Modulation of neutrophil phospholipase C activity and cyclic AMP levels byfMLP-OMe analogues

The N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP)-OMe (1) analogues for-Thp-Leu-Ain-OMe (2), for-Thp-Leu-Phe-OMe (3), for-Met-Leu-Ain-OMe (4), for-Met-Delta (z)Leu-Phe-OMe (5), for-Met-Lys-Phe-For-Met-Lys-Phe (6), for- Met-Leu-Pheol-COMe (7), and for-Nle-Leu-Phe-OMe (8) have been studied. Some of these have been found selective towards the activation of different bio logical responses of human neutrophils. In particular, peptides 2 and 3, wh ich evoke only chemotaxis, are ineffective in enhancing inositol phosphate, as well as cyclic AMP (cAMP) levels. On the contrary, analogues 5 and 7, w hich induce superoxide anion production and degranulation, but not chemotax is, significantly increase the levels of the two intracellular messengers, as is the case of the full agonists 1 and 6. The Ca2+ ionophore A23187 also activates phospholipase C (PLC) and increases the nucleotide levels, when tested in combination with peptide 1 or 5, a supra-additive enhancement of cAMP concentration is obtained. The PLC blocker, U-73122, inhibits the form ylpeptide-induced inositol phosphate formation, as well as cAMP increase. M oreover, this drug drastically reduces superoxide anion release triggered b y 1 or 5, whereas it inhibits to a much lesser extent neutrophil chemotaxis induced by 1 or 2. Our results suggest that: (i) PLC stimulation is involv ed in cAMP enhancement by formylpeptides; (ii) the activation of PLC by for mylpeptides, in conditions of increased Ca2+ influx, induces a supraadditiv e enhancement of the nucleotide; (iii) the inability of pure chemoattractan ts to significantly alter the PLC activity or cAMP level, differently from full agonists or peptides specific in inducing superoxide anion release, ap pears as a general property. Thus, the activation of neutrophil PLC seems e ssential for superoxide anion release, but less involved in the chemotactic response. (C) 2001 Elsevier Science Inc. All rights reserved.