One may wonder why methylxanthines are so abundant in beverages used by humans for centuries, or in cola-drinks that have been heavily consumed since their appearance. It is likely that humans have stuck to any brew containing compounds with psychoactive properties, resulting in a better daily life, i.e., more efficient thinking, exploring, hunting, etc., however, without the serious side effects of drugs of abuse. The physiological effects of methylxanthines have been known for a long time and they are mainly mediated by the so-called adenosine receptors. Caffeine and theobromine are the most abundant methylxanthines in cacao and their physiological effects are notable. Their health-promoting benefits are so remarkable that chocolate is explored as a functional food. The consequences of adenosine receptor blockade by natural compounds present in cacao/chocolate are here reviewed. Palatability and health benefits of methylxanthines, in general, and theobromine, in particular, have further contributed to sustain one of the most innocuous and pleasant habits: chocolate consumption.

The mechanism of action of cannabidiol (CBD), the main non-psychotropic component of Cannabis sativa L., is not completely understood. First assumed that the compound was acting via cannabinoid CB₂ receptors (CB₂Rs) it is now suggested that it interacts with non-cannabinoid G-protein-coupled receptors (GPCRs); however, CBD does not bind with high affinity to the orthosteric site of any GPCR. To search for alternative explanations, we tested CBD as a potential allosteric ligand of CB₂R. Radioligand and non-radioactive homogeneous binding, intracellular cAMP determination and ERK1/2 phosphorylation assays were undertaken in heterologous systems expressing the human version of CB₂R. Using membrane preparations from CB₂R-expressing HEK-293T (human embryonic kidney 293T) cells, we confirmed that CBD does not bind with high affinity to the orthosteric site of the human CB₂R where the synthetic cannabinoid, [³H]-WIN 55,212-2, binds. CBD was, however, able to produce minor but consistent reduction in the homogeneous binding assays in living cells using the fluorophore-conjugated CB₂R-selective compound, CM-157. The effect on binding to CB₂R-expressing living cells was different to that exerted by the orthosteric antagonist, SR144528, which decreased the maximum binding without changing the K_D. CBD at nanomolar concentrations was also able to significantly reduce the effect of the selective CB₂R agonist, JWH133, on forskolin-induced intracellular cAMP levels and on activation of the MAP kinase pathway. These results may help to understand CBD mode of action and may serve to revisit its therapeutic possibilities.

Background and Purpose: Heteromerization ofGPCRs is key to the integration of extracellular signals and the subsequent cell response via several mechanisms including heteromer‐selective ligand binding, trafficking and/or downstream signalling. As the lysophosphatidylinositolGPCR55 (GPR55) has been shown to affect the function of the cannabinoid receptor subtype 2 (CB₂receptor) in human neutrophils, we investigated the possible heteromerization ofCB₂receptorswith GPR55.Experimental Approach: The direct interaction of humanGPR55 andCB₂receptors heterologously expressed inHEK293 cells was assessed by co‐immunoprecipitation and bioluminescence resonance energy transfer assays. The effect of cross‐talk on signalling was investigated at downstream levels by label‐free real‐time methods (Epic dynamic mass redistribution andCellKey impedance assays),ERK1/2‐MAPKactivation and gene reporter assays.Key Results: GPR55 andCB₂receptors co‐localized on the surface ofHEK293 cells, co‐precipitated in membrane extracts and formed heteromers in livingHEK293 cells. Whereas heteromerization led to a reduction inGPR55‐mediated activation of transcription factors (nuclear factor of activatedT‐cells,NF‐κBandcAMPresponse element),ERK1/2‐MAPKactivation was potentiated in the presence ofCB₂receptors.CB₂receptor‐mediated signalling was also affected by co‐expression withGPR55. Label‐free assays confirmed cross‐talk between the two receptors.Conclusions and Implications: Heteromers, unique signalling units, form inHEK293 cells expressingGPR55 andCB₂receptors. The signalling by agonists of either receptor was governed (i) by the presence or absence of the partner receptors (with the consequent formation of heteromers) and (ii) by the activation state of the partner receptor.

Cocoa consumption began in America and in the mid 16th Century it quickly spread to Europe. Beyond being considered a pleasant habit due to its rich sweet lingering taste, chocolate was considered a good nutrient and even a medicine. Traditionally, health benefits of cocoa have been related with the high content of antioxidants of Theobroma cocoa beans. However, the direct psychoactive effect due to methylxanthines in cocoa is notable. Theobromine and caffeine in the proportions found in cocoa are responsible for the liking of the food/beverage. These compounds influence in a positive way our moods and our state of alertness. Theobromine, which is found in higher amounts than caffeine, seems to be behind several effects attributed to cocoa intake. The main mechanisms of action are inhibition of phosphodiesterases and blockade of adenosine receptors. Further mechanisms are being explored to better understand the health benefits associated to theobromine consumption. Unlike what happens in other mammals –pets included-, theobromine is safe for humans and has fewer unwanted effects than caffeine. Therefore, theobromine deserves attention as one of the most attractive molecules in cocoa.

Cell membrane receptors rarely work on isolation, often they form oligomeric complexes with other receptor molecules and they may directly interact with different proteins of the signal transduction machinery. For a variety of reasons, rhodopsin-like class A G-protein-coupled receptors (GPCRs) seem an exception to the general rule of receptor-receptor direct interaction. In fact, controversy surrounds their potential to form homo- hetero-dimers/oligomers with other class A GPCRs; in a sense, the field is going backwards instead of forward. This review focuses on the convergent, complementary and telling evidence showing that homo- and heteromers of class A GPCRs exist in transfected cells and, more importantly, in natural sources. It is time to decide between questioning the occurrence of heteromers or, alternatively, facing the vast scientific and technical challenges that class A receptor-dimer/oligomer existence pose to Pharmacology and to Drug Discovery.