Nitrofuran drugs beyond redox cycling: Evidence of Nitroreduction-independent cytotoxicity mechanism.

Nitrofurans (5-nitro-2-hydrazonylfuran as pharmacophore) are a group of widely used antimicrobial drugs but also associated to a variety of side effects. The molecular mechanisms that underlie the cytotoxic effects of nitrofuran drugs are not yet clearly understood. One-electron reduction of 5-nitro group by host enzymes and ROS production via redox cycling have been attributed as mechanisms of cell toxicity. However, the current evidence suggests that nitrofuran ROS generation by itself is uncapable to explain the whole toxic effects associated to nitrofuran consumption, proposing a nitro-reduction independent mechanism of toxicity. In the present work, a series of nitrated and non-nitrated derivatives of nitrofuran drugs were synthesized and evaluated in vitro for their cytotoxicity, ROS-producing capacity, effect on GSH-S-transferase and antibacterial activity. Our studies showed that in human cells non-nitrated derivatives were less toxic than parental drugs but, unexpectedly preserved the ability to generate intracellular ROS in similar amounts to nitrofurans despite not entering into a redox cycle mechanism. In addition, some non-nitrated derivatives although being uncapable to generate ROS exhibited the highest cell toxicity among all derivatives. Inhibition of cytosolic glutathione-S-transferase activity by some derivatives was also observed. Finally, only nitrofuran derivatives displayed antibacterial effect. Results suggest that the combined 2-hydrazonylfuran moiety, redox cycling of 5-nitrofuran, and inhibitory effects on antioxidant enzymes, would be finally responsible for the toxic effects of the studied nitrofurans on mammalian cells.

NADPH oxidase activity: Spectrophotometric determination of superoxide using pyrogallol red.

A simple and fast spectrophotometric methodology able to quantify superoxide released by NADPH oxidase from differentiated promyelocytic leukaemia (HL-60) cells using pyrogallol red is described.The latter is based on the known stoichiometry of the reaction between superoxide and pyrogallol red and the inability of pyrogallol red to react with hydrogen peroxide. In addition, we developed a 96-wells microplate-based method able to determine NADPH oxidase activity. Using this method, we determined pharmacological properties of the NADPH oxidase inhibitors VAS2870 and diphenyleneiodonium and the obtained IC50 values were in good agreement with previous reported data. NOX2 is highly expressed in differentiated promyelocytic leukaemia cells, whereas other isoforms are not detected or expressed at low amounts. Likewise, this methodology may be a useful assay for NOX2 inhibitor screening. NADPH oxidases are involved in several physiological and pathological processes, rendering its pharmacological modulation an attractive research target. In this context, this simple assay can be used for NADPH oxidase inhibitor screening as well as aiding in the study of different biological conditions that involve NADPH oxidase activity.