Progress in the development of ß-lactams as N-Acylethanolamine Acid Amidase (NAAA) inhibitors: Synthesis and SAR study of new, potent N-O-substituted derivatives.

The anti-inflammatory effects resulting from raising the levels of palmitoylethanolamide (PEA), an endogenous bioactive lipid, led to envisage N-Acylethanolamine Acid Amidase (NAAA), the cysteine hydrolase mainly responsible for PEA degradation, as an attractive target for small molecule inhibitors. Previous work in our group identified serine-derived ß-lactams as potent and systemically active inhibitors of NAAA activity. Aiming to expand the SAR study around this class of compounds, we investigated the effect of the substitution on the endocyclic nitrogen by designing and synthesizing a series of N-substituted ß-lactams. The present work describes the synthesis of new N-O-alkyl and N-O-aryl substituted ß-lactams and reports the results of the structure activity relationship (SAR) study leading to the discovery of a novel, single-digit nanomolar NAAA inhibitor (37). Compound 37 was shown in vitro to inhibit human NAAA via S-acylation of the catalytic cysteine, and to display very good selectivity vs. human Acid Ceramidase, a cysteine amidase structurally related to NAAA. Preliminary in vivo studies showed that compound 37, administered topically, reduced paw edema and heat hyperalgesia in a carrageenan-induced inflammation mouse model. The high in vitro potency of 37 as NAAA inhibitor, and its encouraging in vivo activity qualify this compound as a new tool for the study of the role of NAAA in inflammatory and pain states.

An Important Role for N-Acylethanolamine Acid Amidase in the Complete Freund's Adjuvant Rat Model of Arthritis.

The endogenous lipid amides, palmitoylethanolamide (PEA) and oleoylethanolamide (OEA), exert marked antinociceptive and anti-inflammatory effects in animal models by engaging nuclear peroxisome proliferator-activated receptor-α. PEA and OEA are produced by macrophages and other host-defense cells and are deactivated by the cysteine amidase, N-acylethanolamine acid amidase (NAAA), which is highly expressed in macrophages and B-lymphocytes. In the present study, we examined whether a) NAAA might be involved in the inflammatory reaction triggered by injection of complete Freund's adjuvant (CFA) into the rat paw and b) administration of 4-cyclohexylbutyl-N-[(S)-2-oxoazetidin-3-yl]-carbamate (ARN726), a novel systemically active NAAA inhibitor, attenuates such reaction. Injection of CFA into the paw produced local edema and heat hyperalgesia, which were accompanied by decreased PEA and OEA content (assessed by liquid chromatography/mass spectrometry) and increased NAAA levels (assessed by Western blot and ex vivo enzyme activity measurements) in paw tissue. Administration of undec-10-ynyl-N-[(3S)-2-oxoazetidin-3-yl] carbamate (ARN14686), a NAAA-preferring activity-based probe, revealed that NAAA was catalytically active in CFA-treated paws. Administration of ARN726 reduced NAAA activity and restored PEA and OEA levels in inflamed tissues, and significantly decreased CFA-induced inflammatory symptoms, including pus production and myeloperoxidase activity. The results confirm the usefulness of ARN726 as a probe to investigate the functions of NAAA in health and disease and suggest that this enzyme may provide a new molecular target for the treatment of arthritis.

Pharmacological characterization of the peripheral FAAH inhibitor URB937 in female rodents: interaction with the Abcg2 transporter in the blood-placenta barrier.

BACKGROUND AND PURPOSE: URB937 is a peripherally restricted inhibitor of the anandamide-deactivating enzyme fatty-acid amide hydrolase (FAAH). Despite its limited access to the CNS, URB937 produces marked antinociceptive effects in rodents. URB937 is actively extruded from the CNS by the ATP-binding cassette (ABC) membrane transporter, Abcg2. Tissue Abcg2 levels are markedly different between males and females, and this transporter is known to limit the access of xenobiotics to the fetoplacental unit in gestating female rodents. In the present study, we investigated the tissue distribution and antinociceptive properties of URB937 in female mice and rats. EXPERIMENTAL APPROACH: We studied the systemic disposition of URB937 in female mice and the antinociceptive effects of this compound in models of visceral (acetic acid-induced writhing) and inflammatory nociception (carrageenan-induced hyperalgesia) in female mice and rats. Furthermore, we evaluated the interaction of URB937 with the blood-placenta barrier in gestating mice and rats. KEY RESULTS: Abcg2 restricted the access of URB937 to the CNS of female mice and rats. Nevertheless, URB937 produced a high degree of antinociception in female mice and rats in models of visceral and inflammatory pain. Moreover, the compound displayed a restricted access to placental and fetal tissues in pregnant mice and rats. CONCLUSIONS AND IMPLICATIONS: Peripheral FAAH blockade with URB937 reduces nociception in female mice and rats, as previously shown for males of the same species. In female mice and rats, Abcg2 limits the access of URB937, not only to the CNS, but also to the fetoplacental unit. LINKED ARTICLES This article is part of a themed section on Cannabinoids. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.167.issue-8.

Palmitoylethanolamide stimulation induces allopregnanolone synthesis in C6 Cells and primary astrocytes: involvement of peroxisome-proliferator activated receptor-α.

Palmitoylethanolamide (PEA) regulates many pathophysiological processes in the central nervous system, including pain perception, convulsions and neurotoxicity, and increasing evidence points to its neuroprotective action. In the present study, we report that PEA, acting as a ligand of peroxisome-proliferator activated receptor (PPAR)-α, might regulate neurosteroidogenesis in astrocytes, which, similar to other glial cells and neurones, have the enzymatic machinery for neurosteroid de novo synthesis. Accordingly, we used the C6 glioma cell line and primary murine astrocytes. In the mitochondrial fraction from cells stimulated with PEA, we demonstrated an increase in steroidogenic acute regulatory protein (StAR) and cytochrome P450 enzyme (P450scc) expression, both comprising proteins considered to be involved in crucial steps of neurosteroid formation. The effects of PEA were completely blunted by GW6471, a selective PPAR-α antagonist, or by PPAR-α silencing by RNA interference. Accordingly, allopregnanolone (ALLO) levels were increased in supernatant of PEA-treated astrocytes, as revealed by gas chromatography-mass spectrometry, and this effect was inhibited by GW6471. Moreover, PEA showed a protective effect, reducing malondialdehyde formation in cells treated with l-buthionine-(S,R)-sulfoximine, a glutathione depletor and, interestingly, the effect of PEA was partially inhibited by finasteride, a 5α-reductase inhibitor. A similar profile of activity was demonstrated by ALLO and the lack of an additive effect with PEA suggests that the reduction of oxidative stress by PEA is mediated through ALLO synthesis. The present study provides evidence indicating the involvement of the saturated acylethanolamide PEA in ALLO synthesis through PPAR-α in astrocytes and explores the antioxidative activity of this molecule, confirming its homeostatic and protective role both under physiological and pathological conditions.

AM404, an anandamide transport inhibitor, reduces plasma extravasation in a model of neuropathic pain in rat: role for cannabinoid receptors.

Neuropathic pain consequent to peripheral nerve injury has been associated with local inflammation. Following noxious stimulation afferent fibres release substance P (SP) and calcitonin-gene related peptide (CGRP), which are closely related to oedema formation and plasma leakage. The effect of the anandamide transport blocker AM404 has been studied on plasma extravasation after chronic constriction injury (CCI) which consists in a unilateral loose ligation of the rat sciatic nerve (Bennett and Xie, 1988). AM404 (1-3-10 mg kg(-1)) reduced plasma extravasation in the legated paw, measured as mug of Evans Blue per gram of fresh tissue. A strong effect on vascular permeability was also produced by the synthetic cannabinoid agonist WIN 55,212-2 (0.1-0.3-1 mg kg(-1)). Using specific antagonists or enzyme inhibitors, we demonstrate that cannabinoids act at several levels: data on the 3rd day suggest a strong involvement of substance P (SP) and calcitonin gene-related peptide (CGRP) in the control of vascular tone, whereas at the 7th and 14th days the major role seems to be played by prostaglandins (PGs) and nitric oxide (NO). Capsaicin injection in ligated paws of AM404- or WIN 55,212-2-treated rats resulted in an increase of Evans Blue extravasation, suggesting the involvement of the cannabinergic system in the protective effect of C fibres of ligated paws. Taken together, these data demonstrate the efficacy of cannabinoids in controlling pain behaviour through the modulation of several pain mediators and markers of vascular reactivity, such as SP, CGRP, PGs and NO.