Investigating the uncertainty of prediction accuracy for the application of physiologically based pharmacokinetic models to animal-free risk assessment of cosmetic ingredients.

Physiologically based pharmacokinetic (PBPK) models are considered useful tools in animal-free risk assessment. To utilize PBPK models for risk assessment, it is necessary to compare their reliability with in vivo data. However, obtaining in vivo pharmacokinetics data for cosmetic ingredients is difficult, complicating the utilization of PBPK models for risk assessment. In this study, to utilize PBPK models for risk assessment without accuracy evaluation, we proposed a novel concept-the modeling uncertainty factor (MUF). By calculating the prediction accuracy for 150 compounds, we established that using in vitro data for metabolism-related parameters and limiting the applicability domain increase the prediction accuracy of a PBPK model. Based on the 97.5th percentile of prediction accuracy, MUF was defined at 10 for the area under the plasma concentration curve and 6 for Cmax. A case study on animal-free risk assessment was conducted for bisphenol A using these MUFs. As this study was conducted mainly on pharmaceuticals, further investigation using cosmetic ingredients is pivotal. However, since internal exposure is essential in realizing animal-free risk assessment, our concept will serve as a useful tool to predict plasma concentrations without using in vivo data.

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.

Sequential breakdown of 3-phosphorylated phosphoinositides is essential for the completion of macropinocytosis.

Macropinocytosis is a highly conserved endocytic process by which extracellular fluid and solutes are internalized into cells. Macropinocytosis starts with the formation of membrane ruffles at the plasma membrane and ends with their closure. The transient and sequential emergence of phosphoinositides PI(3,4,5)P3 and PI(3,4)P2 in the membrane ruffles is essential for macropinocytosis. By making use of information in the Caenorhabditis elegans mutants defective in fluid-phase endocytosis, we found that mammalian phosphoinositide phosphatase MTMR6 that dephosphorylates PI(3)P to PI, and its binding partner MTMR9, are required for macropinocytosis. INPP4B, which dephosphorylates PI(3,4)P2 to PI(3)P, was also found to be essential for macropinocytosis. These phosphatases operate after the formation of membrane ruffles to complete macropinocytosis. Finally, we showed that KCa3.1, a Ca(2+)-activated K(+) channel that is activated by PI(3)P, is required for macropinocytosis. We propose that the sequential breakdown of PI(3,4,5)P3 → PI(3,4)P2 → PI(3)P → PI controls macropinocytosis through specific effectors of the intermediate phosphoinositides.