Fluoroquinolones lower constitutive H2AX and ATM phosphorylation in TK6 lymphoblastoid cells via modulation of the intracellular redox status.

Accumulation of reactive oxygen species (ROS)-induced damage and mutations in the genomic DNA is considered the primary etiology of aging and age-related pathologies including cancer. Strategies aimed at slowing these conditions often involve protecting against oxidative DNA damage via modulation of the intracellular redox state. Recently, a biomarker of DNA double-strand breaks (DSBs), serine 139-phosphorylated histone H2AX (gammaH2AX), and its upstream mediator, activated PI-3-related kinase, ATM (ATM(P1981)), were shown to be constitutively expressed in cells and modulated by antioxidant treatment. Thus, both constitutive histone H2AX phosphorylation (CHP) and constitutive ATM activation (CAA) are thought to reflect a cell's response to endogenous ROS-induced DSBs. In the present study, we investigated the effects of a battery of fluoroquinolone (FQ) compounds, namely ciprofloxacin, enrofloxacin, gatifloxacin, lomefloxacin and ofloxacin, on CHP and CAA in human TK6 lymphoblastoid cells. All FQs tested reduced CHP and CAA compared to controls following 6 and 24 h treatment with CAA being more sensitive to their effects at both time points. In addition, intracellular ROS levels and mitochondrial activities were also lowered in FQ-treated cells at 6 and 24 h.We presume that FQs mediate this effect via a combination of ROS-scavenging and mitochondrial suppression and therefore may protect against the onset or may slow the progression of numerous oxidative pathophysiological conditions.