Anti-Inflammatory Activities of Constituents from Cinnamomum insularimontanum Hayata Leaves and Their Mechanisms

Cinnamomum insularimontanum is an endemic species of Taiwan. Although most Cinnamomum plants have significant biological activity, the bioactivity investment of C. insularimontanum is rare. Since inflammation plays an important role in many diseases, anti-inflammatory compounds can be developed into healthcare products. Therefore, we first conducted a study on the anti-inflammatory activity of C. insularimontanum leaves. First, we examined the antiinflammation activity of essential oil from C. insularimontanum leaves, and it revealed potent anti-inflammatory activity. A total of 23 volatile compounds were identified in C. insularimontanum leaves' essential oil by using GC/MS analysis. Among them were 1,8-cineole (35.94%), α-eudesmol (6.17%), pinene (7.55%), sabinene (5.06%), and isobornyl acetate (4.81%). According to previous studies, 1,8-cineole might be an anti-inflammation principal compound of C. insularimontanum leaves. Next, the ethanolic extracts of C. insularimontanum leaves also exhibited good anti-inflammatory activity. Two bioactive compounds, isoburmanol (F1) and burmanol (F2), were isolated from the ethyl acetate soluble fraction by using the bioactivity-guided separation protocol and spectroscopic analysis. F1 was obtained from C. insularimontanum for the first time, and F2 was isolated for the first time from natural resources. Both F1 and F2 could inhibit the production of nitric oxide (NO), and the IC50 values were 14.0 μM and 43.8 μM, RAW 264.7 cells after induction of lipopolysaccharide. Furthermore, F1 and F2 also revealed significant inhabitation effects on iNOS and COX-2 protein expression. The anti-inflammation activity of F1 and F2 was different from the common pathway of inhibiting NF-κB. Both of them could inhibit the production of NO and PGE2 by directly inhibiting the AP-1 (c-Jun) protein and then inhibiting the downstream iNOS and COX-2. Although both F1 and F2 possessed significant anti-inflammatory activity, the activity of F1 was better than F2. Through molecular docking simulation analysis, the results show that F1 and F2 interact with AP-1, inhibit the binding of AP-1 to DNA, and cause AP-1 to fail to transcribe the related factors of inflammation. The binding ability of AP-1 and F1 was stronger than F2, and that is the reason why F1 exhibited better activities in both downstream proteins and inflammatory cytokines. Based on the results obtained in this study, the essential oil and F1 and F2 isolated from C. insularimontanum leaves have good anti-inflammatory activities, and it is expected to be used as a reference for the development of medical care products in the future.