The impact of postmenopausal osteoporosis on aortic valve stenosis in an animal model

Abstract

Abstract Background Aortic valve stenosis (AVS) is the most prevalent heart valve disease worldwide and mainly affects the elderly. In observational clinical studies, postmenopausal osteoporosis, which affects 30 % of all women, is associated with increased aortic valve calcification and stenosis. However, there are no pathomechanistic investigations that link these diseases. In this study, we analyzed the impact of postmenopausal osteoporosis in ovariectomized C57BL6/J mice on the occurrence and progression of wire injury-induced aortic valve stenosis. Methods To induce postmenopausal osteoporosis, we performed bilateral ovariectomy (OVX) or sham operation in C57BL6/J mice. Successful OVX was confirmed by measuring the uterine weight. To distinguish the impact of estrogen deprivation from osteoporosis effects, 100 µg of the bisphosphonate zoledronic acid (ZA) or vehicle were applied i.p. weekly. Bone density was assessed through histological and µCT-analysis of the distal femur. 14 days after ovariectomy, AVS (or sham-procedure) was induced through a standardized, echocardiography-controlled injury of the aortic valve with a spring wire. Primary endpoint was the increase of peak velocity 2, 4 and 6 weeks after AVS-procedure. 8 weeks after OVX, mice were sacrificed and organs were harvested for further analysis (Fig. 1A). Results Bone mineral density and relative bone volume was significantly reduced 8 weeks after OVX. ZA led to a significant increase in bone mineral density, trabecular thickness and relative bone volume in comparison to the sham/vehicle and OVX/vehicle-groups (Fig. 1B-C). AVS was successfully induced, as shown by a significant increase in peak velocity (PV; Fig. 2A-B) 2, 4 and 6 weeks after wire injury. PV and mean pressure gradient (MPG) showed no difference between OVX- or Sham-operated mice (Fig. 2A). ZA did not significantly affect PV or MPG after AVS-procedure (Fig. 2B). Histological analysis revealed significantly greater cusp area in mice with AVS, but no difference for OVX- or ZA-groups (Fig. 2C). Picrosirius red staining showed a significantly decreased relative and absolute collagen content in aortic valves derived from mice with AVS, but no difference between OVX- or ZA-groups was detectable. Immature/degraded collagen was increased in mice with AVS. Conclusion Estrogen depletion and reduction in bone mineral density did affect AVS development in C57BL6/J mice. Application of ZA was effective in preventing bone loss, but did not change AVS-severity. Further histological analysis of the aortic valves could reveal potential differences in cardiovascular osteoclast- and immune cell-infiltration.Figure 1Figure 2