An ex-vivo human intestinal model to study Entamoeba histolytica pathogenesis

Amoebiasis (a human intestinal infection affecting 50 million people every year) is caused by the protozoan parasite Entamoeba histolytica. To study the molecular mechanisms underlying human colon invasion by E. histolytica, we have set up an ex vivo human colon model to study the early steps in amoebiasis. Using scanning electron microscopy and histological analyses, we have established that E. histolytica caused the removal of the protective mucus coat during the first two hours of incubation, detached the enterocytes, and then penetrated into the lamina propria by following the crypts of Lieberkühn. Significant cell lysis (determined by the release of lactodehydrogenase) and inflammation (marked by the secretion of pro-inflammatory molecules such as interleukin 1 beta, interferon gamma, interleukin 6, interleukin 8 and tumour necrosis factor) were detected after four hours of incubation. Entamoeba dispar (a closely related non-pathogenic amoeba that also colonizes the human colon) was unable to invade colonic mucosa, lyse cells or induce an inflammatory response. We also examined the behaviour of trophozoites in which genes coding for known virulent factors (such as amoebapores, the Gal/GalNAc lectin and the cysteine protease 5 (CP-A5), which have major roles in cell death, adhesion (to target cells or mucus) and mucus degradation, respectively) were silenced, together with the corresponding tissue responses. Our data revealed that the signalling via the heavy chain Hgl2 or via the light chain Lgl1 of the Gal/GalNAc lectin is not essential to penetrate the human colonic mucosa. In addition, our study demonstrates that E. histolytica silenced for CP-A5 does not penetrate the colonic lamina propria and does not induce the host's pro-inflammatory cytokine secretion.

Entamoeba histolytica is the causative agent of amoebiasis, a human disease. Like other enteric infections, the lack of animal models enhances the difficulty of studying the development of amoebiasis. To date, no experimental model has been developed that reproduces the invasive intestinal amoebic lesions seen in human colon. We present the first study that examines, using human colon explants, the early steps of the human colonic barrier invasion by E. histolytica. With this ex vivo integrative model we have investigated both parasite behaviour and the human tissue response. Remarkably, in this model E. histolytica was able to cross and destroy the intestinal barrier evoking a tissue inflammatory response, while E. dispar, a non-pathogenic species, was unable to penetrate nor induce tissue responses. Furthermore, we have explored the role of three virulence factors during the invasive process, using gene-silenced E. histolytica trophozoites, particularly the kinetics of invasion, tissue destruction and induction of an early inflammatory responses. This is, to our knowledge, the first time that their role is highlighted in a complex human system. Our study provides new insights in the molecular mechanisms involved in the early steps of human colon invasion by E. histolytica.

[Ischemic colitis. A surgical series of 88 cases]

We report our experience in 88 cases of ischemic colitis including 76 cases of gangrene with 17 perforations, 6 cases with stenosis and 6 cases which regressed. The left colon was involved in 59 cases with extension to the transverse colon in 20 the right colon in 10 and global involvement in 18. Abdominal pain, diarrhea, and meteorism occurred in 81, 62 and 78% of the cases respectively. Coloscopy was performed in 61 cases, a barium study in 27. A colectomy was required in 77 patients: 50 left colectomies with 16 extensions to the transverse colon, 17 total colectomies and 10 right colectomies. Morbidity was 53% in cases with perforated gangrene and 28% without perforation. There was no morbidity in stenosis and regressive forms. Normal tube flow was conserved or reestablished in 51 of the 62 survivors. The 88 patients were referred from cardiovascular units (36%), intensive care (28.5%), or internal medicine (22%). All had intramural ischemia due to local or general lesions which progressed to parietal gangrene in 76 cases. The diagnosis was based on clinical signs and confirmed by coloscopy which determined the stage and extension. Stage II ischemia required rapid colectomy adapted to the endoscopic lesions and not the exterior aspect of the colon; immediate anastomosis is usually not used.