Damian E. Myers

Leptin inhibits osteoclast generation.

Originally, leptin was described as a product of adipocytes that acts on the hypothalamus to regulate appetite. However, subsequently, it has been shown that leptin receptors are distributed widely and that leptin has diverse functions, including promotion of hemopoietic and osteoblastic differentiation. It has been recognized for some time that both serum leptin and bone mass are correlated positively to body fat mass and, recently, we have shown a direct positive relationship between serum leptin and bone mass in nonobese women. We now report that leptin inhibits osteoclast generation in cultures of human peripheral blood mononuclear cells (PBMCs) and murine spleen cells incubated on bone in the presence of human macrophage colony‐stimulating factor (hM‐CSF) and human soluble receptor activator of NF‐κB ligand (sRANKL). The half‐maximal concentration inhibitory of leptin was approximately 20 nM in the presence of sRANKL at 40 ng/ml but decreased to approximately 2 nM when sRANKL was used at 5 ng/ml. The majority of the inhibitory effect occurred in the first week of the 3‐week cultures. Inhibition did not occur when the PBMC cultures were washed vigorously to remove nonadherent cells or when purified CD14+ monocytes were used to generate osteoclasts, indicating an indirect or permissive effect via CD14− PBMC. Leptin increased osteoprotegerin (OPG) messenger RNA (mRNA) and protein expression in PBMC but not in CD14+ cells, suggesting that the inhibitory effect may be mediated by the RANKL/RANK/OPG system. Leptin may act locally to increase bone mass and may contribute to linkage of bone formation and resorption.

The molecular pathogenesis of osteosarcoma: a review.

Osteosarcoma is the most common primary malignancy of bone. It arises in bone during periods of rapid growth and primarily affects adolescents and young adults. The 5-year survival rate for osteosarcoma is 60%–70%, with no significant improvements in prognosis since the advent of multiagent chemotherapy. Diagnosis, staging, and surgical management of osteosarcoma remain focused on our anatomical understanding of the disease. As our knowledge of the molecular pathogenesis of osteosarcoma expands, potential therapeutic targets are being identified. A comprehensive understanding of these mechanisms is essential if we are to improve the prognosis of patients with osteosarcoma through tumour-targeted therapies. This paper will outline the pathogenic mechanisms of osteosarcoma oncogenesis and progression and will discuss some of the more frontline translational studies performed to date in search of novel, safer, and more targeted drugs for disease management.

The Heat Shock Protein 90 Inhibitor, 17-Allylamino-17-demethoxygeldanamycin, Enhances Osteoclast Formation and Potentiates Bone Metastasis of a Human Breast Cancer Cell Line

Breast cancer metastasis to the bone occurs frequently, causing numerous complications including severe pain, fracture, hypercalcemia, and paralysis. Despite its prevalence and severity, few effective therapies exist. To address this, we examined whether the heat shock protein 90 (Hsp90) inhibitor, 17-allylamino-17-demethoxygeldanamycin (17-AAG), would be efficacious in inhibiting breast cancer metastasis to bone. Utilizing the human breast cancer subline, MDA-MB-231SA, previously in vivo selected for its enhanced ability to generate osteolytic bone lesions, we determined that 17-AAG potently inhibited its in vitro proliferation and migration. Moreover, 17-AAG significantly reduced MDA-MB-231SA tumor growth in the mammary-fat pad of nude mice. Despite these findings, 17-AAG enhanced the incidence of bone metastasis and osteolytic lesions following intracardiac inoculation in the nude mouse. Consistent with these findings, 17-AAG enhanced osteoclast formation 2- to 4-fold in mouse bone marrow/osteoblast cocultures, receptor activator of nuclear factor kappaB ligand (RANKL)-stimulated bone marrow, and RAW264.7 cell models of in vitro osteoclastogenesis. Moreover, the drug enhanced osteoclastogenesis in human cord blood progenitor cells, demonstrating that its effects were not limited to mouse models. In addition to 17-AAG, other Hsp90 inhibitors, such as radicicol and herbimycin A, also enhanced osteoclastogenesis. A pro-osteolytic action of 17-AAG independent of tumor presence was also determined in vivo, in which 17-AAG-treated tumor-naive mice had reduced trabecular bone volume with an associated increase in osteoclast number. Thus, HSP90 inhibitors can stimulate osteoclast formation, which may underlie the increased incidence of osteolysis and skeletal tumor incidence caused by 17-AAG in vivo. These data suggest an important contraindication to the Hsp90 targeted cancer therapy currently undergoing clinical trial.

Bioactive coatings for orthopaedic implants-recent trends in development of implant coatings.

Joint replacement is a major orthopaedic procedure used to treat joint osteoarthritis. Aseptic loosening and infection are the two most significant causes of prosthetic implant failure. The ideal implant should be able to promote osteointegration, deter bacterial adhesion and minimize prosthetic infection. Recent developments in material science and cell biology have seen the development of new orthopaedic implant coatings to address these issues. Coatings consisting of bioceramics, extracellular matrix proteins, biological peptides or growth factors impart bioactivity and biocompatibility to the metallic surface of conventional orthopaedic prosthesis that promote bone ingrowth and differentiation of stem cells into osteoblasts leading to enhanced osteointegration of the implant. Furthermore, coatings such as silver, nitric oxide, antibiotics, antiseptics and antimicrobial peptides with anti-microbial properties have also been developed, which show promise in reducing bacterial adhesion and prosthetic infections. This review summarizes some of the recent developments in coatings for orthopaedic implants.

Experimental traumatic brain injury induces a pervasive hyperanxious phenotype in rats

Mood disturbances, including depression and anxiety disorders, are common and disabling long-term sequelae of traumatic brain injury (TBI). These psychiatric conditions have generally been considered psychosocial consequences of the trauma, but neurobiological alterations and causes have also been implicated. Using a rat model of TBI (lateral fluid-percussion injury), this longitudinal study seeks to assess anxiety and depression-like behaviors following experimental TBI. Male Wistar rats (n = 20) received a severe (approximately 3.5 atmosphere) pressure pulse directed to the right sensorimotor cortex, or sham surgery (n = 15). At 1, 3, and 6 months following injury, all rats underwent four assessments of anxiety and depression-like behaviors: exposure to an open field, elevated plus maze test, the forced swim test, and the sucrose preference test. Injured animals displayed increased anxiety-like behaviors throughout the study, as evidenced by reduced time spent (p = 0.014) and reduced entries (p < 0.001) into the center area of the open field, and reduced proportion of time in the open arms of the plus maze (p = 0.015), compared to sham-injured controls. These striking changes were particularly evident 1 and 3 months after injury. No differences were observed in depression-like behaviors in the forced swim test (a measure of behavioral despair) and the sucrose preference test (a measure of anhedonia). This report provides the first evidence of persistent anxiety-like disturbances in an experimental model of TBI. This finding indicates that the common occurrence of these symptoms in human sufferers is likely to have, at least in part, a neurobiological basis. Studies in this model could provide insight into the mechanisms underlying affective disturbance in brain-injured patients.

Refracting Röntgen’s rays: Propagation-based x-ray phase contrast for biomedical imaging

Absorption-contrast x-ray imaging serves to visualize the variation in x-ray attenuation within the volume of a given sample, whereas phase contrast allows one to visualize variations in x-ray refractive index. The former imaging mechanism has been well known and widely utilized since the time of Rontgen’s Nobel prize winning work, whereas the latter mechanism—sought for, but not found, by Rontgen himself—has laid the foundation for a revolution in x-ray imaging which is the central topic of this review. We consider the physical imaging mechanisms underlying both absorption contrast and phase contrast, together with the associated inverse problem of how one may obtain quantitative two- or three-dimensional information regarding a sample, given one or more phase-contrast images of the same. Practical questions are considered, regarding optimized phase-contrast imaging geometries as a function of detector resolution, source size, x-ray spectrum, and dose. Experimental examples pertaining to biomedical appli...

Osteoclastic Potential of Human CFU-GM: Biphasic Effect of GM-CSF

Human osteoclasts can be efficiently generated in vitro from cord blood mononuclear cells and derived CFU‐GM colonies. However, CFU‐M colonies are poorly osteoclastogenic. Short‐term (2–48 h) treatment with GM‐CSF stimulates osteoclast formation by proliferating precursors, whereas longer exposure favors dendritic cell formation.

Expression of functional RANK on mature rat and human osteoclasts

Although the important roles of RANK/RANKL in osteoclastogenesis have been established, their roles in the regulation of mature osteoclasts remain uncertain. Microisolation has been used to obtain pure populations of rat and human osteoclasts for RT‐PCR analysis. RANK and calcitonin receptor mRNA was detected in all the samples whereas OPG and ALP mRNA was not present in any. RANKL mRNA was detected in two of eight rat and one of four human samples. Treatment of osteoclasts with soluble RANKL resulted in translocation of NF‐κB to the nucleus and elevation of cytosolic and nuclear calcium levels. We have shown that RANK is highly expressed in mature osteoclasts and that its stimulation by RANKL results in activation of NF‐κB and calcium signalling.

Can structural or functional changes following traumatic brain injury in the rat predict epileptic outcome

Posttraumatic epilepsy (PTE) occurs in a proportion of traumatic brain injury (TBI) cases, significantly compounding the disability, and risk of injury and death for sufferers. To date, predictive biomarkers for PTE have not been identified. This study used the lateral fluid percussion injury (LFPI) rat model of TBI to investigate whether structural, functional, and behavioral changes post‐TBI relate to the later development of PTE.

AMPK activation is fiber type specific in human skeletal muscle: effects of exercise and short-term exercise training

AMP-activated protein kinase (AMPK) has been extensively studied in whole muscle biopsy samples of humans, yet the fiber type-specific expression and/or activation of AMPK is unknown. We examined basal and exercise AMPK-alpha Thr(172) phosphorylation and AMPK subunit expression (alpha(1), alpha(2), and gamma(3)) in type I, IIa, and IIx fibers of human skeletal muscle before and after 10 days of exercise training. Before training basal AMPK phosphorylation was greatest in type IIa fibers (P < 0.05 vs. type I and IIx), while an acute bout of exercise increased AMPK phosphorylation in all fibers (P < 0.05), with the greatest increase occurring in type IIx fibers. Exercise training significantly increased basal AMPK phosphorylation in all fibers, and the exercise-induced increases were uniformly suppressed compared with pretraining exercise. Expression of AMPK-alpha(1) and -alpha(2) was similar between fibers and was not altered by exercise training. However, AMPK-gamma(3) was differentially expressed in skeletal muscle fibers (type IIx > type IIa > type I), irrespective of training status. Thus skeletal muscle AMPK phosphorylation and AMPK expression are fiber type specific in humans in the basal state, as well as during exercise. Our findings reveal fiber type-specific differences that have been masked in previous studies examining mixed muscle samples.