High intra- and inter-individual variability of plasma vitamin K concentrations in patients with atrial fibrillation under warfarin therapy.

BACKGROUND/OBJECTIVES: Vitamin K intake is considered as a controllable contributor to warfarin sensitivity. It is restricted in warfarin-treated patients. However, little study has assessed the vitamin K status in warfarin-treated patients. We directly measured plasma vitamin K in warfarin-treated patients and evaluated its effect on anticoagulation. SUBJECTS/METHODS: A total of 302 plasma vitamin K concentrations were assessed using high-performance liquid chromatography for 203 outpatients with atrial fibrillation under warfarin treatment. Clinical and laboratory information including warfarin dosage, plasma warfarin concentrations, prothrombin time international normalized ratio (PT INR) and CYP2C9/VKORC1 genotypes was reviewed retrospectively. The anticoagulation stability (intra-individual variability, frequency of PT INR tests and complications) was investigated in 163 patients with long-term warfarin therapy. Plasma vitamin K was measured in 40 healthy subjects and in 40 patients before and after initial warfarin treatment. RESULTS: Vitamin K concentrations were significantly decreased after the initiation of warfarin treatment (before treatment: 1.72 ng/ml; after treatment: 0.59 ng/ml, P<0.05). There was a large inter-individual variability in vitamin K levels (0.2-4.2 ng/ml) in warfarin-treated patients. PT INR was more frequently checked in patients with low plasma vitamin K levels than in those with high vitamin K levels (9.5 times/year vs 7.5 times/year, P=0.029). Two patients with gross hematuria showed very low vitamin K levels (<0.4 ng/ml). CONCLUSIONS: We found high inter- and intra-individual variability in vitamin K concentration in warfarin-treated patients. Low vitamin K concentration in warfarin-treated patients suggested excessive dietary restriction. Plasma vitamin K measurement would be helpful for dietary control and anticoagulation stability.

Vitamin C prevents radiation-induced endothelium-dependent vasomotor dysfunction and de-endothelialization by inhibiting oxidative damage in the rat.

1. The present study was undertaken to determine whether endothelial function or morphology was altered in aortic rings of rats after irradiation, to investigate the mechanism of radiation effects on the endothelium and to examine the effect of vitamin C treatment against radiation-induced damage of the endothelium. 2. Female Sprague-Dawley rats were randomized into four groups (control, radiation, radiation + vitamin C, radiation + vitamin C + NG-nitro-L-arginine methyl ester (L-NAME); n = 10 for each group and n = 7 for the control group) and were irradiated with 10 Gy of 137Cs as a radiation source. Segments of the thoracic aorta were obtained and isometric tension, levels of 8-hydroxydeoxyguanosine (OH-dG) and immunohistochemical staining were measured. 3. Irradiation significantly impaired the acetylcholine-induced vasodilation of aortic segments, an effect that could be prevented by pretreatment with vitamin C (500 mg/kg per day). This beneficial effect of vitamin C was abolished by the addition of L-NAME (100 microg/kg per day), an inhibitor of nitric oxide (NO) synthesis. Irradiation significantly increased the level of OH-dG in the aorta (1.02 +/- 0.27 vs 2.61 +/- 0.78 OH-dG/105 deoxyguanosine (dG) for control and irradiated tissues, respectively; P < 0.01), an increase that was prevented by vitamin C treatment (1.59 +/- 0.23 OH-dG/105 dG; P < 0.01). Irradiation caused significant de-endothelialization (von Willebrand factor (vWF) staining was 93 +/- 7 vs 100% in irradiated and control tissues, respectively; P < 0.05) and this was prevented by vitamin C treatment (vWF staining 98 +/- 3%; P < 0.05). 4. Radiation caused endothelial damage and impaired NO production through oxidative injury, resulting in a selective impairment of endothelial-dependent vasodilation that could be prevented by vitamin C, partly through anti-oxidant mechanisms.