Role of angiotensin in the hepatic partial ischaemia-reperfusion injury

• Grant number: 15/10996-1
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: September 01, 2015
• End date: August 31, 2018
• Field of knowledge: Health Sciences - Medicine
• Principal Investigator: Márcia Regina Nagaoka
• Grantee: Raphael Manzato Petrolini
• Host Institution: Instituto de Saúde e Sociedade (ISS). Universidade Federal de São Paulo (UNIFESP). Campus Baixada Santista. Santos , SP, Brazil

Abstract

Ischemia-reperfusion injury is characterized by a period of ischemia, interruption of blood flow and lack of oxygen and nutrients to the cells, followed by restoration of flow and consequently the oxygenation in a process called reperfusion. Reperfusion increases the damage caused by ischemic period and this injury has a direct impact on organ viability. Many clinical settings, including hemorrhagic shock, trauma, liver resection and transplantation, involve this kind of injury and has been studied in the past decades. During ischemia, there is loss of balance between vasoactive mediators causing alteration in the hepatic microcirculation. During reperfusion, there is activation of Kupffer cells and subsequent synthesis of inflammatory cytokines, which further aggravates the changes in microcirculation, and production of reactive oxygen species and nitrogen, recruitment and infiltration of leukocytes, activation of the immune system, and many other effects that increase tissue damage. Cell death, as a final event to damage from ischemia and reperfusion may occur by necrosis or apoptosis and must be controlled, since it is responsible for post-surgical complications. The renin-angiotensin system comprises circulating angiotensinogen synthesized by the liver, which by the action of renin releases a decapeptide angiotensin I (AI). Angiotensin converting enzyme (ACE), in turn, converts AI to a biologically active product, angiotensin II (AII). There are two main types of receptors: Type I (AT1), and type II (AT2). Both are receptors with seven transmembrane domains, but have different pharmacological effects, and the AT1 is considered to be responsible for the main physiological actions of AII. The role of the AT2 receptor is under investigation. Third receptor, which was extensively studied recently, is the MAS receptor, but its role is still controversial. The involvement of MAS receptor in heart ischemia and reperfusion was reported and suggested that its blockade could be a new therapeutic strategy. Recently the role of AII in the cold ischemia, warm reperfusion ex vivo has been studied by our group and we demonstrated increased cell death in the presence of AII and promising results with consequent reduction of cell death when AII action has been blocked. Thus, this project aims to study the role of AII in an experimental model of warm ischemia partial (30-60 min) and reperfusion in vivo (1h, 6h and 24h).For this we will use the isolated liver perfusion system and to assess ischemia and reperfusion injury, biochemical markers will be analyzed, as release of enzymes marker of injury (AST, ALT), bromossulphalein clearance, oxygen consumption, bile secretion and release of glucose by the reperfused livers. Cell death will be assessed by histological analysis using Trypan blue exclusion, cell death by ELISA and cleaved caspase-3 using the Western blot technique. Western blot will also evaluated the role of kinin B1 and B2 receptors and angiotensin AT1 receptor and MAS. This study aims to better understand this injury so that future participation in morbidity and mortality after liver surgery is practically zero or at least controlled.(AU)