Investigation on Pneumotoxicity Induced by Pyrrolizidine AlkaloidsInvestigation on Pneumotoxicity Induced by Pyrrolizidine Alkaloids
Authors: He Yisheng , Song Zijing , Fan Xiaoyu , Ding Liang , Zhang Qing-Yu , Fu Peter P. , Ding Xinxin , Lin Ge 
Published: April 2020

Pyrrolizidine alkaloids (PAs) are most common phytotoxins. Apart from their extensively reported hepatotoxicity, few PAs, such as MCT, are also reported to cause lung injury. However, whether different PAs commonly lead to pneumotoxicity remains largely unknown whether different PAs. PAs require metabolic activation to exert toxicity. Hepatic cytochrome P450s are proposed to be responsible for bioactivation of PAs to reactive dehydro‐PAs, which interact with proteins to form pyrrole‐protein adducts causing intrahepatic cytotoxicity. However, the mechanisms underlying pneumotoxicity of PAs, especially the site of metabolic activation of PAs, have not been delineated. Here we aimed to investigate pneumotoxicity of different types of PAs and also identify the contribution of hepatic P450s and extrahepatic P450s to metabolic bioactivation of PAs.

Pulmonary toxicity of four representative PAs of both retronecine and otonecine types and Gynura Segetum (GS) alkaloid extract containing two retronecine type PAs, to mimic human PA poisoning, were investigated. Rats were orally administered with representative PAs and GS at 0.2 mmol/kg for 48 hours. Biochemical and histological examinations were applied to evaluate PA‐induced toxicity in liver and lung. The results showed that all PAs induced liver injury to varied levels. Significant lung lesions including pulmonary arterial hypertrophy, capillary congestion, endothelium damage, and abnormal proliferation of smooth muscle cells were found in all PA‐treated groups, demonstrating that both retronecine and otonecine types of PAs can cause pulmonary toxicity.

Further to delineate the role of hepatic and extrahepatic CYPs in metabolic bioactivation of PAs, mice with conditional deletion of cytochrome P450 reductase (Cpr) gene and resultant dysfunctional P450s were used. After oral exposure to MCT (120 mg/kg), a well‐known pneumotoxic PA, metabolic activation and pneumotoxicity of MCT among wild‐type (WT), liver‐specific Cpr‐null (LCN), and extrahepatic Cpr‐knockdown (XhCL) mice were compared. The results demonstrated that comparing with WT mice, pyrrole‐protein adducts were significantly decreased (by >60%) in the serum, liver and lungs in LCN mice but unchanged in XhCL mice. In addition, comparing with WT mice, MCT‐exposed LCN mice had significantly higher blood concentration of the intact MCT. Consistently, lung injury represented by vasculature damage was observed in WT and XhCL mice but not in LCN mice. All the data confirmed that hepatic CYPs, not extrahepatic CYPs, were responsible for metabolic activation of PAs.

To conclude, the present study for the first time demonstrated that PAs can commonly induce lung injury, which is dependent on the metabolic activation mediated by functional hepatic CYPs.

Support or Funding Information

The present study was supported by General Research Fund (GRF Project No. 14160817) from Research Grants Council of Hong Kong Special Administrative Region.