Endocannabinoid 2-arachidonylglycerol protects primary cultured neurons against homocysteine-induced impairments in rat caudate nucleus through CB1 receptor

Elevation of Plasma 2-Arachidonoylglycerol Levels in Alzheimer's Disease Patients as a Potential Protective Mechanism against Neurodegenerative Decline

BACKGROUND

Growing evidence suggests that the endocannabinoid system is involved in the pathogenesis of Alzheimer's disease (AD) and atherosclerosis.

OBJECTIVE

The purpose of this study was to investigate the activation of the endocannabinoid system in AD in vivo and the possible intermediate role of atherosclerosis.

METHODS

We enrolled 41 patients with probable AD, and 30 age- and gender-matched controls. All subjects underwent: ultrasound examination of cerebral and neck vessels (including intima-media thickness and plaque stenosis evaluation); blood sampling to measure levels of endocannabinoid [anandamide (AEA), 2-arachidonoylglycerol (2-AG)] and endogenous AEA analogues [N-palmitoyl-ethanolamide (PEA); N-oleoyl-ethanolamide]; neuropsychological evaluation and brain MRI (atrophy, white matter hyperintensity volume).

RESULTS

2-AG levels were higher in AD patients compared to controls (Mann-Whitney test p = 0.021). In the AD group, 2-AG correlated to white matter hyperintensity volume (r = 0.415, p = 0.015) and was higher in patients with chronic heart ischemic disease (p = 0.023). In AD patients, 2-AG was also positively related to memory (r = 0.334, p = 0.05) and attention (r = 0.423, p = 0.018) performances. Constructional praxia test scores were lower in patients with higher levels of PEA (r =-0.389, p = 0.019).

CONCLUSION

AD patients present high plasma 2-AG levels, also in relation to heart ischemic disease and cerebral leukoaraiosis. This may be a protective mechanism hindering neurodegeneration, but it may also play an ambivalent role on cerebrovascular circulation. The increase in 2-AG and PEA levels observed with ongoing pathological processes may differently modulate cognitive performances.

Endocannabinoid 2-Arachidonoylglycerol Suppresses LPS-Induced Inhibition of A-Type Potassium Channel Currents in Caudate Nucleus Neurons Through CB1 Receptor

Inflammation plays a pivotal role in the pathogenesis of many diseases in the central nervous system. Caudate nucleus (CN), the largest nucleus in the brain, is also implicated in many neurological disorders. 2-Arachidonoylglycerol (2-AG), the most abundant endogenous cannabinoid, has been shown to exhibit neuroprotective effects through its anti-inflammatory action from some proinflammatory stimuli. However, the neuroprotective mechanism of 2-AG is complex and has not been fully understood. A-type K(+) channels critically regulate neuronal excitability and have been demonstrated to be associated with some nervous system diseases. The aim of this study was to explore whether A-type K(+) channels were involved in neurotoxicity of lipopolysaccharides (LPS) and the neuroprotective mechanism of 2-AG in CN neurons. Whole cell patch clamp recording was used to investigate the influence of LPS on the function of A-type K(+) channels and its modulation by 2-AG in primary cultured rat CN neurons. Our findings showed that in cultured CN neurons, LPS significantly decreased the A-type potassium currents (I A) in a voltage-insensitive way. The further data demonstrated that an elevation of 2-AG levels by directly applying exogenous 2-AG or inhibiting monoacylglycerol lipase (MAGL) to prevent 2-AG hydrolysis was capable of suppressing the LPS-induced inhibition of IA and the action of 2-AG is mediated through CB1 receptor-dependant way. The study provides a better understanding of inflammation-related neurological disorders and suggests the therapeutic potential for 2-AG for the treatment of these diseases.

Lipopolysaccharide suppresses carboxylesterase 2g activity and 2-arachidonoylglycerol hydrolysis: A possible mechanism to regulate inflammation

Inflammation is an important part of the innate immune response and is involved in the healing of many disease processes; however, chronic inflammation is a harmful component of many diseases. The regulatory mechanisms of inflammation are incompletely understood. One possible regulatory mechanism is the endocannabinoid system. Endocannabinoids such as 2-arachidonoylglycerol (2-AG) and anandamide (AEA) are generally anti-inflammatory via engagement of the cannabinoid receptor 2 (CB2) on innate cells; therefore, preventing the degradation of endocannabinoids by specific serine hydrolases such as fatty acid amide hydrolase (FAAH), monoacylglycerol lipase (MAGL), and carboxylesterases (CES) might decrease inflammation. We hypothesized that the activities of these catabolic enzymes would decrease with a subsequent increase in 2-AG and AEA in a model of inflammation. Mice were injected with lipopolysaccharide (LPS) for 6 or 24h, and inflammation was confirmed by an increase in interleukin-6 (il6) and il17 gene expression. Activity-based protein profiling (ABPP) of serine hydrolases showed no significant difference in various serine hydrolase activities in brain or liver, whereas a modest decrease in Ces activity in spleen after LPS administration was noted. 2-AG hydrolase activity in the spleen was also decreased at 6h post LPS, which was corroborated by LPS treatment of splenocytes ex vivo. ABPP-MudPIT proteomic analysis suggested that the decreased 2-AG hydrolysis in spleen was due to a reduction in Ces2g activity. These studies suggest that the endocannabinoid system could be activated via suppression of a 2-AG catabolic enzyme in response to inflammatory stimuli as one mechanism to limit inflammation.

Effect of Homocysteine on Voltage-Gated Sodium Channel Currents in Primary Cultured Rat Caudate Nucleus Neurons and Its Modulation by 2-Arachidonylglycerol

Homocysteine (Hcy) is an important risk factor for Alzheimer's disease (AD) and other neurodegenerative diseases. Caudate nucleus (CN), the largest nucleus in the brain, is also implicated in many neurological disorders. 2-Arachidonoylglycerol (2-AG), the most abundant endogenous cannabinoid, has been shown to exhibit neuroprotective effects from many stimuli in the central nervous system (CNS). Furthermore, it has been reported that voltage-gated sodium channels (VGSCs) are the common targets of many neuronal damages and drugs. However, it is still not clear whether VGSCs are involved in the neurotoxicity of Hcy and the neuroprotective effect of 2-AG in CN neurons. In the present study, whole-cell patch clamp recording was used to invest the action of Hcy on sodium currents in primary cultured rat CN neurons and its modulation by 2-AG. The results showed that in cultured CN neurons, pathological concentration of Hcy (100 μM) significantly increased the voltage-gated sodium currents (I(Na)) and produced a hyperpolarizing shift in the activation-voltage curve of I(Na). The further data demonstrated 2-AG is capable of suppressing elevation of Hcy-induced increase in I(Na) and hyperpolarizing shift of activation curves most partly through CB1 receptor-dependent way. Our study provides a better understanding of Hcy-associated neurological disorders and suggests the therapeutic potential for 2-AG for the treatment of these diseases.

Monoacylglycerol lipase inhibitor protects primary cultured neurons against homocysteine-induced impairments in rat caudate nucleus through COX-2 signaling

AIMS

URB602 is a selective inhibitor of monoacylglycerol lipase (MAGL), a serine hydrolase involved in the biological deactivation of the endocannabinoid 2-arachidonoyl glycerol (2-AG). It has been described that URB602 significantly enhances depolarization-induced increases in 2-AG. A high level of homocysteine (Hcy) is a modifiable risk factor for developing Alzheimer's disease (AD). The aim of this study was to investigate the protective effects of URB602 on Hcy-induced impairments underlying its cellular and molecular mechanism in primary cultured caudate nucleus (CN) neurons.

MAIN METHODS

The expressions of cyclooxygenase-2 (COX-2), ERK1/2, NF-κB and IκB-α as well as cleaved caspase-3 and p-Bcl-2 in Hcy-, URB602 or SR1 (a selective inhibitor of CB1 receptor)-treated primary cultured neurons in CN were measured by immunoblotting technique and neurotoxicity assays were performed by using Hoechst staining.

KEY FINDINGS

The MAGL inhibitor URB602 exerted a neuroprotective effect on Hcy-induced impairment through suppression of cyclooxygenase-2 (COX-2) elevation and ERK1/2 and NF-κB phosphorylation as well as suppressions of IκB-α degradation in a CB1 receptor-dependent way. Moreover, anti-neuronal impairments of URB602 were mediated by modulating down-regulation of cleaved caspase-3 expression and up-regulation of p-Bcl-2 expression in a CB1 receptor-dependent manner in primary cultured CN neurons.

SIGNIFICANCE

These data suggest that the MAGL inhibitor is a promising therapeutic target for some neurodegenerative disorders, such as AD, via the COX-2 signaling pathway.