Metabolic markers of tongue coating in healthy people with phlegm dampness constitution and damp-heat constitution

Abstract Objective Using tongue coating metabolomics, this study will comprehensively analyze metabolic differences between individuals with Phlegm Dampness Constitution (PDC) and Dampness Heat Constitution (DHC). Methods The samples were categorized into three groups: the Phlegm Dampness Constitution group, the Dampness Heat Constitution group, and the Balanced Constitution (BC) group (each consisting of 50 cases). Metabolites present in the tongue coating of the three groups were identified using GC-TOF-MS and UHPLC-QE-MS. We scrutinized the characteristics of metabolites, identified differential metabolic pathways in the Phlegm Dampness and Dampness Heat groups, and constructed a recognition model for distinguishing between Phlegm Dampness and Dampness Heat. Results A total of 139 different metabolites (75 upregulated, 64 downregulated) were identified in the Phlegm Dampness Constitution group compared to the Balanced Constitution group. Similarly, 157 different metabolites (103 upregulated, 54 downregulated) were observed in the Dampness Heat Constitution group compared to the Balanced Constitution group. Notably, 100 metabolites were common in the differential metabolites obtained from the aforementioned two comparisons, comprising 14 types of substances (mainly lipids and lipid-like molecules) across 6 metabolic pathways. In the comparison between the Phlegm Dampness Constitution and Dampness Heat Constitution groups, 54 different metabolites (15 upregulated, 39 downregulated) were identified, mainly involving 10 types of compounds (primarily lipids and lipid-like molecules and organic heterocyclic compounds) across 10 metabolic pathways. The identification model for distinguishing Phlegm Dampness Constitution and Dampness Heat Constitution groups based on differential metabolites included phenol, N-nitrosopyrrolidine, and triethanolamine. The model exhibited high accuracy (98.4%), specificity (96.0%), and sensitivity (98.0%). Triethanolamine was significantly upregulated in the Phlegm Dampness Constitution group compared to the Dampness Heat Constitution group, while N-nitrosopyrrolidine and phenol were significantly downregulated in the Phlegm Dampness Constitution group. Conclusion Lipids, lipid-like molecules, and organic heterocyclic compounds with abnormal expression play a crucial role in the formation of the Phlegm Dampness Constitution and the Dampness Heat Constitution. These identified differential metabolites hold promise as non-invasive markers for identifying individuals with Phlegm Dampness and Dampness Heat constitutions.