Effects of vitamin K deficiency, warfarin, and inhibitors of protein synthesis upon the plasma levels of vitamin K-dependent clotting factors in the chick

Avian interspecific differences in VKOR activity and inhibition: Insights from amino acid sequence and mRNA expression ratio of VKORC1 and VKORC1L1

Worldwide use of anticoagulant rodenticides (ARs) for rodents control has frequently led to secondary poisoning of non-target animals, especially raptors. In order to suggest some factors that may help considering the mechanism of the incidents, this study focused on the avian vitamin K 2, 3-epoxide reductase (VKOR) that is the target protein of ARs. We addressed the interspecific differences in VKOR activity and inhibition related to amino acid sequence and mRNA expression of VKORC1 and VKORC1-like1 (VKORC1L1). Poultry have been considered to be more tolerant to ARs than mammals. However, VKOR activity of owls, hawks, falcon and surprisingly, canaries, was lower and inhibited by warfarin more easily than that of chickens and turkeys. The amino acid sequence of VKORC1 and VKORC1L1 implied that the value of Ki for VKOR activity to ARs could depend on the amino acid at position 140 in the TYX warfarin-binding motif in VKORC1, and other amino acid mutations in VKORC1L1. The mRNA expression ratio of VKORC1:VKORC1L1 differed between turkey (8:1) and chicken (2:3) liver. VKORC1L1 has been reported to be resistant to warfarin compared to VKORC1. Hence, both the Ki of specific VKORC1 and VKORC1L1, and the mRNA expression ratio would cause avian interspecific difference of the VKOR inhibition. Our study also suggested the high inhibition of VKOR activities in raptors and surprisingly that in canaries as well. These factors are the most likely to contribute to the high sensitivity to ARs found in raptors.

Nutrition and genetics: an expanding frontier

The age of molecular biology began in 1953 with the discovery of the structure of DNA. By 1961 the genetic code for the translation of the sequence of bases in DNA to amino acids in proteins was underway, and a model for the genetic regulation of protein synthesis was proposed. My interest in the genetic regulation of nutrient metabolism began in that year during my sabbatical leave in the laboratory of Sir Hans Krebs at Oxford University. In the present article, I describe 2 episodes in my career during which I used genetic concepts to explain a nutritional phenomenon; the first episode occurred before doing the experimental work, and the second occurred after the experimental work was completed. My first brainstorm, which occurred in 1961, was to investigate the hypothesis that all of the fat-soluble vitamins act by the regulation of a cluster of genes. Unfortunately, I selected vitamin K as my model and discovered that it is the only fat-soluble vitamin that does not work in full or in part by the regulation of a set of genes. In 1967 I undertook a second problem, which was to determine the mode of action of polyunsaturated fatty acids in lowering plasma lipid concentrations in humans. We discovered that linoleic acid reduced the storage and enhanced the oxidation of fatty acids. The genetic interpretation of this study has come only recently: polyunsaturated fats have been shown to down-regulate enzymes that accomplish storage of fatty acids and to up-regulate genes that enhance fatty acid oxidation.