Identification and Quantification of Human Neutrophil Elastase Inhibitory Caffeoylquinic Acids in the Leaves of Aster koraiensis

Abstract

A method for identifying and quantifying caffeoylquinic acids (CQAs) in aqueous extracts of the leaves of Aster koraiensis (AKAE) using high-performance liquid chromatography coupled with diode-array detection and electrospray ionization mass spectrometry was developed. Six CQAs (5-CQA, 3-CQA, 4-CQA, 3,4-diCQA, 3,5-diCQA, and 4,5-diCQA) in AKAE were identified by comparing their retention times and ultraviolet spectra with those of the corresponding standards, and the results were confirmed by ESI/MS. The developed HPLC method was applied to quantitative analyses of the six CQAs in AKAE, whose contents in AKAE were in the range 2.04–4.00 mg/g. The inhibitory activities of the CQAs against human neutrophil elastase (HNE) were also evaluated; all tested di-CQA isomers showed considerable inhibition of HNE activity, with IC₅₀ values ranging from 2.09 to 14.20 μM, while three mono-CQAs exhibited no such activity (IC₅₀ > 100 μM). 3,5-diCQA and 4,5-diCQA inhibited HNE in a mixed-type noncompetitive manner, with inhibition constant (K_i) values of 0.47 and 1.4 μM, respectively.