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In this study we examined the effects of hydroxyethyl starch (HES 200/0.5) on lung capillary permeability in endotoxic rats and explored the possible mechanisms. Male Wistar rats were randomly divided into seven groups treated with saline, lipopolysaccharide (LPS; 6 mg/kg), LPS plus HES (3.75, 7.5, 15, or 30 mL/kg), or HES (30 mL/kg) alone for 4 or 2 h. Lung capillary permeability, lung neutrophil accumulation, expression of CD11b on the blood neutrophil cell surface, lung cytokine-induced neutrophil chemoattractant protein level, and nuclear factor kappa B (NF- B) activation in blood neutrophils and lungs were measured. HES at doses of 3.75 and 7.5 mL/kg significantly reduced LPS-induced increases of lung capillary permeability. HES was found to inhibit lung neutrophil accumulation, cytokine-induced neutrophil chemoattractant protein, and NF- B activation in parallel and to inhibit CD11b expression in a dose-dependent manner. These findings demonstrate that HES has beneficial effects on capillary leak in acute lung injury and that the mechanisms underlying this action involve an antiinflammatory effect of HES, including inhibition of NF- B activation. IMPLICATIONS: A randomized, controlled laboratory experiment indicated that hydroxyethyl starch (HES) could reduce increased lung capillary permeability in endotoxemia. This effect may be due to an antiinflammatory effect of HES.
Hydroxyethyl starch (HES) solutions are modified natural polymers of amylopectin. They are often used as plasma expanders, in part because of their therapeutic safety, stable effects on plasma volume, and few associated incidences of anaphylactic reactions. Some animal studies imply that fractionated HES solutions with a molecular range of 1001000 kDa may be capable of plugging leaky capillaries in inflammatory states (1,2). This potential effect of HES has recently been demonstrated in trauma patients (3). However, there are also studies with contradictory results (4). Therefore, additional studies need to be performed to clarify this protective effect of HES, and, if possible, explore the potential mechanisms that have not yet been interpreted.
Endotoxemia is always accompanied with systemic inflammatory response syndrome, which induces multiple organ failure, including the lung, liver, and kidney. Microvascular injury and increased vascular endothelial permeability are its characteristic features. One crucial event that leads to this injury is neutrophil activation followed by neutrophil infiltration and accumulation in various organs. Bacterial endotoxin (lipopolysaccharide; LPS) can induce the expression of adhesion molecules (E selectin, P selectin, and intercellular adhesion molecule-1 [ICAM-1]) on endothelial cells; activate and upregulate integrins (CD11b/CD18) on the neutrophil cell surface (5); cause the expression of chemokines, including interleukin (IL)-8 and cytokine-induced neutrophil chemoattractant (CINC) in several constitutive cells and resident macrophages (6,7); and release other proinflammatory cytokines (tumor necrosis factor (TNF)-
Nuclear factor-
No studies have investigated the effects of HES on capillary permeability in acute endotoxemia. In this study, we used a third-generation HES with a medium molecular weight and a low degree of substitution (HES 200/0.5) to determine its effect on lung capillary permeability in endotoxic rats, the effects on lung neutrophil accumulation, expression of CD11b on the blood neutrophil cell surface, lung CINC protein level, and NF-
Male Wistar rats weighing 250300 g were purchased from the Animal Center of the Chinese Academy of Science, Shanghai, China. The rats were fed rat chow with free access to tap water and housed in temperature- and humidity-controlled animal quarters with a 12-h light/dark cycle. All procedures were approved by the Institutional Animal Care Committee. Animals were anesthetized with urethane (1250 mg/kg intraperitoneally [IP]). A polyethylene catheter was implanted in the right external jugular vein for the continuous infusion of solutions by using a Razel Model WZ-50C syringe pump. The rats were randomly divided into seven groups (six rats per group): 1) controls, 2) LPS; 36) LPS plus HES 3.75, 7.5, 15, or 30 mL/kg; and 6) HES alone (30 mL/kg). Immediately after the time reading, LPS (6 mg/kg IP; Escherichia coli O55:B5, Sigma Chemical Co., St. Louis, MO) was given over 20 s. HES (HAES-Steril 200/0.5, 6%; Fresenius Kabi) was infused beginning at 1 min at 0.2 mL/min. In the control and HES-alone groups, 0.9% saline vehicle (3 mL/kg IP) was given instead of LPS at Time 0. In the control and LPS groups, saline 30 mL/kg was infused instead of HES. In a pilot study, the blood pressure of rats was measured with a microtip manometer (Millar, Houston, TX) inserted into the femoral artery; no significant hemodynamic instability was encountered during the procedure. The rats were killed by exsanguination 4 h after the LPS challenge, and lung microvascular permeability was assessed by quantitating the extravasation of Evans blue dye into lung parenchyma. In another set of experiments, animals underwent the same treatments. Heparinized blood samples were obtained by a cardiac puncture with a heparin-coated 18-gauge needle either at 2 h (for neutrophil isolation and electrophoretic mobility shift assay [EMSA]) or 4 h (for flow cytometry analysis) after LPS challenge. The lung tissue was also collected either at 2 h (for EMSA) or 4 h (for determination of lung wet/dry weight ratio, myeloperoxidase [MPO] analysis, and enzyme-linked immunosorbent assay [ELISA]) after LPS challenge, frozen in liquid nitrogen, and stored at -80°C. Lung capillary permeability was assessed with the Evans blue dye extravasation method (12). Briefly, animals were injected with 2% Evans blue (20 mg/kg; Sigma Chemical Co.) via the jugular vein 15 min before killing. After the rats were killed, the lungs were removed, and the wet weight was determined. The dye was then extracted from the tissue by incubation with 4 mL of formamide for 24 h at 37°C. The quantity of dye extracted was determined spectrophotometrically at 620 nm and calculated from a standard curve established with known amounts of Evans blue dye. Results are expressed as milligrams of dye per gram of wet tissue. To determine the lung wet/dry weight ratio, lung tissue samples were taken after the rats were killed. Excess fluid was blotted from specimens, and wet weights were measured immediately. Dry weights were measured after drying specimens at 80°C for 72 h to constant weight. The lung wet/dry weight ratio was then calculated. Lung MPO activity was determined as an index of tissue neutrophil accumulation. To measure tissue MPO activity, frozen lungs were thawed, and MPO was extracted by homogenization and sonication, as described previously (13). MPO activity in the supernatant was measured and calculated from the absorbance (at 460 nm) changes resulting from decomposition of H2O2 in the presence of o-dianisidine. The lung tissue CINC content was measured by an ELISA with a Rat GRO/CINC-1 immunoassay kit (Amersham, UK) according to the manufacturers instructions. Blood samples from each animal collected at 4 h after the LPS challenge were prepared for cytometric analysis. After the lysing procedure, the number of leukocytes per sample was counted. Then 5 x 106 cells were incubated with a phycoerythrin-labeled mouse anti-rat CD11b antibody (Serotec, Oxford, UK) on ice for 30 min. After samples were washed, they were cold-centrifuged, and the cell pellet was resuspended in 500 µL of phosphate-buffered saline. The cells were then read on a Becton-Dickinson FACSCalibur. Negative controls were incubated with phycoerythrin-labeled mouse immunoglobulin G2a (Serotec). Neutrophils were isolated by using Ficoll-Paque gradient centrifugation and dextran sedimentation. After hypotonic lysis of residual red blood cells, neutrophils were collected. Viability, as determined by trypan blue exclusion, was consistently >95%. Neutrophil purity, as determined by Wrights staining cytospin preparations, was >98%. Neutrophils were then stored at -80°C.
Nuclear extracts of the lung tissues and neutrophils were prepared by hypotonic lysis followed by high salt extraction. Briefly,
EMSA was performed by using a commercial kit (Gel Shift Assay System; Promega, Madison, WI). The NF- All data were expressed as mean ± SE. Statistical significance was determined by one-way analysis of variance, followed by Tukeys test; P < 0.05 was considered significant.
We used the Evans blue dye extravasation method to study the lung capillary permeability. Challenge with LPS caused a 2-fold increase in the microvascular permeability index in the lung (Fig. 1). Treatment of the LPS-challenged animals with HES 3.75 and 7.5 mL/kg, but not 15 and 30 mL/kg, significantly reduced (P < 0.05) the LPS-induced increase in permeability. HES alone had no effect on permeability index.
The wet/dry weight ratio, which represents the percentage of tissue water, is another index of tissue microvascular permeability. The results of this study were in parallel with those of the Evans blue dye study (Fig. 2). LPS significantly increased the lung wet/dry weight ratio. Rats co-treated with HES 3.75 and 7.5 mL/kg, but not 15 and 30 mL/kg, had decreased ratios compared with rats treated only with LPS. HES alone had no significant effect.
We studied the functional consequence of HES on neutrophil influx into the lungs by using MPO activity as an index of tissue neutrophil accumulation. As shown in Figure 3, MPO levels were significantly increased from 0.38 ± 0.013 U/g in control rats to 0.67 ± 0.029 U/g in the LPS group of rats and were reduced to 0.51 ± 0.015 U/g, 0.48 ± 0.026 U/g, 0.56 ± 0.040 U/g, and 0.60 ± 0.033 U/g in the rats treated with LPS plus HES 3.75, 7.5, 15, or 30 mL/kg. Control rats and rats treated with HES alone had similar lung MPO activities.
Increased surface expression of ß2 adhesion molecules is important for neutrophil adherence to endothelial cells. As shown in Figure 4, LPS caused a more than twofold increase in surface expression of CD11b. Rats given increasing doses of HES progressively decreased the expression. Treatment of the LPS-challenged animals with HES 3.75, 7.5, 15, and 30 mL/kg reduced the LPS-induced increase of CD11b expression by 28%, 33%, 47%, and 50%, respectively. Treatment of control animals with HES did not affect the CD11b level on neutrophils.
CINC plays a pivotal role in neutrophil recruitment and acute lung injury. To address whether HES affects lung CINC expression, we compared CINC protein levels in different groups. ELISA results showed low CINC protein levels in control lungs (Fig. 5); these levels increased by 2.5-fold in lungs of LPS-challenged animals. Treatment with HES 3.75, 7.5, and 15 mL/kg significantly reduced (P < 0.05) the LPS-induced increase in CINC levels. HES alone had no effect on CINC expression.
To investigate the possible mechanism of HES action, we performed the EMSA experiment to examine the effect of HES on the activation of NF- B induced by LPS. We quantitated these NF- B bands by using densitometry. As shown in Figure 6, the NF- B activity was low in nuclear protein from control lungs and neutrophils but was markedly increased in specimens from LPS-challenged rats. This increased NF- B activity was inhibited by treatment with HES in a dose-related manner. The maximal inhibition of LPS-induced increase in NF- B activity was observed at the HES dose of 7.5 mL/kg in both specimens. This was the same dose at which HES maximally inhibited an LPS-induced increase in lung microvascular permeability (Fig. 1), lung wet/dry weight ratio (Fig. 2), lung accumulation of neutrophils (Fig. 3), and lung CINC protein expression (Fig. 5).
The major focus of this study was to determine the effect of HES on lung capillary permeability in endotoxic rats and the mechanistic bases that underlie the possible effect. Our results showed that early treatment of HES (200/0.5) at doses of 3.75 and 7.5 mL/kg significantly reduced LPS-induced increases of lung capillary permeability.
Neutrophils play a central role in experimental models of acute lung leak. After being activated and mediated by adhesion molecules, integrins, and chemotactic factors, neutrophil accumulation is increased in lungs of endotoxic animal models. Neutrophils then release several toxic substances, including reactive oxygen species and proteolytic enzymes, that cause capillary leak and lung injury (9). In this respect, understanding the mechanisms by which HES reduces the increased capillary permeability should provide information on the regulation of processes that can contribute to the pathogenesis of acute lung leak. In this study, we provide evidence that HES could inhibit LPS-induced increases of lung neutrophil accumulation, CD11b expression on the blood neutrophil cell surface, lung CINC protein level, and NF-
Several studies have reported that HES molecules are able to reduce increases in microvascular permeability after ischemic insults in the spinal cord and cremaster muscle or after thermal burn (1,14,15). Our finding in an endotoxic rat model is consistent with these previous reports. In addition, our studies extend these previous observations by showing that the effect of HES is not dose dependent. Although doses of HES 3.75 and 7.5 mL/kg showed a significant reduction in lung capillary permeability, larger doses of 15 and 30 mL/kg did not. The question that arises is as follows: How do starch macromolecules affect the microvascular permeability? Zikria et al. (16) postulated that HES macromolecules act by physically sealing the barrier defects created by the injury. This hypothesis was formed on the basis that increased transport is associated with a widening of the interendothelial cleft in postcapillary venules. However, Suval et al. (17) found increased extravasation of macromolecules in the presence of normal microvascular ultrastructure. Furthermore, electron microscope evidence confirmed that separation of interendothelial clefts is not a necessary element for increases in microvascular permeability (18). Also, the dose-related manner of HES found here is hard to elucidate with only a physically sealing mechanism. There must be additional mechanistic bases that underlie the actions of HES. Oz et al. (14) demonstrated that HES might affect microvascular dysfunction by influencing neutrophil binding to stimulated endothelial cells. However, they did not know the mechanism of this effect. Pascual et al. (19) reported that HES could reduce neutrophil-mediated tissue injury through inhibition of neutrophil L-selectin expression. Our present findings suggest the in vivo linkage between improvement in microvascular permeability of HES and its reduction of neutrophilic inflammation, which involves its inhibition of CD11b expression, CINC level, and NF- Activated neutrophils have been implicated as pathogenic mediators of injury to tissues and, in particular, to the microcirculation system. The critical common step is the adhesion of the activated neutrophils (5). Firm adhesion of neutrophils is mediated by ß2 integrins (CD11b/CD18) and ICAM-1. The role of ß2 integrins in lung injury has been determined by the application of blocking antibodies. Anti-CD11b antibodies were found to reduce complement-mediated lung injury (20). In vitro studies have tested the influence of HES on the expression of the adhesion molecule CD11b on neutrophils and found no significant inhibition effect of HES (21). However, the in vivo function has not been established. We observed that HES could inhibit LPS-induced increases of CD11b expression on neutrophils in a dose-dependent manner. This result is consistent with the hypothesis of Nohe et al. (22). They found that HES did not attenuate adhesion molecule expression but showed an immediate decreasing effect on neutrophil adhesion. They thought that this was due to its inhibition on interactions of neutrophilic ß2 integrins with their endothelial counterreceptors. CINC is structurally and functionally related to human IL-8. It is a potent chemotactic factor for rat neutrophils both in vitro and in vivo. Frevert et al. (23) reported that approximately 50% to 70% of neutrophil chemotaxis in LPS-induced pulmonary inflammation is caused by CINC. Because CINC itself can increase the expression of CD11b/CD18 integrin on rat neutrophils (23) and because expression of leukocyte adhesion molecules such as E selectin is dependent on CINC (24), the inhibition of lung CINC level by HES that we observed in our study may exert both direct and indirect effects on neutrophil vascular adhesion and extravascular migration.
In our study, we found that HES at doses of 3.75 and 7.5 mL/kg significantly reduced LPS-induced NF- Emphasis should be placed on the hemodynamics, which are obviously important during the procedure because reversal of systemic hypotension would also influence microvascular disorders and thus would not allow discrimination between the effects of HES on macrohemodynamics and microcirculation per se. We measured the blood pressure of the rats in our pilot study, and this variable did not differ among the seven groups, indicating that the animals were hemodynamically stable. Minor hemodynamic changes probably could not be excluded because other measurements such as cardiac output (CO) and systemic vascular resistance (SVR) were lacking. We did not study CO and SVR in our experiment because, on the one hand, measurements of CO and SVR were invasive procedures and because repeated blood sampling of >1 mL during the procedure would likely influence the hemodynamics in such a limited circulating blood volume as in the rat; on the other hand, the changes of blood pressure were similar among the seven groups. However, these presumably minor changes would surely not influence hemodynamic stability. The fact that blood pressure differences among the groups were absent in the model used indicates that the improvements of microvascular permeability and reduction of neutrophilic inflammation by HES are not caused by reversal of macrohemodynamics disturbances.
Another noteworthy phenomenon in our experiment is that the maximal effect of HES was observed at a dose of 7.5 mL/kg in most cases. This may be because most mediators are regulated by many factors. Besides NF-
In summary, we have shown that HES (200/0.5) at doses of 3.75 and 7.5 mL/kg significantly reduced LPS-induced increases in lung capillary permeability. The proposed mechanism is that HES inhibits LPS-induced NF-
We thank Dr. Genbao Feng for technical assistance.
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