Experimental trauma models: an update

Confocal Raman Micro-Spectroscopy for Discrimination of Glycerol Diffusivity in Ex Vivo Porcine Dura Mater

Dura mater (DM) is a connective tissue with dense collagen, which is a protective membrane surrounding the human brain. The optical clearing (OC) method was used to make DM more transparent, thereby allowing to increase in-depth investigation by confocal Raman micro-spectroscopy and estimate the diffusivity of 50% glycerol and water migration. Glycerol concentration was obtained, and the diffusion coefficient was calculated, which ranged from 9.6 × 10^-6 to 3.0 × 10^-5 cm²/s. Collagen-related Raman band intensities were significantly increased for all depths from 50 to 200 µm after treatment. In addition, the changes in water content during OC showed that 50% glycerol induces tissue dehydration. Weakly and strongly bound water types were found to be most concentrated, playing a major role in the glycerol-induced water flux and OC. Results show that OC is an efficient method for controlling the DM optical properties, thereby enhancing the in-depth probing for laser therapy and diagnostics of the brain. DM is a comparable to various collagen-containing tissues and organs, such as sclera of eyes and skin dermis.

A Toolbox to Investigate the Impact of Impaired Oxygen Delivery in Experimental Disease Models

Impaired oxygen utilization is the underlying pathophysiological process in different shock states. Clinically most important are septic and hemorrhagic shock, which comprise more than 75% of all clinical cases of shock. Both forms lead to severe dysfunction of the microcirculation and the mitochondria that can cause or further aggravate tissue damage and inflammation. However, the detailed mechanisms of acute and long-term effects of impaired oxygen utilization are still elusive. Importantly, a defective oxygen exploitation can impact multiple organs simultaneously and organ damage can be aggravated due to intense organ cross-talk or the presence of a systemic inflammatory response. Complexity is further increased through a large heterogeneity in the human population, differences in genetics, age and gender, comorbidities or disease history. To gain a deeper understanding of the principles, mechanisms, interconnections and consequences of impaired oxygen delivery and utilization, interdisciplinary preclinical as well as clinical research is required. In this review, we provide a "tool-box" that covers widely used animal disease models for septic and hemorrhagic shock and methods to determine the structure and function of the microcirculation as well as mitochondrial function. Furthermore, we suggest magnetic resonance imaging as a multimodal imaging platform to noninvasively assess the consequences of impaired oxygen delivery on organ function, cell metabolism, alterations in tissue textures or inflammation. Combining structural and functional analyses of oxygen delivery and utilization in animal models with additional data obtained by multiparametric MRI-based techniques can help to unravel mechanisms underlying immediate effects as well as long-term consequences of impaired oxygen delivery on multiple organs and may narrow the gap between experimental preclinical research and the human patient.

Preclinical models for studying immune responses to traumatic injury

Traumatic injury initiates a large and complex immune response in the minutes after the initial insult, comprising of simultaneous pro- and anti-inflammatory responses. In patients that survive the initial injury, these immune responses are believed to contribute towards complications such as the development of sepsis and multiple organ dysfunction syndrome. These post-traumatic complications affect a significant proportion of patients and are a major contributing factor for poor outcomes and an increased burden on healthcare systems. Therefore, understanding the immune responses to trauma is crucial for improving patient outcomes through the development of novel therapeutics and refining resuscitation strategies. In order to do this, preclinical animal models must mimic human immune responses as much as possible, and as such, we need to understand the constraints of each species in the context of trauma. A number of species have been used in this field; however, these models are limited by their genetic background and their capacity for recapitulating human immune function. This review provides a brief overview of the immune response in critically injured human patients and discusses the most commonly used species for modelling trauma, focusing on how their immune response to serious injury and haemorrhage compares to that of humans.

Physiology of Human Hemorrhage and Compensation

Hemorrhage is a leading cause of death following traumatic injuries in the United States. Much of the previous work in assessing the physiology and pathophysiology underlying blood loss has focused on descriptive measures of hemodynamic responses such as blood pressure, cardiac output, stroke volume, heart rate, and vascular resistance as indicators of changes in organ perfusion. More recent work has shifted the focus toward understanding mechanisms of compensation for reduced systemic delivery and cellular utilization of oxygen as a more comprehensive approach to understanding the complex physiologic changes that occur following and during blood loss. In this article, we begin with applying dimensional analysis for comparison of animal models, and progress to descriptions of various physiological consequences of hemorrhage. We then introduce the complementary side of compensation by detailing the complexity and integration of various compensatory mechanisms that are activated from the initiation of hemorrhage and serve to maintain adequate vital organ perfusion and hemodynamic stability in the scenario of reduced systemic delivery of oxygen until the onset of hemodynamic decompensation. New data are introduced that challenge legacy concepts related to mechanisms that underlie baroreflex functions and provide novel insights into the measurement of the integrated response of compensation to central hypovolemia known as the compensatory reserve. The impact of demographic and environmental factors on tolerance to hemorrhage is also reviewed. Finally, we describe how understanding the physiology of compensation can be translated to applications for early assessment of the clinical status and accurate triage of hypovolemic and hypotensive patients. © 2021 American Physiological Society. Compr Physiol 11:1531-1574, 2021.

Mechanical Characterization and Modeling of the Porcine Cerebral Meninges

The cerebral meninges, made up of the dura, arachnoid, and pia mater, is a tri-layer membrane that surrounds the brain and the spinal cord and has an important function in protecting the brain from injury. Understanding its mechanical behavior is important to ensure the accuracy of finite element (FE) head model simulations which are commonly used in the study of traumatic brain injury (TBI). Mechanical characterization of freshly excised porcine dura-arachnoid mater (DAM) was achieved using uniaxial tensile testing and bulge inflation testing, highlighting the dependency of the identified parameters on the testing method. Experimental data was fit to the Ogden hyperelastic material model with best fit material parameters of μ = 450 ± 190 kPa and α = 16.55 ± 3.16 for uniaxial testing, and μ = 234 ± 193 kPa and α = 8.19 ± 3.29 for bulge inflation testing. The average ultimate tensile strength of the DAM was 6.91 ± 2.00 MPa (uniaxial), and the rupture stress at burst was 2.08 ± 0.41 MPa (inflation). A structural analysis using small angle light scattering (SALS) revealed that while local regions of highly aligned fibers exist, globally, there is no preferred orientation of fibers and the cerebral DAM can be considered to be structurally isotropic. This confirms the results of the uniaxial mechanical testing which found that there was no statistical difference between samples tested in the longitudinal and transversal direction (p = 0.13 for μ, p = 0.87 for α). A finite element simulation of a craniotomy procedure following brain swelling revealed that the mechanical properties of the meninges are important for predicting accurate stress and strain fields in the brain and meninges. Indeed, a simulation using a common linear elastic representation of the meninges was compared to the present material properties (Ogden model) and the intracranial pressure was found to differ by a factor of 3. The current study has provided researchers with primary experimental data on the mechanical behavior of the meninges which will further improve the accuracy of FE head models used in TBI.

Modeling trauma in rats: similarities to humans and potential pitfalls to consider

Trauma is the leading cause of mortality in humans below the age of 40. Patients injured by accidents frequently suffer severe multiple trauma, which is life-threatening and leads to death in many cases. In multiply injured patients, thoracic trauma constitutes the third most common cause of mortality after abdominal injury and head trauma. Furthermore, 40-50% of all trauma-related deaths within the first 48 h after hospital admission result from uncontrolled hemorrhage. Physical trauma and hemorrhage are frequently associated with complex pathophysiological and immunological responses. To develop a greater understanding of the mechanisms of single and/or multiple trauma, reliable and reproducible animal models, fulfilling the ethical 3 R's criteria (Replacement, Reduction and Refinement), established by Russell and Burch in 'The Principles of Human Experimental Technique' (published 1959), are required. These should reflect both the complex pathophysiological and the immunological alterations induced by trauma, with the objective to translate the findings to the human situation, providing new clinical treatment approaches for patients affected by severe trauma. Small animal models are the most frequently used in trauma research. Rattus norvegicus was the first mammalian species domesticated for scientific research, dating back to 1830. To date, there exist numerous well-established procedures to mimic different forms of injury patterns in rats, animals that are uncomplicated in handling and housing. Nevertheless, there are some physiological and genetic differences between humans and rats, which should be carefully considered when rats are chosen as a model organism. The aim of this review is to illustrate the advantages as well as the disadvantages of rat models, which should be considered in trauma research when selecting an appropriate in vivo model. Being the most common and important models in trauma research, this review focuses on hemorrhagic shock, blunt chest trauma, bone fracture, skin and soft-tissue trauma, burns, traumatic brain injury and polytrauma.

A systematic review of large animal models of combined traumatic brain injury and hemorrhagic shock

Traumatic brain injury (TBI) and severe blood loss (SBL) frequently co-occur in human trauma, resulting in high levels of mortality and morbidity. Importantly, each of the individual post-injury cascades is characterized by complex and potentially opposing pathophysiological responses, complicating optimal resuscitation and therapeutic approaches. Large animal models of poly-neurotrauma closely mimic human physiology, but a systematic literature review of published models has been lacking. The current review suggests a relative paucity of large animal poly-neurotrauma studies (N = 52), with meta-statistics revealing trends for animal species (exclusively swine), characteristics (use of single biological sex, use of juveniles) and TBI models. Although most studies have targeted blood loss volumes of 35-45%, the associated mortality rates are much lower relative to Class III/IV human trauma. This discrepancy may result from potentially mitigating experimental factors (e.g., mechanical ventilation prior to or during injury, pausing/resuming blood loss based on physiological parameters, administration of small volume fluid resuscitation) that are rarely associated with human trauma, highlighting the need for additional work in this area.

Feasibility of a Portable Abdominal Insufflation Device for Controlling Intraperitoneal Bleeding After Abdominal Blunt Trauma

Uncontrolled bleeding contributes to 30% to 40% of trauma-related deaths and is the leading cause of potentially preventable deaths. Currently, there is no effective method available to first responders for temporary control of noncompressible intraabdominal bleeding while patients are transported to the hospital. Our previous studies demonstrated that abdominal insufflation provides effective temporary bleeding control. The study aims to prove the feasibility (insufflation to a target pressure) and safety (cardiovascular and respiratory effects) of a novel portable abdominal insufflation device (PAID) designed to control the intraperitoneal bleeding caused by abdominal trauma. The PAID prototype is based on a patented design and manufactured via additive manufacturing. PAID contains a 16-g CO2cartridge and an electronic pressure transducer. PAID was tested on a bench top and a swine animal model. For the animal model study, the intraperitoneal pressure as well as cardiorespiratory parameters (hearth rate, SpO2[peripheral capillary oxygen saturation], and blood pressure) were continuously monitored during the insufflation procedure. The prototype functioned according to specifications on both bench top and animal models. CO2insufflation of the peritoneal cavity was delivered up the target 20 mm Hg and maintained for 30 minutes from 1 or 2 cartridges in the swine model. No intraoperative incidents were registered, and all the recorded physiological parameters were within normal limits. The PAID prototype is a feasible, easy to use device that provides quick, controlled, and safe insufflation of the peritoneal cavity. Future studies will focus on testing the next-generation, semiautomatic PAID prototype in a severe intraabdominal injury model.

Role of Hemorrhagic Shock in Experimental Polytrauma

Hemorrhagic shock (HS) after tissue trauma increases the complication and mortality rate of polytrauma (PT) patients. Although several murine trauma models have been introduced, there is a lack of knowledge about the exact impact of an additional HS. We hypothesized that HS significantly contributes to organ injury, which can be reliably monitored by detection of specific organ damage markers. Therefore we established a novel clinically relevant PT plus HS model in C57BL/6 mice which were randomly assigned to control, HS, PT, or PT+HS procedure (n = 8 per group). For induction of PT, anesthetized animals received a blunt chest trauma, head injury, femur fracture, and soft tissue injury. HS was induced by pressure-controlled blood drawing (mean arterial blood pressure of 30 mmHg for 60 min) and mice then resuscitated with ionosterile (4 × volume drawn), monitored, and killed for blood and organ harvesting 4 h after injury. After HS and resuscitation, PT+HS mice required earlier and overall more catecholamine support than HS animals to keep their mean arterial blood pressure. HS significantly contributed to the systemic release of interleukin-6 and high mobility group box 1 protein. Furthermore, the histological lung injury score, pulmonary edema, neutrophil influx, and plasma clara cell protein 16 were all significantly enhanced in PT animals in the presence of an additional HS. Although early morphological changes were minor, HS also contributed functionally to remote acute kidney injury but not to early liver damage. Moreover, PT-induced systemic endothelial injury, as determined by plasma syndecan-1 levels, was significantly aggravated by an additional HS. These results indicate that HS adds to the systemic inflammatory reaction early after PT. Within hours after PT, HS seems to aggravate pulmonary damage and to worsen renal and endothelial function which might overall contribute to the development of early multiple organ dysfunction.

Inflammatory Profile in Response to Uncontrolled Hemorrhage in a Non-Human Primate (Rhesus Macaque) Model

BACKGROUND

Uncontrolled hemorrhage (UH), the leading cause of potentially survivable combat-related death, elicits a deleterious inflammatory response. Our group previously reported an increased secretion of pro-inflammatory cytokines in a novel non-human primate model of UH; however, to better understand the molecular profile of the inflammatory response to UH, we performed a comprehensive evaluation of inflammation at the proteomic and transcriptomic level.

METHODS

Anesthetized rhesus macaques (n = 8) underwent UH by 60% left lobe hepatectomy T = 0 min. At T = 5 min, animals received 11 mL of 5% albumin followed by normal saline infusion to a total resuscitation volume of 20 mL/kg by T = 120 min. Blood (T = 0, 5, 20, 120, 480 min) was collected for qPCR and multiplex cytokine quantification. Results from each non-human primate (NHP) per time-point are shown. Statistical analysis by one-way ANOVA with repeated measures, P <0.05 was considered significant.

RESULTS

Luminex analysis in serum revealed significant up-regulation compared with baseline of 8 cytokines/chemokines starting T = 120 min postinjury and significant down-regulation of 4 cytokines/chemokines as early as T = 20 min postinjury. Gene expression analysis in white blood cells uncovered 10 genes that were up-regulated greater than 3-fold compared with baseline and 29 genes that were down-regulated greater than 3-fold.

CONCLUSION

The present study confirms the presence of systemic inflammation after UH at the proteomic and transcriptomic level providing insight into the inflammatory mediators that are involved as well as their kinetics following UH. The data demonstrates that NHP hemorrhage models may be suitable for evaluating therapeutics to control inflammation following hemorrhage.

Mouse Injury Model of Polytrauma and Shock

Severe injury and shock remain major sources of morbidity and mortality worldwide. Immunologic dysregulation following trauma contributes to these poor outcomes. Few, if any, therapeutic interventions have benefited these patients, and this is due to our limited understanding of the host response to injury and shock. The Food and Drug Administration requires preclinical animal studies prior to any interventional trials in humans; thus, animal models of injury and shock will remain the mainstay for trauma research. However, adequate animal models that reflect the severe response to trauma in both the acute and subacute phases have been limited. Here we describe a novel murine model of polytrauma and shock that combines hemorrhagic shock, cecectomy, long bone fracture, and soft-tissue damage. This model produces an equivalent Injury Severity Score associated with adverse outcomes in humans, and may better recapitulate the human leukocyte, cytokine, transcriptomic, and overall inflammatory response following injury and hemorrhagic shock.

A new multiple trauma model of the mouse

Background

Blunt trauma is the most frequent mechanism of injury in multiple trauma, commonly resulting from road traffic collisions or falls. Two of the most frequent injuries in patients with multiple trauma are chest trauma and extremity fracture. Several trauma mouse models combine chest trauma and head injury, but no trauma mouse model to date includes the combination of long bone fractures and chest trauma. Outcome is essentially determined by the combination of these injuries. In this study, we attempted to establish a reproducible novel multiple trauma model in mice that combines blunt trauma, major injuries and simple practicability.

Methods

Ninety-six male C57BL/6 N mice (n = 8/group) were subjected to trauma for isolated femur fracture and a combination of femur fracture and chest injury. Serum samples of mice were obtained by heart puncture at defined time points of 0 h (hour), 6 h, 12 h, 24 h, 3 d (days), and 7 d.

Results

A tendency toward reduced weight and temperature was observed at 24 h after chest trauma and femur fracture. Blood analyses revealed a decrease in hemoglobin during the first 24 h after trauma. Some animals were killed by heart puncture immediately after chest contusion; these animals showed the most severe lung contusion and hemorrhage. The extent of structural lung injury varied in different mice but was evident in all animals. Representative H&E-stained (Haematoxylin and Eosin-stained) paraffin lung sections of mice with multiple trauma revealed hemorrhage and an inflammatory immune response. Plasma samples of mice with chest trauma and femur fracture showed an up-regulation of IL-1β (Interleukin-1β), IL-6, IL-10, IL-12p70 and TNF-α (Tumor necrosis factor- α) compared with the control group. Mice with femur fracture and chest trauma showed a significant up-regulation of IL-6 compared to group with isolated femur fracture.

Conclusions

The multiple trauma mouse model comprising chest trauma and femur fracture enables many analogies to clinical cases of multiple trauma in humans and demonstrates associated characteristic clinical and pathophysiological changes. This model is easy to perform, is economical and can be used for further research examining specific immunological questions.

Murine Models of Sepsis and Trauma: Can We Bridge the Gap?

Sepsis and trauma are both leading causes of death in the United States and represent major public health challenges. Murine models have largely been used in sepsis and trauma research to better understand the pathophysiological changes that occur after an insult and to develop potential life-saving therapeutic agents. Mice are favorable subjects for this type of research given the variety of readily available strains including inbred, outbred, and transgenic strains. In addition, they are relatively easy to maintain and have a high fecundity. However, pharmacological therapies demonstrating promise in preclinical mouse models of sepsis and trauma often fail to demonstrate similar efficacy in human clinical trials, prompting considerable criticism surrounding the capacity of murine models to recapitulate complex human diseases like sepsis and traumatic injury. Fundamental differences between the two species include, but are not limited to, the divergence of the transcriptomic response, the mismatch of temporal response patterns, differences in both innate and adaptive immunity, and heterogeneity within the human population in comparison to the homogeneity of highly inbred mouse strains. Given the ongoing controversy, this narrative review aims to not only highlight the historical importance of the mouse as an animal research model but also highlight the current benefits and limitations of the model as it pertains to sepsis and trauma. Lastly, this review will propose future directions that may promote further use of the model.

The approximated cardiovascular reserve index complies with haemorrhage related hemodynamic deterioration pattern: A swine exsanguination model

Background

To estimate the cardiovascular reserve we formulated the Cardiovascular Reserve Index (CVRI) based on physiological measurements. The aim of this study was to evaluate the pattern of CVRI in haemorrhage-related haemodynamic deterioration in an animal model simulating combat injury.

Methods

Data were collected retrospectively from a research database of swine exsanguination model in which serial physiological measurements were made under anesthesia in 12 swine of haemorrhagic injury and 5 controls. We calculated the approximated CVRI (CVRI_A). The course of haemodynamic deterioration was defined according to the cumulative blood loss until shock. The ability of heart rate (HR), mean arterial blood pressure (MABP), stroke volume (SV), cardiac output (CO) and systemic vascular resistance (SVR) and the CVRI_A to predict haemodynamic deterioration was evaluated according to three criteria: strength of association with the course of haemodynamic deterioration (r² > 0.5); threshold for haemodynamic deterioration detection; and range at which the parameter remained consistently monotonous course of deterioration.

Results

Three parameters met the first criterion for prediction of haemodynamic deterioration: HR (r² = 0.59), SV (r² = 0.57) and CVRI_A (r² = 0.66). Results were negative for MABP (r² = 0.27), CO (r² = 0.33) and SVR (r² = 0.02). The detection threshold of the CVRI_A was 200–300 ml blood loss whereas HR, SV and CO showed a delay in detection, MABP and CVRI exhibited a wide indicative range toward shock.

Conclusions

The CVRI_A met preset criteria of a potential predictor of haemorrhage-related haemodynamic deterioration. Prospective studies are required to evaluate use of the CVRI in combat medicine.

Level of evidence

Level III.

•

Cardiovascular reserve index (CVRI) estimates the assumed cardiovascular reserve.

•

CVRI is computed by routinely measured physiological parameters.

•

Criteria for haemodynamic deterioration prediction were preset.

•

CVRI met preset criteria (correlation, detecting threshold and indicative range).

OBESITY AND CRITICAL ILLNESS: INSIGHTS FROM ANIMAL MODELS

Critical illness is a major cause of morbidity and mortality around the world. While obesity is often detrimental in the context of trauma, it is paradoxically associated with improved outcomes in some septic patients. The reasons for these disparate outcomes are not well understood. A number of animal models have been used to study the obese response to various forms of critical illness. Just as there have been many animal models that have attempted to mimic clinical conditions, there are many clinical scenarios that can occur in the highly heterogeneous critically ill patient population that occupies hospitals and intensive care units. This poses a formidable challenge for clinicians and researchers attempting to understand the mechanisms of disease and develop appropriate therapies and treatment algorithms for specific subsets of patients, including the obese. The development of new, and the modification of existing animal models, is important in order to bring effective treatments to a wide range of patients. Not only do experimental variables need to be matched as closely as possible to clinical scenarios, but animal models with pre-existing comorbid conditions need to be studied. This review briefly summarizes animal models of hemorrhage, blunt trauma, traumatic brain injury, and sepsis. It also discusses what has been learned through the use of obese models to study the pathophysiology of critical illness in light of what has been demonstrated in the clinical literature.

Ovariectomy-Induced Osteopenia Influences the Middle and Late Periods of Bone Healing in a Mouse Femoral Osteotomy Model

OBJECTIVE

It is known that bone healing is delayed in the presence of osteoporosis in humans. However, due to the complexities of the healing of osteoporotic fractures, animal models may be more appropriate for studying the effects of osteoporosis in more detail and for testing drugs on the fracture repair process. The purpose of this study was to investigate the influence of ovariectomy-induced osteopenia in bone healing in an open femoral osteotomy model, and to test the feasibility of this model for evaluating the healing process under osteopenic conditions.

METHODS

Ovariectomized (OVX) mouse models were employed to assess the effects of osteopenia on fracture healing, A mid-shaft femur osteotomy model was also established 3 weeks after ovariectomy as an osteopenic fracture group (OVX group). Femurs were then harvested at 2 weeks and 6 weeks after fracture for X-ray radiography, micro-computed tomography (micro-CT), histology, and biomechanical analysis. A sham-operated group (sham group) was used for comparison.

RESULTS

The OVX mice had significantly lower bone volume density (BVF), volumetric bone mineral density (vBMD), and tissue mineral density (TMD) in the fracture calluses at 6 weeks (p<0.05), and similar trend was observed in 2 weeks. Additionally, larger calluses in OVX animals were observed via micro-CT and X-ray, but these did not result in better healing outcomes, as determined by biomechanical test at 6 weeks. Histological images of the healing fractures in the OVX mice found hastening of broken end resorption and delay of hard callus remodeling. The impaired biomechanical measurements in the OVX group (p<0.05) were consistent with micro-CT measurements and radiographic scoring, which also indicated delay in fracture healing of the OVX group.

CONCLUSIONS

This study provided evidence that ovariectomy-induced osteopenia impair the middle and late bone healing process. These data also supported the validity of the mouse femoral osteotomy model in evaluating the process of bone healing under osteopenic conditions.

Evaluation of procalcitonin postmortem levels in some models of death: An experimental study

Post-mortem determination of biochemical parameters, especially for obscure cases, has been recognized useful in diagnosis of the underlying causes of death. Procalcitonin (PCT) is known to rise in a response to any proinflammatory stimulus. The present study aims to estimate postmortem PCT levels in serum and kidney, liver, brain; and whether it is similar in different causes of death models (trauma, drowning and freezing) models or not. The study was performed on 60 male rabbits. Rabbits were divided into four different death induced models (15 rabbit each): trauma, infection, drowning and freezing models. At the end of the study, all rabbits were sacrificed; blood samples, kidneys, livers and brains were collected. PCT was measured using ELISA assay. Results showed highly significant increase in PCT levels in all tested samples in different models of death. The infection induced model showed the highest levels in all tested samples compared to other groups mainly in liver; followed by trauma model and drowning model which were increased mainly in brain's samples. The least model which showed increased PCT levels was the freezing model mainly in liver samples. Post Hoc multiple comparisons test showed significant differences between groups in most of liver, brain and kidney samples, while PCT serum blood samples were significant only between trauma and infection groups. It was concluded that PCT can differentiate between sepsis and non-sepsis related deaths and that organs like liver, kidney and brain PCT levels could be an alternative to serum PCT for the diagnosis of postmortem sepsis.

Acute perioperative-stress-induced increase of atherosclerotic plaque volume and vulnerability to rupture in apolipoprotein-E-deficient mice is amenable to statin treatment and IL-6 inhibition

Myocardial infarction and stroke are frequent after surgical procedures and consume a considerable amount of benefit of surgical therapy. Perioperative stress, induced by surgery, is composed of hemodynamic and inflammatory reactions. The effects of perioperative stress on atherosclerotic plaques are ill-defined. Murine models to investigate the influence of perioperative stress on plaque stability and rupture are not available. We developed a model to investigate the influence of perioperative stress on plaque growth and stability by exposing apolipoprotein-E-deficient mice, fed a high cholesterol diet for 7 weeks, to a double hit consisting of 30 min of laparotomy combined with a substantial blood loss (approximately 20% of total blood volume; 400 µl). The innominate artery was harvested 72 h after the intervention. Control groups were sham and baseline controls. Interleukin-6 (IL-6) and serum amyloid A (SAA) plasma levels were determined. Plaque load, vascular smooth muscle cell (VSMC) and macrophage content were quantified. Plaque stability was assessed using the Stary score and frequency of signs of plaque rupture were assessed. High-dose atorvastatin (80 mg/kg body weight/day) was administered for 6 days starting 3 days prior to the double hit. A single dose of an IL-6-neutralizing antibody or the fusion protein gp130-Fc selectively targeting IL-6 trans-signaling was subcutaneously injected. IL-6 plasma levels increased, peaking at 6 h after the intervention. SAA levels peaked at 24 h (n=4, P<0.01). Plaque volume increased significantly with the double hit compared to sham (n=8, P<0.01). More plaques were scored as complex or bearing signs of rupture after the double hit compared to sham (n=5-8, P<0.05). Relative VSMC and macrophage content remained unchanged. IL-6-inhibition or atorvastatin, but not blocking of IL-6 trans-signaling, significantly decreased plaque volume and complexity (n=8, P<0.01). Using this model, researchers will be able to further investigate the pathophysiology of perioperative plaque stability, which can result in myocardial infarction, and, additionally, to test potential protective strategies.

Summary: We developed a model to study the dynamics of atherosclerotic plaque growth and stability following surgery, and show that IL-6 inhibition and statins beneficially affect plaque volume and complexity.

The Effect of Blood Loss in the Presence and Absence of Severe Soft Tissue Injury on Hemodynamic and Metabolic Parameters; an Experimental study

INTRODUCTION

The effect of severe soft tissue injury on the severity of hemorrhagic shock is still unknown. Therefore, the present study was aimed to determine hemodynamic and metabolic changes in traumatic/hemorrhagic shock in an animal model.

METHODS

Forty male rats were randomly divided into 4 equal groups including sham, hemorrhagic shock, soft tissue injury, and hemorrhagic shock + soft tissue injury groups. The changes in blood pressure, central venous pressure (CVP) level, acidity (pH), and base excess were dynamically monitored and comparedsented.

RESULTS

Mean arterial blood pressure decreased significantly in hemorrhagic shock (df: 12; F=10.9; p<0.001) and severe soft tissue injury + hemorrhagic shock (df: 12; F=11.7; p<0.001) groups 15 minutes and 5 minutes after injury, respectively. A similar trend was observed in CVP in severe soft tissue injury + hemorrhagic shock group (df: 12; F=8.9; p<0.001). After 40 minutes, pH was significantly lower in hemorrhagic shock (df: 12; F=6.8; p=0.009) and severe soft tissue injury + hemorrhagic shock (df: 12; F=7.9; p=0.003) groups. Base excess changes during follow ups have a similar trend. (df: 12; F=11.3; p<0.001).

CONCLUSION

The results of this study have shown that the effect of hemorrhage on the decrease of mean arterial blood pressure, CVP, pH, and base excess is the same in the presence or absence of soft tissue injury.

Modeling acute traumatic injury

Acute traumatic injury is a complex disease that has remained a leading cause of death, which affects all ages in our society. Direct mechanical insult to tissues may result in physiological and immunologic disturbances brought about by blood loss, coagulopathy, as well as ischemia and reperfusion insults. This inappropriate response leads to an abnormal release of endogenous mediators of inflammation that synergistically contribute to the incidence of morbidity and mortality. This aberrant activation and suppression of the immune system follows a bimodal pattern, wherein activation of the innate immune responses is followed by an anti-inflammatory response with suppression of the adaptive immunity, which can subsequently lead secondary insults and multiple organ dysfunction. Traumatic injury rodent and swine models have been used to describe many of the underlying pathologic mechanisms, which have led to an improved understanding of the morbidity and mortality associated with critically ill trauma patients. The enigmatic immunopathology of the human immunologic response after severe trauma, however, has never more been apparent and there grows a need for a clinically relevant animal model, which mimics this immune physiology to enhance the care of the most severely injured. This has necessitated preclinical studies in a more closely related model system, the nonhuman primate. In this review article, we summarize animal models of trauma that have provided insight into the clinical response and understanding of cellular mechanisms involved in the onset and progression of ischemia-reperfusion injury as well as describe future treatment options using immunomodulation-based strategies.

Blood-banking techniques for plateletpheresis in swine

During the past several years, trauma resuscitation in human patients has evolved from decreased use of crystalloids to increased use of blood products. Of high interest is the role of platelets in trauma resuscitation. Because conducting prehos- pital resuscitation in human trauma patients is very difficult, swine are often the animal model of choice for such studies because their coagulation and hemodynamic systems are similar to those in humans. However, consistent production of sufficient swine platelets for such studies has not previously been achieved. We developed a method for producing swine platelets by using standard human techniques and equipment. We assessed pH, pO2, pCO2, lactate, thromboelastography, and platelet aggregation over 5 d of storage to determine whether the swine platelet product met the American Association of Blood Banks (AABB) standards for transfusion. Swine platelets met AABB standards at 24 h but not at later time points. In addition, we fluorescently labeled nonautologous platelets and then measured their percentage recovery over 5 h (the time used in subsequent experimental studies) when transfused into a recipient pig. We showed that 80% of the platelets stored for 24 h remained in the circulation and increased the recipient pigs' thromboelastographic responses, indicating that the platelets were viable and active. Therefore, swine platelets stored for 24 h by using standard human products met the AABB criteria and were functional.

Intravenous hemostats: challenges in translation to patients

Excessive bleeding and the resulting complications are a leading killer of young people globally. There are many successful methods to halt bleeding in the extremities, including compression, tourniquets, and dressings. However, current treatments for internal hemorrhage (including from head or truncal injuries), termed non-compressible bleeding, are inadequate. For these non-compressible injuries, blood transfusions are the current treatment standard. However, they must be refrigerated, may potentially transfer disease, and are of limited supply. In addition, time is of the essence for halting hemorrhage, since more than a third of civilian deaths due to hemorrhage from trauma occur before the patient even reaches the hospital. As a result, particles that can cross-link activated platelets through the glycoprotein IIb/IIIa receptor expressed on activated platelets are being investigated as an alternative treatment for non-compressible bleeding. Ideally, these particles would interact specifically with platelets to stabilize the platelet plug. Initial designs used biologically derived microparticles with red blood cell fragment or albumin cores decorated with RGD or fibrinogen, which bind to GPIIb/IIIa. More recently there has been research into the use of fully synthetic nanoparticles with liposomal or polymer cores that crosslink platelets through a targeting peptide bound to the surface. Some of the challenges for the development of these particles include appropriate sizing to prevent blocking the capillaries of the lungs, immune system evasion to prevent strong reactions and increase circulation time, and storage and resuspension so that first responders can easily use the particles. In addition, the effectiveness of the variety of animal bleeding models in predicting outcomes must be examined before test results can be fully understood. Progress has been made in the development of particles to combat hemorrhage, but issues of immune sensitivity and storage must be resolved before these types of particles can be translated for human use.

Towards clinical management of traumatic brain injury: a review of models and mechanisms from a biomechanical perspective

Traumatic brain injury (TBI) is a major worldwide healthcare problem. Despite promising outcomes from many preclinical studies, the failure of several clinical studies to identify effective therapeutic and pharmacological approaches for TBI suggests that methods to improve the translational potential of preclinical studies are highly desirable. Rodent models of TBI are increasingly in demand for preclinical research, particularly for closed head injury (CHI), which mimics the most common type of TBI observed clinically. Although seemingly simple to establish, CHI models are particularly prone to experimental variability. Promisingly, bioengineering-oriented research has advanced our understanding of the nature of the mechanical forces and resulting head and brain motion during TBI. However, many neuroscience-oriented laboratories lack guidance with respect to fundamental biomechanical principles of TBI. Here, we review key historical and current literature that is relevant to the investigation of TBI from clinical, physiological and biomechanical perspectives, and comment on how the current challenges associated with rodent TBI models, particularly those involving CHI, could be improved.

Rapid analytical methods for on-site triage for traumatic brain injury

Traumatic brain injury (TBI) results from an event that causes rapid acceleration and deceleration of the brain or penetration of the skull with an object. Responses to stimuli and questions, loss of consciousness, and altered behavior are symptoms currently used to justify brain imaging for diagnosis and therapeutic guidance. Tests based on such symptoms are susceptible to false-positive and false-negative results due to stress, fatigue, and medications. Biochemical markers of neuronal damage and the physiological response to that damage are being identified. Biosensors capable of rapid measurement of such markers in the circulation offer a solution for on-site triage, as long as three criteria are met: (a) Recognition reagents can be identified that are sufficiently sensitive and specific, (b) the biosensor can provide quantitative assessment of multiple markers rapidly and simultaneously, and (c) both the sensor and reagents are designed for use outside the laboratory.

Systemic inflammatory effects of traumatic brain injury, femur fracture, and shock: an experimental murine polytrauma model

Objective. Despite broad research in neurotrauma and shock, little is known on systemic inflammatory effects of the clinically most relevant combined polytrauma. Experimental investigation in an animal model may provide relevant insight for therapeutic strategies. We describe the effects of a combined injury with respect to lymphocyte population and cytokine activation. Methods. 45 male C57BL/6J mice (mean weight 27 g) were anesthetized with ketamine/xylazine. Animals were subjected to a weight drop closed traumatic brain injury (WD-TBI), a femoral fracture and hemorrhagic shock (FX-SH). Animals were subdivided into WD-TBI, FX-SH and combined trauma (CO-TX) groups. Subjects were sacrificed at 96 h. Blood was analysed for cytokines and by flow cytometry for lymphocyte populations. Results. Mortality was 8%, 13% and 47% for FX-SH, WD-TBI and CO-TX groups (P < 0.05). TNFα (11/13/139 for FX-SH/WD-TBI/CO-TX; P < 0.05), CCL2 (78/96/227; P < 0.05) and IL-6 (16/48/281; P = 0.05) showed significant increases in the CO-TX group. Lymphocyte populations results for FX-SH, WD-TBI and CO-TX were: CD-4 (31/21/22; P = n.s.), CD-8 (7/28/34, P < 0.05), CD-4-CD-8 (11/12/18; P = n.s.), CD-56 (36/7/8; P < 0.05). Conclusion. This study shows that a combination of closed TBI and femur-fracture/ shock results in an increase of the humoral inflammation. More attention to combined injury models in inflammation research is indicated.