Appearance of alveolar protein-rich edema is an early event in the development of acute respiratory distress syndrome (ARDS). Alveolar edema in ARDS results from a significant increase in the permeability of the alveolar epithelial barrier, and represents one of the main factors that contribute to the hypoxemia in these patients. Damage of the alveolar epithelium is considered a major mechanism responsible for the increased pulmonary permeability, which results in edema fluid containing high concentrations of extravasated macromolecules in the alveoli. The breakdown of the alveolar-epithelial barrier is a consequence of multiple factors that include dysregulated inflammation, intense leukocyte infiltration, activation of pro-coagulant processes, cell death and mechanical stretch. The disruption of tight junction (TJ) complexes at the lateral contact of epithelial cells, the loss of contact between epithelial cells and extracellular matrix (ECM), and relevant changes in the communication between epithelial and immune cells, are deleterious alterations that mediate the disruption of the alveolar epithelial barrier and thereby the formation of lung edema in ARDS.

Sepsis is a highly lethal disorder. Organ dysfunction in sepsis is not defined as a clinicopathological entity but rather by changes in clinical, physiological, or biochemical parameters. Pathogenesis and specific treatment of organ dysfunction in sepsis are unknown. The study of the histopathological correlate of organ dysfunction in sepsis will help understand its pathogenesis. We searched in PubMed, EMBASE, and Scielo for original articles on kidney, brain, and liver dysfunction in human sepsis. A defined search strategy was designed, and pertinent articles that addressed the histopathological changes in sepsis were retrieved for review. Only studies considered relevant in the field were discussed. Studies on acute kidney injury (AKI) in sepsis reveal that acute tubular necrosis is less prevalent than other changes, indicating that kidney hypoperfusion is not the predominant pathogenetic mechanism of sepsis-induced AKI. Other more predominant histopathological changes are apoptosis, interstitial inflammation, and, to a lesser extent, thrombosis. Brain pathological findings include white matter hemorrhage and hypercoagulability, microabscess formation, central pontine myelinolysis, multifocal necrotizing leukoencephalopathy, metabolic changes, ischemic changes, and apoptosis. Liver pathology in sepsis includes steatosis, cholangiolitis and intrahepatic cholestasis, periportal inflammation, and apoptosis. There is no information on physiological or biochemical biomarkers of the histopathological findings. Histopathological studies may provide important information for a better understanding of the pathogenesis of organ dysfunction in sepsis and for the design of potentially effective therapies. There is a lack of clinically available biomarkers for the identification of organ dysfunction as defined by the histological analysis.

Patients with liver diseases are at high risk for the development of acute respiratory distress syndrome (ARDS). The liver is an important organ that regulates a complex network of mediators and modulates organ interactions during inflammatory disorders. Liver function is increasingly recognized as a critical determinant of the pathogenesis and resolution of ARDS, significantly influencing the prognosis of these patients. The liver plays a central role in the synthesis of proteins, metabolism of toxins and drugs, and in the modulation of immunity and host defense. However, the tools for assessing liver function are limited in the clinical setting, and patients with liver diseases are frequently excluded from clinical studies of ARDS. Therefore, the mechanisms by which the liver participates in the pathogenesis of acute lung injury are not totally understood. Several functions of the liver, including endotoxin and bacterial clearance, release and clearance of pro-inflammatory cytokines and eicosanoids, and synthesis of acute-phase proteins can modulate lung injury in the setting of sepsis and other severe inflammatory diseases. In this review, we summarized clinical and experimental support for the notion that the liver critically regulates systemic and pulmonary responses following inflammatory insults. Although promoting inflammation can be detrimental in the context of acute lung injury, the liver response to an inflammatory insult is also pro-defense and pro-survival. A better understanding of the liver–lung axis will provide valuable insights into new diagnostic targets and therapeutic strategies for clinical intervention in patients with or at risk for ARDS.

Acute lung injury (ALI) is a life-threatening condition in critically ill patients. Injury to the alveolar epithelium is a critical event in ALI, and accumulating evidence suggests that it is linked to proapoptotic Fas/FasL signals. Active soluble FasL (sFasL) is detectable in the bronchoalveolar lavage (BAL) fluid of patients with ALI, but the mechanisms controlling its bioactivity are unclear. We therefore investigated how the structure of sFasL influences cellular activation in human and mouse lungs and the role of oxidants and proteases in modifying sFasL activity. The sFasL in BAL fluid from patients with ALI was bioactive and present in high molecular weight multimers and aggregates. Oxidants generated from neutrophil myeloperoxidase in BAL fluid promoted aggregation of sFasL in vitro and in vivo. Oxidation increased the biological activity of sFasL at low concentrations but degraded sFasL at high concentrations. The amino-terminal extracellular stalk region of human sFasL was required to induce lung injury in mice, and proteolytic cleavage of the stalk region by MMP-7 reduced the bioactivity of sFasL in human cells in vitro. The sFasL recovered from the lungs of patients with ALI contained both oxidized methionine residues and the stalk region. These data provide what we believe to be new insights into the structural determinants of sFasL bioactivity in the lungs of patients with ALI.

Background & Aims: Body temperature may critically affect mechanisms of liver injury in acetaminophen (APAP) hepatotoxicity. In addition, mild hypothermia is used to treat intracranial hypertension in human liver failure without detailed information on its effects on the injured liver itself. Therefore, we investigated the effects of body temperature on the progression of APAP-induced liver injury in mice. Methods: Male C57BL6 mice treated with saline or APAP (300 mg/kg intraperitoneally) were maintained at normothermia (35.5–37.5°C) by external warming or were allowed to develop mild hypothermia (32.0–35.0°C) after 2 hours from APAP administration. Results: Mild hypothermia resulted in improved survival after APAP intoxication. Liver damage was reduced, as assessed histologically and by plasma alanine aminotransferase levels. Early effects of hypothermia included a reduction of hepatic congestion and improved recovery of glycogen stores. At later time points (8–12 hours), APAP-treated mice that were maintained at normothermia manifested increased hepatocyte apoptosis, as assessed by terminal deoxynucleotidyl transferase–mediated deoxyuridine triphosphate nick-end labeling staining and cleavage of poly(adenosine diphosphate-ribose) polymerase. Mild hypothermia did not affect the formation of APAP-protein adducts or the depletion of glutathione, nor did it abrogate hepatocyte DNA synthesis. Conclusions: Mild hypothermia improved survival and attenuated liver injury and apoptosis in APAP-treated mice by reducing hepatic congestion and improving glycogen recovery without affecting hepatic regeneration. Results of the study underscore the need for a strict control of body temperature in animal models of liver failure and suggest that the benefits of mild hypothermia in liver failure may extend beyond those related to reduced cerebral complications.

Background Pulmonary hypertension (PH) is frequently observed in patients with acute respiratory distress syndrome (ARDS) and it is associated with an increased risk of mortality. Both acid sphingomyelinase (aSMase) activity and interleukin 6 (IL-6) levels are increased in patients with sepsis and correlate with worst outcomes, but their role in pulmonary vascular dysfunction pathogenesis has not yet been elucidated. Therefore, the aim of this study was to determine the potential contribution of aSMase and IL-6 in the pulmonary vascular dysfunction induced by lipopolysaccharide (LPS). Methods Rat or human pulmonary arteries (PAs) or their cultured smooth muscle cells (SMCs) were exposed to LPS, SMase or IL-6 in the absence or presence of a range of pharmacological inhibitors. The effects of aSMase inhibition in vivo with D609 on pulmonary arterial pressure and inflammation were assessed following intratracheal administration of LPS. Results LPS increased ceramide and IL-6 production in rat pulmonary artery smooth muscle cells (PASMCs) and inhibited pulmonary vasoconstriction induced by phenylephrine or hypoxia (HPV), induced endothelial dysfunction and potentiated the contractile responses to serotonin. Exogenous SMase and IL-6 mimicked the effects of LPS on endothelial dysfunction, HPV failure and hyperresponsiveness to serotonin in PA; whereas blockade of aSMase or IL-6 prevented LPS-induced effects. Finally, administration of the aSMase inhibitor D609 limited the development of endotoxin-induced PH and ventilation-perfusion mismatch. The protective effects of D609 were validated in isolated human PAs. Conclusions Our data indicate that aSMase and IL-6 are not simply biomarkers of poor outcomes but pathogenic mediators of pulmonary vascular dysfunction in ARDS secondary to Gram-negative infections.