Why have antioxidants failed in clinical trials?

Area of Science:

• Cardiovascular Research
• Oxidative Stress Biology
• Clinical Pharmacology

Background:

• Antioxidant therapies are widely investigated for chronic disease prevention.
• Clinical trials for chronic antioxidant therapy in atherosclerosis have yielded largely negative results.
• Mechanistic and epidemiological data suggest a role for oxidative stress in atherosclerosis.

Purpose of the Study:

• To critically evaluate the existing evidence for antioxidant therapies in atherosclerosis.
• To reconcile negative findings in chronic trials with encouraging data from acute settings.
• To identify key factors for future research, including optimal antioxidant selection, patient populations, and trial durations.

Main Methods:

• Review of placebo-controlled clinical trials on antioxidant therapies.
• Analysis of data from small-scale trials focusing on acute antioxidant benefits (e.g., N-acetylcysteine).
• Consideration of limitations of commonly used antioxidants like Vitamin E, including potential prooxidant effects.

Main Results:

• Large-scale trials of chronic antioxidant therapy for atherosclerosis prevention have been predominantly negative.
• Smaller trials suggest potential acute benefits of certain antioxidants, such as N-acetylcysteine.
• Commonly available antioxidants like Vitamin E may have limitations and even prooxidant effects.

Conclusions:

• The lack of benefit in chronic trials does not negate the role of oxidative stress in atherosclerosis.
• Further research is needed to identify optimal antioxidant agents, suitable patient cohorts, and appropriate trial lengths.
• Re-evaluation of antioxidant therapy strategies is necessary, focusing on specific clinical contexts and improved therapeutic agents.