Total body phylloquinone and its turnover in human subjects at two levels of vitamin K intake

Vitamin K and the Visual System-A Narrative Review

Vitamin K occupies a unique and often obscured place among its fellow fat-soluble vitamins. Evidence is mounting, however, that vitamin K (VK) may play an important role in the visual system apart from the hepatic carboxylation of hemostatic-related proteins. However, to our knowledge, no review covering the topic has appeared in the medical literature. Recent studies have confirmed that matrix Gla protein (MGP), a vitamin K-dependent protein (VKDP), is essential for the regulation of intraocular pressure in mice. The PREDIMED (Prevención con Dieta Mediterránea) study, a randomized trial involving 5860 adults at risk for cardiovascular disease, demonstrated a 29% reduction in the risk of cataract surgery in participants with the highest tertile of dietary vitamin K1 (PK) intake compared with those with the lowest tertile. However, the specific requirements of the eye and visual system (EVS) for VK, and what might constitute an optimized VK status, is currently unknown and largely unexplored. It is, therefore, the intention of this narrative review to provide an introduction concerning VK and the visual system, review ocular VK biology, and provide some historical context for recent discoveries. Potential opportunities and gaps in current research efforts will be touched upon in the hope of raising awareness and encouraging continued VK-related investigations in this important and highly specialized sensory system.

Vitamin K and cystic fibrosis: A gordian knot that deserves our attention

Cystic fibrosis (CF) is an inherited genetic disorder with multiorgan involvement. Gastrointestinal tract dysfunction leads to fat and fat-soluble vitamins (A,D,E,K) malabsorption and deficiency of these vitamins. Subclinical vitamin K (VK) deficiency seems to be a common problem in CF patients. However, despite the rest of fat-soluble vitamins being routinely supplemented, this is not a universal clinical practice for VK. Inefficient levels of VK may have significant effects on blood coagulation and bone formation. There are also some data indicating that VK may play a key role on regulation of inflammation. Supplementing CF patients with VK seems rational, but the appropriate dosing regimens are still a matter of debate. This review will try to delineate the problem and communicate the latest opinions on this controversial issue.

Vitamin K and osteoporosis: Myth or reality?

Vitamin K is a liposoluble vitamin. The predominant dietary form, phylloquinone or vitamin K1, is found in plants and green vegetables; whereas menaquinone, or vitamin K2, is endogenously synthesized by intestinal bacteria and includes several subtypes that differ in side chain length. Aside from its established role in blood clotting, several studies now support a critical function of vitamin K in improving bone health. Vitamin K is in fact required for osteocalcin carboxylation that in turn regulates bone mineral accretion; it seems to promote the transition of osteoblasts to osteocytes and also limits the process of osteoclastogenesis. Several observational and interventional studies have examined the relationship between vitamin K and bone metabolism, but findings are conflicting and unclear. This systematic review aims to investigate the impact of vitamin K (plasma levels, dietary intake, and oral supplementation) on bone health with a particular interest in bone remodeling, mineral density and fragility fractures.

Dietary reference values for vitamin K

Following a request from the European Commission, the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) derives dietary reference values (DRVs) for vitamin K. In this Opinion, the Panel considers vitamin K to comprise both phylloquinone and menaquinones. The Panel considers that none of the biomarkers of vitamin K intake or status is suitable by itself to derive DRVs for vitamin K. Several health outcomes possibly associated with vitamin K intake were also considered but data could not be used to establish DRVs. The Panel considers that average requirements and population reference intakes for vitamin K cannot be derived for adults, infants and children, and therefore sets adequate intakes (AIs). The Panel considers that available evidence on occurrence, absorption, function and content in the body or organs of menaquinones is insufficient, and, therefore, sets AIs for phylloquinone only. Having assessed additional evidence available since 1993 in particular related to biomarkers, intake data and the factorial approach, which all are associated with considerable uncertainties, the Panel maintains the reference value proposed by the Scientific Committee for Food (SCF) in 1993. An AI of 1 μg phylloquinone/kg body weight per day is set for all age and sex population groups. Considering the respective reference body weights, AIs for phylloquinone are set at 70 μg/day for all adults including pregnant and lactating women, at 10 μg/day for infants aged 7-11 months, and between 12 μg/day for children aged 1-3 years and 65 μg/day for children aged 15-17 years.

Role of prophylactic vitamin K in preventing antibiotic induced hypoprothrombinemia

OBJECTIVE

To determine prophylactic role of single dose of vitamin K in prevention of antibiotic induced hypoprothrombinemia.

METHODS

This prospective comparative study included critically ill children in age group 2 mo to 12 y, admitted to a tertiary care hospital in India, likely to receive prolonged antibiotic therapy. One hundred twenty children, 60 in each group (A & B) were enrolled in the study. Patient allocation was done on alternate basis. Group A children received prophylactic vitamin K while group B did not. Baseline coagulation studies and other investigations were done in all children. Coagulation studies were repeated on day 10 and day 14 of antibiotic therapy and in between if required clinically. Children who developed deranged INR were given therapeutic vitamin K. If deranged INR returns to normal at 12 h of vitamin K administration then it indirectly confirms vitamin K deficiency. Analysis was done by fisher's t test and chi square test.

RESULTS

In children on prolonged antibiotic therapy, vitamin K deficiency was a common problem (15%). It was common in male sex, severe grade of protein energy malnutrition (PEM), N-methylthiotetrazole (NMTT) group containing antibiotics use and duration of antibiotic more than 10 d. It was same in children whether they received or did not receive prophylactic vitamin K on day 1 of antibiotic therapy (95% CI; p value 0.79).

CONCLUSIONS

Vitamin K deficiency is common problem in patients on prolonged antibiotic therapy. There is no role of single dose of prophylactic vitamin K in preventing antibiotic induced hypoprothrombinemia.

Vitamin K metabolism: current knowledge and future research

Vitamin K is an essential fat-soluble micronutrient that is required for the post-translational γ-carboxylation of specific glutamic acid residues in hepatic and extra-hepatic proteins involved in blood coagulation and preventing cartilage and vasculature calcification. In humans, sources of vitamin K are derived from plants as phylloquinone and bacteria as the menaquinones. Menadione is a synthetic product used as a pharmaceutical but also represents an intermediate in the tissue-specific conversion of vitamin K to menaquinone-4, which preferentially resides in tissues such as brain. Research into vitamin K metabolism is essential for the understanding of vitamin K biology in health and disease. Progress in this area, driven by knowledge of vitamin K and the availability of markers of vitamin K status, has already proved beneficial in many areas of medicine and further opportunities present themselves. Areas of interest discussed in this review include prophylactic administration of vitamin K1 in term and preterm neonates, interactions between vitamins K and E, the industrial conversion of vitamin K to dihydro-vitamin K in foods, tissue-specific conversion of vitamin K to menaquinone-4, the biological activity of the five and seven carbon metabolites of vitamin K and circadian variations.

The role of gut microbiota in nutritional status

PURPOSE OF REVIEW

The objective of this review is to outline the contribution of the gut microbiota to nutritional status and to highlight the mechanisms by which this can occur.

RECENT FINDINGS

Historically, research linking intestinal bacteria with nutritional status focused on the degradation of indigestible food components by bacterial enzymes and metabolites. Of late, emerging evidence suggests an independent role of the gut microbiota in the regulation of glucose and energy homeostasis via complex interactions between microbially derived metabolites and specific target tissue cells. In addition, novel findings highlight specific microbial species involved in the production of a number of micronutrient components, which could potentially improve nutritional status in certain population groups, if available to the host at sufficiently abundant levels.

SUMMARY

New insights into the role of the gut microbiota and its holistic effects on the host are now emerging. High-throughput technologies allow for a greater insight into the role of the intestinal microbiota and the mechanisms by which it can contribute to overall nutritional status. Further, exploration of this evolving field of research will advance our understanding of how this complex ecosystem could advance the area of personalized nutrition in the future.

The role of dietary vitamin K in the management of oral vitamin K antagonists

Vitamin K antagonists (VKA) have been the mainstay of oral anticoagulant therapy for over 60years. In this review we critically assess the evidence for the importance of vitamin K nutrition during VKA therapy; the methodologies for measuring dietary intakes; the vitamin K intake data in patients on VKA and healthy people; and the experimental evidence for the influence of vitamin K intakes and biochemical measures of vitamin K status on VKA response. Several studies show that dietary intakes of phylloquinone (vitamin K1) are associated to the sensitivity and stability of anticoagulation during initiation and maintenance dosing with low habitual intakes associated with greater instability of the INR and risk of sub-therapeutic anticoagulation. Preliminary evidence suggests that the stability of anticoagulation therapy may be improved by daily vitamin K supplementation, but further studies are needed to find out whether this, or other dietary interventions, can improve anticoagulant control in routine clinical practice.

Urinary excretion of vitamin K metabolites in term and preterm infants: relationship to vitamin K status and prophylaxis

Little is known about the metabolic turnover and excretion of vitamin K in healthy newborn infants and the metabolic consequences of prophylactic regimens designed to protect against vitamin K deficiency bleeding (VKDB). We measured the excretion of two urinary metabolites (≤ 24 h) of vitamin K (5C- and 7C-aglycones) in term infants before (n = 11) and after (n = 5) a 1000 μg i.m. dose of vitamin K1 (K1) and in preterm infants after 200 μg i.m. (n = 4), 500 μg i.m. (n = 4), or 200 μg i.v. (n = 5). In preterm infants, we also measured serum K1, vitamin K1 2,3-epoxide, and PIVKA-II at 5 d postpartum. Before prophylaxis, the rate of 5C- and 7C-aglycone excretion was 25 times lower than adults, reflecting low vitamin K stores at birth. After prophylaxis, the excretion rate correlated to K1 dose (r = 0.6) but was two orders of magnitude lower than that in adults, probably reflecting the immaturity of neonatal catabolism. All term and 10 of 13 preterm infants mainly excreted 5C-aglycone. We present evidence that increased excretion of the 7C-aglycone was associated with metabolic overload because of the exposure to high-tissue K1 concentrations. Measurement of the 5C- and 7C-aglycones may facilitate longitudinal studies of vitamin K status in neonates and aid the development of improved prophylactic regimens.

Vitamin K absorption and kinetics in human subjects after consumption of 13C-labelled phylloquinone from kale

The absorption and plasma disappearance of vitamin K were investigated by uniformly labelling phylloquinone in kale with carbon-13, and by feeding the kale to study subjects. Seven healthy volunteers ingested a single 400 g serving of kale with 30 g vegetable oil. The kale provided 156 nmol of phylloquinone. Serial plasma samples were collected and analysed for the appearance of 13C-phylloquinone by HPLC-MS. Six of the subjects showed significant amounts of labelled phylloquinone in plasma, though one subject's plasma was not consistently enriched above the detection limit, and this subject's baseline plasma phylloquinone level was the lowest in the group. After ingestion of the labelled kale, plasma 13C-phylloquinone concentration increased rapidly to a peak between 6 and 10 h, and then rapidly decreased. Average peak plasma concentration for the six subjects with detectable 13C-phylloquinone was 2.1 nmol/l. Plasma concentration-time data were analysed by compartmental modelling. Modelling results demonstrated a mean (n 6) bioavailability of phylloquinone from kale to be 4.7%. Plasma and tissue half-times for phylloquinone were found to be 8.8 and 215 h, respectively.

A stable isotope method for the simultaneous measurement of vitamin K1 (phylloquinone) kinetics and absorption

OBJECTIVES

To measure uptake and disposal kinetics and absolute absorption of vitamin K(1) using two stable isotope-labelled forms of vitamin K(1).

SUBJECTS

Ten subjects (nine women and one man) aged between 22 and 31 years, with a mean (+/-standard deviation) body mass index of 22.5+/-2.4 kg/m(2). Subjects took capsules containing 3 microg of methyl-(13)C vitamin K(1), three times a day for six days to reach a steady state for plasma vitamin K(1) isotopic enrichment. On day seven, subjects were given an intravenous dose of Konakion MM to measure disposal kinetics and at the same time, a capsule containing 4 microg of ring-D(4) vitamin K(1) to measure absorption. Plasma vitamin K(1) concentration was measured by high-performance liquid chromatography and isotopic composition by gas chromatography mass spectrometry.

RESULTS

The disposal kinetics of the intravenous dose of vitamin K(1) were resolved into two exponentials with half-times of 0.22 (+/-0.14) and 2.66 (+/-1.69) h. Absorption of oral, deuterated vitamin K(1) was 13 (+/-9)%.

CONCLUSIONS

Two-compartmental kinetic parameters observed in this study are similar to those obtained previously using radioactive tracers, but there may be additional slow-turnover body pools acting as stores of vitamin K(1). The kinetic parameters determined from the intravenous dose allowed determination of the absolute absorption of vitamin K(1) from a bolus oral dose.

Excretion of the urinary 5C- and 7C-aglycone metabolites of vitamin K by young adults responds to changes in dietary phylloquinone and dihydrophylloquinone intakes

The physiological function and putative health roles of vitamin K-dependent proteins now extend beyond their classical role in hemostasis and include bone mineralization, arterial calcification, apoptosis, phagocytosis, growth control, chemotaxis, and signal transduction. Current assessments of vitamin K status do not reflect the variety of molecular forms of vitamin K. We assessed whether urinary excretion of 2-methyl-3-(5'-carboxy-3'-methyl-2'-pentenyl)-1,4-naphthoquinone (7C-aglycone) and 2-methyl-3-(3'-3'-carboxymethylpropyl)-1,4-naphthoquinone (5C-aglycone), vitamin K metabolites common to both phylloquinone and the menaquinone series, reflect dietary vitamin K intake. In a randomized crossover study, 9 adults resided in a metabolic unit for two 30-d periods separated by a free-living period of > or = 4 wk. During each residency, subjects consumed 3 sequential diets: a control diet (93 microg phylloquinone/d) for 5 d, a phylloquinone-restricted diet (11 microg/d) for 15 d, followed by a randomly assigned repletion diet for 10 d with either phylloquinone (206 microg/d) or dihydrophylloquinone (240 microg/d). During the second residency, the alternative repletion diet was assigned. Urinary excretion of the 5C- and 7C-aglycones was measured in sequential 24-h collections. The 5C-aglycone accounted for approximately 75% of total excretion and declined in response to phylloquinone restriction (P = 0.001) to approximately 30% of that during the control diet period. Repletion with phylloquinone and dihydrophylloquinone doubled the excretion rate of the major 5C-aglycone by 24 h (P < 0.001), and tripled excretion by 4 d. There was a linear relationship between the logarithm of total urinary excretion and dietary vitamin K intake (r = 0.699, P < 0.001). We conclude that the urinary excretion of vitamin K metabolites reflects dietary phylloquinone intake and offers the first candidate marker of global vitamin K status.

Plasma phylloquinone (vitamin K1) concentration and its relationship to intake in British adults aged 19-64 years

Plasma phylloquinone (vitamin K1) concentration from non-fasted blood samples was examined by season, smoking status, socio-demographic factors and phylloquinone intake in a nationally representative sample of 1154 British individuals aged 19-64 years from the 2000-1 National Diet and Nutrition Survey. Geometric mean plasma phylloquinone concentration was 0.94 (95% CI 0.88, 1.00) nmol/l, with 95% of values in the range 0.10-8.72 nmol/l. Plasma phylloquinone concentrations of 530 men were significantly higher than those of 624 women (1.13 (95% CI 1.04, 1.22) v. 0.81 (95% CI 0.74, 0.88) nmol/l; P<0.001), independent of other factors. Women aged 19-34 years had significantly lower plasma phylloquinone concentration than their older counterparts. Women were also found to have lower plasma phylloquinone concentrations during summer compared with winter and spring (each P<0.01). In contrast, plasma phylloquinone concentration in men did not vary significantly by season or any of the socio-demographic or lifestyle factors. Plasma phylloquinone concentrations were positively correlated with phylloquinone intake in men and women (r 0.26 and 0.32 respectively; each P<0.001). Overall, forward stepwise multiple regression analysis revealed that 8% of the variation in plasma phylloquinone concentration was explained by phylloquinone intake, with a further 10% of its variation explained by plasma concentrations of gamma-tocopherol (6%) and retinyl palmitate (4%). After adjustment for age and corresponding nutrient intakes, plasma phylloquinone concentration was significantly associated (each P<0.01) with plasma concentrations of total and LDL-cholesterol, alpha- and gamma-tocopherols, retinyl palmitate, beta-carotene, lycopene and lutein plus zeaxanthin in men and women.

Analysis of isotope ratios in vitamin K1 (phylloquinone) from human plasma by gas chromatography/mass spectrometry

Vitamin K(1) is a fat-soluble vitamin required for the gamma-carboxylation of vitamin K-dependent proteins. Recent work has suggested an important role for vitamin K(1) in bone health beyond its more established function in the control and regulation of blood coagulation. However, current UK recommended intakes do not reflect this recent evidence. The use of stable isotopes provides a powerful tool to investigate vitamin K kinetics, turnover and absorption in man, although published methods have reported difficulties in the extraction and analysis of isotope ratios of vitamin K in human plasma. In this paper, we report a new methodology for the extraction and measurement of isotope ratios in vitamin K(1). Sample clean-up is achieved with liquid-liquid extraction, enzyme hydrolysis with lipase and cholesterol esterase, and solid-phase extraction. Isotopic analysis of the pentafluoropropionyl derivative of vitamin K(1) is performed by gas chromatography/mass spectrometry (GC/MS). The limit of quantitation is equivalent to at least 0.3 nmol/L and the method is demonstrated to be linear over a range of enrichments. This method provides a robust alternative to previous work requiring the use of semi-preparative high-performance liquid chromatography (HPLC).

Vitamin K, bone turnover, and bone mass in girls

BACKGROUND

Vitamin K has been suggested to have a role in bone metabolism, and low vitamin K intake has been related to low bone density and increased risk of osteoporotic fracture.

OBJECTIVE

The objective of this study was to determine whether phylloquinone (vitamin K(1)) intake and biochemical indicators of vitamin K status are related to bone mineral content (BMC) and markers of bone formation and bone resorption in girls.

DESIGN

Vitamin K status [plasma phylloquinone concentration and percentage of undercarboxylated osteocalcin (%ucOC)] was measured at baseline in a study of 245 healthy girls aged 3-16 y. Cross-linked N-telopeptide of type 1 collagen (NTx) breakdown, osteocalcin, and bone-specific alkaline phosphatase were measured to reflect bone resorption and formation. BMC of the total body, lumbar spine, and hip and dietary phylloquinone intake were measured annually for 4 y.

RESULTS

Phylloquinone intake (median: 45 microg/d) was not consistently associated with bone turnover markers or BMC. Better vitamin K status (high plasma phylloquinone and low %ucOC) was associated with lower bone resorption and formation. Plasma phylloquinone was inversely associated with NTx and osteocalcin concentrations (P < 0.05), and %ucOC was positively associated with NTx and bone-specific alkaline phosphatase concentrations (P < 0.05). Indicators of vitamin K status were not consistently associated with current BMC or gain in BMC over the 4-y study period.

CONCLUSIONS

Better vitamin K status was associated with decreased bone turnover in healthy girls consuming a typical US diet. Randomized phylloquinone supplementation trials are needed to further understand the potential benefits of phylloquinone on bone acquisition in growing children.

Plasma transport of vitamin K in men using deuterium-labeled collard greens

The plasma transport of stable isotope-labeled phylloquinone at physiologic doses from food was studied. A single bolus of 100 g (396 +/- 28 microg phylloquinone) deuterium-labeled collard greens was fed with a breakfast containing 24 g fat to 5 men (26 to 71 years). Eleven blood samples were obtained over 216 hours. Phylloquinone concentrations in plasma and lipoprotein subfractions were measured using high-performance liquid chromatography (HPLC), and the ion abundances of deuterated and endogenous phylloquinone were determined using gas chromatography/mass spectrometry (GC/MS). Plasma total phylloquinone concentrations peaked at 6 to 9 hours (10.51 +/- 4.38 to 8.30 +/- 4.64 nmol/L) and returned to baseline by 24 hours (1.26 +/- 0.38 nmol/L). The triglyceride-rich lipoprotein (TRL) fraction was the major carrier of phylloquinone; low-density lipoprotein (LDL) and high-density lipoprotein (HDL) fractions contained smaller amounts. Maximum enrichment of plasma and TRL phylloquinone with deuterium (88% and 89%, respectively) was reached at 6 hours, respectively; t(1/2) was 22.8 hours (n = 3). Deuterated-phylloquinone was not detectable in plasma or TRL fraction at 72 hours. These results suggest rapid uptake and transport of physiologic doses of phylloquinone.

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.