Loss of Bone Strength is Dependent on Skeletal Site in Disuse Osteoporosis in Rats

Abstract

Intramuscular injection with botulinum toxin A (BTX) leads to a transient paralysis of the muscles, resulting in a rapid loss of muscle mass and function as well as rapid bone loss (disuse osteoporosis). The purpose of this study was to investigate the temporal development and the site specificity of BTX-induced immobilization on bone strength at five skeletal sites. Three-month-old rats (n = 108) were randomized into nine groups: one served as baseline, while four were injected with BTX and four with saline in the right hind-limb musculature. Animals were killed after 1, 2, 3, or 4 weeks. BTX-induced a significant loss of rectus femoris muscle mass (-61%) and muscle cell cross-sectional area (-59%) as well as bone strength at the femoral neck (-31%), femoral diaphysis (-6%), distal femoral metaphysis (-17%), proximal tibial metaphysis (-31%), and tibial diaphysis (-13%) after 4 weeks. Muscle atrophy occurred in parallel with the bone loss at the femoral neck and proximal tibia, whereas it occurred earlier than the bone loss at the other skeletal sites. At the proximal tibial metaphysis BTX significantly decreased BV/TV (-10%), trabecular thickness (-13%), and bone formation (MS/BS -25%, BFR/BS -50%) and increased osteoclast covered surfaces (+97%) after 4 weeks. In conclusion, BTX-induced a time-dependent loss of bone strength. Moreover, the loss of bone strength differed significantly at the five tested skeletal sites.

Role of endoplasmic reticulum stress in disuse osteoporosis

“…The tail-suspended animal model has been widely accepted as an effective disuse osteoporosis model for simulating bone loss [15,22,41]. In the current tail suspension experiment, bone formation was mildly inhibited and bone resorption was markedly increased in unloaded mice, these 20 changes are in accord with previous study [14,[42][43][44]. Our correlation analysis and linear regression showed that the expression level of p-eIF2α was positively associated with the number of bone-forming osteoblasts, and negatively associated with that of bone-resorbing osteoclasts.…”

Immobilization induced osteopenia is strain specific in mice

“…We have previously shown losses of bone density, microstructure, and strength in rats following BTX injection (Vegger et al, 2014, Thomsen et al, 2012, Brüel et al, 2013, Grubbe et al, 2014), and these findings are similar to what has been shown in mice (Warner et al, 2006a, Warden et al, 2013, Ellman et al, 2014, Manske et al, 2010a, Aliprantis et al, 2012, Grimston et al, 2007, Ausk et al, 2013, Manske et al, 2010b, Manske et al, 2012, Poliachik et al, 2010, Warner et al, 2006b). Furthermore, it has been demonstrated that the bone deterioration following BTX-induced muscle paralysis is paralleled by an increase in osteoclast activity and osteoclastogenesis, and these two factors are believed to play key roles for the rapidly occurring bone loss in this model of immobilization (Aliprantis et al, 2012, Warner et al, 2006b).…”

Osteocyte lacunar properties in rat cortical bone: Differences between lamellar and central bone

“…The bone samples were obtained from 4-months-old female Wistar rats used as controls in previous studies (Bach-Gansmo et al, 2013;Thomsen et al, 2012). The animals were sacrificed, the hind legs removed, and the femora were carefully cleaned.…”

“…The femora had previously been used for ascertaining bone strength using three point bending tests (Thomsen et al, 2012) and were cut into rods for SR µCT investigations. The proximal half of femurs were embedded in Epofix (Struer, Ballerup, Denmark) and rectangular bone bars were cut from the femoral mid-diaphysis using a water cooled Exakt 300 CL diamond band saw (Exakt Apparatebau, Norderstedt, Germany).…”