Agonist and antagonist activities on human NPFF(2) receptors of the NPY ligands GR231118 and BIBP3226

Abstract

Neuropeptide FF (NPFF) is a part of a neurotransmitter system acting as a modulator of endogenous opioid functions. At this time, no non-peptide or peptide NPFF-antagonists have been discovered. Here, we demonstrate that Neuropeptide Y (NPY) ligands, in fact possess significant ability to interact with the human NPFF(2) receptors. NPY Y(1) antagonist BIBP3226 and mixed Y(1) antagonist/Y(4) agonist GR231118 are able to displace with low affinity, 50 -- 100 nM, the specific binding on NPFF receptors expressed in CHO cells as well as in rat dorsal spinal cord, an affinity however superior to those determined against Y(2), Y(4) or Y(5) receptors. Furthermore, BIBP3226 which is unable to inhibit the forskolin-stimulated cyclic AMP production mediated by NPFF(2) receptors, antagonizes the effect of NPFF, revealing the first antagonist of NPFF receptors. These properties of NPY ligands on Neuropeptide FF receptors must be considered when evaluating pharmacological activities of these drugs.

Figure 1

Displacement of [¹²⁵I]-EYF (0.05 nM) specific binding on membranes of recombinant CHO cells (A) and accumulation of intracellular cyclic AMP (B) in CHO cells expressing the human NPFF₂ receptor. Each curve represents the means±s.e.mean of at least three experiments performed in triplicate.

Figure 2

Effect of increasing concentrations of BIBP3226 on the inhibition by NPFF of forskolin-induced cyclic AMP accumulation in CHO cells expressing the human NPFF₂ receptor. Intracellular cyclic AMP content induced by 2 μM forskolin (black bar) was inhibited (80 – 90%) by 10 nM NPFF (white bar), and increasing concentrations of BIBP3226 (grey bar) reversed this effect. The bars represent the means±s.e.mean of triplicate determinations of one representative experiment among three.