Bioavailability of phylloquinone and menaquinones after oral and colorectal administration in vitamin K-deficient rats

Emerging connections between gut microbiome bioenergetics and chronic metabolic diseases

The conventional viewpoint of single-celled microbial metabolism fails to adequately depict energy flow at the systems level in host-adapted microbial communities. Emerging paradigms instead support that distinct microbiomes develop interconnected and interdependent electron transport chains that rely on cooperative production and sharing of bioenergetic machinery (i.e., directly involved in generating ATP) in the extracellular space. These communal resources represent an important subset of the microbial metabolome, designated here as the "pantryome" (i.e., pantry or external storage compartment), that critically supports microbiome function and can exert multifunctional effects on host physiology. We review these interactions as they relate to human health by detailing the genomic-based sharing potential of gut-derived bacterial and archaeal reference strains. Aromatic amino acids, metabolic cofactors (B vitamins), menaquinones (vitamin K2), hemes, and short-chain fatty acids (with specific emphasis on acetate as a central regulator of symbiosis) are discussed in depth regarding their role in microbiome-related metabolic diseases.

Vitamin K and cardiovascular complications in CKD patients

Vitamin K, well known for its role in coagulation, encompasses two major subgroups: Vitamin K1 is exclusively synthesized by plants, whereas vitamin K2 mostly originates from bacterial synthesis. Vitamin K serves as a cofactor for the enzyme γ-glutamyl carboxylase, which carboxylates and thereby activates various vitamin K dependent proteins. Several vitamin K-dependent proteins are synthesized in bone but the role of vitamin K for bone health in CKD patients, in particular the prevention of osteoporosis is still not firmly established. Here we focus on another prominent action of vitamin K, in particular vitamin K2, namely the activation of matrix Gla protein (MGP), the most potent inhibitor of cardiovascular calcifications. Multiple observational studies link relative vitamin K deficiency or low intake to cardiovascular calcification progress, morbidity and mortality. Patients with advanced chronic kidney disease (CKD) are particularly vitamin K deficient, in part because of dietary restrictions but possibly also due to impaired endogenous recycling of vitamin K. At the same time this population is characterized by markedly accelerated cardiovascular calcifications and mortality. High dose dietary supplementation with vitamin K2, in particular the most potent form menaquinone-7 (MK7), can potently reduce circulating levels of dephosphorylated uncarboxylated, i.e. inactive MGP in patients with end stage kidney disease. However, despite this compelling data basis, several randomized controlled trials with high dose MK7 supplements in patients with advanced CKD have failed to confirm cardiovascular benefits. Here we discuss potential reasons and solutions for this.

Vitamin K in CKD Bone Disorders

Vitamin K is principally known because it is involved in blood coagulation. Furthermore, epidemiological studies showed that its deficit was associated with increased fragility fractures, vascular calcification and mortality. There are two main types of vitamin K vitamers: Phylloquinone (or PK) and Menaquinones (MKn). Vitamin K acts both as coenzyme of y-glutamyl carboxylase (GGCX) transforming undercarboxylated in carboxylated vitamin K-dependent proteins (e.g., Osteocalcin and Matrix Gla Protein) and as a ligand of the nuclear steroid and xenobiotic receptor (SXR) (in murine species Pregnane X Receptor: PXR), expressed in osteoblasts. It has been highlighted that the uremic state is a condition of greater vitamin K deficiency than the general population with resulting higher prevalence of bone fractures, vascular calcifications and mortality. The purpose of this literature review is to evaluate the protective role of Vitamin K in bone health in CKD patients.

Ball ME, McDonald E, Hull GLJ, Danaher M, Cashman KD. Biofortification of Chicken Eggs with Vitamin K-Nutritional and Quality Improvements

National nutrition surveys have shown that over half of all adults in Ireland, the United Kingdom (UK), and the United States of America (USA) have low vitamin K intakes. Thus, dietary strategies to improve vitamin K intakes are needed, and vitamin K biofortification of food may be one food-based approach. The primary aim of our study was to establish whether increasing the vitamin K3 content of hen feed can increase the vitamin K content of eggs, and the secondary aims were to examine the effects on hen performance parameters, as well as egg and eggshell quality parameters. A 12 week hen feeding trial was conducted in which Hyline chickens were randomized into four treatment groups (n = 32/group) and fed diets containing vitamin K3 (as menadione nicotinamide bisulfite) at 3 (control), 12.9, 23.7, and 45.7 mg/kg feed. Vitamin K1, menaquinone (MK)-4, MK-7, and MK-9 were measured in raw whole eggs via a liquid chromatography tandem mass spectrometry method. MK-4 was the most abundant form of vitamin K (91-98%) found in all eggs. Increasing the vitamin K3 content of hen feed over the control level significantly (p < 0.001) enhanced the MK-4 content of eggs (mean range: 46-51 µg/100 g, representing ~42-56% of US Adequate Intake values). Vitamin K biofortification also led to significant (p < 0.05) increases in the yellowness of egg yolk and in eggshell weight and thickness, but no other changes in egg quality or hen performance parameters. In conclusion, high-quality vitamin K-biofortified eggs can be produced with at least double the total vitamin K content compared to that in commercially available eggs.

Sevelamer Use in End-Stage Kidney Disease (ESKD) Patients Associates with Poor Vitamin K Status and High Levels of Gut-Derived Uremic Toxins: A Drug-Bug Interaction?

Gut microbial metabolism is not only an important source of uremic toxins but may also help to maintain the vitamin K stores of the host. We hypothesized that sevelamer therapy, a commonly used phosphate binder in patients with end-stage kidney disease (ESKD), associates with a disturbed gut microbial metabolism. Important representatives of gut-derived uremic toxins, including indoxyl sulfate (IndS), p-Cresyl sulfate (pCS), trimethylamine N-oxide (TMAO), phenylacetylglutamine (PAG) and non-phosphorylated, uncarboxylated matrix-Gla protein (dp-ucMGP; a marker of vitamin K status), were analyzed in blood samples from 423 patients (65% males, median age 54 years) with ESKD. Demographics and laboratory data were extracted from electronic files. Sevelamer users (n = 172, 41%) were characterized by higher phosphate, IndS, TMAO, PAG and dp-ucMGP levels compared to non-users. Sevelamer was significantly associated with increased IndS, PAG and dp-ucMGP levels, independent of age, sex, calcium-containing phosphate binder, cohort, phosphate, creatinine and dialysis vintage. High dp-ucMGP levels, reflecting vitamin K deficiency, were independently and positively associated with PAG and TMAO levels. Sevelamer therapy associates with an unfavorable gut microbial metabolism pattern. Although the observational design precludes causal inference, present findings implicate a disturbed microbial metabolism and vitamin K deficiency as potential trade-offs of sevelamer therapy.

Naturally Occurring PCSK9 Inhibitors

Genetic, epidemiological and pharmacological data have led to the conclusion that antagonizing or inhibiting Proprotein convertase subtilisin/kexin type 9 (PCSK9) reduces cardiovascular events. This clinical outcome is mainly related to the pivotal role of PCSK9 in controlling low-density lipoprotein (LDL) cholesterol levels. The absence of oral and affordable anti-PCSK9 medications has limited the beneficial effects of this new therapeutic option. A possible breakthrough in this field may come from the discovery of new naturally occurring PCSK9 inhibitors as a starting point for the development of oral, small molecules, to be used in combination with statins in order to increase the percentage of patients reaching their LDL-cholesterol target levels. In the present review, we have summarized the current knowledge on natural compounds or extracts that have shown an inhibitory effect on PCSK9, either in experimental or clinical settings. When available, the pharmacodynamic and pharmacokinetic profiles of the listed compounds are described.

The Role of Gut Dysbiosis in the Bone-Vascular Axis in Chronic Kidney Disease

Patients with chronic kidney disease (CKD) are at increased risk of bone mineral density loss and vascular calcification. Bone demineralization and vascular mineralization often concur in CKD, similar to what observed in the general population. This contradictory association is commonly referred to as the 'calcification paradox' or the bone-vascular axis. Mounting evidence indicates that CKD-associated gut dysbiosis may be involved in the pathogenesis of the bone-vascular axis. A disrupted intestinal barrier function, a metabolic shift from a predominant saccharolytic to a proteolytic fermentation pattern, and a decreased generation of vitamin K may, alone or in concert, drive a vascular and skeletal pathobiology in CKD patients. A better understanding of the role of gut dysbiosis in the bone-vascular axis may open avenues for novel therapeutics, including nutriceuticals.

Long-chain vitamin K2 production in Lactococcus lactis is influenced by temperature, carbon source, aeration and mode of energy metabolism

Background

Vitamin K2 (menaquinone, MK-n) is a lipid-soluble vitamin that functions as a carboxylase co-factor for maturation of proteins involved in many vital physiological processes in humans. Notably, long-chain vitamin K2 is produced by bacteria, including some species and strains belonging to the group of lactic acid bacteria (LAB) that play important roles in food fermentation processes. This study was performed to gain insights into the natural long-chain vitamin K2 production capacity of LAB and the factors influencing vitamin K2 production during cultivation, providing a basis for biotechnological production of vitamin K2 and in situ fortification of this vitamin in food products.

Results

We observed that six selected Lactococcus lactis strains produced MK-5 to MK-10, with MK-8 and MK-9 as the major MK variant. Significant diversities between strains were observed in terms of specific concentrations and titres of vitamin K2. L. lactis ssp. cremoris MG1363 was selected for more detailed studies of the impact of selected carbon sources tested under different growth conditions [i.e. static fermentation (oxygen absent, heme absent); aerobic fermentation (oxygen present, heme absent) and aerobic respiration (oxygen present, heme present)] on vitamin K2 production in M17 media. Aerobic fermentation with fructose as a carbon source resulted in the highest specific concentration of vitamin K2: 3.7-fold increase compared to static fermentation with glucose, whereas aerobic respiration with trehalose resulted in the highest titre: 5.2-fold increase compared to static fermentation with glucose. When the same strain was applied to quark fermentation, we consistently observed that altered carbon source (fructose) and aerobic cultivation of the pre-culture resulted in efficient vitamin K2 fortification in the quark product.

Conclusions

With this study we demonstrate that certain LAB strains can be employed for efficient production of long-chain vitamin K2. Strain selection and optimisation of growth conditions offer a viable strategy towards natural vitamin K2 enrichment of fermented foods, and to improved biotechnological vitamin K2 production processes.

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1179-9) contains supplementary material, which is available to authorized users.

Modular Pathway Engineering of Bacillus subtilis To Promote De Novo Biosynthesis of Menaquinone-7

Menaquinone-7 (MK-7), a valuable vitamin K₂, plays an important role in the prevention of osteoporosis and cardiovascular calcification. We chose B. subtilis 168 as the chassis for the modular metabolic engineering design to promote the biosynthesis of MK-7. The biosynthetic pathway of MK-7 was categorized into four modules, namely, the MK-7 pathway (Module I), the shikimate (SA) pathway (Module II), the methylerythritol phosphate (MEP) pathway (Module III), and the glycerol metabolism pathway (Module IV). Overexpression of menA (Module I) resulted in 6.6 ± 0.1 mg/L of MK-7 after 120 h fermentation, which was 2.1-fold that of the starting strain BS168NU (3.1 ± 0.2 mg/L). Overexpression of aroA, aroD, and aroE (Module II) had a negative effect on the synthesis of MK-7. Simultaneous overexpression of dxs, dxr, yacM, and yacN (Module III) enabled the yield of MK-7 to 12.0 ± 0.1 mg/L. Moreover, overexpression of glpD (Module IV) resulted in an increase of the yield of MK-7 to 13.7 ± 0.2 mg/L. Furthermore, deletion of dhbB reduced the consumption of the intermediate metabolite isochorismate, thus promoting the yield of MK-7 to 15.4 ± 0.6 mg/L. Taken together, the final resulting strain MK3-MEP123-Gly2-Δ dhbB with simultaneous overexpression of menA, dxs, dxr, yacM-yacN, glpD and deletion of dhbB enabled the yield of MK-7 to 69.5 ± 2.8 mg/L upon 144 h fermentation in a 2 L baffled flask.

Tissue Concentrations of Vitamin K and Expression of Key Enzymes of Vitamin K Metabolism Are Influenced by Sex and Diet but Not Housing in C57Bl6 Mice

BACKGROUND

There has been limited characterization of biological variables that impact vitamin K metabolism. This gap in knowledge can limit the translation of data obtained from preclinical animal studies to future human studies.

OBJECTIVE

The purpose of this study was to determine the effects of diet, sex, and housing on serum, tissue, and fecal vitamin K concentrations and gene expression in C57BL6 mice during dietary vitamin K manipulation.

METHODS

C57BL6 4-mo-old male and female mice were randomly assigned to conventional or suspended-wire cages and fed control [1400 ± 80 μg phylloquinone (PK)/kg] or deficient (31 ± 0.45 μg PK/kg) diets for 28 d in a factorial design. PK and menaquinone (MK) 4 plasma and tissue concentrations were measured by HPLC. Long-chain MKs were measured in all matrices by LC-atmospheric pressure chemical ionization-mass spectrometry. Gene expression was quantified by reverse transcriptase-polymerase chain reaction in the liver, brain, kidney, pancreas, and adipose tissue.

RESULTS

Male and female mice responded differently to dietary manipulation in a tissue-dependent manner. In mice fed the control diet, females had ∼3-fold more MK4 in the brain and mesenteric adipose tissue than did males and 100% greater PK concentrations in the liver, kidney, and mesenteric adipose tissue than did males. In mice fed the deficient diet, kidney MK4 concentrations were ∼4-fold greater in females than in males, and there were no differences in other tissues. Males and females differed in the expression of vitamin K expoxide reductase complex 1 (Vkorc1) in mesenteric adipose tissue and the pancreas and ubiA domain-containing protein 1 (Ubiad1) in the kidney and brain. There was no effect of housing on serum, tissue, or fecal concentrations of any vitamin K form.

CONCLUSIONS

Vitamin K concentrations and expression of key metabolic enzymes differ between male and female mice and in response to the dietary PK concentration. Identifying factors that may impact study design and outcomes of interest is critical to optimize study parameters examining vitamin K metabolism in animal models.

GGCX and VKORC1 inhibit osteocalcin endocrine functions

Cell-specific gene inactivation experiments delineate the functions of the enzymes required for osteocalcin modification and demonstrate that it is its uncarboxylated form that acts as a hormone.

Osteocalcin (OCN) is an osteoblast-derived hormone favoring glucose homeostasis, energy expenditure, male fertility, brain development, and cognition. Before being secreted by osteoblasts in the bone extracellular matrix, OCN is γ-carboxylated by the γ-carboxylase (GGCX) on three glutamic acid residues, a cellular process requiring reduction of vitamin K (VK) by a second enzyme, a reductase called VKORC1. Although circumstantial evidence suggests that γ-carboxylation may inhibit OCN endocrine functions, genetic evidence that it is the case is still lacking. Here we show using cell-specific gene inactivation models that γ-carboxylation of OCN by GGCX inhibits its endocrine function. We further show that VKORC1 is required for OCN γ-carboxylation in osteoblasts, whereas its paralogue, VKORC1L1, is dispensable for this function and cannot compensate for the absence of VKORC1 in osteoblasts. This study genetically and biochemically delineates the functions of the enzymes required for OCN modification and demonstrates that it is the uncarboxylated form of OCN that acts as a hormone.

Menaquinones, bacteria, and the food supply: the relevance of dairy and fermented food products to vitamin K requirements

Vitamin K exists in the food supply as phylloquinone, a plant-based form and as menaquinones (MKs), a collection of isoprenologues mostly originating from bacterial synthesis. Although multiple bacterial species used as starter cultures for food fermentations synthesize MK, relatively little is known about the presence and distribution of MK in the food supply and the relative contribution of MK to total dietary vitamin K intake. Dairy products may be a predominant source of dietary MK in many regions of the world, and there is recent interest in enhancing the MK content of dairy products through identification and selection of MK-producing bacteria in dairy fermentations. This interest is increased by emerging evidence that current dietary recommendations based on the classic role of vitamin K as an enzyme cofactor for coagulation proteins may not be optimal for supporting vitamin K requirements in extrahepatic tissues and that MK may have unique bioactivity beyond that as an enzyme cofactor. Observational studies have reported favorable associations between MK intake and bone and cardiovascular health. Although randomized trials have provided some evidence to support the beneficial effects of MK on bone, the evidence to date is not definitive, and randomized trials have not yet examined MK intake in relation to cardiovascular outcomes. Food production practices provide a means to enhance dietary MK availability and intake. However, parallel research is needed to optimize these production practices, develop comprehensive food MK content databases, and test hypotheses of unique beneficial physiological roles of MK beyond that achieved by phylloquinone.

Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women

Background

Vitamin K₂ contributes to bone and cardiovascular health. Therefore, two vitamin K₂ homologues, menaquinone-4 (MK-4) and menaquinone-7 (MK-7), have been used as nutrients by the food industry and as nutritional supplements to support bone and cardiovascular health. However, little is known about the bioavailability of nutritional MK-4. To investigate MK-4 and MK-7 bioavailability, nutritional doses were administered to healthy Japanese women.

Findings

Single dose administration of MK-4 (420 μg; 945 nmol) or MK-7 (420 μg; 647 nmol) was given in the morning together with standardized breakfast. MK-7 was well absorbed and reached maximal serum level at 6 h after intake and was detected up to 48 h after intake. MK-4 was not detectable in the serum of all subjects at any time point. Consecutive administration of MK-4 (60 μg; 135 nmol) or MK-7 (60 μg; 92 nmol) for 7 days demonstrated that MK-4 supplementation did not increase serum MK-4 levels. However, consecutive administration of MK-7 increased serum MK-7 levels significantly in all subjects.

Conclusions

We conclude that MK-4 present in food does not contribute to the vitamin K status as measured by serum vitamin K levels. MK-7, however significantly increases serum MK-7 levels and therefore may be of particular importance for extrahepatic tissues.

Vitamin K deficiency of germfree mice caused by feeding standard purified diet sterilized by gamma-irradiation

Germfree mice died when they were fed a purified diet of AIN-76 formula sterilized by gamma-irradiation. Vitamin K deficiency was suspected and this study was performed to confirm the cause of the death. Germfree mice were fed purified diets of AIN-76 or AIN-93M formula, which were pelleted and sterilized by gamma-irradiation at a dose of 50 kGy. One half of the mice fed the AIN-76 diet died within two weeks and the surviving animals were also in poor health, while 91% of mice fed the AIN-93M diet survived. No hemorrhage was observed grossly in any organs of the surviving animals. Histologically, degeneration with inflammatory cell infiltration was observed as well as hemorrhage and fibrosis in the heart muscles of mice fed the AIN-76 diet. No microscopic lesions were observed in the other organs. Prothrombin time (PT) and activated partial thromboplastin time (APTT) were extremely prolonged when mice were fed the AIN-76 diet. The animals totally recovered when they were intragastrically administered 1 microg/day of vitamin K(3) from the third day of feeding of the AIN-76 diet, except for PT and APTT which were still slightly longer than in mice fed the AIN-93M diet. The concentration of vitamin K(3) supplied in the AIN-76 diet decreased to an undetectable level after gamma-irradiation, while the AIN-93M diet contained 240 microg/kg of vitamin K(1). These results indicate that the deaths of the germfree mice fed the gamma-irradiated AIN-76 diet were caused by vitamin K deficiency. Vitamin K deficiency may cause fatal degeneration of cardiac muscle cells.

Difference in the metabolism of vitamin K between liver and bone in vitamin K-deficient rats

The difference between vitamin K metabolism in the liver and that in the bone of vitamin K-deficient rats was examined. After 17 d administration of vitamin K-deficient food, vitamin K in the liver was almost depleted, and prothrombin time (PT) was prolonged. Serum total osteocalcin level was slightly decreased by vitamin K deficiency, whereas serum undercarboxylated osteocalcin level did not change. The level of menaquinone (MK)-4 as well as that of phylloquinone was decreased, but approximately 40 % of the initial level still existed in the femur after the 17 d period. A single-dose administration of vitamin K (250 nmol/kg body weight) markedly increased vitamin K level in the liver but not in the femur. These results suggest that the turnover of vitamin K in the bone is slower than that in the liver, and bone metabolism may be little affected by the short period of intake of vitamin K-deficient food. However, intake of a larger amount of vitamin K is required for its accumulation in the bone than in the liver. Furthermore, the counteracting effect of MK-7 on prolonged PT in vitamin K-deficient rats was found to be higher than phylloquinone or MK-4.

Intestinal, hepatic, and circulating vitamin K levels at low and high intakes of vitamin K in rats

The aim of the present study was to assess how high doses of dietary vitamin K influence the intestinal profile of K-vitamins in vitamin K-deficient rats, and whether the induced changes are reflected in the hepatic vitamin K store. Vitamin K-deficient rats were fed for 10 d on diets containing different forms of vitamin K, and it was determined how these diets affected the vitamin K concentration at various sites of the instestine, serum, and the liver. It was found that the absorption of phylloquinone from standard food is not more than 10 %, while the absorption of pharmacological doses of oil-solubilized phylloquinone and menaquinone-4 was also far from complete (18 and 55 % respectively). High intakes of phylloquinone suppress the colonic production of all higher menaquinones. High menaquinone-4 intake induces very high menaquinone-8 concentrations, both in the colonic contents as well as in the liver. These data suggest that menaquinone-4 may be converted into menaquinone-8 (but not into other menaquinones) via a metabolic pathway which has not been reported previously.

Pleiotropic actions of vitamin K: protector of bone health and beyond?

Vitamin K is a nutrient that was originally identified as an essential factor for blood coagulation. Recently, vitamin K has emerged as a potential protector against osteoporosis, atherosclerosis, and hepatocarcinoma. Accumulated evidence indicates that subclinical non-hemostatic vitamin K deficiency in extrahepatic tissues, particularly in bone and possibly in vasculature, exists widely in the otherwise healthy adult population. Vitamins K1 and K2 have been shown to exert protective effects against osteoporosis, although it is important that the beneficial effects will be further confirmed by large-scale, randomized, clinical trials. Increasing evidence implicates a role for vitamin K in calcification of arteries and atherogenesis. Moreover, the therapeutic potential of vitamin K2 as an antihepatoma drug has recently been highlighted. Most of the new biological functions of vitamin K in bone, vasculature, and hepatoma cells are considered attributable to promotion of gamma-carboxylation of glutamic acid residues in vitamin K-dependent proteins, which is shared by vitamins K1 and K2. In contrast, vitamin K2-specific, gamma-carboxylation-unrelated functions have also been demonstrated. Thus, biological differences between vitamins K1 and K2 and potential involvement of gamma-carboxylation-independent actions in the new roles of vitamin K remain open issues. Molecular bases of coagulation-unrelated pleiotropic actions of vitamin K and its implications in human health deserve further investigations.

Production of menaquinone (vitamin K2)-7 by Bacillus subtilis

Menaquinone-7 (MK-7) is a highly bioactive homologue of vitamin K. We obtained a diphenylamine-resistant mutant strain D200-41 from Bacillus subtilis strain MH-1 which was isolated from fermented soybeans, natto. The mutant strain exhibited decreased production of MK-6. Using strain D200-41, efficient production of MK-7 was achieved. We found that, compared with an agitated and aerated culture, production of MK-7 was increased by static culture. The sporulation of the cells progressed more slowly in a static culture than in an agitated culture. The maximum concentration of MK reached about 60 mg/l in a medium containing 10% soybean extract, 5% glycerol, 0.5% yeast extract and 0.05% K2HPO4 (pH 7.3) when D200-41 cells as well as MH-1 cells were statically cultured at 45 degrees C for 5 d after being cultured with shaking at 37 degrees C for 1 d.

Biodisponibilidade de vitaminas lipossolúveis

O termo biodisponibilidade representa a parte do nutriente ingerido que tem o potencial de suprir as demandas fisiológicas em tecidos alvos; por definição, não corresponde, na maioria das vezes, à quantidade ingerida. Apesar da concordância entre alguns pesquisadores no que se refere ao conceito de biodisponibilidade, vários termos são comumente utilizados em trabalhos científicos como sinônimos desse, em função das peculiaridades dos métodos empregados na sua determinação. Estudos de balanço, relação dose-efeito e uso de isótopos são alguns dos métodos mais comumente utilizados para determinar a biodisponibilidade de vitaminas. Tais metodologias, além de avaliar a biodisponibilidade do nutriente, devem tanto quanto possível procurar elucidar ou levar em consideração os fatores que interferem na sua absorção e utilização. Dentre esses fatores, estão a interação com outros nutrientes ou componentes da dieta e as condições fisiológicas dos organismos submetidos ao estudo. As vitaminas lipossolúveis, devido ao seu metabolismo complexo, diversidade funcional e mecanismo de absorção relacionado a lipoproteínas, apresentam alguns problemas específicos no que se refere à avaliação de sua biodisponibilidade em alimentos ou dietas, necessitando, por ocasião dos ensaios, de um criterioso planejamento e análise de resultados. Dessa forma, ressaltaram-se, nesta revisão, alguns aspectos importantes com relação à biodisponibilidade das vitaminas lipossolúveis, como: diversidade de termos usados, metodologia para avaliação, fatores que interferem na absorção e utilização, entre outros, visto que a avaliação da biodisponibilidade de algumas vitaminas lipossolúveis ainda não possui métodos validados, gerando uma grande variação nos resultados obtidos nas pesquisas realizadas nesta área.

Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study

Vitamin K-dependent proteins, including matrix Gla-protein, have been shown to inhibit vascular calcification. Activation of these proteins via carboxylation depends on the availability of vitamin K. We examined whether dietary intake of phylloquinone (vitamin K-1) and menaquinone (vitamin K-2) were related to aortic calcification and coronary heart disease (CHD) in the population-based Rotterdam Study. The analysis included 4807 subjects with dietary data and no history of myocardial infarction at baseline (1990-1993) who were followed until January 1, 2000. The risk of incident CHD, all-cause mortality, and aortic atherosclerosis was studied in tertiles of energy-adjusted vitamin K intake after adjustment for age, gender, BMI, smoking, diabetes, education, and dietary factors. The relative risk (RR) of CHD mortality was reduced in the mid and upper tertiles of dietary menaquinone compared to the lower tertile [RR = 0.73 (95% CI: 0.45, 1.17) and 0.43 (0.24, 0.77), respectively]. Intake of menaquinone was also inversely related to all-cause mortality [RR = 0.91 (0.75, 1.09) and 0.74 (0.59, 0.92), respectively] and severe aortic calcification [odds ratio of 0.71 (0.50, 1.00) and 0.48 (0.32, 0.71), respectively]. Phylloquinone intake was not related to any of the outcomes. These findings suggest that an adequate intake of menaquinone could be important for CHD prevention.

Factors affecting intestinal absorption of highly lipophilic food microconstituents (fat-soluble vitamins, carotenoids and phytosterols)

Highly lipophilic food microconstituents (HLFMs) with octanol-water partition coefficients log10 P(c) > 8 include the fat-soluble vitamins (A, E, D and K) and phytochemicals with potential health benefits, the carotenoids and phytosterols. It has been assumed that these compounds have the same metabolism in the human upper gastrointestinal tract and that they follow the same fate as lipids. However, a literature review shows that the metabolism of HLFMs in the upper gastrointestinal tract depends on each HLFM species. For example, some HLFM esters are hydrolyzed mainly by pancreatic lipase, others by bile salt-stimulated lipase; some HLFMs are apparently absorbed by passive diffusion, others by a transporter. Also, although some factors (HLFM molecular species, fat, food matrix) affect absorption efficiency of most HLFMs, other factors (fibers, microconstituents) apparently affect absorption only of some HLFMs. The mnemonic acronym SLAMENGHI, previously proposed to list the factors affecting the bioavailability of carotenoids, was used here to review current knowledge of the factors suspected to affect the intestinal absorption of HLFMs. The available data reveal numerous gaps in the knowledge of the metabolism of HLFMs and the factors that affect their absorption. These gaps need to be filled to be able to formulate HLFMs so as to promote greater absorption efficiency.

Vitamin K-dependent and vitamin K-independent hypocoagulant effects of dietary fish oil in rats

In rats, dietary fish oil causes a plasma triglyceride-lowering as well as hypocoagulant effect. The latter is apparent from reduced levels of vitamin K-dependent coagulation factors and a decreased thrombin-forming potential of the coagulating plasma. Here, we describe that intervention with low levels of n-3 polyunsaturated fatty acids (n-3 PUFAs, about 2.5% of digestible energy, en%) resulted in no more than a small reduction in coagulation factors, when supplied as part of a high-fat diet relatively rich in vitamin K. Plasma triglycerides also remained unchanged. On the other hand, when feeding rats with low- or high-fat diets restricted in vitamin K, intervention with 3 en% of n-3 PUFAs acids (fish oil) caused only a lowering in triglycerides in combination with high fat. The fish caused a reduction in coagulation potential and levels vitamin K-dependent coagulation factors (prothrombin and factor VII) that was most prominent with the low-fat diet. Fish oil, in combination with low fat but not with high fat, reduced the vitamin K levels in the liver of the animals. In addition, regardless of the fat content, the vitamin K-independent coagulation factor V was decreased in the fish oil groups. Taken together, these results indicate that, in the rat, the hypocoagulant effect of a low dose of n-3 PUFAs is most apparent at low intakes of both vitamin K and fat, is not linked to the triglyceride plasma level, but involves modulation of both vitamin K-dependent and -independent coagulation factors.

A comprehensive review of vitamin K and vitamin K antagonists

For more than 60 years, vitamin K-dependent proteins have been known to play an important role in regulating blood coagulation. During recent years it has become clear, however, that vitamin K is also involved in other physiologic processes, including bone metabolism and vascular biology. Because the vitamin K requirement of bone and vessel wall is higher than that of the liver (where the clotting factors are produced) recommended daily allowance (RDA) values for K vitamins must be redefined. According to the new definition, a substantial part of the population is mildly deficient in vitamin K, and at later ages this deficiency may contribute to increased bone fracture risk, arterial calcification, and cardiovascular disease.

Induction of prothrombin synthesis by K-vitamins compared in vitamin K-deficient and in brodifacoum-treated rats

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.

Modulation of arterial thrombosis tendency in rats by vitamin K and its side chains

Vitamin K is involved in the biosynthesis of a number of blood coagulation factors and bone proteins. It has been suggested that the vitamin K requirement of bone tissue is higher than that of the liver. Here we report that in rats very high doses of vitamin K affected neither the blood coagulation characteristics nor the blood platelet aggregation rate. This was observed for both phylloquinone and menaquinone-4. Both vitamers were also tested for their effects on the arterial thrombosis tendency in the rat aorta loop model. The mean obstruction times were prolonged at a high intake of menaquinone-4 (250 mg/kg body weight/day), and shortened after a similarly high phylloquinone regimen. Since (a) both vitamers only differ in their aliphatic side chains; and (b) a similar trend was observed after administration of phytol and geranylgeraniol, we conclude that the modulation of the arterial thrombosis tendency is accomplished by the side chain of vitamin K.

Effect of food composition on vitamin K absorption in human volunteers

The human vitamin K requirement is not known precisely, but the minimal requirement is often assumed to be between 0.5 and 1 x 10(-6) g/kg body weight. In the present study we addressed the question to what extent circulating vitamin K concentrations are influenced by the form in which the vitamer is consumed. The experimental group consisted of five healthy volunteers who received phylloquinone after an overnight fast. On the first day of three successive weeks the participants consumed 1 mg (2.2 mumol) phylloquinone, either in the form of a pharmaceutical preparation (Konakion), or in the form of spinach + butter, or as spinach without added fat. Circulating phylloquinone levels after spinach with and without butter were substantially lower (7.5- and 24.3-fold respectively) than those after taking the pharmaceutical concentrate. Moreover, the absorption of phylloquinone from the vegetables was 1.5 times slower than from Konakion. In a second experiment in the same five volunteers it was shown that relatively high amounts of menaquinone-4 enter the circulation after the consumption of butter enriched with this vitamer. It is concluded that the bioavailability of membrane-bound phylloquinone is extremely poor and may depend on other food components, notably fat. The bioavailability of dietary vitamin K (phylloquinone + menaquinones) is lower than generally assumed, and depends on the form in which the vitamin is ingested. These new insights may lead to a revision of the recommended daily intake for vitamin K.