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Gert Folkerts

Publications and source records attributed to Gert Folkerts.

At least 19 recordsLinked to original sources
PubMed2006

Toll-like receptor-4 mediates cigarette smoke-induced cytokine production by human macrophages.

BACKGROUND: The major risk factor for the development of COPD is cigarette smoking. Smoking causes activation of resident cells and the recruitment of inflammatory cells into the lungs, which leads to release of pro-inflammatory cytokines, chemotactic factors, oxygen radicals and proteases. In the present study evidence is found for a new cellular mechanism that refers to a link between smoking and inflammation in lungs. METHODS: Employing human monocyte-derived macrophages, different techniques including FACS analysis, Cytometric Bead Array Assay and ELISA were achieved to evaluate the effects of CS on pro-inflammatory cytokine secretion including IL-8. Then, Toll-like receptor neutralization was performed to study the involvement of Toll-like receptor-4 in IL-8 production. Finally, signaling pathways in macrophages after exposure to CS medium were investigated performing ELISA and Western analysis. RESULTS: We demonstrate that especially human monocytes are sensitive to produce IL-8 upon cigarette smoke stimulation compared to lymphocytes or neutrophils. Moreover, monocyte-derived macrophages produce high amounts of the cytokine. The IL-8 production is dependent on Toll-like receptor 4 stimulation and LPS is not involved. Further research resolved the cellular mechanism by which cigarette smoke induces cytokine production in monocyte-derived macrophages. Cigarette smoke causes subsequently a concentration-dependent phosphorylation of IRAK and degradation of TRAF6. Moreover, IkappaBalpha was phosphorylated which suggests involvement of NF-kappaB. In addition, NFkappaB-inhibitor blocked cigarette smoke-induced IL-8 production. CONCLUSION: These findings link cigarette smoke to inflammation and lead to new insights/therapeutic strategies in the pathogenesis of lung emphysema.

Cells, Cultured↗
PubMed2006

Overexpression of endothelial nitric oxide synthase suppresses features of allergic asthma in mice.

BACKGROUND: Asthma is associated with airway hyperresponsiveness and enhanced T-cell number/activity on one hand and increased levels of exhaled nitric oxide (NO) with expression of inducible NO synthase (iNOS) on the other hand. These findings are in paradox, as NO also relaxes airway smooth muscle and has immunosuppressive properties. The exact role of the endothelial NOS (eNOS) isoform in asthma is still unknown. We hypothezised that a delicate regulation in the production of NO and its bioactive forms by eNOS might be the key to the pathogenesis of asthma. METHODS: The contribution of eNOS on the development of asthmatic features was examined. We used transgenic mice that overexpress eNOS and measured characteristic features of allergic asthma after sensitisation and challenge of these mice with the allergen ovalbumin. RESULTS: eNOS overexpression resulted in both increased eNOS activity and NO production in the lungs. Isolated thoracic lymph nodes cells from eNOS overexpressing mice that have been sensitized and challenged with ovalbumin produced significantly less of the cytokines IFN-gamma, IL-5 and IL-10. No difference in serum IgE levels could be found. Further, there was a 50% reduction in the number of lymphocytes and eosinophils in the lung lavage fluid of these animals. Finally, airway hyperresponsiveness to methacholine was abolished in eNOS overexpressing mice. CONCLUSION: These findings demonstrate that eNOS overexpression attenuates both airway inflammation and airway hyperresponsiveness in a model of allergic asthma. We suggest that a delicate balance in the production of bioactive forms of NO derived from eNOS might be essential in the pathophysiology of asthma.

Animals↗
PubMed2006

A novel peptide CXCR ligand derived from extracellular matrix degradation during airway inflammation.

We describe the tripeptide neutrophil chemoattractant N-acetyl Pro-Gly-Pro (PGP), derived from the breakdown of extracellular matrix (ECM), which shares sequence and structural homology with an important domain on alpha chemokines. PGP caused chemotaxis and production of superoxide through CXC receptors, and administration of peptide caused recruitment of neutrophils (PMNs) into lungs of control, but not CXCR2-deficient mice. PGP was generated in mouse lung after exposure to lipopolysaccharide, and in vivo and in vitro blockade of PGP with monoclonal antibody suppressed PMN responses as much as chemokine-specific monoclonal antibody. Extended PGP treatment caused alveolar enlargement and right ventricular hypertrophy in mice. PGP was detectable in substantial concentrations in a majority of bronchoalveolar lavage samples from individuals with chronic obstructive pulmonary disease, but not control individuals. Thus, PGP's activity links degradation of ECM with neutrophil recruitment in airway inflammation, and PGP may be a biomarker and therapeutic target for neutrophilic inflammatory diseases.

Animals↗
PubMed2006

Reactive nitrogen species in the respiratory tract.

Endogenous Nitric Oxide (NO) plays a key role in the physiological regulation of airway functions. In response to various stimuli activated inflammatory cells (e.g., eosinophils and neutrophils) generate oxidants ("oxidative stress") which in conjunction with exaggerated enzymatic release of NO and augmented NO metabolites produce the formation of strong oxidizing reactive nitrogen species, such as peroxynitrite, in various airway diseases including asthma, chronic obstructive pulmonary diseases (COPD), cystic fibrosis and acute respiratory distress syndrome (ARDS). Reactive nitrogen species provoke amplification of inflammatory processes in the airways and lung parenchyma causing DNA damage, inhibition of mitochondrial respiration, protein dysfunction and cell damage ("nitrosative stress"). These effects alter respiratory homeostasis (such as bronchomotor tone and pulmonary surfactant activity) and the long-term persistence of "nitrosative stress" may contribute to the progressive deterioration of pulmonary functions leading to respiratory failure. Recent studies showing that protein nitration can be dynamic and reversible ("denitration mechanisms") open new horizons in the treatment of chronic respiratory diseases affected by the deleterious actions of "nitrosative stress".

Animals↗
PubMed2006

Modified approach of administering cytostatics to the lung: more efficient isolated lung perfusion.

BACKGROUND: Isolated lung perfusion (ILuP) is an experimental technique for the treatment of pulmonary metastases. We hypothesized that part of the drug taken up by the lung during ILuP is washed out during the flush procedure. Therefore, we investigated gemcitabine uptake at different inflow concentrations, and the effect of delayed clamp release after ILuP on lung levels was studied. METHODS: Thirty rats had ILuP during 30 minutes using gemcitabine perfusate levels of 1.3, 2.7, 4.0, 5.3, and 6.7 mg/mL. Another 37 rats underwent ILuP with gemcitabine perfusate levels of 6.7 mg/mL during 6 minutes followed by a 5-minute flush and 30 or 60 minutes of reperfusion, while two other groups had ILuP and delayed clamp release for 30 or 60 minutes followed by a 5-minute flush. All effluent and lung samples were stored for later analysis. Results were evaluated using Friedmann two-way analysis and two-way analysis of variance. RESULTS: At 6 minutes, steady-state of gemcitabine uptake was achieved for all inflow concentrations and a linear relation (r = 0.933, p < 0.0001) between effluent and lung levels was observed. Delayed clamp release resulted in significantly higher lung levels compared with immediate restoration of blood circulation after ILuP (456% at 30 minutes and 828% at 60 minutes). CONCLUSIONS: Effective gemcitabine lung levels are already achieved after 6 minutes of ILuP with 6.7 mg/mL followed by delayed clamp release during 30 minutes instead of the clinically applied 30 minutes ILuP.

Animals↗
PubMed2006

Nitric oxide in asthma therapy.

The discovery of the delicate role of endogenous nitric oxide in the homeostasis of various cellular functions and the dynamic behaviour of the airways, has led to a new, rapidly progressing area of physiological science, that has direct bearing for our understanding of multiple airway diseases. The potentially protective effects of nitric oxide include: neuromodulation by mediating inhibitory non-cholinergic non-adrenergic nerve activity; smooth muscle relaxation, attenuating airway hyperresponsiveness to bronchoconstrictor stimuli and immune-suppression. NO itself or SNO can be administered directly to the airways, and the development of gene transfer therapy seems to become a realistic approach in the treatment of airway diseases. However, NO has also harmful effects, especially when it interacts with other molecules. At present, there are novel opportunities to modulate nitric oxide-synthesis aimed to restore the balance between the protective and deleterious effects of nitric oxide. This is potentially beneficial in both airway and alveolar diseases. Such interventions might be targeted in various ways, e.g. by using selective reactive nitrogen- and oxygen- scavengers, selective NO donors and selective nitric oxide synthase inhibitors. The possible therapeutical opportunities are reviewed in this paper. Nitric oxide has already made it from the bench to the bedside, and it is likely that new developments in this area will drastically change respiratory medicine during the coming 5-10 years.

Animals↗
PubMed2006

Nitric oxide synthase (NOS) as therapeutic target for asthma and chronic obstructive pulmonary disease.

In the respiratory tract, NO is produced by residential and inflammatory cells. NO is generated via oxidation of L-arginine that is catalysed by the enzyme NO synthase (NOS). NOS exists in three distinct isoforms: neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS). NO derived from the constitutive isoforms of NOS (nNOS and eNOS) and other NO-adduct molecules (nitrosothiols) are able to modulate bronchomotor tone. NO derived from the inducible isoform of NO synthase, up-regulated by different cytokines via NF-kappaB-dependent pathway, seems to be a pro-inflammatory mediator with immunomodulatory effects. The production of NO under oxidative stress conditions secondarily generates strong oxidising agents (reactive nitrogen species) that may amplify the inflammatory response in asthma and COPD. Moreover, NO can be exhaled and levels are abnormal in stable atopic asthma and during exacerbations in both asthma and COPD. Exhaled NO might therefore be a non-invasive tool to monitor the underlying inflammatory process. It is suggested that NOS regulation provides a novel target in the prevention and treatment of chronic inflammatory diseases of the airways such as asthma and COPD.

Animals↗
PubMed2005

Pulmonary intravascular volume can be used for dose calculation in isolated lung perfusion.

INTRODUCTION: Isolated lung perfusion (ILuP) is an experimental surgical technique for the treatment of pulmonary metastases. Phase I trials showed a wide range in drug lung levels. This may be due to the variance of lung size and pulmonary intravascular volume (PIV). Therefore, we developed a method to assess PIV and investigated the relation of PIV and dry lung weight (DLW). MATERIAL AND METHODS: Thirty-two rats of 555+/-8 and 199+/-5g underwent left ILuP two, four and eight minutes. Venous effluent was analyzed for haemoglobin, red blood cells (RBC), leucocytes, platelets, albumin and creatinine. PIV was calculated by dividing the product of perfusate volume and post-ILuP parameter by the difference between post-ILuP and pre-ILuP parameter. RESULTS: No significant differences in PIV for all perfusion times were noted between the different variables (P=0.14). Based on haemoglobin (P<0.0009), RBC (P=0.006), leucocytes (P=0.0003), platelets (P=0.017) and creatinine (P=0.003) analysis, PIV was significantly smaller in rats of 199g while PIV/DLW ratio was not significantly different. CONCLUSION: Because PIV/DLW ratio is independent of body weight, we advocate PIV calculation using haemoglobin and RBC as an excellent parameter for drug dose calculation during ILuP intraoperatively in order to achieve more reproducible local drug levels and higher efficacy.

Albumins↗
PubMed2004

Airway nitrergic pathways: is there therapeutic potential in asthma and COPD?

Airway diseases such as asthma and chronic obstructive pulmonary disease (COPD) are characterised by airway hyperresponsiveness, epithelial damage, oxidative stress and airway inflammation. Inflammatory cells, including macrophages, neutrophils, eosinophils and lymphocytes, are crucial in the pathogenesis of asthma and COPD. The prevalence of asthma and COPD is increasing, especially in Western countries. Symptomatic treatment is based on reduction of airway obstruction by inhalation of beta(2)-receptor agonists and attenuation of the underlying inflammatory reactions by inhalation of corticosteroids. Because these agents only suppress symptoms, there is a need for medicines that remove the cause of these airway diseases.

Adrenergic beta-Agonists↗
PubMed2004

Neuropeptide Y (NPY).

Neuropeptides such as neuropeptide Y (NPY) have long been proposed to play a role in the pathogenesis of inflammatory diseases. NPY is a 36 amino acid neuropeptide which participates in the regulation of a large number of physiological and pathophysiological processes in the cardiorespiratory system, immune system, nervous system and endocrine system. Serum levels of NPY are increased during exacerbations of asthma, whereas the number of NPY-immunoreactive nerves in the airways remains constant in the airways of patients with inflammatory airway diseases such asthma or rhinitis. Next to a role in the regulation of glandular activity, NPY exerts a major influence on humoral and cellular immune functions. In this respect, NPY is known to modulate potent immunological effects such as immune cell distribution, T helper cell differentiation, mediator release, or natural killer cell activation. In addition to these direct effects, NPY also acts as an immunomodulator by influencing the effects of a variety of other neurotransmitters. Whereas the peptide has been focused for therapeutic options in the central nervous system, a potential use in the treatment of pulmonary inflammatory disorders has not been revealed so far due to the complex pulmonary effects of NPY. However, since selective antagonists and agonists and gene-depleted animals for the different receptors are now available, NPY may be of value for future strategies in airway nerve modulation.

Animals↗
PubMed2004

Specific modulation of calmodulin activity induces a dramatic production of superoxide by alveolar macrophages.

Airway inflammation is a characteristic feature in airway diseases such as asthma and chronic obstructive pulmonary disease. Oxidative stress, caused by the excessive production of reactive oxygen species by inflammatory cells like macrophages, eosinophils and neutrophils, is thought to be important in the complex pathogenesis of such airway diseases. The calcium-sensing regulatory protein calmodulin (CaM) binds and regulates different target enzymes and proteins, including calcium channels. In the present study, we investigated whether CaM, via the modulation of calcium channel function, influences [Ca(2+)](i) in pulmonary inflammatory cells, and consequently, modulates the production of reactive oxygen species by these cells. This was tested with a peptide termed calcium-like peptide 2 (CALP2), which was previously shown to regulate such channels. Specifically, radical production by purified broncho-alveolar lavage cells from guinea-pigs in response to CALP2 was measured. CALP2 was a strong activator of alveolar macrophages. In contrast, CALP2 was only a mild activator of neutrophils and did not induce radical production by eosinophils. The CALP2-induced radical production was mainly intracellular, and was completely blocked by the NADPH-oxidase inhibitor DPI, the superoxide inhibitor SOD and the CaM antagonist W7. Furthermore, the calcium channel blocker lanthanum partly inhibited the cellular activation by CALP2. We conclude that alveolar macrophages, but not neutrophils or eosinophils, can produce extremely high amounts of reactive oxygen species when stimulated via the calcium/CaM pathway. These results may contribute to new therapeutic strategies against oxidative stress in airway diseases.

Animals↗
PubMed2004

Mycobacteria, genes and the 'hygiene hypothesis'.

PURPOSE OF REVIEW: The 'hygiene hypothesis' suggests that a relationship exists between improved hygiene and an increase in allergic diseases. As an underlying mechanism for this hypothesis it is proposed that due to the lack of microbial stimulation either a misbalance in T helper type responses or a misbalance in regulatory mechanisms develops. As yet, however, a specific infectious factor responsible for the hygiene hypothesis has not been found. RECENT FINDINGS: Animal models have lent support for mycobacteria as important candidates in the hygiene hypothesis. These animal studies have also suggested that mycobacterial treatment generated regulatory mechanisms which restored the immune balance. In contrast, the relationship between mycobacterial infection or treatment and the development of allergy and asthma in humans is unclear and highly controversial. SUMMARY: Mycobacteria have been found to unambiguously reduce allergic and asthmatic manifestations, suggesting that mycobacteria perhaps can be used as an 'anti-asthma' vaccine. Conflicting results in humans, however, confirm that the complex and multifactorial interactions between the environment and the genetic background of the individual contribute to the development of allergic disease. Therefore, the hygiene hypothesis should involve the genetic and the environmental background of the individual.

Animals↗
PubMed2004

Nitric oxide in health and disease of the respiratory system.

During the past decade a plethora of studies have unravelled the multiple roles of nitric oxide (NO) in airway physiology and pathophysiology. In the respiratory tract, NO is produced by a wide variety of cell types and is generated via oxidation of l-arginine that is catalyzed by the enzyme NO synthase (NOS). NOS exists in three distinct isoforms: neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS). NO derived from the constitutive isoforms of NOS (nNOS and eNOS) and other NO-adduct molecules (nitrosothiols) have been shown to be modulators of bronchomotor tone. On the other hand, NO derived from iNOS seems to be a proinflammatory mediator with immunomodulatory effects. The concentration of this molecule in exhaled air is abnormal in activated states of different inflammatory airway diseases, and its monitoring is potentially a major advance in the management of, e.g., asthma. Finally, the production of NO under oxidative stress conditions secondarily generates strong oxidizing agents (reactive nitrogen species) that may modulate the development of chronic inflammatory airway diseases and/or amplify the inflammatory response. The fundamental mechanisms driving the altered NO bioactivity under pathological conditions still need to be fully clarified, because their regulation provides a novel target in the prevention and treatment of chronic inflammatory diseases of the airways.

Administration, Inhalation↗
PubMed2003

Ca2+ sensors modulate asthmatic symptoms in an allergic model for asthma.

We previously described two novel peptides, Ca2+-like peptide (CALP) 1 and CALP2, which interact with Ca2+-binding EF hand motifs, and therefore have the characteristics to define the role of the Ca2+-sensing regulatory protein calmodulin in asthma. In the present study, the effects of the calcium-like peptides were investigated in an animal model for allergic asthma. For that purpose, sensitized guinea pigs were intratracheally pretreated with CALP1 or CALP2. Thirty minutes later, the animals were challenged with aerosolized ovalbumin. Acute bronchoconstriction was measured as well as characteristic features of asthma 6 and 24 hours (h) after challenge. Neither CALP1 nor CALP2 prevented the anaphylactic response elicited by ovalbumin challenge. However, CALP1 pretreatment attenuated the influx of inflammatory cells in the lungs 6 h after challenge. Furthermore, radical production by these cells was diminished both 6 and 24 h after challenge. Moreover, CALP1 completely inhibited airway hyperresponsiveness in vitro 24 h after challenge. We conclude that CALP1, as a selective calmodulin agonist, inhibits the development of asthmatic features probably via the attenuation of mast cell degranulation and radical production. Specific modulation of calmodulin activity might therefore be a potential new target for the treatment of allergic asthma.

Animals↗
PubMed2003

The Slc11a1 (Nramp1) gene controls efficacy of mycobacterial treatment of allergic asthma.

Genes controlling antibacterial resistance may be important in the hygiene hypothesis, which states that lack of bacterial infections during childhood would favor development of allergic disease. We, therefore, studied whether Nramp1 (Slc11a1) alleles, which determine susceptibility (Nramp1(s)) or resistance (Nramp1(r)) to intracellular bacteria, affect the efficacy of heat-killed Mycobacterium vaccae in the treatment of allergic asthma in a mouse model. Treatment of OVA-sensitized Nramp1(s) mice with M. vaccae suppressed airway hyperresponsiveness, airway eosinophilia, Ag-specific IgE, and IL-4 and IL-5 production after OVA aerosol challenge. In contrast, M. vaccae hardly affected these parameters in Nramp1(r) mice. In addition, The Nramp1 gene affected both T cell-mediated responses to M. vaccae in vivo and the level of macrophage activation after stimulation with M. vaccae in vitro. In conclusion, the efficacy of M. vaccae in preventing allergic and asthmatic manifestations in a mouse model is strongly affected by Nramp1 alleles. These findings could have important implications for the future use of mycobacteria and their components in the prevention or treatment of allergic asthma. A new link is described between genes, the environment, and the development of allergy, in which the Nramp1 gene fine tunes the hygiene hypothesis.

Allergens↗
PubMed2003

Therapeutic treatment with heat-killed Mycobacterium vaccae (SRL172) in a mild and severe mouse model for allergic asthma.

The hypothesis that a lack of early childhood bacterial infections would favor the development of allergic disease suggests that bacteria can be used as a potential treatment for allergic asthma. Therefore, in this study, we investigated the therapeutic potential of heat-killed Mycobacterium vaccae in two mouse models of allergic asthma. For this purpose, mice were sensitized i.p. with ovalbumin/alum (severe model) or ovalbumin alone (mild model) and challenged on days 77, 80 and 83 by inhalation of either ovalbumin or saline aerosols. Treatment of mice with M. vaccae (s.c. 10(7) or 10(8) colony-forming units) on days 56 and 63, however, did not reduce airway hyperresponsiveness and eosinophilia, IgE and interleukin-5 production 24 h after ovalbumin challenge in either mouse model. We therefore conclude that treatment of sensitized mice with M. vaccae before allergen exposure is not able to reduce the allergic and asthma-like response in a mild and a severe model of allergic asthma.

Allergens↗
PubMed2002

Eotaxin protein levels and airway pathology in a mouse model for allergic asthma.

Eotaxin is a chemokine implicated in eosinophil trafficking and may be involved in the development of airway hyperresponsiveness. The role of eotaxin in a mouse model for allergic asthma was investigated. Challenging ovalbumin-sensitised mice with ovalbumin aerosol leads to airway hyperresponsiveness and airway eosinophilia 24 h after the last challenge. Furthermore, eotaxin concentrations were markedly increased in lungs and broncho-alveolar lavage fluid of ovalbumin-challenged mice compared to vehicle treated mice. This could mean that eotaxin is implicated in the pathology of this model. To further investigate the role of eotaxin in this murine model for allergic asthma, the ovalbumin response was modulated by either treatment with eotaxin antibodies or additional eotaxin, to suppress or promote the development of airway hyperresponsiveness and inflammation. Administration of eotaxin antibodies or an additional intravenous eotaxin injection did not alter the development of ovalbumin-induced airway hyperresponsiveness and eosinophilia. In conclusion, eotaxin concentrations were increased in a murine model for allergic airway inflammation. However, anti-eotaxin antibodies or additive intravenous murine eotaxin did not influence airway inflammation and hyperresponsiveness in this mouse model for allergic asthma.

Allergens↗