Abstract: Establishing a scientific quality evaluation system for traditional Chinese medicine is crucial for its internationalization and industrialization. By identifying quality marker components through the linkage chain of efficacy–chemical basis–quality control, and by correlating chemical constituents with clinical therapeutic effects, we can assess the efficacy and safety of TCM and thereby achieve a holistic quality evaluation. Starting from the evolution of TCM quality evaluation systems, this paper analyzes both the traditional quality assessment model based on macroscopic characteristics and the modern model centered on active ingredients. Drawing on the organic integration of quality markers (Q-Markers) with multidisciplinary knowledge, the study explores the establishment of a Q-Marker–based quality evaluation framework and proposes innovative approaches to guide the future development of TCM quality assessment.

1 Development History of the Quality Evaluation System for Traditional Chinese Medicine

1.1 Development of the Traditional Chinese Medicine Quality Evaluation System

The authenticity and quality of traditional Chinese medicines directly affect the efficacy and safety of clinical use. In ancient texts on TCM, it is common to assess the authenticity and quality of herbs based on their morphological, coloristic, olfactory, and gustatory characteristics. Drawing on long-term clinical experience and accumulated knowledge, ancient Chinese pharmacologists developed a comprehensive system for evaluating the quality of TCM that links these macroscopic traits to the intrinsic properties of the herbs. With the advent of modern precision instruments such as microscopes, the identification of herbal characteristics has advanced to the cellular and molecular levels, thereby reducing the influence of subjective factors on evaluators’ judgments and imbuing the process with greater accuracy and scientific rigor. Renowned TCM scholar Professor Xie Zongwan, building on the theoretical essence and empirical insights passed down through millennia, systematically reviewed and highly endorsed the traditional TCM quality-assessment framework, articulating the principle of “distinguishing quality through characteristic appraisal.” However, systematic research on the correspondence and correlation between “characteristics” and “quality” remains lacking. ^[2-3] The traditional “morphological identification and quality assessment” system is characterized by its intuitive presentation and ease of operation, thereby playing a crucial role in the quality evaluation of traditional Chinese medicines. However, it suffers from significant limitations, including strong subjectivity on the part of the assessor, difficulties in objectively articulating morphological attributes, and challenges in quantifying quality attributes. Fortunately, the use of modern electronic sensory instruments—such as electronic noses, electronic tongues, and texture analyzers—has made it possible to achieve objective, data-driven representation of certain morphological characteristics. ^[4-6] The core principle of “identifying characteristics and discussing quality” emphasizes, on the basis of empirical observation, the exploration of the relationship between the morphological characteristics of Chinese medicinal materials and their overall quality. However, at present, the intrinsic mechanisms underlying this relationship remain scientifically unexplained; thus, this approach constitutes a rather vague method of evaluation that overlooks the importance of research into formula compatibility, the material basis, and the mechanisms of action of Chinese medicinal prescriptions.

1.2 Development of Modern Quality Evaluation Systems for Traditional Chinese Medicine

2 Based on Q-Marker Research Approach to Quality Assessment

2.1 The Theory of Medicinal Properties in Traditional Chinese Medicine Q-Marker Quality Assessment

The theory of medicinal properties in traditional Chinese medicine constitutes the epistemology and methodology within the TCM theoretical system. It is a systematic summary derived from objective observations of the body’s responses to herbal medicines, analyzed, generalized, and interpreted through the TCM theoretical framework. This theory is characterized by the mutual interdependence of “nature” and “efficacy,” and primarily encompasses the four natures—warm, hot, cold, and cool; the five flavors—pungent, sour, bitter, sweet, and salty; as well as the principles of ascending, descending, floating, and sinking, and the meridian tropism of herbs. ^[20-21] Under the guidance of the theoretical system of traditional Chinese medicine, the efficacy and properties of herbal medicines are inextricably linked; for instance, in cases of heat syndromes, the use of cold or cool herbs can alleviate or eliminate the symptoms. By analyzing the correlations between the chemical structures of plant-derived TCM herbs and their pharmacological properties, it has been found that compounds from herbs with similar properties exhibit a high degree of structural similarity. Using metabolomics approaches, the mechanisms underlying the warming and heating effects of Astragalus and its fractionated constituents were investigated, thereby establishing a “property–efficacy–compound” relationship. The results indicate that calycosin exerts its warming effect by upregulating the expression of key proteins in the peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α)/nuclear respiratory factor 1 (NRF1) signaling pathway, thereby modulating glycerophospholipid and unsaturated fatty acid metabolism and influencing energy metabolism—this constitutes the material basis for the warming and heating effects of Astragalus. ^[22-23] Conducting Q-Marker research, guided by the theoretical framework of traditional Chinese medicine, can begin with an analysis of the correlation between the properties of Chinese medicinal materials and their material basis, focusing on the “property–efficacy–component” relationship to achieve precise identification of Q-Markers, thereby enabling quality evaluation that reflects the “property–efficacy–component” triad.

2.2 Principles of Traditional Chinese Medicine Compatibility Q-Marker Quality Assessment

Traditional Chinese medicinal formulas are a crucial manifestation and primary therapeutic modality of TCM, grounded in the principles of syndrome differentiation and individualized treatment as well as the holistic perspective. As the saying goes, “A formula is composed through the combination of herbs,” and the rules governing herb compatibility are employed to guide the formulation of these prescriptions, with particular emphasis on the principles of “seven emotions and six harmonies” and the hierarchical structure of “sovereign, minister, assistant, and messenger.” ^[24] In traditional Chinese medicine, formulae are composed by selecting herbs in accordance with the pattern, symptoms, and disease, while taking into account the primary and secondary aspects of the pathological changes, the relationship between root and manifestation, the urgency of the condition, and the vertical hierarchy. The careful combination of herbs, tailored to their individual properties, embodies the holistic and dynamic perspective of TCM. ^[25] The formulation of herbal prescriptions emphasizes a hierarchical and orderly arrangement of principal and auxiliary ingredients: the chief herb is typically used in the largest dosage to address the patient’s primary disease or principal syndrome, while the assistant herbs, when combined with the chief herb either synergistically or as facilitators, can enhance the formula’s therapeutic efficacy against the primary condition or provide supportive treatment for concomitant diseases or syndromes. The adjuvant herbs further assist the chief and assistant herbs in exerting their therapeutic effects and help harmonize the entire formula. This “chief–assistant–adjuvant–facilitator” compositional structure underscores the hierarchical distinction among the herbs in a prescription, reflecting the systematic nature of herbal compatibility as well as the reciprocal relationship between dosage and efficacy—features that can guide the discovery and identification of Q-Markers for both formulas and pharmaceutical preparations. By applying network pharmacology techniques and leveraging the characteristics of Q-Markers, we have preliminarily identified rhein, aloe-emodin, physcion, chrysophanol, sennoside B, (±)-catechin, and gallic acid as the Q-Markers of Taohu Chengqi Tang and its chief herb, rhubarb, which exerts its blood-activating and stasis-resolving effects in the context of stroke. ^[26] 。

2.3 Structure-activity relationship Q-Marker Quality Assessment

For single-compound drugs, since the therapeutic efficacy is directly proportional to the content of the active ingredient, quality evaluation can be achieved through quantitative determination of that ingredient. However, due to the multi-component nature of traditional Chinese medicines and the complex formulation and compatibility inherent in TCM compound prescriptions, controlling only a single component fails to accurately reflect the true quality of the preparation. The TCM fingerprint profile is a widely accepted method for evaluating the quality of TCM in China; it provides a visual representation of the chemical constituents and their relative amounts, thereby revealing the chemical characteristics of the medicinal material. This approach enables quality assessment from a chemical-information perspective. Furthermore, spectrum–effect relationship analysis integrates the chemical information conveyed by the fingerprint profile with the pharmacological effects, making it a valuable tool for identifying biomarkers that truly reflect the intrinsic quality of the product. ^[27-28] Traditional Chinese medicine fingerprinting technology, combined with chemometric techniques such as cluster analysis, principal component analysis, and similarity evaluation, can comprehensively characterize the relative relationships among the chemical constituents of medicinal materials, thereby enabling quality assessment of both crude TCM herbs and TCM products. ^[29-30] . Using the spectrum–effect relationship research approach, by establishing the Tibetan medicinal plant Saussurea integrifolia Meconopsis integrifolia (Maxim.) Fingerprint profile of Franch’s whole herb (excluding the floral parts used in medicinal applications) (HMI) extract, with its constituent components analyzed by liquid–mass spectrometry; principal component analysis and grey relational analysis were employed to establish the relationship between the common peaks in the HMI extract fingerprint and its antioxidant activity; high-speed counter-current chromatography was used for separation, providing a reference for research on HMI quality evaluation and quality-control indicators. ^[31] 。

2.4 Network pharmacology Q-Marker Quality Assessment

The identification of Q-Markers should comprehensively consider as many chemical constituents as possible in traditional Chinese medicines, with those identified through preliminary screening being selected for further analysis. Literature retrieval is a commonly used approach for pinpointing the sources of Q-Markers; however, it suffers from incomplete knowledge integration, a lack of systematic analysis, and unclear relational networks. Network pharmacology, a novel methodology rooted in systems biology, pharmacology, and molecular network science, constructs “component–target” interaction networks to uncover the latent relationships between active constituents and their mechanisms of action. At both the molecular and systemic levels, this approach can identify bioactive components along with their potential targets and underlying mechanisms, thereby demonstrating the feasibility of predicting the specific disease-targets and mechanistic pathways through which traditional Chinese medicines exert therapeutic effects. ^[32-34] This clarifies the “efficacy–component–mechanism” relationship. In recent years, network pharmacology has been widely applied to research on the source identification of Q-Markers. By employing fingerprinting techniques, five chemical constituents in the aqueous decoction of Paeonia lactiflora and in Danggui Sini Tang were identified, elucidating the patterns of component transmission and demonstrating the traceability and measurability of Q-Markers. Furthermore, network pharmacology was used to analyze the regulatory signaling pathways of ten core targets, thereby constructing a “component–target–pathway” network to evaluate their efficacy and provide a scientific basis for predicting Q-Marker profiles. ^[35] 。

2.5 Drug Metabolism Q-Marker Quality Assessment

The effective absorption of chemical constituents in the body and their pharmacokinetic patterns constitute the material basis and objective rationale for the therapeutic efficacy of traditional Chinese medicines. The spectrum–effect relationship links chemical constituents to the pharmacological actions of TCM, reflecting the intrinsic quality of the formulation as a whole; however, it does not account for the in vivo metabolic processes of the drugs. Only when a drug is sufficiently absorbed and reaches its target sites can it exert a therapeutic effect. Therefore, it is necessary to integrate information on chemical constituents, pharmacological effects of TCM, and the metabolic processes of absorbed components—i.e., to conduct research on the “spectrum–effect–metabolism” relationship. In recent years, numerous biomarkers have been identified through analysis of blood metabolites, which are of great significance for the discovery of Q-markers and for the quality evaluation of TCM. ^[36-37] Tangzhiqing tablets can be used in the treatment of diabetes; however, their quality assessment remains at a preliminary stage. Based on qualitative, quantitative, and dose–exposure–response analyses, it was found that the glucose-lowering efficacy of Tangzhiqing tablets increases with increasing dosage. Furthermore, liquid chromatography–tandem mass spectrometry (LC–MS/MS) was employed to identify potential Q-markers in plasma, and the results indicated that nuciferine and paeoniflorin exhibit a clockwise hysteresis relative to the glucose-lowering effect of Tangzhiqing tablets. ^[38] 。

2.6  Q-Marker Establishment of a Quality Evaluation Model