Natural Potent NAAA Inhibitor Atractylodin Counteracts LPS-Induced Microglial Activation.

N-acylethanolamine-hydrolyzing acid amidase (NAAA) is a lysosomal enzyme that inhibits the degradation of palmitoylethanolamide (PEA), an endogenous lipid that induces analgesic, anti-inflammation, and anti-multiple sclerosis through PPARα activation. Only a few potent NAAA inhibitors have been reported to date, which is mainly due to the restricted substrate-binding site of NAAA. Here, we established a high-throughput fluorescence-based assay for NAAA inhibitor screening. Several new classes of NAAA inhibitors were discovered from a small library of natural products. One of these is atractylodin, a polyethylene alkyne compound from the root of Atractylodes lancea (Thunb) DC., which significantly inhibits NAAA activity and has an IC50 of 2.81 µM. Kinetic analyses and dialysis assays suggested that atractylodin engages in competitive inhibition via reversible reaction to the enzyme. Docking assays revealed that atractylodin occupies the catalytic cavity of NAAA, where the atractylodin furan head group has a hydrophobic-related interaction with the backbone of the Trp181 and Leu152 residues of human NAAA. Further investigation indicated that atractylodin significantly increases PEA and OEA levels and dose-dependently inhibits LPS-induced nitrate, TNF-α, IL-1ß, and IL-6 pro-inflammatory cytokine release in BV-2 microglia. Our results show that atractylodin elevates cellular PEA levels and inhibits microglial activation by inhibiting NAAA activity, which in turn could contribute to NAAA functional research.

Inhibition of N-acylethanolamine acid amidase reduces nicotine-induced dopamine activation and reward.

Tobacco smoke is the leading preventable cause of death in the world and treatments aimed to increase success rate in smoking cessation by reducing nicotine dependence are sought. Activation of peroxisome proliferator-activated receptor-alpha (PPARα) by synthetic or endogenous agonists was shown to suppress nicotine-induced activation of mesolimbic dopamine system, one of the major neurobiological substrates of nicotine dependence, and nicotine-seeking behavior in rats and monkeys. An alternative indirect way to activate PPARα is inhibition of N-acylethanolamine acid amidase (NAAA), one of the major hydrolyzing enzyme for its endogenous agonists palmitoylethanolamide (PEA) and oleoylethanolamide (OEA). We synthetized a novel specific brain permeable NAAA inhibitor, AM11095. We administered AM11095 to rats and carried out brain lipid analysis, a functional observational battery (FOB) to assess toxicity, in vivo electrophysiological recording from dopamine cells in the ventral tegmental area, brain microdialysis in the nucleus accumbens shell and behavioral experiments to assess its effect on nicotine -induced conditioned place preference (CPP). AM11095 (5 and 25 mg/kg, i.p.) was devoid of neurotoxic and behavioral effects and did not affect motor behavior and coordination. This NAAA inhibitor (5 mg/kg i.p.) increased OEA and PEA levels in the hippocampus and cortex, prevented nicotine-induced activation of mesolimbic dopamine neurons in the ventral tegmental area, nicotine-induced elevation of dopamine levels in the nucleus accumbens shell and decreased the expression of nicotine CPP. Our results indicate that NAAA inhibitors represent a new class of pharmacological tools to modulate brain PEA/PPARα signalling and show potential in the treatment of nicotine dependence.

Inflammation-restricted anti-inflammatory activities of a N-acylethanolamine acid amidase (NAAA) inhibitor F215.

N-Acylethanolamine acid amidase (NAAA) is a cysteine enzyme that catalyzes the hydrolysis of palmitoylethanolamide (PEA). Pharmacological blockage of NAAA elevates PEA levels and exerts powerful anti-inflammatory activities. We have recently identified a highly potent NAAA inhibitor F215. Here, we demonstrated that F215 was an unusual inflammation-restricted NAAA inhibitor. In lipopolysaccharides (LPS) induced acute lung injury (ALI) model, F215 markedly accelerated inflammation resolution, promoted clearance of neutrophils infiltration and alveolar repair in the lungs. F215 efficiently inhibited NAAA and protected endogenous PEA from degradation in ALI model, but it cannot readily suppress the NAAA activity in naïve mice. The inflammation-restricted effect of F215 was further confirmed in the alveolar macrophage, F215 only increased PEA levels and exerted anti-inflammatory effects in activated macrophages, but not in unstimulated macrophages. Moreover, we also showed that the pharmacological effects of F215 were restricted to the local inflamed skin elicited by 12-o-tetradecanoylphorbol-13-acetate (TPA), but not the normal tissues. We believe that F215 could be a useful probe to investigate the function of NAAA, as well as a potent anti-inflammatory agent, and its inflammation-restricted feature might offer a new approach to prevent potential side effects of systemic enzyme inhibition.

Identification of highly potent N-acylethanolamine acid amidase (NAAA) inhibitors: Optimization of the terminal phenyl moiety of oxazolidone derivatives.

N-acylethanolamine acid amidase (NAAA) is a cysteine hydrolase that participates in the deactivation of fatty acid ethanolamides, such as palmitoylethanolamide (PEA). NAAA inhibition may provide a potential therapeutic strategy for the treatment of diseases in which higher PEA level is desired. In the present study, we reported the structure-activity relationship (SAR) studies for oxazolidone derivatives as NAAA inhibitors. A series of substituents or alkyl replacements for the terminal phenyl ring of oxazolidone derivatives were examined. The results showed that the inhibition potency of these oxazolidone derivatives towards NAAA depends on the sizes, flexibility, and lipophilicity of the terminal groups. SAR results suggested that small lipophilic 3-phenyl substituents or hydroxy-containing 4-phenyl substituents were preferable for optimal potency. Furthermore, the distal aliphatic replacement is also preferred for high inhibitory potency. Rapid dilution and kinetic analysis suggested that oxazolidone derivatives with different terminal phenyl moieties inhibited NAAA via different mechanisms. This study identified several highly potent NAAA inhibitors, including 1a (F215, IC50 = 0.009 µM), 1o (IC50 = 0.061 µM) and 2e (IC50 = 0.092 µM), and also determined structural requirements of oxazolidone derivatives for potent inhibition against NAAA.