'Entourage' effects of N-acyl ethanolamines at human vanilloid receptors.: Comparison of effects upon anandamide-induced vanilloid receptor activation and upon anandamide metabolism

1 The abilities of a series of saturated N-acyl ethanolamines and related compounds to affect the ability of anandamide (AEA) to produce a Ca2+ influx into human embryonic kidney cells expressing the human vanilloid receptor (hVR1-HEK293 cells) has been investigated. 2 The C3:0, C4:0, C6:0 and C10:0 ethanolamides neither affected basal Ca2+-influx, nor the influx in response to a submaximal concentration of AEA (1 muM). In contrast, the C12:0, C17:0, C18:0 ethanolamides and the monounsaturated compound oleoylethanolamide (C18:1) greatly potentiated the response to AEA. Palmitoylethanolamide (C16:0) produced both a response per se and an augmentation of the response to AEA. 3 Lauroylethanolamide (C12:0) produced a leftward shift in the dose-response curve for AEA. EC50 values for AEA to produce Ca2+ influx into hVR1-HEK293 cells were 1.8, 1.5, 1.1 and 0.22 muM in the presence of 0, 1, 3 and 10 muM lauroylethanolamide, respectively. Lauroylethanolamide did not affect the dose-response curves to capsaicin. 4 Palmitoylethylamide was synthesized and found to be a mixed-type inhibitor (K-i(slope) 4.1 muM, K-i(intercept) 66 muM) of [H-3]-AEA metabolism by rat brain membranes. 5 The -amide, -ethylamide, -isopropylamide, -butylamide, -cyclohexamide and -trifluoromethyl ketone analogues of palmitoylethanolamide had little or no effect on the Ca2+ influx response to 1 muM AEA. 6 There was no obvious relation between the abilities of the compounds to enhance the Ca2+-influx response to 1 muM EA into hVR1-HEK293 cells and to prevent the hydrolysis of AEA by rat brain membranes. 7 It is concluded that although palmitoylethanolamide has entourage-like effects at VR1 receptors expressed on hVR1-HEK293 cells, other N-acyl ethanolamines have even more dramatic potentiating effects. It is possible that they may play an important role under conditions where their synthesis is increased, such as in severe inflammation.