Endocannabinoid System Modulation By Natural Products From Ancient Medicinal Plants

Herbal drugs have been important for the treatment of multiple pathological conditions since ancient times. A multitude of historical texts document the importance of plant-based therapies, but the therapeutic effectiveness of many described applications remains questionable. Concomitantly, the pharmacological properties and the associated chemistry of many herbal drugs described in ancient texts remain poorly studied. The development of modern pharmacology and analytical tools in the past century has led to the discovery of a plethora of novel plant-derived compounds and propelled advancements in medicine and pharmacology. The identification of (-)-trans-Δ9-tetrahydrocannabinol (THC) as the active principle of Cannabis sativa L., triggered research activities conductive to the elucidation of the endocannabinoid system (ECS). The ECS is a major modulatory system involved in a variety of physiological functions including the regulation of appetite, pain perception, memory, mood, and the modulation of inflammation and immune responses. A deregulation of the ECS is commonly associated with pathological conditions such as mood disorders, pain, inflammation, and neurodegenerative and immune diseases. Therefore, identifying target specific agonists, antagonists and inhibitors constitutes a promising strategy to tackle these conditions. The inhibition of fatty acid amide hydrolase (FAAH), the major enzyme involved in the termination of endocannabinoid signalling via the degradation of the endocannabinoid anandamide (AEA), represents a pharmacological strategy to treat conditions such as anxiety, depression or metabolic disorders. Besides the main cannabinoid type-1 (CB1) receptors, activation of cannabinoid type-2 (CB2) receptors represents as well an interesting pharmacological approach to treat diverse disorders such as diabetes, and neurodegenerative and immune diseases. Therefore, the main aim of this doctoral thesis was to identify and characterize plant-derived compounds able to target and modulate specific components of the ECS. As a starting point to address this objective, a plant extract library of drug samples mainly associated with the herbal drugs described in Dioscorides’ De Materia Medica (DMM; ex Matthioli, 1568) was built up. The extracts were tested for in vitro inhibition of FAAH and affinity towards CB2 receptors. In addition, as an indication of non-specific cytotoxicity, their antiproliferative activity was evaluated. For the screened extracts, the possible relationship between investigated bioactivity and plant phylogeny was first questioned. From the results of the FAAH inhibition screening, it emerged that extracts with significant FAAH inhibitory activity are phylogenetically clustered, as they are associated preponderantly with herbal drugs derived from the Fabaceae family. Isoflavonoids and prenylated derivatives, secondary metabolites commonly produced in Fabaceae, were proposed as potential FAAH inhibitors. Among the isoflavonoids tested, the prenylated luteone and neobavaisoflavone proved to be highly potent, selective, competitive and reversible FAAH inhibitors at the nanomolar range. In addition, preliminary results from the screening of the extract library towards CB2 receptors suggested the identification of sesquiterpene coumarins as a new class of CB2 receptor ligands at the low micromolar range. In conclusion, in this thesis project we have identified two classes of natural products showing in vitro pharmacological interaction with the ECS. Moreover, the compounds may prove promising scaffolds for the development of new therapeutic agents with anti-inflammatory, anti-nociceptive, anxiolytic, anti-diabetic or immunomodulatory activities.