Christopher G. Schultz

The tyrosine kinase inhibitor dasatinib dysregulates bone remodeling through inhibition of osteoclasts in vivo

Dasatinib is a potent tyrosine kinase inhibitor that is used to treat chronic myeloid leukemia in patients resistant or intolerant to imatinib mesylate. While designed to inhibit Abl and Src kinases, dasatinib shows multitarget effects, including inhibition of the macrophage colony‐stimulating factor (M‐CSF) receptor c‐fms. We have shown previously that dasatinib abrogates osteoclast formation and activity in vitro owing, in part, to its specificity for c‐fms. In this study we examined whether dasatinib could significantly alter bone volume in a model of physiologic bone turnover. Sprague‐Dawley rats were administered dasatinib (5 mg/kg/day) or vehicle by gavage or zoledronic acid (ZOL; 100 µg/kg/6 weeks) subcutaneously. Following 4, 8, and 12 weeks of treatment, serum biochemical, bone morphometric, and histologic analyses were performed. Whole‐body bone mineral density and tibial cortical thickness where unchanged in the dasatinib‐ or ZOL‐treated animals relative to controls. However, micro–computed tomographic (µCT) analysis of cancellous bone at the proximal tibias showed that trabecular volume (BV/TV) and thickness (Tb.Th) were increased in dasatinib‐treated animals at levels comparable with those of the ZOL‐treated group. These changes were associated with a decrease in osteoclast numbers (N.Oc/B.Pm) and surface (Oc.S/BS) and decreased serum levels of the osteoclast marker c‐terminal collagen crosslinks (CTX‐1). Mineral apposition rate (MAR), bone‐formation rate (BFR), and levels of the serum osteoblast markers osteocalcin and N‐terminal propeptide of type I procollagen (P1NP) were not altered significantly in the dasatinib‐treated animals relative to controls. These studies show that dasatinib increases trabecular bone volume at least in part by inhibiting osteoclast activity, suggesting that dasatinib therapy may result in dysregulated bone remodeling.

Heavy metal toxicity of kidney and bone tissues in South Australian adult bottlenose dolphins (Tursiops aduncus).

Metallothioneins (MT) concentration, renal damage, and bone malformations were investigated in 38 adult Tursiops aduncus carcasses to determine any associations with cadmium, copper, zinc, mercury, lead and selenium. Significantly higher concentrations of cadmium, copper, and zinc in the liver were observed in dolphins showing evidence of more advanced renal damage. No significant differences in metal or selenium concentrations in the liver were observed between groups differing in level of bone malformations. Some dolphins displayed evidence of toxicity and knowledge of metal toxicity pathways were used to elucidate the cause of these abnormalities. Two dolphins had high metal burdens, high MT concentrations, renal damage, and evidence of bone malformations, indicating possible severe and prolonged metal toxicity. One dolphin showed evidence of renal damage, but the lack of any other symptoms suggests that this was unlikely to be caused by metal toxicity. We recommend examining a range of metal toxicity symptoms simultaneously to aid in distinguishing metal toxicity from unrelated aetiologies.

Low muscle mass and sarcopenia: common and predictive of osteopenia in inflammatory bowel disease

Body composition is poorly studied in inflammatory bowel disease (IBD). Sarcopenia describes a loss of muscle mass and strength.

Plasma Adiponectin Levels Are Markedly Elevated in Imatinib-Treated Chronic Myeloid Leukemia (CML) Patients: A Mechanism for Improved Insulin Sensitivity in Type 2 Diabetic CML Patients?

CONTEXT The mechanism(s) by which imatinib improves glycemic control in chronic myeloid leukemia (CML) patients with type 2 diabetes remains unclear. OBJECTIVE Adiponectin is an important regulator of insulin sensitivity that is secreted exclusively by adipocytes. We previously reported that imatinib promotes adipocytic differentiation of mesenchymal stromal cells. We therefore hypothesized that imatinib therapy would be associated with an increase in peripheral and intramedullary adiposity and elevated plasma adiponectin levels. RESEARCH DESIGN AND METHODS Adiponectin levels in CML patient plasma, at diagnosis and then during imatinib mesylate therapy, was measured using an ELISA. Adiponectin multimers in plasma were analyzed using nondenaturing PAGE and immunoblotting. Intramedullary adiposity and adipose tissue mass was determined using histomorphometry and dual-energy X-ray absorptiometry, respectively. RESULTS In CML patients, an increase in intramedullary and peripheral adiposity was observed after 6 months of imatinib therapy and plasma adiponectin levels, in the form of high- and low-molecular-weight complexes, were elevated 3-fold, compared with pretreatment levels, after 3, 6, and 12 months of therapy. CONCLUSIONS Elevated adiponectin levels in imatinib-treated CML patients provide a possible mechanism for improved glucose and lipid metabolism reported for some imatinib-treated patients.

Effect of placental restriction and neonatal exendin-4 treatment on postnatal growth, adult body composition, and in vivo glucose metabolism in the sheep.

Intrauterine growth restriction (IUGR) increases the risk of adult type 2 diabetes (T2D) and obesity. Neonatal exendin-4 treatment can prevent diabetes in the IUGR rat, but whether this will be effective in a species where the pancreas is more mature at birth is unknown. Therefore, we evaluated the effects of neonatal exendin-4 administration after experimental restriction of placental and fetal growth on growth and adult metabolic outcomes in sheep. Body composition, glucose tolerance, and insulin secretion and sensitivity were assessed in singleton-born adult sheep from control (CON; n = 6 females and 4 males) and placentally restricted pregnancies (PR; n = 13 females and 7 males) and in sheep from PR pregnancies that were treated with exendin-4 as neonates (daily sc injections of 1 nmol/kg exendin-4; PR + exendin-4; n = 11 females and 7 males). Placental restriction reduced birth weight (by 29%) and impaired glucose tolerance in the adult but did not affect adult adiposity, insulin secretion, or insulin sensitivity. Neonatal exendin-4 suppressed growth during treatment, followed by delayed catchup growth and unchanged adult adiposity. Neonatal exendin-4 partially restored glucose tolerance in PR progeny but did not affect insulin secretion or sensitivity. Although the effects on glucose tolerance are promising, the lack of effects on adult body composition, insulin secretion, and insulin sensitivity suggest that the neonatal period may be too late to fully reprogram the metabolic consequences of IUGR in species that are more mature at birth than rodents.

Prospective Histomorphometric and DXA Evaluation of Bone Remodeling in Imatinib-Treated CML Patients: Evidence for Site-Specific Skeletal Effects

CONTEXT Imatinib is a tyrosine kinase inhibitor that has been successfully used to treat Philadelphia chromosome-positive chronic myeloid leukemia (CML) and Kit(+) gastrointestinal stromal tumors. We have previously shown that imatinib therapy is associated with an increase in trabecular bone volume. OBJECTIVE In the present study, we performed a prospective analysis of bone indices in imatinib-treated CML patients to determine the mechanism responsible for this altered bone remodeling. DESIGN, PATIENTS, AND INTERVENTION: This study assessed the effects of high-dose (600 mg/d) imatinib on bone parameters in newly diagnosed chronic-phase Philadelphia chromosome-positive CML patients (n = 11) enrolled in the TIDEL II study. At baseline and after 6, 12, and 24 months of treatment, serum markers of bone remodeling were quantitated, dual-energy x-ray absorptiometry analysis of bone mineral density (BMD) was carried out, and a bone biopsy was collected for histological and micro-computed tomography analysis. RESULTS Our studies show that the increase in trabecular bone volume and trabecular thickness after imatinib treatment was associated with a significant decrease in osteoclast numbers, accompanied by a significant decrease in serum levels of a marker of osteoclast activity. In contrast, osteoblast numbers were not altered by up to 24 months of imatinib treatment. Notably, we also found that imatinib caused a site-specific decrease in BMD at the femoral neck. CONCLUSIONS These data suggest that imatinib therapy dysregulates bone remodeling, causing a generalized decrease in osteoclast number and activity that is not counterbalanced by a decrease in osteoblast activity, leading to increased trabecular bone volume. Further long-term investigations are required to determine the causes and consequences of the site-specific decrease in BMD at the femoral neck.

Recombinant human bone morphogenetic protein-type 2 (rhBMP-2) enhances local bone formation in the lumbar spine of osteoporotic sheep.

The failure of orthopedic implants in osteoporotic patients is attributed to the lack of sufficient bone stock and regenerative capacity but most treatments for osteoporosis fail to address this issue. rhBMP‐2 is known to promote bone formation under normal conditions but has not been used clinically in the osteoporotic condition. Osteoporosis was induced in 19 ewes using ovariectomy, low calcium diet, and steroid injection. After induction, the steroid was withdrawn and pellets containing inert carrier with rhBMP‐2 in either slow or fast‐release formulation were implanted into the lumbar vertebrae of each animal. After 2, 3, and 6 months the spines were harvested and assessed for changes in BMD and histomorphometric indices. BMD did not change after cessation of steroid treatment. After 2 months BV/TV increased in the vicinity of the pellets containing the fast‐release rhBMP‐2 and was sustained for the duration of the study. Focal voids surrounding all implants, particularly the slow‐release formulation, were observed initially but resolved with time. Increased BV/TV adjacent to rhBMP‐2 pellets suggests it could be used for localized treatment of osteoporosis. Refinement of the delivery system and supplementary treatments may be necessary to overcome the initial catabolic effects of rhBMP‐2.

Correlations between the mechanical properties, radiology and histomorphometry of human femoral bone

Initial fixation of the femoral components of total hip replacements is related to the mechanical integrity of the bone within the proximal femur. This preliminary study examined the correlations between the mechanical properties, histomorphometry, and radiology of bone core specimens taken from the proximal femora of cadavers and of patients undergoing total hip replacement surgery. Measurements and subjective assessments of the femoral bone from radiographs were shown to have poor correlation with both compressive mechanical properties and bone volume measurements. However, the mechanical properties of the bone core specimens and the histomorphometric measurements correlated well with the bone density measured by single-photon absorptiometry, indicating that this type of imaging technique may be of value in determining bone quality prior to surgery. The prediction of the mechanical properties of the proximal femur by preoperative imaging may have direct bearing on the type of femoral component to be used in total hip replacement. Preoperative assessment of bone quality would allow the surgeon to predict the likely fixation obtainable with different designs.

Osteoporotic Characteristics Persist in the Spine of Ovariectomized Sheep after Withdrawal of Corticosteroid Administration

A validated ovine model of osteoporosis achieves severe bone loss in a relatively short period. This study investigated if osteoporotic features persist in this model after cessation of corticosteroid administration. Methods. Osteoporosis was induced in nine ewes by chronic corticosteroid injection, ovariectomy, and low calcium diet. Six ewes were used as controls. Bone mineral density (BMD) of the lumbar spine (LS) and body weight were assessed at regular intervals. After five months, corticosteroid treatment was withdrawn systematically over one month. Three months later, all animals were euthanised, and the LS was collected for histomorphometric analysis. Results. BMD in the LS of osteoporotic sheep was 25% lower than control sheep. Body weight of osteoporotic sheep was reduced in the first month of the corticosteroid withdrawal period but returned to baseline level thereafter. Trabecular bone volume of LS in osteoporotic sheep was 27% lower than controls and showed a heterogeneous structure. Conclusions. Osteoporotic characteristics remain in the vertebra after ceasing corticosteroid administration providing an opportunity to evaluate potential systemic or local treatments in vivo under realistic physiological conditions. The microstructural arrangement of vertebral trabecular bone in sheep is similar to humans demonstrating further relevance of this model for preclinical investigations.

Obesity in Inflammatory Bowel Disease: Gains in Adiposity despite High Prevalence of Myopenia and Osteopenia

Background: Rising rates of obesity have been reported in patients with inflammatory bowel disease (IBD); however, prospective data is lacking. The aim of this study is to prospectively evaluate body composition in adults with IBD over 24 months. Methods: Whole body dual energy X-ray absorptiometry (DXA) data was performed at 0 months, 12 months, and 24 months. Bone mineral density (BMD), fat mass index (FMI (kg)/height (m2)), appendicular skeletal muscle index (ASMI (kg)/height (m2)), visceral adipose tissue and the visceral adipose height index (VHI, VAT area (cm3)/height (m2)), and clinical and anthropometric assessments were performed at each time point. Multivariable linear mixed effects regression analyses were performed. Results: Initially, 154 participants were assessed at baseline (70% Crohn’s disease, 55% male, median age 31 years), of whom 129 underwent repeated DXA at 12 months, and 110 underwent repeated DXA at 24 months. Amongst those undergoing repeated DXA, their body mass index (BMI) significantly increased over time, such that by 24 months, 62% of patients were overweight or obese (annual change BMI β = 0.43, 95%CI = [0.18, 0.67], p = 0.0006). Gains in BMI related to increases in both FMI and VHI (β = 0.33, 95%CI = [0.14, 0.53], p = 0.0007; β = 0.08, 95%CI = [0.02, 0.13], p = 0.001; respectively), whereas ASMI decreased (β = −0.07, 95%CI = [−0.12, −0.01], p = 0.01) with a concordant rise in rates of myopenia (OR = 3.1 95%CI = [1.2, 7.7]; p = 0.01). Rates of osteopenia and osteoporosis were high (37%), but remained unchanged over time (p = 0.23). Conclusion: Increasing rates of obesity in patients with IBD coincide with decreases in lean muscle mass over time, while high rates of osteopenia remain stable. These previously undocumented issues warrant attention in routine care to prevent avoidable morbidity.