CD44 disruption attenuates murine hepatic ischemia/reperfusion injury

Liver ischaemia-reperfusion injury: a new understanding of the role of innate immunity

Liver ischaemia-reperfusion injury (LIRI), a local sterile inflammatory response driven by innate immunity, is one of the primary causes of early organ dysfunction and failure after liver transplantation. Cellular damage resulting from LIRI is an important risk factor not only for graft dysfunction but also for acute and even chronic rejection and exacerbates the shortage of donor organs for life-saving liver transplantation. Hepatocytes, liver sinusoidal endothelial cells and Kupffer cells, along with extrahepatic monocyte-derived macrophages, neutrophils and platelets, are all involved in LIRI. However, the mechanisms underlying the responses of these cells in the acute phase of LIRI and how these responses are orchestrated to control and resolve inflammation and achieve homeostatic tissue repair are not well understood. Technological advances allow the tracking of cells to better appreciate the role of hepatic macrophages and platelets (such as their origin and immunomodulatory and tissue-remodelling functions) and hepatic neutrophils (such as their selective recruitment, anti-inflammatory and tissue-repairing functions, and formation of extracellular traps and reverse migration) in LIRI. In this Review, we summarize the role of macrophages, platelets and neutrophils in LIRI, highlight unanswered questions, and discuss prospects for innovative therapeutic regimens against LIRI in transplant recipients.

Long Term Response to Circulating Angiogenic Cells, Unstimulated or Atherosclerotic Pre-Conditioned, in Critical Limb Ischemic Mice

Critical limb ischemia (CLI), the most severe form of peripheral artery disease, results from the blockade of peripheral vessels, usually correlated to atherosclerosis. Currently, endovascular and surgical revascularization strategies cannot be applied to all patients due to related comorbidities, and even so, most patients require re-intervention or amputation within a year. Circulating angiogenic cells (CACs) constitute a good alternative as CLI cell therapy due to their vascular regenerative potential, although the mechanisms of action of these cells, as well as their response to pathological conditions, remain unclear. Previously, we have shown that CACs enhance angiogenesis/arteriogenesis from the first days of administration in CLI mice. Also, the incubation ex vivo of these cells with factors secreted by atherosclerotic plaques promotes their activation and mobilization. Herein, we have evaluated the long-term effect of CACs administration in CLI mice, whether pre-stimulated or not with atherosclerotic factors. Remarkably, mice receiving CACs and moreover, pre-stimulated CACs, presented the highest blood flow recovery, lower progression of ischemic symptoms, and decrease of immune cells recruitment. In addition, many proteins potentially involved, like CD44 or matrix metalloproteinase 9 (MMP9), up-regulated in response to ischemia and decreased after CACs administration, were identified by a quantitative proteomics approach. Overall, our data suggest that pre-stimulation of CACs with atherosclerotic factors might potentiate the regenerative properties of these cells in vivo.

Protective role of heme oxygenase-1 in fatty liver ischemia-reperfusion injury

Ischemia-reperfusion (IR) injury is a kind of injury resulting from the restoration of the blood supply after blood vessel closure during liver transplantation and is the main cause of graft failure. The pathophysiological mechanisms of hepatic IR include a variety of oxidative stress responses. Hepatic IR is characterized by ischemia and hypoxia inducing oxidative stress, immune response and apoptosis. Fat-denatured livers are also used as donors due to the lack of liver donors. Fatty liver is less tolerant to IR than normal liver. Heme oxygenase (HO) is an enzyme that breaks down hemoglobin to bilirubin, ferrous iron and carbon monoxide (CO). Inducible HO subtype HO-1 is an important protective molecule in mammalian cells used to improve acute and chronic liver injury owing to its characteristic anti-inflammatory and anti-apoptotic qualities. HO-1 degrades heme, and its reaction product CO has been shown to reduce hepatic IR injury and increase the survival rate of grafts. As an induced form of HO, HO-1 also exerts a protective effect against liver IR injury and may be useful as a new strategy of ameliorating this kind of damage. This review summarizes the protective effects of HO-1 in liver IR injury, especially in fatty liver.

Neutrophils: a cornerstone of liver ischemia and reperfusion injury

Ischemia-reperfusion injury (IRI) is the main cause of morbidity and mortality due to graft rejection after liver transplantation. During IRI, an intense inflammatory process occurs in the liver. This hepatic inflammation is initiated by the ischemic period but occurs mainly during the reperfusion phase, and is characterized by a large neutrophil recruitment to the liver. Production of cytokines, chemokines, and danger signals results in activation of resident hepatocytes, leukocytes, and Kupffer cells. The role of neutrophils as the main amplifiers of liver injury in IRI has been recognized in many publications. Several studies have shown that elimination of excessive neutrophils or inhibition of their function leads to reduction of liver injury and inflammation. However, the mechanisms involved in neutrophil recruitment during liver IRI are not well known. In addition, the molecules necessary for this type of migration are poorly defined, as the liver presents an atypical sinusoidal vasculature in which the classical leukocyte migration paradigm only partially applies. This review summarizes recent advances in neutrophil-mediated liver damage, and its application to liver IRI. Basic mechanisms of activation of neutrophils and their unique mechanisms of recruitment into the liver vasculature are discussed. In particular, the role of danger signals, adhesion molecules, chemokines, glycosaminoglycans (GAGs), and metalloproteinases is explored. The precise definition of the molecular events that govern the recruitment of neutrophils and their movement into inflamed tissue may offer new therapeutic alternatives for hepatic injury by IRI and other inflammatory diseases of the liver.

CCR2 dependent neutrophil activation and mobilization rely on TLR4-p38 axis during liver ischemia-reperfusion injury

Liver ischemia-reperfusion injury (IRI) is a common clinical problem in which neutrophil recruitment is an essential event. Our previous study revealed the important role of C-C motif chemokine receptor 2 (CCR2) in neutrophils during liver IRI. The aim of the present study was to further investigate the underlying mechanisms mediating the changes in CCR2 expression in neutrophils during this pathophysiological process. Herein, we found that TLR4 ablation reduced neutrophil mobilization from the bone marrow and the subsequent infiltration into the liver during liver IRI; neutrophil-derived CCR2 expression was also repressed. In addition, neutrophil mobilization was dependent on CCR2 expression in neutrophils, which in turn relied on activation of the TLR4-p38 axis during liver IRI. In conclusion, neutrophil-derived CCR2 expression regulates neutrophil mobilization from the bone marrow and infiltration into the liver, which requires activation of the TLR4-p38 axis during liver IRI.

Oral administration of cilostazol improves survival rate after rat liver ischemia/reperfusion injury

BACKGROUND

Cilostazol is a type III phosphodiesterase inhibitor used to treat the symptoms of intermittent claudication. Recent studies have shown that cilostazol decreases ischemia/reperfusion (I/R) injury in several organs.

MATERIALS AND METHODS

We evaluated the effects of cilostazol in a rat model of liver I/R injury. Thirty male Wistar rats with liver I/R injury were divided into a cilostazol or saline (control) group (n = 15 each). Each rat was orally administered cilostazol or saline for 3 d before I/R injury. Liver I/R injury was induced via 1 h of warm ischemia of the median and left lateral liver lobes, followed by 3 h of reperfusion. The rats were then euthanized. Serum aspartate aminotransferase, alanine aminotransferase, interleukin (IL)-1β, IL-6, and tumor necrosis factor-α levels were measured. The Mann-Whitney U test was used to compare the differences between the treatment groups. Histologic examination was performed on the liver tissues. We also conducted a survival study to confirm the effect of cilostazol on the mortality rate in rats. For the survival study, a liver I/R injury model with an ischemia time of 1.5 h was used, and the rats were observed for 1 wk.

RESULTS

Serum aspartate aminotransferase, alanine aminotransferase, IL-1β, and IL-6 levels were significantly lower in the cilostazol group than in the saline group. Treatment with cilostazol significantly improved pathological findings associated with liver I/R injury and increased survival rate compared to that in controls.

CONCLUSIONS

Cilostazol reduced mortality and alleviated the effects of liver I/R injury in Wistar rats.

Role of the endothelial surface layer in neutrophil recruitment

Neutrophil recruitment in most tissues is limited to postcapillary venules, where E- and P-selectins are inducibly expressed by venular endothelial cells. These molecules support neutrophil rolling via binding of PSGL-1 and other ligands on neutrophils. Selectins extend ≤ 38 nm above the endothelial plasma membrane, and PSGL-1 extends to 50 nm above the neutrophil plasma membrane. However, endothelial cells are covered with an ESL composed of glycosaminoglycans that is ≥ 500 nm thick and has measurable resistance against compression. The neutrophil surface is also covered with a surface layer. These surface layers would be expected to completely shield adhesion molecules; thus, neutrophils should not be able to roll and adhere. However, in the cremaster muscle and in many other models investigated using intravital microscopy, neutrophils clearly roll, and their rolling is easily and quickly induced. This conundrum was thought to be resolved by the observation that the induction of selectins is accompanied by ESL shedding; however, ESL shedding only partially reduces the ESL thickness (to 200 nm) and thus is insufficient to expose adhesion molecules. In addition to its antiadhesive functions, the ESL also presents neutrophil arrest-inducing chemokines. ESL heparan sulfate can also bind L-selectin expressed by the neutrophils, which contributes to rolling and arrest. We conclude that ESL has both proadhesive and antiadhesive functions. However, most previous studies considered either only the proadhesive or only the antiadhesive effects of the ESL. An integrated model for the role of the ESL in neutrophil rolling, arrest, and transmigration is needed.

Rodent models of hepatic ischemia-reperfusion injury: time and percentage-related pathophysiological mechanisms

Ischemia and reperfusion (IR) injury remains one of the major problems in liver surgery and transplantation, which determines the viability of the hepatic tissue after resection and of the grafted organ. This review aims to elucidate the mechanisms involved in IR injury of the liver in rodent experimental studies and the preventative methods and pharmacologic agents that have been applied. Many time- and percentage-related liver IR injury rodent models have been used to examine the pathophysiological mechanisms and the parameters implicated with different morbidity, mortality, and pathology findings. The most preferred experimental rodent model of liver IR is the induction of 70% IR for 45 min, which is associated with almost 100% survival. In this model, plasma levels of several parameters such as alanine transaminase, aspartate aminotransferase, gamma-glutamyltransferase, endothelin-1, malonodialdehyde, tumor necrosis factor α, interleukin 1b, inducible nitric oxide synthase, and caspases are increased. The increase of caspases is associated with the initiation of hepatic cellular apoptosis. The main injuries observed 24 h after reperfusion are nuclear pyknosis, cytoplasmic hypereosinophilia, severe necrosis, and loss of intercellular borders. Both ischemic pre- and post-conditioning preventative methods and pharmacologic agents are successfully applied to alleviate the IR injuries. The selection of the time- and percentage-related liver IR injury rodent model and the potential preventative method should be related to the clinical question being answered.

The role of neutrophils in the development of liver diseases

Liver disease encompasses a wide variety of liver conditions, including liver failure, liver cirrhosis and a spectrum of acute and chronic hepatitis, such as alcoholic, fatty, drug, viral and chronic hepatitis. Liver injury is a primary causative factor in liver disease; generally, these factors include direct liver damage and immune-mediated liver injury. Neutrophils (also known as neutrophilic granulocytes or polymorphonuclear leukocytes (PMNs)) are the most abundant circulating white blood cell type in humans, and PMNs are a major innate immune cell subset. Inappropriate activation and homing of neutrophils to the microvasculature contributes to the pathological manifestations of many types of liver disease. This review summarizes novel concepts of neutrophil-mediated liver injury that are based on current clinical and animal model studies.

The role of neutrophils in the development of liver diseases

Liver disease encompasses a wide variety of liver conditions, including liver failure, liver cirrhosis and a spectrum of acute and chronic hepatitis, such as alcoholic, fatty, drug, viral and chronic hepatitis. Liver injury is a primary causative factor in liver disease; generally, these factors include direct liver damage and immune-mediated liver injury. Neutrophils (also known as neutrophilic granulocytes or polymorphonuclear leukocytes (PMNs)) are the most abundant circulating white blood cell type in humans, and PMNs are a major innate immune cell subset. Inappropriate activation and homing of neutrophils to the microvasculature contributes to the pathological manifestations of many types of liver disease. This review summarizes novel concepts of neutrophil-mediated liver injury that are based on current clinical and animal model studies.