Dietary-induced metabolic acidosis decreases bone mineral density in mature ovariectomized ewes

Use of ammonium chloride to prevent urolithiasis in sheep

ABSTRACT Urolithiasis has a high incidence among confined sheep. It is multifactorial and may cause economic damage. Our aim was to determine the capacity of urinary acidification using ammonium chloride in sheep. Twenty-five 3-month-old male sheep were confined and randomly divided into three groups; the G200 and G500 groups received 200mg/kg/GW and 500mg/kg/GW of ammonium chloride daily for 56 consecutive days, respectively, whereas the CG group did not receive ammonium chloride. Sampling times and clinical evaluation were performed weekly, starting from the 14th day of confinement (M1 or immediately before administering ammonium chloride) until the 17th day (M9) of the feedlot. Hemogasometry, biochemical examination of serum urea and creatinine concentration and ultrasound evaluation of the urinary tract were performed. The urinalysis indicated a higher incidence of ammonium magnesium phosphate crystals at the beginning of the study, showing a migration to urate crystal formation, mainly in the G500 group because of urinary acidification. No hemogasometric, serum biochemistry, ruminal fluid, or ultrasonographic changes were observed. Urinary acidification was achieved and maintained after M7 during the administration of ammonium chloride in the G500 group, but not in the other study groups.

The old sheep: a convenient and suitable model for senile osteopenia

INTRODUCTION

Existing osteoporosis models in sheep exhibit some disadvantages, e.g., challenging surgical procedures, serious ethical concerns, failure of reliable induction of substantial bone loss, or lack of comparability to the human condition. This study aimed to compare bone morphological and mechanical properties of old and young sheep, and to evaluate the suitability of the old sheep as a model for senile osteopenia.

MATERIALS AND METHODS

The lumbar vertebral body L3 of female merino sheep with two age ranges, i.e., old animals (6-10 years; n = 41) and young animals (2-4 years; n = 40), was analyzed concerning its morphological and mechanical properties by bone densitometry, quantitative histomorphometry, and biomechanical testing of the corticalis and/or central spongious region.

RESULTS

In comparison with young sheep, old animals showed only marginally diminished bone mineral density of the vertebral bodies, but significantly decreased structural (bone volume, - 15.1%; ventral cortical thickness, - 11.8%; lateral cortical thickness, - 12.2%) and bone formation parameters (osteoid volume, osteoid surface, osteoid thickness, osteoblast surface, all - 100.0%), as well as significantly increased bone erosion (eroded surface, osteoclast surface). This resulted in numerically decreased biomechanical properties (compressive strength; - 6.4%).

CONCLUSION

Old sheep may represent a suitable model of senile osteopenia with markedly diminished bone structure and formation, and substantially augmented bone erosion. The underlying physiological aging concept reduces challenging surgical procedures and ethical concerns and, due to complex alteration of different facets of bone turnover, may be well representative of the human condition.

Preclinical and Translational Studies in Small Ruminants (Sheep and Goat) as Models for Osteoporosis Research

PURPOSE OF THE REVIEW

This review summarizes research on the use of sheep and goats as large animal models of human osteoporosis for preclinical and translational studies.

RECENT FINDINGS

The most frequent osteoporotic sheep model used is the ovariectomized sheep with 12 months post-operatively or more and the combined treatment of ovariectomized sheep associated to calcium/vitamin D-deficient diet and glucocorticoid applications for 6 months, but other methods are also described, like pinealectomy or hypothalamic-pituitary disconnection in ovariectomized sheep. The goat model for osteoporosis research has been used in a very limited number of studies in osteoporosis research relative to sheep. These osteoporotic small ruminant models are applied for biomaterial research, bone augmentation, efficacy of implant fixation, fragility fracture-healing process improvement, or bone-defect repair studies in the osteopenic or osteoporotic bone. Sheep are a recognized large animal model for preclinical and translational studies in osteoporosis research and the goat to a lesser extent. Recently, the pathophysiological mechanism underlying induction of osteoporosis in glucocorticoid-treated ovariectomized aged sheep was clarified, being similar to what occurs in postmenopausal women with glucocorticoid-induced osteoporosis. It was also concluded that the receptor activator of NF-κB ligand was stimulated in the late progressive phase of the osteoporosis induced by steroids in sheep. The knowledge of the pathophysiological mechanisms at the cellular and molecular levels of the induction of osteoporosis in small ruminants, if identical to humans, will allow in the future, the use of these animal models with greater confidence in the preclinical and translational studies for osteoporosis research.

Bone turnover markers in sheep and goat: A review of the scientific literature

Bone turnover markers (BTMs) are product of bone cell activity and are generally divided in bone formation and bone resorption markers. The purpose of this review was to structure the available information on the use of BTMs in studies on small ruminants, especially for monitoring their variations related to diet, exercise, gestation and metabolic lactation state, circadian and seasonal variations, and also during skeletal growth. Pre-clinical and translational studies using BTMs with sheep and goats as animal models in orthopaedic research studies to help in the evaluation of the fracture healing process and osteoporosis research are also described in this review. The available information from the reviewed studies was systematically organized in order to highlight the most promising BTMs in small ruminant research, as well as provide a wide view of the use of sheep and goat as animal models in orthopaedic research, type of markers and commercial assay kits with cross-reactivity in sheep and goat, method of sample and storage of serum and urine for bone turnover markers determination and the usefulness and limitations of bone turnover markers in the different studies, therefore an effective tool for researchers that seek answers to different questions while using BTMs in small ruminants.

The Effect of Osteoporosis Treatments on Fatigue Properties of Cortical Bone Tissue

Bisphosphonates are commonly prescribed for treatment of osteoporosis. Long-term use of bisphosphonates has been correlated to atypical femoral fractures (AFF). AFFs arise from fatigue damage to bone tissue that cannot be repaired due to pharmacologic treatments. Despite fatigue being the primary damage mechanism of AFFs, the effects of osteoporosis treatments on fatigue properties of cortical bone are unknown. To examine if fatigue-life differences occur in bone tissue after different pharmacologic treatments for osteoporosis, we tested bone tissue from the femurs of sheep given a metabolic acidosis diet to induce osteoporosis, followed by treatment with a selective estrogen reception modulator (raloxifene), a bisphosphonate (alendronate or zoledronate), or parathyroid hormone (teriparatide, PTH). Beams of cortical bone tissue were created and tested in four-point bending fatigue to failure. Tissues treated with alendronate had reduced fatigue life and less modulus loss at failure compared to other treatments, while tissue treated with PTH had a prolonged fatigue life. No loss of fatigue life occurred with zoledronate treatment despite its greater binding affinity and potency compared to alendronate. Tissue mineralization measured by microCT did not explain the differences seen in fatigue behavior. Increased fatigue life with PTH suggests that current treatment methods for AFF could have beneficial effects for restoring fatigue life. These results indicate that fatigue life differs with each type of osteoporosis treatment.

Long-term effects of ovariectomy on the properties of bone in goats

Large animal models of osteoporosis are essential for osteoporosis research. However, the time required to establish an accurate osteoporosis model is unknown. Therefore, the aim of the present study was to establish a large animal model of osteoporosis in goats. In total, 14 Chinese goats were divided into an ovariectomized (OVX, n=7) or sham-operated (SHAM, n=7) group. Vertebral bodies were used to measure the bone mineral density (BMD) prior to the ovariectomy and at 24 months after the ovariectomy. In addition, the BMD of the femoral neck, femoral diaphysis and tibial diaphysis were measured 24 months postoperatively. Bone samples from the vertebral body, femoral head and femoral neck were scanned by micro-computed tomography (CT) to visualize the trabecular and cortical microstructure. Furthermore, the vertebral body, femoral head, femoral neck and tibial diaphysis were analyzed for mechanical strength. The BMD of vertebral body of the OVX group decreased significantly (P<0.01) at 24 months after the ovariectomy when compared with the baseline measurements. Micro-CT scans of the vertebral body revealed that the bone volume fraction, trabecular number, trabecular thickness and the degree of anisotropy decreased by 37.1, 36.7, 10.5 and 16.5%, respectively (P<0.01) in the OVX group when compared with the SHAM group. Additionally, the specific bone surface and trabecular spacing significantly increased by 37.7 and 62%, respectively in the OVX group (P<0.001). Cortical bone porosity in the vertebral body and femoral neck was greater in the OVX group when compared with the SHAM group (P<0.05). In addition, mechanical testing revealed a statistically significant difference between the vertebral bodies of the OVX group and the SHAM group. In conclusion, the present study demonstrated that an ovariectomy was able to induce significant osteoporosis and deterioration of mechanical properties in the bones of goats.

Sheep model for osteoporosis: sustainability and biomechanical relevance of low turnover osteoporosis induced by hypothalamic-pituitary disconnection

Hypothalamo-pituitary disconnection (HPD) leads to low bone turnover and osteoporosis in sheep. To determine the sustainability of bone loss and its biomechanical relevance, we studied HPD-sheep 24 months after surgery (HPD + OVX-24) in comparison to untreated control (Control), ovariectomized sheep (OVX), and sheep 12 months after HPD (HPD + OVX-12). We performed histomorphometric, HR-pQCT, and qBEI analyses, as well as biomechanical testing of all ewes studied. Twenty-four months after HPD, histomorphometric analyses of the iliac crest showed a significant reduction of BV/TV by 60% in comparison to Control. Cortical thickness of the femora measured by HR-pQCT did not change between 12 and 24 months after HPD but remained decreased by 30%. These structural changes were caused by a persisting depression of osteoblast and osteoclast cellular activity. Biomechanical testing of the femora showed a significant reduction of bending strength, whereas calcium content and distribution was found to be unchanged. In conclusion, HPD surgery leads to a persisting low turnover status with negative turnover balance in sheep followed by dramatic cortical and trabecular bone loss with consequent biomechanical impairment.

Variations in nanomechanical properties and tissue composition within trabeculae from an ovine model of osteoporosis and treatment

Osteoporosis and treatment may affect both composition and nanomechanical properties and their spatial distributions within the individual trabeculae of cancellous bone at length scales that cannot be captured by bulk measurements. This study utilized 25 mature adult ewes divided into 5 treatment groups. Four treatment groups were given a dietary model for human high-turnover osteoporosis, and two of these were treated with antiresorptive drugs, either zoledronate (ZOL) or raloxifene (RAL), to examine their effects on bulk tissue properties and nanoscale tissue composition and mechanical properties within trabeculae. Treatment effects were most pronounced at the nanoscale, where RAL increased indentation modulus and hardness throughout trabeculae by 10% relative to the osteoporosis model. In comparison, ZOL increased these properties exclusively at the surfaces of trabeculae (indentation modulus +12%, hardness +16%). Nanomechanical alterations correlated with changes in tissue mineralization, carbonate substitution, crystallinity, and aligned collagen. Despite only minimal changes in bulk tissue tBMD, the nanomechanical improvements within trabeculae with both treatments greatly improved the predicted theoretical bending stiffness of individual trabeculae when idealized as cylindrical struts. Hence, small tissue-level alterations in critical locations for resisting trabecular failure could account for some of the discrepancy between the large reductions in fracture risk and the only modest changes in BMD with antiresorptive treatments.

A proteomic study of protein variation between osteopenic and age-matched control bone tissue

The focus of this study was to identify changes in protein expression within the bone tissue environment between osteopenic and control bone tissue of human femoral neck patients with osteoarthritis. Femoral necks were compared from osteopenic patients and age-matched controls. A new method of bone protein extraction was developed to provide a swift, clear view of the bone proteome. Relative changes in protein expression between control and osteopenic samples were quantified using difference gel electrophoresis (DIGE) technology after affinity chromatographic depletion of albumin and IgG. The proteins that were determined to be differentially expressed were identified using standard liquid chromatography mass spectrometry (LC/MS/MS) and database searching techniques. In order to rule out blood contamination, blood from age-matched osteoporotic, osteopenic and controls were analyzed in a similar manner. Image analysis of the DIGE gels indicated that 145 spots in the osteopenic bone samples changed at least ± 1.5-fold from the control samples ( P < 0.05). Three of the proteins were identified by LC/MS/MS. Of the proteins that increased in the osteopenic femurs, two were especially significant: carbonic anhydrase I and phosphoglycerate kinase 1. Apolipoprotein A–I was the most prominent protein that significantly decreased in the osteopenic femurs. The blood samples revealed no significant differences between groups for any of these proteins. In conclusion, carbonic anhydrase I, phosphoglycerate kinase 1 and apolipoprotein A–I appeared to be the most significant variations of proteins in patients with osteopenia and osteoarthritis.

Fourier transform infrared imaging analysis of cancellous bone in alendronate- and raloxifene-treated osteopenic sheep

Fourier transform infrared imaging spectroscopy (FTIRI)-assessed bone composition parameters (mineral content, collagen maturity, crystal size and perfection, and carbonate content) describe bone quality and correlate to bone fracture risk. The challenge with studying bone quality in patients treated with antiresorptive drugs such as bisphosphonates (e.g., alendronate) and selective estrogen receptor modulators (SERMs) (e.g. raloxifene) is being able to test bone mechanical performance and material properties pre- and posttreatment. The purpose of this study was to evaluate the FTIRI changes in a large animal model of osteoporosis (female sheep with dietary induced metabolic acidosis; MA). Previous studies have investigated the relationship between bone material properties and bone strength in humans and smaller animals and have shown that changes in compositional properties influence fracture risk. Here we characterize the MA model at 6 and 12 months, demonstrate the loss of bone and changes in compositional properties, and show that 6 months of treatment with both antiresorptives ameliorate the bone loss as assessed by bone mineral density and FTIRI. This preliminary data suggest that the MA sheep model allows investigation of whether drug treatments preserve bone properties that exist at the time of treatment or if they induce further beneficial changes.

Osteopenia in the maxillofacial area: a study in sheep

Osteoporosis is a major public health problem worldwide. Its significance in the fields of traumatology and implantology of the maxillofacial area requires investigation. A large animal model was used to assess bone loss in the lumbar spine and mandible.

INTRODUCTION

Osteoporosis is a prevalent disease characterized by low bone mass and microarchitectural deterioration of bone tissue. Osteoporosis-related fractures represent a major public health burden. The presence and relevance of osteoporosis in the maxillofacial area remain controversial. Research in humans is limited by difficulties in finding large homogenous study groups and, due to ethical considerations, numerous animal models have been used in osteoporosis research. The aim of this study was to assess a sheep model of generalized osteopenia for changes in the maxillofacial area.

METHODS

Bone loss was induced in ten Merino sheep by ovariectomy, intramuscular administration of glucocorticoids, and a calcium-reduced diet. Five untreated animals served as controls. Bone mineral density (BMD) was assessed by dual-energy X-ray absorptiometry at the lumbar spine at baseline and after 1, 3, 6, 9, and 12 months. Lumbar and mandibular bone biopsies were obtained and analyzed with microcomputed tomography.

RESULTS

Lumbar BMD decreased progressively in the intervention group and was most significantly low after 6 months (p < 0.001). Lumbar trabecular bone showed a significant decrease in bone volume (BV)/tissue volume (TV; p < 0.05) in the inducted group. Significant changes were found in both analyzed mandibular regions for BV/TV (p < 0.05). Regional variations were found for other parameters in the mandible. The cortical width was substantially reduced in the intervention group (p < 0.001).

CONCLUSIONS

Microstructural changes occurring in sheep as a result of induction seem to have a generalized nature. This sheep model meets the criteria for further investigation in the maxillofacial area.

Sustained-release rhBMP-2 increased bone mass and bone strength in an ovine model of postmenopausal osteoporosis

OBJECTIVE

The purpose of this study was to analyze the local treatment effects of rhBMP-2 combined with fibrin sealant (FS) on bone mineral density, microarchitectural and mechanical properties in osteoporotic ovine spine.

MATERIALS AND METHODS

Postmenopausal osteoporosis was induced in eight sheep through ovariectomy (OVX) and a low-calcium diet for a period of 12 months. According to the Latin square design, L3-L6 vertebrae were randomly assigned to four treatment groups: A (rhBMP-2/FS), B (rhBMP-2), C (FS) and D (blank control). All materials were injected into the assigned vertebra transpedicularly. All animals were euthanized 3 months after treatment. Bone mineral density (BMD), microarchitectural and mechanical properties were assessed. ANOVA analysis of variance was used to determine effects of rhBMP-2/FS (α = 0.05).

RESULTS

The BMD in group A (rhBMP-2/FS) was 18.8, 30.4 and 27.9% higher than that in group B, C and D, respectively. Analysis of bone structure by micro-CT revealed higher trabecular bone volume (BV/TV), trabecular thickness (Tb.Th) and trabecular number (Tb.N) in the rhBMP-2/FS group (P < 0.01). In addition, vertebrae treated with rhBMP-2/FS exhibited higher yield stress, ultimate stress, energy absorption and bone modulus compared to the control groups.

CONCLUSIONS

Local administration of rhBMP-2/FS showed a positive trend in improving BMD, microarchitectural parameters and mechanical strength of osteoporotic vertebra. Slow release of rhBMP-2 using FS appeared to be an effective method of protein delivery. The local treatment of osteoporosis in the spine can increase bone strength and reduce fracture risk quickly.

Biomechanical and histological evaluation of an expandable pedicle screw in osteoporotic spine in sheep

Transpedicular fixation can be challenging in the osteoporotic spine as reduced bone mineral density compromises the mechanical stability of the pedicle screw. Here, we sought to investigate the biomechanical and histological properties of stabilization of expandable pedicle screw (EPS) in the osteoporotic spine in sheep. EPSs and standard pedicle screws, SINO screws, were inserted on the vertebral bodies in four female ovariectomized sheep. Pull-out and cyclic bending resistance test were performed to compare the holding strength of these pedicle screws. High-resolution micro-computed tomography (CT) was performed for three-dimensional image reconstruction. We found that the EPSs provided a 59.6% increase in the pull-out strength over the SINO screws. Moreover, the EPSs withstood a greater number of cycles or load with less displacement before loosening. Micro-CT image reconstruction showed that the tissue mineral density, bone volume fraction, bone surface/bone volume ratio, trabecular thickness, and trabecular separation were significantly better in the expandable portion of the EPSs than those in the anterior portion of the SINO screws (P < 0.05). Furthermore, the trabecular architecture in the screw-bone interface was denser in the expandable portion of the EPS than that in the anterior portion of the SINO screw. Histologically, newly formed bone tissues grew into the center of EPS and were in close contact with the EPS. Our results show that the EPS demonstrates improved biomechanical and histological properties over the standard screw in the osteoporotic spine. The EPS may be of value in treating patients with osteoporosis and warrants further clinical studies.

Femoral Cortical Bone Mineral Density and Biomechanical Properties in Sheep Consuming an Acidifying Diet

Dietary acidity is a likely contributor to the development of osteoporosis. Dietary acidosis in an ovine model has effects on trabecular bone that have been previously shown to mimic human osteoporosis. Effects on cortical bone using this model have not been investigated. The objective of this study was to examine the effects of dietary acidosis on cortical bone mineral density and material properties.

Skeletally mature ovariectomized (OVX) sheep consumed either a normal diet (ND) or a metabolic acidosis diet (MA) for 6 or 12 months. Whole femoral and cortical bone beam BMD was determined using dual energy x-ray absorptiometry (DEXA). Beams were then subjected to three point flexure monotonically to failure to determine strength and modulus and then ashed to determine percent mineralization.

Femoral BMD in adult OVX ND 6 mo sheep was significantly greater than those in the non-OVX ND group. The BMD in the MA groups was lower than the control non-OVX ND group. Cortical beams had significantly decreased modulus in all MA and OVX groups when compared with the non-OVX ND group and a tendency towards decreased strength in all groups with significance only in the OVX ND 6 mo sheep. Percent mineralization increased in MA and OVX groups when compared to the non-OVX ND group and was significantly increased in the OVX ND 6 mo and OVX MA 12 mo groups. A significant correlation was seen between BMD of the beam and breaking strength and modulus. Dietary acidity impacts cortical bone and results in reduced material properties that may contribute to failure.

Effect of Dietary Induced Metabolic Acidosis on Bone Mineral Acquisition in 2-8 Month Old Lambs

Dietary induced metabolic acidosis (MA) results in a negative calcium balance in normal animals. In order to maintain acid-base homeostasis the body's primary base buffer source calcium is mobilized from bone. This study examined the impact of dietary induced MA on bone in an adolescent ovine model. We hypothesized that a MA diet would reduce bone mineral density (BMD) in growing sheep.

Twelve 2 month old lambs of mixed sex were divided into 2 groups. The MA group consumed a ration that was relatively acidogenic compared to the control diet (CD) for 6 months. DXA was performed on days 0 and 180. Arterial blood samples were evaluated on days 0, 30, 120, 150 and 180 for pH, pCO2, pO2, HCT, Na, K, ionized Ca, HCO3–, TCO2, base excess (BE), and O2 saturation. Histomorphometry of the femoral diaphysis was performed from samples harvested at 180 days. Statistical analysis consisted of a 2-way ANOVA for sex and diet with repeated measures for bone mineral content (BMC) and blood parameters, a 2-way ANOVA for one time measurements at 180 d including BMD of the whole body, radii, femora and lumbar vertebrae, and 1-way ANOVA to compare histomorphometric measurements.

Percent increase from baseline for BMD of the whole body was 1.8x greater in the CD group than the MA group. BMC of the whole body and lumbar vertebrae was significantly less in the MA group. Lumbar BMD on day 180 was 30% less in the MA group. Cortical bone was less affected. Radii and femora BMD was 18% and 21% less, respectively, in the MA group than in the CD group. MA treatment significantly decreased pH, HCT, iCa, HCO3–, TCO2 and BE. However, no blood parameters were outside the normal range for this species. Histomorphometry revealed significantly decreased cortical area and thickness and increased mineral apposition rate and endosteal active surface length in the femoral cortex of the MA group compared to the CD group.

This study demonstrated a well compensated dietary induced MA that resulted in a significant decrease in bone mineral acquisition in juvenile sheep. Diets that induce MA may have a profound impact on lowering peak BMD in adolescents and therefore predispose individuals to osteoporosis later in life.

Validation of the sheep as a large animal model for the study of vertebral osteoporosis

Rats have long been the animal of choice for research in the field of osteoporosis. In the search for a complementary large animal model the sheep appears useful but hitherto the extent of bone loss from the spine has failed to reach a level that is generally accepted as osteoporotic in humans. Osteoporosis was induced in ten sheep using ovariectomy, low calcium diet and steroid injection for 6 months. Bone samples of iliac crest (IC), lumbar spine (LS), and proximal femur (PF) from the osteoporotic sheep were compared with those from four normal sheep using densitometry, histomorphometry, biochemistry and basic mechanical testing. The differences were examined using an analysis of variance with Tukey-Kramer test. Overall, the bone mineral density at LS and PF decreased more than 25% after treatment. Trabecular bone volume decreased by 29.2, 33.4 and 42.6% in IC, LS and PF, respectively. The failure load of the LS in axial compression was reduced to 2,003 from 6,140 N. The extent of bone loss was sufficient to categorise these sheep as osteoporotic although the pattern of bone loss varied between sites. Reduced mechanical competence in LS confirmed the suitability of this model for evaluation of potential treatments for osteoporosis.

Role of transparency in managing outcome successes

Purpose

Healthcare is both the largest (17 + percent) and the most rapidly growing (three plus times the consumer product index (measure of inflation) and half a percent of gross domestic product each year) segment of the US economy. The purpose of this paper is to focus on outcome successes that illustrate application of a previously reported health equation. The health equation allows an organized and more transparent assessment of healthcare outcomes.

Design/methodology/approach

The approach includes “end use/least cost” techniques that identifies healthful care as a big unmet need (BUN) and equally attractive business opportunity in identifying health promotion that improves outcome at lower net costs.

Findings

Opportunity exists to reduce costs while also reducing adverse events, healthcare morbidity and morality. Transparency is essential to find what works more effectively to yield desired outcomes. Metrics and measures, particularly more precise tools to assess true outcome in promoting health or managing ill health, are given priority as they allow quantified and, often econometric, outcome opportunities in the midst of current uncertainties.

Practical implications

This paper is for consumers and businesses, managers and administrators, professionals and allied health professionals. The successes described herein illustrate fundamental opportunities driving change and innovation within healthcare and in our society.

Originality/value

Attention is called to opportunity areas that can fund out of savings the transition from the authors' current “sickness care” system to a healthful care, proactive prevention approach to delivering care. Novel application of transparency and end use/least cost can help guide choices to achieve healthier outcomes.

Review of nonprimate, large animal models for osteoporosis research

Large animal models are required for preclinical prevention and intervention studies related to osteoporosis research. The challenging aspect of this requirement is that no single animal model exactly mimics the progression of this human-specific chronic condition. There are pros and cons associated with the skeletal, hormonal, and metabolic conditions of each species that influence their relevance and applicability to human physiology. Of all larger mammalian species, nonhuman primates (NHPs) are preeminent in terms of replicating important aspects of human physiology. However, NHPs are very expensive, putting them out of reach of the vast majority of researchers. Practical, cost-effective alternatives to NHPs are sought after among ungulate (porcine, caprine, and ovine) and canine species that are the focus of this review. The overriding caveat to using large lower-order species is to take the time in advance to understand and appreciate the limitations and strengths of each animal model. Under these circumstances, experiments can be strategically designed to optimize the potential of an animal to develop the cardinal features of postmenopausal bone loss and/or yield information of relevance to treatment.

Low-grade metabolic acidosis may be the cause of sodium chloride-induced exaggerated bone resorption

Stepwise increase in NaCl intake in healthy male test subjects led to a low-grade metabolic acidosis. This was most likely the cause for increased bone resorption during high sodium chloride intake, as determined by analyzing bone resorption markers.

INTRODUCTION

We examined the effect of increased dietary sodium chloride (NaCl) on bone metabolism and acid-base balance.

MATERIALS AND METHODS

Subjects were nine healthy men (mean age, 25.7 +/- 3.1 yr; mean body weight [BW], 71.5 +/- 4.0 kg). During the first period (6 days), subjects received 0.7 mEq NaCl/kg BW per day (phase 1), during the second period (6 days) 2.8 mEq NaCl/kg BW per day (phase 2), during the third period (10 days) 7.7 mEq NaCl/kg BW per day (phase 3), and during the fourth period (6 days) 0.7 mEq NaCl/kg BW per day (phase 4).

RESULTS

Twenty-four-hour urinary excretion of calcium and sodium rose significantly with increasing NaCl intake (p < 0.001 for both). Urinary excretion of bone resorption markers C- and N-terminal telopeptide of type I collagen (CTX, NTX) increased from phase 2 to phase 3 (CTX, p = 0.013; NTX, p < 0.001) and decreased from phase 3 to phase 4 (CTX, p < 0.001; NTX, p = 0.002). Bone formation markers N-terminal propeptide of type I procollagen, bone-specific alkaline phosphatase, and osteocalcin remained unchanged from low to high NaCl intake. Blood pH levels decreased (p = 0.04) between phases 1 and 3. Blood bicarbonate (HCO(3)(-)) and base excess (BE) decreased from phases 1 to 3 (p < 0.001 for both) and from phases 2-3 (HCO(3)(-), p = 0.003; BE, p = 0.015). Nearly all bone resorption markers and acid-base variables reached their baseline levels in phase 4.

CONCLUSIONS

We conclude that low-grade metabolic acidosis may be the cause of NaCl-induced exaggerated bone resorption.

Staged-injection procedure to prevent cement leakage during vertebroplasty: an in vitro study

STUDY DESIGN

Fibrin sealant (FS) combined with or without growth factor was used to improve the micro-architectural and biomechanical properties of vertebral body in osteoporotic ovine spine.

OBJECTIVE

To analyze the treatment effects of bovine bone morphogenetic protein (bBMP) combined with FS on osteopenic ovine vertebral architecture, bone mineral density, and biomechanics in vivo.

SUMMARY OF BACKGROUND DATA

Vertebroplasty and kyphoplasty were used to treat spinal osteoporosis. They can increase strength of vertebrae physically. However, each has specific disadvantages. bBMP could rapidly increasing bone formation and suppressing bone resorption, but little is known about its effect on ovariectomized-induced osteoporosis.

METHODS

Six sheep underwent ovariectomy and were placed on a low-calcium diet. Twelve months later, according to Ladin square design, L4-L6 vertebrae in all sheep were randomly assigned to 3 treatment groups: A (30 mg bBMP/1.5 mL FS), B (30 mg bBMP) and C (1.5 mL FS). All materials were injected into the assigned vertebra transpedicularly. Animals were killed 3 months after injection, and bone mineral density (BMD), biomechanics, and histomorphometry were assessed. Analysis of variance was used to determine effects of bBMP/FS (alpha = 0.05).

RESULTS

The BMD in Group 1 was 17.1% and 14.7% higher than that in Group 2 and Group 3, respectively. The micro-CT reconstruction analysis showed that the density and connectivity of trabecular bone in bBMP/FS treated vertebrae were higher than those in control groups. The mechanical properties (yield stress, ultimate stress, energy absorption, bone modulus) of the vertebrae were also significantly higher. In this study, local bBMP/FS treatment showed a positive trend in improving BMD, histomorphometric parameters, and mechanical strength of osteoporotic vertebra. Slow release of bBMP using FS appeared to be an effective method of protein delivery.

CONCLUSION

The use of bBMP/FS in the treatment of vertebral osteoporosis in an attempt to enhance bone strength merits further study.

In vivo BMP-7 (OP-1) enhancement of osteoporotic vertebral bodies in an ovine model

BACKGROUND CONTEXT

Prevention of osteoporotic vertebral fractures could help at-risk individuals avoid the pain and morbidity associated with these fractures. Currently, patients with osteoporosis are treated with systemic medications to reduce fracture risk. Although effective, these therapies do not eliminate fractures and also tend to have a gradual time-dependent effect on fracture risk. The mechanism of action of the bone morphogenetic protein (BMP) family theoretically makes these molecules candidates for rapidly enhancing local bone structure.

STUDY DESIGN

An in vivo study analyzing the effects of BMP-7 (osteogenic protein 1 [OP-1]) treatment on osteopenic ovine vertebral architecture and biomechanics.

PURPOSE

We tested the hypothesis that local injection of OP-1 into osteopenic ovine vertebrae will improve bone mass and trabecular distribution, thereby reducing bone fragility and fracture risk. We specifically evaluated compressive biomechanics and morphology of osteopenic ovine vertebral bodies 6 months after local OP-1 treatment.

STUDY DESIGN

In vivo animal study.

METHODS

Skeletally mature sheep (n=24) underwent ovariectomy and were placed on low cation relative to anion diet. These interventions reduce bone density and induce skeletal fragility. After 6 months, sheep were randomly assigned to six treatment groups based on OP-1 dose (370 mg or 0 mg) and carrier with 4 animals/treatment group. Carriers A and B were poly-L-glycolic acid (PLGA) biospheres with different release kinetics (B allowing sustained BMP release); Carrier C was carboxymethylcellulose. After creating an 8-mm-diameter defect in the midvertebral body, sheep underwent intravertebral body implantation at two nonadjacent levels. Animals were euthanized 6 months after implantation and bone mineral density (BMD), biomechanics, and histomorphometry were assessed. Two-way analysis of variance was used to determine effects of OP-1 (alpha=0.05).

RESULTS

An 81.9%, 333.2%, and 39.9% increase in stiffness was seen for OP-1 treated vertebra with Carriers A, B, and C respectively. Although these effects did not reach statistical significance, trends toward improvement were evident. Histology showed varied degrees of bony healing in the injection sites. Histomorphometrically, OP-1 treated vertebrae showed improvements in percent bone of up to 38% and star volume of up to 55% (with Carrier B). Improvements in whole vertebral body BMD were not detected for any treatment.

CONCLUSION

In this study, local OP-1 treatment showed a positive trend in improving mechanical strength and histomorphometric parameters of osteopenic vertebra, despite the absence of consistent change in BMD. Controlled slow release of OP-1 using PLGA microspheres appeared to be the most effective method of protein delivery. In conclusion, we feel that the pilot data suggest that the use of OP-1 in the treatment of vertebral osteoporosis in an attempt to enhance bone strength merits further study.