Multiple Dietary Vitamin K Forms Are Converted to Tissue Menaquinone-4 in Mice

Beyond the Coagulation Cascade: Vitamin K and Its Multifaceted Impact on Human and Domesticated Animal Health

Vitamin K (VK) is an essential micronutrient impacting many systems in the body. This lipid-soluble vitamin is found in various plant and animal products and is absorbed via the lymphatic system. This biomolecule's importance to human health includes but is not limited to its promotion of brain, cardiovascular, bone, and immune functions. These biological properties are also necessary for maintaining domesticated animal health. The synergistic impact of both VK and vitamin D (VD) maximizes these health benefits, specifically for the circulatory and skeletal systems. This manuscript reviews VK's properties, molecular structures, nutrikinetics, mechanisms of action, daily requirements, safety in supplemental form, biomarkers used for its detection, and impacts on various organs. The purpose of synthesizing this information is to evaluate the potential uses of VK for the treatment or prevention of diseases.

Reduction of neutral lipid reservoirs, bioconversion and untargeted metabolomics reveal distinct roles for vitamin K isoforms on lipid metabolism

Vitamin K isoforms are known as co-factors for the synthesis of blood-clotting proteins, but several other bioactivities were reported. In this work, we isolated a vitamin K1-analogue (OH-PhQ) from the cyanobacterium Tychonema sp. LEGE 07196 with lipid reducing activity. OH-PhQ reduced neutral lipid reservoirs with an EC50 value of 31 μM after 48 h exposure in zebrafish larvae, while other vitamin K isoforms had EC50 values of 21.1 μM (K2) and 1.2 μM (K3). No lipid reducing activity was observed for K1 up to 50 μM. The presence of vitamin K isoforms was studied in zebrafish after exposure (OH-PhQ, K1, K2 and K3), and a clear preference for bioconversion was observed to retain K1 and OH-PhQ. Untargeted metabolomics revealed different biological effects for vitamin K isoforms on the subclass and metabolite level, but similarities were present on the compound class level, particularly on the regulation of glycerophospholipids. Our data showed for the first time a lipid reducing activity of OH-PhQ and performed a comparative analysis of vitamin K isoforms, which could be important for the development of future nutraceuticals or food supplements.

Revisiting the interconnection between lipids and vitamin K metabolism: insights from recent research and potential therapeutic implications: a review

Vitamin K is a lipophilic vitamin, whose absorption, transportation, and distribution are influenced by lipids. The plasma vitamin K level after supplementation is predominantly a lipid-driven effect and independent of existing vitamin K status. However, previous studies examining the efficacy of vitamin K supplementation often overlooked the influence of lipid levels on vitamin K absorption, resulting in inconsistent outcomes. Recent research discovered that impaired transportation of vitamin K2 within uremic high-density lipoproteins (HDL) in individuals with uremia might elucidate the lack of beneficial effects in preventing calcification observed in multiple trials involving menaquinone-7 (MK-7) supplementation among patients with chronic kidney disease. Clinical findings have shown that drugs used to regulate hyperlipidemia interact with the vitamin K antagonist warfarin, because cholesterol and vitamin K share common transport receptors, such as Niemann-Pick C1-like 1 (NPC1L1) and ATP-binding cassette protein G5/G8 (ABCG5/ABCG8), in enterocytes and hepatocytes. Additionally, cholesterol and vitamin K share a common biosynthetic intermediate called geranylgeranyl pyrophosphate (GGPP). It is important to note that statins, which hinder cholesterol synthesis, can also impede vitamin K conversion, ultimately impacting the functionality of vitamin K-dependent proteins. Furthermore, certain studies have indicated that vitamin K supplementation holds potential in managing hyperlipidemia, potentially opening a novel avenue for controlling hyperlipidemia using dietary vitamin K supplements. Therefore, attaining a more comprehensive understanding of the intricate interplay between vitamin K and lipids will yield valuable insights concerning the utilization of vitamin K and lipid regulation.

Natto consumption suppresses atherosclerotic plaque progression in LDL receptor-deficient mice transplanted with iRFP-expressing hematopoietic cells

Natto, known for its high vitamin K content, has been demonstrated to suppress atherosclerosis in large-scale clinical trials through a yet-unknown mechanism. In this study, we used a previously reported mouse model, transplanting the bone marrow of mice expressing infra-red fluorescent protein (iRFP) into LDLR-deficient mice, allowing unique and non-invasive observation of foam cells expressing iRFP in atherosclerotic lesions. Using 3 natto strains, we meticulously examined the effects of varying vitamin K levels on atherosclerosis in these mice. Notably, high vitamin K natto significantly reduced aortic staining and iRFP fluorescence, indicative of decreased atherosclerosis. Furthermore, mice administered natto showed changes in gut microbiota, including an increase in natto bacteria within the cecum, and a significant reduction in serum CCL2 expression. In experiments with LPS-stimulated macrophages, adding natto decreased CCL2 expression and increased anti-inflammatory cytokine IL-10 expression. This suggests that natto inhibits atherosclerosis through suppression of intestinal inflammation and reduced CCL2 expression in macrophages.

Vitamin K and Calcium Chelation in Vascular Health

The observation that the extent of artery calcification correlates with the degree of atherosclerosis was the background for the alternative treatment of cardiovascular disease with chelator ethylenediamine tetraacetate (EDTA). Recent studies have indicated that such chelation treatment has only marginal impact on the course of vascular disease. In contrast, endogenous calcium chelation with removal of calcium from the cardiovascular system paralleled by improved bone mineralization exerted, i.e., by matrix Gla protein (MGP) and osteocalcin, appears to significantly delay the development of cardiovascular diseases. After post-translational vitamin-K-dependent carboxylation of glutamic acid residues, MGP and other vitamin-K-dependent proteins (VKDPs) can chelate calcium through vicinal carboxyl groups. Dietary vitamin K is mainly provided in the form of phylloquinone from green leafy vegetables and as menaquinones from fermented foods. Here, we provide a review of clinical studies, addressing the role of vitamin K in cardiovascular diseases, and an overview of vitamin K kinetics and biological actions, including vitamin-K-dependent carboxylation and calcium chelation, as compared with the action of the exogenous (therapeutic) chelator EDTA. Consumption of vitamin-K-rich foods and/or use of vitamin K supplements appear to be a better preventive strategy than EDTA chelation for maintaining vascular health.

Vitamin K - a scoping review for Nordic Nutrition Recommendations 2023

Vitamin K occurs in dietary supply in two major forms: phylloquinone (vitamin K1) and menaquinones (collectively referred as vitamin K2). Phylloquinone is derived from plants. There are at least 10 forms of menaquinones varying in chain length and they are produced by bacteria except menaquinone-4. Menaquinone-4 is formed from phylloquinone or other menaquinone forms. Phylloquinone is considered to be the major contributor and menaquinones are thought to contribute less to vitamin K intake in Western diets. However, less is known about the content of menaquinones than phylloquinones in foods. Vitamin K is known to function as an enzymatic cofactor in the gamma-carboxylation of vitamin K dependent proteins (VKDPs). Hepatic VKDPs are involved in coagulation. Extrahepatic VKDPs have a role e.g. in bone health and vascular calcification. However, the amount of vitamin K needed for optimal functioning of the different VKDPs is not known.

Effects of Menaquinone-7 on the Bone Health of Growing Rats under Calcium Restriction: New Insights from Microbiome-Metabolomics

Insufficient calcium intake during growth is a global public health concern. The aim of this study was to investigate the effects of dietary menaquinone-7 (MK-7) on bone accrual in growing Sprague-Dawley rats under calcium restriction. Following 13 weeks of treatment, various bone quality parameters, including microarchitecture, were measured. Fecal and cecal samples were subjected to microbiome (16S rRNA gene sequencing) analyses, while metabolomics analysis of the cecum and humerus samples was analyzed based on UHPLC-Q/TOF-MS. We found that calcium deficiency diminished the richness of the microbiome and disrupted microbiome composition, accompanied by an elevation in the relative abundance of Parasutterella. Furthermore, calcium insufficiency escalated the level of isovaleric acid and modified the metabolic profiles. MK-7 supplementation significantly increased the cortical thickness, cortical bone area, and the calcium content of the femur. Apart from improving bone calcium deposition and diminishing bone resorption, the mechanisms underlying the beneficial effects of MK on bone quality also involve the modulation of the host's metabolic pathways and the composition of gut microbiota. The gut-bone axis holds promise as an efficacious target for ameliorating calcium deficiency in children's bone quality, and MK-7 is a promising dietary supplement from this perspective.

Vitamin K2 enhances the tumor suppressive effects of 1,25(OH)2D3 in triple negative breast cancer cells

K vitamins are well known as essential cofactors for hepatic γ-carboxylation of coagulation factors, but their potential role in chronic diseases including cancer is understudied. K2, the most abundant form of vitamin K in tissues, exerts anti-cancer effects via diverse mechanisms which are not completely understood. Our studies were prompted by previous work demonstrating that the K2 precursor menadione synergized with 1,25 dihydroxyvitamin D3 (1,25(OH)2D3) to inhibit growth of MCF7 luminal breast cancer cells. Here we assessed whether K2 modified the anti-cancer effects of 1,25(OH)2D3 in triple negative breast cancer (TNBC) cell models. We examined the independent and combined effects of these vitamins on morphology, cell viability, mammosphere formation, cell cycle, apoptosis and protein expression in three TNBC cell models (MDA-MB-453, SUM159PT, Hs578T). We found that all three TNBC cell lines expressed low levels of the vitamin D receptor (VDR) and were modestly growth inhibited by 1,25(OH)2D3 in association with cell cycle arrest in G0/G1. Induction of differentiated morphology by 1,25(OH)2D3 was observed in two of the cell lines (MDA-MB-453, Hs578T). Treatment with K2 alone reduced viability of MDA-MB-453 and SUM159PT cells but not Hs578T cells. Co-treatment with 1,25(OH)2D3 and K2 significantly reduced viable cell number relative to either treatment alone in Hs578T and SUM159PT cells. The combination treatment induced G0/G1 arrest in MDA-MB-453 cells, Hs578T and SUM159PT cells. Combination treatment altered mammosphere size and morphology in a cell specific manner. Of particular interest, treatment with K2 increased VDR expression in SUM159PT cells suggesting that the synergistic effects in these cells may be secondary to increased sensitivity to 1,25(OH)2D3. The phenotypic effects of K2 in TNBC cells did not correlate with γ-carboxylation suggesting non-canonical actions. In summary, 1,25(OH)2D3 and K2 exert tumor suppressive effects in TNBC cells, inducing cell cycle arrest leading to differentiation and/or apoptosis depending on the specific cell line. Further mechanistic studies to clarify common and unique targets of these two fat soluble vitamins in TNBC are warranted.

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.

Exclusively breastmilk-fed preterm infants are at high risk of developing subclinical vitamin K deficiency despite intramuscular prophylaxis at birth

BACKGROUND

There is near-global consensus that all newborns be given parenteral vitamin K1 (VK1 ) at birth as prophylaxis against VK deficiency bleeding (VKDB). Breastmilk has a low VK content and cases of late VKDB are reported in exclusively breastmilk-fed preterm infants despite VK prophylaxis at birth.

OBJECTIVES

To assess the prevalence of functional VK insufficiency in preterm infants based on elevated under-γ-carboxylated (Glu) species of Gla proteins, factor II (PIVKA-II), and osteocalcin (GluOC), synthesized by liver and bone, respectively.

PATIENTS/METHODS

Prospective, multicenter, observational study in preterm infants born <33 weeks' gestation. Blood samples and dietary history were collected before hospital discharge, and after discharge at 2-3 months' corrected age. Outcome measures were serum VK1 , PIVKA-II, and %GluOC (GluOC as a percentage of the sum of GluOC plus GlaOC) compared between exclusively breastmilk-fed and formula/mixed-fed infants after discharge.

RESULTS

After discharge, breastmilk-fed babies had significantly lower serum VK1 (0.15 vs. 1.81 μg/L), higher PIVKA-II (0.10 vs. 0.02 AU/ml) and higher %GluOC (63.6% vs. 8.1%) than those receiving a formula/mixed-feed diet. Pre-discharge (based on elevated PIVKA-II), only one (2%) of 45 breastmilk-fed infants was VK insufficient. After discharge, eight (67%) of 12 exclusively breastmilk-fed babies were VK insufficient versus only one (4%) of 25 formula/mixed-fed babies.

CONCLUSIONS

Preterm infants who remain exclusively or predominantly human breastmilk-fed after neonatal unit discharge are at high risk of developing subclinical VK deficiency in early infancy. Routine postdischarge VK1 supplementation of breastfed infants to provide intakes comparable to those from formula milks should prevent this deficiency.

Synthesis, function, and regulation of sterol and nonsterol isoprenoids

Cholesterol, the bulk end-product of the mevalonate pathway, is a key component of cellular membranes and lipoproteins that transport lipids throughout the body. It is also a precursor of steroid hormones, vitamin D, and bile acids. In addition to cholesterol, the mevalonate pathway yields a variety of nonsterol isoprenoids that are essential to cell survival. Flux through the mevalonate pathway is tightly controlled to ensure cells continuously synthesize nonsterol isoprenoids but avoid overproducing cholesterol and other sterols. Endoplasmic reticulum (ER)-localized 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase (HMGCR), the rate limiting enzyme in the mevalonate pathway, is the focus of a complex feedback regulatory system governed by sterol and nonsterol isoprenoids. This review highlights transcriptional and post-translational regulation of HMGCR. Transcriptional regulation of HMGCR is mediated by the Scap-SREBP pathway. Post-translational control is initiated by the intracellular accumulation of sterols, which causes HMGCR to become ubiquitinated and subjected to proteasome-mediated ER-associated degradation (ERAD). Sterols also cause a subfraction of HMGCR molecules to bind the vitamin K₂ synthetic enzyme, UbiA prenyltransferase domain-containing protein-1 (UBIAD1). This binding inhibits ERAD of HMGCR, which allows cells to continuously synthesize nonsterol isoprenoids such as geranylgeranyl pyrophosphate (GGPP), even when sterols are abundant. Recent studies reveal that UBIAD1 is a GGPP sensor, dissociating from HMGCR when GGPP thresholds are met to allow maximal ERAD. Animal studies using genetically manipulated mice disclose the physiological significance of the HMGCR regulatory system and we describe how dysregulation of these pathways contributes to disease.

New insights into vitamin K biology with relevance to cancer

Phylloquinone (vitamin K1) and menaquinones (vitamin K2 family) are essential for post-translational γ-carboxylation of a small number of proteins, including clotting factors. These modified proteins have now been implicated in diverse physiological and pathological processes including cancer. Vitamin K intake has been inversely associated with cancer incidence and mortality in observational studies. Newly discovered functions of vitamin K in cancer cells include activation of the steroid and xenobiotic receptor (SXR) and regulation of oxidative stress, apoptosis, and autophagy. We provide an update of vitamin K biology, non-canonical mechanisms of vitamin K actions, the potential functions of vitamin K-dependent proteins in cancer, and observational trials on vitamin K intake and cancer.

Dietary Vitamin K1 intake is associated with lower long-term fracture-related hospitalization risk: the Perth longitudinal study of ageing women

This study examined the association between dietary Vitamin K1 intake with fracture-related hospitalizations over 14.5 years in community-dwelling older Australian women (n = 1373, ≥70 years). Dietary Vitamin K1 intake at baseline (1998) was estimated using a validated food frequency questionnaire and a new Australian Vitamin K nutrient database, which was supplemented with published data. Over 14.5 years, any fracture (n = 404, 28.3%) and hip fracture (n = 153, 10.7%) related hospitalizations were captured using linked health data. Plasma Vitamin D status (25OHD) and the ratio of undercarboxylated osteocalcin (ucOC) to total osteocalcin (tOC) from serum was assessed at baseline. Estimates of dietary Vitamin K1 intake were supported by a significant inverse association with ucOC : tOC; a marker of Vitamin K status (r = -0.12, p < 0.001). Compared to women with the lowest Vitamin K1 intake (Quartile 1, <61 μg d^-1), women with the highest Vitamin K1 intake (Quartile 4, ≥99 μg d^-1) had lower hazards for any fracture- (HR 0.69 95%CI 0.52-0.91, p < 0.001) and hip fracture-related hospitalization (HR 0.51 95%CI 0.32-0.79, p < 0.001), independent of 25OHD levels, as part of multivariable-adjusted analysis. Spline analysis suggested a nadir in the relative hazard for any fracture-related hospitalizations at a Vitamin K1 intake of approximately 100 μg day^-1. For hip fractures, a similar relationship was apparent. Higher dietary Vitamin K1 is associated with lower long-term risk for any fracture- and hip fracture-related hospitalizations in community-dwelling older women.

Role of Vitamin K in Selected Malignant Neoplasms in Women

The main function of vitamin K in the human organism is its activity in the blood clotting cascade. Epidemiological studies suggest that reduced intake of vitamin K may contribute to an increased risk of geriatric diseases such as atherosclerosis, dementia, osteoporosis, and osteoarthritis. A growing number of studies also indicate that vitamin K may be involved not only in preventing the development of certain cancers but it may also support classical cancer chemotherapy. This review article summarizes the results of studies on the anticancer effects of vitamin K on selected female malignancies, i.e., breast, cervical, and ovarian cancer, published over the past 20 years. The promising effects of vitamin K on cancer cells observed so far indicate its great potential, but also the need for expansion of our knowledge in this area by conducting extensive research, including clinical trials.

Inverse Association between Plasma Phylloquinone and Risk of Ischemic Stroke in Chinese Adults with Hypertension and High BMI: A Nested Case-Control Study

BACKGROUND

Evidence on the association between phylloquinone status and cardiovascular diseases is scarce and conflicting. These inconsistencies may be due to differences in individual characteristics of the study populations, which may modify the association.

OBJECTIVE

This study aimed to evaluate the association between plasma phylloquinone and the risk of first total stroke and its subtypes, and to examine potential effect modifications by BMI in patients with hypertension.

METHODS

We performed a nested case-control study including 604 first stroke cases and 604 matched controls. The mean age was 62.2 y (range, 45 to 75). Lower BMI was defined as <25 kg/m2  and higher BMI was defined as ≥25 kg/m2. The risks of the first stroke were estimated by ORs and 95% CIs using conditional logistic regression. The primary outcome was total stroke or ischemic stroke.

RESULTS

The relation between log-transformed phylloquinone concentration and stroke or ischemic stroke was modified by BMI. Higher phylloquinone concentrations were associated with lower stroke risk in those with a higher BMI. When plasma phylloquinone was assessed as tertiles, the adjusted ORs of first stroke and ischemic stroke for participants with a high BMI in tertile 2-3 were 0.70 (95% CI: 0.46, 1.08) and 0.57 (95% CI: 0.35, 0.92) compared with those in tertile 1, respectively. However, there was no significant association between plasma phylloquinone and risk of first total stroke or ischemic stroke for those with a lower BMI. Patients with a higher BMI and lower phylloquinone concentrations had the highest risk of ischemic stroke and showed a statistically significant difference compared with the reference group with a lower BMI and higher phylloquinone (OR = 1.80, 95% CI: 1.06, 3.10; P-interaction: 0.017).

CONCLUSIONS

In Chinese patients with hypertension, there was an inverse association between baseline plasma phylloquinone and risk of first ischemic stroke among those with a higher BMI. This trial was registered at clinicaltrials.gov as NCT00794885.

Vitamin K Status and Cognitive Function in Adults with Chronic Kidney Disease: The Chronic Renal Insufficiency Cohort

Vitamin K is linked to cognitive function, but studies in individuals with chronic kidney disease (CKD), who are at risk for vitamin K insufficiency and cognitive impairment, are lacking. The cross-sectional association of vitamin K status biomarkers with cognitive performance was evaluated in ≥55-y-old adults with CKD (N = 714, 49% female, 44% black). A composite score of a cognitive performance test battery, calculated by averaging the z scores of the individual tests, was the primary outcome. Vitamin K status was measured using plasma phylloquinone and dephospho-uncarboxylated matrix Gla protein [(dp)ucMGP]. Participants with low plasma (dp)ucMGP, reflecting higher vitamin K status, had better cognitive performance than those in the two higher (dp)ucMGP categories based on the composite outcome (P = 0.03), whereas it did not significantly differ according to plasma phylloquinone categories (P = 0.08). Neither biomarker was significantly associated with performance on individual tests (all P > 0.05). The importance of vitamin K to cognitive performance in adults with CKD remains to be clarified.

Estimation of Vitamin K Content and Its Sources in the Diet of the Polish Participants of the PURE Study

The aim of the study was to estimate the content of K1, K2 (MK-n) as well as total K vitamins and their sources in the diets of 1985 PURE Poland study participants based on the FFQ questionnaire. Due to the pleiotropic effect of K vitamins, it is important to know their food sources depending on different eating habits. Total vitamin K in the diets amounted to 331.1 ± 151.5 µg/d and 358.6 ± 181.0 µg/d for men and women, respectively. Dietary patterns (DPs) were identified in the study group, and the relationship between them and vitamin K intake was assessed. The proportion of dominant products as sources of vitamin K in the fourth quartile of each of the three identified DPs did not change significantly compared to the proportion of these products as sources of vitamin K in all subjects. In the fourth quartile of individual DPs, vitamin K1 came mainly from vegetables (56.5-76.8%); K2 mainly from processed meat and high-fat cheese and cream (70.1-77.6%); and total K mainly from vegetables and processed meat (57.6-67.8%). Intakes of K vitamins were high and similar in terms of predominant vitamin K provider products, in groups of subjects whose diets were most consistent with the particular DP. In the absence of global findings on the most appropriate dietary content of MK-n vitamins other than phylloquinone, the estimated high content of these vitamins in the diets of the subjects compared with other nations suggests that their level in diets was satisfactory. Future studies should aim to determine the need for MK-n vitamins in terms of fulfilling all their functions in the body.

Association of vitamin K with cognitive decline and neuropathology in community‐dwelling older persons

Higher vitamin K intakes have been associated with better cognitive function, suggestive of a vitamin K mechanistic effect or simply reflective of a healthy diet. To test the hypothesis that brain vitamin K is linked to cognitive decline and dementia, vitamin K concentrations were measured in four brain regions, and their associations with cognitive and neuropathological outcomes were estimated in 325 decedents of the Rush Memory and Aging Project. Menaquinone‐4 (MK4) was the main vitamin K form in the brain regions evaluated. Higher brain MK4 concentrations were associated with a 17% to 20% lower odds of dementia or mild cognitive impairment (MCI) (P‐value < .014), with a 14% to 16% lower odds of Braak stage ≥IV (P‐value < 0.045), with lower Alzheimer's disease global pathology scores and fewer neuronal neurofibrillary tangles (P‐value < 0.012). These findings provide new and compelling evidence implicating vitamin K in neuropathology underlying cognitive decline and dementia.

Naturally occurring UBIAD1 mutations differentially affect menaquinone biosynthesis and vitamin K-dependent carboxylation

UbiA prenyltransferase domain-containing protein-1 (UBIAD1) is responsible for the biosynthesis of menaquinone-4 (MK-4), a cofactor for extrahepatic carboxylation of vitamin K-dependent (VKD) proteins. Genetic variations of UBIAD1 are mainly associated with Schnyder corneal dystrophy (SCD), a disease characterized by abnormal accumulation of cholesterol in the cornea. Results from in vitro studies demonstrate that SCD-associated UBIAD1 mutations are defective in MK-4 biosynthesis. However, SCD patients do not exhibit typical phenotypes associated with defects of MK-4 or VKD carboxylation. Here, we coupled UBIAD1's biosynthetic activity of MK-4 with VKD carboxylation in HEK293 cells that stably express a chimeric VKD reporter protein. The endogenous Ubiad1 gene in these cells was knocked out by CRISPR-Cas9-mediated genome editing. The effect of UBIAD1 mutations on MK-4 biosynthesis and VKD carboxylation was evaluated in Ubiad1-deficient reporter cells by determining the production of MK-4 or by measuring the efficiency of reporter-protein carboxylation. Our results show that the hot-spot mutation N102S has a moderate impact on MK-4 biosynthesis (retained ˜ 82% activity) but does not affect VKD carboxylation. However, the G186R mutation significantly affected both MK-4 biosynthesis and VKD carboxylation. Other mutations exhibit varying degrees of effects on MK-4 biosynthesis and VKD carboxylation. These results are consistent with in vivo results obtained from gene knock-in mice and SCD patients. Our findings suggest that UBIAD1's MK-4 biosynthetic activity does not directly correlate with the phenotypes of SCD patients. The established cell-based assays in this study provide a powerful tool for the functional studies of UBIAD1 in a cellular milieu.