The anti-inflammatory potential of Cinnamomum camphora (L.) J.Presl essential oil in vitro and in vivo

Ethnopharmacological relevance: Borneol was widely used in traditional Chinese medicine formulas due to its pharmacological activities, e.g. sedative, anti-inflammatory, and anti-ischemic properties. Cinnamomum camphora (L.) J.Presl essential oil (BEO) is a by-product of natural crystalline borneol (NCB) production obtained by steam distillation of Cinnamomum camphora (L.) J.Presl leaves, and borneol was the main component of BEO. This study aims to investigate the anti-inflammatory effect of BEO and its corresponding mechanisms through in vitro and in vivo studies.

Materials and methods: Human erythrocyte membrane stability assay and the acute inflammation murine model (xylene-induced ear edema) were chosen to evaluate the anti-inflammatory effect of BEO. Expression of inflammatory mediators, including interleukin (IL)-1β, IL-6, and tumor necrosis factor α (TNF-α) was determined by real-time quantitative polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assays (ELISA). The functional compounds in the BEO were identified by using gas chromatography-mass spectrometry (GC-MS). The steady-state transdermal diffusion rates of BEO and BEO nano-emulsion with were also determined in this study. Cytotoxicity of BEO was analyzed by cell counting kit-8 (CCK-8) assay.

Results: The BEO showed a high human erythrocyte membrane stabilization by inhibiting heat-induced hemolysis (IC₅₀ = 5.29 mg/mL) and hypotonic solution-induced hemolysis (IC₅₀ = 0.26 mg/mL) in vitro. The BEO was topically applied to mice auricles, both single and repeated administration significantly reduced xylene-induced auricle swelling (p < 0.0001). Expression of inflammatory mediators, including interleukin (IL)-1β, IL-6, and tumor necrosis factor α (TNF-α) in serum and tissue was significantly downregulated (p < 0.05), so as to the mRNA expression of IL-1β (p＜0.05) and TNF-α (p < 0.001). A total of 43 components were identified and quantified by GC-MS. The most abundant was borneol [178.3 mg/mL, 20.9% (m/v)], followed by β-caryophyllene (116.3 mg/mL), camphor (115.2 mg/mL), and limonene (89.4 mg/mL). For determining the skin permeability of BEO, the steady-state transdermal diffusion rates of BEO and BEO nano-emulsion were determined to be 6.7 and 8.9 mg/cm²·h, respectively.

Conclusion: It is suspected that the anti-inflammatory effects in vivo and in vitro were derived from the above-mentioned components in the BEO. These findings will facilitate the development of BEO as a new and natural therapeutic agent for inflammatory skin conditions.