Tissue-specific metabolite profiling of alkaloids in Sinomenii Caulis using laser microdissection and liquid chromatography-quadrupole/time of flight-mass spectrometry

Secondary metabolites accumulated in different tissues and cells of herbs are usually bioactive components of herbal medicines. Thus, tissue- and cell-specific phytochemical profiling should be useful for indicating relationship between herbal tissues and chemicals, and evaluating the quality of a medicinal herb. Here, a method that combining laser microdissection and ultra-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry (LMD with UPLC-Q/TOF-MS) was established to achieve simultaneous localization and determination of bioactive components in herbal medicines. Sinomenii Caulis, sourced from the stems of Sinomenium acutum (Thunb.) Rehd. et Wils., was set as an illustrative case, and its phytochemicals were profiled by the present method through analyses of different microdissected tissues and cells, involving epidermis, cortex, stone cells, pericycle, vascular bundles and pith. Results revealed that different tissues and cells contained varied alkaloids, among which six alkaloids, i.e. 6-Me-ether-12-O-β-D-glucopyranoside-laudanosoline (peak 4), sinomenine (peak 6), N-norsinoacutine (peak 7), magnoflorine (peak 11), laurifoline (peak 16) and menisperine (peak 17) were detected in all microdissected parts, and sinomenine and magnoflorine were the two most abundant components. By further quantitative determination, alkaloids were generally demonstrated to distribute in the outer part of the cortex, phloem and xylem. According to the relationship between alkaloids and tissues revealed in our study, Sinomenii Caulis of larger diameter has proportionately more bioactive components, and is therefore of higher quality for medicinal use. The method of LMD with UPLC-Q/TOF-MS developed in this study was initially applied to the research of medicinal herbs, and proved to be high sensitive, low cost, convenient and practical.