Galantamine is not a positive allosteric modulator of human α4ß2 or α7 nicotinic acetylcholine receptors.

BACKGROUND AND PURPOSE: The alkaloid galantamine was originally isolated from the green snowdrop Galanthus woronowii and is currently marketed as a drug for treatment of mild to moderate dementia in patients with Alzheimer's disease. In addition to a well-documented proficiency to inhibit acetylcholinesterase, galantamine has been reported to increase neuronal nicotinic ACh (nACh) receptor function by acting as a positive allosteric modulator. Yet there remains controversy regarding these findings in the literature. To resolve this conundrum, we evaluated galantamine actions at α4ß2 and α7, which represent the nACh receptors most commonly associated with mammalian cognitive domains. EXPERIMENTAL APPROACH: α4ß2 [in (α4)3 (ß2)2 and (α4)2 (ß2)3 stoichiometries] and α7 nACh receptors were expressed in Xenopus laevis oocytes and subjected to two-electrode voltage-clamp electrophysiological experiments. Galantamine (10 nM to 100 µM) was evaluated for direct agonist effects and for positive modulation by co-application with sub-maximally efficacious concentrations of ACh. In addition, similar experiments were performed with α7 nACh receptors stably expressed in HEK293 cells using patch-clamp electrophysiology. KEY RESULTS: In concentrations ranging from 10 nM to 1 µM, galantamine did not display direct agonism nor positive modulatory effects at any receptor combination tested. At concentrations from 10 µM and above, galantamine inhibited the activity with a mechanism of action consistent with open-channel pore blockade at all receptor types. CONCLUSION AND IMPLICATIONS: Based on our data, we conclude that galantamine is not a positive allosteric modulator of α7 or α4ß2 receptors, which represent the majority of nACh receptors in mammalian brain.

Cannabinoid effects on ß amyloid fibril and aggregate formation, neuronal and microglial-activated neurotoxicity in vitro.

Cannabinoid (CB) ligands have demonstrated neuroprotective properties. In this study we compared the effects of a diverse set of CB ligands against ß amyloid-mediated neuronal toxicity and activated microglial-conditioned media-based neurotoxicity in vitro, and compared this with a capacity to directly alter ß amyloid (Aß) fibril or aggregate formation. Neuroblastoma (SH-SY5Y) cells were exposed to Aß1-42 directly or microglial (BV-2 cells) conditioned media activated with lipopolysaccharide (LPS) in the presence of the CB1 receptor-selective agonist ACEA, CB2 receptor-selective agonist JWH-015, phytocannabinoids Δ(9)-THC and cannabidiol (CBD), the endocannabinoids 2-arachidonoyl glycerol (2-AG) and anandamide or putative GPR18/GPR55 ligands O-1602 and abnormal-cannabidiol (Abn-CBD). TNF-α and nitrite production was measured in BV-2 cells to compare activation via LPS or albumin with Aß1-42. Aß1-42 evoked a concentration-dependent loss of cell viability in SH-SY5Y cells but negligible TNF-α and nitrite production in BV-2 cells compared to albumin or LPS. Both albumin and LPS-activated BV-2 conditioned media significantly reduced neuronal cell viability but were directly innocuous to SH-SY5Y cells. Of those CB ligands tested, only 2-AG and CBD were directly protective against Aß-evoked SH-SY5Y cell viability, whereas JWH-015, THC, CBD, Abn-CBD and O-1602 all protected SH-SY5Y cells from BV-2 conditioned media activated via LPS. While CB ligands variably altered the morphology of Aß fibrils and aggregates, there was no clear correlation between effects on Aß morphology and neuroprotective actions. These findings indicate a neuroprotective action of CB ligands via actions at microglial and neuronal cells.

Prostaglandin ethanolamides attenuate damage in a human explant colitis model.

Endocannabinoids are protective in animal colitis models. As endocannabinoids also form novel prostaglandin ethanolamides (prostamides) via COX-2, we investigated the effects of prostamides and other COX-2 mediators on tissue damage in an ex vivo human mucosal explant colitis model. Healthy human colonic mucosae were incubated with pro-inflammatory cytokines TNF-α and IL-1ß to elicit colitis-like tissue damage. The PGF-ethanolamide analogue, bimatoprost decreased colitis scores which were reversed by a prostamide-specific antagonist AGN 211334, but not the FP receptor antagonist AL-8810. PGF-ethanolamide and PGE-ethanolamide also reduced cytokine-evoked epithelial damage. Anandamide was protective in the explant colitis model; however COX-2 inhibition did not alter its effects, associated with a lack of COX-2 induction in explant mucosal tissue. These findings support an anti-inflammatory role for prostamides and endocannabinoids in the human colon.

Contrasting protective effects of cannabinoids against oxidative stress and amyloid-ß evoked neurotoxicity in vitro.

Cannabinoids have been widely reported to have neuroprotective properties in vitro and in vivo. In this study we compared the effects of CB1 and CB2 receptor-selective ligands, the endocannabinoid anandamide and the phytocannabinoid cannabidiol, against oxidative stress and the toxic hallmark Alzheimer's protein, ß-amyloid (Aß) in neuronal cell lines. PC12 or SH-SY5Y cells were selectively exposed to either hydrogen peroxide, tert-butyl hydroperoxide or Aß, alone or in the presence of the CB1 specific agonist arachidonyl-2'-chloroethylamide (ACEA), CB2 specific agonist JWH-015, anandamide or cannabidiol. Cannabidiol improved cell viability in response to tert-butyl hydroperoxide in PC12 and SH-SY5Y cells, while hydrogen peroxide-mediated toxicity was unaffected by cannabidiol pretreatment. Aß exposure evoked a loss of cell viability in PC12 cells. Of the cannabinoids tested, only anandamide was able to inhibit Aß-evoked neurotoxicity. ACEA had no effect on Aß-evoked neurotoxicity, suggesting a CB1 receptor-independent effect of anandamide. JWH-015 pretreatment was also without protective influence on PC12 cells from either pro-oxidant or Aß exposure. None of the cannabinoids directly inhibited or disrupted preformed Aß fibrils and aggregates. In conclusion, the endocannabinoid anandamide protects neuronal cells from Aß exposure via a pathway unrelated to CB1 or CB2 receptor activation. The protective effect of cannabidiol against oxidative stress does not confer protection against Aß exposure, suggesting divergent pathways for neuroprotection of these two cannabinoids.