Development of a Murine Model of Blunt Hepatic Trauma

Despite the prevalence of blunt hepatic trauma in humans, there are few rodent models of blunt trauma that can be used to study the associated inflammatory responses. We present a mouse model of blunt hepatic trauma that was created by using a cortical contusion device. Male mice were anesthetized with ketamine–xylazine–buprenorphine and placed in left lateral recumbency. A position of 2 mm ventral to the posterior axillary line and 5 mm caudal to the costal margin on the right side was targeted for impact. An impact velocity of 6 m/s and a piston depth of 12 mm produced a consistent pattern of hepatic injury with low mortality. All mice that recovered from anesthesia survived without complication for the length of the study. Mice were euthanized at various time points (n = 5 per group) until 7 d after injury for gross examination and collection of blood and peritoneal lavage fluids. Some mice were reanesthetized for serial monitoring of hepatic lesions via MRI. At 2 h after trauma, mice consistently displayed laceration, hematoma, and discoloration of the right lateral and caudate liver lobes, with intraabdominal hemorrhage but no other gross injuries. Blood and peritoneal lavage fluid were collected from all mice for cytokine analysis. At 2 h after trauma, there were significant increases in plasma IL10 as well as peritoneal lavage fluid IL6 and CXCL1/KC; however, these levels decreased within 24 h. At 7 d after trauma, the mice had regained body weight, and the hepatic lesions, which initially had increased in size during the first 48 h, had returned to their original size. In summary, this technique produced a reliable, low mortality, murine model that recreates features of blunt abdominal liver injury in human subjects with similar acute inflammatory response.Abbreviation: CXCL1/KC, keratinocyte-derived chemokineTrauma is the most frequent cause of mortality worldwide,¹¹ and in cases of blunt abdominal trauma, the liver is the most frequently injured organ.⁴ In humans, traumatic injuries to the liver are graded (I through VI) according to the American Association for the Surgery of Trauma Liver Injury Scale, which is based on the severity of lesions, including hematomas, lacerations and vascular disruption.¹⁰ Parenchymal injuries (grades I through III) are more common than are major vascular injuries (grades V and VI), correlating with the greater hemodynamic stability and lower early mortality rates of parenchymal damage.⁴ Although early mortality rates may be low in low-grade injuries, the overall mortality rates for abdominal traumas involving liver are greater than that of abdominal trauma without liver damage. Late mortality after liver injury is associated with immunologic dysfunction, leading to systemic inflammatory response syndrome, sepsis, and multiple-organ failure.⁶To study the complex immune responses surrounding blunt hepatic trauma, an appropriate animal model is imperative, but few animal models of liver trauma have been described. Swine traditionally have been the preferred model because of similarity of the liver anatomy and lesions to those of human cases.² Nonpenetrating models have been developed in swine and involve impact by crossbow or other blunted projectiles.²⁰ The first rodent model of trauma was developed by positioning anesthetized rats under a column containing a flat weight.³ In that model, the severity of injury could be adjusted by the height of the column. This model was distinctive in its use of the least sentient species to date. The large animal models and even the rat model would readily support studies of treatment modalities and the measurement of hemodynamic parameters. For extensively characterizing the immunopathology associated with liver trauma, a murine model could offer distinct advantages, including the ready availability of transgenic mice and the extensive array of reagents for immunologic studies.The purpose of the current study was to develop a reliable and reproducible, closed abdominal, murine model of blunt hepatic trauma that is suitable for studies of posttraumatic immune dysfunction and related complications. Our first aim was to develop a low-mortality model that demonstrated gross and microscopic hepatic lesions similar to those seen in humans. The second study aim was to define selected systemic and local immune responses, including immune cell counts and cytokine levels. In addition, we examined the potential use of a noninvasive imaging technique (MRI) for the sequential evaluation of hepatic lesions.