Elsevier

Food Chemistry

Volume 299, 30 November 2019, 125102
Food Chemistry

Chemical compositions and α-glucosidase inhibitory effects of anthocyanidins from blueberry, blackcurrant and blue honeysuckle fruits

https://doi.org/10.1016/j.foodchem.2019.125102Get rights and content

Highlights

  • Anthocyanidins exhibited higher α-glucosidase inhibition effects than anthocyanins.

  • Anthocyanidins were mixed-type inhibitors and inhibited through a static procedure.

  • Anthocyanidins occupied the active site of enzyme and avoided the entrance of pNPG.

  • Anthocyanidins from berry fruits can be used as potential α-glucosidase inhibitors.

Abstract

The chemical compositions and α-glucosidase inhibitory activities of anthocyanins extracted from blueberry, blackcurrant and blue honeysuckle fruits and their acid hydrolysates (anthocyanidins) were analysed. Those anthocyanins were glycosidic anthocyanins that converted to anthocyanidins during acid hydrolysis, leading to increases in their α-glucosidase inhibitory activities (expressed as IC50 values) from 0.232, 0.152 and 0.188 to 0.113 to 0.005 and 0.025 mg/mL. The potential inhibitory mechanism of these anthocyanidins was then investigated through inhibition kinetics, fluorescence quenching and docking simulations. The results showed the following: 1) all anthocyanidins were mixed-type inhibitors of α-glucosidase and they bind more tightly to free α-glucosidase as compared to the α-glucosidase-substrate complex; 2) anthocyanidin inhibition of α-glucosidase was a static procedure, presumably driven by hydrophobic associations and hydrogen bonding; and 3) all anthocyanidins were inserted into the active site of α-glucosidase and avoided the entrance of p-nitrophenyl-a-D-glucopyranoside. This study is valuable for anthocyanidins as potential α-glucosidase inhibitors.

Introduction

Diabetes mellitus is a well-known chronic disease that affects 415 million people and kills 5 million people worldwide in 2015 (Söhretoglu et al., 2018, Zhao et al., 2018). The population of diabetes mellitus patients is soaring globally, and the worldwide prevalence of diabetes is expected to increase to 642 million by 2040 (Wang et al., 2017, Zhao et al., 2018). Type 2 diabetes mellitus, which accounts for 90% of all cases of diabetes, is a complex metabolic disorder characterized by hyperglycaemia due to insulin resistance and impaired islet β-cell function, which together result in an inability to supply sufficient insulin to meet the body’s demands, eventual β-cell loss, and serious diabetes-related complications such as cardiovascular diseases, nephropathy and retinopathy (Zaharudin et al., 2019, Zhao et al., 2018).

Polyphenols are a large group of phytochemicals widely distributed in plant sources, especially in fruits and vegetables (Scalbert, Manach, Morand, Rémésy, & Jiménez, 2005). It has been reported that dietary polyphenols are effective antidiabetic agents for managing and preventing type 2 diabetes and its complications (Cao et al., 2018, Xiao and Högger, 2015). The potential of dietary polyphenols, especially individual compounds, in type 2 diabetes can be summarized as follows: protection of pancreatic β-cells against glucose toxicity, anti-inflammatory and antioxidant effects, inhibition of starch and carbohydrate digestion by inhibition of digestion enzymes (e.g., α-amylases and α-glucosidases), improvement of insulin resistance, and inhibition of advanced glycation end product formation (Aguirre et al., 2011, Cao et al., 2014, Xiao and Högger, 2015). Xiao and Högger (2015) published an excellent review of current insights and future perspectives on these aspects.

Anthocyanins are a major subclass of flavonoids that could be used as effective inhibitors against α-glucosidase, the most important enzyme in carbohydrate digestion located in the brush-border surface membrane of intestinal cells (Xiao, Kai, Yamamoto, & Chen, 2013). For example, Xu, Xie, Xie, Liu, and Chen (2018) isolated pelargonidin 3-rutinoside from strawberries and revealed its inhibitory effects on α-glucosidase by enzymatic kinetics and molecular docking analysis. You, Chen, Wang, Luo, and Jiang (2011) investigated the inhibitory effect of muscadine anthocyanins on α-glucosidase regarding their antidiabetic activities. It has been reported that anthocyanins are most abundant in coloured berries such as blueberries and blackcurrants (Liobikas, Skemiene, Trumbeckaite, & Borutaite, 2016). Hence, these coloured berry fruits could be important sources of α-glucosidase inhibitory anthocyanins. Various coloured berries, especially those of blueberry, blackcurrant and blue honeysuckle, are widely distributed in the Greater Khingan Mountains region, one of the largest natural distribution areas of berries in China. However, to the best of our knowledge, limited information is available on the α-glucosidase inhibitory activities of anthocyanins in these three berry fruits.

The majority (more than 65%) of anthocyanins, including those found in many berries, are glycosidic anthocyanins, i.e., they contain glycoside ligands (Liobikas et al., 2016, Lohachoompol et al., 2008), which lowers the bioactivities of anthocyanins such as antioxidant activities, α-glucosidase activity and pancreatic lipase inhibition (You et al., 2011, Zheng et al., 2011). Therefore, considering that certain anthocyanins are absorbed into the gastrointestinal wall in their intact form (Liobikas et al., 2016), it is important to compare the α-glucosidase inhibitory activities of anthocyanins and anthocyanidins with the aim of selecting more effective α-glucosidase inhibitors. Meanwhile, berries belonging to different geographical places within the same genus may also exhibit considerable differences in the concentration of various anthocyanidins and the levels of glycosylation within these compounds (Li, Meng, & Li, 2016). Therefore, insight into the composition of anthocyanins and anthocyanidins in berry fruits should be obtained before studying their α-glucosidase inhibitory activities.

The objective of the present study was to investigate the α-glucosidase inhibition activities of anthocyanins and anthocyanidins in three berry fruits (blueberry, blackcurrant and blue honeysuckle) grown in the Greater Khingan Mountains region and to study the potential mechanism of inhibition.

Section snippets

Plant materials

Fully ripened blueberry, blackcurrant and blue honeysuckle fruits were randomly collected from the Greater Khingan Mountains region (Latitude, 52°34′ N; Longitude, 123°14′ E; Altitude, 600 m), Heilongjiang Province, China in 2018. The fruits were handpicked and transported with ice bags to our laboratory. They were freeze dried, crushed into powders, and sieved through a 40-mesh sieve. The powdered samples were stored at −20 °C until use.

Chemical reagents

α-Glucosidase from Saccharomyce cerevisiae (EC 3.2.1.20)

Composition and content of anthocyanins

The chromatographic fingerprints of anthocyanins in the samples before acid hydrolysis were initially analysed using HPLC-DAD and are presented in Fig. 1A. Thirteen, four and five peaks were detected in blueberry, blackcurrant and blue honeysuckle samples, respectively. Individual anthocyanins were then identified using HPLC-ESI-ToF-MS/MS by comparing the detailed MS data with published values (Celli et al., 2015, Cruz et al., 2018, Li et al., 2016). Fragment (M+ - 162) corresponded to the loss

Discussion

It is expected that the composition of anthocyanins between the samples was different because berry fruits from various genera exhibit specific anthocyanin profiles (Fraige, Pereira-Filho, & Carrilho, 2014). The biosynthesis of anthocyanins was strictly controlled by the genes of the corresponding enzymes involved in the relevant biosynthetic pathways (Wang et al., 2018). It was found that all the anthocyanins in the three berry samples were glycosidic forms (Table 1A). The 3-position in the C

Conclusions

In summary, this study analysed the composition of anthocyanins and anthocyanidins in blueberry, blackcurrant and blue honeysuckle and studied their α-glucosidase inhibition activities. The results showed that the anthocyanins in the fruits were glycosidic anthocyanins, but their corresponding anthocyanidins exhibited higher inhibition effects against α-glucosidase. Through kinetic analysis, it was found that the three anthocyanidins were mixed-type inhibitors. The fluorescence quenching showed

Declaration of Competing Interest

There are no conflicts of financial and personal relationships in this work.

Acknowledgments

This work was financially supported by China Agriculture Research System (CARS-27) and Fundamental Research Funds for Sate Central Universities (2017TS043).

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