Warfarin poisoning and vitamin K antagonism in rat and human liver. Design of a system in vitro that mimics the situation in vivo

Abstract

The present paper describes a sytem in vitro that has been developed to mimic vitamin K metabolism and vitamin K function in liver. In this system the two pathways that are known to participate in vitamin K reduction are active and the vitamin K-dependent carboxylase accepts a synthetic pentapeptide as substrate. With this system in vitro the effect of warfarin on both pathways was examined under conditions which simulated a warfarin-poisoned liver. Identical experiments were completed with rat and human liver. All activities currently associated with vitamin K metabolism and vitamin K function were similar in the rat and human systems. Warfarin neutralized the ability of pathway I (the vitamin K epoxide reductase pathway) to produce reduced and active vitamin K cofactor for the carboxylase. In both the rat and the human system, however, when warfarin was present, reduced vitamin K cofactor was produced by pathway II (the dehydrogenase pathway). The data are consistent with observations in vivo on the effect of vitamin K1 when used as an antidote. This suggests that the system in vitro reflects the mechanism in vivo by which vitamin K1 overcomes warfarin poisoning.

Recent trends in the metabolism and cell biology of vitamin K with special reference to vitamin K cycling and MK-4 biosynthesis

“…However, GGCX activity was again abolished in HEK293 cells in which both VKOR and its paralog VKOR-like 1 (VKORL1) had been knocked out. The data suggested Furthermore, in rat liver, pathway II comprised at least two dehydrogenases ( 73,78 ), both present in microsomes ( 76 ). Recent and informative functional studies of the vitamin K cycle in mammalian cells are described in more detail below.…”

“…Although physicians were well aware of the antidotal properties of vitamin K, it was the pioneering and extensive investigations by Wallin and colleagues that provided the fi rst insights into the existence and properties of a vitamin K dehydrogenase that was insensitive to coumarin antagonists (75)(76)(77)(78). In brief, Wallin proposed that vitamin K reduction could be achieved by two independent pathways: a "physiological" disulfhydryl-dependent reductase pathway that was highly sensitive to warfarin (pathway I) and a NAD(P)H-dependent reductase pathway (pathway II) that was less sensitive to warfarin and was responsible for the antidotal effect of vitamin K ( 73,78 ). inhibit vitamin K reductases (see below).…”

“…A paradigm of the nature of the antagonism by coumarin anticoagulants in humans and animals is that even when VKOR is completely inhibited in vivo, the coagulation function (but not necessarily other functions in extrahepatic tissues) can be rescued by providing high doses of vitamin K (72)(73)(74). Although physicians were well aware of the antidotal properties of vitamin K, it was the pioneering and extensive investigations by Wallin and colleagues that provided the fi rst insights into the existence and properties of a vitamin K dehydrogenase that was insensitive to coumarin antagonists (75)(76)(77)(78).…”

Comparison of warfarin sensitivity between rat and bird species

“…Vitamin K 1 epoxide was prepared according to the method of Tishler et al (1940) and the concentration of vitamin K 1 epoxide was determined spectrophotometrically using a molar absorption coefficient of 30,800 M -1 cm -1 at 266 nm (Wallin and Martin, 1987). The vitamin K 1 8 epoxide was kept at 4°C and was shielded from light until use.…”

The genetic mechanisms of warfarin resistance in Rattus rattus found in the wild in Japan

“…The concentration of vitamin K epoxide was determined by spectrophotometry using molar absorption coefficients of 30800 M -1 cm -1 at 226 nm (spectrophotometer: U-3300 Hitachi) [21].…”