Nitroxide Hormesis in Yeast: 4-Hydroxy-TEMPO Modulates Aging, and Cell Cycle.

4-hydroxy-TEMPO is a water-soluble nitroxide radical with potent antioxidant and redox-modulating properties. Its small molecular weight and membrane permeability enable it to act as a superoxide dismutase mimetic, efficiently scavenging reactive oxygen species and mitigating oxidative damage. In this study, we investigated the physiological and transcriptomic effects of 4-hydroxy-TEMPO in <i>Saccharomyces cerevisiae</i>, using wild-type and mutant strains deficient in key redox and DNA repair pathways (<i>sod1Δ</i>, <i>sod2Δ</i>, <i>yap1Δ</i>, <i>rad52Δ</i>). RNA-Seq analysis revealed widespread transcriptional reprogramming. Treatment with 4-hydroxy-TEMPO impaired cell growth, induced accumulation of cells with 1C (G1 phase) DNA content, and modulated chronological aging in a strain-dependent manner. Notably, low concentrations delayed aging in wild-type, <i>yap1Δ</i>, and <i>rad52Δ</i> strains, while accelerating it in <i>sod1Δ</i> mutants, consistent with a hormetic response. Unlike TEMPO, 4-hydroxy-TEMPO exhibited markedly reduced translational toxicity, preserved polysome structure at high doses, and triggered a non-canonical, redox-dependent transcriptional program characterized by induction of stress-response genes together with unexpected up-regulation of multiple ribosomal protein genes. This was accompanied by a biphasic, genotype-specific hormetic response and a measurable genoprotective effect. RT-qPCR confirmed key transcriptional changes, linking transcriptome remodeling to functional outcomes.