PARP1 and gastrointestinal disease: Genes-metabolites networks corresponding to the “tRNA Charging” canonical pathway and to the “Cancer and Gastrointestinal Disease” canonical disease revealed key ‘hub’ compounds also present in our list of interest (Table 3 and complete Additional file 9: Table S5); such as, respectively, pyrophosphate, in relation to numerous genes of the RNA polymerases family (Figure 3A), and nicotinamide, in relation to numerous genes of the poly(ADP-ribose) polymerases (PARP) families, as well as Sirt-6 histone deacetylase (Figure 3B).