Cellular and molecular mechanisms of hepatic ischemia-reperfusion injury: The role of oxidative stress and therapeutic approaches

Abstract

Ischemia-reperfusion (IR) or reoxygenation injury is the paradoxical exacerbation of cellular impairment following restoration of blood flow after a period of ischemia during surgical procedures or other conditions. Acute interruption of blood supply to the liver and subsequent reperfusion can result in hepatocyte injury, apoptosis, and necrosis. Since the liver requires a continuous supply of oxygen for many biochemical reactions, any obstruction of blood flow can rapidly lead to hepatic hypoxia, which could quickly progress to absolute anoxia. Reoxygenation results in the increased generation of reactive oxygen species and oxidative stress, which lead to the enhanced production of proinflammatory cytokines, chemokines, and other signaling molecules. Consequent acute inflammatory cascades lead to significant impairment of hepatocytes and nonparenchymal cells. Furthermore, the expression of several vascular growth factors results in the heterogeneous closure of numerous hepatic sinusoids, which leads to reduced oxygen supply in certain areas of the liver even after reperfusion. Therefore, it is vital to identify appropriate therapeutic modalities to mitigate hepatic IR injury and subsequent tissue damage. This review covers all the major aspects of cellular and molecular mechanisms underlying the pathogenesis of hepatic ischemia-reperfusion injury, with special emphasis on oxidative stress, associated inflammation and complications, and prospective therapeutic approaches.

Keywords: 4-Hydroxy-2-nonenal; Free radicals; Ischemia-reperfusion injury; Malondialdehyde; Oxidative stress; γ-glutamyl transpeptidase.

Graphical abstract

Fig. 1

The γ−glutamyl cycle indicating elevated levels of γ-glutamyl activity and increased degradation of glutathione during hepatic ischemia-reperfusion. γ-Glutamyl transpeptidase (γ-GT) is present in the outer surface of the cell membrane and transfers the γ-glutamyl moiety of glutathione into glutamate and γ-glutamyl-amino acids with a byproduct cysteinylglycine. The cysteinylglycine is a highly reactive thiol compound and reduces Fe³⁺ (ferric iron) into Fe²⁺ (ferrous ion) with the donation of an electron. In the subsequent redox reaction, oxygen (O₂) takes away an electron from Fe²⁺ and transform to Fe³⁺ with the generation of superoxide. Molecular oxygen (dioxygen) is a diradical containing two unpaired electrons, and superoxide is generated from the addition of an electron that fills one of the two degenerate molecular orbitals, leaving a charged ionic species with a single unpaired electron and a net negative charge of −1. The repeated redox cycling causes elevation of reactive oxygen species (ROS) which in turn results in intracellular oxidative stress.

Fig. 2

Immunohistochemical staining for high mobility group box 1 (HMGB1) (antibody used (GeneTex Cat# GTX127344, RRID:AB_11164700): in rat liver with hepatic steatosis. (A) Control liver showing the complete absence of HMGB1 staining. (B) Marked and prominent staining of HMGB1 after ischemia-reperfusion in the necrotic zone as a response to hepatic inflammation (x200). HMGB1 is a nuclear protein that translocates to the cytoplasm and extracellular compartments during ischemia-reperfusion injury. Tissue oxidative stress is a major factor that induces the secretion of HMGB1 from the nucleus and its relocation to the extracellular matrix to perform pivotal roles in the regulation of cellular response to inflammation. (Originally published as a Figure panel in Br J Pharmacol 2020; 177: 5195–5207 by the authors).

Fig. 3

Immunohistochemical staining for tumor necrosis factor-α (TNF-α) (antibody used: Cat# ab6671, Abcam, Tokyo, Japan) in rat liver sections after ischemia-reperfusion injury. (A) Control liver showing complete absence of TNF-α staining. (B) Intense and strong staining of TNF-α in macrophages that infiltrated into the necrotic zone (x100). TNF-α is a pro-inflammatory cytokine produced by activated macrophages during acute inflammation and serves as a marker for the degree of hepatic injury during ischemia-reperfusion. (Originally published as a Figure panel in Am J Physiol Gastrointest Liver Physiol 2016; 311: G305–G312 by the authors).

Fig. 4

Lipid peroxidation of polyunsaturated fatty acids depicting the production of toxic end products malondialdehyde (MDA) and 4-hydroxy-2-nonenal (4-HNE). The toxic aldehydes MDA and 4-HNE can react with the -NH2 group of proteins and DNA bases to form adducts that can cause mutations. (A) Oxidative degradation of arachidonic acid and formation of MDA. (B) Oxidative breakdown of linoleic acid to hydroperoxynonenal and then to hydroxynonenal.

Fig. 5

Schematic presentation of the prospective therapeutic approaches to attenuate ischemia-reperfusion injury, promote repair of impaired hepatocytes, and regenerate the injured liver tissue. Various pharmacological agents, potent antioxidants, and mesenchymal stem cells from different sources could be used for the purpose.