The Effects And Mechanism Of Dietary Lactose Ingestion On Pathogenesy Of Irritable Bowel Syndrome With Diarrhea

Irritable bowel syndrome (IBS) is one of the most common chronic functional intestinal disorders that impairing the sufferer's quality of life and patients with IBS constitute a great quantity of the load for the healthcare system. The pathogenesis and pathophysiology of IBS is complex and still incompletely clear. As an important factor for provocating or aggravating symptoms of IBS, dietary factor, especially dairy was associated closely with irritable bowel syndrome with diarrhea (IBS-D).Lactose deficiency (LD) affects the majority of Chinese people. In recent year the availability and popularity of milk products and commercially prepared foods containing lactose is increasing rapidly. Given the high prevalence of LD in this population, this change in diet may cause abdominal symptoms and diarrhea in large numbers of consumers, especially those with a predisposition to developing IBS-D. Some sufferers may not identify these foods as the cause of their symptoms and seek medical advice for symptoms, request investigation and treatment. with large direct and indirect health care costs. Therefore, it is urgent and important to study LI and identity the effects of lactose on pathogenesy of IBS in China.The Lactose Hydrogen Breath Test (HBT) provides objective evidence of LM and LI. result of HBT is correlated with the dose of lactose used in test, however.there was no unify, standard dosage of lactose. A 40-50g lactose dose is standard for HBT in populations with low prevalence of lactase deficiency, but many reports suggested 20g or even 10g dosage. It was unclear which dosage used in HBT not only can detect LM completely, but also discriminate IBS-D patients with healthy people (physiogenic lactose intolerance) significantly in Chinese people, the relevant study about this is seldom, especially high quality design, comparative study. Breath hydrogen was detected with 15 min interval for 3-4 hours in routine protocol, which was tesious and time-consuming, so how to simplify the frequence of hydrogen is another clinical issue about LHBT.The effects of dietary lactose on pathogenesy of IBS were controversial. Our previous study on epidemiological investigation about IBS showed:the increased prevalence of IBS in China may relate to increased ingestion of food containing lactose. However, there was seldom study to investigate the lactose intake and the effection of diet interference on abdominal symptoms in IBS patients.Our previous study showed patients with IBS-D have an obvious tendency to report more symptoms after lactose ingestion compared with healthy volunteers (HVs), although LM is as prevalent in D-IBS population as in HVs. And even among the group of patients, the threshold dose of lactose they can ingest without symptom onset varies from person to person. However, the potential mechanisms for those findings are still unclear. Visceral hypersensitivity could explain this finding; however the mechanism that underlies this pathogenic mechanism remains unclear. The role of mucosal immune activation and psychological factors has been advocated in recent studies to explain visceral hypersensitivity in the gut. But there was scarely study to investigate the association between LI with mucosal immune activation and psychological factors in IBS patients.In conclusion, The present study aimed to (1) determine the appropriate dose of lactose and simplified protocol in LHBT in Chinese people by compared results of LHBT with 10g,20g, and 40g three different dosage in a double blind, randomized controlled trial; (2) identify the impact of dietary lactose on symptoms of IBS-D occurrence by investigate amount of lactose ingestion in IBS-D patients and observe the effects of lactose restricted diet on abdominal symptoms; (3) explore the effects of intestinal mucosal immunocyte and psychological factors on lactose sensitivity in IBS-D patients by analyzed the relationship between variety of visceral sensitivity, psychological factor and intestinal mucosal immunocyte.The main body of the present study consists of three parts detailed below:Part?. Appropriate lactose dose and simplified hydrogen test methods for lactose hydrogen breath test in Chinese peopleAim:To establish the most appropriate dose and HBT protocol for assessment of lactose malabsorption and intolerance in populations with a high prevalence of lactase deficiency.Methods:63 Chinese patients with IBS-D and 64 healthy volunteers (HVs) underwent HBT at 10g,20g.40g lactose on three days in a double blind, randomized controlled trial. Breath samples and abdominal symptoms were assessed at 15min intervals for 3hr.Results:LM prevalence on HBT was similar in HVs and IBS-D patients and increased with lactose dose from lOg (41.6%v.35.0%) to 20g (86.7%v.80.0%) and 40g (93.3%v.91.6%). LI prevalence was lower in HVs than IBS-D at 10g (3.3%v.18.3, P=0.008) to 20g (21.7%v.46.7%, P=0.004) and 40g (68.3%v.85%. P=0.031). Moreover. HVs reported fewer and less severe symptoms compared to IBS-D patients. At 20g lactose HBT a cutoff of 2.5 symptoms or 4.5 on the total symptom scale demonstrated excellent specificity (92.3%) to discriminate IBS-D patients from HVs on ROC analysis (P<0.05). Finally, compared to the full protocol, a simplified HBT with 4 breath samples at 30 min intervals from 90min to 180 min maintained high diagnostic sensitivity (LM:92%-98%, LI:91%-96%).Conclusion:Intermediate 20g dose lactose HBT is appropriate to diagnose LM and LI in a population with a high prevalence of lactase deficiency. It is feasible to using a simplified HBT (30 min intervals from 90min to 180 min) in clinic.Part II. Investigation of lactose intake and the effection of diet interference on abdominal symptoms in IBS patients Aim:To (1) investigate effect of dietary lactose on abdominal symptoms in patients with IBS-D; (2)compare directive effect of diet intervention between subjective lactose intolerance with objective lactose intolerance detected by 10g,20g LHBT.Methods:246 IBS-D patients and 60 HVs underwent (1) food containing lactose consumption questionnaire and GI symptom questionnaire to evaluate daily average amount of lactose ingestion and severity of gastrointestinal symptom; (2) lOg or 20g lactose LHBT with LI measured by a validated total symptom score (TSS). IBS-D patients were divided two groups after LHBT:lactose restriction or not-restriction, and re-evaluated the severity of GI symptom after 6 months through telephone or clinical follow-up with questionnaire.Results:(1) The differences in age, gender between IBS-D patients and HVs were no statistical significance (p>0.05); (2) IBS-D patients consumed more less lactose from dairy (13.8(0-27.2) vs.20.3(8.8-39.4), P=0.006) and more other food containing lactose (27.0 (14.4-40.5) vs.17.8(3-37.2), P=0.005) than HVs. (3) IBS patients who was in lactose restriction group have higher improvement rate of abdominal symptoms than those in non-restriction group (71.6% vs.45%, P=0.000), and the improvement rate of abdominal symptoms by lactose restriction in patients diagnosed LM or LI in 20g LHBT was higher than those in non-restriction (LM:69.2% vs 47.8%, P=0.012; LI:65.9% vs 43.9%, P=0.041). (4) The improvement rate of symptoms between lactose restriction and non-restriction in patient with subjective lactose intolerance was no statistical significant (69.7% vs.54.8%, P=0.083), on the contrary, the improvement rate of symptoms in lactose restriction in patients with subjective lactose tolerance was higher than non-restriction (75.0% vs.49.1%, P=0.011)Conclusion:(1) IBS-D patients intake more lactose from containing lactose food besides dairy, and the symptoms were improved significantly through dietary lactose restriction; (2) it was fallibility to direct lactose restriction according to subjective lactose intolerance.20g LHBT had a commendable effect of direct lactose restriction. Part III. Lactose Intolerance in Patients with IBS-D is associated with mucosal immune activation and anxietyAim:To explore the association of visceral sensitivity induced by LI with mucosal immune activation and psychological factors in D-IBS patients.Methods:55 outpatients with D-IBS and 18 healthy volunteers (HVs) underwent a 20g lactose Hydrogen Breath Test (HBT) and were categorized as LM or LI on the basis of a validated total symptom score (TSS). Further assessment included (1) Evaluation of psychological status and psychosocial stress by validated questionnaire. (2) Assessment of rectal sensitivity before and after HBT. (3) Colonoscopy with biopsy of sigmoid colon, ascending colon and terminal ileum with quantification of intraepithelial T lymphocytes (IEL; CD4+, CD8+). mast cells (MCs) and enterochromaffin cells (ECCs) /high-power field. (4) Assay of serum cytokine levels (TNF-a.IFN-y,IL-4,IL-10,IL-17). Comparisons were made between D-IBS patients with LI phenotype and HVs with corrections for multiple comparisons.Results:Most participants in all groups (-90%) had a positive 20g lactose HBT (P=0.856):however LI was more prevalent in D-IBS patients than HVs (45.5%(25/55) vs 16.7%(3/18), P=0.029). (1) Demographic factors, levels of depression and stress were similar in all groups; however D-IBS patients were more anxious than HVs (P<0.001). (2) Rectal discomfort thresholds were reduced after lactose HBT in IBS patients with LI but not in LM patients or HVs (P<0.001). (3) Histology showed normal mucosal architecture. MCs in the terminal ileum were elevated in LI patients compared to LM patients and HVs (both P<0.001) (4) Serum TNF-a in LI patients was higher than in LM patients (P=0.034) and HVs (p<0.001). On multivariate logistic regression. MCs in terminal ileum (OR=1.403.95%CI:1.066-1.845. P=0.016). first sensation during HBT (OR=0.612,95%CI:0.392-0.956. P=0.031) were risk factors for LI. Severity of intolerance symptoms (TSS) was associated with visceral hypersensitivity to rectal distension induced by LI (reduction in discomfort threshold pressure:r=0.611. p=0.000). MCs in terminal ileum (r=0.656.p=0.000) and anxiety (r=0.539. P=0.000).Conclusions:Intolerance of lactose in D-IBS patients is associated with increased mucosal immune activation and higher anxiety scores. These findings provide insight into the mechanism by which lactose and, likely, other poorly fermentable carbohydrates cause symptoms in D-IBS and may identify a phenotype that may respond to dietary management and specific medical treatments.