Probiotics: An ideal anti-inflammatory treatment for IBS?

Irritable bowel syndrome (IBS) is one of the most common reasons for consultation and yet there are few treatments with proven efficacy. Thus, even modestly effective treatments would be acceptable provided that they are free from significant side effects. Probiotics start with an advantage over drug treatments in this respect, being living nonpathogenic organisms, which experience to date suggests are extremely safe. Furthermore, patients appear to like the idea, and such products are widely consumed. Probably the strongest effect, confirmed by a recent meta-analyses, is a reduction in the duration of acute infectious diarrhea in children, an effect particularly robust in studies using Lactobacilli sp.1Huang J.S. Bousvaros A. Lee J.W. Diaz A. Davidson E.J. Efficacy of probiotic use in acute diarrhea in children a meta-analysis.Dig Dis Sci. 2002; 47: 2625-2634Google Scholar Reestablishing colonization with nonpathogenic bacteria appears to inhibit secondary overgrowth of urease-producing bacteria that follow acute viral gastroenteritis.2Isolauri E. Kaila M. Mykkanen H. Ling W.H. Salminen S. Oral bacteriotherapy for viral gastroenteritis.Dig Dis Sci. 1994; 39: 2595-2600Google Scholar Benefits relevant to other clinical scenarios include inhibition of pathogenic bacteria from adhering to enterocytes, invading the epithelium or colonizing the gut, and exerting favorable influences on the immune system.3Isolauri E. Sutas Y. Kankaanpaa P. Arvilommi H. Salminen S. Probiotics effects on immunity.Am J Clin Nutr. 2001; 73: 444S-450SGoogle Scholar These vary according to the precise probiotic but include increasing the secretion of defensins, decreasing interleukin (IL) 8 secretion, and inhibiting nuclear factor κB production. Initially, oral delivery of live bacteria was considered vital, but DNA from killed probiotics can inhibit the production of IL-8 and interferon γ by enterocytes in response to Escherichia coli DNA.4Jijon H. Backer J. Diaz H. Yeung H. Thiel D. McKaigney C. De Simone C. Madsen K. DNA from probiotic bacteria modulates murine and human epithelial and immune function.Gastroenterology. 2004; 126: 1358-1373Google Scholar Furthermore, the bacteria can also exert an anti-inflammatory effect when administered parenterally,5Sheil B. McCarthy J. O’Mahony L. Bennett M.W. Ryan P. Fitzgibbon J.J. Kiely B. Collins J.K. Shanahan F. Is the mucosal route of administration essential for probiotic function? Subcutaneous administration is associated with attenuation of murine colitis and arthritis.Gut. 2004; 53: 694-700Google Scholar indicating that the effects are not purely local to the gut. These anti-inflammatory effects are associated with modest clinical benefits, reducing the relapse rate of pouchitis6Gionchetti P. Rizzello F. Venturi A. Brigidi P. Matteuzzi D. Bazzocchi G. Poggioli G. Miglioli M. Campieri M. Oral bacteriotherapy as maintenance treatment in patients with chronic pouchitis a double-blind, placebo-controlled trial.Gastroenterology. 2000; 119: 305-309Abstract Full Text Full Text PDF Scopus (1292) Google Scholar, 7Mimura T. Rizzello F. Helwig U. Poggioli G. Schreiber S. Talbot I.C. Nicholls R.J. Gionchetti P. Campieri M. Kamm M.A. Once daily high dose probiotic therapy (VSL#3) for maintaining remission in recurrent or refractory pouchitis.Gut. 2004; 53: 108-114Google Scholar and chronic ulcerative colitis.8Kruis W. Fric P. Pokrotnieks J. Lukas M. Fixa B. Kascak M. Kamm M.A. Weismueller J. Beglinger C. Stolte M. Wolff C. Schulze J. Maintaining remission of ulcerative colitis with the probiotic Escherichia coli Nissle 1917 is as effective as with standard mesalazine.Gut. 2004; 53: 1617-1623Google Scholar Evidence of benefit in IBS has been less than compelling. The best documented double-blind, randomized, placebo-controlled study in 60 unselected patients with IBS found that flatulence was the only symptom to specifically respond.9Nobaek S. Johansson M.L. Molin G. Ahrne S. Jeppsson B. Alteration of intestinal microflora is associated with reduction in abdominal bloating and pain in patients with irritable bowel syndrome.Am J Gastroenterol. 2000; 95: 1231-1238Google Scholar However, a detailed follow-up study using the same Lactobacillus plantarum preparation was unable to show any change in colonic fermentation, nor did it confirm any clinical benefit.10Sen S. Mullan M.M. Parker T.J. Woolner J.T. Tarry S.A. Hunter J.O. Effect of Lactobacillus plantarum 299v on colonic fermentation and symptoms of irritable bowel syndrome.Dig Dis Sci. 2002; 47: 2615-2620Google Scholar L plantarum was also used in a study that showed a benefit for pain, with a 100% response rate in the treatment group versus just 16% in the control.11Niedzielin K. Kordecki H. Birkenfeld B. A controlled, double-blind, randomized study on the efficacy of Lactobacillus plantarum 299V in patients with irritable bowel syndrome.Eur J Gastroenterol Hepatol. 2001; 13: 1143-1147Google Scholar This remarkable response rate is an outlier among all IBS studies and needs repeating using more conventional endpoints. Another study used VSL#3, a probiotic mixture including lactobacilli and bifidobacteria, in 25 patients with diarrhea-predominant IBS. Bloating was the only symptom to improve, but, again, this was underpowered and vulnerable to a type II error. The study in this issue of Gastroenterology12O’Mahony L. McCarthy J. Kelly P. Hurley G. Luo F. Chen K. O’Sullivan G.C. Kiely B. Collins J.K. Shanahan F. Quigley E.M.M. Lactobacillus and bifidobacterium in irritable bowel syndrome symptom responses and relationship to cytokine profiles.Gastroenterology. 2005; 128: 541-551Abstract Full Text Full Text PDF Scopus (1142) Google Scholar was a double-blind, randomized, placebo-controlled, parallel group design examining the effect of 2 probiotics: Lactobacillus salivarius against Bifidobacterium infantis. Previously, work had shown that L salivarius had favorable properties,13Dunne C. O’Mahony L. Murphy L. Thornton G. Morrissey D. O’Halloran S. Feeney M. Flynn S. Fitzgerald G. Daly C. Kiely B. O’Sullivan G.C. Shanahan F. Collins J.K. In vitro selection criteria for probiotic bacteria of human origin correlation with in vivo findings.Am J Clin Nutr. 2001; 73: 386S-392SGoogle Scholar, 14O’Mahony L. Feeney M. O’Halloran S. Murphy L. Kiely B. Fitzgibbon J. Lee G. O’Sullivan G. Shanahan F. Collins J.K. Probiotic impact on microbial flora, inflammation and tumour development in IL-10 knockout mice.Aliment Pharmacol Ther. 2001; 15: 1219-1225Google Scholar, 15Sheil B. McCarthy J. O’Mahony L. Bennett M.W. Ryan P. Fitzgibbon J.J. Kiely B. Collins J.K. Shanahan F. Is the mucosal route of administration essential for probiotic function? Subcutaneous administration is associated with attenuation of murine colitis and arthritis.Gut. 2004; 53: 694-700Google Scholar including the ability to inhibit colonic inflammation.15Sheil B. McCarthy J. O’Mahony L. Bennett M.W. Ryan P. Fitzgibbon J.J. Kiely B. Collins J.K. Shanahan F. Is the mucosal route of administration essential for probiotic function? Subcutaneous administration is associated with attenuation of murine colitis and arthritis.Gut. 2004; 53: 694-700Google Scholar The treatment evaluated was a malted drink with or without 1 × 1010 live bacteria of either L salivarius or B infantis taken each morning for 2 months. Patients satisfying the Rome II criteria for IBS were enrolled; 64% were women with an average age of 44 years (range, 18–73). The treatment phase was 2 months, preceded by a 4-week run-in period and followed by a 4-week washout period during which symptoms were recorded in a daily diary. Outcomes were symptom scores for abdominal pain, bloating, and “bowel movement difficulty” (either straining or urgency). Quality of life was also assessed by using an IBS-specific questionnaire. In addition to these subjective assessments, blood samples were also obtained before and after treatment for measurement of unstimulated peripheral blood mononuclear cell (PBMC) production of the regulatory cytokines IL-10 and IL-12 during 72 hours of culture. Patients taking B infantis had lower composite symptom scores for every week during treatment and during the 4-week washout period, whereas the L salivarius appeared no different from placebo (malted drink alone). The effect appeared within the first week of treatment and reached its maximum effect after 2 weeks. Somewhat surprisingly, we are told that the effects on quality of life were modest and largely nonsignificant, although the data is not shown. Perhaps the most striking finding was, for the first time, a marked immunologic difference between controls and IBS patients was shown. PBMCs from IBS patients showed a ratio of IL-10/IL-12 basal production rates that was 39% of age and gender-matched healthy volunteers. Treatment with B infantis led to normalization of this ratio, which was, however, unaltered by either placebo or L salivarius treatment. Studies in IBS that use subjective outcomes such as symptoms need very substantial numbers, typically 10 times the number of patients studied here, to avoid either inconsistent chance findings or missing small but relevant effects. The small numbers in this study resulted by chance in an unequal randomization so that the placebo group was symptomatically worse at baseline. The statistical analysis included baseline as a covariate in an attempt to control for this but this is always second best to starting from the same baseline. However, despite the small numbers, the effect reported here is unlikely to have arisen by chance and is consistent across all 3 measures, but is it important? The most clinically meaningful outcome of a trial of treatment of a polymorphous condition like IBS is what proportion of patients consider themselves to have experienced adequate relief of their symptoms. Most authors and regulatory authorities dislike arbitrary scoring systems such as used here because it is hard to relate changes in these to the percentage with adequate relief.16Whitehead W.E. Corazziari E. Prizont R. Senior J.R. Thompson W.G. Veldhuyzen van Zanten S.J. Definition of a responder in clinical trials for functional gastrointestinal disorders report on a symposium.Gut. 1999; 45: II78-II79Google Scholar Equally important, one cannot calculate the number needed to treat and thus get a feel for how such treatments compare with others. The lack of effect on quality of life suggests that the overall benefit may be small. Perhaps the most exciting aspect of this study what it tells us about immune mechanisms in IBS. There is currently great interest in how the balance between IL-10 and IL-12 in the gut mucosa determines T-cell responses. IL-10 derived from both regulatory T cells and other immunocytes acts to limit the immune response and minimize collateral damage in the mucosa17O’Garra A. Vieira P.L. Vieira P. Goldfeld A.E. IL-10-producing and naturally occurring CD4+ Tregs limiting collateral damage.J Clin Invest. 2004; 114: 1372-1378Google Scholar by inhibiting secretion of tumor necrosis factor α, IL-6, and interferon γ. IL-10 also inhibits antigen-presenting cell function by inhibiting MHCII and B7 expression and hence T-cell activation and IL-12 production. The finding in this study of reduced basal IL-10/IL-12 ratio in IBS and its normalization by B infantilis is highly novel but does it explain the clinical response? The authors claim that the benefit was not due to a change in bowel habit but to an anti-inflammatory effect. However, no supporting evidence is given to confirm that any patients had low-grade gastrointestinal inflammation. There are several recent reports of low-grade mucosal inflammation in IBS with increased mucosal T-lymphocytes in both unselected diarrhea-predominant IBS.18Chadwick V.S. Chen W. Shu D. Paulus B. Bethwaite P. Tie A. Wilson I. Activation of the mucosal immune system in irritable bowel syndrome.Gastroenterology. 2002; 122: 1778-1783Abstract Full Text Full Text PDF Scopus (703) Google Scholar as well as those whose IBS begins with an acute episode of bacterial gastroenteritis.19Wang L.H. Fang X.C. Pan G.Z. Bacillary dysentery as a causative factor of irritable bowel syndrome and its pathogenesis.Gut. 2004; 53: 1096-1101Google Scholar, 20Spiller R.C. Postinfectious irritable bowel syndrome.Gastroenterology. 2003; 124: 1662-1671Google Scholar These are supported by 2 studies in postinfective IBS that show increased expression of IL-1β messenger RNA, indicating chronic activation of the mucosal immune system.19Wang L.H. Fang X.C. Pan G.Z. Bacillary dysentery as a causative factor of irritable bowel syndrome and its pathogenesis.Gut. 2004; 53: 1096-1101Google Scholar, 21Gwee K.A. Collins S.M. Read N.W. Rajnakova A. Deng Y. Graham J.C. McKendrick M.W. Moochhala S.M. Increased rectal mucosal expression of interleukin 1beta in recently acquired post-infectious irritable bowel syndrome.Gut. 2003; 52: 523-526Google Scholar The key remaining question is why do most infected individuals show speedy resolution of infection whereas a few persist with chronic symptoms that can last many years?22Neal K.R. Barker L. Spiller R.C. Prognosis in post-infective irritable bowel syndrome a six-year follow-up study.Gut. 2002; 51: 410-413Google Scholar Could the decreased IL-10/IL-12 ratio, as found in the current study, be the missing link? The authors studied IL-10 production by PBMCs, but it is not entirely clear how this relates to what is happening in the gut. PBMC IL-10 secretion is unaltered in IBD, but reduced levels are found in the inflamed mucosa23Gasche C. Bakos S. Dejaco C. Tillinger W. Zakeri S. Reinisch W. IL-10 secretion and sensitivity in normal human intestine and inflammatory bowel disease.J Clin Immunol. 2000; 20: 362-370Google Scholar and may allow the chronic inflammatory response thought to be directed against resident flora.24Duchmann R. Kaiser I. Hermann E. Mayet W. Ewe K. Meyer zum Buschenfelde K.H. Tolerance exists towards resident intestinal flora but is broken in active inflammatory bowel disease (IBD).Clin Exp Immunol. 1995; 102: 448-455Google Scholar PBMC production of IL-10 is largely genetically determined by polymorphisms in the IL-10 promoter region.25Eskdale J. Gallagher G. Verweij C.L. Keijsers V. Westendorp R.G. Huizinga T.W. Interleukin 10 secretion in relation to human IL-10 locus haplotypes.Proc Natl Acad Sci U S A. 1998; 95: 9465-9470Google Scholar There has been one recent study of particular relevance to this current study that suggested that high producers of IL-10 were underrepresented in an unselected IBS group.26Gonsalkorale W.M. Perrey C. Pravica V. Whorwell P.J. Hutchinson I.V. Interleukin 10 genotypes in irritable bowel syndrome evidence for an inflammatory component?.Gut. 2003; 52: 91-93Google Scholar If IBS sufferers have genetically reduced levels of IL-10 then how would a probiotic help? The IL-10 knockout mouse has been widely used as a model of IBD, driven by an inappropriate immune response to resident bacterial flora. L salivarius, as used in the current trial, reduces both the associated inflammation and the number of fecal coliforms and enterococci in this model. Regrettably, this probiotic was not the one shown to be effective in the human trial, showing once again the difficulty in extrapolating from genetically modified mice to humans. Plainly, there are many missing pieces to this jigsaw puzzle. What is now needed is a larger study using B infantis, stratifying IBS patients on the basis of inflammatory and immune markers measured before and after treatment. Ideally, these markers would include both blood and mucosal assessments focusing on IL-10/IL-12 balance but would also include quantitative histology. It would be useful in such a gut-oriented study to exclude those with extreme psychologic disturbance, whose symptoms would be expected to be less well linked to events in the mucosa. Objective measures such as stool consistency should also be included because one would predict that those with diarrhea predominance might do best.