Difference between revisions of "Team:BIT-China/Background"

Reactive oxygen species (ROS) refers to substances that have strong oxidative properties in living organisms. ROS are mainly divided into four categories: hydrogen peroxide(H₂O₂), superoxide anion(O₂^-), hydroxyl radicals(OH^-), and single-line oxygen(¹[O₂]). ^[1]

Antioxidants are compounds that inhibit oxidation.

Antioxidants can scavenge the excess ROS in the organisms. The antioxidants mentioned here is not antioxidants for food preservation, nor reductants, but working in organisms. ^[3]

To better study the performance of antioxidants in the market, we divide them into two categories: direct antioxidants and indirect antioxidants, according to the mechanism of antioxidant action. Direct antioxidants exert antioxidant effects by redox reaction to scavenging or inhibiting free radicals, such as vitamin C, vitamins E and proanthocyanidins. And indirect antioxidants achieve antioxidant activity by regulating gene expression and intracellular metabolism in cell endogenous antioxidant system, such as the natural antioxidants oleuropein, ^[4]quercetin, and the synthetic antioxidant probucol. The antioxidants that are commonly found in cosmetics and health products on the market today are vitamin C, vitamin E, tea polyphenols, etc.

In these existing assays for detection of antioxidants, human studies and animal models could give us the most truthful and reliable measurement results could. However, these are expensive and time-consuming and not available for initial screening antioxidants. ^[9]

Chemistry methods were widely-used, including oxygen radical absorbance capacity (ORAC) ^[10] , total radical-trapping antioxidant parameter (TRAP) ^[11] , Trolox equivalent antioxidant capacity (TEAC) ^[12] , total oxyradical scavenge capacity (TOSC) ^[13] , the peroxyl scavenging capacity (PSC) ^[14] , the ferric reducing/antioxidant power assay (FRAP) ^[15] , and the DPPH free radical method ^[16] . Although these chemistry methods are currently widely-use, their main measurement principle is to characterize the reducibility of antioxidants by virous artificially synthesized exogenous free radical occurring redox reactions with the antioxidants. As a result, chemistry methods have the shortcoming of low biological relevance, their detecting conditions are almost different from the physiological environment of cell living in, and these assays can’t evaluate the effects of antioxidants in the complicated metabolic process. That means, chemical methods are unable tot evaluate indirect antioxidants properly. ^[17][18] Therefore, the authenticity of the experimental results of chemistry methods is questioned. ^[19] For example, USDA's Nutrient Data Laboratory (NDL) removed the USDA ORAC Database for Selected Foods from the NDL website in 2012, because of the poor authenticity and low credibility of the chemistry methods. ^[20]

Compared to human studies and animal models, our program has shorter cycles, lower costs and lower detection difficulty. Compared to chemistry methods, our project is compatible with complex metabolic processes in cells, and biological relevance and data reliability have been greatly improved. In addition, our project can also detect the indirect antioxidants that can’t be evaluate by chemistry methods, such as antioxidants that functions by stimulating the endogenous antioxidant system in cells, which have not antioxidant capacity without cells.

Cell-based methods for evaluating antioxidants are a novel field. Cell-based antioxidants detection methods that people have developed can be roughly divided into three types. The first type is the CAA assay and MTT assay developed from the traditional chemistry methods. The second type is the cell-based electrochemical method evolved from the traditional electrochemical methods. The third type is the engineered cells that we use to synthesize biology. The third one utilize the engineering cells transformed by synthetic biological methods, which can detect and evaluate the antioxidants.

CAA assay ^[21] is cell-based assay, but it still doesn’t break through the limitations of traditional chemistry methods. Firstly, it still produces free radicals using artificial synthetic materials used in traditional chemistry methods, such as ABAP (Azo compound) which are criticized for cells. ^[22]

Secondly, the CAA assay uses an artificial synthetic fluorescent probe DCFH-DA, which is widely used to detect ROS currently, but the authenticity of the data obtained by this probe is questioned. ^[23]

MTT assay ^[24][25] breaks through the defect that the traditional chemical method can only detect single free radical, and the cell survival rate is used as the standard to characterize the antioxidant activity. However, the evaluation of MTT assay is not very good, because its detection condition is too critical for the cell and the cell survival pressure is very high. ^[26]

Cell-based electrochemical detection method, ^[27] which is based on the traditional electrochemistry and the bio-electrochemical probe. This kind of method has high sensitivity and can realize real-time monitoring which is its unique feature. But the high cost and critical requirement of equipment limits this method used widely.