Heat shock preconditioning on mitochondria during warm ischemia in rat livers

Heat Stress Induces Extended Plateau of Hsp70 Accumulation--A Possible Cytoprotection Mechanism in Hepatic Cells

The relevance of heat preconditioning resides in its ability to protect cells from different kinds of injury by induction of heat shock proteins, a process in which the intensity of heat stress (HS) and duration of subsequent recovery are vital. This study evaluates the effects of moderate HS (45 min/43°C) and the time-dependent changes during recovery period of HSP70, Bcl-2 and p53 gene and protein expression in HepG2 cells. We also evaluated the effects of 0.4 mM aspirin (ASA) as a potential pharmacological co-inducer of HSP, both alone and in a combination with HS (ASA + HS). HS alone and ASA + HS caused a major up-regulation of HSP70 mRNA in the first 2 h, while HSP70 protein increased gradually and was especially abundant from 2 h to 24 h. Regarding Bcl-2, all treatments rendered similar results: gene expression was down-regulated in the first 2 h, after which there was protein elevation (12-48 h after HS). mRNA expression of p53 in HS- and (ASA + HS)-cells was down-regulated in the first 12 h. The immediate decrease of p53 protein after HS was followed by a biphasic increase. In conclusion, 0.4 mM ASA + HS does not act as a co-inducer of HSP70 in HepG2 cells, but promotes Bcl-2 protein expression during prolonged treatment. Our suggestion is that hepatic cells are most vulnerable in the first 2-6 h, but may have a high capacity for combating stress 12-24 h after HS. Finally, short-term exposure HS might be a "physiological conditioner" for liver cells to accumulate HSP and Bcl-2 proteins and thus obtain cytoprotection against an additional stress.

Ischemic preconditioning results in an ATP-dependent inhibition of cytochrome C oxidase

PURPOSE

This study addresses the effect of short myocardial ischemia on inhibitory effect of ATP for mitochondrial cytochrome c oxidase (CytOx) activity in myocardium and subsequent hemodynamic alterations. The activity of CytOx is inhibited by ATP (primary substrate control). This additional mechanism was proposed to be switched off at higher mitochondrial membrane potential values in case of stress. The ATP-dependent allosteric enzyme inhibition (second respiratory control) is suggested to reduce the formation of reactive oxygen species and thus is pivotal for cytoprotection. This report addresses the possible involvement of this mechanism in case of myocardial preconditioning.

METHODS

Rat hearts were perfused in a Langendorff system (n = 5 each group). The first two groups underwent short recurrent ischemic periods (three times 5 min) and subsequent high or low reperfusion for 40 min. Besides four control groups, hearts were exposed to an ischemia of 15 min and high flow reperfused for 30 min, in addition. Hemodynamic data were evaluated in parallel. Mitochondria were separated for the polarographic respiration measurements in the presence of ADP or ATP, respectively. Phosphorylation patterns of the CytOx subunits were studied by immunoblotting with P-Ser, P-Thr, and P-Tyr antibodies.

RESULTS

Short recurrent episodes of ischemia result in an ATP-dependent inhibition of CytOx. Electrophoretic analysis and blotting techniques reveal different phosphorylation patterns of the enzyme. Frequent short-lasting ischemic impacts and subsequent increased coronary flow seem to be essential for this effect.

CONCLUSION

The procedure of preconditioning is likely to be dependent on the mechanism of ATP-dependent inhibition of CytOx activity.

Intermittent hypoxia protects cerebral mitochondrial function from calcium overload

Hypoxia leads to Ca(2+) overload and results in mitochondrial uncoupling, decreased ATP synthesis, and neuronal death. Inhibition of mitochondrial Ca(2+) overload protects mitochondrial function after hypoxia. The present study was aimed to investigate the effect of intermittent hypoxia on mitochondrial function and mitochondrial tolerance to Ca(2+) overload. Wistar rats were divided into control and intermittent hypoxia (IH) groups. The IH group was subject to hypoxia for 4 h daily in a hypobaric cabin (5,000 m) for 7 days. Brain mitochondria were isolated on day 7 following hypoxia. The baseline mitochondrial functions, such as ST3, ST4, and respiratory control ratio (RCR = ST3/ST4), were measured using a Clark-type oxygen electrode. Mitochondrial adenine nucleotide concentrations were measured by HPLC. Mitochondrial membrane potential was determined by measuring rhodamine 123 (Rh-123) fluorescence in the absence and presence of high Ca(2+) concentration (0.1 M), which simulates Ca(2+) overload. Our results revealed that IH did not affect mitochondrial respiratory functions, but led to a reduction in AMP and an increase in ADP concentrations in mitochondria. Both control and IH groups demonstrated decreased mitochondrial membrane potential in the presence of high Ca(2+) (0.1 M), while the IH group showed a relative higher mitochondrial membrane potential. These results indicated that the neuroprotective effect of intermittent hypoxia was resulted partly from preserving mitochondrial membrane potential, and increasing mitochondrial tolerance to high calcium levels. The increased ADP and decreased AMP in mitochondria following intermittent hypoxia may be a mechanism underlying this protection.

Avaliação da regeneração hepática com modulação pelo pré-condicionamento isquêmico após isquemia e reperfusão e hepatectomia parcial

OBJETIVO: Avaliar a regeneração hepática com modulação pelo pré-condicionamento isquêmico após isquemia, reperfusão e hepatectomia parcial. MÉTODOS: Foram usadas 24 ratas Wistar, de 12 semanas de idade, distribuídas randomicamente em quatro grupos: Grupo Controle (SHAM), Grupo Hepatectomia (HEP), Grupo Isquemia e Reperfusão (GIR) e Grupo Pré-condicionamento Isquêmico (PRE). Foi feita a análise das enzimas hepáticas ALT e AST, avaliação da regeneração através dos pesos inicial e final do fígado e da proliferação dos hepatócitos pela análise imunoistoquímica com o Proliferating Cell Nuclear Antigen (PCNA). RESULTADOS: Em todos os grupos ocorreu regeneração do fígado, não havendo significância estatística entre eles. Houve diferenças significativas em relação a ALT e AST entre os grupos HEP-SHAM, GIR-PRE, GIR-SHAM E PRE-SHAM (p< 0,05). Também houve diferença significativa em relação à marcação de PCNA do grupo SHAM quando comparado aos demais grupos (p< 0,05). CONCLUSÃO: O pré-condicionamento isquêmico diminuiu a lesão hepática, mas não influenciou na regeneração até 48 horas.

Preactivation of NKT cells with alpha-GalCer protects against hepatic ischemia-reperfusion injury in mouse by a mechanism involving IL-13 and adenosine A2A receptor

Hepatic preconditioning has emerged as a promising strategy of activating natural pathways to augment tolerance to liver ischemia-reperfusion (IR) injury. Liver-resident natural killer T (NKT) cells play an important role in modulating the local immune and inflammatory responses. This work was aimed to investigate whether preactivation of NKT cells could provide a beneficial "preconditioning" effect to ameliorate the subsequent hepatic IR injury. To selectively activate NKT cells, C57BL/6 mice were treated intraperitoneally with the glycolipid antigen alpha-galactosylceramide (alpha-GalCer) 1 h prior to hepatic ischemia. Significantly reduced liver IR injury was observed in mice pretreated with alpha- GalCer, and this protective effect was specifically abrogated by a CD1d blocking antibody. Serum TNF-alpha, IFN-gamma, and IL-13 levels were markedly increased shortly after alpha-GalCer injection. Pretreatment with a neutralizing antibody against TNF-alpha or IFN-gamma did not influence the protective effect of alpha-GalCer preconditioning, whereas preadministration of an IL-13 neutralizing antibody completely abolished the effect. Treatment with alpha-GalCer also led to an increased expression of adenosine A2A receptor (A2AR) in the liver, and blockade of A2AR by SH58261 diminished alpha-GalCer pretreatment-mediated attenuation of liver IR injury. In contrast, administration of the selective A2AR agonist CGS21680 reversed the counteracting effect of the IL-13 neutralizing antibody on alpha-GalCer preconditioning. Additionally, alpha-GalCer pretreatment was associated with a decreased neutrophil accumulation in the ischemic liver. These findings provide the first evidence that hepatic preconditioning by preactivation of NKT cells with alpha-GalCer protects the liver from IR injury via an IL-13 and adenosine A2AR-dependent mechanism.

Endogenous microRNAs induced by heat-shock reduce myocardial infarction following ischemia-reperfusion in mice

We investigated the role of microRNAs (miRNA) in protection against ischemia/reperfusion (I/R) injury in heart. Mice subjected to cytoprotective heat-shock (HS) showed a significant increase of miRNA-1, miRNA-21 and miRNA-24 in the heart. miRNAs isolated from HS mice and injected into non-HS mice significantly reduced infarct size after I/R injury, which was associated with the inhibition of pro-apoptotic genes and increase in anti-apoptotic genes. Chemically synthesized miRNA-21 also reduced infarct size, whereas a miRNA-21 inhibitor abolished this effect. Overall, these studies for the first time provide evidence for the potential role of endogenously synthesized miRNA's in cardioprotection following I/R injury.

Role of ischaemic preconditioning in liver regeneration following major liver resection and transplantation

Liver ischaemic preconditioning (IPC) is known to protect the liver from the detrimental effects of ischaemic-reperfusion injury (IRI), which contributes significantly to the morbidity and mortality following major liver surgery. Recent studies have focused on the role of IPC in liver regeneration, the precise mechanism of which are not completely understood. This review discusses the current understanding of the mechanism of liver regeneration and the role of IPC in this setting. Relevant articles were reviewed from the published literature using the Medline database. The search was performed using the keywords “liver”, “ischaemic reperfusion”, “ischaemic preconditioning”, “regeneration”, “hepatectomy” and “transplantation”. The underlying mechanism of liver regeneration is a complex process involving the interaction of cytokines, growth factors and the metabolic demand of the liver. IPC, through various mediators, promotes liver regeneration by up-regulating growth-promoting factors and suppresses growth-inhibiting factors as well as damaging stresses. The increased understanding of the cellular mechanisms involved in IPC will enable the development of alternative treatment modalities aimed at promoting liver regeneration following major liver resection and transplantation.

Improvement of nutritive perfusion after free tissue transfer by local heat shock-priming-induced preservation of capillary flowmotion

BACKGROUND

Capillary flowmotion protects pedicled flaps during critical perfusion conditions. However, free tissue transfer, causing ischemia-reperfusion and surgical trauma, have been shown to blunt these protective blood flow fluctuations. Because heat shock priming protects tissue after transfer, we herein studied whether heat shock protein expression is capable to preserve critical perfusion-induced capillary flowmotion in transferred composite flaps.

METHODS

In Sprague Dawley rats (n = 16), osteomyocutaneous flaps were subjected to critical perfusion after harvest and 1 h and 4 h after free transfer. In eight animals additional heat shock priming was induced 24 h before flap harvest. Microcirculation including capillary flowmotion was analyzed using intravital fluorescence microscopy.

RESULTS

After harvest, critical perfusion induced capillary flowmotion in skeletal muscle tissue of all flaps. By this, functional capillary density (FCD), an indicator of nutritive perfusion, was maintained not only in muscle but also in periosteum, subcutis, and skin. In contrast, 1 h after flap transfer muscle capillary flowmotion was completely abrogated, resulting in a significant decrease of FCD in all tissues. Heat shock-priming completely restored capillary flowmotion, and, by this, maintained tissue FCD.

CONCLUSIONS

The loss of muscle capillary flowmotion after free tissue transfer-associated ischemia-reperfusion can be prevented by heat shock-priming. This may represent the mechanism of protection by local heat application.

The essential role of PKCalpha in the protective effect of heat-shock pretreatment on TNFalpha-induced apoptosis in hepatic epithelial cell line

During sepsis, hepatic apoptosis occurred, which is associated with inactivation of PKCalpha and elevation of tumor necrosis factor-alpha (TNFalpha), an apoptosis trigger. Heat shock, accompanied by the increase of heat-shock protein (Hsp72), has been shown to exhibit a protective role on cell survival. However, Hsp72 was unable to express during sepsis when the apoptosis was markedly increased. We hypothesized that hepatic apoptosis during sepsis may be due to the failure to induce expression of Hsp72, which is activated by PKC-phosphorylated HSF. This study was designed to examine the role of PKCalpha in Hsp72 expression and the anti-apoptotic effect of Hsp72 on hepatic epithelial cells by analyzing a TNFalpha-induced apoptosis system. The following results were observed: (1) Hsp72 was highly expressed at 8 h after heat-shock treatment in a clone 9 hepatic epithelial cell line; (2) the protein expression of PKCalpha in membrane-associated fraction was decreased by TNFalpha treatment; (3) the TNFalpha-induced cell death, especially apoptosis, was diminished by heat-shock pretreatment; (4) in the presence of PKCalpha antisense, which blocks the PKCalpha resynthesis, no protective effect of heat-shock pretreatment was observed, and the protein expression of Hsp72 was significantly suppressed. These results suggest that PKCalpha plays a critical role in the expression of Hsp72, which subsequently protects against TNFalpha-induced hepatic apoptosis.

Protection of the liver by ischemic preconditioning: a review of mechanisms and clinical applications

Ischemic preconditioning refers to the endogenous mechanism of protection against a sustained ischemic insult following an initial, brief ischemic stimulus. Ischemia-reperfusion injury of the liver is a major cause of morbidity and mortality in liver surgery and transplantation and ischemic preconditioning is a promising strategy for improving the outcome of liver surgery. The preconditioning phenomenon was first described in a canine model of myocardial ischemia-reperfusion injury in 1986 and since then has been shown to exist in other organs including skeletal muscle, brain, kidneys, retina and liver. In the liver, the preconditioning effect has been demonstrated in rodents and a recent study has demonstrated human clinical benefits of preconditioning during hemihepatectomies. Ischemic preconditioning has been described as an adaptive response and although the precise mechanism of hepatoprotection from preconditioning is unknown it is likely to be a receptor-mediated process. Several hypotheses have been proposed and this review assesses possible mechanisms of ischemic preconditioning and its role in hepatic surgery and liver transplantation. The future lies in defining the mechanisms of the ischemic preconditioning effect to allow drug targeting to induce the preconditioning response.

Recent insights on the mechanisms of liver preconditioning

Ischemia/reperfusion is the main cause of hepatic damage consequent to temporary clamping of the hepatoduodenal ligament during liver surgery as well as graft failure after liver transplantation. In recent years, a number of animal studies have shown that pre-exposure of the liver to transient ischemia, hyperthermia, or mild oxidative stress increases the tolerance to reperfusion injury, a phenomenon known as hepatic preconditioning. The development of hepatic preconditioning can be differentiated into 2 phases. An immediate phase (early preconditioning) occurs within minutes and involves the direct modulation of energy supplies, pH regulation, Na(+) and Ca(2+) homeostasis, and caspase activation. The subsequent phase (late preconditioning) begins 12-24 hours after the stimulus and requires the synthesis of multiple stress-response proteins, including heat shock proteins HSP70, HSP27, and HSP32/heme oxygenase 1. Hepatic preconditioning is not limited to parenchymal cells but ameliorates sinusoidal perfusion, prevents postischemic neutrophil infiltration, and decreases the production of proinflammatory cytokines by Kupffer cells. This latter effect is important in improving systemic disorders associated with hepatic ischemia/reperfusion. The signals triggering hepatic preconditioning have been partially characterized, showing that adenosine, nitric oxide, and reactive oxygen species can activate multiple protein kinase cascades involving, among others, protein kinase C and p38 mitogen-activated protein kinase. These observations, along with preliminary studies in humans, give a rationale to perform clinical trials aimed at verifying the possible application of hepatic preconditioning in preventing ischemia/reperfusion injury during liver surgery.

Hypothermic preservation of hepatocytes

This paper presents a review of recent research on the hypothermic storage of hepatocytes. The first focus is on the diversity of methodologies currently employed in this area. The cell damage caused by hypothermic preservation and its possible mechanism are then investigated on both morphological and molecular biology. Later, the gene expressions on a mRNA level or enzyme level after hypothermic preservation are further discussed. Finally, the improvement of hypothermic storage by preconditioning, such as by increasing temperature, is explored.

Ischemic preconditioning in a rodent hepatocyte model of liver hypothermic preservation injury

Ischemic preconditioning (IPC) is a phenomenon of protection in various tissues from normothermic ischemic injury by previous exposure to short cycles of ischemia-reperfusion. The ability of IPC to protect hepatocytes from a model of hypothermic transplant preservation injury was tested in this study. Rat hepatocytes were subjected to 30min of warm ischemia (37 degrees C) followed by 24 or 48h of hypothermic (4 degrees C) storage in UW solution and subsequent re-oxygenation at normothermia for 1h. Studies were performed with untreated control cells and cells treated with IPC (10min anoxia followed by 10min re-oxygenation, 1 cycle). Hepatocytes exposed to IPC prior to warm ischemia released significantly less LDH and had higher ATP concentrations, relative to untreated ischemic hepatocytes. IPC significantly reduced LDH release after 24h of cold storage before reperfusion and after 48h of cold storage and after 60min of warm re-oxygenation, relative to the corresponding untreated hepatocytes. ATP levels were also significantly higher when IPC was used prior to the warm and cold ischemia-re-oxygenation protocols. In parallel studies, IPC increased new protein synthesis and lactate after cold storage and reperfusion compared to untreated cells but no differences in the patterns of protein banding were detected on electrophoresis between the groups. In conclusion, IPC significantly improves hepatocyte viability and energy metabolism in a model of hypothermic preservation injury preceded by normothermic ischemia. These protective effects on viability may be related to enhanced protein and ATP synthesis at reperfusion.

Cytochrome c release into cytosol with subsequent caspase activation during warm ischemia in rat liver

Apoptosis plays an important role in liver ischemia and reperfusion (I/R) injury. However, the molecular basis of apoptosis in I/R injury is poorly understood. The aims of this study were to ascertain when and how apoptotic signal transduction occurs in I/R injury. The apoptotic pathway in rats undergoing 90 min of warm ischemia with reperfusion was compared with that of rats undergoing prolonged ischemia alone. During ischemia, mitochondrial cytochrome c was released into the cytosol in a time-dependent manner in hepatocytes and sinusoidal endothelial cells, and caspase-3 and an inhibitor of caspase-activated DNase were cleaved. However, apoptotic manifestation and DNA fragmentation were not observed. After reperfusion, nuclear condensation, cells positive for terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling, and DNA fragmentation were observed and caspase-8 and Bid cleavage occurred. In contrast, prolonged ischemia alone induced necrosis rather than apoptosis. In summary, our results show that release of mitochondrial cytochrome c and caspase activation proceed during ischemia, although apoptosis is manifested after reperfusion.

Protective effect of heat preconditioning of rat liver graft resulting in improved transplant survival

BACKGROUND

The protective effect of heat preconditioning of the liver against ischemia-reperfusion injury has been reported mostly in models of transient ischemia in relation to heat shock protein 70 (HSP70). We estimated the effect of heat preconditioning of liver grafts on the transplant survival rate and on apoptosis of sinusoidal endothelial cells (SEC) as well as hepatocytes in a rat model of liver transplantation.

METHODS

Donor rats of the heat shock (HS) group were subjected to heat preconditioning 48 hr before graft harvest, and HSP70 levels were estimated by. Western blot analysis and immunohistochemistry. The liver isografts from the HS group and control (C) group were preserved in Euro-Collins solution for 6 or 8 hr and transplanted orthotopically. Serum hyaluronic acid and alanine aminotransferase were measured, and apoptosis of the SEC and hepatocytes was analyzed by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling staining and electron microscopy.

RESULTS

HSP70 expression was detected not only in hepatocytes but also in SEC. In the 8-hr preservation model, the 1-week survival rate was 60% in the HS group and 0% in the C group. Serum hyaluronic acid and alanine aminotransferase levels in the HS group were significantly lower than those in the C group at 3 hr after reperfusion, and the number of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling-positive SEC in the C group (35.2%) was markedly increased compared with the HS group (10.1%). Electron microscopic examination confirmed the features of apoptosis of SEC.

CONCLUSIONS

Heat preconditioning of the graft improved the survival rate of the liver transplants. Induction of HSP70 in SEC as well as in hepatocytes might attenuate preservation-reperfusion injury by inhibiting apoptosis of SEC.