The Rac1 splice form Rac1b favors mouse colonic mucosa regeneration and contributes to intestinal cancer progression.

We previously have identified the ectopic expression of Rac1b, an activated and novel splice variant of Rac1, in a subset of human colorectal adenocarcinomas, as well as in inflammatory bowel diseases and in colitis mouse model. Rac1b overexpression has been further evidenced in breast, pancreatic, thyroid, ovarian, and lung cancers. In this context, the aim of our study was to investigate the physiopathological implications of Rac1b in intestinal inflammation and carcinogenesis in vivo. The ectopic expression of Rac1b was induced in mouse intestinal epithelial cells after crossing Rosa26-LSL-Rac1b and villin-Cre mice. These animals were let to age or were challenged with dextran sulfate sodium (DSS) to induce experimental colitis, or either received azoxymethane (AOM)/DSS treatment, or were bred with ApcMin/+ or Il10-/- mice to trigger intestinal tumors. Rac1b ectopic expression increased the intestinal epithelial cell proliferation and migration, enhanced the production of reactive oxygen species, and promoted the Paneth cell lineage. Although Rac1b overexpression alone was not sufficient to drive intestinal neoplasia, it enhanced Apc-dependent intestinal tumorigenesis. In the context of Il10 knockout, the Rac1b transgene strengthened colonic inflammation due to induced intestinal mucosa permeability and promoted cecum and proximal colon carcinogenesis. In contrast, Rac1b alleviated carcinogen/acute inflammation-associated colon carcinogenesis (AOM/DSS). This resulted at least partly from the early mucosal repair after resolution of inflammation. Our data highlight the critical role of Rac1b in driving wound-healing after resolution of intestinal inflammation, and in cooperating with Wnt pathway dysregulation and chronic inflammation to promote intestinal carcinogenesis.

Metronidazole or Cotrimoxazole therapy is associated with a decrease in intestinal bioavailability of common antiretroviral drugs.

Metronidazole (MTZ) and Cotrimoxazole (CTX) are used in HIV/AIDS patients eligible for antiretroviral treatment. The objective of this animal study was to determine whether pre-treatment with antibiotics affects the intestinal bioavailability of Atazanavir (ATV) and Ritonavir (RTV). After oral administration of 1 mg MTZ and CTX for 7 days, the rat colonic mucosa were analyzed for mucus thickness or placed in Ussing chambers to measure ATV and RTV net transepithelial fluxes (Jnet). 1. In control rats, the mucus thickness was 43.3±7.6 µm and 40.7±6.9 µm, in proximal and distal colon, respectively. In proximal colon, the thickness was 57.2±8.8 and 58.2±6.9 µm after MTZ and CTX, respectively whereas in distal colon, the thickness was 121.1±38.4 and 170.5±35.0 µm (P<0.05) respectively. 2. Transepithelial conductance was reduced after MTZ or CTX in the proximal and distal colon. 3. In control, net ATV secretion was observed both in proximal (-0.36±0.02 µg.hr(-1) cm(-2)) and distal colon (-0.30±0.08 µg.hr(-1) cm(-2)). After MTZ and CTX, it was increased in the proximal colon by two 2 fold and 4 fold, respectively and in the distal colon by 3 fold and 5 fold, respectively. 4. In control, there was no net active RTV transport either in proximal (+0.01±0.01 µg.hr(-1) cm(-2)) or distal colon (+0.04±0.01 µg.hr(-1) cm(-2)). After MTZ and CTX, secretion was increased 5 fold and 10 fold, respectively, in the proximal colon and two fold and 5 fold, respectively in the distal colon (p<0.001). In conclusion, after MTZ and CTX therapy, the mucus layer was enlarged, passive permeability was decreased and ATV and RTV were actively secreted by the colonic epithelium suggesting that, in rat, the intestinal bioavailability of ATV and RTV is impaired after antibiotic therapy.

Antisecretory effect of prescribed appetite stimulator drug cyproheptadine in rat intestine.

Cyproheptadine (Cph) is an antiserotoninergic and antihistaminergic agent with alpha-blocking activity and central sedative effect. Cph has been found to be effective in stimulating appetite, but to our knowledge, its direct effects on the intestine have not been documented. We aimed to assess the antisecretory effects of Cph in rat proximal colon using Ussing chambers' technique. In basal and serotonin (5-HT)-stimulated conditions, Cph induced a dose-dependent reduction in short-circuit current (Isc). This effect was different in fed vs. fasted rats (EC50 = 1.9 × 10(-5 ) m and 4.9 × 10(-5 ) m, respectively). As expected, Cph induced a marked dose-dependent rightward shift of the concentration-response curve to 5-HT (pA2 = 5.4). The effect of Cph was found to be close to that of antisecretory agents in the following sequence: peptide YY > somatostatin > clonidine > Cph > C7-sorbin. To our knowledge, this is the first demonstration that Cph has a direct effect on the inhibition of electrogenic ionic secretion in intestinal epithelium in vitro. Our results indicate that Cph can modulate the intestinal transport of electrolytes and provide a new insight into the peripheral effects of this drug, which is frequently prescribed as appetite stimulator in developing countries.