Eugenol, bis-eugenol and synthesized related-dimer compounds produce antinociception in the acetic acid-induced-writhing responses

Eugenol and its symmetrical dimer bis-eugenol as well as the bromo-bis-eugenol derivative (±)-2,2’-dihydroxy-3,3’-dimethoxy-5,5’-diallyl-6,6’-dibromo-1,1’-biphenyl [(±)-1] and both its enantiomers, (aR)-(+)-2,2’-dihydroxy-3,3’-dimethoxy-5,5’-diallyl-6,6’-dibromo-1,1’-biphenyl [(aR)-(+)1] and (aS)-(+)-2,2’-dihydroxy-3,3’-dimethoxy-5,5’-diallyl-6,6’-dibromo-1,1’-biphenyl [(aS)-(-)1], previously synthesized, were tested in the carrageenin-induced paw oedema in the rat and in the writhing induced by acetic acid in the mouse. Experimental data indicate that acute systemic admin-istration of assayed compounds, at the dose of 50 mg/kg, did not inhibit oedema development whereas all caused a significant effect in visceral pain as revealed by the reduction of the number of writhing responses. At the dose tested, no significant differences were ob-served between the racemate form (±)-1 and the (aR)-(+)-1 and (aS)-(-)-1 enantiomers and between eugenol and bis-eugenol. In addition, the antinociception of the racemate (±)-1 and its respective enantiomers (aR)-(+)-1 and (aS)-(-)-1 was not mediated by the opioid receptors since opioid receptor antagonist, naloxone did not reverse bromo-bis-eugenol derivatives-produced antinociception. Moreover, to further characterise the antinociceptive profile of bromo-bis-eugenol derivatives we have also examined the effects on carrageenin-induced thermal hyperalgesia in rat paw. All bromo-bis-eugenol derivatives did not increase the paw with-drawal latency on both paws, the site of carrageenin in-jection and the contralateral side. In conclusion, eugenol, bis-eugenol and bromo-bis-eugenol derivatives produced a reduction of visceral pain but had no effect on inflammation. Moreover, bromo-bis-eugenol derivatives failed in reducing the inflammatory pain showing also a lack of antinociceptive effect on thermal pain. These interesting findings provide some infor-mation that will be useful for further studying and development of these compounds for clinical use.