Isomer-Dependent Pharmacokinetic Behavior and VKOR Interactions of Second-Generation Anticoagulant Rodenticides: An...

Second-generation anticoagulant rodenticides (SGARs) were developed to overcome warfarin resistance in rodent populations; however, their prolonged hepatic retention has raised concerns regarding secondary poisoning of non-target wildlife. All major SGARs exist as cis-trans isomeric pairs, and differences in biological half-life between isomers have been reported, yet the molecular basis for such isomer-dependent pharmacokinetic behavior remains poorly understood. In this study, we conducted an integrated evaluation of cis and trans isomers of SGARs using in vivo, in vitro, and in silico approaches, with vitamin K epoxide reductase (VKOR) serving as the molecular target. The individual compounds exhibited distinct isomer-dependent profiles in hepatic retention, inhibitory potency (IC₅₀), and VKOR interaction-related properties. Molecular dynamics simulations further revealed isomer-dependent differences in torsional flexibility around specific rotatable bonds and in ligand-VKOR interaction fractions. For flocoumafen and bromadiolone, the presence of an ether oxygen was associated with increased torsional and orientational flexibility and enhanced hydrogen-bonding potential, which may facilitate metabolic processing and contribute to the relatively faster elimination of cis isomers. Collectively, these results suggest that isomer-specific VKOR interaction patterns may contribute, in a compound-dependent manner, to isomer-dependent pharmacokinetic behavior, offering structural perspectives for the design of rodenticides with reduced ecological risk.