Bone is a target for the antidiabetic compound rosiglitazone

Abstract

Rosiglitazone is an FDA-approved oral antidiabetic agent for the treatment of type 2 diabetes. This compound improves insulin sensitivity through the activation of the nuclear receptor, peroxisome proliferator-activated receptor-gamma (PPAR-gamma). In addition to sensitizing cells to insulin, the PPAR-gamma2 isoform appears to be critical for the regulation of osteoblast and adipocyte differentiation from common mesenchymal bone marrow progenitors. We have demonstrated previously that PPAR-gamma2 activated with rosiglitazone acts as a dominant inhibitor of osteoblastogenesis in murine bone marrow in vitro. Here, we show that in vivo, rosiglitazone administration results in significant bone loss. When rosiglitazone (20 microg/g body weight/d) was given to 6-month-old, nondiabetic C57BL/6 mice for 7 wk, a significant decrease in total body bone mineral density was observed. Analysis of bone microarchitecture, using micro-computed tomography, demonstrated a decrease in bone volume, trabecular width, and trabecular number and an increase in trabecular spacing. Histomorphometric analysis showed a decrease in bone formation rate, with a simultaneous increase in fat content in the bone marrow. Changes in bone morphology and structure were accompanied by changes in the expression of osteoblast- and adipocyte-specific marker genes; the expression of the osteoblast-specific genes Runx2/Cbfa1, Dlx5, and alpha1(I)collagen were decreased, whereas the expression of the adipocyte-specific fatty acid binding protein aP2, was increased. These in vivo data suggest that rosiglitazone therapy may pose a significant risk of adverse skeletal effects in humans.

Fig. 1

Body and organ weights of animals fed for 7 wk with either nonsupplemented (gray bar) or rosiglitazone-supplemented (black bar) diet. Each bar represents a mean weight (± SD) of eight animals or tissues derived from eight animals. *, Significant difference (P < 0.05) between control and rosiglitazone-fed group. A, Body weights; B, wet weight of livers; C, epididymal WAT and interscapular BAT.

Fig. 2

Liver histological cross-sections representative for each group. Snap-frozen specimens were sectioned, fixed with formalin, and stained with Oil Red O for fat and counterstained with methyl green. Magnification, ×40.

Fig. 3

DXA of total-body BMD. Values represent a mean of eight animals per group (±SD) *, Significant differences (P < 0.05) between control (gray bar) and rosiglitazone-fed (black bar) groups. A, Total BMD, measured at the end of the experiment, of animals fed with either nonsupplemented or rosiglitazone-supplemented diet. B, Percent change in BMD within groups based on the measurements at the beginning and end of experiment and calculated as described in Materials and Methods.

Fig. 4

Micro-CT representative renderings of proximal tibia from control and rosiglitazone-treated animals were generated as described in Materials and Methods.

Fig. 5

Representative photomicrographs of cancellous tibia. Numbers represent average of six representative fields examined from the same bone. A, Bone sections stained with Goldner trichrome stain. Mineralized bone tissue is stained blue, whereas the unstained area in the bone marrow represents empty spaces previously occupied by adipocytes. Photomicrographs were obtained on the Osteometrics system using a ×10 objective. B, Tetracycline-labeled section of the proximal tibia. The distance between two layers of tetracycline labels (arrows) visualized by epifluorescence represents bone formation that occurred during the 5-d period between tetracycline injections. Photomicrographs were obtained on the Osteometrics system using a ×40 objective. AD/HFP, Number of adipocytes per high-power field.