Abandon the mouse research ship? Not just yet!

A Neutrophil Phenotype Model for Extracorporeal Treatment of Sepsis

Neutrophils play a central role in eliminating bacterial pathogens, but may also contribute to end-organ damage in sepsis. Interleukin-8 (IL-8), a key modulator of neutrophil function, signals through neutrophil specific surface receptors CXCR-1 and CXCR-2. In this study a mechanistic computational model was used to evaluate and deploy an extracorporeal sepsis treatment which modulates CXCR-1/2 levels. First, a simplified mechanistic computational model of IL-8 mediated activation of CXCR-1/2 receptors was developed, containing 16 ODEs and 43 parameters. Receptor level dynamics and systemic parameters were coupled with multiple neutrophil phenotypes to generate dynamic populations of activated neutrophils which reduce pathogen load, and/or primed neutrophils which cause adverse tissue damage when misdirected. The mathematical model was calibrated using experimental data from baboons administered a two-hour infusion of E coli and followed for a maximum of 28 days. Ensembles of parameters were generated using a Bayesian parallel tempering approach to produce model fits that could recreate experimental outcomes. Stepwise logistic regression identified seven model parameters as key determinants of mortality. Sensitivity analysis showed that parameters controlling the level of killer cell neutrophils affected the overall systemic damage of individuals. To evaluate rescue strategies and provide probabilistic predictions of their impact on mortality, time of onset, duration, and capture efficacy of an extracorporeal device that modulated neutrophil phenotype were explored. Our findings suggest that interventions aiming to modulate phenotypic composition are time sensitive. When introduced between 3–6 hours of infection for a 72 hour duration, the survivor population increased from 31% to 40–80%. Treatment efficacy quickly diminishes if not introduced within 15 hours of infection. Significant harm is possible with treatment durations ranging from 5–24 hours, which may reduce survival to 13%. In severe sepsis, an extracorporeal treatment which modulates CXCR-1/2 levels has therapeutic potential, but also potential for harm. Further development of the computational model will help guide optimal device development and determine which patient populations should be targeted by treatment.

Sepsis occurs when a patient develops a whole body immune response due to infection. In this condition, white blood cells called neutrophils circulate in an active state, seeking and eliminating invading bacteria. However, when neutrophils are activated, healthy tissue is inadvertently targeted, leading to organ damage and potentially death. Even though sepsis kills millions worldwide, there are still no specific treatments approved in the United States. This may be due to the complexity and diversity of the body’s immune response, which can be managed well using computational modeling. We have developed a computational model to predict how different levels of neutrophil activation impact survival in an overactive inflammatory conditions. The model was utilized to assess the effectiveness of a simulated experimental sepsis treatment which modulates neutrophil populations and activity. This evaluation determined that treatment timing plays a critical role in therapeutic effectiveness. When utilized properly the treatment drastically improves survival, but there is also risk of causing patient harm when introduced at the wrong time. We intend for this computational model to support and guide further development of sepsis treatments and help translate these preliminary results from bench to bedside.

New paradigms in sepsis: from prevention to protection of failing microcirculation

Sepsis, also known as septicemia, is one of the 10 leading causes of death worldwide. The rising tide of sepsis due to bacterial, fungal and viral infections cannot be stemmed by current antimicrobial therapies and supportive measures. New paradigms for the mechanism and resolution of sepsis and consequences for sepsis survivors are emerging. Consistent with Benjamin Franklin's dictum 'an ounce of prevention is worth a pound of cure', sepsis can be prevented by vaccinations against pneumococci and meningococci. Recently, the NIH NHLBI Panel redefined sepsis as 'severe endothelial dysfunction syndrome in response to intravascular and extravascular infections causing reversible or irreversible injury to the microcirculation responsible for multiple organ failure'. Microvascular endothelial injury underlies sepsis-associated hypotension, edema, disseminated intravascular coagulation, acute respiratory distress syndrome and acute kidney injury. Microbial genome products trigger 'genome wars' in sepsis that reprogram the human genome and culminate in a 'genomic storm' in blood and vascular cells. Sepsis can be averted experimentally by endothelial cytoprotection through targeting nuclear signaling that mediates inflammation and deranged metabolism. Endothelial 'rheostats' (e.g. inhibitors of NF-κB, A20 protein, CRADD/RAIDD protein and microRNAs) regulate endothelial signaling. Physiologic 'extinguishers' (e.g. suppressor of cytokine signaling 3) can be replenished through intracellular protein therapy. Lipid mediators (e.g. resolvin D1) hasten sepsis resolution. As sepsis cases rose from 387 330 in 1996 to 1.1 million in 2011, and are estimated to reach 2 million by 2020 in the US, mortality due to sepsis approaches that of heart attacks and exceeds deaths from stroke. More preventive vaccines and therapeutic measures are urgently needed.

Early severe impairment of hematopoietic stem and progenitor cells from the bone marrow caused by CLP sepsis and endotoxemia in a humanized mice model

Introduction

An effective immune response to severe bacterial infections requires a robust production of the innate immunity cells from hematopoietic stem and progenitor cells (HSPCs) in a process called emergency myelopoiesis. In sepsis, an altered immune response that leads to a failure of bacterial clearance is often observed. In this study, we aimed to evaluate the impact of sepsis on human HSPCs in the bone marrow (BM) microenvironment of humanized mice subjected to acute endotoxemia and polymicrobial sepsis.

Methods

Humanized mice (hu-NSG) were generated by transplanting NOD.Cg-Prkdc/scidIL2rγ (NSG) mice with the human cord blood CD34⁺ cells. Eight weeks after the transplantation, hu-NSG mice were subjected to sepsis induced by endotoxemia—Escherichia coli lipopolysaccharide (LPS)—or by cecal ligation and puncture (CLP). Twenty-four hours later, HSPCs from BM were analyzed by flow cytometry and colony-forming unit (CFU) assay. CLP after inhibition of Notch signaling was also performed. The effects of LPS on the in vitro proliferation of CD34⁺ cells from human BM were tested by CellTrace Violet dye staining.

Results

The expression of Toll-like receptor 4 receptor was present among engrafted human HSPCs. Both CLP and endotoxemia decreased (by 43 % and 37 %) cellularity of the BM. In addition, in both models, accumulation of early CD34⁺ CD38⁻ HSCs was observed, but the number of CD34⁺ CD38⁺ progenitors decreased. After CLP, there was a 1.5-fold increase of proliferating CD34⁺ CD38⁻Ki-67⁺ cells. Moreover, CFU assay revealed a depressed (by 75 % after LPS and by 50 % after CLP) production of human hematopoietic colonies from the BM of septic mice. In contrast, in vitro LPS stimulated differentiation of CD34⁺ CD38⁻ HSCs but did not induce proliferation of these cells in contrast to the CD34⁺ CD38⁺ progenitors. CLP sepsis modulated the BM microenvironment by upregulation of Jagged-1 expression on non-hematopoietic cells, and the proliferation of HSCs was Notch-dependent.

Conclusions

CLP sepsis and endotoxemia induced a similar expansion and proliferation of early HSCs in the BM, while committed progenitors decreased. It is suggestive that the Notch pathway contributed to this effect. Targeting early hematopoiesis may be considered as a viable alternative in the existing arsenal of supportive therapies in sepsis.

Low-dose cyclophosphamide improves survival in a murine treatment model of sepsis

Sepsis is a complex medical condition characterized by a systemic inflammatory response in the setting of infection. We hypothesized that combining antibiotics plus an immunosuppressant would protect against the morbidity and mortality of polymicrobial sepsis in mice better than would antibiotics alone. We used a murine cecal-ligation-and-puncture model in which mice were treated either with imipenem plus cyclophosphamide or imipenem alone. Titration to a low cyclophosphamide dose revealed that combination therapy increased survival by 20% compared with imipenem alone (56% vs. 36%, P < 0.001). To investigate the mechanism by which combination therapy did this, we reviewed quantitative and qualitative markers of the systemic immune response, end-organ damage, and the local immune response at the site of injury. Cyclophosphamide treatment was not associated with depletion of peripheral leukocytes or differences in pulmonary damage. However, mice that received combination therapy had higher plasma granulocyte colony-stimulating factor levels than did those treated with antibiotics alone. In addition, mice treated with cyclophosphamide had higher levels of bacterial colonization in intestinal Peyer's patch lymph nodes at 72 h after the septic insult. Intraperitoneal macrophage phenotypes and phagocytosis activity did not differ between groups. We conclude that the inflammatory response plays a significant role in the mortality of polymicrobial sepsis and that the regulation of this element is both feasible and beneficial in this disease model.

Passenger Mutations Confound Interpretation of All Genetically Modified Congenic Mice

Targeted mutagenesis in mice is a powerful tool for functional analysis of genes. However, genetic variation between embryonic stem cells (ESCs) used for targeting (previously almost exclusively 129-derived) and recipient strains (often C57BL/6J) typically results in congenic mice in which the targeted gene is flanked by ESC-derived passenger DNA potentially containing mutations. Comparative genomic analysis of 129 and C57BL/6J mouse strains revealed indels and single nucleotide polymorphisms resulting in alternative or aberrant amino acid sequences in 1,084 genes in the 129-strain genome. Annotating these passenger mutations to the reported genetically modified congenic mice that were generated using 129-strain ESCs revealed that nearly all these mice possess multiple passenger mutations potentially influencing the phenotypic outcome. We illustrated this phenotypic interference of 129-derived passenger mutations with several case studies and developed a Me-PaMuFind-It web tool to estimate the number and possible effect of passenger mutations in transgenic mice of interest.

Location, location, location: cytokine concentrations are dependent on blood sampling site

OBJECTIVE

Considerable breakthroughs in the field of sepsis have been made using animal models. Sepsis exhibits a wide array of derangements that may be evaluated in the blood, including the release of proinflammatory and anti-inflammatory cytokines. The Shock journal adheres to the ARRIVE guidelines regarding reporting in vivo results to allow reproducibility of data findings. It is generally assumed that blood cytokine concentrations collected from typical sampling sites will be similar, but there are no data validating that this is true. The main purpose of the present study was to determine if the location of blood sampling results in cytokine concentration differences following inflammatory insults.

METHODS

Two different models of acute inflammation were studied. Adult, female ICR (Institute of Cancer Research) mice were injected with Escherichia coli lipopolysaccharide (n = 28) or subjected to cecal ligation and puncture (n = 16). They were killed at early time points following these inflammatory challenges for the collection of blood from the facial vein, retro-orbital sinus, and heart. Additional samples were collected in EDTA and heparin. Plasma cytokines from the same mouse were collected from each sampling site and evaluated by enzyme-linked immunosorbent assay. Clinical chemical parameters including plasma blood urea nitrogen and total protein were also analyzed.

RESULTS

Regardless of model, time of collection, or cytokine measured, cytokine values from heart blood were higher than facial vein values from the same mouse. Interleukin (IL-6) collected from the heart relative to the facial vein demonstrated elevated concentrations following injection of lipopolysaccharide. In a similar manner, higher concentrations of IL-6, macrophage inflammatory protein 2, IL-10, and IL-1 receptor antagonist were found in cardiac puncture samples compared with other sampling sites 24 h after sepsis induced by cecal ligation and puncture. Similar differences were not seen when comparing blood urea nitrogen and total protein values from the two different sites. Using plasma IL-6 collected from the heart would incorrectly stratify predicted-to-live mice into the predicted-to-die category. Therefore, a simple linear regression model was developed to correctly restratify mice to their predicted fate. These data demonstrate that proinflammatory and anti-inflammatory cytokine concentrations are dramatically elevated when drawn centrally from the heart compared with collection from peripheral locations such as the facial vein. It is critical for publications to document the sampling location when evaluating plasma cytokines and attempting to compare studies.

Skeletal muscle dysfunction is associated with derangements in mitochondrial bioenergetics (but not UCP3) in a rodent model of sepsis

Muscle dysfunction is a common feature of severe sepsis and multiorgan failure. Recent evidence implicates bioenergetic dysfunction and oxidative damage as important underlying pathophysiological mechanisms. Increased abundance of uncoupling protein-3 (UCP3) in sepsis suggests increased mitochondrial proton leak, which may reduce mitochondrial coupling efficiency but limit reactive oxygen species (ROS) production. Using a murine model, we examined metabolic, cardiovascular, and skeletal muscle contractile changes following induction of peritoneal sepsis in wild-type and Ucp3(-/-) mice. Mitochondrial membrane potential (Δψm) was measured using two-photon microscopy in living diaphragm, and contractile function was measured in diaphragm muscle strips. The kinetic relationship between membrane potential and oxygen consumption was determined using a modular kinetic approach in isolated mitochondria. Sepsis was associated with significant whole body metabolic suppression, hypothermia, and cardiovascular dysfunction. Maximal force generation was reduced and fatigue accelerated in ex vivo diaphragm muscle strips from septic mice. Δψm was lower in the isolated diaphragm from septic mice despite normal substrate oxidation kinetics and proton leak in skeletal muscle mitochondria. Even though wild-type mice exhibited an absolute 26 ± 6% higher UCP3 protein abundance at 24 h, no differences were seen in whole animal or diaphragm physiology, nor in survival rates, between wild-type and Ucp3(-/-) mice. In conclusion, this murine sepsis model shows a hypometabolic phenotype with evidence of significant cardiovascular and muscle dysfunction. This was associated with lower Δψm and alterations in mitochondrial ATP turnover and the phosphorylation pathway. However, UCP3 does not play an important functional role, despite its upregulation.

Lymph node fibroblastic reticular cell transplants show robust therapeutic efficacy in high-mortality murine sepsis

Sepsis is an aggressive inflammatory syndrome and a global health burden estimated to kill 7.3 million people annually. Single-target molecular therapies have not addressed the multiple disease pathways triggered by septic injury. Cell therapies might offer a broader set of mechanisms of action that benefit complex, multifocal disease processes. We describe a population of immune-specialized myofibroblasts derived from lymph node tissue, termed fibroblastic reticular cells (FRCs). Because FRCs have an immunoregulatory function in lymph nodes, we hypothesized that ex vivo-expanded FRCs would control inflammation when administered therapeutically. Indeed, a single injection of ex vivo-expanded allogeneic FRCs reduced mortality in mouse models of sepsis when administered at early or late time points after septic onset. Mice treated with FRCs exhibited lower local and systemic concentrations of proinflammatory cytokines and reduced bacteremia. When administered 4 hours after induction of lipopolysaccharide endotoxemia, or cecal ligation and puncture (CLP) sepsis in mice, FRCs reduced deaths by at least 70%. When administered late in disease (16 hours after CLP), FRCs still conveyed a robust survival advantage (44% survival compared to 0% for controls). FRC therapy was dependent on the metabolic activity of nitric oxide synthase 2 (NOS2) as the primary molecular mechanism of drug action in the mice. Together, these data describe a new anti-inflammatory cell type and provide preclinical evidence for therapeutic efficacy in severe sepsis that warrants further translational study.

Why do they die? Comparison of selected aspects of organ injury and dysfunction in mice surviving and dying in acute abdominal sepsis

Background

The mechanisms of sepsis mortality remain undefined. While there is some evidence of organ damage, it is not clear whether this damage alone is sufficient to cause death. Therefore, we aimed to examine contribution of organ injury/dysfunction to early deaths in the mouse abdominal sepsis.

Methods

Female OF-1 mice underwent either medium-severity cecal ligation and puncture (CLP-Only) or non-lethal CLP-ODam (CLP with cisplatin/carbontetrachloride to induce survivable hepatotoxicity and nephrotoxicity). In the first experiment, blood was collected daily from survivors (SUR; CLP-Only and CLP-ODam groups) or until early death (DIED; CLP-Only). In the second experiment (CLP-Only), early outcome was prospectively predicted based on body temperature (BT) and pairs of mice predicted to survive (P-SUR) and die (P-DIE) were sacrificed post-CLP. The overall magnitude of organ injury/dysfunction was compared in retrospectively and prospectively stratified mice.

Results

At day 7 post-CLP, survival in CLP-Only was 48%, while CLP-ODam was non-lethal. In CLP-Only mice within 24 h of death, urea increased to 78 (versus 40 mg/dl in SUR), ALT to 166 (vs. 108 U/l), LDH to 739 (vs. 438 U/l) and glucose declined to 43 (vs. 62 mg/dl). In CLP-ODam, hypoglycemia was exacerbated (by 1.5-fold) and ALT and LDH were 20- and 8-fold higher versus DIED (CLP-Only) mice. In CLP-Only, predicted deaths (P-DIE) were preceded by a significant rise only in cystatin C (268 vs. 170 ng/ml in P-SUR) but not in creatinine and troponin I. Respiratory function of mitochondria in the liver and kidney of P-SUR and P-DIE CLP-Only mice was not impaired (vs. controls) and ATP level in organs remained similar among all groups. Histologic injury scores in the liver, kidney, heart and lung showed no major disparities among dying, surviving and control mice.

Conclusions

In CLP-Only mice, although the deregulation of parameters indicative of organ injury/dysfunction was greater in dying versus surviving mice, it never exceeded the changes in surviving CLP-ODam animals, and it was not followed by histopathological damage and/or mitochondrial dysfunction. This shows that interpretation of the contribution of the organ injury/dysfunction to early deaths in the CLP model is not straightforward and depends on the pathophysiological origin of the profiled disturbances.

Electronic supplementary material

The online version of this article (doi:10.1186/s40635-015-0048-z) contains supplementary material, which is available to authorized users.

Human metabolic response to systemic inflammation: assessment of the concordance between experimental endotoxemia and clinical cases of sepsis/SIRS

Introduction

Two recent, independent, studies conducted novel metabolomics analyses relevant to human sepsis progression; one was a human model of endotoxin (lipopolysaccharide (LPS)) challenge (experimental endotoxemia) and the other was community acquired pneumonia and sepsis outcome diagnostic study (CAPSOD). The purpose of the present study was to assess the concordance of metabolic responses to LPS and community-acquired sepsis.

Methods

We tested the hypothesis that the patterns of metabolic response elicited by endotoxin would agree with those in clinical sepsis. Alterations in the plasma metabolome of the subjects challenged with LPS were compared with those of sepsis patients who had been stratified into two groups: sepsis patients with confirmed infection and non-infected patients who exhibited systemic inflammatory response syndrome (SIRS) criteria. Common metabolites between endotoxemia and both these groups were individually identified, together with their direction of change and functional classifications.

Results

Response to endotoxemia at the metabolome level elicited characteristics that agree well with those observed in sepsis patients despite the high degree of variability in the response of these patients. Moreover, some distinct features of SIRS have been identified. Upon stratification of sepsis patients based on 28-day survival, the direction of change in 21 of 23 metabolites was the same in endotoxemia and sepsis survival groups.

Conclusions

The observed concordance in plasma metabolomes of LPS-treated subjects and sepsis survivors strengthens the relevance of endotoxemia to clinical research as a physiological model of community-acquired sepsis, and gives valuable insights into the metabolic changes that constitute a homeostatic response. Furthermore, recapitulation of metabolic differences between sepsis non-survivors and survivors in LPS-treated subjects can enable further research on the development and assessment of rational clinical therapies to prevent sepsis mortality. Compared with earlier studies which focused exclusively on comparing transcriptional dynamics, the distinct metabolomic responses to systemic inflammation with or without confirmed infection, suggest that the metabolome is much better at differentiating these pathophysiologies. Finally, the metabolic changes in the recovering patients shift towards the LPS-induced response pattern strengthening the notion that the metabolic, as well as transcriptional responses, characteristic to the endotoxemia model represent necessary and “healthy” responses to infectious stimuli.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-0783-2) contains supplementary material, which is available to authorized users.

CHRFAM7A, a human-specific and partially duplicated α7-nicotinic acetylcholine receptor gene with the potential to specify a human-specific inflammatory response to injury

Conventional wisdom presumes that the α7nAChR product of CHRNA7 expression mediates the ability of the vagus nerve to regulate the inflammatory response to injury and infection. Yet, 15 years ago, a 2nd structurally distinct and human-specific α7nAChR gene was discovered that has largely escaped attention of the inflammation research community. The gene, originally called dupα7nAChR but now known as CHRFAM7A, has been studied exhaustively in psychiatric research because of its association with mental illness. However, dupα7nAChR/CHRFAM7A expression is relatively low in human brain but elevated in human leukocytes. Furthermore, α7nAChR research in human tissues has been confounded by cross-reacting antibodies and nonspecific oligonucleotide primers that crossreact in immunoblotting, immunohistochemistry, and RT-PCR. Yet, 3 independent reports show the human-specific CHRFAM7A changes cell responsiveness to the canonical α7nAChR/CHRNA7 ion-gated channel. Because of its potential for the injury research community, its possible significance to human leukocyte biology, and its relevance to human inflammation, we review the discovery and structure of the dupα7nAChR/CHRFAM7A gene, the distribution of its mRNA, and its biologic activities and then discuss its possible role(s) in specifying human inflammation and injury. In light of emerging concepts that point to a role for human-specific genes in complex human disease, the existence of a human-specific α7nAChR regulating inflammatory responses in injury underscores the need for caution in extrapolating findings in the α7nAChR literature to man. To this end, we discuss the translational implications of a uniquely human α7nAChR-like gene on new drug target discovery and therapeutics development for injury, infection, and inflammation.

The reproducibility of biomedical research: Sleepers awake!

There is increasing concern about the reliability of biomedical research, with recent articles suggesting that up to 85% of research funding is wasted. This article argues that an important reason for this is the inappropriate use of molecular techniques, particularly in the field of RNA biomarkers, coupled with a tendency to exaggerate the importance of research findings.

Overexpression of GTP cyclohydrolase 1 feedback regulatory protein is protective in a murine model of septic shock

Overproduction of nitric oxide (NO) by inducible NO synthase contributes toward refractory hypotension, impaired microvascular perfusion, and end-organ damage in septic shock patients. Tetrahydrobiopterin (BH4) is an essential NOS cofactor. GTP cyclohydrolase 1 (GCH1) is the rate-limiting enzyme for BH4 biosynthesis. Under inflammatory conditions, GCH1 activity and hence BH4 levels are increased, supporting pathological NOS activity. GCH1 activity can be controlled through allosteric interactions with GCH1 feedback regulatory protein (GFRP). We investigated whether overexpression of GFRP can regulate BH4 and NO production and attenuate cardiovascular dysfunction in sepsis. Sepsis was induced in mice conditionally overexpressing GFRP and wild-type littermates by cecal ligation and puncture. Blood pressure was monitored by radiotelemetry, and mesenteric blood flow was quantified by laser speckle contrast imaging. Blood biochemistry data were obtained using an iSTAT analyzer, and BH4 levels were measured in plasma and tissues by high-performance liquid chromatography. Increased BH4 and NO production and hypotension were observed in all mice, but the extents of these pathophysiological changes were attenuated in GFRP OE mice. Perturbations in blood biochemistry were similarly attenuated in GFRP OE compared with wild-type controls. These results suggest that GFRP overexpression regulates GCH1 activity during septic shock, which in turn limits BH4 bioavailability for iNOS. We conclude that the GCH1-GFRP axis is a critical regulator of BH4 and NO production and the cardiovascular derangements that occur in septic shock.

The Future of Preclinical Animal Models in Pharmaceutical Discovery and Development

Animal models have provided an important tool to help make the decision to take potential therapies from preclinical studies to humans. In the past several years, the strong reliance of the pharmaceutical discovery and development process on the use of animal models has come under increasing scrutiny for ethical and scientific reasons. Several prominent and widely publicized articles have reported limited concordance of animal experiments with subsequent human clinical trials. Recent assessments of the quality of animal studies have suggested that this translational failure may be due in part to shortcomings in the planning, conduct, and reporting of in vivo studies. This article will emphasize methods to assure best practice rigor in animal study methods and reporting. It will introduce the so-called scientific 3Rs of relevance, robustness, and reproducibility to the in vivo study approach and will review important new trends in the animal research and pharmaceutical discovery and development communities.

Loss of the endothelial glucocorticoid receptor prevents the therapeutic protection afforded by dexamethasone after LPS

Glucocorticoids are normally regarded as anti-inflammatory therapy for a wide variety of conditions and have been used with some success in treating sepsis and sepsis-like syndromes. We previously demonstrated that mice lacking the glucocorticoid receptor in the endothelium (GR EC KO mice) are extremely sensitive to low-dose LPS and demonstrate prolonged activation and up regulation of NF-κB. In this study we pre-treated these GR EC KO mice with dexamethasone and assessed their response to an identical dose of LPS. Surprisingly, the GR EC KO mice fared even worse than when given LPS alone demonstrating increased mortality, increased levels of the inflammatory cytokines TNF-α and IL-6 and increased nitric oxide release after the dexamethasone pre-treatment. As expected, control animals pre-treated with dexamethasone showed improvement in all parameters assayed. Mechanistically we demonstrate that GR EC KO mice show increased iNOS production and NF-κB activation despite treatment with dexamethasone.

Effects of intra-abdominal sepsis on atherosclerosis in mice

Introduction

Sepsis and other infections are associated with late cardiovascular events. Although persistent inflammation is implicated, a causal relationship has not been established. We tested whether sepsis causes vascular inflammation and accelerates atherosclerosis.

Methods

We performed prospective, randomized animal studies at a university research laboratory involving adult male ApoE-deficient (ApoE^−/−) and young C57B/L6 wild-type (WT) mice. In the primary study conducted to determine whether sepsis accelerates atherosclerosis, we fed ApoE^−/− mice (N = 46) an atherogenic diet for 4 months and then performed cecal ligation and puncture (CLP), followed by antibiotic therapy and fluid resuscitation or a sham operation. We followed mice for up to an additional 5 months and assessed atheroma in the descending aorta and root of the aorta. We also exposed 32 young WT mice to CLP or sham operation and followed them for 5 days to determine the effects of sepsis on vascular inflammation.

Results

ApoE^−/− mice that underwent CLP had reduced activity during the first 14 days (38% reduction compared to sham; P < 0.001) and sustained weight loss compared to the sham-operated mice (−6% versus +9% change in weight after CLP or sham surgery to 5 months; P < 0.001). Despite their weight loss, CLP mice had increased atheroma (46% by 3 months and 41% increase in aortic surface area by 5 months; P = 0.03 and P = 0.004, respectively) with increased macrophage infiltration into atheroma as assessed by immunofluorescence microscopy (0.52 relative fluorescence units (rfu) versus 0.97 rfu; P = 0.04). At 5 months, peritoneal cultures were negative; however, CLP mice had elevated serum levels of interleukin 6 (IL-6) and IL-10 (each at P < 0.05). WT mice that underwent CLP had increased expression of intercellular adhesion molecule 1 in the aortic lumen versus sham at 24 hours (P = 0.01) that persisted at 120 hours (P = 0.006). Inflammatory and adhesion genes (tumor necrosis factor α, chemokine (C-C motif) ligand 2 and vascular cell adhesion molecule 1) and the adhesion assay, a functional measure of endothelial activation, were elevated at 72 hours and 120 hours in mice that underwent CLP versus sham-operations (all at P <0.05).

Conclusions

Using a combination of existing murine models for atherosclerosis and sepsis, we found that CLP, a model of intra-abdominal sepsis, accelerates atheroma development. Accelerated atheroma burden was associated with prolonged systemic, endothelial and intimal inflammation and was not explained by ongoing infection. These findings support observations in humans and demonstrate the feasibility of a long-term follow-up murine model of sepsis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-014-0469-1) contains supplementary material, which is available to authorized users.

Intestine-specific deletion of microsomal triglyceride transfer protein increases mortality in aged mice

Background

Mice with conditional, intestine-specific deletion of microsomal triglyceride transfer protein (Mttp-IKO) exhibit a complete block in chylomicron assembly together with lipid malabsorption. Young (8–10 week) Mttp-IKO mice have improved survival when subjected to a murine model of Pseudomonas aeruginosa-induced sepsis. However, 80% of deaths in sepsis occur in patients over age 65. The purpose of this study was to determine whether age impacts outcome in Mttp-IKO mice subjected to sepsis.

Methods

Aged (20–24 months) Mttp-IKO mice and WT mice underwent intratracheal injection with P. aeruginosa. Mice were either sacrificed 24 hours post-operatively for mechanistic studies or followed seven days for survival.

Results

In contrast to young septic Mttp-IKO mice, aged septic Mttp-IKO mice had a significantly higher mortality than aged septic WT mice (80% vs. 39%, p = 0.005). Aged septic Mttp-IKO mice exhibited increased gut epithelial apoptosis, increased jejunal Bax/Bcl-2 and Bax/Bcl-X_L ratios yet simultaneously demonstrated increased crypt proliferation and villus length. Aged septic Mttp-IKO mice also manifested increased pulmonary myeloperoxidase levels, suggesting increased neutrophil infiltration, as well as decreased systemic TNFα compared to aged septic WT mice.

Conclusions

Blocking intestinal chylomicron secretion alters mortality following sepsis in an age-dependent manner. Increases in gut apoptosis and pulmonary neutrophil infiltration, and decreased systemic TNFα represent potential mechanisms for why intestine-specific Mttp deletion is beneficial in young septic mice but harmful in aged mice as each of these parameters are altered differently in young and aged septic WT and Mttp-IKO mice.