Falk A. Gonnert

Liver Dysfunction and Phosphatidylinositol-3-Kinase Signalling in Early Sepsis: Experimental Studies in Rodent Models of Peritonitis

Experimental studies in a rat model of fecal peritonitis conducted by Michael Bauer and colleagues show that in this model, changes in liver function occur early in the development of sepsis, with potential implications for prognosis and development of new therapeutic approaches.

Characteristics of Clinical Sepsis Reflected in a Reliable and Reproducible Rodent Sepsis Model

BACKGROUND Sepsis models are frequently based on induction of peritonitis, with cecal ligation and puncture reflecting the prototypical model. However, there is an ongoing discussion about the limitations of these models due to their variability in progression and outcome. Since standardization is a cornerstone of experimental models, we aimed to develop a reliable and reproducible procedure for induction of peritonitis. MATERIALS AND METHODS A human stool batch was processed for -80° storage. For induction of peritonitis in fluid-resuscitated rats, a defined volume of stool suspension from this batch was injected intraperitoneally. For characterization of the model, physiologic and inflammatory changes were evaluated after sepsis induction. Survival analyses with the same batch were repeated in four independent experiments over a time period of 16 mo. RESULTS The polymicrobial infection resulted in severe peritoneal inflammation with a systemic increase in cytokines. The mortality rate at 15 h was 29% and this was reproducible over a 16 mo time period. If antibiotic treatment was applied, a 50% survival was achieved. Laboratory markers indicated a progressive multi-organ dysfunction, while blood gas analysis showed respiratory compensation of a metabolic acidosis, and maintenance of PaO(2). Intravital microscopy of the liver revealed an impaired microcirculation. A decreased hemostatic potential was demonstrated by rotational thromboelastometry. Despite clinical recovery within 3 d, surviving animals showed laboratory and histologic signs of persisting inflammation even after 2 wk. CONCLUSIONS This model reflects many features of human sepsis. Application of an infectious focus that is both quantitatively and qualitatively defined assures high reproducibility. Moreover, the procedure is simple and can be easily standardized.

Hepatic Fibrosis in a Long-term Murine Model of Sepsis.

ABSTRACT Chronic sequelae of sepsis represent a major, yet underappreciated clinical problem, contributing to long-term mortality and quality-of-life impairment. In chronic liver disease, inflammation perpetuates fibrogenesis, but development of fibrosis in the post–acute phase of systemic inflammation has not been studied. Therefore, a mouse model of post–acute sequelae of sepsis was established based on polymicrobial peritonitis under antibiotic protection. Survival decreased to approximately 40% within 7 days and remained constant until day 28 (post–acute phase). In survivors, clinical recovery was observed within 1 week, whereas white blood cell and platelet count, as well as markers of liver injury, remained elevated until day 28. Macroscopically, inflammation and abscess formation were detected in the peritoneal space and on/in the liver. Microscopically, acute-chronic inflammation with ductular proliferation, focal granuloma formation in the parenchyma, and substantial hepatic fibrosis were observed. Increased numbers of potentially pathogenetic macrophages and &agr;-smooth muscle actin–positive cells, presumably activated hepatic stellate cells, were detected in the vicinity of fibrotic areas. Fibrosis was associated with the presence of elastin and an augmented production/deposition of collagen types I and III. Microarray analyses revealed early activation of canonical and noncanonical pathways of hepatic stellate cell transdifferentiation. Thus, chronic sequelae of experimental sepsis were characterized by abscess formation, persistent inflammation, and substantial liver injury and fibrosis, the latter associated with increased numbers of macrophages/&agr;-smooth muscle actin–positive cells and deposition of collagen types I and III. This suggests persistent activation of stellate cells, with consecutive fibrosis—a hallmark of chronic liver disease—as a result of acute life-threatening infection.

In vivo imaging of hepatic excretory function in the rat by fluorescence microscopy.

Applying intravital fluorescence microscopy, we assessed sinusoidal delivery and biliary clearance of two different polymethine dyes. DY635, a benzopyrylium-based hemocyanine dye with shorter excitation wavelength than indocyanine green (ICG), was validated for assessment of hepatic excretory function. Decrease of DY635 and ICG reflecting transcellular transport was 83 ± 4% (DY635) and 14 ± 2% (ICG; p < 0.05) over 35 minutes, respectively. In cholestasis, hepatobiliary excretion of DY635 was markedly impaired (control 3176 ± 148 pmol vs. cholestatic 1929 ± 179 pmol; p < 0.05). DY635 even enabled an analysis at high resolution suggesting 1.) hepatocyte uncoupling and 2.) failure of primarily the canalicular pole, allowing in vivo insights into molecular mechanisms of this critical facet of hepatobiliary function.

Mechanisms and functional consequences of liver failure substantially differ between endotoxaemia and faecal peritonitis in rats.

Many of the concepts describing molecular mechanisms of sepsis‐induced liver failure are derived from endotoxin models. However, the biological significance of such models is questionable as the complexity of clinical sepsis and associated organ failure is only partially replicated.

Phosphoinositide 3-Kinase γ Affects LPS-Induced Disturbance of Blood–Brain Barrier Via Lipid Kinase-Independent Control of cAMP in Microglial Cells

AbstractThe breakdown of the blood–brain barrier (BBB) is a key event in the development of sepsis-induced brain damage. BBB opening allows blood-born immune cells to enter the CNS to provoke a neuroinflammatory response. Abnormal expression and activation of matrix metalloproteinases (MMP) was shown to contribute to BBB opening. Using different mouse genotypes in a model of LPS-induced systemic inflammation, our present report reveals phosphoinositide 3-kinase γ (PI3Kγ) as a mediator of BBB deterioration and concomitant generation of MMP by microglia. Unexpectedly, microglia expressing lipid kinase-deficient mutant PI3Kγ exhibited similar MMP regulation as wild-type cells. Our data suggest kinase-independent control of cAMP phosphodiesterase activity by PI3Kγ as a crucial mediator of microglial cell activation, MMP expression and subsequent BBB deterioration. The results identify the suppressive effect of PI3Kγ on cAMP as a critical mediator of immune cell functions.

Hepatic excretory function in sepsis: implications from biophotonic analysis of transcellular xenobiotic transport in a rodent model.

IntroductionHepatobiliary elimination of endo- and xenobiotics is affected by different variables including hepatic perfusion, hepatocellular energy state and functional integrity of transporter proteins, all of which are altered during sepsis. A particular impairment of hepatocellular transport at the canalicular pole resulting in an accumulation of potentially hepatotoxic compounds would have major implications for critical care pharmacology and diagnostics.MethodsHepatic transcellular transport, that is, uptake and hepatobiliary excretion, was studied in a rodent model of severe polymicrobial sepsis by two different biophotonic techniques to obtain insights into the handling of potentially toxic endo- and xenobiotics in sepsis. Direct and indirect in vivo imaging of the liver was performed by intravital multifluorescence microscopy and non-invasive whole-body near-infrared (NIRF) imaging after administration of two different, primarily hepatobiliary excreted xenobiotics, the organic anionic dyes indocyanine green (ICG) and DY635. Subsequent quantitative data analysis enabled assessment of hepatic uptake and fate of these model substrates under conditions of sepsis.ResultsFifteen hours after sepsis induction, animals displayed clinical and laboratory signs of multiple organ dysfunction, including moderate liver injury, cholestasis and an impairment of sinusoidal perfusion. With respect to hepatocellular transport of both dyes, excretion into bile was significantly delayed for both dyes and resulted in net accumulation of potentially cytotoxic xenobiotics in the liver parenchyma (for example, specific dye fluorescence in liver at 30 minutes in sham versus sepsis: ICG: 75% versus 89%; DY635 20% versus 40% of maximum fluorescence; P < 0.05). Transcutaneous assessment of ICG fluorescence by whole body NIRF imaging revealed a significant increase of ICG fluorescence from the 30th minute on in the bowel region of the abdomen in sham but not in septic animals, confirming a sepsis-associated failure of canalicular excretion.ConclusionsHepatocytes accumulate organic anions under conditions of sepsis-associated organ dysfunction. These results have potential implications for monitoring liver function, critical care pharmacology and the understanding of drug-induced liver injury in the critically ill.

Comparison of sepsis-induced transcriptomic changes in a murine model to clinical blood samples identifies common response patterns

Experimental models, mimicking physiology, and molecular dynamics of diseases in human, harbor the possibility to study the effect of interventions and transfer results from bench to bedside. Recent advances in high-throughput technologies, standardized protocols, and integration of knowledge from databases yielded rising consistency and usability of results for inter-species comparisons. Here, we explored similarities and dissimilarities in gene expression from blood samples of a murine sepsis model (peritoneal contamination and infection, PCI) and patients from the pediatric intensive care unit (PICU) measured by microarrays. Applying a consistent pre-processing and analysis workflow, differentially expressed genes (DEG) from PCI and PICU data significantly overlapped. A major fraction of DEG was commonly expressed and mapped to adaptive and innate immune response related pathways, whereas the minor fraction, including the chemokine (C–C motif) ligand 4, exhibited constant inter-species disparities. Reproducibility of transcriptomic observations was validated experimentally in PCI. These data underline, that inter-species comparison can obtain commonly expressed transcriptomic features despite missing homologs and different protocols. Our findings point toward a high suitability of an animal sepsis model and further experimental efforts in order to transfer results from animal experiments to the bedside.

Hyperresponsiveness of mice deficient in plasma-secreted sphingomyelinase reveals its pivotal role in early phase of host response

Plasma secretion of acid sphingomyelinase is a hallmark of cellular stress response resulting in the formation of membrane embedded ceramide-enriched lipid rafts and the reorganization of receptor complexes. Consistently, decompartmentalization of ceramide formation from inert sphingomyelin has been associated with signaling events and regulation of the cellular phenotype. Herein, we addressed the question of whether the secretion of acid sphingomyelinase is involved in host response during sepsis. We found an exaggerated clinical course in mice genetically deficient in acid sphingomyelinase characterized by an increased bacterial burden, an increased phagocytotic activity, and a more pronounced cytokine storm. Moreover, on a functional level, leukocyte-endothelial interaction was found diminished in sphingomyelinase-deficient animals corresponding to a distinct leukocytes’ phenotype with respect to rolling and sticking as well as expression of cellular surface proteins. We conclude that hydrolysis of membrane-embedded sphingomyelin, triggered by circulating sphingomyelinase, plays a pivotal role in the first line of defense against invading microorganisms. This function might be essential during the early phase of infection leading to an adaptive response of remote cells and tissues.

Comparative suitability of CFDA-SE and rhodamine 6G for in vivo assessment of leukocyte-endothelium interactions.

Intravital fluorescence microscopy (IVM) is a predestined tool for investigating the fate of leukocytes during the process of leukocyte recruitment. In the present study, the commonly used dye for this purpose, rhodamine 6G, and carboxyfluorescein diacetate succinimidyl ester (CFDA-SE) were compared for leukocytes labelling with respect to suitability for IVM studies. Their potential in labelling different leukocytes subpopulations as well as their fluorescence intensities were assessed by flow cytometry revealing distinct differences between both dyes. These differences had a profound impact on their application for in vivo imaging of leukocyte-endothelium interactions. In summary, CFDA-SE revealed superior in labelling leukocytes for in vivo microscopy with respect to image quality. In addition, we could show the efficiency of CFDA-SE also under disease condition in an animal model of sepsis.