subject: The Effect of a Novel Cytokine, High Mobility Group Box 1 [print this page] The Effect of a Novel Cytokine, High Mobility Group Box 1
Protein, on the Development of Traumatic Sepsis*
YAO Yong-ming, SHENG Zhi-yong, and HUANG Li-feng
Sepsis and subsequent multiple organ dysfunction syndrome (MODS) are frequent complications after severe traumata or burns involving a large area, and these remain as the two most common causes of morbidity and mortality in critical illnesses. Despite the recent rapid advances in intensive care technologies and the use of costly treatments with new antibiotics, the mortality in patients with severe sepsis still reaches as high as 40% to 50% in many countries. Therefore, our efforts to understand the pathogenesis of sepsis after severe burns and to seek a novel intervention strategy to prevent and treat sepsis seem more urgent. Modern viewpoints believe that the activation of the systemic inflammatory system plays a key role in the incidence of sepsis. The data have confirmed that the nosogenetic components from bacteria, including lipopolysaccharide (LPS) from gram-negative bacteria and exotoxins from gram-positive bacteria, as well as bacterial DNA, are important factors in inducing inflammatory responses. Pathogenic microorganisms and their toxic products can quickly activate the body's natural immune system, thus, leading to over-synthesis and release of pro-inflammatory cytokines, such as tumor necrosis factor (TNF)- and interleukin (IL)-1. In recent years, the antagonists of these cytokines have been studied in clinical trials to treat patients with severe sepsis or septic shock. Unfortunately, the results were not satisfactory. The main reason was that these cytokines are released in the early stages of sepsis into the blood, thus, leaving little time for intervention or a narrow therapeutic window for drug administration. Therefore, the clinical intervention is too late to be effective.
A Late-stage Inflammatory Mediator in the Process of Sepsis, High Mobility Group Box I Protein
High mobility group box 1 (HMGB1) protein has recently aroused great interests. It belongs to DNA-binding nuclear protein, and may stabilize nucleosomes and promote gene transcription. Activated monocytes and macrophages may release a large amount of HMGB1 when stimulated by LPS, TNF-or IL-1. Nine to 16 h after the attack, blood HMGB1 level significantly increased in patients with endotoxemia and sepsis, and the increase time obviously lagged behind such "early" inflammatory mediators as TNF-, IL-1 , and so on. HMGB1 can also activate monocytes and neutrophils, contributing to a variety of cytokine production and further stimulating cells to secrete more HMGBI. This process belongs to the autocrine pathway, which further leads to the cascade effect of the body's inflammatory response. Thus, HMGB1 acts as a late mediator of the inflammatory reaction in the human body. It is reported that the serum HMGB1 level in dead patients was markedly higher than that in survivors. The significant increase in serum HMGB1 level after hemorrhagic shock in animal models and the enhanced HMGB1 expression in pulmonary tissues at the same time suggest that HMGB1 may be involved in the pathological process of hemorrhagic shock induced acute lung injury. One prospective study in a population of patients with severe sepsis or septic shock shows that HMGB1 level obviously elevated and lasted in the majority of patients for a week after the onset. The existence of HMGB1 may exacerbate and prolong the process of the inflammation process of the body. Further experiments demonstrated that after treatment with anti-HMGB1 antibody or other HMGB1 antagonists, animals can
*Supported, in part, by Grants from the National Basic Research Program of China (No. 2005CB522602), National Natural Science Foundation of China (No. 30672178, 30872683, 30800437), and National Natural Science Outstanding Youth Foundation of China (No. 30125020)
avoid suffering from MODS secondary to sepsis and the inflammatory response. Besides, the obvious efficacy was still observed when the medication time was obviously later than intervention by other cytokines. Even when anti-HMGB1 intervention was conducted 24 h after infection, the mortality of sepsis significantly reduced, which undoubtedly provided a sufficient time window for the clinical treatment of fatal sepsis.
HMGB1 Expression and Its Regulatory Mechanism after Acute Injury
Our study revealed that thermal injury induced a delayed increase of HMGB1 mRNA expression in various tissues. During the early post-burn phase, HMGB1 mRNA levels were not significantly different between animals in the normal control group and the burned animals group, but the HMGB1 mRNA expression was significantly enhanced 24 h after burns, and lasted 72 h after burns. Similarly, recent schlors reported that serum HMGB1 concentration was significantly elevated within the first 24 h after the onset of hemorrhagic shock and lasted for 72 h. Furthermore, we noted that plasma HMGB1 level was significantly elevated in patients with sepsis, and was markedly lower in the survival group than in the deceased group, suggesting that timely monitoring of the circulatory HMGB1 level may be beneficial to the observations in severe burns care course and the judgment of prognosis. The aforementioned data indicated that HMGB1 level could be up-regulated by various injuries. HMGB1 release was a delayed, continuous process and the dynamic characteristics were significantly different from early inflammatory mediators, such as TNF- , IL-1 , etc.
Recent in vitro studies demonstrated that LPS or LPS induced inflammatory mediators could stimulate the release of HMGB1. Our previous studies have shown that burns can lead to gut-derived endotoxi
n translocation and accumulation in different tissues. Based on these findings, we further explored the effect of gut-derived endotoxin translocation on the HMGB1 expression in tissues after thermal injury. It was found that the application of recombinant bactericidal/ permeability-increasing protein (a natural protein with anti-endotoxin activity) significantly reduced the level of toxins in each organ, and the expression level of HMGB1 also decreased. Therefore, the endotoxin translocation plays an important role in regulating HMGB1 expression after acute injury. It was reported that the concentration of HMGB1 significantly increased in animals after an LPS challenge. In recent clinical studies, no significant correlation been found between HMGB1 levels and the burned area, but plasma HMGB1 levels were positively correlated with endotoxin concentrations on day 3, 5, 7, 21 after severe burns. These findings indicate that up-regulation of HMGB1 expression may be closely correlated with endotoxin-mediated sepsis after severe trauma.
Relationship between HMGB1 and Cellular Immunity
As a new late-stage inflammatory mediator, HMGB1's effect on immune function after trauma has not been fully explored. In view of this, we investigated the effects of HMGB1 on T lymphocyte-mediated immunity secondary to severe burns. Animal experimental results showed that the proliferative response of splenic CD3+ T lymphocytes was obviously inhibited from the 1st day to the 7th day after injury, and the plasma HMGB1 level was significantly negatively correlated with spleen T lymphocyte proliferative activity. After the application of HMGB1 inhibitor, the plasma HMGB1 level markedly decreased from the 1st to the 5th day after injury. Meanwhile, the proliferative activity of spleen T lymphocytes increased from the 1st to the 7th day. Clinical data shows that lymphocyte proliferation response and IL-2 production in the peripheral blood, and the ratio of CD4+/CD8+ T lymphocytes in MODS group were markedly lower than those in the non-MODS group on PBDs (post-burn days) 1, 14, 21 and 28. It was also revealed that the plasma HMGB1 level was negatively correlated with T cellular immune function parameters, including the lymphoproliferation response, IL-2 release and the ratio of CD4+/CD8+ T lymphocytes in patients suffering from severe burns. These findings support that HMGB1 release in a large amount might possibly be associated with the dysfunction of T lymphocyte after a severe injury. In addition, we investigated the effect and mechanism of HMGB1 on the immune function of human T lymphocytes in vitro. The results demonstrated that HMGB1 had a bi-directional effect on the immune function of T lymphocytes. On one hand, a low dose of HMGB1 could initiate an inflammatory response by inducing secretion of Thl type cytokines from T lymphocytes. On the other hand, along with the increase in the concentration as well as the action duration of HMGB1, HMGB1 may promote a Th2-polarizing stimulus to suppress T-cell-mediated immune function.
Effect of Xuebijing Injection on HMGB1 Expression and Immune Function after Trauma
Xuebijing Injection is a traditional Chinese preparation with the main ingredients extracted from Flos Carthami, Radix Paeoniae Rubra, Rhizoma Chuanxiong, Radix Salviae Miltiorrhizae and Radix Angelicae Sinensis, etc. It is a prescription for removing blood stasis and relieving toxic substance, mainly used for the treatment of epidemic febrile diseases. The recommended dosage is 50 mL Xuebijing Injection added in 100 mL saline for intravenous dripping (completing the dripping within 30-40 min) for patients with systemic inflammatory response syndrome, 2-3 times a day. Currently, it has been reported that Xuebijing Injection can effectively prevent and treat sepsis and multiple organ dysfunction both in experimental as well as clinical settings, while the precise mechanism remains to be elucidated. To address this issue, we investigated the effects of Xuebijing Injection on HMGB1 expression and multiple organ dysfunctions in rats with delayed resuscitation after burn shock. The results show that both mRNA and protein expressions of HMGB1 were significantly enhanced in the lung, liver and kidney from 8 to 72 h after burns. Xuebijing Injection could significantly down-regulate tissue HMGB1 mRNA as well as protein expressions, and lower the values of parameters pertaining to the function of multiple organs following injury. Moreover, the mortality of animals receiving Xuebijing Injection 12 h after burns was significantly lower than that of burn controls (40% vs 75%, P
