Fig. 4

Metabolomic analysis of synovial fluid in the knee joint of patients with gout and normal group. A: PCA model plot for all samples obtained by sevenfold cross-validation. B: PLS-DA (partial least squares-discriminant analysis PLS-DA is a supervised discriminant statistical method). C: Orthogonal partial least squares-discriminant analysis OPLS-DA is a supervised discriminant statistical method in which there is only one predictive principal component and multiple orthogonal principal components. There can be more than one. The between-group variation is maximized on t1 so that between-group variation is directly distinguished from t1, while within-group variation is reflected in the orthogonal principal component. The two groups are significantly different on the OPLS-DA score plot. D: Volcanic map can be used to visualize p value and Fold change value, which is beneficial to screen differential metabolites. The red origin represents the significantly up-regulated differential metabolites in the experimental group, the blue origin represents the significantly down-regulated differential metabolites, and the gray point represents the insignificant differential metabolites. E: TOP-50 differential metabolite heat map, visualization of top50 differential metabolite expression based on VIP values (horizontal coordinates indicate sample names, vertical coordinates indicate differential metabolites. The color ranges from green to red indicating low to high metabolite expression abundance, i.e., redder indicates higher expression abundance of the differential metabolite)