Modeling sepsis, with a special focus on large animal models of porcine peritonitis and bacteremia

In this article, we reviewed the use of photodynamic therapy (PDT) for breast cancer (BC) in animal models. These in vivo models imitate the cancer disease progression, aid diagnosis, as well as create opportunities to assess treatment during the approval process for the new drug. BC ranks first among women's cancers. Nowadays, there are many diagnostic methods and therapy options for BC but the majority of them have severe side effects. This article discusses the advantages and some disadvantages of the use of small and large animals used for BC models. A literature review showed that the majority of studies have used large animal models, and recently there has been more interest in developing BC in small animal models. BC cell lines such as MCF-7, BT-474, MDA-MB-231, and 4T1 are commercially available for two-dimensional and three-dimensional in vitro cell cultures and subcutaneous models. The purpose of this article is to discuss the performance of PDT in animal models and its further clinical implications. PDT is known to be a non-invasive therapy, which uses monochromatic light and energy to excite photosensitizers (PSs) for the generation of reactive oxygen species as the required factors. Herein, we discuss the use of five photosensitizers in BC models such as chlorin e6 (Ce6), methylene blue, indocyanine green, 5-aminolevulinic acid, and meta-tetra(hydroxyphenyl)chlorin. The database PubMed and Scopus were searched for keywords: 'photodynamic therapy', 'breast cancer', 'animal model', 'clinical studies', and 'photosensitizer(s)'. The PDT search results in animal experiments and its effect on a living organism indicate the possibility of its application in clinical trials on women with local and disseminated BC. The availability and accessibility of small and large BC animal models enable the progress and trial of cancer drugs for innovative technologies and new diagnostics and treatments.

Treatment of brain injury following circulatory arrest is a challenging health issue with no viable therapeutic options. Based on studies in a clinically relevant large animal (canine) model of hypothermic circulatory arrest (HCA)-induced brain injury, neuroinflammation and excitotoxicity have been identified as key players in mediating the brain injury after HCA. Therapy with large doses of valproic acid (VPA) showed some neuroprotection but was associated with adverse side effects. For the first time in a large animal model, we explored whether systemically administered polyamidoamine (PAMAM) dendrimers could be effective in reaching target cells in the brain and deliver therapeutics. We showed that, upon systemic administration, hydroxyl-terminated PAMAM dendrimers are taken up in the brain of injured animals and selectively localize in the injured neurons and microglia in the brain. The biodistribution in other major organs was similar to that seen in small animal models. We studied systemic dendrimer–drug combination therapy with two clinically approved drugs, N-acetyl cysteine (NAC) (attenuating neuroinflammation) and valproic acid (attenuating excitotoxicity), building on positive outcomes in a rabbit model of perinatal brain injury. We prepared and characterized dendrimer-NAC (D-NAC) and dendrimer-VPA (D-VPA) conjugates in multigram quantities. A glutathione-sensitive linker to enable for fast intracellular release. In preliminary efficacy studies, combination therapy with D-NAC and D-VPA showed promise in this large animal model, producing 24 h neurological deficit score improvements comparable to high dose combination therapy with VPA and NAC, or free VPA, but at one-tenth the dose, while significantly reducing the adverse side effects. Since adverse side effects of drugs are exaggerated in HCA, the reduced side effects with dendrimer conjugates and suggestions of neuroprotection offer promise for these nanoscale drug delivery systems.

Recommendations of the National Heart, Lung and Blood Institute Heart and Lung Tolerance Working Group.

Thoracoabdominal aortic replacement, necessary in case of injuries, aneurysms and dissections, shows a high complication rate as a consequence of the perioperative ischemia / reperfusion-sequence (I/R). Clamping above and below the lesion leads to the spinal cord suffering from ischemia. Clamping times of less than 30 minutes show only a small risk of neurological deficit, while longer periods increase paraplegia rates disproportionately. The subsequent reperfusion as a second hit causes additional damage to the spinal cord. Up to 30 % of all patients who require being treated in the thoracoabdominal part of the aorta suffer from paraplegia within the first 24 postoperative hours (Kahn et al., 2012). While paraplegia following ischemia can be explained by the consequent death of motor neurons, reperfusion period is still poorly studied and understood. High metabolic activity and a need for substrate of the motor neurons aggravate I/R damage to the spinal cord (Sakurai et al., 1998). One of the triggers is free radicals that consume the available buffer enzymes (Gelman, 1995). Due to the loss of cellular energy (ATP), mediated by inhibition of mitochondrial phosphorylation, membrane pumps are inhibited. This in turn leads to a disequilibrium of the Na+ / K+ balance within the cell. What follows is an intracellular hyperkalemia with cellular edema and intracellular acidosis. Via other cellular mechanisms, this results in programmed cell death, namely apoptosis (Abe et al., 1995). Currently, there is no prophylaxis to avoid this damage in clinical practice of thoracic or abdominal aortic reconstruction. Although there are different approaches to this, no method has been implemented yet (Zvara, 2002). Hence, there is a need for better experimental approaches that can support the clinical treatment, in order to reduce the complication rate for thoracoabdominal aortic replacement. A crucial part in planning such an experimental project is to choose the best fitting model. It should be a combination of being as near to humans and to the clinical setting as possible. Furthermore it should give answers to present questions and upcoming more specific questions in the future. One animal model cannot serve all this demand so that several models are needed in order to choose the best fitting one for each experimental question. Therefore, inspired by experimental set-ups described in literature, our study group established three animal models to elucidate I/R of the spinal cord resulting in paraplegia. The large animal model was developed to offer the opportunity to map pathophysiology of aortic clamping in a clinical relevant porcine model to test potentially protective substances during I/R of the spinal cord. In this setting pigs were anesthetized and mechanically ventilated. In order to introduce two inflatable balloon catheters, femoral arteries were prepared via inguinal surgical cut downs. One of these balloon catheters was placed at the height of the left subclavian artery and the second one directly upstream of the aortic bifurcation (Figure 1). By inflating the balloons the blood flow was stopped by means of aortic occlusion in order to mimic an aortic crossclamping.Figure 1: Aortic anatomy with clamping locations.(1) Large animal model: One balloon catheter was placed at the height of the left subclavian artery and the second one directly upstream of the aortic bifurcation. (2) Medium sized animal model: Because of the strict segmental blood supply to the spinal cord in rabbits only infrarenal aortic crossclamping is needed. (3) Small animal model: Clamping of the aorta and left subclavian artery.When using such a model permission by the local authorities to let animals wake up again is not necessarily given, so other solutions need to be found in order to be able to control spinal cord function during anesthesia. Therefore motor evoked potentials (MEP) were recorded, reflex status was tested and histological staining was performed after harvesting of the spinal cord. The recording of the MEPs of the lower extremities presented potential damage of the spinal cord while the upper limbs served as technical proof. Corresponding to the low ischemic tolerance of the spinal cord, aortic occlusion was limited to 30 minutes and the follow-up period was extended up to 10 hours. Tissue damage was evaluated using hematoxylin and eosin, Nissl, and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) staining. In addition several plasma parameters for inflammation and oxidative stress were taken during the experiments (Simon et al., 2008; Simon et al., 2011). The advantages of such an animal model are plain to see, because there are two complementary aspects. On the one hand, anatomy and physiology of these animals are close enough to mimic the clinical situation of human patients and on the other hand one can use clinical equipment without special adjustments because of animal size. As anatomy is a very important factor in animal studies the pig is one of the most ideal animals to study ischemia and reperfusion of the spinal cord. Like humans, these animals provide blood to the spinal cord via many vessels of different origin. In humans the spinal cord receives blood supply through the unpaired anterior spinal artery and the two posterior spinal arteries. Both originate from the vertebral arteries. The anterior spinal artery also receives blood from segmental arteries of the aorta. Perfusion in pigs differs slightly from humans as the anterior spinal artery gets additional blood influx by an anastomosis with the median sacral artery that is much more pronounced in pigs than in humans. Therefore, as pigs are concerned, terminology is "aortic trifurcation" rather than bifurcation. Another advantage of a large animal model is that enough tissue and/or blood samples can be taken for several examinations whereas in small animal models these options are much more limited. At the same time, there are also clear disadvantages when pigs or sheep are being used for experimental models. Expenses for animals and for experimental set-up are much higher and it takes a lot more of manpower to realise such elaborate projects. Compared to mouse models costs can be several hundred times higher for each experiment. The required aortic occlusion near to the heart causes major hemodynamic imbalances and ischemia of all abdominal organs. Therefore, the large animal model should be carried out as a terminal test. For a better observation of the postoperative outcome and the effectiveness of various neuroprotective substances a rabbit model was established in which postoperative observation times up to 96 hours were performed. Even longer observation times are possible when needed for answering specific questions. Due to its special anatomy with strict segmental blood supply to the spinal cord the rabbit is an easy to use experimental model for studying clinical spinal ischemia-reperfusion injury (DeGirolami et al., 1982). Because of this segmental blood supply only infrarenal aortic crossclamping is needed to gain neuronal damage in the spinal cord level comparable to the thoracic crossclamping of the aorta in humans and pigs (Figure 1). The surgical impact can therefore be reduced to the size of a laparotomy. Due to the limited surgical trauma and the avoided ischemia of the kidney and visceral organs blood pressure could be kept stable and postoperative awakening was possible due to intact visceral organ function. The neurological examinations were done at 0, 6, 24, 36, 48, 60, 72, 84 and 96 hours postoperatively, using a modified Tarlov score. After 96 hours, the spinal cord was harvested for histopathological examination like hematoxylin-eosin staining. In literature different clamping times were mentioned, so, in this case, clamping times between 17 and 25 minutes were tested. Here, 22 minutes of aortic clamping was found to be the perfect ischemia duration to gain reproducible paraplegia. The rabbit model provides, in contrast to terminal experiments on large animals, important statements concerning the clinical effectiveness of pharmacological conditioning. Clear benefits of such a model using medium sized animals are the possibility for long reperfusion observation, relatively low costs in combination with reduced manpower needed. This model offers the opportunity to gain enough tissue and/or blood for examinations. Another positive effect is that administration of drugs that have to be given intravenously can be applied much easier than in animals of smaller size. Best vein in most of the cases is certainly one of the ear veins that can be cannulised with human peripheral venous catheter. Furthermore, more abstract results can be found than in a large animal model. Reasons for this can certainly be found at DNA level. One can see the differences among the species already in macroscopic anatomy as already described above, e.g. of the blood supply of the spinal cord. Additionally, when wanting to perform immunohistological stainings, it is very complicated to find working antibodies. The reason is that many antibodies are produced in rabbits and therefore are not specific working on rabbit tissue. So laboratory possibilities are limited by using this kind of animal model (Simon et al., 2015). Mouse models have some important advantages. The vascular anatomy in mice is more similar to humans than in other animals such as rabbits. In mice there is one anterior and two posterior spinal arteries responsible for the spinal cord blood supply (Lang-Lazdunski et al., 2000) while e.g., in rabbits there is a strict segmental blood supply. The anatomical vessel structure in mice is the reason for the clamping of the thoracic aorta that induces an ischemia of the associated spinal cord sections, accordingly to humans and the clinical problems. Despite in large animal models clamping procedure in mice only needs 7 minutes to produce paraplegia, which causes less damage to the visceral organs compared to 30 minutes occlusion procedure in pigs. Due to the size of the animals only direct clamping of the aorta via a thoracotomy is possible, since murine blood vessels are too small for balloon occlusion (Figure 1). After the clamping procedure (including closing chest and skin), it is possible to awaken these animals and to observe the experiment for several days. Furthermore, mouse models offer also the advantage of the variety of genetically altered mouse strains. This is a clear advantage of mouse models for human diseases compared to rabbits or pigs and, therefore, should be taken into account. An additional factor in planning experimental models, although of only from a financial viewpoint, is, that animal models in mice are ten times cheaper and even more when considering following costs like keeping of animals. A single mouse (weight 20–25 g; C57BL/6J mice) costs approx. € 24, while a New Zealand White Rabbit (weight 2.5–3 kg) of the same company costs about €204 each. Finally, it is rather obvious that small animal models have model typical disadvantages. As the animal is of smallest size your experiment is limited if it is based on many or large amounts of blood or tissue samples. As already mentioned above, a small animal size needs special equipment or procedures. For example when performing a thoracotomy, intubation and ventilation is a challenge for the inexperienced scientist and takes time to be learned. Special equipment is not only needed for doing anesthesia like e.g., special inhaling units etc., but also offers a broad spectrum of experimental possibilities like e.g., whole body laser doppler imaging, which becomes the more difficult the larger the animal is. All together, there are several aspects one should consider if thinking about building up an animal model. First of all it is important to understand that experimental models are only an attempt to mimic clinical situation and require a lot of discussion when conclusions are to be drawn with a view to humans. There will never be an ideal model. For a deeper understanding of a clinic problem or side-effect several models are needed so that the best fitting one can be chosen. This indicates that a precise formulation of the question to be answered is needed in advance. It requires a rather big budget, a lot of time and manpower to realise a large animal model that should take place in an animal intensive care. At the same time this has the benefit of more clinical relevant data acquisition. For those needing a simple model that is easy to learn and only needs an animal operation theatre but no animal intensive care unit, the rabbit model might be the right choice. It combines the small surgical impact with the possibility of long-time postoperative observation. When looking at questions dealing with DNA focus or needing animals of genetically altered strains the mouse model will fit best as it offers these advantages that normally cannot be found in other animal models. Eventually, when building up a new model one should take into account that research in literature will not replace teamwork with already experienced scientists in this field. Results will always differ from literature of other groups, because micromanagement differs. So each new experiment, especially when using a new animal model, needs a learning curve for building up one's own know-how.

The purpose of this review is to evaluate the effectiveness of large animal models in gynecology research and provide future perspectives. Gynecological diseases are diverse and pose a serious threat to women's physical and mental health. In addition to the commonly used small animal models, large animal models have gradually entered the field of gynecological research. Results suggest that large animal models offer significant advantages in simulating human physiological processes, despite ethical and practical challenges. This paper reviews the application of large animal models in the study of gynecological diseases, provides a summary of the research characteristics of large animal models, analyses the advantages and challenges of these models in disease research, and compares the research differences between large and small animal models. It also discusses the relationship between these models and new alternative models, with a view to providing more new ideas for the selection of animal models in the study of gynecological diseases.

Animal Models of Sepsis

Nanofiber vascular grafts have been shown to create neovessels made of autologous tissue, by in vivo scaffold biodegradation over time. However, many studies on graft materials and biodegradation have been conducted in vitro or in small animal models, instead of large animal models, which demonstrate different degradation profiles. In this study, we compared the degradation profiles of nanofiber vascular grafts in a rat model and a sheep model, while controlling for the type of graft material, the duration of implantation, fabrication method, type of circulation (arterial/venous), and type of surgery (interposition graft). We found that there was significantly less remaining scaffold (i.e., faster degradation) in nanofiber vascular grafts implanted in the sheep model compared with the rat model, in both the arterial and the venous circulations, at 6months postimplantation. In addition, there was more extracellular matrix deposition, more elastin formation, more mature collagen, and no calcification in the sheep model compared with the rat model. In conclusion, studies comparing degradation of vascular grafts in large and small animal models remain limited. For clinical translation of nanofiber vascular grafts, it is important to understand these differences.

The translation of bone tissue engineering (BTE) research to clinical use has been absymal1. Outside of bone void filler biomaterials, only Bone Morphogenetic Protein 2 (BMP2) has made significant inroads to clinical practice, and even BMP2 use has been associated with significant complications including death, dysphagia, and ectopic bone formation. The dearth of BTE products can be attributed to two main causes: (1) the need to develop BTE systems, that successfully integrate scaffolds, growth factors like BMP2 and cells and (2) the need to adapt and implement such systems for a wide variety of clinical indications in CranioMaxilloFacial (CMF), Spine and Orthopedic Surgery. Of course, to fully develop BTE systems (Issue 1) and adapt them to realistic clinical indications, we must be able to test such systems in bone defects that are as close to the human situation as possible. Thus, the use of domestic large animals for bone tissue engineering is critical, as these animals provide challenges in both defect volume and functional loading that can mimic the human situation. In addition, FDA approval for BTE products either through a 510K or IDE/IND/PMA pathway requires the use of a large pre-clinical animal model. However, despite this need, only approximately 60 large animal bone tissue-engineering studies have been published in the past 10 years. Furthermore, NIH has funded only 8% of these studies, and of the 17 bone tissue engineering studies supported by NIH in 2010, only three utilized a large animal model, and none of these used an animal larger than a rabbit. Clearly, increased translation and regulatory approval of BTE therapies will require greater testing in large animal models. We will discuss the current dearth of relevant pre-clinical studies in BTE, and present our work addressing these issues by developing BTE systems (integrated scaffold, growth factor and stem-cell constructs) and testing these systems for realistic clinical applications using the Yorkshire and other swine species as a large pre-clinical animal model. We will detail our work in developing BTE systems for CMF reconstruction and spine fusion in the swine model. Reference Hollister S. J. and Murphy W. L. Scaffold translation: barriers between concept and clinic. Tissue Eng. B. (in press).

Percutaneous Transendocardial Delivery of Self-complementary Adeno-associated Virus 6 Achieves Global Cardiac Gene Transfer in Canines

Acute respiratory distress syndrome (ARDS) is a life-threatening, high mortality pulmonary condition characterized by acute lung injury (ALI) resulting in diffuse alveolar damage. Despite progress regarding the understanding of ARDS pathophysiology, there are presently no effective pharmacotherapies. Due to the complexity and multiorgan involvement typically associated with ARDS, animal models remain the most commonly used research tool for investigating potential new therapies. Experimental models of ALI/ARDS use different methods of injury to acutely induce lung damage in both small and large animals. These models have historically played an important role in the development of new clinical interventions, such as fluid therapy and the use of supportive mechanical ventilation (MV). However, failures in recent clinical trials have highlighted the potential inadequacy of small animal models due to major anatomical and physiological differences, as well as technical challenges associated with the use of clinical co-interventions [e.g., MV and extracorporeal membrane oxygenation (ECMO)]. Thus, there is a need for larger animal models of ALI/ARDS, to allow the incorporation of clinically relevant measurements and co-interventions, hopefully leading to improved rates of clinical translation. However, one of the main challenges in using large animal models of preclinical research is that fewer species-specific experimental tools and metrics are available for evaluating the extent of lung injury, as compared to rodent models. One of the most relevant indicators of ALI in all animal models is evidence of histological tissue damage, and while histological scoring systems exist for small animal models, these cannot frequently be readily applied to large animal models. Histological injury in these models differs due to the type and severity of the injury being modeled. Additionally, the incorporation of other clinical support devices such as MV and ECMO in large animal models can lead to further lung damage and appearance of features absent in the small animal models. Therefore, semi-quantitative histological scoring systems designed to evaluate tissue-level injury in large animal models of ALI/ARDS are needed. Here we describe a semi-quantitative scoring system to evaluate histological injury using a previously established porcine model of ALI via intratracheal and intravascular lipopolysaccharide (LPS) administration. Additionally, and owing to the higher number of samples generated from large animal models, we worked to implement a more sustainable and greener histopathological workflow throughout the entire process.

Background and Aims with the worldwide dialysis population growing rapidly, improving haemodialysis (HD) outcomes is crucial and HD innovations are urgently needed. Prior to clinical application, novel HD technologies must undergo extensive preclinical testing. However, to date there is no consensus on the induction method of kidney failure in animal models nor which animal species is most suitable for research on HD innovations. Moreover, there is no consensus on which parameters should be used to validate adequate induction of kidney failure and functioning of novel HD devices. Using a systematic review approach, we summarized available literature of HD in kidney failure animal models. Method we performed a systematic search on PubMed and Embase for relevant studies up to February 4th 2022. After removal of duplicates, 5723 abstracts were screened for eligibility by three independent reviewers (JdV, KW and MK). Inclusion was based on publication of a HD intervention in an animal model with adequate (acute or chronic) kidney failure (independent of induction method). Detailed in- and exclusion criteria were registered in PROSPERO 2022 CRD42022307144. Data from individual reports, including animal species and sex, kidney injury parameters and HD details, were extracted in a pre-set data extraction form. Future efforts will focus on risk of bias and key quality indicators. Results of the 5723 abstracts screened, 195 records were included as full text and 41 full text articles were included for data-extraction (Figure 1). Current data extraction is completed for 31 articles (75%). Publication years range from 1973 to 2021 with over half (16/31) published after 2000. HD experiments were most frequently performed on dogs (45%), followed by rats (29%), goats (13%), pigs (10%), and sheep (3%) respectively. Parameters such as weight (81% reported), sex (58%) and age (29%) were not systematically reported. Most studies (67% of records reporting sex) used male animals only. Dog models were found in older studies, with no records after 2009. Other large animal studies were almost exclusively (88%) performed from the year 2007 onwards. Independent of animal species, studies mainly used acute kidney injury (AKI) models (84%), induced by bilateral nephrectomy (48%) or bilateral ureteral ligation (29%). The majority confirmed kidney failure by an increase in BUN and/or plasma creatinine. In AKI models, dialysis was on average initiated on AKI day 2 ± 0.8, and generally either HD (61%) or veno-venous hemofiltration as a single session (35%) was applied. Except for one clearance study, dialysis efficiency was reported as reduction ratios of BUN and/or plasma creatinine. Conclusion both large and small animal models have been used in HD research and preclinical validation of dialysis innovations. The use of dogs to test HD innovations has seen a sharp decline over the past decades, possibly resulting from a shift in public ethical perception. However, large animal models such as goat, sheep and pigs remain popular. A pressing issue appears the overall lack of adequate ARRIVE guideline adherence for reporting of animal parameters. We found no apparent improvement in reporting over time, emphasizing the need for clear guidelines to drive innovative HD research. Further (quantitative) analysis and meta-analysis are ongoing.

In liver surgery, biliary obstruction can lead to secondary biliary cirrhosis, a life-threatening disease with liver transplantation as the only curative treatment option. Mesenchymal stromal cells (MSC) have been shown to improve liver function in both acute and chronic liver disease models. This study evaluated the effect of allogenic MSC transplantation in a large animal model of repeated biliary obstruction followed by partial hepatectomy. MSC transplantation supported the growth of regenerated liver tissue after 14 days (MSC group, n = 10: from 1087 ± 108 (0 h) to 1243 ± 92 mL (14 days); control group, n = 11: from 1080 ± 95 (0 h) to 1100 ± 105 mL (14 days), p = 0.016), with a lower volume fraction of hepatocytes in regenerated liver tissue compared to resected liver tissue (59.5 ± 10.2% vs. 70.2 ± 5.6%, p < 0.05). Volume fraction of connective tissue, blood vessels and bile vessels in regenerated liver tissue, serum levels of liver enzymes (AST, ALT, ALP and GGT) and liver metabolites (albumin, bilirubin, urea and creatinine), as well as plasma levels of IL-6, IL-8, TNF-α and TGF-β, were not affected by MSC transplantation. In our novel, large animal (pig) model of repeated biliary obstruction followed by partial hepatectomy, MSC transplantation promoted growth of liver tissue without any effect on liver function. This study underscores the importance of translating results between small and large animal models as well as the careful translation of results from animal model into human medicine.

The complex pathogenesis of sepsis and septic shock involves myocardial depression, the pathophysiology of which, however, remains unclear. In this study, cellular mechanisms of myocardial depression were addressed in a clinically relevant, large animal (porcine) model of sepsis and septic shock. Sepsis was induced by fecal peritonitis in eight anesthetized, mechanically ventilated, and instrumented pigs of both sexes and continued for 24 h. In eight control pigs, an identical experiment but without sepsis induction was performed. In vitro analysis of cardiac function included measurements of action potentials and contractions in the right ventricle trabeculae, measurements of sarcomeric contractions, calcium transients and calcium current in isolated cardiac myocytes, and analysis of mitochondrial respiration by ultrasensitive oxygraphy. Increased values of modified sequential organ failure assessment score and serum lactate levels documented the development of sepsis/septic shock, accompanied by hyperdynamic circulation with high heart rate, increased cardiac output, peripheral vasodilation, and decreased stroke volume. In septic trabeculae, action potential duration was shortened and contraction force reduced. In septic cardiac myocytes, sarcomeric contractions, calcium transients, and L-type calcium current were all suppressed. Similar relaxation trajectory of the intracellular calcium-cell length phase-plane diagram indicated unchanged calcium responsiveness of myofilaments. Mitochondrial respiration was diminished through inhibition of Complex II and Complex IV. Defective calcium handling with reduced calcium current and transients, together with inhibition of mitochondrial respiration, appears to represent the dominant cellular mechanisms of myocardial depression in porcine septic shock.

Introduction: Man-machine interfacing remains the main challenge for accurate and reliable control of bionic prostheses. Implantable electrodes in nerves and muscles may overcome some of the limitations by significantly increasing the interface's reliability and bandwidth. Before human application, experimental preclinical testing is essential to assess chronic in-vivo biocompatibility and functionality. Here, we analyze available animal models, their costs and ethical challenges in special regards to simulating a potentially life-long application in a short period of time and in non-biped animals.Methods: We performed a literature analysis following the PRISMA guidelines including all animal models used to record neural or muscular activity via implantable electrodes, evaluating animal models, group size, duration, origin of publication as well as type of interface. Furthermore, behavioral, ethical, and economic considerations of these models were analyzed. Additionally, we discuss experience and surgical approaches with rat, sheep, and primate models and an approach for international standardized testing.Results: Overall, 343 studies matched the search terms, dominantly originating from the US (55%) and Europe (34%), using mainly small animal models (rat: 40%). Electrode placement was dominantly neural (77%) compared to muscular (23%). Large animal models had a mean duration of 135 ± 87.2 days, with a mean of 5.3 ± 3.4 animals per trial. Small animal models had a mean duration of 85 ± 11.2 days, with a mean of 12.4 ± 1.7 animals.Discussion: Only 37% animal models were by definition chronic tests (>3 months) and thus potentially provide information on long-term performance. Costs for large animals were up to 45 times higher than small animals. However, costs are relatively small compared to complication costs in human long-term applications. Overall, we believe a combination of small animals for preliminary primary electrode testing and large animals to investigate long-term biocompatibility, impedance, and tissue regeneration parameters provides sufficient data to ensure long-term human applications.

BackgroundThe lack of a reliable scoring system that predicts the development of septic shock and death precludes comparison of disease and/or treatment outcomes in animal models of sepsis. We developed a murine sepsis score (MSS) that evaluates seven clinical variables, and sought to assess its validity and reliability in an experimental mouse model of polymicrobial sepsis.MethodsStool collected from the cecum of C57BL/6 (B6) mice was dissolved in 0.9% normal saline (NS) and filtered, resulting in a fecal solution (FS) which was injected intraperitoneally into B6 mice. Disease severity was monitored by MSS during the experimental timeline. Blood and tissue samples were harvested for the evaluation of inflammatory changes after sepsis induction. The correlation between pro-inflammatory markers and MSS was assessed by the Spearman rank correlation coefficient.ResultsMice injected with FS at a concentration of 90 mg/mL developed polymicrobial sepsis with a 75% mortality rate at 24 hours. The MSS was highly predictive of sepsis progression and mortality, with excellent discriminatory power, high internal consistency (Cronbach alpha coefficient = 0.92), and excellent inter-rater reliability (intra-class coefficient = 0.96). An MSS of 3 had a specificity of 100% for predicting onset of septic shock and death within 24 hours. Hepatic dysfunction and systemic pro-inflammatory responses were confirmed by biochemical and cytokine analyses where the latter correlated well with the MSS. Significant bacterial dissemination was noted in multiple organs. Furthermore, the liver, spleen, and intestine demonstrated histopathological evidence of injury.ConclusionsThe MSS reliably predicts disease progression and mortality in an animal model of polymicrobial sepsis. More importantly, it may be used to assess and compare outcomes among various experimental models of sepsis, and serve as an ethically acceptable alternative to death as an endpoint.