Oxidative Stress
Valid from 1 Nov 2019 to 30 Jan 2020
A Guide to Finding the Right Biomarker to Detect in Your Application
Oxidative stress can be evaluated directly by measuring reactive oxygen species (ROS) or indirectly by the associated damage to lipids, proteins, and nucleic acids that occurs upon overproduction of ROS. 
Although direct measurement of ROS is ideal, the indirect methods are often relied on more heavily due to the relative stability of damage markers on biomolecules compared to the transient nature of ROS. To help you determine which is best to use in your experimental system, here is a breakdown of the assay technology used to detect the most common oxidative damage biomarkers.
Oxygen is electronically reduced as part of normal metabolism, resulting in the formation of various ROS, including hydrogen peroxide (H2O2) and superoxide (O2*−). Damage to cellular macromolecules occurs when uncontrolled oxidation stresses a biological system. Assays for ROS do not discern the source of ROS production (i.e., normal versus disease state), but if the experimental model is under stress, an increase in ROS and alteration to molecular components is probable.
Reactive nitrogen species (RNS) are also produced during oxidative stress. High levels of nitric oxide (NO*), synthesized by nitric oxide synthase (NOS), and O2*− lead to the formation of peroxynitrite. NO* itself also reacts with thiols and iron-sulfur enzymes, whereas peroxynitrite reacts with tyrosine residues to form nitrotyrosine.
DNA/RNA Damage
Guanine is the base that is most prone to oxidation when DNA and RNA are damaged. The repair processes that are initiated to correct this damage release the following oxidized guanine species into the urine:
8-hydroxyguanine - the ribose-free base
8-hydroxyguanosine - the nucleoside from RNA
8-hydroxy-2'-deoxyguanosine - the deoxynucleoside from DNA
Assays that can detect multiple oxidized guanine species capture a more complete set of biologically relevant products of oxidative damage than do assays that are restricted to analysis of only one
(e.g., 8-hydroxy-2'-deoxyguanosine).
Protein Oxidation and Nitration
The most common marker of protein oxidation is protein carbonyl content. Redox cycling cations bind to proteins and, in conjunction with attack by ROS, lead to the formation of amino acid derivatives containing carbonyl groups (ketones, aldehydes). Cigarette smoke and aldehydes also introduce carbonyls into proteins. Alternatively, ROS exposure to a protein's methionine residues generates protein methionine sulfoxide (MetO), an oxidative modification, that if not reversed by MetO reductases is further oxidized to methionine sulfone and can lead to protein dysfunction. The presence of nitrotyrosine on proteins is used as a marker of peroxynitrite formed in vivo when NO* reacts with O2*−. As peroxynitrite undergoes heterolytic cleavage, freed nitronium ions nitrate protein tyrosine residues. NO* can directly modify proteins through the RNS-mediated process of S-nitrosylation wherein an NO* group binds to thiol groups of protein cysteine residues resulting in the formation of an S-NO moiety.
Kit Recommendations (10% OFF)
703302 Glutathione S-Transferase Assay Kit
700340 Thiol Detection Assay Kit
706002 Superoxide Dismutase Assay Kit
10007892 Thioredoxin Reductase Colorimetric Assay Kit
389549 Nitrotyrosine Affinity Sorbent
501110 8-Isoprostane Affinity Purification Kit
600320 Sulfenylated Protein Cell-Based Detection Kit
600360 Glutathione Cell-Based Detection Kit (Blue Fluorescence)
700910 Catalase Assay Kit (without Hydrogen Peroxide)
703002 Glutathione Assay Kit
703102 Glutathione Peroxidase Assay Kit
703202 Glutathione Reductase Assay Kit
707002 Catalase Assay Kit
709001 Antioxidant Assay Kit
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