Phosphodiesterase 4-dependent regulation of cyclic AMP levels and leukotriene B 4 biosynthesis in human polymorphonuclear leukocytes

Abstract

Several selective phosphodiesterase 4 inhibitors were found to be potent inhibitors of the N-formyl-Met-Leu-Phe (fMLP)-induced leukotriene B 4 biosynthesis by human polymorphonuclear leukocytes with IC 50s in the nanomolar range (0.09–26 nM). The rank order of potency was 6-(4-pyridylmethyl)-8-(3-nitrophenyl)quinoline (RS-14203)>3-benzyl-5-phenyl-3 H-imidazo[4,5- c][1,8]naphthyridin-4(5 H)-one (KF18280)>8-aza-1-(3-nitrophenyl)-3-(4-pyridylmethyl)-2,4-quinazoline dione (RS-25344)>3-cyclo-pentyloxy- N-[3,5-dichloro-4-pyridyl]-4-methoxybenzamide (RP-73401)> R-rolipram> R-4-[2-(3-cyclopentyloxy-4-methoxyphenyl)-2-phenylethyl] pyridine (CDP840)> S-rolipram. Isoproterenol (IC 50=350 nM) and prostaglandin E 2 (IC 50=59 nM) also suppressed leukotriene B 4 biosynthesis. Inhibitors of the phosphodiesterase 1 (8-methoxymethyl-1-methyl-3-(2-methylpropyl)xanthine (8-MeOMe-IBMX)), phosphodiesterase 2 ( erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA)), phosphodiesterase 3 (quazinone and milrinone) and phosphodiesterase 5 (zaprinast and dipyridamole) had no inhibitory effects on the fMLP-induced leukotriene B 4 biosynthesis (IC 50s>20 μM). All phosphodiesterase 4 inhibitors caused an accumulation of cellular cyclic AMP to 140–185% over the basal level of fMLP-treated control cells, comparable to that observed with high concentrations of isoproterenol and prostaglandin E 2. In contrast, the complete inhibition of leukotriene B 4 production by 5-lipoxygenase and 5-lipoxygenase-activating protein (FLAP) inhibitors had no effect on cyclic AMP levels. Phosphodiesterase 1, 2, 3 and 5 inhibitors had little effect on the level of cellular cyclic AMP (89–126% of the basal cyclic AMP level). Dose-dependencies for R-rolipram, RS-14203 and CDP840 indicated that the maximal accumulation of cyclic AMP occurred at concentrations of phosphodiesterase 4 inhibitors higher than those required for the inhibition of leukotriene B 4 production. The presence of a mixture of 8-MeOMe-IBMX, EHNA, milrinone and zaprinast to inhibit phosphodiesterase 1, 2, 3 and 5 had little effect on the dose-dependence of R-rolipram for the inhibition of leukotriene B 4 biosynthesis or cyclic AMP accumulation. These data demonstrate that selective phosphodiesterase 4 inhibitors can inhibit the fMLP-induced leukotriene B 4 biosynthesis in human polymorphonuclear leukocytes with a potency similar or greater than that of potent 5-lipoxygenase or FLAP inhibitors. This inhibition is accompanied by small variations in the levels of cellular cyclic AMP and appears to proceed independently of the other phosphodiesterases.