Systemic inhibition or global deletion of CaMKK2 protects against post-traumatic osteoarthritis

OBJECTIVE

To investigate the role of Ca^2+/calmodulin-dependent protein kinase 2 (CaMKK2) in post-traumatic osteoarthritis (PTOA).

METHODS

Destabilization of the medial meniscus (DMM) or sham surgeries were performed on 10-week-old male wild-type (WT) and Camkk2^-/- mice. Half of the DMM-WT mice and all other cohorts (n = 6/group) received tri-weekly intraperitoneal (i.p.) injections of saline whereas the remaining DMM-WT mice (n = 6/group) received i.p. injections of the CaMKK2 inhibitor STO-609 (0.033 mg/kg body weight) thrice a week. Study was terminated at 8- or 12-weeks post-surgery, and knee joints processed for microcomputed tomography imaging followed by histology and immunohistochemistry. Primary articular chondrocytes were isolated from knee joints of 4-6-day-old WT and Camkk2^-/- mice, and treated with 10 ng/ml interleukin-1β (IL)-1β for 24 or 48 h to investigate gene and protein expression.

RESULTS

CaMKK2 levels and activity became elevated in articular chondrocytes following IL-1β treatment or DMM surgery. Inhibition or absence of CaMKK2 protected against DMM-associated destruction of the cartilage, subchondral bone alterations and synovial inflammation. When challenged with IL-1β, chondrocytes lacking CaMKK2 displayed attenuated inflammation, cartilage catabolism, and resistance to suppression of matrix synthesis. IL-1β-treated CaMKK2-null chondrocytes displayed decreased IL-6 production, activation of signal transducer and activator of transcription 3 (Stat3) and matrix metalloproteinase 13 (MMP13), indicating a potential mechanism for the regulation of inflammatory responses in chondrocytes by CaMKK2.

CONCLUSIONS

Our findings reveal a novel function for CaMKK2 in chondrocytes and highlight the potential for its inhibition as an innovative therapeutic strategy in the prevention of PTOA.

The contribution of global aviation to anthropogenic climate forcing for 2000 to 2018

Global aviation operations contribute to anthropogenic climate change via a complex set of processes that lead to a net surface warming. Of importance are aviation emissions of carbon dioxide (CO₂), nitrogen oxides (NO_x), water vapor, soot and sulfate aerosols, and increased cloudiness due to contrail formation. Aviation grew strongly over the past decades (1960-2018) in terms of activity, with revenue passenger kilometers increasing from 109 to 8269 billion km yr^-1, and in terms of climate change impacts, with CO₂ emissions increasing by a factor of 6.8 to 1034 Tg CO₂ yr^-1. Over the period 2013-2018, the growth rates in both terms show a marked increase. Here, we present a new comprehensive and quantitative approach for evaluating aviation climate forcing terms. Both radiative forcing (RF) and effective radiative forcing (ERF) terms and their sums are calculated for the years 2000-2018. Contrail cirrus, consisting of linear contrails and the cirrus cloudiness arising from them, yields the largest positive net (warming) ERF term followed by CO₂ and NO_x emissions. The formation and emission of sulfate aerosol yields a negative (cooling) term. The mean contrail cirrus ERF/RF ratio of 0.42 indicates that contrail cirrus is less effective in surface warming than other terms. For 2018 the net aviation ERF is +100.9 milliwatts (mW) m^-2 (5-95% likelihood range of (55, 145)) with major contributions from contrail cirrus (57.4 mW m^-2), CO₂ (34.3 mW m^-2), and NO_x (17.5 mW m^-2). Non-CO₂ terms sum to yield a net positive (warming) ERF that accounts for more than half (66%) of the aviation net ERF in 2018. Using normalization to aviation fuel use, the contribution of global aviation in 2011 was calculated to be 3.5 (4.0, 3.4) % of the net anthropogenic ERF of 2290 (1130, 3330) mW m^-2. Uncertainty distributions (5%, 95%) show that non-CO₂ forcing terms contribute about 8 times more than CO₂ to the uncertainty in the aviation net ERF in 2018. The best estimates of the ERFs from aviation aerosol-cloud interactions for soot and sulfate remain undetermined. CO₂-warming-equivalent emissions based on global warming potentials (GWP* method) indicate that aviation emissions are currently warming the climate at approximately three times the rate of that associated with aviation CO₂ emissions alone. CO₂ and NO_x aviation emissions and cloud effects remain a continued focus of anthropogenic climate change research and policy discussions.

Parathyroid suppression therapy normalizes chronic kidney disease-induced elevations in cortical bone vascular perfusion: a pilot study

Interventions that alter PTH levels in an animal model of chronic kidney disease have effects on the perfusion of bone and bone marrow.

INTRODUCTION

Patients with chronic kidney disease (CKD) have accelerated bone loss, vascular calcification, and abnormal biochemistries, together contributing to an increased risk of cardiovascular disease and fracture-associated mortality. Despite evidence of vascular pathologies and dysfunction in CKD, our group has shown that cortical bone tissue perfusion is higher in a rat model of high-turnover CKD. The goal of the present study was to test the hypothesis that parathyroid hormone (PTH) suppressive interventions would normalize cortical bone vascular perfusion in the setting of CKD.

METHODS

In two separate experiments, 35-week-old CKD animals and their normal littermates underwent intra-cardiac fluorescent microsphere injection to assess the effect of 10 weeks of PTH suppression (Experiment 1: calcium supplementation, Experiment 2: calcimimetic treatment) on alterations in bone tissue perfusion.

RESULTS

In Experiment 1, CKD animals had serum blood urea nitrogen (BUN) and PTH levels significantly higher than NL (+ 182% and + 958%; p < 0.05). CKD+Ca animals had BUN levels that were similar to CKD, while PTH levels were significantly lower and comparable to NL. Both femoral cortex (+ 220%, p = 0.003) and tibial cortex (+ 336, p = 0.005) tissue perfusion were significantly higher in CKD animals when compared to NL; perfusion was normalized to those of NL in CKD+Ca animals. MicroCT analysis of the proximal tibia cortical porosity showed a trend toward higher values in CKD (+ 401%; p = 0.017) but not CKD+Ca (+ 111%; p = 0.38) compared to NL. Experiment 2, using an alternative method of PTH suppression, showed similar results as those of Experiment 1.

CONCLUSIONS

These data demonstrate that PTH suppression-based interventions normalize cortical bone perfusion in the setting of CKD.

Effects of treadmill running in a rat model of chronic kidney disease

Chronic kidney disease (CKD) progression results in musculoskeletal dysfunction that is associated with a higher likelihood of hospitalization and is predictive of hospitalizations and mortality. Despite this, there is a lack of effective interventions to treat the musculoskeletal dysfunction. We studied treadmill running as an intervention to improve musculoskeletal health in a translational rat model that has slowly progressive CKD. CKD rats were subjected to treadmill exercise or no treadmill exercise for 10 weeks (n = 8 each group). Animals ran for 60 min, 5 times per week starting at a speed of 8 m/min and ending at 18 m/min (1 m/min increase/week). Treadmill training had no effect on muscle strength (assessed as maximally stimulated torque), half-relaxation time (time from peak torque to 50%) or muscle cross-sectional area. Overall, there were no biochemical improvements related to CKD progression. Skeletal muscle catabolism was higher than non-exercised animals without a concomitant change in muscle synthesis markers or regeneration transcription factors. These results suggest that aerobic exercise, achieved via treadmill running was not protective in CKD animals and actually produced potentially harmful effects (increased catabolism). Given the high prevalence and dramatic musculoskeletal mobility impairment in patients with CKD, there is a clear need to understand how to effectively prescribe exercise in order to benefit the musculoskeletal system.

Skeletal accumulation of fluorescently tagged zoledronate is higher in animals with early stage chronic kidney disease

This work examines the skeletal accumulation of fluorescently tagged zoledronate in an animal model of chronic kidney disease. The results show higher accumulation in 24-h post-dose animals with lower kidney function due to greater amounts of binding at individual surfaces.

INTRODUCTION

Chronic kidney disease (CKD) patients suffer from increased rates of skeletal-related mortality from changes driven by biochemical abnormalities. Bisphosphonates are commonly used in reducing fracture risk in a variety of diseases, yet their use is not recommended in advanced stages of CKD. This study aimed to characterize the accumulation of a single dose of fluorescently tagged zoledronate (FAM-ZOL) in the setting of reduced kidney function.

METHODS

At 25 weeks of age, FAM-ZOL was administered to normal and CKD rats. Twenty-four hours later, multiple bones were collected and assessed using bulk fluorescence imaging, two-photon imaging, and dynamic histomorphometry.

RESULTS

CKD animals had significantly higher levels of FAM-ZOL accumulation in the proximal tibia, radius, and ulna, but not in lumbar vertebral body or mandible, based on multiple measurement modalities. Although a majority of trabecular bone surfaces were covered with FAM-ZOL in both normal and CKD animals, the latter had significantly higher levels of fluorescence per unit bone surface in the proximal tibia.

CONCLUSIONS

These results provide new data regarding how reduced kidney function affects drug accumulation in rat bone.

Measuring and modeling surface sorption dynamics of organophosphate flame retardants on impervious surfaces

Understanding the sorption mechanisms for organophosphate flame retardants (OPFRs) on impervious surfaces is important to improve our knowledge of the fate and transport of OPFRs in indoor environments. The sorption processes of semivolatile organic compounds (SVOCs) on indoor surfaces are heterogeneous (multilayer sorption) or homogeneous (monolayer sorption). In this study, we adopted simplified Langmuir isotherm and Freundlich isotherm in a dynamic sink model to characterize the sorption dynamics of OPFRs on impervious surfaces such as stainless steel and made comparisons between the two models through a series of empty chamber studies. The tests involve two types of stainless steel chambers (53-L small chambers and 44-mL micro chambers) using tris(2-chloroethyl)phosphate (TCEP) and tris(1-chloro-2-propyl)phosphate (TCPP) as target compounds. Our test results show that the dynamic sink model using Freundlich isotherm can better represent the sorption process in the empty small chamber. Micro chamber test results from this study show that the sink model using both simplified Langmuir isotherm and Freundlich isotherm can well fit the measured gas-phase concentrations of OPFRs. We further applied both models and the parameters obtained to predict the gas phase concentrations of OPFRs in a small chamber with an emission source. Comparisons between model predictions and measurements demonstrate the reliability and applicability of the sorption parameters.

A real-time Global Warming Index

We propose a simple real-time index of global human-induced warming and assess its robustness to uncertainties in climate forcing and short-term climate fluctuations. This index provides improved scientific context for temperature stabilisation targets and has the potential to decrease the volatility of climate policy. We quantify uncertainties arising from temperature observations, climate radiative forcings, internal variability and the model response. Our index and the associated rate of human-induced warming is compatible with a range of other more sophisticated methods to estimate the human contribution to observed global temperature change.

Zoledronate treatment has different effects in mouse strains with contrasting baseline bone mechanical phenotypes

Two strains of mice with distinct bone morphologies and mechanical properties were treated with zoledronate. Our results show a different response to drug treatment in the two strains providing evidence that baseline properties of structure/material may influence response to zoledronate.

INTRODUCTION

Bisphosphonates are highly effective in reducing fracture risk, yet some individuals treated with these agents still experience fracture. The goal of this study was to test the hypothesis that genotype influences the effect of zoledronate on bone mechanical properties.

METHODS

Skeletally mature male mice from genetic backgrounds known to have distinct baseline post-yield properties (C57/B6, high post-yield displacement; A/J, low post-yield displacement) were treated for 8 weeks with saline (VEH) or zoledronate (ZOL, 0.06 mg/kg subcutaneously once every 4 weeks) in a 2 × 2 study design. Ex vivo μCT and mechanical testing (4-pt bending) were conducted on the femur to assess morphological and mechanical differences.

RESULTS

Significant drug and/or genotype effects were found for several mechanical properties and significant drug × genotype interactions were found for measures of strength (ultimate force) and brittleness (total displacement, strain to failure). Treatment with ZOL affected bone biomechanical measures of brittleness (total displacement (-25 %) and strain to failure (-23 %)) in B6 mice significantly differently than in A/J mice. This was driven by unique drug × genotype effects on bone geometry in B6 animals yet likely also reflected changes to the tissue properties.

CONCLUSION

These data may support the concept that properties of the bone geometry and/or tissue at the time of treatment initiation play a role in determining the bone's mechanical response to zoledronate treatment.

Simulating the Lunar Environment: Partial Weightbearing and High-LET Radiation-Induce Bone Loss and Increase Sclerostin-Positive Osteocytes

Exploration missions to the Moon or Mars will expose astronauts to galactic cosmic radiation and low gravitational fields. Exposure to reduced weightbearing and radiation independently result in bone loss. However, no data exist regarding the skeletal consequences of combining low-dose, high-linear energy transfer (LET) radiation and partial weightbearing. We hypothesized that simulated galactic cosmic radiation would exacerbate bone loss in animals held at one-sixth body weight (G/6) without radiation exposure. Female BALB/cByJ four-month-old mice were randomly assigned to one of the following treatment groups: 1 gravity (1G) control; 1G with radiation; G/6 control; and G/6 with radiation. Mice were exposed to either silicon-28 or X-ray radiation. (28)Si radiation (300 MeV/nucleon) was administered at acute doses of 0 (sham), 0.17 and 0.5 Gy, or in three fractionated doses of 0.17 Gy each over seven days. X radiation (250 kV) was administered at acute doses of 0 (sham), 0.17, 0.5 and 1 Gy, or in three fractionated doses of 0.33 Gy each over 14 days. Bones were harvested 21 days after the first exposure. Acute 1 Gy X-ray irradiation during G/6, and acute or fractionated 0.5 Gy (28)Si irradiation during 1G resulted in significantly lower cancellous mass [percentage bone volume/total volume (%BV/TV), by microcomputed tomography]. In addition, G/6 significantly reduced %BV/TV compared to 1G controls. When acute X-ray irradiation was combined with G/6, distal femur %BV/TV was significantly lower compared to G/6 control. Fractionated X-ray irradiation during G/6 protected against radiation-induced losses in %BV/TV and trabecular number, while fractionated (28)Si irradiation during 1G exacerbated the effects compared to single-dose exposure. Impaired bone formation capacity, measured by percentage mineralizing surface, can partially explain the lower cortical bone thickness. Moreover, both partial weightbearing and (28)Si-ion exposure contribute to a higher proportion of sclerostin-positive osteocytes in cortical bone. Taken together, these data suggest that partial weightbearing and low-dose, high-LET radiation negatively impact maintenance of bone mass by lowering bone formation and increasing bone resorption. The impaired bone formation response is associated with sclerostin-induced suppression of Wnt signaling. Therefore, exposure to low-dose, high-LET radiation during long-duration spaceflight missions may reduce bone formation capacity, decrease cancellous bone mass and increase bone resorption. Future countermeasure strategies should aim to restore mechanical loads on bone to those experienced in one gravity. Moreover, low-doses of high-LET radiation during long-duration spaceflight should be limited or countermeasure strategies employed to mitigate bone loss.

Changes in skeletal collagen cross-links and matrix hydration in high- and low-turnover chronic kidney disease

Chronic kidney disease (CKD) increases fracture risk. The results of this work point to changes in bone collagen and bone hydration as playing a role in bone fragility associated with CKD.

INTRODUCTION

Clinical data have documented a clear increase in fracture risk associated with chronic kidney disease (CKD). Preclinical studies have shown reductions in bone mechanical properties although the tissue-level mechanisms for these differences remain unclear. The goal of this study was to assess collagen cross-links and matrix hydration, two variables known to affect mechanical properties, in animals with either high- or low-turnover CKD.

METHODS

At 35 weeks of age (>75% reduction in kidney function), the femoral diaphysis of male Cy/+ rats with high or low bone turnover rates, along with normal littermate (NL) controls, were assessed for collagen cross-links (pyridinoline (Pyd), deoxypyridinoline (Dpd), and pentosidine (PE)) using a high-performance liquid chromatography (HPLC) assay as well as pore and bound water per volume (pw and bw) using a (1)H nuclear magnetic resonance (NMR) technique. Material-level biomechanical properties were calculated based on previously published whole bone mechanical tests.

RESULTS

Cortical bone from animals with high-turnover disease had lower Pyd and Dpd cross-link levels (-21% each), lower bw (-10%), higher PE (+71%), and higher pw (+46%) compared to NL. Animals with low turnover had higher Dpd, PE (+71%), and bw (+7%) along with lower pw (-60%) compared to NL. Both high- and low-turnover animals had reduced material-level bone toughness compared to NL animals as determined by three-point bending.

CONCLUSIONS

These data document an increase in skeletal PE with advanced CKD that is independent of bone turnover rate and inversely related to decline in kidney function. Although hydration changes occur in both high- and low-turnover disease, the data suggest that nonenzymatic collagen cross-links may be a key factor in compromised mechanical properties of CKD.

Calcium and vitamin D intake maintained from preovariectomy independently affect calcium metabolism and bone properties in Sprague Dawley rats

The interaction of habitual Ca and vitamin D intake from preovariectomy to 4 months postovariectomy on bone and Ca metabolism was assessed. Higher Ca intake suppressed net bone turnover, and both nutrients independently benefitted trabecular structure. Habitual intake of adequate Ca and ~50 nmol/L vitamin D status is most beneficial.

INTRODUCTION

Dietary strategies to benefit bone are typically tested prior to or after menopause but not through menopause transition. We investigated the interaction of Ca and vitamin D status on Ca absorption, bone remodeling, Ca kinetics, and bone strength as rats transitioned through estrogen deficiency.

METHODS

Sprague Dawley rats were randomized at 8 weeks to 0.2 or 1.0 % Ca and 50, 100, or 1,000 IU (1.25, 2.5, or 25 μg) vitamin D/kg diet (2 × 3 factorial design) and ovariectomized at 12 weeks. Urinary (45)Ca excretion from deep-labeled bone was used to assess net bone turnover weekly. Ca kinetics was performed between 25 and 28 weeks. Rats were killed at 29 weeks. Femoral and tibiae structure (by μCT), dynamic histomorphometry, and bone Ca content were assessed.

RESULTS

Mean 25(OH)D for rats on the 50, 100, 1,000 IU vitamin D/kg diet were 32, 54, and 175 nmol/L, respectively. Higher Ca intake ameliorated net bone turnover, reduced fractional Ca absorption and bone resorption, and increased net Ca absorption. Tibial and femoral trabecular structures were enhanced independently by higher Ca and vitamin D intake. Tibial bone width and fracture resistance were enhanced by higher vitamin D intake. Dynamic histomorphometry in the tibia was not affected by either nutrient. A Ca × vitamin D interaction existed in femur length, tibial Ca content, and mass of the soft tissue/extracellular fluid compartment.

CONCLUSIONS

Adequate Ca intake and serum 25(OH)D level of 50 nmol/L provided the most benefit for bone health, mostly through independent effects of Ca and vitamin D.

Intracortical bone remodeling variation shows strong genetic effects

Intracortical microstructure influences crack propagation and arrest within bone cortex. Genetic variation in intracortical remodeling may contribute to mechanical integrity and, therefore, fracture risk. Our aim was to determine the degree to which normal population-level variation in intracortical microstructure is due to genetic variation. We examined right femurs from 101 baboons (74 females, 27 males; aged 7-33 years) from a single, extended pedigree to determine osteon number, osteon area (On.Ar), haversian canal area, osteon population density, percent osteonal bone (%On.B), wall thickness (W.Th), and cortical porosity (Ct.Po). Through evaluation of the covariance in intracortical properties between pairs of relatives, we quantified the contribution of additive genetic effects (heritability [h (2)]) to variation in these traits using a variance decomposition approach. Significant age and sex effects account for 9 % (Ct.Po) to 21 % (W.Th) of intracortical microstructural variation. After accounting for age and sex, significant genetic effects are evident for On.Ar (h (2) = 0.79, p = 0.002), %On.B (h (2) = 0.82, p = 0.003), and W.Th (h (2) = 0.61, p = 0.013), indicating that 61-82 % of the residual variation (after accounting for age and sex effects) is due to additive genetic effects. This corresponds to 48-75 % of the total phenotypic variance. Our results demonstrate that normal, population-level variation in cortical microstructure is significantly influenced by genes. As a critical mediator of crack behavior in bone cortex, intracortical microstructural variation provides another mechanism through which genetic variation may affect fracture risk.

Skeletal effects of zoledronic acid in an animal model of chronic kidney disease

Bisphosphonates reduce skeletal loss and fracture risk, but their use has been limited in patients with chronic kidney disease. This study shows skeletal benefits of zoledronic acid in an animal model of chronic kidney disease.

INTRODUCTION

Bisphosphonates are routinely used to reduce fractures but limited data exists concerning their efficacy in non-dialysis chronic kidney disease. The goal of this study was to test the hypothesis that zoledronic acid produces similar skeletal effects in normal animals and those with kidney disease.

METHODS

At 25 weeks of age, normal rats were treated with a single dose of saline vehicle or 100 μg/kg of zoledronic acid while animals with kidney disease (approximately 30% of normal kidney function) were treated with vehicle, low dose (20 μg/kg), or high dose (100 μg/kg) zoledronic acid, or calcium gluconate (3% in the drinking water). Skeletal properties were assessed 5 weeks later using micro-computed tomography, dynamic histomorphometry, and mechanical testing.

RESULTS

Animals with kidney disease had significantly higher trabecular bone remodeling compared to normal animals. Zoledronic acid significantly suppressed remodeling in both normal and diseased animals yet the remodeling response to zoledronic acid was no different in normal and animals with kidney disease. Animals with kidney disease had significantly lower cortical bone biomechanical properties; these were partially normalized by treatment.

CONCLUSIONS

Based on these results, we conclude that zoledronic acid produces similar amounts of remodeling suppression in animals with high turnover kidney disease as it does in normal animals, and has positive effects on select biomechanical properties that are similar in normal animals and those with chronic kidney disease.

Three years of alendronate treatment does not continue to decrease microstructural stresses and strains associated with trabecular microdamage initiation beyond those at 1 year

The effects of a 3-year alendronate treatment on trabecular stresses/strains associated with microdamage initiation were investigated using finite element modeling (FEM). Severely damaged trabeculae in the low-dose treatment group were associated with increased stresses compared with the high-dose treatment group (p = 0.006) and approached significance in the control group (p = 0.02).

INTRODUCTION

Alendronate, a commonly prescribed anti-remodeling agent, decreases fracture risk in the vertebrae, hip, and wrist of osteoporotic individuals. However, evaluation of microdamage accumulation in animal and human studies shows increased microdamage density relative to controls. Microstructural von Mises stresses associated with severe and linear damage have been found to decrease after 1 year of alendronate treatment. In the present study, stresses/strains associated with damage were assessed after 3 years of treatment to determine whether they continued to decrease with increased treatment duration.

METHODS

Microdamaged trabeculae visualized with fluorescent microscopy were associated with stresses and strains obtained using image-based FEM. Stresses/strains associated with severe, diffuse, and linearly damaged and undamaged trabeculae were compared among groups treated for 3 years with an osteoporotic treatment dose of alendronate, a Paget's disease treatment dose of alendronate, or saline control. Architectural characteristics and mineralization were also analyzed from three-dimensional microcomputed tomography reconstructed images.

RESULTS

Severely damaged trabeculae in the osteoporotic treatment dose group were associated with increased stress compared with the Paget's disease treatment dose group (p = 0.006) and approached significance compared to the control group (p = 0.02). Trabecular mineralization in severely damaged trabeculae of the low-dose treatment group was significantly greater compared to severely damaged trabeculae in the high-dose treatment and control group, suggesting that changes at the tissue level may play a role in these findings.

CONCLUSIONS

Trabecular level stresses associated with microdamage do not continue to decrease with prolonged alendronate treatment. Changes in mineralization may account for these findings.

Ovariectomy stimulates and bisphosphonates inhibit intracortical remodeling in the mouse mandible

OBJECTIVE

The pathophysiology of osteonecrosis of the jaw (ONJ) is thought to be linked to suppression of intracortical remodeling. The aim of this study was to determine whether mice, which normally do not undergo appreciable amounts of intracortical remodeling, could be stimulated by ovariectomy to remodel within the cortex of the mandible and if bisphosphonates (BPs) would suppress this intracortical remodeling.

MATERIAL AND METHODS

Skeletally mature female C3H mice were either ovariectomized (OVX) or SHAM operated and treated with two intravenous doses of zoledronic acid (ZOL, 0.06 mg/kg body weight) or vehicle (VEH). This ZOL dose corresponds to the dose given to patients with cancer on a mg/kg basis, adjusted for body weight. Calcein was administered prior to sacrifice to label active formation sites. Dynamic histomorphometry of the mandible and femur was performed.

RESULTS

Vehicle-treated OVX animals had significantly higher (eightfold) intracortical remodeling of the alveolar portion of the mandible compared to sham--this was significantly suppressed by ZOL treatment. At all skeletal sites, overall bone formation rate was lower with ZOL treatment compared to the corresponding VEH group.

CONCLUSIONS

Under normal conditions, the level of intracortical remodeling in the mouse mandible is minimal but in C3H mice it can be stimulated to appreciable levels with ovariectomy. Based on this, if the suppression of intracortical remodeling is found to be part of the pathophysiology of ONJ, the ovariectomized C3H mouse could serve as a useful tool for studying this condition.

Compromised osseous healing of dental extraction sites in zoledronic acid-treated dogs

The goal of this study was to document how treatment with high doses of zoledronic acid affects dental extraction healing. Our results, showing significantly compromised osseous healing within the socket as well as presence of exposed bone and development of a sequestrum in one animal, provide a building block toward understanding osteonecrosis of the jaw.

PURPOSE

The goal of this study was to document how treatment with a bisphosphonate affects the bone tissue following dental extraction.

METHODS

Skeletally mature female beagle dogs were either untreated controls (CON) or treated with intravenous zoledronic acid (ZOL). Following the extraction of the fourth premolars, healing was allowed for 4 or 8 weeks. Properties of the extraction site were assessed using microcomputed tomography (micro-CT) and dynamic histomorphometry.

RESULTS

The initial infilling of the extraction socket with bone was not affected by ZOL, but subsequent removal of this bone was significantly suppressed compared to CON. After 8 weeks of healing, the alveolar cortical bone adjacent to the extraction socket had a remodeling rate of ∼50% per year in CON animals while ZOL-treated animals had a rate of <1% per year. One ZOL-treated animal developed exposed bone post-extraction which eventually led to the formation of a sequestrum. Assessment of the sequestrum with micro-CT and histology showed that it had features consistent with those reported in humans with osteonecrosis of the jaw.

CONCLUSIONS

These results, showing significantly compromised post-extraction osseous healing as well as presence of exposed bone and development of a sequestrum in one ZOL animal, provide a building block toward understanding the pathophysiology of osteonecrosis of the jaw.

Heritability of lumbar trabecular bone mechanical properties in baboons

Genetic effects on mechanical properties have been demonstrated in rodents, but not confirmed in primates. Our aim was to quantify the proportion of variation in vertebral trabecular bone mechanical properties that is due to the effects of genes. L3 vertebrae were collected from 110 females and 46 male baboons (6-32 years old) from a single extended pedigree. Cranio-caudally oriented trabecular bone cores were scanned with microCT then tested in monotonic compression to determine apparent ultimate stress, modulus, and toughness. Age and sex effects and heritability (h(2)) were assessed using maximum likelihood-based variance components methods. Additive effects of genes on residual trait variance were significant for ultimate stress (h(2)=0.58), toughness (h(2)=0.64), and BV/TV (h(2)=0.55). When BV/TV was accounted for, the residual variance in ultimate stress accounted for by the additive effects of genes was no longer significant. Toughness, however, showed evidence of a non-BV/TV-related genetic effect. Overall, maximum stress and modulus show strong genetic effects that are nearly entirely due to bone volume. Toughness shows strong genetic effects related to bone volume and shows additional genetic effects (accounting for 10% of the total trait variance) that are independent of bone volume. These results support continued use of bone volume as a focal trait to identify genes related to skeletal fragility, but also show that other focal traits related to toughness and variation in the organic component of bone matrix will enhance our ability to find additional genes that are particularly relevant to fatigue-related fractures.

Mandibular necrosis in beagle dogs treated with bisphosphonates

OBJECTIVES - To test the effect of bisphosphonate (BP) treatment for up to 3 years on bone necrosis and osteocyte death in the mandible using a canine model. MATERIALS AND METHODS - Dogs were treated with clinical doses of oral alendronate (ALN, 0.2 or 1.0 mg/kg/day) for 1 or 3 years. In a separate study, dogs were treated with i.v. zoledronate (ZOL) at 0.06 mg/kg/day for 6 months. En bloc staining was used to identify necrotic areas in the mandible; viable osteocytes were identified using lactate dehydrogenase. RESULTS - None of the treatments was associated with exposed bone, but 17-25% of dogs treated for 1 year and 25-33% of dogs treated for 3 years with ALN showed pockets of dead bone. Necrotic areas had no viable osteocytes and were void of patent canaliculi. No control animals demonstrated necrotic bone. ZOL treatment for 6 months was associated with osteocyte death greater than that seen in animals treated with ALN or saline. It is not clear whether osteocyte death occurs because of direct toxic effects of BPs, or because suppressed remodelling fails to renew areas that naturally undergo cell death. Necrotic areas are also associated with bone other than the mandible, e.g. the rib, which normally undergo high rates of remodelling. CONCLUSIONS - Reduced remodelling rate using BPs may contribute to the pathogenesis of bone matrix necrosis. The development of an animal model that mimics important aspects of BP-related osteonecrosis of the jaw is important to understanding the pathogenesis of osteonecrosis.

Changes in non-enzymatic glycation and its association with altered mechanical properties following 1-year treatment with risedronate or alendronate

SUMMARY

One year of high-dose bisphosphonate (BPs) therapy in dogs allowed the increased accumulation of advanced glycation end-products (AGEs) and reduced postyield work-to-fracture of the cortical bone matrix. The increased accumulation of AGEs in these tissues may help explain altered bone matrix quality due to the administration of BPs in animal models

INTRODUCTION

Non-enzymatic glycation (NEG) is a posttranslational modification of the organic matrix that results in the formation of advanced glycation end-products (AGEs). In bone, the accumulation of AGEs play an important role in determining fracture resistance, and elevated levels of AGEs have been shown to adversely affect the bone's propensity to brittle fracture. It was thus hypothesized that the suppression of tissue turnover in cortical bone due to the administration of bisphosphonates would cause increased accumulation of AGEs and result in a more brittle bone matrix.

METHODS

Using a canine animal model (n = 12), we administered daily doses of a saline vehicle (VEH), alendronate (ALN 0.20, 1.00 mg/kg) or risedronate (RIS 0.10, 0.50 mg/kg). After a 1-year treatment, the mechanical properties, intracortical bone turnover, and the degree of nonenzymatic cross-linking of the organic matrix were measured from the tibial cortical bone tissue of these animals.

RESULTS

There was a significant accumulation of AGEs at high treatment doses (+49 to + 86%; p < 0.001), but not at doses equivalent to those used for the treatment of postmenopausal osteoporosis, compared to vehicle. Likewise, postyield work-to-fracture of the tissue was significantly reduced at these high doses (-28% to -51%; p < 0.001) compared to VEH. AGE accumulation inversely correlated with postyield work-to-fracture (r (2) = 0.45; p < 0.001), suggesting that increased AGEs may contribute to a more brittle bone matrix.

CONCLUSION

High doses of bisphosphonates result in the accumulation of AGEs and a reduction in energy absorption of cortical bone. The increased accumulation of AGEs in these tissues may help explain altered bone matrix quality due to the administration of BPs in animal models.

The climateprediction.net BBC climate change experiment: design of the coupled model ensemble

Perturbed physics experiments are among the most comprehensive ways to address uncertainty in climate change forecasts. In these experiments, parameters and parametrizations in atmosphere-ocean general circulation models are perturbed across ranges of uncertainty, and results are compared with observations. In this paper, we describe the largest perturbed physics climate experiment conducted to date, the British Broadcasting Corporation (BBC) climate change experiment, in which the physics of the atmosphere and ocean are changed, and run in conjunction with a forcing ensemble designed to represent uncertainty in past and future forcings, under the A1B Special Report on Emissions Scenarios (SRES) climate change scenario.

Strontium ranelate does not stimulate bone formation in ovariectomized rats

INTRODUCTION

Strontium ranelate (SrR) is suggested to function as a dual-acting agent in the treatment of postmenopausal osteoporosis with anti-resorptive and anabolic skeletal benefits. We evaluated the effects of SrR on the skeleton in ovariectomized (OVX) rats and evaluated the influence of dietary calcium.

METHODS

Three-month old virgin female rats underwent ovariectomy (OVX, n = 50) or SHAM surgery (SHAM, n = 10). Four weeks post-surgery, rats were treated daily by oral gavage with distilled water (10 ml/kg/day) or SrR (25 or 150 mg/kg/day) for 90 days. Separate groups of animals for each dose of SrR were fed a low (0.1%) or normal (1.19%) calcium (Ca) diet. Static and dynamic histomorphometry, DXA, mu-CT, mechanical testing, and serum and skeletal concentrations of strontium were assessed.

RESULTS

SrR at doses of 25 and 150 mg/kg/day did not increase bone formation on trabecular or periosteal bone surfaces, and failed to inhibit bone resorption of trabecular bone regardless of Ca intake. There were no improvements in bone mass, volume or strength with either dose of SrR given normal Ca.

CONCLUSION

These findings demonstrate that SrR at dosages of 25 and 150 mg/kg/day did not stimulate an anabolic bone response, and failed to improve the bone biomechanical properties of OVX rats.

Bisphosphonates alter trabecular bone collagen cross-linking and isomerization in beagle dog vertebra

Changes in organic matrix may contribute to the anti-fracture efficacy of anti-remodeling agents. Following one year of treatment in beagle dogs, bisphosphonates alter the organic matrix of vertebral trabecular bone, while raloxifene had no effect. These results show that pharmacological suppression of turnover alters the organic matrix component of bone.

INTRODUCTION

The collagen matrix contributes significantly to a bone's fracture resistance yet the effects of anti-remodeling agents on collagen properties are unclear. The goal of this study was to assess changes in collagen cross-linking and isomerization following anti-remodeling treatment.

METHODS

Skeletally mature female beagles were treated for one year with oral doses of vehicle (VEH), risedronate (RIS; 3 doses), alendronate (ALN; 3 doses), or raloxifene (RAL; 2 doses). The middle dose of RIS and ALN and the lower dose of RAL approximate doses used for treatment of post menopausal osteoporosis. Vertebral trabecular bone matrix was assessed for collagen isomerization (ratio of alpha/beta C-telopeptide [CTX]), enzymatic (pyridinoline [PYD] and deoxypyridinoline [DPD]), and non-enzymatic (pentosidine [PEN]) cross-links.

RESULTS

All doses of both RIS and ALN increased PEN (+34-58%) and the ratio of PYD/DPD (+14-26%), and decreased the ratio of alpha/beta CTX (-29-56%) compared to VEH. RAL did not alter any collagen parameters. Bone turnover rate was significantly correlated to PEN (R = -0.664), alpha/beta CTX (R = 0.586), and PYD/DPD (R = -0.470).

CONCLUSIONS

Bisphosphonate treatment significantly alters properties of bone collagen suggesting a contribution of the organic matrix to the anti-fracture efficacy of this drug class.

Changes in vertebral strength-density and energy absorption-density relationships following bisphosphonate treatment in beagle dogs

We aimed to determine the effects of bisphosphonates on mechanical properties independent of changes in bone density. Our results show that at equivalent bone densities, vertebrae from beagles treated with bisphosphonate have equivalent bone strength and reduced bone energy absorption compared to those from untreated animals.

INTRODUCTION

Assessing the relationship between mechanical properties and bone density allows a biomechanical evaluation of bone quality, with differences at a given density indicative of altered quality. The purpose of this study was to evaluate the strength-density and energy absorption-density relationships in vertebral bone following a one-year treatment with clinical doses of two different bisphosphonates in beagle dogs.

METHODS

Areal bone mineral density (aBMD) and compressive mechanical properties (ultimate load and energy absorption) were assessed on lumbar vertebrae from skeletally mature beagle dogs treated with vehicle (VEH), alendronate (ALN), or risedronate (RIS). Relationships among properties were assessed using analyses of covariance.

RESULTS

Neither treatment altered the strength-density relationship compared to VEH, suggesting increases in vertebral strength with bisphosphonate-treatment are explained by increased density. The energy absorption-density relationship was altered by ALN, resulting in significantly lower energy absorption capacity at a given aBMD compared to both VEH (-22%) and RIS (-14%).

CONCLUSIONS

These data document that after adjusting for increased aBMD, vertebrae from animals treated with bisphosphonates have similar strength as those from untreated animals. Conversely, when adjusted for increased aBMD, alendronate treatment, but not risedronate treatment, significantly reduces the energy required for vertebral fracture, indicative of an alteration in bone quality.

Probabilistic climate forecasts and inductive problems

The development of ensemble-based 'probabilistic' climate forecasts is often seen as a promising avenue for climate scientists. Ensemble-based methods allow scientists to produce more informative, nuanced forecasts of climate variables by reflecting uncertainty from various sources, such as similarity to observation and model uncertainty. However, these developments present challenges as well as opportunities, particularly surrounding issues of experimental design and interpretation of forecast results. This paper discusses different approaches and attempts to set out what climateprediction.net and other large ensemble, complex model experiments might contribute to this research programme.

Confidence, uncertainty and decision-support relevance in climate predictions

Over the last 20 years, climate models have been developed to an impressive level of complexity. They are core tools in the study of the interactions of many climatic processes and justifiably provide an additional strand in the argument that anthropogenic climate change is a critical global problem. Over a similar period, there has been growing interest in the interpretation and probabilistic analysis of the output of computer models; particularly, models of natural systems. The results of these areas of research are being sought and utilized in the development of policy, in other academic disciplines, and more generally in societal decision making. Here, our focus is solely on complex climate models as predictive tools on decadal and longer time scales. We argue for a reassessment of the role of such models when used for this purpose and a reconsideration of strategies for model development and experimental design. Building on more generic work, we categorize sources of uncertainty as they relate to this specific problem and discuss experimental strategies available for their quantification. Complex climate models, as predictive tools for many variables and scales, cannot be meaningfully calibrated because they are simulating a never before experienced state of the system; the problem is one of extrapolation. It is therefore inappropriate to apply any of the currently available generic techniques which utilize observations to calibrate or weight models to produce forecast probabilities for the real world. To do so is misleading to the users of climate science in wider society. In this context, we discuss where we derive confidence in climate forecasts and present some concepts to aid discussion and communicate the state-of-the-art. Effective communication of the underlying assumptions and sources of forecast uncertainty is critical in the interaction between climate science, the impacts communities and society in general.

Antiremodeling agents influence osteoblast activity differently in modeling and remodeling sites of canine rib

Antiremodeling agents reduce bone loss in part through direct actions on osteoclasts. Their effects on osteoblasts and bone formation activity are less clear and may differ at sites undergoing modeling vs. remodeling. Skeletally mature intact beagles, 1-2 years old at the start of the study, were treated daily with clinically relevant doses of alendronate (0.10 or 0.20 mg/kg), risedronate (0.05 or 0.10 mg/kg), raloxifene (0.50 mg/kg), or vehicle (1 mL/kg). Dynamic bone formation parameters were histologically assessed on periosteal, endocortical/trabecular, and intracortical bone envelopes of the rib. Raloxifene significantly increased periosteal surface mineral apposition rate (MAR), a measure of osteoblast activity, compared to all other treatments (+108 to +175%, P < 0.02), while having no significant effect on MAR at either the endocortical/trabecular or intracortical envelope. Alendronate (both 0.10 and 0.20 doses) and risedronate (only the 0.10 dose) significantly (P < or = 0.05) suppressed MAR on the endocortical/trabecular envelope, while none of the bisphosphonate doses significantly altered MAR at either the periosteal or intracortical envelopes compared to vehicle. Based on these results, we conclude that (1) at clinically relevant doses the two classes of antiremodeling agents, bisphosphonates and selective estrogen receptor modulators, exert differential effects on osteoblast activity in the canine rib and (2) this effect depends on whether modeling or remodeling is the predominant mechanism of bone formation.

Differential bone and muscle recovery following hindlimb unloading in skeletally mature male rats

This study was designed to track the recovery of bone and muscle properties after 28 days of hindlimb unloading (HU) in skeletally mature male rats in order to quantify the degree and timing of the expected mismatch between bone and muscle properties. Outcome variables were in vivo plantarflexor peak isometric torque and proximal tibial volumetric bone mineral density (vBMD). Proximal tibia vBMD was significantly lower than age-matched controls (-7.8%) after 28 days of HU, continued to decrease through day 28 of recovery (-10%) and did not recover until day 84 of recovery. Plantarflexor peak isometric torque was significantly reduced after 28 days of HU (-13.9%). Further reductions of isometric torque occurred after 7 days of recovery (-15%), but returned to age-matched control levels by day 14. The functional relationship between bone and muscle (vBMD/isometric torque) tended to increase after 28 days of HU (+7.8%), remained elevated after 7 days of reloading (+9.1%) and was significantly lower than age-matched controls on day 28 (-13.6%). This relatively rapid return of muscle strength, coupled with continued depression of bone density at the proximal tibia metaphysis, may increase the risk for skeletal injury during recovery from prolonged periods of reduced mechanical loading.

Uncertainty in predictions of the climate response to rising levels of greenhouse gases

The range of possibilities for future climate evolution needs to be taken into account when planning climate change mitigation and adaptation strategies. This requires ensembles of multi-decadal simulations to assess both chaotic climate variability and model response uncertainty. Statistical estimates of model response uncertainty, based on observations of recent climate change, admit climate sensitivities--defined as the equilibrium response of global mean temperature to doubling levels of atmospheric carbon dioxide--substantially greater than 5 K. But such strong responses are not used in ranges for future climate change because they have not been seen in general circulation models. Here we present results from the 'climateprediction.net' experiment, the first multi-thousand-member grand ensemble of simulations using a general circulation model and thereby explicitly resolving regional details. We find model versions as realistic as other state-of-the-art climate models but with climate sensitivities ranging from less than 2 K to more than 11 K. Models with such extreme sensitivities are critical for the study of the full range of possible responses of the climate system to rising greenhouse gas levels, and for assessing the risks associated with specific targets for stabilizing these levels.

Effects of eccentric exercise training on cortical bone and muscle strength in the estrogen-deficient mouse

The purpose of this study was to determine whether eccentrically biased exercise training could attenuate changes in muscle and bone function associated with estrogen deficiency in the mouse model. Four groups of ICR mice were used: control (Con), sham ovariectomized (Sham), ovariectomized (OVX), and ovariectomized + high-force resistance training (OVX+Train). All groups except Con were implanted with a nerve cuff surrounding the peroneal nerve to stimulate the left ankle dorsiflexors. Training consisted of 30 stimulated eccentric contractions of the left ankle dorsiflexors at approximately 150% of peak isometric torque every third day for 8 wk. After the training period, groups were not significantly different with regard to peak torque or muscle size. However, the tibial midshaft of the trained leg in the OVX+Train mice exhibited greater stiffness (+15%) than that in the untrained OVX mice, which could not be explained by changes in cross-sectional geometry of the tibia. Scaling of bone mechanical properties to muscle strength were not altered by ovariectomy or training. These data indicate that eccentric exercise training in adult mice can significantly increase bone stiffness, despite the absence of ovarian hormones.

Human contribution to the European heatwave of 2003

The summer of 2003 was probably the hottest in Europe since at latest ad 1500, and unusually large numbers of heat-related deaths were reported in France, Germany and Italy. It is an ill-posed question whether the 2003 heatwave was caused, in a simple deterministic sense, by a modification of the external influences on climate--for example, increasing concentrations of greenhouse gases in the atmosphere--because almost any such weather event might have occurred by chance in an unmodified climate. However, it is possible to estimate by how much human activities may have increased the risk of the occurrence of such a heatwave. Here we use this conceptual framework to estimate the contribution of human-induced increases in atmospheric concentrations of greenhouse gases and other pollutants to the risk of the occurrence of unusually high mean summer temperatures throughout a large region of continental Europe. Using a threshold for mean summer temperature that was exceeded in 2003, but in no other year since the start of the instrumental record in 1851, we estimate it is very likely (confidence level >90%) that human influence has at least doubled the risk of a heatwave exceeding this threshold magnitude.

Functional recovery of the plantarflexor muscle group after hindlimb unloading in the rat

Research into skeletal muscle's response to hindlimb unloading (HU) of the rodent has focused on that of the markedly affected slow-twitch anti-gravity muscles (e.g., soleus). However, the ability of the animal to locomote following HU should be best determined by the in vivo functional properties of the muscle groups involved and, to our knowledge, this has not been investigated. Our objective was to determine how the in vivo functional properties of the rat ankle plantarflexor group change after 28 days of HU and during a subsequent 28-day recovery. Rats ( n=48) were unloaded for 28 days after which they were either tested immediately or allowed to recover for 7, 14, or 28 days before being tested. Control rats ( n=61) were tested at comparable times. In vivo functional properties of the ankle plantarflexors were assessed under anesthesia using an isokinetic dynamometer and included determination of the isometric torque-frequency relationship, the concentric torque-ankle angular velocity relationship, and fatigability. Immediately after HU, plantarflexor muscle weight was reduced by 24% but isometric torque production was reduced by 7-9% only at > or =100 Hz and concentric torque production was not significantly affected. However, after 7 days of recovery, in vivo function was more adversely affected; isometric and concentric torques were reduced by 12-33% and 16-36%, respectively, relative to control levels. In vivo plantarflexor function was recovered by 14 days. In conclusion, 28 days of HU has minor adverse effects on the in vivo function of the rat ankle plantarflexors. During the first week of recovery from HU, injury apparently occurs to the plantarflexors resulting in a transient impairment of functional capacity.

Biglycan-deficient mice have delayed osteogenesis after marrow ablation

Biglycan (bgn) is a small proteoglycan in skeletal tissue that binds and regulates collagen and TGF-beta activities. Mice deficient in bgn (bgn-KO) develop age-dependent osteopenia and have multiple metabolic defects in their bone marrow stromal cells including increased apoptosis, reduced numbers of colony-forming units-fibroblastic (CFU-F) and decreased collagen production. In the present study we tested the hypothesis that bone formation capability in response to a physiological stress is compromised in bgn deficiency. We tested this theory using an in vivo bone marrow ablation assay. Ablation was performed on 6-week-old wild type (wt) and bgn-KO mice and bones were analyzed at days 7, 10, and 17 postsurgery. X-ray analysis showed that bone marrow ablation in femora induced vigorous new bone formation within 10 days in both genotypes but appeared greater in the wt compared to the bgn-KO. In order to quantitate the changes in bone formation in the ablated animals, bone densities of the proximal, midshaft, and distal femora were assessed using peripheral quantitative computed tomography (pQCT). The ratio of cancellous bone density at the midshaft (ablated limb/control limb) was significantly higher in wt compared to bgn-KO at day 10 postsurgery. Wt and bgn-KO femora had similar total and cancellous bone densities at days 7 and 17 postsurgery at all three locations indicating that the ablation effects were temporal and limited to the cancellous bone of the mid-shaft region. These data indicate that the absence of bgn directly impeded bone formation. Our results support the concept that bgn is important in controlling osteogenesis following marrow ablation.

Inducible, brain region-specific expression of a dominant negative mutant of c-Jun in transgenic mice decreases sensitivity to cocaine

Administration of cocaine induces the Fos family of transcription factors in the striatum, including the nucleus accumbens (NAc), a brain region important for the rewarding effects of addictive drugs. Several Fos proteins are induced acutely by cocaine, with stable isoforms of DeltaFosB predominating after chronic drug administration. However, it has been difficult to study the functional consequences of these Fos responses in vivo. Fos proteins heterodimerize with members of the Jun family to form active AP-1 transcription factor complexes. In the present study, we took advantage of this property and generated transgenic mice, using the tetracycline gene regulation system, that support the inducible, brain region-specific expression of a dominant negative mutant form of c-Jun (Deltac-Jun), which can antagonize the actions of Fos proteins. Expression of Deltac-Jun in the striatum and certain other brain regions of adult mice decreases their development of cocaine-induced conditioned place preference, suggesting reduced sensitivity to the rewarding effects of cocaine. In contrast, Deltac-Jun expression had no effect on cocaine-induced locomotor activity or sensitization. However, expression of Deltac-Jun in adult mice blocked the ability of chronic cocaine administration to induce three known targets for AP-1 in the NAc: the AMPA glutamate receptor subunit GluR2, the cyclin-dependent protein kinase Cdk5, and the transcription factor nuclear factor-kappaB (NFkappaB), without affecting several other proteins examined for comparison. Taken together, these results provide further support for an important role of AP-1-mediated transcription in some of the behavioral and molecular mechanisms underlying cocaine addiction.

The role of estrogen receptor-beta, in the early age-related bone gain and later age-related bone loss in female mice

The molecular and cellular mechanism of estrogen action in skeletal tissue remains unclear. The purpose of this study was to understand the role of estrogen receptor-beta, (ERbeta) on cortical and cancellous bone during growth and aging by comparing the bone phenotype of 6- and 13-month-old female mice with or without ERbeta. Groups of 11-14 wild-type (WT) controls and ERbeta knockout (BERKO) female mice were necropsied at 6 and 13 months of age. At both ages, BERKO mice did not differ significantly from WT controls in uterine weight and uterine epithelial thickness, indicating that ERbeta does not regulate the growth of uterine tissue. Femoral length increased significantly by 5.5% at 6 months of age in BERKO mice compared with WT controls. At 6 months of age, peripheral quantitative computerized tomography (pQCT) analysis of the distal femoral metaphysis (DFM) and femoral shafts showed that BERKO mice had significantly higher cortical bone content and periosteal circumference as compared with WT controls at both sites. In contrast to the findings in cortical bone, at 6 months of age, there was no difference between BERKO and WT mice in trabecular density, trabecular bone volume (TBV), or formation and resorption indices at the DFM. In 13-month-old WT mice, TBV (-41%), trabecular density (-27%) and cortical thickness decreased significantly. while marrow cavity and endocortical circumference increased significantly compared with 6-month-old WT mice. These age-related decreases in cancellous and endocortical bone did not occur in BERKO mice. At 13 months of age, BERKO mice had significantly higher total, trabecular and cortical bone, while having significantly lower bone resorption, bone formation and bone turnover in DFM compared with WT mice. These results indicate that deleting ERbeta protected against age-related bone loss in both the cancellous and endocortical compartments by decreasing bone resorption and bone turnover in aged female mice. These data demonstrate that in female mice, ERbeta plays a role in inhibiting periosteal bone formation, longitudinal and radial bone growth during the growth period, while it plays a role in stimulating bone resorption, bone turnover and bone loss on cancellous and endocortical bone surfaces during the aging process.

Site- and compartment-specific changes in bone with hindlimb unloading in mature adult rats

The purpose of this study was to examine site- and compartment-specific changes in bone induced by hindlimb unloading (HU) in the mature adult male rat (6 months old). Tibiae, femora, and humeri were removed after 14, 21, and 28 days of HU for determination of bone mineral density (BMD) and geometry by peripheral quantitative computed tomography (pQCT), mechanical properties, and bone formation rate (BFR), and compared with baseline (0 day) and aging (28 day) controls. HU resulted in 20%-21% declines in cancellous BMD at the proximal tibia and femoral neck after 28 day HU vs. 0 day controls (CON). Cortical shell BMD at these sites was greater (by 4%-6%) in both 28 day HU and 28 day CON vs. 0 day CON animals, and nearly identical to that gain seen in the weight-bearing humerus. Mechanical properties at the proximal tibia exhibited a nonsignificant decline after HU vs. those of 0 day CON rats. At the femoral neck, a 10% decrement was noted in ultimate load in 28 day HU rats vs. 28 day CON animals. Middiaphyseal tibial bone increased slightly in density and area during HU; no differences in structural and material properties between 28 day HU and 28 day CON rats were noted. BFR at the tibial midshaft was significantly lower (by 90%) after 21 day HU vs. 0 day CON; this decline was maintained throughout 28 day HU. These results suggest there are compartment-specific differences in the mature adult skeletal response to hindlimb unloading, and that the major impact over 28 days of unloading is on cancellous bone sites. Given the sharp decline in BFR for midshaft cortical bone, it appears likely that deficits in BMD, area, or mechanical properties would develop with longer duration unloading.

Presence of the acute phase protein, bikunin, in the endometrium of gilts during estrous cycle and early pregnancy

Noninvasive, epitheliochorial placental attachment in the pig is regulated through endometrial production of protease inhibitors. The objective of the present study was to determine if the light-chain serine protease inhibitor of the inter-alpha-trypsin inhibitor family, bikunin, is produced by the porcine endometrium during the estrous cycle and early pregnancy. Western blot analysis revealed the presence of bikunin in uterine flushings of gilts collected during the luteal phase of the estrous cycle and early pregnancy (Days 12-18). However, bikunin unbound to the inter-alpha-trypsin heavy chains was detected only in endometrial explant culture medium obtained from estrus and pregnant (Days 12, 15, and 18) gilts. Endometrial bikunin gene expression was lowest on Day 10 of the estrous cycle and pregnancy, followed by a 30- to 77-fold increase on Day 15 of the estrous cycle and pregnancy. Bikunin gene expression decreased on Day 18 of the estrous cycle, whereas endometrial bikunin gene expression continued to increase in pregnant gilts. Bikunin mRNA was localized to the uterine glands between Days 15 and 18 of the estrous cycle and pregnancy. In addition to its role as a protease inhibitor, bikunin functions in stabilization of the extracellular matrix, which suggests that bikunin could be involved with facilitating placental attachment to the uterine epithelial surface in the pig.

External control of 20th century temperature by natural and anthropogenic forcings

A comparison of observations with simulations of a coupled ocean-atmosphere general circulation model shows that both natural and anthropogenic factors have contributed significantly to 20th century temperature changes. The model successfully simulates global mean and large-scale land temperature variations, indicating that the climate response on these scales is strongly influenced by external factors. More than 80% of observed multidecadal-scale global mean temperature variations and more than 60% of 10- to 50-year land temperature variations are due to changes in external forcings. Anthropogenic global warming under a standard emissions scenario is predicted to continue at a rate similar to that observed in recent decades.

Harmonic imaging: echocardiographic enhanced contrast intensity and duration

The intensity and duration of contrast effect within the left ventricular cavity after an intravenous bolus of Levovist Injection were observed with both harmonic and fundamental imaging in nine patients with known or suspected coronary artery disease. Contrast intensity was assessed by a qualitative grading system (0, none; 1, weak; 2, moderate; 3, good) and by videodensitometric analysis of pixel intensity. Duration of left ventricular contrast effect was determined by measuring time from the initial visual appearance of contrast agent to its disappearance. The mean increase in pixel intensity within the left ventricular cavity from precontrast to peak contrast was significantly greater for second harmonic than for fundamental imaging (25.5 vs 7.1; P < 0.012). The mean contrast intensity qualitative score with harmonic imaging was higher (2.6 +/- 0.73 vs 1.2 +/- 0.44; P < 0.01) and the duration of contrast effect was longer (242 +/- 131 s vs 53 +/- 33 s; P < 0.004). Second harmonic imaging significantly enhanced contrast intensity and prolonged visible duration of contrast effect after a peripheral venous injection of Levovist.

Sex differences in ventricular function in patients with right bundle branch block

BACKGROUND

Left ventricular function in patients with right bundle branch block is variable and depends on the population under study. This study assessed the implications of right bundle branch block for the estimation of resting left ventricular function in patients with right bundle branch and suspected coronary artery disease.

METHODS AND RESULTS

Seventy-four patients with right bundle branch block, symptoms suggestive of coronary artery disease, and no electrocardiographic Q waves were compared with 649 patients with entirely normal electrocardiograms to assess the implications of right bundle branch block on resting left ventricular function. Resting ejection fraction was determined by radionuclide ventriculography. Patients with right bundle branch block were older (mean 65.0+/-10.2 years vs 53.8+/-11.1; P< .001) and had a lower mean ejection fraction (60%+/-11% vs 63%+/-9%; P< .005) compared with patients with normal electrocardiograms. There was a highly significant interaction between right bundle branch block and sex with respect to resting ejection fraction (P< .001). The mean ejection fraction for men with right bundle branch block was 57%+/-10% (17% with abnormal resting ejection fraction) compared with 62%+/-8% (7% with abnormal resting ejection fraction) for normal men. In contrast, the mean ejection fraction for women with right bundle branch block was 68%+/-9% (0% with abnormal resting ejection fraction) compared with 65%+/-9% (5% with abnormal resting ejection fraction) for normal women.

CONCLUSIONS

Male patients with right bundle branch block and symptoms suggestive of coronary artery disease have a lower resting ejection fraction than mole patients with normal electrocardiograms. This difference is not seen in female patients.

Permanent pacing in Ebstein's anomaly

Patients with Ebstein's anomaly present unique challenges to permanent pacing due to anatomical variations and tricuspid valve replacement. We retrospectively reviewed our experience with permanent pacing in patients with Ebstein's anomaly between 1976 and 1993. We identified 401 patients with Ebstein's anomaly, of whom 15 (3.7%) required permanent pacing (1 of the 15 was implanted elsewhere). Of the 15, there were 8 females and 7 males (mean age 32 years [range 7-74]); the indications for pacing were AV block in 11 and sinus node dysfunction in 4. Eight patients were programmed with VVI and seven with DDD. All VVI patients were paced epicardially. Two patients with DDD pacemakers had transvenous atrial and ventricular leads, 4 DDD patients had transvenous atrial leads and epicardial ventricular leads, and 1 patient had both epicardial and transvenous systems. Associated surgical procedures included tricuspid valve replacement in 14 of 15, atrial septal defect repair in 10 of 15, atrioplasty in 7 of 15, prior tricuspid annuloplasty in 4 of 15, pulmonary vein dilation in 1 of 15, and conduction system ablation in 2 of 15. Patients had a mean follow-up of 35 months (range 1-168 months). Complications requiring operative intervention occurred in four patients. One patient had displacement of a transvenous ventricular lead. A second patient had an epicardial lead failure. A third patient had a nonfunctioning atrial lead that displaced across the tricuspid valve, causing severe tricuspid regurgitation. The fourth patient had multiple epicardial and endocardial leads exit block with secondary diaphragmatic stimulation. Permanent pacemakers were required in 3.7% of patients with Ebstein's anomaly, with the indication being intrinsic conduction disease in the majority of patients. Ninety-three percent of patients required tricuspid valve replacement, suggesting more severe manifestation of Ebstein's anomaly. Twenty-seven percent had complications requiring surgical intervention. Thus, permanent pacing in patients with Ebstein's anomaly can be challenging and should be approached by an experienced physician.

Human Influence on the Atmospheric Vertical Temperature Structure: Detection and Observations

Recent work suggests a discernible human influence on climate. This finding is supported, with less restrictive assumptions than those used in earlier studies, by a 1961 through 1995 data set of radiosonde observations and by ensembles of coupled atmosphere-ocean simulations forced with changes in greenhouse gases, tropospheric sulfate aerosols, and stratospheric ozone. On balance, agreement between the simulations and observations is best for a combination of greenhouse gas, aerosol, and ozone forcing. The uncertainties remaining are due to imperfect knowledge of radiative forcing, natural climate variability, and errors in observations and model response.