The role of high mobility group box-1 protein in severe sepsis

Pathophysiology of Disseminated Intravascular Coagulation in Sepsis: A Clinically Focused Overview

Sepsis is a major global health problem that results from a dysregulated and uncontrolled host response to infection, causing organ failure. Despite effective anti-infective therapy and supportive treatments, the mortality rate of sepsis remains high. Approximately 30-80% of patients with sepsis may develop disseminated intravascular coagulation (DIC), which can double the mortality rate. There is currently no definitive treatment approach for sepsis, with etiologic treatment being the cornerstone of therapy for sepsis-associated DIC. Early detection, diagnosis, and treatment are critical factors that impact the prognosis of sepsis-related DIC. Over the past several decades, researchers have made continuous efforts to better understand the mechanisms of DIC in sepsis, as well as improve its quantitative diagnosis and treatment. This article aims to provide a comprehensive overview of the current understanding of sepsis-related DIC, focusing on common causes and diagnoses, with the goal of guiding healthcare providers in the care of patients with sepsis.

Inflammasome-Dependent Coagulation Activation in Sepsis

Sepsis is a potentially life-threatening, pathological condition caused by a dysregulated host response to infection. Pathologically, systemic inflammation can initiate coagulation activation, leading to organ dysfunction, and ultimately to multiple organ failure and septic death. The inflammasomes are cytosolic multiprotein signaling complexes that control the host response to diverse pathogen-associated molecular patterns (PAMPs) from microorganisms as well as damage-associated molecular patterns (DAMPs) from dead or dying host cells. Recent studies highlight that the activation of canonical and non-canonical inflammasomes not only mediate the maturation and secretion of interleukin-1 (IL1) family cytokines, but also trigger the release of coagulation factor III, tissue factor (F3, best known as TF) in activated macrophages and monocytes. These emerging functions of inflammasomes in immunocoagulation are further positively regulated by stimulator of interferon response cGAMP interactor 1 (STING1, also known as STING or TMEM173, a hub of the innate immune signaling network) and high mobility group box 1 (HMGB1, a nuclear DAMP). This mini-review will discuss the regulation and function of inflammasome-dependent coagulation activation in sepsis.

Recombinant human soluble thrombomodulin is associated with attenuation of sepsis-induced renal impairment by inhibition of extracellular histone release

Multiple organ dysfunction induced by sepsis often involves kidney injury. Extracellular histones released in response to damage-associated molecular patterns are known to facilitate sepsis-induced organ dysfunction. Recombinant human soluble thrombomodulin (rhTM) and its lectin-like domain (D1) exert anti-inflammatory effects and neutralize damage-associated molecular patterns. However, the effects of rhTM and D1 on extracellular histone H3 levels and kidney injury remain poorly understood. Our purpose was to investigate the association between extracellular histone H3 levels and kidney injury, and to clarify the effects of rhTM and D1 on extracellular histone H3 levels, kidney injury, and survival in sepsis-induced rats. Rats in whom sepsis was induced via cecal ligation and puncture were used in this study. Histone H3 levels, histopathology of the kidneys, and the survival rate of rats at 24 h after cecal ligation and puncture were investigated. Histone H3 levels increased over time following cecal ligation and puncture. Histopathological analyses indicated that the distribution of degeneration foci among tubular epithelial cells of the kidney and levels of histone H3 increased simultaneously. Administration of rhTM and D1 significantly reduced histone H3 levels compared with that in the vehicle-treated group and improved kidney injury. The survival rates of rats in rhTM- and D1-treated groups were significantly higher than that in the vehicle-treated group. The results of this study indicated that rhTM and its D1 similarly reduce elevated histone H3 levels, thereby reducing acute kidney injury. Our findings also proposed that rhTM and D1 show potential as new treatment strategies for sepsis combined with acute kidney injury.

Astragaloside IV attenuates inflammatory reaction via activating immune function of regulatory T-cells inhibited by HMGB1 in mice

CONTEXT

High-mobility group box 1 (HMGB1) protein is a highly abundant protein that can promote the pathogenesis of inflammatory. Some experiments have demonstrated a vital role for HMGB1 to modulate the immune function of regulatory T-cells (Tregs). Astragaloside IV (AST IV), an extract from Astragalus membranaceus Moench (Leguminosae), has been shown to exert potent cardioprotective and anti-inflammatory effects. It is still unclear whether AST IV has a latent effect on the proinflammatory ability of HMGB1 with subsequent activation of Tregs in vivo.

OBJECTIVE

This research explores the antagonism of different doses of AST IV on the immunologic function of Tregs mediated by HMGB1.

MATERIALS AND METHODS

Mouse models (BALB/c) were constructed by which normal saline or AST IV was administered i.p. at 2, 4 and 6 days after the administration i.p. of 20 μg recombinate HMGB1. Spleen was used to procure Treg and CD4 ⁺ CD25^- T-cells which were co-cultured with Treg. Cell phenotypes of Tregs(Foxp3) were examined, and the cytokine levels in supernatants and the proliferation of T-cells were assayed. Gene expression was measured by RT-PCR.

RESULTS

(1) The expression levels of Foxp3 in Treg on post-stimulus days (PSD) 1-7 were significantly decreased in the HMGB1 group in comparison to those in the control group mice (p < 0.01). The Foxp3 expression was markedly increased in a dose-dependent manner in the AST group as compared with those in the HMGB1 group (p < 0.0 1-0.05). The same results were found in the contents of cytokines (IL-10 and TGF-β) released into supernatants by Treg. (2) When CD4 ⁺ CD25^- T-cells were co-cultured with Treg stimulated by HMGB1, the cell proliferation and the levels of cytokines (IL-2 and IFN-γ) in supernatant were markedly increased as compared with those in the HMGB1 group. The level of IL-4 was markedly decreased as compared with that in the HMGB1 group. The same results were found when CD4 ⁺ CD25^- T-cells were co-cultured with Treg in the NS group. Compared with those in the NS group, the contrary results were shown in a dose-dependent manner in the AST group.

DISCUSSION AND CONCLUSION

These results showed that AST IV has a therapeutic effect on inflammation promoted by HMGB1, and it should be studied as a new drug for the treatment of sepsis.

The coagulopathy of acute sepsis

PURPOSE OF REVIEW

Sepsis, defined by the presence of infection and host inflammation, is a lethal clinical syndrome with an increasing mortality rate worldwide. In severe disease, the coagulation system becomes diffusely activated, with consumption of multiple clotting factors resulting in disseminated intravascular coagulation (DIC). When present, DIC portends a higher mortality rate. Understanding the mechanisms that tie inflammation and diffuse thrombosis will allow therapeutic interventions to be developed. The coagulopathy of acute sepsis is a dynamic process that is time and disease burden specific. Whole-blood testing of coagulation may provide more clinically useful information than the classical tests. Natural anticoagulants that regulate thrombosis are downregulated in sepsis. Patients may benefit from the modulation of the coagulation system when systemic inflammation and hypercoagulopathy exist. Proper timing of anticoagulant therapy may ultimately lead to decreased incidence of multisystem organ dysfunction.

RECENT FINDINGS

The pathogenesis of coagulopathy in sepsis is driven by an upregulation of procoagulant mechanisms and simultaneous downregulation of natural anticoagulants. Inflammation caused by the invading organism is a natural host defense that cannot be eliminated during treatment. Successful strategies to prevent multisystem organ dysfunction center on stratifying patients at high risk for DIC and restoring the balance of inflammation and coagulation.

SUMMARY

The prevention of DIC in septic patients is a key therapeutic target in preventing death from multisystem organ failure. Stratifying patients for therapy using thromboelastometry, specific markers for DIC, and composite scoring systems is an area of growing research.

NKT cell modulates NAFLD potentiation of metabolic oxidative stress-induced mesangial cell activation and proximal tubular toxicity

Obesity and nonalcoholic fatty liver disease (NAFLD) are associated with the development and progression of chronic kidney disease. We recently showed that NAFLD induces liver-specific cytochrome P-450 (CYP)2E1-mediated metabolic oxidative stress after administration of the CYP2E1 substrate bromodichloromethane (BDCM) (Seth RK, Das S, Kumar A, Chanda A, Kadiiska MB, Michelotti G, Manautou J, Diehl AM, Chatterjee S. Toxicol Appl Pharmacol 274: 42-54, 2014; Seth RK, Kumar A, Das S, Kadiiska MB, Michelotti G, Diehl AM, Chatterjee S. Toxicol Sci 134:291-303, 2013). The present study examined the effects of CYP2E1-mediated oxidative stress in NAFLD leading to kidney toxicity. Mice were fed a high-fat diet for 12 wk to induce NAFLD. NAFLD mice were exposed to BDCM, a CYP2E1 substrate, for 4 wk. NAFLD + BDCM increased CYP2E1-mediated lipid peroxidation in proximal tubular cells compared with mice with NAFLD alone or BDCM-treated lean mice, thus ruling out the exclusive role of BDCM. Lipid peroxidation increased IL-1β, TNF-α, and interferon-γ. In parallel, mesangial cell activation was observed by increased α-smooth muscle actin and transforming growth factor-β, which was blocked by the CYP2E1 inhibitor diallyl sulphide both in vivo and in vitro. Mice lacking natural killer T cells (CD1d knockout mice) showed elevated (>4-fold) proinflammatory mediator release, increased Toll-like receptor (TLR)4 and PDGF2 mRNA, and mesangial cell activation in the kidney. Finally, NAFLD CD1D knockout mice treated with BDCM exhibited increased high mobility group box 1 and Fas ligand levels and TUNEL-positive nuclei, indicating that higher cell death was attenuated in TLR4 knockout mice. Tubular cells showed increased cell death and cytokine release when incubated with activated mesangial cells. In summary, an underlying condition of progressive NAFLD causes renal immunotoxicity and aberrant glomerular function possibly through high mobility group box 1-dependent TLR4 signaling and mesangial cell activation, which, in turn, is modulated by intrinsic CD1D-dependent natural killer T cells.

Recombinant human soluble thrombomodulin prevents peripheral HMGB1-dependent hyperalgesia in rats

BACKGROUND AND PURPOSE

High-mobility group box 1 (HMGB1), a nuclear protein, is actively or passively released during inflammation. Recombinant human soluble thrombomodulin (rhsTM), a medicine for treatment of disseminated intravascular coagulation (DIC), sequesters HMGB1 and promotes its degradation. Given evidence for involvement of HMGB1 in pain signalling, we determined if peripheral HMGB1 causes hyperalgesia, and then asked if rhsTM modulates the HMGB1-dependent hyperalgesia.

EXPERIMENTAL APPROACH

Mechanical nociceptive threshold and swelling in rat hindpaw were determined by the paw pressure test and by measuring paw thickness, respectively, and HMGB1 levels in rat hindpaw plantar tissue, dorsal root ganglion (DRG) and serum were determined by Western blotting or elisa.

KEY RESULTS

Intraplantar (i.pl.) administration of HMGB1 rapidly evoked paw swelling and gradually caused hyperalgesia in rats. Systemic administration of rhsTM abolished HMGB1-induced hyperalgesia, and partially blocked paw swelling. LPS, administered i.pl., rapidly produced mild paw swelling, and gradually caused hyperalgesia. The anti-HMGB1 neutralizing antibody abolished LPS-induced hyperalgesia, but partially inhibited paw swelling. rhsTM at a high dose, 10 mg kg(-1) , prevented both hyperalgesia and paw swelling caused by LPS. In contrast, rhsTM at low doses, 0.001-1 mg kg(-1) , abolished the LPS-induced hyperalgesia, but not paw swelling. HMGB1 levels greatly decreased in the hindpaw, but not DRG. Serum HMGB1 tended to increase after i.pl. LPS in rats pretreated with vehicle, but not rhsTM.

CONCLUSION AND IMPLICATIONS

These data suggest that peripheral HMGB1 causes hyperalgesia, and that rhsTM abolishes HMGB1-dependent hyperalgesia, providing novel evidence for therapeutic usefulness of rhsTM as an analgesic.

Clinical evaluation of high mobility group box 1 protein in Legionella pneumophila pneumonia

High mobility group box 1 (HMGB-1) protein is involved in acute lung injury due to various etiologies. We evaluated HMGB-1 levels in sera and bronchoalveolar fluids in patients with pneumonia caused by Legionella pneumophila. Levels of HMGB-1 in the sera of patients with L. pneumophila pneumonia (32 cases) and control subjects (24 cases) were determined. Serum HMGB-1 levels in Legionella pneumonia were similar to those of the control subjects. No significant correlation between HMGB-1 levels and other biomarkers and the outcome of cases was observed. In contrast, HMGB-1 levels, as well as interferon-γ, in bronchoalveolar (BA) fluids from severe L. pneumophila pneumonia (7 cases) were significantly higher than those in the sera of identical patients. HMGB-1 levels in BA fluids were relatively higher in pneumonia cases with ALI than those without ALI. Our findings suggest that intra-pulmonary HMGB-1 may be involved in the pathophysiology of pneumonia caused by L. pneumophila.

Combination of antithrombin and recombinant thrombomodulin attenuates leukocyte-endothelial interaction and suppresses the increase of intrinsic damage-associated molecular patterns in endotoxemic rats

INTRODUCTION

Both antithrombin (AT) and thrombomodulin are key players in physiological anticoagulant systems. Because the levels of both factors are known to decrease significantly during severe sepsis, we hypothesized that a combination therapy would be effective.

METHODS

A sepsis model was established using the intravenous infusion of lipopolysaccharide (LPS). A dose of 125 IU/kg of AT, 0.25 mg/kg of recombinant thrombomodulin, or a combination of both agents was injected immediately after LPS infusion (n = 7, each). Intravital observation of the mesenteric microcirculation was performed, and leukocyte adhesion and blood flow were calculated at 3 h after LPS infusion. Immediately after the observation, blood samples were obtained and coagulation markers, organ damage markers, the circulating levels of nucleosome and high-mobility group box 1 were measured.

RESULTS

Microscopic findings revealed the suppression of leukocyte adhesion and thrombus formation in the combination group. The number of adhesive leukocytes on the endothelium was significantly suppressed (P < 0.01), and the blood flow in venules was better maintained in the combination group compared with the placebo control (P < 0.01). The blood samples showed the suppressed activation in coagulation, no significant changes were observed in the organ damage markers in the treatment groups. The circulating levels of nucleosome and high-mobility group box 1 were both decreased significantly in the combination group compared with the placebo control (P < 0.01).

CONCLUSIONS

The coadministration of AT and recombinant thrombomodulin is effective for the suppression of leukocyte activation and cell death during sepsis.

Attenuation of sepsis-induced organ injury in mice by vitamin C

BACKGROUND

Multiple organ dysfunction syndrome (MODS) is the principal cause of death in patients with sepsis. Recent work supports the notion that parenteral vitamin C (VitC) is protective in sepsis through pleiotropic mechanisms. Whether suboptimal levels of circulating VitC increase susceptibility to sepsis-induced MODS is unknown.

MATERIALS AND METHODS

Unlike mice, humans lack the ability to synthesize VitC because of loss of L-gulono-γ-lactone oxidase (Gulo), the final enzyme in the biosynthesis of VitC. To examine whether physiological levels of VitC are required for defense against a catastrophic infection, we induced sepsis in VitC sufficient and VitC deficient Gulo(-/-) mice by intraperitoneal infusion of a fecal stem solution (FIP). Some VitC deficient Gulo(-/-) mice received a parenteral infusion of ascorbic acid (AscA, 200 mg/kg) 30 minutes after induction of FIP. We used molecular, histological, and biochemical analyses to assess for MODS as well as abnormalities in the coagulation system and circulating blood cells.

RESULTS

FIP produced injury to lungs, kidneys and liver (MODS) in VitC deficient Gulo(-/-) mice. MODS was not evident in FIP-exposed VitC sufficient Gulo(-/-) mice and attenuated in VitC deficient Gulo(-/-) mice infused with AscA. Septic VitC deficient Gulo(-/-) mice developed significant abnormalities in the coagulation system and circulating blood cells. These were attenuated by VitC sufficiency/infusion in septic Gulo(-/-) mice.

CONCLUSIONS

VitC deficient Gulo(-/-) mice were more susceptible to sepsis-induced MODS. VitC sufficiency or parenteral infusion of VitC, following induction of sepsis, normalized physiological functions that attenuated the development of MODS in sepsis.

The effect of Astragaloside IV on immune function of regulatory T cell mediated by high mobility group box 1 protein in vitro

High mobility group box 1 protein (HMGB1), a potent pro-inflammatory cytokine, contributes to the pathogenesis of diverse inflammatory and infectious disorders. Some studies have illustrated the potential effect of HMGB1 on regulatory T cells (Tregs). Astragaloside IV (AST IV) isolated from a Chinese herb, Astragalus mongholicus, is known to have a variety of immunomodulatory activities. However, it is not yet clear whether AST IV possesses potential regulatory effect on the pro-inflammatory ability of HMGB1 with subsequent activation of Tregs. This study was carried out to investigate the antagonistic effects of different doses of AST IV on the immune function of Tregs mediated by HMGB1 in vitro. Tregs isolated from the spleens of mice were co-cultured with HMGB1 and/or AST IV. Cell phenotypes of Tregs were analyzed, and the contents of various cytokines in the cell supernatants as a result of co-culture and the proliferation of CD4(+)CD25(-) T cells were determined. Results showed that HMGB1 stimulation resulted in significantly down-regulation of expressions of Tregs cell phenotypes. However, AST IV can rival the suppressing effect of HMGB1 on immune function of Tregs with a dose-dependent in vitro. These results indicate that AST IV has the potential therapeutic action on inflammation augmented by HMGB1.

Intravenous immunoglobulin preparation attenuates LPS-induced production of pro-inflammatory cytokines in human monocytic cells by modulating TLR4-mediated signaling pathways

Intravenous immunoglobulin (IVIG) has been used for the treatment of inflammatory and autoimmune diseases. The ability to modulate cytokine production has been formerly described as one of the mechanisms of its action. This study aimed to investigate the effect of IVIG on the production of pro-inflammatory cytokines in lipopolysaccharide (LPS)-stimulated monocytic cells. Peripheral blood mononuclear cells (PBMCs) or THP-1 cells treated with phorbol myristate acetate (PMA) were stimulated with LPS. The protein levels of pro-inflammatory cytokines [tumor necrosis factor (TNF)-α, interleukin (IL)-6, and high-mobility group box 1 (HMGB1)] in the culture supernatants were determined using appropriate enzyme-linked immunosorbent assay kits. The mRNA of TNF-α was determined by reverse transcription-polymerase chain reaction. The phosphorylation of nuclear factor kappa B (NF-κB) and the mitogen-activated protein kinases was examined by Western blot analyses. IVIG suppressed the production of pro-inflammatory cytokines such as TNF-α and IL-6 in LPS-stimulated PBMCs. Furthermore, IVIG inhibited TNF-α, IL-6, and HMGB1 production from LPS-stimulated THP-1 cells treated with PMA. In addition, Fc fragment prepared from the IVIG inhibited production of these cytokines from the cells to the same degree as IVIG, whereas Fab and F(ab')(2) fragments inhibited this only partially. We showed that IVIG and Fc fragments suppressed LPS-induced signal transduction pathways involving phosphorylation of NF-κB, p38, and c-Jun N-terminal kinase (JNK). Taken together, our results suggest that IVIG attenuates LPS-induced cytokine production predominantly mediated by its Fc region. The activity might be regulated by inhibiting NF-κB, p38, and JNK pathways in human monocytic cells.

The kynurenine system and immunoregulation

There is developing interest in the role of the kynurenines in the immune function. A considerable amount of evidence has accumulated as concerns interactions between the kynurenine pathway, cytokines and the nervous system. Indoleamine 2,3-dioxygenase (IDO) occupies a key position connecting the immune system and the kynurenine pathway. There are evidences of the immunosuppressive effect of IDO. Following the interferon (IFN)-mediated activation of antigen presenting cells, the induction of IDO and the kynurenine system exerts a counter-regulating effect, maintaining the homeostasis. Inhibition of T cell functions, activation of the regulatory T cells, and the inhibition of Natural Killer cells are among the important factors in the immunosuppressive effects of IDO and kynurenines. There is a close connection between cytokines (IFN-α, IFN-γ, TNF-α, TGF-β, IL-4 and IL-23) and the kynurenine system, and an imbalance in the TH1/TH2 cytokine profile may possibly lead to neurologic or psychiatric disorders. As the tryptophan metabolic pathway is activated by pro-inflammatory stimuli, the anti-inflammatory effect of kynurenic acid provides a further feedback mechanism in modulating the immune responses.

Astragalus polysaccharides attenuate postburn sepsis via inhibiting negative immunoregulation of CD4+ CD25(high) T cells

BACKGROUND

Astragalus polysaccharides (APS) isolated from one of the Chinese herbs, Astragalus mongholicus, are known to have a variety of immunomodulatory activities. However, it is not yet clear whether APS can exert an effect on the immune functions of regulatory T cells (Tregs). This study was carried out to investigate the effect of APS on the immune function of peripheral blood Tregs in postburn sepsis.

METHODOLOGY/PRINCIPAL FINDINGS

BALB/C mice were randomly divided into six groups as follows: sham burn group, burn control (burn without infection animals) group, burn plus P. aeruginosa group, burn plus P. aeruginosa with APS (50 mg/kg) treatment group, burn plus P. aeruginosa with APS (100 mg/kg) treatment group, and burn plus P. aeruginosa with APS (200 mg/kg) treatment group, and they were sacrificed on postburn day 1, 3, 5, and 7, respectively, with seven animals at each time point. Magnetic microbeads were used to isolate peripheral blood Tregs and CD4(+) T cells. Phenotypes were analyzed by flow cytometry, and cytokine levels were determined with ELISA. In the burn plus P. aeruginosa group, forkhead/winged helix transcription factor p3 (Foxp3) expression on CD4(+)CD25(+)Tregs were strongly enhanced in comparison to the sham group, and the capacity of CD4(+)CD25(+)Tregs to produce interleukin (IL)-10 was markedly increased. Administration of APS to inhibit CD4(+)CD25(+)Tregs could significantly decrease expression of Foxp3 on CD4(+)CD25(+)Tregs, and IL-10 production in burned mice with P. aeruginosa infection. At the same time, proliferative activity and expression of IL-2 and IL-2Rα on CD4(+) T cells were restored. In contrast, anti-Toll-like receptor 4 (TLR4) antibody could block the effect of APS on Tregs immune function.

CONCLUSION

APS might suppress CD4(+)CD25(+)Treg activity, at least in part, via binding TLR4 on Tregs and trigger a shift of Th2 to Th1 with activation of CD4(+) T cells in burned mice with P. aeruginosa infection.

Astragalus polysaccharides attenuate postburn sepsis via inhibiting negative immunoregulation of CD4+ CD25(high) T cells

Backgroud

Astragalus polysaccharides (APS) isolated from one of the Chinese herbs, Astragalus mongholicus, are known to have a variety of immunomodulatory activities. However, it is not yet clear whether APS can exert an effect on the immune functions of regulatory T cells (Tregs). This study was carried out to investigate the effect of APS on the immune function of peripheral blood Tregs in postburn sepsis.

Methodology/Principal Findings

BalB/c mice were randomly divided into six groups as follows: sham burn group, burn control(burn without infection animals) group, burn plus P. aeruginosa group, burn plus P. aeruginosa with APS (50 mg/kg) treatment group, burn plus P. aeruginosa with APS (100 mg/kg) treatment group, and burn plus P. aeruginosa with APS (200 mg/kg) treatment group, and they were sacrificed on postburn day 1, 3, 5, and 7, respectively, with seven animals at each time point. Magnetic microbeads were used to isolate peripheral blood Tregs and CD4⁺ T cells. Phenotypes were analyzed by flow cytometry, and cytokine levels were determined with ELISA. In the burn plus P. aeruginosa group, forkhead/winged helix transcription factor p3 (Foxp3) expression on CD4⁺CD25⁺Tregs were strongly enhanced in comparison to the sham group, and the capacity of CD4⁺CD25⁺Tregs to produce interleukin (IL)-10 was markedly increased. Administration of APS to inhibit CD4⁺CD25⁺Tregs could significantly decrease expression of Foxp3 on CD4⁺CD25⁺Tregs, and IL-10 production in burned mice with P. aeruginosa infection. At the same time, proliferative activity and expression of IL-2 and IL-2Rα on CD4⁺ T cells were restored. In contrast, anti-Toll-like receptor 4 (TLR4) antibody could block the effect of APS on Tregs immune function.

Conclusion

APS might suppress CD4⁺CD25⁺Treg activity, at least in part, via binding TLR4 on Tregs and trigger a shift of Th2 to Th1 with activation of CD4⁺ T cells in burned mice with P. aeruginosa infection.

Different inhibitory effects of kynurenic acid and a novel kynurenic acid analogue on tumour necrosis factor-α (TNF-α) production by mononuclear cells, HMGB1 production by monocytes and HNP1-3 secretion by neutrophils

Kynurenic acid (KynA), a broad spectrum antagonist of excitatory amino acid receptors, may serve as a protective agent in neurological disorders. The potential anti-inflammatory effect of KynA in human leukocytes has not been characterized. The aim of this study was to compare the effects of KynA with those of a new analogue, 2-(2-N,N-dimethylaminoethylamine-1-carbonyl)-1H-quinolin-4-one hydrochloride on tumour necrosis factor-α (TNF-α) production and high mobility group box protein 1 (HMGB1) secretion. The effects of KynA on granulocyte activation were investigated via the secretion of human neutrophil peptide 1-3 (HNP1-3). Peripheral blood mononuclear cells and granulocytes or CD14 positive monocytes were applied as effector cells, or whole blood cultures were used. TNF-α, HMGB1 and HNP1-3 concentrations were determined by ELISA, TNF-α and HNP1-3 mRNA expressions were quantified by reverse transcription PCR. KynA attenuated the TNF-α production of human mononuclear cells activated by heat-inactivated Staphylococcus aureus, inhibiting TNF-α production at the transcription level. Furthermore, KynA diminished HMGB1 secretion by U 937 monocytic cells and by peripheral blood monocytes. KynA inhibited the HNP1-3 secretion in whole blood and in granulocyte cultures. The suppressive effect of the KynA analogue was more potent than that of an equimolar concentration KynA in TNF-α, HMGB1 and HNP1-3 inhibition. These results suggest that the new KynA analogue has a more potent immunoregulatory effect than KynA on human mononuclear cells, monocytes and granulocytes and indicate the potential benefits of further exploration of its uses in human inflammatory disease.

High mobility group box 1 protein suppresses T cell-mediated immunity via CD11c(low)CD45RB(high) dendritic cell differentiation

AIM

High mobility group box 1 protein (HMGB1) has been identified as a late proinflammatory cytokine and plays a key role in immune regulation. However, it is not yet clear whether HMGB1 can induce the activation and differentiation of dendritic cell (DC) subsets and subsequently modulate immune function of T cells. This study was performed to investigate the effect of HMGB1 on the differentiation of splenic DCs and its influence on T cell-mediated immunity in terms of DC subsets CD11c(low)CD45RB(high) DCs and CD11c(high)CD45RB(low) DCs in male BALB/c mice spleens in vitro.

RESULTS

MACS microbeads were used to isolate splenic DCs, CD11c(low)CD45RB(high) DCs, CD11c(high)CD45RB(low) DCs and CD4(+) T cells. The percentage of CD11c(low)CD45RB(high) DCs was significantly increased after treatment with HMGB1 compared to their counterparts (CD11c(high)CD45RB(low) DCs). It was found that unlike the gradually increasing interleukin (IL)-12 secretion of CD11c(high)CD45RB(low) DCs induced by HMGB1, CD11c(low)CD45RB(high) DCs showed a obvious dose-dependent response between IL-10 production and HMGB1 stimulation. In order to verify whether the alteration of CD4(+) T cells was mainly associated with the differentiation of splenic DCs mediated by HMGB1 to CD11c(low)CD45RB(high) DCs, anti-IL-12 receptor (IL-12R) or anti-IL-10R monoclonal antibody was used to inhibit the effect of CD11c(high)CD45RB(low) DCs or CD11c(low)CD45RB(high) DCs in CD4(+) T cells mixed lymphocyte reaction culture. After treatment with anti-IL-12R or anti-IL-10 monoclonal antibody in CD4(+) T cells+CD11c(high)CD45RB(low) DCs or CD11c(low)CD45RB(high) DCs mixed lymphocyte reaction, the induction of these DCs on T cells was inhibited dramatically.

CONCLUSION

These data demonstrated that HMGB1 might induce the differentiation of splenic DCs to CD11c(low)CD45RB(high) DCs followed by shifting of Th1 to Th2 with enhancement of T lymphocyte immune function in vitro. Also, the effect of HMGB1 on T cell differentiation to Th2 was not associated with the inhibition of IL-12 production in CD11c(high)CD45RB(low) DCs.

Association between high-mobility group box-1 protein release and immune function of dendritic cells in thermal injury

The present study was performed to investigate in vivo the effect of high-mobility group box-1 protein (HMGB1) on the maturation of dendritic cell (DC) and the influence on T-cell-mediated immunity after thermal injury. Rats were randomly divided into 3 groups as follows: sham burn group, burn group, and burn with ethyl pyruvate (EP) treatment group, and they were sacrificed on post burn days (PBD) 1, 3, 5, and 7 respectively. MACS microbeads were used to isolate splenic DCs and column of nylon wool to obtain T cells. Phenotypes were analyzed by flow cytometry and cytokines were determined with ELISA kits. The expression levels of splenic HMGB1 were significantly elevated during PBD 1-7. DC expressed similar CD80 levels, strongly enhanced CD86, and slightly elevated MHC class II levels in comparison to DC from sham-injured rats, and protein levels of IL-12 were not increased after thermal injury. Administration of EP to inhibit HMGB1 could significantly enhance expression levels of CD80, MHC class II on DC surface, and IL-12 production after burns. Simultaneously, proliferative activity and expression levels of IL-2 as well as IL-2R alpha of T cell were restored. These results suggested that the excessively released HMGB1 might stimulate splenic DC to mature abnormally and down-regulate the IL-12 production, and further shifting of Th1 to Th2 with suppression of T-lymphocyte immune function following burn injury.

Stepwise release of biologically active HMGB1 during HSV-2 infection

BACKGROUND

High mobility group box 1 protein (HMGB1) is a major endogenous danger signal that triggers inflammation and immunity during septic and aseptic stresses. HMGB1 recently emerged as a key soluble factor in the pathogenesis of various infectious diseases, but nothing is known of its behaviour during herpesvirus infection. We therefore investigated the dynamics and biological effects of HMGB1 during HSV-2 infection of epithelial HEC-1 cells.

METHODOLOGY/PRINCIPAL FINDINGS

Despite a transcriptional shutdown of HMGB1 gene expression during infection, the intracellular pool of HMGB1 protein remained unaffected, indicating its remarkable stability. However, the dynamics of HMGB1 was deeply modified in infected cells. Whereas viral multiplication was concomitant with apoptosis and HMGB1 retention on chromatin, a subsequent release of HMGB1 was observed in response to HSV-2 mediated necrosis. Importantly, extracellular HMGB1 was biologically active. Indeed, HMGB1-containing supernatants from HSV-2 infected cells induced the migration of fibroblasts from murine or human origin, and reactivated HIV-1 from latently infected T lymphocytes. These effects were specifically linked to HMGB1 since they were blocked by glycyrrhizin or by a neutralizing anti-HMGB1 antibody, and were mediated through TLR2 and the receptor for Advanced Glycation End-products (RAGE). Finally, we show that genital HSV-2 active infections also promote HMGB1 release in vivo, strengthening the clinical relevance of our experimental data.

CONCLUSIONS

These observations target HMGB1 as an important actor during HSV-2 genital infection, notably in the setting of HSV-HIV co-infection.

Sepsis-associated disseminated intravascular coagulation and thromboembolic disease

Sepsis is almost invariably associated with haemostatic abnormalities ranging from subclinical activation of blood coagulation (hypercoagulability), which may contribute to localized venous thromboembolism, to acute disseminated intravascular coagulation (DIC), characterized by massive thrombin formation and widespread microvascular thrombosis, partly responsible of the multiple organ dysfunction syndrome (MODS), and subsequent consumption of platelets and coagulation proteins causing, in most severe cases, bleeding manifestations. There is general agreement that the key event underlying this life-threatening sepsis complication is the overwhelming inflammatory host response to the infectious agent leading to the overexpression of inflammatory mediators. Mechanistically, the latter, together with the micro-organism and its derivatives, causes DIC by 1) up-regulation of procoagulant molecules, primarily tissue factor (TF), which is produced mainly by stimulated monocytes-macrophages and by specific cells in target tissues; 2) impairment of physiological anticoagulant pathways (antithrombin, protein C pathway, tissue factor pathway inhibitor), which is orchestrated mainly by dysfunctional endothelial cells (ECs); and 3) suppression of fibrinolysis due to increased plasminogen activator inhibitor-1 (PAI-1) by ECs and likely also to thrombin-mediated activation of thrombin-activatable fibrinolysis inhibitor (TAFI). Notably, clotting enzymes non only lead to microvascular thrombosis but can also elicit cellular responses that amplify the inflammatory reactions. Inflammatory mediators can also cause, directly or indirectly, cell apoptosis or necrosis and recent evidence indicates that products released from dead cells, such as nuclear proteins (particularly extracellular histones), are able to propagate further inflammation, coagulation, cell death and MODS. These insights into the pathogenetic mechanisms of DIC and MODS may have important implications for the development of new therapeutic agents that could be potentially useful particularly for the management of severe sepsis.

High-mobility group box-1 protein serum levels do not reflect monocytic function in patients with sepsis-induced immunosuppression

BACKGROUND

High-mobility group box-1 (HMGB-1) protein is released during "late sepsis" by activated monocytes. We investigated whether systemic HMGB-1 levels are associated with indices of monocytic activation/function in patients with sepsis-induced immunosuppression.

METHODOLOGY

36 patients (31 male, 64 +/- 14 years) with severe sepsis/septic shock and monocytic deactivation (reduced mHLA-DR expression and TNF-alpha release) were assessed in a subanalysis of a placebo-controlled immunostimulatory trial using GM-CSF. HMGB-1 levels were assessed over a 9-day treatment interval. Data were compared to standardized biomarkers of monocytic immunity (mHLA-DR expression, TNF-alpha release).

PRINCIPLE FINDINGS

HMGB-1 levels were enhanced in sepsis but did not differ between treatment and placebo groups at baseline (14.6 +/- 13.5 versus 12.5 +/- 11.5 ng/ml, P = .62). When compared to controls, HMGB-1 level increased transiently in treated patients at day 5 (27.8 +/- 21.7 versus 11.0 +/- 14.9, P = .01). Between group differences were not noted at any other point of assessment. HMGB-1 levels were not associated with markers of monocytic function or clinical disease severity.

CONCLUSIONS

GM-CSF treatment for sepsis-induced immunosuppression induces a moderate but only transient increase in systemic HMGB-1 levels. HMGB-1 levels should not be used for monitoring of monocytic function in immunostimulatory trials as they do not adequately portray contemporary changes in monocytic immunity.

High-mobility group box-1 protein, lipopolysaccharide-binding protein, interleukin-6 and C-reactive protein in children with community acquired infections and bacteraemia: a prospective study

Introduction

Even though sepsis is one of the common causes of children morbidity and mortality, specific inflammatory markers for identifying sepsis are less studied in children. The main aim of this study was to compare the levels of high-mobility group box-1 protein (HMGB1), Lipopolysaccharide-binding protein (LBP), Interleukin-6 (IL-6) and C-reactive protein (CRP) between infected children without systemic inflammatory response syndrome (SIRS) and children with severe and less severe sepsis. The second aim was to examine HMGB1, LBP, IL6 and CRP as markers for of bacteraemia.

Methods

Totally, 140 children with suspected or proven infections admitted to the Children's Clinical University Hospital of Latvia during 2008 and 2009 were included. Clinical and demographical information as well as infection focus were assessed in all patients. HMGB1, LBP, IL-6 and CRP blood samples were determined. Children with suspected or diagnosed infections were categorized into three groups of severity of infection: (i) infected without SIRS (n = 36), (ii) sepsis (n = 91) and, (iii) severe sepsis (n = 13). They were furthermore classified according bacteraemia into (i) bacteremia (n = 30) and (ii) no bacteraemia (n = 74).

Results

There was no statistically significant difference in HMGB1 levels between children with different levels of sepsis or with and without bacteraemia. The levels of LBP, IL-6 and CRP were statistically significantly higher among patients with sepsis compared to those infected but without SIRS (p < 0.001). Furthermore, LBP, IL-6 and CRP were significantly higher in children with severe sepsis compared to those ones with less severe sepsis (p < 0.001). Median values of LBP, IL6 and CRP were significantly higher in children with bacteraemia compared to those without bacteraemia. The area under the receiver operating curve (ROC) for detecting bacteraemia was 0.87 for both IL6 and CRP and 0.82 for LBP, respectively.

Conclusion

Elevated levels of LBP, IL-6 and CRP were associated with a more severe level of infection in children. Whereas LBP, IL-6 and CRP seem to be good markers to detect patients with bacteraemia, HMGB1 seem to be of minor importance. LBP, IL-6 and CRP levels may serve as good biomarkers for identifying children with severe sepsis and bacteraemia and, thus, may be routinely used in clinical practice.

Clinical review: the role of biomarkers in the diagnosis and management of community-acquired pneumonia

In patients with community-acquired pneumonia, traditional criteria of infection based on clinical signs and symptoms, clinical scoring systems, and general inflammatory indicators (for example, leukocytosis, fever, C-reactive protein and blood cultures) are often of limited clinical value and remain an unreliable guide to etiology, optimal therapy and prognosis. Procalcitonin is superior to other commonly used markers in its specificity for bacterial infection (allowing alternative diagnoses to be excluded), as an indicator of disease severity and risk of death, and mainly as a guide to the necessity for antibiotic therapy. It can therefore be viewed as a diagnostic, prognostic, and perhaps even theragnostic test. It more closely matches the criteria for usefulness than other candidate biomarkers such as C-reactive protein, which is rather a nonspecific marker of acute phase inflammation, and proinflammatory cytokines such as plasma IL-6 levels that are highly variable, cumbersome to measure, and lack specificity for systemic infection. Elevated levels of pro-adrenomedullin, copeptin (which is produced in equimolar amounts to vasopressin), natriuretic peptides and cortisol are significantly related to mortality in community-acquired pneumonia, as are other prohormones such as pro-atrial natriuretic peptide, coagulation markers, and other combinations of inflammatory cytokine profiles. However, all biomarkers have weaknesses as well as strengths. None should be used on its own; and none is anything more than an aid in the exercise of clinical judgment based upon a synthesis of available clinical, physiologic and laboratory features in each patient.

Circulating levels of a soluble form of receptor for advanced glycation end products and high-mobility group box chromosomal protein 1 in patients with acute pancreatitis

OBJECTIVES

To study in patients with acute pancreatitis (AP) the plasma soluble form of the receptor for advanced glycation end products (sRAGE) and high-mobility group box chromosomal protein 1 (HMGB1) levels, followed-up for 12 days after hospitalization, in relation to the occurrence of organ failure and mortality.

METHODS

Thirty-eight patients with severe AP and organ failure (grade 2). A control group (127 patients) consisted of 38 patients with severe AP without organ failure (grade 1) and 89 patients with mild AP (grade 0). Plasma samples for determination of HMGB1 and sRAGE levels were collected on admission and on days 1 and 2, days 3 and 4, and days 7 and 12 after admission.

RESULTS

The median of the highest sRAGE levels was higher in grade 2 patients (472 pg/mL; interquartile range [IQR], 259-912) than in grade 0 plus grade 1 patients (349 pg/mL; IQR, 209-544; P = 0.024). Among the patients with detectable HMGB1, the median of the highest HMGB1 levels was 117 ng/mL (IQR, 56-212; n = 24) in grade 2 patients and 87 ng/mL (IQR, 54-161; n = 62) in grade 0 plus grade 1 patients (P = 0.310).

CONCLUSIONS

We demonstrate that sRAGE level, but not HMGB1 level, is significantly higher in AP patients who develop organ failure than in AP patients without organ failure who recover.

NLRP3 (NALP3, Cryopyrin) facilitates in vivo caspase-1 activation, necrosis, and HMGB1 release via inflammasome-dependent and -independent pathways

Bacterial infection elicits a range of beneficial as well as detrimental host inflammatory responses. Key among these responses are macrophage/monocyte necrosis, release of the proinflammatory factor high-mobility group box 1 protein (HMGB1), and induction of the cytokine IL-1. Although the control of IL-1beta has been well studied, processes that control macrophage cell death and HMGB1 release in animals are poorly understood. This study uses Klebsiella pneumonia as a model organism because it elicits all three responses in vivo. The regulation of these responses is studied in the context of the inflammasome components NLRP3 and ASC, which are important for caspase-1 activation and IL-1beta release. Using a pulmonary infection model that reflects human infection, we show that K. pneumonia-induced mouse macrophage necrosis, HMGB1, and IL-1beta release are dependent on NLRP3 and ASC. K. pneumoniae infection of mice lacking Nlrp3 results in decreased lung inflammation and reduced survival relative to control, indicating the overall protective role of this gene. Macrophage/monocyte necrosis and HMGB1 release are controlled independently of caspase-1, suggesting that the former two responses are separable from inflammasome-associated functions. These results provide critical in vivo validation that the physiologic role of NLRP3 and ASC is not limited to inflammasome formation.

Recombinant human soluble thrombomodulin decreases the plasma high-mobility group box-1 protein levels, whereas improving the acute liver injury and survival rates in experimental endotoxemia

OBJECTIVE

In addition to the hyperactivation of the inflammatory cytokines, high-mobility group box-1 protein (HMGB1), recently identified as a lethal late-phase mediator is suspected to be closely correlated with the development of sepsis. Therefore, the therapeutic efficacy of recombinant human soluble thrombomodulin (ART-123) administration on the production of inflammatory cytokines and the plasma level of HMGB1 was investigated in experimental endotoxemia.

DESIGN

Prospective, comparative, experimental study.

SETTING

Laboratory animal research center at a university.

SUBJECTS

Male Sprague-Dawley rats (250-300 g).

INTERVENTIONS

Endotoxemia was induced in rats by a bolus intravenous injection of lipopolysaccharide (LPS) at a dosage of 4 mg/kg (LPS group). ART-123 (1 mg/kg) was administered as a bolus injection 30 minutes before or 4 hours after injection of LPS (ART-123 pretreated/treated group). As a control, an equal volume of physiologic saline was administered instead of LPS and ART-123 (control group).

MEASUREMENTS AND MAIN RESULTS

Rats were randomly divided into ART-123 pretreated group, ART-123 treated group, and LPS group, respectively. After the injection of LPS, the levels of inflammatory cytokines and thrombin-antithrombin III complex, plasma HMGB1 concentrations, liver immunohistochemical and histopathologic characteristics, liver dysfunction, and survival rate were examined. The increased levels of inflammatory cytokines and plasma HMGB1 induced by LPS in this rat model were improved by the administration of ART-123; additionally, reduced liver dysfunction and increased survival rate were observed.

CONCLUSIONS

This study demonstrated that ART-123 inhibits the expression of inflammatory cytokines and decreases the plasma HMGB1 levels in experimental endotoxemia. In addition, ART-123 administration markedly reduced liver dysfunction and mortality even with delayed treatment of ART-123. The use of ART-123 may therefore be a beneficial treatment for septic patients.

Plasma concentrations of high-mobility group box protein 1, soluble receptor for advanced glycation end-products and circulating DNA in patients with acute pancreatitis

AIMS

High-mobility group box protein 1 (HMGB1), a late-acting proinflammatory cytokine, is secreted actively by inflammatory cells, and released passively from necrotic cells. From the aspect that both inflammation and necrosis are involved in the pathogenesis in acute pancreatitis, the aim of the study was a joint investigation of the plasma concentrations of HMGB1, its soluble receptor for advanced glycation end-products (sRAGE), and the circulating DNA as a marker of cell death.

METHODS

62 patients with acute pancreatitis (30 mild, 32 severe), 20 patients with sepsis, and 20 healthy controls were enrolled in the study. HMGB1 and sRAGE plasma levels were measured by means of ELISA. Plasma DNA concentrations were estimated by real-time quantitative PCR for the beta-globin gene.

RESULTS

The circulating HMGB1 level was significantly higher in patients with severe acute pancreatitis (13.33 +/- 2.11 ng/ml) than in healthy controls (0.161 +/- 0.03 ng/ml) or than in patients with mild pancreatitis (2.64 +/- 0.185 ng/ml). The plasma concentration of sRAGE was highest in patients with sepsis (2,210 +/- 252 pg/ml), while the levels of sRAGE correlated inversely with that of HMGB1 in patients with acute pancreatitis. The plasma DNA level was significantly elevated in patients with severe acute pancreatitis (2,206 +/- 452 ng/ml).

CONCLUSION

A complex study of the plasma levels of HMGB1, sRAGE and circulating DNA can be informative in evaluations of acute pancreatitis with different levels of severity.

The effect of high-mobility group box 1 protein on activity of regulatory T cells after thermal injury in rats

The aim of the present study was to investigate in vivo the effect of high-mobility group box 1 protein (HMGB1) on activity of regulatory T cells (Tregs) and the influence on T-cell-mediated immunity after thermal injury. Male Wistar rats were randomly divided into four groups as follows: sham burn group, burn group, burn with ethyl pyruvate treatment group, and burn with antireceptor for advanced glycation end products (RAGE) antibody treatment group, and they were killed on postburn days 1, 3, 5, and 7, respectively, with eight animals at each time point. Magnetic cell sorting microbeads were used to isolate splenic Tregs and a column of nylon wool to obtain T cells. Phenotypes, including cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), forkhead/winged helix transcription factor p3 (Foxp3), RAGE, and IL-2Ralpha, were analyzed by flow cytometry. Levels of HMGB1, IL-10, IL-2, IL-4 and interferon gamma were determined by enzyme-linked immunosorbent assay kits, and real-time reverse transcription-polymerase chain reaction was performed to detect mRNA expression of IL-10, IL-2, and IL-2Ralpha. Serum HMGB1 levels were significantly elevated during postburn days 1 to 7. In the burn group, CTLA-4 and Foxp3 expression levels of Tregs were strongly enhanced in comparison to the sham-injured group, and the capacity of Tregs to produce IL-10 was markedly increased. Administration of ethyl pyruvate to inhibit HMGB1 or anti-RAGE antibody could significantly decrease expression levels of CTLA-4, Foxp3 on Tregs, and IL-10 production after burns. Simultaneously, proliferative activity and expression levels of IL-2 and IL-2Ralpha of T cell were restored. The excessively released HMGB1 might stimulate CD4+CD25+Treg activity via binding RAGE on the surface of Tregs and trigger a shift of T(H)1 to T(H)2 with suppression of T-lymphocyte immune function after burn injury.

Quercetin prevents LPS-induced high-mobility group box 1 release and proinflammatory function

The pathogenesis of sepsis is mediated in part by the pathogen-associated molecular pattern molecule bacterial endotoxin, which stimulates macrophages to sequentially release early (e.g., TNF-alpha, IL-1beta) and late (e.g., high-mobility group box [HMGB] 1 protein) proinflammatory mediators. The recent discovery of HMGB1 as a late mediator of lethal sepsis has prompted investigation into development of several new experimental therapeutics that limit release, either blocking HMGB1 itself or its nominal receptors. Quercetin was recently identified as an experimental therapeutic that significantly protects against oxidative injury. Here, we report that quercetin attenuates lethal systemic inflammation caused by endotoxemia, even if treatment is started after the early TNF response. Quercetin treatment reduced circulating levels of HMGB1 in animals with established endotoxemia. In macrophage cultures, quercetin inhibited release as well as the cytokine activities of HMGB1, including limiting the activation of mitogen-activated protein kinase and NF-kappaB, two signaling pathways that are critical for HMGB1-induced subsequent cytokine release. Quercetin and autophagic inhibitor, wortmannin, inhibited LPS-induced type-II microtubule-associated protein 1A/1B-light chain 3 production and aggregation, as well as HMGB1 translocation and release, suggesting a potential association between autophagy and HMGB1 release. Quercetin delivery, a strategy to pharmacologically inhibit HMGB1 release that is effective at clinically achievable concentrations, now warrants further evaluation in sepsis and other systemic inflammatory disorders.

KLF4 promotes the expression, translocation, and releas eof HMGB1 in RAW264.7 macrophages in response to LPS

Krüppel-like factor 4 (KLF4) is an evolutionarily conserved zinc finger-containing transcription factor with diverse regulatory functions in cell growth, proliferation, differentiation, and embryogenesis. In our previous study, we found that KLF4 mRNA was up-regulated more than 10-fold in adult mice lung tissues after endotoxin stimuli, and that KLF4 can regulate the expression of IL -10, an early inflammatory mediator. To determine whether KLF4 influences the expression and release of high-mobility group box 1 (HMGB1), an important late inflammatory mediator, which contains two potential KLF4-binding elements in its promoter, pcDNA3.1-KLF4 expression plasmid or KLF4 antisense oligonucleotide was transfected into RAW264.7 macrophages, the expression and release of HMGB1 were examined by reverse-transcriptase-polymerase chain reaction and Western blot, respectively. Electrophoretic mobility shift assay was performed to detect the binding activity of KLF4 to the HMGB1 promoter. The results showed that KLF4 overexpression led to an increased expression of HMGB1 in both cytoplasm and nucleus, whereas KLF4 deficiency led to a decrease in HMGB1. Moreover, compared with the control group, the release of HMGB1 was increased after KLF4 overexpression after LPS treatment, whereas the release of HMGB1 was decreased after KLF4 deficiency in response to LPS. Electrophoretic mobility shift assay results showed the binding of KLF4 to the oligonucleotides designed according to the HMGB1 promoter, and the binding activity was increased in response to LPS stimulation. These results indicate that KLF4 plays an important role in regulating the expression of HMGB1 in normal condition, as well as the translocation and release of HMGB1 in response to LPS.

A high-sensitivity method for detection and measurement of HMGB1 protein concentration by high-affinity binding to DNA hemicatenanes

BACKGROUND

Protein HMGB1, an abundant nuclear non-histone protein that interacts with DNA and has an architectural function in chromatin, was strikingly shown some years ago to also possess an extracellular function as an alarmin and a mediator of inflammation. This extracellular function has since been actively studied, both from a fundamental point of view and in relation to the involvement of HMGB1 in inflammatory diseases. A prerequisite for such studies is the ability to detect HMGB1 in blood or other biological fluids and to accurately measure its concentration.

METHODOLOGY/PRINCIPAL FINDINGS

In addition to classical techniques (western blot, ELISA) that make use of specific anti-HMGB1 antibodies, we present here a new, extremely sensitive technique that is based on the fact that hemicatenated DNA loops (hcDNA) bind HMGB1 with extremely high affinity, higher than the affinity of specific antibodies, similar in that respect to DNA aptamers. DNA-protein complexes formed between HMGB1 and radiolabeled hcDNA are analyzed by electrophoresis on nondenaturing polyacrylamide gels using the band-shift assay method. In addition, using a simple and fast protocol to purify HMGB1 on the basis of its solubility in perchloric acid allowed us to increase the sensitivity by suppressing any nonspecific background. The technique can reliably detect HMGB1 at a concentration of 1 pg per microliter in complex fluids such as serum, and at much lower concentrations in less complex samples. It compares favorably with ELISA in terms of sensitivity and background, and is less prone to interference from masking proteins in serum.

CONCLUSION

The new technique, which illustrates the potential of DNA nanoobjects and aptamers to form high-affinity complexes with selected proteins, should provide a valuable tool to further investigate the extracellular functions of HMGB1 and its involvement in inflammatory pathologies.

High mobility group box-1 protein--one step closer to the clinic?

High mobility group box (HMGB)1, originally described as a nuclear protein that binds to and modifies DNA, is now regarded as a central mediator of inflammation by acting as a cytokine. HMGB1 is postulated to be particularly important as a late acting mediator of lethal septicaemia in mice. Furthermore, it has been suggested that HMGB1 plays a role in clinical conditions such as autoimmunity, acute ischaemia-reperfusion injury, cardiovascular disease and cancer. HMGB1 has emerged as a candidate for therapeutic intervention in various disease conditions. However, further basic and clinical studies are warranted to confirm the roles played by HMGB1 in clinical medicine.

NLRs at the intersection of cell death and immunity

Inflammation is a crucial element of the host response to cellular insult. Pathogen-induced inflammation includes a molecular pathway which proceeds through activation of the protease caspase-1 to the release of the inflammatory cytokines interleukin-1 (IL-1) and IL-18. Importantly, pathogens may also induce forms of cell death that have inherently pro-inflammatory features. Here, we review recent evidence demonstrating that NLR (nucleotide-binding domain, leucine-rich repeat containing) family proteins serve as a common component of both caspase-1-activated apoptotic pathways and caspase-independent necrotic pathways. Parallels are drawn between NLR protein function and the activity of structurally similar proteins involved in cell death: the apoptotic mediator APAF1 (apoptotic-protease-activating factor 1) and the plant disease resistance NBS-LRR (nucleotide-binding site leucine-rich repeats) proteins.

High-dose intravenous immunoglobulin G improves systemic inflammation in a rat model of CLP-induced sepsis

OBJECTIVE

Intravenous immunoglobulin therapy has been proposed as an advanced treatment for sepsis. Yet, its benefit remains unclear and the mechanism of action is poorly understood. One key mediator in the development of sepsis is high mobility group box 1 (HMGB1). Therefore, we examined the serum and lung tissue levels of HMGB1 in a rat model of sepsis.

DESIGN AND SETTING

Prospective controlled animal study in a university laboratory.

MATERIALS

Rats received either cecal ligation and puncture-induced sepsis or had additional intravenous immunoglobulin treatment in boluses of 100, 300, or 1,000 mg/kg.

MEASUREMENTS AND RESULTS

After induction of sepsis and respective treatment conditions, histopathology, wet/dry weight ratios, and signaling molecules were examined in pulmonary tissue. Serum and pulmonary levels of cytokine and HMGB1 were measured. High dose intravenous immunoglobulin (1,000 mg/kg)-treated animals demonstrated significantly improved survival and pulmonary histopathology compared to the control rats. Serum and pulmonary HMGB1 levels were lower over time among intravenous immunoglobulin-treated animals. Furthermore, administration of intravenous immunoglobulin resulted in inhibition of NF-kappaB activity.

CONCLUSIONS

High-dose intravenous immunoglobulin decreased the mortality and pulmonary pathology in a rat model of sepsis. A significant reduction in HMGB1 levels was also observed, which may be mediated by inhibition of inflammation and NF-kappaB.

DESCRIPTOR

23. Acute respiratory distress syndrome (ARDS) and acute lung injury (ALI): experimental models.

High mobility group box 1 protein induction by Mycobacterium bovis BCG

High mobility group box 1 protein (HMGB1), a nuclear protein, is a critical cytokine that mediates the response to infection, injury, and inflammation. The aim of our study was to elaborate a reliable in vitro model to investigate whether Mycobacterium bovis BCG is able to induce HMGB1 secretion from the monocytic U-937 cells. Western blot technique was applied for the detection of HMGB1 from supernatants of cells, following induction with Mycobacterium bovis BCG. Densitometric analysis revealed higher concentrations of HMGB1 in cell supernatants stimulated with BCG than in the supernatants of the control, nonstimulated cells. Further quantitation of the secreted HMGB1 was performed by ELISA. The BCG strain resulted in a higher amount of secreted HMGB1 (450 ± 44 ng/mL) than that of LPS (84 ± 12 ng/mL) or Staphylococcus aureus (150 ± 14 ng/mL). BCG and Phorbol −12-myristate −13 acetate (PMA), added together, resulted in the highest HMGB1 secretion (645 ± 125 ng/mL). The translocation of the HMGB1 towards the cytoplasm following infection of cells with BCG was demonstrated by immunofluorescence examinations. Conclusion: Our pilot experiments draw attention to the HMGB1 inducing ability of Mycobacterium bovis. Assesment of the pathophysiological role of this late cytokine in mycobacterial infections demands further in vitro and in vivo examinations.

RECOMBINANT BACTERICIDAL/PERMEABILITY-INCREASING PROTEIN INHIBITS ENDOTOXIN-INDUCED HIGH-MOBILITY GROUP BOX 1 PROTEIN GENE EXPRESSION IN SEPSIS

We investigated in vivo the effect of recombinant bactericidal/permeability-increasing protein (rBPI21) on high-mobility group box 1 protein (HMGB1) expression in sepsis and its potential mechanism. Using a sepsis model induced by cecal ligation and puncture (CLP), rats were randomly divided into four groups as follows: normal control group, sham-operated group, CLP group, and BPI treatment group. Animals were killed at designated time points, and blood and tissue samples from liver, lungs, kidneys, and small intestine were harvested to determine related variables. In addition, we observed the effect of treatment with rBPI21 on survival rate in septic rats. The results showed that endotoxin content and expression levels of HMGB1 and LPS binding protein/CD14 mRNA in various organs were significantly increased at 12 and 24 h after CLP, which can be attenuated by treatment with rBPI21 (P<0.05-0.01). Meanwhile, treatment with rBPI21 in septic rats can markedly reduce serum alanine aminotransferase, creatinine levels, and pulmonary myeloperoxidase activity at 12 and 24 h after CLP, increase diamine oxidase activity at both time points (P<0.05-0.01), and improve the 1- to 10-day survival rates in animals subjected to CLP (P=0.012). These findings suggest that treatment with rBPI21 can significantly reduce endotoxin contents and expression levels of HMGB1 and LPS binding protein/CD14 mRNA in various organs in sepsis induced by CLP, and can protect against multiple organ damage resulting from sepsis. The effect of rBPI21 inhibiting HMGB1 gene expression in sepsis might be associated with endotoxin-dependent mechanisms.

Mycobacterium bovis BCG induces high mobility group box 1 protein release from monocytic cells

High mobility group box 1 protein (HMGB-1), a nuclear protein is a critical cytokine that mediates the response to infection, injury and inflammation. The aim of our study was to elaborate a reliable in vitro model to investigate whether Mycobacterium bovis BCG is able to induce HMGB-1 secretion from the monocytic U-937 cells. Western blot technique was applied for the detection of HMGB-1 from supernatants of cells, following induction with LPS, Staphylococcus aureus, and Mycobacterium bovis BCG. HMGB-1 was subjected to MALDI-TOF mass and PSD analysis. Quantitation of the secreted HMGB-1 was performed by ELISA. The BCG strain induced higher amounts of secreted HMGB-1 than LPS or Staphylococcus aureus. The translocation of the HMGB-1 to the cytoplasm following infection of cells with BCG was demonstrated by immunofluorescence examinations.

CONCLUSION

Our pilot experiments draw attention the to HMGB-1-inducing ability of Mycobacterium bovis. Assessment of the pathophysiological role of this late cytokine in mycobacterial infections demands further in vitro and in vivo examinations.

The induction of HMGB1 release from RAW 264.7 cells by transfected DNA

High mobility group protein 1 (HMGB1) is a non-histone nuclear protein that can activate innate immunity when in an extracellular location. As shown in in vitro studies, while polyinosinic-polycytidylic acid [poly (I:C)] and LPS, TLR3 and TLR4 ligands, respectively, can induce HMGB1 release from macrophages, CpG DNA, a TLR 9 ligand, does not. Since DNA displays distinct immunostimulatory activity when transfected into cells, we investigated whether transfected DNA can induce HMGB1 release from macrophages. In these experiments, using RAW 264.7 cells as model, we show that DNA, either natural DNA or synthetic oligonucleotides, can induce HMGB1 release when used to stimulate cells with the transfection reagent Lipofectamine 2000; release occurred irrespective of the intrinsic activity of the DNA. The induction of HMGB1 release by transfected DNA was dependent on IFN-beta as shown by the inhibitory effects of an antibody. In addition, JNK activation mediated HMGB1 release induced by a transfected phosphorothioate oligonucleotide but not by transfected natural DNA. Together, these findings indicate that transfected DNA can stimulate macrophages to release HMGB1 under conditions in which free DNA is inactive and suggest a role of DNA in inducing inflammation when bound to molecules that influence its entry into cells.

High dose antithrombin III inhibits HMGB1 and improves endotoxin-induced acute lung injury in rats

OBJECTIVE

High mobility group box 1 (HMGB1) is an important factor in the development of sepsis. Previous work suggests that antithrombin III (ATIII) inhibits inflammation, but the mechanism of action is still poorly understood.

DESIGN AND SETTING

Prospective controlled animal study in a university laboratory.

MATERIALS

Rats were randomly divided into a lipopolysaccharide (LPS)-induced sepsis control group and an ATIII-treated experimental group. Animals in the experimental group received a bolus of 250 units/kg of ATIII injected into the tail vein.

MEASUREMENTS AND RESULTS

Animals receiving high-dose ATIII (250 units/kg) had significantly improved lung histopathology and survival compared to the control rats. We measured serum and lung levels of various cytokines and HMGB1 at regular intervals from 0 to 12 h after the induction of sepsis and demonstrated lower HMGB1 levels over time in ATIII-treated animals. In an in vitro experiment, we stimulated the mouse macrophage cell line RAW 264.7 with LPS in the presence or absence of ATIII. Subsequent measurement of HMGB1 concentrations in the supernatant and cell signaling molecules in cell lysates revealed an ATIII dose-dependent decrease in HMGB1 release. Furthermore, inhibition of IkB and p42 phosphorylation was observed with the administration of ATIII, suggestive of downstream signaling pathways.

CONCLUSIONS

High-dose ATIII decreases lung pathology and reduces mortality in a rat sepsis model. This finding may be mediated by the inhibition of HMGB1.

Ethyl pyruvate improves survival and ameliorates distant organ injury in rats with severe acute pancreatitis

OBJECTIVE

To evaluate the effect of ethyl pyruvate (EP) in improving the survival and ameliorating distant organ damage and to investigate the role of high-mobility group box (HMGB) 1 in rats with established severe acute pancreatitis (SAP).

METHODS

Severe acute pancreatitis was induced by retrograde infusion of sodium taurodeoxycholate (5%, 1 mL/kg) into the biliopancreatic ducts in male Wistar rats. The rats were infused intravenously with EP of 40 mg/kg, 4 mg/kg, and 0.4 mg/kg initiating 12 hours, and EP of 40 mg/kg was administered beginning 2 hours before surgery (-2 hours) and 12, 24, and 36 hours after induction of SAP; then, the mortality was recorded. Serum tumor necrosis factor alpha, interleukin (IL) 6, and IL-1beta were measured using enzyme-linked immunosorbent assay. High-mobility group box 1 levels were measured using Western immunoblotting analysis.

RESULTS

Serum HMGB1 levels were increased dramatically after 12 hours, remained at high levels for 72 hours, and were significantly higher in rats with SAP than in those with mild and moderate pancreatitis (P < 0.01). Treatment with EP (40 mg/kg) conferred protection from lethality of SAP (EP survival [63%] vs vehicle survival [6.3%]; P < 0.001). No survival advantage occurred when treatment was initiated 36 hours after surgery, but administration beginning 2 hours before operation (-2 hours) and 12 and 24 hours after induction of SAP significantly increased survival. Ethyl pyruvate treatment significantly decreased serum HMGB1, tumor necrosis factor alpha, IL-1beta, and IL-6 levels and ameliorated extrapancreatic organ dysfunction in rats with SAP.

CONCLUSIONS

Ethyl pyruvate improves survival and ameliorates distant organ injury of SAP. These beneficial effects of EP are because of the modulation of HMGB1 and other inflammatory cytokine responses.

The anti-inflammatory effects of heat shock protein 72 involve inhibition of high-mobility-group box 1 release and proinflammatory function in macrophages

High-mobility-group box 1 (HMGB1), a nuclear protein, has recently been identified as an important mediator of local and systemic inflammatory diseases when released into the extracellular milieu. Anti-inflammatory regulation by the stress response is an effective autoprotective mechanism when the host encounters harmful stimuli, but the mechanism of action remains incompletely delineated. In this study, we demonstrate that increases in levels of a major stress-inducible protein, heat shock protein 72 (Hsp72) by gene transfection attenuated LPS- or TNF-alpha-induced HMGB1 cytoplasmic translocation and release. The mechanisms involved inhibition of the chromosome region maintenance 1 (CRM1)-dependent nuclear export pathway. Overexpression of Hsp72 inhibited CRM1 translocation and interaction between HMGB1 and CRM1 in macrophages post-LPS and TNF-alpha treatment. In addition, overexpression of Hsp72 strongly inhibited HMGB1-induced cytokine (TNF-alpha, IL-1beta) expression and release, which correlated closely with: 1) inhibition of the MAP kinases (p38, JNK, and ERK); and 2) inhibition of the NF-kappaB pathway. Taken together, these experiments suggest that the anti-inflammatory activity of Hsp72 is achieved by interfering with both the release and proinflammatory function of HMGB1. Our experimental data provide important insights into the anti-inflammatory mechanisms of heat shock protein protection.

Inhibition of tumor angiogenesis by HMGB1 A box peptide

High mobility group box 1 protein (HMGB1) is a highly conserved, ubiquitous non-histone nuclear protein, which participates in maintaining nucleosome structure, regulation of gene transcription, and modulating the activity of steroid hormone receptors. Substantial evidence demonstrated that HMGB1 could be secreted into the extracellular milieu, acts as a proinflammatory cytokine and mediates the downstream inflammatory responses in endotoxemia, arthritis and sepsis. Recently, several reports suggested that HMGB1 plays a key role in tumor angiogenesis through multiple mechanisms, including up-regulation of proangiogenic factors, promoting endothelial progenitor cells homing to ischemic tumor tissues and induction of endothelial cell migration and sprouting. And blockade of HMGB1 binding to the receptor for advanced glycation end products (RAGE) with anti-HMGB1 antibody, soluble RAGE or anti-RAGE neutralizing antibody has been proved to inhibit angiogenesis efficiently. Since HMGB1 A box peptide could antagonize the HMGB1 whole length protein by competitively binding to RAGE and has been considered as a HMGB1 specific antagonist, we postulate that the HMGB1 A box peptide could function as an anti-angiogenic agent to inhibit tumor angiogenesis. In our opinion, if the hypothesis proved to be practical, HMGB1 A box peptide could be widely used in clinical settings to treat malignant tumors.

Protective effects of ethyl pyruvate against acute lung injury induced by acute necrotizing pancreatitis in rats

AIM: To investigate the effects of ethyl pyruvate (EP) on the levels of tumor necrosis factor-α (TNF-α), interleukin-1b (IL-1β) in serum and mRNA expression of high mobility group box 1 (HMGB1) in lung tissues, and explore the mechanisms of ethyl pyruvate in protecting the lungs against acute injury induced by acute necrotizing pancreatitis (ANP).

METHODS: ANP model was induced by retrograde injection of 50 g/L sodium taurocholate into pancreatic duct. Animals were divided randomly into 3 groups: control group, ANP group, and EP treatment group. EP solution was administered intravenously every 6 hours (40 mg/kg once). The serum levels of TNF-α and IL-1β were measured by enzyme-linked immunosorbent assay (ELISA). The mRNA expression of HMGB1 in lung tissues was detected by reverse transcription-polymerase chain reaction (RT-PCR). The partial pressure of blood oxygen (PaO₂) was measured, and histological examination of the lungs was also performed.

RESULTS: The serum levels of TNF-α and IL-6 were rapidly increased after ANP model was induced, and reached peak at the 6^th hour, but they were decreased at the 12^th hour. In comparison with those in ANP group, the serum levels of TNF-α and IL-1β were markedly lowered in EP group 6 and 12 hours after ANP model was induced (TNF-α: 131.6 ± 29.6 ng/L vs 196.3 ± 16.3 ng/L, 65.0 ± 16.6 ng/L vs 90.2 ± 20.1 ng/L, P < 0.05; IL-1β: 194.9 ± 26.8 ng/L vs 223.0 ± 34.8 ng/L, 105.2 ± 24.0 ng/L vs 130.4 ± 23.0 ng/L, P < 0.05). The mRNA expression of HMGB1 in lung tissues was increased significantly at the 12th hour and maintained to the 24^th hour after ANP model was induced, whereas in EP group, HMGB1 mRNA expression was significantly lower than that in ANP group at each time point (0.68 ± 0.11 vs 0.88 ± 0.11, 0.81 ± 0.11 vs 1.04 ± 0.10, 1.08 ± 0.08 vs 1.33 ± 0.15, all P < 0.05). The injury of lung tissues in EP group was milder than that in ANP group, and the value of PaO₂ was also obviously higher in EP group than that in ANP group (P < 0.05).

CONCLUSION: EP can inhibit the release of TNF-α and IL-1β, down-regulate HMGB1 mRNA expression in lung tissues of ANP rats, and protect lungs from acute injury induced by ANP.