Resveratrol Impairs the Release of Steroid-resistant Cytokines from Bacterial Endotoxin-Exposed Alveolar Macrophages in Chronic Obstructive Pulmonary Disease

Authors

  • Jürgen Knobloch,

    1. Medical Clinic III for Pneumology, Allergology and Sleep Medicine, University Hospital Bergmannsheil, Bochum, Germany
    2. Department of Pneumology, Clinic III for Internal Medicine, University of Cologne, Cologne, Germany
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  • Haitham Hag,

    1. Department of Pneumology, Clinic III for Internal Medicine, University of Cologne, Cologne, Germany
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  • David Jungck,

    1. Medical Clinic III for Pneumology, Allergology and Sleep Medicine, University Hospital Bergmannsheil, Bochum, Germany
    2. Department of Pneumology, Clinic III for Internal Medicine, University of Cologne, Cologne, Germany
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  • Katja Urban,

    1. Department of Pneumology, Clinic III for Internal Medicine, University of Cologne, Cologne, Germany
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  • Andrea Koch

    1. Medical Clinic III for Pneumology, Allergology and Sleep Medicine, University Hospital Bergmannsheil, Bochum, Germany
    2. Department of Pneumology, Clinic III for Internal Medicine, University of Cologne, Cologne, Germany
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Author for correspondence: Andrea Koch, Medical Clinic III for Pneumology, Allergology and Sleep Medicine, University Hospital Bergmannsheil, Bürkle-de-la-Camp Platz 1, D-44789 Bochum, Germany (fax +49 234 302 6420, e-mail andrea.koch@bergmannsheil.de).

Abstract

Abstract:  Airway inflammation in chronic obstructive pulmonary disease (COPD) is believed to be insensitive to corticosteroids. However, corticosteroids are recommended in COPD (GOLD stages III, IV) with frequent exacerbations. Resveratrol has anti-inflammatory properties and could be an alternative to corticosteroids in COPD therapy. We investigated the effect of dexamethasone versus resveratrol on the release of COPD-related inflammatory mediators (IL-6, IL-8, GM-CSF and MCP-1) and matrix-metalloprotease-9 (MMP-9) from alveolar macrophages exposed to gram-negative bacterial endotoxin (lipopolysaccharide, LPS). We compared never-smokers, current smokers without airway obstruction and current smokers with COPD. The cytokines and MMP-9 were measured in cell culture supernatants with ELISA. The release of IL-8 and MMP-9 from LPS-exposed alveolar macrophages was increased in COPD, the release of GM-CSF and IL-6 was decreased in COPD and the release of MCP-1 was without differences between the cohorts. Dexamethasone impaired the release of all cytokines and MMP-9 from LPS-exposed alveolar macrophages of all cohorts, but for IL-8 and GM-CSF this effect was reduced in COPD. In alveolar macrophages of COPD, there was an almost complete reduction in IL-6 release but only a partial reduction in IL-8, GM-CSF, MCP-1 and MMP-9 release demonstrating a partial corticosteroid-insensitivity. In contrast, resveratrol almost completely reduced the release of all cytokines and MMP-9 without significant differences between the cohorts. Our data provide evidence for a corticosteroid resistance of alveolar macrophage-dependent inflammatory responses induced by gram-negative bacteria in COPD and thus question the utility of corticosteroids in COPD therapy. Instead, resveratrol may prove an alternative.

Chronic obstructive pulmonary disease (COPD) is one of the leading causes of death worldwide with mortality rates continuing to rise. COPD is primarily characterized by irreversible airflow limitation as a result of chronic airway inflammation with cigarette smoking as the major risk factor. Airway inflammation in stable COPD is perpetuated by the release of inflammatory mediators from immunoreactive cells, such as alveolar macrophages and airway smooth muscle cells [1–3]. Amongst others, interleukin-6 (IL-6), IL-8, granulocyte-macrophage colony-stimulating factor (GM-CSF) and monocyte chemotactic protein (MCP-1/CCL2) are of particular relevance in COPD. Matrix metalloproteases such as MMP-9 contribute to inflammation and tissue destruction in COPD and thus to disease progression [1–3]. The release of these factors from immunoreactive cells is induced by cigarette smoke and inflammatory cytokines like IL-1β and tumour necrosis factor α (TNFα), both of which are up-regulated in COPD [2–4]. Immunogenic bacterial components like lipopolysaccharide (LPS), an endotoxin formed in gram-negative bacteria, can additionally stimulate alveolar macrophages to release inflammatory mediators important in COPD [5,6]. Thus, infection with gram-negative bacteria enhances airway inflammation resulting in accelerated and irreversible disease progression (COPD exacerbation) [7].

Corticosteroids efficiently reduce airway inflammation in allergic asthma. However, airway inflammation in COPD has been shown to be insensitive to corticosteroids [8]. On the cellular level, a resistance of the release of inflammatory mediators to corticosteroids has been demonstrated for alveolar macrophages and airway smooth muscle cells exposed to cytokines and/or cigarette smoke [3,4]. According to the current GOLD (Global Initiative for Chronic Obstructive Lung Disease) treatment guidelines, corticosteroids are not applied in milder COPD but, notably, in advanced COPD with frequent exacerbations to reduce airway inflammation (http://www.goldcopd.com). This implies that the inflammatory processes induced by infection of the airways, e.g., with bacteria are not corticosteroid-resistant in COPD. However, this hypothesis and, consequently, the utility of corticosteroids in severe stages of COPD is under discussion – particularly as a recent clinical trial, the TORCH study, reported serious side effects such as an increased risk of pneumonia [9,10]. Thus, studies investigating the corticosteroid sensitivity of inflammatory mediator release in response to immunogenic bacterial compounds in COPD are urgently required to support (or challenge) the utility of corticosteroids in COPD.

The problem of corticosteroid resistance also raises the question of alternative therapeutic approaches. Resveratrol (3,5,4′-trihydroxystilbene), a polyphenolic molecule and compound of red wine extract, exhibits anti-oxidative and anti-inflammatory properties and is discussed as an alternative in COPD therapy [3,11–14].

Here, we investigated whether cigarette smoking and/or COPD pathogenesis modulate the LPS-induced release of IL-6, IL-8, GM-CSF, MCP-1 and MMP-9 from alveolar macrophages. We investigated the reductive effect of dexamethasone, a model corticosteroid, on LPS-induced cytokine/MMP-9 release in comparison with resveratrol in never-smokers (NS), current smokers without airway obstruction (S) and current smokers with COPD.

Material and Methods

Power calculation and study patients.  Power calculation (with the SAS program fpower) was based on the following primary outcome: differences in the effect of dexamethasone at 10−6 M (represents a medium concentration in terms of clinical relevance [3]) on cytokine release from LPS-exposed alveolar macrophages between NS and current smokers (S, >10 pack years), both without respiratory symptoms or airflow limitation, and current smokers with COPD. It was estimated by preliminary experiments with n = 4 patients of each group that the sample size to achieve a power of 1-β = 0.8 for a one-way anova test at α = 0.05 would be n = 12 patients in each group for GM-CSF (n < 12 for IL-8). Thus, the study population consisted of 12 NS, 12 S and 12 COPD (GOLD stage II) (table 1). None of the patients received oral or inhaled corticosteroids or immunosuppressive treatment and none reported any other serious illness or acute viral disease during the 2 months preceding the test or had tuberculosis or parasite infections or histories of allergies or asthma. COPD was diagnosed according to the criteria recommended by the National Institutes of Health as described before [15]. The study was approved by the Ethics Committee of the University of Cologne, Germany.

Table 1. 
Demographics of patients.
 NSSCOPD
  1. NS, non-smoker; S, current smoker without COPD (≥10 py); FEV1: forced expiratory volume in 1 sec.; FVC: forced vital capacity; COPD, chronic obstructive pulmonary disease.

  2. *p < 0.001 versus NS and S.

  3. The difference in pack years between S and COPD is not statistically significant (p = 0.79).

  4. COPD patients were all GOLD stage II.

N121212
Age (year)65.8 ± 3.361.3 ± 2.367.4 ± 3.1
Gender (m:f)10:27:59:3
FEV1 (% pred.)101.0 ± 4.095.3 ± 4.467.4 ± 3.3*
FEV1/FVC (%)87.5 ± 2.087.5 ± 2.460.9 ± 1.4*
FVC (% pred.)89.0 ± 4.092.7 ± 4.582.7 ± 4.5
Pack years52.9 ± 12.048.8 ± 8.2

Fibreoptic bronchoscopy.  Patients were sedated with intravenous midazolam (5–10 mg). Oxygen (3 l/min.) was administered via nasal prongs, and oxygen saturation was monitored by digital pulse oximetry. Using local anaesthesia with lidocaine [2% weight (w)/volume (v)] applied to the upper airways and larynx, a fibreoptic bronchoscope (Olympus BF10; Olympus, Hamburg, Germany) was passed through the nasal passages into the trachea. The bronchoscope was wedged in the right middle lobe, and four 60-ml aliquots of pre-warmed sterile 0.9% NaCl were instilled. This solution was aspirated through the bronchoscope, collected in pre-chilled bottles and stored on ice. Bronchoalveolar lavage fluid recovery was 150–180 ml.

Isolation of alveolar macrophages from bronchoalveolar lavage fluid.  Isolation of alveolar macrophages from bronchoalveolar lavage fluid was performed as described before [5,6]. Briefly, the bronchoalveolar lavage fluid was filtered through sterile gauze to exclude mucus plugs and then centrifuged for 10 min. at 1000 × g at 4°C. The cell pellet was washed once in 50 ml Ca2+/Mg2+-free Hank’s balanced salt solution (HBSS; Sigma, Munich, Germany). Alveolar macrophages were counted using a haemocytometer (Neubauer chamber) slide and counterstaining with Kimura. Viability was assessed by trypan blue exclusion. Alveolar macrophages were resuspended in Roswell Park Memorial Institute (RPMI) 1640 medium (Sigma) supplemented with 10% (v/v) heat-inactivated foetal calf serum (Sigma), 2 mM l-glutamine (Sigma), 100 U/ml penicillin (Sigma) and 100 μg/ml streptomycin (Sigma). Alveolar macrophages were plated at 1 × 106 cells/well on to 12-well plates and allowed to adhere overnight in a humidified atmosphere containing 5% CO2 at 37°C. Non-adherent cells were removed by washing with RPMI 1640, leaving the adherent alveolar macrophages, which were >99% pure as assessed by staining and morphological analysis.

Cell culture.  Alveolar macrophages were cultured in medium and under the conditions described above. After 12 hr, cells were stimulated with LPS (S-form of Salmonella minnesota; without any protein or DNA contaminants with agonistic toll-like receptor activity; Alexis, EnzoLifeSciences GmbH cat#-581-020-L002) at 1 μg/ml for 24 hr in fresh medium at 1 × 106 cells/ml. Dexamethasone or resveratrol (both from Sigma) were added 60 min. before stimulation with LPS. Cell viability (≥85%) was determined by trypan blue dye exclusion [5,6].

ELISA (enzyme-linked immunosorbent assay).  Concentrations of IL-6, IL-8, GM-CSF, MCP-1 and MMP-9 in culture supernatants were measured by ELISA using commercially available kits (cat#: DY206, DY208, DY215, DY279, DY911; R&D Systems, Minneapolis, MN, USA) according to standard protocols as described before [16]. Resveratrol has previously been reported not to affect cytokine ELISAs [12].

Results

IL-8.

Baseline release of IL-8 from alveolar macrophages cultivated for 24 hr was 93.9 ± 37.7 ng/ml (mean ± S.E.M.) in NS, 89.4 ± 27.8 ng/ml in S, and 85.1 ± 28.8 ng/ml in COPD without significant differences between the cohorts (fig. 1A). LPS-induced IL-8 release was increased in COPD (18 times increase above baseline up to 1524 ± 207 ng/ml) compared with S (13 times; 1168 ± 155 ng/ml) and was also increased in S compared with NS (8.5 times; 802 ± 90.9 ng/ml) (fig. 1A). As the cohorts S and COPD were comprised exclusively of current smokers, these data demonstrate that LPS-induced IL-8 release is not only enhanced by cigarette smoking but also by other factors related to COPD pathogenesis.

Figure 1.

 Effects of dexamethasone and resveratrol on LPS-induced IL-8, GM-CSF, IL-6, MCP-1 and MMP-9 release from alveolar macrophages. Alveolar macrophages were stimulated with LPS at 1 μg/ml for 24 hr. Dexamethasone (middle column) or resveratrol (right column) was added at the indicated concentrations to the medium 1 hr before LPS stimulation. After incubation, the amounts of indicated soluble factors in supernatants were determined by ELISA. Data are presented as mean ± S.E.M. Values in the middle and right column express the per cent decrease related to cells stimulated with LPS alone (LPSmax). Concentration–response curves were created by performing non-linear regression sigmoid curve fit analyses with no constant parameter; r2, goodness of fit. EC50, logEC50 and Emax values are given in table 2. Note that in C and F Emax values are below −100% in all cohorts and in O values are below −100% in never-smokers (NS) and chronic obstructive pulmonary disease (COPD). Thus, these concentration–response curves were re-calculated with a constant bottom value of −100% (not shown) for determining EC50, logEC50 and Emax values (see table 2). One-way anova: p < 0.0001 (A–I, K–O), p = 0.0081 (J). Post hoc Bonferroni–Holm tests in the left column: *p < 0.05; **p < 0.01; ***p < 0.001. Post hoc Bonferroni–Holm tests in middle and right columns were performed to analyse the differences of drug effects between the cohorts at the same concentrations: NS versus COPD, *p < 0.05; **p < 0.01; ***p < 0.001; NS versus S, #p < 0.05; S versus COPD, +p < 0.05; +++p < 0.001.

Dexamethasone concentration dependently reduced IL-8 release from LPS-exposed alveolar macrophages down to baseline in NS. This effect was reduced in S compared with NS and also reduced in COPD compared with S (fig. 1B, table 2). In contrast, resveratrol concentration dependently reduced IL-8 release from LPS-exposed alveolar macrophages almost down to baseline without differences between the three cohorts (fig. 1C, table 2).

Table 2. 
Emax and EC50 values for the effects of dexamethasone and resveratrol on LPS-induced cytokine release from alveolar macrophages.
CytokineCohortEC50 (M)LogEC50 ± S.E.Emax ± S.E.M. (% reduction)EC50 (M)LogEC50 ± S.E.Emax ± S.E.M. (% reduction)
DexamethasoneDexamethasoneDexamethasoneResveratrolResveratrolResveratrol
  1. Values were determined from concentration–response curves in fig. 1. Emax values for resveratrol effects on IL-8 and GM-CSF in all cohorts and on MMP-9 in NS and COPD were below −100% (100% reduction) by calculating sigmoid concentration–response curves with variable bottom values (see fig. 1C, F, O). Thus, these curves were re-calculated for determining Emax and EC50 values with constant bottom values of −100% (graphs not shown). NS, non-smokers; S, smokers; S.E., standard error; S.E.M., standard error of the mean; COPD, chronic obstructive pulmonary disease.

IL-8NS1.7 × 10−8−7.770 ± 0.3437102 ± 96.3 × 10−6−5.200 ± 0.7051100
S3.7 × 10−8−7.437 ± 0.804385 ± 173.4 × 10−5−4.440 ± 0.3571100
COPD3.1 × 10−8−7.515 ± 0.626960 ± 104.0 × 10−5−4.406 ± 0.3732100
GM-CSFNS3.9 × 10−9−8.405 ± 0.313990 ± 6.14.0 × 10−6−5.400 ± 0.3254100
S2.3 × 10−9−8.634 ± 0.137390 ± 2.16.5 × 10−6−5.189 ± 0.1320100
COPD2.7 × 10−9−8.565 ± 0.213369 ± 3.03.9 × 10−6−5.409 ± 0.4481100
IL-6NS5.0 × 10−6−5.303 ± 1.4600100 ± 511.8 × 10−6−5.750 ± 0.352993 ± 13
S3.3 × 10−7−6.483 ± 0.253088 ± 9.61.5 × 10−6−5.839 ± 0.245595 ± 8.5
COPD3.6 × 10−7−6.443 ± 0.303494 ± 131.3 × 10−6−5.872 ± 0.304592 ± 10
MCP-1NS3.0 × 10−7−6.519 ± 0.501558 ± 122.7 × 10−6−5.567 ± 0.218489 ± 9.3
S5.8 × 10−7−6.240 ± 0.362867 ± 101.8 × 10−6−5.749 ± 0.188388 ± 6.9
COPD2.5 × 10−7−6.608 ± 0.193356 ± 4.47.1 × 10−6−5.149 ± 0.233494 ± 11
MMP-9NS7.9 × 10−8−7.101 ± 0.398258 ± 7.42.8 × 10−6−5.548 ± 0.2593100
S2.0 × 10−8−7.704 ± 0.317455 ± 4.73.9 × 10−6−5.407 ± 0.415291 ± 17
COPD6.5 × 10−8−7.191 ± 0.658071 ± 158.4 × 10−7−6.076 ± 0.4781100

GM-CSF.

Baseline release of GM-CSF from alveolar macrophages cultivated for 24 hr was 30.6 ± 6.3 pg/ml in NS, 24.4 ± 3.6 pg/ml in S, and 17.5 ± 1.7 pg/ml in COPD without significant differences between the cohorts (fig. 1D). LPS-induced GM-CSF release was reduced in S (105 times increase above baseline up to 2.55 ± 0.43 ng/ml) and COPD (102 times; 1.78 ± 0.22 ng/ml) compared with NS (130 times; 3.97 ± 0.73 ng/ml) (fig. 1D). This demonstrates that cigarette smoking impairs LPS-induced GM-CSF release.

Dexamethasone concentration dependently reduced GM-CSF release from LPS-exposed alveolar macrophages almost down to baseline in NS and S; however, this effect was reduced in COPD (fig. 1E, table 2). In contrast, resveratrol concentration dependently reduced GM-CSF release from LPS-exposed alveolar macrophages down to baseline without differences between the three cohorts (fig. 1F, table 2).

IL-6.

Baseline release of IL-6 from alveolar macrophages cultivated for 24 hr was 1547 ± 427 pg/ml in NS, 870 ± 242 pg/ml in S and 377 ± 140 pg/ml in COPD without significant differences between the cohorts (fig. 1G). The relative effect of LPS on IL-6 release was increased in COPD (21 times increase above baseline) compared with S (12 times) and NS (9.4 times). However, the total amount of IL-6 measured in culture supernatants from LPS-exposed alveolar macrophages was significantly reduced in COPD (7.84 ± 0.87 ng/ml) compared with NS (14.5 ± 3.23 ng/ml) and without significant difference between S (10.6 ± 1.32 ng/ml) and COPD or NS and S, respectively (fig. 1G). This demonstrates that the COPD pathogenesis modulates LPS-induced GM-CSF release.

Dexamethasone as well as resveratrol both concentration dependently reduced IL-6 release from LPS-exposed alveolar macrophages almost down to baseline in all cohorts without differences (fig. 1H, I, table 2).

MCP-1.

Baseline release of MCP-1 from alveolar macrophages cultivated for 24 hr was 805 ± 172 pg/ml in NS, 773 ± 291 pg/ml in S and 789 ± 238 pg/ml in COPD without significant differences between the cohorts (fig. 1J). LPS-induced MCP-1 release was without differences between NS (2.3 times increase above baseline up to 1.88 ± 0.37 ng/ml), S (3.1 times; 2.42 ± 0.72 ng/ml) and COPD (3.4 times; 2.68 ± 0.76 ng/ml).

Dexamethasone partially reduced MCP-1 release from LPS-exposed alveolar macrophages without differences between the cohorts. (fig. 1K, table 2). In contrast, resveratrol reduced MCP-1 release from LPS-exposed alveolar macrophages almost completely without differences between the three cohorts (fig. 1L, table 2).

MMP-9.

Baseline release of MMP-9 from alveolar macrophages cultivated for 24 hr was 25.8 ± 4.0 ng/ml in NS, 22.8 ± 3.8 ng/ml in S and 35.6 ± 7.6 ng/ml in COPD without significant differences between the cohorts (fig. 1M). MMP-9 release from LPS-exposed alveolar macrophages was increased in COPD (6.4 times increase above baseline up to 229 ± 42 ng/ml) compared with S (5.7 times; 131 ± 25 ng/ml) and NS (3.4 times; 87.9 ± 13 ng/ml) (fig. 1M). This demonstrates that factors of COPD pathogenesis independent from direct effects of cigarette smoking enhance LPS-induced MMP-9 release.

Dexamethasone partially reduced MMP-9 release from LPS-exposed alveolar macrophages without differences between the cohorts. (fig. 1N, table 2). In contrast, resveratrol reduced MMP-9 release from LPS-exposed alveolar macrophages almost completely without differences between the three cohorts (fig. 1O, table 2).

Discussion

Total levels of IL-6, IL-8, GM-CSF, MCP-1 and MMP-9 are increased in the airways of patients with stable or exacerbated COPD [2,17]. Our data show that alveolar macrophage activation by LPS contributes to the increase in IL-8 and MMP-9 but not to the increase in IL-6, GM-CSF and MCP-1 levels in COPD. For MMP-9, this is in agreement with a previous study [18]. These data might be of particular relevance for bacteria-induced COPD exacerbations, as they suggest an increase in IL-8- and MMP-9-dependent inflammation and tissue destruction upon infection with gram-negative bacteria.

Nonetheless, therapeutic reduction not only in IL-8 and MMP-9 but also in the other inflammatory mediators measured in our study is believed to be of benefit in stable and exacerbated COPD [2,4,12,17]. Thus, we also take the effects of resveratrol and dexamethasone on IL-6, GM-CSF and MCP-1 into consideration. We have shown that the release of all measured inflammatory mediators from alveolar macrophages can be reduced by corticosteroids. However, with the exception of IL-6, dexamethasone is unable to completely abolish the release of these mediators from alveolar macrophages of COPD. This demonstrates that LPS-induced IL-8, GM-CSF, MCP-1 and MMP-9 release from alveolar macrophages is partially resistant to corticosteroids in COPD. For MCP-1 and MMP-9, this partial corticosteroid resistance is independent from smoking and COPD as dexamethasone is also unable to completely reduce the release of these factors in non-smokers and smokers without airway obstruction. Disease-independent differences in the corticosteroid sensitivity of inflammatory genes have previously been postulated to be based on differences in the impact of corticosteroid-sensitive and -insensitive transcription mechanisms [19]. For example, LPS-regulated cytokine gene transcription in alveolar macrophages usually depends on nuclear factor-κB (NF-κB) signaling, whose activity is sensitive to corticosteroids, and on the mitogen-activated protein kinases (MAPK)/activator protein 1 (AP-1) pathway, which has been postulated to be insensitive to corticosteroids [19]. Thus, the level of corticosteroid resistance of a specific cytokine might depend on the ratio of corticosteroid-insensitive and -sensitive signaling mechanisms required for the full transcriptional activation of its gene. Notably, the partial corticosteroid resistance of IL-8 and GM-CSF release from alveolar macrophages is characteristic of COPD and (in the case of IL-8) of smokers, as dexamethasone completely abolishes the release of these cytokines from alveolar macrophages of healthy non-smokers. Mechanistically, this can be explained by the decreased expression and activity of histone deacetylases in alveolar macrophages of COPD caused by cigarette smoke-induced oxidative and nitrosative stress, as histone deacetylase activity is required for the anti-inflammatory properties of corticosteroids [1].

As introduced above, the effectiveness of corticosteroids in severe and exacerbated COPD remains controversial. Randomized controlled trials, meta-analyses, medication withdrawal studies and observational reports have examined this question, with mixed results [10]. Moreover, post hoc analyses of the TORCH study, a large randomized controlled trial, suggest an increased risk of pneumonia after corticosteroid use in COPD [9]. Thus, the anti-inflammatory effects of corticosteroids in severe and exacerbated COPD have to be clearly proven in the future for the risk of such side effects to be acceptable. Our data demonstrate that the bacterial endotoxin-induced release of COPD-related inflammatory mediators is partially insensitive to corticosteroids. Thus, they provide a strong argument against the use of corticosteroids in COPD exacerbated by infection with gram-negative bacteria.

As resveratrol but not dexamethasone reduced LPS-induced IL-8, GM-CSF, MCP-1 and MMP-9 release from alveolar macrophages of COPD down to or down below baseline, resveratrol could be superior to corticosteroids in reducing airway inflammation in COPD exacerbated by infection with gram-negative bacteria. As resveratrol is also more efficient than dexamethasone in the reduction in IL-8 and GM-CSF release from IL-1β-activated alveolar macrophages and TNFα-activated human airway smooth muscle cells of COPD, it might also be useful in the therapy of stable COPD [3,12]. In contrast to corticosteroids (see above), resveratrol cannot only block NF-κB but also MAPK signaling [3,20]. This could explain the improved efficiency of resveratrol to reduce cytokine release from alveolar macrophages.

Notably, the anti-inflammatory effects of resveratrol require relatively high concentrations in vitro, and plasma concentrations of free resveratrol after a single administration are comparatively low in human beings, indicating rapid metabolism and limited bioavailability [21]. However, free resveratrol plasma levels might be seriously underestimated because of large amounts potentially contained in the cellular fraction. This has not been assessed in the corresponding studies. Moreover, repeated resveratrol administration increases half-life and plasma concentration in human beings and might decrease its effective dose for anti-inflammatory effects [3,21]. Finally, great effort is currently made to increase resveratrol bioavailability, e.g., by structural modification. Thus, the anti-inflammatory effects of resveratrol on alveolar macrophages of COPD shown here in a culture model of bacterial infection are nonetheless of relevance for COPD therapy.

In summary, our data support the hypothesis that the anti-inflammatory properties of corticosteroids are of limited utility in COPD therapy and suggest resveratrol or its derivatives as an alternative.

Acknowledgements

We thank Nina Mehling for technical support. The study was financially supported by the Moritz-Stiftung (#36460040), Cologne, Germany.

Conflict of interests

The authors declare to have no conflict of interest related to this study.

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