Cannabidiol Protects Dopaminergic Neuronal Cells from Cadmium
Jacopo Junio Valerio Branca, Gabriele Morucci, Matteo Becatti, Donatello Carrino, Carla Ghelardini, Massimo Gulisano, Lorenzo Di Cesare Mannelli Alessandra Pacini
International Journal of Environmental Research and Public Health, 2019, 16, 4420.
doi : 10.3390/ijerph16224420
The protective effect of cannabidiol (CBD), the non-psychoactive component of Cannabis sativa, against neuronal toxicity induced by cadmium chloride (CdCl2 10 M) was investigated in a retinoic acid (RA)-dierentiated SH-SY5Y neuroblastoma cell line. CBD (1 M) was applied 24 h before and removed during cadmium (Cd) treatment. In dierentiated neuronal cells, CBD significantly reduced the Cd-dependent decrease of cell viability, and the rapid reactive oxygen species (ROS) increase. CBD significantly prevented the endoplasmic reticulum (ER) stress (GRP78 increase) and the subcellular distribution of the cytochrome C, as well as the overexpression of the pro-apoptotic protein BAX. Immunocytochemical analysis as well as quantitative protein evaluation by western blotting revealed that CBD partially counteracted the depletion of the growth associated protein 43 (GAP43) and of the neuronal specific class III -tubulin (3 tubulin) induced by Cd treatment. These data showed that Cd induced neuronal injury was ameliorated by CBD treatment and it was concluded that CBD may represent a potential option to protect neuronal cells from the detrimental eects of Cd toxicity.
Keywords : cadmium; cannabidiol; ER stress; ROS; SH-SY5Y; neurotoxicity
Cadmium (Cd) is a transition heavy metal, chemically similar to zinc and mercury, the two other metals in group 12, whose preferential oxidation state is +2. As an important component of industrial processes such as metal plating, production of nickel-cadmium batteries, pigments, plastics, and other synthetics, Cd has been seen as an occupational hazard . On the other hand, tobacco smoking, air pollution, and consumption of Cd-contaminated drinking water are the major sources of non-occupational Cd exposure [2,3]. If the primary route of exposure in industrial settings is inhalation of Cd-containing fumes, food and water are generally the largest sources of Cd exposure in a non-smoker population . Epidemiological and experimental studies have linked the occupational Cd exposure with lung cancer and other cancers such as the prostate, renal, liver, hematopoietic system, urinary bladder, pancreatic, testis, and stomach cancers [5–7].
Exposure to Cd also severely aects the function of the nervous system [8–11], with symptoms including headache and vertigo, olfactory and motor dysfunction, peripheral neuropathy, decreased equilibrium and ability to concentrate, and learning disabilities [12–15]. Although studies on the central nervous system (CNS) Cd distribution demonstrated that this metal could not easily get into the brain due to the presence of the blood brain barrier (BBB) [16,17], a Cd-induced BBB dysfunction and permeability increase has been demonstrated in in vivo models . Also, authors reported the presence of BBB impairment in several neurodegenerative diseases, such as Alzheimer’s disease (AD) and Parkinson’s disease (PD) [19,20]. Cd was shown to adversely influence the functions of cholinergic and catecholaminergic systems , as well as the balance between excitation–inhibition in synaptic neurotransmission . Also, it has been proposed that chronic exposure to Cd can be associated with an increased risk of developing PD . Parkinson’s disease is a neurodegenerative condition characterized by loss of dopaminergic neurons in the substantia nigra pars compacta with resulting neurochemical imbalance throughout the basal ganglia . Interestingly, this heavy metal shows similar mechanisms of toxicity with other pollutants: they accumulate in the substantia nigra and generate oxidative stress by increasing the production of reactive oxygen species (ROS) and/or deregulating the antioxidant enzymes. This, in turn, produces the activation of the glia inducing neuroinflammation, which increases the generation of further oxidative stress, leading to a self-perpetuating cycle [25,26].
Although the mechanisms of Cd toxicity are poorly understood, the neurotoxicity of Cd is attributable to the generation of ROS. Oxidative stress is generally defined as an imbalance that favors the production of ROS and reactive nitrogen species (RNS) [27–29]. The major consequence induced by Cd through oxidative stress is a ROS-mediated attack of double bonds in membrane lipids that results in increased lipid peroxidation (LPO) as well as interference with the endogenous antioxidant defenses in several organs and systems [27,30–33]. Indeed, Cd is known to induce a mitochondrial membrane potential decrease and the consequent release of cytochrome C, eventually leading to the activation of caspase-3 . Furthermore, it has been demonstrated that Cd induces ER stress [21,35].
Previous in vitro and in vivo studies showed that Cd neurotoxicity was significantly attenuated by antioxidants, anti-inflammatory, and metal-chelating agents [21,36–39]. Cannabis sativa has been used for medicinal/recreational purposes for many years . The two major components are D9-tetrahydro-cannabinol (D9-THC), the main psychoactive ingredient, and cannabidiol (CBD), the major non-psychoactive component [41–43].
The adverse effects of cannabis are attributed to D9-THC , whereas CBD exhibits a variety of therapeutic properties: anti-inflammatory, antidepressant, anxiolytic, immunomodulatory, antioxidant,
and neuroprotective eects [45–52]. CBD has been shown to reverse the increased excitotoxicity, inflammation, and oxidative stress in ischemic brain damage and to protect PC12 and SH-SY5Y cells from tert-butyl-hydroperoxide-induced oxidative stress . Also, recent studies demonstrated that CBD was able to reverse the reductions in synaptophysin levels and increases in caspase-3 levels induced by iron .
For this purpose, SH-SY5Y cell line presents many advantages including that can be dierentiated using retinoic acid (RA). Recently, Korecka and colleagues  have characterized the molecular phenotype of RA-dierentiated SH-SY5Y cells and concluded that these cells exhibit a dopaminergic phenotype. The use of dierentiated SH-SY5Y cells is well established as a cell culture model of PD .
In the present study, we provide evidence that CBD oers protection to neuronal cells against Cd-induced oxidative stress by decreasing ROS production. Finally, we demonstrate the protective effects of CBD against Cd-induced ER stress, pro-apoptotic BAX upregulation, cytochrome C release, and the modifications in the expression levels and in the cellular distribution of the growth associated protein 43 (GAP43) and of the neuronal specific class III -tubulin (3 tubulin), two proteins involved in the neuronal sprouting.