Irritable bowel syndrome pathophysiology
Pathophysiology
Pathogenesis
IBS occurs as a result of an interplay between four main factors:
| CNS dysregulation and psychosocial factors | |||||||||||||||||||||||||||||
| Intrinsic gastrointestinal factors: • Motor abnormalities • Visceral hypersensitivity • Immune activation and mucosal inflammation • Altered gut microbiota • Abnormal serotonin pathways | IRRITABLE BOWEL SYNDROME | Genetic factors: • Twin concordance • Familial aggregation • Single nucleotide polymorphisms(SNPs) • TNF polymorphism | |||||||||||||||||||||||||||
| Environmental factors: •Diet •Infections | |||||||||||||||||||||||||||||
Environmental factors
- Diet
- Fermentable oligosaccharides, monosaccharides, disaccharides, and polyols (FODMAPs) are present in stone fruits, artificial sweeteners, lactose-containing foods, and legumes. Changes in diet such as increased amounts (FODMAPs) can alter gut microflora.[1]
- Fermentation and osmotic effects of FODMAPs produce abdominal discomfort and diarrhea in IBS.
- FODMAPs yield carbon dioxide, methane, and hydrogen that are responsible for bloating.
- Osmotically active carbohydrate by products lead to diarrhea by enhancing intestinal contractions and precipitating fluid secretion.[2][3][4][5][6][7][8][9]
- Infection
- Infectious gastroenteritis triggers micro inflammation, and up to one third of irritable bowel syndrome cases follow acute gastroenteritis.
- Micro inflammation of the gut causes activation of the lymphocytes, mast cells and pro inflammatory cytokines that stimulate the enteric nervous system and lead to abnormal visceral and motor responses within the gastrointestinal tract.
- Immune activation due to GI infection also increases enteroendocrine cells, calprotectin-positive macrophages, intraepithelial lymphocytes, and lamina propria T cells which contribute directly to abdominal pain perception. [10][11][12][13][14][15][16][17][18]
Intrinsic gastrointestinal factors
- Motor abnormalities:
- IBS is referred to as ‘spastic colon’ due to changes in colonic motor function.
- Manometry recordings from the transverse, descending and sigmoid colon have shown that IBS leads to altered colonic and small intestinal motor function, such as increased frequency and irregularity of luminal contractions.
- Motor changes lead to symptoms of diarrhea and constipation.[19][20][21]
- Diarrhea-prone IBS patients have increased responses to ingestion, CRH (corticotropin releasing hormone), CCK (cholecystokinin), which increase the peak amplitude of high-amplitude propagating contractions (HAPCs) and lead to abdominal discomfort with accelerated transit through the colon. [22][23][24][25][26]
- Constipation-prone IBS patients show fewer high-amplitude propagating contractions (HAPCs) as compared to diarrhea prone IBS patients, delayed transit through the colon and decreased motility.
- Changes in the motor function of the colon are responsible for producing the gastrointestinal symptoms of IBS such as altered bowel habits and abdominal pain.[25]
- Visceral hypersensitivity:
- IBS is associated with a decreased threshold for perception of visceral stimuli (i.e. visceral hypersensitivity)[25][27][28]
- Rectal distension produces painful and non-painful sensations at lower volumes in IBS patients as compared to healthy controls, suggesting the presence of afferent pathway disturbances in visceral innervation[29][30][31][32].
- Visceral hypersensitivity contributes to IBS by involving the following:
- Spinal hyperexcitability
- Secondary to activation of neurotransmitters such as:
- N-methyl D aspartate (NMDA) receptor
- nitric oxide
- Activation of specific gastrointestinal mediators that lead to afferent nerve fiber sensitization:
- Central (brainstem and cortical) modulation with increased activation of anterior cingulate cortex, thalamus and insula.
- These structures are involved in processing of pain.
- Cortical and brain stem modulation translate into long term hypersensitivity due to neuroplasticity.
- Semi permanent changes(seen on functional magnetic resonance imaging and positron emission tomography) in the neural response to visceral stimulation contribute to visceral hypersensitivity.[27][33]
- Recruitment of peripheral silent nociceptors cause increased end organ sensitivity due to
- hormonal activation ( increased serotonin affects gastrointestinal motility and visceral pain perception)
- immune activation(recruitment of inflammatory mediators)[27]
- Spinal hyperexcitability
| Spinal hyperexcitability | Activation of • N-methyl D aspartate (NMDA) receptor • nitric oxide | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Central (brainstem and cortical) modulation | Increased activation of: • Anterior cingulate cortex • Thalamus • insula | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Visceral hypersensitivity | |||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Activation of specific gastrointestinal mediators | Kinins and serotonin activation lead to afferent nerve fiber sensitization | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Recruitment of peripheral silent nociceptors | Increased end organ sensitivity due to hormonal or immune activation | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
- Immune activation and mucosal inflammation
Mast cells IMMUNE ACTIVATION AND MUCOSAL INFLAMMATION Lymphocytes Proinflammatory cytokines - IBS in patients with history of inflammatory bowel disease, celiac disease or microscopic colitis points towards the fact that immune activation and local GI mucosal inflammation play an important role in its pathogenesis.[34][35][36][37][38][39][36]
- IBS patients have higher mucosal counts of lymphocytes (T cells, B cells), mast cells and immune mediators such as prostanoids, proteases, cytokines and histamines.[36][40][41][42][43]
- Lymphocytes:
- Activation of humoral immunity in IBS is specific for the gastrointestinal tract. Increased number of lymphocytes have been found in the small intestine and colon of IBS patients.[35][37][44][45]
- IBS patients with diarrhea have enhanced mucosal humoral activity, associated with activation and proliferation of B cells and immunoglobulin production, identified by microarray profiling.[45]
- IBS patients with severe disease have an increase in lymphocyte infiltration in the myentric plexus.[37]
- Mediators released by lymphocytes include histamine, proteases and nitric oxide. The stimulation of the enteric nervous system by these mediators leads to abnormal visceral and motor responses within the gastrointestinal tract.[35]
- Stool in patients with diarrhea prominent IBS demonstrates high levels of serine protease activity, which is produced by lymphocytes.[46][47]
- In response to high levels of serine protease, there is increased visceral pain and colonic cellular permeability. [46]
- Serine protease inhibitors prevent effects mediated by high levels of serine protease in IBS patients.[47][46]
- Mast cells:
- IBS leads to an increased number of mast cells in IBS patients in the jejunum, terminal ileum and colon.[39]
- Higher numbers of activated mast cells are found in proximity to colonic nerve fibres in the mucosa of the gastrointestinal tract of IBS patients. [39][38]
- Proinflammatory cytokines:
- Cytokines are protein mediators of the immune response. Increased levels of cytokines have been found in IBS patients.[43][42]
- Higher amounts of tumor necrosis factor are produced by the peripheral blood mononuclear cells of IBS patients.[48][36]
- Other cytokines such as interleukin 1β, interleukin 6, interleukin10, and TNFα are raised in IBS patients.
- Increased concentration of cytokines is directly proportional to the severity and frequency of pain.[36][49][48]
- The TNF antagonist infliximab counteracts pain in IBS patients, proving TNF involvement in mechanical hypersensitivity of the colonic afferent nerve endings . [49]
- Altered gut microbiota
- Fecal microflora in IBS patients differ from healthy individuals. Some IBS patients have colonic spirochaetosis, with a unique pathology of increased lymphoid follicles and eosinophils on histology.[40][50][51][52][53][54][14][55]
- Acute GI infection alters gut microflora switches on a T-helper-2 immune-cell response with increased numbers of CD8 and CD4RA-positive intraepithelial lymphocytes, causing increased susceptibility to the development of IBS. [56][57][58]
- Altered gut microbiota causes increased colonic hypersensitivity. [59]
- Abnormal serotonin pathways
- Serotonin(5-HT) is an important neurotransmitter produced by the enterochromaffin cells in the colon, in response to chemical stimuli (short chain fatty acids produced by gastrointestinal microflora ) and mechanical stimuli ( food) and is increased in IBS patients.[60][61][62][63][64][65][66]
- Serotonin affects gastrointestinal motility and visceral pain perception. Spontaneous release of 5-HT correlates with abdominal pain severity.[67]
- There is an established relationship between IBS and polymorphisms in the gene for serotonin transport causing alteration in intestinal peristalsis due to change in the serotonin reuptake efficacy.[68][69][70][71]
- Increased serotonin production contributes to postprandial symptoms in IBS patients, hence providing the rationale for the therapeutic efficacy of 5-HT 3 receptor antagonists and 5-HT 4 receptor agonists on symptoms in IBS patients.[72][73]
Psychosocial factors and CNS dysregulation
- Symptom exacerbation occurs in IBS patients with emotional disturbances,stress, anxiety or depression. Traumatic experiences before 18 years of age directly shape adult connectivity in the executive control network consisting of structures such as the insula, anterior cingulate cortex and the thalamus.
- Semipermanent/permanent changes in complex neural circuits lead to central pain amplification and contribute to abdominal pain in IBS patients.[74][75]
- The dorsolateral prefrontal cortex activity (responsible for vigilance and alertness of the human brain) and the mid-cingulate cortex (engaged in attention pathways and responses) is reduced in IBS patients, seen on advanced brain imaging techniques as irregularities in the mid- cingulate cortex and prefrontal cortex on diffusion tensor imaging. [76]
- prefrontal cortex modulation may lead to increased perception of visceral pain.
- Modulation of the mid-cingulate cortex is associated with alterations in the subjective sensations of pain.[77][78]
- Patients with IBS have aberrant processing of central information, with decreased feedback on the emotional arousal network that controls the autonomic activity of the gastrointestinal tract and changes gut motility.[79][80]
- IBS is a brain gut disorder as rectal distension in patients causes increased engagement of regions of the brain associated with attentional and behavioral responses.[77][81][82]
- Psychological stress also impacts the release of gut proinflammatory cytokines, contributing to pain in IBS patients.[34]
- ↑ Muir JG, Gibson PR (2013). "The Low FODMAP Diet for Treatment of Irritable Bowel Syndrome and Other Gastrointestinal Disorders". Gastroenterol Hepatol (N Y). 9 (7): 450–2. PMC 3736783. PMID 23935555.
- ↑ Böhn L, Störsrud S, Törnblom H, Bengtsson U, Simrén M (2013). "Self-reported food-related gastrointestinal symptoms in IBS are common and associated with more severe symptoms and reduced quality of life". Am. J. Gastroenterol. 108 (5): 634–41. doi:10.1038/ajg.2013.105. PMID 23644955.
- ↑ Young E, Stoneham MD, Petruckevitch A, Barton J, Rona R (1994). "A population study of food intolerance". Lancet. 343 (8906): 1127–30. PMID 7910231.
- ↑ David LA, Maurice CF, Carmody RN, Gootenberg DB, Button JE, Wolfe BE, Ling AV, Devlin AS, Varma Y, Fischbach MA, Biddinger SB, Dutton RJ, Turnbaugh PJ (2014). "Diet rapidly and reproducibly alters the human gut microbiome". Nature. 505 (7484): 559–63. doi:10.1038/nature12820. PMC 3957428. PMID 24336217.
- ↑ Francis CY, Whorwell PJ (1994). "Bran and irritable bowel syndrome: time for reappraisal". Lancet. 344 (8914): 39–40. PMID 7912305.
- ↑ Elli L, Tomba C, Branchi F, Roncoroni L, Lombardo V, Bardella MT, Ferretti F, Conte D, Valiante F, Fini L, Forti E, Cannizzaro R, Maiero S, Londoni C, Lauri A, Fornaciari G, Lenoci N, Spagnuolo R, Basilisco G, Somalvico F, Borgatta B, Leandro G, Segato S, Barisani D, Morreale G, Buscarini E (2016). "Evidence for the Presence of Non-Celiac Gluten Sensitivity in Patients with Functional Gastrointestinal Symptoms: Results from a Multicenter Randomized Double-Blind Placebo-Controlled Gluten Challenge". Nutrients. 8 (2): 84. doi:10.3390/nu8020084. PMC 4772047. PMID 26867199.
- ↑ Coletta M, Gates FK, Marciani L, Shiwani H, Major G, Hoad CL, Chaddock G, Gowland PA, Spiller RC (2016). "Effect of bread gluten content on gastrointestinal function: a crossover MRI study on healthy humans". Br. J. Nutr. 115 (1): 55–61. doi:10.1017/S0007114515004183. PMID 26522233.
- ↑ Yang J, Fox M, Cong Y, Chu H, Zheng X, Long Y, Fried M, Dai N (2014). "Lactose intolerance in irritable bowel syndrome patients with diarrhoea: the roles of anxiety, activation of the innate mucosal immune system and visceral sensitivity". Aliment. Pharmacol. Ther. 39 (3): 302–11. doi:10.1111/apt.12582. PMID 24308871.
- ↑ Staudacher HM, Irving PM, Lomer MC, Whelan K (2014). "Mechanisms and efficacy of dietary FODMAP restriction in IBS". Nat Rev Gastroenterol Hepatol. 11 (4): 256–66. doi:10.1038/nrgastro.2013.259. PMID 24445613.
- ↑ Ohman L, Simrén M (2010). "Pathogenesis of IBS: role of inflammation, immunity and neuroimmune interactions". Nat Rev Gastroenterol Hepatol. 7 (3): 163–73. doi:10.1038/nrgastro.2010.4. PMID 20101257.
- ↑ Simrén M, Barbara G, Flint HJ, Spiegel BM, Spiller RC, Vanner S, Verdu EF, Whorwell PJ, Zoetendal EG (2013). "Intestinal microbiota in functional bowel disorders: a Rome foundation report". Gut. 62 (1): 159–76. doi:10.1136/gutjnl-2012-302167. PMC 3551212. PMID 22730468.
- ↑ Ohman L, Simrén M (2013). "Intestinal microbiota and its role in irritable bowel syndrome (IBS)". Curr Gastroenterol Rep. 15 (5): 323. doi:10.1007/s11894-013-0323-7. PMID 23580243.
- ↑ Posserud I, Stotzer PO, Björnsson ES, Abrahamsson H, Simrén M (2007). "Small intestinal bacterial overgrowth in patients with irritable bowel syndrome". Gut. 56 (6): 802–8. doi:10.1136/gut.2006.108712. PMC 1954873. PMID 17148502.
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- ↑ Spiller R, Garsed K (2009). "Postinfectious irritable bowel syndrome". Gastroenterology. 136 (6): 1979–88. doi:10.1053/j.gastro.2009.02.074. PMID 19457422.
- ↑ Joo YE (2015). "Alteration of fecal microbiota in patients with postinfectious irritable bowel syndrome". J Neurogastroenterol Motil. 21 (1): 135–7. doi:10.5056/jnm14133. PMC 4288086. PMID 25611066.
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- ↑ Nielsen HL, Engberg J, Ejlertsen T, Nielsen H (2014). "Psychometric scores and persistence of irritable bowel after Campylobacter concisus infection". Scand. J. Gastroenterol. 49 (5): 545–51. doi:10.3109/00365521.2014.886718. PMID 24646319.
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- ↑ 25.0 25.1 25.2 Camilleri M, McKinzie S, Busciglio I, Low PA, Sweetser S, Burton D, Baxter K, Ryks M, Zinsmeister AR (2008). "Prospective study of motor, sensory, psychologic, and autonomic functions in patients with irritable bowel syndrome". Clin. Gastroenterol. Hepatol. 6 (7): 772–81. doi:10.1016/j.cgh.2008.02.060. PMC 2495078. PMID 18456567.
- ↑ Kellow JE, Phillips SF (1987). "Altered small bowel motility in irritable bowel syndrome is correlated with symptoms". Gastroenterology. 92 (6): 1885–93. PMID 3569764.
- ↑ 27.0 27.1 27.2 Barbara G, Cremon C, De Giorgio R, Dothel G, Zecchi L, Bellacosa L, Carini G, Stanghellini V, Corinaldesi R (2011). "Mechanisms underlying visceral hypersensitivity in irritable bowel syndrome". Curr Gastroenterol Rep. 13 (4): 308–15. doi:10.1007/s11894-011-0195-7. PMID 21537962.
- ↑ Whitehead WE, Holtkotter B, Enck P, Hoelzl R, Holmes KD, Anthony J, Shabsin HS, Schuster MM (1990). "Tolerance for rectosigmoid distention in irritable bowel syndrome". Gastroenterology. 98 (5 Pt 1): 1187–92. PMID 2323511.
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- ↑ 34.0 34.1 Coëffier M, Gloro R, Boukhettala N, Aziz M, Lecleire S, Vandaele N, Antonietti M, Savoye G, Bôle-Feysot C, Déchelotte P, Reimund JM, Ducrotté P (2010). "Increased proteasome-mediated degradation of occludin in irritable bowel syndrome". Am. J. Gastroenterol. 105 (5): 1181–8. doi:10.1038/ajg.2009.700. PMID 19997094.
- ↑ 35.0 35.1 35.2 Chadwick VS, Chen W, Shu D, Paulus B, Bethwaite P, Tie A, Wilson I (2002). "Activation of the mucosal immune system in irritable bowel syndrome". Gastroenterology. 122 (7): 1778–83. PMID 12055584.
- ↑ 36.0 36.1 36.2 36.3 36.4 Liebregts T, Adam B, Bredack C, Röth A, Heinzel S, Lester S, Downie-Doyle S, Smith E, Drew P, Talley NJ, Holtmann G (2007). "Immune activation in patients with irritable bowel syndrome". Gastroenterology. 132 (3): 913–20. doi:10.1053/j.gastro.2007.01.046. PMID 17383420.
- ↑ 37.0 37.1 37.2 Törnblom H, Lindberg G, Nyberg B, Veress B (2002). "Full-thickness biopsy of the jejunum reveals inflammation and enteric neuropathy in irritable bowel syndrome". Gastroenterology. 123 (6): 1972–9. doi:10.1053/gast.2002.37059. PMID 12454854.
- ↑ 38.0 38.1 Guilarte M, Santos J, de Torres I, Alonso C, Vicario M, Ramos L, Martínez C, Casellas F, Saperas E, Malagelada JR (2007). "Diarrhoea-predominant IBS patients show mast cell activation and hyperplasia in the jejunum". Gut. 56 (2): 203–9. doi:10.1136/gut.2006.100594. PMC 1856785. PMID 17005763.
- ↑ 39.0 39.1 39.2 Barbara G, Stanghellini V, De Giorgio R, Cremon C, Cottrell GS, Santini D, Pasquinelli G, Morselli-Labate AM, Grady EF, Bunnett NW, Collins SM, Corinaldesi R (2004). "Activated mast cells in proximity to colonic nerves correlate with abdominal pain in irritable bowel syndrome". Gastroenterology. 126 (3): 693–702. PMID 14988823.
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- ↑ 47.0 47.1 Gecse K, Róka R, Ferrier L, Leveque M, Eutamene H, Cartier C, Ait-Belgnaoui A, Rosztóczy A, Izbéki F, Fioramonti J, Wittmann T, Bueno L (2008). "Increased faecal serine protease activity in diarrhoeic IBS patients: a colonic lumenal factor impairing colonic permeability and sensitivity". Gut. 57 (5): 591–9. doi:10.1136/gut.2007.140210. PMID 18194983.
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- ↑ 49.0 49.1 Hughes PA, Moretta M, Lim A, Grasby DJ, Bird D, Brierley SM, Liebregts T, Adam B, Blackshaw LA, Holtmann G, Bampton P, Hoffmann P, Andrews JM, Zola H, Krumbiegel D (2014). "Immune derived opioidergic inhibition of viscerosensory afferents is decreased in Irritable Bowel Syndrome patients". Brain Behav. Immun. 42: 191–203. doi:10.1016/j.bbi.2014.07.001. PMID 25063707.
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