Inhibition of IL-8 release from CFTR-deficient lung epithelial cells following pre-treatment with fenretinide

Decreased plasma levels of sphingolipids and total cholesterol in adult cystic fibrosis patients

BACKGROUND

Sphingolipid species in the lung epithelium have a critical role for continuity of membrane structure, vesicular transport, and cell survival. Sphingolipid species were reported to have a role in the inflammatory etiology of cystic fibrosis by previous work. The aim of the study was to investigate the levels of plasma sphingomyelin and ceramide in adult cystic fibrosis (CF) patients and compared with healthy controls.

MATERIALS AND METHODS

Blood samples were obtained from CF patients at exacerbation (n = 15), discharge (n = 13) and stable periods (n = 11). Healthy individuals (n = 15) of similar age served as control. Levels of C16-C24 sphingomyelin and C16-C24 ceramide were measured in the plasma by LC-MS/MS. Also, cholesterol and triglyceride levels were determined in plasma samples of the patients at stable period.

RESULTS

All measured sphingomyelin and ceramide levels in all periods of CF patients were significantly lower than healthy controls except C16 sphingomyelin level in the stable period. However, plasma Cer and SM levels among exacerbation, discharge, and stable periods of CF were not different. CF patients had significantly lower cholesterol levels compared to healthy individuals. We found significant correlation of cholesterol with C16 sphingomyelin.

CONCLUSION

We observed lower plasma Cer and SM levels in adult CF patients at exacerbation, discharge, and stable periods compared to healthy controls. We didn't find any significant difference between patient Cer and SM levels among these three periods. Our limited number of patients might have resulted with this statistical insignificance. However, percentage of SM16 levels were increased at discharge compared to exacerbation levels, while percentage of Cer16 and Cer 20 decreased at stable compared to exacerbation. Inclusion of a larger number of CF patients in such a follow up study may better demonstrate any possible difference between exacerbation, discharge, and stable periods.

Treatment With LAU-7b Complements CFTR Modulator Therapy by Improving Lung Physiology and Normalizing Lipid Imbalance Associated With CF Lung Disease

Cystic fibrosis (CF) is the most common autosomal recessive genetic disease in Caucasians, affecting more than 100,000 individuals worldwide. It is caused by pathogenic variants in the gene encoding CFTR, an anion channel at the plasma membrane of epithelial and other cells. Many CF pathogenic variants disrupt the biosynthesis and trafficking of CFTR or reduce its ion channel function. The most frequent mutation, loss of a phenylalanine at position 508 (F508del), leads to misfolding, retention in the endoplasmic reticulum, and premature degradation of the protein. The therapeutics available for treating CF lung disease include antibiotics, mucolytics, bronchodilators, physiotherapy, and most recently CFTR modulators. To date, no cure for this life shortening disease has been found. Treatment with the Triple combination drug therapy, TRIKAFTA®, is composed of three drugs: Elexacaftor (VX-445), Tezacaftor (VX-661) and Ivacaftor (VX-770). This therapy, benefits persons with CF, improving their weight, lung function, energy levels (as defined by reduced fatigue), and overall quality of life. We examined the effect of combining LAU-7b oral treatment and Triple therapy combination on lung function in a F508deltm1EUR mouse model that displays lung abnormalities relevant to human CF. We assessed lung function, lung histopathology, protein oxidation, lipid oxidation, and fatty acid and lipid profiles in F508deltm1EUR mice.

Current evidence on the effect of highly effective CFTR modulation on interleukin-8 in cystic fibrosis

INTRODUCTION

Cystic fibrosis (CF) is a genetically inherited disease, with mortality and morbidity associated with respiratory disease. The inflammatory response in CF is characterized by excessive neutrophil influx to the airways, mainly due to the increased local production and retention of interleukin-8 (IL-8), a potent neutrophil chemoattractant.

AREAS COVERED

We discuss how the chemokine IL-8 dominates the inflammatory profile of the airways in CF lung disease. Cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapies are designed to correct the malfunctioning protein resulting from specific CFTR mutations. This review covers current evidence on the impact of CFTR impairment on levels of IL-8 and outlines the influence of effective CFTR modulation on inflammation in CF with a focus on cytokine production. Review of the literature was carried out using the PUBMED database, Google Scholar, and The Cochrane Library databases, using several appropriate generic terms.

EXPERT OPINION

Therapeutic interventions specifically targeting the defective CFTR protein have improved the outlook for CF. Accumulating studies on the effect of highly effective CFTR modulation on inflammation indicate an impact on IL-8 levels. Further studies are required to increase our knowledge of early onset innate inflammatory dysregulation and on anti-inflammatory mechanisms of CFTR modulators.

Novel Anti-Inflammatory Approaches for Cystic Fibrosis Lung Disease: Identification of Molecular Targets and Design of Innovative Therapies

Cystic fibrosis (CF) is the most common genetic disorder among Caucasians, estimated to affect more than 70,000 people in the world. Severe and persistent bronchial inflammation and chronic bacterial infection, along with airway mucus obstruction, are hallmarks of CF lung disease and participate in its progression. Anti-inflammatory therapies are, therefore, of particular interest for CF lung disease. Furthermore, a better understanding of the molecular mechanisms involved in airway infection and inflammation in CF has led to the development of new therapeutic approaches that are currently under evaluation by clinical trials. These new strategies dedicated to CF inflammation are designed to treat different dysregulated aspects such as oxidative stress, cytokine secretion, and the targeting of dysregulated pathways. In this review, we summarize the current understanding of the cellular and molecular mechanisms that contribute to abnormal lung inflammation in CF, as well as the new anti-inflammatory strategies proposed to CF patients by exploring novel molecular targets and novel drug approaches.

Plasma Ceramides and Sphingomyelins of Pediatric Patients Increase in Primary Ciliary Dyskinesia but Decrease in Cystic Fibrosis

We investigated plasma sphingomyelin (CerPCho) and ceramide (Cer) levels in pediatric patients with cystic fibrosis (CF) and primary ciliary dyskinesia (PCD). Plasma samples were obtained from CF (n = 19) and PCD (n = 7) patients at exacerbation, discharge, and stable periods. Healthy children (n = 17) of similar age served as control. Levels of 16-24 CerPCho and 16-24 Cer were measured by LC-MS/MS. Concentrations of all CerPCho and Cer species measured at exacerbation were significantly lower in patients with CF than PCD. 16, 18, 24 CerPCho, and 22, 24 Cer in exacerbation; 18, 24 CerPCho, and 18, 20, 22, 24 Cer at discharge; 18, 24 CerPCho and 24 Cer at stable period were significantly lower in CF patients than healthy children (p < 0.001 and p < 0.05). All CerPCho and Cer levels of PCD patients were significantly higher except 24 CerPCho and 24 Cer during exacerbation, 24 CerPCho at discharge, and 18, 22 CerPCho levels at stable period (p < 0.001 and p < 0.05) compared with healthy children. There was no significant difference among exacerbation, discharge, and stable periods in each group for Cer and CerPCho levels. This is the first study measuring plasma Cer and CerPCho levels in PCD and third study in CF patients. The dramatic difference in plasma levels of most CerPCho and Cer species found between two diseases suggest that cilia pathology in PCD and CFTR mutation in CF seem to alter sphingolipid metabolism possibly in opposite directions.

Efficacy of Optimized Treatment Protocol Using LAU-7b Formulation against Ovalbumin (OVA) and House Dust Mite (HDM) -Induced Allergic Asthma in Atopic Hyperresponsive A/J Mice

PURPOSE

To assess the efficacy of the novel clinical formulation of fenretinide (LAU-7b) for the treatment of allergic asthma. To study the association between LAU-7b treatment in allergic asthma and the modulation of very long chain ceramides (VLCC).

METHODS

We used two allergens (OVA and HDM) to induce asthma in mouse models and we established a treatment protocol with LAU-7b. The severity of allergic asthma reaction was quantified by measuring the airway resistance, quantifying lung inflammatory cell infiltration (Haematoxylin and eosin stain) and mucus production (Periodic acid Schiff satin). IgE levels were measured by ELISA. Immunophenotyping of T cells was done using Fluorescence-activated cell sorting (FACS) analysis. The analysis of the specific species of lipids and markers of oxidation was performed using mass spectrometry.

RESULTS

Our data demonstrate that 10 mg/kg of LAU-7b was able to protect OVA- and HDM-challenged mice against increase in airway hyperresponsiveness, influx of inflammatory cells into the airways, and mucus production without affecting IgE levels. Treatment with LAU-7b significantly increased percentage of regulatory T cells and CD4⁺ IL-10-producing T cells and significantly decreased percentage of CD4⁺ IL-4-producing T cells. Our data also demonstrate a strong association between the improvement in the lung physiology and histology parameters and the drug-induced normalization of the aberrant distribution of ceramides in allergic mice.

CONCLUSION

9 days of 10 mg/kg of LAU-7b daily treatment protects the mice against allergen-induced asthma and restores VLCC levels in the lungs and plasma.

Druggable Sphingolipid Pathways: Experimental Models and Clinical Opportunities

Intensive research in the field of sphingolipids has revealed diverse roles in cell biological responses and human health and disease. This immense molecular family is primarily represented by the bioactive molecules ceramide, sphingosine, and sphingosine 1-phosphate (S1P). The flux of sphingolipid metabolism at both the subcellular and extracellular levels provides multiple opportunities for pharmacological intervention. The caveat is that perturbation of any single node of this highly regulated flux may have effects that propagate throughout the metabolic network in a dramatic and sometimes unexpected manner. Beginning with S1P, the receptors for which have thus far been the most clinically tractable pharmacological targets, this review will describe recent advances in therapeutic modulators targeting sphingolipids, their chaperones, transporters, and metabolic enzymes.

Fenretinide prevents inflammation and airway hyperresponsiveness in a mouse model of allergic asthma

Arachidonic acid (AA) and docosahexaenoic acid (DHA) play important roles in inflammation and disease progression, where AA is viewed as proinflammatory and DHA as antiinflammatory. We observe in our model of allergic asthma that the AA/DHA ratio is significantly skewed in a proinflammatory direction. Fenretinide, a vitamin A derivative, has been shown to correct fatty acid imbalances in other diseases. Therefore, we explored if fenretinide can have a protective effect in allergic asthma. To accomplish this, we measured the levels of AA and DHA in the lungs of nonallergic, ovalbumin-induced allergic, and fenretinide-treated allergic mice. We also investigated the effect of allergic asthma and fenretinide treatment on markers of oxidative stress, levels of metabolites, IgE production, airway hyperresponsiveness, and histological changes. Our data demonstrate that treatment of allergen-sensitized mice with fenretinide before allergen challenge prevents ovalbumin-induced changes in the AA/DHA ratio. The levels of several metabolites, such as serotonin, and markers of cellular stress, which are increased after ovalbumin challenge, are also controlled by fenretinide treatment. We observed the protective effect of fenretinide against ovalbumin-induced airway hyperresponsiveness and inflammation in the lungs, illustrated by a complete block in the infiltration of inflammatory cells to the airways and dramatically diminished goblet cell proliferation, even though IgE remained high. Our results demonstrate that fenretinide is an effective agent targeting inflammation, oxidation, and lung pathology observed in allergic asthma.

Phenomics of cardiac chloride channels

Forward genetic studies have identified several chloride (Cl-) channel genes, including CFTR, ClC-2, ClC-3, CLCA, Bestrophin, and Ano1, in the heart. Recent reverse genetic studies using gene targeting and transgenic techniques to delineate the functional role of cardiac Cl- channels have shown that Cl- channels may contribute to cardiac arrhythmogenesis, myocardial hypertrophy and heart failure, and cardioprotection against ischemia reperfusion. The study of physiological or pathophysiological phenotypes of cardiac Cl- channels, however, is complicated by the compensatory changes in the animals in response to the targeted genetic manipulation. Alternatively, tissue-specific conditional or inducible knockout or knockin animal models may be more valuable in the phenotypic studies of specific Cl- channels by limiting the effect of compensation on the phenotype. The integrated function of Cl- channels may involve multiprotein complexes of the Cl- channel subproteome. Similar phenotypes can be attained from alternative protein pathways within cellular networks, which are influenced by genetic and environmental factors. The phenomics approach, which characterizes phenotypes as a whole phenome and systematically studies the molecular changes that give rise to particular phenotypes achieved by modifying the genotype under the scope of genome/proteome/phenome, may provide more complete understanding of the integrated function of each cardiac Cl- channel in the context of health and disease.

Anti-inflammatory action of lipid nanocarrier-delivered myriocin: therapeutic potential in cystic fibrosis

BACKGROUND

Sphingolipids take part in immune response and can initiate and/or sustain inflammation. Various inflammatory diseases have been associated with increased ceramide content, and pharmacological reduction of ceramide diminishes inflammation damage in vivo. Inflammation and susceptibility to microbial infection are two elements in a vicious circle. Recently, sphingolipid metabolism inhibitors were used to reduce infection. Cystic fibrosis (CF) is characterized by a hyper-inflammation and an excessive innate immune response, which fails to evolve into adaptive immunity and to eradicate infection. Chronic infections result in lung damage and patient morbidity. Notably, ceramide content in mucosa airways is higher in CF mouse models and in patients than in control mice or healthy subjects.

METHODS

The therapeutic potential of myriocin, an inhibitor of the sphingolipid de novo synthesis rate limiting enzyme (Serine Palmitoyl Transferase, SPT),was investigated in CF cells and mice models.

RESULTS

We treated CF human respiratory epithelial cells with myriocin, This treatment resulted in reduced basal, as well as TNFα-stimulated, inflammation. In turn, TNFα induced an increase in SPT in these cells, linking de novo synthesis of ceramide to inflammation. Furthermore, myriocin-loaded nanocarrier, injected intratrachea prior to P. aeruginosa challenge, enabled a significant reduction of lung infection and reduced inflammation.

CONCLUSIONS

The presented data suggest that de novo ceramide synthesis is constitutively enhanced in CF mucosa and that it can be envisaged as pharmacological target for modulating inflammation and restoring effective innate immunity against acute infection.

GENERAL SIGNIFICANCE

Myriocin stands as a powerful immunomodulatory agent for inflammatory and infectious diseases.

Fenretinide corrects the imbalance between omega-6 to omega-3 polyunsaturated fatty acids and inhibits macrophage inflammatory mediators via the ERK pathway

We previously identified Fragile X-related protein 1 (FXR1) as an RNA-binding protein involved in the post-transcriptional control of TNF and other cytokines in macrophages. Macrophages derived from FXR1-KO mice overexpress several inflammatory cytokines including TNF. Recently, we showed that fenretinide (4HPR) is able to inhibit several inflammatory cytokines in the lungs of cystic fibrosis mice, which also have abnormal immune responses. Therefore, we hypothesized that 4HPR might also be able to downregulate excessive inflammation even in macrophages with ablated FXR1. Indeed, our results demonstrate that 4HPR inhibited the excessive production of inflammatory mediators, including TNF, IL-6, CCL2 and CCL-5 in LPS-stimulated FXR1-KO macrophages, by selectively inhibiting phosphorylation of ERK1/2, which is naturally more phosphorylated in FXR1-KO cells. We also found that LPS stimulation of FXR1-KO macrophages led to significantly higher ratio of arachidonic acid/docosahexaenoic acid than observed in FXR1-WT macrophages. Interestingly, treatment with 4HPR was associated with the normalization of arachidonic acid/docosahexaenoic acid ratio in macrophages, which we found to impact phosphorylation of ERK1/2. Overall, this study shows for the first time that 4HPR modulates inflammatory cytokine expression in macrophages by correcting a phospholipid-bound fatty acid imbalance that impacts the phosphorylation of ERK1/2.

Cisplatin-induced ototoxicity: transporters playing a role in cisplatin toxicity

Cisplatin is a potent antineoplastic agent widely used for a variety of cancer types. Unfortunately, its use leads to dose limiting side effects such as ototoxicity. Up to 93% of patients receiving cisplatin chemotherapy will develop progressive and irreversible sensorineural hearing loss which leads to a decreased quality of life in cancer survivors. No treatment is currently available for cisplatin-induced ototoxicity. It appears that cisplatin causes apoptosis by binding DNA, activating the inflammatory cascade as well as generating oxidative stress in the cell. Various studies have aimed to assess the potential protective effects of compounds such as antioxidants, anti-inflammatories, caspase inhibitors, anti-apoptotic agents and calcium channel blockers against the toxicity caused by cisplatin in the inner ear with variable degrees of protection. Nevertheless, the pathophysiology of cisplatin-induced ototoxicity remains unclear. This review summarizes all of the known transporters that could play a role in cisplatin influx, leading to cisplatin-induced ototoxicity. The following were evaluated: copper transporters, organic cation transporters, the transient receptor potential channel family, calcium channels, multidrug resistance associated proteins, mechanotransduction channels and chloride channels.

Fenretinide inhibited de novo ceramide synthesis and proinflammatory cytokines induced by Aggregatibacter actinomycetemcomitans

Ceramides play an essential role in modulating immune signaling pathways and proinflammatory cytokine production in response to infectious pathogens, stress stimuli, or chemotherapeutic drugs. In this study, we demonstrated that Aggregatibacter actinomycetemcomitans, the pathogen for aggressive periodontitis, induced de novo synthesis of ceramide in Raw 264.7 cells. In addition, we identified that fenretinide, a synthetic retinoid, suppressed the de novo synthesis of ceramide induced by A. actinomycetemcomitans. Moreover, fenretinide attenuated interleukin (IL)-1β, IL-6, and cyclooxygenase-2 mRNA expression induced by A. actinomycetemcomitans. Fenretinide also decreased IL-1β, IL-6, and prostaglandin E2 proinflammatory cytokine levels in Raw 264.7 cells induced by A. actinomycetemcomitans. However, fenretinide had no significant effects on tumor necrosis factor alpha mRNA or protein levels. Furthermore, we showed that fenretinide inhibited the janus kinase-signal transducer and activator of transcription, phosphatidylinositol 3-kinase-Akt, protein kinase C, and nuclear factor-kappaB signaling pathways, whereas fenretinide up-regulated the mitogen-activated protein kinase signaling pathways after bacterial stimulation. This study emphasizes the de novo ceramide synthesis pathway in response to bacterial stimulation and demonstrates the anti-inflammatory role of fenretinide in the bacteria-induced immune response.

Ceramide in cystic fibrosis: a potential new target for therapeutic intervention

Patients with cystic fibrosis (CF) are afflicted with many symptoms but the greatest challenge is the fight against chronic bacterial infections, leading to decreased lung function and ultimately death. Our group has recently found reduced levels of ceramides in CF patients and mice. Ceramides are sphingolipids involved in the structure of cell membranes but also participate in the inflammatory response, in cell signalling through membrane microdomains (lipid rafts), and in apoptosis. These characteristics of ceramides make them strong candidates for therapeutic intervention in CF. As more studies have come to evaluate the role of ceramide in CF, conflicting results have been described. This paper discusses various views regarding the potential role of ceramide in CF, summarizes methods of ceramide detection and their role in the regulation of cellular and molecular processes.

Fatty acid metabolism in cystic fibrosis

Despite identification twenty years ago of the gene responsible for cystic fibrosis transmembrane conductance regulator (CFTR), the protein defective in cystic fibrosis (CF), research of this monogenetic disease has not provided an explanation for the divergent symptoms, and a treatment breakthrough is still awaited. This review discusses different aspects of disturbances in lipid metabolism seen in CF. These include increased release of arachidonic acid (AA) from cell membrane phospholipids and a low status of linoleic and docosahexaenoic acids. Recent research has explored more complicated lipid associations. Disturbances in annexins and ceramides might act in concert to explain the impact on inflammation and AA release. The connections to CFTR and between the disturbances in essential fatty acid metabolism are reviewed. The metabolic interactions, some of which might be compensating, possibly explain the difficulties in understanding the fatty acid disturbances in relation to different symptoms and their relation to the defective CFTR.

Ceramide synthases: roles in cell physiology and signaling

Ceramide synthases (CerS) are integral membrane proteins of the endoplasmic reticulum. Six mammalian CerS have been described, with each utilizing fatty acyl CoAs of relatively defined chain lengths for N-acylation of the sphingoid long chain base. In this chapter, we review the main functional features of the CerS proteins, discuss their fatty acid specificity, kinetics, tissue distribution and mode of inhibition, as well as possible posttranslational modifications. We then address the reason that mammals contain six distinct CerS, whereas most other enzymes in the sphingolipid biosynthetic pathway only occur in one or two isoforms. Finally, we discuss the putative roles of CerS and the ceramide derived from the CerS, in signaling pathways and in development of disease.

Mechanisms of the noxious inflammatory cycle in cystic fibrosis

Multiple evidences indicate that inflammation is an event occurring prior to infection in patients with cystic fibrosis. The self-perpetuating inflammatory cycle may play a pathogenic part in this disease. The role of the NF-κB pathway in enhanced production of inflammatory mediators is well documented. The pathophysiologic mechanisms through which the intrinsic inflammatory response develops remain unclear. The unfolded mutated protein cystic fibrosis transmembrane conductance regulator (CFTRΔF508), accounting for this pathology, is retained in the endoplasmic reticulum (ER), induces a stress, and modifies calcium homeostasis. Furthermore, CFTR is implicated in the transport of glutathione, the major antioxidant element in cells. CFTR mutations can alter redox homeostasis and induce an oxidative stress. The disturbance of the redox balance may evoke NF-κB activation and, in addition, promote apoptosis. In this review, we examine the hypotheses of the integrated pathogenic processes leading to the intrinsic inflammatory response in cystic fibrosis.

Lipid metabolism in cystic fibrosis

PURPOSE OF REVIEW

Expression of defective cystic fibrosis transmembrane conductance regulator (CFTR), the cause for cystic fibrosis, affects fatty acid, cholesterol and sphingolipid metabolism. This review summarizes recent observations and evaluates current understanding of mechanisms.

RECENT FINDINGS

Recent observations implicate CFTR, in addition to known effects on fatty acid and cholesterol metabolism, in the regulation of sphingolipid metabolism and suggest that this pathway is relevant to inflammation and infection. A common mechanism on how CFTR affects such a wide spectrum of lipid classes is currently not known. One mechanism for low linoleic acid, amenable to inhibition by docosahexaenoic acid, is increased metabolism in the n-6 fatty acid pathway. Accumulation of free cholesterol in distinct perinuclear compartments, reversible by overexpression of rab9, suggests that cystic fibrosis and the lysosomal storage disease Niemann-Pick-C could share similar cell signaling defects, in addition to increased cAMP signaling and sterol-regulatory element binding protein (SREBP) expression that affect cholesterol metabolism. Novel is the recognition that CFTR modulates ceramide mass and uptake of sphingosine-1- phosphate. Experiments in different cystic fibrosis-mouse models, although not able to establish whether ceramide mass is increased or decreased, suggest that normalization of ceramide decreases infection and selected parameters of inflammation, of relevance to the complex phenotype that characterizes cystic fibrosis.

SUMMARY

Expression of defective CFTR has profound effects on fatty acid, cholesterol and sphingolipid metabolism, for which mechanisms are currently poorly understood. Recent studies in different cystic fibrosis models suggest a causal relationship between altered ceramide mass and increased inflammation and susceptibility to infection. Studies in cystic fibrosis knockout mouse models suggest that normalization of ceramide decreases infection and inflammation. Studies that evaluate the diagnostic and clinical relevance of sphingolipids in patients with cystic fibrosis are needed.

Phenomics of cardiac chloride channels: the systematic study of chloride channel function in the heart

Recent studies have identified several chloride (Cl-) channel genes in the heart, including CFTR, ClC-2, ClC-3, CLCA, Bestrophin, and TMEM16A. Gene targeting and transgenic techniques have been used to delineate the functional role of cardiac Cl- channels in the context of health and disease. It has been shown that Cl- channels may contribute to cardiac arrhythmogenesis, myocardial hypertrophy and heart failure, and cardioprotection against ischaemia-reperfusion. The study of physiological or pathophysiological phenotypes of cardiac Cl- channels, however, may be complicated by the compensatory changes in the animals in response to the targeted genetic manipulation. Alternatively, tissue-specific conditional or inducible knockout or knockin animal models may be more valuable in the phenotypic studies of specific Cl- channels by limiting the effect of compensation on the phenotype. The integrated function of Cl- channels may involve multi-protein complexes of the Cl- channel subproteome and similar phenotypes can be attained from alternative protein pathways within cellular networks, which are influenced by genetic and environmental factors. Therefore, the phenomics approach, which characterizes phenotypes as a whole phenome and systematically studies the molecular changes that give rise to particular phenotypes achieved by modifying the genotype (such as gene knockouts or knockins) under the scope of genome/proteome/phenome, may provide a more complete understanding of the integrated function of each cardiac Cl- channel in the context of health and disease.

Defective acid sphingomyelinase pathway with Pseudomonas aeruginosa infection in cystic fibrosis

Acid sphingomyelinase (ASMase) is a key enzyme in sphingolipid metabolism, which can be activated by various cellular stress mechanisms including bacterial pathogens. Activation of ASMase generates ceramide, which is important for innate immune response to eliminate infected pathogens. The current study reveals a defective ASMase pathway after Pseudomonas aeruginosa infection in both a cystic fibrosis (CF) bronchial epithelial cell line (IB3-1 cell) and in the lungs of CF transmembrane conductance regulator (CFTR) knockout (KO) mice as compared with S9 cells and wild-type C57BL/6 mice. ASMase activity and total ceramide levels significantly increased in S9 cells and C57BL/6 mice with P. aeruginosa infection, but not in IB3-1 cells and CFTR KO mice. The silencing of CFTR by CFTR RNAi in S9 cells significantly decreased ASMase activity after bacterial infection as compared with controls. This study also demonstrates that induction of ASMase is responsible for modulating the immune response to bacterial infection. Blocking ASMase activity with specific ASMase RNAi, an ASMase inhibitor, or an ASMase antibody in S9 cells significantly increased IL-8 levels with P. aeruginosa infection compared with controls. Reciprocally, adding exogenous bacterial sphingomyelinase to IB3-1 cells significantly decreased IL-8 levels compared with untreated cells. In addition, silencing of ASMase in S9 cells also significantly decreased bacterial internalization. Adding exogenous bacterial sphingomyelinase to IB3-1 cells reconstituted the cell death response to P. aeruginosa infection. This study demonstrates that the defective ASMase pathway in CF is a key contributor to the unabated IL-8 response with P. aeruginosa infection and to the compromised host response failing to eradicate bacteria.

Defective CFTR increases synthesis and mass of sphingolipids that modulate membrane composition and lipid signaling

Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator (CFTR) that affect protein structure and channel function. CFTR, localized in the apical membrane within cholesterol and sphingomyelin rich regions, is an ABC transporter that functions as a chloride channel. Here, we report that expression of defective CFTR (DeltaF508CFTR or decreased CFTR) in human lung epithelial cell lines increases sphingolipid synthesis and mass of sphinganine, sphingosine, four long-chain saturated ceramide species, C16 dihydroceramide, C22, C24, C26-ceramide, and sphingomyelin, and decreases mass of C18 and unsaturated C18:1 ceramide species. Decreased expression of CFTR is associated with increased expression of long-chain base subunit 1 of serine-palmitoyl CoA, the rate-limiting enzyme of de novo sphingolipid synthesis and increased sphingolipid synthesis. Overexpression of DeltaF508CFTR in bronchoalveolar cells that do not express CFTR increases sphingolipid synthesis and mass, whereas overexpression of wild-type CFTR, but not of an unrelated ABC transporter, ABCA7, decreases sphingolipid synthesis and mass. The data are consistent with a model in which CFTR functions within a feedback system that affects sphingolipid synthesis and in which increased sphingolipid synthesis could reflect a physiological response to sequestration of sphingolipids or altered membrane structure.

Fenretinide Corrects Newly Found Ceramide Deficiency in Cystic Fibrosis

Chronic and persistent lung infections cause the majority of morbidity and mortality in patients with cystic fibrosis (CF). Galactosyl ceramide has been previously shown to be involved in Pseudomonas internalization. Therefore, we assessed ceramide levels in the plasma of patients with CF and compared them to healthy volunteers using high-performance liquid chromatography followed by mass spectrometry. Our results demonstrate that patients with CF display significantly lower levels of several ceramide sphingolipid species, specifically C14:0, C20:1, C22:0, C22:1, and C24:0 ceramides, and dihydroxy ceramide (DHC16:0). We report that Cftr-knockout mice display diminished ceramide levels in CF-related organs (lung, pancreas, ileum, and plasma) compared with their littermate controls. Since it has been previously reported that in vitro treatment with fenretinide induced ceramide in neuroblastoma cell lines, we decided to test this drug in vivo using our Cftr-knockout mice in an attempt to correct this newly identified defect in ceramide levels. We demonstrate that treatment with fenretinide is able to increase ceramide concentrations in CF-related organs. We further assessed the biological effect of fenretinide on the ability of Cftr-knockout mice to combat lung infection with P. aeruginosa. Our data show dramatic improvement in the ability of Cftr-knockout mice to control P. aeruginosa infection. Overall, these findings not only document a novel deficiency in several ceramide species in patients with CF, but also demonstrate a pharmacologic means to correct this defect in Cftr-knockout mice. Our data provide a strong rationale for clinical intervention that may benefit patients with CF suffering from CF lung disease.

Nutrition in pediatric lung disease

The respiratory system exists in an oxygenated milieu and is recurrently exposed to both endogenous and exogenous oxidants and irritants. A variety of dietary-dependent defenses have evolved to protect the lungs. These comprise vitamins, proteins, polyphenols, fatty acids and co-factors. This is a brief review of oxidant sources and the antioxidant system, as pertains to the respiratory system. The challenge to both clinicians and investigators is to understand how defenses are integrated and coordinated so that enhanced protection can be delivered.

Exaggerated apoptosis and NF-kappaB activation in pancreatic and tracheal cystic fibrosis cells

The pathophysiologic mechanisms causing inflammation in cystic fibrosis (CF) remain obscure. The effects of proapoptotic agents on pancreatic and tracheal cell lines expressing wild-type CFTR (PANC-1 and NT-1, respectively) or the homozygous CFTRDeltaF508 mutation (CFPAC-1 and CFT-2, respectively) were assessed. An increased susceptibility to apoptosis was observed in CFPAC-1 and CFT-2 cells. Apoptosis was reduced by treatment with a pan-caspase inhibitor and by incubation at 27 degrees C, allowing recruitment of CFTR deltaF508 at the plasma membrane. Inhibition of CFTR function in wild-type cells induced an increase of apoptosis. Apoptosis in CFPAC-1, but not in CFT-2 cells, was associated with overexpression of the proinflammatory mediators interleukin-6 and interleukin-8. In CF cells, apoptosis was linked to NF-kappaB pathway activation. Conditioned medium from actinomycin D-treated CFPAC-1 cells produced an increase in apoptosis of wild-type cells, suggesting that proinflammatory mediators secreted by mutant cells promote apoptosis. This was confirmed through the induction of apoptosis in wild-type cells by exogenous interleukin-6 and interleukin-8. These results suggest that CFTR deltaF508 mutation, apoptosis, and activation of the NF-kappaB pathway contribute to the self-perpetuating inflammatory cycle, at least in pancreatic cells, and provide evidence that excessive apoptosis may account for the exaggerated proinflammatory response observed in CF patients.