Differential effects of thermal injury on circulating insulin-like growth factor binding proteins in burn patients

The results of this report provide evidence that insulin-like growth factor-1 binding proteins (IGFBPs) in human sera are differentially regulated as a result of severe burn injury. Using the ligand binding technique,¹²⁵I-IGF-1 visualizes 5 different protein bands corresponding to those previously reported for IGFBP-1 to 4 with apparent sizes of 23–42 kd in serum samples prepared from severely burned patients and healthy individuals. The level of IGFBP-3 was significantly decreased within 3–5 days of injury and remained depressed for up to 20 days post injury. The average level of this binding protein reached its lowest value within 3–5 days of the injury (3.8±1.48% relative to day 0–1 value, n=4, p<0.001). Serum samples from 3 to 4 patients showed no recovery within 20 days post injury and the level of IGFBP-3 remained significantly depressed (p<0.01). In contrast, the levels of IGFBP-2 and IGFBP-4 increased 2 and 3 fold in the same serum samples within 3–5 days of the burn injury, respectively. This increase returns to normal (day 0–1 value) within 7–10 days for IGFBP-2, but the level of IGFBP-4 remained elevated 4 fold relative to the day 0–1 (p<0.01). However, the abundance of IGFBP-1 in these serum samples was not significantly altered by the burn injury. By controlling for protein loading, these apparent alterations of IGFBPs in the sera of burned patients were not due to hemodilution. Similarly, significant reductions in IGFBP-3 were not likely due to IGFBP-3 specific protease activity in the sera of burn patients since incubation of sera from burn patients and normal individuals at 37° C did not alter the pattern of IGFBPs in sera obtained from normal individuals. Of interest, the level of IGF-1 protein in these samples was also markedly reduced following severe burn injury similar to IGFBP-3. The results of this study suggest that a marked reduction of serum IGF-1 seen in burn patients is associated with a significant reduction of IGFBP-3, a major IGF-1 binding protein in human serum.