Nootkatone Inhibits Acute and Chronic Inflammatory Responses in Mice

Abstract

Nootkatone (NTK) is a sesquiterpenoid found in essential oils of many species of Citrus (Rutaceae). Considering previous reports demonstrating that NTK inhibited inflammatory signaling pathways, this study aimed to investigate the effects of this compound in mice models of acute and chronic inflammation. Murine models of paw edema induced by carrageenan, dextran, histamine, and arachidonic acid, as well as carrageenan-induced peritonitis and pleurisy, were used to evaluate the effects of NTK on acute inflammation. A murine model of granuloma induced by cotton pellets was used to access the impact of NTK treatment on chronic inflammation. In the acute inflammation models, NTK demonstrated antiedematogenic effects and inhibited leukocyte recruitment, which was associated with decreased vascular permeability, inhibition of myeloperoxidase (MPO), interleukin (IL)1-β, and tumor necrosis factor (TNF)-α production. In silico analysis suggest that NTZ anti-inflammatory effects may also occur due to inhibition of cyclooxygenase (COX)-2 activity and antagonism of the histamine receptor type 1 (H₁). These mechanisms might have contributed to the reduction of granuloma weight and protein concentration in the homogenates, observed in the chronic inflammation model. In conclusion, NTK exerted anti-inflammatory effects that are associated with inhibition of IL1-β and TNF-α production, possibly due to inhibition of COX-2 activity and antagonism of the H1 receptor. However, further studies are required to characterize the effects of this compound on chronic inflammation.

Keywords: acute inflammation; anti-inflammatory; granuloma; nootkatone.

Figure 1

(+)-Nootkatone (NTK) [8].

Figure 2

Time-point analysis of treatment with different NTK doses on paw edema formation induced by carrageenan (a) or dextran (c). These data are also represented as area under the curve (AUC) ((b,d), respectively)). a4 = p < 0.0001 vs. saline; b3 = p < 0.001 vs. NTK 100 mg/kg group; c4 = p < 0.0001 vs. NTK 10 mg/kg group. Statistical significance was determined with two-way ANOVA (a,c) and post hoc Tukey test.

Figure 2

Time-point analysis of treatment with different NTK doses on paw edema formation induced by carrageenan (a) or dextran (c). These data are also represented as area under the curve (AUC) ((b,d), respectively)). a4 = p < 0.0001 vs. saline; b3 = p < 0.001 vs. NTK 100 mg/kg group; c4 = p < 0.0001 vs. NTK 10 mg/kg group. Statistical significance was determined with two-way ANOVA (a,c) and post hoc Tukey test.

Figure 3

Potential mechanisms associated with NTK-mediated paw edema inhibition. The antiedematogenic effect is expressed as a percentage of edema induced by histamine (a) or arachidonic acid (b). a4 = p < 0.0001 vs. saline; a3 = p < 0.001 vs. saline and a2 = p < 0.01 vs. saline. Statistical significance was determined with two-way ANOVA and post hoc Tukey test.

Figure 4

The effects of NTK on carrageenan-induced peritonitis. (a) The number of total leukocytes; (b) concentrations of myeloperoxidase (MPO), and (c) concentrations of albumin in the peritoneal fluid of mice. a4 = p < 0.0001 vs. saline and a3 = p < 0.001 vs. saline. Statistical significance was determined with one-way ANOVA and post hoc Tukey test.

Figure 5

The effects of NTK on carrageenan-induced pleurisy. (a) The number of total leukocytes; (b) concentrations of Interleukin (IL)-1β, and (c) concentrations of Tumor Necrosis Factor (TNF)-α in the pleural lavages of mice. a4 = p < 0.0001 vs. saline and a2 = p < 0.01 vs. saline. Statistical significance was determined with one-way ANOVA and post hoc Tukey test.

Figure 5

The effects of NTK on carrageenan-induced pleurisy. (a) The number of total leukocytes; (b) concentrations of Interleukin (IL)-1β, and (c) concentrations of Tumor Necrosis Factor (TNF)-α in the pleural lavages of mice. a4 = p < 0.0001 vs. saline and a2 = p < 0.01 vs. saline. Statistical significance was determined with one-way ANOVA and post hoc Tukey test.

Figure 6

The binding poses of best stability between NTK and diclofenac into the cyclooxygenase (COX)-2 enzyme binding site (a) and between NTK and doxepin into the binding site of the H₁ receptor (b).

Figure 7

Maps of amino acid residues within the binding pocket of COX-2 (a,b) and the H1 receptor (c,d). The interactions of NKT (a,c), Diclofenac (b), and Doxepin (d) with these amino acids is illustrated.

Figure 8

The effects of NTK treatment on cotton pellet-induced granuloma in mice. (a) Final weight of the granuloma. (b) Protein concentration in the homogenates. a4 = p < 0.0001 vs. saline and a1 = p < 0.05 vs. saline. Statistical significance was determined with T test.