Bioprospecting of Artemisia genus: from artemisinin to other potentially bioactive compounds

Abstract

Species from genus Artemisia are widely distributed throughout temperate regions of the northern hemisphere and many cultures have a long-standing traditional use of these plants as herbal remedies, liquors, cosmetics, spices, etc. Nowadays, the discovery of new plant-derived products to be used as food supplements or drugs has been pushed by the exploitation of bioprospection approaches. Often driven by the knowledge derived from the ethnobotanical use of plants, bioprospection explores the existing biodiversity through integration of modern omics techniques with targeted bioactivity assays. In this work we set up a bioprospection plan to investigate the phytochemical diversity and the potential bioactivity of five Artemisia species with recognized ethnobotanical tradition (A. absinthium, A. alba, A. annua, A. verlotiorum and A. vulgaris), growing wild in the natural areas of the Verona province. We characterized the specialized metabolomes of the species (including sesquiterpenoids from the artemisinin biosynthesis pathway) through an LC-MS based untargeted approach and, in order to identify potential bioactive metabolites, we correlated their composition with the in vitro antioxidant activity. We propose as potential bioactive compounds several isomers of caffeoyl and feruloyl quinic acid esters (e.g. dicaffeoylquinic acids, feruloylquinic acids and caffeoylferuloylquinic acids), which strongly characterize the most antioxidant species A. verlotiorum and A. annua. Morevoer, in this study we report for the first time the occurrence of sesquiterpenoids from the artemisinin biosynthesis pathway in the species A. alba.

Keywords: Artemisia spp.; Antioxidants; Artemisinin; Bioprospection; Dicaffeoylquinic acids; Sesquiterpenes.

Figure 1

Geolocation of the sampling spots in the northern area of the Verona province (A) and pictures of the five Artemisia spp. plants collected (B). The maps were obtained from Google Maps (2023).

Figure 2

Secondary metabolomes of Artemisia spp. Exemplificative base peak chromatograms recorded in LC–MS–ESI⁻ (intensity scaled to 2.5 × 10⁵) of leaves (left) and stems (right) are shown together with pie charts representing the metabolite classes according to the total LC–MS signal detected. Peak annotation numbers refer to Table 2. HBA hydroxybenzoic acid, HCA hydroxycinnamic acid derivatives.

Figure 3

Heat map showing the average relative percentage abundance (respect to the total LC–MS signal of each metabolome) of all metabolites tentatively identified in Artemisia spp. Leaves (L) and stems (S) over a 3-year sampling period (2019, 2020, 2021). The metabolite identification numbers match those in the dataset. Aab, A. absinthium; Aal, A. alba; Aan, A. annua; Ave, A. verlotiorum; Avu, A. vulgaris. Cf caffeoyl, CfQa caffeoylquinic acids, CfHa caffeoylhexaric acids, HBA hydroxybenzoic acid, HCA hydroxycinnamic acid, der derivatives. This heatmap was created manually from the dataset with the conditional formatting tool of Microsoft Excel (v. 2401; https://www.microsoft.com/it-it/microsoft-365/excel).

Figure 4

Antioxidant activity of extracts from Artemisia spp. leaves and stems, sampled in three independent growing seasons, and determined by FRAP (A, B) and DPPH (C, D) assays, and expressed as Trolox Equivalent Antioxidant Capacity (TEAC), in millimoles of Trolox Equivalents/kg of tissue (leaves or stem), fr. wt. Values are expressed as mean +/− standard deviation (n = 9). Significant differences were calculated with one-way ANOVA.

Figure 5

Antioxidant activity of extracts from Artemisia spp. leaves and stems, sampled in three independent growing seasons, and determined by FRAP (A, C, G, I) and DPPH (B, D, F, H, J) assays, and expressed as Trolox Equivalent Antioxidant Capacity (TEAC), in millimoles of Trolox Equivalents/kg of tissue (leaves or stem), fresh weight. Values are expressed as mean +/− standard deviation (n = 9). Aab, absinthium; Aal, alba; Aan, annua; Ave, verlotiorum; Avu, vulgaris. Significant differences calculated with two-way ANOVA.

Figure 6

Scatter plot of OPLS analysis that correlates antioxidant activity (u) (FRAP on the left and DPPH on the right) with metabolic composition (t). Samples are colored according to the species.

Figure 7

Scatter plot of OPLS analysis that correlates antioxidant activity (u) (FRAP on the left and DPPH on the right) with metabolic composition (t). Samples are colored according to the organs. (A) A. absinthium (Aab); (B) A. alba (Aal); (C) A. annua (Aan); (D) A. verlotiorum (Ave); (E) A. vulgaris (Avu).

Figure 8

Relative comparison of the final sesquiterpenoid products from the artemisinin biosynthesis pathway in the five Artemisia species. Y axis: peak area arbitrary units. Bars represent SD (n = 3).