Double edge redox-implications for the interaction between endogenous thiols and copper ions: In vitro studies

Area of Science:

• Biochemistry
• Oxidative Stress Research
• Metal Ion Interactions

Background:

• Endogenous thiols (RSH) play crucial roles in cellular redox homeostasis.
• Copper ions (Cu2+) are essential micronutrients but can induce oxidative stress.
• The interaction between thiols and copper ions influences their respective redox properties.

Purpose of the Study:

• To investigate the redox consequences of interactions between various endogenous thiols and Cu(2+).
• To assess the impact on free radical-scavenging, ascorbate-oxidizing, and superoxide (O2(*-))-generating properties.
• To determine how molar ratios and incubation times affect these properties.

Main Methods:

• Incubation of endogenous thiols (glutathione, cysteine, homocysteine, gamma-glutamyl-cysteine, cysteinyl-glycine) with Cu(2+) at different molar ratios.
• Measurement of free radical-scavenging activity using ABTS(*)(+) and DPPH(*).
• Electron Paramagnetic Resonance (EPR) spectroscopy to characterize copper complex formation (Cu(II) and Cu(I)).
• Assays for ascorbate reduction and O2(*-) generation (cytochrome c and lucigenin reduction).

Main Results:

• Incubation with Cu(2+) significantly decreased thiol-titratable groups and free radical-scavenging properties of thiols.
• Equimolar RSH/Cu(2+) mixtures formed stable, ascorbate-reducible Cu(II)-complexes, redox-inactive towards oxygen.
• A 3:1 thiol-to-Cu(2+) ratio yielded stable, EPR-silent Cu(I)-complexes, unreactive towards ascorbate and oxygen.
• Glutathione was an exception, forming Cu(2+) mixtures that generated O2(*-).

Conclusions:

• The interaction between Cu(2+) and thiols generates distinct copper complexes based on molar ratios.
• These complexes exhibit varying redox activities, influencing antioxidant and radical-scavenging capacities.
• Glutathione uniquely retains O2(*-)-generating capacity upon interaction with Cu(2+), highlighting thiol-specific effects.