Effect of the hydrophilic α-tocopherol analog MDL 74,405 on detection of hydroxyl radicals in stunned myocardium in dogs

We have previously shown in dogs that the hydrophilic α-tocopherol analog, MDL 74,405, attenuates postischemic myocardial dysfunction (“stunning”) and generation of free radicals as assessed with the spin trap α-phenyl N-tert-butyl nitrone (PBN). However, we could not discern whether this drug acts on primary radicals (such as hydroxyl radical [•OH]) or on secondary radicals. The goal of this study was to directly determine whether the beneficial effects of MDL 74,405 result from actions against •OH. Open-chest dogs undergoing a 15-minute coronary artery occlusion and 3 hours of reperfusion received an intravenous infusion of either saline solution (control group, n = 7) or MDL 74,405 (n = 6) starting 30 minutes before coronary occlusion and ending 60 minutes after reflow at a dose of 0.3 mg/kg/hr. Formation of •OH was estimated by the technique of aromatic hydroxylation of phenylalanine. Phenylalanine was infused intravenously, and the plasma concentrations of the hydroxylated products ortho-, meta-, and para-tyrosines (o-, m-, and p-tyr) in the coronary venous effluent and in the arterial blood were measured with high-performance liquid chromatography. In the control group a dramatic increase in the myocardial release of o-, m-, and p-tyr was observed immediately after reperfusion; the release of tyrosines peaked at 1 minute of reflow and continued up to 10 minutes after reperfusion. MDL 74,405 abolished the release of o-tyr throughout the first 10 minutes of reperfusion but had a less pronounced effect on the production of m- and p-tyr. These results demonstrate that MDL 74,405 is effective in inhibiting •OH-initiated reactions in the postischemic stunned myocardium in the dog, suggesting that the anti-•OH action of MDL 74,405 is an important mechanism of action of this antioxidant.