The elmiric acids: biologically active anandamide analogs

Abstract

As chemical entities, lipoamino acids have been known for some time. However, more recently their occurrence and importance in mammalian species has been discovered. They appear to have close relationships with the endocannabinoids not only structurally but also in terms of biological actions. The latter include analgesia, anti-inflammatory effects, inhibition of cell proliferation and calcium ion mobilization. To date about 40 naturally occurring members of this family have been identified and, additionally, several synthetic analogs have been prepared and studied. To facilitate their identity, a nomenclature system has been suggested based on the name elmiric acid (EMA). The prototypic example, N-arachidonoyl glycine, does not bind to CB1, however it does inhibit the glycine transporter GLYT2a and also appears to be a ligand for the orphan G-protein-coupled receptor GPR18. It may also have a role in regulating tissue levels of anandamide by virtue of its inhibitory effect on FAAH the enzyme that mediates inactivation of anandamide. Its concentration in rat brain is several-fold higher than anandamide supporting its possible role as a physiological mediator. Future studies should be aimed at elucidating the actions of all of the members of this interesting family of molecules.

Figure 1. Effects of elmiric acids on the proliferation of mouse macrophage RAW cells

The data shown were previously reported in Burstein et al. (2007). The cells were treated with 1 and 10 uM elmiric acid whose identity is shown on the Y axis (designated as 1 or 10 on the Y axis). Luminometer units are directly proportional to the number of metabolically active cells and are a measure of ATP levels.

Figure 2. Effects of elmiric acids on the ratio of iPGJ/iPGE* in RAW cell media

The data shown were previously reported in Burstein et al. (2007). All of the ratio values greater than 20 are significant at the 95% confidence level when compared to the DMSO-LPS control by ANOVA. Note: see Table 1 for structures. *i denotes immunoreactive.

Figure 3. Effects of elmiric acids in the mouse subcutaneous pouch assay

The data shown were previously reported in Burstein et al. (2007). P<0.05 by ANOVA vs. the oil control. Note: see Table 1 for structures.

Figure 4. Effects of elmiric acids on ear edema compared with increases in prostaglandin ratio

The data presented here were previously reported in Burstein et al. (2007). The values shown in this comparison represent the maximum response in each case. Note: EMA-1 = glycine; EMA-2 = alanine; EMA-22 = 1,1-dimethylglycine; EMA-25 = 1-amino-cyclohexane-carboxylic acid. *i = immunoreactive.

Figure 5. EMA-1 (20:4) – induced stimulation of arachidonic acid release from RAW cells (Burstein, unpublished findings)

Cells were grown and maintained as described previously (Pestonjamasp and Burstein, 1998). Following a 2 hr labeling period with ¹⁴C-arachidonic acid, the media (RPMI+0.1% BSA) were changed and the cells treated for 1 hr with EMA-1 (20:4) in 10 ul of DMSO. The control was 10 ul of DMSO and there were 4 replicates of each treatment concentration. Release was measured by liquid scintillation counting on a 0.1 ml aliquot of medium. Values shown are the means (∓) SD. Note: The cells were treated with non-radioactive EMA-1 (20:4).

Figure 6. Putative mechanism for the anti-inflammatory actions of the elmiric acids

Induction of inflammation. A wide range of pro inflammatory agonists can activate various forms of phospholipase A₂ causing the release of free arachidonic acid from pools of phospholipids. Several routes of regulated biotransformation can then lead to elevated levels of various mediators of inflammation. Resolution by elmiric acids. An elmiric acid, activating a receptor, promotes the mobilization of Ca⁺⁺ that in turn causes the release of free arachidonic acid. COX-2 action then results in the production of PGG₂ and PGH₂ that is converted by a terminal synthetase to PGD₂. In a non-enzymic process, PGD₂ is transformed into 15-deoxy-PGJ₂, a potent anti inflammatory mediator.