Inhibitor Binding to Type 4 Phosphodiesterase (PDE4) Assessed Using [³H]Piclamilast and [³H]Rolipram

Abstract

Piclamilast is a type 4 phosphodiesterase (PDE4) inhibitor with equal affinity for the high-affinity rolipram binding site (HARBS) and low-affinity rolipram binding site (LARBS ICI 63,197, and Ro 20-1724 were better described by a two-site model, while the competition curves for piclamilast, cilomilast, roflumilast, and CDP 840 were adequately described by a one-site model. Inhibitors of other PDE families were much less potent. The inhibition of [ 3 H]piclamilast was further tested in the presence of 1 M rolipram to isolate the LARBS. Under this condition, the competition curves for all the inhibitors were adequately described by a one-site model, with K i values close to that for the LARBS. The results indicated that [ 3 H]piclamilast is a useful tool to directly study inhibitor interaction with the HARBS and the LARBS in rat brain.

Vascular Smooth Muscle Cell Phenotype-Dependent Phosphodiesterase 4D Short Form Expression: Role of Differential Histone Acetylation on cAMP-Regulated Function

“…Second, we propose that development of PDE4D splice-variant selective inhibitors may provide greater specificity when PDE enzymes are targeted therapeutically in situations in which different effects in contractile/quiescent and synthetic/activated VSMCs are desired, such as in attempts to limit in-stent restenosis. There is now substantial evidence that some PDE4 inhibitors, such as rolipram, bind to long and short PDE4 variants with different affinities, whereas other PDE4 inhibitors, such as piclamilast, do not possess this ability (Zhao et al, 2003). Thus, based on these differences in rolipram binding to long and short forms of PDE4D, studies are currently underway to identify PDE4 inhibitors that might selectively inhibit PDE4D short forms and thus selectively augment cAMP signaling in synthetic/activated VSMC but not contractile/ quiescent VSMC in the same artery in animal models of in-stent restenosis.…”

Antidepressant-Induced Increase in High-Affinity Rolipram Binding Sites in Rat Brain: Dependence on Noradrenergic and Serotonergic Function

“…The HARBS and the LARBS in preparations of rat brain were assessed using (Jacobitz et al, 1996;Zhao et al, 2003 3 H]piclamilast binding. The up-regulation of the HARBS was observed using both rat hippocampal and cerebral cortical membranes, with the effect in the hippocampus being somewhat greater.…”

“…Data were analyzed by nonlinear regression (O'Donnell et al, 1984;Zhao et al, 2003). B max and K d values were determined for saturation experiments.…”

“…3 H]piclamilast and [ 3 H]rolipram (Zhao et al, 2003). To determine whether their actions depend on enhanced monoaminergic function, the effects of the antidepressants also were determined following noradrenergic or serotonergic lesions.…”

“…Given that factors such as phosphorylation and interaction with other proteins can affect inhibitor affinity (Hoffmann et al, 1998;McPhee et al, 1999), it appears likely that the HARBS and the LARBS are regulated to different degrees by antidepressant treatment. Such a finding might suggest that antidepressant treatment alters cAMP-mediated signaling in the central nervous system via this mechanism, since the HARBS is present in brain, but not peripheral tissues (Schneider et al, 1986;Zhao et al, 2003).…”