Antinociceptive and Anti-Inflammatory Effects of Bixin, a Carotenoid Extracted from the Seeds of Bixa orellana.

Bixin is the main natural apocarotenoid extracted from the seeds of Bixa orellana, widely used as a cosmetic and textile colorant. Despite the description of several pharmacological properties of B. orellana extracts, little has been studied regarding the pharmacological properties of bixin. Then we aimed to investigate the potential anti-inflammatory and antinociceptive effect of bixin in preclinical models of inflammation and acute pain. The anti-inflammatory activity of bixin (15 or 30 mg/kg, orally) was determined using carrageenan-induced paw edema and the myeloperoxidase (MPO) activity in male Wistar rats. The antinociceptive effect of bixin was assessed in the formalin and hot plate tests in rats (at same doses) and in the acetic acid-induced writhing test in Swiss albino male mice (at doses of 27 or 53 mg/kg). General locomotor activity was evaluated in the open field test. Only the higher dose of bixin significantly decreased the carrageenan-induced paw edema and the MPO activity and increased the latency time in the hot plate. Both doses of bixin significantly reduced the number of flinches in both phases of the formalin test and the number of acetic acid-induced writhings without changing the locomotor performance in the open field test. This study validates the use of bixin as an anti-inflammatory trough mechanism related to the reduction of neutrophil migration. Furthermore, this is the first report showing the antinociceptive property of bixin, which does not appear to be related to the sedative effect. Further studies are necessary to characterize the mechanisms involved in these effects.

Cannabidiol attenuates mechanical allodynia in streptozotocin-induced diabetic rats via serotonergic system activation through 5-HT1A receptors.

Most diabetic patients describe moderate to severe pain symptoms whose pharmacological treatment is palliative and poorly effective. Cannabidiol (CBD) has shown promising results in painful conditions. Then, we aimed to investigate the potential antinociceptive effect of CBD over the mechanical allodynia in streptozotocin-induced diabetic (DBT) rats, as well as its involved mechanisms. Wistar adult male diabetic rats were treated acutely or sub-chronically (for 14 days) with CBD (0.1, 0.3 or 3 mg/kg, intraperitoneal; i.p.) and had their mechanical threshold assessed using the electronic Von Frey. Acute treatment with CBD (at doses of 0.3 and 3 mg/kg) exerted a significant anti-allodynic effect, which is not associated with locomotor impairment. The antinociceptive effect of CBD (3 mg/kg) was not altered by the pre-treatment with CB1 or CB2 receptor antagonists (AM251 and AM630; respectively; both at a dose of 1 mg/kg, i.p.) nor by glycine receptor antagonist (strychnine hydrochloride, 10 µg/rat, intrathecal, i.t.). However, this effect was completely prevented by the pre-treatment with the selective 5-HT1A receptor antagonist WAY 100135 (3 µg/rat, i.t.). Sub-chronic treatment with CBD (0.3 or 3 mg/kg) induced a sustained attenuation of the mechanical allodynia in DBT rats. DBT rats presented significantly lower spinal cord levels of serotonin, which was prevented by the daily treatment with CBD (0.3 mg/kg). Taken together, our data suggest that CBD may be effective in the treatment of painful diabetic neuropathy and this effect seems to be potentially mediated by the serotonergic system activation through 5-HT1A receptors.