Adenosine monophosphate-activated protein kinase and nitric oxide in rat steatotic liver transplantation

Relevance of the GH-VEGFB/VEGFA axis in liver grafts from brain-dead donors with alcohol-associated liver disease

Introduction

Grafts with alcohol-associated liver disease (ALD) subjected to prolonged cold ischaemia from donors after brain death (DBD) are typically unsuitable for transplantation. Here, we investigated the role of growth hormone (GH) in livers with ALD from DBDs and its relationship with vascular endothelial growth factor A (VEGFA) and VEGFB.

Methods

Livers from rats fed ethanol for 6 weeks and with brain death (BD) were cold stored for 24 h and subjected to ex vivo reperfusion. Hepatic damage and proliferative and inflammatory parameters were analysed after BD, before graft retrieval, and after reperfusion. Survival was monitored using an in vivo transplantation model.

Results

In DBDs, the administration of GH, which increased the levels in the intestine but not in the liver, induced the generation of both VEGFA and VEGFB in the intestine and protected against hepatic damage caused by BD before retrieving liver grafts from donors. However, VEGFA was the only factor that protected against damage after cold ischemia and reperfusion, which also increased the survival of the recipients.

Discussion

In conclusion, the signalling pathway and beneficial properties of the GH-VEGFA/VEGFB pathway, in which the intestine-liver axis plays a key role, were disrupted when grafts with ALD from DBDs were retrieved from donors and subjected to cold ischemia and reperfusion.

Regulation of Adiponectin and Resistin in Liver Transplantation Protects Grafts from Extended-Criteria Donors

The donor shortage increases liver transplantation (LT) waiting lists, making it crucial to consider extended-criteria donors, such as steatotic donors after brain death (DBDs) or cardiocirculatory death (DCDs). Nevertheless, steatosis, brain death, and cardiocirculatory death are key risk factors for poor LT outcomes. We investigated the role and therapeutic usefulness of several adipocytokines to protect such grafts from extended-criteria donors. Sprague rats with nutritionally induced steatosis were used in an experimental LT model with grafts from DBDs or DCDs. Adiponectin, resistin, and visfatin were measured and pharmacologically modulated, and effects on liver injury were assessed. Visfatin played no role under conditions of neither DBD nor DCD LT. Brain death increased adiponectin and reduced resistin. Adiponectin harmed steatotic and nonsteatotic DBD grafts, via a resistin-dependent mechanism; restraining adiponectin increased resistin, reducing damage. Resistin treatment protected both types of DBD grafts, whereas suppressing it increased damage. This adiponectin-resistin pathway was dependent on protein kinase C. In DCD LT, adiponectin and resistin were not modified in nonsteatotic grafts, but reduced in steatotic ones. Adiponectin or resistin treatments protected steatotic grafts: hepatic adiponectin activated AMPK; hepatic resistin increased phosphatidylinositol 3-kinase-Akt. Concomitant administration of both adipocytokines increased both signaling pathways, intensifying protection. Therefore, pharmacologic modulation of adiponectin and resistin resulted in therapies that potentially might be translated to clinical studies to improve surgical outcomes for LT from extended-criteria donors.

Steatotic Donor Transplant Livers: Preservation Strategies to Mitigate against Ischaemia-Reperfusion Injury

Liver transplantation (LT) is the only definitive treatment for end-stage liver disease, yet the UK has seen a 400% increase in liver disease-related deaths since 1970, constrained further by a critical shortage of donor organs. This shortfall has necessitated the use of extended criteria donor organs, including those with evidence of steatosis. The impact of hepatic steatosis (HS) on graft viability remains a concern, particularly for donor livers with moderate to severe steatosis which are highly sensitive to the process of ischaemia-reperfusion injury (IRI) and static cold storage (SCS) leading to poor post-transplantation outcomes. This review explores the pathophysiological predisposition of steatotic livers to IRI, the limitations of SCS, and alternative preservation strategies, including novel organ preservation solutions (OPS) and normothermic machine perfusion (NMP), to mitigate IRI and improve outcomes for steatotic donor livers. By addressing these challenges, the liver transplant community can enhance the utilisation of steatotic donor livers which is crucial in the context of the global obesity crisis and the growing need to expand the donor pool.

Effectiveness of metformin for the reversal of cold-ischemia-induced damage in hepatosteatosis

BACKGROUND

Primary dysfunction and rejection are more common in donor liver tissues with steatosis. AMP-activated protein kinase (AMPK) assumes organ-protective functions during ischemia. Metformin was used for the activation of AMPK in hepatocytes. The aim of this study is to investigate the effectiveness of metformin administration for the reversal of cold-ischemia-induced damage in hepatosteatosis.

MATERIAL AND METHODS

Seven-week-old C7BL56 male-mice (n = 109) were separated into four groups depending on diet type and metformin use. A specific diet model was followed for 10 weeks to induce hepatosteatosis. A group of the animals was administered with metformin for the last four weeks via oral gavage. After resection, the liver tissues were perfused and kept for 0-6-12-24 h in the UW solution. Histopathological examinations were performed, and Western blot was utilized to analyze p-AMPK and AMPK expression levels.

RESULTS

Hepatosteatosis decreased significantly with metformin. The steatotic liver group had more prominent pericentral inflammation, necrosis as well as showing a decreased and more delayed AMPK response than the non-fat group. All these alterations could be corrected using metformin.

CONCLUSION

Metformin can increase the resistance of livers with hepatosteatosis to cold-ischemia-induced damage, which in turn may pave the way for successful transplantation of fatty living-donor livers.

NO-IL-6/10-IL-1β axis: a new pathway in steatotic and non-steatotic liver grafts from brain-dead donor rats

Introduction

Brain death (BD) and steatosis are both risk factors for organ dysfunction or failure in liver transplantation (LT).

Material and methods

Here, we examine the role of interleukin 6 (IL- 6) and IL-10 in LT of both non-steatotic and steatotic liver recovered from donors after brain death (DBDs), as well as the molecular signaling pathways underlying the effects of such cytokines.

Results

BD reduced IL-6 levels only in nonsteatotic grafts, and diminished IL-10 levels only in steatotic ones. In both graft types, BD increased IL-1β, which was associated with hepatic inflammation and damage. IL-6 administration reduced IL-1β only in non-steatotic grafts and protected them against damage and inflammation. Concordantly, IL-1β inhibition via treatment with an IL-1 receptor antagonist caused the same benefits in non-steatotic grafts. Treatment with IL-10 decreased IL-1β only in steatotic grafts and reduced injury and inflammation specifically in this graft type. Blockading the IL-1β effects also reduced damage and inflammation in steatotic grafts. Also, blockade of IL-1β action diminished hepatic cAMP in both types of livers, and this was associated with a reduction in liver injury and inflammation, then pointing to IL-1β regulating cAMP generation under LT and BD conditions. Additionally, the involvement of nitric oxide (NO) in the effects of interleukins was evaluated. Pharmacological inhibition of NO in LT from DBDs prompted even more evident reductions of IL-6 or IL-10 in non-steatotic and steatotic grafts, respectively. This exacerbated the already high levels of IL-1β seen in LT from DBDs, causing worse damage and inflammation in both graft types. The administration of NO donors to non-steatotic grafts potentiated the beneficial effects of endogenous NO, since it increased IL-6 levels, and reduced IL-1β, inflammation, and damage. However, treatment with NO donors in steatotic grafts did not modify IL-10 or IL-1β levels, but induced more injurious effects tan the induction of BD alone, characterized by increased nitrotyrosine, lipid peroxidation, inflammation, and hepatic damage.

Conclusion

Our study thus highlights the specificity of new signaling pathways in LT from DBDs: NO-IL-6-IL-1β in non-steatotic livers and NO-IL-10-IL-1β in steatotic ones. This opens up new therapeutic targets that could be useful in clinical LT.

How to Preserve Steatotic Liver Grafts for Transplantation

Liver allograft steatosis is a significant risk factor for postoperative graft dysfunction and has been associated with inferior patient and graft survival, particularly in the case of moderate or severe macrovesicular steatosis. In recent years, the increasing incidence of obesity and fatty liver disease in the population has led to a higher proportion of steatotic liver grafts being used for transplantation, making the optimization of their preservation an urgent necessity. This review discusses the mechanisms behind the increased susceptibility of fatty livers to ischemia-reperfusion injury and provides an overview of the available strategies to improve their utilization for transplantation, with a focus on preclinical and clinical evidence supporting donor interventions, novel preservation solutions, and machine perfusion techniques.

Transcriptome Profiling of the Liver in Nellore Cattle Phenotypically Divergent for RFI in Two Genetic Groups

The identification and selection of genetically superior animals for residual feed intake (RFI) could enhance productivity and minimize environmental impacts. The aim of this study was to use RNA-seq data to identify the differentially expressed genes (DEGs), known non-coding RNAs (ncRNAs), specific biomarkers and enriched biological processes associated with RFI of the liver in Nellore cattle in two genetic groups. In genetic group 1 (G1), 24 extreme RFI animals (12 low RFI (LRFI) versus 12 high RFI (HRFI)) were selected from a population of 60 Nellore bulls. The RNA-seq of the samples from their liver tissues was performed using an Illumina HiSeq 2000. In genetic group 2 (G2), 20 samples of liver tissue of Nellore bulls divergent for RFI (LRFI, n = 10 versus HRFI, n = 10) were selected from 83 animals. The raw data of the G2 were chosen from the ENA repository. A total of 1811 DEGs were found for the G1 and 2054 for the G2 (p-value ≤ 0.05). We detected 88 common genes in both genetic groups, of which 33 were involved in the immune response and in blocking oxidative stress. In addition, seven (B2M, ADSS, SNX2, TUBA4A, ARHGAP18, MECR, and ABCF3) possible gene biomarkers were identified through a receiver operating characteristic analysis (ROC) considering an AUC > 0.70. The B2M gene was overexpressed in the LRFI group. This gene regulates the lipid metabolism protein turnover and inhibits cell death. We also found non-coding RNAs in both groups. MIR25 was up-regulated and SNORD16 was down-regulated in the LRFI for G1. For G2, up-regulated RNase_MRP and SCARNA10 were found. We highlight MIR25 as being able to act by blocking cytotoxicity and oxidative stress and RMRP as a blocker of mitochondrial damage. The biological pathways associated with RFI of the liver in Nellore cattle in the two genetic groups were for energy metabolism, protein turnover, redox homeostasis and the immune response. The common transcripts, biomarkers and metabolic pathways found in the two genetic groups make this unprecedented work even more relevant, since the results are valid for different herds raised in different ways. The results reinforce the biological importance of these known processes but also reveal new insights into the complexity of the liver tissue transcriptome of Nellore cattle.

Effect of arginine supplementation on the production of milk fat in dairy cows

Arginine, one of the conditionally essential AA, has been reported to affect fat synthesis and metabolism in nonruminant animals by influencing adenosine monophosphate activated protein kinase (AMPK) in some organs. In dairy cows, the effect of Arg on milk fat production is not clear, and any potential mechanism that underlies the effect is unknown. We tested the hypothesis that Arg infusion would improve the production of milk fat, and explored possible mechanism that might underlie any effect. We used 6 healthy lactating cows at 20 ± 2 d in milk, in fourth parity, with a body weight of 508 ± 14 kg, body condition score of 3.0 ± 0, and a milk yield of 30.6 ± 1.8 kg/d (mean ± standard deviation). The cows were blocked by days in milk and milk yield and each cow received 3 treatments in a replicated 3 × 3 Latin square design, with each of the experimental periods lasting 7 d with a 14-d washout between each period. The treatments, delivered in random order, were (1) infusion of saline (control); (2) infusion of 0.216 mol/d of l-Arg in saline (Arg); (3) infusion of 0.868 mol/d of l-Ala in saline (the Arg and Ala treatments were iso-nitrogenous) through a jugular vein. On the last day of each experimental period, blood was sampled to measure insulin, nitric oxide, glucose, and nonesterified fatty acid, and the liver and mammary gland were biopsied to measure the expression of genes. Milk yield was recorded, and milk fat percentage was measured daily during each of the experimental periods. The yield and composition of fatty acid (FA) in milk was measured daily on the last 3 d during each of the experimental periods. The data were analyzed using a mixed model with treatment as a fixed factor, and cow, period, and block as random factors. The daily milk yield and milk fat yield when the cows were infused with Arg were 2.2 kg and 76 g, respectively, higher than that in control, and 1.8 kg and 111 g, respectively, higher than that in Ala. When the cows were infused with Arg they had higher concentration and yield of de novo synthesized FA, than when they received the control or Ala infusions, although milk fat percentage, daily feed intake, and the digestibility of nutrients were not affected by treatment. The serum concentration of nitric oxide and insulin were higher during Arg than during control or Ala, with no difference between control and Ala. In the liver, the expression of the genes coding for AMPK (PRKAA1, PRKAB1, and PRKAG1) and genes related to the oxidation of FA were higher during Arg than during control or Ala, whereas in the mammary gland the expression PRKAB1 was lowest, and the expression of genes involved in the synthesis of milk fat were highest, during Arg infusion. The results suggest the intravenous infusion of Arg enhanced the production of milk fat by promoting the de novo synthesis of FA and increasing milk yield.

The Role of Neuregulin-1 in Steatotic and Non-Steatotic Liver Transplantation from Brain-Dead Donors

Background. Brain death (BD) and steatosis are key risk factors to predict adverse post-transplant outcomes. We investigated the role of Neuregulin-1 (NRG1) in rat steatotic and non-steatotic liver transplantation (LT) from brain death donors (DBD). Methods: NRG1 pathways were characterized after surgery. Results: NRG1 and p21-activated kinase 1 (PAK1) levels increased in steatotic and non-steatotic grafts from DBDs. The abolishment of NRG1 effects reduced PAK1. When the effect of either NRG1 nor PAK1 was inhibited, injury and regenerative failure were exacerbated. The benefits of the NRG-1-PAK1 axis in liver grafts from DBDs were associated with increased vascular endothelial growth factor-A (VEGFA) and insulin growth factor-1 (IGF1) levels, respectively. Indeed, VEGFA administration in non-steatotic livers and IGF1 treatment in steatotic grafts prevented damage and regenerative failure resulting from the inhibition of either NRG1 or PAK-1 activity in each type of liver. Exogenous NRG1 induced greater injury than BD induction. Conclusions: This study indicates the benefits of endogenous NRG1 in liver grafts from DBDs and underscores the specificity of the NRG1 signaling pathway depending on the type of liver: NRG1-PAK1-VEGFA in non-steatotic livers and NRG1-PAK1-IGF1 in steatotic livers. Exogenous NRG1 is not an appropriate strategy to apply to liver grafts from DBD.

New Insights Into the Role of Autophagy in Liver Surgery in the Setting of Metabolic Syndrome and Related Diseases

Visceral obesity is an important component of metabolic syndrome, a cluster of diseases that also includes diabetes and insulin resistance. A combination of these metabolic disorders damages liver function, which manifests as non-alcoholic fatty liver disease (NAFLD). NAFLD is a common cause of abnormal liver function, and numerous studies have established the enormously deleterious role of hepatic steatosis in ischemia-reperfusion (I/R) injury that inevitably occurs in both liver resection and transplantation. Thus, steatotic livers exhibit a higher frequency of post-surgical complications after hepatectomy, and using liver grafts from donors with NAFLD is associated with an increased risk of post-surgical morbidity and mortality in the recipient. Diabetes, another MetS-related metabolic disorder, also worsens hepatic I/R injury, and similar to NAFLD, diabetes is associated with a poor prognosis after liver surgery. Due to the large increase in the prevalence of MetS, NAFLD, and diabetes, their association is frequent in the population and therefore, in patients requiring liver resection and in potential liver graft donors. This scenario requires advancement in therapies to improve postoperative results in patients suffering from metabolic diseases and undergoing liver surgery; and in this sense, the bases for designing therapeutic strategies are in-depth knowledge about the molecular signaling pathways underlying the effects of MetS-related diseases and I/R injury on liver tissue. A common denominator in all these diseases is autophagy. In fact, in the context of obesity, autophagy is profoundly diminished in hepatocytes and alters mitochondrial functions in the liver. In insulin resistance conditions, there is a suppression of autophagy in the liver, which is associated with the accumulation of lipids, being this is a risk factor for NAFLD. Also, oxidative stress occurring in hepatic I/R injury promotes autophagy. The present review aims to shed some light on the role of autophagy in livers undergoing surgery and also suffering from metabolic diseases, which may lead to the discovery of effective therapeutic targets that could be translated from laboratory to clinical practice, to improve postoperative results of liver surgeries when performed in the presence of one or more metabolic diseases.

Association between temperament related traits and single nucleotide polymorphisms in the serotonin and oxytocin systems in Merino sheep

Animal temperament is defined as the consistent behavioral and physiological differences that are seen between individuals in response to the same stressor. Neurotransmitter systems, like serotonin and oxytocin in the central nervous system, underlie variation in behavioral traits in humans and other animals. Variations like single nucleotide polymorphisms (SNPs) in the genes for tryptophan 5-hydroxylase (TPH2), the serotonin transporter (SLC6A4), the serotonin receptor (HTR2A), and the oxytocin receptor (OXTR) are associated with behavioral phenotype in humans. Thus, the objective of this study was to identify SNPs in those genes and to test if those variations are associated with the temperament in Merino sheep. Using ewes from the University of Western Australia temperament flock, which has been selected on emotional reactivity for more than 20 generations, eight SNPs (rs107856757, rs107856818, rs107856856 and rs107857156 in TPH2, rs20917091 in SLC6A4, rs17196799 and rs17193181 in HTR2A, and rs17664565 in OXTR) were found to be distributed differently between calm and nervous sheep. These eight SNPs were then genotyped in 260 sheep from a flock that has never been selected on emotional reactivity, followed by the estimation of the behavioral traits of those 260 sheep using an arena test and an isolation box test. We found that several SNPs in TPH2 (rs107856757, rs107856818, rs107856856 and rs107857156) were in strong linkage disequilibrium, and all were associated with behavioral phenotype in the nonselected sheep. Similarly, rs17196799 in HTR2A was also associated with the behavioral phenotype.

Bardallo R, Calvo M, Folch-Puy E, Carbonell T, Palmeira C, Roselló Catafau J, Adam R. Polyethylene Glycol 35 as a Perfusate Additive for Mitochondrial and Glycocalyx Protection in HOPE Liver Preservation

Organ transplantation is a multifactorial process in which proper graft preservation is a mandatory step for the success of the transplantation. Hypothermic preservation of abdominal organs is mostly based on the use of several commercial solutions, including UW, Celsior, HTK and IGL-1. The presence of the oncotic agents HES (in UW) and PEG35 (in IGL-1) characterize both solution compositions, while HTK and Celsior do not contain any type of oncotic agent. Polyethylene glycols (PEGs) are non-immunogenic, non-toxic and water-soluble polymers, which present a combination of properties of particular interest in the clinical context of ischemia-reperfusion injury (IRI): they limit edema and nitric oxide induction and modulate immunogenicity. Besides static cold storage (SCS), there are other strategies to preserve the organ, such as the use of machine perfusion (MP) in dynamic preservation strategies, which increase graft function and survival as compared to the conventional static hypothermic preservation. Here we report some considerations about using PEG35 as a component of perfusates for MP strategies (such as hypothermic oxygenated perfusion, HOPE) and its benefits for liver graft preservation. Improved liver preservation is closely related to mitochondria integrity, making this organelle a good target to increase graft viability, especially in marginal organs (e.g., steatotic livers). The final goal is to increase the pool of suitable organs, and thereby shorten patient waiting lists, a crucial problem in liver transplantation.

Exercise Improves Outcomes of Surgery on Fatty Liver in Mice: A Novel Effect Mediated by the AMPK Pathway

OBJECTIVE

To investigate whether exercise improves outcomes of surgery on fatty liver, and whether pharmacological approaches can substitute exercising programs.

SUMMARY OF BACKGROUND DATA

Steatosis is the hepatic manifestation of the metabolic syndrome, and decreases the liver's ability to handle inflammatory stress or to regenerate after tissue loss. Exercise activates adenosine monophosphate-activated kinase (AMPK) and mitigates steatosis; however, its impact on ischemia-reperfusion injury and regeneration is unknown.

METHODS

We used a mouse model of simple, diet-induced steatosis and assessed the impact of exercise on metabolic parameters, ischemia-reperfusion injury and regeneration after hepatectomy. The same parameters were evaluated after treatment of mice with the AMPK activator 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR). Mice on a control diet served as age-matched controls.

RESULTS

A 4-week-exercising program reversed steatosis, lowered insulin levels, and improved glucose tolerance. Exercise markedly enhanced the ischemic tolerance and the regenerative capacity of fatty liver. Replacing exercise with AICAR was sufficient to replicate the above benefits. Both exercise and AICAR improved survival after extended hepatectomy in mice challenged with a Western diet, indicating protection from resection-induced liver failure.

CONCLUSIONS

Exercise efficiently counteracts the metabolic, ischemic, and regenerative deficits of fatty liver. AICAR acts as an exercise mimetic in settings of fatty liver disease, an important finding given the compliance issues associated with exercise. Exercising, or its substitution through AICAR, may provide a feasible strategy to negate the hepatic consequences of energy-rich diet, and has the potential to extend the application of liver surgery if confirmed in humans.

AICAR prolongs corneal allograft survival via the AMPK-mTOR signaling pathway in mice

Immune rejection is a critical complication that results in the graft failure after corneal transplantation. Thus, there remains a need for new therapies for allograft rejection. AICAR (aminoimidazole-4-carboxamide ribonucleoside) is an, as adenosine monophosphate-activated protein kinase (AMPK) activator and a purine nucleoside with a wide range of metabolic effects, including activation of AMPK. More recently, it was reported that it is possible to inhibiting organs rejection and prolong the graft survival time in various models of organ transplantation. In this study, we systematically evaluated the efficacy of AICAR as a treatment modality for inhibiting allograft rejection in a mouse model of corneal transplantation. We found that AICAR significantly suppressed the opacity, edema, and vascularization of the graft, resulting in prolonged corneal allograft survival. AICAR treatment also significantly decreased central corneal thickness. Moreover, the AICAR-treated group showed decreased expression of IB4 and VEGF as compared to the control group. In addition, the mRNA expression of T helper 1 cytokines (IL-2, INF-γ, and TNF-α) was suppressed, and the expression of T helper 2 cytokines (IL-4, IL-5, and IL-13) was elevated by AICAR. Furthermore, the western blotting results revealed that AICAR stimulated AMPK activation and inhibited angiogenesis and inflammation possibly by subsequently suppressing mTOR phosphorylation. By contrast, the AMPK inhibitor Compound C (also called dorsomorphin) had the opposite effect. Our results showed that Compound C blocked AMPK-mTOR signaling and promoted the angiogenesis and inflammation, thus compromising the graft survival. These results suggest that AICAR may be a potential option for inhibiting the corneal graft rejection and for prolonging the graft survival.

Glycocalyx Preservation and NO Production in Fatty Livers-The Protective Role of High Molecular Polyethylene Glycol in Cold Ischemia Injury

Improving the protection of marginal liver grafts during static cold storage is a major hurdle to increase the donor pool of organs. The endothelium glycocalyx quality of preservation influences future inflammatory and oxidative responses. One cellular pathway responsible for the formation of nitric oxide by endothelial cells is dependent on the stimulation of proteoglycans present in the glycocalyx. We investigated the impact of the glycocalyx preservation in static cold storage of fatty liver preserved in different preservation solutions on the endothelium-mediated production of NO. Zucker fatty rat livers were preserved 24 h in static cold storage in either Institut Georges Lopez-1 (IGL-1) (n = 10), IGL-0 (i.e., without PEG35) (n = 5) or Histidine-Tryptophan-Ketoglutarate (HTK) (n = 10) preservation solutions before being processed for analysis. For Sham group (n = 5), the fatty livers were immediately analyzed after procurement. The level of transaminases and nitrites/nitrates were measured in the washing perfusate. Glycocalyx proteins expressions, Syndecan-1, glypican-1 and heparan sulfate (HS), were determined in the tissue (ELISA). Steatotic livers preserved 24 h in IGL-1 preservation solution have a significant lower level of transaminases (aspartate aminotransferase (AST), alanine aminotransferase (ALT)) and less histological damages than steatotic livers preserved 24 h with HTK (p = 0.0152). The syndecan-1 is significantly better preserved in IGL-1 group compared to HTK (p < 0.0001) and we observed the same tendency compared to IGL-0. No significant differences were observed with glypican-1. HS expression in HTK group was significantly higher compared to the three other groups. HS level in IGL-1 was even lower than IGL-0 (p = 0.0005) which was similar to Sham group. The better protection of the glycocalyx proteins in IGL-1 group was correlated with a higher production of NO than HTK (p = 0.0055) or IGL-0 (p = 0.0433). IGL-1 protective mechanisms through the formation of NO could be due to its better protective effects on the glycocalyx during SCS compared to other preservation solutions. This beneficial effect could involve the preservation state of syndecan-1 and the internalization of HS.

Short-term and long-term outcomes of liver transplantation using moderately and severely steatotic donor livers: A systematic review

BACKGROUND

The aim of this study was to perform a systemic review of the studies addressing the use of moderately and severely steatotic donor livers for liver transplantation.

METHODS

We searched the following electronic databases from January 1, 1989, to August 1, 2017: PubMed, EMBASE, Science Citation Index Expanded, and the Cochrane Library. In addition, reference lists were scanned to identify any additional reports. The quality of published papers was assessed. The main outcomes of the use of moderately and severely steatotic donor livers for liver transplantation, including primary nonfunction, short-term mortality, and long-term mortality, were extracted for pooled analysis.

RESULTS

Literature searches identified 16 studies that met the inclusion criteria. There were no randomized controlled studies, and all of the studies were retrospective or prospective case series. From a total of 3226 subjects (532 moderately and severely steatotic donor livers and 2694 controls), we found a significant increase in primary nonfunction [odds ratio (OR): 2.47, 95% confidence interval (95% CI): 1.44-4.27], and a trend of increase in 1-month patient mortality (OR: 1.90, 95% CI: 0.98-3.71) with the use of moderately and severely steatotic donor livers, whereas the 1-year mortality was relatively less influenced.

CONCLUSION

The use of moderately and severely steatotic livers is associated with unfavorable short-term outcomes, but long-term outcomes are relatively less influenced.

AMPK activation promotes gastroprotection through mutual interaction with the gaseous mediators H2S, NO, and CO

Activation of 5' adenosine monophosphate-activated protein kinase (AMPK) stimulates production of the gaseous mediators nitric oxide (NO) and carbon monoxide (CO), which are involved in mucosal defense and gastroprotection. As AMPK itself has gastroprotective effects against several gastric ulcer etiologies, in the present study, we aimed to elucidate whether AMPK may also prevent ethanol-induced injury and play a key role in the associated gastroprotection mediated by hydrogen sulfide (H₂S), NO, and CO. Mice were pretreated with AICAR (20 mg/kg, an AMPK activator) alone or with 50% ethanol. Other groups were pretreated with respective gaseous mediator inhibitors PAG, l-NAME, or ZnPP IX 30 min prior to AICAR, or with gaseous mediator donors NaHS, Lawesson's reagent and l-cysteine (H₂S), SNP, l-Arginine (NO), Hemin, or CORM-2 (CO) 30 min prior to ethanol with or without compound C (10 mg/kg, a non-selective AMPK inhibitor). H₂S, nitrate/nitrite (NO₃^-/NO₂^-), bilirubin levels, GSH and MDA concentration were evaluated in the gastric mucosa. The gastric mucosa was also collected for histopathological analysis and AMPK expression assessment by immunohistochemistry. Pretreatment with AICAR attenuated the ethanol-induced injury and increased H₂S and bilirubin levels but not NO₃^-/NO₂^- levels in the gastric mucosa. In addition, inhibition of H₂S, NO, or CO synthesis exacerbated the ethanol-induced gastric damage and inhibited the gastroprotection by AICAR. Pretreatment with compound C reversed the gastroprotective effect of NaHS, Lawesson's reagent, l-cysteine, SNP, l-Arginine, CORM-2, or Hemin. Compound C also reversed the effect of NaHS on H₂S production, SNP on NO₃^-/NO₂^- levels, and Hemin on bilirubin levels. Immunohistochemistry revealed that AMPK is present at basal levels mainly in the gastric mucosa cells, and was increased by pretreatment with NaHS, SNP, and CORM-2. In conclusion, our findings indicate that AMPK activation exerts gastroprotection against ethanol-induced gastric damage and mutually interacts with H₂S, NO, or CO to facilitate this process.

The Relevance of the UPS in Fatty Liver Graft Preservation: A New Approach for IGL-1 and HTK Solutions

The 26S proteasome is the central proteolytic machinery of the ubiquitin proteasome system (UPS), which is involved in the degradation of ubiquitinated protein substrates. Recently, UPS inhibition has been shown to be a key factor in fatty liver graft preservation during organ cold storage using University of Wisconsin solution (UW) and Institute Georges Lopez (IGL-1) solutions. However, the merits of IGL-1 and histidine-tryptophan-ketoglutarate (HTK) solutions for fatty liver preservation have not been compared. Fatty liver grafts from obese Zücker rats were preserved for 24 h at 4 °C. Aspartate aminotransferase and alanine aminotransferase (AST/ALT), glutamate dehydrogenase (GLDH), ATP, adenosine monophosphate protein kinase (AMPK), e-NOS, proteasome activity and liver polyubiquitinated proteins were determined. IGL-1 solution prevented ATP breakdown during cold-storage preservation of steatotic livers to a greater extent than HTK solution. There were concomitant increases in AMPK activation, e-NOS (endothelial NOS (NO synthase)) expression and UPS inhibition. UPS activity is closely related to the composition of the solution used to preserve the organ. IGL-1 solution provided significantly better protection against ischemia-reperfusion for cold-stored fatty liver grafts than HTK solution. The effect is exerted through the activation of the protective AMPK signaling pathway, an increase in e-NOS expression and a dysregulation of the UPS.

The impact of cortisol in steatotic and non-steatotic liver surgery

The intent of this study was to examine the effects of regulating cortisol levels on damage and regeneration in livers with and without steatosis subjected to partial hepatectomy under ischaemia–reperfusion. Ultimately, we found that lean animals undergoing liver resection displayed no changes in cortisol, whereas cortisol levels in plasma, liver and adipose tissue were elevated in obese animals undergoing such surgery. Such elevations were attributed to enzymatic upregulation, ensuring cortisol production, and downregulation of enzymes controlling cortisol clearance. In the absence of steatosis, exogenous cortisol administration boosted circulating cortisol, while inducing clearance of hepatic cortisol, thus maintaining low cortisol levels and preventing related hepatocellular harm. In the presence of steatosis, cortisol administration was marked by a substantial rise in intrahepatic availability, thereby exacerbating tissue damage and regenerative failure. The injurious effects of cortisol were linked to high hepatic acethylcholine levels. Upon administering an α7 nicotinic acethylcholine receptor antagonist, no changes in terms of tissue damage or regenerative lapse were apparent in steatotic livers. However, exposure to an M3 muscarinic acetylcholine receptor antagonist protected livers against damage, enhancing parenchymal regeneration and survival rate. These outcomes for the first time provide new mechanistic insight into surgically altered steatotic livers, underscoring the compelling therapeutic potential of cortisol–acetylcholine–M3 muscarinic receptors.

The Effect of High-Mobility Group Box 1 in Rat Steatotic and Nonsteatotic Liver Transplantation From Donors After Brain Death

High-mobility group box 1 (HMGB1) has been described in different inflammatory disorders, and the deleterious effects of brain death (BD) may counteract the protection conferred by ischemic preconditioning (IP), the only surgical strategy that is being applied in clinical liver transplantation. Our study examined how HMGB1 may affect preconditioned and unpreconditioned steatotic and nonsteatotic liver grafts from donors after BD (DBDs) for transplantation. HMGB1 was pharmacologically modulated in liver grafts from DBDs, and HMGB1-underlying mechanisms were characterized. We found that BD decreased HMGB1 in preconditioned and unpreconditioned livers and was associated with inflammation and damage. Exogenous HMGB1 in DBDs activates phosphoinositide-3-kinase and Akt and reduces hepatic inflammation and damage, increasing the survival of recipients. Combination of IP and exogenous HMGB1 shows additional benefits compared with HMGB1 alone. This study provides new mechanistic insights into the pathophysiology of BD-derived liver graft damage and contributes to the development of novel and efficient strategies to ultimately improve liver graft quality.

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.

Mitochondrial dysfunction in steatotic rat livers occurs because a defect in complex i makes the liver susceptible to prolonged cold ischemia

Steatotic livers are susceptible to cold ischemia, which is thought to be secondary to mitochondrial dysfunction. Ischemic preconditioning (IPC) has been reported to improve liver function in the setting of warm ischemia/reperfusion injury, but the effect of IPC on steatotic liver mitochondrial function (MF) with cold ischemia has not been previously evaluated. We aimed to evaluate MF with various severities of hepatic steatosis after various durations of cold ischemia storage with or without IPC. Male Sprague-Dawley rats were fed a normal diet or a high-fat/high-sucrose diet for 1, 2, or 4 weeks to induce mild (<30%), moderate (30%-60%), or severe (>60%) macrovesicular steatosis, respectively. Liver MF was tested with high-resolution respirometry after 1.5, 4, 8, 12, 18, and 24 hours of cold ischemia. Rats in each group (n = 10) underwent 10 minutes of IPC or no IPC before cold ischemia. The baseline (time 0) respiration was similar for lean and severely steatotic livers despite decreased mitochondrial complex I (C-I) activity in severely steatotic livers. Hepatic steatosis was associated with increased C-I-mediated leaks and decreased respiratory control ratios (RCRs) after cold ischemia. Mildly, moderately, and severely steatotic livers showed significantly lower RCRs after 8, 1.5, and 1.5 hours of cold ischemia, respectively, in comparison with lean livers. IPC restored RCRs in mildly steatotic livers to levels comparable to those in lean livers for up to 24 hours of cold ischemia via the attenuation of C-I-mediated leaks, but it had no beneficial effect on moderately and severely steatotic livers. In conclusion, steatotic livers exhibited apparent mitochondrial dysfunction through an alteration in C-I activity, and this made them more susceptible to prolonged cold ischemia. The clinically based IPC protocol used here restored MF in cases of mild hepatic steatosis by attenuating C-I-mediated leaks after prolonged cold ischemia, but it did work not in livers with moderate or severe steatosis.

Impact of ischaemic preconditioning on experimental steatotic livers following hepatic ischaemia-reperfusion injury: a systematic review

BACKGROUND

Steatotic livers are vulnerable to the deleterious effects of ischaemia-reperfusion injury (IRI) that occur after hepatic surgery. Ischaemic preconditioning (IPC) has been shown to abrogate the effects of IRI in patients undergoing hepatic surgery. Experimental studies have suggested that IPC may be beneficial in steatotic livers subjected to IRI.

OBJECTIVE

The aim of this systematic review was to evaluate the effects of IPC on steatotic livers following hepatic IRI in experimental models.

METHODS

An electronic search of the OVID Medline and EMBASE databases was performed to identify studies that reported clinically relevant outcomes in animal models of hepatic steatosis subjected to IPC and IRI.

RESULTS

A total of 1093 articles were identified, of which 18 met the inclusion criteria. There was considerable heterogeneity in the type of animal model, and duration and type of IRI. Increased macrovesicular steatosis (> 30%) was associated with a poor outcome following IRI. Ischaemic preconditioning was found to be beneficial in > 30% steatotic livers and provided for decreased histological damage, improved liver function findings and increased survival.

CONCLUSIONS

Experimental evidence supports the use of IPC in steatotic livers undergoing IRI. These findings may be applicable to patients undergoing liver surgery. However, clinical studies are required to validate the efficacy of IPC in this setting.

Polyethylene glycol rinse solution: An effective way to prevent ischemia-reperfusion injury

AIM: To test whether a new rinse solution containing polyethylene glycol 35 (PEG-35) could prevent ischemia-reperfusion injury (IRI) in liver grafts.

METHODS: Sprague-Dawley rat livers were stored in University of Wisconsin preservation solution and then washed with different rinse solutions (Ringer’s lactate solution and a new rinse solution enriched with PEG-35 at either 1 or 5 g/L) before ex vivo perfusion with Krebs-Heinseleit buffer solution. We assessed the following: liver injury (transaminase levels), mitochondrial damage (glutamate dehydrogenase activity), liver function (bile output and vascular resistance), oxidative stress (malondialdehyde), nitric oxide, liver autophagy (Beclin-1 and LCB3) and cytoskeleton integrity (filament and globular actin fraction); as well as levels of metalloproteinases (MMP2 and MMP9), adenosine monophosphate-activated protein kinase (AMPK), heat shock protein 70 (HSP70) and heme oxygenase 1 (HO-1).

RESULTS: When we used the PEG-35 rinse solution, reduced hepatic injury and improved liver function were noted after reperfusion. The PEG-35 rinse solution prevented oxidative stress, mitochondrial damage, and liver autophagy. Further, it increased the expression of cytoprotective heat shock proteins such as HO-1 and HSP70, activated AMPK, and contributed to the restoration of cytoskeleton integrity after IRI.

CONCLUSION: Using the rinse solution containing PEG-35 was effective for decreasing liver graft vulnerability to IRI.

Silent information regulator 1 protects the liver against ischemia-reperfusion injury: implications in steatotic liver ischemic preconditioning

Ischemia-reperfusion (IR) injury is an important problem in liver surgery especially when steatosis is present. Ischemic preconditioning (PC) is the only surgical strategy that has been applied in patients with steatotic livers undergoing warm ischemia. Silent information regulator 1 (SIRT1) is a histone deacetylase that regulates various cellular processes. This study evaluates the SIRT1 implication in PC in fatty livers. Homozygous (Ob) Zucker rats were subjected to IR and IR + PC. An additional group treated with sirtinol or EX527 (SIRT1 inhibitors) before PC was also realized. Liver injury and oxidative stress were evaluated. SIRT1 protein levels and activity, as well as other parameters involved in PC protective mechanisms (adenosine monophosphate protein kinase, eNOS, HSP70, MAP kinases, apoptosis), were also measured. We demonstrated that the protective effect of PC was due in part to SIRT1 induction, as SIRT1 inhibition resulted in increased liver injury and abolished the beneficial mechanisms of PC. In this study, we report for the first time that SIRT1 is involved in the protective mechanisms induced by hepatic PC in steatotic livers.

Adiponectin and resistin protect steatotic livers undergoing transplantation

BACKGROUND & AIMS

Numerous steatotic livers are discarded for transplantation because of their poor tolerance to ischemia-reperfusion. Controversial roles for adiponectin and related adipocytokines visfatin and resistin have been described in different liver pathologies, nevertheless it is unknown their possible implication in ischemia-reperfusion injury associated with liver transplantation. Our study aimed at characterizing the role of the adiponectin-derived molecular pathway in transplantation with steatotic and non-steatotic liver grafts.

METHODS

Steatotic and non-steatotic liver transplantation was carried out and the hepatic levels of adiponectin, visfatin and resistin were measured and modulated either pharmacologically or surgically.

RESULTS

Steatotic liver grafts exhibited downregulation of both adiponectin and resistin when subjected to transplantation. Adiponectin pre-treatment only protected steatotic grafts and did it so through a visfatin-independent and resistin-dependent mechanism. Adiponectin-derived resistin accumulation activated the PI3K/Akt pathway, unravelling AMPK as an upstream mediator of adiponectin's actions in steatotic grafts. Strategies aimed at increasing adiponectin including either AMPK activators or the induction of ischemic preconditioning (which activates AMPK) increased resistin accumulation, prevented the downregulation of PI3K/Akt pathway and protected steatotic liver grafts. Conversely, PI3K/Akt pathway upregulation and hepatic protection induced by adiponectin were abolished when resistin action was inhibited.

CONCLUSIONS

Our findings reveal a new protective pathway in steatotic liver transplantation, namely AMPK-adiponectin-resistin-PI3K/Akt, which may help develop new strategies aimed at increasing either adiponectin or resistin in the steatotic liver undergoing transplant to ultimately increase organ donor pool and reduce waiting list.

Hepatic ischemia and reperfusion injury: effects on the liver sinusoidal milieu

Ischemia-reperfusion injury is an important cause of liver damage occurring during surgical procedures including hepatic resection and liver transplantation, and represents the main underlying cause of graft dysfunction post-transplantation. Cellular and biochemical processes occurring during hepatic ischemia-reperfusion are diverse and complex, and include the deregulation of the healthy phenotype of all liver cellular components. Nevertheless, a significant part of these processes are still unknown or unclear. The present review aims at summarizing the current knowledge in liver ischemia-reperfusion, but specifically focusing on liver cell phenotype and paracrine interaction deregulations. Moreover, the most updated therapeutic strategies including pharmacological, genetic and surgical interventions, as well as some of the scientific controversies in the field will be described. Finally, the importance of considering the subclinical situation of liver grafts when translating basic knowledge to the bedside is discussed.

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.

AMPK involvement in endoplasmic reticulum stress and autophagy modulation after fatty liver graft preservation: a role for melatonin and trimetazidine cocktail

Ischemia/reperfusion injury (IRI) associated with liver transplantation plays an important role in the induction of graft injury. Prolonged cold storage remains a risk factor for liver graft outcome, especially when steatosis is present. Steatotic livers exhibit exacerbated endoplasmic reticulum (ER) stress that occurs in response to cold IRI. In addition, a defective liver autophagy correlates well with liver damage. Here, we evaluated the combined effect of melatonin and trimetazidine as additives to IGL-1 solution in the modulation of ER stress and autophagy in steatotic liver grafts through activation of AMPK. Steatotic livers were preserved for 24 hr (4°C) in UW or IGL-1 solutions with or without MEL + TMZ and subjected to 2-hr reperfusion (37°C). We assessed hepatic injury (ALT and AST) and function (bile production). We evaluated ER stress (GRP78, PERK, and CHOP) and autophagy (beclin-1, ATG7, LC3B, and P62). Steatotic livers preserved in IGL-1 + MEL + TMZ showed lower injury and better function as compared to those preserved in IGL-1 alone. IGL-1 + MEL + TMZ induced a significant decrease in GRP78, pPERK, and CHOP activation after reperfusion. This was consistent with a major activation of autophagic parameters (beclin-1, ATG7, and LC3B) and AMPK phosphorylation. The inhibition of AMPK induced an increase in ER stress and a significant reduction in autophagy. These data confirm the close relationship between AMPK activation and ER stress and autophagy after cold IRI. The addition of melatonin and TMZ to IGL-1 solution improved steatotic liver graft preservation through AMPK activation, which reduces ER stress and increases autophagy.

Proteasome inhibitors protect the steatotic and non-steatotic liver graft against cold ischemia reperfusion injury

BACKGROUND

The dramatic shortage of organs leads to consider the steatotic livers for transplantation although their poor tolerance against ischemia reperfusion injury (IRI). Ubiquitin proteasome system (UPS) inhibition during hypothermia prolongs myocardial graft preservation. The role of UPS in the liver IRI is not fully understood. Bortezomib (BRZ) treatment at non-toxic doses of rats fed alcohol chronically has shown protective effects by increasing liver antioxidant enzymes. We evaluated and compared both proteasome inhibitors BRZ and MG132 in addition to University of Wisconsin preservation solution (UW) at low and non-toxic dose for fatty liver graft protection against cold IRI.

EXPERIMENTAL

Steatotic and non-steatotic livers have been stored in UW enriched with BRZ (100 nM) or MG132 (25 μM), for 24h at 4°C and then subjected to 2-h normothermic reperfusion (37 °C). Liver injury (AST/ALT), hepatic function (bile output; vascular resistance), mitochondrial damage (GLDH), oxidative stress (MDA), nitric oxide (NO) (e-NOS activity; nitrates/nitrites), proteasome chymotrypsin-like activity (ChT), and UPS (19S and 20S5 beta) protein levels have been measured.

RESULTS

ChT was inhibited when BRZ and MG132 were added to UW. Both inhibitors prevented liver injury (AST/ALT), when compared to UW alone. BRZ increased bile production more efficiently than MG132. Only BRZ decreased vascular resistance in fatty livers, which correlated with an increase in NO generation (through e-NOS activation) and AMPK phosphorylation. GLDH and MDA were also prevented by BRZ. In addition, BRZ inhibited adiponectin, IL-1, and TNF alpha, only in steatotic livers.

CONCLUSION

MG132 and BRZ, administrated at low and non toxic doses, are very efficient to protect fatty liver grafts against cold IRI. The benefits of BRZ are more effective than those of MG132. This evidenced for the first time the potential use of UPS inhibitors for the preservation of marginal liver grafts and for future applications in the prevention of IRI.

Tauroursodeoxycholic acid affects PPARγ and TLR4 in Steatotic liver transplantation

Numerous steatotic livers are discarded for transplantation because of their poor tolerance to ischemia-reperfusion (I/R). We examined whether tauroursodeoxycholic acid (TUDCA), a known inhibitor of endoplasmic reticulum (ER) stress, protects steatotic and nonsteatotic liver grafts preserved during 6 h in University of Wisconsin (UW) solution and transplanted. The protective mechanisms of TUDCA were also examined. Neither unfolded protein response (UPR) induction nor ER stress was evidenced in steatotic and nonsteatotic liver grafts after 6 h in UW preservation solution. TUDCA only protected steatotic livers grafts and did so through a mechanism independent of ER stress. It reduced proliferator-activated receptor-γ (PPARγ) and damage. When PPARγ was activated, TUDCA did not reduce damage. TUDCA, which inhibited PPARγ, and the PPARγ antagonist treatment up-regulated toll-like receptor 4 (TLR4), specifically the TIR domain-containing adaptor inducing IFNβ (TRIF) pathway. TLR4 agonist treatment reduced damage in steatotic liver grafts. When TLR4 action was inhibited, PPARγ antagonists did not protect steatotic liver grafts. In conclusion, TUDCA reduced PPARγ and this in turn up-regulated the TLR4 pathway, thus protecting steatotic liver grafts. TLR4 activating-based strategies could reduce the inherent risk of steatotic liver failure after transplantation.

Ubiquitin-proteasome system inhibitors and AMPK regulation in hepatic cold ischaemia and reperfusion injury: possible mechanisms

In the present Hypothesis article, we summarize and present data from the literature that support our hypothesis on the potential mechanisms by which UPS (ubiquitin-proteasome system) inhibitors reduce I/R (ischaemia/reperfusion) injury in the liver. I/R is the main cause of primary liver failure and, consequently, minimizing the detrimental effects of this process could increase the number of suitable transplantation grafts and also enhance the survival rate of patients after liver transplantation. A potential strategy to reduce I/R injury is the use of UPS inhibitors either as additives to preservation solutions or as drugs administered to patients. However, there is still controversy over whether the use of UPS inhibitors is beneficial or deleterious with regard to liver injury. From our experience and the few studies that have investigated the role of UPS in hepatic I/R, we believe that the use of UPS inhibitors is a potential strategy to reduce I/R injury in liver transplantation and graft preservation. We hypothesize that one of the main mechanisms of action of UPS inhibitors may be the up-regulation of AMPK (AMP-activated protein kinase) activity and the consequent down-regulation of mTOR (mammalian target of rapamycin), which may finally influence autophagy and preserve the energy state of the cell.

The current state of knowledge of hepatic ischemia-reperfusion injury based on its study in experimental models

The present review focuses on the numerous experimental models used to study the complexity of hepatic ischemia/reperfusion (I/R) injury. Although experimental models of hepatic I/R injury represent a compromise between the clinical reality and experimental simplification, the clinical transfer of experimental results is problematic because of anatomical and physiological differences and the inevitable simplification of experimental work. In this review, the strengths and limitations of the various models of hepatic I/R are discussed. Several strategies to protect the liver from I/R injury have been developed in animal models and, some of these, might find their way into clinical practice. We also attempt to highlight the fact that the mechanisms responsible for hepatic I/R injury depend on the experimental model used, and therefore the therapeutic strategies also differ according to the model used. Thus, the choice of model must therefore be adapted to the clinical question being answered.

The nitric oxide pathway--evidence and mechanisms for protection against liver ischaemia reperfusion injury

Ischaemia reperfusion (IR) injury is a clinical entity with a major contribution to the morbidity and mortality of liver surgery and transplantation. A central pathway of protection against IR injury utilizes nitric oxide (NO). Nitric oxide synthase (NOS) enzymes manufacture NO from L-arginine. NO generated by the endothelial NOS (eNOS) isoform protects against liver IR injury, whereas inducible NOS (iNOS)-derived NO may have either a protective or a deleterious effect during the early phase of IR injury, depending on the length of ischaemia, length of reperfusion and experimental model. In late phase hepatic IR injury, iNOS-derived NO plays a protective role. In addition to NOS consumption of L-arginine during NO synthesis, this amino acid may also be metabolized by arginase, an enzyme whose release is increased during prolonged ischaemia, and therefore diverts L-arginine away from NOS metabolism leading to a drop in the rate of NO synthesis. NO most commonly acts through the soluble guanylyl cyclase-cyclic GMP- protein kinase G pathway to ameliorate hepatic IR injury. Both endogenously generated and exogenously administered NO donors protect against liver IR injury. The beneficial effects of NO on liver IR are not, however, universal, and certain conditions, such as steatosis, may influence the protective effects of NO. In this review, the evidence for, and mechanisms of these protective actions of NO are discussed, and areas in need of further research are highlighted.

Ischemia-reperfusion injury in rat steatotic liver is dependent on NFκB P65 activation

BACKGROUND

Steatotic liver grafts tolerate ischemia-reperfusion (I/R) injury poorly, contributing to increased primary graft nonfunction following transplantation. Activation of nuclear factor kappa-B (NFκB) following I/R injury plays a crucial role in activation of pro-inflammatory responses leading to injury.

METHODS

We evaluated the role of NFκB in steatotic liver injury by using an orthotopic liver transplant (OLT) model in Zucker rats (lean to lean or obese to lean) to define the mechanisms of steatotic liver injury. Obese donors were treated with bortezomib to assess the role of NF-κB in steatotic liver I/R injury. Hepatic levels of NF-κB and pro-inflammatory cytokines were analyzed by ELISA. Serum transaminase levels and histopathological analysis were performed to assess associated graft injury.

RESULTS

I/R injury in steatotic liver results in significant increases in activation of NF-κB (40%, p<0.003), specifically the p65 subunit following transplantation. Steatotic donor pretreatment with proteasome inhibitor bortezomib (0.1mg/kg) resulted in significant reduction in levels of activated NF-κB (0.58±0.18 vs. 1.37±0.06O.D./min/10 μg protein, p<0.003). Bortezomib treatment also reduced expression of pro-inflammatory cytokines MIP-2 compared with control treated steatotic and lean liver transplants respectively (106±17.5 vs. 443.3±49.9 vs. 176±10.6 pg/mL, p=0.02), TNF-α (223.8±29.9 vs. 518.5±66.5 vs. 264.5±30.1 pg/2 μg protein, p=0.003) and IL-1β (6.0±0.91 vs. 19.8±5.2 vs. 5±1.7 pg/10 μg protein, p=0.02) along with a significant reduction in ALT levels (715±71 vs. 3712.5±437.5 vs. 606±286 U/L, p=0.01).

CONCLUSION

These results suggest that I/R injury in steatotic liver transplantation are associated with exaggerated activation of NFκB subunit p65, leading to an inflammatory mechanism of reperfusion injury and necrosis. Proteasome inhibition in steatotic liver donor reduces NFκB p65 activation and inflammatory I/R injury, improving transplant outcomes of steatotic grafts in a rat model.

Diet-induced obesity suppresses sevoflurane preconditioning against myocardial ischemia-reperfusion injury: role of AMP-activated protein kinase pathway

Obesity is a major risk factor for coronary artery disease, but its impact on anesthetic-induced cardioprotective actions is unexplored. We tested whether obesity inhibits anesthetic sevoflurane-induced preconditioning and whether this effect is mediated via the AMP-activated protein kinase (AMPK) signaling pathway. Sprague-Dawley rats were fed a high-fat (HF, 45% kcal as fat) or low-fat (LF, 10% kcal as fat) diet for 12 weeks. HF-fed rats developed metabolic disturbances including visceral obesity, hyperinsulinemia, hyperleptinemia and dyslipidemia. HF- or LF-fed rats subjected to 25 min of myocardial ischemia followed by 120 min of reperfusion were assigned to the following groups: control, sevoflurane preconditioning, sevoflurane plus AMPK inhibitor ara-A or AMPK activator A769662 alone. Infarct size was similar between the two control groups. Sevoflurane preconditioning significantly reduced infarct size in LF-fed rats but failed to induce cardioprotection in HF-fed rats. Phosphorylation of AMPK and endothelial nitric oxide synthase, as well as myocardial nitrite and nitrate, were also increased by sevoflurane preconditioning in LF-fed rats but not in HF-fed rats. Pretreatment with ara-A inhibited phosphorylation of AMPK and reversed sevoflurane preconditioning-induced cardioprotection in LF-fed rats, whereas it had no effects in HF-fed rats. In addition, sevoflurane preconditioning failed to enhance reactive oxygen species (ROS) generation in the myocardium of HF-fed rats compared with LF-fed rats. Direct activation of AMPK with A769662 equally increased phosphorylation of AMPK and reduced infarct size in both LF- and HF-fed rats. The results suggest that diet-induced obesity suppresses sevoflurane preconditioning-induced cardioprotective action, probably due to a diminished effect of sevoflurane preconditioning on activation of the ROS-mediated AMPK signaling pathway.

How to protect liver graft with nitric oxide

Organ preservation and ischemia reperfusion injury associated with liver transplantation play an important role in the induction of graft injury. One of the earliest events associated with the reperfusion injury is endothelial cell dysfunction. It is generally accepted that endothelial nitric oxide synthase (e-NOS) is cell-protective by mediating vasodilatation, whereas inducible nitric oxide synthase mediates liver graft injury after transplantation. We conducted a critical review of the literature evaluating the potential applications of regulating and promoting e-NOS activity in liver preservation and transplantation, showing the most current evidence to support the concept that enhanced bioavailability of NO derived from e-NOS is detrimental to ameliorate graft liver preservation, as well as preventing subsequent graft reperfusion injury. This review deals mainly with the beneficial effects of promoting “endogenous” pathways for NO generation, via e-NOS inducer drugs in cold preservation solution, surgical strategies such as ischemic preconditioning, and alternative “exogenous” pathways that focus on the enrichment of cold storage liquid with NO donors. Finally, we also provide a basic bench-to-bed side summary of the liver physiology and cell signalling mechanisms that account for explaining the e-NOS protective effects in liver preservation and transplantation.

Retinol-binding protein 4 and peroxisome proliferator-activated receptor-γ in steatotic liver transplantation

Numerous steatotic livers are discarded for transplantation because of their poor tolerance of ischemia-reperfusion (I/R). The injurious effects of retinol-binding protein 4 (RBP4) in various pathologies are well documented. RBP4 levels are reduced by peroxisome proliferator-activated receptor-γ (PPARγ) agonists. Strategies aimed at increasing PPARγ protect steatotic livers under warm ischemia. Ischemic preconditioning (PC) based on brief periods of I/R protects steatotic liver grafts against I/R injury, but the responsible mechanism is poorly understood. We examined the roles of RBP4 and PPARγ in I/R injury associated with steatotic liver transplantation and the benefits of PC in such situations. We report that RBP4 and PPARγ expression levels in nonsteatotic livers were similar to those found in the sham group. However, reduced RBP4 and increased PPARγ levels were observed in steatotic livers. Treatment with either RBP4 or a PPARγ antagonist was effective only in steatotic livers. PC, which increased RBP4 levels, and RBP4 treatment both reduced PPARγ levels and hepatic injury in steatotic livers. When PPARγ was activated, neither RBP4 treatment nor PC (despite RBP4 induction) protected steatotic livers. In conclusion, steatotic liver grafts are more predisposed to down-regulate RBP4 and overexpress PPARγ. RBP4 treatment and PC, through RBP4 induction, reduced PPARγ levels in steatotic liver grafts, thus protecting them from the PPARγ detrimental effects.

Isoform-selective 5'-AMP-activated protein kinase-dependent preconditioning mechanisms to prevent postischemic leukocyte-endothelial cell adhesive interactions

We previously demonstrated that preconditioning induced by ethanol consumption at low levels [ethanol preconditioning (EPC)] or with 5-aminoimidazole-4-carboxamide 1-β-d-ribofuranoside (AICAR-PC) 24 h before ischemia-reperfusion prevents postischemic leukocyte-endothelial cell adhesive interactions (LEI) by a mechanism that is initiated by nitric oxide formed by endothelial nitric oxide synthase. Recent work indicates that 1) ethanol increases the activity of AMP-activated protein kinase (AMPK) and 2) AMPK phosphorylates endothelial nitric oxide synthase at the same activation site seen following EPC (Ser1177). In light of these observations, we postulated that the heterotrimeric serine/threonine kinase, AMPK, may play a role in triggering the development of the anti-inflammatory phenotype induced by EPC. Ethanol was administered to C57BL/6J mice by gavage in the presence or absence of AMPK inhibition. Twenty-four hours later, the numbers of rolling and adherent leukocytes in postcapillary venules of the small intestine were recorded using an intravital microscopic approach. Following 45 min of ischemia, LEI were recorded after 30 and 60 min of reperfusion or at equivalent time points in control animals. Ischemia-reperfusion induced a marked increase in LEI relative to sham-operated control mice. The increase in LEI was prevented by EPC, an effect that was lost with AMPK inhibition during the period of ethanol exposure. Studies conducted in AMPK α(1)- and α(2)-knockout mice suggest that the anti-inflammatory effects of AICAR are not dependent on which isoform of the catalytic α-subunit is present because a deficiency of either isoform results in a loss of protection. In sharp contrast, EPC appears to be triggered by an AMPK α(2)-isoform-dependent mechanism.

Intermittent ischaemia maintains function after ischaemia reperfusion in steatotic livers

BACKGROUND

Ischaemic preconditioning (IPC) and intermittent ischaemia (INT) reduce liver injury after ischaemia reperfusion (IR). Steatotic livers are at a higher risk of IR injury, but the protection offered by IPC and INT is not well understood. The aim of the present study was to determine the effectiveness of IPC and INT in maintaining liver function in steatotic livers.

MATERIAL AND METHODS

A model of segmental hepatic ischaemia (45 min) and reperfusion (60 min) was employed using lean and obese Zucker rats. Bile flow recovery was measured to assess dynamic liver function, hepatocyte fat content quantified and blood electrolytes, metabolites and bile calcium measured to assess liver and whole body physiology. Liver marker enzymes and light and electron microscopy were employed to assess hepatocyte injury.

RESULTS

IPC was not effective in promoting bile flow recovery after IR in either lean or steatotic livers, whereas INT promoted good bile flow recovery in steatotic as well as lean livers. However, the bile flow recovery in steatotic livers was less than that in lean livers. In steatotic livers, ischaemia led to a rapid and substantial decrease in fat content. Steatotic livers were more susceptible to IR injury than lean livers, as indicated by increased blood ALT concentrations and major histological injury.

CONCLUSION

INT is more effective than IPC in restoring liver function in the acute phase of IR in steatotic livers. In obese patients, INT may be useful in promoting better liver function after IR after liver resection.

Addition of carvedilol to University Wisconsin solution improves rat steatotic and nonsteatotic liver preservation

Here we examine the effect of adding carvedilol (CVD) to University of Wisconsin (UW) solution on the preservation of steatotic and nonsteatotic livers during cold ischemia and after normothermic reperfusion. We used an isolated perfused rat liver model. The following protocols were evaluated. Protocol 1 concerned the effect of CVD after cold ischemia. Steatotic and nonsteatotic livers were preserved for 24 hours in UW solution alone or with CVD. Livers without cold ischemia were used as controls. Transaminases were evaluated in the flushing effluent. Protocol 2 involved the effect of CVD after reperfusion. Both liver types were preserved for 24 hours in UW solution alone or with CVD and then perfused ex vivo for 2 hours at 37 degrees C. Livers flushed and perfused without ischemia were used as controls. Hepatic injury and functionality [transaminases, bile production, and hepatic clearance of sulfobromophthalein (BSP)] were evaluated after reperfusion. In addition, factors potentially involved in hepatic ischemia-reperfusion injury, including oxidative stress (malondialdehyde and superoxide anion levels), mitochondrial damage (glutamate dehydrogenase activity), microcirculatory disorders (flow rate and vascular resistance), and adenosine triphosphate (ATP) depletion, were evaluated after reperfusion. After cold ischemia, steatotic livers preserved in UW solution showed higher transaminase levels than nonsteatotic livers. After reperfusion, steatotic livers preserved in UW solution showed higher transaminase levels and lower bile production and BSP clearance than nonsteatotic livers. Alterations in the perfusion flow rate and vascular resistance, mitochondrial damage, and reduced ATP content were more evident in steatotic livers preserved in UW solution. The addition of CVD to UW solution reduced hepatic injury, obstructed its mechanisms, and improved hepatic functionality in both liver types. We conclude that CVD is a useful additive for UW solution that improves the preservation of steatotic and nonsteatotic livers subjected to prolonged cold ischemia.

Variable activation of phosphoinositide 3-kinase influences the response of liver grafts to ischemic preconditioning

BACKGROUND/AIMS

The efficacy of ischemic preconditioning (IPC) in preventing reperfusion injury in human liver transplants is still questioned. Phosphoinositide-3-kinase (PI3K) is essential for IPC development in rodent livers. This work investigates whether PI3K-dependent signals might account for the inconsistent responses to IPC of transplanted human livers.

METHODS

Forty livers from deceased donors were randomized to receive or not IPC before recovery. PI3K activation was evaluated in biopsies obtained immediately before IPC and 2 h after reperfusion by measuring the phosphorylation of the PI3K downstream kinase PKB/Akt and the levels of the PI3K antagonist phosphatase tensin-homologue deleted from chromosome 10 (PTEN).

RESULTS

IPC increased PKB/Akt phosphorylation (p = 0.01) and decreased PTEN levels (p = 0.03) in grafts, but did not significantly ameliorate post-transplant reperfusion injury. By calculating T(2h)/T(0) PKB/Akt phosphorylation ratios, 10/19 (53%) of the preconditioned grafts had ratios above the control threshold (IPC-responsive), while the remaining nine grafts showed ratios comparable to controls (IPC-non-responsive). T(2h)/T(0) PTEN ratios were also decreased (p < or = 0.03) only in IPC-responsive grafts. The patients receiving IPC-responsive organs had ameliorated (p < or = 0.05) post-transplant aminotransferase and bilirubin levels, while prothrombin activity was unchanged.

CONCLUSIONS

Impaired PI3K signaling might account for the variability in the responses to IPC of human grafts from deceased donors.

AICAR preconditioning prevents postischemic leukocyte rolling and adhesion: role of K(ATP) channels and heme oxygenase

OBJECTIVE

We previously demonstrated that pharmacologic activation of AMP-activated protein kinase (AMPK) with 5-aminoimidazole-4-carboxamide 1-beta-D-ribofuranoside (AICAR) 24 hours prior to (AICAR preconditioning; AICAR-PC) ischemia/reperfusion (I/R) prevents postischemic leukocyte-endothelial cell adhesive interactions (LEI) by a mechanism initiated by endothelial nitric oxide synthase (eNOS)-dependent NO production during the period of AICAR-PC. The major aim of this study was to examine the role of ATP-sensitive potassium (K(ATP)) channels and heme oxygenase as mediators of the antiadhesive effects of AICAR-PC during I/R 24 hours later.

METHODS

Intravital fluorescence microscopy was used to quantify LEI in the small intestine of AICAR-preconditioned C57BL/6J mice treated with K(ATP) channel or heme oxygenase inhibitors during I/R 24 hours after AICAR-PC in separate experiments.

RESULTS

I/R induced marked increases in LEI relative to sham control mice, proadhesive responses that were prevented by AICAR-PC 24 hours prior to I/R. The effects of AICAR-PC to prevent postischemic LEI were abolished by K(ATP) channel or heme oxygenase inhibition during I/R.

DISCUSSION/CONCLUSION

Our results indicate that the antiadhesive effects of AICAR-PC are mediated by K(ATP) channel- and heme oxygenase-dependent mechanisms during I/R.

Therapeutic targets in liver transplantation: angiotensin II in nonsteatotic grafts and angiotensin-(1-7) in steatotic grafts

Numerous steatotic livers are discarded as unsuitable for transplantation because of their poor tolerance of ischemia-reperfusion(I/R). The injurious effects of angiotensin (Ang)-II and the benefits of Ang-(1-7) in various pathologies are well documented. We examined the generation of Ang II and Ang-(1-7) in steatotic and nonsteatotic liver grafts from Zucker rats following transplantation. We also studied in both liver grafts the effects of Ang-II receptors antagonists and Ang-(1-7) receptor antagonists on hepatic I/R damage associated with transplantation. Nonsteatotic grafts showed higher Ang II levels than steatotic grafts, whereas steatotic grafts showed higher Ang-(1-7) levels than nonsteatotic grafts. Ang II receptor antagonists protected only nonsteatotic grafts against damage, whereas Ang-(1-7) receptor antagonists were effective only in steatotic grafts. The protection conferred by Ang II receptor antagonists in nonsteatotic grafts was associated with ERK 1/2 overexpression, whereas the beneficial effects of Ang-(1-7) receptor antagonists in steatotic grafts may be mediated by NO inhibition. Our results show that Ang II receptor antagonists are effective only in nonsteatotic liver transplantation and point to a novel therapeutic target in liver transplantation based on Ang-(1-7), which is specific for steatotic liver grafts.

Are angiotensin II receptor antagonists useful strategies in steatotic and nonsteatotic livers in conditions of partial hepatectomy under ischemia-reperfusion?

We examined whether angiotensin (Ang) II receptor antagonists could be considered a therapeutic strategy in steatotic and nonsteatotic livers in conditions of partial hepatectomy under ischemia-reperfusion (I/R), which is commonly applied in clinical practice to reduce blood loss. We report that Ang II type I receptor (AT1R) antagonist, but not Ang II type II receptor (AT2R) antagonist, increased regeneration in nonsteatotic livers. In the presence of steatosis, both AT1R and AT2R antagonists increased liver regeneration. This effect was stronger when the two were combined. Neither of the Ang II receptor antagonists protected nonsteatotic livers against damage. Only the AT1R antagonist, through nitric oxide inhibition, reduced damage in steatotic livers. The combination of the AT1R and AT2R antagonists in steatotic livers conferred a similar degree of protection to AT1R antagonist alone. Herein, we show that p38 mitogen-activated protein kinase (p38) was a key mechanism in the regeneration induced by the Ang II receptor antagonists in both liver types because when this signaling pathway was inhibited, the beneficial effects of the Ang II receptor antagonists on liver regeneration disappeared, regardless of hepatocyte growth factor or transforming growth factor beta-hepatic levels. In conclusion, in conditions of partial hepatectomy under I/R, the AT1R antagonist for nonsteatotic livers and the AT1R and AT2R antagonists for steatotic livers improved regeneration in the remnant liver through p38 activation. In addition, the combination of the AT1R and AT2R antagonists in steatotic livers led to stronger liver regeneration than either antagonists used separately and also provided the same protection against damage as that afforded by AT1R antagonist alone.

2-Deoxy-d-glucose protects neural progenitor cells against oxidative stress through the activation of AMP-activated protein kinase

2-Deoxy-d-glucose (2DG) is an analog of glucose that is effectively taken up by cells competing with normal glucose but cannot be further utilized to produce energy. It was previously reported that 2DG can mimic the beneficial effects of dietary restriction in experimental models of neurodegenerative disorders and cancer. In the present study, we report that pretreatment with 2DG increases the resistance of neural progenitor cells (NPC) to oxidative insults. 2DG significantly suppressed the proliferation of NPC, and high concentrations of 2DG were toxic to NPC. However, a treatment with a moderate concentration of 2DG protected the NPC against tBHP-induced oxidative stress suggesting that this chemical had hormetic action mimicking dietary restriction. Furthermore, we showed that the protective mechanism of 2DG involved the activation of AMP-activated protein kinase. Our findings demonstrate that 2DG can modulate the cellular responses to oxidative stress and confer cellular resistance in NPC by activating the metabolic regulator.

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.

Inhibition of angiotensin II action protects rat steatotic livers against ischemia-reperfusion injury

OBJECTIVE

We examined whether pharmacologic strategies blocking angiotensin II actions protect steatotic livers against ischemia-reperfusion (I/R) injury. The effects of ischemic preconditioning (PC) on angiotensin II were also evaluated.

DESIGN

Randomized and controlled animal study.

SETTING

Experimental laboratory.

SUBJECTS

Zucker rats.

INTERVENTIONS

The following experimental groups were studied: I/R, ischemia-reperfusion + angiotensin-converting enzyme inhibitor (I/R+ACE inhibitor), ischemia-reperfusion + angiotensin II type I receptor antagonist (I/R+AT1R antagonist), ischemia-reperfusion + angiotensin II type II receptor antagonist (I/R+AT2R antagonist), and PC (5 mins of ischemia + 10 mins of reperfusion before I/R). In some of these groups, the action of bradykinin (BK) and/or peroxisome-proliferator-activated receptor-gamma (PPARgamma) was altered pharmacologically.

MEASUREMENTS AND MAIN RESULTS

I/R+ACE inhibitor, I/R+AT1R antagonist, and I/R+AT2R antagonist reduced hepatic injury in steatotic livers compared with the I/R group. PC reduced angiotensin II generation and hepatic injury in steatotic livers in comparison to I/R group. Our results revealed that I/R+ACE inhibitor, I/R+AT1R antagonist, I/R+AT2R antagonist, and PC increased BK compared with the I/R group. In addition, the effects of PC on BK and hepatic injury were abolished when angiotensin II was administered. Furthermore, administration of BK receptor antagonists to the I/R+ACE inhibitor, I/R+AT1R antagonist, I/R+AT2R antagonist, and PC groups resulted in hepatic injury similar to the I/R group, indicating that the benefits of ACE inhibitor, AT1R antagonist, AT2R antagonist, and PC were abolished when the action of BK was inhibited. Experiments aimed at investigating why BK was protective in steatotic livers indicated that BK acts as a positive regulator of PPARgamma. If PPARgamma action was inhibited, BK did not protect steatotic livers against hepatic injury.

CONCLUSIONS

Pharmacologic blockers of angiotensin II action (ACE inhibitors, AT1R antagonists, and AT2R antagonists) and PC, which reduced angiotensin II generation, increased BK generation in steatotic livers after I/R. This in turn increased PPARgamma and protected this type of liver against I/R injury.

Autofluorescence properties of rat liver under hypermetabolic conditions

Autofluorescence response to oxygen supply modulation has been investigated in livers of rats under the hypermetabolic state associated to a pathological condition-hyperthyroidism-that is known to enhance hepatocyte metabolic activities involving both NAD, i.e. oxidative pathways engaged in ATP synthesis, and NADP, i.e. reductive bio-synthesis and antioxidant functions. Experiments have been performed on rats in normal condition or submitted to long-term thyroxine (T(4)) administration. Histological inspection did not show any appreciable morphological alteration in liver parenchyma; biochemical analysis indicated an increase in both NADP(+) and NADPH contents. Autofluorescence properties have been monitored in vivo, via a fiber optic probe, on exposed livers both during induction of global ischemia and after restoration of blood circulation. Alteration of oxygen supply modulated liver autofluorescence properties, mainly as to NAD(P)H contribution, in dependence of changes in pyridine coenzymes redox state. With respect to euthyroid, hyperthyroid rat livers exhibited higher autofluorescence signals in all phases of the experiment, and a faster signal decay time upon reoxygenation. The results have been interpreted on the basis of a larger content of NADPH-the coenzyme not directly oxidized in respiratory processes and likely providing an almost constant autofluorescence background contribution-and of uncoupling effects facilitating the respiratory NADH oxidation, associated with the hyperthyroid condition. The results obtained in the liver hypermetabolic model provide interesting perspectives for a further improvement of the diagnostic implications of autofluorescence.