What Are Reactive Oxygen Species?

Reactive oxygen species (ROS) are the single-electron reduction products of a group of oxygen in the body. They are generated by the electrons that leak out of the respiratory chain and consume about 2% of the oxygen before they can be delivered to the terminal oxidase. The reduction products are superoxide anions (O2 ·-), two-electron reduction products, hydrogen peroxide (H2O2), three-electron reduction products, hydroxyl radicals (· OH), and nitric oxide. ^[1]

Oxygen is an indispensable gas in the process of life. Once people are in an environment of hypoxia or insufficient oxygen supply, they will feel the pain of thoron and even die. Therefore, since the discovery of oxygen by Joseph Priestley, an Englishman in the early 1770s, oxygen has been considered as a gas that is beneficial to the human body and harmless. However, today, with the rapid development of science and technology, we know that both oxygen in the air and dissolved oxygen in water have high oxidizing properties. Like ordinary metal iron, all parts of the human body in the air are constantly growing. It is "rusted" by the corrosion of oxygen. Of course, this corrosion is different from iron. It is reflected at the cellular level of the human body. In particular, the continuous aging of various organs of the human body with age is an intuitive manifestation of this "rust" of corrosion. In 1969, McCord and Fridovich discovered that during the biochemical reaction, O2 obtained an electron reduction to generate superoxide radical (O-2), and then was separated and purified by red blood cells to obtain O-2 scavenging and inactivating enzyme, and named it superoxidation. Superoxide dismultase (SOD). This discovery has inspired a large number of scientific researchers to devote themselves to the research on the formation process, reactivity, toxicity, physiology, and pathology of O-2 in order to explore the physiological significance of SOD. At the same time, hydrogen peroxide (H2O2), hydroxyl radical (· OH), and excited oxygen (single state oxygen or singlet oxygen, O2) derived from O-2 have also attracted people's attention.

The so-called reactive oxygen, in a nutshell, refers to the general term for substances that are composed of oxygen in the body or in the natural environment: oxygen-containing and active properties: there is mainly an excited oxygen molecule, that is, a singlet oxygen molecule or singlet oxygen Molecule (O2); 3 kinds of oxygen-containing free radicals, namely superoxide anion radical (O-2), hydroxyl radical (· OH) and hydroperoxy radical (HO2); 2 kinds of peroxides, namely Hydrogen oxide (H2O2) and lipid peroxide (ROOH) and a nitrogen-containing oxide (NO). These substances have strong chemical reactivity and short lifespan. For example, the average life of O2 is 2 s, · OH radical 200 s, and O-2 radical 5 s. Because of their short lifespan and high reactivity, the determination of other reactive oxygen species besides H2O2 is still an international problem, and there is no particularly specific and effective method. Generally, the analysis methods used can be chemical reaction method, capture method and direct measurement method. ^[2]

Oxidative damage to nucleic acids

The oxidative damage of DNA mainly includes: First, the modification of bases. Hydroxyl radicals can add 5,6-double bonds to thymine to form thymine radicals. Changes in bases can disrupt many of the biochemical and protein synthesis processes under their group control. The second is the breaking of the bond. The free radical captures the hydrogen atom from the pentose of DNA, and forms a free radical with an unpaired electron at the C4 position. Then, the free radical undergoes a chain break at the -position. O2 can also break down nucleotides, especially guanylic acid.

Chemical reaction

Due to the high reactivity of reactive oxygen species, they can chemically react with many different compounds, resulting in a variety of different reaction products, which can be quantitatively or qualitatively analyzed according to the degree of change of these reaction products or reactants. The commonly used instrumental analysis methods are chemiluminescence, ultraviolet-visible absorption spectrophotometry, fluorescence spectrometry, electron spin probe, and selective electrode method. The chemical reaction method is characterized by high measurement sensitivity, low cost, and simple operation. However, the specificity of the chemical reaction method is relatively poor. Some redox reactions or enzyme-catalyzed reactions often affect the determination of the determination results. Generally, other analytical methods are required for comparison to obtain satisfactory conclusions. ^[2]

Chemiluminescence method

Chemiluminescence is one of the most sensitive methods in instrumental analysis, and has been widely used in many fields such as medicine, environment, and industrial analysis. Chemiluminescence research on active oxygen is also one of the more active branches in the field of active oxygen measurement. Especially for the determination of H2O2, there are many chemiluminescence systems with high sensitivity and selectivity. In recent years, the author has developed a series of high-sensitivity chemiluminescence analysis methods for the determination of H2O2. In addition, the currently successful active oxidative luminescence assays include luminol, lucigenin, and cypridina luciferin analog (CLA).

Spectrophotometry

The most commonly used methods for the spectrophotometric determination of active oxygen include the cytochrome C superoxide radical reduction method and the nitro blue tetrazolium (NBT) reduction method. After the oxidative cytochrome C is reduced by O-2, a ferrous cytochrome with strong absorption at a wavelength of 550 nm is formed, which can be used for the direct measurement of O-2. In the presence of SOD, O-2 is subjected to The catalytic formation of SOD by H2O2 and O2 was developed as an indirect quantitative analysis method for SOD. ^[2]

However, there are other reducing substances such as HADPA and reducing enzymes in the cytochrome c reduction method of reactive oxygen species. Generally, they cannot be directly used for the qualitative analysis of O-2. It is necessary to compare whether or not There is a result of the reaction between O-2 and cytochrome C, so as to judge whether O-2 is produced or not.

Fluorophotometry

Like chemiluminescence, fluorescence spectrophotometry is one of the analytical methods with high sensitivity and easy operation. A typical example is that in the presence of peroxidase, dichlorofluorescein (DCFH) is oxidized by H2O2 or HO-2 to form DCF with fluorescence, which can be effectively applied to the quantitative analysis of H2O2 [23]. By using 2, 3-diaminonaphthalene (DAN) to react with NO-2 under acidic conditions to form a fluorescent 1- (H) -naphthalenetriazene ring, it has been proposed to use 2, 3-diaminonaphthalene (DAN) ) As a method for measuring NO. ^[2]

Electron spin resonance method

Electron spin resonance method (ESR method) As a detection method after the chemical reaction of active oxygen, it can be understood as a radical identification reaction, that is, the freedom to add asymmetric electrons to the reaction system of active oxygen generation Group, this additive loses asymmetric electrons after reacting with active oxygen, resulting in changes in the ESR signal. ^[2]