Cell experiment:

The essential oil and eugenol are diluted in aqueous solution of Tween 20 (0.5%) in the following concentrations: 0.0625, 0.12, 0.25, 0.5 and 1.0% to be used in the egg hatch test[1].

Animal experiment:

Rats: The treatment groups of arthritic rats are given either ingwerol (0.33 mL/kg or 33 mg/kg) or eugenol (0.33 mL/kg or 33 mg/kg) orally 1 day prior to the induction of arthritis. This treatment is continued for 26 days on a daily basis. Mycobaterium trated rats receive physiological saline orally[4].

Eugenol, a phenylpropanoid class compounds, is a colourless to pale yellow oily liquid extracted from certain essential oils, such as clove oil, cinnamon, nutmeg, basil and bay leaf.

In vitro: Previous study showed that eugenol could deplete intracellular GSH, inhibit GJIC and ROS generation, and had a modest effect on MMP at concentrations of 10 to 100 μM. Eugenol at high concentrations was also able to affecte [Ca2+i, PMP, as well as nd pH. The earliest and most potent effects of either was found on GSH levels and GJIC. In addition, the coadministration of glutathione ethyl ester enhanced intracellular GSH levels by almost 100% and protected cells from cell death caused by eugenol completely. Such results indicated that eugenol exhibited its hepatotoxic effects mainly via depletion of cytoprotective thiols and disruptioin in thiol-dependent processes [1].

In vivo: Animal study showed that the pretreatment with a single dose of eugenol that was 1 h before indomethacin administration was fond to cause significant reductions in gastric acid outputs, gastric mucosal lesions, as well as pepsin activity with a obvioius increase in mucin concentration. In addition, eugenol could also attenuate the elevations in gastric mucosal malondialdehyde and total nitrite significantly [2].

Clinical trial: Clinical study has been conducted to evaluate the effects of zinc oxide eugenol and metapex in root canal treatment of primary teeth. Results showed that both zinc oxide eugenol and metapex had encouraging results, however, metapex could be more safely used whenever there was a doubt about the patient's follow-up return [3].

References:
[1] Thompson DC,Barhoumi R,Burghardt RC.  Comparative toxicity of eugenol and its quinone methide metabolite in cultured liver cells using kinetic fluorescence bioassays. Toxicol Appl Pharmacol.1998 Mar;149(1):55-63.
[2] Morsy MA,Fouad AA.  Mechanisms of gastroprotective effect of eugenol in indomethacin-induced ulcer in rats. Phytother Res.2008 Oct;22(10):1361-6.
[3] Gupta S,Das G.  Clinical and radiographic evaluation of zinc oxide eugenol and metapex in root canal treatment of primary teeth. J Indian Soc Pedod Prev Dent.2011 Jul-Sep;29(3):222-8.