•  doi: 10.3390/molecules26247692
• Published online 2021 Dec 20

Piotr Sugier,¹ Łukasz Sęczyk,² Danuta Sugier,^2,* Rafał Krawczyk,³ Małgorzata Wójcik,⁴ Joanna Czarnecka,¹ Sylwia Okoń,⁵ and Andrzej Plak⁶

Oksana Sytar , Academic Editor and Iryna Smetanska, Academic Editor

Abstract

The bearberry (Arctostaphylos uva-ursi L. Spreng.) is a source of herbal material—bearberry leaf (Uvae ursi folium), which is highly valued and sought by pharmaceutical and cosmetic industries. For many years, leaves of this plant have been used in traditional medicine as a diuretic, antimicrobial, and anti-inflammatory agent for various diseases of the urogenital tract. The bearberry has also been proposed as a natural antioxidant additive due to the high contents of phenolic compounds in its leaves. The study was focused on characterization of the basic phytochemical composition and antioxidant activity of extracts derived from bearberry leaves collected from plants located at the southern border of the geographical range of the species in Europe. The investigated herbal material is characterized by a different chemical profile compared to the chemical profiles of bearberry found in other parts of the continent. Bearberry extracts from plants growing in two different habitat types—heathlands and pine forests showed a wide range of variation, especially in the concentration of hyperoside, corilagin, and methylartutin and the total flavonoid contents. In addition to arbutin, bearberry can be a valuable source of phenolic compounds, which are mainly responsible for the antioxidant properties of extracts. The high content of phenols and high values of antioxidant parameters indicate a high potential of bearberry leaves to be used as a powerful natural source of antioxidants in herbal preparations. Therefore, the A. uva-ursi populations can be a source of plant material for pharmaceutical, cosmetic, and food industries.

Keywords: bearberry, arbutin, natural antioxidants, heathlands, pine forests

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1. Introduction

Many Ericaceae plant species have a long history of ethnopharmacological use and are important for medicinal and pharmacological purposes [1]. This family is represented, e.g., by the bearberry (Arctostaphylos uva-ursi L. Spreng.), which has been used in folk medicine for centuries as a rich source of raw material abundant in secondary metabolites. This plant species is an evergreen dwarf shrub. It can be found at high and mid-latitudes in Europe, Asia, and North America. This circumpolar plant reaches the southern limit of its compact range in the south of Poland [2]. In southern and south-western Europe, the bearberry is noted in mountainous regions [3,4,5]. In Central Europe, it occurs mainly in the lowlands—in pine forests on podsolic soils and heathlands situated on sandy dunes [6].

In the last decades, the use of medicinal plants has been growing rapidly in the world due to the increasing demand for natural health products, herbal drugs, and secondary metabolites [7,8]. Natural products and their derivatives are important sources of novel therapeutic substances [9]. Therefore, widespread pressure to obtain plant material from areas of natural occurrence is observed; however, it is very often limited by the legal restrictions of conservation and sustainable use of medicinal plants [8,10,11]. At the same time, new sources of secondary metabolites are widely being searched [12,13], and plant cultivation trials are carried out to obtain enough raw material with a new chemical profile in controlled conditions [13,14]. The present study focuses on the bearberry, i.e., an endangered species in Europe [15] included in the European red list of medicinal plants [16]. Presently, this species is under strict law protection and is placed on the red lists in Poland, the Czech Republic, Slovakia, and Bulgaria [17,18,19]. Moreover, investigations have shown that harvesting aerial biomass in unprotected areas decreases the regenerative capacity of A. uva-ursi populations [20,21]. Therefore, recommendations or guidelines for harvesting as part of the sustainable management of the population of this species in natural habitats have been formulated [22]. It should be mentioned that, in Europe, the need to acquire new chemotypes of herbal plants is emphasized as the most effective way to meet the industry’s demand for raw material and to reduce the pressure exerted by harvesting in countries where it is possible to obtain material from natural populations.

The bearberry is a source of herbal material—bearberry leaf (Uvae ursi folium), which is highly valued and sought by pharmaceutical and cosmetic industries both in Poland and in Europe [23,24]. During the last years, the chemical composition of bearberry leaves has been intensively studied [25,26,27]. It has been found that Uvae ursi folium is a rich source of phytochemicals, especially phenolic compounds. Phenolic glycoside arbutin is considered the main bioactive compound of this plant. Moreover, the chemical profile of bearberry leaves is characterized by the presence of ursolic acid, tannic acid, gallic acid, p-coumaric acid, syringic acid, galloylarbutin, gallotannins, and glycosidic forms of flavonoids, e.g., quercetin, kaempferol, and myricetin glycosides, penta-O-galloyl-β-d-glucose, hyperoside, corilagin, and picein [1,25,26,27,28]. The health benefits of the bearberry are provided by the compounds comprised in its valuable composition.

For many years, leaves of this plant have been used in traditional medicine as a diuretic, antimicrobial, and anti-inflammatory agent for various diseases of the urogenital tract [27]. Arctostaphylos uva-ursi leaf extracts are characterized by antioxidant [4,29] and antimicrobial activity [30,31] and have been used as skin-whitening agents and antioxidant agents in food and food packaging formulations [4,32,33]. In recent decades, many studies have shown that bearberry leaf extracts have strong antibacterial activity against bacterial strains that cause urinary tract infections [34]. They are remedies for several diseases, including diuresis [35,36] and have antiproliferative effects against human carcinoma cell lines [37].

The accumulation of secondary metabolites is strongly dependent on genetic, ontogenic, morphogenetic, and various environmental factors such as light, temperature, soil water capacity, soil fertility, and salinity. Changes in one factor may alter the content of secondary metabolites even if the other factors remain constant [38]. In literature, there are reports of diversified and changeable responses of various plant species to different environmental stresses in terms of production of secondary metabolites [38]. In the case of the bearberry from the Iberian Peninsula, such factors as altitude, UV-radiation, the date of collection, and location of plants have been proven to influence the chemical composition [3,4,5]. Therefore, it can be assumed that the acid and poor sandy soils, characteristic vegetation, and climatic conditions at the southern border of the geographical range of the species in Europe can affect the chemical profile in the bearberry and, in consequence, the antioxidant activity of its extracts.

Generally, there are scarce investigations of the chemical profiles in bearberry populations occurring in natural habitats in Europe. In many studies on the chemistry of the raw material and biological activity, raw material from pharmacies, supermarkets, and collections was used. In Europe, very detailed characteristics, such as the chemical composition and biological activity, have recently been presented from the Iberian Peninsula in the context of selection of plant material for pharmaceutical, cosmetic, and food industries [4,5], where plant material was collected from the typical bearberry habitats located in mountain communities (424–1410 m a. s. l.). Conversely, the A. uva-ursi populations selected in this study come from extremely and harsh sites situated at the southern border of the dense geographical range of the species in Europe. This is the first analysis of raw material originating from populations growing in completely different conditions (acid and poor sandy soils of heathlands and pine forests) (Figure 1). It is very often observed that stress and disturbances in harsh habitat conditions affect the response of plants through accumulation of secondary metabolites [38]. This yields plant material with a valuable chemical composition, which can exhibit new properties and, in consequence, new activities that can be used in medicine, pharmacy, or cosmetic industry. In the case of the Polish populations of A. uva-ursi, the knowledge of the chemical characteristics and biological activity of leaves is still insufficient. Therefore, the objective of this study was to characterize the basic phytochemical composition and antioxidant activity of extracts derived from bearberry leaves collected from plants located at the southern border of the geographical range of the species in Europe. The results presented in this paper can contribute to appropriate selection of plant material for pharmaceutical, cosmetic, and food industries.

Reference:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8707569/