Jürg Andreas Gasser

This chapter provides information for the in vivo use of peripheral quantitative computed tomography in rats and mice to determine bone density and cortical geometric data, including suggestions for study design, instrument setting, and data interpretation. This update also provides guidance for the use of pQCT to extract muscle and fat cross-sectional area information from the bone scans.

PTH is indicated for the treatment of severe osteoporosis. Elderly osteoporotic patients frequently suffer from protein malnutrition, which may contribute to bone loss. It is unknown whether this malnutrition may affect the response to PTH. Therefore, the aim of the present study was to assess whether an isocaloric low-protein (LP) diet may influence the bone anabolic response to intermittent PTH in 6-month-old female rats. Six-month-old female rats were either pair fed an isocaloric LP diet (2.5% casein) or a normal-protein (NP) diet (15% casein) for 2 weeks. The rats continued on their respective diet while being treated with 5- or 40-μg/kg recombinant human PTH amino-terminal fragment 1-34 (PTH-[1-34]) daily, or with vehicle for 4 weeks. At the end of this period, areal bone mineral density, bone mineral content, microstructure, and bone strength in axial compression of proximal tibia or 3-point bending for midshaft tibia tests were measured. Blood was collected for the determination of IGF-I and osteocalcin. After 4 weeks of PTH-(1-34), the dose-dependent increase of proximal tibia bone mineral density, trabecular microstructure variables, and bone strength was attenuated in rats fed a LP diet as compared with rats on a NP intake. At the level of midshaft tibia cortical bone, PTH-(1-34) exerted an anabolic effect only in the NP but not in the LP diet group. Protein malnutrition was associated with lower IGF-I levels. Protein malnutrition attenuates the bone anabolic effects of PTH-(1-34) in rats. These results suggest that a sufficient protein intake should be recommended for osteoporotic patients undergoing PTH therapy.

Chronic metabolic acidosis (CMA) might result in a decrease in vivo in bone mass based on its reported in vitro inhibition of bone mineralization, bone formation, or stimulation of bone resorption, but such data, in the absence of other disorders, have not been reported. CMA also results in negative nitrogen balance, which might decrease skeletal muscle mass. This study analyzed the net in vivo effects of CMA's cellular and physicochemical processes on bone turnover, trabecular and cortical bone density, and bone microarchitecture using both peripheral quantitative computed tomography and μCT. CMA induced by NH₄Cl administration (15 mEq/kg body wt/day) in intact and ovariectomized (OVX) rats resulted in stable CMA (mean Δ[HCO₃⁻]_p = 10 mmol/l). CMA decreased plasma osteocalcin and increased TRAP5b in intact and OVX animals. CMA decreased total volumetric bone mineral density (vBMD) after 6 and 10 wk ( week 10: intact normal +2.1 ± 0.9% vs. intact acidosis −3.6 ± 1.2%, P < 0.001), an effect attributable to a decrease in cortical thickness and, thus, cortical bone mass (no significant effect on cancellous vBMD, week 10) attributed to an increase in endosteal bone resorption (nominally increased endosteal circumference). Trabecular bone volume (BV/TV) decreased significantly in both CMA groups at 6 and 10 wk, associated with a decrease in trabecular number. CMA significantly decreased muscle cross-sectional area in the proximal hindlimb at 6 and 10 wk. In conclusion, chronic metabolic acidosis induces a large decrease in cortical bone mass (a prime determinant of bone fragility) in intact and OVX rats and impairs bone microarchitecture characterized by a decrease in trabecular number.

Coronal clefts—a radiolucent band running through at least one vertebral body, visualized in the lateral spinal radiograph and discussed as a physiological variation of the fetal vertebral ossification pattern—are often found in fetal autopsies with trisomies. Published studies are missing concerning the question of whether this finding could serve as a diagnostic radiological or even ultrasonographic sign. We studied the incidence of radiological coronal clefts and their association with chromosomal aberrations in 443 fetuses (mostly medically induced abortions). In 42 of the 443 fetuses (9.5%), coronal clefts were visualized. The majority (71%) were localized in the lumbar spine. No cervical or singular sacral clefts were detected. Twenty-five of the 42 fetuses (60%) displaying coronal clefts had chromosomal aberrations, either as a trisomy (13 or 21) or as monosomy X. Histologically, coronal clefts showed a missing central ossification of the vertebral body. Remnants of the notochord could be excluded. Hence, coronal clefts represent a variant ossification of vertebral bodies in fetal development that is found almost exclusively in fetuses with chromosomal aberrations or severe congenital malformations. This finding could be a helpful supplement to prenatal diagnostics and fetal autopsy. On the other hand, the genetic diagnosis of chromosomal aberration, especially trisomy, does not automatically imply the presence of coronal clefts.

Once-yearly administration of intravenous zoledronic acid for 3 years in humans affects the kinetics of matrix filling in by mineral, independent of bone turnover.

The efficacy of 3 years of annual intravenous administration of zoledronic acid (ZOL) in reducing vertebral and nonvertebral fractures in postmenopausal osteoporosis has been shown by the HORIZON pivotal fracture trial. Histomorphometric analysis of transiliac bone biopsies from the HORIZON participants revealed significantly improved trabecular architecture and reduced bone remodeling for the ZOL-treated versus placebo-treated patients. The aim of our study was to evaluate the cancellous and cortical bone mineralization density distribution (BMDD) in these biopsies by quantitative backscattered electron imaging (qBEI). The study cohort comprised 82 patients on active treatment (ZOL, yearly doses of 5 mg) and 70 treated with placebo, and all received adequate Ca and VitD supplementation. Comparison of ZOL-treated versus placebo-treated cancellous (Cn.) and cortical (Ct.) BMDD-derived variables resulted in significantly higher average (Cn.CaMean + 3.2%, Ct.CaMean + 2.7%) and mode calcium concentrations (Cn.CaPeak + 2.1%, Ct.CaPeak + 1.5%), increased percentages of highly mineralized bone areas (Cn.CaHigh + 64%, Ct.CaHigh + 31%), lower heterogeneity of mineralization (Cn.CaWidth −14%, Ct.CaWidth −13%), and decreased percentages of low mineralized bone areas (Cn.CaLow −22%, Ct.CaLow −26%) versus placebo (all p < 0.001). Cn. BMDD from the patients on active treatment also revealed a statistically significant shift to higher Ca concentrations when compared to a historical normal reference BMDD. These differences in BMDD from ZOL patients compared to the other groups were in line with the correlation of BMDD variables with previously determined cancellous mineralizing surface per bone surface (Cn. MS/BS, a primary histomorphometric index for bone turnover), showing that those with lower Cn. MS/BS had a higher degree of bone matrix mineralization. However, the differences in BMDD variables between the study groups remained when adjusted for Cn. MS/BS, suggesting that other factors in addition to reduced bone turnover might contribute to the higher bone matrix mineralization after ZOL treatment. © 2013 American Society for Bone and Mineral Research.