Characterization of a model of systemic inflammation in humans in vivo elicited by continuous infusion of endotoxin

Mathematical model of the inflammatory response to acute and prolonged lipopolysaccharide exposure in humans

One in five deaths worldwide is associated with sepsis, which is defined as organ dysfunction caused by a dysregulated host response to infection. An increased understanding of the pathophysiology of sepsis could provide improved approaches for early detection and treatment. Here we describe the development and validation of a mechanistic mathematical model of the inflammatory response, making use of a combination of in vitro and human in vivo data obtained from experiments where bacterial lipopolysaccharide (LPS) was used to induce an inflammatory response. The new model can simulate the responses to both acute and prolonged inflammatory stimuli in an experimental setting, as well as the response to infection in the clinical setting. This model serves as a foundation for a sepsis simulation model with a potentially wide range of applications in different disciplines involved with sepsis research.

Characterization of differences in immune responses during bolus and continuous infusion endotoxin challenges using mathematical modelling

Endotoxin administration is commonly used to study the inflammatory response, and though traditionally given as a bolus injection, it can be administered as a continuous infusion over multiple hours. Several studies hypothesize that the latter better represents the prolonged and pronounced inflammation observed in conditions like sepsis. Yet very few experimental studies have administered endotoxin using both strategies, leaving significant gaps in determining the underlying mechanisms responsible for their differing immune responses. We used mathematical modelling to analyse cytokine data from two studies administering a 2 ng kg-1 dose of endotoxin, one as a bolus and the other as a continuous infusion over 4 h. Using our model, we simulated the dynamics of mean and subject-specific cytokine responses as well as the response to long-term endotoxin administration. Cytokine measurements revealed that the bolus injection led to significantly higher peaks for interleukin (IL)-8, while IL-10 reaches higher peaks during continuous administration. Moreover, the peak timing of all measured cytokines occurred later with continuous infusion. We identified three model parameters that significantly differed between the two administration methods. Monocyte activation of IL-10 was greater during the continuous infusion, while tumour necrosis factor α $ {\alpha} $ and IL-8 recovery rates were faster for the bolus injection. This suggests that a continuous infusion elicits a stronger, longer-lasting systemic reaction through increased stimulation of monocyte anti-inflammatory mediator production and decreased recovery of pro-inflammatory catalysts. Furthermore, the continuous infusion model exhibited prolonged inflammation with recurrent peaks resolving within 2 days during long-term (20-32 h) endotoxin administration.

Evaluation of Systemic Inflammation Before and After Standard Anti-tuberculosis Treatment in Patients With Active Pulmonary Tuberculosis and Diabetes Mellitus

Background Diabetes mellitus (DM) is a common comorbidity of active pulmonary tuberculosis (APTB) that increases the risk of treatment failure during anti-tuberculosis chemotherapy. Evaluating systemic inflammatory response could help determine differences in response to treatment between APTB patients and those with APTB and DM. Methodology To explore changes in systemic inflammation, measured by a set of inflammatory mediators in subjects with APTB and TBDM before and after six months of anti-tuberculosis chemotherapy, 30 APTB and nine TBDM subjects underwent cytokine testing, including interleukin (IL)-6, IL-8, IL-10, interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), and transforming growth factor-beta 1 (TGF-β1) by enzyme-linked immunosorbent assay, C-reactive protein by nephelometry, and sialic acid by colorimetric assay at baseline and following six months of standard anti-tuberculosis treatment. Sputum smear microscopy or molecular biology (Xpert MTB/RIF) was used for diagnosis, and sputum smear microscopy was performed monthly during the treatment of the patient with pulmonary tuberculosis to evaluate his evolution. Principal component analysis examined changes in the inflammatory status. Results Both groups showed negative sputum smear microscopy in the sixth month after starting anti-tuberculosis chemotherapy. TGF-β1 was found to be significantly higher in subjects with TBDM before treatment compared to APTB patients (p<0.001), and systemic inflammation continued only in TBDM subjects after treatment (accumulation and persistence of inflammatory mediators like IL-6, IL-8, IL-10, IFN-γ, TNF-α, TGF-β1, C-reactive protein, and sialic acid in blood). On the other hand, the mediators IFN-γ, C-reactive protein, and total sialic acid were found to be most influential in distinguishing pre- and post-treatment inflammatory response in subjects with APTB without DM. Conclusions Inflammatory mediators analyzed in combination, including IFN-γ, CRP, and total sialic acid, may be useful in evaluating the systemic inflammatory response in subjects with APTB and TBDM before and after anti-tuberculosis treatment. Determining these mediators revealed persistent systemic inflammation in TBDM subjects after six months of standard tuberculosis treatment, despite negative sputum smear microscopy results and good glycemic control. This suggests a need for inflammation-modulating therapies during tuberculosis control. Finally, monitoring sputum smear microscopy results alongside the determination of proposed inflammatory mediators (IFN-γ, CRP, and total sialic acid) are effective in evaluating the response to anti-tuberculosis treatment in APTB subjects without DM, warranting further investigation.

Processing stimulus dynamics by the NF-κB network in single cells

Cells at the site of an infection experience numerous biochemical signals that vary in amplitude, space, and time. Despite the diversity of dynamic signals produced by pathogens and sentinel cells, information-processing pathways converge on a limited number of central signaling nodes to ultimately control cellular responses. In particular, the NF-κB pathway responds to dozens of signals from pathogens and self, and plays a vital role in processing proinflammatory inputs. Studies addressing the influence of stimulus dynamics on NF-κB signaling are rare due to technical limitations with live-cell measurements. However, recent advances in microfluidics, automation, and image analysis have enabled investigations that yield high temporal resolution at the single-cell level. Here, we summarize the recent research which measures and models the NF-κB response to pulsatile and fluctuating stimulus concentrations, as well as different combinations and sequences of signaling molecules. Collectively, these studies show that the NF-κB network integrates external inflammatory signals and translates these into downstream transcriptional responses.

Altered response to Toll-like receptor 4 activation in fibromyalgia: A low-dose, human experimental endotoxemia pilot study

In this pilot study, a human intravenous injection of low-dose endotoxin (lipopolysaccharide, LPS) model was used to test if fibromyalgia is associated with altered immune responses to Toll-like receptor 4 (TLR4) activation. Eight women with moderately-severe fibromyalgia and eight healthy women were administered LPS at 0.1 ng/kg in session one and 0.4 ng/kg in session two. Blood draws were collected hourly to characterize the immune response. The primary analytes of interest, leptin and fractalkine, were assayed via commercial radioimmunoassay and enzyme-linked immunosorbent assay kits, respectively. Exploratory analyses were performed on 20 secreted cytokine assays by multiplex cytokine panels, collected hourly. Exploratory analyses were also performed on testosterone, estrogen, and cortisol levels, collected hourly. Additionally, standard clinical complete blood counts with differential (CBC-D) were collected before LPS administration and at the end of the session. The fibromyalgia group demonstrated enhanced leptin and suppressed fractalkine responses to LPS administration. In the exploratory analyses, the fibromyalgia group showed a lower release of IFN-γ, CXCL10, IL-17A, and IL-12 and higher release of IL-15, TARC, MDC, and eotaxin than the healthy group. The results of this study suggest that fibromyalgia may involve an altered immune response to TLR4 activation.

NF-κB memory coordinates transcriptional responses to dynamic inflammatory stimuli

Many scenarios in cellular communication require cells to interpret multiple dynamic signals. It is unclear how exposure to inflammatory stimuli alters transcriptional responses to subsequent stimulus. Using high-throughput microfluidic live-cell analysis, we systematically profile the NF-κB response to different signal sequences in single cells. We find that NF-κB dynamics store the short-term history of received signals: depending on the prior pathogenic or cytokine signal, the NF-κB response to subsequent stimuli varies from no response to full activation. Using information theory, we reveal that these stimulus-dependent changes in the NF-κB response encode and reflect information about the identity and dose of the prior stimulus. Small-molecule inhibition, computational modeling, and gene expression profiling show that this encoding is driven by stimulus-dependent engagement of negative feedback modules. These results provide a model for how signal transduction networks process sequences of inflammatory stimuli to coordinate cellular responses in complex dynamic environments.

Effects of Early Initiation of High-Dose Dexamethasone Therapy on Pro-Inflammatory Cytokines and Mortality in LPS-Challenged Mice

This study aims to explore the effects of early dexamethasone therapy at low to high doses on the survival and inflammatory responses in lipopolysaccharide (LPS)-challenged mice. We performed two-series experiments to explore the impact of early dexamethasone therapy at different doses (0.5 mg/kg, 1.5 mg/kg, and 5 mg/kg; PO) on pro-inflammatory cytokine levels, including tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6), as well as survival in LPS-treated mice (10 mg/kg, IP). Dexamethasone was administered daily from 24 h before and 5 days after LPS challenge. Dose-dependent improved survival was demonstrated with dexamethasone (p < 0.05). Body weight was significantly decreased within 24 h of LPS injection, with significantly greater weight loss in the dexamethasone groups (p < 0.05). Weight changes were significantly associated with the days after LPS administration (p < 0.01), but not with the dexamethasone dose (p > 0.05). Mice treated with high-dose dexamethasone (5 mg/kg) had a significantly lowered serum TNF-α (134.41 ± 15.83 vs. 408.83 ± 18.32) and IL-6 (22.08 ± 4.34 vs. 91.27 ± 8.56) compared with those without dexamethasone. This study provides essential insights that the suppression of early-phase hyperactivation of pro-inflammatory activities through the early initiation of high-dose dexamethasone therapy increases sepsis-related prognosis.

Understanding the role of endotoxin tolerance in chronic inflammatory conditions and periodontal disease

OBJECTIVE

This review aims to present the current understanding of endotoxin tolerance (ET) in chronic inflammatory diseases and explores the potential connection with periodontitis.

SUMMARY

Subsequent exposure to lipopolysaccharides (LPS) triggers ET, a phenomenon regulated by different mechanisms and pathways, including toll-like receptors (TLRs), nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB), apoptosis of immune cells, epigenetics, and microRNAs (miRNAs). These mechanisms interconnect ET with chronic inflammatory diseases that include periodontitis. While the direct correlation between ET and periodontal destruction has not been fully elucidated, emerging reports point towards the potential tolerization of human periodontal ligament cells (hPDLCs) and gingival tissues with a significant reduction of TLR levels.

CONCLUSIONS

There is a potential link between ET and periodontal diseases. Future studies should explore the crucial role of ET in the pathogenesis of periodontal diseases as evidence of a tolerized oral mucosa may represent an intrinsic mechanism capable of regulating the oral immune response. A clear understanding of this host immune regulatory mechanism might lead to effective and more predictable therapeutic strategies to treat chronic inflammatory diseases and periodontitis. This article is protected by copyright. All rights reserved.

Endotoxin for Alcohol Research: A Call for Experimental Medicine Using Lipopolysaccharide Challenge

Studies of inflammation in alcohol use disorder (AUD) are overwhelmingly preclinical, and translation to clinical samples is necessary. Endotoxin administration has been used successfully in humans to study mood disorders, offering a translational, reliable and safe model that may be validated in AUD research. We argue for the use of endotoxin challenge to elucidate the interplay between AUD and inflammation.

Biomarker-Guided Individualization of Antibiotic Therapy

Treatment failure of antibiotic therapy due to insufficient efficacy or occurrence of toxicity is a major clinical challenge, and is expected to become even more urgent with the global rise of antibiotic resistance. Strategies to optimize treatment in individual patients are therefore of crucial importance. Currently, therapeutic drug monitoring plays an important role in optimizing antibiotic exposure to reduce treatment failure and toxicity. Biomarker-based strategies may be a powerful tool to further quantify and monitor antibiotic treatment response, and reduce variation in treatment response between patients. Host response biomarkers, such as CRP, procalcitonin, IL-6, and presepsin, could potentially carry significant information to be utilized for treatment individualization. To achieve this, the complex interactions among immune system, pathogen, drug, and biomarker need to be better understood and characterized. The purpose of this tutorial is to discuss the use and evidence of currently available biomarker-based approaches to inform antibiotic treatment. To this end, we also included a discussion on how treatment response biomarker data from preclinical, healthy volunteer, and patient-based studies can be further characterized using pharmacometric and system pharmacology based modeling approaches. As an illustrative example of how such modeling strategies can be used, we describe a case study in which we quantitatively characterize procalcitonin dynamics in relation to antibiotic treatments in patients with sepsis.

Kinetics of Neutrophil Subsets in Acute, Subacute, and Chronic Inflammation

At homeostasis the vast majority of neutrophils in the circulation expresses CD16 and CD62L within a narrow expression range, but this quickly changes in disease. Little is known regarding the changes in kinetics of neutrophils phenotypes in inflammatory conditions. During acute inflammation more heterogeneity was found, characterized by an increase in CD16^dim banded neutrophils. These cells were probably released from the bone marrow (left shift). Acute inflammation induced by human experimental endotoxemia (LPS model) was additionally accompanied by an immediate increase in a CD62L^low neutrophil population, which was not as explicit after injury/trauma induced acute inflammation. The situation in sub-acute inflammation was more complex. CD62L^low neutrophils appeared in the peripheral blood several days (>3 days) after trauma with a peak after 10 days. A similar situation was found in the blood of COVID-19 patients returning from the ICU. Sorted CD16^low and CD62L^low subsets from trauma and COVID-19 patients displayed the same nuclear characteristics as found after experimental endotoxemia. In diseases associated with chronic inflammation (stable COPD and treatment naive HIV) no increases in CD16^low or CD62L^low neutrophils were found in the peripheral blood. All neutrophil subsets were present in the bone marrow during homeostasis. After LPS rechallenge, these subsets failed to appear in the circulation, but continued to be present in the bone marrow, suggesting the absence of recruitment signals. Because the subsets were reported to have different functionalities, these results on the kinetics of neutrophil subsets in a range of inflammatory conditions contribute to our understanding on the role of neutrophils in health and disease.

Ultra-High Packing Density Next Generation Microtube Array Membrane for Absorption Based Applications

Previously, we successfully developed an extracorporeal endotoxin removal device (EERD) that is based on the novel next generation alternating microtube array membrane (MTAM-A) that was superior to the commercial equivalent. In this article, we demonstrated multiple different parameter modifications that led to multiple different types of novel new MTAM structures, which ultimately led to the formation of the MTAM-A. Contrary to the single layered MTAM, the MTAM-A series consisted of a superior packing density fiber connected in a double layered, alternating position which allowed for the greater fiber count to be packed per unit area. The respective MTAM variants were electrospun by utilizing our internally developed tri-axial electrospinning set up to produce the novel microstructures as seen in the respective MTAM variants. A key uniqueness of this study is the ability to produce self-arranged fibers into the respective MTAM variants by utilizing a single spinneret, which has not been demonstrated before. Of the MTAM variants, we observed a change in the microstructure from a single layered MTAM to the MTAM-A series when the ratio of surfactant to shell flow rate approaches 1:1.92. MTAM-A registered the greatest surface area of 2.2 times compared to the traditional single layered MTAM, with the greatest tensile strength at 1.02 ± 0.13 MPa and a maximum elongation of 57.70 ± 9.42%. The MTAM-A was selected for downstream immobilization of polymyxin B (PMB) and assembly into our own internally developed and fabricated dialyzer housing. Subsequently, the entire setup was tested with whole blood spiked with endotoxin; and benchmarked against commercial Toraymyxin fibers of the same size. The results demonstrated that the EERD based on the MTAM-A performed superior to that of the commercial equivalent, registering a rapid reduction of 73.18% of endotoxin (vs. Toraymyxin at 38.78%) at time point 15 min and a final total endotoxin removal of 89.43% (vs. Toraymyxin at 65.03%).

NF-κB responds to absolute differences in cytokine concentrations

Cells receive a wide range of dynamic signaling inputs during immune regulation, but how gene regulatory networks measure such dynamic inputs is not well understood. Here, we used microfluidic single-cell analysis and mathematical modeling to study how the NF-κB pathway responds to immune inputs that vary over time such as increasing, decreasing, or fluctuating cytokine signals. We found that NF-κB activity responded to the absolute difference in cytokine concentration and not to the concentration itself. Our analyses revealed that negative feedback by the regulatory proteins A20 and IκBα enabled differential responses to changes in cytokine dose by providing a short-term memory of previous cytokine concentrations and by continuously resetting kinase cycling and receptor abundance. Investigation of NF-κB target gene expression showed that cells exhibited distinct transcriptional responses under different dynamic cytokine profiles. Our results demonstrate how cells use simple network motifs and transcription factor dynamics to efficiently extract information from complex signaling environments.

Sick for science: experimental endotoxemia as a translational tool to develop and test new therapies for inflammation-associated depression

Depression is one of the global leading causes of disability, but treatments remain limited and classical antidepressants were found to be ineffective in a substantial proportion of patients. Thus, novel effective therapies for the treatment of depression are urgently needed. Given the emerging role of inflammation in the etiology and pathophysiology of affective disorders, we herein illustrate how experimental endotoxemia, a translational model of systemic inflammation, could be used as a tool to develop and test new therapeutic options against depression. Our concept is based on the striking overlap of inflammatory, neural, and affective characteristics in patients with inflammation-associated depression and in endotoxin-challenged healthy subjects. Experimental administration of endotoxin in healthy volunteers is safe, well-tolerated, and without known long-term health risks. It offers a highly standardized translational approach to characterize potential targets of therapies against inflammation-associated depression, as well as to identify characteristics of patients that would benefit from these interventions, and, therefore, could contribute to improve personalization of treatment and to increase the overall rate of responders.

Monitoring coherence between the macro and microcirculation in septic shock

PURPOSE OF REVIEW

Currently, the treatment of patients with shock is focused on the clinical symptoms of shock. In the early phase, this is usually limited to heart rate, blood pressure, lactate levels and urine output. However, as the ultimate goal of resuscitation is the improvement in microcirculatory perfusion the question is whether these currently used signs of shock and the improvement in these signs actually correspond to the changes in the microcirculation.

RECENT FINDINGS

Recent studies have shown that during the development of shock the deterioration in the macrocirculatory parameters are followed by the deterioration of microcirculatory perfusion. However, in many cases the restoration of adequate macrocirculatory parameters is frequently not associated with improvement in microcirculatory perfusion. This relates not only to the cause of shock, where there are some differences between different forms of shock, but also to the type of treatment.

SUMMARY

The improvement in macrohemodynamics during the resuscitation is not consistently followed by subsequent changes in the microcirculation. This may result in both over-resuscitation and under-resuscitation leading to increased morbidity and mortality. In this article the principles of coherence and the monitoring of the microcirculation are reviewed.

Challenging the challenge: A randomized controlled trial evaluating the inflammatory response and pain perception of healthy volunteers after single-dose LPS administration, as a potential model for inflammatory pain in early-phase drug development

BACKGROUND AND AIMS

Following an infection, cytokines not only regulate the acute immune response, but also contribute to symptoms such as inflammatory hyperalgesia. We aimed to characterize the acute inflammatory response induced by a human endotoxemia model, and its effect on pain perception using evoked pain tests in two different dose levels. We also attempted to determine whether combining a human endotoxemia challenge with measurement of pain thresholds in healthy subjects could serve as a model to study drug effects on inflammatory pain.

METHODS AND RESULTS

This was a placebo-controlled, randomized, cross-over study in 24 healthy males. Twelve subjects were administered a bolus of 1 ng/kg LPS intravenously, and twelve 2 ng/kg LPS. Before days of placebo/LPS administration, subjects completed a full study day without study drug administration, but with identical pain threshold testing. Blood sampling and evoked pain tests (electrical burst and -stair, heat, pressure, and cold pressor test) were performed pre-dose and at frequent intervals up to 10hr post-dose. Data were analysed with a repeated-measures ANCOVA. For both dose levels, LPS induced an evident acute inflammatory response, but did not significantly affect any of the pain modalities. In a post-hoc analysis, lowering of pain thresholds was observed in the first 3 h after dosing, corresponding with the peak of the acute inflammatory response around 1-3 h post-dose.

CONCLUSION

Mild acute systemic inflammation, as induced by 1 ng/kg and 2 ng/kg LPS intravenous administration, did not significantly change pain thresholds in this study. The endotoxemia model in combination with evoked pain tests is not suitable to study acute inflammatory hyperalgesia in healthy males.

Pharmacodynamics of immune response biomarkers of interest for evaluation of treatment effects in bacterial infections

This mini-review discusses the pharmacodynamics of immune-related biomarkers in the area of bacterial infectious diseases that could be of interest from a pharmacokinetic (PK) and pharmacokinetic/pharmacodynamic (PK/PD) perspective in the evaluation of treatment effects. The host response to an infection is often poorly defined both in preclinical assessments and in clinical practice when it comes to characterisation of PK and PK/PD relationships. Through population modelling, the time courses and variability of immune response variables can be quantified. Incorporation of such biomarker information into PK and PK/PD models may guide the evaluation of individual response to treatment (right antibiotic, more antibiotic, less antibiotic) and when to stop treatment. Furthermore, translation of results from preclinical systems to clinical scenarios may be improved with the incorporation of biomarker information. Potential biomarkers for these purposes are discussed and a few modelling examples are provided.

Treatment With Acetylsalicylic Acid Reverses Endotoxin Tolerance in Humans In Vivo: A Randomized Placebo-Controlled Study

OBJECTIVE

To investigate immunostimulatory effects of acetylsalicylic acid during experimental human endotoxemia and in sepsis patients.

DESIGN

Double-blind, randomized, placebo-controlled study in healthy volunteers and ex vivo stimulation experiments using monocytes of septic patients.

SETTING

Intensive care research unit of an university hospital.

SUBJECTS

Thirty healthy male volunteers and four sepsis patients.

INTERVENTIONS

Healthy volunteers were challenged IV with endotoxin twice, at a 1-week interval, with each challenge consisting of a bolus of 1 ng/kg followed by continuous administration of 1 ng/kg/hr during 3 hours. Volunteers were randomized to acetylsalicylic acid prophylaxis (80 mg acetylsalicylic acid daily for a 14-d period, starting 7 d before the first endotoxin challenge), acetylsalicylic acid treatment (80 mg acetylsalicylic acid daily for the 7-d period in-between both endotoxin challenges), or the control group (receiving placebo). Furthermore, monocytes of sepsis patients were incubated with acetylsalicylic acid preexposed platelets and were subsequently stimulated with endotoxin.

MEASUREMENTS AND MAIN RESULTS

Acetylsalicylic acid prophylaxis enhanced plasma tumor necrosis factor-α concentrations upon the first endotoxin challenge by 50% compared with the control group (p = 0.02) but did not modulate cytokine responses during the second endotoxin challenge. In contrast, acetylsalicylic acid treatment resulted in enhanced plasma levels of tumor necrosis factor-α (+53%; p = 0.02), interleukin-6 (+91%; p = 0.03), and interleukin-8 (+42%; p = 0.02) upon the second challenge, whereas plasma levels of the key antiinflammatory cytokine interleukin-10 were attenuated (-40%; p = 0.003). This proinflammatory phenotype in the acetylsalicylic acid treatment group was accompanied by a decrease in urinary prostaglandin E metabolite levels (-27% ± 7%; p = 0.01). Ex vivo exposure of platelets to acetylsalicylic acid increased production of tumor necrosis factor-α (+66%) and decreased production of interleukin-10 (-23%) by monocytes of sepsis patients.

CONCLUSIONS

Treatment, but not prophylaxis, with low-dose acetylsalicylic acid, partially reverses endotoxin tolerance in humans in vivo by shifting response toward a proinflammatory phenotype. This acetylsalicylic acid-induced proinflammatory shift was also observed in septic monocytes, signifying that patients suffering from sepsis-induced immunoparalysis might benefit from initiating acetylsalicylic acid treatment.

Challenges of using lipopolysaccharides for cancer immunotherapy and potential delivery-based solutions thereto

Despite being one of the earliest Toll-like receptor (TLR)-based cancer immunotherapeutics discovered and investigated, the full extent of lipopolysaccharide (LPS) potentials within this arena remains hitherto unexploited. In this review, we will debate the challenges that have complicated the improvement of LPS-based immunotherapeutic approaches in cancer therapy. Based on their nature, those will be discussed with a focus on side effect-related, tolerance-related and in vivo model-related challenges. We will then explore how drug delivery strategies can be integrated within this domain to address such challenges in order to improve the therapeutic outcome, and will present a summary of the studies that have been dedicated thereto. This paper may inspire further developments based on reconciling the advantages of drug delivery and LPS-based cancer immunotherapy.

Norepinephrine Contributes to Enterocyte Damage in Septic Shock Patients: A Prospective Cohort Study

OBJECTIVES

In septic patients, both systemic inflammation and splanchnic hypoperfusion may cause enterocyte damage. Catecholamines may exert additional detrimental effects on mesenteric blood flow in these patients, and thereby contribute to this damage. Enterocyte damage itself results in impairment of gut barrier function and consequent translocation of bacteria/toxins. This may contribute to multiple organ failure and death by sustaining or amplifying the systemic inflammatory response. The aim of the study was 2-fold: to investigate which factors contribute to enterocyte damage in septic patients, and to assess whether enterocyte damage is associated with a sustained or amplified systemic inflammatory response.

METHODS

In this prospective observational cohort study in 129 patients with septic shock admitted to the ICU, we serially measured plasma levels of Intestinal Fatty Acid-Binding Protein (I-FABP, a marker for enterocyte damage) and of cytokines Tumor Necrosis Factor (TNF)-α, Interferon (IFN)-y, Interleukin (IL)-1β, IL-6, IL-8, IL-1 Receptor Antagonist (RA), and IL-10. Clinical data were collected from electronic patient files.

RESULTS

A total of 129 patients were included in the study. The median age of the patients was 67 years [56-74]. The median norepinephrine infusion rate was 0.2 μg/kg/min [0.1-0.5]. Overall, 28-day mortality was 31 (24%). Similar to previous work, I-FABP levels at admission were independently associated with mortality (odds ratio 3.101 [1.138-8.448]). Acute Physiology and Chronic Health Evaluation II score and an increase in norepinephrine infusion rate between days 1 and 3 were independently associated with area under curve I-FABP levels, whereas mean arterial pressure and creatinine levels were not. No correlations were found between any of the measured cytokines and plasma I-FABP levels. Furthermore, high I-FABP levels were not related with the subsequent course of cytokine levels.

CONCLUSIONS

In patients with septic shock, norepinephrine use is associated with more enterocyte damage. Although enterocyte damage is associated with increased 28-day mortality, it is not associated with a sustained or amplified systemic inflammatory response.

Comparison of different lots of endotoxin and evaluation of in vivo potency over time in the experimental human endotoxemia model

The experimental human endotoxemia model is used to study the systemic inflammatory response in vivo. The previously used lot of endotoxin, which was used for over a decade, is no longer approved for human use and a new Good Manufacturing Practices-grade batch has become available. We compared the inflammatory response induced by either bolus or continuous administration of either the previously used lot #1188844 or new lots of endotoxin (#94332B1 and #94332B4). Compared with lot #1188844, bolus administration of lot #94332B1 induced a more pronounced systemic inflammatory response including higher plasma levels of pro-inflammatory cytokines and more pronounced clinical signs of inflammation. In contrast, continuous infusion of lot #94332B4 resulted in a slightly less pronounced inflammatory response compared with lot #1188844. Furthermore, we evaluated whether lot #1188844 displayed in vivo potency loss by reviewing inflammatory parameters obtained from 17 endotoxemia studies performed in our centre between 2007 and 2016. Despite inter-study variability in endotoxemia-induced effects on temperature, heart rate, symptoms, and leukocyte counts, the magnitude of these effects did not decrease over time. In conclusion, although all lots of endotoxin induce a pronounced inflammatory response, the magnitude differs between lots. We observed no potency loss of endotoxin over time.

The influence of esmolol on right ventricular function in early experimental endotoxic shock

The mechanism by which heart rate (HR) control with esmolol improves hemodynamics during septic shock remains unclear. Improved right ventricular (RV) function, thereby reducing venous congestion, may play a role. We assessed the effect of HR control with esmolol during sepsis on RV function, macrocirculation, microcirculation, end-organ-perfusion, and ventricular-arterial coupling. Sepsis was induced in 10 healthy anesthetized and mechanically ventilated sheep by continuous IV administration of lipopolysaccharide (LPS). Esmolol was infused after successful resuscitation of the septic shock, to reduce HR and stopped 30-min after reaching targeted HR reduction of 30%. Venous and arterial blood gases were sampled and the small intestines' microcirculation was assessed by using a hand-held video microscope (CytoCam-IDF). Arterial and venous pressures, and cardiac output (CO) were recorded continuously. An intraventricular micromanometer was used to assess the RV function. Ventricular-arterial coupling ratio (VACR) was estimated by catheterization-derived single beat estimation. The targeted HR reduction of >30% by esmolol infusion, after controlled resuscitation of the LPS induced septic shock, led to a deteriorated RV-function and macrocirculation, while the microcirculation remained depressed. Esmolol improved VACR by decreasing the RV end-systolic pressure. Stopping esmolol showed the reversibility of these effects on the RV and the macrocirculation. In this animal model of acute severe endotoxic septic shock, early administration of esmolol decreased RV-function resulting in venous congestion and an unimproved poor microcirculation despite improved cardiac mechanical efficiency.

Safety, tolerability and pharmacokinetics/pharmacodynamics of the adrenomedullin antibody adrecizumab in a first-in-human study and during experimental human endotoxaemia in healthy subjects

AIMS

Adrenomedullin (ADM) is an important regulator of endothelial barrier function and vascular tone, and may represent a novel treatment target in sepsis. The non-neutralizing ADM antibody adrecizumab has shown promising results in preclinical sepsis models. In the present study, we investigated the safety, tolerability and pharmacokinetics (PK)/pharmacodynamics of adrecizumab in a first-in-man study and in a second study during experimental human endotoxaemia.

METHODS

Forty-eight healthy male volunteers were enrolled in two randomized, double-blind, placebo-controlled phase I studies. In both studies, subjects received placebo or one of three doses of adrecizumab (n = 6 per group). In the second study, a bolus of 1 ng kg-1 endotoxin was followed by infusion of 1 ng kg-1 h-1 endotoxin for 3 h to induce systemic inflammation, and the study medication infusion started 1 h after endotoxin bolus administration.

RESULTS

Adrecizumab showed an excellent safety profile in both studies. PK analyses showed proportional increases in the maximum plasma concentration of adrecizumab with increasing doses, a small volume of distribution, a low clearance rate and a terminal half-life of ~14 days. adrecizumab elicited a pronounced increase in plasma ADM levels, whereas levels of mid-regional pro-adrenomedullin remained unchanged, indicating that de novo synthesis of ADM was not influenced. In the second study, no effects of adrecizumab on cytokine clearance were observed, whereas endotoxin-induced flu-like symptoms resolved more rapidly.

CONCLUSIONS

Administration of adrecizumab is safe and well tolerated in humans, both in the absence and presence of systemic inflammation. These findings pave the way for further investigation of adrecizumab in sepsis patients.

Experimental human endotoxemia as a model of systemic inflammation

Systemic inflammation plays a pivotal role in a multitude of conditions, including sepsis, trauma, major surgery and burns. However, comprehensive analysis of the pathophysiology underlying this systemic inflammatory response is greatly complicated by variations in the immune response observed in critically ill patients, which is a result of inter-individual differences in comorbidity, comedication, source of infection, causative pathogen, and onset of the inflammatory response. During experimental human endotoxemia, human subjects are challenged with purified endotoxin (lipopolysaccharide) intravenously which induces a short-lived, well-tolerated and controlled systemic inflammatory response, similar to that observed during sepsis. The human endotoxemia model can be conducted in a highly standardized and reproducible manner, using a carefully selected homogenous study population. As such, the experimental human endotoxemia model does not share the aforementioned clinical limitations and enables us to investigate both the mechanisms of systemic inflammation, as well as to evaluate novel (pharmacological) interventions in humans in vivo. The present review provides a detailed overview of the various designs, organ-specific changes, and strengths and limitations of the experimental human endotoxemia model, with the main focus on its use as a translational model for sepsis research.

Pro-Inflammatory Th1 and Th17 Cells Are Suppressed During Human Experimental Endotoxemia Whereas Anti-Inflammatory IL-10 Producing T-Cells Are Unaffected

Objective

Sepsis is one of the leading causes of the deaths in hospitals. During sepsis, patients are exposed to endotoxemia, which may contribute to the dysregulation of the immune system frequently observed in sepsis. This dysregulation leads to impaired pro-inflammatory responses and may increase the risk for secondary infections in sepsis. The experimental human endotoxemia model is widely used as a model system to study the acute effects of endotoxemia. Under physiological circumstances, the immune system is tightly regulated. Effector T-cells exert pro-inflammatory function and are restrained by regulatory T-cells (Tregs), which modulate pro-inflammatory effector responses. Endotoxemia may induce inadequate Treg activity or render effector T-cells dysfunctional. It was the aim of the study to investigate effector T-cell and Treg responses in an experimental human endotoxemia model.

Methods

In a cross-over designed placebo-controlled study, 20 healthy male volunteers received an intravenous injection of either lipopolysaccharide (LPS) (0.8 ng/kg body weight) or a placebo (saline 0.9%). CD3⁺ T-cells, CD4⁺ T-cells, CD8⁺ T-cells, and intracellular cytokine profiles were measured with flow cytometry at baseline and at repeated points after LPS/placebo injection. Complete blood cell counts were obtained with an automated hematology analyzer and cytokines were quantified by ELISA.

Results

Circulating neutrophils were significantly increased 2 h after LPS injection (p < 0.001) while absolute number of CD3⁺ T-cells, CD4⁺ T-cells, and CD8⁺ T-cells decreased (p < 0.001). Effector T-helper-cells (THs) showed a significant—but transient—decrease of pro-inflammatory IFNγ, interleukin (IL)-2, TNFα, and IL-17A production after LPS injection (p < 0.001). In contrast, the frequency of Treg and the capacity to produce IL-10 were unchanged (p = 0.21).

Conclusion

Effector THs fail to produce pro-inflammatory Th1-/Th17-associated cytokines after LPS challenge. In contrast, IL-10 production by Treg is not affected. Thus, endotoxemia-induced suppression of pro-inflammatory THs might be considered as a contributing factor to immunoparalysis in sepsis.

Development and Characterization of an Endotoxemia Model in Zebra Fish

Endotoxemia is a condition in which endotoxins enter the blood stream and cause systemic and sometimes lethal inflammation. Zebra fish provides a genetically tractable model organism for studying innate immunity, with additional advantages in live imaging and drug discovery. However, a bona fide endotoxemia model has not been established in zebra fish. Here, we have developed an acute endotoxemia model in zebra fish by injecting a single dose of LPS directly into the circulation. Hallmarks of human acute endotoxemia, including systemic inflammation, extensive tissue damage, circulation blockade, immune cell mobilization, and emergency hematopoiesis, were recapitulated in this model. Knocking out the adaptor protein Myd88 inhibited systemic inflammation and improved zebra fish survival. In addition, similar alternations of pathways with human acute endotoxemia were detected using global proteomic profiling and MetaCore™ pathway enrichment analysis. Furthermore, treating zebra fish with a protein tyrosine phosphatase nonreceptor type 11 (Shp2) inhibitor decreased systemic inflammation, immune mobilization, tissue damage, and improved survival in the endotoxemia model. Together, we have established and characterized the phenotypic and gene expression changes of a zebra fish endotoxemia model, which is amenable to genetic and pharmacological discoveries that can ultimately lead to a better mechanistic understanding of the dynamics and interplay of the innate immune system.