Protective role of gambogic acid in experimental pulmonary fibrosis in vitro and in vivo.
Background: Idiopathic pulmonary fibrosis (IPF) is a progressive disorder with poor prognosis. The treatment options for IPF are very limited. Gambogic acid (GA) has anticancer effect and anti-proliferative activity which is extracted from a dried yellow resin of the Garcinia hanburyi Hook.f. [Clusiaceae (Guttiferae)] in Southeast Asia. However, the anti-fibrotic activities of GA have not been previously investigated.
Methods: In this study, the effects of GA on TGF-[beta]1-mediated epithelial-mesenchymal transition (EMT) in A549 cells and endothelial-mesenchymal transition (EndoMT) in human pulmonary microvascular endothelial cells (HPMECs), on the proliferation of human lung fibroblasts (HLF-1) were investigated in vitro, and on bleomycin (BLM)-induced pulmonary fibrosis was investigated in vivo.
Results: In TGF-[beta]1 stimulated A549 cells, treatment with GA resulted in a reduction of EMT with a decrease in vimentin and p-Smad3 and an increase in E-cadherin instead. In TGF-[beta]1 stimulated HPMECs, treatment with GA resulted in a reduction of EndoMT with a decrease in vimentin, and an increase in VE-cadherin instead. In the hypoxic HPMECs, treatment with GA reduced Vasohibin-2 (VASH-2), whereas increased VASH-1. In TGF-[beta]1 stimulated HLF-1, treatment with GA reduced HLF-1 proliferation with a decrease in platelet-derived growth factor (PDGF) and fibroblast growth factor (FGF-2) expressions. In vivo, treatment with GA for 2 weeks resulted in an amelioration of the BLM-induced pulmonary fibrosis in rats with a lower VASH-2. Instead, it was observed a higher VASH-1 expression at early stage of fibrosis at 1 mg/kg, with reductions of the pathological score, collagen deposition, [alpha]-SMA, PDGF and FGF-2 expressions at fibrotic stage at 0.5 mg/kg and 1 mg/kg.
Conclusion: In summary, GA reversed EMT and EndoMT, as well as HLF-1 proliferation in vitro and prevented pulmonary fibrosis in vivo by modulating VASH-2/VASH-1 and suppressing the TGF-[beta]1/Smad3 pathway.
Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, irreversible and usually lethal lung disease, with unpredictable acute exacerbations that are often fatal. However, the cause is unknown (Ley et al. 2011; Raghu et al. 2011). The latest evidences indicated that the fibrotic response is driven by abnormally activated alveolar epithelial cells resulting in epithelial to mesenchymal transition (EMT) and formation of fibroblast and myofibroblast foci. The fibroblast and myofibroblast foci secrete amounts of extracellular matrix (ECM) resulting in scarring and destruction of the lung architecture (King et al. 2011). Several tyrosine kinase receptors were activated and involved the progression of IPF, and nintedanib (BIBF 1120) was approved for treatment of IPF (Myllarniemi et al. 2015).
Pulmonary arterial hypertension (PAH) is an increase of blood pressure in the pulmonary artery, pulmonary vein, or pulmonary capillaries, together known as the lung vasculature, leading to shortness of breath, dizziness, fainting, leg swelling and other symptoms. PAH is common in IPF patients, and the early development of PAH is associated with increased fibrotic cell mediators, abnormal vasculature or response to intermittent hypoxia. IPF patients benefit from treatment of PH (Corte et al. 2009). Vasohibin-1 (VASH-1), a unique endogenous angiogenesis inhibitor is induced in endothelial cells by proangiogenic factors and is a negative feedback regulator of angiogenesis (Nasu et al. 2009), knockdown of VASH-1 in cancer cells promoted cell growth, adhesion and migration in vitro and enhanced angiogenesis in vivo (Liu et al. 2015). Vasohibin-2 (VASH-2), an endogenous and vascular endothelial growth factor (VEGF)-independent angiogenic factor is highly expressed in tumor vessels which regulates tumor angiogenesis (Kitahara et al. 2014).
Gamboge is a dry resin secreted by Garcinia hanburyi Hook.f. [Clusiaceae (Guttiferae)] in Southeast Asia, and gambogic acid (GA, Fig. 1) is the main active compound of gamboge with the content from 22.5% to 34.58% in different areas of China (Yang et al. 1999). GA has various bioactivities including detoxification and anti-inflammatory (Zhao et al. 2010), anti-tumor and antiproliferation (Wu et al. 2004; Cascao et al. 2014). Up to now, no pharmacological activity of GA has been reported in experimental pulmonary fibrosis. Therefore, we investigated the effects of GA on experimental pulmonary fibrosis in vitro and in vivo and proposed a mechanism of action.
Materials and methods
GA (CAS NO: 116064-77-8, molecular formula; C18H1802, purity >98.9%, provided by Paipai biological company, (Guangzhou, PR China); ponatinib (AP, purity >99.0%, CAS NO.: 1232836-257, provided by NCE biomedical company, Wuhan, PR China.); SIS3 (CAS NO: 1009104-85-1, molecular formula: [C.sub.28][H.sub.27][N.sub.3][0.sub.3], purity >98.9%, Santa Cruz Biotechnology, sc-222318); TGF-[beta]1 (T7039, purity >98.0%, Sigma).
Human lung fibroblasts (HLF-1), human pulmonary microvascular endothelial cells (HPMECs) and human type II alveolar epithelial cells (A549 cell line) were purchased from the cell bank of the Chinese Academy of Sciences.
Adult male Sprague-Dawley rats (180-200 g, body weight) were housed individually under constant temperature (22[+ or -]2[degrees]C) and humidity with a 12 h light/dark cycle and with free access to chow and water. All animal experimental procedures in this study were performed in accordance with the Institutional Animal Care and the National Institutes of Health Guide for the Care and Use of Laboratory Animals (Maryland, USA). The protocol was approved by the Committee on the Ethics of Animal Experiments of Binzhou Medical University (Permit Number: SCXK 20110003).
Epithelial-to-mesenchymal transition (EMT) of A549 cells in vitro
The A549 cell line was maintained in Dulbecco's modified Eagle's medium (DMEM) /F12 containing 10% (v/v) fetal bovine serum, 100kU/l penicillin and 100 mg/l streptomycin at 37 [degrees]C in a humidified 5% C[0.sub.2]. The cells were cultured at approximately 70% confluency and starved in the serum-free DMEM overnight. GA was incubated at concentrations of 0, 0.15 and 0.5 |xM or AP at 0.3 [micro]M or a Smad3 inhibitor, SIS3 with or without TGF-[beta]1 5ng/ml for 48 h. Pictures were taken in five random fields under inverted microscope, then the proteins were extracted to detect the expression of vimentin, E-cadherin, Smad3 and p-Smad3 by western blots. Data were normalized against those of the corresponding [beta]-actin bands. Results were expressed as fold increase over the normal.
Endothelial-mesenchymal transition (EndoMT) of HPMECs in vitro
HPMECs were maintained in DMEM (high glucose) containing 10% (v/v) fetal bovine serum, 100kU/l penicillin and 100mg/l streptomycin at 37 [degrees]C in a humidified 5% C[0.sub.2]. The cells were cultured at approximately 70% confluency and starved in serum-free DMEM overnight. GA was incubated at concentrations of 0, 0.15 and 0.5 [micro]M or AP at 0.3 [micro]M with or without TGF-[beta]1 5ng/ml in A549 cells for 48 h, pictured five random fields in the inverted microscope camera, then extracted the protein to detect the expression of vimentin (ab45939) and VE-cadherin (ab1l9785) by western blots. Data were normalized against those of the corresponding [beta]-actin bands. Results were expressed as fold increase over the normal.
HPMECs were cultured in vitro during the hypoxic condition
The HPMECs were maintained in DMEM/F12 containing 10% (v/v) fetal bovine serum, 100kU/l penicillin and 100mg/l streptomycin at 37 [degrees]C in a humidified 5% C[0.sub.2] atmosphere. The cells were cultured at approximately 80% confluency in DMEM, GA were incubated at concentrations of 0, 0.15 and 0.5 [micro]M for 48 h in the hypoxic condition (5% C[0.sub.2], 93% [N.sub.2], 2% [0.sub.2]), then collected the HPMECs, lysed and analyzed VASH-1 and VASH-2 expression. Data were normalized against those of the corresponding [beta]-actin bands. Results were expressed as fold increase over the normal.
HLF-1 proliferation assay
For the proliferation assays in vitro, HLF-1 were seeded into 96-well (1 x [10.sup.5] cells/well) flat bottom plates with medium alone (control) or medium containing the different concentrations of GA (0, 0.15, 0.5 and 1 [micro]M), with or without TGF-[beta]1 5 ng/ml. Cell proliferation was tested by MTT methods. Briefly, the serum-starved cells were treated with GA for 48 h. The absorbance was recorded at 490 nm (Spectramax/M5 multi-detection reader, molecular devices, USA), and calculated as a ratio against the untreated cells. The cells were treated in the same way. PDGF and FGF-2 expression were measured by Western blot.
HLF-1 cells were exposed to cobalt chloride (Co[Cl.sub.2], 100[micro]M) in order to mimic hypoxia. The viability of HLF-1 cells was determined by MTT methods. These HLF-1 cells were seeded into 6-well flat bottom plates. One blank well in every plate was left which was filled with normal HLF-1 cells without Co[Cl.sub.2] and with medium alone as the control. The others were with medium containing the different concentrations of GA (0, 0.15, 0.5 [micro]M) or AP at 0.3 [micro]M (Qu et al. 2015) for 48 h maintained in DMEM (high glucose) containing 10% (v/v) fetal bovine serum, 100kU/l penicillin and 100 mg/1 streptomycin at 37 [degrees]C in a humidified 5% C[O.sub.2]. The expression of PDGF and FGF-2 was measured by Western blot. Data were normalized against those of the corresponding [beta]-actin bands. Results were expressed as fold increase over the normal.
Bleomycin (BLM)-induced pulmonary fibrosis model at the early stage and the fibrotic stage
Seventy SD rats with the mean weight of 150 g were acclimatized for 7 days. The pulmonary fibrosis model was established except for the control animals, and induced according to previous method (Wang et al. 2002; Tanaka et al. 2010) which was induced by a single intratracheal instillation of 5mg/kg bleomycin (BLM) within 0.3 ml of saline (Zhao et al. 2002). The control rats received an equal volume of saline only. Beginning on the day 3, twenty BLM-instilled rats randomly divided into two groups, the BLM-treated group and GA 1 mg/kg group, each group contains 10 rats; on the day 21, the rest forty BLM-instilled rats randomly divided into four groups, the BLM-treated group, GA 0.5 mg/kg group, GA 1 mg/kg group and AP 1 mg/kg group (Qu et al. 2015), each group contains 10 rats. Each GA-treated animal was orally administered daily with GA. The lung was removed at day 17 and day 35, and divided into two parts: one part was frozen in liquid nitrogen, the others fixed in 10% formalin for further analysis.
The collected lung tissue was fixed in 10% formalin and embedded in paraffin, then was sectioned and stained with hematoxylin and eosin (HE) after fixation. Each field was individually assessed for the degree of interstitial fibrosis and graded from 0 to 8 for the increasing extent of fibrosis in lung histological samples. Grade 0, normal lung; grade 1, isolated alveolar septa with gentle fibrotic changes; grade 2, fibrotic changes of alveolar septa with knot-like formation; grade 3, contiguous fibrotic walls of alveolar septa; grade 4, single fibrotic masses; grade 5, confluent fibrotic masses; grade 6, large contiguous fibrotic masses; grade 7, air bubbles; grade 8, fibrous obliteration (Ashcroft et al. 1988). The researcher was blinded to the experimental groups and the mean score of all fields examined was taken as the fibrosis score of each animal. The sections were prepared 4 [micro]m in thickness and stained with Masson's trichrome to investigate the collagen deposition. The percentage of fibrosis in the lung was evaluated by counting the number of pixels corresponding to stained collagen areas from digital images using Adobe Photoshop CS4 as previously described (Loughlin et al. 2007).
The tissue sections (4 [micro]m) were deparaffinized and rehydrated, then treated in 0.01 M citric acid at 400 W in a microwave for 10 min, endogenous peroxidase was inactivated with 5% [H.sub.2][O.sub.2] in methanol for 30 min at room temperature in the dark. Next, the sections were sealed by a serum cap for 30 min and incubated with a rabbit polyclonal anti-VASH-1 or anti-von Willebrand Factor for 16 h at 4 [degrees]C, then washed and incubated with anti-rabbit horseradish peroxidase-conjugated antibody for 60 min at 37 [degrees]C. The samples were viewed by light microscopy.
Measurement of hydroxyproline (Hyp)
The lung tissues were washed with saline and hydrolyzed with 6 ml/1 hydrochloric acid at 100 [degrees]C for 5h. The Hyp content was determined at 560 nm with p-dimethylaminobenzaldehyde and was expressed as milligrams per gram of the wet lung tissue.
Western blots analysis of lung tissue
Lung samples were suspended in a buffer that contained 10 mM Tris (pH 7.5), 1.5 mM MgCl2, 10 mM KC1, and 0.1% Triton X-100 and lysed by homogenization, the supernatant were collected and stored at -80 [degrees]C for western blot analysis. The protein concentration was measured by a bicinchoninic acid (BCA) assay (Smith et al., 1985). After the determination of protein concentration, equal amounts of the protein (about 50 [micro]g) was isolated by SDS-PAGE and transferred to PDVF membrane. Then the membrane was closed by TBST containing 5% skimmed milk power. A variety of proteins were analyzed by western blot using the specific antibodies to [alpha]-SMA (ab5694), PDGF (ab21234), FGF-2 (ab8880), VASH1 (ab176114), VASH-2 (ab199732) and [beta]-actin, after being washed three times by TBST. Optical densities of the bands were scanned and quantified with a Gel Doc 2000. Densities were normalized against those of the corresponding [beta]-actin bands. Results as percentage increase over the sham animal.
Histopathological scores between groups were assessed using sum of ranks test. Quantitative data from experiments were expressed as mean [+ or -] S.D., significance was determined by one-way analysis of ANOVA followed by Dunnett's test. P < 0.05 was considered statistically significant.
Effects of GA on EMT in A549 cells
EMT was enhanced in A549 cells treated with 5 ng/ml of TGF-[beta] 1 for 48 h, as shown in Fig. 2A2. When A549 cells were exposed to GA at 0.15 [micro]M, 0.5 [micro]M, 1.0 [micro]M (Fig. 2A3-2A5) or the positive drug AP at 0.3 [micro]M (Fig. 2A6) for 48 h, the EMT was attenuated. To demonstrate that the alveolar EMT in response to GA or AP in TGF-[beta]1 stimulated A549 cells, the effects of GA at 0.15 or 0.5 [micro]M or AP at 0.3 [micro]M on the expressions of epithelial cell marker E-cadherin and mesenchymal cell marker vimentin in trans-differentiated A549 cells were investigated by western blot. The representative western blot was shown in Fig. 2B. The results showed that E-cadherin was decreased to 58.1%, whereas vimentin was increased to 146.5% after 48 h in TGF-[beta]1 stimulated A549 cells. Comparing to that of TGF-[beta]1 stimulated A549 cells plus GA 0.15 [micro]M and 0.5 [micro]M or AP 0.3 [micro]M, E-cadherin was increased to 77%, 93% and 95%, while vimentin was decreased to 123%, 116% and 113%, shown in Fig. 2C.
In order to clarify the mechanism of GA on the EMT, a Smad3 Inhibitor, SIS3 at 3 [micro]M was used. In addition, the effects of GA at 0.15 [micro]M and 0.5 [micro]M on the TGF-[beta]1/Smad3 pathway were investigated and the representative western blots were shown in Fig. 2D. The results showed that p-Smad3 expression was reduced to 157% and 148% with GA at 0.15 [micro]M and 0.5 [micro]M, as shown in Fig. 2E. GA at the tested concentration didn't affect total Smad3 expression. In addition, GA at 0.15 [micro]M or 0.5 [micro]M plus SIS3 at 3 [micro]M had no significantly different effect compared to GA alone, as shown in Fig. 2F. It suggested that GA attenuated the EMT by modulating the TGF-beta]1/Smad3 pathway.
Effects of GA on EndoMT in HPMECs
EndoMT was enhanced in HPMECs for 48 h, as shown in Fig. 3A2. When trans-differentiated HPMECs were exposed to GA at 0.15 [micro]M, 0.5 [micro]M, 1.0 [micro]M (Fig. 3A3-2A5) or the positive drug AP at 0.3 [micro]M (Fig. 3A6) for 48 h, EndoMT of the HPMECs were attenuated. To demonstrate that the EndoMT of HPMECs in response to GA in the TGF-[beta]1 stimulated HPMECs, the effects of GA at 0.15 [micro]M, 0.5 [micro]M or AP at 0.3 [micro]M on the expressions of the vascular endothelial cell marker VE-cadherin, and the mesenchymal cell marker vimentin in trans-differentiated HPMECs were investigated, as shown in Fig. 3B. The results showed that VE-cadherin expression was decreased to 49%, whereas vimentin was increased to 190% after 48 h in the TGF-[beta]1 stimulated HPMECs. However, GA at 0.15 [micro]M, 0.5 [micro]M or AP at 0.3 [micro]M dramatically attenuated the decrease of VE-cadherin to 70%, 88% and 90%, inhibited the increase of vimentin to 143%, 122% and 117%, as shown in Fig. 3C.
Effects of GA on HPMECs during the hypoxic condition
Compared with no hypoxic condition, the hypoxic condition significantly promoted VASH-2 expression to reach 145%, while VASH-1 expression was significantly decreased to 52% in HPMECs during the hypoxic condition for 24 h, as shown in Fig. 4A. When the hypoxic HPMECs were exposed to GA at 0.15 [micro]M, 0.5 [micro]M or the positive drug AP at 0.3 [micro]M for 24 h. VASH-2 expression was reduced to 123%, 110% and 116%, while VASH-1 expression was increased to 77%, 88% and 94%, as shown in Fig. 4B. It suggested that GA could modulate the rate of VASH-2/ VASH-1 of HPMECs during the hypoxic condition.
Effects of GA on HLF-1 proliferation
The HLF-1 cells were tested in the absence or presence of TGF-[beta]1 to mimic a pro-fibrotic environment. TGF-[beta]1 induced proliferation of the HLF-1, as shown in Fig. 5A2. GA at 0.15-1.0 [micro]M (Fig. 5A3-A5) or the positive drug AP at 0.3 [micro]M (Fig. 5A6) has apparent inhibitory effects on fibroblast proliferation, and the results were shown in Fig. 5B. PDGF and FGF-2 expression was enhanced to 168% and 186% after TGF-[beta]1 stimulated for 48 h, while GA at 0.15 [micro]M, 0.5 [micro]M or AP at 0.3 [micro]M reduced PDGF to 125%, 111% and 110%, and FGF-2 expression to 129%, 114% and 112%, as shown in Fig. 5C and Fig. 5D.
The HLF-1 cells were exposed to Co[Cl.sub.2] (100 [micro]M) in order to mimic the hypoxia condition in IPF. Hypoxia stimulates cell proliferation, up-regulating the expression of PDGF and FGF, resulting in the development of pulmonary fibrosis. However, GA at 0.15 [micro]M, 0.5 [micro]M or AP at 0.3 [micro]M prevented cell proliferation induced by hypoxia with reducing PDGF expression to 128%, 108% and 107%, and reducing FGF-2 to 132%, 112% and 110%, as shown in Fig. 6A and Fig. 6B.
Effects of GA on bleomycin-induced vascular remodeling during the early stage of pulmonary fibrosis
In order to investigate the mechanism of GA on vascular remodeling during the early stage of the BLM-induced pulmonary fibrosis, von Willebrand factor (vWF) and VASH-1 were staining by immunohistochemical staining method. The biomarker of angiogenesis, vVF, is expressed on the endothelial cell largely. The vWF positive cells were significantly increased in the BLM-treated animals. VASH-2 was increased, whereas VASH-1 was decreased in the BLM-treated animals. The vWF and VASH-2 were significantly attenuated in the GA-treated animals compared to the BLM-treated animals, and higher VASH-1 was found in GA-treated animals, as shown in Fig. 7A and Fig. 7B. In addition, VASH-1 and VASH-2 expression were determined by Western blot analysis. The results showed that GA-treated animals have higher VASH-1, whereas lower VASH-2 was noted, as shown in Fig. 7D and Fig. 7E.
The grades of histopathological change at day 17 in the three groups are presented in Fig. 7C. In the semi-quantitative assessment of lung sections, no inflammatory or fibrotic changes were observed in lungs of the sham rats. The BLM-treated animal produced a significant increase in the pathology score as compared to the sham animals. Continuous GA treatment for 14 days decreased the BLM-induced pathology scores by 45%, as shown in Table 1. Those results suggested that GA inhibited histopathological change at the early stage of pulmonary fibrosis by improving vascular remodeling.
Effects of GA on histopathological change and collagen content in pulmonary fibrosis model
The grades of histopathological changes at day 35 in these groups are presented in Fig. 8A, Fig. 8B and Table 1. In the semi-quantitative assessment of the lung sections, no inflammatory or fibrotic changes were noted in the lungs of the control rats, as shown in Fig. 8A1. At day 35, a significant increase in the pathology score was noted in the BLM-treated animals, compared to the control animals, as shown in Fig. 8A2. Continuous GA 0.5mg/kg (Fig. 8A3), GA 1 mg/kg (Fig. 8A4) or AP 1 mg/kg (Fig. 8A5) treatment for 14 days decreased the BLM-induced pathology score by 29%, 49% and 47 %, as shown in Table 1.
The collagen content was observed with Masson's trichrome staining, as shown in Fig. 8B. The interstitial lungs of the rats in the BLM-treated animal exhibited a large amount of collagen, as shown in Fig. 8B2. The collagen content was significantly reduced in GA-treated (Fig. 8B3 and Fig. 8B4) or AP-treated (Fig. 8B5) rats. Significant increases in the collagen and Hyp content were noted in the BLM-treated animals, compared to the control animals. Continuous GA 0.5 mg/kg, GA 1 mg/kg or AP 1 mg/kg treatment for 14 days decreased the BLM-induced collagen content by 48%, 55% and 59%, decreased the BLM-induced Hyp levels by 37%, 47% and 46% as shown in Fig. 8C and Table 1.
Effects of GA on [alpha]-SMA, FGF-2 and PDGF expression in pulmonary fibrosis model
At day 35, FGF-2, [alpha]-SMA and PDGF expressions increased in BLM-treated lung tissue were determined by western blot. We compared the effects of AP on FGF-2, [alpha]-SMA and PDGF expression with GA. Results exhibited GA 1 mg/kg has similar potency in reducing FGF-2, [alpha]-SMA and PDGF expression with AP, as shown in Fig. 8D and Fig. 8E. The results of in vitro and in vivo studies showed that GA inhibited the EMT and the fibroblast proliferation. The results of in vitro and in vivo studies all showed that GA could inhibit the trans-differentiation and fibroblast proliferation.
IPF is a progressive disorder with poor prognosis. The treatment options for IPF are very limited. At present, the main aim of IPF treatment is to relieve symptoms as much as possible and to slow down the progression. Therefore, the identification of a novel therapeutic target in predinical tests is greatly needed. GA administered orally at dosages of 120 mg/kg for 13 weeks can lead to the damage on the kidney and liver (Qi et al. 2008). A safe dose was established to be 60 mg/kg which is approximately 18.0 (body weight) or 9.6 (body surface area) times higher than that of the dose (200 mg) used for human trials (Qi et al. 2008). In our studies, each GA-treated rat was only orally administered daily with GA 0.5 and 1 mg/kg for 2 weeks. This dose and the route of administration are considered safe to use in clinic.
The latest evidences indicate that the fibrotic response is activated by abnormally type II AEC which boosts EMT. Fibroblasts are differentiated into myofibroblasts, which were noted both in animal model and clinic (King et al. 2011). Among them, Smad3 is a critical mediator. The signaling of Smad3 is modulated via phosphorylation and cytosol-nucleus translocation and regulated the lung phenotype in pulmonary fibrosis. Inhibition of Smad3 or pSmad3 can reduce TGF-[beta]1-induced EMT and fibrosis (Derynck et al. 2003; Wang et al. 2013). The results showed that GA reduced EMT with lower p-Smad3 and vimentin and higher E-cadherin expression. It suggested that GA attenuated the EMT by modulating the TGF-[beta]1/Smad3 pathway.
PAH, a life-threatening disease is characterized by elevated pressure in the pulmonary artery and abnormal remodeling of the lung vasculature. The early development of PAH is associated with increased fibrotic cell mediators, abnormal vasculature or response to hypoxia, seen in IPF. PAH worsens the prognosis of patients with IPF. It means that PAH and IPF are a dangerous duo (Adir et al. 2014). EndoMT is a newly recognized type of cellular transdifferentiation, and is another possible source of myofibroblasts which plays an important role in the pathogenesis of PH, so inhibition of EndoMT may represent a novel therapeutic target for PH including IPF (Piera et al. 2012; Piera et al. 2011). GA treatment resulted in inhibition of EndoMT and normalization of vimentin and VE-cadherin expression. The HPMECs treated with GA in majority, are resistant to the TGF-[beta]1-induced EndoMT, whereas GA-untreated controls are more vulnerable to EndoMT. It suggested that GA reduced the TGF-[beta]1-induced EndoMT, thus reduced the incidence of PAH and delayed IPF.
The specific marker of endothelial cells vWF, is expressed in large amounts on endothelial cells which controls and regulates angiogenesis (Randi et al. 2013) during PAH. An endothelium-derived angiogenesis inhibitor, VASH-1, is produced by the endothelial cells (ECs). VASH-2, a homologue of VASH-1, which was transcriptionally activated can promote angiogenesis (Kimura et al. 2009; Sato et al. 2013; Xue et al. 2013). Down-regulation of VASH-2 suppresses tumor growth by inhibiting angiogenesis (Koyanagi et al. 2013). During the phase of PAH formation, the aberrant pulmonary microvascular endothelial cells were activated largely, VASH-2 was largely expressed which leads to an abnormal angiogenesis. Our study showed that GA treatment reduced VASH-2 expression, while increased VASH-1 expression in the hypoxic HPMECs and the BLM-induced PAH animals. These results suggested that GA modulated VASH-1 and VASH-2 expression to ease PAH by ameliorating the abnormal vascular remodeling.
Compared with the normal lung tissue-derived fibroblasts, pulmonary fibrosis-derived fibroblasts or myofibroblasts synthesize more ECM, especially the collagen (Bocchino et al. 2010). The Hyp level is another indicator to show the degree of collagen deposition in fibrotic lung (Tanaka et al. 2010). Therefore, the effect of GA on the changes of both Hyp levels and the collagen deposition in BLM-treated lungs were investigated. The results showed enhanced collagen deposition and Hyp levels in the BLM-treated lungs, whereas the situation was ameliorated after GA treatment. This suggested that GA exerts anti-pulmonary fibrosis effects by reducing the collagen deposition.
The percentage of [alpha]-SMA is higher in myofibroblasts of IPF samples (Ramos et al. 2001). PDGF and FGF-2 play important roles in IPF. Inhibition of PDGF and FGF-2 expression attenuates fibrosis (Chaudhary et al. 2007). A gradual increase of PDGF and FGF-2 was observed both in TGF-[beta]1 stimulated HLF-1 cells and BLM-treated lungs. The Smad3 signaling has been demonstrated in TGF-[beta]1-mediated regulation of cell proliferation (Nicolas et al. 2003). Our study showed GA reduced PDGF and FGF2 in the TGF-[beta]1 stimulated HLF-1 cells and Co[Cl.sub.2] stimulated HLF-1 cells, reduced PDGF and FGF-2 in the BLM-treated animals. These findings suggested that GA ameliorated proliferation and pulmonary fibrosis by suppressing the TGF-[beta]1/Smad3 pathway.
AP prevented the EMT, inhibited HLF-1 proliferation and ameliorated pulmonary fibrosis by TGF-[beta]1/Smad3 pathway (Qu et al. 2015). We compared the anti-fibrotic effects of AP with GA. Results exhibited GA has similar potency in inhibiting EMT, endoMT, HLF-1 proliferation, PDGF and FGF-2 expression in vitro, ameliorating fibrosis severity in fibrotic lung in vivo.
In summary, it demonstrated that GA prevented the EMT and endoMT, modulated the rate of VASH-1/VASH-2 at early stage of BLM-induced pulmonary fibrosis, inhibited TGF-[beta]1 and Co[Cl.sub.2] stimulated HLF-1 proliferation with reduction of PDGF and FGF-2 in vitro, and ameliorated BLM-induced pulmonary fibrosis with a lower rate of VASH-2/VASH-1 at early stage of fibrosis, with reductions of the pathological score, collagen deposition, [alpha]-SMA, PDGF and FGF-2 expressions at fibrotic stage.
In conclusion, GA has potentially antifibrotic effect; the mechanism might be due to the inhibition of the TGF-[beta]1/Smad3 pathway. These findings suggest that GA can be a new multi-target drug to use in pulmonary fibrosis therapy during the early stage and the fibrotic stage.
Abbreviations: [alpha]-SMA, alpha smooth muscle actin; AP, ponatinib; AT I, Human type 1 alveolar epithelial cell line; BLM, bleomycin; ECM, extracellular matrix; EMT, epithelial-mesenchymal transition; EndoMT, endothelial-mesenchymal transition; FGF-2, fibroblast growth factor; GA, gambogic acid; HE, hematoxylin and eosin; HPMEC, human pulmonary microvascular endothelial cells; Hyp, hydroxyproline; IPF, idiopathic pulmonary fibrosis; PAH, pulmonary arterial hypertension; PDGF, platelet-derived growth factor; VASH-1, vasohibin-1 ; VASH-2, vasohibin-2; vWF, von Willebrand factor.
Received 20 August 2015
Revised 12 January 2016
Accepted 24 January 2016
Conflict of interest
The authors confirmed that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.
The study was supported by the National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809 (grant N0.31270391), in part financially supported by the domestic visiting scholar project funding of Shandong Province outstanding young teachers and Taishan Scholar Project to Fang Han.
Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.phymed.2016.01.011.
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Yubei Qu (1), Guanghua Zhang (1), Yunxia Ji Haibo Zhua, Changjun Lv, Wanglin Jiang*
The Key Laboratory of Traditional Chinese Medicine Prescription Effect and Clinical Evaluation of State Administration of Traditional Chinese Medicine, School of Pharmacy, Binzhou Medical University, Yantai, P.R. China
* Corresponding authors. Tel.: +86 535 6912036; fax: +86 535 6912036.
E-mail addresses: Lucky_lcj@sina.com (C. Lv), firstname.lastname@example.org (W. Jiang).
(1) These authors contributed equally to this work and should be considered co-first authors.
Table 1 Effects of GA on grade of lung fibrosis and Hyp content in BLM-induced fibrosis model. Groups Grade of fibrosis Day 17 Day 35 Sham 0.2 [+ or -] 0.4 0.3 [+ or -] 0.7 BLM-treated 5.4 [+ or -] 0.9# 4.5 [+ or -] 0.9# AP 1 mg/kg -- 2.4 [+ or -] 0.6 ** GA 0.5 mg/kg -- 3.2 [+ or -] 1.2 * GA 1 mg/kg 3.3 [+ or -] 0.7 ** 2.3 [+ or -] 0.7 ** Groups Hyp (mg/g tissue) Sham 0.83 [+ or -] 0.11 BLM-treated 5.45 [+ or -] 1.12# AP 1 mg/kg 2.95 [+ or -] 0.48 ** GA 0.5 mg/kg 3.43 [+ or -] 0.87 ** GA 1 mg/kg 2.87 [+ or -] 0.53 ** All data were shown as mean [+ or -] S.D., n = 10 in each group. Hyp, hydroxyproline; AP, ponatinib; GA, gambogic acid; BLM, bleomycin. # P < 0.01 versus the Sham group; * P < 0.05, ** P < 0.01 versus the BLM-treated group. Grade of fibrosis between groups were compared using sum of ranks test. The significance of Hyp content was determined by one-way analysis of ANOVA followed by Dunnett's test.
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|Author:||Qu, Yubei; Zhang, Guanghua; Ji, Yunxia; Zhua, Haibo; Lv, Changjun; Jiang, Wanglin|
|Publication:||Phytomedicine: International Journal of Phytotherapy & Phytopharmacology|
|Date:||Apr 15, 2016|
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