Effects of thermal injury on skeletal metabolism in two strains of mice

Bone mineral density and low bone mass in severely burned patients: A retrospective cohort study

INTRODUCTION

Severe burns can alter bone metabolism through different mechanisms. Despite prior published studies describing the association between burns and a decrease in bone mineral density (BMD), no clinical guidelines currently exist recommending the systematic evaluation of bone health in patients after severe burns. This study aims to describe the BMD of individuals with severe burn injuries and healthy controls and determine the frequency of low-to-normal bone mass (LNBM) and BMD below the expected range for age (BEA).

MATERIALS AND METHODS

We conducted a retrospective cohort of patients with either severe thermal or electrical burns and healthy controls paired by gender and age. We performed a dual-energy X-ray absorptiometry at least 90 days after the burn and collected data from each patient's clinical evaluation and clinical file.

RESULTS

A total of 77 patients (64 men and 13 women) and their paired controls were included in the study (age [mean ± standard deviation, SD]: 30.37 ± 8.66 years). Patients participated in the study an average of 315 ± 438 days after their burn. The BMD (grs/cm2) in total hip burned vs controls was: 0.998 ± 0.135 vs 1.059 ± 0.12 (p = 0.004); femoral neck 0.876 ± 0.121 vs 0.915 ± 0.097 (p = 0.031), spine 0.977 ± 0.127 vs 1.003 ± 0.076 (p = 0.132).The Z-scores for total hip were - 0.06 ± 1.05 vs 0.41 ± 0.80 (p = 0.002); for neck -0.39 ± 0.89 vs -0.01 ± 0.77 (p = 0.005); and for spine -0.75 ± 1.11 vs -0.32 ± 0.73 (p = 0.005). The proportion of subjects with BMD BEA in burns vs controls was 5.2 vs 1.2% (p = 0.05) in total hip, 3.9 vs 0% (p = 0.045) in the neck, and 18.2 vs 1.2% (p = 0.001) in the spine. The logistic regression model found-in burn patients vs controls-an OR of 9.83 for BMD BEA (CI 95%: 2.17-44.45, p = 003), OR = 4.05 for electrical burns (CI 95%: 1.72-20.89, p = 004) and OR = 15.16 for thermal burns (CI 95%: 2.91-79.00, p = 001). The model also found an OR = 2.48 for LNBM (CI 95%: 1.25-4.93, p = 0.009). The burn variables associated with BMD BEA at any site in the patients were BMI >25 Kg/m2 with an OR = 0.180 (CI 95%: 0.046-0.710, p = 0.014); and the lower limb amputation with an OR = 7.33 (CI 95%; 1.12-48.33, p = 0.038). Five burn patients had a fragility fracture.

CONCLUSION

BMD was significantly lower in severely burned patients than in controls, and the proportion BMD BEA cases was significantly higher in the burn patient sample. Severe burns are a strong independent predictor of bone loss, and this risk is maintained for an extended period after the burn.

Burn Injury Has Skeletal Site-Specific Effects on Bone Integrity and Markers of Bone Remodeling

To further understand the mechanisms of perturbations in bone remodeling following severe burn injury, the biomechanical properties, genetic expression, and serological markers were evaluated in rodents at six time intervals within 6 weeks following injury. Moreover, these effects were observed in rodent tibia and lumbar vertebrae to explore possible skeletal site localization of this pathologic bone loss. Rodents underwent either thermal injury (100°C water, 30 seconds, 30% BSA) or sham burn. Bone mineral density was evaluated though peripheral quantitative computer tomography, and specialized apparatus measured the weight bearing capacity of tibia and lumbar vertebrae. Markers of bone resorption (RANK ligand, osteocalcin) and bone formation (osteoprotegerin, procollagenase type 1 alpha 2) were measured at 7, 14, and 21 days following injury, and serum RANK-ligand levels were observed at these time intervals. Rodent body mass, bone mineral density, and weight bearing capacity were negatively influenced both acutely and several weeks following burn injury. Moreover, a genetic expression profile favoring increased bone resorption and lower bone formation was demonstrated. Our serum analysis findings of significantly increased RANKL 1 and 2 weeks following injury support the increased expression of bone resorption markers. Furthermore, these effects occurred sooner and were more pronounced in the rodent lumbar vertebrae than tibia. These results suggest that severe burn injury results in perturbations in bone remodeling secondary to increased bone resorption and diminished bone formation, impacting both bone mineral density and weight bearing capacity. Furthermore, these processes had a skeletal site effect more pronounced in the lumbar vertebrae. With a better understanding of the mechanisms of burn-injury bone loss, targeted therapies can be implemented to improve long-term clinical outcomes.

5-Androstene-3β,7β,17β-triol (β-AET) slows thermal injury induced osteopenia in mice: relation to aging and osteoporosis

5-androstene-3β,7β,17β-triol (β-AET), an active metabolite of dehydroepiandrosterone (DHEA), reversed glucocorticoid (GC)-induced suppression of IL-6, IL-8 and osteoprotegerin production by human osteoblast-like MG-63 cells and promoted osteoblast differentiation of human mesenchymal stem cells (MSCs). In a murine thermal injury model that includes glucocorticoid-induced osteopenia, β-AET significantly (p<0.05) preserved bone mineral content, restored whole body bone mineral content and endochondral growth, suggesting reversal of GC-mediated decreases in chondrocyte proliferation, maturation and osteogenesis in the growth plate. In men and women, levels of β-AET decline with age, consistent with a role for β-AET relevant to diseases associated with aging. β-AET, related compounds or synthetic derivatives may be part of effective therapeutic strategies to accelerate tissue regeneration and prevent or treat diseases associated with aging such as osteoporosis.

Bone loss during the acute stage following burn injury

The aim of this study was to investigate the effect of burn injury on bone metabolism and bone densitometry in the early period. Twenty-one patients with >25% total body surface area (TBSA) burns and 20 healthy controls participated. TBSA burned, ambulation, and functional status were recorded. After 30 days, we measured bone mineral densities of the L1-L4 vertebrae, the left distal forearm, and the left proximal femur in the patients. At 1 and 4 weeks after the burn, changes in bone turnover were assessed in patients by changes in deoxypyridinoline levels in the urine and osteocalcin in the serum and compared with the values of control group. In patients, Z-scores < -1 were found in 71.42% of left distal forearm, 23.80% of left proximal femur, and in 42.85% of L1-L4 vertebrae measurements. No significant correlations existed between Z-scores and TBSA, Functional Ambulation Scale, or Functional Independent Measure. When compared with controls, there was no statistically significant decrease of osteocalcin (a marker of bone formation) levels in patients 1 and 4 weeks after burn injury. However, when compared with controls, a statistically significant difference was found regarding deoxypyridinoline (a marker for bone resorption) in patients 1 and 4 weeks after burn injury (P < .001 and P < .001, respectively). Decreases in bone mineral density occurred during the first month following burn injury, which seemed to be linked with increases in bone resorption during this period. No correlation existed between reduction in bone mineral density and functional status.

Effects of long-term oxandrolone administration in severely burned children

BACKGROUND

Severe burns cause exaggerated catabolism of muscle protein and inhibit bone deposition. Weakness and bony growth arrest interfere with rehabilitation. The purpose of this study was to determine whether oxandrolone administration for 1 year after the burn reverses muscle and bone catabolism in hypermetabolic pediatric burn patients.

METHODS

Children with burns greater than 40% total body surface area were enrolled into a randomized controlled trial to receive oxandrolone as a long-term anabolic agent. All patients received similar clinical care. Subjects were studied at discharge (95% healed) and at 6, 9, and 12 months after the burn, after treatment with 0.1 mg/kg po bid or placebo. Serum hepatic transaminases were measured. Lean body mass (LBM), bone mineral content (BMC,) and bone mineral density (BMD) were measured by dual energy x-ray absorptiometry. Patients completed a safety questionnaire and were reviewed clinically at intervals.

RESULTS

The groups were similar in age, weight, and total body surface area burned. LBM was significantly greater with oxandrolone at 6, 9, and 12 months after the burn (P < .001) and BMC at 12 months (P < .016). Age- and gender-matched BMD z scores were significantly better with oxandrolone (P < .039). Liver transaminases were unaffected.

CONCLUSIONS

Long-term administration of oxandrolone safely improves LBM, BMC, and BMD in severely burned children.

Cortical bone dynamics, strength, and densitometry after induction of emphysema in hamsters

Recent evidence suggests that patients suffering from chronic obstructive pulmonary disease are also at an increased risk of developing osteoporosis. The pathophysiological mechanism(s) linking these progressive diseases is unknown. The goal of this investigation was to determine whether there were alterations in bone mineral density and content, cortical bone structure and strength, and indexes of bone formation and resorption in the elastase-induced emphysematous hamster. At 3 wk after induction of emphysema, the femoral bone mineral content was 8% less (P = 0.026) and the femoral fracture strength was 6% less (P = 0.032) in the emphysematous hamster than in controls. The cortical area was 8.4% less (P = 0.013) and the periosteal mineral appositional rate was 27% less (P = 0.05) than in controls. Additionally, the endocortical eroded surface in the emphysematous group was about twice that in the control group (P = 0.003). Differences in some indexes of bone formation and resorption, paralleled by differences in bone structure and strength, were observed 3 wk after induction of emphysema. These differences in skeletal metabolism and strength may help explain some of the skeletal changes associated with chronic obstructive pulmonary disease in humans.