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A series of phenothiazines was synthesized and evaluated as in vitro inhibitors of iron-dependent lipid peroxidation. The MIC (minimum tested concentration that gave greater than or equal to 50% inhibition) for 2-(10H-phenothiazin-2-yloxy)-N,N-dimethylethanolamine methanesulfonate (6) was 0.26 microM. Whereas methyl substitution at N-10 diminished activity nearly 100-fold, other structural modifications such as varying the amine group, the distance separating the amine substituent from the phenothiazine nucleus, and the linking group had little effect. Compound 6 was more effective than probucol, a known antioxidant, in blocking Cu2+ catalyzed oxidation of low-density lipoprotein (LDL) as measured by competitive scavenger receptor mediated degradation of 125I-labeled acetyl-LDL by mouse peritoneal macrophage cells in vitro. At a concentration of 5 microM, compound 6 also protected primary cultures of rat hippocampal neurons exposed to hydrogen peroxide (50 microM) when assessed 18 h later by fluorescein diacetate and propidium iodide uptake.

In the rat four-vessel occlusion model with 30 minutes of ischemia most agents have failed to be of benefit when given after ischemia. Because postischemia administration is more clinically relevant, we evaluated the antioxidant LY231617 (2,6-bis(1,1-dimethylethyl)-4-[[(1-ethyl)amino]methyl]phenol hydrochloride]) when administered after 30 minutes of four-vessel occlusion. Male Wistar rats were subjected to 30 minutes of four-vessel occlusion. LY231617 was either given orally 30 minutes before ischemia or intravenously beginning at 30 minutes after the onset of ischemia. Hippocampal CA1 layer and striatal damage were rated on a scale of 0-3 (0, no damage; 3, > 90% cell loss). We also evaluated the ability of LY231617 to prevent iron-dependent lipid peroxidation and to prevent hydrogen peroxide-induced neuronal death of hippocampal neurons in primary culture by exposing cultures to a 50-microM concentration of hydrogen peroxide for 15 minutes in the presence of LY231617. Oral administration of LY231617 reduced both striatal and hippocampal CA1 damage by > 75% (p < 0.0001). In two separate experiments in which LY231617 was given intravenously beginning 30 minutes after occlusion, hippocampal and striatal damage were reduced by approximately 50% (p < 0.03) in the first experiment and by approximately 41% (p < 0.02) in the second experiment. Addition of 5 microM of LY231617 to primary hippocampal neuronal cultures antagonized the lethal effect of hydrogen peroxide (p < 0.05). Iron-dependent lipid peroxidation was also inhibited in a dose-related fashion. The significant reduction of ischemia-induced or hydrogen peroxide-induced neuronal damage and inhibition of lipid peroxidation by LY231617 observed in this study suggest that reactive oxygen intermediates play an important role in the events leading to neuronal death after global ischemia/reperfusion.

1 -4 Although a considerable amount of scientific evidence suggests a role for free radicals in the pathology of ischemia, the actual presence of free radicals during ischemia and reperfusion in the brain, unlike in the heart and other organs, has been difficult to demonstrate.Increases in the amounts of free fatty acids 5 after ischemia and during early reperfusion can provide the substrate for lipid peroxidation and for the formation of products of the arachidonic acid cascade. These products, in particular thromboxane and platelet activating factor, are believed to play a deleterious role in ischemic brain. Received September 20, 1990; accepted April 11, 1991. let activating factor at the receptor level reduced the volume of focal cortical infarcts.