Table 1.
Biomarkers for oxidative stress status.
| Substrate of damage | Oxidative stress evaluation |
|---|---|
| DNA | 8-hydroxyl-deoxyguanosine (8-OHdG) |
| • The 8-OHdG is the end product of guanine oxidation through hydroxyl radicals [23] | |
| Comet assay | |
| • Very sensitive method for measuring DNA strand breaks in individual cells | |
| • Used in environmental toxicology, cancer research, and radiation biology to assess DNA damage | |
| • Damaged DNA migrates during electrophoresis from the nucleus towards the anode, forming a shape of a ‘comet’ with a head (cell nucleus with intact DNA) and a tail (relaxed and broken DNA) | |
| • The proportion of DNA in the tail is indicative of the frequency of breaks [23,24] | |
| 5-Hydroxyluracil (5-OHUra) | |
| • Presumed to form in DNA via deamination and loss of water from the oxidative DNA lesion cytosine glycol | |
| • A modified pyrimidine, 5-OHUra is a substrate for hNTH1, accounting for an earlier observation of repair of this lesion in human cell extracts [25,26] | |
| Proteins | Protein carbonyls |
| • Conventional assay: colorimetric procedure that involves dinitrophenylhydrazine | |
| • ELISA method: correlates well with the colorimetric assay for quantifying protein carbonyls in plasma samples [27] | |
| Lipids | Thiobarbituric acid-reactive substances (TBA-RS) |
| • Malondialdehyde (MDA) is a secondary product of lipid peroxidation by enzymatic via | |
| • It is a β-rupture byproduct of polyunsaturated fatty acids, such as linoleic, arachidonic and docosahexaenoic acids | |
| • Based on the reaction of TBA with MDA, one of the aldehyde products of lipid peroxidation | |
| • More specific technique for MDA quantification is by high performance liquid chromatography (HPLC), where the particles are separated and only MDA is detected [28] | |
| F2 isoprostanes | |
| • Produced by free radical-related peroxidation of arachidonic acid [16] | |
| • Formed in phospholipids and are then cleaved and released into the circulation before excretion in the urine as free isoprostanes | |
| • Most abundant is 8-isoprostaglandin F2α (8-iso-PGF2α), which has been suggested to be a promising marker for oxidation injury [29] | |
| Reduced/oxidized glutathione (GSH/GSSH) | |
| • Major anti-oxidant in human tissues that provides reducing equivalents for the glutathione peroxidase catalysed reduction of hydrogen peroxide and lipid hydroperoxides to water and the respective alcohol [21] | |
| • During this process GSH becomes oxidized glutathione. The GSSG is then recycled into GSH by gutathione reductase (GR) and NADPH | |
| • Mammalian cells are exposed to increased oxidative stress, the ratio of GSH/GSSG will decrease as a consequence of GSSG accumulation [11] | |
| • Measurement of the GSSG level and determination of the GSH/GSSG ratio are an useful indicators of oxidative stress and can be used to monitor the effectiveness of anti-oxidant intervention strategies [30] |
ELISA, enzyme-linked immunosorbent assay; NADPH, nicotinamide adenine dinucleotide phosphate.