Contribution of Individual Polyphenols to Antioxidant Activity of Cotoneaster bullatus and Cotoneaster zabelii Leaves—Structural Relationships, Synergy Effects and Application for Quality Control

Abstract

Cotoneaster plants are sources of traditional medicines and dietary products, with health benefits resulting from their phenolic contents and antioxidant activity. In this work, active markers of the leaves of C. bullatus and C. zabelii were characterized and evaluated in an integrated phytochemical and biological activity study. Based on UHPLC-PDA-ESI-MS3 analysis, twelve analytes were preselected from the constituents of the hydromethanolic leaf extracts, and two of them—caffeoylmalic acid and quercetin 3--O-β-d-(2″--O-β-d-xylopyranosyl)galactopyranoside (QPH)—were isolated for full identification (NMR spectroscopy: 1H, 13C, COSY, HMBC, HMQC). All selected phenolics contributed to the antioxidant activity of the extracts, which was demonstrated in chemical in vitro tests (DPPH, FRAP, and TBARS) and in a biological model of human plasma exposed to oxidative/nitrative stress induced by peroxynitrite. This contribution was partly due to the synergy between individual polyphenols, evidenced by an isobolographic analysis of the interactions of (–)-epicatechin, chlorogenic acid, and QPH as representatives of three classes of Cotoneaster polyphenols. All twelve markers, including also neochlorogenic acid, cryptochlorogenic acid, procyanidin B2, procyanidin C1, rutin, hyperoside, isoquercitrin, and quercitrin, were thus applied as calibration standards, and a fast, accurate, reproducible, and fully validated RP-HPLC-PDA method for quality control and standardization of the target extracts was proposed.

An Overview of the Genus Cotoneaster (Rosaceae): Phytochemistry, Biological Activity, and Toxicology

“…As the major bioactive constituents of Cotoneaster species are represented by flavonoids, most of the literature reports are focused on their identification and quantification. Numerous isolation studies have been carried out [ 8 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ] to explore the rich composition of flavonoids found in the leaves, leafy twigs, flowers, fruits, and roots of several Cotoneaster species. As presented in Table 1 , and Figure 3 , the structurally diverse flavonoids are derivatives of flavonol ( 1–9 ), flavone ( 10–15 ), flavanone ( 16–19 ), flavanol ( 23–25 ), and isoflavone ( 20–22 ).…”

“…As presented in Table 1 , and Figure 3 , the structurally diverse flavonoids are derivatives of flavonol ( 1–9 ), flavone ( 10–15 ), flavanone ( 16–19 ), flavanol ( 23–25 ), and isoflavone ( 20–22 ). The leaves, flowers, and fruits were found to be particularly rich in flavonols, mainly kaempferol and quercetin mono- and diglycosides, containing glucose, galactose, and rhamnose as the sugar moiety [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. Regarding individual components, isoquercitrin ( 2 ), hyperoside ( 3 ), quercitrin ( 4 ), and rutin ( 5 ) were identified as the dominant flavonoids of the leaves, flowers, and fruits ( Table 1 ).…”

“…(-)-Epicatechin ( 24 ) and (+)-catechin ( 23 ), as markers of proanthocyanidin occurrence, have been detected in several Cotoneaster species, suggesting the presence of procyanidins in this genus. Although the available literature on this phenolic group is limited to a few reports [ 9 , 17 , 19 , 20 , 21 , 22 ] and requires more extensive research, it is known that B-type procyanidins are characteristic of the Cotoneaster species, mostly present in the form of di-, tri-, and tetramers of (-)-epicatechin, and that (-)-epicatechin ( 24 ), procyanidins B2 ( 26 ), and C1 ( 27 ) are the dominant components of the leaves and fruits.…”

“…The typical representatives of these phenolics are caffeoylquinic acids such as chlorogenic acid ( 28 ) and its isomers, ferulic ( 29 ), caffeic ( 30 ), p -coumaric ( 31 ), cinnamic acids ( 32 ) as well as benzoic ( 33 ), protocatechuic ( 34 ), vanillic ( 35 ), gentisic ( 36 ), syringic ( 37 ), p -hydroxybenzoic ( 38 ), and salicylic acids ( 39 ) [ 5 , 7 , 13 , 15 , 20 , 21 , 23 , 26 ]. In addition, a gentisic acid 2- O -glucoside named orbicularin ( 40 ) was isolated from the leafy twigs of C. orbicularis , while caffeoylmalic acid ( 41 ) was obtained from the leaves of C. zabelii [ 15 , 17 ]. Nevertheless, in a set of identified phenolic acids, chlorogenic ( 28 ) and ferulic ( 29 ) acids were noted as the most abundant phenolics in the twigs and fruits of C. integerrimus [ 24 ], the leaves of C. meyeri [ 23 ], the leafy twigs of C. nummularia [ 7 ], and the leafy twigs of C. horizontalis [ 26 ].…”

“…Among the numerous methods employed for the quantification of the antioxidant capacity of Cotoneaster species are the assays based on the single electron transfer (SET) and/or hydrogen atom transfer (HAT) reaction mechanisms. In vitro SET-based assays such as free radical scavenging with DPPH (2,2-diphenyl-1picrylhydrazyl radical), ABTS (2,2-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) radical cation), DMPD ( N , N -dimethyl- p -phenylenediamine radical cation), FRAP (ferric ion reducing antioxidant power), CUPRAC (cupric-reducing antioxidant capacity) as well as HAT-based methods for scavenging superoxide anions (O 2 •− ), hydrogen peroxide (H 2 O 2 ), and for the inhibition of linoleic acid peroxidation, are the most frequently methods used to assess the antioxidant properties of the leaves of 12 Cotoneaster species, including the most active C. bullatus , C. zabelii and C. integerrimus [ 17 , 19 , 20 , 22 ]; the leaves of C. melanocarpus , C. meyeri , C. morulus , C. nummularia , C. mongolica [ 5 , 18 , 23 ]; the fruits of nine Cotoneaster species [ 21 ] and the fruits of C. pannosus [ 25 ], the leafy twigs of C. nummularia and C. afghanicus [ 7 , 49 ]; the twigs, fruits of C. integerrimus [ 24 ] and sarcocarp of C. multiflorus [ 50 ]. As demonstrated in Table 2 , in most applied tests, the Cotoneaster extracts displayed significant antioxidant effects, depending on the polarity of the extraction solvent.…”