U-78517F: A potent inhibitor of lipid peroxidation with activity in experimental brain injury and ischemia

U-78517F {2-[4-[2,6-di-(1-pyrrolidinyl)-4-pyrimidinyl)-1-piperazinyl]-3,4 -dihydro-2,5,7,8-tetramethyl-2H-1-benzopyran-6-ol, dihydrochloride}, which combines the antioxidant ring portion of α-tocopherol together with the amine of the previously described 21-aminosteroids (e.g., U-74006F), is a novel inhibitor of iron-catalyzed lipid peroxidation. U-78517F was found to have a 50% inhibitory concentration (IC₅₀) of 0.6 μM against 200 μM ferrous chloride-initiated lipid peroxidation in rat brain homogenates, compared to 8 μM for U-74006F, 28 μM for α-tocopherol and 43 μM for the ring portion of α-tocopherol (i.e., trolox). Both stereoisomers of the racemic U-78517F proved to be equally active antioxidants. Against lipid peroxidation initiated by xanthine/xanthine oxidase, U-78517F was even more potent, with an IC₅₀ of 0.01 μM. U-78517F was also observed to protect cultured mouse spinal neurons against iron-induced damage, with an IC₅₀ of approximately 0.5 μM. When administered to male CF-1 mice i.v. at 5 min after a severe concussive head injury, U-78517F produced a dose-related improvement in the 1-hr neurological recovery. The minimum effective i.v. dose was 1.0 μg/kg. Measurement of U-78517 concentrations in the brains of mice after administration of a 10-mg/kg i.v. dose revealed effective antioxidant levels for as long as 2 hr. Evidence of an in vivo antioxidant action was provided by the attenuation of iron-induced blood-brain barrier disruption (i.e., Evans' blue extravasation) in rats pretreated with U-78517F. When administered to male gerbils at an i.p. dose of 10 mg/kg at 10 min before, and again at the end of a 3-hr period of unilateral carotid artery occlusion, U-78517F was shown to decrease 24-hr postischemic cortical neuronal necrosis. In the medial portion of the cortex, neuronal density was increased from 34.2% of normal in vehicle-treated animals to 86.3% in the U-78517F-treated animals. In the lateral cortical area, the vehicle group showed only 3.3% neuronal survival vs. 48.2% in the drug-treated group. U-78517F neither exhibited hypothermic activity nor antagonized excitatory amino acid (e.g., N-methyl-D-aspartate, kainate, quisqualate)-induced seizures in mice. Moreover, it showed no significant interaction with known neurotransmitter receptors (e.g., acetylcholine, norepinephrine, dopamine, 5-hydroxytryptamine, opiate and benzodiazepine). These results document the cerebroprotective efficacy of a novel and potent inhibitor of iron-catalyzed lipid peroxidation, and further support a key role of oxygen radicals in post-traumatic and postischemic pathophysiology.