Free radicals and antioxidants at a glance using EPR spectroscopy

Abstract

The delicate balance between the advantageous and detrimental effects of free radicals is one of the important aspects of human (patho)physiology. The controlled production of reactive oxygen and nitrogen species has an essential role in the regulation of various signaling switches. On the other hand, imbalanced generation of radicals is highly correlated with the pathogenesis of many diseases which require the application of selected antioxidants to regain the homeostasis. In the era of growing interest for redox processes, electron paramagnetic resonance (EPR) spectroscopy is arguably the best-suited technique for such research due to its ability to provide a unique insight into the world of free radicals and antioxidants. Herein, I present the principles of EPR spectroscopy and the applications of this method in assessing: (i) the oxidative status of biological systems, using endogenous long-lived free radicals (ascorbyl radical (Asc^•), tocopheroxyl radical (TO^•), melanin) as markers; (ii) the production of short-lived radicals (hydroxyl radical (OH^•), superoxide radical anion (O₂^•−), sulfur- and carbon-centered radicals), which are implicated in both, oxidative stress and redox signaling; (iii) the metabolism of nitric oxide (NO^•); (iv) the antioxidative properties of various drugs, compounds, and natural products; (v) other redox-relevant parameter. Besides giving a comprehensive survey of up-to-date literature, I also provide illustrative examples in sufficient detail to provide a means to exploit the potential of EPR in biochemical/physiological/medical research. The emphasis is on the features and characteristics (both positive and negative) relevant for EPR application in clinical sciences. My aim is to encourage fellow colleagues interested in free radicals and antioxidants to expand their base knowledge or methods used in their laboratories with data acquired by EPR or some of the EPR techniques outlined in this review, in order to boost up the exciting area of redox science.

Keywords::

• Ascorbyl radical
• hydroxyl radical
• nitric oxide
• oxidative status
• reactive nitrogen species
• reactive oxygen species
• redox signaling
• spin-labeling
• spin-trapping
• superoxide radical anion

Acknowledgements

I am very thankful to Prof. David M. Goldberg. I would like to dedicate this paper to my father Bogoljub.

Declaration of interest

This work was supported by the Ministry of Science of the Republic of Serbia, Grant number OI 173014 “Molecular mechanisms of redox signaling in homeostasis, adaptation and pathology”.