Deciphering the multitarget protective mechanisms of melatonin in cadmium-induced male reproductive toxicity via a computational approach.

Cadmium (Cd) is a widespread environmental contaminant that has a detrimental impact on male reproductive toxicity (MRT) due to oxidative stress, endocrine imbalance, inflammation and cell death processes. Despite the known potential of melatonin (MLT) to ameliorate the adverse effects of Cd on MRT, the exact molecular mechanisms of such multistep action are still obscure. In this work, an integrated computational approach based on network pharmacology, protein-protein interaction (PPI) network analysis, molecular docking, MM-GBSA binding energy calculation, molecular dynamics (MD) simulation, and functional annotation was used for understanding of the molecular basis of MLT-mediated protection. Forty shared targets were found between MLT-related genes and MRT-related genes caused by cadmium exposure. Ten hub genes (PTGS2, ESR1, MAPK8, EGFR, AR, NR3C1, PGR, CCND1, MMP9, and NFKB1) were selected based on network topology analysis. Functional annotation revealed that these targets are mostly involved in steroid hormone signaling, reproductive system development, transcription regulation, inflammatory signaling, and cancer pathways. Molecular docking identified that MAPK8 and PGR are the two best-binding proteins of MLT with docking scores of -7.783 and -6.830kcal/mol, respectively and MM-GBSA binding energies of -66.10 and -63.63kcal/mol, respectively. Further MD simulations over 300ns proved to be successful in achieving a stable ligand-protein complex, maintaining structural stability, and stable binding during the course of the simulations. Taken together, these results indicate that MLT might operate via modulation of the oxidative stress-related, endocrine-related, and inflammation-related pathways simultaneously instead of operating through one specific target.