The Anti-Inflammatory Effect of Smilax china L. Extract on LPS-Stimulated THP-1 via Downregulation of MAPK and NF-κB Signaling Pathway

Background Traditional Chinese medicine Smilax is the rhizome of liliaceous plant Smilax china L., which is used to treat pelvic inflammatory disease and anxieties. Purpose To investigate the mechanism of anti-inflammatory activity of the extract from Smilax china L. (ES). Methods The components of ES were identified by UPLC-QTOF-MS/MS. The anti-inflammatory activities were evaluated in xylene-induced ear oedema and egg white-induced plantar swelling test. Cell viability was examined by CCK-8 assay. The inflammatory mediators, proinflammatory cytokines, and MAPK and NF-κB signals in LPS-stimulated THP-1 cells were determined using ELISA, real-time PCR, and Western blot, respectively. Results 20 compounds of ES were confirmed by comparing with the reference substance. ES displayed more prominent anti-inflammatory activity than the positive control “Jin Gang Teng” capsule in the in vivo acute inflammatory model. ES suppressed the expression of PGE2 and 6-Keot-PGF1α, and the ratio of IC50 (COX-1)/IC50 (COX-2) of ES was 3.15, which indicated that ES could selectively inhibit COX-2. ES dose-dependently (12.5, 25, and 50 mg/L) decreased the production and mRNA levels of proinflammatory cytokines IL-1β, IL-6, and TNF-α. Furthermore, ES significantly decreased LPS-induced phosphorylation of p38, JNK, ERK1/2, and p65, inhibiting the expression of IKKα and the degradation of IκBα. Conclusion The results suggested that ES could selectively inhibit the activity of COX-2, and the anti-inflammatory effect of ES was associated with the inhibition of IL-1β, IL-6, and TNF-α via negative regulation of MAPK and NF-κB signaling pathways in LPS-induced THP-1 cells.


Introduction
Inflammation is the first response occurring after damage or infection, which was regulated by many inflammatory mediators, including cyclooxygenase-2 (COX-2), prostaglandin E2 (PGE 2 ), and proinflammatory cytokines (IL-1β, IL-6, and TNF-α) [1][2][3]. It has been generally accepted that the excessive production of proinflammatory cytokines and mediators due to monocytes and macrophages activation plays an important role in the progression of many inflammatory disease, such as rheumatic arthritis, chronic bronchitis, colitis, and glomerulonephritis [4]. During the inflammatory condition, monocytes and macrophages are activated; they secrete massive proinflammatory cytokines to regulate immune responses. Simultaneously, a large amount of PGE 2 is generated by the inducible proteins COX-2, which induces the body's response to pain and inflammation [5].
LPS-induced THP-1 cells have been widely used as an in vitro model because THP-1 which is a human leukemia monocytic cell line can be stimulated by LPS to trigger the activation of multiple inflammatory signals such as mitogen-activated protein kinases (MAPKs) and nuclear transcription factor kappa-B (NF-κB) [6,7]. MAPKs containing p38 MAPK, ERK, and JNK have important functions on regulation of cell differentiation, cell growth, and cellular response to cytokines in the immune system [8]. NF-κB signaling pathway plays a crucial role in regulating inflammation through transcription of COX and cytokine genes [9]. NF-κB is normally located in the cytoplasm with its inhibitor IκBα. However, LPS stimulation induces phosphorylation of IκBα leading to translocation of NF-κB into the nucleus where it activates transcription [10]. e activation of MAPK and NF-κB triggers the expression of genes encoding downstream inflammatory mediators and eventually causes inflammatory actions [11]. Smilax china L., also known as "Jin Gang Teng," belongs to Liliaceae family. As a commonly used traditional Chinese medicine, the herb has been collected in the Chinese Pharmacopoeia (2015 version) and generally used to treat pelvic inflammatory disease, adnexitis, lump, and other diseases of gynecology clinically [12]. e efficacy of Smilax china L. has been declared on anti-inflammation [13], antinociception [14], and anticancer [15]. "Jin Gang Teng" capsule made from water extract of the herb has a good effect on gynecological inflammation, and its annual sales exceed 100 million. But the extraction rate of active components in water extract is low, and the mechanism of action is not entirely clear. e herb contains many chemical ingredients such as flavonoids, saponins, stilbene glycosides, polyphenols, etc. Previous research results showed that the flavonoids, saponins, and polyphenols of the herb are active ingredients inhibiting inflammation [16]. Our research group prepared extract using ethanol extraction and macroporous adsorption resin purification and improved the extraction and concentration rate of chemical compositions including flavonoids, saponins, tannins, etc. Although it has been reported that the herb can decrease the production of PGE 2 and inhibit COX-2 activity [13], its anti-inflammatory mechanisms as well as the associated signaling pathways have not yet been fully illuminated. erefore, in the present study, the components of ES were identified by UPLC-QTOF-MS/MS, and anti-inflammatory mechanisms of ES were investigated in LPS-induced THP-1 cells.

Preparation of ES.
e dried powdered rhizomes of Smilax china L. (100 g) were firstly treated with 800 ml 60% ethanol 2 hours and subsequently with 600 ml 60% ethanol 1 hour for two more times. e extracts of the three treatments were collected, concentrated under reduced pressure, and filtered to get the total extracts. 70 ml 3% gelatin solution was added to the total extracts and placed statically for 24 h and then filtered. Distilled water was added to get filtrate at the concentration of 0.2 g/ml, which was subjected to D101 macroporous adsorption resin (2 BV/h) and successively eluted with 3 BV distilled water (2 BV/h) until the Molisch reaction was negative and then successively eluted with 5 BV 70% ethanol (2 BV/h). e eluate of 70% ethanol was collected and dried by rotary evaporation to obtain ES.

Xylene-Induced Ear
Oedema. Forty female Kunming mice were randomly divided into four groups: model group (saline), JGTgroup (the extract at the dose equalling to 13.5 g herb/kg), and two doses of ES (the extract at the doses equalling to 13.5 and 27 g herb/kg). Four groups were administered orally once a day for 4 days. 1 h after the last administration, the left ear was coated with 0.1 mL xylene in all mice and the right ear was considered as control. After 15 min, the animals were sacrificed, the ears were cut off and weighed. e swelling degree of ear was calculated using formula: degree of era oedema (%) � (the weight of the left ear − the weight of the right ear)/the weight of the right ear × 100%; inhibiting rate of inflammation (%) � mean of model group − mean of test group.

Egg White-Induced Plantar Swelling. Forty female
Wistar rats were randomly divided into four groups: model group (saline), JGT group (the extract at the dose equalling to 10 g herb/kg), and two doses of ES (the extract at the doses equalling to 10 and 20 g herb/kg). Four groups were administered orally once a day for 14 days. On the 14th day, the volume of left hind paw of rats was measured. 1 h after the last administration, 0.05 mL of freshly prepared 10% fresh egg white aqueous solution was injected subcutaneously into the left hind paw of rats in each group. After 6 h, the volume of left hind paw was measured and the swelling rate of paw 6-Keot-PGF 1 α was measured as an indicator of COX-1 activity, while PGE 2 was measured as an indicator of COX-2 activity. e inhibition percentage of 6-Keot-PGF 1 α and PGE 2 was calculated and the half-maximal inhibitory concentration (IC 50 ) values were determined by regression analysis.

Real-Time PCR.
Total RNA was extracted by Trizol RNA isolation reagent (Invitrogen). e cDNA was generated using the First-Strand cDNA Synthesis Kit (TOYOBO). e synthesized cDNA was amplified by using SYBR ® Premix Ex Taq ™ (Takara) and quantitative real-time PCR assays were carried out in a Bio-Rad CFX96 touch q-PCR system (Bio-Rad, USA). e primer sequences (Invitrogen Biotechnology Co., Ltd., China) used for IL-1β, IL-6, TNF-α, and GAPDH are shown in Table 2. e PCR reaction consisted of denaturation at 95°C for 1 min, followed by 40 cycles of 15 s at 95°C, 20 s at 58°C, and 20 s at 72°C. All signals were normalized with GAPDH and the mRNA relative expression was calculated according to the methods of 2 −△△Ct (where △△Ct � △Ct sample − △Ct reference).

Western
Blot. THP-1 cells were seeded in 6-well plates at 1.5 × 10 6 cells/mL. e cells were pretreated with or without LPS (1 μg/mL) for 1 h and then treated with ES (0, 12.5, 25, and 50 μg/mL) for 1 h. After incubation, the cells were harvested by centrifugation (1500 rpm, 5 min). Proteins were extracted by RIPA lysis Kit (Beyotime) containing phenylmethanesulfonyl fluoride (PMSF). Protein concentration in the supernatant was measured using BCA protein assay kit (Takara, Japan). Equal amounts of proteins were loaded on 10% SDS-polyacrylamide gel and transferred onto nitrocellulose membranes (Amersham Biosciences, UK). After blocking in Tris-buffered saline with 0.05% Tween 20 (TBST) containing 5% nonfat milk for 1.5 h, the membranes were incubated with primary antibodies (Cell Signaling Technology) at 4°C overnight. After washing, the membranes were incubated with HRP-conjugated IgG antibodies (Cell Signaling Technology) for 1 h. Membranes were developed using ECL Western blotting detection reagent (Bio-Rad). e band intensity was measured using the FluorChem 8000 system.

Statistical Analysis.
e results were presented as means ± SD. Statistical significance was determined by ANOVA and Student's t-test using SPSS software (IBM SPSS Statistics version 19.0, IBM Company). Values of P < 0.05 were considered as statistically significant.

UPLC-QTOF-MS/MS Analysis of ES.
58 compounds from ES were identified by UPLC-QTOF-MS/MS, 47 compounds were deduced by secondary mass spectrometry information, and 20 compounds were confirmed by comparing with the reference substance. e total ion chromatogram (TIC) is shown in Figure 1. e UPLC-QTOF-MS/MS information and structures of 20 compounds are shown in Figure 2 and Table 3, respectively.

In Vivo Anti-Inflammatory Activity.
Applying of xyleneinduced ear oedema in mice (Figure 3(a)), indicating acute inflammation. ES (the extract at the doses equalling to 13.5 and 27 g herb/kg) and JGT (the extract at the dose equalling to 13.5 g herb/kg) inhibited ear oedema with inhibiting rates of 9.70, 13.77, and 7.74%, respectively (Figure 3(a)).
Subcutaneous injection of egg white aqueous solution induced plantar swelling in rats (Figure 3(b)), indicating acute inflammation. ES (the extract at the doses equalling to 10 and 20 g herb/kg) and JGT (the extract at the dose equalling to 10 g herb/kg) inhibited plantar swelling with inhibiting rates of 8.74, 11.26, and 3.75%, respectively (Figure 3(b)).

Cytotoxicity of ES on THP-1 Cells.
e effects of ES on THP-1 growth were examined by CCK-8 assay, and no cytotoxic effect was observed at 100 μg/mL concentration, while there was significant proliferation when the cells were treated with 200 and 400 μg/mL ES ( Figure 4). erefore, sample treatments between 6.25 and 100 μg/mL were used in the subsequent experiments.
ese results implied that ES had selective COX-2 inhibitory activity.

Effect of ES on MAPK Signaling Pathway in LPS-Induced
THP-1 Cells. As presented in Figure 8, the phosphorylation levels of p38, JNK, and ERK1/2 were increased in THP-1 cells treated with LPS alone, and ES decreased LPS-induced phosphorylation of p38, JNK, and ERK1/2.

Effect of ES on NF-κB Signaling Pathway in LPS-Induced
THP-1 Cells. To further explore the inhibiting effect of ES, its effect on NF-κB signaling pathway was investigated. e expression levels of IKKα, IκBα, and p-p65 were evaluated Table 2: qRT-PCR primer sequences.

Discussion
e extract from Smilax china L. has been confirmed to have anti-inflammatory activities, which are likely related to flavonoids, saponins, and polyphenols. In this study, the activities of ES in equal doses were significantly better than the positive control "Jin Gang Teng" capsule in the in vivo acute inflammatory model. Furthermore, ES selectively inhibited LPS-induced overrelease of COX-2, as well as suppressed the transcription and expression of IL-1β, IL-6, and TNF-α in THP-1 cells. ES exerted this anti-inflammatory effect through negative regulating MAPK and NF-κB pathways.
Prostaglandins are important mediators of the body's response to pain and inflammation and are formed from essential fatty acids found in cell membranes. is reaction is catalysed by cyclooxygenase, a membrane-associated enzyme occurring in two isoforms: COX-1 and COX-2 [17]. e physiological prostaglandins are produced by catalytic COX-1, represented by PGI 2 , and PGI 2 is very unstable in the body, which will be metabolized to stable 6-Keot-PGF 1 α. erefore, the secretion of 6-Keot-PGF 1 α can reflect the activity of COX-1. e pathological prostaglandins are produced by catalytic COX-2, represented by PGE 2 , so the secretion of PGE 2 can reflect the activity of COX-2 [18].
COX-2 is closely related to inflammation and its product PGE 2 is an important inflammatory medium [19]. Classic epoxy enzyme inhibitors such as aspirin, indomethacin, and many other nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit both COX-1 and COX-2, which play antiinflammatory effect accompanied by gastrointestinal and renal side effects [20]. COX-2 selective inhibitors such as meloxicam have a weak inhibitory activity of COX-1, consequently reducing the adverse reactions.    Figure 3: In vivo anti-inflammatory activity of ES. ES and JGT capsule inhibited xylene-induced ear oedema in mice (a) and egg whiteinduced plantar swelling in rats (b). Saline (model group), ES (the extract at the doses equalling to 13.5 and 27 g/kg in mice, 10 and 20 g/kg in rats), and JGT (the extract at the dose equalling to 13.5 g/kg in mice, 10 g/kg in rats) were orally administered, respectively. e mouse ear oedema and rat plantar swelling were induced, and the inhibitory activities were calculated as described in Materials and Methods, respectively. Data are presented as means ± SD (n � 10). * P < 0.05 and * * P < 0.01 versus the model group.  Evidence-Based Complementary and Alternative Medicine ES inhibited overproduction of 6-Keot-PGF 1 α and PGE 2 induced by LPS, and the inhibition rate of PGE 2 was greater than 6-Keot-PGF 1 α at the same concentration ( Figure 5). Moreover, it showed that IC 50 (COX-1)/IC 50 (COX-2) of ES was 3.15, which was greater than 1 and close to the IC 50 (COX-1)/IC 50 (COX-2) of meloxicam ( Figure 6). ese results suggested that ES had selective COX-2 inhibitory activity; therefore, ES may be used as a potentially developable drug for inflammation diseases.

Evidence-Based Complementary and Alternative Medicine
Proinflammatory cytokines such as IL-1β, IL-6, and TNF-α, which play crucial roles in the development of inflammatory diseases, are also involved in the innate immunity and autoimmune diseases [21]. us, blocking the effects of proinflammatory mediators offers an attractive   Evidence-Based Complementary and Alternative Medicine therapeutic strategy. In this study, ES suppressed LPS-induced overproduction of IL-1β, IL-6, and TNF-α in a dosedependent manner (Figures 7(a)-7(c)).
Activation of MAPKs is known to be associated with the expression of multiple genes that together regulate the inflammatory processes. MAPK family with three major components p38, JNK, and ERK has been reported to play an important role in the upregulation of biosynthesis of IL-1β, IL-6, and TNF-α and transcriptional target enzymes (e.g., COX-2 and iNOS) [23]. erefore, the effects of ES on LPSinduced phosphorylation of MAPKs in THP-1 cells were evaluated using Western blot analysis. As shown in Figure 8, the phosphorylation levels of p38, JNK, and ERK were increased in cells treated with LPS alone. Importantly, ES treatment significantly inhibited phosphorylation of p38, JNK, and ERK at all concentrations from 12.5 μg/mL to 50 μg/mL. ese results revealed that the high activity of ES against the LPS-induced inflammatory stimuli was attributed to the inhibition of the phosphorylation of p38, JNK, and ERK, which may downregulate the levels of inflammatory mediators and cytokines in THP-1 cells. Interestingly, ES exhibited high activity at 25 μg/mL, a much better inhibition potential in comparison to the concentration of 50 μg/mL. e more pronounced effect at intermediate concentration than high concentration may be due to the multicomponent and multitarget synergistic effect, which is very common in traditional Chinese medicines [24,25].
During the immune cells rest stage, NF-κB remains inactive as part of a complex with p65, p50, and IκBα. IκBα is an inhibitory protein that binds to the p50/p65 heterodimer in the cytoplasm. Upon stimulation by LPS or certain cytokines, IκBα is phosphorylated by the IκB kinase (IKK) and degraded, promoting the activation and phosphorylation of p65 subunit that allows the translocation of NF-κB into the nucleus and leads to the transcription of proinflammatory mediators [26]. us, the underlying inhibitory mechanism was then focused on the LPS-stimulated cellular NF-κB pathway and changes in the content and forms of IKK, IκBα, and p65 were investigated. Western blot analysis indicated that NF-κB pathway was activated upon the addition of LPS with significant overexpression of IKKα and phosphorylated p65 protein as well as degradation of IκB-α ( Figure 9). Moreover, there was observable inhibition of IKKα overproduction by ES at three concentrations. Simultaneously, ES treatment increased level of IκB-α and decreasd phosphorylated p65 ( Figure 9). Because activation of IKK allows IκBα to be phosphorylated and ubiquitinated from p50/p65 complex, which leads to phosphorylation of p65, it is likely that ES downregulated expression of IKKα that resulted in the prevention of the degradation of IκB-α and phosphorylation of p65. In addition, this was consistent with the results of LPS-stimulated cellular MAPK pathway showing that ES was more effective at intermediate concentration on NF-κB regulated proteins. All these results implied that ES blocked the activation of the NF-κB pathway in LPS-induced THP-1 cells through inhibition of IKKα overexpression. Based on UPLC-QTOF-MS/MS, 20 compounds from ES were explored and verified by the reference substance, which mainly were flavonoids, saponins, and tannins including taxifolin, astilbin, rutin, resveratrol, polydatin, oxyresveratrol, engeletin, quercitrin, quercetin, and methylprotodioscin. Many flavonoids, saponins, and tannins have been shown to participate in the regulation of inflammatory mediators and signal transduction pathways [27][28][29]. For example, resveratrol suppressed the expression of TNF-α, IL-6, and COX-2 through a decrease in the intracellular levels of ERK1/2, as well as activation of NF-κB in activated HMC-1 cells [30]. Polydatin effectively inhibited NO and PGE 2 production and reduced iNOS and COX-2 expression at protein and transcriptional levels through NF-κB and MAPK pathways in LPS-induced RAW264.7 cells [31]. However, some compounds play an anti-inflammatory role by regulating specific targets. In previous studies, taxifolin suppressed expression of IL-1β and IL-6 mRNA in LPS-activated RAW264.7 cells, but not that of TNF-α [32]. Astilbin significantly suppressed production of NO and TNF-α, as well as mRNA expression of iNOS and TNF-α in LPS-induced RAW 264.7 cells, but did not affect IL-6 release or its mRNA expression [33]. Oxyresveratrol inhibited iNOS expression rather than iNOS enzyme activity through downregulation of NF-κB binding activity and significant inhibition of COX-2 activity [34]. Methylprotodioscin inhibited the activation of JNK and c-Jun while the activation of p38 MAPK, ERK, and NF-κB was not significantly affected [35]. Rutin protected spinal cord cells by reducing oxidative stress and inflammation and by decreasing the expression of proapoptotic proteins via inhibition of the p38 MAPK pathway [36]. e composition of ES is complex, and the targets and effects of each component are different. us, the anti-inflammatory effect of ES is likely achieved by multiple components and multiple targets.

Conclusions
In conclusion, ES prepared using ethanol extraction and macroporous adsorption resin purification mainly contained flavonoids, saponins, and tannins, and 20 compounds from ES were confirmed by comparing with the reference substance. ES inhibited the overproduction of 6-Keot-PGF 1 α and PGE2 induced by LPS and showed selective COX-2 inhibitory activity. ES decreased production and mRNA levels of proinflammatory cytokines (IL-1β, IL-6, and TNFα). ES also blocked the activation of the MAPK and NF-κB pathways, which may be closely related to the inhibitory effects of ES on inflammatory mediators ( Figure 10). Moreover, ES may exert anti-inflammatory effect through multiple components and multiple targets. Jin Gang Teng COX-2: Cyclooxygenase-2 PGE 2 : Prostaglandin E2 NF-κB: Nuclear factor kappa-B MAPKs: Mitogen-activated protein kinases ERK: Extracellular signal-regulated kinase JNK: C-jun N-terminal kinase IL-1β: Interleukin-1β IL-6: Interleukin-6 TNF-α: Tumor necrosis factor IC 50 : e half-maximal inhibitory concentration TIC: Total ion chromatogram PGI 2 : Prostaglandin I2.

Data Availability
e data used to support the findings of this study are available from the corresponding author upon request.

Disclosure
Some research work in this manuscript has been presented as a poster in the 18th World Congress of Basic and Clinical Pharmacology (WCP2018).