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      Inflammatory Response to Different Toxins in Experimental Sepsis Models

      review-article
      1 , 1 , 2 , 3 , 4 , *
      International Journal of Molecular Sciences
      MDPI
      inflammation, sepsis, endotoxemia, infection

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          Abstract

          Sepsis is defined as life-threatening organ dysfunction caused by the dysregulated host response to infection. Despite serious mortality and morbidity, no sepsis-specific drugs exist. Endotoxemia is often used to model the hyperinflammation associated with early sepsis. This model classically uses lipopolysaccharide (LPS) from Gram-negative pathogens to activate the immune system, leading to hyperinflammation, microcirculatory disturbances and death. Other toxins may also be used to activate the immune system including Gram-positive peptidoglycan (PG) and lipoteichoic acid (LTA). In addition to these standard toxins, other bacterial components can induce inflammation. These molecules activate different signaling pathways and produce different physiological responses which can be taken advantage of for sepsis modeling. Endotoxemia modeling can provide information on pathways to inflammation in sepsis and contribute to preclinical drug development.

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          Most cited references64

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          Long Term Outcomes Following Hospital Admission for Sepsis Using Relative Survival Analysis: A Prospective Cohort Study of 1,092 Patients with 5 Year Follow Up

          Background Sepsis is a leading cause of death in intensive care units and is increasing in incidence. Current trials of novel therapeutic approaches for sepsis focus on 28-day mortality as the primary outcome measure, but excess mortality may extend well beyond this time period. Methods We used relative survival analysis to examine excess mortality in a cohort of 1,028 patients admitted to a tertiary referral hospital with sepsis during 2007–2008, over the first 5 years of follow up. Expected survival was estimated using the Ederer II method, using Australian life tables as the reference population. Cumulative and interval specific relative survival were estimated by age group, sex, sepsis severity and Indigenous status. Results Patients were followed for a median of 4.5 years (range 0–5.2). Of the 1028 patients, the mean age was 46.9 years, 52% were male, 228 (22.2%) had severe sepsis and 218 (21%) died during the follow up period. Mortality based on cumulative relative survival exceeded that of the reference population for the first 2 years post admission in the whole cohort and for the first 3 years in the subgroup with severe sepsis. Independent predictors of mortality over the whole follow up period were male sex, Indigenous Australian ethnicity, older age, higher Charlson Comorbidity Index, and sepsis-related organ dysfunction at presentation. Conclusions The mortality rate of patients hospitalised with sepsis exceeds that of the general population until 2 years post admission. Efforts to improve outcomes from sepsis should examine longer term outcomes than the traditional primary endpoints of 28-day and 90-day mortality.
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            MD-2, a Molecule that Confers Lipopolysaccharide Responsiveness on Toll-like Receptor 4

            Toll-like receptor 4 (TLR4) is a mammalian homologue of Drosophila Toll, a leucine-rich repeat molecule that can trigger innate responses against pathogens. The TLR4 gene has recently been shown to be mutated in C3H/HeJ and C57BL/10ScCr mice, both of which are low responders to lipopolysaccharide (LPS). TLR4 may be a long-sought receptor for LPS. However, transfection of TLR4 does not confer LPS responsiveness on a recipient cell line, suggesting a requirement for an additional molecule. Here, we report that a novel molecule, MD-2, is requisite for LPS signaling of TLR4. MD-2 is physically associated with TLR4 on the cell surface and confers responsiveness to LPS. MD-2 is thus a link between TLR4 and LPS signaling. Identification of this new receptor complex has potential implications for understanding host defense, as well as pathophysiologic, mechanisms.
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              Hexokinase Is an Innate Immune Receptor for the Detection of Bacterial Peptidoglycan.

              Degradation of Gram-positive bacterial cell wall peptidoglycan in macrophage and dendritic cell phagosomes leads to activation of the NLRP3 inflammasome, a cytosolic complex that regulates processing and secretion of interleukin (IL)-1β and IL-18. While many inflammatory responses to peptidoglycan are mediated by detection of its muramyl dipeptide component in the cytosol by NOD2, we report here that NLRP3 inflammasome activation is caused by release of N-acetylglucosamine that is detected in the cytosol by the glycolytic enzyme hexokinase. Inhibition of hexokinase by N-acetylglucosamine causes its dissociation from mitochondria outer membranes, and we found that this is sufficient to activate the NLRP3 inflammasome. In addition, we observed that glycolytic inhibitors and metabolic conditions affecting hexokinase function and localization induce inflammasome activation. While previous studies have demonstrated that signaling by pattern recognition receptors can regulate metabolic processes, this study shows that a metabolic enzyme can act as a pattern recognition receptor. PAPERCLIP.
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                Author and article information

                Journal
                Int J Mol Sci
                Int J Mol Sci
                ijms
                International Journal of Molecular Sciences
                MDPI
                1422-0067
                05 September 2019
                September 2019
                : 20
                : 18
                : 4341
                Affiliations
                [1 ]Department of Microbiology and Immunology, Dalhousie University, Halifax, NS B3H 4R2, Canada
                [2 ]Department of Physiology and Biophysics, Dalhousie University, Halifax, NS B3H 4R2, Canada
                [3 ]Department of Pharmacology, Dalhousie University, Halifax, NS B3H 4R2, Canada
                [4 ]Department of Anesthesia, Pain Management and Perioperative Medicine, Dalhousie University, Halifax, NS B3H 4R2, Canada
                Author notes
                [* ]Correspondence: chlehmann@ 123456dal.ca ; Tel.: +1-902-494-1287
                Author information
                https://orcid.org/0000-0001-6419-9168
                Article
                ijms-20-04341
                10.3390/ijms20184341
                6770119
                31491842
                f2a64799-6799-42e6-a285-e716ebeddb96
                © 2019 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 31 July 2019
                : 02 September 2019
                Categories
                Review

                Molecular biology
                inflammation,sepsis,endotoxemia,infection
                Molecular biology
                inflammation, sepsis, endotoxemia, infection

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