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

BACKGROUND "Vitamin K" is a family of structurally-related quinones, phylloquinone (PK) and the menaquinones (MKn), that share a common naphthoquinone ring but vary in sidechain length (n) and saturation. Dietary PK is a biosynthetic precursor to tissue menaquinone-4 (MK4), but little is known about the absorption and metabolism of dietary MKn. OBJECTIVE To characterize absorption and metabolism of dietary MKn relative to PK. METHODS In the 4-week diet study, 10-wk old male and female C57BL/6 mice were pair-fed a vitamin K deficient diet (control) or a diet supplemented with 5.0 μmol/kg total PK, MK4, and/or MK9 (separately and in combination). In the 1-week stable isotope study, 12-wk old mice were pair-fed diets containing 2.2 μmol/kg PK (unlabeled control), 2H7PK, 13C11MK4, 2H7MK7, or 2H7MK9. Vitamin K tissue content was quantified by HPLC and/or LC-MS, and concentrations were compared by sex and diet group using 2-factor ANOVA. RESULTS Regardless of the form(s) of vitamin K provided in the feed, tissue MK4 concentrations did not differ across equimolar supplemented groups in kidney, adipose, reproductive organ, bone, and pancreas, in either males or females in the diet study (all P > 0.05). Isotopic labeling confirmed the naphthoquinone ring of MK4 in tissues originated from the administered dietary PK or MKn. Despite equimolar supplementation, accumulation of the administered dietary form differed across diet groups in small intestinal segments (all P < 0.002) and liver (P < 0.001). Female mice had greater total vitamin K than males in every tissue examined (P < 0.05). CONCLUSION Dietary PK, MK4, MK7, and MK9 all served as precursors to tissue MK4 in mice. This study expands our understanding of vitamin K metabolism and supports a common conversion mechanism of all dietary vitamin K forms to MK4. Further investigation of the metabolism and physiological roles of MK4 that may be independent of classical vitamin K function are warranted.