ABSTRACT
Vitamin K has been implicated in skeletal health because vitamin K-dependent proteins are present in bone. While there are multiple forms of vitamin K, most research has focused on phylloquinone, which is found mainly in plant-based foods, and its metabolite menaquinone-4 (MK4). However, there are additional forms of vitamin K that are bacterially produced that appear to influence bone health but have not yet been studied extensively. Herein, we evaluated the effects of menaquinone-9 (MK9), a bacterially produced form of vitamin K on bone tissue quality and density in young mice. Four-week-old male (n=32) and female (n=32) C57BL/6 mice were supplemented with 0.06 mg/kg diet or 2.1 mg/kg diet of MK9 for 12 weeks. During week 11, a sub-group of mice (n=7/sex/group) received daily deuterium-labeled MK9 to trace its metabolic fate in bone. Liver MK4 and MK9 were significantly higher in mice fed 2.1 mg MK9/kg compared to those receiving 0.06 mg MK9/kg, regardless of sex (all p ≤ 0.017). MK4 was the only vitamin K form detected in bone, with 63-67% of skeletal MK4 in mice fed 2.1 mg MK9/kg derived from deuterium-labeled MK9. Femoral tissue strength, maximum bending moment, section modulus, and bone mineral density did not differ significantly across diet groups in either sex (all p≥0.083). Cross-sectional area (p=0.003) and moment of inertia (p=0.001) were lower in female mice receiving 2.1 mg MK9/kg compared to those receiving 0.06 mg MK9/kg, but no differences were found in male mice. Higher bone MK4 concentrations did not correlate with higher bone tissue quality or density. Despite dietary MK9 being a dietary precursor to MK4 in bone, dietary MK9 supplementation did not affect bone tissue quality or bone mineral density.
Lay summary Most research about vitamin K and bone health has focused on phylloquinone, the plant-based vitamin K form, and its metabolite menaquinone-4. Because interest in bacterially produced forms of vitamin K, which are abundant in the intestinal microbiome, is growing, we evaluated the effect of menaquinone-9 (a bacterially-produced form of vitamin K) on skeletal health. We supplemented mice with low and high doses of menaquinone-9 and also used stable-isotope labeled menaquinone-9 to trace its conversion to menaquinone-4 in bone. We found menaquinone-9 served as a precursor to menaquinone-4 in bone, but menaquinone-9 supplementation did not improve bone health.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Supported by NIA R01 R01AG067997 and USDA Agricultural Research Service under Cooperative Agreement 58-8050-3-003. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the view of the USDA.
Abbreviations
- 2H7MK9
- deuterium-labeled MK9
- BMD
- bone mineral density
- CBU
- Comparative Biology Unit
- DEXA
- dual-energy X-ray absorptiometry
- HNRCA
- Tufts University Human Nutrition Research Center on Aging
- LC-MS
- liquid chromatography mass spectrometry
- MK
- menaquinone
- PBS
- phosphate-buffered saline
- PK
- phylloquinone
- Q-TOF-MS
- time-of-flight mass spectrometry