Investigating the role of microRNA on warfarin response

Warfarin is the most commonly prescribed oral anticoagulant for the prevention and treatment of thromboembolism in patients with atrial fibrillation, venous thrombosis or with cardiac valve prostheses. However, warfarin remains a challenging drug to prescribe due to its narrow therapeutic index and large inter-individual variability. At least 30% of warfarin dose variability is attributable to genetic polymorphisms in CYP2C9, the primary metabolizing enzyme of warfarin’s S-enantiomer, and VKORC1, the drug target of warfarin which mediates the vitamin K-dependent coagulation pathway (1, 2). CYP4F2, a vitamin K oxidase, has been shown to account for an additional 1-7% of warfarin dose variability (3, 4). Combinations of age, body weight and polymorphisms in CYP2C9, VKORC1 and CYP4F2 account for up to 65% of warfarin dose variability, but 30-40% of warfarin dose variance still remains poorly understood, suggesting that other factors might be involved in warfarin’s pharmacological effect. Interestingly, a recent in vitro study has shown that miR-133a down-regulates VKORC1 mRNA expression in HepG2 cells (5). More recently, a genetic variant in MIR133A2 was demonstrated to have a potential effect on warfarin dose variability (6). The role of circulating microRNA (miRNA) in warfarin dose variability however has never been investigated. To evaluate the effect of miRNA on warfarin dose variability, we conducted a pilot study comparing the baseline serum levels of miRNA in patients who have achieved warfarin stable dose (n=10) to those who did not achieve warfarin stability (n=10), using the Affymetrix GeneChip® miRNA Array 4.1. Statistical analyses were conducted using the T-test in Multi Experiment Viewer (MeV) v4.9, with 180k permutations. Six miRNAs showed significant association (p < 0.05) with fold change > 1.5 but no association was found with miR-133a. Target genes of the significant miRNAs were identified using Affymetrix® Transcriptome Analysis Console (TAC) software v3.0. Bioinformatics analysis using DAVID pathway viewer v6.7 suggests target genes of miR-548a-3p are involved in the coagulation pathwayFigure has been removed due to lack of space., suggesting that this miRNA could play a role in warfarin dose variability. Work is currently underway to validate and replicate the effect of circulating miR-548a-3p on warfarin response in our prospective cohort of warfarin-treated patients (n=1000). Given the functional and genetic associations previously reported with miR-133a (5, 6), we are also including miR-133a in our validation process. Any miRNAs found to affect warfarin dose requirement will be incorporated into a warfarin dosing algorithm to determine their effect on warfarin dosing accuracy.

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