Diversified Cassane Family Diterpenoids from the Leaves of Caesalpinia Minax Exerting Anti-Neuroinflammatory Activity Through Suppressing MAPK and NF-κB Pathways in BV-2 Microglia

Abstract

Ethnopharmacological relevance: Caesalpinia minaxHance, whose seeds are known as 'ku-shi-lian' in China, have been used in Chinese folk medicine for treatment of rheumatism, dysentery, and skin itching. However, the anti-neuro-inflammatory constituents of its leaves and their mechanism are rarely reported.

Aim of the study: To search for new anti-neuro-inflammatory compounds from the leaves of C. minax and elucidate their mechanism on anti-neuro-inflammatory effect.

Materials and methods: The main metabolites of the ethyl acetate fraction from C. minax were analyzed and purified via HPLC and various column chromatography techniques. Their structures were elucidated on the basis of 1D and 2D NMR, HR-ESE-MS, and single crystal X-ray diffraction analysis. Anti-neuro-inflammatory activity was evaluated in BV-2 microglia cells induced by LPS. The expression levels of molecules in NF-κB and MAPK signaling pathways were analyzed through western blot. Meanwhile, the time- and dose-dependent expression of associated proteins such as iNOS and COX-2 were detected by western blotting. Furthermore, Compounds 1 and 3 were performed on the NF-κB p65 active site using molecular docking simulation to elucidate the molecular level inhibition mechanism.

Results: 20 cassane diterpenoids, including two novel ones (caeminaxins A and B) were isolated from the leaves of Caesalpinia minax Hance. Caeminaxins A and B possessed a rare unsaturated carbonyl moiety in their structures. Most of the metabolites exhibited potent inhibition effects with an IC50 values ranging from 10.86 ± 0.82 to 32.55 ± 0.47μM. Among them, caeminaxin A inhibited seriously the expression of iNOS and COX-2 protein and restrained the phosphorylation of MAPK and the activation of NF-κB signaling pathways in BV-2 cells. The anti-neuro-inflammatory mechanism of caeminaxin A has been studied systematically for the first time. Furthermore, biosynthesis pathways for compounds 1-20 were discussed.

Conclusions: The new cassane diterpenoid, caeminaxin A, alleviated the expression of iNOS and COX-2 protein and down-regulated of intracellular MAPK and NF-κB signaling pathways. The results implied that cassane diterpenoids had potential to be developed into therapeutic agents for neurodegenerative disorders such as Alzheimer’s disease.

Note:
Funding declaration: This work was partially financed by the National Natural Science Foundation of China (No. 31500275). And the Scientific Research Foundation of Yunnan Key Laboratory of Screening and Research on Anti-pathogenic Plant Resources from West Yunnan (APR202201) is also gratefully acknowledged.

Conflict of Interests: The authors declare no conflict of interest.

Keywords: Cassane diterpenoids, Anti-neuroinflammatory activity, NF-κB, MAPK, NEURODEGENERATIVE DISEASES