Hepatotoxic pyrrolizidine alkaloids induce DNA damage response in rat liver in a 28-day feeding study

Abstract

Pyrrolizidine alkaloids (PA) are secondary plant metabolites that occur as food and feed contaminants. Acute and subacute PA poisoning can lead to severe liver damage in humans and animals, comprising liver pain, hepatomegaly and the development of ascites due to occlusion of the hepatic sinusoids (veno-occlusive disease). Chronic exposure to low levels of PA can induce liver cirrhosis and liver cancer. However, it is not well understood which transcriptional changes are induced by PA and whether all hepatotoxic PA, regardless of their structure, induce similar responses. Therefore, a 28-day subacute rat feeding study was performed with six structurally different PA heliotrine, echimidine, lasiocarpine, senecionine, senkirkine, and platyphylline, administered at not acutely toxic doses from 0.1 to 3.3 mg/kg body weight. This dose range is relevant for humans, since consumption of contaminated tea may result in doses of ~ 8 µg/kg in adults and cases of PA ingestion by contaminated food was reported for infants with doses up to 3 mg/kg body weight. ALT and AST were not increased in all treatment groups. Whole-genome microarray analyses revealed pronounced effects on gene expression in the high-dose treatment groups resulting in a set of 36 commonly regulated genes. However, platyphylline, the only 1,2-saturated and, therefore, presumably non-hepatotoxic PA, did not induce significant expression changes. Biological functions identified to be affected by high-dose treatments (3.3 mg/kg body weight) comprise cell-cycle regulation associated with DNA damage response. These functions were found to be affected by all analyzed 1,2-unsaturated PA. In conclusion, 1,2-unsaturated hepatotoxic PA induced cell cycle regulation processes associated with DNA damage response. Similar effects were observed for all hepatotoxic PA. Effects were observed in a dose range inducing no histopathological alterations and no increase in liver enzymes. Therefore, transcriptomics studies identified changes in expression of genes known to be involved in response to genotoxic compounds at PA doses relevant to humans under worst case exposure scenarios.

Transcriptomics analysis of hepatotoxicity induced by the pesticides imazalil, thiacloprid and clothianidin alone or in binary mixtures in a 28-day study in female Wistar rats

“…Those three studies indicated a clastogenic potential, which is in line with the different regulators included in the network predicted by IPA, such as BRCA1, ATR, MDC1, MCPH1 and H2AX (Bonner et al 2008 ; Hustedt and Durocher 2016 ). Interestingly, a study on pyrrolizidine alkaloids reported the induction of a DNA damage response involving the up-regulation of Rad51 and Ddias that were also induced our study (Ebmeyer et al 2020 ). For THI or IMZ, no specific networks or evident GO enrichment patterns were observed.…”

Toxic Prediction of Pyrrolizidine Alkaloids and Structure‐Dependent Induction of Apoptosis in HepaRG Cells

“…Pyrrolizidine alkaloids (PAs), a group of secondary plant metabolites, belong to the most widely distributed natural toxins [ 1 ]. Intake of PAs present in plants and/or contaminated foodstuffs causes numerous cases of toxicity [ 2 , 3 ].…”

“…Intake of PAs present in plants and/or contaminated foodstuffs causes numerous cases of toxicity [ 2 , 3 ]. Tea, honey, and herbal spices were identified as the primary sources contributing to human exposure to PAs [ 1 , 4 , 5 ]. Different doses of PAs could cause acute toxicity and chronic toxicity [ 6 ].…”

Hepatotoxicity of pyrrolizidine alkaloids in rats in relation to human exposure

“…Recently, Ebmeyer and colleagues published a 28-day feeding study with six pyrrolizidine alkaloids in rats (Ebmeyer et al 2020 ). Pyrrolizidine alkaloids occur in honey, tea and herbal spices, which represent the main sources of human exposure (Bodi et al 2014 ; EFSA 2017 ; Mulder et al 2018 ).…”

“…Liver enzymes were not increased in the exposed rats. However, at the highest tested doses, gene array analyses showed clear expression changes (Ebmeyer et al 2020 ). A set of 36 commonly regulated genes was observed for the high-dose groups of four structurally different pyrrolizidine alkaloids.…”