49, P = 0.038). No association between FD and the genotype of the insertion/deletion polymorphism in the promoter of SERT (SERT-P) or HTR3A C178T polymorphism was observed. Tertiary referral FD is associated with the 825T allele of the GNB3 gene. The increased signal transduction associated with this allele may contribute to the abnormalities in gastroduodenal sensory and motor function observed in FD.

Relationship between genetic polymorphism and irritable bowel syndrome pathogenesis

Irritable bowel syndrome is a common functional disorder, whose etiology remains unknown. Previous researches indicated that its pathogenesis might be associated such factors as gastrointestinal motor abnormality, altered visceral sensation, psychological factors, neurotransmitter and imbalance of gastrointestinal flora, intestinal infection and food intolerance, etc. Besides, recent research has touched on relationship between genetics and IBS. This paper reviewed relationship between the inheritance, gene-linked polymorphism and irritable bowel syndrome pathogenesis.

Updates on treatment of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a highly prevalent gastrointestinal disorder characterized by abdominal pain and discomfort in association with altered bowel habits. It is estimated to affect 10%-15% of the Western population, and has a large impact on quality of life and (in)direct healthcare costs. IBS is a multifactorial disorder involving dysregulation within the brain-gut axis, and it is frequently associated with gastrointestinal motor and sensory dysfunction, enteric and central nervous system irregularities, neuroimmune dysregulation, and post-infectious inflammation. As with other functional medical disorders, the treatment for IBS can be challenging. Conventional therapy for those with moderate to severe symptoms is largely unsatisfactory, and the development of new and effective drugs is made difficult by the complex pathogenesis, variety of symptoms, and lack of objective clinical findings that are the hallmark of this disorder. Fortunately, research advances over the past several decades have provided insight into potential mechanisms responsible for the pathogenesis of IBS, and have led to the development of several promising pharmaceutical agents. In recent years there has been much publicity over several of these new IBS medications (alosetron and tegaserod) because of their reported association with ischemic colitis and cardiovascular disease. While these agents remain available for use under restricted prescribing programs, this highlights the need for continued development of safe and effective medication for IBS. This article provides a physiologically-based overview of recently developed and frequently employed pharmaceutical agents used to treat IBS, and discusses some non-pharmaceutical options that may be beneficial in this disorder.

Exploring possible mechanisms for primary bile acid malabsorption: evidence for different regulation of ileal bile acid transporter transcripts in chronic diarrhoea

OBJECTIVES

Chronic diarrhoea resulting from primary idiopathic bile acid malabsorption (IBAM) is common, but its aetiology is largely unknown. We investigated possible mechanisms, first looking for common sequence variations in the cytoplasmic ileal bile acid-binding protein (IBABP, gene symbol FABP6), and secondly, determining the expression of ileal mucosal transcripts for the apical sodium-linked bile acid transporter (ASBT), IBABP, the putative basolateral transporters, OSTalpha and OSTbeta, and regulatory factors.

METHODS

Genomic DNA was prepared from two cohorts of patients and two control groups; the promoter and exonic regions of FABP6 were sequenced. In intestinal biopsies, transcript expression was measured by quantitative real time-PCR, using ileum from 17 patients and 21 controls.

RESULTS

Sequence variations were identified in FABP6, but overall frequencies were similar in patients and controls. Transcripts of ASBT and IBABP, but not OSTalpha and OSTbeta, were expressed at higher levels in ileum than duodenum. The transcription factors farnesoid-X-receptor (FXR) and liver-receptor-homologue (LRH-1) were also more abundant in ileum, as was fibroblast growth factor 19 (FGF19), unlike short heterodimer partner (SHP), c-Fos, or CDX2. No significant differences in mean or median values were found between the groups for any of these transcripts. However, findings on regression analysis suggested that these transporters differ in their regulation, particularly in the relationships of CDX2, LRH-1 and FXR with OSTalpha.

CONCLUSION

Most cases of IBAM are unlikely to be caused by genetic variation in FABP6 or by major differences in transporter transcript expression. Our evidence indicates that other factors, such as regulation of expression of the basolateral bile acid transporter, should be considered as possible causes.

Serotonin pharmacology in the gastrointestinal tract: a review

Serotonin (5-hydroxytryptamine or 5-HT) plays a critical physiological role in the regulation of gastrointestinal (GI) function. 5-HT dysfunction may also be involved in the pathophysiology of a number of functional GI disorders, such as chronic constipation, irritable bowel syndrome and functional dyspepsia. This article describes the role of 5-HT in the enteric nervous system (ENS) of the mammalian GI tract and the receptors with which it interacts. Existing serotonergic therapies that have proven effective in the treatment of GI functional disorders and the potential of drugs currently in development are also highlighted. Advances in our understanding of the physiological and pathophysiological roles of 5-HT in the ENS and the identification of selective receptor ligands bodes well for the future development of more efficacious therapies for patients with functional GI disorders.

An exploratory study of the association of adrenergic and serotonergic genotype and gastrointestinal motor functions

Adrenergic and serotonergic mechanisms alter human gut motor functions. Genotype variation influences phenotype. Our aim was to test the hypothesis that variation in genes that control these functions is associated with gastrointestinal (GI) motor functions in humans with functional GI disorders (FGID). A database of 251 people was assembled by combining genotype data with measurements of gut transit and gastric volumes. Genetic variations evaluated were: alpha(2A) adrenergic (C-1291G), alpha(2C) (Del 332-325), 5-HT transporter (SLC6A4) and GNbeta3 (C825T). We sought associations between motor function or disease groups and genotypes, adjusting for age, gender and body mass index. Among 251 participants, 82 were healthy, 20 with irritable bowel syndrome (IBS) with mixed bowel habit, 49 with constipation-predominant IBS, 67 with diarrhoea-predominant IBS and 33 with functional dyspepsia. For all candidate genes, there was no significant association between motor function and wildtype vs non-wildtype gene status. There were significant interactions between genotype and motility phenotype, specifically GNbeta3 and alpha(2A) and gastric emptying at 4 h. Borderline associations were noted for SCL6A4 and alpha(2A) and postprandial gastric volume, and for alpha(2C) and gastric emptying at 2 h. We conclude that genotype variation may affect gastric motor functions in different FGID phenotypes. However, these candidate genes account for only a limited amount of the variance in gastric function of patients with FGID.

Pharmacogenomics in gastrointestinal disorders

It is anticipated that unraveling the human genome will have a direct impact on the management of specific diseases. Variations or mutations in genes involved in drug metabolism or disease pathophysiology in gastroenterology and hepatology are expected to have effect on response to therapy. The spectrum of diseases is vast. Thus, we focus this review on clinical pharmacogenetics of inflammatory bowel disease, Helicobacter pylori infections, gastroesophageal reflux disease, irritable bowel syndrome, liver transplantation, and colon cancer. Although only a few genotyping tests are used regularly in clinical practice, we anticipate that in the future there will be more routine use of many of the tests described in this review.

Novel procedure for genotyping of the human serotonin transporter gene-linked polymorphic region (5-HTTLPR)--a region with a high level of allele diversity

BACKGROUND

The serotonin transporter, the target of a group of antidepressant drugs, is involved in the regulation of the availability and reuptake of serotonin. A variable number of tandem repeats in the promoter region of the serotonin transporter gene, designated 5-HTTLPR, affects the transcription of this gene and appears to modulate the susceptibility to a variety of diseases including depression. Of importance, 5-HTTLPR alleles composed of the same number of basic units may differ at single nucleotide positions providing an additional source of variation.

OBJECTIVE

To develop a procedure for detailed genotyping of 5-HTTLPR based upon simultaneous analysis of tandem repeat size variation and single nucleotide variations.

METHODS

We elaborated a list of all known 5-HTTLPR alleles to provide an overview of the allele repertoire at this polymorphic locus. Fragments of 5-HTTLPR were PCR-amplified in reaction mixtures prepared with and without 7-deaza-dGTP. The amplified fragments were treated with NciI and NlaIII and subjected to agarose gel electrophoresis. Alleles were identified by comparison of the observed electrophoretic patterns with the predicted patterns. Two hundred samples of human genomic DNA representing a variety of different 5-HTTLPR alleles were included in the study.

MAIN RESULTS

We were able to amplify fragments of 5-HTTLPR, which are GC-rich, without the use of 7-deaza-dGTP. This is an advantage as modified nucleotides may inhibit restriction enzymes and interfere with allele determination. After having developed a 5-HTTLPR genotyping assay, we examined all samples of DNA in two separate rounds of analyses and found complete agreement between the results from these two rounds.

CONCLUSION

On the basis of simultaneous analysis of tandem repeat size variation and variation of single nucleotides we designed a reliable assay for the determination of the major alleles and several of the rare alleles at the polymorphic locus 5-HTTLPR.

The association of serotonin transporter genetic polymorphisms and irritable bowel syndrome and its influence on tegaserod treatment in Chinese patients

The aims of this study were to investigate the relationship of genetic polymorphisms of the serotonin reuptake transporter and the clinical subtypes of irritable bowel syndrome and its influence on the efficacy of tegaserod in Chinese irritable bowel syndrome patients with constipation. Genetic polymorphisms were analyzed in 87 patients and 96 controls, then 41 irritable bowel syndrome patients with constipation received tegaserod for 4 weeks. The primary efficacy variable was the responder rate measured by Subject's Global Assessment of Relief. Secondary efficacy assessed the changes of individual symptoms weekly. There was no significant difference in genotype frequencies between the patients as a whole and the control group. The frequency of the L/L genotype in the serotonin transporter gene-linked polymorphic region was significantly higher in patients with constipation than in controls (25.0% vs. 7.3%). Responder rates to tegaserod were significantly higher in the S/S (85.0%) and L/S (70.0%) than in the L/L genotype (36.4%). All secondary variables also significantly improved in the S/S and L/S groups compared to the L/L group. This study suggests the hypothesis that individuals with the L/L genotype are vulnerable to development of irritable bowel syndrome with constipation, and patients with the L/L genotype respond poorly to treatment with a routine dose of tegaserod.

Relationship of SERT polymorphisms to depressive and anxiety symptoms in irritable bowel syndrome

This study investigates the association of psychological symptoms with the distribution of two serotonin transporter gene (SERT) polymorphisms, located in the promoter region (5-HTTLPR) and in intron 2 (STin2 VNTR), in patients with irritable bowel syndrome (IBS). Participants, 21 men and 117 women, were assessed for mental health history and current psychological distress. A blood sample was used for genotyping. Participants who were homozygous for the short allele of 5-HTTLPR or carried a STin2.9 VNTR allele were significantly more likely to have a history of depression. Participants did not differ by genotype in their history of anxiety or suicidal ideation nor in their current levels of depression, anxiety, or general psychological distress. The results support a biopsychosocial model of IBS in which SERT genotype modifies the risk for depressive episodes. Long term, practitioners may individualize treatment of patients with IBS using genotype as one of the factors.

Meta-analysis: a functional polymorphism in the gene encoding for activity of the serotonin transporter protein is not associated with the irritable bowel syndrome

BACKGROUND

Serotonin is associated with symptoms of the irritable bowel syndrome, its action is terminated by the serotonin transporter protein.

AIM

To assess the association between a functional polymorphism in the gene encoding for activity of the serotonin transporter protein and the irritable bowel syndrome.

METHODS

Meta-analysis of studies identified through a Medline, PubMed and Web of Science search, describing the prevalence of a polymorphism in the serotonin transporter gene creating long and short alleles.

RESULTS

Eight eligible studies described a total of 1034 patients with the irritable bowel syndrome, and 1377 healthy controls. Presence of the short allele is not associated with an increased risk for the irritable bowel syndrome: OR 1.0; 95% CI: 0.7-1.4 for homozygous subjects, and OR 1.0; 95% CI: 0.8-1.2 for homozygous subjects and heterozygotes together. Although Caucasians and Asians had diverging genotypic frequencies, no association with the shot allele and irritable bowel syndrome was observed in subgroups: Asians OR 1.2; 95% CI: 0.9-1.6 and OR 1.1; 95% CI: 0.2-5.9; Caucasians OR 0.9; 95% CI: 0.5-1.7 and OR 0.9; 95% CI: 0.7-1.2, respectively, for homozygous subjects alone and for homozygous subjects and heterozygotes together.

CONCLUSION

A genetic polymorphism in the gene encoding for activity of the serotonin transporter protein is not associated with the irritable bowel.

Twin studies used to prove that the comorbidity of major depressive disorder with IBS is NOT influenced by heredity

Twin studies have traditionally been used to assess the heritability of diseases such as irritable bowel syndrome (IBS) by comparing concordance rates in monozygotic twins (identical genetic endowment) to dizygotic twins (half of genes shared). Wojczynski et al. used twins in a novel way-they studied monozygotic twins who were discordant for IBS (but who shared identical genes) to show that the comorbidity of IBS with major depressive disorder could NOT be due to genetic influences. This paradigm provides the most rigorous method for separating genetic from environmental influences and should be adopted by other researchers. However, the authors' conclusion that major depressive disorder and IBS are part of the same pathophysiological process is questioned on the basis of (a) incomplete co-occurrence of IBS and major depressive disorder (13-45% co-occurrence) and (b) lack of specificity-the authors show that chronic widespread pain (related to fibromyalgia) and chronic fatigue are also strongly associated with IBS. This study provides precise, generalizable estimates from a large population-based study for the comorbidity of IBS with major depressive disorder, chronic widespread pain, and chronic fatigue.

Genetics of chronic pain states

Chronic pain states are common in the general population. Genetic factors can explain a significant amount of the variability in the perception of pain. Fibromyalgia syndrome (FMS) and related conditions are syndromes characterized by generalized pain sensitivity as well as a constellation of other symptoms. Family studies show a strong familial aggregation of FMS and related conditions, suggesting the importance of genetic factors in the development of these conditions. Recent evidence suggests a role for polymorphisms of genes in the serotoninergic, dopaminergic and catecholaminergic systems in the pathogenesis of FMS and related conditions. Environmental factors may trigger the development of these disorders in genetically predisposed individuals. Future large well-designed studies are needed to further clarify the role of genetic factors in FMS and related conditions. The knowledge of these gene polymorphisms may help with better subgrouping of FMS patients and in designing a more specific pharmacologic treatment approach.

Pharmacogenomics and serotonergic agents: research observations and potential clinical practice implications

Pharmacogenomics of serotonin are potentially relevant in research and clinical practice. There are few proven examples of the importance of pharmacogenetics of serotonin-modifying agents used in functional gastrointestinal or motility disorders. Drug metabolism is dependent on function of the cytochrome P450 enzymes, such as 2D6 and 3A4. Genetic variations in transporters and translation mechanisms have been associated with responses to treatment in irritable bowel syndrome and in obesity. Research on the impact of polymorphisms of key proteins on the pharmacokinetics and pharmacodynamics of drugs that alter serotonin-mediated signalling will assist in explaining diverse responses to those drugs and ultimately improve clinical practice, individualizing medicine.

5-HT and the brain-gut axis: opportunities for pharmacologic intervention

Interactions between the enteric nervous system of the gut and the brain occur bidirectionally over sympathetic and parasympathetic pathways. Coordinated actions of the central, autonomic and enteric nervous systems modulate intestinal motor, sensory and secretory activities by neuromodulators, including 5-HT, noradrenaline and dopamine. 5-HT is an important signaling molecule in the brain-gut axis and the 5-HT released from enterochromaffin cells modulates peristaltic, secretory, vasodilatory, vagal and nociceptive reflexes. Irritable bowel syndrome is associated with altered motility, secretion and sensation; enteric 5-HT signaling may be defective in this disorder. In this editorial, recent data are reviewed and the potential for the development of pharmacologic intervention is assessed.

The psyche and the gut

Research on gut-brain interactions has increased over the last decade and has brought about a number of new topics beyond "classical" subjects, such as "stress" and "personality", which have dominated the psychosomatic literature on gastrointestinal disorders over the past century. These novel topics include brain imaging of intestinal functions, placebo responses in gastroenterology, learning of gastrointestinal symptoms, quality of life in patients with intestinal complaints, and psychotherapy and familial aggregation of functional intestinal disorders. Currently, these new topics appear with a frequency of 1% to 3% in leading gastroenterological journals, either as data presentation or review papers. Increasing focus underlines the importance of enhancing our understanding on how the psyche and the brain communicate in order to better meet the needs of our patients.

Alteration of gastric functions and candidate genes associated with weight reduction in response to sibutramine

BACKGROUND & AIMS

It is unclear whether weight loss with the noradrenergic (norepinephrine) and serotonergic (5-hydroxytryptamine) reuptake inhibitor, sibutramine, is associated with altered stomach functions and whether genetics influence treatment response.

METHODS

Forty-eight overweight and obese but otherwise healthy participants were randomized to placebo or sibutramine (15 mg/day for 12 weeks). At baseline and posttreatment we measured the following: gastric emptying for solids and liquids by scintigraphy, gastric volumes by single-photon emission computed tomography, maximum tolerated volume and 30-minute postnutrient challenge symptoms, and selected gastrointestinal hormones. All participants received structured behavior therapy for weight management. The influence of candidate gene polymorphisms involved in norepinephrine and 5-hydroxytryptamine or receptor function (phenylethanolamine N-methyltransferase, guanine nucleotide binding protein beta polypeptide 3, alpha2A adrenoreceptor, and solute carrier family 6 [neurotransmitter transporter, serotonin] member 4 [homo sapiens] [SLC6A4]) on weight loss and gastric functions was evaluated.

RESULTS

The overall average weight loss posttreatment was 5.4 +/- 0.8 (SEM) kg with sibutramine and 0.9 +/- 0.9 kg with placebo (P < .001). The sibutramine group showed significant retardation in gastric emptying of solids (P = .03), reduced maximum tolerated volume (P = .03), and increased postprandial peptide YY compared with the placebo group. Obese females showed greater effects of sibutramine on weight loss and gastric emptying of solids and liquids. Gastric volumes and postchallenge symptoms were not significantly different in the 2 treatment groups. The LS/SS genotype of the promoter for SLC6A4 was associated with enhanced weight loss with sibutramine.

CONCLUSIONS

Weight reduction with sibutramine is associated with altered gastric functions and increased peptide YY and is significantly associated with SLC6A4 genotype. The role of genetic variation in SLC6A4 on weight loss in response to sibutramine deserves further study.

Fibromyalgia and Overlapping Disorders: The Unifying Concept of Central Sensitivity Syndromes

OBJECTIVES

To discuss fibromyalgia syndrome (FMS) and overlapping conditions, eg, irritable bowel syndrome, headaches, and chronic fatigue syndrome, within the concept of central sensitivity syndromes (CSS).

METHODS

A critical overview of the literature and incorporation of the author's own views.

RESULTS

The concept of CSS seems viable. It is based on mutual associations among the CSS conditions as well as the evidence for central sensitization (CS) among several CSS members. However, such evidence is weak or not available in other members at this time, requiring further studies. The biology of CSS is based on neuroendocrine aberrations, including CS, that interact with psychosocial factors to cause a number of symptoms.

CONCLUSIONS

CSS is an important new concept that embraces the biopsychosocial model of disease. Further critical studies are warranted to fully test this concept. However, it seems to have important significance for new directions for research and patient care involving physician and patient education. Each patient, irrespective of diagnosis, should be treated as an individual considering both the biological and psychosocial contributions to his or her symptoms and suffering.

Regional distribution of solute carrier mRNA expression along the human intestinal tract

Intestinal absorption of drugs, nutrients, and other compounds is mediated by uptake transporters expressed at the apical enterocyte membrane. These compounds are returned to the intestinal lumen or released into portal circulation by intestinal efflux transporters expressed at apical or basolateral membranes, respectively. One important transporter superfamily, multiple members of which are intestinally expressed, are the solute carriers (SLCs). SLC expression levels may determine the pharmacokinetics of drugs that are substrates of these transporters. In this study we characterize the distribution of 15 human SLC transporter mRNAs in histologically normal biopsies from five regions of the intestine of 10 patients. The mRNA expression levels of CNT1, CNT2, apical sodium-dependent bile acid transporter (ABST), serotonin transporter (SERT), PEPT1, and OCTN2 exhibit marked differences between different regions of the intestine: the first five are predominantly expressed in the small intestine, whereas OCTN2 exhibits strongest expression in the colon. Two transporter mRNAs studied (OCTN1, OATP2B1) are expressed at similar levels in all gut sections. In addition, ENT2 mRNA is present at low levels across the colon, but not in the small intestine. The other six SLC mRNAs studied are not expressed in the intestine. Quantitative knowledge of transporter expression levels in different regions of the human gastrointestinal tract could be useful for designing intestinal delivery strategies for orally administered drugs. Furthermore, changes in transporter expression that occur in pathological states, such as inflammatory bowel disease, can now be defined more precisely by comparison with the expression levels measured in healthy individuals.

New insights into the pathogenesis and pathophysiology of irritable bowel syndrome

The pathogenesis and pathophysiology of irritable bowel syndrome is complex and still incompletely known. Potential pathogenetic factors include genes, infectious events, psychological symptoms and other loosely defined environmental factors. Both alterations at the central and peripheral level are thought to contribute to the symptoms of irritable bowel syndrome, including psychosocial factors, abnormal gastrointestinal motility and secretion, and visceral hypersensitivity. Today irritable bowel syndrome is viewed upon as a disorder of dysregulation of the so-called brain-gut axis, involving abnormal function in the enteric, autonomic and/or central nervous systems, with peripheral abnormalities probably dominating in some patients and disturbed central processing of signals from the periphery in others. Lines of evidence also suggest that inflammation within the gastrointestinal tract may be of great importance in at least subgroups of irritable bowel syndrome patients. To conclude, a complex picture of the pathogenesis and pathophysiology of irritable bowel syndrome is emerging, with interactions between several different alterations resulting in the divergent symptom pattern in these patients.

Influence of positive family history on clinical characteristics of functional constipation

BACKGROUND & AIMS

We observed that there is familial aggregation in patients with functional constipation. Their clinical characteristics have not been studied. The aim of this study was to investigate the clinical characteristics of patients with functional constipation with and without a positive family history.

METHODS

Patients with functional constipation satisfying Rome II criteria were recruited. A Rome II questionnaire on constipation was given to the patients' families to identify whether there were any family members with idiopathic constipation. The clinical characteristics between those with and without positive family history were evaluated.

RESULTS

There were 118 patients with at least one first-degree relative with idiopathic constipation and 114 patients without a positive family history. The patients in the 2 groups were comparable in mean age (P = .3) and sex distribution (P = .09). Patients with positive family history had a younger age of onset (median, 11-20 years vs 21-30 years, P < .0001); longer duration of constipation (20 +/- 14 vs 15 +/- 13, P = .016); more complications, eg, symptomatic hemorrhoids, anal fissure, and rectal prolapse (54.2% vs 40.4%, P = .034); less precipitating factors leading to the onset of constipation (35.6% vs 49.1%, P = .037); more frequent use of digital evacuation (27.1% vs 13.2%, P = .008), but no difference in the association with psychological disorders (P = .3); transit time (P = .5); or manometric dyssynergia (P = .5).

CONCLUSIONS

Patients with idiopathic constipation and with a positive family history exhibited different clinical characteristics. This might be related to the early age of onset of the symptoms, which might, in turn, give clues to the underlying etiology.

Mechanisms of Disease: genetics of functional gastrointestinal disorders—searching the genes that matter

There is evidence to suggest that genetic factors contribute to the manifestation of functional gastrointestinal disorders (FGID). As such, it is important to note that FGID are heterogeneous; they have quite different clinical features and (probably) different underlying pathophysiologic mechanisms. Evidence from family and twin studies indicates that there is clustering of FGID in families and increased concordance in monozygotic compared with dizygotic twins. The clinical features of FGID implicate polymorphisms in the genes that encode adrenergic, opioidergic or serotonergic receptors, as well as in the G-protein beta3 subunit (GNB3) gene and serotonin-transporter genes, in their manifestations. As mediators or regulators of mucosal inflammation can trigger events that ultimately result in manifestations of FGID, polymorphisms in genes that encode proteins with immunomodulatory and/or neuromodulatory features (e.g. OPRM1, IL4, IL4R, TNF) might also have a role in the manifestation of FGID. A two-step model for the role of genetic factors in the manifestation of functional gastrointestinal pain can, therefore, be proposed. In the presence of specific hereditary factors, environmental factors that do not usually cause long-term functional alterations are linked to the manifestation of symptoms.

The genetics of fibromyalgia syndrome

Fibromyalgia syndrome (FMS) is a common chronic widespread pain syndrome mainly affecting women. Although the etiology of FMS is not completely understood, varieties of neuroendocrine disturbances, as well as abnormalities of autonomic function, have been implicated in its pathogenesis. The exposure of a genetically predisposed individual to a host of environmental stressors is presumed to lead to the development of FMS. Fibromyalgia overlaps with several related syndromes, collectively compromising the spectrum of the functional somatic disorder. FMS is characterized by a strong familial aggregation. Recent evidence suggests a role for polymorphisms of genes in the serotoninergic, dopaminergic and catecholaminergic systems in the etiopathogenesis of FMS. These polymorphisms are not specific for FMS and are similarly associated with additional comorbid conditions. The mode of inheritance in FMS is unknown, but it is most probably polygenic. Recognition of these gene polymorphisms may help to better subgroup FMS patients and to guide a more rational pharmacological approach. Future genetic studies conducted in larger cohorts of FMS patients and matched control groups may further illuminate the role of genetics in FMS.

Mechanisms of hypersensitivity in IBS and functional disorders

General introduction The concept of visceral hypersensitivity is accepted as being germane to several functional gastrointestinal disorders (FGIDs). The causes or risk factors associated with this hypersensitivity are unclear. This article addresses the proposed mechanisms leading to hypersensitivity: from genetic to inflammatory disorders, from central to peripheral alterations of function. However, in order to place visceral hypersensitivity in a more global perspective as an aetiological factor for FGIDs, it also provides a review of recent evidence regarding the role of other peripheral mechanisms (the intraluminal milieu), as also genetic factors in the pathophysiology of these disorders. The article has been divided into five independent sections. The first three sections summarize the evidence of visceral hypersensitivity as a biological marker of functional gut disorders, the peripheral and central mechanisms involved, and the role of inflammation on hypersensitivity. In opposition to visceral hypersensitivity as an isolated phenomenon in functional gut disorders, the last two sections focus on the importance of peripheral mechanisms, like motor disturbances, specifically those resulting on altered transport of intestinal gas, and alterations of the intraluminal milieu and genetics.

Serotonergic and non-serotonergic targets in the pharmacotherapy of visceral hypersensitivity

Visceral hypersensitivity is considered a key mechanism in the pathogenesis of functional gastrointestinal (GI) disorders. Targeting visceral hypersensitivity seems an attractive approach to the development of drugs for functional GI disorders. This review summarizes current knowledge on targets for the treatment of visceral hypersensitivity, and the status of current and future drug and probiotic treatment development, and the role of pharmacogenomic factors.

Familial aggregation in constipated subjects in a tertiary referral center

OBJECTIVES

Clinical observation showed that there is family aggregation in constipated subjects, but formal data are lacking. This prompted us to conduct a formal family study in constipated subjects.

METHODS

Constipated subjects (probands) were identified according to the Rome II and Chinese constipation questionnaire criteria, healthy subjects were chosen as controls. Living first-degree relatives (parents, siblings, and children) and spouses (as internal controls) from both groups were identified. The questionnaire on Rome II criteria was given to the relatives either through the index subjects or by mail. The questionnaire was received by mailing back or through the index subjects. Any nonresponders were chased.

RESULTS

There were 132 probands with constipation and 114 controls. The Rome II questionnaire was sent to a total of 677 relatives of the probands and 591 of the controls. Relatives were comparable in mean age, sex distribution, family size, and marital status in the two groups. Constipation prevalence was 16.4% in probands' relatives versus 9.1% in controls' relatives, i.e., 13% in the relatives from both proband and controls. Among the constipated relatives, 6.3%versus 9.3% of the relatives were spouses of the probands and controls (P = 0.5). Subjects with more family members having constipation will have higher risk of constipation: OR 2.02, CI 1.14-3.65, P = 0.0177 for at least one family member; OR 3.99, CI 1.86-9.23, P = 0.0006 for at least two family members.

CONCLUSIONS

Familial aggregation of constipation occurs, supporting a genetic or intrafamilial environment component.

Role of infection in irritable bowel syndrome

Infection by pathogenic organisms leads to mucosal damage and disruption of the gut's extensive commensal flora, factors which may lead to prolonged bowel dysfunction. Six to 17% of unselected irritable bowel syndrome (IBS) patients believe their symptoms began with an infection, which is supported by prospective studies showing a 4%-31% incidence of postinfectious IBS-(PI) following bacterial gastroenteritis. The wide range of incidence can be accounted for by differences in risk factors, which include in order of magnitude; severity of initial illness > bacterial toxigenicity > hypochondriasis, depression and neuroticism, and adverse life events in the previous 3 months. PI-IBS has been reported after Campylobacter, Salmonella, and Shigella infections. Serial biopsies after Campylobacter jejuni gastroenteritis show an initial inflammatory infiltrate, with an increase in enterochromaffin (EC) cells, which in most cases subsides over the next 6 months. Those who go on to develop IBS show increased numbers of EC and lymphocyte cell counts at 3 months compared with those who do not develop IBS. Interleukin-1beta mRNA levels are increased in the mucosa of those who develop PI-IBS, who also show increased gut permeability. Recover can be slow, with approximately 50% still having symptoms at 5 years. Recent studies suggest an increase in peripheral blood mononuclear cell cytokine production in unselected IBS, an abnormality that may be ameliorated by probiotic treatment. The role of small-bowel bacterial overgrowth in IBS is controversial, but broad-spectrum antibiotics do have a temporary benefit in some patients. More acceptable long-term treatments altering gut flora are awaited with interest.

Genes and environment in irritable bowel syndrome: one step forward

Both low birth weight and genetic factors may be integral to the aetiological pathway in irritable bowel syndrome

5-HT in the enteric nervous system: gut function and neuropharmacology

In recent times, the perception of functional gastrointestinal disorders such as irritable bowel syndrome (IBS) has shifted fundamentally. Such disorders are now thought of as serious diseases characterized by perturbations in the neuronal regulation of gastrointestinal function. The concept of visceral hypersensitivity, the characterization of neuronal networks in the 'brain-gut axis' and the identification of several novel 5-HT-mediated mechanisms have contributed to this shift. Here, we review how some of the more promising of these new mechanisms (e.g. those involving 5-HT transporters and the 5-HT(2B), 5-HT(7) and putative 5-HT(1p) receptors) might lead to a range of second-generation therapies that could revolutionize the treatment of functional gastrointestinal disorders, particularly IBS.

Serotonin transporter gene polymorphism and irritable bowel syndrome

Polymorphisms in the promoter region of the serotonin reuptake transporter (SERT) gene may underlie the disturbance in gut function in patients with irritable bowel syndrome (IBS). Association studies of SERT polymorphisms and IBS have shown diverse results among different countries, which might be due to racial and subject composition differences. The aim of this study was to assess the potential association between SERT polymorphisms and IBS in Koreans. A total of 190 IBS patients, who met the Rome II criteria, and 437 healthy controls were subjected to genotyping. SERT polymorphisms differed in the IBS and control groups (P = 0.014). The SERT deletion/deletion genotype occurred with greater frequency in the diarrhoea-predominant IBS group than in the controls. A strong genotypic association was observed between the SERT deletion/deletion genotype and diarrhoea-predominant IBS (P = 0.012). None of the clinical symptoms analysed was significantly associated with the SERT genotypes. The frequency of the SERT insertion/insertion genotype was much lower than that of the other two genotypes. A significant association was observed between the SERT polymorphism and IBS, especially diarrhoea-predominant IBS, suggesting that the SERT gene is a potential candidate gene involved in IBS in Korea.

Acute tryptophan depletion alters gastrointestinal and anxiety symptoms in irritable bowel syndrome

OBJECTIVES

To assess the effect of acute changes in serotonin (5-HT) synthesis using the acute tryptophan depletion (ATD) paradigm on gastrointestinal (GI) and mood symptoms in irritable bowel syndrome (IBS).

METHODS

In a randomized double-blind crossover study, 29 subjects (18 patients with ROME II defined IBS and 11 age-matched controls) were studied under ATD and acute tryptophan increase (ATI) conditions. GI symptoms, mood and anxiety ratings, as well as plasma tryptophan concentrations were measured.

RESULTS

Total (and free) plasma tryptophan concentrations decreased on the ATD day in patients (73%[82%]) and controls (73%[80%]), and increased on the ATI day in patients (59%[143%]) and controls (61%[381%]). Compared with the ATD day, IBS patients reported more GI symptoms on the ATI day at +210 (p < 0.001) and at +270 (p < 0.05) min post drink. IBS patients also reported less anxiety on the ATI day compared with the ATD day at +270 min (p < 0.001). ATD and ATI did not affect these ratings in control participants. IBS patients had a lower mood compared with controls (p < 0.05), but this did not differ between the ATI and ATD days in either group.

CONCLUSIONS

IBS patients' GI and anxiety responses to changes in tryptophan load differ from controls. This suggests a difference in serotonergic functioning between these two groups and provides evidence to support the hypothesis that 5-HT dysfunction is involved in IBS.