Mechanistic insights into the effect of CYP2C9*2 and CYP2C9*3 variants on the 7-hydroxylation of warfarin

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From: Pharmacogenomics(Vol. 16, Issue 4)
Publisher: Future Medicine Ltd.
Document Type: Report
Length: 4,176 words
Lexile Measure: 1500L

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Author(s): Addepalli Pavani aff1 , Shaik Mohammad Naushad aff2 , Balraj Alex Stanley aff2 , Renganathan Gnanambal Kamakshi aff2 , Krishnan Abinaya aff2 , Malempati Amaresh Rao aff3 , Addepally Uma aff4 , Vijay Kumar Kutala [*] aff1

Keywords:

7-hydroxy warfarin; CYP2C9*2 ; CYP2C9*3 ; multiple linear regression; warfarin

Background

CYP2C9 (MIM:*601130) is one of the major drug-metabolizing enzyme of the CYP450 superfamily of monooxygenases, which is involved in the metabolism of more than 100 therapeutic drugs [1 ]. CYP2C9 gene is highly polymorphic with several SNPs reported in its regulatory and coding regions. Some of these SNPs are associated with reduced enzyme activity compared with wild-type both in vitro and in vivo [2-5 ].

Warfarin is an oral anticoagulant frequently prescribed to prevent thrombotic events in patients with deep vein thrombosis, atrial fibrillation and valve replacement therapy. Warfarin is a racemic mixture of R- and S-enantiomers. S-warfarin is more potent than R-warfarin in producing an anticoagulant response [6 ]. CYP2C9 catalyzes the 7-hydroxylation of S-warfarin to form 7-hydroxy warfarin [6 ]. Two polymorphisms in CYP2C9 , that is, CYP2C9*2 (rs1799853) and CYP2C9*3 (rs1057910) were reported to decrease CYP2C9 activity [7 ]. Adverse drug reactions were observed in the subjects harboring these two polymorphisms upon treatment with the standard empirical doses of warfarin [ 8 ]. Typically, they exhibit a phenomenon termed as 'warfarin sensitivity,' requiring lower doses of warfarin for achieving therapeutic international normalized ratio (INR) due to poor 7-hydroxylation [9 ].

The CYP2C9*2 and CYP2C9*3 variants are being used widely as predictors of warfarin dose in different pharmacogenomic algorithms [10,11 ]. Our recent studies also highlighted potential utility of these genetic variants in warfarin dose optimization [12,13 ]. These polymorphisms result in the following amino acid substitutions, that is, R144C and I359L, respectively. Although, these amino acids are located away from the active catalytic site of CYP2C9, they are influencing S-warfarin metabolism significantly. The existing simulation models proposed following molecular effects of CYP2C9*2 and CYP2C9*3 variants: an increased fluctuation of residues near the substrate recognition site/active site [14 ], reduction in the substrate access channel size hindering the entry of substrate to the active site [15 ] and increased distance between hydroxylation site of S-warfarin and reactive oxyferryl heme than wild-type structure [16 ].

In the current study, we have generated PyMOL based structural ensembles of each variant using crystal structure of CYP2C9 with flurbiprofen bound form (PDB ID: 1R9O) as a template. This has better resolution (2 Å) compared with other two crystal structures of CYP2C9, that is, 1OG2 (2.60 Å) and 1OG5 (2.55 Å). Glide (grid-based ligand docking with energetics) score was used for docking and binding affinity prediction in wild and variant forms of CYP2C9 with S-warfarin to provide more insights into the CYP2C9 mediated molecular dynamics and warfarin pharmacokinetics.

Materials & methods

Patients & data collection

A total of 199 patients (110 men and 89 women) who are receiving therapeutic dose of warfarin as a preventive measure for thrombotic events for clinical indications, that is, valve replacement (n = 195), deep vein thrombosis (n...

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Gale Document Number: GALE|A416964382