Irritable Bowel Syndrome: Pathophysiology and Current Therapeutic Approaches

Electroacupuncture Improving Intestinal Barrier Function in Rats with Irritable Bowel Syndrome Through Regulating Aquaporins

BACKGROUND

Intestinal mucosal barrier dysfunction plays a crucial role in the pathogenesis of irritable bowel syndrome with diarrhea (IBS-D). In order to explore the mechanism of electroacupuncture (EA) treatment on intestinal mucosal barrier, this study observed the effect of EA on aquaporins (AQPs), tight junctions (TJs), NF-κB pathway and the gut microbiota in IBS-D rats.

METHODS

The IBS-D model was established by acetic acid enema combined with chronic restraint method. The effects of EA on the treatment of IBS-D were examined by the abdominal withdrawal reflex score, Bristol's fecal character score, fecal water content, small intestine propulsion rate and HE staining. AQPs, TJs and inflammation-related molecular mechanisms were explored. The fecal samples were applied for 16S rRNA sequencing to assess the effect of EA intervention to the intestinal bacterial abundance.

RESULTS

EA reduced intestinal sensitization, restored intestinal motility and improved inflammatory cell infiltration. Furthermore, EA improved intestinal inflammation and flora environment significantly, inhibited NF-κB signaling and inflammatory factors (IL-1β and TNF-α). It can also increase the gene and protein expression of AQPs (AQP1, AQP3, and AQP8) and the gene levels of TJs (ZO-1 and Occludin).

CONCLUSION

EA has an inhibitory effect on the NF-κB signaling pathway, and regulates the proteins of AQP1, AQP3, AQP8, and TJs to restore the balance of water metabolism and intestinal permeability in IBS-D, which also restored the function of the intestinal mucosa by regulating the intestinal flora.

Chronic Sacral Nerve Stimulation Inhibits Visceral Hypersensitivity in Diarrhea-Predominant Irritable Bowel Syndrome Rats Model

OBJECTIVE

Sacral nerve stimulation (SNS) is emerging as a novel treatment for irritable bowel syndrome (IBS). However, its effects are limited, and the underlying mechanisms remain largely unknown.

MATERIALS AND METHODS

In this study, rats were divided into three groups (n = 12 rats per group): 1) the SNS group; 2) the sham SNS group (the sham group for short); and 3) the control group. The SNS and sham groups were exposed to chronic and acute stress to establish an IBS model. Electrode implantation surgery was performed in rats with the IBS model. The SNS group received electrical stimulation for 30 minutes every day for seven days. Abdominal withdrawal reflex (AWR) was used to evaluate the effect of SNS on visceral sensitivity in diarrhea-predominant IBS (IBS-D) rats. The frequency domain of heart rate variability (HRV) was analyzed to assess the effect of SNS on regulating the autonomic function. The expression of transient receptor potential vanilloid 1 (TRPV1) in the colon, spinal cord, and hippocampus was detected by immunohistochemistry to explore the mechanism of SNS in IBS-D rats.

RESULTS

Compared with the sham group, AWR scores were significantly decreased under different gas volumes of stimulation of 0.4, 0.6, and 0.8 ml for rectal distention in the SNS group (all p < 0.05). However, there was no significant difference <1.0 ml between the two groups (p > 0.05). Compared with the sham group, the frequency domain indexes of HRV were significantly altered. Normalized low-frequency power and low frequency-to-high frequency ratio were significantly decreased, and normalized high-frequency power was significantly increased in the SNS group (all p < 0.05). Moreover, the expression of TRPV1 in the spinal cord and colon in the SNS group was significantly decreased compared with the sham group (both p < 0.05). These results suggested that chronic SNS not only improved the visceral sensitivity and autonomic dysfunction but also decreased the expression of TRPV1 in the spinal cord-gut tissue in IBS-D rats.

CONCLUSION

Chronic SNS was found to have an inhibitory effect on visceral hypersensitivity in IBS-D rats, providing experimental evidence for its potential clinical application in IBS.

Genomic analysis and in vivo efficacy of Pediococcus acidilactici as a potential probiotic to prevent hyperglycemia, hypercholesterolemia and gastrointestinal infections

Lactic acid bacteria are the well acknowledged probiotics that can cure a variety of diseases. In this study, we observed the in vivo potentials of Pediococcus to treat hyperglycemia, hypercholesterolemia and gastrointestinal infections. A total of 77 Lactobacillus were isolated from the milk of 10 cows and 10 goats, four of those strains inhibited both carbohydrates-hydrolyzing enzymes, α-glucosidase, and α-amylase. They all showed antagonistic effects on pathogenic E. coli and S. Typhimurium which were confirmed by performing pathogen challenge test and visualizing on Electron microscopy. 16S rRNA gene sequence identified that all four strains belong to Pediococcus genus which were further distinguished as Pediococcus acidilactici by pheS gene sequence. Whole genome sequence analysis revealed their non-pathogenic properties for human and the presence of probiotic genes responsible for stress resistance, immunomodulation, adhesion, metal and drug resistance. In vivo trial with diabetes-induced mice ascertained that all Pediococcus acidilactici had significant potentials to reduce elevated glucose and low-density lipoprotein level in blood. Interestingly, two out of four strains were significantly more effective (p < 0.0001 each) than metformin in reducing the blood glucose level. This in vivo study demonstrated that Pediococcus acidilactici might be a promising probiotic to prevent hyperglycemia, hypercholesterolemia and gastrointestinal infections.

Bile Acid and Gut Microbiota in Irritable Bowel Syndrome

Gut microbiota and their metabolites like bile acid (BA) have been investigated as causes of irritable bowel syndrome (IBS) symptoms. Primary BAs are synthesized and conjugated in the liver and released into the duodenum. BA biotransformation by gut microbiota begins in the intestine and results in production of a broad range of secondary BAs. Deconjugation is considered the gateway reaction for further modification and is mediated by bile salt hydrolase, which is widely expressed by the gut microbiota. However, gut bacteria that convert primary BAs to secondary BAs belong to a limited number of species, mainly Clostridiales. Like gut microbiota modify BA profile, BAs can shape gut microbiota via direct and indirect actions. BAs have prosecretory effects and regulates gut motility. BAs can also affect gut sensitivity. Because of the vital role of the gut microbiota and BAs in gut function, their bidirectional relationship may contribute to the pathophysiology of IBS. Individuals with IBS have been reported to have altered microbial profiles and modified BA profiles. A significant increase in fecal primary BA and a corresponding decrease in secondary BA have been observed in IBS with predominant diarrhea. In addition, primary BA was positively correlated with IBS symptoms. In IBS with predominant diarrhea, bacteria with reduced abundance mainly belonged to the genera in Ruminococcaceae and exhibited a negative correlation with primary BAs. Integrating the analysis of the gut microbiota and BAs could better understanding of IBS pathophysiology. The gap in this field needs to be further filled in the future.

Comparing probiotic and drug interventions in irritable bowel syndrome: a meta-analysis of randomised controlled trials

Clinical decisions made by health professionals to recommend either drug or probiotic interventions for irritable bowel syndrome (IBS) should be supported by proper knowledge of the efficacy rates of both types of interventions. In this article, we performed a systematic review and meta-analysis to examine the efficacy of both probiotic- and drug interventions in IBS. Medline was searched between January 2015 - January 2021. Randomised controlled trials (RCT) recruiting participants > 18 years old with IBS and examining the effect of probiotics or drugs were eligible for inclusion. The data of the primary outcome, i.e. the persistence of IBS symptoms (dichotomous symptom data), were pooled to obtain a relative risk (RR), with a 95% confidence interval (CI). Secondary outcomes, abdominal pain- and bloating scores (continuous data), were pooled using a standardised mean difference with a 95% CI. The search identified 269 citations of which 32 RCTs were eligible. Our meta-analysis indicated that both probiotic and drug interventions are able to improve the persistence of IBS symptoms (RR 0.60 [0.51; 0.92] versus 0.87 [0.81; 0.92], respectively) and abdominal pain scores (standardised mean difference (SMD) -0.35 [-0.56; -0.14] versus -0.10 [-0.20; 0.00], respectively). However, determining the overall efficacy of both intervention types is inherently complex and such results should be interpreted with care, due to the large diversity of probiotic- and drug types and doses, which is also complicated by variety in IBS subtypes. Hence, as a first step, more large scale randomised double blind placebo-controlled trials focussing on a specific IBS subtype targeted with specific probiotic strains or specific pharmaceutical modalities should be executed, enabling a more proper comparison between trials.

Antibiotics, gut microbiota, and irritable bowel syndrome: What are the relations?

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder in which recurrent abdominal pain is associated with defecation or a change in bowel habits (constipation, diarrhea, or both), and it is often accompanied by symptoms of abdominal bloating and distension. IBS is an important health care issue because it negatively affects the quality of life of patients and places a considerable financial burden on health care systems. Despite extensive research, the etiology and underlying pathophysiology of IBS remain incompletely understood. Proposed mechanisms involved in its pathogenesis include increased intestinal permeability, changes in the immune system, visceral hypersensitivity, impaired gut motility, and emotional disorders. Recently, accumulating evidence has highlighted the important role of the gut microbiota in the development of IBS. Microbial dysbiosis within the gut is thought to contribute to all aspects of its multifactorial pathogenesis. The last few decades have also seen an increasing interest in the impact of antibiotics on the gut microbiota. Moreover, antibiotics have been suggested to play a role in the development of IBS. Extensive research has established that antibacterial therapy induces remarkable shifts in the bacterial community composition that are quite similar to those observed in IBS. This suggestion is further supported by data from cohort and case-control studies, indicating that antibiotic treatment is associated with an increased risk of IBS. This paper summarizes the main findings on this issue and contributes to a deeper understanding of the link between antibiotic use and the development of IBS.

Associations of Habitual Dietary Intake With Fecal Short-Chain Fatty Acids and Bowel Functions in Irritable Bowel Syndrome

BACKGROUND GOALS

Diet may contribute to symptoms of irritable bowel syndrome (IBS) and luminal production of putative IBS biomarkers including short-chain fatty acids (SCFAs). Study aims were to to assess relationships of habitual fiber or starch intake with fecal SCFAs in patients with IBS and healthy volunteers (HVs).

STUDY

In 18 HVs and 30 patients with IBS (13 constipation-predominant [IBS-C] and 17 diarrhea-predominant [IBS-D]), habitual diet using a food frequency questionnaire; bowel functions using a validated bowel diary; and fecal SCFAs by HPLC-mass spectrometry were assessed. Associations of fiber and starch with SCFAs were analyzed using Spearman (rs) and Pearson (R) correlations. Relationships between other dietary endpoints, SCFAs, and bowel functions were explored.

RESULTS

Habitual fiber or starch intakes were not significantly correlated with SCFAs or bowel functions in all participants or HVs nor with SCFAs in IBS. Starch was negatively correlated (R=-0.53; P=0.04) with complete evacuation in IBS-D. Fiber (rs=0.65; P=0.02) and starch (rs=0.56; P=0.05) were correlated with ease of passage in IBS-C. Stool form, frequency, and ease of passage were positively correlated with total SCFAs (all P<0.05), acetate (all P<0.01), propionate (all P<0.05), and butyrate (form P=0.01; ease of passage P=0.05) among all participants, but not in IBS. Complete evacuation was negatively correlated with propionate (R=-0.34; P=0.04) in all participants. Total (P=0.04) and individual SCFAs (all P<0.05) were positively correlated with stool form in HVs.

CONCLUSIONS

Habitual fiber and starch intake does not influence fecal SCFAs but may influence bowel functions in IBS. Fecal SCFAs correlate with bowel functions among all participants including HVs.

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

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

Gluten-Free Diet Reduces Symptoms, Particularly Diarrhea, in Patients With Irritable Bowel Syndrome and Antigliadin IgG

BACKGROUND & AIMS

Many patients with irritable bowel syndrome (IBS) perceive that their symptoms are triggered by wheat-containing foods. We assessed symptoms and gastrointestinal transit before and after a gluten-free diet (GFD) in unselected patients with IBS and investigated biomarkers associated with symptoms.

METHODS

We performed a prospective study of 50 patients with IBS (ROME III, all subtypes), with and without serologic reactivity to gluten (antigliadin IgG and IgA), and 25 healthy subjects (controls) at a university hospital in Hamilton, Ontario, Canada, between 2012 and 2016. Gastrointestinal transit, gut symptoms, anxiety, depression, somatization, dietary habits, and microbiota composition were studied before and after 4 weeks of a GFD. HLA-DQ2/DQ8 status was determined. GFD compliance was assessed by a dietitian and by measuring gluten peptides in stool.

RESULTS

There was no difference in symptoms among patients at baseline, but after the GFD, patients with antigliadin IgG and IgA reported less diarrhea than patients without these antibodies (P = .03). Compared with baseline, IBS symptoms improved in 18 of 24 patients (75%) with antigliadin IgG and IgA and in 8 of 21 patients (38%) without the antibodies. Although constipation, diarrhea, and abdominal pain were reduced in patients with antigliadin IgG and IgA, only pain decreased in patients without these antibodies. Gastrointestinal transit normalized in a higher proportion of patients with antigliadin IgG and IgA. Anxiety, depression, somatization, and well-being increased in both groups. The presence of antigliadin IgG was associated with overall reductions in symptoms (adjusted odds ratio compared with patients without this antibody, 128.9; 95% CI, 1.16-1427.8; P = .04). Symptoms were reduced even in patients with antigliadin IgG and IgA who reduced gluten intake but were not strictly compliant with the GFD. In controls, a GFD had no effect on gastrointestinal symptoms or gut function.

CONCLUSIONS

Antigliadin IgG can be used as a biomarker to identify patients with IBS who might have reductions in symptoms, particularly diarrhea, on a GFD. Larger studies are needed to validate these findings. ClinicalTrials.gov: NCT03492333.

Effect of psychological problems and interventions on gastrointestinal diseases

Many gastrointestinal diseases may develop under the social-psychological-biomedical model; their onset is closely related to psychological factors, and psychological intervention can improve the therapeutic efficacy. This paper reviews the effects of psychological problems and interventions on gastroesophageal reflux disease, irritable bowel syndrome, peptic ulcer, inflammatory bowel disease, and gastrointestinal tumors.

Disruption of the pro-inflammatory, anti-inflammatory cytokines and tight junction proteins expression, associated with changes of the composition of the gut microbiota in patients with irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a pathologic condition characterized by changes in gut microbiome composition, low-grade inflammation, and disruption of intestinal wall permeability. The interaction between the gut microbiome and the disease manifestation remains unclear. The changing of tight junction proteins and cytokines expression throughout the gastrointestinal tract in IBS patients has not been studied yet.

AIM OF THE STUDY

To assess the changes of gut microbiome composition, tight junction proteins, and cytokines expression of intestinal mucosa from the duodenum to the distal part of the colon in IBS patients and healthy volunteers.

METHODS

In 31 IBS patients (16 patients with IBS-D; 15 patients with IBS-C) and 10 healthy volunteers the expression of CLD-2, CLD-3, CLD-5, IL-2, IL-10, and TNF-α in mucosal biopsy specimens was determined by morphological and immune-histochemical methods. The qualitative and quantitative composition of the intestinal microbiota was assessed based on 16S rRNA gene sequencing in both groups of patients.

RESULTS

The expression of IL-2 and TNF-α was significantly increased in IBS patients compared with the controls (p<0.001), with a gradual increase from the duodenum to the sigmoid colon. The expression of IL-10, CLD-3, and CLD-5 in mucosal biopsy specimens of these patients was lower than in the control group (p<0.001). Increased ratios of Bacteroidetes and decreased ratios of Firmicutes were noted in IBS patients compared to healthy volunteers (p<0.05).

CONCLUSION

IBS patients have impaired gut permeability and persisting low-grade inflammation throughout the gastrointestinal tract. Changes in the gut microbiota may support or exacerbate these changes.

Review article: diagnosis, management and patient perspectives of the spectrum of constipation disorders

BACKGROUND

Chronic constipation is a common, heterogeneous disorder with multiple symptoms and pathophysiological mechanisms. Patients are often referred to a gastroenterology provider after laxatives fail. However, there is limited knowledge of the spectrum and management of constipation disorders.

AIM

To discuss the latest understanding of the spectrum of constipation disorders, tools for identifying a pathophysiologic-based diagnosis in the specialist setting, treatment options and the patient's perspective of constipation.

METHODS

Literature searches were conducted using PubMed for constipation diagnostic criteria, diagnostic tools and approved treatments. The authors provided insight from their own practices.

RESULTS

Clinical assessment, stool diaries and Rome IV diagnostic criteria can facilitate diagnosis, evaluate severity and distinguish between IBS with constipation, chronic idiopathic constipation and dyssynergic defecation. Novel smartphone applications can help track constipation symptoms. Rectal examinations, anorectal manometry and balloon expulsion, assessments of neuromuscular function with colonic transit time and colonic manometry can provide mechanistic understanding of underlying pathophysiology. Treatments include lifestyle and diet changes, biofeedback therapy and pharmacological agents. Several classes of laxatives, as well as prokinetic and prosecretory agents, are available; here we describe their mechanisms of action, efficacy and side effects.

CONCLUSIONS

Constipation includes multiple overlapping subtypes identifiable using detailed history, current diagnostic tools and smartphone applications. Recognition of individual subtype(s) could pave the way for optimal, evidence-based treatments by a gastroenterology provider.

Compositional and Functional Changes in the Gut Microbiota in Irritable Bowel Syndrome Patients

Background/Aims

This study aimed to characterize the changes in the gut microbiota of irritable bowel syndrome (IBS) patients and to investigate the consequent alterations in bacterial functions.

Methods

We performed 16S rRNA metagenomic sequencing and a phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) analyses using fecal samples from control (n=12) and diarrhea-dominant IBS patients (n=7).

Results

The samples were clustered by the principal coordinates analysis depending on the presence of IBS (p=0.003). In the IBS patients, the abundances of Acidaminococcaceae, Sutterellaceae, and Desulfovibrionaceae were significantly increased, while those of Enterococcaceae, Leuconostocaceae, Clostridiaceae, Peptostreptococcaceae, and Lachnospiraceae were significantly decreased. The PICRUSt results indicated that two orthologues involved in secondary bile acid biosynthesis were significantly decreased in IBS patients. Modules involved in multidrug resistance, lipopolysaccharide biosynthesis, the reductive citrate cycle, and the citrate cycle were significantly increased in the IBS patients. In contrast, modules involved in cationic antimicrobial peptide resistance, and some transport systems were more abundant in controls than in IBS patients.

Conclusions

Changes in the gut microbiota composition in IBS patients lead to alterations in bacterial functions, such as bile acid transformation and the induction of inflammation, which is a known pathophysiological mechanism of IBS.

Diagnosing Constipation Spectrum Disorders in a Primary Care Setting

Understanding pathophysiological causes of constipation is worthwhile in directing therapy and improving symptoms. This review aims to identify and fill gaps in the understanding of the pathophysiology of constipation, understand its prevalence, review diagnostic tools available to primary care physicians (PCPs), and highlight patients’ expectations for the management of this common spectrum of disorders. Literature searches conducted via PubMed included terms related to constipation, diagnosis, and patient perceptions. Case studies were developed to highlight the differences between patients who may be appropriately managed in the primary care setting and those requiring specialty consultation. Myriad pathophysiological factors may contribute to constipation, including stool consistency, altered intestinal motility, gut microbiome, anorectal abnormalities, as well as behavioral and psychological factors. Common diagnoses of “primary constipation” include slow-transit constipation, defecation disorders, irritable bowel syndrome with constipation, and chronic idiopathic constipation. A detailed medical history should be conducted to exclude alarm features and PCPs should be familiar with pathophysiological factors that cause constipation, available diagnostic tools, alarm signs, and the various classification criteria for constipation subtypes in order to diagnose and treat patients accordingly. PCPs should understand when a referral to a gastroenterologist, anorectal specialist, pelvic floor physical therapist, and/or mental health specialist is appropriate.

Scientific Evidence for the Treatment of Children with Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is one of the most common functional gastro-intestinal disorders which significantly impacts the quality of life of affected children. Abdominal pain improved by defecation, associated with a change in stool form and frequency, represents its specific clinical marker. Even if a number of potential patho-physiological mechanisms have been described, the exact underlying etiology of IBS is so far unclear. Likewise, no optimal treatment has ever been found neither for adult nor for pediatric patients. Current therapeutic options include drugs, dietary interventions and biopsychosocial therapies. The present review aims at evaluating the scientific evidence supporting the efficacy of these treatments for children with IBS.

The Relationship Between the Serotonin Metabolism, Gut-Microbiota and the Gut-Brain Axis

BACKGROUND

Serotonin (5-HT) has a pleiotropic function in gastrointestinal, neurological/psychiatric and liver diseases. The aim of this review was to elucidate whether the gut-microbiota played a critical role in regulating peripheral serotonin levels.

METHODS

We searched for relevant studies published in English using the PubMed database from 1993 to the present.

RESULTS

Several studies suggested that alterations in the gut-microbiota may contribute to a modulation of serotonin signalling. The first indication regarded the changes in the composition of the commensal bacteria and the intestinal transit time caused by antibiotic treatment. The second indication regarded the changes in serotonin levels correlated to specific bacteria. The third indication regarded the fact that decreased serotonin transporter expression was associated with a shift in gut-microbiota from homeostasis to inflammatory type microbiota. Serotonin plays a key role in the regulation of visceral pain, secretion, and initiation of the peristaltic reflex; however, its altered levels are also detected in many different psychiatric disorders. Symptoms of some gastrointestinal functional disorders may be due to deregulation in central nervous system activity, dysregulation at the peripheral level (intestine), or a combination of both (brain-gut axis) by means of neuro-endocrine-immune stimuli. Moreover, several studies have demonstrated the profibrogenic role of 5-HT in the liver, showing that it works synergistically with platelet-derived growth factor in stimulating hepatic stellate cell proliferation.

CONCLUSION

Although the specific interaction mechanisms are still unclear, some studies have suggested that there is a correlation between the gut-microbiota, some gastrointestinal and liver diseases and the serotonin metabolism.

Subthreshold Psychiatric Psychopathology in Functional Gastrointestinal Disorders: Can It Be the Bridge between Gastroenterology and Psychiatry?

Background and Aims

Functional gastrointestinal disorders (FGDs) are multifactorial disorders of the gut-brain interaction. This study investigated the prevalence of Axis I and spectrum disorders in patients with FGD and established the link between FGDs and psychopathological dimensions.

Methods

A total of 135 consecutive patients with FGD were enrolled. The symptoms' severity was evaluated using questionnaires, while the psychiatric evaluation by clinical interviews established the presence/absence of mental (Diagnostic and Statistical Manual-4th edition, Axis I Diagnosis) or spectrum disorders.

Results

Of the 135 patients, 42 (32.3%) had functional dyspepsia, 52 (40.0%) had irritable bowel syndrome, 21 (16.2%) had functional bloating, and 20 (15.4%) had functional constipation. At least one psychiatric disorder was present in 46.9% of the patients, while a suprathreshold panic spectrum was present in 26.2%. Functional constipation was associated with depressive disorders (p < 0.05), while functional dyspepsia was related to the current major depressive episode (p < 0.05). Obsessive-compulsive spectrum was correlated with the presence of functional constipation and irritable bowel syndrome (p < 0.05).

Conclusion

The high prevalence of subthreshold psychiatric symptomatology in patients with FGD, which is likely to influence the expression of gastrointestinal symptoms, suggested the usefulness of psychological evaluation in patients with FGDs.

Description of analytical method and clinical utility of measuring serum 7-alpha-hydroxy-4-cholesten-3-one (7aC4) by mass spectrometry

BACKGROUND

Imbalance of bile acids (BA) homeostasis in the gastrointestinal tract can lead to chronic diarrhea or constipation when BA in the colon are in excess or low, respectively. Since both disturbances of bowel function can result from other etiologies, identifying BA imbalance is important to tailor treatment strategies. Serum concentrations of 7-alpha-hydroxy-4-cholesten-3-one (7aC4), a precursor in bile acid synthesis, reflect BA homeostasis. Here we describe a method to accurately measure serum 7aC4 and evaluate the clinical utility in patients with diarrhea or constipation phenotypes.

METHODS

Serum 7aC4 is measured after acetonitrile protein precipitation using C18 liquid chromatography, tandem mass spectrometry, and deuterium-labeled 7aC4 internal standard. Assay performance including linearity, precision, and accuracy was assessed using waste serum samples. The reference interval was established in healthy individuals without BA-altering conditions or medications. Clinical performance was assessed in patients with irritable bowel syndrome.

RESULTS

The method precisely and accurately measured 7aC4 in human serum from 1.4-338ng/mL with no ion suppression or interference from related 7-keto-cholesterol. Central 95th percentile reference interval was 2.5-63.2ng/mL. Lower serum 7aC4 was found in patients with constipation with sensitivity/specificity of 79%/55% compared to healthy controls. Higher 7aC4 was found in patients with bile acid diarrhea (BAD) compared to those without BAD with sensitivity/specificity of 82%/53%.

CONCLUSIONS

We have developed a sensitive and precise assay for measuring the concentration of 7aC4 in serum. The assay can be used to screen for diarrhea caused by bile acid malabsorption.