Abstract
Pyrrolizidine alkaloids (PAs) are a large group of plant constituents of which especially
the 1,2- unsaturated PAs raise a concern because of their liver toxicity and potential
genotoxic carcinogenicity. This toxicity of PAs depends on their kinetics. Differences
in absorption, distribution, metabolism, and excretion (ADME) characteristics of PAs
may substantially alter the relative toxicity of PAs. As a result, kinetics will also
affect relative potency (REP) values. The present review summarizes the current state-of-the
art on PA kinetics and resulting consequences for toxicity and illustrates how physiologically-based
kinetic (PBK) modelling can be applied to take kinetics into account when defining
the relative differences in toxicity between PAs in the in vivo situation. We conclude that toxicokinetics play an important role in the overall
toxicity of pyrrolizidine alkaloids. and that kinetics should therefore be considered
when defining REP values for
combined risk assessment. New approach methodologies (NAMs) can be of use to
quantify these kinetic differences between PAs and their N-oxides, thus contributing
to the 3Rs (Replacement, Reduction and Refinement) in animal studies.
Key words
Toxicokinetics - pyrrolizidine alkaloids - pyrrolizidine alkaloid N-oxides - relative
potency (REP) value - Physiologically-based kinetic (PBK) models