β-lactolin, a Monoamine Oxidase B Inhibitory Lactopeptide, Suppresses Reactive Oxygen Species Production in Lipopolysaccharide-Stimulated Astrocytes

Shiori Akiyama,Yasuhisa Ano,Chika Takahashi,Rena Ohya,Tatsuhiro Ayabe

doi:10.3390/app11073034

Abstract

Astrocytes are known to regulate normal brain function. Monoamine oxidase B (MAO-B), an enzyme highly expressed in astrocytes, metabolizes dopamine (DA) and induces reactive oxygen species (ROS) production. We have previously reported that β-lactolin, a whey-derived glycine–threonine–tryptophan–tyrosine tetrapeptide, improves memory impairment in mice by regulating the dopaminergic system; however, the effects of β-lactolin on astrocytes remain unclear. Herein, we investigated the effects of β-lactolin on cultured murine astrocytes. First, we measured intracellular ROS production in lipopolysaccharide-stimulated reactive astrocytes treated with or without β-lactolin, and then determined the role of β-lactolin in DA metabolism in astrocytes by measuring MAO-B enzyme activity and the levels of DA, and its metabolites, in DA-pretreated astrocytes. We found that β-lactolin significantly suppressed ROS production in lipopolysaccharide-stimulated reactive astrocytes (p = 2.76 × 10−6), inhibited MAO-B activity (p = 2.65 × 10−2) and increased intracellular DA levels (p = 1.08 × 10−3), suggesting that β-lactolin could inhibit DA metabolism in astrocytes. These results illustrate the novel protective effects of β-lactolin on reactive astrocytes and suggest their involvement in the memory-improving effects of β-lactolin via the dopaminergic system.

Highlights

The cells were seeded in 6-well plates (IWAKI, Shizuoka, Japan) for reverse transcription quantitative polymerase chain reaction (RT-qPCR) and monoamine analysis or in 10-cm plates (Corning, Corning, NY, USA) for MAO and COMT activity assays at a density of 3.0 × 105 cells/mL and incubated overnight. β-lactolin (GTWY peptide; purity: 98%) was purchased from Bachem (Bubendorf, Switzerland). β-lactolin was dissolved in dimethyl sulfoxide (Wako, Osaka, Japan) and diluted in phosphate-buffered saline (PBS; TaKaRa Bio, Shiga, Japan), such that the final concentration in the culture medium was less than 1%
Astrocytes perform various crucial functions in the central nervous system (CNS) and reactive astrocytes are considered as therapeutic targets in neurodegenerative diseases
This study showed that β-lactolin suppresses intracellular reactive oxygen species (ROS) production in LPS-treated astrocytes

Summary

Introduction

Astrocytes are the most abundant glial cells with fundamental physiological functions in the brain, such as supporting neurons, modulating synaptic activities, and regulating the clearance of neurotransmitters, including dopamine (DA) [1,2,3]. Reactive astrocytes are induced in response to pathological conditions, such as ischemia, brain injury, infection, and neurodegenerative diseases, such as Alzheimer’s (AD), Parkinson’s (PD) and Huntington’s disease [6]. The induced astrocytes become harmful, as they lose their normal functions, upregulate the expression of inflammatory genes, and produce higher levels of reactive oxygen species (ROS) than astrocytes under resting conditions, causing further neurotoxicity and cell death [6]. Reactive astrocytes are considered as preventive and therapeutic targets in neurodegenerative diseases

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