Unraveling pyrrolizidine alkaloid-induced liver damage with an integrative spatial lipidomics framework

Pyrrolizidine alkaloids (PAs), a class of secondary metabolites widely distributed in plants and the accidental ingestion or improper use of foods and herbs containing PAs, can lead to irreversible liver damage. Considering that the toxic mechanism of PAs is closely associated with metabolism, the hepatotoxicity was analyzed from the perspective of lipid metabolism. An integrated analytical approach was employed, combining mass spectrometry imaging (MSI) with liquid chromatography-mass spectrometry (LC-MS), to comprehensively investigate the spatial and temporal dynamics of lipid metabolites during PA exposure. The final lipidomics results combined with RNA sequencing showed that time-dependent changes in metabolite levels after the administration of PAs, involving the pathways of fatty acids, glycerophospholipids, glycerolipids and sphingolipids. Among them, phosphatidylcholines (PC), phosphatidylethanolamines (PE), phosphatidylinositols (PI) and sphingomyelins (SM) were downregulated to varying degrees within 0 to 24 h, while phosphatidylglycerol (PG), ceramides (Cer), diacylglycerols (DG) and triacylglycerols (TG) were upregulated. Notably, certain lipids exhibited distinct spatial distributions; for example, elevated levels of TG (56:13) were localized near the hepatic portal vein. Subsequently, the changes of lipid subclasses recovered within 24 to 48 h. Transcriptome RNA sequencing was used to enrich for key pathway-related differential genes Pemt, Gpat, etc. to explain the regulation of the hepatotoxic lipid pathway. The integration of MSI with LC-MS spectroscopy of endogenous metabolites provided intuitive insights into the alterations and spatial distribution of lipid metabolism in mice. Consequently, this study may enhance specific assessments and facilitate early diagnosis of acute toxicity associated with PAs.