Open Access

Effects in cigarette smoke stimulated bronchial epithelial cells of a corticosteroid entrapped into nanostructured lipid carriers

  • Maria Luisa Bondì1Email author,
  • Maria Ferraro2,
  • Serena Di Vincenzo2,
  • Stefania Gerbino2,
  • Gennara Cavallaro3,
  • Gaetano Giammona3,
  • Chiara Botto3,
  • Mark Gjomarkaj2 and
  • Elisabetta Pace2
Journal of Nanobiotechnology201412:46

https://doi.org/10.1186/s12951-014-0046-4

Received: 2 September 2014

Accepted: 23 October 2014

Published: 29 November 2014

Abstract

Background

Nanomedicine studies have showed a great potential for drug delivery into the lung. In this manuscript nanostructured lipid carriers (NLC) containing Fluticasone propionate (FP) were prepared and their biocompatibility and effects in a human bronchial epithelial cell line (16-HBE) stimulated with cigarette smoke extracts (CSE) were tested.

Results

Biocompatibility studies showed that the NLC did not induce cell necrosis or apoptosis. Moreover, it was confirmed that CSE increased intracellular ROS production and TLR4 expression in bronchial epithelial cells and that FP-loaded NLC were more effective than free drug in modulating these processes. Finally, the nanoparticles increased GSH levels improving cell protection against oxidative stress.

Conclusions

The present study shows that NLC may be considered a promising strategy to improve corticosteroid mediated effects in cellular models associated to corticosteroid resistance. The NLC containing FP can be considered good systems for dosage forms useful for increasing the effectiveness of fluticasone decreasing its side effects.

Keywords

Nanostructured lipid carriers Corticosteroid Fluticasone propionate Cigarette smoke Airway epithelial cell Chronic obstructive pulmonary disease Asthma

Background

Pulmonary drug delivery is an important research area with a potential high impact in the treatment of various obstructive pulmonary diseases including asthma and chronic obstructive pulmonary disease. It can provide rapid responses and can minimize the required drug dose being the drug delivered directly into the lungs and specifically at the site of activity [1].

Nanomedicine is used for modified and targeted drug delivery. It is based on nanostructured materials at colloidal size (1–500 nm) and is able to release biologically active agents, chemically or physically incorporated, into specific sites and within very well defined time frames. These systems are characterized by: 1) nanoscaled dimensions, able to allow their direct interaction at molecular levels with cell components of the damaged tissue; 2) the ability to incorporate elevated amounts of active molecules with subsequent increase of the efficiency of the drug delivery systems; 3) the ability to deliver the drugs by increasing their bioavailability and decreasing administered doses; 4) the ability to obtain an efficient localization of the drug in the target site [2]. Nanomedicine provides new solutions to clinical problems, particularly in pulmonary diseases, promising better delivery of therapeutics to disease sites [3],[4]. These advantages can be properly exploited for the administration of inhaled corticosteroids, especially during long-term therapies like in patients with chronic obstructive pulmonary disease (COPD); potentially, it might be possible to utilise these nanosystems in inhalatory therapies in order to maximize local effects into the lung and to reduce systemic effects as well as the frequency of administration. Moreover, long-term use of high-dose inhaled corticosteroids (ICS) has the potential to cause undesirable side effects. Conversely, a modified delivery system provides constant levels of drug at the prime site of action for a prolonged time and it would enable better control of the disease [5],[6].

To obtain these results it is important the choice of the material forming the nanodevices. In particular the use of pegylated lipid for the production of Nanostructured Lipid Carrier (NLC) combines the advantages of the safety of lipids and the possibility of large-scale production, with the mucoadhesive properties useful for improving residence time of nanodevices on airways surface and to contrast the effect of the abnormal production of mucus, occurring in COPD, with the consequent dramatic reduction of corticosteroids absorption [7]. In this context, colloidal lipid nanoparticles such as NLC could give great benefit in designing new drug delivery systems with great potential advantages.

The aim of the present work was to realize a novel drug delivery system to improve the drug bioavailability, making the drug able to achieve an increase of permeability through the membrane cell and consequently to reduce the administered dose. In this paper we report the preparation and characterization of NLC by using a pegylated lipid such as Compritol HD5 ATO, for the delivery through inhalator route of Fluticasone propionate (FP). Pegylated NLC containing Fluticasone (FP-loaded NLC) as well as empty NLC, as control, were prepared and characterized in terms of size, polydispersity index (PDI), surface charge, stability, and in vitro drug release. Moreover, the biological efficiency of this new drug delivery system was evaluated in vitro by using the human bronchial epithelial cell line (16-HBE) considering the effects of the drug, in the loaded-NLC or free form on Reactive Oxygen Species (ROS) production, GSH levels, and TRL4 expression in cigarette smoke extracts (CSE) stimulated cells.

Results and discussion

In this paper, in order to improve the FP efficacy in the treatment of respiratory diseases such as COPD, FP-loaded NLC were developed. Due to the lypophilic characteristics of FP, FP-loaded NLC were prepared by the precipitation method [8]-[10]. In particular, Compritol HD5 ATO was chosen as lipid matrix for obtaining NLC with or without FP because of its good biocompatibility and the presence of PEG in its structure. In this regards, it has been shown that the PEG chains can play an important role in transport across mucosae of nanoparticles since their presence can improve their transport across the nasal epithelia [7],[11]-[13].

Since some physicochemical and technological properties are quite critical for biopharmaceutical behaviour of NLC, either empty and drug-loaded samples, after preparation and purification, were characterized in terms of particle size, PDI and ζ potential in three different dispersing aqueous media by light scattering measurements, and analytical data are reported in Table 1.
Table 1

Mean size (nm), polydispersity index (PDI) and ζ-potential (mV) in bi-distilled water, phosphate buffer solution (PBS) and NaCl 0.9 wt% of empty and Fluticasone propionate (FP)-loaded nanoparticles

Sample

Dispersing medium

Mean size (nm)

PDI

Zeta potential (mV)(± S.D.)

EE%(w/w)

Empty

PBS pH 7.4

133.7

0.243

−15.1 ± 3.78

-----

 

NaCl 0.9%

132.5

0.215

−12.3 ± 4.16

-----

 

H2O

115.9

0.285

−27.8 ± 3.21

-----

FP-loaded

PBS pH 7.4

178.7

0.266

−14.3 ± 2.44

76.8 ± 0.04

 

NaCl 0.9%

189.6

0.244

−13.3 ± 4.56

76.8 ± 0.05

 

H2O

129.9

0.330

−31.3 ± 4.50

76.8 ± 0.04

Empty 4 months)

H2O

137.9

0.247

−26.6 ± 3.13

-----

Empty (10 months)

H2O

149.9

0.235

−25.4 ± 2.15

-----

FP-loaded (4 months)

H2O

143.2

0.323

−28.3 ± 2.72

74.7 ± 0.06

FP-loaded (10 months)

H2O

145.6

0.334

−27.5 ± 4.50

72.5 ± 0.03

Efficiency entrapment % (EE%) of FP-loaded NLC.

Empty and drug loaded-NLC have size of about 116 and 130 nm in bi-distilled water respectively, and greater in the all other investigated media; these differences could be attributed to the different ionic strength of the media. Moreover, all these systems possessed quite low PDI values, which indicated a good dimensional homogeneity of particles that, together with small size, make them suitable for inhalatory administration.

The ζ potential values of these structures, also reported in Table 1, were rather high (absolute value) in bi-distilled water and decreased when they were determined in PBS and NaCl 0.9% aqueous solution. The presence of electrolytes causes a diminution of surface charge for the potential screening effect of solution ions. The surface charge of nanoparticles is important because it makes the nanosystems more stable when dispersed into an aqueous solution, reducing the occurrence of the aggregation phenomenon. Several systems were prepared with different size and surface characteristics (data not shown) but for the in vitro tests the system with better physical-chemical characteristics was chosen.

In order to confirm the nanometer size and to investigate the morphology of empty or FP-loaded NLC, SEM was used and the obtained images are reported in Figure 1.
Figure 1

Scanning electron microscopy. Representative SEM images of NLC, empty (A) and loaded with FP (B), respectively. The bars represent 500 nm.

These images were consistent with the findings obtained from dimensional analysis and also revealed a spherical shape of investigated samples.

Moreover, an important aspect to be taken into account in the formulations of NLC as possible carrier to be aerosolized for the pulmonary delivery of drugs is their capability to give colloidal dispersions stable during storage. The occurrence of aggregation phenomena can lead to a significant worsening of the biopharmaceutical features of colloidal suspensions, above all in terms of ability to be uptaken into the cells.

Therefore in order to evaluate the stability of these systems during storage empty and FP-loaded NLC were kept for 4 months and 10 months at 4°C and subsequently characterized in terms of size, PDI, and ζ potential. The results (Table 1) showed that either empty or FP-loaded NLC were stable during storage under tested conditions.

DL % and EE % of FP loaded in NLC were equal to about as 4.8% and 76.8% respectively. In order to evaluate the ability of these NLC of retaining the encapsulated drug under sink conditions and to release it slowly in physiological media, a release study was carried out in PBS at pH 7.4/ethanol mixture 80:20 (v/v) by evaluating the amount of released drug from NLC at prefixed time intervals across a dialysis tube (Spectra/Por®, MWCO 12,000-14,000 Da), in accordance to the European Pharmacopoeia [14],[15]. In Figure 2, the drug release profile from FP-loaded NLC was reported until 72 hrs incubation.
Figure 2

Drug release profile from FP- loaded NLC.

As shown, after 1 hr, the amount of FP released from NLC was equal to 15%. An initial burst effect in the drug-release profile of FP-NLC is evident and it can be probably ascribed to the presence of the drug absorbed on the nanoparticle surface. Moreover, these studies revealed that in a physiological-mimicking medium, FP was not completely released from nanoparticles until 72 hrs, supporting the hypothesis that these systems at the contact with the airways mucosae, could efficiently enter in the colloidal form improving then the drug internalization into the cells and its accumulation into human bronchial epithelial cells. The drug burst release shown in this study could be exploited to deliver a high initial dose when desired. The gradual release after the initial burst would also be important in order to maintain an effective drug concentration in the target organ.

An innovative drug delivery system has to be tested for its safety. This aspect is much more relevant in the case of pulmonary delivery, since several side effects may result from an unsafe material [16]. Taking also into account the possibility to incorporate into aerosol droplets the FP-loaded pegylated nanoparticles and to administer them by inhalation, safety of empty NLC and FP-loaded NLC was evaluated in vitro by using 16-HBE cells as a model of epithelial cells.

Cytotoxicity of FP-loaded pegylated nanoparticles in 16-HBE cells (Figures 3 and 4) was evaluated by using the PI/Annexin V binding method [17].
Figure 3

Biocompatibility of empty and FP- loaded NLC: dose–response experiments. Bronchial epithelial cells (16-HBE) were cultured in the presence and in the absence of NLC and FP-loaded NLC (10−8M, 10−10M, 10−12M) for 24 hours and cell necrosis and cell apotosis were assessed using the PI/Annexin V method by flow cytometry. Representative dot plots were shown.

Figure 4

Biocompatibility of empty and FP- loaded NLC: time-dependent experiments. Bronchial epithelial cells (16-HBE) were cultured in the presence and in the absence of FP, NLC and FP-loaded NLC (10−8M) for 48 (A) and 72 (B) hours and cell necrosis and cell apotosis were assessed using the PI/Annexin V method by flow cytometry. Representative dot plots were shown.

Neither FP-loaded NLC nor empty NLC at both tested concentrations and time points induced relevant numbers of necrotic (PI positive) or of apoptotic (Annexin V positive) 16-HBE cells (Figures 3 and 4), evidencing the high biocompatibility of obtained nanoparticles.

Our results indicate the potential of the obtained NLC as carriers for FP delivered by intra-bronchial route.

The increased oxidative stress present in COPD patients is related to the increased burden of inhaled oxidants such as cigarette smoke and to the increase in ROS generated by several inflammatory, immune, and structural airways cells [18]. We initially tested the effect of CSE in ROS production by bronchial epithelial cells. When the cells were exposed to CSE, an increased ROS expression occurred. The presence of free FP tended to increase ROS expression in CSE stimulated cells but this increase was not statistically different. FP-loaded NLC significantly reduced the CSE induced ROS expression and the effect was significantly greater than that exerted by free FP (Figure 5A and B).
Figure 5

Effects of FP-loaded NLC on ROS production. Bronchial epithelial cells (16-HBE) were cultured in the presence and in the absence of CSE (10%), FP, NLC and FP-loaded NLC for 24 hours and then were used for assessing ROS production by flow cytometry (see Materials and methods for details). (A) Data are expressed as percentage of ROS positive cells ± SD. *p < 0.05. (B) Representative histogram plots are shown.

Glutathione (GSH) is one of the most important defensive mechanisms against oxidative stress [19],[20]. The effects of unloaded FP and FP-loaded NLC as GSH expression in CSE stimulated bronchial epithelial cells were explored. CSE did not significantly increase GSH expression in bronchial epithelial cells. Free FP and empty NLC did not significantly induce GSH expression (data not shown). On the contrary FP-loaded NLC significantly increased GSH expression in CSE stimulated bronchial epithelial cells (Figure 6).
Figure 6

Effects of FP-loaded NLC on GSH expression. Bronchial epithelial cells (16-HBE) were cultured in the presence and in the absence of CSE (10%), FP, NLC and FP-loaded NLC for 24 hours and then were used for assessing GSH content (see Materials and methods for details). Data are expressed as GSH μmoles/mg proteins ± SD. *p < 0.05.

Therefore the increase of GSH suggests a protective effect against oxidative stress into the cells induced by FP when it is administered by NLC.

A key component of the innate immunity and of the innate defence mechanisms against infections is represented by the toll like receptor (TLR4) family. After stimulation of these receptors the cell is triggered to produce inflammatory mediators. Since CSE increased TLR4 expression in bronchial epithelial cells [21],[22], the effect of free FP and FP-loaded NLC in CSE induced TLR4 expression was assessed. FP-loaded NLC at 10−8M concentration was more effective in reducing TLR4 expression in CSE stimulated cells in comparison to the other two tested concentrations (Figure 7). According to the results of these experiments, 24 hours of incubation was selected as the best time point (Figure 8). Free FP as well as empty NLC did not significantly affect the CSE induced TLR4 expression while FP-loaded NLC significantly reduced the CSE induced TLR4 expression (Figure 9A and B).
Figure 7

Dose–response experiments for TLR4 expression. Bronchial epithelial cells (16-HBE) were cultured in the presence and in the absence of CSE (10%) and FP-loaded NLC at different drug concentrations (10−8M, 10−10M, 10−12M) for 24 hours. Representative histogram plots were shown.

Figure 8

Time-dependent experiments for TLR4 expression. Bronchial epithelial cells (16-HBE) were cultured in the presence and in the absence of CSE (10%) and FP-loaded NLC (10−8M) for different time points (24, 48 and 72 hours). Representative histogram plots were shown.

Figure 9

Effects of FP-loaded NLC on TLR4 expression. Bronchial epithelial cells (16-HBE) were cultured in the presence and in the absence of CSE (10%), FP, NLC and FP-loaded NLC (10−8M) for 24 hours and then were used for assessing TLR4 expression by flow cytometry. (A) Representative histogram plots are shown. (B) Data are expressed as percentage of TLR4 positive cells ± SD. *p < 0.05.

To further investigate why the use of FP-loaded NLC was more effective than the free drug in reducing CSE-mediated effects, the intracellular and extracellular contents of FP in 16-HBE cells treated with unloaded FP or with FP-loaded NLC were assessed by UV analysis. The content of FP was higher within the cells treated with FP-loaded NLC than within the cells treated with free FP at all time points. These results further supported the obtained biological data. Figure 10 shows that the intracellular concentrations of FP loaded into the NLC were always higher than those found in cells treated with free FP. Furthermore, the intracellular and extracellular concentrations were lower than the ones used for the experiments because an aliquot of FP was probably degraded by enzymes present in the cells, thus confirming the data reported in the literature [23].
Figure 10

Intracellular and extracellular concentrations of FP at 24, 48 and 72 hrs. Data are expressed as Molarity.

Cigarette smoking is the major cause of chronic obstructive pulmonary disease, which is associated with increased oxidative stress and altered innate and adaptive immunity [24].

Cigarette smoke-mediated oxidative stress other than producing protein denaturation [25], lipid peroxidation, and DNA damage, contributes to reducing corticosteroid activity [26]. In the presence of mucus hypersecretion, a phenomenon frequently present in the airways of COPD patients, lipophilic substances, such as corticosteroids, can be remarkably impeded in reaching their receptors, which are localized within the cytoplasm of bronchial epithelial cells. A modified delivery system that provides constant levels of drug at the prime site of action for a prolonged time can contribute to better control this disease [27]. Lipid nanoparticles such as NLC may increase cell uptake of the drug and may improve drug stability and these events may contribute to increased efficacy of the drug. By varying the composition of lipids, structure and size, they could offer a controlled and prolonged duration of the effect of the encapsulated drugs as well as a regional and cell-specific drug targeting within the airways. This kind of drug carriers presents many advantages [28],[29].

On the basis of the well-known capability of the NLC to solubilize adequate amounts of hydrophobic drugs, to pass through the mucus layer associated with bronchial inflammatory diseases escaping from pulmonary phagocytosis due to their bulky hydrophilic outer shell [11], the potential of NLC containing PEG chains as inhalatory delivery systems for FP, was investigated.

The present study describes the preparation of NLC loaded with FP and demonstrates their biocompatibility and their efficacy in controlling oxidative stress and innate immune responses in bronchial epithelial cells exposed to cigarette smoke extracts. The method used for preparing cigarette smoke extracts was previously validated [30],[31] and samples of CSE were filtered to remove bacteria and other macromolecules. These large particles in vivo do not reach the deeper airways because they are deposited in the oral cavity or in the upper respiratory tract. Furthermore, CSE 10% was selected because we showed that this concentration was not toxic for the cells and was able to significantly increase both ROS production [17] and TLR4 expression [21] in bronchial epithelial cells. In addition, this concentration as mentioned in a previous study [32] corresponds to exposures associated with smoking equivalent to two packs per day of cigarettes.

Lungs are unique because they have a large epithelial surface area that is at risk for oxidant-mediated attack. The tracheobronchial tree and the alveolar space are exposed to reactive oxidizing species in the form of inhaled airborne pollutants, tobacco smoke, and products of inflammation. The ROS play an integral role in the modulation of several physiological functions but can also be destructive if produced in excessive amounts. Cigarette smoke results in an imbalance between oxidants and antioxidants in favor of oxidants thus promoting increased oxidative stress [33]. Oxidative stress leads to cause oxidative lung damage including apoptosis [34], senescence and inflammation, all of which have been described in the airways of smokers with COPD [23]. Signal transducers and activators of transcription (STAT), nuclear factor-κB, and transcription factor activator protein-1 (AP-1) are activated in epithelial cells and inflammatory cells during oxidative stress [35]. Increased oxidative stress leads to reduced histone deacetylase (HDAC) activity contributing to the low response to corticosteroids [36]. Upon the exposure of cigarette smoke extracts in airway epithelial cells, the ubiquitin proteasome system is unable to cope with severely damaged proteins that accumulate in the cell in the form of insoluble polyubiquitinated aggregates [37]. In the present study we confirm that CSE increase ROS and here we provide data supporting the efficacy of FP when it is entrapped into NLC containing PEG reducing TLR4 expression any more than compared to NLC without PEG (see below) and thus suggesting an important role of the PEG nanoparticles in reducing the effects of CSE in the modulation of innate immunity responses. Although the majority of COPD cases can be directly related to smoking, only a quarter of smokers actually develop the disease. A potential reason for the disparity between smoking and COPD may involve an individual’s ability to mount a protective adaptive response to cigarette smoke. The GSH system belongs to enzymatic anti-oxidant systems. It is highly concentrated in the lung epithelial lining fluid and protects against many inhaled oxidants. The exposure to cigarette smoke in airway epithelial cells leads to the exhaustion of the pool of reduced GSH thus promoting a lack of antioxidant protection [38]. Under our experimental conditions in vitro CSE do not increase GSH levels as well as no effect on GSH levels were recorded by using free FP. On the contrary we provide data supporting the efficacy of FP-loaded NLC in increasing GSH levels in the presence of CSE.

Furthermore, the surface of the airway epithelium represents a battleground in which the host intercepts signals from pathogens and external insults and activates epithelial defences mainly represented by the innate host immune system. Innate immunity relies on pattern recognition receptors that recognize molecular structures common to many micro-organisms, such as lipopolysaccharides (LPS), and endogenous ligands such as heat shock proteins. TLR4 is a transmembrane protein that participates in the recognition of LPS and plays a crucial role in the activation of innate host immune system. LPS via TLR4 activation increases inflammatory responses and stimulates MUC5AC expression thus contributing to airway mucus hypersecretion [39]. TLR4 expression is increased in the bronchial epithelium of smokers [40] and cigarette smoke increases TLR4 expression in bronchial epithelial cells [21] and, via activation of the TLR4 signaling cascade, mediates MMP-1 expression [41] and increases IL-8 release [42]. All together these findings suggest that the over-expression and over-activation of TLR4 can contribute to many phenomena associated to COPD pathogenesis. In the present study we confirm that CSE increase TLR4 expression and demonstrate that FP-loaded NLC, but not unloaded FP, significantly reduce the effects of CSE in increasing TLR4 expression. Moreover, when FP is entrapped into the pegylated NLC is more effective than FP entrapped into the un-pegylated NLC (data not shown).

Conclusions

In the present study NLC based on a pegylated lipid have been prepared and tested as carrier of FP. Either empty and drug-loaded NLC showed negative ζ potential values and a mean size in the nanometer scale with low PDI values, which indicated a good dimensional homogeneity of particles such as make them suitable for inhalatory administration.

Excellent stability was also showed by this system during storing in the dried form at 4°C, being unchanged their size, PDI and ζ potential.

The release study showed that the investigated carrier had a great stability, being able to retain about 80% of initially entrapped corticosteroid even after 72 h. This result is in agreement with the hypothesis that this system, able to keep inside the drug, at the contact with airways mucosae, could improve drug cell uptake because FP-loaded NLC could enter the cells by endocytosis.

On the other hand a greater amount of FP was found into bronchial epithelial cells treated with FP-loaded NLC in comparison with that treated with free FP.

In vitro studies on 16-HBE cells revealed that neither unloaded FP nor FP-loaded NLC induced relevant numbers of necrotic or of apoptotic cells. In 16-HBE cells exposed to CSE, FP-loaded NLC were able to control oxidative stress increasing oxidant/anti-oxidant balance in favour of anti-oxidant responses and to limit innate immune responses, and were similar or superior to unloaded FP in these effects. These observations suggest the use of this system for the FP administration in inhalation therapies because of the ability of NLC to solubilize an adequate amount of the drug and to penetrate into the airway epithelial cells. These findings suggest a potential role of these nanocarriers in the therapy of chronic obstructive pulmonary diseases such as COPD.

Experimental

Materials and methods

Fluticasone propionate, sodium taurocholate, and acetonitrile for HPLC were purchased from Sigma Aldrich (Milan, Italy). Dichlorometane for HPLC was obtained from Merck (Germany). Compritol HD5 ATO (behenoyl polyoxyl-8 glycerides) was a gift sample from Gattefossè (France). Epikuron 200 (soybean lecithin) was a gift sample from Lucas Meyer Company (Germany). HPLC (UFLC-Prominence system, Shimadzu Instrument, Japan) was equipped with two pumps LC-20 AD, an UV-visible detector SPD-20 AV, an autosample SIL-20A HT and a column Gemini® C18 Phenomenex (250 mm, 5 μm particle size, 110 Å pores size).

Preparation of NLC

Pegylated NLC, empty or FP-loaded were prepared by the precipitation method [8]-[10]. Briefly, Compritol HD5 ATO (180 mg) was heated at 5–10°C above its melting point (m.p. 60°-67°C). For obtaining drug-loaded NLC, FP (10 mg; m.p. 272°-273°C) was added, under mechanical stirring, to the melted lipid phase. An ethanolic solution (2 ml) of Epikuron 200 (78.5 mg) was then added to the melted lipid phase containing FP and the resulting organic dispersion was dispersed into bidistilled water (100 ml) containing sodium taurocholate (177.4 mg) at 2-3°C and stirred by using an Ultraturrax T125 (IKA Labortechnik, Germany) at 13,500 rpm for 10 minutes. Finally, the colloidal aqueous dispersion of NLC was purified by exhaustive dialysis (dialysis tube with 12,000/14,000 Dalton cut-off (Spectra/Por®, USA) and freeze-dried. NLC samples (m.p. about 70°C) were stored at 4 ± 1°C for successive characterization.

Scanning Electron Microscopy (SEM) analysis

For morphological studies, freeze-dried samples were observed by using an ESEM FEI Quanta 200F scanning electron microscope. Samples were dusted on a double-sided adhesive tape, previously applied on a stainless steel stub. All samples were then sputter-coated with gold prior to microscopy examination.

Particle size analysis

The hydrodynamic diameter (z-average) and the width of distribution (polydispersity index, PDI) of the nanosuspensions were investigated by Photon Correlation Spectroscopy (PCS) by using a Zetasizer Nano ZS (Malvern Instrument Ltd, UK). The nanoparticles were diluted until the appropriate concentration and then the measurements performed at a temperature of 25°C, at a fixed angle of 173° (NIBS = non-invasive backscattering detection) in respect to the incident beam. Bidistilled water, isotonic aqueous solution (NaCl 0.9% w/w), and phosphate buffered saline solution (PBS) at pH 7.4 as suspending media were used. When the measurement was carried out in NaCl 0.9 wt%, the instrument setting conditions were: μ = 0.902, RI = 1.331; in PBS at pH 7.4, the setting conditions were: μ = 0.980, RI = 1.334. Results of light scattering experiments are given as the average values obtained using samples from three different batches. Each sample was measured in triplicate.

ζ potential measurements

The surface charge or ζ potential is considered as one of the benchmark of stability of a colloidal system. It indicates the degree of repulsion between similarly charged particles into a dispersion. For the nanoparticles, a high value of ζ potential will confer stability and the nanosuspensions will resist aggregation phenomena. When the ζ potential is low, attraction exceeds repulsion and the dispersions will flocculate.

The analysis was performed at a temperature of 25 ± 1°C using appropriately diluted samples in the same media used for size measurements. Instrument setting conditions were equal to those described above for size measurements.

Results of these experiments are given as the average values obtained using samples from three different batches. Each sample was measured in triplicate.

HPLC analysis

An adequate HPLC method was developed to reveal FP and to study its stability in PBS at pH 7.4, as well as Loading Capacity (LC%) and drug release profiles from drug-loaded NLC. The HPLC analysis was performed at room temperature by using the instrument described above. A column Gemini® C18 Phenomenex (above described) was used as stationary phase and a mixture of CH3CN/H2O 80/20 (v/v), with a flow rate of 0.8 ml/min, was used as mobile phase with an isocratic method. The drug peak was measured at wavelength of 239 nm and quantitatively determined by comparison with a standard curve obtained using FP organic solutions in a mixture of CH2Cl2:CH3CN 3:2 (v/v) at known concentrations (tr =7.03 min). The straight-line equation was: y = 4 • 105 × and the linear regression value was: r2 = 0.9993. The linearity of the method was studied in the range 0.30-1.20 μg/ml.

Drug loading and entrapment efficiency determination

Loading capacity (LC%) was determined by solubilizing the nanoparticles into an organic mixture (CH2Cl2:CH3CN 3:2 (v/v)), filtered with 0.45 μm PTFE syringe filters (Puradisc Whatman) and analyzed by the HPLC method described above. Drug loading capacity (DL%) was calculated as drug analyzed in the nanoparticles versus the total amount of the drug and the lipid added during preparation, according to the following equation, where W drug is the amount drug found inside nanoparticles and W NPS is the weight of drug-loaded nanoparticle:
D L % = W drug W N P s × 100
Results are given as the average values obtained using samples from three different batches and were expressed as the percentage of the FP amount contained in 100 mg of dried material (LC%). Moreover, entrapment efficiency (EE%) was determined using the HPLC method above described on purified NLC following their disruption with a mixture of CH2Cl2 and CH3CN (3:2 v/v). The encapsulated amount of FP was expressed dividing the found amount of FP and the total amount used to prepare the nanoparticles. The following equation was used to calculate the EE%, where W f is the amount drug found and W i is the initial amount of drug for the preparation:
E E % = W f W i × 100

Stability studies in PBS/ethanol

In order to obtain a release profile of FP from NLC under sink conditions, a mixture of PBS at pH 7.4 and ethanol 80:20 (v/v) was used. The term “sink conditions” refers to release conditions in which the volume of the buffer used is sufficient to dissolve all drug present into NLC. Such conditions are used to assure that the amount of drug released is not limited by the degree of solubility in the buffer or solvent used. In particular, lyophilized FP-loaded nanoparticles (5 mg) were suspended into the mixture release medium above described (5 ml) and transferred inside of a Spectra/Por® dialysis membrane that was immersed into the same pre-heated medium (25 ml) and incubated at 37 ± 0.1°C, under continuous stirring, in a Benchtop Incubator Orbital Shaker model 420 (Thermo-Scientific Instruments, CA).

At scheduled time, solution aliquots were taken out from the outside of the dialysis membrane and replaced with equal volumes of the fresh PBS/ethanol mixture. In order to determine the released FP amount, the drawn samples were filtered by 0.2 μm cellulose syringe filters (Millipore) and analyzed by HPLC, following the method above described. Profile releases were determined by comparing the amount of released drug as a function of incubation time with the total amount of drug loaded into the nanoparticles.

Moreover, in order to determine the amount of FP entrapped into residual NLC samples, the PBS suspension containing FP-loaded NLC was freeze-dried (FreeZone®Freeze Dry System, Labconco Corporation, Missouri, USA). Successively, an organic mixture (CH2Cl2:CH3CN 3:2 (v/v)), was added to lyophilized product, which was filtered through 0.2 μm (PTFE membrane) filters and analysed by HPLC, as reported above.

Finally, in order to determine the diffusion behaviour of the unloaded drug a control experiment was also performed. At this purpose, an appropriate amount of FP (equal to whom of FP-loaded nanoparticles) was dispersed in the mixture release medium (5 ml), placed inside a dialysis tube (MWCO 12,000-14,000 Da) and immersed into the same medium (25 ml). The amount of FP was detected by HPLC, as reported above.

Storage and colloidal stability evaluation

Both lyophilised empty and FP-loaded NLC were stored at 4°C for 4 and 10 months in the dark. The stability test was carried only at 4°C and not at room temperature because the NLC are prepared with lipids that must be stored at a temperature not exceeding 10°C so as reported in the data sheet of the supplier of Gattefosse Compritol HD5 ATO. After this period of storage, samples were dispersed in bidistilled water and characterized in terms of mean size, PDI, ζ potential and drug stability.

Preparation of cigarette smoke extracts (CSE)

Commercial cigarettes (Marlboro) were used in this study. Cigarette smoke solution was prepared as described previously [21]. Each cigarette was smoked for 5 min and two cigarettes were used per 20 ml of PBS to generate a CSE-PBS solution. The CSE solution was filtered through a 0.22 μm-pore filter to remove bacteria and large particles as previously described and standardised [30],[31]. The smoke solution was then adjusted to pH 7.4 and used within 30 minutes of preparation. This solution was considered to be 100% CSE and diluted to obtain the desired concentration in each experiments. The concentration of CSE was calculated spectrophotometrically measuring the optical density (OD) as previously described at the wavelength of 320 nm [21]. The presence of contaminating LPS on undiluted CSE was assessed by a commercially available kit (Cambrex Corporation, East Rutherfort, New Jersey, USA) and was below the detection limit of 0.1 EU/ml.

Stimulation of bronchial epithelial cell lines

The SV40 large T antigen-transformed 16-HBE cell line (16-HBE) was used for these studies [21]. 16-HBE is a cell line that retains the differentiated morphology and function of normal airway epithelial cells. 16-HBE was maintained in Eagle’s minimum essential medium (MEM) supplemented with 10% heat-inactivated (56°C, 30 min) fetal bovine serum (FBS), 1% MEM (non-essential amino acids, Euroclone), 2 mM L-glutamine and gentamicin 250 μg/ml. Cell cultures were maintained in a humidified atmosphere of 5% CO2 in air at 37°C. 16HBE were plated in 12-well plates. 70.000 cells in 1ml MEM 10% FBS were seeded for each well. At confluence 16-HBE cells were treated in 1 ml MEM 1% FBS in presence of CSE (10%) and with or without FP (10−8M), empty-NLC or FP-loaded NLC (10−8M) for 24 hrs. 1% FBS was used during cell stimulation to limit the basal activation of the cells due to serum proteins. Preliminary experiments aimed to identify the best time point (24, 48 and 72 hrs) as well as the best drug concentration (FP-loaded NLC 10−8M, 10−9M, 10−10M) were performed. At the end of stimulation, cells were collected for further evaluations.

Cell apoptosis by annexin V binding method

Cell apoptosis in the presence of free FP (10−8M), empty NLC and FP-loaded NLC (10−8M) was evaluated by staining with annexin V-fluorescein isothiocyanate and propidium iodide (PI) using a commercial kit (Bender MedSystem, Vienna, Austria) following the manufacturer's directions. Cells were analyzed using a FACS Calibur (Becton Dickinson, Mountain View, CA) analyzer equipped with an Argon ion Laser (Innova 70 Coherent) and Consort 32 computer support.

Analysis of intracellular reactive oxygen species (ROS)

Intracellular ROS were measured by the conversion of the non-fluorescent dichlorodihydrofluorescein diacetate (DCFH-DA; Sigma Aldrich, Milan, Italy) in a highly fluorescent compound, dichlorofluorescein (DCF), by monitoring the cellular esterase activity in the presence of peroxides. The ROS generation was assessed by uptake of 1 μM DCFH-DA, incubation for 10 min at room temperature in the dark, followed by flow cytometric analysis.

Measurement of cellular glutathione (GSH) content

Intracellular total GSH content was assessed in cell extracts as previously reported [43]. Briefly, cell extracts were prepared in 0.1 M potassium phosphate extraction buffer containing 0.6% (w/v) sulfosalicylic acid, 0.1% (v/v) Triton X-100, 5 mM EDTA. After harvesting and resuspension in extraction buffer, cells were sonicated in ice-cold water and underwent two cycles of freezing and thawing. Supernatants/extracts were collected by centrifugation and used for the following colorimetric assay: 10 μl of extracts were incubated in presence of 60 μl 0.6 mg/ml 5,5′-Dithiobis(2-nitrobenzoic acid) (DTNB) and 60 μl of 250 U/ml glutathione reductase for 30 seconds at room temperature; 50 μl of 0.6 mg/ml β-NADPH were added and formation of 2-nitro-5-thiobenzoic acid was immediately evaluated by measuring the absorbance at 412 nm in a microplate reader. Concentration of GSH in cell extracts was calculated using a standard curve, normalized by the total protein content and expressed as nmol/mg protein.

Expression of TLR4 in 16-HBE

The total TLR4 protein expression (inside the cells and on their surface) was assessed in permeabilized cells. For cell permeabilization, a commercial fix-perm cell permeabilization kit (Caltag Laboratories, Burlingame, CA, USA) was used. Cells were incubated in the dark (30 min, 4°C) with PE anti-human TLR4 monoclonal mouse antibody (eBioscence San Diego CA) and then evaluated by flow-cytometry (FACS Calibur).

Negative controls were performed using mouse immunoglobulins negative control (Dako). Data are expressed as percentage of positive cells.

Intracellular and extracellular concentrations of FP and NLC-FP

Cell cultures were maintained in a humidified atmosphere of 5% CO2 in air at 37 ± 1°C. Cell lines were cultured in the presence and in the absence of free FP (10−8M) and FP-loaded NLC (10−8M) for 24, 48 and 72 hrs. At the end of stimulation, cells and supernatants were collected for assessing the intracellular and extracellular content of FP by UV analysis. In particular, the supernatants were sucked from the wells and then collected by centrifugation at 1300 rmp for 10 min. Cells were detached from the wells by tripsin, washed with PBS and stored as dry pellet at −20°C. After several cycles of freezing and thawing, the cells as well as the previously recovered culture supernatants, were used for testing their FP content. FP was extracted both from the cells from the supernatants with an organic solution (4 ml) of CH2Cl2:CH3CN (3:2 v/v), filtered with 0.45 μm PTFE syringe filters (Puradisc Whatman) and the absorbance was determined by ultraviolet–visible (UV–vis) Spectrophotometer (UV-1800 Shimadzu, Kyoto, Japan) at 239 nm.

Statistics

Data are expressed as mean counts ± standard deviation. Comparison between different experimental conditions was evaluated by paired t test. P < 0.05 was accepted as statistically significant.

Abbreviations

AP-1: 

Activator protein-1

COPD: 

Chronic obstructive pulmonary disease

CSE: 

Cigarette smoke extracts

DCF: 

Dichlorofluorescein

DCFH-DA: 

Dichlorodihydrofluorescein diacetate

DL: 

Drug loading capacity

DTNB: 

5,5′-Dithiobis(2-nitrobenzoic acid)

EDTA: 

Ethylenedyaminetetraacetic acid

EE: 

Entrapment efficiency

FP: 

Fluticasone propionate

FBS: 

Fetal bovine serum

GSH: 

Glutathione

16-HBE: 

Human bronchial epithelial cell line

HDAC: 

Histone deacetylase

HPLC: 

High pressure liquid chromatography

ICS: 

Inhaled corticosteroids

LC: 

Loading capacity

LPS: 

Lipopolysaccharides

MEM: 

Eagle’s minimum essential medium (MEM)

NADPH: 

Nicotinamide adenine dinucleotide phosphate

NLC: 

Nanostructured lipid carriers

OD: 

Optical density

PBS: 

Phosphate buffered saline solution

PCD: 

Photon correlation spectroscopy

PDI: 

Polydispersity index

PI: 

Propidium iodide

ROS: 

Reactive oxygen species

SEM: 

Scanning electron microscopy

STAT: 

Signal transducers and activators of transcription

TLR4: 

Toll-like receptor 4

Declarations

Acknowledgements

Maria Luisa Bondì and Maria Ferraro contributed equally to this manuscript.

This work was supported by the Italian National Research Council.

Authors thanks also FFR 2012 of University of Palermo for funding.

Authors’ Affiliations

(1)
Istituto per lo Studio dei Materiali Nanostrutturati- U.O.S. di Palermo-Consiglio Nazionale delle Ricerche-via Ugo La Malfa
(2)
Istituto di Biomedicina e Immunologia Molecolare-Consiglio Nazionale delle Ricerche – via Ugo La Malfa
(3)
Laboratory of Biocompatible Polymers-Dipartimento di Scienze e Tecnologie, Biologiche, Chimiche e Farmaceutiche (STEBICEF), Università di Palermo -via Archirafi

References

  1. Chaturvedi NP, Solanki H: Pulmonary drug delivery system: review. Nit J Appl Pharm. 2013, 5: 7-10.Google Scholar
  2. Torchilin VP: Nanocarriers. Pharm Res. 2007, 24: 2333-2334. 10.1007/s11095-007-9463-5.View ArticleGoogle Scholar
  3. Terzano C, Allegra L, Alhaique F, Marianecci C, Carafa M: Non-phospholipid vesicles for pulmonary glucocorticoid delivery. Eur J Pharm Biopharm. 2005, 59: 57-62. 10.1016/j.ejpb.2004.06.010.View ArticleGoogle Scholar
  4. Buxton DB: Nanomedicine for the management of lung and blood diseases. Nanomedicine (Lond). 2009, 4: 331-339. 10.2217/nnm.09.8.View ArticleGoogle Scholar
  5. Nassimi M, Schleh C, Lauenstein HD, Hussein R, Hoymann HG, Koch W, Pohlmann G, Krug N, Sewald K, Rittinghausen S, Braun A, Müller-Goymannet C: A toxicological evaluation of inhaled solid lipid nanoparticles used as a potential drug delivery system for the lung. Eur J Pharm Biopharm. 2010, 75: 107-116. 10.1016/j.ejpb.2010.02.014.View ArticleGoogle Scholar
  6. Doktorovová S, Araújo J, Garcia ML, Rakovský E, Souto EB: Formulating fluticasone propionate in novel PEG-containing nanostructured lipid carriers (PEG-NLC). Colloids Surf B Biointerfaces. 2010, 75: 538-542. 10.1016/j.colsurfb.2009.09.033.View ArticleGoogle Scholar
  7. Üner M, Yener G: Importance of solid lipid nanoparticles (SLN) in various administration routes and future perspectives. Int J Nanomedicine. 2007, 2: 289-300.Google Scholar
  8. Bondì ML, Craparo EF, Giammona G, Cervello M, Azzolina A, Diana P, Martorana A, Cirrincione G: Nanostructured lipid carriers-containing anticancer compounds: preparation, characterization, and cytotoxicity studies. Drug Deliv. 2007, 14: 61-67. 10.1080/10717540600739914.View ArticleGoogle Scholar
  9. Bondì ML, Azzolina A, Craparo EF, Capuano G, Lampiasi N, Giammona G, Cervello M: Solid lipid nanoparticles (SLNs) containing nimesulide: preparation, characterization and in cytotoxicity studies. Curr Nanosci. 2009, 5: 39-44. 10.2174/157341309787314575.View ArticleGoogle Scholar
  10. Bondì ML, Craparo EF, Picone P, Di Carlo M, Di Gesù R, Capuano G, Giammona G: Curcumin entrapped into lipid nanosystems inhibits neuroblastoma cancer cell growth and activate Hsp70 protein. Curr Nanosci. 2010, 6: 439-445. 10.2174/157341310797575005.View ArticleGoogle Scholar
  11. Alonso MJ: Nanomedicine for overcoming biological barriers. Biomed Pharmacother. 2004, 58: 168-172. 10.1016/j.biopha.2004.01.007.View ArticleGoogle Scholar
  12. Tobío M, Gref R, Sánchez A, Langer R, Alonso MJ: Stealth PLA-PEG nanoparticles as protein carriers for nasal administration. Pharm Res. 1998, 15: 270-275. 10.1023/A:1011922819926.View ArticleGoogle Scholar
  13. Vila A, Sánchez A, Tobío M, Calvo P, Alonso MJ: Design of biodegradable particles for protein delivery. J Control Release. 2002, 78: 15-24. 10.1016/S0168-3659(01)00486-2.View ArticleGoogle Scholar
  14. Craparo EF, Teresi G, Bondì ML, Licciardi M, Cavallaro G: Phospholipid-polyaspartamide micelles for pulmonary delivery of corticosteroids. Int J Pharm. 2011, 406: 135-144. 10.1016/j.ijpharm.2010.12.024.View ArticleGoogle Scholar
  15. Pitarresi G, Casadei MA, Mandracchia D, Paolicelli P, Palumbo FS, Giammona G: Photocrosslinking of dextran and polyaspartamide derivatives: a combination suitable for colon-specific drug delivery. J Control Release. 2007, 119: 328-338. 10.1016/j.jconrel.2007.03.005.View ArticleGoogle Scholar
  16. Marianecci C, Paolino D, Celia C, Fresta M, Carafa M, Alhaique F: Non-ionic surfactant vesicles in pulmonary glucocorticoid delivery: characterization and interaction with human lung fibroblast. J Control Release. 2010, 147: 127-135. 10.1016/j.jconrel.2010.06.022.View ArticleGoogle Scholar
  17. Pace E, Ferraro M, Di Vincenzo S, Cipollina C, Gerbino S, Cigna D, Caputo V, Balsamo R, Lanata L, Gjomarkaj M: Comparative cytoprotective effects of carbocysteine and fluticasone propionate in cigarette smoke extract-stimulated bronchial epithelial cells. Cell Stress Chaperones. 2013, 18: 733-743. 10.1007/s12192-013-0424-0.View ArticleGoogle Scholar
  18. Faux SP, Tai T, Thorne D, Xu Y, Breheny D, Gaca M: The role of oxidative stress in the biological responses of lung epithelial cells to cigarette smoke. Biomarkers. 2009, 14: 90-96. 10.1080/13547500902965047.View ArticleGoogle Scholar
  19. Biswas SK, Rahman I: Environmental toxicity, redox signaling and lung inflammation: the role of glutathione. Mol Aspects Med. 2009, 30: 60-76. 10.1016/j.mam.2008.07.001.View ArticleGoogle Scholar
  20. Ghezzi P: Role of glutathione in immunity and inflammation in the lung. Int J Gen Med. 2011, 4: 105-113. 10.2147/IJGM.S15618.View ArticleGoogle Scholar
  21. Pace E, Ferraro M, Siena L, Melis M, Montalbano A, Johnson M, Bonsignore MR, Bonsignore G, Gjomarkaj M: Cigarette smoke increases TLR4 and modifies LPS mediated responses in airway epithelial cells. Immunology. 2008, 124: 401-411. 10.1111/j.1365-2567.2007.02788.x.View ArticleGoogle Scholar
  22. Pace E, Ferraro M, Uasuf CG, Giarratano A, La Grutta S, Liotta G, Johnson M, Gjomarkaj M: Cilomilast counteracts the effects of cigarette smoke in airway epithelial cells. Cell Immunol. 2011, 268: 47-53. 10.1016/j.cellimm.2011.02.004.View ArticleGoogle Scholar
  23. Olsson B, Bondesson E, Borgström L, Edsbäcker S, Eirefelt S, Ekelund K, Gustavsson L, Hegelund-Myrbäck T: Pulmonary Drug Metabolism, Clearance, and Absorption. Controlled Pulmonary Drug Delivery. Edited by: Smith HDC, Hickey AJ. 2011, Springer, Germany, 21-50. 10.1007/978-1-4419-9745-6_2.View ArticleGoogle Scholar
  24. Brusselle GG, Joos GF, Bracke KR: New insights into the immunology of chronic obstructive pulmonary disease. Lancet. 2011, 378: 1015-1026. 10.1016/S0140-6736(11)60988-4.View ArticleGoogle Scholar
  25. Kelsen SG, Duan X, Ji R, Perez O, Liu C, Merali S: Cigarette smoke induces an unfolded protein response in the human lung: a proteomic approach. Am J Respir Cell Mol Biol. 2008, 38: 541-550. 10.1165/rcmb.2007-0221OC.View ArticleGoogle Scholar
  26. Smola M, Vandamme T, Sokolowski A: Nanocarriers as pulmonary drug delivery systems to treat and to diagnose respiratory and non respiratory diseases. Int J Nanomedicine. 2008, 3: 1-19. 10.2217/17435889.3.1.1.View ArticleGoogle Scholar
  27. Rouse JJ, Whateley TL, Thomas M, Eccleston GM: Controlled drug delivery to the lung: influence of hyaluronic acid solution conformation on its adsorption to hydrophobic drug particles. Int J Pharm. 2007, 330: 175-182. 10.1016/j.ijpharm.2006.11.066.View ArticleGoogle Scholar
  28. Jaspart S, Bertholet P, Piel G, Dogné JM, Delattre L, Evrard B: Solid lipid microparticles as a sustained release system for pulmonary drug delivery. Eur J Pharm Biopharm. 2007, 5: 47-56. 10.1016/j.ejpb.2006.07.006.View ArticleGoogle Scholar
  29. Bondì ML, Montana G, Craparo EF, Di Gesù R, Giammona G, Bonura A, Colombo P: Lipid nanoparticles as delivery vehicles for the Parietaria judaica major allergen Par j 2. Int J Nanomedicine. 2011, 6: 2953-2962. 10.2147/IJN.S24264.View ArticleGoogle Scholar
  30. Liu X, Conner H, Kobayashi T, Kim H, Wen F, Abe S, Fang Q, Wang X, Hashimoto M, Bitterman P, Rennardt SI: Cigarette smoke extract induces DNA damage but not apoptosis in human bronchial epithelial cells. Am J Respir Cell Mol Biol. 2005, 33: 121-129. 10.1165/rcmb.2003-0341OC.View ArticleGoogle Scholar
  31. Moretto N, Facchinetti F, Southworth T, Civelli M, Singh D: Patacchini R: α, β-Unsaturated aldehydes contained in cigarette smoke elicit IL-8 release in pulmonary cells through mitogen-activated protein kinases. Am J Physiol Lung Cell Mol Physiol. 2009, 296: 839-848. 10.1152/ajplung.90570.2008.View ArticleGoogle Scholar
  32. Su Y, Han W, Giraldo C, De Li Y, Block ER: Effect of cigarette smoke extract on nitric oxide synthase in pulmonary artery endothelial cells. Am J Respir Cell Mol Biol. 1998, 19: 819-825. 10.1165/ajrcmb.19.5.3091.View ArticleGoogle Scholar
  33. MacNee W: Oxidants/antioxidants and COPD. Chest. 2000, 117: 303-317. 10.1378/chest.117.5_suppl_1.303S-a.View ArticleGoogle Scholar
  34. Baglole CJ, Bushinsky SM, Garcia TM, Kode A, Rahman I, Sime PJ, Phipps RP: Differential induction of apoptosis by cigarette smoke extract in primary human lung fibroblast strains: implications for emphysema. Am J Physiol Lung Cell Mol Physiol. 2006, 291: 19-29. 10.1152/ajplung.00306.2005.View ArticleGoogle Scholar
  35. Rahman I, MacNee W: Oxidative stress and regulation of glutathione in lung inflammation. Eur Respir J. 2000, 16: 534-544. 10.1034/j.1399-3003.2000.016003534.x.View ArticleGoogle Scholar
  36. Barnes PJ: Theophylline for COPD. Thorax. 2006, 61: 742-744. 10.1136/thx.2006.061002.View ArticleGoogle Scholar
  37. Luppi F, Aarbiou J, van Wetering S, Rahman I, de Boer WI, Rabe KF, Hiemstra PS: Effects of cigarette smoke condensate on proliferation and wound closure of bronchial epithelial cells in vitro: role of glutathione. Respir Res. 2005, 6: 140-151. 10.1186/1465-9921-6-140.View ArticleGoogle Scholar
  38. Van der Toorn M, Smit-de Vries MP, Slebos DJ, de Bruin HG, Abello N, Van Oosterhout AJ, Bischoff R, Kauffman HF: Cigarette smoke irreversibly modifies glutathione in airway epithelial cells. Am J Physiol Lung Cell Mol Physiol. 2007, 293: 1156-1162. 10.1152/ajplung.00081.2007.View ArticleGoogle Scholar
  39. Chen L, Wang T, Zhang JY, Zhang SF, Liu DS, Xu D, Wang X, Chen YJ, Wen FQ: Toll-like receptor 4 relates to lipopolysaccharide-induced mucus hypersecretion in rat airway. Arch Med Res. 2009, 40: 10-17. 10.1016/j.arcmed.2008.10.005.View ArticleGoogle Scholar
  40. Pace E, Ferraro M, Minervini MI, Vitulo P, Pipitone L, Chiappara G, Siena L, Montalbano AM, Johnson M, Gjomarkaj M: Beta defensin-2 is reduced in central but not in distal airways of smoker COPD patients. PLoS One. 2012, 7: e33601-10.1371/journal.pone.0033601.View ArticleGoogle Scholar
  41. Geraghty P, Dabo AJ, D’Armiento J: TLR4 protein contributes to cigarette smoke-induced matrix metalloproteinase-1 (MMP-1) expression in chronic obstructive pulmonary disease. J Biol Chem. 2011, 286: 30211-30218. 10.1074/jbc.M111.238824.View ArticleGoogle Scholar
  42. Mortaz E, Henricks PA, Kraneveld AD, Givi ME, Garssen J, Folkerts G: Cigarette smoke induces the release of CXCL-8 from human bronchial epithelial cells via TLRs and induction of the inflammasome. Biochim Biophys Acta. 1812, 2011: 1104-1110.Google Scholar
  43. Rahman I, Kode A, Biswas SK: Assay for quantitative determination of glutathione and glutathione disulfide levels using enzymatic recycling method. Nat Protoc. 2006, 1: 3159-3165. 10.1038/nprot.2006.378.View ArticleGoogle Scholar

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© Bondì et al.; licensee BioMed Central. 2014

This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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