Chukrasia tabularis limonoid plays anti-inflammatory role by regulating NF-κB signaling pathway in lipopolysaccharide-induced macrophages

Background

Chukrasia tabularisis, a well-known tropical tree native to southeastern China, has anti-inflammatory and antioxidant activities, and contains large amounts of limonoids and triterpenoids.

Objective

The aim of this study was to investigate the potential anti-inflammatory activity of limonoids from C. tabularis on lipopolysaccharide (LPS)-mediated RAW264.7 cells.

Methods and results

Using a bioassay-guided approach, the chemical fraction with high anti-inflammatory activity was found and its chemical constituents were investigated. Phytochemical studies on active extracts resulted in the separation of three novel phragmalin limonoids (1-3), together with two known limonoids (4-5) and 11 tirucallane triterpenes (6-16). The activity of these isolated compounds in the production of nitric oxide (NO) on LPS-reated macrophages was evaluated. Limonoid 2 indicated significant anti-inflammatory activities with IC50 value of 4.58 μM. Limonoid 2 notably inhibited the production of NO, interleukin- 6 and tumor necrosis factor-α on macrophage. Signal transduction and activation of STAT and NF-κB activators were effectively blocked by limonoid 2.

Conclusions

These results indicate that limonoid 2 has an anti-inflammatory effect by the inhibiting JAK2/STAT3, iNOS/eNOS, and NF-κB signaling pathways and regulating inflammatory mediators.

Research progress of meliaceous limonoids from 2011 to 2021

Covering: July 2010 to December 2021Limonoids, a kind of natural tetranortriterpenoids with diverse skeletons and valuable insecticidal and medicinal bioactivities, are the characteristic metabolites of most plants of the Meliaceae family. The chemistry and bioactivities of meliaceous limonoids are a continuing hot area of natural products research; to date, about 2700 meliaceous limonoids have been identified. In particular, more than 1600, including thirty kinds of novel rearranged skeletons, have been isolated and identified in the past decade due to their wide distribution and abundant content in Meliaceae plants and active biosynthetic pathways. In addition to the discovery of new structures, many positive medicinal bioactivities of meliaceous limonoids have been investigated, and extensive achievements regarding the chemical and biological synthesis have been made. This review summarizes the recent research progress in the discovery of new structures, medicinal and agricultural bioactivities, and chem/biosynthesis of limonoids from the plants of the Meliaceae family during the past decade, with an emphasis on the discovery of limonoids with novel skeletons, the medicinal bioactivities and mechanisms, and chemical synthesis. The structures, origins, and bioactivities of other new limonoids were provided as ESI. Studies published from July 2010 to December 2021 are reviewed, and 482 references are cited.

Two new phragmalin-type limonoids from Chukrasia tabularis and their α-glucosidase inhibitory activity

Phytochemical investigation on the stems of C. tabularis (Meliaceae) led to the isolation of two new phragmalin-type limonoids, named tabularisins S and T (1-2), along with five known ones (3-7). The structures of the new limonoids were established by spectroscopic methods including UV, IR, HRESIMS, and 1D and 2D NMR. All the compounds were evaluated for α-glucosidase inhibitory activity in vitro. Compounds 2 and 3 exhibited significant inhibitory activity against α-glucosidase with IC50 values of 0.15 and 0.03 mM, respectively (acarbose as positive control, IC50 0.95 mM).

New Phragmalin-Type Limonoids from Chukrasia tabularis and Their α-Glucosidase Inhibitory Activity

Phytochemical investigation on the stems of C. tabularis led to the isolation of five new phragmalin-type limonoids and six known ones. The structures of the new compounds 1–5, named chukbularisins A–E, were elucidated by spectroscopic techniques (IR, HRESIMS, 1D and 2D NMR) and comparisons with published data. All the compounds were evaluated for in vitro α-glucosidase inhibitory activity. Compounds 2, 3, 4, 5, and 8 exhibited inhibitory activity against α-glucosidase with IC₅₀ values of 0.06 ± 0.008, 0.04 ± 0.002, 0.52 ± 0.039, 1.09 ± 0.040, and 0.20 ± 0.057 mM, respectively (using acarbose as positive control, IC₅₀ 0.95 ± 0.092 mM).

Varioxiranols A-G and 19-O-Methyl-22-methoxypre-shamixanthone, PKS and Hybrid PKS-Derived Metabolites from a Sponge-Associated Emericella variecolor Fungus

Chemical examination of a sponge (Cinachyrella sp.)-associated Emericella variecolor fungus resulted in the isolation of seven new polyketide derivatives, namely, varioxiranols A-G (1-7), and a new hybrid PKS-isoprenoid metabolite, 19-O-methyl-22-methoxypre-shamixanthone (8), together with nine known analogues. Their structures were elucidated on the basis of extensive spectroscopic analyses, including ECD effects, Mosher's method, X-ray diffraction, and chemical conversion for the determination of absolute configurations. Varioxiranols F and G were found for the first time to link a xanthone moiety with a benzyl alcohol via an ether bond, while the dioxolanone group of 5 is unusual in nature. A cell-based lipid-lowering assay revealed that pre-shamixanthone (12) exerted significant inhibition against lipid accumulation in HepG2 cells without cytotoxic effects, accompanying the potent reduction of total cholesterol and triglycerides. Real-time quantitative PCR indicated that pre-shamixanthone (12) mediated the reduction of lipid accumulation related to the down-regulation of the expression of the key lipogenic transcriptional factor SREBP-1c and its downstream genes encoding FAS and ACC.

Triterpenoids

This review covers the isolation and structure determination of triterpenoids reported during 2012 including squalene derivatives, lanostanes, holostanes, cycloartanes, cucurbitanes, dammaranes, euphanes, tirucallanes, tetranortriterpenoids, quassinoids, lupanes, oleananes, friedelanes, ursanes, hopanes, serratanes, isomalabaricanes and saponins; 348 references are cited.

Two new phragmalin-type limonoids from Chukrasia tabularis var. velutina

Two new phragmalin-type limonoids with different structural skeletons, chuktabrin K (1) and tabulalin J (2), were isolated from the stem barks of Chukrasia tabularis var. velutina in the course of our ongoing research work in this area. Compound 1 was a 16-norphragmalin with an enolic alkyl appendage at C-15, and the carbonate moiety in 1 was also rare in natural organic molecules. The basic skeleton of compound 2 was a D-ring-opened phragmalin. Their structures were elucidated on HR-ESI-MS, ¹H and ¹³C-NMR, HSQC, HMBC, and ROESY experiments.