Glucocorticoids affect bone mineral density and bone remodelling in OVX sheep: A pilot study

Abstract

The aim of this study was to validate the combination of ovariectomy and glucocorticoid treatment in sheep as a large animal model for osteoporosis by measuring the concentration of specific biomarkers in the blood of the sheep and measuring bone loss over five months. Aged Merino ewes were randomly allocated into four groups: control, ovariectomy (OVX), and two OVX groups receiving glucocorticoids-one group once-monthly for five months (OVXG), and the other for two months followed by no treatment for three months (OVXG2). Parameters measured were biochemical markers of bone turnover, areal bone mineral density, volumetric bone mineral density, and total and trabecular bone parameters. Ovariectomy increased the concentrations of bone resorption marker C-terminal telopeptides of type 1 collagen (CTx-1) and bone turnover marker serum osteocalcin (OC) concentrations in the OVX group compared to control sheep. The combination of ovariectomy and glucocorticoid treatment increased the concentrations of CTx-1 and decreased serum OC concentrations in the OVXG group compared to OVXG2. Femur and lumbar spine bone density were lower in experimentally treated groups when compared with the control group. Total and trabecular _vBMD in the proximal tibia were significantly lower in the treatment groups when compared with the control group. A significant negative correlation between femoral bone density and CTx-1 was found. The results of this study suggest that the combination of OVX and glucocorticoids induces bone loss in a short period of time in sheep.

Keywords: Bone mineral density; Bone turnover markers; Glucocorticoids; Osteoporosis; Ovariectomy; Sheep.

Fig. 1

Flow diagram of the experimental study. Merino ewes were randomly divided into groups, 10 underwent no treatment (control group), 12 ewes underwent ovariectomy (OVX), and the remaining 6 ewes underwent OVX and received an injectable suspension of 400 mg methylprednisolone (OVXG group). Half of the ewes in the OVXG group received the methylprednisolone treatment for five months, while the other half received this treatment for only two months (OVXG2 group). Blood samples were collected monthly. BMD measurements were done at baseline (month zero) by pQCT, and at post-cull (month two or month five) by pQCT and DXA. Half of the sheep in the control group and OVX group were euthanised after two months, and the remaining sheep for each group were euthanised after five months. All the sheep in the OVXG group and OVXG2 were euthanised after five months.

Fig. 2

The concentrations of OC and CTx-1 in the serum of the OVX sheep. Percentage change in the bone turnover marker serum OC (A) and percentage change in the bone resorption marker CTx-1 (B) compared with the pretreatment baseline from Merino ewes that were either ovariectomised (OVX), ovariectomised and given five doses of glucocorticoid at monthly intervals (OVXG), ovariectomised and given two doses glucocorticoid at monthly intervals (OVXG2), or received no treatments (Control). OC and CTx-1 were measured at two months and five months after initiation of the treatments. The results are presented as serum OC and CTx-1 mean percent change from baseline. *p-value <0.05. Error bars denote standard error of mean.

Fig. 3

Bone parameters of lumbar spine and femur at month two and month five measured by DXA. (A) lumbar spine aBMD, (B) lumbar spine BMC, (C) femoral aBMD and (D) femoral BMC are shown for half of the ewes euthanised at month two in the control group and OVX group, and for the remaining ewes at month five for each group. Data is presented as mean and 95% confidence intervals.

Fig. 4

Bone variables at the proximal metaphysis of the tibia at month two and month five measured by pQCT. Total and trabecular tibial vBMD, area and BMC (A), (C) and (E), respectively, at month two. Total and trabecular tibial vBMD, area and BMC (B), (D) and (F), respectively, at month five are shown for half of the ewes euthanised at month two in the control group and OVX group; and the remaining ewes at month five for each group. Data is presented as mean and 95% confidence intervals. *p-value <0.05 was considered as statistically significant.