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

Several selective phosphodiesterase 4 inhibitors were found to be potent in hibitors of the N-formyl-Met-Leu-Phe (fMLP)-induced leukotriene B-4 biosynt hesis by human polymorphonuclear leukocytes with IC(50)s in the nanomolar r ange (0.09-26 nM). The rank order of potency was 6-(4-pyridylmethyl)-8-(3-n itrophenyl)quinoline (RS-14203) > 3-benzyl-5-phenyl-3 H-imidazo[4,5-c][1,8] naphthyridin-4(5H)-one (KF18280)> 8-aza-1-(3-nitrophenyl)-3-(4-pyridylmethy l)-2,4-quinazoline dione (RS-25344)> 3-cyclo-pentyloxy-N-[3,5-dichloro-4-py ridyl]-4-methoxybenzamide (RP-73401) > R-rolipram > R-4-[2-(3-cyclopentylox y-4-methoxyphenyl)-2-phenylethyl] pyridine (CDP840)> S-rolipram. Isoprotere nol (IC50 = 350 nM) and prostaglandin E-2 (IC50 = 59 nM) also suppressed le ukotriene B-4 biosynthesis. Inhibitors of the phosphodiesterase 1 (8-methox ymethyl-1-methyl-3-(2-methylpropyl)xanthine (8-MeOMe-IBMX)), phosphodiester ase 2 (erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA)), phosphodiesterase 3 (q uazinone and milrinone) and phosphodiesterase 5 (zaprinast and dipyridamole ) had no inhibitory effects on the fMLP-induced leukotriene B-4, biosynthes is (IC(50)s> 20 mu M). All phosphodiesterase 4 inhibitors caused an accumul ation of cellular cyclic AMP to 140-185% over the basal level of fMLP-treat ed control cells, comparable to that observed with high concentrations of i soproterenol and prostaglandin E-2,. In contrast, the complete inhibition o f leukotriene B-4, production by 5-lipoxygenase and 5-lipoxygenase-activati ng protein (FLAP) inhibitors had no effect on cyclic AMP levels. Phosphodie sterase 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 hig her 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-depe ndence of R-rolipram for the inhibition of leukotriene B-4, biosynthesis or cyclic AMP accumulation. These data demonstrate that selective phosphodies terase 4 inhibitors can inhibit the fMLP-induced leukotriene B-4, biosynthe sis 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 ap pears to proceed independently of the other phosphodiesterases. (C) 1999 El sevier Science B.V. All rights reserved.