Radiation-induced enteropathy: Molecular basis of pentoxifylline–vitamin E anti-fibrotic effect involved TGF-β1 cascade inhibition

Background: Radiation-induced fibrosis is a serious late complication of radiotherapy. Pentoxifylline–vitamin E has proven effective and safe in clinical trials in the treatment of fibrosis, while the molecular mechanism of its activity is yet unexplored. Methods: Ten patients suffering from radiation-induced enteropathy were treated with pentoxifylline–vitamin E combination with SOMA score as the primary endpoint. In parallel, primary smooth muscle cells isolated from intestinal samples isolated from humans with radiation enteropathy were incubated with pentoxifylline, trolox (vit. E hydrophilic analogous) or their combination. Activation of the TGF-β1/Smad and Rho/ROCK pathways was subsequently investigated using Q-RT-PCR, gene reporter, Western-blot, ELISA and immunohistochemistry. Results: Pentoxifylline–vitamin E combination induces regression of symptoms (SOMA) by −41% and −80% at 6 and 18 months. In vitro, pentoxifylline and trolox synergize to inhibit TGF-β1 protein and mRNA expression. This inhibitory action is mediated at the transcriptional level and leads to subsequent inhibition of TGF-β1/Smad targets (Col Iα1, FN1, PAI-1, CTGF), while it has no effect on the Rho/ROCK pathway. Conclusions: The anti-fibrotic effect of combined pentoxifylline–vitamin E is at least in part mediated by inhibition of the TGF-β1 cascade. It strengthens previous clinical data showing pentoxifylline–vitamin E synergy and supports its use as a first-line treatment of radiation-induced fibrosis.