Early reduced bone formation following burn injury in rats is not inversely related to marrow adiposity

OBJECTIVES: The objective of the study was to determine whether postburn reduction of bone formation occurred earlier than 2–3 weeks after burn injury and whether that reduction was inversely related to marrow adiposity. METHODS: Using a rat model of burn injury with sacrifice at 3 days postburn, we measured serum osteocalcin, a biomarker of bone formation, as well as a regulator of glucose metabolism, and counted tibial marrow adipocytes. RESULTS: Serum osteocalcin was reduced as early as 3 days postburn, coinciding with a trend toward decline in marrow adipocyte number rather than demonstrating an inverse relationship with adipocyte count. CONCLUSIONS: Factors that may be responsible for the dissociation include lack of circulating sclerostin, previously reported, increased energy demands following burn injury, increased sympathetic tone and perhaps oxidative stress. The relationship between bone formation and marrow adiposity is complex and subject to a variety of influences.

Calcemic response to burns differs between adults and children: A review of the literature

OBJECTIVES: The calcemic and parathyroid hormone (PTH) responses to severe burn injury appear to differ between children and adults. In our limited studies children exhibited hypocalcemic hypoparathyroidism consistent with up-regulation of the parathyroid calcium-sensing receptor (CaSR) while adults did not, suggesting a developmental cutoff in cytokine-mediated up-regulation of the CaSR. This difference may be clinically important as published studies indicate that extracellular calcium (Ca) may stimulate the inflammatory response. The aim of this study was to examine the existing literature on burns to see if the differences between pediatric and adult calcemic and PTH responses to burn supported our findings providing stronger evidence to support this developmental difference. METHODS: We reviewed the National Library of Medicine database using the terms burns, PTH and ionized calcium and found 9 articles from 8 different medical centers; one was eliminated due to mixing of adults and children. RESULTS: There were 245 burn patients reported from the literature, 178 pediatric and 67 adults. The data are mostly consistent with our reported findings. Of the 10 pediatric patients with severe burns that we studied, mean ionized Ca concentration was below the lower limit of normal of 1.10 mM. The 67 adult burn patients reported in the literature had a mean blood ionized Ca concentration that was within the adult normal range or was lower than normal but with secondary hyperparathyroidism. Moreover, serum PTH concentrations were uniformly low in the 178 children in the burn literature but normal or mildly elevated in the 67 adults. CONCLUSIONS: These results support the hypothesis that the difference between pediatric and adult victims is consistent with an age-related CaSR response to cytokine stimulation and may be consistent with a lower level of inflammation in children. Ionized Ca and PTH might serve as possible therapeutic targets to lower the inflammatory response in burn victims.