Changes in micro-CT 3D bone parameters reflect effects of a potent cathepsin K inhibitor (SB-553484) on bone resorption and cortical bone formation in ovariectomized mice.

Cathepsin K is a cysteine proteinase that is highly expressed by osteoclasts and is being pursued as a potential drug target for the treatment of osteoporosis. We have reported that microcomputed tomography (micro-CT) analysis of bone microarchitecture may serve as a valuable tool for evaluating both antiresorptive and anabolic agents in ovariectomized (OVX) mice. The purpose of this study was to evaluate the effect of SB-553484, a novel cathepsin K inhibitor (human Ki,app=0.14 nM, mouse Ki,app=26 nM), on the OVX mice by micro-CT bone morphometric analysis. Seven weeks female BALB/c mice were OVX or sham-operated. OVX animals were treated with SB-553484 (30 mg/kg, sc) or Rolipram (10 mg/kg, po), a phosphodiesterase 4 inhibitor used as a positive bone anabolic agent, twice a day for 2 weeks. Both SB-553484 and Rolipram significantly prevented the decrease of trabecular bone volume as well as the deterioration of trabecular architecture in OVX mice. Interestingly, SB-553484 demonstrated a more pronounced effect in improvement of trabecular separation, number and connectivity, and a weaker effect in improvement of trabecular thickness compared to that of Rolipram. These differences indicate that SB-553484 mainly acted as an antiresorptive agent in OVX-induced loss of trabecular bone. On the other hand, SB-553484 significantly increased cortical bone volume and cortical thickness as well as Rolipram in OVX mice indicating an unexpected stimulatory effect of SB-553484 on cortical bone formation. These data suggest that targeting cathepsin K may prove therapeutically beneficial in the treatment of diseases with accelerated bone loss such as postmenopausal osteoporosis not only by inhibiting bone resorption but also by potentially stimulating cortical bone formation.

Analysis of change patterns of microcomputed tomography 3-dimensional bone parameters as a high-throughput tool to evaluate antiosteoporotic effects of agents at an early stage of ovariectomy-induced osteoporosis in mice.

OBJECTIVES: The purposes of this study were to develop an osteoporosis model in a short period of 2 weeks after ovariectomy in mice and to investigate whether analysis of microcomputed tomography (muCT) 3-dimensional bone parameters could provide useful information on the mechanism of action of antiosteoporotic agents. MATERIALS AND METHODS: Mice were ovariectomized (OVX) or sham-operated, and the OVX mice were treated daily with 17beta-estradiol (E2), parathyroid hormone (PTH[1-34]), raloxifene, rolipram, or vehicle for 2 weeks. On day 14 post-OVX, the left femur bones were removed and then the distal metaphyseal bone was analyzed by both muCT and histomorphometry. RESULTS: The trabecular bone volume, thickness, number, and connectivity significantly decreased and the number of osteoclasts increased in OVX mice. Treatment of OVX animals with each of the 4 antiosteoporotic agents significantly increased the bone volume and improved the bone architecture. However, the improvement of trabecular thickness in the rolipram-treated group and that of cortical thickness in the PTH(1-34)-treated group were the most marked, whereas the improvement of connectivity in the rolipram-treated group was the least among the drug-treated groups. These different improving effects of agents on the bone parameters reflect the differential effects of these agents on bone formation and bone resorption. CONCLUSIONS: This study demonstrated the feasibility of evaluating the effect of the antiosteoporotic agents within 2 weeks after ovariectomy in mice. The muCT analysis may serve as a valuable tool, specifically in a high-throughput pharmacological screening test, offering useful information regarding the effects of test compounds on both bone resorption and formation.

Quantitative image analysis in adipose tissue using an automated image analysis system: differential effects of peroxisome proliferator-activated receptor-alpha and -gamma agonist on white and brown adipose tissue morphology in AKR obese and db/db diabetic mice.

Morphometric analysis of adipocytes is widely used to demonstrate the effects of antiobesity drugs or anti-diabetic drugs on adipose tissues. However, adipocyte morphometry has been quantitatively performed by manual object extraction using conventional image analysis systems. The authors have developed an automated quantitative image analysis method for adipose tissues using an innovative object-based quantitative image analysis system (eCognition). Using this system, it has been shown quantitatively that morphological features of adipose tissues of mice treated with peroxisome proliferator-activated receptor (PPAR) agonists differ dramatically depending on the type of PPAR agonist. Marked alteration of morphological characteristics of brown adipose tissue (BAT) treated with GI259578A, a PPAR-alpha agonist, was observed in AKR/J (AKR) obese mice. Furthermore, there was a 22.8% decrease in the mean size of adipocytes in white adipose tissue (WAT) compared with vehicle. In diabetic db/db mice, the PPAR-gamma agonist GW347845X decreased the mean size of adipocytes in WAT by 15.4% compared with vehicle. In contrast to changes in WAT, GW347845X increased the mean size of adipocytes in BAT greatly by 96.1% compared with vehicle. These findings suggest that GI259578A may activate fatty acid oxidation in BAT and that GW347845X may cause adipocyte differentiation in WAT and enhancement of lipid storage in BAT.