Biophysical characterization of PEI/DNA complexes

Area of Science:

• Biochemistry
• Biophysics
• Gene Delivery

Background:

• Polyethylenimine (PEI) is a cationic polymer used for gene delivery.
• Understanding the relationship between PEI structure, physical properties, and transfection efficiency is crucial for optimizing gene delivery systems.

Purpose of the Study:

• To investigate the effects of PEI molecular weight and structure on PEI/DNA complex properties.
• To determine the influence of the nitrogen/phosphate (N/P) molar ratio on complex formation and stability.
• To correlate physical properties with transfection efficiencies in different cell lines.

Main Methods:

• Fourier transform infrared spectroscopy (FTIR) to assess DNA conformation.
• Circular dichroism (CD) spectroscopy to detect alterations in DNA structure.
• Differential scanning calorimetry (DSC) to evaluate DNA stability.
• Isothermal titration calorimetry (ITC) to study protonation changes.
• Transfection assays in COS-7 and CHO-K1 cells.

Main Results:

• DNA maintained B conformation in all PEI complexes.
• PEI complexation altered DNA's CD spectra and destabilized supercoiled DNA at N/P ratios below 3/1.
• Protonation changes were observed via ITC at low ionic strength.
• 25 kDa branched and 25 kDa linear PEI showed highest transfection efficiencies at an N/P ratio of 6:1 in respective cell lines.
• Physical properties did not directly correlate with transfection efficiencies.

Conclusions:

• PEI molecular weight, structure, and N/P ratio significantly influence PEI/DNA complex physical properties.
• These physical alterations do not consistently predict transfection efficiency.
• Further biophysical analysis is recommended to explore potential subpopulations affecting transfection activity.