4-Aminocyclopentane-1,3-diols as platforms for diversity: synthesis of anandamide analogs.

Starting from cyclopentadiene, two racemic mixtures of 4-aminocyclopentane-1,3-diols were prepared in 8 steps and characterized. Structure determination proved the anticipated trans-orientation of the two oxygen atoms with respect to the plane of the ring. The fragment-like new compounds are small and hydrophilic, devoid of rotatable bonds, and offer stereochemically defined attachment points for substituents. Thus, these platforms for diversity are suitable starting points for the construction of combinatorial libraries of lead-like 4-amidocyclopentane-1,3-diols or natural product analogs. As a proof of concept, cyclopentanoid anandamide analogs were prepared using these molecular platforms and evaluated as tools for the investigation of unresolved issues in the molecular biology of anandamide.

Effects of acute and repeated restraint stress on endocannabinoid content in the amygdala, ventral striatum, and medial prefrontal cortex in mice.

Endocannabinoid signaling has been implicated in habituation to repeated stress. The hypothesis that repeated exposures to stress alters endocannabinoid signaling in the limbic circuit was tested by restraining male mice for 30 min/day for 1, 7, or 10 days and measuring brain endocannabinoid content. Amygdalar N-arachidonylethanolamine was decreased after 1, 7, and 10 restraint episodes; 2-arachidonylglycerol was increased after the 10th restraint. A similar pattern occurred in the medial prefrontal cortex (mPFC): N-arachidonylethanolamine was decreased after the 7th and 10th restraints and 2-arachidonylglycerol was increased after the 10th restraint. In the ventral striatum, the pattern reversed: N-arachidonylethanolamine was increased after the 10th restraint and 2-arachidonylglycerol was decreased after the 7th restraint. Palmitoylethanolamide contents changed in parallel with N-arachidonylethanolamine in the amygdala and ventral striatum. A single restraint episode did not affect the activity of fatty acid amide hydrolase (FAAH) in any of the brain regions examined. After the 10th restraint, both V(max) and K(m) for N-arachidonylethanolamine were increased in the mPFC; while only the V(max) was increased in the amygdala. On the other hand, the V(max) of FAAH was decreased in ventral striatum after the 10th restraint. After the 10th restraint, the maximum velocity for 2-oleoylglycerol hydrolysis was increased in mPFC; no other changes in 2-oleoylglycerol hydrolysis occurred. Repeated exposure to restraint produced no changes in CB(1) receptor density in any of the areas examined. These studies are consistent with the hypothesis that stress exposure alters endocannabinoid signaling in the brain and that alterations in endocannabinoid signaling occur during habituation to stress.

Accumulation of anandamide: evidence for cellular diversity.

The endocannabinoid N-arachidonylethanolamine (AEA) is accumulated by many cell types, but the mechanisms are unknown. Data from several laboratories are consistent with the hypothesis that the accumulation of AEA occurs via the action of a transmembrane carrier that binds and transports AEA. However, other data suggest that AEA is sufficiently lipophilic to transverse plasma membranes by passive diffusion and will accumulate if it is catabolized intracellularly. The controversy is muddied by the use of different cellular models and assays, all of which are assumed to be studying the same phenomena. The purpose of the studies reported herein was: first, to compare AEA accumulation and accumulation inhibitors in cerebellar granule neurons with a glioma cell line; and, second, to compare the neuronal accumulation of AEA with a closely related analog, N-palmitoylethanolamine (PEA). We have found that the accumulation of AEA by neurons and C6 glioma exhibits different affinity for AEA and inhibitor profiles. In addition, we find that the accumulation of AEA and PEA by neurons differs in the amount accumulated and in heterologous inhibition. These studies add to the evidence that the neuronal accumulation of AEA uniquely requires more than passive diffusion and fatty acid amide-mediated catabolism of intracellular AEA.

Cellular accumulation of anandamide: consensus and controversy.

The endocannabinoids N-arachidonylethanolamine (AEA or anandamide) and 2-arachidonylglycerol (2-AG) are hypothesized to function in the brain as interneuronal signaling molecules. Prevailing models of the actions of these molecules require that they traverse cellular plasma membranes twice; first, following cellular synthesis and second, prior to enzymatic hydrolysis. The transmembrane movement of AEA has been studied in multiple laboratories with a primary focus on its cellular accumulation following extracellular administration. Although there are areas of consensus among laboratories regarding AEA accumulation, several aspects are very unclear. In particular, there is a lack of consensus in the literature regarding the importance of AEA hydrolysis by fatty acid amide hydrolase in maintaining the driving force for accumulation. Furthermore, evidence for and against a transmembrane carrier protein has been published. We have reviewed the available literature and present a working model of the processes that are involved in the cellular accumulation of AEA. It is our hypothesis that transmembrane movement of AEA is regulated by concentration gradient between extracellular and intracellular free AEA. Furthermore, it is our view that a significant portion of the intracellular AEA in most cells is sequestered either by a protein or lipid compartment and that AEA sequestered in this manner does not equilibrate directly with the extracellular pool. Finally, we discuss the available data that have been presented in support of a transmembrane carrier protein for AEA.