Glugacon-like peptide-2: broad receptor expression, limited therapeutic effect on intestinal inflammation and novel role in liver regeneration.

The glucagon-like peptide 2 (GLP-2) is an intestinotrophic hormone with growth promoting and anti-inflammatory actions. However, the full biological functions of GLP-2 and the localization of its receptor (GLP-2R) remain controversial. Among cell lines tested, the expression of GLP-2R transcript was detected in human colonic myofibroblasts (CCD-18Co) and in primary culture of rat enteric nervous system but not in intestinal epithelial cell lines, lymphocytes, monocytes, or endothelial cells. Surprisingly, GLP-2R was expressed in murine (GLUTag), but not human (NCI-H716) enteroendocrine cells. The screening of GLP-2R mRNA in mice organs revealed an increasing gradient of GLP-2R toward the distal gut. An unexpected expression was detected in the mesenteric fat, mesenteric lymph nodes, bladder, spleen, and liver, particularly in hepatocytes. In two mice models of trinitrobenzene sulfonic acid (TNBS)- and dextran sulfate sodium (DSS)-induced colitis, the colonic expression of GLP-2R mRNA was decreased by 60% compared with control mice. Also, GLP-2R mRNA was significantly downregulated in intestinal tissues of inflammatory bowel disease patients. Therapeutically, GLP-2 showed a weak restorative effect on intestinal inflammation during TNBS-induced colitis as assessed by macroscopic score and inflammatory markers. Finally, GLP-2 treatment accelerated mouse liver regeneration following partial hepatectomy as assessed by histological and molecular analyses. In conclusion, the limited therapeutic effect of GLP-2 on colonic inflammation dampens its utility in the management of severe inflammatory intestinal disorders. However, the role of GLP-2 in liver regeneration is a novelty that might introduce GLP-2 into the management of liver diseases and emphasizes on the importance of elucidating other extraintestinal functions of GLP-2.

The 5-aminosalicylic acid antineoplastic effect in the intestine is mediated by PPARγ.

Epidemiological evidences suggested that 5-aminosalicylic acid (5-ASA) therapy may prevent the development of colorectal cancer in inflammatory bowel disease patients. Our aim is to investigate whether peroxisome proliferator-activated receptor-γ (PPARγ) mediates the antineoplastic effects of 5-ASA. HT-29 and Caco-2 cells were treated by 5-ASA, rosiglitazone (PPARγ ligand) or etoposide (anticarcinogenic drug). Epithelial cell growth, proliferation and apoptosis were assessed by cell count, Ki-67 staining and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay, respectively. The antineoplastic effect of 5-ASA was evaluated in a xenograft tumor model in SCID mice and in azoxymethane (AOM)-induced colon carcinogenesis in A/JOlaHsd mice. The role of PPARγ was examined by administration of PPARγ antagonist, GW9662 and in PPAR knockdown cells. Compared with untreated cells, treatment of HT-29 cells by 5-ASA inhibited significantly cell growth and cell proliferation (respectively, 60% and 63%) and induced apoptosis in 75% of cells. These effects were abolished by co-treatment with GW9662 and blunted in PPAR knockdown cells. Contrarily to etoposide, similar inhibitory effects of GW9662 were obtained in HT-29 cells treated with rosiglitazone. In the xenograft model, GW9662 abolished the therapeutic effect of 5-ASA, which decreased tumor weight and volume by 80% in SCID mice compared with untreated mice. In A/JOlaHsd mice, 5-ASA suppressed colon carcinogenesis by decreasing the number of aberrant crypt foci (75%) and aberrant crypts (22%) induced by AOM treatment with an absence of 5-ASA response after GW9662 administration. In conclusion, 5-ASA exerts potent antineoplastic effects that are mediated through PPARγ. These data provide new rational for designing more effective and safe antineoplastic PPARγ ligands with topical effects.

In vivo imaging reveals selective PPAR activity in the skin of peroxisome proliferator-activated receptor responsive element-luciferase reporter mice.

Peroxisome proliferator-activated receptors (PPARs) have been revealed as key regulators of several skin disorders. This has led to a growing interest in the development of drugs targeting PPARs as therapeutics for skin diseases. To evaluate skin PPAR activity, we developed peroxisome proliferator responsive element-luciferase (PPRE-Luc) mice, a mouse model in which the luciferase gene expression is under the control of a PPAR-inducible promoter in all organs. Our aim was to define and validate experimental conditions to establish PPRE-Luc mice as a valuable tool for in vivo non-invasive evaluation of PPARs activation in the skin. We demonstrated by optical imaging that topical application of 40 mm of Luciferin for 10 min was enough to reveal the optimal luciferase activity in mice skin. The treatment of mice skin with the PPARγ and PPARα agonists, pioglitazone and WY14643, was associated with significant increase in photons emission reaching maximal signalling at 6 h. We have performed dose response studies by testing a large range of pioglitazone and WY14643 concentrations on mouse skin. The specificity of bioluminescence signal induced by pioglitazone and WY14643 was assessed using PPARγ and PPARα antagonists, GW9662 and GW6471, respectively. This approach revealed that the isoform specificity of PPARs agonists decreased when high ligand concentrations were applied on mouse skin. These results were further confirmed by in vitro measurement of luciferase activity in skin extracts. Overall, our results demonstrated that PPRE-Luc mice represent a valuable reporter mouse model for the in vivo pharmacological profiling of drugs targeting PPARs in the skin.