Effects of homologues and analogues of palmitoylethanolamide upon the inactivation of the endocannabinoid anandamide.

• The ability of a series of homologues and analogues of palmitoylethanolamide to inhibit the uptake and fatty acid amidohydrolase (FAAH)-catalysed hydrolysis of [3H]-anandamide ([3H]-AEA) has been investigated.Palmitoylethanolamide and homologues with chain lengths from 12–18 carbon atoms inhibited rat brain [3H]-AEA metabolism with pI50 values of ∼5. Homologues with chain lengths eight carbon atoms gave <20% inhibition at 100 μM.R-palmitoyl-(2-methyl)ethanolamide, palmitoylisopropylamide and oleoylethanolamide inhibited [3H]-AEA metabolism with pI50 values of 5.39 (competitive inhibition), 4.89 (mixed type inhibition) and 5.33 (mixed type inhibition), respectively.With the exception of oleoylethanolamide, the compounds did not produce dramatic inhibition of [3H]-WIN 55,212-2 binding to human CB2 receptors expressed on CHO cells. Palmitoylethanolamide, palmitoylisopropylamide and R-palmitoyl-(2-methyl)ethanolamide had modest effects upon [3H]-CP 55,940 binding to human CB1 receptors expressed on CHO cells.Most of the compounds had little effect upon the uptake of [3H]-AEA into C6 and/or RBL-2H3 cells. However, palmitoylcyclohexamide (100 μM) and palmitoylisopropylamide (30 and 100 μM) produced more inhibition of [3H]-AEA uptake than expected to result from inhibition of [3H]-AEA metabolism alone.In intact C6 cells, palmitoylisopropylamide and oleoylethanolamide inhibited formation of [3H]-ethanolamine from [3H]-AEA to a similar extent as AM404, whereas palmitoylethanolamide, palmitoylcyclohexamide and R-palmitoyl-(2-methyl)ethanolamide were less effective.These data provide useful information upon the ability of palmitoylethanolamide analogues to act as 'entourage' compounds. Palmitoylisopropylamide may prove useful as a template for design of compounds that reduce the cellular accumulation and metabolism of AEA without affecting either CB1 or CB2 receptors.

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