Endothelial structural integrity is maintained during endotoxic shock in an interleukin-1 type 1 receptor knockout mouse

Multisystem Inflammatory Syndrome in Children (MIS-C), a Post-viral Myocarditis and Systemic Vasculitis-A Critical Review of Its Pathogenesis and Treatment

MIS-C is a newly defined post-viral myocarditis and inflammatory vasculopathy of children following COVID-19 infection. This review summarizes the literature on diagnosis, parameters of disease severity, and current treatment regimens. The clinical perspective was analyzed in light of potential immunopathogenesis and compared to other post-infectious and inflammatory illnesses of children affecting the heart. In this paradigm, the evidence supports the importance of endothelial injury and activation of the IL-1 pathway as a common determinant among MIS-C, Kawasaki disease, and Acute Rheumatic fever.

Pathophysiology of Acute Illness and Injury

The pathophysiology of acute illness and injury recognizes three main effectors: infection, trauma, and ischemia-reperfusion injury. Each of them can act by itself or in combination with the other two in developing a systemic inflammatory reaction syndrome (SIRS) that is a generalized reaction to the morbid event. The time course of SIRS is variable and influenced by the number and severity of subsequent insults (e.g., reparative surgery, acquired hospital infections). It occurs simultaneously with a complex of counter-regulatory mechanisms (compensatory anti-inflammatory response syndrome, CARS) that limit the aggressive effects of SIRS. In adjunct, a progressive dysfunction of the acquired (lymphocytes) immune system develops with increased risk for immunoparalysis and associated infectious complications. Both humoral and cellular effectors participate to the development of SIRS and CARS. The most important humoral mediators are pro-inflammatory (IL-1β, IL-6, IL-8, IL-12) and anti-inflammatory (IL-4, IL-10) cytokines and chemokines, complement, leukotrienes, and PAF. Effector cells include neutrophils, monocytes, macrophages, lymphocytes, and endothelial cells. The endothelium is a key factor for production of remote organ damage as it exerts potent chemo-attracting effects on inflammatory cells, allows for leukocyte trafficking into tissues and organs, and promotes further inflammation by cytokines release. Moreover, the loss of vasoregulatory properties and the increased permeability contribute to the development of hypotension and tissue edema. Finally, the disseminated activation of the coagulation cascade causes the widespread deposition of microthrombi with resulting maldistribution of capillary blood flow and ultimately hypoxic cellular damage. This mechanism together with increased vascular permeability and vasodilation is responsible for the development of the multiple organ dysfunction syndrome (MODS).

Discordance between microvascular permeability and leukocyte dynamics in septic inducible nitric oxide synthase deficient mice

Introduction

Microvascular dysfunction causing intravascular leakage of fluid and protein contributes to hypotension and shock in sepsis. We tested the hypothesis that abrogation of inducible nitric oxide synthase (iNOS) activation would decrease leukocyte rolling, leukocyte adhesion, and microvascular leakage in sepsis. We compared wild-type mice made septic by cecal ligation and puncture with mice deficient in iNOS.

Methods

Leukocyte dynamics and microvascular permeability were assessed simultaneously by fluorescence intravital microscopy in the cremaster muscle 15 to 20 hours after induction of sepsis by cecal ligation and puncture in C57Bl/6 mice. Rolling and adhesion of leukocytes labeled with rhodamine and leakage of fluorescein isothiocyanate-conjugated albumin was measured in single nonbranching venules (25 to 40 μm) and compared among septic wild-type, septic iNOS-deficient transgenic, and sham-operated control mice.

Results

Leukocyte rolling and adhesion were increased in septic animals (61.6 ± 14.4 cells/minute and 4.1 ± 0.6 cells/100 μm per minute, respectively) as compared with control animals (8.5 ± 2.3 cells/minute and 1.1 ± 0.2 cells/100 μm per minute, respectively; P < 0.001 for both). Rolling increased in iNOS-deficient septic mice (to 105.5 ± 30.0 cells/minute, P = 0.048, versus wild-type septic); adhesion was unchanged (5.1 ± 0.5 cells/100 μm per minute, P = 0.30). Sepsis produced an increase in leakage ratio in wild-type septic mice compared with controls (0.36 ± 0.05 versus 0.08 ± 0.01, P < 0.001). Leakage was attenuated in iNOS-deficient septic mice (0.12 ± 0.02, P < 0.001, versus wild-type septic mice).

Conclusion

Leukocyte adhesion and vascular leakage were discordant in this setting. The finding that septic iNOS-deficient mice exhibited less microvascular leakage than wild-type septic mice despite equivalent increases in leukocyte adhesion suggests an important role for nitric oxide in modulating vascular permeability during sepsis.

The inflammasome, autoinflammatory diseases, and gout

IL-1beta is a cytokine with major roles in inflammation and innate immune responses. IL-1beta is produced as an inactive proform that must be cleaved within the cell to generate biologically active IL-1beta. The enzyme caspase-1 catalyzes the reaction. Recent work showed that caspase-1 must be activated by a complex known as the inflammasome. The inflammasome comprises NALP, which is an intracellular receptor involved in innate immunity, and an ASC adapter that ensures caspase-1 recruitment to the receptor. The most extensively described inflammasome to date is formed by the NALP3 receptor within monocytes. Mutations involving the NALP3 gene cause hereditary periodic fever syndromes in humans. Increased inflammasome activity responsible for uncontrolled IL-1beta production occurs in these syndromes. Inhibition of the IL-1beta pathway by IL-1 receptor antagonist (anakinra) is a highly effective treatment for inherited periodic fever syndromes. A major role for inflammasome activity in the development of gout attacks was established recently. Urate monosodium crystals are specifically detected via the NALP3 inflammasome, which results in marked IL-1beta overproduction and initiation of an inflammatory response. This finding opens up new possibilities for the management of gouty attacks.

Beneficial effects of statins on the microcirculation during sepsis: the role of nitric oxide

This review describes the laboratory evidence and microvascular mechanisms responsible for the beneficial effects of statins in sepsis. During sepsis, changes occur within the microcirculation including alterations in arteriolar tone influencing blood pressure, adaptations to endothelial cell integrity causing leakage of proteins and macromolecules, and adhesion and migration of leucocytes through the vascular endothelium. Statins are widely used as cholesterol-lowering agents, but appear to have anti-inflammatory actions during sepsis. We have discussed the effects of statins on specific pathological processed within the microcirculation and focused on the role of nitric oxide (NO). The main mechanism by which statins appear to be an effective treatment for sepsis is increased expression of endothelial nitric oxide synthase (eNOS), in conjunction with down-regulation of inducible nitric oxide synthase. Combined, this results in an increase in physiological concentrations of NO, thus restoring endothelial function. Laboratory studies have therefore suggested that enhancement of eNOS activity during sepsis may lead to restoration of microvascular tone, maintenance of microvascular integrity, and inhibition of cell adhesion molecules. However, other mechanisms independent of lipid-lowering effects, including antioxidant activity and alterations in the development of vascular atherosclerosis, may also contribute to the beneficial effects of statins. We have also addressed the influence on the effects of statins of lipid solubility and pre- and pro-phylactic administration.

Microvascular responses to sepsis: clinical significance

Sepsis can be defined as a phenomenon related to the host's response to infection. Sepsis is considered an uncontrolled, unregulated, and self-sustaining intravascular inflammation, resulting from an imbalance between systemic proinflammatory reaction and excessive anti-inflammatory response. Microcirculatory dysfunction lies at the center of sepsis pathogenesis and involves all three elements of the microcirculation: arterioles, capillaries, and venules. Endothelium plays a pivotal role in the pathogenesis of sepsis, not only because it modulates the inflammatory response but also because endothelial cells activated with excessive amounts of inflammatory mediators become dysfunctional. In response to various stimuli, the endothelium exhibits a wide range of responses that may lead to local as well as systemic changes, giving rise to the phenotypic heterogeneity seen in sepsis. Therapeutic approaches, such as targeting the coagulation system, nitric oxide synthesis or intracellular signal transduction, have been considered. The administration of activated protein C has been associated with a dramatic reduction in mortality and ongoing studies with tissue factor pathway inhibitor seem promising. Glucocorticoids also seem promising for use in sepsis as a result of their anti-inflammatory effects.

The role of cytokines in the pathogenesis of acute pancreatitis

BACKGROUND

The systemic manifestations of acute pancreatitis are responsible for the majority of pancreatitis-associated morbidity and mortality and are now believed to be due to the actions of specific inflammatory cytokines. This report summarizes what is known about the role of cytokines in the pathogenesis of acute pancreatitis.

METHODS

Comprehensive literature review of experimental pancreatitis as well as all reports of cytokine involvement during clinical pancreatitis.

RESULTS

Several cytokines and other noncytokine inflammatory mediators are produced rapidly during pancreatitis. These mediators arise in many tissues in a predictable fashion independent of the animal model used or the underlying etiology in human disease. Preventing the activities of these mediators has a profound beneficial effect in experimental animals.

CONCLUSIONS

A few recently described inflammatory mediators are believed to be primarily responsible for the systemic manifestations of acute pancreatitis and its associated distant organ dysfunction. The predictable nature in which they are produced may allow for novel approaches to treating this disease. Am J Surg.