The effect of black cohosh extract and risedronate coadministration on bone health in an ovariectomized rat model

Abstract

Preparations of black cohosh extract are sold as dietary supplements marketed to relieve the vasomotor symptoms of menopause, and some studies suggest it may protect against postmenopausal bone loss. Postmenopausal women are also frequently prescribed bisphosphonates, such as risedronate, to prevent osteoporotic bone loss. However, the pharmacodynamic interactions between these compounds when taken together is not known. To investigate possible interactions, 6-month-old, female Sprague-Dawley rats underwent bilateral ovariectomy or sham surgery and were treated for 24 weeks with either vehicle, ethinyl estradiol, risedronate, black cohosh extract or coadministration of risedronate and black cohosh extract, at low or high doses. Bone mineral density (BMD) of the femur, tibia, and lumbar vertebrae was then measured by dual-energy X-ray absorptiometry (DEXA) at weeks 0, 8, 16, and 24. A high dose of risedronate significantly increased BMD of the femur and vertebrae, while black cohosh extract had no significant effect on BMD individually and minimal effects upon coadministration with risedronate. Under these experimental conditions, black cohosh extract alone had no effect on BMD, nor did it negatively impact the BMD-enhancing properties of risedronate.

Keywords: bisphosphonates; black cohosh; bone mineral density; dietary supplements; postmenopausal osteoporosis; risedronate.

FIGURE 1

Study design to evaluate changes in bone quality in the ovariectomized rat, an established model of postmenopausal osteoporosis. (A) At 6 months of age, female Sprague Dawley rats underwent sham or bilateral ovariectomy (OVX). Following a 7-day recovery period, animals were treated with vehicle or test articles for 24 weeks. (B) Representative DEXA images show regions of interest in shaded red boxes used to quantify bone mineral density (BMD) for the femur, lumbar vertebrae (L1-L4), and tibia. All images depicted are from the same rat. (C) Estradiol levels, measured by ELISA, were significantly greater in sham animals compared to OVX-vehicle animals (p < 0.0001, n = 12). The lower limit of detection in the assay was 3 pg/mL (dashed line).

FIGURE 2

Longitudinal body, terminal body, and absolute organ weight measurements. (A) Mean weekly body weight measurements are plotted for each treatment group. Due to significant reductions in body weight, doses of EE2 were adjusted downward to 2.5 and 15 μg/kg body weight per day after three or four weeks of treatment for load one and load two animals. Animals in loads three and four only received the lowered doses. (B) Sham surgery and EE2 treatment groups had significantly lower body weight measurements at week 24, while all risedronate and black cohosh extract treatment groups showed no significant differences compared to OVX-vehicle control. (C–E) Uterine, liver and kidney weights at week 24 showed no significant differences associated with risedronate or black cohosh extract treatments compared to OVX-vehicle. Data plotted as mean ± SD. Significance was evaluated by one-way ANOVA with Sidak’s post-hoc for multiple comparisons. * Indicates difference vs. OVX-vehicle control; *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001; n = 16–18. EE2 = ethinyl estradiol; BC = black cohosh extract; Ris = risedronate sodium; Veh = OVX-vehicle control.

FIGURE 3

BMD of femur, vertebrae and tibia following treatment with black cohosh extract and/or risedronate. (A) Longitudinal measurement of BMD at 0, 8, 16, and 24 weeks of treatment is plotted to show the effects of EE2, risedronate, black cohosh extract and risedronate + black cohosh extract combination treatments, with sham and vehicle data shown on each graph. Data plotted as mean ± SEM; n = 9–10. (B–D) BMD at week 24 was normalized to week 0 for each animal. After normalization, significant differences in BMD were associated with Hi EE2, Hi Ris and combined BC + Ris treatments, as compared to vehicle control. No statistically significant differences were observed between Lo Ris vs. Lo/Hi BC + Lo Ris or between Hi Ris vs. Lo/Hi BC + Hi Ris groups. Data plotted as mean ± SD. Significance was evaluated by one-way ANOVA with Sidak’s post-hoc for multiple comparisons. * Indicates difference vs. OVX-vehicle control; *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001; n = 14–18. EE2 = ethinyl estradiol; BC = black cohosh extract; Ris = risedronate sodium; Veh = OVX-vehicle control.