Original ContributionMitochondrial reactive oxygen species generation triggers inflammatory response and tissue injury associated with hepatic ischemia–reperfusion: Therapeutic potential of mitochondrially targeted antioxidants
Graphical abstract
Highlights
▸ Ischemia–reperfusion (I/R) injury is a pivotal mechanism of organ damage/dysfunction. ▸ The exact role and timing of mitochondrial oxidant generation in liver I/R are elusive. ▸ Mitochondrial oxidant generation triggers I/R-induced liver inflammation and injury. ▸ Mitochondrial antioxidants (MTAs) prevent I/R-induced oxidative/nitrative injury. ▸ MTAs prevent I/R-induced acute/delayed inflammatory response and cell death.
Introduction
Ischemia–reperfusion (I/R) inflicted by transient ischemia followed by reperfusion is a pivotal mechanism of organ injury during various pathological conditions (e.g., myocardial infarction, stroke, vascular surgeries, circulatory shock, and organ transplantation). Surgical interventions in the liver, transplantation, inflammatory and vascular diseases, circulatory shock, or various toxic insults may lead to hepatic I/R injury resulting in organ dysfunction or failure, depending on the duration of the insult [1], [2], [3]. Early generation of reactive oxygen (e.g., superoxide and hydrogen peroxide) and nitrogen (e.g., peroxynitrite) species (ROS and RNS) during reperfusion is considered to play a pivotal role in initiating a chain of deleterious cellular responses leading to inflammation and cell death, which eventually culminate in target organ dysfunction/failure [3], [4], [5], [6], [7], [8], [9], [10], [11]. Mitochondrial proteins are particularly sensitive targets for ROS/RNS [12], and their inactivation by oxidants may contribute to dysfunction and injury during hepatic [13] and other forms of liver injury [14]. Dysfunctional mitochondria may also generate significant amounts of ROS during hepatic I/R in addition to activated xanthine oxidoreductases and NADPH oxidases in various key cell types of the liver (e.g., hepatocytes, endothelial, Kupffer, and infiltrating immune cells) [15], [16], [17].
Despite numerous reports on the role of oxidative stress and mitochondrial dysfunction in hepatic I/R injury, and on the beneficial effects of global antioxidants, the exact role of mitochondrial ROS generation in liver I/R injury is still largely elusive. Furthermore, there is very limited information on the spatial–temporal relationship of the oxidative and nitrative stress and the inflammatory response during hepatic I/R or on the main cellular sources/targets of ROS/RNS generation. In this study, we used a well-established mouse model of in vivo segmental hepatic I/R injury [13], [18], [19], [20] and two well-characterized mitochondrially targeted small-molecule antioxidants, MitoQ and Mito-CP [21], [22], [23], [24], to investigate the roles of oxidative stress and mitochondrial oxidant generation during the course of hepatic I/R.
Section snippets
Hepatic ischemia–reperfusion
The study was approved by the Institutional Animal Care and Use Committees of the NIAAA and was carried out in line with the National Institutes of Health (NIH) Guidelines for the Care and Use of Laboratory Animals. Male C57BL/6J mice (25–30 g; The Jackson Laboratory, Bar Harbor, ME, USA) were anesthetized with pentobarbital sodium (65 mg/kg ip). In our study, the model of segmental (70%) hepatic ischemia–reperfusion was used as described [13], [18], [19], [20], [25], [26]. Two mitochondrially
Mitochondrially targeted antioxidants attenuate markers of hepatic I/R injury (ALT, AST) and histological damage
After 1 h of ischemia and a subsequent 2 or 6 h of reperfusion (I/R 2 h or I/R 6 h), a dramatic increase in the serum transaminase enzyme activities (AST and ALT, markers of hepatocellular damage/necrosis) were observed in vehicle-treated C57BL/6J mice (peaking at 6 h of reperfusion), compared with sham-operated controls (Fig. 1B–D). At 24 h of reperfusion (I/R 24 h) the transaminase activities declined compared to I/R 6 h, but were still elevated compared to sham-operated controls (Fig. 1D).
Discussion
In this study we explored the therapeutic potential of mitochondrially targeted antioxidants in a well-established mouse model of segmental hepatic I/R injury[13], [18], [19], [20], [26]. Previous in vitro, ex vivo, and in vivo studies using this and other models of hepatic I/R have implicated important roles for oxidative/nitrative stress, mitochondrial dysfunction, and inflammation in hepatic I/R injury and demonstrated beneficial effects of various global antioxidants [5], [7], [13], [15],
Acknowledgments
This study was supported by the Intramural Research Program of the NIAAA/NIH (to P.P.). Dr. Béla Horváth is the recipient of a Hungarian Research Council Scientific Research Fund Fellowship (OTKA-NKTH-EU MB08-80238). The authors are indebted to Dr. George Kunos, the Scientific Director of the NIAAA/NIH, for providing key resources and support.
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These authors contributed equally to this work.