Effects of Redox State on the Efficient Uptake of Cell Permeable Peptide in Mammalian Cells

Shayne Squires1, *, Elisabeth Christians1, Michael Riedel1, David Timothy2, Christopher K Rodesch3, James Marvin, Ivor Benjamin1, 4, *
1 Division of Cardiology, University of Utah School of Medicine, Salt Lake City, Utah, USA
2 Department of Chemistry, University of Utah, Salt Lake City, Utah, USA
3 Department of Pathology, University of Utah School of Medicine, Salt Lake City, Utah, USA
4 Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, Utah, USA

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© Squires et al.; Licensee Bentham Open.

open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

* Address correspondence to these authors at the Department of Internal Medicine. 1900 E., Rm. 4A100, Salt Lake City, Utah 84132, USA; E-mail: Shayne.squires@hsc.utah.eduCorrespondence: Departments of Internal Medicine & Biochemistry, 30 N. 1900 E., Rm. 4A100, Salt Lake City, Utah 84132, USA; Tel: +1 801-581-6785, Fax: +1 801-585-1082; E-mail:


We investigated whether a cell-penetrating peptide linked via a disulfide bond to a fluorophore-labeled cargo peptide can be used to interrogate changes in cellular redox state. A fluorescence resonance energy transfer (FRET) pair was constructed so that the cargo peptide was labeled with fluorescein amidite (FAM) and the cell-penetrating peptide was attached to a quencher. Incubation of cells in culture with the FRET construct was visualized using live-cell, time-lapse imaging, which demonstrated earlier cellular uptake of the construct when cells were treated with the reducing agent n-acetylcysteine (NAC). The FRET peptide construct was easily detected in cells cultured in 96-well plates using a plate-reader. Treatment of cells with various classes of reducing or oxidizing agents resulted in an increase or decrease in FAM fluorescence, respectively. Changes in FAM fluorescence correlated significantly with redox-sensitive green fluorescent protein ratios in cells treated with hydrogen peroxide but not NAC. Detection of relative changes in cellular redox state was enhanced by the fact that uptake of the cell-penetrating peptide occurred more quickly in relatively reduced compared with oxidized cells. We conclude that cell-penetrating peptides coupled via disulfide bonds to detectable cargo is a novel and specific approach for assessment of relative changes in cellular thiol redox state.

Keyword: Redox, cell-penetrating peptides, model amphipathic peptide, glutathione, FRET.