Free radical-induced chitosan depolymerized products protect calf thymus DNA from oxidative damage

Area of Science:

• Biochemistry
• Polymer Science
• Molecular Biology

Background:

• Chitosan derivatives, including low molecular weight chitosan (LMWC) and chitooligosaccharides (COs), are derived from chitosan via depolymerization.
• These compounds possess inherent antioxidant properties, crucial for cellular protection against oxidative stress.

Purpose of the Study:

• To investigate the free radical scavenging and DNA protective capabilities of LMWC and COs.
• To compare the efficacy of LMWC and COs in preventing oxidative damage to DNA.
• To elucidate the mechanism of LMWC interaction with DNA.

Main Methods:

• Persulfate-induced depolymerization of chitosan to obtain LMWC and COs.
• Assays for hydroxyl (OH) and superoxide (O2.-) radical scavenging activity.
• Calf thymus DNA protection assays against oxidative damage.
• Circular dichroism (CD), Transmission Electron Microscopy (TEM), and melting curve (Tm) analyses for DNA condensation and stability.
• Fluorescence spectroscopy to determine LMWC binding interactions with DNA.

Main Results:

• Both LMWC and COs exhibited significant scavenging of OH. and O2.- radicals, with over 85% inhibition observed.
• LMWC demonstrated a markedly stronger inhibitory activity against free radicals and superior protection of calf thymus DNA compared to COs.
• LMWC induced reversible condensation of calf thymus DNA, enhancing its stability, as confirmed by CD, TEM, and Tm analyses.
• Fluorescence studies indicated that LMWC binds to the minor groove of DNA, forming hydrogen bonds with phosphate backbones without distorting the double helix.

Conclusions:

• LMWC is a potent antioxidant and exhibits significant DNA protective effects, outperforming COs.
• LMWC stabilizes DNA through reversible condensation, interacting with the minor groove via hydrogen bonding.
• These findings highlight the potential of LMWC as a therapeutic agent against oxidative stress and DNA damage.