Intestinal flora is not an intermediate in the phylloquinone-menaquinone-4 conversion in the rat

To elucidate the role of intestinal bacteria in the conversion of phylloquinone into menaquinone-4 (MK-4) we investigated the tissue distribution of vitamin K in germ-free rats. The rats were made vitamin K deficient by feeding a vitamin K-free diet for 13 days. In a subsequent period of 6 days, phylloquinone and menadione were supplied via the drinking water in concentrations of 10 and 50 micromol l(-1). Menadione supplementation led to high levels of tissue MK-4, particularly in extrahepatic tissues like pancreas, aorta, fat and brain. Liver and serum were low in MK-4. Phylloquinone supplementation resulted in higher phylloquinone levels in all tissues when compared with vitamin K-deficient values. The main target organs were liver, heart and fat. Remarkably, tissue MK-4 levels were also higher after the phylloquinone supplementation. The MK-4 tissue distribution pattern after phylloquinone intake was comparable with that found after menadione intake. Our results demonstrate that the conversion of phylloquinone into MK-4 in extrahepatic tissues may occur in the absence of an intestinal bacterial population and is tissue specific. A specific function for extrahepatic MK-4 or a reason for this biochemical conversion of phylloquinone into MK-4 remains unclear thus far.

Phylloquinone and menaquinone-4 distribution in rats: synthesis rather than uptake determines menaquinone-4 organ concentrations

To clarify the origin of organ menaquinone-4 (MK-4), the distributions of phylloquinone and MK-4 were investigated in rats fed diets containing phylloquinone, MK-4 or menadione (1.1, 2.2 and 31 mumol/kg diet, respectively, 6 rats per group). Warfarin (2 x 1 mg/kg subcutaneously) was given (3 rats per group) to study the effect of vitamin K cycle blockage. In rats fed phylloquinone the vitamin accumulated mainly in liver and heart. Additionally, the diet resulted in significantly higher organ MK-4 concentrations compared with the vitamin K-deficient controls. The epoxide of MK-4 also was significantly higher in some organs. The MK-4 diet increased MK-4 concentration primarily in the heart, liver and lung. Rats fed menadione had significantly higher MK-4 and MK-4 epoxide concentrations in all organs examined. The greatest accumulations were in nonhepatic organs, particularly the pancreas, salivary gland and brain. Generally, liver and plasma had low MK-4 concentrations. Warfarin treatment lowered significantly the MK-4 concentrations, whereas MK-4 epoxide accumulated. The study shows the following: 1) dietary phylloquinone is accumulated mainly in the heart and liver, 2) the MK-4 accumulation in nonhepatic organs is due to synthesis rather than uptake and 3) MK-4 rather than phylloquinone may be the functional vitamin in nonhepatic organs.

Vitamin K status in human tissues: tissue-specific accumulation of phylloquinone and menaquinone-4

We measured the vitamin K status in postmortem human tissues (brain, heart, kidney, liver, lung, pancreas) to see if there is a tissue-specific distribution pattern. Phylloquinone (K1) was recovered in all tissues with relatively high levels in liver, heart and pancreas (medians, 10.6 (4.8), 9.3 (4.2), 28.4 (12.8) pmol(ng)/g wet weight tissue); low levels (< 2 pmol/g) were found in brain, kidney and lung. Menaquinone-4 (MK-4) was recovered from most of the tissues; its levels exceeded the K1 levels in brain and kidney (median, 2.8 ng/g) and equalled K1 in pancreas. Liver, heart and lung were low in MK-4. The higher menaquinones, MK-6-11, were recovered in the liver samples (n 6), traces of MK-6-9 were found in some of the heart and pancreas samples. The results show that in man there are tissue-specific, vitamin-K distribution patterns comparable to those in the rat. Furthermore, the accumulation of vitamin K in heart, brain and pancreas suggests a hitherto unrecognized physiological function of this vitamin.

Vitamin K distribution in rat tissues: dietary phylloquinone is a source of tissue menaquinone-4

The present study was undertaken to determine whether there is selective tissue distribution of vitamin K in the rat and whether this distribution mirrors the distribution of tissue vitamin K metabolism. The effects of feeding a vitamin K-free diet followed by resupplementation with phylloquinone (K1) were studied. K1 was recovered in all tissues. In K1-supplemented rats, most tissues accumulated K1 relative to plasma K1 with the highest levels in liver, heart, bone, and cartilaginous tissue (sternum). Low K1 levels were found in the brain. In the K1-free rats, relatively high K1 levels were still found in heart, pancreas, bone and sternum. Surprisingly, menaquinone-4 (MK-4) was detected in all tissues, with low levels in plasma and liver, and much higher levels in pancreas, salivary gland and sternum. MK-4 levels exceeded K1 levels in brain, pancreas, salivary gland and sternum. Supplementation with K1, orally and by intravenous infusion, caused MK-4 levels to rise. Some accumulation of K1 and MK-4 in the mitochondrial fraction was found for kidney, pancreas and salivary gland. In the liver the higher menaquinones (MK-6-9) accumulated in the mitochondria. The results indicate that: (1) there is selective tissue distribution of K1 and MK-4, (2) dietary K1 is a source of MK-4. The results also suggest there may be an as yet unrecognized physiological function for vitamin K (MK-4).

Vitamin K status and parenteral nutrition; the effect of Intralipid on plasma vitamin K1 levels

Parenteral nutrition may affect the patient's vitamin K status. This imposes a risk when using drugs that interfere with the vitamin K-dependent clotting factor synthesis, such as N-methyl-thiotetrazole-containing cephalosporins. Intravenous lipid emulsions based on plant oils may contain phylloquinone (vitamin K1). We estimated the vitamin K1 content of the intravenous lipid emulsion product Intralipid (20%), an emulsion based on soybean oil, and estimated the vitamin K1 status of recipient patients. The emulsion was found to contain 0.6-0.7 micrograms/ml of the vitamin. Patients supplied with the product per continuous intravenous infusion, showed a steady increase of their plasma vitamin K1 levels, 3-30-fold over 4 days of infusion. In conclusion, the study shows that fat emulsions prepared from plant oils may contain vitamin K1 in sufficient amounts to meet the daily requirement.

Vitamin K metabolism and vitamin K1 status in human liver samples: a search for inter-individual differences in warfarin sensitivity

Vitamin K-dependent parameters in human liver samples were investigated to find a clue to the inter-individual differences in sensitivity for oral anticoagulants. Vitamin K epoxide reductase and vitamin K-dependent carboxylase activity differed 2-3-fold between the samples. Microsomal warfarin binding correlated significantly with the reductase activity. Microsomal vitamin K epoxide reductase of the different samples showed equal sensitivity for warfarin inhibition, I50 about 0.1 microM. Vitamin K epoxide reductase activity stimulated by NADH/lipoamide and microsomal lipoamide dehydrogenase activity showed higher inter-subject variability than the reductase activity by itself. Liver vitamin K1 levels varied 4-5-fold. Total and liver microsomal vitamin K1 levels were correlated. One of the liver samples was obtained from a donor anticoagulated with phenprocoumon and additionally treated with vitamin K1. High levels of the vitamin and its epoxide were present. Phenprocoumon was essentially irreversibly bound to the microsomes. In general the results confirm inter-individual differences in the hepatic vitamin K-dependent systems; the differences as such were found to be small. However, as the various parameters can work synergistically in the same direction, they may well account for the wide dose range observed in oral anticoagulant therapy.

The effect of S-warfarin administration on vitamin K 2,3-epoxide reductase activity in liver, kidney and testis of the rat

The dithiothreitol-dependent vitamin K 2,3-epoxide (vitamin KO) reductase activity was assayed in rat liver, kidney and testis microsomes. Rat kidney and testis showed vitamin KO reductase activity. The activity was about one tenth of the activity present in liver microsomes. The effect of in vivo S-warfarin was investigated after single doses, i.e. 0.2, 0.4 and 1 mg/kg, and after its chronic administration, i.e. 4.8 micrograms/kg/hr for 3 days. At 20 hr following the acute warfarin administration vitamin KO reductase in liver microsomes was depressed in a dose-dependent way, 50, 30 and 20% of control activity. Vitamin KO reductase in testis was not affected, and in kidney reductase activity was only reduced after the highest warfarin dose, 40% of control activity. Following chronic administration of warfarin, vitamin KO reductase activity was reduced in liver as well as in kidney and testis microsomes, 15-20, 40 and 60% of control activity in liver, kidney and testis, respectively. Blood clotting activity was about 14% of normal (thrombotest). Vitamin KO reductase activity in tissue microsomes was inhibited by warfarin added in vitro. Tissue and microsomal warfarin concentration were assayed. Following the acute administration, warfarin was poorly distributed into kidney and testis. Following the chronic administration, warfarin tissue to plasma ratio was about 3 for liver, but 0.5 for kidney and testis. The results indicate that during chronic therapy with oral anticoagulants vitamin K-dependent systems in non-hepatic tissues are reduced. However, this reduction is less than the reduction of the hepatic system. This is determined mainly by the pharmacokinetic behaviour of the 4-hydroxycoumarins.

B16 tumor cells contain a warfarin sensitive vitamin K1 2,3 epoxide reductase

Using an adapted assay that requires an enzyme aliquot that forms only 5 pmoles vitamin K, we were able to demonstrate vitamin K1 2,3 epoxide reductase activity in cultured B16 mouse melanoma cells. The enzyme uses dithiothreitol, but not NADH as a reducing cofactor and is sensitive to inhibition by warfarin (2% residual activity at 10 micrograms/ml warfarin). Incubation of B16 cells in culture with 30 micrograms/ml warfarin leads to an 45% residual reductase as compared to normally cultured B16 cells. Combined with the reported presence of vitamin K dependent carboxylase in B16 cells and the cytotoxicity of warfarin towards B16 cells this suggests an active vitamin K cycle in these melanoma cells that may be essential for survival.

Stereoselective aspects in the pharmacokinetics and pharmacodynamics of acenocoumarol and its amino and acetamido derivatives in the rat

The stereoselectivity of the pharmacokinetics and of the pharmacodynamics of the oral anticoagulant acenocoumarol (AC) and of two of its potential metabolites, the amino (AM) and the acetamido (AA) derivatives, were investigated in the rat. The pharmacokinetics and pharmacodynamics were investigated following the acute subcutaneous (1 mg/kg) administration of the pure enantiomers. For AC and AA, the S(-)-enantiomer was preferentially eliminated, whereas for AM the R(+)-enantiomer showed the shortest half-life. The differences in elimination between the AC enantiomers were entirely due to differences in total clearance, 183 +/- 14 and 714 +/- 148 ml X h-1 X kg-1 (+/- SD) for R(+)- and S(-)-AC. Also the differences in elimination between the AM enantiomers were mainly due to differences in body clearance, 50 +/- 13 and 18 +/- 4 ml X h-1 X kg-1 for R(+)- and S(-)-AM. For S(-)-AA the higher total clearance as well as the smaller volume of distribution accounted for its 2-fold higher rate of elimination. Acetylation of AM, i.e. the conversion to AA, which accounted for about 50% of its total clearance was stereoselective for R(+)-AM. The renal clearance of AA which accounted for 50-60% of the AA clearance was not selective for one of the AA enantiomers. Stereoselectivity in plasma protein binding was observed, the differences, however, were small. Thus, stereoselectivity in plasma protein binding did not account for the observed differences in the pharmacokinetics. The differences in anticlotting activity between the enantiomers of AC and AM were determined mainly by their pharmacokinetics.(ABSTRACT TRUNCATED AT 250 WORDS)