Harald S. Hansen

International Union of Basic and Clinical Pharmacology. LXXIX. Cannabinoid Receptors and Their Ligands: Beyond CB1 and CB2

There are at least two types of cannabinoid receptors (CB1 and CB2). Ligands activating these G protein-coupled receptors (GPCRs) include the phytocannabinoid Δ9-tetrahydrocannabinol, numerous synthetic compounds, and endogenous compounds known as endocannabinoids. Cannabinoid receptor antagonists have also been developed. Some of these ligands activate or block one type of cannabinoid receptor more potently than the other type. This review summarizes current data indicating the extent to which cannabinoid receptor ligands undergo orthosteric or allosteric interactions with non-CB1, non-CB2 established GPCRs, deorphanized receptors such as GPR55, ligand-gated ion channels, transient receptor potential (TRP) channels, and other ion channels or peroxisome proliferator-activated nuclear receptors. From these data, it is clear that some ligands that interact similarly with CB1 and/or CB2 receptors are likely to display significantly different pharmacological profiles. The review also lists some criteria that any novel “CB3” cannabinoid receptor or channel should fulfil and concludes that these criteria are not currently met by any non-CB1, non-CB2 pharmacological receptor or channel. However, it does identify certain pharmacological targets that should be investigated further as potential CB3 receptors or channels. These include TRP vanilloid 1, which possibly functions as an ionotropic cannabinoid receptor under physiological and/or pathological conditions, and some deorphanized GPCRs. Also discussed are 1) the ability of CB1 receptors to form heteromeric complexes with certain other GPCRs, 2) phylogenetic relationships that exist between CB1/CB2 receptors and other GPCRs, 3) evidence for the existence of several as-yet-uncharacterized non-CB1, non-CB2 cannabinoid receptors; and 4) current cannabinoid receptor nomenclature.

Influence of dietary fatty acids on endocannabinoid and N-acylethanolamine levels in rat brain, liver and small intestine.

Endocannabinoids and N-acylethanolamines are lipid mediators regulating a wide range of biological functions including food intake. We investigated short-term effects of feeding rats five different dietary fats (palm oil (PO), olive oil (OA), safflower oil (LA), fish oil (FO) and arachidonic acid (AA)) on tissue levels of 2-arachidonoylglycerol, anandamide, oleoylethanolamide, palmitoylethanolamide, stearoylethanolamide, linoleoylethanolamide, eicosapentaenoylethanolamide, docosahexaenoylethanolamide and tissue fatty acid composition. The LA-diet increased linoleoylethanolamide and linoleic acid in brain, jejunum and liver. The OA-diet increased brain levels of anandamide and oleoylethanolamide (not 2-arachidonoylglycerol) without changing tissue fatty acid composition. The same diet increased oleoylethanolamide in liver. All five dietary fats decreased oleoylethanolamide in jejunum without changing levels of anandamide, suggesting that dietary fat may have an orexigenic effect. The AA-diet increased anandamide and 2-arachidonoylglycerol in jejunum without effect on liver. The FO-diet decreased liver levels of all N-acylethanolamines (except eicosapentaenoylethanolamide and docosahexaenoylethanolamide) with similar changes in precursor lipids. The AA-diet and FO-diet had no effect on N-acylethanolamines, endocannabinoids or precursor lipids in brain. All N-acylethanolamines activated PPAR-alpha. In conclusion, short-term feeding of diets resembling human diets (Mediterranean diet high in monounsaturated fat, diet high in saturated fat, or diet high in polyunsaturated fat) can affect tissue levels of endocannabinoids and N-acylethanolamines.

INTAKE OF MARINE FAT, RICH IN (n-3)-POLYUNSATURATED FATTY ACIDS, MAY INCREASE BIRTHWEIGHT BY PROLONGING GESTATION

Birthweights in the Faroe Islands are among the highest in the world. Compared with Denmark, the average birthweight of liveborn singleton infants of primiparous mothers is 194 g higher, and a substantial part of this difference seems to be attributable to longer gestation. Prostaglandins play an important part in the timing of parturition in human beings. Dietary (n-3)-polyunsaturated fatty acids (PUFA) in high amounts influence endogenous prostaglandin metabolism. Owing to the large consumption of marine fat, the average intake of (n-3)-PUFA in the Faroes by far exceeds that in Denmark. The hypothesis proposed is that dietary (n-3)-PUFA in high amounts prolong gestation in human beings by interfering with uterine production of prostaglandins, possibly by inhibiting the production of dienoic prostaglandins, primarily PGF2 alpha and PGE2, which are mediators of uterine contractions and cervical ripening.

Anandamide, but not 2-arachidonoylglycerol, accumulates during in vivo neurodegeneration

Endogenous cannabinoid receptor ligands (endocannabinoids) may rescue neurons from glutamate excitotoxicity. As these substances also accumulate in cultured immature neurons following neuronal damage, elevated endocannabinoid concentrations may be interpreted as a putative neuroprotective response. However, it is not known how glutamatergic insults affect in vivo endocannabinoid homeostasis, i.e. N‐arachidonoylethanolamine (anandamide) and 2‐arachidonoylglycerol (2‐AG), as well as other constituents of their lipid families, N‐acylethanolamines (NAEs) and 2‐monoacylglycerols (2‐MAGs), respectively. Here we employed three in vivo neonatal rat models characterized by widespread neurodegeneration as a consequence of altered glutamatergic neurotransmission and assessed changes in endocannabinoid homeostasis. A 46‐fold increase of cortical NAE concentrations (anandamide, 13‐fold) was noted 24 h after intracerebral NMDA injection, while less severe insults triggered by mild concussive head trauma or NMDA receptor blockade produced a less pronounced NAE accumulation. By contrast, levels of 2‐AG and other 2‐MAGs were virtually unaffected by the insults employed, rendering it likely that key enzymes in biosynthetic pathways of the two different endocannabinoid structures are not equally associated to intracellular events that cause neuronal damage in vivo. Analysis of cannabinoid CB1 receptor mRNA expression and binding capacity revealed that cortical subfields exhibited an up‐regulation of these parameters following mild concussive head trauma and exposure to NMDA receptor blockade. This may suggest that mild to moderate brain injury may trigger elevated endocannabinoid activity via concomitant increase of anandamide levels, but not 2‐AG, and CB1 receptor density.

N-Acylethanolamines and precursor phospholipids — relation to cell injury

The present review focuses on the relationship between formation of N-acylethanolamine phospholipids (NAPEs) and N-acyletransferase (NAEs) catalyzed by N-acyltranferase and NAPE-hydrolyzing phospholipase D, respectively, and cell injury in tissues like brain, heart, and testis. A number of mechanisms are proposed by which these two groups of lipids may have cytoprotective properties. The mechanisms may involve activation of cannabinoid receptors, as well as non-receptor-mediated effects such as stabilization of membrane bilayers, antioxidant mechanisms, inhibition of calcium leakage from mitochondria, and direct inhibition of ceramidase. Anandamide (20:4-NAE) is formed as a minor component along with other NAEs during cell injury. Whether 20:4-NAE has a separate physiological role is at present not known, but some data suggest that 20:4-NAE may be formed, e.g. in the uterus, by a more selective mechanism without being accompanied by a vast majority of saturated and monounsaturated NAEs.

2-Oleoyl Glycerol Is a GPR119 Agonist and Signals GLP-1 Release in Humans

OBJECTIVE Dietary fat is thought to stimulate release of incretin hormones via activation of fatty acid receptors in the intestine. However, dietary fat (triacylglycerol) is digested to 2-monoacylglycerol and fatty acids. Activation of G protein-coupled receptor 119 (GPR119) stimulates glucagon-like peptide-1 (GLP-1) release from the intestinal L-cells. We aimed to investigate if 2-oleoyl glycerol (2OG) can activate GPR119 in vitro and stimulate GLP-1 secretion in vivo. RESEARCH DESIGN AND METHODS Agonist activity for various lipids was tested on transiently expressed human GPR119 in COS-7 cells. The effect of a jejunal bolus of 2 g 2OG on plasma levels of GLP-1 was evaluated in eight healthy human volunteers. The effect of 2OG was compared to an equimolar amount of oleic acid, a degradation product from 2OG, and the vehicle, glycerol. Digestion of 5 ml olive oil with pancreatic lipase will result in formation of approximately 2 g 2OG and 3.2 g oleic acid. RESULTS 2OG and other 2-monoacylglycerols increased intracellular concentrations of cAMP in GPR119-expressing COS-7 cells (2OG EC(50) = 2.5 μm). Administration of 2OG to humans significantly increased plasma GLP-1 (0-25 min) when compared to the two controls, oleic acid and vehicle. Plasma levels of glucose-dependent insulinotropic polypeptide also increased. CONCLUSION 2OG and other 2-monoacylglycerols formed during fat digestion can activate GPR119 and cause incretin release from the human intestine. This mechanism is likely to contribute to the known stimulatory effect of dietary fat on incretin secretion, and it indicates that GPR119 is a fat sensor.

Essential function of linoleic acid esterified in acylglucosylceramide and acylceramide in maintaining the epidermal water permeability barrier. Evidence from feeding studies with oleate, linoleate, arachidonate, columbinate and α-linolenate

Essential fatty acid-deficient rats were supplemented with 300 mg per day of pure fatty acid esters: oleate (O), linoleate (L), arachidonate (A), and columbinate (C) for 10 days. During this period, the rats in groups L, A, and C all showed a decrease in their initially high trans-epidermal water loss, a classical essential fatty acid-deficiency symptom, to a level seen in non-deficient rats (group N). The trans-epidermal water loss in rats of group O was unaffected by the supplementation. Fatty acid composition of two epidermal sphingolipids, acylglucosylceramide and acylceramide, from the skin were determined. The results indicate that re-establishment of a low trans-epidermal water loss was associated with incorporation of linolenate into the two epidermal sphingolipids. Supplementation with columbinate resulted in relatively high amounts of this fatty acid in the investigated epidermal sphingolipids. Analysis of pooled skin specimens from a previous study in which weanling rats were fed a fat-free diet and supplemented orally with pure alpha-linolenate for 13 weeks (Hansen, H.S. and Jensen, B. (1983) Lipids 18, 682-690) revealed very little polyunsaturated fatty acid in the two sphingolipids. These rats showed increased evaporation which was comparable to that of essential fatty acid-deficient rats. We interpret these results as strong evidence for a very specific and essential function of linoleic acid in maintaining the integrity of the epidermal water permeability barrier. This function of linoleate is independent of its role as precursor for arachidonate and icosanoids.

Dynamic changes of the endogenous cannabinoid and opioid mesocorticolimbic systems during adolescence : THC effects

Adolescence is a critical phase of active brain development often characterized by the initiation of marijuana (Cannabis sativa) use. Limited information is known regarding the endogenous cannabinoid system of the adolescent brain as well as related neurotransmitters that appear sensitive to cannabis exposure. We recently observed that adult rats pre-exposed to Delta-9-tetrahydrocannabinol (THC) during adolescence self-administered higher amounts of heroin and had selective impairments of the enkephalin opioid system within the nucleus accumbens (NAc) implicated in reward-related behavior. To explore the ontogeny of the cannabinoid and opioid neuronal systems in association with adolescence THC exposure, rats were examined at different adolescent stages during an intermittent THC paradigm (1.5 mg/kg i.p. every third day) from postnatal days (PNDs) 28-49. Rat brains were examined 24 h after injection at PND 29 (early adolescence), PND 38 (mid adolescence) and PND 50 (late adolescence) and analyzed for endocannabinoids (anandamide and 2-arachidonoylglycerol), Met-enkephalin, cannabinoid CB(1) receptors and micro opioid receptors (microOR) in the NAc, caudate-putamen and prefrontal cortex (PFC). Of the markers studied, the endocannabinoid levels had the most robust alterations throughout adolescence and were specific to the PFC and NAc. Normal correlations between anandamide and 2-arachidonoylglycerol concentrations in the NAc (positive) and PFC (negative) were reversed by THC. Other significant THC-induced effects were confined to the NAc - increased anandamide, decreased Met-enkephalin and decreased microORs. These findings emphasize the dynamic nature of the mesocorticolimbic endocannabinoid system during adolescence and the selective mesocorticolimbic disturbance as a consequence of adolescent cannabis exposure.

Long-term characterization of the diet-induced obese and diet-resistant rat model: a polygenetic rat model mimicking the human obesity syndrome.

The availability of useful animal models reflecting the human obesity syndrome is crucial in the search for novel compounds for the pharmacological treatment of obesity. In the current study, we have performed an extensive characterization of the obesity syndrome in a polygenetic animal model, namely the selectively bred diet-induced obese (DIO) and diet-resistant (DR) rat strains. We show that they constitute useful models of the human obesity syndrome. DIO and DR rats were fed either a high-energy (HE) or a standard chow (Chow) diet from weaning to 9 months of age. Metabolic characterization including blood biochemistry and glucose homeostasis was examined at 2, 3, 6, and 9 months of age. Furthermore, in 6-month-old HE-fed DIO rats, the anti-obesity effects of liraglutide and sibutramine were examined in a 28-day study. Only HE-fed DIO rats developed visceral obesity, hyperleptinemia, hyperinsulinemia, and dyslipidemia, and showed a worsening of glucose tolerance over time. In line with the hyperlipidemic profile, a severe hepatic fat infiltration was observed in DIO rats at 6 months of age. The effects of liraglutide and sibutramine were tested in 6-month-old DIO rats. Both compounds effectively reduced food intake and body weight in DIO rats. Liraglutide furthermore improved glucose tolerance when compared with sibutramine. Our data highlights the usefulness of a polygenetic animal model for screening of compounds affecting food intake, body weight, and glucose homeostasis. Furthermore, the results underscore the effectiveness of GLP-1 mimetics both as anti-diabetes and anti-obesity agents.

Gestation length and birth weight in relation to intake of marine n -3 fatty acids

It has been hypothesized that marine n-3 fatty acids ingested during pregnancy prolong duration of pregnancy and increase fetal growth rate in humans. By a combined self-administered questionnaire and interview applied in the 30th week of gestation we assessed dietary intake of marine n-3 fatty acids and energy in a population-based sample of 965 pregnant Danish women; in a random 14% subsample we also measured marine n-3 fatty acids relative to arachidonic acid (FA-ratio) in erythrocytes. Mean intake of marine n-3 fatty acids was 0.25 (95% range 0-0.75) g/d. We could detect no association between n-3 fatty acid intake and FA-ratio on the one hand, and gestation length, birth weight and birth length on the other. The analyses were adjusted for maternal height, prepregnant weight, parity and smoking. The conclusion from the study was that within the intake range of this population, marine n-3 fatty acids ingested in the weeks prior to the 30th week of pregnancy seem not to be a predictor of gestation length or fetal growth rate.