Bone Loss in the Intensive Care Unit

Bisphosphonates and lifespan

Bisphosphonates are first line agents used to treat osteoporosis and reduce fracture rate. They bind to areas of exposed calcium in the skeleton and cause osteoclast apoptosis, thereby leading to a reduction in remodelling rates. They are also used to decrease skeletal complications of some cancers including a reduction in bone metastases. Following the landmark randomised controlled trial of zoledronate post hip fracture (HORIZON) in which an unexpected survival benefit was found, there has been increasing interest in their potential ability to increase lifespan. This review will consider the clinical evidence for their effect on mortality in both the osteoporosis and non-osteoporosis settings, the latter including studies in intensive care, cancer and cardiovascular disease. Where evidence exists, this review will briefly discuss some of the postulated mechanisms for this survival benefit.

Sepsis Reduces Bone Strength Before Morphologic Changes Are Identifiable

OBJECTIVES

Survivors of critical illness have an increased prevalence of bone fractures. However, early changes in bone strength, and their relationship to structural changes, have not been described. We aimed to characterize early changes in bone functional properties in critical illness and their relationship to changes in bone structure, using a sepsis rodent model.

DESIGN

Experimental study.

SETTING

Animal research laboratory.

SUBJECTS

Adult Sprague-Dawley rats.

INTERVENTIONS

Forty Sprague-Dawley rats were randomized to cecal ligation and puncture or sham surgery. Twenty rodents (10 cecal ligation and puncture, 10 sham) were killed at 24 hours, and 20 more at 96 hours.

MEASUREMENTS AND MAIN RESULTS

Femoral bones were harvested for strength testing, microCT imaging, histologic analysis, and multifrequency scanning probe microscopy. Fracture loads at the femoral neck were significantly reduced for cecal ligation and puncture-exposed rodents at 24 hours (83.39 ± 10.1 vs 103.1 ± 17.6 N; p = 0.014) and 96 hours (81.60 ± 14.2 vs 95.66 ± 14.3 N; p = 0.047). Using multifrequency scanning probe microscopy, collagen elastic modulus was lower in cecal ligation and puncture-exposed rats at 24 hours (1.37 ± 0.2 vs 6.13 ± 0.3 GPa; p = 0.001) and 96 hours (5.57 ± 0.5 vs 6.13 ± 0.3 GPa; p = 0.006). Bone mineral elastic modulus was similar at 24 hours but reduced in cecal ligation and puncture-exposed rodents at 96 hours (75.34 ± 13.2 vs 134.4 ± 8.2 GPa; p < 0.001). There were no bone architectural or bone mineral density differences by microCT. Similarly, histologic analysis demonstrated no difference in collagen and elastin staining, and C-X-C chemokine receptor type 4, nuclear factor kappa beta, and tartrate-resistant acid phosphatase immunostaining.

CONCLUSIONS

In a rodent sepsis model, trabecular bone strength is functionally reduced within 24 hours and is associated with a reduction in collagen and mineral elastic modulus. This is likely to be the result of altered biomechanical properties, rather than increased bone mineral turnover. These data offer both mechanistic insights and may potentially guide development of therapeutic interventions.