Reactive oxygen species mediate human hepatocyte injury during hypoxia/reoxygenation

Abstract

Increasing evidence shows that reactive oxygen species (ROS) may be critical mediators of liver damage during the relative hypoxia of ischemia/reperfusion injury (IRI) associated with transplant surgery or of the tissue microenvironment created as a result of chronic hepatic inflammation or infection. Much work has been focused on Kupffer cells or liver resident macrophages with respect to the generation of ROS during IRI. However, little is known about the contribution of endogenous hepatocyte ROS production or its potential impact on the parenchymal cell death associated with IRI and chronic hepatic inflammation. For the first time, we show that human hepatocytes isolated from nondiseased liver tissue and human hepatocytes isolated from diseased liver tissue exhibit marked differences in ROS production in response to hypoxia/reoxygenation (H-R). Furthermore, several different antioxidants are able to abrogate hepatocyte ROS-induced cell death during hypoxia and H-R. These data provide clear evidence that endogenous ROS production by mitochondria and nicotinamide adenine dinucleotide phosphate oxidase drives human hepatocyte apoptosis and necrosis during hypoxia and H-R and may therefore play an important role in any hepatic diseases characterized by a relatively hypoxic liver microenvironment. In conclusion, these data strongly suggest that hepatocytes and hepatocyte-derived ROS are active participants driving hepatic inflammation. These novel findings highlight important functional/metabolic differences between hepatocytes isolated from normal donor livers, hepatocytes isolated from normal resected tissue obtained during surgery for malignant neoplasms, and hepatocytes isolated from livers with endstage disease. Furthermore, the targeting of hepatocyte ROS generation with antioxidants may offer therapeutic potential for the adjunctive treatment of IRI and chronic inflammatory liver diseases. Liver Transpl 16:1303-1313,

Factors affecting hepatocyte isolation, engraftment, and replication in an in vivo model

“…Our group also has good experience with human hepatocyte isolation. 2 We have 2 points to raise with respect to this excellent study. The authors used human hepatocytes isolated from resected normal liver tissue in their study (51 cancer specimens and 39 specimens of benign etiology).…”

“…Our data show that such hepatocytes differ in their response to hypoxia and hypoxia/reoxygenation in comparison with hepatocytes isolated from normal livers. 2 Did the authors note any phenotypic differences between hepatocytes isolated from cancer specimens and those isolated from benign livers? Moreover, did this have a bearing on transplant success?…”

“…We concur with Kawahara et al that human hepatocytes isolated from extended criteria donors are suitable for cell transplantation, but we also stress that human hepatocytes isolated from diseased livers can be a valuable source of cells for functional studies. 2 We again congratulate the authors on their excellent work within this challenging area, and we hope that with continuing research in human hepatocyte isolation, clear parameters and protocols can be established so that hepatocytes can be harvested from all available livers. …”

Hepatic liver ischemia/reperfusion injury: Processes in inflammatory networks - A review

“…3 Our recent study has conclusively shown that hepatocytes are also important sources of ROS during hepatic IRI. 4 This latter point has not been included in the review by Abu-Amara et al Indeed, hepatocytes may also be important sources of ROS along with Kupffer cells and neutrophils in the late stage of hepatic IRI. 2 We suggest that models of hepatic IRI should include the significant contribution of hepatocytes to the evolution of the injury.…”

“…First, hepatocytes generate significant levels of intracellular ROS during hypoxia and hypoxia/reoxygenation. 4 The subsequent release of intracellular ROS by necrotic hepatocytes into the liver parenchyma will perpetuate hepatocyte cell death. 5 Second, hepatocytes can secrete proinflammatory cytokines and chemokines during hepatic inflammation, which can then propagate liver injury.…”