Biomedical subjects

Christopher Haslett

Publications and source records attributed to Christopher Haslett.

25 records · Page 2Linked to original sources

PubMed2002

Sphingosine kinase: a point of convergence in the action of diverse neutrophil priming agents.

Neutrophils are a vital component of the early acute inflammatory response, but can cause profound tissue damage when activated to excess or prevented from undergoing apoptosis. However, much remains unknown about the intracellular signaling pathways regulating neutrophil activity. The structurally diverse neutrophil-priming agents platelet-activating factor, TNF-alpha, and the substance P analog [D-Arg(6), D-Trp(7,9),N(me)Phe(8)]-substance P(6-11) (SP-G) stimulated a rapid increase in sphingosine kinase activity in freshly isolated human neutrophils. This activity was blocked by preincubation with the sphingosine kinase inhibitor N,N-dimethylsphingosine (DMS). DMS also inhibited the increase in intracellular calcium concentration stimulated by platelet-activating factor, fMLP, and SP-G. This suggests that the increase in intracellular calcium concentration by these agents is dependent on sphingosine kinase activation and the generation of sphingosine-1-phosphate. Changes in cell polarization and the augmentation of the fMLP-induced superoxide anion generation, by all priming agents were also inhibited by DMS, while only the superoxide anion release was blocked by the phosphatidylinositol 3-kinase inhibitor LY294002. Moreover, SP-G and GM-CSF inhibited constitutive neutrophil apoptosis which was completely blocked by DMS. These results suggest a novel role for sphingosine kinase in the regulation of neutrophil priming.

Adult↗

PubMed2002

Kinetics of lung macrophages monitored in vivo following particulate challenge in rabbits.

The ligand PK11195 binds specifically in macrophages. We have assessed the use of positron emission tomography (PET) of [(11)C]R-PK11195 to monitor macrophage disposition following particulate challenge to the lung. Repeated PET scanning was performed over 4 weeks following iv [(11)C]R-PK11195 in rabbits treated with 5-microm particles of either amorphous (aSiO(2)) or microcrystalline (xSiO(2)) silica instilled into right upper pulmonary lobes. aSiO(2) resulted in increased macrophages, few neutrophils, and no fibrosis, while xSiO(2) increased macrophages and neutrophils and caused fibrosis. After both stimuli, (11)C localized to the challenged area and correlated with macrophage numbers. Radioactive counts in challenged/control lung regions peaked at 4 days for aSiO(2) (2.88, n = 2) and 6 days for xSiO(2) (4.62, n = 2). The signal remained elevated throughout the study (aSiO(2), 2.33 +/- 0.77 SD, n = 14; xSiO(2), 3.99 +/- 1.29 SD, n = 9), as did macrophage accumulation. (11)C also localized to regions consistent with macrophage traffic through lymph ducts 6 days after aSiO(2) challenge, but not until 4 weeks after xSiO(2). Specific binding of R-PK11195 in macrophages was demonstrated by microautoradiography in lavage fluid from an inflamed rabbit knee-joint model. These data suggest that PET scanning after [(11)C]PK11195 provides a new noninvasive approach for the study of macrophage kinetics in the lung.

Animals↗

PubMed2002

Prostaglandin D2 and its metabolites induce caspase-dependent granulocyte apoptosis that is mediated via inhibition of I kappa B alpha degradation using a peroxisome proliferator-activated receptor-gamma-independent mechanism.

Many inflammatory mediators retard granulocyte apoptosis. Most natural PGs studied herein (e.g., PGE(2), PGA(2), PGA(1), PGF(2 alpha)) either delayed apoptosis or had no effect, whereas PGD(2) and its metabolite PGJ(2) selectively induced eosinophil, but not neutrophil apoptosis. This novel proapoptotic effect does not appear to be mediated via classical PG receptor ligation or by elevation of intracellular cAMP or Ca(2+). Intriguingly, the sequential metabolites Delta(12)PGJ(2) and 15-deoxy-Delta(12,) Delta(14)-PGJ(2) (15dPGJ(2)) induced caspase-dependent apoptosis in both granulocytes, an effect that did not involve de novo protein synthesis. Despite the fact that Delta(12)PGJ(2) and 15dPGJ(2) are peroxisome proliferator-activated receptor-gamma (PPAR-gamma) activators, apoptosis was not mimicked by synthetic PPAR-gamma and PPAR-alpha ligands or blocked by an irreversible PPAR-gamma antagonist. Furthermore, Delta(12)PGJ(2) and 15dPGJ(2) inhibited LPS-induced I kappa B alpha degradation and subsequent inhibition of neutrophil apoptosis, suggesting that apoptosis is mediated via PPAR-gamma-independent inhibition of NF-kappa B activation. In addition, we show that TNF-alpha-mediated loss of cytoplasmic I kappa B alpha in eosinophils is inhibited by 15dPGJ(2) in a concentration-dependent manner. The selective induction of eosinophil apoptosis by PGD(2) and PGJ(2) may help define novel therapeutic pathways in diseases in which it would be desirable to specifically remove eosinophils but retain neutrophils for antibacterial host defense. The powerful proapoptotic effects of Delta(12)PGJ(2) and 15dPGJ(2) in both granulocyte types suggest that these natural products control the longevity of key inflammatory cells and may be relevant to understanding the control and resolution of inflammation.

Apoptosis↗

PubMed2002

Inhibition of nuclear factor-kappaB activation un-masks the ability of TNF-alpha to induce human eosinophil apoptosis.

Apoptosis renders eosinophils functionally effete and marks them for "silent" removal from inflamed sites by macrophages. We show, for the first time, that eosinophils exposed to TNF-alpha rapidly lose their cytoplasmic levels of IkappaBalpha, the inhibitory subunit of NF-kappaB. Consequently, TNF-alpha triggers NF-kappaB mobilization from the cytoplasm to the nucleus, as determined by tracking the NF-kappaB subunit p65 by immunofluorescence and Western blot analysis. Inhibition of TNF-alpha-mediated IkappaBalpha degradation and NF-kappaB activation by gliotoxin or the proteasome inhibitor MG-132 un-masks the caspase-dependent pro-apoptotic properties of TNF-alpha. In addition, cycloheximide similarly renders TNF-alpha pro-apoptotic, suggesting that NF-kappaB activation controls the production of a protein(s) that protects eosinophils from the cytotoxic effects of TNF-alpha. Evidence is presented suggesting that TNF-alpha triggered apoptosis is more susceptible to NF-kappaB inhibition than constitutive apoptosis, leading to the possibility of the specific targeting of apoptosis in eosinophil sub-populations. Prior to morphological signs of apoptosis, TNF-alpha-induced IL-8 synthesis is abrogated by inhibition of NF-kappaB. We propose that NF-kappaB activation plays a critical role in controlling eosinophil responsiveness and apoptosis, and speculate that selective inhibitors of eosinophil NF-kappaB activation may ultimately provide alternative therapeutic agents for the treatment of eosinophilic diseases, including asthma and allergic rhinitis.

Apoptosis↗

PubMed2002

Cross-linking CD98 promotes integrin-like signaling and anchorage-independent growth.

CD98, an early marker of T-cell activation, is an important regulator of integrin-mediated adhesion events. Previous studies suggest that CD98 is coupled to both cellular activation and transformation and is involved in the pathogenesis of viral infection, inflammatory disease, and cancer. Understanding of the molecular mechanisms underlying CD98 activity may have far-reaching practical applications in the development of novel therapeutic strategies in these disease states. Using small cell lung cancer cell lines, which are nonadherent, nonpolarized, and highly express CD98, we show that, in vitro, under physiological conditions, CD98 is constitutively associated with beta1 integrins regardless of activation status. Cross-linking CD98 with the monoclonal antibody 4F2 stimulated phosphatidylinositol (PI) 3-kinase, PI(3,4,5)P(3), and protein kinase B in the absence of integrin ligation or extracellular matrix engagement. Furthermore, cross-linking CD98 promoted anchorage-independent growth. Using fibroblasts derived from beta1 integrin null stem cells (GD25), wild-type GD25beta1, or GD25 cells expressing a mutation preventing beta1 integrin-dependent FAK phosphorylation, we demonstrate that a functional beta1 integrin is required for CD98 signaling. We propose that by cross-linking CD98, it acts as a "molecular facilitator" in the plasma membrane, clustering beta1 integrins to form high-density complexes. This results in integrin activation, integrin-like signaling, and anchorage-independent growth. Activation of PI 3-kinase may, in part, explain cellular transformation seen on overexpressing CD98. These results may provide a paradigm for events involved in such diverse processes as inflammation and viral-induced cell fusion.

Amino Acids↗

PubMed2002

Anti-interleukin-8 autoantibodies in patients at risk for acute respiratory distress syndrome.

OBJECTIVE: To test the hypothesis that elevated concentrations of interleukin-8 associated with anti-interleukin-8 autoantibodies (anti-interleukin-8:interleukin-8 complexes) are found in patients at risk for acute respiratory distress syndrome who developed the disease. DESIGN: Measurement of anti-interleukin-8:interleukin-8 complex concentrations in previously collected bronchoalveolar lavage fluids. These fluids were obtained from patients at risk for acute respiratory distress syndrome who subsequently either recovered or developed acute respiratory distress syndrome. PATIENTS: A unique population of patients at risk for acute respiratory distress syndrome was studied. There were 26 patients at risk for acute respiratory distress syndrome who were divided into three groups. Group I patients had high interleukin-8 concentrations and developed acute respiratory distress syndrome, group II had high interleukin-8 concentrations and did not develop acute respiratory distress syndrome, and group III had low interleukin-8 concentrations and did not develop acute respiratory distress syndrome. These patients were selected to test the hypothesis that presence of elevated concentrations of anti-interleukin-8:interleukin-8 complexes differentiates patients at risk for acute respiratory distress syndrome who developed acute respiratory distress syndrome from patients who did not. MEASUREMENTS AND MAIN RESULTS: Bronchoalveolar lavage fluid concentrations of interleukin-8 associated with the anti-interleukin-8 autoantibodies were significantly different between groups (p <.03). The amount of interleukin-8 bound to the anti-interleukin-8 autoantibody was higher in group I than in group II and group III. CONCLUSIONS: Bronchoalveolar lavage fluid concentration of anti-interleukin-8:interleukin-8 complexes may serve as a marker of disease progression in patients at risk for acute respiratory distress syndrome.

Antigen-Antibody Complex↗

PubMed2002

Increased virulence of a fibronectin-binding protein mutant of Staphylococcus aureus in a rat model of pneumonia.

Fibronectin-binding proteins mediate Staphylococcus aureus internalization into nonphagocytic cells in vitro. We have investigated whether fibronectin-binding proteins are virulence factors in the pathogenesis of pneumonia by using S. aureus strain 8325-4 and isogenic mutants in which fibronectin-binding proteins were either deleted (DU5883) or overexpressed [DU5883(pFnBPA4)]. We first demonstrated that fibronectin-binding proteins mediate S. aureus internalization into alveolar epithelial cells in vitro and that S. aureus internalization into alveolar epithelial cells requires actin rearrangement and protein kinase activity. Second, we established a rat model of S. aureus-induced pneumonia and measured lung injury and bacterial survival at 24 and 96 h postinoculation. S. aureus growth and the extent of lung injury were both increased in rats inoculated with the deletion mutant (DU5883) in comparison with rats inoculated with the wild-type (8325-4) and the fibronectin-binding protein-overexpressing strain DU5883(pFnBPA4) at 24 h postinfection. Morphological evaluation of infected lungs at the light and electron microscopic levels demonstrated that S. aureus was present within neutrophils from both 8325-4- and DU5883-inoculated lungs. Our data suggest that fibronectin-binding protein-mediated internalization into alveolar epithelial cells is not a virulence mechanism in a rat model of pneumonia. Instead, our data suggest that fibronectin-binding proteins decrease the virulence of S. aureus in pneumonia.

Adhesins, Bacterial↗