Biol. Pharm. Bull. 28(3) 515—519 (2005)

way inflammation associated with the accumulation and activation of inflammatory cells, such as eosinophils, in the bronchial wall and airway lumen. Eosinophils at the site of inflammation release preformed and newly synthesized mediators, including eosinophil cationic protein, major basic protein, leukotriene C4, and reactive oxygen. These mediators contribute to the formation of the pathological features of asthmatic airways such as bronchoconstriction, mucus hypersecretion, microvascular leakage, submucosal edema, and epithelial shedding, which lead to the clinical features of asthma, hyperresponsiveness, and airway narrowing. Eosinophils cultured in the absence of hematopoietic cytokines such as granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-5 undergo apoptosis, which is physiologic cell death characterized by morphologic changes such as membrane blebbing and nuclear condensation, and by the degradation of DNA into oligonucleosomesized fragments showing a “ladder” pattern on agarose gel. Apoptotic eosinophils have been shown to be removed from the tissue without releasing inflammatory mediators after ingestion by macrophages, which is believed to be one of the important mechanisms in the resolution of inflammation. GM-CSF and IL-5, which have been detected in sputum, bronchoalveolar lavage fluid, and bronchial tissues from asthmatics, prolong the survival of tissue eosinophils through the prevention of apoptosis, leading to the development and maintenance of airway inflammation. Therefore the induction of apoptosis in eosinophils would be beneficial in the treatment of asthma. The induction of apoptosis in airway eosinophils by the administration of anti-Fas antibody or inhaled steroid is reported to be associated with the reduction or termination of asthmatic airway inflammation in vivo. cAMP is well known as a second messenger mediating intracellular signal transduction evoked by the binding of agonists to their cell-surface receptors. The concentration of intracellular cAMP is dependent on the catalysis rate of ATP to cAMP by adenylate cyclase and of cAMP to 5 -adenosine monophosphate by cyclic nucleotide phosphodiesterases (PDEs). PDEs comprise at lease 11 families containing, in total, more than 50 different PDE enzyme variants, the differentiation of which is based on the primary protein and cDNA sequences, substrate specificity, regulation of enzymatic activity, and calcium/calmodulin dependence. The increased concentration of intracellular cAMP is known to suppress the functions of inflammatory cells. With regard to eosinophils of which the PDE isoenzyme is exclusively type 4, selective inhibitors of PDE 4 and theophylline, a nonselective PDE inhibitor, have been shown to inhibit chemotaxis, adhesion, degranulation, and the release of active oxygen by an increase in the cAMP content. Furthermore, PDE 4 inhibitors and theophylline, as well dibutyryl cAMP (d-cAMP), a cAMP analogue, have been also demonstrated to reduce eosinophil survival prolonged by GM-CSF or IL5. Together with the pathogenic roles of eosinophils in asthma, there has been increased interest in the therapeutic benefit of these agents in asthma. However, the mechanisms by which PDE 4 inhibitors suppress eosinophil survival remain to be elucidated, while theophylline and d-cAMP were shown to decrease the survival rate via the induction of apoptosis. Therefore, to evaluate whether PDE 4 inhibitors have the ability to cause eosinophils to undergo apoptosis, we examined the effects of selective PDE isoenzyme inhibitors on eosinophil survival proloned by GM-CSF. March 2005 Notes Biol. Pharm. Bull. 28(3) 515—519 (2005) 515