HMGB1 translocation and expression is caused by warm ischemia reperfusion injury, but not by partial hepatectomy in rats

EP4 activation ameliorates liver ischemia/reperfusion injury via ERK1/2‑GSK3β‑dependent MPTP inhibition

Prostaglandin E receptor subtype 4 (EP4) is widely distributed in the heart, but its role in hepatic ischemia/reperfusion (I/R), particularly in mitochondrial permeability transition pore (MPTP) modulation, is yet to be elucidated. In the present study, an EP4 agonist (CAY10598) was used in a rat model to evaluate the effects of EP4 activation on liver I/R and the mechanisms underlying this. I/R insult upregulated hepatic EP4 expression during early reperfusion. In addition, subcutaneous CAY10598 injection prior to the onset of reperfusion significantly increased hepatocyte cAMP concentrations and decreased serum ALT and AST levels and necrotic and apoptotic cell percentages, after 6 h of reperfusion. Moreover, CAY10598 protected mitochondrial morphology, markedly inhibited mitochondrial permeability transition pore (MPTP) opening and decreased liver reactive oxygen species levels. This occurred via activation of the ERK1/2-GSK3β pathway rather than the janus kinase (JAK)2-signal transducers and activators of transcription (STAT)3 pathway, and resulted in prevention of mitochondria-associated cell injury. The MPTP opener carboxyatractyloside (CATR) and the ERK1/2 inhibitor PD98059 also partially reversed the protective effects of CAY10598 on the liver and mitochondria. The current findings indicate that EP4 activation induces ERK1/2-GSK3β signaling and subsequent MPTP inhibition to provide hepatoprotection, and these observations are informative for developing new molecular targets and preventative therapies for I/R in a clinical setting.

Hypoxia protects the liver from Small For Size Syndrome: A lesson learned from the associated liver partition and portal vein ligation for staged hepatectomy (ALPPS) procedure in rats

Portal hyperperfusion and "dearterialization" of the liver remnant are the main pathogenic mechanisms for Small For Size syndrome (SFSS). Associating liver partition and portal vein ligation for staged hepatectomy (ALPPS) induces rapid remnant hypertrophy. We hypothesized a similar increase in portal pressure/flow into the future liver remnant in ALPPS and SFSS-setting hepatectomies. In a rodent model, ALPPS was compared to SFSS-setting hepatectomy. We assessed mortality, remnant hypertrophy, hepatocyte proliferation, portal and hepatic artery flow, hypoxia-induced response, and liver sinusoidal morphology. SFSS-hepatectomy rats were subjected to local (hepatic artery ligation) or systemic (Dimethyloxalylglycine) hypoxia. ALLPS prevented mortality in SFSS-setting hepatectomies. Portal hyperperfusion per liver mass was similar in ALLPS and SFSS. Compared to SFSS, efficient arterial perfusion of the remnant was significantly lower in ALPPS causing pronounced hypoxia confirmed by pimonidazole immunostaining, activation of hypoxia sensors and upregulation of neo-angiogenic genes. Liver sinusoids, larger in ALPPS, collapsed in SFSS. Induction of hypoxia in SFSS reduced mortality. Hypoxia had no impact on hepatocyte proliferation but contributed to the integrity of sinusoidal morphology. ALPPS hemodynamically differ from SFSS by a much lower arterial flow in ALPPS's FLR. We show that the ensuing hypoxic response is essential for the function of the regenerating liver by preserving sinusoidal morphology.

Ischemic preconditioning attenuates ischemia/reperfusion injury in rat steatotic liver: role of heme oxygenase-1-mediated autophagy

Steatotic livers are more susceptible to ischemia/reperfusion (I/R) injury, which is ameliorated by ischemic preconditioning (IPC). Autophagy possesses protective action on liver I/R injury and declines in steatotic livers. The aim of this study was to test the hypothesis that the increased susceptibility of steatotic livers to I/R injury was associated with defective hepatic autophagy, which could be restored by IPC via heme oxygenase-1 (HO-1) signaling. Obesity and hepatic steatosis was induced using a high fat diet. Obesity impaired hepatic autophagy activity and decreased hepatic HO-1 expression. Induction of HO-1 restored autophagy activity and inhibited calpain 2 activity. Additionally, suppression of calpain 2 activity also restored autophagy activity. Mitochondrial dysfunction and hepatocellular injury were significantly increased in steatotic livers compared to lean livers in response to I/R injury. This increase in sensitivity to I/R injury was associated with defective hepatic autophagy activity in steatotic livers. IPC increased autophagy and reduced mitochondrial dysfunction and hepatocellular damage in steatotic livers following I/R injury. Furthermore, IPC increased HO-1 expression. Inhibition of HO-1 decreased the IPC-induced autophagy, increased calpain 2 activity and diminished the protective effect of IPC against I/R injury. Inhibition of calpain 2 restored autophagic defect and attenuated mitochondrial dysfunction in steatotic livers after I/R. Collectively, IPC might ameliorate steatotic liver damage and restore mitochondrial function via HO-1-mediated autophagy.

Cross-Talk Between Sirtuin 1 and High-Mobility Box 1 in Steatotic Liver Graft Preservation

BACKGROUND

Sirtuin 1 (SIRT1) is a nicotinamide adenine dinucleotide +-dependent histone deacetylase that regulates various pathways involved in ischemia-reperfusion injury (IRI). Moreover, high-mobility group box 1 protein (HMGB1) has also been involved in inflammatory processes during IRI. However, the roles of both SIRT1 and HMGB1 in liver preservation is poorly understood. In this communication, we evaluated the potential relationship between SIRT1 and HMGB1 in steatotic and non-steatotic liver grafts preserved in Institute Georges Lopez solution (IGL-1) preservation solution enriched or not enriched with trimetazidine (TMZ).

METHODS

Steatotic and non-steatotic livers were preserved in IGL-1 preservation solution (24 hours, 4°C), enriched or not enriched with TMZ (10 μmol/L), and then submitted to ex vivo reperfusion (2 hours; 37°C). Liver injury (AST/ALT) and function (bile output, vascular resistance) were evaluated. SIRT1, HMGB1, autophagy parameters (beclin-1, LC3B), PPAR-γ, and heat-shock protein (HO-1, HSP70) expression were determined by means of Western blot. Also, we assessed oxidative stress, mitochondrial damage (glutamate dehydrogenase), and TNF-α levels.

RESULTS

Elevated SIRT1 and enhanced autophagy were found after reperfusion in steatotic livers preserved in IGL-1+TMZ when compared with IGL-1. However, these changes were not seen in the case of non-steatotic livers. Also, HO-1 increases in the IGL-1 + TMZ group were evident only in the case of steatotic livers, whereas HSP70 and PPAR-γ protein expression were enhanced only in non-steatotic livers. All reported changes were consistent with decreased liver injury diminution, ameliorated hepatic function, and decreased TNF-α and HMGB levels. In addition, the oxidative stress and mitochondrial damage were efficiently prevented by the IGL-1 + TMZ use.

CONCLUSIONS

SIRT1 is associated with HMGB1 decreases and increased autophagy in steatotic livers, contributing to increased tolerance to cold IRI.

Silybin Against Liver Ischemia-Reperfusion Injury: Something Old, Something New…

Ischemia reperfusion injury (IRI) is a life threatening condition that may develop after elective liver surgery or liver transplantation. Numerous surgical and pharmacological approaches have shown varying degrees of protection against liver IRI. A group of protective compounds are the flavonoids but their intestinal absorbtion and bioavailability are low and impredictible. In this issue Tsaroucha et al. reports significantly decreased hepatocellular injury, Fas/FasL expression and inhibited HMGB1 release in rats receiving a hydrosoluble, lyophilized complex of SLB and hydroxypropyl-β-cyclodextrin (SLB-HP-β-CD) intravenously.

Relevance of proteolysis and proteasome activation in fatty liver graft preservation: An Institut Georges Lopez-1 vs University of Wisconsin appraisal

AIM

To compare liver proteolysis and proteasome activation in steatotic liver grafts conserved in University of Wisconsin (UW) and Institut Georges Lopez-1 (IGL-1) solutions.

METHODS

Fatty liver grafts from male obese Zücker rats were conserved in UW and IGL-1 solutions for 24 h at 4 °Cand subjected to “ex vivo” normo-thermic perfusion (2 h; 37 °C). Liver proteolysis in tissue specimens and perfusate was measured by reverse-phase high performance liquid chromatography. Total free amino acid release was correlated with the activation of the ubiquitin proteasome system (UPS: measured as chymotryptic-like activity and 20S and 19S proteasome), the prevention of liver injury (transaminases), mitochondrial injury (confocal microscopy) and inflammation markers (TNF 1 alpha, high mobility group box-1 (HGMB-1) and PPAR gamma), and liver apoptosis (TUNEL assay, cytochrome c and caspase 3).

RESULTS

Profiles of free AA (alanine, proline, leucine, isoleucine, methionine, lysine, ornithine, and threonine, among others) were similar for tissue and reperfusion effluent. In all cases, the IGL-1 solution showed a significantly higher prevention of proteolysis than UW (P < 0.05) after cold ischemia reperfusion. Livers conserved in IGL-1 presented more effective prevention of ATP-breakdown and more inhibition of UPS activity (measured as chymotryptic-like activity). In addition, the prevention of liver proteolysis and UPS activation correlated with the prevention of liver injury (AST/ALT) and mitochondrial damage (revealed by confocal microscopy findings) as well as with the prevention of inflammatory markers (TNF1alpha and HMGB) after reperfusion. In addition, the liver grafts preserved in IGL-1 showed a significant decrease in liver apoptosis, as shown by TUNEL assay and the reduction of cytochrome c, caspase 3 and P62 levels.

CONCLUSION

Our comparison of these two preservation solutions suggests that IGL-1 helps to prevent ATP breakdown more effectively than UW and subsequently achieves a higher UPS inhibition and reduced liver proteolysis.

Mechanistic Modelling of Drug-Induced Liver Injury: Investigating the Role of Innate Immune Responses

Drug-induced liver injury (DILI) remains an adverse event of significant concern for drug development and marketed drugs, and the field would benefit from better tools to identify liver liabilities early in development and/or to mitigate potential DILI risk in otherwise promising drugs. DILIsym software takes a quantitative systems toxicology approach to represent DILI in pre-clinical species and in humans for the mechanistic investigation of liver toxicity. In addition to multiple intrinsic mechanisms of hepatocyte toxicity (ie, oxidative stress, bile acid accumulation, mitochondrial dysfunction), DILIsym includes the interaction between hepatocytes and cells of the innate immune response in the amplification of liver injury and in liver regeneration. The representation of innate immune responses, detailed here, consolidates much of the available data on the innate immune response in DILI within a single framework and affords the opportunity to systematically investigate the contribution of the innate response to DILI.

Quercetin attenuates the activation of hepatic stellate cells and liver fibrosis in mice through modulation of HMGB1-TLR2/4-NF-κB signaling pathways

This study aimed to investigate the effects of quercetin on liver fibrogenesis in mice and to elucidate the underlying molecular mechanisms. Mice were administered with carbon tetrachloride (CCl₄) for eight weeks to induce liver fibrosis and concomitantly orally treated with quercetin (50mgkg^-1day^-1). Here, we demonstrated that quercetin dramatically ameliorated liver injury, inflammation, and hepatic fibrogenesis induced by CCl₄. Quercetin also inhibited the activation of hepatic stellate cells (HSC) in vivo and in vitro, as evaluated by α-smooth muscle actin (α-SMA) expression, which is a specific marker of HSC activation. Moreover, reduced fibrosis was associated with decreased high-mobility group box 1 (HMGB1), toll like receptor (TLR) 2 and TLR4 genes, and protein expression. Quercetin also inhibited the cytoplasmic translocation of HMGB1 in hepatocytes of fibrotic livers. Further investigation demonstrated that quercetin treatment significantly attenuated CCl₄-induced nuclear translocation of the nuclear factor-κB (NF-κB) p65 and inhibited degradation of IκBα (an inhibitor of NF-κB) expression in the liver compared with vehicle-treated fibrotic mice. Considered together, our data indicate that quercetin has hepatoprotective and anti-fibrotic effects in animal models of liver fibrosis, the mechanism of which may be involved in modulating the HMGB1-TLR2/4-NF-κB signaling pathways.

Changes in expression of high mobility group protein B1 in acute liver failure in rats

AIM: To observe the changes in the expression of high mobility group protein B1 (HMGB1) and other inflammatory cytokines in acute liver failure (ALF) in rats.

METHODS: D-galactosamine (D-Gal) and lipopolysaccharide (LPS) were used to establish a model of ALF by intraperitoneal injection. Rats were treated with normal saline alone in a control group. Serum and liver tissues were collected at different time points (3, 6, 12, 48, 72 and 96 h). Serum biochemical indicators were detected, and HMGB1 expression in liver tissue was observed by immunohistochemical analysis. HE staining was performed to evaluate the severity of liver damage. The changes of HMGB1, interleukin 1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α) mRNA expression were determined by real-time fluorescent quantitative PCR, and the levels of HMGB1, IL-1β, IL-6 and TNF-α were measured using ELISA kits. rHMGB1 was injected via the tail vein alone or combined with D-Gal and LPS by intraperitoneal injection, and the changes of symptoms and signs and survival rates of rats were observed.

RESULTS: ALF was successfully induced in rats using D-Gal and LPS. In ALF rats, the peak of HMGB1 gene expression and serum levels of HMGB1 were later but lasted longer than IL-1β, IL-6 and TNF-α. Cytoplasmic translocation of HMGB1 was observed as early as 3 h after D-Gal and LPS administration. In 24-48 h, normal liver tissue structures disappeared, and HMGB1 was overflowed from necrotic liver cells and showed diffused yellow staining, full of the entire field of vision. Administration of exogenous rHMGB1 reduced the time to death and increased mortality rates .

CONCLUSION: HMGB1 may be passively leaked by necrosis hepatic cells, which appeared later compared with other inflammatory cytokines. The interaction of HMGB1 and other inflammatory cytokines can promote the inflammation progression in ALF.

Ischemic preconditioning protects against liver ischemia/reperfusion injury via heme oxygenase-1-mediated autophagy

OBJECTIVES

Ischemic preconditioning exerts a protective effect in hepatic ischemia/reperfusion injury. The exact mechanism of ischemic preconditioning action remains largely unknown. Recent studies suggest that autophagy plays an important role in protecting against ischemia/reperfusion injury. However, the role of autophagy in ischemic preconditioning-afforded protection and its regulatory mechanisms in liver ischemia/reperfusion injury remain poorly understood. This study was designed to determine whether ischemic preconditioning could protect against liver ischemia/reperfusion injury via heme oxygenase-1-mediated autophagy.

DESIGN

Laboratory investigation.

SETTING

University animal research laboratory.

SUBJECTS

Male inbred Lewis rats and C57BL/6 mice.

INTERVENTIONS

Ischemic preconditioning was produced by 10 minutes of ischemia followed by 10 minutes of reperfusion prior to 60 minutes of ischemia. In a rat model of hepatic ischemia/reperfusion injury, rats were pretreated with wortmannin or rapamycin to evaluate the contribution of autophagy to the protective effects of ischemic preconditioning. Heme oxygenase-1 was inhibited with tin protoporphyrin IX. In a mouse model of hepatic ischemia/reperfusion injury, autophagy or heme oxygenase-1 was inhibited with vacuolar protein sorting 34 small interfering RNA or heme oxygenase-1 small interfering RNA, respectively.

MEASUREMENTS AND MAIN RESULTS

Ischemic preconditioning ameliorated liver ischemia/reperfusion injury, as indicated by lower serum aminotransferase levels, lower hepatic inflammatory cytokines, and less severe ischemia/reperfusion-associated histopathologic changes. Ischemic preconditioning treatment induced autophagy activation, as indicated by an increase of LC3-II, degradation of p62, and accumulation of autophagic vacuoles in response to ischemia/reperfusion injury. When ischemic preconditioning-induced autophagy was inhibited with wortmannin in rats or vacuolar protein sorting 34-specific small interfering RNA in mice, liver ischemia/reperfusion injury was worsened, whereas rapamycin treatment increased autophagy and mimicked the protective effects of ischemic preconditioning. Furthermore, ischemic preconditioning increased heme oxygenase-1 expression. The inhibition of heme oxygenase-1 with tin protoporphyrin IX in rats or heme oxygenase-1-specific small interfering RNA in mice decreased ischemic preconditioning-induced autophagy and diminished the protective effects of ischemic preconditioning against ischemia/reperfusion injury.

CONCLUSIONS

Ischemic preconditioning protects against liver ischemia/reperfusion injury, at least in part, via heme oxygenase-1-mediated autophagy.

Curcumin protects against concanavalin A-induced hepatitis in mice through inhibiting the cytoplasmic translocation and expression of high mobility group box 1

The aims of this study were to examine the anti-inflammatory effect of curcumin on concanavalin A (ConA) induced hepatitis in mice, and to elucidate its underlying molecular mechanisms. Mice received curcumin by gavage before ConA intravenous administration. The results showed that curcumin pretreatment attenuated ConA-induced hepatitis. Enzyme linked immunosorbent assay (ELISA) results showed that serum levels of high mobility group box 1 (HMGB1) increased at 4 h and reached its peak value at 12 h after challenge with ConA; but this increase was significantly inhibited by curcumin. Furthermore, curcumin significantly decreased the HMGB1 translocation from nucleus to cytoplasm of hepatocytes in ConA-induced mice. The levels of HMGB1 mRNA and protein expression in the liver were also significantly lowered in curcumin-treated mice. In addition, curcumin inhibited intrahepatic expression of tumor necrosis factor-α (TNF-α), interleukin (IL)-1β and IL-6 protein. In conclusion, the results indicated that curcumin protected against ConA-induced hepatitis in mice; and the beneficial effects may be partly through inhibition of HMGB1 translocation in hepatocytes, release into the plasma and expression in livers.

Chronic lithium treatment protects against liver ischemia/reperfusion injury in rats

Lithium has long been widely used in the treatment of bipolar mood disorders. Recent studies have demonstrated that lithium is able to decrease ischemia/reperfusion (I/R) injury in the brain, kidneys, and heart. Because lithium may act on a number of stress and survival pathways, it is of great interest to explore this compound also in the setting of liver I/R injury. In this study, we aimed to evaluate the effects of lithium in a model of liver I/R injury in rats. Chronic treatment with lithium (2 mmol/kg for 3 days before ischemia) decreased I/R injury, whereas acute treatment with a single dose of lithium (2 mmol/kg 1 hour before ischemia) did not confer any protection in a partial hepatic I/R model. Furthermore, rats subjected to chronic lithium treatment had a significantly better survival rate (60%) than saline-treated rats (27%) in a total hepatic I/R survival model. Chronic lithium treatment protected against liver I/R injury, as indicated by lower serum aminotransferase levels, fewer I/R-associated histopathological changes, lower hepatic inflammatory cytokine levels, less neutrophil infiltration, and lower hepatic high-mobility group box expression and serum levels. The mechanism of action of lithium appears to involve its ability to inhibit glycogen synthase kinase 3β activation, modulate mitogen-activated protein kinase activation, inhibit hepatic apoptosis, and induce autophagy. On the basis of these data, we conclude that lithium treatment may be a simple and applicable preconditioning intervention for protecting against liver I/R injury.

Dual role of chloroquine in liver ischemia reperfusion injury: reduction of liver damage in early phase, but aggravation in late phase

The anti-malaria drug chloroquine is well known as autophagy inhibitor. Chloroquine has also been used as anti-inflammatory drugs to treat inflammatory diseases. We hypothesized that chloroquine could have a dual effect in liver ischemia/reperfusion (I/R) injury: chloroquine on the one hand could protect the liver against I/R injury via inhibition of inflammatory response, but on the other hand could aggravate liver I/R injury through inhibition of autophagy. Rats (n=6 per group) were pre-treated with chloroquine (60 mg/kg, i.p.) 1 h before warm ischemia, and they were continuously subjected to a daily chloroquine injection for up to 2 days. Rats were killed 0.5, 6, 24 and 48 h after reperfusion. At the early phase (i.e., 0–6 h after reperfusion), chloroquine treatment ameliorated liver I/R injury, as indicated by lower serum aminotransferase levels, lower hepatic inflammatory cytokines and fewer histopathologic changes. In contrast, chloroquine worsened liver injury at the late phase of reperfusion (i.e., 24–48 h after reperfusion). The mechanism of protective action of chloroquine appeared to involve its ability to modulate mitogen-activated protein kinase activation, reduce high-mobility group box 1 release and inflammatory cytokines production, whereas chloroquine worsened liver injury via inhibition of autophagy and induction of hepatic apoptosis at the late phase. In conclusion, chloroquine prevents ischemic liver damage at the early phase, but aggravates liver damage at the late phase in liver I/R injury. This dual role of chloroquine should be considered when using chloroquine as an inhibitor of inflammation or autophagy in I/R injury.

Profound impact of gut homeostasis on chemically-induced pro-tumorigenic inflammation and hepatocarcinogenesis in rats

BACKGROUND & AIMS

Due to its anatomic connection, the liver is constantly exposed to gut-derived bacterial products or metabolites. Disruption of gut homeostasis is associated with many human diseases. The aim of this study was to determine the role of gut homeostasis in initiation and progression of hepatocellular carcinoma (HCC).

METHODS

Disruption of intestinal homeostasis by penicillin or dextran sulfate sodium (DSS) and its restoration by probiotics were applied in a diethylnitrosamine (DEN) model of rat hepatocarcinogenesis.

RESULTS

Patients with liver cirrhosis and HCC had significantly increased serum endotoxin levels. Chronic DEN treatment of rats was associated with an imbalance of subpopulations of the gut microflora including a significant suppression of Lactobacillus species, Bifidobacterium species and Enterococcus species as well as intestinal inflammation. Induction of enteric dysbacteriosis or intestinal inflammation by penicillin or DSS, respectively, significantly promoted tumor formation. Administration of probiotics dramatically mitigated enteric dysbacteriosis, ameliorated intestinal inflammation, and most importantly, decreased liver tumor growth and multiplicity. Interestingly, probiotics not only inhibited the translocation of endotoxin, which bears pathogen-associated molecular patterns (PAMPs) but also the activation of damage-associated molecular patterns (DAMPs) such as high-mobility group box 1 (HMGB1). As a result, the production of pro- and anti-inflammatory cytokines was skewed in favor of a reduced tumorigenic inflammation in the liver.

CONCLUSIONS

The data highlights the importance of gut homeostasis in the pathogenesis of HCC. Modulation of the gut microbiota by probiotics may represent a new avenue for therapeutic intervention to treat or prevent HCC development.

Protective effects of curcumin against hepatic fibrosis induced by carbon tetrachloride: modulation of high-mobility group box 1, Toll-like receptor 4 and 2 expression

The aim of the study was to investigate the effect of curcumin on the liver fibrosis induced by carbon tetrachloride (CCl(4)) in rats, and to elucidate its underlying molecular mechanisms. Rats were administered with CCl(4) together with or without curcumin for 6 weeks. Hepatic damage was evaluated by analysis of liver function tests in serum. Hepatic histopathology and collagen content were employed to quantify liver fibrosis; and activated hepatic stellate cells were assessed. Moreover, the mRNA and protein expression levels of interleukin (IL)-6, tumor necrosis factor (TNF)-α, monocyte chemotactic protein (MCP)-1, high-mobility group box 1 (HMGB1), Toll like receptor (TLR) 2 and TLR4 were determined by quantitative real time PCR, Western blot or immunohistochemistry. Treatment with curcumin significantly attenuated CCl(4)-induce liver injury, hepatic inflammation and reduced the levels of proinflammatory mediators (TNF-α, IL-6 and MCP-1). Moreover, curcumin significantly inhibited extracellular matrix deposition, reduced the number of activated stellate cells, and decreased the levels of HMGB1, TLR4 and TLR2 expression in the rat model of fibrogenesis. These results suggest that curcumin could be an effective agent for preventing liver fibrosis and its mechanism may in part be a consequence of the reduction TLR2, TLR4 and HMGB1 expression.

High mobility group box chromosomal protein 1 in acute-on-chronic liver failure patients and mice with ConA-induced acute liver injury

High mobility group box chromosomal protein 1 (HMGB1) is an important proinflammatory molecule in many inflammatory disorders, but little is known about its role in acute-on-chronic liver failure (ACLF). Here, we investigated the relationship between the expression of HMGB1 and the disease onset and severity of ACLF patients and mice with acute liver injury/failure induced by concanavalin A (ConA). Peripheral blood mononuclear cells (PBMCs) and serum from ACLF patients were collected, and a mouse model of acute liver injury/failure was induced by ConA. HMGB1 mRNA expression in patient PBMCs or in murine livers and serum HMGB1 protein in ACLF patients and mice were assayed by RT-PCR and Western blotting, respectively. HMGB1 translocation in hepatocytes of ConA-treated mice was assessed by immunohistochemical staining. Up-regulated HMGB1 mRNA levels in PBMCs and accumulated protein in serum were both correlated with disease severity in ACLF patients. In the animal model, HMGB1 levels increased at 4 h and reached its peak value at 8-12 h after challenge with ConA, which suggests that HMGB1 is a relatively late proinflammatory cytokine compared with TNF-α. Translocation of HMGB1 from the nucleus to the cytoplasm in hepatocytes was correlated with the severity of liver injury in mice. While specific anti-HMGB1 antibodies and nicotine protected mice from acute liver injury/failure by reducing mortality and improving liver tissue injury, treatment with recombinant HMGB1 led to an increased mortality due to ConA challenge. Thus, the data from the present study suggest that HMGB1 plays a critical role in the systemic inflammation of ACLF and could be a potential therapeutic target in the treatment of ACLF.

Oxidation of HMGB1 causes attenuation of its pro-inflammatory activity and occurs during liver ischemia and reperfusion

High mobility group box 1 (HMGB1) is a nuclear transcription factor. Once HMGB1 is released by damaged cells or activated immune cells, it acts as danger molecule and triggers the inflammatory signaling cascade. Currently, evidence is accumulating that posttranslational modifications such as oxidation may modulate the pro-inflammatory potential of danger signals. We hypothesized that oxidation of HMGB1 may reduce its pro-inflammatory potential and could take place during prolonged ischemia and upon reperfusion.

Liver grafts were cold preserved for 24 h and flushed with saline in hourly intervals to collect the effluent. Liver grafts, cold-preserved for 6 h, were transplanted into syngeneic recipients to obtain serum and liver samples 24 h after initiation of reperfusion. Addition of the effluent to a macrophage culture induced the synthesis of tumor necrosis factor-alpha (TNF-α) and interleukin (IL)-6. The stimulatory activity of graft effluent was reduced after depletion of HMGB1 via immunoprecipitation. Oxidation of the effluent HMGB1 using H₂O₂ attenuated its stimulatory activity as well. Liver transplantation of cold preserved grafts caused HMGB1 translocation and release as determined by immunohistochemistry and ELISA-assay, respectively. Using Western blot with non-reducing conditions revealed the presence of oxidized HMGB1 in liver samples obtained after 12 h and in effluent samples after 16 h of cold preservation as well as in liver and serum samples obtained 24 h after reperfusion.

These observations confirm that post-translational oxidation of HMGB1 attenuates its pro-inflammatory activity. Oxidation of HMGB1 as induced during prolonged ischemia and by reoxygenation during reperfusion in vivo might also attenuate its pro-inflammatory activity. Our findings also call for future studies to investigate the mechanism of the inhibitory effect of oxidized HMGB1 on the pro-inflammatory potential.