Neutrophil chemotactic activity of sputum from patients with COPD: role of interleukin 8 and leukotriene B4

Alveolar Macrophages as Orchestrators of COPD

Alveolar macrophages play a critical role in the pathophysiology of COPD and are a major target for future anti-inflammatory therapy. Macrophage numbers are markedly increased in the lung and alveolar space of patients with COPD and are localized to sites of alveolar destruction. The increased numbers of macrophages may result from increased recruitment of blood monocytes, prolonged survival in the lung and to a lesser extent to increased proliferation in the lung. Alveolar macrophages from COPD patients have an increased baseline and stimulated secretion of inflammatory proteins, including certain cytokines, chemokines, reactive oxygen species and elastolytic enzymes, which together could account for all of the pathophysiological features of COPD. Alveolar macrophages form COPD appear to be resistant to the anti-inflammatory effects of corticosteriods and this is linked to reduced activity and expression of histone deacetylase 2, a nuclear enzyme that switches off inflammatory genes activated through the transcription factor nuclear factor-KB. Alternative anti-inflammatory therapies that inhibit macrophages are therefore needed in the future to deal with the chronic inflammation of COPD. These drugs may include resveratrol, theophylline derivatives, MAP kinase inhibitors and phosphodiesterase-4 inhibitors.

Therapy for chronic obstructive pulmonary disease in the 21st century

Chronic obstructive pulmonary disease (COPD) is a common, smoking-related, severe respiratory condition characterised by progressive, irreversible airflow limitation. Current treatment of COPD is symptomatic, with no drugs capable of halting the relentless progression of airflow obstruction. Better understanding of the airway inflammation, oxidative stress and alveolar destruction that characterise COPD has delineated new disease targets, with consequent identification of novel compounds with therapeutic potential. These new drugs include aids to smoking cessation (e.g. bupropion) and improvements to existing therapies, for example long-acting rather than short-acting bronchodilators, as well as combination therapy. New antiproteases include acyl-enzyme and transition state inhibitors of neutrophil elastase (e.g. sivelestat and ONO-6818), matrix metalloprotease inhibitors (e.g. batimastat), cathepsin inhibitors and peptide protease inhibitors (e.g. DX-890 [EPI-HNE-4] and trappin-2). New antioxidants include superoxide dismutase mimetics (e.g. AEOL-10113) and spin trap compounds (e.g. N-tert-butyl-alpha-phenylnitrone). New anti-inflammatory interventions include phosphodiesterase-4 inhibitors (e.g. cilomilast), inhibitors of tumour necrosis factor-alpha (e.g. humanised monoclonal antibodies), adenosine A(2a) receptor agonists (e.g. CGS-21680), adhesion molecule inhibitors (e.g. bimosiamose [TBC1269]), inhibitors of nuclear factor-kappaB (e.g. the naturally occurring compounds hypoestoxide and (-)-epigallocatechin-3-gallate) and activators of histone deacetylase (e.g. theophylline). There are also selective inhibitors of specific extracellular mediators such as chemokines (e.g. CXCR2 and CCR2 antagonists) and leukotriene B(4) (e.g. SB201146), and of intracellular signal transduction molecules such as p38 mitogen activated protein kinase (e.g. RWJ67657) and phosphoinositide 3-kinase. Retinoids may be one of the few potential treatments capable of reversing alveolar destruction in COPD, and a number of compounds are in clinical trial (e.g. all-trans-retinoic acid). Talniflumate (MSI-1995), an inhibitor of human calcium-activated chloride channels, has been developed to treat mucous hypersecretion. In addition, the purinoceptor P2Y(2) receptor agonist diquafosol (INS365) is undergoing clinical trials to increase mucus clearance. The challenge to transferral of these new compounds from preclinical research to disease management is the design of effective clinical trials. The current scarcity of well characterised surrogate markers predicts that long-term studies in large numbers of patients will be needed to monitor changes in disease progression.

Cloning and Pharmacological Characterization of CXCR1 and CXCR2 fromMacaca fascicularis

Two genes with high sequence homology to human CXCR1 (hCXCR1) and CXCR2 (hCXCR2) were cloned from blood of cynomolgus monkey (Macaca fascicularis). Comparison of the expression pattern of these receptors in different species demonstrated that, like in humans, cynomolgus CXCR1 (cCXCR1) and CXCR2 (cCXCR2) are highly expressed in blood. Membranes from transfected BaF3 cells expressing cCXCR1 bind interleukin (IL)-8 with an affinity similar to hCXCR1 (Kd values, 170 +/- 87 and 103 +/- 37 pM, respectively) and show low binding affinity to Gro-alpha. Cynomolgus CXCR2 also binds hIL-8 but with somewhat higher affinity than the hCXCR2 (46 +/- 28 and 220 +/- 14 pM, respectively). Surprisingly, cCXCR2 has a reduced binding affinity to hGro-alpha (3.7 +/- 2.2 nM), a specific ligand of hCXCR2 (540 +/- 140 pM). Furthermore, the CXCR2-specific antagonist SB225002 [N-(2-hydroxy-4-nitrophenyl)-N'-(2-bromophenyl)urea] is 10-fold more potent in inhibiting IL-8 binding to hCXCR2 than to cCXCR2, suggesting that some of the observed differences in the amino acid sequences of the human and monkey receptor affect ligand binding sites or the conformation of the receptor. Both cynomolgus receptors were functionally active in inducing guanosine 5'-O-(3-thio)triphosphate exchange on membranes in response to IL-8 and Gro-alpha and in mediating chemotactic activity of recombinant BA/F3 cells in response to IL-8 and Gro-alpha. These results identify the products of the novel cynomolgus genes as functional homologs of hCXCR1 and hCXCR2.

Circulating monocytes from healthy individuals and COPD patients

Background

Chronic obstructive pulmonary disease (COPD) is characterized by incompletely reversible airflow obstruction associated with inflammation in which monocytes/macrophages are the predominant inflammatory cells. The only known genetic factor related to COPD is inherited PiZZ deficiency of α1-antitrypsin (AAT), an inhibitor of serine proteases.

Methods

We investigated the basal and LPS-stimulated release of pro-inflammatory molecules from blood monocytes isolated from age and gender matched healthy (n = 30) and COPD (n = 20) individuals with and without AAT deficiency.

Results

After 18 h of cell culture the basal release of MMP-9 was 2.5-fold, p < 0.02 greater, whereas IL-8 was 1.8-fold (p < 0.01) lower from COPD patient monocytes than from controls. LPS-stimulated release of IL-6 and MCP-1 was greater from COPD patient's monocytes relative to controls, while activation of control cells resulted in enhanced secretion of ICAM-1 and MMP-9 compared to COPD patients. Independent of disease status, monocytes from PiZZ AAT carriers released less TNFα (by 2.3-fold, p < 0.03).

Conclusions

The basal and LPS-stimulated secretion of specific pro-inflammatory molecules from circulating monocytes differs between healthy and COPD subjects. These findings may be valuable for further studies on the mechanisms involved in recruitment and activation of inflammatory cells in COPD.