1. Introduction
Inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn’s disease (CD), is a worldwide healthcare problem characterized by chronic and recurring inflammation in the intestinal tract [
1,
2]. Up to date, the pathogenesis of IBD has not been clearly clarified, which may be relevant to genetic susceptibility, environmental factors, and intestinal flora, subsequently affecting the immune response, resulting in inflammation [
2,
3]. Also, oxidative stress could activate inflammatory mediators, which should not be neglected [
4]. More seriously, it has been widely accepted that IBD is an important risk factor for the development of colorectal cancer [
5]. Current treatments of IBD mainly rely on the usage of aminosalicylic acids, corticosteroids, thiopurines, and biologic drugs [
6]. However, these drugs are often expensive and associated with side effects or undesirable clinical efficacy [
7]. Therefore, investigation of novel therapeutic drugs for IBD treatment is needed.
Finding potential therapeutic candidates from natural products based on food and complementary and alternative medicine has become attractive, due to their long history of use. In recent years, a series of herbal compounds with anti-inflammatory effects have been reported with the possibility of treatment for IBD, such as gingerol, curcumin, resveratrol and anthocyanins [
8,
9,
10]. Plant-derived substances capable of ameliorating IBD symptoms could potentially enlarge the scope of drug candidates.
Angelica sinensis and
Zingiber officinale Roscoe are two common dietetic Chinese herbs which are traditionally applied for complementary treatment of gastrointestinal disorders [
11]. The major components of them in common are volatile oils, which are a group of constituents with various bioactivities, including anti-inflammatory, anti-oxidant, and anti-cancer activities [
12,
13]. Previous studies proved the anti-inflammatory effects of
Angelica sinensis’s volatile oils on acute inflammation model rats [
14], and essential oils from
Zingiber officinale Roscoe could inhibit leukocyte migration to exert an anti-inflammatory effect [
15]. In addition, gingerols and their derivatives, as important constituents in
Zingiber officinale Roscoe, are non-volatile pungent compounds with multiple functions, which have been reviewed by Butt et al. [
16]. Specifically, gingerols showed protective effects on IBD mice and rats by reducing cytokines and adjusting oxidative stress [
17,
18]. A random clinical trial indicated that the supplementation of ginger powder orally could improve treatment of UC patients with significant reduction of malonic dialdehyde (MDA) [
19]. Furthermore, our previous study proved the chemo-preventive potential of
Angelica sinensis on an Azoxymethane/Dextran sodium sulphate induced colorectal cancer model [
20]. Taken together, the combination of
Angelica sinensis and
Zingiber officinale Roscoe have potential for the treatment of IBD.
It is well known that choosing the proper extract method is necessary for the improvement of extract quality and yield. Supercritical fluid extraction is an efficient and environmentally friendly method to extract non-polar constituents from vegetal sources, especially for those thermal unstable compounds [
21]. It is a great choice to extract potential anti-colitis components from the two above mentioned herbs by this method.
Many animal models have been applied to study IBD, such as chemical-induced colitis models, models of spontaneous colitis, and genetically engineered animal models. Among them, chemically induced models are most commonly used due to their reproducibility and ease of operation [
22]. The chemical substance 2,4,6-trinitrobenzenesulfonic acid (TNBS) is commonly used for induction of IBD, and many previous studies used a TNBS-induced rodent model to evaluate the therapeutic potency of various substances on IBD [
7,
23].
Therefore, the first aim of this study was to obtain the supercritical fluid extract of Angelica sinensis and Zingiber officinale Roscoe (AZ-SFE) after optimization of extraction process parameters by orthogonal experimental design and to characterize it. In addition, the anti-inflammatory potential of AZ-SFE in vitro was investigated by detecting NO production on lipopolysaccharide (LPS)-induced RAW264.7 cells. Moreover, the anti-colitis effects of AZ-SFE on a TNBS-induced colitis rat model were evaluated through different biological activities.
3. Discussion
Natural products from medicinal and edible plants are supposed to be alternative treatments for chronic inflammatory diseases [
24,
25]. The multiple active constituents in plants are considered to act simultaneously on different targets to exert therapeutic effect [
23]. In the present study, we optimized the extraction process of AZ-SFE, and analyzed the extract both qualitatively and quantitatively by GC/MS and HPLC methods, respectively. Subsequently, the obtained AZ-SFE with a stable quality was applied to the ensuing bioactivity evaluation.
Macrophages as important immune cells play a vital role in the inflammation response. Shin et al. found that macrophages could be accumulated and activated in dextran sodium sulphate (DSS)-induced colonic tissues [
26]. Activated macrophages can secrete many kinds of inflammatory mediators, resulting in the progression of inflammatory diseases. LPS-induced RAW264.7 macrophages are classically used to evaluate the anti-inflammatory effect in vitro. NO, a pro-inflammatory mediator synthesized by iNOS, can be overproduced under the stimulation of LPS. Therefore, the inhibitory ability of AZ-SFE on NO production was assessed to preliminarily evaluate the anti-inflammatory effect. Results proved the anti-inflammatory activity of AZ-SFE, because of the significant and dose-dependent suppression of NO production. The in vitro study encouraged us to further investigate the anti-colitis activity of AZ-SFE on TNBS-induced rat model.
Immunological abnormity is one of the factors involving the pathogenesis of IBD [
27]. Immunosuppressors like azathioprine have been applied for the treatment of moderate to severe patients [
6]. The spleen is an important immune organ, containing a large number of T lymphocytes which can be non-specifically stimulated by Con A. IFN-γ can induce macrophages to produce TNF-α, IL-1β, IL-2, and IL-6, which together aggravate inflammation and magnify Th1 response in a positive feedback regulation [
7]. The proliferation of ex vivo splenocytes induced by Con A was suppressed by AZ-SFE. Additionally, the levels of IFN-γ and IL-2 in cell cultures were reduced by AZ-SFE in a dose-dependent manner. Based on our findings, it could be speculated that the immunoregulating effect of AZ-SFE is related to the modulation of Th1 response, and the anti-colitis mechanism of AZ-SFE involves immunoregulation.
In vivo study revealed an anti-inflammatory effect of AZ-SFE in TNBS-induced rats with the alleviation of disease activity and macroscopic damage. Furthermore, histological evaluation supported the reduction of pathological changes by AZ-SFE intervention. It has been widely accepted that oxidative stress is one of the important pathogenic factors involving the development of IBD [
28]. Oxidative stress and the resulting lipid peroxidation could exacerbate free radical chain reactions, disrupt the integrity of intestinal mucosa, and activate inflammatory mediators [
29]. SOD is an important antioxidant enzyme which is able to scavenge free radicals, and hinder oxidative damage [
30]. MDA is a major product of lipid peroxidation as a consequence of oxidative stress [
31]. Our results showed that AZ-SFE increased SOD activity and decreased MDA concentration in colonic tissue of TNBS-induced rats, indicating the amelioration of intestinal injury was at least partly related to the reduction of oxidative stress. Neutrophil infiltration is one of the most prominent histological features observed in IBD [
29]. MPO activity can be used to evaluate the degree of neutrophil infiltration [
32,
33]. Our findings revealed that increased MPO activity induced by TNBS could be weakened after administration of AZ-SFE at test doses, showing the protective effect of AZ-SFE against tissue injury in experimental colitis.
Pro-inflammatory cytokines are important in the pathogenesis of IBD. Increased levels of pro-inflammatory cytokines have been detected in IBD patients [
34,
35]. TNF-α takes part in tissue inflammation through recruitment of leukocytes in an inflamed area, stimulation of expression of cytokines, and induction of cascade effects for other cytokines [
36]. IL-6 also plays a vital role in the progression of colonic inflammation, which can promote lymphocyte proliferation, and is important in acute phase inflammation response [
36,
37]. IL-1β is another important cytokine to accelerate intestinal inflammation by facilitating the production of IL-17A, indicating IL-1β to be a promising target in IBD therapy [
38]. Taken together, targeting pro-inflammatory cytokines is one of the therapeutic approaches for IBD treatment. In the current study, the production of IL-6, TNF-α, and IL-1β in serum of TNBS-induced rats was increased. Treatment with AZ-SFE in two doses significantly reduced the expression of tested cytokines, with the dose of 60 mg/kg showing the better effect.
Anemia is one of the symptoms of IBD, whose pathogenesis is related to the abnormal elevation of hepcidin, the key modulator of systemic iron homeostasis [
39]. Hepcidin is an antimicrobial peptide which is mainly generated in liver in response to iron overload, or upregulation by pro-inflammatory stimuli, such as IL-6 [
40]. The cellular iron export protein ferroportin is the receptor of hepcidin. The combination of hepcidin and ferroportin contributes to the reduction of circulating iron. Therefore, it is supposed that increased level of hepcidin leads to decreased serum iron, consequentially iron-restricted impairment of erythropoiesis, and even anemia [
41]. Many researchers have been interested in finding the correlation between hepcidin and IBD, which up till now has not been fully clarified. Some reported the elevated expression of hepcidin in IBD patients, while others claimed no differences or even decreased hepcidin levels compared with healthy controls [
42,
43,
44]. In the TNBS-induced rat colitis model, the expression of hepcidin in the colon could be increased associated with the activation of IL-6/STAT 3 pathway [
45]. Also, hepcidin has been proposed to be directly involved in IBD pathogenesis, since the severity of experimental colitis could be relieved in
Hfe knockout mice with low hepcidin expression [
46]. Taken together, we intended to investigate the effect of AZ-SFE on the regulation of hepcidin in our study.
To some extent, our results support the explanation that the higher hepcidin level in TNBS group is the consequence of the more severe inflammation state, as Toblli et al. described [
47]. Administration of AZ-SFE and mesalazine decreased the production of hepcidin, indicating the potency of AZ-SFE on the regulation of iron homeostasis. The expression of hepcidin was related to the production of IL-6, as shown in our research, which was consistent with former research. Also, the serum iron level was decreased in the TNBS group, while it was significantly increased by the administration of mesalazine and AZ-SFE (60 mg/kg). On one hand, the increased expression of hepcidin lead to the decrease of serum iron [
41]. On the other hand, infiltrating cells may enter the blood and utilize serum iron for their proliferation, and the sequestration of serum iron by iron storage proteins may lead to the low level of serum iron [
48]. These findings indicated that AZ-SFE could involve in the regulation of system iron homeostasis, which may be related to its anti-inflammatory activity.
Furthermore, intestinal epithelial cells provide a physical barrier to protect the body from pathogens as well as toxins [
49]. The dysfunction of intestinal barrier, such as increased intestinal permeability plays an important role in the pathogenesis of IBD. Therefore, the protection and improvement of intestinal barrier function may be a potential therapeutic strategy for IBD [
50]. The effects of AZ-SFE on the intestinal barrier will be investigated in our further research.
4. Materials and Methods
4.1. Chemicals and Reagents
Ligustilide (S13M9D55861) was obtained from Shanghai Yuanye Biotechnology Co., Ltd., (Shanghai, China). 6-gingerol (MUST-16122205) was purchased from Chengdu Man Site Biotechnology Co. Ltd., (Chengdu, China). Methanol and Acetonitrile were HPLC grade (Sigma-Aldrich, USA). High glucose DMEM was purchased from Corning Incorporated (Corning, NY, USA). Fetal bovine serum (FBS) was obtained from Biological Industries Ltd. (Herzliya, Israel). Penicilin/streptomycin was obtained from Invitrogen (Carlsbad, CA, USA). TNBS (P2297–10 mL) was purchased from Sigma-Aldrich (St. Louis, MO, USA). Mesalazine was obtained from Ethypharm Pharmaceutical Co. Ltd., (Shanghai, China). All other reagents used were of analytical grade.
4.2. Plant Material and Preparation of AZ-SFE
Fresh Zingiber officinale Roscoe roots were bought in a local market (Beijing, China). Angelica sinensis was purchased from Beijing Sanhe Yaoye Co., Ltd. (Beijing, China). They were identified at the Beijing University of Chinese Medicine as per the identification standard of Pharmacopoeia of the People’s Republic of China, 2015. Fresh Zingiber officinalle Roscoe roots were cut into slices and dried at 40 °C. Then they were smashed into 40 mesh. Extraction was conducted using a HA220-50-06 supercritical fluid extraction system (Hua’an Supercritical Extraction Co., Ltd. Nantong, China). Ground powders (40 mesh) of Angelica sinensis and Zingiber officinalle Roscoe were weighted and extracted together at a ratio of 7:4 which is based on a traditional usage. When the temperatures in both extraction and separation vessels met the requirement, liquid CO2 was pumped into the extraction system at a flow rate of 25 L/h. The pressure of first separation vessel was 8 MPa; the temperature of first separation vessel was 55 °C; while those of second separation vessel were system tail pressure and 35 °C. After extraction, the products were collected from the first separation vessel, weighted and stored at −20 °C for further analysis.
4.3. GC/MS Analysis of AZ-SFE
GC/MS analysis of AZ-SFE was carried out on Agilent 7890B GC system coupled with 5977A mass selective detector (Agilent Technologies Inc., Santa Clara, CA, USA) in electronic ionization mode (ionization energy: 70 eV). The GC column was Agilent HP-5ms (30 m × 0.25 mm, 0.25 μm). AZ-SFE was dissolved in chloroform for analysis. The heating temperature was as follows: Hold at 50 °C for 5 min, rise to 170 °C at the rate of 10 °C/min, and hold for 5 min; then rise to 230 °C at the rate of 3 °C/min and hold for 3 min; finally rise to 280 °C at the rate of 5 °C/min and hold for 5 min. Inlet temperature and transmission line temperature were both 250 °C. Helium was used as carrier gas at a flow rate of 1 mL/min. The injection volume was 1 μL with a split ratio of 10:1. Ion source temperature was 230 °C and quadrupole the temperature was at 150 °C. The scan scale was 30–600 amu.
4.4. HPLC Analysis of AZ-SFE
The contents of ligustilide and 6-gingerol in AZ-SFE were detected by HPLC in a Thermo Ultimate 3000 HPLC system with a variable wavelength detector (Thermo Fisher Scientific Inc., San Francisco, CA, USA) using an Inertsil ODS-C18 column (4.6 mm × 250 mm, 5 μm). The column temperature was 30 °C, and 10 μL of the sample solution was injected for detection. AZ-SFE, ligustilide and 6-gingerol were dissolved in methanol as a sample solution and reference solution, respectively. The flow rate was 1 mL/min. For detection of ligustilide, the mobile phase was methanol-water (70:30), and the detection wavelength was 326 nm. For detection of 6-gingerol, the mobile phase was acetonitrile-methanol-water (40:5:55), and the detection wavelength was 280 nm [
51]. The specificity, linearity, precision, repeatability, stability, and recovery rate of analytical methods were validated.
4.5. Optimization of Extraction Process of AZ-SFE
An L
9 (3
4) orthogonal experiment design was conducted to investigate the optimum parameters in the extraction process. The factors and levels were listed in
Table 4 according to pre-experiments and literature review. The extract yield, ligustilide content and 6-gingerol content were chosen as evaluation indexes with weight coefficients of 0.5, 0.3, and 0.2, respectively. The colligation score of each extraction was calculated based on weight coefficient after data normalization. Optimum extraction parameters were screened by both visual analysis and analysis of variance by SAS 8.0.
4.6. Cell Culture and MTT Cell Viability Assay
The RAW264.7 cell line was obtained from the Cell Resource Center, Chinese Academy of Medical Sciences (Beijing, China). RAW264.7 cells were cultured in high glucose DMEM supplemented with 10% FBS and 1% penicillin/streptomycin (complete medium) at 37 °C, 5% CO
2. AZ-SFE was dissolved in DMSO to be 10 mg/mL as stock solution. MTT cell viability assay was conducted at first to select concentrations without cytotoxicity based on the method of Mosmann with minor modifications [
52]. RAW264.7 cells were seeded in 96-well plates (1 × 10
4 cells/well) and cultured for 24 h. Then cells were incubated with gradient concentrations of AZ-SFE (0.625 to 40 μg/mL), ligustilide (2.5 to 160 μM), and 6-gingerol (2.5 to 160 μM) for 24 h. Then 10 μL of MTT solution (5 mg/mL) was added to each well and the cells were cultured for another 4 h. The supernatants were discarded and the formazan crystals formed in living cells were dissolved in DMSO. The plate was shaken in orbital shaker for 10 min, after which the optical density was measured at 490 nm using a microplate reader system (SPECTROstar Nano, BMG LABTECH, Ortenberg, Germany). The medium group contained only complete medium, and vehicle group contained 0.5% DMSO in complete medium. The cell viability was calculated as follows:
Where OD represents the average optical density of samples at the same concentration, and OD
0 represents for the average optical density of vehicle controls (0.5% DMSO in medium).
4.7. Measurement of NO Production in RAW264.7 Cells
RAW264.7 cells were seeded into 96-well plates (1 × 10
5 cells/well) and precultured for 24 h at 37 °C, 5% CO
2. After discarding the supernatants, cells were treated with different concentrations of AZ-SFE (0.625 to 20 μg/mL) or the combinations of ligustilide and 6-gingerol, at their corresponding concentrations in AZ-SFE for 1 h. After stimulation with or without LPS (1 μg/mL) for 24 h, the cell supernatants were collected and detected for NO production by Griess method using a commercial kit (Beijing BioDee Biotechnology Co. Ltd., Beijing, China) [
53]. Briefly, 50 μL of supernatant was mixed with the same volume of Griess reagent I and II. After incubation at room temperature for 5 min, the optical density was measured at 540 nm. The concentration of NO was calculated by comparing with sodium nitrite standard curve. The inhibition rate of NO was calculated as follows:
Where C
1 represents the average concentration of model controls (1 μg/mL LPS in medium), C
0 represents the average concentration of blank control and C represents the average concentration of samples at the same concentration.
4.8. Experimental Animals
Thirty male Sprague Dawley rats (180–200 g) were purchased from SPF Biotechnology Co., Ltd. (Beijing, China) and maintained in the animal experiment center of Beijing University of Chinese medicine. Animals were housed under controlled conditions of temperature (25 ± 2 °C) and humidity (50 ± 10%) with a 12-h light-dark cycle, and fed with standard diet and water. The experimental procedures were approved by the Animal Care and Research Ethics Committee of the Beijing University of Chinese Medicine.
4.9. Induction of Experimental Colitis and Intervention with AZ-SFE
Rats were randomly divided into 5 groups (
n = 6): Control group, TNBS group, positive drug (mesalazine, 400 mg/kg) group, and AZ-SFE (30 and 60 mg/kg) groups. Colitis was induced by intrarectal administration of a single dose of TNBS, as described previously, with modifications [
54]. Briefly, rats were anesthetized by 10% chloral hydrate (3 mL/kg), and TNBS (100 mg/kg) dissolved in ethanol (50%,
v/v) was instilled into the colon, using a gavage needle lubricated by liquid paraffin, and inserted into 8 cm from anus. To ensure the agent within the entire colon and avoid drug leakage, rats were held in a head-down position for 3 min. Control group received only saline by the same method.
From the next day after modeling, drugs were administered once a day by gavage (1 mL/100 g body weight) for seven consecutive days. Then the rats were anesthetized and blood were collected from abdominal aorta. The entire colons were collected, and washed in cold saline. All specimens were stored at −80 °C before analysis.
4.10. Splenocyte Proliferation and Cytokine Detection
The spleens of rats in the TNBS group were aseptically taken out, and they were ground with PBS and filtered through 200 mesh. After removing red blood cells by lysis and centrifugation, splenocytes were obtained. Cells were precultured in RPMI 1640 complete medium (supplemented with 10% FBS and 1% penicillin/streptomycin) for 2 h to remove adherent cells. Then cells in suspension were counted and seeded into 96-well plates (5 × 105 cells/well). Cells were stimulated with 5 μg/mL Con A to maintain inflammation status, and AZ-SFE (5, 10 and 20 μg/mL) were supplemented and incubated for 24 h. Cells treated with Con A were named the Con A group, and cells without any intervention were labelled blank control group. After incubation, culture medium in each well was collected and centrifuged. Supernatants were collected for cytokine detection, and cells were cultured with MTT in medium for another 4 h, for proliferation detection. The optical density was measured at 550 nm. The levels of IL-2 and IFN-γ in supernatants were measured using ELISA kits (RayBiotech Inc., Norcross, GA, USA) according to the manufacturer’s instructions.
4.11. Evaluation of DAI
Body weight, stool consistency and fecal bleeding of rats were monitored daily, and the DAI was calculated as the average score of three above mentioned aspects. In weight loss, score 0 was assigned for no weight loss compared with the original body weight, 1 for loss of 1–5%, 2 for loss of 5–10%, 3 for loss of 10–20% and 4 for loss > 20%. For stool consistency, score 0 was assigned for normal stool, 2 was assigned for loose stool and 4 was assigned for diarrhea. For fecal bleeding, score 0 represented no blood, 2 represented occult blood and 4 represented obvious bleeding [
55].
4.12. Evaluation of Macroscopic Damage
The colon was cut longitudinally and cleaned by cold saline for macroscopic observation. The macroscopic severity of colonic mucosal damage was determined according to the criteria of Luk et al. [
56]. Briefly, the score was on a 0–10 scale. The more severe the damage was, the higher the score was.
4.13. Histological Analysis
Colon samples were fixed in 10% formalin at room temperature for 48 h, and embedded in paraffin blocks. Sliced sections (3 μm) were deparaffinized and stained with H&E. The sections were observed and photographed under an ECLIPSE Ts2R microscope (Nikon Corp., Tokyo, Japan). Colonic damage was evaluated according to previous standard [
57] with a total score of 10.
4.14. Measurement of SOD, MDA and MPO in Colonic Tissue
Colonic tissues were homogenized, and the supernatants were collected for detection. The activities of SOD and MPO, as well as the level of MDA were analyzed with commercial test kits (Nanjing Jiancheng Bioengineering Institute, Nanjing, China).
4.15. Measurement of Pro-inflammatory Cytokines in Serum
Blood samples collected from abdominal aorta were placed at room temperature for 2 h to clot, and they were centrifuged at 3000 rpm for 10 min in order to collect serum. The levels of IL-6, TNF-α and IL-1β in serum were detected using ELISA kits, according to the manufacturer’s instructions. The kit for IL-6 was purchased from Cloud Clone Corp., (Wuhan, China), and those for TNF-α and IL-1β were obtained from RayBiotech Inc. (Norcross, GA, USA).
4.16. Measurement of Hepcidin and Serum Iron
Serum hepcidin was measured by competitive ELISA (Cloud Clone Corp., Wuhan, China). Concentrations of serum iron were detected by colorimetry using a test kit (Nanjing Jiancheng Bioengineering Institute, Nanjing, China).
4.17. Statistic Analysis
Data obtained were presented as the mean ± standard deviation (SD). Statistical analyses were performed using one-way ANOVA, followed by Dunnett’s multiple comparisons tests for multiple comparisons using in SAS 8.0. p < 0.05 was considered statistically significant.
