Vivien Y Chen1, Sonya M Khersonsky, Kerby Shedden
1Department of Pharmaceutical Sciences, University of Michigan College of Pharmacy, Ann Arbor, Michigan 48109, USA.
This study explores how small molecules move within cells using fluorescent probes and advanced imaging. Researchers found that molecules often accumulate in cytoplasmic vesicles, following a two-step transport pattern. Hydrophobic molecules prefer to stay in these vesicles. The findings challenge the idea that cells are simple barriers and suggest transport dynamics should be considered in drug modeling. This could improve how we predict drug concentrations and effects in the body.
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Area of Science:
Background:
Traditional pharmacokinetic models often treat cells as static permeability barriers, simplifying them to a single compartment. However, this approach overlooks the complex dynamics of subcellular transport. Prior research has shown that molecules can move through various intracellular compartments, but the mechanisms remain poorly understood. No prior work had resolved how small molecules distribute within cells over time. This gap motivated the use of advanced imaging techniques to observe transport in real time. Classical models fail to capture the spatiotemporal variations of probe distribution. Researchers needed a way to visualize transport beyond plasma membrane permeability. Fluorescent probes offer a solution for tracking molecules in living cells. This study introduces a kinetic imaging system to address these limitations.
Purpose Of The Study:
The goal was to investigate subcellular transport dynamics of small molecules using fluorescent probes. The researchers aimed to challenge the static boundary model of classical pharmacokinetics. They wanted to determine if cells function as a single compartment or multiple interacting compartments. The study focused on spatiotemporal variations in probe distribution. The team sought to identify patterns in how molecules accumulate within cells. They aimed to test if hydrophobicity influences sequestration preferences. The study also aimed to assess the role of cytoplasmic vesicles in transport. This approach could refine pharmacokinetic models by incorporating intracellular dynamics.
The study found that subcellular transport follows a nested two-compartment dynamical system, with probes partitioning from extracellular to cytosol and then to cytoplasmic vesicles.
Hydrophobic molecules preferentially partition into cytoplasmic vesicles, according to the study's findings.
The system allows real-time monitoring of spatiotemporal changes in probe distribution, revealing transport dynamics that static models miss.
Cytoplasmic vesicles serve as accumulation sites for most probes, suggesting they are key compartments in small molecule transport.
Main Methods:
The team used a combinatorial library of fluorescent small molecules. These probes were introduced into living cells for real-time observation. A kinetic, high-content imaging system tracked intracellular distribution. The system monitored spatiotemporal changes in probe localization. Cytoplasmic vesicles were identified as accumulation sites for most probes. Researchers analyzed probe kinetics using a two-compartment dynamical model. Steady-state partitioning was measured between extracellular and intracellular compartments. Hydrophobicity effects on sequestration were evaluated using probe partitioning data.
Main Results:
Most probes accumulated in cytoplasmic vesicles at steady state. Probe kinetics followed a nested two-compartment system model. Extracellular to cytosol transport was a primary partitioning pathway. Cytosol to vesicle transport was a secondary partitioning pathway. Hydrophobic molecules showed a stronger preference for vesicle sequestration. The study found a general organizing principle for subcellular transport. Classical pharmacokinetic models underestimated intracellular dynamics. These findings suggest transport phenomena influence cytosolic drug concentrations.
Conclusions:
The study challenges the classical pharmacokinetic boundary model of cells. Subcellular transport phenomena influence small molecule concentrations in the cytosol. The nested two-compartment model better explains probe distribution patterns. Hydrophobicity affects sequestration preferences in cytoplasmic vesicles. These findings suggest transport dynamics should be considered in pharmacokinetic models. Direct imaging reveals that cells are not static permeability barriers. The results support a revised framework for drug transport modeling. Authors propose that subcellular transport mechanisms are integral to pharmacokinetics.
The study shows cells are not static permeability barriers but dynamic systems with complex transport mechanisms influencing drug concentrations.
The findings suggest pharmacokinetic models should incorporate subcellular transport dynamics to better predict drug concentrations in the cytosol.