Effect of polymyxin B-immobilized fiber hemoperfusion on serum high mobility group box-1 protein levels and oxidative stress in patients with acute respiratory distress syndrome. ASAIO J. 2009;55:395-399. [PMID: 19506468 DOI: 10.1097/mat.0b013e3181a5290f]

Transcriptomic Mapping of Neurotoxicity Pathways in the Rat Brain in Response to Intraventricular Polymyxin B

Intraventricular or intrathecal administration of polymyxins are increasingly used to treat multidrug-resistant (MDR) Gram-negative bacteria caused infections in the central nervous system (CNS). However, our limited knowledge of the mechanisms underpinning polymyxin-induced neurotoxicity significantly hinders the development of safe and efficacious polymyxin dosing regimens. To this end, we conducted transcriptomic analyses of the rat brain and spinal cord 1 h following intracerebroventricular administration of polymyxin B into rat lateral ventricle at a clinically relevant dose (0.5 mg/kg). Following the treatment, 66 differentially expressed genes (DEGs) were identified in the brain transcriptome while none for the spinal cord (FDR ≤ 0.05, fold-change ≥ 1.5). DEGs were enriched in signaling pathways associated with hormones and neurotransmitters, including dopamine and (nor)epinephrine. Notably, the expression levels of Slc6a3 and Gabra6 were decreased by 20-fold and 4.3-fold, respectively, likely resulting in major perturbations of dopamine and γ-aminobutyric acid signaling in the brain. Mass spectrometry imaging of brain sections revealed a distinct pattern of polymyxin B distribution with the majority accumulating in the injection-side lateral ventricle and subsequently into third and fourth ventricles. Polymyxin B was not detectable in the left lateral ventricle or brain tissue. Electrophysiological measurements on primary cultured rat neurons revealed a large inward current and significant membrane leakage following polymyxin B treatment. Our work demonstrates, for the first time, the key CNS signaling pathways associated with polymyxin neurotoxicity. This mechanistic insight combined with pharmacokinetic/pharmacodynamic dosing strategies will help guide the design of safe and effective intraventricular/intrathecal polymyxin treatment regimens for CNS infections caused by MDR Gram-negative pathogens.

Targeting circulating high mobility group box-1 and histones by extracorporeal blood purification as an immunomodulation strategy against critical illnesses

Both high mobility group box-1 (HMGB1) and histones are major damage-associated molecular patterns (DAPMs) that mediate lethal systemic inflammation, activation of the complement and coagulation system, endothelial injury and multiple organ dysfunction syndrome in critical illnesses. Although accumulating evidence collectively shows that targeting HMGB1 or histones by their specific antibodies or inhibitors could significantly mitigate aberrant immune responses in multiple critically ill animal models, routine clinical use of such agents is still not recommended by any guideline. In contrast, extracorporeal blood purification, which has been widely used to replace dysfunctional organs and remove exogenous or endogenous toxins in intensive care units, may also exert an immunomodulatory effect by eliminating inflammatory mediators such as cytokines, endotoxin, HMGB1 and histones in patients with critical illnesses. In this review, we summarize the multiple immunopathological roles of HMGB1 and histones in mediating inflammation, immune thrombosis and organ dysfunction and discuss the rationale for the removal of these DAMPs using various hemofilters. The latest preclinical and clinical evidence for the use of extracorporeal blood purification to improve the clinical outcome of critically ill patients by targeting circulating HMGB1 and histones is also gathered.

Angiotensin-converting enzyme 2 attenuates inflammatory response and oxidative stress in hyperoxic lung injury by regulating NF-κB and Nrf2 pathways

OBJECTIVE

To investigate the role of angiotensin-converting enzyme 2 (ACE2) in hyperoxic lung injury.

METHODS

Adult mice were exposed to 95% O2 for 72 h to induce hyperoxic lung injury, and simultaneously treated with ACE2 agonist diminazene aceturate (DIZE) or inhibitor MLN-4760. ACE2 expression/activity in lung tissue and angiotensin (Ang)-(1-7)/Ang II in bronchoalveolar lavage fluid (BALF), and the severity of hyperoxic lung injury were evaluated. The levels of inflammatory factors in BALF and lung tissue and the expression levels of phospho-p65, p65 and IkBα were measured. Oxidative parameter and antioxidant enzyme levels in lung tissue were measured to assess oxidative stress. Finally, the expression levels of nuclear factor-erythroid-2-related factor (Nrf2), NAD(P)H quinine oxidoreductase 1 (NQO1) and heme oxygenase-1 (HO-1) were measured using Western blotting.

RESULTS

Hyperoxia treatment significantly decreased lung ACE2 expression/activity and increased the Ang II/Ang-(1-7) ratio, while co-treatment with hyperoxia and DIZE significantly increased lung ACE2 expression/activity and decreased the Ang II/Ang-(1-7) ratio. By contrast, co-treatment with hyperoxia and MLN-4760 significantly decreased lung ACE2 expression/activity and increased the Ang II/Ang-(1-7) ratio. Hyperoxia treatment induced significant lung injury, inflammatory response and oxidative stress, which were attenuated by DIZE but aggravated by MLN-4760. The NF-κB pathways were activated by hyperoxia and MLN-4760 but inhibited by DIZE. The Nrf2 pathway and its downstream proteins NQO1 and HO-1 were activated by DIZE but inhibited by MLN-4760.

CONCLUSION

Activation of ACE2 can reduce the severity of hyperoxic lung injury by inhibiting inflammatory response and oxidative stress. ACE2 can inhibit the NF-κB pathway and activate the Nrf2/HO-1/NQO1 pathway, which may be involved in the underlying mechanism.

Recombinant human soluble thrombomodulin prevents acute lung injury in a rat cardiopulmonary bypass model

BACKGROUND

Cardiopulmonary bypass (CPB) may induce systemic inflammatory responses causing acute lung injury. Recombinant human soluble thrombomodulin (rTM) is reported to attenuate the secretion of inflammatory cytokines and the high-mobility group box 1 (HMGB1) protein, which is critical in controlling systemic inflammation and apoptosis. We investigated the protective effects of rTM on CPB-induced lung injury in a rat model.

METHODS

Eighteen male Sprague-Dawley rats were divided into 3 groups: sham, control (CPB alone), and rTM (CPB + rTM). CPB was conducted in the control group and the rTM group. A bolus of rTM (3 mg/kg) was administered to the rTM group rats before CPB establishment.

RESULTS

The ratio of partial pressure of arterial oxygen to the fraction of inspired oxygen only dropped markedly from before CPB in the control group (P < .001). Serum tumor necrosis factor α, interleukin (IL) 6, and HMGB1 levels were significantly higher in the control group after CPB. Pathologic study revealed significantly more severe congestion, alveolar hemorrhage, neutrophil accumulation, and edema, and the number of lung cells expressing HMGB1 increased in the control group. The mRNA expression levels of tumor necrosis factor α, IL-6, IL-1β, and HMGB1 in the control group were significantly higher than those in other groups. According to Western blot analysis, nuclear factor-κB p65 in lung tissue was significantly downregulated in the rTM group. The number of apoptotic cells and the protein of cleaved Caspase-3 were reduced in the rTM group.

CONCLUSIONS

These results suggest that rTM prevents acute lung injury through attenuating inflammation and apoptosis during and after CPB in a rat model.

High-mobility group box 1 protein and its role in severe acute pancreatitis

The high mobility group box 1 (HMGB1), which belongs to the subfamily of HMG-1/-2, is a highly conserved single peptide chain consisting of 215 amino acid residues with a molecular weight of approximately 24894 Da. HMGB1 is a ubiquitous nuclear protein in mammals and plays a vital role in inflammatory diseases. Acute pancreatitis is one of the most common causes of acute abdominal pain with a poor prognosis. Acute pancreatitis is an acute inflammatory process of the pancreas (duration of less than six months), for which the severe form is called severe acute pancreatitis (SAP). More and more studies have shown that HMGB1 has a bidirectional effect in the pathogenesis of SAP. Extracellular HMGB1 can aggravate the pancreatic inflammatory process, whereas intracellular HMGB1 has a protective effect against pancreatitis. The mechanism of HMGB1 is multiple, mainly through the nuclear factor-κB pathway. Receptors for advanced glycation end-products and toll-like receptors (TLR), especially TLR-2 and TLR-4, are two major types of receptors mediating the inflammatory process triggered by HMGB1 and may be also the main mediators in the pathogenesis of SAP. HMGB1 inhibitors, such as ethyl pyruvate, pyrrolidine dithiocarbamate and Scolopendra subspinipes mutilans, can decrease the level of extracellular HMGB1 and are the promising targets in the treatment of SAP.

HMGB1 in health and disease

Complex genetic and physiological variations as well as environmental factors that drive emergence of chromosomal instability, development of unscheduled cell death, skewed differentiation, and altered metabolism are central to the pathogenesis of human diseases and disorders. Understanding the molecular bases for these processes is important for the development of new diagnostic biomarkers, and for identifying new therapeutic targets. In 1973, a group of non-histone nuclear proteins with high electrophoretic mobility was discovered and termed high-mobility group (HMG) proteins. The HMG proteins include three superfamilies termed HMGB, HMGN, and HMGA. High-mobility group box 1 (HMGB1), the most abundant and well-studied HMG protein, senses and coordinates the cellular stress response and plays a critical role not only inside of the cell as a DNA chaperone, chromosome guardian, autophagy sustainer, and protector from apoptotic cell death, but also outside the cell as the prototypic damage associated molecular pattern molecule (DAMP). This DAMP, in conjunction with other factors, thus has cytokine, chemokine, and growth factor activity, orchestrating the inflammatory and immune response. All of these characteristics make HMGB1 a critical molecular target in multiple human diseases including infectious diseases, ischemia, immune disorders, neurodegenerative diseases, metabolic disorders, and cancer. Indeed, a number of emergent strategies have been used to inhibit HMGB1 expression, release, and activity in vitro and in vivo. These include antibodies, peptide inhibitors, RNAi, anti-coagulants, endogenous hormones, various chemical compounds, HMGB1-receptor and signaling pathway inhibition, artificial DNAs, physical strategies including vagus nerve stimulation and other surgical approaches. Future work further investigating the details of HMGB1 localization, structure, post-translational modification, and identification of additional partners will undoubtedly uncover additional secrets regarding HMGB1's multiple functions.

Effect of hemoperfusion using polymyxin B-immobilized fibers on acute lung injury in a rat sepsis model

Direct hemoperfusion using polymyxin B-immobilized column (PMX-DHP) is recognized as an effective treatment for septic shock. However, whether its efficacy is limited to cardiovascular dysfunction remains unknown. Therefore, we planned to examine the effects of PMX-DHP in an acute lung injury model. [Materials and methods] Rats were assigned to either PMX-DHP group or control group (n= 7 in each). A lung injury was created by the intratracheal instillation of LPS. In PMX-DHP group, an arteriovenous extracorporeal circuit using PMX column was applied for three hours. The same procedure using a dummy column was applied in control group. The lung microcirculation was observed, and adherent leukocytes, RBC velocity, and the arterial PaO2 were calculated. Pathological changes and the wet/dry weight ratio of the lungs were examined. [Results] Adherent leukocytes and platelets to the lung venules were recognized at 3 hours, and their numbers increased over time. Treatment with PMX-DHP significantly suppressed these events and helped maintenance of the blood flow and PaO2 levels. The lung edema and the histologic damages were also suppressed. [Conclusions] PMX-DHP improved the microcirculation by suppressing leukocyte and platelet adhesion. PMX-DHP had beneficial effects in a model for acute lung injury.

[Usefulness of haemoperfusion in the treatment of the severe septic patient: an update]

Haemoperfusion is an extracorporeal technique that removes endotoxin and/or inflammatory mediators by means of an adsorptive mechanism during the passage of the blood through a porous filter. Most of the studies in the literature use polymyxin B as the adsorptive agent. This treatment is based on the assumption that the removal of endotoxin and inflammatory mediators from the circulation attenuates the inflammatory response in sepsis. This review summarizes the theoretical basis, and the experimental and clinical results published to date with the use of haemoperfusion. Although most of the studies show positive results, some doubts have arisen about the suitability of the methods described (small number of cases, low quality of the experimental design, and excessive mortality in the control groups). There are also some inconsistencies regarding the theoretical basis of its use (lack of positive effects after the removal of endotoxin from the circulation using alternative mechanisms, discrepancies regarding the best moment to initiate the therapy, unexplained beneficial effects in the absence of increased endotoxin levels). It is the opinion of the authors that haemoperfusion represents a promising therapy for the treatment of sepsis, but consider that its usefulness requires confirmation in well designed studies before being included in protocols.

Nuclear antigens and auto/alloantibody responses: friend or foe in transplant immunology

In addition to cellular immune responses, humoral immune responses, mediated by natural antibodies, autoantibodies, and alloantibodies, have increasingly been recognized as causes of organ transplant rejection. In our previous studies, we have demonstrated the induction of antinuclear antibodies against histone H1 and high-mobility group box 1 (HMGB1), in both experimental and clinical liver transplant tolerance. The active induction of antinuclear antibodies is usually an undesirable phenomenon, but it is often observed after liver transplantation. However, the release of nuclear antigens and its suppression by neutralizing antibodies are proposed to be important in the initiation and regulation of immune responses. In this review article, we summarize the current understanding of nuclear antigens and corresponding antinuclear regulatory antibodies (Abregs) on infection, injury, inflammation, transplant rejection, and tolerance induction and discuss the significance of nuclear antigens as diagnostic and therapeutic targets.

Reduction in serum high mobility group box-1 level by polymyxin B-immobilized fiber column in patients with idiopathic pulmonary fibrosis with acute exacerbation

BACKGROUND/AIM

Recent reports suggest that polymyxin B (PMX)-immobilized fiber may have beneficial effects in idiopathic pulmonary fibrosis (IPF) with acute exacerbation (AE). High mobility group box-1 (HMGB-1) is an important pro-inflammatory mediator that contributes to acute lung inflammation. This study was aimed to investigate whether PMX treatment affects serum HMGB-1 levels and oxygenation in IPF patients with AE.

MATERIALS AND METHODS

Twenty IPF patients with AE were treated by PMX. PMX treatment was carried out once daily for 2 successive days. Serum HMGB-1 levels were measured before and after PMX treatment. We also monitored arterial oxygen tension (PaO(2))/inspiratory oxygen fraction (FiO(2)) (P/F) ratio. PMX fiber columns were analyzed to examine whether HMGB-1 was absorbed by PMX.

RESULTS

PMX treatment significantly improved both the serum HMGB-1 level and P/F ratio. HMGB-1 was detected in washing medium from the PMX column.

CONCLUSION

PMX treatment may reduce serum HMGB-1 and improve oxygenation in patients with IPF with AE.

HMGB1 is a therapeutic target for sterile inflammation and infection

A key question in immunology concerns how sterile injury activates innate immunity to mediate damaging inflammation in the absence of foreign invaders. The discovery that HMGB1, a ubiquitous nuclear protein, mediates the activation of innate immune responses led directly to the understanding that HMGB1 plays a critical role at the intersection of the host inflammatory response to sterile and infectious threat. HMGB1 is actively released by stimulation of the innate immune system with exogenous pathogen-derived molecules and is passively released by ischemia or cell injury in the absence of invasion. Established molecular mechanisms of HMGB1 binding and signaling through TLR4 reveal signaling pathways that mediate cytokine release and tissue damage. Experimental strategies that selectively target HMGB1 and TLR4 effectively reverse and prevent activation of innate immunity and significantly attenuate damage in diverse models of sterile and infection-induced threat.

Production of recombinant human HMGB1 and anti-HMGB1 rabbit serum

High-mobility group box-1 (HMGB1) plays important roles in inflammation, immune responses, and tumor progression. Since HMGB1 and its components have been shown to be mediators of a number of diseases but several sources of recombinant HMGB1 showed controversial biological activity, it is important to obtain recombinant HMGB1 with properties that resemble the native protein. For this purpose, we cloned genes coding for human HMGB1 and its active components A box and B box by PCR and inserted the cloned genes into pET28a vectors for transformation of Escherichia coli BL21. The E. coli expressed proteins were then purified with a Ni(2+)-NTA column and the endotoxin content was removed. Recombinant human HMGB1 (rhHMGB1) and its B box thus obtained stimulated, but A box inhibited, the production of the chemokine CXCL8/IL-8 by THP-1 monocytic cell line. We also used purified rhHMGB1 to immunize rabbits and generated potent anti-sera, which was capable of neutralizing the activity of rhHMGB1 in vitro and detecting the increased HMGB1 expression in inflammatory tissues in mice and humans. Thus, we have established essential means to produce biologically active rhHMGB1 that will facilitate us to study its role in diseases and to explore its potential as a therapeutic agent.

A case of successful treatment with polymyxin B-immobilized fiber column direct hemoperfusion in acute respiratory distress syndrome after influenza A infection

We report a case of acute respiratory distress syndrome (ARDS) after influenza A infection who was successfully treated with combined treatment including direct hemoperfusion with polymyxin B-immobilized fiber (PMX-DHP) column. A 56-year-old Japanese man was admitted to our hospital in January 2010 because of progressive dyspnea, hypoxemia, fever and bilateral diffuse infiltration on chest radiograph after pandemic influenza A infection. His chest computed tomography showed diffuse and patchy bilateral ground-glass opacities, and we diagnosed ARDS after influenza A infection. The patient was successfully treated with PMX-DHP in addition to the treatment with oseltamivir, corticosteroid, sivelestat and antibiotics with mechanical ventilation, and the patient recovered with only minor pulmonary fibrotic change. Although the efficacy of PMX-DHP treatment in patients with acute lung injury (ALI)/ARDS after influenza virus infection is not well established, this treatment could be a possible therapeutic modality in treating the patients with this disease.

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.

Targeting endotoxin in the treatment of sepsis

The role of endotoxin in the genesis of sepsis has long been recognized and multiple treatments aimed at neutralizing it have been studied. Endotoxin can be bound by antibodies (whose role as a therapeutic agent is unlikely), binding proteins such as BPI or human lactoferrin (effectiveness debated and promising respectively) and phospholipid emulsion (which has not improved outcomes in a recent study). Alternatively, the action of endotoxin could be blocked by lipid A analogs (initial study showed no overall benefit and another large trial is near completion targeting a subpopulation of that study). Finally, endotoxin can be bound by polymyxin B embedded in hemoperfusion cartridges. The later treatment has been used for more than a decade in Japan. Since both pre-clinical rationale and studies support the targeting of endotoxin to ameliorate the pro-inflammatory and pro-coagulation response of severe sepsis, this therapeutic intervention is being pursued.

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.