Bone remodeling in experimental diabetes mellitus and surgical menopause in Wistar rats

BACKGROUND: Osteoporosis is metabolic skeletal disease characterized with low bone mass, bone microarchitecture disturbance that together lead to high prevalence of fragility fractures. Postmenopausal osteoporosis accounts for about 80% of the osteoporosis structure in women over 50 years. Diabetes mellitus (DM) is an independent risk factor for low-traumatic fractures. The incidence of both type 2 DM and osteoporosis increases during menopause. Therefore, the study of bone metabolism in experimental diabetes and surgical menopause seems important.THE AIM of the study was to investigate bone metabolism parameters during menopause and experimental type 2 DM.MATERIALS AND METHODS: The half of female Wistar rats had been subjected to bilateral ovariectomy at the beginning of the experiment. Diabetes mellitus (DM) was modelled using a high-fat diet and streptozotocin+nicotinamide. Four weeks after the following groups were formed: «Сontrol» (females without any interventions receiving standard chew, n=5) «OE» (females after ovariectomy n=5), «DM» (females with DM, n=4), «OE+DM» (females after ovariectomy with DM, n=4). The observation period lasted 8 weeks. Bone turnover and calcium-phosphorus metabolism markers (osteocalcin, osteoprotegerin (OPG), nuclear factor-kappa-beta receptor activator ligand (RANKL), sclerostin, fibroblast growth factor-23 (FGF-23), calcium, phosphorus) were measured in the end of experiment. Bone histomorphometry was performed after euthanasia.RESULTS: Phosphorus level was significantly lower both in the «OE» group (1.63 [1.58; 1.65] mmol/L) and in the «DM» group (2.81 [2.57; 2.83] mmol /l) compared to the «Control» group (3.12 [2.55; 3.24] mmol/l) (p<0.001). This marker was significantly higher in the «OE+DM» group (2.79 [2.46; 2.81] mmol/l) in comparison to the «OE» group (2.79 [2.46; 2.81] mmol /l), p=0.025. Osteocalcin level was significantly lower in the «DM» group (8.1 [7.8; 9.2] ng/ml) compared to the «Control» group (16.97 [14.07; 17.07] ng/ml ), p=0.005. A weak negative correlation (r= -0.5, p<0,05) was found between glucose and osteocalcin levels (p=0.03). RANKL level was significantly lower in the «OE+DM» group (278,1 [273.1; 289.7] pg/mL) compared to the «OE» group (400.6 [394.5; 415.1] pg/mL), besides the OPG/RANKL ratio was higher in this group (0.03 [0.02; 0.035] and 0.01 [0.004; 0.014], respectively), p=0.05. In the «OE» group lower OPG level (5.1 [1.5; 5.6] pmol/L) and OPG/RANKL ratio (0.01 [0.003; 0.014]) were obtained in comparison to the «Control» group (12.3 [8.8; 14.2] pmol/l and (0.34[0.33; 0.4], p=0.025 and p=0.07, respectively. The area of bone trabeculae in the epiphyseal zone was the largest in the «Control» group (42 [39; 45]) %; the difference was significant compared to the «OE» group (29 [25; 33] %, p=0.011) and the «OE+DM» group (30 [23; 25] %, p=0.016). The area of bone trabeculae in the metaepiphyseal zone was also the largest in the «Control» group (49 [46; 52] %) compared to the «OE» (35 [25; 39] %), «DM» (31 [26; 34] %), «OE+DM» (35 [33; 38] %), p<0.001. There was no difference in the thickness of the bone trabeculae among the groups.CONCLUSION: DM induction can significantly inhibit bone remodeling in animals without menopause, which is reflected in a lower osteocalcin level. Bone turnover during DM and surgical menopause is characterized by lower RANKL levels and higher OPG/RANKL ratio. The effect of ovariectomy on bone metabolism was manifested in more extensive decrease in bone trabeculae area than in DM.