Heat-shock preconditioning protects fatty livers in genetically obese Zucker rats from microvascular perfusion failure after ischemia reperfusion

Combination of liver graft sonographic grading and point shear wave elastography to reduce early allograft dysfunction after liver transplantation

OBJECTIVE

To analyze the performance of a liver graft sonographic grading system and point shear wave elastography (PSWE) in predicting early allograft dysfunction (EAD) after liver transplantation (LT).

METHODS

Successive brain-dead donors and liver recipients in our hospital from March 2017 to May 2018 were retrospectively recruited. All donors underwent PSWE examination, abdominal ultrasonography, and sonographic grading (grade 0 to grade 5). Donors with ≥ 10 valid PSWE examinations and a failure rate of < 60% were included. For all recipients, abdominal ultrasonography and blood tests for biologic parameters were performed preoperatively and daily postoperatively to screen for EAD. The recipients and their grafts were classified into EAD and non-EAD groups. Statistical analyses were performed to analyze the correlations among liver stiffness (LS), liver graft sonographic grading, and EAD.

RESULTS

Thirty-two donors and 32 corresponding liver recipients were enrolled (15 cases in the EAD group; 17 in the non-EAD group). There were no grade 0, 1, or 2 cases in the two groups. For prediction of EAD in recipients after LT, the AUC for PSWE was 0.929 and the AUC for combination of PSWE and sonographic grading system was 0.935.

CONCLUSIONS

Combination of PSWE and sonographic grading system can predict postoperative EAD in LT recipients with high sensitivity. Abnormal results may suggest a need for liver biopsy preoperatively, thus avoiding unnecessary surgical preparation for liver procurement.

KEY POINTS

• Combination of PSWE with new sonographic grading system is useful for preoperative evaluation of liver grafts from brain-dead donors. • EAD is as a criterion for evaluating the diagnostic value of PSWE and sonographic grading system. • Combination of PSWE and sonographic grading system can predict postoperative EAD in LT recipients with high sensitivity.

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.

Metabolic Flux Distribution during Defatting of Steatotic Human Hepatoma (HepG2) Cells

Methods that rapidly decrease fat in steatotic hepatocytes may be helpful to recover severely fatty livers for transplantation. Defatting kinetics are highly dependent upon the extracellular medium composition; however, the pathways involved are poorly understood. Steatosis was induced in human hepatoma cells (HepG2) by exposure to high levels of free fatty acids, followed by defatting using plain medium containing no fatty acids, or medium supplemented with a cocktail of defatting agents previously described before. We measured the levels of 28 extracellular metabolites and intracellular triglyceride, and fed the data into a steady-state mass balance model to estimate strictly intracellular fluxes. We found that during defatting, triglyceride content decreased, while beta-oxidation, the tricarboxylic acid cycle, and the urea cycle increased. These fluxes were augmented by defatting agents, and even more so by hyperoxic conditions. In all defatting conditions, the rate of extracellular glucose uptake/release was very small compared to the internal supply from glycogenolysis, and glycolysis remained highly active. Thus, in steatotic HepG2 cells, glycolysis and fatty acid oxidation may co-exist. Together, these pathways generate reducing equivalents that are supplied to mitochondrial oxidative phosphorylation.

Ischemia–reperfusion injury in patients with fatty liver and the clinical impact of steatotic liver on hepatic surgery

Hepatic steatosis is one of the most common hepatic disorders in developed countries. The epidemic of obesity in developed countries has increased with its attendant complications, including metabolic syndrome and non-alcoholic fatty liver disease. Steatotic livers are particularly vulnerable to ischemia/reperfusion injury, resulting in an increased risk of postoperative morbidity and mortality after liver surgery, including liver transplantation. There is growing understanding of the molecular and cellular mechanisms and therapeutic approaches for treating ischemia/reperfusion injury in patients with steatotic livers. This review discusses the mechanisms underlying the susceptibility of steatotic livers to ischemia/reperfusion injuries, such as mitochondrial dysfunction and signal transduction alterations, and summarizes the clinical impact of steatotic livers in the setting of hepatic resection and liver transplantation. This review also describes potential therapeutic approaches, such as ischemic and pharmacological preconditioning, to prevent ischemia/reperfusion injury in patients with steatotic livers. Other approaches, including machine perfusion, are also under clinical investigation; however, many pharmacological approaches developed through basic research are not yet suitable for clinical application.

Strategies to rescue steatotic livers before transplantation in clinical and experimental studies

The shortage of donor livers has led to an increased use of organs from expanded criteria donors. Included are livers with steatosis, a metabolic abnormality that increases the likelihood of graft complications post-transplantation. After a brief introduction on the etiology, pathophysiology, categories and experimental models of hepatic steatosis, we herein review the methods to rescue steatotic donor livers before transplantation applied in clinical and experimental studies. The methods span the spectrum of encouraging donor weight loss, employing drug therapy, heat shock preconditioning, ischemia preconditioning and selective anesthesia on donors, and the treatment on isolated grafts during preservation. These methods work at different stages of transplantation process, although share similar molecular mechanisms including lipid metabolism stimulation through enzymes or nuclear receptor e.g., peroxisomal proliferator-activated receptor, or anti-inflammation through suppressing cytokines e.g., tumor necrosis factor-α, or antioxidant therapies to alleviate oxidative stress. This similarity of molecular mechanisms implies possible future attempts to reinforce each approach by repeating the same treatment approach at several stages of procurement and preservation, as well as utilizing these alternative approaches in tandem.

Liver defatting: an alternative approach to enable steatotic liver transplantation

Macrovesicular steatosis in greater than 30% of hepatocytes is a significant risk factor for primary graft nonfunction due to increased sensitivity to ischemia reperfusion (I/R) injury. The growing prevalence of hepatic steatosis due to the obesity epidemic, in conjunction with an aging population, may negatively impact the availability of suitable deceased liver donors. Some have suggested that metabolic interventions could decrease the fat content of liver grafts prior to transplantation. This concept has been successfully tested through nutritional supplementation in a few living donors. Utilization of deceased donor livers, however, requires defatting of explanted organs. Animal studies suggest that this can be accomplished by ex vivo warm perfusion in a time scale of a few hours. We estimate that this approach could significantly boost the size of the donor pool by increasing the utilization of steatotic livers. Here we review current knowledge on the mechanisms whereby excessive lipid storage and macrosteatosis exacerbate hepatic I/R injury, and possible approaches to address this problem, including ex vivo perfusion methods as well as metabolically induced defatting. We also discuss the challenges ahead that need to be addressed for clinical implementation.

Are hepatic steatosis and carotid intima media thickness associated in obese patients with normal or slightly elevated gamma-glutamyl-transferase?

BACKGROUND

Hepatic steatosis (HS) has been associated with obesity and metabolic syndrome (MS), conditions carrying a high risk of coronary artery disease. We aimed to determine whether HS was an independent factor of atherogenic risk beyond its association with MS and its components.

METHODS

We assessed the circulating levels of the heat shock protein-70 (HSP-70), a chaperone involved in inflammation, endoplasmic reticulum stress and apoptosis at liver and endothelial level and the gamma-glutamyl transferase activity (γ-GT) correlating them to carotid intima-media thickness (IMT), along with lipid profile, HOMA, C-reactive protein, fibrinogen, ferritin, adiposity type as well as spleen volume in 52 obese pts with grade 1, 128 with grade 2, and 20 with grade 3 of HS evaluated by sonography.

RESULTS

Patients with different grade of HS demonstrated overlapping HSP-70 levels; similarly performed obese subjects regarding IMT. Using multiple regression analysis, IMT was predicted by age, visceral adiposity and by HOMA (β = 0.50, p < 0.0001, β = 0.30, p = 0.01 and β = 0.18, p = 0.048 respectively, while the severity of HS was predicted by visceral and subcutaneous adiposity and HOMA (β = 0.50, p < 0.0001 and β = 0.27, p = 0.001 and β = 0.18, p = 0.024, respectively).

CONCLUSION

In our series of patients with normal or mild elevation of γ-GT, the severity of HS does not entail higher IMT, which may be linked to MS stigmata.

Ischemia/reperfusion injury in liver resection: a review of preconditioning methods

Ischemic preconditioning is one of the therapeutic interventions aiming at preventing ischemia/reperfusion-related injury. Numerous experimental studies and a few clinical series have shown that during liver resections, ischemic preconditioning is a promising strategy for optimizing the postoperative outcome. Moreover, various types of pharmacological intervention as well as different types of preconditioning, such as remote preconditioning, the use of heat shock, and hyperbaric oxygen, have been developed to attenuate the functional impairment accompanying ischemia/reperfusion injury. This review summarizes the various forms of preconditioning, thus suggesting that close cooperation between surgeons and anesthesiologists paves the way to apply novel strategies to improve the outcome of liver resection.

Comparison of the response of human embryonic stem cells and their differentiated progenies to oxidative stress

OBJECTIVE

To investigate effects of oxidative stress on human embryonic stem cells (hESC) and their spontaneously differentiated fibroblastic progenies (at passage 5).

BACKGROUND DATA

In ischemic disease models, high levels of free radicals and reactive oxygen species are critical factors in decreasing survivability and engraftment of transplanted/transfused cells. Hence, it is imperative to characterize response of hESC and their differentiated progenies to oxidative stress.

METHODS

Oxidative stress was induced either by (i) varying durations (0 to 40 min) of photodynamic treatment (diode laser, 664 nm, 30 mW) in the presence of 10 microM methylene blue as a photosensitizer, or by (ii) exposure to varying concentrations of hydrogen peroxide (0 to 50 microM) for a fixed duration of 40 min. Additionally, the effects of heat shock and mild oxidative stress preconditioning on oxidative stress response was also investigated.

RESULTS

Consistently higher survivability (MTT assay) of hESC was observed compared to their differentiated fibroblastic progenies, upon exposure to equivalent levels of oxidative stress. Further experiments demonstrated that heat-shock pretreatment (42 degrees C for 90 min) did not enhance the resistance of either hESC or their differentiated progenies to oxidative stress (photodynamic treatment), but in fact had a slightly detrimental effect on their survivability upon subsequent exposure to oxidative stress. Similarly, preconditioning of both undifferentiated hESC and their differentiated progenies with low levels of oxidative stress also did not enhance cellular survivability upon subsequent exposure to much higher levels of oxidative stress induced by photodynamic treatment.

CONCLUSIONS

Undifferentiated hESC are intrinsically more resistant to oxidative stress compared to their spontaneously differentiated fibroblastic progenies.

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.

Modified mild heat shock modality attenuates hepatic ischemia/reperfusion injury

BACKGROUND

Hepatic ischemia/reperfusion (I/R) injury is a pathologic process caused by hepatic surgery and transplantation, and still remains a severe clinical problem. It was shown that preconditioning by hyperthermia might protect tissues against I/R injury. But hyperthermia could be laborious and time-consuming. Alternatively, the application of mild electrical stimulation (MES) has been reported to have positive effects in clinical settings on several medical ailments. Thus, we modified the preconditioning approach by combining short-term mild heat shock (HS) and MES, and evaluated the effect of HS+MES pretreatment on hepatic injury induced by I/R.

MATERIALS AND METHODS

C57BL/6J mice were sham treated or treated three times with HS (42 degrees C) and/or MES (12V) for 20min, carried out every other d within 1 wk. After the last treatment, mice were subjected to hepatic ischemia for 30 or 60min and reperfusion for 6h. Liver injury was assessed by evaluating the levels of serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST). The expressions of pro-inflammatory cytokines and heat shock protein (Hsp) 72 in liver tissues were also assessed by real-time PCR and Western blotting analyses, respectively.

RESULTS

HS+MES pretreatment suppressed the hepatic I/R-induced release of serum AST and ALT and the mRNA levels of some pro-inflammatory cytokines. In addition, HS+MES up-regulated the expression of Hsp72 in mice liver.

CONCLUSIONS

HS+MES preconditioning ameliorated hepatic I/R injury possibly through Hsp72 induction, and suppressed pro-inflammatory cytokine expression in mice liver.

Current studies on therapeutic approaches for ischemia/reperfusion injury in steatotic livers

Steatotic livers are particularly vulnerable to ischemia/reperfusion (I/R) injury, resulting in poor outcomes following liver surgery and transplantation. Therapeutic approaches for I/R injury in steatotic livers are currently under intensive investigation. This review summarizes and discusses the approaches developed during the last few years to prevent hepatic I/R injury in steatotic livers. Among the proposed approaches, ischemic preconditioning and intermittent clamping are the two most promising approaches that have been applied in some clinical centers for liver surgery and transplantation, but most of others have not reached clinical application yet.

Enhanced iNOS Gene Expression in the Steatotic Rat Liver after Normothermic Ischemia

BACKGROUND

Impaired hepatic microcirculation in the steatotic liver has been identified as a considerable factor for increased vulnerability after ischemia/reperfusion (I/R). Changes in regulation and synthesis of vasoactive mediators, such as nitric oxide (NO) and endothelin (ET-1), may result in functional impairment of postischemic sinusoidal perfusion. The aim of the current study was to assess the impact of I/R injury on postischemic gene expression of NO and ET-1 in steatotic livers.

MATERIALS AND METHODS

Male Sprague-Dawley rats with or without hepatic steatosis (induced by carbon tetrachloride treatment) were subjected to normothermic I/R injury. Steady-state mRNA levels were assessed using RT-PCR to study the expression of genes encoding ET-1, NO synthase (endothelial cell NO synthase and inducible NO synthase, iNOS). Immunohistochemistry was performed for detection of iNOS.

RESULTS

I/R injury was followed by increased iNOS gene expression (RT-PCR/immunohistochemistry) in animals with hepatic steatosis, predominately in hepatocytes with fatty degeneration. A mild increase in mRNA levels for ET-1 was found in steatotic rat livers. I/R induced a further increase in ET-1 gene expression in some but not all reperfused steatotic livers.

CONCLUSIONS

We show an enhanced gene expression of iNOS in postischemic steatotic rat livers. Hepatocytes with fatty degeneration appear to be the major source for NO generation. Furthermore, I/R may also induce ET-1 gene expression. Dysregulation of sinusoidal perfusion by NO and ET-1 is therefore likely to contribute to I/R injury of the steatotic liver.

Steatosis as a risk factor in liver surgery

OBJECTIVE

To review present knowledge of the influence of hepatic steatosis in liver surgery as derived from experimental and clinical studies.

SUMMARY BACKGROUND DATA

Hepatic steatosis is the most common chronic liver disease in the Western world, and it is associated with obesity, diabetes, and metabolic syndrome. Fatty accumulation affects hepatocyte homeostasis and potentially impairs recovery of steatotic livers after resection. This is reflected clinically in increased mortality and morbidity after liver resection in patients with any grade of steatosis. Because of the epidemic increase of obesity, hepatic steatosis will play an even more significant role in liver surgery.

METHODS

A literature review was performed using MEDLINE and key words related to experimental and clinical studies concerning steatosis.

RESULTS

Experimental studies show the increased vulnerability of steatotic livers to various insults, attributed to underlying metabolic and pathologic derangements induced by fatty accumulation. In clinical studies, the severity of steatosis has an important impact on patient outcome and mortality. Even the mildest form of steatosis increases the risk of postoperative complications.

CONCLUSIONS

Hepatic steatosis is a major factor determining patient outcome after surgery. Further research is needed to clarify the clinical relevance of all forms and severity grades of steatosis for patient outcome. Standardized grading and diagnostic methods need to be used in future clinical trials to be able to compare outcomes of different studies.

Heat shock preconditioning reduces ischemic tissue necrosis by heat shock protein (HSP)-32-mediated improvement of the microcirculation rather than induction of ischemic tolerance

INTRODUCTION

Supraphysiologic stress induces a heat shock response, which may exert protection against ischemic necrosis. Herein we analyzed in vivo whether the induction of heat shock protein (HSP) 32 improves survival of chronically ischemic myocutaneous tissue, and whether this is based on amelioration of microvascular perfusion or induction of ischemic tolerance.

METHODS

The dorsal skin of mice was subjected to local heat preconditioning (n = 8) 24 hours before surgery. In additional heat-preconditioned animals (n = 8), HSP-32 was inhibited by tin-protoporphyrin-IX. Unconditioned animals served as controls (n = 8). A random-pattern myocutaneous flap was elevated in the back of the animals and fixed into a dorsal skinfold chamber. The microcirculation, edema formation, apoptotic cell death, and tissue necrosis were analyzed over a 10-day period using intravital fluorescence microscopy.

RESULTS

HSP-32 protein expression was observed only in heat-preconditioned but not in unconditioned flaps. Heat preconditioning induced arteriolar dilation, which was associated with a significant improvement of both arteriolar blood flow and capillary perfusion in the distal part of the flap. Further, heat shock reduced interstitial edema formation, attenuated apoptotic cell death, and almost completely abrogated the development of flap necrosis (4% +/- 1% versus controls: 53% +/- 5%; P[r] < 0.001). Most strikingly, inhibition of HSP-32 by tin-protoporphyrin-IX completely blunted the preconditioning-induced improvement of microcirculation and resulted in manifestation of 72% +/- 4% necrosis.

CONCLUSION

Local heat preconditioning of myocutaneous tissue markedly increases flap survival by maintaining adequate nutritive perfusion rather than inducing ischemic tolerance. The protection is caused by the increased arteriolar blood flow due to significant arteriolar dilation, which is mediated through the carbon monoxide-associated vasoactive properties of HSP-32.

Synergistic effects of brain death and liver steatosis on the hepatic microcirculation

BACKGROUND

The routine transplantation of steatotic livers could potentially mitigate the donor shortage, but so far is associated with a high rate of graft dysfunction. Steatosis and brain death have been perceived as independent risk factors, but they may synergistically target the hepatic microcirculation. This study compares the effects of brain death on the microcirculation of steatotic and normal livers.

METHODS

Brain death was induced in obese and lean Zucker rats. Lean and obese sham-operated animals served as controls. Liver microcirculation was investigated using intravital fluorescence microscopy. Serum liver enzyme and reduced glutathione, expression of P-selectin, ICAM-1 and VCAM-1 mRNA in the liver were determined. The ultrastructural alterations were compared by electron microscopy.

RESULTS

In nonbrain-dead animals, liver steatosis was associated with smaller sinusoidal diameters, but did not impair sinusoidal perfusion. During brain death, sinusoidal diameter and perfusion were reduced in normal and, to a greater extent, in steatotic livers. Also, more leukocytes were recruited to the microvasculature of steatotic livers than to normal livers in brain-dead state. The highest liver enzyme activities and the lowest hepatic GSH concentrations were measured in brain-dead animals with steatotic livers; only in these organs was endothelial cell swelling regularly observed. In brain-dead state, only the P-selectin mRNA expression was increased in steatotic livers as compared to normal livers.

CONCLUSIONS

Brain death amplifies the adverse effects of steatosis on the hepatic microcirculation. Our results underline the need for therapeutic intervention in brain-dead state when steatotic livers are to be used for transplantation.