Anti-Inflammatory Effects of the Essential Oils of Ginger (Zingiber officinale Roscoe ) in Experimental Rheumatoid Arthritis

Abstract

Ginger and its extracts have been used traditionally as anti-inflammatory remedies, with a particular focus on the medicinal properties of its phenolic secondary metabolites, the gingerols. Consistent with these uses, potent anti-arthritic effects of gingerol-containing extracts were previously demonstrated by our laboratory using an experimental model of rheumatoid arthritis, streptococcal cell wall (SCW)-induced arthritis. In this study, anti-inflammatory effects of ginger's other secondary metabolites, the essential oils (GEO), which contain terpenes with reported phytoestrogenic activity, were assessed in female Lewis rats with SCW-induced arthritis. GEO (28 mg/kg/d ip) prevented chronic joint inflammation, but altered neither the initial acute phase of joint swelling nor granuloma formation at sites of SCW deposition in liver. Pharmacologic doses of 17-β estradiol (200 or 600 μg/kg/d sc) elicited the same pattern of anti-inflammatory activity, suggesting that GEO could be acting as a phytoestrogen. However, contrary to this hypothesis, GEO had no in vivo effect on classic estrogen target organs, such as uterus or bone. En toto, these results suggest that ginger's anti-inflammatory properties are not limited to the frequently studied phenolics, but may be attributable to the combined effects of both secondary metabolites, the pungent-tasting gingerols and as well as its aromatic essential oils.

Keywords: arthritis; essential oil; estradiol; estrogen; ginger; gingerol; inflammation; mice; phytoestrogen; rats.

Figure 1

HPLC-UV profiles (λ = 250 nm) of GEO (A), a gingerol-only fraction (B), and the crude DCM extract from which the GEO and gingerol fractions were derived (C). The 3 major gingerols (1, [6]-gingerol; 2, [8]-gingerol; 3, [10]-gingerol) and a primary gingerol degradation product (4, [6]-shogaol) are not present in the GEO fraction.

Figure 2

Effects of GEO or E₂ on joint inflammation. Female Lewis rats were injected on day 0 with SCW (or vehicle) to induce arthritis with daily GEO, E₂, or vehicle treatments starting 4 days prior to SCW injection as described in Methods and Materials. Joint swelling in limbs of SCW-injected rats was assessed at times indicated and expressed as mean arthritic index (AI, mean ± SEM)) (scale 0-4/limb for total possible score of 16) with statistical significance assessed by ANOVA with Mann Whitney analysis. *p < 0.05, treated vs. vehicle control. A. GEO (28 mg/kg, n = 19) or vehicle alone (DMSO, 1 μl/g, n = 18) were dosed ip daily 5-7 times a week. B. E₂ (200 μg/kg, n = 9) or vehicle alone (sesame seed oil, μl/g, n = 9) were dosed sc daily 5 times a week. C. E₂ (600 μg/kg, n = 9) or vehicle alone (sesame seed oil, μl/g, n = 9) were dosed sc daily 5 times a week.

Figure 3

Effects of GEO or E₂ on incidence of hepatic granuloma formation. Female Lewis rats were injected on day 0 with SCW (or vehicle) to induce arthritis with daily GEO, E₂, or vehicle treatments starting 4 days prior to SCW injection as described in Methods and Materials. The incidence of granuloma formation on day 28-30 was assessed histologically as described in SCW-injected animals. Statistical significance was determined by Fisher's exact test. NS = non-significant. A. GEO (28 mg/kg, n = 8) or vehicle alone (DMSO, 1 μl/g, n = 8) were dosed ip daily 5-7 times a week. B. E₂ (200 μg/kg or 600 μg/kg, n = 12) or vehicle alone (sesame seed oil, μl/g, n = 10) were dosed sc daily 5 times a week. The E₂ doses tested did not alter granuloma incidence when analyzed separately (data not shown) or in combination, as demonstrated here.

Figure 4

Effects of GEO or E₂ on femoral BMD. Female Lewis rats were injected on day 0 with vehicle (control) or SCW to induce arthritis with daily GEO, E₂, or vehicle treatments starting 4 days prior to SCW injection as described in Methods and Materials. Femoral BMD (mean ± SEM, n = 8-36/group) was assessed at time of sacrifice on day 28-30 using a Piximus densitometer as described in Materials and Methods. Statistical significance was determined by ANOVA with post-hoc testing. * p < 0.05 vs. control. ** p < 0.01 vs. SCW. *** p < 0.001 vs. control or SCW, as indicated. NS = non significant. A. GEO (28 mg/kg) or vehicle alone (DMSO, 1 μl/g) were dosed ip daily 5-7 times a week. B. E₂ (200 μg/kg) or vehicle alone (sesame seed oil, μl/g) were dosed sc daily 5 times a week. C. E₂ (600 μg/kg) or vehicle alone (sesame seed oil, μl/g) were dosed sc daily 5 times a week.

Figure 5

Effects of GEO or E₂ on uterine weights. Female Lewis rats were injected on day 0 with vehicle (control) or SCW to induce arthritis with daily GEO, E₂, or vehicle treatments starting 4 days prior to SCW injection as described in Methods and Materials. Uterine weights, expressed as a ratio of body weight (mg uterus/kg body weight, average ± SEM with n = 8-13/group), were assessed at time of sacrifice on day 28-30. Statistical significance was determined by ANOVA with post-hoc testing. ** p < 0.01 vs control. *** p < 0.001 vs control. NS = non significant. A. GEO (28 mg/kg) or vehicle alone (DMSO, 1 μl/g) were dosed ip daily 5-7 times a week. B. E₂ (200 μg/kg) or vehicle alone (sesame seed oil, μl/g) were dosed sc daily 5 times a week.

Figure 6

Effects of GEO or E₂ on circulating lymphocyte counts. Female Lewis rats were injected on day 0 with vehicle (control) or SCW to induce arthritis with daily GEO, E₂, or vehicle treatments starting 4 days prior to SCW injection as described in Methods and Materials. Lymphocyte counts (mean ± SEM, n = 4-16/group) were assessed at time of sacrifice on day 28-31 as described in Materials and Methods. Statistical significance was determined by ANOVA with post-hoc testing. * p < 0.05 vs. control or SCW, as indicated. ** p < 0.01 vs. control or SCW, as indicated. NS = non significant. A. GEO (28 mg/kg) or vehicle alone (DMSO, 1 μl/g) were dosed ip daily 5-7 times a week. B. E₂ (200 μg/kg) or vehicle alone (sesame seed oil, μl/g) were dosed sc daily 5 times a week. C. E₂ (600 μg/kg) or vehicle alone (sesame seed oil, μl/g) were dosed sc daily 5 times a week.