Effect of nitric oxide donors on membrane tritium accumulation of endocannabinoids and related endogenous lipids

Transport of endocannabinoids across the plasma membrane and within the cell

Endocannabinoids are readily accumulated from the extracellular space by cells. Although their uptake properties have the appearance of a process of facilitated diffusion, it is by no means clear as to whether there is a plasma membrane transporter dedicated to this task. Intracellular carrier proteins that shuttle the endocannabinoid anandamide from the plasma membrane to its intracellular targets such as the metabolic enzyme, fatty acid amide hydrolase, have been identified. These include proteins with other primary functions, such as fatty-acid-binding proteins and heat shock protein 70, and possibly a fatty acid amide hydrolase-like anandamide transporter protein. Thus, anandamide uptake can be adequately described as a diffusion process across the plasma membrane followed by intracellular carrier-mediated transport to effector molecules, catabolic enzymes and sequestration sites, although it is recognized that different cells are likely to utilize different mechanisms of endocannabinoid transport depending upon the utility of the endocannabinoid for the cell in question.

Fine-tuning of defensive behaviors in the dorsal periaqueductal gray by atypical neurotransmitters

This paper presents an up-to-date review of the evidence indicating that atypical neurotransmitters such as nitric oxide (NO) and endocannabinoids (eCBs) play an important role in the regulation of aversive responses in the periaqueductal gray (PAG). Among the results supporting this role, several studies have shown that inhibitors of neuronal NO synthase or cannabinoid type 1 (CB1) receptor agonists cause clear anxiolytic responses when injected into this region. The nitrergic and eCB systems can regulate the activity of classical neurotransmitters such as glutamate and _γ-aminobutyric acid (GABA) that control PAG activity. We propose that they exert a ‘fine-tuning’ regulatory control of defensive responses in this area. This control, however, is probably complex, which may explain the usually bell-shaped dose-response curves observed with drugs that act on NO- or CB1-mediated neurotransmission. Even if the mechanisms responsible for this complex interaction are still poorly understood, they are beginning to be recognized. For example, activation of transient receptor potential vanilloid type-1 channel (TRPV1) receptors by anandamide seems to counteract the anxiolytic effects induced by CB1 receptor activation caused by this compound. Further studies, however, are needed to identify other mechanisms responsible for this fine-tuning effect.

Biochanin A, a naturally occurring inhibitor of fatty acid amide hydrolase

BACKGROUND AND PURPOSE

Inhibitors of fatty acid amide hydrolase (FAAH), the enzyme responsible for the metabolism of the endogenous cannabinoid (CB) receptor ligand anandamide (AEA), are effective in a number of animal models of pain. Here, we investigated a series of isoflavones with respect to their abilities to inhibit FAAH.

EXPERIMENTAL APPROACH

In vitro assays of FAAH activity and affinity for CB receptors were used to characterize key compounds. In vivo assays used were biochemical responses to formalin in anaesthetized mice and the 'tetrad' test for central CB receptor activation.

KEY RESULTS

Of the compounds tested, biochanin A was adjudged to be the most promising. Biochanin A inhibited the hydrolysis of 0.5 microM AEA by mouse, rat and human FAAH with IC(50) values of 1.8, 1.4 and 2.4 microM respectively. The compound did not interact to any major extent with CB(1) or CB(2) receptors, nor with FAAH-2. In anaesthetized mice, URB597 (30 microg i.pl.) and biochanin A (100 microg i.pl.) both inhibited the spinal phosphorylation of extracellular signal-regulated kinase produced by the intraplantar injection of formalin. The effects of both compounds were significantly reduced by the CB(1) receptor antagonist/inverse agonist AM251 (30 microg i.pl.). Biochanin A (15 mg.kg(-1) i.v.) did not increase brain AEA concentrations, but produced a modest potentiation of the effects of 10 mg.kg(-1) i.v. AEA in the tetrad test.

CONCLUSIONS AND IMPLICATIONS

It is concluded that biochanin A, in addition to its other biochemical properties, inhibits FAAH both in vitro and peripherally in vivo.