Free-radical formation by mitomycin C and its novel analogs in cardiac microsomes and the perfused rat heart

Abstract

Using a spin-trapping technique, we have examined free-redical formation by mitomycin C and its analogs, BMY 25282 and BMY 25067, in rat cardiac microsomes and isolated perfused rat hearts. All three drugs stimulated 2–4-fold .OH radical formation in cardiac microsomes which was inhibited by SOD and catalase. Superoxide anion radical was also detected in the presence of diethylenetraaminopentaacetic acid. Addition of DMSO yielded methyl radicals, thus indicating the production of free .OH under these conditions. Similar stimulation of .OH formation (2–3-fold) in the perfusates from rat hearts was detected with all three drugs. Perfusion with catalase (550 U/ml) completely suppressed the .OH signal both in the presence and absence of the drugs, thus suggesting the intermediacy of hydrogen peroxide. However, BMY 25067-induced .OH formation was more sensitive to inhibition by superoxide dismutase (SOD) and the iron chelator ICRF-187. Perfusion with DMSO produced methyl radicals at the expense of .OH in the presence of all three drugs. SOD and catalase inhibited DMPO-OH signals, indicating that most of the .OH formation was extracellular in this setting. While mitomycin C and BMY 25067 (up to 10 μM) did not affect the heart rate, perfusion with 10 μM BMY 25282 caused acute arrhythmia and cardiac standstill within 20 min. An initial surge in .OH formation (2-fold) accompanied this cardiotoxic effect. Both the arrhythmia and the free radical signal were partially blocked by SOD, catalase and ICRF-187, indicating that iron-dependent oxygen radical formation from BMY-25282 (and possibly other compounds) is involved, in part, in inducing toxic manifestations in the rat heart and possibly in clinic.