Protective Effect of Vitamin K2 (MK-7) on Acute Lung Injury Induced by Lipopolysaccharide in Mice.

Vitamin K2 (MK-7) has been shown to cause significant changes in different physiological processes and diseases, but its role in acute lung injury (ALI) is unclear. Therefore, in this study, we aimed to evaluate the protective effects of VK2 against LPS-induced ALI in mice. The male C57BL/6J mice were randomly divided into six groups (n = 7): the control group, LPS group, negative control group (LPS + Oil), positive control group (LPS + DEX), LPS + VK2 (L) group (VK2, 1.5 mg/kg), and LPS + VK2 (H) group (VK2, 15 mg/kg). Hematoxylin-eosin (HE) staining of lung tissue was performed. Antioxidant superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) activities, and the Ca2+ level in the lung tissue were measured. The effects of VK2 on inflammation, apoptosis, tight junction (TJ) injury, mitochondrial dysfunction, and autophagy were quantitatively assessed using Western blot analysis. Compared with the LPS group, VK2 improved histopathological changes; alleviated inflammation, apoptosis, and TJ injury; increased antioxidant enzyme activity; reduced Ca2+ overload; regulated mitochondrial function; and inhibited lung autophagy. These results indicate that VK2 could improve tight junction protein loss, inflammation, and cell apoptosis in LPS-induced ALI by inhibiting the mitochondrial dysfunction and excessive autophagy, indicating that VK2 plays a beneficial role in ALI and might be a potential therapeutic strategy.

Effects of vitamin K2 administration on guided bone regeneration in diabetic rats.

AIM: The present study aimed to investigate the histomorphometric and immunohistochemical impacts of vitamin K2 on guided bone regeneration (GBR) in calvarial critical-size defects (CSDs) in diabetic rats. METHODS: A total of 30 rats were used in this study, comprising 12 non-diabetic (control) rats and 18 with streptozotocin-nicotinamide-induced experimental Diabetes mellitus (DM). In all rats, two calvarial CSDs were created: one defect was left empty (E), the other was treated with bovine-derived bone graft and collagen-based resorbable membrane (GM). Study groups were as follows: control rats administered saline (n = 6, C-E and C-GM groups) or vitamin K2 (n = 6, CK-E and CK-GM groups) and diabetic rats administered saline (n = 6, DM-E and DM-GM groups) or vitamin K2 (n = 6, DMK-E and DMK-GM groups). After 4 weeks of saline or vitamin K2 administration, the rats were euthanized. Bone defect healing and new bone formation were assessed histomorphometrically, and osteocalcin and osteopontin levels were examined immunohistochemically. RESULTS: Percentage of new bone formation was greater in CK-GM vs. CK-E and in DMK-GM vs. DMK-E [d = 3.86 (95% CI = 16.38-28.61), d = 1.86, (95% CI = 10.74-38.58), respectively, p < .05]. Bone defect healing scores were higher in CK-GM vs. CK-E and in DMK-GM vs. DMK-E [d = 2.69 (95% CI = -2.12 to -0.87), d = 3.28 (95% CI = 0.98-1.91), respectively, p < .05]. Osteocalcin expression levels were elevated in CK-GM vs. CK-E, in DMK-GM vs. DMK-E [d = 1.19 (95% CI = 0.08-1.41), d = 1.10 (95% CI = 0.02-1.22), respectively p < .05]. Vitamin K2 enhanced osteocalcin expression levels in DMK-E vs. DM-E [d = 2.78, (95% CI = 0.56-1.53), p < .05] and in DMK-GM vs. DM-GM [d = 2.43, (95% CI = 0.65-2.10), p < .05]. Osteopontin expression was enhanced in defects treated with GM vs. E defects [C-GM vs. C-E, d = 1.56 (95% CI = 0.38-2.01); CK-GM vs. CK-E, d = 1.91 (95% CI = 0.49-1.72); DM-GM vs. DM-E, d = 2.34 (95% CI = -1.12 to -0.50); DMK-GM vs. DMK-E, d = 2.00 (95% CI = 0.58-1.91), p < .05]. CONCLUSION: The research findings suggest that administering vitamin K2 in GBR for rats with DM favorably impacts bone healing in CSDs, presenting an adjunctive strategy for bone regeneration.

Enhancing menaquinone-7 biosynthesis through strengthening precursor supply and product secretion.

Menaquinone-7 (MK-7) is an important class of vitamin K2 that is essential in human health and can prevent osteoporosis and cardiovascular disease. However, due to the complex synthesis pathway, the synthesis efficiency is low. The main objective of this study was to explore the effect of enhanced supply of precursors in Bacillus natto. Three precursors of pyruvate, shikimic acid, and sodium glutamate were chosen to investigate the effect of enhanced supply of precursors on MK-7 synthesis. Then, the optimal concentrations, different combinations, and different adding times were systematically studied, respectively. Results showed that the combination of shikimic acid and sodium glutamate could boost MK-7 production by 2 times, reaching 50 mg/L of MK-7 titer and 0.52 mg/(L·h) of MK-7 productivity. Furthermore, adding shikimic acid and sodium glutamate initially and feeding pyruvate at 48 h and 72 h increased MK-7 production to 58 mg/L. At the same time, the expression of the three related genes was also significantly upregulated. Subsequently, a new fermentation strategy combining the precursors enhancement and product secretion was proposed to enhance MK-7 yield and MK-7 productivity to 63 mg/L and 0.45 mg/(L·h). This study proposed a new fermentation regulation strategy for the enhancement of vitamin K2 biosynthesis.

Vitamin K2 and D in Patients With Aortic Valve Calcification: A Randomized Double-Blinded Clinical Trial.

BACKGROUND: Menaquinone-7 (MK-7), also known as vitamin K2, is a cofactor for the carboxylation of proteins involved in the inhibition of arterial calcification and has been suggested to reduce the progression rate of aortic valve calcification (AVC) in patients with aortic stenosis. METHODS: In a randomized, double-blind, multicenter trial, men from the community with an AVC score >300 arbitrary units (AU) on cardiac noncontrast computer tomography were randomized to daily treatment with tablet 720 µg MK-7 plus 25 µg vitamin D or matching placebo for 24 months. The primary outcome was the change in AVC score. Selected secondary outcomes included change in aortic valve area and peak aortic jet velocity on echocardiography, heart valve surgery, change in aortic and coronary artery calcification, and change in dp-ucMGP (dephosphorylated-undercarboxylated matrix Gla-protein). Safety outcomes included all-cause death and cardiovascular events. RESULTS: From February 1, 2018, to March 21, 2019, 365 men were randomized. Mean age was 71.0 (±4.4) years. The mean (95% CI) increase in AVC score was 275 AU (95% CI, 225-326 AU) and 292 AU (95% CI, 246-338 AU) in the intervention and placebo groups, respectively. The mean difference on AVC progression was 17 AU (95% CI, -86 to 53 AU; P=0.64). The mean change in aortic valve area was 0.02 cm2 (95% CI, -0.09 to 0.12 cm2; P=0.78) and in peak aortic jet velocity was 0.04 m/s (95% CI, -0.11 to 0.02 m/s; P=0.21). The progression in aortic and coronary artery calcification score was not significantly different between patients treated with MK-7 plus vitamin D and patients receiving placebo. There was no difference in the rate of heart valve surgery (1 versus 2 patients; P=0.99), all-cause death (1 versus 4 patients; P=0.37), or cardiovascular events (10 versus 10 patients; P=0.99). Compared with patients in the placebo arm, a significant reduction in dp-ucMGP was observed with MK-7 plus vitamin D (-212 pmol/L versus 45 pmol/L; P<0.001). CONCLUSIONS: In elderly men with an AVC score >300 AU, 2 years MK-7 plus vitamin D supplementation did not influence AVC progression. REGISTRATION: URL: https://www. CLINICALTRIALS: gov; Unique identifier: NCT03243890.

Vitamin K2 supplementation improves impaired glycemic homeostasis and insulin sensitivity for type 2 diabetes through gut microbiome and fecal metabolites.

BACKGROUND: There is insufficient evidence for the ability of vitamin K2 to improve type 2 diabetes mellitus symptoms by regulating gut microbial composition. Herein, we aimed to demonstrate the key role of the gut microbiota in the improvement of impaired glycemic homeostasis and insulin sensitivity by vitamin K2 intervention. METHODS: We first performed a 6-month RCT on 60 T2DM participants with or without MK-7 (a natural form of vitamin K2) intervention. In addition, we conducted a transplantation of the MK-7-regulated microbiota in diet-induced obesity mice for 4 weeks. 16S rRNA sequencing, fecal metabolomics, and transcriptomics in both study phases were used to clarify the potential mechanism. RESULTS: After MK-7 intervention, we observed notable 13.4%, 28.3%, and 7.4% reductions in fasting serum glucose (P = 0.048), insulin (P = 0.005), and HbA1c levels (P = 0.019) in type 2 diabetes participants and significant glucose tolerance improvement in diet-induced obesity mice (P = 0.005). Moreover, increased concentrations of secondary bile acids (lithocholic and taurodeoxycholic acid) and short-chain fatty acids (acetic acid, butyric acid, and valeric acid) were found in human and mouse feces accompanied by an increased abundance of the genera that are responsible for the biosynthesis of these metabolites. Finally, we found that 4 weeks of fecal microbiota transplantation significantly improved glucose tolerance in diet-induced obesity mice by activating colon bile acid receptors, improving host immune-inflammatory responses, and increasing circulating GLP-1 concentrations. CONCLUSIONS: Our gut-derived findings provide evidence for a regulatory role of vitamin K2 on glycemic homeostasis, which may further facilitate the clinical implementation of vitamin K2 intervention for diabetes management. TRIAL REGISTRATION: The study was registered at https://www.chictr.org.cn (ChiCTR1800019663).

The impact of gut bacteria producing long chain homologs of vitamin K2 on colorectal carcinogenesis.

Colorectal cancer (CRC) is one of the foremost causes of cancer-related deaths. Lately, a close connection between the course of CRC and the intestinal microbiota has been revealed. Vitamin K2 (VK2) is a bacterially derived compound that plays a crucial role in the human body. Its significant anti-cancer properties may result, inter alia, from a quinone ring possessing a specific chemical structure found in many chemotherapeutics. VK2 can be supplied to our body exogenously, i.e., through dietary supplements or fermented food (e.g., yellow cheese, fermented soybeans -Natto), and endogenously, i.e., through the production of bacteria that constantly colonize the human microbiome of the large intestine.This paper focuses on endogenous K2 synthesized by the most active members of the human gut microbiome. This analysis tested 86 intestinally derived bacterial strains, among which the largest VK2 producers (Lactobacillus, Bifidobacterium, Bacillus) were selected. Moreover, based on the chosen VK2-MK4 homolog, the potential of VK2 penetration into Caco-2 cells in an aqueous environment without the coexistence of fats, pancreatic enzymes, or bile salts has been displayed. The influence of three VK2 homologs: VK2-MK4, VK2-MK7 and VK2-MK9 on apoptosis and necrosis of Caco-2 cells was tested proving the lack of their harmful effects on the tested cells. Moreover, the unique role of long-chain homologs (VK2-MK9 and VK2-MK7) in inhibiting the secretion of pro-inflammatory cytokines such as IL-8 (for Caco-2 tissue) and IL-6 and TNFα (for RAW 264.7) has been documented.

Effect of asciminib and vitamin K2 on Abelson tyrosine-kinase-inhibitor-resistant chronic myelogenous leukemia cells.

BACKGROUND: Abelson (ABL) tyrosine kinase inhibitors (TKIs) are effective against chronic myeloid leukemia (CML); however, many patients develop resistance during ABL TKI therapy. Vitamin K2 (VK2) is a crucial fat-soluble vitamin used to activate hepatic coagulation factors and treat osteoporosis. Although VK2 has demonstrated impressive anticancer activity in various cancer cell lines, it is not known whether VK2 enhances the effects of asciminib, which specifically targets the ABL myristoyl pocket (STAMP) inhibitor. METHOD: In this work, we investigated whether VK2 contributed to the development of CML cell lines. We also investigated the efficacy of asciminib and VK2 by using K562, ponatinib-resistant K562 (K562 PR), Ba/F3 BCR-ABL, and T315I point mutant Ba/F3 (Ba/F3 T315I) cells. RESULTS: Based on data from the Gene Expression Omnibus (GEO) database, gamma-glutamyl carboxylase (GGCX) and vitamin K epoxide reductase complex subunit 1 (VKORC1) were elevated in imatinib-resistant patients (GSE130404). UBIA Prenyltransferase Domain Containing 1 (UBIAD1) was decreased, and K562 PR cells were resistant to ponatinib. In contrast, asciminib inhibited CML cells and ponatinib resistance in a dose-dependent manner. CML cells were suppressed by VK2. Caspase 3/7 activity was also elevated, as was cellular cytotoxicity. Asciminib plus VK2 therapy induced a significantly higher level of cytotoxicity than use of each drug alone. Asciminib and VK2 therapy altered the mitochondrial membrane potential. CONCLUSIONS: Asciminib and VK2 are suggested as a novel treatment for ABL-TKI-resistant cells since they increase treatment efficacy. Additionally, this treatment option has intriguing clinical relevance for patients who are resistant to ABL TKIs.

Ameliorating Effects of Vitamin K2 on Dextran Sulfate Sodium-Induced Ulcerative Colitis in Mice.

Ulcerative colitis (UC) is a chronic recurrent inflammatory illness of the gastrointestinal system. The purpose of this study was to explore the alleviating effect of vitamin K2 (VK2) on UC, as well as its mechanism. C57BL/6J mice were given 3% DSS for seven days to establish UC, and they then received VK2 (15, 30, or 60 mg/kg·bw) and 5-aminosalicylic acid (100 mg/kg·bw) for two weeks. We recorded the clinical signs, body weights, colon lengths, and histological changes during the experiment. We detected the inflammatory factor expressions using enzyme-linked immunosorbent assay (ELISA) kits, and we detected the tight junction proteins using Western blotting. We analyzed the intestinal microbiota alterations and short-chain fatty acids (SCFAs) using 16S rRNA sequencing and targeted metabolomics. According to the results, VK2 restored the colon lengths, improved the colonic histopathology, reduced the levels of proinflammatory cytokines (such as IL-1ß, TNF-α, and IL-6), and boosted the level of the immunosuppressive cytokine IL-10 in the colon tissues of the colitis mice. Moreover, VK2 promoted the expression of mucin and tight junction proteins (such as occludin and zonula occludens-1) in order to preserve the intestinal mucosal barrier function and prevent UC in mice. Additionally, after the VK2 intervention, the SCFAs and SCFA-producing genera, such as Eubacterium_ruminantium_group and Faecalibaculum, were elevated in the colon. In conclusion, VK2 alleviated the DSS-induced colitis in the mice, perhaps by boosting the dominant intestinal microflora, such as Faecalibaculum, by reducing intestinal microflora dysbiosis, and by modulating the expression of SCFAs, inflammatory factors, and intestinal barrier proteins.

Advances in regulating vitamin K2 production through metabolic engineering strategies.

Vitamin K2 (menaquinone, VK2, MK) is an essential lipid-soluble vitamin that plays critical roles in inhibiting cell ferroptosis, improving blood clotting, and preventing osteoporosis. The increased global demand for VK2 has inspired interest in novel production strategies. In this review, various novel metabolic regulation strategies, including static and dynamic metabolic regulation, are summarized and discussed. Furthermore, the advantages and disadvantages of both strategies are analyzed in-depth to highlight the bottlenecks facing microbial VK2 production on an industrial scale. Finally, advanced metabolic engineering biotechnology for future microbial VK2 production will also be discussed. In summary, this review provides in-depth information and offers an outlook on metabolic engineering strategies for VK2 production.

[Distribution of vitamin K_2 content in Chinese traditional fermented soybean products].

OBJECTIVE: To determine the content of vitamin K_2 in different types of fermented bean products and analyze the difference of vitamin K_(2 )content. METHODS: A total of 98 kinds of typical fermented bean products were included in Chinese traditional fermented bean products(Douchi, Sufu, soybean paste). Process, region, sales volume, raw materials and flavor were considered, and the content of vitamin K_2 in fermented bean products was determined by high performance liquid chromatography. RESULTS: Chinese bean fermented foods generally contained vitamin K_2, and the subtype menaquinone-7(MK-7)was the main one. The content of vitamin K_2 in Douchi was the highest(437.55 µg/100 g), the content of vitamin K_2 in Sufu and Soybean paste were lower(7.48 µg/100 g and 2.47 µg/100 g). The content of vitamin K_2 in bacterial Douchi was higher than that in Mucor type and Aspergillus oryzae type which were 403.94, 232.98 and 81.00 µg/100 g(P<0.05). Soybean type Douchi was higher than that in black bean type of Douchi which were 610.41, 178.08 µg/100 g(P<0.05), and the content of vitamin K_2 in dry Douchi was higher than the content of vitamin K_2 in water Douchi which were 1 517.45 µg/100 g, 297.58 µg/100 g(P<0.05). However, there were no significant difference in the content of vitamin K_2 in Soybean paste and Sufu in different types and regions(P > 0.05). CONCLUSION: Vitamin K_2 is widely contained in Chinese fermented bean products, and its content is mainly affected by fermentation microorganisms and processing technology.

Combining phosphate binder therapy with vitamin K2 inhibits vascular calcification in an experimental animal model of kidney failure.

BACKGROUND: Hyperphosphataemia is strongly associated with cardiovascular disease and mortality. Recently, phosphate binders (PBs), which are used to bind intestinal phosphate, have been shown to bind vitamin K, thereby potentially aggravating vitamin K deficiency. This vitamin K binding by PBs may offset the beneficial effects of phosphate reduction in reducing vascular calcification (VC). Here we assessed whether combining PBs with vitamin K2 supplementation inhibits VC. METHODS: We performed 3/4 nephrectomy in rats, after which warfarin was given for 3 weeks to induce vitamin K deficiency. Next, animals were fed a high phosphate diet in the presence of low or high vitamin K2 and were randomized to either control or one of four different PBs for 8 weeks. The primary outcome was the amount of thoracic and abdominal aorta VC measured by high-resolution micro-computed tomography (µCT). Vitamin K status was measured by plasma MK7 levels and immunohistochemically analysed in vasculature using uncarboxylated matrix Gla protein (ucMGP) specific antibodies. RESULTS: The combination of a high vitamin K2 diet and PB treatment significantly reduced VC as measured by µCT for both the thoracic (P = 0.026) and abdominal aorta (P = 0.023), compared with MK7 or PB treatment alone. UcMGP stain was significantly more present in the low vitamin K2-treated groups in both the thoracic (P < 0.01) and abdominal aorta (P < 0.01) as compared with high vitamin K2-treated groups. Moreover, a high vitamin K diet and PBs led to reduced vascular oxidative stress. CONCLUSION: In an animal model of kidney failure with vitamin K deficiency, neither PB therapy nor vitamin K2 supplementation alone prevented VC. However, the combination of high vitamin K2 with PB treatment significantly attenuated VC.

Phosphocalcic metabolism and the role of vitamin D, vitamin K2, and nattokinase supplementation.

Calcium is involved in bone metabolism, regulation of nerve signaling, and release of neurotransmitters. Phosphorus is a structural component of ATP, participates in metabolic energy regulation, and ensures stability to biological membranes and cells. Vitamin D and vitamin K are important for intestinal absorption and renal excretion of calcium and phosphorus. Vitamin D plays a regulatory role in bone formation, carbohydrate metabolism, immune responses, and cardiovascular regulation. Research has linked vitamin D deficiency to the development of diabetes mellitus, hypertension, cancer, and osteoporosis. Vitamin K has been associated with a reduced risk of osteoporosis, cancer, and cardiovascular diseases (due to improved vascular elasticity). This review highlights the importance of vitamins D and K in the metabolism of calcium and phosphorus and explores various molecular mechanisms that help maintain the system's mineral homeostasis. Moreover, the paper reviews the enzyme nattokinase's role in thrombotic prevention due to its fibrinolytic activity.

Engineering microbial consortia of Elizabethkingia meningoseptica and Escherichia coli strains for the biosynthesis of vitamin K2.

BACKGROUND: The study and application of microbial consortia are topics of interest in the fields of metabolic engineering and synthetic biology. In this study, we report the design and optimisation of Elizabethkingia meningoseptica and Escherichia coli co-culture, which bypass certain limitations found during the molecular modification of E. meningoseptica, such as resistance to many antibiotics and fewer available molecular tools. RESULTS: The octaprenyl pyrophosphate synthase from E. meningoseptica sp. F2 (EmOPPS) was expressed, purified, and identified in the present study. Then, owing to the low vitamin K2 production by E. coli or E. meningoseptica sp. F2 monoculture, we introduced the E. meningoseptica and E. coli co-culture strategy to improve vitamin K2 biosynthesis. We achieved production titres of 32 mg/L by introducing vitamin K2 synthesis-related genes from E. meningoseptica sp. F2 into E. coli, which were approximately three-fold more than the titre achieved with E. meningoseptica sp. F2 monoculture. This study establishes a foundation for further engineering of MK-n (n = 4, 5, 6, 7, 8) in a co-cultivation system of E. meningoseptica and E. coli. Finally, we analysed the surface morphology, esterase activity, and membrane permeability of these microbial consortia using scanning electron microscopy, confocal laser scanning microscopy, and flow cytometry, respectively. The results showed that the co-cultured bacteria were closely linked and that lipase activity and membrane permeability improved, which may be conducive to the exchange of substances between bacteria. CONCLUSIONS: Our results demonstrated that co-culture engineering can be a useful method in the broad field of metabolic engineering of strains with restricted molecular modifications.

Efficacy and safety of vitamin K2 for postmenopausal women with osteoporosis at a long-term follow-up: meta-analysis and systematic review.

INTRODUCTION: Vitamin K2 supplementation has been revealed to be effective in the prevention and treatment of osteoporosis in Japan, but further proof for the effectiveness of this practice is still needed. OBJECTIVE: To investigate whether vitamin K2 supplementation plays a role in maintaining bone mineral density (BMD) and reducing the incidence of fractures for postmenopausal women with osteoporosis at a long-term follow-up. MATERIALS AND METHODS: We searched systematically throughout the databases of PubMed, Cochrane library, and EMBASE from the dates of their inception to November 16 2021 in this meta-analysis and systematic review, using keywords vitamin K2 and osteoporosis. RESULTS: Nine RCTs with 6853 participants met the inclusion criteria. Vitamin K2 was associated with a significantly increased percentage change of lumbar BMD and forearm BMD (WMD 2.17, 95% CI [1.59-2.76] and WMD 1.57, 95% CI [1.15-1.99]). There were significant differences in undercarboxylated osteocalcin (uc-OC) reduction (WMD -0.96, 95% CI [-0.70 to 0.21]) and osteocalcin (OC) increment (WMD 26.52, 95% CI [17.06-35.98]). Adverse reaction analysis showed that there seemed to be higher adverse reaction rates in the vitamin K2 group (RR = 1.33, 95% CI [1.11-1.59]), but no serious adverse events related to vitamin K2 supplementation. CONCLUSION: This meta-analysis and systematic review seemed to support the hypothesis that vitamin K2 plays an important role in the maintenance and improvement of BMD, and it decreases uc-OC and increases OC significantly at a long-term follow-up. Vitamin K2 supplementation is beneficial and safe in the treatment of osteoporosis for postmenopausal women.

Effect of vitamin K2 administration on depression status in patients with polycystic ovary syndrome: a randomized clinical trial.

BACKGROUND: Patients with Polycystic ovary syndrome (PCOS) are predisposed to the development of several mental comorbidities such as depression. According to several studies, PCOS can be managed by improving insulin sensitivity. The insulin-sensitizing effect of vitamin K has been reported in recent studies. Therefore, in the current trial, we assessed the effect of administrating vitamin K2 (Menaquinone-7) on depression status in women afflicted with PCOS. METHODS: Eighty-four PCOS women were allocated into the intervention and comparison groups; the intervention group (n = 42) administered 90 µg/day Menaquinone-7, and the comparison group (n = 42) consumed placebo capsules (containing avesil) for 8 weeks. In this randomized, double blind, placebo-controlled clinical trial, depression status was measured by BECK depression inventory-II (BDI-II) before and after 8 weeks of intervention. RESULTS: Consumption of Menaquinone-7 in comparison with the placebo capsules significantly improved depression status (P = 0.012). CONCLUSION: This clinical study reported the advantageous effect of Menaquinone-7 administration on depression status in PCOS patients. Trial registration The present study was registered at http://www.IRCT.ir on 06/06/2018 (registration number: IRCT20170916036204N5).

Role of vitamin K2 in bone-vascular crosstalk.

Vitamin K (VK) is a fat-soluble vitamin that is indispensable for the activation of vitamin K-dependent proteins (VKDPs). It has been shown to play an important role in the proper calcium deposit at the bone level, hindering that on the vascular walls. The deficiency of this vitamin in European populations is frequent and unknown. It is related to several factors, poor dietary intake, altered intestinal absorption or altered production by bacteria, indicating possible dysbiosis. For Vitamin K2 (VK2), there is currently no official reference daily intake (RDI). However, the effects of VK2 on the improvement of health in cardiovascular diseases, on bone metabolism, on chronic kidney diseases have been the subject of research in recent decades. The microbiota in the gastrointestinal tract plays an important role: Bacteroides are primarily capable of synthetizing very long chain forms of menaquinones and, in addition to the bacteria present in the intestinal flora, VK2 is also produced by bacteria used in food fermentation processes. This review provides an update on the current literature regarding the origin of VK2 and its implications in what is called the "calcium paradox", namely the lack of calcium in the bone and its storage in the wall of the vessel.

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OBJECTIVES: To study the level of serum vitamin K2 (VitK2) and its association with bone metabolism markers osteocalcin (OC), type I procollagen amino-terminal peptide (PINP), and type I collagen carboxy-terminal peptide (CTX) in children. METHODS: A prospective analysis was performed on 1 732 children who underwent routine physical examination from October 2020 to October 2021. The serum levels of VitK2 and 25-hydroxy vitamin D [25(OH)D] were measured. According to age, they were divided into four groups: <1 year, 1-3 years group, >3-6 years group, and >6-14 years. A total of 309 children with 25(OH)D≥50 nmol/L were screened out, and serum levels of OC, PINP, and CTX were measured to investigate the correlation of the serum levels of OC, PINP, and CTX with serum VitK2 levels in different age groups. RESULTS: The prevalence rate of serum VitK2 deficiency was 52.31% (906/1 732). The VitK2 deficiency group had higher prevalence rates of overweight/obesity and growth pain (≥3 years of age) than the normal VitK2 group (P<0.05). There were differences in the prevalence rate of serum VitK2 deficiency (P<0.0083) and the serum level of VitK2 (P<0.05) between the 1-3 years group and the >6-14 years group. The <1 year group had a higher serum level of CTX and a lower serum level of PINP than the >3-6 years group and the >6-14 years group (P<0.05). The <1 year group had a lower serum level of OC than the >6-14 years group (P<0.05). Serum VitK2 level was positively correlated with OC level (rs=0.347, P<0.01), and CTX level was negatively correlated with PINP level (rs=-0.317, P<0.01). CONCLUSIONS: Serum VitK2 deficiency may be associated with overweight/obesity. Serum VitK2 may affect the level of OC and even bone health.

Allosteric regulation of menaquinone (vitamin K2) biosynthesis in the human pathogen Mycobacterium tuberculosis.

Menaquinone (vitamin K2) plays a vital role in energy generation and environmental adaptation in many bacteria, including the human pathogen Mycobacterium tuberculosis (Mtb). Although menaquinone levels are known to be tightly linked to the cellular redox/energy status of the cell, the regulatory mechanisms underpinning this phenomenon are unclear. The first committed step in menaquinone biosynthesis is catalyzed by MenD, a thiamine diphosphate-dependent enzyme comprising three domains. Domains I and III form the MenD active site, but no function has yet been ascribed to domain II. Here, we show that the last cytosolic metabolite in the menaquinone biosynthesis pathway, 1,4-dihydroxy-2-naphthoic acid (DHNA), binds to domain II of Mtb-MenD and inhibits its activity. Using X-ray crystallography of four apo- and cofactor-bound Mtb-MenD structures, along with several spectroscopy assays, we identified three arginine residues (Arg-97, Arg-277, and Arg-303) that are important for both enzyme activity and the feedback inhibition by DHNA. Among these residues, Arg-277 appeared to be particularly important for signal propagation from the allosteric site to the active site. This is the first evidence of feedback regulation of the menaquinone biosynthesis pathway in bacteria, identifying a protein-level regulatory mechanism that controls menaquinone levels within the cell and may therefore represent a good target for disrupting menaquinone biosynthesis in M. tuberculosis.

The effects of the chemical environment of menaquinones in lipid monolayers on mercury electrodes on the thermodynamics and kinetics of their electrochemistry.

The effects of the chemical environment of menaquinones (all-trans MK-4 and all-trans MK-7) incorporated in lipid monolayers on mercury electrodes have been studied with respect to the thermodynamics and kinetics of their electrochemistry. The chemical environment relates to the composition of lipid films as well as the adjacent aqueous phase. It could be shown that the addition of all-trans MK-4 to TMCL does not change the phase transition temperatures of TMCL. In case of DMPC monolayers, the presence of cholesterol has no effect on the thermodynamics (formal redox potentials) of all-trans MK-7, but the kinetics are affected. Addition of an inert electrolyte (sodium perchlorate; change of ionic strength) to the aqueous phase shifts the redox potentials of all-trans MK-7 only slightly. The formal redox potentials of all-trans MK-4 were determined in TMCL and nCL monolayers and found to be higher in nCL monolayers than in TMCL monolayers. The apparent electron transfer rate constants, transfer coefficients and activation energies of all-trans MK-4 in cardiolipins have been also determined. Most surprisingly, the apparent electron transfer rate constants of all-trans MK-4 exhibit an opposite pH dependence for TMCL and nCL films: the rate constants increase in TMCL films with increasing pH, but in nCL films they increase with decreasing pH. This study is a contribution to understand environmental effects on the redox properties of membrane bond redox systems.

New aspects of microbial vitamin K2 production by expanding the product spectrum.

Vitamin K2 (menaquinone, MK) is an essential lipid-soluble vitamin with critical roles in blood coagulation and bone metabolism. Chemically, the term vitamin K2 encompasses a group of small molecules that contain a common naphthoquinone head group and a polyisoprenyl side chain of variable length. Among them, menaquinone-7 (MK-7) is the most potent form. Here, the biosynthetic pathways of vitamin K2 and different types of MK produced by microorganisms are briefly introduced. Further, we provide a new aspect of MK-7 production, which shares a common naphthoquinone ring and polyisoprene biosynthesis pathway, by analyzing strategies for expanding the product spectrum. We review the findings of metabolic engineering strategies targeting the shikimate pathway, polyisoprene pathway, and menaquinone pathway, as well as membrane engineering, which provide comprehensive insights for enhancing the yield of MK-7. Finally, the current limitations and perspectives of microbial menaquinone production are also discussed. This article provides in-depth information on metabolic engineering strategies for vitamin K2 production by expanding the product spectrum.