Role And Mechanisms Of High Mobility Group Box1Protein In Acute Lung Injury Of Severely Burned Rats With Delayed Fluid Resuscitation

1. IntroductionAcute lung injury (ALI) is one of the major complications of major burns,especially in the patients with inhalation injury, shock, and delayed resuscitation. It mayresult in anoxia, which will lead to distant organ damage and the development ofmultiple organ dysfunction syndrome (MODS), accounting for significant morbidityand mortality in severe burns. It has been documented that the diffused alveolarcapillary injuries resulted from uncontrolled inflammatory response played a centralrole in the development of ALI.High mobility group box chromosomal protein1(HMGB1), known as an abundant,non-histone architectural chromosomal protein, is highly conserved across differentspecies. It was originally discovered as a DNA binding protein that facilitates DNAreplication and repair. During inflammation and trauma, it can be releasedextracellularly by macrophages and other immune cells. Recent studies showed thatHMGB1can also be "passively released" into the extracellular milieu by necrotic anddamaged somatic cells. HMGB1induces endothelial cytokine expression, causesepithelial barrier dysfunction, and activates macrophages and neutrophils to releaseinflammatory mediators. It not only initiates the early inflammation, but also canaggravate the late inflammation. However, it has been little information regarding therole of HMGB1in the acute lung injury of severe burns.In this study, severely burned rats with delayed resuscitation were utilized toinvestigate the pulmonary HMGB1expression, the TNF-α and IL-8levels in serum and bronchoalveolar lavage fluid, and the activations of MAPKs. Sodium butyrate, ashort-chain fatty acid was used to inhibit the expression of HMGB1. The findings of thepresent study will provide a new insight into the development of ALI postburn.2. ObjectiveThis study aimed to investigate the role and preliminary mechanisms of HMGB1inacute lung injury of severe burns with delayed fluid resuscitation.3. Materials and MethodsPart Ⅰ Role of HMGB1in acute lung injury of severe burns with delayed fluidresuscitation.Female Sprague–Dawley rats weighing200to250g were purchased from theExperimental Animal Center of Anhui Medical University and housed at constanttemperature for one week. All rats were randomly divided into three groups:1)shamgroup(n=8);2) burn plus Lactated Ringer’s group (n=24);3) burn plus LactatedRinger’s solution and sodium butyrate-treated group (n=24). The rats were anesthetizedwith3%pentobarbital sodium (30mg/kg) by IP injection. The dorsal hair of the animalswas shaved to allow direct skin contact to hot water. We developed a device for creatingburn injury on the back of rats. It consists of a wooden plate with a circular opening thatexposes30%TBSA. After anesthesia, the animals were placed on the device in thesupine position. Each rat, along with the device, was immersed into hot water (98°C) for12seconds, resulting in a full-thickness skin burn injury. Sham animals were subjectedto identical procedure but were immersed into water at room temperature. The burnedrats were then resuscitated with an IP injection of2ml/kg/TBSA of Lactated Ringer’ssolution at6,12,36hours postburn. Sodium butyrate was diluted1:150in Ringer’slactate fluid. The rats in sodium butyrate group were treated with sodium butyratelactated Ringer’s solution in the same manner. That is, the amount of sodium butyrategiven was400mg/kg. Subsequently, burned animals were scarified at12h,24h and48h postburn for bronchoalveolar lavage (BAL), histologic evidence, and pulmonaryHMGB1and intercellular adhesion molecule-1(ICAM-1) expressions. A separate groupof sham burn rats were subjected to an identical preparation except that they wereimmersed in room temperature water and were not given any fluid resuscitation.Part Ⅱ The role and mechanism of HMGB1in the pulmonary lipid peroxidationdamage after severe burns with delayed fluid resuscitation.The animal divisions, burn procedures, and treatment methods were identical toPart one. The lung was harvested for the examination of the activity of MPO and thecontent of MDA. The pulmonary expressions of p38MAPK and JNK were detected byimmunohistochemistry. The process of sham rats was also identical to Part one.4. ResultsPart ⅠA30%TBSA full-thickness burns trauma followed by delayed fluid resuscitationresulted in elevated lung water content, worsen histologic condition, and increasedTNF-α and IL-8levels in serum and BALF. HMGB1and ICAM-1expressions in lungwere also increased after severe burn and delayed resuscitation. All these events weresignificantly abolished by the administration with sodium butyrate.Part ⅡA30%TBSA full-thickness burns trauma followed by delayed fluid resuscitationresulted in increased MPO activities and elevated MDA content in the lung. Thepulmonary expressions of p38MAPK and JNK were also increased after severe burnand delayed resuscitation. All these events were significantly abolished by theadministration with sodium butyrate.5. ConclusionHMGB1mediates the release of TNF-α, IL-8and ICAM-1, the activation of PMN, andlipid peroxidation damage, involving the activation of p38MAPK and JNK signal pathways, and contributes to burn and delayed resuscitation-induced acute lung injury.