3.2 The lipid profiles of placenta collected from ICP patients
The collected placenta samples were used for lipidomic analysis through UHPLC-Q Exactive MS as described in the method section. We separately analyzed the lipid profiles between the 30 women with mild ICP or severe ICP and 30 women with normal pregnancies. To distinguish the overall differences in lipid metabolite profiles between groups, we conducted multivariate statistical modeling by using OPLS-DA. The score scatter plot of the OPLS-DA model indicated that the difference between the normal group and the mild or severe ICP group was obvious (Fig 1A and Fig 2A), the samples from the ICP-M/ICP-S group and control groups were separated along the x-axis. Permutation test was used to confirm the accuracy of the model. All Q2 values (green) on the left were lower than the original value on the right, and the regression line of Q2 values intersects the vertical axis (left) below zero, which indicates high effectiveness and good prediction ability of the OPLS-DA model (Fig 1B and Fig 2B).
A total of 61 lipids (VIP >1 and P <0.05) were found to be significantly different between mild ICP and control groups, which included 27 downregulated and 34 upregulated lipids in the ICP-M group. The expression levels of the 61 differential lipids were used to draw a volcano plot (Fig 1C), the blue dots represent remarkably downregulated lipids, while the red dots represent significantly upregulated lipids. The relative contents of the top 50 differentially expressed lipids were observed through a hierarchical cluster heatmap (Fig 1D). All of the differentially expressed lipids can be classified into 16 categories, including: 15 PE species, 10 PC species, seven PS species, 12 SM species, three TG species, two FA species, two dMePE species, and one OAHFA, MGDG, Cer, GM3, phSM, LPE, ChE, PG , PI species. Detailed information about these differential lipids is shown in Data S1.
We also obtained 88 differential lipids between severe ICP and the control group according to the conditions of VIP >1 and P<0.05. A total of 46 lipids exhibited increased levels, and 42 exhibited decreased levels in the ICP-S group, and the detailed information between these two groups was shown in Data S2. The heatmap and volcano plots were conducted to display differences in lipid metabolites between the two groups (Fig 2C and Fig 2D). All the 88 differential lipids can be classified into 17 categories, including 20 PC species, 19 PE species, 15 PS species, 13 SM species, seven TG species, two dMePE species, two So species, and one OAHFA, MGDG, Cer, GM3, phSM, LPE, ChE, PG , PI ,FA species, respectively.