Background Acute lung injury(ALI) has a high death rate reaching up to 30~40%,because of acute respiratory failure.Experimental evidence has documented the protective effect of hydroxyethyl starch(HES) 200/0.5 on ALI.HES130/0.4 is a novel preparation of colloid with the narrow molecular weight distribution.This study was designed to investigate the effect of HES130/0.4 on lipopolysaccharide(LPS)-induced ALI.

Materials and methods Adult male Sprague-Dawley(SD) rats were randomly divided into six groups(12 rats/group): (a) Sham(saline 30ml/kg); (b) LPS alone(5mg/kg);(c,d and e) LPS(5mg/kg) plus HES (7.5ml/kg, 15ml/kg, 30ml/kg); and (f)HES alone (30ml/kg). HES130/0.4 was infused 1h before administration of LPS.Arterial blood gas,inflammation-related factors,pulmonary capillary permeability,pulmonary neutrophils infiltration and pathological examination were measured 4h after infusing LPS.

Results We demonstrated that administration LPS could provoke severe injury in lung,characterized by PaO₂/FiO₂≦300mmHg.Pretreatment with HES at three different doses of 7.5ml/kg, 15ml/kg, 30ml/kg respectively increased PaO₂ ,while reduced pulmonary neutrophils infiltration, pulmonary capillary permeability and inflammatory factors.The changes of pathology were consistent with the results above,which attenuated lung injury,whereas,administration HES alone had no influence.

Conclusions Pretreatment with 6%HES 130/0.4 at the dose of 15ml/kg most significantly mitigated LPS-induced ALI. The resultant effect might be that HES could downregulate expression of imflammatory factor,block aggregation of PMNs in lung ,reduce generation of oxygen free radicals

Discussion

Severe hypoxemia was the main character of ALI, the pathological changes of which were the high vascular permeability and pulmonary edema induced by non-microvascular endothelial cells injury. The ALI model of rats had been established by LPS at 5mg/kg intravenously in this study and PaO₂/FiO₂≦300mmHg was thought to be one of the crucial standards described previously^[9]. According to the result especially the blood gas ,the rats with ALI were successfully rescued in our study.

ALI participated by pyrogen cells(most of mononuclear cells/macrophages) produce proinflammatory factors (including TNF-α,IL-1,interferon(IFN),IL-6),which causes pyrogen effect in the body and the quantitative change of polymorphonuclear neutrophils(PMNs),provokes various acute phase reactive proteins and destroys pulmonary tissues in the end. TNF-α ,as one of initial critical proinflammatory factors, causes the systematic inflammation through the cooperation with IL-1,which has a amplified effect in the process of inflammation,as called immuno-inflammatory waterfall effect^[10].The elevation of IL-10,as one of endogenous antagonists of TNF-α,restrains the production of proinflammatory factors and their biologic activity^[11].In this study,the values of TNF-α,IL-1β had a significant decrease in the 3 groups of LPS+HES, particularly in LPS+HES₂ group(HES 15ml/kg).At the same time, the value of IL-10 increased significantly in LPS+HES₂ group, implying the protective mechanism of HES ,in part, restrained proinflammatory factors.

Within cellular signaling pathway, NF-κB is one of the critical transcription factors and plays an important role in the physiological or pathological processes of immunity, inflammation and stress response. The main function of NF-κB in these processes is to promote gene expression of diverse cytokines through binding to the definite sites in DNA molecule after entering into the nucleus, and causing inflammation. Many articles have presented the protective effect of HES on LPS-related ALI by reducing the expression of NF-κB^[12~14].The decrease of TNF-α,IL-1β in three groups of LPS+HES may be caused by downregulation of NF-κB expression induced by HES.

The mechanism of capillary permeability syndrome in the processes of injury, shock, ischemic reperfusion or spesis is PMN aggregation and adhesion to endotheliocyte^[15].Activated PMNs that increase the permeability of capillary in lung released a great quantity of reactive oxygen  species and proteinases which induced tissue injury.In ALI, PMNs aggregation in lung play a critical role in increasing capillary permeability^[16].MPO is the specific enzyme in PMNs and the quantity of the MPO in lung determines the extent of PMN aggregation. SOD , a scavenger of hyperoxide radical anion(O₂^¯•), protected pulmonary histiocyte in ALI. MDA, the oxidative product of cellular membrane, could reflect the damage of cellular membrane. In this study, the content of MPO in lung increased, PMNs aggregated in interstitium and the serum level of MDA increased in contrast to decreased  SOD 4h after injecting LPS. Taken above, PMNs aggregation and subsequently increasing oxidative free radicals induced damage and high permeability of pulmonary capillary ,which cascadely result in ALI finally. Administration of HES could decrease the heightened levels of MPO, MDA in serum and raise the activity of SOD. Pathological examination was consistent with the results. Interestingly, group LPS+HES₂ had the best result, indicating administration 6%HES 130/0.4 at the dose of 15ml/kg restrained PMNs aggregation and activation, reduced the generation of oxygen free radicals, mitigated membrane lipid peroxidation and reduced pulmonary injury to the most significant degree among  these 3 groups finally.

PMPI,BALFpro and W/D increased 4h after infusing LPS,impling high pulmonary capillary permeability.Pretreatment with 6%HES 130/0.4 refrained the heightening of PMPI,BALFpro,W/D,which reduced capillary permeability and pulmonary injury.On one hand,HES,a giant molecule,might have the potential to block capillary endothelial cell gaps.On the other hand,HES,which reduced expression of L-selection in PMNs^[17],could restrain adhesion between PMNs and vascular endothelicytes.

In the study, it was designed that in the three groups pretreating with HES at low,medium and high dose respectively,however,it was found that the protective effect of HES on ALI was non-dose-dependent. Tian^[5]et al noted that the activity of NF-κB reduced while using HES at a high dose. Activity of NF-κB might be regulated by several kinds of pathways of mitogen-activated protein kinases. HES could activate different mitogen-activated protein kinases under different doses, which could explain the effect of HES on ALI .Deeply researches should be done for clarifing the mechanism of HES.

,onclusion dosesd withgroups se In conclusion, pretreatment with 6%HES 130/0.4 at the dose of 15ml/kg most significantly mitigated LPS-induced ALI. The resultant effect might be that HES could downregulate expression of imflammatory factor,block aggregation of PMNs in pulmonary,reduce generation of oxygen free radicals and lower microvascluar permeability.

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