ROS scavenging before 27°C ischemia protects hearts and reduces mitochondrial ROS, Ca²⁺ overload, and changes in redox state

Abstract

In this study, we determined 1) whether ROS scavenging only during cold perfusion before global ischemia improves mitochondrial and myocardial function, and 2) which ROS leads to compromised cardiac function during ischemia and reperfusion (I/R) injury. Using fluorescence spectrophotometry, we monitored redox balance (NADH and FAD), O 2•Ϫ levels and mitochondrial Ca 2ϩ (m[Ca 2ϩ ]) at the left ventricular wall in 120 guinea pig isolated hearts divided into control (Con), MnTBAP (a superoxide dismutase 2 mimetic), MnTBAP (M) ϩ catalase (C) ϩ glutathione (G) (MCG), CϩG (CG), and N G -nitro-L-arginine methyl ester (L-NAME; a nitric oxide synthase inhibitor) groups. After an initial period of warm perfusion, hearts were treated with drugs before and after at 27°C. Drugs were washed out before 2 h at 27°C ischemia and 2 h at 37°C reperfusion. We found that on reperfusion the MnTBAP group had the worst functional recovery and largest infarction with the highest m [Ca 2ϩ ], most oxidized redox state and increased ROS levels. The MCG group had the best recovery, the smallest infarction, the lowest ROS level, the lowest m [Ca 2ϩ ], and the most reduced redox state. CG and L-NAME groups gave results intermediate to those of the MnTBAP and MCG groups. Our results indicate that the scavenging of cold-induced O 2•Ϫ species to less toxic downstream products additionally protects during and after cold I/R by preserving mitochondrial function. Because MnTBAP treatment showed the worst functional return along with poor preservation of mitochondrial bioenergetics, accumulation of H 2 O 2 and/or hydroxyl radicals during cold perfusion may be involved in compromised function during subsequent cold I/R injury. hypothermic ischemia; mitochondrial Ca 2ϩ ; reactive oxygen species HYPOTHERMIA of the arrested, ischemic heart improves its function on reperfusion compared with the normothermic arrested ischemic heart. The strategy behind hypothermic protection against ischemia, i.e., better tissue perfusion, and improved metabolic and mechanical function on reperfusion, is the reduced mitochondrial respiration and oxidative phosphorylation during ischemia that results in better mitochondrial respiration and regeneration of ATP on reperfusion. For example, we demonstrated that NADH, m [Ca 2ϩ ], and reactive O 2 species (ROS) levels were less altered during and after 30 min of ischemia at 17°C vs. 37°C (39). We reported that the more severe the hypothermia, the later is the onset of deleterious changes in mitochondrial function (1,2,16,22,31).Although hypothermia is very protective against ischemia, hypothermic perfusion, e.g., before subsequent cardiac ischemia, may cause injury due to altered cellular ion homeostasis resulting from impaired membrane ion pumps and exchangers and/or to reduced activity of enzymes responsible for mitochondrial respiration, scavenging of ROS, and contractile activity. A well-known effect of hypothermia is hypercontracture with elevated cytosolic [Ca 2ϩ ] (42). Another is a decreasing temperature-depende...

Reactive Oxygen Species in the Regulation of Synaptic Plasticity and Memory

“…It has long been established that ROS are produced in association with traumatic brain injury (TBI), during ischemia and hypoxia, as well as during the reperfusion and reoxygenation after these events (23,75,420,425). Ischemia is characterized by a transient block in blood flow that leads to decreased glucose and oxygen perfusion to the brain, resulting in energy failure, neuronal dysfunction and death, and impairments in cognitive functions, especially if the focal point of the ischemia was in learning and memory regions of the brain.…”

Mitochondrial Pathways, Permeability Transition Pore, and Redox Signaling in Cardioprotection: Therapeutic Implications

“…Excessive oxidative stress, besides contributing to irreversible myocardial injury, inducing prolonged mPTP opening, and leading to cellular dysfunction and cell death, may also induce reversible injury during ischemia and during reperfusion (17, 206, 300, 363). As said above, oxidative stress occurring during ischemia may be also important in reperfusion injury (20,49,364,365). Moreover, the reversible contractile dysfunction after myocardial I/R (stunning) is clearly a manifestation of oxidative stress (125).…”

“…Therefore, reperfusion injury limitation remains a major therapeutic target (174,179,269,368,392). Nevertheless, it must be borne in mind that attenuation of mitochondrial redox potential, ROS production, and mitochondrial Ca 2 + overload are also observed in ischemia/hypoxia (17,49,191,(363)(364)(365), as we will discuss in the next section.…”

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“…The recent paradoxical findings, erroneously interpreted to be due to increased superoxide production under complete global ischemia [10][11][12][13][14][15] could be explained by the above-described properties of 2-OH-E + and other cationic oxidation products of DHE. The time course of oxidized DHE species fluorescence in isolated perfused heart resembles with surprising fidelity the temporal pattern of fluorescence of the mitochondrial membrane potential probe safranin during ischemia and reperfusion previously described by us [58], i.e.…”