SMPD1 and erectile dysfunction: We propose that during the evolution of parenchymal tissue damage after radiation, ASMase/ceramide-dependent endothelial apoptosis likely represents a feed-forward process, which, once disrupted, even for a brief period, initiates a previously unknown tissue reparative process as shown recently with Sildenafil in erectile dysfunction (ED) and in cardiovascular disease (CVD) [29] https://www.biorxiv.org/content/10.1101/2021.04.08.438992v1.