Ciprofloxacin-Induced Oxidative Stress Promotes a Senescence-like Phenotype in Human Fibroblasts In Vitro

Fluoroquinolones are effective synthetic broad-spectrum antibiotics, but their use can be associated with persistent adverse effects, sometimes described as fluoroquinolone-induced disability. The molecular mechanisms underlying these effects remain incompletely understood, although accumulating evidence implicates mitochondrial dysfunction, oxidative stress, and DNA damage. We hypothesized that the convergence of these stress responses may promote cellular senescence and thereby contribute to persistent fluoroquinolone-associated adverse effects. We examined three clinically used fluoroquinolones—ciprofloxacin, moxifloxacin, and levofloxacin—in primary human fibroblasts in vitro. Exposure for 7 days revealed that 200 µM ciprofloxacin, but not 200 µM moxifloxacin or 500 µM levofloxacin, induced a senescence-like phenotype characterized by increased senescence-associated β-galactosidase (SA-β-Gal) activity and an elevated senescence index (SI), which integrates increased cell size and autofluorescence measured by imaging flow cytometry. At 7 days, ciprofloxacin did not induce a broad canonical senescence-associated secretory phenotype (SASP) at either the transcriptional or secretory level, consistent with a non-canonical senescence-like state; only a modest increase in IL-1β secretion emerged after 14 days. The ciprofloxacin-induced phenotype was not accompanied by a robust increase in the canonical p53, p16, or p21 protein markers, but was associated with reduced retinoblastoma protein (RB) phosphorylation at Ser795. However, ciprofloxacin removal from the culture medium after 1 or 2 weeks of incubation resulted in the recovery of the resazurin signal to approximately control values by the end of the 3-week experimental period. Ciprofloxacin also increased oxidative stress, as assessed using dihydroethidium and dichlorodihydrofluorescein diacetate. Both the antioxidant Trolox and the mitochondria-targeted antioxidant SkQ3 attenuated the ciprofloxacin-induced increase in SA-β-Gal activity and SI. These findings identify oxidative stress as a putative mediator of ciprofloxacin-induced senescence-like remodeling in human fibroblasts and support further investigation of drug-induced cellular senescence as a potential contributor to persistent fluoroquinolone-associated adverse effects.