Extracellular hemin crisis triggers acute chest syndrome in sickle mice
01 Nov 2013-Journal of Clinical Investigation (American Society for Clinical Investigation)-Vol. 123, Iss: 11, pp 4809-4820
TL;DR: A mechanism that helps to explain the pathogenesis of acute chest syndrome is revealed, and proof of principle for therapeutic strategies to prevent and treat this condition in mice is provided.
Abstract: The prevention and treatment of acute chest syndrome (ACS) is a major clinical concern in sickle cell disease (SCD). However, the mechanism underlying the pathogenesis of ACS remains elusive. We tested the hypothesis that the hemolysis byproduct hemin elicits events that induce ACS. Infusion of a low dose of hemin caused acute intravascular hemolysis and autoamplification of extracellular hemin in transgenic sickle mice, but not in sickle-trait littermates. The sickle mice developed multiple symptoms typical of ACS and succumbed rapidly. Pharmacologic inhibition of TLR4 and hemopexin replacement therapy prior to hemin infusion protected sickle mice from developing ACS. Replication of the ACS-like phenotype in nonsickle mice revealed that the mechanism of lung injury due to extracellular hemin is independent of SCD. Using genetic and bone marrow chimeric tools, we confirmed that TLR4 expressed in nonhematopoietic vascular tissues mediated this lethal type of acute lung injury. Respiratory failure was averted after the onset of ACS-like symptoms in sickle mice by treating them with recombinant hemopexin. Our results reveal a mechanism that helps to explain the pathogenesis of ACS, and we provide proof of principle for therapeutic strategies to prevent and treat this condition in mice.
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TL;DR: It is concluded that intravascular hemolysis in SCD releases heme that activates endothelial TLR4 signaling leading to WPB degranulation, NF-κB activation, and vaso-occlusion, and heme lethality.
520 citations
Cites background from "Extracellular hemin crisis triggers..."
...Intravenous heme was recently shown to induce acute lung injury and death in sickle mice that can be averted by TLR4 inhibition, TLR4 knockout in nonhematopoietic tissues, or hemopexin replacement therapy.(53) Suppression of TLR4-induced vaso-occlusion in the pulmonary vasculature may explain the survival of HbSS mice treated with TAK-242....
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TL;DR: Intravascular hemolysis represents an intrinsic mechanism for human vascular disease that manifests clinical complications in sickle cell disease and other chronic hereditary or acquired hemolytic anemias.
Abstract: Hemolysis is a fundamental feature of sickle cell anemia that contributes to its pathophysiology and phenotypic variability. Decompartmentalized hemoglobin, arginase 1, asymmetric dimethylarginine, and adenine nucleotides are all products of hemolysis that promote vasomotor dysfunction, proliferative vasculopathy, and a multitude of clinical complications of pulmonary and systemic vasculopathy, including pulmonary hypertension, leg ulcers, priapism, chronic kidney disease, and large-artery ischemic stroke. Nitric oxide (NO) is inactivated by cell-free hemoglobin in a dioxygenation reaction that also oxidizes hemoglobin to methemoglobin, a non-oxygen-binding form of hemoglobin that readily loses heme. Circulating hemoglobin and heme represent erythrocytic danger-associated molecular pattern (eDAMP) molecules, which activate the innate immune system and endothelium to an inflammatory, proadhesive state that promotes sickle vaso-occlusion and acute lung injury in murine models of sickle cell disease. Intravascular hemolysis can impair NO bioavailability and cause oxidative stress, altering redox balance and amplifying physiological processes that govern blood flow, hemostasis, inflammation, and angiogenesis. These pathological responses promote regional vasoconstriction and subsequent blood vessel remodeling. Thus, intravascular hemolysis represents an intrinsic mechanism for human vascular disease that manifests clinical complications in sickle cell disease and other chronic hereditary or acquired hemolytic anemias.
429 citations
Cites background from "Extracellular hemin crisis triggers..."
...Heme species appear to activate innate immune sterile inflammation pathways through TLR4 and NALP inflammasome signaling (104, 105, 124, 125)....
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TL;DR: The role of cellular and molecular factors that contribute to the pathophysiology of SCD are reviewed and the opportunities for therapeutic intervention are discussed.
289 citations
Cites background from "Extracellular hemin crisis triggers..."
...TLR4 inhibition, suggesting that extracellular heme/hemin may signal through TLR4 to trigger an inflammatory response.(57,58) In addition, hemolytic transfusion reactions (HTRs) induce lethal acute vaso-occlusion in a model of alloimmune, IgG-mediated HTRs in SCD mice....
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TL;DR: It is suggested that NETs significantly contribute to SCD pathogenesis and can serve as a therapeutic target for treating SCD.
282 citations
TL;DR: This review provides an exhaustive overview of the current understanding of the molecular pathophysiology of SCD, how this pathophysiological contributes to complications of the central nervous and cardiopulmonary systems, and how this knowledge is being harnessed to develop current and potential therapies.
Abstract: Since the discovery of sickle cell disease (SCD) in 1910, enormous strides have been made in the elucidation of the pathogenesis of its protean complications, which has inspired recent advances in targeted molecular therapies. In SCD, a single amino acid substitution in the β-globin chain leads to polymerization of mutant hemoglobin S, impairing erythrocyte rheology and survival. Clinically, erythrocyte abnormalities in SCD manifest in hemolytic anemia and cycles of microvascular vaso-occlusion leading to end-organ ischemia-reperfusion injury and infarction. Vaso-occlusive events and intravascular hemolysis promote inflammation and redox instability that lead to progressive small- and large-vessel vasculopathy. Based on current evidence, the pathobiology of SCD is considered to be a vicious cycle of four major processes, all the subject of active study and novel therapeutic targeting: ( a) hemoglobin S polymerization, ( b) impaired biorheology and increased adhesion-mediated vaso-occlusion, ( c) hemolysis-mediated endothelial dysfunction, and ( d) concerted activation of sterile inflammation (Toll-like receptor 4- and inflammasome-dependent innate immune pathways). These molecular, cellular, and biophysical processes synergize to promote acute and chronic pain and end-organ injury and failure in SCD. This review provides an exhaustive overview of the current understanding of the molecular pathophysiology of SCD, how this pathophysiology contributes to complications of the central nervous and cardiopulmonary systems, and how this knowledge is being harnessed to develop current and potential therapies.
275 citations
References
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TL;DR: Modeling revealed that in patients with sickle cell anemia, the acute chest syndrome, renal failure, seizures, a base-line white-cell count above 15,000 cells per cubic millimeter, and a low level of fetal hemoglobin were associated with an increased risk of early death.
Abstract: Background Information on life expectancy and risk factors for early death among patients with sickle cell disease (sickle cell anemia, sickle cell-hemoglobin C disease, and the sickle cell-β-thalassemias) is needed to counsel patients, target therapy, and design clinical trials. Methods We followed 3764 patients who ranged from birth to 66 years of age at enrollment to determine the life expectancy and calculate the median age at death. In addition, we investigated the circumstances of death for all 209 adult patients who died during the study, and used proportional-hazards regression analysis to identify risk factors for early death among 964 adults with sickle cell anemia who were followed for at least two years. Results Among children and adults with sickle cell anemia (homozygous for sickle hemoglobin), the median age at death was 42 years for males and 48 years for females. Among those with sickle cell-hemoglobin C disease, the median age at death was 60 years for males and 68 years for females. Amo...
2,941 citations
"Extracellular hemin crisis triggers..." refers background in this paper
...Acute chest syndrome (ACS) is the second most common reason for hospital admission of SCD patients (2) and the leading cause of referral to intensive care units (3), and it is associated with a high mortality rate (4)....
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TL;DR: Identification of distinct mutations involving the same gene at the Lps locus in two different hyporesponsive inbred mouse strains strongly supports the hypothesis that altered Tlr4 function is responsible for endotoxin tolerance.
Abstract: Bacterial lipopolysaccharide (LPS) provokes a vigorous, generalized proinflammatory state in the infected host. Genetic regulation of this response has been localized to the Lps locus on mouse chromosome 4, through study of the C3H/HeJ and C57BL/10ScCr inbred strains. Both C3H/HeJ and C57BL/10ScCr mice are homozygous for a mutant Lps allele (Lpsd/d) that confers hyporesponsiveness to LPS challenge, and therefore exhibit natural tolerance to its lethal effects. Genetic and physical mapping of 1,345 backcross progeny segregating this mutant phenotype confined Lps to a 0.9-cM interval spanning 1.7 Mb. Three transcription units were identified within the candidate interval, including Toll-like receptor 4 (Tlr4), part of a protein family with members that have been implicated in LPS-induced cell signaling. C3H/HeJ mice have a point mutation within the coding region of the Tlr4 gene, resulting in a nonconservative substitution of a highly conserved proline by histidine at codon 712, whereas C57BL/ 10ScCr mice exhibit a deletion of Tlr4. Identification of distinct mutations involving the same gene at the Lps locus in two different hyporesponsive inbred mouse strains strongly supports the hypothesis that altered Tlr4 function is responsible for endotoxin tolerance.
1,648 citations
"Extracellular hemin crisis triggers..." refers background in this paper
...B10ScN-Tlr4lps–del/JthJ (referred to herein as B6TLR4–/–), with a small deletion in the mouse Tlr4 gene, and its wild-type control (B6TLR4+/+) (37)....
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TL;DR: The goal of this review is to summarize the strengths and weaknesses of existing models of lung injury and help guide investigators in the design and interpretation of animal studies of acute lung injury.
Abstract: Acute lung injury in humans is characterized histopathologically by neutrophilic alveolitis, injury of the alveolar epithelium and endothelium, hyaline membrane formation, and microvascular thrombi. Different animal models of experimental lung injury have been used to investigate mechanisms of lung injury. Most are based on reproducing in animals known risk factors for ARDS, such as sepsis, lipid embolism secondary to bone fracture, acid aspiration, ischemia-reperfusion of pulmonary or distal vascular beds, and other clinical risks. However, none of these models fully reproduces the features of human lung injury. The goal of this review is to summarize the strengths and weaknesses of existing models of lung injury. We review the specific features of human ARDS that should be modeled in experimental lung injury and then discuss specific characteristics of animal species that may affect the pulmonary host response to noxious stimuli. We emphasize those models of lung injury that are based on reproducing risk factors for human ARDS in animals and discuss the advantages and disadvantages of each model and the extent to which each model reproduces human ARDS. The present review will help guide investigators in the design and interpretation of animal studies of acute lung injury.
1,453 citations
"Extracellular hemin crisis triggers..." refers methods in this paper
...In addition, key features of ALI are substantially different for the hemin model described here and for LPS (47)....
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...Next, we assessed the prophylactic potential of recombinant human Hx (rhHx), and to exclude the potential contribution of LPS contamination of hemin to ALI....
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...TAK-242 did not rescue these SS mice, analogous to prior findings in a mouse endotoxin model when the drug was given after the disease process involving LPS was already well underway (38)....
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...Importantly, we excluded LPS, a potential contaminant of commercial preparations of hemin, as the source of ALI in our model....
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TL;DR: A treatment protocol that included matched transfusions, bronchodilators, and bronchoscopy was evaluated and it was found that infection and fat embolism are underdiagnosed in patients with the syndrome.
Abstract: Background The acute chest syndrome is the leading cause of death among patients with sickle cell disease. Since its cause is largely unknown, therapy is supportive. Pilot studies with improved diagnostic techniques suggest that infection and fat embolism are underdiagnosed in patients with the syndrome. Methods In a 30-center study, we analyzed 671 episodes of the acute chest syndrome in 538 patients with sickle cell disease to determine the cause, outcome, and response to therapy. We evaluated a treatment protocol that included matched transfusions, bronchodilators, and bronchoscopy. Samples of blood and respiratory tract secretions were sent to central laboratories for antibody testing, culture, DNA testing, and histopathological analyses. Results Nearly half the patients were initially admitted for another reason, mainly pain. When the acute chest syndrome was diagnosed, patients had hypoxia, decreasing hemoglobin values, and progressive multilobar pneumonia. The mean length of hospitalization was 10....
1,024 citations
TL;DR: The acute chest syndrome (ACS), a pneumonia-like illness in sickle cell patients, is one of the most frequent causes of their morbidity and hospitalizations, and a positive association between ACS rate and steady-state leukocyte count is found.
683 citations