Lung injury induced by pyrrolizidine alkaloids depends on metabolism by hepatic cytochrome P450s and blood transport of reactive metabolites

Yisheng He, Wei Lian, Liang Ding, Xiaoyu Fan, Jiang Ma, Qing Yu Zhang, Xinxin Ding, Ge Lin

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


Pyrrolizidine alkaloids (PAs) are common phytotoxins with both hepatotoxicity and pneumotoxicity. Hepatic cytochrome P450 enzymes are known to bioactivate PAs into reactive metabolites, which can interact with proteins to form pyrrole-protein adducts and cause intrahepatic cytotoxicity. However, the metabolic and initiation biochemical mechanisms underlying PA-induced pneumotoxicity remain unclear. To investigate the in vivo metabolism basis for PA-induced lung injury, this study used mice with conditional deletion of the cytochrome P450 reductase (Cpr) gene and resultant tissue-selective ablation of microsomal P450 enzyme activities. After oral exposure to monocrotaline (MCT), a pneumotoxic PA widely used to establish animal lung injury models, liver-specific Cpr-null (LCN) mice, but not extrahepatic Cpr-low (xh-CL) mice, had significantly lower level of pyrrole-protein adducts in the serum, liver and lungs compared with wild-type (WT) mice. While MCT-exposed LCN mice had significantly higher blood concentration of intact MCT, compared to MCT-exposed WT or xh-CL mice. Consistent with the MCT in vivo bioactivation data, MCT-induced lung injury, represented by vasculature damage, in WT and xh-CL mice but not LCN mice. Furthermore, reactive metabolites of MCT were confirmed to exist in the blood efflux from the hepatic veins of MCT-exposed rats. Our results provide the first mode-of-action evidence that hepatic P450s are essential for the bioactivation of MCT, and blood circulating reactive metabolites of MCT to the lung causes pneumotoxicity. Collectively, this study presents the scientific basis for the application of MCT in animal lung injury models, and more importantly, warrants public awareness and further investigations of lung diseases associated with exposure to not only MCT but also different PAs.

Original languageEnglish (US)
Pages (from-to)103-116
Number of pages14
JournalArchives of Toxicology
Issue number1
StatePublished - Jan 2021


  • Cpr-null mice
  • Cytochromes P450
  • Lung injury
  • Metabolism-based pneumotoxicity
  • Monocrotaline
  • Pyrrolizidine alkaloids

ASJC Scopus subject areas

  • Toxicology
  • Health, Toxicology and Mutagenesis


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