Pharmacological properties of rat brain fatty acid amidohydrolase in different subcellular fractions using palmitoylethanolamide as substrate

In the present study, the pharmacological properties of fatty acid amide hydrolase (FAAH) in subcellular fractions of rat brain were investigated using palmitoylethanolamide (PEA) and arachidonyl ethanolamide (anandamide, AEA) as substrates. FAAH hydrolysed [H-3]PEA in crude homogenates with median K-m and V-max values of 2.9 mu M and 2.14 nmol.(mg protein)(-1).min(-1), respectively. [H-3]PEA hydrolysis was inhibited both by non-radioactive AEA (with a K-i Value very similar to the K-m Value for [H-3]AEA as substrate using the same assay) and by R(-)ibuprofen (mixed-type inhibition K-i and K-i' values 88 and 720 mu M, respectively). FAAH activity towards both [H-3]PEA and [H-3]AEA was in the order microsomal > synaptosomal = mitochondrial > crude nuclear > myelin = cytosol, but there were no differences between the relative activities towards the two substrates in any of the fractions. [H-3]PEA hydrolysis in mitochondrial, myelin, microsomal, and synaptosomal fractions was inhibited by oleyl trifluoromethylketone, phenylmethylsulphonyl fluoride, and the R(-)- and S(+)-enantiomers of the nonsteroidal anti-inflammatory drug ibuprofen, with mean IC50 Values in the ranges 0.028-0.041, 0.31-0.52, 67-110, and 130-260 mu M, respectively. It is concluded that the pharmacological properties of FAAH in the different subcellular fractions are very similar. (C) 2000 Elsevier Science Inc.