Hepatic ischemia-reperfusion injury: histological determinants studied from light and electron microscopy of pig livers under experimental transplantation

Abstract

Background During 1985-1998, there have been 45 cases of orthotopic liver transplant (OLT) conducted at 16 European centers in patients with alveolar echinococcosis, a rare parasitic disease caused by intrahepatic growth of Echinococcus multilocularis larvae (Koch et al., 2003). In USA alone, each year more than 4,000 patients undergo OLT surgery, the treatment of choice for most end-stage/incurable liver diseases (Keeffe, 2001). Although survival rate has drastically improved, surgeons still have difficulties in determining whether, and how much, the donor organs are involved in ischemia-reperfusion (I/R) injury, one of the most confounding factors affecting the initial graft function and the subsequent organ integrity. We, therefore, examined the livers under I/R in order to characterize the nature of the injury microscopically and to evaluate the organ from morphological viewpoint. Materials and methods Of ten pigs studied, six pigs were subject to I/R experiment prepared for an OLT. The injury was induced by a Pringle’s maneuver, i.e., 30-min ischemia and 10-min reperfusion. Three livers underwent double vessel injection with colored gelatin. The organs were removed and cut perpendicular to their longitudinal axis into 12-14 segments to map the position of major blood vessels. The tissue blocks obtained thereof were processed for light microscopy (LM). The other three livers were injected with Batson#17 plastic mixture for microcorrosion study under scanning electron microscopy (SEM). Four animals were sham-operated and used as LM and SEM control. Results Under LM, the lobular profiles were distinguished into two types, occluded lobules and unoccluded lobules. The occluded lobules, recognized with diffusely collapsed sinusoids and distinctly shrinked central veins, vastly prevailed the lobule population, while the unoccluded lobules, recognized with open sinusoids and widened central veins, represented only a minor only a minor proportion. Morphoquantitative mapping revealed that occluded lobules in different segments accounted for 80% rostrally and 60% caudally. White cell aggregations were frequently encountered along the narrowed sinusoids, forming chains and clusters. The chains were formed by 3-6 cells of lymphocytes and neutrophils, while the clusters size ranged from 40-60 µm containing exclusively polymorphonuclear cell. Endothelial cells showed varying degrees of swelling as evidenced by the thickened cytoplasm and enlarged nuclei. Kupffer cells and arachnocytes were observed unaltered. Hydropic swelling was striking in parenchymal cells. Hepatocyte shapes were found variously, e.g., rounded, columnar, elongate, or stellate. Round-shaped cells mostly resided in intermediate zone. In portal tracts, dilated hepatic arteries and recoiled portal veins were common. The isolated arterioles were found with a prominent diameter. Hepatic vein’s wall was filled with dilated vasa venarum which emptied through the transintimal vasal outlets measuring 20-25 µm in width. Under SEM, the dense plexus of vasa venarum were observed. Their drainage through vassal outlets were found as plastic globes sprouting into the luminal surface of hepatic vein, continuous with the venules of the vasa via a slender connector. Discussion and Conclusion Results are clear that livers with I/R injury exhibit certain histological landmarks usually not seen in unaffected livers. These include the narrowing of sinusoids, white cell sequestration, endothelial cell swelling, deformed hepatocytes, recoiled portal veins, dilated hepatic arteries, and distended vasa venarum of hepatic vein wall. The isolated arteries which are uncommon to encounter in control are easily identified in the injured liver. The data from SEM show an increased arterial circulation in the extraportal compartment, indicative of a functional arterosystemic shunt pathway. With the increasing practice of partial liver transplantation, such as reduced-size, spilt-liver, and living-related donor, the implication of unequal injury in different organ segments, as revealed by the two lobular populations, would significantly matter the process of making decision in selecting donor grafts to best fit recipient individuals of years to come. (Supported by Thailand Research Fund #BRG4380002; RBD Project Grant #4703, National Science and Technology Development Agency; Mahidol University Medical Scholars Program, Thailand, and; SFB Grant #405 Heidelberg; Germany).