Anti-inflammatory and analgesic activities of Neolamarckia cadamba and its bioactive monoterpenoid indole alkaloids

Ethnopharmacological relevance: Neolamarckia cadamba has been used traditionally to treat inflammation, fever, and pruritus in the Dai ethnopharmacy in Yunnan province, P.R. China. However, according to literature survey, the action basis of anti-inflammatory and analgesic activities of this plant were rarely reported, which accounts for the original intentions of this investigation.

Aim of the study: The study aimed to investigate the anti-inflammatory and analgesic action of methanolic extract (ME), ethyl acetate (EA), and aqueous (AQS) fractions of N. cadamba and further explore the accurate compounds responsible for the activities of EA fraction.

Materials and methods: The in vivo anti-inflammatory and analgesic activities of ME, EA, and AQS fractions at the doses of 200 and 400 mg/kg and two major constituents (compounds 5 and 7) at 50 and 100 mg/kg via intragastrically administrated, respectively, were evaluated by carrageenan-induced paw edema and acetic acid-stimulated writhing animal models. Aspirin (ASP) was used as the positive control at the dose of 200 mg/kg. The monoterpenoid indole alkaloids (MIAs) in EA fraction were phytochemically studied utilizing chromatographic techniques, and their structures and absolute configurations were established on the basis of multiple spectroscopic analyses and quantum computational chemistry method. Moreover, the in vitro anti-inflammatory activities of all the isolates were assessed by suppressing releases of LPS-activated inflammatory mediators (TNF-α, IL-1β, and COX-2) in RAW 264.7 macrophage cells at a concentration of 10 μg/mL. Dexamethasone (DXM) was used as the positive control.

Results: Three fractions (ME, EA, and AQS) significantly ameliorated the paw edema caused by carrageenan and reduced the number of writhing induced by acetic acid in comparison to the control group at the doses of 200 and/or 400 mg/kg (in vivo). Subsequent phytochemical investigation of EA fraction led to the structural characterization of four new monoterpenoid indole alkaloids, neocadambines A-D (1-4), as well as eight known analogues (5-12). Neocadambine A possesses a novel 14-nor-MIA skeleton that could be derived from the corynantheine-type MIAs via oxidative cleavage of C3-C14 bond and subsequently degradation of C14. Moreover, the structure of a bioactive known MIA, cadambine acid (6), was reassigned by analysis of its NMR spectroscopic data. Further biological assays revealed that the major constituent 3β-dihydrocadambine (7) significantly relieved the paw edema and decreased the number of writhing at 100 mg/kg in vivo. In addition, most of the isolates displayed remarkable in vitro anti-inflammatory effects by inhibiting the secretion of aforementioned inflammatory mediators (COX-2, IL-1β, and TNF-α) at a concentration of 10 μg/mL, and compounds 4, 7, and 9 showed better anti-inflammatory effects than that of positive control, dexamethasone.

Conclusions: This study further validated the anti-inflammatory and analgesic activities of N. cadamba, and revealed that monoterpenoid indole alkaloids could partly contribute to the efficacy of this ethnodrug. The major constituent 3β-dihydrocadambine (7) showed significant anti-inflammatory activities both in vitro and in vivo, which suggested that it could be a promising anti-inflammatory lead compound. Our findings provided scientific justification to support the traditional application of N. cadamba for treating inflammatory and nociceptive disorders.

Keywords: Analgesic activity; Anti-inflammatory activity; Monoterpenoid indole alkaloids; Neolamarckia cadamba.