Safety and toxicological evaluation of a synthetic vitamin K2, menaquinone-7

Menaquinone-7 (MK-7) is part of a family of vitamin K that are essential co-factors for the enzyme γ-glutamyl carboxylase, which is involved in the activation of γ-carboxy glutamate (Gla) proteins in the body. Gla proteins are important for normal blood coagulation and normality of bones and arteries. The objective of this study was to examine the potential toxicity of synthetic MK-7 in BomTac:NMRI mice and in Sprague-Dawley rats. In an acute oral toxicity test, mice were administered a single oral dose of 2000 mg/kg body weight (limit dose) and no toxicity was observed during the 14-day observation period. In the subchronic oral toxicity test in rats, animals were administered MK-7 for 90 days by gavage at the following doses: 0 (vehicle control, corn oil), 2.5, 5, and 10 mg/kg body weight/day. All generated data, including clinical observations, ophthalmology, clinical pathology, gross necropsy, and histopathology, revealed no compound-related toxicity in rats. Any statistically significant findings in clinical pathology parameters and/or organ weights noted were considered to be within normal biological variability. Therefore, under the conditions of this experiment, the median lethal dose (LD50) of MK-7 after a single oral administration in mice was determined to be greater than the limit dose level of 2000 mg/kg body weight. The no observed adverse effect level (NOAEL) of MK-7, when administered orally to rats for 90 days, was considered to be equal to 10 mg/kg body weight/day, the highest dose tested, based on lack of toxicity during the 90-day study period

Vitamin K epoxide reductase and its paralogous enzyme have different structures and functions

Abstract Vitamin K epoxide reductase (VKOR) is an essential enzyme for vitamin K-dependent carboxylation, while the physiological function of its paralogous enzyme VKOR-like (VKORL) is yet unknown. Although these two enzymes share approximately 50% protein sequence homology, the membrane topology of VKOR is still in debate. Here, we explored the differences in the membrane topology and disulfide-linked oligomerization of these two enzymes. Results from mutating the critical amino acid residues in the disputed transmembrane (TM) regions revealed that the second TM domain in the proposed 4-TM model of VKOR does not function as an authentic TM helix; supporting VKOR is a 3-TM protein, which is different from VKORL. Additionally, altering the loop sequence between the two conserved cysteine residues of VKORL affects its activity, supporting the notion that the conserved loop cysteines of VKORL are involved in its active site regeneration. However, a similar mutation in VKOR does not affect its enzymatic activity. Finally, our results show that although both VKOR and VKORL form disulfide-linked oligomers, the cysteine residues involved in the oligomerization appear to be different. Overall, the structural and functional differences between VKOR and VKORL shown here indicate that VKORL might have a different physiological function other than recycling vitamin K