COPD is an increasingly prevalent disease, affecting up to 10% of adults aged over 40 years[1]. Current therapies include long acting β₂-receptor agonists (LABAs) and muscarinic receptor antagonists, which increase lung function by relaxing airway smooth muscle. Corticosteroids are also used, and have been shown to decrease exacerbations as well as improving other clinical parameters such as FEV₁[2]. However, the use of inhaled steroids in COPD is somewhat controversial due to inconsistent clinical effects and reports that these agents have limited effects on lung inflammation in COPD patients. For example, a meta-analysis of the effects of inhaled corticosteroids on inflammatory cells in the sputum of stable COPD patients showed evidence of reductions in neutrophils and lymphocytes but no effect on macrophages[3]. A similar analysis conducted recently on bronchial biopsies and bronchoalveolar lavage (BAL) fluid from stable patients showed reductions in neutrophils and lymphocytes in BAL but an increase in macrophages. The biopsy analysis indicated no effect on neutrophil and macrophage counts but a reduction in CD4⁺ and CD8⁺ lymphocytes[4]. In accordance with these results, macrophages from COPD patients have been reported to be insensitive to steroids[5, 6]. Various mechanisms for this steroid insensitivity have been proposed, including up-regulation of NF-kB signaling and increased oxidative stress[7]. If specific mechanisms are indeed responsible for the poor efficacy of steroids in COPD, then alternative anti-inflammatory approaches may be more successful. One such approach currently being considered is inhibition of PDEIV, by drugs such as Roflumilast and Cilomilast. The former drug has recently been approved as an add-on therapy for the maintenance treatment of severe COPD in the European Union and as a treatment to reduce the risk of exacerbations in the United States. These cAMP elevating agents have been shown to reduce recruitment of macrophages and CD8⁺ T-cells in COPD biopsies[8] and improve FEV₁, alone or in combination with a bronchodilator therapy[9, 10]. p38 MAP kinase is involved in transducing a number of inflammatory stimuli[11] and inhibitors of this enzyme have broad anti-inflammatory potential. Indeed, p38 inhibitors have shown evidence of anti-inflammatory effects and improvements in clinical parameters in COPD patients[12, 13]. Such agents have also been shown to inhibit cytokine release from human AMs derived from patients with COPD[14, 15], but the effectiveness of p38 inhibitors, steroids and PDEIV inhibitors has not been directly compared in the same donors.

In the present study we compared the ability of Cilomilast, Budesonide and BIRB-796 to inhibit cytokine release from AMs isolated from patients undergoing COPD lung transplant surgery for severe end stage disease (GOLD IV). This allowed us to directly compare the effectiveness of different mechanisms in modulating cytokine release, and assess donor to donor variability in response.

We have investigated the pharmacological profile of three different anti-inflammatory agents in COPD lung macrophages. We used LPS as a stimulus, given the strong links between bacterial colonization and exacerbations of COPD[16]. TNF and IL-6 are both pleiotropic, pro-inflammatory cytokines which are elevated in COPD patients[17, 18]. Furthermore, genetic polymorphisms in both these cytokines have been linked to development of COPD[19, 20]. The response to the PDEIV inhibitor, Cilomilast, was poor, consistent with published data showing limited effects of PDEIV inhibitors in inhibiting cytokine production from human macrophages[21, 22]. Such data suggests that suppression of macrophage function is not a key contributor to the observed clinical efficacy of PDEIV inhibitors in COPD, which may instead lie with anti-inflammatory effects on other cells such as neutrophils or epithelial cells. Alternatively, the modest potency of cilomilast may have limited the effects of this agent and therefore it would be interesting to evaluate the properties of other PDEIV inhibitors. The steroid Budesonide and the p38 inhibitor BIRB-796 were effective anti-inflammatory agents in alveolar macrophages although their effectiveness was dependent on the particular cytokine readout. TNFα release was significantly inhibited by both compounds, but IL-6 was more resistant to inhibition. Other studies have also demonstrated efficacy of steroids in reducing cytokine release from COPD macrophages, with the magnitude of the effect varying between readouts[15, 23] . In our study, AMs exhibited a broad spectrum of sensitivities to Budesonide ranging from one donor which failed to show any inhibition of cytokine release, to donors in which the steroid gave over 75% inhibition of TNFα release. This data suggests that cellular steroid insensitivity may not be characteristic of COPD. Rather, there appears to be a significant proportion of individuals whose show a poor cellular response to steroid. Increasingly, physicians and payers are looking towards personalized healthcare approaches, so that individuals likely to respond or fail to respond to treatment can be identified. Steroid treatment is linked to a range of serious side effects, and if those patients who are steroid insensitive could be identified, an alternative treatment option could be selected, thus avoiding unnecessary exposure to steroid.

Of particular interest is our observation that BIRB-796 inhibited TNFα release from AMs equally well in COPD donors that were good or poor responders to Budesonide. This data indicates that p38 inhibitors might be effective in patients which respond poorly to steroids. p38 MAPK pathways have been shown to be active in COPD[24] and a p38 inhibitor has been shown to down-regulate a different panel of mediators to steroids, which may also provide an advantage in a disease setting[15]. Although a number of oral p38 MAPK inhibitors have ceased development due to unwanted side-effects, inhaled p38 inhibitors may have an acceptable therapeutic window and thus represent useful new anti-inflammatory agents. Indeed, PF-03715455 is being developed as an inhaled agent for the treatment of COPD[25]. Such agents could be considered as steroid replacements, or as a second-line treatment option in patients with a poor response to steroid. Recent studies have demonstrated additive effects of steroids and p38 inhibitors in reducing cytokine release from bronchoalveolar lavage (BAL) macrophages and PBMCs from asthmatics[26] and COPD patients[27]. Our data confirms and extends these results, demonstrating additive effects of BIRB-796 and Budesonide in macrophages from a different compartment (lung tissue versus BAL) and to severe (GOLD stage IV) COPD patients, as compared to mild/moderate disease. Thus, our data adds to a growing body of evidence suggesting that a combination of steroid plus p38 inhibitor, on the background of standard bronchodilator therapy, could deliver increased clinical efficacy in severe COPD patients.

In a subset of subjects with GOLD IV stage COPD, steroids are ineffective in reducing cytokine release from tissue macrophages, yet the inhibitory response to the p38 MAPK inhibitor BIRB-796 is maintained in these cells. Use of inhaled p38 MAPK inhibitors may therefore provide a more effective therapy than steroids in some COPD patients. In addition, combination of steroid with a p38 inhibitor provides additive anti-inflammatory effects in COPD lung tissue macrophages.