ESR1 and rheumatoid arthritis: The formation of peroxynitrite inside RBCs from RA patients is conceivable as a result of the increased 1) NO synthesis by the eNOS stimulated by ER-α activation and 2) O2• formed as a result of hemoglobin auto-oxidation and activation of the NADH oxidases following the RBCs continuous exposition to exogenous oxidative insult (Mahdi et al., 2021; Mohanty et al., 2014).