Two-year combination antibiotic therapy with clarithromycin, rifabutin, and clofazimine for Crohn's disease

Commensal bacteria, traditional and opportunistic pathogens, dysbiosis and bacterial killing in inflammatory bowel diseases

PURPOSE OF REVIEW

The authors present evidence published during the past 2 years of the roles of commensal and pathogenic bacteria in the pathogenesis of the inflammatory bowel diseases.

RECENT FINDINGS

Rodent models conclusively implicate commensal enteric bacteria in chronic, immune-mediated, experimental colitis, and genetically determined defects in bacterial killing by innate immune cells are found in a subset of patients with Crohn's disease. There is no evidence that a single pathogen, including Mycobacterium avium subspecies paratuberculosis, causes Crohn's disease or ulcerative colitis. However, adherent/invasive Escherichia coli are associated with ileal Crohn's disease, with the mechanisms and genetics of adherent/invasive E. coli virulence being elucidated. Molecular characterization of the microbiota in patients with inflammatory bowel diseases reveals decreased biodiversity of commensal bacteria, most notably the phyla Bacteroidetes and Firmicutes, including the clinically relevant Faecalibacterium prausnitzii, and increased E. coli concentrations. VSL#3 is one probiotic preparation shown to be efficacious in certain clinical situations in small clinical trials.

SUMMARY

Further characterization of altered microbiota in patients with inflammatory bowel diseases and linking dysbiosis with host genetic alterations in immunoregulation, innate microbial killing and barrier function are critical, so that individualized treatments to increase beneficial commensals and their metabolic products (probiotic and prebiotic administration) and diminish deleterious species such as adherent/invasive E. coli can be tailored for defined patient subsets.

Crohn's disease in India: a multicenter study from a country where tuberculosis is endemic

Although Crohn's disease is thought to be rare and intestinal tuberculosis common in India, Crohn's disease is being reported more often. However, there is a lack of systematic study on Crohn's disease from India. In this analysis of data from three inflammatory bowel disease clinics (two in northern India and one in eastern India), criteria for Crohn's disease were applied retrospectively: (1) World Health Organization (WHO) criteria; or (2) compatible histology (European Crohn's and Colitis Organization) or failure of response to 4-8 weeks of anti-tuberculosis therapy (Asia-Pacific guidelines); or (3) compatible macroscopic, radiologic, colonoscopic features (European Crohn's and Colitis Organization). Others were classified as probable Crohn's disease. The Montreal classification was used for disease phenotype. Age at onset and duration of symptoms (182 patients, 117 male) were 34.5 (+/-13.6; 7-73) years and 3.0 (+/-5.8; 0.1-36) years, respectively. Diarrhea (68%), abdominal pain (62%), and weight loss (57%) were common. The common intestinal complications were occult (27%) and overt (40%) gastrointestinal bleeding and obstruction (28%). There were 141 (78%) and 41 (22%) with definite and probable Crohn's disease respectively. Of 147 (81%) available histopathology specimens (endoscopic biopsy in 110; 75%), 31 (21%) had granuloma. Seventy-one out of 166 (43%) had received anti-tuberculosis therapy in the past. Results from the Montreal classification were as follows: age at onset, A1:A2:A3 6%:64%:30%; location of disease, L1:L2:L3:L4 32%:41%:23%:4%, and disease behavior, B1:B2:B3 51%:24%:25%. Twenty-six (15%) and 31 (17%) patients had upper gastrointestinal and perianal modifiers. The drugs used were: aminosalicylates (128, 70%), steroids (76, 42%), azathioprine (53, 29%), methotrexate (4, 2%), and salazopyrine (14, 8%). Sixty-six (36%) patients underwent surgical treatment. We concluded that the phenotype of Crohn's disease in India is very similar to that described in other regions of Asia and the West, except for a delay in diagnosis and a more complicated disease at diagnosis.

Targeting the human microbiome with antibiotics, probiotics, and prebiotics: gastroenterology enters the metagenomics era

Studies of metagenomics and the human microbiome will tremendously expand our knowledge of the composition of microbial communities in the human body. As our understanding of microbial variation and corresponding genetic parameters is refined, this information can be applied to rational remodeling or "tailoring" of human-associated microbial communities and their associated functions. Physiologic features such as the development of innate and adaptive immunity, relative susceptibilities to infections, immune tolerance, bioavailability of nutrients, and intestinal barrier function may be modified by changing the composition and functions of the microbial communities. The specialty of gastroenterology will be affected profoundly by the ability to modify the gastrointestinal microbiota through the rational deployment of antibiotics, probiotics, and prebiotics. Antibiotics might be used to remove or suppress undesirable components of the human microbiome. Probiotics can introduce missing microbial components with known beneficial functions for the human host. Prebiotics can enhance the proliferation of beneficial microbes or probiotics, to maximize sustainable changes in the human microbiome. Combinations of these approaches might provide synergistic and effective therapies for specific disorders. The human microbiome could be manipulated by such "smart" strategies to prevent and treat acute gastroenteritis, antibiotic-associated diarrhea and colitis, inflammatory bowel disease, irritable bowel syndrome, necrotizing enterocolitis, and a variety of other disorders.

Differentiating intestinal tuberculosis from Crohn's disease: a diagnostic challenge

With the changing epidemiology of Crohn's disease (CD) and intestinal tuberculosis (ITB), we are in an era where the difficulty facing physicians in discriminating between the two diseases has increased, and the morbidity and mortality resulting from a delayed diagnosis or misdiagnosis is considerably high. In this article, we examine the changing trends in the epidemiology of CD and ITB, in addition to clinical features that aid in the differentiation of both diseases. The value of various laboratory, serological, and the tuberculin skin tests are reviewed as well. The use of an interferon-gamma-release assay, QuantiFERON-TB Gold, in the workup of these patients and its value in populations where the bacillus Calmette-Guérin vaccine is still administered is discussed. Different radiological, endoscopic, and pathological similarities and features that can aid the clinician in reaching a rapid diagnosis are reviewed as well. The association between mycobacteria and CD, the concerns with the practice of antituberculosis medication trials in areas where tuberculosis (TB) is endemic, as well as extrapulmonary TB induced by the use of antitumor necrosis factor-alpha agents are delineated in this article. Furthermore, we propose an algorithm for the investigation of patients in whom the differential diagnosis encompasses CD and ITB.

On the effect of thalidomide on Mycobacterium avium subspecies paratuberculosis in culture

BACKGROUND

Without known mechanisms of action, thalidomide is used to treat a variety of non-malignant 'idiopathic' diseases. There is increasing concern that Mycobacterium avium subspecies paratuberculosis (MAP) may be zoonotic. Recently, methotrexate, azathioprine, 6-mercaptopurine (6-MP), 5-aminosalicylic acid (5-ASA), cyclosporine A, rapamycin, and tacrolimus have been shown to inhibit MAP growth in culture, indicating that, unknowingly, MAP infections may have been treated for decades. We herein test the hypothesis that thalidomide may inhibit MAP growth.

METHODS

Using the radiometric 14CO2 (Bactec) system we quantified growth kinetics of thalidomide (+/-), (+), and (-) and two components for thalidomide, phthalimide and 1-hydroxypiperidine-2,6-dione (HPD). We studied four MAP strains (three human isolates, 'Ben', 'Dominic', and UCF-4, and a bovine MAP isolate 19698) and three mycobacterial controls (Mycobacterium avium and bacillus Calmette-Guérin (BCG)). Growth was quantified as growth index (GI) and inhibition as percent decrease in cumulative GI (%-DeltacGI).

RESULTS

Phthalimide had no dose-dependent inhibition on any strain. Neither thalidomide nor HPD inhibited M. avium or BCG. MAP inhibition varied; at 64 microg/ml, amongst human isolates, Dominic was most susceptible: thalidomide (+)=58%-DeltacGI and HPD=46%-DeltacGI. UCF-4 was next: thalidomide (-)=37%-DeltacGI and HPD=40%-DeltacGI. Ben was least susceptible: HPD=24%-DeltacGI.

CONCLUSIONS

We have shown, in culture, the heretofore-undescribed inhibition of MAP growth by thalidomide and its enantiomers. Phthalimide was found to have no anti-MAP activity, whereas HPD was found to inhibit MAP growth. These data are compatible with the hypothesis that thalidomide, like other 'anti-inflammatories' and 'immunomodulators' may act, in part, as an anti-MAP antibiotic.

Intestinal dendritic cells and epithelial barrier dysfunction in Crohn's disease

Crohn's disease (CD) is a chronic gastrointestinal inflammatory disorder considered to be the result of an inappropriate and exaggerated mucosal immune reaction to yet undefined triggers from the gut flora in genetically predisposed individuals. This inflammatory phenomenon has been characterized by an adaptive T-cell response in addition to an abnormal function of the innate immune system. Dendritic cells (DCs) are constituents of this innate system, inducing T-cell activation via antigen presentation. In the gut, mucosal DCs are separated from the luminal milieu by a monolayer of cylindrical epithelial cells that forms an anatomical and physiological barrier that controls the normal traffic of antigens between both compartments. An imbalance of colonic and ileal DC distribution in tissues from CD patients as well as functional differences between DCs isolated from normal and diseased intestinal samples have been demonstrated. Moreover, a gut barrier defect in the para- and transepithelial routes in addition to a significant reduction in the intestinal secretion of epithelial products involved in barrier function has been well documented in CD. Therefore, this may expose the diseased mucosa to overwhelming amounts of antigens, resulting in abnormal DC activation and a subsequent imbalance in their distribution. In conclusion, this review provides a summary of relevant progress in CD, intestinal epithelial permeability, and DCs highlighting a potential relationship between increased epithelial permeability and abnormal DC distribution during the pathogenesis of intestinal inflammation.

Monensin causes dose dependent inhibition of Mycobacterium avium subspecies paratuberculosis in radiometric culture

Background

Mycobacterium avium subspecies paratuberculosis (MAP) causes a chronic wasting diarrheal disease in ruminants called Johne's disease, that is evocative of human inflammatory bowel disease (IBD). Agents used to treat IBD, called "anti-inflammatories", immuno-modulators" and "immuno-suppressants" inhibit MAP growth in culture. We concluded that, unknowingly, the medical profession has been treating MAP since sulfasalazine's introduction in 1942. Monensin, called a "Growth Enhancer" in cattle, ameliorates Johne's disease without a documented mechanism of action. We hypothesized that Monensin would inhibit MAP in culture.

Methods

Using the radiometric ¹⁴CO₂ Bactec^® system, that expresses mycobacterial growth in arbitrary growth index (GI) units, we studied the effect of Monensin on the growth kinetic of MAP isolated from humans with IBD ("Dominic", "Ben" & UCF-4) and cattle with Johne's disease (303 & ATCC 19698.) Results are expressed as percent inhibition of cumulative GI (%–ΔcGI).

Results

The positive control Clofazimine inhibits every strain tested. The negative controls Cycloheximide & Phthalimide, have no inhibition on any MAP strain. Monensin has dose dependent inhibition on every MAP strain tested. The most susceptible human isolate was UCF-4 (73% – ΔcGI at 1 μg/ml) and bovine isolate was 303 (73% – ΔcGI at 4 μg/ml.) Monensin additionally inhibits M. avium ATCC 25291 (87% – ΔcGI at 64 μg/ml) & BCG (92% – ΔcGI at 16 μg/ml).

Discussion

We show that in radiometric culture the "Growth Enhancer" Monensin causes dose dependent inhibition of mycobacteria including MAP. We posit that the "Growth Enhancer" effect of Monensin may, at least in part, be due to inhibition of MAP in clinical or sub-clinical Johne's disease.

Management of Crohn's disease in adults

Guidelines for clinical practice are intended to suggest preferable approaches to particular medical problems as established by interpretation and collation of scientifically valid research, derived from extensive review of published literature. When data that will withstand objective scrutiny are not available, a recommendation may be made based on a consensus of experts. Guidelines are intended to apply to the clinical situation for all physicians without regard to specialty. Guidelines are intended to be flexible, not necessarily indicating the only acceptable approach, and should be distinguished from standards of care that are inflexible and rarely violated. Given the wide range of choices in any health-care problem, the physician should select the course best suited to the individual patient and the clinical situation presented. These guidelines are developed under the auspices of the American College of Gastroenterology and its Practice Parameters Committee. Expert opinion is solicited from the outset for the document. The quality of evidence upon which a specific recommendation is based is as follows: Grade A: Homogeneous evidence from multiple well-designed randomized (therapeutic) or cohort (descriptive) controlled trials, each involving a number of participants to be of sufficient statistical power. Grade B: Evidence from at least one large well-designed clinical trial with or without randomization, from cohort or case-control analytic studies, or well-designed meta-analysis. Grade C: Evidence based on clinical experience, descriptive studies, or reports of expert committees. The Committee reviews guidelines in depth, with participation from experienced clinicians and others in related fields. The final recommendations are based on the data available at the time of the production of the document and may be updated with pertinent scientific developments at a later time.

Mycobacterium avium subspecies paratuberculosis and its relationship with Crohn’s disease

The hypothesis postulating that Mycobacterium avium paratuberculosis (MAP) is the cause of Crohn’s disease (CD) has been circulating for many years. Advances in molecular techniques, such as polymerase chain reaction and culture methods, have enabled researchers to demonstrate that there is an association between MAP and CD. Recently, genome-wide association studies have identified novel susceptibility genes for CD, which are critical for generation of an adaptive immune response that is protective against intracellular pathogens, including M. tuberculosis infection. However, the role of MAP as a cause of CD suffered a setback with the report that administration of antimycobacterial therapy failed to lead to a sustained response in CD patients. Accordingly, this review sought neither to confirm nor refute this, but instead to survey recent literature on the role of MAP in CD.

Intestinal barrier dysfunction in inflammatory bowel diseases

The etiology of human inflammatory bowel diseases (IBDs) is believed to involve inappropriate host responses to the complex commensal microbial flora in the gut, although an altered commensal flora is not completely excluded. A multifunctional cellular and secreted barrier separates the microbial flora from host tissues. Altered function of this barrier remains a major largely unexplored pathway to IBD. Although there is evidence of barrier dysfunction in IBD, it remains unclear whether this is a primary contributor to disease or a consequence of mucosal inflammation. Recent evidence from animal models demonstrating that genetic defects restricted to the epithelium can initiate intestinal inflammation in the presence of normal underlying immunity has refocused attention on epithelial dysfunction in IBD. We review the components of the secreted and cellular barrier, their regulation, including interactions with underlying innate and adaptive immunity, evidence from animal models of the barrier's role in preventing intestinal inflammation, and evidence of barrier dysfunction in both Crohn's disease and ulcerative colitis.

Clofazimine inhibits human Kv1.3 potassium channel by perturbing calcium oscillation in T lymphocytes

The Kv1.3 potassium channel plays an essential role in effector memory T cells and has been implicated in several important autoimmune diseases including multiple sclerosis, psoriasis and type 1 diabetes. A number of potent small molecule inhibitors of Kv1.3 channel have been reported, some of which were found to be effective in various animal models of autoimmune diseases. We report herein the identification of clofazimine, a known anti-mycobacterial drug, as a novel inhibitor of human Kv1.3. Clofazimine was initially identified as an inhibitor of intracellular T cell receptor-mediated signaling leading to the transcriptional activation of human interleukin-2 gene in T cells from a screen of the Johns Hopkins Drug Library. A systematic mechanistic deconvolution revealed that clofazimine selectively blocked the Kv1.3 channel activity, perturbing the oscillation frequency of the calcium-release activated calcium channel, which in turn led to the inhibition of the calcineurin-NFAT signaling pathway. These effects of clofazimine provide the first line of experimental evidence in support of a causal relationship between Kv1.3 and calcium oscillation in human T cells. Furthermore, clofazimine was found to be effective in blocking human T cell-mediated skin graft rejection in an animal model in vivo. Together, these results suggest that clofazimine is a promising immunomodulatory drug candidate for treating a variety of autoimmune disorders.

Is there a link between food and intestinal microbes and the occurrence of Crohn's disease and ulcerative colitis?

The pathogenesis of Crohn's disease (CD) and ulcerative colitis (UC) is not fully understood. The interaction between intestinal environmental factors of food and intestinal microbes and the immunological system of hosts seems to be an important aspect. We have reviewed the relationship of the daily consumption of dietary animal meat and fats, dairy products, sugar, and other factors that may be linked to the occurrence of CD and UC from the literature and Japanese epidemiological data. In the present study, we reviewed the association between food and intestinal microbes and other factors contributing to the occurence of inflammatory bowel disease (IBD) from epidemiological data and case-control studies of IBD in the literature that appeared on Medline, and assessed the reports of intestinal microbes involved in the occurrence of IBD. We found several papers describing the positive association of animal meat and sweets and sugar with the occurrence of CD and UC. An analysis of Japanese epidemiological data suggested that the registered number of patients with CD or UC started to increase more than 20 years after an increased daily consumption of dietary animal meat and fats, and milk and dairy products, and after a decreased consumption of rice. Many studies implied a positive role of intestinal microbes in the occurrence of IBD. Intestinal environmental factors, such as Westernized food and intestinal microbes, seem to be involved in the increased occurrence of IBD.

Molecular pathogenesis of inflammatory bowel disease: relevance for novel therapies

The immense load of microorganisms within the gastrointestinal tract is a great challenge for the mucosal immune system. Whereas the vast majority of commensal bacteria should be tolerated, pathogenic organisms have to be attacked. During inflammatory bowel disease, the balanced interaction between the mucosal flora and the intestinal immune system is disturbed. Various defective components of this complex interaction have been described, such as different susceptibility genes, impaired innate immune responses and environmental factors, suggesting that inflammatory bowel diseases are multifactorial diseases. Based on new insights into the pathogenesis of inflammatory bowel disease, various targets for future drugs have been identified and new substances are emerging. The following article will review the current understanding of inflammatory bowel disease pathogenesis in context with genetic risk factors, imbalanced innate and acquired immune responses, and altered barrier function. Clinical treatment of the diseases will be summarized and emerging therapies as well as individual management based on recent insights into pathogenesis will be discussed.

Association between Mycobacterium avium subsp. paratuberculosis DNA in blood and cellular and humoral immune response in inflammatory bowel disease patients and controls

BACKGROUND

Similarities between human inflammatory bowel disease (IBD) and ruminant paratuberculosis have fueled a heated discussion on the role of Mycobacterium avium subsp. paratuberculosis (MAP) in the etiology of IBD.

METHODS

In order to determine microbiological and immunological evidence of an association between MAP and IBD, blood from 222 inflammatory bowel disease patients and 80 healthy donors from the Basque Country (Spain) were subjected to nested PCR for MAP-specific insertion sequence IS900, interferon-gamma (IFN-gamma) release test with PPA-3 MAP antigen (IFNMAP) or phosphate-buffered saline (IFNPBS), and antibody ELISA with PPA-3 MAP antigen (ABMAP).

RESULTS

Highly significant differences in the proportion of PCR-positive IBD patients (17%) and healthy controls (43%) as well as lower IFNMAP and higher ABMAP and IFNPBS responses were observed. Treatment was associated with decreases in IFNMAP and PCR-positive frequency.

CONCLUSIONS

These results indicate the existence of immune responses and treatment interactions with MAP that strongly support an etiological role of this agent in IBD.

On the prevalence of M. avium subspecies paratuberculosis DNA in the blood of healthy individuals and patients with inflammatory bowel disease

Background

Mycobacteria, such as M. leprae and M. tuberculosis infect billions of humans. However, because of appropriate immune responses and antibiotic therapy, overt mycobacterial diseases occur far less frequently. M. avium subspecies paratuberculosis (MAP) causes Johne's disease in ruminants, an affliction evocative of inflammatory bowel disease (IBD). Several agents used to treat IBD (5-ASA, methotrexate, azathioprine and its metabolite 6-MP) have recently been shown to be antiMAP antibiotics. We herein evaluate the prevalence of MAP DNA in healthy individuals and compare them with IBD patients on antiMAP antibiotics.

Methods

We studied 100 healthy individuals (90 blood donors) and 246 patients with IBD. IS900 MAP DNA was identified using a nested primer PCR in the buffy coat of blood. Positive signal was confirmed as MAP by DNA sequence analysis. PCR positive results frequencies were compared according to medications used. Significance was accepted at p<0.05.

Results

47% (47/100) healthy controls and 16% (40/246) IBD patients were IS900 positive (p<0.0001). MAP DNA was identified in 17% of 143 patients receiving mesalamine and 6% of 16 receiving sulfasalazine. None of the IBD patients receiving methotrexate (n = 9), 6-MP (n = 3), ciprofloxacin (n = 5) or Tacrolimus® (n = 3) had MAP DNA detectable in their blood.

Discussion

We found a disquietingly large percentage of healthy individuals have MAP DNA in their blood, the significance of which remains to be determined. Counter-intuitively, the incidence of MAP DNA was significantly lower in patients with IBD. Agents with the most potent in vitro antiMAP activity were associated with clearance of blood MAP DNA. We posit that the use antiMAP antibiotics was responsible for the decreased prevalence of MAP DNA in patients with IBD.

Pathogenic agents in inflammatory bowel diseases

PURPOSE OF REVIEW

Infectious agents are still thought to be involved in the origin of inflammatory bowel disease. The focus in recent years has been more on Mycobacterium avium subsp paratuberculosis, adherent-invasive Escherichia coli or yeasts.

RECENT FINDINGS

A metaanalysis has shown a significant association of M. avium subsp paratuberculosis and Crohn's disease and a large randomized placebo-controlled trial reported an absence of sustained beneficial effects of combined antibiotic therapy on remission of active Crohn's disease. Adherent-invasive E. coli adhere via type 1 pili to carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6), abnormally expressed by intestinal epithelial cells in Crohn's disease patients. Both colonization of the ileal mucosa and stimulation of ileal epithelial cells by tumour necrosis factor-alpha induce overexpression of CEACAM6, leading to an amplification loop of colonization and inflammation. Anti-Saccharomyces cerevisiae mannan antibodies are the most prevalent serologic marker in Crohn's disease. Major oligomannose epitopes supporting antibody formation are expressed by Candida albicans in human tissues, suggesting that a loss of tolerance to C. albicans could lead to antibody formation in a subset of Crohn's disease patients who are genetically predisposed.

SUMMARY

M. avium subsp paratuberculosis, adherent-invasive E. coli and Candida are good candidates for an infectious aetiology of Crohn's disease on the basis of genetic susceptibility, which relates to impaired function in the defence against intracellular bacteria.

On the action of cyclosporine A, rapamycin and tacrolimus on M. avium including subspecies paratuberculosis

Background

Mycobacterium avium subspecies paratuberculosis (MAP) may be zoonotic. Recently the “immuno-modulators” methotrexate, azathioprine and 6-MP and the “anti-inflammatory” 5-ASA have been shown to inhibit MAP growth in vitro. We concluded that their most plausible mechanism of action is as antiMAP antibiotics. The “immunosuppressants” Cyclosporine A, Rapamycin and Tacrolimus (FK 506) treat a variety of “autoimmune” and “inflammatory” diseases. Rapamycin and Tacrolimus are macrolides. We hypothesized that their mode of action may simply be to inhibit MAP growth.

Methodology

The effect on radiometric MAP ¹⁴CO₂ growth kinetics of Cyclosporine A, Rapamycin and Tacrolimus on MAP cultured from humans (Dominic & UCF 4) or ruminants (ATCC 19698 & 303) and M. avium subspecies avium (ATCC 25291 & 101) are presented as “percent decrease in cumulative GI” (%-ΔcGI.)

Principal Findings

The positive control clofazimine has 99%-ΔcGI at 0.5 µg/ml (Dominic). Phthalimide, a negative control has no dose dependent inhibition on any strain. Against MAP there is dose dependent inhibition by the immunosuppressants. Cyclosporine has 97%-ΔcGI by 32 µg/ml (Dominic), Rapamycin has 74%-ΔcGI by 64 µg/ml (UCF 4) and Tacrolimus 43%-ΔcGI by 64 µg/ml (UCF 4)

Conclusions

We show heretofore-undescribed inhibition of MAP growth in vitro by “immunosuppressants;” the cyclic undecapeptide Cyclosporine A, and the macrolides Rapamycin and Tacrolimus. These data are compatible with our thesis that, unknowingly, the medical profession has been treating MAP infections since 1942 when 5-ASA and subsequently azathioprine, 6-MP and methotrexate were introduced in the therapy of some “autoimmune” and “inflammatory” diseases.

Analysis of bacterial bowel communities of IBD patients: what has it revealed?

The bacterial community, in whole or in part, resident in the bowel of humans is considered to fuel the chronic immune inflammatory conditions characteristic of Crohn's disease and ulcerative colitis. Chronic or recurrent pouchitis in ulcerative colitis patients is responsive to antibiotic therapy, indicating that bacteria are the etiological agents. Microbiological investigations of the bacterial communities in stool or of biopsy-associated bacteria have so far failed to reveal conclusively the existence of pathogens or bacterial communities of consistently altered composition in IBD patients relative to control subjects. Confounding factors need to be eliminated from future studies by using better-defined patient populations of newly diagnosed and untreated individuals and by improved sampling procedures.

Clinical trial: randomized study of clarithromycin versus placebo in active Crohn's disease

BACKGROUND

Crohn's disease is characterized by defective innate immune responses to intestinal bacteria. Clarithromycin is a broad-spectrum antibiotic that has good penetration into macrophages.

AIM

To assess the efficacy of clarithromycin in active Crohn's disease.

METHODS

Patients with Crohn's disease activity index > 200 and serum C-reactive protein > or = 10 mg/L were randomized to receive clarithromycin 1 g o.d. or placebo for 3 months. Patients taking more than 10 mg/day prednisolone or 3 mg/day budesonide were excluded. Primary outcome was remission (CDAI < or = 150) or response (fall in CDAI > or = 70 from pre-treatment level) at 3 months.

RESULTS

The trial was stopped after 41 patients had been recruited because of poor overall efficacy. There was no difference in combined remission or response rates at 3 months between clarithromycin: 26% (five of 19) and placebo: 27% (six of 22) (P = 1.00). The mean (s.d.) fall in Crohn's disease activity index was 35 (80) clarithromycin and -2 (114) placebo (P = 0.24). However, post hoc analysis showed a significant difference in response/remission determined by Crohn's disease activity index after 1 month: 53% (10 of 19) clarithromycin vs. 14% (three of 22) placebo (P = 0.01).

CONCLUSION

Clarithromycin 1 g for 3 months is ineffective in active Crohn's disease but possible benefit was observed at 1 month, suggesting that an initial effect may be attenuated by subsequent bacterial resistance.

Interplay of commensal and pathogenic bacteria, genetic mutations, and immunoregulatory defects in the pathogenesis of inflammatory bowel diseases

Enteric microbiota can contribute to Crohn's disease and ulcerative colitis in several ways. Pathogenic or functionally altered commensal bacteria with increased mucosal adherence, invasion and intracellular persistence can activate pathogenic T cells and chronic intestinal inflammation. Compositional changes in intestinal microbiota can lead to decreased protective and increased aggressive species. Genetic polymorphisms resulting in increased mucosal permeability, decreased microbial killing, ineffective clearance of bacteria, biased TH1 and TH17 immune responses and loss of immunological tolerance are probably key contributors to IBD. Future therapies for these heterogeneous diseases should be individualized based on the patient-specific subset.

Microbial host interactions in IBD: implications for pathogenesis and therapy

Crohn's disease (CD), ulcerative colitis (UC), and pouchitis appear to be caused by pathogenic T-cell responses to discrete antigens from the complex luminal microbiota, with susceptibility conferred by genetic polymorphisms that regulate bacterial killing, mucosal barrier function, or immune responses. Environmental triggers initiate or reactivate inflammation and modulate genetic susceptibility. New pathogenesis concepts include defective bacterial killing by innate immune cells in CD, colonization of the ileum in CD with functionally abnormal Escherichia coli that adhere to and invade epithelial cells and resist bacterial killing, and alterations in enteric microbiota composition in CD, UC, and pouchitis detected by molecular probes. The considerable therapeutic potential of manipulating the enteric microbiota in inflammatory bowel disease patients has not been realized, probably due to failure to recognize heterogenic disease mechanisms that require individualized use of antibiotics, probiotics, prebiotics, combination therapies, and genetically engineered bacteria to restore mucosal homeostasis.

Correlation between rpoB gene mutation in Mycobacterium avium subspecies paratuberculosis and clinical rifabutin and rifampicin resistance for treatment of Crohn’s disease

AIM: To investigate overlapping regions of the rpoB gene previously involved with rifamycin resistance in M. tuberculosis and seek correlation between rpoB mutations in clinical MAP strains with susceptibility to RIF and RFB.

METHODS: We designed a molecular-based PCR method for the evaluation of rifabutin (RFB) and rifampicin (RIF) resistance based on probable determinant regions within the rpoB gene of MAP, including the 81 bp variable site located between nucleotides 1363 and 1443. The minimum inhibitory concentration (MIC) for RIF was also determined against 11 MAP isolates in attempt to seek correlation with rpoB sequences.

RESULTS: We determined that MAP strain 18 had an MIC of > 30 mg/L and ≤ 5 mg/L for RIF and RFB respectively, and a significant and novel rpoB mutation C1367T, compared to an MIC of ≤ 1.0 mg/L for both drugs in the wild type MAP. The 30-fold increase in the MIC was a direct result of the rpoB mutation C1367T, which caused an amino acid change Thr456 to Ile456 in the drug’s binding site. In addition, MAP strain 185 contained five silent rpoB mutations and exhibited an MIC comparable to the wild-type. Moreover, our in vitro selected mutation in MAP strain UCF5 resulted in the generation of a new resistant strain (UCF5-RIF16r) that possessed T1442C rpoB mutation and an MIC > 30 mg/L and > 10 mg/L for RIF and RFB respectively. Sequencing of the entire rpoB gene in MAP strains UCF4, 18, and UCF5-RIF16r revealed an rpoB mutation A2284C further downstream of the 81 bp variable region in UCF4, accounting for observed slight increase in MIC. In addition, no other significant mutations were found in strains 18 and UCF-RIF16r.

CONCLUSION: The data clearly illustrates that clinical and in vitro-selected MAP mutants with rpoB mutations result in resistance to RIF and RFB, and that a single amino acid change in the beta subunit may have a significant impact on RIF resistance. Unconventional drug susceptibility testing such as our molecular approach will be beneficial for evaluation of antibiotic effectiveness. This molecular approach may also serve as a model for other drugs used for treatment of MAP infections.

Incidence of Mycobacterium avium subspecies paratuberculosis in a population-based cohort of patients with Crohn's disease and control subjects

OBJECTIVE

To define the incidence of Mycobacterium avium subspecies paratuberculosis (MAP) in patients with Crohn's disease (CD) and in control subjects.

METHODS

Blood samples from 361 CD patients from a previously described population-based inflammatory bowel disease (IBD) cohort and 200 blood donor controls, of known NOD2 genotype, were screened by PCR for MAP-specific IS900 DNA. These results were correlated with NOD2 genotype.

RESULTS

The PCR assay was capable of detecting 20 fg of purified MAP DNA, equivalent to roughly 100 MAP cells/mL of blood. MAP-specific IS900 DNA was detected in 33.8% of CD cases and 21.5% of controls (OR 1.86, 95% CI 1.247-2.785, P= 0.002). All study participants were genotyped for the NOD2 mutations 2104C>T (R702W), 2722G>C (G908R), and 3020insC (1007fs). Carriage of one or two NOD2 mutations was not associated with a significantly higher risk of CD (OR 0.75, 95% CI 0.465-1.207, P= 0.234). No significant association was seen in the CD cohort for carriage of one or two NOD2 mutations and MAP status (OR 0.883, 95% CI 0.494-1.579, P= 0.675).

CONCLUSIONS

Screening peripheral blood using IS900 PCR indicated that MAP DNA could be detected in a significant proportion of CD cases from a large population-based cohort, and also, in control subjects. The over-representation of MAP DNA in CD suggests either a role or a probable role for MAP in the etiology of CD.

Evidence for the involvement of infectious agents in the pathogenesis of Crohn's disease

Many advances have been made in the understanding of Crohn's disease (CD) pathogenesis during the last decade. CD is currently seen as a predominantly T-lymphocyte-driven disease characterized by the presence of a complex cocktail of interacting cytokines, chemokines and other mediators produced by a variety of cell types. Prevailing theories of CD pathogenesis suggest that patients' T-lymphocytes are inappropriately activated in the setting of an immune imbalance, which is itself caused by an unfortunate confluence of genetic and environmental factors. The T-cell response then leads to the chronic inflammation characteristic for the disease. Various environmental factors may play a role in the development of CD, but microbes are most consistently implied. This theory is based on epidemiological, clinicopathological, genetic and experimental evidence. Despite the abundance of arguments for the implication of bacteria in the aetiopathogenesis of CD, the precise role of bacteria in this disease still remains elusive. Three not necessarily mutually exclusive theories have been proposed: (1) an unidentified persistent pathogen; (2) an abnormally permeable mucosal barrier leading to excessive bacterial translocation; and (3) a breakdown in the balance between putative "protective" versus "harmful" intestinal bacteria ("dysbiosis"). At present, one cannot exclude with certainty any of these three proposed hypotheses; they may all apply to CD to a certain extent.

Microbial influences in inflammatory bowel diseases

The predominantly anaerobic microbiota of the distal ileum and colon contain an extraordinarily complex variety of metabolically active bacteria and fungi that intimately interact with the host's epithelial cells and mucosal immune system. Crohn's disease, ulcerative colitis, and pouchitis are the result of continuous microbial antigenic stimulation of pathogenic immune responses as a consequence of host genetic defects in mucosal barrier function, innate bacterial killing, or immunoregulation. Altered microbial composition and function in inflammatory bowel diseases result in increased immune stimulation, epithelial dysfunction, or enhanced mucosal permeability. Although traditional pathogens probably are not responsible for these disorders, increased virulence of commensal bacterial species, particularly Escherichia coli, enhance their mucosal attachment, invasion, and intracellular persistence, thereby stimulating pathogenic immune responses. Host genetic polymorphisms most likely interact with functional bacterial changes to stimulate aggressive immune responses that lead to chronic tissue injury. Identification of these host and microbial alterations in individual patients should lead to selective targeted interventions that correct underlying abnormalities and induce sustained and predictable therapeutic responses.

The evidence for Mycobacterium paratuberculosis in Crohn's disease

PURPOSE OF REVIEW

Though long hypothesized, the putative link between Mycobacterium avium paratuberculosis and Crohn's disease remains neither confirmed nor refuted. This article reviews published contributions that directly or indirectly address this question.

RECENT FINDINGS

Epidemiologic studies, looking for M. avium paratuberculosis DNA in Crohn's tissue, show a strong association between the agent and this disease. Supporting data, however, are presently inconclusive on a causal role. Genetic studies provide indirect support for a role of mycobacteria in Crohn's disease, by identifying susceptibility genes that encode proteins implicated in innate immunity to intracellular bacteria. Clinical trial data support at least a short-term benefit for antimycobacterial therapy in Crohn's disease, but the microbial specificity of this response is presently unknown.

SUMMARY

There appears to be a strong association between M. avium paratuberculosis and Crohn's disease, but the causality of this association is unknown. Consequently, the therapeutic implications of this association require further study. A number of critical questions about the biology of M. avium paratuberculosis remain unanswered. Data from studies of this organism, and its interaction with the immune system, can help address proposed reasons for or against a role of M. avium paratuberculosis in the etiology of Crohn's disease.

Review article: the evidence base for interventions used to maintain remission in Crohn's disease

BACKGROUND

Crohn's disease is characterised by recurrent flare-ups alternating with periods of remission. A number of interventions are currently used in clinical practice to try and maintain remission in Crohn's disease but the evidence base for some of them may be questionable.

AIM

To review the available evidence on interventions, which are currently used to maintain remission in Crohn's disease.

METHODS

The Cochrane Library and Medline (Pubmed) were searched for level 1 evidence on specific interventions. Search terms included 'Crohn's disease or synonyms', 'remission or synonyms' and the names of specific interventions.

RESULTS

Azathioprine, infliximab and adalimumab are effective at maintaining remission in Crohn's disease. Natalizumab is also effective, but there are concerns about its potential association with progressive multifocal leukoencephalopathy. Long-term enteral nutritional supplementation, enteric-coated omega-3 fatty acids and intramuscular methotrexate may also be effective but the evidence for these is based on relatively small studies. The available evidence does not support the use of oral 5-aminosalicylates agents, corticosteroids, anti-mycobacterial agents, probiotics or ciclosporin as maintenance therapy in Crohn's disease.

CONCLUSION

A better understanding of the evidence base of existing interventions could result in the use of treatments, which are more likely to lead to improved patient outcomes.

Inflammatory bowel disease: progress and current concepts of etiopathogenesis

Over the past few years, none of the numerous conditions that are grouped under the broad designation of 'chronic inflammatory or autoimmune disorders' has undergone as much scientific and clinical progress as the two main forms of inflammatory bowel disease (IBD), Crohn's disease (CD) and ulcerative colitis (UC). Progress has occurred in all major areas relevant to IBD pathogenesis, which include the external environment, genetics, microbial factors, and the immune system. This review presents an update on the specific major advances that have occurred in each of these four areas, briefly discusses the therapeutic implications of the observed progress, and points out the additional work that needs to be accomplished in the next few years to reach a full understanding of IBD etiopathogenesis.