Evaluation of Polyphenol Anthocyanin-Enriched Extracts of Blackberry, Black Raspberry, Blueberry, Cranberry, Red Raspberry, and Strawberry for Free Radical Scavenging, Reactive Carbonyl Species Trapping, Anti-Glycation, Anti-β-Amyloid Aggregation, and Microglial Neuroprotective Effects.

Hang Ma,Susan Meschwitz,Nicholas Dasilva,Joel Dain,Navindra Seeram,Weixi Liu,Shelby Johnson

doi:10.3390/ijms19020461

Abstract

Glycation is associated with several neurodegenerative disorders, including Alzheimer’s disease (AD), where it potentiates the aggregation and toxicity of proteins such as β-amyloid (Aβ). Published studies support the anti-glycation and neuroprotective effects of several polyphenol-rich fruits, including berries, which are rich in anthocyanins. Herein, blackberry, black raspberry, blueberry, cranberry, red raspberry, and strawberry extracts were evaluated for: (1) total phenolic and anthocyanins contents, (2) free radical (DPPH) scavenging and reactive carbonyl species (methylglyoxal; MGO) trapping, (3) anti-glycation (using BSA-fructose and BSA-MGO models), (4) anti-Aβ aggregation (using thermal- and MGO-induced fibrillation models), and, (5) murine microglia (BV-2) neuroprotective properties. Berry crude extracts (CE) were fractionated to yield anthocyanins-free (ACF) and anthocyanins-enriched (ACE) extracts. The berry ACEs (at 100 μg/mL) showed superior free radical scavenging, reactive carbonyl species trapping, and anti-glycation effects compared to their respective ACFs. The berry ACEs (at 100 μg/mL) inhibited both thermal- and MGO-induced Aβ fibrillation. In addition, the berry ACEs (at 20 μg/mL) reduced H2O2-induced reactive oxygen species production, and lipopolysaccharide-induced nitric oxide species in BV-2 microglia as well as decreased H2O2-induced cytotoxicity and caspase-3/7 activity in BV-2 microglia. The free radical scavenging, reactive carbonyl trapping, anti-glycation, anti-Aβ fibrillation, and microglial neuroprotective effects of these berry extracts warrant further in vivo studies to evaluate their potential neuroprotective effects against AD.

Highlights

Glycation is a non-enzymatic process which starts with a reaction between sugar molecules and the free amino groups of proteins to produce unstable aldimine and ketoamine structures
We confirmed the identities of the individual anthocyanins in each berry Anthocyanin-Enriched Extracts (ACEs) by conducting high performance liquid chromatography with ultraviolet (HPLC-UV) analyses and by comparison of the elution orders and their retention times based on our previous report [26]
The chromatograms for each of the berry ACEs (Supplementary Materials Figures S1A–S6A shown at 520 nm, the characteristic wavelength of anthocyanins), confirmed the presence of anthocyanins which were in agreement with literature [26]

Summary

Introduction

Glycation is a non-enzymatic process which starts with a reaction between sugar molecules and the free amino groups of proteins to produce unstable aldimine and ketoamine structures. Over time, these structures can transform to a heterogenous group of compounds collectively known as advanced glycation endproducts (AGEs). Accumulated AGEs can magnify the production of reactive oxygen species (ROS) by binding to transmembrane receptors known as RAGE (receptor for AGEs), triggering intracellular signaling pathways, and stimulating the production of cytokines, which leads to neuronal oxidative stress, inflammation, and apoptosis. ROS and RCS can mediate cellular oxidative and inflammatory stresses, leading to the dysfunction of neuronal cells which greatly contributes towards the development of neurodegenerative diseases including AD [4,5]

Objectives

Methods

Results

Discussion

Conclusion