Animal models as the basis of pharmacologic intervention in trauma and sepsis patients

Relevance of induced and accidental hypothermia after trauma-haemorrhage-what do we know from experimental models in pigs?

Recent experimental research has either focused on the role of accidental hypothermia as part of the lethal triad after trauma or tried to elucidate the effects of therapeutically induced hypothermia on the posttraumatic course. Induced hypothermia seems to reduce the mortality in experimental models of trauma-haemorrhage. As potential mechanisms, a decrease of cellular metabolism, beneficial effects on haemodynamic function and an attenuation of the inflammatory response have been described. However, negative side effects of hypothermia have to be considered, such as impairment of the coagulatory function and immunosuppressive effects. Furthermore, the optimal strategy for the induction of hypothermia (magnitude, duration, timing, cooling rate, etc.) and subsequent rewarming remains unclear. Nevertheless, this piece of information is essential before considering hypothermia as a treatment strategy for severely injured patients. This review aims to elaborate the differences between accidental and induced hypothermia and to summarize the current knowledge of the potential therapeutic use of induced hypothermia suggested in porcine models of trauma-haemorrhage.

Combined hemorrhage/trauma models in pigs-current state and future perspectives

The majority of injury combinations in multiply injured patients entail the chest, abdomen, and extremities. Numerous pig models focus on the investigation of posttraumatic pathophysiology, organ performance monitoring and on potential treatment options. Depending on the experimental question, previous authors have included isolated insults (controlled or uncontrolled hemorrhage, chest trauma) or a combination of these injuries (hemorrhage with abdominal trauma, chest trauma, traumatic brain injury, and/or long-bone fractures). Combined trauma models in pigs can provide a high level of clinical relevance, when they are properly designed and mimicking the clinical situation. Most of these models focus on the first hours after trauma, to assess the acute sequel of traumatic hemorrhage. However, hemorrhagic shock and the associated mass transfusion are also major causes for organ failure and mortality in the later clinical course. Thus, most models lack information on the pathomechanisms during the late posttraumatic phase. Studying new therapies only during the early phase is also not reflective of the clinical situation. Therefore, a longer observation period is required to study the effects of therapeutic approaches during intensive care treatment when using animal models. These long-term studies of combined trauma models will allow the development of valuable therapeutic approaches relevant for the later posttraumatic course. This review summarizes the existing porcine models and outlines the need for long-term models to provide real effective novel therapeutics for multiply injured patients to improve organ function and clinical outcome.

Role of glutathione in immunity and inflammation in the lung

Reactive oxygen species and thiol antioxidants, including glutathione (GSH), regulate innate immunity at various levels. This review outlines the redox-sensitive steps of the cellular mechanisms implicated in inflammation and host defense against infection, and describes how GSH is not only important as an antioxidant but also as a signaling molecule. There is an extensive literature of the role of GSH in immunity. Most reviews are biased by an oversimplified picture where “bad” free radicals cause all sorts of diseases and “good” antioxidants protect from them and prevent oxidative stress. While this may be the case in certain fields (eg, toxicology), the role of thiols (the topic of this review) in immunity certainly requires wearing scientist’s goggles and being prepared to accept a more complex picture. This review aims at describing the role of GSH in the lung in the context of immunity and inflammation. The first part summarizes the history and basic concepts of this picture. The second part focuses on GSH metabolism/levels in pathology, the third on the role of GSH in innate immunity and inflammation, and the fourth gives 4 examples describing the importance of GSH in the response to infections.

Characterization of an animal model of severe sepsis associated with respiratory dysfunction

PURPOSE

Pathophysiological studies in humans regarding sepsis are difficult to perform due to ethical and methodological concerns. In this context, animal models of sepsis can be useful to better understand this condition and to test therapeutic strategies. The purpose of this study was to characterize a feasible and clinically relevant model of sepsis in pigs that could be useful for testing different therapeutic interventions.

METHODS

5 White Large pigs were anesthetized, arterial and pulmonary catheters were introduced, and sepsis was induced by fecal peritonitis. Several biochemical indicators of organ dysfunction and infectious parameters were measured. The pigs were monitored until death, when fragments of organs were removed for pathology. Three animals without peritonitis served as controls and were sacrificed 24 hours after surgery without developing significant changes in organ function.

RESULTS

Septic pigs survived 17 hours on average (range, 16-18 h), and Escherichia coli was recovered from blood cultures. They developed a significant decrease in left ventricular work and a nonsignificant reduction in mixed venous oxygen saturation. Respiratory dysfunction was characterized by a decrease in the PaO2/FiO2 ratio and respiratory compliance. Pathology of the lungs revealed areas of pulmonary collapse, hemorrhage, pulmonary congestion, and discrete neutrophil infiltrate.

CONCLUSIONS

Fecal peritonitis in pigs is a clinically relevant model of sepsis associated with acute lung injury without direct pulmonary insult. This model may prove to be useful for studying pathogenic aspects of secondary lung injury as well as for validating ventilatory or pharmacologic interventions.

Large animal models: baboons for trauma, shock, and sepsis studies

A few limited examples of large animal models are outlined, with the main emphasis on baboon models. The baboon offers all the advantages of a large animal and is comparable with humans in nearly all physiological and immunological aspects. In addition, cross-reactivity with human therapeutic and diagnostic reagents allows testing of new species-specific therapies such as antihuman antibodies, on the one hand, and monitoring with available human analytical procedures, on the other.

Opportunities to Replace the Use of Animals in Sepsis Research

Sepsis and multiple organ failure are common causes of death in patients admitted to intensive care units. The incidence of sepsis and associated mortalities has been steadily increasing over the past 20 years. Sepsis is a complex inflammatory condition, the precise causes of which are still poorly understood. Animal models of sepsis have the potential to cause substantial suffering, and many of them have been poorly representative of the human syndrome. However, a number of non-animal approaches, including in vitro, in silico and clinical studies, show promise for addressing this situation. This report is based on discussions held at an expert workshop convened by Focus on Alternatives and held in 2004 at the Wellcome Trust, London. It provides an overview of some non-animal approaches to sepsis research, including their strengths and weaknesses, and argues that they should be prioritised for further development.

Can one use biologic modifiers to prevent multiple organ dysfunction syndrome after abdominal infections?

Postoperative or trauma-induced intra-abdominal infections can result in sepsis and multiple organ dysfunction syndrome (MODS). Enteric bacteria and endotoxin released from the gut into the peritoneal cavity in response to injury can directly stimulate the inflammatory cascade responsible for the development of systemic inflammation and subsequent MODS. Therapeutic strategies, such as biologic modifiers that are aimed at blocking or enhancing specific mediators of the inflammatory response, have been developed and tested in animal models with varying efficacy in preventing mortality. Specific therapies that have shown beneficial effects in animal models have not proved successful in prospective, randomized human studies, and it is as yet unclear whether cytokine-based therapies will ultimately have a role in preventing MODS. Testing novel therapies in appropriate animal models that closely simulate human intra-abdominal infection is crucial in developing drugs that will be beneficial in preventing sepsis-induced mortality in critically ill patients.

Toxicities of hemoglobin solutions: in search of in-vitro and in-vivo model systems

Several hemoglobin-based oxygen carriers (HBOCs) have been developed with a rationale focused on exploiting one or more physicochemical properties (e.g., oxygen affinity, molecular weight, viscosity, and colloid osmotic pressure) resulting from the chemical or recombinant modification of hemoglobin (Hb). Several chemically modified Hbs have reached late stages of clinical evaluation in the United States and Canada. These Hbs, in general, demonstrated mixed preclinical safety and efficacy, and reasonable safety in Phase I trials. However, as clinical development shifted into later stages, an undesirable safety and efficacy profile became clear in patient populations studied, and as a result some products were withdrawn from further clinical pursuit. Several questions still remain unanswered regarding the safety of Hb products for their proposed clinical indication(s). For example, 1) were preclinical studies predictive of clinical outcome? And, 2) were the most appropriate preclinical studies performed to predict clinical outcome? The primary objectives of this analysis are to explore prelinical safety issues associated with HBOCs and provide an overview of the in-vitro and in-vivo models employed. The methods for obtaining data to serve as a basis for discussion are compiled from a literature-based survey of safety and efficacy derived from biochemical, cellular, and whole animal assessment of HBOCs. Results from this overview of a vast body of published data may provide a means for identifying critical preclinical safety issues, which may ultimately lead to identification of potential limitations in the effective clinical use of certain HBOCs.

Chronic left heart catheterization for microvascular blood flow determination in the rabbit: a minimally invasive technique using specially designed port devices

BACKGROUND

This study describes a modified catheterization technique with subcutaneously implanted port catheters to be inserted in a retrograde manner across the aortic valve into the left heart ventricle through the right carotid artery to measure organ perfusion.

MATERIALS AND METHODS

The specially designed arterial port catheters were implanted in New Zealand rabbits (n = 11, 3.7 +/- 0.1 kg [mean +/- SEM]) under iv anesthesia (medetomidine/ketamine) and single-shot perioperative antibiotic therapy. Hemodynamics were registered continuously during the operation via an ear artery catheter.

RESULTS

Implantation of ports was performed in all animals (11/11) without major complications (mean operation time: 70 +/- 3 min). We did not observe catheter-associated arrhythmia, fall in mean arterial pressure (MAP before and post OP: 70 +/- 2 and 68 +/- 2 Torr, respectively), or change in arterial oxygen saturation (SaO2 before and post OP: 89 +/- 3 and 95 +/- 2%, respectively). With a specifically modified microsurgical insertion technique, cerebral blood supply was effectively preserved as evidenced from postmortem histological examinations, cerebral blood flow determination with fluorescent microspheres, and measurement of S-100b protein serum concentrations, a specific marker of neuronal damage. The positioning of the catheter tip in the left ventricle was found to be correct in 10/11 animals.

CONCLUSIONS

Repeated and atraumatic microsphere injections into the left ventricle have become feasible by transcutaneous puncture of subcutaneous port systems over several weeks under light sedation. Hence, this new approach (i) avoids the necessity of repeated intracardiac injections and port insertions via thoracotomy, thus reducing the perioperative stress for the animals, and (ii) allows for the first time minimally invasive repetitive and chronic measurements of regional organ blood flow under various experimental settings.

Multiple organ dysfunction in ulcerative colitis

OBJECTIVE

The mortality rate in severe ulcerative colitis (UC) is commonly attributed to major colonic complications or surgical procedures. Early recognition of the severity of the colitis, intensive medical treatment, and prompt surgery have all contributed to improving its outcome over the past 40 yr. Recently, we have observed some fatal cases of severe UC in which death was related to multiple organ dysfunction syndrome (MODS). This complication, associated with a very high mortality rate, may occur in several acute critical diseases, both infectious and noninfectious, but has so far not been reported in UC. The aim of this study was to evaluate the prevalence and outcome of MODS in severe UC.

METHODS

The records of 180 consecutive patients admitted to the Gastrointestinal Unit, University of Rome for an acute severe attack of UC during the period 1976-1998 were retrospectively analyzed. Severity of UC was defined according to the criteria of Truelove and Witts. MODS was defined according to the original criteria of the American College of Chest Physicians/Society of Critical Care Medicine Consensus Conference 1992. All patients were on a standard intensive regimen consisting of total parenteral nutrition and hydrocortisone 100 mg q.i.d. Colectomy was performed according to the timing of the Oxford intensive regimen.

RESULTS

Of these 180 severe UC patients, 11 (6.1%) experienced clinical and laboratory features of MODS. The lung was involved in five patients, the kidney in three, the liver in seven, the central nervous system in three, the hematological system in three, and the pancreas in one. MODS was preceded by toxic megacolon in five patients and by so-called "impending megacolon" in four, whereas in two patients no previous complications of UC were observed. MODS developed during the first attack of colitis in seven patients and during relapse in four. The overall mortality rate was 12/180 (6.6%). Of the 12 patients who died, eight (72.7%) had MODS.

CONCLUSIONS

These data indicate that UC must be included among the causes of MODS. In our referral center for inflammatory bowel diseases, MODS was responsible for the majority of UC cases with a fatal outcome. The timely identification of signs of MODS should prompt admission to an intensive care unit and emergency surgery.

Protective effect of bactericidal/permeability-increasing protein (rBPI21) in baboon sepsis is related to its antibacterial, not antiendotoxin, properties

OBJECTIVE AND SUMMARY BACKGROUND DATA

The recombinant fragment of bactericidal/permeability-increasing protein, rBPI21, has potent bactericidal activity against gram-negative bacteria as well as antiendotoxin (lipopolysaccharide [LPS]) action. On the basis of these activities, the authors sought to discover whether rBPI21 would be protective in baboons with live Escherichia coli-induced sepsis and whether the potential protective effects of rBPI21 (together with antibiotics) would be more closely related to its antibacterial or LPS-neutralizing effects.

METHODS

In a prospective, randomized, placebo-controlled subchronic laboratory study, the efficacy of rBPI21 or placebo was studied over 72 hours in chronically instrumented male baboons infused with live E. coli under antibiotic therapy.

RESULTS

Intravenous rBPI21 attenuated sepsis-related organ failure and increased survival significantly. Bacteremia was significantly reduced in the rBPI21 group at 2 hours after the start of the E. coli infusion, whereas circulating LPS was less affected. The in vivo formation of tumor necrosis factor was significantly suppressed by the rBPI21 treatment regimen. Microcirculation and organ function were improved.

CONCLUSIONS

In baboon live E. coli sepsis, the salutary effect of rBPI21 results from a more prevalent antibacterial than antiendotoxin activity.