Origin of the gender differences of the natural resistance to antivitamin K anticoagulants in rats

Abstract

Vitamin K antagonists (VKA) are used either in human medicine to prevent thromboembolic disorders or as rodenticides for pest control management. In rodents, female rats are described to be more tolerant to the action of vitamin K antagonists than males. Nevertheless, the mechanism of this greatest tolerance is still unknown and this study aims to identify the origin of this greatest tolerance after VKA administration. Therefore, difethialone, one of the most powerful VKA was used in this study. A possible difference in the pharmacokinetics of difethialone between males and females was first investigated. The determination of the pharmacokinetic parameters allowed to exclude a pharmacokinetic origin of the greatest tolerance of females to VKA. Thus, a natural resistance to difethialone of the liver VKOR activity, which is the target of VKA, was thus explored in females. The determination of Ki towards difethialone in liver microsomes allowed to also exclude this hypothesis. Therefore, equipment in vitamin K-dependent clotting factors and properties of vitamin K-dependent clotting factors were explored. Basal activity of clotting factors VII and X were found significantly higher in females of respectively 43% and 21%. Moreover, after VKA administration, half-lives of clotting factors II and X were found significantly longer in females of respectively 27% and 10% and a lag time of 4h before the beginning of the decay of factor VII was observed only in females after difethialone administration. The greater tolerance of female rats to VKA is thus due a stronger basal pool of vitamin K-dependent clotting factors VII and X and to a slower decline of vitamin K-dependent clotting factors II, VII and X after VKA administration.

Thrombin generation test: A reliable tool to evaluate the pharmacodynamics of vitamin K antagonist rodenticides in rats

“…VKA rodenticides are characterized by a wide interindividual variability of response between rats due to gender, environmental and genetic factors 1,5,6 . The origin of the gender differences in the response to VKA rodenticides has been reported in different rat strains: in Sprague-Dawley rats, a higher basal activity of FVII and FX has been found in females compared to males, in agreement with results of older studies in Wistar rats 6,7 . Besides, resistance to VKA rodenticides due to genetic factors has been reported in both genders from many countries in Europe but also in United States, Canada, Japan and Australia resulting in a serious concern for pest control [8][9][10] ].…”

“…Half-lives of the vitamin K dependent factors following difethialone intoxication had been previously estimated in aliquots collected during this same study 7 and reported: 2.9h for FVII, 5.5h for FX, 11h for FII and 12.6h for FIX. Based on the time to halving values, ETP and PH were ranked: in both genders, FVII decreased first, followed by FX, then ETP, PH, and FII then finally by FIX.…”

“…Published data on the rodent PD profile of VKA rodenticides are scarce and report results obtained using coagulation tests of human clinical practice performed with rodent plasma samples 5,7,14,15 . Semi-global coagulation assays, namely prothrombin time (PT) and activated partial thromboplastin time are reliable tools for the exploration of coagulation system in rodents, especially to assess the anticoagulant resistance 16 .…”

Missense mutation of VKORC1 leads to medial arterial calcification in rats

“…In our model, the limited intake of vitamin K associated with the presence of the VKORC1 mutation leads to decrease of the pool of activated vitamin K-dependent clotting factors but not sufficiently to lead to hemorrhagic syndrome. Indeed, to modify the prothrombin time in rats, it was demonstrated that reduction of at least 70% of activity of factor II was required 46 . This reduction in our model is only of 40%.…”

Study of the efficiency of anticoagulant rodenticides to controlMus musculus domesticusintrogressed withMus spretus Vkorc1

“…Microsomal VKOR activity was assayed as described previously, and characterisation of VKOR activity was performed by determining K m , V max and K i towards various AVKs, as described previously . The resistance factor of VKOR activity catalysed by VKORC1 spr was calculated by dividing the K i obtained for VKORC1 spr by the corresponding K i obtained for VKORC1 dom .…”