Functional consequences of abnormal fatty acid profiles in cultured airway epithelial cells

Membrane lipid composition of bronchial epithelial cells influences antiviral responses during rhinovirus infection

Lipids and their mediators have important regulatory functions in many cellular processes, including the innate antiviral response. The aim of this study was to compare the lipid membrane composition of in vitro differentiated primary bronchial epithelial cells (PBECs) with ex vivo bronchial brushings and to establish whether any changes in the lipid membrane composition affect antiviral defense of cells from donors without and with severe asthma. Using mass spectrometry, we showed that the lipid membrane of in vitro differentiated PBECs was deprived of polyunsaturated fatty acids (PUFAs) compared to ex vivo bronchial brushings. Supplementation of the culture medium with arachidonic acid (AA) increased the PUFA-content to more closely match the ex vivo membrane profile. Rhinovirus (RV16) infection of AA-supplemented cultures from healthy donors resulted in significantly reduced viral replication while release of inflammatory mediators and prostaglandin E2 (PGE2) was significantly increased. Indomethacin, an inhibitor of prostaglandin-endoperoxide synthases, suppressed RV16-induced PGE2 release and significantly reduced CXCL-8/IL-8 release from AA-supplemented cultures indicating a link between PGE2 and CXCL8/IL-8 release. In contrast, in AA-supplemented cultures from severe asthmatic donors, viral replication was enhanced whereas PTGS2 expression and PGE2 release were unchanged and CXCL8/IL-8 was significantly reduced in response to RV16 infection. While the PTGS2/COX-2 pathway is initially pro-inflammatory, its downstream products can promote symptom resolution. Thus, reduced PGE2 release during an RV-induced severe asthma exacerbation may lead to prolonged symptoms and slower recovery. Our data highlight the importance of reflecting the in vivo lipid profile in in vitro cell cultures for mechanistic studies.

Heparin can improve the viability of transfected cystic fibrosis cell lines in vitro

Cationic liposomes are widely used as gene transfer agents in in vitro and in vivo studies of cystic fibrosis. In this study we report comparative results of cationic mediated transfection in several cell lines. We have tested epithelial cell lines expressing the wild-type cystic fibrosis transmembrane protein CFTR (bronchial epithelium-16HBE14o-, submucosal gland-Calu3) and their cystic fibrosis counterparts (CFBE41o-, CFSMEo-), as well as baby hamster kidney fibroblast cell lines (BHK) heterologously expressing human CFTR. The cells were transfected with a green fluorescent protein plasmid complexed with commercial cationic liposome (Geneporter2, GP) and 25 kDa polyethylenimine (PEI). At the end of the incubation (2 hours), low molecular weight heparin was added in order to reduce the toxicity of the lipoplexes. Transfection efficiency and cell viability were measured by flow cytometry. Determination of fatty acid composition of cellular phospholipids was performed by capillary gas chromatography. The short incubation time was sufficient to obtain satisfactory transfection in all cell lines studied. Cells treated with PEI-complexes had lower transfection efficiency and viability compared to GP in all tested cell lines. DeltaF508 CFTR carrying airway epithelial cells were easier to transfect but had lower viability compared to their healthy counterparts. This was, however not the case for the BHK cells. The fatty acid analysis showed characteristic polyunsaturated fatty acid patterns, which correlated with the viability of the transfected cells. Low molecular mass heparin added at the end of the lipoplex incubation time could help to maintain the viability of the cells, without interfering with the transfection efficiency.

The effects of chronic sidestream cigarette smoke exposure on eicosanoid production by tracheal epithelium

Environmental exposure to sidestream cigarette smoke (SSCS) has been associated with an increased incidence of pulmonary infection and bronchospasm. Chronic exposure to SSCS could modify the release of bronchoreactive eicosanoids by tracheal epithelium, the site of initial contact by lung with inhaled toxins. To assess this possibility, New Zealand white rabbits were placed in an environmental chamber flushed with 3 L of SSCS, 15 min/day for 20 days. Eighteen hours after the last exposure the animals were sacrificed and the tracheas were explanted. At 7 days, the epithelial cell outgrowths were exposed to media containing endotoxin (10 micrograms/mL) or acrolein (50 microM), an aldehyde commonly found in smoke, or to control media. After a 2-h exposure, media were assayed for eicosanoids by radioimmunoassay. PGE2 was produced in epithelium from normal animals (5.7 +/- 1.3 ng/10(6) cells), and was not significantly different in SSCS-exposed epithelium. When incubated in medium containing acrolein, PGE2 production increased significantly in SSCS-exposed epithelium (14.9 +/- 2.5, p < .05) but not in control groups. Endotoxin also increased PGE2 production in SSCS-exposed cells (12.6 +/- 3.3 ng/10(6), p < .05). Baseline production of 6-keto PGF1 alpha was 10.8 +/- 3.2 ng/10(6) cells in non-SSCS controls and did not change significantly in these cells with the addition of endotoxin or acrolein. In acrolein plus SSCS-exposed cells, 6-keto PGF1 alpha increased, in a dose-dependent manner, to 88.1 +/- 26.1 ng/10(6) (p < .05 compared to all normals, SSCS-exposed controls, and SSCS plus LPS). TxB2 release in control, non-SSCS-exposed cells was 13.3 +/- 2.8 ng/10(6) cells and was significantly increased (P < .05) only in the SSCS plus acrolein group (60.7 +/- 16.2 ng/10(6) cells). The results indicate that even brief, recurrent exposure to SSCS can change the production of cyclooxygenase products, particularly PGE2, 6- keto PGF1 alpha, and TxB2. This may reflect an altered ability of SSCS-exposed tracheal epithelium to respond to environmental (e.g., acrolein) or bacterial (e.g., endotoxin) insults.

Essential fatty acid metabolism in cultured human airway epithelial cells

To characterize essential fatty acid metabolism of human airway epithelium, we examined the capacity of epithelial cells to incorporate and desaturate/elongate 18:2(n - 6) and the turnover of phospholipid fatty acyl chains in these cells. Epithelial cells were cultured for 5-7 days and incubated with [1-14C]18:2(n - 6) (1 microCi, 100 nmol). The essential fatty acid profile of the cells was readily modified by 18:2(n - 6) supplementation to culture medium. After 4 h incubation, 32 +/- 5.6 nmol of [1-14C]18:2(n - 6) was incorporated into phospholipids (65 +/- 9.5%, of which 74% was incorporated into phosphatidylcholine (PC)) and neutral lipid (31 +/- 10%) per mg protein of cultured cells. 30 +/- 8% of [1-14C]18:2(n - 6) incorporated, was converted to homologous trienes, tetraenes and pentaenes, the major products being 20:3(n - 6) and 20:4(n - 6). The conversion of 18:2(n - 6) was time-dependent and donor age-related. A higher proportion of 20:3(n - 6) and 20:4(n - 6) was incorporated into phosphatidylinositol (PI) and phosphatidylethanolamine (PE). About 10-15% of total products formed from 18:2(n - 6) was released from membrane to culture medium. Both 20:4(n - 6) and 20:5(n - 3) inhibited 18:2(n - 6) incorporation and desaturation. Rate of incorporation of 18:2(n - 6) was more than either 18:1(n - 9) or 16:0. With pulse-chase studies, the half-life of 18:2(n - 6) in PC, PI and PE was estimated to be 5.5, 6.0 and 7.3 h, respectively. These data indicate active metabolism of essential fatty acids in human airway epithelial cells. This metabolism may play a key role in the regulation of membrane properties and function in these cells.