Long-term effects of a new
selective estrogen receptor modulator (
SERM)
arzoxifene were examined in ovariectomized (OVX) rats.
Arzoxifene was administered postoperatively (po) at 0.1 mg/kg per day or 0.5 mg/kg per day to 4-month-old rats, starting 1 week after OVX for 12 months. At study termination,
body weights for
arzoxifene groups were 16-17% lower than OVX control, which was caused by mainly reduced gain of fat mass. Longitudinal analysis of the proximal tibial metaphysis (PTM) by computed tomography (CT) at 0, 2, 4, 6,9, and 12 months showed that OVX induced a 22% reduction in bone mineral density (BMD) at 2 months, which narrowed to a 12% difference between
sham-operated (
sham) and OVX rats by 12 months. Both doses of
arzoxifene prevented the OVX-induced decline in BMD. Histomorphometry of the PTM showed that
arzoxifene prevented bone loss by reducing osteoclast number in OVX rats.
Arzoxifene maintained bone formation indices at
sham levels and preserved trabecular number above OVX controls. Micro-CT analysis of lumbar vertebrae showed similar preservation of BMD compared with OVX, which were not different from
sham. Compression testing of the vertebra and three-point bending testing of femoral shaft showed that strength and toughness were higher for
arzoxifene-treated animals compared with OVX animals.
Arzoxifene reduced serum
cholesterol by 44-59% compared with OVX. Uteri wet weight from
arzoxifene animals was 38-40% of
sham compared with OVX rats, which were 29% of
sham. Histology of the uterine endometrium showed that cell heights from both doses of
arzoxifene were not significantly different from OVX controls. In summary, treatment of OVX rats with
arzoxifene for nearly one-half of a lifetime maintained beneficial effects on
cholesterol and the skeleton. These data suggest that
arzoxifene may be a useful therapeutic agent for
osteoporosis in postmenopausal women.