Antioxidant and Anti-Inflammatory Activities Of
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antioxidants Article Antioxidant and Anti-Inflammatory Activities of Flavanones from Glycyrrhiza glabra L. (licorice) Leaf Phytocomplexes: Identification of Licoflavanone as a Modulator of NF-kB/MAPK Pathway Luca Frattaruolo 1 , Gabriele Carullo 1 , Matteo Brindisi 1 , Sarah Mazzotta 1,2, Luca Bellissimo 1, Vittoria Rago 1, Rosita Curcio 1, Vincenza Dolce 1, Francesca Aiello 1,* and Anna Rita Cappello 1,* 1 Department of Pharmacy Health and Nutritional Sciences, Department of Excellence 2018–2022, University of Calabria, Edificio Polifunzionale, 87036 Arcavacata di Rende (CS), Italy; [email protected] (L.F.); [email protected] (G.C.); [email protected] (M.B.); [email protected] (S.M.); [email protected] (L.B.); [email protected] (V.R.); [email protected] (R.C.); [email protected] (V.D.) 2 Department of Organic and Medicinal Chemistry, University of Seville, C/Prof García González, n. 2, 41012 Seville, Spain * Correspondence: [email protected] (F.A.); [email protected] (A.R.C.); Tel.: +39-0984-493154 (F.A.); +39-0984-493177 (A.R.C.) Received: 28 May 2019; Accepted: 18 June 2019; Published: 20 June 2019 Abstract: Inflammation represents an adaptive response generated by injuries or harmful stimuli. Natural remedies represent an interesting alternative to traditional therapies, involving several biochemical pathways. Besides, the valorization of agrochemical wastes nowadays seems to be a feasible way to reduce the health spending and improve the accessibility at bioactive natural compounds. In this context, the chemical composition of three Glycyrrhiza glabra L. (licorice) leaf extracts, obtained through maceration or ultrasound-assisted method (fresh and dried leaves) was investigated. A guided fractionation obtained three main components: pinocembrin, glabranin and licoflavanone. All the extracts showed similar antioxidant properties, evaluated by 2,20-diphenyl-1-picrylhydrazyl (DPPH) or 2,20-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) Diammonium Salt (ABTS) assay, while, among the isolated compounds, licoflavanone exhibited the best antioxidant activity. The anti-inflammatory activity of the extracts and the purified compounds was investigated in lipopolysaccharide (LPS)-stimulated RAW 264.7 murine macrophages. Extract C and licoflavanone showed a good anti-inflammatory activity without affecting cell viability, as they decreased nitrite levels even when used at 12.5 µg/mL (p < 0.005) and 50 µM concentration (p < 0.001), respectively. Interestingly, licoflavanone markedly decreased pro-inflammatory cytokines and cyclooxygenase 2/inducible nitric oxide synthase (COX-2/iNOS) expression levels (p < 0.001). A modulation of nuclear factor kappa B/mitogen-activated protein kinases (NF-kB/MAPK) pathway underlay such behavior, highlighting the potential of this natural compound as a new scaffold in anti-inflammatory drug research. Keywords: pinocembrin; licoflavanone; Glycyrrhiza glabra; antioxidant activity; anti-inflammatory activity; NF-kB/MAPK pathway 1. Introduction Inflammation is a physio-pathological condition characterized by a complex biological response of body tissues to physical, chemical and biological stimuli. This process involves immune cells, Antioxidants 2019, 8, 186; doi:10.3390/antiox8060186 www.mdpi.com/journal/antioxidants Antioxidants 2019, 8, 186 2 of 15 blood vessels and molecular mediators in order to remove damage and to start tissue repair but, on the other hand, chronic inflammation can favor the onset of various diseases [1,2]. Over the years, many anti-inflammatory drugs have been developed with the aim to reduce inflammatory mediators’ levels in the body [3]. Most of these molecules act as cyclooxygenase (COX) inhibitors. They belong to a class of drugs that evolved over time to include selective inhibitors of COX-2, the isoform induced in inflammatory conditions, in order to reduce side effects of traditional nonsteroidal anti-inflammatory drugs (NSAID) therapy [4]. In addition, in the last decades, many natural compounds were used as templates for the development of new anti-inflammatory agents [5–7]. Plant phenols, particularly flavonoids, feature a wide range of biological activity, mainly including antioxidant and anti-inflammatory activity, useful as alternative medicaments [8–11]. Many studies highlighted that different phytocomplexes derived from Glycyrrhiza glabra L. are endowed with multiple biological activities, including antioxidant and anti-inflammatory activity, which were studied in different experimental models [12–14]. Although for a long time the most utilized parts of G. glabra were the roots, many studies reported that also its aerial parts, usually treated as an agrochemical waste, contained many bioactive compounds such as dihydrostilbenes [15–17], pinocembrin [18,19], licoflavanone, formononetin, isoquercitrin, genistein, prunetin, wighteone, 6-prenylnaringenin and lupiwighteone [19]. Dihydrostilbenes derived from Glycyrrhiza glabra leaves are structurally related to flavonoids and exhibit antigenotoxic, antioxidant and anti-inflammatory activity [16,17]. In previous studies, performed on autochthonous Glycyrrhiza glabra L., pinocembrin was recovered in leaf extracts, also assayed for their anti-proliferative, antioxidant and antibacterial activities [18,20]. Pinocembrin resulted as the principal component of the total extract, recoverable from methanol fraction after column chromatography. Literature data report that pinocembrin is a flavonoid endowed with antioxidant [21] and anti-inflammatory properties, exerted by downregulating tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1β), and interleukin 6 (IL-6). These activities are also achieved by significantly suppressing the phosphorylation and activation of extracellular signal-regulated kinase (ERK), c-Jun NH2-terminal kinase (JNK) and p38MAPK, as well as by reducing the phosphorylation of IkBα, directly involved in nuclear factor kappa B (NF-kB) regulation, as demonstrated by in vitro and in vivo studies [22]. In Glycyrrhiza glabra L. extracts, several bioactive metabolites were also identified [23], including flavonoids able to inhibit the production of nitric oxide (NO), interleukin-6 (IL-6) and prostaglandin E2 (PGE2) in lipopolysaccharide (LPS)-induced macrophages [24]. In this work, an efficient and fast method to recover pinocembrin, an emergent tool in pharmaceutical research [25], was firstly apprehended. For this purpose, ultrasound-assisted extraction (UAE) was applied both to fresh and dried leaves of Glycyrrhiza glabra. Furthermore, this procedure allowed us to isolate two prenylated flavanones, known as glabranin and licoflavanone, whose anti-inflammatory activities were also tested. Our outcomes revealed a strong biological potential of licoflavanone, whose molecular mechanisms underlying its anti-inflammatory effects were elucidated for the first time. 2. Materials and Methods 2.1. Plant Material Leaves of Glycyrrhiza glabra L. were collected in the Botanic Garden, University of Calabria, Rende (Cosenza province, Southern Italy) (39◦3507400 N, 16◦2209400 E) in May 2017. The cultivation generally requires soil 1.4 m deep or more, having a light, loamy and stone-free texture. As a perennial plant, it is grown continuously on the same land, with pieces of stolons planted in March at 0.91 m distance. Two prunings are necessary during the year (in May and October, generally). Fresh leaves recovered in May [18] were used to prepare the extract named B (see later). The remaining leaves were stored at room temperature, in the dark far from light and heat sources, for 5 months before the extraction. Antioxidants 2019, 8, 186 3 of 15 Antioxidants 2019, 8, x FOR PEER REVIEW 3 of 15 2.2. ChemicalEthanol Reagents96%, n-hexane, and Instrumentation and ethyl acetate (analytical grade) were obtained from Levanchimica srl (Bari, Italy). Silica gel (0.040–0.063 and 0.063–0.200 mm) and thin-layer chromatography (TLC, Ethanol 96%, n-hexane, and ethyl acetate (analytical grade) were obtained from Levanchimica silica gel plates 60 F254) were acquired from Merck (Darmstadt, Germany). TLC were visualized at srl (Bari, Italy). Silica gel (0.040–0.063 and 0.063–0.200 mm) and thin-layer chromatography (TLC, 254 nm. Ultrasound-bath Branson model 3800-CPXH (Milan, Italy) was used to perform the silica gel plates 60 F254) were acquired from Merck (Darmstadt, Germany). TLC were visualized at extractions. Organic solutions were dried over MgSO4 and evaporated on a rotary evaporator (Büchi 254 nm. Ultrasound-bath Branson model 3800-CPXH (Milan, Italy) was used to perform the extractions. RII) under reduced pressure. Melting points were obtained using a Gallenkamp melting point Organic solutions were dried over MgSO4 and evaporated on a rotary evaporator (Büchi RII) under apparatus. reduced pressure. Melting points were obtained using a Gallenkamp melting point apparatus. 2.3.2.3. Extraction Procedures TheThe extractextract AA waswas obtainedobtained as as previously previously described described [13 [13].]. Di Differentfferent procedures procedures were were performed performed to obtainto obtain extracts extracts B and B and C. Fresh C. Fresh or dried or dried leaves leaves (10 g), (10 previously g), previously triturated, triturated, were extracted were extracted with ethanol with ethanol 96% (250 mL) at 50 °C (10 cycles/s) for 1.5 h, at an ultrasonic frequency of 40 kHz. Leaves 96% (250 mL) at 50 ◦C (10 cycles/s) for 1.5 h, at an ultrasonic frequency of 40 kHz. Leaves were filtered were filtered