NF-κB-Associated Redox Signaling and Intrinsic Apoptotic Activation in Polystyrene Nanoplastic–Induced Testicular Toxicity and Modulatory Effects of Nelumbo nucifera

Polystyrene nanoplastics (PS-NPs) are emerging environmental contaminants increasingly linked to male reproductive toxicity; however, the molecular mechanisms underlying testicular damage remain unclear. This study evaluated PS-NP-associated testicular damage in rats after 55 days of exposure and assessed the modulatory effects of Nelumbo nucifera leaf, flower, and rhizome extracts, with quercetin as a reference. PS-NP exposure reduced spermatogenic cell populations, testicular, epididymal weights, and sperm motility. These changes were accompanied by increased NOX4 and NF-κB expression, upregulation of intrinsic apoptosis-related genes (Tp53, Bax, Caspase-9, and Caspase-3), elevated caspase-3 and caspase-9 protein levels, and enhanced cleaved caspase-3 immunoreactivity. In contrast, Fas and Caspase-8 were downregulated, confirming intrinsic mitochondrial apoptosis. PS-NP exposure also altered reproductive hormone receptor expression (LHr, FSHr, and AR) and dysregulated chromatin-regulatory genes, with increased Dnmt1, Dnmt3a, and Ehmt2 (G9a) and decreased Hdac1 and Ep300. Co-administration of N. nucifera attenuated most of these alterations, with the rhizome extract exhibiting the most pronounced protective effect. GO and PPI network analyses suggested functional connectivity among stress-responsive, apoptotic, and chromatin-modifying proteins. Docking simulations indicated phytochemical-apoptosis-related protein interactions. PS-NPs may impair testicular homeostasis through coordinated stress, apoptosis, endocrine disturbance, and epigenetic dysregulation, with possible relevance to male reproductive health, while N. nucifera shows promise as a protective modulator.