Chapter 7 Cannabinoid Receptor CB1 Antagonists

Exploring the Therapeutic Potential of Cannabinoid Receptor Antagonists in Inflammation, Diabetes Mellitus, and Obesity

Recently, research has greatly expanded the knowledge of the endocannabinoid system (ECS) and its involvement in several therapeutic applications. Cannabinoid receptors (CBRs) are present in nearly every mammalian tissue, performing a vital role in different physiological processes (neuronal development, immune modulation, energy homeostasis). The ECS has an essential role in metabolic control and lipid signaling, making it a potential target for managing conditions such as obesity and diabetes. Its malfunction is closely linked to these pathological conditions. Additionally, the immunomodulatory function of the ECS presents a promising avenue for developing new treatments for various types of acute and chronic inflammatory conditions. Preclinical investigations using peripherally restricted CBR antagonists that do not cross the BBB have shown promise for the treatment of obesity and metabolic diseases, highlighting the importance of continuing efforts to discover novel molecules with superior safety profiles. The purpose of this review is to examine the roles of CB1R and CB2Rs, as well as their antagonists, in relation to the above-mentioned disorders.

Recent challenges and trends in forensic analysis: Δ9-THC isomers pharmacology, toxicology and analysis

Δ9-tetrahydrocannabinol (Δ9-THC) isomers, especially Δ8-tetrahydrocannabinol (Δ8-THC), are increasing in foods, beverages, and e-cigarettes liquids. A major factor is passage of the Agriculture Improvement Act (AIA) that removed hemp containing less than 0.3 % Δ9-THC from the definition of "marijuana" or cannabis. CBD-rich hemp flooded the market resulting in excess product that could be subjected to CBD cyclization to produce Δ8-THC. This process utilizes strong acid and yields toxic byproducts that frequently are not removed prior to sale and are currently inadequately studied. Pharmacological activity is qualitatively similar for Δ8-THC and Δ9-THC, but most preclinical studies in mice, rats, and monkeys documented greater ∆9-THC potency. Both isomers caused graded dose-response effects on euphoria, blurred vision, mental confusion and lethargy, although Δ8-THC was at least 25 % less potent. The most common analytical methodologies providing baseline resolution of ∆8-THC and ∆9-THC in non-biological matrices are liquid-chromatography coupled to diode-array detection (LC-DAD or LC-PDA), while liquid chromatography coupled to mass spectrometry is preferred for biological matrices. Other available analytical methods are gas-chromatography-mass spectrometry (GC-MS) and quantitative nuclear magnetic resonance (QNMR). Current knowledge on the pharmacology of ∆8-THC and other ∆9-THC isomers are reviewed to raise awareness of the activity of these isomers in cannabis products, as well as analytical methods to discriminate ∆9-THC qualitatively, and quantitatively and ∆8-THC in biological and non-biological matrices.

The Complex Interplay between Endocannabinoid System and the Estrogen System in Central Nervous System and Periphery

The endocannabinoid system (ECS) is a lipid cell signaling system involved in the physiology and homeostasis of the brain and peripheral tissues. Synaptic plasticity, neuroendocrine functions, reproduction, and immune response among others all require the activity of functional ECS, with the onset of disease in case of ECS impairment. Estrogens, classically considered as female steroid hormones, regulate growth, differentiation, and many other functions in a broad range of target tissues and both sexes through the activation of nuclear and membrane estrogen receptors (ERs), which leads to genomic and non-genomic cell responses. Since ECS function overlaps or integrates with many other cell signaling systems, this review aims at updating the knowledge about the possible crosstalk between ECS and estrogen system (ES) at both central and peripheral level, with focuses on the central nervous system, reproduction, and cancer.

DARK Classics in Chemical Neuroscience: Synthetic Cannabinoids (Spice/K2)

This Review covers the background, pharmacology, adverse effects, synthesis, pharmacokinetics, metabolism, and history of synthetic cannabinoid compounds. Synthetic cannabinoids are a class of novel psychoactive substances that act as agonists at cannabinoid receptors. This class of compounds is structurally diverse and rapidly changing, with multiple generations of molecules having been developed in the past decade. The structural diversity of synthetic cannabinoids is supported by the breadth of chemical space available for exploitation by clandestine chemists and incentivized by attempts to remain ahead of legal pressures. As a class, synthetic cannabinoid products have a more serious adverse effect profile than that of traditional phytocannabinoids, including notable risks of lethality, as well as a history of dangerous adulteration. Most synthetic cannabinoids are rapidly metabolized to active species with prolonged residence times and peripheral tissue distribution, and analytical confirmation of use of these compounds remains challenging. Overall, the emergence of synthetic cannabinoids serves as a noteworthy example of the pressing public health challenges associated with the increasing development of easily synthesized, structurally flexible, highly potent, psychoactive drugs.

Pathophysiology of human visceral obesity: an update

Excess intra-abdominal adipose tissue accumulation, often termed visceral obesity, is part of a phenotype including dysfunctional subcutaneous adipose tissue expansion and ectopic triglyceride storage closely related to clustering cardiometabolic risk factors. Hypertriglyceridemia; increased free fatty acid availability; adipose tissue release of proinflammatory cytokines; liver insulin resistance and inflammation; increased liver VLDL synthesis and secretion; reduced clearance of triglyceride-rich lipoproteins; presence of small, dense LDL particles; and reduced HDL cholesterol levels are among the many metabolic alterations closely related to this condition. Age, gender, genetics, and ethnicity are broad etiological factors contributing to variation in visceral adipose tissue accumulation. Specific mechanisms responsible for proportionally increased visceral fat storage when facing positive energy balance and weight gain may involve sex hormones, local cortisol production in abdominal adipose tissues, endocannabinoids, growth hormone, and dietary fructose. Physiological characteristics of abdominal adipose tissues such as adipocyte size and number, lipolytic responsiveness, lipid storage capacity, and inflammatory cytokine production are significant correlates and even possible determinants of the increased cardiometabolic risk associated with visceral obesity. Thiazolidinediones, estrogen replacement in postmenopausal women, and testosterone replacement in androgen-deficient men have been shown to favorably modulate body fat distribution and cardiometabolic risk to various degrees. However, some of these therapies must now be considered in the context of their serious side effects. Lifestyle interventions leading to weight loss generally induce preferential mobilization of visceral fat. In clinical practice, measuring waist circumference in addition to the body mass index could be helpful for the identification and management of a subgroup of overweight or obese patients at high cardiometabolic risk.

Cannabinoid receptor expression in HIV encephalitis and HIV-associated neuropathologic comorbidities

AIMS

Cannabinoids have been proposed for treating various neurodegenerative disorders and as adjunct therapy for HIV+ patients with neurologic sequelae. The expression of cannabinoid receptors (CB1 and CB2) has been reported in neurodegenerative diseases and in simian immunodeficiency virus encephalitis, yet the receptor expression in the central nervous system of HIV+ individuals is not known.

METHODS

An anti-CB1 antibody and two anti-CB2 antibodies were employed for immunohistochemistry in the cerebral cortex and white matter of HIV encephalitis (HIVE) and HIV-associated comorbidities, as well as control brains (HIV- and HIV+).

RESULTS

By quantitative image analysis, we observed that CB1 was increased in HIVE brains and those with comorbidities, while CB2 was significantly increased in the white matter of HIVE. Morphologically, CB1 was present in neurones, and both CB1 and CB2 were present in meningeal macrophages and subpial glia in all brains. In HIVE, CB1 was found in white matter microglia and perivascular cells, while CB2 was increased in microglia, astrocytes and perivascular macrophages. Double immunofluorescence with cell-specific markers and immunoblots on primary cultured microglia and astrocytes substantiated the glial localization of the cannabinoid receptors and specificity of the antibodies.

CONCLUSIONS

Our study indicates that cannabinoid receptor expression occurs in glia in HIVE brains, and this may have ramifications for the potential use of cannabinoid ligands in HIV-infected patients.

Natural prenylated resveratrol analogs arachidin-1 and -3 demonstrate improved glucuronidation profiles and have affinity for cannabinoid receptors

RATIONALE

The therapeutic promise of trans-resveratrol (tRes) is limited by poor bioavailability following rapid metabolism. We hypothesise that trans-arachidin-1 (tA1) and trans-arachidin-3 (tA3), peanut hairy root-derived isoprenylated analogs of tRes, will exhibit slower metabolism/enhanced bioavailability and retain biological activity via cannabinoid receptor (CBR) binding relative to their non-prenylated parent compounds trans-piceatannol (tPice) and tRes, respectively.

RESULTS

The activities of eight human UDP-glucuronosyltransferases (UGTs) toward these compounds were evaluated. The greatest activity was observed for extrahepatic UGTs 1A10 and 1A7, followed by hepatic UGTs 1A1 and 1A9. Importantly, an additional isoprenyl and/or hydroxyl group in tA1 and tA3 slowed overall glucuronidation. CBR binding studies demonstrated that all analogs bound to CB1Rs with similar affinities (5-18 µM); however, only tA1 and tA3 bound appreciably to CB2Rs. Molecular modelling studies confirmed that the isoprenyl moiety of tA1 and tA3 improved binding affinity to CB2Rs. Finally, although tA3 acted as a competitive CB1R antagonist, tA1 antagonised CB1R agonists by both competitive and non-competitive mechanisms.

CONCLUSIONS

Prenylated stilbenoids may be preferable alternatives to tRes due to increased bioavailability via slowed metabolism. Similar structural analogs might be developed as novel CB therapeutics for obesity and/or drug dependency.

Attenuation of food intake in chicks by an inverse agonist of cannabinoid receptor 1 administered by either injection or ingestion in hydrocolloid carriers

The cannabinoid receptor (CB(1)) was studied primarily in mammals where it was found to comprise a link between reward processes and addictive behavior such as food consumption. The purpose of this study was twofold: first to characterize the effect of the chicken CB(1) receptor inverse agonist AM251 on food intake, and second, to establish a stress-free approach for application of AM251 to birds using hydrocolloid carriers, which can be mixed with food. A single administration of AM251 by intravenous injection (at 0.85 or 5 mg kg(-1)BW) or by ingestion of hydrocolloid carriers entrapping AM251 at a concentration of 5 mg kg(-1)BW led to a transient attenuation of food intake. The consequent reduced cumulative food intake and BW were observed in the treated chicks for at least 7h post-administration, with no gender differences. Circulating levels of AM251, assessed by LC-MS following 48 h of continuous feeding with hydrocolloid carriers containing 50mg AM 251 kg(-1) BW day(-1), were physiologically significant at 186 ± 73 pmol ml(-1). It is concluded that unlike some other factors, which act differently in birds compared to mammals such as ghrelin, CB(1) inverse agonists attenuate food intake in chicks similar to its effect in mammals. In addition, the new approach for administration of AM251 to birds in hydrocolloid carriers could provide a simple and stress-free tool for prolonged studies of this control mechanism in birds.

Rimonabant-induced apoptosis in leukemia cell lines: activation of caspase-dependent and -independent pathways

Rimonabant (SR141716), a cannabinoid CB1 receptor antagonist known for anti-obesity activity, has more recently been shown to inhibit tumor cell growth. Here we demonstrated the antitumor potential of SR141716 in leukemia-derived cell lines and its low toxicity in normal cells (PBMC). SR141716 (1-20microM range of doses) reduced Jurkat and U937 cell number by activating death signals as well as affecting cell cycle progression. The most prominent response in U937 to SR141716 was a G(0)/G(1) block, while in Jurkat cells there was activation of cell death processes. SR141716-treated cells exhibited the morphological and biochemical features of apoptosis and to some extent necrosis. Apoptotic mode of cell death was confirmed in both cell lines by analysis of cell morphology, phosphatidylserine exposure and DNA fragmentation. Moreover, the drug was found to induce an early and robust mitochondrial membrane depolarization. In Jurkat cells the apoptotic process was typically caspase-dependent, while in U937 caspase-independent pathways were also activated. The contribution of PARP activation to SR141716-induced apoptosis in U937 was suggested by protein PARylation, AIF release and apoptosis reversal by PARP inhibitors. Moreover, SR141716 negatively modulated, especially in U937, the PI3K/AKT pathways. In conclusion, our data indicate that SR141716 elicits alternative response and/or cell death pathways depending on the cell type affected.

Rimonabant (SR141716) induces metabolism and acquisition of fertilizing ability in human sperm

BACKGROUND AND PURPOSE

The endocannabinoid system and the cannabinoid CB(1) receptor have been identified in human sperm, and it is well known that endocannabinoids have pronounced adverse effects on male and female reproduction. In order to elucidate further the pathophysiological role of the endocannabinoid system in male fertility, we investigated the activity of the CB(1) receptor antagonist rimonabant (SR141716) on the fertilizing ability of human sperm.

EXPERIMENTAL APPROACH

We evaluated in vitro the effects of rimonabant on motility, survival, capacitation, acrosin activity and metabolism of human sperm. Particularly, capacitation was studied by using three different approaches: intracellular free Ca(2+) content assay, cholesterol efflux assay and protein tyrosine phosphorylation analysis.

KEY RESULTS

Rimonabant significantly increased sperm motility and viability through the induction of pAkt and pBcl2, key proteins of cell survival and metabolism, and it induced acrosome reaction and capacitation as well. Rimonabant reduced the triglyceride content of sperm, while enhancing lipase and acyl-CoA dehydrogenase activities, implying an overall lipolytic action in these cells. Rimonabant also affected sperm glucose metabolism by decreasing phosphorylation of glycogen synthase kinase 3 and increasing glucose-6-phosphate dehydrogenase activity, suggesting a role in inducing sperm energy expenditure. Intriguingly, agonism at the CB(1) receptor, with an anandamide analogue or a selective inhibitor of fatty acid amide hydrolase, produced opposing effects on human sperm functions.

CONCLUSIONS AND IMPLICATIONS

Our data suggest that blockade of the CB(1) receptor by rimonabant induces the acquisition of fertilizing ability and stimulates energy expenditure in human sperm.

Biochemical effects of SIRT1 activators

SIRT1 is the closest mammalian homologue of enzymes that extend life in lower organisms. Its role in mammals is incompletely understood, but includes modulation of at least 34 distinct targets through its nicotinamide adenine dinucleotide (NAD(+))-dependent deacetylase activity. Recent experiments using small molecule activators and genetically engineered mice have provided new insight into the role of this enzyme in mammalian biology and helped to highlight some of the potentially relevant targets. The most widely employed activator is resveratrol, a small polyphenol that improves insulin sensitivity and vascular function, boosts endurance, inhibits tumor formation, and ameliorates the early mortality associated with obesity in mice. Many of these effects are consistent with modulation of SIRT1 targets, such as PGC1alpha and NFkappaB, however, resveratrol can also activate AMPK, inhibit cyclooxygenases, and influence a variety of other enzymes. A novel activator, SRT1720, as well as various methods to manipulate NAD(+) metabolism, are emerging as alternative methods to increase SIRT1 activity, and in many cases recapitulate effects of resveratrol. At present, further studies are needed to more directly test the role of SIRT1 in mediating beneficial effects of resveratrol, to evaluate other strategies for SIRT1 activation, and to confirm the specific targets of SIRT1 that are relevant in vivo. These efforts are especially important in light of the fact that SIRT1 activators are entering clinical trials in humans, and "nutraceutical" formulations containing resveratrol are already widely available.