Caspases are reversibly inactivated by hydrogen peroxide

Area of Science:

• Biochemistry
• Cell Biology
• Oxidative Stress

Background:

• Hydrogen peroxide (H2O2) exhibits dual roles in apoptosis, capable of both inducing and inhibiting the process.
• The precise molecular mechanisms underlying H2O2's effects on apoptosis, particularly its inhibitory actions, remain incompletely understood.

Purpose of the Study:

• To investigate the direct inhibitory effects of hydrogen peroxide on caspase activity.
• To elucidate the mechanisms by which H2O2 influences caspase function in cellular contexts.

Main Methods:

• Assessed the inhibitory concentration of H2O2 on recombinant caspase-3 and caspase-8 activity.
• Examined the protective and reversing effects of dithiothreitol and glutathione on H2O2-induced inhibition.
• Investigated H2O2's impact on caspase activity in macrophages following nitric oxide or serum withdrawal.
• Studied the effects of NADPH oxidase activation and catalase on cellular caspase inactivation.

Main Results:

• Hydrogen peroxide significantly inhibited recombinant caspase-3 and caspase-8 activity, with half-maximal inhibition at approximately 17 microM.
• Dithiothreitol effectively prevented and reversed H2O2-induced caspase inhibition, whereas glutathione offered minimal protection.
• H2O2 addition to macrophages post-caspase activation substantially inhibited enzymatic activity.
• Activation of NADPH oxidase led to catalase-sensitive inactivation of cellular caspases.

Conclusions:

• Hydrogen peroxide directly and reversibly inhibits the activity of caspases.
• This H2O2-mediated caspase inhibition occurs in both cell-free systems and cellular environments.
• The findings suggest a novel mechanism for regulating apoptosis through direct modulation of caspase activity by hydrogen peroxide.