Akari ISHISAKA

ABSTRACT Flavonoids are present in plant foods such as vegetables and fruits and exhibit various physiological effects, including antioxidant and anti-inflammatory properties. Ingested flavonoids are absorbed from the intestinal tract and circulated in the blood. Some studies have indicated the presence of flavonoids in breast milk. However, information on their metabolites and concentrations in breast milk and the subsequent transfer to and physiological functions in infants is limited. Therefore, this review presents a compilation of recent findings on the transfer of flavonoids to infants via breast milk and their bioactivities.

This is the first study that quantified quercetin (QUE) and its 16 metabolites in the breast milk of QUE-fed maternal mice, the plasma and urine of that, and neonatal mice. Interestingly, the QUE aglycone concentration in the milk was much higher than in the plasma of maternal mice, suggesting that QUE may exert biological activity in neonates.

Green tea catechins have thus far been demonstrated to have antiobesity effects in a variety of experimental models. However, upstream molecular events triggering those phenomena remain to be identified. In this study, we found that (-)-epigallocatechin-3-O-gallate (EGCG) promoted lipolysis in lipid-loaded Huh7 human hepatoma cells. Notably, EGCG at a high concentration induced both oxidative stress and protein stress (proteo-stress), leading to activation of stress defense mechanisms, such as mRNA expressions of antioxidant and phase-2 detoxifying enzymes, and heat shock proteins. Furthermore, EGCG decreased the level of intracellular ATP, while glucose uptake from culture media was promoted possibly for energy homeostasis. EGCG also upregulated the expression of adipose triglyceride lipase, and activated AMP-activated protein kinase. Collectively, these results suggest that EGCG induces lipolysis to compensate for ATP reduction derived from activation of stress defense systems against its oxidative and proteo-stress properties.

Leptosperin (methyl syringate β-d-gentiobioside) is abundantly found in manuka honey, which is widely used because of its antibacterial and possible anti-inflammatory activities. The aim of this study was to examine the molecular mechanism underlying the metabolism of leptosperin. Five phytochemicals (leptosperin, methyl syringate (MSYR), glucuronate conjugate of MSYR (MSYR-GA), sulfonate conjugate of MSYR (MSYR-S), and syringic acid (SYR)) were separately incubated with HepG2 and Caco-2 cells. After incubation, we found that the concentration of MSYR decreased, whereas the concentrations of SYR, MSYR-GA, and MSYR-S increased. By profiling with inhibitors and carboxylesterases (CES1, 2), we found that the conversion from MSYR to SYR was mediated by CES1. Lipopolysaccharide-stimulated RAW264.7 cells restored MSYR-GA to MSYR possibly by the secreted β-glucuronidase. All of the mice administered with leptosperin, MSYR, or manuka honey showed higher MSYR (13.84 ± 11.51, 14.29 ± 9.19, or 6.66 ± 2.30 nM) and SYR (1.85 ± 0.66, 6.01 ± 1.20, or 8.16 ± 3.10 nM) levels in the plasma compared with that of the vehicle controls (3.33 ± 1.45 (MSYR) and 1.85 ± 0.66 (SYR) nM). The findings of our study indicate that the unique metabolic pathways of these compounds may account for possible functionalities of manuka honey.