Microbial lung infections are the major cause of morbidity and mortality in the hereditary metabolic disorder cystic fibrosis, yet the molecular mechanisms leading from the mutation of cystic fibrosis transmembrane conductance regulator (CFTR) to lung infection are still unclear. Here, we show that ceramide age-dependently accumulates in the respiratory tract of uninfected Cftr-deficient mice owing to an alkalinization of intracellular vesicles in Cftr-deficient cells. This change in pH results in an imbalance between acid sphingomyelinase (Asm) cleavage of sphingomyelin to ceramide and acid ceramidase consumption of ceramide, resulting in the higher levels of ceramide. The accumulation of ceramide causes Cftr-deficient mice to suffer from constitutive age-dependent pulmonary inflammation, death of respiratory epithelial cells, deposits of DNA in bronchi and high susceptibility to severe Pseudomonas aeruginosa infections. Partial genetic deficiency of Asm in Cftr(-/-)Smpd1(+/-) mice or pharmacological treatment of Cftr-deficient mice with the Asm blocker amitriptyline normalizes pulmonary ceramide and prevents all pathological findings, including susceptibility to infection. These data suggest inhibition of Asm as a new treatment strategy for cystic fibrosis.-1 - infection. These data suggest inhibition of Asm as a novel treatment strategy in CF.
Ceramide accumulation mediates inflammation, cell death and infection susceptibility in cystic fibrosis-4 -
Employing genetic mouse models we have recently shown that ceramide accumulation is critically involved in the pathogenesis of cystic fibrosis (CF) lung disease. Genetic or systemic inhibition of the acid sphingomyelinase (Asm) is not feasible for treatment of patients or might cause adverse effects. Thus, a manipulation of ceramide specifically in lungs of CF mice must be developed. We tested whether inhalation of different acid sphingomyelinase inhibitors does reduce Asm activity and ceramide accumulation in lungs of CF mice. The efficacy and specificity of the drugs was determined. Ceramide was determined by mass spectrometry, DAG-kinase assays, and fluorescence microscopy. We determined pulmonary and systemic Asm activity, neutral sphingomyelinase (Nsm), ceramide, cytokines, and infection susceptibility. Mass spectroscopy, DAG-kinase assays, and semiquantitative immune fluorescence microscopy revealed that a standard diet did not influence ceramide in bronchial respiratory epithelial cells, while a diet with Peptamen severely affected the concentration of sphingolipids in CF lungs. Inhalation of the Asm inhibitors amitriptyline, trimipramine, desipramine, chlorprothixene, fluoxetine, amlodipine, or sertraline restored normal ceramide concentrations in murine bronchial epithelial cells, reduced inflammation in the lung of CF mice and prevented infection with Pseudomonas aeruginosa. All drugs showed very similar efficacy. Inhalation of the drugs was without systemic effects and did not inhibit Nsm. These findings employing several structurally different Asm inhibitors identify Asm as primary target in the lung to reduce ceramide concentrations. Inhaling an Asm inhibitor may be a beneficial treatment for CF, with minimal adverse systemic effects.
SummaryChronic pulmonary colonization with bacterial pathogens, particularly Pseudomonas aeruginosa, is the primary cause of morbidity and mortality in patients with cystic fibrosis (CF). We observed that β1-integrins accumulate on the luminal membrane of upper-airway epithelial cells from mice and humans with CF. β1-integrin accumulation is due to increased ceramide and the formation of ceramide platforms that trap β1-integrins on the luminal pole of bronchial epithelial cells. β1-integrins downregulate acid ceramidase expression, resulting in further accumulation of ceramide and consequent reduction of surface sphingosine, a lipid that kills bacteria. Interrupting this vicious cycle by triggering surface β1-integrin internalization via anti-β1-integrin antibodies or the RGD peptide ligand—or by genetic or pharmacological correction of ceramide levels—normalizes β1-integrin distribution and sphingosine levels in CF epithelial cells and prevents P. aeruginosa infection in CF mice. These findings suggest a therapeutic avenue to ameliorate CF-associated bacterial infections.
Colistin-tobramycin combinations are more efficient than respective single antibiotics for killing P. aeruginosa in biofilms in vitro, and they significantly reduced P. aeruginosa cell counts in a rat lung infection model and in patients with cystic fibrosis.
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