TNF and major depressive disorder: In MDD, increased levels of oxidative stress markers—such as malondialdehyde (MDA) and 8-hydroxy-2-deoxyguanosine (8-OHdG)—telomere shortening, dysregulated nitric oxide signaling, cyclooxygenase-2 (COX-2) activation, and elevated concentrations of proinflammatory cytokines (IL-1, IL-6, TNF-α) have been reported.