Comparative UPLC-QTOF-MS-based metabolomics and bioactivities analyses of Garcinia oblongifolia

Highlights

• A strategy for the comparative metabolic profiling and bioactivities of leaf, branch, and fruit extracts of G. oblongifolia is describe.

• Forty compounds were identified by UPLC-QTOF-MS and MS^E, including 15 compounds reported for the first time from this species.

• Heatmap and chemometrics analyses were performed to reveal the distribution and relationship of the chemical constituents among different plant parts.

Abstract

Garcinia oblongifolia Champ. ex Benth. (Clusiaceae) is a well-known medicinal plant from southern China, with edible fruits. However, the phytochemistry and bioactivity of the different plant parts of G. oblongifolia have not been studied extensively. Comparative metabolic profiling and bioactivities of the leaf, branch, and fruit of G. oblongifolia were investigated. A total of 40 compounds such as biflavonoids, xanthones, and benzophenones were identified using UPLC-QTOF-MS and MS^E, including 15 compounds reported for the first time from this species. Heatmap analyses found that benzophenones, xanthones, and biflavonoids were predominately found in branches, with benzophenones present in relatively high concentrations in all three plant parts. Xanthones were found to have limited distribution in fruit while biflavonoids were present at only low levels in leaves. In addition, the cytotoxic (MCF-7 breast cancer cell line) and antioxidant (ABTS and DPPH chemical tests) activities of the crude extracts of G. oblongifolia indicate that the branch extract exhibits greater bioactivity than either the leaf or the fruit extracts. Orthogonal partial least squares discriminate analysis was used to find 12 marker compounds, mainly xanthones, from the branches, including well-known antioxidants and cytotoxic agents. These G. oblongifolia results revealed that the variation in metabolite profiles can be correlated to the differences in bioactivity of the three plant parts investigated. This UPLC-QTOF-MS strategy can be useful to identify bioactive constituents expressed differentially in the various plant parts of a single species.

Introduction

Garcinia species in the Clusiaceae family are well-known for their polyisoprenylated benzophenones and xanthones derivatives, exhibiting a wide range of biological activities such as apoptotic, anti-cancer, antioxidant, antifungal, anti-viral, antimicrobial, antiviral, and anti-protozoal [1], [2]. The fruits of some species in this genus are edible, such as Garcinia mangostana, a well-known tropical fruit, and there have been many studies recently about the phytochemical and pharmacological differences among Garcinia species [3], [4].

Garcinia oblongifolia Champ. ex Benth. is mainly distributed in tropical regions of China including Guangxi, Guangdong, and Hainan. Our ethnobotanical investigation found that the ripe fresh fruits are eaten locally and have a well-known local name “Huang Ya Guo” since the fruits can stain teeth yellow after eating. The bark and leaf are made into folk medicine used in the treatment of pain, burns, and inflammation [5]. Previous phytochemical investigations on the bark of this species lead to the discovery of numerous new compounds including oblongifolin A–G, oblongixanthones A–C and 12 known compounds, exhibiting apoptotic effects against HeLa-C3 cells and cytotoxicity against cervical cancer cell in vitro [6], [7], [8]. In a recent study, bioassay-guided isolation led to the discovery of 12 new prenylated benzoylphloroglucinols, oblongifolins J–U from G. oblongifolia leaves in which two compounds have exhibited significant anti-EV71 activity [9]. Most studies of G. oblongifolia have focused on the bark and leaves, but no studies have been published on the chemical constituents of the edible fruits. Bioactive constituents of certain species are well known to be expressed differentially in various plant parts/organs, and these differences can be significant at times. Although previous research has looked at the bioactive constituents from the bark, stem, twig, leaf, fruit, seed, pericarp, and root of Garcinia species [2], systematic metabolic profiling among the plant parts of Garcinia species has been limited. Understanding the metabolite profile of different parts of plant could enable their better and potentially sustainable use, especially in ethnobotanically important species like Garcinia.

UPLC coupled with QTOF-MS to investigate natural products provides efficient separation and good sensitivity, and also allows for the identification of the fragmentation pathways of metabolites [10], [11], by employing newer mass spectrometry ^{Elevated energy} (MS^E) methods to acquire MS/MS (without specific precursor ion selection) data at both low and high energy from a single injection [12]. Therefore, UPLC-QTOF-MS^E is a very versatile technique and is increasingly important in metabolomics [13]. In recent years, UPLC-QTOF-MS has been used to characterize the polycyclic polyprenylated acylphloroglucinols from Garcinia species [14], and 16 compounds were qualitatively and quantitatively analyzed from G. oblongifolia [15]. A rapid characterization of caged xanthone and polyprenylated xanthones from G. hanburyi and G. xipshuanbannaensis have been described as well [16], [17], [18]. However, these studies focused only on a single class of compounds, and not the metabolite profile of a selected species.

Herein we present a comparative analysis of the metabolite profile of leaves, branches, and fruits of G. oblongifolia using UPLC-QTOF-MS. We also conducted in vitro bioactivity tests (cytotoxicity and antioxidant assays) to better understand and correlate the relationship between the metabolite profile and the bioactivity of various plant parts of G. oblongifolia.