The anti-nociceptive and anti-inflammatory effects of Pelargonium graveolens essential oil nanoemulsion in mice

Pain and inflammation are the severe problems of the world. Essential oils (EOs) have been considered for treating pain and inflammation. As EOs are unstable and insoluble in water, nanoemulsions can improve bioavailability and efficacy. This study formulated Pelargonium graveolens essential oil nanoemulsion (PGEO-NE) using Tween 80 as a carrier. The activity of PGEO-NE (50 and 100 mg/kg) and the involvement of the opioid pathway were investigated in different models of nociception and inflammation in mice. The droplets in PGEO-NE are spherical, with a particle size of around 553 nm and a polydispersity index of 0.113. GC/MS analysis of PGEO revealed citronellol (34.9%), geraniol (16.1%), citronellyl formate (12.3%), and linalool (6.8%) as the main constituents. PGEO-NE significantly reduced the duration of formalin-induced paw licking/biting in both phases and the number of acetic acid-induced writhings, and increased the hot plate latency, compared to vehicle and PGEO (10 mg/kg), equivalent to the PGEO-NE dose of 100 mg/kg. The anti-nociceptive potential of PGEO-NE (100 mg/kg) in the hot plate and acetic acid tests was reversed by the opioid antagonist. After formalin and carrageenan injections, PGEO-NE significantly inhibited paw edema, but PGEO (10 mg/kg) had no effect. These results confirm that PGEO-NE inhibits pain and inflammation via the opioid pathway.