Investigation of Pyrrolizidine Alkaloid‐Induced Pulmonary Toxicity

Abstract

IntroductionPyrrolizidine alkaloids (PAs) are widely present in plants, and about half of them had been reported to induce toxicity in different organs. The previous study has proved that PAs exert their toxicity by metabolic activation to form dehydro‐PAs (DHPAs), which interact with proteins to form pyrrole‐protein adducts leading to toxicity. Monocrotaline (MCT) and retrorsine (RTS) are two representative toxic PAs. MCT is known to cause pneumotoxicity, while other PAs, including RTS, induced pneumotoxicity is unknown. The present study aimed to investigate whether other PAs can also cause pneumotoxicity and the mechanism initiating PA‐induced pneumotoxicity.MethodsMCT and RTS in rat liver and lung microsomal incubation were tested to compare the metabolic site of these two PAs. Then, the transport of DHPAs in blood after a single dose of MCT or RTS in rats was studied by using LC‐MS/MS analysis. DHPAs in blood fractions were detected by addition of glutathione (GSH) to form pyrrole‐GSH conjugate, and the addition of saline was used as the control. The biomarker of PA‐induced toxicity, pyrrole‐protein adducts in liver and lung of MCT or RTS treated rats were also determined. The histological study was performed to examine RTS‐induced pneumotoxicity in rats.ResultsThe microsomal incubation results showed that DHPAs were primarily generated in liver. Comparing with the control group, significant increase in the formation of pyrrole‐GSH conjugate was found in GSH‐added red blood cells (RBC) and plasma of both PA‐treated rats. Further, hepatic pyrrole‐protein adducts level in RTS‐treated rats was found about 3‐folds of that in MCT‐treated rats, while pyrrole‐protein adducts levels in lung were similar in both PA‐treated groups. Mild to severe vascular medial hypertrophy was observed along with the time after RTS treatment from 2 days to 4 weeks.These findings proved that RTS could cause pneumotoxicity. Furthermore, it provided, for the first time, that for both PAs, 1) DHPAs were present in the blood circulation; 2) DHPAs were transported by not only RBC as demonstrated previously but also by plasma; and 3) the transport of DHPAs by both RBC and plasma may be common for different toxic PAs rather than solely for MCT.ConclusionsOur study delineated the mechanism initiating PA‐induced pneumotoxicity via migration of DHPAs in blood circulation, and also revealed a potential risk of PA‐induced pulmonary toxicity.Support or Funding InformationThis study was supported by RGC HKSAR (GRF Project No. 469712 and 14111816), CUHK Direct Grant (No. 4054215 and 4054302) and CUHK One‐off Funding for Joint Lab/Research Collaboration (Project Code: 3132968)