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Inhibition of LDL oxidation by melatonin requires supraphysiologic concentrations
P B Duell1, D L Wheaton, A Shultz
1Division of Endocrinology, Diabetes and Clinical Nutrition, Oregon Health Sciences University, Portland 97201-3098, USA. duellb@ohsu.edu
Clinical Chemistry
|September 11, 1998
Summary
Melatonin shows minimal antioxidant activity, even at extremely high doses, unlike alpha-tocopherol, ascorbic acid, and tryptophan. This study questions melatonin's proposed role as a potent antioxidant in preventing diseases like atherosclerosis and cancer.
Area of Science:
- Biochemistry
- Oxidative Stress Research
Background:
- Melatonin is hypothesized to possess potent antioxidant properties, potentially protecting against atherosclerosis and cancer.
- However, evidence supporting these claims is limited and debated.
Purpose of the Study:
- To evaluate the antioxidant capacity of melatonin compared to alpha-tocopherol, ascorbic acid, tryptophan, and serotonin.
- To assess their efficacy in inhibiting low-density lipoprotein (LDL) oxidation.
Main Methods:
- Assessed antioxidant activity by measuring the inhibition of metal ion-mediated and macrophage-mediated LDL oxidation.
- Compared melatonin's efficacy against alpha-tocopherol, ascorbic acid, tryptophan, and serotonin.
Main Results:
- Melatonin exhibited weak antioxidant activity, requiring concentrations 10,000- to 100,000-fold higher than physiological levels.
- Alpha-tocopherol was 50- to 100-fold more potent than melatonin and effective at physiological concentrations.
- Ascorbic acid and tryptophan also demonstrated significant antioxidant activity at physiological concentrations, surpassing melatonin's efficacy.
Conclusions:
- Melatonin possesses only weak antioxidant activity, even at supraphysiological concentrations.
- Its antioxidant potential is considerably lower than that of alpha-tocopherol, ascorbic acid, and tryptophan.
- The study suggests that melatonin's role as a potent antioxidant in preventing diseases like atherosclerosis and cancer is not supported by current evidence.