HMG-1 as a late mediator of endotoxin lethality in mice

The role of HMGB-1 on the development of necrosis during hepatic ischemia and hepatic ischemia/reperfusion injury in mice

BACKGROUND

High-mobility group 1 (HMGB-1) is a late mediator of endotoxin lethality in mice. The release of HMGB-1 is delayed compared to other proinflammatory cytokines that mediate shock and tissue injury. The purpose of this study was to investigate the role of HMGB-1 levels in response to hepatic ischemia, hepatic I/R injury, and the relationship between changes in HMGB-1 and other cytokines.

MATERIALS AND METHODS

Three murine models were employed: our robust model of segmental hepatic warm ischemia (SHWI), a model of partial hepatic ischemia/reperfusion injury (PHIRI), and a model of total hepatic ischemia/reperfusion injury (THIRI). Over a 48-h period following ischemic insult and reperfusion using these models, serum HMGB-1 concentrations, concentrations of HMGB-1 in ischemic and nonischemic lobes, and serum concentrations of TNF-alpha and IL-6 levels were determined in mice. An anti-HMGB-1 antibody treatment was used in SHWI and THIRI to evaluate what aspects of response to ischemia and reperfusion were potentially mediated by HMGB-1.

RESULTS

Hepatic HMGB-1 tissue concentrations exhibited biphasic changes in SHWI mice, which were increased in the ischemic lobes relative to nonischemic lobes at 12 h but decreased relative to nonischemic lobes at 24 h after ischemic insult. These results suggested that HMGB-1 was released into the systemic circulation by necrotic cells over the first 12 h but this process may be complete by 24 h postischemia. By 6 to 12 h after SHWI, serum TNF-alpha began to increase significantly and continued to increase for 18 h, followed by a sudden decline. Similarly, serum IL-6 increased over 1-3 h after SHWI and then decreased over the next 6 h. Treatment with an anti-HMGB-1 antibody significantly prolonged survival time in SHWI and THIRI.

CONCLUSIONS

HMGB-1 plays a significant role in the response to hepatic ischemia and hepatic ischemia/reperfusion injury. The present study demonstrated a time-dependent production of HMGB-1 following hepatic warm ischemia in mice. The inherent HMGB-1 in ischemic areas was exhausted and HMGB-1 may be released by necrotic cells. HMGB-1 activation is involved in immediate proinflammatory stress response to I/R and anti-HMGB-1 antibody treatment remarkably improved survival. We demonstrated that systemic HMGB-1 accumulation was measured at an earlier phase of the hepatic ischemia and ischemia/reperfusion injury model than LPS-induced endotoxemia.

High mobility group box 1 (HMGB1) protein: possible amplification signal in the pathogenesis of falciparum malaria

High mobility group box 1 (HMGB1) protein, a DNA-binding protein that can also act as a pro-inflammatory cytokine if released from cells, is an important amplification signal in various forms of inflammation. The concentration of HMGB1 in serum taken at admission was increased in falciparum malaria in sixteen African children, more so in fatal cases than in those who subsequently recovered (P<0.001). Serum from both non-fatal (P=0.0048) and fatal (P<0.001) cases contained significantly more circulating HMGB1 than did serum from healthy Caucasian adults. These data provide an additional argument that malaria is fundamentally a systemic inflammatory state. In keeping with its developing role in sepsis, HMGB1 may enhance and prolong the inflammatory processes, and thus illness, in malaria.

RAGE is the major receptor for the proinflammatory activity of HMGB1 in rodent macrophages

Abstract High-mobility group box chromosomal protein 1 (HMGB1) is a protein with both intranuclear functions and extracellular cytokine-like effects. In this report, we study possible candidate receptors for HMGB1 on macrophages (Mphi) and define pathways activated by HMGB1 binding. Bone marrow Mphi were prepared from Dark Agouti (DA) rats and stimulated in vitro with HMGB1. The kinetics of tumour necrosis factor (TNF) production, NO production, activation of p38 mitogen-activated protein kinase (MAPK), p44/42 MAPK- and SAPK/JNK-signalling pathways, nuclear translocation of nuclear factor kappa B (NF-kappaB) and HMGB1-induced upregulation of major histocompatibility complex (MHC) class II and CD86 were analysed. Mphi from interleukin (IL)-1 receptor type I-/-, Toll-like receptor 2 (TLR2-/-) and RAGE-/- mice were used to investigate the role of these receptors in HMGB1 signalling. HMGB1 induced TNF and NO production by Mphi, phosphorylation of all investigated MAP kinase pathways and NF-kappaB translocation, and expression of MHC class II was increased. Mphi from RAGE-/- mice produced significantly lower amounts of TNF, IL-1beta and IL-6, while IL-1RI-/- and TLR2-/- Mphi produced cytokine levels comparable with wildtype controls in response to HMGB1 stimulation. We conclude that HMGB1 has the potential to induce a proinflammatory phenotype in Mphi, with RAGE as the major activation-inducing receptor.

Longitudinal study of cytokine and immune transcription factor mRNA expression in septic shock

Success in treating severe sepsis will require relevant tools to monitor the patient immunoinflammatory status. This study aimed to investigate the feasibility of measuring a panel of immunological mediator mRNAs in whole blood and to study their prognostic values in septic shock patients. At the onset of shock, compared to healthy volunteers, mRNA levels in septic shock patients were increased for IL-10, IL-1beta, and high mobility group B1 (HMGB1) and decreased for transforming growth factor beta 1, the Th1, and Th2 transcription factors, T-bet and GATA-3, respectively. Single parameter analysis highlighted an increased expression of IL-10 and HMGB1 mRNA in nonsurvivors and a significant rise over time of GATA3 in survivors. Combining the expression levels of four genes, hierarchical cluster analysis showed that up to 95% of the patients with a similar outcome displayed transcriptional similarities. These results illustrate both the potential of whole blood mRNA quantification assays and the interest of a multiparametric strategy to better stratify septic patients.

Pathogenic role of HMGB1 in SARS?

High mobility group box 1 protein (HMGB1) is released by necrotic cells or activated macrophages/monocytes, and functions as a late mediator of lethal systemic and local pulmonary inflammation. Passive immunization with anti-HMGB1 antibodies confers significant protection against lethal endotoxemia, sepsis, and acute lung injury, even when antibodies are administered after the onset of these diseases. In light of observations that three Chinese herbal formulations recommended for treatment of severe acute respiratory syndrome (SARS) specifically inhibited the release of HMGB1 from innate immune cells, we hypothesize that HMGB1 might occupy a pathogenic role in SARS by mediating an injurious pulmonary inflammatory response.

Atherosclerosis and restenosis: is there a role for RAGE?

Diabetic vascular complications are a major cause of morbidity and mortality. Furthermore, such vascular disease is only incompletely explained by "traditional" risk factors in the nondiabetic complications. This situation has prompted the search for factors contributing to the pathogenesis of accelerated and more severe vascular disease in patients with diabetes. We review evidence that receptor for advanced glycation end products (RAGE), via its interaction with ligands, serves as a cofactor exacerbating diabetic vascular disease. RAGE is a member of the immunoglobulin superfamily of cell surface molecules with a diverse repertoire of ligands reminiscent of pattern recognition receptors. In the diabetic milieu, two classes of RAGE ligands, products of nonenzymatic glycoxidation and S100 proteins, appear to drive receptor-mediated cellular activation and, potentially, acceleration of vascular disease.

Activation of human umbilical vein endothelial cells leads to relocation and release of high-mobility group box chromosomal protein 1

The nuclear protein high-mobility group box chromosomal protein 1 (HMGB1) was recently described to act as a pro-inflammatory cytokine and as a late mediator of severe sepsis and septic shock. The protein is released from monocytes in response to endotoxin and activates monocytes and endothelial cells through nuclear factor kappa B. We have previously demonstrated that the B-box of HMGB1 mediates a pro-inflammatory effect on endothelial cells including the upregulation of cell-adhesion molecules and release of interleukin (IL)-8 and granulocyte colony-stimulating factor. Here, we report that HMGB1 is released from human umbilical vein endothelial cells (HUVEC) in response to lipopolysaccharide (LPS) and tumour necrosis factor (TNF)-alpha. A nuclear relocation of HMGB1 to the cytoplasm was seen at 4 h. Subsequently, high amounts of HMGB1 could be seen in the supernatants from stimulated cells after 16 h. It was also observed that the pro-inflammatory activity of HMGB1 is sensitive to dexamethasone. Interestingly, the HMGB1-induced TNF-alpha release from monocytes could be inhibited by either the A-box of the protein or the p38 inhibitor CNI-1493, but neither had any inhibitory effects on the HMGB1-dependent upregulation of cell-adhesion molecules on HUVEC. Altogether, these results suggest that HUVEC may be an important source of HMGB1 secretion in response to systemic infection and that endothelial cells and monocytes may use different signalling pathways.

Suppression of HMGB1 release by stearoyl lysophosphatidylcholine:an additional mechanism for its therapeutic effects in experimental sepsis

Stearoyl lysophosphatidylcholine (LPC) has recently been proven protective against lethal sepsis by stimulating neutrophils to eliminate invading pathogens through an H2O2-dependent mechanism. Here, we demonstrate that stearoyl LPC, but not caproyl LPC, significantly attenuates circulating high-mobility group box 1 (HMGB1) levels in endotoxemia and sepsis by suppressing endotoxin-induced HMGB1 release from macrophages/monocytes. Neutralizing antibodies against G2A, a potential cell surface receptor for LPC, partially abrogated stearoyl LPC-mediated suppression of HMGB1 release. Thus, stearoyl LPC confers protection against lethal experimental sepsis partly by facilitating the elimination of the invading pathogens and partly by inhibiting endotoxin-induced release of a late proinflammatory cytokine, HMGB1.

HMGB1 contributes to the development of acute lung injury after hemorrhage

High mobility group box 1 (HMGB1) is a novel late mediator of inflammatory responses that contributes to endotoxin-induced acute lung injury and sepsis-associated lethality. Although acute lung injury is a frequent complication of severe blood loss, the contribution of HMGB1 to organ system dysfunction in this setting has not been investigated. In this study, HMGB1 was detected in pulmonary endothelial cells and macrophages under baseline conditions. After hemorrhage, in addition to positively staining endothelial cells and macrophages, neutrophils expressing HMGB1 were present in the lungs. HMGB1 expression in the lung was found to be increased within 4 h of hemorrhage and then remained elevated for more than 72 h after blood loss. Neutrophils appeared to contribute to the increase in posthemorrhage pulmonary HMGB1 expression since no change in lung HMGB1 levels was found after hemorrhage in mice made neutropenic with cyclophosphamide. Plasma concentrations of HMGB1 also increased after hemorrhage. Blockade of HMGB1 by administration of anti-HMGB1 antibodies prevented hemorrhage-induced increases in nuclear translocation of NF-kappa B in the lungs and pulmonary levels of proinflammatory cytokines, including keratinocyte-derived chemokine, IL-6, and IL-1 beta. Similarly, both the accumulation of neutrophils in the lung as well as enhanced lung permeability were reduced when anti-HMGB1 antibodies were injected after hemorrhage. These results demonstrate that hemorrhage results in increased HMGB1 expression in the lungs, primarily through neutrophil sources, and that HMGB1 participates in hemorrhage-induced acute lung injury.

Increased expression of the novel proinflammatory cytokine high mobility group box chromosomal protein 1 in skin lesions of patients with lupus erythematosus

OBJECTIVE

To investigate the role of the novel cytokine high mobility group box chromosomal protein 1 (HMGB-1) in the pathogenesis of cutaneous lupus erythematosus (CLE).

METHODS

Punch biopsy specimens of lesional and unaffected skin from 10 patients with CLE and 3 healthy control subjects were investigated. Immunohistochemical staining for HMGB-1, tumor necrosis factor alpha (TNFalpha), and interleukin-1beta (IL-1beta) was performed on consecutive sections. Analysis of single-nucleotide polymorphisms of -308 TNF was performed on DNA extracted from peripheral blood mononuclear cells.

RESULTS

An altered expression of HMGB-1 was observed both in the epidermis and in the dermal infiltrates of lesional skin. Expression of HMGB-1 in the epidermis and dermis was increased (P < 0.01 and P < 0.001, respectively, versus unaffected skin), and translocation to the cytoplasm as well as the extracellular presence of secreted HMGB-1 were found. Increased levels of TNFalpha and IL-1beta were also observed in the dermal infiltrates of lesional skin (P < 0.01 and P < 0.05, respectively, versus unaffected skin). The carrier frequency of the -308A TNF polymorphism was 80% in patients with subacute CLE, but this was not related to higher expression of TNFalpha in biopsy specimens from the CLE group.

CONCLUSION

The high amount of extracellular HMGB-1 observed in skin lesions indicates that HMGB-1 is involved in the inflammatory process of CLE. TNFalpha and IL-1beta may form a proinflammatory loop with HMGB-1, since they can induce the release of each other. The extracellular HMGB-1 observed by immunostaining of the epidermis indicates that keratinocytes may be an as yet unrecognized source of secreted HMGB-1, underscoring the role of the target organ in the rheumatoid autoimmune inflammatory process.

The effect of inflammation on the generation of plasma DNA from dead and dying cells in the peritoneum

To assess the effects of inflammation on the generation of circulating DNA from dead and dying cells, plasma DNA levels were determined in BALB/c mice, administered apoptotic or necrotic Jurkat cells following induction of peritonitis by treatment with thioglycollate (TG), peptone (PT), or sodium periodate (NaIO(4)). In mice receiving TG or NaIO(4), plasma DNA levels following intraperitoneal administration of Jurkat cells were significantly reduced compared with controls, whereas they were not affected in mice receiving PT. To determine the basis of these differences, the cellular composition of peritoneal fluids prior to the administration of the dead cells was analyzed. Among agents tested, TG administration led to the largest increase in cells, both neutrophils and monocytes. As shown by flow cytometry, the exudates contained apoptotic neutrophils and macrophages, with the highest levels in the TG-induced exudates. Analysis of DNA and caspase 3 in the fluids also showed differences. TG exudates showed increases in DNA and caspase 3, while NaIO(4)-induced exudates had an increase only in DNA. Fluid from PT-treated mice did not have increases in DNA or caspase 3. Together, these results indicate that prior inflammation can affect the generation of blood DNA from apoptotic or necrotic cells, although this effect may vary depending on the composition of the exudates with respect to cells as well as DNA.

[Stress proteins and regulation of microglial amyloid-beta phagocytosis]

Recent studies have indicated that prolonged dysfunction and/or stress in the endoplasmic reticulum (ER) may contribute to pathogenesis and neurodegeneration. The disorder caused by misfolding and aggregation of proteins has been referred to as conformational disease, including Alzheimer's disease (AD). AD is characterized by the accumulation of extracellular amyloid-beta1-42 (A beta 42) fibrils with reactive microglia. Understanding the balance of production and clearance of A beta 42 is the key to elucidating amyloid plaque homeostasis. We have recently found that microglial phagocytosis of A beta 42 may be essentially driven by dynamic reorganization of the actin cytoskeleton through the pathway of WAVE and Rac1. In addition, an extracellular stress protein, such as Hsp90, enhances A beta 42 phagocytosis. HMGB1 inhibits microglial phagocytosis of A beta 42, and it binds A beta 42 and stabilizes the oligomerization. These results suggest that microglial clearance of A beta 42 may be another option for investigations in the search for a therapeutic strategy for AD, in addition to the study of production and degradation of A beta 42.

Importance of Tumor Necrosis Factor-α Cleavage Process in Post-Transplantation Lung Injury in Rats

Tumor necrosis factor-alpha (TNF-alpha) has two forms with apparently different biological activities: a membrane-associated form and a soluble form. TNF-alpha-converting enzyme (TACE) mediates a cleavage of membrane-associated TNF-alpha to induce its bioactive soluble form. We hypothesized that inhibition of TACE might prevent TNF-alpha-induced tissue injury while preserving the benefits of TNF-alpha. In this study, we evaluated the role of TACE in acute inflammation using an inhibitor of the enzyme in a rat model of lung transplantation. Inbred Lewis rats underwent left lung isotransplantation, and the donor lungs were kept in Euro-Collins solution with or without the inhibitor. After 6 hours of ischemia, the left lung was transplanted into the recipient rat and reperfused for 4 hours. Inhibition of TACE significantly attenuated endothelial and alveolar septal damage, as assessed by radiolabeled albumin leakage after transplantation. The inhibition also attenuated neutrophil accumulation in the alveolar space and other histopathologic findings, including intercellular adhesion molecule-1 expression. In addition, significantly lower levels of monocyte chemotactic protein-1, cytokine-induced neutrophil chemoattractant-1, high mobility group box-1, and soluble epithelial cadherin and decreased neutrophil elastase activity were observed in bronchoalveolar lavage fluid from the rats treated with the inhibitor. We conclude that TACE mediates a critical step in the development of post-transplantation lung injury.

Polymyxin B-immobilized fiber hemoperfusion after emergency surgery in patients with chronic renal failure

The purpose of this study was to evaluate the effect of direct hemoperfusion using a Polymyxin B (PMX) immobilized fiber column in septic patients with chronic renal failure after emergency surgery. Twenty-four renal failure patients, including 19 dialysis patients, with sepsis or septic shock were treated with direct hemoperfusion after emergency surgery. The 24 consecutive patients included nine with necrotic enterocolitis, six with colonic perforation due to diverticulitis, three with ruptured suture after colectomy, one with duodenal perforation, four with blood access infection, and one with an infected abdominal aortic aneurysm. The acute physiology and chronic health evaluation II score ranged from 13 to 26 (19 +/- 3). After completion of the first and the second hemoperfusion, mean blood pressure was significantly elevated from 69 +/- 12 mm Hg to 89 +/- 15 mm Hg and from 78 +/- 14 mm Hg to 95 +/- 13 mm Hg, respectively (P < 0.01). In addition, the catecholamine dosage needed to maintain the circulation could be decreased markedly after the treatment. The blood concentration of endotoxin in patients with Gram-negative sepsis, before and after the treatment, significantly decreased from 36 +/- 19 pg/mL to 19 +/- 19 pg/mL (P < 0.05). PMX was effective in patients with Gram-positive sepsis as well as Gram-negative sepsis. The 28-day mortality rate in patients who had emergency abdominal surgery was 10% (2/20), whereas that in patients with dialysis access infection was 50% (2/4). There was a significant difference in the Sequential Organ Failure Assessment (SOFA) score of all patients before and after treatment using PMX (9.2 +/- 3.3 vs. 7.5 +/- 3.5, P < 0.05). Furthermore, the SOFA score of survivors decreased significantly after PMX treatment (8.4 +/- 3.5 vs. 6.7 +/- 2.6, P < 0.01). Our results suggest that the early application of PMX may prevent multiple organ failure and improve survival in patients with chronic renal failure and sepsis/septic shock after emergency abdominal surgery, regardless of the type of pathogenic bacteria involved.

Bench to bedside: HMGB1-a novel proinflammatory cytokine and potential therapeutic target for septic patients in the emergency department

Overwhelming gram-negative bacterial infection and life-threatening systemic inflammation are widespread problems in critically ill emergency department patients. Currently, the treatment of these patients is largely supportive, focusing on antibiotics, fluids, hemodynamic and ventilatory support, and intensive monitoring. The only Food and Drug Administration-approved pharmaceutical agent for the treatment of sepsis is activated protein C, with its use largely relegated to the intensive care unit. The subject thus remains an active area of exploration for emergency medicine research. During sepsis and inflammation, innate immune cells release excessive amounts of proinflammatory cytokines such as tumor necrosis factor (TNF) and interleukin-1beta. If delivered early enough, anti-TNF antibodies can be an effective therapy in experimental models of septic shock. Anti-TNF antibodies have been developed for clinical use in rheumatoid arthritis and Crohn's disease. However, anti-TNF treatment for sepsis has been difficult to achieve in the clinical setting, perhaps because TNF's early release and transient appearance in the serum create a narrow therapeutic window. An alternative strategy would be to identify "late" mediators that may be clinically more accessible. High mobility group box 1 (HMGB1), a protein previously known only as a nuclear transcription factor, is now implicated as a late mediator of sepsis. Targeting late mediators of lethal systemic inflammation represents a novel approach that may widen the therapeutic window and lead to new strategies for inhibiting the deleterious effects of the inflammatory cascade. Here the authors review the studies that led to the discovery of HMGB1 as a late mediator of systemic inflammation and discuss the possibility of HMGB1 as a therapeutic target for septic patients in the emergency department.

Time course of nitric oxide production after endotoxin challenge in mice

Nitric oxide (NO) regulates numerous processes during endotoxemia and inflammation. However, the sequential changes in whole body (Wb) nitric oxide (NO) production during endotoxemia in vivo remain to be clarified. Male Swiss mice were injected intraperitoneally with saline (control group) or lipopolysaccharide (LPS group). After 0, 2, 4, 6, 9, 12, and 24 h, animals received a primed constant infusion of L-[guanidino-(15)N(2)-(2)H(2)]arginine, L-[ureido-(15)N]citrulline, L-[5-(15)N]glutamine, and L-[ring-(2)H(5)]phenylalanine in the jugular vein. Arterial blood was collected for plasma arginine (Arg), citrulline (Cit), glutamine (Gln), and phenylalanine (Phe) concentrations and tracer-to-tracee ratios. NO production was calculated as plasma Arg-to-Cit flux, Wb de novo Arg synthesis as plasma Cit-to-Arg flux, and Wb protein breakdown as plasma Phe flux. LPS reduced plasma Arg and Cit and increased Gln and Phe concentrations. Two peaks of NO production were observed at 4 and 12 h after LPS. Although LPS did not affect total Arg production, de novo Arg production decreased after 12 h. The second peak of NO production coincided with increased Wb Cit, Gln, and Phe production. In conclusion, the curve of NO production in both early and late phases of endotoxemia is not related to plasma Arg kinetics. However, because Wb Cit, Gln, and Phe fluxes increased concomitantly with the second peak of NO production, NO production is probably related to the catabolic phase of endotoxemia.

Cholinergic agonists inhibit HMGB1 release and improve survival in experimental sepsis

Physiological anti-inflammatory mechanisms can potentially be exploited for the treatment of inflammatory disorders. Here we report that the neurotransmitter acetylcholine inhibits HMGB1 release from human macrophages by signaling through a nicotinic acetylcholine receptor. Nicotine, a selective cholinergic agonist, is more efficient than acetylcholine and inhibits HMGB1 release induced by either endotoxin or tumor necrosis factor-alpha (TNF-alpha). Nicotinic stimulation prevents activation of the NF-kappaB pathway and inhibits HMGB1 secretion through a specific 'nicotinic anti-inflammatory pathway' that requires the alpha7 nicotinic acetylcholine receptor (alpha7nAChR). In vivo, treatment with nicotine attenuates serum HMGB1 levels and improves survival in experimental models of sepsis, even when treatment is started after the onset of the disease. These results reveal acetylcholine as the first known physiological inhibitor of HMGB1 release from human macrophages and suggest that selective nicotinic agonists for the alpha7nAChR might have therapeutic potential for the treatment of sepsis.

Linking the "two-hit" response following injury to enhanced TLR4 reactivity

Severe injury can initiate an exaggerated systemic inflammatory response and multiple organ failure (MOF) if a subsequent immune stimulus, "second hit", occurs. Using a mouse thermal injury model, we tested whether changes in innate immune cell reactivity following injury can contribute to the development of heightened inflammation and MOF. Using high-purity Escherichia coli lipopolysaccharide (LPS) to selectively stimulate Toll-like receptor 4 (TLR4), we demonstrate augmented interleukin (IL)-1beta, tumor necrosis factor alpha (TNF-alpha), and IL-6 production by 1 day but particularly, at 7 days after injury. The in vivo significance of enhanced TLR4 responsiveness was explored by challenging sham or burn mice with LPS at 1 or 7 days after injury and determining mortality along with in vivo cytokine and chemokine levels. Mortality was high (75%) in LPS-challenged burn but not sham mice at 7 days, although not at 1 day, after injury. Death was associated with leukocyte sequestration in the lungs and livers along with increased proinflammatory cytokine and chemokine levels in these organs. Blocking TNF-alpha activity prevented this mortality, suggesting that excessive TNF-alpha production contributes to this lethal response. These findings demonstrate the potential lethality of excessive TLR4 reactivity after injury and provide an explanation for the exaggerated inflammatory response to a second hit, which can occur following severe injury.

Depletion of tumor-infiltrating macrophages is associated with amphoterin expression in colon cancer

Macrophage infiltration into colon cancer and amphoterin expression in cancer cells was examined in 42 human colon cancers invading the subserosa. The mean number of infiltrating macrophages was significantly higher in Dukes' B cases than in Dukes' C cases (p = 0.0065). Tumors with few infiltrating macrophages (macrophage depletion) were significantly more frequent in Dukes' C cases than in Dukes' B cases (p = 0.0014). No Dukes' C cases with relevant macrophage infiltration showed macrophage-cancer cell contact, whereas 5 Dukes' B cases showed such contact (p < 0.0001). In human colon cancer cells implanted in the cecum of nude mice, KM12SM (highly metastatic) tumors yielded less macrophage infiltration and more liver metastases than KM12C (low risk of metastasis) tumors (14 +/- 3 vs. 78 +/- 32 and 24 +/- 6 vs. 5 +/- 3 per liver, respectively). Amphoterin expression was detected at high frequency in both Dukes' B and C cases (p = 0.0684). In macrophage-depleted cases, amphoterin expression was significantly higher than that in non-depleted cases (p = 0.0015). To confirm biological effects of amphoterin on macrophages, an infiltration assay using the cell-layered Boyden chamber was done. Infiltration of PMA-treated U937 monocytes through the KM12SM cell layer was increased by pretreatment of KM12SM cells with amphoterin antisense S-oligodeoxynucleotide exposure. Moreover, extracted amphoterin inhibited PMA-U937 monocyte infiltration in a dose-dependent manner. Thus, amphoterin may play an important role in the inhibition of macrophage infiltration into colon cancer.

Increased expression of the DNA-binding cytokine HMGB1 in human atherosclerotic lesions: role of activated macrophages and cytokines

OBJECTIVE

Atherosclerosis is a chronic inflammatory response of the arterial wall to injury. High-mobility group box 1 (HMGB1) is a DNA-binding protein, which on release from cells exhibits potent inflammatory actions. We examined its expression in atherosclerotic lesions and regulation by cytokines.

METHODS AND RESULTS

In atherosclerotic lesions, HMGB1 protein is expressed by endothelial cells, some intimal smooth muscle cells, and macrophages. As atherosclerosis develops and progresses from fatty streaks to fibrofatty lesion, the number of HMGB1-producing macrophages increases markedly. Studies using the THP-1 cell line indicated that HMGB1 mRNA expression could be markedly upregulated by inflammatory cytokines, interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha and also transforming growth factor (TGF)-beta. IFN-gamma, TNF-alpha, TWEAK, and TGF-beta induced an intracellular redistribution of HMGB1 and stimulated secretion by THP-1 cells and human blood monocytes. Inhibitors of MEK1/MEK2, protein kinase C, and PI-3/Akt, which inhibit lysosomal degranulation and mRNA translation, attenuated cytokine-induced HMGB1 secretion.

CONCLUSIONS

Macrophage is the major cell type responsible for HMGB1 production in human atherosclerotic lesions. Inflammatory cytokines and TGF-beta increase HMGB1 expression and secretion by monocyte/macrophages. HMGB1 appears to be a common mediator of inflammation induced by inflammatory cytokines and is likely to contribute to lesion progression and chronic inflammation.

Contributions of high mobility group box protein in experimental and clinical acute lung injury

This study was performed to examine the putative role of high mobility group box (HMGB) protein in the pathogenesis of acute lung injury (ALI). Observations were made (1) in 21 patients who were septic with ALI and 15 patients with normal lung function and (2) in a mouse model 24 hours after intratracheal instillation of lipopolysaccharide (LPS). The concentrations of HMGB1 were increased in plasma and lung epithelial lining fluid of patients with ALI and mice instilled with LPS. LPS-induced ALI was mitigated by anti-HMGB1 antibody. Although this protein was not detected in the plasma of control humans or mice, the concentrations of HMGB1 in lung epithelial lining fluid or in bronchoalveolar lavage fluid were unexpectedly high. The nuclear expression of HMGB1 was apparent in epithelial cells surrounding terminal bronchioles in normal mice, whereas its nuclear and cytoplasmic expression was observed in alveolar macrophages in LPS-instilled mice. Lung instillation of HMGB2 did not cause as much inflammation as HMGB1. Extracellular HMGB1 may play a key role in the pathogenesis of clinical and experimental ALI. However, its expression in normal airways is noteworthy and suggests that it also plays a physiologic role in the lung.

The systemic inflammatory response syndrome

Sepsis and septic shock are the leading causes of death in intensive care units in developed countries despite recent advances in critical care medicine. Sepsis is the systemic inflammatory response to infection frequently associated with hypoperfusion followed by tissue injury and organ failure. The activation of monocytes/macrophages and neutrophils, with the consecutive release of pro-inflammatory mediators and activation of the coagulation cascade, seems to play a key role in the pathogenesis of sepsis. Elimination of the septic focus, anti-microbial therapy and supportive treatment are the cornerstones of sepsis therapy. In addition, the application of small doses hydrocortisone to patients with refractory septic shock and the treatment of patients with septic multiple organ failure with activated protein C are two adjunctive therapeutic strategies. Promising new experimental treatment options are interference with MIF, HMGB1, C5a or TREM-1 signal transduction pathways and an inhibition of apoptosis, which may further improve the prognosis of septic patients in the future.

[Pathophysiological role of endotoxins, a common denominator to various diseases]

A growing number of investigations point to endotoxin or lipopolysaccharide as a central player in many pathophysiological states and diseases. Endotoxins are one of the most toxic biological contaminants continuously shed by both dead and live Gram negative bacteria. Endotoxins induce the primitive form of defense called innate immunity. Endotoxins have been related to inflammatory reactions observed in patients suffering from respiratory distress syndrome, multiorgan failure and septic shock, hepatic diseases, or in subjects affected by graft versus host disease after allogeneic transplantation. As our understanding of the molecular mechanisms underlying pathologies progresses, more diseases involving endotoxins emerge. Although these illnesses are multifactorial, the objective of this article is to review some of the common and distinct processes involving endotoxins in various disease states.

High mobility group box 1 protein, a cue for stem cell recruitment

High mobility group box 1 (HMGB1) is a non-histone protein required to maintain chromatin architecture. Recent observations demonstrated that HMGB1 can also act as a cytokine to regulate different biological processes such as inflammation, cell migration and metastasis. We showed previously that HMGB1 can be released passively by cells that die in a traumatic and unprogrammed way, and can serve a signal of tissue damage. More recently, we showed that HMGB1 can recruit stem cells: HMGB1 induces stem cell transmigration through an endothelial barrier; moreover, when beads containing HMGB1 are implanted into healthy muscle, they recruit stem cells injected into the general circulation. The inflammatory and tissue-regenerating roles of HMGB1 may be strictly interconnected, and are discussed here.

Insulin attenuates the systemic inflammatory response in endotoxemic rats

Insulin decreases the mortality and prevents the incidence of infection and sepsis in critically ill patients. The molecular and cellular mechanisms by which insulin improves survival have not been defined. The purpose of the present study was to determine the effect of insulin on the inflammatory reaction during endotoxemia. Endotoxemic rats were randomly divided into two groups to receive either saline or insulin. The effects of insulin on hepatic signal transcription factor mRNA expression, proinflammatory and antiinflammatory cytokine mRNA and protein concentration were determined. Insulin administration did not change glucose or electrolyte levels, but significantly decreased proinflammatory signal transcription factors [CCAAT/enhancer-binding protein-beta, signal transducer and activator of transcription-3 and-5, RANTES (regulated on activation, normal T cell expressed and secreted)] and cytokine expression in the liver and serum levels of IL-1beta, IL-6, macrophage inflammatory factor, and TNFalpha. Insulin administration further decreased high mobility group 1 protein in the serum compared with controls. In addition, insulin increased antiinflammatory cytokine expression in the liver; serum levels of IL-2, IL-4, and IL-10; and hepatic suppressor of cytokine signaling-3 mRNA expression. Insulin modulates the inflammatory response by decreasing the proinflammatory and increasing the antiinflammatory cascade. Because glucose and electrolyte levels did not differ between insulin-treated patients and controls, we hypothesize that the effects are direct antiinflammatory mechanisms of insulin, rather than indirect, through modulation of glucose or electrolyte metabolism.

Bacterial endotoxin stimulates macrophages to release HMGB1 partly through CD14- and TNF-dependent mechanisms

Bacterial endotoxin [lipopolysaccharide (LPS)] stimulates macrophages to sequentially release early [tumor necrosis factor (TNF)] and late [high mobility group box 1 (HMGB1)] proinflammatory cytokines. The requirement of CD14 and mitogen-activated protein kinases [MAPK; e.g., p38 and extracellular signal-regulated kinase (ERK)1/2] for endotoxin-induced TNF production has been demonstrated previously, but little is known about their involvement in endotoxin-mediated HMGB1 release. Here, we demonstrated that genetic disruption of CD14 expression abrogated LPS-induced TNF production but only partially attenuated LPS-induced HMGB1 release in cultures of primary murine peritoneal macrophages. Pharmacological suppression of p38 or ERK1/2 MAPK with specific inhibitors (SB203580, SB202190, U0126, or PD98059) significantly attenuated LPS-induced TNF production but failed to inhibit LPS-induced HMGB1 release. Consistently, an endogenous, immunosuppressive molecule, spermine, failed to inhibit LPS-induced activation of p38 MAPK and yet, still significantly attenuated LPS-mediated HMGB1 release. Direct suppression of TNF activity with neutralizing antibodies or genetic disruption of TNF expression partially attenuated HMGB1 release from macrophages induced by LPS at lower concentrations (e.g., 10 ng/ml). Taken together, these data suggest that LPS stimulates macrophages to release HMGB1 partly through CD14- and TNF-dependent mechanisms.

HMGB1 as a mediator of necrosis-induced inflammation and a therapeutic target in arthritis

For the second time in recent history, studies directed at the pathogenesis of infectious disease have led to the identification of an endogenous mediator of arthritis. HMGB1, a 30-kD nuclear and cytoplasmic protein widely studied as a DNA-binding protein, is a newly described cytokine and a necessary and sufficient mediator of lethal sepsis. HMGB1 is passively released during cell necrosis, but not apoptosis; it activates an inflammatory response to necrosis,but not apoptosis. Furthermore, HMGB1 can also be actively secreted by stimulated macrophages or monocytes in a process that requires acetylation of the molecule, enabling a translocation from the nucleus to secretory lysosomes. Recent evidence indicates that HMGB1 is a mediator of arthritis because of the following: (1) it is produced at the site of joint inflammation, (2) it causes the development of arthritis when applied to normal joints, and (3) therapies that inhibit HMGB1 prevent the progression of collagen-induced arthritis in rodents. Anti-HMGB1 may be studied in future clinical trials of diseases of excessive production of HMGB1, such as severe sepsis and arthritis.

HMGB1 is an endogenous immune adjuvant released by necrotic cells

Immune responses against pathogens require that microbial components promote the activation of antigen-presenting cells (APCs). Autoimmune diseases and graft rejections occur in the absence of pathogens; in these conditions, endogenous molecules, the so-called 'innate adjuvants', activate APCs. Necrotic cells contain and release innate adjuvants; necrotic cells also release high-mobility group B1 protein (HMGB1), an abundant and conserved constituent of vertebrate nuclei. Here, we show that necrotic HMGB1(-/-) cells have a reduced ability to activate APCs, and HMGB1 blockade reduces the activation induced by necrotic wild-type cell supernatants. In vivo, HMGB1 enhances the primary antibody responses to soluble antigens and transforms poorly immunogenic apoptotic lymphoma cells into efficient vaccines.

High mobility group box protein 1: an endogenous signal for dendritic cell maturation and Th1 polarization

High mobility group box protein 1 (HMGB1), a DNA binding nuclear and cytosolic protein, is a proinflammatory cytokine released by monocytes and macrophages. This study addressed the hypothesis that HMGB1 is an immunostimulatory signal that induces dendritic cell (DC) maturation. We show that HMGB1, via its B box domain, induced phenotypic maturation of DCs, as evidenced by increased CD83, CD54, CD80, CD40, CD58, and MHC class II expression and decreased CD206 expression. The B box caused increased secretion of the proinflammatory cytokines IL-12, IL-6, IL-1alpha, IL-8, TNF-alpha, and RANTES. B box up-regulated CD83 expression as well as IL-6 secretion via a p38 MAPK-dependent pathway. In the MLR, B box-activated DCs acted as potent stimulators of allogeneic T cells, and the magnitude of the response was equivalent to DCs activated by exposure to LPS, nonmethylated CpG oligonucleotides, or CD40L. Furthermore, B box induced secretion of IL-12 from DCs as well as IL-2 and IFN-gamma secretion from allogeneic T cells, suggesting a Th1 bias. HMGB1 released by necrotic cells may be a signal of tissue or cellular injury that, when sensed by DCs, induces and/or enhances an immune reaction.

Pathogenesis of malaria and clinically similar conditions

There is now wide acceptance of the concept that the similarity between many acute infectious diseases, be they viral, bacterial, or parasitic in origin, is caused by the overproduction of inflammatory cytokines initiated when the organism interacts with the innate immune system. This is also true of certain noninfectious states, such as the tissue injury syndromes. This review discusses the historical origins of these ideas, which began with tumor necrosis factor (TNF) and spread from their origins in malaria research to other fields. As well the more established proinflammatory mediators, such as TNF, interleukin-1, and lymphotoxin, the roles of nitric oxide and carbon monoxide, which are chiefly inhibitory, are discussed. The established and potential roles of two more recently recognized contributors, overactivity of the enzyme poly(ADP-ribose) polymerase 1 (PARP-1) and the escape of high-mobility-group box 1 (HMGB1) protein from its normal location into the circulation, are also put in context. The pathogenesis of the disease caused by falciparum malaria is then considered in the light of what has been learned about the roles of these mediators in these other diseases, as well as in malaria itself.

Receptor for advanced glycation end products (RAGE) regulates sepsis but not the adaptive immune response

While the initiation of the adaptive and innate immune response is well understood, less is known about cellular mechanisms propagating inflammation. The receptor for advanced glycation end products (RAGE), a transmembrane receptor of the immunoglobulin superfamily, leads to perpetuated cell activation. Using novel animal models with defective or tissue-specific RAGE expression, we show that in these animal models RAGE does not play a role in the adaptive immune response. However, deletion of RAGE provides protection from the lethal effects of septic shock caused by cecal ligation and puncture. Such protection is reversed by reconstitution of RAGE in endothelial and hematopoietic cells. These results indicate that the innate immune response is controlled by pattern-recognition receptors not only at the initiating steps but also at the phase of perpetuation.

Further characterization of high mobility group box 1 (HMGB1) as a proinflammatory cytokine: central nervous system effects

High mobility group box 1 (HMGB1), an abundant, highly conserved cellular protein, is widely known as a nuclear DNA-binding protein. HMGB1 has been recently implicated as a proinflammatory cytokine because of its role as a late mediator of endotoxin lethality and ability to stimulate release of proinflammatory cytokines from monocytes. Production of central cytokines is a critical step in the pathway by which endotoxin and peripheral proinflammatory cytokines, including interleukin-1beta (IL-1) and tumor necrosis factor-alpha (TNF), produce sickness behaviors and fever. Intracerebroventricular (ICV) administration of HMGB1 has been shown to increase TNF expression in mouse brain and induce aphagia and taste aversion. Here we show that ICV injections of HMGB1 induce fever and hypothalamic IL-1 in rats. Furthermore, we show that intrathecal administration of HMGB1 produces mechanical allodynia (lowering of the response threshold to calibrated stimuli). Finally, while endotoxin (lipopolysaccharide, LPS) administration elevates IL-1 and TNF mRNA in various brain regions, HMGB1 mRNA is unchanged. It remains possible that HMGB1 protein is released in brain in response to LPS. Nonetheless, these data suggest that HMGB1 may play a role as an endogenous pyrogen and support the concept that HMGB1 has proinflammatory characteristics within the central nervous system.

Receptor for advanced glycation end products (RAGE) regulates sepsis but not the adaptive immune response

While the initiation of the adaptive and innate immune response is well understood, less is known about cellular mechanisms propagating inflammation. The receptor for advanced glycation end products (RAGE), a transmembrane receptor of the immunoglobulin superfamily, leads to perpetuated cell activation. Using novel animal models with defective or tissue-specific RAGE expression, we show that in these animal models RAGE does not play a role in the adaptive immune response. However, deletion of RAGE provides protection from the lethal effects of septic shock caused by cecal ligation and puncture. Such protection is reversed by reconstitution of RAGE in endothelial and hematopoietic cells. These results indicate that the innate immune response is controlled by pattern-recognition receptors not only at the initiating steps but also at the phase of perpetuation.

Ethyl pyruvate decreases sepsis-induced acute renal failure and multiple organ damage in aged mice

BACKGROUND

Sepsis is a common cause of acute renal failure (ARF). The incidence of sepsis increases dramatically after 50 years of age; however, most ARF studies are performed in young mice.

METHODS

We performed two common sepsis models, lipopolysaccharide (LPS) administration and cecal ligation puncture (CLP) in aged mice. We developed a fully treated CLP model in aged mice by treating mice with fluid resuscitation and antibiotics.

RESULTS

LPS induced renal injury in aged but not young mice. However, volume resuscitation starting within 6 hours decreased renal injury. We then used this fluid resuscitation scheme, along with antibiotics, to develop a fully treated CLP model in aged mice. Mice subjected to CLP developed functional and histologic ARF and multiple organ damage. Treatment with ethyl pyruvate, even when started 12 hours after surgery, decreased serum creatinine, tubular damage, and multiple organ injury at 24 hours. Ethyl pyruvate decreased plasma tumor necrosis factor-alpha (TNF-alpha), and kidney mRNA for TNF alpha, tissue factor, and plasminogen activator inhibitor-1 (PAI-1), and increased mRNA for urokinase-like plasminogen activator.

CONCLUSION

CLP in aged mice causes functional and histologic changes consistent with human ARF. A single dose of ethyl pyruvate inhibits renal and multiple organ damage, and is still effective when given 12 hours after surgery.

Sepsis: avoiding its deadly toll

Systemic bacterial infection may culminate in a frequently fatal septic shock syndrome. The underlying pathology is the result of an uncontrolled inflammatory response, stimulated by the pathogen and its products. Toll-like receptors (TLRs) are critically involved in sensing bacteria and, in the case of sepsis, stimulate a pathogenic response by the innate immune system. A new study reports a successful attempt to inhibit systemic inflammation in mice by disrupting the formation of complexes between Gram-positive bacteria and their cognate receptor, TLR2.

Antagonistic antibody prevents toll-like receptor 2-driven lethal shock-like syndromes

Hyperactivation of immune cells by bacterial products through toll-like receptors (TLRs) is thought of as a causative mechanism of septic shock pathology. Infections with Gram-negative or Gram-positive bacteria provide TLR2-specific agonists and are the major cause of severe sepsis. In order to intervene in TLR2-driven toxemia, we raised mAb's against the extracellular domain of TLR2. Surface plasmon resonance analysis showed direct and specific interaction of TLR2 and immunostimulatory lipopeptide, which was blocked by T2.5 in a dose-dependent manner. Application of mAb T2.5 inhibited cell activation in experimental murine models of infection. T2.5 also antagonized TLR2-specific activation of primary human macrophages. TLR2 surface expression by murine macrophages was surprisingly weak, while both intra- and extracellular expression increased upon systemic microbial challenge. Systemic application of T2.5 upon lipopeptide challenge inhibited release of inflammatory mediators such as TNF-alpha and prevented lethal shock-like syndrome in mice. Twenty milligrams per kilogram of T2.5 was sufficient to protect mice, and administration of 40 mg/kg of T2.5 was protective even 3 hours after the start of otherwise lethal challenge with Bacillus subtilis. These results indicate that epitope-specific binding of exogenous ligands precedes specific TLR signaling and suggest therapeutic application of a neutralizing anti-TLR2 antibody in acute infection.

Pre-B cell colony-enhancing factor inhibits neutrophil apoptosis in experimental inflammation and clinical sepsis

Pre-B cell colony-enhancing factor (PBEF) is a highly conserved 52-kDa protein, originally identified as a growth factor for early stage B cells. We show here that PBEF is also upregulated in neutrophils by IL-1beta and functions as a novel inhibitor of apoptosis in response to a variety of inflammatory stimuli. Induction of PBEF occurs 5-10 hours after LPS exposure. Prevention of PBEF translation with an antisense oligonucleotide completely abrogates the inhibitory effects of LPS, IL-1, GM-CSF, IL-8, and TNF-alpha on neutrophil apoptosis. Immunoreactive PBEF is detectable in culture supernatants from LPS-stimulated neutrophils, and a recombinant PBEF fusion protein inhibits neutrophil apoptosis. PBEF is also expressed in neutrophils from critically ill patients with sepsis in whom rates of apoptosis are profoundly delayed. Expression occurs at higher levels than those seen in experimental inflammation, and a PBEF antisense oligonucleotide significantly restores the normal kinetics of apoptosis in septic polymorphonuclear neutrophils. Inhibition of apoptosis by PBEF is associated with reduced activity of caspases-8 and -3, but not caspase-9. These data identify PBEF as a novel inflammatory cytokine that plays a requisite role in the delayed neutrophil apoptosis of clinical and experimental sepsis.

RAGE axis: Animal models and novel insights into the vascular complications of diabetes

Receptor for AGE (RAGE) is a multi-ligand member of the immunoglobulin superfamily of cell surface molecules. Engagement of RAGE by its signal transduction ligands evokes inflammatory cell infiltration and activation in the vessel wall. In diabetes, when fueled by oxidant stress, hyperglycemia, and superimposed stresses such as hyperlipidemia or acute balloon/endothelial denuding arterial injury, the ligand-RAGE axis amplifies vascular stress and accelerates atherosclerosis and neointimal expansion. In this brief synopsis, we review the use of rodent models to test these concepts. Taken together, our findings support the premise that RAGE is an amplification step in vascular inflammation and acceleration of atherosclerosis. Future studies must rigorously test the potential impact of RAGE blockade in human subjects; such trials are on the horizon.

Chromatin and cell death

HMGB1, a very mobile chromatin protein, leaks out from necrotic cells and signals to neighbouring cells that tissue damage has occurred. At least one receptor for extracellular HMGB1 exists, and signals to different cells to divide, migrate, activate inflammation or start an immune response. Remarkably, apoptotic chromatin binds HMGB1 irreversibly, thereby ensuring that it will not diffuse away to activate responses from neighbouring cells. Thus, dying cells use their own chromatin to signal how they have died. We argue that the nuclear events in apoptosis serve to control the molecular signals that dying cells send out.

Cloning and characterization of granulosa cell high-mobility group (HMG)-box protein-1, a novel HMG-box transcriptional regulator strongly expressed in rat ovarian granulosa cells

Specific events in the ovary are dependent on gene expression in the tissue. By screening a rat ovarian granulosa cell cDNA library, a cDNA clone encoding a novel transcription factor-like protein containing a high-mobility group-box, referred to as granulosa cell high-mobility group-box protein-1 (GCX-1), was identified. The expression of GCX-1 is restricted to the hypothalamus, pituitary, testis, uterus, and ovary but was not detected in the adrenal gland. An in situ hybridization study revealed that the expression of GCX-1 was restricted to granulosa cell layers in early-stage follicles, and the expression was very low in large antral follicles and the corpus luteum, but localized expression in the testis or pituitary was not clear. Endogenous GCX-1 protein in the granulosa cells was identified by a Western blot analysis, and an analysis using the green fluorescence protein-GCX-1 fusion protein revealed that the GCX-1 protein was localized in the cell nucleus. GAL4 fusion protein-based assays demonstrated that GCX-1 is a potent transcriptional activator, and its putative transactivation domain was mapped to the region between amino acid residues 25 and 63 from the N terminus. These data strongly suggest that GCX-1 is likely a novel transcriptional activator that is exclusively expressed in reproductive tissues involving the hypothalamo-pituitary-gonadal axis, and functions as a specific regulator of follicular development, and may also participate in other specific events related to reproduction, particularly in the female.

RAGE and its ligands: a lasting memory in diabetic complications?

The complications of diabetes are myriad and represent a rising cause of morbidity and mortality, particularly in the Western world. The update of the Diabetes Control and Clinical Trials Group/Epidemiology of Diabetes Interventions and Complications Research Group (DCCT/EDIC) suggested that previous strict control of hyperglycaemia was associated with reduced carotid atherosclerosis compared to conventional treatment, even after levels of glycosylated haemoglobin between the two treatment groups became indistinguishable. These intriguing findings prompt the key question, why does the blood vessel 'remember'? This review focuses on the hypothesis that the ligand/RAGE axis contributes importantly to glycaemic 'memory'. Studies in rodent models of diabetes suggest that blockade or genetic modification of RAGE suppress diabetes-associated progression of atherosclerosis, exaggerated neointimal expansion consequent to acute arterial injury, and cardiac dysfunction. We propose that therapeutic RAGE blockade will intercept maladaptive diabetes-associated memory in the vessel wall and provide cardiovascular protection in diabetes.

Glycation, inflammation, and RAGE: a scaffold for the macrovascular complications of diabetes and beyond

The cardiovascular complications of diabetes represent the leading cause of morbidity and mortality in affected subjects. The impact of hyperglycemia may be both direct and indirect: indirect consequences of elevated blood glucose lead to generation of advanced glycation endproducts, the products of nonenzymatic glycation/oxidation of proteins/lipids that accumulate in the vessel wall, and are signal transduction ligands for Receptor for AGE (RAGE). Although enhanced in diabetes, AGE accumulation also occurs in euglycemia and aging, albeit to lower degrees, driven by oxidant stress and inflammation. In hyperglycemia, production of 3-deoxyglucosone, at least in part via the polyol pathway, provides an amplification loop to sustain AGE generation, oxidant stress, and vascular activation. Furthermore, recruitment of inflammatory cells bearing S100/calgranulins, also ligands for RAGE, augments vascular dysfunction. We hypothesize that activation of RAGE is a final common pathway that transduces signals from these diverse biochemical and molecular species, leading to cardiovascular perturbation. Ultimately, these pathways synergize to construct a scaffold on which the complications of diabetes in the vasculature and heart may be built. We propose that antagonism of RAGE will provide a unique means to dismantle this scaffold and, thereby, suppress initiation/progression of vascular disease and cardiac dysfunction that accompany diabetes and aging.

The dark side of C5a in sepsis

Sepsis is a major clinical problem for which therapeutic interventions have been largely unsuccessful, in spite of promising strategies that were successful in animals, especially rodents. There is new evidence that sepsis causes excessive activation of the complement system and that this induces paralysis of innate immune functions in phagocytic cells due to effects of the powerful complement-activation product, C5a. This review describes our present understanding of how and why sepsis is a life-threatening condition and how it might be more effectively treated.