Heterogeneity of the coumarin anticoagulant targeted vitamin K epoxide reduction system. Study of kinetic parameters in susceptible and resistant mice (Mus musculus domesticus)
✍ Scribed by Romain Lasseur; Agnès Grandemange; Christiane Longin-Sauvageon; Philippe Berny; Etienne Benoit
- Publisher
- John Wiley and Sons
- Year
- 2006
- Tongue
- English
- Weight
- 259 KB
- Volume
- 20
- Category
- Article
- ISSN
- 1095-6670
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✦ Synopsis
Vitamin K epoxide reductase (VKOR) activity in liver microsomes from a susceptible and a genetically warfarin-resistant strain of mice (Mus Musculus domesticus) was analyzed to determine the mechanism of resistance to this 4-hydroxycoumarin derivative. Kinetic parameters for VKOR were calculated for each strain by incubating liver microsomes with vitamin K epoxide ± warfarin. In susceptible mice, an Eadie-Hofstee plot of the data was not linear and suggested the involvement of at least two different components. Apparent kinetic parameters were obtained by nonlinear regression using a Michaelis-Menten model, which takes into account two enzymatic components. Component A presents a high K m and a high V m , and as a consequence only an enzymatic efficiency V m /K m was obtained (0.0024 mL/min/mg). Estimated warfarin K i was 0.17 µ µM. Component B presented an apparent K m of 12.73 µ µM, an apparent V m of 0.32 nmol/min/mg, and an apparent K i for warfarin of 6.0 µ µM. In resistant mice, the enzymatic efficiency corresponding to component A was highly decreased (0.0003-0.00066 mL/min/mg) while the K i for warfarin was not modified. The apparent V m of component B was poorly modified between susceptible and resistant mice. The apparent K m of component B observed in resistant mice was similar to the K m observed in susceptible mice. These modifications of the catalytic properties are associated with a single nucleotide polymorphism (T175G) in the VKOR-C1 gene, which corresponds to a Trp59Gly mutation in the protein.