# Dielectric Responses of Cytosolic Water Change with Aging of Circulating Red Blood Cells

## TL;DR

This study shows that the dielectric properties of water inside red blood cells change as the cells age, offering a new way to track cellular aging.

## Contribution

The study introduces dielectric spectroscopy as a novel method to detect age-related changes in red blood cell cytosolic water.

## Key findings

- Dielectric parameters correlate with red blood cell age and deformability.
- Aging RBCs show distinct dielectric responses due to changes in free-to-bound water ratios.
- MDS can serve as a sensitive marker for cytosolic changes during RBC aging.

## Abstract

Water molecules in the cytosol of red blood cells (RBCs) may exist in a free or bound state. The ratio between the free and bound water depends on the composition of the cytoplasm, particularly on the hemoglobin concentration. Microwave dielectric spectroscopy (MDS) provides information on the state of intracellular water in red blood cell suspension and the erythrocyte cytosol state. In the presented study, we used MDS to assess the differences in the free-to-bound water ratio in subpopulations of freshly donated human erythrocytes of different ages (young, mature, and senescent cells) obtained by fractionation in a Percoll density gradient. The obtained MDS parameters (dielectric strength ∆ε, the relaxation time τ, and the broadening parameter α) were compared with the red blood cell indices and single cell deformability measurements obtained for each subpopulation. We demonstrated that the unique hematological indices and deformability of red blood cells of different ages are well-correlated with the specific values of dielectric fitting parameters. The obtained results indicate that the dielectric properties of cytosolic water can serve as a sensitive marker of changes occurring in the cytosol of red blood cells during cell aging.