Abstract

Pearl and nacre have been used in traditional medicines for treating brain dysfunctions, such as epilepsy, myopia, palpitations and convulsions. We previously showed that a pearl oyster nacre extract improves scopolamine-induced memory impairments using the Y-maze, Banes maze and object recognition tests. In this study, we aimed to isolate the memory-improving substance using ion-exchange column chromatography and reverse-phase column chromatography and elucidate the molecular mechanism underlying its memory-improving activity. The isolated substance was found to be a sulfated polysaccharide with a molecular weight of approximately 750 kDa. Monosaccharide composition analysis showed that it was rich in galactose, glucose, mannose and uronic acid. Furthermore, the mRNA expression levels of oxidative stress, inflammatory response and neuroprotective factors in the cerebral cortex were investigated. Treatment with the polysaccharide increased the expression levels of the antioxidant enzymes Cu, Zn -superoxide dismutase (SOD) and catalase and attenuated the scopolamine-mediated upregulation of the inflammatory cytokines interleukin-1 and interleukin-6. In addition, the polysaccharide suppressed the decrease in the expression levels of brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF). These findings strongly suggest that the polysaccharide in the nacre extract mediated its antiamnesic effects by preventing oxidative stress and inflammation and increasing the expression levels of BDNF and NGF.

Highlights

  • Pearl oyster shells are composed of a nacreous layer and a prismatic layer

  • We previously showed the memory-improving activity of the nacre extract against scopolamine-induced memory impairment

  • We isolated a bioactive substance with memory-improving activity against scopolamine-induced memory impairment, which was assessed using the Y-maze and novel object recognition tests

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Summary

Introduction

Pearl oyster shells are composed of a nacreous layer and a prismatic layer. Pearls, composed of the nacreous layer, are produced by mollusks, such as pearl oysters. Pearl and nacre consist of CaCO3 (>90%), proteins, peptides, glycoproteins, chitin and lipids [1]. Pearl powder has been used in traditional Chinese medicine to treat brain dysfunctions, such as epilepsy and myopia [2,3,4]. Pearl powder has been used in food supplements and cosmetics. Pearl oysters are widely used in the pearl-producing industry. Approximately 100,000 tons of pearl oyster shells are generated as industrial waste per year, and most shells containing a nacreous layer are discarded in Japan [5]. Effective utilization of pearl oyster shells is strongly desired

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