Expression of cannabinoid receptors and neurotrophins in human gliomas

Recent studies have shown an anti-tumour activity of cannabinoid receptors CB1 and CB2 in gliomas. This effect was mediated by neurotrophins in breast and prostate carcinoma, while in gliomas this relationship has not yet been considered. The aim of this study was to investigate the expression of cannabinoid receptors CB1 and CB2, neurotrophin NGF and NT-3 and their receptors TrkA and TrkC in glioma and endothelial cells. The analysis was performed in 14 gliomas and 2 non-tumour brain specimens by immunohistochemistry and real-time quantitative-polymerase chain reaction (RTQ-PCR). Gliomas showed a weak immunoreactivity for CB1 and CB2 in tumour and in endothelial cells, and for NGF/TrkA mainly in tumour cells, while a moderate/diffuse immunoreactivity was found for NT-3/TrkC. CB2 was expressed on 3 out of 6 low-grade gliomas and in all high-grade gliomas. Non-tumour brain tissues were weakly positive in astrocytes and endothelium for CB1, CB2, NT-3 and TrkC and negative for NGF and TrkA. By RTQ-PCR, gliomas showed low mRNA levels of NGF/TrkA and moderate levels of CB1, NT-3 and TrkC. CB2 mRNA expression was low or absent. A potential role of cannabinoids, particularly of CB2 agonists devoid of psychotropic side effects, in glioma therapy could have a basis in glioblastomas, because they were all positive, though weakly, to CB2. The presence of neurotrophins and their receptors, mainly NT-3 and TrkC, suggests a possible role of these pathways in glioma growth/invasion, but further investigations are required to verify this hypothesis and a potential relationship between cannabinoids and neurotrophins.