Tyrosine Is a Booster of Leucine-Induced Muscle Anabolic Response.

Leucine (Leu), an essential amino acid, is known to stimulate protein synthesis in the skeletal muscle via mTOR complex 1 (mTORC1) activation. However, the intrinsic contribution of other amino acids to Leu-mediated activation of mTORC1 signaling remains unexplored. This study aimed to identify amino acids that can promote mTORC1 activity in combination with Leu and to assess the effectiveness of these combinations in vitro and in vivo. We found that tyrosine (Tyr) enhanced Leu-induced phosphorylation of S6 kinase (S6K), an indicator of mTORC1 activity, although it exerted no such effect individually. This booster effect was observed in C2C12 cells, isolated murine muscle, and the skeletal muscles of mice orally administered the amino acids. To explore the molecular mechanisms underlying this Tyr-mediated booster effect, the expression of the intracellular Leu sensors, Sestrin1 and 2, was suppressed, and the cells were treated with Leu and Tyr. This suppression enabled Tyr alone to induce S6K phosphorylation and enhanced the booster effect, suggesting that Tyr possibly contributes to mTORC1 activation when Sestrin-GAP activity toward Rags 2 (GATOR2) is dissociated through Sestrin knockdown or the binding of Sestrins to Leu. Collectively, these results indicate that Tyr is a key regulator of Leu-mediated protein synthesis.

Monodemethylated Metabolites of Orally Administered Nobiletin: Identification and Quantitation in Rat Plasma and Tissues.

Although nobiletin (Nob) is a promising functional food component in view of its multifaceted physiological activity, the metabolism of this flavonoid remains underexplored. Herein, we examine the pharmacokinetics and tissue distribution of orally ingested Nob in rats, focusing on the six monodemethylnobiletin (MDNob) isomers as the main Nob metabolites. Two of these metabolites, namely, 6-MDNob and 8-MDNob, are chemically prepared for the first time, and a method for the simultaneous determination of all six MDNobs is developed. The obtained results demonstrate the production of 8-MDNob as a novel Nob metabolite and confirm the previously reported generation of 6-MDNob and 7-MDNob as oral metabolites of Nob in vivo. Finally, a quantitative relationship is established between the amount of metabolically generated MDNobs and that of administered Nob. Thus, this work paves the way for the broad applications and safe usage of Nob.

4″-Sulfation Is the Major Metabolic Pathway of Epigallocatechin-3-gallate in Humans: Characterization of Metabolites, Enzymatic Analysis, and Pharmacokinetic Profiling.

Epigallocatechin-3-gallate (EGCG), a major green tea polyphenol, has beneficial effects on human health. This study aimed to elucidate the detailed EGCG sulfation process to better understand its phase II metabolism, a process required to maximize its health benefits. Results show that kinetic activity of sulfation in the human liver and intestinal cytosol is 2-fold and 60- to 300-fold higher than that of methylation and glucuronidation, respectively, suggesting sulfation as the key metabolic pathway. Moreover, SULT1A1 and SULT1A3 are responsible for sulfation in the liver and intestine, respectively. Additionally, our human ingestion study revealed that the concentration of EGCG-4″-sulfate in human plasma (Cmax: 177.9 nmol·L-1, AUC: 715.2 nmol·h·L-1) is equivalent to free EGCG (Cmax: 233.5 nmol·L-1, AUC: 664.1 nmol·h·L-1), suggesting that EGCG-4″-sulfate is the key metabolite. These findings indicate that sulfation is a crucial factor for improving EGCG bioavailability, while also advancing the understanding of the bioactivity and toxicity of EGCG.

Development of nobiletin-methyl hesperidin amorphous solid dispersion: Novel application of methyl hesperidin as an excipient for hot-melt extrusion.

A novel amorphous solid dispersion (ASD) of poorly water-soluble nobiletin (Nob) with highly water-soluble methyl hesperidin (MeHes) was developed. Mixtures of Nob and excipients (MeHes, cellulose derivatives, and synthetic polymers) were processed by hot-melt extrusion (HME). Powder X-ray diffraction analysis proved that most of the HME products were fully amorphized. In dissolution studies, Nob-MeHes ASD showed a prominently higher Nob concentration than other HME products with polymeric excipients. Nob concentration upon dissolution of Nob-MeHes ASD was 400 and 7.5 times higher than that upon dissolution of crystalline Nob and a Nob-MeHes physical mixture, respectively. In addition, Nob-MeHes ASD showed good preservation stability for 6 months under an accelerated condition of 40 °C and 80% relative humidity. Permeation studies using a Caco-2 cell monolayer showed that Nob-MeHes ASD markedly increased the amount of Nob transported. In mice, the plasma Nob concentration and accumulated amount of Nob in various tissues drastically increased after administration of Nob-MeHes ASD. This is the first successful application of MeHes, with a relatively low glass-transition temperature, as an excipient for an ASD formulation prepared by hot-melt extrusion. The drastic improvement in Nob concentration with a small-molecule excipient may be an important finding.

Synthesis and evaluation of lysophosphatidylserine analogues as inducers of mast cell degranulation. Potent activities of lysophosphatidylthreonine and its 2-deoxy derivative.

In response to various exogenous stimuli, mast cells (MCs) release a wide variety of inflammatory mediators stored in their cytoplasmic granules and this release initiates subsequent allergic reactions. Lysophosphatidylserine (lysoPS) has been known as an exogenous inducer to potentiate histamine release from MCs, though even at submicromolar concentrations. In this study, through SAR studies on lysoPS against MC degranulation, we identified lysoPT, a threonine-containing lysophospholipid and its 2-deoxy derivative as novel strong agonists. LysoPT and its 2-deoxy derivative induced histamine release from MCs both in vitro and in vivo at a concentration less than one-tenth that of lysoPS. Notably, lysoPT did not activate a recently proposed lysoPS receptor on MCs, GPR34, demonstrating the presence of another undefined receptor reactive to both lysoPS and lysoPT that is involved in MC degranulation. Thus, the present strong agonists, lysoPT and its 2-deoxy derivative, will be useful tools to understand the mechanisms of lysoPS-induced activation of degranulation of MCs.