Anti-high-mobility group box chromosomal protein 1 antibodies improve survival of rats with sepsis

HMGB1 release by inflammasomes

High-mobility group box 1 (HMGB1) was originally identified as a highly conserved nuclear DNA-binding protein that participates in DNA replication, repair and transcriptional regulation of gene expression. Although the nuclear role of HMGB1 is not quite understood, recent studies characterized the emerging role of extracellular HMGB1 as a prototypical danger signal that regulates inflammatory and repair responses. Under conditions of infection, injury and sterile inflammation, HMGB1 can be passively released from damaged cells or actively secreted from activated immune cells. Inflammasomes, large caspase-1-activating protein complexes, were recently shown to play a critical role in mediating the extracellular release of HMGB1 from activated and infected immune cells.

HMGB1 contributes to kidney ischemia reperfusion injury

High-mobility group box 1 (HMGB1), a nuclear factor released extracellularly as an inflammatory cytokine, is an endogenous ligand for Toll-like receptor 4 (TLR4). TLR4 activation mediates kidney ischemia-reperfusion injury (IRI), but whether HMGB1 contributes to IRI is unknown. Here, treating wild-type mice with neutralizing anti-HMGB1 antibody protected them against kidney IRI, evidenced by lower serum creatinine and less tubular damage than untreated mice. Mice treated with anti-HMGB1 had significantly less tubulointerstitial infiltration by neutrophils (day 1) and macrophages (day 5) and markedly reduced apoptosis of tubular epithelial cells. Furthermore, anti-HMGB1 antibody-treated IRI kidneys had significantly lower levels of IL-6, TNFα, and monocyte chemoattractant protein 1 (MCP1). mRNA, which are downstream of HMGB1. Conversely, administration of rHMGB1 after reperfusion exacerbated kidney IRI in wild-type mice. TLR4 deficient (TLR4(-/-)) mice were protected against kidney IRI; administration of neither anti-HMGB1 antibody nor rHMGB1 affected this renoprotection. In conclusion, endogenous HMGB1 promotes kidney damage after IRI, possibly through the TLR4 pathway. Administration of a neutralizing antibody to HMGB1 either before or soon after ischemia-reperfusion affords significant protection, suggesting therapeutic potential for acute kidney injury.

The C-terminal acidic tail is responsible for the inhibitory effects of HMGB1 on efferocytosis

HMGB1 was described originally as a nuclear protein involved in DNA binding and transcriptional regulation. However, HMGB1 also has an extracellular role as a potent mediator of inflammation and can diminish the uptake of apoptotic cells by phagocytes, a process called efferocytosis. To explore the mechanism responsible for the ability of HMGB1 to inhibit efferocytosis, we examined the role of the C-terminal acidic tail, a region of HMGB1 that has been shown to participate in specific intramolecular interactions. Deletion of the C-terminal tail abrogated the ability of HMGB1 to decrease murine macrophage ingestion of apoptotic neutrophils and to diminish phagocytosis-induced activation of Erk and Rac-1 in macrophages. We found that RAGE plays a major role in efferocytosis, and deletion of the C-terminal tail of HMGB1 prevented binding of HMGB1 to RAGE but not to other macrophage receptors involved in efferocytosis, such as the α(V)β(3) integrin. Whereas HMGB1 decreased ingestion of apoptotic neutrophils significantly by alveolar macrophages under in vivo conditions in the lungs of mice, this effect was lost when the C-terminal acidic tail was absent from HMGB1. These results demonstrate that the HMGB1 C-terminal tail is responsible for the inhibitory effects of HMGB1 on phagocytosis of apoptotic neutrophils under in vitro and in vivo conditions.

Role of Apoptosis in Amplifying Inflammatory Responses in Lung Diseases

Apoptosis is an important contributor to the pathophysiology of lung diseases such as acute lung injury (ALI) and chronic obstructive pulmonary disease (COPD). Furthermore, the cellular environment of these acute and chronic lung diseases favors the delayed clearance of apoptotic cells. This dysfunctional efferocytosis predisposes to the release of endogenous ligands from dying cells. These so-called damage-associated molecular patterns (DAMPs) play an important role in the stimulation of innate immunity as well as in the induction of adaptive immunity, potentially against autoantigens. In this review, we explore the role of apoptosis in ALI and COPD, with particular attention to the contribution of DAMP release in augmenting the inflammatory response in these disease states.

DAMPening inflammation by modulating TLR signalling

Damage-associated molecular patterns (DAMPs) include endogenous intracellular molecules released by activated or necrotic cells and extracellular matrix (ECM) molecules that are upregulated upon injury or degraded following tissue damage. DAMPs are vital danger signals that alert our immune system to tissue damage upon both infectious and sterile insult. DAMP activation of Toll-like receptors (TLRs) induces inflammatory gene expression to mediate tissue repair. However, DAMPs have also been implicated in diseases where excessive inflammation plays a key role in pathogenesis, including rheumatoid arthritis (RA), cancer, and atherosclerosis. TLR activation by DAMPs may initiate positive feedback loops where increasing tissue damage perpetuates pro-inflammatory responses leading to chronic inflammation. Here we explore the current knowledge about distinct signalling cascades resulting from self TLR activation. We also discuss the involvement of endogenous TLR activators in disease and highlight how specifically targeting DAMPs may yield therapies that do not globally suppress the immune system.

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.

Targeting HMGB1 in inflammation

High mobility group box 1 (HMGB1), a highly conserved, ubiquitous protein present in the nuclei and cytoplasm of nearly all cell types, is a necessary and sufficient mediator of inflammation during sterile and infection-associated responses. Elevated levels of HMGB1 in serum and tissues occur during sterile tissue injury and during infection, and targeting HMGB1 with antibodies or specific antagonists is protective in established preclinical inflammatory disease models including lethal endotoxemia or sepsis, collagen-induced arthritis, and ischemia-reperfusion induced tissue injury. Future advances in this field will stem from understanding the biological basis for the success of targeting HMGB1 to therapeutic improvement in the treatment of inflammation, infection and ischemia-reperfusion induced injury.

Role of macrophage colony-stimulating factor in polymicrobial sepsis according to studies using osteopetrotic (op/op) mice

BACKGROUND

The specific purpose of this study was to investigate the role of macrophage colony-stimulating factor (M-CSF)-induced macrophages in mouse polymicrobial sepsis model.

MATERIALS AND METHODS

M-CSF deficient (op/op) mice and their littermate mice w ere subjected the cecal ligation and puncture (CLP). Survival was assessed for the following 7 d after the CLP operation, and histopathologic findings were evaluated 12h after CLP. After CLP, expression of inflammatory mediators in serum was assessed by enzyme immunosorbent assay (ELISA). Furthermore, isolated peritoneal macrophages were stimulated with lipopolysaccharide (LPS) (10μg/mL) for 4h, and cytokine concentration in the supernatant was then measured by ELISA. Moreover, phagocytosis of isolated macrophages was assessed using fluorescent rates beads. In another set of experiments, effects of neutralization antibodies against high mobility group box 1 (HMGB1) were investigated in CLP model.

RESULTS

Mortality was increased in op/op mice compared with op/? mice after CLP. Furthermore, serum HMGB1 levels were also significantly greater in op/op mice than op/? mice. Production of HMGB1 by isolated peritoneal macrophages was significantly greater in op/op mice than op/? mice. Furthermore, the phagocytosis index was significantly blunted in op/op mice compared with op/? mice. Importantly, treatment with neutralization antibodies against HMGB1 markedly prevented acute lung injury and mortality in op/op mice.

CONCLUSION

Matured macrophages by M-CSF play pivotal role by scavenging endotoxin in inflammation. Furthermore, HMGB1 is involved in pathophysiology in polymicrobial sepsis, consistent with previous reports.

High mobility group box 1 as a mediator of endotoxin administration after hemorrhagic shock-primed lung injury

High mobility group box 1 (HMGB1) was discovered as a novel late-acting cytokine that contributes to acute lung injury (ALI). However, the contribution of HMGB1 to two-hit-induced ALI has not been investigated. To examine the participation of HMGB1 in the pathogenesis of ALI caused by the two-hit hypothesis, endotoxin was injected intratracheally in a hemorrhagic shock-primed ALI mouse model. Concentrations of HMGB1 in the lung of the shock group were markedly increased at 16 h (1.63 +/- 0.05, compared to the control group: 1.02 +/- 0.03; P < 0.05), with the highest concentration being observed at 24 h. In the sham/lipopolysaccharide group, lung HMGB1 concentrations were found to be markedly increased at 24 h (1.98 +/- 0.08, compared to the control group: 1.07 +/- 0.03; P < 0.05). Administration of lipopolysaccharide to the hemorrhagic shock group resulted in a notable HMGB1 increase by 4 h, with a further increase by 16 h. Intratracheal lipopolysaccharide injection after hemorrhagic shock resulted in the highest lung leak at 16 h (2.68 +/- 0.08, compared to the control group: 1.05 +/- 0.04; P < 0.05). Compared to the hemorrhagic shock/lipopolysaccharide mice, blockade of HMGB1 at the same time as lipopolysaccharide injection prevented significantly pulmonary tumor necrosis factor-alpha, interleukin-1beta and myeloperoxidase. Lung leak was also markedly reduced at 16 h; blockade of HMGB1 24 h after lipopolysaccharide injection failed to alter lung leak or myeloperoxidase at 48 h. Our observations suggest that HMGB1 plays a key role as a late mediator when lipopolysaccharide is injected after hemorrhagic shock-primed ALI and the kinetics of its release differs from that of one-hit ALI. The therapeutic window to suppress HMGB1 activity should not be delayed to 24 h after the disease onset.

High-mobility group box 1 contributes to lethality of endotoxemia in heme oxygenase-1-deficient mice

High-mobility group box 1 (HMGB1) is a nuclear protein that has been found to be a critical mediator of lethality in endotoxemia and sepsis. During the systemic inflammatory response, circulating levels of HMGB1 are increased, but in a delayed fashion compared with early inflammatory mediators. To counteract the inflammatory response of endotoxemia, a secondary anti-inflammatory response ensues in an attempt to prevent inflammation-induced tissue injury. One such cytoprotective gene that is induced during endotoxemia is heme oxygenase (HO)-1. HO-1, and its products of heme metabolism, possess anti-inflammatory and antioxidant properties to counter the damaging effects of endotoxemia. In the present study, we wanted to determine whether tissue and circulating levels of HMGB1 are increased further in the absence of HO-1 during endotoxemia, and whether this increase may contribute to the pathobiology of endotoxemia. Lung inflammation, HMGB1 protein levels, and expression of HMGB1 in inflammatory cells were increased in HO-1(-/-) mice compared with HO-1+/+ mice. After the administration of LPS, tissue levels of HMGB1 were not increased further in HO-1(-/-) mice; however, circulating levels of HMGB1 were higher when compared with HO-1+/+ mice. HO-1(-/-) mice treated with a carbon monoxide-releasing molecule or biliverdin showed a reduction in plasma HMGB1, which was associated with a marked improvement in survival. HO-1(-/-) mice given HMGB1-neutralizing antibody showed improvement in survival compared with control antibody. These data suggest that exaggerated circulating levels of HMGB1 contribute to endotoxin-induced mortality in the absence of HO-1.

Therapeutic potential of HMGB1-targeting agents in sepsis

Sepsis refers to a systemic inflammatory response syndrome resulting from a microbial infection. The inflammatory response is partly mediated by innate immune cells (such as macrophages, monocytes and neutrophils), which not only ingest and eliminate invading pathogens but also initiate an inflammatory response upon recognition of pathogen-associated molecular patterns (PAMPs). The prevailing theories of sepsis as a dysregulated inflammatory response, as manifested by excessive release of inflammatory mediators such as tumour necrosis factor and high-mobility group box 1 protein (HMGB1), are supported by extensive studies employing animal models of sepsis. Here we review emerging evidence that support extracellular HMGB1 as a late mediator of experimental sepsis, and discuss the therapeutic potential of several HMGB1-targeting agents (including neutralising antibodies and steroid-like tanshinones) in experimental sepsis.

Role of high-mobility group box 1 protein in post-infarction healing process and left ventricular remodelling

AIMS

High-mobility group box 1 protein (HMGB1) is one of the recently defined damage-associated molecular pattern molecules derived from necrotic cells and activated macrophages. We investigated clinical implications of serum HMGB1 elevation in patients with acute myocardial infarction (MI). Then, we evaluated the effect of HMGB1 blockade on post-MI left ventricular (LV) remodelling in a rat MI model.

METHODS AND RESULTS

Serum HMGB1 levels were examined in patients with ST-elevation MI (n = 35). A higher peak serum HMGB1 level was associated with pump failure, cardiac rupture, and in-hospital cardiac death. Then, an experimental MI model was induced in male Wistar rats. The mRNA and protein expression of HMGB1 were increased in the infarcted area compared with those values observed in sham-operated rats. We administered neutralizing anti-HMGB1 antibody (MI/anti-H) or control antibody (MI/C) to MI rats subcutaneously for 7 days. The mRNA levels of tumour necrosis factor-alpha and interleukin-1beta and the number of macrophages in the infarcted area were reduced on day 3 in MI/anti-H rats compared with MI/C rats. Interestingly, HMGB1 blockade resulted in thinning and expansion of the infarct scar and marked hypertrophy of the non-infarcted area on day 14.

CONCLUSION

Elevated serum HMGB1 levels were associated with adverse clinical outcomes in patients with MI. However, HMGB1 blockade in a rat MI model aggravated LV remodelling, possibly through impairment of the infarct-healing process. HMGB1, a novel predictor of adverse clinical outcomes after MI, may have an essential role in the appropriate healing process after MI.

Potential role of high-mobility group box 1 in cystic fibrosis airway disease

RATIONALE

High-mobility group box 1 (HMGB1) is a potent inflammatory mediator elevated in sepsis and rheumatoid arthritis, although its role in cystic fibrosis (CF) lung disease is unknown.

OBJECTIVES

To determine whether HMGB1 contributes to CF lung inflammation, including neutrophil chemotaxis and lung matrix degradation.

METHODS

We used sputum and serum from subjects with CF and a Scnn1b-transgenic (Scnn1b-Tg) mouse model that overexpresses beta-epithelial Na(+) channel in airways and mimics the CF phenotype, including lung inflammation. Human secretions and murine bronchoalveolar lavage fluid (BALF) was assayed for HMGB1 by Western blot and ELISA. Neutrophil chemotaxis was measured in vitro after incubation with human neutrophils. The collagen fragment proline-glycine-proline (PGP) was measured by tandem mass spectroscopy.

MEASUREMENTS AND MAIN RESULTS

HMGB1 was detected in CF sputum at higher levels than secretions from normal individuals. Scnn1b-Tg mice had elevated levels of HMGB1 by Western blot and ELISA. We demonstrated that dose-dependent chemotaxis of human neutrophils stimulated by purified HMGB1 was partially dependent on CXC chemokine receptors and that this could be duplicated in CF sputum and BALF from Scnn1b-Tg mice. Neutralization by anti-HMGB1 antibody, in both the sputum and BALF-reduced chemotaxis, which suggested that HMGB1 contributed to the chemotactic properties of these samples. Intratracheal administration of purified HMGB1 induced neutrophil influx into the airways of mice and promoted the release of PGP. PGP was also elevated in Scnn1b-Tg mice and CF serum.

CONCLUSIONS

HMGB1 expression contributes to pulmonary inflammation and lung matrix degradation in CF airway disease and deserves further investigation as a biomarker and potential therapeutic target.

Bench-to-bedside review: High-mobility group box 1 and critical illness

High-mobility group box 1 (HMGB1) is a DNA-binding protein that also exhibits proinflammatory cytokine-like activity. HMGB1 is passively released by necrotic cells and also is actively secreted by immunostimulated macrophages, dendritic cells, and enterocytes. Although circulating HMGB1 levels are increased relative to healthy controls in patients with infections and severe sepsis, plasma or serum HMGB1 concentrations do not discriminate reliably between infected and uninfected critically ill patients. Nevertheless, administration of drugs that block HMGB1 secretion or of anti-HMGB1 neutralizing antibodies has been shown to ameliorate organ dysfunction and/or improve survival in numerous animal models of critical illness. Because HMGB1 tends to be released relatively late in the inflammatory response (at least in animal models of endotoxemia or sepsis), this protein is an attractive target for the development of new therapeutic agents for the treatment of patients with various forms of critical illness.

Functional roles for C5a receptors in sepsis

The function of the C5a receptors, C5ar (encoded by C5ar) and C5l2 (encoded by Gpr77), especially of C5l2, which was originally termed a 'default receptor', remains a controversial topic. Here we investigated the role of each receptor in the setting of cecal ligation and puncture-induced sepsis by using antibody-induced blockade of C5a receptors and knockout mice. In 'mid-grade' sepsis (30-40% survival), blockade or absence of either C5ar or C5l2 greatly improved survival and attenuated the buildup of proinflammatory mediators in plasma. In vivo appearance or in vitro release of high mobility group box 1 protein (HMGB1) required C5l2 but not C5ar. In 'high-grade' sepsis (100% lethality), the only protective condition was the combined blockade of C5l2 and C5ar. These data suggest that C5ar and C5l2 contribute synergistically to the harmful consequences in sepsis and that C5l2 is required for the release of HMGB1. Thus, contrary to earlier speculation, C5l2 is a functional receptor rather than merely a default receptor.

Systemic and local high mobility group box 1 concentrations during severe infection

OBJECTIVE

High mobility group box 1 (HMGB1) has been implicated as a late mediator in sepsis. We here sought to determine the extent of HMGB1 release in patients with sepsis stratified to the three most common infectious sources and to determine HMGB1 concentrations at the site of infection during peritonitis or pneumonia.

DESIGN

Observational studies in patients and healthy humans challenged with lipopolysaccharide.

SETTING

Three intensive care units and one clinical research unit.

PATIENTS AND SUBJECTS

Three patient populations were studied: 1) 51 patients with sepsis due to pneumonia (n = 29), peritonitis (n = 12), or urinary tract infection (n = 10); 2) 17 patients with peritonitis; and 3) four patients with community-acquired pneumonia. In addition, eight healthy subjects were studied after intravenous injection of lipopolysaccharide (4 ng/kg).

INTERVENTIONS

One population of healthy volunteers received lipopolysaccharide intravenously.

MEASUREMENTS AND MAIN RESULTS

Patients with severe sepsis due to pneumonia displayed elevated circulating HMGB1 concentrations at both days 0 and 3 after inclusion. Patients with sepsis due to peritonitis had elevated HMGB1 levels at day 0 but not at day 3, whereas urinary tract infection was associated with a delayed HMGB1 response, with elevated levels only at day 3. HMGB1 concentrations did not differ between survivors and nonsurvivors and were not correlated to either disease severity or concurrently measured cytokine levels. In line with these observations, although intravenous lipopolysaccharide injection clearly elevated plasma cytokine levels, HMGB1 remained undetectable. In patients with peritonitis, HMGB1 concentrations in abdominal fluid were more than ten-fold higher than in concurrently obtained plasma. In pneumonia patients, HMGB1 levels were higher in bronchoalveolar lavage fluid obtained from the site of infection than in lavage fluid from healthy controls.

CONCLUSIONS

In severe sepsis, the kinetics of HMGB1 release may differ depending on the primary source of infection. In patients with severe infection, HMGB1 release may predominantly occur at the site of infection.

Blockade of high mobility group box-1 protein attenuates experimental severe acute pancreatitis

AIM: To examine the effects of anti-high mobility group box 1 (HMGB1) neutralizing antibody in experimental severe acute pancreatitis (SAP).

METHODS: SAP was induced by creating closed duodenal loop in C3H/HeN mice. SAP was induced immediately after intraperitoneal injection of anti-HMGB1 neutralizing antibody (200 μg). Severity of pancreatitis, organ injury (liver, kidney and lung), and bacterial translocation to pancreas was examined 12 h after induction of SAP.

RESULTS: Anti-HMGB1 neutralizing antibody significantly improved the elevation of the serum amylase level and the histological alterations of pancreas and lung in SAP. Anti-HMGB1 antibody also significantly ameliorated the elevations of serum alanine aminotransferase and creatinine in SAP. However, anti-HMGB1 antibody worsened the bacterial translocation to pancreas.

CONCLUSION: Blockade of HMGB1 attenuated the development of SAP and associated organ dysfunction, suggesting that HMGB1 may act as a key mediator for inflammatory response and organ injury in SAP.