Investigação do efeito do canabidiol sobre a ativação de células da glia em modelos de nocicepção induzida por paclitaxel e LPS

Abstract

Throughout life, pain, both acute and chronic, is one of the reasons for the higher frequency of medical visits and one of the most common reasons for using medications, in addition to being a major cause of disability at work. Chronic pain affects physical and mental functioning, quality of life and productivity of affected individuals. Studies have shown that pain causes activation of glial cells with increased expression of Tool-like receptors (TRL4). TLR4 recognize endogenous and exogenous ligands DAMPS (molecular patterns associated with damage) and PAMPS (molecular patterns associated with pathogens) not only involved with infection or injury, but also with other pathophysiological processes such as pain. Thus, several treatment strategies have been developed to control this symptom, such as treatment with cannabidiol (CBD), a ficanabinoid. Cannabinoid type 2 (CB2) receptors, expressed in peripheral tissues and inflammatory cells, appear to be involved in CBD-induced antinociception. In addition, studies have shown that such receptors are also expressed in the Central Nervous System (CNS), including glial cells. Thus, the present study investigated the effect of CBD on neuropathic pain induced by paclitaxel (PTX) and on nociception induced by lipopolysaccharide (LPS). For this, Swiss mice were used, weighing between 25 and 30g. The nociceptive threshold was assessed by the Von frey filament test. The neuropathic pain model was induced by intraperitoneal injection of PTX and the nociception model induced by PAMP, by intrathecal injection of LPS. The ELISA assay was performed to verify the levels of pro-inflammatory cytokines, IL-1β and TNF-α. The drugs, AM630, were used to investigate the participation of CB2 receptors, the dosage of anandamide (AEA) and 2-arachidonoylglycerol (2-AG), to evaluate the participation of endocannabinoids, minocycline and

fluorocitrate, to investigate the involvement of microglia and astrocyte and LPS- RS to verify the participation of the TRL4 receptor. The western blot assay was

also performed to investigate the effect of CBD on the levels of CB2, IBA-1, GFAP and TRL4 receptor expression, in addition to immunofluorescence to assess the co-location of CB2 / TRL4 receptors in the dorsal root horn of the spinal cord. After 4 days of treatment with PTX, the animals presented a mechanical allodynia and this was reversed by the CBD. The same occurred with the animals that were treated with LPS, the mechanical allodynia was reversed by the CBD. AM630

inhibited CBD-induced antinociception in both nociceptive models. CBD increased levels of AEA and 2-AG in the spinal cord in the models studied. Minocycline and fluorocitrate blocked nociception in both models. LPS-RS also inhibited nociception in both models. The results of the ELISA assay demonstrated that CBD reduced the levels of TNF-α and IL-1β in the models studied. CBD increased CB2 expression in the PTX-induced nociception model and had no effect on the LPS-induced nociception model, reduced IBA-1 levels

in the PTX-induced nociception model, and had no effect on the nociception- induced model LPS. In GFAP expression, CBD had no effect on any of the

models and in TRL4 expression, CBD reduced its expression in the nociception model induced by PTX and had no effect in the nociception model induced by LPS. Thus, we conclude that CBD reduces nociception in models induced by PTX and LPS, the endocannabinoid system participates in this effect and glial cells appear to be involved in the genesis and maintenance of pain, by activating TRL4, with consequent release of cytokines pro-inflammatory TNF-α andIL-1β.