Fatty acid amide hydrolase (FAAH) regulates hypercapnia/ischemia-induced increases in n-acylethanolamines in mouse brain

Circulating Endocannabinoids and N-Acylethanolamines in Individuals with Cannabis Use Disorder-Preliminary Findings

BACKGROUND

Endocannabinoids and related N-acylethanolamines (NAEs) are bioactive lipids with important physiological functions and putative roles in mental health and addictions. Although chronic cannabis use is associated with endocannabinoid system changes, the status of circulating endocannabinoids and related NAEs in people with cannabis use disorder (CUD) is uncertain.

METHODS

Eleven individuals with CUD and 54 healthy non-cannabis using control participants (HC) provided plasma for measurement by high-performance liquid chromatography-mass spectrometry of endocannabinoids (2-arachidonoylglycerol (2-AG) and N-arachidonoylethanolamine (AEA)) and related NAE fatty acids (N-docosahexaenoylethanolamine (DHEA) and N-oleoylethanolamine (OEA)). Participants were genotyped for the functional gene variant of FAAH (rs324420, C385A) which may affect concentrations of AEA as well as other NAEs (OEA, DHEA).

RESULTS

In overnight abstinent CUD, AEA, OEA and DHEA concentrations were significantly higher (31-40%; p < 0.05) and concentrations of the endocannabinoid 2-AG were marginally elevated (55%, p = 0.13) relative to HC. There were no significant correlations between endocannabinoids/NAE concentrations and cannabis analytes, self-reported cannabis use frequency or withdrawal symptoms. DHEA concentration was inversely related with marijuana craving (r = -0.86; p = 0.001). Genotype had no significant effect on plasma endocannabinoids/NAE concentrations.

CONCLUSIONS

Our preliminary findings, requiring replication, might suggest that activity of the endocannabinoid system is elevated in chronic cannabis users. It is unclear whether this elevation is a compensatory response or a predating state. Studies examining endocannabinoids and NAEs during prolonged abstinence as well as the potential role of DHEA in craving are warranted.

Measuring brain docosahexaenoic acid turnover as a marker of metabolic consumption

Docosahexaenoic acid (DHA, 22:6n-3) accretion in brain phospholipids is critical for maintaining the structural fluidity that permits proper assembly of protein complexes for signaling. Furthermore, membrane DHA can by released by phospholipase A₂ and act as substrate for synthesis of bioactive metabolites that regulate synaptogenesis, neurogenesis, inflammation, and oxidative stress. Thus, brain DHA is consumed through multiple pathways including mitochondrial β-oxidation, autoxidation to neuroprostanes, as well as enzymatic synthesis of bioactive metabolites including oxylipins, synaptamide, fatty-acid amides, and epoxides. By using models developed by Rapoport and colleagues, brain DHA loss has been estimated to be 0.07-0.26 μmol DHA/g brain/d. Since β-oxidation of DHA in the brain is relatively low, a large portion of brain DHA loss may be attributed to synthesis of autoxidative and bioactive metabolites. In recent years, we have developed a novel application of compound specific isotope analysis to trace DHA metabolism. By the use of natural abundance in ¹³C-DHA in food supply, we are able to trace brain phospholipid DHA loss in free-living mice with estimates ranging from 0.11 to 0.38 μmol DHA/g brain/d, in reasonable agreement with previous methods. This novel fatty acid metabolic tracing methodology should improve our understanding of the factors that regulate brain DHA metabolism.

Biosynthesis and metabolism of endocannabinoids and their congeners from the monoacylglycerol andN-acyl-ethanolamine families

The endocannabinoids 2-arachidonoyl-glycerol (2-AG) and N-arachidonoyl-ethanolamine (AEA) are eicosanoids implicated in numerous physiological processes like appetite, adipogenesis, inflammatory pain and inflammation. They mediate most of their physiological effect by activating the cannabinoid (CB) receptors 1 and 2. Other than directly binding to the CB receptors, 2-AG and AEA are also metabolized by most eicosanoid biosynthetic enzymes, yielding many metabolites that are part of the oxyendocannabinoidome. Some of these metabolites have been found in vivo, have the ability to modulate specific receptors and thus potentially influence physiological processes. In this review, we discuss the biosynthesis and metabolism of 2-AG and AEA, as well as their congeners from the monoacyl-glycerol and N-acyl-ethanolamine families, with a special focus on the metabolism by oxygenases involved in arachidonic acid metabolism. We highlight the knowledge gaps in our understanding of the regulation and roles the oxyendocannabinoidome mediators.

Tetracosahexaenoylethanolamide, a novel N-acylethanolamide, is elevated in ischemia and increases neuronal output

N-acylethanolamines (NAEs) are endogenous lipid-signaling molecules derived from fatty acids that regulate numerous biological functions, including in the brain. Interestingly, NAEs are elevated in the absence of fatty acid amide hydrolase (FAAH) and following CO₂-induced ischemia/hypercapnia, suggesting a neuroprotective response. Tetracosahexaenoic acid (THA) is a product and precursor to DHA; however, the NAE product, tetracosahexaenoylethanolamide (THEA), has never been reported. Presently, THEA was chemically synthesized as an authentic standard to confirm THEA presence in biological tissues. Whole brains were collected and analyzed for unesterified THA, total THA, and THEA in wild-type and FAAH-KO mice that were euthanized by either head-focused microwave fixation, CO₂ + microwave, or CO₂ only. PPAR activity by transient transfection assay and ex vivo neuronal output in medium spiny neurons (MSNs) of the nucleus accumbens by patch clamp electrophysiology were determined following THEA exposure. THEA in the wild-type mice was nearly doubled (P < 0.05) following ischemia/hypercapnia (CO₂ euthanization) and up to 12 times higher (P < 0.001) in the FAAH-KO compared with wild-type. THEA did not increase (P > 0.05) transcriptional activity of PPARs relative to control, but 100 nM of THEA increased (P < 0.001) neuronal output in MSNs of the nucleus accumbens. Here were identify a novel NAE, THEA, in the brain that is elevated upon ischemia/hypercapnia and by KO of the FAAH enzyme. While THEA did not activate PPAR, it augmented the excitability of MSNs in the nucleus accumbens. Overall, our results suggest that THEA is a novel NAE that is produced in the brain upon ischemia/hypercapnia and regulates neuronal excitation.

Lower brain fatty acid amide hydrolase in treatment-seeking patients with alcohol use disorder: a positron emission tomography study with [C-11]CURB

The endocannabinoid enzyme, fatty acid amide hydrolase (FAAH), has been proposed as a therapeutic target for alcohol use disorder (AUD) and co-morbid psychiatric illnesses. Investigating this target in the living human brain and its relationship to clinical outcome is a critical step of informed drug development. Our objective was to establish whether brain FAAH levels are low in individuals with AUD and related to drinking behavior. In this pilot study, treatment-seeking patients with AUD completed two PET scans with the FAAH radiotracer [C-11]CURB after 3-7 days (n = 14) and 2-4 weeks (n = 9) of monitored abstinence. Healthy controls (n = 25) completed one scan. FAAH genetic polymorphism (rs324420) and blood concentrations of anandamide and other N-acylethanolamines metabolized by FAAH were determined and AUD symptoms assessed. In AUD, brain FAAH levels were globally lower than controls during early abstinence (F(1,36) = 5.447; p = 0.025)) and FAAH substrates (anandamide, oleoylethanolamide, and N-docosahexaenoylethanolamide) were significantly elevated (30-67%). No significant differences in FAAH or FAAH substrates were noted after 2-4 weeks abstinence. FAAH levels negatively correlated with drinks per week (r = -0.57, p = 0.032) and plasma concentrations of the three FAAH substrates (r > 0.57; p < 0.04)). Our findings suggest that early abstinence from alcohol in AUD is associated with transiently low brain FAAH levels, which are inversely related to heavier alcohol use and elevated plasma levels of FAAH substrates. Whether low FAAH is an adaptive beneficial response to chronic alcohol is unknown. Therapeutic strategies focusing on FAAH inhibition should consider the possibility that low FAAH during early abstinence may be related to drinking.

Ethanolamides of essential α-linolenic and linoleic fatty acids suppress short-term food intake in rats

Food source has a significant impact on levels of fatty acids and their derivatives, fatty acid ethanolamides (FAEs), in the small intestine and brain. Among non-essential fatty acids, oleic acid and its FAE acutely reduce food intake. However, effects of the essential α-linolenic acid, linoleic acid, and their FAEs on appetite regulation remain undefined. This study tested the hypothesis that α-linolenic acid and linoleic acid mediate acute suppression of food intake through their corresponding FAEs, α-linolenoylethanolamide and linoleoylethanolamide, respectively. To allow for the differentiation of the effects of FAEs and their parent fatty acids, male Wistar rats were injected intraperitoneally with α-linolenic acid, linoleic acid, α-linolenoylethanolamide and linoleoylethanolamide after a 12-hour overnight fast. Short-term food intake, plasma and brain FAE status, and plasma concentrations of insulin and leptin were measured to determine whether these hormones mediate the anorectic effect of FAEs. Both ethanolamides, but not their parent fatty acids, acutely suppressed food intake up to one hour post-treatment and this effect was independent of insulin and leptin hormones. In conclusion, essential α-linolenic and linoleic fatty acids mediate acute suppression of food intake through their corresponding FAEs. These findings may aid in the further research of FAEs as potential therapeutic agents for the management and treatment of obesity.

Clinical Efficacy and Biological Regulations of ω-3 PUFA-Derived Endocannabinoids in Major Depressive Disorder

BACKGROUND

Endocannabinoids (ECs) are one type of bioactive endogenous neuroinflammatory mediator derived from polyunsaturated fatty acids (PUFAs), which may regulate the emotional processes. Here, we assessed the effect of ω-3 PUFAs on EC levels, which may be the novel targets for the ω-3 PUFAs' antidepressive effects.

METHODS

We conducted a 12-week double-blind, nonplacebo, randomized controlled trial. Eighty-eight major depressive disorder (MDD) participants were randomly assigned to receive eicosapentaenoic acid (EPA, 3.0 g/day), docosahexaenoic acid (DHA, 1.4 g/day), or a combination of EPA (1.5 g/d) and DHA (0.7 g/day). Eighty-five participants completed the trial, and their clinical remission and plasma PUFA-derived EC levels (pmol/mL) were measured.

RESULTS

The cumulative rates of clinical remission were significantly higher in the EPA and EPA + DHA groups than the DHA group (51.85 and 53.84 vs. 34.37%; p =0.027 and p =0.024, respectively). EPA and EPA + DHA treatments increased the eicosapentaenoylethanolamide (EPEA) levels compared to DHA treatment (0.33 ± 0.18 and 0.35 ± 0.24 vs. 0.08 ± 0.12; p =0.002 and p =0.001, respectively), while EPA + DHA treatment increased the docosahexaenoylethanolamide levels more than EPA treatment (1.34 ± 2.09 vs. 0.01 ± 1.79; p =0.006). Plasma EPEA levels were positively correlated with rates of clinical remission (hazard ratio: 1.60, 95% confidence interval: 1.08-2.39).

CONCLUSIONS

Treatments enriched with EPA increased plasma EPEA levels, which was positively associated with clinical remission. This finding may suggest that levels of plasma EPEA play a potential novel endogenous therapeutic target in MDD.

Dietary fatty acids augment tissue levels of n-acylethanolamines in n-acylphosphatidylethanolamine phospholipase D (NAPE-PLD) knockout mice

N-acylethanolamines (NAEs) are lipid signaling mediators, which can be synthesized from dietary fatty acids via n-acylphosphatidylethanolamine-phospholipase D (NAPE-PLD) and in turn influence physiological outcomes; however, the roles of NAPE-PLD upon dietary fatty acid modulation are not fully understood. Presently, we examine if NAPE-PLD is necessary to increase NAEs in response to dietary fatty acid manipulation. Post-weaning male wild-type (C57Bl/6), NAPE-PLD (-/+) and NAPE-PLD (-/-) mice received isocaloric fat diets containing either beef tallow, corn oil, canola oil or fish oil (10% wt/wt from fat) for 9 weeks. Brain docosahexaenoic acid (DHA) levels were higher (P<.01) in NAPE-PLD (-/+) (10.01±0.31 μmol/g) and NAPE-PLD (-/-) (10.89±0.61 μmol/g) than wild-type (7.72±0.61 μmol/g) consuming fish oil. In NAPE-PLD (-/-) mice, brain docosahexaenoylethanolamide (DHEA) levels were higher (P<.01) after fish oil feeding suggesting that NAPE-PLD was not necessary for DHEA synthesis. Liver and jejunum arachidonoylethanolamide, 1,2-arachidonoylglycerol and DHEA levels reflected their corresponding fatty acid precursors suggesting that alternate pathways are involved in NAE synthesis. NAPE-PLD (-/-) mice had lower oleoylethanolamide levels in the jejunum and a leaner phenotype compared to wild-type mice. Overall, these results demonstrate that dietary fatty acid can augment tissue NAEs in the absence of NAPE-PLD.

Brain docosahexaenoic acid uptake and metabolism

Docosahexaenoic acid (DHA) is the most abundant n-3 polyunsaturated fatty acid in the brain where it serves to regulate several important processes and, in addition, serves as a precursor to bioactive mediators. Given that the capacity of the brain to synthesize DHA locally is appreciably low, the uptake of DHA from circulating lipid pools is essential to maintaining homeostatic levels. Although, several plasma pools have been proposed to supply the brain with DHA, recent evidence suggests non-esterified-DHA and lysophosphatidylcholine-DHA are the primary sources. The uptake of DHA into the brain appears to be regulated by a number of complementary pathways associated with the activation and metabolism of DHA, and may provide mechanisms for enrichment of DHA within the brain. Following entry into the brain, DHA is esterified into and recycled amongst membrane phospholipids contributing the distribution of DHA in brain phospholipids. During neurotransmission and following brain injury, DHA is released from membrane phospholipids and converted to bioactive mediators which regulate signaling pathways important to synaptogenesis, cell survival, and neuroinflammation, and may be relevant to treating neurological diseases. In the present review, we provide a comprehensive overview of brain DHA metabolism, encompassing many of the pathways and key enzymatic regulators governing brain DHA uptake and metabolism. In addition, we focus on the release of non-esterified DHA and subsequent production of bioactive mediators and the evidence of their proposed activity within the brain. We also provide a brief review of the evidence from post-mortem brain analyses investigating DHA levels in the context of neurological disease and mood disorder, highlighting the current disparities within the field.