Cannabinoid Delivery Systems for Pain and Inflammation Treatment
Natascia Bruni, Carlo Della Pepa, Simonetta Oliaro-Bosso, Enrica Pessione, Daniela Gastaldi and Franco Dosio
Molecules, 2018, 23, 2478
doi:10.3390/molecules23102478 www.mdpi.com/journal/molecules
Abstract : There is a growing body of evidence to suggest that cannabinoids are beneficial for a range of clinical conditions, including pain, inflammation, epilepsy, sleep disorders, the symptoms of multiple sclerosis, anorexia, schizophrenia and other conditions. The transformation of cannabinoids from herbal preparations into highly regulated prescription drugs is therefore progressing rapidly. The development of such drugs requires well-controlled clinical trials to be carried out in order to objectively establish therapeutic efficacy, dose ranges and safety. The low oral bioavailability of cannabinoids has led to feasible methods of administration, such as the transdermal route, intranasal administration and transmucosal adsorption, being proposed. The highly lipophilic nature of cannabinoids means that they are seen as suitable candidates for advanced nanosized drug delivery systems, which can be applied via a range of routes. Nanotechnology-based drug delivery strategies have flourished in several therapeutic fields in recent years and numerous drugs have reached the market. This review explores the most recent developments, from preclinical to advanced clinical trials, in the cannabinoid delivery field, and focuses particularly on pain and inflammation treatment. Likely future directions are also considered and reported.
Keywords : cannabinoids; delivery system; pain treatment; inflammation; cannabidiol; D9-tetrahydrocannabinol
1. Introduction
Cannabis (Cannabis sativa) is a dioic plant that belongs to the Cannabaceae family (Magnoliopsida, Urticales). Knowledge of the medical and psychoactive properties of cannabis dates back to 4000 B.C. All of the different varieties of cannabis, including the one known as Cannabis indica, belong to the same species. All C. sativa plants produce active compounds, but each variety produces these compounds in different concentrations and proportions, which do not only depend on genomic background, but also on growing conditions and climate, meaning that they can be referred to as chemical varieties or chemovars, rather than strains [1]. Each chemovar contains varying concentrations of cannabinoids, a class of mono- to tetracyclic C21 (or C22) meroterpenoids. While more than 100 different cannabinoids can be isolated from C. sativa, the primary psychoactive compound is D9-tetrahydrocannabinol (THC), which was first isolated in its pure form by Gaoni and Mechoulam in 1964 [2]. Other pharmacologically important analogues are cannabidiol (CBD), cannabinol, cannabinoid acids, cannabigerol, and cannabivarins. In addition to cannabinoids, other components, such as the monoterpenoids myrcene, limonene, and pinene and the sesquiterpenoid -caryophyllene, can also mediate the pharmacological effects of C. sativa [3].
Although phytocannabinoids have similar chemical structures, they can elicit different pharmacological actions. The identification of THC paved the way for the discovery, in 1988, of cannabinoid receptor type 1 (CB1) [4], and, later, of cannabinoid receptor type 2 (CB2) [5]. CB1 and CB2 belong to a family of seven transmembrane Guanosine Binding Protein-Coupled Receptors, are widely expressed and distinguished by their specific functions, localization and signalling mechanisms. They are one of the important endogenous lipid signalling pathways, named the ‘endocannabinoid system’, which consists of cannabinoid receptors, the endogenous ligands of cannabinoid receptors (endocannabinoids) and the enzymes that regulate the biosynthesis and inactivation of endocannabinoids. This lipid signalling system is involved in many important physiological functions in the central and peripheral nervous system and in the endocrine and immune systems [6,7].
The psychotropic effects of cannabis are principally mediated by CB1, which is widely distributed throughout the brain, but mainly in the frontal cortex, basal ganglia and cerebellum. CB1 is also present in several tissues and organs, including adipose tissue, the gastrointestinal tract, the spinal cord, the adrenal and thyroid glands, liver, reproductive organs and immune cells. The presence of CB1 receptors on chondrocytes and osteocytes, as well as evidence for their presence on fibroblast-like synoviocytes, makes CB1 particularly interesting in the study of rheumatic diseases [8]. CB1 activation inhibits adenylate cyclase and reduces cAMP levels and protein kinase A (PKA) activity, resulting in the activation of the A-type potassium channels and decreased cellular potassium levels [9].
CB2 is principally expressed in immune cells, but can also be found in various other cell types, including chondrocytes, osteocytes and fibroblasts, meaning that it can be considered the peripheral cannabinoid receptor. It is also present in some nervous tissues, such as dorsal root ganglia and microglial cells. CB2 shows 44% amino acid similarity with CB1, and similarly inhibits adenylate cyclase as well as activating mitogen-activated protein kinase. Moreover, CB2 activation can increase intracellular calcium levels via phospholipase C. While both CB1 and CB2 are coupled to G-proteins, the transduction pathways that they activate can be different, for example, in their interactions with ion channels [10]. The association of a particular variant of CB2, known as Q63R, with coeliac disease, immune thrombocytopenic purpura and juvenile idiopathic arthritis is particularly interesting for the field of autoimmune and rheumatic diseases [11].
Overall, seven different endogenous ligands have been identified as acting within the endocannabinoid system to date. The first two endocannabinoids are the derivatives of arachidonic acid N-arachidonoyl ethanolamide (anandamide) and 2-arachidonoyl glycerol [12]. A third endocannabinoid, 2-arachidonoyl glyceryl ether (noladin ether) was discovered in 2001. N-arachidonoyl dopamine, O-arachidonoyl-ethanolamide (virodhamine), docosatetraenoylethanolamide, lysophosphatidylinositol and oleoylethanolamide have since been described as ligands of endocannabinoid receptors [7].
The endocannabinoid system’s contribution to the regulation of such a variety of processes makes phytocannabinoid pharmacological modulation a promising therapeutic strategy for many medical fields, including the studies of analgesic, neuroprotective, anti-inflammatory and antibacterial activity [13,14].
THC is the primary psychoactive component of cannabis and works primarily as a partial agonist of CB1 (Ki = 53 nM) and CB2 (Ki = 40 nM) receptors [15] and has well-known effects on pain, appetite enhancement, digestion, emotions and processes that are mediated through the endocannabinoid system [7]. Adverse psychoactive events can be caused by THC, depending on dose and previous patient tolerance. By contrast CBD, which is the major non-psychoactive phytocannabinoid component of C. sativa, has little affinity for these receptors, (Ki for human CB1 and CB2 of 1.5 and 0.37 M, respectively), and acts as a partial antagonist CB1 and as a weak inverse CB2 agonist (Ki as antagonist of CP55940 from 4.2 2.4 to 0.75 0.3 M in different human cell lines) [16].
In a recent paper, experiments based on the functional effects of CBD on PLC 3, ERK, arrestin2 recruitment and CB1 internalization, show a negative allosteric modulation of CB1 at concentration below 1 M [17].
Additionally, other non-CB1 receptor mechanisms of CBD have been proposed, among them its agonism at serotonin 1A receptor (or 5-TH1A), vanilloid receptor 1 (TRPV1) and adenosine A2A receptors [18,19]. The complex physiological and pharmacological mechanisms and interaction of CBD with the endocannabinoid system and other molecular targets are extensively reviewed by McPartland et al. [20]. These data may help explain some of the observed CBD effects including analgesic, anti-inflammatory, anti-anxiety and anti-psychotic activity [21]. The combination of THC and CBD with other phytocannabinoids and other components, such as terpenoids and flavonoids, in cannabis may have a synergistic effect on pain treatment [22,23].
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