Distribution of bioactive compounds in different tissues of Paeonia lactiflora roots by DESI-MSI and UPLC

Abstract

The quality of Paeoniae Radix Alba and Paeoniae Radix Rubra is evaluated by root thickness, and paeoniflorin serves as a common quality indicator of them. However, the correlation between the content of bioactive compounds and the root size is still unclear. Therefore, this study characterized the distribution patterns and content of seven bioactive compounds including paeoniflorin in different tissues of Paeonia lactiflora roots, analyzed the correlation between the root size and the content of bioactive compounds based on the xylem-to-bark ratio, and further determined the index components for quality assessment. Nine samples of fresh P. lactiflora roots were collected from the genuine cultivation area. The distribution of bioactive compounds in different tissues on the cross-section of the root was firstly analyzed by desorption electrospray ionization-mass spectrometry imaging(DESI-MSI). Subsequently, the content of bioactive compounds was determined in the xylems and barks of the roots by UPLC. The compounds with the largest difference between the xylem and the bark were selected by orthogonal partial least squares discriminant analysis(OPLS-DA). The results indicated that paeoniflorin, benzoylpaeoniflorin, oxypaeoniflorin, gallic acid, and 1,2,3,4,6-pentagalloylglucose were significantly accumulated in the xylems, while albiflorin and catechin were mainly distributed in the barks. Paeoniflorin and albiflorin, with the largest differences in the xylem and the bark, had the highest content in the two tissues. The root diameter was positively correlated with paeoniflorin content and negatively correlated with albiflorin content. As isomers with different efficacies, paeoniflorin or albiflorin can be chosen as the quality marker corresponding to specific clinical application to launch quality classification evaluation of multi-functional Chinese medicines.