Dietary Intake of Rosmarinic Acid Increases Serum Inhibitory Activity in Amyloid A Aggregation and Suppresses Deposition in the Organs of Mice

Abstract

Serum amyloid A (SAA) is one of the most important precursor amyloid proteins and plays a vital step in AA amyloidosis, although the underlying aggregation mechanism has not been elucidated. Since SAA aggregation is a key step in this pathogenesis, inhibitors are useful to prevent and treat AA amyloidosis, serving as tools to investigate the pathogenic mechanism. In this study, we showed that rosmarinic acid (RA), which is a well-known inhibitor of the aggregation of amyloid β (Aβ), displayed inhibitory activity against SAA aggregation in vitro using a microliter-scale high-throughput screening (MSHTS) system with quantum-dot nanoprobes. Therefore, we evaluated the amyloid aggregation inhibitory activity of blood and the deposition of SAA in organs by feeding mice with Melissa officinalis extract (ME) containing RA as an active substance. Interestingly, the inhibitory activity of ME-fed mice sera for SAA and Aβ aggregation, measured with the MSHTS system, was higher than that of the control group. The amount of amyloid deposition in the organs of ME-fed mice was lower than that in the control group, suggesting that the SAA aggregation inhibitory activity of serum is associated with SAA deposition. These results suggest that dietary intake of RA-containing ME enhanced amyloid aggregation inhibitory activity of blood and suppressed SAA deposition in organs. This study also demonstrated that the MSHTS system could be applied to in vitro screening and to monitor comprehensive activity of metabolized foods adsorbed by blood.

Aggregation of Mouse Serum Amyloid A Protein Was Promoted by Amyloid-Enhancing Factors with the More Genetically Homologous Serum Amyloid A

“…However, the SD value did not increase after 168 h of incubation in this condition (Figure 2B). Our previous report [6] showed that SAA spontaneously aggregates with increasing concentration, reaching a maximum SD value when the concentration is 50 µM. These results suggest that mSAA cannot spontaneously aggregate at a low concentration of about 10 µM.…”

“…Amyloid A (AA) amyloidosis, one of the most common forms of clinically important amyloidosis, is related to chronic inflammatory diseases and chronic infections. The structure of these amyloid fibrils may affect their ability to spread to different sites in a cell and between organisms in a prion-like mechanism, but the mechanism by which amyloid fibrils form in vivo and in vitro remains largely unclear although the structure of many precursors has been elucidated [5][6][7][8].…”

“…2021, 22, x FOR PEER REVIEW 2 of 13 Serum amyloid A (SAA), an evolutionarily highly conserved acute phase protein in vertebrates and invertebrates, is predominantly secreted by hepatocytes in the liver and is also produced by a variety of cells and tissues [9][10][11]. In fields of regulating inflammation and immunity and lipid metabolism, SAA protein plays an important role that benefits the body [6,11,12]. SAA is an important amyloid precursor and plays a key role in AA amyloidosis which impacts ∼1% of patients with chronic inflammation [13,14].…”

“…Moreover, QDs are useful for long-term, single-molecule imaging in vitro. In the MSHTS system, a sample of 5 μL in volume is needed for analysis in a 1536-well plate, and the inhibitory activity is estimated by half-maximal effective concentration Previously, we reported a real-time imaging method of various amyloid proteins such as amyloid β (Aβ 42 ), tau, α-synuclein, and SAA aggregation with quantum-dot (QD) nanoprobes, which was using fluorescence probes in imaging by confocal and fluorescent microscopy, and developed a microliter-scale high-throughput screening system (MSHTS) to search for substances that exhibit aggregation inhibitory activity by applying this imaging method [6,[25][26][27]. Moreover, QDs are useful for long-term, single-molecule imaging in vitro.…”

“…Moreover, QDs are useful for long-term, single-molecule imaging in vitro. In the MSHTS system, a sample of 5 µL in volume is needed for analysis in a 1536-well plate, and the inhibitory activity is estimated by half-maximal effective concentration (EC 50 ) [6,26,28]. These imaging techniques that employ QDs serve as quick, easy, and powerful tools to apply to in vitro screening and monitoring.…”