Background
Heart failure (HF) after myocardial infarction (MI) is a common clinical syndrome with high morbidity and mortality [
1]. Although traditional risk factors partially account for the development of HF, other new factors have recently been implicated. Evidence suggests that inflammation is important in the development and progression of HF. Chronic heart failure (HF) is characterized by an ongoing inflammatory response that correlates with HF disease severity and prognosis [
2]. Given the importance of inflammatory pathways in HF, new treatment modalities that target inflammatory mediators may be effective. Recently, a series of experimental studies has reported the improvement of myocardial infraction and HF through anti-arachidonic acid (AA) metabolism therapy, specifically by suppressing cyclooxygenase 1 (COX1) and COX2 [
3]. However, these drugs have side effects, such as increased gastrointestinal and adverse cardiovascular events [
4].
Traditional Chinese medicine has been applied to treat HF for thousands of years, and some herbal formulas have been proved to be effective [
5]. Among them, the ancient DanQi Pill (DQP), prepared from a basic formula of two Chinese herbs (i.e., Salvia miltiorrhiza and Panax notoginseng), is widely produced in China in accordance with the China Pharmacopoeia standard of quality control [
6]. DQP is commonly prescribed in routine treatment of HF in China. Large-scale randomized and controlled clinical trials have proved that DQP has a definite effect in improving heart function [
7]. Until now, many studies are being conducted to investigate the effect of active monomers in DQP on HF. For example, panax notoginseng saponins (PNS, monomer of P. notoginseng) were found to affect ischemia-induced myocardial apoptosis [
8]; tanshinone IIA (monomer of S. miltiorrhiza bunge) was found to have cardioprotective effects and to attenuate myocardial hypertrophy [
9]. However, most of these studies examined only one or several pharmacological effects of the monomer. Studies on the comprehensive effects of all of the compounds are rare.
In recent years, researchers have developed some bioinformatic methods to infer drug–target interactions [
10‐
15], which provide opportunities to conduct more efficient research on the efficacy of the entire formula. Recent advances on the databases cataloguing chemical components of herbs and the interactions between drugs and targets have contributed to predicting the drug targets of herbs.
DrugCIPHER-CS is an efficient drug–target prediction method that was successfully applied to our recent work [
16,
17]. In the current paper, we investigated the pharmacological mechanism of DQP using DrugCIPHER-CS to predict drug targets, followed by experimental validation. Specifically, after obtaining the potential targets of DQP, the significantly enriched Kyoto Encyclopedia of Genes and Genomes (KEGG) biological pathways and Gene Ontology (GO) biological processes involved in these potential targets were analyzed. AA metabolism pathway was selected to elucidate the special efficacy patterns of DQP. This study applied novel and effective methods and provided insight into the complicated multi-targets mechanism of herbs.
Methods
Drug–target prediction and analyses
We used DrugCIPHER-CS to predict the drug targets of the main compounds of DQP, following the procedure described in [
17]. The herbal compounds were first identified in the Modern Chinese materia medica database [
18]. The identified compounds were then typed into the durgbank (
http://www.drugbank.ca/) to search their structural information including their canonical and isomeric SMILES. Then we applied DrugCIPHER-CS to predict the potential drug targets of these compounds. DrugCIPHER-CS achieved good prediction performance in our previous study and can infer drug-targets in the genome-wide scale [
17]. This method is based on the hypotheses that i) drugs with similar chemical structure usually bind functionally related proteins, and ii) functional relationship between the proteins can be measured by their distance in the protein interaction network. Given a set of known drug (drug space)-target (target space) interactions, for a query drug and a candidate target-gene, drugCIPHER-CS will measure the likelihood of their interaction based on the correlation between the query drug’s structure similarity vector with the drug space and the candidate gene’s functional similarity vector with the target space. For a query compound, drugCIPHER-CS will prioritize the proteins in the protein interaction network (i.e. candidate proteins) according to the order of the decreasing drug-target interaction likelihood, and the candidate proteins with high likelihood will be hypothesized as the potential drug-targets [
16].
Here known drug-target interactions are obtained from DrugBank database [
19]. We only use those drug-target interactions whose drugs are FDA-approved and have InChI identifiers [
20]. The chemical structure similarity is calculated based on compounds’ MOLPRINT 2D descriptors and Tanimoto coefficient [
21].
After obtaining the potential drug targets, we analyzed the significantly enriched KEGG biological pathways and GO biological processes of these potential targets using the hypergeometric cumulative distribution test [
22]. A pathway was significantly enriched with candidate target-genes when its corresponding upper-tailed P-value of hypergeometric cumulative distribution was smaller than 0.05. The pathways were ranked according to the order of the increasing P-values. Then, GO annotations of human proteins were obtained from the GO project Web site (
http://www.geneontology.org/) [
23]. The top 0.1% candidate target-genes were significantly enriched with genes annotated with a GO term when its corresponding upper-tailed P-value of hypergeometric cumulative distribution was smaller than 0.05. These GO terms were ranked according to the order of the increasing P-values. KEGG biological pathway data were downloaded from the KEGG database [
24].
HF model preparation and grouping
Studies were performed in accordance with the China Physiological Society’s “Guiding Principles in the Care and Use of Animals” and with approval of the Animal Care Committee of Beijing Medical Center (SCXK: 2006-0009). A total of 80 male Specific Pathogen Free (SPF)-grade Sprague–Dawley (SD) rats weighing 240 ± 10 g were selected (purchased from Beijing Vital River Laboratory Animal Technology Co. Ltd.). HF was induced by direct coronary ligation as previously described [
25]. Briefly, sixty SD rats were anaesthetized with pentobarbital sodium (1%, 50 mg kg − 1 intraperitoneally). The left anterior descending coronary artery (LAD) was ligated with a 5–0 polypropylene suture (Surgipro, CT, USA) directly proximal to its main branching point. After electrocardiograph testing, rats that averaged QT-interval prolongation in three pre-cordial leads were included in the study. Sham-operated groups of the rest twenty rats were prepared following an identical procedure, but without the actual tying of the polypropylene suture. The overall mortality of rats that underwent induction of HF during the entire experimental period (up to 28 days after operation) was 30%. The majority of death occurred on the day of or the day after the surgery, probably because of acute pump failure or lethal arrhythmias. The operated rats were then randomly divided into two groups: 20 in the model group, 20 in the DQP group. Meanwhile, 20 in sham-operated group were investigated together. The rats were fed with a standard diet and water, and were maintained on a 12 h light and dark cycle. The DQP group was treated for 28 days, with the total daily dosage of 1.5 g/kg of the concentrated DQP (Tongren Tang, Beijing, China) dissolved in water. The sham and model groups received the same volume of water through oral gavage as the DQP vehicle. At the end of the study, all animals were anaesthetized using pentobarbital sodium following an overnight fast. Blood samples were collected through abdominal aorta puncture and were placing on ice. After centrifugation, plasma was collected, aliquoted, and stored at -80°C until analysis of each indicator. The heart was excised and incubated in ice-cold PBS to wash out blood. Each left ventricle was then carefully dissected to remove all the necrotic/scarred zones to keep only the viable myocardium in the marginal zone of the infarct region in model animals. The left ventricular myocardial below ligation bit in sham animals were also dissected.
Echocardiographic assessment of the left ventricle (LV) function
Echocardiography was used to detect left ventricle (LV) end-systolic diameter (LVEDs), LV end-diastolic diameter (LVEDd), ejection fraction (EF) and fractional shortening (FS). A sector scanner (PST 65A, Toshiba Company, Japan), which generates two-dimensional images at a frame rate of 300 frames/s to 500 frames/s, was used. Fractional shortening (FS%) was calculated by the following equation: FS% = [( LVEDd- LVEDs)/LVEDd]*100%.
Preparation and dose consideration of concentrated DQP
The DQP (Series: 6128006) used in this study was manufactured by Tongrentang company (Beijing, China) with the roots of 150 g S. miltiorrhiza and 150 g P. notoginseng. Briefly, the residue of P. notoginseng was mixed with all S. miltiorrhiza bunge, followed by extraction with hot water (twice at 2 h each). The water extract was then concentrated to form a paste, and ethanol was added. After 24 h, the filtrate, which was the final product, was collected. Based on the recommendation of daily human dosage (20 g/d) and the equivalent conversion between animal and people by body surface area and body weight, dosage of 1.5 g/kg was chosen in the present study.
Measurement of plasma indicators by Enzyme Linked Immunosorbent Assay (ELISA)
Levels of plasma indicators were quantified in duplicate using commercial ELISA kits (Abcam Inc., Cambridge, MA, USA). Each assay was performed following the kits’ instructions. Standards at a series of concentrations were run parallel to the samples. The concentrations of the samples were calculated in reference to their corresponding standard curves and expressed as ng/mL.
Measurement of indicators by Western blot
The heart tissue was homogenized in RIPALYSIS buffer (i.e., 50 mM Tris-HCl pH7.4, 150 mM NaCl, 2 mM EDTA, 1% NP-40, and 0.1% SDS), and total protein was extracted from this homogenate. The protein concentration in each extract was measured using a protein assay kit (Pierce; Rockford, IL) and was then adjusted to the same value in all samples with 2× 4% Sodium dodecyl sulfate (SDS) sample buffer. The samples were boiled for 5 min, followed by loading on a 12.5% SDS-Polyacrylamide gel electrophoresis (PAGE) gel (30 mg protein/10 ml per well) for electrophoresis using a Bio-Rad mini gel apparatus at 100 V for 2 h. The fractionated protein on the gel was transferred onto an NC membrane (Millipore) and electrophoresed at 300 mA for 90 min. The membrane was first probed with COX1 primary antibody (anti-COX Type 1 antibody, ab18801, Abcam, 1:500) and secondary antibody (donkey polyclonal secondary antibody to rabbit IgG-HRP,ab97064, Abcam, 1:5000), and then treated with ECL (ECL plus Western blotting detection reagent, GE Healthcare) for 1 min at room temperature. The bands in the membrane were visualized and analyzed using UVP BioImaging Systems. After obtaining the COX1 blot density, the membrane was then treated using Restore Western Blot Stripping Buffer (Thermo Scientific) to remove the COX1signal, followed by probing with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) primary antibodies (GAPDH mouse monoclonal IgG, ab8245, Abcam, 1:2000). The COX2, prostaglandin E2 receptor 4 (EP4), and leukotrienes B4 receptor (LTB4R) antibody blot densities were determined using the same process. The final reported data were the normalized COX1 band densities by GAPDH.
Statistical analysis
ANOVA using SAS 9.2 statistical software (SAS Institute, NC, USA) was applied to evaluate between-group differences in the outcome variables, follow-up least significant differences (LSD) analysis verified these differences were significant. P < 0.05 was considered statistically significant. Results were presented as mean values with their corresponding standard deviations.
Discussion
In the present study, drug target prediction was applied to reveal the underlying mechanism of DQP. A potential target pathway seldom studied, AA metabolism, was investigated. After experimental validation, COXs and LTB4 were determined to be the targets of DQP.
Both nonselective and COX-specific inhibitors called nonsteroidal anti-inflammatory drugs are commonly used in relieving pain associated with medical conditions [
37]. COX (prostaglandin G/H synthase) is a key enzyme in prostaglandin synthesis; it has two isoforms (i.e., COX1 and COX2) [
38]. COX1 is constitutively expressed and is probably responsible for prostaglandin release under physiological conditions, and COX2 is expressed at high levels upon induction. COX activation produces prostaglandin H2, which is subsequently converted to PGE2, PGI2, or thromboxane A2 (TXA2). Then, the PGI2 and TXA2 are unstable in plasma, and quickly metabolized to 6-Keto-PGF1α and TXB2 respectively [
39]. Imbalance between TXA2 and PGI2 is considered as a critical cause of HF. Anti-COXs therapy with aspirin, which at low doses acts as a selective inhibitor of COX activity, is well established. However, a major limitation of aspirin treatment is its gastrointestinal toxicity, which is considered linked to its disruption of the balance between TXA2 and PGI2. Newly developed dual COX2 and LTB4 inhibitors not only share the anti-inflammatory effect of COX1 inhibitors but also inhibit the 5-lipoxygenase (LOX)-mediated synthesis of gastrotoxic leukotrienes. Dual inhibitors may be beneficial in the treatment of HF with fewer side effects [
40].
In the present study, using DrugCipher-CS software, AA metabolism was predicted to be altered by DQP. An experiment using an animal model validated that the alteration of the levels of proteins in the AA metabolism pathway with the occurrence of HF and administration of DQP to HF rats could suppress these protein levels. Consistent with previous reports, the LAD-induced HF animals were characterized by declined diastolic and systolic myocardial performance (i.e., decreased EF and FS values) and myocardial fibrosis. Our results also agree with those of previous studies that demonstrate the enhanced activation of cardiac AA metabolism in HF, such as PGI2 and TXB2 [
41]. Moreover, COXs and LTB4 are the products of two AA metabolism pathways mediated by COX and LOX, respectively. Levels of COXs and LTB4R increased in HF models because of the activation of AA metabolism.
DQP treatment was able to regulate the AA metabolism in different ways. First, COX1 and COX2 are downregulated, thus suppressing AA activation and avoiding its gastrointestinal toxicity. Downregulation of LTB4R also occurs. LTB4 produced from AA by 5-LOX is a potent chemo-attractant of leukocytes [
42]. Therefore, the cardioprotective effect on HF by DQP is partly due to its inhibition of LTB4R. These results also support the emerging role of inflammation in the development and progression of HF [
33,
43].
PGI2 and TXA2 belong to metabolites of AA pathway, and they have critical and contradictory roles in the progression of HF. PGI2 exhibits cardioprotective effects by inhibiting the aggravation of HF. However, TXA2, which is metabolized into TXB2, increases the risk of cardiovascular events. The dynamic balance between the metabolites is considered a critical biomarker of thrombosis regulation in HF [
44]. Although DQP cannot directly reduce the concentration of TXB2, DQP can significantly upregulate the cardioprotective PGI2 and recover the imbalance of P/T ratio, thus providing a synthetic effect on HF.
Conclusions
Our results suggest that DQP exerts a synthetic cardiac protective role by targeting multiple targets in the treatment of HF. Particularly, DQP can attenuate the activation of AA metabolism in HF by reducing the levels of COXs and LTB4R while increasing the levels of PGE2 receptor EP4 and PGI2. The combination of drug target prediction and experimental validation provides new insights into the complicated mechanism of DQP in the treatment of HF.
Limitations
There are some limitations in our study. For example, the search for DQP compounds has been done through the Chinese Materia Medica only, which is far from comprehensive. We presume all components of herbal formulation compounds are absorbed and utilized; improvement should be made in our future work.
Acknowledgements
The authors would like to thank Associate Editor and the anonymous reviewers for their valuable comments and suggestions. We also thank Shao Li for the guidance on drugCIPHER. Y Wang, C. Li, Z. Liu and T Shi contributed equally to this work. We also thank the Grants from the National Natural Science Foundation of China (no.81202788); the National Science & Technology Pillar Program (no. 2012BAI29B07) and Creation for Significant New Drugs Project of China (no. 2012ZX09103-201-011).
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (
http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (
http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
Conceived and designed the experiments: WW and BT. Performed the experiments: YW, CL and TS. Analyzed the data: ZL, DL and SG. Contributed reagents/materials/analysis tools: YW, JH. Wrote the paper: YW, ZL and QW. All authors read and approved the final manuscript.