3.1 Clinical characteristics of DF
The clinical characteristics of the enrolled 50 patients showed in Table 1. There were 21 males and 29 females. The average admission days was 4.9 (3.9-7) days. Fever, nausea and vomiting, asthenia, skin hyperemia were the most common clinical symptoms. Regarding the comorbidities, hypertension (26%, 13/50), fatty liver (14%, 7/50), diabetes mellitus (10%, 5/50) were the most prevalent comorbidities. The results of the laboratory examinations showed that leukopenia (76%, 38/50), thrombocytopenia (92%, 46/50), increase of transaminase (alanine aminotransferase 29/50, aspartate aminotransferase 48/50, γ-glutamyl transpeptadase 23/50), increase of free fatty acids (FFA) (68%, 34/50), increase of creatine kinase (CK) (44%, 22/50) were more common. The management for most symptomatic DF patients were supportive treatments including.
3.2 Quality Control (QC) analysis and metabolites annotation
There was no statistical difference in age and gender between DF group and HC group. The QC samples were used to evaluate the repeatability and stability of UPLC-Q-TOF MS spectrometer. The Pearson correlation coefficient was calculated based on the peak area. The results of QC analysis indicated the experiment conditions exhibited high reliability (Supplementary Figure 1).
A total of 20 classes of metabolites were annotated and 631 types were lipids and lipid-like molecules (Figure 1a). According to the LIPID MAPS, flavonoids, glycerophosphoinositols and glycerophosphocholines were three most metabolites (Figure 1b).
3.3 Multivariate analysis
PCA was initially applied to evaluate the distribution pattern among all samples. As shown in Figure 2a, DF group and HC group showed good aggregation and classification. PLS-DA was further carried out to investigate the discrimination between the two groups (Figure 2b). The model parameters for the classification were R2Y = 0.87, Q2Y = 0.79 by 7-fold cross-validation. There was no obvious overfitting in model validation by randomly shuffled 200 times of the class membership (Figure 2c). The well fit PLS-DA models showed a significant separation in the scores plot between DF patients and HC, indicating the endogenous metabolites were changed as a result of DENV infection. Base on VIP and log2FC, a total of 619 metabolites significantly up-regulated and 64 metabolites down-regulated (Figure 2d).
3.4 Identification of potential biomarkers
Based on OPLS-DA, 17 metabolites in the upper-right quadrant of S-plot were tentatively identified, with 2 up-regulated and 15 down-regulated (Figure 2e) (Table 2). The relationship of 17 potential metabolites was evaluated by correlation analysis. Among them, LysoPC (18:2(9Z,12Z)) were highly positive correlated with PE (21:0/20:5(5Z,8Z,11Z,14Z,17Z)) and 13'-Hydroxy-alpha-tocopherol. Further metabolic pathways were analyzed by MetPA. The results from pathway analysis were presented in Figure 2e. Glycerophospholipid metabolism pathway was the main pathway of metabolic disorder in DF.