Abstract
BackgroundDespite plausible biological mechanisms, the differential abilities of phylloquinone (PK) and menaquinones (MKn) to prevent bone loss remain controversial. The objective of the current study was to compare the effects of PK, menaquinone-4 (MK-4) and menaquinone-7 (MK-7) on the rate of bone loss in ovariectomized (OVX) Norway rats. A secondary aim was to compare the effects of vitamin K with those of bisphosphonates (BP) on bone loss.MethodsRats (n = 96) were randomized to 6 dosing groups [n = 16/group; Sham; OVX; OVX + BP (100 μg/kg/100 μg/mL saline sc); OVX + PK; OVX + MK-4; and OVX + MK-7] for 6 wk. Equimolar daily doses of 107 mg PK/kg, 147 mg MK-4/kg, and 201 mg MK-7/kg diet were provided.ResultsBP significantly increased bone strength and bone mineral density (BMD) vs. OVX (P < 0.05). However, PK, MK-4 or MK-7 did not change bone strength or BMD compared to the OVX group. Whereas supplementation of PK, MK-4 and MK-7 increased serum and tibia concentrations of each respective form, PK concentrations were consistently higher despite equimolar intakes.ConclusionPK, MK-4, and MK-7 do not appear to prevent bone loss in OVX rats when administered concurrent with adequate intake of other nutrients.
Highlights
IntroductionThe differential abilities of phylloquinone (PK) and menaquinones (MKn) to prevent bone loss remain controversial
Despite plausible biological mechanisms, the differential abilities of phylloquinone (PK) and menaquinones (MKn) to prevent bone loss remain controversial
Recent evidence suggests that vitamin K promotes the expression of osteoblastic markers through steroid and xenobiotic receptors (SXR)/pregnane X receptor (PXR)-modulated gene transcription [2,6]
Summary
The differential abilities of phylloquinone (PK) and menaquinones (MKn) to prevent bone loss remain controversial. Vitamin K is essential for the g-carboxylation of specific glutamate residues in bone-specific proteins, including osteocalcin (OC). Without this modification, OC lacks the ability to bind to the mineral hydroxyapatite [4]. Vitamin K exists in two primary forms in the diet: phylloquinone (PK) and menaquinones (MKn). PK, menaquinone-4 (MK-4) and menaquinone-7 (MK-7) have been collectively identified by various investigators as forms of vitamin K that have a potential role in preventing bone loss [7,8,9,10]. MK-4 is unique in that it is converted from PK and menadione [12,13,14,15], the exact mechanisms of conversion have yet to be elucidated
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