Pyrrolizidine alkaloids (PAs) are widely occurring phytotoxins which can induce severe liver damage in humans and other mammalian species by mechanisms that are not fully understood. Therefore, we investigated the development of PA hepatotoxicity in vivo, using an acutely toxic dose of the PA
senecionine in mice, in combination with intravital two-photon microscopy, histology, clinical chemistry, and in vitro experiments with primary mouse hepatocytes and liver sinusoidal endothelial cells (LSECs). We observed pericentral LSEC
necrosis together with elevated sinusoidal marker
proteins in the serum of
senecionine-treated mice and increased sinusoidal platelet aggregation in the damaged tissue regions. In vitro experiments showed no cytotoxicity to freshly isolated LSECs up to 500 µM
senecionine. However, metabolic activation of
senecionine by preincubation with primary mouse hepatocytes increased the cytotoxicity to cultivated LSECs with an EC50 of approximately 22 µM. The
cytochrome P450 (CYP)-dependency of
senecionine bioactivation was confirmed in CYP
reductase-deficient mice where no PA-induced hepatotoxicity was observed. Therefore, toxic metabolites of
senecionine are generated by hepatic CYPs, and may be partially released from hepatocytes leading to destruction of LSECs in the pericentral region of the liver lobules. Analysis of hepatic
bile salt transport by intravital two-photon imaging revealed a delayed uptake of a fluorescent
bile salt analogue from the hepatic sinusoids into hepatocytes and delayed elimination. This was accompanied by transcriptional deregulation of hepatic
bile salt transporters like Abcb11 or Abcc1. In conclusion,
senecionine destroys LSECs although the toxic metabolite is formed in a CYP-dependent manner in the adjacent pericentral hepatocytes.