Metabolic profiles among the control group, sepsis group and XBJ group
A series of metabolites were obtained at 2h, 6h and 12h post CLP in rats with or without XBJ injection treatment via GC-MS analysis. All of these differential metabolites detected were showed in supplementary table 1, 2 and 3, respectively.
Screening of differential metabolites in serum samples
PLS-DA, a multivariate statistical analysis, acted to find differential metabolites and discriminate different groups. Our results showed that the PLS-DA model demonstrated a distinct separation in the metabolic profiles among the control group, sepsis group, and XBJ group (Figure 1).
To explore the effect of XBJ injection in the dynamic changes of CLP-induced septic rat. Statistical tests, including fold change (FC), P-values and VIP scores, were applied to detect the significant metabolites in the sepsis group and XBJ injection group. Before analysis, the raw data acquired by GC-MS were normalized by median (supplementary figure 1). Based on VIP scores(VIP >1.5), fold change(FC>1.5 or <0.67), P value (P<0.05), 11, 33 and 26 differential metabolites were identified at 2h, 6h, and 12h post CLP between the sepsis group and the control group(Table 1). Besides, 32, 23, and 28 differential metabolites were observed at 2h, 6h and 12h post CLP between the XBJ group and the sepsis group (Table 2). We also found 3, 6 and 6 differential metabolites overlapped between the XBJ group and the sepsis group at different time points post CLP (Figure 2 and Table 3). In addition, the heat map and VIP scores of differential expressed metabolites at different time points in the control group, sepsis group, and XBJ group were presented in Figure 3 and Figure 4.
Related metabolic pathway analysis for the identified differential metabolites
To explore the potential metabolic pathways in which the identified differential metabolites were involved, all of the identified metabolites with significant differences in each group were imported into MetaboAnalyst5.0 to detect the metabolic pathways via KEGG. The pathway analysis results are shown in Figure 5. Cut-off value >0.1 was utilized to identify the significant metabolic pathways and filter the less important pathways. In our work, 1, 4 and 5 important metabolic pathways were investigated at 2h, 6h and 12h post CLP in the sepsis group compared with that of the control group. The related pathways of differential metabolites were galactose metabolism in 2h post CLP; aminoacyl-tRNA biosynthesis, arginine, and proline metabolism, selenocompound metabolism, starch and sucrose metabolism in 6h post CLP; aminoacyl-tRNA biosynthesis, arginine biosynthesis, arginine and proline metabolism, glyoxylate and dicarboxylate metabolism, glycine, serine, and threonine metabolism in 12h post CLP. Besides, 5, 1 and 1 significantly metabolic pathways were observed at 2, 6 and 12h post CLP in the rats with XBJ injection treatment compared with that of the rats without XBJ injection treatment. The related pathways of differential metabolites were tyrosine metabolism and galactose metabolism in 2h post CLP; aminoacyl-tRNA biosynthesis, arginine and proline metabolism, selenocompound metabolism, starch, and sucrose metabolism in 6h post CLP; aminoacyl-tRNA biosynthesis, arginine biosynthesis, arginine and proline metabolism, glyoxylate and dicarboxylate metabolism, glycine, serine and threonine metabolism in 12h post CLP in the sepsis group compared with the control group (Figure 5). Besides, compared with the sepsis group, glutathione metabolism, arginine biosynthesis, arginine, and proline metabolism, sphingolipid metabolism, phenylalanine, tyrosine, and tryptophan biosynthesis changed markedly at 2h; arginine and proline metabolism changed significantly at 6 and 12h post CLP in the XBJ group compared with that of the sepsis group (Figure 5). According to the related metabolic pathway we identified, we found that XBJ injection can affect arginine and proline metabolism in CLP-induced septic rat (Table 3).