In vitro α-glucosidase and α-amylase inhibitory activities of acorn, acorn shell and cupule extracts of Quercus robur L.

Diabetes is a serious disease characterized by high blood sugar level and associated with dysfunction and failure in several organs in the long term. One of therapeutic approaches in type II diabetes is inhibition of α-glucosidase and α-amylase enzymes [1,2].

Quercus genus is represented with 24 species in Turkish flora [3]. Quercus robur L. that is known as common oak or pedunculate oak is one of the most economically and ecologically important hardwood species belonging to Fagaceae family [4,5]. Cortex and seed parts of Quercus robur have been used in Turkish folk medicine as antidiarrheal internally and its cortex has been also used as antiseptic externally [6]. It was reported to have astringent, antiphlogistic, antiviral, anthelmintic, antimicrobial and antioxidant effects [7]. Quercus robur L. was shown to contain the seconder metabolites such as tannins [8], saponins [9], triterpenoids, steroids, phenolcarboxylic acids, coumarins, flavonoids, catechins [10].

In the present study, in vitro α-glucosidase and α-amylase inhibitory activities of methanol extracts from acorn, acorn shell and cupule of Quercus robur L. were investigated. They indicated 94.28, 37.14 and 26.86% α-glucosidase inhibitory activity with IC₅₀ values 0.0071, 0.0259 and 0.0303 mg/mL, respectively at 20 µg/mL. Standard compound acarbose displayed 1.62% inhibitory activity against α-glucosidase (IC₅₀= 2.3631 mg/mL) at the same concentration. The extracts showed significant α-glucosidase inhibitory activity. However, none of them inhibited α-amylase.

Keywords: Diabetes, Quercus robur, α-glucosidase, α-amylase.

References:

[1] Mahajan RP, Mahire RR, More DH. Phytochemical screening of aqueous and ethanol extracts of some medicinal plants and in-vitro study of inhibition of α- amylase. Int J Pharm 2014; 1: 501 – 506

[2] Hamid HA, Yusoff MM, Liu M, Karim MR. α-Glucosidase and α-amylase inhibitory constituents of Tinospora crispa: Isolation and chemical profile confirmation by ultra-high performance liquid chromatography-quadrupole time-of-flight/mass spectrometry. J Funct Foods 2015; 16: 74 – 80

[3] Güner A, Aslan S, Ekim T, Vural M, Babaç MT, editors. Türkiye Bitkileri Listesi (Damarlı Bitkiler). İstanbul: Nezahat Gökyiğit Botanik Bahçesi ve Flora Araştırmaları Derneği Yayını, 2012; 506 – 511

[4] Plitta BP, Michalak M, Naskret-Barciszewska MZ, Barciszewski J, Chmielarz P. DNA methylation of Quercus robur L. plumules following cryopretreatment and cryopreservation. Plant Cell Tiss Organ Cult 2014; 117: 31 – 37

[5] PDR for Herbal Medicines, 4th ed., Thomson Medical Economics, Montvale, NJ, 2007.

[6] Baytop T. Türkiye'de Bitkilerle Tedavi (Geçmişte ve Bugün). İstanbul: İstanbul Üniversitesi, 1999; 295

[7] Uddin G, Rauf A. Phytochemical screening, antimicrobial and antioxidant activities of aerial parts of Quercus robur L. J Med Plants Res 2012; 1: 1 – 4

[8] Paaver U, Matto V, Raal A. Total tannin content in distinct Quercus robur L. galls. J Med Plants Res 2010; 4: 702 – 705

[9] Arramon G, Saucier C, Colombani D, Glories Y. Identification of triterpene saponins in Quercus robur L. and Q. petraea Liebl. Heartwood by LC-ESI/MS and NMR. Phytochem Anal 2002; 13: 305 – 310

[10] Nishanbaev SZ, Bobakulov KM, Abdullaev ND, Sham'yanov ID. Phenolcarboxylic acids from Quercus robur growing in Uzbekistan. Chem Nat Compd 2015; 5: 537 – 539