Olaparib: A Clinically Applied PARP Inhibitor Protects from Experimental Crohn's Disease and Maintains Barrier Integrity by Improving Bioenergetics through Rescuing Glycolysis in Colonic Epithelial Cells

Crohn's disease (CD) is an inflammatory disorder of the intestines characterized by epithelial barrier dysfunction and mucosal damage. The activity of poly(ADP-ribose) polymerase-1 (PARP-1) is deeply involved in the pathomechanism of inflammation since it leads to energy depletion and mitochondrial failure in cells. Focusing on the epithelial barrier integrity and bioenergetics of epithelial cells, we investigated whether the clinically applied PARP inhibitor olaparib might improve experimental CD. We used the oral PARP inhibitor olaparib in the 2,4,6-trinitrobenzene sulfonic acid- (TNBS-) induced mouse colitis model. Inflammatory scoring, cytokine levels, colon histology, hematological analysis, and intestinal permeability were studied. Caco-2 monolayer culture was utilized as an epithelial barrier model, on which we used qPCR and light microscopy imaging, and measured impedance-based barrier integrity, FITC-dextran permeability, apoptosis, mitochondrial oxygen consumption rate, and extracellular acidification rate. Olaparib reduced the inflammation score, the concentration of IL-1β and IL-6, enhanced the level of IL-10, and decreased the intestinal permeability in TNBS-colitis. Blood cell ratios, such as lymphocyte to monocyte ratio, platelet to lymphocyte ratio, and neutrophil to lymphocyte ratio were improved. In H(2)O(2)-treated Caco-2 monolayer, olaparib decreased morphological changes, barrier permeability, and preserved barrier integrity. In oxidative stress, olaparib enhanced glycolysis (extracellular acidification rate), and it improved mitochondrial function (mitochondrial coupling efficiency, maximal respiration, and spare respiratory capacity) in epithelial cells. Olaparib, a PARP inhibitor used in human cancer therapy, improved experimental CD and protected intestinal barrier integrity by preventing its energetic collapse; therefore, it could be repurposed for the therapy of Crohn's disease.