Spatial chemo-profiling of hypericin and related phytochemicals in Hypericum species using MALDI-HRMS imaging

Abstract

Advanced analytical imaging techniques, including matrix-assisted laser desorption/ionization high-resolution mass spectrometry (MALDI-HRMS) imaging, can be used to visualize the distribution, localization, and dynamics of target compounds and their precursors with limited sample preparation. Herein we report an application of MALDI-HRMS imaging to map, in high spatial resolution, the accumulation of the medicinally important naphthodianthrone hypericin, its structural analogues and proposed precursors, and other crucial phytochemical constituents in the leaves of two hypericin-containing species, Hypericum perforatum and Hypericum olympicum. We also investigated Hypericum patulum, which does not contain hypericin or its protoforms. We focused on both the secretory (dark glands, translucent glands, secretory canals, laminar glands, and ventral glands) and the surrounding non-secretory tissues to clarify the site of biosynthesis and localization of hypericin, its possible precursors, and patterns of localization of other related compounds concomitant to the presence or absence of hypericin. Hypericin, pseudohypericin, and protohypericin accumulate in the dark glands. However, the precursor emodin not only accumulates in the dark glands but is also present outside the glands in both hypericin-containing species. In hypericin-lacking H. patulum, however, emodin typically accumulates only in the glands, thereby providing evidence that hypericin is possibly biosynthesized outside the dark glands and thereafter stored in them. The distribution and localization of related compounds were also evaluated and are discussed concomitant to the occurrence of hypericin. Our study provides the basis for further detailed investigation of hypericin biosynthesis by gene discovery and expression studies.

Phenotyping the genus Hypericum by secondary metabolite profiling: emodin vs. skyrin, two possible key intermediates in hypericin biosynthesis

“…In general, phloroglucinols were most abundant in Hypericum spp. that lack hypericins ( H. androsaemum , H. stellatum , and H. kouytchense ), which is in accordance with previous studies [6, 7, 15, 18]. In contrast, species with a higher abundance of naphthodianthrones contained fewer or no phloroglucinols, except for H. perforatum , which was determined to have a high content of both of these metabolite groups.…”

Occurrence and Distribution of Phytochemicals in the Leaves of 17 In vitro Cultured Hypericum spp. Adapted to Outdoor Conditions

“…Samples for MALDI measurement were prepared according to Kusari et al (2015). Extensive method optimization was also performed according to Kusari et al (2015).…”

“…Extensive method optimization was also performed according to Kusari et al (2015). Before starting the measurements with leaves, reference standard (where available) solutions at concentrations of 50 μg mL −1 were prepared.…”

“…Different positions of the leaf tissues were morphologically demarcated based on our earlier study (Kusari et al, 2015), with emphasis on secretory and non-secretory structures that could be identified in each Hypericum species. Notably, leaf tissue areas containing and lacking dark glands on adaxial and abaxial leaf surfaces of the 17 Hypericum species were targeted with laser spots (with laser scan mode: Repetition) of ca.…”

“…This work was followed-up by Li et al (2013) with direct DESI analyses of the leaves and petals of H. perforatum . Recently, we employed matrix-assisted laser desorption/ionization-HRMS (MALDI-HRMS) imaging to reveal, in high spatial resolution with limited sample preparation, the distribution, localization, and subtleties of hypericins and structural analogs and proposed precursors in the secretory as well as non-secretory tissues of three wild-growing Hypericum species ( H. perforatum, H. olympicum , and H. patulum ) (Kusari et al, 2015). More recently, we explored the interspecific variation in localization of hypericins and phloroglucinols as well as some new compounds using indirect DESI-MSI in the leaves of seventeen different in vitro cultured Hypericum species (Kucharíková et al, 2016).…”