Uncoupling protein-2 deficiency provides protection in a murine model of endotoxemic acute liver failure

Malvidin alleviates mitochondrial dysfunction and ROS accumulation through activating AMPK-α/UCP2 axis, thereby resisting inflammation and apoptosis in SAE mice

This study aimed to explore the protective roles of malvidin in life-threatened sepsis-associated encephalopathy (SAE) and illustrate the underlying mechanism. SAE mice models were developed and treated with malvidin for subsequently protective effects evaluation. Malvidin restored neurobehavioral retardation, declined serum S100β and NSE levels, sustained cerebrum morphological structure, improved blood-brain barrier integrity with elevated tight junction proteins, and decreased evans blue leakage, and finally protect SAE mice from brain injury. Mechanistically, malvidin prevented cerebrum from mitochondrial dysfunction with enhanced JC-1 aggregates and ATP levels, and ROS accumulation with decreased lipid peroxidation and increased antioxidant enzymes. UCP2 protein levels were found to be decreased after LPS stimulation in the cerebrum and BV-2 cells, and malvidin recovered its levels in a ROS dependent manner. In vivo inhibition of UCP2 with genipin or in vitro interference with siRNA UCP2 both disrupted the mitochondrial membrane potential, decreased ATP levels and intensified DCF signals, being a key target for malvidin. Moreover, dorsomorphin block assays verified that malvidin upregulated UCP2 expression through phosphorylating AMPK in SAE models. Also, malvidin alleviated SAE progression through inhibition of ROS-dependent NLRP3 inflammasome activation mediated serum pro-inflammatory cytokines secretion and mitochondrial pathway mediated apoptosis with weakened apoptosis body formation and tunel positive signals, and decreased Bax, cytochrome C, caspase-3 and increased Bcl-2 protein levels. Overall, this study illustrated that malvidin targeted AMPK-α/UCP2 axis to restore LPS-induced mitochondrial dysfunction and alleviate ROS accumulation, which further inhibits NLRP3 inflammasome activation and mitochondrial apoptosis in a ROS dependent way, and ultimately protected SAE mice, providing a reference for the targeted development of SAE prophylactic approach.

Combined physical exercise reverses the reduced expression of Bmal1 in the liver of aged mice

Aging can modify the morphology and function of the liver, such as generating a decrease in the mitochondria content, autophagy, and cell senescence. Although exercise training has several beneficial effects on hepatic metabolism, its actions on autophagy processes, mitochondrial function, and cellular senescence need to be more widely explored. The present study verified the effects of aging and exercise on hepatic circadian markers, autophagy, and mitochondria activity in 24-month-old mice with a combined exercise training protocol. In addition, we used public datasets from human livers in several conditions and BMAL1 knockout mice. C57BL/6 mice were distributed into Control (CT, young, 6-month-old mice), sedentary old (Old Sed, sedentary, 24-month-old mice), and exercised old (Old Ex, 24-month-old mice submitted to a combined exercise training protocol). The exercise training protocol consisted of three days of endurance exercise - treadmill running, and two days of resistance exercise - climbing a ladder, for three weeks. At the end of the protocol, the liver was removed and prepared for histological analysis, reverse transcription-quantitative polymerase chain reaction (RT-qPCR), immunoblotting technique, and oxygen consumption. Heatmaps were built using a human dataset and Bmal1 knockout samples. In summary, the Old Sed had reduced strength, coordination, and balance, as well as a decrease in Bmal1 expression and the presence of degenerated liver cells. Still, this group upregulated the transcription factors related to mitochondrial biogenesis. The Old Ex group had increased strength, coordination, and balance, improved glucose sensitivity, as well as restored Bmal1 expression and the mitochondrial transcription factors. The human datasets indicated that mitochondrial markers and autophagy strongly correlate with specific liver diseases but not aging. We can speculate that mitochondrial and autophagy molecular markers alterations may depend on long-term training.

Drug-induced-acute liver failure: A critical appraisal of the thioacetamide model for the study of hepatic encephalopathy

Hepatic encephalopathy (HE) following acute and chronic liver failure is defined as a complex of neuropsychiatric abnormalities, such as discrete personal changes, sleep disorder, forgetfulness, confusion, and decreasing the level of consciousness to coma. The use and design of suitable animal models that represent clinical features and pathological changes of HE are valuable to map the molecular mechanisms that result in HE. Among different types of animal models, thioacetamide (TAA) has been used extensively for the induction of acute liver injury and HE. This agent is not directly hepatotoxic but its metabolites induce liver injury through the induction of oxidative stress and produce systemic inflammation similar to that seen in acute HE patients. In this short review article, we shortly review the most important pathological findings in animal models of acute HE following the administration of TAA.

Melatonin Balance the Autophagy and Apoptosis by Regulating UCP2 in the LPS-Induced Cardiomyopathy

To explore the mechanism of mitochondrial uncoupling protein 2 (UCP2) mediating the protective of melatonin when septic cardiomyopathy. UCP2 knocked out mice and cardiomyocytes were used to study the effect of melatonin in response to LPS. Indicators of myocardial and mitochondria injury including mitochondrial membrane potential, mitochondrial permeability transition pore, calcium loading, ROS, and ATP detection were assessed. In addition cell viability and apoptosis as well as autophagy-associated proteins were evaluated. Melatonin was able to protect heart function from LPS, which weakened in the UCP2-knockout mice. Consistently, genipin, a pharmacologic inhibitor of UCP2, augmented LPS-induced damage of AC16 cells. In contrast, melatonin upregulated UCP2 expression and protected the cells from the changes in morphology, mitochondrial membrane potential loss, mitochondrial Ca²⁺ overload, the opening of mitochondrial permeability transition pore, and subsequent increased ROS generation as well as ATP reduction. Mitophagy proteins (Beclin-1 and LC-3β) were increased while apoptosis-associated proteins (cytochrome C and caspase-3) were decreased when UCP2 was up-regulated. In conclusion, UCP2 may play a protecting role against LPS by regulating the balance between autophagy and apoptosis of cardiomyocytes, and by which mechanisms, it may contribute to homeostasis of cardiac function and cardiomyocytes activity. Melatonin may protect cardiomyocytes through modulating UCP2.

The Role of Uncoupling Protein 2 During Myocardial Dysfunction in a Canine Model of Endotoxin Shock

To explore the role of uncoupling protein 2 (UCP2) during myocardial dysfunction in a canine model of endotoxin shock, 26 mongrel canines were randomly divided into the following four groups: A (control group; n = 6), B2 (shock after 2 h; n = 7), B4 (shock after 4 h; n = 7), and B6 (shock after 6 h; n = 6). Escherichia coli endotoxin was injected into the canines via the central vein, and hemodynamics were monitored. Energy metabolism, UCP2 mRNA and protein expression, and UCP2 localization were analyzed, and the correlation between energy metabolism changes, and UCP2 expression was determined. After the canine endotoxin shock model was successfully established, the expression of UCP2 mRNA and protein was found to increase, with later time points showing significant increases (P < 0.05). Immunofluorescence assays of UCP2 in heart tissue showed that UCP2 was localized in the cytoplasm, and its expression pattern was the same as that found in the mRNA and protein analyses. The energy metabolism results revealed that the ADP levels increased, but the ATP and phosphocreatine (PCr) levels and ATP/ADP and PCr/ATP ratios decreased in the model. In particular, the PCr/ATP ratio was significantly different from that of the control group 6 h after shock (P < 0.05). Furthermore, correlation analysis showed that the UCP2 protein and mRNA levels were negatively correlated with myocardial energy levels. In summary, decreased energy synthesis can occur in the myocardium during endotoxin shock, and UCP2 may play an important role in this process. The negative correlation between UCP2 expression and energy metabolism requires further study, as the results might contribute to the treatment of sepsis with heart failure.

The therapeutic effect of CORM-3 on acute liver failure induced by lipopolysaccharide/D-galactosamine in mice

BACKGROUND

Acute liver failure (ALF) is a severe and life-threatening clinical syndrome resulting in a high mortality and extremely poor prognosis. Recently, a water-soluble CO-releasing molecule (CORM-3) has been shown to have anti-inflammatory effect. The present study was to investigate the effect of CORM-3 on ALF and elucidate its underlying mechanism.

METHODS

ALF was induced by a combination of LPS/D-GalN in mice which were treated with CORM-3 or inactive CORM-3 (iCORM-3). The efficacy of CORM-3 was evaluated based on survival, liver histopathology, serum aminotransferase activities (ALT and AST) and total bilirubin (TBiL). Serum levels of inflammatory cytokines (TNF-alpha, IL-6, IL-1beta and IL-10) and liver immunohistochemistry of NF-kappaB-p65 were determined; the expression of inflammatory mediators such as iNOS, COX-2 and TLR4 was measured using Western blotting.

RESULTS

The pretreatment with CORM-3 significantly improved the liver histology and the survival rate of mice compared with the controls; CORM-3 also decreased the levels of ALT, AST and TBiL. Furthermore, CORM-3 significantly inhibited the increased concentration of pro-inflammatory cytokines (TNF-alpha, IL-6 and IL-1beta) and increased the anti-inflammatory cytokine (IL-10) productions in ALF mice. Moreover, CORM-3 significantly reduced the increased expression of iNOS and TLR4 in liver tissues and inhibited the nuclear expression of NF-kappaB-p65. CORM-3 had no effect on the increased expression of COX-2 in the ALF mice. An iCORM-3 failed to prevent acute liver damage induced by LPS/D-GalN.

CONCLUSION

These findings provided evidence that CORM-3 may offer a novel alternative approach for the management of ALF through anti-inflammatory functions.

Silencing of uncoupling protein 2 by small interfering RNA aggravates mitochondrial dysfunction in cardiomyocytes under septic conditions

Uncoupling protein 2 (UCP2) regulates the production of mitochondrial reactive oxygen species (ROS) and cellular energy transduction under physiological or pathological conditions. In this study, we aimed to determine whether mitochondrial UCP2 plays a protective role in cardiomyocytes under septic conditions. In order to mimic the septic condition, rat embryonic cardiomyoblast-derived H9C2 cells were cultured in the presence of lipopolysaccharide (LPS) plus peptidoglycan G (PepG) and small interfering RNA (siRNA) against UCP2 (siUCP2) was used to suppress UCP2 expression. Reverse transcription quantitative-polymerase chain reaction (RT-qPCR), western blot analysis, transmission electron microscopy (TEM), confocal microscopy and flow cytometry (FCM) were used to detect the mRNA levels, protein levels, mitochondrial morphology and mitochondrial membrane potential (MMP or ΔΨm) in qualitative and quantitative analyses, respectively. Indicators of cell damage [lactate dehydrogenase (LDH), creatine kinase (CK), interleukin (IL)-6 and tumor necrosis factor (TNF)-α in the culture supernatant] and mitochondrial function [ROS, adenosine triphosphate (ATP) and mitochondrial DNA (mtDNA)] were detected. Sepsis enhanced the mRNA and protein expression of UCP2 in the H9C2 cells, damaged the mitochondrial ultrastructure, increased the forward scatter (FSC)/side scatter (SSC) ratio, increased the CK, LDH, TNF-α and IL-6 levels, and lead to the dissipation of MMP, as well as the overproduction of ROS; in addition, the induction of sepsis led to a decrease in ATP levels and the deletion of mtDNA. The silencing of UCP2 aggravated H9C2 cell damage and mitochondrial dysfunction. In conclusion, our data demonstrate that mitochondrial morphology and funtion are damaged in cardiomyocytes under septic conditions, while the silencing of UCP2 using siRNA aggravated this process, indicating that UCP2 may play a protective role in cardiomyocytes under septic conditions.

Role of age and uncoupling protein-2 in oxidative stress, RAGE/AGE interaction and inflammatory liver injury

The objective of this study is to clarify whether age-related oxidative stress enhances hepatic vulnerability via increased interaction of advanced glycation endproducts (AGE) with their receptor RAGE. To further address the role of uncoupling of mitochondrial respiration, mitochondrial uncoupling protein-2 wild-type (UCP2+/+) and knock out (UCP2-/-) mice were used and studied at an age of 8 (young), 38 (adult) and 76 weeks (senescent). First, we could show that UCP2 protein expression increased with age in UCP2+/+ mice. Second, in both mouse strains oxidative stress, as measured by malondialdehyde concentrations and the ratio of glutathione to glutathione disulfide, as well as hepatic RAGE expression and highly modified AGE accumulation significantly increased with age. This, however, was far more pronounced in UCP2-/- mice, in particular at the young age of 8 wk. In addition, the hepatic activity of the AGE precursor detoxifying enzyme glyoxalase-I was significantly decreased in 8 wk old UCP2-/- animals and concomitantly caused 2-fold higher levels of methylglyoxal-modified AGE in these animals. We further showed that the numbers of hepatic cells expressing sRAGE which acts as a decoy for RAGE ligands decreased with age and were markedly lower in the UCP2-/- than the UCP2+/+ mice. As a consequence, young 8 wk old UCP2-/- mice benefited from treatment with recombinant mouse RAGE to block the RAGE/AGE interaction, when challenged with galactosamine/lipopolysaccharide for the induction of acute liver injury. They showed less pronounced tissue damage and slightly lower mortality rate, while older UCP2+/+ and UCP2-/- mice revealed comparably high mortality rates and extent of liver injury, irrespective of their treatment with rRAGE. Taken together, the present study underlines the role of UCP2 in the age-related increase of oxidative stress and the oxidative stress-related RAGE/AGE interaction. In young animals, blockade of the RAGE/AGE interaction is of benefit, while in older animals, this protective effect is lost, supposedly due to the fact that with age other factors than enhanced hepatic glycation products predominantly determine liver injury and injury-related mortality rate.

Mutation of mitochondrial ATP8 gene improves hepatic energy status in a murine model of acute endotoxemic liver failure

AIMS

Mitochondria not only generate and modulate bioenergy but also serve as biosensors for oxidative stress, and eventually become effector organelles for cell viability. Therefore, the implications of mitochondrial (dys)function in the development of multiple organ failure are profound. We investigated whether a mutation in the ATPase subunit-8 gene affects the course of endotoxemic acute liver failure.

MAIN METHODS

C57BL/6J (ATP8 wild type) and C57BL/6J-mt(FVB/N) (ATP8 mutant) mice were challenged with d-galactosamine (GalN) and Escherichia coli lipopolysaccharide (LPS) for induction of acute liver failure, and studied 6 h thereafter. Control mice received physiological saline only. Analysis included in vivo fluorescence microscopy of hepatic microcirculation and levels of hepatocellular apoptosis, hepatic adenosine nucleotides and oxidative stress. Additionally, survival rates were assessed.

KEY FINDINGS

Induction of endotoxemic liver failure provoked marked liver damage, which was coexistent with a drop of total adenosine nucleotide levels and increased oxidative stress. Of interest, oxidative stress was higher in the GalN/LPS challenged ATP8 mutants compared to wild types. Concomitantly, adenosine triphosphate (ATP) levels in livers of mice carrying the ATP8 mutation remained higher than those in wild type mice. As net result, ATP8 mutants showed lower transaminase release and a tendency to better survival rate upon GalN/LPS exposure compared to wild types.

SIGNIFICANCE

Our findings demonstrate that mutation in the ATPase subunit-8 partially protects mice against endotoxemic stress, most probably due to better hepatic energy status despite elevated oxidative stress. Thus, modulating mitochondrial function to preserve bioenergetic status may be an effective strategy to protect against sepsis-induced multiorgan dysfunction.

Temporal increase of platelet mitochondrial respiration is negatively associated with clinical outcome in patients with sepsis

Introduction

Mitochondrial dysfunction has been suggested as a contributing factor to the pathogenesis of sepsis-induced multiple organ failure. Also, restoration of mitochondrial function, known as mitochondrial biogenesis, has been implicated as a key factor for the recovery of organ function in patients with sepsis. Here we investigated temporal changes in platelet mitochondrial respiratory function in patients with sepsis during the first week after disease onset.

Methods

Platelets were isolated from blood samples taken from 18 patients with severe sepsis or septic shock within 48 hours of their admission to the intensive care unit. Subsequent samples were taken on Day 3 to 4 and Day 6 to 7. Eighteen healthy blood donors served as controls. Platelet mitochondrial function was analyzed by high-resolution respirometry. Endogenous respiration of viable, intact platelets suspended in their own plasma or phosphate-buffered saline (PBS) glucose was determined. Further, in order to investigate the role of different dehydrogenases and respiratory complexes as well as to evaluate maximal respiratory activity of the mitochondria, platelets were permeabilized and stimulated with complex-specific substrates and inhibitors.

Results

Platelets suspended in their own septic plasma exhibited increased basal non-phosphorylating respiration (state 4) compared to controls and to platelets suspended in PBS glucose. In parallel, there was a substantial increase in respiratory capacity of the electron transfer system from Day 1 to 2 to Day 6 to 7 as well as compared to controls in both intact and permeabilized platelets oxidizing Complex I and/or II-linked substrates. No inhibition of respiratory complexes was detected in septic patients compared to controls. Non-survivors, at 90 days, had a more elevated respiratory capacity at Day 6 to 7 as compared to survivors. Cytochrome c increased over the time interval studied but no change in mitochondrial DNA was detected.

Conclusions

The results indicate the presence of a soluble plasma factor in the initial stage of sepsis inducing uncoupling of platelet mitochondria without inhibition of the electron transfer system. The mitochondrial uncoupling was paralleled by a gradual and substantial increase in respiratory capacity. This may reflect a compensatory response to severe sepsis or septic shock, that was most pronounced in non-survivors, likely correlating to the severity of the septic insult.

Uncoupling protein-2 deficient mice are not protected against warm ischemia/reperfusion injury of the liver

BACKGROUND

Uncoupling protein-2 (UCP2) might play an important role in mediating ischemia/reperfusion (I/R) injury due to its function in uncoupling of oxidative phosphorylation and in the proton leak-associated increase of reactive oxygen species (ROS) production. The aim of this study was to elucidate the role of UCP2 in hepatic I/R injury.

MATERIALS AND METHODS

UCP2 wild type and UCP2 deficient mice were subjected to I/R of the left liver lobe. Sham-operated animals without I/R served as controls. Intravital fluorescence microscopy was used for assessing postischemic microcirculatory dysfunction. Indicators of hepatic inflammatory response, oxidative stress, and bioenergetic status as well as histomorphology were investigated.

RESULTS

Under sham conditions UCP2-/-mice presented slightly but not significantly higher levels of hepatic ATP and energy charge than wild type mice. In addition, they exhibited higher systemic IL-6 levels and intrahepatic leukocyte adherence. After exposure to I/R, the extent of reperfusion injury did not differ between UCP2+/+ and UCP2-/-mice, as indicated by a comparable loss of sinusoidal perfusion, hepatic ATP, and energy charge levels, as well as rise of transaminases and disintegration of liver structures. Intrahepatic leukocyte adherence and plasma IL-6 levels of postischemic UCP2-/-mice still exceeded those of UCP2+/+mice.

CONCLUSIONS

UCP2 appears to be of minor relevance for the manifestation and extent of postischemic reperfusion injury in nondiseased livers with the increased ATP availability being counteracted by the higher pro-inflammatory IL-6 levels in UCP2 deficient mice.

An overview of animal models for investigating the pathogenesis and therapeutic strategies in acute hepatic failure

Acute hepatic failure (AHF) is a severe liver injury accompanied by hepatic encephalopathy which causes multiorgan failure with an extremely high mortality rate, even if intensive care is provided. Management of severe AHF continues to be one of the most challenging problems in clinical medicine. Liver transplantation has been shown to be the most effective therapy, but the procedure is limited by shortage of donor organs. Although a number of clinical trials testing different liver assist devices are under way, these systems alone have no significant effect on patient survival and are only regarded as a useful approach to bridge patients with AHF to liver transplantation. As a result, reproducible experimental animal models resembling the clinical conditions are still needed. The three main approaches used to create an animal model for AHF are: surgical procedures, toxic liver injury and infective procedures. Most common models are based on surgical techniques (total/partial hepatectomy, complete/transient devascularization) or the use of hepatotoxic drugs (acetaminophen, galactosamine, thioacetamide, and others), and very few satisfactory viral models are available. We have recently developed a viral model of AHF by means of the inoculation of rabbits with the virus of rabbit hemorrhagic disease. This model displays biochemical and histological characteristics, and clinical features that resemble those in human AHF. In the present article an overview is given of the most widely used animal models of AHF, and their main advantages and disadvantages are reviewed.