The neuroprotection of cannabidiol against MPP+-induced toxicity inPC12 cells involves trkA receptors, upregulation of axonal and synapticproteins, neuritogenesis, and might be relevant to Parkinson’s disease
Toxicology in Vitro, 2015, 30, 231–240.
a b s t r a c t
Cannabidiol (CBD) is a non-psychoactive constituent of Cannabis sativa with potential to treat neurodegenerative diseases. Its neuroprotection has beenmainly associated with anti-inflammatory and antioxidant events; however, other mechanisms might be involved. We investigated the involvement of neuritogenesis, NGF receptors (trkA), NGF, and neuronal proteins in the mechanism of neuroprotection of CBD against MPP+ toxicity in PC12 cells. CBD increased cell viability, differentiation, and the expression of axonal (GAP-43) and synaptic (synaptophysin and synapsin I) proteins. Its neuritogenic effect was not dependent or additive to NGF, but it was inhibited by K252a (trkA inhibitor). CBD did not increase the expression of NGF, but protected against its decrease induced by MPP+, probably by an indirect mechanism.We also evaluated the neuritogenesis in SH-SY5Y cells, which do not express trkA receptors. CBD did not induce neuritogenesis in this cellular model, which supports the involvement of trkA receptors. This is the first study to report the involvement of neuronal proteins and trkA in the neuroprotection of CBD. Our findings suggest that CBD has a neurorestorative potential independent of NGF that might contribute to its neuroprotection against MPP+, a neurotoxin relevant to Parkinson’s disease.
Keywords : Cannabidiol (CBD), trkA receptors, GAP-43, Synaptophysin, Synapsin I, Neuroprotection
Cannabidiol (CBD) is a non-psychoactive compound of Cannabis sativa with anti-inflammatory and antioxidant properties and consequently, a potential for neuroprotection (Zuardi et al., 2006; Fernandez-Ruiz et al., 2013). Several studies have suggested the potential of CBD in the treatment of neurodegenerative diseases (ND) such as Parkinson’s disease (PD) (Chagas et al., 2014), Alzheimer’s disease (AD) (Fernandes-Ruiz et al., 2005) and Huntington’s disease (HD) (Sagredo et al., 2007).Despite that, the precisemolecularmechanisms underlying the therapeutic potential of CBD remain unclear. Many targets of CBD such as receptors, ion channels, enzymes and transporters have been identified (Fernandez-Ruiz et al., 2013); however, the role of neuritogenesis in the neuroprotection of CBD has not been clarified yet. Neurite loss is an early event in neurodegenerative diseases and the regeneration of the network of neurites constitutes a strategy for the treatment of such disorders. Neurotrophic factors play a critical role in neuronal regeneration, but their clinical use is limited by their inability to cross the blood brain barrier (Gottlieb et al., 2010). It is noteworthy that, CBD is not psychoactive, but it can readily cross the blood brain barrier and exert its beneficial effects on the brain (Deiana et al., 2012). The trophic signaling of nerve growth factor (NGF) has been associated with the prevention of neuronal apoptosismediated by activation of the anti-apoptotic protein Bcl2. The lack of stimulation by NGF and the resulting inactivation of Bcl2 trigger the intrinsic pathway (mitochondrial) of apoptosis through mitochondrial permeability transition (MPT), release of cytochrome c and activation of the caspase cascade (Wolozin and Behl, 2000).
Loss and dysfunction of trophic factors seem to be involved in the pathogenesis of AD and PD (Connor and Dragunow, 1998; Siegel and Chauhan, 2000). Decrease of neurotrophic factors such as BDNF and NGF has been reported in the brain and cerebrospinal fluid of PD patients (Mogi et al., 1999; Nagatsu et al., 2000). Additionally, a study showed significant reduction of serum levels of NGF in parkinsonian rats and in patients with PD. Interestingly, NGF levels in early stages of the disease (Grades I–II)were lower in comparison to those found in advanced stages (Grades III–IV) (Lorigados Pedre et al., 2002).
Based on these premises, the present study investigated the neurorestorative potential of CBD and the pathways that mediate it by using PC12 cells treated with the neurotoxin MPP+, a metabolite of MPTP (1-methyl-4-phenyl-1,2,5,6tetrahydropyridine), known to induce Parkinsonism in vivo. The involvement of the NGF-pathway was evaluated by using a specific inhibitor of trk receptors and two cell lines (PC12 and SH-SY5Y)with distinct phenotypes for these receptors. The role of NGF in the protective mechanism of CBD was also investigated.