An in vitro trial on the effect of arch form on connector size requirements in long span anterior zirconia fixed dental prostheses.

PURPOSE: To test the fracture resistance of maxillary canine to canine fixed partial denture with four missing incisors, with increasing anterior-cantilevers of the pontics and varying connector sizes. MATERIALS AND METHODS: Two 3D-printed titanium alloy (Ti6Al4V) models mimicking a maxillary canine to canine fixed partial denture (FPD) with four pontics replacing the incisors were used as master models. Zirconia FPDs were digitally designed and milled with two different connector sizes (9 and 12 mm2 ) each with three different anterior cantilevers (7, 10, and 13 mm) accounting for 6 test groups. Seven samples were milled for each group generating a total of 42 samples. The zirconia FPDs were cemented on the titanium model using resin modified glass ionomer cement and the model fixated to a variable angle vice. A sinusoidal cyclic waveform load from 50 to 280N was applied using a universal testing machine at a frequency of 30 cycles per second and a total of 5 million cycles. RESULTS: The results of Fisher's exact tests showed that the difference in the proportion of fractured versus nonfractured fixed partial dentures was not statistically significant when comparing the 9 with the 12 mm2 connector size (p = 1.00), as well as when comparing the six test groups (p = 0.2338); on the other hand, it proved to be statistically significant when comparing the 7 mm cantilever with the 10 and 13 mm cantilevers combined (p = 0.0407) indicating that a 7 mm anterior spread of the pontics showed a significantly greater proportion of fixed partial dentures that fractured. CONCLUSIONS: Fracture susceptibility was not a function of cantilever length in this testing configuration for anterior FPDs. Retainer crown thickness seems to be a more important parameter than connector size thickness. Based on the results, a smaller connector size (9 mm2 ) can be used to improve the esthetics of pontics in long span anterior FPDs.

Human periodontal ligament fibroblast responses to compression in chronic periodontitis.

AIM: Test whether human periodontal ligament fibroblasts (PDLFs) retain homeostatic responses to a physiological compressive force during chronic periodontitis. MATERIAL AND METHODS: Six cell lines were established from periodontally healthy individuals (H-PDLFs) and another six were cultured from patients diagnosed with chronic periodontitis (D-PDLFs). Compressive force at 150 psi was applied to H-and D-PDLFs for 3 h on 2 consecutive days. After compression, comparisons between H-and D-PDLFs were performed by gene expression analysis of IL-6, proteases and 84 inflammation-related targets using real-time PCR. RESULTS: Compression of H-PDLFs resulted in a significant increase only in MMP-1 mRNA. In contrast, the same compressive force on D-PDLFs produced significant increases in the expression of MMPs-1,-7,-9 and -16. Moreover, compression of H-PDLFs resulted in down-regulation of IL-6, while IL-6 was significantly up-regulated in compressed D-PDLFs. Compression of H-PDLFs slightly up-regulated 3 and significantly down-regulated 15 inflammation-related genes, while the same treatment strongly up-regulated 21 inflammation-related genes in D-PDLFs. CONCLUSION: These results suggest a fundamental difference in the inflammatory response of healthy versus diseased PDLFs under physiological compression. Maintenance of these characteristics in vitro suggests that these cells may be at least partly responsible for the persistence of inflammation and localized susceptibility in chronic periodontitis.

Myostatin (GDF-8) inhibits chondrogenesis and chondrocyte proliferation in vitro by suppressing Sox-9 expression.

Here, we investigate a possible direct role for myostatin in chondrogenesis. First, we examined the effects of myostatin on the proliferation of bone marrow stromal cells (BMSCs) and epiphyseal growth plate (EGP) chondrocytes (EGPCs) isolated from myostatin-deficient mice. Results show that myostatin deficiency is associated with a significant (P < 0.001) increase in proliferation of both BMSCs (+25%) and EGPCs (+35%) compared with wild-type cells. Next, we examined the effects of myostatin treatment on chondrogenic differentiation of BMSCs. These experiments show that myostatin treatment starting at either 0 or 48 h induces a significant decrease in collagen type II protein synthesis by 31% (P < 0.001) and 25% (P < 0.05), respectively. Real-time PCR reveals significant (P < 0.01) down regulation of Sox9 mRNA expression with 10 and 100 ng/ml treatments. Together, these findings suggest that myostatin has direct effects on chondrogenesis, and may, therefore, represent a potential therapeutic target for improving bone repair.

Repair and remodeling of partial-weightbearing, uninstrumented long bone fracture model in mice treated with low intensity vibration therapy.

BACKGROUND: While vibration therapy has shown encouraging results across many fields of medicine in the last decade, its role as originally envisioned for bone health remains uncertain. Especially regarding its efficacy in promoting fracture healing, mixed and incomplete outcomes suggest a need to clarify its potential. In particular, the definitive effect of vibration, when isolated from the confounding mechanical inputs of gait and stabilizing instrumentation, remains largely unknown. METHODS: Four cohorts of C57BL/6 male mice underwent single-leg, open fibula fracture. Vibration was applied at 0.3 g to two groups for 20 min/d. At 3 and 6 weeks, fibulae were harvested for microcomputed tomography and 3-point bending to failure. FINDINGS: In bone volume and tissue volume, the groups at each healing time point were statistically not different. At 3 weeks, however, the ratio of bone-to-tissue volume was lower for the vibrated group than control. Likewise, while bone mineral density did not differ, tissue volume density was lowest with vibration. At 6 weeks, mean differences were nominal. Biomechanically, vibration consistently trended ahead of control in strength and stiffness, but did not achieve statistical significance. INTERPRETATION: At this stage of therapeutic development, vibration therapy in isolation does not demonstrate a clear efficacy for bone healing, although further treatment permutations and translational uses remain open for investigation.

Ingestion of gastrolith mineralized matrix increases bone volume and tissue volume in mouse long bone fracture model.

PURPOSE: Fracture healing often requires extended convalescence as the bony fragments consolidate into restored viable tissue for load-bearing. Development of interventions to improve healing remains a priority for orthopaedic research. The goal of this study was to evaluate the ability of a naturally occurring matrix of amorphous calcium carbonate to affect fracture healing in an uninstrumented long bone model. METHODS: Complete transverse fracture was induced in the fibula of mature mice, followed by daily gavage of crushed gastrolith from crayfish at doses of 0 (control), 1 (1 MG), and 5 (5 MG) mg/kg. At Day 17, bones and sera were harvested. RESULTS: Morphologically, the 1 MG treated group had greater bone volume (BV), and both 1 MG and 5 MG had greater tissue volume (TV) than control (p < 0.05), as determined by µCT; BV/TV and mineral density did not yield a statistical difference. Histologically, regional variations in mineralized matrix were evident in all specimens, indicating a broad continuum of healing within the callus. Among serum proteins, bone-specific alkaline phosphatase, indicative of active mineralization, was greater in 5 MG than control (p < 0.05). Sclerostin, an inhibitor of osteogenesis, was lower in 5 MG than control (p < 0.05), also suggestive of enhanced healing. CONCLUSIONS: An increase in bone volume, tissue volume and cellular signaling for osteogenesis at 17 days following fibula fracture in this mouse model suggests that gastrolith treatment holds potential for improving fracture healing. Further study at subsequent time points is warranted to determine the extent to which the increase in callus size with gastrolith treatment may accelerate restoration of tissue integrity.

Loop and knot security of a novel arthroscopic sliding-locking knot using high-strength sutures.

OBJECTIVE: We evaluated the loop and knot security of a novel arthroscopic knot, the Wiese knot, using different types of sutures. METHODS: The Wiese knot was tied using four different brands of braided sutures (Ethibond, Orthocord, FiberWire, and UltraBraid) with and without a series of three reversing half-hitches (RHAPs) and tested for loop and knot security. RESULTS: Orthocord provided the greatest amount of loop security. FiberWire delivered the highest knot security. UltraBraid had the greatest ultimate force. Three half-hitches increased the maximal load to clinical failure. CONCLUSION: The biomechanical characteristics of the Wiese knot are affected by suture material qualities.

Determination of joint loads using new sensate scaffolds for regenerating large cartilage defects in the knee.

Two complete unicondylar surface replacement scaffold designs to support tissue-engineered cartilage growth that utilized adult endogenous stem cells were 3D printed and tested in a dog stifle model. Integrated rosette strain gauges were calibrated and used to determine shear loading within stifle joints for up to 12 months. An activity index that compared extent of daily activity with tissue formation showed differences in the extent and quality of new tissue with the most active animal having the most new tissue formation. Shear loads were highest early and decreased with time indicating that cartilage tissue formation begins while tissues experience high shear loads and continues as the loads decrease toward normal physiological levels. Scaffolds with biomimetic support pegs facilitated the most rapid bone ingrowth and were noted to have more cartilage formation with better quality cartilage as measured using both indentation testing and histology. Comparison of implant placement depth to previous studies suggested that placement depth affects the amount of tissue formation. This study provides measurements of loading patterns and cartilage regeneration on a complete medial condylar surface replacement that can be used for preclinical testing of a tissue engineering approach for the most common form of early stage osteoarthritis, unicondylar disease. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 1409-1421, 2017.

Characterization of primary osteocyte-like cells from rat mandibles.

OBJECTIVE: The mandible is continuously undergoing remodeling as a result of mechanobiologic factors, such as chewing forces, tooth loss, orthodontic forces, and periodontitis. The effects of mechanical stress and biologic signals in bone homeostasis have been the focus of many investigations. However, much of this research utilized osteocytes derived from long bones, but little is known about the mandible-derived osteocytes. This study tests a protocol to isolate and grow osteocytes from rat mandible. STUDY DESIGN: Rat mandibles were harvested, sectioned into small pieces, and subjected to a sequence chemical treatment and enzymatic digestion. The treated tissues were cultured for a few weeks while cells emerged. Cells were sorted by using the osteocyte marker podoplanin, an early marker for osteocyte differentiation. The cells were then characterized according to morphology, biochemical markers (osteocalcin, podoplanin, and sclerostin), and alkaline phosphatase activity and compared with an isotype cell line MLO-Y4 cells. RESULTS: The mandibular osteocytic cells had stellate shape and were positive for osteocalcin, podoplanin, and sclerostin and lower alkaline phosphatase activity compared with MLO-Y4 osteocyte-like cells. CONCLUSIONS: The protocol to isolate osteocyte-like cells will allow the investigators to investigate the mechanobiologic differences in biomechanical response between these mandibular and long bone osteocyte-like cells under various conditions.

Whole-Body Vibration Mimics the Metabolic Effects of Exercise in Male Leptin Receptor-Deficient Mice.

Whole-body vibration (WBV) has gained attention as a potential exercise mimetic, but direct comparisons with the metabolic effects of exercise are scarce. To determine whether WBV recapitulates the metabolic and osteogenic effects of physical activity, we exposed male wild-type (WT) and leptin receptor-deficient (db/db) mice to daily treadmill exercise (TE) or WBV for 3 months. Body weights were analyzed and compared with WT and db/db mice that remained sedentary. Glucose and insulin tolerance testing revealed comparable attenuation of hyperglycemia and insulin resistance in db/db mice following TE or WBV. Both interventions reduced body weight in db/db mice and normalized muscle fiber diameter. TE or WBV also attenuated adipocyte hypertrophy in visceral adipose tissue and reduced hepatic lipid content in db/db mice. Although the effects of leptin receptor deficiency on cortical bone structure were not eliminated by either intervention, exercise and WBV increased circulating levels of osteocalcin in db/db mice. In the context of increased serum osteocalcin, the modest effects of TE and WBV on bone geometry, mineralization, and biomechanics may reflect subtle increases in osteoblast activity in multiple areas of the skeleton. Taken together, these observations indicate that WBV recapitulates the effects of exercise on metabolism in type 2 diabetes.

Inherent physical characteristics and gene expression differences between alveolar and basal bones.

OBJECTIVES: The objective of this study was to evaluate the baseline differences between alveolar and basal areas of the rat mandible. STUDY DESIGN: Rat mandibular alveolar and basal bones were evaluated using histology and micro-computed tomography to compare osteocyte number as well as bone density and architecture and polymerase chain reaction to measure gene expression levels. RESULTS: Micro-computed tomography data indicated that basal bone is denser and less porous than alveolar bone. Histologic analysis showed that alveolar bone has more osteocytes per unit area compared with basal bone. Real-time polymerase chain reaction results showed higher levels of expression of the following genes in basal bone than in alveolar bone: SOST, E-11, DMP-1, and MEPE. CONCLUSIONS: Three of these gene products are associated with mature osteocytes, and this suggests that basal bone has more mature osteocyte phenotypes compared with alveolar bone. These findings are suggestive of fewer bone mineralization units and therefore a slower remodeling rate.

In vivo telemetric determination of shear and axial loads on a regenerative cartilage scaffold following ligament disruption.

Recent interest in repair of chondral and osteochondral cartilage defects to prevent osteoarthritis caused by ligament disruption has led to the research and development of biomimetic scaffolds combined with cell-based regeneration techniques. Current clinical focal defect repair strategies have had limited success. New scaffold-based approaches may provide solutions that can repair extensive damage and prevent osteoarthritis. This study utilized a novel scaffold design that accommodated strain gauges for shear and axial load monitoring in the canine stifle joint through implantable telemetry technology. Loading changes induced by ligament disruption are widely implicated in the development of injury-related osteoarthritis. Seeding the scaffold end with progenitor cells resulted in higher shear stress than without cell seeding and histology showed significantly more bone and cartilage formation. Biomechanically, the effect of transecting the anterior cruciate ligament was a significant reduction in braking load in shear, but no change axially, and conversely a significant reduction in push-off load axially, but no change in shear. This is the first study to report shear loads measured directly in knee joint tissue. Further, advances of these measurement techniques are critical to developing improved regeneration strategies and personalizing reliable rehabilitation protocols.

Sodium-coupled vitamin C transporter (SVCT2): expression, function, and regulation in intervertebral disc cells.

BACKGROUND CONTEXT: Vitamin C (ascorbic acid [AA]) is essential for the synthesis of collagen and also acts as an antioxidant in the intervertebral disc (IVD). However, there is very little information currently available on the identity of the transporter that facilitates AA entry into IVD cells and the factors that mediate the transport process. PURPOSE: To investigate the expression of the two known isoforms of Na+ -coupled vitamin C transporter, SVCT1 and SVCT2, in IVD cells and its regulation by insulin-like growth factor 1 (IGF-1) and the steroid hormone dexamethasone. STUDY DESIGN: To identify the expression and functional activity of the sodium-dependent vitamin C transporter (SVCT) in the IVD. METHODS: Uptake studies were carried out with rabbit annulus fibrosis and nucleus pulposus cells in 24-well plates using [14C]-AA. To characterize SVCT transporter, uptake was done in the presence and absence of Na+ in the uptake buffer. Time dependency, Na+ activation kinetics, saturation kinetics, and substrate selectivity studies were performed. Regulatory studies were performed in the presence of IGF-1 and the steroid hormone dexamethasone. Gene expression was analyzed by quantitative polymerase chain reaction. RESULTS: Our real-time polymerase chain reaction results showed the presence of SVCT2 but not SVCT1 in IVD cells. Uptake of vitamin C in IVD cells is Na+ dependent and saturable. The Michaelis constant for the process is 96±11 µM. The activation of vitamin C uptake by Na+ exhibits a sigmoidal relationship, indicating involvement of more than one Na+ in the activation process. The uptake system does not recognize any other water-soluble vitamin as a substrate. Immunocytochemical analysis shows robust expression of SVCT2 protein in IVD cells. The growth factors IGF-1 and the steroid hormone dexamethasone upregulate the expression of SVCT2 in IVD cells. CONCLUSIONS: Our studies demonstrate that the active SVCT2 is expressed in IVD cells and that the expression of this transporter is regulated by growth factors IGF-1 and dexamethasone.

New technology applications: Knotless barbed suture for tracheal resection anastomosis.

OBJECTIVES/HYPOTHESIS: Tracheal resection anastomoses are often under tension and can be technically challenging. New suture materials such as V-loc (barbed, knotless wound closure device) may offer advantages over conventional methods. The objective of this study is to determine if a running V-loc suture is of comparable tensile strength to conventional closure. STUDY DESIGN: Laboratory based study of human cadaveric tissue. METHODS: Fresh human cadaveric tracheas were dissected and incised into segments. Anastomosis of adjacent segments was then performed with either submucosal interrupted 3-0 Vicryl, or a running submucosal 3-0 V-loc suture. Anastomosed specimens were stretched to failure on an Instron force tension machine. Surgeon satisfaction was recorded by visual analog scale (VAS). RESULTS: The tensile strength of 12 tracheal anastomoses was tested. Video documentation of V-loc suture technique and anastomosis failure was recorded. In both Vicryl (80%) and V-loc (100%) anastomoses, failure occurred at the membranous intercartilaginous region. In 20% of the Vicryl anastomoses, the suture was noted to break prior to tissue failure. Anastomoses with V-loc suture had equivalent failure force (mean, 59 N) compared to interrupted Vicryl (51 N), with P = .57. On VAS, surgeons were more satisfied with V-loc suture closure compared to interrupted Vicryl closure (paired t test, P = .003). CONCLUSIONS: Tracheal anastomosis with running v-loc suture is a feasible alternative to conventional closure with interrupted Vicryl suture. V-loc suture provided a surgical advantage by improved ease of use.

Pneumatic pressure bioreactor for cyclic hydrostatic stress application: mechanobiology effects on periodontal ligament cells.

A bioreactor system was developed to provide high-amplitude cyclic hydrostatic compressive stress (cHSC) using compressed air mixed commercially as needed to create partial pressures of oxygen and carbon dioxide appropriate for the cells under investigation. Operating pressures as high as 300 psi are achievable in this system at cyclic speeds of up to 0.2 Hz. In this study, ligamentous fibroblasts from human periodontal ligaments (n = 6) were compressed on two consecutive days at 150 psi for 3 h each day, and the mRNA for families of extracellular matrix protein and protease isoforms was evaluated by real-time PCR array. Several integrins were significantly upregulated, most notably alpha-3 (6.4-fold), as was SPG7 (12.1-fold). Among the collagens, Col8a1 was highly upregulated at 53.5-fold, with Col6a1, Col6a2, and Col7a1 also significantly upregulated 4.4- to 8.5-fold. MMP-1 was the most affected at 122.9-fold upregulation. MMP-14 likewise increased 17.8-fold with slight reductions for the gelatinases and a significant increase of TIMP-2 at 5.8-fold. The development of this bioreactor system and its utility in characterizing periodontal ligament fibroblast mechanobiology in intermediate-term testing hold promise for better simulating the conditions of the musculoskeletal system and the large cyclic compressive stresses joints may experience in gait, exertion, and mastication.

Lower uncarboxylated osteocalcin concentrations in children with prediabetes is associated with beta-cell function.

CONTEXT: Although animal studies suggest that it is the uncarboxylated rather than carboxylated form of osteocalcin that affects glucose homeostasis, the human data are scant and equivocal. OBJECTIVE: This study investigated associations of uncarboxylated and carboxylated forms of osteocalcin with insulin sensitivity and ß-cell function in 140 overweight prepubertal children (43% female, 46% black, 84% obese) with normal glucose levels (n = 99) and prediabetes (n = 41). METHODS: An oral glucose tolerance test was used to identify prediabetes and for measurement of insulin sensitivity (Matsuda index), ß-cell function [oral glucose tolerance test derived insulinogenic index and disposition index (DI(OGTT))] and uncarboxylated and carboxylated forms of osteocalcin. Visceral adipose tissue (VAT) was assessed using magnetic resonance imaging. RESULTS: After controlling for age, sex and race, lower uncarboxylated osteocalcin concentrations, Matsuda index, insulinogenic index, and DI(OGTT) and higher VAT levels were found in the prediabetes vs. normal-glucose group (all P < 0.03). Carboxylated osteocalcin levels were not different between groups. Multiple linear regression adjusting for age, sex, race, and VAT revealed that uncarboxylated osteocalcin was associated with insulinogenic index and DI(OGTT) (ß = 0.34, 0.36, respectively, both P < 0.04) in the prediabetes group but not the normal-glucose group. In both the normal-glucose and prediabetes groups, carboxylated osteocalcin was associated with insulin sensitivity (ß = 0.26, 0.47, respectively, both P < 0.02). CONCLUSIONS: These data suggest that the lower uncarboxylated osteocalcin concentrations found in children with prediabetes may be associated with ß-cell dysfunction. In addition, our findings between carboxylated osteocalcin and insulin sensitivity suggest that carboxylated osteocalcin plays a role in human glucose homeostasis.

Role of myostatin (GDF-8) signaling in the human anterior cruciate ligament.

Myostatin, also referred to as growth and differentiation factor-8 (GDF-8), is expressed in muscle tissue where it functions to suppress myoblast proliferation and myofiber hypertrophy. Recently, myostatin and its receptor, the type IIB activin receptor (ActRIIB), were detected in the leg tendons of mice, and recombinant myostatin was shown to increase cellular proliferation and the expression of type 1 collagen in primary fibroblasts from mouse tendons. We sought to determine whether myostatin and its receptor were present in human anterior cruciate ligament (ACL) tissue, and if myostatin treatment had any effect on primary ACL fibroblasts. ACL tissue samples were obtained from material discarded during ACL reconstruction surgery. Real-time PCR and immunohistochemistry demonstrate that both myostatin and its receptor are abundant in the human ACL. Primary fibroblasts isolated from human ACL specimens were treated with recombinant myostatin, and myostatin treatment increased fibroblast proliferation as well as the expression of tenascin C (TNC), type 1 collagen, and transforming growth factor-beta1. Real-time PCR analysis of TNC and type 1 collagen expression in ACL specimens from normal mice and mice lacking myostatin supported these findings by showing that both TNC and type 1 collagen were downregulated in ACL tissue from myostatin-deficient mice. Together, these data suggest that myostatin is a pro-fibrogenic factor that enhances cellular proliferation and extracellular matrix synthesis by ACL fibroblasts. Recombinant myostatin may therefore have therapeutic applications in the area of tendon and ligament engineering and regeneration.

Periodontal ligament fibroblasts sustain destructive immune modulators of chronic periodontitis.

BACKGROUND: In healthy periodontal tissue, innate immune responses effectively confine and suppress a bacterial insult. However, a disruption of the host-bacterial equilibrium may produce an overexpression of cytokines and lead to permanent, host-mediated tissue damage. Although such periodontal destruction primarily results from activated immune mechanisms, the site-specific damage suggests that local tissues participate in these pathologic changes. Periodontal ligament fibroblasts (PDLFs) are prominent in the periodontium and are critical in homeostasis and regeneration because they have the ability to produce multiple cytokines in response to a bacterial insult. These cells could play a role in the local pathogenesis of periodontal disease. METHODS: We studied alkaline phosphatase (ALP) activity, interleukin (IL)-6 production, and morphologic characteristics of cultured PDLFs that were isolated from periodontally healthy sites (H-PDLFs) and diseased sites (D-PDLFs) in humans. Quantitative analyses of 84 genes that are related to inflammation were performed using real-time polymerase chain reaction arrays. RESULTS: A mineralizing medium induced a significant increase of ALP in H-PDLFs, but no significant enzymatic changes were detected in D-PDLFs after such treatment. The protein and gene expression of IL6 showed a significant upregulation in D-PDLFs, which also demonstrated a significant upregulation of 54% of genes in the inflammatory gene arrays. CONCLUSIONS: To our knowledge, these results represent the first biologic evidence that D-PDLFs retain uniquely inflammatory phenotypes that could maintain localized destructive signals in periodontitis. The overexpression of proinflammatory cytokines by PDLFs could amplify local inflammation by the continuous triggering of immune responses. In addition, the location of these cells could be critical in the progression of the inflammatory front into the deeper tissues.

Lower bone mass in prepubertal overweight children with prediabetes.

Childhood studies of the fat-bone relationship are conflicting, possibly reflecting the influence of metabolic abnormalities in some but not all obese children. Bone mass was compared between prepubertal overweight children with (n = 41) and without (n = 99) prediabetes. Associations of bone mass with measures of total and central adiposity, glucose intolerance, insulin sensitivity, lipid profile, systemic inflammation, and osteocalcin also were determined. In 140 overweight children aged 7 to 11 years, an oral glucose tolerance test was used to identify those with prediabetes and for determination of glucose, 2-hour glucose, glucose area under the curve (AUC), insulin, 2-hour insulin, and insulin AUC. Blood samples also were assessed for lipids, C-reactive protein, and osteocalcin. Total-body bone mineral content (BMC), fat-free soft tissue mass (FFST), and fat mass (FM) were measured by dual-energy X-ray absorptiometry (DXA). Visceral adipose tissue (VAT) and subcutaneous abdominal adipose tissue (SAAT) were assessed using MRI. Total-body BMC was 4% lower in overweight children with prediabetes than in those without prediabetes after controlling for sex, race, height, and weight (p = .03). In the total sample, FM was positively related with BMC (ß = 0.16, p = .01) after adjusting for sex, race, height, and FFST. However, VAT (ß = -0.13, p = .03) and SAAT (ß = -0.34, p = .02) were inversely associated with BMC after controlling for sex, race, height, FFST, FM, and SAAT or VAT. No significant associations were found between BMC and the biochemical measurements. Prepubertal overweight children with prediabetes may be at risk for poor skeletal development. In addition, it appears that greater levels of central rather than total adiposity may be deleterious for developing bone.

Effect of whole-body vibration on bone properties in aging mice.

Recent studies suggest that whole-body vibration (WBV) can improve measures of bone health for certain clinical conditions and ages. In the elderly, there also is particular interest in assessing the ability of physical interventions such as WBV to improve coordination, strength, and movement speed, which help prevent falls and fractures and maintain ambulation for independent living. The current study evaluated the efficacy of WBV in an aging mouse model. Two levels of vibration--0.5 and 1.5g--were applied at 32Hz to CB57BL/6 male mice (n=9 each) beginning at age 18 months and continuing for 12 weeks, 30 min/day, in a novel pivoting vibration device. Previous reports indicate that bone parameters in these mice begin to decrease substantially at 18 months, equivalent to mid-fifties for humans. Micro-computed tomography (micro-CT) and biomechanical assessments were made in the femur, radius, and lumbar vertebra to determine the effect of these WBV magnitudes and durations in the aging model. Sera also were collected for analysis of bone formation and breakdown markers. Mineralizing surface and cell counts were determined histologically. Bone volume in four regions of the femur did not change significantly, but there was a consistent shift toward higher mean density in the bone density spectrum (BDS), with the two vibration levels producing similar results. This new parameter represents an integral of the conventional density histogram. The amount of high density bone statistically improved in the head, neck, and diaphysis. Biomechanically, there was a trend toward greater stiffness in the 1.5 g group (p=0.139 vs. controls in the radius), and no change in strength. In the lumbar spine, no differences were seen due to vibration. Both vibration groups significantly reduced pyridinoline crosslinks, a collagen breakdown marker. They also significantly increased dynamic mineralization, MS/BS. Furthermore, osteoclasts were most numerous in the 1.5 g group (p≤ 0.05). These findings suggest that some benefits of WBV found in previous studies of young and mature rodent models may extend to an aging population. Density parameters indicated 0.5 g was more effective than 1.5 g. Serological markers, by contrast, favored 1.5 g, while biomechanically and histologically the results were mixed. Although the purported anabolic effect of WBV on bone homeostasis may depend on location and the parameter of interest, this emerging therapy at a minimum does not appear to compromise bone health by the measures studied here.

Myostatin (GDF-8) deficiency increases fracture callus size, Sox-5 expression, and callus bone volume.

Myostatin (GDF-8) is a negative regulator of skeletal muscle growth and mice lacking myostatin show increased muscle mass. We have previously shown that myostatin deficiency increases bone strength and biomineralization throughout the skeleton, and others have demonstrated that myostatin is expressed during the earliest phase of fracture repair. In order to determine the role of myostatin in fracture callus morphogenesis, we studied fracture healing in mice lacking myostatin. Adult wild-type mice (+/+), mice heterozygous for the myostatin mutation (+/-), and mice homozygous for the disrupted myostatin sequence (-/-) were included for study at two and four weeks following osteotomy of the fibula. Expression of Sox-5 and BMP-2 were significantly upregulated in the fracture callus of myostatin-deficient (-/-) mice compared to wild-type (+/+) mice at two weeks following osteotomy. Fracture callus size was significantly increased in mice lacking myostatin at both two and four weeks following osteotomy, and total osseous tissue area and callus strength in three-point bending were significantly greater in myostatin -/- mice compared to myostatin +/+ mice at four weeks post-osteotomy. Our data suggest that myostatin functions to regulate fracture callus size by inhibiting the recruitment and proliferation of progenitor cells in the fracture blastema. Myostatin deficiency increases blastema size during the early inflammatory phase of fracture repair, ultimately producing an ossified callus having greater bone volume and greater callus strength. While myostatin is most well known for its effects on muscle development, it is also clear that myostatin plays a significant, direct role in bone formation and regeneration.