EFFECT OF LONG TERM ADMINISTRATION OF VITAMIN D3 ANALOGS ON MICE

Participants: E.A. Smith, E.P. Frankenburg, P. Koeffler, S.A. Goldstein

Keywords: bone mechanics, Vitamin D3, drug treatment

Introduction

Vitamin D3 analogs are able to inhibit growth of a variety of malignant cells, but the effect of long-term administration of these compounds is unknown. Metabolites of vitamin D3 are instrumental in regulating calcium homeostasis; both its absorption in the small intestine and resorption of bone. Therefore, it is possible that long-term administration of vitamin D3 analogs could have profound effects on bone properties. The goal of this study was to quantify the mechanical and geometrical consequences of long-term administration of vitamin D3 analogs on bone.

Materials and Methods

Forty 8 week old female Balb/c mice received treatments of one of 5 vitamin D3 analogs or sham by IP injections 3 times per week for one year. The vitamin D3 analogs that were tested are: 1,25(OH)2D3 (Compound C, n=4), 1,25(OH)2-16ene-23yne-D3 (Compound V, n=8), 1,25(OH)2-16ene-23yne-26,27,F6-D3 (Compound EO, n=5), 1,25(OH)2-16ene-23yne-19-nor-26,27-F6-D3 (Compound LH, n=8), and 1,25(OH)2-16,22R,23-triene-D3 (Compound LA, n=8). After sacrifice, the right femur was dissected free of surrounding muscle and soft tissue and was scanned on the µCT system at a resolution of 20 µm. Cross-sectional area, cortical thickness and moments of inertia were measured from these digital images. Femora were then tested in four-point bending on an MTS servohydraulic testing machine at a displacement rate of 1 mm/sec. Stiffness, and loads and displacements to yield and failure were determined from load-displacement data. Statistical analysis was performed using a one-way ANOVA with Tukey's post-hoc, and p<0.05 considered statistically significant.

Progress

All mechanical testing and µCT analysis has been completed, and a manuscript entitled "Effect of Long-Term Administration of Vitamin D3 Analogs to Mice" has been submitted to the Journal of Endocrinology which has been recently published.

Results

The geometry results showed that Compound C resulted in significantly smaller bones, as cross-sectional area, cortical thickness were decreased when compared to control (see Figure 1). Moments of inertia, however, showed a trend towards a slight increase. In contrast, Compound EO resulted in significantly larger bones, as this group showed an increase in cross-sectional area, cortical thickness and moments of inertia. The geometrical properties of groups treated with Compounds LA, LH and V were not significantly changed. The group treated with Compound EO showed similar increases in mechanical properties as in geometry (see Figure 2), indicating that the majority of the mechanical property alterations could be explained by an increased moment of inertia. Compound C, however, resulted in significant decreases in mechanical properties despite the slight increase in moment of inertia. This indicates that Compound C severely decreased the quality of bone tissue.

Figure 1

*p<0.05 vs. Control *p<0.05 vs. Control

Figure 2

+, * p<0.05 vs. Control + p<0.05 vs. Control