Mechanism of action
While warfarin is one of several drugs popularly referred to as a "blood thinner", this is a misnomer, since it does not affect the viscosity of blood.Warfarin inhibits the vitamin K-dependent synthesis of biologically active forms of the clotting factors II, VII, IX and X, as well as the regulatory factors protein C, protein S, and protein Z. Other proteins not involved in blood clotting, such as osteocalcin, or matrix Gla protein, may also be affected. The precursors of these factors require gamma carboxylation of their glutamic acid residues to allow the coagulation factors to bind to phospholipid surfaces inside blood vessels, on the vascular endothelium. The enzyme that carries out the carboxylation of glutamic acid is gamma-glutamyl carboxylase. The carboxylation reaction proceeds only if the carboxylase enzyme is able to convert a reduced form of vitamin K (vitamin K hydroquinone) to vitamin K epoxide at the same time. The vitamin K epoxide is, in turn, recycled back to vitamin K and vitamin K hydroquinone by another enzyme, the vitamin K epoxide reductase (VKOR). Warfarin inhibits VKOR (specifically the VKORC1 subunit), thereby diminishing available vitamin K and vitamin K hydroquinone in the tissues, which decreases the carboxylation activity of the glutamyl carboxylase. When this occurs, the coagulation factors are no longer carboxylated at certain glutamic acid residues, and are incapable of binding to the endothelial surface of blood vessels, and are thus biologically inactive.
Next, Links student, Mark A. Stahmann, took over the project and initiated a large-scale extraction, isolating 1.8 g of recrystallized anticoagulant in about 4 months. This was enough material for Stahmann and Charles F. Huebner to check their results against Campbells, and to thoroughly characterize the compound. Through degradation experiments, they established that the anticoagulant was 3,3-methylenebis-(4-hydroxycoumarin), which they later named dicoumarol. They confirmed their results by synthesizing dicoumarol and proving in 1940 that it was identical to the naturally occurring agent.Dicoumarol was a product of the plant molecule coumarin (not to be confused with Coumadin, a later tradename for warfarin). Coumarin is now known to be present in many plants, and produces the notably sweet smell of freshly cut grass or hay and plants suc as sweet grass; in fact, the plants high content of coumarin is responsible for the original common name of "sweet clover", which is named for its sweet smell, not its bitter taste. They are present notably in woodruff (Galium odoratum, Rubiaceae), and at lower levels in licorice, lavender, and various other species. The name coumarin comes from the French pronunciation of coumarou, the Indian name for the tree of the tonka bean, which notably contains a high concentration of coumarin. However, coumarins themselves do not influence clotting or warfarin-like action, but must first be metabolized by various fungi into compounds such as 4-hydroxycoumarin, then further (in the presence of naturally occurring formaldehyde) into dicoumarol, to have any anticoagulant properties.