Assessment of inflammatory response and sequestration of blood iron transferrin complexes in a rat model of lung injury resulting from exposure to low-frequency shock waves.

OBJECTIVE: Impact of air blast overpressure waves (OPW), or shock wave, with the body wall or body armor produces two types of energy waves: high-frequency low-amplitude stress waves and long-duration low-frequency share waves. These types of energy waves are characterized by different mechanisms of primary tissue injury that mostly affect lung. Systemic inflammation and resultant acute respiratory distress syndrome are known major secondary causative agents of delayed multiple organ failure and subsequent death after OPW exposure. However, association of each pattern of the blast OPW-produced energy waves with postexposure inflammatory events has not yet been delineated. The objectives of the present research were a) establishment of a rat model for assessment of the inflammatory response following lung injury produced by exposure to medium-amplitude (approximately 120 kPa) low-frequency (260+/-5 Hz) OPWs; and b) assessment of the dynamics of alteration in polymorphonuclear leukocyte counts and expression of CD11b adhesion molecules on the surface of polymorphonuclear leukocytes and status of iron-transferrin complexes in peripheral blood after OPW exposure. DESIGN: This study focused on the OPW effects at different time periods, using a sequential approach to postexposure events. Lung injury in rat was induced by OPW generated in a laboratory shock tube. Animals were exposed to OPW (at peak overpressure of 118+/-7 kPa) that produced "moderate" lung injury. SETTING: Military research institute. SUBJECTS: Twenty-seven CVF Sprague-Dawley rats were subjected to OPW exposures, and 17 sham-treated animals were used as control. INTERVENTIONS: Lung tissue and blood samples were collected at 1, 3, 6, 12, and 24 hrs following OPW exposures and compared with samples collected from nonexposed animals. MEASUREMENTS AND MAIN RESULTS: OPW-induced lung injury caused a 2.7-fold increase in the number of circulatory polymorphonuclear leukocytes as early as 1 hr postexposure, which is indicative of mobilization of the pool of marginated polymorphonuclear leukocytes into the free circulation. Polymorphonuclear leukocyte counts increased through the following 3- and 6-hr periods, when they were, respectively, 5-fold and 3.5-fold higher than in controls. These effects were accompanied by a pronounced expression of CD11b in polymorphonuclear leukocytes and tissue sequestration of blood iron-transferrin complexes during the entire 24-hr period of observations. The increase in circulatory polymorphonuclear leukocytes was accompanied by a decrease in iron-transferrin complex concentrations that apparently reflected implication of blood plasma iron in the inflammatory cell response to OPW-induced injury. CONCLUSIONS: The observed dynamics in polymorphonuclear leukocyte alterations in peripheral blood after OPW exposure were similar to those found recently in clinical observations of nonpenetrating injury and in animal models of infectious insults. Therefore, our data suggest that the main pattern of proinflammatory alterations in the rat model of lung injury induced by exposure to long-duration shock wave is similar to patterns that are characteristic of major trauma. The data further suggest that the expression of polymorphonuclear leukocyte CD11b and the response of iron-transferrin complex can be considered as potential surrogate markers in blood for systemic alterations following OPW-induced injury and, therefore, warrant further investigation in a human pilot study.

Electron paramagnetic resonance analysis of transferrin-bound iron in animal models of blunt trauma.

BACKGROUND: Blood iron sequestration is known to be implicated in the systemic acute-phase response to trauma injury. The objective of the present research was to assess the effect of iron sequestration in animal models of blunt trauma by means of electron paramagnetic resonance spectroscopy of iron in complex with transferrin, a main iron-transporting protein in blood, and to correlate this effect with the extent of induced injury. METHODS: Two animal models of blunt trauma were explored in the present study. Blunt trauma in the rat model was produced by exposure of 14 animals to blast overpressure (BOP) (at peak BOP of either 86 +/- 5 kPa or 112 +/- 2 kPa) generated in a shock tube. Blunt trauma in the porcine model was produced by impact of high-speed projectiles made from a rubber-tipped, plastic composite weighing 28.64 +/- 0.12 g (mean +/- SEM, n = 8) with a length of approximately 6 cm and a diameter of approximately 4 cm. The projectiles were propelled by compressed helium onto eight animals at a velocity of 101.8 +/- 3.8 m/s (mean +/- SEM, n = 8) at the point of impact. Each experiment was accompanied by a pathology assessment using an injury scoring system developed for blunt trauma injuries to derive a severity score for whole-body involvement. Amounts of transferrin-bound iron (TRF-[Fe3+]) in whole blood and blood plasma samples were measured using quantitative electron paramagnetic resonance spectroscopy. The observed alterations in the amounts of blood TRF-[Fe3+] were correlated with estimated injury score ratios in each animal. RESULTS: Blunt trauma produced by either BOP exposure of rats or projectile impacts in pigs was accompanied by TRF-[Fe3+] sequestration observed in both blood and blood plasma. The amount of TRF-[Fe3+] in blood was shown to have inverse correlation with the extent of injury (Pearson r = -0.90 in the rat model and r = -0.93 in the porcine model) estimated by injury score ratios and was not dependent on location of the injury (lung, liver, spleen, or jejunum). CONCLUSION: The presented data suggest that assessment of TRF-[Fe3+] in blunt trauma can provide a good deal of information on severity of injury. The response of TRF-[Fe3+] can be considered as a potential surrogate marker of the systemic alterations in blunt trauma and, therefore, warrants further investigation in a human pilot study.