Effect of Hyperbaric Oxygen on Liver Regeneration in a Rat Model E.C. Tolentino, O. Castro e Silva, S. Zucoloto, M.E.J. Souza, M.C.J. Gomes, A.K. Sankarankutty, G.R. Oliveira, and O. Feres ABSTRACT Hyperbaric oxygen therapy is a treatment that has been gradually implemented for the treatment of several pathologic conditions. The present study evaluated the effect of hyperbaric oxygen therapy for hepatic regeneration and its relationship to mitochondrial function. Male Wistar rats underwent partial hepatectomy (70%) and subsequently underwent two sessions of hyperbaric oxygen (90 minutes each, at a pressure of 2 ATA). The animals were sacrificed at 24 and 48 hours after surgery. Hepatic regeneration was evaluated by the dry weight of the remaining liver, the hepatic regeneration rate, the hepatic DNA content, and the hepatocyte proliferation rate using the “proliferating cell nuclear antigen” (PCNA) content. Function of the mitochondria was evaluated by its oxygen consumption during respiratory states 3 and 4, its respiratory control ratio (RCR), its membrane potential, as well as its osmotic swelling. We also measured serum levels of aminotransferases. The results revealed an increased dry weight of the remaining liver, regeneration rate, and DNA content at 24 and 48 hours after hepatectomy. The hepatocyte proliferation rate was significantly higher among animals treated with hyperbaric oxygen therapy at 48 hours after surgery. There was no significant difference in aminotransferase levels. Mitochondrial respiration revealed reduced oxygen consumption in state 3 after 48 hours. These results demonstrated that hyperbaric oxygen stimulates hepatic regeneration at 24 and 48 hours after 70% hepatectomy. The effect of hyperbaric oxygen on hepatic tissue occurs without tissue damage and protects mitochondria after 48 hours. T HE PROCESS OF LIVER REGENERATION that takes place after tissue loss recruits fully differentiated hepatocytes into the proliferative cycle. Although adult liver hepatocytes rarely divide under normal conditions, they may be transformed from a quiescent to a prereplica- tion state, which is followed by DNA synthesis and mitosis, with cell division completing the sequence. 1–4 Hyperbaric oxygen therapy (HBO) is an increasingly utilized therapeu- tic method that employs inhalation of 100% oxygen at a pressure of more than one atmosphere in a hyperbaric chamber. 5,6 The most important effect of HBO treatment is tissue hyperoxygenation starting from oxygen dissolved in plasma. Extracellular matrix deposition, angiogenesis, epithelializa- tion, and bacterial phagocytosis require molecular oxygen for wound repair. The presence of O 2 is essential for lysine and proline hydroxylation, a fundamental step for collagen release by cells. Collagen maturation and binding increase linearly with the elevation of oxygen concentration in the environment. 5 In 1966, Karasewich et al 6 reported the increased survival of dogs treated with HBO after hepatic artery ligation. Brettschneider et al 7 used HBO to preserve liver grafts in humans. Mazariegos et al 8 published a study comparing the clinical course of children undergoing liver transplantation who were or were not treated with HBO following early hepatic artery thrombosis. There was no significant differ- ence in survival or in the rate of retransplantation. How- ever, in the cases that required retransplantation, the procedure was performed after a longer time and under From the Special Liver Transplantation Unit, Departments of Surgery and Anatomy (G.R.O., O.F., E.C.T., O.C., M.E.J.S., M.C.J.G., A.K.S.), and Pathology (S.Z.), Ribeirão Preto School of Medicine, University of São Paulo, São Paulo, Brazil. Supported by FAPESP and CNPq. Address reprint requests to Orlando de Castro e Silva, Pro- fessor, Departamento de Cirurgia e Anatomia, Faculdade de Medicina de Ribeirão Preto, Avenida Bandeirantes, 3.900 - CEP 14049-900 - Ribeirão Preto - SP - Brasil. E-mail: orlando@fmrp. usp.br © 2006 by Elsevier Inc. All rights reserved. 0041-1345/06/$–see front matter 360 Park Avenue South, New York, NY 10010-1710 doi:10.1016/j.transproceed.2006.06.066 Transplantation Proceedings, 38, 1947–1952 (2006) 1947