Evaluation of the anti-inflammatory effects of β-adrenoceptor agonists on human lung macrophages

The principal mechanism by which bronchodilator β-adrenoceptor agonists act is to relax airways smooth muscle although they may also be anti-inflammatory. However, the extent of anti-inflammatory activity and the cell types affected by these agonists are uncertain. The purpose of this study was to evaluate whether β-adrenoceptor agonists prevent pro-inflammatory cytokine generation from activated human lung macrophages. Macrophages were isolated and purified from human lung. The cells were pre-treated with both short-acting (isoprenaline, salbutamol, terbutaline) and long-acting (formoterol, salmeterol, indacaterol) β-agonists before activation with lipopolysaccharide (LPS) to induce cytokine (TNFα, IL-6, IL-8 and IL-10) generation. The experiments showed that short-acting β-agonists were poor inhibitors of cytokine generation. Of the long-acting β-agonists studied, formoterol was also a weak inhibitor of cytokine generation whereas only indacaterol and salmeterol showed moderate inhibitory activity. Further experiments using the β2-adrenoceptor antagonist ICI-118,551 suggested that the effects of indacaterol were likely to be mediated by β2-adrenoceptors whereas those of salmeterol were not. These findings were corroborated by functional desensitization studies in which the inhibitory effects of indacaterol appeared to be receptor-mediated whereas those of salmeterol were not. Taken together, the data indicate that the anti-inflammatory effects of β-adrenoceptor agonists on human lung macrophages are modest

The anti-inflammatory effects of prostaglandin E 2 on human lung macrophages are mediated by the EP 4 receptor

Background and purpose: Prostaglandin E2 (PGE2) has been shown to inhibit cytokine generation from human lung macrophages. However, the EP receptor that mediates this beneficial anti-inflammatory effect of PGE2 has not been elucidated definitively. The aim of this study was to identify the EP receptor by which PGE2 inhibits cytokine generation from human lung macrophages. This was determined by using recently-developed EP receptor ligands. Experimental approach: The effects of PGE2 and EP-selective agonists on lipopolysaccharide (LPS) induced tumour necrosis factor-α (TNFα) and interleukin-6 (IL-6) generation from macrophages were evaluated. The effects of EP2-selective (PF-04852946, PF-04418948) and EP4-selective (L-161,982, CJ-042794) antagonists on PGE2 responses were studied. The expression of EP receptor subtypes by human lung macrophages was determined by RT-PCR. Key results: PGE2 inhibited LPS-induced and Streptococcus pneumoniae-induced cytokine generation from human lung macrophages. Analysis of mRNA levels indicated that macrophages expressed EP2 and EP4 receptors. L-902,688 (EP4-selective agonist) was considerably more potent than butaprost (EP2-selective agonist) as an inhibitor of TNFα generation from macrophages. EP2-selective antagonists had marginal effects on the PGE2 inhibition of TNFα generation whereas EP4-selective antagonists caused rightward shifts in the PGE2 concentration-response curves. Conclusions and implications: These studies demonstrate that the EP4 receptor is the principal receptor that mediates the anti-inflammatory effects of PGE2 on human lung macrophages. This suggests that EP4 agonists could be effective anti-inflammatory agents in human lung disease

Prostaglandin D2 generation from human lung mast cells is catalysed exclusively by cyclooxygenase-1

Mast cells are an exceptionally rich source of prostaglandin D2 (PGD2). PGD2 is pro-inflammatory and can cause bronchoconstriction. The enzyme cyclooxygenase (COX) is central to the generation of prostanoids such as PGD2. Non-steroidal anti-inflammatory drugs (NSAIDs) inhibit COX. COX exists as two isoforms, COX-1 and COX-2. The principal aim of this study was to establish whether COX-1 and/or COX-2 mediates PGD2 generation from human lung mast cells. Mast cells were isolated from human lung tissue and purified by flotation over Percoll and immunomagnetic bead separations. The cells were activated with anti-IgE or Stem Cell Factor (SCF). The generation of PGD2 was determined by ELISA. The effects of NSAIDs (aspirin, ibuprofen, diclofenac, naproxen, indomethacin), COX-1 selective (FR122047), and COX-2 selective (celecoxib) inhibitors on PGD2 generation were determined. The expression of COX-1 and COX-2 in mast cells was determined by Western blotting. All the NSAIDs tested abrogated stimulated PGD2 generation from mast cells except aspirin which was only weakly effective. FR122047 was an effective inhibitor of PGD2 generation (EC50 ~25 nM) from mast cells whereas celecoxib was ineffective. Immunoblotting indicated that COX-1 was strongly expressed in all mast cell preparations while COX-2 expression was weak. No induction of COX-2 was observed following activation of mast cells. These findings indicate that COX-1 is the principal isoform involved in generating PGD2 from human lung mast cells. These studies provide insight into the potential behaviour of NSAIDs in the context of respiratory diseases