menaquinone-9 and menatetrenone

The acid-base and redox properties of the menaquinones MK-4, MK-7, and MK-9 (vitamin K

Topics: Dimyristoylphosphatidylcholine; Electrodes; Hydrogen-Ion Concentration; Mercury; Oxidation-Reduction; Vitamin K 2

Vitamin K is a group name for K1 (phylloquinone) and K2 (menaquinones). Both forms contribute to the tissue vitamin K status. Following intestinal absorption, the serum transport of these lipophilic compounds to their target tissues takes place via lipoproteins. In previous studies we have found that K1 is preferentially accumulated in the liver, whereas menaquinones have a more widespread distribution pattern. Here we have tested whether these differences may be explained by the different liposolubility of the various K-vitamers, resulting in their association with different lipoprotein particles. Six healthy male volunteers received a mixture containing 2 micromol of each of three K vitamers (K1, MK-4, and MK-9) dissolved in corn oil. Blood was obtained at baseline and at different time intervals after intake for the measurement of vitamin K in serum and in the lipoprotein fractions. During the first 4 h after intake all K-vitamins were found to be associated predominantly with the triacylglycerol-rich lipoprotein (TGRLP) fraction. Since the TGRLP fraction is mainly cleared by the liver, this suggests that initially most of the K-vitamins are transported to the liver. In contrast to K1, however, both menaquinones investigated were also found in TGRLP and low-density lipoprotein, whereas MK-4 was even present in high-density lipoprotein. This explains why menaquinones may have a different distribution profile and suggests a relatively large impact of menaquinones on extra-hepatic vitamin K status than generally assumed. Moreover, the very long half-life time of MK-9 in the circulation indicates that it may form a more constant source of vitamin K than are either K1 or MK-4.

Topics: Humans; Lipoproteins; Lipoproteins, HDL; Lipoproteins, LDL; Liver; Postprandial Period; Protein Transport; Triglycerides; Vitamin K; Vitamin K 1; Vitamin K 2

Vitamin K is a group name for a number of prenylated 2-methyl-1,4-naphtoquinones, which may differ in their ability to function as a cofactor for prothrombin biosynthesis. To quantify the bioactivity of different forms of vitamin K, two experimental animal systems are frequently used: vitamin K-deficient rats and anticoagulated rats. In this paper both models are compared, and it is shown that the results obtained depend on the model used. The main reason for this discrepancy is the difference in recycling of vitamin K-epoxide, which results in a 500 times higher vitamin K requirement in anticoagulated rats. Absorption and hepatic accumulation of long chain menaquinones seem to be restricted to a maximum, whereas also the lipophilic nature of long chain menaquinones may hamper the quinone-quinol reduction in anticoagulated animals. If these data may be extrapolated to patients, food items rich in K1 and MK-4 would be expected to influence the stability of oral anticoagulation to a much larger extent than food items primarily containing higher menaquinones.

Topics: 4-Hydroxycoumarins; Absorption; Animals; Anticoagulants; Blood Coagulation; Disease Models, Animal; Male; Prothrombin; Rats; Rats, Inbred Lew; Vitamin K; Vitamin K 1; Vitamin K 2; Vitamin K Deficiency

Rats were made vitamin K-deficient by feeding them a diet devoid of vitamin K and by rigorously preventing coprophagy. After one week, circulating prothrombin concentrations were between 5 and 10% of initial values, and various amounts of phylloquinone, menaquinone-4, and menaquinone-9 were given in a single dose either subcutaneously, orally, or colorectally. The relative 'vitamin K activities' of these compounds were assessed by comparing their ability to support prothrombin synthesis after subcutaneous injection. Intestinal and colonic absorption were deduced from the difference between subcutaneous and either oral or colorectal administration of the vitamers. It is concluded that the colonic absorption of all three forms of vitamin K is extremely poor, suggesting that physiological menaquinones in the colon do not contribute substantially to vitamin K status in rats. Furthermore, the stimulation of prothrombin synthesis by menaquinone-9 lasted much longer than that by the two other K-vitamers, resulting in a substantially higher 'vitamin K activity' of menaquinone-9.

Topics: Animals; Biological Availability; Hemostatics; Intestinal Absorption; Male; Prothrombin; Rats; Vitamin K; Vitamin K 1; Vitamin K 2; Vitamin K Deficiency

The colonic absorption of menaquinones was examined in rats by the in situ loop method. The overall disappearance of [14C]menaquinone-4 from the colonal loop was approximately 6% at 3 h and much slower than that of menadione. After administration of [14C]menaquinone-4 into the jejunal loop with bile, approximately 17% of unchanged menaquinone-4 was recovered in the lymph after 6 h, but none was found when the administration had been into the colonal loop. Portal absorption of menaquinone-4 from the colon was detected and the unchanged form (approximately 23% of the absorbed radioactivity) was identified in the mesenteric venous blood. When menaquinone-9 was administered into the colon, almost all was recovered from the colonal loop. No transfer of menaquinone-9 from the colon into the lymph or blood was observed at 6 h after dosing. The present observations indicate that only a part of bacterially produced menaquinones is absorbed from the colon via the portal pathway, but the absorption rates of menaquinones decrease markedly with an increase in the number of isoprenoid units.

Topics: Animals; Bacteria; Bile; Colon; Intestinal Absorption; Intestine, Large; Jejunum; Liver; Lymph; Male; Rats; Rats, Inbred Strains; Tissue Distribution; Vitamin K; Vitamin K 2