Clove (Syzygium aromaticum) essential oil contains between 72 and 90 percent eugenol, while cinnamon oil may contain 30 percent eugenol and basil oil up to 10 percent eugenol. This essential oil constituent is known to possess analgesic, antioxidant, and neuroprotective properties. Also known is eugenol’s anti-inflammatory effects. But it seems there is just one research paper on eugenol exhibiting anti-rheumatic effects.
A joint study1 of the Brazilian State University of Maringá and Georgia Health Sciences University in Augusta, Georgia, tested eugenol from clove essential oil on mice with collagen-induced arthritis. The experimental model of collagen-induced arthritis (CIA) was used in this animal study because it resembles the arthritis that humans experience.
The researchers had previously determined that clove oil, with its major compound eugenol, has an immunomodulatory effect. So this study would see if eugenol had any effect on established arthritis in mice. All of the study mice received 100 μg of bovine collagen type II to induce arthritis. “Vehicle-treated” mice received saline containing 1 percent Tween 80, v/v (percentage by volume) orally, while another group of mice received 100 μg of eugenol. “Normal” mice received the CII but without treatment or vehicle.
While the eugenol showed beneficial effects against the collagen-induced arthritis at the very beginning of treatment, there was a significant reduction by the 35th to the 40th day of treatment. The title of Figure 1 in the paper told the story well: “Eugenol Reduced the Progression and Severity of CIA and Cellular Recruitment in Knee Joints from Arthritic Mice.”
As the inflammatory rush of leukocytes (white blood cells) to areas affected by arthritis “plays an essential role in experimental arthritis and could contribute to articular damage,” the researchers tested “whether eugenol could modulate leukocyte recruitment (the inflammatory rush) to the knee joint when compared with the vehicle-treated arthritic mice.” After testing cell viability in eugenol-treated cells versus the control cells, the study states, “Our results show that cells treated with eugenol remain viable (>80%) even when exposed to the highest concentration (90 μg/mL).”
Since cytokines (signaling molecules) have direct cell-to-cell communication and are involved in the tissue damage detected in rheumatoid arthritis, this study also investigated how eugenol affected concentrations of the cytokines TNF-_ (tumor necrosis factor alpha, the cytokine that can cause cell death: apoptosis), IFN-_ (interferon gamma, macrophageactivating factor), TGF-_ (transforming growth factor beta), which can also induce apoptosis, and IL-10 (Interleukin-10) an anti-inflammatory cytokine.
The study reported that paw samples from the vehicle-treated arthritic mice had significantly higher concentrations of all the cytokines mentioned above. While the eugenol-treated mice showed a significant reduction in TNF- _, IFN-_, and TGF-_. A surprisingly positive find was that the researchers “found a slight tendency for eugenol to enhance levels of the anti-inflammatory cytokine IL-10 when compared with the vehicletreated mice.”
1. Grespan R, et al. Anti-arthritic Effect of Eugenol on Collagen-Induced Arthritis Experimental Model,” Biol Pharm Bull. 2012;35(10):1818-20. The full study is available free online at: https://www.jstage.jst.go.jp/article/bpb/35/10/35_b12-00128/_pdf.