William R. Hunt

Hyperglycemia impedes lung bacterial clearance in a murine model of cystic fibrosis-related diabetes

Cystic fibrosis-related diabetes (CFRD) is the most common comorbidity associated with cystic fibrosis (CF), impacting more than half of patients over age 30. CFRD is clinically significant, portending accelerated decline in lung function, more frequent pulmonary exacerbations, and increased mortality. Despite the profound morbidity associated with CFRD, little is known about the underlying CFRD-related pulmonary pathology. Our aim was to develop a murine model of CFRD to explore the hypothesis that elevated glucose in CFRD is associated with reduced lung bacterial clearance. A diabetic phenotype was induced in gut-corrected CF transmembrane conductance regulator (CFTR) knockout mice (CFKO) and their CFTR-expressing wild-type littermates (WT) utilizing streptozotocin. Mice were subsequently challenged with an intratracheal inoculation of Pseudomonas aeruginosa (PAO1) (75 μl of 1-5 × 10(6) cfu/ml) for 18 h. Bronchoalveolar lavage fluid was collected for glucose concentration and cell counts. A portion of the lung was homogenized and cultured as a measure of the remaining viable PAO1 inoculum. Diabetic mice had increased airway glucose compared with nondiabetic mice. The ability to clear bacteria from the lung was significantly reduced in diabetic WT mice and control CFKO mice. Critically, bacterial clearance by diabetic CFKO mice was significantly more diminished compared with nondiabetic CFKO mice, despite an even more robust recruitment of neutrophils to the airways. This finding that CFRD mice boast an exaggerated, but less effective, inflammatory cell response to intratracheal PAO1 challenge presents a novel and useful murine model to help identify therapeutic strategies that promote bacterial clearance in CFRD.

Insulin signaling via the PI3-kinase/Akt pathway regulates airway glucose uptake and barrier function in a CFTR-dependent manner

Cystic fibrosis-related diabetes is the most common comorbidity associated with cystic fibrosis (CF) and correlates with increased rates of lung function decline. Because glucose is a nutrient present in the airways of patients with bacterial airway infections and because insulin controls glucose metabolism, the effect of insulin on CF airway epithelia was investigated to determine the role of insulin receptors and glucose transport in regulating glucose availability in the airway. The response to insulin by human airway epithelial cells was characterized by quantitative PCR, immunoblot, immunofluorescence, and glucose uptake assays. Phosphatidylinositol 3-kinase/protein kinase B (Akt) signaling and cystic fibrosis transmembrane conductance regulator (CFTR) activity were analyzed by pharmacological and immunoblot assays. We found that normal human primary airway epithelial cells expressed glucose transporter 4 and that application of insulin stimulated cytochalasin B-inhibitable glucose uptake, consistent with a requirement for glucose transporter translocation. Application of insulin to normal primary human airway epithelial cells promoted airway barrier function as demonstrated by increased transepithelial electrical resistance and decreased paracellular flux of small molecules. This provides the first demonstration that airway cells express insulin-regulated glucose transporters that act in concert with tight junctions to form an airway glucose barrier. However, insulin failed to increase glucose uptake or decrease paracellular flux of small molecules in human airway epithelia expressing F508del-CFTR. Insulin stimulation of Akt1 and Akt2 signaling in CF airway cells was diminished compared with that observed in airway cells expressing wild-type CFTR. These results indicate that the airway glucose barrier is regulated by insulin and is dysfunctional in CF.

Advanced glycation end products are elevated in cystic fibrosis-related diabetes and correlate with worse lung function.

BACKGROUND The onset of cystic fibrosis-related diabetes (CFRD) exacerbates lung function decline and increases mortality. One pathway that may worsen the lung dysfunction associated with CFRD is that of the receptor for advanced glycation end products (RAGE) and its ligands. METHODS Human plasma was obtained from age-matched healthy, CF and CFRD patients. Plasma RAGE ligands (i.e. advanced glycation end products, S100A12, and high-mobility group protein B1) and soluble RAGE (sRAGE) levels were measured. RESULTS CFRD patients had elevated plasma levels of AGEs and S100A12. Soluble RAGE, a RAGE ligand decoy receptor, was not significantly different between groups. Plasma AGE levels and S100A12 levels had significantly negative correlations with FEV1. CONCLUSIONS AGEs are significantly elevated in CFRD and correlate negatively with FEV1. CFRD patients did not have significant increases in the decoy sRAGE, suggesting there may be heightened binding and activation of RAGE in CFRD exacerbating activation of proinflammatory pathways.

Cystic Fibrosis: An Overview of the Past, Present, and the Future

Cystic fibrosis (CF) is the most common lethal genetic disorder amongst Caucasians with a current life expectancy of about 40 years. A dysfunctional CF transmembrane conductance regulator chloride channel is the single primary cause of this complex systemic disease that negatively affects every secretory organ in the body. In this chapter, we present our current understanding of CF through model systems that shed light on the pathophysiological consequences of the disease. In particular, we discuss its epidemiological and clinical impact with a focus on the identified and exploratory defects within airway epithelial cells. Finally, we discuss therapeutic approaches as they relate to the underlying disease pathophysiology.

A 22-Year-Old Woman With Bronchiectasis and a Mediastinal Mass

A 22-year-old woman presented to the ED following several days of worsening shortness of breath and chest tightness associated with tachypnea and palpitations. Her past medical history was significant for several months of nausea and vomiting, crampy abdominal pain, intermittent loose stool, and weight loss. Severe gastritis and pyloric ulcers were discovered during an upper endoscopy approximately 1 month prior; she was treated with a proton pump inhibitor and sucralfate. She had previously been healthy and did not have a history of alcohol consumption, smoking, or intake of nonsteroidal antiinflammatory drugs. Her initial chest radiograph and chest CT scan are shown in Figures 1 and ​and2.2. She denied frequent respiratory illness as a child. Figure 1. Posteroanterior chest radiograph demonstrates upper lobe predominant scarring, architectural distortion, and subtle cystic and cylindrical bronchiectasis. Contour deformity of the right upper mediastinum with silhouetting of the ascending aortic contour ... Figure 2. A, Representative axial CT image displayed with lung window settings demonstrates architectural distortion and bilateral cystic and cylindrical bronchiectasis in the upper lobes and superior portion of the lower lobes. B, Mediastinal window demonstrates ... Physical Examination Findings On physical examination the patient was afebrile, with a heart rate of 113 beats/min, BP of 101/65 mm Hg, respiratory rate of 22 breaths/min, and oxygen saturation of 99% on room air. Neck examination revealed no thyromegaly, jugular venous distention, or cervical lymphadenopathy. Cardiac examination was notable for tachycardia. Bilateral inspiratory crackles were noted on lung auscultation. On abdominal examination she had diffuse mild tenderness to palpation without organomegaly. The rest of the physical examination was unremarkable. Laboratory Findings Laboratory findings showed a normal chemistry panel and normocytic anemia (hemoglobin=10.4 g/dL). Thyrotropin and free T4 levels were normal. Serum immunoglobulin levels showed IgG 354 mg/dL (normal, 694-1,698 mg/dL), IgA 40 mg/dL (normal, 63-378 mg/dL), and IgM 19 mg/dL (normal, 60-263 mg/dL). HIV test was negative. A bronchoscopy with BAL and transbronchial biopsy did not isolate any organisms and showed normal lung parenchyma. What is the next diagnostic step? What is the probable diagnosis? Next diagnostic step: Biopsy of the mediastinal mass Diagnosis: Good syndrome