Eugenol

The flower of Syzygium aromaticum

Eugenol is an essential oil found in cloves with antibacterial, anthelmintic and antioxidant activity. Eugenol is shown to inhibit lipid peroxidation.

In Vitro:The essential oil of O. gratissimum, as well as eugenol, are efficient in inhibiting eclodibility of H. contortus eggs, showing possible utilizations in the treatment of gastrointestinal helmintosis of small ruminants. At 0.50% concentration, the essential oil and eugenol show a maximum eclodibility inhibition[1]. Eugenol inhibits superoxide anion generation in xanthine-xanthine oxidase system to an extent of 50% at concentrations of 250 μM. Eugenol also inhibits the generation of hydroxyl radicals to an extent of 70%. The OH-radical formation measured by the hydroxylation of salicylate to 2, 3-dihydroxy benzoate is inhibited to an extent of 46% by eugenol at 250 μM[2]. Eugenol protects against RS-induced development of IBS-like gastrointestinal dysfunction through modulation of HPA-axis and brain monoaminergic pathways apart from its antioxidant effect. Eugenol (50 mg/kg) reduces 80% of RS-induced increase in fecal pellets similar to that of ondansetron. Eugenol attenuates 80% of stress-induced increase in plasma corticosterone and modulates the serotonergic system in the PFC and amygdala. Eugenol attenuates stress-induced changes in norepinephrine and potentiates the antioxidant defense system in all brain regions[3].

In Vivo:Eugenol (33 mg/kg) administered orally for 2 days causes significant suppression of knee joint edema, which continues to be significantly reduced at the end of the treatment. After 2 days, eugenol-treated mycobacterial arthritic rats show a marked reduction in paw swelling[4].

References:
[1]. Pessoa LM, et al. Anthelmintic activity of essential oil of Ocimum gratissimum Linn. and eugenol against Haemonchus contortus. Vet Parasitol. 2002 Oct 16;109(1-2):59-63. [2]. Reddy AC, et al. Studies on the inhibitory effects of curcumin and eugenol on the formation of reactive oxygenspecies and the oxidation of ferrous iron. Mol Cell Biochem. 1994 Aug 17;137(1):1-8. [3]. Garabadu D, et al. Protective effect of eugenol against restraint stress-induced gastrointestinal dysfunction: Potential use in irritable bowel syndrome. Pharm Biol. 2015 Jul;53(7):968-74. [4]. Sharma JN, et al. Suppressive effects of eugenol and ginger oil on arthritic rats. Pharmacology. 1994 Nov;49(5):314-8.

Eugenol suppresses cyclooxygenase-2 expression in lipopolysaccharide-stimulated mouse macrophage RAW264.7 cells.[Pubmed:12757841]

Life Sci. 2003 Jun 6;73(3):337-48.

Inducible cyclooxygenase (COX-2) has been implicated in the processes of inflammation and carcinogenesis. Thus, the potential COX-2 inhibitors have been considered as anti-inflammatory or cancer chemopreventive agents. In this study, the methanolic extract of the cortex of Eugenia caryophyllata Thunberg (Myrtaceae) was found to potently inhibit the prostaglandin E(2) production in lipopolysaccharide (LPS)-activated mouse macrophage RAW264.7 cells (98.3% inhibition at the test concentration of 10 microg/ml). Further, hexane-soluble layer was the most active partition compared to ethyl acetate, n-butanol, and water-soluble parts. By bioassay-guided fractionation of hexane-soluble partition, Eugenol was isolated and exhibited a significant inhibition of PGE(2) production (IC(50) = 0.37 microM). In addition, Eugenol suppressed the cyclooxygenase-2 (COX-2) gene expression in LPS-stimulated mouse macrophage cells. On the line of COX-2 playing an important role in colon carcinogenesis further study was designed to investigate the effect of Eugenol on the growth and COX-2 expression in HT-29 human colon cancer cells. Eugenol inhibited the proliferation of HT-29 cells and the mRNA expression of COX-2, but not COX-1. This result suggests that Eugenol might be a plausible lead candidate for further developing the COX-2 inhibitor as an anti-inflammatory or cancer chemopreventive agent.

Eugenol (an essential oil of clove) acts as an antibacterial agent against Salmonella typhi by disrupting the cellular membrane.[Pubmed:20435121]

J Ethnopharmacol. 2010 Jul 6;130(1):107-15.

AIM OF THE STUDY: To evaluate the antibacterial activity of Eugenol and its mechanism of bactericidal action against Salmonella typhi. MATERIALS AND METHODS: The antibacterial activity was checked by disc-diffusion method, MIC, MBC, time course assay and pH sensitivity assay. The chemo-attractant property of Eugenol was verified by chemotaxis assay. The mode of action of Eugenol was determined by crystal violet assay, measurement of release of 260 nm absorbing material, SDS-PAGE, FT-IR spectroscopy, AFM and SEM. RESULTS: Treatment with Eugenol at their MIC (0.0125%) and MBC (0.025%) reduced the viability and resulted in complete inhibition of the organism. Eugenol inactivated Salmonella typhi within 60 min exposure. The chemo-attractant property of Eugenol combined with the observed high antibacterial activity at alkaline pH favors the fact that the compound can work more efficiently when given in vivo. Eugenol increased the permeability of the membrane, as evidenced by crystal violet assay. The measurement of release of 260 nm absorbing intracellular materials, SDS-PAGE, SEM and AFM analysis confirmed the disruptive action of Eugenol on cytoplasmic membrane. The deformation of macromolecules in the membrane, upon treatment with Eugenol was verified by FT-IR spectroscopy. CONCLUSION: The results suggest that the antibacterial activity of Eugenol against Salmonella typhi is due to the interaction of Eugenol on bacterial cell membrane.

Inhibitory effects of eugenol on RANKL-induced osteoclast formation via attenuation of NF-kappaB and MAPK pathways.[Pubmed:25405641]

Connect Tissue Res. 2015 Jun;56(3):195-203.

Bone loss diseases are often associated with increased receptor activator of NF-kappaB ligand (RANKL)-induced osteoclast formation. Compounds that can attenuate RANKL-mediated osteoclast formation are of great biomedical interest. Eugenol, a phenolic constituent of clove oil possesses medicinal properties; however, its anti-osteoclastogenic potential is unexplored hitherto. Here, we found that Eugenol dose-dependently inhibited the RANKL-induced multinucleated osteoclast formation and TRAP activity in RAW264.7 macrophages. The underlying molecular mechanisms included the attenuation of RANKL-mediated degradation of IkappaBalpha and subsequent activation of NF-kappaB pathway. Furthermore, increase in phosphorylation and activation of RANKL-induced mitogen-activated protein kinase pathways (MAPK) was perturbed by Eugenol. RANKL-induced expression of osteoclast-specific marker genes such as TRAP, cathepsin K (CtsK) and matrix metalloproteinase-9 (MMP-9) was remarkably downregulated by Eugenol. These findings provide the first line of evidence that Eugenol mediated attenuation of RANKL-induced NF-kappaB and MAPK pathways could synergistically contribute to the inhibition of osteoclast formation. Eugenol could be developed as therapeutic agent against diseases with excessive osteoclast activity.

Eugenol-inhibited root growth in Avena fatua involves ROS-mediated oxidative damage.[Pubmed:25752432]

Pestic Biochem Physiol. 2015 Feb;118:64-70.

Plant essential oils and their constituent monoterpenes are widely known plant growth retardants but their mechanism of action is not well understood. We explored the mechanism of phytotoxicity of Eugenol, a monoterpenoid alcohol, proposed as a natural herbicide. Eugenol (100-1000 microM) retarded the germination of Avena fatua and strongly inhibited its root growth compared to the coleoptile growth. We further investigated the underlying physiological and biochemical alterations leading to the root growth inhibition. Eugenol induced the generation of reactive oxygen species (ROS) leading to oxidative stress and membrane damage in the root tissue. ROS generation measured in terms of hydrogen peroxide, superoxide anion and hydroxyl radical content increased significantly in the range of 24 to 144, 21 to 91, 46 to 173% over the control at 100 to 1000 microM Eugenol, respectively. The disruption in membrane integrity was indicated by 25 to 125% increase in malondialdehyde (lipid peroxidation byproduct), and decreased conjugated diene content (~10 to 41%). The electrolyte leakage suggesting membrane damage increased both under light as well as dark conditions measured over a period from 0 to 30 h. In defense to the oxidative damage due to Eugenol, a significant upregulation in the ROS-scavenging antioxidant enzyme machinery was observed. The activities of superoxide dismutases, catalases, ascorbate peroxidases, guaiacol peroxidases and glutathione reductases were elevated by ~1.5 to 2.8, 2 to 4.3, 1.9 to 5.0, 1.4 to 3.9, 2.5 to 5.5 times, respectively, in response to 100 to 1000 microM Eugenol. The study concludes that Eugenol inhibits early root growth through ROS-mediated oxidative damage, despite an activation of the antioxidant enzyme machinery.

Studies on the inhibitory effects of curcumin and eugenol on the formation of reactive oxygen species and the oxidation of ferrous iron.[Pubmed:7845373]

Mol Cell Biochem. 1994 Aug 17;137(1):1-8.

The spice principles curcumin (from turmeric) and Eugenol (from cloves) are good inhibitors of lipid peroxidation. Lipid peroxidation is known to be initiated by reactive oxygen species. The effect of curcumin and Eugenol on the generation of reactive oxygen species in model systems were investigated. Both curcumin and Eugenol inhibited superoxide anion generation in xanthine-xanthine oxidase system to an extent of 40% and 50% at concentrations of 75 microM and 250 microM respectively. Curcumin and Eugenol also inhibited the generation of hydroxyl radicals (.OH) to an extent of 76% and 70% as measured by deoxyribose degradation. The .OH-radical formation measured by the hydroxylation of salicylate to 2,3-dihydroxy benzoate was inhibited to an extent of 66% and 46%, respectively, by curcumin and Eugenol at 50 microM and 250 microM. These spice principles also prevented the oxidation of Fe2+ in Fentons reaction which generates .OH radicals.

Eugenol inhibits the GABAA current in trigeminal ganglion neurons.[Pubmed:25635877]

PLoS One. 2015 Jan 30;10(1):e0117316.

Eugenol has sedative, antioxidant, anti-inflammatory, and analgesic effects, but also serves as an irritant through the regulation of a different set of ion channels. Activation of gamma aminobutyric acid (GABA) receptors on sensory neurons leads to the stabilization of neuronal excitability but contributes to formalin-induced inflammatory pain. In this study, we examined the effect of Eugenol on the GABA-induced current in rat trigeminal ganglia (TG) neurons and in human embryonic kidney (HEK) 293 cells expressing the GABAA receptor alpha1beta2gamma2 subtype using the whole-cell patch clamp technique. RT-PCR and Western blot analysis were used to confirm the expression of GABAA receptor gamma2 subunit mRNA and protein in the TG and hippocampus. Eugenol decreased the amplitude ratio of the GABA-induced current to 27.5 +/- 3.2% (p < 0.05) in TG neurons, which recovered after a 3-min washout. In HEK 293 cells expressing the alpha1beta2gamma2 subtype, Eugenol inhibited GABA-induced currents in a dose-dependent manner. Application of Eugenol also decreased the GABA response in the presence of a G-protein blocker. Eugenol pretreatment with different concentrations of GABA resulted in similar inhibition of the GABA-induced current in a non-competitive manner. In conclusion, Eugenol inhibits the GABA-induced current in TG neurons and HEK 293 cells expressing the GABAA receptor in a reversible, dose-dependent, and non-competitive manner, but not via the G-protein pathway. We suggest that the GABAA receptor could be a molecular target for Eugenol in the modulation of nociceptive information.

Anthelmintic activity of essential oil of Ocimum gratissimum Linn. and eugenol against Haemonchus contortus.[Pubmed:12383625]

Vet Parasitol. 2002 Oct 16;109(1-2):59-63.

The ovicidal activity of the essential oil of Ocimum gratissimum Linn. (Labideae) and its main component Eugenol was evaluated against Haemonchus contortus, gastrointestinal parasite of small ruminants. The oil and Eugenol were diluted in Tween 20 (0.5%) at five different concentrations. In the egg hatch test, H. contortus eggs were obtained from feces of goats experimentally infected. At 0.50% concentration, the essential oil and Eugenol showed a maximum eclodibility inhibition. These results suggest a possible utilization of the essential oil of O. gratissimum as an aid to the control of gastrointestinal helmintosis of small ruminants.

Eugenol is an essential oil found in cloves with antibacterial, anthelmintic and antioxidant activity. Eugenol is shown to inhibit lipid peroxidation.

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