Effects of Menaquinone-7 on Bone Turnover Markers, Femoral Mechanical Resistance, and Histology in Young Ovariectomized Rats

Background: Osteoporosis is a major skeletal disorder, particularly affecting postmenopausal women. Young ovariectomized rat models are commonly used to investigate estrogen deficiency-related skeletal changes, although they do not fully reproduce osteoporosis in a mature postmenopausal skeleton. Established pharmacological therapies remain the cornerstone of osteoporosis management, while nutritional factors continue to be investigated for their potential supportive role in bone metabolism. Menaquinone-7 (MK-7), a form of vitamin K2, has been investigated for potential skeletal effects through vitamin k-dependent mechanisms, particularly osteocalcin carboxylation. The aim of this study was to evaluate the dose-dependent effects of MK-7 on bone turnover markers, femoral mechanical resistance, qualitative histological findings, and hepatic safety in a young ovariectomized rat model. Methods: Forty female Wistar rats that were 8 weeks old, and thus still undergoing skeletal maturation, were assigned to four groups: sham-operated controls, ovariectomized controls, ovariectomized rats treated with low-dose MK-7, and ovariectomized rats treated with high-dose MK-7. Treatment was administered every 48 h for 12 weeks. At study completion, 35 rats survived; standardized analysis included eight animals per group. Plasma bone turnover markers (BTMs) and alanine aminotransferase were measured, femoral strength was assessed by the three-point bending test, and bone and liver histology was analyzed. Results: Biomechanical testing showed that high-dose MK-7 was associated with greater femoral mechanical resistance compared with untreated ovariectomized rats, while qualitative histology suggested differences in cortical architecture among groups. Biochemically, MK-7 treatment reduced undercarboxylated osteocalcin, suggesting vitamin K-dependent target engagement, whereas conventional turnover markers showed discordant findings. Overall, hepatic architecture was preserved, although mild hepatocellular apoptosis was observed. Conclusions: In this young OVX rat model, high-dose MK-7 was associated with improved femoral mechanical resistance compared with untreated OVX controls. However, because ovariectomy was performed during skeletal maturation, these findings should be interpreted as preliminary and cannot be directly extrapolated to established postmenopausal osteoporosis in a mature skeleton, and further studies are needed to clarify its activity pathways and safety profile.