The effect of conjugated equine estrogens on ovariectomy-induced osteopenia in the rat

Piper sarmentosum enhances fracture healing in ovariectomized osteoporotic rats: a radiological study

INTRODUCTION

Osteoporotic fractures are common during osteoporotic states. Piper sarmentosum extract is known to possess antioxidant and anti-inflammatory properties.

OBJECTIVES

To observe the radiological changes in fracture calluses following administration of a Piper sarmentosum extract during an estrogen-deficient state.

METHODS

A total of 24 female Sprague-Dawley rats (200-250 g) were randomly divided into 4 groups: (i) the sham-operated group; (ii) the ovariectomized-control group; (iii) the ovariectomized + estrogen-replacement therapy (ovariectomized-control + estrogen replacement therapy) group, which was supplemented with estrogen (100 μg/kg/day); and (iv) the ovariectomized + Piper sarmentosum (ovariectomized + Piper sarmentosum) group, which was supplemented with a water-based Piper sarmentosum extract (125 mg/kg). Six weeks after an ovariectomy, the right femora were fractured at the mid-diaphysis, and a K-wire was inserted. Each group of rats received their respective treatment for 6 weeks. Following sacrifice, the right femora were subjected to radiological assessment.

RESULTS

The mean axial callus volume was significantly higher in the ovariectomized-control group (68.2 ± 11.74 mm³) than in the sham-operated, estrogen-replacement-therapy and Piper sarmentosum groups (20.4 ± 4.05, 22.4 ± 4.14 and 17.5 ± 3.68 mm³, respectively). The median callus scores for the sham-operated, estrogen-replacement-therapy and Piper sarmentosum groups had median (range, minimum - maximum value) as 1.0 (0 - 2), 1.0 (1 - 2) and 1.0 (1 - 2), respectively, which were significantly lower than the ovariectomized-control group score of 2.0 (2 - 3). The median fracture scores for the sham-operated, estrogen-replacement-therapy and Piper sarmentosum groups were 3.0 (3 - 4), 3.0 (2 - 3) and 3.0 (2 - 3), respectively, which were significantly higher than the ovariectomized-control group score of 2.0 (1 - 2) (p<0.05).

CONCLUSION

The Piper sarmentosum extract improved fracture healing, as assessed by the reduced callus volumes and reduced callus scores. This extract is beneficial for fractures in osteoporotic states.

Utility of the ovariectomized rat as a model for human osteoporosis in drug discovery

Ovariectomy-induced osteopenia in the rat produces skeletal responses similar to that in a post-menopausal woman. In the ovariectomized (ovx) rat, high bone turnover, and subsequent bone loss, like in the human post-menopausal condition, can be prevented by estrogen replacement. Because of the striking resemblance of skeletal responses in humans and rats in the state of estrogen deficiency, the ovx rat is considered to be a gold standard model for evaluating drugs for prevention and reversal of osteoporosis. This chapter describes the procedure for performing ovariectomy on the rat and the utility of the ovx rat model we have utilized over the last two decades in our laboratory.

Effect of weight manipulation on bone loss due to ovariectomy and the protective effects of estrogen in the rat

While characterizing the effects of estrogen on an ovariectomized (OVX) rat model of bone loss, we examined several weight-matching regimens [e.g., ad libitum (feed bins continually full), weight matched (rate of weight gain for OVX and Sham-OVX groups was equalized), and weight restricted (weight gain rates for all groups were equalized to that of estrogen-treated OVX rats)] for possible effects. Bone loss following ovariectomy is primarily the result of an increase in bone resorption and is extremely sensitive to the effects of estrogens. Thus, in all of our analyses, treatment with 17 beta-estradiol served as a positive control for the prevention of bone loss. Each weight-matching study had three groups: control (Sham-OVX), OVX, and OVX + 17 beta-estradiol (0.1 mg/kg/day), and lasted for either 2, 4, or 6 weeks. Throughout the study, each Sprague Dawley rat was weighed every other day, and following sacrifice, a femur was removed for bone mineral density (BMD) analysis at the distal metaphysis by single photon absorptiometry. Following 2 weeks of dietary modifications, no significant differences were detected in BMD among the ad lib or weight matched groups. However, an estradiol-preventable reduction in BMD in restricted OVX rats was detected at 2 weeks postovariectomy. Additionally, OVX rats in all three dietary regimens displayed an estrogen-preventable reduction in proximal femur BMD at 4 and 6 weeks postovariectomy. These results indicate that a 4-week rat ovariectomized model of bone loss, under conditions of ad libitum feeding, shows great potential for pharmacologic manipulation.

Loss of cancellous bone mass and connectivity in ovariectomized rats can be restored by combined treatment with parathyroid hormone and estradiol

To evaluate the potential use of a combination of antiresorption and bone formation-promoting agents as a treatment for postmenopausal osteoporosis, we examined the effects of combined and separate administration of estrogen (17 beta-estradiol, 30 micrograms/kg per d, s.c.) and parathyroid hormone (rPTH [1-34], 40 micrograms/kg per d, s.c.) on the proximal tibia of ovariectomized (Ovx) rats. The treatments lasted for 4 wk and were initiated 1, 3, and 5 wk after surgery. Ovx resulted in rapid loss of cancellous bone volume (Cn-BV/TV) as well as trabecular connectivity, as determined by two dimensional strut analysis. When administered in a preventive mode, treatment beginning 1 wk post-Ovx, estrogen or PTH treatment alone preserved Cn-BV/TV and trabecular connectivity, and combined estrogen and PTH treatment caused a 40% increment in Cn-BV/TV while maintaining comparable trabecular connectivity with that seen in the Sham-operated animals. When administered in a curative mode to rats with established osteoporosis, treatments beginning 3 or 5 wk post-Ovx, estrogen or PTH treatment alone prevented further loss of connectivity and Cn-BV/TV, whereas the combined treatment resulted in as much as a 300% improvement in one of the parameters of trabecular connectivity, node to node strut length, and a 106% increase in Cn-BV/TV, with respect to the bone status at the initiation of treatment. The beneficial effects of this combined treatment derive from estrogen's ability to prevent accelerated bone resorption and, simultaneously, PTH's promotion of bone formation. These data demonstrate, in an animal model, that therapies can be devised to cure the skeletal defects associated with established osteoporosis.