The role of the fecal stream in Crohn's disease: an historical and analytic review

Inflammatory bowel disease: immunodiagnostics, immunotherapeutics, and ecotherapeutics

Treatment options for inflammatory bowel disease (IBD) reflect a continuing shift from empiricism to strategies based on improved understanding of the pathophysiology of disease. In susceptible individuals, IBD appears to be the result of defective regulation of mucosal immune interactions with the enteric microflora. This has prompted research directed at the interface of the traditional disciplines of immunology, microbiology, and epithelial cell biology. Whereas immunodiagnostics have been of limited clinical value in IBD, assessments of mucosal rather than systemic immune function are promising. Therapeutically, there is an increasing trend toward more aggressive and earlier use of immunomodulatory agents, particularly for prevention of relapse, with cytokine manipulation as a bridge therapy to achieve remission in patients with acute severe disease. Although most drug treatments are directed toward altering the host response, the rationale for manipulating the enteric flora appears sound and will be the basis of additional future therapeutic strategies. Notwithstanding the widening range of options for drug therapy in IBD, other outcome modifiers and well-established principles of managing chronic disease are as important as ever.

Role of a defunctioning stoma in the management of large bowel Crohn's disease

BACKGROUND

The faecal stream plays a significant role in the pathogenesis of Crohn's disease. This retrospective study aimed to assess the effect of faecal diversion on the natural history of refractory Crohn's colitis (RCC) and severe perianal disease (PAD).

METHODS

All patients undergoing a defunctioning stoma without resection for RCC or PAD between 1970 and 1997 were studied. Indications for surgery, acute clinical response, subsequent outcome and stoma rates were recorded.

RESULTS

Some 73 patients underwent a defunctioning stoma (55 RCC and 18 PAD). Acute remission was achieved in 63 patients (48 RCC, 15 PAD). Twenty-nine patients had subsequent closure of the defunctioning stoma (25 of 48 acute responders with RCC and four of 15 acute responders with PAD). Eleven patients with RCC and two with PAD achieved good long-term function without disease relapse (median follow-up 36 months). Overall 52 patients have undergone proctocolectomy or remain with a defunctioning stoma (37 with RCC and 15 with PAD).

CONCLUSION

Faecal diversion is associated with acute clinical remission in the majority of patients with RCC and PAD, but sustained benefit occurs less often. For selected patients, diversionary surgery alone offers a realistic alternative to major bowel resection.

Identification of a novel bacterial sequence associated with Crohn's disease

BACKGROUND & AIMS

Enteric microorganisms are implicated in the pathogenesis of Crohn's disease (CD), but no clear bacterial or viral species has been identified. In this study, representational difference analysis (RDA) was used to isolate DNA segments preferentially abundant in lamina propria mononuclear cells of lesional mucosa vs. adjacent uninvolved mucosa.

METHODS

Two RDA-derived microbial sequences were isolated (I1 and I2) and identified as novel homologues of the ptxR and tetR bacterial transcription-factor families.

RESULTS

Quantitative competitive polymerase chain reaction of paraffin-embedded intestinal specimens from 212 patients showed that I2 DNA was present in many CD colonic lesions (43%), but was infrequent in other colonic specimens (9% of ulcerative colitis lesions and 5% of non-inflammatory bowel disease diseases; P<0.0001). I2 was prevalent in ileal specimens, regardless of disease status (43%-54%). Enzyme-linked immunosorbent assay analysis of 150 individuals with an I2 glutathione-S-transferase fusion protein showed frequent immunoglobulin A seroreactivity in CD (54% of patients), but infrequent seroreactivity in patients with ulcerative colitis, other inflammatory enteric diseases, or normals (10%, 19%, and 4%, respectively; P<0.001 to 0.00001).

CONCLUSIONS

These findings relate CD to a novel lesion-localized and immunologically associated bacterial sequence, suggesting that the microorganism expressing the I2 gene product may be related to CD pathogenesis.

Probiotics and inflammatory bowel disease: is there a scientific rationale?

Most conventional forms of drug therapy suppress or modify the host immunoinflammatory response and neglect the other contributor to disease pathogenesis-the environmental microflora. Probiotics are live microbial food ingredients that alter the enteric microflora and have a beneficial effect on health. The rationale for using probiotics in IBD is mainly based on evidence from human studies and experimental animal models implicating intestinal bacteria in the pathogenesis of these disorders. The relationship between bacteria and intestinal inflammation is complex and does not appear to reflect a simple cause and effect. Similarly, the field of probiotics is complex and in need of rigorous research. Until the indigenous flora are better characterized and mechanisms of probiotic action defined, the promise of probiotics in IBD is unlikely to be fulfilled. Because of strain-specific variability and clinical and therapeutic heterogeneity within Crohn's disease and ulcerative colitis, it cannot be assumed that a given probiotic is equally suitable for all individuals. Although preliminary results of probiotic therapy in animal models and humans with ulcerative colitis and pouchitis have been encouraging, their efficacy in treatment or maintenance of remission of Crohn's disease remains to be clarified. However, the circumstantial evidence for some form of biotherapeutic modification of the enteric flora in Crohn's disease seems compelling. In the future, probiotics may offer a simple adjunct to conventional therapy with the emphasis on diet shifting from one of nutritional replenishment alone to a more functional role.

Medical therapy to reduce postoperative Crohn's disease recurrence

Clinical recurrence of Crohn's disease after surgical resection is a significant problem, with reported rates as high as 55% at 5 yr and 76% at 15 yr. Specific factors that predispose to postoperative recurrence of Crohn's disease have not been well defined. In addition, the underlying pathophysiology of recurrent disease and the reason for its localization to the neoterminal ileum are not well understood. Various operative techniques have been evaluated but none, aside from formation of an ostomy, has been shown to reduce the risk of recurrence. In contrast, there is increasing evidence that postoperative medical therapy has the potential to decrease the risk of postoperative recurrence. Historically, sulfasalazine may have a modest effect on reducing postoperative recurrence of ileal or ileocolonic disease. However, 5-ASA preparations that can selectively deliver mesalamine to the small bowel or anastomotic margin should be more effective. Indeed, in several studies and as confirmed by a meta-analysis, mesalamine has been demonstrated to reduce significantly postoperative recurrence of Crohn's disease. Metronidazole and 6-mercaptopurine or azathioprine also seem to be of benefit in postoperative prophylaxis of disease recurrence, but additional controlled studies are required to define better the efficacy and dose-response of these agents. Corticosteroids are ineffective at reducing postoperative recurrence.

Colonic bacteria express an ulcerative colitis pANCA-related protein epitope

Bacteria are a suspected pathogenic factor in inflammatory bowel disease, but the identity of the relevant microbial species remains unresolved. The pANCA autoantibody is associated with most cases of ulcerative colitis (UC) and hence reflects an immune response associated with the disease process. This study addresses the hypothesis that pANCA identifies an antigen(s) expressed by bacteria resident in the human colonic mucosa. Libraries of colonic bacteria were generated using aerobic and anaerobic microbiologic culture conditions, and bacterial pools and clonal isolates were evaluated for cross-reactive antigens by immunoblot analysis using the pANCA monoclonal antibody Fab 5-3. Two major species of proteins immunoreactive to pANCA monoclonal antibodies were detected in bacteria from the anaerobic libraries. Colony isolates of the expressing bacteria were identified as Bacteroides caccae and Escherichia coli. Isolation and partial sequencing of the B. caccae antigen identified a 100-kDa protein without database homologous sequences. The E. coli protein was biochemically and genetically identified as the outer membrane porin OmpC. Enzyme-linked immunosorbent assay with human sera demonstrated elevated immunoglobulin G anti-OmpC in UC patients compared to healthy controls. These findings demonstrate that a pANCA monoclonal antibody detects a recurrent protein epitope expressed by colonic bacteria and implicates colonic bacterial proteins as a target of the disease-associated immune response.