Lipid peroxidation as molecular mechanism of liver cell injury during reperfusion after ischemia

Ferroptosis and Intrinsic Drug-induced Liver Injury by Acetaminophen and Other Drugs: A Critical Evaluation and Historical Perspective

Drug-induced hepatotoxicity is a significant clinical issue worldwide. Given the limited treatment options for these liver injuries, understanding the mechanisms and modes of cell death is crucial for identifying novel therapeutic targets. For the past 60 years, reactive oxygen species and iron-dependent lipid peroxidation (LPO) have been hypothesized to be involved in many models of acute drug-induced liver injury. However, this mechanism of toxicity was largely abandoned when apoptosis became the primary focus of cell death research. More recently, ferroptosis-a novel, non-apoptotic form of cell death-was identified in NRAS-mutant HT-1080 fibrosarcoma cells exposed to erastin and other NRLs. Ferroptosis is characterized by glutathione depletion and the impairment of glutathione peroxidase 4 activity, which hinders the detoxification of lipid hydroperoxides. These hydroperoxides then serve as substrates for iron-dependent LPO propagation. This cell death mechanism is now receiving widespread attention, extending well beyond its original identification in cancer research, including in the field of drug-induced liver injury. However, concerns arise when such mechanisms are applied across different cell types and disease states without sufficient validation. This review critically evaluated the historical evidence for iron-dependent LPO as a mechanism of drug-induced hepatotoxicity and explored how these earlier findings have led to the current concept of ferroptosis. Overall, the published data support the idea that multi-layered endogenous antioxidant defense mechanisms in the liver limit the occurrence of pathophysiologically relevant LPO under normal conditions. Only when these defense mechanisms are severely compromised does ferroptosis become a significant mode of drug-induced cell death.

Ferroptosis: action and mechanism of chemical/drug-induced liver injury

Drug-induced liver injury (DILI) is characterized by hepatocyte injury, cholestasis injury, and mixed injury. The liver transplantation is required for serious clinical outcomes such as acute liver failure. Current studies have found that many mechanisms were involved in DILI, such as mitochondrial oxidative stress, apoptosis, necroptosis, autophagy, ferroptosis, etc. Ferroptosis occurs when hepatocytes die from iron-dependent lipid peroxidation and plays a key role in DILI. After entry into the liver, where some drugs or chemicals are metabolized, they convert into hepatotoxic substances, consume reduced glutathione (GSH), and decrease the reductive capacity of GSH-dependent GPX4, leading to redox imbalance in hepatocytes and increase of reactive oxygen species (ROS) and lipid peroxidation level, leading to the undermining of hepatocytes; some drugs facilitated the autophagy of ferritin, orchestrating the increased ion level and ferroptosis. The purpose of this review is to summarize the role of ferroptosis in chemical- or drug-induced liver injury (chemical/DILI) and how natural products inhibit ferroptosis to prevent chemical/DILI.

Programmed cell death, from liver Ischemia-Reperfusion injury perspective: An overview

Liver ischemia-reperfusion injury (LIRI) commonly occurs in liver resection, liver transplantation, shock, and other hemorrhagic conditions, resulting in profound local and systemic effects via associated inflammatory responses and hepatic cell death. Hepatocyte death is a significant component of LIRI and its mechanism was previously thought to be limited to apoptosis and necrosis. With the discovery of novel types of programmed cell death (PCD), necroptosis, ferroptosis, pyroptosis, autophagy, NETosis, and parthanatos have been shown to be involved in LIRI. Understanding the mechanisms underlying cell death following LIRI is indispensable to mitigating the widespread effects of LIRI. Here, we review the roles of different PCD and discuss potential therapy in LIRI.

Response of the nuclear xenobiotic receptors to alleviate glyphosate-based herbicide-induced nephrotoxicity in weaned piglets

Glyphosate-based herbicides (GBHs) are widely used worldwide. Glyphosate (GLP) is the main active component of GBHs. The presence of GBH residues in the environment has led to the exposure of animals to GBHs, but the mechanisms of GBH-induced nephrotoxicity are not clear. This study investigated the effects of GBHs on piglet kidneys. Twenty-eight healthy female hybrid weaned piglets (Duroc × Landrace × Yorkshire) with an average weight of 12.24 ± 0.61 kg were randomly divided into four treatment groups (n=7 piglets/group) that were supplemented with Roundup® (equivalent to GLP concentrations of 0, 10, 20, and 40 mg/kg) for a 35-day feeding trial. The results showed that the kidneys in the 40-mg/kg GLP group suffered slight damage. Roundup® significantly decreased the activity of catalase (CAT) (P=0.005) and increased the activity of superoxide dismutase (SOD) (P=0.029). Roundup® increased the level of cystatin-C (Cys-C) in the plasma (linear, P=0.002 and quadratic, P=0.015). The levels of neutrophil gelatinase-associated lipocalin (NGAL) in plasma increased linearly (P=0.007) and quadratically (P=0.003) as the dose of GLP increased. The mRNA expression of intercellular cell adhesion molecule-1 (ICAM-1) in the 20-mg/kg GLP group was increased significantly (P<0.05). There was a significant increase in the mRNA levels of pregnenolone X receptor (PXR), constitutive androstane receptor (CAR), and uridine diphosphate glucuronosyltransferase 1A3 (UGT1A3) (P<0.05). Our findings found that kidney nuclear xenobiotic receptors (NXRs) may play an important role in defense against GBHs.

Recommendations for the use of the acetaminophen hepatotoxicity model for mechanistic studies and how to avoid common pitfalls

Acetaminophen (APAP) is a widely used analgesic and antipyretic drug, which is safe at therapeutic doses but can cause severe liver injury and even liver failure after overdoses. The mouse model of APAP hepatotoxicity recapitulates closely the human pathophysiology. As a result, this clinically relevant model is frequently used to study mechanisms of drug-induced liver injury and even more so to test potential therapeutic interventions. However, the complexity of the model requires a thorough understanding of the pathophysiology to obtain valid results and mechanistic information that is translatable to the clinic. However, many studies using this model are flawed, which jeopardizes the scientific and clinical relevance. The purpose of this review is to provide a framework of the model where mechanistically sound and clinically relevant data can be obtained. The discussion provides insight into the injury mechanisms and how to study it including the critical roles of drug metabolism, mitochondrial dysfunction, necrotic cell death, autophagy and the sterile inflammatory response. In addition, the most frequently made mistakes when using this model are discussed. Thus, considering these recommendations when studying APAP hepatotoxicity will facilitate the discovery of more clinically relevant interventions.

Ferroptosis and Acetaminophen Hepatotoxicity: Are We Going Down Another Rabbit Hole?

Acetaminophen (APAP) hepatotoxicity is the most frequent cause of acute liver failure in the US. The mechanisms of APAP-induced liver injury have been under extensive investigations for decades, and many key events of this necrotic cell death are known today. Initially, two opposing hypotheses for cell death were proposed: reactive metabolite and protein adduct formation versus reactive oxygen and lipid peroxidation (LPO). In the end, both mechanisms were reconciled, and it is now generally accepted that the toxicity starts with formation of reactive metabolites that, after glutathione depletion, bind to cellular proteins, especially on mitochondria. This results in a mitochondrial oxidant stress, which requires amplification through a mitogen-activated protein kinase cascade, leading ultimately to enough reactive oxygen and peroxynitrite formation to trigger the mitochondrial membrane permeability transition and cell death. However, the earlier rejected LPO hypothesis seems to make a comeback recently under a different name: ferroptosis. Therefore, the objective of this review was to critically evaluate the available information about intracellular signaling mechanisms of APAP-induced cell death and those of ferroptosis. Under pathophysiologically relevant conditions, there is no evidence for quantitatively enough LPO to cause cell death, and thus APAP hepatotoxicity is not caused by ferroptosis. However, the role of mitochondria-localized minor LPO remains to be further investigated.

Monoacylglycerol Acyltransferase 1 Knockdown Exacerbates Hepatic Ischemia/Reperfusion Injury in Mice With Hepatic Steatosis

Nonalcoholic fatty liver disease (NAFLD) is becoming the most common indication for liver transplantation. The growing prevalence of NAFLD not only increases the demand for liver transplantation, but it also limits the supply of available organs because steatosis predisposes grafts to ischemia/reperfusion injury (IRI) and many steatotic grafts are discarded. We have shown that monoacylglycerol acyltransferase (MGAT) 1, an enzyme that converts monoacylglycerol to diacylglycerol, is highly induced in animal models and patients with NAFLD and is an important mediator in NAFLD-related insulin resistance. Herein, we sought to determine whether Mogat1 (the gene encoding MGAT1) knockdown in mice with hepatic steatosis would reduce liver injury and improve liver regeneration following experimental IRI. Antisense oligonucleotides (ASO) were used to knockdown the expression of Mogat1 in a mouse model of NAFLD. Mice then underwent surgery to induce IRI. We found that Mogat1 knockdown reduced hepatic triacylglycerol accumulation, but it unexpectedly exacerbated liver injury and mortality following experimental ischemia/reperfusion surgery in mice on a high-fat diet. The increased liver injury was associated with robust effects on the hepatic transcriptome following IRI including enhanced expression of proinflammatory cytokines and chemokines and suppression of enzymes involved in intermediary metabolism. These transcriptional changes were accompanied by increased signs of oxidative stress and an impaired regenerative response. We have shown that Mogat1 knockdown in a mouse model of NAFLD exacerbates IRI and inflammation and prolongs injury resolution, suggesting that Mogat1 may be necessary for liver regeneration following IRI and that targeting this metabolic enzyme will not be an effective treatment to reduce steatosis-associated graft dysfunction or failure.

Hyperoside Attenuates Hepatic Ischemia-Reperfusion Injury by Suppressing Oxidative Stress and Inhibiting Apoptosis in Rats

PURPOSE

Hepatic ischemia-reperfusion (IR) injury is a serious complication of many clinical conditions, which may lead to liver or multiple organ failure. Hyperoside, a flavonoid compound, has been reported to protect against myocardial and cerebral injury induced by IR. This study aimed to investigate the protective effects of hyperoside on hepatic IR injury in rats.

METHODS

Using the 70% hepatic IR injury model, we divided 32 male Wistar rats into 4 groups (n = 8): sham-operated, IR+saline (saline/p.o.), IR+vehicle (carboxy methyl cellulose/p.o.), and IR+hyperoside (50 mg/kg/d/p.o.). At 24 hours after reperfusion, blood and liver tissue were collected. The effects of hyperoside on hepatic IR injury were assessed through tests of serum transaminase, hepatic histopathology, and measurement of markers of oxidative stress and apoptosis.

RESULTS

Pretreatment with hyperoside protected the liver from IR injury by a reduction in serum aspartate aminotransferase/alanine aminotransferase levels and a decrease in the severity of histologic changes. Hyperoside treatment also decreased the activity of malondialdehyde, increased the activities of superoxide dismutase and glutathione peroxidase, up-regulated the expression of heme oxygenase 1 and NAD(P)H:quinone oxidoreductase 1, and reduced the apoptotic index after IR injury. A decrease in the expression of caspase-3 and an increase in the ratio of B cell lymphoma 2 to B cell lymphoma 2-associated X also were observed.

CONCLUSION

Hyperoside has a protective effect on hepatic IR injury in rats, which may be due to its antioxidant and antiapoptotic properties.

Emerging and established modes of cell death during acetaminophen-induced liver injury

Acetaminophen (APAP)-induced liver injury is an important clinical and toxicological problem. Understanding the mechanisms and modes of cell death are vital for the development of therapeutic interventions. The histological and clinical features of APAP hepatotoxicity including cell and organelle swelling, karyolysis, and extensive cell contents release lead to the characterization of the cell death as oncotic necrosis. However, the more recent identification of detailed signaling mechanisms of mitochondrial dysfunction, the amplification mechanisms of mitochondrial oxidant stress and peroxynitrite formation by a mitogen-activated protein kinase cascade, mechanisms of the mitochondrial permeability transition pore opening and nuclear DNA fragmentation as well as the characterization of the sterile inflammatory response suggested that the mode of cell death is better termed programmed necrosis. Additional features like mitochondrial Bax translocation and cytochrome c release, mobilization of lysosomal iron and the activation of receptor-interacting protein kinases and the inflammasome raised the question whether other emerging modes of cell death such as apoptosis, necroptosis, ferroptosis and pyroptosis could also play a role. The current review summarizes the key mechanisms of APAP-induced liver injury and compares these with key features of the newly described modes of cell death. Based on the preponderance of experimental and clinical evidence, the mode of APAP-induced cell death should be termed programmed necrosis; despite some overlap with other modes of cell death, APAP hepatotoxicity does not fulfill the characteristics of either apoptosis, necroptosis, ferroptosis, pyroptosis or autophagic cell death.

Upregulation of Carbonyl Reductase 1 by Nrf2 as a Potential Therapeutic Intervention for Ischemia/ Reperfusion Injury during Liver Transplantation

Currently, liver transplantation is the only available remedy for patients with end-stage liver disease. Conservation of transplanted liver graft is the most important issue as it directly related to patient survival. Carbonyl reductase 1 (CBR1) protects cells against oxidative stress and cell death by inactivating cellular membrane-derived lipid aldehydes. Ischemia-reperfusion (I/R) injury during living-donor liver transplantation is known to form reactive oxygen species. Thus, the objective of this study was to investigate whether CBR1 transcription might be increased during liver I/R injury and whether such increase might protect liver against I/R injury. Our results revealed that transcription factor Nrf2 could induce CBR1 transcription in liver of mice during I/R. Pre-treatment with sulforaphane, an activator of Nrf2, increased CBR1 expression, decreased liver enzymes such as aspartate aminotransferase and alanine transaminase, and reduced I/R-related pathological changes. Using oxygenglucose deprivation and recovery model of human normal liver cell line, it was found that oxidative stress markers and lipid peroxidation products were significantly lowered in cells overexpressing CBR1. Conversely, CBR1 knockdown cells expressed elevated levels of oxidative stress proteins compared to the parental cell line. We also observed that Nrf2 and CBR1 were overexpressed during liver transplantation in clinical samples. These results suggest that CBR1 expression during liver I/R injury is regulated by transcription factor Nrf2. In addition, CBR1 can reduce free radicals and prevent lipid peroxidation. Taken together, CBR1 induction might be a therapeutic strategy for relieving liver I/R injury during liver transplantation.

Oxidative Stress and Acute Hepatic Injury

Reactive oxygen species have long been implicated in the pathophysiology of acute liver injury. However, the translation of these findings to the clinic and the development of therapeutic agents have been slow mainly due to the poor mechanistic understanding of the pathophysiology and the many indirect approaches used to characterize the role of oxidant stress in liver injury. The current review discusses in depth the sources of reactive oxygen, the oxidants involved and the impact of this oxidant stress in the mechanism of cell death in 3 different clinically relevant acute liver injury models.

Alpha-lipoic acid protects mice against concanavalin A-induced hepatitis by modulating cytokine secretion and reducing reactive oxygen species generation

BACKGROUND

Alpha-lipoic acid (α-LA), which exits in almost all types of prokaryotic and eukaryotic cells, is a key regulator of energy metabolism in mitochondria. This study was designed to explore the protective effect of α-LA against concanavalin A (Con A)-induced hepatitis in mice and explore the potential mechanism.

METHODS

Acute autoimmune hepatitis was induced by intravenous (IV) injection of Con A (15mg/kg) in C57BL/6 mice. α-LA (100mg/kg) was administered four days before Con A injection. Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) and histopathological change of the liver tissue were measured. Serum cytokine TNF-α, IL-6, IFN-γ and IL-10 were detected by ELISA. The mRNA levels of these inflammatory cytokines in the liver were detected by RT-PCR. Malondialdehyde (MDA), myeloperoxidase (MPO), superoxide dismutase (SOD) and reduced/oxidized glutathione (GSH/GSSG) in liver were determined using commercial kits. Phosphorylated NF-κB p65, IκBα and phosphorylated MAPK were measured by Western blot.

RESULTS

Con A injection induced severe immune responses and extensive hepatocellular apoptosis within 12h. Pretreatment of α-LA markedly reduced the serum ALT and AST activity and the increase of plasma TNF-α, IL-6, IFN-γ and IL-10. In addition, α-LA pretreatment decreased the tissue MPO activity and lipid peroxidation, but increased SOD and GSH levels. α-LA inhibited the phosphorylation of NF-κB p65, IκBα and JNK.

CONCLUSION

Pretreatment of α-LA markedly attenuated Con A-induced hepatitis by modulating cytokine secretion and reducing reactive oxygen species generation.

Hearing, reactive metabolite formation, and oxidative stress in cochleae after a single acute overdose of acetaminophen: an in vivo study

CONTEXT

Although the liver is the primary target organ in acetaminophen (APAP) toxicity, other organs are affected. Previous data suggested that chronic APAP abuse can be ototoxic and the mechanism involves APAP-induced oxidative stress and reactive metabolite (N-acetyl-p-benzoquinone imine, NAPQI)-induced endoplasmic reticulum stress. However, the effect of a single acute overdose on hearing has not been tested.

OBJECTIVES

To determine if a single acute APAP overdose causes hearing damage, and to explore possible mechanisms of APAP ototoxicity.

MATERIALS AND METHODS

Male C57BL/6 J mice were treated with a single human-relevant overdose of APAP (300 mg APAP per kg bodyweight). Blood, liver and cochleae were harvested at 0, 2, 6 and 24 h post-APAP. In some mice, auditory brainstem responses (ABRs) to a range of frequencies were measured at 24 h. The furosemide plus kanamycin (FS/K) model of drug ototoxicity was used as a positive control for hearing loss. NAPQI formation after APAP was assessed by measuring glutathione depletion and covalent protein binding, and oxidative stress was assessed by measuring glutathione disulfide.

RESULTS

There was no evidence of reactive metabolite formation or hearing loss after a single overdose of APAP at a clinically relevant dose. However, there was a transient increase in oxidative stress.

DISCUSSION

Although a single acute overdose was not ototoxic, there was evidence of oxidative stress which may support a role for oxidative stress in hearing loss due to chronic APAP abuse.

CONCLUSION

A single human-relevant acute overdose of APAP causes transient oxidative stress in cochleae but not hearing loss.

The relationship between plasma lipid peroxidation products and primary graft dysfunction after lung transplantation is modified by donor smoking and reperfusion hyperoxia

BACKGROUND

Donor smoking history and higher fraction of inspired oxygen (FIO2) at reperfusion are associated with primary graft dysfunction (PGD) after lung transplantation. We hypothesized that oxidative injury biomarkers would be elevated in PGD, with higher levels associated with donor exposure to cigarette smoke and recipient hyperoxia at reperfusion.

METHODS

We performed a nested case-control study of 72 lung transplant recipients from the Lung Transplant Outcomes Group cohort. Using mass spectroscopy, F2-isoprostanes and isofurans were measured in plasma collected after transplantation. Cases were defined in 2 ways: grade 3 PGD present at day 2 or day 3 after reperfusion (severe PGD) or any grade 3 PGD (any PGD).

RESULTS

There were 31 severe PGD cases with 41 controls and 35 any PGD cases with 37 controls. Plasma F2-isoprostane levels were higher in severe PGD cases compared with controls (28.6 pg/ml vs 19.8 pg/ml, p = 0.03). Plasma F2-isoprostane levels were higher in severe PGD cases compared with controls (29.6 pg/ml vs 19.0 pg/ml, p = 0.03) among patients reperfused with FIO2 >40%. Among recipients of lungs from donors with smoke exposure, plasma F2-isoprostane (38.2 pg/ml vs 22.5 pg/ml, p = 0.046) and isofuran (66.9 pg/ml vs 34.6 pg/ml, p = 0.046) levels were higher in severe PGD compared with control subjects.

CONCLUSIONS

Plasma levels of lipid peroxidation products are higher in patients with severe PGD, in recipients of lungs from donors with smoke exposure, and in recipients exposed to higher Fio2 at reperfusion. Oxidative injury is an important mechanism of PGD and may be magnified by donor exposure to cigarette smoke and hyperoxia at reperfusion.

Iron-induced oxidative rat liver injury after non-heart-beating warm ischemia is mediated by tumor necrosis factor α and prevented by deferoxamine

This study investigated iron-induced injury after warm ischemia in a non-heart-beating (NHB) rat liver model and the effects of deferoxamine (DFO). Livers from heart-beating (HB) rats or rats that were NHB for 60 minutes were stored in University of Wisconsin solution for 5 hours at 4°C [cold storage (CS)] and then were subjected to 2 hours of machine reperfusion (MRP) at 37°C. Three NHB groups were compared: (1) no DFO, (2) DFO 30 minutes before cardiac arrest and during CS and MRP, and (3) DFO during CS and MRP. Aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) levels in the NHB perfusate were significantly elevated (P < 0.01) in comparison with levels in HB controls after CS and MRP. After CS, the levels of iron and tumor necrosis factor α (TNF-α) were 0.077 ± 0.007 μmol/g and 151 ± 26 pg/g, respectively, in the NHB group and 0.022 ± 0.004 μmol/g and 17 ± 7 pg/g, respectively, in the HB group (P < 0.01). After MRP, LDH significantly correlated with iron (R(2)  = 0.81, P < 0.01). The DFO pretreatment of NHB donors decreased AST (7.3 ± 0.8 versus 4.0 ± 0.5 U/g of liver, P < 0.05) and LDH (42.5 ± 4.1 versus 20.4 ± 2.5 U/g of liver, P < 0.05) with 2 hours of MRP and increased bile flow during MRP (142 ± 34 versus 240 ± 18 μL/g, P < 0.05). It also reduced the levels of iron (0.077 ± 0.007 versus 0.050 ± 0.008 μmol/g, P < 0.05) and TNF-α (151 ± 26 versus 51 ± 13 pg/g, P < 0.05) after CS and the levels of lipid peroxidation products F2-isoprostane (149 ± 11 versus 99 ± 10 ng/g, P < 0.05) and malondialdehyde (1.58 ± 0.1 versus 1.14 ± 0.08 μmol/g, P < 0.05) after MRP. In conclusion, iron-initiated oxidative stress is likely involved in NHB donor liver injury, and importantly, DFO pretreatment reduces liver damage.

The effect of RHIZOMA COPTIDIS and COPTIS CHINENSIS aqueous extract on radiation-induced skin injury in a rat model

BACKGROUND

Radiation-induced skin injury is a common complication of radiotherapy. The RHIZOMA COPTIDIS and COPTIS CHINENSIS aqueous extract (RCE) can ameliorate radiation-induced skin injury in our clinical observation. But, the protective mechanism of RHIZOMA COPTIDIS and COPTIS CHINENSIS in radiation-induced skin injury remains unclear.

METHODS

In this experiment, we developed a radiation-induced skin injury rat model to study the mechanism. The animals were randomly divided into control group, treatment group, radiation group, and treatment and radiation group. 5 rats in each group were separately executed on 2 d and 49 d post-radiation. The semi-quantitative skin injury score was used to measure skin reactions by unblinded observers, and hematoxylin and eosin staining was used to evaluate the damage areas by irradiation. The MDA content, SOD activity of skin and serum were measured to detect the oxidative stress.

RESULTS

Acute skin reactions were caused by a single dose of 45 Gy of β-ray irradiation, and the skin injury could be found in all rats receiving irradiation based on the observation of HE staining of skin at different time-points, while RCE could significantly ameliorate those changes. The MDA content in serum and skin of control rats was 4.13±0.12 mmol/ml and 4.95±0.35 mmol/mgprot on 2 d post-radiation. The rats receiving radiation showed an increased content of MDA (5.54±0.21 mmol/ml and 7.10±0.32 mmol/mgprot), while it was 4.57±0.21 mmol/ml and 5.95±0.24 mmol/mgprot after treated with RCE (p<0.05). Similar changes of the MDA content could be seen on 49 d post-radiation. However, the SOD activity of rats receiving radiation decreased compared with control group on both time-points, which was inhibited by RCE (p<0.05). Meanwhile, no valuable changes could be found between control group and treatment group on 2 d and 49 d.

CONCLUSIONS

Our study provides evidences for the radioprotective role of RCE against radiation-induced skin damage in rats by modulating oxidative stress in skin, which may be a useful therapy for radiation-induced skin injury.

Models of drug-induced liver injury for evaluation of phytotherapeutics and other natural products

Extracts from medicinal plants, many of which have been used for centuries, are increasingly tested in models of hepatotoxicity. One of the most popular models to evaluate the hepatoprotective potential of natural products is acetaminophen (APAP)-induced liver injury, although other hepatotoxicity models such as carbon tetrachloride, thioacetamide, ethanol and endotoxin are occasionally used. APAP overdose is a clinically relevant model of drug-induced liver injury. Critical mechanisms and signaling pathways, which trigger necrotic cell death and sterile inflammation, are discussed. Although there is increasing understanding of the pathophysiology of APAP-induced liver injury, the mechanism is complex and prone to misinterpretation, especially when unknown chemicals such as plant extracts are tested. This review discusses the fundamental aspects that need to be considered when using this model, such as selection of the animal species or in vitro system, timing and dose-responses of signaling events, metabolic activation and protein adduct formation, the role of lipid peroxidation and apoptotic versus necrotic cell death, and the impact of the ensuing sterile inflammatory response. The goal is to enable researchers to select the appropriate model and experimental conditions for testing of natural products that will yield clinically relevant results and allow valid interpretations of the pharmacological mechanisms.

Breath pentane as a potential biomarker for survival in hepatic ischemia and reperfusion injury--a pilot study

Background

Exhaled pentane, which is produced as a consequence of reactive oxygen species-mediated lipid peroxidation, is a marker of oxidative stress. Propofol is widely used as a hypnotic agent in intensive care units and the operating room. Moreover, this agent has been reported to inhibit lipid peroxidation by directly scavenging reactive oxygen species. In this study, using a porcine liver ischemia-reperfusion injury model, we have evaluated the hypothesis that high concentrations of breath pentane are related to adverse outcome and that propofol could reduce breath pentane and improve liver injury and outcome in swine in this situation.

Methodology/Principal Findings

Twenty male swine were assigned to two groups: propofol (n = 10) and chloral hydrate groups (n = 10). Hepatic ischemia was induced by occluding the portal inflow vessels. Ischemia lasted for 30 min, followed by reperfusion for 360 min. Exhaled and blood pentane concentrations in the chloral hydrate group markedly increased 1 min after reperfusion and then decreased to baseline. Breath and blood pentane concentrations in the propofol group increased 1 min after reperfusion but were significantly lower than in the chloral hydrate group. A negative correlation was found between breath pentane levels and survival in the chloral hydrate group. The median overall survival was 251 min after reperfusion (range 150–360 min) in the chloral hydrate group. All of the swine were alive in the propofol group.

Conclusions

Monitoring of exhaled pentane may be useful for evaluating the severity of hepatic ischemia-reperfusion injury and aid in predicting the outcome; propofol may improve the outcome in this situation.

Current strategies to minimize hepatic ischemia-reperfusion injury by targeting reactive oxygen species

Ischemia-reperfusion is a major component of injury in vascular occlusion both during liver surgery and during liver transplantation. The pathophysiology of hepatic ischemia-reperfusion includes a number of mechanisms including oxidant stress that contribute to various degrees to the overall organ damage. A large volume of recent research has focused on the use of antioxidants to ameliorate this injury, although results in experimental models have not translated well to the clinic. This review focuses on critical sources and mediators of oxidative stress during hepatic ischemia-reperfusion, the status of current antioxidant interventions, and emerging mechanisms of protection by preconditioning. While recent advances in regulation of antioxidant systems by Nrf2 provide interesting new potential therapeutic targets, an increased focus must be placed on more in-depth mechanistic investigations in hepatic ischemia-reperfusion injury and translational research in order to refine current strategies in disease management.

Oxidant stress, mitochondria, and cell death mechanisms in drug-induced liver injury: lessons learned from acetaminophen hepatotoxicity

Hepatotoxicity is a serious problem during drug development and for the use of many established drugs. For example, acetaminophen overdose is currently the most frequent cause of acute liver failure in the United States and Great Britain. Evaluation of the mechanisms of drug-induced liver injury indicates that mitochondria are critical targets for drug toxicity, either directly or indirectly through the formation of reactive metabolites. The consequence of these modifications is generally a mitochondrial oxidant stress and peroxynitrite formation, which leads to structural alterations of proteins and mitochondrial DNA and, eventually, to the opening of mitochondrial membrane permeability transition (MPT) pores. MPT pore formation results in a collapse of mitochondrial membrane potential and cessation of adenosine triphosphate synthesis. In addition, the release of intermembrane proteins, such as apoptosis-inducing factor and endonuclease G, and their translocation to the nucleus, leads to nuclear DNA fragmentation. Together, these events trigger necrotic cell death. Alternatively, the release of cytochrome c and other proapoptotic factors from mitochondria can promote caspase activation and apoptotic cell death. Drug toxicity can also induce an inflammatory response with the formation of reactive oxygen species by Kupffer cells and neutrophils. If not properly detoxified, these extracellularly generated oxidants can diffuse into hepatocytes and trigger mitochondrial dysfunction and oxidant stress, which then induces MPT and necrotic cell death. This review addresses the formation of oxidants and the defense mechanisms available for cells and applies this knowledge to better understand mechanisms of drug hepatotoxicity, especially acetaminophen-induced liver injury.

The evolutionarily conserved longevity determinants HCF-1 and SIR-2.1/SIRT1 collaborate to regulate DAF-16/FOXO

The conserved DAF-16/FOXO transcription factors and SIR-2.1/SIRT1 deacetylases are critical for diverse biological processes, particularly longevity and stress response; and complex regulation of DAF-16/FOXO by SIR-2.1/SIRT1 is central to appropriate biological outcomes. Caenorhabditis elegans Host Cell Factor 1 (HCF-1) is a longevity determinant previously shown to act as a co-repressor of DAF-16. We report here that HCF-1 represents an integral player in the regulatory loop linking SIR-2.1/SIRT1 and DAF-16/FOXO in both worms and mammals. Genetic analyses showed that hcf-1 acts downstream of sir-2.1 to influence lifespan and oxidative stress response in C. elegans. Gene expression profiling revealed a striking 80% overlap between the DAF-16 target genes responsive to hcf-1 mutation and sir-2.1 overexpression. Subsequent GO-term analyses of HCF-1 and SIR-2.1-coregulated DAF-16 targets suggested that HCF-1 and SIR-2.1 together regulate specific aspects of DAF-16-mediated transcription particularly important for aging and stress responses. Analogous to its role in regulating DAF-16/SIR-2.1 target genes in C. elegans, the mammalian HCF-1 also repressed the expression of several FOXO/SIRT1 target genes. Protein–protein association studies demonstrated that SIR-2.1/SIRT1 and HCF-1 form protein complexes in worms and mammalian cells, highlighting the conservation of their regulatory relationship. Our findings uncover a conserved interaction between the key longevity determinants SIR-2.1/SIRT1 and HCF-1, and they provide new insights into the complex regulation of FOXO proteins.

The nematode C. elegans has been instrumental in identifying and characterizing genetic components that influence aging. Studies in worms have been successfully extended to complex mammalian organisms allowing for the identification of genetic factors that impact longevity in mammals. DAF-16/FOXO transcription factors are among the best characterized longevity factors, and their increased activity leads to a longer lifespan and improved stress resistance in many organisms. Elucidating how the activities of DAF-16/FOXO are regulated will provide new insights into the basic biology of aging and will aid future therapeutic developments aiming to improve healthy aging and alleviate age-related diseases in humans. We utilized both C. elegans and mammalian cell culture systems to dissect the functional and molecular interactions between two important DAF-16 regulators, HCF-1 and SIR-2.1/SIRT1. We demonstrated that HCF-1 and SIR-2.1/SIRT1 physically associate and antagonize each other to properly regulate DAF-16/FOXO-mediated expression of genes important for longevity and stress response. We further showed that the functional relationships among these three proteins are conserved in mammals. Our work implicates HCF-1 as an important player in the regulation of FOXO by SIRT1, and thereby a potential longevity determinant in humans, and prompts further characterization of HCF-1's functions in aging and age-related pathologies.

Current issues with acetaminophen hepatotoxicity--a clinically relevant model to test the efficacy of natural products

There is a significant need to evaluate the therapeutic potential of natural products and other compounds purported to be hepatoprotective. Acetaminophen-induced liver injury, especially in mice, is an attractive and widely used model for this purpose because it is both clinically relevant and experimentally convenient. However, the pathophysiology of liver injury after acetaminophen overdose is complex. This review describes the multiple steps and signaling pathways involved in acetaminophen-mediated cell death. The toxicity is initiated by the formation of a reactive metabolite, which depletes glutathione and binds to cellular proteins, especially in mitochondria. The resulting mitochondrial oxidant stress and peroxynitrite formation, in part through amplification by c-jun-N-terminal kinase activation, leads to mitochondrial DNA damage and opening of the mitochondrial permeability transition pore. Endonucleases from the mitochondrial intermembrane space and lysosomes are responsible for nuclear DNA fragmentation. Despite the oxidant stress, lipid peroxidation is not a relevant mechanism of injury. The mitochondrial dysfunction and nuclear DNA damage ultimately cause oncotic necrotic cell death with release of damage-associated molecular patterns that trigger a sterile inflammatory response. Current evidence supports the hypothesis that innate immune cells do not contribute to injury but are involved in cell debris removal and regeneration. This review discusses the latest mechanistic aspects of acetaminophen hepatotoxicity and demonstrates ways to assess the mechanisms of drug action and design experiments needed to avoid pitfalls and incorrect conclusions. This review should assist investigators in the optimal use of this model to test the efficacy of natural compounds and obtain reliable mechanistic information.

Reactive oxygen and mechanisms of inflammatory liver injury: Present concepts

Liver cell death induced by stresses such as ischemia-reperfusion, cholestasis and drug toxicity can trigger a sterile inflammatory response with activation of innate immune cells through release of damage-associated molecular patterns (DAMPs). A similar inflammatory response can be induced by pathogen-associated molecular patterns (PAMPs) such as endotoxin. Both DAMPs and PAMPs activate through toll-like receptors the resident macrophages (Kupffer cells) and recruit activated neutrophils and monocytes into the liver. Central to this inflammatory response is promotion of reactive oxygen species (ROS) formation by these phagocytes. ROS are the principal toxic mediators by which inflammatory cells kill their targets, e.g. bacteria during host defense but also hepatocytes and other liver cells. The mechanism of ROS-induced cell killing during inflammation involves the promotion of mitochondrial dysfunction through an intracellular oxidant stress in hepatocytes leading mainly to oncotic necrosis and less apoptosis. The additional release of cell contents amplifies the inflammatory injury. However, an inflammatory oxidant stress insufficient to directly cause cell damage can induce transcription of stress defence genes including antioxidant genes. This preconditioning effect of ROS enhances the resistance against future inflammatory oxidant stress and promotes the initiation of tissue repair processes. Despite the substantial progress in our understanding of mechanisms of inflammatory liver injury during the last decade, more research is necessary to better understand the role of ROS in acute liver inflammation and to develop clinically applicable therapeutic strategies that selectively target the detrimental effects of oxidant stress without compromising the vital function of ROS in host defense.

The hepatic microcirculation: mechanistic contributions and therapeutic targets in liver injury and repair

The complex functions of the liver in biosynthesis, metabolism, clearance, and host defense are tightly dependent on an adequate microcirculation. To guarantee hepatic homeostasis, this requires not only a sufficient nutritive perfusion and oxygen supply, but also a balanced vasomotor control and an appropriate cell-cell communication. Deteriorations of the hepatic homeostasis, as observed in ischemia/reperfusion, cold preservation and transplantation, septic organ failure, and hepatic resection-induced hyperperfusion, are associated with a high morbidity and mortality. During the last two decades, experimental studies have demonstrated that microcirculatory disorders are determinants for organ failure in these disease states. Disorders include 1) a dysregulation of the vasomotor control with a deterioration of the endothelin-nitric oxide balance, an arterial and sinusoidal constriction, and a shutdown of the microcirculation as well as 2) an overwhelming inflammatory response with microvascular leukocyte accumulation, platelet adherence, and Kupffer cell activation. Within the sequelae of events, proinflammatory mediators, such as reactive oxygen species and tumor necrosis factor-alpha, are the key players, causing the microvascular dysfunction and perfusion failure. This review covers the morphological and functional characterization of the hepatic microcirculation, the mechanistic contributions in surgical disease states, and the therapeutic targets to attenuate tissue injury and organ dysfunction. It also indicates future directions to translate the knowledge achieved from experimental studies into clinical practice. By this, the use of the recently introduced techniques to monitor the hepatic microcirculation in humans, such as near-infrared spectroscopy or orthogonal polarized spectral imaging, may allow an early initiation of treatment, which should benefit the final outcome of these critically ill patients.

An insight into the protection of rat liver against ischemia/reperfusion injury by 2-selenium-bridged beta-cyclodextrin

AIM

The reperfusion following liver ischemia results in the damage and apoptosis of hepatocytes. The aim of this study was to investigate the possible effects and mechanism of a new synthesized glutathione peroxidase (GPX) mimic, 2-selenium-bridged beta-cyclodextrin (2-SeCD), on rat liver ischemia-reperfusion (I/R) injury.

METHODS

Male Wistar rats (n = 32) were randomly divided into four groups: I. sham-operated group, II. I/R group, III. I/R +2-SeCD group, IV. I/R + Ebselen group. Hepatic I/R was administered by 90 min of ischemia and 12 h of reperfusion. Liver tissues were collected at the end of reperfusion period for measurement of various biochemical parameters.

RESULTS

The serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) activity and tissue malondialdehyde, myeloperoxidase levels were increased in I/R group, while the increase was significantly reduced by 2-SeCD treatment. The glutathione level, depressed by I/R, was elevated back to normal levels by treatment with 2-SeCD. Severe hepatic damage were observed by light and transmission electron microscopy whilst pretreatment with 2-SeCD resulted in tissue and cellular preservation. Furthermore, 2-SeCD reduced cytochrome c release from mitochondria and subsequent DNA fragmentation by regulating Bcl-2/Bax expression ratio. RESULTS suggested that 2-SeCD was more effective than ebselen in the reversal of the alteration in tissue structural and biochemical parameters caused by I/R injury.

CONCLUSION

2-selenium-bridged beta-cyclodextrin playes an important role in the protection of liver against I/R injury and this treatment may be a novel pharmacological agent for liver surgery.

Condition-adapted stress and longevity gene regulation by Caenorhabditis elegans SKN-1/Nrf

Studies in model organisms have identified regulatory processes that profoundly influence aging, many of which modulate resistance against environmental or metabolic stresses. In Caenorhabditis elegans, the transcription regulator SKN-1 is important for oxidative stress resistance and acts in multiple longevity pathways. SKN-1 is the ortholog of mammalian Nrf proteins, which induce Phase 2 detoxification genes in response to stress. Phase 2 enzymes defend against oxygen radicals and conjugate electrophiles that are produced by Phase 1 detoxification enzymes, which metabolize lipophilic compounds. Here, we have used expression profiling to identify genes and processes that are regulated by SKN-1 under normal and stress-response conditions. Under nonstressed conditions SKN-1 upregulates numerous genes involved in detoxification, cellular repair, and other functions, and downregulates a set of genes that reduce stress resistance and lifespan. Many of these genes appear to be direct SKN-1 targets, based upon presence of predicted SKN-binding sites in their promoters. The metalloid sodium arsenite induces skn-1-dependent activation of certain detoxification gene groups, including some that were not SKN-1-upregulated under normal conditions. An organic peroxide also triggers induction of a discrete Phase 2 gene set, but additionally stimulates a broad SKN-1-independent response. We conclude that under normal conditions SKN-1 has a wide range of functions in detoxification and other processes, including modulating mechanisms that reduce lifespan. In response to stress, SKN-1 and other regulators tailor transcription programs to meet the challenge at hand. Our findings reveal striking complexity in SKN-1 functions and the regulation of systemic detoxification defenses.

Breath pentane: an indicator for early and continuous monitoring of lipid peroxidation in hepatic ischaemia-reperfusion injury

BACKGROUND AND OBJECTIVE

Lipid peroxidation plays an important role during liver ischaemia-reperfusion injury. Pentane in breath is often used as an index of lipid peroxidation. We observed the changes in levels of breath pentane during the lipid peroxidation process caused by liver ischaemia-reperfusion injury.

METHODS

Ten male swine were anaesthetized with chloral hydrate 0.3-0.5 g kg(-1) min(-1). Total hepatic ischaemia was induced by occluding the portal inflow vessels. Ischaemia lasted 30 min followed by reperfusion for 180 min. Breath samples were sampled from the anaesthesia circuit and blood samples were collected from the inferior vena cava. Pentane concentrations in breath and blood were quantified by means of solid phase microextraction and gas chromatography-mass spectrography technique.

RESULTS

Exhaled pentane concentrations (means +/- SE) increased markedly after reperfusion for 1 min (244.13 +/- 33.3 pmol l(-1)) and decreased gradually to initial levels after reperfusion for 60 min. Blood pentane concentrations (means +/- SE) increased significantly after reperfusion for 1 min (333.46 +/- 63.05 pmol l(-1)) and then decreased to basal level. Breath pentane concentrations showed a correlation with blood (r = 0.709, P < 0.05).

CONCLUSION

Breath pentane analysis could provide early, rapid, noninvasive and continuous assessment of lipid peroxidation during hepatic ischaemia-reperfusion injury.

New Hope for an Old Cure: A Pilot Animal Study on Selective Venesection in Attenuating the Systemic Effects of Ischaemic-Reperfusion Injury

Introduction: Reperfusion of acutely ischaemic tissue may, paradoxically, lead to systemic complications. This phenomenon is believed to be initiated by humoral factors that have accumulated in the ischaemic tissue. The ancient art of venesection may reduce the load of these mediators at the point of reperfusion. The aim of this study is to test if selective venesection, by removing the initial venous return from the ischaemic tissue, can attenuate the systemic effects of the ischaemic-reperfusion injury using a porcine model of acute limb ischaemia. Materials and Methods: The right femoral arteries of anaesthetised female pigs were clamped. Twelve pigs were divided into 2 groups (n = 6 per group). In the treatment group, 5% of blood volume was venesected from the ipsilateral femoral vein upon reperfusion; the other arm served as control. The animals were sacrificed after 4 days for histological examination. A pathologist, blinded to the experimental groups, graded the degree of microscopic injury. Results: For the control group, the kidneys showed glomeruli and tubular damage. The livers demonstrated architectural distortion with cellular oedema. There was pulmonary oedema as well as extensive capillary congestion and neutrophil infiltration. Such findings were absent or reduced in the venesected animals. Consequently, the injury scores for the kidney, lung, liver and heart were significantly less for the venesected animals. Conclusion: Selective venesection reduces the remote organ injuries of the ischaemic-reperfusion phenomenon. Key words: Acute ischaemia, Humoral factors, MODS, Pulmonary oedema

Oxidant stress-induced liver injury in vivo: role of apoptosis, oncotic necrosis, and c-Jun NH2-terminal kinase activation

Oxidant stress is critically involved in various liver diseases. Superoxide formation causes c-Jun NH2-terminal kinase (JNK)- and caspase-dependent apoptosis in cultured hepatocytes. To verify these findings in vivo, male Fisher rats were treated with diquat and menadione. The oxidant stress induced by both compounds was confirmed by increased formation of glutathione disulfide and 4-hydroxynonenal protein adducts. Plasma alanine aminotransferase activities increased from 46+/-4 U/l in controls to 955+/-90 U/l at 6 h after diquat treatment. Hematoxylin and eosin staining of liver sections revealed large areas of necrotic cells at 3 and 6 h. DNA strandbreaks, evaluated with the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay, showed clusters of TUNEL-positive cells, where the staining was predominantly cytosolic and the cells were swollen, indicating oncotic necrosis. There was no significant increase in caspase-3 activities or relevant release of DNA fragments into the cytosol at any time between 0 and 6 h after diquat treatment. Despite the activation of JNK after high doses of diquat, the JNK inhibitor SP-600125 did not protect against diquat-induced necrosis. Menadione alone did not cause liver injury, but, in combination with phorone and FeSO4, induced moderate oncotic necrosis. On the other hand, if animals were treated with galactosamine/endotoxin as positive control for apoptosis, caspase-3 activities were increased by 259%, the number of TUNEL-positive cells with apoptotic morphology was increased 103-fold, and DNA fragmentation was enhanced 6-fold. The data indicate that liver cell death initiated by diquat-induced superoxide formation in vivo is mediated predominantly by oncotic necrosis and is independent of JNK activation.

Laennec protects murine from concanavalin A-induced liver injury through inhibition of inflammatory reactions and hepatocyte apoptosis

The effect of Laennec, a hydrolyte of human placenta, on immune-mediated liver injury was investigated in vivo and in vitro in murine. Vena caudalis administration of concanavalin A (Con A) was employed to establish an in vivo liver-injury model, and in vitro hepatotoxicity was induced by 8 h interaction between Con A pre-treated hepatocytes and Con A-stimulated autologous splenic lymphocytes. Laennec was used for pre-treatment in the two models. Laennec decreased biochemical marker activity (alanine aminotransferase, ALT; lactate dehydrogenase, LDH) in serum and recovered the activity of superoxide dismutase (SOD) and myeloperoxidase (MPO), as well as the content of malondialdehyde (MDA) and nitric oxide (NO) in liver tissue. We also found that the DNA ladder induced by Con A in vivo was attenuated by Laennec. Furthermore, the leakage of aspartate aminotransferase (AST) and LDH in the supernatant of the co-culture system was decreased by addition of Laennec. Potential protective mechanisms were elucidated by DNA fragmentation assay and intercellular adhesion molecule-1 (ICAM-1) induction/inhibition experiments. Results showed that ICAM-1, which is related to the interaction between hepatocytes and lymphocytes, was inhibited by Laennec. These findings indicated that Laennec has potent activity against immune-mediated liver injury.

[Hemodynamic effects of N-acetylcysteine and ischemic preconditioning in a liver ischemia-reperfusion model]

The aim of the study was to investigate whether repeated ischemic preconditioning or N-acetylcysteine (NAC) prevents ischemic-reperfusion injury as determined by having favourable hemodynamic effects during reperfusion in canine livers.

METHODS

The control group ( n = 10) underwent 60 minutes of hepatic ischemia followed by 180 minutes reperfusion. In the NAC group ( n = 5) 150 mg kg -1 of NAC was administered intravenously before inducing ischemia. In the preconditioned group ( n = 5) animals received ischemic preconditioning (10 minutes of ischemia followed by 10 minutes of reperfusion repeated three times) before clamping the portal triad.

RESULTS

18 dogs survived the study period. One dog in the NAC group died due to circulatory failure unresponsive to inotropic drugs. The cardiac index and the intrathoracic blood volume index were significantly higher in the preconditioning group compared to the controls throughout the study period.

CONCLUSIONS

Repeated ischemic preconditioning might improve hemodynamic parameters, whereas we were unable to find any significant differences between the groups regarding N-acetylcysteine.

Short-term effects of N-acetylcysteine and ischemic preconditioning in a canine model of hepatic ischemia-reperfusion injury

AIMS

We evaluated the possibility that repeated ischemic preconditioning or N-acetylcysteine (NAC) could prevent ischemia-reperfusion injury as determined by indocyanine green plasma disappearance rate (ICG-PDR) or has favorable hemodynamic effects during reperfusion in an in vivo canine liver model.

METHODS

Under general anesthesia, 3 groups of mongrel dogs (n = 5 per group) were subjected to (1) 60-min hepatic ischemia, (2) same ischemia preceded by intravenous administration of 150 mg kg(-1) NAC, and (3) three episodes of IPC (10-min ischemia followed by 10-min reperfusion) prior to same ischemia. Hepatic reperfusion was maintained for a further 180 min, with hemodynamic and hepatic function parameters monitored throughout.

RESULTS

Plasma disappearance rate of indocyanine green and serum levels of aspartate transferase and alanine transferase showed no significant differences between groups. Although liver injury was obvious, reflected by hemodynamic, blood gas, and liver function tests, NAC and IPC failed to prevent decay in hepatic function in this canine model.

CONCLUSION

The results do not support the hypothesis that short-term use of NAC and IPC is beneficial in hepatic surgery.

Roles of nuclear factor-kappaB in postischemic liver

Hepatic ischemia/reperfusion (I/R) results in a chain of events that culminate in liver dysfunction and injury. I/R injury is characterized by early oxidant stress followed by an intense acute inflammatory response that involves the transcription factor nuclear factor (NF)-kappaB. In addition to being a primary regulator of pro-inflammatory gene expression, NF-kappaB may play other roles in the hepatic response to I/R, such as mediating the expression of anti-apoptotic genes, preventing the accumulation of damaging reactive oxygen species, facilitating liver regeneration, and mediating the protective effects of ischemic preconditioning. In the present study, we review the diverse functions of NF-kappaB during hepatic I/R injury.

F2-isoprostanes are not just markers of oxidative stress

F(2)-isoprostanes are not just markers of oxidative stress. The discovery of F(2)-isoprostanes (F(2)-IsoPs) as specific and reliable markers of oxidative stress in vivo is briefly summarized here. F(2)-IsoPs are also agonists of important biological effects, such as the vasoconstriction of renal glomerular arterioles, the retinal vessel, and the brain microcirculature. In addition to the F(2)-IsoPs, E(2)- and D(2)-IsoPs can be formed by rearrangement of H(2)-IsoP endoperoxides and can give rise to cyclopentenone IsoPs, which are very reactive alpha,beta-unsaturated aldehydes. The same type of reactivity is also shown by acyclic gamma-ketoaldehydes formed as products of the IsoP pathway. Because previous studies suggested a relation between oxidative stress and collagen hyperproduction, it was investigated whether collagen synthesis is induced by F(2)-IsoPs, the most proximal products of lipid peroxidation. In contrast to aldehydes, F(2)-IsoPs act through receptors able to elicit definite signal transduction pathways. In a rat model of carbon tetrachloride-induced hepatic fibrosis, plasma F(2)-IsoPs were markedly elevated for the entire experimental period; hepatic collagen content was also increased. When hepatic stellate cells from normal liver were cultured up to activation (expression of smooth muscle alpha-actin) and then treated with F(2)-IsoPs in the concentration range found in the in vivo studies (10(-9) to 10(-8) M), a striking increase in DNA synthesis, cell proliferation, and collagen synthesis was observed. Total collagen content was similarly increased. All these stimulatory effects were reversed by the specific antagonist of the thromboxane A(2) receptor, SQ 29 548, whereas the receptor agonist, I-BOP, also had a stimulatory effect. Therefore F(2)-IsoPs generated by lipid peroxidation in hepatocytes may mediate hepatic stellate cell proliferation and collagen hyperproduction seen in hepatic fibrosis.

JunD protects the liver from ischemia/reperfusion injury by dampening AP-1 transcriptional activation

The AP-1 transcription factor modulates a wide range of cellular processes, including cellular proliferation, programmed cell death, and survival. JunD is a major component of the AP-1 complex following liver ischemia/reperfusion (I/R) injury; however, its precise function in this setting remains unclear. We investigated the functional significance of JunD in regulating AP-1 transcription following partial lobar I/R injury to the liver, as well as the downstream consequences for hepatocellular remodeling. Our findings demonstrate that JunD plays a protective role, reducing I/R injury to the liver by suppressing acute transcriptional activation of AP-1. In the absence of JunD, c-Jun phosphorylation and AP-1 activation in response to I/R injury were elevated, and this correlated with increased caspase activation, injury, and alterations in hepatocyte proliferation. The expression of dominant negative JNK1 inhibited c-Jun phosphorylation, AP-1 activation, and hepatic injury following I/R in JunD-/- mice but, paradoxically, led to an enhancement of AP-1 activation and liver injury in JunD+/- littermates. Enhanced JunD/JNK1-dependent liver injury correlated with the acute induction of diphenylene iodonium-sensitive NADPH-dependent superoxide production by the liver following I/R. In this context, dominant negative JNK1 expression elevated both Nox2 and Nox4 mRNA levels in the liver in a JunD-dependent manner. These findings suggest that JunD counterbalances JNK1 activation and the downstream redox-dependent hepatic injury that results from I/R, and may do so by regulating NADPH oxidases.

Malondialdehyde as an indicator of oxidative stress during abdominal aortic aneurysm repair

Ischemia-reperfusion injury significantly contributes to abdominal aortic aneurysm (AAA)- related mortality and morbidity; therefore, we measured oxidative stress during open AAA repair and investigated any potential associations with intraoperative or perioperative events (aortic clamping time, blood loss, and the need to transfer to the intensive care unit). Blood samples were collected at specific time points from 53 patients undergoing open AAA repair: (1) before induction of anesthesia; (2) 15, 30, 60, and 120 minutes after aortic clamping; (3) 15 and 60 minutes after clamp removal; and (4) 24 hours postoperatively. Malondialdehyde (MDA) levels were measured by a spectrophotometric method. Baseline MDA values in patients with AAA were significantly higher than in controls (P < .0001). A positive correlation was found between preoperative MDA levels and the size of AAAs (Pearson correlation = 0.578, P < .001). No difference was observed in MDA levels between ruptured and nonruptured AAAs; however, when all symptomatic patients (ruptured and elective symptomatic AAAs, n = 18) were considered, there was a significant elevation in MDA levels (P < .001). There was also a significant increase in MDA values in patients transferred postoperatively to the intensive care unit (P < .001). Finally, a positive association was found between the duration of aortic clamping with MDA values at 15 and 60 minutes after declamping, but not after 24 hours (Pearson correlation = 0.467, P < .001). MDA levels may predict the postoperative course of elective and ruptured AAAs.

Endothelium-dependent and -independent hepatic artery vasodilatation is not impaired in a canine model of liver ischemia-reperfusion injury

We investigated whether hepatic artery endothelium may be the earliest site of injury consequent to liver ischemia and reperfusion. Twenty-four heartworm-free mongrel dogs of either sex exposed to liver ischemia/reperfusion in vivo were randomized into four experimental groups (N = 6): a) control, sham-operated dogs, b) dogs subjected to 60 min of ischemia, c) dogs subjected to 30 min of ischemia and 60 min of reperfusion, and d) animals subjected to 45 min of ischemia and 120 min of reperfusion. The nitric oxide endothelium-dependent relaxation of hepatic artery rings contracted with prostaglandin F2a and exposed to increasing concentrations of acetylcholine, calcium ionophore A23187, sodium fluoride, phospholipase-C, poly-L-arginine, isoproterenol, and sodium nitroprusside was evaluated in organ-chamber experiments. Lipid peroxidation was estimated by malondialdehyde activity in liver tissue samples and by blood lactic dehydrogenase (LDH), serum aspartate aminotransferase (AST) and serum alanine aminotransferase (ALT) activities. No changes were observed in hepatic artery relaxation for any agonist tested. The group subjected to 45 min of ischemia and 120 min of reperfusion presented marked increases of serum aminotransferases (ALT = 2989 +/- 1056 U/L and AST = 1268 +/- 371 U/L; P < 0.01), LDH = 2887 +/- 1213 IU/L; P < 0.01) and malondialdehyde in liver samples (0.360 +/- 0.020 nmol/mgPT; P < 0.05). Under the experimental conditions utilized, no abnormal changes in hepatic arterial vasoreactivity were observed: endothelium-dependent and independent hepatic artery vasodilation were not impaired in this canine model of ischemia/reperfusion injury. In contrast to other vital organs and in the ischemia/reperfusion injury environment, dysfunction of the main artery endothelium is not the first site of reperfusion injury.

Baicalin protects mouse from Concanavalin A-induced liver injury through inhibition of cytokine production and hepatocyte apoptosis

BACKGROUND

Baicalin (BA) exhibits an anti-inflammatory effect in vivo and in vitro and is used to treat chronic hepatitis. However, the mechanism by which BA exerts the liver-protective effect remains largely unknown.

AIMS

The present study reports that BA inhibits cytokine production and hepatocyte apoptosis to protect mice from liver injury induced by concanavalin A (Con A), a T-cell-dependent liver injury model.

RESULTS

Con A injection of mice induced severe immune responses and extensive hepatocellular apoptosis within 24 h. Pretreatment of 200 or 100 mg/kg BA markedly reduced serum aminotransferase activities, protected hepatoycte apoptosis and reduced the increase of plasma cytokine levels, including tumor necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma) and interleukin-6 (IL-6). Furthermore, BA pretreatment decreased tissue myeloperoxidase activity and lipid peroxidation, but increased the superoxide dismutase level. In vitro studies indicated that the beneficial effect of BA was associated with reduced cytokine production from lymphocytes and reduced TNF-alpha-induced hepatocyte apoptosis.

CONCLUSION

These results suggest that BA has therapeutic potential for T-cell-mediated liver injury.

Effects of mannitol in the prevention of lipid peroxidation during liver resection with hepatic vascular exclusion

STUDY OBJECTIVE

To examine the efficacy of mannitol in the prevention of lipid peroxidation during major liver resections performed during hepatic inflow occlusion.

DESIGN

Prospective, randomized, open-label study.

SETTING

Aretaieion Hospital, a university-affiliated hospital.

PATIENTS

30 ASA physical status II and III patients, less than 75 years of age, scheduled for elective liver resection.

INTERVENTIONS

All patients received combined general and epidural anesthesia. Laparotomy was performed through a bilateral subcostal incision, and hepatectomy was performed by inflow vascular exclusion (Pringle's maneuver). Before this maneuver, and if the patients were hemodynamically stable, they were randomized to receive either mannitol 20% 1.5 mL kg(-1) (group M) or normal saline 1.5 mL kg(-1) (group S) intravenously for 30 minutes.

MEASUREMENTS

Venous blood malondialdehyde (MDA) concentration, as an index of lipid peroxidation, was measured spectrophotometrically at selected time points.

MAIN RESULTS

Patients in both groups presented with raised MDA values (P < 0.05) for the period starting before the release of vascular occlusion until 6 days postoperatively. In patients receiving mannitol, lower MDA values were observed (P < 0.05) compared with group S at the end of operation.

CONCLUSION

Mannitol has an antioxidant activity, but we were unable to confirm a positive impact on the postoperative clinical course.

Role of neutrophils in acute inflammatory liver injury

Hepatic infiltration of polymorphonuclear leukocytes (neutrophils) is an early response to tissue injury, cellular stress or systemic inflammation. Neutrophil activation is vital for host-defense and the removal of cell debris but can also cause additional tissue damage or even liver failure. In order to prevent the detrimental effects of neutrophils without compromising host-defense reactions, it is important to understand the mechanisms of neutrophil hepatotoxicity. The first step in the pathophysiology is the priming and recruitment of neutrophils into the liver vasculature by inflammatory mediators, e.g. cytokines, chemokines, or complement factors. Most critical for parenchymal cell damage is the accumulation in sinusoids, which does not depend on cellular adhesion molecules. The next step is the extravasation into the parenchyma. This process requires a chemotactic signal from hepatocytes or already extravasated neutrophils and depends on cellular adhesion molecules on neutrophils (beta(2) or beta(1) integrins) and on endothelial cells (intercellular or vascular cell adhesion molecules). The third step is the direct contact with target cells (hepatocytes), which involves beta(2) integrins and triggers the full activation of the neutrophil with a long-lasting adherence-dependent oxidant stress and degranulation. The oxidants diffuse into hepatocytes and trigger an intracellular oxidant stress, mitochondrial dysfunction and eventually cause oncotic necrotic cell death. Neutrophil-derived proteases facilitate extravasation and are involved in the regulation of inflammatory mediator production. Based on these mechanisms, it appears that strengthening of the intracellular defense mechanisms in hepatocytes may be the most promising therapeutic approach to selectively prevent neutrophil-mediated tissue damage without compromising their host-defense function.

Oxidant injury occurs rapidly after cardiac arrest, cardiopulmonary resuscitation, and reperfusion

OBJECTIVE

Investigations conducted in cellular models show that reperfusion of ischemic tissue is associated with a burst of reactive oxidant species within minutes after reperfusion. Oxidant injury may play a role in the poor outcome typical of people resuscitated from cardiac arrest. The objective of the present study was to determine the presence and timing of oxidant injury in an in vivo model of cardiac arrest.

DESIGN

Randomized controlled.

SETTING

University medical center laboratory.

SUBJECTS

Domestic swine.

INTERVENTIONS

We evaluated oxidant injury during and after 8 mins of cardiac arrest using a gas chromatography/mass spectrometry F2-isoprostane assay and compared these results with a matched control group.

MEASUREMENTS AND MAIN RESULTS

Baseline mean arterial, venous, and brain tissue F2-isoprostane levels were not significantly different when the cardiac arrest group was compared with the control group. However, in the group subjected to cardiac arrest and cardiopulmonary resuscitation we found significant (p < .0006) two- to three-fold increases in venous and arterial F2-isoprostane levels, which peaked between 15 and 30 mins after reperfusion and returned to baseline within 90 mins (p < .0006). Overall mean (+/- SE) brain tissue F2-isoprostane levels increased significantly to 370 +/- 60 vs. 140 +/- 60 ng/g tissue in the cardiac arrest group compared with the control group (p = .026).

CONCLUSION

This study shows that F2-isoprostane measurement could be used to assess oxidant injury in an animal model of cardiac arrest and that oxidant injury occurs rapidly after cardiac arrest and reperfusion.

Generation of hypochlorite-modified proteins by neutrophils during ischemia-reperfusion injury in rat liver: attenuation by ischemic preconditioning

Although it is well documented that neutrophils are critical for the delayed phase of hepatic ischemia-reperfusion injury, there is no direct evidence for a specific neutrophil-derived oxidant stress in vivo. Therefore, we used a model of 60 min of partial hepatic ischemia and 0-24 h of reperfusion to investigate neutrophil accumulation and to analyze biomarkers for a general oxidant stress [glutathione disulfide (GSSG) and malondialdehyde (MDA)] and for a neutrophil-specific oxidant stress [hypochlorite (HOCl)-modified epitopes] in rats. Plasma alanine transaminase activities and histology showed progressively increasing liver injury during reperfusion, when hepatic GSSG and soluble MDA levels were elevated. At that time, few neutrophils were present in sinusoids. However, the number of hepatocytes positively stained for HOCl-modified epitopes increased from 6 to 24 h of reperfusion, which correlated with the bulk of hepatic neutrophil accumulation and extravasation into the parenchyma. Consistent with a higher oxidant stress at later times, hepatic GSSG and protein-bound MDA levels further increased. Treatment with the NADPH oxidase inhibitor diphenyleneiodonium chloride attenuated postischemic oxidant stress (GSSG, protein-bound MDA, and hepatocytes positively stained for HOCl-modified epitopes) and liver injury at 24 h of reperfusion. Ischemic preconditioning suppressed all oxidant stress biomarkers, liver injury, and extravasation of neutrophils. In conclusion, extravasated neutrophils generate HOCl, which diffuses into hepatocytes and causes oxidative modifications of intracellular proteins during the neutrophil-mediated reperfusion injury phase. Ischemic preconditioning is an effective intervention for reduction of the overall inflammatory response and, in particular, for limitation of the cytotoxic activity of neutrophils during the later reperfusion period.

Involvement of peroxiredoxin I in protecting cells from radiation-induced death

Peroxiredoxin I (Prx-I), a key member of the peroxiredoxin family, reduces peroxides and equivalents through the thioredoxin system. Our previous work has shown that expression of Prx-I in mammalian cells increases following ionizing radiation (IR), indicating that Prx-I actively responds to IR-induced reactive oxygen species (ROS) and suggesting that Prx-I plays an important role in protecting cells from IR-induced death. To test this hypothesis, we suppressed the expression of Prx-I in SW480 cells by RNA interference. Our results show that IR induces the expression of Prx-I in SW480 cells in a dose- and time-dependent manner. The recombinant siRNA vector targeting Prx-I dramatically reduced the expression of Prx-I in SW480 cells. When Prx-I was knocked down in SW480 cells, the cells exhibited a decreased growth rate, a reduced antioxidant capability following IR and became more sensitive to IR-induced apoptosis. Together, our results demonstrate that Prx-I plays an important role in protecting cells from IR-induced cell death, which might be through scavenging IR-induced ROS in the cells.

A atividade respiratória mitocondrial é um bom parâmetro para a lesão por isquemia e reperfusão hepática?

RACIONAL: A atividade respiratória das mitocôndrias está associada à lesão por isquemia e reperfusão do fígado. OBJETIVO: Investigar in vitro se há obrigatoriedade de impedimento da respiração mitocondrial para que a lesão por isquemia e reperfusão do fígado possa ser detectada. MATERIAIS E MÉTODOS: Vinte e quatro cães de ambos os gêneros foram divididos nos seguintes grupos: controle, cães operados sem sofrer isquemia ou reperfusão hepática; I60, cães submetidos a 60 minutos de isquemia do fígado; I30/R60, cães submetidos a 30 minutos de isquemia e 60 minutos de reperfusão do fígado e I45/R120, cães submetidos a 45 minutos de isquemia e 120 de reperfusão do fígado. Amostras de fígado foram obtidas para dosagem de malondialdeído, para estudo da respiração mitocondrial por meio de traços polarográficos e para avaliação do potencial de membrana mitocondrial. Sangue foi obtido para dosagem de transaminases e desidrogenase lática. RESULTADOS: O grupo I45/R120 apresentou evidente aumento dos valores de transaminases, desidrogenase lática, aumento dos valores de malondialdeído e tendência à diminuição da respiração mitocondrial estimulada por adenosina difosfato, sem haver prejuízo irreversível para a fosforilação oxidativa ou para o potencial de membrana mitocondrial. CONCLUSÃO: A lesão por isquemia e reperfusão do fígado do cão pode ser documentada sem que haja prejuízo demonstrável para a função mitocondrial. Dados referentes à respiração mitocondrial podem não mostrar diferenças significativas em relação aos controles, mesmo em situações de evidente lesão tecidual por isquemia e reperfusão do fígado.

The pulmonary biology of isoprostanes

Isoprostanes were first recognized as convenient markers of oxidative stress, but their powerful effects on a variety of cell functions are now also being increasingly appreciated. This is particularly true of the lung, which is comprised of a wide variety of different cell types (smooth muscle, innervation, epithelium, lymphatics, etc.), all of which have been shown to respond to exogenously applied isoprostanes. In this review, we summarize these biological responses in the lung, and also consider the roles that isoprostanes might play in a range of pulmonary clinical disorders.