Recent Advance in Applications of Proteomics Technologies on Traditional Chinese Medicine Research

Proteomics technology, a major component of system biology, has gained comprehensive attention in the area of medical diagnosis, drug development, and mechanism research. On the holistic and systemic theory, proteomics has a convergence with traditional Chinese medicine (TCM). In this review, we discussed the applications of proteomic technologies in diseases-TCM syndrome combination researches. We also introduced the proteomic studies on the in vivo and in vitro effects and underlying mechanisms of TCM treatments using Chinese herbal medicine (CHM), Chinese herbal formula (CHF), and acupuncture. Furthermore, the combined studies of proteomics with other “-omics” technologies in TCM were also discussed. In summary, this report presents an overview of the recent advances in the application of proteomic technologies in TCM studies and sheds a light on the future global and further research on TCM.


Introduction
Traditional Chinese medicine (TCM), emphasizing most importantly the holistic concept, has been applied in the diagnosis, treatment, and prevention of illnesses in China and other Asian countries for more than 3000 years. Because of the complexity of the concept, the technology limitations, and the current investigation methodology, TCM diagnosis and treatment lack objective evaluation, and the essence and the mechanisms of TCM theory remain unclear.
Since proteins are the major executers of biological information, proteomic analysis provides a direct reflection of gene expression. Generally, proteomics is defined as the genome-scale analysis of protein abundance, structure, localization, modification, and activity. Currently, as a major component of systems biology, proteomics has gained comprehensive attention in the field of medical diagnosis, drug development, and mechanism studies [1,2]. Proteomics technology is an important research tool for elucidating the differential expressions of proteins in peripheral body fluids, cells, tissues, blood, and urine samples [3]. Blood and urine are the most widely used specimens because their molecular compositions fluctuate in response to the dynamic physiological and pathological conditions of the body. Technically, proteomic analysis requires the combination of several technologies, that is, protein processing and separation such as two-dimensional polyacrylamide gel electrophoresis (2DE), high-performance liquid chromatography (HPLC), mass spectrography (MS) such as MALDI-TOF-MS, SELDI-TOF-MS, and MS/MS, isobaric tags for relative and absolute quantification-(iTRAQ-) based quantitative proteomic analysis, and bioinformatics [4].
TCM diagnosis and therapy depend on the intuition and experience of the TCM theory trained physicians. Compared with biomolecular science and western medicine, TCM appears to be nonobjective and lacking accuracy and reproducibility. In accordance with the holistic and systemic theory, proteomics has a convergence with TCM and can overcome biases in TCM research. Proteomics can be helpful in exploring the scientific connotation of TCM and the modernization of Chinese herbal medicine (CHM). First, proteomics could be used to characterize the differential 2 Evidence-Based Complementary and Alternative Medicine expression profiles between healthy individuals and patients with different TCM syndromes. For example, apolipoprotein A1 and apolipoprotein A4 expression levels analyzed by plasma proteomics were found to be the potential diagnostic and prognostic markers for chronic viral hepatitis B (CHB) with damp-heat retention in Middle-Jiao syndrome (DRMS) [5]. Similar findings [6][7][8][9][10] can discover other molecular markers of TCM syndromes in clinical applications.
Secondly, proteomics can help discover molecular targets, develop new bioactive compounds, and elucidate the underlying mechanisms of TCM treatment. For instance, a recent proteomic study showed that Tianma promoted neuroregenerative processes by inhibiting stress-related proteins and mobilizing neuroprotective genes such as Nucleoredoxin (Nxn), Drebrin-like protein (Dbnl), Ki67 protein, and Baxin mouse N2a cells [11]. This and other similar proteomic studies provide important insights into the molecular mechanisms underlining the beneficial effects of TCM treatments [12][13][14][15].
In this report, we reviewed the current proteomic approaches in TCM research including clinical TCM diagnosis and treatment and in vitro and in vivo mechanistic studies and shed light on future utilization of proteomics for TCM research ( Figure 1).

Proteomics Studies on Disease-TCM Syndrome Combination
TCM syndrome, also called ZHENG in Chinese, is a profile of clinical symptoms and signs, which reflect the essence of pathological changes in the occurrence and development of diseases, provide great insights in understanding the human homeostasis, and guide specific TCM treatments. TCM syndrome differentiation, that is, the diagnosis of TCM syndrome, is to differentiate diseases by analyzing the information of each patient, for example, patients' symptoms and physical status, which were collected by four diagnostic methods: inspection, auscultation and olfaction, inquiry, and palpation [16]. Currently, although the applications of proteomic technologies in TCM are much less common than those in western medicine, clinical TCM studies using proteomic technologies have already achieved some great successes, with several biomarkers and the mechanisms of TCM syndrome differentiation being discovered in various diseases, such as hepatorenal, cardiocerebrovascular, and lung diseases.
Song et al. [19] studied correlation between the states of Zang-Fu organs and the levels of plasma biomarker proteins and found differential plasma protein profiles in hyperlipidemia and atherosclerosis of different patterns of phlegm stasis syndrome and blood stagnation syndrome. For example, the levels of albumin, adrenomedullin binding protein precursor, and haptoglobin precursor in patients with phlegm syndrome were different from those in the patients with blood stagnation syndrome and also correlated with kidney-Qi deficiency and heart-Qi deficiency, while the complement component C4 is independent of the deficient Zang-Fu organs. Zhao et al. [20] uncovered common proteomic characteristics in unstable angina with Qi deficiency and blood stasis syndrome (QBS) and phlegm stasis crossblocking syndromes (PSS), indicating a correlation of these proteins with inflammatory reaction and metabolic disturbance. For instance, actin was found only expressed in Qi deficiency blood stasis syndrome (QDBS), while FN, ApoH, and ANXA6 are highly expressed in QDBS. Wang et al. [21] found that energy metabolism and myocardial structural injury associated proteins, isocitrate dehydrogenase 3 (NAD+) alpha, NADH dehydrogenase (NAD) Fe-S protein 1, chain A, heat shock protein 27 (HSP27), and oxidoreductase (NAD-binding protein), may be biomarkers for the diagnosis of chronic myocardial ischemia with QBS.  for TCM syndrome differentiation in TB. By combining SELDI-TOF-MS techniques with a decision tree model, nine upregulated and six downregulated proteins were identified in lung cancer patients with Qi deficiency syndrome and phlegm and blood stasis syndrome. Two candidate protein peaks, 2284.97 m/z, were selected to establish a predictive model, which can be applied in the TCM syndrome differentiation in lung cancer [23].

Lung Diseases and TCM
Other studies have also provided the evidence of syndrome differentiation using proteomic technologies in chronic stomach disease [24], myasthenia gravis [25], and systemic lupus erythematosus [26]. All these studies suggested that the rapid growth of proteomics has made it possible for the integration of diseases-TCM syndrome with modern technology, thereby supplying the diagnostic or prognostic markers for TCM syndrome differentiation, as well as TCM therapy targets.

Proteomic Studies of Clinical TCM Treatments Using Chinese Herbal Medicine (CHM), Chinese Herbal Formula (CHF), and Acupuncture
TCM treatment is based on the holistic characterization of patients' disease status, which is diagnosed to certain TCM syndrome type. Most of the TCM therapeutic methods, CHM, CHF, or acupuncture, provide modern medicine with a collection of complementary remedies for disease treatment and health maintenance. Although some of CHM, CHF, or acupuncture methods are known to have beneficial effects on the diseases, their therapeutic efficacy could not be well evaluated. Recently, proteomic technologies have been utilized to measure the therapeutic effect of TCM treatments [74]. Lian et al. [75] demonstrated that the favorable effects of Liuwei Dihuang granule (LDG) on infertility of women with Kidney-yin deficiency syndrome might be through regulating the expression levels of retinol binding protein 4, transthyretin, apolipoprotein, and complement C4-B, all being associated with HPT axis, lipid metabolism, estrogen level, and cellular immunity, and activation function of complement system-pathways might be the actionable targets for the treatment of infertility with LDG. To identify the drug targets of TCM formulae Yin-Chen-Hao-Tang (YCHT), which was used to treat hepatic injury, Sun et al. [76] performed 2DE and MALDI-TOF/TOF-MS analysis and found that YCHT modulated the expression levels of several proteins, that is, zinc finger protein 407, haptoglobin, transthyretin, and vitamin D-binding protein, all being involved in metabolism, energy generation, chaperone, antioxidation, signal transduction, protein folding, and apoptosis. Pan et al. [77] investigated the effects of acupuncture on serum protein levels in a total of 35 acute ischemic stroke (IS) patients, with the acupuncture treatment being performed on eight acupuncture points once a day for 10 consecutive days. After acupuncture, SerpinG1 protein expression in patients' serum was downregulated while those of gelsolin, complement component I, C3, C4B, and beta-2-glycoprotein I proteins were upregulated. iTRAQ-based quantitative proteomics was performed to identify key proteins in the blood sample for acupuncture at "Zusanli" acupoint (ST-36) in patients, and a total of seven related proteins were identified. These proteins, aldolase A protein, hCG2008184, ATP synthase, ATP5A1 protein, and hexokinase type 1, were involved in the regulation of multiple metabolism pathways, which may help elucidate the action mechanism of ST-36 acupuncture [78].
Although proteomic studies in clinical TCM medicine have been successful, such studies in clinical TCM treatment still remain few. Ideally, proteomic studies should be conducted in both the diagnosis of a TCM syndrome and its corresponding treatment including CHM, CHF, and acupuncture. A large number of experimental proteomic studies are currently under way to uncover the molecular mechanisms of TCM treatment.

Proteomic Studies on Mechanisms of TCM Treatments In Vitro and In Vivo
The complex nature of TCM determines that a thorough investigation on the mechanisms and physical basis of TCM will not be so easy. Luckily, development of modern biotechnologies is constantly providing novel and powerful tools. Proteomic technologies can reveal statistically significant changes in the levels of proteins, identify novel target molecules, and provide clues for the underlying mechanisms of TCM treatments. Herein, we will focus mainly on the application of proteomics in the research of TCM treatment using in vitro and in vivo models over the past years [79].

Evaluation of TCM Treatment In Vitro.
Proteomic technologies can be applied to screen target molecules and explore the effective mechanisms of TCM treatments in various cell lines originated from various diseases, such as cancers and cardiocerebrovascular and inflammatory diseases. TCM treatment includes CHM, CHM compounds, and CHF. As shown in Table 1, proteomics is often applied to investigate the change of proteins and of various related signaling pathways in TCM treatments in vitro.
In gastric adenocarcinoma, Lin et al. [35] revealed that Tanshinone IIA suppressed gastric cancer AGS cell growth by blocking glucose metabolism via the downregulation of the levels of intracellular ATP, glucose-6-phosphate isomerase, and L-lactate dehydrogenase B chains, as well as altering the p53 and AKT expression. Zhu et al. [15] found in human gastric adenocarcinoma SGC-7901 cells that Celastrus orbiculatus suppressed TGF-1-induced epithelial-mesenchymal transition by inhibiting HSP27 expression, and further investigation showed that the downregulation of HSP27 was associated with TNF--induced NF-B/Snail signaling pathway.
In breast cancer, proteomic analysis by Fang et al. [14] identified 12 differentially expressed proteins, of which the downregulated proteins TDP-43, SF2/ASF, and eIF3i, as well as upregulated proteins including 3-PGDH, ERP29, and platelet-activating factor acetylhydrolase IB subunit beta, positively contributed to the anticancer activity of Curcumin in human breast cancer MCF-7 cells. In addition, a study by Chou et al. [36] illustrated that berberine induced apoptosis of MCF-7 cells, and a link between ROS generation and cell death was identified using lysine-and cysteine-labeling 2D-DIGE combined with MS.

Cardiocerebrovascular Diseases.
In heart disease, Fan et al. [38] revealed that Shuanglong formula (SLF) induced autologous mesenchymal stem cells (MSCs) into cardiomyocyte-like cells, and 36 proteins, which functioned in cytoskeleton, cell tissue energy metabolism, and signal transduction, showed distinct differential expression patterns before and after SLF treatment. Feng et al. [39] clarified the signaling impact of salvianolic acid B (SB) in H9C2 cells using proteomic assay and bioinformatic analysis and found the signal cascade from EGFR to heat shock protein 27 (HSP27) and mitofilin might be the most important cascade that was affected by SB.

Inflammatory Diseases.
In inflammatory diseases, the proteome profiler array analyses [44] displayed that 8 cytokines were downregulated while 6 were upregulated by Bi-Qi capsule in lipopolysaccharide-stimulated RAW 264.7 macrophages. The same research group [45] also found that Zuojin pill inhibited the levels of inflammatory mediators such as inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), TNF-, IL-6, and interleukin 1 (IL-1 ) in lipopolysaccharide-stimulated RAW 264.7 mouse macrophages. Additionally, Jiang et al. [12] established that Acanthopanax senticosus extract (ASE) suppressed LPSinduced nitrosative stress in BV-2 cells, and proteomic quantitative analyses revealed that the levels of 17 proteins significantly changed in response to ASE.
In other diseases, by proteomic analysis, several important molecular mechanisms of TCM treatment have been found, such as Lithospermi radix on wound healing [46], isopsoralen on oxidative damage [47], Tao Hong Si Wu decoction (THSWD) on cerebral ischemia reperfusion injury [48], and Curcumin on postcataracts [49].
One may know that in vitro studies may not reflect the actual effects of TCM treatments, as in vivo body environment and the influencing factors are very complex and hard to control. To better understand the effective mechanisms of TCM treatments, in vivo animal models and tests are highly desired.

Evaluation of TCM Treatments In Vivo.
Presently, the in vivo proteomic research involves mainly the rat and mouse models. Recent studies focused mostly on the following diseases: cardiocerebrovascular diseases, hepatorenal diseases, diabetes, and so on. In addition, proteomic technologies were also applied to study the effective mechanisms of acupuncture on diseases such as asthma. As shown in Table 2, the proteomics was applied to investigate the mechanisms of TCM treatments including CHF, CHM, and CHM compound in vivo.
By the differential proteomic analysis in platelet samples of SD rats, Ma et al. [52] proposed that salvianolic acid B (SB) caused regulation of 20 proteins such as heat shockrelated 70 kDa protein 2 (HSP70), LIM domain protein CLP-36, copine I, peroxiredoxin-2, coronin-1B, and cytoplasmic dynein intermediate chain 2C. Furthermore, SB bound with integrin 2 1 to regulate intracellular Ca 2+ level and the levels of cytoskeleton-related protein coronin-1B and to affect cytoskeleton structure of platelets. In addition, Yue et al. [53] from the same studying group demonstrated that salvianolic acids (SA) and notoginsenoside (NG) showed both similarity and difference in their protein targets involved in cardioprotective effects.
Lo et al. [54] investigated the effect of Uncaria rhynchophylla (UR) on the differentially expressed proteins in SD rats with kainic acid-(KA-) induced epileptic seizures using a proteomic analysis and found that macrophage migration inhibitory factor (MIF) and cyclophilin A were underexpressed in frontal cortex by an average of 0.19-and 0.23fold, respectively, suggesting that both MIF and cyclophilin A at least partially participated in the anticonvulsive effect of UR. Zhang et al. [55] explored the effective mechanisms of Yizhijiannao granule (YZJN) in treating Alzheimer's disease (AD) with proteomic tools, and the results indicated that YZJN regulated multiple protein expressions in entorhinal cortex tissues of SAMP8, suggesting that it had multitarget therapeutic action and the mechanism in treating AD is possibly via improving mitochondria function, antagonizing oxidation stress, preventing nerve cell apoptosis, and protecting neurons. Koh [56] has identified the proteins differentially expressed in cerebral cortexes of Ginkgo biloba extract-(EGb761-) treated rats in a middle cerebral artery occlusion model, and the results showed that EGb761 protected neuronal cells against ischemic brain injury through the specific up-and downmodulation of various proteins.
Manavalan et al. [43] found that Gastrodia elata (Tianma) affected synaptic plasticity and neurorestorative processes and thus might be a novel candidate agent for the treatment of neurodegenerative diseases by regulating the brain proteome. In detail, the long-term treatment with Tianma modulated the brain protein metabolism at the proteome level by downregulating the expressions of various proteins, such as Gnao1 and Dctn2, which are related to neuronal growth cone control and synaptic activities. Tianma treatment also induced the upregulation of molecular chaperons and proteins related to the misfolded protein response, such as Pacsin1 and Arf3 involved in Huntington's disease (HD).
Evidence-Based Complementary and Alternative Medicine 7  [57] investigated the effects of Yiguanjian decoction on rats with cirrhosis and found that increasing expression of proteins that were related to antioxidative stress such as Cu/Zn SOD and DJ-1 is probably the mechanism of Yiguanjian decoction in treating CCl4 induced cirrhosis. Xie et al. [58] proposed that the action mechanism of anti-liver fibrosis effect of Fuzheng Huayu (FZHY) may be due to modulation of proteins associated with metabolism and stress response, as well as myofibroblast activation, including aldehyde dehydrogenase, vimentin isoform (CRA b), gamma-actin, vimentin, fructose-bisphosphate aldolase B, aldo-keto reductase, Sadenosyl homocysteine hydrolase isoform, and HSP90. Wang et al. [80] studied the effects of Isoline on mouse liver protein profile and showed that the liver samples from mice of Isoline group had about 13 differentially expressed proteins compared with the normal. These proteins may be involved in Isoline-induced liver injury, as 9 of them were involved in the process of oxidative stress or cellular energy metabolism. Sun et al. [60] investigated mechanisms of the protective effects of Salvia miltiorrhiza polysaccharide (SMPS) against lipopolysaccharide-(LPS-) induced immunological liver injury (ILI) in Bacille Calmette-Guérin-(BCG-) primed mice, and the results showed that SMPS antagonized liver injury by upregulating the enzymes of the citric acid cycle, namely, malate dehydrogenase (MDH) and 2-oxoglutarate dehydrogenase complex, as well as inhibiting the NF-B activation by upregulation of PRDX6 and the subsequent attenuation of lipid peroxidation, iNOS expression, and inflammation.
Liu et al. [61] observed the effect of Tanshinone II A sodium sulfonate (TSNIIA-SS) on oxidative stress in mice and used two-dimensional electrophoresis (2DE) to find that TSNIIA-SS treatment not only improved DXR lesion but also regulated the expression of several proteins associated with the cytoskeleton, oxidative stress, and protein synthesis or degradation.

Diabetes.
In diabetes research, Guo and Xiong [62] observed changes of serum proteome in model rats treated with Granules of Eliminating Phlegm and Removing Blood Stasis (GEPRB). It suggested that 13 proteins changed in response to GEPRB in vivo, and these proteins may play key roles in the GEPRB treatment of diabetes deafness. Among them, 2 highly differentially expressed proteins apolipoprotein E (apoE) and C3 may be potential drug targets of GEPRB.
Shi et al. [63] investigated the effects of the Chinese medicine ZiBuPiYin recipe (ZBPYR) on the hippocampus in a rat model of diabetes-associated cognitive decline and found that 13 protein spots were altered between control and diabetes groups and 12 spots were changed between diabetes and DM/ZBPYR groups. Nine proteins were involved in energy metabolism, cytoskeleton regulation, and oxidative stress. The protein alterations observed in the diabetes group were ameliorated to varying degrees following ZBPYR treatment.
Another proteomic study of serum proteins in a type 2 diabetes mellitus (T2DM) rat model by Chinese traditional medicine Tianqijiangtang capsule was performed by Zhang et al. [64], and the distinct effect of T2DM on rat serum protein patterns included the downregulation of apolipoprotein E, apolipoprotein A-I, and Ig gamma-2A chain C region and upregulation of transthyretin (TTR), haptoglobin (Hp), serum amyloid P-component (SAP), and prothrombin. The majority of those protein levels were restored to those of healthy rats after Tianqijiangtang capsule treatment.
In other diseases, the proteomics was also applied to uncover the effective mechanisms of TCM treatments in in vivo models, such as chronic restraint stress-induced liver stagnancy syndrome rats [65], stressed rats treated with Wei Kangning [66], spontaneously hypertensive rats treated with CHM compound PingganQianyang [67], airway inflammatory mice treated with Xiao-Qing-Long-Tang [81], silica exposing rats treated with Gymnadenia conopsea alcohol extract [69], and anxious rats treated with polysaccharides extracted from Shudihuang [70]. In addition, the proteomics was also performed to study the effect of acupuncture on different diseases, such as the effects of acupuncture at Taixi acupoint (KI3) on kidney proteome [71], the nonspecific physiological background effects of acupuncture revealed by proteomic analysis in normal rats [72], and the proteomic analysis in acupuncture-treated rats with asthma onset [73].
In summary, from the in vivo models, using proteomics method, the researchers can successfully identify novel candidate proteins involved in the development of disease and define potential targets for TCM treatment. Further studies are required to investigate the exact role of these selected proteins and validate their potential as therapeutic targets.

Combination of Proteomics and Other (-Omics) Technologies in TCM Researches
Because of the complexity of TCM and the differential expression profiles of various biomolecules, that is, DNAs, RNAs, proteins, and metabolites, there are indeed numerous regulatory mechanisms and signaling pathways awaiting to be investigated for TCM research. Systematically integrating collected information from genomics, transcriptomics, proteomics, and metabolomics will greatly help explore the molecular mechanisms of TCM, as well as finding biomarkers or targets for future research and clinical practice.
Over the past few years, several researchers have combined the use of transcriptomics and proteomics in TCM researches. Using next-generation RNA sequencing and iTRAQ, in gastric cancer cell line AGS treated with TIIA, Lin et al. [35] characterized 16,603 unique transcripts and 102 proteins, which were involved in carbohydrate metabolism, cell cycle, apoptosis, DNA damage, and cytoskeleton reorganization. Intracellular ATP levels, the levels of glucose-6-phosphate isomerase, L-lactate dehydrogenase B chains, p53, and AKT were characterized to be associated with these changes. Moreover, proteomics and transcriptomic analysis coupled with pharmacological tests were employed to reveal the diversity of antithrombosis proteins from the medicinal Evidence-Based Complementary and Alternative Medicine 9 insect, Eupolyphaga sinensis. By this approach, Wang et al. [82] found that serine proteases contained both plasminand plasminogen-activating-like activities, the excellent candidates for antithrombosis medicines.
Recently, an integrated proteomic and metabolomic study found that three principal components of Yin-Chen-Hao-Tang, Artemisia annua L., Gardenia jasminoides Ellis, and Rheum palmatum L., contained major active ingredients 6,7dimethylesculetin (D), geniposide (G), and rhein (R), respectively. Wang et al. [83] found that the DGR combination had a better therapeutic effect through intensifying dynamic changes in metabolic biomarkers, regulating target proteins, and activating both intrinsic and extrinsic pathways.
However, what needs to be emphasized is that, because of the high cost of "-omics" technologies, the studies combining proteomics with other "-omics" still remain of a small number, especially in TCM research, but it is a very promising approach since the combined "-omics" can provide much more information.

Prospects and Challenges
Recent technological advances in "-omics" including genomics, transcriptomics, proteomics, and metabolomics have helped cast light on the essence and molecular basis of TCM syndrome. High-throughput proteomics technologies assist the researchers to identify candidate proteins, which play key roles in TCM treatment response and toxicity. Subsequently, pharmacoproteomics emerges, seeking to characterize the molecules affecting the response to drugs in individual patients and helping target-based therapy. Furthermore, disease susceptibility proteins representing potential new drug targets could also be identified by pharmacoproteomics methods. All these novel approaches provide very useful tools for TCM drug discovery and individualized application of TCM therapy.
Proteomics can combine tightly with other technologies to better understand the essences of TCM [84]. For example, combining proteomics and bioinformatics to study protein signaling pathways and protein-drug interactions would be favorable to molecular evidence-based TCM research. Posttranslational modifications by small compounds, lipids, or even a group of chemicals can regulate the protein activity and its function. Proteomics could be applied to detect the posttranslational modifications and protein-protein interactions after TCM treatment. With the development of the latest proteomics techniques in TCM research, more and more researchers begin focusing on how proteomics can determine the mechanism of TCM treatment for various diseases including cancers, cardiocerebrovascular diseases, hepatorenal diseases, lung diseases, and diabetes. Proteomics could also be applied to determine the anticancer mechanisms of CHM compounds or CHM and CHF extracts. In addition, many researchers have paid more attention to proteomics studies based on treatment-TCM syndrome animal models. analysis of gastric mucosa in chronic gastritis rats of Spleen-Stomach Damp-Heat syndrome treated by Sanren decoction [86]. These studies greatly help understand the molecular basis of TCM treatment based on syndrome differentiation.
However, every coin has two sides; proteomics technology has its limitation or disadvantage. Presently, the identified proteins from the proteomics technology are relatively fewer in comparison with the data from genomics and transcriptomics. The proteomics results are frequently instable and variable, which means that the reproducibility of proteomics data is poor. To obtain the ideal results, it is necessary to integrate all the proteomic technology such as 2DE, HPLC, MALDI-TOF-MS, SELDI-TOF-MS, MS/MS, iTRAQ, and the bioinformatics.
Furthermore, there are still many limitations for the application of proteomics in TCM research. For example, most studies have identified differentially expressed proteins among different TCM syndromes or TCM treatments. Few identified molecules were investigated in depth from the aspects of function and mechanism. Moreover, although many in vivo animal models associated with TCM syndromes have been established based on TCM theory, it remains unknown whether these models accurately simulate the real human environment and reflect human body conditions [87]. In addition, many CHM or CHF compounds are very complex and not stable because of the origin and production process; the proteomics results could not keep consistent, which affect greatly the further mechanism investigation of CHMs and CHFs.
Nowadays, proteomics bridges TCM and modern life sciences, greatly facilitates the quality evaluation and standardization of TCM, and promotes the modernization and internationalization of TCM. Although the application of proteomics in TCM research is full of challenges, it also provides very good opportunity.